Uplift and Isostasy

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Uplift and Isostasy
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Uplift-displacement opposite gravity vector
exhumation is greater than rock uplift surface
elevation decreases
US UR - e
Rock uplift (UR) -vertical displacement of rock
w.r.t. sea level Exhumation (e) -thickness of
rock removed by tectonics/erosion (inferred from
geobarometers, geothermometers, and the
geotherm, e.g., garnets and metamorphic facies
rates inferred by radiometric dating) Surface
uplift (US) -resultant change in ground-surface
elevation w.r.t. sea level (value can be or
-)
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Isostasy
Condition of equilibrium, comparable to floating,
of the lithosphere atop the asthenosphere
Isostatic compensation
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American West
NRM
BHM
YNP
BH
GSL
FR
WM
D
SRM
Basin Range
GV
SNM
CCR
LV
SJM
SCM
GC
CO Plateau
RGR
WSNP
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Physiographic Provinces
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CO Plateau
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CO Plateau Rock Uplift 2.1 km
0.4 km of exhumation since Late Cretaceous
Rocky Mts. display 5-7 km of rock uplift
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Rate of CO Plateau Uplift
Stage 1 25-5 Ma (40 m/m.y.) Stage 2 5-0 Ma
(220 m/m.y.)
Vesicle size in basalt (f) altitude
Geology (9/02)
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River Incision and Rock Uplift
Eastern Himalayas
40Ar/39Ar biotite is age of mineral since cooling
below 300-335ºC
Tsangpo River
(U-Th)/He zircon is age of mineral since
cooling below 185-210ºC
Note the superposed patterns of relief (gt3300
m), sediment deposition, river power, and cooling
ages
GSA Bulletin 1/08
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Uplift of Andes
Central Andean plateau began uplifting rapidly
about 8 Ma (as fast as 1.5 km/m.y.) Why?
Delamination of dense mantle lithosphere and
eclogite (80-140 km worth) after protracted
thickening by tectonic shortening
Science 6/6/08
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India A Tale of Loss and Tears
Hindu Kush region
Boudin in gneiss
Slab is deforming by ductile necking
Earthquake foci beneath Hindu Kush suggest
active delamination of slab from Indian plate
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India A Tale of Loss and Tears
Q Why rapid sea floor spreading (20 cm/yr) in
Indian Ocean after deconstruction of
Gondwanaland (130-50 Ma)?
A India lost its mantle lithosphere today, its
100 km thicknormal Archean age litho. is 250
km thick
Gondwanaland with present-day cont. litho.
thickness
Nature 10/18/07