Enthalpies in (Na,Ca)- and (K,Ca)-feldspar binaries: a high-temperature solution calorimetric study

Benisek, Artur; Kroll, Herbert; Cemič, Ladislav; Kohl, V.; Breit, Udo; Heying, Birgit

doi:10.1007/s00410-002-0436-8

Cited by 20 publications

(15 citation statements)

References 13 publications

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“…The interaction parameters are similar to those of Newton et al (1980), who reported W H AbAn = 28.2 kJ/mol and W H AnAb = 8.5 kJ/mol. Giving higher weight to end-member enthalpies, Benisek et al (2003) obtained larger W H values: 40 kJ/mol and 14 kJ/mol, respectively. In the thermometer fi t, these values resulted in a pronounced sensitivity of the temperature T(Ab) to slight compositional shifts.…”

Section: Revision Of Interaction Parametersmentioning

confidence: 94%

“…The enthalpies of solution, ΔH sol , measured in these studies are plotted in Figure 1a. Although Benisek et al (2003) provided a complex fi t to these data, which took account of phase transitions at X An ≈ 0.2 and X An ≈ 0.7, the curve shown in Figure 1a assumes that solution enthalpies can be described by a simple mixing model. This provides a practical way of handling mixing properties for petrological purposes like geothermometry.…”

Section: Revision Of Interaction Parametersmentioning

confidence: 99%

“…The enthalpic mixing properties of high structural-state plagioclase feldspars have been investigated by Newton et al (1980), Carpenter et al (1985, and Benisek et al (2003) using high-temperature solution calorimetry. The enthalpies of solution, ΔH sol , measured in these studies are plotted in Figure 1a.…”

Section: Revision Of Interaction Parametersmentioning

confidence: 99%

“…By analogy to the plagioclases, a two-parameter Margules model has been chosen to describe the solution enthalpies yielding W H OrAn = 91 ± 14 kJ/mol and W H AnOr = 60 ± 10 kJ/mol. W V parameters of (Na,Ca)-and (K,Ca)-feldspars were calculated from the data of Kroll and Müller (1980) and Benisek et al (2003). Using Equation 2 of Fuhrman and Lindsley (1988), the ternary W V parameter was fi tted to three disordered series of Kroll et al (1986) and Hovis (1997).…”

Section: Revision Of Interaction Parametersmentioning

confidence: 99%

“…From high-temperature plagioclase feldspars, Benisek et al (2003) prepared a metastable Or-An series by K-exchange and determined their solution enthalpies. Because the Al,Si ordering state is not affected by the K-exchange, both series have similar enthalpy characteristics.…”

Section: Revision Of Interaction Parametersmentioning

confidence: 99%

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New developments in two-feldspar thermometry

Benisek

Kroll

Cemič

2004

American Mineralogist

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The thermodynamic model of the two-feldspar thermometer has been revised. From recent enthalpy and volume measurements in the (Na,Ca)-and (K,Ca)-feldspar binaries, new interaction parameters have been derived and previous ones have been updated. Entropy parameters have been fi tted to the phase equilibrium data of Seck (1971) and Elkins and Grove (1990). The two data sets could be suitably combined into one. Ideal Ab, Or, and An activities have been expressed in terms of both the molecular mixing and Al-avoidance models.Two-feldspar pairs from high-grade metamorphic rocks that cooled slowly under dry conditions suffer from a distinct type of retrograde resetting. Whereas the original An content in both the plagioclase and the alkali feldspar is preserved because the intercrystalline Ca + Al ↔ (Na,K) + Si diffusion is sluggish, Na and K may be freely exchanged between phases. Mathematical reversal of the Na-K exchange at constant An yields the temperature at which the two feldspars originally coexisted. The shifts in Ab and Or contents obtained from the reversal refl ect the relative plagioclase/alkali feldspar proportions observed in thin sections. Good agreement between calculated and measured ratios was found for feldspar pairs from Sri Lankan granulites. This observation represents a successful test of the reliability of the calculated Ab-Or shifts.In contrast to dry metamorphic rocks, similar application of chemical constraints is not indicated in the case of volcanic rocks. Then the two-feldspar thermometer delivers three, usually incongruent temperatures: T(Ab), T(Or), and T(An). From the abundance of temperatures, Fuhrman and Lindsley (1988) suggested adjusting compositions within assumed chemical uncertainties (e.g., ±2 mol%) so that congruent temperatures could be obtained. However, the result is not unique. Depending on minute variations in the starting compositions, the temperatures may vary by several tens of degrees. In addition, temperatures vary to a similar extent depending on the type of search algorithm. Therefore, we advise users to completely abandon this practice. Instead, a statistical procedure is suggested: Two-feldspar compositions are randomly generated according to Gaussian distributions with their means at the observed compositions and standard errors chosen according to the quality of the chemical analysis. This procedure returns normally distributed temperatures [T(Ab), T(Or), T(An)] together with means and standard deviations. From the overlap of the three Gaussian curves the question of equilibrium or non-equilibrium crystallization of feldspar pairs may be addressed.

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Section: Revision Of Interaction Parametersmentioning

confidence: 94%

Section: Revision Of Interaction Parametersmentioning

confidence: 99%

Section: Revision Of Interaction Parametersmentioning

confidence: 99%

Section: Revision Of Interaction Parametersmentioning

confidence: 99%

Section: Revision Of Interaction Parametersmentioning

confidence: 99%

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New developments in two-feldspar thermometry

Benisek

Kroll

Cemič

2004

American Mineralogist

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Plagioclase composition by Raman spectroscopy

Bersani

Aliatis

Tribaudino

et al. 2018

J Raman Spectroscopy

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Plagioclase undergoes complex exsolution and ordering and phase transition processes during their evolution in nature, and this has hindered attempts to define simple trends relating the major peaks of their Raman spectra with composition. Here, the peak position and linewidth of major Raman features have been calibrated for a set of 20 plagioclases, spanning from albite to anorthite in composition, with symmetry and ordering states that were already well characterized. Point group symmetry is the most important factor determining the Raman peak behaviour with composition, though C true1¯, I true1¯, and P true1¯ plagioclases show different trends for the position of the main peak νa at ~500 cm−1. Using a simplifying approach, which merges the effect of Al–Si ordering and incommensurate modulations, a method has been developed to estimate the plagioclase composition from calibration of a few determinative Raman peaks. This makes use of the wavenumber difference Δab between the most intense peaks νa and νb around 500 cm−1, the linewidth Гa of the strongest νa peak, and the wavenumber difference Δcb between νc and νb peaks, where νc is a Raman feature at ~560–580 cm−1. The calibration was completed from data sets composed of spectra from metamorphic to pegmatitic plagioclase. The results were then tested against a further data set, mostly made by volcanic plagioclase. In most samples, the difference between electron micro probe analysis (EMPA) and Raman compositions is less than 5%. Higher residuals (beyond 10%) are observed for intermediate plagioclase, suggesting that some differences in Δab exist between volcanic and metamorphic plagioclase of intermediate compositions. The Raman compositional results for a plagioclase from Marsili submarine volcano agree with composition and zoning found from the analysis by laser ablation.

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8.1.6.3 Feldspars

Burzo¹

2011

Tectosilicates

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Enthalpies in (Na,Ca)- and (K,Ca)-feldspar binaries: a high-temperature solution calorimetric study

Cited by 20 publications

References 13 publications

New developments in two-feldspar thermometry

New developments in two-feldspar thermometry

Plagioclase composition by Raman spectroscopy

8.1.6.3 Feldspars

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