Pétrologie du granite peralcalin du lac Brisson, Labrador central, Nouveau-Québec. II. Minéralogie et modalités de cristallisation

1993 ◽  
Vol 30 (12) ◽  
pp. 2423-2435 ◽  
Author(s):  
D. Pillet ◽  
M. Chenevoy ◽  
M. Bélanger
Keyword(s):  
Late Stage ◽  
Fluid Phase ◽  
Alkali Feldspar ◽  
Stability Field ◽  
Residual Liquid ◽  
Accessory Minerals ◽  
Mafic Mineral ◽  
Peralkaline Granite ◽  
Zirconium Silicate

Mineral zonation in the Québec–Labrador Brisson Lake peralkaline granite displays quartzose and feldspathic lithofacies arranged concentrically, the latter occupying the centre of the intrusion. The zonation is the result of successive magmatic pulses. In the feldspathic facies, agpaitic crystallization began under hypersolvus conditions around 720 °C with PF = 0.1 GPa. Subsolvus crystallization involving enrichment of the residual liquid in F continued to below 500 °C. The quartzose facies is more differentiated and its composition was controlled by feldspar fractionation. Early quartz crystallization is partly explained by the high content of F in the magma. The mafic mineral succession is, in both facies: Li- and Zn-rich arfvedsonite with an important ferrorichtérite component, which crystallized along with alkali feldspar under low [Formula: see text]; aenigmatite contemporary of amphibole or anterior, destabilized to form neptunite, astrophyllite, aegirine, or arfvedsonite; primary titaniferous aegyrine, contemporary with the amphibole and replaced by secondary aegyrine; neptunite and astrophyllite replacing aenigmatite. This succession is in accordance with the increase of Na and F in the fluid phase, and the increase of [Formula: see text] near the end of crystallization. Among the accessory minerals, euhedral zircon is indicative of the initial richness of the magma in Zr. Magmatic vlasovite, and elpidite formed from late fluid, are evidence that residual system entered the zirconium silicate stability field. Zircon with a fibrous, radiating texture, and gittinsite are indicative of the postmagmatic evolution of the pluton and the presence of a late stage residual fluid which was enriched in Ca and Sr.

Uranium content, distribution, and migration in the Glendessarry syenite, Inverness-shire

1981 ◽  
Vol 44 (336) ◽  
pp. 443-448 ◽  
Author(s):  
M. B. Fowler
Keyword(s):  
Late Stage ◽  
Fission Track ◽  
Content Distribution ◽  
Fluid Phase ◽  
Uranium Content ◽  
Rich Phase ◽  
Accessory Minerals ◽  
Track Method ◽  
Metamorphic Fluids ◽  
And Migration

AbstractThe distribution of uranium in a suite of variably deformed and metamorphosed rocks from the leucocratic member of the Glendessarry syenite has been determined using the fission track method. The uranium content of the magma increased during crystallization and uranium was concentrated in accessory minerals such as monazite, zircon, sphene, allanite, apatite, and microinclusions of a Zr- and Ti-rich phase. Contamination of the magma by pelitic metasediment enhanced the uranium content and monazite and zircon formed instead of sphene, allanite, and apatite.Evidence of subsolidus uranium mobility in late stage magmatic or metamorphic fluids is presented here and shows: (a) Intracrystalline redistribution of uranium, especially in grains of sphene. (b) Intergranular mobility in a fluid phase, which affected the uraniferous accessory minerals in several ways.

Mineralogy of vesicles in an olivine leucitite at Cosgrove, Victoria, Australia

1980 ◽  
Vol 43 (329) ◽  
pp. 597-603 ◽  
Author(s):  
W. D. Birch
Keyword(s):  
Late Stage ◽  
Rock Type ◽  
Early Stage ◽  
Coarse Grained ◽  
Residual Liquid ◽  
Cooling History ◽  
History Of

SummaryAn olivine-titanomagnetite-apatite-clinopyroxene-mica-nepheline-feldspar assemblage occurs in late-stage vesicles in a small outcrop of olivine leucitite at Cosgrove, Victoria. The vesicles were formed by exsolution of volatiles at an early stage in the cooling history of the lava. Subsequently, a volatile-rich residual liquid filled cavities and fractures, giving rise to a coarse-grained pegmatoid rock type similar in over-all mineralogy to the vesicles. The volatiles facilitating crystallization in both the vesicles and the pegmatoid were probably enriched in F, CO2, and P. A number of geothermometers applied to the vesicle assemblage failed to agree on likely crystallization temperatures.

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.

Petrology of the alkali syenites of the Mundwara magmatic suite, Sirohi, Rajasthan, India

1973 ◽  
Vol 110 (5) ◽  
pp. 457-466 ◽  
Author(s):  
M. K. Bose ◽  
D. K. Das Gupta
Keyword(s):  
Comparative Study ◽  
Alkali Feldspar ◽  
Western India ◽  
Variable Degree ◽  
Deccan Volcanic Province ◽  
Volcanic Province ◽  
Mafic Mineral ◽  
Magmatic Suite ◽  
Calciferous Amphibole ◽  
North Western

SummaryThe alkali syenites of the Mundwara magmatic suite, Sirohi district, Rajasthan, in north-western India, are chiefly developed in the Musala hill of the complex. They comprise three principal varieties representing different stages of crystallization, viz. nepheline-sodalite syenite, nepheline-barkevikite microsyenite, and nepheline poor leucosyenite. The dominant constituent of these hypersolvus syenites is alkali feldspar, an orthoclase microperthite showing a variable degree of exsolution. The chief mafic mineral is a distinctly green and zoned sodic pyroxene, close to aegirine-augite in composition. A brown calciferous amphibole, identified as a barkevikite, is developed in addition in the microsyenites. Reddish brown biotite of the phlogopite-annite series is common to all the syenites. The petrography and mineralogy of the syenites are discussed, and a comparative study of the Mundwara syenites with similar rocks of the Deccan volcanic province is presented. Chemistry and mineralogy of the syenites of the Mundwara suite suggest that they are related to those associated with the Deccan volcanic province.

scholarly journals Using mineral equilibria to estimate H2O activities in peridotites from the Western Gneiss Region of Norway

2017 ◽  
Vol 102 (5) ◽  
pp. 1021-1036 ◽  
Author(s):  
Patricia Kang ◽  
William M. Lamb ◽  
Martyn Drury
Keyword(s):  
Physical Properties ◽  
Fluid Pressure ◽  
Fluid Phase ◽  
Stability Field ◽  
Lithostatic Pressure ◽  
Free Fluid ◽  
Western Gneiss Region ◽  
Mineral Equilibria ◽  
Earth’S Mantle ◽  
Absent Condition

Abstract The Earth’s mantle is an important reservoir of H2O, and even a small amount of H2O has a significant influence on the physical properties of mantle rocks. Estimating the amount of H2O in rocks from the Earth’s mantle would, therefore, provide some insights into the physical properties of this volumetrically dominant portion of the Earth. The goal of this study is to use mineral equilibria to determine the activities of H2O (aH2O) in orogenic mantle peridotites from the Western Gneiss Region of Norway. An amphibole dehydration reaction yielded values of aH2O ranging from 0.1 to 0.4 for these samples. Values of fO2 of approximately 1 to 2 log units below the FMQ oxygen buffer were estimated from a fO2-buffering reaction between olivine, orthopyroxene, and spinel for these same samples. These results demonstrate that the presence of amphibole in the mantle does not require elevated values of aH2O (i.e., aH2O≈1) nor relatively oxidizing values of fO2 (i.e., >FMQ). It is possible to estimate a minimum value of aH2O by characterizing fluid speciation in C-O-H system for a given value of oxygen fugacity (fO2). Our results show that the estimates of aH2O obtained from the amphibole dehydration equilibrium are significantly lower than values of aH2O estimated from this combination of fO2 and C-O-H calculations. This suggests that fluid pressure (Pfluid) is less than lithostatic pressure (Plith) and, for metamorphic rocks, implies the absence of a free fluid phase. Fluid absent condition could be generated by amphibole growth during exhumation. If small amounts of H2O were added to these rocks, the formation of amphibole could yield low values of aH2O by consuming all available H2O. On the other hand, if the nominally anhydrous minerals (NAMs) contained significant H2O at conditions outside of the stability field of amphibole they might have served as a reservoir of H2O. In this case, NAMs could supply the OH necessary for amphibole growth once retrograde P-T conditions were consistent with amphibole stability. Thus, amphibole growth may effectively dehydrate coexisting NAMs and enhance the strength of rocks as long as the NAMs controlled the rheology of the rock.

scholarly journals On the compositional variability of dalyite, K2ZrSi6O15: a new occurrence from Terceira, Azores

2016 ◽  
Vol 80 (4) ◽  
pp. 547-565 ◽  
Author(s):  
A. J. Jeffery ◽  
R. Gertisser ◽  
R. A. Jackson ◽  
B. O'Driscoll ◽  
A. Kronz
Keyword(s):  
Solid State ◽  
Late Stage ◽  
Octahedral Site ◽  
Pore Wall ◽  
Zirconium Silicate ◽  
Quantitative Analyses ◽  
Compositional Variability ◽  
First Time ◽  
Potassic Rocks ◽  
Bimodal Variation

AbstractThe rare potassium zirconium silicate dalyite has been identified for the first time on Terceira, Azores, within syenitic ejecta of the Caldeira-Castelinho Ignimbrite Formation. New quantitative analyses of this dalyite were combined with the small number of published analyses from various locations worldwide to evaluate the mineral's compositional variability. Additionally, solid-state modelling has been applied to assess the site allocations of substituting elements. The new analyses yield the average formula (K1.84Na0.15)∑=1.99(Zr0.94Ti0.012Hf0.011Fe0.004)∑=0.967Si6.03O15. Model results predict the placement of substituting Hf and Ti in the octahedral site, and highlight the overall complexity in the incorporation of Fe, Mg and Ba. The combined dataset reveals that dalyite found within peralkaline granites and syenites is generally defined by higher Na↔K substitution and lower Ti↔Zr substitution relative to dalyite from highly potassic rocks. The Terceira dalyite exhibits a bimodal variation in the degree of Na↔K substitution which is attributed to a K-enrichment trend induced by late-stage pore wall crystallization and albitization, coupled with the control of pore size upon the degree of supersaturation required to initiate nucleation of dalyite in pores of varying size.

Iron-rich and iron-poor prehnites from the Way Linggo epithermal Au-Ag deposit, southwest Sumatra, and the Heber geothermal field, California

2001 ◽  
Vol 65 (3) ◽  
pp. 397-406 ◽  
Author(s):  
R. S. Wheeler ◽  
P. R. L. Browne ◽  
K. A. Rodgers
Keyword(s):  
Electron Microprobe ◽  
Late Stage ◽  
Hydrothermal Fluid ◽  
Geothermal Field ◽  
Stability Field ◽  
Octahedral Sites ◽  
The Stability ◽  
Hydrothermal Environment ◽  
Epithermal Au ◽  
The Way

AbstractElectron microprobe analyses of prehnites from the Way Linggo low-sulphidation epithermal Au-Ag deposit of southern Sumatra, show that the mole fraction of octahedral Fe3+, expressed as Fe3+/(Fe3++AlVI), ranges from 0.0 to ~0.6, the higher values being among the most iron-rich reported for prehnite in a hydrothermal environment. Prehnites from a diabase sill in the Heber geothermal field of California have mole fractions of octahedral Fe3+ ranging from 0.03 to 0.3. The Way Linggo prehnites formed below 220°C, some 20–30°C lower than those at the Heber field; the lower crystallization temperatures perhaps enhanced the opportunity for Fe3+ to substitute in octahedral sites. In both occurrences, prehnite predates late-stage calcite, consistent with the need for waters depositing prehnite to have aCO2 <0.01 moles. At higher CO2 activities the stability field of calcite would swamp the range of aCa2+/aH+ values appropriate for crystallizing prehnite. Consequently, the presence of prehnite in a hydrothermal environment primarily indicates that degassing of the hydrothermal fluid in CO2 occurred prior to deposition.

Petrology and geodynamic significance of deerite-bearing metaquartzites from the Escambray Massif, Cuba

2006 ◽  
Vol 70 (5) ◽  
pp. 545-564 ◽  
Author(s):  
C. Grevel ◽  
W. V. Maresch ◽  
K.-P. Stanek ◽  
F. Grafe ◽  
S. Hoernes
Keyword(s):  
High Pressure ◽  
North America ◽  
Oxygen Isotope ◽  
Late Stage ◽  
Direct Application ◽  
Stability Field ◽  
Western Cordillera ◽  
First Occurrence ◽  
Ideal Composition ◽  
Crystallization Conditions

AbstractDeerite, a typical mineral of Fe-rich metacherts metamorphosed under blueschist conditions, is not rare, but known occurrences have up to now been restricted mainly to the Tethyan collisional zone and the Western Cordillera of North America. We describe a first occurrence in the high-pressure nappes of the Escambray Massif, Cuba, in the assemblage deerite + Mg-Al-poor riebeckite + magnetite + quartz ± garnet ± phengite ± aegirine. This assemblage typically forms during exhumation and accompanies late, stress-free annealing of the quartz matrix. Mg-Al-poor riebeckite overgrows older, large, oriented crystals of glaucophane, ferroglaucophane and Mg-Al-rich riebeckite (‘crossite’) during deerite formation. Early-formed hematite was largely replaced by magnetite. Deerite is very close to ideal composition, attaining >99% Si12O40(OH)5, allowing direct application of the experimentally determined P-T-fO2 stability field (Lattard and Le Breton, 1994). In combination with oxygen-isotope thermometry on magnetite-quartz, the crystallization conditions of the deerite-bearing assemblage can be constrained to ∼470°C, >15 kbar, and an oxygen fugacity restricted closely to the quartz-fayalite-magnetite buffer (fO2 ≈ 10−23 bar). Thus, the late-stage P-T path ofthe metacherts mirrors a steep P-T gradient of 10°C/km or less, requiring subduction ofthis part ofthe Antillean Island Arc to be still active during exhumation of the Escambray nappes.

Gahnite and columbite in an alkali-feldspar granite from New Zealand

1981 ◽  
Vol 44 (335) ◽  
pp. 275-278 ◽  
Author(s):  
A. J. Tulloch
Keyword(s):  
New Zealand ◽  
Fractional Crystallization ◽  
Alkali Feldspar ◽  
Mafic Mineral ◽  
Granitoid Rocks ◽  
Highly Evolved

AbstractGahnite and columbite with compositions (Zn5.96Fe1.55Mg0.21Mn0.13)Σ7.85Al16.09O32 and (Nb7.36Ta0.60Mn2.95Fe0.98Ti0.09)Σ11.98O24 occur as accessory phases in a highly evolved garnetiferous muscovite alkalifeldspar granite. Both phases have developed as a result of a concentration of Zn, Nb, and Ta during the fmal stages of the fractional crystallization which led to the formation of the pluton, and the lack of a major mafic mineral such as biotite, in which these elements are normally camouflaged in granitoid rocks.

Garnet-quartz intergrowths in graphitic pelites: the role of the fluid phase

1986 ◽  
Vol 50 (358) ◽  
pp. 611-620 ◽  
Author(s):  
Kevin W. Burton
Keyword(s):  
Oxygen Fugacity ◽  
Fluid Phase ◽  
Garnet Growth ◽  
Stability Field ◽  
Lattice Orientation ◽  
Crystal Face ◽  
Interphase Boundaries ◽  
New Material ◽  
The Stability

AbstractGarnets with an unusual inclusion pattern of cylindrical quartz intergrowths have been found to develop exclusively in the presence of graphite. The intergrowths consist of quartz rods, 1–5 µm in diameter, originating at the sector-zone interfaces in the garnet with the long axes normal to the crystal faces. The lattice orientation and continuity of the quartz suggests that the interphase boundaries between the quartz and garnet are epitaxially related and that new material was added to the tube as the crystal face of the garnet grew. In the presence of a C-O-H fluid, at the temperatures and pressures recorded, (P = 6.5 kbar, T = 500°C), the amount of CO2 present restricts the solubility of SiO2 in the intergranular fluid phase, where the oxygen fugacity (fo2) is below the Quartz-fayalite-magnetite (QFM) buffer, and within the stability field of graphite. The reduced solubility will lower the concentration of SiO2 in solution, and hence restrict its ease of transport via the fluid, resulting in an excess of SiO2at the site of garnet growth. Under such conditions the SiO2 is incorporated in the growing garnet in the form of the cylindrical quartz intergrowths.

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