Abstract
The East Africa rifts and the Red Sea spreading center are characterized
by uplifted shoulders and sunken median valleys. The Dead Sea transform,
on the northern extension of the Arabian-African plate boundary,
has a similar morphological character despite its well-documented
strike-slip motion. To understand the 'rift' morphology and the crustal
structure beneath the transform we compiled a 320 km long gravity
and topography profile perpendicular to the Dead Sea transform. The
gravity field and the topography in the region surrounding the profile
are generally parallel to the trend of the Dead Sea transform, justifying
the two-dimensional approximation of the analysis. The gravity profile
was modeled using constraints from seismic refraction, borehole and
surface geology data. The observed gravity anomaly can be explained
by the juxtaposition of two different sedimentary and crustal sections
which have been offset by a 105 km left-lateral displacement across
the transform boundary, suggesting a step in the depth to Moho. The
existence of a significant density anomaly under the median valley
is not required by the model. The current elevation of the transform
shoulders appears not to be compensated locally. Assuming a state
of local isostasy prior to the development of the transform, the
magnitude of the uplift in the vicinity of the profile is estimated
at 700-900 m, with a half width of 100-125 km. This topography (uplift)
can be fitted equally well by models which assume either dynamic
support or regional compensation. It is suggested that if the source
of the uplift is thermal, it is located within the upper mantle,
since there is no requirement for a shallow density anomaly under
the rift itself or in the crust nearby.
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