【摘要】 湘西隘口地区基性-超基性岩墙锆石LA-ICP-MSU-Pb年龄为831.6±9.7Ma,与桂北、赣东北基性岩墙具有相似的形成时代(约830～825Ma),组成了扬子陆块南缘新元古代呈带状断续分布的基性岩墙群。隘口地区的基性-超基性岩墙化学成分上属于碱性系列,超基性岩具有比基性岩明显高的MgO、Cr和Ni含量,所有样品都展示出相似的稀土和微量元素配分模式,部分样品具有轻微的Nb的负异常和明显的P、Ti的负异常,表明岩浆在演化的过程中遭受过不同程度的地壳的混染。该区基性-超基性样品具有明显高的相似于软流圈地幔的εNd(t)值,则暗示其母岩浆来源于长期亏损的软流圈地幔。结合其微量元素及其对应的比值和εNd(t)值与板内裂谷碱性玄武岩和洋岛玄武岩非常相似的特征,以及扬子周缘大规模相同时代岩浆作用的特点,我们认为这些新元古代火成岩是地幔柱有关的裂谷岩浆作用的产物,地幔柱或超级地幔柱的作用导致了Rodinia超大陆最终的裂解。更多还原

【Abstract】 The geochronological result of the mafic-ultramafic dykes from Aikou in the western Hunan Province dated at 831.6±9.7 Ma by the technique of LA-ICP-MS,which is similar to those of basic-ultrabasic rocks from the northern Guangxi and Northeastern Jiangxi provinces.These rocks display an affinity of alkaline basalts in chemical compositions.Compared with the mafic dykes,the ultramafic rocks have prominently high MgO,Cr and Ni contents.All samples show similar REE and trace-element patterns.Part of them have negative anomalies in Nb,P and Ti and possess variable εNd(t) values,indicating the slight involving of continental crustal materials during magma ascending.On the basis of the fact that the least contaminated samples have relatively high εNd(t) values(>4),it is clear that their parental magma are derived from partial melting of long-term depleted asthenospheric mantle.In addition,their characteristics of elemental and isotopic geochemistry akin to those of ocean island basalts and alkaline basalts generated within the continental rift,together with the feature of large-scale magmatism occurring synchronously around the margin of Yangtze Block,it is likely possible that the Neoproterozoic magmatism are the products of plume-related rifting.Mantle plume or superplume beneath the Yangtze Block resulted in the ultimate breakup of Rodinia supercontinent.更多还原