Graduation Year


Document Type




Degree Name

Master of Science (M.S.)

Degree Granting Department


Major Professor

Zachary Atlas, Ph.D.

Co-Major Professor

Aurélie Germa, Ph.D.

Committee Member

Jeffrey G. Ryan, Ph.D.


FTIR, Mid-Ocean Ridge, Mid-Ocean Ridge Structure, Sea Floor Spreading Center, Cocos-Nazca Spreading Center


The Hess Deep Rift in the East Pacific Rise is a mid-ocean ridge spreading center that produces melts which exhibit geochemical characteristics of evolved MORB. Using basaltic glass samples collected from multiple dive cruises that explored Hess Deep geology, volatile and chemical data were collected at USF using FTIR and EMPA, respectively. In addition, a data suite of samples of glass from Hess Deep were compiled from the EarthChem database. The intention was to use the data suite and models to compare the Hess Deep regime to analog models for mid-ocean ridge crystallization regimes and tectonic structures. The USF and EarthChem samples were then compared to various crystallization models generated in Petrolog3 (Danyushevsky and Plechov, 2011) and COMAGMAT (Ariskin and Barmina, 2004). The starting compositions using depleted, normal, and enriched MORB (Gale et al, 2013) were modeled at depths reflecting an upper and lower melt lens along the rift axis. The volatile components of the USF samples were compared to models for water and carbon dioxide behavior in basalt made using VolatileCalc (Newman and Lowenstern, 2002). Based on the comparison of the samples to the forward modeling in Petrolog3, it appears that the geochemical behavior of major and trace elements most closely resembles that of small amounts of fractional crystallization and re-assimilation of accessory minerals. The VolatileCalc models suggest that the USF samples most likely followed a degassing pathway at depths corresponding to the shallow melt lens. When considering the analog models for ophiolite sequences and melt flow beneath a fast-spreading ridge, it appears that the melt regime at Hess Deep deviates from both standing theories. Instead the most likely mechanisms are shallow crystallization, at depths equal to or less than an upper melt lens, and shallow dynamic degassing.