| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
|
| Initial Amendment Date: | July 16, 2010 |
| Latest Amendment Date: | June 4, 2012 |
| Award Number: | 1019229 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Jennifer Wade
jwade@nsf.gov (703)292-4739 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | July 15, 2010 |
| End Date: | June 30, 2014 (Estimated) |
| Total Intended Award Amount: | $350,000.00 |
| Total Awarded Amount to Date: | $350,000.00 |
| Funds Obligated to Date: |
FY 2011 = $117,280.00 FY 2012 = $121,812.00 |
| History of Investigator: |
|
| Recipient Sponsored Research Office: |
1 PROSPECT ST PROVIDENCE RI US 02912-9100 (401)863-2777 |
| Sponsor Congressional District: |
|
| Primary Place of Performance: |
1 PROSPECT ST PROVIDENCE RI US 02912-9100 |
| Primary Place of
Performance Congressional District: |
|
| Unique Entity Identifier (UEI): |
|
| Parent UEI: |
|
| NSF Program(s): | Petrology and Geochemistry |
| Primary Program Source: |
01001112DB NSF RESEARCH & RELATED ACTIVIT 01001213DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
|
| Program Element Code(s): |
|
| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
The motions of the Earth's interior control and organize much of what goes on at the surface. From earthquakes and volcanoes, to oil and mineral deposits, even the evolution of life itself; the world humans live in is largely the product of the deep processes within our planet's interior. Because one cannot directly sample the deep Earth, one has to use indirect physical and chemical measurements to understand what is happening below our feet. The proposed study seeks to further our understanding of the inner motions and composition of the Earth's interior using the concentrations of noble gases (He, Ne, Ar, Kr, Xe) and their isotopes in lavas as probes of the high pressure processes that have such a large effect on our lives.
Due to their lack of charge, it has generally been assumed that noble gases are inert and are not retained in mantle minerals. A number of paradigms about the Earth use this as a key assumption: from the understanding structure of mantle convection to quantifying the volatile content of the planet. However, recent high-pressure experimental studies suggest that in fact noble gases have surprisingly high solubilities in the mantle, potentially requiring a wide range of theories to be revamped. In fact, there are few experimental measurements of noble gas behavior at mantle conditions. Utilizing new analytical and experimental advances, this study will measure the partitioning and diffusivities of noble gases in a range of mantle minerals, many for the first time, including orthopyroxene, garnet, wadsleyite, ringwoodite and majorite. A range of high-pressure devices (piston-cylinder, multi-anvil, internally-heated gas pressure) will be employed to produce pressures over 20 GPa and temperatures up to 2000 oC, simulating conditions in the upper and lower mantle. Samples will be measured by new generation laser-ablation mass spectrometry. The unprecedented data set will be used to reevaluate current ideas about the structure and composition of the Earth.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
Note:
When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external
site maintained by the publisher. Some full text articles may not yet be available without a
charge during the embargo (administrative interval).
Some links on this page may take you to non-federal websites. Their policies may differ from
this site.
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.
Overview
Our study set out to measure the partitioning of noble gases (He, Ne, Ar, Kr and Xe) between minerals and melts in the mantle. These elements, and particularly their isotope ratios, are key to understanding the geochemical evolution and structure of the Earth's interior. Prior to our study, despite their importance, only two minerals (olivine and clinopyroxene) had any noble gas partitioning data at pressures and temperature relevant to the mantle. Our project was highly successful in its goals and we have measured noble gas partitioning into 14 minerals, including the minerals involved in mantle melting (olivine, orthopyroxene, clinopyroxene and spinel) and in minerals important for recycling of noble gases back into the mantle by subduction (amphibole, serpentine). The data have fundamental implications for the noble gas composition of basaltic lavas, the noble gas isotopic evolution of the mantle and the degassing of volatiles into the atmosphere.
Noble gas behavior during mantle melting
The study produced the first comprehensive and self-consistent data set of partitioning data for He, Ne and Ar for all minerals involved mid-ocean ridge melting: olivine, orthopyroxene, clinopyroxene and spinel (Figure 1). The results show that noble gases have similar partitioning into different mantle minerals, quite different than most trace elements, which are highly concentrated in clinopyroxene. This has major implications for fractionation of noble gases from the parent isotopes. As melting proceeds, noble gases should become increasingly compatible compared to their parents. Thus at high degrees of melting, perhaps relevant for the early Earth or in plumes, noble gases are likely to be more compatible than their parent isotopes, and so depleted mantle could preserve unradiogenic isotope signatures, which are typically interpreted to be evidence of undegassed mantle.
This work was published in an EPSL paper (Jackson et al, 2013) and in numerous presentations given at international conferences.
Noble gas solubility in ring-structured minerals
Partitioning during mantle melting is a main control on how noble gases are extracted from the mantle. But are they returned to the mantle? Subduction of oceanic lithosphere recycles large amounts of H2O and CO2. But until recently, most models assumed that noble gases were not recycled by subduction, because they have no charge and so were thought not to be bound into minerals as H2O and CO2 are.
We measured partitioning of noble gases into amphibole, a common mineral in hydrated oceanic crust. We found that, contrary to previous assumptions, noble gases are highly soluble in amphibole, more than 3 orders of magnitude higher than in olivine or other mantle minerals. This means that hydrated oceanic crust could hold substantial amounts of noble gases, which would require existing models of noble gas evolution of the mantle to be reworked to include a recycling pathway. This could explain the similarity of Ar, Kr and Xe isotopic composition between the atmosphere and mantle. Fractionation by minerals may also explain why He and Ne have not been strongly recycled.
One of the most interesting aspects of the amphibole experiments is that they allowed us to identify where the noble gases were located in the mineral structure, for the first time to our knowledge. We varied the composition of the amphibole such that the number of vacant ring(A)-sites in the structure varied. The solubility of noble gases showed a clear correlation with the number of vacant ring-sites. This is a key observation, as many other minerals have ring-structures, such as serpentine.
Based on this we have m...
Please report errors in award information by writing to: awardsearch@nsf.gov.
