Fluid/melt inclusions in Cenozoic mantle xenoliths from Linqu, Shandong Province, eastern China: Implications for asthenosphere-lithosphere interactions

Abstract

Fluid and melt inclusions in mantle xenoliths are thought as direct samples to study mantle liquids. Here we apply Raman microspectroscopy and microthermometry to fluid/melt inclusions in lherzolite xenoliths in Qiaoshan basalts, a Miocene volcano in Linqu, Shandong Province, eastern China. These inclusions include (1) early CO2 fluid inclusions, (2) early carbonate melt inclusions, (3) late CO2 fluid inclusions, and (4) late silicate melt inclusions. Among the early CO2 fluid inclusions, most consist of high-density pure CO2, while others have small amounts of other components besides of CO2, including graphite, magnesite, Mg-calcite, CO and N2. The lowest trapping pressures are estimated to be 1.42 GPa and 0.80 GPa for the early and the late fluid inclusions, respectively. Because orthopyroxene is the main host mineral for the early carbonate melt inclusions, we propose that the formation of these carbonate melts is genetically associated with the interactions between CO2 fluids and silicate minerals, e.g. olivine and clinopyroxene. The diversity of minor components in the early CO2 fluid inclusions indicates that mantle peridotites had undergone redox reactions with penetrating fluids/melts. These observations suggest that the compositions of the lithospheric mantle beneath the studied area had been changed by asthenosphere-derived CO2-rich fluids/melts.