scholarly journals The Oka carbonatite complex: Magnetite compositions and the role of immiscible silicate liquids

2019 ◽  
Keyword(s):  
Carbonatite Complex ◽  
Silicate Liquids

scholarly journals The Syenite–Carbonatite Complex of Ihouhaouene (Western Hoggar, Algeria): Interplay Between Alkaline Magma Differentiation and Hybridization of Cumulus Crystal Mushes

2021 ◽  
Vol 8 ◽  
Author(s):  
A. Djeddi ◽  
F. Parat ◽  
J.-L. Bodinier ◽  
K. Ouzegane ◽  
J.-M. Dautria
Keyword(s):  
Alkaline Complex ◽  
Carbonatite Complex ◽  
Slow Cooling ◽  
Silicate Minerals ◽  
Rock Types ◽  
Evolutionary Scheme ◽  
Silicate Liquids ◽  
Rock Suite ◽  
Highly Evolved ◽  
Carbonate Melt

The 2 Ga-old Ihouhaouene alkaline complex (Western Hoggar, Algeria) is among the oldest known carbonatite occurrences on Earth. The carbonatites are calciocarbonatites hosted by syenites, the predominant rock type in the complex. Both rock types are characterized by medium-grained to pegmatitic textures and contain clinopyroxene, apatite, and wollastonite, associated with K-feldspar in syenites and a groundmass of calcite in carbonatites. The rock suite shows a continuous range of compositions from 57–65 wt.% SiO2 and 0.1–0.4 wt.% CO2 in red syenites to 52–58 wt.% SiO2 and 0.1–6.5 wt.% CO2 in white syenites, 20–35 wt.% SiO2 and 11–24 wt.% CO2 in Si-rich carbonatites (>10% silicate minerals), and <20 wt.% SiO2 and 24–36 wt.% CO2 in Si-poor carbonatites (<5% silicate minerals). Calculation of mineral equilibrium melts reveals that apatite and clinopyroxene are in disequilibrium with each other and were most likely crystallized from different parental magmas before being assembled in the studied rocks. They are subtle in the red syenites, whereas the white syenites and the Si-rich carbonatites bear evidence for parental magmas of highly contrasted compositions. Apatite was equilibrated with LREE-enriched (Ce/Lu = 1,690–6,182) carbonate melts, also characterized by elevated Nb/Ta ratio (>50), whereas clinopyroxene was precipitated from silicate liquids characterized by lower LREE/HREE (Ce/Lu = 49–234) and variable Nb/Ta ratios (Nb/Ta = 2–30). The Si-poor carbonatites resemble the Si-rich carbonatites and the white syenites with elevated REE contents in apatite equilibrium melts compared to clinopyroxene. However, apatite equilibrium melt in Si-poor carbonatite shows a majority of subchondritic values (Nb/Ta<10) and clinopyroxene has chondritic-to-superchondritic values (Nb/Ta = 15–50). Although paradoxical at first sight, this Nb-Ta signature may simply reflect the segregation of the carbonatite from highly evolved silicate melts characterized by extremely low Nb/Ta values. Altogether, our results suggest an evolutionary scheme whereby slow cooling of a silico-carbonated mantle melt resulted in the segregation of both cumulus minerals and immiscible silicate and carbonate melt fractions, resulting in the overall differentiation of the complex. This process was however counterbalanced by intermingling of partially crystallized melt fractions, which resulted in the formation of hybrid alkaline cumulates composed of disequilibrium cumulus phases and variable proportions of carbonate or K-feldspar.

The role of mafic dykes in the petrogenesis of the Archean Siilinjärvi carbonatite complex, east-central Finland

Lithos ◽  
2019 ◽  
Vol 342-343 ◽  
pp. 468-479 ◽  
Author(s):  
Hannes B. Mattsson ◽  
Karin Högdahl ◽  
Matias Carlsson ◽  
Alireza Malehmir
Keyword(s):  
Carbonatite Complex ◽  
East Central ◽  
Mafic Dykes

scholarly journals Major, Trace, and Rare-Earth Element Geochemistry of Nb-V Rich Andradite-Schorlomite-Morimotoite Garnet from Ambadungar-Saidivasan Alkaline Carbonatite Complex, India: Implication for the Role of Hydrothermal Fluid-Induced Metasomatism

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 756
Author(s):  
Amiya K. Samal ◽  
Rajesh K. Srivastava ◽  
Dewashish Upadhyay
Keyword(s):  
Rare Earth ◽  
Rare Earth Element ◽  
Hydrothermal Fluid ◽  
Earth Element ◽  
Primary Source ◽  
Active Role ◽  
Carbonatite Complex ◽  
Element Geochemistry ◽  
Convex Upward

In situ major, trace and rare-earth element composition of Ti-rich garnets from Ambadungar-Saidivasan alkaline carbonatite complex (ASACC) are presented to constrain its likely genesis. The garnets are characterized by high andradite (42.7–57.3), schorolomite (22.0–31.0), and morimotoite (15.6–26.5) end members. No distinct chemical zonation is noticed except for minor variations in Ti content. The garnets are enriched in LREE (average 731 ppm) and relatively depleted in HREE (average 186 ppm) and show an M-type first tetrad that leads to a convex upward pattern between Ce and Gd. Mildly positive to no Eu anomalies are observed (Eu/Eu* = 1.06–1.17). The REE patterns (LaN/YbN = 1.11–2.11) are similar to those of garnets from skarn deposits. The presence of tetrad effect in the LREE pattern suggests an active role of metasomatic processes involving hydrothermal fluids during the growth of the garnets. These garnets also contain high Nb (282–2283 ppm) and V (1083–2155 ppm) concentrations, which stand out against the composition of the host rock. Therefore, late-stage metasomatic reactions of earlier formed minerals with hydrothermal fluid enriched in Fe, Si, LREE, Nb, V, and Ti led to the formation of garnet. The primary source for these elements could be magnetite, ilmenite, and pyrochlore present in different varieties of carbonatites in the ASACC, with the required elements being released during their interaction with the hydrothermal fluid. The hydrothermal fluid was likely to be moderately acidic, and having fluoride and sulfate as the primary ligands.

Role of CO2 on differentiation of ultramafic alkaline series: liquid immiscibility in carbonate-bearing phonolitic dykes (Polar Siberia)

1997 ◽  
Vol 61 (407) ◽  
pp. 549-556 ◽  
Author(s):  
L. N. Kogarko
Keyword(s):  
Fluid Phase ◽  
Liquid Immiscibility ◽  
Aqueous Fluid ◽  
Magma Ascent ◽  
Carbonatite Complex ◽  
Incongruent Dissolution ◽  
Central Type ◽  
The North ◽  
Crustal Magma

AbstractThe Maimecha-Kotui province in the North of Siberian platform is the largest province of ultramafic alkaline rocks in the world. The province comprises thirty-seven central-type complexes together with numerous dykes. The majority of dykes are radially disposed around the ultramafic alkaline massifs. Data are presented for dykes of the Dolbykha carbonatite complex, which comprises olivine and melilite nephelinites; nosean, calcite and cancrinite phonolites; calcite trachytes and calcite carbonatites.Some peralkaline phonolitic dykes contain carbonate-bearing globules with sizes of 1−2 mm to 17−20 mm. Globules consist of polycrystalline calcitic aggregates together with albite, phlogopite, apatite, Sr-lueshite, zircon, ancylite, ilmenite and strontianite. The phonolites have phenocrysts of albite, phlogopite and ilmenite. Albite, phlogopite, calcite and nepheline are also present in the groundmass. Analysis of these materials in the light of experimental data on the liquid immiscibility in carbonate-silicate systems suggests that separation of carbonatite from phonolitic melts took place due to immiscibility in the liquid state. I propose that carbonate melts contained originally significantly higher alkali contents which were subsequently lost into the fluid phase due to the incongruent dissolution of calcium-sodium carbonates in aqueous fluid at low temperatures. The discovery of nyerereite in the carbonatite of Polar Siberia confirms this conclusion. I infer that one of the mechanisms for the genesis of carbonatite melt in Polar Siberia was liquid immiscibility in strongly differentiated phonolitic magmas.The generation of the carbonatites was probably controlled by the depth (and PCO2) of the crustal magma chamber where differentiation took place and probably also by the alkalinity of melts, and the rapidity of magma ascent to the surface.

Dewetting of Liquids on Ceramic Surfaces at High Temperatures

2002 ◽  
Vol 8 (4) ◽  
pp. 257-267 ◽  
Author(s):  
N. Ravishankar ◽  
Shelley R. Gilliss ◽  
C. Barry Carter
Keyword(s):  
Surface Roughness ◽  
Model Systems ◽  
Length Scale ◽  
Solute Redistribution ◽  
Surface Complex ◽  
Dewetting Process ◽  
Ceramic Surfaces ◽  
Silicate Liquids ◽  
Effect Of Surface

The influence of surface structure and chemistry on high-temperature dewetting of silicate liquids on ceramic surfaces has been investigated. Model systems based on well-defined crystallography and known chemistry have been used to illustrate the effect of surface roughness and chemistry on the dewetting process. Reconstructed ceramic surfaces provide ideal substrates to study effects of surface roughness. It has been shown that the morphology of dewet droplets depend on the length scale and the crystallography of the facets on the surface. Complex pattern formation due to solute redistribution during dewetting is illustrated in the case of SiO2 dewetting on (001) rutile substrates. The role of kinetics on the dewetting process has also been clarified.

Role of dactinomycin in the improved survival of children with Wilms' tumor

JAMA ◽  
1966 ◽  
Vol 195 (12) ◽  
pp. 1005-1009 ◽  
Author(s):  
D. J. Fernbach
Keyword(s):  
Wilms Tumor

Role of the allergist in diagnosis and management of patients with uveitis

JAMA ◽  
1966 ◽  
Vol 195 (3) ◽  
pp. 167-172 ◽  
Author(s):  
T. E. Van Metre
Keyword(s):  
Diagnosis And Management
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