Australia: The Land Where Time Began

A biography of the Australian continent 

The Southwest Indian Ridge - Continuous exhumation of rocks derived from the Mantle for 11 My

It has traditionally been believed that the global mid-ocean ridge system is the largest single volcanic feature on the Earth, though in the Indian Ocean, in the easternmost part of the Southwest Indian Ridge the hummocky morphology typical of submarine volcanism is missing, in its place is a wide expanse of smooth sea floor. The sea floor can extend by faulting existing lithosphere along 1 side of the ridge axis at other ridges that are slow-spreading. The smooth sea floor in the easternmost Southwest Indian Ridge does not have the corrugated texture produced by faulting, the sea floor being smooth on both sides of the ridge axis, and is believed to be mantle rock that has been altered. In this article the authors¹ report the results of their study using side-scan sonar to image the sea floor and they dredged samples to be used in determining the composition of 2 sections of the Southwest Indian Ridge between 62^o 05' E and 64^o 40' E, the sea floor in the area having formed during the past 11 My. The authors¹ have shown that the smooth sea floor is almost entirely composed of rock that was derived from the mantle and altered by seawater after being brought to the surface by large detachment faults on both sides of the ridge axis. Almost 100 % of plate divergence has been accommodated by faulting, and the detachment faults have flipped polarity repeatedly. The authors¹ suggest that the exhumation of rocks derived from the mantle at the margins, that are magma-poor, of continents that have rifted could be explained by this tectonic process.

Sources & Further reading

1. Sauter, Daniel, Mathilde Cannat, Stephane Roumejon, Muriel Andreani, Dominique Birot, Adrien Bronner, Daniele Brunelli, et al. "Continuous Exhumation of Mantle-Derived Rocks at the Southwest Indian Ridge for 11 Million Years." Nature Geosci 6, no. 4 (04//print 2013): 314-20.