The pyroxenite-diamond connection

Kiseeva, Ekaterina S.; Wood, B. J.; Ghosh, Sujoy; Stachel, Thomas

doi:10.7185/geochemlet.1601

Cited by 25 publications

(15 citation statements)

References 17 publications

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“…The majorite inclusions show a clear excess of Si [3.15 to 3.22 per formula unit (pfu)] and concomitant Al deficit (~0.6 pfu) and contain relatively high MgO [~27.16 weight % (wt %)] and low CaO (~1.35 wt %) contents compared with the host garnet (Grt-II). In contrast to Grt-I and Grt-II, the majorite inclusions appear to be from a peridotitic protolith, on the basis of the low CaO and high Cr 2 O 3 contents and the relationships among the divalent, trivalent, and quadrivalent cations ( 5 , 8 ). …”

Section: Resultsmentioning

confidence: 92%

Recovery of an oxidized majorite inclusion from Earth’s deep asthenosphere

Kynický

Tao

et al. 2017

Sci. Adv.

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Section: Resultsmentioning

confidence: 92%

Recovery of an oxidized majorite inclusion from Earth’s deep asthenosphere

Kynický

Tao

et al. 2017

Sci. Adv.

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“…As far as we are aware, no majoritic garnets of peridotitic composition have yet been reported as inclusions in diamond from the mantle transition zone. This implies a genetic connection, explored in more detail elsewhere 17,18 between the minor mantle rock type pyroxenite, and the diamond host. Our measurements show an increase in Fe 3+ /(Fe 2+ +Fe 3+ ) with increasing amount of majorite substitution and hence pressure ( Fig.…”

Section: Introductionmentioning

confidence: 94%

“…Pyroxenite lenses are common in mantle peridotites 16 and considered to be produced by reaction between peridotitic and eclogitic compositions, possibly through the agency of carbonated melts 17,18 . Although following the "peridotitic" trend of Fig 1,pyroxenitic garnets are lower in Cr2O3 and Mg# (=Mg/Mg+Fe) and higher in CaO than peridotitic garnets.…”

Section: Introductionmentioning

confidence: 99%

Oxidized iron in garnets from the mantle transition zone

et al. 2018

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The oxidation state of iron in Earth's mantle is well known to depths of ~200km, but has not been measured in samples from the lowermost upper mantle (200-410 km depth) or the transition zone (410-660 km). Here we use Synchrotron Mössbauer Source spectroscopy complemented by single crystal X-ray diffraction to make the first measurements of the oxidation state of Fe in inclusions of ultrahigh pressure majoritic garnet in diamond. The garnets show a pronounced increase in oxidation state with depth, with Fe 3+ /(Fe 3+ + Fe 2+) increasing from 0.08 at ~240 km depth to 0.30 at ~500 km depth. The latter majorites, which come from pyroxenitic bulk compositions, are twice as rich in Fe 3+ as the most oxidised garnets from the shallow mantle. Corresponding oxygen fugacities are above the upper stability limit of Fe metal. This observation implies that the increase in oxidation state is not linked to the putative disproportionation of Fe 2+ to Fe 3+ plus Fe metal. Instead, the Fe 3+ increases with depth are consistent with the hypothesis that carbonated fluids or melts are the oxidising agents responsible for the high Fe 3+ contents of the inclusions.

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“…Rather, they span a continuous compositional spectrum, and many samples have intermediate compositions. Whilst this could be evidence for a large reservoir of pyroxenite within the transition zone (Kiseeva et al, 2013b), it is more likely to be the consequence of interaction between metabasic and ambient mantle components (Thomson et al, 2016;Kiseeva et al, 2016). Indeed, experiments demonstrate that intermediate garnet chemistries, similar to inclusions, are generated during the reaction of MORB-derived carbonatite melts with ambient peridotite (Thomson et al, 2016).…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

“…However, both natural samples (Kopylova et al, 1997;Stachel et al, 2000b) and experiments (Brey et al, 2004;Thomson et al, 2016) demonstrate the stability of ferropericlase with a range of compositions in equilibrium with diamond throughout the upper mantle in regions of low silica activity. Kiseeva et al (2016;2013b) and Thomson et al (2016) have recently demonstrated that many diamond-hosted majoritic garnet inclusions are neither ultrabasic or basic endmembers, despite their assignments based on CaO and Cr 2 O 3 contents. Rather, they span a continuous compositional spectrum, and many samples have intermediate compositions.…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

Trace element composition of silicate inclusions in sub-lithospheric diamonds from the Juina-5 kimberlite: Evidence for diamond growth from slab melts

Thomson

Kohn

Bulanova

et al. 2016

Lithos

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Trace element composition of silicate inclusions in sublithospheric diamonds from the juina-5 kimberlite: Evidence for diamond growth from slab melts, LITHOS (2016), doi: 10.1016/j.lithos.2016.08.035 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E DM A N U S C R I P T ACCEPTED MANUSCRIPT ABSTRACTThe trace element compositions of inclusions in sub-lithospheric diamonds from the Juina-5 kimberlite, Brazil, are presented. Literature data for mineral/melt partition coefficients were collated, refitted and employed to interpret inclusion compositions. As part of this process an updated empirical model for predicting the partitioning behaviour of trivalent cations for garnet-melt equilibrium calibrated using data from 73 garnet-melt pairs is presented. High levels of trace element enrichment in inclusions interpreted as former calcium silicate perovskite and majoritic garnet preclude their origin as fragments of an ambient deep mantle assemblage. Inclusions believed to represent former bridgmanite minerals also display a modest degree of enrichment relative to mantle phases. The trace element composition of 'NAL' and 'CF phase' minerals are also reported. Negative Eu, Ce, and Y/Ho anomalies alongside depletions of Sr, Hf and Zr in many inclusions are suggestive of formation from a low-degree carbonatitic melt of subducted oceanic crust. Observed enrichments in garnet and 'calcium perovskite' inclusions limit depths of melting to less than ~ 600 km, prior to calcium perovskite saturation in subducting assemblages. Less enriched inclusions in sub-lithospheric diamonds from other global localities may represent deeper diamond formation. Modelled source rock compositions that are capable of producing melts in equilibrium with Juina-5 'calcium perovskite' and majorite inclusions are consistent with subducted MORB. Global majorite inclusion compositions suggest a common process is responsible for the formation of many superdeep diamonds, irrespective of geographic locality. Global transition zone inclusion compositions are reproduced by fractional crystallisation from a single parent melt, suggesting that they record the crystallisation sequence and melt evolution during this interaction of slab melts with ambient mantle. All observations are consistent with the previous hypothesis that many superdeep diamonds are created as slab-derived carbonatites interact with peridotitic mantle in the transition zone.

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The pyroxenite-diamond connection

Cited by 25 publications

References 17 publications

Recovery of an oxidized majorite inclusion from Earth’s deep asthenosphere

Recovery of an oxidized majorite inclusion from Earth’s deep asthenosphere

Oxidized iron in garnets from the mantle transition zone

Trace element composition of silicate inclusions in sub-lithospheric diamonds from the Juina-5 kimberlite: Evidence for diamond growth from slab melts

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