Petrogenesis of Dashenshan I-type granodiorite: implications for Triassic crust-mantle interaction, South China

Triassic granodiorites in South China (SC) provide an opportunity to examine crust-mantle interactions that may have been caused by a mantle plume. Here we present a combined study of chronological, geochemical, and Sr-Nd-Hf isotopic compositions for Dashenshan granodiorites. These are high-K, calc-alkaline, I-type granodiorites that yield a U-Pb zircon age of 211 +/- 3Ma. They are metaluminous to weakly peraluminous (A/CNK< 1.1), with 3.04-3.89wt.% Na2O and 3.24-3.86wt.%K2O, and Na2O/K2O ratio ranging from 0.79 to 1.11. These granodiorites contain 67.7-72.6wt.% SiO2 but show moderate Mg-# values (44.2-57.8) and variable contents of Ni (3.6-29.9ppm) and Cr (7.6-53.5ppm). They exhibit light rare earth element (REE) enrichment and flat, heavy REE patterns with negative Eu anomalies (Eu/Eu*=0.52-0.87). They also display strongly negative Ba, Sr, Nb, Ta, P, and Ti anomalies and positive Rb, Th, K, and Pb anomalies. Dashenshan granodiorites have high whole-rock initial Sr-87/Sr-86 ratios (0.7121-0.7172), negative epsilon(Nd) (t) values (-8.8 to -6.8), and negative zircon epsilon(Hf) (t) values (-6.6 to -3.3). These results suggest that the Dashenshan granodiorites were generated by a mixing between crustal melt and mantle-derived magma in an extensional setting. We conclude that generation of the Dashenshan pluton may reflect an interaction between a mantle plume and the overlying SC crust.