秦岭南缘勉略带构造属性及晚古生代地质背景:来自碎屑锆石U-Pb年代学的制约  

Tectonic attributes and Late Paleozoic geological background of Mian-Lue belt in the southern margin of Qinling:Constraints from U-Pb geochronology of zircon

作　　者：李小兵[1,2] 裴先治 李佐臣[1] 李瑞保[1] 裴磊[1] 高峰[1] 王盟[1] LI XiaoBing;PEI XianZhi;LI ZuoChen;LI RuiBao;PEI Lei;GAO Feng;WANG Meng(School of Earth Science and Resources,Chang'an University,Xiaon 710054,China;College of Geographical Sciences,Shanxri Normal Unversity,Linfen 041004,China;MOE Key Laboratory of Westem China’s Mineral Resoures and Geological Engineering,Chang'an Univesity,Xi’an 710054,China)

机构地区：[1]长安大学地球科学与资源学院,西安710054 [2]山西师范大学地理科学学院,临汾541454 [3]长安大学西部矿产资源与地质工程教育部重点实验室,西安710054

出　　处：《岩石学报》2021年第5期1444-1468,共25页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41872233、41872235);中国地质调查局地质调查项目(1212011120161);中央高校基本科研业务费专项资金项目(CHD2011TD020、2013G1271091、2013G1271092、310827161002、310827161006、310827173702);陕西省公益性地质专项(20150102)联合资助。

摘　　要：勉略构造带作为秦岭造山带内重要的构造边界,关于其构造属性及晚古生代以来的地质背景,一直是学术界争论的焦点。碎屑锆石U-Pb年代学在限定地层单元的最大沉积年龄、研究区域构造岩浆事件及约束构造地质背景等方面行之有效。基于此,通过对勉略带内五郎坪北侧两河口变沉积地层和侵入其中的变形花岗岩脉体进行LA-ICP-MS锆石U-Pb年代学研究。获得2件变形花岗岩脉的结晶年龄均为406±1Ma。碎屑锆石主年龄谱分别为422~456Ma和558~826Ma,峰值年龄为441Ma和771Ma、813Ma,次级年龄谱分别为942~1495Ma和1658~2981Ma,峰值年龄不明显。依据最小一组碎屑锆石的峰值年龄(441Ma),和侵入其中的变形花岗岩脉(406±0.6Ma),限定该变沉积地层形成时代为406~441Ma(S_1-D_1)。碎屑锆石年龄谱显示该套变沉积地层物质来源较为复杂,其中秦岭造山带及扬子板块北缘早古生代、新元古代岩浆岩为其提供了74%±的物源,古老变质基底为其提供了26%±的物源。通过与区域上已有资料对比,认为勉略构造带内晚古生代沉积地层形成环境与邻区大致相同,且本次所获得的变沉积岩碎屑锆石年龄谱也与邻区泥盆系相似。综合认为,勉略构造带与邻区在晚古生代应属同一构造环境,晚古生代"勉略海盆"应当包括整个南秦岭。Mian-Lue tectonic belt is an important tectonic boundary in the Qinling orogenic belt,and its structural attributes and geological backgrounds since the Late Paleozoic have been the focus of debate in academic circles.The U-Pb chronology of detrital zircons is effective in defining the maximum sedimentary age of stratigraphic units,studying regional tectono-magmatic events,and constructing tectonic and geological settings.Based on this,the LA-ICP-MS zircon U-Pb geochronology study was carried out on the meta-sedimentary rocks and granite intrusions within the Lianghekou on the north side of Wulangping in Mian-Lue belt.We obtained406±0.6 Ma crystallization ages of two granite veins in the meta-sedimentary rocks,indicating that their formation age should not be later than 406 Ma.Detrital zircon U-Pb age spectrum can be explicitly divided into Early Paleozoic and Neoproterozoic two main age spectrum and the Paleoproterozoic,Mesoproterozoic,Early Neoproterozoic secondary age spectrum.The main age spectra were within ranges of 422~456 Ma and 558~844 Ma,with three peak ages of 441 Ma,771 Ma and 813 Ma,respectively.The secondary age spectra were 942~1495 Ma and 1658~2981 Ma respectively,without any obvious peak age.Based on the peak age of the smallest group of detrital zircons(441 Ma),and the age of the deformation granite dike(406 Ma),we infer that the metasedimentary strata were formed at 406~441 Ma(S_(1)-D_(1)).Combined with geological data in the study area and its adjacent areas,the meta-sedimentary rocks on the north side of Wulangping in Mian-Lue belt has a multiple supplying sources from different time periods,namely,Early Paleozoic,Neoproterozoic,Mesoproterozoic,Palaeoproterozoic and Archean.Furthermore,the Early Paleozoic magmatic rocks and Neoproterozoic magmatic rocks in Qinling orogenic belt and the northern margin of the Yangtze provide about 74%±of sediment source,while the old metamorphic basement provides only about 26%±of sedimentary debris for meta-sedimentary rocks.In addition,by comparing with t

关 键 词：碎屑锆石U-PB年龄 沉积物源 构造属性 勉略带 秦岭南缘 

分 类 号：P534.4[天文地球—古生物学与地层学] P597.3[天文地球—地质学]