The petrogenesis of modern and ophiolitic lavas reconsidered:Ti-V and Nb-Th  

作　　者：John W.Shervais 

机构地区：[1]Department of Geosciences,Utah State University,Logan,UT 84322-4500,United States

出　　处：《Geoscience Frontiers》2022年第2期90-109,共20页地学前缘（英文版）

基　　金：supported in part by the National Science Foundation(OCE-1558689)。

摘　　要：Tectonic discrimination diagrams are a key tool for understanding ancient volcanic rock origins.In this contribution we compile over 15,000 whole rock compositions to re-evaluate the Ti-V discrimination diagram and compare it to another commonly used tool,the Nb/Yb-Th/Yb diagram.We have reformulated the Ti-V diagram into a log-log plot to distinguish samples more clearly at lower concentrations.The compilation shows that MORB are dominated by Ti/V=20-43,whereas juvenile arc tholeiites and boninites are characterized by Ti/V<20 generally,although there is minor overlap at the boundary(Ti/V=20-22).Plume-related volcanic rocks(ocean island basalts,oceanic plateaux,and continental flood basalts)generally have Ti/V>43,although there may be significant overlap with MORB-like ratios for ridgecentered OIB and for some oceanic plateaux.About 56%of alkaline OIB have Ti/V>70.Back-arc basins are dominantly MORB-like.Melt models show that MORB and juvenile arc volcanics most likely formed under different fO;conditions,but are permissive of similar fO_(2)if the arc rocks form by much higher melt fractions.The Nb/Yb vs.Th/Yb plot clearly distinguishes most oceanic basalts(MORB,plateaux,OIB)from subduction-related volcanic rocks(boninite,juvenile arc tholeiite,calc-alkaline)and from flood basalts.We propose here a new two-proxy diagram of Ti/V vs.Th/Nb,which incorporates the advantages of both.

关 键 词：OPHIOLITE Discrimination diagrams Trace element geochemistry VANADIUM 

分 类 号：P587[天文地球—岩石学]