Research On Disintegration And Chronology Of Xilin Gol Complex In Xiwuqi, Inner Mongolia

Xiwuqi，Inner Mongolia is between Hegenshan suture zone to the north andSolon-Xar Moron River suture to the south, which is located in the mid-east of Xing’anMongolian orogenic belt. Xilin Gol Complex emerged in the area is a suite ofmetamorphic rocks which have endured strong metamorphism and deformation. Thisarticle recovers its protolith and tectonic settings by analyzing its field geological,petrologic and geochemical features. The forming time and tectonic significance arealso discussed. Based on the differences of rock associations, metamorphic anddeformation characteristics as well as the forming time, this article d isintegrates XilinGol Complex into four parts: Buyant Group of Proterozoic era, Bulongshan Formationof Ordovician, Chagannor volcanic rocks of early Carboniferous and intrusive rocks ofUpper Ordovician and Carboniferous epoch. Buyant Group is a suite of strongmetamorphic-geologic body belongs to amphibolitfacies which comprises schist,gneiss, leptynite, leuco leptite and quartzite. Chagannor volcanic rocks are mainlyandesite, dacite and rhyolite which belong to calc-alkalic series with a zircon U-Pb ageof336Ma and formed during early Carboniferous epoch. The intrusive rocks comprisegabbro diorite belongs to low-K tholeiitic rock series of Upper Ordovician,peraluminous and high potassium calc-alkaline adamellite of early Carboniferous, highpotassium calc-alkaline syengranite and diorite dikes of late Carboniferous epoch.The protolith of Buyant Group is a suite of clastic sedimentary rock whichconsists of shaly sand, arkoses, and greywacke. It formed in the active continentalmargin and arc settings. The zircon U-Pb ages of440Ma and950Ma indicate thatBuyant Group experienced at least two metamorphic events. According to the detri talzircon U-Pb age between1367-2369Ma and regional geology research status, it issuggested that the metamorphic rocks possibly formed during Mesoproterozoic, which proves the existence of Precambrian metamorphic basement rock series in the region,and indicates that the existence of Xilinhot microblocks.The protolith of Bulongshan formation is also a suite of clastic sedimentary rockwhich formed in the arc-active continental margin settings. It includes quartzsandstone, arkoses, and greywacke with clay. The minimum of the detrital zircon U-Pbage is449Ma, and the age of420Ma indicates Bulongshan formation experienc ed ametamorphic event and formed during middle to late Ordovician. In combination withthe regional geology research, the provenance of Bulongshan formation is from SonidLeft Banner-Xilinhot early Paleozoic magmatic belts or Xilin Gol Complex (BuyantGroup described in this article). The provenance is probably a fore-arc sedimentaryformation and may be formed during the subduction state of Paleo-Asian Ocean inearly Paleozoic era.