Abstract

Northwest of Karachi, the Bela ophiolite zone is the southernmost exposure in a string of three major ophiolitic occurrences in the Axial fold-thrust belt, which extends generally south and southwest from northern Pakistan to the Arabian Sea. Allochthonous and para-allochthonous Jurassic rock units are tectonically associated with this ophiolite zone. These units contain massive deposits of lead-zinc sulfides and barite, whereas the ophiolite zone hosts chromite, manganese, massive copper sulfide, and related mineral deposits. This study describes the regional tectonic setting and relationship to local geological features of the mineral deposits using gravity and aeromagnetic data. These geophysical studies provide a basis for interpreting the emplacement models and deformation history of the Bela ophiolite zone and associated Jurassic rocks. These models and their supporting geologic data suggest that hydrothermal solutions containing barite and massive sulfides rich in zinc and lead rose on the sea floor through crustal faults developed in areas of divergent tectonism and deposited these minerals in the Jurassic sedimentary sequence on the western margin of Indo-Pakistan subcontinental plate. The Cretaceous Neotethyan spreading center, however, gave rise to metallic mineralizations. The Tertiary convergence between the rifted western margin of the Indian subcontinent and the Neotethyan oceanic plate (a segment of the Arabian oceanic plate) obducted the Bela ophiolite zone (consisting of, e.g., chromite, manganese, massive copper sulfide) along the overriding edge of the subcontinental plate, which contained massive sulfides rich in zinc-lead and barite. These convergent phases through Paleocene to Pleistocene time intensely deformed the divergent products and created a geologically complex region.

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