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Encyclopedia of geology, five volume set, volume 1 5 (encyclopedia of geology series) ( PDFDrive ) 719

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EUROPE/Variscan Orogeny 83 Figure Simplified tectonic cross sections through the Variscan belt in (A) the Iberian peninsula and (B) France: pink, pre Palaeozoic basement and early Palaeozoic granitoids (undifferentiated); yellow, Early Palaeozoic sediments; green, thrust sheets with Early Palaeozoic ophiolites; dots, Carboniferous foreland basin deposits; VF, Variscan Front; Bray F, Bray Fault, NASZ, North Armoricn Shear Zone; SASZ, South Armorican Shear Zone; CCSZ, Coimbra Cordoba Shear Zone by major faults and/or sutures and are discussed below The Central Iberian Zone is the southern continuation of the autochthonous series of the northern Iberian section, with Early Palaeozoic rocks unconformably overlying low-grade Proterozoic sediments A very important intracontinental sinistral shear zone separates the Central Iberian Zone from the Ossa Morena Zone and marks the boundary between tectonic domains with north-east and south-west vergences This shear zone either represents or overprints the suture zone in which the north-west Iberian allochthon is rooted There is evidence of very peculiar Ordovician magmatism with alkaline to peralkaline gneisses The Ossa Morena Zone shows a relatively complete fossiliferous Early Palaeozoic record from the lowermost Cambrian through to the Silurian and Devonian Lower Cambrian sandstones and limestones unconformably overlie Upper Proterozoic rocks that are characterized by the presence of black cherts metamorphosed and intruded by Cadomian granitoids (550–500 Ma) as in northern Brittany In some places (e.g Cordoba) calc-alkaline andesites erupted during the latest Proterozoic/Early Cambrian The Ossa Morena Zone shows large south-west-facing recumbent folds emplaced before the Early Carboniferous (which is, in part, coal-bearing) The Variscan metamorphism (epizonal to catazonal) is of a hightemperature–low-pressure type, and an important Variscan magmatism (diorites and granodiorites) is present The present-day southern boundary of the Ossa Morena Zone is considered to be a suture, based on the existence of a belt of oceanic amphibolites (Beja-Acebuches) thrust over a possibly Devonian accretionary prism with slices of oceanic metabasalts This north-west–south-east-trending boundary with the South Portuguese Zone has been reworked as a sinistral wrench fault The South Portuguese Zone exposes only Devonian and Carboniferous sediments and is characterized by important bimodal Tournaisian volcanic deposits, which contain the largest copper ore bodies in Western Europe (the South Portuguese Pyrite Belt) Timeequivalent volcanic rocks are known from south-west England and are widespread in the Rheno-Hercynian Belt of Germany The Rheno-Hercynian and, hence, Avalonian affinities of the South Portuguese Zone are also suggested by a thick turbidite sequence deposited in a foreland basin (‘Culm’ facies), with a change towards paralic deposits in the south-west It comprises the Vise´ an to Westphalian D The South Portugese Zone is characterized by south-west-facing folds and thrusts Deformation occurred during the Late Carboniferous The French section (see Figure for location) can be subdivided into three segments The Massif Central segment is the most complete section on the southern flank of the Variscan belt and is exposed over a distance of 400 km from the Montagne Noire to the southern margin of the Paris Basin The Paris Basin segment is buried beneath Mesozoic sediments, but has been sampled in rare drillings and imaged at depth by a wide-angle reflection profile Potentially equivalent rocks are exposed to the west in central Brittany The Ardennes section is partly buried beneath the sediments of the Paris Basin, but is well known at depth from drilling, coal mining, and a

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