Petrogenesis of Early Cretaceous granitic rocks from the Haobugao area, southern Great Xing'an Range, northeast China: Geochronology, geochemistry and Sr-Nd-Hf-O isotope constraints

Abstract

Early Cretaceous granitic rocks are widespread in the southern Great Xing'an Range (SGXR) in the eastern part of the Central Asia Orogenic Belt where they have been interpreted to have formed by remelting of juvenile materials derived from a depleted mantle source. We present new U-Pb ages, geochemistry and Sr-Nd-Hf-O isotopic data for ~140 Ma granitic rocks from the Haobugao area. The Xiaohanshan (XHS) quartz monzonite porphyry formed at 140 ± 2 Ma, the Wulanba (WLB) biotite granite formed at 142 ± 2 Ma, and the Wulanchulute (WLCLT) granite formed at 139 ± 2 Ma. They are A-type granites characterised by enrichment of light rare earth and high field strength elements. Based on the geochemistry and Sr-Nd-Hf-O isotope data, the quartz monzonite porphyry with elevated δ18O (6.6‰–7.4‰), high εNd(t) (5.8) and high εHf(t) (5.0–8.4) formed by the partial melting of juvenile material ultimately derived from depleted mantle which had been modified by melts derived from sediment on the downgoing slab. The biotite granite and granite with mantle-like δ18O (4.6‰–6.5‰, one value of 2.7‰), positive εNd(t) (1.4–1.8) and high εHf(t) (3.6–9.4) formed from partial melting of juvenile material derived from depleted mantle. The one low δ18O value from the biotite granite is probably the result of post magmatic alteration. The geochemical data suggest that the granitic rocks of the Haobugao area were not contaminated by older crust and formed in an extensional environment related to Paleo-Pacific oceanic slab rollback.