Ridge Segmentation, Tectonic Evolution and Rheology of Slow-Spreading Oceanic Crust

Slow spreading ridges are composed of ridge segments, which are fundamental units of magmatic accretion and tectonic deformation. The objective of this thesis is to characterize these tectonic processes, identify factors controlling segment propagation, and constrain lithospheric strength with deformation experiments. In chapter 2, bathymetry and gravity analyses show that here is a marked asymmetry in bathymetry and gravity near segment offsets. A model of faulting explains these observations suggests that low angle faults may accommodate extension at inside corners of ridge offset intersections, resulting in uplifted and thinned crust with respect to outside corners or segment centers. Statistical and spectral analyses of bathymetry and gravity in Chapter 3 indicate that the crust magmatically emplaced on axis is reshaped by tectonism along the rift valley walls. Satellite gravity data in Chapter 4 reveal the history of segmentation is controlled mainly by the geometry of the ridge axis, and secondarily by hot spots. Segments migrate down regional gradients associated with hot spot swells. However offset propagation up gradient suggests that additional factors control propagation e.g., lithospheric strength. Most non-transform offsets are short lived and migrating, while transform offsets are long lived and stable. Both the propagation of segments and tectonism depend on lithospheric rheology. In Chapter 5, I present results from deformation experiments on serpentinites, which demonstrate that serpentinites are considerably weaker than peridotites, and display a non-delatant type of brittle deformation. Serpentinites may weaken the lithosphere, and control the faulting style.