Supercontinent

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In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia[1] qualifies as a supercontinent today.

Contents

History

Most commonly, paleogeographers employ the term supercontinent to refer to a single landmass consisting of all the modern continents. The earliest known supercontinent was Vaalbara. It formed from proto-continents and was a supercontinent by 3.1 billion years ago (3.1 Ga). Vaalbara broke up ~2.8 Ga ago. The supercontinent Kenorland was formed ~2.7 Ga ago and then broke sometime after 2.5 Ga into the proto-continent Cratons called Laurentia, Baltica, Australia, and Kalahari. The supercontinent Columbia or Nuna formed during a period of 2.0–1.8 billion years and broke up about 1.5–1.3 billion years ago [2][3].

The supercontinent Rodinia formed about 1100 million years ago and broke up roughly 750 million years ago. One of the fragments included large parts of the continents now located in the southern hemisphere. Plate tectonics brought the fragments of Rodinia back together in a different configuration during the late Paleozoic era about 300 million years ago, forming the best-known supercontinent, Pangaea. Pangaea subsequently broke up into the northern and southern supercontinents, Laurasia and Gondwana, about 200 million years ago.

Mechanism of generation and dispersal

The continental lithosphere is 80–160 kilometres (50–99 mi) thick.[4]:94 When continents rift into separate plates, the thicker lithosphere gives way to thinner lithosphere of the oceans.[4]:94 Also, the transition from a continental rift to an oceanic rift is accompanied by block faulting, where blocks of continental crust drop down along extensional faults where the crust is being pulled apart.[4]:94 This results in a deep rift valley and a thinning of the crust.[4]:94 The African rift valley is an active rifting event. Rifting of a continent begins with hot-spot volcanism at rift valleys.[4]:94 Hot spots burn holes through the crust and cause it to weaken.[4]:94 The crust under a rift is only 30–50 kilometres (19–31 mi) thick.[4]:94

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