The Case for Primary, Mantle-derived Carbonatite Magma

Harmer, R. E.; Gittins, J.

doi:10.1093/petroj/39.11-12.1895

Cited by 190 publications

(56 citation statements)

References 32 publications

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“…There are two main hypotheses for their formation (i) primary melting of carbonated peridotite (Bell et al, 1998;Harmer and Gittins, 1998) and (ii) partial melting and differentiation from carbonated silicate melts (Burke and Khan, 2006). Primary melting of carbonated peridotite is thought to occur in the mantle at depths greater than 70 km giving a high temperature and pressure formation regime, while differentiation from carbonated silicate melts likely occurs within the shallow mantle or crust.…”

Section: Carbonatites As a Geologic Testmentioning

confidence: 99%

“…Evidence for high temperature crystallization regimes (ca. 550-900°C) from calcite-dolomite geothermometry and oxygen isotope fractionations between calcite and associated silicate minerals (Gittins, 1979;Haynes et al, 2003), along with the mantle-like Sr and Nd signatures (Bell et al, 1998;Harmer and Gittins, 1998), provide support for formation by primary mantle melting while the association of alkaline igneous provinces with suture zones suggests carbonatites may be generated within the crust (Burke et al, 2003;Burke and Khan, 2006). Either scenario produces carbonate minerals crystallized at much higher temperatures than the sedimentary carbonates found abundantly on the Earth's surface and in deep-sea sediment cores.…”

Section: Carbonatites As a Geologic Testmentioning

confidence: 99%

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Clumped isotope thermometry of carbonatites as an indicator of diagenetic alteration

Dennis

Schrag

2010

Geochimica et Cosmochimica Acta

269

279

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Section: Carbonatites As a Geologic Testmentioning

confidence: 99%

Section: Carbonatites As a Geologic Testmentioning

confidence: 99%

Clumped isotope thermometry of carbonatites as an indicator of diagenetic alteration

Dennis

Schrag

2010

Geochimica et Cosmochimica Acta

269

279

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“…Wallace and Green 1988;Thibault et al 1992;Dalton and Wood 1993), by compositions of carbonatite bodies that show no connection to alkaline silicate magmatism (Bailey 1990;Harmer and Gittins 1998) and by studies of mantle xenoliths (Yaxley et al 1998). At depth (P > 2.5 GPa) the melts appear to be dolomitic (Bailey 1993;Gittins 1989;Wyllie 1989).…”

Section: Soè Vite and Parental Melts Of Plutonic Carbonatitesmentioning

confidence: 99%

Partitioning of Mg, Ca, and Na between carbonatite melt and hydrous fluid at 0.1–0.2 GPa

Veksler

Keppler

2000

Contrib Mineral Petrol

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Experimental studies of the element distribution between carbonatite melts and hydrous¯uids are hampered by the fact that neither the¯uid nor the melt can be isochemically quenched in conventional highpressure vessels. In order to overcome this problem, we used a double-capsule technique to separate immisciblē uid and melt phases during and after the runs. The inner platinum capsules were charged with carbonate mixtures (CaCO 3 , MgCO 3 and Na 2 CO 3 ) and placed inside the outer capsules charged with distilled water and diamond powder. The latter was used as an inert trap for solids precipitating from the¯uid on quenching. Carbonate melt and hydrous¯uid equilibrated through a small hole left in the upper end of the inner capsule. The runs were performed in rapid-quench cold-seal pressure vessels at 0.1±0.2 GPa and 700±900°C in the two-phase (¯uid + melt) stability region. Both quenched melt and quenched¯uid were dissolved in dilute HCl and analysed by inductively coupled plasma atomic emission spectroscopy. The results show that under all conditions investigated,¯uid/melt partition coecients for Ca and Mg are similar and several times smaller than those for Na. At 0.1 GPa and a water/carbonatite ratio of 1 (by weight), the partition coecients are D Na = 0.35 0.02, D Ca = 0.09 0.02, and D Mg = 0.13 0.01. Between 700 and 900°C, the eect of temperature on partitioning is negligible. However, D Na increases signi®cantly with decreasing water/carbonatite ratio in the system. Our data show that the release of a hydrous¯uid enriched in sodium and simultaneous crystallisation of calcite can transform an alkaline, vapour-saturated carbonatite melt into a body of pure calcite surrounded by zones of sodium metasomatism. Thus, it is quite possible that carbonate magmas with substantial amounts of alkalies were common parental liquids of plutonic carbonatites.

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“…Although Hanang volcano did not erupt sensus stricto carbonatite lavas, nephelinite lavas have bulk-rock composition and isotopic signature close to the Natron carbonatite-nephelinite (e.g. Bell and Tilton 2001;Harmer and Gittins 1998) and mineral crystallization records magmatic differentiation of carbonated-rich silicate liquid. Melilitite magmas evolved to nephelinite magmas at 9-12 km through fractional crystallization, carbonate-silicate immiscibility and replenishment.…”

Section: Carbonatite-nephelinite Association In North Tanzanian Divermentioning

confidence: 99%

Nephelinite lavas at early stage of rift initiation (Hanang volcano, North Tanzanian Divergence)

Baudouin

Parat

Denis

et al. 2016

Contrib Mineral Petrol

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International audienceNorth Tanzanian Divergence is the first stage of continental break-up of East African Rift (<6 Ma) and is one of the most concentrated areas of carbonatite magmatism on Earth, with singular Oldoinyo Lengai and Kerimasi volcanoes. Hanang volcano is the southernmost volcano in the North Tanzanian Divergence and the earliest stage of rift initiation. Hanang volcano erupted silica-undersaturated alkaline lavas with zoned clinopyroxene, nepheline, andradite-schorlomite, titanite, apatite, and pyrrhotite. Lavas are low MgO-nephelinite with low Mg# and high silica content (Mg# = 22.4–35.2, SiO2 = 44.2–46.7 wt%, respectively), high incompatible element concentrations (e.g. REE, Ba, Sr) and display Nb–Ta fractionation (Nb/Ta = 36–61). Major elements of whole rock are consistent with magmatic differentiation by fractional crystallization from a parental melt with melilititic composition. Although fractional crystallization occurred at 9–12 km and can be considered as an important process leading to nephelinite magma, the complex zonation of cpx (e.g. abrupt change of Mg#, Nb/Ta, and H2O) and trace element patterns of nephelinites recorded magmatic differentiation involving open system with carbonate–silicate immiscibility and primary melilititic melt replenishment. The low water content of clinopyroxene (3–25 ppm wt. H2O) indicates that at least 0.3 wt% H2O was present at depth during carbonate-rich nephelinite crystallization at 340–640 MPa and 1050–1100 °C. Mg-poor nephelinites from Hanang represent an early stage of the evolution path towards carbonatitic magmatism as observed in Oldoinyo Lengai. Paragenesis and geochemistry of Hanang nephelinites require the presence of CO2-rich melilititic liquid in the southern part of North Tanzanian Divergence and carbonate-rich melt percolations after deep partial melting of CO2-rich oxidized mantle source

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The Case for Primary, Mantle-derived Carbonatite Magma

Cited by 190 publications

References 32 publications

Clumped isotope thermometry of carbonatites as an indicator of diagenetic alteration

Clumped isotope thermometry of carbonatites as an indicator of diagenetic alteration

Partitioning of Mg, Ca, and Na between carbonatite melt and hydrous fluid at 0.1–0.2 GPa

Nephelinite lavas at early stage of rift initiation (Hanang volcano, North Tanzanian Divergence)

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