Gravity and magnetic surveys in Northern Tanzania and Southern Kenya

Abstract

The main results of gravity surveys carried out in 1968 and 1969 are presented with occasional reference to magnetic surveys carried out at the same time. The long wavelength negative Bouguer anomaly associated with the northern part of the rift zone is found to terminate at about 4S and the shorter wavelength positive anomaly over the Gregory Rift floor dies out at about 2°S. The negative anomaly is thought to be due to a low density asthenolith and the positive anomaly to be an intrusive zone penetrating the upper crust suggesting extreme thinning of the lithosphère beneath the eastern rift north of 2°S. The negative Bouguer anomaly over the Speke Gulf region is interpreted in terms of a simple rift; reasons are given for considering this to be a Precambrian structure which is presently being rejuvenated. The negative Bouguer anomalies found over the west-east volcanic chain which includes Meru and Kilimanjaro are considered to be due to low density lava piles.