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
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Authors: Jason Ott, Cailey Condit, Matej Pec, Baptiste Journaux
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References:
-Bachmann, F., Hielscher, R., & Schaeben, H. (2010). Texture Analysis with MTEX – Free and Open Source Software Toolbox. Solid State Phenomena, 160, 63–68. https://doi.org/10.4028/www.scientific.net/SSP.160.63
-Grove, M., & Bebout, G. E. (1995). Cretaceous tectonic evolution of coastal southern California: Insights from the Catalina Schist. Tectonics, 14(6), 1290–1308. https://doi.org/10.1029/95TC01931
-Grove, M., Bebout, G. E., Jacobson, C. E., Barth, A. P., Kimbrough, D. L., King, R. L., et al. (2008). The Catalina Schist: Evidence for middle Cretaceous subduction erosion of southwestern North America. In A. E. Draut, Peter. D. Clift, & D. W. Scholl (Eds.), Formation and Applications of the Sedimentary Record in Arc Collision Zones (Vol. 436, p. 0). Geological Society of America. https://doi.org/10.1130/2008.2436(15)
-Harvey, K.M., Penniston-Dorland, S.C., Kohn, M.J., & Piccoli, P.M. (2021). Assessing P-T variability in melange blocks from the Catalina Schist: Is there differential movement at the subduction interface? Journal of Metamorphic Geology, 39, 3. https://doi.org/10.1111/jmg.12571
-Hirth, G., & Tullis, J. (1992). Dislocation creep regimes in quartz aggregates. Journal of Structural Geology, 14(2), 145–159. https://doi.org/10.1016/0191-8141(92)90053-Y
-Mainprice, D., Bachmann, F., Hielscher, R., & Schaeben, H. (2015). Descriptive tools for the analysis of texture projects with large datasets using MTEX : strength, symmetry and components. Geological Society, London, Special Publications, 409(1), 251–271. https://doi.org/10.1144/SP409.8
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-Platt, J.P., & Schmidt, W.L. (2024). Is the inverted field gradient in the Catalina Schist terrane primary or constructional? Tectonics, 43, e2023TC008021. https://doi.org/10.1029/2023TC008021
-Prior, D. J., Boyle, A. P., Brenker, F., Cheadle, M. C., Day, A., Lopez, G., et al. (1999). The Application of Electron Backscatter Diffraction and Orientation Contrast Imaging in the SEM to Textural Problems in Rocks. American Mineralogist, 84(11–12), 1741–1759. https://doi.org/10.2138/am-1999-11-1204
-Reynard, B., Gillet, P., & Willaime, C. (1989). Deformation mechanisms in naturally deformed glaucophanes: a TEM and HREM study. European Journal of Mineralogy, 1(5), 611–624. https://doi.org/10.1127/ejm/1/5/0611
-Stern, R.J., 2002. Subduction zones. Rev. Geophys. 40, 1012. doi:10.1029/2001RG000108
-Tokle, L., Hufford, L. J., Behr, W. M., Morales, L. F. G., & Madonna, C. (2023). Diffusion Creep of Sodic Amphibole-Bearing Blueschist Limited by Microboudinage. Journal of Geophysical Research: Solid Earth, 128(9), e2023JB026848. https://doi.org/10.1029/2023JB026848
-Wheeler, J., Prior, D., Jiang, Z., Spiess, R., & Trimby, P. (2001). The petrological significance of misorientations between grains. Contributions to Mineralogy and Petrology, 141(1), 109–124. https://doi.org/10.1007/s004100000225
-Wheeler, J., Mariani, E., Piazolo, S., Prior, D. j., Trimby, P., & Drury, M. r. (2009). The weighted Burgers vector: a new quantity for constraining dislocation densities and types using electron backscatter diffraction on 2D sections through crystalline materials. Journal of Microscopy, 233(3), 482–494. https://doi.org/10.1111/j.1365-2818.2009.03136.x
-Wheeler, J., Piazolo, S., Prior, D. J., Trimby, P. W., & Tielke, J. A. (2024). Using crystal-lattice distortion data for geological investigations: the weighted Burgers vector method. Journal of Structural Geology, 179, 105040. https://doi.org/10.1016/j.jsg.2023.105040
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Oral Presentation: GSA 2023 Cordilleran Section Meeting, Friday, May 19
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Abstract:
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Preliminary Experimental Constraints on the
Rheology of Mafic Blueschists
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Authors: Jason Ott, Cailey Condit, Matej Pec, and Angelica Bonanno
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The strength and deformation behavior of the subduction-interface plays a central role in generating geological hazards. Yet, the rheology of many subduction lithologies that deform along the plate interface remain poorly constrained. Between the base of the subduction seismogenic zone and the sub-arc (~35-100 km), high-P low-T metamorphism of subducting ocean crust produces mafic blueschist. Observations of naturally deformed blueschists exhumed from these depths suggest they accommodate significant strain—largely partitioned into the ubiquitous sodic amphibole glaucophane (gln). Thus, constraining the absolute strength of gln, and by extension blueschist, will improve our understanding of plate interface rheology at these depths.
In order to provide these rheological constraints, we experimentally deformed gln in a high-P high-T deformation apparatus at relevant P-T conditions. Fine grained gln aggregates (10-20 µm) were hot-pressed for 16 hours at T=650℃ and P=1.5 GPa, then deformed at temperatures from 650-750℃ at strain rates (γ ̇) of 10-3-10-4 s-1. Glaucophane’s peak strength decreases substantially from τ~1000 to ~200 MPa with a 100℃ temperature increase. Preliminary calculations estimate an activation energy (Q) of ~200-400 kJ/mol. Stress-stepping experiments yield a stress-exponent of n ≈ 5, consistent with deformation by dislocation-assisted motion. Compared to the hot-pressed starting material, microstructures in deformed samples show increased evidence of intragranular deformation, subgrain boundary recrystallization, and strong crystallographic preferred orientations supporting the activation of dislocation-creep-accommodated deformation. Similar microstructures in our lab-deformed samples and exhumed, naturally deformed blueschists from various subduction zones imply that our experiments accessed the deformation regime experienced by these naturally-deformed blueschists. This suggests that deformation along the subduction interface at blueschist conditions is largely accommodated by dislocation creep in gln. Based on the high temperature-sensitivity of gln’s peak strength in the dislocation-creep regime, we propose that blueschist strength along the plate interface rapidly decreases with increasing temperature/depth in the subduction zone.
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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
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Authors: Jason Ott, Cailey Condit, Rachel Bernard, Vera Schulte-Pelkum, Matej Pec
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DOI: 10.5281/zenodo.7530437
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References:
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-Mainprice, D., Bachmann, F., Hielscher, R., & Schaeben, H. (2015). Descriptive tools for the analysis of texture projects with large datasets using MTEX : strength, symmetry and components. Geological Society, London, Special Publications, 409(1), 251–271. https://doi.org/10.1144/SP409.8
-Mainprice, D., Hielscher, R., & Schaeben, H. (2011). Calculating anisotropic physical properties from texture data using the MTEX open-source package. Geological Society, London, Special Publications, 360(1), 175–192. https://doi.org/10.1144/SP360.10
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-Reynard, B., Gillet, P., & Willaime, C. (1989). Deformation mechanisms in naturally deformed glaucophanes: a TEM and HREM study. European Journal of Mineralogy, 1(5), 611–624. https://doi.org/10.1127/ejm/1/5/0611
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Oral Presentation: AGU 2022 Fall Meeting, Monday, December 12
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Abstract:
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Experimental constraints on the strength and deformation
mechanisms of glaucophane at subduction zone conditions
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Authors: Jason Ott, Cailey Condit, Matej Pec, and Angelica Bonanno
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Subduction zones are complex tectonic systems that generate significant geological hazards tied directly to subduction-interface strength and deformation behavior. However, the rheology and deformation mechanisms active in typical subduction lithologies remain poorly constrained. Mafic blueschists are the product of high-P/low-T metamorphism of oceanic crust during subduction and are ubiquitous along the plate interface from the seismogenic zone to the sub-arc depths. Observations of naturally deformed blueschists suggests strain is largely partitioned into the sodic amphibole glaucophane, typically a major modal component of these rocks.
To evaluate the role of glaucophane in subduction-interface rheology, we performed deformation experiments in a Sanchez-type triaxial press at relevant P-T conditions. Fine-grained glaucophane aggregates (10-20 µm) were hot-pressed for 16 hours at T=650℃ and P=1.5 GPa, then deformed at temperatures from 650-750℃ at shear strain rates () of 10-3-10-4 s-1. Preliminary results show that glaucophane reaches a peak shear stress of τ~1 GPa at T=650℃ and ~10-3 s-1. Further deformation experiments are needed to accurately determine the activation energy (Q) governing glaucophane deformation, but the preliminary observations show the peak shear stress of the material decreases by ~60% with a 100℃ temperature-increase. Stress-stepping experiments suggest deformation by dislocation-assisted motion, with a stress-exponent of n ≈ 5 at T=650℃. EBSD data collected on the recovered deformed samples confirm dislocation-facilitated deformation through preserved microstructures including increased (1) intragranular misorientation gradients, (2) subgrain formation, and (3) bulging recrystallization when compared to the hot-pressed starting material. Together, these data indicate dislocation-creep-accommodated deformation. Similarities between crystallographic preferred orientations and these observed microstructures in experimentally-deformed samples and naturally-deformed blueschists, including subgrain formation and misorientations suggest deformation along the subduction interface at blueschist conditions is largely accommodated by dislocation creep in glaucophane.
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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
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Authors: Jason Ott, Cailey Condit, Matej Pec, and Angelica Bonanno
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References:
-Elyaszadeh, R., Prior, D.J., Sarkarinejad, K., Mansouri, H., 2018. Different slip systems controlling crystallographic preferred orientation and intracrystalline deformation of amphibole in mylonites from the Neyriz mantle diapir, Iran. J. Struct. Geol. 107, 38–52. doi:10.1016/j.jsg.2017.11.020
-​Kim, J., & Jung, H. (2019). New Crystal Preferred Orientation of Amphibole Experimentally Found in Simple Shear. Geophysical Research Letters, 46(22), 12996–13005. https://doi.org/10.1029/2019GL085189
-Mainprice, D., Hielscher, R., & Schaeben, H. (2011). Calculating Anisotropic Physical Properties from Texture Data using the MTEX Open-Source Package. Geological Society, London, Special Publications, 360(1), 175–192. https://doi.org/10.1144/SP360.10
-Mainprice, D., & Humbert, M. (1994). Methods of Calculating Petrophysical Properties from Lattice Preferred Orientation Data. Surveys in Geophysics, 15(5), 575–592. https://doi.org/10.1007/BF00690175
-Peacock, S. M. (2009), Thermal and metamorphic environment of subduction zone episodic tremor and slip, J. Geophys. Res., 114, B00A07, doi:10.1029/2008JB005978.
-Pec, M., & Al Nasser, S. (2021). 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, e2020JB021262. https://doi.org/10.1029/2020JB021262
-Prior, D. J., Boyle, A. P., Brenker, F., Cheadle, M. C., Day, A., Lopez, G., et al. (1999). The Application of Electron Backscatter Diffraction and Orientation Contrast Imaging in the SEM to Textural Problems in Rocks. American Mineralogist, 84(11–12), 1741–1759. https://doi.org/10.2138/am-1999-11-1204
-Reynard, B., Gillet, P., & Willaime, C. (1989). Deformation mechanisms in naturally deformed glaucophanes: a TEM and HREM study. European Journal of Mineralogy, 1(5), 611–624. https://doi.org/10.1127/ejm/1/5/0611
-Stern, R.J., 2002. Subduction zones. Rev. Geophys. 40, 1012. doi:10.1029/2001RG000108
-Wheeler, J., Prior, D., Jiang, Z., Spiess, R., & Trimby, P. (2001). The petrological significance of misorientations between grains. Contributions to Mineralogy and Petrology, 141(1), 109–124. https://doi.org/10.1007/s004100000225
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Poster Presentation: AGU 2021 Fall Meeting, Thursday, December 16, 4-6 p.m.
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Abstract:
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Seismic anisotropy of mafic blueschists: constraints from exhumed glaucophane-
rich blueschists with implications for the subduction interface
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Authors: Jason Ott, Cailey Condit, and Vera Schulte-Pelkum
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Subduction zones generate some of Earth’s most significant geological hazards including megathrust earthquakes, tsunami, and arc volcanism. The interconnected mechanical and chemical processes controlling the dynamics of these complex systems remain poorly understood in part because we have limited exhumed subduction exposures to provide geologic constraints on remote geophysical observations. One such geophysical tool, seismic anisotropy, informs our understanding of subduction zone structure and can link deep processes to their expression as hazards at the surface. Here we provide essential geologic constraints from the rock record to better interpret observations of slab seismic anisotropy. Mafic blueschists, the glaucophane-rich product of high-P/low-T metamorphism of hydrated oceanic crust, occur along the slab top between the seismogenic zone and the sub-arc and can develop significant seismic anisotropy. This observed anisotropy is likely produced by crystallographic preferred orientations (CPO) of glaucophane and white mica formed during ductile subduction deformation. We present results from a suite of electron backscatter diffraction (EBSD)-based seismic anisotropy values from an exhumed global blueschist collection to illustrate the bounds of the range of seismic anisotropy signatures along the deforming plate interface at blueschist facies conditions. Our suite of samples exhibit variable mineralogies and represent diverse P-T conditions of metamorphism and deformation, together spanning much of the blueschist facies stability field. EBSD- constrained modal mineralogies and CPO strength together with the elastic properties of each phase are used to calculate the bulk elastic properties and resultant seismic anisotropy (in Vp and Vs) of each sample. We present trends in calculated seismic anisotropy relating to the varying phase volumes and CPO strength. This compilation improves the interpretation and construction of seismic models of the subducting oceanic lithosphere in subduction zones, increases accuracy in imaging of blueschist-metamorphosed oceanic crust, and may better constrain the depth of the blueschist-eclogite transition in individual subduction zones.
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References:
-Almqvist, B. S. G., & Mainprice, D. (2017). Seismic Properties and Anisotropy of the Continental Crust: Predictions Based on Mineral Texture and Rock Microstructure. Reviews of Geophysics, 55(2), 367–433. https://doi.org/10.1002/2016RG000552
-Ashley, K. T., Caddick, M. J., Steele-MacInnis, M. J., Bodnar, R. J., & Dragovic, B. (2014). Geothermobarometric History of Subduction Recorded by Quartz Inclusions in Garnet. Geochemistry, Geophysics, Geosystems, 15(2), 350–360. https://doi.org/10.1002/2013GC005106
-Bebout, G. E., Scholl, D. W., Stern, R. J., Wallace, L. M., & Agard, P. (2018). Twenty Years of Subduction Zone Science: Subduction Top to Bottom 2 (ST2B-2). GSA Today, 4–10. https://doi.org/10.1130/GSATG354A.1
-Bezacier, L., Reynard, B., Bass, J. D., Wang, J., & Mainprice, D. (2010). Elasticity of Glaucophane, Seismic Velocities and Anisotropy of the Subducted Oceanic Crust. Tectonophysics, 494(3), 201–210. https://doi.org/10.1016/j.tecto.2010.09.011
-Black, P. M. (1974). Oxygen Isotope Study of Metamorphic Rocks from the Ouégoa District, New Caledonia. Contributions to Mineralogy and Petrology, 47(3), 197–206. https://doi.org/10.1007/BF00371539
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-Brownlee, S. J., Schulte-Pelkum, V., Raju, A., Mahan, K., Condit, C., & Orlandini, O. F. (2017). Characteristics of Deep Crustal Seismic Anisotropy from a Compilation of Rock Elasticity Tensors and Their
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