内蒙古贺根山缝合带后造山作用——满克头鄂博组火山岩锆石U-Pb年龄和地球化学制约

以出露于贺根山缝合带梅劳特乌拉蛇绿岩中的白音瑞满克头鄂博组火山岩为研究对象,通过野外地质调查、岩石学、地球化学和LA-ICP-MS锆石U-Pb年代学研究,探讨火山岩成因、构造环境与贺根山缝合带后造山作用。岩石地球化学研究表明,白音瑞地区满克头鄂博组火山岩主要为流纹岩,岩石具有较高SiO_2、K_2O和Na_2O+K_2O含量,以及较高Ga/Al值,相对贫CaO、MgO、Sr、Ba、Eu、Ti和P的特征。稀土元素含量较低,配分曲线为微弱右倾的海鸥式分布。岩石学和地球化学特征表明,该区满克头鄂博组流纹岩为A型流纹岩,形成于后造山伸展构造环境,为后造山A型花岗岩浆作用的产物。LA-ICP-MS锆石U-Pb同位素定年结果显示,该流纹岩的形成年龄为158.0±0.7Ma,表明满克头鄂博组流纹岩喷发于晚侏罗世,反映了贺根山缝合带晚侏罗世后造山A型花岗岩浆作用事件。结合二连-贺根山缝合带石炭纪蛇绿岩、石炭纪—二叠纪岛弧岩浆岩和中三叠世—早白垩世后造山A型岩浆岩的时空分布与演化关系,认为二连-贺根山缝合带在中三叠世—早白垩世经历了后造山伸展作用演化过程。

Post-orogeny of the Hegenshan suture zone: Zircon U-Pb age and geochemical constraints from volcanic rocks of the Manketouebo Formation

Based on field geological survey, petrology, geochemistry and LA-ICP-MS zircon U-Pb geochronology of the Baiyinrui volcanic rocks of the Manketouebo Formation exposed in the Meilaotewula SSZ-type ophiolite of the Hegenshan suture zone in Xi Ujimqin Banner of Inner Mongolia, this paper discusses the petrogenesis and tectonic setting of the volcanic rocks and post-orogeny of the Hegenshan suture zone. Petrogeochemical studies show that the volcanic rocks of the Manketouebo Formation in Baiyinrui area are mainly rhyolite with high SiO₂, K₂O and Na₂O+K₂O content, higher Ga/Al ratio and relatively poor CaO, MgO, Sr, Ba, Eu, Ti and P content. The REE content is relatively low. The REE distribution curve exhibits weak right-inclined gull-wing distribution. Petrological and geochemical characteristics show that the rhyolite of the Manketouebo Formation in this area is of Atype rhyolite origin, formed in post-orogenic extensional tectonic setting, and is a product of post-orogenic A-type magmatism, reflecting post-orogenic extensional process. The results of LA-ICP-MS zircon U-Pb isotope dating show that the rhyolite was formed at 158.0±0.7Ma, indicating that the rhyolite of the Manketouebo Formation erupted in the Late Jurassic, reflecting the Late Jurassic post-orogenic A-type magmatism event in the Hegenshan suture zone. Combined with the study of the time and space evolution of the Carboniferous ophiolites, Carboniferous-Permian island arc magmatic rocks and Middle Triassic-Early Cretaceous post-orogenic A-type magmatic rocks in the Erenhot-Hegenshan suture zone, it is considered that the Erenhot-Hegenshan suture zone underwent the evolution stage and dynamic process of post-orogenic extension during the Middle Triassic-Early Cretaceous after the final suture stretching in the Late Permian-Early Triassic.