Deep carbon through time: Earth’s diamond record and its implications for carbon cycling and fluid speciation in the mantle

Howell, D.; Stachel, Thomas; Stern, Richard A.; Pearson, D. Graham; Nestola, Fabrizio; Hardman, Matthew F.; Harris, Jeff W.; Jaques, A. L.; Shirey, Steven B.; Cartigny, Pierre; Smit, Karen V.; Aulbach, Sonja; Brenker, Frank E.; Jacob, Dorrit E.; Thomassot, Émilie; Walter, Michael J.; Navon, O.

doi:10.1016/j.gca.2020.02.011

Cited by 32 publications

(30 citation statements)

References 105 publications

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“…We can only speculate as to the exact mechanism by which release of hydrated and/or carbonated fluids at transition zone depths induces seismicity (e.g., dehydration embrittlement), but we suggest there is a link between sublithospheric diamonds that are now forming in the mantle (Figure 8) and where deep‐focus earthquakes occur. If deep subduction with slab stalling is a product of the post‐Archean Earth (e.g., Klein et al., 2017), then the potentially younger ages of sublithospheric diamonds implied by the current sparse data (Bulanova et al., 2010; Harte & Richardson, 2012; Hutchison et al., 2012) compared with the more ancient lithospheric diamonds (e.g., Howell et al., 2020) is consistent with such a growth environment.…”

Section: Discussionmentioning

confidence: 87%

Slab Transport of Fluids to Deep Focus Earthquake Depths—Thermal Modeling Constraints and Evidence From Diamonds

et al. 2021

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The nature and cause of deep earthquakes remain enduring unknowns in the field of seismology. We present new models of thermal structures of subducted slabs traced to mantle transition zone depths that permit a detailed comparison between slab pressure/temperature (P/T) paths and hydrated/carbonated mineral phase relations. We find a remarkable correlation between slabs capable of transporting water to transition zone depths in dense hydrous magnesium silicates with slabs that produce seismicity below ∼300‐km depth, primarily between 500 and 700 km. This depth range also coincides with the P/T conditions at which oceanic crustal lithologies in cold slabs are predicted to intersect the carbonate‐bearing basalt solidus to produce carbonatitic melts. Both forms of fluid evolution are well represented by sublithospheric diamonds whose inclusions record the existence of melts, fluids, or supercritical liquids derived from hydrated or carbonate‐bearing slabs at depths (∼300–700 km) generally coincident with deep‐focus earthquakes. We propose that the hydrous and carbonated fluids released from subducted slabs at these depths lead to fluid‐triggered seismicity, fluid migration, diamond precipitation, and inclusion crystallization. Deep focus earthquake hypocenters could track the general region of deep fluid release, migration, and diamond formation in the mantle. The thermal modeling of slabs in the mantle and the correlation between sublithospheric diamonds, deep focus earthquakes, and slabs at depth demonstrate a deep subduction pathway to the mantle transition zone for carbon and volatiles that bypasses shallower decarbonation and dehydration processes.

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Section: Discussionmentioning

confidence: 87%

Slab Transport of Fluids to Deep Focus Earthquake Depths—Thermal Modeling Constraints and Evidence From Diamonds

et al. 2021

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“…If preserved in diamond inclusions and returned to the surface, heavy CaCO 3 could be used to trace the presence of oxidized carbon in the lowermost mantle. The potential of CaCO 3 to be a signature of an ultradeep carbon cycle reaching the core–mantle-boundary region may help to reveal other mysteries of the deep mantle, such as heat budget related to radioactive elements stored in Ca-bearing silicates 52 , and compositions of heterogeneities that may record Earth’s early history 48 , 53 .…”

Section: Discussionmentioning

confidence: 99%

Reversal of carbonate-silicate cation exchange in cold slabs in Earth’s lower mantle

Dorfman

Badro

et al. 2021

Nat Commun

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The stable forms of carbon in Earth’s deep interior control storage and fluxes of carbon through the planet over geologic time, impacting the surface climate as well as carrying records of geologic processes in the form of diamond inclusions. However, current estimates of the distribution of carbon in Earth’s mantle are uncertain, due in part to limited understanding of the fate of carbonates through subduction, the main mechanism that transports carbon from Earth’s surface to its interior. Oxidized carbon carried by subduction has been found to reside in MgCO3 throughout much of the mantle. Experiments in this study demonstrate that at deep mantle conditions MgCO3 reacts with silicates to form CaCO3. In combination with previous work indicating that CaCO3 is more stable than MgCO3 under reducing conditions of Earth’s lowermost mantle, these observations allow us to predict that the signature of surface carbon reaching Earth’s lowermost mantle may include CaCO3.

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“…A correlation of δ 13 C values with relative time has been proposed based on rim growth zones of diamonds that record heavier δ 13 C than their cores (Bulanova et al 2014;Chinn et al 2018;Thomson et al 2014). Moreover, the internal range in δ 13 C values was found to become smaller (towards heavier values) in dated diamonds from 3.0 to 2.1 to 1.0 Ga (Howell et al 2020), indicating some homogenization of carbon isotope compositions in the SCLM. Globally, significant changes in δ 13 C values within individual diamonds (4% has > 3‰) are rare (Howell et al 2020).…”

Section: Implications For the Deep Carbon Cyclementioning

confidence: 99%

“…1f) clearly demonstrate formation of adjacent growth zones from different metasomatic fluids e.g., in LK09 δ 13 C varies from − 10.0‰ (core: 1110 ± 64 Ma; T MR : 1109 °C) to − 5.0‰ (rim). Review of the global dataset establishes that limited intra-diamond C isotope variation is typical (96% have < 3‰) suggesting that the oxidation state and carbon speciation of diamond-forming fluids have been similar throughout history (Howell et al 2020;Jablon and Navon 2016;Weiss et al 2014). Local variations do exist, however, and, potentially in combination, changes in the scale and mechanism of diamond formation, may be depth or time dependent.…”

Section: Implications For the Deep Carbon Cyclementioning

confidence: 99%

“…Diamonds and incorporated inclusions allow researchers to investigate large-scale processes such as plate tectonics and crustal recycling (Farquhar et al 2002;Gurney et al 2010;Schulze et al 2003;Shirey and Richardson 2011). They provide samples of Earth's otherwise inaccessible sub-continental lithospheric mantle (SCLM) and a record of deep cycling of volatile elements (Cartigny et al 1999;Deines 1980;Howell et al 2020;Shirey et al 2019). Together, these observations have led to the current paradigm that diamond formation involves metasomatic processes in the mantle comprising volatile-rich, supercritical high-density fluids, possibly triggered by tectono-magmatic events (Deines Communicated by Dante Canil.…”

Section: Introductionmentioning

confidence: 99%

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Two billion years of episodic and simultaneous websteritic and eclogitic diamond formation beneath the Orapa kimberlite cluster, Botswana

Gress

Timmerman

Chinn

et al. 2021

Contrib Mineral Petrol

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The Sm–Nd isotope systematics and geochemistry of eclogitic, websteritic and peridotitic garnet and clinopyroxene inclusions together with characteristics of their corresponding diamond hosts are presented for the Letlhakane mine, Botswana. These data are supplemented with new inclusion data from the nearby (20–30 km) Orapa and Damtshaa mines to evaluate the nature and scale of diamond-forming processes beneath the NW part of the Kalahari Craton and to provide insight into the evolution of the deep carbon cycle. The Sm–Nd isotope compositions of the diamond inclusions indicate five well-defined, discrete eclogitic and websteritic diamond-forming events in the Orapa kimberlite cluster at 220 ± 80 Ma, 746 ± 100 Ma, 1110 ± 64 Ma, 1698 ± 280 Ma and 2341 ± 21 Ma. In addition, two poorly constrained events suggest ancient eclogitic (> 2700 Ma) and recent eclogitic and websteritic diamond formation (< 140 Ma). Together with sub-calcic garnets from two harzburgitic diamonds that have Archaean Nd mantle model ages (TCHUR) between 2.86 and 3.38 Ga, the diamonds studied here span almost the entire temporal evolution of the SCLM of the Kalahari Craton. The new data demonstrate, for the first time, that diamond formation occurs simultaneously and episodically in different parageneses, reflecting metasomatism of the compositionally heterogeneous SCLM beneath the area (~ 200 km2). Diamond formation can be directly related to major tectono-magmatic events that impacted the Kalahari Craton such as crustal accretion, continental breakup and large igneous provinces. Compositions of dated inclusions, in combination with marked variations in the carbon and nitrogen isotope compositions of the host diamonds, record mixing arrays between a minimum of three components (A: peridotitic mantle; B: eclogites dominated by mafic material; C: eclogites that include recycled sedimentary material). Diamond formation appears dominated by local fluid–rock interactions involving different protoliths in the SCLM. Redistribution of carbon during fluid–rock interactions generally masks any potential temporal changes of the deep carbon cycle.

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Deep carbon through time: Earth’s diamond record and its implications for carbon cycling and fluid speciation in the mantle

Cited by 32 publications

References 105 publications

Slab Transport of Fluids to Deep Focus Earthquake Depths—Thermal Modeling Constraints and Evidence From Diamonds

Slab Transport of Fluids to Deep Focus Earthquake Depths—Thermal Modeling Constraints and Evidence From Diamonds

Reversal of carbonate-silicate cation exchange in cold slabs in Earth’s lower mantle

Two billion years of episodic and simultaneous websteritic and eclogitic diamond formation beneath the Orapa kimberlite cluster, Botswana

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