DefinePK

Abstract

 Gravity data along a NNW-SSE profile from western Pakistan and eastern Afghanistan has been incorporated with recent structural interpretations based on seismic reflection, borehole and surface geological data from the Sulaiman fold belt to infer the gross crustal structure across the Indian! Afghan collision zone. Seismic reflection profiles reveal that the stratigraphic thickness ofthe rocks at the deformation front of the Sulaiman fold belt is aboutlO km. The wedge thickens northward and may have a thickness of 20 km in the hinterland. Gravity modeling depicts the depth to the Moho at about 35 km at the deformation front of the southern Sulaiman fold belt. The Moho depth decreases northward with a gentle gradient of 1.10 (20 m/km) below the Sulaiman fold belt, and then deepens abruptly with a gradient of about 7.So (136 m/km) across the Chaman fault zone, attaining a depth of about 57 km in eastern Afghanistan. Interpretation of the model suggests that the Sulaiman Cold belt is underlain by transitional crust, in contrast to the full thickness of crystalline crust underneath the Cold-and-thrust belt ofthe Himalayan collision zone in northern Pakistan.