The Evolution of Lithospheric Deformation and Crustal Structure from Continental Margins to Oceanic Spreading Centers

Mark Behn, Ph.D., 2002
Jian Lin and Maria Zuber, Advisors

This thesis investigates the evolution of lithospheric deformation and crustal structure from continental margins to mid-ocean ridges. Chapter 2 examines segmentation along the U.S. East Coast Margin and investigates the relationship between incipient margin structure and segmentation at the modern Mid-Atlantic Ridge. In Chapter 3, I show that incorporating strain-rate softening in continuum models results in localized zones of high strain rate that develop in response to the rheology and boundary conditions. I use this approach to quantify the effects of thermal state, crustal thickness, and crustal rheology on the style of extension deformation. The mechanics of fault initiation and propagation at mid-ocean ridges is investigated in Chapter 4. Two modes of fault development are identified: faults that initiate near the segment center and faults that initiate at the segment ends. Numerical results from Chapter 5 predict that over time scales longer than an earthquake cycle transform faults behave as zones of significant weakness. Furthermore, these models indicate that faults formed at the inside-corner of a ridge-transform intersection will experience preferential growth due to their proximity to the weak transform. Finally, Chapter 6 presents a new method to quantify the relationship between the seismic velocity and composition of igneous rocks.