Phase relations of a Carbonated High-CaO Nephelinite at 0.2 and 0.5 GPa

Kjarsgaard, B A

doi:10.1093/petroj/39.11-12.2061

Cited by 112 publications

(102 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The results and conclusions presented here are supported by the experimental data from Kjarsgaard 39 , which suggest that a minimum of B5-7 wt% of (Na 2 O þ K 2 O) is present in carbonatite melts produced at pressures between 0.2 and 0.5 GPa (these correspond to crustal levels). In addition, the experimentally quenched sodic dolomitic carbonatite liquids produced at high temperature (930-1,030°C) and high pressure (21-30 kbar) by Wallace and Green 3 contain 0.5% P 2 O 5 , 3% SiO 2 , 2% Al 2 O 3 , 5% FeO, 5% Na 2 O and 0.4% K 2 O, which allow for the crystallization of the non-carbonate minerals (for example, phosphates, oxides and silicates).…”

Section: Discussionsupporting

confidence: 85%

Evidence for the alkaline nature of parental carbonatite melts at Oka complex in Canada

2013

View full text Add to dashboard Cite

The Earth's sole active carbonatite volcano, Oldoinyo Lengai (Tanzania), is presently erupting unique natrocarbonatite lavas that are characterized by Na-and K-bearing magmatic carbonates of nyerereite [Na 2 Ca(CO 3 ) 2 ] and gregoryite [(Na 2 ,K 2 ,Ca)CO 3 ]. Contrarily, the vast majority of older, plutonic carbonatite occurrences worldwide are dominated by Ca-(calcite) or Mg-(dolomite)-rich magmatic carbonates. Consequently, this leads to the conundrum as to the composition of primary, mantle-derived carbonatite liquids. Here we report a detailed chemical investigation of melt inclusions associated with intrusive (plutonic) calcite-rich carbonatites from the B120 Ma carbonatite complex of Oka (Canada). Melt inclusions are hosted by magnetite (Fe 3 O 4 ), which crystallizes through a significant period of carbonatite melt solidification. Our results indicate mineral assemblages within the melt inclusions that are consistent with those documented in natrocarbonatite lavas. We propose therefore that derivation of alkali-enriched parental carbonatite melts has been more prevalent than that preserved in the geological record.

show abstract

Section: Discussionsupporting

confidence: 85%

Evidence for the alkaline nature of parental carbonatite melts at Oka complex in Canada

2013

View full text Add to dashboard Cite

show abstract

“…This implies that silicate and carbonate liquids were miscible under the temperature and pressure conditions prevailing in the environment where the ejecta plume formed. Experiments on liquid immiscibility (Lee and Wyllie 1996;Kjarsgaard 1998) show that, with increasing pressure, the immiscibility field broadens and the stability field of carbonate melt increases drastically, while the stability field of silicate melt gets very small at 2.5 GPa (Lee and Wyllie 1996). On the other hand, high pressure and temperature experiments on carbonate liquids by Moore and Wood (1998) show that, at 3 GPa and temperatures between 1475°C and 1525°C, the SiO 2 content dramatically increases, while the CO 2 content decreases, even up to temperatures >1700°C.…”

Section: Carbonate Meltsmentioning

confidence: 99%

The suevite of drill hole Yucatàn 6 in the Chicxulub impact crater

Claeys

Heuschkel²,

Lounejeva

et al. 2003

Meteorit & Planetary Scien

110

View full text Add to dashboard Cite

The suevite of drill hole Yucatàn 6 in the Chicxulub impact craterPhilippe CLAEYS, 1* Sabine HEUSCHKEL, 2 Elena LOUNEJEVA-BATURINA, 3 Gerardo SANCHEZ-RUBIO, 3 Abstract-The suevite breccia of the Chicxulub impact crater, Yucatàn, Mexico, is more variable and complex in terms of composition and stratigraphy than suevites observed at other craters. Detailed studies (microscope, electron microprobe, SEM, XRF) have been carried out on a noncontinuous set of samples from the drill hole Yucatàn 6 (Y6) located 50 km SW from the center of the impact structure. Three subunits can be distinguished in the suevite: the upper unit is a fine-grained carbonate-rich suevite breccia with few shocked basement clasts, mostly altered melt fragments, and formerly melted carbonate material; the middle suevite is a coarse-grained suevite with shocked basement clasts and altered silicate melt fragments; the lower suevite unit is composed of shocked basement and melt fragments and large evaporite clasts. The matrix of the suevite is not clastic but recrystallized and composed mainly of feldspar and pyroxene. The composition of the upper members of the suevite is dominated by the sedimentary cover of the Yucatàn target rock. With depth in well Y6, the amount of carbonate decreases and the proportion of evaporite and silicate basement rocks increases significantly. Even at the thin section scale, melt phases of different chemistry can be identified, showing that no widespread homogenization of the melt took place. The melt compositions also reflect the heterogeneity of the deep Yucatàn basement. Calcite with characteristic feathery texture indicates the existence of formerly pure carbonate melt. The proportion of carbonate to evaporite clasts is less than 5:1, except in the lower suevite where large evaporite clasts are present. This proportion constrains the amount of CO 2 and SO X released by the impact event.

show abstract

“…Among the few experimental studies performed to constrain phase assemblage of nephelinite magmas, phase equilibria of Shombole nephelinite (Peterson 1989), with whole-rock composition and mineral assemblage close to the Hanang nephelinite (Fig. 3), corroborate that cpx and garnet are liquidus phases at low pressure (100-500 MPa) and nepheline is a sub-liquidus phase co-precipitating with cpx, garnet, titanite, Fe-spinel and calcite at 950 °C (Kjarsgaard 1998). The low-pressure carbonate precipitation reported in experimental run products occurred at low temperature (<950 °C) in Si-poor and Ca-rich melt composition (e.g.…”

Section: Petrogenesis Of Hanang Nephelinitesmentioning

confidence: 79%

“…Modified after Thomas (1966) Page 3 of 20 64 magmatic differentiation, including fractional crystallization and liquid immiscibility (e.g. Dawson 1998;Freestone and Hamilton 1980;Kjarsgaard 1998).…”

Section: Electronic Supplementary Materialsmentioning

confidence: 99%

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

Baudouin

Parat

Denis

et al. 2016

Contrib Mineral Petrol

View full text Add to dashboard Cite

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

show abstract

Phase relations of a Carbonated High-CaO Nephelinite at 0.2 and 0.5 GPa

Cited by 112 publications

References 20 publications

Evidence for the alkaline nature of parental carbonatite melts at Oka complex in Canada

Evidence for the alkaline nature of parental carbonatite melts at Oka complex in Canada

The suevite of drill hole Yucatàn 6 in the Chicxulub impact crater

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

Contact Info

Product

Resources

About