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Abstract To understand the effects of secondary minerals on changes in the mechanical properties of upper mantle rocks due to phase mixing, we conducted high‐strain torsion experiments on aggregates of iron‐rich olivine + orthopyroxene (opx) with opx volume fractions offopx = 0.15, 0.26, and 0.35. For samples with larger amounts of opx,fopx = 0.26 and 0.35, the value of the stress exponent decreases with increasing strain fromn ≈ 3 for γ ≲ 5 ton ≈ 2 for 5 ≲ γ ≲ 25, indicating that the deformation mechanism changes as strain increases. In contrast, for samples withfopx = 0.15, the stress exponent is constant atn ≈ 3.3 for 1 ≲ γ ≲ 25, suggesting that no change in deformation mechanism occurs with increasing strain for samples with smaller amounts of opx. The microstructures of samples with larger amounts of opx provide insight into the change in deformation mechanism derived from the mechanical data. Elongated grains align subparallel to the shear direction for samples of all three compositions deformed to lower strains. However, strain weakening with grain size reduction and the formation of a thoroughly mixed, fine‐grained texture only develops in samples withfopx = 0.26 and 0.35 deformed to higher strains of γ ≳ 16. These mechanical and associated microstructural properties imply that rheological weakening due to phase mixing only occurs in the samples with largerfopx, which is an important constraint for understanding strain localization in the upper mantle of Earth.
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Texture Development and Stress–Strain Partitioning in Periclase + Halite Aggregates
Multiphase materials are widely applied in engineering due to desirable mechanical properties and are of interest to geoscience as rocks are multiphase. High-pressure mechanical behavior is important for understanding the deep Earth where rocks deform at extreme pressure and temperature. In order to systematically study the underlying physics of multiphase deformation at high pressure, we perform diamond anvil cell deformation experiments on MgO + NaCl aggregates with varying phase proportions. Lattice strain and texture evolution are recorded using in-situ synchrotron x-ray diffraction and are modeled using two-phase elasto-viscoplastic self-consistent (EVPSC) simulations to deduce stress, strain, and deformation mechanisms in individual phases and the aggregate. Texture development of MgO and NaCl are affected by phase proportions. In NaCl, a (100) compression texture is observed when small amounts of MgO are present. In contrast, when deformed as a single phase or when large amounts of MgO are present, NaCl develops a (110) texture. Stress and strain evolution in MgO and NaCl also show different trends with varying phase proportions. Based on the results from this study, we construct a general scheme of stress evolution as a function of phase proportion for individual phases and the aggregate.
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- Award ID(s):
- 1654687
- PAR ID:
- 10162352
- Date Published:
- Journal Name:
- Minerals
- Volume:
- 9
- Issue:
- 11
- ISSN:
- 0560-9178
- Page Range / eLocation ID:
- 679
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/min9110679
