Strain localization processes at a magma-starved ridge ... · Strain localization processes at a...
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Strain localization processes at a magma-starved ridge: from micro-scale to macro-scale Bickert 1 , M., Cannat 1 , M., Tommasi 2 , A., Jammes 3 , S., Lavier 4 , L. [modified from Cannat et al., 2008] ? Detachment faults exhume mantle-derived rocks from the base on the brittle lithosphere to the seafloor. § What are the strain localization mechanisms in the deep axial lithosphere when there is no magma ? § How to make detachments in a thick lithosphere (≥ 15 km) ? 1
Transcript of Strain localization processes at a magma-starved ridge ... · Strain localization processes at a...
Strainlocalizationprocessesatamagma-starvedridge:frommicro-scaletomacro-scaleBickert1,M.,Cannat1,M.,Tommasi2,A.,Jammes3,S.,Lavier4,L.
[modifiedfromCannatetal.,2008]
?
Detachment faults exhume mantle-derived rocks fromthebaseonthebrittlelithospheretotheseafloor.
§ What are the strain localizationmechanismsinthedeepaxiallithospherewhenthereisnomagma?
§ How to make detachments in a thicklithosphere(≥15km)?
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2[Bickertetal.,tobesubmitted]
TheEasternSouthWestIndianRidge(SWIR)
40% of the samples are stronglydeformed,withplanarfine-grainedzones.
385samplesofultramaficrocks
99partiallyserpentinizedsamples
4059 Weakly
deformedStronglydeformed
Partiallyserpentinizedsamples(99)
Dredges realized on and off-axis recovered variablyserpentinizedperidotites,withminoramountsofgabbros(<4%)andbasalt(16%).
B C
ExtractingP-Tconditionsfromgrainsizereductionzones[Bickerteta
l.,to
besubm
itted]
Heterogeneousdeformationcombiningbrittleandductilemechanisms(Fig.A):
§ Pressuresinthespinelfieldi.e.atdepths>20km(Fig.B)§ Hightemperature(800-1000°C,Fig.B)fromorthopyroxenethermometry§ Highdeviatoricstresses(80-270MPa,Fig.C)fromolivinegrainsize
WeproposethatthisdeformationcharacterizestherootofSWIRaxialdetachments.A
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[Sauter et al., 2013]
Isitpossibletoobtainflipflopdetachmentfaultswithsimilarlife-spamsasthoseobservedinnaturebyconsidering:§ Athickbrittlelithosphere(~20km)
§ Twostrainsofteningmechanismsobservedinthesamples:ü Serpentinization(T≤350°C)ü Grainsizereduction(800-1000°C)
Fromthemicroscaletothemacroscale:Platescaledeformationmodels
4059 Weakly
deformedStronglydeformed
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T ~350°C
[Bickerteta
l.,to
besubm
itted]
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Serpentinizationalone… doesnotproduceflipflopdetachments.
T≤350°C
εII.σII=108J
1) When conditions are appropriate:
2) Decrease of cohesion and friction:
3) Decrease of activation energy:
[Bickert et al., 2020]
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Grainsizereductionalone…doesproduceflipflopdetachments.
T=800–1000°C
1) When conditions are appropriate:
2) Set up of new grain size:
3) New viscosity using diffusion creep law:
[VanderWaletal.,1993]
[Bickert et al., 2020]
Modelswithserpentinization+grainsizereduction…
Ø … develop four faulting modes,including2detachmentmodes.
Ø Serpentinization alone does not
produceflipflopdetachments.Ø Grain size reduction makes
flipflopdetachmentspossible inathicklithosphere.
Ø By combining the two, theresulting fault patterns approachthe flipflop detachment faultingpatternattheEasternSWIR.
7 [Bickert et al., 2020]
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Bickert1,M.,Cannat1,M.,Tommasi2,A.,Jammes3,S.,Lavier4,L.
Questions?Comments?Feelfreetocontacttheauthors:
[email protected]/[email protected],InstitutdePhysiqueduGlobedeParis,UMR7154-CNRS,UniversitédeParis,[email protected]éosciencesMontpellier–CNRS&UniversitédeMontpellier,[email protected],TexasStateUniversity,SanMarcos,Texas78666,[email protected],InstituteforGeophysics,JacksonSchoolofGeosciences,TheUniversityofTexasatAustin,UnitedStates
