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An experimental investigation of the relative strength of the silica polymorphs quartz, coesite and stishovite

Hunt, S; Whitaker, ML; Bailey, E; Mariani, E; Stan, CV; Dobson, D; (2019) An experimental investigation of the relative strength of the silica polymorphs quartz, coesite and stishovite. Geochemistry, Geophysics, Geosystems , 20 (4) pp. 1975-1989. 10.1029/2018GC007842. Green open access

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Abstract

In this study, quartz, coesite and stishovite were deformed concurrently with an olivine reference sample at high pressure and 850±50°C. Olivine deformed with an effective stress exponent (n) of 6.0_{+3.1}^{-2.2}, which we interpret to indicate that the Peierls creep deformation mechanism was active in the olivine. Quartz and coesite had very similar strengths and deformed by a mechanism with n = 2.8_{+1.2}^{-0.9} and 2.9_{+1.3}^{-0.9} respectively, which are consistent with previous measurements of power‐law creep in these phases. Stishovite deformed with n = 8.1_{+3.7}^{-2.7} and was stronger than both olivine and the other silica polymorphs. The high stress exponent of stishovite is greater than that typically observed for power‐law creep, indicating it is probably (but not certainly) deforming by Peierls creep. The rheology of SiO₂ minerals appears therefore to be strongly affected by the change in silicon‐coordination and density from 4‐fold in quartz and coesite to 6‐fold in stishovite. If the effect of Si‐coordination can be generalised, the increase in Si‐coordination (and density) associated with bridgmanite formation may explain the 10‐100 fold viscosity increase around 660km depth in the Earth.

Type: Article
Title: An experimental investigation of the relative strength of the silica polymorphs quartz, coesite and stishovite
Open access status: An open access version is available from UCL Discovery
DOI: 10.1029/2018GC007842
Publisher version: https://doi.org/10.1029/2018GC007842
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: quartz, rheology, silicon‐coordination, coesite, stishovite, bridgmanite
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10070979
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