Early Neoproterozoic syncollisional S-type granites from the western Yangtze Block, South China: Implications for final closure of the back-arc basin

Abstract

Records of Neoproterozoic magmatic activity in the western margin of the Yangtze Block are widely distributed, although considerable debate remains regarding the petrogenesis and tectonic setting of this region. We performed zircon U-Pb geochronologic, zircon Hf isotope and whole-rock geochemical analyses on Jinkouhe granite (JKHG) samples from the western margin of the Yangtze Block. The zircon U-Pb dating results show that the age of the JKHG formation is 860±4 Ma (MSWD=0.23). The JKHG is classified as high-K calc-alkaline strongly peraluminous S-type granite, and the samples have positive zircon ε Hf (t) values of 3.95 to 5.77. Based on the zircon ε Hf (t) values and the geochemical characteristics, we conclude that the JKHG is sourced from the mixture of partial melts of metagraywackes and partial melts of juvenile crust. The geochemical analysis shows that the JKHG has the characteristics of syncollisional granitic magmatism. Integrating previous studies with the regional correlations among magma records in this contribution, we propose that the Shimian-Ebian region was a back-arc basin system along the western margin of the Yangtze Block ca. 1070~940 Ma and that the JKHG may be related to the final closure of the back-arc basin.

Detrital zircon in the Huashan Group, northern Yangtze Block: Implications for the nature of Neoproterozoic sedimentary basins and Precambrian crustal evolution

“…The Yangtze Block is bounded by the Neoproterozoic Jiangnan (or Jinning‐Sibao) orogenic belt during ca. 830 Ma to the southeast, by the Qinlin‐Dabie‐Sulu orogen to the north, by the Ailaoshan‐Red River Fault to the southwest, and by the Longmenshan Thrust Fault Zone to the northwest (Figure 1a; Deng et al, 2019; Deng, Wang, Wang, et al, 2016; Li et al, 2019; Zhao & Cawood, 2012). Generally, the Yangtze Block made up of an Archean to Palaeoproterozoic basement, and is overlain bylow‐grade to unmetamorphosed Mesoproterozoic‐Neoproterozoic volcano‐sedimentary sequences, and is overlain by Neoproterozoic‐Palaeozoic volcanic‐sedimentary units (Wang & Li, 2003; Zhao & Cawood, 2012).…”