P–T–X controls on phase stability and composition in LTMP metabasite rocks – a thermodynamic evaluation
Identifieur interne : 000D94 ( Main/Exploration ); précédent : 000D93; suivant : 000D95P–T–X controls on phase stability and composition in LTMP metabasite rocks – a thermodynamic evaluation
Auteurs : G. Phillips [Australie] ; M. Hand [Australie] ; R. Offler [Australie]Source :
- Journal of Metamorphic Geology [ 0263-4929 ] ; 2010-06.
Descripteurs français
- Wicri :
- topic : Sciences de la terre, Pétrologie.
English descriptors
- KwdEn :
- Accretionary, Accretionary wedge, Actinolite, Albite, Alvi, Amphibole, Assemblage, Augite, Australian journal, Barometer, Basic rocks, Blackwell publishing, Bulk composition, Bulk compositions, Cation, Chlorite, Compatibility, Compatibility diagram, Compositional, Compositional data, Compositional isopleths, Current study, Dirk, Earth sciences, Eastern australia, Eld, England orogen, Epidote, Facies, Geological society, Groundmass, Hematite, Holland powell, Idioblastic, Isopleth, Kbar, Leitch, Liou, Ltmp, Ltmp metabasic rocks, Ltmp metamorphism, Maruyama, Metabasic, Metabasic rocks, Metabasite, Metabasites, Metamorphic, Metamorphic geology, Metamorphics, Metamorphism, Mineral assemblages, Mineral equilibria, Minor quartz, Modelling, Na2o, Ncfmashto, Newcastle, Orogen, Petrology, Phase diagram, Phase diagram calculations, Phase diagrams, Phase relations, Phase stability, Pumpellyite, Pumpellyite stability, Pyroxene, Quartz, Relict, Relict augite, Riebeckite, Sio2, Sodic, Sodic amphibole, System ncfmashto, Tectonic, Thermodynamic, Thermodynamic approach, Thermodynamic calculations, Tio2, Titanite.
- Teeft :
- Accretionary, Accretionary wedge, Actinolite, Albite, Alvi, Amphibole, Assemblage, Augite, Australian journal, Barometer, Basic rocks, Blackwell publishing, Bulk composition, Bulk compositions, Cation, Chlorite, Compatibility, Compatibility diagram, Compositional, Compositional data, Compositional isopleths, Current study, Dirk, Earth sciences, Eastern australia, Eld, England orogen, Epidote, Facies, Geological society, Groundmass, Hematite, Holland powell, Idioblastic, Isopleth, Kbar, Leitch, Liou, Ltmp, Ltmp metabasic rocks, Ltmp metamorphism, Maruyama, Metabasic, Metabasic rocks, Metabasite, Metabasites, Metamorphic, Metamorphic geology, Metamorphics, Metamorphism, Mineral assemblages, Mineral equilibria, Minor quartz, Modelling, Na2o, Ncfmashto, Newcastle, Orogen, Petrology, Phase diagram, Phase diagram calculations, Phase diagrams, Phase relations, Phase stability, Pumpellyite, Pumpellyite stability, Pyroxene, Quartz, Relict, Relict augite, Riebeckite, Sio2, Sodic, Sodic amphibole, System ncfmashto, Tectonic, Thermodynamic, Thermodynamic approach, Thermodynamic calculations, Tio2, Titanite.
Abstract
The stability of pumpellyite + actinolite or riebeckite + epidote + hematite (with chlorite, albite, titanite, quartz and H2O in excess) mineral assemblages in LTMP metabasite rocks is strongly dependent on bulk composition. By using a thermodynamic approach (THERMOCALC), the importance of CaO and Fe2O3 bulk contents on the stability of these phases is illustrated using P–T and P–X phase diagrams. This approach allowed P–T conditions of ∼4.0 kbar and ∼260 °C to be calculated for the growth of pumpellyite + actinolite or riebeckite + epidote + hematite assemblages in rocks containing variable bulk CaO and Fe2O3 contents. These rocks form part of an accretionary wedge that developed along the east Australian margin during the Carboniferous–Triassic New England Orogen. P–T and P–X diagrams show that sodic amphibole, epidote and hematite will grow at these conditions in Fe2O3‐saturated (6.16 wt%) metabasic rocks, whereas actinolite and pumpellyite will be stable in CaO‐rich (10.30 wt%) rocks. With intermediate Fe2O3 (∼3.50 wt%) and CaO (∼8.30 wt%) contents, sodic amphibole, actinolite and epidote can coexist at these P–T conditions. For Fe2O3‐saturated rocks, compositional isopleths for sodic amphibole (Al3+ and Fe3+ on the M2 site), epidote (Fe3+/Fe3+ + Al3+) and chlorite (Fe2+/Fe2+ + Mg) were calculated to evaluate the efficiency of these cation exchanges as thermobarometers in LTMP metabasic rocks. Based on these calculations, it is shown that Al3+ in sodic amphibole and epidote is an excellent barometer in chlorite, albite, hematite, quartz and titanite buffered assemblages. The effectiveness of these barometers decreases with the breakdown of albite. In higher‐P stability fields where albite is absent, Fe2+‐Mg ratios in chlorite may be dependent on pressure. The Fe3+/Al and Fe2+/Mg ratios in epidote and chlorite are reliable thermometers in actinolite, epidote, chlorite, albite, quartz, hematite and titanite buffered assemblages.
Url:
DOI: 10.1111/j.1525-1314.2010.00874.x
Affiliations:
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controls on phase stability and composition in LTMP metabasite rocks – a thermodynamic evaluation</title>
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<profileDesc><textClass><keywords scheme="KwdEn" xml:lang="en"><term>Accretionary</term>
<term>Accretionary wedge</term>
<term>Actinolite</term>
<term>Albite</term>
<term>Alvi</term>
<term>Amphibole</term>
<term>Assemblage</term>
<term>Augite</term>
<term>Australian journal</term>
<term>Barometer</term>
<term>Basic rocks</term>
<term>Blackwell publishing</term>
<term>Bulk composition</term>
<term>Bulk compositions</term>
<term>Cation</term>
<term>Chlorite</term>
<term>Compatibility</term>
<term>Compatibility diagram</term>
<term>Compositional</term>
<term>Compositional data</term>
<term>Compositional isopleths</term>
<term>Current study</term>
<term>Dirk</term>
<term>Earth sciences</term>
<term>Eastern australia</term>
<term>Eld</term>
<term>England orogen</term>
<term>Epidote</term>
<term>Facies</term>
<term>Geological society</term>
<term>Groundmass</term>
<term>Hematite</term>
<term>Holland powell</term>
<term>Idioblastic</term>
<term>Isopleth</term>
<term>Kbar</term>
<term>Leitch</term>
<term>Liou</term>
<term>Ltmp</term>
<term>Ltmp metabasic rocks</term>
<term>Ltmp metamorphism</term>
<term>Maruyama</term>
<term>Metabasic</term>
<term>Metabasic rocks</term>
<term>Metabasite</term>
<term>Metabasites</term>
<term>Metamorphic</term>
<term>Metamorphic geology</term>
<term>Metamorphics</term>
<term>Metamorphism</term>
<term>Mineral assemblages</term>
<term>Mineral equilibria</term>
<term>Minor quartz</term>
<term>Modelling</term>
<term>Na2o</term>
<term>Ncfmashto</term>
<term>Newcastle</term>
<term>Orogen</term>
<term>Petrology</term>
<term>Phase diagram</term>
<term>Phase diagram calculations</term>
<term>Phase diagrams</term>
<term>Phase relations</term>
<term>Phase stability</term>
<term>Pumpellyite</term>
<term>Pumpellyite stability</term>
<term>Pyroxene</term>
<term>Quartz</term>
<term>Relict</term>
<term>Relict augite</term>
<term>Riebeckite</term>
<term>Sio2</term>
<term>Sodic</term>
<term>Sodic amphibole</term>
<term>System ncfmashto</term>
<term>Tectonic</term>
<term>Thermodynamic</term>
<term>Thermodynamic approach</term>
<term>Thermodynamic calculations</term>
<term>Tio2</term>
<term>Titanite</term>
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<term>Accretionary wedge</term>
<term>Actinolite</term>
<term>Albite</term>
<term>Alvi</term>
<term>Amphibole</term>
<term>Assemblage</term>
<term>Augite</term>
<term>Australian journal</term>
<term>Barometer</term>
<term>Basic rocks</term>
<term>Blackwell publishing</term>
<term>Bulk composition</term>
<term>Bulk compositions</term>
<term>Cation</term>
<term>Chlorite</term>
<term>Compatibility</term>
<term>Compatibility diagram</term>
<term>Compositional</term>
<term>Compositional data</term>
<term>Compositional isopleths</term>
<term>Current study</term>
<term>Dirk</term>
<term>Earth sciences</term>
<term>Eastern australia</term>
<term>Eld</term>
<term>England orogen</term>
<term>Epidote</term>
<term>Facies</term>
<term>Geological society</term>
<term>Groundmass</term>
<term>Hematite</term>
<term>Holland powell</term>
<term>Idioblastic</term>
<term>Isopleth</term>
<term>Kbar</term>
<term>Leitch</term>
<term>Liou</term>
<term>Ltmp</term>
<term>Ltmp metabasic rocks</term>
<term>Ltmp metamorphism</term>
<term>Maruyama</term>
<term>Metabasic</term>
<term>Metabasic rocks</term>
<term>Metabasite</term>
<term>Metabasites</term>
<term>Metamorphic</term>
<term>Metamorphic geology</term>
<term>Metamorphics</term>
<term>Metamorphism</term>
<term>Mineral assemblages</term>
<term>Mineral equilibria</term>
<term>Minor quartz</term>
<term>Modelling</term>
<term>Na2o</term>
<term>Ncfmashto</term>
<term>Newcastle</term>
<term>Orogen</term>
<term>Petrology</term>
<term>Phase diagram</term>
<term>Phase diagram calculations</term>
<term>Phase diagrams</term>
<term>Phase relations</term>
<term>Phase stability</term>
<term>Pumpellyite</term>
<term>Pumpellyite stability</term>
<term>Pyroxene</term>
<term>Quartz</term>
<term>Relict</term>
<term>Relict augite</term>
<term>Riebeckite</term>
<term>Sio2</term>
<term>Sodic</term>
<term>Sodic amphibole</term>
<term>System ncfmashto</term>
<term>Tectonic</term>
<term>Thermodynamic</term>
<term>Thermodynamic approach</term>
<term>Thermodynamic calculations</term>
<term>Tio2</term>
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<front><div type="abstract" xml:lang="en">The stability of pumpellyite + actinolite or riebeckite + epidote + hematite (with chlorite, albite, titanite, quartz and H2O in excess) mineral assemblages in LTMP metabasite rocks is strongly dependent on bulk composition. By using a thermodynamic approach (THERMOCALC), the importance of CaO and Fe2O3 bulk contents on the stability of these phases is illustrated using P–T and P–X phase diagrams. This approach allowed P–T conditions of ∼4.0 kbar and ∼260 °C to be calculated for the growth of pumpellyite + actinolite or riebeckite + epidote + hematite assemblages in rocks containing variable bulk CaO and Fe2O3 contents. These rocks form part of an accretionary wedge that developed along the east Australian margin during the Carboniferous–Triassic New England Orogen. P–T and P–X diagrams show that sodic amphibole, epidote and hematite will grow at these conditions in Fe2O3‐saturated (6.16 wt%) metabasic rocks, whereas actinolite and pumpellyite will be stable in CaO‐rich (10.30 wt%) rocks. With intermediate Fe2O3 (∼3.50 wt%) and CaO (∼8.30 wt%) contents, sodic amphibole, actinolite and epidote can coexist at these P–T conditions. For Fe2O3‐saturated rocks, compositional isopleths for sodic amphibole (Al3+ and Fe3+ on the M2 site), epidote (Fe3+/Fe3+ + Al3+) and chlorite (Fe2+/Fe2+ + Mg) were calculated to evaluate the efficiency of these cation exchanges as thermobarometers in LTMP metabasic rocks. Based on these calculations, it is shown that Al3+ in sodic amphibole and epidote is an excellent barometer in chlorite, albite, hematite, quartz and titanite buffered assemblages. The effectiveness of these barometers decreases with the breakdown of albite. In higher‐P stability fields where albite is absent, Fe2+‐Mg ratios in chlorite may be dependent on pressure. The Fe3+/Al and Fe2+/Mg ratios in epidote and chlorite are reliable thermometers in actinolite, epidote, chlorite, albite, quartz, hematite and titanite buffered assemblages.</div>
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