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We present a study of the deformation pattern along the Canary archipelago through the analysis of continuous GNSS data. We use data spanning 2011–2017 period to retrieve precise horizontal displacements and a broad calculation of the strain. Geodetic data are interpreted in light of the regional tectonics, which is proven to play a key role in the volcanic eruptions that take place in the archipelago. The common-mode component filtering technique is applied to improve the signal-to-noise ratio of the time series of the GNSS daily solutions before retrieving the geodetic velocities. Through a triangular segmentation approach, we retrieve the 2D infinitesimal strain from the velocities along the Canaries and map deformation patterns in various sectors of the volcanic archipelago. We found areas of maximum deformation west of Tenerife, Gran Canaria and Fuerteventura Islands. A sharp change in shear strain between Tenerife and Gran Canaria is recognized, delineating a sector of intense seismicity, which is mostly associated with a well-known major submarine fault that separates the two insular edifices. On this submarine tectonic structure, we have performed a tentative simulation of the horizontal deformation and strain caused by one of the strongest (mbLg 5.2) earthquakes of the region. Our strain analysis supports the possibility that the main tectonic lineaments are being influenced by the regional stress field. Furthermore, the seismic areas between islands seem mainly influenced by the regional tectonic stress, rather than by the local volcanic activity. This is in accordance with the extensional and compressional tectonic regimes, already identified by other authors, which might favour episodes of volcanism in this volcanic archipelago.

An aeromagnetic data set from the island of La Gomera was studied through two inverse modeling approaches that produced complementary views of the inner structure of this volcanic island: (1) a variable magnetization model that identified the main lateral magnetization contrasts and (2) a constant magnetization model that imaged the main magnetic source by assuming that it was a uniformly magnetized body. The modeling reveals intense magnetizations beneath the northern part of La Gomera, which occupy an important portion of the northern submarine edifice, correspond well with outcrops of the submarine volcano (Basal Complex), and confirm that most of the magnetic signal revealed by aeromagnetic mapping in the Canary Islands is due to the intense magnetizations of the intrusive complexes (plutonic bodies and dike complexes) emplaced during the initial stages of growth of the volcanic edifices. The consistency of our models with the results of a previous gravimetric study suggests that these intrusive complexes are denser and more magnetic than the surrounding rocks. The location of the main magnetic source reinforces the interpretation, first suggested by geological evidence, that the submarine and early subaerial growth of La Gomera started to the north of the present island. The elongated shape of these intrusive complexes with a nearly E-W strike agrees with the orientation of analogous structures on Tenerife and Gran Canaria, suggesting that the initial formation of the central islands of the Canary Archipelago was controlled by a set of regional fractures in a strike-slip tectonic framework., Spanish Ministry of Science, Innovation and Universities (Project CGL2015-63799-P) and by the Junta de Castilla y León and the European Regional Development Fund (ERD) (Project BU235P18).

The 3-D inverse modelling of a magnetic anomaly measured over the NW submarine edifice of the volcanic island of Gran Canaria revealed a large, reversely-magnetized, elongated structure following an ENE-WSW direction, which we interpreted as a sill-like magmatic intrusion emplaced during the submarine growth of this volcanic island, with a volume that could represent up to about 20% of the whole island. The elongated shape of this body suggests the existence of a major crustal fracture in the central part of the Canary Archipelago which would have favoured the rapid ascent and emplacement of magmas during a time span from 0.5 to 1.9 My during a reverse polarity chron of the Earth’s magnetic field prior to 16 Ma. The agreement of our results with those of previous gravimetric, seismological and geodynamical studies strongly supports the idea that the genesis of the Canary Islands was conditioned by a strike-slip tectonic framework probably related to Atlas tectonic features in Africa. These results do not contradict the hotspot theory for the origin of the Canary magmatism, but they do introduce the essential role of regional crustal tectonics to explain where and how those magmas both reached the surface and built the volcanic edifices., This research was funded by project CGL2015-63799-P of the Spanish Ministry of Economy and Competitiveness.

Following the 2004 seismic unrest at Tenerife and the 2011-2012 submarine eruption at El Hierro, the number of GNSS observation sites in the Canary Islands (Spain) has increased, offering scientists a useful tool with which to infer the kinematics and present-day surface deformation of the Canary sector of the Atlantic Ocean. We take advantage of the common mode component filtering technique to improve the signal-to-noise ratio of the velocities retrieved from the daily solutions of 18 permanent GNSS stations distributed in the Canaries. The analysis of GNSS time series spanning the period 2011-2017 enabled us to characterize major regions of deformation along the archipelago through the mapping of the 2D infinitesimal strain field. By applying the triangular segmentation approach to GNSS velocities, we unveil a variable kinematic behaviour within the islands. The retrieved extension pattern shows areas of maximum deformation west of Tenerife, Gran Canaria and Fuerteventura. For the submarine main seismogenic fault between Tenerife and Gran Canaria, we simulated the horizontal deformation and strain due to one of the strongest (mbLg 5.2) earthquakes of the region. The seismic areas between islands, mainly offshore Tenerife and Gran Canaria, seem mainly influenced by the regional tectonic stress, not the local volcanic activity. In addition, the analysis of the maximum shear strain confirms that the regional stress field influences the E-W and NE-SW tectonic lineaments, which in accordance with the extensional and compressional tectonic regimes identified, might favour episodes of volcanism in the Canary Islands., Project CGL2015-63799-P

SUMMARY El Hierro is the youngest of the Canary Islands, a volcanic archipelago in the central Atlantic, near the African coast. The subaerial part of the island shows the characteristic shape of three convergent ridges that has been interpreted as a triple-arm rift system. At least four giant landslides formed wide, horseshoe embayments that separate these ridges. Recent studies based on high-resolution bathymetry, however, showed that the submarine rift structure is much more complex. We analysed an aeromagnetic anomaly data set acquired in 1993 by the Spanish National Geographic Institute in order to obtain a structural model of the island from a magnetic point of view. A digital elevation model of the volcanic edifice was divided into a mesh of prismatic cells, each of them with a top corresponding to the topographic height (or bathymetric depth in the marine area) and a bottom at a constant depth of 4000 m below sea level. A three-dimensional (3-D) inversion algorithm and forward modelling along representative profiles provided us with a magnetization distribution containing valuable information about the inner structure of the island. The magnetic model cast new light on the rift structure of El Hierro. In particular, high magnetization values have been mainly interpreted as intrusive complexes on which rift zones are rooted. Their location confirms the hypothesis of a complex rift structure in the marine area. The inverse magnetization that characterizes the NE submarine rift area implies that this part of the volcanic edifice formed during the Matuyama and, therefore, predates the NW submarine rift zone, which is normally magnetized. The N‐S rift zone extending southwards from the island seems to be shifted to the west with respect to the bathymetric high in this area. This result suggests that the original rift zone was located in the area where the highest magnetizations presently occur so that the present morphology may reflect the westward collapse of the original ridge. In addition, very low magnetizations characterize the areas affected by giant landslides, indicating that magnetic anomalies can provide important constraints on the distribution of these catastrophic events.

We present a modelling method to estimate the 3-D geometry and location of homogeneously magnetized sources from magnetic anomaly data. As input information, the procedure needs the parameters defining the magnetization vector (intensity, inclination and declination) and the Earth’s magnetic field direction. When these two vectors are expected to be different in direction, we propose to estimate the magnetization direction from the magnetic map. Then, using this information, we apply an inversion approach based on a genetic algorithm which finds the geometry of the sources by seeking the optimum solution from an initial population of models in successive iterations through an evolutionary process. The evolution consists of three genetic operators (selection, crossover and mutation), which act on each generation, and a smoothing operator, which looks for the best fit to the observed data and a solution consisting of plausible compact sources. The method allows the use of non-gridded, non-planar and inaccurate anomaly data and non-regular subsurface partitions. In addition, neither constraints for the depth to the top of the sources nor an initial model are necessary, although previous models can be incorporated into the process. We show the results of a test using two complex synthetic anomalies to demonstrate the efficiency of our inversion method. The application to real data is illustrated with aeromagnetic data of the volcanic island of Gran Canaria (Canary Islands)., This research was supported by: Project CGL2011-25494 of the Spanish Ministry of Economy and Competitiveness, Project 320/2011 of the Spanish Ministry of Agriculture, Food and Environment, and Programa de Financiación para Grupos de Investigación UCM-BSCH. I. Blanco-Montenegro is grateful to the Ministry of Education of Spain for funding her research at Universidad Complutense de Madrid (Ayuda de movilidad ref. PR2010-0498).

In this paper, we present a magnetic model of the subsurface structure of Vulcano island based on high-resolution aeromagnetic data. Three profiles across the most intense magnetic anomalies over the Piano and Fossa calderas were selected for the magnetic modelling, which was constrained by structural and volcanological data, previous geophysical models, paleomagnetic data, and borehole stratigraphy obtained from two deep wells. The interpretation of the magnetic sources represents a significant contribution to the understanding of the Piano and Fossa calderas’ underlying structure, providing us with evidence of the lateral discontinuity between them at depth. We propose that the positive magnetic anomalies in the Piano caldera area are caused by: (a) the remnants of an early submarine volcano; (b) an outcropping dyke swarm related to the feeding system of the Primordial Vulcano phase (beneath Mt. Saraceno); and (c) the presence of a non-outcropping dyke system intruded along a NE–SW-oriented intra-caldera fault (beneath the eastern part of the Piano caldera). Offshore, to the west, the magnetic anomaly map suggests the presence of a submarine volcanic structure, not revealed by bathymetric data, which could represent the eruptive centre, the presence of which has been indirectly deduced from the outcrop of eastern-dipping lavas on the western seashore. Magnetic modelling of the Fossa caldera points to the presence of a highly magnetized cone-like body inside the Fossa cone, centred beneath the oldest crater rims. We interpret this body as a pile of tephritic lavas emplaced in an early phase of activity of the Fossa cone, suggesting that the volume of mafic lavas that erupted at the beginning of the construction of the Fossa edifice was more significant than has previously been deduced. Furthermore, the presence of a magnetized body inside the Fossa cone implies that high temperatures are contained in very limited spaces, do not affect its bulk inner structure, and are restricted to fumarolic conduits and vents. In addition, structures beneath the western and northern part of the Fossa caldera are revealed to have null or low magnetization, which can be ascribed to the presence of pyroclasts and hyaloclastites in this area as well as to a large volume of hydrothermally altered materials. This suggests that the hydrothermal system, with a very limited extension at present, affected a larger area in the past, especially beneath the western part of the caldera.

In this paper we present a crustal magnetic model of the volcanic island of Gran Canaria based on aeromagnetic data. This magnetic study has made it possible to constrain the location and geometry of: (1) the mafic core of Gran Canaria, built as the result of the crystallization of magmas which rose from the mantle during the submarine and shield basaltic stages of its evolution. The most intense magnetic high, displayed over the NW part of the island likely shows the main feeding system of the shield volcano; (2) the residual syenitic shallow magma chamber which fed the salic volcanic activity in the center of the island, linked to the formation of the Tejeda caldera and to the intrusion of felsic rocks which made up a cone sheet; (3) a reversely magnetized linear intrusion located in the marine area to the NW of the island, which could be related to the magmatic source of the submarine volcanism between Gran Canaria and Tenerife. Most of these magnetic sources show a linear pattern with trends that are in close agreement with the orientations of previously identified fractures. The magmatic intrusion to the NW of the island could be related with a WSW–ENE active fault between Gran Canaria and Tenerife, while the main trend and location of the mafic core agree with a NW–SE fault suggested by geological studies. This means that these magnetic sources are the result of the ascent and intrusion of magma along regional fractures. Therefore, this study provides fresh data which demonstrate the influence of regional tectonics on the growth of Gran Canaria during its entire evolution. Finally, the spectral analysis of the magnetic anomaly map suggests that it is possible that rocks located at mantle-like depths (from the Moho to about 23 km) behave as magnetic sources, a fact that can be related with the magmatic underplating detected by other geophysical techniques.

We present 3-D magnetic models of Tenerife based on a high-resolution aeromagnetic survey carried out in 2006. Two different inverse modeling techniques have been applied: (1) a linear method aimed at imaging lateral magnetization contacts and (2) a nonlinear method aimed at obtaining a 3-D description of deep intrusive bodies, in which a constant magnetization value characterizes the main sources. Magnetic models show that deep intrusive structures are located beneath the northern part of the island and aligned along the E-W direction. This arrangement of intrusive bodies does not support the hypothesis of a three-armed rift system that has been present since the early formation of the island. The shallow portion of the intrusive structures shows a round geometry that agrees with the previously proposed location of some of the landslide headwalls, suggesting that collapse scars have acted as preferential sites for magma upwelling. Our magnetic model probably provides the first geophysical evidence of the location of the headwall of the Icod landslide beneath the Teide-Pico Viejo complex, thus supporting the vertical collapse hypothesis for the origin of the Cañadas caldera. The largest intrusive complex is located to the northwest of Teide and Pico Viejo, revealing the presence of a very high dike density in this area. This complex probably resulted from the intrusion of magma over the span of millions of years, beginning with the early phases of basaltic shield volcanism in central Tenerife and lasting until the building of Teide and Pico Viejo stratovolcanoes.

This study presents magnetic anomaly data from a new high-resolution, low-altitude helicopter-borne magnetic survey recently collected on and offshore Tenerife in the Canary Archipelago. The Italian Istituto Nazionale di Geofisica e Vulcanologia (INGV) in collaboration with the Museo Nacional de Ciencias Naturales of the CSIC of Spain conducted the survey in 2006. The data for Tenerife and surrounding marine areas were processed into digital total intensity magnetic anomalies for geomagnetic epoch 2006.4. Relative to previously available higher altitude magnetic survey data, the new survey mapped higher resolution anomalies with significantly improved spatial details, especially over the Las Cañadas caldera and Teide-Pico Viejo complex in the central part of the island. A good correlation is evident between known structural geology and the magnetic anomalies, where the new shorter wavelength anomalies facilitate more detailed and comprehensive geologic interpretations.

[1] The active Vulcano Island (Southern Tyrrhenian Sea) represents the southernmost portion of a NW-SE elongated volcanic ridge that includes also Lipari and Salina islands. The ridge is affected by a regional, NW-SE to N-S striking fault system. The elaboration and analysis of data from three high-resolution aeromagnetic surveys carried out between 1999 and 2004 on Vulcano and offshore allow us to recognize high intensity magnetic anomalies related to volcanic centers/conduits or shallow intrusions. Previously unreported offshore submarine vents have been also recognized. Some of them may correspond with source areas of outcropping exotic pyroclastics on Vulcano. The spatial analysis of the recognized magnetic anomalies and volcanic structures shows that they are preferably aligned along the strikes of the main regional faults that affect the volcanic ridge. Submarine volcanic conduits revealed by the aeromagnetic survey might represent potential sources for future submarine, effusive or explosive activity.

The Bouguer and aeromagnetic anomaly maps of Lanzarote show a gravity high and a dipolar magnetic anomaly over the central part of the island, indicating one isolated source. Assuming that the structure responsible for both anomalies is the same, a methodology has been designed to estimate the total magnetization vector of the source, which is interpreted as a large intrusive body (mafic core) positioned as a result of magma rising to the surface during the early stages of growth of Lanzarote. Considering its geometry to be known from a previous three-dimensional (3-D) gravity model, the approach proposed in this paper is based on the delineation of magnetic contacts through analysis of the horizontal gradient of the reduced-to-the-pole anomaly map, comparison between the gravity and the pseudogravity anomalies, and 3-D forward magnetic modeling. The total magnetization vector obtained by this method is defined by a module of 4.5 A m(-1) and a direction D = -20 degrees and I = 30 degrees. Comparing the paleomagnetic pole, obtained from this direction, with the apparent polar wander path of Africa for the last 160 Myr, it is concluded that the main component of the total magnetization vector is probably a primary natural remanent magnetization (NRM) which could have been acquired between 60 and 100 Ma. This result suggests that the emplacement of magmas at shallow depths linked to the beginning of volcanism in Lanzarote took place during the Upper Cretaceous, thus providing the first evidence of a timeline for the early formative stages of this volcanic island.