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Tephra layers are interstratified in the ice caps of the South Shetland Islands. Although previously poorly investigated, they are potential targets for the application of tephrochronology and, hence, may provide temporal constraints on glaciological models for the region. Several tephra layers crop out in the coastal ice-cliffs and ablation ramps of Livingston Island. Using stratigraphical position, granulometry and bulk sample geochemistry, the tephra layers can be divided into three groups (TPH1, TPH2 and TPH3, from top to base). The source for all of the tephras is unequivocally identified as Deception Island, a large active volcano in Bransfield Strait, situated about 35 km south of Livingston Island. TPH1 (a single layer) is strongly correlated compositionally with tephra erupted in 1970 from centres close to Telefon Bay. This is the first time it has been possible to correlate a distal tephra with a pyroclastic unit in the source volcano in the Antarctic Peninsula region. TPH2 (usually two layers, sometimes only one) was probably erupted from a tuff cone centre within the Crater Lake cluster of vents. From historical accounts, it is deduced that the numerous co-eruptive Crater Lake vents were active prior to 1829 and, from their relatively fresh appearance, an eighteen-century age for the eruptions is possible. TPH3 comprises at least four discrete tephra layers with a much wider compositional range than either TPH1 or TPH2. It may have been erupted during successive months or years. Compositional comparisons of TPH3 with possible source vents on Deception Island are ambiguous, but there is a reasonably good similarity with tephras erupted at Wensleydale Beacon and/or Vapour Col. However, it is also conceivable that the source(s) for TPH3 are no longer preserved on Deception Island. The age of the TPH3 eruptions is unknown but it must be prior to 1829 and is unlikely to be more than a few centuries.

Keywords:Pre-Variscan Late Ordovician magmatism SHRIMP geochronology U-Pb zircon

International audienceThe volcanism hosted by the Ediacaran–Terreneuvian Canaveilles Group of the Eastern Pyrenees displays two distinct geochemical affinities: (1) metabasites of the Nyer and Olette formations reflect the emplacement of a tholeiitic magmatism linked to extensional conditions, whereas (2) subsequent felsic and calc-alkaline magmatic rocks marking the top of the Olette Formation and forming the overlying Fabert and Finestrelles members represent Cadomian magmatic events. Based on U–Pb zircon dating constraints, palaeotopographic relationships linked to onlap geometries and distance from vent sources, three volcanosedimentary edifices can be distinguished, the so-called Tregurà (ca. 565–552 Ma), Cap de Creus (ca. 558 Ma) and Coll d’Ares (ca. 542–532 Ma) edifices. The top of their palaeoreliefs recorded locally the nucleation of centres of microbial carbonate productivity (Puig Sec Member) linked to synsedimentary tilting and karstification. Throughout West Gondwana, the presence of carbonate production across the Ediacaran–Cambrian transition is exclusively located in back-arc settings (Central-Iberian Zone) and areas far from the Cadomian subduction trench and devoid of significant terrigenous input, such as those reported in the Eastern Pyrenees and the neighbouring Montagne Noire

Two deformational events which developed prior to the Variscan structures can be characterized in the Palaeozoic rocks of the Pyrenees

Geochronological U-Pb (LA-ICP-MS), geochemical and isotopic data from metavolcanic felsic rocks of the Canigó and Cap de Creus massifs in the Eastern Pyrenees provide evidence of an Ediacaran magmatic event lasting 30 m.y. in NE Iberia. Data also constrain the age of the Late Neoproterozoic succession in the Cap de Creus massif, where depositional ages range from 577 to 558 Ma, and in the Canigó massif, where the data (575 to 568 Ma) represent minimum ages. Geochemistry indicates that the rocks were formed in a back-arc environment and record a fragment of a long-lived subduction-related magmatic arc (620 to 520 Ma) in the active northern Gondwana margin. The homogeneity shown by all these crustal fragments along this margin suggests that the individualization of the Pyrenean basement from the Iberian Massif started later, probably during its transition from an active to a passive margin in Cambro-Ordovician times.

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