
NSF Org: |
OCE Division Of Ocean Sciences |
Recipient: |
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Initial Amendment Date: | August 3, 2015 |
Latest Amendment Date: | April 15, 2019 |
Award Number: | 1538121 |
Award Instrument: | Standard Grant |
Program Manager: |
Deborah K. Smith
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
Start Date: | August 15, 2015 |
End Date: | July 31, 2020 (Estimated) |
Total Intended Award Amount: | $275,379.00 |
Total Awarded Amount to Date: | $275,379.00 |
Funds Obligated to Date: |
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History of Investigator: |
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Recipient Sponsored Research Office: |
2425 CAMPUS RD SINCLAIR RM 1 HONOLULU HI US 96822-2247 (808)956-7800 |
Sponsor Congressional District: |
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Primary Place of Performance: |
1680 East-West Rd Honolulu HI US 96822-2234 |
Primary Place of
Performance Congressional District: |
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Unique Entity Identifier (UEI): |
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Parent UEI: |
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NSF Program(s): | Marine Geology and Geophysics |
Primary Program Source: |
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Program Reference Code(s): |
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Program Element Code(s): |
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Award Agency Code: | 4900 |
Fund Agency Code: | 4900 |
Assistance Listing Number(s): | 47.050 |
ABSTRACT
This project is a study of subduction zone volcanic rocks to understand how they form. Subduction zones are places where materials from Earth's surface (sediments, volcanic rocks, and other rocky materials) are returned to the mantle. During this process fluids are drawn from the "slab" of subducting material while it descends, causing the overlying mantle to melt, producing magmas that drive a significant portion of Earth's volcanism. Despite 50 years of research about how and where this magmatic activity occurs, the range of volcanic styles and products, and their contributions to human society (hazards, ore formation, landscape evolution, etc.), numerous questions remain about the conditions and timescales of melting in the mantle, the different types of rocks that might melt, and the sizes and shapes of these different subterranean rock regions. In addition scientists still have a very incomplete picture of how all of these things contribute to what type of magma is ultimately erupted and what style the eruptions take (for example, how big, how frequent, how explosive). This research project addresses these questions using recently erupted, rare, volcanic rocks called boninites. These rocks form when H2O is added to the shallow mantle under very high temperature conditions. The tools of geochemistry, isotope geochemistry, and naturally-occurring radioactive element distributions in these rocks will be used to analyze an already existing, unique, set of samples. Project goals are to determine: (1) the variety and spatial scale of mantle compositions beneath this subduction zone, (2) the timescales over which they melt, (3) how magma forms and migrates to the surface, and (4) how this contributes to volcanic activity. Answers to these questions have broader impacts to society and the national interest because they provide information on processes leading to magmatism and volcanism (and associated hazards and benefits) at subduction zones, which occur both off the western coast of the United States and along the coasts of many of our partner nations in the Americas, Caribbean and Pacific Rim, like Japan, Taiwan and New Zealand. In addition, the project will fund an institution in an EPSCoR state (Hawaii), support an early career researcher, and carry out public outreach through the NOAA outreach engine and U Hawaii websites.
This project will study interoceanic subduction zone volcanism, using a unique set of young boninite and related mafic/ultramafic samples from the nine Mata Volcanoes and neighboring rear arc and back arc volcanoes (Northeast Lau and Fonualei Spreading Centers). U-series disequilibria and analyses of Sr-Nd-Pb-Hf isotopes, and major/trace element abundances in already-collected volcanic glasses, minerals and whole rocks will be used to investigate high resolution (km-scale) mantle wedge heterogeneity at an active inter-oceanic arc/backarc, sub-millennial variations in subduction fluid inputs, and conditions of boninite and other magma petrogenesis. Hypotheses will be tested to address how fluids from the subducting slab induce melting in the overlying mantle, how different compositions of mantle melt, how different magmas are delivered to the surface in a way that preserves large variations in magma composition over small spatial scales, and the timescales of these various processes, which prelimimary data indicates is likely to be much faster in some cases than heretofore realized.
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Introduction/Project Motivation
Volcanoes provide windows into a planetary interior (how hot it is, what it is made of, and how internal forces and processes affect the planetary surface). This research focused on modern submarine volcanism, a spectacular but difficult to study form of volcanism because of the remoteness and complicated environmental parameters in the deep sea. Active deep sea volcanism and volcanic ecosystems illustrate part of the wide range of Earth's geological and biological conditions and captivate peoples' imaginations with their "otherworldly" character.
The main project goal was to study the causes and consequences of submarine Boninite. We used geological, geochemical and geophysical tools in the field and laboratory. What makes Boninite unusual is it's rareness in the modern geological record, it's very unusual composition (e.g., very rich in Si-Mg-H2O, and very poor in other common magmatic components), and the very high estimated eruption temperatures (perhaps >1600oC). It is thought to represent an "endmember" (rare extreme) magma composition that can teach us much about Earth's interior.
Ancient (millions of years old) examples of Boninite were first discovered in Japan's Bonin Islands several decades ago and subsequently at a handful of other localities. Age and weathering often make those imperfect for detailed compositional analysis. In 2009 a NSF/NOAA sponsored research team, including Rubin, discovered Earth's only known modern Boninite Volcanism locality at West Mata Volcano, in the northern submarine reaches of Tonga. This allowed collection of the first geologically and geochemically pristine boninite specimens, as well as the very first observations of erupting lava in the deep sea [see NSF News Release 09-243, Marine-Scientists Discover-Deepest-Undersea-Erupting-Volcano]. That discovery, the unusualness of the rocks, sample collections on 4 subsequent NSF/NOAA expeditions (2010 to 2012), and on a new public-private partnership expedition with Schmidt Ocean Institute (SOI) in 2017, were all motivating factors in this research.
Nitty Gritty Details
This research includes a variety of compositional attributes in volcanic rocks and minerals, including natural radioactivity (U, Th and their daughter isotopes), stable and radiogenic isotopes (Sr-Nd-Pb-Hf and Fe), and major and trace element abundances. Collectively these chemical tracers allow us to study the rates of deep earth processes, the diversity of compositions there, how magma is made and transported, and how seemingly small differences in mantle chemistry, mineralogy and history can greatly impact magmatism and volcanism.
Why Boninite and why Tonga?
Boninite is thought to form by melting of Earth's mantle, primarily at subduction zones. While the entire Pacific Ocean is ringed by subduction zones, boninite has only been detected at inter-oceanic arcs and not observed at continental subduction zones (such as most of the western coasts of North and South America). The Northeast Lau basin and adjacent Tofua arc (see the map) has widespread boninite volcanism. It is a very dynamic geological environment (i.e., the fastest converging tectonic plates on the planet and the fastest opening back-arc basin) forming many closely spaced active volcanoes.
You can learn about the study site and boninite in this public outreach video on YouTube, produced with SOI during the 2017 expedition. It is narrated by Rubin and animated by a media specialist. That video and a lot of other video, blogs and photos are also at the cruise website.
Boninite is thought to form by melting of mantle that has already experienced prior melting episodes, making it very difficult to re-melt ("refractory" mantle). However, adding water to refractory mantle can lower its melting point, allowing it to producing Boninite. In this instance the water comes from dehydration of the subducting tectonic plate, percolating upward as the plate descends beneath a wedge-shaped region of refractory mantle. Not all Boninite is the same, with important regional differences starting to emerge, as well as difference between modern and more ancient occurrences, so that Boninite is best thought of as a category of related rock types, rather than a singular composition.
Major Findings - summarized in Figure 4.
The Team
This research involved an integrated team of geologists, petrologists and geochemists, including the thee PIs, two graduate students, a postdoc, NOAA research partners, and a public private partnership with SOI (a philanthropic organization and excellent partner for extending the reach of NSF funded research by maximizing public engagement, and promoting basic scientific research, exploration of the sea, and use of cutting edge technologies in the sea).
Public Outreach
Rubin frequently communicates to the public about volcanoes through (1) websites and social media (@kenhrubin or @kenhrubingeo on your favorite platform); public presentations at museums and universities, and (3) as an occasional contributor to major broadcast media and print media outlets. Two notable outreach papers about this research are in ECO Magazine (2017) and Environmental SCIENTIST (2018) "Exploring submarine volcanoes" (story 4). Rubin and 2017 expedition co chief Chadwick also narrated ROV dive data (live streamed on SOI's Facebook and YouTube channels).
Last Modified: 07/29/2021
Modified by: Kenneth H Rubin
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