Tectonic Environment And Geological Significance Of Neoproterozoic Magmatic Rocks In Lueyang Area,Southern Shaanxi

The Mianlue Tectonic Belt is the important component of the Qinling Orogenic Belt,the large amount of Neoproterozoic magmatic rocks discovered in it is of great significance for the study of the Neoproterozoic tectonic evolution of the Mianlue Tectonic Belt.The following progress has been made in this study for the Tianba diabase,Sanchazi area,Lueyang in the Mianlue Tectonic Belts and a set of metamorphic basaltic andesite-dacite combinations in Jieguanting area which in the south of the Mianlue Tectonic Belts,Lueyang,through comprehensive research such as field geology,petrology,rock geochemistry and LA-ICP-MS zircon U-Pb dating,the main results and progress achieved are as follows:1.Based on LA-ICP-MS zircon U-Pb dating,the crystallization age of the Tianba diabase is 805.9±2.6 Ma,indicative of a middle Neoproterozoic formation age.The geochemical research shows that the Tianba diabase belongs to the calc-alkaline series,the chondritenormalized REE patterns show enriched LREEs and flat HREEs with weak negative Eu anomaly(the average ?Eu is 0.91)and the primitive mantle-normalized trace elements show enrichment in LILEs,such as Rb,Ba,Sr,etc.,and LREEs,and depletion of HFSEs such as Nb,Ta,relatively depletion of P and Ti.Comprehensive study shows that the Tianba diabase has the geochemical characteristics of arc magmatic rocks,which was formed by partial melting of the subduction fluid metasomatised enriched mantle in a convergent setting.2.A set of metamorphic basaltic andesite-dacite combinations has developed in Jieguanting area,Lueyang.Based on LA-ICP-MS zircon U-Pb dating,the crystallization age of the Jieguanting metamorphic basaltic andesite is 845±8.5 Ma,indicative of an early-middle Neoproterozoic formation age,and the crystallization age of the Jieguanting metamorphic dacite is 844.0±6.0 Ma and 843.1±5.2 Ma,which shows great agreement with the Jieguanting metamorphic basaltic andesite.The geochemical research shows that the Jieguanting metamorphic basaltic andesite belongs to the calc-alkaline series,the chondrite-normalized REE patterns show enriched LREEs and flat HREEs with weak negative Eu anomaly(the average ?Eu is 1.06)and the primitive mantle-normalized trace elements show enrichment in LILEs,such as Rb,Ba,Pb,etc.,and LREEs,and depletion of HFSEs such as Nb,Th,relatively depletion of P and Ti.Comprehensive study shows that the Jieguanting metamorphic basaltic andesite has the geochemical characteristics of arc magmatic rocks,which was formed by partial melting of the subduction fluid metasomatised enriched mantle in a convergent setting.The geochemical research shows that the Jieguanting metamorphic dacite shows the characteristics of medium potassium to low potassium tholeiitic series and peraluminous.Comprehensive study shows that the Jieguanting metamorphic dacite was formed by partial melting of the crust in a convergent setting,which was heated by basaltic andesite magma when its ascent.3.Combining with regional geological data,this study explores the tectonic evolution process of the Mianlue Tectonic Belt and its adjacent areas in the Neoproterozoic period.The Mianlue Tectonic Belt and its adjacent areas were in a subduction-convergence tectonic environment during mid Neoproterozoic(ca.845?800 Ma).