Abstract Low δ18O felsic igneous rocks are reported for the first time in the northwestern margin of the South China Block. Zircon U-Pb dating indicates that intermediate to felsic plutons were emplaced at 780 Ma and 750 Ma, respectively, and rhyolite was erupted at about 750 Ma. Compared with other rock-forming minerals that have variable δ18O values (−2.3‰ to 8.7‰ for quartz; −5.4‰ to 6.3‰ for plagioclase, −7.6‰ to 2.5‰ for K-feldspar), zircon δ18O values mainly range from 1.0‰ to 4.7‰ with a few negative values of −7.7‰ to −2.9‰. A two-stage 18O-depletion scenario was proposed, 1) high-temperature meteoric water–rock reaction in a continental rift setting, generating low δ18O melt from which precipitated zircons with significant lower δ18O values than normal mantle; 2) post-crystallization sub-solidus high-T meteoric-hydrothermal alteration, resulting in varying δ18O values for rock-forming minerals that leads to δ18O-disequilibrium between zircon and other minerals. In addition, zircons from these rocks show positive eHf(t) values of 4.6 to 11.2 with Hf model ages of ca. 1.0–1.4 Ga, suggesting a magma source of juvenile crust due to mantle melting during the Grenvillian subduction of oceanic lithosphere in response to accretion of the South China Block to Rodinia in the Late Mesoproterozoic. The occurrence of low δ18O felsic rocks in the northwestern margin of the South China Block indicates the development of a low δ18O magmatic belt during the rifting of the South China Block away from Rodinia at about 750 Ma. The coeval occurrence of Neoproterozoic low δ18O magmatism in NW India, South China, Madagascar and Seychelles suggests a link between these continental blocks in the Rodinia configuration.

中文翻译：

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华南地块西北缘新元古代低δ18O火成岩的赋存对罗迪尼亚构造的启示

摘要 华南地块西北缘首次报道了低δ18O长英质火成岩。锆石 U-Pb 测年表明，中长英质岩体分别在 780 Ma 和 750 Ma 就位，流纹岩在 750 Ma 左右喷发。与其他δ18O值可变的造岩矿物（石英为-2.3‰至8.7‰；斜长石为-5.4‰至6.3‰，钾长石为-7.6‰至2.5‰）相比，锆石δ18O值主要在1.0之间‰ 到 4.7‰ 与几个负值 -7.7‰ 到 -2.9‰。提出了一个两阶段的 18O 耗竭情景，1）大陆裂谷环境中的高温大气水岩反应，产生低 δ18O 熔体，从中沉淀出 δ18O 值明显低于正常地幔的锆石；2) 结晶后亚固相线高温大气热液蚀变，导致造岩矿物的 δ18O 值发生变化，从而导致锆石和其他矿物之间的 δ18O 不平衡。此外，这些岩石中的锆石显示出 4.6 至 11.2 的正 eHf(t) 值，Hf 模型年龄约为 1.0-1.4 Ga，表明在中元古代晚期华南地块向罗迪尼亚岛的增生过程中，大洋岩石圈的格伦维尔俯冲过程中地幔熔融形成了新生地壳的岩浆来源。华南地块西北缘低δ18O长英质岩的赋存表明华南地块在750 Ma左右从Rodinia裂谷开裂时发育了低δ18O岩浆带。印度西北部、华南地区新元古代低δ18O岩浆作用的同时发生