Melt Generation and Fluid Flow in the Thermal Aureole of the Bushveld Complex |
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Authors: | HARRIS NIGEL; McMILLAN ANDY; HOLNESS MARIAN; UKEN RON; WATKEYS MIKE; ROGERS NICK; FALLICK ANTHONY |
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Affiliation: | 1 DEPARTMENT OF EARTH SCIENCES, OPEN UNIVERSITY, MILTON KEYNES MK7 6AA, UK
2 DEPARTMENT OF EARTH SCIENCES, UNIVERSITY OF CAMBRIDGE, CAMBRIDGE CB2 3EQ, UK
3 SCHOOL OF GEOLOGICAL AND COMPUTER SCIENCES, UNIVERSITY OF NATAL, DURBAN 4041, SOUTH AFRICA
4 SCOTTISH UNIVERSITIES ENVIRONMENTAL RESEARCH CENTRE, EAST KILBRIDE, GLASGOW G75 0QF, UK |
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Abstract: | Granite sheets emplaced into the migmatite zone of the easterncontact aureole of the Bushveld Complex resulted from fluid-enhanced,incongruent biotite melting of the underlying Silverton Formationshales during prograde metamorphism. Ba concentrations are extremein both the sheets (>1000 ppm) and the hornfels (>800ppm) into which they have been emplaced. We conclude that aBa-rich, hydrothermal fluid induced melting in the aureole,and that fluid transport of Ba2+, and to a lesser extent, Sr2+and Eu2+, persisted in the melt zones under subsolidus conditions.Sr-isotope systematics from high-Ba localities define an errorchronof 2161 ± 106 Ma with an initial (87Sr/86Sr) ratio of0·705 ± 0·001. Metasedimentary rocks unaffectedby fluid infiltration were homogenized at the same time butwith an increased initial ratio, suggesting that whereas isotopehomogenization was achieved between outcrops permeated by fluids,there is no evidence of regional homogenization. Oxygen-isotopecompositions of psammitic metasediments in the aureole are uncorrelatedwith distance from the contact, suggesting the infiltratingfluid equilibrated isotopically with the metasediments. Theirelevated |
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