Formation of Nanocrystalline and Amorphous Materials Causes Parallel Brittle‐Viscous Flow of Crustal Rocks: Experiments on Quartz‐Feldspar Aggregates
The brittle-viscous transition in the lithosphere occurs in a region where many large earthquakes nucleate. To study this transition, we sheared bimineralic aggregates with varying ratio of quartz and potassium feldspar. We deformed the samples in a solid-medium deformation apparatus at temperature,...
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| Format: | Article |
| Language: | English |
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American Geophysical Union (AGU)
2021
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| Online Access: | https://hdl.handle.net/1721.1/133157 |
| _version_ | 1826213544333410304 |
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| author | Pec, Matej Al Nasser, Saleh Mohammed |
| author2 | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences |
| author_facet | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Pec, Matej Al Nasser, Saleh Mohammed |
| author_sort | Pec, Matej |
| collection | MIT |
| description | The brittle-viscous transition in the lithosphere occurs in a region where many large earthquakes nucleate. To study this transition, we sheared bimineralic aggregates with varying ratio of quartz and potassium feldspar. We deformed the samples in a solid-medium deformation apparatus at temperature, T = 750°C and pressure, Pc = 800 MPa under either constant displacement rate or constant load boundary conditions. Under constant displacement rate, samples reach high shear stress (τ = 0.4–1 GPa depending on mineral ratio) and then weaken. Under constant load, the strain rate shows low sensitivity to stress below τ ≈ 400 MPa, followed by a higher stress sensitivity (stress exponent, n = 9–13) at higher stresses irrespective of mineral ratio. Strain is localized along “slip zones” in a C and C′ orientation. The material in the slip zones shows extreme grain size reduction and flow features. At peak strength, 1–2 vol% of the sample is composed of slip zones that are straight and short. With increasing strain, the slip zones become anastomosing and branching and occupy up to 9 vol%; this development is concomitant with strain-weakening of the sample. Slip zones delimit larger cataclastic lenses, which develop a weak foliation. Our results suggest that strain localization leads to microstructural transformation of the rocks from a crystalline solid to a fluid-like material in the slip zones. The measured rheological response is a combination of viscous flow in the slip zones and cataclastic flow in coarser-grained lenses and can be modeled as a frictional slider coupled in parallel with a viscous dashpot. |
| first_indexed | 2024-09-23T15:50:58Z |
| format | Article |
| id | mit-1721.1/133157 |
| institution | Massachusetts Institute of Technology |
| language | English |
| last_indexed | 2024-09-23T15:50:58Z |
| publishDate | 2021 |
| publisher | American Geophysical Union (AGU) |
| record_format | dspace |
| spelling | mit-1721.1/1331572022-10-02T04:34:46Z Formation of Nanocrystalline and Amorphous Materials Causes Parallel Brittle‐Viscous Flow of Crustal Rocks: Experiments on Quartz‐Feldspar Aggregates Pec, Matej Al Nasser, Saleh Mohammed Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences The brittle-viscous transition in the lithosphere occurs in a region where many large earthquakes nucleate. To study this transition, we sheared bimineralic aggregates with varying ratio of quartz and potassium feldspar. We deformed the samples in a solid-medium deformation apparatus at temperature, T = 750°C and pressure, Pc = 800 MPa under either constant displacement rate or constant load boundary conditions. Under constant displacement rate, samples reach high shear stress (τ = 0.4–1 GPa depending on mineral ratio) and then weaken. Under constant load, the strain rate shows low sensitivity to stress below τ ≈ 400 MPa, followed by a higher stress sensitivity (stress exponent, n = 9–13) at higher stresses irrespective of mineral ratio. Strain is localized along “slip zones” in a C and C′ orientation. The material in the slip zones shows extreme grain size reduction and flow features. At peak strength, 1–2 vol% of the sample is composed of slip zones that are straight and short. With increasing strain, the slip zones become anastomosing and branching and occupy up to 9 vol%; this development is concomitant with strain-weakening of the sample. Slip zones delimit larger cataclastic lenses, which develop a weak foliation. Our results suggest that strain localization leads to microstructural transformation of the rocks from a crystalline solid to a fluid-like material in the slip zones. The measured rheological response is a combination of viscous flow in the slip zones and cataclastic flow in coarser-grained lenses and can be modeled as a frictional slider coupled in parallel with a viscous dashpot. 2021-10-27T16:43:08Z 2021-10-27T16:43:08Z 2021-05 2021-03 2021-10-26T18:19:39Z Article http://purl.org/eprint/type/JournalArticle 2169-9313 2169-9356 https://hdl.handle.net/1721.1/133157 Pec, Matej and Saleh Al Nasser. "Formation of nanocrystalline and amorphous materials causes parallel brittle-viscous flow of crustal rocks: Experiments on quartz-feldspar aggregates." Journal of Geophysical Research: Solid Earth 126, 5 (May 2021): e2020JB021262. © 2021 American Geophysical Union en http://dx.doi.org/10.1029/2020jb021262 Journal of Geophysical Research: Solid Earth Creative Commons Attribution-Noncommercial-Share Alike http://creativecommons.org/licenses/by-nc-sa/4.0/ application/pdf American Geophysical Union (AGU) Prof. Pec |
| spellingShingle | Pec, Matej Al Nasser, Saleh Mohammed Formation of Nanocrystalline and Amorphous Materials Causes Parallel Brittle‐Viscous Flow of Crustal Rocks: Experiments on Quartz‐Feldspar Aggregates |
| title | Formation of Nanocrystalline and Amorphous Materials Causes Parallel Brittle‐Viscous Flow of Crustal Rocks: Experiments on Quartz‐Feldspar Aggregates |
| title_full | Formation of Nanocrystalline and Amorphous Materials Causes Parallel Brittle‐Viscous Flow of Crustal Rocks: Experiments on Quartz‐Feldspar Aggregates |
| title_fullStr | Formation of Nanocrystalline and Amorphous Materials Causes Parallel Brittle‐Viscous Flow of Crustal Rocks: Experiments on Quartz‐Feldspar Aggregates |
| title_full_unstemmed | Formation of Nanocrystalline and Amorphous Materials Causes Parallel Brittle‐Viscous Flow of Crustal Rocks: Experiments on Quartz‐Feldspar Aggregates |
| title_short | Formation of Nanocrystalline and Amorphous Materials Causes Parallel Brittle‐Viscous Flow of Crustal Rocks: Experiments on Quartz‐Feldspar Aggregates |
| title_sort | formation of nanocrystalline and amorphous materials causes parallel brittle viscous flow of crustal rocks experiments on quartz feldspar aggregates |
| url | https://hdl.handle.net/1721.1/133157 |
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