Dear Yong-Fei,
What P-T conditions range are we talking about?
Best
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Jaroslaw Majka Ph.D., Docent
Department of Earth Sciences
Uppsala University
Villavägen 16
SE-752 36 Uppsala, Sweden
Mobile: (+46) 702823330
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From: Metamorphic Studies Group [[log in to unmask]] on behalf of Yong-Fei?Zheng [[log in to unmask]]
Sent: Thursday, August 29, 2019 4:38 PM
To: [log in to unmask]
Subject: Re: [geo-metamorphism] Eclogite question
Dear eclogite colleagues,
I was informed that during eclogitization of mafic rocks, plagioclase is not stable any more with decomposition of albite to jadeite and quartz, and diopside is transformed to omphacite by incorporating jadeite. In this regard, the mineralogical reaction of Ab to Jd + Qtz marks the lower limit of eclogite facies metamorphism. Furthermore, it is not only the boundary between eclogite and garnet amphibolite at lower temperatures of <900°C for the retrogression of pyroxene to amphibole (hydration) but also the boundary between eclogite and garnet pyroxenite at higher temperatures of >900°C for the exsolution of Na cations from omphacite. However, I am puzzled now by metamorphic conditions for the formation of some eclogites in a P-T range below the metamorphic reaction of albite to jadeite and quartz. Are such eclogites really produced by eclogitization at lower pressures but slightly higher temperatures? Or are they just metastable at reduced pressures? Any comment is welcome.
Best regards,
Yong-Fei
--
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Dr. Yong-Fei Zheng
Professor of Geochemistry
School of Earth and Space Sciences
University of Science and Technology of China
Hefei 230026, China
Tel & Fax: +86 551 63603554
Email: [log in to unmask]<mailto:[log in to unmask]>
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