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 dia-gram 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 boni-nites 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 ridge-centered 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 fO2 conditions,but are permissive of similar fO2 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.