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Collisional Belts and Intra-Continental Convergence (A-type Subduction) |
Department of Geology, CB# 3315, University of North Carolina, Chapel Hill, NC 27599, USA afg{at}unc.edu
A numerical model of the interplay between viscous sinking and erosion predicts that the ultimate fate of dense rock bodies in the crust is a sensitive function of erosion rate and of the body’s radius, density, and initial depth of emplacement. If all of these variables save one are held constant, the trajectories taken by the body on a depth-time plot diverge widely about a critical value of the remaining variable. For example, if erosion rate, depth, and density are held constant, there is a critical value of the body’s radius below which it will be carried to the Earth’s surface by erosion and above which it will plummet to neutral buoyancy in the deep crust. This critical sensitivity may explain, for example, why dense plutons larger than a few kilometres in diameter are rare in plutonic terranes. The calculations indicate that exceptionally high erosion or tectonic denudation rates, on the order of 10 km Ma–1 or more, may be necessary to bring dense bodies to the surface before they sink through less dense crust.
