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.