内蒙古四子王旗地区古生代—早中生代侵入岩活动期次、特征及构造背景

Geochronology,Geochemistry and Tectonic Setting of the Paleozoic-Early Mesozoic Intrusive in Siziwangqi,Inner Mongolia

通过对内蒙古四子王旗地区近年来获得的古生代-早中生代侵入岩锆石U_Pb及少量Rb—Sr测年结果的分析，认为该区古生代-早中生代至少经历了奥陶纪、石炭纪-早二叠世、中晚二叠世以及三叠纪等4期明显的岩浆作用过程。奥陶纪岩浆活动时限在508-454Ma，出露面积少，岩性主要为闪长岩、石英闪长岩，经历较强的变质变形作用。石炭纪-早二叠世岩浆活动时限在331～299Ma，分布面积最少，岩石组合为辉长岩、闪长岩及石英闪长岩，有弱变形或未变形。中晚二叠世岩浆活动时限为271～253Ma，出露面积最大，岩石组合有富含暗色包体的花岗闪长岩、正长花岗岩、二长花岗岩及少量的角闪正长岩。三叠纪岩浆活动时限为250～224Ma，出露面积较大，岩石组合有白云母花岗岩、二长花岗岩及碱性岩。这些广泛分布的多期次岩浆活动表明四子王旗地区在此期间经历了复杂的岩浆及构造作用过程。奥陶纪岩浆活动和石炭纪-早二叠世岩浆活动可能与古亚洲洋多次俯冲作用相关。中晚二叠世岩浆活动可能与西伯利亚板块和华北板块的碰撞作用有关。三叠纪岩浆活动与造山后伸展作用及岩石圈拆沉有关。

A summary of the recently obtained zircon U-Pb or Rb-Sr ages of the Paleozoic-Early Mesozoic intrusive rocks in the Siziwangqi area indicates that at least four stages of magmatism including Cambrian to Ordovician, Carboniferous to Early Permian, Middle to Late Permian, Triassic occurred during the Paleozoic to Early Mesozoic period. The main components of the Cambrian to Ordovician intrusive are diorite and quarta diorite. The Carboniferous to Early Permian intrusive rocks consist mainly of gabbro, diorite and quarta diorite. Rocks from Middle to Late Permian intrusive suite are composed mainly of granodiorite, monzogranite, syenogranite with some hornblende-syenite. The main components of the Triassic intrusive are muscovite granite, monzogranite, and alkaline rocks. Compared with the Cambrian to Ordovician, Carboniferous to Early Permian, the Middle to Late Permian and Triassic intrusive rocks show much more extensive distribution. The wide distribution of the Paleozoic-Early Mesozoic intrusive rocks indicates a very complex tectonomagmatic history of the Siziwangqi area during the Paleozoic-Early Mesozoic period. The Cambrian to Ordovician and Carboniferous to Early Permian rocks are probably related to the subduction of the Paleo-Asian Ocean. The Middle to Late Permian rocks are interpreted as collision between North China Craton and Siberia plate. The Triassic intrusive rocks might have resulted from post-collisional lithospheric extension after final collision, represented the ending of orogeny.