为探讨张广才岭北部构造格架及其演变,对张广才岭北部二长花岗岩、正长花岗岩及碱长花岗岩进行LA-MC-ICP-MS锆石U-Pb年代学、岩石学、岩石地球化学等方面的研究,确定了其形成时代及岩石成因.研究结果表明:2件二长花岗岩、1件正长花岗岩及1件碱长花岗岩样品的锆石U-Pb年龄分别为(191.4±1.1)、(202.6±1.0)、(190.8±1.5)、和(198.1±1.0)Ma,总体年龄介于 202～190 Ma 之间,时代为早侏罗世;二长花岗岩、正长花岗岩和碱长花岗岩总体属于低铝质,以高钾钙碱性系列为主,显示富集Rb、Ba、K等大离子亲石元素和轻稀土元素,亏损Nb、P、Ti等高场强元素和重稀土元素;二长花岗岩、正长花岗岩和碱长花岗岩显示出Ⅰ型花岗岩特征.结合区域对比及综合研究,初步认为张广才岭北部早侏罗世花岗岩的构造环境为古太平洋板块向欧亚大陆俯冲形成的活动大陆边缘环境.
Geochronology,Geochemistry and Geological Significance of Early Jurassic Granites in Nothern Zhangguangcai Mountains
In order to discuss the tectonic framework and evolution of the Northern Zhangguangcai Mountains,LA-MC-ICP-MS zircon U-Pb chronology,petrology,and petrogeochemistry studies were conducted on monzonitic granite,syenite granite and alkali-feldspar granite in this area.The zircon U-Pb ages of two monzonitic granites,one syenite granite,and one alkali feldspar granite are(191.4±1.1)Ma,(202.6±1.0)Ma,(190.8±1.5)Ma,and(198.1±1.0)Ma,respectively,in Early Jurassic.These granites are mainly classified as low aluminous,high potassium,and calc-alkaline series,have enrichment of large ion lithophile elements and lightly rare earth elements,like Rb,Ba,K,etc.,whlie have depletion of high field strength elements and heavy rare earth elements,such as Nb,P,Ti,etc..They exhibit characteristics of I-type granite,indicative of an active continental margin environment resulting from Paleo-Pacific plate subduction to Eurasia.
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