Abstract The Neoproterozoic Gourma fold and thrust belt exposed in eastern Mali includes in its inner part high-pressure, low-temperature metasediments and scarce metabasites. This high-pressure metamorphic unit is characterized in the Ansongo region by garnet–glaucophane–paragonite assemblages and eclogites of basaltic derivation, whereas phengite–garnet–rutile mineral assemblages characterize the metapelites. Thermobarometric estimates on the metabasites suggest peak pressure around 13–15 kbar and temperature of 500±50 °C for the Seyna Bela garnet glaucophanite and glaucophane-bearing eclogite, and 16 kbar at 600±50 °C for the Tin Hama phengite eclogite, values indicative of palaeogeothermal gradients of about 10 °C km −1 typical of subduction settings. The high-pressure unit may represents a giant allochthon emplaced on top of very low-grade metasediments. It represents the southern extension of the ultrahigh-pressure rocks. Garnet pyriclasites from the Amalaoulaou massif, which represents the roots of a c . 800–730 Ma Neoproterozoic island arc, underwent a medium-temperature metamorphic overprint characterized by barroisite–paragonite assemblages; that is, of same grade as the decompression that affected the eclogites and garnet-blueschists. The Gourma high-pressure metamorphic belt formed as a consequence of the east-dipping subduction of the Neoproterozoic passive palaeo-margin of the West African craton. The presented P – T estimates suggest that subduction-related palaeogeothermal gradients during the late Neoproterozoic period along the main Pan-African suture were similar to those reconstructed for Tertiary Alpine-type belts.

Abstract The Borborema and Benin–Nigeria provinces of NE Brazil and NW Africa, respectively, are key areas in the amalgamation of West Gondwana by continental collision during the Brasiliano/Pan-African orogenies. Both are underlain by complex basement: Nigeria has c. 3.05 Ga Archaean crust but no known Palaeoproterozoic rocks >2.0 Ga; in NE Brazil, 2.6–3.5 Ga Archaean rocks form small cores within Palaeoproterozoic gneiss terrains affected by plutonism at c. 2.17 Ga. Both regions exhibit Late Palaeoproterozoic ( c. 1.8 Ga) rift-related magmatism and metasedimentary sequences overlying the basement. The Seridó Group of NE Brazil (<0.65 Ga) is similar to the Igarra Sequence in SW Nigeria. The Ceará Group, which may date back to c. 0.85 Ga, is a passive margin deposit on crust thinned during initiation of an oceanic domain. In both provinces, basement and sedimentary cover were involved in tangential tectonics that resulted in crust-thickening by nappe-stacking associated with closure of this ocean. Frontal collision between c. 0.66 and 0.60 Ga later evolved to an oblique collision, generating north–south continental strike-slip shear zones at c. 0.59 Ga. In NE Brazil, the main Pan-African suture is probably buried beneath the Parnaíba Basin. The Transbrasiliano Lineament, interpreted as the prolongation of the Kandi–4°50 Lineament in Hoggar, may represent a cryptic suture.