藏南特提斯喜马拉雅带始新世隆子-恰嘎次火山岩区：雅拉香波二云母花岗岩的高位岩浆体系  

The Mid-Eocene subvolcanic field in the Lhunze-Qiaga area,Tethyan Himalaya,southern Tibet:A high-level magmatic suite related to the Yardio two-mica granite

作　　者：胡古月[1] 曾令森[1] 戚学祥[1] 候可军[2] 高利娥[1] 

机构地区：[1]中国地质科学院地质研究所,大陆构造与动力学国家重点实验室,北京100037 [2]中国地质科学院矿产资源研究所,成矿作用与资源评价重点实验室,北京100037

出　　处：《岩石学报》2011年第11期3308-3318,共11页Acta Petrologica Sinica

基　　金：国家自然科学基金(41073024、40921001);中国地质调查局项目(1212011121265);中国地科院地质所所长基金(J1004)联合资助

摘　　要：已有的数据表明,大约在中始新世(44～40Ma),西藏特提斯喜马拉雅带(雅拉香波穹窿地区)经历了一次特别的地壳深熔作用,产生了大量高Sr/Y比值的二云母花岗岩。在雅拉香波穹窿南部的隆子-恰嘎地区,发育一套流纹质次火山岩,以小岩体或岩脉形式侵位于侏罗纪日当组的砂岩和页岩之中。岩相学观察、锆石U-Pb年代学、全岩元素和同位素(Sr、Nd)地球化学数据表明:(1)该次火山岩形成于约43～41Ma,与北部二云母花岗岩体的形成年龄相似;(2)该次火山岩经历了强烈的岩浆演化后期的岩浆-热液作用和钙长石分离结晶作用,导致该套岩浆岩强烈的Eu负异常、明显降低的Sr含量和锆石岩浆增生边的普通Pb和U浓度明显升高;和(3)该套次火山岩和二云母花岗岩属于同一岩浆过程的不同的构造层次,在时间、空间和成岩物质来源上具有一致性,同属于中始新世青藏高原主碰撞时中下地壳部分熔融的产物。Recent studies in the Yardoi gneiss dome（YGD） of the Tethyan Himalaya,have demonstrated that the Tethyan Himalayan belt experienced a major episode of crustal melting at Mid-Eocene（44～40Ma） time,represented by the formation of a suite of high Sr/Y two-mica granites.Further south of YGD,a suite of subvolcanic rocks of rhyolitic composition occurs in the Lhunze-Qiaga area and intruded into black sandstones and yellow-greenish shales of the Tethyan sedimentary sequence.Petrographic observations,zircon U-Pb age and geochemical data show that：（1） the Lhunze-Qiaga rhyolitic subvolcanic rocks formed at ca.43～41Ma and may represent the shallow counterpart of the two-mica granites crystallized at a much deeper level;（2） in contrast with the two-mica granites,the subvolcanic rocks had experienced intensive hydrothermal-magmatic interactions as well as An-rich plagioclase fractional crystallization as evidenced by pronounced negative Eu anomalies,much lower Sr concentrations,and enhanced common Pb and U concentrations in the magmatic zircon;and（3） these two suites of rocks formed a Mid-Eocene igneous edifice under crustal thickened conditions.

关 键 词：特提斯喜马拉雅 次火山岩 锆石U-Pb定年 流体作用 高U锆石 

分 类 号：P588.121[天文地球—岩石学]