In this project, the investigator will explore the evolution of oceanic crust by analyzing the composition of the lava flows from off-axis seamounts near the Juan de Fuca Ridge.
Oceanic crust is created at the axis of mid-ocean ridge spreading centers and is subsequently modified by off-axis volcanism. While mid-ocean ridge basalts erupted on-axis are typically relatively uniform in composition, off-axis seamounts erupt a wide range of compositions suggesting a complex system of melt generation, accumulation, and crystallization beneath these volcanic edifices. The investigator will use geochemical analyses of melt inclusions and associated glasses (including major, trace, and volatile elements) from lavas erupted at several seamounts to geochemically define the magmatic plumbing system beneath off-axis seamounts from melt generation to eruption on the seafloor.
Results will be integrated with an ongoing study of melt inclusions at the adjacent ridge segment, which will provide a direct comparison between on- and off-axis magmatic systems at depth. Thus, the investigator will be able to systematically assess melt generation, accumulation, and the depth of crystallization beneath off-axis seamounts.
The broader impacts include sponsoring an undergraduate student from an under-represented group to work on the research project as a summer intern, and graduate student mentorship. Findings from this project will be presented to the general public in an effort to inspire young scientists at "family science nights" at the New Bedford Ocean Explorium. Data and interpretations will be presented at international conferences. Once published, all data produced will be made available to the scientific community though incorporation into PetDB (www.petdb.org).
This project is supported under the NSF Ocean Sciences Postdoctoral Research Fellowship (OCE PRF) program, with goals to support novel research by early career scientists and increase the diversity of the U.S. ocean sciences workforce and research community. With OCE-PRF support, this project will enable a promising early career researcher to establish themselves in an independent research career related to ocean sciences and broaden participation of under-represented groups in the ocean sciences.
Intellectual Merit: Oceanic crust is primarily created at the axis of mid-ocean ridge spreading centers, however, an important component of ocean crust formation occurs at seamounts or volcanic cones. While lavas erupted on mid-ocean ridges are relatively uniform in composition, seamounts erupt a wide range of compositions suggesting a complex system of melt generation, accumulation, and crystallization beneath these volcanic edifices. However, the structure of the deep magmatic plumbing system and the sources of magmatism feeding these seamounts has not been constrained. In this project geochemical analyses are used to explore the composition of magmas erupted at seamounts to better understand how the ocean crust is formed. Geochemical investigations of lavas erupted on the seafloor provide information on shallow crustal processes, but yield limited insights into the deeper magmatic system because lavas typically reflect pooled melts that have aggregated and fractionated in shallow crustal magma chambers. To overcome this obstacle, I measured the composition of olivine-hosted, glassy melt inclusions instead of lavas. Melt inclusions are droplets of melt that are trapped in a crystal (olivine) as it grows deep in magmatic system. The crystal walls protect the magma from alteration, contamination, homogenization, and/or degassing as it ascends to the seafloor, which preserves the original melt composition. Thus, melt inclusions provide a window into the magmatic processes occurring at depth below the seamounts. Over 200 melt inclusions were hand-picked from 10 basalts erupted at five seamounts associated with Juan de Fuca Ridge. Each melt inclusion was run for volatile concentrations using the WHOI 1280 ion microprobe and for major elements using the MIT electron microprobe. Pressures of crystallization beneath each seamount were determined using vapor saturation calculations. The results were presented at the international American Geophysical Union meeting in San Francisco, CA in 2013 and 2014. Broader Impacts: A major component of this fellow ship was to help educate under-represented groups in ocean science. To accomplish this goal, the PI worked with a team of outreach coordinators from Woods Hole Oceanographic Institution and the New Bedford Explorium on a project aimed at educating the public about ocean science. This included several different outreach events over the course of the year: (1) a series of lectures were given at the New Bedford Explorium, (2) tours of the melt inclusion sample preparation lab, rock storage rooms, and the ion microprobe were given to students (and parents) that attended the lectures, and (3) a ship to shore interview was given by the PI while at sea to discuss life at sea and the adventures of the new Alvin Submersible. Another goal of this grant was to mentor a young geoscientist in the field of ocean science. The PI worked with a PhD graduate student to develop a project to analyze volatiles in melt inclusions from mid-ocean ridges. The student and PI worked together to develop a thesis question and select suitable samples for analyses. She was trained in melt inclusion sample preparation and to independently operate the 1280 ion microprobe. This project was a major component of her PhD research. Results of this project were presented at the international American Geophysical Union meeting in 2013 and have been submitted for publication in Earth and Planetary Science Letters.
