Mesoproterozoic magmatism redefines the tectonics and paleogeography of the SW Yangtze Block, China

Abstract

The geodynamic setting of the Yangtze Block and its paleogeography in the reconstructed Rodinia supercontinent during the late Mesoproterozoic is loosely constrained due to the limited geological information reported. In this contribution, we identify a new suite of amphibolites in the SW Yangtze with an 1175 ± 5 Ma emplacement age. Geochemical modeling demonstrates they were derived from low-degree (3.5%–6.5%) partial melting of spinel lherzolite mantle. Additionally, three suites of late Mesoproterozoic granites in the SW Yangtze Block are revisited by providing new zircon U-Pb-Hf-O isotopes and whole-rock geochemical data. The granites have been dated to emplace during 1060–1042 Ma and have Zr + Nb + Y + Ce and Tzr values mostly at 304–576 ppm and 831–886 ℃, respectively, similar to A-type granites. Zircon Hf-O isotopic data indicate two subgroups of granites, in which one group has suprachondritic εHf(t) values of + 2.4 to + 11.4 with δ18O values of 6.5‰ to 7.4‰ while the other group has εHf (t) values of −3.9 to +1.5 with δ18O values of 10.0‰–11.6‰. The first group of granites was mainly derived from partial melting of mafic tholeiitic rocks while the second group of granites was mainly formed by partial melting of metasedimentary rocks. Integrated with published work, we propose that an intra-continental rift basin was developed in the SW Yangtze Block during ∼ 1.2–1.04 Ga, arguing against a late Mesoproterozoic orogenic event in the SW Yangtze Block. Statistical analyses based on compiled zircon U-Pb-Hf isotopes from Laurentia, Yangzte, and Amazonia show that the Yangtze has an isotopic affinity with west Nuna. These continents likely remained united during the transition from Nuna/Columbia to Rodina along the western periphery of the Rodinia supercontinent.