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Cambrian-early Ordovician volcanism across the South Armorican and Occitan domains of the Variscan Belt in France:Continental break-up and rifting of the northern Gondwana margin
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作者 andre pouclet J.Javier Alvaro +3 位作者 Jacques-Marie Bardintzeff andres Gil Imaz Eric Monceret Daniel Vizcaino 《Geoscience Frontiers》 SCIE CAS CSCD 2017年第1期25-64,共40页
The Cambrian-lower Ordovician volcanic units of the South Armorican and Occitan domains are ana- lysed in a tectonostratigraphic survey of the French Variscan Belt. The South Armorican lavas consist of continental tho... The Cambrian-lower Ordovician volcanic units of the South Armorican and Occitan domains are ana- lysed in a tectonostratigraphic survey of the French Variscan Belt. The South Armorican lavas consist of continental tholeiites in middle Camhrian-Furongian sequences related to continental break-up. A significant volcanic activity occurred in the Tremadocian, dominated by crustal melted rhyolitic lavas and initial rifting tholeiites. The Occitan lavas are distributed into five volcanic phases: (I) basal Cambrian rhyolites, (2) upper lower Cambrian Mg-rich tholeiites close to N-MORBs but crustal contaminated, (3) upper lower-middle Cambrian continental tholeiites, (4) Tremadocian rhyolites, and (5) upper lower Ordovician initial rift tholeiites. A rifting event linked to asthenosphere upwelling took place in the late early Cambrian but did not evolve. It renewed in the Tremadocian with abundant crustal melting due to underplating of mixed asthenospheric and lithospheric magmas. This main tectono-magmatic conti- nental rift is termed the "Tremadocian Tectonic Belt" underlined by a chain of rhyolitic volcanoes from Occitan and South Armorican domains to Central Iberia. It evolved with the setting of syn-rift coarse siliciclastic deposits overlain by post-rift deep water shales in a suite of sedimentary basins that fore- casted the South Armorican-Medio-European Ocean as a part of the Palaeotethys Ocean. 展开更多
关键词 Gondwana margin Cambro-Ordovician volcanic activity Continental tholeiite Rheic Ocean Middle-European Ocean Palaeotethys Ocean
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