AN ABSTRACT OF THE THESIS OF
Mirza Shahid Baig for the degree of Doctor of
Philosophy in Geology presented on June 6, 1990.
Title: Structure and Geochronoloqy of Pre-Himalayan and
Himalayan Oro2enic Events in the Northwest Himalaya,
Pakistan, with Special Reference to the Besham Area. Redacted for Privacy Abstract approved:
Dr. Robert D. Lawrence
In the northwest Himalaya of Pakistan, metamorphism, deformation, and plutonism are the result of collision between the Indo-Pakistan and Asian plates. The timing of pre-Himalayan orogenic events remains uncertain, due to strong, pervasive Himalayan overprinting. This study presents new field, structural, and metamorphic data together with 40Ar/39Ar isotopic age data on hornblende, muscovite, biotite, and K-feldspar for Besham, Mansehra, Swat, and Hazara areas of northern
Pakistan. These data provide the first detailed record of Early Proterozoic to Late Paleozoic events in the northwest
Himalaya and combine with prior U/Pb, Rb/Sr, and fission track data record an orogenic history from the Early
Proterozoic to Cenozoic.
The Early Proterozoic orogenic events in the Besham basement complex occurred at (A) 2,031 ± 6 to 1,997 ± 8 Ma, (B) 1,950 ± 3 Ma, and (C) 1,887 ± 5 to 1,865 ± 3 Ma. These were followed by sodic granite intrusion at 1,517 ± 3 Ma. Subsequently, flysch of the Kurinang, Gandaf, Manki, Hazara, Dogra, and Simla formations was deposited unconforinably on the basement rocks of the Indo-Pakistan plate. These units are unconformably overlain by the molasse of the Tanawal and Manglaur formations. The area underwent metamorphism and deformation at 664 to 625 Ma, and volcanism and plutonism at 850 to 600 Ma (Hazaran orogeny). Later metamorphism and deformation at >466 ± 3 Ma and plutonism at 550 to 450 Ma record an Early Paleozoic orogeny. Alkaline magmatisni (315 ± 15 to 297 ± 4 Ma), sodic granites (>272 ± 1 Ma), mafic Panjal volcanism (284 ± 4 to 262 ± 1 Ma), and metamorphism (333 ± 1 Ma), occurred during early rifting of the Cimmerian microcontinent from Gondwana. The early Himalayan metamorphism and deformation in northern Pakistan occurred between 84 to 64 Ma. 40Ar/39Ar dates of 51 to36 Ma, 36 to 30 Ma, and 30 to 24 Ma from shear zones, date successive shearing, and 24 to 5 Ma fission track dates show unroof ing and tectonic erosion, during the development of the Indus syntaxis. The presence of active faults, seismicity, and newly recognized 1600 in of uplifted Indus river terraces, show that the Indus syntaxis is an active feature, which has an uplift rate of about 1 nun/yr since 5.2 Ma. Structure and Geochronology of Pre-Himalayan and Himalayan Orogenic Events in the Northwest Himalaya, Pakistan, with
Special Reference to the Beshain Area
by
Hirza Shahid Baig
A THESIS
submitted to Oregon State University
in partial fulfillment of
the requirements for the
degree of
Doctor of Philosophy
Completed June 6, 1990
Commencement June, 1991 APPROVED:
Redacted for Privacy
Associate Professor of Geology in charge of major Redacted for Privacy
Cha- of Departm- t of eoscie bes
Redacted for Privacy
Dean of the G ate Schol
Date thesis is presented: June 6,1990
Typed by: Mirza Shahid Baig DEDICATED TO NY LATE MOTHER RAZIA ACKNOWLEDGEMENTS
I deeply appreciate my family for encouragement, financial, and moral support during the course of this study. This work would not have been possible without financial support of NSF fliT 86-09914 and NSF EAR 86-17543 to Robert. D. Lawrence, and scholarship from the Government of Pakistan and University of Azad Jammu and Kashinir to undertake this project at Oregon State University.
Thesis committee members Robert D. Lawrence, Lawrence W. Snee, John H. Dilles, and Robert J. Lillie provided insight, direction, and critically reviewed the manuscripts.
Special thanks to Robert D. Lawrence, who served as thesis advisor. I appreciate his encouragement and support through out this study. The analytical work was supported by the Branch of Isotope Geology, U.S. Geological Survey, Denver. Argon work was done under the supervision of Lawrence W. Snee for more than two years. I appreciate discussions with Larry during and after the analytical work. Fruitful discussions with Dr. R. D. Lawrence, Dr. L. W. Snee, Dr. M. Ashraf, Dr. M. N. Chaudhry, Dr. N. A. Latif, J. A. DiPietro, K. Pogue, A. Hussain, I. Ahmad, and R. J.
LaFortune are acknowledged. Field work in rugged areas of Swat and Allai-Kohistan was not possible without the cooperation and help of the tribal peoples of Kohistan. I deeply acknowledge my field guide Fazal Karim, drivers Mohsoom Shah and Russul Shah for their sincere support during the field work. All the personals from S.D.A. at Besham are acknowledged for their
logistic support. Professors Munir Chazanfar, Arif Au Khan Ghauri, and Imtiaz Ahmad of the Punjab and Peshawar Universities were helpful in arranging field equipment and transport. Mazhar Qayyum is acknowledged for his sincere constant support during the preparation of this thesis. I thank all the friends who were source of encouragement and extended moral support during my stay at Oregon State University. Therese and Hazal were supportive through out my stay at the Geosciences Department. I deeply acknowledge Therese's help in typing argon data table.
During last ix months of this study I -was without financial support. The financial help by my family, Amin Molvai, Razawan Ahmed, Mazhar Qayyum, Larry Snee, and Oregon State University is particularly acknowledged. I sincerely appreciate Dr. Cyrus Field and Dr. Anita Grunder for their help and support.
I will not forget the hospitality of Karen Lund, Larry Snee, and Gary Davidson during my stay at Denver. I sincerely appreciate technical help by Rass, Dave, and Ed of the mineral separation and argon labs of the U.S.G.S. TABLE OF CONTENTS
SECTION 1
INTRODUCTION 1 SECTION 2 EVIDENCE FOR LATE PRECAMBRIAN TO EARLY CAMBRIAN OROGENY IN NORTHWEST HIMALAYA, PAKISTAN 7
ABSTRACT 7
INTRODUCTION 8
HAZARA-SWAT THRUST BELT 10 DISCUSSION 15 CONTRIBUTIONS OF THE AUTHORS 17 SECTION 3 EARLY PROTEROZOIC TO CENOZOIC TECTQNICISTORY OF THE NORTHWEST HIMALAYA: GEOLOGIC AND Ar/3 Ar THERMOCHRONOLOGIC EVIDENCE FROM NORTHERN PAKISTAN 18
ABSTRACT 18
INTRODUCTION 22 TECTONIC SETTING 27
NOMENCLATURE USED 34
BESHAK BLOCK 35 (1). Beshain block stratigraphy 37 Besham group 38 Intrusive rocks 44 Karora group 53 Post-Karora group sodic granites and inafic dikes and sills 58 (2). Beshain block deformation, metamorphism, and plutonism 59 (a). Pre-Karora group sedimentation plutonism, metamorphism, and deformation 59 (1). Field evidence 66 (ii). Inferred history 70 TABLE OF CONTENTS (CONTINUED)
(b).Post-Karora group plutonism, metamorphism, and deformation 81 (1). Beshain basement complex 81 Karora group 84 Recent deformation and Indus syntaxis 88 SWAT BLOCK 90 Mingora and Peshawar basin areas 90 Alpurai, Puran, and Ajmar areas 94 Stratigraphy 94 Metamorphism and deformation 96
MANSEHRA BLOCK 99 (1). Tarbela and Mansehra areas 99 (2) .Allai-Kohistan 101 Stratigraphy 101 Inferred deformation, metamorphism, and plutonism 104 NEOTETHYS TERRANE 121 KOKISTAN ISLAND ARC TERRANE 123 40Ar/39Ar GEOCHRONOLOGY 125 40Ar/39Ar dating techniques 125 Analytical methods 130 40Ar/39Ar RESULTS 137
BESHA1' BLOCK 144 Ainphibolites of the Besham basement complex 144 Metasediments of the Besham basement complex 168 Intrusive rocks of the Besham basement complex 171 Metasediments of the Karora group 176 Post-Karora group sodic granites 177 TABLE OF CONTENTS (CONTINUED)
SWAT BLOCK 178 Low-grade units of the Peshawar basin 180 High-grade to medium-grade metamorphic units of the Alpurai and Swat areas west of the Puran fault 183
MANSEHRA BLOCK 186
NEOTETHYS TERRANE 198
KOHISTAN ISLAND ARC TERRANE 198
DISCUSSION AND IMPLICATIONS OF 40Ar/39Ar DATA 202
(1). Besham block 202 Geologic implications 202 Timing of Pb/Zn mineralization 219 Thermal/cooling history of the Besham block 221
(2). Swat block 224 Geologic implications 224 Thermal/cooling history of the Swat block 234
(3). Mansehra block 237 Geologic implications 237 Thermal/cooling history of the Mansehra block 257
(4). Neotethys terrane 259
(5). Kohistan island arc terrane 265
(6). Timing of melange emplacement and suturing in the northwest Himalaya of Pakistan 268 (7). 40Ar/39Ar constraints for the development of the Indus syntaxis 271 (8). Uplift rates and tectonic erosion since 5.2 Ma in the Indus syntaxis 274 TABLE OF CONTENTS (CONTINUED)
SECTION 4
CONCLUSIONS 277 Section 2: Evidence for Late Precambrian to Early Cambrian orogeny in northwest Himalaya, Pakistan 277 Section 3: Early Proterozoic to Cenozoic tectonic History of th norwest Himalaya: Geologic and °Ar/ Ar thermochronologic evidence from northern Pakistan 278
BIBLIOGRAPHY 283 APPENDICES 40Ar/39Ar Age-Spectrum Data front rocks of the Indus syntaxis, Besham area, northwest Himalaya Pakistan 315 Measured production ratios for Ca- and K-derived argon isotopes for the U.S Geological Survey TRIGA reactor, Denver 396 Major element chemistry of granitic rocks of the Besham block 397 LIST OF FIGURES
FIGURE PAGE #
1.1. Tectonic map of the northwest Himalaya, showing Besham, Hazara, and Tanakki study areas 3
2.1 (a). Geologic map of the Tanakki village area, Hazara District, Pakistan, showing the unconformity between the Tanakki conglomerate at the base of the Abbottabad Group of Cambrian age and the underlying Hazara Formation 12
2.1 (b). Geological cross-section along line C-C' on Figure 2.la showing unconformity at the base of the Tanakki conglomerate 12
3.1. Tectonic map of the northwest Himalaya, showing Besham (Figure 3.2) and Tanakki study areas 23
3.2. Geologic and tectonic map of the Indus syntaxis, Besham area, Pakistan 28
3.3. Geologic map of the Besham and Allai- Kohistan areas of the Indus syntaxis 39
3.4. The magmatic history of the Besham basement complex 46 The metapyroxenite of the Besham group 46
Lahor sodic granite gneiss intrudes the metasediments of the Besham group 46 Xenoliths of the Thakot formation of the Besham group in the Lahor sodic granite gneiss 46 Apophyses of the Lahor sodic granite gneiss intrude the amphibolite of the Besham basement complex 46 Sharp intrusive contact of the hornblende-biotite granite gneiss with the Lahor sodic granite gneiss 46 LIST OF FIGURES (CONTINUED)
FIGURE PAGE #
Dubair hornblende-biotite granite gneiss with a xenolith of the Lahor granite gneiss and associated pegmatite 46 The Middle Proterozoic graphic equigranular tourmaline-muscovite sodic granite intrudes the metasediments of the Besham basement complex, and postdates the gneissic fabric of the Besham basement complex to be pre-Middle Prderozoic in age... 47 The very weakly to undeformed equigranular Karora sodic granite is intruded by a tourmaline pegmatite (87MB47A) 47
Photomicrograph of the tourmaline pegmatite (87MB47A), showing a inagmatic texture 47
The very weakly to undeformed equigranular Karai sodic granite intrudes the quartzo-feldspathic garnet-biotite gneiss of the Thakot formation, and shows sharp intrusive contact 47
3.5. Field relation of Karora group and the Besham basement complex 54 Geological field sketch map, showing field relations of the Karora group and the Besham basement complex, about 4 km west of Besham along the Besham Mingora road (modified after Baig and Lawrence, 1987) 54 The gneissic metasediments of the Besham basement complex are truncated by the Amlo basal conglomerate of the Karora group 54 LIST OF FIGURES (CONTINUED)
FIGURE PAGE #
3.6. Deformation, metamorphism, and plutonism in the Karora group 60 Multiply deformed graphitic phyllite of the Kurmang formation of the Karora group 60
Phyllite of the Kurmang formation preserves the remanent of SKi fabric in the hinge of an intrafolial FK fold, which is strongly transpose parallel to SK2 fabric 60 The Ranial granite intrudes the metamorphic rocks of the Karora group and has a hornfelsic aureole 60 FK2 fold in the phyllite of the Kurmang formation 60 F3 crenulation folds in the phyllite o! the Kurmang formation 60 Carbonates of the Kandoana formation define strong lineations parallel to the handle of the hammer 60 Carbonate of the Kandoana formation showing one strong mica fabric close to the Chakesar fault zone 61
3.7. Middle Proterozoic tourmaline granite boulder 68 Field photograph showing a boulder of tourmaline-muscovite granite in phyllitic to schistose matrix of the basal Amlo conglomerate of the Karora group 68 Photomicrograph of graphic tourmaline-muscovite granite boulder, showing maginatic texture 68
3.8. The folding, fabric, and metamorphic events in the Besham basement complex 72 LIST OF FIGURES (CONTINUED)
FIGURE PAGE #
Two sets of Early Proterozoic folds in the metasediments of the Besham basement complex 72 Photomicrograph showing a hook of FB sheath or intrafolial foldtransposes parallel to the S12 main penetrative fabric of the Besriam metasediments.... 72
A relict MB2 garnet with inclusions of sillimanite needles 72
A relict MB2 garnet, showing well developed sillimanite inclusions 72 A F3 north-striking,steeply west-dipping, eas-verging, north-plunging tight to isoclinal fold in the metasediments of the Besham basement complex 72 Photomicrograph showing FB3 fold in the left top corner of photograph 73
Photoinicrograph of amphibolite of the Besham basement complex 73 The amphibolite of the Besham basement complex, showing MB3 generation hornblendes (Hb) and later MB4 actinolite rims Photomicrograph showing two spaced fabrics in the quartz-muscovite-biotite- garnet schist 73 The hornblende-biotite granite, showing M3 generation hornblende, surroundea by MB4 actinolite rims
3.9. Deformation, metamorphism, and magmatism of the Mansehra block 105 (a). Xenoliths of the Tanawal Formation in the late Cambrian Mansehra granite gneiss indicate that the Tanawal Formation is older than the late Cambrian 105 LIST OF FIGURES (CONTINUED)
FIGURE PAGE
An amphibolite xenolith in the Mansehra granite gneiss indicates that one episode of mafic activity predated the intrusion of the late Cambrian Mansehra granite.. 105
A photomicrograph of aiuphibolite (87MB253) which intrudes parallel to main SM2 fabric of the Mansehra granite gneiss 105
Photomicrograph of garnet-biotite- muscovite gneiss (87MB272) of the Tanawal Formation 105
The unmetamorphosed Early Permian Panjal diabase sill (87MB33A) intrudes parallel to the SM., gneissic fabric of the Mansehra granite gneiss 105 Photomicrograph of diabase sill (87MB33A) showing magmatic texture, and does not record any fabric 105
An unmetainorphosed Jurassic basalt dike (87MB61) which intrudes the folded Tanawal Formation 106
3.10. Field and fabric relations showing deformation along the Thakot fault zone 114 A brittle shear zone along the Thakot fault 114 Blocks and lenses of peridotite of the Indus suture zone in the shear zone of the Thakot fault 114 (C). Photomicrograph of an epidote amphibolite (87M323) of the Besham basement complex close to the Thakot fault, showing hornblende, biotite, epidote, and quartz growth during ductile deformation 114 LIST OF FIGURES (CONTINUED)
FIGURE PAGE #
Photomicrograph of a garnet amphibolite lens (87MB1O1) in a shear zone of the Tanawal Formation, east of Thakot fault, showing syntectonic growth of garnet, hornblende, biotite, and quartz 114
The matrix (87MB102) of shear zone has two mica fabrics 114
The mylonitized Nansehra granite gneiss from a ductile shear zone, east of the Thakot fault, showing ribbon structures.. 115
A tourmaline granite (87MS824) from a shear zone of the Mansehra block 115
3.11. Summary diagram showing Early Proterozoic to Cenozoic metamorphic/thermal events in the Besham block 148
3.12. Proterozoic hornblende (Hb), biotite (Bt), and muscovite (Mu) age spectra from the Besham basement complex 150
3.13. The thermal release data and mineral phase relations of the sample 87MSB45 153 Age spectrum of sample 87MSB45, showing different ages for low- to high- temperature steps 153 The 39Ar/37Ar verses 39ArK percent released diagram, showing relation between degassing behavior of the hornblende (Hb), actinolite rims (AR), and chlorite (Chi) or biotite (Bt) at different temperature steps 153 A thin section sketch of a hornblende from sample 87MSB45 showing phase relations of the hornblende, actinolite rims, biotite, and chlorite 153
3.14. Amphibolite (87MB6A) of the Besham basement complex 158 LIST OF FIGURES (CONTINUED)
FIGURE PAGE 3.15. Phanerozoic biotite (Bt) 40Ar/39Ar age spectra from granites, granite gneisses, metasediments, shear zones, amphibolites, and mafic dikes of the Mansehra, Besham, and Swat blocks 160 3.16. Phanerozoic passin feldspar (K) and biotite (Bt) Ar/Ar age spectra from granites, granite gneisses, peginatites, amphibolites, and xnetasediments of the Beshain and Mansehra blocks 163 3.17. Phanerozoic hornblende (Hb) 40Ar/39Ar age spectra from amphibolites and basalt dikes of the Mansehra, Besham, and Swat blocks and Kohistan island arc terrane 166 3.18. Phanerozoic muscovite (Mu) 40Ar/39Ar age spectra from granites, peginatites, and inetasediments of the Besham, Swat, and Mansehra blocks 169 3.19. te oterozoic to Tertiary muscovite (Mu) Ar/Ar age spectra from the Besham block, Swat block, Mansehra block, Neotethys terrane, and the Kohistan island arc terrane 172 3.20. Summary diagram showing Late Carboniferous to Cenozoic thermal/metamorphic events in the Swat block 179 3.21. The Late Proterozoic to Cenozoic potassium feldspar (K), hornbnde Hb), Biotite (Bt), and Muscovite (Mu) Ar!3 Ar age spectra from the Swat block, Kohistan island arc terrane, and Hazara area 181 3.22. Phyllite of the Panj Pir formation (D) showing two fabrics 184 3.23. Composite 40Ar/39Ar hornblende age spectra from the amphibolites of the Alpurai group of Swat, showing 36-40 Ma dates 187 3.24. Composite 40Ar/39Ar muscovite age spectra from the Alpurai group of Swat, showing 36-40 Ma dates 189 LIST OF FIGURES (CONTINUED)
FIGURE PAGE # 3.25. Summary diagram showing Early Ordovician to Cenozoic metamorphic and thermal events in the Mansehra block 191 3.26. Cooling age profile along line A-A' across the Mansehra, Besham, and Swat blocks, showing sharp break in the cooling ages across the Thakot and Puran faults 193 3.27. Fuchsite-bearing schist from the Mingora ophiolitic melange of the Indus suture zone 199 3.28. A garnet amphibolite dike (87MB401) which intrudes the Jijal complex 201 3.29. Composite 40Ar/39Ar hornblende age spectra from the amphibolites of the Besham basement complex, showing 1997 ± 8 Ma to 2031 ± 6 Ma MB1 metamorphic event 204 3.30. Composite cooling, metamorphic (MB and MB3), fabric (SB1,SB2, and SBt, anMB folding events (FBi, FB2, and FB3J diagram 206 3.31. Composite 40Ar/39Ar hornblende age spectra from the amphibolites of the Besham basement complex, showing 1950 ± 3 Ma MB2 metamorphic event 208 3.32. Composite 40Ar/39Ar hornblende age spectra from the ainphibolites of the Beshain basement complex, showing 1865 ± 3 Ma to 1887 ± 5 Ma MB3 metamorphic event 210 3.33. Composite 40Ar/39Ar hornblende age spectra from the ainphibolites of the Beshain basement complex close to the Tahkot fault, showing 36-51 ± 2 Ma epidote amphibolite fades ductile shearing along the Tahkot fault 218 3.34. Composite 40Ar/39Ar age spectra of biotite (87MB2) and muscovite (87MB4) showing 36 Ma to 29 Ma Himalayan shearing along the Chakesar fault zone 220 LIST OF FIGURES (CONTINUED)
FIGURE PAGE #
3.35. Tertiary cooling history of the Besham block 222
3.36. Composite 40Ar/39Ar muscovite age spectra showing 36 Ma and 30-24 Ma Himalayan shearing in the Indus syntaxis 225
3.37. Tertiary cooling history of the Swat block 236
3.38. A clast of quartzite of the Tanawal Formation in the Early Cambrian Tanakki conglomerate 243
3.39. Showing field relations of the Cambrian Abbottabad Group and the Precambrian Hazara Formation near Tanakki area of Hazara 245
Geological map of the Tanakki area, showing the angular unconformity at the base of Tanakki conglomerate of the Cambrian Abbottabad Group (Modified after Latif, 1970) 245 Geological cross-section along the line C-C' on Figure (a) showing the unconformity at the base of the Tanakki conglomerate 245
3.40. Field and petrographic evidence for the Late Proterozoic deformation and metamorphism in the Tanakki area of Hazara.. 248 Randomly oriented low-grade metamorphic clasts of the Hazara Formation, in clast supported sedimentary matrix of the Early Cambrian Tanakki conglomerate 248 A folded phyllite clast of the Manki or Kurniang formation in the Early Cambrian Tanakki conglomerate 248 (C). Photomicrograph of the Early Cambrian Tariakki conglomerate, showing randomly oriented low-grade metamorphic clasts of slate of the Hazara Formation 248 LIST OF FIGURES (CONTINUED)
FIGURE PAGE #
3.41. Location map forthe Lesser Himalayan granite belt 252
3 .42. Tertiary cooling history of the Mansehra block 260
3.43. Composite 40Ar/39Ar muscovite age spectra from the Kohistan island arc, Neotethys, and Gondwana terranes of the NW Himalaya, showing Late Cretaceous metamorphic and deformational events at 80-84 ± 4 Ma and 70 Ma 262 LIST OF TABLES
TABLE PAGE #
3.1. Pre-Himalayan and Himalayan fabric relation near the Indus syntaxis 36
3.2. Precambrian pre-Himalayan events in NW Pakistan 82
33. The Paleozoic and Mesozoic pre-Hinialayan events in NW Pakistan 85
3.4. Interpretation of 40Ar/39Ar Age-Spectrum data from the Indus syntaxis, NW Himalaya Pakistan 138
3.5. Temperature, age, and 39Ar/37Ar ratios data for the Early Proterozoic amphibolites of the Beshain basement complex 145
3.6. Rb/Sr isotopic Age Data from the Himalaya and the southern Indo-Pakistan plate 239 LIST OF APPENDICES
APPENDIX PAGE # 4O,39 Age-Spectrum Data from rocks of the Indus syntaxis, Besham area, northwest Himalaya Pakistan 315 Measured production ratios for Ca- and K-derived argon isotopes for the U.S. Geological Survey TRIGA reactor, Denver 396 Major element chemistry of granitic rocks of the Besham block 397 STRUCTURE AND GEOCHRONOLOGY OF PRE -HIMALAYAN AND HIMALAYAN
OROGENIC EVENTS IN THE NORTHWEST HIMALAYA, PAKISTAN, WITH SPECIAL REFERENCE TO THE BESHAN AREA
SECTION 1
INTRODUCTION
The Himalayan mountain belt is the result of collision between the Indo-Pakistan and Eurasian plates (Stocklin, 1977; Tahirkheli et al., 1979; Windley, 1983; Farah et al., 1984). The Indo-Pakistan plate collided with the Kohistan island arc and Eurasian plate between the Late Cretaceous and Eocene and initiated the Himalayan fold-and-thrust belt (Molnar and Tapponnier, 1975; Stocklin, 1977; Tahirkheli et al., 1979; Windley, 1983; Peterson and Windley, 1985; Farah et al., 1984; Yeats and Hussian, 1987; Baig and Lawrence,
1987) In the northwest Himalaya of Pakistan, deformation and metamorphism in the Precambrian to Phanerozoic shelf and platform sediments of the Indo-Pakistan plate have been considered to be the result of Himalayan collision, which occurred sometime between the Late Cretaceous and Eocene (Gansser, 1964; Martin et al., 1962; Shams, 1969; Calkins et
al., 1975; Zeitler, 1983; 1985; Maluski and Matte, 1984; Coward et al., 1987; Zeitler et al., 1989; Chamberlain et al., 1989; Greco et al., 1989; Hubbard and Harrison, 1989). 2 Himalayan collision caused pervasive high-grade metamorphism and deformation that has mostly obscured evidence for pre-Himalayan orogenic events in the shelf and platform sediments. In contrast, where the Himalayan metamorphism and deformation decreases in the foreland fold-and-thrust belt, pre-Hixnalayan orogenic events can be recognized through the weak or absent Himalayan overprint (Baig and Lawrence, 1987; Baig et al., 1988; Baig and Snee, 1989; Baig et al., 1989). Earlier workers mostly inferred the existence of pre-Hiinalayan deformation and metamorphism on the basis of geologic and petrographic evidence (Kumar et al., 1978; Bhargava, 1980; Jamet al., 1980, Saxena, 1980; Kazmi et al., 1984; Garzenti et al., 1986; Baig and Lawrence, 1987; Baig et al., 1988; LaFortune, 1988; Pognante and Loinbardo, 1989; Williams et al., 1988; Treloar et al., l989b) and provided no conclusive 40Ar/39Ar constraints for these pre-Himalayan events- South of the Main Mantle thrust near the village of Besham (Figure 1.1), a polyphase pre-Himalayan dynamothermal metamorphic and plutonic history can be documented for the unusual Besham basement block in the core of the Indus syntaxis (Baig and Lawrence, 1987; Baig and Snee, 1989; Baig et al., 1989). This basement block is fault bounded on all sides. To the east the Thakot fault separates the Besham 3
Figure 1.1. Tectonic map of the northwest Himalaya, showing
Beshani, Hazara, and Tanakki study areas. Modified from
Wadia, 1931; Gansser 1964; Latif, 1970; Calkins et al.,
1975; Tahirkheli and Jan, 1979; Seeber and Armbruster, 1979;
Kazmi and Rana, 1982; Baig and Lawrence, 1987; Verplanck,
1987; Bossart et al., 1988; Baig et al., 1989; Madin et al.,
1989; Pogue et al.(in prep.), and this study. Abbreviations are: Besham (B), NP syntaxis (Nanga-Parbat syntaxis), H-K syntaxis (Hazara-Kashmir syntaxis), Indus Kohistan seismic zone (IKSZ), Jhelum fault (JF), Main boundary thrust (MBT),
Puran fault (PF), Panjal thrust (PT), and Thakot fault (TF).
Ophiolite along Main Mantle thrust zone (black). U&R. This Figure Chltrai Iran 36° Kohistan island N China r4 ArcTerrane Pakistan 7 rn, India w Ladakh IslandAro Besham Area
Main Hazara Area Swat /abui a Srinagar Peshawar ,___ Jalalabad Basin 4 Basin * . hy 34° a Peshawar - annkI , ,", N , Isiamaba ,, ' MBT
Potwar - Piateau
n 0 50 100 I I kilometers 32° ) I rN 7Q0 E 72° E 74° E Figure 1.1. 5 block from low- to high-grade metamorphosed Late Proterozoic to Mesozoic rock units of the Mansehra block. To the west, the Beshain block is separated by the Puran fault from Swat block (Baig and Lawrence, 1987; Baig and Snee, 1989; Baig et al., 1989). To the north it is separated by the Main Mantle thrust from the Kohistan island arc terrane lying to the north. To the south, the Beshain block is separated from low-grade to unmetamorphosed sedimentary rocks by thrust faults. A series of north-trending high-angle oblique-slip faults and shear zones first recognized in this study are present in the Indus syntaxis. Some of these faults offset the Indus suture zone arid contain lenses and blocks of mafic and ultramafic rocks (Baig and Lawrence, 1987; Baig and Snee, 1989; Baig et al., 1989). The Besham block is exposed as a tectonic window through the overlying Himalayan thrust sheets of the Mansehra and Swat blocks. It is the westernmost exposed basement of the Indo-Pakistan plate in the hinterland of the northwest Himalaya of Pakistan. The Besham block records a pre-Hiivalayan stratigraphic, plutonic, metamorphic, deformational, and geochronologic history not as completely preserved in the adjoining Mansehra and Swat blocks (Section 3) The Besham and the Hazara areas (Figure 1.1) have been investigated to document the pre-Hixnalayan and Himalayan 6 orogenic events on the basis of field, fabric, metamorphic, structural, stratigraphic, and geochronologic data. This thesis is written as two manuscripts. The first paper "Evidence for late Precambrian to early Cambrian Orogeny in northwest Himalaya, Pakistan" (Section 2) presents the field, metamorphic, stratigraphic, and paleontologic evidence to document Late Precambrian to Early
Cambrian metamorphism and deformation in the northwest
Himalaya of Pakistan.
The second paper "Early Proterozoic to Cenozoic Tectonic History of the Northwest Himalaya: Geologic and 40Ar/39Ar Thermochronologic Evidence from Northern Pakistan"
(Section 3) presents new 40Ar/39Ar dating results accompanied with field, structure, fabric, metamorphic, stratigraphic, and plutonic studies to document Early
Proterozoic, Middle Proterozoic, Late Proterozoic to Early
Cambrian, Caxnbro-Ordovician, Late Carboniferous, Early Permian, Late Jurassic, Late Cretaceous, Paleocene, Eocene, and Oligocene tectonic events. Section 4 presents the conclusions of this study. Section 5 includes combined bibliography of sections 1, 2, and 3.40Ar/39Ar and major element chemistry data is presented in appendices 1,2, and 3. 7
SECTION 2
EVIDENCE FOR LATE PRECAMBRIAN TO EARLY CAMBRIAN OROGENY IN NORTHWEST HIMALAYA, PAKISTAN by Mirza ShahidBaig*
ABSTRACT
An angular unconformity below Cambrian rocks is present in the northwest Himalaya in the Hazara district, Pakistan.
Low-grade metamorphism and folding with axial planar cleavage present in Precambrian rocks below the unconformity, but not in those above it, confirm orogenic deformation at this time. This is the first clear evidence for such a deformation episode, and it may be referred to locally as the Hazaran orogeny. Anatectic peraluminous granites of the Himalaya are of only slightly younger age and may be related to this orogenic episode.
*Co-authored by R.D. Lawrence and L.W. Snee. Published in the Geological Magazine, v. 125/1, pp. 83-86, 1988; (Received April 10, 1987; accepted May 6, 1987), copyright
Cambridge University Press, U.K. 8
INTRODUCTION
The Himalayan Mountains are one of the prime examples of a collision mountain belt where shortening processes are continuing. It is generally considered that the foreland fold-and-thrust belt of the range is comprised of deformed rocks of the Indian margin of Gondwana including both shelf sediment and basement elements largely of Precambrian age with only thin younger units (Gansser, 1964; Le Fort, 1975;
Singh, 1978; Ahinad and Alam, 1978; Valdiya, 1980, 1984). Orogenic events of Himalayan age are generally considered to begin in Late Cretaceous time and continue to the present
(Raina et al., 1980; Windley, 1983; Molnar, 1986). Various investigators (Kuinar et al., 1978; Bhargava, 1980; Jam et al., 1980; and Saxena, 1980) have discussed the possibility of important pre-Himalayandeformation based on stratigraphic and isotopic age data. However, the generally unfossiliferous nature of Lesser Himalayan stratigraphic units has made definite evidence for such deformation difficult to obtain. The principal arguments for such deformation have been scattered isotopic dates (Metha, 1977,
1980; Saxena, 1980) and apparent tracing of Indian shield structures and events into the Himalaya, where they are considered to have exerted control on major elements of Himalayan structure (Gupta, 1964; Valdiya, 1976, 1984).
Kumar et al.(1978) report a contact with two metamorphic 9 foliations below and only one foliation in Cambrian rocks above, but find no other stratigraphic evidence to confirm an unconformity. Faced with these uncertainties, many authors have argued that no good evidence for pre-Himalayan orogenic deformation exists, and that at most epeirogenic granite intrusion is recorded (Powell and Conaghan, 1973, 1978; Powell et al., 1979; Gansser, 1981; Windley, 1983).
Orogenic deformation can be distinguished from epeirogenic deformation by the presence of metamorphism and related intense shortening. Polymetamorphic deformation is common in the Himalaya (Gansser, 1964; Krummenacher, 1966;
Naha and Ray, 1971; Kumar and Pande, 1972; Virdi, 1981; Maruo and Kizaki, 1983; Ghazanfar et al., 1983; Windley, 1983; Coward et al., 1986), and in all previously reported cases the most recent metamorphic events are clearly
Himalayan. A central question arises whether any important pre-Himalayan metamorphic episode can be recognized through the Himalayan overprint. What stratigraphically controlled evidence can be offered for metamorphism prior to the well- documented Himalayan events? In this paper, I am for the first time presenting stratigraphic and palaeontological evidence from the Hazara-Swat thrust belt to show that at least one metamorphic and tectonic episode is of late Precambrian to earliest Cambrian age, andthus unrelated to
Himalayan orogenesis. 10
HAZARA-SWAT THRUST BELT
The Hazara-Swat foreland fold-and--thrust belt occurs west of the Hazara-Kashmir syntaxis in Pakistan (Kazmi and
Rana, 1982; Yeats and Lawrence, 1984). The rock units and tectonic setting correspond to the Lesser Himalayan subdivision of the central Himalaya. This belt lies south of the Main Mantle Thrust, which is the major suture separating the Cretaceous-Cenozoic Kohistan andesitic arc terrane from the deformed and metamorphosed rocks of the northern margin of Gondwana in the Indo-Pakistan plate. It lies north of the
Margala and Kala Chitta thrust faults which separate Precambrian to Cenozoic rocks of the upper thrust sheets from Murree and Siwalik molasse. The evidence for Precambrian metamorphism and deformation is exposed in this terrane. The Precambrian to Cenozoic rocks in Hazara and Swat range from unmetainorphosed in the south to high-grade metamorphic rocks in the north. The stratigraphy of the Hazara area is well constrained by the presence of Cambrian to Cenozoic fossiliferous rocks
(M.A. Latif, unpub. Ph.D. thesis, Univ. London, 1969; Latif, 1970, 1972; Calkins et al., 1975; Ghaznavi et al., 1983) which unconformably overlie the late Precambrian Tanawal and Hazara Formations. These units are thrust south in a series of imbricated sheets and duplexes. Late Precambrian and/or early Cambrian tectonism and metamorphism are recorded by an 11 angular unconformity between the Hazara Formation, in which new metamorphic mica has grown and a clear cleavage is developed, and Cambrian sediments of the Abbottabad Group, which are uncleaved. The unconformity has considerable relief, reflecting rolling hills, and the Tanakki conglomerate represents subaerial debris-flow deposits in valleys of this terrain (Figures 2.la and 2.lb). The transition from subaerial to marine conditions occurs within the Abbottabad Group. The Abbottabad Group is disconformably overlain by the Hazira Formation bearing Cambrian Hyolithes and Chancelloria fossils (Figure 2.la; Latif, 1972, 1974; Rushton, 1973). These are unconformably overlain by Jurassic units. The unconformity is well developed in the Hazara areas of Khoti-Di-Qaber, Tanakki (Figure 2.la); Mirpur Public School, Abbottabad; Sobrah; and Sangargali where it was initially mapped in detail by Latif (1969, 1970). The base of the Cambrian section is marked by a basal conglomerate, the Tanakki conglomerate, which has clasts of metamorphosed metasedimentary rocks, derived from the underlying Precambrian Hazara Formation. Hazara is the only
known area in the Himalayas where the Cambrian to Cenozoic
rocks above the angular unconformity are unmetamorphosed, whereas the Precambrian rocks below the unconformity are metamorphosed up to lower greenschist fades. The Hazara Formation with strongly developed cleavage is truncated by 12
Figure 2.1.(a) Geologic map of the Tanakki village area, Hazara District, Pakistan, showing the unconformity between the Tanakki conglomerate at the base of the Abbottabad Group of Cambrian age and the underlying Hazara Formation. Units are: 1 = Hazara Formation, 2 = Tanakki conglomerate, 3 = Sangargali sandstone, Mumdhagali sandy dolomite, and Mirpur sandstone, 4 = Sirban dolomite, 5 = Hazira Formation, 6 = Jurassic units, and 7 = Quaternary deposits. Units 2 to 4 comprise the Abbottabad Group. 'F' marks Cambrian fossil locality. For location of Tanakki village area, see Figure
1.1.
(b) Geological cross-section along lineC-C'on Figure 2.la showing unconformity at the base of the Tanakki conglomerate. 13
348,
- .-'-2jfr w. Quaternary Deposits 7 / J*WZ 7' iVa Jurassic Units 6 , _.__v_w
Hazira Formation 5
Sirban Dolomite 4 Mirpur Sandstone '.umdtagaIi Sandy Dolomite 3 Sangargali Sandstone
Tanakki Conglomerate 2
Hazara Formation i
Concealed Tflrust 34'4, Figure 2.la.
C, C ood
3000
1000
Figure2.lb. 14
Tanakki conglomerate in an angular unconformity. No cleavage is observed in the matrix of the conglomerate or in the overlying Cambrian rocks. At least this episode of new mica growth and cleavage development occurred prior to deposition of the Abbottabad Group in Cambrian time. This presence of metamorphic clasts of the underlying Precambrian strata in the unmetamorphosed Tanakki conglomerate above an angular unconformity confirms that the tectonisiu and metamorphism occurred before deposition of the Tanakki conglomerate. In this area the entire Tanawal Formation has been removed from above the Hazara Formation by erosion before the Tanakki conglomerate was deposited (Calkins et al., 1975). The only available indication of the time of deposition
of the Hazara Formation is from isotopic dates. Crawford and Davies (1975) dated three samples of slate from the Hazara Formation by the Rb/Sr whole-rock method. Their data did not
define a whole-rock isochron so they calculated model dates
for each sample. I recalculated these model ages to be 752 ±
20, 728 ± 20, and 951 ± 20 Ma by using Crawford and Davies, assumed initial 87Sr/86Sr ratio of 0.700 and a post-1977 decay constant of 1.42 x l011/yr. Because these samples are high-Rb, low-Sr slates whose Rb/Sr system is controlled by mica or clay, and because the data do not fit an isochron,
it is difficult to assign these model dates to the Precambrian metamorphic event. These dates more likely show
the age of provenance of the Hazara Formation clastic 15 materials to be late Precambrian; alternatively, the provenance dates could have been partially disturbed by
later metamorphism.
DISCUSSION
Prior workers have discussed the probability of orogenic deformation in very late Precambrian to early Paleozoic time. They have based this suggestion on two major arguments. First, they interpret much of the unfossiliferous
Lesser Himalayan stratigraphy to correlate to that of the
Vindhyan basin of the northern Indian shield (Jam et al.,
1980; Valdiya, 1984). Mild internal and more intense marginal deformation terminated deposition in this basin
during late Precambrian or early Paleozoic time, but related unconformities in the Himalaya cover most of the Paleozoic
span (Jam et al., 1980), leaving the time and nature of the deformation indefinite. Second, a significant number of Rb/Sr isochrons and related dates are now available from the
Lesser Himalaya indicating that peraluminous granites intruded during the period from 600 to 500 Ma (Metha, 1977;
Jam at al., 1980; Sharma, 1983; Le Fort et al., 1983; Le Fort, 1986), and that the Malani silicic volcanic suite in northwestern India erupted at a somewhat earlier time (Pareek, 1981). Such granites are also present in the
Mansehra area north of Hazara where they intrude 16 metamorphosed Precambrian basement. Available isotopic dates include a516 ± 16Ma Rb/Sr isochron (Le Fort et al.,1980), and a500Ma U/Pb isochron (Zartman and Zeitler, pers. comm. 1986).These confirm an igneous episode in late Precambrian and/or Cambrian time, but Himalayan age metamorphism has prevented prior workers from demonstrating that orogenic deformation accompanied this igneous activity. It is on this basis that some workers (Powell and Conaghan,1978)deny the existence of pre-Himalayan metamorphism. There is no doubt that the age of the Hazara Formation is Precambrian, based on the isotopic dates, the succeeding Tanawal unit, and the unconformably overlying rocks containing Cambrian fossils. The stratigraphic, palaeontological, and isotopic data confirm the presence of a late Precambrian to very early
Cambrian metamorphism at least to lower greenschist facies with accompanying deformation and cleavage development in the Hazara Himalaya. This deformation apparently occurred somewhat prior to the Cambrian intrusion of the Mansehra and related granites. The dating of this event in Hazara, combined with prior worker's less definite arguments for such an event elsewhere in the Lesser Himalaya and the widespread occurrence of early Paleozoic granites, suggests that this was a widespread event in the Himalaya. As this tectonic episode is most definitely recorded in the Hazara area, it may be useful to refer to it locally asthe Hazaran Orogeny. The500-600Ma plutons may be either a late Hazaran 17 orogenic phase or they may be post-Hazaran. These late Precambrian to early Cambrian events may be related to the assembly of Gondwana as a supercontinent.
CONTRIBUTIONS OF TkU AUTHORS
This parer was written as a result of the collaboration of three people. Shahid Baig was the principal author and leader of the effort. Lawrence and Baig visited the principal Tariakki section in the field together and discussed the significance of the section. Baig collected information on other exposures, most of which he had visited himself. Snee assisted Baig in recalculating the Rb/Sr dates published in earlier work. The basic interpretation in the end was made by Baig and discussed at length with his co-authors. Baig prepared the first draft of the manuscript and altered it according to the comments of his co-authors. 18
SECTION 3
EARLY PROTEROZOIC TO CENOZOIC TECTONIC HISTORY OF THE
NORTHWEST HIM7LAYA: GEOLOGIC AND40Ar/39Ar THERMOCHRONOLOGIC EVIDENCE FROM NORTHERN PAKISTAN
by
Mirza Shahid Baig
ABSTRACT
In the northwest Himalaya of Pakistan, metamorphism and deformation are the result of collision between the Indo-
Pakistan and Asian plates. The presence, timing, and significance of pre-Himalayan orogenic events has previously been uncertain, due to the pervasive high-grade Himalayan tectonic overprint which obscures any prior record. This study of the Besham area of northern Pakistan, has discovered earlier pre-Hinialayan events which are dateable due to weaker Himalayan overprinting. The new field, structural, metamorphic, and stratigraphic data together with 40Ar/39Ar isotopic age data on hornblende, muscovite, biotite, and K-feldspar are presented for the Besham, Swat, Allai-Kohistan, and Hazara areas. These data, together with prior published U/Pb, Rb/Sr, and fission track data, reveal a lengthy pre-Himalayañ as well as Himalayanorogenic 19 history initiated at least in the Early Proterozoic and perhaps in the Archean. The Besham basement complex, in the core of the Indus syntaxis, consists of multiply-intruded high-grade metasediments, mainly psammitic. 40Ar/39Ar dating of these basement rocks confirms the following Early Proterozoic events:(1) sediment deposition and rift-related ultrainafic flows,(2) mafic dike intrusion,(3) potassic and sodic granite intrusions,(4) orogeny at 2,031 ± 6 to 1,997 ± 8
Ma,(5) orogeny at 1,950 ± 3 Ma,(6) granite intrusion, (7) mafic dike intrusion, and (8) orogeny at 1,887 ± 5 to 1,865
± 3. These were followed in the Middle Proterozoic by sodic granites intruded at 1,517 ± 3 Ma.
The Karora group was deposited subsequently with an angular unconformity on the Besham basement complex in the early Middle to early Late Proterozoic. It is composed of basal Amlo conglomerate, Kurmang formation, and Kandoana formation. The Kurmang formation mainly graphitic, pelitic, and psammitic phyllite of flyschoid character, is widely correlative in northern Pakistan and NW India (Hazara, Manki, Gandaf, Dakhner, Landikotal, Simla, and Dogra formations), and this is the only place where the base of these units is exposed. These units are unconformably overlain by the Late Proterozoic molasse of the Tanawal and Manglaur formations. Granites intruded the area between 850 20 to 600 Ma and metamorphism and deformation occurred between 664 to 625 Ma (Hazaran orogeny).
The Hazaran orogeny was followed by the unconformable deposition of the Early Cambrian fossil-bearing sedimentary strata in the Hazara Himalaya of Pakistan. Plutonism at 550 to 450 Ma and metamorphism and deformation at >466 ± 3 Ma record a separate Cambro-Ordovician orogenic event.
Early Permian irtafic Panjal dikes cross-cut all the above units and record early rifting of the Cimmerian microcontinent from the northern margin of Gondwana. Dated events which are interpreted to relate to this rifting include alkaline magmatisxn (315 ± 15 to 297 ± 4 Ma), sodic granites (>272 ± 1 Ma), metamorphism (333 ±.l Ma), and maf Ic
Panjal volcanism (284 ± 4 to 262 ± 1 Ma).
The earliest Himalayan deformation and metamorphism in northern Pakistan occurred between 84 to 64 Ma. The earliest Himalayan thrust sheets were emplaced on the top of the
Besham block before 51 Ma, and were subsequently folded against the pre-Himalayan and Himalayan north-trending structures of the Besham block to form the Indus syntaxis. The overlying thrust sheets escaped east and west of the Besham block, due to indentation, vertical uplift, and escape-block tectonics. This indicates that both compressional and extensional processes are responsible for the development of the Indus syntaxis. 21
Shearing related to the development of the Indus syntaxis is recorded at 51 to 36 Ma, 36 to 30 Ma, and 30 to 24 Ma. Previously published fission track dates of 24 to
5 Na record uplift and unroof ing of the Himalayan thrust
sheets above the Besham block.
The presence of all Besham block lithologies in Quaternary terraces confirms that the Beshain block existed as an erosional/tectonic window before the Quaternary. Newly recognized Quaternary terraces 1600 m above the current
Indus river level, active faults, and seisinicity indicate a continuing uplift rate for the Indus syntaxis of about
1 mm/yr since 5.2 Ma. 22
INTRODUCTION
The Himalaya, the world's tallest mountain belt, is a clear manifestation of the collision between the continental and microcontinental fragments of Gondwana and Eurasia
(Stocklin, 1977; Tahirkheli et al., 1979; Farah et al.,
1984). The Indus-Tsangpo suture (ITS) is commonly believed to be the major structure that marks this collision zone.
The ITS is clearly defined as a boundary between different northern and southern tectonostratigraphic terranes which are commonly separated by intervening dismembered ophiolite lithologies of the Neotethys terrane (Gansser, 1964, 1981; Brookfield and Reynolds, 1981; Honegger et al., 1982; Searle et al., 1987).
In northern Pakistan, the Indus-Tsangpo suture bifurcates into the Main Mantle thrust (MMT) and the Main
Karakorum thrust (MKT)(Tahirkheli et al., 1979). The MKT marks the northern suture between the Kohistan island arc terrane and the Karakorum micro plate, and the MMT marks the southern suture between the Kohistan island arc terrane and the Indo-Pakistan plate (Figure 3.1). The collision of India and Kohistan is commonly considered to have occurred in the Eocene (Molnar and Tapponnier, 1975; Tahirkheli et al.,
1979; Patriet and Achache, 1984; Klootwijk et al., 1985; Coward et al., 1986, 1987). However, other worker (Stocklin,
1977; Raina et al., 1980; Brookfield and Reynolds, 1981; 23
Figure 3.1. Tectonic map of the northwest Himalaya, showing
Besham (Figure 3.2) and Tanakki study areas. Modified from
Wadia, 1931; Gansser, 1964; Latif, 1970; Calkins et al.,
1975; Tahirkheli and Jan, 1979; Seeber and Ariabruster, 1979; Kazmi and Rana, 1982; Madin, 1986; Baig and Lawrence, 1987;
Verplanck, 1987; Bossart et al., 1988; Madin et al., 1989;
Pogue et al.(in prep.), and this study. Abbreviations are: Besham (B), NP syntaxis (Nanga-Parabat syntaxis), H-K syntaxis (Hazara-Kashmir syntaxis), Indus Kohistan seismic zone (IKSZ), Jhelum fault (JF), Panjal thrust (PT), Main boundary thrust (MBT), Puran fault (PF), and Thakot fault (TF). Ophiolite along Main Mantle thrust zone (black).
Sample locations for Figure 3.21 are:
1 87MB43 2 =D 3 =E
4 = Pak9
5 = PaklO
SN1= close to location 3. This Figure Chitra Iran Kohitan Island aii9it China Al-c Terrane
Pakistan (
India .4 ) Ladaich \ Island Art Figure \ Terrane 3-2
-o Main 04_-"I Swat
JKabui Ft Srinagar Peshawar "4- Jaiaiabad Basin 1 Basin 340 hybe Phawa Tannki r7 N ' 1 islamaba - MBT C -4
Plateau
- / r e' / N
'"''/s 0 50 100 1 I I \ kilometers 320 J [N I / I 70° E 72°E 74°E Figure 3.1. 25
Windley, 1983; Yeats and Hussian, 1987; Baig and Lawrence,
1987) have suggested that the initial Himalayan collision started as early as the Late Cretaceous and is continuing even today.
This Himalayan collision caused polyphase deformation and metamorphism in the Precambrian to Phanerozoic shelf and platform sediments of the Himalaya (Gansser, 1964, 1981; Martin et al., 1962; Calkins et al., 1975; Shams, 1969; Baig, 1980; Ghazanfar et al., 1983; Chaudhry et al., 1986; Ghazanfar and Chaudhry, 1986; Coward et al., 1986; Greco et al., 1989). 40Ar/39Ar dates of 40 to 4 Ma and fission track cooling ages of 30 to 5 Ma, indicate that Himalayan metamorphism and related post-metamorphic cooling affected most of the Himalayan rocks (Metha, 1980; Zeitler et al., 1982; Maluski and Matte, 1984; Snee in Rosenberg, 1985; Lawrence et al., 1985; Zeitler, 1985; Maluski et al., 1988;
Zeitler et al., 1989; Baig and Snee, 1989; Hubbard and Harrison, 1989). However, even within the collision zone, a pre-Himalayan intrusive history is preserved in plutonic rocks that have U/Pb zircon and Rb/Sr whole rock isochron dates ranging from approximately 2,500 to 450 Ma (Le Fort et al., 1980, 1983; Bhanot et al., 1979; Frank, 1977; Metha,
1977; Valdiya, 1983; Sharma, 1983; Zartman and Zeitler in
Baig et al., 1988; Zeitler et al., 1989). Earlier workers who suspected at least one pre-
Himalayan deformation and metamorphism presented geologic 26
and petrographic evidence to support their contentions
(Kumar et al., 1978; Bhargava, 1980; Jam et al., 1980,
Saxena, 1980; Kazmi et al., 1984; Baig and Lawrence, 1987; Baig et al., 1988; LaFortune, 1988; Williams et al., 1988; Pognante and Lombardo, 1989). Despite the Rb/Sr and U/Pb dates mentioned above, there has been no conclusive
40Ar/39Ar geochronologic evidence for the pre-Himalayan metamorphic events, and it has been difficult to conclusively demonstrate the existence of the pre-Himalayan metamorphic overprints through the high-grade pervasive Himalayan metamorphism and deformation. No thermochronologic
study within, or adjacent to, the Himalayan collision zone, conclusively demonstrates that the Himalayan collision records a lengthy pre-Himalayan metamorphic and deformational history. The contribution of this paper is to present new field,
structural, metamorphic, and 40Ar/39Ar thermochronologic data that document an extended and complicated pre-Hinialayan
and Himalayan tectonic history in the rocks of the Indian plate south of the MMT in Swat, Besham, Allai-Kohistan, and Hazara areas. Samples from these rocks preserve evidence for
Early Proterozoic to Early Cambrian, Cambro-Ordovician, Late Carboniferous, Early Permian, Late Jurassic, and Cretaceous to Cenozoic tectonic events. Thus, the evidence for pre-
Himalayan tectonic events in the northwest Himalaya of Pakistan was not completely obliterated during Himalayan 27
deformation and metamorphism. In addition, this study
reveals that, in the northwest Himalaya of Pakistan, between
the Late Cretaceous and the Early Paleocene, the Indo- Pakistan plate collided with the Kohistan island arc, and
initiated the Himalayan foreland fold-and--thrust belt. These
data are in direct conflict with most of tectonic models for
the origin of Himalaya in northwest Pakistan.
TECTONIC SETTING
In northwest Pakistan, the Himalayan mountain belt makes a major bend in structural trends from northwest to
northeast. This change is partially accomplished by a series of syntaxes, sharp bends in mapped structural trends that are convex into the orogenic belt, such as the Hazara- Kashmir syntaxis (Wadia, 1931; Gansser, 1964; Calkins et al., 1975; Bossart et al., 1988) and the Nanga-Parbat syntaxis (Wadia, 1933; Tahirkheli and Jan, 1979; Coward et al., 1982, 1987; Verplanck et al., 1985; Verplanck, 1987; Madin, 1986; Madin et al., 1989). Along the Indus River, in Allai and Swat Kohistan, the structural trend of the Himalayan thrusts makes a bend from
northwest to northeast around the Beshant block forming a
feature herein called the Indus syntaxis (Figures 3.1 and 3.2). Himalayan thrust sheets of the Mansehra and Swat blocks and the Neotethys terrane are bent against the 28
Figure 3.2. Geologic and tectonic map of the Indus syntaxis,
Beshain area, Pakistan. Box showing location for Figure 3.3. For abbreviated fault names see Figure 3.3. The black lenses along faults are Neotethys terrane rocks. This map is based on detailed and reconnaissance mapping by Mirza Shahid Baig during 1986-1987, on 1:50,000 scale toposheets 43B/13,
43B19, 43B/10, 43A/12, 43A116and43F11,and 1:40,000 scale areal photographs and satellite imagery. East of Alpurai and Puran, the geology is modified after Martin et al., (1962),
Kazini et al., (1984), DiPietro (1990), and reconnaissance work by Baig. Age Rock Units of the Lfl(IUS SyntaXis Terrane
1Kohistan Er,cerre uItirrei tsland Arc flue Ct rut Neethys
flue, All urrrr,, Alluurrrru
Thkot I/Ivor1 ' bf I M A N S E1jR A s,'w -r BESiHA-M / -- BLOCK Late rCrpIC. fireboat, I2I Middle to' Prcteroroie t / / o I L. Block Swat Besham Mansehra \ \ kilometers 723O \ \ \73E ii \ Figure 3.2. 30 north-trending pre-Himalayan and Himalayan structures of the Besham block in a north-plunging antiformal structure. The Indus syntaxis is a Precambrian basement cored syntaxis similar to the Nanga-Parbat syntaxis. In contrast, the Hazara-Kashinir syntaxis differs from the Indus and Nanga- Parbat syntaxes by having Tertiary Murree molasse in the core (Baig et al., in prep.). A northwest-trending zone of seisinicityextending west of the Hazara-Kashmir syntaxis is called the Indus Kohistan seismic zone (IKSZ; Seeber and Jacob, 1977; Seeber and Armbruster, 1979). The IKSZ extends into the Pattan area (Seeber and Jacob, 1977; Seeber and Arinbruster, 1979), parallel to the eastern limb of the Indus syntaxis (Figure 3.1). It may be related to a subsurface right-lateral blind thrust north of Mansehra (Seeber and Jacob, 1977; Seeber and Armbruster, 1979). However, no active fault related to the IKSZ has been previously mapped. A series of newly recognized north-trending right-lateral thrust and oblique- slip faults are present along the eastern limb of the Indus syntaxis (Figures 3.2 and 3.3). Some of these faults offset the Neotethys terrane and have evidence for neotectonic activity. Newly recognized Quaternary Indus River terraces that lie 2120 meters above the present Indus River level (520 meters above sea level), emplacement of sheared metasediments of the Tanawal Formation on the Indus River gravels by the reverse Piplai fault (PPF), and the presence 31 of a knick point in Allai Khwar (valley) at the right- lateral Chail Sar thrust (CST)(Figures 3.2 and 3.3), collectively show that the Indus syntaxis is an active feature (Baig, in prep.). The Neotethys terrane is offset by the out-of-sequence CST 14 km to the south (Figures 3.2 and
3.3). The CST along the eastern limb of the Indus syntaxis is the previously unrecognized surface rupture of IKSZ in
Allai-Kohistan (Figures 3.1 and 3.2). Other syntaxes of northern Pakistan also have active boundary faults. The Jhelum fault (JF) on the western limb of the Hazara-Kashmir syntaxis (Baig and Lawrence, 1987) and the CST on the eastern limb of the Indus syntaxis, form the active left-lateral and right-lateral ramps respectively
(Baig, in prep.). North of the Hazara-Kashmir syntaxis (Figure 3.1), the Nanga-Parabat syntaxis is bounded to the east by the active (?) Stak fault (Verplanck et al., 1985;
Verplanck, 1987) and to the west by the active Raikot fault
(Lawrence and Ghauri, 1983; Madin, 1986; Madin et al., 1989). The presence of active faults along the limbs of these syntaxes, indicate that their recent development is controlled by active ramp faults (Baig, in prep.).
In the Indus syntaxis, the Himalayan collision zone is composed of three fault-bounded tectonostratigraphic terranes (Figure 3.2):(1) the Gondwana terrane,(2) the Neotethys terrane, and (3) the Kohistan island arc terrane. These terranes record different stratigraphic, plutonic, 32 structural, and metamorphic histories reflecting their origins in significantly different tectonic and geographic settings.
The Gondwana terrane is mainly composed of rocks of the Indo-Pakistan subcontinent that were deposited prior to and during the Carboniferous-Triassic beakup of Gondwana. The Gondwana terrane is further subdivided from west to east into the Swat, Besham, and Mansehra blocks, which are separated by major faults, the Puran and Thakot faults (Figure 3.2), and have different Himalayan tectonic histories. This study reveals that the Late Archean (?) metasedimentary rocks of the Besham block record an Early Proterozoic to Cenozoic history of metamorphism, deformation, and plutonism which is preserved both geologically and thermochronologically. In contrast, the Paleozoic to Mesozoic shelf and platform sediments of the
Swat and Mansehra blocks record deformation and metamorphism mainly related to the Himalayan collision. In addition, Late
Proterozoic to Early Cambrian and Cambro-Ordovician pre- Himalayan tectonic events predated the intrusion of Late
Carboniferous alkaline rocks (Le Bas et al., 1987), Airibela granite (Rafiq, 1987), Late Carboniferous sodic granites, and Early Permian mafic Panjal volcanism in the Gondwana terrane.
The Neotethys terrane is a complex of dismembered ophiolite, greenschist, blueschist, phyllite, zeolite-grade 33 metasediinentary rocks, inetavolcanics, and limestone blocks that form the Indus suture zone between the Gondwana and Kohistan Island arc terranes (Figure 3.2). It is equivalent to the Indus-Tsangpo suture zone of Ladakh east of the Nanga-Parbat syntaxis (Tahirkheli et al., 1979; Gansser, 1979). Herein, the north and south bounding faults of the
Neotethys terrane are referred to as the Main Mantle thrust
and the Kishora thrust respectively. The thrusts between the Main Mantle thrust (NNT) and the Kishora thrust (KT)
constitute the Main Mantle thrust zone (MMTZ).
The Kohistan island arc terrane is composed of abundant igneous and metaigneous rocks, and less common metasedimentary rocks of island arc affinity (Tahirkheli et al., 1979; Majid and Paracha, 1980; Bard, 1983; Pudsey et al., 1985; Coward et al., 1987; Jan, 1988). These were formed along the southern margin of the developing Asian continent during the late Mesozoic (Tahirkheli et al., 1979; Pudsey et al., 1985; Coward et al., 1987). In the study area (Figures 3.1 and 3.2), the Kohistan island arc terrane is mainly composed of complexly deformed and intruded amphibolites locally structurally underlain by garnet granulites and ultramafic rocks of the Jijal complex (Jan,
1979; Jan and Howie, 1981). The Jijal ultramafics are bounded to the east by the
Besham fault (BF) and to the west by the Chakesar fault zone
(CFZ) and do not extend into Allai and Swat Kohistan. The 34
Jijal ultramafics are not part of the ophiolitic melange of the Neotethys terrane. They are generally considered to be
the base of the Kohistan island arc terrane (Jan, 1979;
Tahirkheli et al., 1979; Jan and Howie, 1981; Coward et al.,
1987)
NONENCLATURE USED
This study involves 4 areas with different structural histories, and I have adopted several conventions to refer
to structures and events from different blocks of the Indus syntaxis (Table 3.1). I have used the conventional symbols S, N, and F of metamorphic structural analysis for S-planes,
metamorphic recrystallization events, and fold sets respectively. Each symbol is composed as follows:
XAi where "X" relates to S, N, and F and "A" refers to the area and block and "i" is a number referring to the sequence of feature or event. The area symbols are: Swat Block (S),
Ainbela area, Swat block (P), Attock hills west of Indus river (A), Karora group, Besham block (K), Besham basement complex, Besham block (B), Allai-Kohistan area, Mansehra block (N), Hazara Formation, Abbottabad area (H). The term penetrative fabric is used for penetrative deformation and
spaced fabric for less penetrative deformation. ThusSB2 refers to the second S-plane fabric developed in the Besham basement complex of the Besham block. 35
Deformation and metamorphism occurred variously in the different blocks. A tentative correlation of these events to provide an overall regional history is presented in the event column of table 3.1, D1 to Dxi. This deformation chronology works very well for the pre-Himalayan history where correlation between blocks is not a problem because the events occurred only in one block or they can be matched with other blocks. Correlation within the Himalayan events is less clear largely because more detail is known, smaller chronologic interval is possible, and the rocks have been moved relative to one another during Himalayan thrust motion. Correlation of events is not always clear between blocks which had different thermochronologic and fabric histories. Caution in using these correlations, Dvii to is essential.
BESHAM BLOCK
Along the Indus River in the Besham area of northern Pakistan an assemblage of rocks is exposed south of the
Neotethys terrane which is unlike units found elsewhere in the Gondwana terrane of Swat and Mansehra (Figure 3.2). These rocks are herein called the Besham block. This block is bounded by high-angle oblique-slip north-trending faults
(Baig and Lawrence, 1987; Baig and Snee, 1989; Baig et al.,
1989), the right-lateral Thakot fault to the east and the 36
Table 3.1. Pre-Hiivalayan and Himalayan fabric relation near the Indus syntaxis.
INFERRED FABRIC RELATIONS NEAR THE INDUS SYNTAXIS EVENT SWAT BLOCK BESHAM BLOCK MANSHERA KARORA GROUP BESHAM COMPLEX BLOCK Himalayan Fabrics Fss Fx4 - FB6 Dx, Development of lndus Development of lrrdus syntaxis; Development of Indus syritaxis; Development of Indus syntaxis; syntaxis; shear fabrics only; shear fabrics only; NS shear shear fabrics only; NS shear shear fabrics only; NS shear NS shear zones; W flank of zones; NS-trending, N plunging, zones; NS-trending, N plunging, zones; thrust faults folded ; E syntaxial structure upriqht folds upright folds flank of syntaxial structure S4 SK3 SM4 Dx Crenulation cleavage; EW- Crenulationcleavage; EW- Crenulationcleavage; EW- trending,S-ver gent folds; trending, south-vergent open trending open folds; S-directed main episode of S-directed folds; south directed thrusts; thrust faults; static retrograde thrusts;staticretrograde Babai thrust overprint overprint 5K2 Crenulation cleavage; NS- Main phytlitic to fine schistose MB$ trendinguprightto west- foliation; DIX NS-trending, open, No cleavage; retrogradechlorite overturned folds; greenschist upright folds; W dips West of and biotite; static overgrowth of facies Besham fault, E dips east of biotite on uctinolite rims S2 fault; lower gre055chist fames Dv,,, Main schistose fabric: NNW- trending W-vergent recumbent folds: WSW-directed thrusts(?); arnphibolae facies Sp2 Secondary cleavage in Panj Fir Formation near Ambela; low qreerrschist fames s1 SM3 D vu Fabric within porphyroblasts Spaced fabric; may correlate only in Swat may correlate with S51; greenschist facies with SM3; greenuchist fades <------?------?------> Spi Phyllitic cleavage in Panj Fir Formation near Ambela; low qreenschist facies Pre-Himalayan Fabrics
DV, Rift Deformation No fabrics developed
SM2 Dv Main shistose fabric in Tanawal Formation; amphibolile facies SAl SKi SB4 SM1 Slateycleavage in Manki Fm Intrafolial foliation; folds rotated Spaced foliation; tower Fabricwithin porphyroblasts and D IV nearly parallel to F folds; lower greenschist faciesconditions; intrafolial told noses in Tanawal greenschist fades actinolite rims grow on Formation: formed under hornblendes greenschist facies f?) conditions SN1 Slatey cleavage in Manki & Hazura Fms.
3 D Spaced foliation formed under epidoteamphibolitefacies conditions: NS trending, tight to isolinal folds 5B2 Main gnieasic and schistose D foliationformed under upper amphibolite facies conditions; NS striking, steeply dipping; small- scale, tight to isoclinal folds 5B1 DL Intrafolial fabric; associated with sheath folds and microlithons; upper amohibolitel') facies 37 left-lateral Puran fault to the west. These faults dip steeply away from the Besham block, so the Swat and Mansehra rocks are in their hanging walls, and converge south of the study area so that the Besham block is exposed as a tectonic window (Figure 3.1). Along most of its northern margin the Besham block is directly juxtaposed against Kohistan island arc terrane rocks. Internally, the Besham block is broken by additional north-trending, steeply dipping faults, the Chakesar fault zone, Pir Sar fault, Besham fault, Farid Garhi fault, Pazang fault, Mamdin Sar fault, and Sakergah fault zone, many of which include slivers and slices of mafic and ultramafic rocks similar to rocks of the Neotethys terrane. Several of these faults significantly offset the Kishora and Main Mantle thrust of the suture zone.
(1). Besham block stratigraphy
The Beshaiu block consists of metasedilnentary and metaigneous rocks of the Besham basement complex which is unconformably overlairi by marine inetasedimentary rocks of the I (a). Beshain group The Besham group has not been separately mapped in most of the Besham block because psaminitic sedimentary rocks and granites are intimately mixed in migmatitic masses that are a single mappable unit, the Besham basement complex. The most abundant material of psainmitic sedimentary origin is now mediuin-grained quartzo-feldspathic gneiss intruded by amphibolites, granite gneisses, leucogranites, and pegmatites. Locally, lenses of graphitic schist, mica schist, and marble are present. Along the eastern margin of the study area (Figure 3.3) more metasediinentary rocks are 39 Figure 3.3. Geologic map of the Beshani and Allai-Kohistan areas of the Indus syntaxis. For location of this Figure see Figure 3.2. Abbreviations are: Main Mantle thrust (MMT), Alpurai fault (AF), Makhad thrust (MT), Karshat fault (KRF), Chakesar fault zone (CFZ), Pir Sar fault (PSF), Babai thrust (BT), Babai klippe (BK), Besham fault (BF), Farid Garhi fault (FGF), Pazang fault (PF), Mantdin Sar fault (MSF), Sakergah fault zone (SFZ), Piplai fault (PLF), Sherghar Sar thrust (SGT), Chail Sar thrust (CST), and Rashang fault (RF). The gneissic fabric of the Besham basement complex is truncated by the basal Ainlo conglomerate of the Karora group. The Early to Middle Proterozoic granites and granite gneisses of the Besham basement complex do not intrude the rocks of the Mansehra block, Swat block, Neotethys terrane, and the Kohistan island arc terrane. For legend of the Mansehra block, Swat block, Neotethys terrane, and Kohistan island arc terrane see Figure 3.2. ROCK UNITS OF THE BESHAM BLOCK 40 ALLUVIUM Clays, siltssands, cobbles, pebbles, & boulders ofindus river & ifs tributaries. OUATERNARY derived fromthe Kohistanisland arc terrace,Neotethys terrane. Mansehra block Besham block.& Swat block SUTURE ROCKS talc-carbonate, JURASSIC 0.25-10 m thicklensesofperidotite,serpentinite.pyroxenite,talc, CRETACEOUS meta-gabbro, amphibolite, banded chert, greenschist. & btueschist along faults. POST-KARORA GROUP SODIC GRANITES 'n fl\\O Undeformed to weakly deformed,fine-to medium-grained. equigranular. leucocratic muscovite & biotite-bearing granites, containing rare tourmaline & xenolitflS of Karora PALEOZOIC /1 group & Besham basement complex & amphibolites Intruded by tourmaline-rich . pegmatites Dated bodies shown by KARAt BIOTITE GRANITE (>272 Ma) open triangle & KARORA BIOTITE GRANITE (>493 Ma) solid triangle. KARORA GROUP Undifferentiated Karora group (KG) C.) 0 r' r KANDOANA FORMATION: Low-grade dolomitic limestone & sandy dolomite with minor N layers of quartzite, & graphitic phyllite. 0 KURMANG FORMATION: Mainll graphific phyltite with interbedded psammitic layers uJw Metasandstonenear baseMinor bandedtomassivequartzite.intratormational 00 conglomerate. & calc.pelite present.Abundant quartz veining AMLO CONGLOMERATE: Angulartorounded, boulders, cobbles. & pebbles of SI metasedimentary & metaigneous rocks of the Besham basement complex. in a phyllific to schistose clast-supportedmatrix BASEMENT COMPLEX www Undifferentiated basement complex (BC) INTRUSIVE ROCKS /_y_ .JABRAI GRANITE GNEISS: Medium-tocoarse-grained. equigranular.massiveto foliated, hornblende, & biotite-bearing granite 9neiss (betweenf .887 andf .950 Ma) Includesxenolifhs & screensof Besham group. Lahor sodicgranitegneiss. & amphibolitex.Intruded by amphibolife dikes LAHOR SODIC GRANITE GNEISS: Fine- to medium-grained, equigranular. massive to + + foliated, biotife-bearing granite gneiss with rare tourmaline (>2.03t Ma metamorphism). + Contains screens & senoliths of the Besham group & amphibotifes Intruded bysilts & + dikes of middle Proterozoic graphic, tourmatine-muscovite sodic granites (too small to map) & amphibolite dikes. DARWAZA SAR POTASSIC GRANITE GNEISS: Medium- to coarse-grained. foliated, biotite granite gneiss (>2,031 Mx metamorphism) Intruded by blue-gray pegroatites of the Lahor sodic granite gneiss BESHAM GROUP Ail intruded by amphibohtes, sodic & potassic granites, & associated pegmatites PAZANG FORMATION: Mainlyfremolite-& diopside-bearingmarbles,banded quartzites, 4 psammitic gneissesMinor talc schist, actinoliteschist. graphitic schist & gneiss. & metapyroxenhte withstratitormPb/Zn mineralization Locally contains magnesife & barite THAKOT FORMATION: Mainly quartzo-feldspathic gneiss with minor graphiticpeliuc, & albitic schists & gneisses Obitqu.-stlp f.utts.dashed where SB Screens of Besham group _.. approximate, dotted where concealed. XL Xenotith of Lahor sodic granite bar and bati on downthrown block. gneiss arrows show strike-slip motion XA Xenolifh of amphibolite Normal fault, dashed where approximate, G Glaucophane-bearing bar and batl on downthrown block blueschist -.4-. Thrust tautts. dashed where approximate SlitSitlimanhte/Fibroihte teeth on upper plate Ky Kyaniie Contacts, dashed where approximate. Gt Garnet dotted where concealed Cht Chlorite GradatIonal contacts, approximate B Sante T Tourmaline granite gnelss (Tertiary) Uncorrsolldatsdcontacts, approximate. SB2/SB3 gn.lsslc fabrIcof Bestram basement complex SK2 phyttlttcto schlstose fabric of Karora group FK2 synform, arrow shows direction of plunge FK2 antitorm, arrow shows direction of plunge Mafic dlkas and slits (Early Perman to late Jurassic) Figure 3.3. 41 72 4 5 73OO M T / liiii / /1_ \ liii P - Zr I ThL!LioJ& JJP q'/ / -:i // 35 G 0Shn-Karner g --- - oo 35 oo \Cc / XA 52Orn- 34 34 45 45 73OO Figure 3.3 continued. 42 present. The metasedixnents are relatively more abundant than the intrusive rocks in the Besham basement complex. In the areas of best preserved and non-migmatized inetasediments of the Beshain basement complex, the Besham group is further subdivided into the Thakot and Pazang formations (Figure 3.3). The Thakot formation is the oldest unit of the Besham group. It is dominantly composed of quartzo-feldspathic gneisses and also includes albite gneiss, graphitic schist and gneiss, and minor calcareous and pelitic schists. It grades into the overlying Pazang formation. The Pazang formation consists of psaminite, caic-pelite, banded quartzite, and tremolite-diopside-bearing marbles. Locally, the Pazang formation contains Pb/Zn skarn (Ashraf et al., 1980; Chaudhry et al., 1983; Butt, 1983) and stratiforin Pb/Zn mineralization (Fletcher et al., 1986), graphite- actinolite schist, barite, ivagnesite (M. N. Chaudhry, verbal communication, 1987), and inetapyroxenitic komatiitic flows. In skarn zones, clinopyroxene, diopside, garnet, magnetite, forsterite, sphalerite, galena, molybdenite, pyrrhotite, and pyrite are well developed (Ashraf et al., 1980; Butt, 1983; Chaudhry et al., 1983; and Fletcher et al., 1986). Metapyroxenites (Figure 3.4a), which are not within the skarn zones are herein interpreted as komatiite flows based on chemical composition and mineralogy. Mineralogically, these are composed of amphibole, epidote, biotite, quartz, and ± plagioclase. Komatiitic metapyroxenitic flows of the 43 Pazang formation alternate with banded quartz ites and psammites and show concordant field relationships with the country rocks. Komatiitic volcanic spinifex texture is not preserved probably due to later metamorphism and deformation. Komatiites are noncumulate ultramafic rocks which can be distinguished from common ultramafic rocks by (1) noncumulate lavas of high ultramafic compositions (2) volcanic spinifex texture,(3) high Si02,(4) low Fe/Mg ratio at a given Al203,(5) low Ti02 at a given Si02, (6) low alkali elements (K20 < 0.5 wt. % ),(7) high CaO/Al203 ratio (> 1), and (8) high MgO (12-30 wt. %)(Viljoen and Viljoen, 1969a and 1969b; Brooks and Hart, 1974; and Arndt et al., 1977). The major element chemistry (in weight percent) for one inetapyroxenite (87MB307) from the Besham area has been obtained (Analyst: U.S.G.S) and is as follows: Si02 55.0 % Al203 3.77 % FeOT 10.9 % MgO 15.94 % CaO 13.0 % Na20 0.56 % K20 0.24 % Ti02 0.25 % <0.05 % MnO 0.24 % Total 99.95 % 44 This analysis is appropriate for a pyroxene komatiite because of high Sb2 (55 wt. %), high MgO (15.94 wt. %), low K20 (0.24 wt. %), and high CaO/Al203 ratio (3.45). Komatiitic lava flows are known in the Precanibrian shields of India (Viswanathan, 1974), Australia (Williams, 1972), Africa (Bickle et al., 1975), and Canada (Arndt et al., 1977). They are characteristic of the Late Archean to Early Proterozoic rifts of the Precambrian shields. The geological setting of Besham group apparently resembles that of Late Archean to Early Proterozoic (2,500 to 2,000 Ma) Aravalli Supergroup of Rajastan, India (Heron, 1917, 1953; Murthy et al., 1980; Sen, 1983; Choudhary et al., 1984). (b). Intrusive rocks The Beshamn group of metasedirnentary rocks are intruded by two episodes of basic dikes and sills (now aniphibolites) and four episodes of granitic rocks. The magmatic nature of these rocks is documented by intrusive contact relationships with the country rocks and the presence of included xenoliths and mnetasedimentary screens (Figures 3.3 and 3.4). Locally, shearing has altered these contacts, and the intrusive field relationships are obliterated. The intrusive sequence from oldest to youngest as determined in the field and confirmed by isotopic dates discussed below is (1) mafic dikes and sills (Figure 3.4d),(2) Darwaza Sar potassic 45 biotite granite,(3) Lahor sodic granite (Figures 3.4b, 3.4c, and 3.4d),(4) Jabrai, Shang, and Dubair hornblende- biotite granites (Figures 3.4e and 3.4f),(5) inafic dikes, and (6) unnamed equigranular graphic muscovite-tourmaline- bearing sodic granites (Figure 3.4g). All except the muscovite-tourmaline-bearing sodic granites are now metamorphosed rocks. Only bodies large enough to show on the geologic map are named (Figure 3.3). The major (Appendix 3) and trace element chemistry (not included here) indicate that these potassic and sodic granites are not comagmatic in nature. The youngest equigranular graphic muscovite- tourmaline-bearing sodic granites intrude after metamorphism and deformation of the Besham basement complex (Figure 3.4g). The Pb/Zn skarn mineralization is associated with the intrusion of these granites and associated pegmatites (units 3,6, and post-Karora group granites) into the carbonates of the Pazang formation. These potassic and sodic granites of the Beshain basement complex and their associated pegmatites intrude neither the Karora group of the Besham block nor the Tanawal and Manglaur formations of the Mansehra and Swat blocks (Figures 3.2 and 3.3). In addition, Himalayan tourmaline granites and two-mica porphyritic granites of the Swat block (Martin et al., 1962; 46 Figure 3.4. The magmatic history of the Besham basement complex. The metapyroxenite of the Besham group. These metapyroxenites predated the intrusion of mafic dikes, Darwaza Sar potassic granite, and Lahor sodic granite. Lahor sodic granite gneiss intrudes the metasediments of the Besham group. These relations show that the Lahor granite is younger than the Besham group. (C). Xenoliths of the Thakot formation of the Besham group in the Lahor sodic granite gneiss. These xenoliths and apophyses of the granite into one xenolith confirm the magmatic origin for the body. Apophyses of the Lahor sodic granite gneiss intrude the amphibolite of the Besham basement complex. It indicate that the mafic activity predated the Lahor granite. Sharp intrusive contact of the hornblende-biotite granite gneiss with the Lahor sodic granite gneiss. Hornblende-biotite granite has a xenolith of Lahor granite in the left top corner of photograph. These relations indicate that the hornblende-biotite granite is younger than the Lahor granite. Dubair hornblende-biotite granite gneiss with a xenolith of the Lahor granite gneiss and associated pegmatite. This shows that the Lahor granite and pegmatite are older than the Dubair granite. 47 The Middle Proterozoic graphic equigranular tourmaline-muscovite sodic granite intrudes the metasedixnents of the Besham basement complex, arid postdates the gneissic fabric of the Besham basement complex to be pre-Middle Proterozoic in age. The very weakly to undeformed equigranular Karora sodic granite is intruded by a tourmaline pegmatite (87MB47A) Photomicrograph of the tourmaline pegmatite (87MB47A), showing a magmatic texture. Orthoclase from pegmatite yields a 40Ar/39Ar date of 493 ± 1 Ma. Magnification - lox; crossed nicols; 1.3 mm field of view. The very weakly to undeformed equigranular Karai sodic granite (>272 ± 1 Ma) intrudes the quartzo-feldspathic garnet-biotite gneisses of the Thakot formation, and shows sharp intrusive contact. The garnet to cordierite (?) horrifelses are developed along the hornfelses aureole. Note the gneissic xenoliths of the Thakot formation in the granite body along its contact. This indicates that the gneissic fabric of the Thakot formation predated the late Carboniferous intrusion of the Karai granite. 52 Figure 3.4 continued. 53 Chaudhry et al., 1974, 1976, 1984; KazTni et al., 1984; Lawrence et al., 1989) and Mansehra block are not found in the Besham block. These blocks were juxtaposed along the Thakot and Puran faults and have different magmatic histories. (C). Karora group The marine metaseditnents of the Karora group unconformably overlie the rocks of the Besham basement complex (Jan and Tahirkheli, 1969; Gansser, 1979; Ashraf et al., 1980; Coward et al., 1982; Butt, 1983; Fletcher et al., 1986; LaFortune, 1988; Baig and Lawrence, 1987; Baig et al., 1989; Baig and Snee, 1989). The Karora group of Fletcher et al.(1986) is herein divided into three informal formations: the basal Ainlo metaconglomerate, the Kurmang formation, and the uppermost Kandoana formation (Figure 3.3). The Amlo metaconglomerate overlies the Beshain basement complex on an angular unconformity (Figures 3.3 and 3.5) and is composed of clasts of 2 to 45 cm Besham basement complex. The transition from subareal conglomerate deposits to marine psammitic, pelitic, graphitic, and minor calcareous deposits occurs in the Kurmang formation. The metaconglomerate grades upward into metasandstone at the base of the Kurmang formation. The Kurmang formation consists of inetasandstone, graphitic-pelitic phyllite and schist, quartzite, minor 54 Figure 3.5. Field relation of Karora group and the Besham basement complex. For location of Figure 3.5 see Figure 3.3. Geological field sketch map, showing field relations of the Karora group and the Besham basement complex, about 4 km west of Besham along the Besham Mingora road (modified after Baig arid Lawrence, 1987). The thickness of units is approximate. Contact between the Karora group and the Besham basement complex is marked by an angular unconformity. The Early Proterozoic amphibolite and pegmatite do not intrude the overlying Karora group. The dashed lines in the Karora and Besham basement complex show the general trend of foliation. The gneissic foliation in the Besham basement complex is truncated by overlying Ainlo basal conglomerate of the Karora group. The gneissic metasediments of the Beshain basement complex are truncated by the Amlo basal conglomerate of the Karora group. Note cobbles, pebbles, and boulders of granites, granite gneisses, schists, psammitic gneisses, and amphibolites of Besham basement complex in the basal conglomerate. 55 (a) Graphitic phyilite Amlo conglomerate Angular unconformity 0 Pegmatite j- N --00 Amphibolite <00 CC Otzo-feldspathic J gneiss Gneissic fabric of Besham Group -;0 _._ Phyllitic fabnc of I. Karora Group BESHAM JG° APPROXIMATE SCALE (b). 0 meters 15 Fioure 3.5 56 layers and lenses of intraforinational conglomerate, and caic-pelite. It is conformably succeeded by dolomitic limestone, sandy dolomite, minor quartzite, and graphitic phyllite of the Kandoana formation. The Karora group lithologically and stratigraphyically correlates with rock units in the following areas: Ganaghar Range (Riaz, 1990; Hylland, 1990), Attock Hills (Tahirkheli, 1970; Yeats and Hussain, 1987), eastern Peshawar basin (Calkins et al., 1975), Hazara (Latif, 1970, 1974; Calkins et al., 1975; Baig and Lawrence, 1987; Baig et al., 1988), and Kashmir (Ashraf et al., 1983; Baig and Lawrence, 1987). The Kurmang formation of the Karora group on the basis of lithology and stratigraphy is herein correlated with the Manki formation (Tahirkheli, 1970; Yeats and Hussian, 1987), Gandaf formation (Pogue in prep.), Dakhner formation (Yeats and Hussian, 1987; Riaz, 1990; Hylland, 1990), Hazara Formation (Latif, 1970, 1974; Calkins et al., 1975; Baig and Lawrence, 1987; Baig et al., 1988), Landikotal Formation (Shah, 1977), Dogra formation (Ashraf et al., 1983; Baig and Lawrence, 1987), Sixnla Formation, and other related units in the northwest Himalaya (Baig and Lawrence, 1987). The Kandoana formation correlates on the basis of lithology and stratigraphy with Shahkot formation of Tahirkheli (1970), Yeats and Hussian (1987), Riaz (1990), and Hylland (1990) in Gandghar and Attock Cherat Ranges. In Hazara/Attock/Besham area, Hazara and Dakhner formations, sandyturbidites on the 57 south, Manki formation, slaty turbidites in the middle, and Kurmang and Gandaf formations, graphitic phyllites and schists, in the north, are interpreted as change in shallow water sedimentation in the south to deep water sedimentation in the north. The Aznlo conglomerate is the first known exposure at the base of this widespread unit in the northwest Himalaya of Pakistan. These units represent Proterozoic flysch related to the early phases of the Hazaran orogeny (Baig and Lawrence, 1987). The rock units equivalent to the Tanawal (Tanol) Formation or Manglaur formation, and their unconforinably overlying Paleozoic to Mesozoic sequence are not present above the Karora group (Figures 3.2 and 3.3). Three alternative explanations can be proposed.(1) These units were eroded from the top of the Karora group during pre-Himalayan uplift of the Besham horst block along pre-Himalayan Thakot and Puran faults as a result of Carboniferous-Triassic rift related normal faulting. Possible buried (?) rift-related extensional faults have also been inferred in Swat and Peshawar basin (Pogue et al., in prep.). This explanation implies that the Besham block was established as a unique tectonic element early and has persisted through Himalayan metamorphism and deformation. (2) The sequence was present on the top of Karora group and has been eroded during post-Himalayan thrusting and uplift which exposed the Besham block as a tectonic window. This 58 explanation seems unlikely since these units are entirely absent under the MMT Jijal section.(3) These rocks were previously on the top of the Besham horst block and were tectonically scraped off during Himalayan thrusting. This explanation :Lmplies that the Besham block developed very late during the development of the hinterland of the Himalayan thrust system. (d). Post-Karora group sodic granites and inafic dikes and sills Both the Besham basement complex and the Karora group of rocks were intruded by sodic leucocratic, equigranular, tourmaline-and muscovite-bearing biotite granites (Figures 3.3 and 3.4j) and pegmatites. These granites are weakly deformed to undeformed with no pervasive fabric development. They produced a contact metamorphic aureole in the country rocks. At places hornfelses of actinolite (Figure 3.6c), tremolite, diopside, wollastonite, cordierite (?), and garnet overprint the pre-Himalayan fabric in the inetasediments of the Besham block. However, where these granites and associated hornfelses are involved in the Himalayan shearing, they develop shear fabrics. In the vicinity of Besham, no mafic dikes and sills have been seen intruding the Karora group. However, in the south, rocks of the Karora group are intruded by 59 unmetamorphosed mafic dikes and sills of possible Panjal volcanics. (2). Beshain block deformation, metamorphism, and plutonism (a). Pre-Karora group sedimentation, plutonism, metamorphism, and deformation Until recently major deformation and metamorphism in the Besham block has been considered to be the result of Himalayan orogeny (Coward et al., 1982; Fletcher et al., 1986; LaFortune, 1988; Treloar et al., 1989a). Earlier workers did recognize the basal conglomerate and angular unconformity between the Karora group and the Besham basement complex (Tahirkheli and Jan, 1969; Gansser, 1979; Ashraf et al., 1980; Coward et al., 1982; Butt, 1983; La Fortune, 1988; Baig and Lawrence, 1987; Baig and Snee, 1989; Baig et al., 1989; Treloar et al., 1989a). At least one pre-Himalayan metamorphic event has recently been inferred on the basis of the basal conglomerate without any absolute time constrain (LaFortune, 1988; Baig and Lawrence, 1987; Williams et al., 1988; Treloar et al., l989a). 40Ar/39Ar dating of the Besham basement complex during this study confirms five metamorphic events. Present field, fabric, petrographic, and 40Ar/39Ar studies confirm three phases of pre-Karora group metamorphism (MB1, MB2, and MB3), fabric 60 Figure 3.6. Deformation, metamorphism, and plutonism in the Karora group. Multiply deformed graphitic phyllite of the Kurmang formation of the Karora group. Phyllite of the Kurmang formation preserves the reinanents of SKi fabric in the hinge of an intrafolial FK1 fold, which is strongly transposed parallel to SK2 fabric. Magnification - 4x; crossed nicols; 3.3 mm field of view. (C). The Ranial granite intrudes the metamorphic rocks of the Karora group and has a hornfelsic aureole. The actinolites of this aureole overprints the SK1 fabric of the Karora group. Magnification - 4x; crossed nicols; 3.3 mm field of view. F2 fold in the phyllite of the Kurmang formation. The earlier quartz vein of SK1 fabric is folded to form FK2 fold. The axial plane to FK2 fold defines SK2 penetrative fabric which angles about400down from the left. Magnification - 4x; crossed nicols; 3.3 mm field of view. FK3 crenulation folds in the phyllite of the Kurmang formation. The SK2 main fabric in the photograph is folded into crenulation folds, and a spaced crenulation cleavage SK3 is developed about parallel to axial planes of these broad folds. Magnification - lox; crossed nicols; 1.3 mm field of view. Carbonates of the Kandoana formation define strong lineations parallel to the handle of the hammer. 61 These lineations were formed during deformation along the Chakesar fault zone. (g). Carbonate of the Kandoana formation showing one strong mica fabric close to the Chakesar fault zone. The earlier mica fabrics of the Karora group are completely obliterated and new mica fabric is formed. Muscovite from new mica fabric yields a 40Ar/39Ar date of 36 Ma (87MB4). Magnification - 4x; crossed nicols; 33 mm field of view. c) 0 j I 1) LU 66 development (SE1, SB2, and SB3), and folding (FBi, FB2, and FB3) in the Besham basement complex (Table 3.1). Two additional phases (SB4 and MB5) formed after unconformable deposition of the Karora group. The post-Karora group lower greenschist facies metamorphism and deformation did not obliterate the evidence for pre-JIimalayan amphibolite fades metamorphism and deformation in the Besham basement complex (Baig and Lawrence, 1987; Baig and Snee, 1989; Baig et al., 1989) (i). Field evidence A complex history occurred before deposition of the basal Amlo metaconglomerate of the Karora group. This unit truncates the SB2/SB3 gneissic fabrics of the Besham basement complex (Figures 3.3 and 3.5). All lithologies of metasedimentary, metaigneous, and igneous rocks of the Besham basement complex are present, in the Amlo basal metaconglomerate (Figures 3.5b and 3.7a). The metapyroxenite, sodic and potassic granite gneisses, hornblende-biotite granite gneisses (Figure 3.3), amphibolites (Figure 3.5a), and graphic muscovite- tourmaline-bearing sodic granites of the Besham basement complex do not intrude the Karora group. All of this confirms that the sedimentation, metamorphism, and plutonism 67 of the Besham basement complex occurred before the deposition of the Karora group. There is a major change in metamorphic grade across the Karora unconformity. The rocks above the unconformity have phyllitic to schistose fabric (Figures 3.6a, 3.6b, 3.6d, and 3.6e) formed during lower greenschist facies metamorphism (chlorite to biotite zone). Those below the unconformity have gneissic fabrics formed during epidote amphibolite to upper amphibolite facies metamorphism (garnet to sillimanite zone). Gneissic clasts of the Amlo conglomerate have fabrics randomly oriented with respect to the systematic phyllite fabric of the matrix which indicates that the gneissic fabric formed before the deposition of the Karora group. Garnet, kyanite, fibrolite or sillimanite, and rare relict garnets with sillimanite inclusions (Figures 3.8c and 3.8d) are present in the Besham basement complex, and have not been observed in the Karora group (Figures 3.6b, 3.6d, and 3.6e). Thus, the garnet to sillimanite zone metamorphism below the unconformity is pre-Karora in age. At least three phases of folds FB1, FB2, and FB3 are recorded in the Besham basement complex (Figures 3.8a and 3.8e). The FBi folds are locally preserved as east-west- striking, east-plunging, and north-vergent asymmetric folds (Figure 38a). The axial planes (SB1) to these folds are south dipping. Where, strong SB2 penetrative deformation in the Besham basement complex occurred, the east-west-striking 68 Figure 3.7. Middle Proterozoic tourirnaline granite boulder. Field photograph showing a boulder of tourmaline- muscovite granite in phyllitic to schistose matrix of the basal Amlo conglomerate of the Karora group. Photomicrograph of graphic tourmaline-muscovite granite boulder, showing niagmatic texture. Magmatic muscovite (5JL059B; collected by R.J. LaFortune, 1986) from this boulder yields a date of 1517± 3 Ma. Magnification - 2x; crossed nicols; 6.7 mm field of view. 69 Figure 3.7. 70 FBi folds are rotated into north- or south-plunging intrafolial or sheath folds, parallel to SB2 penetrative gneissic fabric. The FB2 folds (Figure 3.8a) are north- northeast or north-northwest-striking, north- or south- plunging, east-southeast or west-southwest vergent, and tight to isoclinal. Their axial planes dip moderately to the east or west. The SB2 main penetrative gneissic fabric of the Besham basement complex is folded to form FE3 north- northeast or north-northwest-striking, north- or south- plunging, east-southeast or west-southwest vergent, recumbent, tight to isoclinal folds (Figure 3.8e). The axial planes dip moderately to steeply to the east or west. The axial planes to these folds define a regional spaced fabric in the Besham basement complex. Axial planes of FBi, FE2, and FE3 folds do not cross the Karora group unconformity, and confirm that these were formed before the deposition of the Karora group. (ii). Inferred history The three deformations (D1, D11, and and associated metamorphisins are separated by various depositional and igneous events (Tables 3.1 and 3.2) that help determine the sequence of events and provide the basis for controls on the40Ar/39Ar dating that is the main topic of this paper. The earliest event is deposition of the 71 Besham group sediments, including ultramaf ic flows. These were intruded, In order, by maf Ic dikes and sills, the Darwaza Sar potassic granite and Lahor sodic granite (Table 3.2). The earliest metamorphism and deformation (D1) occurred next (Tables 3.1 and 3.2). Evidence for this event is preserved as inclusions of sillimanite needles in uncommon MB2 garnet cores (Figures 3.8c and 3.8d) and the local preservation of FB1 intrafolial or sheath folds which preserve SB1 fabric (Figure 3.8b). This event probably reached the sillimanite zone of the upper ainphibolite facies. In most places it has been completely overprinted by 1B2 During D11, which followed D1 without any recognized intervening events (Tables 3.1 and 3.2), biotite, muscovite, garnet, rare kyanite, and fibrolite or sillimariite (in metasediments), and andesine to labradorite plagioclase and hornblende (in amphibolites), define the main regional penetrative gneissic fabric SB2 of the Besham basement complex. Kyanite and fibrolite or sillimanite are only locally developed in favorable lithologies. They are rare in the abundant psammitic and granitic rocks of the Besham basement complex. This mineral assemblage indicates that the MB2 metamorphism is of upper amphibolitefacies. Syn-or post-D11, the Jabrai, Shang, and Dubair hornblende-biotite 72 Figure 3.8. The folding, fabric, and metamorphic events in the Besham basement complex. Two sets of Early Proterozoic folds in the metasediments of the Besham basement complex. The earlier asymmetric FBi fold is east-trending, north-vergent, and gently east-plunging. It is refolded by recumbent to isoclinal north-trending, east-vergent, and moderately south-plunging FB2 fold. The pencil is parallel to the FE2 fold axis. North is to the right of photograph. Photomicrograph showing a hook of FBi sheath or intrafolial fold transposed parallel to the SB2 main penetrative fabric of the Besham metasediments. The hinge area of fold preserves the SB1 fabric. Magnification - 2x; crossed nicols; 6.7 nun field of view. (C). A relict MB2 garnet has inclusions of sillixnanite needles. The MB2 garnet is consumed by late MB3 biotite. Magnification - lox; crossed nicols; 1.3 nun field of view. A relict NB2 garnet, showing well developed sillimanite inclusions. Magnification - 40x; crossed nicols; 0.33 nun field of view. A FE3 north-striking, steeply west-dipping, east- verging, north-plunging tight to isoclinal fold in the metasediments of the Besham basement complex. Note that the FE3 fold deforms the main SB2 gneissic fabric of the Besham basement complex. View in photograph is slightly to the east of north. 73 Photomicrograph showing FB3 fold in the left top corner of photograph. The SB2 fabric is folded by FE3 fold. The axial planes to FE3 folds define the SB3 spaced fabric. Magnification - 2x; crossed nicols; 6.7 nun field of view. Photomicrograph of amphibolite of the Besham basement complex. Note that the hornblende defines the SB2 penetrative fabric oriented from the lower left to the upper right corner of the photograph, and that it is cut by SB3 spaced fabric oriented approximately in the plane of the photograph. Note light greenish areas around some of the hornblendes are reaction rims of actinolite, related to M34 lower greenschist facies metamorphism. Magnification - lox; crossed nicols; 1.3 mm field of view. The amphibolite of the Besham basement complex, showing MB3 generation hornblendes (Hb) and later MB4 actinolite rims (AR). Magnification - lox; crossed nicols; 1.3 mm field of view. (1). Photomicrograph showing two spaced fabrics in the quartz-muscovite-biotite-garnet schist. The S33 spaced fabric is oriented from the lower left to the upper right corners of the photograph while the weak SB4 spaced fabric is oriented from the lower right to the upper left corners of the photograph. Magnification - lox; crossed nicols; 1.3 mm field of view. (j). The hornblende-biotite granite, showing N33 generation hornblende surrounded by N34 actinolite rims. 74 Note that the MB5 static growth of biotite (Bt) MB4 actinolite rtms (AR) and MB3 hornblendes (Hb). Magnification - lOx; plan polarized light; 1.3 nun field of view. 75 (a) Figure 3.8. ci) 77 (e) - Figure 3.8 continued. 78 (g). (h).. Figure 3.8 continued. 79 (1) (j) Figure 3.8 continued. 80 granites and later inafic dikes intruded the Besham basement complex (Table 3.2). These were metamorphism and deformed during D111 (Tables 3.1 and 3.2). This metamorphism and related deformation produced the SB3 regional spaced fabric (Table 3.1) associated with FB3 folds in the rocks of the Besham basement complex (Figures 3.8e and 3.f). The MB3 epidote amphibolite facies metamorphism is defined by the development of chlorite, epidote, zoisite, biotite, and muscovite (in metasediment), oligoclase to andesine plagioclase and hornblende (in hornblende-biotite granites and amphibolites). The MB2 garnets are also partially consumed in pressure shadows by chlorite and biotite (Figure 3.8c) that developed during the MB3 metamorphism. D111 was followed by intrusion of equigranular graphic muscovite- tourmaline-bearing sodic granites (Table 3.2 and Figure 3.4g) and then uplift, erosion, and deposition of the Karora group. These pre-Karora group metamorphic, deformational (Table 3.1), and plutonic events (Figure 3.3 and Table 3.3) of the Besham basement complex are absent in the rocks of the Marisehra and Swat blocks. 81 (b). Post-Karora group plutonism, metamorphism, and deformation (i). Besham basement complex The Besham basement complex was metamorphosed after the deposition of the Karora group during Div (Tables 3.1 and 3.2). MB4 lower greenschist facies metamorphism and related SB4 spaced fabric is defined by weak development of muscovite (Figure 3.8i), chlorite, and epidote in more pelitic metasediments, and by actinolite rims around the MB2 and M generation hornblendes of amphibolites (Figures 3.8g and 3.8h) or by actinolite rims around the MB3 generation hornblendes of the hornblende-biotite granites (Figure 3.8j) of the Besham basement complex. MB5 (Table 3.1) is only preserved asstatic overgrowth of chlorite in biotites and hornblendes or as static overgrowth of biotite and epidote in actinolite rims of MB4 and MB3 hornblendes (Figure 3.8j) of the rocks of the Besham basement complex. In the Besham basement complex no fabric was developed during MBS. MBS may correlate with S3 and SK2 (Table 3.1). MB4 and MBS metamorphic events are poorly recorded in the quartzo-feldspathic gneisses and granite gneisses of the Besham basement complex and remain obscure events. 82 Table 3.2. Precambrian pre-Himalayari events in NW Pakistan. Notations used: Ar/Ar hornblende mineral isochron dates (Ar/Ar H Is), Ar/Ar hornblende dates (Ar/Ar H), Ar/Ar muscovite dates (Ar/Ar M), Rb/Sr whole rock isochron (Rb/Sr Is; recalculated from Davies and Crawford, 1971), Ar/Ar sericite date (Ar/Ar S), actinolite rim development around the hornblendes of the Besham amphibolites (AR), Beshain block (BS), Nansehra block (MN), and Swat block (SW). Roman numbers relate to deformation chronology of the Table 3.1. For Rb/Sr whole rock isochron data of Malani volcanicsnear Kirana Hills see Table 3.6. 83 Table 3.2. PRECAMBRAIW PRE-HIMALAYAN EVENTS IN NW PAKISTAN 00'ow HLU '- SEDIMENTATION IGNEOUS METAMORPHISM DATES ACTIVITY & DEFORMATION (Ma) 0 Div Greenschist facies Ar/Ar S. 650 ± 2 Malani volcanics in metamorphism forms Ar/ArM, 623 ± I Kirana Hills c- Mafic dikes (MN, SW) 0 o Psammitic Tanawal E and Manglaur o Formations (SW & MN) 0 LU 0° Erosion =>- Karora, Manki, Hazara, Dakhnar Fms. > (SW,BS,MN) 0 w Tourmaline-muscovite Ar/ArM, 1517 ± 3 o w sodic granites 0I Dni Epidote-amphibolite Ar/Ar H, 1865 ± 3 fades metamorphism Ar/Ar H, 1884 ± 3 forms spaced foliation Ar/Ar H, 1887 ± 5 (BS) Ar/ArHIs, 1883 130/-167 z Mafic dikes (BS) LU Horn blendo-biotjte 0 granites (Shang, Jabrai wI I- and Dubair plutons) I0 (BS) 0 Dii Upper amphibolite Ar/Ar H, 1950 ± 3 - I facies metamorphism Ar/Ar H Is, 1950 95/-i 13 LU forms main foliation (BS) Ar/Ar H Is, 1931 +751-88 Di Upper amphibolite Ar/Ar H, 1997± 8 metamorphism forms Ar/Ar H, 1998 ± 6 intrafolial foliation (BS) Ar/Ar H, 2031 ± 6 Ar/Ar, H Is, 2005 +53/-63 Potassic and sodic grariites (Darwaza Sar 0 and Lahor plutons) )BS) z Mafic dikes (DS) 0 Quar0o-feldspathic clastic sediments, minor carbonates, 1 0 & ultramafic (komat- Ui iltic) lava (BS) (Aravalli equivalent?) 84 (ii). Karora qrou The Karora group records three widespread phases of fabric development (SKi, SK2 and Sx3) which formed during lower greenschist facies metamorphism (chlorite to biotite zone) (Table 3.1). Where, the Himalayan shearing has affected the Karora group and Besham basement complex, all fabrics are strongly transposed. The SK1 fabric development, MK1 metamorphism, and Div deformation (Table 3.1) occurred after the unconformable deposition of the Karora group on the Besham basement complex. Remnants of SKi are preserved in sheath folds (FK1) and microlithons (Figure 3.6b), which are strongly transposed parallel to SK2 penetrative fabric. The FK1 small scale folds are rotated nearly parallel to north-northeast or north-northwest-striking FK2 folds. South of the Besham area, the Manki and Hazara formations which are correlative with the Kurmang formation of the Karora group have cleavages, 5A1 and SH1, developed prior to deposition of Cambrian rocks (Baig and Lawrence, 1987; Baig et al., 1988). SKi and SB4 are tentatively correlated with SH1 and SAl fabrics (Table 3.1). During Dv and Dvi, Paleozoic granites and maf Ic dikes intruded the Besham basement complex (Table 3.3 and Figures 3.4h and 3.4j) and Karora group. No fabric is associated with Dv and Dvi events in the Besham block (Table 3.1). The hornfelsic aureoles of these granites, overprint the earlier 85 Table 3.3. The Paleozoic and Mesozoic pre-Himalayan events in NW Pakistan. Notations used: Ar/Ar hornblende mineral isochron dates (Ar/Ar H IS), Ar/Ar hornblende dates (Ar/Ar H), Rb/Sr whole rock isochron (Rb/Sr IS), U/Pb zircon date (U/Pb Z), Ar/Ar biotite dates (Ar/Ar B), Ar/Ar potassium feldspar dates (Ar/Ar K), Ar/Ar whole rock basalt date (Ar/Ar WR), Besham block (BS) Mansehra block (MN), and Swat block (SW). Roman numbers relate to deformation chronology of the Table 3.1. Dates in parentheses are from previous workers (LeFort et al., 1980; Le Bas, 1987; Zartman in Lawrence et al., 1989; Zartman and Zeitler in Baig et al., 1988) Table 3.3. z o 0H PALEOZOIC AND MESOZOIC PRE-HIMALAYAN EVENTS IN NW PAKISTAN Fu:ow Cu- wro W SEDIMENTATION IGNEOUS METAMORPHISM DATES z ACTIVITY & DEFORMATION (Ma) 0 o Shelf sediments mainly carbonates 3 Mafic dikes (MN) Ar/Ar WR, 159 ± 0.42 (S W & MN) a probably not on BS Ar/Ar H Is, 284 ± 4 Mafic dikes (SW, MN, BS) Dvi Normal faults z Ar/Ar H, 268 ± 26 0 PanjaI traps (MN,SW) (SW, BS) wN< Ar/Ar B, 262 ± I Karai sodic granites (BS) Ar/Ar K,> 272 ± 1 a Ambela alkaline granites (SW) (Rb/Sr Is, 297 ± 4, 315 ± 15) Metamorphism (?) (BS) Ar/Ar B, 333 ± 1 o cc Cambrian to Carbor,i- NI 0 Ou.. ferous shelf sediments W H and Permian basalt -j u-a flows (SW) Dv Upper amphibolite Ar/Ar H,> 466 ± 2 facies metamorphism No Ar/Ar H Is, 464 ± 1 wzo > forms main foliation (MN) _J w a0 Mafic dikes (MN) >-cc Karora sodic granite (85) Ar/Ar K,> 493 ±1 W Mansehra granite (M (Rb/Sr IS, 516 ± 16) (U/Pb Z, 470, 500) 87 fabrics of the Besham basement complex and Karoragroup (Figure 3.6c), and thus established that the earlierBesham basement complex (Figure 3.4j) and Karoragroup (Figure 3.6c) fabrics are pre-Paleozoic in age.Dvii and Dviii are not present in the Besham basement complex (Table3.1). During the second recognizable deformation(Dix) of the Karora group (Table 3.1), north-northeastor north- northwest-striking, open and upright,FK2 folds developed, which are east-southeast vergent west of Besham faultand west-southwest vergent east of Besham fault (Figure 3.3). The SK2 deformation accompanied theMK2 lower greenschist fades metamorphism (chlorite to biotite zone). Earlyquartz veins of SK1 are folded to form theFK2 folds (Figure 3.6d). The axial planes to these folds define the main penetrative phyllitic to schistose fabric,SK2, of the Karora group (Figure 3.6d).5K2 probably correlates with the S3 and MBS fabric of the Swat block (Table 3.1). The later SK3 fabric and relatedDx deformation (Table 3.1) is marked by the crenulation cleavage related tomap scale east-west-striking and south-vergentopen folds. These folds are recognized by the change in plunge ofFK2 folds or by folding of Karora outcrops along east-westaxes on map scale (Figure 3.3). However, in outcropsFK3 is recorded by east-west-striking kink bands and crenulation folds. in thin sections, the SK2 fabric is folded into kink bandsor crenulation folds (Figure 3.6e), the axial planes of these 88 folds define SK3. Along the north-south trending faults and shear zones earlier fabrics of the Karora group are transposed (Figure 3.6g). SK3 correlates with the S54 and SM4 (Table 3.1). Evidence for south-directed thrusting in the Besham block is documented by the Babai thrust (BT), a klippe of Besham basement complex that lies tectonically on the top of Karora group (Figures 3.2 and 3.3). In addition, presence of mafic and ultraniafic slivers and lenses 30 km south of the present exposure of the Neotethys terrane, in north- trending faults and shear zones (black lenses; Figures 3.2 and 3.3), indicate that these are remanents of once overlying Neotethys melanges or Kohistan ultramafic rockson the top of Besham block. They were trapped in these faults and shear zones during the development of the Indus syntaxis. However, note that some of the mnafic and ultramafic rocks are directly related to the offset of the Neotethys terrane (Figures 3.2 and 3.3). The Babai thrust is probably coeval with the development of SK3. (iii). Recent deformation and Indus syntaxis During the Fs5, FR4, FB6, and FMS structural development of the Indus syntaxis occurred (Table 3.1). Overall the feature has the form of a north-plunging antiform with limbs largely controlled by steeply dipping, 89 north-striking faults and shear zones (Figures 3.2 and 3.3). New fabrics related to this structure are shear fabrics developed only within these shear zones and faults. These shear zone fabrics formed under lower greenschist to epidote aiuphibolite facies metamorphism. In the large oxbow bend of the Indus river in the Thakot area, terraces are extensive. These terraces contain clasts of all lithologies of the Beshain block and Kohistan island arc terrane indicate that they were deposited by the Indus River. North of Thakot they rise from 520 meters at river level to 2120 meters, recording very rapid downcutting by the river in this area. Nick points in side streams to the Indus River, as at the Chail Sar thrust on Allai Khwar, the Thakot fault on Nandinar Khwar, the Chakesar fault zone on Chakesar Khwar, and the Puran fault in Puran valley (Figures 3.2 and 3.3). These faults are important in the development of the Indus syntaxis and show that it is an active feature. The presence of all the lithologies of the Beshain block in Indus river terraces, show that it was exposed as an erosional/tectonic window through the overlying Himalayan thrust sheets, as a result of post-Himalayan thrusting, uplift and tectonic erosion, before the Quaternary deposition of Indus River terraces. The gradually uplifted Quaternary Indus River terraces from 520 meters to 2120 meters in the Indus syntaxis (Figure 90 3.3), indicate that these were rejuvenated during the Quaternary uplift of the Indus syntaxis. The 1600 meters uplifted Indus River terraces, active Piplai fault and Chail Sar thrust, nick points at the Chail Sar thrust, Chakesar fault zone, and Puran fault (Figures 3.2 and 3.3), and seismicity (IKSZ; Figure 3.1, Seeber and Armbuster, 1979) in the Indus syntaxis, show that it is a neotectortic feature. SWAT BLOCK (1). Mingora and Peshawar basin areas The Swat block extends west from the Indus syntaxis to the border of Afghanistan west of Malakand Pass. The most important prior studies were those of Martin et al.(1962), King (1964), Au (1962), Calkins et al. (1975), and Chaudhry et al. (1974, 1976, and 1984). These workers initially mapped different stratigraphic and granitic units of the Swat block. The shelf and platform sequence of the Swat block near Mingora and the Peshawar basin have been recently remapped (Kazmi et al., 1984; Rosenberg, 1985; Ahmad, 1986; Ahmad et al., 1987; DiPietro, 1990; Pogue et al., in prep.). In this region, the shelf and platform sequence iscomposed of Manglaur formation, of probable Late Proterozoic age, intruded by Late Cambrian to Early Ordovician (?) Swat granite gneiss. Low-grade shelf and platform sedimentary 91 rocks in the eastern Peshawar basin and the hills west and east of the Indus River (Au, 1962; Calkins et al., 1975; Pogue et al., in prep.) were intruded by Carboniferous alkaline rocks (with Rb/Sr whole rock ages of 315 ± 15 Ma to 297 ± 4 Ma; Le Bas et al., 1987), Ainbela granite (Rafiq, 1987), and probable basic dikes and sills of Panjal volcanics (Coulson, 1936, 1937; Baig and Lawrence, 1987). The Manglaur formation is in the center of a structural dome southeast of Mingora and south of Manglaur village (Kazini et al., 1984; Lawrence et al., 1989; and DiPietro, 1990). It is mainly composed of quartz-mica-garnet schist, quartz-mica-kyanite schist, quartzo-feldspathic schist, quartz ite, with minor layers of graphitic and hornblende schist, and calc-silicates (Kazmi et al., 1984; DiPietro, 1990) These units are unconformably overlain by the Alpurai group of Carboniferous to Triassic or younger age (Kazmi et al., 1984; Lawrence et al., 1989; DiPietro, 1990; Pogue et al., in prep.) which is intruded by Tertiary Himalayan syntectonic tourmaline granites and post-tectonic Malakand and related granites (Chaudhry et al., 1974, 1976, 1984; Lawrence et al., 1989). The Alpurai group of rocks are informally subdivided into the Marghazar, Kashala, Saidu, and Nikanai Ghar formations (DiPietro, 1990). The Marghazar formation is composed of psairtmitic schists, quartzo-feldspathic schists, 92 feldspathic quartzites, amphibolitic schist, amphibolites, calcite marbles, phiogopite-bearing marbles, pelitic schist, and rare graphitic schist (DiPietro, 1990). The Marghazar formation is lithologic equivalent to Jafar Kandao formation (DiPietro, 1990), which unconforinably overlies the Early to early Late Devonian Nowshera formation in the Peshawar basin (Pogue et al., in prep.). On the basis of conodonts, the Jafar Kandao formation ranges in age from Early Mississippian to Middle Pennsylvanian (Pogue et al., in perp.a). The Marghazar formation is overlain by an axnphibolite horizon in Swat (Martin et al., 1962; Rosenberg, 1985; Ahmad, 1986; Ahmad et al., 1987; DiPietro, 1990) and its stratigraphic equivalent Karapa greenschist (metamorphosed lava flows) is on the top of the Jafar Kandao formation in the Peshawar basin (Pogue et al., in prep.). The age of Karapa greenschist is broadly constrained from Middle Pennsylvanian to Late Triassic by underlying Early Mississippian to Middle Pennsylvanian Jafar Kandao formation and by overlying Late Triassic Kashala formation (Pogue et al., in prep.a). On the basis of geochemistry and field relations Ahmad (1986) suggested that the ainphibolite horizon in Swat is a metamorphosed tholeiitic basalt flow. The mafic sills and dikes intrude the Precambrian to Carboniferous rocks in the Peshawar basin, which are considered to be feeder dikes and sills to Karapa greenschist (Pogue et al., in prep.a). Pogue et al. (in 93 prep.a) suggested on the basis of the above relations and major and trace element chemistry that the amphibolite horizon of Swat and Peshawar basin correlate with the Panjal volcanics. However, no absolute dating of mafic dikes and sills has constrained the time of mafic Panjal volcanism in the Peshawar basin, Swat, and northwest Himalaya. The amphibolite horizon and Karapa greenschist are overlain by the Kashala formation (DiPietro, 1990; and Pogue et al., in prep.). The Kashala formation is composed of garnetiferous calc-schists, schistose marbles and pelitic schists, without amphibolites, psammitic schists, and quartzites (DiPietro, 1990). The low-grade marbles of Kashala formation in the Peshawar basin yielded Late Triassic conodonts (Pogue et al., in prep.). The Saidu formation is dominantly composed of gray to black phyllites and schists with minor layers and lenses of marbles and silty material (Kazmi et al., 1984; DiPietro, 1990). Locally, lenses of green phyllite and talc schist of the Indus suture zone are structurally inthricated within the Saidu formation below the Kishora thrust (Kazmi et al., 1984). The Nikanai Ghar formation is the youngest unit of the Alpurai group and is composed of massive marbles, dolomitic marbles, minor quartzite, calc-schist, and graphitic schist (Ahmad et al., 1987). The Saidu and Nikanai Ghar formations are tentatively assigned Late Triassic or younger ages (Pogue et al., in prep., and DiPietro, 1990). 94 These rocks were multiply deformed and metamorphosed during the Himalayan orogeny (Martin et al., 1962; King, 1964; Rosenberg, 1985; Ahmad et al., l987a; Lawrence et al., 1989; DiPietro, 1990). The grade of metamorphism ranges from chlorite zone in the south to kyanite zone in the north (Martin et al., 1962; King, 1964; Kazmi et al., 1984; DiPietro, 1990) Recently, four phases of folding (F51, Fs2, Fs3, and Fs4) and fabric (Ss1, S2, S53, and Ss4) forming events have been interpreted in the Mingora area (DiPietro, 1990). The earliest superposed north-northwest- and south-southeast plunging small-scale F51 and Fs2 folds are associated with a single set of west-southwest vergent large scaleFs2 folds. The F53 north-plunging folds are superposed on the F51 and Fs2 folds. These folds are upright, open, and west-vergent. The Fs4 folds are east-west- striking, upright, tight to open, and south-vergent. All of these folds and fabric forming events are considered to be related to Himalayan deformation and metamorphism (DiPietro, 1990). (2). Alpurai, Puran, and Ajmar areas (a). Stratigraphy In the course of this study, the rock units of the Swat block between the Alpurai fault and the Puran fault have 95 been mapped. Significant differences from the Mingora area were observed. Three major units are recognized in the Puran, Alpurai, and Ajmar areas:(1) Manglaur formation, (2) Choga granite gneiss (unit of the Swat granite gneiss), and (3) Alpurai group. The Manglaur formation and Alpurai group occur on either side of the Alpurai anticline which has a sheet of Choga granite gneiss (Swat granite gneiss) in its core (Figure 3.2). The Manglaur formation is identified on the basis of recognition of xenoliths of this unit in the Choga granite gneiss. It has lithologies similar to those reported for Manglaur formation in the Mingora area (Kazmi et al., 1984; Dipietro, 1990). The Manglaur formation is intruded by a porphyritic Choga granite. It contains muscovite, biotite, garnet, kyanite, fibrolite or sillimanite, microcline, and quartz as significant metamorphic minerals. At places along contacts, a strong cataclastic foliation is developed, however, no significant stratigraphic displacement is observed between the Manglaur formation and the Choga granite gneiss. The age of the Choga granite gneiss is probably Late Cambrian to Early Ordovician (7) based on stratigraphic position and lithologic correlation with the Late Cambrian to Early Ordovician Mansehra granite gneiss. The Manglaur formation is intruded by mafic dikes and sills, and the Choga granite has mafic xenoliths, indicate that an earlier phase of basic magma intruded the Manglaur 96 formation in the Proterozoic. Subsequently, the Alpurai group was deposited unconformably on the Manglaur formation and the Choga granite gneiss. The Alpurai group is mapped as a single stratigraphic unit, and Marghazar, Kashala, Saidu, and Nikanaj Ghar formations are not differentiated in this study (Figure 3.2). The Nikanai Ghar formation is not well developed in this area, and is a discontinuous unit. On the basis of lithology the Alpurai group of study area correlates with similar rock units in the Peshawar basin (Pogue et al., in prep.) and Mingora area (DiPietro, 1990). In the study area, the Middle Pennsylvanian to Late Triassic Karapa greenschist of Peshawar basin or amphibolite horizon of Swat is absent between the Marghazar and Kashala formations. However, below the Kashala formation, dikes and sills of amphibolite intrude the Narghazar formation. The absence of amphibolite horizon is evidence that the basalt flows of probable Panjal volcanics did not extend this far east or that they were eroded away before the deposition of Kashala formation. Small bodies of probable Tertiary tourmaline granites also intrude the Manglaur formation and the Alpurai group. (b). Metamorphism and deformation Overall, the metamorphic grade is higher in the Puran, Alpurai, and Ajmar areas. Garnet, kyanite, and sillimanite- 97 bearing rocks are present in the Alpurai group, Choga granite gneiss, and Manglaur formation. The kyanite- sillixnanite zone of metamorphism in the core of the Alpurai anticline decreases to the chlorite zone of metamorphism towards the Puran and Alpurai faults. In contrast to conclusions by Treloar et al. (1989a), isograds between the Aipurai and Puran faults do not appear to be significantly displaced by post-metamorphic faulting. The Swat block records five deformations (Dvii, Dviii, Dix, Dx, and Dxi) ,four fabrics (Ssi, S2, S53, and Ss4), and four folding events (Fs2, Fs3,Fs4,andFss)(Table 3.1). Dvii formed S1. The earliest recognizable fabric (Ssi) is preserved as inclusion trials of zoisite, quartz, muscovite, and rare biotite and hornblende in S2 garnets. Inclusion trails are straight or rotated within garnets, and are always oblique to the external S2 fabric. No macroscopic folding event related to S1 fabric has been recognized. This event probably occurred under greenschist facies metamorphism. s1 may correlate with the S1 and SM3 (Table 3.1). During Dviii, Fs2 folds were formed. These are small scale, north-northeast-striking, north- or south- plunging, and east-southeast vergent. The axial planes to these folds are west-northwest dipping and are defined by the main penetrative schistose fabric (Ss2)(Table 3.1). S2 is defined by muscovite, biotite, zoisite, clinozoisite, garnet, plagioclase, K-feldspar, kyanite, and fibrolite or 98 sillimanite. The grade of metamorphism varies from greenschist to airiphibolite facies. Dix formed the F53 folds. These are north-northeast- striking, north- or south-plunging, upright,open, and east- southeast vergent. In thin sections, F53 are preservedas crenulation folds which fold the S2. S3 defines the axial plane to F53 folds, and is marked by the presence of muscovite, biotite, plagioclase, and hornblendeor actinolite. This metamorphic event occurred under greenschist facies metamorphism. On the regional scale, F53 folds the chlorite/garnet/kyanite/sillimanitezone rocks on either side of the Alpurai anticline. in contrast to this area, the vergence of Fs2 and F53 structures is west- southwestward in the Mingora area. Dx formed F54 folds (Table 3.1). These are open, east- west-striking folds, recognized by the change in plunge of F52 and F53 and/or by folding of Alpurai group, Manglaur formation, and Choga granite along east-west axison map scale (Figure 3.2). in outcropFs4 is preserved as kink bands or crenulation folds. S54 crenulation cleavage is axial plane to Fs4 folds. This event is contemporaneous with retrograde greenschist facies metamorphism. Dxi event folded the shelf and platform sediments of the Swat block with the melanges of the Neotethys terrane to form antiforinal and synformal structures (Fss) of the Shangla area along the west flank of the Indus syntaxis 99 (Figure 3.2). Dxi is recorded by shear fabrics, in north- south shear zones, associated with the development of the Indus syntais. These shear fabrics strongly transpose the earlier fabrics, and were formed under greenschist to amphibolite facies conditions. MANS EHRA BLOCK The lithologies of the Swat block reappear east of the Indus syntaxis in the Mansehra block (Figures 3.2 and 3.3). Earlier studies of the Mansehra block mainly dealt with the areas around and south of Mansehra and near Tarbela reservoir (Wyrine, 1879; Middlemiss, 1896; Shams, 1961, 1969; All, 1962; Offield et al., 1966; and Calkins et al., 1975). This study provides new data on the Allai-Kohistan area in the northwestern corner of the block. (1). Tarbela and Mansehra areas In the Tarbela area, the Tanawal Formation unconformably overlies the Hazara Formation (Calkins et al., 1975) and is, in turn, unconformably overlain by the Sherwan Formation (Baig and Lawrence, 1987), which composed of a basal inetaconglomerate, quartz-mica phyllite, quartzose sandstone, and phosphorite-bearing dolomites which contain hyolithes fossils of Cambrian age (M.I. Ghaznavi, verbal 100 communication, 1986). This unit correlates lithologically and stratigraphically with the Cambrian (?) knibar formation of Pogue and Hussian (1986) and Cambrian Abbottabad Group of Latif (1974) In the Mansehra area to the north the dominant rock is the Mansehra granite gneiss (Shams, 1961, 1969; Off ield et al., 1966; Calkins et al., 1975). Shams (1961, 1969, and 1983), Offield et al. (1966), and Ashraf (1974) have recognized multiple intrusive phases to the Mansehra granite that indicate most of the granite lithologies found in Swat: augen gneisses, K-feldspar granite porphyries, albitites, and tourmaline granites. The Mansehra granite has a 516± 16 Ma Rb/Sr whole rock isochron date (Le Fort et al., 1980), and 500 to 470 Ma U/Pb dates (Zartman and Zeitler in Baig et al., 1988; Zartman in Lawrence et al., 1989). These data suggest intrusion of the granite in the Late Cambrian to Early Ordovician. The Mansehra granite intrudes a sequence of psammitic metasediinents that are correlated with the Tanawal Formation of the Tarbela area on the basis of lithology (Shams, 1961, 1969; Calkins et al., 1975). Metamorphic grade ranges from chlorite to sillimanite. In the lower grade rocks around Mansehra town, hornfelsic fabric produced during intrusion of the Mansehra granite (Shams, 1969, 1983; LeFort et al., 1980; Baig and Lawrence, 1987) and essentially unaffected by younger Himalayan metamorphism are preserved (Williams et 101 al., 1988; Trelaor et al., 1989b). The rocks of the Mansehra area and north were multiply deformed and metamorphosed during the Himalayan orogeny. Since the granite history and stratigraphy are more poorly understood than in Swat, a detailed deformation history is not yet possible here. (2). Allai-Kohjstan (a). Stratigraphy Earlier reconnaissance studies in Allai-Kohistan include Tahirkheli, (l979a), Ashraf et al. (1980), Baig and Lawrence, (1987), Baig and Snee, (1989), Baig et al., (1989), and Treloar et al., (1989b). Initially, Ashraf et al.(1980) mapped various rock units in Allai-Kohistan. However, during this study (1986-1987), the area has been reinapped. Its revised stratigraphic, metamorphic, and deformational history is presented here. The Thakot fault to the west separates the Mansehra and Beshain blocks and the Kishora thrust to the north separates the Neotethys terrane and Mansehra block (Figures 3.2 and 3.3). The Thakot fault marks a distinct structural, metamorphic, stratigraphic (Baig and Lawrence, 1987; Baig and Snee, 1989; Baig et al.,, 1989), and geochronologic break between the Mansehra and Besham blocks. 102 Principal units of the Mansehra block are:(1) the Tanawal Formation,(2) Mansehra granite gneiss, and (3) Bana group (Figures 3.2 and 3.3). The Tanawal Formation is mainly composed of quartz-mica-garnet schist, quartz-mica-garnet- kyanite schist, quartz-mica-kyanite schist, quartz- muscovite-kyariite-sjlljmanjte schist, quartzo-feldspathic schist, quartzite, and minor layers of hornblende and graphitic schists, and caic-silicates. It lithologically correlates with the Manglaur formation. The contact between the Tanawal Formation and the Mansehra granite gneiss at places is sheared and a strong cataclastic foliation is developed, however, no significant stratigraphic displacement is observed between the Mansehra granite gneiss and the Tanawal Formation. The Mansehra granite is porphyritic, mainly with large K-feldspar phenocrysts. It is composed of quartz, microcline, biotite, muscovite, garnet, kyanite, and fibrolite or sillimanite. The Bana group (Tahirkheli 1979a) is mainly composed of quartzo-feldspathic schist, garnet ainphibolite, zoisite- garnet-kyanite-calc-schist, schistose marble, and garnetiferous caic-graphitic schist in the lower part, and graphitic phyllite, slate, and dolomitic limestone in the upper part. These lithologies are present in a fault-block between the Chail sar and Kishora thrusts (Figure 3.3). Near Bana, the amphibolite facies lower part of the Bana group is 103 faulted out along Rashang fault, and the lower greenschist facies upper part is in fault contact with the amphibolite facies Tanawal Formation. Lithologically, the lower part of the Bana group correlates with the Marghazar and Kashala formations and the upper part with the Saidu and Nakanai Ghar formations of the Alpurai group. The Hansehra granite gneiss and Tanawal Formation are in fault contact with the Bana group along the Rashang fault (Figures 3.2). The inferred unconformity between the Bana group and the Tanawal Formation is faulted out by the Rashang fault. This unconformity is documented between the Manglaur (Tanawal) formation and the Alpurai (Bana) group by regional mapping in Mingora (DiPietro, 1990) and Alpurai areas (Figure 3.2). The Bana group is not found around Abbottabad area south in the Hazara-Swat thrust belt as suggested by Treloar et al (1989b). Four phases of mafic intrusive activity can be documented in Allai-Kohistan. These are (1) pre-Mansehra activity recorded by mafic xenoliths in the granite (Figure 3.9b),(2) garnet amphibolite dikes and sills that are metamorphic equivalents of inafic dikes and sills which accompanied or postdated the intrusion of Mansehra granite during Late Cambrian time,(3) very weakly metamorphosed to unmetamorphosed diabase dikes and sills of possible Panjal volcanics postdate the main SM2 gneissic fabric of the Mansehra granite gneiss (Figure 3.9e) and Tanawal Formation, 104 and (4) unmetainorphosed basalt dikes which postdate the FM2 structures (Figure 3.9g). Subsequently, the Mansehra granite and the Tanawal Formation were intruded by small bodies of probable Tertiary tourmaline granites (Figure 3.3). (b). Inferred deformation, metamorphism, and plutonisin A chronology of deformation and prograde metamorphism has been inferred for the Nansehra block by Trelaor et al. (l989b) that is mainly related to south-vergent folds, ductile shears, and iinbricate thrusts. The medium to high- grade metamorphism has been largely considered to be synchronous with the early phases of the Himalayan deformation (Treloar et al., l989b). The Mansehra block in Allai-Kohistan not only preserves a record of Himalayan deformation and metamorphism, but also provides field, fabric, and 40Ar/39Ar evidence (see below) for pre-Himalayan metamorphism, deformation, plutonisxn, and sedimentation (Tables 3.1, 3.2, and 3.3). Initially, the clastic sediments of the Tanawal and Manglaur formations were deposited unconformably on the flysch deposits of the Hazara, Dakhner, and Manki formations (Table 3.2). Subsequently, these were intruded by mafic dikes and sills (Table 3.2). The Div event formed SM1 fabric in the Tanawal Formation and enhanced the SH1 fabric in the underlying 105 Figure 3.9. Deformation, metamorphism, and magmatisin ofthe Mansehra block. (a). Xenoliths of the Tanawal Formation in the late Cambrian Mansehra granite gneiss indicate that the Tanawal Formation is older than the late Cambrian. (b) An amphibolite xenolith in the Mansehra granite gneiss indicates that one episode of mafic activitypredated the intrusion of the late Cambrian Mansehra granite. A photomicrograph of amphibolite (87MB253) which Intrudes parallel to mainSM2 fabric of the Mansehra granite gneiss. Hornblende, biotite, labradorite, andquartz defines the SM2 gneissic fabric. Hornblende fromSM2 yields a 40Ar/39Ar dateof 466 ± 2 Ma. Magnification- lOx; crossed nicols; 1.31 nun field of view. Photomicrograph of garnet-biotite-muscovite gneiss (87MB272) of the Tanawal Formation. Note Earlier biotite (Bt) of SM2 gneissic fabric is overprinted by muscovite (Mu) of SM3 fabric. Biotite yields 40Ar/39Ar date of 434± 1 Ma and muscovite is dated at 70 ± 0.2 Ma. Magnification- 4x; crossed nicols; 3.3 mm field of view. The unmetamorphosed Early Permian Panjal diabase sill (87MB33A) intrudes parallel to theSM2 gneissic fabric of the Nansehra granite gneiss. Photomicrograph of diabase sill (87MB33A) showing maginatic texture, and does not record any fabric. Note a maginatic biotite in the center of the photomicrograph. The 106 biotite yields a 40Ar/39Ar date of 262± 1 Ma. The diabase sill postdates theSM2 gneissic fabric of the Mansehra granite gneiss to be pre-Early Permian inage. Magnification - lox; crossed nicols; field of view - 1.31 irun. (g). An unmetainorphosed Jurassic basalt dike (87MB61) which intrudes the folded metasedjinents of theTanawal Formation. Note in the lower left corner of the photographa limb of south-plungingFM2 fold is truncated by the basalt dike. This indicate that theFM2 folding event in the Mansehra block is pre-Jurassic inage. North to the top of photograph. 107 (a). :l p L - (b). Figure 3.9. 108 Figure 3.9 continued. 111 units (Table 3.1). S11 isan intrafolial fabric, in locally preserved noses of FM1 small scale north-or south-plunging sheath folds or as inclusion trials inSM2 garnets. The inclusion trials, reinanents of earlierSM1 fabric, are straight or rotated within garnets,but are always oblique to SN2 main phase fabric. The grade ofmetamorphism was probably greenschist facies.SM1 may correlate with SB4, SKi, SAl, and SH1 (Table 3.1). Subsequently, Late Cambrian to Early Ordoviciari Nansehra granite intruded the Mansehrablock. Mafic dikes and sills intrude the Mansehra granite,and may have predated or accompanied its intrusion. Thesewere metamorphosed and deformed byDv event (Tables 3.1 and 3.3). No dating evidence has previously been availableto document that the Dv deformation and metamorphism accompaniedthe intrusion of the Mansehra granite. Dv formed FM2 folds in the Tanawal Formation (Figure 3.9g) of the Alli-Kohistanarea. FM2 folds are north- northeast to north-northwest-striking, east-southeastto west-southwest vergent, and north- or south-plunging.SM2 is axial plane to these folds. the main fabric of the unit, is defined by the development of muscovite, biotite, plagioclase (An30-An45), hornblende, garnet, kyanite, sillimanite, and K-feldspar. This metamorphic eventoccurred under amphibolite facies. 112 After Dv event (Table 3.3), the Late Paleozoic to Jurassic mafic dikes and sills cross-cut and postdate the SM2 fabric of the Nansehra granite gneiss (Figure 3.9e)and Tanawal Formation (Figure 3.9g). These mafic dikes and sills accompanied no fabric development. During Dvii, the SM2 penetrative fabric was folded to form FM3 folds, the axial planes to these folds define a spaced fabric, SM3. These are preserved as upright folds. These folds are north-northeast to north-northwest-striking, east-southeast or west-southwest vergent, and north- or south plunging. SM3 formed during greenschist facies conditions. This event did not develop fabric in mafic dikes and sills (Figures 3.9e, 3.9f, and 3.9g), but where these are involved in Himalayan shear zones, they have shear fabrics. During Dx, east-west-striking, south-vergent folds, shear zones, and south-directed thrusts were formed. These are preserved as east-west-striking crenulation folds. This event is related to the retrograde greenschist facies metamorphism. The south-directed thrusting and related east- west-striking, south-vergent folds are the major style of deformation in the Hazara-Swat foreland fold-and-thrust belt to the south. Dxi deformed the Main Mantle thrust, Kishora thrust, and Rashang fault into the FM5 north-plunging antiforms and synforms of the eastern limb of the Indus syntaxis (Figure 113 3.2). During this deformational eventshear fabrics formed in north-trending shearzones related to the development of the Indus syntaxis. The grade of metamorphismin these shear zones varies from greenschist to amphibolite fades.Where, strong shear fabrics are developed, theearlier fabrics are transposed. Parallel to and east of the Thakot fault,a series of shear zones are present; these shearzones vary in width from a few feet to 0.5 km. Thedeformation in these shear zones varies from ductile to brittle, indicatingthat deformation occurred at different structurallevels during the development of the Indus syntaxis.At deep structural levels, ductile deformation ismarked by the development of mylonite, which shows ribbon structures(Figure 3.lOf). However, at shallow structural levels,phyllonite, fault breccia, and faultgouge mark the brittle deformation (Figures 3.l0a and 3.lOb). Earliergarnet and kyanite crystals are broken and/or stretched and strainedin shear zones (Figure 3..22d). Fibrolite, garnet, hornblende, zoisite, epidote, muscovite, biotite,quartz, and plagioclase define the shear fabrics (Figures3.lOc, 3.lOd, 3.lOe, 3.lof, and 3.log). At places, amphiboliteblocks are ductiley deformed and rotated inan amphibolite facies shear zone matrix with a right-lateral sense of shear. The ainphibolite blocks show strong syntectonicgrowth of garnet, hornblende, biotite, and quartz (Figure 3.lOd).Garnet 114 Figure 3.10. Field and fabric relationsshowing deformation along the Thakot fault zone. A brittle shear zone along the Thakot fault. Blocks and lenses of peridotite of the Indus suture zone in the shear zone of the Thakotfault. These rocks are present about 21 Kin south of thepresent exposure of the Indus suture zone. For locationsee Figures 3.2 and 3.3, a black lens is mapped along theThakot fault. (C). Photomicrograph of an epidote ainphibolite(87MB23) of the Besham basement complex close tothe Thakot fault, showing hornblende, biotite, epidote,and quartz growth during ductile deformation. Thehornblende is dated by 40Ar/39Armethod at 51 ± 2 Ma. Magnification- 4x; crossed nicols; 3.3 mm field of view. Photomicrograph of a garnet amphibolite lens (87MBlol) in a shear zone of the TariawalFormation east of Thakot fault, showing syntectonic growthof garnet, hornblende, biotite, and quartz. Garnet inthe middle of photograph has rotated inclusion trial of biotiteand quartz. Biotite (87MB101) from this lens yieldsa preferred date of 51 ± 0.23 Ma and minor Ar-loss at35 Ma. Magnification - 2x; crossed nicols; 6.7mm field of view. The matrix (B7MB1O2) of shear zone has two mica fabrics. Note early fabric in hinge ofan asymmetric fold. The later mica fabric is related with the ductile deformation and syntectonic garnet growth. The evidencefor 115 early fabric is also present ingarnets as rotated inclusion trials. Biotite (87MB102)from shear zone matrix yieldsa maximum date of 68± 0.2 Ma and a minimum date of 46 ± 0.2 Ma and muscovite yieldsa close to plateau date of 28 ± 0.13 Ma. The mylonitized Mansehra granite gneissfrom a ductile shear zone, east of theThakot fault, showing ribbon structures. Note in the middle of thephotograph, early garnets are stretched and strained duringductile deformation in the shear zone. Magnification- 4x; crossed nicols; 3.3 mm field of view. A tourmaline granite (87MS824) froma shear zone of the Mansehra block. The earliermuscovjtes in the shear zone have been reset to 30± 0.1 Ma. Magnification - 4x; crossed nicols; 3.3 mm field of view. (j HN C.) 118 (e). (f). Figure 3.10 continued. 120 contains relicts of early fabricas rotated inclusion trials of biotite and quartz; however, quartz isalso polygonized in its pressure shadows (Figure 3.lOd).In the shear zone matrix, two sets of mica fabricsare clearly seen (Figure 3.lOe). The earlier mica fabric is preserved in hingesof asymmetric folds and as rotated inclusion trials ingarnets. The later mica fabric is marked by syntectonicgrowth of garnet, muscovite, biotite, zosite, and quartz.The shear sense indicators such as S-C structures, asymmetric folds, mica-fish, and offset of mafic dikes and sillsand stratigraphic units (Figures 3.2 and 3.3), showa right- lateral sense of shear for these shearzones. The ductile deformation within the Thakot faultzone occurred under epidote ainphibolite fades conditions (3.lOc). The metamorphic grade decreases tolower greenschist facies metamorphism in the adjacentblocks. This is interpreted as deformation and metamorphismrelated to different structural levels, developed duringformation of the Indus syntaxis. Thus, the Thakot fault hasa complex metamorphic and deformational history. Dxii event is the Quaternary uplift of the Indus River terraces and initiation of the active right-lateral Chail Sar thrust and reverse Piplai fault in the Indus syntaxis (Figures 3.2 and 3.3). Some of these faults offsetthe suture zone and contain lenses and blocks of mafic and 121 ultraniafic rocks dragged several kilometers to the south (Figures 3.2 and 3.3). NEOTETHYS TERBANE The shelf and platform inetasediiuentary rocks of the Nansehra and Swat blocks of the Indus syntaxis are tectonically overlainbyJurassic to Cretaceous melanges of the Neotethys terrane along the Kishora thrust of the Indus suture zone (Figures 3.2). The Indus suture zone, the western extension of the Indus Tsangpo suture zone of Ladakh, marks the Neotethys suture in the northwest Himalaya of Pakistan (Tahirkheli et al.,1979;Gansser, 1979). The Swat inelanges of the Neotethys terrane (Kazmi et al.,1984; Baig et al., in prep.) in the west are correlated with the Allai iuelanges in the east of the Indus syntaxis (Figure 3.2). At the apex of the Indus syntaxis, the rocks of the Mansehrablock,Swat block, and Neotethys terrane are absent (Figure 3.2). The Jijal ultramafic complex is generally considered to be part of the base of the Kohistan island arc terrane (Tahirkheli et al., 1979; Jan and Howie,1981). Various types of fault bounded terranes/melange units are present in Swat (Kazmi et al.,1984;Baig et al., in prep.) and Allai-Kohistan (Baig et al., in prep.), which include blueschist melange, ophiolitic melange, and greenschist melange (Figures 3.2 and 3.3). The melange zone contains 122 lenses and blocks of Paleocene toEocene fossil-bearing limestones (Chaudhry et al., 1984). The blueschist melange constitutes lenses andblocks of metaigneous and metasedimentary glaucophane-bearing blueschists (Shams, 1972, Kazmi et al.,1984; Majid and Shah, 1985; Baig et al., in prep.), metatuff, phyllitic schist, metabasalts, iuetagabbro, inetagraywacke,quartz- muscovite-chlorite schist, and minor blocks of peridotite, serpentinite, talc, and limestone ina sheared phyllitic to greenschist matrix. During this study,new inetaigneous and metasediinentary glaucophane-bearing blueschist localities were also found near Shin-Kainer and Marineareas of the Allai-Kohistan (Figure 3.3). This melange showsNeotethys trench affinity. The greenschist melange is composed of blocks of greenschist, greenstorie metabasalts, epidote aiuphibolite, and metasedimentary rocks (Kazmi et al., 1984; Baiget al., in prep.). The greenschist melange, at thebase, in Swat and Allai-Kohistan, is interleaved with the rocks of the Alpurai and Bana groups, along the Kishora thrust. The ophiolitic melange is composed of tectonic blocks and lenses of greeristone metabasalt, greenschist, metagabbro, peridotite, clinopyroxenite, serpentinized peridotite, pillow lava, talc-carbonate, limestone, metachert, and metasedinients, in a greenschist, talc- 123 carbonate, or serpentinite matrix (Kaziui et al., 1984; Baig et al., in prep.). The melanges were metamorphosed from blueschist to lower greenschist fades, whereas, the underlying shelf and platform sediments of Gondwana terrane were metamorphosed from greenschist to amphibolite fades. KOHISTAN ISLAND ARC TERRANE The Kohistan island arc terrane and its equivalent Ladakh island arc to the east of the Nanga-Parbat syntaxis (Figure 3.1) is interpreted to be a Jurassic to Cenozoic island arc (Tahirkhelj et al., 1979; Majid and Paracha, 1980; Honegger et al., 1982; Bard, 1983; Verplanck, 1987; Coward et al., 1987; Windley, 1988). The Kohistan island arc is bounded in the north by Main Karakoruin thrust with the Karakorum microcontinent and in the south by Main Mantle thrust with the Indo-Pakistan plate (Figure 3.1; Tahirkheli et al., 1979). The Kohistan island arc terrane is considered to have been accreted to the Karakorum inicrocontinent in the Late Cretaceous (Pudsey et al., 1985; Peterson and Windley, 1985; Coward et al., 1986; 1987; Treloar et al., 1989). The Kohistan island arc terrane contains ultramafic:s and garnet granulites of the Jijal complex; axnphibolites (Jan, 1979; Jan and Howie, 1981; Jan, 1988; Bard, 1983; Butt, 1983a; Chaudhry et al., 1984); norites, layered 124 gabbros, and two pyroxene granulites of the Chilas complex (Khan et al,, 1989); Rakaposhi volcanics; caic-alkaline diorite, granodiorite, and granites of the Kohistan batholith; and Eocene volcanics and mnetasediments (Tahirkheli et al., 1979; Majid and Paracha, 1980; Pudsey, 1986; Peterson and Windley, 1985; Windley, 1988). 125 40Ar/3 9ArGEOCHRONOLOGY (1).4O39 dating techniques The 40Ar/39Ar dating technique is a variant of the conventional K-Ar method. To obtaina date by this technique, the sample of unknown age anda standard of known age are irradiated together in a nuclear reactor to produce 39Ar from 39Kby fast neutron bombardment. After irradiation, the 40Ar/39Ar ratios of sample aridstandard are measured. The isotopic date of a sample can be calculated from its 40Ar/39Ar ratio when compared to the 40Ar/39Ar ratioof the standard. Most importantly, only the isotopic composition of the argon needs to be measured and this is done by gas-source mass-spectrontetry, potentiallya very precise analytical technique. In contrast, for a conventional K-Ar date, both 40K and 40Arare determined. To do this, argon in one aliquant of sample is measured by isotope-dilution and gas-source mass-spectrometry. Potassium in a different aliquant of a sample is determined bysome other analytical method such as flame photometry,x-ray fluorescence, or isotope-dilution and solid-source mass-spectrometry. Thus, one inherent problem of the conventional K-Ar technique is the necessity of measuring isotopic abundances for separate aliquants ofa sample. This poses the danger that, because of sample inhomogeneity, 126 different potassium and/or argon contents may exist in each aliquant. Two major advantages of the 40Ar/39Ar dating method are:(1) only isotopic ratios of argon need to be determined and (2) all measurements are made on the same sample aliquant, thus avoiding the question of inhoniogeneity. In addition, by the 40Ar/39Ar method, it is possible to obtain a series of dates from a single sample when argon is extracted by step-heating. The combination of these advantages potentially increases the accuracy and precision of the 40Ar/39Ar method over the conventional K-Ar technique. However, the 40Ar/39Ar technique will suffer if proper corrections are not made for interfering radiation-induced isotopes. These corrections are now well-known and routinely made. 40Ar/39Arage-spectrum dating of hornblende, muscovite, biotite, and orthoclase, which form during metamorphism or crystallization from a magma, is currently the best method for determining thermal history of complex metamorphic and plutonic terranes. Combined with structural studies, it can also provide valuable constraints on the timing of deformation events. Ideally, a 40Ar/39Ar mineral date marks the time when that mineral closed to diffusion of argon. Closure of a particular mineral to argon diffusion is controlled mainly by temperature, to a lesser extent by cooling rate (Dodson, 1973), and possibly by chemical compositional variation or strain. Commonly used 127 potassium-bearing minerals have characteristic closure temperatures (or retention temperatures) that are knownwith precisions of about ± 20°C. The closure temperature is higher for minerals that cooled rapidly, and conversely. Commonly accepted closure-temperatures range for rapid (1000°C/Ma) to slow cooling (5°C/Ma) are 580-480°C for hornblende (Harrison, 1981),325-270°C for muscovite (Snee et al., 1988), 300-260°C for biotite (Harrison and McDougall, 1980; Sriee, 1982), and160-100°C for microcline (Harrison and McDougall, 1982). Closure temperatures for potassium feldspars that are structurally different from microcline are less well known but are certainly higher than that of microcline. End-member orthoclase has a closure temperature near that of biotite (L.W. Snee, U.S. Geological Survey, personal communication 1989). For simplicity, intermediate closure temperatures (i.e., for intermediate cooling rates of 500-100°C/Ma) are assumed for this study (5300, 300°, 2800, and 280°C for hornhlende, muscovite, biotite, and orthoclase respectively). The 40Ar/39Ar method was first used in "total-fusion" experiments in which an irradiated sample was completely melted and all isotopes of argon measured in asingle analysis to calculate an "age" for the sample. This total-fusion date is roughly analogous to a conventional K-Ar date for the sample except that noisotopic concentration measurements are required. Very soon afterthe 128 first uses of the 40Ar/39Ar method, it was realized thata sample could be progressively degassed in temperature increments (Merrihue and Turner, 1966) A date could be calculated for each increment of gas released and the dates could be plotted against percent of released argon to form an age spectrum. The character of the spectrum can be evaluated within a theoretical framework to interpret the apparent distribution of potassium and argon within the sample. Ideally, if a mineral has had a simple thermal history, the distribution of argon in the sample will be homogeneous and nearly identical apparent ages will be calculated for each increment of gas released during step-heating. If the calculated apparent ages of several contiguous gas fractions are the same within analytical uncertainty, a "plateau date" is achieved and is generally interpreted to be the best estimate of the time when the mineral closed to argon diffusion. In contrast, ifa mineral has had a complex thermal history, a disturbed spectrum is commonly observed, in which apparent ages for different temperature steps are discordant. Some discordant spectra exhibit a distinct increase in dates for the temperature increments from low-temperature to high-temperature extraction-steps in the experiment. Turner (1968) showed theoretically that an age spectrum will exhibit a step-up in dates if argon was lost from the sample in the geologic environment by volume diffusion. In some cases, the minimum 129 apparent age for the low temperature steps may provide information about the time when argon was lost from the mineral. Beside argon-loss, other discordant spectra result from inclusion of "excess-40Ar" in the sample. Several studies (e.g. Lanphere and Dairymple, 1971, Lanphere 1976; Kaneoka, 1974) have documented that large quantities of excess-40Ar ina sample will produce a "saddle-shaped" 40Ar/39Ar age-spectrum with anomalously old dates for the low-temperature and high-temperature extraction-steps. Small quantities of excess-40Ar commonly only effect the low-temperature steps and form "L-shaped" spectrum. Since these early experiments, many studies have shown that meaningful ages of samples could be determined by the age-spectrum technique even though some loss or gain of 40Ar had occurred during the geologic history of the sample. However, loss or gain of 40Ar by a sample will result in an erroneous conventional K-Ar "age" and because loss or gain of 40Ar by a sample is primarily thermally controlled, samples from thermally complex areas such as metamorphic and plutonic complexes should be analyzed by the 40Ar/39Ar age-spectrum technique. Similarly, conventional K-Ar data from complex geologic settings like northwest Himalaya of Pakistan should be viewed with caution. 130 (2). Analytical methods Mineral separates for 40Ar/39Ar analyses were prepared using standard mineral separation techniques. Rock samples were crushed and sieved, for most samples, the 80- to 120- mesh size fraction (180-l25im) were collected for mineral separation except for sample 87MS801A in which inicas of 1- to 3-mm size were hand picked. The samples were washed in water and acetone and dried in an oven between 40-50°C. Initial separations were done using heavy liquids (bronioform and niethylene iodide), the Frantz magnetic separator, water shaking, and paper shaking. Final separates were carefully hand-picked to ensure sample purity. Samples were then washed in acetone, ethanol, and deionized water in a small ultrasonic bath. Mica separates from carbonates and whole-rock samples were washed in 10 % dilute HCL to remove calcite. Samples were dried in an oven at 40-50°C. Samples of 50-400 mg of hornblende and whole-rock and 20-100 nig of biotite, muscovite, and potassium feldspar were loaded in aluminum capsules for irradiation. The sample capsules were then loaded in silica glass vials. Capsules containing 5-10 mg of hornblende standard MMhb-1 (K-Ar date = 520.4 Ma, %K = 1.555, and 40ArK = 1.624 x 10 mol/g; Alexander et al., 1978; and Samson and Alexander, 1987) were loaded every 1-2 samples and at the top and bottom of the vials to ensure adequate monitoring of the neutron flux during irradiation. 131 In addition, salts of potassium (K2SO4) and calcium (CaY2) were included in all irradiation packages in order to monitor the production of interfering argon isotopes produced from K and Ca during irradiation. After loading, the quartz vials were sealed under vacuum and placed in an aluminum irradiation canister that was cold-welded to prevent leakage. Samples were irradiated discontinuously at 1 NW power in the central thimble facility in the core of the U.S. Geological Survey TRIGA Reactor in Denver, Colorado. The total length of irradiation for 3 packages (DD8, DD1O, and DD12) was 30 hours and package DD9 was irradiated for 100 hours. The irradiation canisters were centered as well as possible on the centerline of the reactor and rotated at 1 rph throughout the irradiation to optimize the neutron flux distribution. Argon isotopic analyses were performed in the 40Ar/39Ar laboratory, at the Branch of Isotope Geology of the U.S. Geological Survey, Denver, Colorado. Samples were experimentally degassed in a double-vacuum resistance furnace via step-heating under ultra-high vacuum for about 20 minutes at each temperature step. Each degassing temperature was reached within 1-2 minutes and maintained by a furnace controller for the duration of the heating step. The temperature of the sample crucible was monitored using a digital voltmeter connected to a thermocouple at the base of the crucible; temperature during heating is known to about ±10°C. The evolved gas was 132 then scrubbed using Zr-V-Fe, Zr-Al, Ti getters, and molecular sieve desiccant. The mass 40, 39, 38, 37, and 36 isotopes of argon were analyzed using a Mass Analyzer Products series 215 rare gas mass spectrometer with on-line digital data acquisition system. Raw isotopic data were corrected for volume, mass discrimination, trap current, radioactive decay of 37Ar and 39Ar, and interfering argon isotopes. Average reactor production ratios used to correct for irradiation-induced 36Ar and 39Ar from Ca and 40Ar for K based on analyses of two samples of each salt in each irradiation package are presented in Appendix 2. Corrections were also made f or36Ar produced from chlorine using the interfering isotopes of argon produced from irradiation of chlorine using the method described by Roddick (1983). Mass discrimination and atmospheric argon corrections were done using a measured atmospheric 40Ar/36Ar ratio of 298.9 for a sample of air argon with 40Ar/36Ar ratio of 295.5, determined for the system by replicate analyses during the period when samples were analyzed. 40Ar/39Ar isotopic dates were calculated according to the relationship tu = l/\ ln (JF + 1) where t is the calculated date of the sample, >.. is the decay constant for decay of40K to 40Ar and 40Ca, J is related to neutron flux during irradiation, and F is the ratio of 40ArR (radiogenic 40Ar) to 39ArK (potassium-derived 133 39Ar) of the sample. The recommended decay constants used in 40Ar/39Ar datingare; = 0.581 xl00/yr, N3= 4.962 xl00/yr, and)'=> +-= 5.543 x100/yr (Steiger and Jager, 1977). The flux parameter, J, was determined according to the relationship J ( e)- 1) / (40ArR/39ArK)m where tm is the age of the primary flux "monitor" (i.e., standard) and (40ArR/39ArK)Th is the measured ratio of the flux monitor (hornblende standard MMhb-1 in this study). In order to determine the actual 40ArR /39Ar ratio of a sample or standard, however, it is necessary to correct for the presence of atmospheric40Ar and irradiation-produced interfering isotopes such as 40Ar (from 40K), 39Ar (from 42Ca), and 36Ar (from 40Ca and 35Cl). Detailed discussion of the technical aspects of the 40Ar/39Ar technique are presented in Dairyinpie et al.(1981) and McDougall and Harrison (1988). Isotopic data for samples analyzed in this study are presented in Tables 3.4 and 3.5 and Appendices 1 and 2. Table 3.4 summarizes the interpreted 40Ar/39Ar data. Table 3.5 shows the temperature, age, and 39Ar/37Ar ratio data for the amphibolites of the Besham basement complex. Appendix 1 presents the 40Ar/39Ar data from the Indus syntaxis, northwest Himalaya Pakistan. In Appendix 1 radiogenic40Ar is total 40Ar derived from natural radioactive decay of4 after all corrections for non-decay-derived40Ar have been 134 made. K-derived 39Ar is total 39Ar derived from the epithermal neutron-induced reaction 39K(n,p)39Ar after corrections for non-39K-derjved 39Ar are made. F is the quantity resulting from the division of the amount of radiogenic 40Ar by the amount of K-derived 39Ar. Quantities for radiogenic 40Ar and K-derived 39Ar are given in volts of signal measured on a Faraday detector by a digital voltmeter. Appendix 2 is the measured production ratios for Ca- and K-derived isotopes for the U.S. Geological Survey TRIGA Reactor, Denver. Mass spectrometer sensitivity at time of measurement was 9.736 x moles Ar per volt of signal. All reported errors in this study represent 1 sigma (68% confidence interval) unless otherwise stated. Estimated error for J-value is 0.25% and was determined experimentally by calculating the reproducibility of multiple monitors. Data for samples are presented in standard 40Ar/39Ar age-spectrum diagrams in which apparent ages (calculated dates for each degassing step for a sample) are plotted versus cumulative percent 39ArK. Age spectra are interpreted to define a plateau if apparent ages from adjacent heating steps with 50% or more gas are analytically indistinguishable at the 2 sigma level (95% confidence interval). Samples in this study show a range from simple plateaus to strongly discordant age spectra. For samples that yield plateau age spectra, the plateau date (Tn) is interpreted to represent the best estimate of the time when 135 the mineral closed to argon diffusion. In some cases where age spectra are more complex and apparent ages do not define a plateau, argon isochron analyses were used to further evaluate whether the argon isotopic data for a given sample provides meaningful geochronologic information. Some of the isochron dates show large uncertainty errors, because of scatter of data points on the isochron diagrams or due to some excess-Ar steps included in the isochron analyses. Strongly discordant age spectra are interpreted individually in combination with other information. Where average apparent ages are reported as preferred dates (Tf)F average apparent ages are weighted according to the percent 39Ar released for each step included in the calculation. The uncertainty reported represents 1 standard deviation from the mean apparent age. The maximum (Tmax) and minimum (Tmin) dates are assigned to the argon-loss and U-shaped spectra. A common feature of many hornblende age spectra is the presence of excess 40Ar (resulting in anomalously old apparent ages) for a small proportion of the total 39ArK released in the lowest temperature steps. This is likely due to adhesion of minor excess 40Ar on mineral grain surfaces, in defects or fluid inclusions, or in loosely bound sites and, because this excess argon is evolved during low-temperature heating, it has no negative effect on apparent ages calculated for the bulk of the argon released at higher temperatures. Therefore, these steps are ignored 136 in interpreting the age spectra. In some cases, 39Ar/37Ar ratios provide additional information pertaining to the interpretation of discordant age spectra (particularly in the case of amphiboles), because, during irradiation, 39Ar is produced from potassium and 37Ar is produced from calcium, corrected 39Ar/37Ar ratios are proportional to K/Ca (estimates of K/Ca can be calculated by multiplying 39Ar/37Ar ratio by an empirically determined factor of about 0.5; Dalrymple et al., 1981). For amphiboles of this study, 39Ar/37Ar ratiosare typically between 0.05 and 0.35 (Table 3.5 and Appendix 1). The occurrence of steps with anomalously high 39Ar/37Ar ratios suggests that, during these degassing steps, a high-K impurity (possibly trace biotite, chlorite, or actinolite) is contributing to the evolved gas. Such steps can reasonably be ignored when interpreting the isotopic data for the mineral of interest unless there is evidence for significant contamination of the sample. 137 4O39 RESULTS An 40Ar/39Ar age-spectrum study on 79 samples from Gondwana, Neotethys, and Kohistan island arc terranes of the Indus syntaxis has been completed; the data are compiled in Appendix 1 and summarized in Table 3.4. From rocks of the Gondwana terrane 74 samples comprising 21 hornblendes, 26 biotites, 21 muscovites, 5 potassium feldspars, and 1 whole rock were analyzed. One sample of green mica from fuchsite schist of the ophiolitic melange of the Neotethys terrane, 2 samples of hornblendes, 1 potassium feldspar, and 1 sodic mica from the Kohistan island arc terrane were analyzed. These new results are summarized in the following section. Because of the large amount of data, the following presentation of the40Ar/39Ar results is subdivided into the sections on the Besham block, Swat block, Mansehra block, Kohistan island arc terrane, and Neotethys terrane. To make any complex set of analytical data, including thermochronologic data, useful for geologic applications, there are several levels of interpretation that must be completed. In the following discussion of results it can be assumed that every 40Ar/39Ar date that is cited has been evaluated primarily by examining the character of its age spectrum. In most cases, in addition, an inverse isochron (Table 3.4) and the relative distribution of potassium and Table 3.4. Interpretation of40Ar/39ArAge-spectrum data from the Indus syntaxis, NW Himalaya Pakistan. Sample Block! Rock Type Mineral Total gasInverse 40Ar/36Ar Iochron Interpreted Ax-Arspectrumtype No. Terrane date (Ma)lsocbron Initial date (Ma) date (Ma) on temp. (C°) steps 87MSB45 Besham aniphibolite horablende 1975±6 950-1450 321+171-15 2005+571-63 Tm=2031±6 Ar-loss block Tp1998±6 87MB135 amphibolite hornblende 1812±7 1075-1450 334+45/36 1989+129/ Tmayl997±8 Ar-loss -163 5JLOO7C amphibolite hornblende 1904±4 1150-1450 30129/-24 1950+951-113 Tm=1951±4 Ar-loss 5JLOI2C amphibolite hornblende 2035±4 975-1200 5650+11500/ 1887775/ Tm=l9SO±3 Excess Ar -3740 -2390 87MB385 amphibolite hornblende 2026±4 Tma,2l6O±4 distwbed xenolith Tmin= 1950±3 5JL042 amphibolite hornblende 1983±4 500-1450 2470+2730/ 1539+347/ Tm=l89S±3 Excess Ar -849 -1120 87MB6A amphibolite hornblende 1873±4 Tm=l922±3 Ar-loss T=1865±3 87MB6A amphibolite blotite 67±0.3 Tm=64±02 reset 87MB310 amphibolite hornblende 1893±4 Tm=19S0±3 Ar-loss 87MB310 amphibolite biotlte 56±2 Tm=485±29 severe Ar-loss Tmin2S±5 87MB307 melapyro- amphibole 1927±6 950-1150 316+451-35 1883130/ Tp1887±5 Ar-loss xenite -167 1200-1450 307+22/-20 1931+751-88 Tmal9SS±4 87MB374 amphibolite hornblende 1769±3 Tm=19l0±4 Ar-loss Tmtnrl4l7±3 87MB336 ainphibolite hornblende 1602±3 TpF1884±3.5 Ar-loss Tminr664± 12 87MB23 epidote hornblende 52±1 950-1450 2953/-3 510.131-0.13T=51±2 undisturbed amphibolite Table 3.4 continued. Sample Blockl Rock Type Mineral Total gas Inverse 40Arf36Ar Isochron Interpreted Ar-Ar spectrum type No. Terrane date (Ma) isochron initial date (Ma) date (Ma) on temp. (C°) steps 87MB155 Besham epidote hornblende 50±0.341050-1450 297+0.61-0.6 46+0.131-0.13 Tm=46±I Ar-loss . excess Ar at Block amphibolite lower temp. steps Tmin=39.SO± 0.38 87MB148 epidote hornblende 37±0.45 500-1075 285+8/-7 33+0.191-0.19 T=38±0.25 undisturbed amphibolite T=36±0.26 87MB144 epidote amphibole 108±5 850-1450 491+93/-67 37+6/-8 Tm=SO±2 Excess Ar amphibolite 87MS726 garnet-biotitebiotlte 148±1 Tm=233±I Ar-loss quartzo-felds- pathic schist Tm!n=92-'+ 87MB7 biotite- muscovite 29.69± T=31±0.11 L-shapcd muscovite 0.18 quartzo-felds- T=26±0. 13 pathic schist 87MS450 Uhor sodic muscovite 530±1 T,=623± 1.5 excess at lowest temp. granite gnelss T=188±0.5 steps, partial Ar-loss 87MS450 Lahor sodic blotite 90±1 T,=99±0.34 severe Ar-loss granite gneiss Tmin_64±2 87MS473 Darwaza Sar muscovite 38±0.20 T=30±0.l2 broad U-shaped potassic granite gneiss 87MS473 Darwaza Sar blotite 82±0.30 T.=73±0.2 severe Ar-loss potassic granite gneiss 87MS691 Jabrai blotite 1750±3 Tm=1782±3 Ar-loss hornblende - biotite granite Tminl73I±3 gneiss 5JL049B Xenollth of biotite 339±1 Tp333±l severe Ar-loss Lahor granite gneiss PAK5 Dubair hornblende 1321±4 Tm1966±16Ar-loss hornblende -with biotite blotite granite intergrowth Tmin4OS±3 Table 3.4 continued. Sample Bloek/ Rock Type Mineral Total ga.Inverse 40/38M Isochron Interpreted Ar-Ar spectrum type No. Terrane date (Ma)lsochron initial date (Ma) date (Ma) on temp. (C°) steps 5JL059B Besham Tourmaline- muscovite 1476±3 Tm 1517±3 minor Ar-loss at block muscovite graphic 1037±2 Ma granite 87MB6C peginatite of biotite 61±0.25 T=53±0.2 broad U-shaped Labor granite gnelss 87MB4 low-grade muscovite 34±0.22 T=36±0.25 Ar-loss with minor carbonate excess Ar in low-temp. Tm1n29±0.4 steps 87MB20A low-grade muscovite 143±0.44 carbonate T=130± 0.35broad U-shaped 87MB5 19 graphitic muscovite 49±0.26 650-850 5533767-159 288/-iS T=30±0.24 broad U-shaped phyllite 87MB47A Tourmaline K-feldspar 450±1 pegmatite Tm493± I excess Ar In low-temp. T143±0.5 steps 87MB47A Tourmaline blotite 122±0.34 T=66±0.2 severely disturbed pegmatite 87MB47 Karora blotite 83±0.25 T=63±0.20 U-shaped granite 87MB380 Karai graniteK-feldspar 233±1 Tm272±1 partial Ar-loss with excess Ar In low-temp. T=56.5± steps 0.23 87MB380 Karat granitebiotite 53±0.32 400-850 33623/ -20 37+2/-2 T=38±0.2 broad U-shaped 87MB2 Ranial graniteblotite 36±0.20 400-1050 29647-4 360.307-0.30TpF36±0.2 undisturbed D Swat blockphyllite muscovite 70±1 500-1050 329+75/-52 618/42 T=83±3 Ar-loss . partial resetting at 63±0.4 Ma PAK9 Swat granite K-feldspar 33±0.14 T=45±0.2 Ar-loss with minor gneiss excess at low-temp. steps Tmin22±O. 1 PAK9 Swat granite blotlte 31±0. 13 T32±0. 13 Ar-loss with minor gneiss resetting at 28±0.13 Ma PAK9 Swat granite muscovite 28±0.15 T=28±0.2 gneiss plateau Table 3.4 continued. Sample Block/ Rock Type Mineral Total gaaInverse 40Ar/3Ar Iaochron Interpreted Ar-Ar spectrwn type No. Terrane date (Ma)Isochron Initial date (Ma) date (Ma) on temp. (Ci steps 87MS801A Swat blockmarble muscovite 28±0.18 TpF28±O.l minor resetting at 25±1 Ma E - diabase dike hornblende 956±27 700-850 294+4/ 4 284+41-4 Tm=26S±26 U-shaped SNI -" Shewa sanidine 62.5±2.15 850-1250 293+1621-77 61+141-30 Tm=8S±4 porphyry Tm39±2 87MS758 - garnet blotite- muscovite 27±0.40 T=28.5±0.4Ar-loss muscovite schist T0=24.6±0. 12 87MS758 ' garnet blotite- blotlte 20±0.25 T,=22±0.3 Ar-loss muscovite schist Tm1n12±0.3 87MB42 muscovite- muscovite 24±0.10 Tp24.4±0. 1 slIghtly disturbed, close blotite to plateau graphitic schist 87MB42 " muscovite- blotite 23±0.10 Tp=23±O.2 plateau biotite graphitic schist PAK8 - Choga granitemuscovite 23±0.11 T=23±0. 1 excess Ar at low and high gneiss temp. steps PAK8 - Choga graniteblotite T,p29.4±O. 12 excess Ar at low-temp. gnelss steps 87MS785 - garnet hornblende 32±0.19 Tm=32± 1 undisturbed with minor amphibollte Ar at low-temp. 950-1450 297+4/-4 31+0.251-0.25Tmtn=31±0.1 e:5 87MSB43 Manshera Hazara slate sericite cone. 612±1 Tp650 Ar-loss block 87MB272 " garnet-blotiteblotlte 408±1 Tma,434±l Ar-loss gneiss Tmin3O3± 1 87MB272 garnet-blotiteblotite 406±1 Total fusion date gneiss 87MB272 garnet-blotltemuscovite 70±0.21 Tpf=70±0.2 slightly disturbed, close H gneiss to plateau H Table 3.4 continued. Sample Block! Rock Type Mineral Total gasInverse 4Op/36M Isochron Interpreted Ar-Ar spectrum type No. Terrane date (Ma)isochron Initial date (Ma) date (Ma) on temp. (C°) steps 87MB253 Mansheragarnet hornblende 597± 1 950, 1075. 3060.66/ 4641/-i TpF466±2 minor excess Ar at low- block amphibolite and 1200 -0.66 temp. steps 87MB33A diabase sill blotite 250±1 Tr=262±1 minor resetting at 75±0.35 Ma 87MB54 psammitic biotite 90±0.29 TPF9O±0.3 minor resetting at 68±1 schist Ma 87MB56 psammitic blotite 115±0.32 Tm i38± 1 severe Ar-loss schist T= 109±0.3 87MB56 psamrnitic muscovite 34±0.13 T=42±0. 15 severe Ar-loss schist T=30±0.24 87MB 101 garnet blotite 48±0.25 Tp15l±0.23 Ar-loss with partial amphibolite resetting at 35±0.18 Ma 87MB102 garnet blotite-blotite 54±0.15 T=68±0.2 Ar-loss with minor muscovite excess at low-temp. steps schist Tmt046±O.2 87MB 102 garnet blotite-muscovite 29±0.11 Tp28±0. 13 close to plateau some muscovite excess Ar at low-temp. schist steps 87MB 104 psammitic blotite 174± 1 Tm2O2±2 Ar-loss schist Tmin62± 1 87MB65 metamor- K-feldspar 135±0.43 190±0.5 severely disturbed phosed tourmaline Tmin33±O.2 pegmatite 87MB65 metamor- muscovite 26±0.14 T=29.5±0. 13Ar-loss phosed tourmaline Tmin24±O.3 pegmatite 87MB249 graphitic muscovite 24±0.14 Tp24.3±0.2 plateau phyllite 87MB283 graphitic muscovite 36±0.20 TpF3l.5±O. 13 dIsturbed phyllite 87MS824 sheared muscovite 30±0.10 500-1400 304+58/-42 31+3/-4 T3O±O. 10 minor resetting at 27±0.2 tourmaline Ma granite Table 3.4 continued. Sample fllock/ Rock Type Mineral Total gas Inverse 40Ar/36M Isochron Interpreted Ar-Al spectrum type No. Terrane date (Ma) Isocliron Initial date (Ma) date (Ma) on temp. (C°) steps 87MB55 Mansheragarnet hornblende 226±1 925-1400 324+631-45 block amphibolite 189+241-34 Tm=221±1 disturbedexcess Ar at T= 129±1 low-temp. steps 87MB55 garnet blotite 179±1 amphibolite Tm=232±1 Ar-loss TmQl±2 87MB60 amphibolite hornblende 290±1 1025-1450 296+ 15/-13 258+ 10/-11 Tma,c=28 1±1 Ar-loss with excess Ar at low-temp. steps mfn 67±1 87MB60 aniphiboilte blottte 195±1 Tpi98±l Ar-loss 87MB61 basalt dike whole rock 279±1 basalt T=159±0.4 U-shaped 87MB400 Neotethys fuchsite fuchslte 82±0.26 700-950 292+12/-ill terrane schist 81+31-3 Tp=82±0.22 plateau 87MB401 Kohistan garnet hornblende 119±1 1025-1250 296+1/-i 117+0.60/ T1i7±0.4 L-shaped island Arc amphibolite -0.60 terrarie 87MB401 garnet sodie mica 70±2 400-1100 324+39/-31 48+3/-4 Tm=83±2 Ar-loss with minor amphibolite resetting at 34±4 Ma Tmtnr34±4 PA110 Kalam quartz- K-feldspar 41±0. 18 diorite T=49±0.2 Ar-loss 1-nIn"--'-'-1.'-' PAKIO Kalam quartz- hornblende 111±1 diorite T=88±0.4 U-shaped 144 calcium within the sample based on 39Ar/37Ar ratios (Table 3.5) have also been used to constrain the interpretation of the age spectrum. These three analytical interpretations can be further constrained by consideration of the character (composition, structural state, number of phases, etc.) and quality of the dated material. The details of this process are exhibited in the following discussion of the first sample. Discussions of subsequent samples will not be as comprehensive but the analysis for each has been as rigorous. The next level of interpretation, which includes incorporation with geologic data, is presented in the subsequent interpretation section. BESIiAX BLOCK The rock samples from the Besham block show thermal and metamorphic events varying from the Early Proterozoic to Cenozoic (Figure 3.11). (1).Amphibolites of the Beshaiubasement complex Hornblende is the most reliable and retentive mineral used in argon thermochronology. Because the closure temperature for argon diffusion in hornblende is about 500-550°C, 40Ar/39Ar dates on hornblende may retain a record of thermal events that occurred before subsequent Table 3.5. Temperature, age, and 39Ar/37Ar ratio data for the Early Proterozoic amphibolites of the Besham basement complex. Sample87MS45 87MB135 5JLOO7C 5JLO12C 5JL042 No. Temp. Date (Ma) 39Ar/ Date (Ma) 39Ar/ Date (Ma) 39Ar/ Date (Ma) 39Ar/ Date (Ma) 39Ar/ C° 37Ar 37Ar 37Ar 37Ar 37Ar 500 3176±11 0.34 4268±53 0.74 2380±8 0.67 5340±15 0.37 6009±36 0.37 600 917±3 0.87 1750±10 0.53 1875±9 1.01 1748±7 0.57 4033±9 0.61 650 573±4 1.14 760±6 1.17 856±9 2.86 1286±11 0.68 1850±17 0.41 700 846±4 0.86 898±5 0.F1 782±6 0.85 1653±19 0.40 1970±17 0.68 750 1016±4 0.51 1199±6 0.26 807±20 0.95 1697±20 0.24 2421±16 0.46 800 1110±3 0.27 1322±6 0.18 1098±9 0.50 1963±13 0.13 2613±14 0.27 825 850 1518±4 0.11 1331±5 0.14 1438±11 0.24 2349±20 0.C*3 2503±16 0.16 875 900 1915±5 0.10 1176±5 0.16 1608±7 0.16 2535±5 0.07 2692±11 0.13 925 1966±5 0.17 2348±4 0.10 950 2003±6 0.21 1545±7 0.21 1684±4 0.16 2163±3 0.14 2146±3 0.16 975 2022±3 0.16 2156±3 0.18 1000 1998±8 0.23 1738±9 022 1796±3 0.19 1964±3 0.16 2122±4 0.18 1025 1994±4 02.3 1894±3 0.21 1950±3 0.16 1979±3 0.19 1050 1993±7 022 1923±8 0.21 1932±3 022 1964±3 0.16 1895±3 0.19 1075 2004±6 0.21 2005±10 022 1934±3 0.23 1897±3 0.19 1100 2013±7 022 1997±9 0.22 1928±3 022 1980±3 0.18 1923±3 0.19 1125 1994±8 0.22 1150 2031±6 022 1979±9 022 1951±3 022 1989±3 0.16 1918±3 0.19 1175 1979±10 0.22 1200 2014±9 0.21 1951±3 0.23 1988±4 0.16 1922±3 0.20 1250 2001±5 022 1990±8 0.22 1950±4 0.22 1941±3 0.19 1300 1950±3 0.23 1961±6 0.19 1450 2025±4 022 1998±10 022 1952±3 0.23 1944±4 0.19 Total 1975±6 1812±7 1904±3 2035±4 1983±3 Gas Date Table 3.5 continued. Sample87MB6A 87MB310 87MB307 87MB374 87MB336 87MB385 No. Temp. Date (Ma) 39Ar/ Date (Ma) 39Ar/ Date (Ma) 39Ar/ Date (Ma) Ar/ Date (Ma) 39Ar/ Date (Ma) 39Ar/ C0 37Ar 37Ar 37Ar 37Ar 37Ar 31Ar 500 4713±10 0.65 4364±11 0.48 5590±42 0.36 2497±5 0.91 2963±10 0.90 5998±13 0.51 600 1666±5 1.18 2870±11 0.95 1537±22 0.29 744±8 0.61 814±7 0.79 5211±24 0.77 650 622±6 1.13 819±9 0.78 560±37 046 535±20 0.81 316±11 0.91 700 748±4 0.77 575±13 0.90 535±95 032 686±19 0.43 533±18 0.41 2840±8 750 1197±8 0.29 791±11 0.38 592±50 0.21 921±8 022 596±33 0.24 1439±11 0.50 800 1519±5 0.13 1014±40 0.10 1049±8 0.11 606±10 0.14 1682±11 0.34 825 1792±12 022 850 1803±5 0.10 1358±5 0.07 1652±45 0.04 1417±3 0.09 664±12 0.13 1690±12 0.17 875 1848±3 0.11 900 1827±3 0.13 1472±3 0.07 1610±3 0.15 971±2 0.13 1610±3 0.19 925 1864±3 0.15 1770±3 0.17 950 1871±3 0.16 1736±3 0.12 1887±4 0.05 1858±3 0.18 1308±3 0.16 1841±3 0.23 975 1846±4 0.14 1881±3 0.05 1867±3 0.17 1738±3 0.18 1000 1894±3 0.15 1902±3 0.14 1889±3 0.06 1903±3 0.17 1984±3 0.24 1025 1899±3 0.13 1895±9 0.06 191 1±4 0.18 1851±3 0.18 1952±3 0.24 1050 1923±3 0.15 1932±3 0.14 1879±5 0.05 1899±3 0.17 1818±3 0.16 1949±4 0.23 1075 1909±5 0.15 1940±3 0.13 1882±5 0.05 1901±4 0.17 1846±4 0.16 2019±3 0.23 1100 1890±8 0.15 1932±4 0.13 1881±4 0.05 1900±4 0.17 1877±3 0.17 2093±4 0.23 1125 2160±4 0.23 1150 1903±0.15 0.15 1930±4 0.15 1892±3 0.05 1911±4 0.18 1892±3 0.18 2136±4 0.23 1175 1200 1910±3 0.05 1911±3 0.18 1875±4 0.18 2116±4 0.23 1250 1897±5 0.15 1950±3 0.15 1957±3 0.05 1910±4 0.18 1887±3 0.18 2096±5 0.23 1300 1450 1935±50 0.15 1969±4 0.06 1881±4 0.18 2105±4 0.23 Total 1873±4 1893±4 1927±6 1796±3 1602±3 2026±4 Gas Date 147 dynamothermal events, depending on the grade of those events. Abundant amphibolite is exposed within the Besham basement complex. To constrain the timing of pre-Hiinalayan and Himalayan thermal events, 15 hornblende and 2 biotite mineral separates from these amphibolites were dated by the 40Ar/39Arage-spectrum technique. Most of the age spectra display minor to moderate argon loss due to the polyphase dynamother-xnal history of rocks of the Besham block. However, two distinctly different groups of apparent ages are present in the hornblende data. The older group ranges from 2031-1865 Ma and the younger group ranges from 51-36 Ma (Table 3.4). These two groups of dates are the first clear evidence that a geological record of one or more pre-Himalayan thermal events is preserved despite the apparent complex thermal history of rocks within the Besham block. Apparently the oldest hornblende sample from the amphibolites of the Besham block is 87MSB45 (Figure 3.12), which exhibits a complex history in its 40Ar/39Ar age spectrum. Because this is the oldest sample from the Beshain block and because of the complexity of the age spectrum, in the following discussion, the thermal release data will be examined in order to limit possible geochronologic interpretations. The apparent age of argon extracted in the lowest temperature heating steps from 500 to 650°C drops from over 3 Ga to 573 4 Ma (Figure 3.l3a). From 650 to 148 THERMAL & METAMORPHIC EVENTS OF BESHAM BLOCK 0 600 Hb (7) 500 f Mu Mu Mu Bt K\ Zr St St K Bt Ap AR 100 0 1 10 100 1000 10000 AGE (Ma) Figure 3.11. Summary diagram showing Early Proterozoic to Cenozoic metamorphic/thermal events in the Besham block. Hornblende from amphibolites of the Besham basement complex (Hb), actinolite rim growth around hornblende of the amphibolite of the Besham basement complex (AR), Muscovite from Lahor granite gneiss and metasediments (Mu), biotite from granites and granite gneisses (Bt), potassium feldspar from Paleozoic granites (K), zircon (Zr), and apatite (Ap). Fission track data from Zeitler (1983, 1985) 149 9500C, the dates increase to just over 2.0 Ga. A plateau date of 1998 ± 6 Ma is defined by the intermediate temperature steps (950-10750C; 58% released 39Ar). From 1100 to 1450°C, the age spectrum steps up in apparent age to 2031 ± 6 Ma. To help in the interpretation of the age spectrum, an inverse isochron and39Ar/37Ar ratios are useful. An isochron of all data for this sample reveals at least three components of contained argon. Excess is present in the 500 to 600°C lowest temperature steps; from 650 to 950°C is evidence for argon loss; finally, the temperature steps from 950 to 1450°C yield an isochron date of 2005 ± 60 Ma with an initial 40Ar/36Ar ratio of 321 ± 16, ratio similar to that of argon in present-day atmosphere. No evidence for excess argon is indicated in the temperature steps above 1075°C. In addition, the 39Ar/37Ar ratio (Table 3.5) can be used to evaluate relative distribution of K and Ca in the sample and composition of the phase degassing during various parts of the spectrum (Figure 3.l3b). From 950 to14500C, sample 87MSB45 has a relatively constant39Ar/37Ar ratio of 0.22, which is typical of hornbleride. From 950 to850°C, the ratio drops to 0.11, suggesting that the argon degassed within this temperature interval was, at least in part, controlled by a different phase, probably actinolite. In the lowest temperature part(800-650°C) of the age spectrum, the 39Ar/37Ar is between 0.27 and 1.14, which may 150 Figure 3.12. Proterozoic hornblende (Hb), biotite (Bt), and muscovite (Mu) age spectra from the Besham basement complex. Hornblende from amphibolites, biotite from Jabrai hornblende-biotite granite gneiss, and muscovite from sodic granite boulder of the kmlo conglomerate. 2500 2500 2500 2500 1500 1500 1500 Hb 87M065 Hb OAKS Hb Si [042 Bt SJMS6SI 500 -1- - - I - 500 -- -J 500 _a 500 U = I A II U 0 50 tOO 50 - IOU 50 100 0 50 100 1 2500 7± 2500 AN 0 ARC 'I 7' 1500 1;44, - LI / / / LI // LI / LI / Mu 5JL05913 / Hb 5JLOO7C 500 IA__I _I i I-----I - I _I _I i_A _I AL_ 0 50 100 50 100 2500 1500 Hb 87M0310 Hb 57M0385 500 j ----I 500 __1 __I----U _n__L_i a__i 0 50 0 50 100 2500 2500 \ /iA,verj1 1500 H' 34 45 I b \. :3, I Hb 55 Hb 87M13135 ( 5001 J I_ J_ I_ \ I' L_ r ! A_ 0 50 N'SgRA B E \SIH A M" M A 50 1013 2500 B1LO C K" B L 0 C K 1500 - I -- - oLIe1eIS Hb 87MB336 / \ Hb MSII45 500 1 I__U-L LA jj_ A 500 I__I_U_A±___U1_U_ 0 50 IOo 0 50 100 2500 w 2500 01 I- 1500 Figure 3.12. Hb 5J[012C Hb 87MB374 '0500_L._1 -1U _L_ A I 5001 _II__J_------50 100 0 50 100 39ArK RELEASED 152 be due to a higher 1< phase such as alteration chlorite or included biotite. Thus, the interpreted apparent age of sample 87MSB45 is complex. From 950 to 1450°C a single phase, hornblende, controls the degassing characteristics of the sample (Figure 3.13b). The apparent age of the majority of this portion of the age spectrum is 1998 ± 6 Ma but the apparent age increases to 2031 ± 6 Ma in the highest temperature steps (Figure 3.13a). Using a model of volume diffusion (Turner,, 1968) to explain degassing characteristics of argon retained within hornblende (Harrison, 1981), this part of the age spectrum indicates that the hornblende cooled below about 530 ± 20°C after some thermal event at or before 2031 ± 6 Ma but was partially thermally rest at 1998 ± 6 Ma. The apparent argon loss from 2003 ± 6 to 573 ± 4 Ma (Figure 3.13a) is a result of the mixing of argon from actinolite, chlorite or biotite, and to a lesser extent, hornblende, because this temperature range is within the normal range for argon degassing from actinolite, chlorite, and biotite but below that for hornblende. Because the 39Ar/37Ar ratio of the sample rises above 0.11 below 850°C (Figure 3.l3b), 1518 ± 4 Ma (the date at850°C; Figure 3.l3a and Table 3.5) is a maximum estimate of the time of actinolite cooling. The remainder of the age spectrum is controlled by chlorite and biotite and of no significance for the interpretation. Figure 3.13c shows the mineral 153 Figure 3.13. The thermal release data and mineral phase relations of the sample 87MSB45. Age spectrum of the sample 87MSB45, showing different ages for low- to high-temperature steps. The 39Ar/37Ar ratio verses 39ArK percent released diagram, showing relation between degassing behavior of the hornblende (Hb), actinolite rims (AR), and chlorite (Chi) or biotite (Bt) at different temperature steps. A thin section sketch of a hornblende from sample 87MSB45 showing phase relations of the hornblende, actinolite rims, biotite, and chlorite. Actinolite rims (AR) grow along the margins of the hornblende and in fractures. The minor chlorite and biotite inclusions occurs along cleavages or fractures. 154 (a). 1100°C 950°C 1075 C 1 45 (IC Plateau Age 1998±6 2031±6 2000 -d 3±6) 1500 r 950°C (± 4) 00 -.--050°C573'4) I I 10 20 30 40 50 90 70 90 90 100 39 ArkReleased(%) 1450°C 950°C I-lb I I I 100 20 3039 40 50 60 70 80 90 Ark Released(%) Figure 3.13. 155 Figure 313 continued. 156 relations observed in thin section, shows actiriolite rims on hornblende that contains a very small percentage of biotite within inclusions and/or minor chlorite alteration along fractures and supports this interpretation. Hornblende from sample 87MB135 (Figure 3.12) yielded an argon loss spectrum with a maximum date of 1997 ± 8 Ma in the higher temperature steps (l075-14500C) defined by 36.1% of gas of the total released 39Ar and a minimum date of 1331 ± 5 Ma at 850°C. An isochron analysis of this sample yields a date of 1989 ± 146 Ma with an 40Ar/36Ar initial ratio of 334 ± 40 for the same part of theage spectrum (1075-1450°C) and evidence for argon loss in the lower temperatures. The 39Ar/37Ar ratios of this sample are nearly identical to those of hornblende 87MSB45. The 1997 ± 8 Ma date is interpreted to be a minimum estimate of original time of cooling of the hornblende and 1331± 5 Ma is a maximum estimate of time of actinolite cooling. The age spectrum for hornblende sample 5JLOO7C (Figure 3.12) has a maximum date of 1951± 4 Ma (1150- 1450°C; 43.2%released 39Ar) and an isochron date for the same temperature steps of 1950 ± 104 Ma with an 40Ar/36Ar initial ratio of 301 ± 27 Ma. The age spectrum displays argon loss to 1438 ± 11 Ma; the isochron corroborates this apparent argon loss. The 39Ar/37Ar ratios are very similar to those of hornblende 87MB135 and 87MB45. Therefore, 1951 157 ± 4 Ma is a minimum time of hornblende cooling and 1438 ± 11 Ma is a maximum for time of actinolite cooling. The age spectrum for hornblende sample 5JLO12C (Figure 3.12) is typical for a sample containing excess argon. An isochron analysis on whole sample yields a date of 1887 ± 1600 Ma and an40Ar/36Ar initial ratio of 5650 ± 8000; the extremely large errors are due to scatter about the isochron resulting from variable amounts of excess argon. The age spectrum is "saddle-shaped"; the lowest apparent age, intermediate temperature step yields a date of 1950 ± 3 Ma, which commonly would be interpreted to represent a maximum estimate of the cooling age. Hornblende sample 5JL042 also contains excess argon. The age spectrum is very similar to that of sample 5JLO12C but the 39Ar/37Ar ratios of 5JL042 are higher than those of 5JLO12C. The isochron of 5JL042 hornblende yields a date of 1539 ± 750 Ma with much scatter resulting from variable amounts of excess argon and an40Ar/36Ar initial ratio of 2470 ± 1800. The lowest apparent age, intermediate temperature step has a date of 1895 ± 3 Ma and can be interpreted to be a maximum estimate of the cooling age. Hornblende and biotite from amphibolite samples 87M36A and 87MB310 have been dated. The age spectrum of pre-Hiinalayan hornblende from B7MB6A (Figures 3.12 and 3.14) exhibits a plateau date of 1865 ± 3 Ma (52.5% released 39Ar) and a maximum date of 1922 ± 3 Ma. 158 Figure 3.14. Amphibolite (87MB6A) of the Besham basement complex. Note the MB3 hornblende is overprinted by the MBS biotite. Hornblende (87MB6A) yields a plateau date of 1865 ± 3 Ma and biotite (87MB6A) yields aminimum date of 64 ± 0.2 Ma. 159 The age spectrum shows argon loss at 1803 ± 5 Ma at the lowest 39Ar/37Ar ratio step. In contrast, biotite from 87MB6A (Figures 3.15 and 3.14) yields a minimum date of 64 ± 0.2 Ma (40.5% released39Ar). Hornblende 87MB310 (Figure 3.12) has an argon loss spectrum. It yields a maximum date of 1950 ± 3 Ma and shows minor resetting at 1358 ± 5 Ma at the lowest 39Ar/37Ar ratio step. The 1950 ± 3 Ma is interpreted to be the minimum cooling age of the hornblende. In contrast, biotite 87MB310 (Figure 3.16) shows severe argon loss with a maximum date of 485 ± 29 Ma and a minimum date of 25 ± 5 Ma. The low-potassium amphibole sample 87MB307 (Figure 3. 12), from a metapyroxenite yields a plateau date of 1887 ± 5 Ma (70% released 39Ar) and a maximum date of 1958 ± 4 Ma (16.5% released 39Ar). The isochron shows three components. The plateau portion (950-11500C) has an isochron date of 1883 ± 150 Ma with an 40Ar/36Ar initial ratio of 316 ± 40. The high temperature part (1200-14500C) of the age spectrum has an :Lsochron date of 1931 ± 81 Ma with an 40Ar/36Ar initial ratio of 307 ± 21. Finally, the lowest temperature part of the age spectrum shows argon loss that occurred at or later than 1652 ± 45 Ma. This age spectrum shows that an earlier thermal event occurred at or before 1958 ± 4 Ma and the sample was thermally reset at 1887 ± 5 Ma. Hornblendes have been dated from samples 87MB374 and 87MB336, a group of amphibolite dikes which intrude the 160 Figure :3.15. Phanerozoic biotite (Bt)40Ar/39Ar age spectra from granites, granite gneisses, metasediments, shear zones, amphibolites, and inafic dikes of the Mansehra, Besham, and Swat blocks. 00 000 Bt 5JLO490 200 1000 50 4170 I - 100 - BOO Bt -- B7MRBA --- Bt 67M1333A !_. .1 - -- 200 - L_i ------i.s_L U 50 IOU 50400 0/ 50 100 0 50 100 100 600 SLANDI------ARC-1 - A.. i (4,/ /7// 5 /7/ Bt - 87M)355 I B 7M17 I 1)2 2 / Bt .... - ..L-.r_J...t _.j -- 0 50 00 50 100 (00 0 Bt 87M1142 - 81 87MR56 0 L i __± A __rn .L----- 0 50 100 0 50 100 35 600 111R, ye,7 30 4317 St SAKS ElI 117MR272 i_... I . 25 . _L L r _I_I I i 0 50 SI'HAM/\MANSE1iRA 50 400 100 BLOCK Bt 57MS758 B1LOCK' \ 50 0 10 4] kilo rioters 7230 73 F St 57MR54 .....j 0 _r_.j.j_.L _.i _j -I- ' 0 50 100 50 100 '5 600 200 (2 F I- 300 Z 100 Ui cr H Bt 87ME1104 Figure 3.15. Bt 87MR60 0 1_ 4__i . L__1. 50 100 50 100 39Ar6 RELEASED 1%) 162 Lahor sodic granite gneiss and hornblende-biotite granite grleiss of the Beshain basement complex. Hornblende sample 87MB374 (Figure 3.12) yields an argon loss spectrum with a maximum date of 1910 ± 4 Ma and shows minimum date of 1417 ± 3 Ma at the lowest39Ar/37Ar ratio step. Sample 87MB336 shows partial argon loss and has a preferred/maximum date of 1884 + 3 Ma and a minimum date of 664 ± 12 Ma (Table 3.5) An amphibolite xenolith sample 87MB385 (Figure 3.12) was collected from the Late Carboniferous Karai sodic granite (see below), which intrudes the Besham basement complex (Figure 3.4j). Hornblende from this sample yields an apparent argon loss spectrum with a maximum date of 2160 ± 4 Ma and a minimum date of 1950 ± 4 Ma. An isochron analysis of this sample has not been conducted but 2160 ± 4 Ma is interpreted to represent the original time of cooling of the mafic rock protolith and 1950 ± 4 Ma is interpreted to be the age of metamorphism. The age spectra of most of hornblende samples (87MSB45, 87MB135, 5JLOO7C, 87MB6A, 87MB310, 87MB307, 87MB374, and 87MB336) show minor to partial argon loss which ranges between 1803 ± 5 Ma to 664 ± 12 Ma (Table 3.5) related to later actinolite rim development. The youngest date with lowest 39Ar/37Ar ratio, therefore, is the most reset age for the hornblende. Thus, the maximum age of 163 Figure 3.16. Phanerozoic potassium feldspar (K)arid biotite (Bt) 40Ar/39Ar age spectra from granites, granite gneisses, pegmatites, amphibolites, and inetasediments of the Beshairi and Mansehra blocks. 200 100200 20010 too 87MB2 I - 81 47MS473 0 131 87MS450 tOO 0 0 81 50 87MS728 tOO 50 100 0 ------i__Li_j___i__j 50 100 0 7 JLL I ------1--- 1 50 I ------c __ 200too SLAND AFC / / / / / / / 87MB6CI 0 50 100 -/ / taSt I 50 8 7Mtt 380] tOO 400800 St 50 87M1347A 100 r 00 400200 -f 'TRive1./ 0 Bt''I 50 87M047A 100 B IE S1I'H A M ,. I bi -! J' M A N S E'ij R A = L_=_I 50 87MI380 I I tOO (0ILl 400 I IJJJ '5 BLOC K zLI' - 200 \ BLO C Kf kiIornI1erS _10 a- 0 I L_L _r 8 7MB4 7 I \73E 50 8 7MI6 tOO 39Ar, IFLEASED 1%) 50 100 Figure 3.16. \ 165 actinolite rim development is inferred to be 664 ± 12 Ma in the Besham basement complex. Based on petrographic and field relations pre-Himalayan deformational fabrics were obliterated and new hornblende growth occurred in amphibolites of the Besham basement complex whenever the amphibolites were deformed within Himalayan shear zones (Figures 3.lOc and 3.lOd). To determine the age of this Himalayan shearing, four hornblende samples (87MB23, 87MB155, 87MB144, and 87MB148; Figure 3.17 and Table 3.4) from amphibolites along the Thakot fault zone were dated. Hornblende sample 87MB23 (Figure 3.lOc) yields a plateau date of 51 ± 2 Ma (73.2% released 39Ar) and an isochron date of 51 ± 0.13 Ma with an 40Ar/36Ar initial ratioof 295 ± 3. Sample 87MB155 yields a maximum date of 46 ± 1 Ma (48.6% released 39Ar) and an isochrori date of 46 ± 0.13 Ma with an 40Ar/36Ar initial ratio of 297 ± 0.6. The age spectrum shows a minimum date of 39.50 ± 0.38 Ma and minor excess argon in lower temperature steps. Sample 87MB148 has a relatively flat age spectrum. Isochron analysis on temperature steps 500-1075°C yields a date of 33 ± 0.2 Ma and 40Ar/36Ar initial ratio of 285 ± 8. The age spectrum shows a minimum date of 36 ± 0.3 Ma (49.7% released 39Ar) and a maximum date of 38 ± 0.3 Ma (27.2% released 39Ar). An isochron date for sample 87MB144 is 37 ± 7 Ma with an 40Ar/36Ar initial ratio of 491 ± 80. The age spectrum and isochron analysis show excess argon 166 Figure 3.17. Phanerozoic hornblende (Hb) 40Ar/39Ar age spectra from amphibolites and basalt dikes of the Manshera, Besham, and Swat blocks and Kohistan island arc terrane. 1000 450- Hb 8 7MB 148 200 200 It 300 500 L 100 100 150 it Hb 875113451 Hb 87510144 Q ....r._j I ------0 I------II..t.__..i-----t IOU (3 50 100 0 / 50 100 SLAND ARC IOU 50 J Hb 87MS785 0 - r - 50 100 50 too 600 200 100 Hb B7MRUO R 0------L 100 0 50 ioU ,#IPP M A N S E'IR A S / W A B E S1/H A M I J ': BLOC 600 200 \B1LOCK-j LU BLOCK 10 F- ¼; / 100 / \ 10 5------1 S 87M823 7230 \73E Hb 87MO253 0 - I I 0 ( I I 50 100 0 50 100 ArK RELEASED 1%) Figure 3.17. 168 but a maximum date of 50 + 2 Ma (23% released 39Ar) can be interpreted from this age spectra. (2). Metasedi]nents of the Besham basement complex To provide lower temperature thermal control on metamorphism of the Besham basement complex, mica samples from the Thakot formation were dated. Muscovite (87MB7) and biotite (87MS726) give information on thermal activity near 300°C. The age spectrum of biotite 87MS726 (Figure 3.16) from garnet-biotite-muscovite guartzofeldspathic schist of the Thakot formation is a disturbed age spectrum. The age spectrum steps up in age from 92 ± 1 Na at low release temperature to 233 ± 1 Ma at the highest release temperature and is typical of argon loss. These data indicate that the sample of pre-Himalayan metasedimentary rock was reheated to 300°C at or younger than 90 Ma. Muscovite from sample 87MB7 (Figure 3.18), a biotite-muscovite quartzofeldspathic schist of the Thakot formation which was collected from close to a shear zone that crosscuts the Besham basement complex also shows a disturbed age spectrum with a maximum date of 31 Ma and a minimum date of 26 Ma. The sample is close to the Mamdin Sar fault (Figures 3.3 and 3.18), a younger structure that crosscuts Besham basement complex. The40Ar/39Ar date and 169 Figure 3.18. Phanerozoic muscovite (Mu) 40Ar/39Ar age spectra from granites, pegmatites, and metasediments of the Besham, Swat, arid Mansehra blocks. Mu 400 Ti - 0 200 Mu 33 7M07 ..L .1.1. 1d .. 0 .1. .J 1_S. 0 50 too 50 tOO SLAND ARC 7. / E 100 Mu 137MS47 I,/1.4 200 /111/ \ 100 Mu 87M3365 0 . ...n / L I ._LJ j_ t_ 0 50 100 50 100 too 400 200 Mu S7MB2OA 1/I oi ye Mu 87M82333 50 100 _L. L _( t 50 100 MA N S E'HR A SWAT B E A M BLOC 100 BL 0 C K B1LoC K' 0 10 Si 0/1/etc/S 8 7M S 7 5 33 7230 Mu 87M856 50 305 -t S L __ 39ArK RELEASED 50 300 H Figure 3.18. 0-1 171 apparent argon loss that occurred between 31 Ma and 26 Ma are related to shearing along this fault. (3). Intrusive rocks of the Besham basement complex In addition to samples of amphibolites and metasedimentary rocks, hornblende, biotite, muscovite, and potassium feldspar from samples of granites and granite gneisses in the Besham basement complex have been dated to evaluate age of metamorphism and thermal history. These data are complicated and clearly show the complex history of the Besham block. A sample of the Dubair hornblende-biotite granite gneiss was collected within 100 meter of the IYINT (Figure 3.12). Pak5 hornblende from this sample yields an argon loss spectrum from 1966 ± 16 Ma to 405 ± 3 Ma. This sample is at least a hornblende concentrate because biotite and hornbleride are iritergrown with each other and were impossible to perfectly separate. Because of severe biotite contamination, the age spectrum can not be strictly interpreted except that the Dubair granite gneiss is certainly Early Proterozoic in age. An amphibolite xenolith (sample N686) from the same body was dated by Treloar et al.(1989) and yielded an excess argon age spectrum with a maximum date of 1920 ± 24 Ma which was interpreted to be the age of metamorphism. However, this date does not define 172 Figure 3.19. Late Proterozoic to Tertiary muscovite (Mu) 40Ar/39Arage spectra from the Besham block, Swat block, Mansehra block, Neotethys terrane, and the Kohistan island arc terrane. Location 1 = 84 ± 1.7 Ma K/Ar date (Shams, 1980) arid location 2 = 83.6 ± 2 Ma 40Ar/39Ar plateau date (Maluski and Matte, 1984). 2000 200 200 1000 <00 <00 Fuchoite 87M54[J0 odic mica 87M11401 [7MS450 0 -----LLJ - U 0 50 100 - 50 <00 I- 100 100 --- - S L AN D AR . F? 50 / 50 // .4 // // Mu 87Mf34 // Mu 87MS824 0 r _L L 2 t L I I 0 50 50 <00 <00 K 25 50 Mu P0K 8 Mu 87M13249 20 i _L < 50 100 50 100 100 C 10 34 _45_ Mu 87M3801A I ±_U_t------M A N S ERA o 50 100 AT B E A M ' 100----- \BILOCK1 \ BLOCK too------LU - BLOCK 10 50 z I 0 <0 Ui It kIlo/IletlIrs Mu 87M842 7230 \ \ \73E Mu 0- / I II - J 0 51< 100 50 39ArK REIEASED 1%) <00 Figure 3.19. 174 with certainty the age of metamorphism because of the extreme excess argon and because no plateau or isochron dates were documented. In addition, Treloar et al. (1989) presented no geological or fabric evidence to constrain this date as age of metamorphism. The age spectrum for muscovite 87MS450 (Figure 3.19) from a sample of Lahor sodic granite gneiss is disturbed and yie:lds a total gas date of 530 ± 1 Na. This age spectrum is interpreted to be the result of partial argon loss and steps up from a minimum date of 188 ± 0.50 Ma to a maximum date of 623 ± 2 Na (24% released 39Ar). A previously reported K-Ar date (Treloar et al., 1989) of 530 ± 20 Ma from a biotite granite (sample N686) of the Besham basement complex has been interpreted as the age of major magmatism in the Indo-Pakistan plate. The 530 ± 20 Ma K/Ar date is within one sigma error of total gas date of the 530 ± 1 Ma of muscovite sample 87MS450. The total gas date is meaningless because the age spectrum shows partial argon loss from 623 ± 2 Ma to 188 ± 1 Ma and the total gas date is integrated over this total spectrum. The biotite sample of Treloar et al. (1989) may be equally disturbed as expected in this multiply metamorphosed and deformed Precambrian Besham basement complex but unrecognized by the K/Ar analysis. Therefore, the contention of Treloar et al. (1989) that a major period of magmatism occurred at 530 Ma, based on their K/Ar date, should be viewed with caution. In 175 addition, biotite from sample 87MS450 (Figure 3.16) shows severe argon loss with a maximum date of 99 ± 0.34 Ma and a minimum date of 64 ± 2 Ma and confirms the complex thermal history that affected these rocks. Biotite sample 87MB6C (Figure 3.16) from a pegniatite which intrudes amphibolite 87MB6A yields a maximum date of 53 ± 0.21 Na. Biotite and muscovite from sample 87MS473 (Figures 3.18 and 3.16) from sheared Darwaza Sar granite gneiss have also been dated. The biotite age spectrum shows an argon loss spectrum with a maximum date of 221.5 ± 6 Ma and minimum date of 73 ± 0.20 Ma. In contrast, muscovite, which formed in the ductile shear fabric along the Chakesar - fault zone, yields a broad U-shaped spectrum with a maximum date of 30 ± 0.12 Ma. Biotite sample 5JL049B (Figure 3.15) from a xenolith of Lahor sodic granite gneiss in the Dubair hornblende- biotite granite gneiss has a severe argon loss spectrum but yields a plateau date of 333 ± 1 Ma. Two very important samples that provide evidence for cooling of Besham basement complex rocks below300°C in the Proterozoic are biotite 87MS691 and muscovite 5JL049B. Biotite sample 87MS691 (Figure 3.12) is from the Jabrai hornblende-biotite granite gneiss. The biotite defines the SB3 gneissic fabric of this rock. The age spectrum ofthis biotite is only slightly disturbed and typical of argon loss from a maximum of 1782 ± 3 Ma to a minimum of 1731 ± 3 176 Ma. The significance of this age spectrum is the clear evidence that the Besham basement complex rocks cooled below 300°C by 1782 Ma. All younger dates record events that occurred after this initial cooling and are clearly related to later thermal activity and not prolonged cooling after Proterozoic metamorphism Muscovite 5JL059B (Figure 3.12) is also important because it was separated from a sample of a boulder of graphic tourmaline-bearing muscovite sodic granite from the basal Amlo metaconglomerate of the Karora group (Figure This conglomerate lies upon the metamorphosed Besham basement complex and is itself metamorphosed to low-grade. The age spectrum of the muscovite yields a maximum date of 1517 ± 3 Ma with a minor argon loss at 1036 ± 2 Ma. The granite boulder from which the sample was taken shows no metamorphic fabric and a clear magmatic texture (Figure Therefore the 1517 + 3 Ma muscovite date is a cooling age of the sodic granite and also clearly shows that the Besham basement complex rocks cooled below 300°C in the Proterozoic. (4). Metasediments of the Karora group Muscovites from the graphitic phyllite of the Kurmang formation and the low-grade carbonates of the Kandoana formation have also been dated. Muscovite 87MB4 (Figure 177 3.19) from lineated low-grade carbonate of the Karidaona formation (Figure 3.6f), close to the Chakesar fault zone, yields an argon loss spectrum with a maximum date of 36 ± 0.3 Ma (35.3% released 39Ar) and a minimum date of 29.4 ± 0.4 Ma. The presence of one strong fabric (Figure 3.6g) in the sample is evidence that the earlier fabric in the Kandoana formation was transposed and/or muscovite regrown between 29 to 36 Ma during a major episode of shearing along the Chakesar fault zone. Muscovite sample 87MB20A (Figure 3.18) from low-grade carbonate of the Kandoana formation yields a broad U-shaped excess argon spectrum, with a maximum date of 130 ± 0.4 Ma. Muscovite 87MB5l9 (Figure 3.18) from highly deformed graphitic phyllite of the Kurmang formation, yields a broad U-shaped spectrum with a maximum date of 30 ± 0.24 Na, and an isochron date of 28 ± 13 Ma with an 40Ar/36Ar initial ratio of 553 ± 268. The 40Ar/36Ar initial ratio clearly shows that the age spectrum records excess argon but the scatter of points about the isochron makes interpretation of the data difficult. (5). Post'-Karora group sodic granites Potassium feldspar (orthoclase) sample 87MB47A (Figure 3.16) from a tourmaline-bearing pegniatite (Figure 3.4i), which intrudes the Karora granite (Figures 3.4h and 3.4i) 178 yields a maximum 40Ar/39Ar date of 493 ± 1 Ma (46.2% released 39Ar) and a minimum date of 143 ± 0.5 Ma. Biotite sample 87MB47A (Figure 3.16) from the same unit, shows a disturbed spectrum, with a maximum date of 66 ± 0.2 Ma. Potassium feldspar (orthoclase), 87MB380 (Figure 3.12), from the Karai biotite granite (Figure 3.3), yields a maximum date of 272 ± 1 Ma (35.6% released 39Ar) and a minimum date of 56.5 ± 0.23 Ma. Biotite sample 87MB380 (Figure 3.16) from the same unit yields an argon loss spectrum with minor excess at lower temperature steps. The biotite age spectrum defines a maximum date of 38 ± 0.2 Ma and an isochron date of 37 ± 2 Ma with an 40Ar/36Ar initial ratio of 336 ± 22. Biotite sample 87MB2 (Figure 3.16) from sheared Ranial biotite granite close to the Chakesar fault zone (Figure 3.3) yields a preferred date of 36 ± 0.2 Ma (42.8% released 39Ar) and an isochron date of 36 ± 0.30 Ma with an 40Ar/36Ar initial ratio of 296 ± 4. SWAT BLOCK Horriblende, potassium feldspar, biotite, and muscovite from inetasediments, aniphibolites, Swat/Choga granite gneiss, and diabase dikes of the Swat block, yield 40Ar/39Ar cooling ages of Early Permian, Late Cretaceous, Paleocene, Eocene, and Oligocene (Figure 3.20). 179 THERMAL & METAMORPHIC EVENTS OF SWAT BLOCK 600 500 Hb(2) Hb Hb I- 400 Mu Mu Mu w K a. 300 Bt w Bt 200 w Ap Zr 100 0C') ) 0 0 10 100 1000 AGE (Ma) Figure 3.20. Suitnuary diagram showing Late Carboniferous to Cenozoic thermal/metamorphic events in the Swat block. Hornblende from djabase dike (Hb), muscovite from inetasediments and granites (Mu), biotite from metasediments and granites (Bt), potassium feldspar from granite gneisses (K), zircon (Zr), and apatite (Ap). Fission track data from Zeitler (1983, 1985). 180 The older cooling ages preserved in Besham block rocks compared to these data of the Swat rocks are indisputable evidence for different thermal histories in these two crustal blocks. (1). Low-grade units of the Peshawar basin Hornblende (E)(Figure 3.21 and location 3 on Figure 3.1) from a diabase dike which intrudes the Ambela granite yields a total gas date of 956 ± 27 Ma. An isochron analysis on all temperature steps yields an isochron date of 160 ± 15 Ma with an 40Ar/36Ar initial ratio of 368 ± 45. The isochron analysis shows that 160 Ma date has no geologic meaning, because the 40Ar/36Ar initial ratio records excess argon. However, temperature steps 700-850°C with an 39Ar/37Ar initial ratio of 0.17 to 0.08, yield a maximum date of 268 ± 26 Ma. Isochron analysis of these temperature steps yields an isochron date of 284 ± 4 Ma with an 40Ar/36Ar initial ratio of 294 ± 4. As the 40Ar/ 36Ar initial ratioof 294 ± 4 is within one sigma error of 295.5 initial ratio of air, the 284 ± 4 Ma isochron date is the best estimate for the inafic magmatisin that was source of this dike. Muscovite (D)(Figure 3.21 and location 2 on Figure 3.1) from a chlorite-grade phyllite of the Middle Ordovician (?) to Late Silurian Panj Pir formation of Pogue 181 Figure :3.21. The Late Proterozoic to Cenozoic potassium feldspar (K), hornblende (Hb), Biotite (Bt), and Muscovite (Mu) 40Ar/39Ar age spectra from the Swat block, Kohistan island arc terrane, and Hazara area. For samples location see Figure 3.1. 1500 2505 200 w 1000 (5 Z (000 ISO w j 500 E D SolIcits COliC 87MSB43 0 - - - 0 50 100 50 100 50 100 35 35 300 50 Si ::r.c:rrrccun_.r5+ 200 (5 40 -= -35 30 z (1 Ui 150 Mu PAK9 llBt PAK9 20 K PAK1O Hb PAK1O 25 .J. 1. tJ. I....I .J.L_ 25U------r I ------r r - 00 ° 0 50 100 00 - 50 100 RELEASED 39ArK RELEASED 39AIK RELEASED 39AR RELEASED Figure 3.21. 183 and Hussian, (1986) has been dated. The fabric of this sample records two deformational events (Figure 3.22). An isochron analysis on all temperature steps yields a date of 61 ± 10 Ma with an 40Ar/36Ar initial ratio of 329 ± 64. The 40Ar/36Ar initial ratio is within 1 sigmaerror of 295.5 initial ratio of air, thus the maximum date of 83 ± 3 Ma (30% released 39Ar) and a minimum date of 63 ± 0.4 Ma (46.7% released 39Ar) represent argon loss, not excess argon. Sanidine SN1 (Figure 3.1 and location close to sample E) from metamorphosed Shewa porphyry has been dated. Isochron analysis on temperature steps 850-1250°C yields an isochron date of 61 ± 22 Ma with an 40Ar/36Ar initial ratio of 293 ± 120. Thus, a maximum date of 85 ± 4 Ma and a minimum date of 39 ± 2 Ma can be interpreted from this argon loss spectrum. (2). High-grade to medium-grade metamorphic units of the Alpurai and Swat areas west of the Puran fault Potassium feldspar, muscovite, and biotite from a sample of sheared Swat granite gneiss (Pak9) have been dated (Figure 3.21 and location 4 on Figure 3.1). The potassium feldspar shows minor excess argon at lower temperature steps and shows an argon loss profile with a maximum date of 45 ± 0.2 Ma and a minimum date of 184 Figure 3.22. Phyllite of the Panj Pir formation (D) showing two fabrics. The early fabric is dated at 83 ± 3 Ma and later fabric shows partial resetting at 63 ± 0.4 Ma. Magnification - lox; crossed nicols; 1.31 mm field ofview. 185 22 ± 0.1 Ma. Biotite shows a preferred date of 32 ± 0.1 Ma (86.1% released 39Ar) with minor argon loss at 28 ± 0.12 Ma, however, muscovite yields a plateau date of 28 ± 0.2 Ma (93.4% released 39Ar). Biotite and muscovite have been dated from sheared Choga granite gneiss (Pak8; also known as the Swat granite gneiss) west of the Puran fault. The biotite (Figure 3.15) yields a preferred date of 29.4 ± 0.1 Ma (70% released 39Ar) with minorexcess argon at lower temperature steps; however, the muscovite (Figure 3.19) yields a preferred date of 23 ± 0.1 Ma (92.7% released 39Ar) with minor excess argon at lower temperature steps. Muscovite sample 87MS8O1A (Figure 3.19) from marble of the Marghazar formation, yields a flat age spectrum with a preferred date of 28 Ma (87% released 39Ar) and minor resetting at 25 ± 1 Na. Biotite 87MS758 (Figure 3.15) from Manglaur formation yields an argon loss spectrum with a maximum date of 22 ± 0.3 Ma (27.4% released 39Ar) and minimum date of 12 ± 0.3 Ma. However, muscovite sample 87MS758 (Figure 3.18) yields a maximum date of 28.5 ± 0.4 Ma (21.8% released 39Ar) and a minimum date of 24.6 ± 0.12 Ma (38.9% of gas). Muscovite 87MB42 (Figure 3.19) from the muscovite- biotite graphitic schist of the Saidu formation, yields a preferred or close to plateau date of 24.4 ± 0.1 Ma (100% 186 released 39Ar) and the coexisting biotite (Figure 3.15) yields a plateau date of 23 ± 0.2 Ma (92.3% released 39Ar). Hornblende 87MS785 (Figure 3.17) from a garnet amphibolite dike which intrudes the Marghazar formation, yields an isochron date of 31 ± 0.25 Ma with an 40Ar/36Ar initial ratio of 297 ± 4 (temperature steps 950-1450°C). The isochron analysis shows that this portion of the age spectrum does not record excess-Ar, thus 32 ± 1 Ma maximum date (28.3% released 39Ar) and 31 ± 0.1 Ma minimum date (49.8% released 39Ar) can be interpreted from the age spectrum. The amphibolites of the Alpurai group around Mingora in Swat yield maximum hornblende dates of 39 Ma to 40 Ma and minimum dates of 36 Ma (L.W. Snee, in Rosenberg, 1985; Figure 3.23) and muscovite from metasediments of the Alpurai group yield dates between 35-30 (L.W. Snee, in Rosenberg, 1985; Figure 3.24). MANS EHRA BLOCK Hornblende, muscovite, biotite, and potassium feldspar from amphibolite, mafic dikes and sills, peginatite, tourmalirie-bearing granite gneiss, Tanawal Formation, and Bana group metasediments, all from Allai-Kohistan have been dated by the 40Ar/39Ar method. These rocks yield cooling ages ranging from Early Ordovician to Cenozoic 187 0Co .01 60 50 100 Ark Released (%) Figure 3.23. Composite 40Ar/39Ar hornblende age spectra from the amphibolites of the Alpurai group of Swat, showing 36-40 Ma dates (Snee, in Rosenberg, 1985). 188 (Figure 3.25). These cooling ages are different from those of the Besham basement complex, as with the case of Swat block, are indisputable evidence for different cooling history in these crustal blocks. The Thakot and puran faults between the Mansehra block to the east and Swat block to the west of the Besham block, respectively, mark the distinct geochronologic break between different thermal histories of these blocks (Figure 3.26). South of the Mansehra block in the Hazara area, SH1 pre-Himalayan fabric (Table 3.1) in the Hazara Formation predates the unconformable deposition of the Cambrian Abbottabad Group (Baig and Lawrence, 1987; Baig et al., 1988). Sericite mica concentrate (87MSB43; Figure 3.21 and location 1 on Figure 3.1) has been dated from SH1 low-grade fabric of the Hazara Formation. The age spectrum shows argon loss from 900 ± 4 Ma to 106 ± 0.34 Ma with an intermediate age mean plateau. Even though this spectrum is complex, three dates can be interpreted from it. A preferred date of 650 ± 2 Ma and a maximum date of 900 ± 4 Ma can be interpreted from the age spectrum. A preferred date of 650 ± 2 Ma from the intermediate part of the age spectrum with 39Ar/37Ar ratio of 58-66 (temperature steps 600-7000C) is interpreted to be the time of major thermal resetting. Beside the high 39Ar/37Ar ratio, the preferred date also records 54.4% of the total gas of the age spectrum. The maximum date of the age spectrum of 900 Ma 189 100 10 0 60 C) t,) 40 Tn,ax 35.14.i5 Ma Tt= 29-30 Ma 50 100 Ark Re'eased (%) Figure 3.24. Composite 40Ar/39Ar muscovite age spectra from the Alpurai group of Swat, showing 36-40 Ma dates (Snee, in Rosenberg, 1985). 190 (with low 39Ar/37Ar ratio of 21.68) can be interpreted to represent a minimum estimate of original cooling or the age of provenance of the Hazara Formation mica. I preferred later interpretation. The small amount of argon loss to 106 ± 0.3 Ma in the low temperature part of the age spectrum is interpreted to be a maximum estimate of the time of later, low-temperature thermal effect. Hornblende sample 87MB253 (Figure 3.17) from amphibolite, which defines the SM2 fabric (Figure 3.9c), yields a preferred date of 466 ± 2 Ma (57.8% released 39Ar). Theage spectrum shows excess argon in lower temperature steps (500-9000C). The isochron analysis on non-excess argon portion of the age spectrum (Temp. steps 950°C, 1075°C, and 1200°C), yields an isochron date of 464 ± 1 Ma with an40Ar/36Ar initial ratio of 306 ± 0.66, ratio similar to that of argon in present-day atmosphere. The isochron date of 464 ± 1 Ma is within one sigma error of the preferred date of 466 ± 2 Ma (Temp. steps,950°C, 1075°C, and 1200°C). Therefore this ainphibolite cooled below 530 ± 20°C closure temperature of hornblende at 466 ± 2 Ma. These results show that the isochron analysis is useful to separate the non-excess argon portion of the age spectrum to yield meaningful geochronoiogical information. Biotite and hornblende from a sample of garnet amphibolite (87MB55) which is transposed parallel to the SM2 fabric of the Tanawal Formation,yield disturbed age 191 THERMEL & METAMORPHIC EVENTS OF MANSEHRA BLOCK 600 500 Hb 400 Mu Mu Bt 300 Bt 200 Zr 100 - Ap 0 10 100 1000 AGE (Ma) Figure 3.25. Summary diagram showing Early Ordovician to Cenozoic metamorphic and thermal events in the Mansehra block. Hornblende from amphibolite (Hb), muscovite from shear zones (Mu), biotite from metasediments and diabase sill (Bt), zircon (Zr), and apatite (Ap). Fission track data from Zeitler (1983, 1985). 192 spectra. The hornblende age spectrum (Figure 3.17) has a maximum date of 221 Ma (temp. steps925-1400°C) and an isochron date of 189 ± 29 Ma for the same temperature steps with an 40Ar/36Ar initial ratio of 324 ± 54. The age spectrum yields a minimum date of 129 ± 1 Ma. The age spectrum for coexisting biotite of sample 87MB55 (Figure 3.15) is also typical of argon loss with a maximum date of 232 ± 1 Ma and a minimum date of 91±2 Ma. In comparison, hornblende sample 87MB60 (Figure 3.17) from amphibolite parallel to SM2 fabric of the Tanawal Formation yields an isochron date of 258±11 Ma (temp. steps1025_14500)with an40Ar/36Ar initial ratio of 296±14. A maximum date of 281±1 Ma and a minimum date of 167±1 Ma are interpreted from this age spectrum. The coexisting biotite of sample 87MB60 (Figure 3.15) yields a preferred date of 198±1 Ma (64.9% released 39Ar). These disturbed biotite and hornblende dates do not define a metamorphic event, and only show that the pre-Hiinalayan SM2 fabric is partially reset during Himalayan deformation. Biotite 87MB272 from SM2 fabric and muscovite 87MB272 from SM3 fabric, which overprints the SM2 biotite of the Tanawal Formation (Figure 3.9d), yield the Early Ordovician and Late Cretaceous dates respectively. The biotite (Figure 3.15) yields a total fusion date of 406±1 Ma and a total gas date of 408±1 Ma. These two separate runs confirm that the total gas and total fusion dates are 193 COOLING AGE PROFILE ALONG LINE A-A' 10000 BESHAM BLOCK SWAT MANSEHRA Hb I-lb Hb 1000 BLOCK BLOCK Hb -J I Bt LU OHb 100 C Mu Hb Hb(4) 10 0 10 20 30 40 50 60 DISTANCE (Km) Figure 3.26. Cooling age profile along line A-A'on Figure 312 across the Mansehra, Besham, and Swat blocks, showing sharp break in the cooling ages across the Thakot and Puran faults. The Early Proterozoic cooling ages are reset between 32-51 Ma along the Thakot and Puran faults. Data points from Figures 3.12, 3.17, 3.18, and 3.19. 194 within 2 sigma error. The step heating age-spectrum shows argon loss profile, with a maximum date of 434 ± 1 Na (28.4% released 39Ar) and a minimum date of 303 ± 1 Ma. These results show that the total fusion, total gas, and K/Ar dates must be evaluated before use, to determine whether they show argon loss or argon excess in a multiply deformed and metamorphosed terrane. In contrast, SM3 muscovite 87MB272 (Figures 3.19 and 3.9d) yields relatively flat spectrum with a preferred or close to plateau date of 70 ± 0.2 Ma (95% released 39Ar). The age discordant between these coexisting minerals is herein interpreted to be real even though it is normally expected that biotite would be reset if younger muscovite grows later. My interpretation is that this rock had cooled below 300°C biotite closure temperature before 434 Na, and was reheated to300°Cor less at 70 Na. At the time of reheating muscovite formed but biotite did not recrystallized. This indicates that the Late Cretaceous metamorphism and deformation was related to a thermal event which was close to300°C. A series of fresh basalt to diabase dikes and sills postdate the SM2 gneissic fabric of the Mansehra granite gneiss and the metasediments of the Tanawal Formation (Figures 3.9e and 3.9g). Magmatic biotite sample 87MB33A (Figures 3.15 and 3.9f) from a diabase sill (Figure 3.9e), which is not affected by the Himalayan penetrative 195 shearing, yields a preferred date of 262 ± 1 Ma and shows minor argon loss at 75 ± 0.4 Ma. A fresh basalt dike 87MB61 (Figure 3.17) which postdates the FM2 structures of the Tanawal Formation (Figure 3.9g) and yields an U-shaped spectrum. A maximum date of 159 ± 0.4 Ma can be interpreted from the age spectrum. The interpreted date has 41% of the total gas with an 39Ar/37Ar ratio of 0.24. Biotite 87MB54 (Figure 3.15) from the sheared Tanawal Formation yields an argon loss spectrum with a preferred date of 90 ± 0.3 Ma (47.3% released 39Ar) and minor argon loss at 68 + 1 Ma. Biotite 87MB56 (Figure 3.15) from the sheared Tanawal Formation yields an argon loss with a maximum date of 138 ± 1 Ma and a minimum date of 109 ± 0.3 Ma. Muscovite 87MB56 (Figure 3.18) yields a severe argon loss spectrum with a maximum date of 42 ± 0.15 Ma and a minimum date of 30 ± 0.26 Ma. To the east of Thakot fault, a one-and-a-half-meter- thick ductile shear zone is present within the Tanawal Formation; the shear zone cuts the main SM2 fabric of the country rock. In epidote amphibolite facies shear zone matrix, lenses of garnet-amphibolites are ductilely rotated with a right lateral sense of motion. Two foliations defined by mica are present in the shear zone matrix, the earlier foliation is rotated and transposed parallel to the later foliation (Figure 3.lOe). Biotite 87MB101 from 196 rotated lens of garnet-amphibolite (Figure 3.lOd), biotite and muscovite 87MB102 from the ductile shear zone matrix (3.lOe), and biotite 87MB104 from the SM2 fabric of the country rock have been dated to evaluate local thermal effects across this local shear zone. Biotite 87MB1O1 (Figure3.15)from a garnet amphibolite lens yields an argon loss spectrum with a preferred date of 51 ±0.19Ma and shows argon loss at35± 0.18 Ma. Biotite 87MB102 (Figure3.15)from the matrix of the ductile shear zone yields an argon loss spectrum with minor excess argon in the lower temperature steps. A maximum date of 68 ± 0.2 Ma and a minimum date of 46 ± 0.2 Ma are interpreted from this age spectrum. Muscovite 87MB102 (Figure3.19)yields a preferred or close to plateau date of 28 ± 0.13 Ma (82.6% released 39Ar). Biotite 87MB104 (Figure3.15)from the country rock shows argon loss from 202 ± 2 to 62 ± 1 Ma. These data show that the shear fabric in the shear zone formed between51Ma to35Ma and reactivation of shear zone occurred at 28 Ma, which is similar to the shear history in the Besham block along Thakot fault. Potassium feldspar (orthoclase), 87MB65 (Figure3.16), from a sheared tourmaline peginatite of the Nansehra granite, yields a severely disturbed age spectrum, with a maximum date of190 ± 0.5Ma and a minimum date of33± 0.2 Ma. The muscovite 87MB65 (Figure3.18),which was disturbed during shearing, yields an argon loss spectrum. The maximum 197 date of 29.5 ± 0.13 Ma and a minimum date of 24 ± 0.3 Ma can be interpreted from this age spectrum. Muscovite, 87MB249 (Figure 3.19), from sheared graphitic phyllite of the Bana group along the Chail Sar thrust yields a plateau date of 24.3 ± 0.2 Ma (77.2% released 39Ar). This date show that the Chail Sar thrust was active at 24 Ma. Muscovite, 87MB283 (Figure 3.18), from phyllite of the Bana group yields a preferred date of 32 ± 0.13 Ma, with minor excess at lower and higher temperature steps. Muscovite, 87MS824 (Figure 3.19), from sheared tourmaline granite (Figure 3.log) in a shear zone, yields a preferred date of 30 ± 0.10 Ma (90.5% released 39Ar) and minor argon loss at 27 ± 0.2 Ma. Isochron analysis on this sample yields a date of 31 ± 4 Ma with an 40Ar/36Ar initial ratio of 304 ± 50. The preferred date of 30 ± 0.10 Ma is within one sigma error of the isochron date of 31 ± 4 Ma and record the time of shear zone development in the Mansehra block. The 24 Ma to 30 Ma muscovite dates from the shear zones and faults indicate that these structures were active during the development of the Indus syntaxis. 198 NEOTETHYS TERRANE Fuchsite, 87MB400 (Figure 3.19), from a schist (Figure 3.27) in the ophiolitic melange yields a plateau date of 82 ± 0.22 Ma (73.5% released39Ar) and an isochron date of 81 ± 3 Ma with an40Ar/36Ar initial ratio of 292 ± 12. These dates are within one sigma error and thus record the time of lower greenschist facies metamorphism in the melange. KOHISTAN ISLAND ARC TERRANE Hornblende and sodic mica (Figure 3.28) from a garnet- paragasite-and-plagioclase-bearing amphibolite dike, which intrudes the Jijal complex have been dated by the40Ar/39Ar method. Hornblende 87MB401 (Figure 3.17) yields a L-shaped spectrum. The age-spectrum has a preferred date of 117 ± 0.4 Ma (40.5% released 39Ar) and an isochron date of 117 ± 0.6 Ma with an 40Ar/36Ar initial ratio of 296 ± 1. The 117 ± 0.4 Ma date is the cooling age for this hornblende.Sodic mica 87MB401 (Figure 3.19) which overprints earlier honrblende and was formed during greenschist facies retrogression of the amphibolite dike (Figure 3.28), yields an argon loss spectrum. The isochron date of 48 4 Ma with an40Ar/36Ar initial ratio of 324 ± 35 shows that it is not an excess age spectrum. Thus, the age spectrumshows a maximum date of 83 ± 2 Ma and minimum date of 34 ± 4 Ma. 199 Figure 3.27. Fuchsite-bearing schist from the Mingora ophiolitic melange of the Indus suture zone.Fuchsite (87MB400) yields a plateau date of 82 ± 0.22 Ma. Magnification - lox; crossed nicols; 1.31 mm field ofview. 200 Hornblende, Paklo (Figure 3.21 and location 5 on Figure 3.1), from the Kalam quartz diorite of the Kohistari batholith, yields a maximum date of 88 ± 0.4 Ma. Coexisting potassium feldspar from this sample (Figure 3.21) yields a maximum date of 49 ± 0.2 Ma and a minimum date of 17 ± 0.1 Ma. 201 Figure 3.28. A garnet ainphibolite dike (87MB401)which intrudes the Jijal complex. Early hornblende (Hb)is overprinted by garnet (Gt), epidote (Ep), andsodic mica (Sm). Hornblende (87MB401) is dated at 117 ±0.4 Ma and sodic mica (87MB401) is dated at 83 ± 2 Ma.Magnification lOx; crossed nicols; 1.31 mm field ofview. 202 DISCUSSION AND IMPLICATIONS OF4°ir/39Ar DATA In this section the40Ar/39Ar data are combined with field, fabric, and metamorphic data to constrain the timing of pre-Himalayan and Himalayan orogenic events in the northwest Himalaya of Pakistan. (1). Beshain block (a). Geologic implications The Besham block in the core of the Indus syntaxis (Baig et al., 1989) records evidence of the earliest events known in the Himalaya west of the Indus syntaxis and in the Aravalli orogenic belt of Rajastan India. The 2500-1850 Ma U/Pb and Rb/Sr isotopic data from these areas have been interpreted the timing of pre-Himalayan intrusive events (Bhanot et al., 1979; Divakara and Rama, 1982; Valdiya, 1983; Sharma, 1983; Choudhary et al., 1984; Zeitler etal., 1989). However, no40Ar/39Ar isotopic age data is available from the Himalayan collision zone to document adetail history of pre-Himalayan metamorphism and deformation. The timing of these pre-Himalayan events in theBeshain block is interpreted here on the basis of thestratigraphic, intrusive, and fabric history interpreted above and the related plateau, maximum, and isochron40Ar/39Ar isotopic 203 dates. Hornblende and biotite 40Ar/39Ar data from three sets of amphibolites of the Besham basement complex constrain the timing of four Precambrian thermal events involving both deformation and metamorphism (D1, D11, D111, arid D1vTables 3.1 and 3.2). These metamorphic and deformational events are separated by various depositional and igneous events. The first three occurs only in the Beshain block. The time of the earliest event is best determined from particularly good dates on two samples (87MSB45 and 87MB135). The maximum date of 2031 ± 6 Ma (87MSB45) and 1997 ± 8 Ma (87MB135) and a plateau date of 1998 ± 6 Ma (87MB45) are within 1 sigma error of isochron dates of 2005 ± 60 Ma (87MSB45) and 1989 ± 146 Ma (87MB135). These data show that the D1 (MBI) event occurred between 1997 ± 8 Na to 2031 ± 6 Na (Figures 3.29 and 3.30, Tables 3.1 and 3.2). was preceded by deposition of the Thakot and Pazang formations of the Besham basement complex, ultramafic flows, intrusion of mafic dikes, and intrusion of the Darwaza Sar and Lahor granites all of which are metamorphosed during D1 (Table 3.2). Thus deposition of these formations and associated ultrainafic flows and intrusion of these granites are at least Early Proterozoic in age (>2031 Ma) and may have been Late Archean (>2500 Ma). The granite gneisses of the Beshain basement complex may correlate with the similar 2500 Ma granite gneisses reported from the Nanga-Parbat syntaxis (Zeitler et al., 1989), Himalaya (Ehanot et al., 204 2500 MB1 = 1997 ± 8 - 2031 ± 6 Ma 500 0 50 100 ArKReleased (%) Figure 3.29. Composite 40Ar/39Ar hornblende age spectra from the ainphibolites of the Besham basement complex, showing 1997 ± 8 Ma to 2031 ± 6 Ma M1 metamorphic event. 205 1979; Valdiya, 1983; Sharina, 1983; Divakara and Rama, 1982), and Rajastan (Choudhary et al., 1984). U/Pb dating of the Besham basement complex is needed to define crystallization ages of these plutons. Samples those record two fabrics (SB2 and SB3; Figure 3.8g) provide data on the timing of D11 which has no known sedimentary or igneous events separating it from D1. Maximum hornblende dates on such samples are 1951 ± 4 Na (5JLOO7C), 1950 ± 3 Ma (87MB310), 1950 ± 3 Ma (5JLO12C), and 1958 ± 4 Na. These are within 1 sigma error of isochron dates of 1950 ± 104 Ma (53L007C) and 1931 ± 81 Na (87MB307), and thus define a minimum age of 1950 + 3 Ma for D11 (MB2) upper amphibolite facies metamorphism (Baig and Snee, 1989) (Figures 3.31 and 3.30, Tables 3.2 and 3.1). Two interpretations of the relation between and are possible. My preferred interpretation is that these are distinct events, because they are separated by 47 Ma to 81 Ma and the structures formed during each event have very different geometries and styles. D1 folds are east-west trending and north vergent while D11 are north-south trending and either east or west vergent. Alternatively, 1997 ± 6 Ma to 2031 ± 6 Ma dates can be interpreted as the maximum ages for upper amphibolite facies metamorphism and 1950 ± 3 Na dates to be the post-metamorphic cooling after 1997 ± 8 Ma to 2031 ± 6 Na metamorphic event. 206 600 Hb Hb Hb Hb Hb I 1 1 500 M83 MB2 MEl SB3 SB2 SE1 400 FB3 FB2 FBi 81 300 Post-MB3 metamorphic cooling 200 1 /25 1825 1925 2025 AGE (MA) Figure 3.30. Composite cooling, metamorphic (MEl, H32, and N33), fabric and and folding events (F31, FB2, and FB3) diagram. 207 Treloar et al.(1989a) report pressure and temperature data for what they consider the earliest Himalayan deformation of the Besham block but which is descriptively as used herein. Their results indicate a peak temperature of 650 ± 500C and pressure of 9 ± 2 kbar for which supports the interpretation that 1950 Ma is a cooling age for the end of this event. Syn- or post-D11, hornblende-biotite granites intruded the Besham basement complex (Figure 3.3). subsequently both were intruded by mafic dikes. Hornblendes in these dikes (Figure 3.8h) and hornblende-biotite granites (Figure 3.8j) record no fabric earlier than 5B3 which developed during under epidote amphibolite facies conditions in contrast to the earliest mafic dike set which records multiple fabrics. These hornblerides date D111 (MB3; Figures 3.32 and 3.30) between 1865 ± 3 Ma and 1887 ± 5 Ma based on the following dates: a preferred/maximum date of 1884 ± 4 Na (87MB336), plateau dates of 1865 ± 3 Ma (87MB6A) and 1887 ± 5 Na (87MJ3307), and an isochron date of 1883 ± 150 Ma (87NB307). The ages determined for and D111 bracket the time of emplacement of the hornblende-biotite granites, the Shang, Jabrai, and Dubair plutons, and associated mafic dikes between 1887 Ma and 1950 Ma. The intensity of deformation and metamorphism during D1, D11, and D111 varies through out the Besham basement complex. Thus the earlier events are dateable in the BeshaTn 208 2500 MB2 = 1950 ± 3 Ma 500 50 100 39ArK Released (%) Figure 3.31. Composite 40Ar/39Ar hornblendeage spectra from the amphibolites of the Besham basement complex, showing 1950 ± 3 Ma MB2 metamorphic event. 209 basement complex where the younger events did not completely obliterate the older events. During D111, the peak metamorphic temperatures were locally above hornblende closure to reset D1 and D11. However, after D111 the Besham block never went above hornblende closure temperatures of 500-550°C except in the local Himalayan shear zones. Zeitler et al.(1989) report a U/Pb date of 1852 ± 14 Ma on the Iskere gneiss of the Nanga-Parbat syntaxis which they interpret as an igneous intrusive age because of the lack of 40Ar/39Ar evidence for Early Proterozoic metamorphism and deformation. The 1852 ± 14 Na U/Pb date is within 1 sigma error of the 40Ar/39Ar plateau date of 1865 ± 3 Na of sample 87MB6A suggests that the U/Pb date reflects an Early Proterozoic metamorphic event in the Nanga-Parbat syntaxis. Biotite 87MB691 (Figure 3.12 and Table 3.4) from the Jabrai hornblende-biotite granite gneiss which defines SB3 developed during D111. It yields an argon loss spectrum with a maximum date of 1782 ± 3 Ma and a minimum of 1731 ± 3 Ma. There is no evidence for an igneous intrusive event at this time which might have reset these biotites. Thus 1782 ± 3 Ma is interpreted as the lower limit for post-M3 metamorphic cooling in the Besham block (Figure 3.30). The most reasonable interpretation of this prolonged cooling would be that the Besham block was deeply buried as part of the 210 2500 MB3 = 1865 ± 3-1887 ± 5 Ma Nb 5ct Nb I J w Hb Bt = 1782 ± 3 Ma <1500 Mu = 1517 ± 3 Ma r 500 0 50 100 39 ArKReleased (%) Figure 3.32. Composite 40Ar/39Ar hornblende age spectra from the amphibolites of the Besham basement complex, showing 1865 ± 3 Ma to 1887 ± 5 Ma MB3 metamorphic event. Biotite (87MS691) show post-metamorphic cooling at 1782 ± 3 Ma, and maginatic muscovite (5J1059B) date of 1517 ± 3 Ma postdates the 1782 ± 3 Ma post-metamorphic MB3 cooling of the Besham basement complex. 211 middle crust (roughly >9 kin)from the time of D111 until about 1782 Ma. was followed by the intrusion of equigranular graphic muscovite-tourmaline sodic granites. Subsequently, uplift, erosion, and unconformable deposition of the Karora group occurred in the Beshani block. The basal Amlo conglomerate of the Karora group contains a boulder of this granite (Figure 3.7a). Muscovite 5JL059B from this boulder (Figure 3.7b) has a maximum date of 1517 ± 3 Ma which is interpreted as a cooling age placing this granite in the Middle Proterozoic (Table 3.2). This date also indicates the deposition of the Karora group and its stratigraphic equivalents, the Manki, Gandaf, Dakhner, Shahkot, Sheikhi, and Hazara formations began after 1517 ± 3 Ma. Div, the Hazaran orogeny (Baig and Lawrence, 1987; Baig et al., 1988; Baig et al., 1989), is dated in the Besham basement complex between 625 and 664 Ma by the development of actinolite rims around Early Proterozoic hornblendes at 664 ± 12 Ma (87M3336) and by a muscovite date of 623 ± 2 Ma (87MS450) from the Lahor sodic granite gneiss. This was a lower greenschist facies event in the Besham block which formed a late spaced cleavage in the Besham basement complex, SB4 (Figure 3.8i), and the oldest preserved cleavage, SK1 (Figure 3.6b), in the Karora group (Table 3.1). 212 The Early proterozoic Beshani orogenic events at Besham partly correlate with the Early proterozoic Aravalli orogeny of Rajastan India. In the main Himalaya, the older north- trending structures of the Aravalli orogenic belt (Sharma, 1983), provide structural control to the younger Himalayan structures (Gupta, 1964; Valdiya, 1984). Similarly in the Besham area of northern Pakistan, the Himalayan structures are folded against the north-trending pre-Himalayan structures of the Besham basement complex. This indicates that the pre-Humalayan structures of the Beshain basement complex are the northwestern most extension of the Aravalli orogenic belt. The next interpreted tectonic event, Dv, is poorly recorded in the Besham block (Table 3.3). The Late Proterozoic Hazaran orogeny was followed by Cambro- Ordovician granite intrusions (Table 3.3). A pegmatite of Karora sodic granite (87MB47A) has a potassium feldspar maximum date of 493 ± 1 Ma, and this is interpreted as the cooling age of pegmatite which is the minimum age of intrusion. This is not greatly different than the earlier published 500 ± 16 Ma Rb/Sr whole rock isochron date on the Mansehra granite (LeFort et al., 1980; Table 3.3). No 40Ar/39Ar dates in the Besham block clearly record the deformation and metamorphism, Dv, that accompanied this intrusive episode in the Nansehra block (Table 3.3). 213 During the Late Carboniferous and Permian, this area of Gondwana underwent a significant episode of rifting that is considered Dvi (Table 3.3). Two dates from the Besham block reflect this event. The potassium feldspar maximum date of 272 ± 1 Ma (87MB380) is the cooling age of the Karai sodic granite. The time of intrusion of this granite was >272 Ma which is within the geological time span of the rift related alkaline magmatism (315 ± 15 to 297 ± 4 Ma; Le Bas et al., 1987; Rafiq, 1987) in the Peshawar basin. The preservation of an Early Proterozoic hornblende maximum date of 2160 ± 4 Ma and a minimum date of 1950 ± 4 Ma in a mafic xenolith (87MB335) in this body confirms that this was a high level intrusive body. Furthermore, the hornfelses aureole of the Karai granite overprints the inetasedinients of the Besham basement complex, and thus postdates the metamorphism and deformation of the Besham basement complex to be pre-Carboniferous in age. A plateau biotite date of 333 ± 1 Ma (5JL0493) from a xenolith of Lahor granite in the Dubair hornblende-biotite granite gneiss may reflect Late Carboniferous reheating during rifting and mafic dike injection. No samples from the Besham block record any dates for events in the Mesozoic. Three Jurassic K/Ar dates reported by Treloar et al.,(1989) of 182 ± 5, 176 ± 6, and 176 ± 6 Ma from granites and inetasedinientswhich are considered to be related to Jurassic extension or inversion of the 214 Neotethys ocean. These K/Ar dates may be disturbed as expected in this multiply metamorphosed and deformed Precambrian Besham basement complex (see samples 87MS726, 87MB6C, and 87MS450, Table 3.4, Figures 3.16 and 3.19) but unrecognized by the K/Ar analysis. In addition no plateau and isochron 40Ar/39Ar dates have been documented by Treloar et al.(1989) to support the Jurassic K/Ar dates. Thus contention of Treloar et al.(1989) that 176 Ma dates relate to Jurassic extension or inversion of Neotethys should be viewed with caution. The remaining dates from the Besham block record events of the Himalayan orogeny. Correlation of these events by fabrics, fold orientations, and metamorphic facies between blocks (Dvii to Dix, Table 3.1) is less confident than the correlation achieved for Precambrian and Paleozoic events. Blocks were significantly separated during early Himalayan events, juxtaposed at some stage along major faults, and experienced quite different thermal histories. No block records a history of all the events that appear to have occurred. The earliest dated Himalayan event in the Beshairi basement complex of the Beshain block is a low grade static metamorphism without fabric development (Figures 3.8j and 3.14), MBS (Dix), at about 64 Ma in the Early Paleocene. The most important dates are on biotites with a minimum date of 64 ± 0.2 Ma from an Early Proterozoic amphibolite (87MB6A; 215 Figure 3.14), a minimum date of 64 ± 2 Ma from the Lahor sodic granite (87MB450), a maximum date of 66 ± 0.2 Ma from tourmaline pegmatite of the Karora granite (87MB47A), and a maximum date of 64 ± 0.2 Ma from the Karora granite (87MB47). All of these biotites occur in rocks in which other minerals are much older, in particular, 87MB6A has biotite of 64 ± 0.2 Ma and hornblende of 1865 ± 3 Ma (Figure 3.14), and in some samples, biotite is only partially reset (87NS691, 87MS473, 87MS726, and 5JL049B) . This shows that the Early Paleocene metamorphic event reached locally temperatures sufficient to reset biotites (>2800C), but not to even partially reset hornblerides with closure temperatures of 500-550°C. MBS is characterized by chlorite overgrowth of biotite and hornblende, and biotite overgrowth of N34 actinolite rims and MB3 hornblendes (Figure 3.8j) without new muscovite growth in the Beshain basement complex (Table 3.1). Thus MB5 (Dix) in the Besham block did not exceed low biotite zone temperatures. This is the last recrystallization event to affect the Besham basement complex regionally. This event correlates with the thrust fault activity prior to Paleocene to Eocene sedimentation reported in the Attock-Cherat Range on the southeastern margin of the Peshawar basin (Yeats and Hussain, 1987). Correlation of Besham basement complex recrystallization, M35, and Karora group fabrics, SK2 and SK3 is not yet clear (Table 3.1), and the dates determined 216 in this study do not resolve these relations. Thin section study confirms new muscovite growth in the Karora group during main foliation development, SK2 (Figure 3.6d), and limited growth during crenulation cleavage development, SK3 (Figure 3.6e). Three Karora group samples were dated, all using muscovite. Sample B7MB2OA has a maximum date of 130 ± 0.35 Ma and may reflect a very early development of SR2. Samples 87MB4 and 87MB519 have muscovites that grew after the 64 Ma biotite growth in the basement complex at maximum dates of 36 ± 0.25 Ma and 30 ± 0.24 Ma, respectively. These samples were taken in or near north-south shear zones and new muscovite formed during shearing (Figure 3.6g). Thus none of the samples dated appear to directly date the SR2 or SR3. Tentatively, SK2 is most likely to have developed during the highest Himalayan temperatures throughout the Besham block, that is, during biotite resetting, MB5, at about 64 Ma. SK3 is largely a crenulation cleavage and involved limited recrystallization some time between 64 and 51 Ma related to Dx south-directed thrust and south vergent folds. Subsequently, Dxi formed the Indus syntaxis (Table 3.1). Shear zones and associated faults are an important structures in the Besham block and dates determined provide important insight into the timing of the development of these structures. Four hornblende samples (87MB23, 87MB155, 87MB148, and 87MB144; Figure 3.17 and Table 3.4) from the 217 Besham block are very close to the Thakot fault and have young isochron, plateau, maximum, and preferred dates between 51 Ma to 36 Ma. The 51 Ma to 36 Ma dates (Figure 3.33) constrain the time of motion of this structure as a shear zone at significant depth which developed epidote ainphibolite facies shear fabrics (Figures 3.lOc and 3.lOd). The pre-Himalayan metamorphic events of the Nansehra and Beshain blocks are partially to completely reset to Eocene-Oligocene close to the Thakot fault (Figure 3.26). The Thakot and Puran faults mark a distinct geologic (Figures 3.2 and 3.3), structural, metamorphic (Table 3.1), and geochronologic break between the Mansehra, Besham, and Swat blocks (Figure 3.26). Two samples from along the Chakesar fault zone constrain the motion of this structure. A preferred biotite date from sheared Ranial granite (87MB2) is 36 ± 0.2 Ma and a maximum muscovite date from a lineated carbonate of the Kandoana formation (87MB4) is 36 ± 0.25 Ma (Figures 3.6f and 3.6g). These are within one sigma error of the isochron date of 36 ± 0.3 Ma with an 40Ar/36Ar initial ratio of 296 ± 4 of sample 87M32. Thus 36 Ma is the best time of lower green- schist facies shear fabric development along the Chakesar fault zone (Figure 3.34). The 29 Ma minimum date of sample 87MB4 show reactivation of Chakesar fault zone at about 29 Na. Two other muscovite samples from the Beshani basement complex and the Darwaza Sar granite are near shear zones. 218 50 Ar Released (%). K Figure 3.33. Composite 40Ar/39Ar hornblende age spectra from the amphibolites of the Besham basement complex close to the Tahkot fault, showing 36-51 ± 2 Ma epidote amphibolite facies ductile shearing along the Tahkot fault. 219 These have maximum dates of 31 ± 0.11 Ma (87M37) and 30 ± 0.12 Ma (87MB473) and are interpreted to reflect the time of shearing. Thus shear zones and faults were active from 51-36 Ma (Figure 3.33; Thakot fault), at 36-29 Ma (Figure 3.34; Chakesar fault), and at 30 Na (minor shears and faults). (b).Timing of Pb/Zn mineralization The results of this study provide broad constraints on the timing of Pb/Zn stratiform and skarn mineralization in the Pazang formation. The Pb/Zn stratiforin mineralization formed in the Early Proterozoic or Late Archean, because it is older than the intrusion of the earliest mafic dikes, the Darwaza Sar and Lahor granites, and D1 (1997-2031 Ma). Pb/Zn skarn mineralization occurred repeatedly in association with the intrusion of granites and their associated peginatites into the Pazang formation dolomites. Dated episodes that developed skarns occurred at >2031, 1517, >493, and >272 Na, that is, from Early Proterozoic to Late Paleozoic. Detailed 40Ar/39Ar and U/Pb dating of granites and peginatites from the skarn zones is needed to more closely bracket the times of Pb/Zn skarn mineralization. 220 100 0 50 100 Ark Released (%) Figure 3.34. Composite 40Ar/39Ar age spectra of biotite (87MB2) and muscovite (87M34) showing 36 Ma to 29 Ma Himalayan shearing along the Chakesar fault zone. 221 (C). Thermal/cooling history of the Beshain block The Beshain block went through a complex thermal/cooling history from the Early Proterozoic to the Pliocene (Figures 3.11, 3.30 and 3.35). Widespread preservation of Early Proterozoic ages in Besham block hornblerides indicates that temperatures above hornblende closure of 500-550°C were confined to this time. The Beshain block cooled below 530 ± 20°C during D1 (MB1; 1997-2031 Ma), D11 (MB2; 1950 Ma), and D111 (MB3; 1865-1887 Ma)(Figure 3.30).After Besham block never went above hornblende closure temperature during later pre-Himalayan and Himalayan deformation and metamorphism. The preferred interpretation of the biotite date of 1782 ± 3 Na is that this records very slow post-D111 (MB3) metamorphic cooling (Figure 3.30) at about 3°C/m.y. during continued deep burial. This date clearly indicates that the Besham basement complex rocks cooled below 300°C by 1782 Ma before the intrusion of the Middle Proterozoic granites (1517 Ma) and unconformable deposition of the Karora group. Temperatures dropped to surface conditions during erosion prior to Karora deposition. Late Proterozoic metamorphism, Div (625-664 Ma), did not reach hornblende closure temperature in the Beshaxa block. It cooled below muscovite closure temperature of 300°C at the end of this episode. Two significant thermal pulses followed during the Paleozoic in conjunction with 222 TERTIARY COOLING HISTORY OF BESHAM BLOCK 000 C-) Hb W 500- Hh <400- cc a 300- U) w 200- cc 100- C-) C 0 10 20 30 40 50 60 AGE (Ma) Figure 3.35. Tertiary cooling history of the Beshain block. Fission track data from Zeitler (1983, 1985). 223 granite intrusions. During these events plutoris cooled below 280°C closuretemperature of potassium feldspar at 493 ± 1 Ma and 272 ± 1 Ma. The partial to complete resetting of most biotites at about 64 Ma in the Beshain block shows that the earliest Himalayan metamorphic temperatures were around biotite grade of metamorphism. This Early Paleocene metamorphism (Dix) locally exceeded 300°C to affect biotite, but did not reset hornblendes in the Besham block. Early Proterozoic hornblendes (87MB6A, 87MB45, 87MB307, and 5JLOO7C) with a closure temperatures of 500-5500C were not even partially reset, suggesting that the tectonic load burying the Besham block during Early Paleocene, due in large part to Himalayan thrust sheets, was about 10 to 12 km. Thus the Besham block did not experience high grade metamorphism which is present in the adjacent Marisehra and Swat blocks. The high grade metamorphism and deformation in the Mansehra and Swat blocks must have occurred before the Early Paleocene further north of the Besham block. These blocks juxtaposed with the Beshain block between 64 Na to 51 Ma. Early Proterozoic hornblendes were reset within the shear zone of the Thakot fault between 51 and 36 Ma (Figures 3.33 and 3.26), and these are taken as the time(s) of shear fabric formation and hence fault motion as a ductile shear zone. These higher temperatures (500-550°C) are found only within the fault zone, and the best interpretation is that 224 either frictional heat produced by shearingor hot hydrothermal fluids travelling in the shear zone or both elevated these temperatures. The biotite and muscovite dates from 36 Ma to 24 Ma (Figures 3.34 and 3.36) relate to shear zones and reflect deformation at shallower structural levels where shearing locally raised temperatures above 300°C and induced muscovite and biotite recrystallization. Fission track dates in the Besham block (Zeitler, 1983 and 1985) record continued cooling and uplift of the Besham block. The 16-22 Ma zircon and 5.2-5.6 Ma apatite dates reflect cooling below 215 ± 25°C and 100 ± 20°C respectively (Figure 3.35). The apatite dates of 5.2-5.6 Ma suggest that about 3.3 km of Himalayan thrust sheets were on the top of Besham block at 5.2-5.6 Ma. The presence of all the lithologies of the Besham block in the Indus River Quaternary shows that the Besham block was exposed to surface conditions before the Quaternary. (2). Swat Block (a). Geologic implications As yet no dates from the Swat area reveal any information about the Precambrian history of this area, and correlation of the stratigraphic sequence to other areas is the only way to approach the times of early events. The 225 100 36 Ma 24-30 Ma 50 100 39 Ar Released (%) K Figure 3.36. Coiiiposite 40Ar/39Ar muscoviteage spectra showing 36 Ma and 30-24 Ma Himalayan shearing inthe Indus syntaxis. 226 oldest stratigraphic unit is the Manki formation along the southeastern margin of the Peshawar basin which has one pre-Hiinalayan main cleavage, SAl (see discussion in Mansehra block below). The next stratigraphic unit in the area is the Manglaur formation, nowhere in direct contact with the Manki formation, but correlated on the basis of lithology with the Tanawal formation of the Tarbela and Mansehra block. The Choga granite and other units of the Swat granite gneiss intrude this unit. In the absence of old dates it is unclear when in the Late Proterozoic to Cambrian these units were intruded. They are tentatively correlated on the basis of lithology with the Cambro-Ordovician Mansehra granite gneiss. These granites have xenoliths of mafic rocks, suggesting an early phase of mafic activity predated the intrusion of these granites. The first event in the Swat area for which new dating information results from this study is late Paleozoic rifting (Pogue et al., in prep..a). Previous evidence for rifting from this area includes the interpretation of the Ainbela granite as a rift intrusive (Rafiq, 1987), Rb/Sr whole rock isochron ages of 315 15 Ma to 297 ± 4 Ma on alkaline granitic rocks which intrude the Ainbela granite (Le Bas et el., 1987), and mafic dikes intruding Paleozoic sedimentary rocks in Swat block. These mafic dikes are considered to be feeders to mafic lava flows of the Karapa 227 greenschist of the Peshawar basin, biostratigraphically between Middle Pennsylvanian and late Triassic (Pogue et al., in prep.a), and the correlative amphibolite horizon of Swat (DiPietro, 1990). Hornblende E (Figure 3.21; location 3, Figure 3.1) from one of these feeder dikes yields an isochron date of 284 ± 4 Ma with an 40Ar/36Ar initial ratio of 294 ± 4. It is noteworthy that the 284 ± 4 Ma date falls within age limit of the Middle Pennsylvanian to late Triassic maf ic lava flows of the Karapa greenschist. Thus 284 ± 4 Ma isochron date provides the maximum age constraint for Early Permian basic magmatism which was source to the Karapa greenschist and amphibolite horizon of Swat. This confirms a correlation of these units with the Permian Panjal traps of Kaghan (Ghazanfar and Chaudhry, 1985; Papritz and Rey 1989) and Zanskar (Gaetani et al., 1990). This dike also intrudes the Aiithela granite and confirms the Late Carboniferous age of this unit. Thus the Late Carboniferous Ambela granite and alkaline rocks predated Early Permian maf Ic Panjal volcanism in the Peshawar basin. Post-rift deposition included the late Triassic or younger Kashala, Saidu, and Nikanai Ghar formations of the Alpurai group in the Swat block. Three additional 40Ar/39Ar dates from the eastern Peshawar basin are important. A phyllite sample D (location 2, Figure 3.1) from the middle Ordovician(?) to Late Silurian Panj Pir formation of Pogue and Hussian, (1986) has 228 two fabrics S1 and S2 developed under chlorite zone conditions of lower greenschist fades (Figure 3.24). Muscovite D from this sample has an argon loss spectrum (Figure 3.21) with an isochron date of 61± 10 Ma and an 40Ar/ 36Ar initial ratioof 329 ± 60. The 40Ar/36Ar initial ratio of 329 ± 60 shows the age spectrum does not record excess argon. The maximum date of 83 ± 3 Ma and a minimum date of 63 ± 0.4 Ma can be interpreted from the age spectrum. Two alternative explanations can be offered for argon loss from 83 3 Ma to 63 ± 0.4 Ma:(1) The 83 Ma maximum date is the minimum age for chlorite zone metamorphism and the 63 Ma date shows diffusive argon loss due to post-metamorphic cooling. This interpretation can only be valid if one metamorphism and related fabric are present, and is, therefore, rejected.(2) The 83 Ma maximum date is the minimum age for the early fabric, S1, which has been partially reset due to later heating during S2 development at 63 ± 0.4 Ma. This interpretation is supported by the presence of the two fabrics (Figure 3.24). Sanidine SN1 from metamorphosed Shewa porphyry (close to location 3, Figure 3.1) has a maximum date of 85 ± 4 Ma. The 85 ± 4 Ma date of Shewa porphyry and 83 + 3 Ma date from phyllite of Panj Pir formation are within one sigma error and thus 85 ± 4 Ma to 83 ± 3 Ma dates are the minimum ages for lower greenschist facies metamorphism and S1 development in the Peshawar basin (Table 3.1). Maluski and Matte (1984) have 229 reported a biotite 40Ar/39Ar date of 47.5 ± 1.5 Ma from a syenite in the Ainbela area which they interpretedas a metamorphic cooling age. This suggests very slow cooling between 63 and 48 Ma in this area. In the Attock-Cherat and Gandghar Ranges of the Peshawar basin a tectonic event occurred before the Paleocene to Eocene sedimentation (Yeats and Hussain, 1987; and Hylland, 1990). This tectonic event correlates with the Late Cretaceous to Early Paleocene (85-63 Ma) deformation and metamorphism of the Peshawar basin. Farther north the main area of Swat metamorphic zone has been studied mainly near and south of Mingora (Martin et al., 1962; Kazmi et al., 1984; Rosenberg, :L985; Lawrence et al., 1985; Ahmad, 1986; Ahmad et al., l987a; Lawrence et al., 1989; Treloar et al., 1989; and DiPietro, 1990), Puran, Alpurai, and Ajmar areas. In the Mingora area, Swat block records four fabrics (Lawrence et al., 1989; DiPietro, 1990), and in the Alpurai and Ajmar areas, it records four fabrics and development of the Indus syntaxis (Table 3.1). S1, S2, and S3 relate to prograde Himalayan deformation and metamorphism (Lawrence et al., 1989; DiPietro, 1990). At present no isotopic dates clearly document the time of S1 and S52 fabrics. S1 and S2 probably relate to early phases of prograde Himalayan deformation (Lawrence et al., 1989; and DiPietro, 1990) but could conceivably be separate earlier events. North of Peshawar basin, S,1 is preserved as 230 S1 greenschist facies relict fabric in S2 generation garnet porphyroblasts. It implies that the S and S1 are equivalent and formed at >83-85 Ma. This would make the low grade equivalent of S2, the main schistosity of Swat, with development ending around 63 Ma. On this basis these events have been designated Dvii and Dvii:r (Table 3.1). The S/S1 may correlate with theSM3 of Mansehra block (Table 3.1). Detailed fabric controlled 40Ar/39Ar dating from the Mingora area is lacking, previously reported resultsare limited and do not provide information about dated fabric history of each sample. It is difficult to correlate published 40Ar/39Ar data with fabric and metamorphic chronology developed in the Mingora area. The reinterpretation of the published 40Ar/39Ar data is basedon the thermochronology and related fabric history developed in the Ambela, Alpurai, Besham, and Allai-Kohistanareas. 40Ar/39Ar dateson biotite of 94.2 ± 1.4 Ma and muscovite of 40.4 ± 0.5 Ma are reported from a granite near Mingora (Zeitler, 1983, 1985) and K/Ar dates on biotite of 60 ± 3 Ma on a garnet gneiss and biotite date of 176± 6 Ma are reported from near Mingora (Treloar et al., 1989). The biotite dates are all much older than the muscovite date. They may reflect excess argon in the minerals, or partial resetting of old biotites. The 40.4 Ma muscovite may date 231 Dix (Ss3), or later shearing, suggesting earlier development of S1 and S2. S2 developed during the main metamorphism in Mingora (Lawrence et al., 1989; DiPietro, 1990), Puran, Alpurai, and Ajmar areas of Swat block. Microprobe data for geothermoinetry and geobarometry on rocks from the Swat block south of Mingora (DiPietro, 1990) and from the Alpurai area (Treloar et al., 1989a) indicate temperatures/pressures of 600-700°C/9-11 kbars and 600-650°C respectively. Only six hornblende results are available from Swat block. A new hornblende date determined during this study from the Alpurai area (87MB785, Figure 3.5) ona garnet amphibolite dike which intrudes the Marghazar formation hasa maximum date of 32 ± 0.1 and a minimum date of 31± 0.1 Ma, and these are metamorphic cooling ages. These amphiboles developed after S4 during shearing along the Puran fault. Three previously reported hornblendes dates (Figure 3.23, Snee in Rosenberg, 1985) from south of Mingora (just east of Location 4, Figure 3.1) varies from 40 Ma to 36 Ma. These dates have been interpreted as metamorphic cooling ages late or after S3 fabric development (DiPietro and Lawrence, in press) or may be shear related post-metamorphic cooling. Because, in the adjacent Beshain block epidote amphibolite facies shear zones were active between 51 Ma to 36 Ma (Figure 3.33). Three hornblende dates have been reported by Treloar et al.(1989). A K/Ar date of 45 ± 2 Ma is on 232 hornblende from near Alpurai. Two 40Ar/39Ar dates of <65 Ma (U-shaped) and 33 ± 1 Ma (plateau) are on hornblendes from near Ningora. The <65 Ma date is from close to the MMT. DiPietro (1990) reports that metamorphic grade drops sharply near the MJvT so that hornblende closure temperatures may not have been reached during early Himalayan deformation and this may represent a partially reset sample recording early Himalayan metamorphism (Dvii and /orDviii). Thus metamorphic cooling below 530 ± 20°C occurred at different times in different parts of the Swat block. Muscovite, biotite, and potassium feldspar data from the Swat block record thermal activity around 300°C. In the Mingora area, three muscovite dates have been previously reported. Two maximum dates on muscovite from near location 4 on Figure 3.1 varies from 30 Ma to 29 Ma (Figure 3.24, Snee in Rosenberg, 1985). The third muscovite date is from near the suture zone north of location 4 on Figure 3.1 (Figure 3.24). It yields an argon loss from 80 ± 0.2 Ma to 35 ± 0.15 Ma. This date hint about Late Cretaceous metamorphic event, reset at about 35 Ma, during Himalayan shearing. New muscovite, biotite, and potassium feldspar have been dated from a sheared sample (PAK9) of Swat granite gneiss (Figure 3.21, Location 4, Figure 3.1, Table 3.4). Potassium feldspar has an argon loss spectrum with a maximum date of 45 ± 0.2 Ma and a minimum date of 22 ± 0.1 Ma. Biotite has a preferred date of 32 ± 0.13 Ma and muscovite 233 has a plateau date of 28± 0.2 Ma. The 45 Ma maximum date from a shear zone which isa late structure supports that it was active under conditions of about 300°C. This indicates that the S1, S2, S3, and S4 formed before 45 Ma. Muscovite date of 40.4 ± 0.5 Ma (Zeitler, 1983, 1985)may relate to this shearing event. The younger biotite and muscovite dates between 32-28 Ma record cooling below 280- 300°C during thedevelopment of lower greenschist facies shear zone. The minimum date of 22 Ma of potassium feldspar (Pak9) may relate to reactivation of shearzone as it does in other areas. In otherareas of the Indus syntaxis, shear zones were also active between 51 Ma to 24 Ma (Figures 3.33, 3.34, and 3.36). This study yields four new muscovite dates and three new biotite dates on four samples from around the Alpurai area (Figures 3.15, 3.18, and 3.19, Table 3.4). Sample 87MB42 has a preferred, near plateau muscovite date of 24.4 ± 0.1 Ma and a plateau biotite date of 23± 0.2 Ma. Sample PAK8 from sheared Choga granite gneiss hasa preferred biotite date of 29.4 ± 0.12 Ma anda preferred muscovite date of 23 + 0.1 Ma. Muscovite 87MB758 hasa maximum date of 28.5 ± 0.4 Ma and minimum date of 24.6± 0.12 Ma, and biotite 87MB758 has a maximum date of 22± 0.3 Ma and a minimum date of 12 ± 0.3 Ma. 87MS8O1A has a preferred muscovite date of 28 ± 0.1 Ma. The biotite and 234 muscovite dates between 29-28 Ma preservea record of cooling below 300-280°C during shear zone development. The single hornblende date in this area at 32-31 Ma supports an interpretation of rapid cooling and uplift below 530 ± 20°C at 32-31 Ma and muscoviteand biotite dates below 300-2800C at 29-28 Na. The older hornblendeK/Ar date of 45 ± 2 Ma (Treloar et al., 1989) from near Alpurai is from close to the N1"IT and may reflect earlier cooling below 530°C. Muscovite and biotite datesbetween 25-22 Na record a second event. Field evidence suggests that this younger event is related to younger uplift and shearing along local faults and not regional heating. (b). Ther]nal/cooling history of the Swat block Data available in this study are adequate to discuss only the Himalayan cooling history of the Swat block inany detail. This history is some what different in three areas, the Ambela, Mingora, and Alpurai areas. The southern Ainbela area cooled below muscovite closure of 300°C at 83 ± 3 Ma and potassium feldspar closure of 280°C at 85± 4 Ma. Close to Indus suture zone in Mingora it locally cooled below muscovite closure temperature at 80 Ma. Thus during >83-85 Ma, the Swat block recorded cooling below 280-300°C in the Late Cretaceous. Himalayan events partially reset micas during the Paleocene around 63 Ma. Zircon and apatite 235 fission track dates (Zeitler, 1983, 1985) indicate cooling to about 200 ± 25°C at 21-25 Ma and 120±20°C at 16-22 Ma. North of Ambela, in the metamorphic zone south of Mingora, temperatures remained locally above hornblende closure of 530 ± 20°C in an interesting pattern. From south to north hornblende closure is recorded at 37, 40 (Figure 3.37), 33, and <65 Ma. This high temperature episode may have begun as early as the Paleocene (<65 Ma) and certainly >45 Ma. The areas that reached the highest temperatures cooled latest (33 Ma) and probably very rapidly. Cooling through potassium feldspar/muscovite/biotite closure of 300-280°C occurred between45 to 28 Ma. Zircon and apatite fission track dates (Zeitler, 1983, 1985) indicate continued cooling to about 200 ± 25°C at 20-21 Ma and 120±20°C at 16 Ma (Figure 3.37). shearing near 22 Ma may have partially reset some micas. In the area east of Alpurai the history is somewhat different. A single hornblende suggests that temperatures locally remained above 530 ± 20°C until 32-31 Ma and then rapidly cooled below muscovite/biotite closure temperatures at 300-280°C by 29-28 Ma. A distinct reheating event that completely reset some samples between 25-22 Ma is related to localized shear zones and faults. Zircon and Apatite fission track dates are not available within this area (Zeitler, 1983 and 1985) but Zeitler's age-contour maps indicate 236 TERTIARY COOLING HISTORY OF SWAT BLOCK 600 500 Hb Hb 400 300 200 100 0 10 20 30 40 50 AGE (Ma) Figure 3.37. Tertiary cooling history of the Swat block. Fission track data from Zeitler (1983, 1985). 237 cooling through 200 ± 25°C at 19 Ma and 120±20°C at 12-10 Ma. (3). Mansehra block (a). Geologic implications Results from two areas of the Mansehra block are important to this study. The main field work was conducted in Allai-Kohistan (Figure 3.2), butan important sample of Hazara slates from near Sobra in Hazara was dated. The Sobra sample is important to constrain deposition and deformation of the Hazara and overlying Tanawal Formations. Sericite sample 87MB43 (Figure 3.21, location 1, Figure 3.1) has a maximum date of 900± 4 Ma and a preferred date of 650 ± 2 Ma. The 650 Ma date is interpreted as the time of development of SH1 (and by correlation ofSAl in the Swat block) and the 900 Ma is a provenance age for detrital micas of the Hazara Formation which were not completely reset during this low grade metamorphism. SK1 in the Karora group, SH1 in the Hazara Formation, SAl in the Manki Formation, and SB4 in the Besham basement complex of the Beshain block developed at the same time, and this widespread metamorphism and cleavage development is Div (Tables 3.1 and 3.2). The 650 Ma metamorphism and deformation of the Hazara and Tanawal Formations indicate that both were deposited 238 before 650 Ma. Previously published Rb/Sr model dates from the upper part of the Hazara Formation range from 728 ± 20 Ma to 951 ± 20 Ma (Table 3.6, recalculated from Crawford and Davies, 1975). These are interpreted as partially reset provenance ages during Late Proterozoic metamorphism and deformation (Baig and Lawrence, 1987; and Baig et al., 1988). These dates provide an upper age limit for the deposition of the Hazara Formation to be late Middle to early Late Proterozoic. However, the Late Proterozoic Tanawal Formation (see below) unconformably overlies the Hazara Formation and puts an upper age limit for the deposition of the Hazara Formation to be Late Proterozoic. Correlation with the Kurmang formation of the Besham block gives a lower age limit for deposition of the Hazara Formation to be later than the 1517 Ma granite clast in the Amlo conglomerate at the base of the Kurmang formation. Thus the Hazara, Kurmang, and stratigraphically equivalent Dakhner, Gandaf, and Manki formations were deposited between the early Middle Proterozoic (<1517 Ma) to early Late Proterozoic (<728-950 Ma), on the Late Archean (?) to Middle Proterozoic basement rocks represented by the Besham basement complex. The clastic sediments of the Tanawal Formation are unconformable on top of the Hazara Formation in Tarbela (Calkins et al., 1975) and are the oldest unit exposed in the Allai-Kohjstan area of the Mansehra block. The Late 239 Table 3.6. Rb/Sr isotopic Age Data from the Himalaya and the southern Indo-Pakistan plate. Rock type Locality Method Calculated Age in Reference 87 Sr/86 Sr Ma years initial Granite Crystalline nappe in Rb/Sr whole 0.7200±0.002 495±16 Frank (1977) South- L.ahul rock isochron Himachal Pradesh Migmatitic Kulu Himachal 0.7190±0.0007 500±8 Mehta (1976) gneisses Pradesh Granite Kangmar South-Tibet 0.7186±0.0018 485±6 Wang etal. (1981) Granite Kangmar South-Tibet 0.7140±0.001 484±7 Debon et al. (1981) Augen Tibetan slab Central Rb/Sr Psuedo0.7097±0.0120 517±62 LeFortetal. gneisses Nepal isochron (1982) Granites Simachar and Plung Rb/Sr 0.7106±0.0027 493±11 Le Fort et al. Central Nepal combined (1983) isochron Granite Palung Central NepalRb/Sr whole 0.720 486±10 Beckinsale (in rock isochron Mitchell, 1981) Gramtes & Behsud Afghanistan 0.7106 496±11 Montenate et al. migmatites (1981) Granite Simachar Cental 0.7205±0.0046 466±40 Le Fort et al. Nepal (1983) Micro- 0.7085±0.0048 511±55 granular inclusions Granite Mansehra Hazara 0.7189±0.0006 516±16 LeFortetal,. Himalaya (1980) Almora Almora nappe Rb/Sr 0.7109±0.0013 560±20 Trivedi et al. granodionte combined (1984) Champawat isochron granite Granite Mandi Himachal Rb/Sr whole 0.7180 510±100 Jager et al. (1971) Pradesh rock isochron Biotite Sarangri & 0.7 190 467±45 Bhanot et al. granites Rungathach. (1979) Manikran Central Rhotang pass Mandi 0.7113±0.0007 600±9 Metha (1977) gneisses area Migmatitic Kulu area 0.7190±0.0007 519±8 gneisses Granite Mandi area 0.7019±0.0015 564±12 Metabasic 0.7001±0.0005 682±20 xenollths in granite 240 Table 3.6 continued. Leucocratic 0.8110±0.0007 321±6 granite Mandi granite Rb/Sr (Mu, Ri)0.7019±0.0015 426±12 mineral date Leucocratic 0.8110±0.0007 333±6 Mandi granite Grey-green Kirana & Bulland Rb/Sr whole 0.712±0.009 831±20 DavIes and fine-grained Hills Pakistan rock lsochron Crawford (1971) rhyolite Brown 838-20 aphanitic volcanic Grey, fine- 809±20 grained rhyolite Fine- grained 865±20 acid volcanic Very fine- 841±20 gramed volcanic Glassy fine- Tobra Form. Salt 786±20 gramed Range porphyry Felsite Barmer India 0.7094±0.0009 729±10 Crawford and Compston (1970) Rhyolite 733±10 Fine- grained 500±10 Crawford and rhyolite Comptson (1970) Agglomerate Miniari India 734±10 Tuff bomb In 719±10 agglomerate Rhyolite Barmer India 724±10 Tuff Bisala India 740±10 Granite Jalor India 4 11±10 Siwana-type Jasai India 701±10 granite Gran lIe 691±10 Granite Jalor India 743±10 Hazara slate 7 miles south of assumed initial 752±20 Crawford and Mansehra 0.7000 Davies (1975) Hazara slate near previous locality 728±20 Hazara slate near Tanakki 951±20 Note: Dates up to 1977 have been recalculated by using Steiger and Jager (1977) decay constant of 1.42x10'1/yr for Rb. Mu = Muscovite, and Bi = Biotite. 241 Archean (?) to Middle Proterozoic sodic and potassic granites of the Besham block do not intrude the Tanawal Formation east of Thakot fault and the Manglaur Formation west of Puran fault and indicate that these Formations are certainly younger than the Middle Proterozoic. Deposition of the Tanawal Formation occurred in the Late Proterozoic (post-Hazara and Kurmang formations). The upper age constraint is based on three arguments:(1) The Late Cambrian Mansehra granite (516 ± 16 Ma, Rb/Sr isochron, LeFort et al., 1980; Table 3.6) intrudes the Tanawal Formation and includes its xenoliths (Figure 3.9a).(2) The Early Cambrian basal conglomerate of the Abbottabad Group (Latif, 1974; Baig and Lawrence, 1987; Baig et al, 1988; and Sherwan Formation (Baig and Lawrence, 1987) contains clasts of the Tanawal formation (Figure 3.38).(3) Three foliations are present in the Tanawal Formation of the Allai-Kohistan area. SM1 is probably correlative with SH1. The main support for this comes from the Mansehra area where contact metamorphic hornfels created during intrusion of the Mansehra granite overprints a low grade fabric in the Tanawal Formation (Treloar et al., 1989b), implying that this fabric is >516 Ma. The dominantly clastic sediments of the Tanawal and its correlative Manglaur formations are herein interpreted the Late Proterozoic molasse of the Hazaran orogeny. 242 The Early Cambrian Tanakki conglomerate at the base of the Abbottabad Group overlies the Hazara Formation with an angular unconformity (Figure 3.39) with significant paleotopography. The Tanawal Formation is eroded before the deposition of the Tanakki conglomerate. Clasts in this conglomerate include Manki or Kurmang formation phyllites (Figure 3.40b), Tanawal Formation quartzites (Figure 3.38), slates of the Hazara Formation (Figure 3.40c), metamorphic quartz veins, graywacke sandstones, and rare iriafic clasts. The underlying Hazara Formation at the Tanakki locality (Figure 3.1) is composed of low grade slates, so the phyllite clasts must have been derived from farther north of the Panjal thrust. The maf Ic clasts indicate that some of the mafic dikes in the Hazara and Tanawal formations were intruded before Early cambrian sedimentation. The fabric of the slate (Figure 3.40c) and phyllite (Figure 3.40b) clasts is randomly oriented between clasts, and the Tanakki matrix is essentially unfoliated (Figure 3.40a) confirming the Late Proterozoic age of the fabric development. SM1, SH1, SK1, SAl, and SB4, therefore , all formed during the Late Proterozoic Hazaran orogeny, Div (Table 3.1 and 3.2) which affected the Besham basement, the Hazara Formation, its equivalents, and the Tanawal Formation. The 664-625 Ma Hazaran deformation and metamorphism accompanied the intrusion of 850-600 Ma felsic volcanic and plutonic rocks in the Indo-Pakistan plate (Table 3.6). 243 of the TanawalFormation Figure 3.38. Aclast of quartzite conglomerate. Thepresence of in the EarlyCambrian Tanakki in the Tanakkiconglomerate clasts of theTanawal Formation has beeneroded before indicates that theTanawal Formation Abbottabad Group. the Cambriandeposition of the 6.7 mm fieldof view. Magnification - 2x;crossed nicols; 244 During the Hazaran orogeny, before the Cambrian sedimentation, the areas to the south of Panjal thrust were significantly uplifted than the areas to the north. The Tanawal Formation has been eroded south of Panjal thrust (Calkins et al., 1975) between the Hazara Formation and the Cambrian Abbottabad group (Figure 3.39). The evidence for erosion of the Tanawal Formation is documented by the presence of Tanawal quartzites (Figure 3.38) in the Early Cambrian Tanakki conglomerate of the Abbottabad Group. In contrast, the Tanawal Formation is present to the north of Panjal thrust (Au, 1962; Calkins et al., 1975) below the Cambrian strata (Pogue and Hussian, 1986; Baig and Lawrence, 1987). This indicates that the substantial pre-Himalayan tectonic uplift, compared to moderate tectonic uplift in the north, has caused the total erosion of the Tanawal Formation to the south of Panjal thrust. The boundary between the Late Proterozoic to Early Cambrian is generally considered to be 570 Ma, and the metamorphism and deformation of the Hazara and Tanawal Formations occurred at 650 Ma. This implies that the 80 Ma of tectonic uplift and erosion caused the erosion of the Tanawal Formation. In the north, the Mansehra granite was intruded into the Tanawal Formation in the Late Cambrian or Early Ordovician. This is based on Rb/Sr whole rock isochron date of 516 ± 16 Ma (LeFort et al., 1980) and U/Pb zircon date of 468 ± 12 Ma (Zartman, written communication, 1985). The 245 Figure 3.39. showing field relations of the Cambrian Abbottabad Group and the Precambrian Hazara Formation near Tanakki area of Hazara. For location of Tanakki area see Figure 3.1. Geological map of the Tanakki area, showing the angu:Lar unconformity at the base of Tanakki conglomerate of the Cambrian Abbottabad Group (Modified after Latif, 1970). "F" marks the Cambrian fossil locality. The Tanawal Formation is eroded between the Abbottabad Group and the Hazara Formation. Geological cross-section along the line C-C' on Figure (a) showing the unconformity at the base of the Tanakki conglomerate. 246 (a). C N 34 °8' \ N Goaterna ry deposits A N \ Samana SubFormation N Middle toate Jurussib N N Datta Formation N Early Jurassic 'N 1-lazira Formation -' 4V A1 Cambrian C?) \ \\' ' Sirban Formation N Ji_.W Cambrian N Mirpyr sandstone 4 aICambrian 00 Miindhaqali sandy dolomite TANAKKt V E Ctimbrian 0 S 0'Sangargali sandstone AI4 Cambrian 4j 7, Tanatchi conglomerate + Cambrian ;, ,- Formation Flazara 340 4 Precambrian 0 4-2 Concealed Lagerban thrust .... .A... Mtte Attitude ot cloanage Attitude oi bedding (b). C 7000 - KHOT}DIQABAR TANAKKI 5000 - 3000 - 1000 Figure 3.39 247 zircon shows inheritance from a middle Proterozoic basement at 1583 ± 120 Ma. Zeitler et al.(1989) also reported 400-500 Ma LI/Pb dates from granite grieisses of the Nanga-Parbat syntaxis. Intrusions of Late Proterozoic to Early Ordovician are well known along the lesser Himalaya (Figure 3.41 and Table 3.6) and previously have been interpreted as a single event based on numerous Rb/Sr whole rock isochron dates (450-865 Ma, Table 3.6). This study demonstrates that at least two separate intrusive events in the Late Proterozoic (>600-850 Ma, average of 17 Rb/Sr isochrons 751 Ma) and Late Cambrian to Early Ordovician (450-550 Ma, average of 18 Rb/Sr isochrons 499 Ma) occurred in the Himalaya. Baig and Lawrence (1987), Baig et al. (1988), and Baig et al.(1989) considered Early Paleozoic intrusive event in the Himalaya related to the late- or post-Hazaran orogenic phase of the Hazaran orogeny. Garzanti et al.(1986) also suggested this event on the basis of Canthro-Ordovician unconformity in the northwest Himalaya. These workers did not provide evidence for deformation and metamorphism at this time to confirm an orogenic event. In the Tanawal Formation, SM1 is considered to have developed during the Hazaran orogeny in the Mansehra area (Tables 3.1 and 3.2). In the Allai-Kohistan, in contrast, four fabrics have been recognized (Table 3.1). SM2 is the main fabric, developed under araphibolite facies conditions (Tables 3.1 and 3.3). Hornblende (87MB253) from SN2 (Figure 248 Figure 3.40. Field and petrographic evidence for the Late Proterozoic deformation and metamorphism in the Tanakki area of Hazara. For location of Tanakki area see Figure 3.1. Randomly oriented low-grade metamorphic clasts of the Hazara Formation, in clast supported sedimentary matrix of the Early Cambrian Tanakki conglomerate. A folded phyllite clast of the Manki or Kurmang formation in the Early Cambrian Tanakki conglomerate. It indicates that the deformation and metamorphism of the clast bccurred before the Early Cambrian deposition of the Tanakki conglomerate. Magnification - 2x; crossed nicols; 6.7 mm field of view. Photomicrograph of the Early Cambrian Tanakki conglomerate, showing randomly oriented low-grade inetainorphic clasts of slate of the Hazara Formation. Note that the clasts do not show preferred orientation, and the fabric between clasts has angular relationship. This indicates that the fabric in clasts formed before the Early Cambrian deposition of the Tanakki conglomerate. Magnification - 2x; crossed nicols; 6.7 mm field of view. 251 yields a preferred date of 466 ± 2 Ma and an isochron date of 464 ± 1 Ma. The preferred and isochron dates are within one sigma error and thus 466 ± 2 Ma date is a minimum age for upper ainphibolite facies metamorphism and development of S2, closely related in time to the intrusion of the Mansehra granite between 516 ± 16 Ma to 468 ± 12 Ma. Geothermometry and geobarometry on kyanite-sillimanite zone rocks from the Tanawal Formation in this area indicate temperatures reached 650-700°C and pressures upto 6-9 Kbars (Treloar et al., 1989b). These conditions were considered by Treloar et al. (l989b) to be related to the early phases of Himalayan orogeny, but instead represent peak temperatures during Dv in the Late Cambrian to Early Ordovician. A biotite 87MB272 from SM2 of the Tanawal Formation (Figure has a maximum date of 434 ± 1 Ma, and is a post- metamorphic cooling age for this event. The 450-550 Ma peraluminous granites, deformation and metamorphism at >466 Ma to 434 Ma, and the development of an unconformity during the Caxubro-Ordovician time confirm that the Late Cambrian to Early Ordovician orogeny occurred in the northwest Himalaya (Table 3.3). This orogenic event correlates with the Pan-African orogeny which affected most of Gondwana. The Early Paleozoic orogeny occurred before the Permo-Triassic breakup of Gondwana, and may relate to its amalgamation as a supper continent (Baig and Lawrence, 1987; Baig et al., 1988; Baig et al., 1989). 252 Figure 3.41. Location map for the Lesser Himalayan granite belt (Modified after, Le Fort et al., 1983). 1 = Main Boundary thrust zone, 2 = thrust, 3 = Early Paleozoic granites, and JF = Jhelum fault. Saidu Sharif (SS = Swat granite), Choga (KA), Utla (UT), Mansehra (MH), Kohistari (KR), Kaghan (KG), Nauseri (NU), Jura (JtJ), Kel (KL), Rashian (RH), Outer band of Daihousie (03), Dalhousie (DH), Dhaola Dar (DD), Kulu (KU), Mandi (MD), Lahul (LU), Axnritpur (AM), Chor (CH), Champawat (CW), Dandeidhura (DA), Dudhatoli (DU), Gwaldam (GW), Ipa (IP), Lansdowne (LD), Narayan Than (NT), Palung (PG), South Almora (SA), Sindhuli Garhi (SG), Siinchar (SR), Timaldana (TD), and Kangmar southern Tibet (Km). Town locations: Srinagar (Sri), Dharamsala (Dhs), Siinla (Sml), Naini Tal (Ntl), Pokhra (Pkr), and Kumaon (KR), and Kumaon (KR) area of Himalaya. KIRANA HILLS Figure 3.41. 254 Dvi upper Paleozoic rifting of northern Gondwana is also recorded in the Nansehra block (Table 3.3). The best result is from magmatic biotite 87MB33A (Figure 3.9f) from a diabase sill, which intrudes SM2 of the Mansehra granite gneiss (Figure 3.9e). It yields a preferred date of 262 ± 1 Ma. The Early Permian date is interpreted as a minimum age of mafic dike and sill feeders to Early Permian inafic Panjal volcanism. The 284 ± 4 Ma, 268 ± 26 Ma, and 262 ± 2 Ma dates from Swat and Mansehra blocks confirm the rift-related mafic Panjal volcanism occurred between 284 ± 4 Ma to 262 ± 1 Ma in the northwest Himalaya of Pakistan. The 284 ± 4 Ma to 262 ± 1 Ma dates provides the absolute time constraints for the Early Perinian Panjal volcanism of Kaghan (Ghazanfar and Chaudhry, 1985; Pipritz and Rey, 1989), Kashinir (Wadia, 1934), and Zanskar (Gaetani et al., 1990). An unmetamorphosed fresh late Jurassic basalt dike 87MB61 cross-cuts SM2 structures of the Tanawal Formation (Figure 3.9g) and yields a maximum date of 159 ± 0.4 Ma. This indicates that the SM2 is older than 159 ± 04 Ma. As this is the maximum age for this basalt dike and it could be younger in age. It may related to continuing Jurassic extension of the margin of the Neotethys ocean. A series of disturbed samples from within the large Indus River meander south of Besham (Figures 3.15 and 3.17, Table 3.4) can be speculatively interpreted as recording 255 Late Paleozoic rifting and Permain-Triassic mafic dike intrusion. Hornblende 87MB60 has a maximum date of 281 ± 1 Ma and SM2 biotite 87MB60 has a preferred date of 198 ± 1 Ma. Hornblende 87MB55 has a maximum date of 221 ± 1 Ma and SM2 biotite 87MB55 has a maximum date of 232 ± 1 Ma. These minerals were formed earlier (probably Cainbro-Ordovician) and have been partially reset. The Permian to Jurassic dates may reflect heating during rift associated intrusions for which Permian dates have been found in the Swat, Besham, and Mansehra blocks. Alternatively all of the resetting may be entirely Himalayan and these spectra are simply very disturbed. Other disturbed samples that preserve younger pre-Himalayan biotite and potassium feldspar are 87MB104, 87MB56, 87MB55, 87NB60, 87MB65 (Figures 3.15 and 3.16) .All of these results definitely confirm that temperatures in the Allai-Kohistan area did not exceed hornblende closure, 530 ± 20°C, and only approached biotite closure temperatures, 280 ±20°C, during Himalayan events. Similar old biotite and muscovite 40Ar/39Ar and Rb/Sr biotite mineral dates (70-215 Ma) from the Mansehra granite in the Mansehra area (Maluski and Matte, 1984; Zeitler, 1983, 1985; LeFort et al., 1980; and Treloar et al., 1989b) confirm the low temperatures of Himalayan metamorphism in the Mansehra block. Himalayan deformation in the Mansehra block began in the Late Cretaceous. Muscovite 87MB272 from the 5M3 fabric (Figure 3.9d) has a preferred or near plateau date of 70 ± 256 0.2 Ma. Similar 40Ar/39Ar dates of 75 ± 3 Ma and 77 ± 3 Ma on biotite from schist and Mansehra granite from southern Allai-Kohistan (Treloar et al., l989b) and of 70.4 ± 0.7 Ma on biotite from the Mansehra granite from near Mansehra (Zeitler, 1983, 1985) have been reported previously. Widespread preservation of older hornblende and biotite dates suggests that muscovite and biotite closure temperatures of 300-280 ± 20°C achieved in the late Cretaceous may be peak temperatures for this lower greenschist event, Dvii (Table 3.1). Activity along the Thakot fault in the Mansehra block is recorded by three samples from a local shear zone (Figure 3.15 and Table 3.4). Biotite 87MB101 from a lens within the shear zone has a preferred age of 51 ± 0.23 Ma and shows partial resetting at 35 ± 0.18 Ma. In the Matrix of the shear zone, biotite 87MB102 has a maximum date of 68 ± 0.2 Ma and a minimum date of 46 ± 0.2 Ma and muscovite 87MB102 has a preferred date of 28 ± 0.13 Ma. These argon loss spectra confirm activity on the Thakot fault over the same range as the Besham block hornblendes previously discussed (51-36 Ma), and suggest continued activity at lower temperatures until 28 Ma. Biotite sample 87MB104, adjacent to but not in the shear zone, has a maximum date of 202 ± 2 Ma and a minimum date of 62 ± 1 Ma confirming that the high temperatures accompanying shearing were confined to the shear zone. 257 All of the younger dates in the Allai-Kohistan area are found in muscovite (Figures 3.18 and 3.19, Table 3.4). Most of these samples come from sheared rocks or shear zones. Where biotite or potassium feldspar are also present, their dates are significantly older than the muscovite dates. Muscovite 87MB56 has a maximum date of 42 ± 0.15 Ma and a minimum date of 30 ± 0.24 Ma. Other samples (87MB65, 87MB249, 87MB824 and 87MB283) have ages between 31.5 ± 0.13 Ma and 24.3 ± 0.2 Ma. Most of these samples reflect shear zone activity during southward thrusting and successive development of the Indus syntaxis, Dx and D. These samples are from west of the Chaji Sar thrust or north of the Rashang fault, while Cretaceous sample 87MB272 is from just below the Rashang fault and the other Cretaceous samples are from farther south. Thus it seems probable that the last normal motion of the Rashang fault occurred after these samples cooled below 300 ± 20°C. (b). Thermal/cooling history of the Mansebra block The thermal history of the Mansehra block begins with the deposition of the Hazara and Tanawal Formations under surface conditions. Muscovite grew during the Hazaran orogeny (650 Ma) in the Hazara area so temperatures exceeded 300°C. Thermal conditions to the north are undocumented but presumably equaled or exceeded those around Hazara. In the 258 Hazara area, the 80 Ma of tectonic uplift and erosion, exposed the area to surface conditions before the Cambrian deposition of the Abbottabad Group. After the subareal unconformable deposition of the Tanakki conglomerate, the marine conditions prevailed during deposition of the rest of the Abbottabad Group in Cambrian time. During the Late Cambrian and Early Ordovician, the Allai-Kohistan area experienced amphibolite facies metamorphism with temperatures of 650-700°C. The area cooled to hornblende closure, 530 ± 20°C, by 466 Ma and to biotite closure, 280 ± 20°C, by 434 Ma. This metamorphic event probably affected most of the northern Mansehra area, but not the Hazara area. Intrusion of mafic dikes occurred during rifting in the Permian to Jurassic(?) and may have induced a minor thermal event. The main Himalaya event to affect the Mansehra block occurred in the Late Cretaceous and influenced all of the blocks studied. Peak temperatures may have been close to biotite and muscovite closure, 280-300 ± 20°C, at 80-70 Ma. Thermal events at 30 Ma and 24 Ma (Figure 3.36) reached muscovite closure (Figure 3.42) and cooled below 300°C north of the Rashang fault and is closely associated with shearing. Fission track data from the Mansehra area (Zeitler, 1983 and 1985) indicate cooling below 200 ± 25°C (zircon) at 259 about 26 Ma and below 120 ± 20°C (apatite) at 19 Ma (Figure 3.42). No fission track samples are reported from the Allai area. (4). Neotethys terrane Muscovite (Figure 3.19, location 1) from blueschist melange has been dated by K/Ar method and yields a date of 84 ± 1.7 Ma Shams (1980). Maluski and Matte (1984) dated phengite mica from the same melange (Figure 3.19, location 2) by 40Ar/39Ar method and yields a plateau date of 83.6 ± 2 Ma. These dates have been interpreted to be the age of blueschist facies metamorphism in the Indus suture zone (Shams, 1980; Maluski and Matte, 1984). Fuchsite mica from sample 87MB400 (Figure 3.19 and Table 3.4) of the ophiolitic melange yields a plateau date of 82 ± 0.22 Ma and an isochron date of 81 ± 3 Na. These dates are within one sigma error, and thus 82 ± 0.22 Ma plateau date is the best estimate of the time of lower greenschist fades metamorphism and deformation in the ophiolitic melange. The 84 ± 1.7 Ma K/Ar (Shams, 1980) and 83.6 ± 2 Ma 40Ar/39Ar (Maluski and Matte, 1984) phengite dates from blueschist melange and 82 ± 0.22 Ma plateau and 81 ± 3 Ma isochron 40Ar/39Ar fuchsite dates from ophiolitic melange are within one sigma error. These dates show that the blueschist and greenschist facies metamorphism occurred within the same 260 TERTIARY COOLING HISTORY OF MANSEHRA BLOCK 400 Mu Mu 300 Zr 200 Ap T 100 0 18 20 22 24 26 28 30 AGE (Ma) Figure 3.42. Tertiary cooling history of the Mansehra block. Fission track data from Zeitler (1983, 1985). 261 geological time span. Two alternative explanation can be offered for these results:(1) The 84 ± 2 Ma high-pressure and low-temperature blueschist facies metamorphism occurred in the trench zone and 82 Ma low-pressure and low- temperature greenschist fades metamorphism occurred in relatively shallow structural levels of the Indus suture zone. This implies that the Indus suture zone was uplifted rapidly within 2 Ma in the Late Cretaceous.(2) The 84 ± 2 Ma phengite dates record the time of lower greenschist facies metamorphism instead of blueschist fades metamorphism. This interpretation is supported by the presence of widespread two mica fabrics in the Indus suture zone. The blueschist facies mica fabric is overprinted by the lower greenschist fades mica fabric. The lower greenschist fades metamorphism is sufficient to reset earlier muscovites developed during blueschist facies metamorphism. Thus the 82-84 ± 4 Ma dates record the timing of lower greenschist fades metamorphism which implies that the blueschist facies metamorphism must be older than 84± 4 Ma. This interpretation can be further supported by the 80 Ma to 84 ± 4 Ma widespread greenschist facies metamorphism and deformation which affected the Indo-Pakistari plate, Neotethys terrane, and Kohistan island arc terrane (Figure 3.43). This metamorphic event is certainly not related to the blueschist facies metamorphism, and thus is a separate metamorphic event. It is herein interpreted to be related to 262 200 C) C) 100 80-64 ± 4Ma C) pf 70 ± .21 Ma 50 100 ArK Released (%) Figure 3.43. Contposite40Ar/39Ar niuscovite age spectra from the Kohistan island arc, Neotethys, and Gondwaria terranesof the NW Himalaya, showing Late Cretaceousmetamorphic and defromational events at 80-84 ± 4 Na and 70 Na. 263 the initial emplacement of the Neotethys and Kohistan island arc terranes on the passive margin of the Indo-Pakistan plate. The 84 to 82 Ma dates in the Neotethys terrane are not affected by the high grade metamorphism of the underlying Gondwana terrane. DiPietro (1990) suggested that the rocks of the Gondwana terrane (Swat block) during or before Eocene were buried to a depth of 35 to 45 Km at temperatures of 600-700°C andpressures of 9-11 Kbars under the Neotethys terrane. If this high-pressure and high-temperature metamorphism is related to the Eocene collision of the Indo-Pakistan plate and Kohistan island arc terrane, than 82 to 84 Ma dates in the Indus suture zone must have been reset to Eocene. The possibility exists that during the subduction of the Swat block under the Neotethys and Kohistan island arc terranes, the high-pressure and high-temperature metamorphism occurred at greater depth in the Swat block while the Late Cretaceous high-pressure low-temperature blueschist and low-pressure low-temperature greenschist facies metamorphism occurred in the trench zone at shallow structural levels of the Neotethys terrane. Subsequently, the Swat block was uplifted during Paleo.cene to Eocene to shallow depth along the Indus suture zone thus recorded post-metamorphic cooling below 530 ± 20°C at <65 Ma and below 280 ± 20°C at 45 Ma. Due to this tectonic uplift, the blueschist to lower greenschist fades 264 metamorphism survived in the upper structural levels of the Indus suture zone. Zeitler (1983 and 1985) reported 58 Ma to 45 Ma zircon dates from the Kohistan island arc terrane which overlies the Indus suture zone, which indicates that the Kohistan island arc terrane was uplifted and cooled below zircon retention temperature of 215 ± 250C during Paleocene to Eocene. This data further support the idea that the Indus suture zone below the Kohistan island arc terrane was uplifted between 58 Ma to 45 Ma. South of Indus suture zone, the aniphibolite fades metamorphism in Swat and Mansehra blocks did not obliterate 2,000 Ma to 64 Ma amphibolite to lower greenschist facies pre-Himalayan and Himalayan metamorphic events in the underlying Besham block. This indicates that the amphibolite facies metamorphism of the overlying blocks must have occurred north of the Besham block before the early Paleocene. The Kohistan and Neotethys terranes, and Swat, Mansehra, and Besham blocks juxtaposed during Dx when south- directed thrusts and south vergent Fs4, FK3,FBG, and folds initiated in the foreland fold-and-thrust belt (Table 3.1). These folds and thrusts were refolded during Fs5, FK4, FB6, and FM5 north-plunging antiformal and synfornial structures, related to the development of the Indus syntaxis (Table 3.1 and Figures 3.2 and 3.3). The sinuous outcrop pattern of the Kishora thrust, at the base of the Swat and 265 Allai melanges (Figures 3.2 and 3.2), shows that it was folded during the development of F55 and FM5 north-plunging antiforms and synforms of the Swat and Mansehra blocks respectively (Figure 3.2). These structures are related to the buttress affects of the basement rocks of the Gondwana terrane with the overlying Neotethys terrane. The presence of melanges in the cores of regional scale Fs5 and FM5 synformal structures in Swat and Allai-Kohistan, respectively, indicates that the melanges were not involved during the early phases of folding in Gondwana terrane (Table 3.6). It implies that the melanges have not seen high grade metamorphism of the underlying Gondwana terrane. (5). Kohistan island arc terrane Three hornblende dates from the garnet granulites of the Jijal complex have been reported by Treloar et al. (1989). All of the age spectra show excess argon with maximum dates of 117 Ma, 213 Ma, and 220 Ma. Hornblende and sodic mica from an amphibolite dike (87MB401; Figure 3.28), which intrudes the Jijal complex, yield Late Cretaceous dates. Hornblende 87MB41O (Figure 3.17 and Table 3.4) yields a L-shaped spectrum with a preferred date of 117 ± 0.4 Ma and an isochron date of 117 ± 0.6 Ma. The preferred and isochron dates are within 1 sigma error, thus 117 ± 0.4 Ma date is the time of epidote amphibolite facies metamorphism, 266 which postdates the garnet granulite facies metamorphism of the Jijal complex. This date shows that the base of the Kohistan island arc terrane was cooled below 530 ± 20°C at 117 ± 0.6 Ma. Sodic mica 87MB401 (Figure 3.19 and Table 3.4) from the same unit, which overprints the earlier hornblendes, during retrograde greenschist facies metamorphism (Figure 3.28), and yields a maximum date of 84 ± 1 Ma and a minimum date of 34 ± 4 Ma. The 34 ± 4 Ma minimum date shows that these micas were partially reset during the development of the Indus syntaxis. The major amphibolite facies metamorphism and deformation in the Komila amphibolite belt which structurally overlies the Jijal complex occurred between 83 Ma to 86 Ma (Zeitler, 1985; Coward et al., 1986; 1987; Treloar et al., 1989) and retrograde greenschist fades metamorphism in the Jijal complex occurred at 84 ± 1 Ma. These data show that the base of the Kohistan island arc terrane was cooled below hornblende closure temperature of 530 ± 20°C at 83 Ma to 86 Ma and below sodic mica closure temperature of about 300°C at 84 ± 1 Ma. This implies that the base of the Kohistan island arc terrane went through rapid cooling between 83-86 Ma. Hornblende PaRlO (Figure 3.21; location 5 on Figure 3.1) from Kalam quartz diorite yields a maximum date of 88 ± 0.37 Ma which is close to 40Ar/39Ar dates of 81 ± 3 Ma to 94 ± 4 Ma reported by Treloar et al. (1989). The 81 Ma to 94 Ma 267 horriblende dates may show the emplacement of Kalam quartz diorite to be pre- to syntectonic with respect to the major deformation of the Kohistan island arc terrane between 80 Ma to 86 Ma reported by Zeitler (1983 and 1985), Coward et al. (1986), and Treloar et al. (1989). Potassium feldspar (Paklo; Figure 3.21, location 5, Figure 3.1) from the same unit yields a maximum date of 49± 0.21 Ma and a minimum date of 17 ± 0.07 Ma. The 49 Ma date may record lower greenschist thermal event and the 17 Na minimum date records local shearing. The Rb/Sr whole rock isochron date on the precollisional deformed pluton at 102 ± 12 Na (Peterson and Windley, 1985) and K/Ar and 40Ar/39Ar hornblende dates from volcanic rocks, precollisional deformed plutons, and postcollisional basic dikes, which intrude both, yield dates of 76-97 and 76 ± 6 Ma, respectively, show that the arc was sutured to Asian plate prior to 76 Ma but after 120 ± 12 Ma (Peterson and Windley, 1985; and Treloar et al., 1989). The late stage undeformed granites and aplite-pegmatite sheets which intrude the Kohistan island arc terrane, yield Rb/Sr whole rock isochron dates of 40 ± 6 Ma to 54 ± 4 Na, and 29 ± 8 Na to 34 ± 14 Ma, respectively, and has been interpreted as postcollisional inagmatism (Peterson and Windley, 1985). The late stage undeformed granites and aplite-pegmatite sheets which intrude the Kohistan island arc terrane, yield Rb/Sr whole rock isochron dates of 40 ± 6 to 54 ± 4 Ma, and 268 29 ± 8 to 34 ± 14 Ma respectively, and has been interpreted as postcollisional magmatisin (Peterson and Windley, 1985). The 58 Ma to 45 Ma fission track zircon dates from the Kohistan island arc terrane indicate that it cooled below zircon retention temperature of 215±25°C at this time. (6). Timing of melange emplacement and suturing in the northwest Himalaya of Pakistan The timing of collision of the Kohistan-Ladahk island arc terrane with the Asian plate, in the north, and the Indo-Pakistan plate, in the south, is controversial. The initial contact between the Indo-Pakistan plate and Kohistan island arc terrane is considered to have occurred at about 53-55 Ma (Powell, 1979; Klootwijk, 1979) arid terminal collision between the Indo-Pakistan and Asian plates occurred between 40-45 Ma (Molnar and Tapponier, 1975; Pierce, 1978; Klootwijk and Radhakrishnamurty, 1981; Klootwijk et al., 1985). Honegger et al. (1982) suggested that the terminal collision of India with Ladakh island arc terrane started in the Mid-Late Eocene. In Pakistan, Tahirkheli et al.(1979) suggested that the Indo-Pakistan plate collided with the Kohistan island arc terrane in the Early Tertiary and sutured to the Asia in the Late Tertiary. In contrast, Pudsey et al. (1986), Peterson and Windley, (1985), Coward et al.(1986, 1987), and Treloar et al. 269 (1989) interpreted that the Kohistan island arc terrane sutured to the Asian plate in the Late Cretaceous and predate the collision of the Indo-Pakistan plate with the Kohistan island arc terrane in the Eocene. The 80-86 Ma metamorphism and deformation in the Kohistan island arc terrane (Zeitler, 1983, 1985; Treloar et al., 1989) has been interpreted to be the result of suturing of Kohistan island arc terrane and Asian plate, which is postdated by the postcollisional basic dikes of about 75 Ma (Treloar et al., 1989) The 80 Ma to 84 ± 4 Ma (Figure 3.43) greenschist facies metamorphism and deformation of the Kohistan island arc, Neotethys, and Gondwana terranes indicates that it was a widespread metamorphic and deformational event in the northwest Himalaya of Pakistan. This metamorphic and deformational event is herein interpreted to be the result of initial emplacement of the Kohistan island arc and Neotethys terranes on the passive margin of the Indo- Pakistan plate. Similarly in Ladakh, ophiolite emplacement occurred on the Irido-Pakistan plate in the Late Cretaceous which is postdated by a 82 ± 4 Ma synite body (Brookfield and Reynolds, 1981). The 70-64 Ma metamorphic and deformational event in the Indo-Pakistan plate is herein interpreted to be the result of initial collision of the Indo-Pakistan plate and the 270 Kohistari island arc terrane. However, the terminal collision between the Kohistan island arc terrane and Indo-Pakistan plate occurred at about55Ma to50Ma. In the Attack Cherat and Gandghar Ranges of Pakistan, south of Indus suture zone, a tectonic event occurred at the end of Cretaceous, and predated the Paleocene to Eocene sedimentation (Yeats and Hussian, 1987; Hylland, 1990). On the western margin of the Indo-Pakistan plate, near Nuslimbagh and Zobe valley, the ophiolite emplacement occurred in the Late Paleocene and predated the Early Eocene sedimentation (Alleinann, 1979; Ahmad and Abbas, 1979). The Paleocene to Early Eocene unconformity is wide spread in the Himalaya (Bhandari and Agarwall, 1966; Latif, 1970, 1976; Singh, 1970, 1973; Terwai and Gupta, 1976; Shah, 1977; Allenmann, 1979; Ahmad and Abbas 1979; Gee, 1983, 1989; Ashraf et al., 1983; Yeats and Hussian, 1987; Wells and Gingerich, 1987) and shows a major paleosole development at this time, indicates that the foreland fold-and-thrust belt of the Himalaya was uplifted and exposed to subareal weathering agents at this time. From the Ladakh and Kohistan areas of the northwest Himalaya to the Wazirastan, Muslim Bagh, and Zob Valley areas of the western margin of the Indo-Pakistan plate, the age of melange emplacement decreases from Late Cretaceous to Late Paleocene respectively. These data show that the southern suture closed in the Late Cretaceous to Early Paleocene, which is 271 contradictory to the earlier studies that the southern suture closed in the Eocene (Coward et al., 1986; 1987; Treloar et al., 1989). Thus the Himalayan collision in northern Pakistan records evidence for the earliest Himalayan deformation and metamorphism between Late Cretaceous to Early Paleocene which is yet to be recorded in the main Himalaya of India. (7). 40Ar/39Ar constraints for the development of the Indus syntaxis In the Besham area of northern Pakistan, south of Neotethys terrane, and in the core of Indus syntaxis, the Besham block of Gondwana is exposed as an erosional/tectonic window, through the Himalayan thrust sheets of the Mansehra and Swat blocks (Figure 3.2). The Besham block is bounded on either side by high- angle north-trending faults, the Thakot and Puran faults (Baig and Lawrence, 1987; Baig and Snee, 1989; Baig et al., 1989; Baig et al., in prep.). The Late Proterozoic to Mesozoic Mansehra and Swat blocks to the east and west, respectively, are in the hanging walls of the Thakot and Puran faults, and the Late Archean (7) to Late Proterozoic Besham block forms the foot wall. The Thakot and Puran faults may have been originated as normal faults during the 272 Carboniferous-Triassic rifting of Gondwana and were reactivated during the Himalayan thrusting. During FK3 (Dx) south-directed thrusting and folding, the thrust sheets of the Mansehra and Swat blocks and Neotethys terrane were emplaced on the top of the Besham block. These were folded against the north-trendingFB2, FB3, and FR1 pre-Himalayan and FK2 Himalayan structures of the Beshain block to form FK4/FB6 north-plunging antiformal structure of the Indus syntaxis. During the development of the Indus syntaxis, the Neotethys terrane, Mansehra block, and Swat block escaped east and west from theapex and top of the Besham block, as a result of indentation and vertical uplift of the Besham block (Baig et al., in prep.). This indicates that the compressional and extensional processes were active during the escape-block tectonics of the Indus syntaxis. During this mini-escape-block tectonics the Beshain block acted as a ridged indenter within the Himalayan thrust sheets. The faults and shear zones those were active during the escape-block tectonics show ductile deformation and those formed late in the development of the Indus syntaxis show brittle deformation. Since Quaternary, a significant normal motion has been accommodated along these faults and shear zones during 1600 meters Quaternary uplift of the Besham block, which is documented by the 2120 meters uplifted Quaternary Indus 273 River terraces from the present river level of 520 meters (Figures 3.2 and 3.3). These shear zones and faults were active under epidote amphibolite facies conditions at 51 Ma to 36 Ma (Thakot fault zone; Figure 3.33) in deep structural levels, and under lower greenschist facies conditions at 36-30 Ma (Chakesar fault zone, Puran fault, and Mamdin Sar fault; Figures 3.34 and 3.36) and 24 Ma (Chail Sar thrust) in shallow structural levels of the Indus syntaxis. These data show that the successive development of the Indus syntaxis occurred between 51 Ma to 24 Ma. The thrust sheets were continuously emplaced since 51 Ma on the top of the Besham block accompanied by contemporaneous uplift and unroofing/tectonjc erosion during the successive development of the Indus syntaxis. The preservation of 2000 Ma to 64 Ma hornblende, biotite, and muscovite dates in the Besham block, indicates that the overlying Himalayan thrust sheet load did not exceed above 10-12 Km (3000C) through out the development of the Indus syntaxis. The 20-25 Na, 19-20 Ma, and 24-26 Ma zircon dates from the Swat, Besham, and Mansehra blocks respectively, and 17- 24 Ma zircon dates from above the Main Mantle thrust (Zeitler, 1983; 1985), indicate that these blocks have seen similar cooling history around 16 to 26 Ma. The 20-26 Na zircon, biotite, and muscovite data from the Swat and Mansehra blocks, suggest that these minerals closed to their 274 respective closure temperatures fairly close in geological time span, due to rapid uplift and tectonic erosion of the Mansehra-Swat thrust sheets above the Besham block. However the apatite dates of 5.2-5.6 Ma from the Besham block with respect to 16-22 Ma apatite dates from the Swat block, and 19-23 Ma apatite dates from the Mansehra block, indicate differential tectonic uplift, erosion, and unroof ing of the Besham block, with respect to the adjacent Mansehra and Swat blocks. Thus the Besham block in the core of the Indus syntaxis cooled below 215 ± 25°C closure temperature of zircon between 19-20 Ma and 100 ± 20°C apatite closure temperature between 5.2 to 5.6 Na. The difference in apatite dates of Beshain block with respect to Swat and Mansehra blocks, indicates that the Besham block records younger uplift with respect to surrounding blocks. The postdating of faults and shear zones those offset the Indus suture zone by Quaternary terraces (Figures 3.2 and 3.3), shows that the present expression of the Indus syntaxis developed before the Quaternary deposition of the Indus River terraces. (8). Uplift rates and tectonic erosion since 5.2 Ma in the Indus syntaxis The newly recognized uplifted Quaternary Indus river terraces in the Indus syntaxis are comprised of rocks of the 275 Besham block, Mansehra block, Neotethys terrane, and the Kohistan island arc terrane. This indicates that the Himalayan thrust sheets were eroded from the top of Besham block before the deposition of the Quaternary terraces, and exposed the Beshain block as an erosional/tectonic window through the overlying thrust sheets (Figures 3.2 and 3.3). Subsequently, the recent uplift of the Quaternary terraces occurred to the present elevation of 1600 meters. The youngest apatite date of 5.2 Ma from Besham block indicates it cooled below 100 ± 20°C at a depth of about 3.3 Km. Since the closure of apatite at 5.2 Ma, about 3.3 Km Himalayan thrust sheets from the top of Besham block have been eroded during 3.6 Ma before the Quaternary deposition of the Indus river terraces at about 1.6 Ma. Thus before the deposition of Quaternary, a minimum uplift/erosion rate of about 0.9 mm/year, since 5.2 Ma, can be calculated for the Besham Block, by assuming the continuous uplift and tectonic erosion of the Besham block. Since 1.6 Ma, the Indus river terraces have been gradually uplifted to a maximum elevation of 2120 meters from the present day 520 meters river level (Figure 3.3). It indicates a maximum uplift of 1600 meters since 1.6 Ma. A minimum uplift/erosion rate of 1 mm/year can be calculated for the Beshain block since 1.6 Ma. Thus since 5.2 Ma to recent the Besham block is continuously uplifting at a rate of about 1 mm/yr. The 1 mm/yr rate for the Besham block in 276 the core of the Indus syntaxis is greater than uplift rates of 0.20 to 0.68 iran/yr reported for the Swat and Mansehra blocks (Zeitler, 1983, 1985). The presences of active faults (Piplai fault and Chail Sar thrust), knick points, and seisinicity (Seeber and Armbuster, 1979) in the Indus syntaxis shows that it is an active feature. The 5 nun/yr uplift rate for the Nanga-Parbat syntaxis (Zeitler, 1983) with respect to 1 nun/yr for the Indus syntaxis, indicates that the Nanga-Parbat syntaxis has five time more uplift rate than the Indus syntaxis. The above 40Ar/39Ar and fission track data, and uplifted Indus river terraces show that the Indus syntaxis has a lengthy development history varying from 51 Ma to recent. 277 SECTION 4 CONCLUS IONS Section 2: Evidence for Late Precambrian to Early Cambrian orogeny in northwest Himalaya, Pakistan There is no conclusive evidence for the timing of pre-Himalayan metamorphism and deformation in the Himalaya, where the Himalayan metamorphism has strongly overprinted the Precambrian basement rocks of the Indo-Pakistan plate. For unambiguous dating of Precambrian metamorphism and deformation in the Himalaya by field criteria, we should look for areas, farther south in the Himalayan foreland fold-and--thrust belt, where fossil-bearing Cambrian sedimentary strata, unconformably overlie deformed and metamorphosed Precambrian basement rocks of the Indo- Pakistan plate. The dating of pre-Himalayan deformation and metamorphism in the Late Proterozoic Hazara Formation by unconformably overlying Cambrian Abbottabad Group, confirms that the Hazaran deformation and metamorphism occurred during Late Proterozoic to. Early Cambrian time. The 500-600 Ma granites of the Himalaya may be a late-Hazaran-or post-Hazaran orogenic phase of the Hazaran orogeny. 278 These orogenic phases occurred on the Indo-Pakistan plate before the Permo-Triassic breakup of Gondwana, and may relate to the amalgamation of Gondwana as a supper continent. The late-or post-Hazaran orogenic phase of the Hazaran orogeny relates to the Pan-African orogeriy which affected most of Gondwaria. Section 3: Early Proterozoic to Cenozoic tectonic history of the northwest Himalaya: Geologic and 40Ar/39Ar thermochronologic evidence from northern Pakistan In polyphase metamorphosed and deformed rocks, relative ages of deformational phases, intrusive age relationships of metaigneous plutons, overprinting of gneissic fabric by weak younger fabric, and an angular unconformity provide relative age constraints, but do not provide absolute dating of metamorphic fabric. Field criteria must be supplemented by isotopic age data to establish absolute age constraints on Himalayan and pre-Himalayan deformational and metamorphic events. 40Ar/39Ar dating of hornblende, potassium feldspar, muscovite, and biotite (this study), accompanied with Rb/Sr, U/Pb, and fission track data published elsewhere, show that the Precambrian to Phanerozoic rocks of the Indo-Pakistan plate record a lengthy pre-Himalayan and Himalayan orogenic 279 history, varying from the Early Proterozoic to Cenozoic. The Besham group of rocks of the Besham basement complex were deposited during Late (?) Archean to Early Proterozoic time and were accompanied by ultrainafic pyroxenitic lava flows, possibly associated with the Late (?) Archean to Early Proterozoic rifting of the Indo- Pakistan plate. The Besham group of rocks may correlate to the Aravalli Supper Group of Rajastari southern India. The Besham basement complex is the northwestern most exposed basement of the Indo-Pakistan plate. The sedimentation of the Besham group occurred before the intrusion of mafic dikes and sills, potassic- biotite granites, and sodic-biotite granites, which were metamorphosed and deformed to upper amphibolite facies between 2031 ± 6 Ma to 1997 ± 8 Ma. A second upper amphibolite fades metamorphism and deformation in the Besham block occurred at 1950 ± 3 Ma and has largely obliterated the fabric evidence for the earlier metamorphism. The next event was intrusion of hornblende-biotite granites and later mafic dikes between 1950 ± 3 Ma to 1887 ± 5 Ma. A third epidote amphibolite facies metamorphism and deformation occurred between 1887 ± 5 Ma to 1865 ± 3 Ma. This was followed by post-tectonic graphic tourmaline-muscovite sodic granites at 1517 ± 3 Ma. 280 The rock units and structural-metamorphic history of the Besham basement complex between the Thakot and Purari faults is different from that of the Nansehra and Swat blocks. The unconformable deposition of the Karora group on the Besham basement complex and of related units, the Hazara, Manki, Dakhner, Sheikhi, and Shahkot formations occurred in the Middle to Late Proterozoic, and postdated the plutonisni, metamorphism, and deformation in the Besham basement complex. After the deposition of Karora group, and its stratigraphic equivalents, the Hazara, Manki, Gandaf, Dakhner, LandiKotal, Dogra, Simla, Sheikhi, and Shahkot formations and unconformably succeeding Tanawal and Manglaur formations, the Indo-Pakistan plate was affected by plutonism and volcanism between 850 Ma to 600 Ma and metamorphism and deformation between 664 Ma to 625 Ma (Hazaran orogeny). This deformation and metamorphism is postdated by the unconformable deposition of the Cambrian fossil-bearing sedimentary strata in the Hazara area of Pakistan. During the Cambro-Ordovician orogeny the Indo- Pakistan plate was affected by major magniatism between 550 Ma to 450 Ma, which was followed closely in time by amphibolite facies metamorphism and deformation >466 Ma. 281 (14) In the Late Carboniferous alkaline rocks (315 ± 15 Ma to 297 ± 4, Le Base et al.,, 1987), Ainbela granite, and sodic granites of Besham (>272 Ma) were intruded, and in the Early Permian (284 Ma to 262 Ma) Panjal mafic dikes and flows were intruded and erupted. These are associated with Late Paleozoic rifting of northern Gondwana to form Cimmerian microcontinent. The diabase dikes of Panjal volcanism intrude at 284 Ma to 262 Ma, and postdate the Early Paleozoic orogenic event. Another group of basalt dikes were intruded in the Jurassic at 159 Ma. These may relate to the Jurassic extension of the Neotethys Ocean. The earliest Himalayan deformation and metamorphism occurred during the Late Cretaceous to early Paleocene in the Indo-Pakistan plate. The Kohistan island arc and Neotethys terranes were initially emplaced on the passive margin of the Indo-Pakistan plate between 80-84 ± 4 Ma. The initial Himalayan collision of the Indo- Pakistan and Kohistan island arc terrane occurred between 70 Ma to 64 Ma. These tectonic events are postdated by the Paleocene to early Eocene unconformity in the foreland fold- and-thrust belt of Himalaya. This study shows that the Himalayan collision in northern Pakistan is musch earlier than the Eocene collision of the main Himalaya of India. 282 The 51 Ma to 36 Ma, 36 Ma to 30 Ma, and 30 Ma to 24 Ma dates from the shear zones of the Indus syntaxis date the timing of oblique-slip faulting, related escape block tectonics, and thrusting during the development of the Indus syntaxis. Tectonic uplift, erosion, and unroofing of the Himalayan thrust sheets from the top of Beshain block took place between 24 Ma to 5 Ma. The current expression of the Indus syntaxis developed before the Quaternary deposition of the Indus river terraces. The presence of cobbles, pebbles, and boulders of Beshain block in the Quaternary deposits of the Indus river terraces shows that the Besham block was exposed as a erosional/tectonic window through the overlying Himalayan thrust sheets during or before the deposition of terraces. The Indus syntaxis records an uplift rate of about 1 mm/yr since 5.2 Ma, which is about five time less than the maximum uplift rate of about 5 mm/yr reported for the Nanga- Parbat syntaxis by Zeitler (1985). The presence of active faults (Chail Sar thrust and Piplai fault), seismicity (Indus Kohistari seismic zone), 1600 m uplifted Quaternary Indus river terraces above the present river level, and an uplift rate of about 1 mm/yr in the Iridus syntaxis show that it is a neotectonic feature. 283 BIBLIOGRAPHY Ahinad, A., and J.M. Alan, The Ganga Basin, its subsurface sequences, their affinity, sedixnentological and tectonic implications, Himalayan Geology, ,583-608, 1978. Ahmnad, Z., and S.G. Abbas, The Muslim Bagh Ophiolites, in Geodynamics of Pakistan, edited by A. Farah and K.A. De Jong, Geological Survey of Pakistan, Quetta, pp.243-249, 1979. Ahmnad, I., Geology of Jowar area, Karakar Pass, Swat District, N.W.FP., Pakistan, Unpublished M.Phil. thesis, National Center of Excellence in Geology University of Peshawar, Pakistan, 144p, 1986. Ahmad, I., P.S. Rosenberg, R.D. Lawrence, A.A.K. Ghauri and M. Majid, Lithostratigraphy of the Karakar Pass section, south of the Main Mantle thrust, Swat, N.W. Pakistan, Geol. Bull. Univ. Peshawar, Pakistan, Q, 199-208, 1987. Ahmnad, I., P.S. Rosenberg, R.D. Lawrence, M Majid, and A.A.K. Ghauri, Evidence of multiple deformation in the rocks of Karakar Pass area, Swat, N.W. Pakistan, Geol. Bull. Univ. Peshawar, Pakistan, 20, 189-198, 1987a. 284 Alexander, E.C., G.M. Michelson, and M.A. Lanphere, MMhb-1:A new40Ar/39Ar dating standard, in Short Papers of the Fourth International Congress, Geochronology Cosmochronoloqy, Isotope Geology, edited by R.E. Zartman, Geological Survey Open-File Report 78-701, pp.6-8, 1978. Ali, C.M.,, The stratigraphy of the southwestern Tanol area, Hazara, West Pakistan. Geol. Bull. Punjab Univ. Lahore, Pakistan, 2, 31-38, 1962. Allemann, F., Time of emplacement of the Zhob Valley ophiolites and Bela Ophiolites, Baluchistan (Preliminary Report), in Geodynamics of Pakistan, edited by F. Farah and K.A. De Jong, Geological Survey of Pakistan, Quetta, pp.215-242, 1979. Arndt, N.T., AJ. Naldrett, and D.R. Pyke, Komattiitic and iron-rich tholeiitic lavas of Munro Township, northeast Ontario, Journal of Petrology, 18J2, 319-369, 1977. Ashraf M., Geochemistry and petrogenesis of acid minor bodies of Nansehra and Batgram area, Hazara District, Unpublished Ph.D. thesis, Panjab University Lahore, Pakistan, 200p, 1974. Ashraf, M., M.N. Chaudhry, and S.S. Hussain, General geology and economic significance of the Lahor granite and rocks of the southern ophiolite belt in Allai-Kohistan area, Geol. Bull. Univ. Peshawar, Pakistan, 13, 207-213, 1980. 285 Ashraf, N., M.N Chaudhry, and K.A. Qureshi, Startigraphy of Kotli area of Azad Kashinir and its correlation with standard type areas of Pakistan, Kashinir Jour. Geol. Azad Kashiuir Univ. Muzaffarabad, Pakistan, ,19-30, 1983. Baig, M.S., Geology of Jura-Doarian area Neeluni Valley, State of Azad Jammu and Kashmir, Unpublished M.Sc. thesis, Institute of Geology, Panjab University Lahore, Pakistan, 223p, 1980. Baig, M.S., and R.D. Lawrence, Precambrian to early Paleozoic orogenesis in the Himalaya, Kashinir Jour. Geol. Azad Kashinir Univ. Muzaffarabad, Pakistan, , 1-22, 1987. Baig, M.S., R.D. Lawrence, and L.W. Snee, Evidence for late Precambrian to early Cambrian orogeny in northwest Himalaya, Pakistan Geological Magazine., 125/1, 83-86, 1988. Baig, N.S., and L. W. Snee, Pre-Himalayan dynamothermal and plutonic activity preserved in the Himalayan collision zone, NW Pakistan: Ar thermochronologic evidence, Geol. Soc. Am. Abst. with Programs, 21/6, p.264, 1989. Baig, M.S., L.W. Snee, R.D. Lawrence, and R.J. La Fortune, Timing of Pre-Hiiaalayan orogenic events in the Northwest Himalaya, accepted in Kashinir Jour. Geol. Azad Kashmir Univ. Huzaffarabad, Pakistan, 7, 1989. 286 Baig, M.S., R.D. Lawrence, and L.W. Snee, Indus syntaxis Besham area, Northwest Himalaya, Pakistan: Implications for syntaxial features, (in prep.). Baig, M.S., Neotectonics of the Indus syntaxis, Northwest Himalaya, Pakistan, (in prep.). Bard, J.P., Metamorphism of an obducted island arc: Example of the Kohistan sequence (Pakistan) in the Himalayan collided range, Earth Planet. Sci. Lett., , 133-144, 1983. Bhandari, L.L., and G.C. Agarwal, Eocene (Subathu Series) of the Himalayan foot hills of north India, Publications of the Center of Advance Study in Geology, Panjab University, Chandigarh. India, 3, 57-58, 1966. Bhanot, yB., A.K. Bhandari, V.P. Singh, and A.K. Kansal, Geochronological and geological studies on a granite of Higher Himalaya, Northwest Manikaran Himachal Pradesh, Jour. Geol. Soc. India, 20, 90-94, 1979. Bhargava, O.N., Pre-Tertiary orogenies in the Himalaya: A review of various evidences, Geologische Rundschau, , 811-823, 1980. Bickle, M.S., A. Martin, and E.G. Nisbet, Basaltic and peridotitic komatiites and stromatolites above a basal unconformity in the Belingwe greenstone belt, Rhodesia, Earth Plant. Sci. Lett., 27, 155-162, 1975. Bossart, P., D. Dietrich, A. Greco, R. Ottiger, and J.G. Ramsay, The tectonic structure of the Hazara-Kashmir 287 syntaxis, southern Himalayas in Hazara Pakistan, Tectonics, 7/2, 273-297, 1988. Brookfield, M.E., and P.H. Reynolds, Late Cretaceous emplacement of the Indus suture zone ophiolitic inelanges and an Eocene-Oligocene inagmatic arc on the northern edge of the Indian plate, Earth Planet. Sci. Lett., 55, 157-162, 1981. Brooks, C., and S.R. Harts, On the significance of komatiite, Geology, 2, 107-110, 1974. Butt K.A., M.N. Chaudhry, and M. Ashraf, An interpretation of petrotectonic asseitthlage west of western Himalayan syntaxis in Dir district and adjoining areas in northern Pakistan, Geol. Bull. Univ. Peshawar, Pakistan, 13, 79-86, 1980. Butt, K.A., Petrology and geochemical evolution of Lahor pegmatiod/granite complex, northern Pakistan, and genesis of associated Pb-Zn-Mo and U mineralization, in Granites of Himalayas. Karakorum and Hindu Kush, edited by F.A. Shams, Institute of Geology Punjab University Lahore, Pakistan, pp.309-326, 1983. Butt, K.A., Komatiltic affinities of ultramafic rocks, serpentinites, and ultramafic amphibolites in the amphibolite belt of northern Pakistan, Kashinir Jour. Geol. Azad Kashinir Univ. Muzaffarabad, Pakistan, 1, 43-48, 1983a. 288 Calkins, J.A., T.W. Offield, S.K.M. Abdullah, and S.T. Au, Geology of the southern Himalayas in Hazara Pakistan, and adjacent areas, U.S.G.S. Prof. Paper, 716-C, 29p, 1975. Chamberlain C.P., M.Q. Jan, and P.K. Zeitler, A petrologic record of the collision between the Kohistan island arc and Indian plate, northwest Himalaya, in Tectonics of the western Himalayas, edited by L.L. Malinconico and R.J. Lillie, U.S.G.S. Spec. Paper, 232, pp.23-32, 1989. Chaudhry, MN., S.A. Jafferi, and B.A. Saleemi, Geology and petrology of the Malakand granite and its environ, Geol. Bull. Punjab Univ. Lahore, Pakistan, , 43-58, 1974. Chaudhry, M.N., M. Ashraf, SS. Hussian, and M. Iqbal, Geology and petrology of Nalakand and a part of Dir (Toposheet 38 N/14), Geol. Bull. Punjab Univ. Lahore, Pakistan, 12, 17-40, 1976. Chaudhry, M.N., M. Ashraf, and S.S. Hussian, Lead-Zinc mineralization of lower Kohistan District, Hazara Division, N.W.F. Province, Pakistan, Kashmir Jour. Geol. Azad Kashmir Univ. Nuzaffarabad, Pakistan, i, 31-42, 1983. Chaudhry, M.N., M. Ghazanfar, N. Ashraf, and S.S. Hussian, Geology of the Shewa-Dir-Yasin area and its plate 289 tectonic interpretation, Kashmir Jour. Geol. Azad Kashir Univ. Muzaffarabad, Pakistan, , 53-63, 1984. Chaudhry, M. N., M. Ghazanfar, and M. Qayyum, Metamorphism at the Indo-Pak plate margin, Kaghan Valley, District Mansehra, Pakistan, Geol. BullPunjab Univ. Lahore, Pakistan, 21, 62-86, 1986. Choudhary, A.K., K. Gopalan, and C. A. Sastry, Present status of the Geochronology of the Precambrian rocks of Rajastan, Tectonophysics, 105, 131-140, 1984 Coulson, A.L., Marble of the North-West Frontier Province, Rec. Geol. Surv. India, 71, 328-344, 1936. Coulson, A.L., Marble and dolomite of Ghundai Tarako, North-West Frontier Province, Rec. Geol. Surv. India, j., 227-234, 1937. Coward, M.P., M.Q. Jan, D.C. Rex, J. Tarney, M.F. Thirlwall, and B.F. Windley, Geotectonic framework of the Himalaya of North Pakistan, Jour. Geol. Soc. London, 299-308, 1982. Coward, M.P., B.F. Windley, RD, Broughton, I.W. Luff, M.G. Peterson, C.J. Pudsey, D.C. Rex, and M.A. Khan, Collision tectonics in the NW Himalayas, in Collision Tectonics, edited by M.P. Coward and A.C. Ries, Geol. Soc. Lond. Spec. Pubi., 19, pp.203-219, 1986. Coward, M.P., R.W.H. Butler, M.A. Khan, and R.J. Knipe, The Tectonic history of Kohistan and its implications for 29 C) Himalayan structure, Jour. Geol. Soc. London, 144, 377-391, 1987. Crawford, A.R., and W. Compston., The age of the Vindhyan System of Peninsular India, Jour. Geol. Soc. London, 125, 351-371, 1970. Crawford, A.R., and Davies, R.G, Ages of Pre-Nesozoic formations of the Lesser Himalaya, Hazara District, northern Pakistan, Geological Maqazine., 112, 509-514, 1975. Dairymple, G. B., E. C. Alexander, M.A. Lanphere, and G. P. Kraker, Irradiation of samples for 40Ar/39Ar dating using the Geological Survey TRIGA reactor, U.S.G.S. Prof. Paper, 1176, 55p, 1981. Davies, R.G., and A.R. Crawford, Petrography and age of the rocks of Bulland Hill and Kirana Hills, Sargodha District, West Pakistan, Geological Magazine, 108/3, 235-246, 1971. Debon, F., P. Le Fort, J. Sonet, G. Liu, C. Jin, and R. Xu, About the lower Paleozoic age of the Kangmar granite (Lhagoi-Kangri plutonic belt, South Tibet, China), Terra Cognita, Special Issue, 1/14, 67-68, 1981. DiPietro, J.A., Stratigraphy, structure, and metamorphism near Saidu Shrif, Lower Swat, Pakistan, Unpublished Ph.D. thesis, Oreqon State University, Corvallis, Oregon, U.S.A., 182p, 1990. 291 DiPietro, J.A., and R.D. Lawrence, Himalayan structure and metamorphism south of the Main Mantle thrust, Lower Swat, Pakistan Jour. Meta. Geol..,(in press, 1990). Divakara Rao, V., and P. Rama Rao, Granitic activity and crustal growth in the Indian shield, Precambrian Research, 16, 257-271, 1982. Dodson, M. H., Closure temperature in cooling geochronological and petrological systems, Contrib. Miner. Petrol., 40, 259-274, 1973. Farah, A., R.D. Lawrence, and K.A. De Jong, An overview of the tectonics of Pakistan, in Marine Geoloqy and Oceanography of Arabian Sea and Coastal Pakistan, edited by B.U. Haq and J.D. Milliinan, Van Nostrand Rienhold company, pp.161-176, 1984. Fletcher, C.J.N., R.C. Leak, and H.W. Haslam, Tectonic setting, mineralogy, and chemistry of a metamorphosed stratiform base metal deposit within Himalayas of Pakistan, Geol. Soc. London, , 521-536, 1986. Frank, W., Geochemistry and isotopic geochemistry in the Himalaya: Discussion, in Colloquies internationaux du CRNS Himalaya, Sci. de la terre, Paris, 268, 250-270, 1977. Gaetani, M., E. Garzanti, and A. Tintori, Perino- Carboniferous stratigraphy in SE Zanskar and NW Lahul (NW Himalaya, India), Eclogae Geol. Helv.., 83/1, 143-161, 1990. 292 Gansser, A., Geology of the Himalaya, Wiley Interecience, New York, 289p, 1964. Gansser, A., A Reconnaissance visit to the ophiolites in Baluchistan and the Himalaya, in Geodynainics of Pakistan, edited by A. Farah and K.A. De Jong, Geological Survey of Pakistan, pp.193-213, 1979. Gansser, A., The geodynamic history of the Himalaya, in Zagros-Hindu Kush Himalaya Geodynaiuic Evolution, edited by H. Gupta and F. Delany, American Geophys. Union, Geodyn. Series, 3, pp.111-121, 1981. Garzanti, E.,, R. Casnedi, and F. Jadoul, Sedimentary evidence of a Caiubro-Ordovician orogenic event in the northwestern Himalaya, Sedimentary Geology, 4, 237- 265, 1986. Gee, E.R., Tectonic problems of the Sub-Himalayan region of Pakistan, Kashmir Jour. Geol. Azad Kashinir Univ. Muzaffarabad, Pakistan,],,11-18, 1983. Gee, E.R., Overview of the geology and structure of the Salt Range, with observations on related areas of northern Pakistan, in Tectonics of the western Himalayas, edited by L.L. Malinconico and R.J. Lillie, U.S.G.S. Spec. Paper, 232, pp.95-112, 1989. Ghazanfar, M., M.S. Baig, and M.N. Chaudhry, Geology of Tithwal-Kel area, Neeluin Valley, Azad Jaminu and Kashmir, Kashmir Jour. Geol. Azad Kashmir Univ. Muzaffarabad, Pakistan, 1, 1-10, 1983. 293 Ghazanfar, M., and N.M. Chaudhry, Geology of Bhunja- Batakundi area, Kaghan Valley, District Mansehra, Pakistan, Geol. Bull. Panjab Univ. Lahore, Pakistan, 20, 76-103, 1985. Ghazanfar, N., andM.N. Chaudhry, Reporting MCT in northwest Himalaya, Pakistan, Geol. Bull. Punjab Univ. Lahore, Pakistan, 21, 10-18, 1986. Ghaznavi, M.I., T. Karim, and J.B. Maynard, A bauxitic paleosol in phosphate-bearing strata of northern Pakistan, Economic Geology, , 144-7, 1983. Greco, A., G. Nartinotti, K. Papritz, J.G. Ramsay and R. Rey, The crystalline rocks of the Kaghan Valley (NE- Pakistan), Eclogae Geol. Helv., 82/2, 629-653, 1989. Gupta, S.S., Possible subsurface structures below the Himalayas and the Gangetic Plains, In Proceedincs 22nd International Geological Congress, Part XI, 335-52, 1964. Harrison, T.M., and I. Mc Dougall, Investigations of an intrusive contact, northwest Nelson, New Zealand: Thermal, chronological, and isotopic constraints, Geochim. Cosinochim. Acta, 46, 1811-1820, 1980. Harrison, T.M., Diffusion of 40Ar in Hornblende, Contrib. Mineral. Petrol. 78, 324-3 31, 1981. Harrison, T.M., and I. McDougall, The thermal significance of potassium feldspar K-Ar ages inferred from40Ar/39Ar 294 age spectrum results, Geochim. Cosmochim. Acta, j, 1811-1820, 1982. Heron, A.M., The geology of north-eastern Rajputana and adjacent Districts, Nem. Geol. Surv. India,4,1-128, 1917. Heron, A.M., The geology of Central Rajputana, Mem. Geol. Surv. India, 79, 1-339, 1953. Honegger, K., V. Dietrich, W. Frank, A. Gansser, M. Thoeni, and V. Trommsdorff, Magmatism and metamorphism in the Ladakh Himalaya (the Indus-Tsangpo suture zone), Earth Planet. Sci. Lett., 60, 253-292, 1982. Hubbard, M.S., and T.M. Harrison, 40Ar/39Ar age constraints on deformation and metamorphism in the Main CentraL thrust zone and Tibetan slab, eastern Nepal Himalaya, Tectonics, 8/4, 865-880, 1989. Hylland, M.D., Structure and Stratigraphy of the southern Gandghar Range, Hazara, District, Pakistan, Unpublished M.S. thesis, Oregon state University, Corvallis, Oregon, U.S.A., 70p, 1990. Jager, E., A.K. Bhandari, and V.B. Bhanot, Rb/Sr age determinations on biotites and whole rock samples from the Mandi and Chor granites Himachal Pradesh, India, Eclogae Geol. Helvi., , 521-527, 1971. Jam, A.K., R.K. Goel, and N.G.K. Nair, Implications of Pre- Mesozoic orogeny in the geologic evolution of the 295 Himalaya and Indo-Gangetic plains, Tectonophysics, 62, 67-86, 1980. Jan, M.Q., and R.AK. Tahirkheli, The geology of the lower part of Indus Kohistan (Swat), west Pakistan, Geol. Bull. Univ. Peshawar, Pakistan, 4, 1-13, 1969. Jan, M.Q., Petrography of amphibolites of Swat and Kohistan, Geol. Bull. Univ. Peshawar, Pakistan, J, 51-64, 1979. Jan, M.Q., and R.A. Howsi, The mineralogy and geochemistry of the metamorphosed basic and ultrabasic rocks of the Jijal complex, Kohistan, NW Pakistan, Journal of Petroloqy, 22, 85-126, 1981. Jan, M.Q., Geology of amphibolites from the southern part of the Kohistan arc, N. Pakistan, Mineralogical Magazine, , 147-159, 1988. Kaneoka, I., Investigations of excess argon in ultramafic rocks from the Kola Peninsula by the 40Ar/39Ar method, Earth Planet. Sci. Lett., , 45-57, 1974. Kazmer, C., S.S. Hussain, and R.D. Lawrence, The Kohistan- Indian plate suture zone at Javan Pass, Swat Pakistan, Geol. Soc. iu. Abst. with Programs, , p.609,1983. Kazmi, A.H., and R.A. Rana, Tectonic Map of Pakistan, 1:2000000, Quetta: Geological Survey of Pakistan, 1982. Kazmi, A.H., R.D. Lawrence, H. Dawood, L.W. Snee, and S.S. Hussain, Geology of the Indus suture zone in the Mingora-Shangla area of Swat, Geol. Bull. Univ. Peshawar, Pakistan, 17, 127-144, 1984. 296 Khan, M.A., M.Q.Jan, B.F. Windley, J. Tarney, and M.F. Thrilwall, The Chilas mafic-ultramafic igneous complex; The root of the Kohistan island arc in the Himalaya of northern Pakistan, in Tectonics of the western Himalayas, edited by L.L. Halinconico and RJ. Lillie, U.S.G.S. Spec. Paper, 232, pp.75-95, 1989. King, B.H., The structure and petrology of part of Lower Swat, West Pakistan, with special reference to the origin of the granitic gneisses, Unpublished Ph.D. thesis, University of London, 250p, 1964. Klootwijk, C.T., A summary of palaeomagnetic data from extrapeninsular Indo-Pakistan and south-central Asia: Implications for collision tectonics, in Structural Geoloqy of the Himalaya, edited by P.S. Saklani, Today and Tomorrow Publisher New Delhi, India, pp.307-360, 1979. Klootwijk, C.T., and Radhakrishnamurthy, Phanerozoic palaeoinagnetism of the Indian plate and the Indo-Asia collision, in Paleoreconstruction of the Continents, Geodynainic Series, 2, 93-105, 1981. Klootwijk, C.T., P.J. Conaghan, and C.M. Powell, The Himalayan Arc; Large-scale continental subduction, oroclinal bending, and backarc spreading, Earth Planet. Sci. Lett., 75, 167-183, 1985. 297 Kruinraenacher, ID., Nepal central. Geochronometrique des series de Lesser Himalaya, Schweiz. Mineral. Petrol. Mitt.,4,43-54, 1966. Kumar, R., and I.C. Pande., Deformation of the rocks of Simla Hills, Geologische Rundschau, , 430-441, 1972. Kuinar, R., A.N. Shah, and S.K. Bingham, Positive evidence of a Precambrian tectonic phase in Central Nepal Himalaya, Jour. Geol. Soc. India, 19, 519-522, 1978. La Fortune, J.R., Geology and geochemistry of Indian plate rocks south of the Indus suture Besham area, Northern Pakistan, Unpublished M.S. thesis. Oregon State University Corvallis, Oregon, U.S.A., 70p, 1988. Lanphere, M.A., and G.B. Dalrymple, A test of the 40Ar/39Ar age spectrum technique on some terrestrial material, Earth Planet. Sci. Lett., , 359-372, 1971. Lanphere, M.A., Identification of excess 40Ar by the 39Ar/40Arage spectrum technique, Earth Planet. Sci. Lett., , 141-148, 1976. Latif, M.A., The stratigraphy of south eastern Hazara and parts of Rawalpindi and Muzaffarabad districts of west Pakistan and Azad Kashmir, Ph.D. thesis London University, 316p, 1969. Latif, M.A., Explanatory notes on the geology of southeastern Hazara, to accompany the revised geological map, Jb. Geol. B.A. Sonder., 15/S, 5-20, 1970. 298 Latif, M.A., Lower Paleozoic (?) Hyolithes from Hazira Shale, Pakistan, Nature Phys. Sci. London, 240/100, p.52, 1972. Latif, M.A., A Cambrian age for the Abbottabad Group of Hazara, Pakistan, Geol. Bull. Punjab Univ. Lahore, Pakistan, , 1-20, 1974. Latif, M.A., Stratigraphy and Micropalaeontology of the Galis Group of Hazara, Geol. Bull. Punjab Univ. Lahore, Pakistan, , 1-63, 1976. Lawrence, R.D., and R.A.K. Ghauri, Evidence of active faulting in Chilas District, Northern Pakistan, Geol. Bull. Univ. Peshawar, Pakistan, , 185-186, 1983. Lawrence, R.D., L.W. Snee, and P.S. Rosenberg, Nappe structure in a crustal scale duplex in Swat, Pakistan, Geol. Soc. Am. Abst. with Programs, , p.640, 1985. Lawrence, R.D., A.H. Kazmi, and L.W. Snee, Geological setting of the emerald deposits of Swat, Northern Pakistan, in Emeralds of Pakistan: Geoloqy, Gemoloqy and Genesis, edited by A.H. Kazmi and L.W. Snee, Van NostrandReinhold, New York, pp.13-38, 1989. Le Base, M.J., I. Mian, and D.C. Rex, Age and nature of carbonatite emplacement in north Pakistan, Geologische Rundschau, 76/2, 317-323, 1987. Le Fort, P., Himalaya: The collided range: Present knowledge of the continental arc, American Jour. Sci., 275A, 55-56, 1975. 299 Le Fort, P., F. Debon, and J. Sonet, The Lesser Himalaya cordierite granite belt: Typology and age of the pluton of Mansehra, Pakistan, Geol. Bull. Univ. Peshawar, Pakistan, 13, 51-61, 1980. Le Fort, P., A. Pecher, and P.H. Vidal., Les gniess oeilles de la dalle du Tibet: un episode magmatique au Paleozoique inferieur en Himalaya du Napal, leme Reun. Annu. Sci. de la Terre, Paris, Soc. Geol. France, p.369, 1982. Le Fort, P., F. Debon, and J. Sonet, The lower Paleozoic "Lesser Himalayan" granitic belt: Emphasis on the Simchar pluton of Central Nepal, in Granites of Himalayas Karakoruin and Hindu Kush, edited by F.A. Shams, Institute of Geology University of Punjab Lahore, Pakistan, pp.235-255, 1983. Le Fort, P., Metamorphism and magmatism during Himalayan collision, in Collision Tectonics, edited by M.P. Coward and A.C. Ries, Geol. Soc. Lond. Spec. Publ., , pp.159-172, 1986. Maj\id, M., and F.A. Paracha, Calc-alkaline magmatisra at destructive plate margin in Kohistan, northern Pakistan, Geol. Bull. Univ. Peshawar, Pakistan, i, 109-120, 1980. Majid, 1., and T. Shah, Mineralogy of the blueschist facies metagraywacke from the Shergarh Sar area, Allai- 300 Kohistan, N. Pakistan, Geol. Bull. Univ. Peshawar, Pakistan, 18, 41-52, 1985. Naluski, H., and P. Matte, Ages of Alpine tectonometamorphic events in the northwestern Himalaya (northern Pakistan), Tectonics, , 1-18, 1984. Maluski, H., P. Matte, and N. Brunel, Argon 39 - Argon 40 dating of metamorphic and plutonic events in the north and high Himalayan belts (southern Tibet-China), Tectonics, 7, 299-326, 1988. Martin, N.R., S.F.A. Siddiqui, and B.H. King, A geological reconnaissance of the region between the lower Swat and Indus River of Pakistan, Geol. Bull. Punjab Univ. Lahore, Pakistan, 2, 1-14, 1962. Maruo, Y., and K. Kizaki, Nappes of the eastern Nepal Himalayas, In Granites of Himalayas Karakorum and Hindu Rush, edited by F.A. Shams, Institute of Geology, Punjab University Lahore, pp.271-286, 1983. Nadin, I., Structure and rieotectonics of the northwestern Nanga Parbat-Haramosh Massif: Unpublished M.S. thesis, Oregon State UniversitI, Corvallis, Oregon, U.S.A., 160p, 1986. Madin, I., R.D. Lawrence, and S.U. Rehman, The northwestern Nanga Parbat-Haramosh Massif; Evidence for crustal uplift at the northwestern corner of the Indian Craton, in Tectonics of the western Himalayas, edited by L.L. 301 Malinconico and R.J. Lillie, U.S.G.S. Spec.Paper, 232, pp.169-182, 1989. Mc Dougall, I., and T.M. Harrison, Geochronology by the 40Ar/39Ar method, Oxford University Press, New York, 212p, 1988. Merrihue, C., and G. Turner, Potassium-argon dating by activation with fast neutrons,Jour. Geophys. R., fl, 2852-2857, 1966. Metha, P.1<., Structural and metamorphic history of the crystalline rocks of Kulu Valley, Hiinachal Pradesh, in relation to the tectonics of the north western Himalaya, InGeotettonica delle zone orogeniche del Kashinir Himalaya-Karakorum-Hindu Kush-Painir, Roma, 1974, Accad. Nas. del Lincei, Roma,pp.215-244, 1976. Metha, P.1<., Rb/Sr geochronology of the Kulu-Mandi Belt: its implications for the Himalayan tectogenesis, Geolociische Rundschau, 66,156-175, 1977. Metha, P.k., Tectonic significance of the young mineral dates and the rates of cooling and uplift in the Himalayas,Tectonophysics,62, 205-217, 1980. Middlemiss, S.S., Geology of Hazara and Black Mountains, Hem. Geol. SUrV. India, 7,1-302, 1896. Mitchell, A.H.G., Himalayan and Trans-Himalayan granitic rocks in and adjacent to Nepal and their mineral potential,Jour. Nepal Geol. Soc., 1/1,41-52, 1981. 302 Molanar, P., and P. Tapponnier, Cenozoic tectonics of Asia: effects of a continental collision, Science, i, 4l9- 426, 1975. Molnar, P., The geologic history and structure of the Himalaya, American Scientist,7,144-154, 1986. Montenate, C., J. Blaise, P. Bordet, F. Debon, U.S. Deutsc., P. Le Fort, and J. Sonet, Metamorphism et plutonisin au Paleozoique ancien er domaine Gondwan sur la marge nordouest des Montagnes Centrales d' Afghanistan, Bull. Soc. Geol. France, 7, t.XXIII, No.1, 101-110, 1981. Murthy, M.V.N., S .N. Gupta, Y . K. Arora, R.K. Mathur, Iqbaluddin, B. Prasad, T.N. Sahai, and S.B. Sharma, Geological map of the Precambrian of the Aravalli region, southern Rajasthan and northeastern Gujarat, India, in 26th International Geological Congress, Paris, 1980. Naha, K., and S.K. Ray, Evidence of overthrusting in the metamorphic terrane of the Simla Himalaya, American Jour. Sci., 270, 30-42, 1971. Offield, T.W., SK.M. Abdullah, and M.S. Zafar, Reconnaissance geology of the Mansehra Quadrangle, Hazara, District, West Pakistan, U.S.G.S. Unpublished Report, No.(IR) PK-10, 3 ip, 1966. Papritz, K., and R. Rey, Evidence for the occurrence of Panjal Trap Basalt in the Lesser-and Higher Himalayas 303 of the Western Syntaxis area, NE Pakistan, Eclogae Geol. Helv., 82/2, 603-627, 1989. Pareek, H.S., Petrochemistry and petrogeriesis of the Malani igneous suit, India, Geol. Soc. i. Bull., , 206-273, 1981. Patriat, P., and J. Achache, India-Eurasia collision chronology has iniplications for crustal shortening and driving mechanism of plates, Nature, 311, 615-621, 1984. Peterson, N.G., and B.F. Windley, Rb-Sr dating of Kohistan arc-batholith in the Trans-Himalaya of North Pakistan and its tectonic implications, Earth Planet. Sci. Lett., 74, 45-57, 1985. Pierce, J. W., The northward motion of India since the late Cretaceous, Geophys. J.R. Astr. Soc., 52, 277-311, 1978. Pognante, U., and B. Lombrado, Metamorphic evolution of the high Himalayan crystallines of SE Zanskar, Jour. Meta. Geol., 7, 9-17, 1989. Pogue, K. R., and A. Hussain, New light on the stratigraphy of Nowshera area and the discovery of early to middle Ordoviciari trace fossils in N.W.F.P., Pakistan, Geol.SUrV.Pak. Infor. Release, 135, 15p, 1986. Pogue, K. R., B. Wardlaw., A. Harris, and A. Hussian, Paleozoic-Nesozoic Tethyan stratigraphy of the Peshawar 304 Basin, Pakistan: Correlations and Implications, Geol. Soc. Am. Bull., (in prep.). Pogue K.R., J.A. DiPietro, S. Hughes, R.D. Lawrence, and S. Rahim, Late Paleozoic rifting in Northern Pakistan, Tectonics, (in prep. a). Powell, C.M., and P.J.Conaghan, Polyphase deformation in Phanerozoic rocks of the Central Himalayan gneiss, northwest India, Journal of Geology, , 127-143, 1973. Powell, C.M., and P.J. Conaghan, Rb/Sr geochronology of the Kulu-Nandi belt: its implications for the Himalayan tectogenesis-discussion, Geologische Rundschau, , 380-3, 1978. Powell, C.M., A.R. Crawford, R.L. Armstrong, R. Prakash, and H.R. Wynne-Edwards, Reconnaissance Rb/Sr dates for the Himalayan Central gneiss, northwest India, Indian Jour. Sci., 6, 139-151, 1979. Powell, C.M., A speculative tectonic history of Pakistan and surroundings: Some constraints from the Indian Ocean, in Geodynamics of Pakistan, edited by A. Farah and K.A. De Jorig, Geological Survey of Pakistan, Quetta, pp.5-24, 1979. Pudsey, C.I., M.P. Coward, I.W. Luff, R.M. Shackleton, B.F. Windley, and M.Q. Jan, Collision zone between the Kohistan arc and the Asian plate in NW Pakistan, Trans. R. Soc. Edinburgh, 76, 463-479, 1985. 305 Pudsey, C.J., The northern suture, Pakistan: margin of a Cretaceous Island arc, Geological Hagazine, , 405-423, 1986. Rafiq, M., Petrology and geochemistry of Ainbela granitic complex, N.W.F.P., Pakistan, Unpublished Ph.D. thesis, University of Peshawar. Pakistan, 272p, 1987. Raina, B.N., U.C. Pati, and N. Sriinal, Phases of Himalayan orogeny, Himalayan Geology, 10, 12-23, 1980. Raiz, M., Structure and Stratigraphy of the northern Gandghar Range, Hazara District, Pakistan, Unpublished M.Ph. thesis, National Center of Excellence in Geology, University of Peshawar, Pakistan, 48p, 1990. Roddick, J.C., High precision intercaliberation of Ar-Ar standards, Geochim. Cosmochim. Acta,41,887-898, 1983. Rosenberg, P.S., Himalayan deformation and metamorphism of rocks south of the Main Mantle thrust, Karakar Pass area, south Swat, Pakistan, Unpublished M.S. thesis, Oregon State Universiy Corvallis, Oregon, U.S.A., 68p, 1985. Rushton, A.W.A., Cambrian fossils from Hazira shale Pakistan, Nature Phys. Sci., 243, 142, 1973. Samson, S.D., and E.C. Alexander, Calibration of the interlaboratory 40Ar/39Ar dating standard, MMh-1, Chemical Geology, ,27-34, 1987 Saxena, M.N., Orogenic and epeirogenic cycles in the Himalaya, Himalayan Geolocry,Q, 191-210, 1980. 306 Searle, M.P., and B.J. Fryer, Garnet, tournialine and muscovite-bearing leucogranites, gneisses and migmatites of the Higher Himalayas from Zanskar, Kulu, Lahul and Kashmir, in Collision Tectonics, edited by K.?. Coward and A.C. Ries, Geol. Soc. Lond. Spec. Pubi. 19, pp.185-201, 1986. Searle, M.P., B.F. Windley, M.P. Coward, D.J.W. Cooper, A.J. Rex, D. Rex, L. Tingdong, X. Xuchang, M.Q. Jan, V.C. Thakur, and S. Kumar, The closing of Tethys and the tectonics of the Himalaya, Bull. Geol. Soc. Am., , 678-701, 1987. Seeber, L., and K.H. Jacob, Microearthquake survey of northern Pakistan: Preliminary results and tectonic implications, in Colloques Internationaux du C.N.R.S., Ecologie et Geologie de L' Himalaya, 268, pp.347-360, 1977. Seeber, L., and J. Armbruster, Seismicity of the Hazara arc in northern Pakistan: Decollement vs. basement faulting, in Geodynainics of Pakistan, edited by A. Farah and K.A. De Jong, Geological Survey of Pakistan, Quetta, pp.131-142, 1979. Seri, S., Stratigraphy of the crystalline Precainbrians of Central and Northern Rajasthan: A review, in Structure and tectonics of Precambrian rocks of India, edited by S.S. Ray, Hindustan Publishers, Dehli, India, pp.26-38, 1983. 307 Shah, S.M.I., Stratigraphy of Pakistan, Mem. Geol. Surv. Pakistan, 12, 138p, 1977. Shams, F.A., A preliminary account of the geology of the Mansehra area, District Hazara, West Pakistan, Geol. Bull. Punlab Univ. Lahore. Pakistan, 1, 57-67, 1961. Shams, F.A., Geology of the Mansehra-Anth State northwest Pakistan, Geol. Bull. Punlal, Univ. Lahore, Pakistan, 8, 1-31, 1969. Shams, F.A., Glaucophane-bearing rocks from near Topsin, Swat, first record from Pakistan, Pakistan Jour. Sci., j, 343-345, 1972. Shams, F.A., Origin of the Shangla blueschist, Swat Himalaya, Pakistan, Geol. Bull. Univ. Peshawar. Pakistan, 13, 67-70, 1980. Shams, F.A., Granites of the NW Himalayas in Pakistan, in Granites of Himalayas. Karakorum and Hundu Kush, edited by F.A. Shams, Institute of Geology University of Punjab Lahore, Pakistan, pp.75-121, 1983. Sharma, K. K., Granitiod belts of the Himalaya, in Granites of Himalayas, Karakoruin and Hindu Kush, edited by F.A. Shams, Institute of Geology University of Punjab Lahore, Pakistan, pp.11-37, 1983. Sharma, R.S., Basement-cover rocks relation in north-central Aravalli Range: A tectonic and metamorphic synthesis, in structure and tectonics of Precambrian rocks of 308 India, edited by S. Sinha-Ray, Hindustan Publication, Dehli, India, pp.53-71, 1983. Singh, I.B., Some thoughts on the evolution of Himalaya and the northern limit of the Indian shield, Geologische Rundschau, 68, 342-350, 1978. Singh, P., Larger foraminif era from the Subathu of Beragua- Jangalgali area, Janimu and Kashmir State, Jour. Geol. Soc. India, 11, 34-44, 1970. Singh, P., Geology of the Subathu Group of Jamittu and Kashmir State, Himalayan Geoloqy, , 284-298, 1973. Snee, L.W., Emplacement and cooling of the Pioneer batholith, southwestern Montana, Unpublished Ph.D. thesis. Columbus. Ohio, The Ohio State University, 320p, 1982. Snee, L.W., J.F. Sutter, and W.C. Kelly, Thermochronology of economic mineral deposits: dating the stages of mineralization at Panasqueira, Portugal by high- precision 40Ar/39Ar age-spectrum techniques on muscovite, Economic Geology, , 335-354, 1988. Steiger, R.H., and E. Jager, Subcommission on geochronology: Convention on the use of decay constants in geo-and cosmo-chronology, Earth Planet. Sci. Lett., , 359-362, 1977. Stocklin, J., Structural correlation of the Alpine ranges between Iran and central Asia, Hem. H. Ser. Soc. Geol. France, 8, 333-353, 1977. 309 Tahirkheli, R.A.K., The geology of the Attock-Cherat Range, West Pakistan, Geol. Bull. Univ. Peshawar, Pakistan, , 1-26, 1970. Tahirkheli, R.AK., M. Mattauer, F. Proust, and P. Tapponier, The India-Eurasia suture zone in northern Pakistan; synthesis and interpretation of recent data at plate scale, in Geodynainics of Pakistan, edited by A. Farah and K.A. De Jong, Geological Survey of Pakistan, Quetta, pp.125-l30, 1979. Tahiricheli, R.A.K., Geotectonic evolution of Kohistan, Geol. Bull. Univ. Peshawar, Pakistan, 11, 113-13 0, 1979. Tahirkheli, R.A.K., Geology of Kohistan and adjoining Eurasian and Indo-Pakistan continents, Pakistan, Geol. Bull. Univ. Peshawar. Pakistan, ]J, 1-30, l979a. Tahirkheli, R.A.K., and M.Q. Jan, A preliminary geological map of Kohistan and adjoining areas, N. Pakistan, Geol. Bull. Univ. Peshawar, Pakistan, 11, in pocket, 1979. Tewari, B.S., and V.J. Gupta, Foraiuinifera from the Subathu Formation, Surkhet Valley, western Nepal, Himalayan Geoloqy, 6, 209-216, 1976. Trivedi, J.R., K. Gopalan, and K.S. Valdiya, Rb/Sr ages of granitic rocks within the Lesser Himalayan nappes, Kumaun, India, Jour. Geol. Soc. India, , 642-654, 1984. 310 Treloar, P.J., D.C. Rex, P.G. Guise, M.P. Coward, M.P. Searle, B.F. Windley, M.G. Peterson, M.Q. Jan, and I.W. Luff, K-Ar and Ar-Ar Geochronology of the Himalayan collision in NW Pakistan: Constraints on the timing of suturing, deformation, metamorphism, and uplift, Tectonics, 8/4, 881-909, 1989. Treloar, P.J., M.P. Coward, M.P. Williams, and M.A. Khan, Basement-cover imbrication south of the Main Mantle thrust, North Pakistan, in Tectonics of the western Himalayas, edited by L.L. Nalinconico and R.J. Lillie, U.S.G.S. Spec. Paper, 232, pp.137-152, 1989a. Treloar, P.3., R.D. Broughton, M.P. Williams, M.P. Coward, and B.F. Windley, Deformation, metamorphism, and imbrication of the Indian plate, south of the Main Mantle thrust, north Pakistan, Jour. Neta. Geol.,2, 11-125, l989b. Turner, G., The distribution of Potassium and argon in chondrites, in Origin and distribution of the elements, edited by L.H. Ahrens, Pergamon Press, New York, pp.387-398, 1968. Valdiya, K.S., Himalayan transverse faults and folds and their parallelism with subsurface structures of north Indian plains, Tectonophysics, , 353-86, 1976. Valdiya, K.S., Geology of Kumaun Lesser Himalaya, Wadia Institute of Himalayan Geoloqy, Dehra Dun, India, 291p, 1980. 311 Valdiya, K.S., Tectonic setting of Himalayan granites, in Granites of Himalayas, Karakoruin and Hindu Kush, edited by F.A. Shams, Institute of Geology University of Punjab Lahore, Pakistan, pp.39-53, 1983. Valdiya, K.S., Evolution of the Himalaya, Tectonophysics, 105, 229-48, 1984. Verplancky P.L., L.W. Snee, and K. Lund, The boundary between the Nanga Parbat massif and the Ladakh island arc Terrain, northern Pakistan; a cross fault on the Main Mantle Thrust, American Geophys. Union, EOS, , p.1074, 1985. Verplanck P.L., Petrology and structure of the eastern portion of the Nanga Parbat-Haramosh massif along the Indus River, northern Pakistan, with special attention to the gem-bearing pegmatites, Unpublished M.S. thesis, Oregon State University, Corvallis, Oregon, U.S.A., 138p, 1987. Viljoen, M.J., and R.P. Viljoen, The geology and geochemistry of the lower ultramafic unit of the Onverwacht Group and a proposed new class of igneous rock, in Upper Mantle Project, Spec. Pubis. Geol. Soc. S. Africa, 2, 221-44, l969a. Viljoen, M.J., and R.P. Viljoen, Evidence for the existence of a mobile intrusive peridotite magma from the Komati Formation of the Onvertwacht Group, in Upper Mantle 312 Project, Spec. Pubis. Geol. Soc. S. Africa, , 87-112, 1969b. Virdi, N.S., Geotectonic evolution of the Indus suture zone, in Contemporary Geoscientific Researches in Himalaya, edited by A.K. Sinha, Dehra Dun India, pp.131-136, 1981. Viswanathan, S., Basaltic koniatiite occurrences in the Kolar gold field of India, Indian Geol. Hag.,JJ,, 353-354, 1974. Wadia, D.N., The Geology of the Poonch State (Kashmir) and adjacent portions of the Punjab, Hem. Geol. Surv. India, , 185-370, 1928. Wadia, D.N., The syntaxis of the northwest Himalaya: Its rocks, tectonics and orogeny, Rec. Geol. Surv. India, 65, 189-220, 1931. Wadia, D.N., Note on the geology of Nanga-Parbat, Mt. Diamir, and adjoining parts of Chilas, Gilgit District, Kashmir, Rec. Geol. Surv. India, 66, 212-234, 1933. Wadia, D.N., The Cambrian-Triassic sequence of Kashinir, Hem. Geol.SUrV.India, 68/2, 76-121, 1934. Wang, J., Z. Chen, X. Gui, R. Xu, and Y. Yang, Rb/Sr isotopic studies of some intermediate-acid plutons in Southern Xizang, in Geological and Ecological studies of Qinghai-Xizang plateau, Proceedings of Symposium on Qinghai-Xizang (Tibet) plateau, Peking 1980, Science Press, Beijing, V.1 pp.515-520, 1981. 313 Wells, N.A., and P.D. Gingerich, Paleoenvironmental interpretation of Paleogene strata near Kotli, Azad Kashmir, Northeastern Pakistan, Kashimr Jour. Geol. Azad Kashinir Univ. Muzaffarabad, Pakistan, , 23-41, 1987. Williams, D.A.C., Archean ultrainafic, maf Ic, and associated rocks, Mt. Monger, western Australia, Jour. Geol. Soc. Australia, , 163-188, 1972. Williams, M.P., P.J. Treloar, and M.P. Coward, More evidence of pre-Himalayan orogenesis in Northern Pakistan, Geological Magazine, 125/6, 651-652, 1988. Windley, B.F., Metamorphism and tectonics of the Himalaya, Jour. Geol. Soc. London, 140, 849-865, 1983. Windley, B.F., Tectonic framework of the Himalaya, Karakorum and Tibet, and problems of their evolution, Phil. Trans. R. Soc. London, A326, 3-16, 1988. Wynne, A.B., Further notes on the geology of the upper Panjab, Rec. Geol. Surv. India, 12, 114-133, 1879. Yeats R.S., and R.D. Lawrence, Tectonics of the Himalayan thrust belt in northern Pakistan, in Marine Geoloqy and Oceanography of Arabian Sea and Coastal Pakistan, edited by B.U.Haq and J.D. Milliman, pp.177-98, New York, Van Nostrand Reinhold, 1984. Yeats, R.S., and A. Hussian, Timing of structural events in the Himalayan Foothills of northwestern Pakistan, Geol. Soc. Am. Bull., 99, 161-176, 1987. 314 Zeitler, P.K., R.A.K. Tahirkeli, C.W. Naeser,and N.M. Johnson, Unroof ing history of a suturezone in the Himalayas of Pakistan by means of fission track annealing ages, Earth Planet. Sci. Lett.,i, 227- 240, 1982. Zeitler, P.K., Uplift and cooling history of theNW Himalaya, northern Pakistan: evidence from fission- track and 40Ar/39Ar cooling ages, Unpublished Ph.D. thesis. Dartmouth College, U.S.A., 266p,1983. Zeitler, P.K., Cooling history of theNorthwest Himalaya, Pakistan, Tectonics, 4, 127-51, 1985. Zeitler, P.1<., J.F. Sutter, I.S. Williams,R. Zartman, and R.A.K. Tahirkheli, Geochronology and temperature history of the Nanga Parbat-Harainosh Massif, Pakistan, in U.S.G.S. Spec. Paper., Tectonics of theWestern Himalayas, edited by L.L. Nalinconjco and R.J. Lillie, 232, 1-22, 1989. APPENDICES 315 Appendix 1. 4°r/39Ar Age-Spectrum Data from rocks of the Indus Syntaxis, Beshain Area, Northwest Himalaya Pakistan. The 40Ar/39i.r data presented below are calculated from measured abundances of 40Ar, 39Ar, 38Ar,:37A.r,and 36Ar volts of signal according procedures summarized in the text. Calculated data are presented for each extraction steps for each sample. Temperature is in °C and has an uncertainty of ±10°C. Abundances of 40ArR and 39ArK are in volts and each abundance has 5 significant figures. F-values (40ArP/39ArK) are significant to 4 figures.39Ar/37Ar values are significant to 2 figures if less than 1; to 3 figures if between 1 and 99.9; and to 4 figures if greater than 100. Any 39Ar/37Ar values greater than 1000 should be considered simply >1000. Values for 40ArR and %39Ar are significant to 4 places. Apparent age is significant to 4 places and errors should be commensurate. All "raw" data, calculated abundances of interfering isotopes of argon, and calculated errors are available from the author. The data arelisted in the order of presentation in the text and subdivided according to crustal block and rock assemblage. 316 BESHAN BLOCK Amphibolites of the Basement Complex 1. Sample 387MSB45/26/DDlO; Amphibolite; Hornblende; 199.7mg; Measured 40Ar/36Ar 298.9; J-value - .007150 ± 0.25% (la); 345O'OO" N latitude; 725l'40" E longitude Temp 40ArR ArK F Ar/37Ar %40ArR %Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 500 7.10947 .01056 673.421 .34 96.1 .3 3175.82 ±11.44 600 3.22976 .03485 92.664 .87 93.5 1.1 917.07 ± 3.23 650 1.16835 .02235 52.269 1.14 69.0 .7 572.81 ± 4.05 700 1.58638 .01897 83.635 .86 90.1 .6 845.62 ± 4.07 750 1.66658 .01575 105.797 .51 93.3 .5 1016.18 ± 4.21 800 2.64583 .02225 118.930 .27 95.7 .7 1110.14 ± 3.11 850 5.24236 .02840 184.599 .11 97.8 .9 1518.09 ± 3.83 900 11.77139 .04450 264.526 .10 99.0 1.5 1915.35 ± 5.08 925 35.71393 .12941 275.971 .17 99.3 4.2 1965.71 ± 5.30 950 89.33898 .31381 284.691 .21 99.7 10,3 2003.14 ± 6.11 1000 179.97952 .63512 283.377 .23 99.8 20.8 1997.55 ± 8.48 1025 164.56934 .58225 282.642 .23 99.9 19.0 1994.42 ± 4.33 1050 19.41260 .06879 282.196 .22 99.8 2.2 1992.51 ± 6.79 1075 48.35304 .16971 284.915 .21 99.8 5.6 2004.10 ± 5.68 1100 85.64747 .29836 287.064 .22 99.8 9.8 2013.20 ± 7.35 1150 167.30898 .57451 291.221 .22 99.9 18.8 2030.68 ± 5.66 1200 8.66471 .03016 287.334 .21 98.8 1.0 2014.34 ± 9.43 1250 5.04911 .01776 284.294 .22 97.8 .6 2001.45 ± 4.58 1450 11.59479 .04000 289.841 .22 80.5 1.3 2024.89 ± 4.40 Total Gas Date 278.021 1974.57 ± 6.15 Plateau Date (950°-1075°C) 57,9 1997.94 ± 6.28 317 2. Sample q/87MB135/63/DD12; Amphibolite; Hornblende; 149.9mg Measured 40Ar/Ar 298.9; J-value .007265 ± .25% (la); 3451'20" N latitude; 7256'l5" E longitude Temp 40ArR ArK F 39Ar/37Ar %40ArA %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 34.47094 .02594 1328.982 .74 98.7 .9 4268.33 ±52.72 600 5.73581 .02544 225.504 1.53 91.5 .9 1750.11 ± 8.46 650 1.27878 .01772 72.150 1.17 83.2 .6 760.30 ± 4.86 700 1.08673 .01224 88.753 .59 89.4 .4 897.70 ± 4.45 750 2.37497 .01828 129.934 .26 94.4 .7 1199.18 ± 4.49 800 3.09211 .02077 148.861 .18 95.7 .8 1322.47 ± 4.53 850 7.71249 .05135 150.180 .14 98.0 1.9 1330.76 ± 3.35 900 21.61752 .17077 126.589 .16 99.0 6.2 1176.49 ± 3.88 950 144.32817 .77372 186.537 .21 99.8 27.9 1545.34 ± 5.42 1000 68.29582 .30627 222.994 .22 99.6 11.1 1737.60 ± 7.65 1050 91.10441 .34762 262.083 .21 99.7 12.6 1923.24 ± 6.29 1075 73.95349 .26362 280.533 .22 99.8 9.5 2006.65 ± 8.04 1100 107.30897 .38507 278.677 .22 99.8 13.9 1996.62 ± 7.29 1125 37.43168 .13463 278.042 .22 99.7 4.9 1993.87 ± 6.41 1150 11.79929 .04298 274.527 .22 99.3 1.6 1978.55 ± 7.82 1175 7.10417 .02588 274.544 .22 98.5 .9 1978.62 ± 8.46 1250 10.47808 .03781 277.127 .22 99.1 1.4 1989.89 ± 6.47 1450 30.23514 .10824 279.325 .22 92.0 3.9 1999.43 ± 8.33 Total Gas Date 238.196 1812.09 ± 6.81 Maximum Date (10750l45O0C) 36.1 1997.17 ± 7.55 318 3. Sample i5JL007C/7L/DD9; Amphibolite; Hornblende; 56mg; Measured 40Ar/Ar 298.9; J-value - .024497 ± .25% (lo; 34°54'30" N latitude; 7255'45" E longitude Temp °ArR ArK F 39Ar/37Ar %40Ar %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 1.74474 .01559 111.880 .67 81.3 .4 2379.98 ± 7.85 600 1.53557 .02059 74.592 1.01 89.3 .6 1874.92 ± 9.01 650 .25610 .01034 24.778 2.86 76.2 .3 855.74 ± 8.78 700 .44604 .02015 22.139 .85 61.5 .5 781.66 ± 6.24 750 .49999 .02171 23.030 .95 68.0 .6 807.02 ±19.62 800 .78301 .02290 34.186 .50 90.1 .6 1097.52 ± 9.30 850 .85014 .01708 49.779 .24 94.8 .5 1438.24 ±10.79 900 .84543 .01440 58.718 .16 93.4 .4 1608.00 ± 7.49 950 2.82638 .04488 62.977 .16 97.0 1.2 1683.57 ± 4.32 1000 24.20953 .34751 69.665 .19 99.6 9.3 1796.22 ± 3.15 1025 29.95356 .39518 75.798 .21 99.7 10.6 1893.68 ± 3.25 1050 51.79501 .66142 78.309 .22 99.8 17.8 1932.11 ± 3.32 1075 28.72374 .36630 78.416 .23 99.7 9.8 1933.72 ± 3.29 1100 12.23460 .15673 78.062 .22 99.6 4.2 1928.36 ± 3.29 1150 51.99151 .65342 79.568 .22 99.8 17.5 1951.08 ± 3.31 1200 55.15623 .69321 79.567 .23 99.8 18.6 1951.06 ± 3.31 1250 3.64490 .04604 79.172 .22 97.5 1.2 1945.13 ± 3.69 1300 9.69076 .12193 79.480 .23 98.3 3.3 1949.75 ± 3.46 1450 7.66472 .09624 79.641 .23 96.0 2.6 1952.17 ± 3.48 Total Gas Date 76.458 1903.86 ± 3.54 Maximum Date (l150°-l450°c) 43.2 1950.86 ± 3.45 319 4. Sample 5JL0l2C/72/DD9; Amphibolite; Hornblende; 52.8 mg; Measured 40Ar/Ara 298.9; J-value .02449 ± .25% (1a); 34°55'35" N latitude; 72°48'50" E longitude Temp 39AR F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 4.80904 .00644 747.150 .37 94.8 .3 5339.82 ±14.80 600 .89731 .01344 66.777 57 85.7 .6 1748.12 ± 7.29 650 .45309 .01067 42.460 .68 58.8 .5 1286.03 ±10.74 700 .43425 .00709 61.224 .40 90.4 .3 1652.53 ±18.96 750 .44375 .00696 63.751 .24 91.7 .3 1696.66 ±20.17 800 .65068 .00809 80.398 .13 95.4 .3 1963.12 ±12.73 850 1.46451 .01340 109.307 .08 96.3 .6 2348.95 ± 9.76 900 2.50575 .01995 125.632 .07 97.9 .9 2535.15 ± 5.48 925 4.61084 .04223 109.192. .10 98.6 1.8 2347.57 ± 4.01 950 15.76435 .16662 94.613 .14 99.5 7.2 2163.15 ± 3.49 975 49.17722 .58263 84.405 .16 99.8 25.2 2021.79 ± 3.43 1000 56.50138 .70240 80.440 .16 99.8 30.4 1963.76 ± 3.49 1025 11.02739 .13867 79.524 .16 99.5 6.0 1950.08 ± 3.38 1050 6.98819 .08686 80.454 .16 99.1 3.8 1963.96 ± 3.40 1100 16.63834 .20411 81.516 .16 99.5 8.8 1979.68 ± 3.33 1150 20.45976 .24896 82.179 .16 99.4 10.8 1989.44 ± 3.34 1200 4.43915 .05410 82.053 .16 98.1 2.3 1987.58 ± 3.99 Total Gas Date 85.300 2034.63 ± 3.65 Maximum Date (1025°C) 6 1950.08 ±3.38 320 5. Sample #87MB385/61/DD9; Amphibolite xenolith; Hornblende; 49.2mg; Measured 40Ar/Ar - 298.9; J-value .024 ± .25% (10'); 3453'50" N latitude; 7257'30" E longitude Temp 40Ar ArK F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 4.09626 .00367 1116.587 .51 95.6 .1 5998.24 ±13.43 600 4.98268 .00705 706.948 .77 99.0 .2 5210.90 ±23.94 700 2.52243 .01581 159.518 .62 86.1 .5 2840.44 ± 8.40 750 .54911 .01080 50.841 .50 94.2 .3 1438.86 ±11.22 800 .68187 .01062 64.204 .34 95.8 .3 1682.26 ±10.97 825 .52813 .00746 70.826 .22 93.4 .2 1791.71 ±11.96 850 .69579 .01076 64.682 .17 97.0 .3 1690.38 ±12.16 900 3.14609 .052LL2 60.019 .19 99.0 1.5 1609.50 ± 3.01 950 36.38534 .49198 73.957 .23 99.6 14.1 1841.24 ± 3.21 1000 76.84682 .92049 83.484 .24 99.8 26.3 1984.08 ± 3.34 1025 49.01850 .60323 81.261 .24 99.8 17.2 1951.73 ± 3.31 1050 20.59941 .25416 81.048 .23 99.8 7.3 1948.62 ± 3.67 1075 10.36565 .12066 85.907 .23 99.5 3.4 2018.66 ± 3.37 1100 13.40039 .14676 91.305 .23 99.7 4.2 2093.43 ± 3.82 1125 16.38747 .17016 96.305 .23 99.6 4.9 2160.02 ± 4.10 1150 6.19919 .06562 94.469 .23 93.3 1.9 2135.84 ± 3.87 1200 12.70420 .13660 93.001 .23 99.5 3.9 2116.29 ± 4.08 1250 20.05181 .21916 91.495 .24 99,4 6.3 2096.00 ± 5.21 1400 23.23762 .25205 92.196 .23 99.5 7.2 2105,47 ± 3.78 Total Gas Date 86.413 2025.80 ± 3.68 Minimum Date (1025-1050°C) 24.5 1950.18 ± 3.49 Maximum Date (1125°C) 4.9 2160.02 ± 4.10 321 6. Sample #5JL042/70/DD9; Amphibolite; Hornblende; 54.2 mg. Measured 40Ar/Ara = 298.9; J-value .02444 ± .25% (10'); 3458'50" N latitude; 7252'20" E longitude Temp 40Ar8 39ArK F Ar/37Ar %40ArR Z39Ar Apparent Age and Error (SC) (Ma at 1 Sigma 500 2.55822 .00232 1103.115 .37 93.4 .1 6008,73 ±35.95 600 1.97281 .00577 341.707 .61 97.6 .2 4032,87 ± 9.14 650 .40704 .00556 73.209 .41 65.6 .2 1850,48 ±17.01 700 .47671 .00589 81.003 .68 68.3 .2 1969.66 ±17.22 750 .68144 .00589 115.692 .46 90.3 .2 2421.36 ±15.83 800 .68814 .00516 133.246 .27 91.5 .2 2613.02 ±13.65 850 .77365 .00629 122.926 .16 88.3 .2 2502.82 ±16.03 900 1.07560 .00763 141.052 .13 94.2 .2 2692.11 ±11.15 950 7.87471 .08418 93.542 .16 98.6 2.6 2146.26 ± 3.48 975 13.45296 .14274 94.246 .18 99.3 4.3 2155.68 ± 3.49 1000 27.39573 .29849 91.782 .18 99.4 9.1 2122.49 ± 3.56 1Q25 43.74800 .53582 81.647 .19 99.6 16.3 1979.16 ± 3.33 1050 59.01151 .77603 76.043 .19 99.7 23.6 1894.72 ± 3.33 1075 18.46351 .24228 76.207 .19 99.3 7.4 1897.25 ± 3.26 1100 9.45673 .12146 77.858 .19 98.7 3.7 1922.51 ± 3.30 1150 31.89161 .41106 77.583 .19 99.6 12.5 1918.33 ± 3.28 1200 40.07271 .51480 77.841 .20 99.7 15.7 1922.25 ± 3.28 1250 3.24351 .04100 79.101 .19 97.8 1.2 1941.29 ± 3.30 1300 1.51410 .01882 80.444 .19 94.2 .6 1961.37 ± 6.23 1450 4.38993 .05537 79.286 .18 95.1 1.7 1944.07 ± 3.70 Total Gas Date 81.893 1982.78 ± 3.46 Maximum Date (1050°-1075°C) 31 1895.33 ± 3.29 322 7. Sample 87MB6A/65/DD9; Amphibolite; Hornblende; 46.3 mg. Measured 40Ar/Ara = 298.9; J-value = .024518 ± .25Z (la) 34°54'30" N latitude; 72°5150" E longitude Temp ArK F Ar/37Ar °Ar %Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 500 5.36487 .01041 515.223 .65 96.3 .5 4712.84 ± 9.54 600 1.48276 .02395 61.911 1.18 98.0 1.2 1665.87 ± 4.76 650 .30181 .01797 16.793 1.13 52.0 .9 622.04 ± 5.61 700 .45682 .02180 20.958 .77 95.0 1.0 748.04 ± 3.48 750 .62637 .01630 38.435 .29 97.1 .8 1197.67 ± 7.52 800 1.25505 .02329 53.891 .13 98.6 1.1 1519.21 ± 5.11 850 2.55817 .03652 70.040 .10 98.5 1.8 1803.31 ± 5.20 875 5.83838 .08017 72.822 .11 99.4 3.9 1848.04 ± 3.21 900 22.30951 .31199 71.508 .13 99.8 15.0 1827.04 ± 3.19 925 64.68448 .87634 73.812 .15 99.8 42.1 1863.69 ± 3.22 950 16.04480 .21608 74.254 .1.6 99.8 10.4 1870.64 ± 3.23 975 4.95395 .06817 72.667 .14 99.3 3.3 1845.57 ± 3.51 1000 8.40769 .11098 75.759 .15 99.6 5.3 1894.07 ± 3.40 1050 12.40944 .15988 77.617 .15 99.8 7.7 1922.62 ± 3.28 1075 2.77804 .03621 76.721 .15 99.6 1.7 1908.90 ± 4.95 1100 1.01900 .01350 75.468 .15 97.7 .6 1889.56 ± 8.48 1150 1.46145 .01915 76.320 .15 98.0 .9 1902.74 ± 7.35 1250 2.80713 .03695 75.973 .15 96.5 1.8 1897.39 ± 5.41 Total Gas Date 74.416 1873.17 ± 3.52 Plateau Date (925C-950°C) 52.5 1865.07 ± 3.23 Maximum Date (1050°C) 7.7 1922.62 ± 3.28 323 8. Sample #87MB6A/66/DD9; Aniphibolite; Biotite; 14.7 mg; Measured 40Ar/Ara - 298.9; J-value - .024474 ± .25% (la); 34°54'30' N latitude; 7251'50" 8 longitude Temp 40Ar ArK F 3Ar/37Ar %40Ar %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .29042 .13366 2,173 23.37 40.2 1.7 93.47 ± .28 600 1.77160 1.19071 1.488 68.83 88.1 15.5 64.52 ± .26 700 3.45664 2.35988 1.465 117.16 87.4 30.6 63.54 ± .18 750 1.13045 .76474 1.478 107.15 93.1 9.9 64.11 ± .27 800 .61006 .40149 1.519 54.66 91.8 5.2 65.87 ± .42 850 .80741 .51439 1.570 39.05 87.7 6.7 68.00 ± .35 900 .78811 .51176 1.540 55.01 88.0 6.6 66.74 ± .33 950 1.08803 .69884 1.557 36.94 92.6 9.1 67.46 ± .31 1000 .89081 .57722 1.543 16.29 90.9 7.5 66.88 ± .51 1050 .51896 .33806 1.535 4.78 89.6 4.4 66.54 ± .38 1150 .36616 .18482 1.981 1.14 81.7 2.4 85.42 ± 1.15 1300 .11640 .03108 3.746 1.74 51.0 .4 158.23 ± 4.47 Total Gas Date 1.536 66.56 ± .30 Maximum Date (700°-750C) 40.5 63.68 ± .23 324 9. Sample j'/87MB310/68/D09; Amphibolite; Hornblende; 62.5 rng; Measured 40Ar/Ar 298.9; J-value .02446 ± .25%(laY 34°53'20N latitude; 72°44'OO" E longitude Temp 40ArR ArK F 39Ar/7Ar Z40ArR Z39Ar Apparent Age and Error (AC) (Ma at 1 Sigma) 500 6.96624 .01665 418.368 .48 97.6 .6 4363,66 ±11.22 600 2.84614 .01781 159.816 .9 98.4 .7 2870.33 ±10.56 650 .31409 .01336 23.508 .78 48.6 .5 819.49 ± 9.21 700 .21133 .01376 15.361 .90 89,6 .5 575.46 ±13.37 750 .24722 .01098 22.507 .38 96.0 .4 791.22 ±10.92 350 1.37079 .02985 45.918 .07 96.3 1.1 1358.23 ± 4.61 900 2.85458 .05537 51.554 .07 98.1 2.0 1471.73 ± 3.02 950 41.25165 .62350 66.162 .12 99.5 23.1 1736.41 ± 3.09 1000 63.19886 .82656 76.461 .14 99.8 30.6 1902.12 ± 3.26 1025 13.05029 .17118 76.238 .13 99.6 6.3 1898.69 ± 3.26 1050 16.95664 .21627 78.403 .14 99.6 8.0 1931.75 ± 3.29 1075 7.69955 .09754 78.941 .13 100.1 3.6 1939.86 ± 3.33 1100 3.02756 .03860 78.436 .13 99.4 1.4 1932.23 ± 4.16 1150 22.65281 .28926 78.312 .15 99.1 10.7 1930.36 ± 3.59 1250 22.20451 .27899 79.588 .15 99.0 10.3 1949.58 ± 3.31 1450 .19676 .00250 78.620 .15 85.4 .1 1935.01 ±49.59 Total Gas Date 75.883 1893.22 ± 3.53 Maximum Date (1250°C) 10.3 1949.58 ± 3.31 325 10. Sample 87MB3l0/l09/DD9; Amphibolite; Biotite; 15.6 mg; Measured 40Ar/Ara 298.9; J-value - .02446 ± .25% (la); 3453'20" N latitude; 72°44'OO" E longitude Temp 40ArR 39ArK F 39Ar/37Ar Z40ArR %39Ar Apparent Age and Error (DC) (Ma at 1 Sigma) 500 .01495 .02618 .571 22.51 2.2 2.3 24.75 ± 4.73 600 .08273 .21023 .869 68.86 44.6 18.3 37.54 ± .83 700 .28513 .24631 1.158 76.82 35.1 21.4 49.83 ± .60 750 .11913 .08716 1.367 57.57 60.2 7.6 58.69 ± 3.03 800 .13376 .08946 1.495 50.01 67.6 7.8 64.10 ± 5.14 850 .11496 .08983 1.280 16.68 45.3 7.8 55.01 ± 1.33 900 .13555 .11969 1.133 21.04 54.6 10.4 48.76 ± .97 950 .17398 .13856 1.256 23.30 59.8 12.0 53.98 ± .79 1000 .13167 .08961 1.469 16.30 58.4 7.8 63.02 ± 2.62 1050 .05556 .02975 1.867 11.34 54.8 2.6 79.71 ± 5.95 1150 .03799 .01542 2.466 4.57 40.1 1.3 104.47 ±11.32 1300 .11114 .00871 12.760 2.07 48.4 .8 485.34 ±29.36 Total Gas Date 1.300 55.88 ± 1.89 Maximum Date (1050°C) 0.8 485.34 ± 29.36 Minimum Date (500°C) 2.3 24.75 ± 4.73 326 11. Sample #87MB307/69/DD9; Metapyroxenite; Amphibole; 52.6 mg. Measured °Ar/Ar - 298.9; J-value .024473 ± .25% (10); 34°53'15" N latitude; 72°44'50" E longitude Temp 40ArR ArK F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at I Sigma) 500 2.86581 .00331 865.018 .30 78.5 .3 5590.09 ±42.02 600 .24409 .00444 54.916 .29 22.1 .5 1536.72 ±22.08 650 .04931 .00332 14.871 .46 7.3 .3 559.93 ±36.78 700 .05359 .00380 14.099 .32 7.1 .4 534.77 ±95.19 750 .05883 .00371 15.868 .21 9.3 .4 591.91 ±49.52 800 .11578 .00376 30.819 .10 15.7 .4 1013.91 ±39.79 850 .32123 .00524 61.252 .04 36.9 .5 1652.29 ±45.31 950 7.91264 .10480 75.505 .05 92.9 10.9 1887.99 ± 3.58 975 13.75465 .18319 75.084 .06 97.0 19.1 1881.46 ± 3.47 1000 11.86407 .15706 75.538 .06 97.6 16.4 1888.50 ± 3.25 1025 4.54340 .05979 75.985 .06 96.8 6.2 1895.41 ± 9.08 1050 2.49335 .03328 74.920 .05 96.3 3.5 1878.90 ± 4.56 1075 1.94179 .02586 75.089 .05 96.3 2.7 1881.53 ± 5.49 1100 1.90587 .02539 75.073 .05 96.0 2.7 1881.28 ± 4.95 1150 6.88180 .09083 75.762 .05 98.4 9.5 1891.98 ± 3.25 1200 7.09260 .09219 76.937 .05 98.5 9.6 1910.06 ± 3.27 1250 7.82170 .09771 80.046 .05 97.2 10.2 1957.05 ± 3.34 1450 4.81500 .06001 80.241 .06 57.2 6.3 1959.96 ± 4.38 Total Gas Date 78.037 1926.82 ± 5.64 P1 ate au Date (950° -ll50C) 71 1886.59 ± 4.70 Max imuni Date (1250°-l450°C) 16.5 1958.16 ± 3.86 327 12. Sample 87MB374/59/DD9; Axnphibolite; Hornblende; 47 mg Measured 40Ar/Ar - 298.9; J-value - .0245 ± .25% (la); 344455" N latitude; 7248'55" E longitude Temp 40Ar ArK F 39Ar/37Ar %40Arç %Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 500 3.27684 .02684 122.103 .91 90.4 1.2 2497.05 ± 4.89 600 .24952 .01198 20.831 .61 41.2 .5 743.87 ± 8.20 650 .11140 .00790 14.095 .81 61.2 .3 535.15 ±19.69 700 .13684 .00725 18.873 .43 86.1 .3 685.65 ±18.80 750 .23721 .00872 27.193 .22 93.6 .4 921.06 ± 7.72 800 .35038 .01089 32.176 .11 94.6 .5 1048.62 ± 7.81 850 2.22645 .04568 48.736 .09 98.4 2.0 1417.47 ± 3.24 900 18.49698 .31458 58.799 .15 99.7 13.8 1609.59 ± 2.95 925 47.00090 .69053 68.065 .17 99.9 30.3 1770.04 ± 3.13 950 36.13996 .49172 73.497 .18 99.8 21.6 1857.88 ± 3.22 975 7.54966 .10187 74.108 .17 99.7 4.5 1867.48 ± 3.23 1000 16.78365 .21972 76.388 .17 99.8 9.6 1902.93 ± 3.26 1025 4.57244 .05946 76.899 .18 99.4 2.6 1910.78 ± 3.61 1050 3.33520 .04380 76.146 .17 99.2 1.9 1899.20 ± 3.26 1075 2.18544 .02866 76.241 .17 99.0 1.3 1900.67 ± 3.60 1100 2.83895 .03726 76.189 .17 98.2 1.6 1899.86 ± 3.95 1L50 3.52159 .04580 76.895 .18 95.8 2.0 1910.72 ± 3.97 1200 8.18563 .10645 76.895 .18 97.9 4.7 1910.71 ± 3.31 1250 1.63633 .02129 76.859 .18 93.3 .9 1910.16 ± 4.39 Total Gas Date 69.652 1796.15 ± 3.44 Maximum Date (1150-1250C) 7.6 1910.62 ± 3.89 328 Sample1/87MB336/62/DD9;Amphibolite; Hornblende; 50.5 mg; Measured 40Ar/Ara 298.9; J-value .024468 ± .25% (la); 34°53'lO" N latitude; 7245'55" E longitude Temp ArK F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 2.24190 .01316 170.363 .90 83.9 .6 2963.20 ± 9.64 600 .35579 .01527 23.300 .79 43.9 .7 813.85 ± 7.14 650 .06679 .00855 7.812 .91 23.5 .4 315.53 ±11.33 700 .09821 .00699 14.051 .41 42.2 .3 533.09 ±18.47 750 .10503 .00657 15.991 .24 50.0 .3 595.71 ±32.88 800 .19092 .01171 16.302 .14 61.7 .5 605.56 ± 9.85 850 .35964 .01977 18.195 .13 75.0 .9 664.33 ±12.07 900 4.35916 .14966 29.127 .13 97.4 6.8 970.67 ± 2.08 950 29.33112 .67376 43.533 .16 99.4 30.6 1308.29 ± 2.58 975 37.17592 .56115 66.249 .18 99.7 25.4 1738.25 ± 3.09 1025 10.97982 .15008 73.160 .18 99.3 6.8 1851.03 ± 3.21 1050 6.83060 .09612 71.067 .16 98.8 4.4 1817.60 ± 3.18 1075 5.94787 .08166 72.836 .16 99.1 3.7 1845.90 ± 3.50 1100 6.49627 .08686 74.789 .17 98.8 3.9 1876.62 ± 3.24 l:L50 10.70337 .14127 75.765 .18 99.3 6.4 1891.78 ± 13.34 1200 2.75908 .03693 74.715 .18 97.7 1.7 1875.47 ± 4.01 1250 3.93215 .05210 75.467 .18 97.2 2.4 1887.17 ± 3.25 1450 7.01219 .09341 75.066 .18 75.9 4.2 1880.94 ± 3.49 Total Gas Date 58.478 1602.38 ± 3.47 Pr e ffe red Date (ll00-l450°C) 18.6 1884.05 ± 3.46 329 14. Sample 87MB23/63/DD9; Epidote amphibolite; Hornblende; 44.1 mg; Measured 40Ar/Ara = 298.9; J-value = .024408 ± .25% (lC); 3448'10" N latitude; 7256'00" E longitude Temp 40ArR 39Ar F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .05195 .00196 26.530 .24 2.8 .1 900.72 ±12.10 600 .01219 .00230 5.306 .16 .7 .1 219.70 ±28.97 800 .01923 .00777 2.474 .13 1.5 .5 105.78 ±11.44 950 .31531 .26231 1.202 .12 20.2 16.1 52.17 ± .71 1000 .75676 .66524 1.138 .13 43.6 40.8 49.41 ± .35 1050 .11690 .10550 1.108 .13 24.5 6.5 48.14 ± 1.79 :Lloo .16145 .13954 1.157 .13 40.2 8.6 50.24 ± 1.51 :L15o .19239 .16102 1.195 .13 58.9 9.9 51.86 ± 1.24 :L200 .05308 .04312 1.231 .13 30.7 2.6 53.41 ± 3.90 1250 .06428 .05424 1.185 .13 21.3 3.3 51.44 ± 5.13 1450 .22819 .18807 1.213 .13 7.3 11.5 52.65 ± 2.34 Total Gas Date 1.209 52.46 ± 1.23 Plateau Date (l000°-l450C) 73.2 51.02 ± 2.12 330 15. Sample q,87MB155/82/DD8; Epidote amphibolite; Hornblende; 32.59 mg; Measured 40Ar/Ar 298.9; J-value .00762 ± .25% (la); 34°48'55" N latitude; 7256'25" E longitude Temp 40ArR ArK F 39Ar/37Ar %40Ar %39Ar Apparent Age and Error ('C) (Ma at 1 Sigma) 500 .56154 .00835 67.215 .22 36.7 .3 746.05 ± 9.80 600 .07027 .00849 8.273 .24 4.9 .3 110.28 ± 4.44 650 .02711 .00678 3.997 .27 3.0 .2 54.12 ±10.74 700 .03807 .00895 4.254 .22 3.9 .3 57.55 ±13.77 750 .07764 .01194 6.501 .17 6.5 .4 87.22 ± 6.48 800 .11062 .01891 5.850 .12 7.5 .6 78.67 ± 4.69 850 .22944 .03450 6.650 .07 10.9 1.0 89.17 ± 1.07 900 .36751 .06351 5.787 .05 12.4 1.9 77.84 ± 1.23 950 2.95579 .78764 3.753 .10 46.2 23.7 50.86 ± .14 975 1.61360 .50608 3.188 .11 28.9 15.2 43.31 ± .12 1000 .73747 .25392 2.904 .11 15.3 7.6 39.49 ± .38 1050 .83850 .24124 3.476 .10 20.7 7.3 47.16 ± .39 1100 1.92495 .56493 3.407 .11 43.4 17.0 46.24 ± .20 1150 2.16648 .64713 3.348 .11 55.8 19.5 45.44 ± .14 1200 .20156 .05693 3.540 .11 9.4 1.7 48.02 ± 2.18 1250 .20715 .05896 3.514 .11 11.9 1.8 47.66 ± 1.12 1450 .15393 .04444 3.464 .11 8.5 1.3 47.00 ± .54 Total Gas Date 3.696 50.11 ± .34 Maximuni Date (l050-1450°C) 48.6 46.19 ± .76 M inimuni Date (1000°C) 7.6 39.49 ± .38 331 16. Sample i87MBl48/91/DD8; Epidote amphibolite; Hornblende; 298.2 mg; Measured 40Ar/Ar8=298.9; J-value .007612 ± .25Z (10); 34°4930" N latitude; 725630" E longitude Temp 40ArR ArK F 39Ar/37Ar ArR 0/Ar Apparent Age and Error (SC) (Ma at 1 Sigma) 500 .02431 .00386 6.295 .22 9.9 .1 84.43 ±31.10 600 .00691 .00483 1.431 .20 1.5 .2 19.54 ±15.01 650 .00636 .00439 1.451 .18 7.1 .2 19.81 ±13.21 700 .00769 .00563 1.365 .14 9.4 .2 18.65 ± 7.90 750 .01512 .00850 1.780 .12 15.0 .3 24.27 ± 5.29 800 .09439 .03288 2.871 .11 52.4 1.2 38.99 ± 2.33 850 .40310 .14542 2.772 .12 77.8 5.4 37.67 ± .57 875 .67083 .25435 2.637 .13 85.7 9.4 35.86 ± .44 900 .96044 .36614 2.623 .13 89.3 13.6 35.67 ± .17 925 1.87218 .71942 2.602 .13 93.5 26.7 35.39 ± .16 1000 .93933 .33730 2.785 .12 91.9 12.5 37.84 ± .23 1025 1.01066 .35885 2.816 .13 92.9 13.3 38.27 ± .25 1050 1.05723 .37412 2.826 .13 93.8 13.9 38.39 ± .25 1075 .21157 .08284 2.554 .13 78.6 3.1 34.74 ± .90 Total Gas Date 2.698 36.67 ± .45 Maximum Date (1Q25-1O5QC) 27.2 38.33 ± .25 Minimum Date (875°-925C) 49.7 35.64 ± .26 232 17. Sample q/87MZ144/64/DD9; Epidote Amphibolite; Horriblende; 49 mg; Measured °Ar/Ar = 298.9; J-value .024465 ± .25% (la); 345l'l0" N latitude; 7256'50" E longitude Temp 40ArR 39ArK F Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 850 .08653 .00475 18.228 .01 40.4 .9 665.26 ±32.95 900 .22192 .02178 10.190 .01 64.3 4.1 401.54 ± 6.94 950 .31711 .08385 3.782 .02 69.9 15.9 159.64 ± 2.94 975 .10268 .06189 1.659 .04 46.8 11.7 71.77 ± 3.58 1000 .08375 .05542 1.511 .04 45.1 10.5 65.50 ± 5.23 1050 .14062 .12222 1.151 .05 62.4 23.1 50.08 ± 1.68 1100 .08890 .04411 2.015 .03 50.0 8.4 86.82 ± 4.32 1150 .10417 .04297 2.425 .03 53.7 8.1 103.95 ± 2.90 1250 .05491 .02489 2.206 .03 33.4 4.7 94.84 ± 6.11 1450 .13538 .06622 2.044 .04 8.5 12.5 88.04 ± 5.65 Total Gas Date 2.530 108.33 ± 4.70 Maximum Date (l000C) 23.1 50.08 ± 1.68 333 Netasediments of the Besham group 18. Sample 1/87MS726/75/DD9; Garnet-biotite quartzo-feldspathic schist; Biotite; 17.6 mg; Measured 40Ar/Ara - 298.9; i-value .02441 ± .25% (10); 34°56'20" N latitude; 7253'50" E longitude Temp 40ArR ArK F 39Ar/37Ar %40ArR %Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 500 .74437 .34715 2.164 19.30 64.5 9.0 92.03 ± .81 600 2.11893 .77666 2.728 22.81 74.7 20.1 116.31 ± .31 700 2.40708 .94273 2.553 26.15 67.7 24.4 109.07 ± .43 750 .59338 .21998 2.697 25.15 74.7 5.7 115.03 ± 1.04 800 .69183 .14904 4.642 19.98 86.0 3.9 193.64 ± 1.34 850 1.57248 .27878 5.641 16.75 86.2 7.2 232.71 ± .76 900 2.79384 .50489 5.534 18.33 86.3 13.1 228.56 ± .62 950 2.21059 .56014 3.947 21.23 79.7 14.5 165.92 ± .46 1000 .21617 .06388 3.384 20.27 70.9 1.7 143.19 ± 2.67 1050 .08522 .01225 6.955 8.18 65.2 .3 282.87 ±13.92 1150 .04223 .00308 13.699 3.79 54.5 .1 520.42 ±70.15 1300 .03115 .00203 15.373 3.29 11.6 .1 574.82 ±67.44 Total Gas Date 3.699 147.84 ± .65 Maximum Date (850) 7.2 232.71 ± .76 Minimum Date (500°C) 9.0 92.03 ± .81 334 19. Sample q/87MB7/74/DD9; Biotite-muscovite quartzo-feldspathic schist; Muscovite; 18 mg; Measured 40Ar/Ara - 298.9; J-value - .024442 ± .25% (la); 34°55'25" N latitude; 72°5410" E longitude Temp 40ArR 39Ar F 39Ar/37Ar %40Ar %mAr Apparent Age and Error (°C) (Ma at 1 Sigma) 450 .02309 .00687 3.360 7.33 67.6 .1 142.39 ±21.31 500 .10357 .04699 2.204 43.19 82.3 .5 94.65 ± 4.01 600 .53212 .50637 1.051 68.88 88.3 5.2 45.75 ± .43 700 .97304 1.41934 .686 144.39 74.8 14.5 29.98 ± .15 750 .89896 1.50281 .598 197.51 91.7 15.3 26.19 ± .13 800 .77211 1.15857 .666 170.32 93,9 11.8 29.15 ± .18 850 1.31366 1.87170 .702 56.75 94.0 19.1 30.68 ± .11 900 .70308 1.13298 .621 74.23 92.3 11.6 27.16 ± .33 950 .93753 1.55588 .603 59.80 91,9 15.9 26.38 ± .08 1000 .39601 .59690 .663 13.64 89.9 6.1 29.02 ± .25 Total Gas Date .679 29.69 ± .18 Maximum Date (850CC) 19.1 30.68 ± .11 Minimum Date (750CC) 15,3 26.19 ± .13 335 Intrusive rocks of the Basement complex 20. Sample 87MS450/l30/DD9; Lahor sodic granite gneiss; Muscovite; 20.3 mg; Measured 40Ar/Ara 298.9; Jvalue .024264 ± .25% (10); 34°59'OO" N latitude; 72°50'OO" E longitude Temp 40ArK ArK F 39Ar/37Ar %40ArR %2Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 26.32142 .23797 110.610 35.42 99.6 2.4 2352.34 ± 5.13 600 10.66127 .70575 15.106 46.25 98.8 7.3 563.36 ± 1.34 700 4.86426 .86351 5.633 83,00 92.5 8.9 231.12 ± .60 750 4.95154 .99007 5.001 82.05 98.3 10.2 206.62 ± .64 800 2.68603 .59331 4.527 58.25 97.6 6.1 188.02 ± .50 900 4.46014 .85212 5.234 53.06 97.8 8.8 215.69 ± .57 1000 13.76215 1.23950 11.103 54.55 99.0 12.7 430.34 ± 1.06 1100 29.15473 1.89092 15.418 40.58 99.1 19.4 573.32 ± 1.36 1200 39.99485 2.35304 16.997 69.38 99.3 24.2 622.93 ± 1.46 Total Gas Date 14.071 529.88 ± 1.30 Maximum Date (1200C) 24.2 622.93 ± 1.46 Minimum Date (800°C) 6.1 188.02 ± .50 336 21. Sample #87MS450/129/DD9; Lahor sodic granite gneiss; Biotite; 20.6 mg; Measured 40Ar/Ara 298.9; J-value .02428 ± .25% (la); 34°59'OO" N latitude; 7250'00" E longitude Temp 40ArR 3ArK F 39Ar/37Ar %Arf %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 400 .20180 .13584 1.486 18.87 39.1 2.2 63.92 ± 1.64 450 .16023 .09553 1.677 22.04 64.7 1.6 72.01 ± 3.23 500 .47026 .26722 1.760 33.82 74.2 4.4 75.48 ± .72 550 1.14736 .58523 1.961 64.62 82.9 9.6 83.89 ± .43 600 1.96222 .97678 2.009 107.45 78.2 16.0 85.91 ± .35 650 2.09068 .98308 2.127 144.21 92.7 16.1 90.83 ± .36 700 1.10518 .49458 2.235 113.56 93.7 8.1 95.32 ± .62 800 .74833 .35118 2.131 46.88 87.1 5.7 91.00 ± .69 850 1.50145 .64762 2.318 25.99 87.2 10.6 98.79 ± .34 950 2.34001 1.12315 2.083 22.23 89.7 18.4 89.02 ± .25 1000 .58175 .27767 2.095 4.99 87.8 4.5 89.51 ± .49 1050 .25978 .10805 2.404 1.59 87.4 1.8 102.35 ± 1.65 1100 .08793 .03313 2.654 2.09 67.2 .5 112.65 ± 2.81 1400 .19732 .03342 5.905 1.14 58.3 .5 241.69 ± 5.92 Total Gas Date 2.103 89.84 ± .53 Maximum Date (850°C) 10.6 98.79 ± .34 Minimum Date (400°C) 2.2 63.92 ± 1.64 337 22. Sample #87MS473/128/DD9; Darwaza Sar potassic granite gneiss; Muscovite.; 20.8 mg; Measured °Ar/Ara 298.9; J-value .02425 ± .25% (la); 3459'l5" N latitude; 72°46'45" E longitude Temp 40ArR Ar F Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 400 .19623 .02598 7.554 12.25 67.6 .2 303.44 ± 5.71 500 .18525 .04388 4.222 15.08 78.7 .4 175.83 ± .83 600 .25770 .14791 1.742 22.97 77.2 1.2 74.65 ± .90 700 .49416 .46114 1.072 43.58 53.4 3.8 46.28 ± .45 750 .60161 .66890 .899 55.24 85.4 5.6 38.92 ± .19 800 1.48774 2.04562 .727 75.84 87.3 17.0 31.54 ± .12 850 1.81597 2.61896 .693 62.16 88.3 21.8 30.08 ± .10 900 1.59146 2.32390 .685 87.26 89.5 19.3 29.71 ± .15 950 1.50891 2.09059 .722 74.32 91.4 17.4 31.30 ± .14 1000 1.05987 1.22622 .864 30.70 91.6 10.2 37.42 ± .30 1050 .41141 .25595 1.607 3.57 87.6 2.1 68.98 ± 1.21 1100 .19667 .06024 3.265 1.04 77.5 .5 137.46 ± :3.87 1150 .20741 .03497 5.932 .68 79.0 .3 242.46 ± 5.34 1400 .44684 .03454 12.935 .36 76.0 .3 492.19 ± 2,21 Total Gas Date .869 37.62 ± .20 Maximum Date (800-850°C) 38.8 29.90 ± .12 338 23. Sample 87MS473/l27/DD9; Darwaza Sar potassic granite gneiss; Biotite; 20.3 mg; Measured 40Ar/Ara - 298.9; J-value .02413 ± .25l (la); 3459'l5" N latitude; 7246'45: E longitude Temp 40ArR 39ArK F 39Ar/37Ar Z40ArR i39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 1.13087 .60060 1.883 21.75 57.4 7.6 80.16 ± .26 600 2.90963 1.70282 1.709 56.81 84.1 21.6 72.89 ± .20 700 3.16821 1.74273 1.818 66.05 83.4 22.1 77.45 ± .21 750 1.06980 .59207 1.807 47.86 90.1 7.5 76.99 ± .38 800 .79207 .44082 1.797 30.31 88.7 5.6 76.57 ± .45 850 1.30215 .73323 1.776 18.73 87.8 9.3 75.70 ± .35 900 1.83604 .97283 1.887 29.10 90.2 12.4 80.34 ± .24 940 1.33632 .68223 1.959 28.62 90,8 8.7 83.31 ± .34 1000 .50013 .20438 2.447 6.06 86.5 2.6 103.49 ± .71 1050 .20742 .06396 3.243 1.38 82.4 .8 135.93 ± 5,50 1150 .56897 .10511 5.413 2.40 86.0 1.3 221.47 ± .93 1300 .39934 .03531 11.310 3.82 82.0 .4 435.32 ± 5.86 Total Gas Date 1.933 82.22 ± .30 Maximum Date (600°C) 21.6 72.89 ± .20 339 Sample#87MS691/131/DD9;Jabrai Hornblende-biotite Biotite; 20.7 mg; Measured 40Ar/Ara 298.9; J-value = .02413 ± .25Z (la); 34°55'05" N latitude; 72°55'15" E longitude Temp 40AER ArK F 39Ar/37Ar Z40ArR Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 4.41043 .07865 56.074 31.74 79.9 .7 1543.72 ± 3.66 700 283.02129 4.23982 66.753 69.16 98.8 39.3 1731.19 ± 3.09 750 143.77972 2.10614 68.267 81.06 99.4 19.5 1756.26 ± 3.11 800 44.09925 .65213 67.623 38.99 99.0 6.0 1745.64 ± 3.10 850 94.89717 1.37610 68.961 43.79 99.5 12.8 1767.63 ± 3.12 900 118.93337 1.70221 69.870 48.27 99.7 15.8 1782.42 ± 3.14 950 39.49355 .57934 68.170 5.51 99.6 5.4 1754.67 ± 3.11 1000 2.76690 .03908 70.809 .14 98.9 .4 1797.58 ± 3.69 1050 .58477 .00686 85.249 .10 95.6 .1 2015.89 ±16.14 Total Gas Date 67.900 1750.21 ± 3.12 Maximum Date (900°C) 15.8 1782.42 ± 3.14 Minimum Date (700°C) 39.3 1713.19 ± 3.09 340 Samplei'5JL049B/73/DD9;Xenolith of Lahorgranite gneiss;Biotite; 21.2 mg; Measured 40Ar/Ar 298.9; J-value .02309 ± .25% (la); 350l'45" N latitude; 725l'30" E longitude Temp 40ArR Ar F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 2.80477 .32509 8.628 19.89 84.3 3.5 327.73 ± .87 700 33,88063 3.86728 8.761 52.07 97.6 41.4 332.34 ± .84 750 7.09092 .80343 8.826 47.98 98.3 8.6 334.60 ± .85 800 8.73764 .78591 8.562 22.44 98.0 8.4 325.45 ± .84 850 11.65986 1.33649 8.722 12.15 98.5 14.3 331.00 ± .84 900 9.85258 1.11134 8.865 23.18 98.7 11.9 335.97 ± .85 950 6.93084 .76936 9.009 10.48 98.7 8.2 340.91 ± .86 1000 1.95421 .20302 9,626 1.50 99.1 2.2 362.06 ± 1.36 1050 .93100 .07301 12.752 .22 98.0 .8 465.56 ± 1.82 1150 1.12997 .04629 24.410 .15 97.9 .5 806.41 ± 3,73 1300 .59774 .01508 39.642 .16 65.7 .2 1172.41 ± 5.62 Total Gas Date 8.950 338.88 ± .87 Plateau Date (700-750C) 50 332.73 ± .84 341 26. Sample q,PAK5/l22/DD9; Dubair 1-Iornblende-Biotite granite gneiss; Hornblende; 50.2 mg; Measured 40Ar/Ara - 298.9; J-value - 0.24 ± .25% (la); 35°0l'45' N latitude; 72°51'l5" E longitude Temp 40ArR 39ArK F 39Ar/37Ar %40Ar %3Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .69746 .05591 12.474 9.40 93.2 5.2 472.45 ± 3.10 600 .76232 .07270 10.486 8.32 88.3 6.8 404.95 ± 3.24 650 .77747 .05063 15.354 5.16 95.2 4,7 565.95 ± 4.86 700 .80874 .04108 19.689 2.80 95,3 3.8 698.12 ± 7.49 750 .83655 .03961 21.119 1.62 95.6 3.7 739.67 ± 3.26 800 1.70943 .07562 22.606 1.15 97.0 7.0 781.93 ± 2.24 825 2.80315 .09636 29.091 .85 98.2 8.9 955.31 ± 2.22 850 8.67961 .17047 50.916 .46 99.4 15.8 1440.31 ± 2.75 875 11.59102 .19225 60.290 .37 99.6 17.9 1614.31 ± 3.16 900 9.17545 .13741 66.776 .32 98.1 12.8 1725.56 ± 3.19 925 4.99197 .07290 68.475 .30 99.5 6.8 1753.60 ± 3,53 950 1.82103 .02540 71.681 .21 99.2 2.4 1805.37 ± 6.09 975 2.39206 .03152 75.901 .16 99.3 2.9 1871.31 ± 51l 1000 .89159 .01084 82.242 .10 98.0 1.0 1966.08 ±16.33 1025 .16732 .00172 97.139 .10 93.1 .2 2170.89 ±53.30 1050 .22223 .00152 146.379 .10 92.2 .1 2718,60 ±32.36 1100 .11233 .00095 118.303 .15 89.5 .1 2426.88 ±81.10 Total Gas Date 44.981 1320.80 ± 4.16 Max imuxn Date (975CC) 1.0 1966.08 ±16.33 Minimum Date (600°C) 6.8 404.95 ± 3.24 342 27. Sample E5JL059B/l08/DD9; Tourmaline-muscovite graphic granite; Muscovite; 19 mg; Measured 40Ar/Ara - 298.9; J-value .024224 ± .25Z (la); 34°56'OO" N latitude; 72°48'20" E longitude Temp ArK F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 400 .35720 .01456 24.539 24.73 83.0 .1 841.59 ± 9.77 500 .60564 .01993 30.385 39.52 89.1 .2 995.09 ± 8.61 600 1.71815 .05836 29.438 99.29 92.9 .5 971.11 ± 2.69 700 8.87954 27706 32.049 336.99 93.5 2.5 1036.51 ± 2.19 725 18.27870 .408 12 44.787 409.67 98.3 3.7 1325.46 ± 2.60 750 59.06577 1. 12899 52.318 572.65 99.4 10.3 1476.77 ± 2.80 775 94.19980 1.77792 52.983 99999.99 99.6 16.2 1489.55 ± 2.81 800 69.64981 1.36136 51.162 328.89 99.5 12.4 1454.35 ± 2.77 825 39.00565 .74437 52.401 327.71 99.5 6.8 1478.37 ± 2.80 850 33.95092 62611 54.226 294.47 99.5 5.7 1513.17 ± 2.84 900 33.91746 .61976 54.727 362.37 99.6 5.6 1522.62 ± 2.85 925 59.20821 1.09606 54.019 809 . 93 99.7 10.0 1509.27 ± 2.84 950 87.37802 1.60632 54. 396 179 . 13 99.7 14.6 1516.39 ± 2.84 1000 67.71477 1. 24310 54.472 219 . 85 99.5 11.3 1517.83 ± 2.85 Total Gas Date 52.261 1475.67 ± 2.81 Maximum Date (9500 -1000°C) 25.9 1517.02 ± 2.85 Minimum Date (700°C) 2.5 1036.51 ± 2.19 343 28. Sample 487MB6C/67/DD9; Pegmatite of Labor granite gneiss; Biotite; 17,9 mg; Measured 40Ar/Ar 298.9; 2-value .023096 ± .25% (lU); 34°54'30" N latitude; 72°52'05" E longitude Temp 40Ar ArK F 39Ar/37Ar %40Ar %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .42706 .23719 1.800 17.89 32.4 2.8 73.50 ± 1.03 600 1.83341 1.28114 1.431 68.09 84.9 15.1 58.66 ± .22 700 2.61828 1.80213 1.453 93.04 85.6 21.2 59.54 ± .16 750 .98204 .65264 1.505 60.43 93.6 7.7 61.63 ± .17 800 .61906 .44376 1.395 43.51 93.5 5.2 57.21 ± .50 850 .98241 .76365 1.286 26.96 92.3 9.0 52.82 ± .21 900 1.11159 .82709 1.344 20.70 92.5 9.7 55.15 ± .25 950 1.64510 1.16310 1.414 41.46 94.2 13.7 57.99 ± .25 1000 1.30895 .90030 1.454 19.23 93.5 10.6 59.58 ± .20 1050 .48539 .28790 1.686 2.68 92.1 3.4 68.91 ± .26 1150 .46005 .11626 3.957 .35 90.0 1.4 157.77 ± 1.61 1300 .21130 .02660 7.945 .29 77.2 .3 303.92 ± 5.05 Total Gas Date 1.492 61.12 ± .25 Maximum Date (850°C) 9 52.82 ± .21 344 Netasediments of the Karora group 29. Sample 487MB4/44/DD8; Low-grade carbonate; Muscovite; 15.4 mg; Measured 40Ar/Ara 298.9; J-value .007418 ± .25% (la); 3453'55' N latitude; 72°46'OO' E longitude Temp 40ArR ArK F 39Ar/37Ar %40ArR %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 700 .60190 .25009 2.407 5.53 5.1 9.7 31.92 ± .16 750 .40984 .18240 2.247 374.57 4.4 7.1 29.82 ± .34 800 .33383 .15072 2.215 494.07 3.9 5.9 29.40 ± .40 850 .45393 .18789 2.416 336.83 6.0 7.3 32.04 ± .13 900 .91749 .35050 2.618 236.42 15.3 13.6 34.69 ± .23 950 1.44260 .54450 2.649 99999.99 31.9 21.2 35.11 ± .18 1000 1.35757 .49430 2.746 99999.99 28.7 19.2 36.38 ± .24 1050 1.13470 .41362 2.743 99999.99 18.6 16.1 36.34 ± .23 Total Gas Date 2.584 34.26 ± .22 Maximum Date (1000° -1050°C) 35.3 36.37 ± .25 Minimum Date (800°C) 5.9 29.40 ± .40 345 30. Sample #87MB20A/46/DD8; Low-grade carbonate; Muscovite; 29 mg; Measured40Ar/Are 298.9; J-value .00743 ± .257 (la); 3457'30" N latitude; 7243'l5 E longitude Temp 40Ar 39Ar F Ar/37Ar Z40Ar %39Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 400 .08778 .00123 71.549 1.29 20.6 .1 769.08 ±37.00 500 .13686 .00552 24.774 .17 20.1 .2 304.81 ± 7.54 600 .50951 .02609 19.525 .03 36.1 1.1 244.38 ± 1.58 700 1.55458 .12038 12.914 7.11 80.5 5.0 165.28 ± .60 750 2.48012 .21210 11.693 27.93 87.6 8.8 150.29 ± .41 800 2.42061 .21817 11.095 34.01 89.4 9.0 142.90 ± .76 850 2.97449 .26458 11.242 9.41 91.8 10.9 144.72 ± .39 900 3.71343 .34762 10.683 3.62 93.6 14.4 137.79 ± .37 950 5.62114 .55555 10.118 2.78 94.5 22.9 130.77 ± .35 1000 4.30729 .42798 10.064 7.92 93.3 17.7 130.09 ± .35 1050 2.20133 .20123 10.939 4.01 88.2 8.3 140.97 ± .41 1100 .65748 .03649 18.018 .45 71,0 1.5 226.66 ± 1.48 1200 .31417 .00423 74.280 .28 50.2 .2 792.82 ±12.27 Total Gas Date 11.143 143.49 ± .44 Maximum Date (950°-1000°C) 40.6 130.43 ± .35 346 31. Sample #87MZ519/47/DD8; Graphitic phyllite; Muscovite; 38.5 mg; Measured 40Ar/Ar - 298.9; J-value .00752 ± .25Z (Ia); 3459'5" N latitude; 724815' E longitude Temp 40ArR 39ArK F 39Ar/37Ar %40Ar8 %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 2.60317 .37565 6.930 79.16 88.8 8.9 91.64 ± .28 550 .82461 .24938 3.307 68.86 83.3 5.9 44.31 ± .56 600 1.39521 .46539 2.998 49.98 77.5 11.0 40.22 ± .22 650 1.05906 .42641 2.484 31.62 90.1 10.1 33.38 ± .18 700 1.02339 .42701 2.397 41.94 89.4 10.1 32.22 ± .16 750 1.00707 .42764 2.355 67.04 86.6 10.1 31.67 ± .12 800 1.08742 .44819 2.426 49.21 82.1 10.6 32.62 ± .16 850 1.43564 .64257 2.234 156.52 89.7 15.2 30.06 ± .24 900 1.35279 .45813 2.953 84,95 91.9 10.8 39.62 ± .16 950 1.85293 .28051 6.605 20.65 93.1 6.6 87.46 ± .33 1000 .99330 .02364 42.015 3.01 88.2 .6 495.30 ± 3.06 1050 .43677 .00715 61.111 7.08 73.4 .2 682.15 ± 3.31 1100 .33355 .00222 150.256 7.28 67.5 .1 1363.98 ±20.41 Total Gas Date 3.638 48.70 ± .26 Maximum Date (850) 15.2 30.06 ± .24 347 Post-Karora group sodic granites 32. Sample /87MB47A/70/DD8; Tourmaline pegmatite; K-feldspar; 29.9 mg; Measured °Ar/Ara - 298.9; J-value .007582 ± .25% (10); 3452'55" N latitude; 72°43'50 E longitude Temp 40ArR ArK F Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 400 12.93807 .01429 905.583 118.61 94.5 .2 3720.87 ±14.72 450 .55331 .00569 97.246 27.50 51.6 .1 996.43 ±24.24 500 14.55268 .06458 225.331 244.87 95.8 1.0 1797.19 ± 4.38 550 7.17204 .09447 75.919 211.25 92.7 1.5 820.19 ± 1.84 600 7.27541 .17800 40.873 227.84 91.7 2,9 486.99 ± 1.18 650 4.59435 .21737 21.136 346.72 85.3 3.5 268.15 ± .69 700 5.39354 .36368 14.831 376.14 90.3 5.8 192.24 ± .51 750 2.93602 .24097 12.184 244.31 88.7 3.9 159.40 ± .51 800 2.85839 .26297 10.870 171.24 87.5 4.2 142.87 ± .45 850 4.83061 .28297 17.071 228.94 91.9 4.5 219.58 ± .57 900 7.94300 .32580 24.380 237.99 93.1 5.2 305.99 ± .78 950 13.48533 .42284 31.892 206.42 95.4 6.8 390.69 ± .97 1000 28.98157 .87205 33.234 221.59 96.8 14.0 405.40 ± 1.01 1050 47.89763 1.15694 41.400 917.61 98.0 18.6 492.49 ± 1.20 1100 71.19231 1.71829 41.432 99999.99 98.1 27.6 492.82 ± 1.20 Total Gas Date 37.391 450.26 ± 1.13 Maximum Date (l050-1l00°C) 46.2 492.68 ± 1.20 Minimum Date (800°C) 4.2 142.87 ± .45 348 33. Sample q/87M347A/71/DD8; Tourmaline pegmatite; Ziotite; 31.2 mg; Measured 40Ar/Ar 298.9; J-value .007379 ± .25Z (ic); 34°52'55" N latitude; 72°43'50" E longitude Temp 40ArR 39ArK F 39Ar/37Ar Z40ArR 7Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .78883 .02417 32.632 19.54 65.3 .6 389.22 ± 3.16 700 4.62143 .71123 6.498 44.60 80.5 16.6 84.49 ± .23 750 4.22770 .55604 7.603 41.76 89.1 13.0 98.47 ± .27 800 4.08334 .62600 6.523 37.54 87.8 14.6 84.81 ± .26 850 3.85078 .76215 5.053 36.06 85.3 17.8 66.03 ± .18 900 4.33431 .60230 7.196 25.74 85.0 14.1 93.34 ± .25 950 8.31199 .61326 13.554 26.82 92.6 14.3 171.96 ± .45 1000 7.53303 .31545 23.880 4.55 90.5 7.4 292.78 ± .75 1050 1.02269 .03624 28.222 .95 62.7 .8 341.26 ± 2.88 1100 .58672 .01717 34.173 1.35 50.3 .4 405.67 ± 3.36 1150 .46755 .00994 47.049 2.39 42.0 .2 537.61 ± 9.11 1300 .80768 .00758 106.548 1.90 56.5 .2 1046.50 ± 4.71 Total Gas Date 9.491 122.11 ± .34 Maximum Date (850CC) 17.8 66.03 ± .18 349 34. Sample #87MB47/69/DD8; Karora granite; Motite; 29.4 mg; Measured °Ar/Ar 298.9; J-value .007209 ± .25% (lu); 34°52'50" N latitude; 72°44'30' E longitude Temp 40ArR 30ArK F 39Ar/37Ar %40ArR 39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 400 .56740 .02999 18.918 12.06 45.2 .7 230.64 ± .79 500 1,31810 .14219 9.270 19.58 59.9 3.5 116,70 ± .61 600 3.15397 .46706 6.753 56.89 66.2 11.4 85.75 ± .23 700 4.31277 .74593 5.782 73.12 81.2 18.1 73.67 ± .24 750 2.25934 .45243 4,994 22.45 74.8 11,0 63.80 ± .22 800 2.68901 .55151 4.876 10.48 76.5 13.4 62.32 ± .18 850 2.48229 .41433 5.991 4.17 79.5 10.1 76.28 ± .26 900 3.97419 .62041 6.406 13.31 85.3 15.1 81.44 ± .24 950 3.92973 .52489 7,487 4.03 87.2 12.8 94.83 ± .44 1000 1.39235 .12844 10.840 .70 71.2 3.1 135.74 ± .56 1050 .23630 .01676 14.095 1.04 28.7 .4 174,58 ± 3.95 1100 .11200 .00610 18.359 .60 19.1 .1 224.23 ± 6.07 1150 .12871 .00596 21.596 .41 20.8 .1 261.03 ± 7.30 1300 .14671 .00446 32.929 .86 21.6 .1 384,25 ±16.52 Total Gas Date 6.496 82.57 ± .29 Max imuin Date (750-800°C) 24.4 63.06 ± .20 350 35. Sample 87MB380/66/DD8; Karai granite; K-feldspar; 33.8 mg; Measured 40Ar/Ara 298.9; J-value .00735 ± .25% (lc); 34°53'30" N latitude; 72°57'35" E longitude Temp 40ArR 39ArK F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 400 5.44436 .06683 81.471 160.19 92.1 .8 846.55 ± 1.93 500 9.61251 .34069 28.215 254.56 94.6 4.3 339.97 ± .86 600 3.76367 .36475 10.318 180.92 85.1 4.6 131.88 ± .43 650 1.21785 .28162 4.324 162.66 77.4 3.5 56.45 ± .23 700 2.46391 .30449 8.092 100.63 86.5 3.8 104.23 ± .31 750 2.46576 .27332 9.022 38.63 87.3 3.4 115.82 ± .32 800 3.16986 .28695 11.047 52.37 88.0 3.6 140.83 ± .38 850 4.01512 .32942 12.188 52.51 90.2 4.1 154.78 ± .41 900 5.09278 .35869 14.198 54.86 91.8 4.5 179.07 ± .47 950 9.24830 .55199 16.754 71.53 93.6 6.9 209.50 ± .55 1000 20.04945 .98241 20.408 176.54 96.2 12.3 252.13 ± .65 1050 62.79482 2.83377 22.159 1607.84 97.5 35.6 272.21 ± .70 1100 19.22637 .94147 20.422 99999.99 96.4 11.8 252.29 ± .65 1150 .86400 .05093 16.965 249.81 63.1 .6 211.99 ± 1.77 Total Gas Date 18.755 232.97 ± .63 Maximum Date (1050°C) 35.6 272.13 ± .70 Minimum Date (650°C) 3.5 56.45 ± .23 351 36. Sample q/87ME380/67/DD8; Karai granite; Biotite; 32.3 mg; Measured 40Ar/Ara 298.9; J-value .00719 ± .25Z (la); 3453'30" N latitude; 72°57'35" E longitude Temp 40ArR 39ArK F 39Ar/37Ar Z40Ar %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 400 .44271 .10300 4.298 10.80 33.3 3.7 54.91 ± .36 500 .79600 .26728 2.978 26.22 42.9 9.6 38.22 ± .32 600 1.48838 .50695 2.936 81.56 54.6 18.3 37.69 ± .19 700 1.20139 .38396 3.129 60.65 61.9 13.8 40.13 ± .28 750 1.06708 .34066 3.132 18.15 60.5 12.3 40.18 ± .28 800 1.09848 .33695 3.260 9.76 61.3 12.1 41,80 ± .22 850 1.37185 .41928 3.272 12.96 63.2 15.1 41,95 ± .21 950 1.83856 .27048 6.797 3.02 70.0 9.7 86.08 ± .29 1000 .90047 .07228 12.458 2.70 60.8 2.6 154,76 ± .56 1050 .84740 .05287 16.029 5.65 55.5 1.9 196.77 ± 1.17 1100 .29998 .01494 20.078 3.45 34.8 .5 243.27 ± 7.74 1150 .14376 .00625 23.000 .65 22.4 .2 276.09 ±25.40 Total Gas Date 4.143 52.95 ± .32 Maximum Date (600CC) 18.3 37.69 ± .19 352 37. Sample )87MB2/64/DD8; Ranial granite; Biotite; 37.8 mg; Measured 40Ar/Ara 298.9; J-value .007315 ± .25% (la); 34°53'45" N latitude; 72°46'30" E longitude Temp 40ArR 39ArK F 39Ar/37Ar %40Ar %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 400 .07611 .03318 2.294 20.84 12.1 .5 30.02 ± 4.69 500 .60389 .21687 2.785 50.92 43,9 3.2 36.38 ± .64 550 1.30761 .45755 2.858 83.72 62.9 6.7 37.32 ± .14 600 2.39980 .85983 2,791 120.48 71,3 12.6 36.46 ± .12 650 2.47241 .89887 2.751 178.72 77.9 13.2 35.94 ± .16 700 1.47456 .54279 2.717 181.86 68.1 8.0 35.50 ± .20 750 .86734 .31955 2.714 83.45 53.3 4.7 35.47 ± .22 800 .98950 .36228 2.731 15.76 56.5 5.3 35.69 ± .36 850 2.32095 .83487 2.780 50.21 74.4 12.2 36.32 ± .12 900 2.21625 .80098 2.767 60.59 64.1 11.7 36.15 ± .12 950 2.56921 .92327 2.783 17.57 79.0 13.5 36,35 ± .11 1000 1.49363 .51794 2.884 2.92 68.6 7.6 37.66 ± .22 1050 .17314 .05362 3.229 2.15 19.1 .8 42.12 ± 1.05 Total Gas Date 2.780 36.32 ± .20 Preferred Date (800-950°C) 42.8 36.20 ± .18 353 SWAT BLOCK Low-grade units of the Peshawar basin 38. Sample 1/D/50/DD8; Phyllite; Muscovite; 34.7 mg; Measured °Ar/Ar - 298.9; J-value - .007538 ± .25% (la); 34lO20 N latitude; 72°15OO. E longitude Temp 40ArR ArK F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .11097 .03411 3.253 2.01 22.3 9.8 4371 ± 1.24 700 .76413 .16268 4.697 2.59 43.3 46.7 62.77 ± .41 750 .15210 .02722 5.587 3.41 40.4 7.8 74.42 ± 2.43 800 .05110 .00808 6.325 1.62 24.2 2.3 84.02 ± 7.18 850 .14237 .02353 6.050 2.44 34.4 6.8 80.45 ± 2.33 950 .46245 .07328 6.310 2.71 53.6 21.0 83.83 ± .71 1050 .14034 .01970 7.124 .53 43.9 5.7 94.36 ± 2.48 Total Gas Date 5.231 69.76 ± 1.08 Maximum Date (800°-950°C) 30.1 83.09 ± 3.40 Minimum Date (700°C) 46.7 62.77 ± 0.41 354 39. Sample /SN1/22/DD10; Shewa porphyry; Sanidine; 35.1 mg; Measured 40Ar/Ar 298.9; J-value - .007103 ± .25Z (la); 3412'30" N latitude; 72°18'25" E longitude Temp 40Ar Ar F 39Ar/37Ar %43ArR Z39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .03909 .00377 10.367 5.12 17.4 .7 128.18 ± 9.19 600 .18432 .01831 10.068 3.11 46.5 3.5 124.60 ± 2.55 700 .34991 .07154 4.891 10.39 36.7 13.8 61.61 ± 1.20 750 .23843 .05546 4.299 46.21 54.7 10.7 54.26 ± 1.1 800 .15714 .04131 3.804 33.09 46.6 8.0 48.09 ± 3.35 850 .10948 .03591 3.048 27.62 35.7 7.0 38.64 ± 1.76 900 .14592 .03916 3.726 29.18 36.3 7.6 47.13 ± 1.64 1000 .19855 .04848 4.095 32.54 62.7 9.4 51.73 ± 1.82 1050 .33132 .06347 5.220 30.09 79.5 12.3 65.68 ± 1.96 1100 .27540 .04821 5.712 37.74 77.2 9.3 71.75 ± 1.00 1150 .28150 .05138 5.479 33.73 80.1 9.9 68.87 ± 1.39 1250 .22782 .03368 6.764 35.25 83.9 6.5 84.66 ± 3.51 1400 .02488 .00584 4.257 30.63 10.1 1.1 53.74 ±14.97 Total Gas Date 4.963 62.50 ± 2.15 Maximum Date (1250°C) 6.5 84.66 ± 3.51 Minimum Date (850°C) 7.0 38.64 ± 1.76 355 40. Sample E/51/DD8; Diabase dike; Hornblende; 177.9 mg; Measured 40Ar/Ara 298.9; J-value .00744 ± .25% (la); 34°15'25" N latitude; 72°1525" E longitude Temp 40AER ArK F 39Ar/37Ar %40Ar %39Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 500 2.28418 .00373 612.878 .07 62.6 4.5 3094.88 ±20.80 600 .12500 .00252 49.680 .16 9.0 3.1 567.42 ±20.19 650 .01939 .00073 26.588 .24 1.7 .9 325.62 ±40.83 700 .08120 .00355 22.899 .17 6.6 4.3 283.81 ±18.48 750 .06430 .00298 21.584 .14 5.5 3.6 268.66 ±39.31 800 .06431 .00334 19.234 .08 5.6 4.1 241.27 ±20.78 850 .11846 .00538 21.999 .04 9.5 6.6 273.46 ±23.62 875 .09756 .00318 30.690 .03 8.4 3.9 371.01 ±15.86 900 .07873 .00223 35.368 .02 6.7 2.7 421.42 ±53.33 925 .09491 .00287 33.120 .02 8.1 3.5 397.37 ±16.11 950 .16170 .00474 34.144 .02 13.6 5.8 408.36 ±11.72 1000 .45146 .01234 36.594 .02 27.3 15.0 434.40 ± 4.69 1025 .92835 .01706 54.415 .02 35.8 20.8 613.23 ± 3.88 1050 .78949 .00927 85.183 .01 46.8 11.3 885.55 ± 5.21 1075 1.35143 .00629 214.732 .01 58.2 7.7 1722.08 ± 9.88 1100 .25617 .00062 415.597 .01 21.3 .7 2541.92 ±63.68 1150 .75728 .00139 542.858 .01 42.2 1.7 2917.39 ±56.95 Total Gas Date 93.962 956.27 ±27.14 Maximum Date (700° -850°C) 18.6 267.87 ±25.55 356 High-grade to medium-grade units of Alpurai and Swat areas west of Puran fault 41. Sample #PAK9/9/D03; Swat granite gneiss; K-feldspar; 31.2 mg; Measured 40Ar/Ar - 300; J-value - .00924 ± .25% (la); 34°3015" N latitude; 72°05'30' E longitude Temp °ArR ArK F 39Ar/37Ar %40ArR %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .48709 .03121 15.607 73.38 27.3 .3 243.02 ± .98 600 .43888 .17307 2.536 267.32 22.1 1.4 41.78 ± .18 700 1.23325 .83145 1.483 664.97 44.9 6.8 24.56 ± .10 750 1.16845 .87796 1.331 1233.87 61.4 7.1 22.05 ± .09 800 1.55165 1.08853 1.425 814.08 70.3 8.8 23.61 ± .10 850 1.29496 .93940 1.378 671.52 58.2 7.6 22.83 ± .10 900 .85139 .57952 1.469 591.64 62.6 4.7 24.32 ± .10 950 1.20036 .75794 1.584 543.40 59.1 6.2 26.21 ± .11 1000 1.25190 .72021 1.738 647.27 61.5 5.8 28.74 ± .12 1100 1.40905 .78632 1.792 728.56 52.9 6.4 29.63 ± .13 1125 1.59645 .77854 2.051 632.18 74.9 6.3 33.86 ± .14 1150 2.56199 1.01025 2.536 1346.31 68.1 8.2 41.78 ± .18 1200 6.09347 2.22687 2.736 2354.25 78.6 18.1 45.04 ± .19 1250 2.89181 1.18628 2.438 2254.57 64.9 9.6 40.18 ± .17 1350 .41329 .20485 2.018 878.96 15.6 1.7 33.32 ± .14 1450 .24308 .12348 1.969 283.97 7.5 1.0 32.52 ± .14 Total Gas Date 2.004 33.11 ± .14 Maximum Date (1200°C) 18.1 45.04 ± .19 Minimum Date (750°C) 7.1 22.05 ± .09 357 42. Sample #PAK9/l8/D03; Swat granite gneiss; Biotite; 39.3 'rig; Measured 40Ar/Ara 300; J-value .009228 ± .25% (10); 3430'l5" N latitude; 72°05'30" E longitude Temp 40ArR 39ArK F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 500 .11870 .11918 .996 73.44 10.3 1.2 16.50 ± .07 600 .98873 .58743 1.683 279.23 42.3 5.9 27.80 ± .12 650 1.17425 .63074 1.862 394.77 63.0 6.3 30.73 ± .13 700 2.44855 1.27541 1,920 563.27 86.7 12.8 31.68 ± .13 750 2.65083 1.38069 1.920 656.44 93.3 13.9 31.68 ± .13 800 1.76388 .91775 1.922 662.60 92.7 9.2 31.71 ± .13 850 1.38093 .71954 1.919 370.58 90.2 7.2 31.67 ± .13 900 2.21174 1.17311 1.885 761.52 90.7 11.8 31.12 ± .13 950 2.81227 1.46292 1.922 1443.09 93.1 14.7 31.72 ± .13 1000 2.09423 1.08302 1.934 995.54 92.4 10.9 31.91 ± .14 1050 .72158 .37606 1.919 295,74 91.7 3.8 31.66 ± .13 1100 .33055 .17418 1.898 221.73 89.4 1.8 31.32 ± .13 1300 .08411 .04035 2.085 156.51 60.9 .4 34.37 ± .46 Total Gas Date 1.889 31.18 ± .13 Preferred Date (700°-1l00°C) 86.1 31.63 ± .13 358 43. Sample #PAK9/20/D03; Swat granite gneiss; Muscovite; 34.2 mg; Measured 40Ar/Ar 300; J-value .009113 ± .25%(laD; 3430'l5" N latitude; 72°05"30" E longitude Temp °ArR ArK F 39Ar/37Ar %Ar %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .06950 .03302 2.105 85.06 10.3 .3 34.28 ± .36 600 .10924 .06042 1.808 138.32 32.4 .6 29.48 ± .31 700 .50130 .29881 1.678 287.43 44.0 3.2 27.37 ± .12 750 .66649 .39161 1.702 510.48 64.4 4.2 27.76 ± .12 800 1.40398 .82365 1.705 1073.20 55.0 8.7 27.81 ± .12 850 4,37416 2.56957 1.702 2353.29 65.0 27.2 27.77 ± .12 900 3.96194 2.32468 1.704 5099.05 70.2 24.6 27.80 ± .12 950 3.10933 1.82928 1.700 2780.68 63,0 19.4 27.73 ± .12 1000 1.49389 .87033 1.716 3891.30 70.4 9.2 28.00 ± .12 1050 .35382 .20994 1.685 30421.42 77.6 2.2 27.50 ± .12 1100 .01388 .01278 1.086 28.65 22.6 .1 17.76 ± .99 1200 .01126 .00464 2.424 4.53 13.7 0,0 39.42 ± 3.35 1400 .27186 .00613 44.368 24.55 58.8 .1 612.56 ± 5.78 Total Gas Date 1.732 28.25 ± .15 Plateau Date (750°-1000°C) 93.4 27.80 ± .17 359 44. Sample 87MS80lA/l04/DD9; Marble; Muscovite; 18.9 mg; Measured 40Ar/Ara - 298.9; J-value .024322 ± .25Z (ic); 345i'45" N latitude; 72°41'45" E longitude Temp 40ArR ArK F 39Ar/37Ar 40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 600 .01384 .02740 .505 4.39 40.9 .2 22.03 ± 5.61 650 .02999 .01994 1.504 1.04 14.0 .2 64.80 ±12.16 700 .02812 .05974 .471 3.23 17.3 .5 20.53 ± 2.82 750 .10264 .17629 .582 153.94 71.4 1.6 25.37 ± .60 800 .50337 .81438 .618 793.55 87.9 7.3 26.92 ± .62 900 1.59385 2,43029 .656 555.53 90.3 21.8 28.55 ± .09 1000 2.25735 3.53748 .638 1238.75 87.4 31.7 27.78 ± .09 1100 2.32952 3.74830 .621 99999.99 86,9 33.6 27.06 ± .09 1200 .19488 .32837 .593 1062.83 32.9 2.9 25.85 ± .48 Total Gas Date .633 27.56 ± .18 Preferred Date (9O0°-l100C) 87.1 27.80 ± .09 360 45. Sample #87MS758/105/DD9; Carnet-biotite-museovite schist; Muscovite; 19.5 mg; Measured 40Ar/Ara 298.9; J-value .024341 ± .25% (la); 34°46'55" N latitude; 7238'30" E longitude Temp 40ArR ArK F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 400 .04899 .04128 1.187 33.85 16.5 .5 51.37 ± 4.79 450 .00428 .02106 .203 39.77 9.2 .3 8.90 ± 7.69 500 .01933 .04120 .469 56.31 34,1 .5 20.48 ± 5.54 550 .02897 .06588 .440 77.23 34.3 .8 19.21 ± 2.29 600 .09812 .15771 .622 83.94 22.9 1.9 27.11 ± 1.05 650 .17634 .29418 .599 116.63 48.6 3.6 26.13 ± .66 700 .63344 1.07660 .588 252.42 48.4 13.0 25.65 ± .14 750 1.34828 2.39456 .563 249.31 80.1 29.0 24.50 ± .15 800 .46113 .81489 .566 82.50 80.1 9.9 24.68 ± .09 850 .34377 .57665 .596 36,60 67.5 7.0 25.99 ± .40 900 .42996 .68371 .629 45.03 65.9 8.3 27.40 ± .33 950 .57463 .87862 .654 96.30 71,2 10.6 28.49 ± .20 1000 .60869 .92776 .656 92.01 82,0 11.2 28.58 ± .53 1050 .23942 .25855 .026 21.94 85.9 3.1 40,21 ± .37 1150 .05248 .02310 2,272 4.84 63,5 .3 97.09 ±18.14 1250 .02651 .00414 6,397 3.91 46.5 .1 261.08 ±42.18 Total Gas Date .617 26.88 ± .40 Maximum Date (950°-l000C) 21,1 28.54 ± 0.4 Minimum Date (750°-800°C) 38,9 24.59 ± .12 361 46. Sample #87MS758/106/DD9; Garnet-biotite-muscovite schist; Biotite; 20 mg; Measured °Ar/Ara 298.9; J-value .02427 ± .25/ (la); 3446'55" N latutide; 72°38'30" E longitude Temp 40ArR ArK F 39Ar/37Ar %40ArR Z39Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 500 .11905 .43450 .274 23.59 9.1 7.1 11.95 ± .26 600 .63369 1.60743 .394 33.87 29.1 26.3 17.18 ± .15 700 .73318 1.61740 .453 42.65 41.8 26.5 19.74 ± .11 800 .09537 .20716 .460 32.33 43.1 3.4 20.04 ± .71 850 .14996 .31017 .483 27.25 41.9 5.1 21.04 ± .44 900 .16062 .31354 .512 25.15 41.0 5.1 22.29 ± .45 950 .35110 .68687 .511 26.84 43.6 11.2 22.24 ± .22 1000 .33743 .67554 .499 28.60 39.9 11.1 21.74 ± .20 1050 .09878 .21919 .451 28.70 31.2 3.6 19.62 ± .91 1150 .06006 .03821 1.572 16.36 53.6 .6 67.53 ± 4.78 Total Gas Date .448 19.52 ± .25 Max imuin Date (900° -1000°C) 27.4 22.05 ± .29 Minimum Date (500°C) 7.1 11.95 ± .26 362 47. Sample 187MB42/2l/DDl0; Muscovite-biotite-graphitic schist; Muscovite; 98.2 mg; Measured 40Ar/Ara 298.9; 2-value .007103 ± .25 (10); 34°5015" N latitude; 72°36'30" E longitude Temp 40Ar ArK F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (SC) (Ma at 1 Sigma) 600 .40563 .20898 1.941 29.87 47.5 1.5 24.70 ± .57 700 1.30450 .67432 1.935 51.79 72.5 4.7 24.62 ± .13 750 6.77850 3.47111 1.953 371.99 91.5 24.3 24.85 ± .07 800 7.75587 4.04796 1.916 223.12 95.3 28.3 24.39 ± .07 850 2.53728 1.34709 1.884 60.82 93.5 9.4 23.98 ± .07 900 1.34798 .71375 1.889 34.35 91.9 5.0 24.04 ± .07 950 1.91837 1.00821 1.903 58.69 92.7 7.1 24.22 ± .10 1000 3.57551 1.87971 1.902 111.12 94.8 13.2 24.21 ± .07 1050 1.61312 .84390 1,912 61.60 96.2 5.9 24.33 ± .09 1100 .17645 .09479 1.861 12.60 85.4 .7 23.69 ± .79 Total Gas Date 1.918 24.42 ± .08 Preferred Date (600-l100°C) 100 24.42 ± .08 363 48. Sample #87MB42/20/DD1O; Muscovite-biotite-graphitic schist; Biotite; 82.1 mg; Measured °Ar/Ara 298.9; J-value .00707 ± .25% (lc; 3450'l5' N latitude; 72°36'30" E longitude Temp 40Ar 39ArK F 39Ar/37Ar %40ArR %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .09730 .08559 1.137 101.36 27.7 .8 14.44 ± 1.06 600 1.15203 .70278 1.639 298.18 74.8 6.9 20.79 ± .13 700 5.81960 3,23784 1.797 1052.24 90.7 31.6 22.78 ± .06 750 1.04194 .57624 1.808 320.54 96.2 5.6 22.92 ± .12 800 1.74606 .96201 1.815 140.99 94.0 9.4 23.00 ± .07 850 1.26001 .69835 1.804 96.28 94.3 6.8 22.87 ± .14 900 3.04568 1.66274 1.832 163.90 96.1 16.2 23.21 ± .08 950 3.08061 1.69230 1.820 347.20 95.9 16.5 23.07 ± .08 1000 .95170 .52290 1.820 66.32 90.1 5.1 23.07 ± .18 1050 .17896 .09602 1,864 16.33 78.2 .9 23.61 ± .68 Total Cas Date 1.795 22.75 ± .10 Plateau Date (700°-1050C) 92.3 22.97 ± .18 364 49. Sample q/Pak8/21/D03; Choga granite gneiss; Muscovite; 34.9 mg; Measured 40Ar/Ara - 300; J-value .009122 ± .25% (la); 3454'45" N latitude; 7239'40" E longitude Temp 40ArR ArK F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 500 .02032 .01585 1.282 43.50 12.3 .2 20.97 ± .83 600 .03507 .02570 1.364 38.58 22.8 .3 22.31 ± .47 700 .26572 .14964 1.776 36.08 34.3 1.6 28.99 ± .19 800 .64474 .43504 1.482 163.83 61.7 4.6 24.23 ± .10 850 3.05163 2.12655 1.435 445.25 61.4 22.3 23.46 ± .10 900 2.20337 1.56624 1.407 443.97 80.8 16.4 23.00 ± .10 950 1.73723 1.24409 1.396 419.91 75.8 13.0 22.83 ± .10 1000 1.25829 .89727 1.402 467.33 73.1 9.4 22.93 ± .10 1050 1.46451 1.02861 1.424 535.24 79.7 10.8 23.28 ± .10 1100 2.07407 1.47818 1.403 979.95 83.2 15.5 22.94 ± .10 1150 .72650 .50897 1.427 439.59 83.5 5.3 23.34 ± .10 1200 .08669 .05830 1.487 138.56 35.6 .6 24.31 ± .30 1400 .05654 .01368 4.133 34.05 22.5 .1 66.76 ± 1.72 Total Gas Date 1.427 23.33 ± .11 Preferred Date (850-ll50°C) 92.7 23.12 ± .10 365 50. Sample 1Pak8/l7/D03; Choga granite gneiss; Biotite; 30.7 mg; Measured 40Ar/Ara - 300; J-value - .00926 ± .25% (lU); 34°54'45" N latitude; 72°39'40" E longitude Temp 40Ar ArK F 39Ar/37Ar Z40ArR %39Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 500 .01830 .01633 1.121 430.38 5.3 .2 18.63 ± .76 600 .50097 .26778 1.871 203.86 17.4 3.4 30.99 ± .13 650 2.10295 1.17247 1.794 724.35 44.2 14.9 29.72 ± .13 700 3.73309 2.10640 1.772 1068.12 85.6 26.8 29.37 ± .12 750 2.76238 1.56666 1.763 1278.41 92.1 19.9 29.22 ± .12 800 .81464 .46545 1.750 885.25 88.3 5.9 29.00 ± .12 850 .36840 .20715 1.778 462.96 83.5 2.6 29.47 ± .12 900 .28932 .16667 1.736 372.00 80.6 2.1 28.77 ± .12 950 .27669 .15985 1.731 359.06 78.9 2.0 28.69 ± .12 1000 .52601 .30756 1.710 379.94 82.1 3.9 28.35 ± .12 1050 1.30586 .73836 1.769 931.43 89.1 9.4 29.30 ± .12 1150 1.20400 .68187 1.766 787.81 87.6 8.7 29.26 ± .12 1300 .02262 .01305 1.734 34.55 10.5 .2 28.73 ± .74 Total Gas Date 1.769 29.32 ± .14 Preferred Date (650°-850°C) 70.1 29.37 ± .12 366 51. Sample #87MS785/27/DD1O; Garnet amphibolite; Hornblende; 357.4 mg; Measured °Ar/Ara 298.9; J-value .00705 ± .25 (1c); 3451'40" N latitude; 72°41'40" E longitude Temp 40ArR ArK F 39Ar/37Ar %40ArR %3Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .08148 .00204 39.965 .15 16.1 .1 447.80 ±21.00 600 .03600 .00270 13.335 .24 16.8 .1 162.09 ±21.90 650 .02162 .00313 6.913 .22 3.3 .1 85.85 ±16.24 700 .02216 .00433 5.112 .22 9.5 .1 63.88 ±10.36 750 .02441 .00517 4.724 .18 12.3 .1 59.10 ±13.19 800 .03327 .00404 8.226 .10 16.3 .1 101.69 ±28.43 850 .06575 .01650 3.985 .12 22.1 .4 49.99 ± 4.13 900 .07387 .01577 4.684 .07 23.1 .4 58.61 ± 3.17 950 .67475 .26102 2.576 .12 57.5 6.7 32.47 ± .28 1000 1.75462 .71313 2.460 .13 72.8 18.1 31.02 ± .09 1050 3.03192 1.24376 2.438 .13 80.0 31.6 30.74 ± .10 1075 .58505 .23454 2.494 .12 51.1 66.0 31.45 ± .41 1100 .76989 .31150 2.472 .12 62.4 7.9 31.16 ± .10 1150 1.67790 .65326 2.569 .13 79.3 16.6 32.37 ± .11 1200 .77026 .30105 2.559 .13 66.0 7.7 32.25 ± .14 1250 .07306 .02857 2.562 .13 11.2 .7 32.30 ± 2.78 1450 .33297 .12955 2.570 .13 29.6 3.3 32.39 ± .33 Total Gas Date 2.551 32.16 ± .19 Maximum Date (1150-l450°C) 28.3 32.34 ± .84 Minimum Date (l000°-l050C) 49.8 30.84 ± .09 367 Mansehra Block 52. Sample 87MSB43/DD9; Hazara slate; Sericite conc. ,20.6 mg; Measured 40Ar/Ara 298.9; J-value .02425 ± .25 (lC); 340515" N latitude; 73°lO'30" E longitude Temp 40Ar ArK F 39Ar/3TAr l°ArR Z39Ar Apparent Age and Error (°C) (Ma at I Sigma) 400 .65917 .26483 2.489 24.43 82.5 5.6 105.73 ± .34 450 1.74889 .22488 7.777 20.30 96.2 4.7 311.68 ± .87 500 4.64505 .34706 13.384 33.52 98.7 7.3 507.07 ± 1.23 550 10.73339 .65433 16.404 48.57 99.3 13.8 604.15 ± 1.42 600 16.40381 .93729 17.501 57.65 99.6 19.8 638.18 ± 1.49 650 16.01282 .90191 17.754 65.87 98.0 19.0 645.93 ± 1.51 700 13.58895 .73870 18.396 64.35 99.6 15.6 665.43 ± 1.54 750 5.78671 .28457 20.335 47.62 89.5 6.0 723.17 ± 1.65 800 3.89590 .17177 22.682 34.77 98.8 3.6 790.64 ± 2.00 850 2.88231 .11579 24.894 29.54 92.5 2.4 852.02 ± 1.88 900 2.55186 .09582 26.632 21.68 97.2 2,0 898.83 ± 3.75 Total Gas Date 16.658 612.09 ± 1.48 Preferred Date (600-700°C) 54.4 650.00 ± 2.00 368 53. Sample #87MB272/61/DD8; Garnet-biotite gneiss; Biotite; 35.3 mg; Measured 40Ar/Ara 298.9; J-value .007265 ± .25% (la); 34°49'25" N latitude; 7Y06'30" E longitude Temp 40Ar 39ArK F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 400 .28309 .02311 12.251 35.33 49.1 .4 153.82 ± 8.15 500 5.06611 .20154 25.137 75.41 87.4 3.6 302.59 ± .77 600 41.50416 1.21115 34.268 120.15 96.6 21.6 401.05 ± 1.00 650 26.82581 .75431 35.564 90.51 68.0 13.5 414.59 ± 1.03 700 13.25258 .39441 33.601 36.09 97.5 7.0 394.04 ± .98 750 11.47626 .36266 31.644 26.99 96.8 6.5 373.30 ± .94 800 8.03246 .24410 32.906 29.10 95.5 4.4 386.70 ± .97 850 24.70297 .67682 36.496 70.66 97.7 12.1 424.30 ± 1.05 900 30.94847 .82864 37.349 252.60 98.3 14.8 433.09 ± 1.07 950 28.80419 .76163 37.557 113.64 98.3 13.6 435.23 ± 1.07 1000 5.42516 .14880 36.459 37.91 94.4 2.7 423.89 ± 1.05 Total Gas Date 34.977 408.47 ± 1.05 Maximum Date (900-950C) 28.4 434.16 ± 1.07 Minimum Date (500CC) 3.6 302.59 ± .77 369 54. Sample /87MB272/85/DDl2; Carnet-biotite gneiss; Biotite; 11.1 mg; Measured °Ar/Ara 298.9; J-value .007292 ± .25%(loD; 34°49'25" N latitude; 73°06'30" E longitude Temp °ArR ArK F 39Ar/3TAr %40Ar %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 550 1.86743 .07501 24.894 56.42 87.6 7.3 300.92 ± 1.26 1100 33.04184 .93259 35.430 66.08. 98.2 91.3 414.57 ± 1.03 1350 .43388 .01394 31.118 17.15 63.9 14 368.92 ± 3.33 Total Gas Date 34.598 405.85 ± 1.06 370 55. Sample 87MB272/86/DDl2; Garnet-biotite gneiss; Muscovite; 30.8 mg; Measured °Ar/Ara 298.9; J-value .00703 ± .25% (la); 344925" N latitude; 73°06'30" 8 longitude Temp 40ArR ArK F 39Ar/37Ar %40Ar %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 700 1.27148 .21561 5.897 37.29 74.6 5.0 73.28 ± 45 750 3.27682 .57685 5.681 72.51 76.8 13.3 70.64 ± .22 800 5.56368 1.00304 5.547 107.82 85.8 23.2 69.01 ± .19 850 2.90343 .52113 5.571 45.56 86.1 12.1 69.31 ± .20 900 2.55677 .44936 5.690 32.36 84.1 10.4 70.75 ± .22 950 2.40314 .42588 5.643 67.91 84.3 9.9 70.18 ± .25 l)00 4.00175 .71272 5.615 185.67 87.9 16.5 69.84 ± .19 1050 2.34916 .41893 5.608 125.44 89.9 9.7 69.75 ± .20 Total Gas Date 5.626 69.98 ± .21 Preferred Date (750°-1050°C) 95 69.81 ± .21 371 56. Sample #87MB253/89/DD8; Garnet amphibolite; Hornblende; 318.5 rug; Measured 40Ar/Ara 298.9; J-value .00758 ± .257 (la); 3447'45' N latitude; 72°58'45" E longitude Temp 40Ar Ar F Ar/37Ar Z°ArR %Ar Apparent Age and Error (AC) (Ma at 1 Sigma) 500 22.93146 .00583 3931.465 .26 97.5 .2 6183.27 ± 4.36 600 15.02886 .00785 1914.836 .25 94.8 .2 4946.16 ±66.46 650 6.76567 .00648 1044.792 .26 96.1 .2 3947.59 ±28.77 700 3.75163 .00757 495.452 .21 91.5 .2 2812.99 ±13.48 750 2.31002 .00791 291.958 .18 91.3 .2 2105.66 ±10.51 800 3.47464 .02241 155.091 .17 93.6 .6 1402.25 ± 4.80 850 11.72338 .28391 41.293 .19 96.7 7.4 491.26 ± 1.19 900 23.61361 .59530 39.667 .17 97,6 15.6 474.24 ± 1.16 950 83.69654 2.16139 38.723 .13 98.4 56.5 464.30 ± 1.14 1000 6.01650 .19251 31.252 .12 96.2 5.0 383.53 ± .96 1050 15.04184 .44204 34.028 .13 97.3 11.6 413.96 ± 1.03 1075 .78220 .02006 38.984 .13 81.0 .5 467.05 ± 3.08 1100 .25455 .00665 38.301 .13 74.5 .2 459.83 ± 4.81 1150 1.30347 .03468 37.591 .13 85.5 .9 452.28 ± 2.28 1200 1.17173 .03003 39.017 .13 79.4 .8 467.40 ± 2.13 Total Gas Date 51.735 596.85 ± 1.47 Preferred Date (950CC, l075C, and l200C) 57.8 466.25 ± 2.12 372 57. Sample #87M.B33A/19/DD1O; Diabase dike; Biotite; 94.8 mg; Measured °Ar/Ara - 298.9; J-value .006907 ± .25% (la); 345l'50" N latitude; 72°58'35" E longitude Temp 40ArR Ar F Ar/37Ar %40Ar %Ar Apparent Age and Error (SC) (Ma at 1 Sigma) 500 .88696 .14419 6.151 9.32 60.9 1.9 75.06 ± .35 600 4.18406 .22905 18.267 24.16 71.6 3.1 214.36 ± .84 700 18.51603 .81988 22.584 35,10 81.0 11.0 261.50 ± .68 750 12.01933 .52950 22.700 41.30 81.9 7.1 262,74 ± .68 800 9.08626 .40131 22.641 34.35 81.8 5.4 262.12 ± .68 850 9.30839 .41307 22.535 20.93 81.5 5.6 260.97 ± .67 900 11.88782 .52689 22.562 4.78 81.7 7.1 261.26 ± .67 950 19.33043 .89630 21.567 1.28 82.6 12.1 250.50 ± .65 1000 28.43296 1.35477 20.987 1,31 83.0 18.2 244.21 ± .63 1050 34.16089 1.57010 21,757 8.47 82.1 21.1 252.56 ± .65 1150 11,21530 .50817 22.070 1.60 81.9 6.8 255.95 ± .66 1300 .85039 .03776 22.523 .45 78.7 .5 260.84 ± 1.14 Total Gas Date 21.515 249.94 ± .66 Preferred Date (700° -900°C) 36.2 261.71 ± .68 373 58. Sample #87MB54/76/DD8; Psammitic schist; Biotite; 32.7 mg; Measured 40Ar/Ara - 298.9; J-value - .007445 ± .25 (Ia); 34°49'05" N latitude; 72°57'45" E longitude Temp 40ArR ArK F Ar/37Ar Z°ArR %Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 600 .43388 .08469 5.123 16.97 60.0 1.8 67.52 ± .68 700 5.35273 .78809 6.792 57.60 86.9 17.0 88.99 ± .24 750 4.24593 .61248 6.932 61.94 95.8 13.2 90.78 ± .25 800 2.82131 .40908 6.897 32.12 94,7 8.8 90.33 ± .30 850 1.49548 .21709 6.889 13.77 91,1 4.7 90.23 ± .28 900 1.17002 .16905 6.921 5.09 87.5 3.6 90.64 ± .43 950 1.60188 .24035 6.665 2.34 90.5 5.2 87.36 ± .43 1000 3.04469 .46677 6.523 6.49 94.3 10.1 85.55 ± .26 1050 4.06364 .59562 6.823 9.04 95.7 12.8 89.3 ± .26 1150 6.83853 .95790 7.139 18.74 96.7 20.6 93.42 ± .25 1300 .65045 .07853 8.283 3.16 77.8 1.7 107.95 ± .76 1400 .22964 .02379 9.651 2.71 56.5 .5 125.17 ± 2.23 Total Gas Date 6.880 90.12 ± .29 Preferred Date (700°-900C) 47.3 90.19 ± .31 374 59. Sample 187MB56/77/DD8; Psaininitic schist; Biotite; 27.2 mg; Measured 40Ar/Ara - 298.9; J-value - .00736 ± .25% (la); 34°49'45" N latutude; 72°57'45' E longitude Temp 40ArK ArK F Ar/37Ar %40ArR %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .15687 .02068 7.586 18.11 45.1 .5 98.01 ± .59 700 6.52819 .77042 8.474 308.82 88.8 18.3 109.14 ± .31 750 5.49272 .62887 8.734 557.04 96.0 15.0 112.39 ± .30 800 3.25073 .38360 8.474 201.06 96.2 9.1 109.15 ± .29 850 2.83652 .34172 8.301 85.33 95.8 8.1 106.98 ± .29 900 2.18786 .25587 8.551 99.41 93.8 6.1 110.10 ± .30 950 3.57403 .40093 8.914 164.59 95.3 9.5 114.64 ± .41 1000 4.59599 .50366 9.125 182.22 96.1 12.0 117.26 ± .31 1050 5.13409 .53390 9.616 142.66 96.9 12.7 123.36 ± .33 1150 2.71142 .27423 9.887 45.88 95.1 6.5 126.72 ± .34 1300 .95216 .08806 10.813 20.10 86.4 2.1 138.14 ± .69 Total Gas Date 8.906 114.54 ± .32 Maximum Date (1300CC) 2.1 138.14 ± .69 Minimum Date (700°C) 18.3 109.14 ± .31 375 60. Sample it87MR56/78/DD8; Psammitic schist; Muscovite; 37.9 nlg; Measured 40Ar/Ara - 298.9; J-value - .00743 ± .25% (1); 34°49'45" N latitude; 72°57'45" E longitude Temp 40ArR ArK F 3Ar/37Ar %40ArR %Ar Apparent Age and Error (CC) (Ma at I Sigma) 600 .20173 .06439 3.133 36.65 57.4 1.0 41.51 ± 1.02 700 .52827 .23104 2.287 95.03 55.5 3.5 30.39 ± .21 750 .60073 .26283 2.286 88.86 78.5 4.0 30.38 ± .26 800 1.55464 .61203 2.540 172.65 80.7 9.4 33.73 ± .13 850 2.89640 1.19486 2.424 667.01 86.9 18.3 32.20 ± .10 900 2.08547 .87305 2.389 262.62 87.2 13.3 31.74 ± .11 950 1.58907 .62700 2.534 385.26 84.4 9.6 33.65 ± .23 1000 1.36853 .50325 2.719 273.96 85.0 7.7 36.09 ± .10 1050 1.56984 .58676 2.675 260.36 86.2 9.0 35.51 ± .12 1100 2.44400 .96815 2.524 464.42 89.7 14.8 33.52 ± .10 1200 1.93265 .61649 3.135 151.68 89.4 9.4 41.54 ± .15 Total Gas Date 2.564 34.05 ± .13 Maximum Date (1200°C) 9.4 41.54 ± .15 Minimum Date (700°-750°C) 7.5 30.39 ± .24 376 61. Sample 87MBl0l/80/DD8; Garnet amphibolite; Biotite; 24.4 mg; Measured 40Ar/Ara - 298.9; J-value - .007468 ± .25% (la); 34°49'25" N latitude; 72°56'50" E longitude Temp 40Ar ArK F Ar/37Ar %°ArR %Ar Apparent Age and Error (SC) (Ma at 1 Sigma) 500 .08527 05735 1.487 20.91 16.8 1.9 19.92 ± 1.37 600 1.05577 40224 2.625 47.71 49.5 13.1 35.02 ± .18 700 2.00543 57018 3.517 117.50 68.4 18.5 46.77 ± .13 750 1.31116 34308 3.822 104.69 78.1 11.1 50.77 ± .20 850 1.03640 27043 3.832 52.32 75.7 8.8 50.91 ± .22 900 1.47682 38878 3.799 43.56 76.1 12.6 50.46 ± .16 950 1.47510 .38280 3.853 29.52 80.4 12.4 51.18 ± .33 1000 1.10400 28461 3.879 12.41 79.4 9.2 51.52 ± .23 1050 .83891 .21325 3.934 33.58 80.6 6.9 52.24 ± .20 1150 .67390 .16697 4.036 8.40 73.7 5.4 53.57 ± .36 Total Gas Date 3.592 47.76 ± .25 Preferred Date (750° -1000°C) 54.1 50.97 ± .23 377 62. Sample 87MB102/63/DD8; Garnet-biotite-muscovite schist; iotite; 66.4 mg; Measured Ar/Are - 298.9; J-value - .007338 ± .25% (lc; 34°49'25" N latitude; 72°56'50' E longitude Temp 40Ar ArK F Ar/37Ar Z40ArR %39Ar Apparent Age and Error (°C) (Ma at I Sigma) 400 2.19054 .06361 34.439 273.86 64.8 .2 406.46 ± 1.29 500 2.01510 .48354 4.167 1091.19 76.8 1.5 54.34 ± .16 600 11.22932 3.18323 3.528 99999.99 91.3 10.2 46.10 ± .13 700 31.24805 8.54938 3.655 99999.99 96.7 27.3 47.75 ± .13 750 14.65620 3.91683 3.742 99999.99 96.2 12.5 48.87 ± .13 800 8.44228 2.21718 3.808 1228.44 94.0 7.1 49.71 ± .14 850 5.50320 1.41514 3.889 569.54 93.6 4.5 50.76 ± .14 900 7.11017 1.77699 4.001 527.72 92.7 5.7 52.20 ± .14 950 8.47066 1.98360 4.270 593.59 93.5 6.3 55.66 ± .15 1000 7.70758 1.66749 4.622 99999.99 93.4 5.3 60.17 ± .16 1050 10.08443 2.02549 4.979 99999.99 94.1 6.5 64.73 ± .18 1150 19.47907 3.73312 5.218 99999.99 95.8 11.9 67.78 ± .18 1300 1.28133 .23969 5.346 387.01 70.4 .8 69.41 ± .53 1400 .30334 .05256 5.772 114.43 41.2 .2 74.83 ± 1.68 Total Gas Date 4.143 54.03 ± .15 Maximum Date (1l50C) 11.9 67.78 ± .18 Minimum Date (600°C) 10.2 46.10 ± .13 378 63. Sample #87MB102/62/DD8; Carnet-biotite-muscovite schist; Muscovite; 58.3 mg; Measured 40Ar/Ara - 298.9; J-value - .007255 ± .25% (la); 34°49'25" N latitude; 72°56'SO" E longitude Temp 40ArR Ar F Ar/37Ar %40ArR %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 400 .27954 .06183 4.521 84.89 26.8 .6 58.23 ± .45 500 .24344 .05850 4.161 169.18 24.7 .5 53.66 ± 1.08 600 .57623 .18568 3.103 222.46 34.0 1.7 40.17 ± .24 700 2.96834 1.24190 2.390 99999.99 66.4 11.6 31.01 ± .10 750 6.43334 2.93437 2.192 99999.99 86.9 27.5 28.47 ± .08 800 2,71920 1.25863 2.160 21995.64 81.3 11.8 28.06 ± .09 850 2,44243 1.12323 2.174 234.90 77.8 10.5 28.24 ± .09 900 2.06458 .95246 2.168 558.74 77.6 8.9 28.15 ± .08 950 4.39153 2.03477 2.158 99999.99 86.2 19.1 28.03 ± .08 1000 1.07889 .50035 2.156 496.99 65.9 4.7 28.00 ± .34 1050 .65648 .28727 2.285 72.85 50.2 2.7 29.66 ± .15 1100 .04232 .01278 3.310 5.90 9.4 .1 42.81 ±10.93 1150 .03316 .00907 3.655 4.74 7.2 .1 47.22 ± 5.98 Total Gas Date 2.245 29.14 ± .11 Preferred Date (750-l000°C) 82.6 28.22 ± .13 379 64. Sample #87MB104/75/DD8; Psammitic schist; Biotite; 35.5 mg; Measured 40Ar/Ara - 298.9; J-value - .00733 ± .25% (la); 34°49'OO" N latitude; 72°56'45" E longitude Temp 40ArR ArK F Ar/37Ar %40Ar %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .22532 .04705 4.789 21.24 33.6 1.6 62.24 ± .66 700 13.38148 1.02057 13.112 50.81 91.2 35.6 165.55 ± .44 750 5.11861 .35257 14.518 191.50 95.5 12.3 182.43 ± .48 800 2.25680 .15602 14.465 75.47 91.7 5.4 181.80 ± .64 850 2.36101 .16884 13.984 105.87 91.6 5.9 176.04 ± .47 900 3.21931 .23217 13.866 67.94 92.3 8.1 174.63 ± .82 950 5.39668 .37724 14.306 227.39 94.3 13.2 179.89 ± .47 1000 6.09000 .41453 14.691 144.07 95.7 14.5 184.50 ± .49 1050 .86514 .05561 15.558 38,25 78.7 1.9 194.82 ± 1.37 1150 .56809 .03509 16.190 12.39 80.3 1.2 202.30 ± 2.09 1300 .13720 .00804 17.067 6.15 41.4 .3 212.64 ± 6.73 Total Gas Date 13.816 174.02 ± .53 Maximum Date (11.50°C) 1.2 202.30 ± 2.09 Minimum Date (500°C) 1.6 62.24 ± .66 380 65. Sample 87MB65/73/DD8; Tourmaline pegmatite; potassium feldspar; 38.2 mg; Measured 40Ar/Ar - 298.9; J-value - .007399 ± .25% (la); 34°50'lO" N latitude; 72°59'45" E longitude Temp ArK F Ar/37Ar %40Ar %Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 500 20.06298 .03270 613.456 34.26 92.9 .4 3088.10 ±13.20 550 1.44207 .12240 11.781 507.07 64.8 1.4 150.77 ± .58 600 1.27867 .31465 4.064 180.48 63.5 3.7 53.44 ± .31 650 1.08657 .43146 2.518 387.15 54.3 5.0 33.31 ± .20 700 3.14716 .94691 3.324 442.21 80.5 11.1 43.83 ± .15 750 2.33698 .58884 3.969 118.19 76.5 6.9 52.21 ± .20 800 2.13406 .32086 6.651 64.36 76.2 3.7 86.66 ± .31 850 5.58488 .43129 12.949 91.03 88.0 5.0 165.06 ± .46 900 9.16590 .61094 15.003 153.76 91.0 7.1 189.90 ± .50 950 12.58454 .97080 12.963 172.30 94.0 11.3 165.23 ± .44 1000 8.26325 .96786 8.538 172.27 91.5 11.3 110.50 ± .30 1050 11.54748 1.26084 9.159 235.03 92.2 14.7 118.28 ± .32 1100 6.52655 .95286 6.849 684.13 79.4 11.1 89.18 ± .25 1150 2.37534 .47082 5.045 613.81 80.5 5.5 66.11 ± .20 1250 1.20406 .08425 14.292 104.26 70.3 1.0 181.34 ± 1.59 1400 1.25497 .05771 21.747 80.37 69.4 .7 269.16 ± 1.16 Total Gas Date 10.507 135.06 ± .43 Maximum Date (9O0C) 7.1 189.90 ± .50 Minimum Date (650C) 5.0 33.31 ± .20 381 66. Sample #87MB65/72/DD8; Tourmaline pegmatite; Muscovite; 38.4 mg; Measured 40Ar/Ar 298.9; J-value - .007379 ± .25% (la); 34°50'lO" N latitude; 72°59'45" E longitude Temp °ArR Ar< F 39Ar/37Ar %40ArR %39Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 700 .46035 .25600 1.798 208.74 45.5 3.2 23.78 ± .50 750 .67695 .36951 1.832 396.41 68.3 4.6 24.22 ± .16 800 2.52143 1.26971 1.986 99999.99 77.0 15.9 26.24 ± .08 850 4.04640 2.12313 1.906 99999.99 81.8 26.6 25.19 ± .10 900 1.83386 .91912 1.995 99999,99 78.3 11.5 26.37 ± .17 950 2.20877 .98878 2.234 1024.92 79.3 12.4 29.49 ± .13 1000 2.51013 1.25965 1.993 6130.10 83.4 15.8 26.33 ± .10 1050 1.57005 .75470 2.080 859.73 83.2 9.5 27.48 ± .20 1100 .15315 .03617 4.234 31.10 49.0 .5 55.50 ± 3.01 1150 .01528 .00563 2.715 13.59 7.6 .1 35.79 ± 7,57 Total Gas Date 2.004 26.48 ± .14 Maximum Date (950CC) 12.4 29.49 ± .13 Minimum Date (700°-750C) 7.8 24,0 ± .33 382 67. Sample 87MZ249/56/DD8; Graphitic phyllite; Muscovite; 55.91 mg; Measured 40Ar/Ar - 298.9; J-value .00745 ± .25% (la); 345ll5' N latitude; 73°0055" E longitude Temp 40Ar Ar F 3Ar/37Ar %40Ar %Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 500 .36687 21114 1.738 32.51 73.0 5.9 23.20 ± .25 600 .82631 45588 1.813 29.69 64.7 12.8 24.20 ± .13 650 .92924 51042 1.821 32.94 89.5 14.4 24.30 ± .09 700 1.06387 58671 1.813 58.21 87.9 16.5 2421 ± .07 750 1.37391 75221 1.827 155.33 91.2 21.2 24.38 ± .11 800 .48502 26804 1.810 83.03 80.4 7.5 24,16 ± .23 850 .30801 16853 1.828 54.11 73.1 4.7 24.40 ± .36 900 .54393 29247 1.860 145.94 84.4 8.2 24.82 ± .20 950 .58344 30740 1.898 154.49 79.1 8.7 25.33 ± .15 Total Gas Date 1.824 24,35 ± .14 Plateau Date (600-85O°C) 77.2 24.28 ± .17 383 68. Sample /87M283/55/DD8; Graphitic phyllite; Muscovite; 50.1 mg; Measured 40Ar/Ara - 298.9; J-value - .00745 ± .25 (la); 34°49'15" N latitude; 73°0205" E longitude Temp 40ArR ArK F Ar/37Ar %40Ar ZAr Apparent Age and Error (CC) (Ma at 1 sigma) 500 .19670 04884 4.027 3.08 58.8 1.6 53.33 ± 1.31 600 .32917 14001 2.351 1.19 76.1 4.7 31.32 ± .57 650 .36284 16246 2.233 .57 76.5 5.4 29.77 ± .28 700 1.02562 42842 2.394 2.18 70.9 14.3 31.89 ± .13 750 1.02268 43043 2.376 10.86 88.7 14.4 31.65 ± .16 800 1.12264 48231 2.328 25.87 91.8 16.1 31.01 ± .09 850 .76523 31360 2.440 17.34 80.5 10.5 32.50 ± .23 900 .58447 22477 2.600 14.70 69.4 7.5 34.61 ± .23 950 1.31280 51871 2.531 19.70 89.4 17.3 33.70 ± .12 1000 .81996 23289 3.521 14.22 83.1 7.8 46.71 ± .24 1050 .47645 01223 38.942 1.48 74.5 .4 459.53 ± 3.73 Total Gas Date 2.678 35.63 ± .20 Preferred Date (700-800C) 44.8 31.52 ± .13 384 69. Sample 87MS824/l8/DDl0; Sheared tourmaline granite; Muscovite; 90.2 mg; Measured 40Ar/Ar - 298.9; J-value - .00706 ± .25% (la); 34°52'OO" N latitude; 7259'40" E longitude Temp 40ArR ArK F Ar/37Ar %40ArR %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 600 .58467 .27754 2.107 162.32 44.6 1.7 26.63 ± .17 700 1.83513 .82740 2.218 319.68 66.8 5.2 28.03 ± .12 750 2.70393 1.17130 2.308 452.67 69.2 7.4 28.16 ± .09 800 5.12608 2.18746 2.343 99999.99 72.0 13.8 29.60 ± .11 850 6.54134 2.81049 2.327 1441.58 80.4 17.7 29.40 ± .08 900 5.08268 2.20297 2.307 1004.68 77.6 13.9 29.15 ± .09 950 5.20907 2.20360 2.364 1796.05 78.6 13.9 29.86 ± .08 1000 6.46007 2.70905 2.385 534.79 83.6 17.1 30.12 ± .08 1050 2.59825 1.08762 2.389 219.77 91.5 6.8 30.17 ± .17 1100 .63914 .24733 2.584 67.16 93.5 1.6 32.62 ± .39 1200 .57014 .16154 3.529 24.88 92.7 1.0 44.40 ± .36 Total Gas Date 2.351 29.70 ± .10 Preferred Date (750-l050°C) 90.5 29.64 ± .10 385 70. Sample #87MB55/86/DD8; Garnet amphibolite; Hornblende; 315 mg; Measured 40Ar/Ara - 298.9; J-value - .007562 ± .25Z (la); 34°49'45" N latitude; 72°57l0" E longitude Temp 40Ar ArK F Ar/37Ar %40ArR %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 5.77267 .01350 427.678 .69 95.7 .3 2603.48 ±32.77 600 2.84770 .02323 122.601 .95 84.1 .5 1183.46 ± 2.64 650 2.13130 .02152 99.040 1.11 92.0 .4 1008.45 ± 3.36 700 2.31710 .02023 114.524 .75 93.7 .4 1125.36 ± 2.32 750 1.37887 .01192 115.684 .42 88.9 .2 1133.82 ± 5.71 800 .93320 .01436 64.900 .22 82.2 .3 720.33 ± 3.57 825 .50046 .01415 35.367 .16 67.5 .3 427.55 ± 4.27 850 .59486 .02031 29.287 .06 71.3 .4 360.90 ± 3.59 875 .63980 .04032 15.870 .17 69.8 .8 204.45 ± .90 900 1.35542 .13403 10.113 .24 78.5 2.8 132.93 ± .58 925 2.61626 .26797 9.763 .23 83.0 5.5 128.50 ± .53 950 11.74637 .84032 12.492 .19 94.8 19.4 162.84 ± .43 975 27.97591 1.62302 17.237 .13 96.3 33.5 221.03 ± .58 1000 4.39690 .31539 13.941 .15 82.3 6.5 180.81 ± .48 1025 3.14420 .20009 15.714 .13 78.5 4.1 202.56 ± .53 1050 7.07314 .49034 14.425 .15 89.6 10.1 186.77 ± .53 1100 5.47222 .38206 14.322 .18 87.9 7.9 185.51 ± .49 1150 1.76300 .12506 14.097 .17 67.6 2.6 182.74 ± .99 1200 1.45737 .09646 15.108 .17 64.2 2.0 195.16 ± .75 1400 1.30441 .08467 15.406 .17 60.2 1.7 198.79 ± .93 Total Gas Date 17.653 226.04 ± .66 Maximum Date (975CC) 33.5 221.03 ± .58 Minimum Date (925°C) 5.5 123.50 ± .53 386 71. Sample i87MB55/86/DD9; Garnet amphibolite; Biotite; 16.6 mg; Measured °Ar/Ara 298.9; J-value .02354 ± .25% (la); 34°49'45" N latitude; 72°57'lO" E longitude Temp ArR ArK F Ar/37Ar %40ArR %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .18395 .08364 2.199 7.64 29.9 1.2 91.06 ± 1.87 600 1.54764 .52053 2.973 46.08 83.1 7.7 122.04 ± .36 700 5.70765 1.47500 3.870 139.88 91.7 21.8 157.27 ± .42 750 2.32637 .53969 4.311 91.22 95.8 8.0 174.35 ± .46 800 1.31687 .28997 4.541 52.69 95.5 4.3 183.23 ± .77 850 1.22482 .25851 4.738 18.95 95.3 3.8 190.75 ± 1.01 900 1.34856 .28855 4.674 7.74 95.4 4.3 188.29 ± .50 950 3.79127 .82146 4.615 6.97 96.6 12.1 186.06 ± .51 1000 5.91245 1.24644 4.743 1.89 97.6 18.4 190.96 ± .50 1050 4.42571 .86978 5.088 6.02 98.3 12.9 204.09 ± .54 1150 1.88501 .32305 5.835 4.70 97.9 4.8 232.19 ± .67 1300 .28018 .04654 6.020 1.46 76.8 .7 239.10 ± 5.01 Total Gas Date 4.428 178.89 ± .54 Maximum Date (1150°C) 4.8 232.19 ± .67 Minimum Date (500°C) 1.2 91.06 ± 1.87 387 72. Sample #87MB60/84/DD8; Amphibolite; Hornblende; 230.6 mg; Measured 40Ar/Ara 298.9; J-value - .007559 ± .25% (la); 34°4930" N latitude; 72°57'25" E longitude Temp 40Ar Ar F Ar/37Ar %°ArR %Ar Apparent Age and Error (°) (Ma at 1 sigma) 500 4.98606 .00327 1524.358 .38 91.3 .1 4559.68 ± 17.32 600 1.44151 .00544 264.822 .64 86.4 .2 1982.97 ± 15.21 650 .67384 .00497 135.687 .49 59.1 .2 1273.44 ± 8.89 700 2.03774 .01122 181.637 .51 82.3 .4 1558.93 ± 7.07 750 2.50738 .01432 175.037 .33 88.6 .5 1520.60 ± 5.65 800 1.43209 .01391 102.952 .22 82.1 .5 1038.40 ± 4.54 825 .46295 .00751 61.606 .20 58.2 .2 689.70 ± 6.03 850 .36321 .00767 47.357 .16 46.9 .2 552.01 ± 9.87 875 .38221 .01254 30.470 .14 49.4 .4 373.92 ± 7.60 900 .66337 .03622 18.314 .16 51.7 1.2 233.90 ± 1.97 925 .94121 .06693 14.062 .18 65.1 2.2 182.23 ± .79 950 2.84013 .22147 12.824 .20 82.0 7.2 166.91 ± .56 975 4.92601 .33743 14.599 .18 87.8 11.0 188.84 ± .50 1000 9.09502 .50527 18.000 .15 90.2 16.4 230.14 ± .60 1025 14.65265 .65655 22.318 .12 93.0 21.4 281.23 ± .72 1050 8.49969 .39183 21.693 .12 87.6 12.7 273.92 ± .70 1075 2.12614 .11658 18.237 .13 62.1 3.8 232.97 ± .67 1100 4.11023 .21371 19.232 .12 74.9 7.0 244.87 ± .75 1150 5.68038 .28813 19.714 .14 55.2 9.4 250.59 ± .65 1200 2.57418 .13226 19.463 .14 73.3 4.3 247.61 ± 1.24 1250 .38510 .01778 21.659 .14 22.2 .6 273.53 ± 3.71 1450 .20729 .00875 23.683 .15 9.9 .3 297.09 ± 8.63 Total Gas Date 23.095 290.27 ± .87 Maximuni Date (1025°C) 21.4 281.23 ± .72 388 73. Sample 87MB60/8l/DD9; Amphibolite; Riotite; 18.7 mg; Measured 40Ar/Ar - 298.9; J-value - .024374 ± .25% (la); 344930' N latitude; 72°5725" E longitude Temp 40ArR Ar F Ar/37Ar %40ArR %3Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .27818 .11385 2.443 12.38 45.9 1.2 104.36 ± 2.73 700 10.29280 2.33485 4.408 176.70 93.9 23.8 184.11 ± .49 750 4.22971 .89212 4.741 242.06 98.5 9.1 197.28 ± .52 800 2.57456 .53786 4.787 178.38 98.0 5.5 199.07 ± .54 850 2.71164 .56685 4.784 80.05 98.0 5.8 198.96 ± .54 900 3.59673 .76151 4.723 38.17 97.7 7.8 196.57 ± .52 950 5.42806 1.15124 4.715 17.30 98.3 11.7 196.25 ± .52 1000 5.79952 1.21914 4.757 4.79 98.7 12.4 197.91 ± .53 1050 5.95906 1.23201 4.837 17.79 98.7 12.6 201.05 ± .53 1300 5.06845 .98972 5.121 24.00 98.0 10.1 212.19 ± .56 Total Gas Date 4.688 195.19 ± .54 Preferred Date (750°-l050C) 64.9 198.15 ± .54 389 74. Sample 87MB6l/88/DD8; Basalt dike; Whole rock; 368.4 mg; Measured 40Ar/Ara - 298.9; J-value - .007679 ± .25% (la); 34°50'30" N latitude; 7258'30" E longitude Temp °Arf ArK F Ar/37Ar %40ArR %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 3.02242 .00273 1108.049 .05 64.9 .1 4062.98 ±44.52 600 3.82759 .01188 322.125 .05 63.2 .4 2246.32 ±10.82 700 6.51193 .04603 119.740 .05 66.1 1.6 1176.31 ± 4.08 800 4.61284 .10936 42.181 .05 58.2 3.7 506.18 ± 1.64 900 12.05812 .65445 18.425 .12 57.3 22.4 238.72 ± .62 950 14.41047 1.19998 12.009 .24 54.4 41.0 159.13 ± .42 1000 4.67878 .28195 16.594 .14 49.2 9.6 216.37 ± .57 1050 9.80832 .46352 21.161 .04 54.2 15.8 271.62 ± .75 1300 5.74239 .15795 36.357 .02 48.8 5.4 444.18 ± 1.09 Total Cas Date 21.747 278.60 ± .74 Maximum Date (950°C) 41 159.13 ± .42 390 Neotethys and Kohistan Island Arc Terraries 75. Sample 87MB400/52/DD8; Fuchsite schist; Fuchsite; 39.5 mg; Measured 40Ar/Ara - 298.9; J-value .00755 ± .25% (10); 35°04'40" N latitude; 72°44'55" E longitude Temp 40ArR ArK F 39Ar/37Ar %°ArR ZAr Apparent Age and Error (SC) (Ma at 1 Sigma) 400 .02299 .00495 4.645 6.89 14.2 .1 62.18 ± 9.32 500 .05938 .00964 6.157 8.69 41.3 .1 81.97 ± 4.05 600 .26222 .04547 5.766 17.00 58.8 .6 76.88 ± 1.38 700 .93355 .15224 6.132 54.41 70.0 2.2 81.64 ± .44 750 1.21691 .20067 6.064 129.39 88.1 2.8 80.76 ± .42 800 3.42204 .56494 6.057 219.91 88.9 8.0 80.67 ± .23 850 13.92004 2.26284 6.152 153.56 93.0 32.0 81.90 ± .22 900 9.06186 1.47285 6.153 201.98 93.4 20.9 81.91 ± .22 950 8.99636 1.45403 6.187 70.97 93.8 20.6 82.36 ± .22 1000 2.74166 .43222 6.343 24.85 93.4 6.1 84.39 ± .25 1050 1.11778 .17580 6.358 33.96 89.1 2.5 84.59 ± .54 1100 .73977 .11874 6.230 29.28 86.7 1.7 82.92 ± .40 1200 .87344 .13927 6.272 14.88 88.0 2.0 83.46 ± .23 1400 .18406 .02818 6.531 6.60 62.0 .4 86.84 ± 1.90 Total Gas Date 6.167 82.10 ± .26 Plateau Date (850°-950C) 73.5 82.03 ± .22 391 76. Sample #87MB401/54/DD8; Garnet amphibolite; Hornblende; 311 mg; Measured 40Ar/Ar 298.9; .3-value .007636 ± .25% (la); 3505'40" N latitude; 7257'l0" E longitude %a9Ar Temp 40ArR ArK F Ar/7Ar %40Ar Apparent Age and Error (G) (Ma at 1 Sigma) 500 .39679 .02362 16.801 .27 15.8 1.4 217.76 ± 1.81 600 .18493 .02486 7.439 .50 10.1 1.5 99.67 ± 3.81 650 .11179 .01337 8.361 .48 6.5 .8 111.64 ± 4.01 700 .14482 .01148 12.614 .39 7.7 .7 165.89 ± 2.49 750 .09276 .00926 10.013 .28 5.3 .5 132.91 ± 8.49 800 .11986 .01832 6.541 .12 5.7 1.1 87.92 ± 3.09 825 .08970 .01218 7.367 .08 3.6 .7 98.73 ± 9.77 850 .14277 .00972 14.693 .02 3.6 .6 191.83 ± 3.91 875 .11339 .01033 10.981 .03 3.9 .6 145.26 ± 7.08 900 .46666 .04672 9.989 .06 12.0 2.8 132.60 ± 2.24 925 1.53050 .16136 9.485 .06 25.4 9.6 126.14 ± .53 950 1.68342 .18366 9.166 .06 24.9 10.9 122.04 ± 1.00 975 2.58309 .30637 8.431 .06 21.0 18.2 112.56 ± .33 1000 .99709 .12616 7.904 .08 9.6 7.5 105.72 ± .41 1025 .41730 .04500 9.273 .07 4.8 2.7 123.41 ± 1.81 1100 2.92777 .33584 8.718 .06 35.8 19.9 116.26 ± .39 1250 3.06775 .34731 8.833 .07 59.6 20.6 117.75 ± .33 Total Gas Date 8.941 119.14 ± .80 Preferred Date (1100°-1250°C) 40.5 117 ± .36 392 77. Sample #87MB401/53/DD8; Garnet amphibolite; Sodic mica; 36 mg; Measured 40Ar/Ar - 298.9; J-value - .00748 ± .25% (10); 35O5'40" N latitude; 72°57'lO" E longitude Temp 40ArR Ar F Ar/37Ar Z°ArR %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 600 .05325 .02115 2.517 5.13 24.6 6.1 33.65 ± 4.06 700 .15935 .04020 3.964 3.04 25.3 11,5 52.71 ± 1.40 750 .29216 .05785 5.050 2.59 44.8 16.6 66.89 ± .90 800 .46266 .08116 5.700 2.28 39.3 23.3 75.33 ± .60 850 .17737 .03340 5.310 1.83 28.8 9.6 70.27 ± .87 900 .06938 .01309 5.299 1.06 24.2 3.8 70.12 ± 2.52 950 .10308 .01864 5.529 .73 27.3 5.3 73.10 ± 1.36 1000 .11621 .01842 6.308 1.44 33.3 5.3 83.17 ± 1.92 1050 .16394 .02628 6.238 1.36 32.8 7.5 82.27 ± 2.11 1100 .24685 .03868 6.382 1.59 45.6 11.1 84.12 ± 1.38 Total Gas Date 5.286 69.95 ± 1.59 Maximum Date (l000°-llOO°C) 23.9 83.33 ± 1.80 Minimum Date (600°C) 6.1 33.65 ± 4.06 393 78. Sample #PaklO/l0/D03; Kalam quartz-diorite; potassium feldspar; 35.7 mg; Measured 40Ar/Ar - 300; J-value - .009422 ± .25 (la) 35l5'l5" N latitude; 72l5'l5' E longitude Temp F Ar/37Ar Z40ArR %Ar Apparent Age and Error (°C) (Ma at 1 Sigma) 500 .44529 .05412 8.228 125.42 63.8 .4 134.70 ± .59 600 .80791 .27638 2.923 126.50 83.0 2.1 49.01 ± .21 700 .93015 .52950 1.757 71.93 65.7 4.0 29.61 ± .13 750 .46795 .46522 1.006 171.52 83.9 3.5 17.02 ± .07 800 .78629 .57156 1.376 135.69 88.4 4.3 23.23 ± .10 850 .69694 .47932 1.454 102.54 87.1 3.6 24.55 ± .10 900 .60254 .35954 1.676 129.55 84.6 2.7 28.26 ± .12 950 .99724 .53462 1.865 109.13 86.3 4.0 31.43 ± .13 1000 1.76341 .85182 2.070 134.49 89.5 6.4 34.85 ± .15 1050 2.31026 1.01515 2.276 194.29 92.0 7.6 38.27 ± .16 1100 3.23864 1.33554 2.425 277.76 92.5 10.0 40.75 ± .17 1150 5.56699 2.10033 2.651 416.77 91.8 15.8 44.50 ± .19 1200 9.90197 3.40317 2.910 749.55 91.8 25.5 48.79 ± .21 1250 3.46957 1.18296 2.933 763.36 85.6 8.9 49.18 ± .21 1350 .27517 .10723 2.566 152.98 44.9 .8 43.10 ± .18 1450 .13237 .05576 2.374 140.62 17.2 .4 39.91 ± .52 Total Gas Date 2.431 40.86 ± .8 Maximum Date (1200°-1250°C) 34.4 48.99 ± .21 Minimum Date (750C) 3.5 17.02 ± .07 394 79. Sample #PaklO/3/D03; Kalam quartz-diorite; Hornblende; 374.4 mg; Measured 40Ar/Ara 300; J-value 00955 ± .25% (1a); 35°15'l5" N latitude; 72°l5'lS' E longitude Temp 40ArR ArK F 39Ar/37Ar Z°Ar %Ar Apparent Age and Error (CC) (Ma at 1 Sigma) 450 .13174 .01616 8.151 .37 4.4 .2 135.23 ± .68 500 2.27124 .07951 28.564 .30 46.0 .9 435.14 ± 1.65 600 1.13442 .07194 15.769 .44 30.3 .8 253.06 ± 1.01 650 .49799 .07136 6,978 .55 17.3 .8 116.39 ± .48 700 .49282 .07217 6.828 .40 12.6 .8 113.96 ± .47 750 .63714 .07903 8,063 .22 11.2 .9 133.81 ± .55 800 .76137 .07771 9.798 .12 12.7 .9 161.37 ± .93 850 3.36729 .31270 10.769 .14 35.4 3.6 176.59 ± .72 900 17.04900 2.45240 6.952 .21 91.5 28.2 115.96 ± .48 925 10.70185 1.91429 5.590 .22 94.0 22.0 93.83 ± .39 950 5.74121 1.10181 5.211 .21 89.1 12.7 87.61 ± .37 975 2.74270 .52565 5.218 .21 69.4 6.0 87.72 ± .37 1000 2.93829 .55348 5.309 .20 75.2 6.4 89.22 ± .37 1025 2.46079 .43953 5.599 .17 83,4 5.1 93.96 ± .39 1050 2.15954 .33244 6.496 .13 79.0 3.8 108.58 ± .45 1100 3.40874 .51232 6.654 .15 81.2 5.9 111.13 ± .46 1150 .39566 .05592 7,076 .14 48.6 .6 117.97 ± .50 1200 .32919 .01651 19.936 .11 40.6 .2 314.39 ± 4.50 1250 .09748 .00492 19.811 .10 25.2 .1 312.60 ±12.33 1450 .75231 .01352 55.645 .11 36.4 .2 768.85 ±27.63 Total Gas Date 6.672 111.44 ± .52 Maximum Date (950°-975°C) 18.7 87.67 ± .37 Note: SampleJ Pak5, D, SN1, and E were collected by Lawrence W. Snee and 395 sample # 5JLOO7C, 5JLO12C, 5JL042, 5JL049B, and 5JL059B were collected by Robert J. LaFortune during 1986, and were prepared and dated by Mirza Shahid Baig. Lawrence W. Snee provided 40Ar/Ar data for sample PaklO, Pak9, and Pak8. Rest of the samples were collected during 1986-1987 and were prepared and dated by Mirza Shahid Baig during 1987-1989. All of the rock samples were collected from the fresh bed rock. Appendix 2. Measured production ratios for Ca- and K-derived argon isotopes for the U.S. Geological Survey TRIGA reactor, Denver. Determination of production ratios is based on analysis of irradiated salts K,SO (for K-derived argon) and CaF2 (for Ca-derived argon). Analytical precisions are available from the author. Irradiation (37Ar/39Ar)K (38Ar/39Ar)K (40Ar/39Ar)K (39Ar/37Ar)Ca(36Ar/37Ar)Ca (38Ar/37Ar)a package DD8 2.20x103 1.30x102 6.27x103 6.73x104 2.64x104 3.17x105 DD9 4.48xlO l.30x102 1.26x102 1.25x103 2.55x104 6.91x105 DD1O 2.00x1O' 1.32x102 1.29x102 7.48x104 2.74x104 4.90x105 DD12 1.82x104 1.30x102 9.07x103 6.99x104 2.66x104 2.75x105 397 Appendix 3. Major element chemistry of granitic rocks of the Besham block. Analytical precisions are available from the author. Unit Darwaza Sar Lahor Jabrai Karora Karora Karai Ranial name. potassic sodic granite biotite biotite biotite sodic granite granite gneiss granitegranite granite granite grneiss gneiss pegmatite Sample (87MS473) (87MS450) (87MS691) (87MB47) (87MB47A) (87MB380) (87MB2) Mo. Si02 71.82 74.12 65.66 73.40 74.14 76.1 67.0 Al203 13.19 12.6 13.7 15.5 15.1 13.7 18.41 FeOT 4.26 3.94 6.93 1.15 0.76 0.55 2.15 MgO 0.64 0.27 1.18 0.28 0.22 0.13 0.79 CaO 1.27 0.29 3.70 1.66 1.15 0.66 2.83 Na20 2.78 4.08 2.82 6.30 5.59 5.10 5.69 K20 5.30 4.36 4.38 1.47 2.85 3.57 2.54 Ti02 0.55 0.24 1.33 0.13 0.09 0.03 0.42 P205 0.11 <0.05 0.22 <0.05 0.06 <0.05 0.10 MnO 0.03 <0.02 0.07 <0.02 <0.02 <0.02 <0.02 Total: 99.85 99.97 99.99 99.96 99.96 100.24 99.91 Note: Sarnpes were collected by Mirza Shahid Baig during 1986-1987 and analyzed by U.S.G.S. at Denver, U.S.A.