东昆仑沙松乌拉环斑花岗岩的时代及地质意义
Age and Geological Implications of Shasongwula Rapakivi Granite in East Kunlun Mountains
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摘要: 东昆仑沙松乌拉环斑花岗岩位于南昆仑结合带，该构造带隶属于秦岭-昆仑造山带的一部分。由似斑状花岗闪长岩、花岗闪长岩和环斑花岗岩组成，主体岩性为环斑花岗岩，具特殊的环斑结构。对似斑状花岗闪长岩和环斑花岗岩进行U-Pb同位素测年，分别获得（440.6±1.1）Ma和（437±1.2）Ma的锆石U-Pb年龄，均显示其时代为早志留世。通过对其地质特征、地球化学特征等资料的研究,结合区域大地构造环境,认为沙松乌拉环斑花岗岩为碰撞造山阶段的产物,是增厚了的造山地壳的部分熔融形成的；沙松乌拉环斑花岗岩时代的精确定年不仅证实了南昆仑结合带存在加里东期花岗质岩浆活动，而且也揭示了该区存在加里东期造山型环斑花岗岩；对认识南昆仑结合带的构造演化特征和物质组成具有重要意义。Abstract: Shasongwula rapakivi granite, located in the South Kunlun suture belt, belongs to a part of Qinling-Kunlun orogenic belt. This rapakivi granite consists of porphyritic granodiorite, granodiorite, rapakivi granite, with special rapakivi texture. The U-Pb isotopic dating of porphyritic granodiorite and rapakivi granite has been carried out, the obtained zircon U-Pb ages are (440.6±1.1)Ma and (437±1.2)Ma respectively, which belong to the Early Silurian. Based on its geological characteristics and geochemical data, the Shasongwula rapakivi granite has been considered as a product of the collision orogenic stage and was formed by the partial melting of thickened orogenic crust through combining with the data regional tectonic environment. The dating of Shasongwula rapakivi granite has confirmed the existence of Caledonian granitic magma activity in South Kunlun suture belt, and has revealed the existence of Caledonian orogenic type rapakivi granite in this studying area. Thus, this study has a great significance to recognize the tectonic evolution haracteristics and composition of South Kunlun suture belt.
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Key words:
- rapakivi granite /
- rapakivi texture /
- collision orogenic /
- Early Silurian
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