Geological Characteristics Of Early Carboniferous Intrusion From Biaoshan Area In Beishan,Inner Mongolia And Their Tectonic Implications

The study area is located in the beishan orogenic belt of Inner Mongolia,north of t he hongliuhe-niuhue-qingchangjing ophiolite belt and south of the hongshishan-baishan-yua nbaoshan ophiolite belt.This paper choose the the latest emplaced age and the widest ra nge of intrusive rocks,and based on the Biaoshan area of Inner Mongolia 1:5 regional g eology survey,and fully collecting related data,to study petrochemistry,geochemistry,LA-MC-ICP-MS zircon U-Pb chronology,petrogenesis and tectonic environment system atically.Petrology and petrochemistry characteristics show that the intrusive rocks of early Carboniferous in study area are the fine-medium grain quartz diorite,fine-medium grain granite diorite and fine grained monzonitic granite,and they have continuous evolution characteristics,which have common mothernal magma evolution.the intrusive rocks of early Carboniferous in study area presents the characteristics of rich silicon,lack aluminum,magnesium and iron which property is a quasi-in weak aluminum-aluminum,high in potassium calc-alkaline series.The intrusive rocks increasing content of SiO2 accompany with the direction of rich alkali,high potassium and aluminum.The geochemical characteristics showed that the total amount of rare earth elements in early Carboniferous intrusive rocks was relatively low(?REE=116.01²10.23 x 10^-6),which belonging to the type of light rare earth enrichment?LR/HR=5.10⁹.32?.Th e?Eu has week negative anomaly??Eu=0.6⁰.85,average value=0.76?and the distribution curve of rare earths was skewed to the right.The rocks relative enrichment of incompati ble elements Rb,Th,La,Hf,while loss of high-field strength elements Nb,Ta,P,Ti w hich show the characteristics of typical island arc granite.The early carboniferous intrusive rocks in the study area belong to highly differentiated i-type granite,and the magmatic source area is derived from the part melting of the basic rocks to part melting of mixed sandstones,and the mantle-derived magmas assimilate and mix a large amount of crust materials to form crust-mantle mixed magmas in the process of upper invasion.U-pb ages of la-mc-icp-ms zircons were obtained in this study,respectively 340.31+0.83Ma?fine-medium grain quartz diorite?,340+1.7ma?fine-medium grain granodiorite?,340.21+0.76Ma and 335.2+3.2ma?fine-grain erachite?,and the age of the intrusive rocks was early carboniferous.The petrochemistry and geochemical characteristics all show that the early Carboniferous intrusive rocks in the study area are the island arc granited formed before plate collision,which is the product of the limited ocean basin subducted from north to south represented by hongshishan-lilian-yubaoshan ophiolite belt.