Mineral equilibria modelling for earth processes

Using calculated chemical potential relationships to account for replacement of kyanite by symplectite in high pressure granulites

JA Baldwin, R Powell, RW White, P Stipska

2015-04-01

Calculated mineral equilibria are used to account for the formation of sapphirine-plagioclase, spinel-plagioclase and corundum-pla..

Interpreting zirconium-in-rutile thermometric

K Taylor-Jones, R Powell

2015-02-01

At first sight, experimental results and observations on rocks suggest that the Zr content in rutile, where equilibrated with quar..

The effect of Mn on mineral stability in metapelites revisited: new a-x relations for manganese-bearing minerals

RW White, R Powell, TE Johnson

2014-10-01

The a-x relations recently presented in White et al. (, Journal of Metamorphic Geology, 32, 261-286) are extended to include MnO. ..

New mineral activity-composition relations for thermodynamic calculations in metapelitic systems

RW White, R Powell, TJB Holland, TE Johnson, ECR Green

2014-04-01

New activity-composition (a-x) relations for minerals commonly occurring in metapelites are presented for use with the internally ..

On parameterizing thermodynamic descriptions of minerals for petrological calculations

R Powell, RW White, ECR Green, TJB Holland, JFA Diener

2014-04-01

A new regularization approach, termed micro-φ{symbol}, is outlined for parameterizing activity-composition (a-x) relations and oth..

Using equilibrium thermodynamics in the study of metasomatic alteration, illustrated by an application to serpentinites

KA Evans, R Powell, BR Frost

2013-05-01

Metasomatic rocks, in which mineralogical change is driven by infiltration of an externally-derived fluid, are challenging for the..

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

ECR Green, TJB Holland, R Powell

2012-08-01

A fully thermodynamic model for mafic melt in CaO-MgO-Al 2O 3-SiO 2 (CMAS) has been calibrated, for calculation of melting equilib..

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

ECR Green, TJB Holland, R Powell, RW White

2012-08-01

The recent publication of an updated thermodynamic dataset for petrological calculations provides an opportunity to illustrate the..

Revised activity-composition models for clinopyroxene and amphibole

JFA Diener, R Powell

2012-02-01

Recent activity-composition models for clinopyroxene and amphibole are revised to provide better consistency with observed phase r..

Stability of sapphirine plus quartz in the oxidized rocks of the Wilson Lake terrane, Labrador: calculated equilibria in NCKFMASHTO

FJ Korhonen, R Powell, JH Stout

2012-01-01

The equilibrium coexistence of sapphirine+quartz is inferred to record temperatures in excess of 980°C, based on the stability of ..

An improved and extended internally consistent thermodynamic dataset for phases of petrological interest, involving a new equation of state for solids

TJB Holland, R Powell

2011-04-01

The thermodynamic properties of 254 end-members, including 210 mineral end-members, 18 silicate liquid end-members and 26 aqueous ..

On the interpretation of retrograde reaction textures in granulite facies rocks

RW White, R Powell

2011-01-01

Retrograde reaction textures, such as partial pseudomorphs, coronae and symplectic coronae are a relatively common feature of gran..

Progress in linking accessory mineral growth and breakdown to major mineral evolution in metamorphic rocks: a thermodynamic approach in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-ZrO2 system

DE Kelsey, R Powell

2011-01-01

Activity-composition (a-x) models have been generated for zirconium-bearing haplogranitic silicate melt and garnet from experiment..

Calculated phase equilibria for a morb composition in a P-T range, 450-650 degrees C and 18-28 kbar: the stability of eclogite

G Rebay, R Powell, JFA Diener

2010-08-01

Lower temperature eclogite (with T = 600 °C) represents a significant part of the occurrences of eclogite in orogenic belts. 'True..

Influence of ferric iron on the stability of mineral assemblages

JFA Diener, R Powell

2010-08-01

Ferric iron is present in all metamorphic rocks and has the ability to significantly affect their phase relations. However, the in..

Retrograde melt-residue interaction and the formation of near-anhydrous leucosomes in migmatites

RW White, R Powell

2010-08-01

Considering physical segregation of melt from its residue, the chemical potentials of the components (oxides) are the same in both..

The role of exhumation in metamorphic dehydration and fluid production

Julie Vry, Roger Powell, Kenneth M Golden, Kellen Petersen

2010-01-01

When mountain belts form, crustal rocks undergo metamorphism, resulting in the breakdown of volatile-bearing minerals and the rele..

Using calculated chemical potential relationships to account for coronas around kyanite: an example from the Bohemian Massif

P Stipska, R Powell, RW White, JA Baldwin

2010-01-01

Corona textures around kyanite, involving for example zoned plagioclase separating kyanite from the matrix, reflect the instabilit..

Formation of gold deposits: Review and evaluation of the continuum model

G Neil Phillips, Roger Powell

2009-05-01

The continuum model has been one of the more widely advocated genetic models for 'gold-only' deposits such as those found in Archa..

Quantitative phase petrology of cordierite-orthoamphibole gneisses and related rocks

JFA Diener, R Powell, RW White

2008-10-01

Cordierite-orthoamphibole gneisses and rocks of similar composition commonly contain low-variance mineral assemblages that can pro..

Contrasting metamorphic histories of lenses of high-pressure rocks and host migmatites with a flat orogenic fabric (Bohemian Massif, Czech Republic): a result of tectonic mixing within horizontal crustal flow?

P Stipska, K Schulmann, R Powell

2008-08-01

Migmatites with sub-horizontal fabrics at the eastern margin of the Variscan orogenic root in the Bohemian Massif host lenses of e..

Granulite facies metamorphism and subsolidus fluid-absent reworking, Strangways Range, Arunta Block, central Australia

JFA Diener, RW White, R Powell

2008-08-01

Orthopyroxene-rich quartz-saturated granulites of the Strangways Range, Arunta Block, central Australia, record evidence of two hi..

Ultrahigh-pressure garnet peridotites from the devolatilization of sea-floor hydrated ultramafic rocks

J-J Yang, R Powell

2008-08-01

Garnet peridotites occur in quartzofeldspathic gneisses in the Northern Qaidam Mountains, western China. They are rich in Mg and C..

Calculated phase equilibria involving chemical potentials to investigate the textural evolution of metamorphic rocks

RW White, R Powell, JA Baldwin

2008-02-01

Evolving pressure-temperature conditions during metamorphism drive changes in the stable mineral assemblage, mineral proportions a..

Garnet-clinopyroxene intermediate granulites in the St. Leonhard massif of the Bohemian Massif: ultrahigh-temperature metamorphism at high pressure or not?

M Racek, P Stipska, R Powell

2008-02-01

Garnet-clinopyroxene intermediate granulites occur as thin layers within garnet-kyanite-K-feldspar felsic granulites of the St. Le..

Establishing the P-T path for Alpine Schist, Southern Alps near Hokitika, New Zealand

JK Vry, R Powell, J Williams

2008-01-01

Pressure-temperature pseudosections for 'greyschist' (metamorphosed greywacke and argillite) from the Alpine Schist (Haast Schist ..

Transforming mylonitic metagranite by open-system interactions during melt flow

P Hasalova, P Stipska, R Powell, K Schulmann, V Janousek, O Lexa

2008-01-01

Gneisses and migmatites of the Gföhl unit (Moldanubian Zone, Bohemian Massif) range from banded mylonitic orthogneiss with recryst..

Formation of eclogite, and reaction during exhumation to mid-crustal levels, Snowbird tectonic zone, western Canadian Shield

JA Baldwin, R Powell, ML Williams, P Goncalves

2007-12-01

A re-evaluation of the P-T history of eclogite within the East Athabasca granulite terrane of the Snowbird tectonic zone, northern..

Understanding K-feldspar Ar-40/Ar-39 data: reconciling models, methods and microtextures

Sandra Mclaren, W James Dunlap, Roger Powell

2007-09-01

Several descriptions of argon diffusion in K-feldspar have been developed, including the quantitative multiple-diffusion-domain (M..

A new thermodynamic model for clino- and orthoamphiboles in the system Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O-O

JFA Diener, R Powell, RW White, TJB Holland

2007-08-01

A recent thermodynamic model for the Na-Ca clinoamphiboles in the system Na2O-CaO-FeO-MgO-Al2O3-SiO2 -H2O-O (NCFMASHO), is improve..

The pressure dependence of the zirconium-in-rutile thermometer

HS Tomkins, R Powell, DJ Ellis

2007-08-01

The solubility of ZrO2 in rutile is strongly temperature-dependent and has been identified as a potentially powerful thermometer w..

DES-code: A metacode to aid calculation of the chemical potential of aqueous solutions at elevated temperatures and pressures

Katy Evans, Roger Powell

2007-06-01

The DH-ASF (Debye-Hückel-asymmetric formalism) model is a recently developed activity-composition model that can be used to calcul..

Progress relating to calculation of partial melting equilibria for metapelites

RW White, R Powell, TJB Holland

2007-06-01

Improved activity-composition relationships for biotite, garnet and silicate liquid are used to construct updated P-T grids and ps..

A method for activity calculations in saline and mixed solvent solutions at elevated temperature and pressure: A framework for geological phase equilibria calculations

Katy Evans, Roger Powell

2006-11-15

Quantitative thermodynamic calculations that involve aqueous fluids have proved difficult because of the complexity of the interac..

The lawsonite paradox: a comparison of field evidence and mineral equilibria modelling

GL Clarke, R Powell, JA Fitzherbert

2006-10-01

Lawsonite equilibria are predicted to occur over a broad P-T spectrum developed during subduction, yet lawsonite-bearing assemblag..

Evolution of H2O content in a polymetamorphic terrane: The Plattengneiss Shear Zone (Koralpe, Austria)

V Tenczer, R Powell, K Stuwe

2006-05-01

The Koralpe of the Eastern European Alps experienced high-temperature/ low-pressure metamorphism (∼650 °C and 6.5 kbar) during the..

Separate or shared metamorphic histories of eclogites and surrounding rocks? An example from the Bohemian Massif

P Stipska, P Pitra, R Powell

2006-04-01

Eclogite boudins occur within an orthogneiss sheet enclosed in a Barrovian metapelite-dominated volcano-sedimentary sequence withi..

A thermodynamic model for Ca-Na clinoamphiboles in Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O-O for petrological calculations

J Dale, R Powell, RW White, FL Elmer, TJB Holland

2005-10-01

A calibration is presented for an activity-composition model for amphiboles in the system Na2O-CaO-FeO-MgO-Al2 O3-SiO2-H2O-O (NCFM..

Modelling of mineral equilibria in ultrahigh-temperature metamorphic rocks from the Anapolis-Itaucu Complex, central Brazil

JA Baldwin, R Powell, M Brown, R Moraes, RA Fuck

2005-09-01

A new quantitative approach to constraining mineral equilibria in sapphirine-bearing ultrahigh-temperature (UHT) granulites throug..