CHROMIAN SPINEL AS A PETROGENETIC INDICATOR: PART 2. PETROLOGIC APPLICATIONS

1967 ◽  
Vol 4 (1) ◽  
pp. 71-103 ◽  
Author(s):  
T. N. Irvine
Keyword(s):  
Oxygen Fugacity ◽  
Peritectic Reaction ◽  
High Pressures ◽  
Volcanic Rocks ◽  
Distribution Coefficients ◽  
Chromian Spinel ◽  
Low Oxygen ◽  
Petrogenetic Indicator

The crystallization of chromium-bearing spinel from silicate magmas is first examined, and then an attempt is made to apply the theory developed in Irvine (1965) to the principal occurrences of the mineral for which data are available. It is concluded that the chromium-rich varieties commonly known as chromite have generally formed simultaneously with olivine, and that their crystallization has in many occurrences been terminated by a peritectic (reaction) relation leading to formation of a pyroxene. The origin of the aluminium-rich varieties is more problematical and perhaps more varied; however, they evidently occur only in alpine-type peridotite bodies and peridotite "nodules" in basaltic volcanic rocks, and their formation may generally have involved high pressures. It is found that there is a rough correlation between the Mg/Fe++ ratios of chromian spinels, olivines, and pyroxenes occurring in the same rock bodies, and there is some evidence that the Mg–Fe++ distribution coefficients of spinel–silicate pairs may significantly be sensitive to temperature. The chromites of stratiform intrusions reflect an appreciable range of oxygen fugacities, whereas the spinels of alpine- type peridotite bodies seem generally to have formed at about the same relatively low oxygen fugacity. Chromites from ultra mafic bodies of the type common to southeastern Alaska have exceptionally high Fe+++/Cr + Al + Fe+++ ratios, probably because the bodies crystallized from magma that was extremely poor in silica.

Crystallization trends of pyroxenes from the alkaline volcanic rocks of Tenerife, Canary Islands

1976 ◽  
Vol 40 (316) ◽  
pp. 805-816 ◽  
Author(s):  
P. W. Scott
Keyword(s):  
Oxygen Fugacity ◽  
Canary Islands ◽  
Nepheline Syenite ◽  
Volcanic Rocks ◽  
Limited Range ◽  
Continuous Series ◽  
Low Oxygen ◽  
Alkali Basalts

SummaryThe alkaline volcanic rocks of Tenerife comprise a compositionally continuous series of ankaramites, alkali basalts, trachybasalts, trachyandesites, trachytes, phonolites, and peralkaline phonolites. Ca-rich pyroxenes occur as phenocrysts throughout the series. They show a limited range of composition from diopside and Ti-rich samite in the basic and intermediate rocks, to sodic sahlite in some phonolites. Features of both the sahlite-aegirine and sahlite-hedenbergite trends are present. Sodic ferrosahlites occur as xenocrystal 'green cores' in phenocrysts from some basic and intermediate rocks. The latter are associated with kaersutite xenocrysts and are similar to pyroxenes in some plutonic xenoliths from Tenerife. During the formation of the 'green cores' conditions were more reducing allowing pyroxene compositions to extend through the range sahlite-hedenbergite.Aegirine-angite and Ti-rich aegirine are present in the groundmass of some phonolites and in pyroclastic boulders of nepheline syenite. The aegirines are associated with magnesioarfvedsonite and aenigmatite, and it is considered that they crystallized under conditions of low oxygen fugacity.

Some high-pressure pyroxenes

1974 ◽  
Vol 39 (307) ◽  
pp. 768-787 ◽  
Author(s):  
R. N. Thompson
Keyword(s):  
High Pressure ◽  
Alkali Basalt ◽  
High Pressures ◽  
Major Element ◽  
Distribution Coefficients ◽  
The Other ◽  
Strong Negative Correlation ◽  
Complex Behaviour ◽  
Complex Variation ◽  
Bulk Chemistry

SummaryMicroprobe analyses of Ca-rich pyroxenes crystallized in the melting ranges of a magnesian alkali basalt, a transitional basalt, an olivine tholeiite, a tholeiitic andesite, and an augite leucitite at pressures between 8 and 45 kb show complex variation. Ca-poor pyroxene precipitated only from the alkali basalt at pressures between 14 and 18 kb. Pyroxene falling near the Di-Hed join in the pyroxene quadilateral formed at all pressures and temperatures from the leucitite, whereas ‘Ca-rich’ pyroxene crystallizing from the other four compositions was Ca-poor augite to sub-calcic augite. The liquidus Ca-rich pyroxenes all show rising Al and Na and falling Ti with increasing pressure and temperature. Other elements show complex behaviour; all but the leucitite pyroxenes tend to make temporary excursions of solid solution towards Ca-poor pyroxene at intermediate pressures, returning to more Ca-rich compositions at high pressures. At sub-liquidus temperatures Na and Ti consistently rise with falling T at constant P and also with rising P at constant T in these pyroxenes. The behaviour of the other elements in these circumstances depends on the nature of the coexisting phases.Fe/Mg distribution between Ca-rich pyroxene and liquid, in the form has a constant value of 0.29 for three separate bulk compositions at widely differing temperatures and pressures. Distribution coefficients for Mg and Fe between pyroxenes and coexisting garnets at high pressures are very similar to those found in garnet pyroxenite xenoliths from Oahu, Hawaii. Systematic shifts in the apparent stoichiometry (all Fe taken as Fe2+) of the augite leucitite pyroxenes are thought to indicate that they have considerable Fe3+ contents at low pressure, decreasing as P rises. If so, they show a strong negative correlation between Na and Fe3+, which negates the customary practice of forming acmite before jadeite component when recalculating the analyses of high-pressure pyroxenes.The sets of pyroxenes crystallized from each composition show consistent trends when plotted on such diagrams as jadeite vs Ca-Tschermak's ‘molecule’, which have often been used in attempts to discriminate natural pyroxenes formed in differing P-T environments. However, these new data show clearly that the bulk chemistry of the magma has a predominating influence on the composition of the pyroxenes crystallizing from it. Unless it is certain that a suite of natural pyroxenes have all precipitated from the same magma, it is probably pointless to attempt to deduce the relative P-T conditions of their formation from their major element chemistry.

scholarly journals Genesis of Volcanic Rocks in the Zijinshan Ore District, SE China: Implications for Porphyry-Epithermal Mineralization

Minerals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 200 ◽  
Author(s):  
Zheng-Zheng Feng ◽  
Zhong-Jie Bai ◽  
Hong Zhong ◽  
Wei-Guang Zhu ◽  
Shi-Ji Zheng
Keyword(s):  
Oxygen Fugacity ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Parental Magma ◽  
High Oxygen ◽  
Magma Source ◽  
High Water Content ◽  
High Oxygen Fugacity ◽  
Epithermal Mineralization ◽  
T Values

Volcanic rocks, as the extrusive counterparts of the mineralized intrusions, can provide important information on the magma source, petrogenesis, and metallogenic conditions of the coeval porphyry-epithermal system. Shanghang Basin volcanic rocks are spatially and temporally related to a series of adjacent porphyry-epithermal Cu–Au deposits, and they can be used as a window to study the related deposits. Two laser-ablation–inductively coupled plasma–mass spectrometry zircon U–Pb analyses of the volcanic rocks yield weighted mean ages of ~105 Ma, identical to the age of the coeval porphyry-epithermal mineralization. Rocks have SiO2 contents of 55.4 to 74.8 wt % and belong to the high-K to shoshonitic series, characterized by strong differentiation of light rare-earth elements (REEs) relative to heavy REEs (mean LaN/YbN = 16.88); enrichment in light REEs, Rb, Th, and U; and depletion in Nb, Ta, Zr, Hf, and Ti. The volcanic rocks display (87Sr/86Sr)i values of 0.709341 to 0.711610, εNd(t) values of −6.9 to −3.3 εHf(t) values of −3.95 to −0.30, and δ18O values of 6.07‰–6.79‰, suggesting that the parental magmas were derived from a mantle source enriched by subduction-related progress. SiO2 content shows a strong negative correlation with the contents of some major and trace elements, indicating that fractional crystallization played an important role in the generation of these rocks. A binary mixing model of Hf–O isotopes gives an estimated degree of crustal contamination of 30%. In addition, magnetite crystallized early, and the samples showed high zircon EuN/EuN* values (0.48–0.68), indicating that the parental magma had a high oxygen fugacity. The inferred suppression of plagioclase crystallization and increasing hornblende crystallization during magma evolution suggest that the magma was water rich. The high-water content and high oxygen fugacity of the magma promoted the dissolving of sulfides containing Cu and Au in the source area and contributed to the migration of ore-forming elements.

Problems of iron gain and loss during experimentation on natural rocks: the experimental crystallization of five lunar basalts at low pressures

1977 ◽  
Vol 286 (1336) ◽  
pp. 313-330 ◽  
Keyword(s):  
Oxygen Fugacity ◽  
Glass Tube ◽  
Oxide Content ◽  
Low Oxygen ◽  
Lunar Basalts ◽  
Purity Iron ◽  
High Purity Iron ◽  
Low Pressures ◽  
Melting Experiments ◽  
Iron Bearing

It is extremely difficult to conduct melting experiments on iron-bearing silicate compositions under conditions where the oxygen fugacity and iron oxide content of the charges are controlled precisely at the relevant values, due to reactions between the charge, the container and the adjacent atmosphere. Possible effects are illustrated by discussion of the experimental data for five lunar basalts. At low oxygen fugacities the techniques using molybdenum capsules in an atmosphere whose oxygen fugacity is controlled by passage of a CO 2 /H 2 mixture, and that of enclosing (better, sealing) the charge inside a high purity iron capsule inside a sealed, evacuated silica glass tube yield results which are relatively close to the desired run conditions.

Chemistry of chromian spinel in volcanic rocks as a potential guide to magma chemistry

1992 ◽  
Vol 56 (383) ◽  
pp. 173-184 ◽  
Author(s):  
Shoji Arai
Keyword(s):  
Volcanic Rocks ◽  
Island Arc ◽  
Chromian Spinel ◽  
Oceanic Plateau ◽  
Magma Type ◽  
Original Magma ◽  
Back Arc

AbstractChromian spinel in volcanic rocks is a potential discriminant for magma chemistry. The TiO2 content of spinel, compared at similar Fe3+/(Cr + Al + Fe3+) ratios, can distinguish island arc basalts from intraplate basalts. MORB spinels are low in this ratio and are intermediate for the TiO2 level at comparable Fe3+ ratios. Spinels from back-arc basin basalts, although similar in TiO2/Fe3+ ratio, are more enriched in Fe3+ than the MORB spinels. Spinels in the oceanic plateau basalts are distinctly lower in TiO2 than other intraplate basalt spinels and even slightly lower in TiO2 than the MORB spinels. The data were successfully applied to estimate the kind of the magma from which spinelbearing cumulates, especially dunites, were formed. Original magma chemistry of altered or metamorphosed volcanics in which spinels survive can also be estimated by the chemistry of relict spinel alone. It is possible to estimate the magma type of source volcanics for detrital spinel particles of volcanic derivation.

scholarly journals Experimental study of amphibole crystallization from the highly magnesian melt of Shiveluch volcano

2019 ◽  
Vol 27 (5) ◽  
pp. 476-495 ◽  
Author(s):  
A. G. Simakin ◽  
V. N. Devyatova ◽  
T. P. Salova ◽  
O. Yu. Shaposhnikova
Keyword(s):  
Experimental Data ◽  
Experimental Study ◽  
Oxygen Fugacity ◽  
Volcanic Rocks ◽  
Maximum Size ◽  
Rapid Quenching ◽  
Shiveluch Volcano ◽  
Modified Technique ◽  
Before And After ◽  
Partial Transfer

The paper reports results of an experimental study of amphibole crystallization from the highly magnesian andesite melt of Shiveluch volcano, Kamchatka. The experiments were carried out in IHPV at 300 MPa and 940–980°С in iron-saturated platinum capsules, using rapid quenching and temperature oscillations (in some experiments). The redox state of iron in the system was measured before and after the experiments using Mössbauer spectroscopy. The maximum size of the experimental amphibole crystals (up to 200 μm) was close to those of natural amphibole phenocrysts in the volcanic rocks of Shiveluch volcano. The experimental data show that the content of octahedrally coordinated Al (Al6) in the amphibole considerably varies with small variations in the intensive parameters (P, T, and fO2) and composition of the melt, and the maximum Al6 concentration can be evaluated only by using a reasonably large dataset of amphibole analyses. A modified 13eCNK method is suggested to calculate the values of Al6 and Fe3+/Fe2+ with regard for the Ti concentration and the probable partial transfer of Mg into site B in high-Mg amphibole. Calculations with this modified technique yield lower Fe3+/Fe2+ and higher Al6 values. Our experimental data show that the temperature of amphibole liquidus crystallization decreases from about 990 to 960°C when the oxygen fugacity drops from NNO + 1.5 to NNO + 0.4. In view of this, the transition from amphibole-bearing to anhydrous mineral assemblage in the magmas of Shiveluch volcano might have been caused by variations of the oxygen fugacity but not water. The application of our geobarometer to amphiboles from Shiveluch volcano (extrusions Krasnaya and Karan) yields the highest pressure estimate of above 1 GPa, corresponding to the P-T conditions of the melting of garnet-bearing amphibolite in the lower crust.

Generation of Calc-Alkaline Magmas During Crystallization at High Oxygen Fugacity: An Experimental and Petrologic Study of Tephras from Buldir Volcano, Western Aleutian Arc, Alaska, USA

2020 ◽  
Author(s):  
L E Waters ◽  
E Cottrell ◽  
M L Coombs ◽  
K A Kelley
Keyword(s):  
Oxygen Fugacity ◽  
Subduction Zones ◽  
Volcanic Rocks ◽  
High Oxygen ◽  
Calc Alkaline ◽  
Edge Structure ◽  
Liquidus Phase ◽  
High Oxygen Fugacity ◽  
Alkaline Volcanism ◽  
Aleutian Arc

Abstract Despite agreement that calc-alkaline volcanism occurs at subduction zones and is responsible for the genesis of continental landmasses, there is no consensus on the source of the Fe-depleted signature hallmark to calc-alkaline volcanism. In this study, we utilize mafic tephras collected from Buldir Volcano to address the genesis of strongly calc-alkaline volcanic rocks (those with a low Tholeiitic Index; ≤0.7) in a segment of the western Aleutian Arc to determine if the eruptions are plausibly part of a liquid line of descent, if they are mixtures of crustal melts and parental magmas, or if they are mixtures of melts of the mantle and the subducting slab. We conducted a series of H2O-saturated phase equilibrium experiments (1175–1000 °C; 100 MPa) in a rapid-quench cold-seal (MHC) apparatus on the most primitive natural lava from Buldir (9.34 wt% MgO) at oxidizing conditions near the Re-ReO2 buffer. We confirmed that all experiments equilibrated 0.3 ± 0.23 log units above the Re-ReO2 buffer (ΔQFM ∼ +2.8) using X-ray Absorption Near Edge Structure (XANES) spectroscopy. Chromite is the liquidus phase, followed by olivine, then plagioclase, then clinopyroxene, and finally hornblende. Once clinopyroxene saturates, spinel composition shifts to magnetite. We compared our experimental results to the major element geochemistry and petrology of six tephras (51.9–54.8 wt% SiO2) from Buldir collected during the 2015 field season of the GeoPRISMS shared platform. Tephras contain olivine + plagioclase + clinopyroxene + spinel ± hornblende; plagioclase comprises most of the crystalline volume, followed by either olivine or hornblende. Spinel is ubiquitous; with Cr- rich spinel inclusions in olivine and hornblende, and magnetite in the groundmass. Variations in phenocryst assemblages and compositions between samples can be attributed to differences in pre-eruptive temperatures, where hotter samples are devoid of hornblende, and contain Fo-rich olivine and plagioclase with lower An-contents, owing to the position of the mineral-in curves at fluid-saturated conditions. Experimental glasses match the depletion in FeOT observed in the tephra whole rock compositions. The continuous depletion in FeOT is attributable to saturation of spinel as a liquidus phase (initially as chromite) and continuous crystallization through the experimental series (changing to magnetite at colder temperatures). In contrast to the natural samples, the experiments show enrichment in TiO2 with decreasing MgO, suggesting that differentiation did not occur at 100 MPa on Buldir. The TiO2 depletion in volcanic rocks from Buldir can be accounted for if hornblende crystallization occurs close to the liquidus of a parental magma; a condition that is met at higher pressures and hydrous conditions. The emerging picture for Buldir Island is that (1) oxidizing conditions are required to drive the observed depletions in FeOT via crystallization of spinel, and (2) elevated H2O contents and high pressures are required to saturate hornblende close to the liquidus to reproduce the entire suite of major elements. Our study provides a mechanism to generate the calc-alkaline trends observed at Buldir without requiring mixing of slab and mantle melts. We conclude that calc-alkaline volcanic rocks with extremely low Tholeiitic Indices (0.7), like those from Buldir, cannot be generated in absence of high oxygen fugacity, even at high pressure and/or elevated water pressures.

scholarly journals Synthesis and Hydrothermal Study of (Na,K)M2(PO4)3 (M = Ti, Zr, Hf) Solid Solutions

2010 ◽  
Vol 12 (3,4) ◽  
pp. 195
Author(s):  
E.A. Asabina ◽  
V.I. Pet'kov ◽  
A.M. Kovalsky ◽  
A.R. Kotelnikov
Keyword(s):  
Solid Solutions ◽  
High Pressures ◽  
Sol Gel ◽  
Distribution Coefficients ◽  
Exchange Reactions ◽  
Sodium Potassium ◽  
Cell Parameters ◽  
Fluid Systems ◽  
Concentration Dependences ◽  
Comparison Of The Results

(Na,K)M2(PO4)3 (M = Ti, Zr, Hf) continuous solid solutions were synthesized by sol-gel and solidstate methods. Cation-exchange reactions in the NaM2(PO4)3–KM2(PO4)3–NaCl–KCl–H2O systems were<br />studied at T = 723 – 973 K and p = 100 – 200 MPa. The concentration dependences of unit cell parameters of the studied phosphates were found. The sodium/potassium distribution coefficients in the phosphate-fluid systems were functions of the solid solution compositions, that is, the systems behave nonideally. The excess volumes and excess Gibbs functions of solid solutions mixing were fitted to thirdorder polynomials and described in terms of the Margules model. From the comparison of the results obtained Ti-, Zr-, and Hf-systems, we made the conclusion that the titanium phosphates show greater<br />nonideality than zirconium and hafnium phosphates and lower thermodynamic stability to decomposition to double phosphates at high pressures and temperatures.

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