The Salt Range and Potwar Plateau are part of the active foreland fold-and-thrust belt of the Himalaya in northern Pakistan. In this region the distance from the Main Boundary Thrust (MBT) to the front of the fold-and-thrust belt is very wide (100-150 km) because a thick evaporite sequence forms the zone of d6collement. Recem studies have combined seismic reflection profiles, petroleum exploration wells, Bouguer gravity anomalies, and surface geology to construct cross sections in the eastern, central, and western Salt Range-Potwar Plateau areas. In this study the sections are compared with a model that considers the mechanics of a fold-and-thrust belt to be analogous to that of a wedge of snow or soil pushed in front of a bulldozer (Chappie, 1978; Davis et al., 1983; Dahlen et al., 1984; Dahlen, 1984). Models which include the effects of evaporites at the base (Chappie, 1978; Davis and Engelder, 1985) suggest that these thruat belts will have (1) narrow (< 1') cross-sectional tapers, (2) larger widths than areas not underlain by evaporites, (3) symmetrical structures, and (4) changes in deformational style at the edge of the evaporite basin. The section across the eastern Potwar Plateau most closely resembles this latter model, having (1) a taper of 0.8' + 0.1', (2) a width of 100-150 km, (3) thrust faults that verge both to the north and south, and (4) structures rotated 30' counterclockwise with respect to the Salt Range. From the observed taper and pore fluid pressures of the eastern Paper number 7T0572. 0278-7407/88/007T-0572510.00 Potwar Plateau, estimates of the values for the yield strength of the evaporites (Xo) and the coefficient of internal friction of the overlying wedge (!,t) are calculated as x o = 1.33-1.50 MPa and !,t = 0.95-1.04, which are then applied to the other cross sections. In the central and western sections a basement uplift, the Sargodha High, interferes with the front of the fold-and-thrust belt. This feature causes the ramping of the Salt Range Thrust and produces a relatively steep basement slope (2'-4') beneath the Potwar Plateau. This dip, in the presence of the weak evaporite d6collement, is sufficient to provide critical taper; no topographic slope is necessary, and the thrust wedge of the southern Potwar Plateau is pushed over the d6collement without significant intemal deformation. The northern Potwar Plateau is strongly folded and faulted, yet the topographic slope remains flat. Although the deformation suggests that evaporites are not present there, the observed taper in the northern Potwar Plateau is best fitted by the model with evaporites at the d6collement. Combining this with published paleomagnetic and geologic constraints, a model for the evolution of the northern Potwar Plateau suggests that the area deformed as a steeply tapered (3.5'-5.5 ø) thrust wedge until approximately 2 million years ago, when the southward propagating d6collement encountered the evaporites. Between 2 Ma and the present, the northern Potwar Plateau has been pushed along the salt d6collement wi...
The Sulaiman foldbelt is an active tectonic feature on the northwestern margin of the Indian plate. Seismic reflection data have been combined with surface geological mapping and drill hole 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 anticlines 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 Cretaceous shales. A steep and highly elevated zone immediately to the west of the frontal folds is interpreted to be underlain by a passive‐roof duplex. The culmination wall of this oblique duplex is separated from the overlying roof sequence by a passive‐roof thrust in Lower Cretaceous shales. The roof‐thrust has a backthrust 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 portion of 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‐Neogene 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 ophiolites and flysch deposits overthrusted on Late Cretaceous shelf strata.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.