Gondwana

About: Gondwana is a research topic. Over the lifetime, 6078 publications have been published within this topic receiving 263050 citations. The topic is also known as: Gondwanaland.

Neoproterozoic geodynamic evolution of SW-Gondwana: a southern African perspective

Abstract: Our current understanding of the tectonic history of the principal Pan-African orogenic belts in southwestern Africa, reaching from the West Congo Belt in the north to the Lufilian/Zambezi, Kaoko, Damara, Gariep and finally the Saldania Belt in the south, is briefly summarized. On that basis, possible links with tectono-stratigraphic units and major structures on the eastern side of the Rio de la Plata Craton are suggested, and a revised geodynamic model for the amalgamation of SW-Gondwana is proposed. The Rio de la Plata and Kalahari Cratons are considered to have become juxtaposed already by the end of the Mesoproterozoic. Early Neoproterozoic rifting led to the fragmentation of the northwestern (in today’s coordinates) Kalahari Craton and the splitting off of several small cratonic blocks. The largest of these ex-Kalahari cratonic fragments is probably the Angola Block. Smaller fragments include the Luis Alves and Curitiba microplates in eastern Brazil, several basement inliers within the Damara Belt, and an elongate fragment off the western margin, named Arachania. The main suture between the Kalahari and the Congo-Sao Francisco Cratons is suspected to be hidden beneath younger cover between the West Congo Belt and the Lufilian/Zambezi Belts and probably continues westwards via the Cabo Frio Terrane into the Goias magmatic arc along the Brasilia Belt. Many of the rift grabens that separated the various former Kalahari cratonic fragments did not evolve into oceanic basins, such as the Northern Nosib Rift in the Damara Belt and the Gariep rift basin. Following latest Cryogenian/early Ediacaran closure of the Brazilides Ocean between the Rio de la Plata Craton and the westernmost fragment of the Kalahari Craton, the latter, Arachania, became the locus of a more than 1,000-km-long continental magmatic arc, the Cuchilla Dionisio-Pelotas Arc. A correspondingly long back-arc basin (Marmora Basin) on the eastern flank of that arc is recognized, remnants of which are found in the Marmora Terrane—the largest accumulation of oceanic crustal material known from any of the Pan-African orogenic belts in the region. Corresponding foredeep deposits that emerged from the late Ediacaran closure of this back-arc basin are well preserved in the southern areas, i.e. the Punta del Este Terrane, the Marmora Terrane and the Tygerberg Terrane. Further to the north, present erosion levels correspond with much deeper crustal sections and comparable deposits are not preserved anymore. Closure of the Brazilides Ocean, and in consequence of the Marmora back-arc basin, resulted from a change in the Rio de la Plata plate motion when the Iapetus Ocean opened between the latter and Laurentia towards the end of the Ediacaran. Later break-up of Gondwana and opening of the modern South Atlantic would have followed largely along the axis of the Marmora back-arc basin and not along major continental sutures.

Were aspects of Pan-African deformation linked to Iapetus opening?

Abstract: The convergence recorded in some Pan-African deformational belts (sensu lato) in South America, Africa, Madagascar, southern India, Sri Lanka, and Antarctica is temporally correlated with opening of the Iapetus ocean. We propose a model in which continent-continent collision and closure of the Adamastor ocean between the Amazon–West African–Rio de La Plata cratons and the Sao Francisco–Congo–Kalahari cratons in the late Neoproterozoic are linked to rifting and orthogonal spreading between Laurentia and the South American cratons. By the Early Cambrian, the cratons in South America and Africa were assembled as West Gondwana. Closure of the Mozambique ocean, which appears to have extended across Antarctica between Lutzow-Holm Bay and the Shackleton Range, resulted in continued convergence between the Congo–Kalahari–Queen Maud Land block and East Gondwana in the Cambrian. Coeval deformation in the Transantarctic Mountains may be related to the obliquity of the Antarctic margin relative to Iapetus spreading directions. Initiation of voluminous arc magmatism along the paleo-Pacific margin of Gondwana in the Early Cambrian is broadly synchronous with the cessation of intra-Gondwana Pan-African deformation, possibly reflecting a change in plate motions at the time of final Gondwana assembly. The new subduction regime along the Gondwana margin in the Early Cambrian may be linked to the closure of the Iapetus ocean basin.

Widespread, prolonged late Middle to Late Ordovician upwelling in North America: A proxy record of glaciation?

Abstract: Late Middle to Late Ordovician subtidal ramp carbonates of New Mexico, Texas, and Oklahoma contain abundant spiculitic chert (to 70% chert by volume) and phosphate (1–5 wt%), indicating that these rocks formed in an extensive upwelling zone. Upwelling began in the late Middle Ordovician (ca. 454 Ma) and persisted until the end of the Ordovician. Late Ordovician cherty carbonates also occur along the U.S. Cordilleran margin, in board of organic-rich graptolitic shale and chert. The widespread occurrence of Late Ordovician cherty and phosphatic carbonates on southern and western Laurentia, in addition to phosphate-rich, cool-water carbonates over much of the North American Midcontinent, suggests vigorous thermohaline circulation related to prolonged (10–14 Ma) Gondwana glaciation.