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A new tetragonal silicate mineral occurring as inclusions in lower-mantle diamonds

Harris, J., Hutchison, M., Hursthouse, M,, Light, M., and Harte, B, (1997) A new tetragonal silicate mineral occurring as inclusions in lower-mantle diamonds. Nature, 387 (6632). pp. 486-488. ISSN 0028-0836 (doi:10.1038/387486a0)

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Publisher's URL: http://dx.doi.org/10.1038/387486a0

Abstract

Aluminium is one of a small group of elements-Si, Mg, Fe, Al, Ca and O-that form the bulk of the Earth's mantle. In the upper mantle, Al is largely contained in minerals with a garnet structure. But the mineral transformations associated with the breakdown of garnet structures in the uppermost lower mantle have been a matter of uncertainty(1-9). Here we report the discovery of a new aluminous mineral, present as inclusions in diamonds of lower-mantle origin found at Sao Luiz, Brazil(10). This phase has a stoichiometric garnet composition similar to pyrope-almandine but has a distinct tetragonal structure (space group I (4) over bar 2d), and is here referred to by the acronym TAPP (tetragonal almandine-pyrope phase). Although TAPP has not been recognized in experimental studies, we suggest that it is nevertheless a primary rather than retrogressive phase and has a limited stability held in relatively aluminous bulk compositions in the uppermost lower mantle. TAPP, like garnet, would lead to relatively low densities for basic rocks compared with peridotites (assumed to be the dominant mantle rocks), and we suggest therefore that it may play an important role in determining density differences and the dynamics of segregation between ultrabasic and basic compositions in the mantle(7,11,12)

Item Type:Article
Status:Published
Refereed:Yes
Glasgow Author(s):Harris, Dr Jeff
Authors: Harris, J., Hutchison, M., Hursthouse, M,, Light, M., and Harte, B,
Subjects:Q Science > QE Geology
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Nature
Publisher:Nature Publications Group
ISSN:0028-0836
Copyright Holders:Copyright © 1997 Macmillan Magazines Ltd
First Published:First published in Nature 387:486-488
Publisher Policy:Reproduced with the permission of the Publisher.

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