Dauphiné twinning and texture memory in polycrystalline quartz. Part 3: texture memory during phase transformation |
| |
| Authors: | Email author" target="_blank">Hans-Rudolf?WenkEmail author N?Barton M?Bortolotti S?C?Vogel M?Voltolini G?E?Lloyd G?B?Gonzalez |
| |
| Institution: | (1) Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA;(2) Lawrence Livermore National Laboratory, Livermore, CA 94550, USA;(3) Lujan Center, Los Alamos National Laboratory, Los Alamos, NM 87545, USA;(4) ESRF, BP 220, 38043 Grenoble, France;(5) School of Earth and Environment, The University of Leeds, Leeds, LS2 9JT, UK;(6) Present address: Department of Physics, DePaul University, Chicago, IL 60614, USA |
| |
| Abstract: | Samples of quartz-bearing rocks were heated above the α (trigonal)–β (hexagonal) phase transformation of quartz (625–950°C)
to explore changes in preferred orientation patterns. Textures were measured both in situ and ex situ with neutron, synchrotron
X-ray and electron backscatter diffraction. The trigonal–hexagonal phase transformation does not change the orientation of
c- and a-axes, but positive and negative rhombs become equal in the hexagonal β-phase. In naturally deformed quartzites measured by
neutron diffraction a perfect texture memory was observed, i.e. crystals returned to the same trigonal orientation they started
from, with no evidence of twin boundaries. Samples measured by electron back-scattered diffraction on surfaces show considerable
twinning and memory loss after the phase transformation. In experimentally deformed quartz rocks, where twinning was induced
mechanically before heating, the orientation memory is lost. A mechanical model can explain the memory loss but so far it
does not account for the persistence of the memory in quartzites. Stresses imposed by neighboring grains remain a likely cause
of texture memory in this mineral with a very high elastic anisotropy. If stresses are imposed experimentally the internal
stresses are released during the phase transformation and the material returns to its original state prior to deformation.
Similarly, on surfaces there are no tractions and thus texture memory is partially lost. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
