南黄海千里岩岛榴辉岩的地球化学特征及成因分析

Geochemistry and Genesis of the Eclogites form Qianliyan Island,South Yellow Sea

南黄海千里岩榴辉岩对研究华北板块和扬子板块碰撞缝合线有重要意义。千里岩榴辉岩变形作用较弱,经历了多期退变质作用。千里岩榴辉岩原岩为拉斑系列的玄武岩,与大别苏鲁造山带榴辉岩相似。千里岩榴辉岩微量与稀土元素配分模式均与大别苏鲁造山带榴辉岩有较大差异。千里岩榴辉岩大离子亲石元素相对于N-MORB富集,高场强元素特征与N-MORB基本一致,无Nb、Ta、Zr、Ti负异常;稀土元素配分形式为LREE亏损的左倾型。千里岩榴辉岩主微量元素判别图与微量元素特征值均指示其形成的构造环境为弧后盆地。榴辉岩的207Pb/204Pb比值不同于华北板块而接近扬子板块,继承性锆石(747±19)Ma的SHRIMP U-Pb年龄说明其原岩经历了仅在扬子板块有记录的晋宁期热事件。该区所在的千里岩隆起区代表了扬子板块的基底。

The eclogites in Qianliyan Island, South Yellow Sea is important to conducting further re- search of Dabie-Sulu Orogen. The degree of eclogite deformation in Qianliyan is low, hut they experienced multistage retrometamorphism. The protolith of eclogite from Qianliyan is tholeiitic basalt, similar to that of Dabie-Sulu orogen. The trace element and REE distribution patterns of eclogite show major differences between Qianliyan and Dabie-Suiu orogen. HFSE of eeiogite from Qianliyan is similar to N-MORB, but LILE is richer than N-MORB. No negative Nb, Ta, Zr, Ti anomalies indicates they are different to IAT. The fractionation between LREE and HREE is not clear and the REE distribution patterns show the depletion of LREE compared with N-MORB. The gneiss shows the relative concentration of LILE and evident depletion of HFSE which is similar to the character of IAT. Its REE distribution patterns are consistent with that of the upper crust. The geochemical discrimination diagrams indicate the eclogites of Qianliyan have both features of N MORB and IAT, formed in back-arc basin setting. The 207Pb/204pb radio shows that the eclogites of Qianliyan are belonged to he Yangtze Cration. The in- herited zircon Shrimp U-Pb age （747±19）Ma implies the eeogites had experienced J inningian magmatic event. In conclusion, the basement of Qianliyan uplift belongs to the Yangtze Cration.