High-temperature fracturing and subsequent grain-size-sensitive creep in lower crustal gabbros: Evidence for coseismic loading followed by creep during decaying stress in the lower crust
The mechanism of shear zone formation in lower crustal, relatively “dry” rocks is still poorly understood. We have studied the high-temperature deformation of the Hasvik gabbro (northern Norway) which commences by fracturing. The 10–20 μm wide fractures show little displacement. The fine-grained pla...
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Online Access: | https://hdl.handle.net/10037/24951 https://doi.org/10.1002/2014JB011708 |
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ftunivtroemsoe:oai:munin.uit.no:10037/24951 2023-05-15T16:33:47+02:00 High-temperature fracturing and subsequent grain-size-sensitive creep in lower crustal gabbros: Evidence for coseismic loading followed by creep during decaying stress in the lower crust Okudaira, Takamoto Jeřábek, Petr Stunitz, Holger Fusseis, Florian 2015 https://hdl.handle.net/10037/24951 https://doi.org/10.1002/2014JB011708 eng eng Wiley Journal of Geophysical Research (JGR): Solid Earth Okudaira, Jeřábek P, Stunitz H, Fusseis F. High-temperature fracturing and subsequent grain-size-sensitive creep in lower crustal gabbros: Evidence for coseismic loading followed by creep during decaying stress in the lower crust. Journal of Geophysical Research (JGR): Solid Earth. 2015;120(5):3119-3141 FRIDAID 1259439 doi:10.1002/2014JB011708 2169-9313 2169-9356 https://hdl.handle.net/10037/24951 openAccess Copyright 2015 The Author(s) Journal article Tidsskriftartikkel Peer reviewed publishedVersion 2015 ftunivtroemsoe https://doi.org/10.1002/2014JB011708 2022-05-04T22:58:43Z The mechanism of shear zone formation in lower crustal, relatively “dry” rocks is still poorly understood. We have studied the high-temperature deformation of the Hasvik gabbro (northern Norway) which commences by fracturing. The 10–20 μm wide fractures show little displacement. The fine-grained plagioclase and orthopyroxene in the fractures lack a crystallographic preferred orientation (CPO) or a systematic crystallographic orientation with respect to the host grains. Fractures grade into narrow shear zones, which are composed of fine (10–20 μm), equant grains of recrystallized plagioclase, amphibole, and pyroxene. Recrystallized plagioclase and pyroxene have compositions different from the magmatic grains, suggesting that they have formed by nucleation and growth. Based on conventional plagioclase-amphibole thermobarometry, the shear zones have formed at temperatures and pressures of 700–750°C and 0.5–0.6 GPa. The observed primary minerals cut by fractures suggest high-temperature fracturing in the absence of high pore pressures, which implies a high strength of the lower crustal gabbros and high stresses at fracturing. The shear zones are characterized by the lack of CPO and a small grain size, suggesting that the mechanism of deformation of the fine-grained plagioclase and orthopyroxene has been grain boundary sliding accommodated by diffusive mass transfer. The amphibole grains have strong CPOs, which most likely result from oriented growth and/or rigid body rotations during deformation. The process that initiated the fracturing and subsequent viscous creep in the Hasvik gabbro may have resulted from a process of coseismic loading followed by creep during decaying stress in the lower crust. Article in Journal/Newspaper Hasvik Northern Norway University of Tromsø: Munin Open Research Archive Hasvik ENVELOPE(22.161,22.161,70.486,70.486) Norway Journal of Geophysical Research: Solid Earth 120 5 3119 3141 |
institution |
Open Polar |
collection |
University of Tromsø: Munin Open Research Archive |
op_collection_id |
ftunivtroemsoe |
language |
English |
description |
The mechanism of shear zone formation in lower crustal, relatively “dry” rocks is still poorly understood. We have studied the high-temperature deformation of the Hasvik gabbro (northern Norway) which commences by fracturing. The 10–20 μm wide fractures show little displacement. The fine-grained plagioclase and orthopyroxene in the fractures lack a crystallographic preferred orientation (CPO) or a systematic crystallographic orientation with respect to the host grains. Fractures grade into narrow shear zones, which are composed of fine (10–20 μm), equant grains of recrystallized plagioclase, amphibole, and pyroxene. Recrystallized plagioclase and pyroxene have compositions different from the magmatic grains, suggesting that they have formed by nucleation and growth. Based on conventional plagioclase-amphibole thermobarometry, the shear zones have formed at temperatures and pressures of 700–750°C and 0.5–0.6 GPa. The observed primary minerals cut by fractures suggest high-temperature fracturing in the absence of high pore pressures, which implies a high strength of the lower crustal gabbros and high stresses at fracturing. The shear zones are characterized by the lack of CPO and a small grain size, suggesting that the mechanism of deformation of the fine-grained plagioclase and orthopyroxene has been grain boundary sliding accommodated by diffusive mass transfer. The amphibole grains have strong CPOs, which most likely result from oriented growth and/or rigid body rotations during deformation. The process that initiated the fracturing and subsequent viscous creep in the Hasvik gabbro may have resulted from a process of coseismic loading followed by creep during decaying stress in the lower crust. |
format |
Article in Journal/Newspaper |
author |
Okudaira, Takamoto Jeřábek, Petr Stunitz, Holger Fusseis, Florian |
spellingShingle |
Okudaira, Takamoto Jeřábek, Petr Stunitz, Holger Fusseis, Florian High-temperature fracturing and subsequent grain-size-sensitive creep in lower crustal gabbros: Evidence for coseismic loading followed by creep during decaying stress in the lower crust |
author_facet |
Okudaira, Takamoto Jeřábek, Petr Stunitz, Holger Fusseis, Florian |
author_sort |
Okudaira, Takamoto |
title |
High-temperature fracturing and subsequent grain-size-sensitive creep in lower crustal gabbros: Evidence for coseismic loading followed by creep during decaying stress in the lower crust |
title_short |
High-temperature fracturing and subsequent grain-size-sensitive creep in lower crustal gabbros: Evidence for coseismic loading followed by creep during decaying stress in the lower crust |
title_full |
High-temperature fracturing and subsequent grain-size-sensitive creep in lower crustal gabbros: Evidence for coseismic loading followed by creep during decaying stress in the lower crust |
title_fullStr |
High-temperature fracturing and subsequent grain-size-sensitive creep in lower crustal gabbros: Evidence for coseismic loading followed by creep during decaying stress in the lower crust |
title_full_unstemmed |
High-temperature fracturing and subsequent grain-size-sensitive creep in lower crustal gabbros: Evidence for coseismic loading followed by creep during decaying stress in the lower crust |
title_sort |
high-temperature fracturing and subsequent grain-size-sensitive creep in lower crustal gabbros: evidence for coseismic loading followed by creep during decaying stress in the lower crust |
publisher |
Wiley |
publishDate |
2015 |
url |
https://hdl.handle.net/10037/24951 https://doi.org/10.1002/2014JB011708 |
long_lat |
ENVELOPE(22.161,22.161,70.486,70.486) |
geographic |
Hasvik Norway |
geographic_facet |
Hasvik Norway |
genre |
Hasvik Northern Norway |
genre_facet |
Hasvik Northern Norway |
op_relation |
Journal of Geophysical Research (JGR): Solid Earth Okudaira, Jeřábek P, Stunitz H, Fusseis F. High-temperature fracturing and subsequent grain-size-sensitive creep in lower crustal gabbros: Evidence for coseismic loading followed by creep during decaying stress in the lower crust. Journal of Geophysical Research (JGR): Solid Earth. 2015;120(5):3119-3141 FRIDAID 1259439 doi:10.1002/2014JB011708 2169-9313 2169-9356 https://hdl.handle.net/10037/24951 |
op_rights |
openAccess Copyright 2015 The Author(s) |
op_doi |
https://doi.org/10.1002/2014JB011708 |
container_title |
Journal of Geophysical Research: Solid Earth |
container_volume |
120 |
container_issue |
5 |
container_start_page |
3119 |
op_container_end_page |
3141 |
_version_ |
1766023486875107328 |