简介：TheTibetanPlateau,knownas“theroofoftheworld”and“thethirdpoleoftheearth”,isaproductofthecollisionbetweenIndiaandAsiaduringthelast~50Ma.Theregionaltectonics–inparticular,growthandexpansionoftheplateau–hasbeenattributedprimarilytodeformationwithinthelithosphere.Theroleandpatternoftheunderlyingasthenosphericflow,however,remainmostlyunaddressed.Inlightofrecentseismictomographicimagesandpublishedseismicanisotropicdescriptionsoftheuppermantle,hereweproposethatanentrainedmantleflowislikelytoexistunderTibet,inducedbythenorthwardadvancingIndianplate.ThedirectionofmantleflowischaracterizedbyagradualrotationfromnorthwardinthesouthtoeastwardinthenorthasaresultofdeflectionbythedeeprootoftheTarimblock.Thepresenceofanunderlyingmantleflowisnotonlyabletoaccountforthewest-eastorientedfast-axisofseismicanisotropyinnorthernTibet,butcanalsoadequatelyexplainthesporadicnullsplittinginsouthernTibet.Specifically,thenullsplittingresults,atleastinpart,fromupwellingsofasthenosphericflowthroughtearsoftheunderthrustingIndianplatethathavebeenrevealedbyvariousseismicobservations.ThemantleflowmayinturnpromotetheblockextrusionunderTibetthathasbeenobservedinGPSmeasurements;hotasthenosphericupwellingsmayalsoleadtowidespreadpost-collisionalmagmatisminsouthernTibet.