Abstract
Enrichment in H (sub 2) O and elevated Fe oxidation states are linked to material recycling in Izu-Bonin-Marianas lavas
American Geophysical Union Fall Meeting, Vol.2019
American Geophysical Union 2019 fall meeting
12/2019
Abstract
Distinct geochemical signatures of subduction related lavas include enrichments in H (sub 2) O and incompatible trace elements, and higher Fe (super 3+) /Fe* ratios. Water and trace element enrichments in subduction lavas clearly reflect the influence of fluids and melts released from subducting slabs, but whether Fe oxidation is similarly linked remains debated. Here, we summarize measurements of major, trace, and volatile contents and Fe (super 3+) /Fe* ratios of submarine glasses and olivine hosted melt inclusions from the Izu-Bonin-Mariana (IBM) to test several recent hypotheses for the cause of Fe oxidation in subduction related lavas. The dataset includes volcanic rocks spanning the life of the arc from 52 ma to the present, and ranging spatially from the fore-arc to the back-arc and along strike from IODP Expedition 352 (c. 28 degrees N) to dredged pillows from the southernmost Mariana trough (c. 12 degrees N). Measurements for all elements are made in situ, and Fe (super 3+) /Fe* ratios are measured via m-x-ray absorption near edge structure spectroscopy (in situ) or micro-colorimetry (bulk glass). Glasses include basalts, basaltic andesites, and boninites with 1-8 wt% MgO, 0.16-6.0 wt% H (sub 2) O, <50-1450 ppm CO (sub 2) , and <50-2100 ppm S. The Fe (super 3+) /Fe* range from 0.136-0.250 (mid ocean ridge basalts = 0.124-0.156), with Ba/La between 3.4 and 62. Independent of age or sample type (i.e., melt inclusion or submarine glass), Fe (super 3+) /Fe* are relatively invariant with decreasing MgO, H (sub 2) O, or S, indicating that low-pressure differentiation does not significantly modify the oxidation state of Fe in subduction related lavas. Erupted samples with Fe (super 3+) /Fe* > 0.18 (i.e., the most oxidized glasses) have from <50 ppm to >1400 ppm S, indicating that S contents at the time of quench does not generate the high Fe (super 3+) /Fe* of arc lavas. Oxidation also appears to be unrelated to crustal thickness. Samples with H (sub 2) O >2 wt% and Ba/La >10 always have Fe (super 3+) /Fe* >0.18. Both modern and Eocene-aged samples define a relationship whereby Fe (super 3+) /Fe* increasing nonlinearly by a factor of approximately 2.3 as Ba/La increases by a factor of approximately 13. The coherence of elevated Fe (super 3+) /Fe* ratios with elevated H (sub 2) O and Ba/La in both space and time strongly links the production of oxidized, hydrous lavas with the release of aqueous slab fluids into the mantle in the IBM system.
Details
- Title: Subtitle
- Enrichment in H (sub 2) O and elevated Fe oxidation states are linked to material recycling in Izu-Bonin-Marianas lavas
- Creators
- Maryjo N BrounceKatherine A Kelley - University of Rhode IslandElizabeth Cottrell - Smithsonian, NMNH USA United StatesMark K Reagan - University of Iowa
- Resource Type
- Abstract
- Publication Details
- American Geophysical Union Fall Meeting, Vol.2019
- Conference
- American Geophysical Union 2019 fall meeting
- Publisher
- American Geophysical Union
- Alternative title
- AGU 2019 fall meeting
- Language
- English
- Date published
- 12/2019
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984230123202771
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