Earthquakes as Precursors of Ductile Shear Zones in the Dry and Strong Lower Crust
The rheology and the conditions for viscous flow of the dry granulite facies lower crust are still poorly understood. Viscous shearing in the dry and strong lower crust commonly localizes in pseudotachylyte veins, but the deformation mechanisms responsible for the weakening and viscous shear localiz...
Published in: | Geochemistry, Geophysics, Geosystems |
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Blackwell Publishing Ltd
2017
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Online Access: | http://hdl.handle.net/11577/3258747 https://doi.org/10.1002/2017GC007189 http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1525-2027 |
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ftunivpadovairis:oai:www.research.unipd.it:11577/3258747 2024-02-27T08:42:39+00:00 Earthquakes as Precursors of Ductile Shear Zones in the Dry and Strong Lower Crust Menegon, L. Pennacchioni, G. Malaspina, N. Harris, K. Wood, E. Menegon, L. Pennacchioni, G. Malaspina, N. Harris, K. Wood, E. 2017 ELETTRONICO http://hdl.handle.net/11577/3258747 https://doi.org/10.1002/2017GC007189 http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1525-2027 eng eng Blackwell Publishing Ltd info:eu-repo/semantics/altIdentifier/wos/WOS:000423230600007 volume:18 issue:12 firstpage:4356 lastpage:4374 numberofpages:19 journal:GEOCHEMISTRY, GEOPHYSICS, GEOSYSTEMS http://hdl.handle.net/11577/3258747 doi:10.1002/2017GC007189 info:eu-repo/semantics/altIdentifier/scopus/2-s2.0-85037652703 http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1525-2027 info:eu-repo/semantics/openAccess deformation mechanism grain-size sensitive creep Lofoten lower crustal earthquake pseudotachylyte shear zone Geophysic Geochemistry and Petrology info:eu-repo/semantics/article 2017 ftunivpadovairis https://doi.org/10.1002/2017GC007189 2024-01-31T17:54:40Z The rheology and the conditions for viscous flow of the dry granulite facies lower crust are still poorly understood. Viscous shearing in the dry and strong lower crust commonly localizes in pseudotachylyte veins, but the deformation mechanisms responsible for the weakening and viscous shear localization in pseudotachylytes are yet to be explored. We investigated examples of pristine and mylonitized pseudotachylytes in anorthosites from Nusfjord (Lofoten, Norway). Mutual overprinting relationships indicate that pristine and mylonitized pseudotachylytes are coeval and resulted from the cyclical interplay between brittle and viscous deformation. The stable mineral assemblage in the mylonitized pseudotachylytes consists of plagioclase, amphibole, clinopyroxene, quartz, biotite,6garnet6K-feldspar. Amphibole-plagioclase geothermobarometry and thermodynamic modeling indicate that pristine and mylonitized pseudotachylytes formed at 650–7508C and 0.7–0.8 GPa. Thermodynamic modeling indicates that a limited amount of H2O infiltration (0.20–0.40 wt. %) was necessary to stabilize the mineral assemblage in the mylonite. Diffusion creep is identified as the main deformation mechanisms in the mylonitized pseudotachylytes based on the lack of crystallographic preferred orientation in plagioclase, the high degree of phase mixing, and the synkinematic nucleation of amphiboles in dilatant sites. Extrapolation of flow laws to natural conditions indicates that mylonitized pseudotachylytes are up to 3 orders of magnitude weaker than anorthosites deforming by dislocation creep, thus highlighting the fundamental role of lower crustal earthquakes as agents of weakening in strong granulites. Article in Journal/Newspaper Lofoten Padua Research Archive (IRIS - Università degli Studi di Padova) Lofoten Norway Nusfjord ENVELOPE(13.348,13.348,68.035,68.035) Geochemistry, Geophysics, Geosystems 18 12 4356 4374 |
institution |
Open Polar |
collection |
Padua Research Archive (IRIS - Università degli Studi di Padova) |
op_collection_id |
ftunivpadovairis |
language |
English |
topic |
deformation mechanism grain-size sensitive creep Lofoten lower crustal earthquake pseudotachylyte shear zone Geophysic Geochemistry and Petrology |
spellingShingle |
deformation mechanism grain-size sensitive creep Lofoten lower crustal earthquake pseudotachylyte shear zone Geophysic Geochemistry and Petrology Menegon, L. Pennacchioni, G. Malaspina, N. Harris, K. Wood, E. Earthquakes as Precursors of Ductile Shear Zones in the Dry and Strong Lower Crust |
topic_facet |
deformation mechanism grain-size sensitive creep Lofoten lower crustal earthquake pseudotachylyte shear zone Geophysic Geochemistry and Petrology |
description |
The rheology and the conditions for viscous flow of the dry granulite facies lower crust are still poorly understood. Viscous shearing in the dry and strong lower crust commonly localizes in pseudotachylyte veins, but the deformation mechanisms responsible for the weakening and viscous shear localization in pseudotachylytes are yet to be explored. We investigated examples of pristine and mylonitized pseudotachylytes in anorthosites from Nusfjord (Lofoten, Norway). Mutual overprinting relationships indicate that pristine and mylonitized pseudotachylytes are coeval and resulted from the cyclical interplay between brittle and viscous deformation. The stable mineral assemblage in the mylonitized pseudotachylytes consists of plagioclase, amphibole, clinopyroxene, quartz, biotite,6garnet6K-feldspar. Amphibole-plagioclase geothermobarometry and thermodynamic modeling indicate that pristine and mylonitized pseudotachylytes formed at 650–7508C and 0.7–0.8 GPa. Thermodynamic modeling indicates that a limited amount of H2O infiltration (0.20–0.40 wt. %) was necessary to stabilize the mineral assemblage in the mylonite. Diffusion creep is identified as the main deformation mechanisms in the mylonitized pseudotachylytes based on the lack of crystallographic preferred orientation in plagioclase, the high degree of phase mixing, and the synkinematic nucleation of amphiboles in dilatant sites. Extrapolation of flow laws to natural conditions indicates that mylonitized pseudotachylytes are up to 3 orders of magnitude weaker than anorthosites deforming by dislocation creep, thus highlighting the fundamental role of lower crustal earthquakes as agents of weakening in strong granulites. |
author2 |
Menegon, L. Pennacchioni, G. Malaspina, N. Harris, K. Wood, E. |
format |
Article in Journal/Newspaper |
author |
Menegon, L. Pennacchioni, G. Malaspina, N. Harris, K. Wood, E. |
author_facet |
Menegon, L. Pennacchioni, G. Malaspina, N. Harris, K. Wood, E. |
author_sort |
Menegon, L. |
title |
Earthquakes as Precursors of Ductile Shear Zones in the Dry and Strong Lower Crust |
title_short |
Earthquakes as Precursors of Ductile Shear Zones in the Dry and Strong Lower Crust |
title_full |
Earthquakes as Precursors of Ductile Shear Zones in the Dry and Strong Lower Crust |
title_fullStr |
Earthquakes as Precursors of Ductile Shear Zones in the Dry and Strong Lower Crust |
title_full_unstemmed |
Earthquakes as Precursors of Ductile Shear Zones in the Dry and Strong Lower Crust |
title_sort |
earthquakes as precursors of ductile shear zones in the dry and strong lower crust |
publisher |
Blackwell Publishing Ltd |
publishDate |
2017 |
url |
http://hdl.handle.net/11577/3258747 https://doi.org/10.1002/2017GC007189 http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1525-2027 |
long_lat |
ENVELOPE(13.348,13.348,68.035,68.035) |
geographic |
Lofoten Norway Nusfjord |
geographic_facet |
Lofoten Norway Nusfjord |
genre |
Lofoten |
genre_facet |
Lofoten |
op_relation |
info:eu-repo/semantics/altIdentifier/wos/WOS:000423230600007 volume:18 issue:12 firstpage:4356 lastpage:4374 numberofpages:19 journal:GEOCHEMISTRY, GEOPHYSICS, GEOSYSTEMS http://hdl.handle.net/11577/3258747 doi:10.1002/2017GC007189 info:eu-repo/semantics/altIdentifier/scopus/2-s2.0-85037652703 http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1525-2027 |
op_rights |
info:eu-repo/semantics/openAccess |
op_doi |
https://doi.org/10.1002/2017GC007189 |
container_title |
Geochemistry, Geophysics, Geosystems |
container_volume |
18 |
container_issue |
12 |
container_start_page |
4356 |
op_container_end_page |
4374 |
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