Geology Reference
In-Depth Information
Modeling the Thermal Evolution of the Andean Edge
A
Altiplano
6
5
4
3
2
1
0
Forearc
Basin
initial
state
present
topography
0.6
B
1.0
Fig. 11.29
Modeling the thermal evolution
of the edge of the Andes.
A. Models of the topography through time,
taking the initial state (left) as a splined fit
across the modern canyon. Second frame
shows 10% of the modern canyon in place;
third frame 30%, and fourth frame 100%.
B. Measured apatite He ages at sample
locations (black diamonds) and modeled
ages for various assumed times and durations
of canyon insertion into the landscape. The
best-fit time for canyon cutting (circles) is
9-5 Ma. Modified after Schildgen
et al.
(2009).
[A color version of this appears as Plate 13.]
1.4
1.8
2.2
2.6
3.0
3.4
0
10
20
30
40
50
60
70
Apatite-He age (Ma)
interior. Gurnis (2001) has argued that such
processes are responsible for the marine
sedimentation in interior Australia (Figs 10.46
and 10.47): even though Australia has seen no
collisional tectonics for a long time, it has none-
theless overridden the sites of several sinking
lithospheric slabs. Modeling of such effects
requires modeling mantle flowfields, which in
turn requires knowledge of the mantle viscosity
structure (e.g., Mitrovica and Forte, 2004).
Another region that has been addressed using
dynamic mantle flow models is the Colorado
Plateau, the enigmatic region in western North
America that has been surprisingly immune to
active tectonism in the Cenozoic. Recent work
of Flowers
et al.
(2008) suggests a complex
pattern of sedimentation and subsequent
exhumation in the last 100 Ma. Their story may
be at least in part corroborated by models
of mantle dynamics (Liu and Gurnis, 2010), as
discussed in commentary to their model
(Flowers, 2010). Using a strategy of “reverse
tectonics,” Liu and Gurnis (2010) roll the clock
backward, and scroll the Farallon slab from its
present location, as deduced from tomographic
images of the mantle beneath North America,
back to where it is likely to have been several
million years ago. They can, therefore, predict
the spatial-temporal pattern of large-scale uplift
and subsidence of the overlying North American
lithosphere. Such calculations suggest that the
Colorado Plateau region should have exp-
erienced broad pre-Laramide subsidence and
Laramide (80-50 Ma) uplift, with amplitudes of
a little more than 1 km (Fig. 11.30). These large-
scale models, and those in which smaller-scale
convection associated with transitions between
the Colorado Plateau and adjacent extending
regions are captured (Moucha
et al.
, 2008; van
Wijk
et al.
, 2010), may go a long way toward
