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Ductile shear deformation of quartzite in an alpine crustal thrust (Ambin Massif)

Authors
Journal
Tectonophysics
0040-1951
Publisher
Elsevier
Publication Date
Volume
78
Identifiers
DOI: 10.1016/0040-1951(81)90006-8
Disciplines
  • Earth Science

Abstract

Abstract In this paper we show that fabric analysis gives good results when the sampling is done in an homogeneous material, in a well-known tectonic environment. A quartzitic layer, situated in the autochtonous basement of the Ambin Massif, below the “Nappe des Schistes Lustrés” (French-Italian Alps), has been choosen because the first ductile deformation phase is clearly defined by the microstructures, and because the metamorphic history is well known. The quartz c-axis diagrams are characterized by two asymmetric crossed girdles, and the one containing the maxima is inclined westwards. We propose that these fabrics result from plastic deformation of the quartzite, occurring with the basal plane as a dominant gliding plane. The fabrics define a shear sense towards the West. The angle between the basal planes and the foliation (which varies from 15 to 40°) is at least qualitatively related to the macroscopic strain. Our study confirms the existence of a regional large crustal thrust which has occurred during the obduction of oceanic material (Schistes lustrés) on the European continent.

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