The global tectonic context of the ca. 2.27-1.96 Ga Birimian Orogen – Insights from comparative studies, with implications for supercontinent cycles

Abstract

The evolution of orogenic systems is a function of their overall tectonic context, and global reconstructions therefore provide a crucial framework for understanding the geodynamic setting of ancient orogens. However, the reverse is also true, as a detailed geodynamic model for an orogenic system can provide valuable insights into its overall tectonic context. Based on a recently proposed geodynamic model for the ca. 2.27-1.96 Ga accretionary-collisional Birimian Orogen in the West African Craton, this study aims to explore its broader tectonic setting, by placing the events outlined on an orogen-scale within a global context. The proposed geodynamic model argues that the Birimian Orogen formed in a plate tectonic setting similar to that which currently characterizes SE Asia, with the orogenic system forming in a wedge-shaped complex plate boundary zone, bordered to the north and south by continental blocks and opening up to face a major oceanic basin. The Neoproterozoic-Paleozoic East African-Antarctic orogen (EAAO) has also been constrained to have formed in such a setting and exhibits significant similarities with the Birimian Orogen with respect to its orogenic evolution. Furthermore, the EAAO and the Birimian Orogen have the same temporal relationship to major environmental perturbations and isotopic excursions in the Neo- and Paleoproterozoic Eras, respectively, which are generally considered to be controlled by global tectonics. Building on previous work, it is argued that this a reflection of how the Paleo- and Neoproterozoic were characterized by an equivalent supercontinent cycle, where the Birimian Orogen assumed an equivalent position to the EAAO. This further requires that the Birimian Orogen formed during the assembly of a Paleoproterozoic equivalent of Gondwana. This is in line with the previous recognition of a ca. 2.1-2.0 Ga continent that included the Birimian Orogen, and which has been referred to as Atlantica. A revised configuration is presented for this continent, which includes crustal domains now present in Africa, South America, Eastern Europe and North China. Gondwana formed during the 1.0 Ga breakup of Rodinia and 0.3 Ga assembly of Pangea, and this cycle forms the basis for a global tectonic reconstruction for the Paleo- and Mesoproterozoic, which places the evolution of the Birimian Orogen within the context of the assembly of Atlantica and global-scale supercontinent cycles. As they are proposed to have formed in an equivalent tectonic setting, the EAAO and the Birimian Orogen also provide an opportunity to study the effect of secular changes during the Proterozoic. Furthermore, since the Birimian Orogen has been noted to have many similarities with Archean orogenic systems, this may indicate that the latter formed in similar complex plate boundary zones, such as currently exist in SE Asia.