Mineral chemistry and origin of ophiolitic rocks from the Waziristan ophiolite complex, NW Pakistan
Abstract
The Waziristan Ophiolite Complex demarcates the spatial disposition of the suture zone between the Indian plate and the Afghan block in the Waziristan area. The complex is located along the western margin of the Indian plate and consists of a chaotically arranged stack of thrust slices. Section(s) showing a complete sequence is not preserved but all members of a typical ophiolite are separately present in the area. Dominant rocks include basic lavas, ultramafics, and gabbros, with subordinate amounts of dikes, granites, and pelagic sediments.
Major minerals (pyroxene, spinel, and plagioclase) within the rocks were analyzed using Jeol Superprobe Microanalyser. Pyroxenes from basalts, apparently crystallized at temperatures above 1000oC, plot in the fields of volcanic arc basalts and ocean floor basalts. Pyroxene and chromite data have been further interpreted to reveal the tectonic environment at the time of generation and emplacement of the ophiolite sequence. The pyroxene data show a transitional character from tholeiitic to calcalkaline, and from ocean floor to island arc type environment. Chromite data, with moderate to high cr#, also exhibit oceanic (abyssal) to arc affinities. The chemical data on pyroxene and chromite suggest an oceanic and/or arc related origin for the Waziristan ophiolite complex.
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