Relict Majoritic Garnet Microstructures from Ultra-Deep Orogenic Peridotites in Western Norway |
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| Authors: | VAN ROERMUND H L M; DRURY M R; BARNHOORN A; DE RONDE A |
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| Institution: | VENING MEINESZ RESEARCH SCHOOL OF GEODYNAMICS, FACULTY OF EARTH SCIENCES, UTRECHT UNIVERSITY, 3508 TA UTRECHT, THE NETHERLANDS |
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| Abstract: | Protogranular, porphyroclastic and equigranular (or equant-polygonal)garnet microstructures from Mg–Cr type orogenic garnetperidotites, Otrøy, Western Gneiss Region, Norway, havebeen studied using naked eye, light-optical, electron-opticaland confocal laser (fluorescence) microscopy techniques. Protogranularand porphyroclastic garnets contain microstructural evidencefor the former existence of majoritic (or super-silicic) garnet.The microstructural evidence consists of exsolution texturesinvolving pyroxene. Two types of exsolution microstructuresoccur—needles parallel to <111>grt and interstitialgrains. The maximum volume percentage for intra-crystallinepyroxene exsolution is 2·7, and 3·6 for inter-crystallinepyroxene exsolution. The maximum pyroxene total volume percentagemeasured in one single protogranular or porphyroclastic garnetis 4·0. This value, at 1200°C, corresponds to minimumpressures of 6·4 GPa ( |
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