Evidence for Early Tonian (Ca. 1000-940 Ma) continental rifting in southern Borborema Province (NE Brazil): tectonic inheritance and shear zone nucleation during assembly of West Gondwana

ABSTRACT

The factors controlling the inception of continental-scale transcurrent shear zones are still under debate. In order to a better understanding of the origin and evolution of the 400 km long West Pernambuco shear zone (WPSZ), we undertook a structural, geochronological and geochemical study in an area around its eastern termination. The WPSZ is one of the most expressive strike-slip shear zones in the Borborema Province of NE Brazil, which resulted from orogenic processes associated with the assembly of western Gondwana in the Late Neoproterozoic. Previous studies have shown that 1000–940 Ma-old granitic orthogneisses are located immediately to the south of the western and central portions of the WPSZ. Based on LA-ICP-MS U-Pb zircon dating, we show that rocks with similar ages (995–956 Ma) also occur to the East. The geochemical characteristics of this magmatism and the alignment of the bodies along a narrow, less than 40 km-wide belt point to emplacement in a continental rift-related setting. The WPSZ thus follows the trend of a pre-existing rheological discontinuity, which induced strain localization during the post-collisional stage of the Brasiliano-Pan-African orogeny.

KEYWORDS:

• Continental rift
• strain localization
• shear zone nucleation
• U-Pb geochronology
• major and trace elements
• Borborema Province

Acknowledgments

This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) of Brazil (grant 449447/2014-6). JPSB and RHMF thank scholarship from CNPq and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), respectively. We thank Roberto G. Oliveira and CPRM (Serviço Geológico do Brasil) for providing access to geophysical data, and two anonymous reviewers for constructive comments.

Disclosure Statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico [449447/2014-6].