Tightening-up NE Brazil and NW Africa connections: New U-Pb/Lu-Hf zircon data of a complete plate tectonic cycle in the Dahomey belt of the West Gondwana Orogen in Togo and Benin

Carlos E. Ganade (1) , Umberto G. Cordani (1) , Yao Agbossoumounde (2) , Renaud Caby (3) , Miguel A. S. Basei (1) , Roberto F. Weinberg (4) , Kei Sato (1)

1 USP - Universidade de São Paulo = University of São Paulo
2 University of Lome
3 Géosciences Montpellier
4 School of Earth, Atmosphere and Environment [Melbourne]

The Dahomey belt in Togo and Benin is an important segment of the larger West Gondwana Orogen. Here, we review the geodynamic evolution of the Dahomey belt and discuss new U–Pb and Lu–Hf zircon data in light of similar data previously acquired on the geologically related Northern Borborema Province, in NE Brazil. Eighteen samples from different tectonic settings and regions within the belt were collected for zircon isotopic investigation. Passive margin deposits of the Atacora Structural Unit and lower units of the Volta Basin have detrital zircon signatures compatible with the flanking West Africa Craton. The arc-related magmatism resulted from the east-dipping subduction of the Goiás-Pharusian oceanic lithosphere and is represented by a variety of granitoids emplaced in the Benino-Nigerian Shield between 670 and 610 Ma. These granitoids were mainly sourced from crustal reservoirs with subordinate juvenile input. Detrital zircon ages from syn-orogenic deposits in Benino-Nigerian Shield suggest that arc development could have started as early as 780 Ma. The main period of melting in the internal part of the belt, the Benino-Nigerian Shield, is related to crustal thickening and occurs only ca. 30 m.y. after initiation of the continental collision, marked by the ca. 610 Ma ultra-high pressure (UHP) metamorphism recorded at Lato Hills. Foreland development represented by the upper units of the Volta basin developed soon after continental collision and persisted with the development of the west-verging thrust front synchronously with the main period of crustal melting due to collision at ca. 580 Ma. The subvertical Transbrasiliano Lineament in South America, that corresponds to the Kandi Lineament in Africa, provides a present-day fit between NW Africa and NE Brazil. Restoration of the movement of the Transbrasiliano-Kandi Lineament (strike-slip plate boundary) places the Dahomey belt and Borborema Province (NE Brazil) along the same section of the West Gondwana Orogen. This configuration would explain some of the misfits previously discussed in the literature and aligns the UHP eclogites in Togo and NE Brazil.

Mots clés: West Gondwana Orogen; Dahomey belt; Zircon geochronology; Brazil-Africa correlation

Domaines: Géochimie

Carlos E. Ganade, Umberto G. Cordani, Yao Agbossoumounde, Renaud Caby, Miguel A. S. Basei, et al.. Tightening-up NE Brazil and NW Africa connections: New U-Pb/Lu-Hf zircon data of a complete plate tectonic cycle in the Dahomey belt of the West Gondwana Orogen in Togo and Benin. Precambrian Research, 2016, 276, pp.24-42. ⟨10.1016/j.precamres.2016.01.032⟩. ⟨hal-01358584⟩