New constraints on megathrust slip stability under subduction zone P-T conditions

Abstract

To understandandmodelsubductionzoneseismogenesis,dataareneededonthefrictionalproperties of (meta)peliticsubductionzonematerialsunderinsitumegathrustconditions.Here,wereportthe results ofrotaryshearfrictionexperimentsonsimulatedillite–quartzfaultgougeataneffectivenormal stress of170MPa,aporefluidpressureof100MPa,at150–500 1C andslidingvelocitiesof1–100 mm/s. The resultsshowthreetemperature-dependentregimes,characterizedbyvelocity-strengtheningat 150–250 1C, velocity-weakeningat250–400 1C andvelocity-strengtheningat400–500 1C. Theregimes are definedbyadecreaseintherateandstatefriction(RSF)parameter(a–b) at150–300 1C followedby an increaseat300–500 1C. ThesetrendscorrelatewithsystematicchangesinotherRSFparameters,as well asanincreaseinfrictioncoefficientabove300 1C. Weexplaintheeffectsofincreasingtemperature in termsofatransitionfromfrictionalgranularflow(150–250 1C), throughgranularflowwhereby dilatation isbalancedbythermallyactivatedcompactioninvolvingstresscorrosioncracking(SCC)of quartz clasts(250–400 1C), tonon-dilatantsliponthephyllosilicateswithaccommodationatquartz clasts bySCC(400–500 1C). Takingintoaccounttheeffectsofslidingvelocity,theobservedvelocity- weakeningregimebroadlyexplainstheextentoftheseismogeniczonewithinsubductionmegathrusts.