阿拉善宗乃山岩体东南缘花岗岩LA－ICP－MS锆石U－Pb年龄与地球化学特征

摘要

There are many types of granites around the southeastern Zongnai Mountain rock mass in Alax,the types of rocks,the characteristics of source rocks,and tectonic setting by using the LA-ICP-MS zircon geochronology, petrographic observation,geochemical methods (major,trace and REE elements)of granites and diorites from southeastern Zongnai Mountain rock in Alax are discussed. The rocks are mainly alkaline-calc-alkaline metaluminous granites and diorites.LA-ICP-MS zircon U-Pb dating yielded ages of 236.8 ±1 .9 Ma to 249.7 ±2.6 Ma for the plagioclase and biotite granite and 268.1 ±1 .1 Ma for the gneissic granite.Therefore,these rocks were formed mainly during the late Variscan and early Indosinian periods and are characteristics of multi-stage intrusions.It indicates that these granites are I-type granites,these rock are mainly derived from volcanic arc crust and locally derived from the collision zone.Due to the subduction of oceanic crust in the southeastern Zongnai mountain,arc margin orogenic granite intrusions and other variations were formed with continental margin arc characteristics.LA-ICP-MS zircon ages provide timing constraints for the subducted oceanic crust and conclude that the collision time is earlier than 236.8 ±1 .9 Ma.%阿拉善宗乃山岩体东南缘分布多种类型的花岗岩，本文主要采用岩相学、激光剥蚀电感耦合等离子体质谱（LA －ICP －MS）锆石 U －Pb 定年、岩石地球化学等技术手段，对宗乃山岩体东南缘岩石类型、年代学、源岩特征以及构造背景进行了研究。结果表明：岩石类型主要为碱性－钙碱性准铝质花岗岩和闪长岩；单颗粒锆石分析获得黑云母斜长花岗岩年龄为236．8±1．9 Ma ～249．7±2．6 Ma，片麻状花岗岩年龄为268．1±1．1 Ma，岩体成岩时期主要为华力西晚期和印支期早期，具有多期侵入的特征。该岩体岩石源岩为 I 型花岗岩，源于地壳火山弧区和同碰撞区，表明由于洋壳俯冲作用，在宗乃山东南缘形成了岛弧花岗岩侵入体。LA －ICP －MS锆石 U －Pb 定年技术为洋壳俯冲提供了年代学约束，确定了研究区碰撞时间为早于236．8±1．9 Ma。