| Reference Type | Journal (article/letter/editorial) |
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| Title | Exsolution structures in calcic pyroxenes from the Bjerkreim-Sokndal lopolith, SW Norway |
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| Journal | Mineralogical Magazine | ISSN | 0026-461X |
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| Authors | Rietmeijer, F. J. M. | Author |
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| Champness, P. E. | Author |
| Year | 1982 | Volume | 45 |
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| Issue | 337 |
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| Publisher | Mineralogical Society |
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| Download URL | https://rruff.info/doclib/MinMag/Volume_45/45-337-11.pdf+ |
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| DOI | doi:10.1180/minmag.1982.045.337.02Search in ResearchGate |
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| Generate Citation Formats |
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| Mindat Ref. ID | 3312 | Long-form Identifier | mindat:1:5:3312:5 |
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| GUID | 0 |
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| Full Reference | Rietmeijer, F. J. M., Champness, P. E. (1982) Exsolution structures in calcic pyroxenes from the Bjerkreim-Sokndal lopolith, SW Norway. Mineralogical Magazine, 45 (337) 11-24 doi:10.1180/minmag.1982.045.337.02 |
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| Plain Text | Rietmeijer, F. J. M., Champness, P. E. (1982) Exsolution structures in calcic pyroxenes from the Bjerkreim-Sokndal lopolith, SW Norway. Mineralogical Magazine, 45 (337) 11-24 doi:10.1180/minmag.1982.045.337.02 |
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| In | (1982) Mineralogical Magazine Vol. 45 (337) Mineralogical Society |
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| Abstract/Notes | AbstractIron-rich (Fs:En βΌ0.8) calcic pyroxenes that have been subjected to granulite-facies metamorphism contain up to seven generations of exsolution lamellae. They can be grouped into four stages. In stage 1 pigeonite exsolved parallel to β001β and β100β (where βhklβ signifies βΌ (hkl)) and mostly inverted later to orthopyroxene. During stage 2 orthopyroxene exsolved parallel to (100), while during stage 3 orthopyroxene was quickly followed by metastable β001β pigeonite. The stage 3 precipitates clearly grew and thickened together for some time. During stage 4 a β100β pigeonite was exsolved. The stage 3 and 4 precipitates show evidence of reheating, dissolution and later, renewed growth. Sometimes orthopyroxenes of stage 3 have crossed a β001β pigeonite lamella and caused it to invert by a shear mechanism.Chemical analysis shows no rotation of the tie lines between Ca-rich and Ca-poor phases, in contrast to previous studies of Skaergaard and Bushveld pyroxenes. The geothermometers of Wood and Banno (1973) and Wells (1977) indicate solidus temperatures of about 850Β°C and 900Β°C respectively, but the geothermometers were found to be unsuitable for subsolidus conditions. We estimate the pressure to have been about 9 kbar during solidification. Estimates of nucleation temperatures obtained from the orientations of the exsolved lamellae (Robinson et al., 1977) were 850β700Β°C for stage 1, and 600β400Β°C for stage 3. We believe this geothermometer to be unreliable for the low temperatures involved in stage 4. |
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