Geoscience Reference
In-Depth Information
Table 2.1
Tectonic settings of arid zones.
Contemporary tectonic setting
Examples
Comments
1. Cratons
Kalahari
Great Karoo
Australian Desert
Relative stability since the Late Tertiary
2. Active continental margins and Cenozoic
orogenic belts
Atacama
Sahara
Sinai-Negev
Arabia-Zagros
Compressional setting, thrust and
transcurrent faulting
3. Older orogenic belts
Sahara
Some reactivation of existing fault zones
4. Interorogenic, intercratonic
Sahara (Afar, Ethiopia)
Mojave
Great Basin
Sonora
Chihuahua
Extensional tectonic setting, 'pull-apart'
basins
5. Passive continental margins
Namib
Patagonian
Note
: The physical extent of the Sahara Desert is such that it features in several different categories.
whereas Burbank and Anderson (2001, p. 131) add extra
factors to give:
tonically active areas show that erosion rates (based on
sediment fluxes in river systems) are broadly comparable
with current rates of uplift (Table 2.2). Both spatial and
temporal scales are important when dealing with erosion
rates. Denudation rates appear to be time-dependent, an
observation facilitated by the recent developments in cos-
mogenic and fission-track thermochronology dating. Von
Blanckenburg (2006) contrasts the results of denudation
rates calculated using sediment gauging data (timescale
10
1
-10
2
yr), cosmogenic nuclides (timescale 10
1
-10
6
yr)
Surface uplift
=
bedrock uplift
+
deposition
−
compaction
−
erosion.
The interplay between uplift and erosion is more com-
plex and subtle than originally thought (Summerfield,
2000; Montgomery and Brandon, 2002). If erosion keeps
pace with gross uplift there is of course no net uplift, but
while incision by a major river may keep pace with up-
lift, as has been the case in the Himalayan region, areal
erosion rates within the catchment may not do so, with
the consequent development of high relative relief (Bur-
bank and Anderson, 2001). In arid zones, the ability of
erosion processes to respond to tectonic displacements is
of course affected by the fact that many geomorphic and
hydrological processes within these zones are ephemeral
in nature.
In an attempt to address the fundamental issue of the
comparative rates of uplift and erosion at the global level,
Schumm (1963) compared data on maximum rates of up-
lift (c. 7 mm/yr) and maximum rates of erosion (c. 1
mm/yr) and concluded that uplift greatly exceeds maxi-
mum erosion. The problem with this approach, as noted
by Vita-Finzi (1986), is that the erosional data are ef-
fectively averaged-out areal data whereas the uplift rates
may be unrepresentative of uplift at a regional level; that
is erosional data maxima are underestimates while up-
Table 2.2
Comparison of uplift and denudation rates.
References
Uplift rates
10 mm/yr (Karakoram,
Pakistan)
Brookfield (1993)
1 mm/yr (Great Himalaya,
India)
Brookfield (1993)
2 mm/yr (Makran, Iran)
Vita-Finzi (1986)
2-10 mm/yr (Zagros, Iran)
Vita-Finzi (1986)
Erosion rates
9 mm/yr (New Zealand)
Hovius , Stark and Allen
(1997)
2.5 mm/yr (Central
Himalaya)
Galy and France-Lenord
(2001)
7 mm/yr (Nanga Parbat)
Shroder and Bishop
(2000)
