Geochemical Characteristics And Tectonic Setting Of The Huimin Formation In Huimin Region, Western Yunnan

The“Sanjiang”area in western Yunnan is located in the southern section of the Tethys tectonic domain.It preserves the stratigraphy,paleontology,volcanic rocks,and ophiolite rock records of the Tethys evolution since the Early Paleozoic,and is also the main polymetallic mineral enrichment area in China.The study of the metamorphic igneous rocks of the Huimin Formation of the Lancang Group in this area plays an important role in understanding the tectonic evolution of the original Tethys in the western Yunnan region.This paper takes the Huimin area of Lancang County in southwestern Yunnan Province as the research area,selects the Huimin Formation of Lancang Group as the main research object,systematically collects and analyzes and studies the regional-related data,and conducts detailed field geological surveys.The Huimin Formation was subjected to petrography,LA-ICP-MS zircon U-Pb isotopic geochronology and rock geochemistry analysis.The geochemical characteristics and tectonic settings of the Huimin Formation of the Lancang Group were discussed and the following were obtained.Research results and understanding:?1?The formation period of the Huimin Formation was ascertained.The LA-ICP-MS zircon U-Pb test results were 482±12 Ma and 471.5±5.4 Ma,respectively,indicating that the formation age was Late Ordovician.?2?The whole rock element analysis of the Huimin Formation sample shows that the Si O₂ content of this group of metamorphic volcanic rocks is 51.27-62.09 wt.%,MgO content is 3.07-7.74 wt.%,P₂O₅ content is 0.09-0.38 wt.%,and TiO₂ is low?0.74-1.12 wt.%?,FeO*is from 10.38 to 16.37%,high-alumina Al₂O₃?14.17 to 17.43wt.%?,and total alkali alk=3.95 to 6.04 wt.%.The rare earth element distribution pattern is a light-medium enriched right-dip curve of light rare earth elements.In the original mantle standard trace element spider pattern,the Huimin Formation metamorphic volcanic rock shows that Rb,Ba and other large ion lithophile elements are relatively enriched,Nb,Ta Features of high field strength elements such as Zr,Hf,etc.?3?The Huimin Formation of Lancang Group has typical island arc environment characteristics on the active continental margin.This group of volcanic rocks was related to the subduction of the original Tethysian ocean of the Early Paleozoic to the Gondwana continent,and provided new evidence for the existence of the original Tethys island arc volcanic rocks in the west of Yunnan.