The implication of two episodic Precambrian supercontinents convergence events from enriched mantle beneath the Yangtze Block: Constraints from the Zhangbaling mafic rocks

Abstract

The Yangtze Block bears witness to a prolonged Precambrian evolutionary history and records the assembly of Precambrian supercontinents. Significantly, compared with the widely recognized ancient continental crustal growth and reconstruction, subduction-related mafic magmatism contains detailed possess of crust-mantle interaction in convergent plate boundaries. This paper reports Neoproterozoic mafic igneous rocks, represented by the 808–787 Ma amphibolites, from the Zhangbaling Uplift, northeastern sector of the Yangtze Block. Their prominent arc-affinity trace-element geochemical compositions with high concentration of LILE, the trough of Th, U, Zr and Hf in the spider diagram as well as natural δ18O values (5.3–6.5‰), indicate an interaction between the lithospheric mantle wedge peridotite and slab-derived fluids during early Neoproterozoic subduction event, and deficient in the involvement of felsic melts from crustal materials and sediments. Analyses of radioisotopes for amphibolites yield extremely low zircon εHf(t) (−25.3 to −3.6) and whole-rock εNd(t) (−17.1 to −10.4) values respectively, corresponding to an enriched mantle source. However, in consideration of the fact that the recycled slab-derived fluids is difficult to alter the isotopic composition (especially hafnium) of lithospheric mantle compared with its geochemical characteristics. Meanwhile, on the compilation of all Precambrian subduction-related magmatism in the Yangtze Block, it appears that the enriched isotopic signature in amphibolites is mainly inherited from the Paleoproterozoic (ca. 2.0 Ga) lithospheric mantle beneath the Yangtze Block, and extremely negative εHf(t) values (–25.3 to –18.4) further reflect prominent crust-mantle interaction correspond to the assembly of Columbia supercontinents. Therefore, the Zhangbaling mafic rocks witness the modification of lithospheric mantle by two episodic subduction events during Paleoproterozoic and Neoproterozoic respectively, which provide new evidence for the Yangtze Block to get involved in the reconstruction of Columbia and Rodinia supercontinents.