Provenance and Hf isotopic variation of Precambrian detrital zircons from the Qilian Orogenic Belt, NW China: Evidence to the transition from breakup of Columbia to the assembly of Rodinia

Abstract

The Qilian Orogenic Belt (QOB) in Northwest China consists of three distinct terranes: North Qilian, Central Qilian, and South Qilian, which have experienced complex rifting and converging. Here, we present new U-Pb ages and Hf isotopes of detrital zircons from the Neoproterozoic and Mesoproterozoic sedimentary rocks in the QOB to constrain the tectonic affinity of the different terranes and provide new evidence to the transition from Columbia to Rodinia. Two Mesoproterozoic zircon samples from the North and the Central Qilian display similar age spectra with a dominant population varying from 1.21 Ga to 1.78 Ga. The population show two age peaks at ~1.5 Ga and ~1.75 Ga and have same range of εHf(t) values from −9.1 to +9.8. Except for this population, the rest zircons yield Paleoproterozoic or even older ages with a peak at ~2.45 Ga. These results suggest that the three terranes were once of a united block in the late Mesoproterozoic. The two Neoproterozoic samples from the Central Qilian and the South Qilian both have a main population of ages at 0.85–1.0 Ga and a minor population peaked at ~2.45 Ga. Their zircon εHf(t) values indicated that the source rocks of the main population were dominantly composed of recycled crustal materials. Because of the comparable and homogeneous age patterns and Hf isotopic compositions of Proterozoic detrital zircons, the QOB has a close relationship to South China from Mesoproterozoic to Early Neoproterozoic. Our zircon ages and Hf isotopic data indicate that the juvenile components increased at 1.6–1.2 Ga, which response to an exterior orogen that newly-formed crust has replaced the lower crust possibly triggered by slab retreat or upwelling of asthenosphere materials related to the breakup of Columbia. In contrast, the abundant addition of the reworking materials at 1.2–0.8 Ga reacts to an interior orogen characteristic because continental collision was involved in the convergent of Rodinia. This changing, therefore, was a response to the transition from breakup of Columbia to the assembly of Rodinia.