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Superposed folding in the Silurian Rocks of Co. Mayo, Eire
Author(s) -
Dewey J. F.,
McManus J.
Publication year - 1964
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.3350040106
Subject(s) - syncline , geology , fold (higher order function) , flattening , structural geology , anticline , deformation (meteorology) , pluton , slip (aerodynamics) , geometry , crenulation , seismology , tectonics , mathematics , mechanical engineering , oceanography , materials science , physics , shear zone , engineering , composite material , thermodynamics
Silurian strata of Upper Llandoverian and Wenlockian age, lying in a complex synclinorium south of the Highland Boundary Fault Zone in Co. Mayo, are affected by two main structural episodes. A tight, curving, E–W synclinorium, verging to the south, was developed during the first episode of deformation (F 1 ). Large‐scale cross‐buckling, followed by variable flattening in the axial‐planar schistosity, was responsible for a considerable plunge variation of F 1 folds. A mechanism is described whereby primary downward‐facing minor folds may be produced in an upward‐facing major structure. Three slides, of considerable magnitude, are co‐planar with the schistosity. During the second episode of deformation (F 2 ) a slip‐cleavage, dipping steeply to the NNE, was superimposed upon the F 1 synclinorium. It is deduced, partly from an analysis of the geometry of F 2 minor structures, that the arcuate curvature of the F 1 synclinorium is pre‐F 2 and was developed during the F 1 deformation as a response to the presence of an early or pre‐F 1 granite pluton. F 2 folds show a great variability in plunge and facing direction, depending upon their position in the F 1 major structure.