We report Neoproterozoic (ca. 785-780 Ma) granites from the western margin of the Yangtze Block that are characterised by magmatic zircons with ${\delta }^{18}$O values as low as 2.98‰. The lack of low-${\delta }^{18}$O 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-${\delta }^{18}$O 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-${\delta }^{18}$O values resulting from high temperature hydrothermal alteration. The ${\delta }^{18}$O 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-${\delta }^{18}$O signatures that occur in the northern and southern margins of the Yangtze Block and Cathaysia Block, the locations of low-${\delta }^{18}$O magmatic zircons exhibit a Neoproterozoic low-${\delta }^{18}$O 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-${\delta }^{18}$O 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.

我们报告了扬子地块西缘的新元古代（约 785-780 Ma）花岗岩，其特征是岩浆锆石 ${\delta }^{18}$O值低至2.98‰。缺乏低${\delta }^{18}$O 岩浆锆石在约。来自新元古代苏雄组的 820-805 Ma 流纹岩样品表明，在约 785-780 Ma 花岗岩。因此约。785-780 Ma 花岗岩${\delta }^{18}$来自扬子地块西缘的 O 值可以与同岩浆蚀变岩石的同化作用（而不是对预先存在的热液蚀变地壳的同化作用）联系起来。花岗岩的来源受其耗尽的 Hf 同位素和低${\delta }^{18}$由高温热液蚀变产生的 O 值。这${\delta }^{18}$锆石从核心到边缘的 O 值显示出降低，表明在高温下岩浆和水相互作用期间材料的重熔。结合广泛的低${\delta }^{18}$出现在扬子地块和华夏地块的北缘和南缘的 O 特征，这些低地${\delta }^{18}$O 岩浆锆石表现出新元古代低-${\delta }^{18}$O 华南周围的岩浆环。这次大陆尺度的新元古代伸展和岩浆事件不能归因于华南俯冲过程导致长英质火成岩岩浆环的侵位，${\delta }^{18}$O 值。因此，我们提出了一个模型，该模型涉及直径约 1500 公里的新元古代超地幔柱，控制着华南周围裂谷系统的发展。