Genesis of coronas in anorthosites of the upper jotun nappe, indre sogn, Norway

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Coronas in anorthosites have resulted from reactions between plagioclase and olivine. The general types are:. (I) Olivine-Opx-Cpx II-Gnt-Cpx I+Spinel. (II) Olivine-Opx-Cpx II-Hbl-Gnt with inclusions of Cpx I+Spinel. (III) Opx-Cpx II-Hbl-Gnt.The evolutionary sequence appears to be Type I → II → III. Cpx I has low Jd/Ts, whereas Cpx II has lower Al and higher Jd/Ts. The orthopyroxenes are low in Al and appear to be in equilibrium with Cpx II. The garnets resemble those of eclogites; the amphibole is pargasite.A two-stage reaction sequence is suggested:. (1) Oliv+Plag → Al-Opx+Al-Cpx+Spinel. (2) AI-Opx+Al-Cpx+Spinel+Plag → Gnt÷low-Al Opx+low-Al Cpx.Formation of amphibole followed reaction (2) in all cases.Comparisons of the mineralogy with experimental work suggest that the anorthosites crystallized below ∼ 8 kb, and that pressure increased to at least 10 kb during slow cooling. Symplectitic breakdown of garnet to orthopyroxene+plagioclase+spinel±clinopyroxene indicates a rapid drop in P at relatively high T. This decompression is probably related to the formation of the Jotun Nappes.

LanguageEnglish
Pages219-243
Number of pages25
JournalJournal of Petrology
Volume12
Issue number2
DOIs
Publication statusPublished - Jun 1971
Externally publishedYes

Fingerprint

anorthosite
folds (geology)
Olivine
Corona
Norway
nappe
spinel
coronas
corona
Garnets
Amphibole Asbestos
olivine
amphiboles
plagioclase
Mineralogy
garnets
amphibole
garnet
Breakdown
Cooling

Cite this

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title = "Genesis of coronas in anorthosites of the upper jotun nappe, indre sogn, Norway",
abstract = "Coronas in anorthosites have resulted from reactions between plagioclase and olivine. The general types are:. (I) Olivine-Opx-Cpx II-Gnt-Cpx I+Spinel. (II) Olivine-Opx-Cpx II-Hbl-Gnt with inclusions of Cpx I+Spinel. (III) Opx-Cpx II-Hbl-Gnt.The evolutionary sequence appears to be Type I → II → III. Cpx I has low Jd/Ts, whereas Cpx II has lower Al and higher Jd/Ts. The orthopyroxenes are low in Al and appear to be in equilibrium with Cpx II. The garnets resemble those of eclogites; the amphibole is pargasite.A two-stage reaction sequence is suggested:. (1) Oliv+Plag → Al-Opx+Al-Cpx+Spinel. (2) AI-Opx+Al-Cpx+Spinel+Plag → Gnt÷low-Al Opx+low-Al Cpx.Formation of amphibole followed reaction (2) in all cases.Comparisons of the mineralogy with experimental work suggest that the anorthosites crystallized below ∼ 8 kb, and that pressure increased to at least 10 kb during slow cooling. Symplectitic breakdown of garnet to orthopyroxene+plagioclase+spinel±clinopyroxene indicates a rapid drop in P at relatively high T. This decompression is probably related to the formation of the Jotun Nappes.",
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Genesis of coronas in anorthosites of the upper jotun nappe, indre sogn, Norway. / Griffin, W. L.

In: Journal of Petrology, Vol. 12, No. 2, 06.1971, p. 219-243.

Research output: Contribution to journalArticleResearchpeer-review

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