Modeling of subduction components in the Genesis of the Meso-Cenozoic igneous rocks from the South Shetland Arc, Antarctica

Abstract

Isotope data and trace elements concentrations are presented for volcanic and plutonic rocks from the Livingston, Greenwich, Robert, King George and Ardley islands (South Shetland arc, Antarctica). These islands were formed during subduction of the Phoenix Plate under the Antarctica Plate from Cretaceous to Tertiary. Isotopically (Sr-87/Sr-86), ratios vary from 0.7033 to 0.7046 and (Nd-143/Nd-144)(o) ratios from 0.5127 to 0.5129. epsilon Nd values vary from +2.71 to +7.30 that indicate asthenospheric mantle source for the analysed samples. Pb-208/Pb-204 ratios vary from 38.12 to 38.70, Pb-207/Pb-204 ratios are between 15.49 and 15.68, and Pb-206/Pb-204 from 18.28 to 18.81. The South Shetland rocks are thought to be derived from a depleted MORB mantle source (DMM) modified by mixtures of two enriched mantle components such as slab-derived melts and/or fluids and small fractions of oceanic sediment (EM I and EM II). The isotopic compositions of the subduction component can be explained by mixing between at least 4 wt.% of sediment and 96 wt.% of melts and/or fluids derived from altered MORB.