The assembly of Western Gondwana in the late Precambrian involved various continental fragments derived from the break-up of Rodinia Supercontinent during the Brasiliano-Pan-African Orogeny (750-550 Ma., Hoffman, 1991; Dalziel, 1992). Four continental blocks (Amazonia, São Francisco/Congo, West Africa and Kalahari) interacted diachronously in complex kinematic patterns involving collisions, wrench tectonics, and extensive pre-to post-tectonic magmatism (e.g. Alkmim et al., 2001). These collisions resulted in the amalgamation of cratonic nuclei to form the western part of the Gondwana continent.
The Araguaia Fold Belt in central Brazil (Figure 1) occurs along the eastern border of Amazonian Craton and the western border of the São Francisco Craton. It is more than 1000 km long and records interactions between the Amazonia, São-Francisco/ Congo and West African Continents. The Araguaia Belt is a complex and poorly known fold belt. Its outer zone contains bodies of ultramafic rocks that may represent oceanic crustal fragments. The ultramafic rocks have been thrust over sedimentary rocks of unknown age. Also, there is an abrupt change of structural and metamorphic styles between rocks of the outer zone of the belt, where sedimentary and anchimetamorphic rocks prevail, and the inner zone, where metamorphism reaches amphibolite facies.
Figure 1. Tectonic map of Brazil
Tectonic map of Brazil, with the distribution of cratons and fold belts. RDPC, Rio de la Plata Craton; WAC, West African Craton; AC: Amazonian Craton; SFC: São Francisco Craton; GM: Goiás Massif. Fold belts: AG: Araguaia; P: Paraguai; B: Brasília; AR: Araçuaí; R: Ribeira; D: Dom Feliciano; S: Sergipano; BP: Borborema Province.
The structure of the Araguaia Belt formed during a contractional event with two phases of deformation. The first is represented by north-south trending, left-lateral thrusts associated with west vergent folds. These oblique-slip thrust faults have a left-lateral strike-slip component and it has been suggested that they formed by reactivation of normal faults that penetrate basement (Hasui and Costa, 1990; Hasui et al., 1994, and Abreu et al., 1994). The second phase has the same orientation and vergence of the first phase and involves deformation (faulting and folding) of previously formed structures (Abreu et al., 1994). Most authors interpret this event as a result of an advanced stage of continental collision (e.g. Hasui et al., 1994). NNW/SSE-trending brittle wrench shear zones are also reported and are responsible for rotation of previously nucleated structures (Santos and Costa, 1995).
In this paper, we review the structure of the Araguaia Belt and present new structural data and discuss their significance in the context of the interaction of Amazonia, São Francisco-Congo and West Africa continents during the Brasiliano-Pan-African orogeny. This paper is therefore concerned with the larger issue of the tectonic role the Araguaia Belt during the collisional scenario of West Gondwana amalgamation.