Timing of Structural Events in the Himalayan Foothills of Northwestern Pakistan

Timing of structural events in the Himalayan foothills of northwestern Pakistan

ROBERT S. YEATS Department of Geology, Oregon State University, Corvallis, Oregon 97331-5506 AHMAD HUSSAIN Geological Survey of Pakistan, Peshawar, Pakistan

ABSTRACT 1985). The timing of structural events from initial contact with Eurasia to the present is critical to an understanding of displacement rates on thrusts The Attock-Cherat Range forms the southern boundary of the in the collision zone. Peshawar basin and includes rocks transitional between metasedi- Late Cenozoic structural history is difficult to resolve in most of the ments of the Lesser Himalaya and foreland-basin strata to the south. Himalaya because uplift has removed younger strata critical to dating The Attock-Cherat Range comprises three fault-bounded structural faults. In northwest Pakistan, however, the Peshawar and Campbellpore blocks which are, from north to south, (1) Precambrian metaclastic intermontane basins intervene between the foreland thrust belt and the strata overlain by unfossiliferous limestone which is itself apparently interior ranges (Figs. 1 and 2). The Attock-Cherat Range is uplifted less overlain by Paleozoic strata with the contact not exposed; (2) unfossil- than are other ranges along strike, and Tertiary strata preserved down iferous flysch of Precambrian(?) age overlain by Cretaceous and plunge in the eastern and western ends of the range contain evidence Paleogene marine strata and Murree red beds at least in part of early critical to structural timing. Miocene age; and (3) unfossiliferous limestone, argillite, and quartzite In the lower Swat Valley, north of the Peshawar basin, the MMT correlated in part to Paleozoic strata in the Peshawar basin, overlain marks the suture zone between an ensimatic island-arc sequence (Kohistan by a Tertiary sequence generally similar to that in block 2. Farther complex) of Cretaceous age to the north and metamorphic and plutonic south, in the Kala Chitta Range, strata of Triassic to Eocene age occur rocks of the Indian continental margin to the south (Fig. 1), including in south-verging folds and thin thrust sheets. The similarity of the metasediments intruded by granitic augen gneiss which may correlate to Tertiary sequences in the Kala Chitta Range and in blocks 2 and 3 the Mansehra granitic terrane dated as 516 ± 6 Ma (Maluski and Matte, demonstrates that the pre-Tertiary sequences were juxtaposed by 1984; H. Maluski in Jan and others, 1981). Farther south, on the eastern faults prior to deposition of the Paleocene Lockhart Limestone. This margin of the Peshawar basin near Swabi and in small inliers within the may coincide with initial contact of the west-northwest-facing passive basin north and east of Nowshera (Fig. 1), Precambrian Tanawal Quartz- margin of India with Eurasia or nearby microplates. Major late Ter- ite is overlain by a sequence of weakly metamorphosed limestone, tiary imbricate thrusting and folding took place prior to uplift of the dolomite, quartzite, and argillite that locally contains early Paleozoic fos- Attock-Cherat Range and to deposition of Peshawar intermontane sils (Fig. 2; Stauffer, 1967,1968a; Pogue and Hussain, 1986). These rocks basin fill of Pliocene-Pleistocene age. The Peshawar basin formed as were metamorphosed prior to the emplacement of the Malakand granite the Kala Chitta Range was faulted south on the Main Boundary thrust around 23 Ma (Maluski and Matte, 1984). (MBT), forcing Siwalik foreland basins still farther south. Late Qua- South of the Peshawar basin, the Attock-Cherat Range is dominated ternary deformation in the southern Peshawar basin occurred along a by slate, less metamorphosed argillaceous and arenaceous strata, and sub- seismically active zone of en echelon, stepped-left faulted pressure ordinate limestone at least in part of Precambrian age. These rocks are ridges that may reflect a subsurface ramp on the older MBT. overlain unconformably by sediments of Pliocene and Pleistocene age in the Peshawar basin and by lower Tertiary foreland-basin strata within the INTRODUCTION range itself. This sequence is in fault contact with unmetamorphosed Mes- ozoic and lower Cenozoic strata of the Kala Chitta Range (Figs. 1 and 3). The Himalaya is the world's youngest full-scale continental collision Farther south, the Kala Chitta sequence is thrust over folded strata of the zone. Evidence of late Quaternary thrusting is found at the southern mar- Kohat Plateau (A. Hussain, unpub. data). In the Kohat Plateau, middle gin of the Himalaya in India (Nakata, 1972), Nepal (Nakata, 1982; Na- and upper Cenozoic molasse deposits (Murree, Siwalik) are underlain by kata and others, 1984), and Pakistan (Yeats and others, 1984), and Eocene limestone, claystone, gypsum and salt, and Paleocene limestone seismicity confirms that underthrusting of the Indian plate is still in prog- and shale; the pre-molasse sequence reaches the surface mainly in salt- ress (Seeber and others, 1981; Ni and Barazangi, 1984). Yet, much of the cored anticlines (Meissner and others, 1974; Wells, 1984). South of a zone deformation of the Pakistan Himalaya is older. Much of the thrusting in in which the Siwaliks dominate in surface exposure, Mesozoic and Ceno- the Potwar Plateau is Miocene and Pliocene (Raynolds and Johnson, zoic strata similar to those of the Kala Chitta Range occur in the Surghar 1985; Burbank and Raynolds, 1987), and farther north, the Main Mantle Range, along with older strata (Meissner and others, 1974). Rocks of the thrust (MMT) may have undergone major displacement -30 Ma, on the Surghar Range are thrust southward over alluvium near the Indus River basis of thermal histories of rocks on opposite sides of the thrust (Zeitler, (J. McDougall, unpub. data; Fig. 2).

Additional material for this article (lithologie descriptions) may be obtained free of charge by requesting Supplementary Data 87-25 from the GSA Documents Secretary.

Geological Society of America Bulletin, v. 99, p. 161-176, 10 figs., August 1987.

161

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/99/2/161/3998258/i0016-7606-99-2-161.pdf by guest on 01 October 2021 Figure 1. Map of Peshawar basin and adjacent areas, adapted from Burbank and Tahirkheli (1985). Geology east of Tarbela Lake from Calkins and others (1975). Lowlands shown by stipple pattern.

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KILOMETERS

Figure 2. Tectonic map of northern Pakistan, showing Salt Range thrust, Murree fault and its suggested western continuation north of the Kohat Plateau (MBT), Panjal fault and its suggested western continuation as Khairabad fault, and Main Mantle thrust. Dotted lines mark subcrop boundaries of west-dipping strata beneath Paleocene in Potwar Plateau and Salt Range. Salt Range control from Gee (1980); Potwar Plateau control from petroleum exploration and production wells (small circles).

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45' 72° 00 E —r EXPLANATION1 Pir Pai • Nowshera V„ 1 Cantt. « | Q |Post-Murree formations n PirânoQ Q S \ I Tm iMurree Form. (mid. Tertiary) Tangi 60 Khwarw Khwar_ \i-Piran | Je |Palgocene 8 Eocene marine strata ]Cretaceous strata N lJurassic strata 1 "ft iTriassic strata /p€ms

lPzPi jlnzari Limestone p€Ps A' "Jallozai 1 |pzph|Hiss(irtang Formation^Paleozoic? |Pzpd|DqrwazaLimestone J

ipCpU |Utch Khattak Limestone! pre- IP6?8 IShahkot a Shekhai Limest.P cam" fP£?31 Dakhner Formation J p€m jManki Formation (Precambrian) •'Shamshattu

Figure 3. Geology of the Attock-Cherat Range, simplified from geologic maps of the 38 0/13, 43 C/l, 43 C/5, and part of the 38 0/9 15-minute quadrangles, 1:50,000, by the Geological Survey of Pakistan. (The city of Attock was formerly named "Campbellpore.") Formations younger than Minrree Formation not mapped separately. A-A', B-B', C-C' are lines of cross sections shown in Figure 8. (Note overlap in center.)

We show that part of the juxtaposition of dissimilar rock sequences in Nizampur basin, the Attock-Cherat Range merges southward into the and adjacent to the Attock-Cherat Range occurred in latest Cretaceous Kala Chitta Range which farther east, comprises the southern margin of time and that major thrusting in the Attock-Cherat Range was completed the Nizampur basin. The Attock-Cherat Range terminates 8 km east of the prior to 2.8 Ma. Indus River, giving way to the Campbellpore basin. The range consists of three east-trending fault-bounded blocks that PREVIOUS WORK contain folds verging to the south; these blocks are bounded by thrust faults that are folded but, in general, dip north. From north to south, these The geology of the Attock-Cherat Range was first described by blocks consist of (1) argillite, slate, phyllite, and subordinate quartzite of Wynne (1873), who considered the slates and associated rocks to be probable Precambrian age intercalated with and overlain by limestone and Paleozoic, on the basis of similarity with the slates of the Hazara region. intruded by diabase, (2) argillite and quartzite of possible Precambrian age Other early workers included Griesbach (1882), Waagen (1884), Mid- intercalated with subordinate beds of limestone and unconformably over- dlemiss (1896), Wadia (1932), and Cotter (1933). The first detailed map- lain by limestone and shale of Cretaceous, Paleocene, and Eocene age and ping was done by Tahirkheli (1970), and stratigraphic sections in the variegated sandstone and siltstone of the Murree Formation, at least in part westernmost part of the area were described by Meissner and others of early Miocene age (Shah, 1977), and (3) limestone, quartzite, argillite, (1974). Pliocene and Pleistocene sediments of the northern flanks of the and local maroon shale, possibly of Paleozoic age, also unconformably range were described by Burbank (1982, 1983) and Burbank and Tahir- overlain by Paleocene-Eocene limestone and shale and Miocene Murree kheli (1985). Formation. Descriptions of formations in these belts and in the Kala Chitta Range to the south are given in the appendix of lithologie descriptions1 and GEOLOGY OF THE ATTOCK-CHERAT RANGE summarized in Figure 4.

The Attock-Cherat Range lies between the Peshawar basin on the 'The appendix may be obtained free of charge by requesting Supplementary north and the Nizampur basin on the south (Fig. 3). At the west end of the Data 87-25 from the GSA Documente Secretory.

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34° GEOLOGY OF THE 00 ATTOCK - CHERAT N RANGE PAKISTAN O 5 10 15

Figure 3. (Continued).

The northern block consists predominantly of the Manki Formation, confusion with the term "Attock Slates" used by early workers for both mainly argillite, slate, phyllite, and subordinate quartzite, part of a low- the Manki and Dakhner Formations. Furthermore, the Mughal fort at the grade metamorphic belt that includes the Hazara Slate to the east and the locality formerly named "Attock" and now called "Attock Khurd" is built Landi Kotal Formation of Khyber Pass to the west (Stauffer, 1968b; Shah on Manki Formation (Fig. 5). Tahirkheli (1970) considered the age of the and others, 1980). The Hazara Slate is Precambrian, on the basis of Rb/Sr flysch sequence to be "somewhere between Middle Jurassic and the Cre- whole-rock ages of 740 ± 20 and 930 ± 20 Ma (Crawford and Davies, taceous," on the basis of fossils in limestone that he considered to be 1975); basal beds of the overlying Cambrian Abbottabad Formation con- interbedded with the flysch. All fossils found by us, including those at tain clasts of Hazara Slate (Latif, 1974). In the Attock-Cherat Range, the Tahirkheli's locality, are in Cenomanian or Paleocene limestone that over- Utch Khattak Formation contains clasts of Shahkot Formation and Manki lies the Dakhner unconformably or is in thrust contact with the Dakhner. Formation and is therefore younger than both. The formations of the At Hasan Abdal, east of the Attock-Cherat Range (Fig. 1), Jurassic lime- northern block are commonly out of normal stratigraphic sequence owing stone lies unconformably on Dakhner Formation and is itself overlain by to thrust faults; their distribution is best explained by a south-verging Paleocene limestone. Hussain (1984) tentatively suggested a late Precam- isoclinal fold with digitations on its limbs (overturned limb next to Khai- brian age on the basis of the lack of correlation with fossiliferous Phanero- rabad fault, normal limb including the Nowshera sequence to the north) zoic strata, the absence of fossils, and the absence of bioturbation in (Figs. 5, 6, and 8). None of the formations in this block resemble the fine-grained strata of the Dakhner Formation. The Dakhner could be Silurian-Devonian sequence north of Nowshera or the sequence between stratigraphically equivalent to the Manki Formation, differing only in the Cherat and Hissartang faults on the south side of the range. The degree of metamorphism. Unlike the northern and southern blocks, the normal, locally gradational contacts between formations in the block and central block contains no intrusions of diabase (Tahirkheli, 1970) except the absence of fossils led Hussain (1984) to suggest that the formations are for one occurrence in limestone east of the Indus River. Two narrow belts all Precambrian. Diabase intrusions are found in this block as well as in the of limestone similar to the Utch Khattak Formation occur as klippen of the Silurian-Devonian sequence to the north. northern block faulted into the Dakhner Formation east of the Indus River The central block is principally underlain by the Dakhner Formation, (Fig. 5). Near the Cherat Cement Company quarry (Fig. 6), and near Dag predominantly argillite, quartzite, and subordinate siltstone and limestone. (Fig. 3), the Dakhner is overlain unconformably by Paleocene Lockhart The quartzite interbeds have characteristics similar to those of deep-water Limestone which is itself overlain by upper Paleocene to lower Eocene deposits, and Tahirkheli (1970) referred to the sequence as "flysch." We Patala Formation and Oligocene-Miocene Murree red beds. The do not retain Tahirkheli's name "Attock Shale" for this formation to avoid Lockhart-Dakhner unconformity is only locally preserved. In most places,

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VERTICAL SCALE

-L500 METERS Murree redbeds Potala Lockhart

Fm. ""f~uTl Utch Khattak a I .1 Shahkot Fms. Inzari La.

Manki Fm.

Hissartang Fm.

Figure 4, Stratigraphic sequences in Surghar Range, Kala Chitta Range, and Attock-Cherat Range. Lockhart Limestone and Patala Formation common to ail but northern block of Attock-Cherat Range, suggesting that pre-Lockhart strata were juxtaposed along Hissartang and Cherat faults prior to Lockhart Darwaza Fm. deposition. Younger strata not preserved in northern block. De- tails of lithology may be obtained free of charge by requesting Supplementary Data 87-25 from the GSA Documents Secretary. SOUTHERN CENTRAL NORTHERN BLOCK BLOCK BLOCK SURGHAR KALA CHITTA ATTOCK- CHERAT RANGE RANGE RANGE

72° 15'

KILOMETERS

Figure 5. Geologic map of Indus River section of Attock-Cherat Range. For explanation, see Figure 3. Additional symbols: pCs, Shahkot Formation; pCu, Utch Khattak Limestone. Mapping near Dakhner based in part on Parvez and others (1986).

the contact is sheared, with Lockhart or Patala in fault contact with the relatively thin-bedded unfossiliferous Inzari Limestone does not corre- Dakhner (Fig. 6). late with the fossiliferous limestone of Silurian-Devonian age composing The southern block consists of a north-dipping homoclinal sequence the upper part of the Nowshera sequence. Both sequences are intruded by that is right side up on the basis of cross bedding in quartzite of the diabase. Overlying the Inzari Limestone on an unconformity marked by Hissartang Formation. The Darwaza Formation consists of limestone laterite, there are the Lockhart Limestone, Patala Formation, and Murree overlain by maroon shale; this is overlain by interbedded quartzite and Formation. North of Mir Kalan, karst topography was locally developed argillite of the Hissartang Formation which is itself overlain by Inzari in the Inzari Limestone prior to deposition of Paleocene strata such that Limestone (Fig. 5). The sequence is correlated, on the basis of lithology, small caves are filled with brown, red-brown, and ocher deposits related to with the Paleozoic sequence north and northeast of Nowshera as re- the basal Paleocene laterite. The southern and central blocks both plunge mapped by Pogue and Hussain (1986). The Darwaza Formation of the westward such that pre-Tertiary rocks of these blocks at the western end of Attock-Cherat Range is somewhat similar to the basal unfossiliferous lime- the map area plunge beneath the Tertiary (Figs. 3 and 7). Less pronounced stone, dolomite, and overlying maroon shale at Nowshera. The Hissartang eastward plunge at the eastern end of the range results in preservation of Formation is similar to the Misri Banda Quartzite at Nowshera except that remnants of Lockhart Limestone (Fig. 5). the Hissartang contains a higher percentage of argillite. On the other hand, The Hissartang fault separates the southern block from rocks of the

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rTF] PATALA FORMATION, s/ s / < LATERITE AT BASE

p€pd (DAKHNER FORMATION

SHEKHAI FORMATION

Figure 6. Geologic map of Cherat Cement Plant and vicinity. Mapping most detailed for Shekhai Limestone and Utch Khattak Limestone, which are used in plant. Most beds in hanging wall of Khairabad fault are in overturned limb of isoclinal fold that was subsequently refolded.

I Kk |KAWAGARH FM.

I Kl iLUMSHIWAL FM.,

[Ju[ JURASSIC STRATA

|feffi|lNZARI LIMESTONE

|PzPF HISSARTANG FM. PALEOZOIC (?)

PzPd DARWAZA FM.

Figure 7. Geologic map of the western end of the Nizampur basin and adjacent area.

Kala Chitta Range; these rocks comprise a relatively complete, largely sections published by Meissner and others (1974), suggests a north-facing shallow-marine sedimentary sequence of Early Triassic to Late Cretaceous continental margin during the Mesozoic similar to that found in the Teth- (Campanian) age overlain by Lockhart Limestone and Patala Formation. yan Himalaya of India and Nepal (Fig. 4). For example, the Triassic Correlation of these formations with their type localities (compare with Tredian Formation of the Surghar Range and western Salt Range includes Fatmi, 1973; Shah, 1977) is straightforward, based on similar lithologies a variegated sandstone that contains ripple marks and a massive, thick- and fossils. Comparison of the Kala Chitta sequence with strata of the bedded white sandstone (Fatmi, 1973), whereas Tredian equivalents in the same age in the Surghar Range to the south, as shown in stratigraphic Kala Chitta block adjacent to the Attock-Cherat Range are carbonate

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rocks. The Jurassic Datta Formation comprises variegated sandstone, displacement on these faults juxtaposing contrasting pre-Lockhart se- shale, and siltstone of continental origin in the Surghar Range, Trans-Indus quences is pre-Tertiary. Salt Range, and v/estern Salt Range, but Datta equivalents adjacent to the The pre-Lockhart age of the Khairabad fault is not demonstrated Attock-Cherat Ra nge are mainly limestone (Meissner and others, 1974). because Tertiary strata are not preserved north of it. The Manki Formation The shallow-marine to nonmarine nature of the Mesozoic sequence north of the Khairabad fault, however, is correlated northeast to the Haz- suggests that these strata formerly extended much farther north than they ara Slate of the Hazara district (Tahirkheli, 1982). In the Hazara district, do now, although their deeper water equivalents are only rarely found the Hazara Slate occurs in two blocks separated by the Panjal thrust fault north of the Hissartang fault. This contrast could be explained by large- (Calkins and others, 1975). No Mesozoic or Tertiary strata are preserved scale telescoping on the Hissartang fault, pre-Paleocene uplift and erosion northwest of the Panjal fault, but southeast of the fault, the Hazara Slate is of the Attock-Cherat Range, or both. The similarity of the Lockhart Lime- overlain by Jurassic and Tertiary strata similar to those in the Kala Chitta stone and Patala Formation in the Kala Chitta Range and Attock-Cherat Range (Calkins and others, 1975). This leads to the suggestion that the Range strongly suggests that juxtaposition of facies and/or uplift and Attock-Cherat Range was once overlain by Mesozoic strata and that the erosion of the Attock-Cherat Range occurred after the deposition of the absence of the deeper water equivalents of the north-facing Mesozoic Upper Cretaceous Kawagarh Formation but prior to deposition of Paleo- continental-margin sequence of the Kala Chitta Range is due to uplift and cene Lockhart Limestone. erosion prior to deposition of Paleocene strata. If south-verging imbricate thrusting immediately preceded the deposi- STRUCTURAL GEOLOGY tion of the Paleocene Lockhart Limestone, then the Lockhart and Patala Formations should show some expression of tectonic loading of the crust Post-Campanian, Pre-Paleocene Deformation by Cretaceous thrust sheets. Basin analysis of Paleocene strata of the Kohat Plateau by Wells (1984), following earlier work by Meissner and Rahman The Paleocene Lockhart Limestone, containing a laterite at its base, (1973), shows an asymmetric foredeep basin with a gentle south flank and rests unconformably on Kawagarh Formation of Coniacian to Campanian a steep north flank receiving sediments from highlands to the north. The age in the Kala Chitta Range, on unfossiliferous Inzari Limestone in the center of the basin in the Kala Chitta Range was euxinic and received southern block of the Attock-Cherat Range, and on flysch deposits of the abyssal shale. The northern edge of the basin, preserved near Dag at the Precambrian(?) Dakhner Formation in the central block (Figs. 3 and 4). western end of the Attock-Chera* Range, was a shelf platform with nodu- The Lockhart Limestone and the overlying Patala Formation and Murree lar micrite and dolomicrite resting directly on Dakhner Formation (Wells, Formation are relatively similar in facies in all three blocks, suggesting that 1984). The Paleocene sequence in the Attock-Cherat Range is very thin in the post-Murree displacement on the Hissartang and Cherat faults is not comparison with that in the Kala Chitta Range (Fig. 4), apparently due to large. The contrast between pre-Lockhart rocks in these blocks argues, its position at the northern margin of the basin. The Murree red beds however, for large pre-Paleocene displacement on these faults, juxtaposing represent the molasse facies of early-formed thrust sheets, migrating the sequences prior to Lockhart deposition. southward with time. It is surprising, however, that the Lockhart, Patala, and Murree Formations do not contain conglomerate beds derived from At the western end of the Nizampur basin, the Hissartang fault can highlands newly formed on the backs of advancing thrust sheets. The be shown in outcrop to separate the limestone, quartzite, and argillite Patala does contain a basal conglomerate containing subangular chert sequence of the southern block of the Attock-Cherat Range from Jurassic clasts possibly derived from strata formerly overlying the Manki strata of the Kala Chitta foreland sequence (Fig. 7). Throughout most of Formation. the Kala Chitta Range, the Lockhart Limestone overlies the Upper Cre- taceous Kawagarh Formation, but close to the Hissartang fault, the Lock- hart locally rests on older strata. This suggests a south dip of the Mesozoic Pre-Pliocene Tertiary Deformation strata of the Kala Chitta Range near the Hissartang fault prior to Lockhart deposition. The Lockhart Limestone can be shown to overlap successively North of the Khairabad fault, the Manki Formation occupies the core older members of the southern block sequence of the Attock-Cherat of an isoclinal fold, both limbs of which are seen along the Indus River Range at its western and eastern ends, in the directions of plunge. North- (Figs. 5 and 8C). Northwest of Attock Fort (Attock Khurd), at the conflu- west of Qamar Mela (Fig. 7), the Lockhart rests on strata as old as ence of the Kabul River with the north bank of the Indus River, Shahkot Darwaza Limestone. Formation rests on Manki Formation, and to the south, Shahkot Forma- The pre-Paleocene unconformity is also evident in the Potwar Pla- tion is preserved in tight synclines. Farther north, the lower Paleozoic teau and Salt Range, where the Lockhart Limestone is underlain by a basal sequence of Nowshera may also be part of the normal limb of this isoclinal Paleocene sandstone, the Hangu Formation. On the basis of mapping in fold although the contact with Manki Formation is not exposed. Farther the Salt Range (Gee, 1980) and on our study of subsurface data from south, adjacent to the Khairabad fault, the Manki Formation overlies petroleum exploration and production wells, the Hangu Formation over- overturned Utch Khattak Limestone. Because of east plunge of the range laps Jurassic, Triassic, and Permian strata in an east-southeasterly direction near the Indus River, rocks of the northern block are preserved farther and directly overlies Cambrian strata in the easternmost Salt Range south there, including two klippen of Utch Khattak Limestone down- (Fig. 2). folded into the Dakhner Formation (Fig. 5). Minimum separation on the In the downplunge direction at the western end of the Attock-Cherat Khairabad fault at the Indus River is determined from cross section as >5 Range, the Hissartang and Cherat faults can be traced as major features km (Fig. 8C). In the western end of the range, near the Cherat Cement only to the western end of exposure of pre-Lockhart rocks (Figs. 3 and 7). Plant (Fig. 6), an overturned sequence of Shekhai Limestone and Utch Farther west, the Darwaza Formation is locally thrust over Lockhart Khattak Limestone is thrust over Patala, Lockhart, and Dakhner Forma- Limestone, but in general, the Hissartang fault is entirely within the Lock- tions along the Khairabad fault which is strongly folded into an anticline hart, and separation is small (Fig. 7). The Cherat fault disappears westward and syncline. Minimum separation on the fault at the Cherat Cement Plant in Murree red beds, and the contact between Dakhner and Tertiary rocks is 1.5 km, on the basis of cross section A-A' in Figure 8. is a folded and thrust-faulted unconformity. This indicates that most of the In the central block, Dakhner Formation dips homoclinally to the

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/99/2/161/3998258/i0016-7606-99-2-161.pdf by guest on 01 October 2021 B B' Figure 8. Structural \\ cross sections of Attock- Cherat Range, with struc- tures projected into section from up-plunge and Kk down-plunge directions. li!W\ A. Cherat Cement Plant ^ lii^xW Indus to west end of Nizampur River basin. B. Wuch Tangi Khwar section east of Ni- zampur. C. Indus River section. No vertical exag- geration; north is to right. Locations given in Fig- ure 3.

/p€?s

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north in all parts of the range except the west end, where it dips west, cut deep gorges through the ranges bounding the Peshawar basin on the down plunge. The unconformable contact with Tertiary strata has been northwest, and they may be antecedent to uplift of those ranges. At Dag sheared locally into a décollement, and in at least two places, west and (Fig. 3), a distinctive white sandstone of apparent northern provenance south of Pallosai, the contact has been displaced by faults down thrown to near the base of the Pliocene-Pleistocene sequence ~2.5 Ma indicates the south. At the east end of the range, Lockhart Limestone is preserved in contribution from the Himalaya by relatively low-gradient, far-traveled several downfolced and faulted synclines (Fig. 5). The Cherat fault over- streams (Burbank and Tahirkheli, 1985). rides an overturned syncline of predominantly Tertiary strata including In the Campbellpore basin, east of and on strike with the Kala Chitta Murree red beds, but west of Qamar Mela and Cherat town, this fault Range, sediments 1.5 m.y. old show evidence of a southern provenance, changes to a series of overturned folds that cannot be traced up section suggesting uplift of the Kala Chitta Range (Burbank, 1982; Burbank and through the Muriee Formation (Fig. 3). This suggests that the post-Murree Raynolds, 1987). The angular unconformity near Rawalpindi dated be- displacement on the Cherat fault, bringing Dakhner Formation over Ter- tween 2.1 and 1.9 Ma may be related to the ponding of the Campbellpore tiary strata, is small in comparison to pre-Lockhart displacement juxtapos- basin starting ~1.8 Ma, and both may be the result of thrusting and ing Dakhner Formation and the southern-block sequence. ramping on the Main Boundary thrust (MBT) bounding the Kala Chitta The southern block consists of more competent strata than does the Range on the south (Burbank and Raynolds, 1987). Internal deformation central block, and this block behaved rather simply in post-Murree time of the Kala Chitta fold-thrust belt predates the Campbellpore basin sedi- except for the development of a bedding thrust and ramp northwest of ments and thus also predates southward thrusting of the Kala Chitta Range Qamar Mela (Fig. 7). This thrust repeats the Inzari Limestone, Lockhart over the Potwar and Kohat plateaus on the MBT. Limestone, Patala Formation, and part of the Murree Formation. It may The deposition of the Peshawar basin fill, including lacustrine depos- have been a blind thrust, giving way to minor overturned folds that cannot its north of the alluvial fans, terminated -0.6 Ma (Burbank and Tahir- be mapped in the Murrees. Up plunge to the east, the Hissartang Forma- kheli, 1985). During the time of deposition of the Peshawar basin and tion is twice its normal thickness, apparently caused by duplication by Campbellpore basin fill, deposition continued in the Siwalik foredeep thrusting, on the basis of distribution of quartzite interbeds. The thrust basin to the south in the Surghar Range and Trans-Indus Salt Range probably flattens out into bedding within the lower part of the Hissartang (Khan, 1983) and to the southeast in the Potwar Plateau (Raynolds and Formation or at (he top of the Darwaza Limestone. Renewed movement Johnson, 1985). Thrusting occurred in the northern Potwar Plateau south on the Hissartang fault brought Darwaza Limestone over Lockhart Lime- of Rawalpindi between 1.8 and. 2.1 Ma (Raynolds and Johnson, 1985) stone, but this displacement is small compared to the pre-Lockhart and in the eastern Salt Range and in the Trans-Indus Salt Range more displacement juxtaposing Darwaza Limestone and Jurassic strata (Fig. 7). recently than 0.6 Ma (Khan, 1983; Yeats and others, 1984). West of the Darwaza exposures, the Hissartang fault is entirely within Late Quaternary Deformation Tertiary strata, and separation is small. East of the Indus River, fossiliferous Jurassic strata are tectonically intercalated with the southern-block After termination of deposition of Peshawar basin fill at 0.6 Ma, four sequence in a schuppenzone (Parvez and others, 1987). en echelon, left-stepping pressure ridges formed within the Peshawar basin, The Kala Chitta block is characterized by imbricate thrusting with close to and parallel to the front of the Attock-Cherat Range to the south relations best preserved in the Nizampur basin and in the hills south of the (Figs. 1 and 3). These ridges are described elsewhere (R. S. Yeats and A. basin through which the Indus River flows westward (Hussain, 1984) Hussain, unpub. data), and only a brief summary is included here. (Figs. 7 and 8B). The northern part of this block is covered by alluvium Peshawar basin fill, dated as 2.8 to 0.6 Ma by Burbank and Tahir- except for limited exposures of Jurassic limestone. Five kilometres north- kheli (1985), is directly correlated only to the westernmost ridge; however, east of Nizampur, Jurassic strata are thrust over Cretaceous Lumshiwal the fill is more or less contemporary with lacustrine deposits, with fanglom- Formation, and the thrust is folded isoclinally (Fig. 8B). Farther south, the erate that has an Attock-Cherat Range provenance, with loosely consol- Kala Chitta foreland sequence from Triassic Mianwali Formation to Eo- idated river gravel that has rounded clasts of granitic rock, and with cene Patala Formation is exposed in a fold-thrust belt including small-scale micaceous gray sand, also fluvial. The fluvial deposits have a northern disharmonie folds, as shown in Figures 7 and 8B and in Hussain (1984). provenance and were probably deposited by the ancestral Kabul River, flowing parallel to the Attock-Cherat Range but closer to it than at pres- Pliocene-Pleistocene Deposition and Deformation ent. Similar deposits were reported by Said and Majid (1977) in the southwestern Peshawar basin. These sediments are widespread in the Pe- As described by Burbank and Tahirkheli (1985) and Burbank shawar basin, and at most localities, they are flat lying. At the easternmost (1982), southward-verging folding and thrusting in the Attock-Cherat ridge, a normally magnetized sequence of repeated graded beds may have Range ended prier to 2.8 Ma when deposition of the Peshawar basin fill been deposited as catastrophic-flood deposits by the Indus River (Burbank, began and, in the Kala Chitta Range, prior to 1.8 Ma when deposition of 1983; Burbank and Tahirkheli, 1985). An angular unconformity within the Campbellpore basin fill began. The Peshawar basin fill, including the this sequence is evidence of deformation during deposition. Jallozai Formation of Tahirkheli (1970), began with low-energy flood- Local steep dips in the Quaternary sediments adjacent to ridge-front plain deposits containing soil zones succeeded by northward-prograding faults indicate that part of the deformation was by folding. The straight alluvial fans with source in the Attock-Cherat Range, indicating that the traces of some of the ridge-front faults are in contrast to the lobate trace of range ponded the basin at that time (Burbank and Tahirkheli, 1985). The late Quaternary thrusts at the foot of the Salt Range and suggest that these axis of the Peshawar basin may have been close to its southern margin, faults are relatively high angle, involving the basement. The left-stepping which cuts diagonally across the northern, central, and southern blocks of pattern of the three ridges suggests that they were formed by oblique-slip the Attock-Cherat Range (Figs. 1 and 3). The Kabul River and Swat River faulting with a component of left-lateral strike slip and reverse slip.

DISCUSSION the Kala Chitta Range and before the deposition of the Lockhart Lime- stone and Hangu Formation of Paleocene age (66.4 to 57.8 Ma) (Figs. 4 Correlation of Tectonic Events: and 9). We correlated this period of faulting with the westward tilting that Latest Cretaceous Faulting predated the deposition of the Hangu Formation in the Potwar Plateau and Salt Range. We have shown that contrasting pre-Tertiary sequences were juxta- This is slightly younger than obduction of Kohistan island-arc crust posed across the Cherat and Hissartang faults after the deposition of the over the Indian plate (75-80 Ma), as based on ages of blueschist meta- Kawagarh Marl of Coniacian to Campanian age (as young as 74.5 Ma) in morphism at the Main Mantle thrust (MMT) (Maluski and Matte, 1984) and rapid cooling following emplacement of the southern intrusive belt of the Kohistan arc (youngest ages 65 Ma, suggested age 75-80 Ma, Zeitler, 1985). This is earlier than the Eocene age of collision of India and Eurasia WNW accepted by many workers, although Klootwijk and others (1985) argued that obduction of the Asian accretionary complex onto the northern margin of India was complete before the Eocene (58 Ma). Klootwijk and others (1985) summarized isotopic evidence that suturing in Ladakh was complete before 60 Ma and stratigraphic evidence that the Asian accre- MESOZOIC" WNW FACING tionary wedge was emplaced onto the leading edge of India by latest Cretaceous or early Paleocene. A change in the Indian apparent polar- PASSIVE MARGIN wander path around 62 Ma may mark the beginning of suturing in the westernmost Himalaya (Klootwijk and others, 1985). The Mesozoic passive margin in northern Pakistan probably faced west-northwest, on the basis of the strike of Mesozoic units prior to Hangu and Lockhart deposition in the Potwar Plateau (Fig. 2). Jurassic red beds ~Kaia .. . r are found in a belt extending from the Surghar Range northeast to the western Potwar Plateau and Hazara, whereas in the Kala Chitta Range to the northwest, equivalent-age strata are shallow marine. The deeper water PALEOCENE equivalents of the Mesozoic are not found. Shallow-water Jurassic and FOREDEEP Cretaceous strata overlie Precambrian metasediments in Hazara, suggesting that they once overlay the Attock-Cherat Range and were removed by erosion prior to deposition of Paleocene strata. If this part of the passive margin faced west-northwest, then the contact with continental rocks to the north may have had a large component of strike slip, in contrast to the passive margin farther east, where N collision was head-on. The pre-Paleocene tectonic event dated in the Siwalik Peshawar AttocK-Cherat Attock-Cherat Range may have been the initial contact of the west- molasse Range intermontane northwest-facing margin of the Indian plate with microcontinents and not (Salt Range) basin its collision with the main mass of Eurasia, which came later. A predominantly strike-slip boundary would have a lesser tendency than a head-on collision to produce mountainous terrain, and this may explain the small percentage of coarse clastic detritus in Paleocene strata of the Kohat foreland basin and adjacent areas as mapped by Wells (1984). The east-west orientation of the Kohat basin may be a distortion caused by telescoping LATE TERTIARY- j across post-Murree, south-directed imbricate thrusts. The undistorted basin could have been influenced by strike-slip faulting with a reverse-slip IMBRICATE THIN-SKINNEDM component. THRUSTING I O" Correlation of Tectonic Events: Figure 9. Evolution of the Attock-Cherat Range. Top: west- Post-Murree, Pre-Pliocene Thrusting northwest-facing Mesozoic sequence, now preserved only in Kala Chitta Range. Center: juxtaposition of major fault-bounded blocks of The Murree Formation of middle Cenozoic age was involved in Attock-Cherat Range with Kala Chitta sequence, followed by creation folding, imbricate thrusting, and local development of slaty cleavage prior of Paleogene foredeep. Bottom: post-Murree, pre-Pliocene imbricate to deposition of the Peshawar basin fill ~2.8 Ma. This tectonic event thrusting, uplifting Attock-Cherat Range and forming Peshawar correlates with the time of major intracontinental underthrusting on the basin. Thrusts may ramp over north-facing basement faults that later Main Central thrust (MCT) and associated imbricate thrusts of India and could propagate to surface as active tectonic zone in southern Pe- Nepal, with Precambrian crystalline rocks thrust over the Lesser Hima- shawar basin. layan sequence. In the Tansen area of western Nepal, the Lesser Hima-

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layan sequence below the MCT includes nummulitic limestone and edge of the Attock-Cherat Range. This deformation is quite different from overlying red becls (Dumri Formation) that correlate with the Dharamsala the low-angle thrusting at the southern edge of the Salt Range described by Formation of northern India and the Murree Formation of Pakistan Yeats and others (1984). Salt Range thrusting does not involve basement (Sakai, 1984). In the Kathmandu basin of Nepal, major thrusting predated rocks but instead passes into a décollement in Eocambrian salt, with the deposition of the Lukundol Formation, a basin fill dated by paleomagnetic underlying basement dipping gently north. The linear traces of faults asso- stratigraphy as Pliocene (Yoshida and Igarashi, 1984; M. Yoshida, 1984, ciated with the pressure ridges north of the Attock-Cherat Range indicate oral commun.). that the faults are high angle, and they probably penetrate downward into high-strength rocks. Moreover, an east-trending zone of seismicity in the Pliocene-Early Pleistocene History Peshawar basin (Seeber and others, 1981) may be associated with the zone of young faults and folds. The left-stepping, en echelon pattern of the Deposition of the Peshawar basin fill was contemporaneous with pressure ridges suggests that they are the surface expression of left-lateral upper Siwalik deposition in the Potwar Plateau and with intra-Siwalik strike-slip faults with a reverse-slip component. thrusting in the northern Potwar Plateau south of Rawalpindi (Raynolds Facies trends of the Pliocene-Pleistocene basin fill and the distribu- and Johnson, 1985), including thrusting and ramping on the MBT (Bur- tion of the late Quaternary pressure ridges are both parallel to the Attock- bank and Raynolds, 1987). Raynolds and Johnson (1985) documented Cherat Range front, suggesting the same underlying cause for both. What the southeastward migration of the Siwalik depocenter, on the basis of caused the ramping of the Attock-Cherat Range along an underlying thrust changes in deposition rates and on the appearance of conglomerate in the fault? Lillie and Yousuf (1986) and Lillie and others (1987) showed that upper part of the Siwalik sequence. The Peshawar intermontane basin fill the central Salt Range was elevated by ramping of the Salt Range thrust was deposited during this migration of the depocenter, ponded by the over a buried, north-facing fault in basement. A similar north-facing fault uplift of the Attock-Cherat Range to the south which itself responded to may have localized ramping of the underlying thrust and ponding of the ramping on a south-verging thrust. Deposition ended in the Peshawar Peshawar basin fill. In late Quaternary time, this zone of weakness in basin at about the same time as it did in the Siwaliks of the eastern Salt basement could have propagated upward to localize the active pressure Range, about half a million years ago. ridges and faults.

Contemporary Tectonics CONCLUSIONS

We find no evidence of faulting during the time of deposition of the Precambrian rocks of northern Pakistan adjacent to the Himalayan Pliocene-early Pleistocene basin fill of the Peshawar basin. Younger fault- foreland fold-and-thrust belt comprise predominantly stratified rocks ing and folding are associated with pressure ridges parallel to the northern rather than massive crystalline rocks. The Hazara Slate, Tanawal Quartz-

Kohat Kala Attock-Cherat Range Nowslhera Peshawar Plateau Chitta Basin Range

Figure 10. Possible configuration of hinterland-dipping duplex of Kala Chitta and Attock-Cherat Ranges and Hazara region. Mz-Eo, Mesozoic to Eocene foreland sequence; Pz, Paleozoic sequence including Silurian-Devonian strata of Nowshera and rocks of southern block, Attock-Cherat Range; pCm, Manki Formation; p€?s, p€?u, p€?sh, predominantly limestones of Precambrian or early Paleozoic age; p€?d, Dakhner Formation. Khairabad, Cherat, and Hissartang faults are assumed to be thrusts of pre-Lockhart age that were reactivated after Murree deposition. Khairibad fault appears to cover the Dakhner Formation and may rejoin the Cherat fault as a roof thrust. Floor thrust is the Murree fault (MBT), but this is of late Tertiary to early Pleistocene age. On the basis of speculated intersections of Paleozoic sequence with faults, the minimum separation on the combined Khairabad and Cherat faults is 22 km and that on the Hissartang fairit is 22 km. Separation on the younger Murree fault is at least 45 km.

ite, Manki Formation, and Dakhner Formation comprise a clastic that we consider the decoupling of the base of the molasse sequence from sequence free of volcanic rocks, with the basement on which this sequence the underlying Phanerozoic sequence of the Potwar Plateau and Salt is deposited not preserved or not recognized. Even the Precambrian inliers Range less important than the décollement in Eocambrian salt between the of the Kirana Hills south of the Salt Range comprise metasedimentary and Phanerozoic sequence and the Precambrian metaclastic basement (Seeber metavolcanic rocks, and the prominent north-dipping seismic reflector and others, 1981; Yeats and others, 1984; Lillie and others, 1987). Their beneath the Potwar Plateau represents the unconformity at the top of this Main Boundary thrust zone corresponds to our Murree fault. To the north, metamorphosed clastic sequence. The crustal structure of the Pakistani we accept the Panjal thrust as mapped by Calkins and others (1975) but part of the Himalayan foreland is comparable to that of an oceanic plateau are unable to recognize the Nathia Gali, Abbottabad, and Mansehra whereas the structure farther east in the Indian foreland is that of a shield thrusts of Coward and Butler (1985). Present mapping by both the British (Chun, 1986). and American teams and the Geological Survey of Pakistan, however, will These are taken as evidence that the passive margin of the Indian undoubtedly modify our preliminary interpretations as well as those of shield faced west-northwest, not north as it did in India and Nepal. Ac- Coward and Butler (1985). cordingly, the first encounter of this part of the margin may have been with Internal deformation of the Attock-Cherat and Kala Chitta Ranges fringing microplates, not the main mass of Eurasia, and it may have been predated deposition of basin fill of the Peshawar and Campbellpore basins, largely by strike slip and subordinantly by convergence. This encounter but southward thrusting of the Kala Chitta Range over the Potwar and produced the juxtaposition of unlike crustal blocks in the Attock-Cherat Kohat Plateaus ponded these basins in Pliocene and early Pleistocene time. Range and the removal by uplift and erosion of nearly all Mesozoic strata Thrusting migrated southward across the Potwar Plateau, forcing the Si- north of the Hissartang fault. Faults bounding major blocks in the Attock- walik depocenter ahead of it, until it reached its present position at the Salt Cherat Range are now low-angle thrusts, but it is not clear whether the Range. juxtaposition of crustal blocks at the end of the Cretaceous was by thrusts The present tectonic setting, in existence for the past 0.6 m.y. in the or by oblique-slip, high-angle faults. Peshawar basin, perhaps longer elsewhere, is thin-skinned thrusting in the If it is assumed that the sequence in the Attock-Cherat Range be- Salt Range and Potwar Plateau and high-angle faulting and localized tween the Hissartang and Cherat faults can be correlated with the Paleo- folding near the southern margin of the Peshawar basin, the latter involv- zoic sequence at Nowshera and that both sequences are part of the Indian ing basement and being characterized by earthquakes. The active deforma- craton, then an estimate can be made of minimum separation on the tion in the Peshawar basin may occur by left slip with a reverse-slip Hissartang and Cherat faults during both the pre-Lockhart and post- component on a basement fault that previously localized the ramp for the Murree tectonic episodes. A pre-Lockhart strike-slip component would older MBT. This tectonic episode includes the rapid uplift of the Tibetan increase the separation. Figure 10 shows a possible reconstruction of an Plateau in the Quaternary (Li and others, 1979) and uplift of the Nanga imbricate thrust stack comprising the Hissartang, Cherat, and Khairabad Parbat massif at rates as high as several millimetres per year (Zeitler, faults. Map relations illustrated in Figures 1 and 3 suggest that the Khai- 1985). This uplift increased the competence of streams draining the Hima- rabad fault is a roof thrust that the Cherat fault rejoins. If the sequence laya such that conglomerate prograded southward during deposition of the above the Hissartang fault is correlated with the Paleozoic sequence near Upper Siwaliks, and gravel characterizes the modern bedload of the Indus Nowshera, a separation of at least 22 km on the combined Khairabad and River. Cherat faults may be calculated from the projected hanging-wall and footwall cutoffs of the sequence. If it is assumed that the Paleozoic se- ACKNOWLEDGMENTS quence underlies the Kala Chitta sequence at depth, then an additional 22 km of separation is calculated for the Hissartang fault. Figure 10 shows This paper could not have been written without the pioneering map- the Paleozoic sequence cut off at its base by the younger Murree fault, but ping of R. A. Khan Tahirkheli of the University of Peshawar, who has the Paleozoic section at depth may be underlain by Proterozoic clastic encouraged us and offered suggestions throughout the project. strata as it is in the Abbottabad region of Hazara. Hussain's mapping of the 38 0/13,43 C/l, and 43 C/5 15-minute The Kala Chitta sequence, already deformed internally, is thrust quadrangles is part of a long-range program of geologic mapping by the southward over the Kohat Plateau sequence, including Eocene evaporites, Geological Survey of Pakistan (GSP) at 1:50,000 scale (Hussain, 1977, on the MBT (A. Hussain, unpub. data). The MBT is correlated eastward 1984; Hussain and others, 1983). The support of Waheeduddin Ahmad, with the Murree fault (Fig. 1), which brings Mesozoic and lower Cenozoic Director-General of the GSP; M. A. Mirza, Director of Planning of the strata of the Margala Hills over strata of the Potwar Plateau north of GSP; and Hassan Gauhar, Director of the Peshawar office of the GSP, is Islamabad, including a great thickness of Murree Formation. The Murree greatly appreciated. John Talent and Ruth Mawson of Macquarie Univer- fault turns northward west of the Jhelum River and forms the boundary of sity conducted the "negative experiment" of searching for fossils in the the Hazara-Kashmir syntaxis underlain by Murree Formation and subja- Shahkot Formation and Utch Khattak Limestone. At various times, cent Mesozoic and Cenozoic foreland strata (Calkins and others, 1975). A.A.K. Ghauri, Said Rahim Khan, A. Imtiaz, Kevin Pogue, and Jim The syntaxis may be considered as a north-plunging anticlinorium folding McDougall accompanied us in the field, and Tahir Karim has discussed his the Murree and Panjal faults, as shown by Coward and Butler (1985). work in the upper Cenozoic deposits of the southern Peshawar basin. Viewed down the west flank of this anticlinorium, the Panjal fault is seen M. K. Parvez, A.A.K. Ghauri, and M. Riaz allowed us to use their to merge with the younger Murree fault, which constitutes the floor thrust unpublished mapping near Dakhner east of the Indus River. The paper of the imbricate stack (Fig. 10). An even deeper thrust, not shown on benefited from reviews by M. P. Coward, R. D. Lawrence, and R. A. Figure 10, is the presently active Salt Range thrust bringing the entire Khan Tahirkheli. Financial support to Yeats was provided by National Phanerozoic section southward over Precambrian basement (Fig. 2). Science Foundation Grants INT 81-18403, INT 86-09914, and EAR Our reconstruction differs from that of Coward and Butler (1985) in 83-18194 and by the Geological Survey of Pakistan.

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