板内橄榄玄粗岩(shoshonite)地幔流体交代作用及成因的元素地球化学证据：以赣南会昌橄榄玄粗岩为例

Elemental geochemical evidence for genesis of intraplate shoshonite and mantle-derived fluid metasomatism: Shoshonite from Huichang,Southern Jiangxi Province as an example

根据稀土元素和微量元素ICP-MS分析结果,通过对流体作用敏感的元素对比值(U/Th、Pb/Ce、Ba/La、Cs/Rb和Ce/Y等)的研究对比,为赣南会昌橄榄玄粗岩的形成有地幔流体交代作用参与提供了重要的地球化学证据。应用主元素氧化物(K2O、Na2O、FeOT、CaO、MgO和TiO2)与SiO2的变异分析,判明会昌橄榄玄粗岩不是高钾钙碱性岩浆结晶分异的产物。应用Ta/Hf-Th/Hf图解判别会昌橄榄玄粗岩形成于大陆板内构造环境。根据上述地球化学特征,结合Sr-Nd-O-Pb同位素组成及Nd模式年龄研究结果,推断会昌橄榄玄粗岩是古大陆(冈瓦纳?)岩石圈富集地幔与中生代亏损地幔的源区混合产物。

Fluid-sensitive trace element ratios, such as U/Th, Pb/Ce, Ba/La, Cs/Rb and Ce/Y, in shoshonites from Huichang, southern Jiangxi Province, are studied in this paper, providing important evidence for mantle-derived fluid metasomatism in formation of the rocks. Analysis on variations of SiO2 versus K2O, Na2O, FeOT, CaO, MgO and TiO2 shows that the Huichang shoshonite was not formed through crystallization fractionation of a high-K calcalkalic magma. From Ta/Hf-Th/Hf discrimination diagram, it is concluded that it was formed in the intraplate tectonic setting. Based on these elemental characteristics, together with Sr-Nd-O-Pb isotopic compositions and Nd isotopic model ages, it is inferred here that the Huaichang shoshonite, southern Jiangxi Province, was formed by mixing of magmas derived from the enriched paleo-continent （Gondwana？） lithospheric mantle with that from the Mesozoic depleted mantle.