Intracrystalline vorticity record of flow kinematics during shear zone reactivation

• Published in: Journal of structural geology Vol. 140; p. 104134
• Main Authors: Piette-Lauzière, N., Larson, K.P., Kellett, D.A., Graziani, R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2020
• Subjects: Appalachian orogen; Eastern Highlands shear zone; Kinematic flow; Shear zone; Transpression; Vorticity; Kinematic flow; Eastern Highlands shear zone; Appalachian orogen; Transpression; Vorticity; Shear zone
• ISSN: 0191-8141; 1873-1201
• DOI: 10.1016/j.jsg.2020.104134

The vorticity axis of deformation of a shear zone is a rotational axis controlled by the relative movement of its boundaries. When characterized, it is a reliable tool to determine the ductile flow geometry (monoclinic general, monoclinic transpressive, or triclinic) and an asset to identify the kinematics of complex oblique collisions. Advancements in analysis of electron backscattered diffraction (EBSD) maps now permit inference of vorticity axes – known as crystallographic vorticity axes (CVAs) – from the intragranular lattice orientation dispersion of strain-bearing minerals. However, natural shear zones may preserve a record of multiple shear events with contrasting kinematics and it is not understood to which extent the quartz lattice may preserve a kinematic record through multiple deformation events. Herein, we characterize the finite flow kinematic record produced during reactivation of the Eastern Highlands shear zone (EHSZ), in an oblique collision within the Canadian Appalachians. We integrate field and thin section observations, quartz lattice preferred orientations, EBSD maps, and grain classification, leading to a new method to determine and compare CVA within relict and recrystallized quartz grains. Using this method, we were able to conclude that the EHSZ was reactivated in an heterogenous monoclinic flow environment. (1)Characterization of the reactivation flow kinematics of a composite shear zone(2)Calculate the intragranular variation of the crystallographic vorticity axis(4)Relict grains preserve a better record of the vorticity flow than the recrystallized grains(5)Reactivation in a monoclinic heterogenous flow environment related to transpression