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Plastic deformation of lower mantle diamonds by inclusion phase transformations

Nicola J. Cayzer, Shoko Odake, Ben Harte and Hiroyuki Kagi
Plastic deformation of lower mantle diamonds by inclusion phase transformations (in Diamonds, Makoto Arima (editor), Ben Harte (editor) and Nikolay V. Sobolev (editor))
European Journal of Mineralogy (June 2008) 20 (3): 333-339


The changes in pressure (P) and temperature (T) conditions experienced by a natural diamond, as it rises to shallower depths and is eventually erupted at the Earth's surface, give rise to stresses between the diamond and any inclusions it contains as a consequence of their differing changes in volume cell parameters in response to P and T. In the case of diamonds with lower-mantle silicate inclusions such effects will be markedly enhanced by phase transformations by which MgSi-perovskite and CaSi-perovskite transform to pyroxene, pyroxenoid and other phases. Using micro-Raman and SEM-EBSD techniques, we have carried out investigations of the diamond immediately adjacent to inclusions with lower mantle perovskite chemical compositions, and compared them with studies of lower-mantle ferropericlase and upper-mantle inclusions. In the Raman studies evidence of shifts in frequency and width in the diamond Raman spectral band at 1333 cm (super -1) were sought and found to be greater for perovskite than ferropericlase. However, even for MgSi-perovskite the effects only indicated stored residual pressures of ca 0.35 GPa, which have also been found for typical upper mantle inclusions. The EBSD studies showed a marked contrast between diamond adjacent to former perovskite (now transformed to pyroxene and other phases) and ferropericlase. EBSD mapping shows lattice distortions in diamond adjacent to former MgSi-perovskite and CaSi-perovskite of 4 to 7 degrees ; but adjacent to ferropericlase the distortion was only 1-2 degrees . The results show that the large strain changes accompanying decompression and phase transformation of the perovskite inclusions were largely accommodated by plastic strain within the diamonds at high temperatures, and only small residual pressures were retained in the diamonds.

ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 20
Serial Issue: 3
Title: Plastic deformation of lower mantle diamonds by inclusion phase transformations
Title: Diamonds
Author(s): Cayzer, Nicola J.Odake, ShokoHarte, BenKagi, Hiroyuki
Author(s): Arima, Makotoeditor
Author(s): Harte, Beneditor
Author(s): Sobolev, Nikolay V.editor
Affiliation: University of Edinburgh, School of GeoSciences, Edinburgh, United Kingdom
Pages: 333-339
Published: 200806
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 23
Accession Number: 2008-111807
Categories: Geophysics of minerals and rocks
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
S18°00'00" - S07°19'60", W61°30'00" - W50°10'00"
Secondary Affiliation: University of Tokyo, JPN, Japan
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200841
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