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Comment on "Was there an Ediacaran Clymene Ocean in central South America?" By U. G. Cordani and others

2014; Yale University; Volume: 314; Issue: 3 Linguagem: Inglês

10.2475/03.2014.03

1945-452X

E. Tohver, Ricardo I.F. Trindade,

Planetary Science and Exploration

The existence of Gondwana is a subject of historical interest for geologists, since it forms the basis for early scientific theories on the mobility of continents.Textbook examples of the common Gondwanan origin of the southern continents includes the Paleozoic ubiquity of Glossopteris flora and fauna such as Mesosaur, as well as the common paleoclimate history of this supercontinent.However, the facts regarding the assembly of the southern continents into Gondwana are still controversial, as the recent article by Cordani and others (2013) reminds us.The authors describe their view that the supercontinent was assembled by 600 Ma by the closure of the Goia ´s and Pharusian seas.This vision is opposed to that put forward recently by Trindade and others (2006) and Tohver and others (2010, 2012a) who suggest a more piecemeal assembly of the West Gondwana, where the final configuration was completed in Cambrian times after the closure of the Clymene Ocean.The Amazon-West African craton is widely considered to have formed part of the Rodinia supercontinent, sutured to Laurentia by the Grenville-aged collisional belts.The separate drift history of the central Gondwanan blocks recorded by paleomagnetism suggests that major cratons such as the Sa ˜o Francisco-Congo and Rio de la Plata blocks were independent of Rodinia, separated by an oceanic tract (Cordani and others, 2003; Trindade and others, 2006; Tohver and others, 2006).The major point of contention regards the timing of closure of this ocean basin, and the significance of tectonic activity that occurs in central Brazil, where the final suture between the cratonic blocks should be located.The Goia ´s sea is located between the Goia ´s magmatic arc and the Sa ˜o Francisco Craton, being closed at the Ediacaran (fig.1-upper).The Clymene Ocean is located between the Amazon craton and the rest of Gondwana, being closed at the Cambrian (fig.1-lower).The purpose of this comment is to place recent findings into the context of West Gondwana's formation, and to highlight the facts that contradict the more traditional view defended by Cordani and others (2013).The main points raised by Cordani (i-iv in italics below) in refuting the presence of an Ediacaran to Cambrian seaway in central Brazil were:(i) "The assembly of West Gondwana was completed by ca.600 Ma, when the convergence between the Amazonian, São Francisco and Rio de la Plata cratons had already ended.After this, there is no geological evidence of an oceanic lithosphere (for example, ophiolites, magmatic arcs, et cetera), ruling out the possible existence of an Ediacaran or Cambrian Clymene Ocean in Central Brazil."