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

Journal Article · · Journal of Geophysical Research. Solid Earth
DOI:https://doi.org/10.1002/2017JB014400· OSTI ID:1499554
 [1];  [2];  [3];  [4]
  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)
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 of 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.
Research Organization:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
SC0012704
OSTI ID:
1499554
Alternate ID(s):
OSTI ID: 1420982
OSTI ID: 1424756
Report Number(s):
BNL--209558-2018-JACI
Journal Information:
Journal of Geophysical Research. Solid Earth, Journal Name: Journal of Geophysical Research. Solid Earth Journal Issue: 10 Vol. 122; ISSN 2169-9313
Publisher:
American Geophysical UnionCopyright Statement
Country of Publication:
United States
Language:
English

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