Early cretaceous lower crustal reworking in NE China: insights from geochronology and geochemistry of felsic igneous rocks from the Great Xing’an range

Abstract

This paper presents new zircon LA-ICP-MS U–Pb ages and whole-rock geochemical data for two granitic plutons and rhyolites of the Baiyingaolao Formation in the western Xing’an range (NE China). The two syenogranite granitic plutons yield identical zircon U–Pb age of 142 ± 1 Ma, and the Baiyingaolao rhyolites yield zircon U–Pb age of 138 ± 2 Ma. The granites contain some hornblendes, and show low Zr and Zr + Nb + Ce + Y contents, and low A/CNK (0.98–1.11), Mg# (6–55), and FeOT/MgO values. Rhyolite samples show similar geochemical characteristics with A/CNK of 0.99–1.10 and Mg# of 14–21. In combination with the high K2O contents (4.43–5.61 wt%) and negative correlations between P2O5 and SiO2, both the granites and rhyolites were classified as high-K calc-alkaline I-type granitoids. All samples give high zirconium saturation temperature of 794–964 °C with few initially inherited zircons, and belong to high-temperature I-type granitoids. They were generated by dehydration melting of biotite/muscovite from sub-alkaline meta-basalts in lower crust depth, leaving garnet, amphibole, and plagioclase as the major residual minerals. The syenogranites and rhyolites are likely formed in Mongol–Okhotsk oceanic subduction setting. Incorporating other lower crust-originated felsic rocks in Erguna and Xing’an massifs and Songliao basin, it is argued that lower crustal reworking is pronounced in NE China during Early Cretaceous.