The Ca. 1.13–0.92 Ga Magmatism in the Western Yangtze Block, South China: Implications for Tectonic Evolution and Paleogeographic Reconstruction

The tectonic regime of the Yangtze Block in the South China and its palaeogeographic location in the Rodinia supercontinent during the late Mesoproterozoic to early Neoproterozoic remain enigmatic due to limited geological records. In this study, we report late Mesoproterozoic basalts and granodiorites and early Neoproterozoic plagioclase amphibolites in the western Yangtze Block. Zircon LA-ICP-MS U-Pb dating yield concordant ages of 1130-1128 Ma for basalts, 1026 +/- 1.6 Ma for granodiorites, and 917 +/- 1.4 Ma for plagioclase amphibolites. The basalts are tholeiitic in chemical composition and are slightly enriched in LREEs with (La/Yb)N ratios of 2.87-3.99 and exhibit E-MORB-like trace element patterns. They are depleted in whole-rock Nd (+3.3 to +5.9) and zircon Hf isotopes (+11.1 to +12.8). Geochemical compositions showed that the basalts were derived from high-degree (7%-20%) partial melting of spinel lherzolite mantle. The granodiorites belong to the A-type granites and have negative whole rock eNd(t) (-5.5 to -7.8) and zircon eHf(t) (-15.3 to +0.6) values. We suggested that these A-type granites were mainly generated by the partial melting of felsic crustal rocks under low-pressure conditions. The plagioclase amphibolites are tholeiitic and exhibit arc-like geochemical affinities. They show depleted isotopic compositions (zircon eHf(t) = +11.0 to +13.6; whole rock eNd(t) = +0.6 to +2.5) and were interpreted as derived from a lithospheric mantle source that was metasomatized by subduction-related fluids. Geochemical compositions show that basalts were formed in an intracontinental rift setting, whereas granodiorites and plagioclase amphibolites were emplaced into a subduction background. Integrated with published work, we suggest that the late Mesoproterozoic and early Neoproterozoic magmatism in the western Yangtze Block record a tectonic switch from a passive margin to a convergence setting. In addition, we also proposed that the South China may be located at the western periphery of the Rodinia supercontinent.