Terrestial Heat Flow Studies in Kenya

Abstract

Temperature logs have been made at 26 sites in Kenya, in boreholes 100 to 300 metres deep, and thermal conductivities were determined from laboratory measurements on drill cuttings from 13 of the sites. Seven of the logs were seriously disturbed by moving water , and minor disturbances were observed in many others.

On the floor of the Gregory rift near the equator, the measured heat flow is very erratic with values ranging from 40 to 230 mvl.m- 2 in a pattern characteristic of a thermal regime dominated by recent igneous activity and hydrothermal circulation in fault zones. On the flanks, approximately 80 km east and west of the rift axis,

heat flows of 40 to 50 mW.m-2

have been recorded. Isolated high

flank values are apparently associated with zones of weakness in the basement. At a distance of 400km east of the rift in the Lamu Embayment local highs in the vicinity of sub-surface horst- like features are superirnposed on a background heat flow of 50 to , -2 75 mW.m •

Model studies have been used to investigate the effect on surface heat flows of high temperature partial melt zones in the upper mantle, inferred from seismic and geomagnetic variation studies. Steady-state two-dimensional models predict surface

heat,

flows significantly higher than observed flank values, but one-dimensional time-dependent studies have shown that the rift

flank heat flows could still be unaffected by a high temperature melt zone in the mantle.