川西容须卡锂辉石矿床石英闪长岩锆石LA-ICP MS测年及构造意义

ZIRCON LA-ICP-MS U-Pb DATING OF QUARTZ DIORITE OF RONGXUKA LITHIUM DEPOSIT IN WESTERN SICHUANAND ITS TECTONIC IMPLICATION

针对松潘-甘孜造山带中部的容须卡锂辉石矿床中进行了详细的岩石学、地球化学2件石英闪长岩、3件花岗岩闪长岩及锆石U-Pb年代学1件研究,结果表明,岩体具有中-高硅(59.05%～67.67%),高钾(1.64%～2.46%)、富钙(4.11%～7.38%)、贫铝(10.63%～17.61%),铝饱和指数(A/CNK<0.58～1.15)偏低的特征,并且岩体中普遍含角闪石,岩石类型属Ⅰ型花岗岩系列。稀土总量变化较大,稀土配分曲线为右倾型,轻稀土相对富集。δEu为0.75～1.63,平均为0.90,具有较弱的负铕异常。野外观测、镜下鉴定及微量元素地球化学特征均显示该岩体原始岩浆起源于壳-幔混熔或下地壳物质的部分熔融,属下地壳重熔的I型高钾钙碱性花岗岩系列岩石。微量元素构造环境判别投点位于火山弧花岗岩区域,与岛弧型花岗岩具有相似的特征,形成于松潘-甘孜造山带碰撞后构造背景,源区可能来自黑云母的脱水熔融。容须卡黑云母石英闪长岩锆石LA-ICP-MS U-Pb加权平均年龄为214.4Ma±1.2Ma(MSWD=0.064),表明容须卡岩体原始岩浆的初始结晶时代为晚三叠世。容须卡岩体形成于晚三叠世碰撞后构造环境,是壳-幔岩浆的拆沉作用导致壳-幔混熔的产物,(含稀有金属)伟晶岩脉与与该花岗岩体在成因上有联系。

The petrological,geochemical and chronological characteristics of the quartz diorite and granodiorite in the the Rongxuka spodumene deposit in the middle part of the Songpan-Garze fold belt are studied.It shows that the rocks have medium-high content of Si(59.05% ~67.67%),high K(1.64%~2.46%)and Ca(4.11%~7.38%),low Al with aluminum saturation index of 10.63%~17.61%,A/cnk<0.58~1.15.The rocks generally contain amphibole mineral and belong to I-type granite series.The total amount of rare earth elements varies greatly with a right inclined REE distribution curve.Light rare earth elements are relatively enriched,δEu is0.75~1.63(average 0.90)with a weak negative Eu anomaly.The field observation,microscopic identification and geochemical analysis reveal that the Rongxuka magma is originated from crustmantle mixed melting or partial melting of lower crust and belongs to lower crust-remelting I-type and high-potassium calcium-alkaline granite series.Tectonic environment discrimination by trace elements analysis shows that these rocks have similar character to volcanic arc granites and are resulted from the collision of the Songpan-Ganzi organic belt.The zircon LA-ICP-MS U-Pb dating yields a 214.4 Ma±1.2 Ma age(MSWD=0.064),indicating that the initial crystallization time of the original magma is the late Triassic.Therefore,Rongxuka granites are derive from crust-mantle mixed melting by crust-mantle magma delamination and formed in late Triassic period under a collisional tectonic background.The pegmatite veins containing rare metals are originally related to the granite.