皖南鹤城科马提质变玄武岩地球化学特征及大地构造意义

Tectonic significance and geochemistry of Komatiitic meta-basalt in Hecheng, southern Anhui

江南造山带新元古变基性岩为区域构造事件和演化模型的建立提供地质依据。对江南造山带东段皖南鹤城地区变玄武质岩的地球化学及岩石成因进行研究。鹤城变玄武岩呈北东—南西向沿瑶里—鹤城—江潭一带分布。元素地球化学的研究表明:休宁鹤城变玄武岩同科马提质玄武岩及岛弧玄武岩相类似;富集Rb、Ba、Th、U等强不相容元素,亏损高场强元素Nb和Ta,指示其成因可能与富集地幔的部分熔融有关,同时有地壳物质的混染,其可能属于皖南伏川蛇绿岩西延组成部分,与伏川蛇绿岩组成一个弧后杂岩带,形成于与俯冲有关的弧后小洋盆环境。结合区域资料,表明新元古代板块俯冲、岛弧岩浆活动以及拼合是江南造山带形成的比较合理的构造演化过程。

The Neoproterozoic meta-mafic rocks of the Jiangnan Orogen in South China provide a critical geological record for unraveling regional tectonic history and testing previously proposed tectonic models. An integrated study of geochemistry and petrogenesis was carried out for the meta-basaltic rocks from Hecheng, south Anhui Province of the eastern Jiangnan Orogen, which distributed along the NE-SW Yaoli-Hecheng-Jiangtan line. The geochemical features of the Hecheng meta-basalt are similar to those of Komatiitic basalt as well as island arc basalt. The trace elements features,such as the enrichment in strongly incompatible elements(Rb, Ba, Th and U) and the depletion in high field strength elements(Nb and Ta), indicate that the Hecheng meta-basalt is derived from partial melting of enriched mantle, with crust materials contamination, suggesting that Hecheng meta-basalt is a westward extension of Fuchuan ophiolite in southern Anhui Province, and constitute a back-arc complex belt with Fuchuan ophiolite, attributed to the back arc basin environment related to the subduction. Integrating this information with previous studies, the plate subduction-island arc magmatism-assembly model is a more appropriate geodynamic interpretation for the Neoproterozoic tectonic evolution of South China.