Monday, February 25, 2013
More on Microcontinents
Published February 25, 2013
Hidden beneath the brilliant blue waters of the Indian Ocean lies
a secret, scientists say: an entire micro-continent that detached itself some 60 million years ago.
And they found it through a few handfuls of sand.
The islands Reunion and Mauritius, both well-known tourist destinations off the southeastern coast of Africa, are hiding the micro-continent, a fragment known as Mauritia that detached while Madagascar and India drifted apart during the Precambrian era, scientists said.
It had been hidden under huge masses of lava. A group of geoscientists from Norway, South Africa, Britain and Germany published a study that suggests, based on the study of lava sand grains from the
beach of Mauritius, the existence of further fragments.
The sand grains contain semi-precious zircons aged between 660 million and 1.9 billion years, which is explained by the fact that the zircons were carried by the lava as it pushed through subjacent continental crust of this age.
"We found zircons that we extracted from the beach sands, and these are something you typically find in a continental crust. They are very old in age,” Prof. Trond Torsvik, from the
University of Oslo, Norway, told the BBC.
Three-quarters of a billion years ago, the surface of the Earth looked very different than it does today; the planet’s continents were joined in a vast supercontinent called Rodinia. And at the time, India nestled up against the island of Madagascar.
It seems Mauritia was sandwiched between the two.
And it may not have been alone: Such micro-continents in the oceans seem to occur more frequently than previously thought, according to Torsvik’s study.
The break-up of continents is often associated with mantle plumes: giant bubbles of hot rock that rise from the deep mantle and soften the tectonic plates from below, until the plates break apart at the hotspots.
Eastern Gondwana -- another early supercontinent -- broke apart about 170 million years ago in just such a process, the scientists say. At first, one part was separated, which in turn fragmented into Madagascar, India, Australia and Antarctica, which then migrated to their present position.
Plumes currently situated underneath the islands Marion and Reunion appear to have played a role in the emergence of the Indian Ocean.
This dating method was supplemented by a recalculation of plate tectonics, which explains exactly how and where the fragments ended up in the Indian Ocean. Bernhard Steinberger of the GFZ German Research Centre helped calculate the hotspot trail.
"The continent fragments continued to wander almost exactly over the Reunion plume, which explains how they were covered by volcanic rock," he said.