Finding of talc– and kyanite–bearing amphibolite from the Paleoproterozoic Usagaran Belt, Tanzania

We report a newly discovered assemblage of talc–kyanite in an amphibolite from the Isimani Suite of the Paleoproterozoic Usagaran Belt, central Tanzania. The amphibolite is characterized by the mineral assemblage of clinoamphibole, kyanite, talc with minor rutile, quartz, dolomite, and rare barite....

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Bibliographic Details
Published in:Journal of Mineralogical and Petrological Sciences 2018, Vol.113(6), pp.316-321
Main Authors: MORI, Keiko, TSUJIMORI, Tatsuki, BONIFACE, Nelson
Format: Article
Language:English
Subjects:
Amphibolite
Amphibolites
Barite
Bearing
Carbon dioxide
Dolomite
Dolostone
Earth
High–pressure metamorphism
Isotopes
Kyanite
Metamorphism
Metamorphism (geology)
Mineral assemblages
Modelling
Oxidation
Rutile
Talc
Tanzania
Usagaran Belt
Valence
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Summary:We report a newly discovered assemblage of talc–kyanite in an amphibolite from the Isimani Suite of the Paleoproterozoic Usagaran Belt, central Tanzania. The amphibolite is characterized by the mineral assemblage of clinoamphibole, kyanite, talc with minor rutile, quartz, dolomite, and rare barite. The high Fe3+/(Fe3+ + Fe2+) ratio (0.48–0.80) of clinoamphibole and the presence of sulfate (barite) indicate a very–high oxidation state during metamorphism. P–T pseudosection modelling predicts that the studied talc– and kyanite–bearing amphibolites formed at high–pressure conditions (P > 1.0 GPa). Moreover, the modelling suggests formation of talc + kyanite + clinoamphibole at a highly oxidizing condition with CO2 fluid. This talc–kyanite association provides an index of high–pressure metamorphism of the Usagaran Belt and marks the oldest record of the talc–kyanite association in regional metamorphism in the Earth’s history.
ISSN:1345-6296
1349-3825
DOI:10.2465/jmps.180713