Petrology and geochemistry of volcanic and volcanoclastic rocks from Zhob ophiolite, North-Western Pakistan

The Zhob ophiolite is divided into Ali Khanzai, Omzha, and Naweoba blocks. The ophiolite geology comprises various lithological units including basalt–chert and hyaloclastite mudstone units. The basalt–chert and hyaloclastite mudstone units consist of thick lava and pelagic sediments. On the basis of petrology and geochemistry, the lavas of basalt–chert unit can be divided into tholeiitic basalt, trachybasalt, basaltic andesite and dacite, and that of hyaloclastite mudstone unit into more alkaline foidite, picrobasalt, and tephrite-basanite. The tholeiitic rocks have a flat N-MORB-normalized pattern with enrichment of Th and depletion of Nb compared to other immobile elements and thus indicate a subduction zone component in the rocks. They have chondrite-normalized REE patterns typical of N-MORB. The alkaline rocks have depleted chondrite-normalized HREE compared to N-MORB similar to those of OIB. Our geochemical results suggest that the tholeiitic rocks may have formed in a supra-subduction zone setting while the alkaline rocks are intraplate setting that was influenced by a subduction component. The Zhob lavas therefore are likely to represent the floor of a branch of the Ceno-Tethys Ocean and may have obducted over the Indian Plate passive continental margin during the Late Cretaceous. © 2021, Saudi Society for Geosciences.