赣东北蛇绿岩和张村岩群的锆石SHRIMP U-Pb年龄及对江南造山带构造演化的讨论  

SHRIMP U-Pb Zircon Ages of the Northeastern Jiangxi Ophiolites and the Zhangcun Group and a Discussion on the Tectonic Evolution of the Jiangnan Orogen

作　　者：李源[1] 颉颃强[1] 宋志瑞[2] LI Yuan XIE Hangqiang SONG Zhirui(Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037 Geological Survey of Jiangxi Province, Nanchang, 330030)

机构地区：[1]中国地质科学院地质研究所,北京离子探针中心,北京100037 [2]江西省地质调查研究院,南昌330030

出　　处：《地质论评》2017年第4期854-868,共15页Geological Review

基　　金：国家自然科学基金资助项目(编号:41203042、41472168);国家重大科技仪器专项(编号:2011YQ05006909)的成果~~

摘　　要：本文对赣东北樟树墩蛇绿混杂岩中基性—超基性岩的地球化学分析表明,其中辉长岩具有MORB的地球化学特征,蛇纹岩强烈亏损各微量元素。辉长岩的锆石SHRIMP O同位素分析结果给出了非常均一的O同位素组成(5.12‰±0.62‰,2σ),与地幔锆石的O同位素组成(5.3‰±0.3‰)接近。这些地球化学特征和其形成于大洋环境吻合。锆石SHRIMP U-Pb定年给出了辉长岩的形成年龄为1009±5 Ma(MSWD=1.15)。在作为赣东北蛇绿岩的围岩张村岩群中,选取凝灰岩样品进行的锆石SHRIMP U-Pb定年给出了833±10 Ma(MSWD=1.5)的形成年龄,表明蛇绿岩就位时代晚于833 Ma。结合前人的研究,本文指出赣东北蛇绿岩形成于中元古代末—新元古代初的大洋中脊环境,不同于皖南伏川蛇绿岩所代表的弧后小洋盆环境。这些新资料为华南区域大地构造演化研究提供了新的约束。Objectives：The fragmentary ophiolite fragments distributed in the Jiangnan orogenic belt have important geological significance for constraining the tectonic evolution of the Jiangnan orogen. Combined with petrological study and SHRIMP U Pb zircon ages of the northeastern Jiangxi ophiolites and the Zhangcun Group, we briefly discuss the tectonic evolution of the Jiangnan orogen. Methods： Based on the field work, through the microscope observation, the whole rock chemical analysis, the the O isotopic analysis and SHRIMP U Pb zircon dating of the Zhangshudun ophiolite and tuffaceous phyllite of of the Zhangcun Group. Results： The geochemical analyses of mafic—ultramafic rocks in the Zhangshudun ophiolite show that the gabbro yields the MORB like geochemical composition and the serpentinite is strongly depleted in the trace elements. The SHRIMP O isotope analyses of zircons in gabbro yield homogeneous O isotope （5.12‰ ± 0.62‰，2 ）, similar to the O isotope of zircons in mantle （5.3‰ ± 0.3‰）. These geochemical characters support that these rocks represent remnants of ancient oceanic crust and upper mantle. SHRIMP U-Pb zircon analyses yields the formation age of 1009 ± 5 Ma （MSWD = 1.15） for the gabbro in the Zhangshudun ophiolite. As the surrounding rocks of the Northeastern Jiangxi ophiolite, the formation age of the Zhangcun Group is constrained by the SHRIMP U Pb zircon dating of a tuffaceous phyllite which yields the formation age of 833 ± 10 Ma （MSWD = 1.5）. This age suggests the emplacement of Northeastern Jiangxi ophiolite is later than 833 Ma. Conclusions： Combined with the early research, we suggest that the Northeastern Jiangxi ophiolite formed at the mid ocean ridge environment in late Mesoproterozoic to early Neoproterozoic, different from the mid Neoproterozoic back arc basin represented by the Fuchuan ophiolite in the south Anhui province. These new data provide new constrains for tectonic evolution of South China.

关 键 词：蛇绿岩 张村岩群 锆石SHRIMP U-PB定年 樟树墩 赣东北 

分 类 号：P542.2[天文地球—构造地质学] P597.3[天文地球—地质学]