Evidence for non-plane strain flattening along the Moine thrust, Loch Srath nan Aisinnin, North-West Scotland.

Title:
Evidence for non-plane strain flattening along the Moine thrust, Loch Srath nan Aisinnin, North-West Scotland.
Authors:
Strine, Matthew; Wojtal, Steven F. ( 0000-0001-6000-4052 )
Abstract:
We report quartz c-axis patterns, grain-shape fabrics, and microstructures for eleven mylonitic quartzites and quartz-phyllosilicate schists from a transect across the Moine thrust at Loch Srath nan Aisinnin, North-West Scotland. In the footwall samples collected more than 42 m normal distance from the thrust surface, quartz c-axis textures indicate a general flattening strain (i.e. 0 < k < 1). Samples within 19 m normal distance of the thrust are completely recrystallized and exhibit asymmetric c-axis patterns. Recrystallized hangingwall fault rocks exhibit random c-axis patterns on the scale of a standard thin section. Relict footwall grains provide the closest approximation of finite strain; they have octahedral shear strains (ϵs) between 1.10 and 1.47 and exhibit general flattening k-values (0.0524-0.659). The long axis of the mean relict grain shape trends parallel to the regional transport direction and plunges gently to the ESE. In contrast, recrystallized footwall grains have a mean grain shape with the longest axis oriented nearly perpendicular to the transport direction. Furthermore, these samples have grain shape k-values range from 0.157 to 0.295. Recrystallized hangingwall grain shapes exhibit the lowest octahedral shear strains (ϵs = 0.532-0.733) and largest mean k-values (0.351-0.961) of this sample set. The long axes of the mean recrystallized hanging wall grain shapes are parallel to transport, similar to that of relict footwall grains. Unrecrystallized quartz 2 overgrowths about opaque mineral grains suggest concurrent elongation in all directions within the mylonitic foliation and support the inference of general flattening deformation. The mylonitic foliation and penetrative lineation are consistent with a WNW shearing direction; however, both were folded during later deformation increments. Recrystallized grains in footwall quartzites suggest a 305° to 320° azimuth for the shearing direction. The best-fit π-axis of the poles to the foliation is 145:18, close to the mean trend/plunge of mesoscopic fold hinges at this site (153:21). Both suggest a NNW azimuth for the shearing direction. Thus, structural, microstructural and fabric indicators suggest a change in the azimuth of the shearing direction from -286 to -331°.
Citation:
Strine, Matthew, and Steven F. Wojtal. "Evidence for non-plane strain flattening along the Moine thrust, Loch Srath nan Aisinnin, North-West Scotland." Journal of Structural Geology 26, no. 10 (October 2004): 1755-1772.
DATE ISSUED:
2004
Department:
Geology
Type:
article
PUBLISHED VERSION:
10.1016/j.jsg.2004.02.011
PERMANENT LINK:
http://hdl.handle.net/11282/309001

Full metadata record

DC FieldValue Language
dc.contributor.authorStrine, Matthewen_US
dc.contributor.authorWojtal, Steven F.en_US
dc.date.accessioned2013-12-23T15:59:56Zen
dc.date.available2013-12-23T15:59:56Zen
dc.date.issued2004en
dc.identifier.citationStrine, Matthew, and Steven F. Wojtal. "Evidence for non-plane strain flattening along the Moine thrust, Loch Srath nan Aisinnin, North-West Scotland." Journal of Structural Geology 26, no. 10 (October 2004): 1755-1772.en_US
dc.identifier.issn0191-8141en_US
dc.identifier.urihttp://hdl.handle.net/11282/309001en
dc.description.abstractWe report quartz c-axis patterns, grain-shape fabrics, and microstructures for eleven mylonitic quartzites and quartz-phyllosilicate schists from a transect across the Moine thrust at Loch Srath nan Aisinnin, North-West Scotland. In the footwall samples collected more than 42 m normal distance from the thrust surface, quartz c-axis textures indicate a general flattening strain (i.e. 0 < k < 1). Samples within 19 m normal distance of the thrust are completely recrystallized and exhibit asymmetric c-axis patterns. Recrystallized hangingwall fault rocks exhibit random c-axis patterns on the scale of a standard thin section. Relict footwall grains provide the closest approximation of finite strain; they have octahedral shear strains (ϵs) between 1.10 and 1.47 and exhibit general flattening k-values (0.0524-0.659). The long axis of the mean relict grain shape trends parallel to the regional transport direction and plunges gently to the ESE. In contrast, recrystallized footwall grains have a mean grain shape with the longest axis oriented nearly perpendicular to the transport direction. Furthermore, these samples have grain shape k-values range from 0.157 to 0.295. Recrystallized hangingwall grain shapes exhibit the lowest octahedral shear strains (ϵs = 0.532-0.733) and largest mean k-values (0.351-0.961) of this sample set. The long axes of the mean recrystallized hanging wall grain shapes are parallel to transport, similar to that of relict footwall grains. Unrecrystallized quartz 2 overgrowths about opaque mineral grains suggest concurrent elongation in all directions within the mylonitic foliation and support the inference of general flattening deformation. The mylonitic foliation and penetrative lineation are consistent with a WNW shearing direction; however, both were folded during later deformation increments. Recrystallized grains in footwall quartzites suggest a 305° to 320° azimuth for the shearing direction. The best-fit π-axis of the poles to the foliation is 145:18, close to the mean trend/plunge of mesoscopic fold hinges at this site (153:21). Both suggest a NNW azimuth for the shearing direction. Thus, structural, microstructural and fabric indicators suggest a change in the azimuth of the shearing direction from -286 to -331°.en_US
dc.language.isoen_USen_US
dc.identifier.doi10.1016/j.jsg.2004.02.011en
dc.subject.departmentGeologyen_US
dc.titleEvidence for non-plane strain flattening along the Moine thrust, Loch Srath nan Aisinnin, North-West Scotland.en
dc.typearticleen_US
dc.identifier.journalJournal of Structural Geologyen_US
dc.subject.keywordc-Axesen_US
dc.subject.keywordFold–thrust beltsen_US
dc.subject.keywordGrain shape analysisen_US
dc.subject.keywordKinematicsen_US
dc.subject.keywordMoineen_US
dc.subject.keywordMylonitesen_US
dc.subject.keywordNon-plane strainen_US
dc.subject.keywordNorth-West Scotlanden_US
dc.subject.keywordPreferred orientationen_US
dc.subject.keywordX-ray goniometryen_US
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