Characteristics And Tectonic Significance Of Late Paleozoic Intrusive Rocks Along The Tamusu-Wuliji Noel Of Alxa, Inner Mongolia

Alax lies in the northern border of China, crossing the northern margin of North China plate and Xing’an-Mongolian Orogenic belt. Magmatic activities are featured by long-term evolution, complex rock categories and variable tectonic settings.This paper studied the late Paleozoic intrusive rocks along Tamusu-Uligi Engel bordering WuSu ophiolite melange to the north, and concluded the intrusive rocks formed in the Permian.The intrusive rocks in the research area include medium-fine graind quartz diorite, quartz monzodiorite, medium-fine grained granodiorite and monzonitic granite. All rocks above belong to calc-alkaline series. The evolution processes, from the early diorite and quartz diorite to the middle-phrase granodiorite and the late monzonitic granite, from meso-basic magma in early phrase to acidic in late, form a completed magma evolution sequence.Meddle Permian intrusive rocks are dominated by medium-fine grained quartz diorite and monzonitic granite. Chemical characteristics show calc-alkaline series, featured by high SiO2. REE has profound negative Eu anomalies, showing the features of S-type granite originated from crust anatexis. LA-ICP-MS zircon U-Pb results give two mean average ages,266.4±3.7Ma and268±1Ma, indicating the rocks formed in the meddle Permian.Late Permian intrusive rocks are composed by medium-fine grained granodiorite and monzonitic granite. Their chemical characteristics indicated they were the product of crust anatexis, and the source rocks probably were I-type igneous rocks. Chemical elements and zircon feature reflect a cognate magma evolution sequence. The LA-ICP-MS zicorn U-Pb dating result come out as249.7±1.6Ma and249.7±1.7Ma, showing the rocks formed in the late Permian.The research reveals that the meddle-Permian intrusive rocks formed in an active continental margin collision orogenic belt tectonic setting. The evolution process from quartz diorite to monzonitic granite roughly represented the transform from pre-collision to syn-collision. Late-Permian intrusive rocks formed in the continental margin arc, belonged to regular orogenic arc granite, and they were new accretion continental crust formed by fresh magma during the orogenic process. To conclude, magma activities from meddle Permian to late Permian, from medium-fine grained diorite to monzonitic granite, showed an evolution tendency from pre-collision to syn-collision.