Lithosphere extension as a function of mantle strength · patterns of lithosphere...

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Lithosphere extension as a functionof mantle strength

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

Finite-element code: SARPP- F. Gueydan & Y. Leroy

2D modelling- Model Set-up

Small perturbation (100m)- at Brittle-Ductile TransitionsIn 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-MantleDécollementWide 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

EARLimagne-Bresse

Basin&RangeAegeanTibet

Rhine graben

Baikal Deverchere & al.,2001

3- Natural examples SINGLE RIFT

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Brun et al., 1992

LimagneBresse

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

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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 analogiqueen

extension

Enjeux de la modélisation numérique

extension

Beslier & Brun, 1991

extension

Beslier & Brun, 1991

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 riftNarrow 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 of the velocity

� Crustal decollement modetriggered 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 of

crustal thickness

Coupled crust-mantle

Crustal decollement

Lithosphere extension as a function of mantle strength · patterns of lithosphere...

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