Isostatic response of the lithosphere beneath the Mozambique Ridge (SW Indian Ocean) and geodynamic implications

• Published in: Geophysical Journal International
• Main Authors: Maia, M., Diament, M., Recq, M.
• Format: Text
• Language: English
• Published: Oxford University Press 1990
• Subjects: Articles; Antarctic; Astrid Ridge; Indian; The Antarctic; Antarc*; Antarctica
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/100/3/337; https://doi.org/10.1111/j.1365-246X.1990.tb00689.x

The SW Indian Ocean is characterized by the presence of several aseismic features. The Mozambique Ridge, an elongated feature lying roughly parallel to the SE coast of Africa, is by far the least known of those structures, mainly due to the scarcity of marine data. To date, the crustal nature and the origin of the ridge are still controversial points. Since knowledge of the origin of the Mozambique Ridge is important for a better understanding of the evolution of the SW Indian Ocean, the isostatic response of the lithosphere beneath the ridge is analysed in order to characterize its effective elastic thickness and the emplacement process of the feature. Two different approaches are applied, the direct computation of the geoid anomaly over the ridge, by means of a 2.5-dimensional method, and the computation of the admittances between the bathymetry and both the geoid and gravity anomalies. Both approaches point to a local isostatic response of the lithosphere. The crustal thickness beneath the Mozambique Ridge ranges from 17 to 30 km and the average density, from 2.78 to 2.7 × 103 kg m-3, varying with locality, in good agreement with the few existing refraction profiles. Based on our results, on the geochemical similarity between the basalts cored at the DSDP site 249 and the MOR basalts (Erlank & Reid 1974; Thompson et al. 1982) and on the present knowledge of the SW Indian Ocean kinematics (Martin & Hartnady 1986), we propose an on-ridge origin for the Mozambique Ridge. The ridge would have been formed by the anomalous activity of a spreading axis linking the northern Mozambique and the Transkei basins accretion centres, between M10 and M2 times. At the M2 epoch, a ridge jump event would have caused the spreading to cease. The Astrid Ridge, a poorly known aseismic structure lying close to the coast of Antarctica near 15°E, may be the antarctic counterpart of the Mozambique Ridge, formed by the same accretionary phenomenon, the two ridges breaking apart at M2 time due to the ridge jump event. However, ...