Crustal Structure of the Sulaiman Range, Pakistan from Gravity Data

Abstract

  Gravity data along an east-west profile from the Punjab plain of Pakistan to the western border town of Chaman have been incorporated into interpretation of the gross crustal structure underlying the Sulaiman Range. Interpretation of the free-air, Bouguer, and isostatic gravity anomalies suggests that 15 to 25 km thick, transitional crust underlies the 250 km wide fold-andthrust belt. Thick overlying sediments are compensated by shallow mantle material, which leads to a long wavelength (- 200 krn) Bouguer gravity high in the area. Free-air and isostatic anomalies suggest that high topography in the eastern Sulaiman Range lacks roots, as the Moho apparently shallows beneath the thick (15 km) sediments. In the western Sulaiman Range the topography appears to be compensated by thicker crust.
Interpretation of transitional crust in the region suggests that passive margin structures identified along the western edge of the Indo-Pakistani subcontinent continue under the Sulaiman fold belt, and that the region is at an early stage of continental collision. The crust appears to be deformed under the load of the thrust belt and the influence of horizontal compressive forces resulting from the convergence of the Indian subcontinent against the Afghan Block. Crustal thickening is taking place on the west, as the Indo-Pakistani plate is underthrusting continental crust of this block.