皖南蛇绿岩套辉长岩锆石U-Pb定年以及元素和氧同位素研究

Zircon U-Pb Dating and Element and Oxygen Isotope Geochemistry of Gabbro from Ophiolites in South Anhui

对皖南蛇绿岩套辉长岩分别进行锆石微区U-Pb定年、全岩主微量元素分析和Sr-Nd同位素分析、矿物氧同位素分析。结果表明，皖南蛇绿岩存在3个时代的岩浆锆石，对应的U-Pb年龄分别为891±13Ma、826±4Ma和764±10Ma。元素和Sr—Nd同位素地球化学特征显示出明显的岛弧岩浆岩特征，表明辉长岩来源于俯冲带上覆地幔楔的部分熔融。矿物氧同位素分析表明，辉长岩遭受了亚固相高温热液蚀变。笔者解释辉长岩构造就位年龄为891±13Ma，在826±4Ma受到前裂谷期岩浆活动的改造，并在764±10Ma受到同裂谷岩浆活动的影响而发生亚固相热液蚀变。

Zircon U-Pb dating, whole-rock major and trace elements, Sr-Nd isotopes, and mineral O isotopes were determined for samples from ophiolites in south Anhui. LA-ICPMS and SHRIMP zircon U-Pb analysis reveals three age phases of magmatic zircons formed at 891 ± 13 Ma, 826 ± 4 Ma and 764 ± 10 Ma respectively. The features of elements and isotopes display apparent signatures of island-arc magmatic rocks, suggesting that they were derived from partial melting of mantle lithosphere of the supra-subduction zone （SSZ）. O isotope analyses suggest that they experienced different degrees of subsolidus hydrothermal alteration. Based on element and isotope analyses in combination with the records of Neoproterozoic magmatism in this area, the authors interpret 891± 13 Ma as the age of ophiolite emplacement. It is also thought that at 826 ± 4 Ma the rocks were rebuilt by pre-rift magmatic activities, and at 764 ± 10 Ma they were affected by syn-rift magmatism and subsolidus hydmthermal alteration.