A Research For The Metamorphic Properties And Zircon Geochronology Of Crystal Basement In Wuhe-Shimen Mountain Area In Northern Anhui

NCC is mainly composed of the western land mass, central China Orogen and the Eastern Block. Comparatively speaking, research on the western land mass, central China Orogen and the north east region of the Eastern Block are extremely rich and deep, while the research on southeastern margin of the North China Craton that is the southern tip of Eastern Block-Bengbu uplift is extremely poor. On the one hand, it is due to lack of relative research or the emphasis of the research are different, on the other hand, another reason which is the most important aspect go against geological research is that suffering the disadvantage of the bad rocky outcropping condition in this area. Therefore the study on it only stays on the level of field observation. Thus, this study will be to the east of Bengbu uplift area-Shimen mountain area as the research target. Through a large number of field geological survey, detailed petrographic analysis, and evaluation of temperature and pressure chronology research, we will elaborate the metamorphism and evolution law basically. The rocky outcropping condition is relatively available and the lithological characters are continuous, so this place is an ideal natural laboratory to explore the mechanisms and backgrounds of Bengbu uplift.The research mainly divided into three aspects, (1) the construction of rock profile in northern Anhui Wuhe-Shimen mountain area. Through a lot of field work and petrographic analysis, we have worked out three rock sections.① Xi Gudui-Nv mountain Measured geological section, ② Zhuding-Shan Zhangjia area measured geological section, ③ Shimen mountaion-Hung Temple Measured geological section. Studies have shown that Wuhe-Shimen mountain is mainly composed of granitic gneiss, quartzite and a small amount of marble, amphibolite rocks, and in the form of monocline output. The overall occurrence tends to be S-SSE model. In this section, there are paleoproterozoic and Mesozoic granite and tancheng-lujiang fault zone represeted by Zhuding-Shimen mountain area which characterized by brittle type right translation features. (2) Constructing the metamorphic petrology study of rock drill in Zhuding area. According to the petrography and thermodynamic evaluation research on rock samples from drill, that is, garnet-plagioclase amphibolite, plagioclase amphibolite and plagioclase amphibolites, we draw the conclusion as followings, ① T=725～754℃ and P=0.2～1.0Gpa, the verage temperature for pressure conditions are T=743±9.9℃ and P=0.6±0.2GPa, ②T=765～794℃ and P=0.5～0.7Gpa, the average temperature for pressure conditions are T=778°±11℃ and P=0.6±0.1GPa,③ T=731-772℃ and P=1.0-1.1Gpa, the average temperature for pressure conditions are T=754±15℃ and P=1.1±0.03GPa. Basically, all fall into the low pressure granulite facies metamorphism, which shows that Wuhe diamictite generally experienced high grade metamorphism. (3) The metamorphic zircon U-Pb isotopic dating. According to the zircon U-Pb isotope dating study on garnet-plagioclase amphibolite and plagioclase amphibolite, we gained two metamorphic age, that is,2394±29Ma (MSWD=2.0) and 2443±23Ma (MSWD=1.05). The two groups of ages are basically same within the margin of error. Combining previous data analysis, this area generally experienced the north China craton～2.5 Ga granulite facies metamorphism.To sum up, Wuhe-Shimen mountaion region is high-grade metamorphic area, generally experienced granulite facies metamorphism, which has relatively complex rock formations, metamorphic time ranges from 2.4 to 2.5Ga.