A window on the lithospheric mantle beneath the eastern Trans-Mexican volcanic belt: Insights from pargasite-bearing mantle xenocrysts from the Holocene Ocotenco maar volcano

Abstract

In this short communication, we report and discuss for the first time the occurrence of pargasite-bearing pyroxenite mantle macro-xenocrysts in a basaltic-andesite juvenile material erupted from the Holocene Ocotenco maar at the Serdán-Oriental Basin Volcanic field, situated in the eastern sector of the Trans-Mexican Volcanic Belt. Through an integrated approach based on microtextural observations, mineral chemistry, geothermobarometric modelling, and comparisons with the existing literature, we determined the xenocrysts equilibrated at ca. 0.8 GPa and 1100 °C, compatible with a pargasite-bearing, upper lithospheric mantle setting. The different textures (resorbed vs. unzoned) of xenocrysts, not only provide evidence of a mantle melting event, but also enabled the discrimination between disrupted mantle fragments and peritectic solid phase generated during the pargasite breakdown. Moreover, peculiar characteristics of the xenocrysts such as the dark pargasite rims and the melt embayment in clinopyroxene, together with the lack of phenocrysts from magma fractionation, the swallow-tail texture of groundmass plagioclase, and a vesicle-rich textures, cumulatively suggest a short-term (days to months?) eruptive scenario with a fast melt extraction from the source region to a rapid ascent through the crust and a sudden explosive eruption by the intense interaction of the ascending melt with a source of water close to the surface.