Part 2

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S
LH
HHC
TSS
Structure of
the
Himalayas
Modified from Lavé & Avouac, 2001
ITS Indus Tsangpo Suture
TS Tethyan Sedimentary Series
STD South Tibetan Detachment
HHC Higher Himalayan Crystalline
MCT Main Central Thrust
LH Lesser Himalayas
MBT Main Boundary Thrust
Siwaliks
MFT Main Frontal Thrust
Galy, 1999
S
LH
HHC
TSS
Structure of
the
Himalayas
Modified from Lavé & Avouac, 2001
ITS Indus Tsangpo Suture
TS Tethyan Sedimentary Series
STD South Tibetan Detachment
HHC Higher Himalayan Crystalline
MCT Main Central Thrust
LH Lesser Himalayas
MBT Main Boundary Thrust
Siwaliks
MFT Main Frontal Thrust
S
LH
HHC
TSS
Structure of
the
Himalayas
Modified from Lavé & Avouac, 2001
ITS Indus Tsangpo Suture
TS Tethyan Sedimentary Series
STD South Tibetan Detachment
HHC Higher Himalayan Crystalline
MCT Main Central Thrust
LH Lesser Himalayas
MBT Main Boundary Thrust
Siwaliks
MFT Main Frontal Thrust
Looking South towards
the high summits
S
LH
HHC
TSS
Structure of
the
Himalayas
Modified from Lavé & Avouac, 2001
ITS Indus Tsangpo Suture
TS Tethyan Sedimentary Series
STD South Tibetan Detachment
HHC Higher Himalayan Crystalline
MCT Main Central Thrust
LH Lesser Himalayas
MBT Main Boundary Thrust
Siwaliks
MFT Main Frontal Thrust
A HUGE normal fault in the middle of
the largest mountain range on Earth!!!
S
N
S
LH
HHC
TSS
Structure of
the
Himalayas
Modified from Lavé & Avouac, 2001
ITS Indus Tsangpo Suture
TS Tethyan Sedimentary Series
STD South Tibetan Detachment
HHC Higher Himalayan Crystalline
MCT Main Central Thrust
LH Lesser Himalayas
MBT Main Boundary Thrust
Siwaliks
MFT Main Frontal Thrust
S
LH
HHC
TSS
Structure of
the
Himalayas
Modified from Lavé & Avouac, 2001
ITS Indus Tsangpo Suture
TS Tethyan Sedimentary Series
STD South Tibetan Detachment
HHC Higher Himalayan Crystalline
MCT Main Central Thrust
LH Lesser Himalayas
MBT Main Boundary Thrust
Siwaliks
MFT Main Frontal Thrust
S
LH
HHC
TSS
Structure of
the
Himalayas
Modified from Lavé & Avouac, 2001
ITS Indus Tsangpo Suture
TS Tethyan Sedimentary Series
STD South Tibetan Detachment
HHC Higher Himalayan Crystalline
MCT Main Central Thrust
LH Lesser Himalayas
MBT Main Boundary Thrust
Siwaliks
MFT Main Frontal Thrust
This is the very
front of the
Himalayas!
MFT
Lavé et al., 2005
III. Erosion controls the structure of mountains?
2) 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…
The growth of
the Himalayas
did affect
profoundly
atmospheric
circulation 
monsoon +
aridification of
the zone North of
the main divide
Bookhagen and Burbank, 2006
(Tapponnier et al., 2001)
Arid Tibetan plateau: erosion << uplift  the range widens + extrusion
Why the Tibetan plateau
is not getting higher?
Tapponnier, 1982
Tibetan Plateau: crustal
thickness ~70 km
 partial melting of the
lower crust
 ductile behaviour, very
low “coefficient of friction”
 can’t build up topo!
(Tapponnier et al., 2001)
Lithospheric cross-section
III. Erosion controls the structure of mountains?
2) 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?
S
LH
HHC
TSS
Modified from Lavé & Avouac, 2001
Lavé & Avouac, 2001:
maximum fluvial erosion
rate in the HHC zone for
6 main Himalayan rivers
S
LH
HHC
TSS
Lavé & Avouac, 2001:
maximum fluvial erosion
rate in the HHC zone for
6 main Himalayan rivers
Modified from
Lavé & Avouac,
2001
Can focused erosion lead to focused exhumation?
Beaumont et al., 2001
Can focused erosion lead to focused exhumation?
Erosion
Erosion
Erosion
Chemenda
et al., 1995
PHYSICAL
MODELLING
Can focused erosion lead to focused exhumation?
NUMERICAL
MODELLING
Beaumont et al., 2001: the CHANNEL FLOW theory
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?
NUMERICAL
MODELLING
Beaumont et al., 2001: the
CHANNEL FLOW theory
S
LH
HHC
TSS
Modified from Lavé & Avouac, 2001
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…)
IV. To which extent does erosion affect deformation in
mountains? “Revisiting river anticlines”.
Montgomery and Stolar, 2006
Montgomery and Stolar, 2006
Unloading  local rebound / uplift. Can be
isostatic (passive) or fed by channel flow
(active: focused erosion focus exhumation)
IV. To which extent does erosion affect deformation in
mountains? “Revisiting river anticlines”.
Montgomery and Stolar, 2006
The growth and development of Himalayan
river anticlines are not explained well by
classical explanations for relationships
between river courses and geological structure.
Re-examination of the potential role of
differential bedrock erosion suggests that rivers
appear able to influence the development of
geological structures where there are sustained
gradients in erosion rate and either a crustal
rigidity low enough to permit localized
isostatic rebound, or where facilitated by active
feedback between tectonic and erosional
processes such as that leading to channeling of
crustal flow. Consequently, rivers may be the
authors not only of their own valleys, but in
some circumstances of the structural geology
of the surrounding mountains as well.
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