The Rock Association And The Age Assignment Of The Hongqiyingzi Group Within Chongli, North Hebei Province

The Hongqiyingzi Group located in the north side of the Chongli-Chicheng fault belt, which has a E-W extending in general,and mainly distributed in the Hongqiying, Yuanmaoshan, Wangmaoshan, Xishuangtai and Wudaoyingzi. It is consisted of the(garnet) biotite(amphibole) plagioclase gneiss and the(garnet) plagioclase amphibolite as well as some tectonic blocks, such as the(diopside) marble, the garnet quartzites. As the main rocks(strata) unit, the(garnet) biotite(amphibole) plagioclase gneiss and the(garnet) plagioclase amphibolite are mainly interbedded in each layer. The protolith of the(garnet) biotite(amphibole) plagioclase gneiss should be sedimentary and igneous, and mainly is the sedimentary. The protolith of the(garnet) plagioclase amphibolite is the basic volcanic rock. The original rock of diopside marble probably is marine limestone which was formed in the transitional environment from infraneritic environment to epeiric sea environment. The forming environment was of strong oxidizing. The protolith of the garnet quartzites probably be greywacke. The garnet composition profile of the(garnet) biotite(amphibole) plagioclase gneiss and the(garnet) plagioclase amphibolite shows a similar character of deformation, which indicates that they are the original formation of the Hongqiyingzi Group within Chongli, and the Hongqiyingzi Group should be a series of volcanic-sedimentary rock.The Zircon SHRIMP U-Pb dating indicates that the provenance of the Hongqiyingzi Group are complicated, and the detrital zircon age is between 343.4Ma~2057Ma. Its protoliths formed later than 343.4Ma, the age of sedimentary –metamorphic is between 326Ma~343.4Ma. The Hongqiyingzi Group experienced six times tectonothermal events in 326±Ma, 281±Ma, 268±Ma, 250±Ma, 243±Ma and 234±Ma respectively. The Geochronology study of the Hongsqiyingzi Group implicate that it is a series of volcanic-sedimentary rock, which is formed in the Late-Paleozoic, and experienced Multiphase tectonic-thermal event. The multi-stages reformation occurred in 326±Ma, 281±Ma, 268±Ma and 250±Ma has certain corresponding relationship with the magmation in the Late Carboniferous-Middle Permian and the Late Permian-Triassic of the north margin of North China Craton, which results from the southward subduction to the North China Craton of the Paleo-Asian ocean, the collision orogenesis of North China Craton and Siberia plate, and the delamination of the lithosphere. The reformation occurred in 240±Ma and 234±Ma may have relationship with the Pacific plate and the North China Craton intracontinental activities. All types of the rocks within the Hongqiyingzi Group are recorded the reformation occurred in 268±Ma, which indicated that the degree of the metamorphic event in 268±Ma is the strongest.