内蒙古西乌旗南部晚古生代侵入岩年代学、地球化学特征及地质意义

Chronology,Geochemistry and Tectonic Implications of Late Palaeozoic Intrusions from South of Xiwuqi,Inner Mongolia

为探讨兴蒙造山带南蒙古陆块南缘晚古生代的构造演化,对出露于西乌旗南部石英闪长岩、花岗闪长岩和黑云母花岗岩开展了详细的年代学、岩石地球化学及Hf同位素特征研究.结果表明:石英闪长岩、花岗闪长岩和黑云母花岗岩分别形成于330±2Ma、274±1Ma及271±1Ma^282±1Ma.石英闪长岩属高镁闪长岩/安山岩类(HMA),与俯冲洋壳板片上部地幔楔中地幔橄榄岩的熔融作用有关,而花岗闪长岩及黑云母花岗岩的源区可能与新生地壳的部分熔融有关.结合区域成果,推测西乌旗南部晚古生代侵入岩均形成于古亚洲洋向北侧南蒙古陆块持续俯冲的阶段,早石炭世石英闪长岩属活动大陆边缘弧岩浆活动,早二叠世花岗闪长岩和黑云母花岗岩则是俯冲过程中短暂弧后伸展阶段的产物.

In order to discuss the tectonic evolution of the Xing-Meng orogenic belt during the Late Palaeozoic, this study con ducts a systematic study of the chronology, geochemical compositions and Hf isotopic characteristics of the quartz diorite, gran odiorite and biotite granite from the south of Xiwuqi, which is situated at the southern margin of the southern Mongolian terra- ne. Zircon U-Pb dating indicates that the quartz diorite, granodiorite and biotite granite were emplaced at ca. 330＋2 Ma,274 ＋1 Ma and 271＋1 Ma^282＋ 1 Ma, respectively. The quartz diorite shows typical features of HMA and may be formed by melting of the subcontinental lithospheric mantle wedge induced by fluids released from partial melting of the subducted oceanic crust. The source of the studied granodiorite and biotite granite might be related to partial melting of juvenile crustal materials. Considering the regional geology, we infer that the Late Palaeozoic intrusions from the south of Xiwuqi were likely emplaced during the northward subduction of the Paleo-Asian Ocean plate beneath the southern Mongolian terrane. The Early Carbonif erous quartz diorites are components of a continental arc-related magmatism, the Early Perrmian granodiorites and biotite gran- ites are products of magmatism in a temporal back-arc extension setting during the northward subduction.