阿尔泰南缘可可托海地区阿拉尔花岗岩体LA-ICP-MS锆石U-Pb定年、岩石地球化学特征及其源区意义

LA-ICP-MS Zircon U-Pb Dating and Geochemistry of Aral Granitic Plutons in Koktokay Area in the Southern Altay Margin and Their Source Significace

阿拉尔花岗岩体出露于阿尔泰造山带南缘可可托海地区喀依尔特-乌什托克斯一带,主要由斑状黑云钾长花岗岩、斑状黑云二长花岗岩（中心相）,黑云钾长花岗岩、二云钾长花岗岩、二云二长花岗岩（过渡相）和黑云母花岗岩（边缘相）组成。对其进行了LA-ICP-MS锆石U-Pb年代学和岩石地球化学研究。结果显示,中心相的锆石206Pb/238 U年龄加权平均值为210±5Ma和218.7±3.3Ma,限定该岩体的形成时代为晚三叠世。岩石高硅（SiO2=65.33%~74.74%）、富钾（K2O=3.82%~6.02%,K2O/Na2O=1.27~2.32）、铝（Al2O3=12.87%~15.19%,A/CNK=0.85~1.17）、低钛（多小于0.33）和贫镁（MgO=0.16%~1.78%）、铁（Fe2O3T=1.79%~4.98%）,为准铝质到弱过铝质的高钾-钾玄岩系列。稀土元素总量较高（123×10-6~363×10-6）,轻稀土元素相对富集,有明显的负Eu异常（δEu=0.29~0.60）。微量元素Ba、Sr、Ti、Nb、Ta等具负异常,Rb、Th、Sm等具正异常,Rb/Sr比值较高（0.77~3.56,均值为1.57）,显示S型花岗岩特征。结合区域资料,认为阿拉尔花岗岩形成于后碰撞造山向板内环境的转换阶段,是含泥质的变质杂砂岩地壳熔融的产物,且其可能与可可托海3号伟晶岩脉具有成因联系。

Aral granitic plutons extend from Kayierte to Wushituokesi in Koktokay area in the Southern Altaids.Lithological assemblage is composed principally of porphyritic biotite K-feldspar granite,porphyritic biotite adamellite（central facies）,biotite（two-mica）K-feldspar granite,two-mica adamellite（transitional facies）and biotite granite（border facies）.LA-ICP-MS zircon U-Pb geochronological and petrogeochemical studies are determined.The results show that the zircon 206Pb/238 U weighted average ages of the rocks of the central facise are 210±5Ma and 218.7±3.3Ma,indicating the crystallized-age of the plutons in late Triassic epoch.The granites are high in SiO2（SiO2=65.33% ~74.74%）,K2O（K2O =3.82~6.02,K2O/Na2 O =1.27~2.32）and Al2O3（Al2O3=12.87% ~15.19%,A/CNK=0.85~1.17）and low in TiO2（less than 0.33）,MgO（MgO=0.16%~1.78%）and Fe2O3（Fe2O3T=1.79%~4.98%）,belongs to high K-shoshonite series with metaluminous to slightly peraluminous feature.In addition,they are enriched in total REE contents（123×10-6~363×10-6）,with obvious negative Eu anomaly（δEu=0.29~0.60）.The trace elements show enrichment in Rb,Th,Sm and Rb/Sr value（0.77~3.56）,depletion in Ba,Sr,Ti,Nb,Ta,with the characteristics of S-type granite.Combined with the data of southern margin of Altay,the VAral granitic plutons were formed in the transitional tectonic setting from the post-collisional orogeny to intraplate,derived from partially melted of crust dominated by greywacke contain claystone,and the Koktokay pegmatite No.3vein likely has genetic relationship with it.