Geology Reference
In-Depth Information
Non-deposition/erosion
(a)
Elastic
T1
T0
(b)
T2
T1
1
2
T0
(c)
T3
T2
T1
1
2
3
T0
(d)
Relaxation phase - viscoelastic
T4
T3
T2
T1
T0
(e)
Lithospheric heterogeneity
T3
T2
T1
Weak lithosphere
T0
Strong lithosphere
Fig. 1.
Cross-sections of foreland basin evolution for a continuous elastic plate (a-c), a continuous viscoelastic plate (a-d),
and an elastic plate with lithospheric heterogeneities (e) plotted next to their respective Wheeler diagrams. Areas of non-
deposition or erosion over a subaerially exposed peripheral bulge indicated in black on the Wheeler diagrams.
time (Grotzinger & Royden, 1990; Waschbusch &
Royden, 1992a,b). In such cases, the peripheral
bulge may appear as a stationary feature within
the foreland as the basin continues to deepen both
cratonward of the peripheral bulge and in the
foredeep (Fig. 1).
(Nádai, 1963), the vertical defl ection (
w
) at any
distance (
x
) from the load is
(1)
where
w
0
is the vertical displacement at the load,
that is, the maximum vertical displacement and
L
is the fl exural parameter, equal to
SCALING CONSIDERATIONS
(2)
Although peripheral bulges frequently are
depicted in schematic fi gures as topographically
prominent features, fl exural modelling indicates
that they are actually rather subtle. In particu-
lar, peripheral bulges are commonly depicted as
too tall relative to the depth of the basin, as too
narrow relative to the width of the basin, and
consequently, with slopes that are too steep. The
theory of bending of fl at, thin plates offers predic-
tions about the scaling of peripheral bulges. For
an infi nite elastic slab deformed by a line load
where
r
m
is the density of the asthenosphere,
r
f
is the density of the basin fi ll,
g
is gravitational
acceleration and
D
is fl exural rigidity.
Based on this equation, the width of the fore-
land basin (
width
basin
), that is, the distance from
the load to the leading edge of the peripheral
bulge, is
(3)
