Constraining mantle carbon: CO 2 -trace element systematics in basalts and the roles of magma mixing and degassing

Matthews, Simon; Shorttle, Oliver; Rudge, John F.; Maclennan, John

doi:10.1016/j.epsl.2017.09.047

Cited by 34 publications

(51 citation statements)

References 51 publications

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“…However, the low degree of PEC (5‐10%; Table S5) observed in the 1669 melt inclusions and analysis of shrinkage‐bubble‐free MI means that the full range in incompatible element concentrations is not reproducible with this mechanism. Modeling of mid‐ocean ridge volatile systematics has shown that this negative correlation may also arise during concurrent mixing and degassing at a range of pressures (Matthews et al, ), although this mechanism cannot reproduce the CO 2 ‐Sr‐REE systematic we observe for the 1669 melt inclusions.…”

Section: Discussionmentioning

confidence: 82%

Carbon Dioxide in Geochemically Heterogeneous Melt Inclusions From Mount Etna, Italy

Salem

Edmonds

Corsaro

et al. 2019

Geochem Geophys Geosyst

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Mt. Etna is among the largest global volcanic outgassers with respect to carbon and sulfur, yet questions remain regarding the source of these volatiles and their systematics in the crust and mantle. The importance of heterogeneous mantle sources, mixing, crustal assimilation, and disequilibrium degassing is investigated using melt inclusions erupted during the CE 1669 eruption of Mt. Etna, Italy. We find that the melt inclusion compositions define a mixing array between two geochemically distinct melts. One end‐member melt is depleted in light rare Earth elements (LREEs) and enriched in strontium (Sr), carbon, and sulfur; the other is enriched in LREE and depleted in Sr, carbon, and sulfur. We infer, through modeling, that the melts may either have been generated by melting a mantle source that includes a recycled oceanic crustal component or they may have assimilated carbonate material in the crust. The resulting LREE‐depleted, Sr‐enriched melts were also alkali‐rich, which enhanced the solubility of carbon and sulfur. The LREE‐depleted, Sr‐ and volatile‐rich melt ascended through the crust and likely became supersaturated with respect to CO2 and sulfur. The melt intruded into a LREE‐enriched, relatively degassed magma body in the shallow crust, cooled rapidly, and vesiculated, likely triggering eruption. The melt inclusion array trapped by growing olivines during this intrusion process records a snapshot of incomplete mixing between the two melts. Mt. Etna is renowned for the large increases in CO2 gas fluxes shortly before and during eruption. The intrusion of supersaturated, CO2‐enhanced magmas into shallow reservoirs may be a common process at Mt. Etna.

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Section: Discussionmentioning

confidence: 82%

Carbon Dioxide in Geochemically Heterogeneous Melt Inclusions From Mount Etna, Italy

Salem

Edmonds

Corsaro

et al. 2019

Geochem Geophys Geosyst

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“…Volcanic fluxes have long been considered the primary contribution to global degassing, and, as such, there is a substantial body of work dedicated to constraining their magnitudes. Modern mid‐ocean ridge volcanism is estimated to contribute ~1.0 to ~5.0 Tmol CO 2 /year (for reference 1 Tmol C is approximately 0.012 Pg C) (Chavrit et al, ; Dasgupta & Hirschmann, , ; Hirschmann, ; Le Voyer et al, ; Marty & Tolstikhin, ; Matthews et al, ; Saal et al, ). While this range is quite significant, it is possible that this upper limit remains conservative, given the lack of consideration of other factors such as bubble loss (e.g., Chavrit et al, ).…”

Section: Global Carbon Cycle Budgetmentioning

confidence: 99%

Evolution of the Global Carbon Cycle and Climate Regulation on Earth

Isson

Planavsky

Coogan

et al. 2020

Global Biogeochemical Cycles

105

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The existence of stabilizing feedbacks within Earth's climate system is generally thought to be necessary for the persistence of liquid water and life. Over the course of Earth's history, Earth's atmospheric composition appears to have adjusted to the gradual increase in solar luminosity, resulting in persistently habitable surface temperatures. With limited exceptions, the Earth system has been observed to recover rapidly from pulsed climatic perturbations. Carbon dioxide (CO2) regulation via negative feedbacks within the coupled global carbon‐silica cycles are classically viewed as the main processes giving rise to climate stability on Earth. Here we review the long‐term global carbon cycle budget, and how the processes modulating Earth's climate system have evolved over time. Specifically, we focus on the relative roles that shifts in carbon sources and sinks have played in driving long‐term changes in atmospheric pCO2. We make the case that marine processes are an important component of the canonical silicate weathering feedback, and have played a much more important role in pCO2 regulation than traditionally imagined. Notably, geochemical evidence indicate that the weathering of marine sediments and off‐axis basalt alteration act as major carbon sinks. However, this sink was potentially dampened during Earth's early history when oceans had higher levels of dissolved silicon (Si), iron (Fe), and magnesium (Mg), and instead likely fostered more extensive carbon recycling within the ocean‐atmosphere system via reverse weathering—that in turn acted to elevate ocean‐atmosphere CO2 levels.

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“…Rare ultra-depleted glasses erupted in oceanic fracture zones often contain sufficiently low concentrations of CO 2 that they are undersaturated in CO 2 vapour at the pressure of eruption. However, Matthews et al (2017) suggested these magmas formed by mixing of trace-element and CO 2 enriched melts that are partially degassed with trace-element and CO 2 depleted melts; with the significant CO 2 vapour undersaturation of the depleted melts conferring CO 2 undersaturation onto the mixed magma. This process is difficult to definitively identify and could lead to underestimates of mantle CO 2 concentrations.…”

Section: Estimating Mantle Carbonmentioning

confidence: 99%

“…A number of previous studies (Saal et al, 2002;Le Voyer et al, 2017;Hauri et al, 2018) are predicated upon correlations between CO 2 and Ba or Nb indicating a lack of any fractionation between CO 2 and the incompatible trace elements, including the absence of any CO 2 degassing prior to, or after, inclusion entrapment. However, Matthews et al (2017) demonstrated that such correlations are also a natural consequence of degassing and mixing of compositionally diverse near-fractional mantle melts, and such a process can explain the increasing variation in CO 2 /Ba with Ba concentration that many datasets exhibit.…”

Section: Estimating Mantle Carbonmentioning

confidence: 99%

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Melt inclusion constraints on mantle carbon heterogeneity within an individual mantle plume and at the global scale

Matthews¹,

Shorttle²,

Maclennan³

et al. 2019

Preprint

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The Earth’s mantle holds more carbon than its oceans, atmosphere and continents combined, yet the distribution of carbon within the mantle remains uncertain. Global variations in the carbon content of the depleted mantle have been inferred from carbon-trace element systematics of ultra-depleted mid-ocean ridge glasses and melt inclusions, though the origin of mantle carbon variability remains uncertain. A variety of observations suggest that the mantle plumes underlying ocean islands have high bulk carbon contents, but the characterisation of individual mantle plume components has not been possible.We supplement the existing melt inclusion data from Iceland with four new datasets, significantly en- hancing the spatial and geochemical coverage. Within the combined dataset there is significant variation in melt inclusion CO2/Ba ratio, which is tightly correlated with trace element enrichment. The trends in CO2/Ba–Ba space displayed by our new data coincide with the same trends in data compiled from global ocean islands and mid-ocean ridges, forming a global array. The overall structure of the global CO2/Ba array is not a property of the source, instead controlled by CO2 degassing before melt inclusion entrapment, and CO2 loss by decrepitation following inclusion entrapment.The position of melt inclusion datasets within the global array allows us to filter out inclusions likely tohave undergone decrepitation. Providing earlier CO2 degassing and magma mixing have not destroyed themantle signal, the remaining inclusions may preserve mantle CO2/Ba values. Using the observed covariationof the filtered CO2/Ba ratio with radiogenic isotope tracers of mantle source, we find CO2 concentrationsin the Icelandic depleted mantle of 102+53 -27 ppmw, typical of mantle underlying the mid-ocean ridge system,and high CO concentrations of 2.2+3.8 -1.5 wt% associated with the high 3He/4He component of the Iceland plume. However, source and process are difficult to deconvolve for the eruptions most sensitive to enriched, or recycled, mantle components; the presently available data is consistent with recycled material being either enriched or depleted in carbon.Extending our approach globally, we find no systematic variation in CO2/Ba or CO2/Nb with enrichment (in the absence of a primordial mantle contribution). The lack of global co-variation suggests mechanisms recycling CO2 from the surface into the convecting mantle are decoupled from those recycling most trace elements. However, the variation of CO2/Nb with Ba/Nb suggests Ba may behave similarly to CO2 during recycling.

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Constraining mantle carbon: CO 2 -trace element systematics in basalts and the roles of magma mixing and degassing

Cited by 34 publications

References 51 publications

Carbon Dioxide in Geochemically Heterogeneous Melt Inclusions From Mount Etna, Italy

Carbon Dioxide in Geochemically Heterogeneous Melt Inclusions From Mount Etna, Italy

Evolution of the Global Carbon Cycle and Climate Regulation on Earth

Melt inclusion constraints on mantle carbon heterogeneity within an individual mantle plume and at the global scale

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