Viscous anisotropy of textured olivine aggregates, Part 1: Measurement of the magnitude and evolution of anisotropy

The development of crystallographic textures in olivine-rich rocks leads to a marked anisotropy in viscosity of the upper mantle, strongly influencing a variety of large-scale geodynamic processes. Most estimates of the magnitude of viscous anisotropy in the upper mantle are derived from micromechan...

Täydet tiedot

Bibliografiset tiedot
Päätekijät: Hansen, L, Warren, J, Zimmerman, M, Kohlstedt, D
Aineistotyyppi: Journal article
Julkaistu: Elsevier 2016
_version_ 1826263297211498496
author Hansen, L
Warren, J
Zimmerman, M
Kohlstedt, D
author_facet Hansen, L
Warren, J
Zimmerman, M
Kohlstedt, D
author_sort Hansen, L
collection OXFORD
description The development of crystallographic textures in olivine-rich rocks leads to a marked anisotropy in viscosity of the upper mantle, strongly influencing a variety of large-scale geodynamic processes. Most estimates of the magnitude of viscous anisotropy in the upper mantle are derived from micromechanical models that predict textural and mechanical evolution numerically. Unfortunately, relatively few data exist with which to benchmark these models, and therefore their applicability to geodynamic processes remains in question. Here we present the results from a series of laboratory deformation experiments that yield insight into the magnitude and evolution of the anisotropy of olivine aggregates during deformation along complex loading paths. Aggregates of Fo50 olivine were first deformed in extension in a gas-medium apparatus at a temperature of 1473 K, confining pressure of 300 MPa, and a variety of stresses and strain rates. Early in the extension experiments, samples exhibited viscosities similar to those previously determined for isotropic aggregates. Extensional deformation was accompanied by formation of crystallographic textures with [100] axes dominantly aligned with the extension axis. Samples were subsequently deformed in torsion under similar conditions to shear strains of up to 15.5. Early in the torsion experiments, samples supported stresses a factor of ~2 larger than measured at the end of extension experiments, demonstrating a marked anisotropy in viscosity. Textures at the end of torsion experiments exhibited [100] axes dominantly aligned with the shear direction, comparable to previous experimental observations. Evolution of the textures resulting from extension to those resulting from torsion was analyzed through examination of radial sections of torsion samples. Our results confirm that texture produces viscous anisotropy in olivine aggregates, and we provide a simple, calibrated parameterization of viscous anisotropy for use in geodynamic models. Our results also provide an extensive dataset for future calibration of micromechanical models that track the evolution of anisotropy in upper mantle rocks.
first_indexed 2024-03-06T19:49:30Z
format Journal article
id oxford-uuid:237b35db-34be-4668-a1fd-fbd24f64630b
institution University of Oxford
last_indexed 2024-03-06T19:49:30Z
publishDate 2016
publisher Elsevier
record_format dspace
spelling oxford-uuid:237b35db-34be-4668-a1fd-fbd24f64630b2022-03-26T11:44:36ZViscous anisotropy of textured olivine aggregates, Part 1: Measurement of the magnitude and evolution of anisotropyJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:237b35db-34be-4668-a1fd-fbd24f64630bSymplectic Elements at OxfordElsevier2016Hansen, LWarren, JZimmerman, MKohlstedt, DThe development of crystallographic textures in olivine-rich rocks leads to a marked anisotropy in viscosity of the upper mantle, strongly influencing a variety of large-scale geodynamic processes. Most estimates of the magnitude of viscous anisotropy in the upper mantle are derived from micromechanical models that predict textural and mechanical evolution numerically. Unfortunately, relatively few data exist with which to benchmark these models, and therefore their applicability to geodynamic processes remains in question. Here we present the results from a series of laboratory deformation experiments that yield insight into the magnitude and evolution of the anisotropy of olivine aggregates during deformation along complex loading paths. Aggregates of Fo50 olivine were first deformed in extension in a gas-medium apparatus at a temperature of 1473 K, confining pressure of 300 MPa, and a variety of stresses and strain rates. Early in the extension experiments, samples exhibited viscosities similar to those previously determined for isotropic aggregates. Extensional deformation was accompanied by formation of crystallographic textures with [100] axes dominantly aligned with the extension axis. Samples were subsequently deformed in torsion under similar conditions to shear strains of up to 15.5. Early in the torsion experiments, samples supported stresses a factor of ~2 larger than measured at the end of extension experiments, demonstrating a marked anisotropy in viscosity. Textures at the end of torsion experiments exhibited [100] axes dominantly aligned with the shear direction, comparable to previous experimental observations. Evolution of the textures resulting from extension to those resulting from torsion was analyzed through examination of radial sections of torsion samples. Our results confirm that texture produces viscous anisotropy in olivine aggregates, and we provide a simple, calibrated parameterization of viscous anisotropy for use in geodynamic models. Our results also provide an extensive dataset for future calibration of micromechanical models that track the evolution of anisotropy in upper mantle rocks.
spellingShingle Hansen, L
Warren, J
Zimmerman, M
Kohlstedt, D
Viscous anisotropy of textured olivine aggregates, Part 1: Measurement of the magnitude and evolution of anisotropy
title Viscous anisotropy of textured olivine aggregates, Part 1: Measurement of the magnitude and evolution of anisotropy
title_full Viscous anisotropy of textured olivine aggregates, Part 1: Measurement of the magnitude and evolution of anisotropy
title_fullStr Viscous anisotropy of textured olivine aggregates, Part 1: Measurement of the magnitude and evolution of anisotropy
title_full_unstemmed Viscous anisotropy of textured olivine aggregates, Part 1: Measurement of the magnitude and evolution of anisotropy
title_short Viscous anisotropy of textured olivine aggregates, Part 1: Measurement of the magnitude and evolution of anisotropy
title_sort viscous anisotropy of textured olivine aggregates part 1 measurement of the magnitude and evolution of anisotropy
work_keys_str_mv AT hansenl viscousanisotropyoftexturedolivineaggregatespart1measurementofthemagnitudeandevolutionofanisotropy
AT warrenj viscousanisotropyoftexturedolivineaggregatespart1measurementofthemagnitudeandevolutionofanisotropy
AT zimmermanm viscousanisotropyoftexturedolivineaggregatespart1measurementofthemagnitudeandevolutionofanisotropy
AT kohlstedtd viscousanisotropyoftexturedolivineaggregatespart1measurementofthemagnitudeandevolutionofanisotropy