Structure and Geochronology of Pre-Himalayan and Himalayan Orogenic Events in the Northwest Himalaya, Pakistan, With
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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,