Marceliano Lago

Permo-Carboniferous volcanism in Europe and northwest Africa: a superplume exhaust valve in the centre of Pangaea?

Abstract The Permo-Carboniferous transition in the European-northwest African province was characterised by widespread volcanism (calc-alkaline with crustal and/or mantle lithospheric characteristics followed by alkaline/subalkaline with HIMU-type signature) with a maximum in the Stephanian-Autunian (Late Pennsylvannian to Early Permian). Extrusion of volcanics was accompanied by massive S-type synextensional granitic intrusions and hydrothermal mineralisation. The geotectonic framework involved the gravitational collapse of the Variscan Belt by extensional detachment tectonics, and its final disruption by wrench faulting. The characteristics of this volcanism are explained within progressively evolving extensional processes. It is suggested that this Permo-Carboniferous Pangaean volcanic province might be interpreted in terms of a superplume impinging on the base of the lithosphere. This model envisages that magmatism acted as an exhaust valve releasing the heat accumulated beneath the Pangaean supercontinent by insulation and blanketing processes which triggered large-scale mantle-wide upward convection and general instability of the supercontinent.

Age of the Cretaceous alkaline magmatism in northeast Iberia: implications for the Alpine cycle in the Pyrenees

Cretaceous magmatism in northeast Iberia is related to the opening of the Bay of Biscay and counterclockwise rotation of Iberia with respect to Europe and predates the collision between Iberia and Europe that resulted in the formation of the Pyrenees. To better constrain the age of this magmatism, we have undertaken a Ar/Ar study on samples from the Pyrenees and the Catalonian Coastal Ranges. In the Basque-Cantabrian Basin and the North Pyrenean Basins, we have obtained Albian ages (ca. 102 Ma). In the northern Catalonian Coastal Ranges, we have obtained Campanian ages (ca. 79 Ma). We integrate our data with a review of previously published ages and discuss our results in terms of their geodynamic significance. The Cretaceous magmatism in the Pyrenees is Albian-Santonian (mostly occurring between 105 to 85 Ma) and was emplaced in a tectonically unclear context after the opening of the Bay of Biscay and rotation of Iberia. The magmatism in the Catalonian Coastal Ranges is well constrained to ca. 79 Ma and could mark the onset of Alpine shortening in the Pyrenean realm in northeasternmost Iberia. Finally, we describe a Late Triassic (ca. 232 Ma)-Early Jurassic (ca. 180 Ma) phase of magmatism in the Central Pyrenees, previously considered to be Cretaceous, that widens temporally and geographically the extent of the rift-related alkaline magmatism in southwestern Europe at that time. Key Points New Ar/Ar data update the age of the Cretaceous magmatism in NE Iberia Magmatism in the Pyrenees postdates the rotation of Iberia Magmatism in the Catalonian Coastal Ranges could mark the onset of Alpine shortening

Magnetic fabric in folded sills and lava flows. A case study in the Permian basalts of the Anayet Massif (Pyrenean Axial Zone, Spain)

Abstract The shallow intrusive bodies and lava flows emplaced within the Permian upper red unit in the Anayet Massif, represent a magmatic episode that occurred about 255 Ma (Saxonian) in the Pyrenean Axial Zone (northern Spain). Anisotropy of magnetic susceptibility (AMS) measurements, in both igneous bodies and their host rocks, allow us to infer the existence of magnetic fabrics of tectonic origin linked to the main cleavage-related folding episode. The relationship between the susceptibility axes and the field structures is the criterion that permits to differentiate normal from inverse magnetic fabrics in the igneous samples. The structural interpretation of all AMS data taken from the igneous bodies and sedimentary host rocks, is in accordance with a folding model which include: (i) flattening associated with cleavage formation during fold amplification in incompetent layers (host pelites), responsible for a magnetic lineation at high angles with respect to the regional folding axis and (ii) buckling in competent (conglomerates and igneous bodies) levels, responsible for a magnetic lineation parallel to the regional fold axes.

Effect of lithostatic pressure and tectonic deformation on the magnetic fabric (anisotropy of magnetic susceptibility) in low‐grade metamorphic rocks

The role of lithostatic pressure and strain in low-grade metamorphic cover rocks is analyzed through the anisotropy of magnetic susceptibility (AMS) of Jurassic and Cretaceous siltstones and limestones from the Cameros Basin (north Spain). For rocks initially characterized by precleavage magnetic fabric the main change in the magnetic fabric produced by the increase of lithostatic pressure is the increment in the degree of anisotropy (Pj). In rocks affected by syncleavage deformation the magnetic fabric depends on the mechanism of internal deformation involved in fabric development. In siltstones, where cleavage is correlated with synkinematic recrystallization of phyllosilicates and rigid-body rotation of grains, the magnetic fabric is coherent with the internal deformation determined by strain analysis on deformed nodules. On the contrary, in limestones we observe a complete reorganization of the magnetic fabric probably due to the discontinuous character of the cleavage formation mechanism. Detailed analysis of the β parameter (angle between the bedding pole and the minimum susceptibility axis parallel to the cleavage pole) indicates that for rocks characterized by syncleavage magnetic fabric the different variation pattern of Tj and Pj parameters is closely related to the deformation mechanisms responsible for the fabric development.

Petrology of the Azores Islands

This chapter presents an overview of the petrology of the Azores Archipelago, based on a review of the published literature on the mineralogy, petrology and major element geochemistry of the Azores islands and Formigas islets. In this chapter, we describe the mineralogy, petrology and major element chemistry of xenoliths/enclaves including peridotites, gabbros and syenites, and their roles in the magmatic evolution of the islands in which they occur. Where sufficient temporal data are available, we further describe the petrogenesis of the islands within a geochronological context. This synthesis and comparison of the petrology of each island is further combined with new modeling results for depth of melting and melt evolution paths to better understand the origin of the distinct petrologic characteristics of individual islands and the archipelago as a whole.