The Petrology Characteristics Of The Mesozoic Volcanic Rocks In Sonid Zuoqi Area Of Inner Mongolia

This paper is supported by The project“Inner Mongolia1:50000of ZhunheremuyinSumu six pieces of regional geological and minerals survey”,Carry out the research on thepetrology, geochronology and geochemistry of Mesozoic volcanic rocks in Sonid ZuoqiArea of Inner Mongolia. The study area is located in the eastern section of The CentralAsian Orogenic Belt（CAOB）-the northern orogenic belt of Xingmeng orogenic belt. Itbelonged to the paleo Asian tectonic domain when in Paleozoic, located in the southeasterncontinental margin accretionary belt-Dongwuqi-Zhalantun volcano passive continentalmargin,In Its south are Erlian-Hegenshan Ophiolite belt zone and Solonher–Linxi suturein sequence,Changan Obo-Arongqi fault Through the study area. When in Mesozoic, itbelonged to West Pacific tectonic domain.The volcanic rocks in Sonid Zuoqi Area distributes north-eastwards. The rock type isrelatively simple, and the lower part are andesites while the upper part are trachydesites.The two LA-ICP-MS zircon U-Pb dating weighted average age were135.1±5.6Ma and135.2±3.8Ma. we can infer that The volcanic rocks in Sonid Zuoqi Area formation inEarly Cretaceous Epoch and not late Jurassic which previously considered. Combined withthe regional stratigraphic data with new zicorn dating results, This study change the manituformation (J3mn) which previously considered (1:250000hong ge er regional stratigraphicsurvey report) to the baiyingaolao formation (K1b).The contents of SiO2of volcanic rocks in Sonid Zuoqi Area changes between58.23wt%~67.93wt%,They have relatively higher total alkal（i6.22wt%~8.26wt%）and K2O（2.49wt%~4.58wt%）,belonging to the metaluminous to weakly peraluminous（NK<A<CNK）rocks. belonging to the subalkalic series and has the high-k calc-alkalineseries to the shoshonite series tendency. REE diagrams shows the rocks enrichment of lightrare earth elements, loss of heavy rare earth elements, showing a" rightist" trend. The traceelement spider diagrams show that the volcano rocks are enriched in enrichment of Rb, Ba,Th and other large ion lithophile elements (LILE) and loss of Nb、Ta、Ti and other highstrength element (HSFE)for feature. rocks have high Zr（446ppm~789ppm）andY（15.2ppm~24ppm）content.In the（Na2O+K2O）-δEu diagram, rocks mostly distributes inmantle range, Rock samples distributes in mantle source region. Rb-Sr abundance andcrustal thickness diagram shows that lithosphere had thickened process. So we can draw theconclusion that The magma of volcanic rocks in Sonid Zuoqi Area originated fromthickened lithospheric mantle. In Zr/Al2O3-TiO2/Al2O3and Ti/Y-Zr/Y diagram,Volcanorocks all into intraplate environment. In combination with the related data of regional, we conclude that the volcanic rocks in Sonid Zuoqi Area were formed under the post-orogenicof extensional setting.