Primary carbonatite melt from deeply subducted oceanic crust

Walter, Michael J.; Bulanova, G.P.; Armstrong, Lora S.; Keshav, Satish; Blundy, Jon; Guðfinnsson, Guðmundur H.; Lord, O. T.; Lennie, AR; Clark, S. M.; Smith, C. B.; Gobbo, L.

doi:10.1038/nature07132

Cited by 237 publications

(165 citation statements)

References 31 publications

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“…In fact, there has been a growing body of evidence for the ultradeep subduction of carbonates and their participation in the formation of diamonds. This evidence involves the discovery of inclusions in diamonds, consisting of carbonates in association with the superdeep phases CaSiO 3 or MgO + MgSiO 3 , as well as some experimental and geochemical observations (51)(52)(53)(54). Our results suggest that the Ca-rich carbonate melt, which forms through the carbonate-iron interaction and can be generated even in the absence of alkalis and H 2 O, can be considered as a transmantle interstitial melt.…”

Section: Significancementioning

confidence: 51%

Mantle–slab interaction and redox mechanism of diamond formation

Palyanov

Bataleva

Sokol

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

172

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Subduction tectonics imposes an important role in the evolution of the interior of the Earth and its global carbon cycle; however, the mechanism of the mantle-slab interaction remains unclear. Here, we demonstrate the results of high-pressure redox-gradient experiments on the interactions between Mg-Ca-carbonate and metallic iron, modeling the processes at the mantle-slab boundary; thereby, we present mechanisms of diamond formation both ahead of and behind the redox front. It is determined that, at oxidized conditions, a low-temperature Ca-rich carbonate melt is generated. This melt acts as both the carbon source and crystallization medium for diamond, whereas at reduced conditions, diamond crystallizes only from the Fe-C melt. The redox mechanism revealed in this study is used to explain the contrasting heterogeneity of natural diamonds, as seen in the composition of inclusions, carbon isotopic composition, and nitrogen impurity content.carbonate-iron interaction | high-pressure experiment | mantle mineralogy | deep carbon cycle S ubduction of crustal material plays an important role in the global carbon cycle (1-6). Depending on oxygen fugacity and pressure-temperature (P-T) conditions, carbon exists in the Earth's interior in the form of carbides, diamond, graphite, hydrocarbons, carbonates, and CO 2 (7-11). In the upper mantle, the oxygen fugacity (fO 2 ) varies from one to five log units below the fayalitemagnetite-quartz (FMQ) buffer, with a trend of a decrease with depth (6,(12)(13)(14)(15). At a depth of ∼250 km, mantle is reported to become metal saturated (16, 17), which holds true for all mantle regions below, including the transition zone and lower mantle. The subduction of the oxidized crustal material occurs to depths greater than 600 km (4-6). The main carbon-bearing minerals of the subducted materials are carbonates, which are thermodynamically stable up to P-T conditions of the lower mantle (10,11,18). As evidenced by the compositions of inclusions in diamond, which vary from strongly reduced, e.g., metallic iron and carbides (19-23), to oxidized, e.g., carbonates and CO 2 (6,20,(24)(25)(26)(27)(28), carbonates may be involved in the reactions with reduced deep-seated rocks, including Fe 0 -bearing species (29-31). A scale of these reactions is determined mainly by the capacity of subducted carbonate-bearing domains. An important consequence of such an interaction is that it can produce diamond. However, studies on diamond synthesis via the reactions between oxidized and reduced phases are limited (32-35).To understand the mechanisms of the interaction of carbonbearing oxidized-and reduced-mineral assemblages, we performed high-pressure experiments with an iron-carbonate system; an approach was used that enabled the creation of an oxygen fugacity gradient in the capsules (Materials and Methods and SI Materials and Methods). Results and DiscussionThe experimental results and the phase compositions are given in Table 1 and Table S1, respectively. At temperatures of 1,000 and 1,100°C, the iron-car...

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Section: Significancementioning

confidence: 51%

Mantle–slab interaction and redox mechanism of diamond formation

Palyanov

Bataleva

Sokol

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

172

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“…An additional method of estimating bulk compositions using an image analysis technique, whereby the compositions of component phases were added in the proportions revealed by BSE images, was used for inclusions too large for defocussed beam analysis. Estimating inclusion bulk compositions of diamond inclusions in this way has previously been employed in a number of studies (Harte and Cayzer 2007;Walter et al 2008Walter et al , 2011Bulanova et al 2010). However, they are not ideal because (1) there is an implied assumption that the modal mineralogy of the twodimensional section is representative of the whole threedimensional inclusion and (2) the conversion of X-ray count rates into chemical compositions makes assumptions that are not strictly valid.…”

Section: CL Sem and Empa Analysismentioning

confidence: 99%

“…In the years following this original discovery examples of majorite as diamond-hosted inclusions have vastly increased, becoming both numerous and geographically widespread. Multiple samples have been identified in the Monastery Moore et al 1991) and Jagersfontein kimberlites of South Africa (Deines et al 1991), Kankan in Guinea (Stachel et al 2000a), alluvial deposits and kimberlites from the Juina district in Brazil (Wilding 1990;Harte 1992;Hutchinson 1997;Walter et al 2008;Bulanova et al 2010) alongside additional one-off finds in Russia (Sobolev 1977), Tanzania (Stachel et al 1998), Canada (Davies et al 2004) and other South African sources . This population of majoritic garnets is dominated by samples with an eclogitic or pyroxenitic signature (indicated by low Cr 2 O 3 and high CaO), an observation potentially explained by the majority of upper mantle diamond formation occurring within subducting assemblages (Stachel 2001).…”

Section: Introductionmentioning

confidence: 99%

“…Diamonds from multiple sources in the Juina region (Brazil), including both kimberlite pipes and alluvial deposits, have been extensively studied (Harte et al 1999;Kaminsky et al 2009Kaminsky et al , 2001Hutchison et al 2001;Hayman et al 2005;Brenker et al 2007;Walter et al 2008Walter et al , 2011Bulanova et al 2010;Araujo et al 2013;Zedgenizov et al 2014) as they commonly have been found to contain mineral inclusions of sub-lithospheric origin. In fact, more than half of all recognised lower mantle diamonds are from Juina sources (Harte 2010), which makes Juina a unique geological locality.…”

Section: Introductionmentioning

confidence: 99%

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Origin of sub-lithospheric diamonds from the Juina-5 kimberlite (Brazil): constraints from carbon isotopes and inclusion compositions

Thomson

Kohn²,

Bulanova

et al. 2014

Contrib Mineral Petrol

Self Cite

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interpreted as evidence of diamond growth from abiotic organic carbon added to the oceanic crust during hydrothermal alteration. The bulk isotopic composition of the oceanic crust, carbonates plus organics, is equal to the composition of mantle carbon (−5 ‰), and we suggest that recycling/mixing of subducted material will replenish this reservoir over geological time. Several exposed, syngenetic inclusions have bulk compositions consistent with former eclogitic magnesium silicate perovskite, calcium silicate perovskite and NAL or CF phases that have reequilibrated during their exhumation to the surface. There are multiple occurrences of majoritic garnet with pyroxene exsolution, coesite with and without kyanite exsolution, clinopyroxene, Fe or Fe-carbide and sulphide minerals alongside single occurrences of olivine and ferropericlase. As a group, the inclusions have eclogitic affinity and provide evidence for diamond formation at pressures extending to Earth's deep transition zone and possibly the lower mantle. It is observed that the major element composition of inclusions and isotopic compositions of host Juina-5 diamonds are not correlated. The diamond and inclusion compositions are intimately related to subducted material and record a polybaric growth history across a depth interval stretching from the lower mantle to the base of the lithosphere. It is suggested that the interaction of slabderived melts and mantle material combined with subsequent upward transport in channelised networks or a buoyant diapir explains the formation of Juina-5 diamonds. We conclude that these samples, despite originating at great mantle depths, do not provide direct information about the ambient mantle, instead, providing a snapshot of the Earth's deep carbon cycle. Keywords Diamonds · Sub-lithospheric mantle · Carbon cycle · SubductionAbstract Forty-one diamonds sourced from the Juina-5 kimberlite pipe in Southern Brazil, which contain optically identifiable inclusions, have been studied using an integrated approach. The diamonds contain <20 ppm nitrogen (N) that is fully aggregated as B centres. Internal structures in several diamonds revealed using cathodoluminescence (CL) are unlike those normally observed in lithospheric samples. The majority of the diamonds are composed of isotopically light carbon, and the collection has a unimodal distribution heavily skewed towards δ 13 C ~ −25 ‰. Individual diamonds can display large carbon isotope heterogeneity of up to ~15 ‰ and predominantly have isotopically lighter cores displaying blue CL, and heavier rims with green CL. The light carbon isotopic compositions are Communicated by O. Müntener. Electronic supplementary materialThe online version of this article

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“…However, the origin of carbonate melts and their relationship to associated silicate rocks is still controversial. In subduction zones, Sr-Nd-Pb and C-O isotopes have been interpreted to indicate that most carbonate melts associated with alkaline igneous rocks were derived from the recycling of subducted carbonate-rich sediments (e.g., Bell and Simonetti, 1996;van Achterbergh et al, 2002;Walter et al, 2008;Marin-Ceron et al, 2010;Frezzotti et al, 2011). Therefore, the occurrence and genesis of primary carbonate-bearing K-rich igneous rocks in the convergent margins can be utilized to help understanding crust-mantle interaction and can provide insights into the mechanisms of carbon-recycling within the mantle wedge during subduction.…”

Section: Introductionmentioning

confidence: 99%