Brittle–viscous deformation of vein quartz under fluid-rich lower greenschist facies conditions
We studied by Electron BackScatter Diffraction (EBSD) and optical microscopy a coarse-grained (ca. 0.5–6 mm) quartz vein embedded in a phyllonitic matrix to gain insights into the recrystallization mechanisms and the processes of strain localization in quartz deformed under lower greenschist facies...
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ftdoajarticles:oai:doaj.org/article:742f05377f844a74849ba93c9bc0ff94 2023-05-15T17:43:36+02:00 Brittle–viscous deformation of vein quartz under fluid-rich lower greenschist facies conditions H. J. Kjøll G. Viola L. Menegon B. E. Sørensen 2015-06-01T00:00:00Z https://doi.org/10.5194/se-6-681-2015 https://doaj.org/article/742f05377f844a74849ba93c9bc0ff94 EN eng Copernicus Publications http://www.solid-earth.net/6/681/2015/se-6-681-2015.pdf https://doaj.org/toc/1869-9510 https://doaj.org/toc/1869-9529 1869-9510 1869-9529 doi:10.5194/se-6-681-2015 https://doaj.org/article/742f05377f844a74849ba93c9bc0ff94 Solid Earth, Vol 6, Iss 2, Pp 681-699 (2015) Geology QE1-996.5 Stratigraphy QE640-699 article 2015 ftdoajarticles https://doi.org/10.5194/se-6-681-2015 2022-12-30T23:26:38Z We studied by Electron BackScatter Diffraction (EBSD) and optical microscopy a coarse-grained (ca. 0.5–6 mm) quartz vein embedded in a phyllonitic matrix to gain insights into the recrystallization mechanisms and the processes of strain localization in quartz deformed under lower greenschist facies conditions, broadly coincident with the brittle–viscous transition. The vein deformed during faulting along a phyllonitic thrust of Caledonian age within the Porsa Imbricate Stack in the Paleoproterozoic Repparfjord Tectonic Window in northern Norway. The phyllonite hosting the vein formed at the expense of a metabasaltic protolith through feldspar breakdown to form interconnected layers of fine, synkinematic phyllosilicates. In the mechanically weak framework of the phyllonite, the quartz vein acted as a relatively rigid body. Viscous deformation in the vein was initially accommodated by quartz basal < a > slip. Under the prevailing deformation conditions, however, dislocation glide- and possibly creep-accommodated deformation of quartz was inefficient, and this resulted in localized strain hardening. In response to the (1) hardening, (2) progressive and cyclic increase of the fluid pressure, and (3) increasing competence contrast between the vein and the weakly foliated host phyllonite, vein quartz crystals began to deform by brittle processes along specific, suitably oriented lattice planes, creating microgouges along microfractures. Nucleated new grains rapidly sealed these fractures as fluids penetrated the actively deforming system. The grains grew initially by solution precipitation and later by grain boundary migration. We suggest that the different initial orientation of the vein crystals led to strain accommodation by different mechanisms in the individual crystals, generating remarkably different microstructures. Crystals suitably oriented for basal slip, for example, accommodated strain mainly viscously and experienced only minor fracturing. Instead, crystals misoriented for basal slip hardened and ... Article in Journal/Newspaper Northern Norway Directory of Open Access Journals: DOAJ Articles Norway Repparfjord ENVELOPE(24.550,24.550,70.417,70.417) Solid Earth 6 2 681 699 |
institution |
Open Polar |
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Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
Geology QE1-996.5 Stratigraphy QE640-699 |
spellingShingle |
Geology QE1-996.5 Stratigraphy QE640-699 H. J. Kjøll G. Viola L. Menegon B. E. Sørensen Brittle–viscous deformation of vein quartz under fluid-rich lower greenschist facies conditions |
topic_facet |
Geology QE1-996.5 Stratigraphy QE640-699 |
description |
We studied by Electron BackScatter Diffraction (EBSD) and optical microscopy a coarse-grained (ca. 0.5–6 mm) quartz vein embedded in a phyllonitic matrix to gain insights into the recrystallization mechanisms and the processes of strain localization in quartz deformed under lower greenschist facies conditions, broadly coincident with the brittle–viscous transition. The vein deformed during faulting along a phyllonitic thrust of Caledonian age within the Porsa Imbricate Stack in the Paleoproterozoic Repparfjord Tectonic Window in northern Norway. The phyllonite hosting the vein formed at the expense of a metabasaltic protolith through feldspar breakdown to form interconnected layers of fine, synkinematic phyllosilicates. In the mechanically weak framework of the phyllonite, the quartz vein acted as a relatively rigid body. Viscous deformation in the vein was initially accommodated by quartz basal < a > slip. Under the prevailing deformation conditions, however, dislocation glide- and possibly creep-accommodated deformation of quartz was inefficient, and this resulted in localized strain hardening. In response to the (1) hardening, (2) progressive and cyclic increase of the fluid pressure, and (3) increasing competence contrast between the vein and the weakly foliated host phyllonite, vein quartz crystals began to deform by brittle processes along specific, suitably oriented lattice planes, creating microgouges along microfractures. Nucleated new grains rapidly sealed these fractures as fluids penetrated the actively deforming system. The grains grew initially by solution precipitation and later by grain boundary migration. We suggest that the different initial orientation of the vein crystals led to strain accommodation by different mechanisms in the individual crystals, generating remarkably different microstructures. Crystals suitably oriented for basal slip, for example, accommodated strain mainly viscously and experienced only minor fracturing. Instead, crystals misoriented for basal slip hardened and ... |
format |
Article in Journal/Newspaper |
author |
H. J. Kjøll G. Viola L. Menegon B. E. Sørensen |
author_facet |
H. J. Kjøll G. Viola L. Menegon B. E. Sørensen |
author_sort |
H. J. Kjøll |
title |
Brittle–viscous deformation of vein quartz under fluid-rich lower greenschist facies conditions |
title_short |
Brittle–viscous deformation of vein quartz under fluid-rich lower greenschist facies conditions |
title_full |
Brittle–viscous deformation of vein quartz under fluid-rich lower greenschist facies conditions |
title_fullStr |
Brittle–viscous deformation of vein quartz under fluid-rich lower greenschist facies conditions |
title_full_unstemmed |
Brittle–viscous deformation of vein quartz under fluid-rich lower greenschist facies conditions |
title_sort |
brittle–viscous deformation of vein quartz under fluid-rich lower greenschist facies conditions |
publisher |
Copernicus Publications |
publishDate |
2015 |
url |
https://doi.org/10.5194/se-6-681-2015 https://doaj.org/article/742f05377f844a74849ba93c9bc0ff94 |
long_lat |
ENVELOPE(24.550,24.550,70.417,70.417) |
geographic |
Norway Repparfjord |
geographic_facet |
Norway Repparfjord |
genre |
Northern Norway |
genre_facet |
Northern Norway |
op_source |
Solid Earth, Vol 6, Iss 2, Pp 681-699 (2015) |
op_relation |
http://www.solid-earth.net/6/681/2015/se-6-681-2015.pdf https://doaj.org/toc/1869-9510 https://doaj.org/toc/1869-9529 1869-9510 1869-9529 doi:10.5194/se-6-681-2015 https://doaj.org/article/742f05377f844a74849ba93c9bc0ff94 |
op_doi |
https://doi.org/10.5194/se-6-681-2015 |
container_title |
Solid Earth |
container_volume |
6 |
container_issue |
2 |
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681 |
op_container_end_page |
699 |
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1766145718576218112 |