Decratonization by rifting enables orogenic reworking and transcurrent dispersal of old terranes in NE Brazil

Dispersion and deformation of cratonic fragments within orogens require weakening of the craton margins in a process of decratonization. The orogenic Borborema Province, in NE Brazil, is one of several Brasiliano/Pan-African late Neoproterozoic orogens that led to the amalgamation of Gondwana. A common feature of these orogens is that a period of extension and opening of narrow oceans preceded inversion and collision. For the case of the Borborema Province, the Sao Francisco Craton was pulled away from its other half, the Benino-Nigerian Shield, during an intermittent extension event between 1.0-0.92 and 0.9-0.82 Ga. This was followed by inversion of an embryonic and confined oceanic basin at ca. 0.60 Ga and transpressiona I orogeny from ca. 0.59 Ga onwards. Here we investigate the boundary region between the north Sao Francisco Craton and the Borborema Province and demonstrate how cratonic blocks became physically involved in the orogeny. We combine these results with a wide compilation of U-Pb and Nd-isotopic model ages to show that the Borborema Province consists of up to 65% of strongly sheared ancient rocks affiliated with the Sao Francisco/Benino-Nigerian Craton, separated by major transcurrent shear zones, with only approximate to 15% addition of juvenile material during the Neoproterozoic orogeny. This evolution is repeated across a number of Brasiliano/Pan-African orogens, with significant local variations, and indicate that extension weakened cratonic regions in a process of decratonization that prepared them for involvement in the orogenies, that led to the amalgamation of Gondwana.

Automated summary

The dispersion and deformation of cratonic fragments within orogens require weakening of craton margins, leading to a process of decratonization. The Borborema Province in NE Brazil is one example of orogens that led to the amalgamation of Gondwana, with a period of extension and opening of narrow oceans preceding inversion and collision. This process involved the pulling away of the Sao Francisco Craton from the Benino-Nigerian Shield, followed by inversion of an oceanic basin and transpression.