青海小赛什腾山地区达肯大坂岩群中新解体出一套变火山岩系  

Discussion on Newly Disintegrated Metavolcanic Rock Series from the Dakendaban Group in Xiaosaishiteng Mountain Area,Qinghai Province

作　　者：王立轩 何世平[1] 庄玉军 李普涛[1] 段忠志 WANG Lixuan;HE Shiping;ZHUANG Yujun;LI Putao;DUAN Zhongzhi(Xi’an Center of Geological Survey, China Geological Survey, Xi’an 710054, Shaanxi, China;China University of Geosciences, Beijing 100083, China;Chinese Academy of Geological Sciences, Beijing 100037, China)

机构地区：[1]中国地质调查局西安地质调查中心,陕西西安710054 [2]中国地质大学(北京),北京100083 [3]中国地质科学院,北京100037

出　　处：《西北地质》2022年第1期1-18,共18页Northwestern Geology

基　　金：中国地质调查局西安地质调查中心“商丹大柴旦区域地质调查(DD20190069)”二级项目下设:“青海冷湖行委赛什腾山地区1∶5万J46E008015等四幅专项地质调查”子项目。

摘　　要：达肯大坂岩群(Pt1D.)是柴北缘欧龙布鲁克地块的结晶基底,为一套变质程度达角闪岩相的深变质岩系,形成时代为古元古代。通过1∶5万专项地质调查,在柴北缘欧龙布鲁克地块苏干湖南小赛什腾山一带原划归达肯大坂岩群中,新填绘出一套糜棱岩化变中酸性火山岩系与达肯大坂岩群岩石组合存在明显差异。通过LA-ICP-MS锆石U-Pb测年,分别获得其中变流纹岩原岩形成年龄为(435.2±1.5)Ma、变英安岩原岩形成年龄为(430.6±2.6)Ma,表明该套糜棱岩化变中酸性火山岩系形成于早志留世。经综合分析,将其从达肯大坂岩群中解体出来,暂划归滩间山群。同时,获得侵入变英安岩中的糜棱岩化花岗岩脉原岩形成年龄为(269.3±1.8)Ma,并获得(1607±14)Ma上交点年龄,代表其母岩形成年龄或岩浆侵入过程中捕获古老围岩的年龄;此外,获得糜棱岩化变英安岩构造热事件年龄为(265.7±4.0)Ma,晚于发育左行剪切揉皱糜棱岩化花岗岩脉的形成时代,表明新解体出的变火山岩系发生左行剪切作用的时代为花岗岩脉侵入之后的晚华力西期。The Dakendaban Group(Pt1D.)is the crystalline basement of Oulongbulak block in the northern margin of Qaidam Basin.It is a set of deep metamorphic rock series with metamorphic degree of amphibolite facies and formed in Paleoproterozoic.Based on the 1∶50000 special geological survey,a new mylonitization and intermediate-acid metavolcanite series has been delineated from the original Dakendaban group in the Xiaosaishiteng Mountain,south of Sugan Lake,Oulongbulak block in the northern margin of Qaidam Basin,which is obviously different from the rock assemblages of Dakendaban group.LA-ICP-MS zircon U-Pb dating shows that the meta-rhyolite protolith is(435.2±1.5)Ma and meta-dacite protolith is(430.6±2.6)Ma,indicating that the mylonitic metamorphic intermediate-acid volcanic series formed in the Early Silurian.Comprehensive analysis disintegrated it from the Dakendaban Group and temporarily classified it as the Tanjianshan Group.The formation age of mylonitized granitic dikes intruding into meta-dacite is(269.3±1.8)Ma,and the age of upper intercept age is(1607±14)Ma,which represents the formation age of the parent rock or the age of the ancient surrounding rock captured in the process of magmatic intrusion.In addition,the tectonic thermal event age of mylonitized meta-dacite is(265.7±4.0)Ma,which is later than the formation age of left-lateral shearing and crinkling mylonitized granitic dikes,indicating that the newly disintegrated metavolcanic rock series occurred in the late Variscan after the intrusion of granitic dikes.

关 键 词：达肯大坂岩群 变火山岩系 LA-ICP-MS锆石U-PB测年 滩间山群 小赛什腾山 

分 类 号：P534[天文地球—古生物学与地层学]