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Crystal preferred orientation of an amphibole experimentally deformed by simple shear.

Ko B, Jung H - Nat Commun (2015)

Bottom Line: Here we present the results of novel experiments on simple shear deformation of amphibolite at high pressure and temperatures (1 GPa, 480-700 °C).Depending on the temperature and stress, the deformed amphibole produced three types of CPOs and resulted in a strong seismic anisotropy.Our data provide a new understanding of the observed seismic anisotropy.

View Article: PubMed Central - PubMed

Affiliation: Tectonophysics Laboratory, School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, Korea.

ABSTRACT
Seismic anisotropy has been widely observed in crust and mantle materials and plays a key role in the understanding of structure and flow patterns. Although seismic anisotropy can be explained by the crystal preferred orientation (CPO) of highly anisotropic minerals in the crust, that is, amphibole, experimental studies on the CPO of amphibole are limited. Here we present the results of novel experiments on simple shear deformation of amphibolite at high pressure and temperatures (1 GPa, 480-700 °C). Depending on the temperature and stress, the deformed amphibole produced three types of CPOs and resulted in a strong seismic anisotropy. Our data provide a new understanding of the observed seismic anisotropy. The seismic data obtained from the amphibole CPOs revealed that anomalous seismic anisotropy observed in the deep crust, subducting slab and mantle wedge can be attributed to the CPO of amphibole.

No MeSH data available.


Related in: MedlinePlus

Backscattered electron image of starting material.Bi, biotite; Hb, hornblende; Il, ilmenite; Pl, plagioclase; Ti, titanite.
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f2: Backscattered electron image of starting material.Bi, biotite; Hb, hornblende; Il, ilmenite; Pl, plagioclase; Ti, titanite.

Mentions: Amphibolite was deformed using a modified Griggs apparatus at a pressure of 1 GPa and temperatures in the range of 480–700 °C. The experimental conditions and results are shown in Table 1. A typical microstructure of the starting material and the deformed amphibolite at high pressure and temperature are shown by backscattered electron images (Figs 2 and 3). The starting material has an average grain size of 20 μm. Faults and microcracks were formed in the deformed amphibolites (Fig. 3a), and the grain shape is angular with a notably fine grain size (<5 μm; Fig. 3b). Another major feature is the strain localization on the scale of mm to μm, which is intimately related to the generation of faults and the comminution of grains. The localized shear zone surrounding the main faults was generally developed after γ∼1 and produced at 0 to 30° to the shear plane (Fig. 3a). Macroscopically, plagioclase appears to be plastically deformed because of the elongated structure of plagioclase aggregates that are subparallel to the rotated strain marker. In contrast, microscopic observations reflect cracking features, which indicate that the plagioclase was also deformed by brittle or semi-brittle processes. These observations of severe grain-size reduction (to <5 μm from an average grain size of ∼20 μm) and microfracturing in deformed amphibolites (Fig. 3b) imply that the dominant deformation mechanism was cataclastic flow with faulting accompanied by the rotation of hornblende grains. These brittle processes are in good agreement with previous studies on naturally and experimentally deformed amphibole25272829, although certain authors have proposed brittle deformation together with diffusive mass transfer3031 and crystal plasticity as a dominant deformation mechanism of amphibole233132.


Crystal preferred orientation of an amphibole experimentally deformed by simple shear.

Ko B, Jung H - Nat Commun (2015)

Backscattered electron image of starting material.Bi, biotite; Hb, hornblende; Il, ilmenite; Pl, plagioclase; Ti, titanite.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4403317&req=5

f2: Backscattered electron image of starting material.Bi, biotite; Hb, hornblende; Il, ilmenite; Pl, plagioclase; Ti, titanite.
Mentions: Amphibolite was deformed using a modified Griggs apparatus at a pressure of 1 GPa and temperatures in the range of 480–700 °C. The experimental conditions and results are shown in Table 1. A typical microstructure of the starting material and the deformed amphibolite at high pressure and temperature are shown by backscattered electron images (Figs 2 and 3). The starting material has an average grain size of 20 μm. Faults and microcracks were formed in the deformed amphibolites (Fig. 3a), and the grain shape is angular with a notably fine grain size (<5 μm; Fig. 3b). Another major feature is the strain localization on the scale of mm to μm, which is intimately related to the generation of faults and the comminution of grains. The localized shear zone surrounding the main faults was generally developed after γ∼1 and produced at 0 to 30° to the shear plane (Fig. 3a). Macroscopically, plagioclase appears to be plastically deformed because of the elongated structure of plagioclase aggregates that are subparallel to the rotated strain marker. In contrast, microscopic observations reflect cracking features, which indicate that the plagioclase was also deformed by brittle or semi-brittle processes. These observations of severe grain-size reduction (to <5 μm from an average grain size of ∼20 μm) and microfracturing in deformed amphibolites (Fig. 3b) imply that the dominant deformation mechanism was cataclastic flow with faulting accompanied by the rotation of hornblende grains. These brittle processes are in good agreement with previous studies on naturally and experimentally deformed amphibole25272829, although certain authors have proposed brittle deformation together with diffusive mass transfer3031 and crystal plasticity as a dominant deformation mechanism of amphibole233132.

Bottom Line: Here we present the results of novel experiments on simple shear deformation of amphibolite at high pressure and temperatures (1 GPa, 480-700 °C).Depending on the temperature and stress, the deformed amphibole produced three types of CPOs and resulted in a strong seismic anisotropy.Our data provide a new understanding of the observed seismic anisotropy.

View Article: PubMed Central - PubMed

Affiliation: Tectonophysics Laboratory, School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, Korea.

ABSTRACT
Seismic anisotropy has been widely observed in crust and mantle materials and plays a key role in the understanding of structure and flow patterns. Although seismic anisotropy can be explained by the crystal preferred orientation (CPO) of highly anisotropic minerals in the crust, that is, amphibole, experimental studies on the CPO of amphibole are limited. Here we present the results of novel experiments on simple shear deformation of amphibolite at high pressure and temperatures (1 GPa, 480-700 °C). Depending on the temperature and stress, the deformed amphibole produced three types of CPOs and resulted in a strong seismic anisotropy. Our data provide a new understanding of the observed seismic anisotropy. The seismic data obtained from the amphibole CPOs revealed that anomalous seismic anisotropy observed in the deep crust, subducting slab and mantle wedge can be attributed to the CPO of amphibole.

No MeSH data available.


Related in: MedlinePlus