Studies Of Geochronology And Geochemistry Of The Carboniferous Intrusive Rocks In Xilinhot Maodeng Area, Inner Mongolia

Based on1:50,000regional geological survey in Maodeng area, Xilinhot, with the analysis of macrogeologicl features of The Carboniferous intrusive rocks and the data of petrology and geochemistry, this articlediscussing the effect of magmatic activity in the process of plate collision. It analyses the relationship betweenthe petrology and the tectonic setting. The paper provides the deep geological constraints and chronologyevidence for the study of Maodeng area regional structure and plate tectonics collision.The magmatic rocks exposures generous in the study area. Magmatic activity last三from the Devonianto the Cretaceous, formed the intrusion of a different era and lithologies, and the Carboniferous intrusive rocksoccupies an area about a quarter of the region. Through the LA-ICP-MS U-Pb dating and the statisticalanalysis of measuring points with high degree of harmony, in12dating samples indicated that the magmaticactivity of Carboniferous magmatic belt concentrated in the following3stages: the mid-late of EarlyCarboniferous(325-331Ma）, the Early of Late Carboniferous(310-318Ma) and the Late of LateCarboniferous(301-305Ma), with a NE-trending long axis which shares the same direction with the regionaltectonic line and formed the Carboniferous tectonic magmatic belt.The Geochemical analysis results show thatthe Early Carboniferous rocks is granitic rocks, the Late Carboniferous rocks is the mafic to the acidicrocks.The results of mineral assemblages, rock association and geochemistry show the rocks is S-type granites,and I-S type granites.In the tectonic environment discrimination diagram, the samples are located IAG area, indicating that themagma formed in the island arc tectonic environment. The monzogranite has the feature of post-orogenicextensional environment,showing partial extend environment of subduction zone.Based on thecomprehensive analysis of the space-time, and geochemical characteristics of Carboniferoustectonic magmatic rocks, comparing arc magmatic rocks in Dongwuqi area and combining withthe widely spreading calc-alkaline arc volcanic rocks of Chagannuoer Formation, this paperdeems that the Carboniferous tectonic magmatic belt was induced by the subduction of theHegenshan Ocean Basin towards the XilinhaoteIntermediate Massif and may belongs to asignificant part of Hegenshanophiolite-Arc-hyperplasia hybrid zone.