Ordering kinetics of Mg-Fe2+exchange in a Wo43En46Fs11augite

Brizi, E.; Molin, Gianmario; Zanazzi, P. F.; Merli, Marcello

doi:10.2138/am-2001-2-309

Cited by 20 publications

(18 citation statements)

References 28 publications

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“…This value is very close to that of 47.8 kcal/mol obtained by Brizi et al (2001) from ordering experiments involving augite. In terms of the activation energy for the Fe-Mg exchange reaction in orthopyroxene, the value obtained in this study for pigeonite is signifi cantly lower than both the average value of 62.8(± 2.2) kcal/mol obtained by Ganguly and Tazzoli (1994) from selected disordering data taken from the literature and the values of about 70 and 78 kcal/mol very recently obtained by 4.12 ×10 -2 FIGURE 1.…”

Section: Table 1csupporting

confidence: 86%

“…As can be seen, there is a close fi t between the theoretical curves calculated using the C 0 K + dis values in Muellerʼs equation and the experimental points, thus indicating a second-order kinetic law for the Fe-Mg exchange reaction and a high reliability for the measured ordering states. The values of the kinetic constants at 700, 750, and 800 °C appear to be higher than those obtained at the same temperatures by Brizi et al (2001), who applied Muellerʼs method to an augitic clinopyroxene. However, this is consistent with the higher Fe content of the BTS308 pigeonite sample compared to augite (X Fe* = 0.49 vs. X Fe* = 0.15).…”

Section: Table 1ccontrasting

confidence: 55%

“…For C2/c clinopyroxene, the equilibrium of Fe-Mg exchange has been studied in samples with different compositions and at different T enabling geothermometric applications (McCallister et al 1976;Molin and Zanazzi 1991) while the kinetics has been characterized by ordering experiments using an augitic sample with composition ca. Wo 43 En 46 Fs 11 (Brizi et al 2001). For P2 1 /c pigeonite, the temperature dependence of the Fe-Mg order-disorder under equilibrium conditions has been studied by Pasqual et al (2000) using two samples with different Mg/Fe ratios and Ca content.…”

Section: Introductionmentioning

confidence: 99%

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Kinetics of Fe2+-Mg order-disorder in P21/c pigeonite

Domeneghetti

Zema

Tazzoli

2005

American Mineralogist

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The kinetics of the Fe-Mg intracrystalline exchange reaction in P2 1 /c pigeonite (Wo 10 En 47 Fs 43 ) free of exsolved augite, from the Paraná rhyodacite sample BTS308, was studied by single-crystal X-ray diffraction (XRD). Isothermal disordering annealing experiments, with oxygen fugacity controlled at the IW buffer, were performed on two crystals at 650, 700, 750, and 800 °C until the Fe-Mg exchange equilibrium was reached. The XRD data were collected from the two untreated crystals and after each annealing experiment. Structure refi nements were carried out taking into account the recently discovered stronger preference of Mn for the M2 site compared to Fe 2+ . The linear regression of ln k D * vs. 1/T yielded the following equation:ln k D * = -2925(± 110)/T(K) + 0.574(± 0.111); (R 2 = 0.997)The T c values calculated using this equation were 566 (±6) and 571 (±6) °C for the two crystals. Analysis of the kinetic data was performed according to Muellerʼs model, which allowed retrieval of the disordering rate constants C 0 K dis + for all four temperatures. The Arrhenius relation:ln K dis + = ln K 0 -Q/(RT) = 20.45(± 1.91) -25191 (± 1900)/T(K); (R 2 = 0.989) yielded an activation energy of 50.03 (±3) kcal/mol for the Fe-Mg exchange process. Cooling time constants, calculated at the QMF buffer conditions of the host rock were, for the two crystals, η = 0.94 × 10 -1 K -1 year -1 and η = 1.10 × 10 -1 K -1 year -1 , and gave cooling rates on the order of 10 °C/h consistent with very fast lava cooling.

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Section: Table 1csupporting

confidence: 86%

Section: Table 1ccontrasting

confidence: 55%

Section: Introductionmentioning

confidence: 99%

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Kinetics of Fe2+-Mg order-disorder in P21/c pigeonite

Domeneghetti

Zema

Tazzoli

2005

American Mineralogist

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“…The crystal quality was checked using rotation pictures while 360°phi-scans allowed optimization of the scan width and scan time for each data collection. The resolution of data collection was set following Brizi et al (2001) observations. They performed leverage analysis (Prince and Nicholson 1985) on single-crystal data collected up to sin h/k * 1.15 Å -1 in order to analyse the influence of each reflection on the evaluation of refined cation occupancies.…”

Section: Single-crystal X-ray Diffractionmentioning

confidence: 99%

Order–disorder–reorder process in thermally treated dolomite samples: a combined powder and single-crystal X-ray diffraction study

et al. 2012

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A combined powder and single-crystal X-ray diffraction analysis of dolomite [CaMg(CO 3 ) 2 ] heated to 1,200°C at 3 GPa was made to study the order-disorderreorder process. The order/disorder transition is inferred to start below 1,100°C, and complete disorder is attained at approximately 1,200°C. Twinned crystals characterized by high internal order were found in samples annealed over 1,100°C, and their fraction was found to increase with temperature. Evidences of twinning domains combined with probable remaining disordered portions of the structure imply that reordering processes occur during the quench. Twin domains are hereby proposed as a witness to thermally induced intra-layer-type cation disordering.

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“…This is for instance the case of clinopyroxene, for which equilibrium and kinetics of the disordering process has been already well studied by single-crystal XRD for augitic compositions (Brizi et al 2000(Brizi et al , 2001 and for low-Ca pigeonitic compositions (Pasqual et al 2000;Domeneghetti et al 2005;Alvaro et al 2011). Along with orthopyroxenes, the latter are thus considered as potential geospeedometers.…”

Section: Discussionmentioning

confidence: 99%

Ordering state in orthopyroxene as determined by precession electron diffraction

Jacob

Palatinus

Cuvillier

et al. 2013

American Mineralogist

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Fe 2+ and Mg distribution on octahedral M1 and M2 sites of the orthopyroxene structure is an indicator of the cooling rate and closure temperature of the mineral. It is generally obtained by single-crystal X-ray diffraction, which is limited in spatial resolution. In this work, we determine the cationic distribution at a submicrometer scale in a transmission electron microscope using precession electron diffraction. Two orthopyroxene samples coming from the same metamorphic rock are studied, a naturally ordered one and a disordered one. The latter was obtained from the ordered sample by annealing at high temperature and rapid quenching. Both samples have been first studied in X-ray diffraction and then in precession electron diffraction. Intensities recorded in zone-axis precession electron diffraction experiments have been quantitatively analyzed and compared to simulations, taking into account dynamical interactions between diffracted beams. Our structure refinement results are in good agreement with those obtained by single-crystal X-ray diffraction. They enable to distinguish between the ordered sample and the disordered one in terms of the observed molar fractions of Fe at M1 and M2 sites. We discuss the sensitivity of the method as a function of experimental parameters. The larger dispersion of the results obtained on the ordered specimen is attributed to structural heterogeneities inherent to the sample.

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Ordering kinetics of Mg-Fe²⁺exchange in a Wo₄₃En₄₆Fs₁₁augite

Cited by 20 publications

References 28 publications

Kinetics of Fe2+-Mg order-disorder in P21/c pigeonite

Kinetics of Fe2+-Mg order-disorder in P21/c pigeonite

Order–disorder–reorder process in thermally treated dolomite samples: a combined powder and single-crystal X-ray diffraction study

Ordering state in orthopyroxene as determined by precession electron diffraction

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