Interpretation of regional gravity and magnetic data in Peninsular Malaysia

Abstract

Abslra~l: A regional gravity survey covering the portion of Peninsular Malaysia between latitudes 2°N and 4 ON was carried OUl to study the eruSlal structure. The tOlal number of gravity stations obtained by Universiti Sains Malaysia is 450. Some aeromagnetic data covering mainly the south~rn half of the peninsula were also used in the interprelation. In general, the gravity data reflect the regional geology of the area. A gravity maximum of up to 20 mgals, and a broad magnetic minimum wilh ~n amplitude of up to 30 gammas were obtained over the Central Belt. These anomalies may indicate a denser and more basic upper crust underlying the Central Belt. A gravity minimum. with an amplitudeofup to SO mgals. Wllo6 observed over the Main Range. A smaller gravity minimum, with an amplitude or20 to 2S mgals, was also observed over the Eastern Belt granites. These anomalies are probably caused by the granite balholiths in these areas which have lower densities than the surrounding rocks. The gravity values on both coasts orthe peninsula are roughly the same. This indi~ates that the gross tectonic structure beneath both coasts may be similar. The anomalies over the Main Rallge and the Central Belt taper off towards the soulh ill Melaka and Johore. This implies that the Main Range granite batholiths and the denser (possibly oceanic) crust beneath the Central Belt do not continue farther south into Johore. Most of these features seem to be best accounted for by the marginal basin tectonic model of Hutchison (1978), which postulates an oceanic eruSl underlying the Central Belt.