Geochemistry and zircon U-Pb dating of diabase from Qulong copper-molybdenum deposit in Xizang and its geological significance
Gangdese magmatic belt is located in central Xizang,it is the product of the collision between India plate and Eurasia plate during the formation,subduction and subduction of the Neo-Tethys Ocean,which recorded Mesozoic-Cenozoic'tectonic-magma-mineralization'process and geological evolution.In the eastern section of Gangdese magmatic belt,Qulong copper-molybdenum deposit was developed with super-large-scale porphyry and Middle Jurassic Yeba Formation volcanic rocks and Miocene granitic intrusive rocks and diabase dykes.To explore the dynamic evolution in the deep earth and the chemical composition of mantle materials in this area,diabase in the Qulong copper-molybdenum deposit was studied with zircon U-Pb dating,bulk rock major,trace and rare earth elements,so as to provide constrained data support for the Paleogene basic magmatic activity and regional tectonic evolution of the Gangdese magmatic belt.The analysis result indicated that the diabase formation age was(58.9±1.1)Ma,belong to Late Paleocene.It has no genetic relationship with Qulong copper-molybdenum mineralization(16.9～15.8 Ma).Diabase falls in calc-alkaline series with high-Al(Al2O3=15.43%～18.42%),poor-K(K2O=0.02%～1.39%),low-Ti(TiO2=0.74%～1.05%),relatively enriched in Rb,Th,U,La,Sr and depleted in Nb,P,Ti.The REE pattern is weakly right-leaning and with no negative Eu anomaly,showing the characteristics of arc magma.It was believed that the diabase was formed in the third stage(65～41Ma)of the Gangdese magmatic activity,which is the product of the rapid intrusion of the basic magma formed by the partial melting of the lithospheric mantle under the background of the initial collision between the Indian continent and the Eurasian continent.
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