Introduction
Crustal Thickness:
Now & Then Crustal
Thickening Mechanisms Conclusions References |
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| Given the well documented
crustal thickness of the Great Plains, and the constraints on the timing
of uplift and thickening and the options
for describing the mechanisms of thickening, it seems that the western
edge of the North American craton was thickened by lower crustal flow.
It is well accepted that before the Laramide and Sevier orogenies, the
thickness of the present day Great Plains was more like normal continental
crust. This would infer up to 15 km of crustal thickening in the last 75
million years or so or a rate of about 0.2 mm/year. A combination of the
five mechanisms described is most likely the cause of the observed crustal
thickening. Still, lower crustal flow stands out as a likely impetus of
thickening. Furthermore, without a clear consensus on the real orientation
of the Farallon slab’s subduction, it’s hard to say with confidence
that basal shear forces are solely responsible for this lower crustal displacement.
Passive flow however is a good candidate for a model to describe the driving
forces pushing this flow. In addition, there are analogous examples of
similar lower crustal flow in other regions of the world that support the
plausibility of this description. |
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