to Rob and others
type 1 semi brittle shear zones are where the dilational structures
usually tension gashes are orientated towrards the regional
maximum principle strain axis
type2 are where the tension gashes(extensional) not reidels etc
are orientated with the trend of the opposing conjugate shear zone
hence the internal structures of one type seem to represent the
regional stress while the other a localised system.
the original reference is
Beach,A, 1975,the geometry of en-echelon vein arrays,Tectonophysics
Vol. 28,pp245-263
John G Rogers
Department of Geology
University College, Cork
Cork
Ireland
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