松潘-甘孜地体下仓界地区晚三叠世基性岩的发现及其地质意义  

Discovery of Late Triassic basic rocks in the Xiacangjie area of Songpan-Ganzi terrane and its geological significance

作　　者：陈敏 王雁鹤 谷强 马庆 CHEN Min;WANG Yan-he;GU Qiang;MA Qing(Geological Engineering Department of Qinghai University,Xining 810016,China;Xining Natural Resources Investigation Center,China Geological Survey,Xining 810000,China;Xi'an Center of Mineral Resources Survey,China Geological Survey,Xi'an 710100,China)

机构地区：[1]青海大学地质工程系,青海西宁810016 [2]中国地质调查局西宁自然资源综合调查中心,青海西宁810000 [3]中国地质调查局西安矿产资源调查中心,陕西西安710100

出　　处：《岩石矿物学杂志》2023年第1期1-12,共12页Acta Petrologica et Mineralogica

基　　金：中国地质调查局地质调查项目(12120114009001)。

摘　　要：笔者在松潘-甘孜地体下仓界地区发现了晚三叠世基性岩,对其开展了岩相学、地球化学、斜锆石U-Pb年代学等研究。该基性岩由玄武岩和辉绿岩组成,均为钙碱性系列,蚀变较强,形成时代为208.0±7.0 Ma。岩石La/Nb值为1.13~1.95,La/Ta值为7.96~25.79,TiO_(2)含量为1.51%~2.22%,Zr/Nb值为11.35~16.33,指示岩浆源自岩石圈地幔与软流圈地幔的混合源区。根据(Yb/Sm)_(P)-(Tb/Yb)_(P)模型计算结果,推测下仓界基性岩可能源于软流圈物质诱发岩石圈地幔尖晶石-石榴子石过渡相(石榴子石约占0~25%)发生约5%的部分熔融。岩石中发现捕获的古老斜锆石,轻稀土元素富集,重稀土元素亏损,Nb、Ta和Ti元素弱亏损。结合区域地质资料,认为松潘-甘孜地体应该具有陆壳基底,其晚三叠世(<211 Ma)的构造环境为碰撞后的板内伸展环境。Late Triassic basic rocks were discovered in the Xiacangjie area of Songpan-Ganzi terrane,and their petrography,geochemistry and baddeleyite U-Pb chronology were studied.The basic rocks are composed of basalt and diabase,both of which belong to calc-alkaline series with strong alteration,and the formation age of diabase is 208.0±7.0 Ma.La/Nb value is 1.13~1.95,La/Ta value is 7.96~25.79,TiO_(2)content is 1.51%~2.22%,and Zr/Nb value is 11.35~16.33,indicating that the magma of the basic rocks originated from the mixed source region of the lithospheric mantle and the asthenosphere mantle.According to the calculation results of the(Yb/Sm)_(P)-(Tb/Yb)_(P)model,it is speculated that the basic rocks in the Xiacangjie area may be derived from the partial melting of about 5%of the spinel and garnet transition phase(garnet accounts for about 0~25%)in the lithospheric mantle induced by the asthenospheric materials.Ancient baddeleyites captured in the rocks are found.Light rare earth elements are enriched in the rocks,heavy rare earth elements are depleted,and Nb,Ta and Ti elements are weakly depleted.Combined with the regional geological data,it is considered that Songpan-Garze terrane should have a continental crust basement,and its tectonic environment in the Late Triassic(<211 Ma)was the post-collisional intraplate extension environment.

关 键 词：晚三叠世基性岩 斜锆石U-Pb年代学 下仓界地区 松潘-甘孜地体 

分 类 号：P588.145[天文地球—岩石学] P588.124[天文地球—地质学]