TY - JOUR
T1 - Shear zones between rock units with no relative movement
AU - Koyi, Hemin
AU - Schmeling, Harro
AU - Burchardt, Steffi
AU - Talbot, Christopher
AU - Mukherjee, Soumyajit
AU - Sjöström, Håkan
AU - Chemia, Zurab
PY - 2013/5
Y1 - 2013/5
N2 - Shear zones are normally viewed as relatively narrow deformation zones
that accommodate relative displacement between two "blocks" that have
moved past each other in opposite directions. This study reports
localized zones of shear between adjacent blocks that have not moved
past each other. Such deformation zones, which we call wakes, form due
to the movement of exotic blocks within a viscous medium (denser blocks
sinking within a salt structure, (the paths) between separated boudins),
melt in partially molten surroundings (melt movement during
migmatisation), or solid blocks sinking through a partially molten magma
body (stoping). From the fluid dynamics perspective these shear zones
can be regarded as low Reynolds number deformation zones within the wake
of a body moving through a viscous medium. While compact moving bodies
(aspect ratio 1:1:1) generate axial symmetric (cone like) shear zones or
wakes, elongated bodies (vertical plates or horizontal rod-like bodies)
produce tabular shear zones or wakes. Unlike conventional shear zones
across which shear indicators usually display consistent symmetries,
shear indicators on either side of the shear zone or wake reported here
show reverse kinematics. Thus profiles exhibit shear zones with opposed
senses of movement across their center-lines or -planes.We have used
field observations and results from analytical and numerical models to
suggest that examples of wakes are the transit paths that develop where
denser blocks sink within salt structures, bodies of melt rise through
migmatites, between boudins separated by progressive extension and
(perhaps) where slabs of subducted oceanic lithosphere delaminate from
the continental crust and sink into the asthenosphere. We also argue
that such shear zones may be more common than they have been given
credit for and may be responsible for some reverse kinematics reported
in shear zones.
AB - Shear zones are normally viewed as relatively narrow deformation zones
that accommodate relative displacement between two "blocks" that have
moved past each other in opposite directions. This study reports
localized zones of shear between adjacent blocks that have not moved
past each other. Such deformation zones, which we call wakes, form due
to the movement of exotic blocks within a viscous medium (denser blocks
sinking within a salt structure, (the paths) between separated boudins),
melt in partially molten surroundings (melt movement during
migmatisation), or solid blocks sinking through a partially molten magma
body (stoping). From the fluid dynamics perspective these shear zones
can be regarded as low Reynolds number deformation zones within the wake
of a body moving through a viscous medium. While compact moving bodies
(aspect ratio 1:1:1) generate axial symmetric (cone like) shear zones or
wakes, elongated bodies (vertical plates or horizontal rod-like bodies)
produce tabular shear zones or wakes. Unlike conventional shear zones
across which shear indicators usually display consistent symmetries,
shear indicators on either side of the shear zone or wake reported here
show reverse kinematics. Thus profiles exhibit shear zones with opposed
senses of movement across their center-lines or -planes.We have used
field observations and results from analytical and numerical models to
suggest that examples of wakes are the transit paths that develop where
denser blocks sink within salt structures, bodies of melt rise through
migmatites, between boudins separated by progressive extension and
(perhaps) where slabs of subducted oceanic lithosphere delaminate from
the continental crust and sink into the asthenosphere. We also argue
that such shear zones may be more common than they have been given
credit for and may be responsible for some reverse kinematics reported
in shear zones.
U2 - 10.1016/j.jsg.2012.08.008
DO - 10.1016/j.jsg.2012.08.008
M3 - Journal article
SN - 0191-8141
VL - 50
SP - 82
EP - 90
JO - Journal of Structural Geology
JF - Journal of Structural Geology
ER -