Title: Diffusion Creep of Enstatite at High Pressures Under Hydrous Conditions: Diffusion Creep of Hydrous Enstatite

Abstract

Mantle convection and large-scale plate motion depend critically on the nature of the lithosphere-asthenosphere boundary and thus on the viscosity structure of Earth's upper mantle, which is determined by the rheological properties of its constituent minerals. To constrain the flow behavior of orthopyroxene, the second most abundant constituent of the upper mantle, deformation experiments were carried out in triaxial compressive creep on fine-grained (~6 μm) samples of enstatite at high pressures (3.8–6.3 GPa) and high temperatures (1323–1573 K) using a deformation-DIA apparatus. Based on results from this study, the deformation behavior of enstatite is quantitatively presented in the form of a flow law that describes the dependence of deformation rate on differential stress, water fugacity, temperature, and pressure. Specifically, the creep rate depends approximately linearly on stress, indicating deformation in the diffusion creep regime. A least squares regression fit to our data yielded a flow law for diffusion creep with an activation energy of ~200 kJ/mol and an activation volume of ~14 × 10^-6 m³/mol. The magnitude of the water-weakening effect is similar to that for olivine with a water fugacity exponent of r ≈ 0.7. This strong dependence of viscosity on water fugacity (concentration) indicates that the viscosity ofmore » an orthopyroxene-bearing mantle varies from one geological setting to another, depending on the large-scale water distribution. Based on the rheology contrast between olivine and enstatite, we conclude that olivine is weaker than enstatite throughout most of the upper mantle except in some shallow regions in the diffusion creep regime.« less

Authors:

Zhang, Guinan  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-2977-5777"

Mei, Shenghua ^[2]; Song, Maoshuang  ^[3];

• Search DOE PAGES for author "Song, Maoshuang"
• Search DOE PAGES for ORCID "0000-0002-3006-756X"

Kohlstedt, David L.  ^[4]

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• Search DOE PAGES for ORCID "0000-0002-6417-6465"

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+ Show Author Affiliations

1. Chinese Academy of Sciences (CAS), Guangzhou (China). State Key Lab. of Isotope Geochemistry, Guangzhou Inst. of Geochemistry; University of Chinese Academy of Sciences, Beijing China; Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Earth Sciences
2. Chinese Academy of Sciences (CAS), Sanya (China). Key Lab. for Experimental Study under Deep-sea Extreme Conditions, Inst. of Deep-sea Science and Engineering; Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Earth Sciences
3. Chinese Academy of Sciences (CAS), Guangzhou (China). State Key Lab. of Isotope Geochemistry, Guangzhou Inst. of Geochemistry
4. Univ. of Minnesota, Minneapolis, MN (United States)

Publication Date:

Sun Oct 01 00:00:00 EDT 2017

Research Org.:

Brookhaven National Laboratory (BNL), Upton, NY (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1499554

Report Number(s):

BNL-209558-2018-JACI
Journal ID: ISSN 2169-9313

Grant/Contract Number:  

SC0012704

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Geophysical Research. Solid Earth

Additional Journal Information:

Journal Volume: 122; Journal Issue: 10; Journal ID: ISSN 2169-9313

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; enstatite; diffusion creep; water fugacity; mantle viscosity