A Neoproterozoic low-δ18O magmatic ring around South China: Implications for configuration and breakup of Rodinia supercontinent

We report Neoproterozoic (ca. 785-780 Ma) granites from the western margin of the Yangtze Block that are characterised by magmatic zircons with delta O-18 values as low as 2.98 parts per thousand. The lack of low-delta O-18 magmatic zircons in the ca. 820-805 Ma rhyolite samples from the Neoproterozoic Suxiong Formation indicates that there is no recycling of pre-existing hydrothermally altered crust in the study area prior to the emplacement of the ca. 785-780 Ma granites. Thus the ca. 785-780 Ma granites with low-delta O-18 values from the western margin of the Yangtze Block can be linked to assimilation of syn-magmatically altered rocks (rather than the assimilation of a pre-existing hydrothermally altered crust). The granites have a source constrained by their depleted Hf isotopes and low-delta O-18 values resulting from high temperature hydrothermal alteration. The delta O-18 values of the zircons from core to rim exhibit a decrease indicative of the remelting of material during the interaction between magma and water at high temperatures. In combination with the widespread low-delta O-18 signatures that occur in the northern and southern margins of the Yangtze Block and Cathaysia Block, the locations of low-delta O-18 magmatic zircons exhibit a Neoproterozoic low-delta O-18 magmatic ring around South China. This continent-scale Neoproterozoic extensional and magmatic event cannot be attributed to subduction processes in South China resulting in the emplacement of a magmatic ring of felsic igneous rocks with low-delta O-18 values. We therefore propose a model involving a Neoproterozoic super-mantle plume with a diameter of approximately 1500 km controlling the development of the rift systems around South China. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study reports Neoproterozoic (ca. 785-780 Ma) granites with low-delta O-18 values from the western margin of the Yangtze Block, which are linked to assimilation of syn-magmatically altered rocks and have their source constrained by high temperature hydrothermal alteration. The zircons exhibit a decrease in delta O-18 values from core to rim, indicating a remelting process at high temperatures.