长江中下游地区早白垩世埃达克质岩的大地构造背景及其成矿意义  

A perspective on the geotectonic setting of early Cretaceous adakite-like rocks in the Lower Reaches of Yangtze River and its significance for copper-gold mineralization.

作　　者：汪洋[1] 邓晋福[2] 姬广义[3] 

机构地区：[1]中国科学院广州地球化学研究所,广州510640 [2]中国地质大学地球科学与资源学院,北京100083 [3]北京市地质研究所,北京100011

出　　处：《岩石学报》2004年第2期297-314,共18页Acta Petrologica Sinica

基　　金：国家自然科学基金(No.40104003);中国博士后科学基金;中国科学院王宽诚博士后奖励基金资助.

摘　　要：长江中下游地区是中国重要的铜资源基地之一。该成矿带广泛发育与Cu-Au成矿作用密切相关的早白垩世火成岩。大多数与成矿有关的中酸性侵入岩具有类似埃达克岩的地球化学特征,即富集Sr而贫HREE(如:Y和Yb);但它们具有负的εNd(t)值和相对富集的Sr同位素初始比值(>0.704.),因此,被称为埃达克质岩。根据岩石化学数据,研究区埃达克质侵入岩多数属于高钾钙碱性系列,部分属于钙碱性系列;而火山岩和A型花岗岩类由于其高钾和富铁特征而属于钾质碱性系列。岩石地球化学资料显示,与成矿作用有关的中酸性埃达克质侵入岩经历了复杂的成岩过程,至少包括在深位岩浆房(>35～40 km深度)的分离结晶和在高位岩浆房内的分离结晶或AFC过程两个阶段。同时不排除有下地壳直接熔融形成的埃达克质熔体参与的可能性。富钾的火山岩则是原生岩浆在深位岩浆房(>40-50 km深度)经镁铁矿物的分离结晶过程演化而来。基于长江中下游地区及其邻区的区域地质构造、早白垩世岩浆岩的岩石化学和地球化学特征和岩浆活动的时空演变特征的综合分析,推测该成矿带在早白垩世早期处于大陆边缘岩浆弧内陆一侧,岩浆活动与古太平洋板块的斜向俯冲作用有关;晚期由于俯冲板片迁移(变陡),岩浆岩具有弧后环境特征。The Lower Reaches of Yangtze River (LRYR) is one of the major copper resource bases in China. Extensive magmatism occurred in the region during Early Cretaceous epoch, and is strongly related to the copper-gold mineralization. The most ore-forming related intermediate-acid intrusive rocks exhibit the geochemical features with adakite affinity, which contains high s but low HREE ( e. g. Y and Yb). However, these rocks have negative epsilon(Nd) (t) values and more enriched (Sr-87/Sr-16)(i) values ( > 0.704); therefore, they are called as adakite-like rocks. According to the petrochemical data, the adakite - like plutons belong to high-K cale - alkaline series, but some belong to cale - alkaline series. Meanwhile, the volcanic rocks and A-type granitoid plutons belong to potassic alkaline series due to their high potassium abundance and iron enrichment. The complex petrogenetic processes were suggested from the analysis of geochemical data. To form the oreborming related adakite-like pluton, two-stage evolution is required. The parental magma evolved to the potash-rich mafic, magma by fractional crystallization in the deep - level magma chamber (> 35 - 40 km in depth). The evolved magma further experienced fractional crystallization (FC) or assimilation and fractional crystallization (AFC) process with crustal materials in high-level chamber. However, it is possible that some adakitic melt generated by melting of basaltic lower crust involved in the petrogenetic process. The potash-rich volcanic rocks were formed by fractional crystallization of mafic minerals in deep-level chamber (> 40 - 50 km in depth). On the comprehensive analysis of regional tectonics, geochemical characteristics of igneous rocks, and the temporal-spatial variation of magmatism, active continental are was identified as the geotectonic setting for the LRYR and its southeastern surrounding regions. The LRYR lies in the inland portion of the arc during the early stage, and the magmatism in LRYR was related to the oblique subduction of Izanagi pla

关 键 词：埃达克质岩 岩石系列 大地构造背景 成矿作用 早白垩世 长江中下游地区 

分 类 号：P588.121[天文地球—岩石学] P618.41[天文地球—地质学]