The Geochemical Characteristics And Protolith Recovery Of Yungou Formation Metamorphic Rock, Western Yunnan

Western Yunnan is located in the south of Sanjiang-Indosinian orogenicbelt,where metamorphic rocks are widely exposed. The researched area belongs toTethys-Himalayan tectonic,where the belt (domain) is between Gondwana andLaurasia continent. The central of the researched area is Changning tectonic melangebelt, the eastern adjacent to Lanping-Simao foreland basin,and the west as theeastern edge of Baoshan Block.It is an ideal research sites for plate kinematics,dynamics and plate boundaries orogenic and diagenetic mineralization of southwestChina. In this paper, we study Neoproterozoic Erathem Yungou Formationmetamorphic rock.The formation belongs to Mengtong–Daxueshan metamorphicbelt, and the metamorphic belt is part of west Changning-Menglian tectonicbelt,with Baoshan block in the west, Damenglong metamorphic belt in the East,mainly exposing Yumeng Series, falling into larger ductile shear metamorphic belt.In this paper, we carry on research on the petrography, mineralogy,petrogeochemistry and other aspects of Neoproterozoic Erathem Yungou Formationmetamorphic rock, according to metamorphic mineral assemblages andmetamorphism deformation characteristics, combined with major and trace elementsand so on, to restore its protolith combination and protolith formation,and forfurther work，to distinguish the source of nature and tectonic environment.Yungou Formation metamorphic rock has the characteristics of highsilicon-aluminum and potassium-rich; REE showing an overall LREE enrichment,LREE flat.Chondrite-normalized REE curve tilted rightward, and performanced thecharacteristics of nearly parallel, similar to the European shale chondrite-normalizedREE distribution curves. In North America shale normalized graph,the REEcharacteristic of Yungou Formation sample is different from the North Americashale′s,which showed negative Ce anomaly and negative Eu anomaly;in the NorthAmerican shale-normalized trace element graph, the majority of the samples showedthe trend of Sr loss and Th enrichment, and with the increase of SiO2content, thecontent of Cr, Co，Ba、Sr、Ta and other elements showed a negative correlation. Withthe use of original rock discrimination diagrams,we can speculate that, the original rock of Yungou Formation metamorphic rock is mainly clay rock, argillaceoussandstone and feldspathic sandstone, but with the igneous rock geochemicalinformation.Combining major elements, REE and trace element characteristics, with theoriginal rock discrimination diagrams of Yungou Formation, the protolith is mainly aset of basic-acid volcanic rock-combinations of sedimentary rock,where thesedimentary rock is mainly sand shale. In a word, the protolith formation is similarto analogy flysch formation.Thus, the protolith formation of Yungou Formation metamorphic rock, westernYunnan， is analogy flysch formation mixed up with basic-acid volcanicsedimentary formation. The source components of Yungou Formation is mainlyfelsic and quartziferous rocks, and containing igneous rock provenance materials andancient recycle sediments.The tectonic environment should belong to the passivecontinental margin.