Age And Tectonic Properties Of Sporadically Exposed Metamorphic Rock Series In Lincang Granite Base In West Yunnan

Lincang granitic batholith is a famous compound batholith in Sanjiang area of Southwest China.A set of parametamorphic rock series mainly composed of schist is sporadically exposed in the batholith,which was named as the Middle Proterozoic Damenglong group by predecessors.It is considered that it and the Middle Proterozoic Lancang group constitute the basement of "Lincang terrane".In recent years,it has been found that the original age of Lancang group belongs to the early Paleozoic,which is not the basement rock,but the schist age and structural attributes scattered on the Lincang granite base have not been well constrained.In this paper,the study of petrology and zircon U-Pb dating of fragmentary schists in Lincang granitic batholith has been carried out.Combined with regional geological background,published high-precision zircon U-Pb chronology and geochemical data,the formation age,petrogenesis and tectonic significance of schists are discussed.Through the above research,this paper has obtained the following main knowledge:(1)In this paper,high-precision U-Pb zircon dating has been carried out for the mica quartz schist(D1645-TW1)and feldspathic mica quartz schist(17MN21-1)of the "Damenglong group" in Lincang granitic basement.The zircon age of the mica quartz schist(D1645-TW1)is 517-2699 Ma,and the youngest group is 517-550 Ma;the zircon age of the feldspathic mica quartz schist(17MN21-1)is 451-2672 Ma,and the youngest group is 451-477 Ma.The results indicate that the "damongyan group" which was drawn by the people before the Lincang granite base is not a Mesoproterozoic basement rock.(2)Based on the comprehensive comparison of lithology and zircon U-Pb age,it is considered that the schist in Lincang granite base can be compared with the Lancang group in the West.It was originally the early Paleozoic Tethys subduction and accretion complex,and now the schist is the remnant of the invasion and destruction of Lincang granite base.(3)The zircon U-Pb ages of Lincang granites are collected and compared with the metamorphic ages of Lancang group.It is found that the two ages are approximately the same.Combined with the strong upper crust geochemical properties of Lincang granites,it is believed that Lancang group is likely to be the parent rock of Lincang granites.The upwelling of asthenosphere under the background of post middle Triassic collision resulted in the subduction of Lancang group in Early Paleozoic Partial melting of the genetic complex.