The late Palaeozoic volcanism of Castejón de Sos - Laspaúles basin, Southern Pyrenees, Spain

Autor: Lloret, Joan, Galé, C., López-Gómez, José, Arranz, E., Ronchi, Ausonio, Horra, Raúl de la, Barrenechea, J. F.
Rok vydání: 2018
Zdroj: Digital.CSIC. Repositorio Institucional del CSIC
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Popis: Trabajo presentado en el 2nd International congress on Permian and Triassic, celebrado en Casablanca (Marruecos), del 25 al 27 de abril de 2018
The late Palaeozoic continental basins emplaced in the present-day southern Pyrenees (Spain) were the result of a transtensive-extensive regime (Saura and Teixell, 2006) that affected most of the present-day SW Europe. The effects of that tectonic scenario preceded the beginning of Pangea break-up (Matte, 1991) and subsequent creation of continental 59 Abstract Book Quablanca 25 .. ·21" Aprll 2018 basins, including the aforementioned Pyrenean ones. A common feat urerelated to the i nit ial phase of these basins is the magmatic activity. In the Pyrenees, the late Pa laeozolc basins were extended untilthe early Mesozoic. The stratigraphic record is organized in five different units (Gisbert, 1981): the Grey Unit (GU - Upper Carboniferous), the Transition Unit (TU - early Lower Permian), the Lower Red Unit (LRU ¿ late lower Permian), the Upper Red Unit (URU - early Middle Permian) and the Buntsandstein facies (BUNT - lower-Middle Triassic). These units are separated by angular unconformities due to syn-sedimentary tectonic pulses. Our study is focused in the Castejón de Sos - Laspaúles basin, which is placed in the Southern Pyrenees (Spain). lts infill reaches a thickness of 900m, in spite of the absence of the URU Unit, as in i ts neighbour Erill Castell basin. The most probable cause to explain this feature is the non-deposition of this unit, condit ioned by the presence of a topographic high in the zone as a result of the intense tecton ic activity. The volcanic deposits in the studied basin are restricted to the Grey Unit (Upper Carboniferous), in contrast to other contemporary Pyrenean basins. This unit reaches 500 m of t hickness, and it is mainly composed by volcanic and volcano-clastic deposits. Siltstones and sandstones, related to fluvial systems, are recorded in the upper part of the unit. The volcanic and volcano-clastic deposits unconformably overlie the Palaeozoic basement (Devonian limestones) and are arranged in a complex sequence, highly variable from one section to another but composed of two clearly distinct units: a lower rhyolitic one and an upper andesitic unit. The rhyolitic unit (25 to over 100 m in thickness) is mainly of ignimbrit ic nature, but several unlts of volcanic agglomerates and tuff deposits, related to pyroclastic flows and surges can be recognized. The contact between the different units is marked either by an erosive base or by thin ash layers that frequently include coalized plant remnants. In sorne sections, the base of this unit includes a rhyolitic breccia (up to 10 m thick), probably related to gravitational collapse of local rhyolitic domes. Pereira et al (2014) dated similar ignimbrites in the Eriii-Castell (296.1±4 Ma) and Estac (296.2±3.1 M a) basins, which are Asselian in age. The andesitic unit is highly variable in thickness and overlies the rhyolitic unit. lt was built by successive events of either subaerial or subaqueous extrusion with sorne stagnation periods, evidenced by development of hydromorphic soils (Gascón and Gisbert, 1987). The subaerial flows constitute massive bodies sometimes related to breccia/conglomerate levels produced by sedimentary reworking of clasts originated in these flows. Subaqueous intrusion is evidenced by the development of autobreccias with chilled clasts, sometimes including sediment blobs and by generalized vesiculation. This volcanism, related to the opening of the late Palaeozoic continental basins, has acalcalkaline geochemical signature, as is common in orogenic contexts. l ts compositional evolution, from a silicic, relatively shallow crustal source, to more basic composi tions, related to deeper sources probably reflects the progressive evolution from the end of the compressive stage to more extensional conditions.
Databáze: OpenAIRE
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