Lithosphere extension as a function of mantle strength Frdric - - PowerPoint PPT Presentation

Lithosphere extension as a function

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Frédéric Gueydan, Christina Morency & Jean Pierre Brun

Gueydan et al., Tectonophysics, 2008

Role of rheological layering on lithosphere deformation

Buck (1991) Jackson (2002)

EXTENSION COMPRESSION High lithosphere strength Narrow rift Low lithosphere strength Wide rift Mechanical role of each rheological layers? No high strength mantle Crustal strength >> Mantle strenght Crustal and mantle contribution to lithosphere strength?

Single Rifts Distributed extension

1- Mantle and crustal contribution to lithosphere strength

Wet quartz, dry olivine Crustal thick=30 km

1- Mantle and crustal contribution to lithosphere strength

Wet quartz, dry olivine Crustal thick=30 km

1- Mantle and crustal contribution to lithosphere strength

Wet quartz, dry olivine Crustal thick=30 km

Finite-element code: SARPP- F. Gueydan & Y. Leroy 2D modelling- Model Set-up

Small perturbation (100m)- at Brittle-Ductile Transitions In order to initiate strain localization Finite-element code: SARPP- F. Gueydan & Y. Leroy 2D modelling- Model Set-up

Model 1

2D Results- Role of mantle strength

Model 2

Gueydan et al, Tectonophysics, 2008

2D Results- Role of mantle strength Three patterns of lithosphere stretching

Transition between the 3 patterns of lithosphere extension

Coupled crust-Mantle Décollement Wide Rift

Transition between the 3 patterns of lithosphere extension

Map of lithosphere extension modes Transitions

Coupled/décollement TM~500° C At larger TM for larger crustal thickness Décollement/wide rift TM~700° C Absence of high strength mantle

Map of lithosphere extension modes Transitions

Coupled/décollement TM~500° C At larger TM for larger crustal thickness Décollement/wide rift TM~700° C Absence of high strength mantle

3- Natural examples SINGLE RIFT TWO BRANCHES RIFTS REGULARLY SPACED RIFTS

Rhine, Baikal EAR Limagne- Bresse Basin&Range Aegean Tibet

Rhine graben

Baikal

Deverchere & al.,2001

3- Natural examples SINGLE RIFT

• Brun et al., 1992

Limagne Bresse

3- Natural examples TWO BRANCHES RIFTS

Michon & Merle,2003

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Evvia-Corinthe

3- Natural examples REGULARLY SPACED RIFTS

Post-orogenic extension Basin & Range Extension of pre-thickened crust Tibet

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• Latorre et al., 1992

Conclusions

Existence of a high strength mantle Lithosphere necking Strength of the deep crust Amount of crust/mantle coupling Rift spacing is a direct function of mantle strength

Allemand et al 1989

Modélisation analogique en extension

Enjeux de la modélisation numérique

Allemand et al 1989

Modélisation analogique en extension

Beslier & Brun, 1991

Enjeux de la modélisation numérique

Allemand et al 1989

Modélisation analogique en extension

Beslier & Brun, 1991

Enjeux de la modélisation numérique

remaillage grande déformation grand déplacements horizontaux

parallèle aux limites lithologiques rhéologies complexes thermo-mécanique couplé, …

Rift spacing

Rift topography

1 cm/a 1 mm/a Map of lithosphere extension modes Role of the applied velocity

Dry Olivine Wet Olivine Map of lithosphere extension modes Role of the rheological parameter

Existence of a high strength mantle No high strength mantle

Role of the high strength uppermost mantle? Objective Role of the rheological layering (thermal layering) on the patterns of lithosphere extension- Continuum analysis Focus on the role of the high strength mantle

Wide rift Narrow rift Moho offset Flat Moho

Rhine, Brun et al., 1992

Decreases the deep crust strength Increases the amount of Mantle/Crust decoupling 2D Results- Role of the applied velocity

Coupled crust-mantle/Crustal décollement Wide rift Crustal decollement

Decrease

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velocity Crustal decollement mode triggered for lower TM More localized deformation (cf. Wide Rift)

Crustal décollement Crustal decollement

2D Results- Role of the crustal thickness Increase of lithosphere strength (uppermost mantle) Increase the amount of Mantle/Crust Coupling Increase

• f

crustal thickness

Coupled crust-mantle Crustal decollement