Petrogenesis and tectonic setting of the Neoproterozoic Douling dioritic–granodioritic–granitic intrusion in the northern Yangtze Block, Central China

Abstract

Voluminous Neoproterozoic intermediate to felsic rocks intruded the Neoarchean Douling Complex in the South Qinling Belt of Central China, which may provide new constraints on the controversial issue about the nature of the continental margin of the Yangtze Block during the Neoproterozoic. This study presents zircon U–Pb geochronology, whole-rock geochemistry and Sr–Nd isotope of the Douling dioritic–granodioritic–granitic intrusion, aiming to clarify its petrogenesis and tectonic significance. The dioritic–granodioritic–granitic rocks yield similar zircon U–Pb ages ranging from 735 to 705 Ma. The enrichment of light rare earth elements (LREEs) and large-ion lithophile elements (LILEs), and depletion of high- field-strength elements (HFSEs) (e.g., Nb, Ta) are typical features of arc magmatic rocks. The whole-rock Sr–Nd isotopic compositions show initial ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7034 to 0.7059, and ε_Nd(t) values from −7.3 to −1.4. Elemental and isotopic data suggest that the Neoproterozoic dioritic–granodioritic–granitic rocks were co-genetic and were generated by partial melting of lower crust materials combined with mantle-derived melts. The granites were the derivative product of dioritic rocks by fractional crystallization of amphibolite, plagioclase, mica and zircon. Combined with literature data, we infer a subduction-related setting for the northern margin of the Yangtze Block during the Middle Neoproterozoic, and a tectonic model of accretion along an Andean-type active continental margin after the collision of the Douling micro-block with the northern Yangtze Block is further proposed.