Article,
Crustal structure beneath the Kenya rift from axial profile data
Tectonophysics, 236 (1-4): 179--200 (Sep 30, 1994)
DOI: 10.1016/0040-1951(94)90176-7
Abstract
Modelling of the KRISP 90 axial line data shows that major crustal
thinning occurs along the axis of the Kenya Rift from Moho depths
of 35 km in the south beneath the Kenya Dome in the vicinity of Lake
Naivasha to 20 km in the north beneath Lake Turkana. Low Pn velocities
of 7.5-7.7 km/s are found beneath the whole of the axial line. The
results indicate that crustal extension increases to the north and
that the low Pn velocities are probably caused by magma (partial
melt) rising from below and being trapped in the uppermost kilometres
of the mantle. Along the axial line, the rift infill consisting of
volcanics and a minor amount of sediments varies in thickness from
zero where Precambrian crystalline basement highs occur to 5-6 km
beneath the lakes Turkana and Naivasha. Analysis of the Pg phase
shows that the upper crystalline crust has velocities of 6.1-6.3
km/s. Bearing in mind the Cainozoic volcanism associated with the
rift, these velocities most probably represent Precambrian basement
intruded by small amounts of igneous material. The boundary between
the upper and lower crusts occurs at about 10 km depth beneath the
northern part of the rift and 15 km depth beneath the southern part
of the rift. The upper part of the lower crust has velocities of
6.4-6.5 km/s. The basal crustal layer which varies in thickness from
a maximum of 2 km in the north to around 9 km in the south has a
velocity of about 6.8 km/s.
