Abstract
The Sierra Nevada de Santa Marta (SNSM) in northwestern Colombia
is one of the
world’s highest coastal mountains, with an elevation above 5.7 km.
Gravity measurements
show that the SNSM has a high Bouguer anomaly (>+130 mGal),
indicating that the
mountain lacks a crustal root. In this work, we test the hypothesis that
these observa-
tions can be explained by gravitational removal of the dense lower
lithosphere. We use
2D numerical models to examine the dynamics of lithosphere removal and
its effect on
surface elevation, gravity and heat flow. The models consist of
continental lithosphere
that includes a pre-thickened crustal region, representing the SNSM. In
our preferred model,
the dense mantle lithosphere instability and crustal root are
gravitationally unstable and
undergo removal as local drips within ∼10 Ma from the onset of
foundering. This cre-
ates an area of thinned crust (∼38 km) underlain by a buoyant
sublithospheric mantle
where melting and low seismic velocities are predicted. Subsequent
non-isostatic forces
maintain a topography of 3.3 km with a Bouguer gravity anomaly of +103
mGal. Pa-
rameter tests show that a strong lower-crustal rheology provides greater
support for the
high topography and that a weak mantle lithosphere rheology produces
faster removal.
The models demonstrate that local lithosphere dynamics can explain the
first-order ob-
servations in the SNSM. We propose that lithosphere removal could have
occurred at 40-
50 Ma, possibly inducing anomalous short-lived Eocene magmatism, or more
recently
(∼2 Ma), explaining the localized low seismic velocity zone below the
SNSM.
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