Thermal structure, magmatism, and evolution of fast-spreading mid-ocean ridges

We use thin-plate flexural models and high-resolution magnetic field data to constrain magmatic and tectonic processes at fast-spreading mid-ocean ridges, and how these processes evolve over time. Models are constructed to predict axial high topography and gravity for a given thermal structure of the crust and mechanical structure of the lithosphere. Whereas previous models predicted the high is due to a narrow column of buoyant material extending to 10's of kilometers depth in the mantle, we find the high can also be produced by a narrow zone of crustal melt, and lithosphere which thickens rapidly with distance from the axis. We consider the effects of plastic weakening using a yield strength envelope to map bending stresses associated with deflections. Near-surface stresses are extensional at distances which closely resemble regions of normal fault growth at certain axial highs, suggesting bending stresses play a significant role in normal faulting at fast-spreading ridges. We further develop the model to simulate ridge jumps. We fit topography and gravity data of a plume-influenced region which has recently experienced a ridge jump. Steep sides of the new high are best modeled as constructional features. An abandoned ridge remains at the old axis due to plate strengthening associated with crustal cooling. By fitting more than one profile along-axis, we constrain the accretion history at the new ridge. We also predict than an inconsistency between bull's eye mantle Bouguer anomaly lows and a nearly constant along-axis depth can be resolved by assuming a low density zone below the axis widens near the bull's eye center. Finally, we study high-resolution magnetic field data at two regions of the East Pacific Rise with different eruptive histories. The anomalies are used to map relatively fresh pillow mounds, void space created by lava tubes and lobate flows, and dike complexes which extend along the length of recent fissure eruptions. The dikes suggest episodic eruptive histories in these regions, and have implications regarding the migration history of the area.