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

Lithosphere extension as a function of mantle strength Frédéric Gueydan, Christina Morency & Jean Pierre Brun Gueydan et al., Tectonophysics, 2008

Role of rheological layering on lithosphere deformation COMPRESSION EXTENSION Distributed extension Single Rifts Jackson (2002) Buck (1991) High lithosphere strength Narrow rift No high strength mantle Crustal strength >> Mantle strenght Low lithosphere strength Wide rift Mechanical role of each rheological Crustal and mantle contribution to layers? lithosphere strength?

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

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

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

2D Results- Role of mantle strength Model 1 Model 2

2D Results- Role of mantle strength � Three patterns of lithosphere stretching Gueydan et al, Tectonophysics, 2008

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 T M 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 T M for larger crustal thickness Décollement/wide rift � TM~700° C � Absence of high strength mantle

3- Natural examples Rhine, Baikal SINGLE RIFT TWO BRANCHES RIFTS EAR Limagne- Bresse REGULARLY SPACED RIFTS Basin&Range Aegean Tibet

3- Natural examples SINGLE RIFT Rhine graben Brun et al., 1992 Baikal Deverchere & al.,2001 �������� �������������� ������� ��������� ��������� ����� ����� ����� ������� ���������� ����������� ������ ����� ����� ������ ������������

3- Natural examples TWO BRANCHES RIFTS Limagne Bresse Michon & Merle,2003 �������� �������������� ������� ��������� ��������� ������� �������� ����� ����� ���������� ������ ��!�����" ����� ����� ����� #��!�����" �������

3- Natural examples REGULARLY SPACED RIFTS Evvia-Corinthe Latorre et al., 1992 Extension of Post-orogenic extension pre-thickened crust Basin & Range Tibet �������� �������������� ������� ��������� ��������� %��� ����"& �������������� ����� $��� ��!�����"& �������������" ������������� ����� $&����� ����������������� ����� '���� ����� �����������������

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

Enjeux de la modélisation numérique 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 remaillage grande déformation grand déplacements horizontaux Beslier & Brun, 1991 parallèle aux limites lithologiques rhéologies complexes thermo-mécanique couplé, …

Rift spacing

Rift topography

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

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

Role of the high strength uppermost mantle? Narrow rift Wide rift Rhine, Brun et al., 1992 Moho offset Flat Moho Existence of a high strength mantle No high strength 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

2D Results- Role of the applied velocity Coupled crust-mantle/Crustal décollement Crustal decollement Wide rift � Decreases the deep crust � Crustal decollement mode Decrease strength triggered for lower T M of the � Increases the amount of � More localized deformation velocity Mantle/Crust decoupling (cf. Wide Rift)

2D Results- Role of the crustal thickness Crustal decollement Crustal décollement Coupled crust-mantle Crustal decollement Increase � Increase of lithosphere strength (uppermost mantle) of � Increase the amount of Mantle/Crust Coupling crustal thickness