Paleoproterozoic TTG gneisses and granites of the Huai’an Complex: Geochemical and zircon U-Pb-Hf data provide insights into subduction history and crustal growth

Abstract

Tonalite-trondhjemite-granodiorite (TTG) suites and granitoids are major components of the Precambrian continental crust. Here we investigate the Paleoproterozoic TTG gneisses and granites from the Huai’an Complex based on new and published geochemical and geochronological data with a view to trace the tectonic evolution of the North China Craton (NCC). The TTG gneisses show high Mg#, Sr and Sr/Y, low Yb, positive Eu anomalies, as well as enriched light REE (LREE) and depleted heavy REE (HREE) patterns. The magmatic zircons of TTG gneisses show εHf(t) of 9.1 to −2.8 and 176Lu/177Hf of 0.046. Geochemical characteristics suggest that the parental magmas of TTG gneisses were sourced from the partial melting of subducted hydrated oceanic crust and mantle wedge, with fractional crystallization of plagioclase and amphibole. The granites are magnesian, medium-K to high-K calc-alkaline, metaluminous to weakly peraluminous, and have decreasing P2O5, Al2O3, TiO2, MgO, CaO, and Sr with increasing SiO2, increasing Pb with increasing SiO2, decreasing Ta/Nb with increasing TiO2, positive Eu anomalies and low HREE. The magmatic zircons of granites show εHf(t) of 2.72 to −2.6 and 176Lu/177Hf of 0.033. Geochemical characteristics classify the granites into I-type granites and indicate that magma derived through partial melting of infra-crustal igneous rocks and subcontinental lithospheric mantle with fractional crystallization of apatite, K-feldspar, plagioclase and mica. Geochemical characteristics and zircon U-Pb data indicate that the Huai’an Complex was a long-lived magmatic arc and in crustal growth stage during 2.51–2.39 Ga. The crystallization ages of TTG gneisses and granites in the Huai’an Complex show a general younging-trend from north to south along NE-SW direction, likely suggesting a scissor-like subduction model with an oceanic lithosphere subduction earlier beneath the northern part of the Huai’an Complex than the southern part.