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

A new tetragonal silicate mineral occurring as inclusions in lower-mantle diamonds
A new tetragonal silicate mineral occurring as inclusions in lower-mantle diamonds
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).
0028-0836
486-488
Harris, J.
702c54d7-f4cb-41af-b5e9-63a51c8533b8
Hutchison, M. T.
4815b679-104f-41fb-b16e-2eb42e2c771c
Hursthouse, M.
57a2ddf9-b1b3-4f38-bfe9-ef2f526388da
Light, M.
b541bc66-98c9-48e3-85c7-6b47fb338180
Harte, B.
0281ed7d-a7cc-4af4-ac16-f7fa58016474
Harris, J.
702c54d7-f4cb-41af-b5e9-63a51c8533b8
Hutchison, M. T.
4815b679-104f-41fb-b16e-2eb42e2c771c
Hursthouse, M.
57a2ddf9-b1b3-4f38-bfe9-ef2f526388da
Light, M.
b541bc66-98c9-48e3-85c7-6b47fb338180
Harte, B.
0281ed7d-a7cc-4af4-ac16-f7fa58016474

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

Record type: Article

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).

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Published date: 1997

Identifiers

Local EPrints ID: 15327
URI: http://eprints.soton.ac.uk/id/eprint/15327
ISSN: 0028-0836
PURE UUID: f240c70e-c7ee-4715-90f8-790f25af0d42

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Date deposited: 12 Apr 2005
Last modified: 15 Mar 2024 05:38

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Contributors

Author: J. Harris
Author: M. T. Hutchison
Author: M. Hursthouse
Author: M. Light
Author: B. Harte

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