Genetic mechanism of the Permo-Carboniferous high-grade coal-bearing kaolin in the Datong Coalfield
The petrographical,mineralogical,whole-rock geochemical,and zircon U-Pb geochronological and Lu-Hf iso-topic studies were carried out for investigating the provenance and genetic mechanism of the high-grade coal-bearing kaol-in within the coal seams of the Permo-Carboniferous Taiyuan Formation in the Xiaoyu mine of the Datong coalfield,Shanxi Province.The coal-bearing kaolin is composed mainly of well-ordered kaolinite with no detrital quartz,feldspars and muscovite.Some samples contain boehmite that were formed through the desilication of kaolinite.The zircons in the coal-bearing kaolin are typically igneous origin with only one age population of ca.300 Ma,same with the depositional age of the coal,confirming that the coal-bearing kaolin was altered from volcanic ash.Besides,the coal-bearing kaolin commonly contains tabular/columnar and vermicular kaolinite that are also diagnostic feature of alteration from volcanic ash.These coarse-grained kaolinites are thought to be pseudomorphic kaolinite altered from crystal fragments in volcanic ash,such as plagioclase and biotite.The zircon εHf(t)is dominant by a wide range of negative values,indicative of their formation from magma generated by substantial remelting of ancient continental crust,coinciding with that of contempor-aneous magmatic rocks formed from continental arc volcanism in the Inner Mongolia Paleo-Uplift at the northern margin of North China.This suggests their cognate relationship.The geochemical fingerprints of trace element of zircons also in-dicate that they were crystalized from continental arc magma.The northern margin of the North China Craton(NCC)is an Andean-type continental margin in the late Paleozoic.During the coal-accumulating period of the Late Carboniferous to Early Permian in North China,the Paleo-Asian Ocean(PAO)plate was continuously southward subducted beneath the NCC,resulted in a frequent continental arc volcanism.The emitted volcanic ash fell into peat swamps developed in a paralic environment in North China,which were subjected to an intensive leaching and altered to the coal-bearing kaolin.
万方数据
维普
