Geochemistry,Geochronology And Tectonic Significance Of Diabase In Jinchanghe Pb-Zn Deposit,Baoshan Block,Western Yunnan Province

In Baoshan block,there are a lot of basic intrusive rocks in vein(wall)shape,especially diabase in polymetallic mining area.Diabase is a kind of basaltic magma derived from the deep mantle,which is formed by upward emplacement and crystallization through the weak zone of the crust structure,and generally occurs in the tension extension tectonic background.The geochemical characteristics of the rocks can indicate the material characteristics of the deep mantle source area,the magmatic evolution process and the tectonic magmatic background in the area.Therefore,this paper takes the diabase vein in jinchanghe Pb-Zn mine area as the research object,combined with the previous research data,through the research methods of petrology,petrochemistry,geochronology and isotope geology,preliminarily discusses the magmatic emplacement time limit,petrogenesis and tectonic background of the diabase in jinchanghe,in order to study and analyze the basic rocks in the region and the regional magmatic structural back Scenery provides reference.Through research and analysis,the following knowledge is obtained:Diabase is altered diabase,and its main mineral assemblage is plagioclase and pyroxene.At the same time,there are a small amount of secondary amphibole,chlorite,limonite and other altered minerals;The geochemical characteristics of the rocks show that the diabase is characterized by low Si O₂,Mg O,Ti O₂,high TFe O and Ca O,and the rocks are calc alkaline basalt.Rare earth elements are characterized by light rare earth enrichment and heavy rare earth depletion,while EU has no obvious negative anomaly.Trace elements are characterized by the loss of K,Sr and other large ion lithophile elements(LILE),and the enrichment of high field strength elements(HFSE)such as Nb and Ta.On the normalized distribution diagram of rare earth elements and the standard curve diagram of trace elements mantle,the characteristics of jinchanghe diabase and ocean island basalt(OIB)are consistent;LA-ICP-MS zircon U-Pb ages show that the age of emplacement crystallization of jinchanghe diabase is from 214.3±3.8 Ma?213.9±2.9 Ma.It is consistent with the ages of diabase(195.0±5.3 Ma)and diabase porphyrite(212±4.9 Ma)in Hetaoping mining area,indicating that the basic intrusive rocks in the area are the products of Middle-Late Triassic magmatic activities.At the same time,the hydrothermal zircon age of the diabase is 128.5±1.5 Ma,which is consistent with the ore-forming age(117?120 Ma).It shows that diabase was affected by hydrothermal alteration in Early Cretaceous.The characteristics of Hf isotope,trace element and incompatible element ratio show that the magma source area of diabase is the mixed source area of depleted mantle and enriched mantle.It may be the source area of enriched mantle formed by residual subduction crust dehydration and replacement of depleted asthenosphere mantle,which is formed by 5%?20%melting of garnet lherzolite.In the process of magma evolution,it is mainly separated crystallization,and the degree of contamination by the crust is relatively low.The characteristics of trace elements and the structural discrimination map of Th,Nb,Ta,Zr,Hf and other trace elements show that the diabase is formed in an intraplate environment with the characteristics of hot spots or mantle plumes.It indicates that Baoshan block may be in the extensional setting in the Late Triassic.Previous studies on the granites in the Baoshan block also show that the Late Triassic Baoshan block was in an intracontinental tension setting of post collisional orogeny.Therefore,it is further confirmed that Baoshan block was in the stage of intracontinental extension in Late Triassic.