Relationships between strain and quartz crystallographic fabrics in the Roche Maurice quartzites of Plougastel, western Brittany

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doi: 10.1016/0191-8141(86)90001-5
Authors:Law, R. D.
Author Affiliations:Primary:
Univ. Leeds, Dep. Earth Sci., Leeds, United Kingdom
Volume Title:Journal of Structural Geology
Source:Journal of Structural Geology, 8(5), p.493-515. Publisher: Pergamon, Oxford-New York, International. ISSN: 0191-8141
Publication Date:1986
Note:In English. 68 refs.; illus. incl. 2 tables, sketch map
Summary:Strain analysis indicates that fold hinges and cleavage within these quartzites are orientated parallel to the principal extension direction (X) and XY plane of the finite-strain ellipsoid, respectively. This conclusion is strongly supported by quartz c- axis fabric studies. Essentially coaxial deformation within the quartzites is indicated by both microstructural and petrofabric studies. The intensity of c-axis preferred orientation of detrital grains is directly proportional to calculated strain magnitude. A correlation is also established between the pattern of c-axis preferred orientation and strain symmetry. Within individual specimens, the c-axis fabrics are similar for syntectonically recrystallized grains and deformed detrital grains. The c-axes of new grains within detrital hosts are commonly orientated at angles of between 10 and 40° to the c axes of their hosts; they are, in addition, statistically orientated at higher angles to Z than the c axes of their hosts. These relationships are interpreted as indicating that both host grain control and the local strain (and/or stress) field may have influenced the process of recrystallization; the relative influences of these factors is, however, unknown. To achieve large bulk strains in coaxial deformation it is proposed that a cyclic process involving dislocation slip and elimination of locked up grains by syntectonic recrystallization may be necessary. [J.M.H.]
Subjects:Fabric; Metamorphic rocks; Petrofabrics; Preferred orientation; Quartzites; Recrystallization; Strain; Structural analysis; Structural geology; Brittany; Europe; France; Western Europe; Plougastel; Roche Maurice
Abstract Numbers:87M/1709
Record ID:1986073546
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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