The Ca-Eskola component in eclogitic clinopyroxene as a function of pressure, temperature and bulk composition: an experimental study to 15 GPa with possible implications for the formation of oriented SiO2-inclusions in omphacite

Juergen Konzett, Daniel J. Frost, Alexander Proyer, Peter Ulmer

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Abstract

Experiments have been conducted in the P-T range 2.5-15 GPa and 850-1,500 degrees C using bulk compositions in the systems SiO2-TiO2-Al2O3-Fe2O3-FeO-MnO-MgO-CaO-Na2O-K2O-P2O5 and SiO2-TiO2-Al2O3-MgO-CaO-Na2O to investigate the Ca-Eskola (CaEs Ca-0.5 square 0.5AlSi2O6) content of clinopyroxene in eclogitic assemblages containing garnet + clinopyroxene + SiO2 +/- TiO2 +/- kyanite as a function of P, T, and bulk composition. The results show that CaEsss in clinopyroxene increases with increasing T and is strongly bulk composition dependent whereby high CaEs-contents are favoured by bulk compositions with high normative anorthite and low diopside contents. In this study, a maximum of 18 mol% CaEsss was found at 6 GPa and 1,350 degrees C in a kyanite-eclogite assemblage garnet + clinopyroxene + kyanite + rutile + coesite. By comparison, no significant increase in CaEsss with increasing P could be observed. If the formation of oriented SiO2-rods frequently observed in eclogititc clinopyroxenes is due to the retrogressive breakdown of a CaEs-component then these textures are a cooling rather than a decompression phenomenon and are most likely to be found in kyanite-bearing eclogites cooled from temperatures >= 750 degrees C. The presence of clinopyroxene with approx. 4 mol% CaEsss in an experiment conducted at 2.5 GPa/850 degrees C confirms earlier suggestions based on field data that vacancy-rich clinopyroxenes are not necessarily restricted to ultrahigh pressure metamorphic conditions.
Original languageEnglish
Pages (from-to)215-228
Number of pages14
JournalContributions to Mineralogy and Petrology
Volume155
Issue number2
DOIs
Publication statusPublished - 2008

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omphacite
clinopyroxene
kyanite
experimental study
inclusions
phosphorus pentoxide
Garnets
Chemical analysis
garnets
Bearings (structural)
temperature
coesite
garnet
eclogite
Temperature
pressure reduction
rutile
anorthite
Vacancies
suggestion

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title = "The Ca-Eskola component in eclogitic clinopyroxene as a function of pressure, temperature and bulk composition: an experimental study to 15 GPa with possible implications for the formation of oriented SiO2-inclusions in omphacite",
abstract = "Experiments have been conducted in the P-T range 2.5-15 GPa and 850-1,500 degrees C using bulk compositions in the systems SiO2-TiO2-Al2O3-Fe2O3-FeO-MnO-MgO-CaO-Na2O-K2O-P2O5 and SiO2-TiO2-Al2O3-MgO-CaO-Na2O to investigate the Ca-Eskola (CaEs Ca-0.5 square 0.5AlSi2O6) content of clinopyroxene in eclogitic assemblages containing garnet + clinopyroxene + SiO2 +/- TiO2 +/- kyanite as a function of P, T, and bulk composition. The results show that CaEsss in clinopyroxene increases with increasing T and is strongly bulk composition dependent whereby high CaEs-contents are favoured by bulk compositions with high normative anorthite and low diopside contents. In this study, a maximum of 18 mol{\%} CaEsss was found at 6 GPa and 1,350 degrees C in a kyanite-eclogite assemblage garnet + clinopyroxene + kyanite + rutile + coesite. By comparison, no significant increase in CaEsss with increasing P could be observed. If the formation of oriented SiO2-rods frequently observed in eclogititc clinopyroxenes is due to the retrogressive breakdown of a CaEs-component then these textures are a cooling rather than a decompression phenomenon and are most likely to be found in kyanite-bearing eclogites cooled from temperatures >= 750 degrees C. The presence of clinopyroxene with approx. 4 mol{\%} CaEsss in an experiment conducted at 2.5 GPa/850 degrees C confirms earlier suggestions based on field data that vacancy-rich clinopyroxenes are not necessarily restricted to ultrahigh pressure metamorphic conditions.",
author = "Juergen Konzett and Frost, {Daniel J.} and Alexander Proyer and Peter Ulmer",
year = "2008",
doi = "10.1007/s00410-007-0238-0",
language = "English",
volume = "155",
pages = "215--228",
journal = "Contributions to Mineralogy and Petrology",
issn = "0010-7999",
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TY - JOUR

T1 - The Ca-Eskola component in eclogitic clinopyroxene as a function of pressure, temperature and bulk composition: an experimental study to 15 GPa with possible implications for the formation of oriented SiO2-inclusions in omphacite

AU - Konzett, Juergen

AU - Frost, Daniel J.

AU - Proyer, Alexander

AU - Ulmer, Peter

PY - 2008

Y1 - 2008

N2 - Experiments have been conducted in the P-T range 2.5-15 GPa and 850-1,500 degrees C using bulk compositions in the systems SiO2-TiO2-Al2O3-Fe2O3-FeO-MnO-MgO-CaO-Na2O-K2O-P2O5 and SiO2-TiO2-Al2O3-MgO-CaO-Na2O to investigate the Ca-Eskola (CaEs Ca-0.5 square 0.5AlSi2O6) content of clinopyroxene in eclogitic assemblages containing garnet + clinopyroxene + SiO2 +/- TiO2 +/- kyanite as a function of P, T, and bulk composition. The results show that CaEsss in clinopyroxene increases with increasing T and is strongly bulk composition dependent whereby high CaEs-contents are favoured by bulk compositions with high normative anorthite and low diopside contents. In this study, a maximum of 18 mol% CaEsss was found at 6 GPa and 1,350 degrees C in a kyanite-eclogite assemblage garnet + clinopyroxene + kyanite + rutile + coesite. By comparison, no significant increase in CaEsss with increasing P could be observed. If the formation of oriented SiO2-rods frequently observed in eclogititc clinopyroxenes is due to the retrogressive breakdown of a CaEs-component then these textures are a cooling rather than a decompression phenomenon and are most likely to be found in kyanite-bearing eclogites cooled from temperatures >= 750 degrees C. The presence of clinopyroxene with approx. 4 mol% CaEsss in an experiment conducted at 2.5 GPa/850 degrees C confirms earlier suggestions based on field data that vacancy-rich clinopyroxenes are not necessarily restricted to ultrahigh pressure metamorphic conditions.

AB - Experiments have been conducted in the P-T range 2.5-15 GPa and 850-1,500 degrees C using bulk compositions in the systems SiO2-TiO2-Al2O3-Fe2O3-FeO-MnO-MgO-CaO-Na2O-K2O-P2O5 and SiO2-TiO2-Al2O3-MgO-CaO-Na2O to investigate the Ca-Eskola (CaEs Ca-0.5 square 0.5AlSi2O6) content of clinopyroxene in eclogitic assemblages containing garnet + clinopyroxene + SiO2 +/- TiO2 +/- kyanite as a function of P, T, and bulk composition. The results show that CaEsss in clinopyroxene increases with increasing T and is strongly bulk composition dependent whereby high CaEs-contents are favoured by bulk compositions with high normative anorthite and low diopside contents. In this study, a maximum of 18 mol% CaEsss was found at 6 GPa and 1,350 degrees C in a kyanite-eclogite assemblage garnet + clinopyroxene + kyanite + rutile + coesite. By comparison, no significant increase in CaEsss with increasing P could be observed. If the formation of oriented SiO2-rods frequently observed in eclogititc clinopyroxenes is due to the retrogressive breakdown of a CaEs-component then these textures are a cooling rather than a decompression phenomenon and are most likely to be found in kyanite-bearing eclogites cooled from temperatures >= 750 degrees C. The presence of clinopyroxene with approx. 4 mol% CaEsss in an experiment conducted at 2.5 GPa/850 degrees C confirms earlier suggestions based on field data that vacancy-rich clinopyroxenes are not necessarily restricted to ultrahigh pressure metamorphic conditions.

U2 - 10.1007/s00410-007-0238-0

DO - 10.1007/s00410-007-0238-0

M3 - Article

VL - 155

SP - 215

EP - 228

JO - Contributions to Mineralogy and Petrology

JF - Contributions to Mineralogy and Petrology

SN - 0010-7999

IS - 2

ER -