Carbon in the Convecting Mantle

Hauri, E. H.; Cottrell, Elizabeth; Kelley, K. A.; Tucker, J.; Shimizu, K.; Voyer, M. Le; Marske, J. P.; Saal, A. E.

doi:10.1017/9781108677950.009

Cited by 10 publications

(16 citation statements)

References 181 publications

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“…Altered oceanic crust Crustal carbon concentration, subduction zone length, subduction rate - Müller et al, 2016;Müller and Dutkiewicz, 2018 Serpentinized mantle Serpentinite carbon concentration and extent, subduction zone length, subduction rate 681 ± 45 ppm (average serpentinite carbon concentration); 20 ± 10%, 13.5 ± 1.5 km (serpentinization degree and extent) Kelemen and Manning, 2015;Müller et al, 2016;East et al, 2019 Carbonate sediment Subducted carbonate sediment - Dutkiewicz et al, 2018 Continental rifts Rift length, average rift carbon flux 2.5 ± 2.0 kt C km −1 yr −1 (rift carbon length flux) Müller et al, 2016;Brune et al, 2017;Hunt et al, 2017 Mid-ocean ridges Mid-ocean ridge length, present-day mid-ocean ridge carbon flux 0.37 ± 0.23 kt C km −1 yr −1 (ridge carbon length flux) Müller et al, 2016 Plume volcanoes LIP area, basalt carbon concentration 6.0 ± 3.0 Mt C yr −1 (baseline plume flux); 0.8 ± 0.3 wt% (primary plume basalt CO 2 concentration) Müller et al, 2016;Johansson et al, 2018;Hauri et al, 2019;Werner et al, 2019 Arc volcanoes Subduction zone length, carbonate platform distribution, present-day arc flux, expected carbonate-intersecting and non-carbonate-intersecting volcanic carbon fluxes 27 ± 16 Mt C yr −1 (present-day arc flux); 10 7.4−8.0 mol km −1 yr −1 (range for carbonate-intersecting arcs); 10 0.0−6.4 mol km −1 yr −1 (range for non-carbonate-intersecting arcs) Kelemen and Manning, 2015;Müller et al, 2016;Pall et al, 2018;Werner et al, 2019 Input data in italics are provided by GPlates modeling. Density of basaltic rock is taken as 2800 kg m −3 .…”

Section: Conversion Factors Referencesmentioning

confidence: 99%

“…Melt inclusions can therefore provide only a minimum bound to arc carbon fluxes (Wallace, 2005;Wallace et al, 2015). Estimates from melt inclusions are further complicated by the spatial heterogeneity of carbon present in the Earth's upper mantle which is sampled during magmatism, resulting in variable concentrations of CO 2 in mantle-derived magmas (Helo et al, 2011;Le Voyer et al, 2017;Hauri et al, 2019). Carbon fluxes and concentrations averaged both over time and large spatial regions (e.g., over entire arc systems) therefore provide the most robust representation of that region's relative contribution to total carbon outgassing as a whole.…”

Section: Volcanic Degassingmentioning

confidence: 99%

“…This is due to the challenge of estimating carbon fluxes in mid-ocean ridge settings with much less accessibility relative to other volcanic settings, and the subsequent difficulty in measurement of ridge carbon directly. Variability in spreading rate, mantle carbon concentrations and magma flux also produce notable differences in carbon flux along different mid-ocean ridge segments; CO 2 fluxes are known to vary by at least two orders of magnitude as a result of this (Le Voyer et al, 2017Hauri et al, 2019). In addition, there is uncertainty as to whether mantle volatiles liberated during decompression melting beneath mid-ocean ridges are focused toward the ridge axis or distributed along the base of the lithosphere (e.g., Keller et al, 2017).…”

Section: Mid-ocean Ridgesmentioning

confidence: 99%

“…This constant is then multiplied by ridge length as computed according to our reference plate tectonic model. This approach allows for the extrapolation of present-day carbon fluxes through geological time, but neglects both magma production fluxes and primary mantle carbon concentrations (Le Voyer et al, 2017Hauri et al, 2019). We select a present-day total mid-ocean ridge carbon flux of 21 ± 13 Mt C yr −1 , which overlaps with most previous estimates and their uncertainties ( Figure 5).…”

Section: Mid-ocean Ridgesmentioning

confidence: 99%

“…We adapt the LIP erupted area per 1 Myr of Johansson et al (2018) to determine an average annual area flux, which is converted into a corresponding LIP eruption volume flux using an average flood basalt thickness of 2 ± 1 km (which fits the average thickness of most flood basalts, Courtillot and Renne, 2003;Ross et al, 2005;Ernst, 2014). To predict the carbon which is degassed, we select an average intraplate primary CO 2 concentration of 0.8 ± 0.3 wt% (Hauri et al, 2019; Figure 6); this CO 2 concentration lies within the range suggested by Black and Gibson (2019). For our analysis we assume that oceanic and continental LIP basalts degas the entirety of their CO 2 on eruption.…”

Section: Plume-related Volcanismmentioning

confidence: 99%

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Deep Carbon Cycling Over the Past 200 Million Years: A Review of Fluxes in Different Tectonic Settings

et al. 2019

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Carbon is a key control on the surface chemistry and climate of Earth. Significant volumes of carbon are input to the oceans and atmosphere from deep Earth in the form of degassed CO 2 and are returned to large carbon reservoirs in the mantle via subduction or burial. Different tectonic settings (e.g., volcanic arcs, mid-ocean ridges, and continental rifts) emit fluxes of CO 2 that are temporally and spatially variable, and together they represent a first-order control on carbon outgassing from the deep Earth. A change in the relative importance of different tectonic settings throughout Earth's history has therefore played a key role in balancing the deep carbon cycle on geological timescales. Over the past 10 years the Deep Carbon Observatory has made enormous progress in constraining estimates of carbon outgassing flux at different tectonic settings. Using plate boundary evolution modeling and our understanding of present-day carbon fluxes, we develop time series of carbon fluxes into and out of the Earth's interior through the past 200 million years. We highlight the increasing importance of carbonate-intersecting subduction zones over time to carbon outgassing, and the possible dominance of carbon outgassing at continental rift zones, which leads to maxima in outgassing at 130 and 15 Ma. To a first-order, carbon outgassing since 200 Ma may be net positive, averaging ∼50 Mt C yr −1 more than the ingassing flux at subduction zones. Our net outgassing curve is poorly correlated with atmospheric CO 2 , implying that surface carbon cycling processes play a significant role in modulating carbon concentrations and/or there is a long-term crustal or lithospheric storage of carbon which modulates the outgassing flux. Our results highlight the large uncertainties that exist in reconstructing the corresponding in-and outgassing fluxes of carbon. Our synthesis summarizes our current understanding of fluxes at tectonic settings and their influence on atmospheric CO 2 , and provides a framework for future research into Earth's deep carbon cycling, both today and in the past.

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Section: Conversion Factors Referencesmentioning

confidence: 99%

Section: Volcanic Degassingmentioning

confidence: 99%

Section: Mid-ocean Ridgesmentioning

confidence: 99%

Section: Mid-ocean Ridgesmentioning

confidence: 99%

Section: Plume-related Volcanismmentioning

confidence: 99%

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Deep Carbon Cycling Over the Past 200 Million Years: A Review of Fluxes in Different Tectonic Settings

et al. 2019

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Partitioning of Fe2O3 in peridotite partial melting experiments over a range of oxygen fugacities elucidates ferric iron systematics in mid-ocean ridge basalts and ferric iron content of the upper mantle

Davis

Cottrell

2021

Contrib Mineral Petrol

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Basalts and peridotites from mid-ocean ridges record fO2 near the quartz-fayalite-magnetite buffer (QFM), but peridotite partial melting experiments have mostly been performed in graphite capsules (~ QFM-3), precluding evaluation of ferric iron’s behavior during basalt generation. We performed experiments at 1.5 GPa, 1350–1400 °C, and fO2 from about QFM-3 to QFM+3 to investigate the anhydrous partitioning behavior of Fe2O3 between silicate melts and coexisting peridotite mineral phases. We find spinel/melt partitioning of Fe2O3 ($${D}_{\mathrm{Fe}2\mathrm{O}3}^{\mathrm{spl}/\mathrm{melt}}$$ D Fe 2 O 3 spl / melt ) increases as spinel Fe2O3 concentrations increase, independent of increases in fO2, and decreases with temperature, which is consistent with new and previous experiments at 0.1 MPa. We find $${D}_{\mathrm{Fe}2\mathrm{O}3}^{\mathrm{opx}/\mathrm{melt}}$$ D Fe 2 O 3 opx / melt = 0.63 ± 0.10 and $${D}_{\mathrm{Fe}2\mathrm{O}3}^{\mathrm{cpx}/\mathrm{melt}}$$ D Fe 2 O 3 cpx / melt = 0.78 ± 0.30. MORB Fe2O3 and Na2O concentrations are consistent with a modeled MORB source with Fe2O3 = 0.48 ± 0.03 wt% (Fe3+/ΣFe = 0.053 ± 0.003) at potential temperatures (TP) from 1320 to 1440 °C. The temperature-dependence of the $${D}_{\mathrm{Fe}2\mathrm{O}3}^{\mathrm{spl}/\mathrm{melt}}$$ D Fe 2 O 3 spl / melt function alone allows ~ 40% of the variation in MORB compositions. If we allow $${D}_{\mathrm{Fe}2\mathrm{O}3}^{\mathrm{opx}/\mathrm{melt}}$$ D Fe 2 O 3 opx / melt and $${D}_{\mathrm{Fe}2\mathrm{O}3}^{\mathrm{opx}/\mathrm{melt}}$$ D Fe 2 O 3 opx / melt to also vary with temperature by tying them to spinel Fe2O3 through intermineral partitioning, then all the MORB data are within error of the model. Our model Fe2O3 concentration for the MORB source would require that the convecting mantle be more oxidized at a given depth than recorded by continental mantle xenoliths. Our result is supported by thermodynamic models of mantle with Fe3+/ΣFe = 0.03 that predict fO2 of ~ QFM-1 near the garnet-spinel transition, which is inconsistent with fO2 of MORB. Our results support previous suggestions that redox melting may occur between 200 and 250 km depth.

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Volatile‐Rich Magmas Distributed Through the Upper Crust in the Main Ethiopian Rift

Iddon

Edmonds

2020

Geochem Geophys Geosyst

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Understanding magma storage and differentiation in the East African Rift underpins our understanding of volcanism in continental rift settings. Here, we present the geochemistry of melt inclusions erupted in Main Ethiopian Rift transitional basalts, trachytes, and peralkaline rhyolites, produced by fractional crystallization. Basalts stored on-and off-axis are saturated in an exsolved volatile phase at up to 18 km in the upper crust. Much of the CO 2 outgassed from the magmas is likely lost through diffuse degassing. Observed CO 2 fluxes require the intrusion of up to 0.14 km 3 of basalt beneath the rift each year. On-axis peralkaline rhyolites are stored shallowly, at~4-8 km depth. In the Daly Gap, magmas saturate in sulfide and an exsolved volatile phase, which promotes magma rise to shallower levels in the crust. Here, magmas undergo further protracted fractional crystallization and degassing, leading to the formation of a substantial exsolved volatile phase, which may accumulate in a gas-rich cap. The exsolved volatile phase is rich in sulfur and halogens: their projected loadings into the atmosphere during explosive peralkaline eruptions in the MER are predicted to be substantially higher than their metaluminous counterparts in other settings. The high fraction of exsolved volatiles in the stored magmas enhances their compressibility and must be considered when interpreting ground displacements thought to be caused by magma intrusion at depth; otherwise, intruding volumes will be underestimated. Pockets of exsolved volatiles may be present at the roof zones of magma reservoirs, which may be resolvable using geophysical techniques.

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Carbon in the Convecting Mantle

Cited by 10 publications

References 181 publications

Deep Carbon Cycling Over the Past 200 Million Years: A Review of Fluxes in Different Tectonic Settings

Deep Carbon Cycling Over the Past 200 Million Years: A Review of Fluxes in Different Tectonic Settings

Partitioning of Fe2O3 in peridotite partial melting experiments over a range of oxygen fugacities elucidates ferric iron systematics in mid-ocean ridge basalts and ferric iron content of the upper mantle

Volatile‐Rich Magmas Distributed Through the Upper Crust in the Main Ethiopian Rift

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