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Chronology of early Archaean granite-greenstone evolution in the Barberton Mountain Land, South Africa, based on precise dating by single zircon evaporationPrecise Pb-207/Pb-206 single zircon evaporating ages are reported for low-grade felsic metavolcanic rocks within the Onverwacht and Fig Tree Groups of the Barberton Greenstone Belt (BGB), South Africa, as well as for granitoid plutons bordering the belt. Dacitic tuffs of the Hooggenoeg Formation in the upper part of the Onverwacht Group are shown to yield ages between 3445 + or - 3 and 3416 + or - 5 Ma and to contain older crustal components represented by a 3504 + or - 4 Ma old zircon xenocryst. Fig Tree dacitic tuffs and agglomerates have euhedral zircons between 3259 + or - 3 Ma in age which are interpreted to reflect the time of crystallization. The comagmatic relationships between greenstone felsic volcanic units and the surrounding plutonic suites are keynoted. The data adduced show that the Onverwacht and Fig Tree felsic units have distinctly different ages and thus do not constitute a single, tectonically repeated unit as proposed by others. It is argued that conventional multigrain zircon dating may not accurately identify the time of felsic volcanic activity in ancient greenstones, and that the BGB in the Kaapval craton of southern Africa and greenstones in the Pilbara Block of Western Australia may have been part of a larger crustal unit in early Archaean times.
Document ID
19910055021
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Kruener, Alfred
(Mainz, Universitaet Federal Republic of Germany, United States)
Byerly, Gary R.
(Louisiana State University Baton Rouge, United States)
Lowe, Donald R.
(Stanford University CA, United States)
Date Acquired
August 15, 2013
Publication Date
April 1, 1991
Publication Information
Publication: Earth and Planetary Science Letters
Volume: 103
Issue: 4-Jan
ISSN: 0012-821X
Subject Category
Geophysics
Accession Number
91A39644
Funding Number(s)
CONTRACT_GRANT: NAG9-344
CONTRACT_GRANT: NSF EAR-89-14720
Distribution Limits
Public
Copyright
Other

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