Geoscience Reference
In-Depth Information
Figure 9.11.
Gravity
models for the
Mid-Atlantic Ridge: (a)
bathymetry; (b) free-air
gravity anomaly and (c)
density model for the
Mid-Atlantic Ridge at
45
◦
N; (d) Bouguer gravity
anomaly and (e), (f) and
(g) density models that
also all satisfy the
anomaly shown in (d).
These four density
models - (c), (e), (f) and
(g) - illustrate the
non-uniqueness of
models based on gravity
data. A low-density zone
lies beneath the ridge, but
its dimensions need to be
constrained by other
methods also. The
oceanic crust is assumed
to be continuous across
the ridge axis in model (c);
but in models (e), (f) and
(g) there is a zone some
800 km wide and centred
on the ridge axis from
which normal oceanic
crust and uppermost
mantle are absent. The
density model in (c) is in
better agreement with
everything that is known
about mid-ocean-ridge
structure than are the
models in (e), (f) and (g).
Densities are given in
kg m
−3
. (After Talwani
et al
.(1965) and Keen and
Tramontini (1970).)
