索伦-林西缝合带北缘构造属性:来自内蒙古扎鲁特旗北部寿山沟组变沉积岩及其安山岩透镜体的制约

Tectonic attributes of the northern Solonker-Linxi suture zone:Constraints from the Shoushangou Formation metamorphosed sedimentary rocks and its andesite lenticle in northern Jarud Banner,Inner Mongolia

本文选择扎鲁特旗北部达巴艾勒地区出露的一套下二叠统寿山沟组变沉积岩及其安山岩透镜体作为研究对象,在野外地质调查的基础上,通过岩相学、年代学、岩石地球化学等方面的系统研究,深入探讨索伦-林西缝合带北缘晚古生代的构造属性。下二叠统寿山沟组变质沉积岩LA-ICP-MS锆石U-Pb测年结果显示其最小峰值年龄为282.3±4.2Ma和285.9±5.6Ma,限定了沉积下限为早二叠世,另外还含有少量400~500Ma以及个别700~800Ma、1700Ma的单颗粒碎屑锆石年龄,表明其物源区主要来自于北侧的锡林浩特岩浆弧。碎屑锆石年龄图谱反映其沉积背景为汇聚背景下的弧前盆地。地球化学特征表明寿山沟组变质沉积岩物源主要来自中酸性岩浆岩源区,形成于大陆岛弧环境。该套沉积岩中的晚石炭世安山岩透镜体锆石U-Pb测年结果为304.9±4.7Ma,地球化学特征显示其具有高镁安山岩特征,为俯冲洋壳释放含水流体交代地幔楔发生部分熔融的产物,形成于大陆边缘弧构造背景。综合分析,索伦-林西缝合带北缘在晚石炭世-早二叠世处于洋内俯冲向洋陆俯冲过渡的转换环境。

On the basis of detailed investigations,a set of Early Permian Shoushangou Formation metamorphosed sedimentary rocks and the inside andesite lenticle exposed in the Daba Aile area,northern Jarud Banner are selected to study the Late Paleozoic tectonic attributes of the northern Solonker-Linxi suture zone through systematic petrographic,chronologic and geochemical analyses.The LA-ICP-MS zircon U-Pb dating results of the Lower Permian Shoushangou Formation meta-sedimentary rocks show that the minimum peak ages are 282.3±4.2Ma and 285.9±5.6Ma,defining the lower sedimentary limit as the Early Permian.In addition,it also contains a small amount of 400~500Ma and individual 700~800Ma,1700Ma detrital zircon ages,reflecting that its provenance area mainly comes from the Xilinhot magma arc on its north side.The detrital zircon spectra of the meta-sedimentary rocks reflect they are deposited in the convergence tectonic setting of a forearc basin.Geochemical characteristics show that the provenance of the metasedimentary rocks of the Shoushangou Formation mainly comes from the intermediate-acid magmatic rocks,and was formed in the continental island arc environment.The zircon U-Pb dating result from an andesite lenticle inside the sedimentary rocks is 304.9±4.7Ma,and the geochemical characteristics show that it is characterized by high-magnesium andesite,which indicate that the andesite is derived from the partial melting of the mantle wedge metasomatized by an aqueous fluid released from the subducted oceanic crust,and formed in the continental margin arc environment.Comprehensive analysis shows that the northern Solonker-Linxi suture zone was in a transitional environment from intra-ocean subduction to ocean-land subduction during the Late Carboniferous to Early Permian.