Mechanics of the Salt Range-Potwar Plateau, Pakistan: A fold-and-thrust belt underlain by evaporites

摘要: The Salt Range and Potwar Plateau are part of the active foreland fold-and-thrust belt Himalaya in northern Pakistan. In this region distance from Main Boundary Thrust (MBT) to front is very wide (100–150 km) because a thick evaporite sequence forms zone decollement. Recent studies have combined seismic reflection profiles, petroleum exploration wells, Bouguer gravity anomalies, surface geology construct cross sections eastern, central, western Range-Potwar areas. study compared with model that considers mechanics be analogous wedge snow or soil pushed bulldozer (Chapple, 1978; Davis et al., 1983; Dahlen 1984; Dahlen, 1984). Models which include effects evaporites at base Engelder, 1985) suggest these thrust belts will (1) narrow (< 1°) cross-sectional tapers, (2) larger widths than areas not underlain by evaporites, (3) symmetrical structures, (4) changes deformational style edge basin. section across eastern most closely resembles latter model, having taper 0.8° ± 0.1°, width 100–150 km, faults verge both north south, structures rotated 30° counterclockwise respect Range. From observed pore fluid pressures Plateau, estimates values for yield strength (τo) coefficient internal friction overlying (μ) calculated as τo = 1.33–1.50 MPa μ 0.95–1.04, then applied other sections. central basement uplift, Sargodha High, interferes belt. This feature causes ramping produces relatively steep slope (2°–4°) beneath Plateau. dip, presence weak decollement, sufficient provide critical taper; no topographic necessary, southern over decollement without significant deformation. strongly folded faulted, yet remains flat. Although deformation suggests present there, best fitted Combining published paleomagnetic geologic constraints, evolution area deformed steeply tapered (3.5°–5.5°) until approximately 2 million years ago, when southward propagating encountered evaporites. Between Ma present, has been along salt deformation, erosion reduced its original nearly level surface.