Abstract The western margin of the Yangtze Block in South China preserves voluminous arc-like intrusive and extrusive igneous rocks which were formed in an active continental margin during the Neoproterozoic time. Rocks from the ca. 800 Ma Moutuo pluton are calc-alkaline I-type granitoids which have high SiO2 (67.13–77.96 wt%), K2O (2.08–4.32 wt%) and low MgO (0.16–1.81 wt%). They show concave chondrite-normalized rare earth element patterns, and are rich in large ion lithophile elements (e.g. Rb, Ba, Th, U and Pb), but depleted in high field strength elements (e.g. Nb, Ta and Ti). The magmatic zircons have low δ18O (3.29–4.80‰) and high eHf(t) values (+6.10 to +13.16) with two-stage Hf model ages (TDM2) of 0.87 to 1.33 Ga. These lines of evidence suggest that the juvenile mafic crust, protolith of the low-δ18O granitoids, was derived from the sub-arc mantle that was modified by slab-derived materials (~90% altered oceanic crust and ~10% oceanic sediments). Partial melting of the newly formed mafic crust followed by fractional crystallization played an important role in the petrogenesis of the Moutuo granitoids. Based on the available oxygen and hafnium isotopic data for the Neoproterozoic magmatic zircons in this region, the low-δ18O character of the I-type granitoids in active continental margins was probably inherited from the sub-arc mantle that was mixed with the altered oceanic crust and oceanic sedimentary materials.

中文翻译：

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华南扬子地块西缘新元古代低δ18O花岗岩的成因

摘要 华南扬子地块西缘保存着大量新元古代活动大陆边缘形成的弧状侵入和喷出火成岩。来自加州的岩石。800 马穆托岩体为钙碱性 I 型花岗岩，具有高 SiO2（67.13-77.96 wt%）、K2O（2.08-4.32 wt%）和低 MgO（0.16-1.81 wt%）。它们显示出凹球粒陨石归一化稀土元素图案，富含大离子亲石元素（例如 Rb、Ba、Th、U 和 Pb），但缺乏高场强元素（例如 Nb、Ta 和 Ti）。岩浆锆石具有低 δ18O (3.29–4.80‰) 和高 eHf(t) 值（+6.10 到 +13.16），两阶段 Hf 模型年龄 (TDM2) 为 0.87 到 1.33 Ga。这些证据表明幼年基性地壳，低δ18O花岗岩的原岩，来自亚弧地幔，该地幔由板片衍生材料（约 90% 改变的洋壳和约 10% 的海洋沉积物）改性。新形成的基性地壳的部分熔融和分步结晶在牟脱花岗岩的成岩作用中起重要作用。根据该地区新元古代岩浆锆石的可用氧和铪同位素数据，活动大陆边缘I型花岗岩的低δ18O特征可能继承自与蚀变洋壳混合的亚弧地幔和海洋沉积物质。新形成的基性地壳的部分熔融和分步结晶在牟脱花岗岩的成岩作用中起重要作用。根据该地区新元古代岩浆锆石的可用氧和铪同位素数据，活动大陆边缘I型花岗岩的低δ18O特征可能继承自与蚀变洋壳混合的亚弧地幔和海洋沉积物质。新形成的基性地壳的部分熔融和分步结晶在牟脱花岗岩的成岩作用中起重要作用。根据该地区新元古代岩浆锆石的可用氧和铪同位素数据，活动大陆边缘I型花岗岩的低δ18O特征可能继承自与蚀变洋壳混合的亚弧地幔和海洋沉积物质。