A COMPARISON BETWEEN THE STABILITY FIELD OF A CL-RICH SCAPOLITE AND THE END-MEMBER MARIALITE

2016 ◽  
Author(s):  
Kaleo Almeida ◽  
◽  
David M. Jenkins
Keyword(s):  
Stability Field ◽  
The Stability

Eclogite from central Yukon: a record of subduction at the western margin of ancient North America

1983 ◽  
Vol 20 (9) ◽  
pp. 1389-1408 ◽  
Author(s):  
Philippe Erdmer ◽  
Herwart Helmstaedt
Keyword(s):  
North America ◽  
North American ◽  
Stability Field ◽  
Western Margin ◽  
Thrust Sheets ◽  
The Stability ◽  
Basic Igneous Rock ◽  
Inclusion Trails ◽  
Tectonic Boundary ◽  
Host Rocks

Eclogite occurring in central Yukon, at Faro and near Last Peak, as lenses interleaved with muscovite–quartz blastomylonite has the chemical and field characteristics of group C rocks. From sigmoidal inclusion trails in garnet, from geothermometry and geobarometry, and from mineral parageneses, the eclogite is inferred to have a crustal protolith and to have followed a hysteretic, subduction-cycle P–T trajectory. Transformation of basic igneous rock into schist was followed by eclogite metamorphism during which pressure was at least 1000 MPa and temperature was between 600 and 700 °C. Uplifting involved passage through the stability field of glaucophane; the eclogite and its host rocks were then subjected to greenschist fades metamorphism and deformation, with temperature at approximately 400 °C. The rocks were emplaced as thrust sheets against or onto the western North American cratonal margin. The tectonic boundary ranges from nearly vertical, where it is outlined by a zone of steeply dipping mélange, to nearly horizontal beneath klippen of cataclastic rocks that lie on North American miogeoclinal strata. Together with occurrences of eclogite on strike, in Yukon, near Fairbanks (Alaska), and near Pinchi Lake (British Columbia), eclogite at Faro and near Last Peak implies that the Yukon Cataclastic Complex is a deeply eroded collision mélange that borders over 1000 km of the ancient continental margin.

A model of Fe3+-kaolinite, Al3+-goethite, Al3+-hematite equilibria in laterites

Clay Minerals ◽  
1989 ◽  
Vol 24 (1) ◽  
pp. 1-21 ◽  
Author(s):  
F. Trolard ◽  
Y. Tardy
Keyword(s):  
Stability Field ◽  
Equilibrium Conditions ◽  
Dissolved Silica ◽  
Silica Activity ◽  
Proposed Model ◽  
Coexisting Phases ◽  
Activity Temperature ◽  
The Stability ◽  
Fe Substitution ◽  
Mineral Constituents

AbstractThe distribution of Fe3+-kaolinite, Al-goethite and Al-hematite and their contents of Fe and Al in bauxites and ferricretes are controlled by water activity, dissolved silica activity, temperature and particle size. The proposed model, based on ideal solid-solution equilibria in the Fe2O3-Al2O3-SiO2-H2O system, takes into account water and silica activities. By using the same considerations as those previously developed for the Fe2O3-Al2O3-H2O system, the model calculates the amounts of coexisting phases, Al or Fe substitution ratios in goethite, hematite or kaolinite, and the stability field distributions of the minerals under various conditions. Thermodynamic equilibrium conditions and element distributions within the mineral constituents are shown to be dependent on the parameters cited above. The model yields results compatible with natural observations on lateritic profiles.

The chemical stability of mendipite, diaboleïte, chloroxiphite, and cumengéite, and their relationships to other secondary lead(II) minerals

1980 ◽  
Vol 43 (331) ◽  
pp. 901-904 ◽  
Author(s):  
D. Alun Humphreys ◽  
John H. Thomas ◽  
Peter A. Williams ◽  
Robert F. Symes
Keyword(s):  
Chloride Ion ◽  
Stability Diagram ◽  
Chloride Ions ◽  
Ion Concentration ◽  
Stability Field ◽  
Cupric Ion ◽  
Free Energy Of Formation ◽  
High Concentrations ◽  
The Stability ◽  
Ph Range

SummaryThe chemical stabilities of mendipite, Pb3O2Cl2, diaboleïte, Pb2CuCl2(OH)4, chloroxiphite, Pb3CuCl2O2(OH)2, and cumengéite, Pb19Cu24Cl42 (OH)44, have been determined in aqueous solution at 298.2 K. Values of standard Gibbs free energy of formation, ΔGf°, for the four minerals are −740, −1160, −1129, and −15163±20 kJ mol−1 respectively. These values have been used to construct the stability diagram shown in fig. I which illustrates their relationships to each other and to the minerals cotunnite, PbCl2, paralaurionite, PbOHCl, and litharge, PbO. This diagram shows that mendipite occupies a large stability field and should readily form from cold, aqueous, mineralizing solutions containing variable amounts of lead and chloride ions, and over a broad pH range. The formation of paralaurionite and of cotunnite requires a considerable increase in chloride ion concentration, although paralaurionite can crystallize under much less extreme conditions than cotunnite. The encroachment of the copper minerals on to the stability fields of those mineral phases containing lead(II) only is significant even at very low relative activities of cupric ion. Chloroxiphite has a large stability field, and at given concentrations of cupric ion, diaboleïte is stable at relatively high aCl−. Cumengéite will only form at high concentrations of chloride ion.

scholarly journals The effect of solid solution on the stability of talc and 10-Å phase

2019 ◽  
Vol 174 (10) ◽  
Author(s):  
Harriet Howe ◽  
Alison R. Pawley
Keyword(s):  
Subduction Zones ◽  
Rheological Behaviour ◽  
Starting Material ◽  
Stability Field ◽  
Compositional Variation ◽  
Thermal Breakdown ◽  
Large Decrease ◽  
Dehydration Reactions ◽  
The Stability ◽  
Fe Substitution

Abstract Talc and 10-Å phase are hydrous phases that are implicated in fluid processes and rheological behaviour in subduction zones. Natural samples of talc show limited compositional variation away from the MgO–SiO2–H2O (MSH) endmember, with only substitution of Fe2+ for Mg occurring in significant amounts. In experiments at 2 GPa, talc containing 0.48 apfu Fe2+ begins to break down in the divariant field talc + anthophyllite + quartz at ~ 550 °C, a temperature ~ 270 °C lower than in the MSH system. At 4 GPa, Fe-bearing talc breaks down over a wide temperature interval in the divariant field talc + enstatite + coesite. The large decrease in temperature of the beginning of talc breakdown shows that Fe2+ is partitioned strongly into enstatite and anthophyllite with respect to talc. In phase reversal experiments at 6.5 GPa, the beginning of the dehydration of 10-Å phase containing 0.48 apfu Fe2+ was bracketed between 575 °C and 600 °C, a temperature ~ 100 °C lower than the MSH endmember reaction. The relative positions of the talc and 10-Å phase dehydration reactions indicate that the latter is able to accommodate greater Fe substitution, and is, therefore, more stable in Fe-bearing systems. In experiments at 6.2 GPa, 650 °C in the systems MgO–Al2O3–SiO2–H2O (MASH) and Na2O–MgO–Al2O3–SiO2–H2O (NMASH), 10-Å phase was synthesised that contains up to 0.5 apfu Al in the system MASH (compared to 0.8 in the starting material) and up to 0.4 apfu Al + 0.4 apfu Na in the system NMASH (compared to 0.7 of each of Al and Na in the starting material). Further experiments are required to determine if higher Al and Na contents in 10-Å phase are possible. The much higher Al and Na contents than found in talc indicate that, as with Fe, substitution of these elements enlarges the 10-Å phase stability field with respect to talc. In contrast to the effect of Fe, Al and Na also increase the stability of 10-Å phase relative to its thermal breakdown products enstatite + coesite.

Carbonatitic melts in cuboid diamonds from Udachnaya kimberlite pipe (Yakutia): evidence from vibrational spectroscopy

2004 ◽  
Vol 68 (1) ◽  
pp. 61-73 ◽  
Author(s):  
D. A. Zedgenizov ◽  
H. Kagi ◽  
V. S. Shatsky ◽  
N. V. Sobolev
Keyword(s):  
Vibrational Spectroscopy ◽  
Low Temperatures ◽  
Kimberlite Pipe ◽  
Silica Content ◽  
Silicate Glasses ◽  
Stability Field ◽  
The Stability ◽  
Reported Data ◽  
Internal Pressures ◽  
High Internal Pressure

AbstractMicro-inclusions (1 –10 μm) in 55 diamonds of cubic habit from the Udachnaya kimberlite pipe have been studied using vibrational spectroscopy. This has revealed a multiphase assemblage in cuboid diamonds from the Udachnaya kimberlite pipe. This assemblage includes carbonates, olivine, apatite, graphite, water and silicate glasses. The micro-inclusions preserve the high internal pressure and give confidence that the original materials were trapped during growth of the host diamond. The internal pressures, extrapolated to mantle temperatures, lie within the stability field of diamond and the relatively low temperatures are typical for the formation of cuboid diamonds. In contrast to previously reported data for African diamonds, the micro-inclusions in the cuboids from Udachnaya are extremely carbonatitic in composition (H2O/(H2O+CO2) ≈5 –20%) with the observed assemblage of microinclusions similar to some types of carbonatites. The low water and silica content testify that the material in the micro-inclusions of the Udachnaya diamonds was near-solidus carbonatitic melt. Vibrational spectroscopy has provided the evidence of carbonatitic melts in cuboid diamonds.

Thermal stability of metalorganic compounds on volcanic olivine

2020 ◽  
Author(s):  
Joanna Brau ◽  
Marco Matzka ◽  
Philippe Schmitt-Kopplin ◽  
Norbert Hertkorn ◽  
Werner Ertel-Ingrisch ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Thermal Treatment ◽  
Tube Furnace ◽  
Stability Field ◽  
Secondary Phases ◽  
The Stability ◽  
The Individual ◽  
Gas Tight ◽  
Metalorganic Compounds ◽  
Thermal Stability Of

<p>Previously unknown class of metalorganic compounds revealed in meteorites [1] also found on the surfaces of silicate phases such as olivine, may have been involved in the emergence of life.  Here, the thermal stability of such organic compounds has been experimentally investigated under conditions which simulate those extant on the early Earth. We have studied olivines from the Hawaiian eruptions of 1959 and 2018. Individual mineral grains have been hand-picked to be free of secondary phases such as pyroxene or melt. We use a high temperature gas-tight tube furnace under CO-CO<sub>2</sub> gas mixture at temperatures ranging from 950°C to 1350°C and oxygen fugacity ranging from 10<sup>-12</sup> to 10<sup>-10 </sup>bar, within the stability field of olivine. The samples were contained in Pt crucibles and held for dwell times of 1 to 64 h. Quenching was performed by lifting the samples vertically out of the tube furnace. Using EPMA (electron microprobe analyzer) and RAMAN spectroscopy, we have mapped the state of the olivine samples. We observe that the composition of the individual mineral grains remains stable and homogeneous with thermal treatment. We are also investigating the role of impurities and cracks in the natural olivine and synthetic forsterite that might influence our study. The metalorganic cargo of these olivines has been analyzed using FT-ICR-MS (Fourier Transform ion cyclotron mass spectrometry). Preliminary results reveal systematic changes or organic molecular composition depending on time and heat of thermal treatment whose origins will be discussed.</p><p>[1] A. Ruf, B. Kanawati, N. Hertkorn, Q. Yin, F. Moritz, M. Harir, M. Lucio, B. Michalke, J. Wimpenny, S. Shilobreeva, B. Bronsky, V. Saraykin, Z. Gabelica, R. D. Gougeon, E. Quirico, S. Ralew, T. Jakubowski,  H. Haack, M. Gonsior, P. Jenniskens, N. W. Hinman, P. Schmitt-Kopplin. (2017) Previously unknown class of metalorganic compoundsrevealed in meteorites. PNAS 114 (2017) 2819-2824.</p>

An EXAFS study of cation site distortions through the P2/c-P1̄ phase transition in the synthetic cuproscheelite-sanmartinite solid solution

1994 ◽  
Vol 58 (391) ◽  
pp. 185-199 ◽  
Author(s):  
P. F. Schofield ◽  
J. M. Charnock ◽  
G. Cressey ◽  
C. M. B. Henderson
Keyword(s):  
Phase Transition ◽  
Solid Solution ◽  
Stability Field ◽  
Cation Site ◽  
Cu Content ◽  
Square Planar ◽  
Jahn Teller ◽  
Exafs Study ◽  
Four Square ◽  
The Stability

AbstractEXAFS spectroscopy has been used to monitor changes in divalent cation site geometries across the P2/c-P1̄ phase transition in the sanmartinite (ZnWO4)-cuproscheelite (CuWO4) solid solution at ambient and liquid nitrogen temperatures. In the ZnWO4 end member, Zn occupies axially-compressed ZnO6 octahedra with two axial Zn-O bonds at approximately 1.95 Å and four square planar Zn-O bonds at approximately 2.11 Å. The substitution of Zn by Cu generates a second Zn environment with four short square planar Zn-O bonds and two longer axial Zn-O bonds. The proportion of the latter site increases progressively as the Cu content increases. Cu EXAFS reveals that the CuO6 octahedra maintain their Jahn-Teller axially-elongate geometry throughout the majority of the solid solution and only occur as axially-compressed octahedra well within the stability field of the Zn-rich phase with monoclinic long-range order.

Formation of Methane Hydrates from Super-compressed Water and Methane Mixtures

2010 ◽  
Vol 1262 ◽  
Author(s):  
Jing-Yin Chen ◽  
Choong-Shik Yoo
Keyword(s):  
Methane Hydrate ◽  
High Speed ◽  
Energy Resource ◽  
Hydrate Formation ◽  
Methane Hydrates ◽  
Stability Field ◽  
Compression Rate ◽  
Time Resolved ◽  
Optical Images ◽  
The Stability

AbstractUnderstanding the high-pressure kinetics associated with the formation of methane hydrates is critical to the practical use of the most abundant energy resource on earth. In this study, we have studied, for the first time, the compression rate dependence on the formation of methane hydrates under pressures, using dynamic-Diamond Anvil Cell (d-DAC) coupled with a high-speed microphotography and a confocal micro-Raman spectroscopy. The time-resolved optical images and Raman spectra indicate that the pressure-induced formation of methane hydrate depends on the compression rate and the peak pressure. At the compression rate of around 5 to 10 GPa/s, methane hydrate phase II (MH-II) forms from super-compressed water within the stability field of ice VI between 0.9 GPa and 2.0 GPa. This is due to a relatively slow rate of the hydrate formation below 0.9 GPa and a relatively fast rate of the water solidification above 2.0 GPa. The fact that methane hydrate forms from super-compressed water underscores a diffusion-controlled growth, which accelerates with pressure because of the enhanced miscibility between methane and super-compressed water.

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