Arc Assembly and Continental Collision in the Neoproterozoic East African Orogen

Topics: Plate tectonics, Continent, Orogeny Pages: 3 (945 words) Published: August 22, 2013
Arc Assembly and Continental collision in the Neoproterozoic East African Orogen: implications for the consolidation of Gondwanaland The Pan African Orogenic cycle, is derived from Kennedy’s (1964) term, Pan-African Thermo-tectonic episode to characterize the thermal differentiation of Africa into cratons and into mobile belts during the late Precambrian (now known as Neoproterozoic) and earliest Phanerozoic (Palaeozoic) In 1981 McWilliams argued that Gondwanaland was assembled from 2 fragments east and west Gondwanaland and he thought that this occurred along the Mozambican Belt and its extension to the north (Arabian-Nubian Shield) In 1984 Kroner refined this term (Pan-African) to be involving a protracted orogenic cycle from 950 - 450 Ma ( a span of 500 Ma). The tectonism associated with this is not restricted to Africa alone. Events of similar age occur throughout Gondwanaland (all the southern continents) but also Laurasia (made up of Baltica [most of northern Europe and European Russia] Kazakhstan [Central Asia, China and Malaysia, Siberia {475 - 490 Ma} ) and Laurentia (North America and Gondwanaland) with which it collided. The timespan of 500 Ma is much longer than any Phanerozoic orogeny. So reference to the Pan-African orogenic cycle must suffice until the timing and regional extent of discrete tectonic events is better understood and constrained. Uranium-lead dating would be recommended because it has a small error margin of 2 Ma. In 1994 Stern said that with the East African Orogen - Pan African are represented hallmarks of modern plate tectonics.including abundant ophiolites, calc-alkaline batholiths and volcanic sequences, and immature clastic sediments When it comes to ophiolites, the horizontal displacements worked out are huge. The ophiolitic nappes have travelled several 10 and maybe a few 100s of kilometers. Pan-African metamorphism has resulting in granulite formations which suggest crustal over thickening due to continent collision. East...
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