Friday, May 2, 2008
The name "Vaalbara" is given to Earth's theorized first supercontinent. According to radiometric data of the encompassing cratons that comprised Vaalbara, it is known to have existed 3.3 billion years ago (3.3 Ga) and possibly even as far back as 3.6 Ga. Evidence includes geochronological and palaeomagnetic studies between the two Archaean cratons (protocontinents) called the Kaapvaal craton (the Kaapvaal province of South Africa) and the Pilbara craton (the Pilbara province of Western Australia).
Further evidence is the structural sequence similarities of the greenstone belts and gneiss belts of these two cratons. These same Archaean greenstone belts are now spread out across the margins of the Superior craton of Canada and are also spread out across the cratons of the former Gondwana and Laurasia continents. The subsequent drift paths of the Kaapvaal and Pilbara cratons after 2.8 Ga gives further evidence that they were once connected.
It is not certain when Vaalbara began to break up, but geochronological and palaeomagnetic evidence show that the two cratons had a rotational 30 degree latitudinal separation at 2.78 to 2.77 Ga, implying that they were no longer contiguous after ~2.8 Ga.
See also
Supercontinent
Kaapvaal craton
Pilbara craton
Gondwana
Laurasia
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