Abstract The sediments of the Mauges Unit located in the internal zone provide an opportunity of studying the evolution of relief during Palaeozoic time. U–Pb dating on zircon and 39 Ar/ 40 Ar on white mica are used to constrain the age and nature of the sources. The first relief identified is marked by an Early Devonian unconformity interpreted as the opening of a northern back-arc basin. Detrital minerals are first reworked from underlying layers indicating a local supply. Magmatic zircons at c. 400 Ma then record the emergence of a magmatic arc. During the Middle Devonian, the gap in the sedimentary record is attributed to an emersion followed by the disappearance of the relief during the Late Devonian. At the Devonian–Carboniferous boundary, the main collision is followed by the onset of a relief. The continental sedimentation in the Ancenis Basin (late Tournaisian–Viséan) is a coarsening-upwards megasequence indicating an increasing and/or approaching relief. The detrital minerals record the progressive exhumation of Variscan metamorphic (mica at c. 350 Ma) and magmatic rocks (zircons at c. 390–340 Ma). The Serpukhovian–Bashkirian sedimentation records the erosion of a proximal metamorphic source (Champtoceaux with micas at c. 350–340 Ma) showing a much shorter drainage system. Supplementary material: Sample coordinates and U–Pb on zircon and 39 Ar/ 40 Ar on white mica analyses are available at http://www.geolsoc.org.uk/SUP18730 .

Abstract Central Hoggar, within the Tuareg shield to the east of the West African craton, is known for its complexity owing to the interplay of the Eburnean and Pan-African orogenies. The Tidjenouine area in the Laouni terrane belongs to the LATEA metacraton and displays spectacular examples of granulite-facies migmatitic metapelites. Here, we present a detailed petrological study coupled with in situ U–Pb zircon dating by laser-ablation inductively coupled plasma mass spectrometry (ICP-MS) that allows us to constrain the relative role of the Eburnean and Pan-African orogenies and hence to constrain how the LATEA Eburnean microcontinent has been partly destabilized during the Pan-African orogeny; that is, its metacratonic evolution. These metapelites have recorded different metamorphic stages. A clockwise P–T evolution is demonstrated on the basis of textural relationships, modelling in KFMASH and FMASH systems and thermobarometry. The prograde evolution implies several melting reactions involving the breakdown of biotite and gedrite. Peak metamorphic P–T conditions of 860±50 °C and 7–8 kbar (M 1 ) were followed by a decrease of pressure to 4.3±1 kbar and of temperature to around 700 °C, associated with the development of migmatites (M 2 ). After cooling, a third thermal phase at c . 650 °C and 3–4 kbar (M 3 ) occurred. U–Pb zircon laser ablation ICP-MS analysis allows us to date the protolith of the migmatites at 2151±8 Ma, the granulite-facies and migmatitic metamorphisms (M 1 –M 2 ) at 2062±39 Ma and the medium-grade metamorphic assemblage (M 3 ) at 614±11 Ma. This last event is coeval with the emplacement of large Pan-African granitic batholiths. These data show that the main metamorphic events are Eburnean in age. The Pan-African orogeny, in contrast, is associated mainly with medium-grade metamorphism but also mega-shear zones and granitic batholiths, characterized by a high temperature gradient. This can be considered as typical of a metacratonic evolution.

Abstract The Platinum-bearing Belt of the Urals consists of a series of zoned ultramafic bodies obducted onto the passive continental margin of the East European Craton during the Palaeozoic. Conventional U–Pb and secondary ionization mass spectrometry U–Th–Pb analyses of single zircon grains from a pegmatitic gabbro of the Kumba massif provide Mid-Silurian ages of 425 ± 3 Ma and 419 ± 10 Ma, respectively, interpreted as dating crystallization of the gabbroic magma. This contrasts with the c . 360 Ma age of the neighbouring Kytlym massif and indicates that the Uralian Platinum-bearing Belt is best interpreted as remnants of an island-arc oceanic lithosphere that started forming in Mid-Silurian times and had a protracted lifetime of about 70 Ma. The Uralian Platinum-bearing Belt is thus coeval with the Sakmara arc of the Southern Urals, and is of similar age to other ultramafic bodies such as the Kempersai and Mindyak massifs. Ophiolitic fragments, now preserved along the Main Uralian Fault, may thus represent the assemblage of contemporaneous oceanic and arc terranes brought together during the final stages of the evolution of the Uralide orogen. The age of the Kumba massif, in addition, indicates that the Uralian Ocean underwent contractional events as early as the Mid-Silurian, which suggests a possible link with the pivotal rotation of Baltica.