CAREER: Developing noble gases as tracers of metamorphic dehydration

Project: Research project

Project Details

Description

The habitability of Earth is controlled by the distribution of volatile elements (e.g. water, carbon dioxide) between surface (atmosphere + hydrosphere) and interior reservoirs (mantle + core). Metamorphism during burial and heating of oceanic plates at subduction zones regulates the supply of water into the Earth's mantle, critically affecting how the mantle flows. However, the specific pathways and fluxes by which water is transported beyond arc volcanoes are uncertain. While direct tracing of subducted water is made difficult by its small number of isotopes, the noble gases are elementally- and isotopically-rich, are fractionated by physical processes and are ideal tracers for the movement of metamorphic fluids. Application of the noble gases as tracers of the deep water cycle requires development of a linkage between noble gas composition and the magnitudes of water loss during subduction. This project will result in a systematic characterisation of the distribution and composition of noble gas isotopes in ancient samples of subducted oceanic crust, establishing the framework for noble gases to be used as tracers of metamorphic fluids. The integrated research and education program proposed here will result in: 1) quantification of the key physical processes that control subduction-processing of volatiles; 2) career-enhancement for an early career scientist and a graduate student, and 3) broadened participation and enhanced diversity in petrological research via a series of formative research institutes targeting applicants from minority-serving institutions.

Earth's upper mantle contains an indelible elemental abundance pattern of heavy noble gases (Ar, Kr, Xe) that is strikingly similar to seawater. Because this is a unique composition in the solar system, the only credible explanation is that a non-disrupted, seawater-like noble gas signature survives the subduction process, generally thought to exclude more than 95% of input volatiles. Given that the noble gases are between 100 and 100,000 times more soluble in fluids than crustal minerals, even minor amounts of phase separation during release and transport of metamorphic fluids will fractionate the noble gas composition of subducting rock. How, then, do noble gases escape removal and significant fractionation during subduction? And, can the noble gases be used to quantitatively trace the subduction of water? This project will address these questions through the integration of noble gas compositions, mineralogically-bound H2O contents and thermodynamic estimates of pressure and temperature from exhumed subduction-related rocks. The proposed research will systematically test the overarching hypothesis that noble gas composition is principally controlled by the extent of metamorphic dehydration during subduction. At the core of the educational component of this CAREER program is the development and implementation of a series of summer institutes dedicated to enhancing diversity in petrological research. This program will result in the petrological training of a cohort of undergraduates, many of whom will come from minority-serving institutions. Petrological and geochemical datasets collected as part of the proposed research program will be used to nurture interest, and increase comprehension of undergraduate students, from a diverse array of institutions and backgrounds, in metamorphic petrology.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

StatusActive
Effective start/end date7/1/216/30/26

Funding

  • National Science Foundation: $124,694.00

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