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Helene Couvy - One of the best experts on this subject based on the ideXlab platform.
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strain induced seismic anisotropy of wadsleyite polycrystals and flow patterns in the mantle transition zone
Journal of Geophysical Research, 2004Co-Authors: Andrea Tommasi, David Mainprice, Patrick Cordier, Catherine Thoraval, Helene CouvyAbstract:[1] We use forward models based on recent high-pressure experimental data on mantle minerals to predict the seismic anisotropy produced by plastic strain of orthorhombic wadsleyite, the dominant mineral in the upper transition zone. These models predict a weak seismic anisotropy for a polycrystal of pyrolitic composition (60% wadsleyite, 40% garnet) at transition zone conditions: ∼2% for P and ∼1% for S waves for a Shear strain of 1. Both P and S wave anisotropy patterns show an orthorhombic symmetry. P waves propagate faster at low angle to the Shear Direction and slower at high angle to the Shear plane. S wave anisotropy is characterized by faster propagation of waves polarized at low angle to the Shear Direction. Horizontal Shearing results therefore in higher velocities for horizontally propagating P waves (PH) and horizontally polarized S waves (SH), as well as in weak azimuthal variation of SV and SH velocities. On the other hand, vertical flow leads to higher velocities for vertically propagating P waves (PV) and vertically polarized S waves (SV) and to a weak azimuthal variation of SV velocity but to a roughly constant SH velocity. Analysis of global observations of seismic anisotropy in the transition zone in the light of these models supports dominant horizontal flow in the uppermost transition zone, in agreement with predictions of geodynamical models that explicitly introduce phase transitions.
Christopher Goscinak - One of the best experts on this subject based on the ideXlab platform.
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corrigendum to constrains on vorticity and non coaxial Shear Direction in neoarchean l s tectonites an example from northern minnesota usa precambrian res 256 2015 189 200
Precambrian Research, 2015Co-Authors: Jonathan E. Dyess, Vicki L. Hansen, Christopher GoscinakAbstract:Please cite this article in press as: Dyess, J.E., et al., Corrigendum to “Constrains on vorticity and non-coaxial Shear Direction in Neoarchean L-S tectonites, an example from northern Minnesota, USA” [Precambrian Res. 256 (2015) 189–200]. Precambrian Res. (2014), http://dx.doi.org/10.1016/j.precamres.2014.12.006 The authors regret that the original title of this contribution was listed as “Constrains on vorticity and non-coaxial Shear Direction in eoarchean L-S tectonites, an example from northern Minnesota, USA.” The correct title is “Constraints on vorticity and non-coaxial Shear irection in Neoarchean L-S tectonites, an example from northern Minnesota, USA.” The authors would like to apologise for any inconvenience caused.
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Corrigendum to “Constrains on vorticity and non-coaxial Shear Direction in Neoarchean L-S tectonites, an example from northern Minnesota, USA” [Precambrian Res. 256 (2015) 189–200]
Precambrian Research, 2015Co-Authors: Jonathan E. Dyess, Vicki L. Hansen, Christopher GoscinakAbstract:Please cite this article in press as: Dyess, J.E., et al., Corrigendum to “Constrains on vorticity and non-coaxial Shear Direction in Neoarchean L-S tectonites, an example from northern Minnesota, USA” [Precambrian Res. 256 (2015) 189–200]. Precambrian Res. (2014), http://dx.doi.org/10.1016/j.precamres.2014.12.006 The authors regret that the original title of this contribution was listed as “Constrains on vorticity and non-coaxial Shear Direction in eoarchean L-S tectonites, an example from northern Minnesota, USA.” The correct title is “Constraints on vorticity and non-coaxial Shear irection in Neoarchean L-S tectonites, an example from northern Minnesota, USA.” The authors would like to apologise for any inconvenience caused.
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Constrains on vorticity and non-coaxial Shear Direction in Neoarchean L-S tectonites, an example from northern Minnesota, USA
Precambrian Research, 2014Co-Authors: Jonathan E. Dyess, Vicki L. Hansen, Christopher GoscinakAbstract:Abstract We present a detailed kinematic study of seven Neoarchean L-S tectonite samples in order to constrain vorticity and non-coaxial Shear Direction relative to foliation and elongation lineation. Samples are L-S tectonites from the Wawa Subprovince of the Archean Superior Province, more specifically the Vermilion District of NE Minnesota, a NE-trending belt of greenschist grade supracrustal rocks and granitoid bodies. Supracrustal rocks host multiple L-S tectonite packages with a well-developed sub-vertical metamorphic foliation and elongation lineation; elongation lineation generally plunges steeply to gently, although zones of shallow plunge occur locally. The Wawa Subprovince is widely interpreted as a transpressional plate margin with Shear zones recording uniDirectional dextral strike-slip, an interpretation held up as fundamental evidence for Archean plate-tectonic processes. However, vorticity and Shear Direction within Vermilion District L-S tectonites remain unconstrained. We compare data from thin-sections, X-ray computed tomography, and quartz crystallographic fabric analysis to monoclinic Shear models to constrain vorticity and better understand the geometric relationships between vorticity, non-coaxial Shear Direction, foliation, and elongation lineation. Kinematic indicators in thin-section and image slices from X-ray computed tomography consistently record asymmetric microstructural fabrics in foliation-normal/lineation-parallel planes, whereas planes normal to foliation and elongation lineation display dominantly symmetric microstructural fabrics. Mantled porphyroclast 3D-shapes and star-volume distribution analyses indicate that porphyroclast short-axes are normal to foliation and long-axes parallel elongation lineation. Quartz crystallographic preferred orientation data show a-axes maxima sub-parallel to foliation-normal/lineation-parallel planes. Kinematic data consistently show a vorticity vector within the foliation plane and normal to elongation lineation; thus non-coaxial Shear Direction is sub-parallel to elongation lineation. Data are inconsistent with Shear models in which non-coaxial Shear Direction is normal to lineation, or in which the vorticity vector is normal to foliation. Rather, kinematic data indicate that tectonites record non-coaxial Shear broadly parallel to elongation lineation regardless of the geographic orientation of lineation.
Jonathan E. Dyess - One of the best experts on this subject based on the ideXlab platform.
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corrigendum to constrains on vorticity and non coaxial Shear Direction in neoarchean l s tectonites an example from northern minnesota usa precambrian res 256 2015 189 200
Precambrian Research, 2015Co-Authors: Jonathan E. Dyess, Vicki L. Hansen, Christopher GoscinakAbstract:Please cite this article in press as: Dyess, J.E., et al., Corrigendum to “Constrains on vorticity and non-coaxial Shear Direction in Neoarchean L-S tectonites, an example from northern Minnesota, USA” [Precambrian Res. 256 (2015) 189–200]. Precambrian Res. (2014), http://dx.doi.org/10.1016/j.precamres.2014.12.006 The authors regret that the original title of this contribution was listed as “Constrains on vorticity and non-coaxial Shear Direction in eoarchean L-S tectonites, an example from northern Minnesota, USA.” The correct title is “Constraints on vorticity and non-coaxial Shear irection in Neoarchean L-S tectonites, an example from northern Minnesota, USA.” The authors would like to apologise for any inconvenience caused.
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Corrigendum to “Constrains on vorticity and non-coaxial Shear Direction in Neoarchean L-S tectonites, an example from northern Minnesota, USA” [Precambrian Res. 256 (2015) 189–200]
Precambrian Research, 2015Co-Authors: Jonathan E. Dyess, Vicki L. Hansen, Christopher GoscinakAbstract:Please cite this article in press as: Dyess, J.E., et al., Corrigendum to “Constrains on vorticity and non-coaxial Shear Direction in Neoarchean L-S tectonites, an example from northern Minnesota, USA” [Precambrian Res. 256 (2015) 189–200]. Precambrian Res. (2014), http://dx.doi.org/10.1016/j.precamres.2014.12.006 The authors regret that the original title of this contribution was listed as “Constrains on vorticity and non-coaxial Shear Direction in eoarchean L-S tectonites, an example from northern Minnesota, USA.” The correct title is “Constraints on vorticity and non-coaxial Shear irection in Neoarchean L-S tectonites, an example from northern Minnesota, USA.” The authors would like to apologise for any inconvenience caused.
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Constrains on vorticity and non-coaxial Shear Direction in Neoarchean L-S tectonites, an example from northern Minnesota, USA
Precambrian Research, 2014Co-Authors: Jonathan E. Dyess, Vicki L. Hansen, Christopher GoscinakAbstract:Abstract We present a detailed kinematic study of seven Neoarchean L-S tectonite samples in order to constrain vorticity and non-coaxial Shear Direction relative to foliation and elongation lineation. Samples are L-S tectonites from the Wawa Subprovince of the Archean Superior Province, more specifically the Vermilion District of NE Minnesota, a NE-trending belt of greenschist grade supracrustal rocks and granitoid bodies. Supracrustal rocks host multiple L-S tectonite packages with a well-developed sub-vertical metamorphic foliation and elongation lineation; elongation lineation generally plunges steeply to gently, although zones of shallow plunge occur locally. The Wawa Subprovince is widely interpreted as a transpressional plate margin with Shear zones recording uniDirectional dextral strike-slip, an interpretation held up as fundamental evidence for Archean plate-tectonic processes. However, vorticity and Shear Direction within Vermilion District L-S tectonites remain unconstrained. We compare data from thin-sections, X-ray computed tomography, and quartz crystallographic fabric analysis to monoclinic Shear models to constrain vorticity and better understand the geometric relationships between vorticity, non-coaxial Shear Direction, foliation, and elongation lineation. Kinematic indicators in thin-section and image slices from X-ray computed tomography consistently record asymmetric microstructural fabrics in foliation-normal/lineation-parallel planes, whereas planes normal to foliation and elongation lineation display dominantly symmetric microstructural fabrics. Mantled porphyroclast 3D-shapes and star-volume distribution analyses indicate that porphyroclast short-axes are normal to foliation and long-axes parallel elongation lineation. Quartz crystallographic preferred orientation data show a-axes maxima sub-parallel to foliation-normal/lineation-parallel planes. Kinematic data consistently show a vorticity vector within the foliation plane and normal to elongation lineation; thus non-coaxial Shear Direction is sub-parallel to elongation lineation. Data are inconsistent with Shear models in which non-coaxial Shear Direction is normal to lineation, or in which the vorticity vector is normal to foliation. Rather, kinematic data indicate that tectonites record non-coaxial Shear broadly parallel to elongation lineation regardless of the geographic orientation of lineation.
Vicki L. Hansen - One of the best experts on this subject based on the ideXlab platform.
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corrigendum to constrains on vorticity and non coaxial Shear Direction in neoarchean l s tectonites an example from northern minnesota usa precambrian res 256 2015 189 200
Precambrian Research, 2015Co-Authors: Jonathan E. Dyess, Vicki L. Hansen, Christopher GoscinakAbstract:Please cite this article in press as: Dyess, J.E., et al., Corrigendum to “Constrains on vorticity and non-coaxial Shear Direction in Neoarchean L-S tectonites, an example from northern Minnesota, USA” [Precambrian Res. 256 (2015) 189–200]. Precambrian Res. (2014), http://dx.doi.org/10.1016/j.precamres.2014.12.006 The authors regret that the original title of this contribution was listed as “Constrains on vorticity and non-coaxial Shear Direction in eoarchean L-S tectonites, an example from northern Minnesota, USA.” The correct title is “Constraints on vorticity and non-coaxial Shear irection in Neoarchean L-S tectonites, an example from northern Minnesota, USA.” The authors would like to apologise for any inconvenience caused.
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Corrigendum to “Constrains on vorticity and non-coaxial Shear Direction in Neoarchean L-S tectonites, an example from northern Minnesota, USA” [Precambrian Res. 256 (2015) 189–200]
Precambrian Research, 2015Co-Authors: Jonathan E. Dyess, Vicki L. Hansen, Christopher GoscinakAbstract:Please cite this article in press as: Dyess, J.E., et al., Corrigendum to “Constrains on vorticity and non-coaxial Shear Direction in Neoarchean L-S tectonites, an example from northern Minnesota, USA” [Precambrian Res. 256 (2015) 189–200]. Precambrian Res. (2014), http://dx.doi.org/10.1016/j.precamres.2014.12.006 The authors regret that the original title of this contribution was listed as “Constrains on vorticity and non-coaxial Shear Direction in eoarchean L-S tectonites, an example from northern Minnesota, USA.” The correct title is “Constraints on vorticity and non-coaxial Shear irection in Neoarchean L-S tectonites, an example from northern Minnesota, USA.” The authors would like to apologise for any inconvenience caused.
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Constrains on vorticity and non-coaxial Shear Direction in Neoarchean L-S tectonites, an example from northern Minnesota, USA
Precambrian Research, 2014Co-Authors: Jonathan E. Dyess, Vicki L. Hansen, Christopher GoscinakAbstract:Abstract We present a detailed kinematic study of seven Neoarchean L-S tectonite samples in order to constrain vorticity and non-coaxial Shear Direction relative to foliation and elongation lineation. Samples are L-S tectonites from the Wawa Subprovince of the Archean Superior Province, more specifically the Vermilion District of NE Minnesota, a NE-trending belt of greenschist grade supracrustal rocks and granitoid bodies. Supracrustal rocks host multiple L-S tectonite packages with a well-developed sub-vertical metamorphic foliation and elongation lineation; elongation lineation generally plunges steeply to gently, although zones of shallow plunge occur locally. The Wawa Subprovince is widely interpreted as a transpressional plate margin with Shear zones recording uniDirectional dextral strike-slip, an interpretation held up as fundamental evidence for Archean plate-tectonic processes. However, vorticity and Shear Direction within Vermilion District L-S tectonites remain unconstrained. We compare data from thin-sections, X-ray computed tomography, and quartz crystallographic fabric analysis to monoclinic Shear models to constrain vorticity and better understand the geometric relationships between vorticity, non-coaxial Shear Direction, foliation, and elongation lineation. Kinematic indicators in thin-section and image slices from X-ray computed tomography consistently record asymmetric microstructural fabrics in foliation-normal/lineation-parallel planes, whereas planes normal to foliation and elongation lineation display dominantly symmetric microstructural fabrics. Mantled porphyroclast 3D-shapes and star-volume distribution analyses indicate that porphyroclast short-axes are normal to foliation and long-axes parallel elongation lineation. Quartz crystallographic preferred orientation data show a-axes maxima sub-parallel to foliation-normal/lineation-parallel planes. Kinematic data consistently show a vorticity vector within the foliation plane and normal to elongation lineation; thus non-coaxial Shear Direction is sub-parallel to elongation lineation. Data are inconsistent with Shear models in which non-coaxial Shear Direction is normal to lineation, or in which the vorticity vector is normal to foliation. Rather, kinematic data indicate that tectonites record non-coaxial Shear broadly parallel to elongation lineation regardless of the geographic orientation of lineation.
Andrea Tommasi - One of the best experts on this subject based on the ideXlab platform.
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strain induced seismic anisotropy of wadsleyite polycrystals and flow patterns in the mantle transition zone
Journal of Geophysical Research, 2004Co-Authors: Andrea Tommasi, David Mainprice, Patrick Cordier, Catherine Thoraval, Helene CouvyAbstract:[1] We use forward models based on recent high-pressure experimental data on mantle minerals to predict the seismic anisotropy produced by plastic strain of orthorhombic wadsleyite, the dominant mineral in the upper transition zone. These models predict a weak seismic anisotropy for a polycrystal of pyrolitic composition (60% wadsleyite, 40% garnet) at transition zone conditions: ∼2% for P and ∼1% for S waves for a Shear strain of 1. Both P and S wave anisotropy patterns show an orthorhombic symmetry. P waves propagate faster at low angle to the Shear Direction and slower at high angle to the Shear plane. S wave anisotropy is characterized by faster propagation of waves polarized at low angle to the Shear Direction. Horizontal Shearing results therefore in higher velocities for horizontally propagating P waves (PH) and horizontally polarized S waves (SH), as well as in weak azimuthal variation of SV and SH velocities. On the other hand, vertical flow leads to higher velocities for vertically propagating P waves (PV) and vertically polarized S waves (SV) and to a weak azimuthal variation of SV velocity but to a roughly constant SH velocity. Analysis of global observations of seismic anisotropy in the transition zone in the light of these models supports dominant horizontal flow in the uppermost transition zone, in agreement with predictions of geodynamical models that explicitly introduce phase transitions.