Release of subducted sedimentary nitrogen throughout Earth’s mantle
The dynamic process of subduction represents the principal means to introduce chemical heterogeneities into Earth's interior. In the case of nitrogen (N) - atmosphere's most abundant gas - biological-activity converts N2 into ammonium ions (NH4+), which are chemically-bound within seafloor...
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| Format: | Journal article |
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European Association of Geochemistry
2016
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| _version_ | 1797100898594324480 |
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| author | Barry, P Hilton, D |
| author_facet | Barry, P Hilton, D |
| author_sort | Barry, P |
| collection | OXFORD |
| description | The dynamic process of subduction represents the principal means to introduce chemical heterogeneities into Earth's interior. In the case of nitrogen (N) - atmosphere's most abundant gas - biological-activity converts N2 into ammonium ions (NH4+), which are chemically-bound within seafloor sediments and altered oceanic crust that comprise the subducting slab. Although some subducted N re-emerges via arc-related volcanism (Sano et al., 1998; Fischer et al., 2002), the majority likely bypasses sub-arc depths (150-200 km) and supplies the deeper mantle (Li et al., 2007; Mitchell et al., 2010; Johnson and Goldblatt, 2015; Bebout et al., 2016). However, the fate of subducted N remains enigmatic: is it incorporated by the shallow convecting mantle - the source of ridge volcanism, or is the deeper mantle - nominally associated with mantle plumes - its ultimate repository? Here, we present N-He-Ne-Ar isotope data for oceanic basalts from the Central Indian Ridge (CIR)-Réunion plume region to address this issue. All on-axis samples with depleted MORB mantle (DMM) affinities (3He/4He = 8 ± 1 RA; Graham, 2002) have low N-isotopes (mean δ15N = -2.1 ‰), whereas those with plume-like 3He/4He display higher values (mean δ15N = 1.3 ‰). We explain these data within the framework of a new mantle reference model to predict a time-integrated net N regassing flux to the mantle of ~3.4 × 1010 mol/yr, with the plume-source mantle representing the preferential destination by a factor of 2-3. The model has implications for the present-day imbalance between N subducted at trenches and N emitted via arc-related volcanism, the N-content of Earth's early atmosphere, as well as relationships between N2 and the noble gases in mantle reservoirs, including 3He/4He-δ15N relationships in plume-derived lavas. |
| first_indexed | 2024-03-07T05:44:13Z |
| format | Journal article |
| id | oxford-uuid:e6a31b15-4966-4992-9d75-bb5a385803df |
| institution | University of Oxford |
| last_indexed | 2024-03-07T05:44:13Z |
| publishDate | 2016 |
| publisher | European Association of Geochemistry |
| record_format | dspace |
| spelling | oxford-uuid:e6a31b15-4966-4992-9d75-bb5a385803df2022-03-27T10:32:38ZRelease of subducted sedimentary nitrogen throughout Earth’s mantleJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:e6a31b15-4966-4992-9d75-bb5a385803dfSymplectic Elements at OxfordEuropean Association of Geochemistry2016Barry, PHilton, DThe dynamic process of subduction represents the principal means to introduce chemical heterogeneities into Earth's interior. In the case of nitrogen (N) - atmosphere's most abundant gas - biological-activity converts N2 into ammonium ions (NH4+), which are chemically-bound within seafloor sediments and altered oceanic crust that comprise the subducting slab. Although some subducted N re-emerges via arc-related volcanism (Sano et al., 1998; Fischer et al., 2002), the majority likely bypasses sub-arc depths (150-200 km) and supplies the deeper mantle (Li et al., 2007; Mitchell et al., 2010; Johnson and Goldblatt, 2015; Bebout et al., 2016). However, the fate of subducted N remains enigmatic: is it incorporated by the shallow convecting mantle - the source of ridge volcanism, or is the deeper mantle - nominally associated with mantle plumes - its ultimate repository? Here, we present N-He-Ne-Ar isotope data for oceanic basalts from the Central Indian Ridge (CIR)-Réunion plume region to address this issue. All on-axis samples with depleted MORB mantle (DMM) affinities (3He/4He = 8 ± 1 RA; Graham, 2002) have low N-isotopes (mean δ15N = -2.1 ‰), whereas those with plume-like 3He/4He display higher values (mean δ15N = 1.3 ‰). We explain these data within the framework of a new mantle reference model to predict a time-integrated net N regassing flux to the mantle of ~3.4 × 1010 mol/yr, with the plume-source mantle representing the preferential destination by a factor of 2-3. The model has implications for the present-day imbalance between N subducted at trenches and N emitted via arc-related volcanism, the N-content of Earth's early atmosphere, as well as relationships between N2 and the noble gases in mantle reservoirs, including 3He/4He-δ15N relationships in plume-derived lavas. |
| spellingShingle | Barry, P Hilton, D Release of subducted sedimentary nitrogen throughout Earth’s mantle |
| title | Release of subducted sedimentary nitrogen throughout Earth’s mantle |
| title_full | Release of subducted sedimentary nitrogen throughout Earth’s mantle |
| title_fullStr | Release of subducted sedimentary nitrogen throughout Earth’s mantle |
| title_full_unstemmed | Release of subducted sedimentary nitrogen throughout Earth’s mantle |
| title_short | Release of subducted sedimentary nitrogen throughout Earth’s mantle |
| title_sort | release of subducted sedimentary nitrogen throughout earth s mantle |
| work_keys_str_mv | AT barryp releaseofsubductedsedimentarynitrogenthroughoutearthsmantle AT hiltond releaseofsubductedsedimentarynitrogenthroughoutearthsmantle |