Abstract

The Ossa–Morena Zone and the South Portuguese Zone represent the southernmost Hercynian domains of the Iberian Massif. Lithostratigraphic, petrographic and structural differences exist between both zones. The boundary between the Ossa–Morena and the South Portuguese Zones is marked by a narrow belt of amphibolites of tholeiitic affinity and related oceanic sequences, the Beja–Acebuches ophiolites. The southernmost area of the Ossa–Morena Zone, which bounds the Acebuches amphibolites, is composed of medium to high grade metamorphic rocks. The Ossa–Morena Zone-South Portuguese Zone suture preserves a complex story of middle to upper Devonian (?) to upper Stephanian sinistral transpression. The resulting structures were generated in a ductile to brittle regime. Transpressive shear zones affect the ophiolitic remnants and the high grade rocks of the southernmost area of the Ossa–Morena Zone. The late Hercynian faulting combines sinistral strike-slip movements and some thrusting component, which cut the suture to produce fish-like megaboudins. The transpressive regime can be explained by the oblique collision of the two plates now represented by the Ossa–Morena Zone and the South Portuguese Zone during the continental accretion. On the scale of the Hercynian Belt, this sinistral transpression belongs to a network of comparable structures explained by the impingement of the Ibero-Armorican Terranes.

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