Lithosphere extension as a function of mantle strength · patterns of lithosphere extension-Continuum analysis Focus on the role of the high strength mantle Narrow rift Wide rift
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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
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 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
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 analogiqueen
extension
Enjeux de la modélisation numérique
Allemand et al 1989 Modélisation analogiqueen
extension
Beslier & Brun, 1991
Enjeux de la modélisation numérique
Allemand et al 1989 Modélisation analogiqueen
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 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
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