云开地块印支期构造热事件叠加改造:来自片麻岩中多矿物U?Pb年代学的证据  

Reworking of Indosinian Tectono-Thermal Events in the Yunkai Massif:Gneissic Multi-Mineral U-Pb Geochronological Evidence

作　　者：王祥东 徐德明[1] 王磊[1] 周岱[1] 胡军 柯贤忠[1] Wang Xiangdong;Xu Deming;Wang Lei;Zhou Dai;Hu Jun;Ke Xianzhong(Wuhan Center of China Geological Survey,Wuhan A30205,China)

机构地区：[1]中国地质调查局武汉地质调查中心,湖北武汉430205

出　　处：《地球科学》2020年第5期1653-1675,共23页Earth Science

基　　金：中国地质调查局项目(Nos.DD20190047,DD20160035);中国博士后科学基金项目(No.2018M630890)。

摘　　要：云开地块显生宙的构造演化一直是华南板块的研究热点之一.通过对云开地块变质基底中片麻岩进行独居石、磷灰石和锆石LA-ICP-MS U-Pb定年,获得了434±6 Ma(MSWD=3.0)和437±12 Ma(MSWD=6.0)的岩浆锆石年龄,结合镜下观察,认为其代表的是片麻岩原岩(花岗质岩石)的形成时代,与区域上加里东期构造-岩浆-变质-深熔事件的时限基本一致,为武夷-云开加里东造山作用的产物;磷灰石经过普通铅校正后分别给出了241±13 Ma(MSWD=2.2)和242±6 Ma(MSWD=1.4)的变质年龄,独居石则分别获得了236.2±0.8 Ma(MSWD=0.66)和229.4±1.2 Ma(MSWD=2.4)的变质年龄,这些年龄结果与云开地块构造岩云母Ar-Ar年龄相一致,暗示云井地块经历了印支期(230~240 Ma)构造热事件的叠加改造.对片麻岩中黑云母电子探针数据分析显示其具有相对高的Al、Ti和Mg含量,XMg值为0.37~0.45,属于铁质黑云母,其Ti饱和温度计给出温度范围为650~700℃(±50℃),与独居石估算温度580~640℃(±25℃)在误差范围内基本一致,暗示印支期构造热事件对云开地块的叠加改造温度达到了700℃.综上所述,认为云开地块现今的构造格局是在加里东期造山作用基础上叠加了印支期构造塑造而成,叠加温度可能达到了700℃;此外,在利用矿物对温压计恢复加里东期变质作用P-T轨迹时应着重考虑印支期构造热事件对矿物成分的再造作用.The Phanerozoic tectonic evolution of the Yunkai massif has long been one of the hot topics in the South China Block.LA-ICP-MS U-Pb dating was carried out on the monazite,apatite and zircon of two gneiss samples from the Yunkai massif,yielding two magmatic zircon ages of 434±6 Ma(MSWD=3.0)and 437±12 Ma(MSWD=6.0)respectively,which represent the crystallization age of gneiss protolith(granitic rocks)and are basically consistent with the ages of regional Caledonian tectonicmagmatic-metamorphic-anatexis events responding to the Wuyi-Yunkai Caledonian orogenesis.Apatite yields metamorphic ages of241±13 Ma(MSWD=2.2)and 242±6 Ma(MSWD=1.4)respectively;and monazite also yields metamorphic ages of 236.2±0.8 Ma(MSWD=0.66)and 229.4±1.2 Ma(MSWD=2.4)respectively.These U-Pb ages are consistent with the biotite Ar-Ar ages of the tectonite in the Yunkai massif,indicating the Indosinian(230-240 Ma)tectono-thermal reworking in the Yunkai massif.EPMA data of biotite from the gneiss show high Al,Ti and Mg contents,but low Fe content,with XMgratios ranging from 0.37 to 0.45,which indicates ferruginous biotite affinity.The Ti saturation temperature of biotite is 650-700℃(±50℃),agreeing with the monazite estimated temperature of 580-640℃(±25℃),which indicates that the temperature of Indosinian reworking maybe reached up to 700℃.In conclusion,the present tectonic pattern of the Yunkai massif is superimposed by Indosinian tectono-thermal events on the basis of Caledonian orogeny,and the superimposed temperature may reach 700℃.In addition,the effect of Indosinian tectono-thermal events on mineral composition should be taken into account when restoring Caledonian metamorphic P-T path with mineral thermometers and baresthesiometers.

关 键 词：多矿物U-Pb年代学 矿物化学 叠加改造 印支期 云开地块 构造地质 

分 类 号：P597[天文地球—地球化学]