赣中存在中元古代变质基底的岩石地球化学证据及其地质意义

The Geochemical Evidences for Existence of Mesoproterozoic Metamorphic Basement in Central Jiangxi Province

对江西乐安相山地区产出在石榴黑云母片岩内、原岩为拉班玄武质火山岩的斜长角闪岩进行了Sm-Nd同位素组成测定,获得Sm-Nd全岩等时线年龄为1113±49Ma,结合弋阳梅树湾斜长角闪岩及余江马荃斜长角闪岩的同位素定年结果(1159±69Ma,Sm-Nd;1190±19Ma,U-Pb),确认赣中变质岩带原岩属中元古代地层。采用微量元素地球化学比值模糊聚类分析方法对浙西陈蔡群、震旦系及赣中变质岩和震旦系地层进行对比,结合斜长角闪岩Pb-Nd同位素地球化学特征研究,确认赣中变质岩系与陈蔡群相当,从而为赣中变质岩归属于华夏地块变质基底提供了重要佐证。根据崇仁—临川—东乡晚白垩纪断陷红盆两侧深部地球物理重力场、磁场及地层和岩浆岩分布特征的对比,推断遂川深断裂为华夏地块在江西省境内的西北段边界。

The whole-rock Sm-Nd isochron age of the amphibolite occurred in the garnet-mica schist from Le ＇an, Xiangshan and from tholeiitic volcanic rocks is 1113± 49 Ma. In combination with the isotopic dating results of am- phibolites in Meishuwan, Yiyang and Maquan, Yijiang （ 1159 ± 69 Ma, Sm-Nd ; 1190± 19 Ma, U-Pb, respectively ）, it is confirmed that the original rocks of central Jiangxi metamorphic belt belong to Mesoproterozoic strata. By means of fuzzy cluster analysis on trace element geochemical ratios between Chencai Group in west Zhejiang, Sinian System and metamorphic rocks in Jiangxi, coupled with the Pb-Nd isotope geochemical features of amphibolites, it is identified that the central Jiangxi metamorphic belt closely corresponds to the Chencai Group and belongs to Cathaysian block. On the basis of a detailed comparative study on the deep geophysical features of gravitational and magnetic fields and the distribution of stratra and magmatic rocks on both sides of the Congren-Linchuan-Dongxiang Cretaceous red-bed fault basin, it is inferred that the northwest boundary of Cathaysian block in Jiangxi Province may be constrained by the Suichuan deep fault.