One or possibly two overlapping periods of deformation are responsible for the structures observed in the rocks in the Seine River area. This deformation has resulted in the formation of tight to isoclinical, non-plane approximately F1 folds with steeply dipping E-W striking axial surfaces. A late stage deformation has resulted in the formation of a crenulation cleavage, kink bands and minor faulting. There is also limited evidence of a possible pre-F1 folding event.
Two major litholigical groups are present in the study area: shallow water metasedimentary rocks of the Seine Group and metavolcanic rocks. The Seine Group metasedimentary rocks are younger than the metavolcanic rocks in the western part of the area but may be older than similar metavolcanic rocks in the eastern part of the area. Two ages of metavolcanic rocks therefore appear to be present: older metavolcanic rocks in the west which underlie the Seine Group, and younger metavolcanic rocks in the east which overlie the Seine Group.
Regional metamorphism to the chlorite to biotite zone greenschist facies was synkienematic with the deformation of the rocks but may have outlasted the folding in places.
Strain analysis from the metasedimentary rocks reveals that the conglomerate units are more intensely strained than arenite units, although all the stain ellipsoids are of the flattened (K < 1) type.
Average shortening in Z ranges from 52% for arenite units to 75% for conglomerate units. A new empirical approach suggested by the writer and Dr. Borradaile for assessing competence contrasts between strain markers and matrix is outlined. This method uses the effects of competent markers on cleavage traces in the matrix of conglomerates.
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