UC San Diego

The structure and magnetization of the oceanic crust reflect its tectonic and magmatic evolution since its initial formation. The magnetization of the crust also provides a record of the polarity reversals and strength of the Earth's geomagnetic field. In this dissertation I first describe absolute paleointensity measurements made on gabbroic rocks collected from the lower oceanic crust of the Troodos ophiolite, Cyprus. The resultant data-set provides a view into the geomagnetic field during the end of the Cretaceous normal polarity superchron (CNS, 120.6 to 83 million years ago). This data-set is then compared to the locally and globally existing data and predictions made by geodynamo numerical simulations. The results hint that the geomagnetic field had similar properties during times of frequent reversals and times of stable polarity. The second chapter of this dissertation is focused on the marine magnetic anomalies observed across the North Pacific fracture zones. Here I analyze archival and newly collected magnetic anomaly and bathymetric profiles measured across three fracture zones in the Cretaceous Quiet Zone (CNS in age). Forward and inverse modeling indicate that these anomalies arise from remanent magnetization, with enhanced remanence located on one side of each fracture zone. These long-duration enhanced zones require some long-lived asymmetry in crustal construction processes near ridge-transform intersections. The calculated magnetization contrasts provide long-term constraints on the properties of the geomagnetic field during the Cretaceous superchron. Finally, using seismic reflection and magnetic anomaly grids collected in the Adare Basin, Antarctica, I explore the kinematic evolution of the West Antarctic rift system during the Neogene. Correlation of the Adare seismic sequence to the closest drillholes and the Ross Sea seismic stratigraphy establishes the temporal framework of three regional tectonic events. Overall, minimal but significant extensional activity took place in the Adare Basin after seafloor spreading stopped. Comparison of the results with observations from the central and southern parts of the rift system suggests that a major change in plate motion took place in the middle miocene