Mean contents of volatile components, major and trace elements in magmatic melts from main geodynamic settings of the earth. II. Silicic melts

Abstract

As a continuation of our previous study, we estimated the mean contents of volatile, major, and trace components in silicic (>66 wt % SiO2) magmatic melts from main terrestrial geodynamic settings on the basis of our database, which includes (as of middle 2017) more than 1 500 000 determination of 75 elements in melt inclusions and quench glasses from rocks. Among the geodynamic settings are those related to subduction processes (III, island-arc zones originated on oceanic crust and IV, magmatic zones of active continental margins, where continental crust is involved in magma formation) and intracontinent rift and continental hot-spot regions (V). For each geodynamic setting, we calculated the mean contents of elements with confidence limits separately for melt inclusions and groundmass glasses and for the entire data set. Systematic differences were found between the mean compositions of melt inclusions and groundmass glasses from these geodynamic settings. Primitive mantle normalized spider diagrams were constructed for all geodynamic settings. Some ratios of elements and volatile components (H2O/Ce, K2O/Cl, La/Yb, Nb/U, Ba/Rb, Ce/ Pb, etc.) in silicic and mafic melts were compared. Variations in the ratios of various elements to Th, which is one of the most incompatible elements in silicic and mafic melts, were discussed.