Diffusion metasomatism in silica-undersaturated sapphirine-bearing granulite from Rumdoodle Peak, Framnes Mountains, east Antarctica |
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| Authors: | Daniel J Dunkley Geoffrey L Clarke Simon L Harley |
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| Institution: | (1) School of Geosciences, Division of Geology and Geophysics F05, University of Sydney, NSW 2006, Australia Fax: 61 2 9351 0184; E-mail: geoffc@mail.usyd.edu.au, AU;(2) Department of Geology and Geophysics, Grant Institute of Geology, University of Edinburgh, Kings Buildings, West Mains Rd., Edinburgh EH9 3JW, Scotland, GB |
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| Abstract: | At Rumdoodle Peak, near Mawson Base, east Antarctica, an enclave of metasedimentary granulite is enclosed in the Mawson Charnockite,
an extensive c. 960 Ma intrusion. The enclave contains a disrupted layer of black spinel-orthopyroxene-phlogopite gneiss, which was truncated
by a quartz-rich vein. A reaction band that developed between these units is composed of a sequence of mineral zones that
contain spinel, orthopyroxene, sapphirine, cordierite and plagioclase. The sequence of mineral zones approximately matches
that predicted by a model of closed system diffusion metasomatism, involving the exchange of Si for Fe and Mg. The reaction
bands differ from the model in the presence of micro-scale disequilibrium textures, that include “double coronas” composed
of cordierite surrounding sapphirine and sapphirine surrounding spinel. The growth of the reaction band was controlled by
diffusion along intergranular pathways, with local equilibrium maintained adjacent to grain boundaries. The presence of corona
textures is a result of slow reaction rates, due to limited diffusive exchange of Si and Al across mineral grains.
Received: 15 January 1998 / Accepted: 7 September 1998 |
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| Keywords: | Mineral abbreviations as in Kretz (1983) |
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