Strain Within the Ultrahigh‐Pressure Western Gneiss Region of Norway Recorded by Quartz CPOs

Nicolas C. Barth, University of California - Santa Barbara
Bradley R. Hacker, University of California - Santa Barbara
Gareth G.E. Seward, University of California - Santa Barbara
Emily O. Walsh, Cornell College
David Young, University of Texas at San Antonio
Scott Johnston, California Polytechnic State University - San Luis Obispo

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Copyright © 2010 The Geological Society of London. The original publication is available at http://dx.doi.org/10.1144/SP335.27.

Abstract

Electron back‐scatter diffraction was used to measure the crystal preferred orientations (CPOs) from 101 samples across the ultrahigh‐pressure Western Gneiss Region of Norway to assess slip systems, sense of shear, CPO strength, and strain geometry. The CPOs suggest a dominance of prism slip, with lesser amounts of prism [c] slip and basal slip; there are few Type‐I and Type‐II girdles. The major structural feature in the study area—the high‐strain, top‐W, normal‐sense Nordfjord–Sogn Detachment Zone—is characterized by asymmetric and strong CPOs; an eastern domain with strong asymmetric CPOs shows top‐E shear. Strain throughout the study area was characterized by a mix of plane strain and constriction with no evidence of flattening. Adjacent gneiss and quartzite/vein samples have similar CPOs.