B. Grasemann et K. Stuwe, The development of flanking folds during simple shear and their use as kinematic indicators, J STRUC GEO, 23(4), 2001, pp. 715-724
We used a numerical finite element simulation to model the formation of fla
nking folds around rotating planar structures (e.g. veins, faults or dykes)
in a non-linear viscous medium during ideal simple shear. If the planar st
ructure is much more viscous than its host it does not deform and flanking
folds with no displacement along the structure develop. Their vergence is c
onsistent with the overall sense of shear. However, if the planar structure
is much less viscous than its host, strain is concentrated within the stru
cture and a secondary shear zone is developed in which slip is opposite to
the overall sense of shear. Then, flanking folds develop that have a vergen
ce, which is incompatible with the drag on structure. If the deflection of
markers is not clearly preserved, then such flanking folds can be easily mi
sinterpreted as shear bands indicating a wrong shear sense. The deflection
of the foliation in flanking folds is very similar to deformed asymmetric p
ull-aparts and can therefore help to interpret these otherwise ambiguous sh
ear sense criteria. Because our model (ideal simple shear boundary conditio
ns) fails to describe back-rotation of planar structures in rocks we specul
ate that shear band geometries are indicative for general shear. (C) 2001 E
lsevier Science Ltd. All rights reserved.