Carboniferous Tectonic Magmatic Belt And Its Geological Significance In Xiwuqi, Inner Mongolia

The research zone resferenced in this paper is located in Inner Mongolia Xiwuqi;it geotectonicly situated in collision belt of north China Taipei hyperplasia and thesouthern margin of the Siberian platform. The latter is in the east side of the MongoliaGuYaZhou ocean tectonic domain （first-order tectonic units） which is located betweenthe the north China plate and Siberia plate （or plate.）In this paper, on the basis of regional survey, in the study area, detailedspace-time characteristics and geochemical studies was done to research theCarboniferous tectonic magmatic belt of the gabbro, diorite, quartz-diorite rocks andthen to explore its tectonic significance.Through the LA-ICP-MS U-Pb dating and the statistical analysis of measuringpoints （158in total） with high degree of harmony.in8dating samples indicated thatthe magmatic activity of Carboniferous magmatic belt concentrated in the following2stages: the later of Early Carboniferous（319³29Ma） and the mid-late LateCarboniferous（about310ma）, mainly from the later of Early Carboniferous to LateCarboniferous. Major lithologic association contains gabbro, diorite, quartz dioritewith 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 that the Carboniferous gabbro anddiorite belong to the low potassium tholeiitic series, presenting a REE distributionpattern with loss of light rare earth weak. The Carboniferous quartz-diorite belongs tothe calc-alkaline series, presenting the REE distribution pattern with enrichment oflight rare earth weak. But there is similar quality of gabbro, diorite and quartz diorite,that their TiO₂contents are low. And in the standardization of trace elements spiderdiagram, there is rich K Ba Rb Sr and other large ion lithophile elements, and Nb Ti Phigh field strength elements relatively low. Geochemical characteristics indicate thatthe qualities of the rock mass is relavant to the Subduction mechanism; it’s mantlemagma derived from the depleted primitive mantle and it was contaminated bycontinental crust material in the process of rising, its evolution has experienced the different degree of partial melting and crystallization separation.In the tectonic environment discrimination diagram, all the samples are locatedin the island arc tholeiite or the island arc calc-alkaline basalt area, indicating that themagma formed in the island arc tectonic environment or continental marginenvironment that associated with subduction zone.Based on the comprehensive analysis of the space-time and geochemicalcharacteristics of Carboniferous tectonic magmatic rocks,comparing arc magmaticrocks in Dongwuqi area and combining with the widely spreading calc-alkaline arcvolcanic rocks of Dashizhai Formation, this paper deems that the Carboniferoustectonic magmatic belt was induced by the subduction of the Hegenshan Ocean Basintowards the XilinhaoteIntermediate Massif and may belongs to a significant part ofHegenshanophiolite-Arc-hyperplasia hybrid zone.