UC San Diego

Magmatism and hydrothermal processes along mid-ocean ridges are ma- jor paths for heat and mass exchange between the ocean and solid earth, and are fundamental processes for crustal formation and cooling. Previous research has investigated the relationship between magmatism and the formation of crustal structures, including seafloor features, as well as the extent to which hydrothermal flux contributes to global heat loss and chemical flux. However, there remains a significant gap in understanding the specifics of short-term magmatism and the patterns of near-axis hydrothermal flow. The three principal chapters of this disser- tation explore the magmatism and hydrothermal processes in a volcanically active mid-ocean ridge segment at East Pacific Rise 9◦50’N with bathymetric, sidescan, bottom imagery, water column, and other data collected by submersibles with unprecedented coverage and resolution. Chapter 1 provides a brief overview of the magmatism and hydrothermal process in mid-ocean ridges and introduction to the scope of this dissertation. Chapter 2 describes the extent and volume of the most recent magmatic eruption during 2005-2006 at East Pacific Rise 9◦50’N with pre- and post-eruption data collected by submersibles. Chapter 3 describes the accommodation of plate separation by magmatic and tectonic processes, using analysis of fault and fissure geometry on 1-m resolution bathymetry. Chapter 4 describes the spatial distribution and the flux estimate of hydrothermal discharge with 1-m resolution bathymetry, bottom images, and water column measurements during the near-bottom mapping dives. Chapter 5 provides a summary of the key findings among these studies, and outlines potential direction of future research. Appendix A, B, and C provide an additional information on near-bottom magnetic anomalies at East Pacific Rise 9◦50’N to explore the hydrothermal and magmatic processes with an independent geophysical dataset.