Coronavirus Information for the UC San Diego Community

Our leaders are working closely with federal and state officials to ensure your ongoing safety at the university. Stay up to date with the latest developments. Learn more.

The effects of quartz Dauphine twinning on strain localization in a mid-crustal shear zone

TitleThe effects of quartz Dauphine twinning on strain localization in a mid-crustal shear zone
Publication TypeJournal Article
Year of Publication2020
AuthorsMcGinn C., Miranda E.A, Hufford L.J
Volume134
Date Published2020/05
Type of ArticleArticle
ISBN Number0191-8141
Accession NumberWOS:000528183400012
Keywordsaxial-compression; Dauphine twins; deformed quartz; EBSD; example; fabric development; Fiordland; Geology; Grain boundary migration; grain-boundary migration; median batholith; microstructure; natural; plutonic rocks; preferred orientations; Quartz; texture memory; Transpression; zealand field relations
Abstract

We use microstructural, electron backscatter diffraction (EBSD), and crystal vorticity axis (CVA) analyses to evaluate the effects of quartz Dauphine twinning on strain localization. We compare a granodiorite mylonite and a tonalite mylonite from the Grebe Shear Zone, a mid-crustal transpressional shear zone in Fiordland, New Zealand. EBSD analysis reveals identical quartz grain boundary migration dynamic recrystallization microstructures in both samples, with abundant Dauphine twinning only in the granodiorite mylonite. Bulk CVA patterns further distinguish the untwinned and Dauphine-twinned samples, indicating a transition from simple shear-to pure shear-dominated transpression, respectively. The quartz CVA pattern from the Dauphine-twinned sample indicates that twinned and untwinned grains record a transition from simple shear-to pure shear-dominated deformation, respectively. Pole figures of the Dauphine-twinned sample reveal high-temperature slip systems in the untwinned and Dauphine-twinned grains. We conclude that Dauphine twinning formed early in transpression, and rendered the twinned grains less deformable relative to the untwinned grains over time. The effectiveness of Dauphine twinning in localizing strain is therefore strongly influenced by its timing relative to the evolving shear zone kinematic deformation geometry.

DOI10.1016/j.jsg.2020.103980
Student Publication: 
No