Geochemical Characteristics Of Metamorphic Rocks In The Upper Member Of Shigu Group In Badi Area, Northwest

Northwest Shigu group is a part of late Proterozoic basement of Yangtze plate Shigu-Diancangshan-Ailaoshan metamorphic belt. The area has attracted widespread attention at home and abroad scholars. But for many segments of previous studies under Shigu group, while the upper section but few people study them systematically. This paper summarizes the work of their predecessors on the basis of geological surveys, as well as a comprehensive study of indoor segment Shigu group makes a more detailed analysis and combines petrology, petrography, geochemistry, U-Pb geochronology of study, elaborates the geological features of Shigu group, a combination of rock, restores the previous paragraph of the metamorphic rocks of the upper section of Shigu group,and analyzes the characteristics of the original rocks, tectonic setting.Lithological composition of the upper section of Shigu group mainly metamorphic rocks microchip sericite, chlorite, sericite microchip rock, rock sericite quartz microchips, quartz microchips rock, rock microchip cordierite sericite, andalusite silk mica microchip rocks.Major elements, trace elements and REE display segment schist on Shigu group contains a high amount of rare earths, light rare earth fractionation, heavy rare earth fractionation obvious, enriched in LILE and LREE, negative Eu anomaly clear;(La/Yb) N=3.3-12.6,8Eu=0.34-0.67, similar with the upper crust of trace elements and REE composition, reflecting the eroded material source area mianly from above crust ingredients; δ Ce (0.82～1.6),displays original sedimentary environment which is continental margin of the upper schist of Shigu group; SiO2-K2O/Na2O and other tectonic discrimination diagrams display Shigu group formed in the upper part of the tectonic setting of metamorphic active continental margin.Shigu metamorphic belt is one of the most famous metamorphic belt in western Yunnan region,and it has long been considered the Yangtze block Paleoproterozoic crystalline basement. This paper selects microchip chlorite rock (BDL01) and quartz microchip rock (BDS01) Shigu group metamorphic rocks within the previous paragraph. And by studying its LA-ICP-MS zircon U-Pb geochronology, the results show that there are three groups of microchips chlorite rock ages,206Pb/238U weighted average age of365±14, Ma805±18Ma and207Pb/206Pb weighted mean age of2298±33Ma; There are three groups of rock quartz microchips ages,206Pb/238U weighted average age of309±15Ma,767±22Ma and207Pb/206Pb weighted mean age of2185±140Ma; Zircon age of two samples show that the material characteristics of the source region and the main magmatic events of Shigu group is very similar with Yangtze block (western margin),and each tectonic events of the western margin of the Yangtze block have had a certain impact on the Shigu group, Shigu group metamorphic rocks source material characteristics and major magmatic events may be related to the western margin of the Yangtze block formation phylogenetic the role of metamorphism and deformation, therefore, Shigu group metamorphic rocks has a very clear pro Yangtze structure properties.