U-Pb ages on single detrital zircon grains from the Witwatersrand Basin, South Africa: Constraints on the age of sedimentation and on the evolution of granites adjacent to the basin

Journal Article · Tue May 01 00:00:00 EDT 1990 · Journal of Geology; (USA)

DOI:https://doi.org/10.1086/629407· OSTI ID:6224354

Robb, L J ^[1]; Davis, D W; Kamo, S L ^[2]

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1. Univ. of the Witwatersrand, Johannesburg (South Africa)
2. Royal Ontario Museum, Toronto (Canada)

U-Pb ages of single detrital zircon grains from various stratigraphic horizons in the Dominion and Witwatersrand sequences provide constraints on the maximum age of sedimentation as well as indicating the pattern of age distribution in the (granitoid) source area providing detritus into the basin. Zircon ages in the Dominion sediments range from 3,191-3,105 Ma with a geometric mean ({bar X}) t 3,153 Ma. Those from the lower Witwatersrand sediments (West Rand Group) range from 3,305-3,044 Ma with {bar X} = 3,097 Ma, and zircons in the upper Witwatersrand sediments (Central Rand Group) are between 3,207-2,894 Ma old with {bar X} = 3,053 Ma. Ages of detrital zircons generally decrease upward in the stratigraphic record, and <3,000 Ma old zircons are only found in the Central Rand Group. This trend implies that younger granites may have formed at some time subsequent to lower Witwatersrand deposition, or that continued erosion of the hinterland resulted in the unroofing of successively younger granites. The wide spread of zircon ages (411 Ma) evident in the data set indicates that granites formed virtually continuously between circa 3,300-2.900 Ma in the Witwatersrand source area. Of the zircon ages 45% fall within 30 m.y. of the geometric mean of the total data set, suggesting that a major crust-forming event occurred at 3,073 {plus minus} 30 Ma. Granitoids in the source area can be divided into (i) pre-Dominion basement; (ii) Dominion granites, whose emplacement coincided with the extrusion of Dominion volcanics, and (iii) Randian granites, which were emplaced synchronously with Witwatersrand deposition. This sequence of events supports recent tectonic models that view the Witwatersrand sequence as having been deposited in a foreland basin.

• OSTI ID: 6224354
• Journal Information: Journal of Geology; (USA), Vol. 98:3; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
WITWATERSRAND
AGE ESTIMATION
CONTINENTAL CRUST
DEPOSITION
EROSION
GEOLOGIC FORMATIONS
GEOLOGIC MODELS
GRANITES
ISOTOPE DATING
LEAD ISOTOPES
ORIGIN
SEDIMENTARY BASINS
SEDIMENTATION
SEDIMENTS
SOURCE ROCKS
SOUTH AFRICA
STRATIGRAPHY
TECTONICS
URANIUM ISOTOPES
VARIATIONS
VOLCANIC ROCKS
ZIRCON
ACTINIDE ISOTOPES
AFRICA
EARTH CRUST
GEOLOGIC STRUCTURES
GEOLOGY
IGNEOUS ROCKS
ISOTOPES
MINERALS
MOUNTAINS
OXYGEN COMPOUNDS
PLUTONIC ROCKS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES
580000* - Geosciences