A geodynamic model for the Paleoproterozoic (ca. 2.27-1.96 Ga) Birimian Orogen of the southern West African Craton - Insights into an evolving accretionary-collisional orogenic system

摘要

This study presents an updated geodynamic model for the 2270-1960 Ma Birimian Orogen in the southern West African Craton (sWAC), which form part of a large accretionary-collisional orogenic system that extends into the Reguibat shields in northern WAC and southwards into equivalent crust in the Amazon Craton. The early evolution of the orogen was characterized by deposition of volcanic-volcanosedimentary successions and emplacement of limited intrusives, with a significant contribution from juvenile sources. This was followed by a collisional phase, associated with the deposition of large volcano-sedimentary and siliciclastic successions in both deep and shallow water conditions, along with ongoing volcanic activity and widespread emplacement of compositionally diverse intrusives. This occurred contemporaneously with deformation, regional greenschistamphibolite facies metamorphism and juxtaposition of high and low-grade crustal domains, during what is referred to as the Eburnean Orogeny. A key aspect of the collisional phase is its diachronous nature, with the main period of magmatism, sedimentation and tectonothermal activity occurring around ca. 2160-2100 Ma in eastern sWAC, and between ca. 2120-2070 Ma in the west.