Abstract

At long-lived arc volcanic centers, open-system interactions between new magma and the plutonic roots of the arc will increase with time relative to interactions with older crust. Assimilative recycling of mafic plutonic arc roots will have different isotopic consequences than incorporation of aged continental crust. In the Tatara–San Pedro complex, 30 comagmatic basaltic lavas are characterized by xenocrysts and microxenoliths of olivine, augite, and plagioclase derived from solidified cumulates, wide but poorly correlated ranges of incompatible and compatible major and trace elements, and limited isotopic variability. This mineralogical-chemical signature reflects assimilation wherein grain-boundary melting and disaggregation of xenoliths led to blending of incompatible element– enriched melts derived mainly from hornblende, phlogopite, and plagioclase in combination with variable retention of xenocrysts, hence variable but high compatible element concentrations.

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