Gravity modeling of the lithosphere in the Calatrava Volcanic Province (Spain): geodynamic implications

The origin of the intraplate volcanism in the Calatrava Volcanic Province (CVP) is controversial. On the basis of its geochemical signature it has been ascribed to an “aborted” rift, implying lithospheric thinning. However, the volcanism occurred during the generalized Cenozoic NW−SE-oriented compressive tectonic regime. On the other hand, on the basis of evidence for its deep-seated origin, it has been linked to the existence of a baby-plume detached from an active megaplume below the Canary-Azores Islands and the western Mediterranean. In order to understand better the aforementioned geodynamic scenarios for the origin of the CVP, we address here the study of the lithosphere in the CVP and its vicinity by means of gravity analysis and 2+1/2D modeling. Gravity modeling results do not support the rifting model adopted for the intraplate volcanism occurred in the CVP because the crust shows a constant thickness. Density models suggest the existence of a sub-crustal, anomalous low-density block that could be underplated magmatic material at the base of the crust, suggesting that only a minor part of it intruded up into the crust and erupted. The localized magmatism of the CVP can be related to the combination of two factors: one active, the gentle folding of the Iberian lithosphere and associated uplifting of the Variscan basement due to the NW-directed transmission of compressive stresses in the upper plate yielded by the subduction/collision in the south Iberian margin. The formation of the lithospheric folding in the Calatrava region results in a decrease of the pressure beneath the swell of the antiform that is likely to bring about basaltic magmatism below the swell; and one passive, the existence of a Variscan right-lateral shear band, which yields a weakened  crust that facilitates the ascent of the magmatic materials. The relatively small volume, but large extension, of the volcanic outcrops could be associated with the preferential ascent of the magmas along the weakened crust of this NW−SE-trending Variscan shear band.El origen del volcanismo intraplaca en la Provincia Volcánica de Calatrava (CVP) es controvertido. En base a su signatura geoquímica se ha atribuido a la formación de un rift “abortado”, implicando un adelgazamiento litosférico. Sin embargo, el volcanismo se desarrolló durante un régimen tectónico compresivo orientado NW-SE que fue generalizado en la región de Calatrava durante el Cenozoico. Por otro lado, en base a las evidencias de su origen profundo, se le ha relacionado con la existencia de una mini-pluma desconectada de una mega-pluma activa debajo de los archipiélagos de Canarias y Azores, y en el Mediterráneo occidental. Con el propósito de contribuir a la discriminación entre los escenarios geodinámicos mencionados para el origen del volcanismo se ha abordado aquí el estudio de la litosfera en la CVP y en las zonas próximas mediante el análisis gravimétrico y la modelación 2+1/2D. Los modelos gravimétricos no apoyan el modelo de rifting adoptado para el volcanismo intraplaca ocurrido en la CVP porque el espesor de la corteza es cuasi-constante. Los modelos siguieren la existencia de un cuerpo anómalo sub-cortical de baja densidad que podría ser material magmático acrecionado y almacenado en la base de la corteza indicando que sólo una parte menor habría intruido en la corteza y producido erupciones. El volcanismo localizado de la CVP se puede relacionar con la combinación de dos factores: a) Un factor activo correspondiente a un amplio plegamiento de la litosfera (corteza) Ibérica y el consiguiente levantamiento asociado del basamento varisco debido a la transmisión hacia el NW de los esfuerzos compresivos en la placa superior de la subducción/colisión miocena en el margen meridional Ibérico. La formación del anticlinal a escala cortical en la región de Calatrava ha producido la disminución de la presión en el intrados del anticlinal y ha originado probablemente el magmatismo basáltico; b) Un factor pasivo correspondiente a la existencia de una banda de cizalla con dirección próxima a NW-SE, heredada de la deformación varisca, que localiza una zona de debilidad cortical favorecedora del ascenso del magmatismo

Pre-eruptive magmatic processes and their timescales revealed by crystal zoning

EGU2020: Sharing Geoscience Online, 4-8 May 2020Understanding the processes that occur in the magma plumbing systems prior to eruption and how they relate to monitoring data can lead to improved volcanic hazard assessment. Crystal compositions are witnesses of the architecture and dynamics of the plumbing system, and crystal zoning patterns can inform us of the range of magmatic environments, and of the likely processes that lead to eruption. We have studied the petrology and the geochemistry of the monogenetic historical eruptions occurred in Tenerife (Canary Islands) that come out through the rift zones (NW and NE Rifts) as well as the last mafic intra-caldera monogenetic eruption of Montaña Mostaza (15 ka). The deposits from the NE Rift and the intra-caldera contain complexly zoned olivine crystals suggesting open system and magma mixing, while crystals from the NW Rift are mainly normally zoned. By modelling the zonation patterns of the crystals we have calculated the timescales of the magma intrusions and ascent to the surface. We have found that the magmas erupted along the NW rift are more evolved and vary from basanites to phono-tephrites, while the magmas from the NE rift are basanites recording different mixing events between magma pockets occurred around 1-2 years, 3 months and few days before the eruption. The olivine crystals from the intra-caldera eruption display more variety in the zoning patterns than the eruptions from the rift, suggesting a more complex history. Based on the integration of the petrological and modelling results with gravimetric and geophysical data we propose, at least, three main different ascent histories (paths and timescales) for monogenetic eruptions in Tenerife.This research has been partially funded by the EUROVOLC project (Horizon 2020 Grant Agreement: 731070)

Gravity modeling of the lithosphere in the Calatrava Volcanic Province (Spain): geodynamic implications

The origin of the intraplate volcanism in the Calatrava Volcanic Province (CVP) is controversial. On the basis of its geochemical signature, it has been ascribed to an “aborted” rift, implying lithospheric thinning. However, the volcanism occurred during the generalized Cenozoic NW−SE-oriented compressive tectonic regime. On the other hand, on the basis of evidence for its deep-seated origin, it has been linked to the existence of a baby-plume detached from an active megaplume below the Canary-Azores Islands and the western Mediterranean. In order to understand better the aforementioned geodynamic scenarios for the origin of the CVP, we address here the study of the lithosphere in the CVP and its vicinity by means of gravity analysis and 2+1/2D modeling. Gravity modeling results do not support the rifting model adopted for the intraplate volcanism occurred in the CVP because the crust shows a quasi-constant thickness. Density models suggest the existence of a sub-crustal, anomalous low-density block that could be underplated magmatic material at the base of the crust, suggesting that only a minor part of it intruded up into the crust and erupted. The localized magmatism of the CVP can be related to the combination of two factors: active, the gentle folding of the Iberian lithosphere and associated uplifting of the Variscan basement due to the NW-directed transmission of compressive stresses in the upper plate yielded by the subduction/collision in the south Iberian margin. The formation of the lithospheric folding in the Calatrava region results in a decrease of the pressure beneath the swell of the antiform that is likely to bring about basaltic magmatism below the swell; and one passive, the existence of a Variscan right-lateral shear band, which yields a weakened crust that facilitates the ascent of the magmatic materials. The relatively small volume, but large extension, of the volcanic outcrops could be associated with the preferential ascent of the magmas along the weakened crust of this NW−SE-trending Variscan shear band

Gravimetric study of the shallow basaltic plumbing system of Tenerife, Canary Islands

Recent studies on intraplate volcanic islands reveal that magma ascends sub-vertically through these volcanic edifices, following well-defined zones in the lithospheric mantle and oceanic crust, and occasionally suffering lateral propagation along rift zones when it reaches very shallow depths. Visualizing the internal structure of the shallowest part of such magma plumbing systems is crucial to understanding magma transport and the location of basaltic volcanism in these volcanic environments. Tenerife (Canary Islands) is a very good example of an intraplate volcanic island, in which the distribution of basaltic volcanism includes well-defined rift systems, and wider monogenetic fields where cinder cones form clusters along different tectonic alignments. In order to characterize the structure of the uppermost part of the basaltic plumbing system of Tenerife, we conducted a detailed gravimetric study of the north-western, central, and southern sectors of the island. We developed a 3D density contrast model of the subsoil based on the application of a genetic algorithm for the inversion of gravity data. The results of our inverse modelling suggest that the observed gravimetric anomalies below the northwestern rift zone are shallow and aligned parallel to this structure. This is consistent with a shallow character for the rift system and a lateral migration of magma along it that comes from a deeper zone located towards the east of this rift zone. Conversely, the anomalies located in the south are also shallow but are distributed along more than one alignment and are connected to much deeper sub-vertical similar density anomalies. These results support the existence of several main channels at the north and south of the island that allow the ascent of deep basaltic magma to shallower zones of Tenerife. There, magma may be either caught by the rifts systems, being distributed laterally and occasionally erupting, or may continue its ascent to the surface using a secondary system of shallow fractures that dominates the southern part of Tenerife. The results of our inverse model also offer new insights on others aspects of the internal structure of Tenerife, such as the distribution of the basaltic shield or that of Las Cañadas caldera. © 2019 Elsevier B.V.Joan Martí was funded by the MECD ( PRX16/00056 ) grant. This work was partially supported by the Instituto Geográfico Nacional of the Spanish Ministerio de Fomento and through projects CGL2014-53044-R and CGL2015-63799-P of the Spanish Ministry of Economy and Competitiveness .Peer reviewe

Coherence in homotopy group actions

SIGLETIB: RN 7354 (87) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman