U–Pb and Hf isotopic compositions of detrital zircons from the paragneisses of the Quanji Massif, NW China: Implications for its early tectonic evolutionary history

Abstract

The Quanji Massif is a cratonic fragment located on the northeastern margin of the Qinghai-Tibetan Plateau in western Qinghai Province, northwest China (Fig. 1). This massif consists of pre-Neoproterozoic crystalline basement unconformably overlain by mid- to late-Neoproterozoic and Cambrian strata. The basement is dominantly made up of the Delingha complex and the supracrustal Dakendaban Group. The Delingha complex is made up of 2.24–2.39Ga granitic gneisses with enclaves of dominant amphibolite and minor felsic gneisses as well as granulites. The supracrustal Dakendaban group is in tectonic contact with the Delingha Complex, and can be divided into the lower and upper Dakendaban sub-Groups. Data from detrital zircons show that the protolith rocks of these two sub-groups were deposited after ∼2.32Ga, and ∼2.11Ga, respectively. The detrital zircon age and Hf isotopic data and geological correlations suggest that the Quanji Massif was possibly fragmented from the Tarim Craton, and the Delingha complex was probably uplifted to become the major sedimentary source for the upper Dakendaban sub-group at ∼2.11Ga. Our zircon Hf-isotope compositions demonstrate important crustal growth at 2.6–2.7Ga and ∼2.5Ga. Together with the important magmatic activity at ∼2.2–2.4Ga and geological data, our results seem to suggest that the Tarim Craton was part of the North China Craton in its early evolutionary history but rifted away and joined the Yangtze Craton prior to the Neoproterozoic.