See more from this Division: Topical Sessions
See more from this Session: Mid- to Lower Crustal Deformation Processes: Strain, Kinematics and Relationships to Upper Crustal Structures
Abstract:
Quantitative vorticity (Wm) data from the mylonites (~100 samples) indicate the presence of a significant pure shear component (0.47-0.82; 68-38% pure shear), and integrated 3D strain and vorticity analyses on mylonitic Cambrian quartzites in the Loch Eriboll region indicate 24-56% vertical shortening sub-perpendicular to the flat lying mylonite belts and their associated thrusts, and sub-horizontal maximum principal stretches of 22-94% oriented parallel to the WNW trending thrust transport direction. These estimates account for ranges in estimated vorticity values and orogen-parallel stretching (non-plane strain), as indicated by 3D strain analyses, but constant volume is assumed for all deformation within the crystal plastic regime.
Transport parallel stretching within the crystal-plastic regime must be accommodated by either volume loss or extrusion of material towards the topographic surface, thereby directly or indirectly driving tectonic processes above the brittle-ductile transition zone. Interestingly, where hinterland mylonite zones are most prominently developed in Cambrian metasedimentary rocks (from the north coast to northern Assynt), the MTZ is characterized by a west-east succession of brittle to ductile thrusts with an estimated minimum total displacement of >30 km on the brittle structures and >100 km on the ductile structures. To the south of Assynt, no mylonites are recognized in the Cambrian succession, and the MTZ is typically marked by a single brittle fault. The high strain zone junction between these two regimes (Oykel constrictional zone) may represent a ductile lateral fault/shear zone to the north of which displacement was transferred from the extruding hinterland mylonites to the brittle thrusts in the foreland.
See more from this Division: Topical Sessions
See more from this Session: Mid- to Lower Crustal Deformation Processes: Strain, Kinematics and Relationships to Upper Crustal Structures