Geochemical Characteristics And Tectonic Background Of The "Half-tile Type" Diabase In The South And East Yunnan Province(SW China)

The funing area in southeast yunnan is located in the southwest of youjiang basin,it is characterized by intense magmatic activity and a large area of basic-intrusive rocks,which are divided into early diabase,gabbro(half tile type)and late diabase and gabbro(stable type).Among them,the"half-tile type" diabase is an important ore-bearing rock in the carlin type gold deposit,which is closely related to gold mineralization.There are still some disputes about the geotectonic environment and the age of diabase formation in this period.Based on the field survey,this paper studies the petrological and geochemical characteristics of diabase in this period,discusses the source of magma,and distinguishes the tectonic environment.At the same time,regional tectonic evolution characteristics were preliminarily summarized based on zircon u-pb dating data.In order to provide a foundation for the study of diabase in this period.According to the field geological survey,only the early "half-tile" type of diabase was exposed in the study area,and the rock mass was produced in groups and zones.The highest intrusive stratum was the middle Triassic banna formation,which was distributed in the NW direction and nearly east-west direction.According to the analysis results of main elements,the rock belongs to the subbasic basalt series,and the subdivision belongs to the high potassium calc-alkaline series.The geochemical characteristics of trace elements show that the MORB spider diagram shows Ba and Th enrichment and Nb,Ta,Zr and Hf loss,which is similar to the geochemical characteristics of intraplate basalt.The magma may come from the source region of the enriched mantle or metasomatism mantle.The spider diagram of the original mantle shows the same flat distribution to the right,and the anomaly of incompatible elements is not obvious,which shows the characteristics of homologous evolution.The characteristics of rare earth elements are that the total amount of rare earth is high,the LREE is relatively enriched,the HREE is relatively deficient,and the heavy rare earth is obviously differentiated.Eu has a weak positive anomaly,Ce has a weak negative anomaly,the rare earth partition reflects the characteristics of intraplate magmatismThe age of the diabase zircon LA-ICP-MS U-Pb was 206.8±5.3ma,indicating that the diabase was formed in the late TriassicMagma is the product of low degree of partial melting in the source area of the enriched mantle,which may be slightly stained in the source area,and suffer from different degrees of crust mixing in the process of ascending intrusion.Diabase was formed in the tectonic environment of continental plate,indicating the tectonic background of extension and tension of continental riftBased on the comprehensive analysis of the regional geological background,it is concluded that the "half-tile" diabase was influenced by the indochinese movement and related to the evolution of the ancient tethys,and was the product of the magma rising and invading under the extensional background after the collision orogeny in the indochinese period.