Oxygen and hydrogen isotope stratigraphy of the Rustenburg Layered Suite, Bushveld Complex; constraints on crustal contamination

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doi: 10.1093/petrology/egh089
Authors:Harris, Chris; Pronost, Julie J. M.; Ashwal, Lewis D.; Cawthorn, R. Grant
Author Affiliations:Primary:
University of Cape Town, Department of Geological Sciences, Rondebosch, South Africa
Other:
Université Jean Monnet, France
Laboratoire Magmas et Volcans, France
University of the Witwatersrand, South Africa
Volume Title:Journal of Petrology
Source:Journal of Petrology, 46(3), p.579-601. Publisher: Oxford University Press, Oxford, United Kingdom. ISSN: 0022-3530
Publication Date:2005
Note:In English. 87 refs.; illus., incl. 3 tables, sketch map
Summary:New δ18O values for plagioclase, pyroxene and olivine, and limited whole-rock δD values are presented for samples from the Rustenburg Layered Suite of the Bushveld Complex, South Africa. In combination with existing data, these provide a much more complete composite O-isotope stratigraphy for the intrusion. Throughout the layered suite, mineral δ18O values indicate that the magmas from which they crystallized had δ18O values that were about 7.1 per mil, that is, 1.4 per mil higher than expected for mantle-derived magmas, suggesting extensive crustal contamination. More limited H-isotope data suggest that the OH present within whole rocks, regardless of the degree of alteration, is of magmatic origin and not an alteration, phenomenon. There appears to be no systematic change in δ18O value with stratigraphic height and this requires the contamination to have taken place in a "staging chamber" before emplacement of the magma(s) into the present chamber. Large amounts (30-40%) of contamination by the lower to middle crust are needed to explain these δ18O values, which is in general agreement with previous estimates based on Sr- and Nd-isotope data. Alternatively, smaller amounts of contamination (∼20%) by sedimentary rocks, or their partial melts, represented by the country rock can explain the data, but it is not apparent how such material could have been present at the depth of the "staging chamber" in the lower to middle crust.
Sections:Geochemistry; Petrology
Subsections:Igneous petrology; Igneous rocks
Subjects:Chemostratigraphy; Complexes; D/H; Deuterium; Hydrogen; Igneous rocks; Isotope ratios; Isotopes; Magma contamination; Magmas; O-18/O-16; Oxygen; Paleoproterozoic; Precambrian; Proterozoic; Rustenburg Layered Suite; Stable isotopes; Upper Precambrian; Africa; Bushveld Complex; South Africa; Southern Africa
Coordinates:S250000 S250000 E0270000 E0270000
Abstract Numbers:05M/651
Record ID:2005038769
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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