The late Variscan HT/LP metamorphic event in NW and Central Iberia: relationships to crustal thickening, extension, orocline development and crustal evolution

Abstract

The Variscan metamorphic evolution of the autochthonous domain of NW and Central Iberia is characterized by a Barrovian gradient followed by a high-temperature–low-pressure (HT/LP) event associated with voluminous granite magmatism. The structural, metamorphic and magmatic histories of the region are described briefly and the relations between them are explained. A coherent model for evolution of the continental crust is proposed using published radiometric ages, thermal models and seismic reflection profiles. The metamorphic evolution, including the high-temperature event, is explained by crustal thickening resulting from the Gondwana–Laurussia collision followed by a period of thermal relaxation and a long-lasting extensional stage. The fact that the highest temperatures were reached in the core of the Central Iberian arc, partly occupied by remnants of a huge allochthonous nappe stack, is discussed in relation to both the emplacement of the allochthon and subsequent oroclinal bending. The overburden provided by the allochthonous pile was decisive in triggering the high-temperature event. Orocline development mostly occurred later and had no significant effect on the metamorphic evolution, although it was important for the present localization of gneiss domes and granitoids. The possible role of the mantle in supplying additional heat to explain the HT/LP event is also discussed. It would seem that little mantle contribution was needed and there are no strong arguments for mantle delamination, although some kind of mantle–crust interaction is expected beneath the hot regions presently occupying the core of the Central Iberian arc.

The transition from Pangea amalgamation to fragmentation: Constraints from detrital zircon geochronology on West Iberia paleogeography and sediment sources

“…2) played an important role in accommodating the oblique convergence between Laurussia and Gondwana (Ribeiro et al, 1990;Dias and Ribeiro, 1993;Shelley and Bossière, 2000;Simancas et al, 2005;Martínez Catalán et al, 2007;Ribeiro et al, 2007). Other authors, however, consider that these shear zones represent large strike-slip faults that crosscut the original boundaries between the Variscan geotectonic zones (Martínez Catalán, 2011;Ballèvre et al, 2014;Martínez Catalán et al, 2014;Gutiérrez-Alonso et al, 2015). Regardless of their specific roles during Variscan and post-Variscan deformation, they have a dextral sense of movement and are associated with the formation of the Pennsylvanian Buçaco (along the Porto-Tomar Shear Zone; Flores et al, 2010) and Santa Susana (along the Santa Susana Shear Zone; Machado et al, 2012) pull-apart basins (Fig.…”

Exhuming a cold case: The early granodiorites of the northwest Iberian Variscan belt—A Visean magmatic flare-up?

“…The hypotheses that support rather continuous magmatic activity are mainly derived from the combined interpretation of radiometric ages of granitoids obtained by different methods 40 Ar- 39 Ar, K-Ar; e.g., Serrano Pinto et al, 1987;Díaz Alvarado et al, 2013;Martínez Catalán et al, 2014) and the numerical modeling of the thermal evolution of the orogen, including radioactive heat production (e.g., Bea et al, 1999Bea et al, , 2003Bea, 2012;Alcock et al, 2015). In essence, these hypotheses view melt production in the collisional scenario mainly as the result of severe crustal thickening of a fertile (graywacke and pelite rich) crust followed by an interval of thermal relaxation (e.g., Martínez-Catalán et al, 2014) accompanied by melting of the thickened crust.…”

“…In essence, these hypotheses view melt production in the collisional scenario mainly as the result of severe crustal thickening of a fertile (graywacke and pelite rich) crust followed by an interval of thermal relaxation (e.g., Martínez-Catalán et al, 2014) accompanied by melting of the thickened crust.…”

“…The advent of a large amount of more precise U-Pb age data on Variscan granitoids (and some volcanic rocks) from northwest Iberia in recent years (e.g., compilation in Gutiérrez-Alonso et al, 2011;Martínez Catalán et al, 2014) has provided a more focused picture of the magmatic history of the WEVB, providing solid ground for interpretations that link periods of more intense magmatic activity with large-scale crust-mantle processes involved in the collisional orogeny and the subsequent development of the West European Variscan Belt (e.g., Castro et al, 1999Castro et al, , 2000Fernández-Suárez et al, 2000;Villaseca et al, 2009Villaseca et al, , 2011Gutiérrez-Alonso et al, 2011;Orejana et al, 2012;López-Moro et al, 2018).…”

LP-HT anatectic processes and lithological heterogeneity in the Mindelo Migmatite Complex (NW Portugal)

“…In the Variscan Belt the metamorphism occurred mostly under low pressure and high temperature (Martínez et al, 2001;Valle Aguado et al, 2005;Ribeiro et al, 2008;Catalán et al, 2014). In CIZ the high-grade rocks, belonging mainly to the Schist-Greywacke Complex (SGC), are associated with peraluminous granitic plutons and anatectic complexes, materializing thermal domes developed in a late stage of the Variscan Orogeny (Escuder Viruete et al, 1994;Martínez et al, 2001;Bea et al, 2003;Valle Aguado et al, 2005;Ribeiro et al, 2008;Catalán et al, 2014). The association of amphibolite facies metamorphic rocks with migmatites grading into granitic rocks has been described in different sectors of the Iberian Variscan Belt (Pereira & Bea, 1994;Barbero & Villaseca, 1995;Valle Aguado et al, 2010).…”