Late Cretaceous intra-plate volcanism in Ceno-Tethys: evidence from the Kazhaba Volcanics, Balochistan, Pakistan

摘要

Basaltic pillow lavas near Kazhaba village in Balochistan occur as tectonic slivers in the Bagh complex, the mélange zone beneath the Muslim Bagh ophiolite complex.These volcanic rocks are mainly alkali basalts, whose petrography and chemistry suggest that they belong to a mildly to strongly alkaline, intra-plate volcanic rock series.Their low Mg # and low Cr, Ni and Co contents suggest that the parent magma was not directly derived from a partially melted mantle source, but resulted from fractionation in a in an upper level magma chamber before eruption.Their LILE and HFSE, and enriched primordial mantle-normalized patterns with marked positive Nb anomalies further confirm their within-plate geochemical signatures and are consistent with an enriched mantle source.Their highly enriched LREE patterns and high (La/Yb)N and (Ce/Yb)N ratios suggest a partially melted garnet-lherzolite parent magma source.A Zr versus Zr/Y plot suggests that these rocks were derived from about 15％ partial melting of an enriched mantle source.We suggest that these Late Cretaceous intra-plate volcanic rocks may represent mantle plume activity related to the Reunion hotspot, and that they were erupted during passage of the Ceno-Tethys ocean floor over it.