A thermodynamic model for silicate melt in CaO–MgO–Al2O3–SiO2 to 50 kbar and 1800 °C

Green, E. C. R.; Holland, T. J. B.; Powell, R.

doi:10.1111/j.1525-1314.2012.00982.x

Cited by 17 publications

(13 citation statements)

References 43 publications

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“…a), which is comparable to the Ol + Cpx + An + Spl = Liq melting curve that has been well calibrated for the purely magnesian compositions (Green et al. ). As NWA 3164 does not show melting structure, such as melt veins, this limit was probably not overstepped during the metamorphic evolution, while the coronas formed in the solid state.…”

Section: Resultssupporting

confidence: 69%

Evolution of the angrite parent body: Implications of metamorphic coronas in NWA 3164

Baghdadi

Godard

Jambon

2013

Meteorit & Planetary Scien

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Abstract-Northwest Africa 3164 is a coarse-grained angrite that shows reaction coronas, a unique character among achondrites. Olivine (Fo 57 ; 1.2 wt% CaO), fassaitic clinopyroxene, anorthite, and spinel account for 46-47, 28-29, 8-13, and 4-8 vol%, respectively; kamacite is an accessory phase. The spinel grains in contact with clinopyroxene are bounded by discontinuous 20 lm thick coronas of anorthite and olivine, indicating the reaction Cpx + Spl ? Ol + An (R1). In addition, irregular coronas of clinopyroxene and spinel developed around the primary anorthite in contact with primary olivine, during the reaction Ol + An ? Cpx + Spl (R2). R2 also generated clinopyroxene and spinel films between the secondary olivine and anorthite coronas produced during R1, implying that R1 preceded R2. Both are metamorphic reactions that developed in the solid state. Finally, the coronas are cross cut by lm-thick veinlets due to a late shock. A mass-balance study shows that R2 is almost the reverse of R1. The P-T metamorphic evolution of the rock, modeled by calculating a P-T isochemical diagram, indicates an equilibrium T of 940 AE 120°C at P < 0.9 GPa for the initial assemblage, followed by an increase of T up to approximately 1000-1200°C during reaction R1 and a subsequent cooling during R2. Several causes are envisaged to account for this metamorphic evolution. Contact metamorphism due to a hot magmatic intrusion in the angrite parent body is favored, as similar metamorphic coronas are well known in metamorphic terrestrial rocks. In addition to differentiation and magmatism, there is now evidence for metamorphism in the angrite parent body, which would have been a large asteroid or a planetary-sized body.

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Section: Resultssupporting

confidence: 69%

Evolution of the angrite parent body: Implications of metamorphic coronas in NWA 3164

Baghdadi

Godard

Jambon

2013

Meteorit & Planetary Scien

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“…Pending experimental developments, more insight into the MAS/CMAS lherzolite problem may be gained when the core models presented here are extended into larger systems and used in combination with other model phases, further testing the rigour of the models and their underlying assumptions. Driving model extension is the desire to model mafic and ultramafic rocks in equilibrium with melt, and for this purpose, the models presented here are used in the calibration of a mafic melt model in CMAS, in an accompanying paper (Green et al. , 2012).…”

Section: Discussionmentioning

confidence: 99%

Garnet and spinel lherzolite assemblages in MgO–Al₂O₃–SiO₂ and CaO–MgO–Al₂O₃–SiO₂: thermodynamic models and an experimental conflict

Green

Holland

Powell

et al. 2012

Journal Metamorphic Geology

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The recent publication of an updated thermodynamic dataset for petrological calculations provides an opportunity to illustrate the relationship between experimental data and the dataset, in the context of a new set of activity–composition models for several key minerals. These models represent orthopyroxene, clinopyroxene and garnet in the system CaO–MgO–Al2O3–SiO2 (CMAS), and are valid up to 50 kbar and at least 1800 °C; they are the first high‐temperature models for these phases to be developed for the Holland & Powell dataset. The models are calibrated with reference to phase‐relation data in the subsystems CaO–MgO–SiO2 (CMS) and MgO–Al2O3–SiO2 (MAS), and will themselves form the basis of models in larger systems, suitable for calculating phase equilibria in the crust and mantle. In the course of calibrating the models, it was necessary to consider the reaction orthopyroxene + clinopyroxene + spinel = garnet + forsterite in CMAS, representing a univariant transition between simple spinel and garnet lherzolite assemblages. The high‐temperature segment of this reaction has been much disputed. We offer a powerful thermodynamic argument relating this reaction to the equivalent reaction in MAS, that forces us to choose between good model fits to the data in MAS or to the more recent data in CMAS. We favour the fit to the MAS data, preserving conformity with a large body of experimental and thermodynamic data that are incorporated as constraints on the activity–composition modelling via the internally consistent thermodynamic dataset.

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“…Berman et al, 1987;de Capitani and Brown, 1987;Spear, 1988a,b;Spear and Cheney, 1989;Spear and Menard, 1989;Frey et al, 1991;Spear et al, 1991Spear et al, , 1999Connolly, 1995;Spear and Markussen, 1997;Simpson et al, 2000), especially in the form of calculated pseudosections (e.g. Spear and Selverstone, 1983;Connolly, 1990;Powell and Holland, 1990;Xu et al, 1994;Stüwe and Powell, 1995;Mahar et al, 1997;Meyre et al, 1997;White et al, 2000White et al, , 2001Guiraud et al, 2001;Kerrick and Connolly, 2001;Connolly and Petrini, 2002;Kelsey et al, 2004Kelsey et al, , 2005Kelsey et al, , 2008Connolly, 2005;Powell et al, 2005;Gaidies et al, 2006Gaidies et al, , 2008Gaidies et al, , 2011Caddick and Thompson, 2008;Diener et al, 2008a;Caddick et al, 2010;de Capitani and Petrakakis, 2010;Spear, 2010;Spear and Pyle, 2010;Taylor-Jones and Powell, 2010;Diener and Powell, 2012;Green et al, 2012;Moynihan and Pattison, 2013;…”

Section: Pet Stability Of Uht Mineral Assemblagesmentioning

confidence: 96%

On ultrahigh temperature crustal metamorphism: Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

Kelsey

Hand

2015

Geoscience Frontiers

371

285

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a b s t r a c tUltrahigh temperature (UHT) metamorphism is the most thermally extreme form of regional crustal metamorphism, with temperatures exceeding 900 C. UHT crustal metamorphism is recognised in more than 50 localities globally in the metamorphic rock record and is accepted as 'normal' in the spectrum of regional crustal processes. UHT metamorphism is typically identified on the basis of diagnostic mineral assemblages such as sapphirine þ quartz, orthopyroxene þ sillimanite AE quartz and osumilite in MgeAlrich rock compositions, now usually coupled with pseudosection-based thermobarometry using internally-consistent thermodynamic data sets and/or Al-in-Orthopyroxene and ternary feldspar thermobarometry. Significant progress in the understanding of regional UHT metamorphism in recent years includes: (1) development of a ferric iron activityecomposition thermodynamic model for sapphirine, allowing phase diagram calculations for oxidised rock compositions; (2) quantification of UHT conditions via trace element thermometry, with Zr-in-rutile more commonly recording higher temperatures than Ti-in-zircon. Rutile is likely to be stable at peak UHT conditions whereas zircon may only grow as UHT rocks are cooling. In addition, the extent to which Zr diffuses out of rutile is controlled by chemical communication with zircon; (3) more fully recognising and utilising temperature-dependent thermal properties of the crust, and the possible range of heat sources causing metamorphism in geodynamic modelling studies; (4) recognising that crust partially melted either in a previous event or earlier in a long-duration event has greater capacity than fertile, unmelted crust to achieve UHT conditions due to the heat energy consumed by partial melting reactions; (5) more strongly linking UePb geochronological data from zircon and monazite to PeT points or path segments through using Y þ REE partitioning between accessory and major phases, as well as phase diagrams incorporating Zr and REE; and (6) improved insight into the settings and factors responsible for UHT metamorphism via geodynamic forward models. These models suggest that regional UHT metamorphism is, principally, geodynamically related to subduction, coupled with elevated crustal radiogenic heat generation rates.Ó 2014, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

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A thermodynamic model for silicate melt in CaO–MgO–Al₂O₃–SiO₂ to 50 kbar and 1800 °C

Cited by 17 publications

References 43 publications

Evolution of the angrite parent body: Implications of metamorphic coronas in NWA 3164

Evolution of the angrite parent body: Implications of metamorphic coronas in NWA 3164

Garnet and spinel lherzolite assemblages in MgO–Al₂O₃–SiO₂ and CaO–MgO–Al₂O₃–SiO₂: thermodynamic models and an experimental conflict

On ultrahigh temperature crustal metamorphism: Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

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A thermodynamic model for silicate melt in CaO–MgO–Al2O3–SiO2 to 50 kbar and 1800 °C

Cited by 17 publications

References 43 publications

Evolution of the angrite parent body: Implications of metamorphic coronas in NWA 3164

Evolution of the angrite parent body: Implications of metamorphic coronas in NWA 3164

Garnet and spinel lherzolite assemblages in MgO–Al2O3–SiO2 and CaO–MgO–Al2O3–SiO2: thermodynamic models and an experimental conflict

On ultrahigh temperature crustal metamorphism: Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

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Product

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A thermodynamic model for silicate melt in CaO–MgO–Al₂O₃–SiO₂ to 50 kbar and 1800 °C

Garnet and spinel lherzolite assemblages in MgO–Al₂O₃–SiO₂ and CaO–MgO–Al₂O₃–SiO₂: thermodynamic models and an experimental conflict