Quartz exsolution in clinopyroxene is not proof of ultrahigh pressures: Evidence from eclogites from the Eastern Blue Ridge, Southern Appalachians, U.S.A.
-
F. Zeb Page
,
E.J. Essene
Abstract
Oriented quartz needles in clinopyroxene have become one of the diagnostic indicators of ultrahighpressure (UHP) metamorphism. The presence of apparently exsolved quartz is taken as evidence of decompression of a non-stochiometric Ca.Eskola component (Ca0.5⃞0.5AlSi2O6, CaEs) that is presumed to be stable only at UHP conditions. Eclogite from the Eastern Blue Ridge, North Carolina, contains clinopyroxene (Jd20CaTs5Ac5CaEs0Di65Hd5) with oriented needles of quartz and calcic amphibole that appear to have exsolved together. The quartz + amphibole intergrowths are surrounded by 1.5 µm haloes of neoformed pyroxene (Jd10CaTs10Ac5CaEs0Di70Hd5). The modes of quartz, amphibole, and clinopyroxene haloes were determined using BSE images, and reintegrated with the host clinopyroxene. Viewing the quartz and amphibole needles down the c-axis of the pyroxene host provides a better estimate of their proportions than in prismatic sections. Reintegrated pyroxene compositions were nearly identical to the analyzed host pyroxene with no CaEs component. Clinopyroxene with CaEs solid solution has been repeatedly synthesized at UHP conditions. However, examination of the phase equilibria usually cited as evidence for CaEs stability at conditions of ≥25 kbar shows that clinopyroxene with 10 mol% CaEs is stable well within the quartz field, and provides a pressure minimum similar to the albite = jadeite + quartz barometer. Exsolution of quartz and associated amphibole is commonplace in clinopyroxene from the Blue Ridge eclogite that lacks coesite or other evidence for UHP metamorphism. The presence of a diluted (5.10%) CaEs component in clinopyroxene does not require UHP conditions.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- A synthesis of systematic mineralogy
- Oxidation/alteration of pentlandite and pyrrhotite surfaces at pH 9.3: Part 1. Assignment of XPS spectra and chemical trends
- Oxidation of pentlandite and pyrrhotite surfaces at pH 9.3: Part 2. Effect of xanthates and dissolved oxygen
- X-ray Rietveld refinement and FTIR spectra of synthetic (Si,Ge)-richterites
- Influence of crystal chemistry on ideal plastic shear anisotropy in forsterite: First principle calculations
- High-temperature Mössbauer study of Fe-substituted mullite
- Pressure and temperature-dependence of water solubility in Fe-free wadsleyite
- Quartz exsolution in clinopyroxene is not proof of ultrahigh pressures: Evidence from eclogites from the Eastern Blue Ridge, Southern Appalachians, U.S.A.
- The visible and infrared spectral properties of jarosite and alunite
- Wakabayashilite, [(As,Sb)6S9][As4S5]: Crystal structure, pseudosymmetry, twinning, and revised chemical formula
- Compression of albite, NaAlSi3O8
- Effect of polymorphic transition on oxygen isotope fractionation between aragonite, calcite, and water: A low-temperature experimental study
- Effect of current density on the electron microprobe analysis of alkali aluminosilicate glasses
- A high-pressure polytypic transformation in type-I chlorite
- Experimental determination of crystal growth rates in highly supercooled aluminosilicate liquids: Implications for rate-controlling processes
- P-V equation of State, thermal expansion, and P-T stability of synthetic zincochromite (ZnCr2O4 spinel)
- Niksergievite, [Ba1.33Ca0.67Al(CO3)(OH)4][Al2(AlSi3O10)(OH)2]·nH2O, a new phyllosilicate related to the surite-ferrisurite series
- The crystal-chemistry of holmquistites: Ferroholmquistite from Greenbushes (Western Australia) and hints for compositional constraints in BLi amphiboles
- Dissakisite-(La) from the Ulten zone peridotite (Italian Eastern Alps): A new end-member of the epidote group
- Mazzite-Na, a new zeolite from Boron, California: Its description and crystal structure
- Low-temperature illitization of smectite in the late eocene and early oligocene of the Isle of Wight (Hampshire basin), U.K.
- First reported sedimentary occurrence of berlinite (AlPO4) in phosphate-bearing sediments from Cioclovina Cave, RomaniaComment
- Optical and near infrared spectra of ringwoodite to 21.5 GPa: Implications for radiative heat transport in the mantle
- Letter. Observation of nano-clustered calcite growth via a transient phase mediated by organic polyanions: A close match for biomineralization
- Letter. Aluminum coordination and the densification of high-pressure aluminosilicate glasses
- Letter. Crystal chemistry of a high-pressure C2/c clinopyroxene with six-coordinated silicon
Articles in the same Issue
- A synthesis of systematic mineralogy
- Oxidation/alteration of pentlandite and pyrrhotite surfaces at pH 9.3: Part 1. Assignment of XPS spectra and chemical trends
- Oxidation of pentlandite and pyrrhotite surfaces at pH 9.3: Part 2. Effect of xanthates and dissolved oxygen
- X-ray Rietveld refinement and FTIR spectra of synthetic (Si,Ge)-richterites
- Influence of crystal chemistry on ideal plastic shear anisotropy in forsterite: First principle calculations
- High-temperature Mössbauer study of Fe-substituted mullite
- Pressure and temperature-dependence of water solubility in Fe-free wadsleyite
- Quartz exsolution in clinopyroxene is not proof of ultrahigh pressures: Evidence from eclogites from the Eastern Blue Ridge, Southern Appalachians, U.S.A.
- The visible and infrared spectral properties of jarosite and alunite
- Wakabayashilite, [(As,Sb)6S9][As4S5]: Crystal structure, pseudosymmetry, twinning, and revised chemical formula
- Compression of albite, NaAlSi3O8
- Effect of polymorphic transition on oxygen isotope fractionation between aragonite, calcite, and water: A low-temperature experimental study
- Effect of current density on the electron microprobe analysis of alkali aluminosilicate glasses
- A high-pressure polytypic transformation in type-I chlorite
- Experimental determination of crystal growth rates in highly supercooled aluminosilicate liquids: Implications for rate-controlling processes
- P-V equation of State, thermal expansion, and P-T stability of synthetic zincochromite (ZnCr2O4 spinel)
- Niksergievite, [Ba1.33Ca0.67Al(CO3)(OH)4][Al2(AlSi3O10)(OH)2]·nH2O, a new phyllosilicate related to the surite-ferrisurite series
- The crystal-chemistry of holmquistites: Ferroholmquistite from Greenbushes (Western Australia) and hints for compositional constraints in BLi amphiboles
- Dissakisite-(La) from the Ulten zone peridotite (Italian Eastern Alps): A new end-member of the epidote group
- Mazzite-Na, a new zeolite from Boron, California: Its description and crystal structure
- Low-temperature illitization of smectite in the late eocene and early oligocene of the Isle of Wight (Hampshire basin), U.K.
- First reported sedimentary occurrence of berlinite (AlPO4) in phosphate-bearing sediments from Cioclovina Cave, RomaniaComment
- Optical and near infrared spectra of ringwoodite to 21.5 GPa: Implications for radiative heat transport in the mantle
- Letter. Observation of nano-clustered calcite growth via a transient phase mediated by organic polyanions: A close match for biomineralization
- Letter. Aluminum coordination and the densification of high-pressure aluminosilicate glasses
- Letter. Crystal chemistry of a high-pressure C2/c clinopyroxene with six-coordinated silicon
