The Granitoids, Geochronology, Rock Assemblages,Tectonic And Evolution Of The Erenhot City-Abag Banner, Inner Mongolia

According to the1:250,000scale geological survey in Erenhot City-Abag Banner, the main geological characteristics of this region is the wide formation and distribution of paleozoic magmatic rock. Based on materials collected through field work and existing research results, as well as theories and methods in petrology, petrochemistry and geochemistry, combining materials on geological characteristics and isotopic age documents, using the method of defining ages by the high precision zircon U-Pb isotopic ages, this paper establishes the geochronological framework in the study area, analyses and defines the igneous petrotectonic assemblages, and then explores and discusses the geotectonic evolution and continental crust growth in the study area.Based on the chronology of igneous rock evolution (including the intrusive rock and the volcanic rock), the geotectonic evolution in the area can be divided into seven stages, and each stage matches different kinds of igneous rocks and different tectonic settings. The main conclusions area as follows:(1) In O, the rock assemblage was mainly basalt andesite, andesite and dacite, and this stage was the island arc stage.(2) In D1-2, the rock assemblage was mainly mesite and basite(andesite-basalt and andesite), and this stage was the island arc stage.(3)In D3, the rock assemblage was quartz diorite-tonalite-granodiorite, combine for the T1T2G1G2, the which have the characteristics of TTG rock, and this stage was the early subduction orogenic stage.(4)In C1, the rock assemblage was granohndiorite-monzogranite-orthoclase granite, combine for the G1G2, which are highly diversified I type granite, and this stage was the main subduction orogenic stage.(5)In C2, the rock assemblage was fine grained hornblende gabbroâ†'fine grained diorite and fine grained quartz dioriteâ†'ine grained biotite granodioriteâ†'horblende quartz monzoniteâ†'medium-grained biotiteâ†' medium grained biotite monzograniteâ†'medium grained granite, combine for the T2G2, and this stage was the late subduction orogenic stage.(6) In C2-P1, the rock assemblage was neutral-intermediate-acid-acid volcanic lava(mainly basalt andesite-dacite-dacite and volcaniclastic rock and a few sedimentary clastic rocks), and this stage was the late subduction orogenic—ontinent-continent collision transition stage.(7) In P1, Medium-the west with the rock assemblage a granodiorite-tonalite for lord, and this stage was the continent-continent collision the early stage; Medium-the east with the rock assemblage was monzogranite-orthoclase granite, which are calc-alkali granite, and there are also some alkali granite, and this stage was post-orogenic stage.In the orogenic belt of the study area, the formation, spatial distribution and evolution of igneous rock show obvious polarity and directionality. The geotectonic evolution experienced the whole process of immature island arc in the ocean-half mature continentalized island arc-mature continental marginal arc-orogenic belt magmatic arc after continent collision.