Late cretaceous mantle plume activity in Ceno-Tethys: evidences from the Hamrani volcanic rocks, western Pakistan

摘要

Basaltic pillow lavas from near the Muslim Bagh town in northern Balochistan are found in the tectonic slivers of the Bagh Complex, northwest of Muslim Bagh Ophiolite. These volcanic rocks are mainly basanites and tephrites. Their petrography and chemistry suggest that these belong to the mildly-strongly alkaline, intra-plate volcanic rock series. Their low Mg # and low Cr, Ni, and Co contents suggest that the parent magma of these volcanic rocks was not directly derived from a partially melted mantle source but have been modified by fractionation en route to eruption. Their primordial mantle-normalized trace element patterns show enrichment in large ion lithophile elements (LILE) and in high field strength elements (HFSE), with marked positive Nb anomalies, and further confirm their within-plate geochemical signatures consistent with an enriched mantle source. Modeling of their Zr versus Zr/Y trends suggest that these volcanic rocks were derived from about 10-15 % melting of an enriched OIB-style mantle source. It is suggested that these Late Cretaceous intra-plate volcanic rocks may represent the mantle plume activity possibly of the Reunion hotspot. These may have erupted on the Ceno-Tethys Ocean floor prior to the passage of Indian plate over it with subsequent tectonic imbrication during Ceno-Tethyan closure and collision with the Eurasian margin.