Geology Reference
In-Depth Information
A
Geology & Model for the Himalayan Orogeny
monsoon
rainfall
Indus-
Tsangpo
suture
High
Himalaya
Tibetan
plateau
gneiss
domes
Indian
foreland
er
osio
n
LHS
?
pa
rtial melt
zo
ne
Indian
middle crust
Indian plate
converges with Asia
Indian lower crust
Indian upper mantle
~ 40 km
(V:H ~ 2:1)
South
North
B
No Erosion: Tunneling in Lower Crust
strain markers
lower
crustal
flow
underthrusting mantle lithosphere
C
Erosion: Channel Flow Drawn to Surface
surface erosion
lower
crustal
flow
Fig. 1.9
Proposed climate-tectonic coupling in the Himalayan orogeny.
A. Geological observations and conceptual model that connect partial melting in Tibet and lower crustal flow to
climatically driven erosion and major faults in the Himalaya. Monsoon-driven erosion along the southern flank of the
Himalaya is proposed to weaken the underlying crust and to draw the channel flow toward the surface. GHS: Greater
Himalayan Sequence; LHS: Lesser Himalayan Sequence; MCT: Main Central Thrust; MHT: Main Himalayan Thrust; STD:
South Tibetan Detachment. B. In the absence of erosion, numerical modeling suggests simple outward lower crustal
flow within a confined channel (tunneling). C. With intense erosion localized in a specific region, modeling suggests
lower crustal flow is drawn upwards toward the zone of high erosion. Note that this geometry predicts relative motion
along the channel's margins that is consistent with the slip on the major Himalayan faults (MCT and STD in A).
Modified after Beaumont
et al
. (2001).
In recent years, provocative linkages between
climate, erosion, and tectonics have been proposed.
Even at the scale of orogens, the large-scale
organization of major faults and rock uplift
has been attributed to patterns of differential
erosion that are in turn controlled by climate.
Underpinning these interpretations is the
observation that rapid erosion both removes
rock mass, thereby perturbing the stress field
on the underlying rocks, and compresses the
geothermal gradient, thereby heating and
weakening the underlying rocks. Together, these
