Coexisting silicate melt inclusions and H_2O-bearing, CO_2-rich fluid inclusions in mantle peridotite xenoliths from the Carpathian-Pannonian region (central Hungary)

摘要

Coexisting fluid inclusions and silicate melt inclusions, trapped as primary inclusions in clinopyroxene rims and as secondary inclusions along healed fractures in orthopyroxene, were studied in two amphibole-bearing spinel lherzolite peridotite xenoliths from the Bakony-Balaton Highland Volcanic Field (western Hungary). The composition of both Cpx-hosted and Opx-hosted inclusions suggests that they were entrapped from the same silicate melt, which was saturated in volatiles at mantle P-T conditions. Raman spectroscopy, combined with microthermometry and FTIR analyses, proved the existence of CO_2, H_2O and H_2S in the fluid inclusions. Trace element compositions of silicate melt and fluid inclusions were determined by LA-ICP-MS, although the results of fluid inclusions are only semi-quantitative. Trace element distributions revealed significant similarities in the compositions of silicate melt and fluid inclusions, especially with respect to K, Rb, Sr, Pb, Nb, Th and U content. This confirms the same parental melt for both silicate melt and fluid inclusions and suggests that the trace element content of the CO_2-rich end-member (containing some dissolved melt) resulted from high P-T immiscibility in deep lithospheric environments and is controlled by the trace element content of the parent silicate melt.