The Melting of Carbonated Pelites from 70 to 700 km Depth

Grassi, Daniele; Schmidt, Max W.

doi:10.1093/petrology/egr002

Cited by 217 publications

(146 citation statements)

References 95 publications

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“…Furthermore, the suspected increase of network carbonate units in K-rich melt will prevent an efficient immiscibility K-rich carbonatitic melt. Although, we do not have currently natural examples of K-rich (in comparison with Na) carbonatitic melt (Jones et al, 2013), recent experimental work (Thomsen and Schmidt, 2008;Grassi and Schmidt, 2011;Tsuno et al, 2012) witnessed the potential existence of K-rich (relative to Na) carbonatite liquid obtained from the partial melting of carbonated natural pelites.…”

Section: Free Carbonate Clusters As Precursors To Liquid Immiscibilitmentioning

confidence: 96%

Carbon dioxide in silica-undersaturated melt. Part I: The effect of mixed alkalis (K and Na) on CO2 solubility and speciation

Morizet

Paris

Gaillard

et al. 2014

Geochimica et Cosmochimica Acta

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Section: Free Carbonate Clusters As Precursors To Liquid Immiscibilitmentioning

confidence: 96%

Carbon dioxide in silica-undersaturated melt. Part I: The effect of mixed alkalis (K and Na) on CO2 solubility and speciation

Morizet

Paris

Gaillard

et al. 2014

Geochimica et Cosmochimica Acta

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“…Compared to these partition coefficients, our Ono (1999). The solidus of carbonated pelite (GS11) is after Grassi and Schmidt (2011b). The diamond-graphite line is a kinetic boundary showing the conditions of spontaneous diamond nucleation in experiments longer than 24 h; the line of graphite-diamond equilibrium lies beyond the diagram, and all the experiments were conducted in the diamond stability field D REE Cpx/L values are low to very low, especially for the middle and heavy REE.…”

Section: Clinopyroxenementioning

confidence: 99%

“…Its nature has to be inferred from the textural appearance and composition of quench products and comparison to known experiments. Grassi and Schmidt (2011b) and Wu et al (2009) determined the solidus of carbonated pelite with ~1 wt% H 2 O to lie at 900-1000 °C at 7-12 GPa. At lower temperatures, all H 2 O and CO 2 in their experiments are stored in hydrous phases and carbonates.…”

Section: Melt and Fluidmentioning

confidence: 99%

Reduced sediment melting at 7.5–12 GPa: phase relations, geochemical signals and diamond nucleation

Brey

Гирнис

Bulatov

et al. 2015

Contrib Mineral Petrol

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garnet. Clinopyroxene stability depends strongly on the Na content in the starting mixture; it remains in the Na-gloss composition up to 1600 °C at 12 GPa, but was not observed in K-gloss experiments above 1200 °C. The composition of melt or fluid changes gradually with increasing temperature from hydrous carbonate-rich (<10 wt% SiO 2 ) at 800-1000 °C to volatile-rich silicate liquids (up to 40 wt% SiO 2 ) at high temperatures. Trace elements were analyzed in melts and crystalline phases by LA ICP MS. The garnetmelt and clinopyroxene-melt partition coefficients are in general consistent with results from the literature for volatile-free systems and silicocarbonate melts derived by melting carbonated peridotites. Most trace elements are strongly incompatible in kyanite and silica polymorphs (D < 0.01), except for V, Cr and Ni, which are slightly compatible in kyanite (D > 1). Aragonite and Fe-Mg carbonate have very different REE partition coefficients (D Mst-Sd/L ~ 0.01 and D Arg/L ~ 1). Nb, Ta, Zr and Hf are strongly incompatible in both carbonates. The bearthite/melt partition coefficients are very high for LREE (>10) and decrease to ~1 for HREE. All HFSE are strongly incompatible in bearthite. In contrast, Ta, Nb, Zr and Hf are moderately to strongly compatible in ZrSiO 4 and TiO 2 phases. Based on the obtained partition coefficients, the composition of a mobile phase derived by sediment melting in deep subduction zones was calculated. This phase is strongly enriched in incompatible elements and displays a pronounced negative Ta-Nb anomaly but no Zr-Hf anomaly. Although all experiments were conducted in the diamond stability field, only graphite was observed in low-temperature experiments. Spontaneous diamond nucleation and the complete transformation of graphite to diamond were observed at temperatures above 1200-1300 °C. We speculate that the observed character of graphite-diamond transformation is controlled by relationships between the kinetics of metastable graphite Abstract Melting of carbonated sediment in the presence of graphite or diamond was experimentally investigated at 7.5-12 GPa and 800-1600 °C in a multianvil apparatus. Two starting materials similar to GLOSS of Plank and Langmuir (Chem Geol 145:325-394, 1998) were prepared from oxides, carbonates, hydroxides and graphite. One mixture (Na-gloss) was identical in major element composition to GLOSS, and the other was poorer in Na and richer in K (K-gloss). Both starting mixtures contained ~6 wt% CO 2 and 7 wt% H 2 O and were doped at a ~100 ppm level with a number of trace elements, including REE, LILE and HFSE. The near-solidus mineral assemblage contained a silica polymorph (coesite or stishovite), garnet, kyanite, clinopyroxene, carbonates (aragonite and magnesite-siderite solid solution), zircon, rutile, bearthite and hydrous phases (phengite and lawsonite at <9 GPa and the hydrous aluminosilicates topaz-OH and phase egg at >10 GPa). Hydrous phases disappear at ~900 °C, and carbonates persist up to 1000-1100 °C. At temperatures >1200 °C, the ...

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“…The olivine inclusion has a magnesium number of 90 mol%, which is normal for a mantle olivine mineral. The significance of the CAS plus kyanite inclusion is unknown, but it is noted that CAS phase is observed on eclogitic and sediment experiments at transition zone pressures (Litasov and Ohtani 2010;Grassi and Schmidt 2011). Another composite inclusion in Ju5-13 diamond (opx + spinel) might be a non-representative section of a further retrograde magnesium silicate perovskite mineral.…”

Section: Other Silicate Inclusionsmentioning

confidence: 99%

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

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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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The Melting of Carbonated Pelites from 70 to 700 km Depth

Cited by 217 publications

References 95 publications

Carbon dioxide in silica-undersaturated melt. Part I: The effect of mixed alkalis (K and Na) on CO2 solubility and speciation

Carbon dioxide in silica-undersaturated melt. Part I: The effect of mixed alkalis (K and Na) on CO2 solubility and speciation

Reduced sediment melting at 7.5–12 GPa: phase relations, geochemical signals and diamond nucleation

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

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