Geology Reference
In-Depth Information
Total Uplift and Instantaneous Uplift Rates Above Fault-Related Folds
t
o
tal uplift
A
A
A
A
instanta
n
eous uplift
rate
1
1
1
0
0
0
d
d
d
A=Hd
H
A=Hd
H
A=Hd
H
classical fault-bend fold
pure-shear fault-bend fold
detachment fold
total uplift
B
A
1
instantaneous uplift rate
0
d
H
A=Hd
Fig. 4.37
Patterns of rock uplift above folds.
A. Depictions of rock uplift patterns associated with different types of fault-related folds. Instantaneous uplift rate
represents the relative rate of vertical deformation predicted for an additional increment of folding at that instant of
the fold's development. Abrupt rate changes across axial surfaces (dashed lines associated with bends in fault ramp
angles) commonly indicate fold growth through kink-band migration, whereas gradual changes in uplift rates indicate
limb rotation (compare the classical versus the pure-shear fault-bend fold models). Total uplift represents the sum of
each increment of vertical uplift during the history of folding up to the stage depicted. Whereas total uplift and the
instantaneous rate exactly mimic each other for the detachment fold, a mismatch exists for the other folds because
fold shape changes through time. Note the equivalence between the area of total uplift (
A
) and the area of total
shortening (displacement
d
times height
H
). B. Complex fault-bend fold model with growth and shortening
accommodated by kink-band migration. Uplift rate equals sine of the underlying fault dip times the horizontal
displacement as translated upward to the surface via axial surfaces. Pattern of total uplift is poorly correlated with
instantaneous rates. Modified from Hubert-Ferrari
et al.
(2007).
forelimb to thicken and create tight folding in
the trishear zone. Conversely, high values of
propagation-to-slip ratio cause less thickening
and more open folding (Allmendinger, 1998).
As originally described, both fault-bend and
fault-propagation folding were characterized
by axial surfaces that create kink bends in the
hanging wall and that abruptly divide the
hanging wall into contrasting dip domains. In
the real world, it is quite common to observe
these dip domains or “panels” of folded strata
that all display similar dips. The transition from
one dip domain to the next, however, may not
be abrupt (a kink bend), but may occur gradually
through a change in curvature. In recognition of
this curvature, fault-bend and fault-propagation
