Magmatism in the intracratonic Central Iberian basins during the Permian: Palaeoenvironmental consequences

Recent studies have confirmed the important role played by magmatism during the Late Carboniferous-Permian transition. In this report, we describe the characteristics of this magmatism in the Central Iberian realm (Iberian Ranges and eastern Spanish Central System) and discuss its palaeoenvironmental impact. In the studied area, the late-Variscan transtensional to extensional tectonic regime favoured the emplacement of a calc-alkaline magmatism during the Late Stephanian-Permian. This magmatism is expressed both as pyroclastic rocks filling small half-graben basins and hypabyssal intrusions (sills and dykes). Pyroxenic- and amphibolic-andesites are the main rock compositions, while basalt, dacite and rhyolite are less represented. The available K/Ar isotopic data suggests a Lower Permian age for this magmatism, also supported by its complete macro- and microflora content and by features related to its emplacement (hypabyssal intrusions crosscut Stephanian rocks and are in turn overlain by late Permian-Triassic sediments). Frequent xenoliths of middle and lower crustal levels indicate considerable magma-crust interaction. This interaction may have led to substantial crustal assimilation during the first emplacement stages in conditions of a low extension rate. Crustal contamination barely affected the final magmatic products emplaced under conditions of greater extension. The palaeoecological effects of explosive manifestations of this volcanism are expressed in the varied macroflora record in volcaniclastic basins. The number and volume of hypabyssal intrusions suggest that the original geological record of explosive activity in these basins was much greater and was reduced by subsequent erosion processes.