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Concept
Craton de Pilbara
Résumé
The Pilbara Craton is an old and stable part of the continental lithosphere located in the Pilbara region of Western Australia.
The Pilbara Craton is one of only two pristine Archaean 3.8–2.7 Ga (billion years ago) crusts identified on the Earth, along with the Kaapvaal Craton in South Africa. The youngest rocks are 1.7 Ga old in the historic area assigned to the Craton. Both locations may have once been part of the Vaalbara supercontinent or the continent of Ur.
There are two subregional geographical classification regimes used, being:
The Interim Biogeographic Regionalisation for Australia based upon interacting geo-ecosystems
Based on geology alone where the eastern continuous oldest portion is called the Eastern Pilbara Craton and younger surface lithologies within the larger craton have different names.
Eastern Pilbara Craton
The most important part of the Pilbara Craton to understand the early Earth crust is called the Eastern Pilbara Craton, where still exposed today, are crustal rocks that are up to 3.8 billion years old and intrusive granitic domes along with greenstone belts that are about 3.5 to 3.2 billion years old. The geology was reassessed in 2007 with the separation out from the geologically named Pilbara Craton of a thick succession of interbedded clastic or chemical sedimentary rocks and volcanic rocks forming the Fortescue, Hamersley, and Turee Creek basins that are usually aged from 2.78–2.42 billion years old and the younger volcano-sedimentary Ashburton Basin aged from 2.21–1.79 billion years ago. A surface region between the Fortescue and Hamersley basins is even younger, at less than 1.7 billion years old, as are the surrounding geo-ecosystems surface rocks to the Pilbara Craton. It is important to note that to the east and south of the Eastern Pilbara Craton there are significant outcrops of the very old rocks and that these are confined to the traditional area of the Pilbara Craton which is inferred to be subsurface for more than half its area.
Source officielle
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