Evolution of the lithosphere in Pakistan

Abstract

The geological setting of Pakistan in the framework of the modern concept of plate tectonics is unique in the sense that, within an area of about 800,000 km 2, critical tectonic junctions of different interacting plates and microplates are present in an environment where field exposures are excellent. Here we discuss the dynamics of these various plate boundaries. Two types of active plate boundaries are conspicuous: (1) convergent boundaries characterized by continent-continent collision, obduction, and thrusting in the northern region of the Himalaya and by oceanic crust subduction with a volcanic arc and a wide accretionary wedge in the southern region of Chagai and Makran; (2) a transform boundary, the Chaman transform zone, characterized by very large strike-slip and lesser thrusting. The Chaman transform zone connects the Makran convergence zone, where oceanic lithosphere is being subducted beneath the Lut and Afghan microplates, with the Himalayan convergence zone, where the Indo-Pakistan lithosphere is underthrusting Eurasia. The Chaman zone is at present an intracontinental plate boundary with oblique motion, characterized by north-south strike-slip faults and eastward thrusting and folding in the Kirthar-Sulaiman mountain belt. This mountain belt, the northwestern margin of the Indo-Pak subcontinent, was an Atlantic-type margin from the late Paleozoic until the Cretaceous. In the Cretaceous, the continental margin became a plate boundary; a thrust belt was formed in the Paleocene, and fragments of the oceanic crust were obducted, either as thrust sheets (Muslimbagh) or as an ophiolitic melange (Bela and Waziristan).