青海团宝山花岗岩年代学、地球化学特征及其地质意义

Geochronological and Geochemical Characteristics of Tuanbaoshan Granite Pluton in Qinghai and Geological Implications

青海省团宝山花岗岩位于南祁连东段,侵位于古元古代化隆群中。为了解其侵位时代、岩体成因和产出构造环境,利用LA-ICP-MS锆石U-Pb定年和地球化学测试方法对团宝山花岗岩岩体样品进行分析。获得其锆石U-Pb年龄为(776±8)Ma;该岩体SiO_(2)、Al_(2)O_(3)和K_(2)O含量较高,而FeO^(T)、MgO和CaO含量较低,K_(2)O/Na_(2)O大于1,富集Rb、Th等元素,亏损Ba、Zr等元素,具明显的负铕异常,表现为轻稀土富集型稀土配分模式。该岩体为分异程度较高的过铝质钙碱性岩,具S型花岗岩特征,为晚元古代中期陆陆碰撞的产物;源岩为泥质岩或杂砂岩,侵位后在晋宁运动末期和加里东运动中期经历过岩浆热事件。

The Tuanbaoshan granite pluton is located in the eastern South Qilian,and is emplaced into the Paleoproterozoic epimetamorphic rocks.Samples from the granite pluton are LA-ICP-MS zircon U-Pb dated and geochemically analyzed to constrain its emplacement age,petrogenesis and tectonic setting.The zircon U-Pb dating yielded weighted mean age of(776±8)Ma.The rocks contain relatively contents of SiO_(2),Al_(2)O_(3)and K_(2)O,and relatively low contents of FeO^(T),MgO and CaO,with K_(2)O/Na_(2)O>1.The Tuanbaoshan granites are enriched in Rb,Th,and depleted in Ba and Zr,with chondrite-normalized LREE-enriched patterns.Based on these characteristics,we suggest that:the Tuanbaoshan granites are calc-alkalic highly-differentiated S-type,and were emplaced in a Late Proterozoic continent-continent collision setting.Source rocks of the Tuanbaoshan granites may have been argillaceous sandstone or graywacke,and the pluton may have subsequently experienced two magmatic events during the end of Jinning movement and the Mid Caledonian movement.