Composition And Evolution Of The Early Precambrian Basement In Daqingshan Region, Inner Mongolia

Daqingshan Mountain, Inner Mongolia region is an important part of the EarlyPrecambrian basement of North China Craton, and one of the basement rocks to retainbetter areas. The regional geological survey results indicate that the region earlyPrecambrian rock is complete, mainly composed of Archaean granite-greenstoneterrane, Archean granulite-charnockite terrane and Early Proterozoic khondalite. Inaddition, the Department of khondalite also found a large number of early Proterozoicmetavolcanic rocks and intrusive rocks.Granite-greenstone terrane is mainly distributed in the vicinity of theDaqingshan the northern foot of Guyang-Wuchuan. Hongshanzi area exposed granite-greenstone is a typical representative. Hongshanzi Archean intrusive rocks aremainly composed of gneissic quartz diorite, gneissic granodiorite, gneissicplagiogranite and gneissic installed granite. Geochemical features indicate that theregion of Archean intrusive rocks includes not only typical TTG rocks, including thesubduction-related high-Mg diorite, Sanuki rocks. In addition, to also found highalumina granite may represent the same (after) collision stage. The rocks of thegreenstone terrane composed of more complex, according to its composition,suggesting that its Archean ophiolite fragments and island arc volcanic metamorphism.Zircon geochronology show that hongshanzi Granite-greenstone terrane is acomprehensive product of subduction-collision–after collision in2.55-2.4Ga.Archean granulite-charnockite terrane is mainly distributed in Xi Ulanbulang area in the northern foothills of the Daqingshan Mountain. The output of the rocks isdome constructed in the formation, the core rocks of the dome is granitic gneiss,granulite rock series cloth around the dome. The geochemical characteristics ofcharnockite indicate it is the product of granulite anatexis. Metamorphism studieshave shown that the region granulite-charnockite not only retained counterclockwiseisobaric cooling P-T path mineral assemblages, also found that the clockwisethermostat decompression P-T path of the "white eye socket" structure. According tothe chronological study of granulite-charnockite terrane, the protolith formed in2.7-2.5Ga and metamorphism as a continuous chronology recorded, distributed in2.5-2.4Ga. According to the analysis of the chronology and metamorphism, granulite-charnockite terrane, reaction in the study area is a continuous process of evolution inthe2.55-2.4Ga, and experience the evolution of the subduction of the island arc modeland transform to the arc-continent collision or continent-continent collision.The main outputs of the Early Proterozoic rock units in the study area in southernkhondalite band, the close relationship between them. Early Proterozoic metavolcanicrocks mainly composed of plagioclase amphibolite, hornblende plagioclase gneiss,biotite-hornblende gneiss, biotite gneiss and felsic gneiss. The geochemicalcharacteristics show that the metavolcanic rocks related to continental rift activity.Chronology evidence indicate that they formed in the~1980-1950Ma.Early Proterozoic intrusions include a set of A-type granite and a set of biotiteamphibolite granite. A-type granites indicated that they formed in the extensionalSystem. Chronological evidence indicated that their formation time is the same as theEarly Proterozoic metavolcanic. Biotite amphibolite granite formed in intracontinentalorogenic events in the late.Early Proterozoic khondalite is a senior metamorphic Stratum, mainly composedof garnet gneiss, diopside gneiss and marble, three rock series. Geochemical featuresindicate that the khondalite a metamorphic sedimentary strata. Geochronologicalstudies have shown that the source of khondalite series is of~2.0Ga and~2.55-2.4Ga two periods of rock; metamorphic age record more than~1.95-~1.80Ga anddevelopment~1.92Ga UHT metamorphism. Ultra-high temperature metamorphism is different with khondalite series clockwise "P-T" track, showing the evolution ofmetamorphism of the counter-clockwise. Ultra-high temperature metamorphism andmafic gabbro veins accompanied, and that is considered to be the regional extensioncaused by asthenospheric mantle on a large scale.Ultra-high temperature metamorphism, rift-related metavolcanic rocks andA-type granites limit the study area in~1.98-1.90Ga during extensional tectonicsetting, and is a continental rift event. According to khondalitethe distribution ofdetrital zircons, Rift Valley events may~2.0Ga has already begun. Khondalite series,however, eventually showing the collision-related clockwise P-T path, and generallydeveloped a steep EW foliation. These characteristics imply that the hole is herebyrock series experienced a north-south compressional deformation. Therefore, wedetermine an intracontinental orogenesis after the end of the rifting, and the time limitshould be consistent with the collision time of the Trans-North China Orogen(1.85-1.8Ga).These studies have shown that Daqingshan area experience continuous evolutioncfrom the arc-continent subduction-continental collision-stable craton-continentalrift–orogeny in late Neoarchean–late Paleoproterozoic.