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This paper introduces the software solution Bingo‐Antidote for thermodynamic calculations at equilibrium based on iterative thermodynamic models. It describes a hybrid strategy combining the strength of Gibbs energy minimization (GEM) and inverse thermobarometry models based on the comparison between the modelled and observed mineral assemblage, modes and compositions. The overall technique relies on quantitative compositional maps acquired by electron probe micro‐analyser for obtaining a mutually consistent set of observed data such as bulk rock and mineral compositions. Thus it offers the opportunity to investigate metamorphic rocks on a microscale. The scoring part Bingo integrates three statistical model quality factors for the assemblage, for the mineral modes, for the mineral compositions combined in a global evaluation criterion that quantifies how the model reproduces the observations for the investigated volume. The input parameters of GEM affecting the model quality such as pressure, temperature and eventually some components of the bulk composition (e.g. the molar amount of hydrogen, carbon or oxygen) or activity variables of fluids and gases (e.g. , , f (O2)) can be optimized by inversion in Antidote using several mapping stages followed by a direct search optimization. Examples of iterative models based on compositional maps processed with Bingo‐Antidote demonstrate the utility of the program. In contrast to the qualitative interpretation of phase diagrams, the inversion maximizes the benefits of GEM and permits the derivation of statistically ‘optimal’ pressure–temperature conditions for well‐equilibrated samples. In addition, Bingo‐Antidote opens new avenues for petrological investigations such as the generation of chemical potential landscape maps.
Accessory phosphate minerals, such as monazite and xenotime, are commonly used as geochronometers to provide timing constraints on tectonometamorphic events recorded by the host rocks within which they occur. However, the formation and recrystallization of accessory minerals, and their interaction with major mineral phases, are still poorly understood. As a consequence, linking ages obtained from accessory minerals to the metamorphic pressure-temperature (P-T) paths obtained primarily from major mineral phases, such as garnet, remains challenging. While there have been studies that have advanced our understanding of the behaviour of various accessory minerals through thermodynamic modelling, limited examples are available to test their reliability in natural metamorphic rocks. This study incorporates phosphate minerals into one of the most commonly used thermodynamic data sets for phase equilibria modelling. This refined methodology is tested by modelling the detailed P-T-time (t) paths for rocks from two different regions of the Himalaya, one subsolidus and one that experienced suprasolidus conditions. The results obtained from our integrated models yield direct information on the behaviour of monazite and xenotime growth/breakdown along the calculated P-T paths. This allows us to tie different age populations obtained from the accessory minerals directly to the P-T paths derived from major mineral phases and facilitates a refined understanding of the P-T-t histories of those rock specimens.
The astonishing progress of personal computer technology in the past 30 years as well as the availability of thermodynamic data and modeling programs have revolutionized our ability to investigate and quantify metamorphic processes. Equilibrium thermodynamics has played a central role in this revolution, providing simultaneously a physico-chemical framework and efficient modeling strategies to calculate mineral stability relations in the Earth’s lithosphere (and beyond) as well as thermobarometric results. This Perspectives contribution provides a review of the ingredients and recipes required for constructing models. A fundamental requirement to perform thermodynamic modeling is an internally consistent database containing standard state properties and activity–composition models of pure minerals, solid solutions, and fluids. We demonstrate how important internal consistency is to this database, and show some of the advantages and pitfalls of the two main modeling strategies (inverse and forward modeling). Both techniques are commonly applied to obtain thermobarometric estimates; that is, to derive P–T (pressure–temperature) information to quantify the conditions of metamorphism. In the last section, we describe a new modeling strategy based on iterative thermodynamic models, integrated with quantitative compositional mapping. This technique provides a powerful alternative to traditional modeling tools and permits use of local bulk compositions for testing the assumption of local equilibrium in rocks that were not fully re-equilibrated during their metamorphic history. We argue that this is the case for most natural samples, even at high-temperature conditions, and that this natural complexity must be taken into consideration when applying equilibrium models.
================See comments to find a link to the full-text================ Deep mantle plumes and associated increased geotherms are expected to cause an upward deflection of the lower–upper mantle boundary and an overall thinning of the mantle transition zone between about 410 and 660 kilometres depth. We use subsequent forward modelling of mineral assemblages, seismic velocities and receiver functions to explain the common paucity of such observations in receiver function data. In the lower mantle transition zone, large horizontal differences in seismic velocities may result from temperature‐dependent assemblage variations. At this depth, primitive mantle compositions are dominated by majoritic garnet at high temperatures. Associated seismic velocities are expected to be much lower than for ringwoodite‐rich assemblages at undisturbed thermal conditions. Neglecting this ultra‐low‐velocity zone at upwelling sites can cause a miscalculation of the lower–upper mantle boundary on the order of 20 kilometres.
BED92.v1 - "Bermans extended database of 92.version1" This database is build on JUN92d.bs database (based on Berman, 1988 + modifications). Watch the header of the database to find a documentation of all changes.
- Erik Duesterhoeft
- Martin Zaehle
- Christian de Capitani
- Roland Oberhänsli
Thermodynamic databases are an essential tool to predict complex equilibrium mineral assemblages and mineral properties like mineral volumes. They consist of numerous thermodynamic data of various minerals, extracted from experiments. Each database follows its own methodology in calculating chemical and physical properties. Therefore a direct comparision between different database predictions was avoided, due to the contrasting methodolgies and philosophy. Here, we present a direct comparison between the databases of Berman  and Holland & Powell , focusing on mineral volumes . For this propose, a reevaluation of the equation of states was nesscary. In this context, we identify an error also implemented in common thermodynamic softwares, concerning the calculation of excess volume. Even after treating the excess energy correctly, volumes show significant discrepancies between the different database predictions. These discrepancies impact geodynamic interpretations and geothermobarometrical estimations, due to the fact that the Gibbs free energy and rock density depends on mineral volumes. The imagination that pressure can vary by 4 kbar, temperature by 150°C or rock-density up to 30 %, by changing the thermodynamic database is dramatic. These enormous differences must be considered keeping in mind that calculations were done for well studied minerals (e.g. quartz and forsterite). The results play an important role for studies of geodynamic interpretations extracted from thermobarometric software packages like Perple_X, Theriak-Domino or Thermocalc. It is important to estimate the influence of the thermodynamic database on Gibbs free energy, volume and rock density. Summarizing, more experimental data will lead to a better comprehension of these discrepancies.  Berman (1988). Journal of Petrology 29, 445-522.  Holland & Powell (1998) Journal of Metamorphic Geology 16, 309-343.  Holland & Powell (2011) Journal of Metamorphic Geology 29, 333-383.  Duesterhoeft, Zaehle, De Capitani, Oberhänsli & Bousquet (2012, in prep.) Submitted to Contributions to Mineralogy and Petrology.