scholarly journals The South Qôroq Centre nepheline syenites, South Greenland. Petrology, felsic mineralogy and petrogenesis

1976 ◽  
Vol 118 ◽  
pp. 1-55
Author(s):  
D Stephenson
Keyword(s):  
Phase Equilibria ◽  
Trace Element ◽  
Experimental System ◽  
Alkali Feldspar ◽  
Continuous Series ◽  
Small Range ◽  
The South ◽  
Outward Diffusion ◽  
Co Precipitation ◽  
Ring Dyke

The South Qoroq Centre is one of four high-level, major intrusive centres comprising the Igaliko Nepheline Syenite Complex. Three elliptical stocks of foyaite were emplaced in fairly rapid succession by ring fracture and block subsidence, followed by a partial ring· dyke of augite syenite. Inward-dipping microsyenite sheets appear to be associated with the ring-dyke; and four earlier, satellitic stocks occur around the periphery of the centre. Petrographic and mineralogical data show that the intrusions become successively less differentiated with time. Felsic mineral phases (alkali feldspar, nepheline and sodalite) constitute over 80% of most rocks from the centre. Electron-microprobe analyses demonstrate the major role of felsics in the fractionation of the magma and, together with estimates of feldspar structural state from 2V measurements, give indications of the history and conditions of crystallisation. Nepheline compositions fall within a small range of decreasing Si content, but are outside the Morozewicz-Buerger convergence field and are not affected by sub-solidus alkali exchange. Feldspars form a continuous series from Or1Ab67An32 to a K-enriched alkali feldspar Or72Ab28An0. From comparison with other rock suites, this extended feldspar trend seems to be associated with the co-precipitation of nepheline, and increasing peralkalinity of the magma. Major and trace element analyses of the rocks, made by X-ray fluorescence, give variation trends which may be interpreted mainly in terms of fractionation of feldspar and the ferromagnesian phases. In particular, trace element distributions are highly characteristic of fractional crystallisation series, but may not be compatible with fractional melting. Analyses of rocks with co-existing felsic phases compare favourably with phase equilibria in the experimental system Q-ne-ks at 1kb. It is suggested that the centre evolved from an underlying differentiated magma chamber, formed by crystal fractionation and accumulation. Successively lower portions of the chamber were tapped, producing batches of fractionated magma. Later stages of crystallisation were influenced by a build-up in volatiles consisting of H2O, CO2, Cl and F, and post-emplacement differentiation was implemented mainly by outward diffusion of these volatiles together with alkalis under a thermal diffusion gradient. Temperatures of crystallisation deduced from the nepheline geothermometer (Hamilton, 1961) and from phase equilibria in the Ab-Or-H2O system are in reasonable agreement. Assuming a PH2O of about 1 kb, the foyaite feldspars crystallised at about 850°C and augite syenite feldspars slightly higher. Nephelines commenced crystallisation within the range 900-850°C but stabilised at 775-700°C irrespective of rock-type. Physico-chemical conditions during recrystallisation attributable to the later Igdlerfigssalik Centre are inferred from textural, geochemical and mineralogical changes. The recrystallised rocks provide evidence for the behaviour of trace elements during the initial stages of remelting under hydrous conditions in an open system.

Major- and trace-element composition of REE-rich turkestanite from peralkaline granites of the Morro Redondo Complex, Graciosa Province, south Brazil

2010 ◽  
Vol 74 (4) ◽  
pp. 645-658 ◽  
Author(s):  
F. C. J. Vilalva ◽  
S. R. F. Vlach
Keyword(s):  
Trace Element ◽  
Inductively Coupled Plasma ◽  
Alkali Feldspar ◽  
Trace Element Composition ◽  
Inductively Coupled ◽  
Coupled Substitution ◽  
Plasma Mass Spectrometry ◽  
Compositional Variations ◽  
End Members ◽  
South Brazil

AbstractTurkestanite, a rare Th- and REE-bearing cyclosilicate in the ekanite–steacyite group was found in evolved peralkaline granitesfrom the Morro Redondo Complex, south Brazil. It occurswith quartz, alkali feldspar and an unnamed Y-bearing silicate. Electron microprobe analysis indicates relatively homogeneous compositions with maximum ThO2, Na2O and K2O contentsof 22.4%, 2.93% and 3.15 wt.%, respectively, and significant REE2O3 abundances(5.21 to 11.04 wt.%). The REE patterns show enrichment of LREE over HREE, a strong negative Eu anomaly and positive Ce anomaly, the latter in the most transformed crystals. Laser ablation inductively coupled plasma mass spectrometry trace element patterns display considerable depletions in Nb, Zr, Hf, Ti and Li relative to whole-rock sample compositions. Observed compositional variations suggest the influence of coupled substitution mechanisms involving steacyite, a Na-dominant analogue of turkestanite, iraqite, a REE-bearing end-member in the ekanite–steacyite group, ekanite and some theoretical end-members. Turkestanite crystals were interpreted as having precipitated during post-magmatic stages in the presence of residual HFSE-rich fluidscarrying Ca, the circulation of which wasenhanced by deformational events.

scholarly journals Hybrid phase equilibria modelling with conventional and trace element thermobarometry to assess the P–T evolution of UHT granulites: An example from the Highland Complex, Sri Lanka

2020 ◽  
Author(s):  
Prasanna L. Dharmapriya ◽  
Sanjeewa P. K. Malaviarachchi ◽  
Andrea Galli ◽  
Leo M. Kriegsman ◽  
Yasuhito Osanai ◽  
...  
Keyword(s):  
Sri Lanka ◽  
Phase Equilibria ◽  
Trace Element

Fluorine and chlorine in peralkaline liquids and the need for magma generation in an open system

1975 ◽  
Vol 40 (312) ◽  
pp. 405-414 ◽  
Author(s):  
D. K. Bailey ◽  
R. Macdonald
Keyword(s):  
Trace Element ◽  
Evolutionary Process ◽  
Correlation Coefficients ◽  
Fluid Phase ◽  
Alkali Feldspar ◽  
Magma Evolution ◽  
Kenya Rift ◽  
Best Fit ◽  
Very High ◽  
Better Than

SummaryFluorine, chlorine, zinc, niobium, zirconium, yttrium, and rubidium have been deter-mined on fifteen obsidians from Eburru volcano (Kenya Rift Valley), spanning the range from pantel-leritic trachyte to pantellerite. All pairs of elements show positive correlation coefficients, ranging between 0·769 and 0·998, but with most values better than 0·900. In spite of some very high correlations, only two of the twenty-one best-fit lines pass near the origin of the Cartesian coordinates. Linear distributions are found within two separate groups of elements: F, Zr, Rb; and Cl, Nb, Yt. Zn behaves in general as a member of the second group but seems to be subject to an additional variation. When an element from the fluorine group is plotted against one from the chlorine group the resulting pattern is non-linear. Therefore, although the elements in both groups would generally be considered ‘residual’ (partition coefficients between crystals and liquid approaching zero) there are clearly detectable differences in their variation, and hence their behaviour.Major-element variations in the obsidians are such that a vapour (fluid) phase would be needed to account for any magma evolution. The trace-element patterns are also impossible by closed-system crystal fractionation and suggest that this fluid may have been rich in halogens, with the metallic elements forming preferred ‘complexes’ with either F or Cl. The F-Zr-Rb ‘complex’ also varies quite independently of the important major oxides (e.g. A12O3) in the rocks. In the case of Rb this is but one aspect of a more significant anomaly, in which there is no sign of any influence of alkali feldspar (which partitions Rb) in the variation. This is remarkable because trachytes and rhyolites have normative ab+or > 50 %, and any evolutionary process controlled by crystal ⇋ liquid interactions must be dominated by the melting or crystallization of alkali feldspar. The results on the Eburru obsidians show that if they are an evolutionary series then either, the process was not crystal ⇋ liquid controlled, or that any such process has been overriden (or buffered) by other processes that have superimposed the observed trace-element patterns. In the latter event, the buffering phase may have been a halogen-bearing vapour.The same considerations must apply to other pantellerite provinces where Rb appears to have behaved as a ‘residual’ element.

Tectono-stratigraphic evolution of the Early Proterozoic Wisconsin magmatic terranes of the Penokean Orogen

1989 ◽  
Vol 26 (10) ◽  
pp. 2145-2158 ◽  
Author(s):  
P. K. Sims ◽  
W. R. Van Schmus ◽  
K. J. Schulz ◽  
Z. E. Peterman
Keyword(s):  
Subduction Zone ◽  
Continental Margin ◽  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Suture Zone ◽  
Island Arcs ◽  
Calc Alkaline ◽  
The South ◽  
Early Proterozoic ◽  
Felsic Volcanic

The Early Proterozoic Penokean Orogen developed along the southern margin of the Archean Superior craton. The orogen consists of a northern deformed continental margin prism overlying an Archean basement and a southern assemblage of oceanic arcs, the Wisconsin magmatic terranes. The south-dipping Niagara fault (suture) zone separates the south-facing continental margin from the accreted arc terranes. The suture zone contains a dismembered ophiolite.The Wisconsin magmatic terranes consist of two terranes that are distinguished on the basis of lithology and structure. The northern Pembine–Wausau terrane contains a major succession of tholeiitic and calc-alkaline volcanic rocks deposited in the interval 1860–1889 Ma and a more restricted succession of calc-alkaline volcanic rocks deposited about 1835 – 1845 Ma. Granitoid rocks ranging in age from about 1870 to 1760 Ma intrude the volcanic rocks. The older succession was generated as island arcs and (or) closed back-arc basins above the south-dipping subduction zone (Niagara fault zone), whereas the younger one developed as island arcs above a north-dipping subduction zone, the Eau Pleine shear zone. The northward subduction followed deformation related to arc–continent collision at the Niagara suture at about 1860 Ma. The southern Marshfield terrane contains remnants of mafic to felsic volcanic rocks about 1860 Ma that were deposited on Archean gneiss basement, foliated tonalite to granite bodies ranging in age from about 1890 to 1870 Ma, and younger undated granite plutons. Following amalgamation of the two arc terranes along the Eau Pleine suture at about 1840 Ma, intraplate magmatism (1835 Ma) produced rhyolite and anorogenic alkali-feldspar granite that straddled the internal suture.

scholarly journals O STOCK NEFELINA-SIENÍTICO RIO PARDO, PROVÍNCIA ALCALINA DO SUL DO ESTADO DA BAHIA

2012 ◽  
Author(s):  
Rita da Cunha Leal Menezes ◽  
Herbet Conceição ◽  
Maria de Lourdes da Silva Rosa ◽  
Marco Antonio Galarza ◽  
Débora Correia Rios ◽  
...  
Keyword(s):  
Rare Earth ◽  
Trace Element ◽  
Nepheline Syenite ◽  
Crystallization Process ◽  
The South ◽  
Trace Element Contents ◽  
Single Zircon ◽  
Age Range ◽  
Fractional Crystallization Process ◽  
Zircon Evaporation

O Stock Nefelina-Sienítico Rio Pardo se localiza na porção sul do conjunto de intrusões alcalinas que constitui a Província Alcalina do Sul do Estado da Bahia. Esse corpo aflora numa área de 46 km2, sendo constituído por sienito, sienito com nefelina, nefelina sienito e sodalita sienito. A idade Pb-Pb obtida em monocristal de zircão para esse stock foi de 725 ± 2 Ma, a qual se insere no intervalo de idades para o magmatismo da parte sul dessa província alcalina (732 Ma a 720 Ma). Os dados litoquímicos obtidos para esse stock o posicionam na suíte alcalina subsaturada em SiO2 da Província Alcalina do Sul do Estado da Bahia. Os conteúdos de elementos traços asseguram sua afinidade anorogênica. Sua evolução, controlada por cristalização fracionada, se marca por acentuado enriquecimento em Na2O (até 15%) e Al2O3 (até 25%) e marcantes decréscimos em SiO2 (63% a 45%) e Elementos Terras Raras.Palavras-chave: nefelina sienito, idade Pb-Pb, Rio Pardo, BahiaABSTRACT: THE RIO PARDO NEPHELINE-SYENITIC STOCK, SOUTH BAHIA ALKALINE PROVINCE. The Rio Pardo nepheline-syenitic intrusion is located in the southern sector of the South Bahia Alkaline Province. It crops out over an area of 46 km2 and consists of syenite, nepheline-bearing syenite, nepheline syenite and blue-sodalite syenite. The Pb-Pb single-zircon evaporation age of 725 ± 2 Ma obtained for the Rio Pardo stock is in agreement with the age range (732 Ma to 720 Ma) for the southern part of province. Lithochemical data provide evidence to consider the Rio Pardo stock as a body of the SiO2 sub-saturated alkaline suite of the South Bahia Alkaline Province. Trace element contents indicate anorogenic afinity and the stock evolution, controlled by a fractional crystallization process, resulted in an outstanding enrichment of Na2O (up to 15%) and Al2O3 (up to 25%), and an important depletion of SiO2 (63% to 45%) and Rare Earth Elements.Keywords: nepheline syenite, Pb-Pb age, Rio Pardo, Bahia State.,

scholarly journals Radium-228-derived ocean mixing and trace element inputs in the South Atlantic

2020 ◽  
Author(s):  
Yu-Te Hsieh ◽  
Walter Geibert ◽  
E. Malcolm S. Woodward ◽  
Neil J. Wyatt ◽  
Maeve C. Lohan ◽  
...  
Keyword(s):  
Trace Elements ◽  
Continental Shelf ◽  
Trace Element ◽  
Vertical Mixing ◽  
South Atlantic ◽  
Open Ocean ◽  
The South ◽  
Horizontal Mixing ◽  
Cape Basin ◽  
Argentine Basin

Abstract. Trace elements play important roles as micronutrients in modulating marine productivity in the global ocean. The South Atlantic around 40° S is a prominent region of high productivity and a transition zone between the nitrate-depleted Subtropical Gyre and the iron-limited Southern Ocean. However, the sources and fluxes of trace elements to this region remain unclear. In this study, the distribution of the naturally occurring radioisotope 228Ra in the water column of the South Atlantic (Cape Basin and Argentine Basin) has been investigated along a 40° S zonal transect to estimate ocean mixing and trace element supply to the surface ocean. Ra-228 profiles have been used to determine the horizontal and vertical mixing rates in the near-surface open ocean. In the Argentine Basin, horizontal mixing from the continental shelf to the open ocean shows an eddy diffusion of Kx = 1.7 ± 1.4 (106 cm2 s−1) and an integrated advection velocity w = 0.6 ± 0.3 cm s−1. In the Cape Basin, horizontal mixing is Kx = 2.7 ± 0.8 (107 cm2 s−1) and vertical mixing Kz = 1.0–1.5 cm2 s−1 in the upper 600 m layer. Three different approaches (228Ra-diffusion, 228Ra-advection and 228Ra/TE-ratio) have been applied to estimate the dissolved trace-element fluxes from shelf to open ocean. These approaches bracket the possible range of off-shelf fluxes from the Argentine margin to be: 3.8–22 (× 103) nmol Co m−2 d−1, 7.9–20 (× 104) nmol Fe m−2 d−1 and 2.7–6.5 (× 104) nmol Zn m−2 d−1. Off-shelf fluxes from the Cape margin are: 4.3–6.2 (× 103) nmol Co m−2 d−1, 1.2–3.1 (× 104) nmol Fe m−2 d−1 and 0.9–1.2 (× 104) nmol Zn m−2 d−1. On average, at 40° S in the Atlantic, vertical mixing supplies 0.4–1.2 nmol Co m−2 d−1, 3.6–11 nmol Fe m−2 d−1, and 13–16 nmol Zn m−2 d−1 to the euphotic zone. Compared with atmospheric dust and continental shelf inputs, vertical mixing is a more important source for supplying dissolved trace elements to the surface 40° S Atlantic. It is insufficient, however, to provide the trace elements removed by biological uptake. Other inputs (e.g. particulate, or from winter deep-mixing) are required to balance the trace element budgets in this region.

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