Intraplate deformation under boundary forces
Abstract
The deformation of a plate due to boundary stresses is investigated using both the elastic and viscous models for plate deformation. The role of basal shear stress (at the lithosphere-asthenosphere boundary), oblique convergence and strength inhomogeneity are investigated for modifying plate deformation, subjected to lateral stresses, using Beam Deflection Theory and Finite Element analysis. The results are applied to two different geological problems. First is the post-rift deformation of the Midcontinent Rift System (MCR) under the stresses from the Grenville Tectonic Zone, and second is the asymmetric distribution of deformation along the Indian-Eurasian collision boundary. The role of basal shear on intraplate deformation is studied using a discretized form of the equation resulting from elastic beam theory. The results indicate insignificant effect of basal shear on plate deformation when subjected to lateral boundary stresses. It is further concluded that tectonic stresses from the Grenville Tectonic Zone contributed to the post-rift evolution of the MCR. This conclusion is also supported by the 2D, finite-element, viscous model which showed that stresses from the Grenville Tectonic Zone could be responsible for producing laterally varying deformation along the axis of the MCR. The influence of a strength inhomogeneity on deformation of a plate is investigated using the 2D, finite-element, viscous model. A high-strength anomalous zone extends the zone of deformation by acting as a secondary indenter. A low-strength anomalous zone confines deformation between the low-strength zone and the collision boundary. Without the low-strength zone, the region of deformation extends farther from the collision zone. The 2D viscous model also is used to investigate the effect of oblique convergence on plate deformation. It is observed that laterally varying velocity, both magnitude and obliquity angle, along the collision boundary is a better choice for boundary condition than the average velocity, both magnitude and obliquity angle. The 2D viscous modeling of the India-Eurasia collision boundary indicates that laterally varying velocity boundary condition accounts for a small percentage of the asymmetry in topography along this boundary. Most of the asymmetry is due to the presence of high-strength Tarim basin.
Degree
Ph.D.
Advisors
King, Purdue University.
Subject Area
Geophysics|Geophysical engineering
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