Abstract The Cambrian Atlas – Ossa–Morena – North Armorican Rift extended along West Gondwana from the end of the Pan-African and Cadomian orogenies until the diachronous beginning of drift conditions related to the opening of the Rheic Ocean. The along-axis rift cross-cut the western parts of the Anti-Atlas, High Atlas and Coastal Meseta, which were linked to the Ossa–Morena Zone and the North Armorican Domain, whereas several joint tectonic branches connected with off-axis rift transects of the Central Iberian, West Asturian–Leonese and Cantabrian zones (Iberian Massif), the Central and South Armorican domains, the Occitan Domain, the Pyrenees, and southern Sardinia. The pre-rift unconformity, post-dating the orogenic collapse, is characterized by initial (half-)graben development and subsequent infill, with slope-related breccias and conglomerates controlled by the denudation of surrounding uplands. Synrift pulses show regional extension and are distinctly identifiable on the top of rift shoulders, recording episodes of carbonate production due to their association with karst and hydrothermal processes. The break-up unconformity ranges from volcanic-free angular discordances and paraconformities to generalized uplift and denudation of subaerially exposed areas, associated with the onset of granite-dominant large igneous provinces (LIPs). The Furongian–Tremadocian (Toledanian) and Ordovician (Sardic) phases have been interpreted as due to: (i) Andean-type subduction magmatism reaching the crust in an arc–back-arc setting; (ii) post-collisional decompression melting without significant mantle involvement; and (iii) partial melting of the lower continental crust affected by the underplating of hot mafic magmas linked to superplumes.

ABSTRACT The Paleozoic plate boundary zone between Laurussia and Gondwana in western Pangea hosts major magmatic and hydrothermal Sn-W-Ta, Au, and U mineralization. Individual mineral deposits represent the results of the superposition of a series of exogenic and endogenic processes. Exogenic processes controlled (1) the enrichment of the ore elements in sedimentary protoliths via residual enrichment during intense chemical weathering and via climatically or tectonically controlled redox traps, (2) the spatial distribution of fertile protoliths, and, thus, eventually (3) the spatial distribution of mineralization. Endogenic processes resulting in metamorphism and crustal melting controlled the mobilization of Sn-W, Au, and U from these enriched protoliths and, thus, account for the age distribution of Sn-W and Au mineralization and U-fertile granites. It is the sequence of exogenic and endogenic processes that eventually results in the formation of mineralization in particular tectonic zones. Whereas the endogenic processes were controlled by orogenic processes during the assembly of western Pangea itself, the exogenic processes were linked to the formation of suitable source rocks for later mineralization. The contrasting distribution of magmatic and hydrothermal Sn-W-Ta, Au, and U mineralization on the Laurussia and Gondwana sides of the plate boundary zone reflects the contrasting distribution of fertile protoliths and the contrasting tectonic situation on these margins. The Laurussian margin was an active margin during most of the Paleozoic, and the distribution of different mineralization types reflects the distribution of terranes of contrasting provenance. The Gondwanan margin was a passive margin during most of the Paleozoic, and the similar distribution of a wide range of different metals (Sn, W, Ta, Au, and U) reflects the fact that the protoliths for the various metals were diachronously accumulated on the same shelf, before the metals were mobilized during Acadian, Variscan, and Alleghanian orogenic processes.