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Oral Presentation: GSA Connects 2024 Fall Meeting, Wednesday, September 25 ​
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Microstructural Evidence of Dislocation Creep and
Diffusion-Accommodated Deformation of Glaucophane
in a Naturally Deformed Lawsonite Blueschist
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​Authors: Jason Ott, Cailey Condit, Matej Pec, and Baptiste Journaux
​
Abstract:
Blueschist rheology is crucial to the mechanical behavior of subducting oceanic crust. Mafic blueschists are often ubiquitous along the plate interface from the base of the seismogenic zone to sub-arc depths, yet the lithology strength remains poorly constrained. Observations from exhumed subduction terranes suggest that blueschist accommodates significant strain, largely partitioned into the sodic amphibole glaucophane (Gln). However, it remains an open question whether the observed deformation is accommodated by dislocation or diffusion related processes.
We investigated the Gln fabric and deformation mechanisms in a garnet-bearing lawsonite blueschist (LBS) block from the mélange unit of the Catalina Schist subduction complex on Pimu’nga. This block records eclogite facies peak conditions with an LBS-facies overprint. We used electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) to interpret the textural and geochemical record of deformation during subduction. Microstructural analysis of the Gln reveals evidence of dislocation accommodated deformation including: (1) crystallographic preferred orientation (CPO) development, (2) intragranular misorientations, (3) dislocation motion on multiple slip systems, and (4) subgrain boundary formation. Evidence for inherited CPOs in core-mantle structures imply that subgrain boundary recrystallization was active. This microstructural evidence suggests that dislocation-creep-accommodated deformation was active. SEM and EDS maps of Gln reveals evidence of chemical zoning with higher Fe and lower Al and Mg concentrations along microfractures suggesting a fluid-mediated/diffusion-accommodated deformation process such as micro-boudinage and/or coupled dissolution-precipitation. Titanite in the matrix and as inclusions in texturally equilibrated Gln and lawsonite grains signals significant Gln growth and deformation occurred post-peak conditions at lawsonite blueschist conditions. These observations are supported by our pseudosection modelling results for the garnet blueschist block. Together, these results suggest that Gln can readily deform by dislocation creep, and also record diffusion-mediated processes during deformation under lawsonite blueschist facies conditions.
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Poster Presentation: EGU General Assembly, April 14-19, 2024
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Microstructural evidence of dislocation creep and diffusion accommodated
deformation of glaucophane in naturally deformed lawsonite and epidote blueschists
​Authors: Jason Ott, Cailey Condit, Matej Pec, Baptiste Journaux ​
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Oral Presentation: GSA 2023 Cordilleran Section Meeting, Friday, May 19​
​
Preliminary Experimental Constraints on the
Rheology of Mafic Blueschists
​Authors: Jason Ott, Cailey Condit, Matej Pec, and Angelica Bonanno​​
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Poster Presentation: USGS Subduction Zone Science Workshop, January 10-11, 2023
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Seismic Anisotropy of Mafic Blueschists: Constraints from Exhumed
Rock-Record with Implications for the Subduction Interface​
Authors: Jason Ott, Cailey Condit, Rachel Bernard, Vera Schulte-Pelkum, Matej Pec ​
DOI: 10.5281/zenodo.7530437
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Oral Presentation: AGU 2022 Fall Meeting, Monday, December 12​
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Experimental constraints on the strength and deformation
mechanisms of glaucophane at subduction zone conditions​
Authors: Jason Ott, Cailey Condit, Matej Pec, and Angelica Bonanno
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Poster Presentation: GRC Rock Deformation Conference, August 6-12, 2022
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Experimental constraints on the strength and deformation
mechanisms of glaucophane at subduction zone conditions​
Authors: Jason Ott, Cailey Condit, Matej Pec, and Angelica Bonanno
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Poster Presentation: AGU 2021 Fall Meeting, Thursday, December 16, 4-6 p.m.​
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Seismic anisotropy of mafic blueschists: constraints from exhumed glaucophane-
rich blueschists with implications for the subduction interface​
Authors: Jason Ott, Cailey Condit, and Vera Schulte-Pelkum
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