Metamorphism And Geochronology Of The Typical Rocks In The Sides Area Of Tan-Lu Fault,Anhui Province

The Initial startup time, Formation mechanism, Geodynamics and Evolution of Tan-Lu wrench fault has been highly concerned, especially the Initial startup time remains controversial. Numerous investigations about the fault focused on the structure, geochemistry and deformation geochronology, but the researches about metamorphism and geochronology of the metamorphic rocks in the Tan-Lu Fault zone is very scarce, which has limited the comprehension about the fault. So we conducted a meticulous study of in situ zircon U-Pb dating, as well as preliminary P-T condition evaluation about the typical rocks in the sides area of Tan-Lu wrench fault, Anhui Province. The main substance and research progress can be addressed in the following.(1) At present, the Tan-lu fault zone (Anhui section) is considered to be entirely made up by internal material of Yangtze Plate. In order to verify whether a small amount of material of the Tan-Lu Fault zone (Anhui section) is derived from the North China Craton,This study have selected 4 samples, TF001-2 (Magnet garnet amphibole) and TF003-1 (Garnet biotite schist) from Feidong group, outcropped as the tectonic lens, and WS069-1 (Magnet garnet amphibole) and WS070-1 (Garnet biotite schist) from Huoqiu group. The TF001-2 (Magnet garnet amphibole) from Feidong Group contain two metamorphic assemblages from different stages:the P-T condition of 1 stage is T=616?700 ? and P=0.66?0.85 GPa respectively and the average T and P is 653±35? and 0.75±0.09 GPa; Differentially, the 2 stage is T=616?700? and P=0.66?0.85 GPa, and the mean is 653±35? and 0.75±0.09 GPa, which indicated a rapid and slight Isobaric cooling process. According to the Raman Spectral Analysis and the LA-ICP-MS dating, the metamorphic age is 2469± 49 Ma. The sample TF003-1, is the surrounding rock of the Magnet garnet amphibole in the Feidong group, outcropped as the tectonic lens, which the Peak P-T conditions is T=610?697 ? and P=0.72?0.93 Gpa, And the metamorphic age is 2406±49 Ma by the study of in situ zircon U-Pb dating. The mineral assemblages of WS069-1 (Magnet garnet amphibole) from Huoqiu group is very similar with Feidong group, the estimation results of P-T conditions of sample WS070-1 indicates Huoqiu group had suffered from amphibolite facies metamorphism (608?659 ?,0.73?0.85 Gpa). Combined with previous data, the Magnet garnet amphibole from Feidong group concordance with which from Huoqiu group about the mineral compositon, metamorphism characteristics and its forming time. So the Magnet garnet amphibole form Feidong group should belong to the Huoqiu group had suffered the sinistral strike-slip of Tan-Lu Fault zone. Furthermore, the forming time of the archean sedimentary strata of Huoqiu Group can be restricted to the period between 2.74 Ga and 2.71 Ga by the in situ zircon U-Pb dating of WS069-1 and WS070-1.(2) The formation age and evolution process of the juvenile crustal of the Bengbu uplift on the southeastern margin of the North China Cration, and the initial startup time of the Tan-Lu Fault remains controversial. Therefore, We conducted a meticulous study of in situ zircon U-Pb dating, as well as preliminary P-T condition evaluation about the Granitegneiss and Amphibolite obtained from Bengbu uplift and Chihe town Weigang mountain across the Tan-Lu Fault Zone. A total of 4 samples were analyzed, which WS055-1 (Granitegneiss), WS055-3 (Amphibolite) and WS021-1 (Granitegneiss) are from the Bengbu uplift, all of which had experienced granulite-facies metamorphism; the rest sample FDO19-1 (Granitegneiss) was obtained from the Chihe towns area of the west of Zhangling group. The zircon U-Pb age dating shows that the weighted average age of 17 magmatic zircons of Sample WS021-1 is 2886±28Ma, represents the formation age of the juvenile crustal; All zircons within Sample WS055-1 are metamorphic zircon, revealling three metamorphic events at 2440±28Ma (21 zircons),2163±55Ma (1 zircon) and 1944±89Ma (1 zircon); Sample WS055-3 recorded metamorphic time of 2481±18Ma (23 zircons). Specially, The zircons within Sample FDO 19-1 have the clear structure of core-mantle-boundary, corresponding to 271-667Ma (10 zircons),228±3Ma (17 zircons) and 211±2Ma (23 zircons). Combined with the previous research, We can confirm the three former samples obviously belong to North China craton, Yet the remaining sample FD019-1 derived from the Dabie orogenic belt in the Yangtze blocks. So the western boundary of the Tan-lu main fault (Anhui segment) can be set in Zhuding-Shimen mountain fault, Further the initial startup time should be at Jurassic and the late Jurassic period. Meanwhile the zircon U-Pb age datings of 3 samples from Bengbu uplift indicates the presence of the oldest juvenile crustal which formed at the late Mesoarchean, And reveals the complex metamorphic evolution process of the Bengbu uplift:the formation stage of juvenile crustal(2.89Ga) ? the formation stage of basement (2.5-2.6Ga) ? The granulite-facies metamorphism stage caused by mantle magma upweling (2.44-2.48Ga) ? The rifting stage (2.0?2.2Ga)?The orogenic stage (1.9?1.95Ga).