Genesis Of Garnet-bearing Granite And Tectonic Implications Within Kangbao County, North Hebei Province

Kangbao area is located in the northern edge of north margin of the north China craton, which is closed to the northern part of the region Xing Meng orogenic belt and the region has a large number of magmatic rocks' outcrop. Lujiaying, Shipeng, Hounao and other places in the vicinity of Kangbao County have Garnet-bearing granite outcrop. Garnet-bearing granite of the three regions was east-west zonal distribution in Kangbao – Weichang fault. Granite rock contains garnet, muscovite and other characteristics of the minerals,regarded as a typical over-aluminum S-type granites. Garnet's mineral chemistry characteristics show that garnet is almandine-spessartine series, and garnet's MnO content is greater than 6.5%, spessartine's content is greater than 10%, which has magmatic garnet compositional characteristics. The muscovite in garnet granite is wide clintheriform, preferably crystal shape, and mineral chemistry characteristics are also displayed as magmatic origin. In addition, a small amount of sillimanite was found in Shipeng Garnet-bearing granite which was mainly in muscovite.The sillimanite has a clear genetic relationship with muscovite and some differences between sillimanite in Kangbao Hongqiyingzi miscellaneous rocks. In consideration of the sillimanite in muscovite and the surrounding sometimes appears quartz, author presumed that sillimanite in Shipeng granite is not melt residue but late formation fluid which has replaced muscovite.Garnet-bearing granite mainly consists of quartz, plagioclase, alkali feldspar, muscovite, garnet, and a small amount of biotite,and so on, which has a mineral assemblages of typical S-type granites. Whole-rock geochemical characteristics displayed granite K2 O / Na2O> 1, A / CNK> 1, that's strong peraluminous characteristics. Geochemical cast figure shows garnet granite is calc-alkaline over-aluminum S-type granites. Formation of the environment cast figure shows Garnet-bearing granite probably formed in a continent- continent collision with the collision stage, the causes may be that the continent- continent collision leaded to partial melting of the aluminum-rich strata in the crust. REE characteristics was slight LREE enrichment, Eu was obvious negative anomaly.Zircon LA-ICP-MS U-Pb geochronology shows, Shipeng Garnet-bearing granite's zircon 206 Pb / 238 U weighted mean age is 254.5 ± 2Ma(MSWD = 0.51,n = 12), which is on behalf of the rock' emplacement age. Hounao Garnet-bearing granite's zircon 206 Pb / 238 U weighted mean age is 255.8 ± 1.6Ma(MSWD = 0.54,n =13) and consistent with Shipeng Garnet-bearing granite's emplacement age basically. Geochemical characteristics shows that it belongs to collision granites. Thus author presumed that the magmation in the northern edge of the north China plate was caused by collision between the north China plate and Siberia plate. The typical over-aluminum S-type granites which contains garnet should have formed from partial melting of the aluminum-rich strata in the crust.