Residual lattice strain in quartzites as a potential palaeo-piezometer. Issue 2 (9th May 2020)

• Record Type: Journal Article
• Authors: Wenk, Hans-Rudolf; Chandler, Brian Chase; Chen, Kai; Li, Yao; Tamura, Nobumichi; Yu, Rong
• Is Part Of: Geophysical journal international. Volume 222:Issue 2(2020)
• Page Start: 1363
• Page End: 1378
• Publication Date: 2020-05-09
• Subjects: Defects -- Elasticity and anelasticity -- Geomechanics -- Mechanics, theory, and modelling -- Microstructures; Geophysics -- Periodicals; 550
• DOI: 10.1093/gji/ggaa226
• Languages: English
• ISSNs: 0956-540X

Abstract

SUMMARY: If a crystal lattice is subjected to a stress, it becomes distorted and no longer represents the ideal crystal symmetry, and if the stress introduces defects such as dislocations, some of this distortion is preserved after the applied stress is removed. In this study, we investigate lattice distortion in quartz at the micron scale with synchrotron X-ray Laue diffraction. From Laue images the local deviatoric strain tensor is derived and corresponding stresses are calculated based on elastic properties. The method is applied to metasedimentary quartzites from the Bergell Alps that were deformed at conditions of greenschist facies metamorphism. The residual palaeostrain is represented in maps of the deviatoric strain tensor components and with deviatoric strain axis pole figures. Data suggest overall shortening perpendicular to the schistosity plane but with considerable asymmetry relative to foliation and lineation, probably attributed to simple shear. Crystallographic pole figures from Laue diffraction agree with neutron diffraction and EBSD measurements and display quartz c -axes girdle distributions with maxima also perpendicular to schistosity. The method shows promise to be used as a palaeo-piezometer to unravel the stress field during tectonic deformation.