AN ABSTRACT OF THE THESIS OF Mansoor Humayon for the degree of Master of Science in Geology presented on March. 13. 1990. Title: Structural Interpretation of the Eastern Sulaiman Foldbelt and Foredeep. .

Abstract Approved: Redacted for Privacy

Robert J. Lillie

The Sulaiman foldbelt is an active and conspicuous tectonic feature on the northwestern margin of the Indo-Pakistani plate. Seismic reflection data have been combined with surface geological mapping and drillhole data to interpret the structural style and tectonic shortening of the eastern Sulaiman foldbelt and its adjacent foredeep. The data show that the basement is more than 8 km deep near the deformation front and that it deepens towards the west. The foredeep adjacent to the eastern Sulaiman foldbelt is a broad synclinal structure, with a steep western limb; the more gentle eastern limb has monoclinal dips from near zero to 2.5°.Several salt-cored are observed on the eastern part of the monocline, but the salt structures are lacking in the western foredeep and in the frontal part of the Sulaiman foldbelt. The basal decollement under the Sulaiman lobe lies either in ductile Eocambrian salt, or within a deep zone of other material that undergoes ductile behavior. Near the deformation front, ramps from the basal detachment become flats in lower Triassic and lower shales. A steep and highly elevated zone immediately tothe west of frontal folds is interpreted to be underlain by apassive-roof duplex. The culmination wall of this oblique duplex is separatedfrom the overlying roof sequence by a passive-roof thrust in lower Cretaceous shales. The roof-thrust has a back-thrust sense of movement, relative to the forelandward propagating duplex, and may extend obliquely 100 km into the interior of the foldbelt. Fault- propagation and fault-bend folds are present in the frontal portionof the eastern Sulaiman foldbelt. Palinspastic restoration of a balanced cross-section shows 108 km of shortening in the eastern Sulaiman foldbelt east of the Kingri strike-slip fault. The presence of more than 11 km of pre- strata on top of basement suggests that the Mesozoic rifted margin of the Indian subcontinent may lie beneath the Sulaiman foldbelt. This interpretation is also favored by the presence of and flysch deposits overthrusted on late Cretaceous shelf strata.

APPROVED:

Redacted for Privacy

V Assistant Professor of Geosciences incharge of major Redacted for Privacy

,airman of Department of Geosciences

Redacted for Privacy

Dean of Gradu te School

Date thesis is presented March 13. 1990

TABLE OF CONTENTS

INTRODUCTION 1 REGIONAL TECTONIC SETTING 4 PREVIOUS WORK 7 OBJECTIVES AND METHODOLOGY 8

STRATIGRAPHIC SETTING 12 STRUCTURE AND DEFORMATIONAL STYLE OF THE

EASTERN SULAIMAN RANGE 21 Sulaiman Foredeep 22 Sulaiman foldbelt. 2 5 Detachment Levels 32 Passive-roof thrust and duplex 38 Fault-Bend and Fault-Propagation folds 41 Tectonic Shortening 4 4 NATURE OF THE CRUST UNDER THE SULAIMAN FOLDBELT 48 CONCLUSIONS 53 REFERENCES 55 LIST OF FIGURES

1. Regional tectonic setting of Pakistan 2

2. Tectonic map of the Sulaiman Foldbelt 5

3. Geological map of part of the Sulaiman Foldbelt 10

4. Location map of seismic and well data 13

5.Generalized stratigraphic column of the Sulaiman Foldbelt and Foredeep 15

6.Stratigraphic thickness and lithology changes in the Mesozoic sequence of the Sulaiman region 18

7. Regional pattern of strain trajectories 23

8. Composite seismic section in the eastern part of the Sulaiman Foredeep 26

9.Composite seismic section in the western part of the Sulaiman Foredeep 28

10. Structural Cross-Section X-Y 30

11. Detailed and retrodeformed Cross-Section A-A 33 12.Plot of strength versus depth and temperature of different rocks 35

13.Examples of passive-roof thrust and duplexe 39

14.Schematic development of passive roof thrust and duplex....42

15.Scematic diagram showing oblique relation between passive-roof and duplex sequences 45

16.Relative positions of Sulaiman Range and Salt Range/ Potwar Plateau on a modern passive margin 51 STRUCTURAL INTERPRETATION OF THE EASTERN SULAIMAN FOLDBELT AND FOREDEEP, PAKISTAN

INTRODUCTION

Foreland fold-and-thrust belts are active and conspicuous tectonic features of convergent continental plate boundaries, and are very important areas for the exploration of hydrocarbons. The Himalayan orogenic belt is the largest continental convergent zone presently active; as a result of underthrusting of the Indo-Pakistani craton beneath its own sedimentary cover, several fold and thrust belts have formed (Fig.1). These belts are more than 100 Km wide along a series of lobes in Pakistan (Salt, Sulaiman, and Kirthar Ranges), in contrast to India, where the width of the fold and thrust belt is less than 50 Km (Fig.1). Detailed studies of structural style have recently been published for one of these lobes, the Salt Range/Potwar Plateau (Lillie et al, 1987; Baker et al, 1987; Jaume and Lillie, 1988; Pennock et al, 1989). The work presented in this paper is the first step of a similar study of the eastern portion of the Sulaiman lobe and adjacent foredeep, as part of a joint project between Oregon State University (OSU) and the Hydrocarbon Development Institute of Pakistan (HDIP). Approximately 1900 Km of seismic profiles, along with gravity, surface and well data, have been supplied to OSU by HDIP, the Oil & Gas Development Corporation (OGDC), and the Geological Survey of 2

Figure 1.Regional tectonic setting of Pakistan (modified from Stonely,1974; Powel1,1979; Kazmi and Rana, 1982). Note the position and lobate shape of the Sulaiman Range on the western edge of the Indo-Pakistani subcontinent. Also note that the width of the foldbelt in India is very smallas compared with the widths of foldbelts in Pakistan. The shelf edge along the western margin of India bends toward the north near Karachi, and is truncated by the east -west zone. The western passive margin of India extends below the alluvium of the Indus plain and the Kirthar and Sulaiman foldbelts, as evidenced by the Cambay (C) and Kutch (K) grabens, the Talhar horst and grabenzone (TFZ), and the basement highs of Kandkot and . Large arrow shows the general convergence of Indo-Pakistani subcontinent relative to Asia. JB= Jacobabad basement high; MK= Mari- Kandkot basement high; SG= Sargodha basement high. Rectangle indicates the area covered in Fig. 2. 3

60° 70° 80°

30°

20

Figure 1 4

Pakistan (GSP). These data were used to construct structural cross sections in the area of current hydrocarbon interest near the deformation front, and to interpret the structural style, depth to basement and overall crustal structure in the interior of the foldbelt (Fig. 2). Similar data are being used by Ishtiaq Jadoon, a Ph.D student at OSU, for a companion study of the southern portion of the Sulaiman lobe.

REGIONAL TECTONIC SETTING

The Indo-Pakistani subcontinent is interpreted as having separated from Australia and Antarctica about 130 Ma ago and migrated northward, closing the Tethys sea. After consumption of Tethyan along a north-dipping subduction zone, continental crust of the Indo-Pakistani plate collided with Asia about 50 Ma (Powel1,1979). This collision has resulted in the rise of the Himalaya, along with the development of several fold-and-thrust belts that now flank the northern and western margins of the Indo- Pakistani plate (Fig. 1). In Pakistan, the northern boundary of the Indo-Pakistani plate remains a (i.e. in the area of Salt Range and Potwar Plateau), while oblique collision with the Afghan Block formed the Sulaiman and Kirthar Ranges in a transpressional zone on the northwest and west, respectively (Fig. 1). The western boundary of the Sulaiman Range is demarcated by a suture zone through the Zhob valley (Fig. 1 and 2), which consists of a discontinuous belt of ophiolites (Abbas & Ahmed, 1979; Gansser, 5

Figure 2. Tectonic map of the Sulaiman Foldbelt (modified from Kazmi and Rana, 1982). Line A-A'shows the location of the cross sections of figure 11-A and Line B-B' shows the location of the cross section being prepared by Jadoon et al (in prep). Lines C-C' and D-D' are the locations of the cross sections made by Banks and Warburton (1986). Line X-Y shows the location of Fig. 10. Rectangle is the area covered in Fig. 3. 68° 70° 72° 32°

D.I. KHAN

C.1\-% =7":-=-- -- - i>.1",\ 'Cs...... //AI NUMMI 1111W41// /AMEN M LI MB H mamirsil MNIMAIIIII M11111:1111W1/111 111.1111111MW /1 111111J1111/1111111W14111

44:011P-Irw'r--.:51.11111M11111111= MUM NM MOM 1111111111111M b.-I irr., LOR ALAI NEM IL NOM Ban INOMENII ONNIMMIN NEM r 0.9 EIT 74 ME= I WWI MOM smosill111111111MIIIIMIN 'MU Wall= IIIIIIMIIIIIMiki:11111111111111=1111111=11111111111=111A01111111/ 30° /MI MI Illk a IIIMIIIIIIIIWIEMMININ111111611WAM1111/2 Pi MOW MINI MUM MI '-'1= MN= Ell MEW: 111111IIII* 11111111e 1=111111111 I MU/ 1111111101111111=1111M11111100i MEM% Mid D.G. KHAN JIM MI MI MI NB MI MEM MMI MINSIIIPMNIIII30 vim r ,,,, SIMMINIIII Ma ma Noommisem11111411/7.LWAINININWIllX ammimm JandraAMMON AIIIIM111111111111/ 411111MILtt!r- Sakhi SIBI 101111111IMMIIIP ''111111M111/4M1/ /11111EMIIMIIIVA -J1110.1111111NININEWAIII.1111111111011/ S or war -'4111111MUI1111;i1111111111111M 111111M1111111111/4111111111111C 111111111111111111111111P211111111M.1111 AO iENNI NMI.= MN MEM IMF Marot-1 ct =111 11111111-11111111 111 NEWNEW mulsammymmrNMI summimenar 21111=1111., MU 1111111=1/1111 MIIII=1/ MUM,. III WM I I V IR 11111.1111/ MOLASSE IP IN (-RECENT) 11111111111WIMI-11 11111UPF IIIIIII FLYSCH ( LOWER IIIIINIWAIWIA111111111 r=_-1LOWER MIOCENE ) 111IMMIIMIILI 11111111111111111. EOCENE- 0 100 km FAULTS MINEMNIMIOMR A I 11111-1111=111111111 OPHIOLITES CROSS 28° B' SECTIONS Figure 2 0) 7

1979; Farah et at, 1984) and Mesozoic sedimentaryrocks interrupted by numerous faults, unconformities, and facies changes(Jones, 1961). Currently this suture is not active (Farah et al,1984).Instead, the Chaman strike-slip zone, to the west, connects thenorthern Himalayan convergence zone with the Makran convergence zonein the south, where oceanic crust of the Arabian plate isbeing subducted (Farah et at, 1984). The eastern and southern boundariesof the Sulaiman Range are marked by broad folds abuttingalluvial deposits of the Indus river system, which flows through the activeHimalayan foredeep (Fig. 1 and 2).

PREVIOUS WORK

Blanford (1883), Oldham (1890), and La Touche (1893) did early reconnaissance work in the Sulaiman Range (as citedby Eames,1952). Paleogeographic and stratigraphic studies weredone on Cretaceous/ rocks of the Sulaiman Range by Davies(1939), and Pinfold (1939). Eames (1952) worked out the basicstratigraphy in the Fort Munro and Zindapir structures in the easternSulaiman Range. The Hunting Survey carried out major reconnaissancemapping (1:253,000 scale), mainly using aerial photos and supplimentedwith field checks (Jones, 1961). Abdel Gawad (1971) andRowland (1978) interpreted the shape and gross structure of the Sulaimanlobe with the help of satellite images. Hemphill and Kidwai (1973)mapped the northern part of the Sulaiman Range at the scale of 1:250,000and recognized some strike-slip and thrust faults. Sarwar and DeJong (1979) interpreted the arcuate shape of the Sulaiman lobe; they 8 considered the lobe a thin-skinned structure, moving along a decollement thought to lie within Eocambrian evaporites. Gansser (1979), Abbas and Ahmed (1979), Allemann (1979) and Asrarullah et al (1979) have described the various features of the Zhob Valley ophiolites. Banks and Warburton (1986) proposed a passive-roof duplex model to explain the frontal portions of the Sulaiman and Kirthar Ranges (Fig.2). Wells (1984) and Waheed and Wells (in press) carried out sedimentological and paleocurrent studies in the northeastern part of the Sulaiman Range. Ahmed et at (1987) and Malik et at (1988) discussed the petroleum potential and prospects of the Sulaiman foredeep. Lillie et at (1989) and Jadoon et at (1989), have explored the possibility of the presence of thin transitional or oceanic crust beneath the Sulaiman Range, through gravity modelling and by the comparison of the thickness of the platform sequence in the Sulaiman and Salt Ranges. A great deal of work has been done on the Sulaiman Range by GSP, HDIP, OGDC, and other oil companies; results of some of this work were available for this thesis.

OBJECTIVES AND METHODOLOGY

The objectives of the overall Sulaiman study are as follows: 1. Determine the fundamental decollement level (or levels) for the fold- and- thrust system. 2. Determine the depth of the basement as it descends beneath the Sulaiman Range. 9

3. Interpret the structure within the overlying deformed section. 4. Examine the nature of deformation and mechanics responsible for the deformation. 5. Determine the thickness and nature of the crust beneath the sedimentary section in the Sulaiman lobe. 6. Interpret the history of development and destruction of the northwestern margin of the Indo-Pakistani plate in the vicinity of the Chaman transform zone. This thesis focused on objectives (1), (2), and (3) for the eastern part of the Sulaiman Lobe and its adjacent foredeep. A similar thesis is being undertaken by Ishtiaq Jadoon (in prep.) for the southern part of the Sulaiman Lobe. Observations and interpretations from these theses provide important constraints for the more regional studies addressing the other objectives, namely mechanics of thrusting (Davis and Lillie, in prep.), crustal structure (Khurshid (in prep.), and tectonic evolution (Jadoon et al, in prep.; Lillie et al, 1989). The objectives for this thesis were addressed through analysis of the following data sets: Surface Mapping In the project area surface geological mapping was available in bits and pieces. However, there were some crucial gaps between different maps and these maps were not of the same scale. A composite geologic map was prepared on 1:250,000 scale by integrating the available geological mapping and then filling the gaps with the help of field work (during Fall of 1988), aerial photographs, and Landsat images (Fig. 3). 10

Figure 3. Geologic map of part of the Sulaiman Foldbelt. Line AA' is the location of the cross section of figure 11-A. Compiled from the mapping of GSP, OGDC, and the Hunting Survey Report (Jones, 1961). 11

31° 70000' 70°30 00'

30° 30'

re=

MIOCENE AND YOUNGER

EOCENE (Kirthor)

EOCENE (Ghozij)

PALEOCENE

CRETACEOUS

FAULTS ALLUVIUM BOUNDARY 0 15 / CONTACTS -4-- 1 i i i I km PROBABLE CONTACTS1 I Figure 3 12

Seismic Reflection and Well data Approximately 800 km of seismic profiles and information from 13 wells (Fig. 4) were available for the study area. A 250 km long composite seismic time section was prepared and interpreted from the Marot well in the east to the Sakhi Sarwar well in the west (Line X-Y,Fig. 2 and 4). The interpretation is constrained by the stratigraphic information from several wells drilled in the project area (Fig. 4). A depth section was then prepared from this time section. Velocities used for this conversion were mainly obtained from sonic logs of the Marot, Bahawalpur East, Sakhi Sarwar, and Zindapir wells. For the structural interpretation, a detailed cross section was prepared and retrodeformed (Line A-A' in Fig. 2, 3, and 4). Although the overall convergence of the Indo-Pakistani plate with the Afghan block is quite oblique along the section line (Fig. 1), an attempt was still made to balance the detailed cross section. This required the development of a new method of volume balancing a section involving oblique convergence (discussed under tectonic shortening).

STRATIGRAPHIC SETTING

A Permian to sequence of rocks, with few breaks, is exposed at the surface or drilled in the Sulaiman Range (Shah, 1977; Fig. 2, 3, and 5). Sedimentary rocks older than Permian are thought to be in the subsurface (Banks & Warburton, 1986), but this has not been confirmed by drilling. The youngest rocks, of Pleistocene age, are present in the foothills along the eastern and southern edge of the Sulaiman Range (Fig. 2). Surface exposures are generally older towards 13

Figure 4. Location of seismic and well data available for this study. Formation tops for all, and Wire line data for some, of the wells shown here were available. The lines shown in boldare the seismic lines used in Fig. 8, 9, and 10. Lines A-A' and X-Y show the location of Fig. 11-A and Fig. 10, respectively. 0°00, 71°00' 72°00' 73°00' 51 0 1 I OHODAK I Lela h 2 RODHO 2 1 665-56-2/v W15-AP 815 -SK -30 PANJPIR-1 W15-1314 836 -KBR 07 AFIBAND-1 836-K BR- 21 SARA! SIONU-1.& W15-BF NANDPUR -1 Z IN DA PIR -1 805-SK -22 'e 805-SK -23 CD0

NI ..ei>.TOL A -1 11115 - BA

W15 -0 D.G. Khan

30°00 ARAM PUR -1 SAKHI X SARWAR-1 W15-6 * C..

1\ Gs

WI6 - F V/16-AM *4' W15-0 W16 -AR,. B A I-I AWA L PUR EAST-1 L4: Doha wal pur i. KOTRUM 1 MA ROT-1 /fr, -(,)' W16-AT SH /81306" 5N/8/ SR/81-5074 .1. SH/81-5050 SH /81 -5080 Rajanpur SN /8I- 50 F2 0 20 I I I 29°00. km Figure 4 Figure 5.Generalized stratigraphic column of the Sulaiman Foldbelt and Foredeep. Thicknesses in the foredeep are ranges encountered in different wells. In the foldbelt (F.belt), thicknesses are from exposed stratigraphic sections as given by Shah (1977), and the Hunting Survey Report (Jones, 1961). Interval velocities vary from east to west, hence their range is shown. 16

THICKNESS (m)SEISMICSYMBOLS AGEFORMATIONLITHOLOGYTECTONOSTRATI-FOLD- FORE-VELOCITYUSED IN GRAPHIC UNITS BELT DEEP RANGE OTHER (m/s) FIGURES w}Z o 0 0 o0 Z uj Molasse. 2000 t-u 0 SI WA LIKS Final co llision, uplift 300 2000 0 uj ------OCE - - - and rapid erosion tO tO to n i HC ITARWATA.:.:.:.:':.' sequence 3200 2000 2700 11=11=11MMINI.10f---WOMIIIIDIMIPM=11 --- w .M.1==.011M=1.1111 KIRTHAR Initial collision ...... , w sequence of ...... ,==,...,...... (...) ...... ,...... 0 shallow marine ...... AlleeMODIMIIIM u., GHAZIJ =1M010.11=011.11 rocks 1700 200 2300 ::::-3- C: to to to MIIMOIMM101.11111.1M zw E;]El1;1;E; ...... =...... mrma. DUNGAN 4000 1700 3000 ------r = (.) ------INIMINIMINMPM. 1111MellMINO111111M 0 NOMINIIIMAMMINI.11 MINNIIMINDIMMM UJ '2=4= 111.11==.1=MMIMMI -J RANIKOT 11.111111111 1=1==11=11111=NNOIMINNIMIN CL. 111.1=1111011.11111 =IMMINNIIMMINIIIMINO

PA B Post-rift deposits OM0011313110 117.7.11 OM 0 Ia FORT MUNRO%....."---"":::. MIN.MiNOMMIIMMMMIMI=11 Cr) Mall.NIMMIIIIMMNIM D mom,...... IMAlw.i..ffil,M.m 0 MUGHALKOT-r-i-x-r-x-x-x-m Passive 0 0 2700 Uiu ______continental margin illOIMII11.1111MEMOD to to to s-i-x-x-xxx. sequence Cr PA R H a_i_x_i_x_x_z_i deposited during 1900 1500 4600 r..) -x-i-x-x-x-x drift of India

GORU . .... SEMBER :':' .11.1MMINI=1 (..) CHILTAN 01111."--*,,-,%r MIMOMMIMPIN.NO 0 100

Figure 6.Stratigraphic thickness and lithology changes in passive continental margin sequence (Mesozoic) of the Sulaiman Foldbelt and Foredeep. Note the increase in carbonates and deeper water shales from east to west in the Jurassic sequence. Thicknesses shown in the westernmost column are taken from several measured sections in the area aroud , , and Khuzdar. Blank portion in the Zindapir well accounts for the projected thickness of Triassic in that area. Note the change of fades from deeper water marine (west) to near-shore (east) in the Jurassic. Right hand column under Quetta-Loralai area shows the symbols used in other figures. For well and city locations see Fig. 2 and 4. 19

WEST EAST SULAIMAN FOLDBELT 10,14$ SULAIMANFOREDEEEP

QUETTA-LORALAI ZINDAPIR SARAI SIDHU AREA WELL WELL 0 km :: 1= =I K 11111rIIMellr MM.= MI M11,==MI ON. MUMr-110-11r- 1 km 111 K -1 I ......

MI MI ON MO IMI1 2 km --1=11= - -- MD MO 01MOW 111,111111,

101 =I =I MI MI =I MD

MAN M=IIMI 3 krn ANIMIM =MOM= INIMM 11,MI. MID J

4 km ? 111111=la 1111161=-10 11 Il

, , , e arnsrowm. 5 km .111=1 IM1 Tr

6 km MOB IMI IMINPMb =Wan= =I =I1M =I ......

7 km APPROXIMATE HORIZONTAL SCALE 00.0=4600:=80 km

Figure 6 20 to the south, on the west coast of India. Basin studies by Biswas (1982) and refraction studies by Naini and Talwani (1983), along with other geophysical evidence from gravity, magnetic and reflection studies, also suggest that this margin is a rifted continental margin. Paleocurrent studies by Waheed and Wells (in press) in the eastern Sulaiman Foldbelt suggest a pre-orogenic, west facing, open marine shelf during late Cretaceous time. Sedimentation during the Paleocene/Eocene is marine, but its nature is more towards shallow, shelf facies. Paleocurrents also changed from westward in the late Cretaceous to more eastward in the Paleocene/Eocene (Waheed and Wells, in press), indicating the initial collision between India and Asia and emplacement along Zhob suture. At about the same time (53 m.y. ago), a sharp decrease in the rate of northward movement of India (from 15 cm/yr to 5 cm/yr) also suggests the initial collision of India with the Kohistan- (Powell and Conaghan, 1973; Quittmeyer et al, 1979). The main collisional tectonics responsible for the development of the Sulaiman Foldbelt, in response to which the Sulaiman Foredeep was formed, started during the middle Eocene. Marine sedimentation, which remained restricted in the southern part of the Sulaiman foldbelt and foredeep area during the , ceased dramatically during Miocene. From the Miocene onward, continental environments prevailed, as shown by the thick molasse deposits of more than 8000 meters in the Sibi Trough area (Movshvitch and Malik, 1965). This great thickness of Siwalik Group rocks represents high uplift rates of the Himalayan source area (0.8 to 1.0 m/1000 yr, Zeit ler, 1980) and 21 high subsidence and sedimentation rates in the foredeep (0.8 to 1.0 m/1000 yr, Mehta, 1980, and Barndt et al, 1978). The stratigraphic setting described above suggests that the area now underlying the Sulaiman Foldbelt and Foredeep was a partof the stable craton (Gondwana) from late Proterozoic to late Paleozoic. Breakup of Gondwana started in early Mesozoic; the passive margin on the western margin of the Indian subcontinent was formed during middle to late Mesozoic. The northern margin of the subcontinent (Himalaya-Salt Range/Potwar Plateau) experienced a head-on collision with Asia, while the northwestern margin (Sulaiman and Kirthar Range) collided with the Afghan block in an oblique fashion, during the Oligocene to Recent. The Mesozoic margin appears to be in an early stage of collision in the Sulaiman Range, in contrast to the area north of the Salt Range/Potwar Plateau, where the passive margin apppears to have been completely deformed as a result ofhead-on collision.

STRUCTURE AND DEFORMATION STYLE OF THE EASTERN SULAIMAN RANGE

Six of the available seismic lines were used to construct a composite seismic profile from the Marot well in the east to the Sakhi Sarwar well in the west (Fig. 4). Farther west (beyond the frontal folds of the eastern Sulaiman Range), no seismic or well data exist and the 22 only available constraint is the surface geological mapping (Fig. 2, 3 and 4). Selection of the cross section line was made by keeping in view the best use of seismic and well control, and keeping the section perpendicular to structural trends. Although the overall tectonic transport direction of the Sulaiman fold-and-thrust belt trends approximately SIVE (determined using the "bow and arrow rule" of Elliot, 1976), the tectonic strain trajectories show a diverging fan type pattern (Fig. 7). The cross section line was kept parallel to the strain trajectory passing through the eastern Sulaiman fold-and- thrust belt (Fig. 7). Depth and dip of the basement are very important constraints in the construction of balanced cross-sections. Basement has been drilled in only three wells (Marot, Bahawalpur East, and Karampur; Fig. 4) in the Sulaiman foredeep area; the best data control (in terms of seismic reflection profiles and sonic logs) were from the Marot well. The cross section line passes over the Sakhi Sarwar well near the deformation front, mainly because there is continuity of seismic data between undeformed strata of the foredeep and deformed strata of the foldbelt. This continuity was lacking farther to the north near the Zindapir and Rodho wells, due to crucial gaps in seismic coverage and poor data quality (Fig. 4).

SULAIMAN FOREDEEP: Structurally, the Sulaiman foredeep is a broad syncline with a very gentle, undisturbed eastern limb and a steeper western limb. The eastern limb has monoclinal dips of 10 to 2.50 and is over 200 km wide. In the eastern portion of this 23

Figure 7. Solid lines are strike-slip faults and bold dashed lines and arrows indicate the alignment of the axes of greatest principle strain, deduced from the orientation of fold axes. Line A-A' is location of cross section in Fig.11-A. Note position of Kingri strike-slip fault, at the end of section A-A'. Modified from

Hunting Survey Report (Jones,1961). 24

67° 68° 69° 70° 32°

31° \

/ / \ 29°

FOLD AXES 28° AXES OF GREATEST PRINCIPLE STRAIN 1111=MO 11111 MEM* STRIKE SLIP FAULTS -x x

Figure 7 25 monocline, several salt-cored anticlines have been formed (e.g., Marot structure (Fig. 8). This salt is part of the Eocambrian Salt Range Formation. The average thickness of the Salt Range Formation in this area is about 500 meters, with 100 to 200 meters of salt section.But thickness increases in the cores of anticlines due to the flow of salt from beneath adjacent . In the Marot well an 1143 m thick Salt Range Formation was drilled, including more than 400 meter of salt. The monoclinal structure of the Sulaiman foredeep extends 25 km west of the Indus river, where it is separated from the foldbelt by a syncline (Fig. 9 and 10). The depth of the basement beneath this syncline is about 8 km (-5 seconds, two-way travel time; Fig. 9 and 10). West of the synclinal axis, basement reflections extend off the bottom of the time sections, and therefore can not be traced beneath the Sulaiman Foldbelt. Basement is extended below the foldbelt by extrapolating its dip (2.50) from this point.

SULAIMAN FOLDBELT: The overall structure of the eastern Sulaiman foldbelt is different from that of the central part of the Sulaiman lobe. A sharp contrast in structural trends exists across a left-lateral strike slip fault, known as the Kingri Fault (Fig. 7). The trends of the structures are mainly east-west, more or less perpendicular to tectonic transport direction, near the fault on the west. However, structural trends are N-S to NNE-SSW and quite oblique to the tectonic transport direction on the east side of the fault. It appears that the central Sulaiman lobe has moved farther, in a thin- skinned manner, than the eastern part. Low topographic slope and broad concentric folds near the southern deformational front (line BB' 26

Figure 8. Composite seismic section in the eastern part of the Sulaiman Foredeep. Note the thickenning of evaporites (Salt Range Fm.) under the Marot structure. Truncation of the Jurassic and Triassic by Paleocene unconformity is also clear. Lines SH/80-508 and SH/80-5074 are unmigrated, 12 fold, Vibroseis source, recorded and processed in 1980 by Seismograph Service Ltd. for Pakistan Shell Petroleum Company. See Fig. 4 for location of lines. 27

MAROT -1 A. TD-2596m 0-WEST SH/80-5074 SH/80-5080 EAST ""

...... _ - . - . . - - 1 _ ---

, - - . - _ --- : : . u) 2_ r - -. _ . 77- .:" :" za .. 1 I o B. 0 2km o- +Paleocene ,.71,0a., (1)

1

.

-

2 --:Precambian Basemen . : . . .

Figure 8 28

Figure 9.Composite seismic section in the western part of the Sulaiman Foredeep, near Sakhi Sarwar. Note that basement reflections extend below 5 sec at Sakhi Sarwar. Also note the interpreted absence of evaporites on top of the basement. Lines W15-BP, W15-BD, and W15-Q are unmigrated, 24 fold, vibroseis source, recorded and processed in 1974 by WesternGeophysical Company for AMOCO Pakistan Exploration Co. Dashed lines show speculative interpretation. See Fig. 4 for location of lines. Cr) C\J 0 C\J U)

111

1

1111111

..III 4 I W I 1 I I WI 1 I

I :...), 1 S' 1 I 1--

1 L., I4 I, ,L?J I I.-Tx 1 ILwJ I 1 LI-J Cu: 1 I"' 1ris 1 z I aj 1 I 4L-j-) 1 I

I r6"/ I 1 1 E

co . ilea,fiiit,i; iiiri1.6''''''"..'. 41 7,.4,,v,A4. tt1tp ts, 09 r,)tv,Itfek 1 :q ' 1 1,

,;'i' 1. ! :, ii,,,...,Nhi 0I,111'' 11''. 0 .01,' ,:itl; 'At, 1111 .1:q, ':;':' ''Iiii'l:;:4::r.:

. w(t qii 4 1 ,Ay. li,'4,,

i ?4r, 1 1 Iiii P :' 4. k 0 lit, 114111, h It SIDI .141 s'if c0 Al 1 11811101 1 16, 401111111111111 N 114111111).11 T111\fki-:. VilitillIlivpar itilIf Ill Op ,,,,,WV IPIA1 MOM%Q iti2 MT 'Will tmNarsIt30.1,14, le tontiffeLpp11V141 Iran, ,A0

al!' 1'0 1 ilT 1 11,.11 It ' 'U, ki qi. tittignil I ill\it.r;14.A 1 '1111M1 II Im vin l.6t t I 1 fa 111111Ikt21

IN 11 11111117

INIII 1'l1,wli.Ifi lloya \ my.,),. fp t 1iiir i 0,;(iii,,,, l ,,' I,' ',1 h I 9 ..; ;1W 1,:) .,'...11t i,,,,Ii %:. . ,1, ri.:, 1,

A!. I/. ? ,. li,,/. //,(A,,77:://1/ r:f Oil! "' .,'' 1.: ( !tnq 7,:,.(,:,;:: ,,, I hot Iitglq.111 k11141Plillii;.;.41..?;5'.1,1Pdifel;(4: A lofwg 1 VI ift v ),;(,': /, c,,,N k "('II'' ?:{ ,!!':: ' I"', 01; Q_ \*,ik\I.Ui \'.1c\ V ,,C;`, IiItt, ,. 1,,;It,IICIVNt ,.0, cf :,'I \l',, i ,t(),l' 4 1. ..; ,f qii,,l '' ., : .0i I 1 L,/M1t1'I/. LO $1eCill\ 11 A)1.1 0 1).1.. ' i..11!,:., :i') I Pit :iii,')' r V gliA.)1Mg 74).'':$.r::',:';''g:".;',:(A 0,j?';')':$?'1 t: 'I) qii.A. VOiV.,1,,N; rifil: f ,)t (14. .0*, li.1 0 N ro SCIN0038 30

Figure 10.Structural cross-section from Marot well in the east to Sakhi Sarwar well in the west. For location see Fig. 2 and 4. The depth of the basement is more than 8 Km near the deformation front, east of Sakhi Sarwar well. Original completion log of Sakhi Sarwar well shows that well penetrated the Pab Formation of Late Cretaceous age. But Sonic and Gamma Ray log correlation with other subsequently drilled wells (at OGDC) shows that well stopped in Lower Ranikot sandstone and shale sequence which resembles very closely to the Pab Sandstone. 31

W15-BP W15-BD W15-Q W16-AT SH/80-5074 SH/81-5080

WEST SAKHI SARWAR-1 EAST INDUS MAROT-1 RIVER 0

" / / / /\` MIOCENE + YOUNGER 5 N ,/ /\/_ \ /` , \ \' M EOCENE + PALEOCENE \ \/\1 I 5 / "/ I 1CRETACEOUS r I\: //,,f \/,,/, VERTICAL EXAGGERATION WEST I 1JURASSIC / \'\ NI \ /,/\'\,. \ \/, \''\ EAST ,\,/\/ //\/,. ,./.,,j./ 4X ,\/` v t="--! TRIASSIC +PERMIAN v. / '/,//v\-\' " .\'\/ \iz\i',/N / / \'\',\-\ \/,fz \/s` -s \/1-, 10 z "\\.'/ HORIZONTAL SCALE TRIASSIC +OLDER = CAMBRIAN / - 0 20 km N, \i' \ \ EO CAMBRIAN 10 I t I l- \, , ,N (SALT RANGE FMN.) / \''\' \'''/ , /V//,//v / Vs' \,1,, s s s \ \ N1 jA Al \// BASEMENT BASEMENT

Figure 10 32 in Fig. 2; Jadoon et al., in prep) contrast with higher topographic slope and tighter folds near the eastern deformation front (line A-A' in Fig. 2), consistent with this idea. The farther movement of the central Sulaiman lobe appears to be accomodated by left-lateral motion along several strike-slip faults (including the Kingri fault), and by the formation of a passive roof duplex (explained in detail in the next section) in the eastern Sulaiman lobe (Fig. 2, and 11). The deformation front of the Sulaiman foldbelt shows foreland- dipping molassic strata throughout its length, and no thrust appears on the surface. This suggests that blind thrusts are present in the cores of the frontal folds of the Sulaiman foldbelt, as is the case in the Rocky mountains of Canada (Thompson, 1981). Similar situation exists in the frontal part of the eastern Salt Range/Potwar Plateau, where blind thrusts are present in the cores of anticlines (Pennock et at., 1989). This is in contrast to the central and western Salt Range where the lower most detachment (Salt Range Thrust) appears on the surface (Lillie et al., 1987). Detachment Levels: The Sulaiman lobe has been considered a thin-skinned structure moving along a decollement within Eocambrian salt (Sarwar and Dejong, 1979; Banks and Warburton, 1986). The overall topographic slope (-10) of the Sulaiman foldbelt also favors the possibility of a basal detachment in salt (Davis and Engelder, 1985). However, the nearest evidence for the presence of salt is about 200 km east of the deformation front, in the Karampur well (Fig. 4). Seismic reflection data do not favor the continuation of Eocambrian salt beneath the frontal part of the eastern Sulaiman foldbelt. Salt- cored anticlines, which are very clear in the eastern part of the 33

Figure 11.(A) Structural cross-section in the frontal part of the eastern Sulaiman Foldbelt. Note the steep culmination wall of the passive-roof duplex under the Fort Munro structure. The shapes of horses in the duplex structure are highly speculative due to the absence of seismic data. Also note ramping of the basal detachment to lower Trassic shales near the Kingri fault. (B & C) Partially and fully restored sections showing 78 Km of tectonic shortening. Dash and dot line shows the present topographic level. Eocene, Paleocene,and Cretaceous sequence is hypothetically extended (dashed) over the passive-roof thrust. 34

AREA BALANCED LINE BALANCED

A9

- - _

L'-er

60km SHORTENING -__ . _ (BO km AFTER CORRECTING FOR EXTRA VOLUME) !% . 7 _ , / _ _ I _i - .

SEISMIC a WELL DATA SEISMIC DATA ABSENT PROJECTED FROM N. SEISMIC DATA INCORPORATED S. PLUNGE OF KINGRI FAULT FORT MUNRO STRUCTURE ZINDAPIR ANTICLINE SAKHI SARWAR A .4 -1 MIOCENE and YOUNGER JURASSIC ii" , 0 PALEOCENE and EOCENE TRIASSIC and OLDER 5 CRETACEOUS PRECAMBRIAN BASEMENT 10 78 km SHORTENING _ _

(108 km AFTER CORRECTING FOR EXTRA VOLUME) - - I . j - - 15 -7"- , 11"1:171:"..:/ - . ,- / 7: 7 7. 150 140 130 120 110 100 90 80 70 60 50 40 30 20 0 KILOMETERS Figure 11 35

Figure 12. Strength versus depth and temperature for different rocks.For normal geothermal gradients (20-35oC/Km) limestone is as week as halite or anhydrite at depths bolow 14 Km. From Davis and Engelder (1985). 36

foredeep (e.g Marot structure, Fig. 8), are not seen in the western part of the foredeep on the composite seismic section (Fig. 9). The westernmost of such salt-cored anticlines (seen on seismic line W16- AT) is still 120 km away from the deformation front (Fig. 4). In the light of the above discussion, two possibilities arise: 1) the interior of the Sulaiman lobe is underlain by the Eocambrian evaporites; and 2) the sedimentary section is so thick that its lower part deforms ductily, even if the evaporites are not present. Seismicity data show some activity all along the deformation front as well along the Kingri Fault, while the interior of the lobe appears aseismic (Rowland, 1978; Quittmeyer, 1979; Verma et al., 1980). For the first possibility, it may be the case that the Eocambrian evaporites were deposited in smaller, isolated, intracratonic basins (Kozary et al, 1968). One of these basins occupied the areas of the Salt Range/Potwar Plateau, Jhelum plains, and the eastern portion of the Sulaiman Foredeep, while another was present below the area now occupied by the interior of the Sulaiman Range, possibly west of the Kingri Fault. The area between these two basins, i.e, between the Indus River and the Kingri Fault (Fig. 2), is a narrow belt, for which there is no conclusive evidence for evaporites at the base of sedimentary section. In this case, it can also be argued that the formation of the Kingri strike-slip fault may be the result of the thinning or the absence of the evaporites. As discussed earlier, the central Sulaiman lobe appears to have been moving towards the south faster than the part of the foldbelt that lies east of the Kingri fault. This situation can also be explained by the differential drag model of Davis and Engelder (1985) for the edge of a salt basin. Their model is 37 supported by examples from the Appalachian plateau and theFranklin mountains of northern Canada. For the second possibility, the basal decollement is morethan 14 km deep near the Kingri fault (Fig. 11). Atthis depth, (with normal geothermal gradient) a limestone has a low strength, and may be as ductile as salt or anhydrite (Davis and Engelder, 1985; Fig.12). A number of carbonate horizons are present in the Triassic, Permian, and possibly in the Cambrian strata of the Sulaimanfold-and-thrust belt (Fig. 5 and 6). The average geothermal gradient in theSulaiman Range is 2.50C /100 m (Ahmed et al, 1987), which means thatrocks at the depth of 15 km are at a temperature of more than3500C. At this temperature, not only carbonates, but even the sandstones maybe ductile. Davis and Lillie, in prep, are suggesting a low temperature creep mechanism in the fine grained carbonaterocks, at a depth of more than 15 km. Structural interpretation presented in Fig.11-A is consistent with both of the above possibilities. Specifically, the basal detachment near the Kingri fault would logically step up atthe thinning or absence of salt, or at the shallowing of a potential carbonate horizon in the sedimentary section. The basal decollement ramps up and flattens in the clayey shales and mudstone sequence of the Lower Triassic, near the Kingrifault (Fig. 11-A). The thickness of this sequence ranges from 300 to 500 m (Shah, 1977). Another potential detachment horizon exists withinthe Sember/Goru Formation of Early Cretaceous age, in which several shaly intervals are present (Shah, 1977; Banks and Warburton, 1986). 38

In cross section A-A (Fig. 11-A), this is the uppermost detachment level that includes the passive-roof thrust discussed below.

Passive-roof Thrust and Duplex: Seismic data are of limited value in the structural interpretation of the frontal part of the eastern Sulaiman foldbelt. These data cover only the first line of folds (Sakhi Sarwar and Zindapir structures; Fig. 3), leaving only surface geology to constrain the interior of the foldbelt. To the west of the Sakhi Sarwar and Zindapir anticlines, a steep zone of elevated topography and Cretaceous to Pleistocene exposures is present, without any major structural disturbance (Fig. 11-A). Butler (1982) has termed this type of steep zone a major culmination wall of a duplex structure, and his model has been applied (Banks and Warburton, 1986) to a similar structure in the area of the Kirthar Range, Pakistan (Line DD' in Fig. 2 and 13). In the eastern Sulaiman culmination wall, exposed lower Cretaceous rocks are exposed in this steep zone and are 9 km above their regional level (Fig. 11-A). This 9 km gap can be filled by a duplex, bounded on the top and bottom by detachments, under these abnormally elevated strata. The upper detachment has a back-thrust sense of displacement, relative to the forelandward propagating duplex. This type of fault has been referred by Banks and Warburton (1986) as a passive-roof thrust. It is equivalent to the upper detachment of Jones (1982) in the Alberta syncline at the foothills of the Canadian Rockies (Fig. 13). There is no surface outcrop of such a passive-roof thrust near the culmination wall or above the roof of the duplex in the study area. However it is inferred, by studying the outcrop pattern in the interior of the foldbelt, that the passive-roof 39

Figure 13. Examples of passive-roof thrust and duplex geometry. (A) Cross-section in the Bolan Pass area of the Kirthar Range, Pakistan(modified from Banks and Warburton, 1986; Line DD' in Fig.2). Note the frontal culmination wall of the duplex, separated from overlying rocks by a passive-roof back thrust. Roof sequence is elevated for more than 7 Km from its regional level. (B) Cross-section in the Athabasca Valley, Alberta foothills (modified from Jones, 1982). Fault labeled as "upper detachment" is equivalent to the passive-roof thrust of Banks and Warburton (1986). The roof sequence above this detachment is imbricated by several small back thrusts, which sole out in the main detachment. (C) Cross-section across the southern thrust belt (modified from Suppe, 1983). This situation is more or less similar to the frontal part of the eastern Sulaiman Foldbelt. In this case the auther had surface and well dips, and stratigraphic thicknesses as constrints and no seismic data was available. A passive-roof thrust was infered at a certain potential week zone; the space between the passive-roof thrust and basal detachment (known from nearby structures) was filled by a duplex, made up of several horses. 40

A ESE WNW FRONTAL CULMINATION WALL FORMING PASSIVE ROOF THRUST

O 0 0 0 0 0 o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ° 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00 0 .0 0 0 0 0 0 0 0 0 0 0 O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o a 0 0 0 0 0 0 o o 0 0 0 0 0 0

. 10 km o 3 0 10km O 0 0 0 0 MOLASSE ROOF SEQUENCE DUPLEX SEQUENCE

B UPPER DETACHMENT NE SW

TERTIARY MESOZOIC PALEOZOIC NANLIAO ANTICLINE C NW SE

8km

00 0 5km 00 0 0 O 0 0 0 PLEISTOCENE MIOCENE Figure 13 41 thrust must be present near the base of the Cretaceous sequence in the shales of the Sember/Goru Formation. This means that theroof sequence above the back-thrust is composedof Cretaceous and younger rocks. This roof sequence continues anadditional 80 to 90 km to the NW, making the length of the passive-roof thrust at least 100 km. The interpretation of the position and length of the passive- roof thrust is in conformity with a similar feature developed in the southern Sulaiman lobe (Jadoon et al, in prep.). In the Brooks Rangeof Alaska, a passive-roof thrust sequence extends hundreds of kilometers across regional strike (I. R. Vann; cited in Banks andWarburton, 1986). Similar examples of highly elevated roof sequences in which the underlying space filled with a duplex also exist in the southern Taiwan foldbelt (Fig. 13; Suppe, 1983) and in the northern Potwar Plateau of Pakistan (Baker et al, 1988; Jaswal, in prep). Fig. 14 shows the schematic development of a passive-roof thrust and associated duplex. Fault-Propagation and Fault-Bend Folds: The roof sequence has been disturbed by several foreland-dipping thrusts. These back-thrusts have a small throw and sole out in the passive-roof thrust. Formation of these back thrusts is considered to be related to the additon of horses in the underlying passive-roof duplex (Banks and Warburton, 1986; Fig. 14). The shortening produced by these faults is compensated by folds which resemble fault-propagation folds (Suppe, 1985). The Sakhi Sarwar anticline, which is the frontal fold of the eastern Sulaiman foldbelt, is one example (Fig. 11-A). Seismic reflection data show a foreland-dipping thrust, along which displacement decreases up section (Fig. 9). 42

Figure 14. Schematic development of passive-roof thrust and duplex (modified from Jones, 1982; Banks and Warburton, 1986). The length of the passive-roof thrust increases with the propagation of the underlying duplex. Several smaller back thrusts also develop in the roof sequence above the duplex. Formation of these smaller thrusts is considered to be related with the addition of horses in the duplex. Shortening produced by these thrusts is compensated by the formation of fault- propagation folds. 1, 2, and 3, are horses of the duplex structure; I, II, and III are foreland-dipping small back-thrusts developed within the roof-sequence.In study area, foreland- dipping back-thrust, developedin the Sa lchi Sarwar structure (Fig. 9 and 10) corresponds to III, while back-thrust formed near the Kingri Fault (Fig. 11-A) corresponds to I or II. Also note that the main shortening has taken place with in the duplex sequence; roof sequence has been shortened much lesser. 43

HINTERLAND FORELAND I Passive-Roof Thrust

=11...0 Floor Thrust I .. ,LII ,- - MIIEWL 41=1

II Foreland-Dipping Passive-Roof Thrust Backthrust

...... Figure 14 44

Although seismic data across the Zindapir anticline are of poor quality, a fault-bend origin of this fold is inferred with the help of surface geological maps and field observations (Suppe, 1985; Fig. 11-A). The western limb of this anticline is very gentle in contrast to the steep eastern limb, which seems to be further disturbed by small faults. A low angle ramp should be present beneath the western limb, possibly between the basal detachment (discussed above) and lower Triassic shales (Fig.11-A). A similar structure (Pirkoh anticline), also involving a fault-bend origin, is interpreted in the southern Sulaiman Foldbelt (Jadoon et al. in prep).

Tectonic Shortening: As discussed above, structural trends in the eastern Sulaiman foldbelt are quite oblique to the overall transport direction of the Sulaiman lobe. The culmination wall of the duplex also trends oblique to the transport direction of the lobe, and according to Butler (1982) classification, it falls under the category of "oblique culmination wall". Cooper (1983) has discussed the problem of calculating shortening in a balanced section drawn oblique to structural trends within a fold-and-thrust belt with a regularly varying displacement field and with a single displacement direction. Essentially his method involves making a simple trignometric correction for the obliquity of the section. Such an approach is only partly applicable to the eastern Sulaiman section. In the study area the displacement field is not uniform, and can be divided into three fields (Fig. 15). (1) The portion of the section above the passive-roof thrust has shortened only a small amount, in a direction perpendicular Ithe fold axes of the area. (2) Under the 45

Figure 15. Schematic diagram showing the relation of obliquely moving duplex and overlying roof-sequence. Note the difference in the thickness of duplexsequence (in undeformed and deformed state). Also note that displacement field in passive-roof sequence is almost perpendicular to the section A-A', but it is quite oblique in the duplexsequence. ,N,NN \\ \ \ \ \\ \ \ \ \ \ \ \\\ N N N N N N

''...,:=:`=.7:.:\.\\''\\''=\\\\\=\=\\\\\\\\"W\\\,

,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,N,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,N,,, ,,N,,,,,,,,,

Figure 15 47 passive-roof is a duplex zone formed of several horses which have moved mainly S120E; the accumulation of portions of these horses in an anticlinal stack along the edge of the thrust belt creates the culmination. (3) East of the tip line of the triangle zone is the lowest horse block which forms the frontal folds (Zindapir and Sakhi Sarwar anticlines). This third zone has moved eastward, and it appears that the culmination wall is acting as a thrust backstop (Byrne et al., 1988) that drives the thrust motion. The cross section A-A' is approximately perpendicular to the first and third displacement fields and, therefore the shortening in these fields can be determined by a traditional line balance method. This gives shortenings of 3 and 18 km, respectively (Fig. 11). The situation of displacement field 2 above makes it very difficult to estimate the shortening in the area west of frontal folds, where seismic data are lacking and the cross section is oblique to the duplex structure. However, an attempt was still made to balance the cross section (Fig. 11-B and 11-C). One pin line was placed to the east of the Sakhi Sarwar structure, in the undeformed or very slightly deformed strata. The second pin line was placed on the Kingri Fault, a vertically dipping, strike-slip fault which also marks the boundary between the eastern and central Sulaiman foldbelt. It was assumed that that the motion in displacement field 2 is parallel to the Kingri Fault and also that all motion of the eastern Sulaiman foldbelt takes place east of this fault. Then a two stage restoration was performed. First, an equal area method was used to balance the duplex structure underlying the passive-roof thrust as if motion was parallel to the line of section (e.g., see Dahlstrom, 1969; woodward et al., 1989; Fig. 11). 48

By palinspastically restoring the section, 60 km of tectonic shortening was determined in the eastern Sulaiman foldbelt, east of the Kingri Fault. Next, we performed a volume balance of this shortening to correct for the obliquity (Lawrence and Humayon, in prep). For this estimate we assumed that the area of the duplex under the culmination wall was constant laterally for a short distance, producing width of the cross section. We also separated the portion under the culmination produced by a pile-up of horses from the portion of the eastern Sulaiman foldbelt that translated S120E. The separation of these areas is essentially at the Paleocene/Cretaceous contact (below the passive-roof thrust), onthe west flank of the Fort Munro anticline (Fig. 11-A). Taking into account the range of possible stratigraphic thickness of the duplex sequence, we calculated a restored secton of -90 km for displacement field 2. In summary, after three dimensional correction, the shortening for the eastern Sulaiman section is calculated to be 90 km on triangle zone duplex plus 18 km on the frontal folds, a total of 108 km (Fig.

1 1).

NATURE OF THE CRUST UNDER THE SULAIMAN FOLDBELT

The stratigraphic setting of the Sulaiman foldbelt suggests that the Mesozoic sequences are associated with the evolution of a passive (Atlantic type) continental margin. The northern continental margin of the Indian subcontinent has been almost completely obscured during the head-on collision with Asia; a full thickness continental crust, with 49 a very thin (-600 m) platform sequence (Cambrian to Eocene) on its top, is now underthrusting the Salt Range /Potwar Plateau area (Duroy et al.. 1989; Lillie et al., 1987). In contrast, the stratigraphic thickness of the Mesozoic platform sequence at the deformation front of the eastern Sulaiman foldbelt is 8 km (Fig. 10 and 11). This stratigraphic thickness increases to about 11 km towards the northwest (Fig. 6; Banks and Warburton, 1986). This large thickness of platform rocks on a passive continental margin suggests that during deposition the crust below was relatively thin, perhaps oceanic or at least transitional in nature (Jadoon et at.. 1989; Lillie et at., 1989). Gravity modelling of Bouguer anomalies also reveals that the sedimentary thickening is incompatable with underthrusting of a full thickness continental crust (Lillie et al., 1989; Khurshid, in prep.). A sequence of ophiolites and flysch, present to the northwest of the Sulaiman foldbelt, is thrusted over the Cretaceous carbonates of the Sulaiman foldbelt; this is also an indication of the presence of oceanic crust near the Sulaiman foldbelt. An analogy for this situation has also been documented in the Ouachita Mountains of Arkansas (Lillie et at., 1983). Seismic reflection profiles show the presence of a 15 km thick sequence of flysch and molassic sediments; modelling of Bouguer gravity data suggest that the crust beneath these sediments is thin transitional or oceanic in nature. Furthermore, these Bouguer gravity values for the Ouachitas are similar to those recorded in the Sulaiman foldbelt (Lillie et at, 1989; Khurshid, in prep.). Surface wave studies of earthquake data (Chun, 1986) and spatial distribution and fault plane solutions of mantle earthquakes (Verma et at., 1980) also suggest that oceanic lithosphere might underlie the Sulaiman lobe. Typical structural features of a 50 passive continental margin (normal faults bounding grabens) have been interpreted to underlie the southern Sulaiman and Kirthar foredeep (Malik et al., 1988; Fig. 1); these structures appear to be associated with the onland continuation of the western margin of India (Biswas, 1982; Fig.1). Quadri and Shuaib (1986) infered the presence of oceanic crust beneath the Jacobabad basement high, by studying the magnetic anomalies in that area (Fig. 1). Refraction data studies by Naini and Talwani (1983) show the boundary between continental and oceanic crust lies just west of the shelf edge, off the western shore of India (Fig. 1). These observations, collectively suggest that the northwestern margin of the Indian subcontinent is in an early stage of underthrusting the Sulaiman Range. In contrast, the northern margin of the subcontinent lies at least 200 km north of the Salt Range/Potwar Plateau region; the passive margin there has been highly deformed during collision and underthrusting (Lillie et al., 1989). Fig. 16 shows positions (based on sedimentary thicknesses) of the Sulaiman and Salt Range/Potwar Plateau relative to a modern passive continental margin. This comparison also favors the presence of transitional or oceanic crust below the Sulaiman Range, as compared to a full thickness craton beneath the Salt Range/Potwar Plateau. 51

Figure 16. Position of the Sulaiman Range and Salt Range relative to a modern rifted continental margin. (A) Cross section is generalized depiction of rifted continental margin of the eastern United States (from Grow et al., 1979). (B) The positions of the Salt Range/Potwar Plateau and Sulaiman Range are oriented according to thickness of their passive continental margin sequences. This analogy suggests that the Sulaiman Rannge is in a very early stage of continental collision, while the Salt Range/Potwar Plateau lies on full thickness cratonic crust, more than 200 km from continental edge. W. SULAIMAN E. SULAIMAN POTWAR SALT RANGE RANGE PLATEAU RANGE 4 7 ...... J.....i. 0 . . 2-z-\,1-,_2\-1---j-z_-."-:-,75- .. . 7 ,7 7 :: .,..--.... \ 7, ____ _\ _, \- -\ 10 \ V\ z \ OCEANIC CRUST -.N " \ N-/ N N/ / V \ )-V N---- 'N NCONTINENTAL_\ z I ,N N/ /N-N----/ CRUST \ \ '20

/ \,- \ MANTLE - , \ 30 X V Z\

40 km 400km 300 200 100 Figure 16 53

CONCLUSIONS

1. Seismic reflection profiles reveal that: (A) the depth to the basement near the deformation front of the eastern Sulaiman Foldbelt is 8 Km. (B) Salt-cored anticlines are present in the eastern part of the Sulaiman Foredeep, but absent in the western part as well in the frontal part of the Sulaiman Foldbelt. (C) Fault-bend and fault- propagation folds are present in the frontal part of the Sulaiman Foldbelt. 2. The basal decollement is in the lower most part of the sedimentary section. It present beneath the Sulaiman Foldbelt, Eocambrian evaporates are the most likely candidate: however, the extreme thickness of I he sedimentary section may result in ductile behavior of carbonate rocks at temperatures encountered below 14 km. Near the deformation front, the basal detachment may be within lower Triassic shales in the vicinity of the Kingri fault. An upper detachment may be present in lower Cretaceous shales, hosting a passive-roof thrust. 3. An oblique culmination wall of a duplex structure is recognized under the eastern limb of the Fort Munro structure. This duplex is made-up of several horses of Jurassic and older rocks, and is separated by a passive-roof thrust from overlying Cretaceous and younger rocks. This passive-roof sequence might extend northwestward into the Interior of the range over a distance of about 100 km. 54

4.Palinspastic restoration indicates that approximately 108 km of tectonic shortening has occurred in the eastern Sulaiman foldbelt. east of the Kingri Fault. This shortening is mostly within the duplex sequence: the passive-roof sequence is shortened only for about 3 km. 5.Geologic and geophysical evidence suggests that the transition from continental to oceanic crust underlies the Sulaiman foldbelt. Crust. of the Mesozoic rifted margin of the Indian subcontinent plate may still he intact beneath the region. This situation is in contrast. to the Himalayan foreland of Pakistan, where full thickness continental crust extends at least 200 km beyond the deformation front. 55

REFERENCES

Abbas, G. and Ahmed. Z., 1979. The Muslimbagh ophiolites, in A. Farah and K.A. Dejong, eds.. Geodynamics of Pakistan: Geological Survey of Pakistan,Quetta, p.243-250. Abdel Gawad, 1971. Wrench movements in Baluchistan arc and their relation to Himalayan-Indian ocean tectonics: Geol. Soc. Am. Bull., v. 82. Ahmed. R.. ;Ind All. M., Review of petroleum exploration data and evaluation of sedimentary basins of Pakistan: project report. 2, Hydrocarbon Develop. Inst. Pakistan, Islamabad, 27 pp. Allemann. F., 1979. Time of emplacement of the Zhob valley ophiolites and the Bela ophiolites, in A.Farah and K.A.Dejong, eds.. Geodynamics of Pakistan: Geological Survey of Pakistan, Quetta. Pakistan, p.215-242. Asrarullah, Ahmed. Z.. and Abbas, G., 1979, Ophiolites in Pakistan: in A.Farah and K.A.Dejong, eds.. Geodynamics of Pakistan: Geological Survey of Pakistan, Quetta, Pakistan, p.181- 192. Baker. D.M.. Lillie, R.J., Yeats, U.S., Johnson, G.D., Yousuf, M., and Zamin. A.S.I I.,1987. Development of the Himalayan frontal thrust zone: Salt. Range. Pakistan: Geology, V.16, p.3-7. Banks, C. J., and Warburton, J., 1986, Passive-roof duplex geometry in the frontal structures of the Kirthar and Sulaiman mountain belts, Pakistan: J. Struct. Geol., No. 8, p.229-237. Barndt, J., Johnson. N.M., Johnson G.D., Opdyke, N.D., Lindsay, E.H., Pilbeam, D., and Tahirkheli, R.A.K., 1978, The magnetic polarity 56

stratigraphy ;iiid age of Siwalik Group near Dhok Pathan village, Potwar Plateau. Pakistan: Earth Planet Sci. Lett., v.41, p.355-364. Biswas. S.K.. 1982, Rill basins in western margin of India and their hydrocarbon prospects with special reference to Kutch basin: Bull. Amer. Assoc. Petrol. Geol., v.66, p.1497-1513. Blandford, W. T.. 1883, Geological notes on the hills in the neighbourhood of the Sind and Punjab frontier between Quetta and : Geol. Surv. India Mem., v. 20, p.229-237. Butler, R.W.H.. 1982, The terminology of structures in thrust belts: J. Struct. Geol.. v.4, 1).239-245. Byrne, D. E.. Davis, [).M. and Sykes, L. R., 1988. Loci of maximum size of thrust earthquakes and mechanics of the shallow region of subduction zones: Tectonics, v.7, No.4, p.833-857. Chun, 1986. c ;nistal block of the western Ganga basin: A fragment of oceanic affinity? Sets. Soc. Amer. Bull., v.76, No.6, p.1687- 1698. Cooper, M.A.. 1983, The calculation of bulk strain in oblique and inclined sections: J. Struct. Geol., v.5, p.161-165. Dahlstrom, C. D. A.. 1969, Balanced cross sections: Canad. J. Earth Sci., 6,p.743-757. Davies, L.M., 1939, Geographical changes in northwestern India during Late Cretaceous and Early Tertiary times: Sixth Pacific Science Con Ilsrence proceedings, 6(2), p.483-501. Davis. D.. Si ippe, .J., and Dahlen. F. A., 1983, Mechanics of fold-and- thrust belts and accretionary wedges: J. geophys. Res. 88, p.I153-1172. 57

and Engelder, T., 1985, The role of salt in fold-and-thrust belts: Tectonophysics, v.71 (2), p.67-88. and Lillie, R. J., in prep., Structure and mechanics of the foldbelts of Pakistan: proceed. Conference on Thrust Tectonics, April, 4-6, 1990, Royal Holloway and Bedford New College, Univ. of London, London, U.K. Duroy, Y., Farah, A., and Lillie, R.J., 1989, Subsurface densities and lithospheric flexure of the Himalayan foreland in Pakistan: in L.L. Malinconico and R.J. Lillie, eds., Tectonics of western Himalaya: G.S.A. Spec. paper 232. Eames. F. E.. 1952, A contribution to the study of the Eocene in western Pakistan, The Geology of standard sections in western Punjab and in Kohat district: Quart. J. Geol. Soc. London, v.107 (2), p.173-200. Elliot, D., 1976, The energy balance and deformation mechanism of thrust belts: Royal Soc. London, Philos. Trans., ser. A, v.283, p.289-312. and Johnson, M.R.W., 1980, Structural evolution in the northern part of the Moine thrust belt, NW Scotland: Royal Soc. Edenburg, Transactions, v.71 (2), p.69-96. 1983, The construction of balanced cross sections: Jour. Struc. Geology, v.5, p.101. Farah, A., Lawrence, R. D., and Dejong, K. A., 1984, An overview of the tectonics of Pakistan, in Marine Geology and Oceanography of Arabian Sea and Coastal Pakistan, eds., B.U.Haq and J.D.Milliman, Van Nostrand Reinhold, p.161-176. 58

Gansser, A., 1979, Reconnaissance visit to the ophiolites in Baluchistan and the Himalayas: in A.Farah and K.A.Dejong, eds., Geodynamics of Pakistan, Geol. Surv. Pakistan, Quetta, Pakistan, p.193-214. Grow, J.A., Mattick, R.E., and Schlee, J.S., 1979, Multichannel seismic depth sections and interval velocities over outer continental shelf and upper continental slope between Cape Hatteras and Cape Cod: in J.S. Watkins, L.Montadert, and P.W. Dickerson, eds., Geological and geophysical investigations of continental margins: Amer. Assoc. Petrol. Geol. Mem. 29, p.65-83. Hemphill, W. R., and Kidwai, A. H., 1973, Stratigraphy of the Bannu and Dera Ismail Khan areas, Pakistan: United Staes Geol. Surv. Professional paper, 716B, 36pp. Jadoon, I.A.K., 1989, Lillie, R.J., Humayon, M., Lawrence, R.D., Ali, S.M., Cheema, A., 1989, Mechanism of deformation and the nature of the crust underneath the Himalayan foreland fold-and- thrust belts in Pakistan: EOS, Trans., Amer. Geophys. Union, v.70, p.1372-1373. Lillie, R.J., and Lawrence, R.D., in prep., Balanced and retrodeformed geological cross-section from the frontal Sulaiman lobe, Pakistan: Duplex development in thick strata along the western margin of the Indian plate: proceedings, International conference on Thrust tectonics,April, 4-6, 1990, Royal Holloway and Bedford New College, Univer. of London, London, U.K. Jaswal, T.M., 1990, Structure and evolution of the Dhurnal oilfield, North Potwar deformed zone, Pakistan. Master's Thesis, Oregon State University, Corvallis, Oregon, U.S.A. 62 pp. 59

Jaume, S.C., Lillie, R.J., 1988, Mechanics of the Salt Range and Potwar Plateau: A fold-and-thrust belt underlain by evaporites: Tectonics, 7, p.57-71. Jones, A. G.. 1961, ed., Reconnaissance Geology of part of , ed., A Colombo Plan Cooperative project: Hunting Survey Corporation, Maracle Press, Toronto, Ontario, 550 pp. Jones, P.B., 1982, Oil and gas beneath east-dipping thrust faults in the Alberta foothills: In Rocky Mountain Association of Geologists Guidebook. Denver, Colorado, p.61-74. Kazmi, A.H.. and Rana, R.A., 1982, Tectonic Map of Pakistan, 1:2,000,000: Geol. Surv. Pakistan, Quetta, Pakistan. Khurshid, A., in prep, Crustal structure of the Sulaiman Range, Pakistan from gravity data: M.S thesis, Oregon State Univer., Corvallis, Oregon. U.S.A. Klootwijk, C.T., Nazirullah, A., Dejong, K.A., and Ahmed,H., 1981, A paleomagnetic reconnaissance of northeastern Baluchistan, Pakistan: Jour. Goephysical Research, v.86(B1), p.289-306. Kozary, M.T., Dunlap, J.C., Humphrey, W.E., 1968, Incidence of saline deposits in geologic time: Geol. Soc. Amer. Spec. Paper no. 88, p.43-57. La Touche, T, H., 1883, Geology of the Shirani Hills: Geol. Surv. India, Records, v. 26, p.77-96. Lawrence, R. D. and Humayon, M., in prep., Volume balancing of an oblique cross section with different displacement fields. Leathers, M., 1987, Balanced structural section of the western Salt Range and Potwar Plateau: Deformation near the strikeslip 60

terminus of an overthrust sheet, M. S. thesis, Oregon State University, Corvallis, Oregon, 220pp. Lillie, R.J., Nelson, K.D., Voogd, B.D., Brewer, J.A., Oliver, J.E., Brown, L.D., Kaufman, S., and Vie le, G.W., 1983, Crustal structure of Ouachita mountains, Arkansas: A model based on Integration of COCORP reflection profiles and regional geophysical data: Bull., Amer. Assoc. Petrol. Geol., v.67, No 6, p.907-931.

.Johnson, G. D., Yousuf, M., Hamid Zaman,A.S., and Yeats, R. S., 1987. Structural development within the Himalayan foreland fold and thrust belt of Pakistan,in Sedimentary Basins and Basin Forming Mechanisms, edited by C.Beaumont and A.J.Tankard, Canad. Assoc. Petrol.Geol., Memoir 12, pp. 379-392.

, Lawrence, R.D., Humayon, M., and Jadoon, I.A.K., 1989, The Sulaiman thrust lobe of Pakistan: Early stage undertrusting of the Mesozoic rifted margin of the Indian subcontinent: Geol. Soc. America, Abstract with program, v.21, No.6, p.A318. Malik, Z., Kemal, A., Malik, A. and Bodenhausen, J. W., 1988, Petroleum potential and prospects in Pakistan: International Symposium on Petroleum for the Future, Jan. 28-30, Islamabad, Ministry of Petroleum and Natural Resources. Mehta, P.K.. 1980, Tectonic significance of the young mineral dates and rates of cooling and uplift in the Himalaya: Tectonophysics, v.62, p.205-217. Morley, C.K., 1986, A classification of thrust fronts: Amer. Assoc. Petrol. Geol. Bull., v.70, p.12-25. 61

Movshovitch, E.B., and Malik, A., 1965, Thickness and facies variations of mousse sediments of the Sibi re-entrant, West Pakistan: Bull. Geol. Dept. Punjab University, , Pakistan, v.5, p.31-42. Naini. B.R., and Talwani, M.. 1983, Structural framework and evolutionary history of the continental margin of western India: in J.S. Watkins, and C.L. Drake, eds., Studies in continental margin geology: Amer. Assoc. Petrol. Geol. Mem. 34, p.167-192. Oldham, R. D., 1890, Report on geology and economic resources of the country adjoining the Sind-Pishin railway between Sharig and Spintangi: Geol. Surv. India, Records, v. 23, p.93-110. Pennock, E.S.. Lillie. R.J.. Zamin, A.S.H., and Yousuf, M., 1989, Structural intrpretation of seismic reflection data from eastern Salt Range and Potwar Plateau, Pakistan: Amer. Assoc. Petrol. Geol. Bull., v.73, p.841-857. Pinfold, E. S., 1939, The Dunghan Limestone and the Cretaceous unconformity in nothwest India: Geol. Surv. India, Records, v. 74 (2), p.189-198. Powell, C. M., 1979, A speculative tectonic history of Pakistan and surroundings: some constraints from the Indian ocean: in A.Farah and K.A.Dejong, eds., Geodynamics of Pakistan, Geol. Surv. Pakistan, Quetta, Pakistan, p.5-24. Quadri, V. N. and Shuaib, M., 1986, Hydrocarbon prospects of southern Indus basin, Pakistan: Amer. Assoc. Petrol. Geol. Bull. v. 70, p.730-747. Quittmeyer, R.C., Farah, A., and Jacob, K.H., 1979, The seismicity of Pakistan and its relation to surface faults: in A. Farah and K.E. 62

De Jong, eds., Geodynamics of Pakistan, Geol. Surv. Pakistan, Quetta, Pakistan. p.351-358. Rowlands, D.. 1978. The stucture and seismicity of a portion of the southern Sulaiman Range, Pakistan; Tectonophysics, 51, p.41- 56. Sarwar, G.. and Dejong, K.A., 1979, Arcs, oroclines, syntaxis: The curvature of mountain belts in Pakistan, in A.Farah and K.A.Dejong, eds.. Geodynamics of Pakistan, Geol. Surv. Pakistan, Quetta. Pakistan. Shah, S. M. I., 1979, ed., Stratigraphy of Pakistan: Geol. Surv. Pakistan, Mem. v. 12, 138pp. Stone ly, R., 1974, Evolution of the continental margin bounding a former Tethys: in C.L. Drake and C.A. Burke, eds., The Geology of continental margins: New York, Springer-Verlag. Suppe. J., 1980. Imbricated structure of western foothills belt, south central Taiwan. Petroleum Geology of Taiwan, v.17, p. 1-16. 1983. Geometry and kinematics of fault bend folding: Amer. Jour. Science, v.283, p. 684-721. 1985, Principles of structural geology: Prentice-Hall, Inc., Englewood Cliffs. N.J.. U.S.A. Thompson, R.I., 1981. The nature and significance of large blind thrusts within the northern Rocky Mountains of Canada: in Thrust and Nappe Tectonics: eds., K.R. Mc Clay and N.J. Price, Spec. Pubis. Geol. Soc. London. No.9. Verma, R.K., Bhanja, A.K., and Mukhopadhyay, M., 1980, Seismotectonics of the Hindukush and Baluchistan arc: Tectonophysics. 66. p.301-322. 63

Waheed, A., Wells, N.A., in press, Changes in paleocurrents during the development of an obliquely convergent plate boundary (Sulaiman foldbelt. Sw Himalayas, west central Pakistan): Sedimentary geology. Wells, N. A. 1984, Marine and continental sedimentation in the Early Kohat basin and adjacent northwestern Pakistan: Unpublished Ph.D. Dissertation, University of Michigan, 465pp. Woodward. N.B., Boyer. S.E.. and Suppe. J., 1989, Balanced geological cross sections: An essential technique in geological research and exploration. Amer. Geophysical Union, Short course in geology, v. 6, 132 pp. Zeit ler, P.K., Tahirkheli, Naeser, C.W., and Johnson N.M., 1982, Unroofing history of a suture zone in the Himalaya of Pakistan by means of fission-track annealing ages: Earth and Planetary Science Letters. v. 57. p.227-240.