The theory of plate tectonics predicts that the outer layer of the earth is composed of approximately 15 tectonic plates that are in motion with respect to one another, and that the deformation of those plates will be concentrated at the boundary — where plates meet. One of the most interesting things about the central Alaska Range, and Mt. McKinely in particular, is that it's located nearly 500 kilometers away from the boundary.
“There are a lot of different angles that a plate can descend,” says Margarete Jadamec, a US National Science Foundation postdoctoral fellow in the Department of Geological Sciences at Brown University in Providence, RI. “But our work shows that both flat slab subduction and the Denali fault are required to form the intercontinental mountain range." Jadamec’s findings are published in Earth and Planetary Science Letters.
The Earth behaves as a viscoelastic fluid, responding elastically on short timescales from seconds to days. But it behaves viscously over larger time scales of millions of years. “CitcomCU solves the basic conservation of mass momentum and energy for the viscous flow. But what’s different from computational fluid dynamics experiments in other areas of science is that the viscosity of the earth is extremely large; ranging from 1017 to 1024 Pascal-seconds in the million-year time window we work with,” says Jadamec.
A Pascal-second can be thought of as thickness or internal friction. In this window of extremely high viscosity, the Earth’s flow rates are very small, ranging from millimeters to tens of centimeters per year.
For the fourteen 3-D geodynamic models of the Alaska subduction zone Jadamec developed, the viscosity structure varied up to seven to eight orders of magnitude over 100 kilometers within the model
This article originally appeared in iSGTW on October 16, 2013. Read the full article: 3D tectonic modeling answers age-old geology question