Global Cenozoic Picrite Data Mining And Research

Picrite is a type of ultramafic rock,which is usually considered to have a high melting temperature and is the product of melting of the hottest part of the mantle plume.Detailed excavation and analysis about temporal and spatial distribution characteristics and tectonic geochemical differences of Cenozoic picrite are done in this paper based on databases Geo Roc and Pet DB.The Cenozoic picrite has a wide range of distribution all over the world and is almost exposed to all tectonic Settings,and characterized by concentrated more in oceanic environment especially ocean islands than in continental environment.Meanwhile the distribution of the Cenozoic picrite shows certain evolutionary characteristics: From Paleocene to Miocene,picrite mainly located in CFB and after Miocene,picrate mainly scattered in island arc and ocean islands,no longer showed up in CFB.Moreover,picrite can be used as a symbol of mantle plume due to its high temperature during formation stage,based on this point we figured out 10 possible location of modern hot spot,including Hawaiian islands,Cologne islands(Ecuador),Iceland,Canary islands,Mt Fair in Germany of Europe orogenic belt,Red ocean ridge,East African Rift,Reunion island,South China Sea and Kamchatka arc.Continental picrate is very different from oceanic picrite in trace element,and shows a higher total content than oceanic picrite.Meanwhile the difference of major and trace element among three type of continental picrite(CFB,rift,intraplate)and oceanic picrite(MORB,OIB,ARC)is obviously which can be used to effectively restrain the tectonic settings,but it does not fit the classical basaltic discrimination diagrams so well.In this paper,we tried to use the method of mathematical calculation to analyze all the samples data of Cenozoic picrite,and preliminarily determined several effective tectonic discrimination diagrams.Among all the diagrams lg(Fe O/Rb)-lg(K2O/Ta),lg(Fe O/Th)-lg(K2O/Ta),lg(Fe O/Ba)-lg(K2O/Ta)and lg(Fe2O3/Rb)-lg(K2O/Ta)can Completely separate OIB and ARC picrite,furthermore,lg(Fe O/Cs)-lg(Mn O/Hf),lg(Fe O/Hf),lg(V/Hf),lg(Mg O/Gd)and lg(Fe O/Gd)is enough to judge the tectonic background between arbitrary two type picrite,but it is not ideal to distinguish all the three tectonic settings of MORB,OIB and ARC in the same time.