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.

Petrology and geochemistry of Cambrian volcanic rocks from the Avalon Zone in New Brunswick

1985 ◽  
Vol 22 (6) ◽  
pp. 881-892 ◽  
Author(s):  
John D. Greenough ◽  
S. R. McCutcheon ◽  
V. S. Papezik
Keyword(s):  
New Brunswick ◽  
Volcanic Rocks ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Middle Cambrian ◽  
Mafic Rocks ◽  
Rock Types ◽  
Petrology And Geochemistry ◽  
Eastern Seaboard ◽  
Highly Evolved

Lower to Middle Cambrian volcanic rocks occur within the Avalon Zone of southern New Brunswick at Beaver Harbour and in the Long Reach area. The Beaver Harbour rocks are intensely altered, but the major- and trace-element geochemistry indicates that they could be highly evolved (basaltic andesites) within-plate basalts. The mafic flows from the Long Reach area form two chemically and petrologically distinct groups: (1) basalts with feldspar phenocrysts that represent evolved continental tholeiites with some oceanic characteristics; and (2) a group of aphyric basalts showing extremely primitive continental tholeiite compositions, also with oceanic affinities and resembling some rift-related Jurassic basalts on the eastern seaboard. Felsic pyroclastic rocks in the Long Reach area make the suite bimodal. This distribution of rock types supports conclusions from the mafic rocks that the area experienced tension throughout the Early to Middle Cambrian.

Liquid immiscibility and the origin of alkali-poor carbonatites

1988 ◽  
Vol 52 (364) ◽  
pp. 43-55 ◽  
Author(s):  
B. A. Kjarsgaard ◽  
D. L. Hamilton
Keyword(s):  
Liquid Immiscibility ◽  
Raw Material ◽  
Coarse Grained ◽  
Rock Types ◽  
Liquid Fractionation ◽  
Ring Complexes ◽  
The Common ◽  
Melt Cooling ◽  
Carbonate Melt ◽  
Common Sequence

AbstractThe work on liquid immiscibility in carbonate-silicate systems of Freestone and Hamilton (1980) has been extended to include alkali-poor and alkali-free compositions. Immiscibility is shown to occur on the joins albite-calcite and anorthite-calcite at 5 kbar. These results make it possible to interpret ocellar structure between calcite-rich spheroids in lamproite or kimberlite host rock as products of liquid immiscibility. The common sequence of rock types found in carbonatite complexes of melilitite-ijolite-urtite-phonolite is interpreted as being the result of both fractional crystallization and liquid fractionation, the corresponding carbonatite composition changing from nearly pure CaCO3 (±MgCO3) progressively to natrocarbonate. A carbonate melt cooling in isolation will suffer crystal fractionation, the residual liquid producing the rarer ferrocarbonatites, etc., whilst the crystal accumulate of calcite (dolomite) plus other phases such as magnetite, apatite, baryte, pyrochlore, etc., are the raw material for the coarse-grained intrusive carbonatites commonly found in ring complexes.

scholarly journals Nepheline solid solution compositions: stoichiometry revisited, reviewed, clarified and rationalised

2020 ◽  
pp. 1-26 ◽  
Author(s):  
C. Michael B. Henderson
Keyword(s):  
Solid Solution ◽  
Unit Cell ◽  
Alkaline Complex ◽  
High Quality ◽  
Diagnostic Parameters ◽  
Rock Types ◽  
Charge Parameter ◽  
Cation Charge ◽  
Excel File

Abstract Molecular formulae used to recalculate nepheline analyses generally have different numbers of oxygens (e.g. NaAlSiO4 (Ne), KAlSiO4, (Ks), CaAl2Si2O8 (An) and SiO2 (Q)). A 32 oxygen cell has 16 T cations and 8 cavity sites, but ideal nepheline stoichiometry is not necessarily followed. Ca end-member □CaCaAl2Si2O4 (CaNe) and excess silica end-member □SiSi2O4 (Q’) calculation requires inclusion of both vacancy species as cavity cation values. Q’ parameter calculations can involve different assumptions and four parameters are described: Qxs; QSi; Q(Si–Al); and Qcavity; these should have closely similar values for high-quality, stoichiometric analyses. Representative published compositions are recalculated to assess whether authors followed ideal nepheline stoichiometry. Phenocrysts from peralkaline rocks and nephelinites typically exhibit Al deficiencies reflected in negative Δ(Al – cavity cation) parameters (ΔAlcc), negative ‘normative’ corundum (Al2O3, Cn), and anomalously low or negative Qxs parameters; for such rock types Q(Si–Al) provides a better estimate of excess silica contents. A ΔT-site (cation charge) parameter (ΔTcharge), is closely coupled to ΔAlcc and end-member NaAlSiO4 has a ΔAlcc/ΔTcharge ratio of 1.4296; the derivation of this value is controlled by strict stuffed-tridymite, unit-cell constraints. Natural nephelines all contain excess silica with a mean ΔAlcc/ΔTcharge of ~1.134 reflecting their Si/Al ratio being > 1. Nepheline analyses with relatively low Al and Si and high Na (also Ca) contents are common; this might reflect the presence of small amounts (up to ~5%) of cancrinite as an alteration phase or perhaps even in solid solution. The compositions of alteration lamellae of Ca-rich cancrinite in altered nepheline phenocrysts in phonolites from the Marangudzi alkaline complex, Zimbabwe, are used to define diagnostic parameters for recognising such non-stoichiometry. These alteration lamellae formed hydrothermally from Ca-rich and K-poor fluids. An EXCEL file is provided to help researchers to standardise calculation of nepheline end-member molecular proportions.

A Study of Potash Fenitization around the Brent Crater, Ontario,—A Paleozoic Alkaline Complex

1971 ◽  
Vol 8 (5) ◽  
pp. 481-497 ◽  
Author(s):  
K. L. Currie
Keyword(s):  
Geometric Form ◽  
Potash Feldspar ◽  
Alkaline Complex ◽  
Carbonatite Complex ◽  
The West ◽  
Granitoid Gneisses ◽  
Chemical Trends

Fractured and brecciated granitoid gneisses around and within the Brent Crater display progressive chemical and mineralogical changes due to metasomatism, culminating in potassic, silica-undersaturated metasomatic rocks. In the metasomatized rocks, potash feldspar increases in amount and degree of triclinicity with increasing metasomatism, while quartz and plagioclase decline in amount. Calcite of carbonatitic isotopic character is found in some of the breccia matrices. Alkaline ultrabasic dikes, identical in chemistry, petrography, and radiometric age to those of the Nippissing alkaline petrographic province, cut the breccia. Potassic trachyte, which appears to form dikes and lenses within the crater, may be the result of anatexis of potassic metasomatites. The geometric form, petrography, and chemical trends of the metasomatized rocks are virtually identical to those of the fenite aureole of the Callander Bay alkaline carbonatite complex, 42 miles (67.6 km) to the west, suggesting that they result from a fenitization process in which potassium rather than sodium is enriched.

scholarly journals On the age of pyrochlore carbonatites from the Ilmeno-Vishnevogorsky Alkaline Complex, the Southern Urals (insights from Rb-Sr and Sm-Nd isotopic data)

LITOSFERA ◽  
2020 ◽  
Vol 20 (4) ◽  
pp. 486-498
Author(s):  
I. L. Nedosekova ◽  
V. A. Koroteev ◽  
T. B. Bayanova ◽  
P. A. Serov ◽  
V. I. Popova ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Southern Urals ◽  
Tectonic Activity ◽  
Ionization Mass ◽  
Alkaline Complex ◽  
Carbonatite Complex ◽  
The Southern Urals ◽  
Scientific Center ◽  
Linear Type ◽  
Isotopic Compositions

Research subject. In this research, we carried out Sm-Nd- и Rb-Sr-dating of pyrochlore carbonatite from the Vishnevogorsky niobium deposit, Ilmeno-Vishnevogorsky Alkaline Complex, Southern Urals. IVC is located in the Ural fold region and is a carbonatite complex of the linear type. Rare metal (Nb-Zr-TR) deposits and occurrences are related to IVC. The age and the duration of IVC deposits formation remains a matter of debate. To determine the age of IVC carbonatites and related niobium ore, we measured Sm-Nd and Rb-Sr isotopic compositions and concentrations of the elements in the minerals (pyrochlore, calcite, apatite, biotite) and bulk sample of pyrochlore carbonatite. Materials and methods. The Sm and Nd isotopic compositions and concentrations were determined on a Finnigan MAT-262L (RPQ) seven-collector mass spectrometer in the static regime at the Geological Institute of the Kola Scientific Center, Apatity, Russia. The Sr and Rb isotopic compositions and concentrations were determined on thermos-ionization mass spectrometer Triton Plus (“Geoanalitik”, IGG UD RAN, Ekaterinburg, Russia). Results. Age of pyrochlore carbonatites from ore zone 140 (Vishnevogorsky deposit, IVC) defined by Sm-Nd and Rb-Sr isotopic methods. Mineral Sm-Nd-isochron (5 points) indicated age 229 ± 16 Ma, mineral Rb-Sr-isochron (5 points) showed similar age 250.5 ± 1.2 Ma. Conclusions. Results Sm-Nd и Rb-Sr dating indicate that the pyrochlore сarbonatites of ore zone 140 crystallized ≈ 250 Ma ago, at the stage of the postcollisional extension, possibly, in connection with exhumation complex, which was accompanied by decompression, partial melting of rocks, involving fluids, dissolution and precipitation of Ordovician-Silurian alkaline-carbonatitе complex. Thus, the formation of the IVC carbonatites and related Nb-ore, which began in Silurian (S), continued in Permian (P) and Triassic (T1-2) and was associated with the post-collision stage of tectonic activity in the Ural Fold Belt.

scholarly journals MAGNETIC SUSCEPTIBILITY AND GAMMA-RAY SPECTROMETRY ON DRILL CORE: LITHOTYPE CHARACTERIZATION AND 3D ORE MODELING OF THE MORRO DO PADRE NIOBIUM DEPOSIT, GOIÁS, BRAZIL

2015 ◽  
Vol 33 (2) ◽  
Author(s):  
Marta Henriques Jácomo ◽  
Tereza Cristina Junqueira Brod ◽  
Augusto Cesar Bittencourt Pires ◽  
José Affonso Brod ◽  
Matheus Palmieri ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Late Cretaceous ◽  
Gamma Ray ◽  
Gamma Ray Spectrometry ◽  
Drill Core ◽  
Carbonatite Complex ◽  
Central Brazil ◽  
Rock Types ◽  
Drill Holes ◽  
Fresh Rock

ABSTRACT. The Morro do Padre niobium Deposit, in the Late-Cretaceous Catal˜ao 2 alkaline-carbonatite complex, central Brazil, consists of stockworks of nelsonite and carbonatite dykes intruded into Precambrian phyllites, quartzites, and amphibolites. A gamma-ray spectrometry and magnetic susceptibility petrophysical survey was conducted on the cores of 73 drill holes in fresh-rock, producing a total of 1295 geophysical samples. Nelsonite, the host rock of the niobium mineralization in the Morro do Padre Deposit, has a characteristic geophysical signature, with higher gamma-ray spectrometry counting rates and magnetic susceptibility values, compared to other rock types. The studied nelsonites may be divided into N1 and N2 types. N2 nelsonite is richer in K, U and Th than N1. Carbonatites are divided into magnetic (C1) and nonmagnetic (C2) varieties. The nonmagnetic carbonatites can be subdivided into C2a and C2b. The C2a carbonatite is richer in K, U and Th than C2b, which is consistent with the presence of apatite and/or monazite in the former. The geophysical 3Dmodeling has shown that the main mineralized body is elongated in the E-W direction. It is about 100 m wide and 300 m long with a maximum depth of approximately 850 m reached by drilling.Keywords: 3D ore modeling, niobium ore, applied geophysics, alkaline rocks, nelsonite. RESUMO. O depósito de nióbio do Morro do Padre no complexo carbonatítico alcalino de Catalão 2 do Cretáceo Superior, região central do Brasil, consiste em stockworks de nelsonito e diques de carbonatito intrudidos em filitos pré-cambrianos, quartzitos e anfibolitos. A pesquisa petrofísica de gamaespectrometria e de susceptibilidade magnética foi realizada em testemunhos de 73 furos de sondagem em rocha fresca, produzindo um total de 1.295 amostras. Nelsonito, a rocha hospedeira da mineralização de nióbio no depósito Morro do Padre, tem uma assinatura geofisica característica, com maiores taxas de radiação gamaespectrométrica e maiores valores de susceptibilidade magnética em comparação com outros tipos de rochas. Os nelsonitos estudados podem ser divididos em N1 e N2. O nelsonito N2 é mais rico em K, U e Th do que o N1. Carbonatitos são divididos em magnéticos (C1) e não magnéticos (C2). Os carbonatitos não magnéticos podem ser subdivididos em C2a e C2b. O carbonatito C2a é mais rico em K, U e Th do que o C2b, o que é consistente com a presença de apatita e/ou monazita na composição minerológica. O modelamento 3D revela um corpo principal de nelsonito mineralizado, alongado segundo a direção E-W. Este é cerca de 100 m de largura e 300 m de comprimento, com uma profundidade máxima de 850 m.Palavras-chave: modelamento 3D de minério, minério de nióbio, geofísica aplicada, rochas alcalinas, nelsonito.

Brief introduction to the geology of the Ilímaussaq alkaline complex, South Greenland, and its exploration history

2001 ◽  
pp. 7-23 ◽  
Author(s):  
Henning Sørensen
Keyword(s):  
Major Part ◽  
Nepheline Syenite ◽  
Geological Mapping ◽  
Type Locality ◽  
Alkaline Complex ◽  
Precise Description ◽  
Rock Types ◽  
Rare Elements ◽  
Exposed Part ◽  
Radioactive Minerals

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Sørensen, H. (2001). Brief introduction to the geology of the Ilímaussaq alkaline complex, South Greenland, and its exploration history. Geology of Greenland Survey Bulletin, 190, 7-23. https://doi.org/10.34194/ggub.v190.5170 _______________ The Ilímaussaq alkaline complex, the type locality of agpaitic nepheline syenites, is made up of three intrusive phases, (1) augite syenite, (2) alkali acid rocks and (3) agpaitic nepheline syenites which occupy the major part of the complex. The agpaitic phase comprises a roof series, a floor series and an intermediate sequence of rocks. The roof series crystallised from the roof downwards beginning with non-agpaitic pulaskite and ending with distinctly agpaitic naujaite. The exposed part of the floor series is made up of the layered agpaitic nepheline syenite kakortokite. The intermediate sequence consists of several types of distinctly agpaitic lujavrites which are accompanied by occurrences of uranium and other rare elements. The complex was first visited by K.L. Giesecke in 1806 and 1809. The first detailed mapping of the complex was carried out by N.V. Ussing in 1900 and 1908. He presented a precise description of the major rock types and an illuminating discussion of the petrology of the complex in his 1912 memoir. In the period 1912–1955 there was very limited activity in the complex. Exploration for radioactive minerals in Ilímaussaq was initiated in 1955 and in subsequent years followed by geological mapping carried out by the Geological Survey of Greenland. This led to a series of detailed studies of the occurrences of not only U, but also Be, Nb, REE and Zr, and to mineralogical, geochemical and petrological studies as well as commercial evaluation and drilling.

Petrogenesis of the Tarr albitite—carbonatite complex, Sinai Peninsula

1975 ◽  
Vol 40 (309) ◽  
pp. 13-24 ◽  
Author(s):  
Aryeh Ervin Shimron
Keyword(s):  
Carbonate Rocks ◽  
Liquid Immiscibility ◽  
Dead Sea ◽  
Rift System ◽  
Sinai Peninsula ◽  
Carbonatite Complex ◽  
Slow Cooling ◽  
Copper Mineralization ◽  
The Dead ◽  
African Rift

SummaryLarge albitite bodies associated with explosive brecciation, fenite aureoles, intrusive carbonate rocks, olivine dolerites, and copper mineralization are described from the Dead Sea rift region in the south-eastern Sinai Peninsula. The main carbonate phases comprise breunnerite and dolomite with actinolite the main phase in the fenites. Field and isotopic evidence indicates that the intrusive carbonate rocks are of carbonatitic origin. The cogenetic, almost monomineralic main phases can be attributed to fractional crystallization and liquid immiscibility acting on a highly gascharged, slow-cooling gabbroic magma. The complex, which is probably of Cretaceous (or older) age, appears to be related to early continental separation along the Dead Sea branch of the African rift system. The porphyry-type copper deposits resemble others that are located along crustal accretion (Iceland) or subduction (Chile) zones.

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