galy, 1999

Galy, 1999

Structure of the

Himalayas

Modified from Lavé & Avouac, 2001

ITS Indus Tsangpo SutureTS Tethyan Sedimentary SeriesSTD South Tibetan DetachmentHHC Higher Himalayan CrystallineMCT Main Central ThrustLH Lesser HimalayasMBT Main Boundary ThrustSiwaliksMFT Main Frontal Thrust

TSSHHCLHS

Structure of the

Himalayas

Modified from Lavé & Avouac, 2001

ITS Indus Tsangpo SutureTS Tethyan Sedimentary SeriesSTD South Tibetan DetachmentHHC Higher Himalayan CrystallineMCT Main Central ThrustLH Lesser HimalayasMBT Main Boundary ThrustSiwaliksMFT Main Frontal Thrust

TSSHHCLHS

Structure of the

Himalayas

Modified from Lavé & Avouac, 2001

ITS Indus Tsangpo SutureTS Tethyan Sedimentary SeriesSTD South Tibetan DetachmentHHC Higher Himalayan CrystallineMCT Main Central ThrustLH Lesser HimalayasMBT Main Boundary ThrustSiwaliksMFT Main Frontal Thrust

TSSHHCLHS

Looking South towards the high summits

Structure of the

Himalayas

Modified from Lavé & Avouac, 2001

ITS Indus Tsangpo SutureTS Tethyan Sedimentary SeriesSTD South Tibetan DetachmentHHC Higher Himalayan CrystallineMCT Main Central ThrustLH Lesser HimalayasMBT Main Boundary ThrustSiwaliksMFT Main Frontal Thrust

TSSHHCLHS

NSHHC

STD

TSS

A HUGE normal fault in the middle of the largest mountain range on Earth!!!

Structure of the

Himalayas

Modified from Lavé & Avouac, 2001

ITS Indus Tsangpo SutureTS Tethyan Sedimentary SeriesSTD South Tibetan DetachmentHHC Higher Himalayan CrystallineMCT Main Central ThrustLH Lesser HimalayasMBT Main Boundary ThrustSiwaliksMFT Main Frontal Thrust

TSSHHCLHS

Structure of the

Himalayas

Modified from Lavé & Avouac, 2001

ITS Indus Tsangpo SutureTS Tethyan Sedimentary SeriesSTD South Tibetan DetachmentHHC Higher Himalayan CrystallineMCT Main Central ThrustLH Lesser HimalayasMBT Main Boundary ThrustSiwaliksMFT Main Frontal Thrust

TSSHHCLHS

Structure of the

Himalayas

Modified from Lavé & Avouac, 2001

ITS Indus Tsangpo SutureTS Tethyan Sedimentary SeriesSTD South Tibetan DetachmentHHC Higher Himalayan CrystallineMCT Main Central ThrustLH Lesser HimalayasMBT Main Boundary ThrustSiwaliksMFT Main Frontal Thrust

TSSHHCLHS

MFT

This is the very front of the Himalayas!

Lavé et al., 2005

III. Erosion controls the structure of mountains?III. Erosion controls the structure of mountains?2) The curious case of the Himalayas2) The curious case of the Himalayas

Puzzling: a huge plateau behind the range and a gigantic normal fault in the middle of the range?!

Localization of erosion could explain both features…

Bookhagen and Burbank, 2006

The growth of the Himalayas did affect profoundly atmospheric circulation monsoon + aridification of the zone North of the main divide

Arid Tibetan plateau: erosion << uplift the range widens + extrusion

(Tap

ponn

ier

et a

l., 2

001)

Tapponnier, 1982

Why the Tibetan plateau is not getting higher?

Lithospheric cross-section

(Tap

ponn

ier

et a

l., 2

001)

Tibetan Plateau: crustal thickness ~70 km

partial melting of the lower crust ductile behaviour, very low “coefficient of friction” can’t build up topo!

III. Erosion controls the structure of mountains?III. Erosion controls the structure of mountains?2) The curious case of the Himalayas2) The curious case of the Himalayas

Puzzling: a huge plateau behind the range and a gigantic normal fault in the middle of the range?!

Localization of erosion could explain both features…

Bookhagen and Burbank, 2006 Rainfall focused at the front of the range focused erosion focused exhumation?

Modified from Lavé & Avouac, 2001

TSSHHCLHS

Lavé & Avouac, 2001: maximum fluvial erosion rate in the HHC zone for 6 main Himalayan rivers

Modified from Lavé & Avouac, 2001

TSSHHCLHS

Lavé & Avouac, 2001: maximum fluvial erosion rate in the HHC zone for 6 main Himalayan rivers

Beaumont et al., 2001

Can focused erosion lead to focused exhumation?Can focused erosion lead to focused exhumation?

Can focused erosion lead to focused exhumation?Can focused erosion lead to focused exhumation?

Erosion

Erosion

Erosion

Chemenda et al., 1995

PHYSICAL MODELLING

Can focused erosion lead to focused exhumation?Can focused erosion lead to focused exhumation?

Beaumont et al., 2001: the CHANNEL FLOW theory

NUMERICALMODELLING

demijohn.co.uk

Erosion rate: H high (> 14 mm/yr), M medium (4-14 mm/yr) or L low (< 4 mm/yr).Effective internal angle of friction for the upper crust: 5 or 15 degrees.Upper crustal rheology: viscosity with respect to Wet Quartzite Flow Law (WQz).

Can focused erosion lead to focused exhumation?Can focused erosion lead to focused exhumation?

Beaumont et al., 2001: the CHANNEL FLOW theory

NUMERICALMODELLING

Modified from Lavé & Avouac, 2001

TSSHHCLHS

Good agreement between model, thermochronologic and PTt data! But

why is the angle of friction for the upper crust so low, and where is the channel

flow now? (the MCT is now inactive…)

Montgomery and Stolar, 2006

IV. To which extent does erosion affect deformation in IV. To which extent does erosion affect deformation in mountains? “Revisiting river anticlines”.mountains? “Revisiting river anticlines”.

Montgomery and Stolar, 2006

Unloading local rebound / uplift. Can be isostatic (passive) or fed by channel flow

(active: focused erosion focus exhumation)

Montgomery and Stolar, 2006

IV. To which extent does erosion affect deformation in IV. To which extent does erosion affect deformation in mountains? “Revisiting river anticlines”.mountains? “Revisiting river anticlines”.

The growth and development of Himalayan The growth and development of Himalayan river anticlines are not explained well by river anticlines are not explained well by classical explanations for relationships classical explanations for relationships between river courses and geological structure. between river courses and geological structure. Re-examination of the potential role of Re-examination of the potential role of differential bedrock erosion suggests that differential bedrock erosion suggests that rivers appear able to influence the rivers appear able to influence the development of geological structures where development of geological structures where there are sustained gradients in erosion rate there are sustained gradients in erosion rate and either a crustal rigidity low enough to and either a crustal rigidity low enough to permit localized isostatic rebound, or where permit localized isostatic rebound, or where facilitated by active feedback between tectonic facilitated by active feedback between tectonic and erosional processes such as that leading to and erosional processes such as that leading to channeling of crustal flow. Consequently, channeling of crustal flow. Consequently, rivers may be the authors not only of their own rivers may be the authors not only of their own valleys, but in some circumstances of the valleys, but in some circumstances of the structural geology of the surrounding structural geology of the surrounding mountains as well.mountains as well.