Tectonic switch of the north Yangtze Craton at ca. 2.0 Ga: Implications for its position in Columbia supercontinent

Abstract

Two episodes of magmatism with zircon U-Pb ages of 2.46 Ga and 2.0 Ga were studied in the Jinpan Complex in the north Yangtze Craton of South China. The ca. 2.46 Ga gneissic granites with various chemical compositions were formed by remelting of different crustal materials in a collisional event. The occurrence of both negative and positive whole-rock εNd(t) and εHf(t) values in these rocks indicates the growth of juvenile crust and reworking of Archean crust during early Paleoproterozoic. The ca. 2.0 Ga trondhjemites have high (La/Yb)N and Sr/Y ratios as well as negative whole-rock εNd(t), εHf(t) and zircon εHf(t) values, suggesting that they were formed by remelting of thickened lower crust in a collisional orogen. The ca. 2.0 Ga A-type granites have high Zr, Nb, Y contents and Ga/Al, Y/Nb ratios, belonging to A2 type granite. Their negative whole-rock εNd(t), εHf(t) and zircon εHf(t) values are similar to those of the ca. 2.0 Ga trondhjemites. These evidences suggest that they were produced by remelting of the residue after extraction of earlier granitic magma in an extensional tectonic setting. The 2.0 Ga mafic dykes show significant enrichment in LILEs but weak negative Nb, Ta anomalies and various Nb/U ratios. This is consistent with a parent magma similar to continental flood basalts and experienced different degrees of crust contamination. The co-occurrence of 2.0 Ga trondhjemites, A-type granites and mafic dykes implies a tectonic switch from convergence to extension at ca. 2.0 Ga in the north Yangtze Craton. Based on the similarities of the ca. 2.0 Ga magmatic rock association and metamorphic records in the north Yangtze Craton and south Siberia, the position of the Yangtze Craton in Columbia supercontinent is proposed to be close to south Siberia.