Bela ophiolite zone of southern Pakistan: Tectonic setting and associated mineral deposits

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 m assive deposits of lead-zinc sulfides and barite, whereas the ophiolite zon e hosts chromite, manganese, massive copper sulfide, and related mineral de posits. This study describes the regional tectonic setting and relationship to local geological features of the mineral deposits using gravity and aer omagnetic data, These geophysical studies provide a basis for interpreting the emplacement models and deformation history of the Bela ophiolite zone a nd associated Jurassic rocks. These models and their supporting geologic da ta suggest that hydrothermal solutions containing barite and massive sulfid es rich in zinc and lead rose on the sea floor through crustal faults devel oped in areas of divergent tectonism and deposited these minerals in the Ju rassic sedimentary sequence on the western margin of Indo-Pakistan subconti nental plate. The Cretaceous Neotethyan spreading center, however, gave ris e 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 sulfi des 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.