Catalan Volcanic Zone Research Articles

Morphometric analysis of monogenetic volcanoes in the Garrotxa Volcanic Field, Iberian Peninsula

The Garrotxa Volcanic Field is situated in the northeast region of the Iberian Peninsula. It represents the most recent volcanic area within the Catalan Volcanic Zone, which is one of the volcanic provinces of the European Rift System, featuring over 50 dispersed eruptive vents.This study presents a comprehensive morphometric analysis of volcanic edifices, aiming to enhance our understanding of both volcanostratigraphy and the geomorphology of landforms within the Garrotxa Volcanic Field. Our methodology involved extensive fieldwork and detailed analysis of Digital Elevation Models (DEMs) to precisely determine the spatial distribution and morphometric parameters of the best-preserved volcanic structures in the area. The Garrotxa Volcanic Field exhibits an uneven spatial distribution of various volcanic landforms, with approximately 50 % comprising magmatic cones, primarily formed through Strombolian eruptions. The remaining 50 % is evenly divided between magmatic-phreatomagmatic volcanoes and phreatomagmatic tuff rings-maars. The morphometric characteristics of the three genetic types overlap significantly, showing no clear differences, although a few distinctions can sometimes be identified.The Garrotxa Volcanic Field displays a variety of eruption styles: 46 % of the identified eruptive sequences begin with phreatomagmatic activity, while 54 % start with predominantly magmatic explosive activity. Most eruptions show a transition through different phases.Data also indicate that the morphometric variability at the Garrotxa Volcanic Field stems from differences in the properties of pyroclastic sequences, resulting from their diverse eruption styles, as well as pre- and post-eruptive factors. Consequently, the results of the morphometric analysis are deemed insufficient for establishing a reliable chronology for the Garrotxa Volcanic Field.

CatVolc: A new database of geochemical and geochronological data of volcanic-related materials from the Catalan Volcanic Zone (Spain)

The Catalan Volcanic Zone (CVZ) (NE Spain) consists of an intraplate alkaline volcanic zone associated with the opening of the Western Mediterranean and the development of the European Rift System. Volcanic activity in the CVZ started in the L'Empordà area (ca. > 12–8 Ma), extended to La Selva (7.9–1.7 Ma), and finally migrated to the Garrotxa Volcanic Field (< 0.7–0.01 Ma). Despite the scientific interest in the CVZ since the early 19th century, certain aspects remain poorly constrained. These include a full understanding of the spatial and temporal evolution of the magma plumbing system(s) and ascent mechanisms, as well as the chronology of volcanism across the CVZ. Addressing these unresolved questions requires geochemical, petrological, and geochronological data, which, in the case of the CVZ, are scattered and have never been integrated or analysed within a unified framework. Here, we present the CatVolc (Catalan Volcanism) database, which compiles available geochemical and geochronological data of volcanic-related materials from the CVZ. The current version of the database contains geochemical analyses from 405 rock samples (296 juvenile magmatic rocks -including lavas and pyroclasts- and 109 xenoliths), and radiometric/thermoluminescence dating data from 57 rocks (55 volcanogenic and two dykes), 4 paleosols samples developed between volcanic deposits and 1 sample from sediments. For each sample, the CatVolc database lists general information about the sampling site, sample lithology, whole-rock analyses (including major and trace elements), isotopic ratios, mineral chemistry, and radiometric/thermoluminescence dating information, if available. A preliminary analysis of the information contained in the CatVolc database highlights the critical limitations of the current state of knowledge and allows suggesting potential future directions for volcanic-driven investigations in the CVZ. Additionally, the results obtained validate the CatVolc database as a key tool for comprehending the spatial and temporal evolution of the magmatic system(s) and volcanic activity in the CVZ, particularly in the Garrotxa Volcanic Field. This aspect is critical for advancing in the assessment of the volcanic hazards in the region and for gaining a comprehensive understanding of future volcanic activity.

Eruptive evolution and 3D geological modeling of Camp dels Ninots maar-diatreme (Catalonia) through continuous intra-crater drill coring

Camp dels Ninots is a mixed hard-soft maar-diatreme located in the Catalan Volcanic Zone (NE of Iberia), in which intra-maar lake sediments have preserved one of the most remarkable Pliocene fossil records in Europe. Geophysical surveys combined with the geological map and 11 boreholes, including two new continuous intra-crater drill cores, have enabled the construction of a 3D geological model of this maar-diatreme and its basement. The formation of this maar-diatreme started with a vent-opening phreatomagmatic explosion at the intersection between a regional fault and the Paleozoic groundwater level at a depth of 210 m. We infer and calculate the geometry, dip direction and dip angle of this regional fault. During the eruption, mixed Strombolian and phreatomagmatic episodes occurred, forming the tuff ring and filling the diatreme with minimum estimated volumes of 0.012 and 0.004 km3, respectively. The diatreme infill is composed of three main lithofacies that include tuff-breccias, welded scoriae, and mafic intrusions into the phreatomagmatic breccias. Thus, the stratigraphy of the diatreme succession suggests a progression of explosive events from deeper to shallower zones with short lateral migration of explosion vents, which control its final morphology, without evidence for significant deep enlargement of the diatreme during the later phases. This generated a wide funnel-shaped with low diatreme wall angles that differs from kimberlite pipes with great depths and sharp slope geometries. Hence, such 3D geological model helps to understand the complex architecture of maar-diatreme structures, highlighting the lack of geological modeling of this type of monogenetic system.

Deformation and seismic anisotropy of the subcontinental lithospheric mantle in NE Spain: EBSD data on xenoliths from the Catalan Volcanic Zone

Mantle xenoliths in Neogene-Quaternary basaltic rocks related to the European Cenozoic Rift System serve to assess the evolution of the subcontinental lithospheric mantle beneath the Catalan Volcanic Zone in NE Spain. Crystallographic preferred orientations, major element composition of minerals, and temperature and pressure estimates have been used to this end. The mantle consists of spinel lherzolites, harzburgites and subordinate websterites. Protogranular microstructures are found in all peridotites and websterites, but lherzolites also display finer-grained porphyroclastic and equigranular microstructures. The dominant olivine deformation fabric is [010] fiber, but subordinate orthorhombic and [100]-fiber types are also present, especially in porphyroclastic and equigranular lherzolites. The fabric strength (J index=10.12–1.91), equilibrium temperature and pressure are higher in xenoliths with [010]-fiber fabric and decrease in those with orthorhombic and [100]-fiber type. Incoherence between olivine and pyroxene deformation fabric is mostly found in porphyroclastic and equigranular lherzolites. Seismic anisotropy, estimated from the crystal preferred orientations, also decreases (AVp=10.2–2.60%; AVs max=7.95–2.19%) in porphyroclastic and equigranular lherzolites. The olivine [010]-fiber fabric points to deformation by simple shear or transpression which is likely to have occured during the development of late-Hercynian strike-slip shear zones, and to subsequent annealing during late Hercynian decompression, Permian and Cretaceous rifting. Also, it cannot be excluded that the percolation of mafic magmas during these extensional events provoked the refertilization of the lithospheric mantle. However, no clear relationship has been observed between fabric strength and mineral mode and composition. Later transtensional deformation during late Alpine orogenesis, at higher stress and decreasing temperature and pressure, transformed the earlier fabric into orthorhombic and [100]-fiber type.Comparison of seismic anisotropy estimates with the available SKS-wave splitting data suggests that most of the measured seismic anisotropy would be explained by the lithospheric contribution, if the lithospheric mantle fabrics record mainly transpression and transtensional deformation.

Reconstructing the eruptive history of a monogenetic volcano through a combination of fieldwork and geophysical surveys: the example of Puig d’Àdri (Garrotxa Volcanic Field)

Puig d’Àdri is a complex volcano in the Garrotxa Volcanic Field (0.7–0.01 Ma), the youngest part of the Catalan Volcanic Zone (NE Iberian Peninsula). The construction of this volcano involved the superimposition of three volcanic edifices with five lithostratigraphic units, in which several Strombolian and phreatomagmatic episodes alternated. Geological and geophysical surveys performed using electrical resistivity tomography and self-potential have contributed to revealing the internal structure of the volcano and the succession of deposits. The ring–cone morphology of the phreatomagmatic part of the structure shows how a number of variables including the way in which magma and water interacted greatly influenced the eruptive dynamics and the mechanisms of formation. A further major issue reflected in the final structure of the edifice is the process of vent migration, which was controlled by the characteristics of the substrate and its interaction with the magma as it rose. Supplementary material: Granulometric and component histograms of the samples not shown in Figure 4 are available at http://doi.org/10.6084/m9.figshare.c.3262498

Structure of the Pliocene Camp dels Ninots maar-diatreme (Catalan Volcanic Zone, NE Spain)

Maar volcanoes expose shallower or deeper levels of their internal structure as a function of the degree of erosion. In El Camp dels Ninots maar-diatreme (Catalan Volcanic Zone, Spain), the tephra ring has been largely eroded, and the remaining volcanic deposits infilling the diatreme are hidden under a lacustrine sedimentary infill of the crater. The volcano shows hardly any exposure, so its study needs the application of direct (e.g., boreholes) and indirect (shallow geophysics) subsurface exploration techniques. Additionally, this maar-diatreme was built astride two different substrates (i.e., mixed setting) as a result of its location in a normal fault separating Neogene sediments from Paleozoic granites. In order to characterize the internal structure and post-eruption stratigraphy of the maar-diatreme, we did geological studies (mapping, continuous core logging, and description of the tephra ring outcrops) and near-surface geophysics, including nine transects of electric resistivity tomography and a gravity survey. Results show that the deeper part of the diatreme is excavated into granites and is relatively steep and symmetrical. The uppermost diatreme is asymmetrical because of mechanical contrast between granites and Pliocene sands. The maar crater contained a lake permanently isolated from the surrounding relief and was deep enough to host anoxic bottom waters while its margins had shallower waters. These lake conditions preserved the remarkable Pliocene fossil record found in the lacustrine sediments.

Studying monogenetic volcanoes with a terrestrial laser scanner: case study at Croscat volcano (Garrotxa Volcanic Field, Spain)

Erosional processes (natural or anthropogenic) may partly destroy the relatively small-sized volcanic edifices characteristic of monogenetic volcanic zones, leaving their internal structure well exposed. Nevertheless, the study of these outcrops may be extremely challenging due to restricted accessibility or safety issues. Digital representations of the outcrop surface have been lately used to overcome such difficulties. Data acquired with terrestrial laser scanning instruments using Light Detection and Ranging technology enables the construction of such digital outcrops. The obtained high-precision 3-D terrain models are of greater coverage and accuracy than conventional methods and, when taken at different times, allow description of geological processes in time and space. Despite its intrinsic advantages and the proven satisfactory results, this technique has been little applied in volcanology-related studies. Here, we want to introduce it to the volcanological community together with a new and user-friendly digital outcrop analysis methodology for inexperienced users. This tool may be useful, not only for volcano monitoring purposes, but also to describe the internal structure of exposed volcanic edifices or to estimate outcrop erosion rates that may be helpful in terms of hazard assessment or preservation of volcanic landscapes. We apply it to the Croscat volcano, a monogenetic cone in the La Garrotxa Volcanic Field (Catalan Volcanic Zone, NE Spain), quarrying of which leads to a perfect view of its interior but restricts access to its uppermost parts. Croscat is additionally one of the most emblematic symbols of the La Garrotxa Volcanic Field Natural Park, and its preservation is a main target of the park administration.

Volcanic stratigraphy of the Quaternary La Garrotxa Volcanic Field (north‐east Iberian Peninsula)

ABSTRACTThe monogenetic Quaternary La Garrotxa Volcanic Field forms part of the Catalan Volcanic Zone (north‐east Iberian Peninsula), one of the alkaline volcanic provinces of the European rift system. It harbours more than 50 basaltic monogenetic cones that range in age from the Middle Pleistocene to the Early Holocene and include cinder and scoria cones, lava flows, tuff rings and maars. This study is the result of extensive fieldwork, including the study of ephemeral outcrops and the stratigraphic logging of new water wells and geotechnical drill holes, also taking into account existing information gathered by recent geophysical studies that have applied shallow geophysical methods to establish the substrate geology of this volcanic field. We have obtained a comprehensive volcanic stratigraphy of the area that identifies the products of each single eruption, their relative stratigraphy and their surface area. This volcanic stratigraphy constitutes an essential tool for understanding the evolution of this volcanic field and for establishing a correct volcanic hazard assessment for the area, but it also provides a precise reference for the Quaternary tephrochronology of the lake sediments in neighbouring areas.

Melting and metasomatism in the lithospheric mantle of NE Spain: Geochemical and Sr[sbnd]Nd isotopic characteristics

The study of major and trace element compositions of whole rocks and minerals, along with SrNd isotopes on separated clinopyroxene crystals, from mantle xenoliths in Neogene–Quaternary basaltic rocks, serves to evaluate the processes which have affected the subcontinental lithospheric mantle in the Catalan Volcanic Zone of NE Spain, and to compare it to other mantle domains in Europe. These xenoliths are mainly anhydrous spinel lherzolites and harzburgites, with rare olivine websterites. Concentrations of Al2O3, CaO, TiO2 and mildly incompatible trace elements decrease gradually from lherzolites to harzburgites. Light rare earth elements (LREE) and other incompatible trace elements display scatter vs. depletion indexes and usually increase from depleted lherzolites to much enriched harzburgites, indicating that metasomatism affected mainly the latter. Clinopyroxene rare earth element (REE) patterns show slight LREE depletion in most lherzolites and LREE–middle rare earth element (MREE) enrichment in harzburgites. The exceptions are a few clinopyroxene patterns from lherzolites with significant LREE–MREE depletion or LREE enrichment and u-shapes. The SrNd isotopic compositions of clinopyroxene also show a gradual variation from depleted MORB mantle (DMM) lherzolites to very enriched mantle (EM) harzburgites (87Sr/86Sr: 0.702486–0.709772; 143Nd/144Nd: 0.513359–0.512411). Most of these compositions match those for off-craton xenoliths. They are also similar to compositions observed in xenoliths of anhydrous spinel lherzolites and harzburgites from the neigbouring subcontinental lithospheric mantle of SE Spain and the southern part of the Massif Central, France. Fractional melting estimates from a Primitive Mantle source indicate that melt extraction was under 12% and 26% for lherzolites and harzburgites respectively. Melting took place in the spinel lherzolite field except for a few lherzolites that may have started to melt in the presence of garnet and continued in the spinel field. The formation of DMM lherzolites as refertilisation products, via percolation and reaction of N-MORB type basalts with refractory and ancient isotopically enriched harzburgites, cannot be ruled out. However, there is no definitive compositional evidence of such a process. It is suggested that harzburgites would have undergone multi-stage metasomatism. An earlier episode would have been caused by subduction-related hydrous fluids or melts related to the Variscan orogeny or an earlier orogenic episode. This is deduced from the time integrated low 143Nd/144Nd and very enriched 87Sr/86Sr values of harzburgite clinopyroxene. A later metasomatic episode is mainly cryptic and would have been related to the percolation of alkaline silicate melts and carbonatite derivatives. It would have affected lherzolites and especially harzburgites, causing opposite isotopic trends in the former compared to the latter. The SrNd isotopic compositions of the metasomatic agents would be close to that of a websterite xenolith. The age of this second metasomatism is also uncertain, since magmatic alkaline episodes have been registered since the Permo-Triassic periods.

Structural control of monogenetic volcanism in the Garrotxa volcanic field (Northeastern Spain) from gravity and self-potential measurements

We report new geophysical observations on the distribution of subsurface structures associated with monogenetic volcanism in the Garrotxa volcanic field (Northern Spain). As part of the Catalan Volcanic Zone, this Quaternary volcanic field is associated with the European rifts system. It contains the most recent and best preserved volcanic edifices of the Catalan Volcanic Zone with 38 monogenetic volcanoes identified in the Garrotxa Natural Park. We conducted new gravimetric and self-potential surveys to enhance our understanding of the relationship between the local geology and the spatial distribution of the monogenetic volcanoes. The main finding of this study is that the central part of the volcanic field is dominated by a broad negative Bouguer anomaly of around −0.5 mGal, within which a series of gravity minima are found with amplitudes of up to −2.3 mGal. Inverse modelling of the Bouguer data suggests that surficial low-density material dominates the volcanic field, most likely associated with effusive and explosive surface deposits. In contrast, an arcuate cluster of gravity minima to the NW of the Croscat volcano, the youngest volcano of this zone, is modelled by vertically extended low-density bodies, which we interpret as a complex ensemble of fault damage zones and the roots of young scoria cones. A ground-water infiltration zone identified by a self-potential anomaly is associated with a steep horizontal Bouguer gravity gradient and interpreted as a fault zone and/or magmatic fissure, which fed the most recent volcanic activity in the Garrotxa. Gravimetric and self-potential data are well correlated and indicate a control on the locations of scoria cones by NNE–SSW and NNW–SSE striking tectonic features, which intersect the main structural boundaries of the study area to the north and south. Our interpretation of the data is that faults facilitated magma ascent to the surface. Our findings have major implications for understanding the relationship between subsurface structures and potential future volcanic activity in the Garrotxa volcanic field.

Investigation of the inner structure of La Crosa de Sant Dalmai maar (Catalan Volcanic Zone, Spain)

La Crosa de Sant Dalmai volcano is the largest volcanic edifice of the Catalan Volcanic Zone (NE Spain). It is a very well preserved maar-type structure, 1.5km in diameter, excavated at the contact between a hard substrate and a soft substrate formed by Palaeozoic granites and Pliocene and Quaternary gravels, respectively. In order to infer the uppermost inner structure of La Crosa de Sant Dalmai maar and to characterise its main geological and tectonic constraints, we have performed a multiparametric geophysical study including gravimetry, magnetometry, self-potential, and electrical resistivity tomography. The results obtained together with a field geology revision and additional geological data from two drill cores, provide a detailed picture of the post-eruptive maar infill sequence as well as of the uppermost part of the maar-diatreme structure. This information helps in understanding the origin and subsequent evolution of the volcano, which included an alternation of phreatomagmatic and Strombolian phases. Geophysical data show that the last Strombolian phase, which culminated with the formation of a scoria cone inside the maar, was associated with a NW–SE trending regional fault. The little erosion and degradation of the original tephra ring suggest a much younger age of La Crosa de Sant Dalmai maar than was previously stated.

Origin and implications of mafic xenoliths associated with Cenozoic extension-related volcanism in the V�lencia Trough, NE Spain

The Valencia Trough of northeastern Spain represents a poorly understood region of Cenozoic extension-related magmatism in western Europe. We present chemical data on mafic xenoliths and their host basalt from the Roca Negra cinder cone in the Catalan Volcanic Zone in the Valencia Trough. The xenoliths consist of augite+hornblende+ oxides±plagioclase±apatite±olivine::Lbiotitelorthopyroxene, and range from clinopyroxenites and hornblendites to gabbroic rocks. The major and trace element compositions of the xenoliths are compatible with formation as cumulates from a range of olivine tholeiitic to strongly alkaline magmas, and show a strong affinity to the Middle Miocene to Recent rift-related magmatism in the Catalan Volcanic Zone. The xenoliths formed at temperatures of 1110–1180 °C, pressures of 2–7 kb (with 10 kb as the upper limit), and oxygen fugacities corresponding to 1–2 log units above the NNO oxygen buffer. The estimated pressure range implies formation in magma chambers within the crust, possibly also near the crust/mantle boundary (underplating). The presence of crustal cumulates indicates that the total volume of magmas emplaced into the crust in the Catalan Volcanic Zone may be significantly larger than indicated by surface exposures. Isotopic compositions of the xenoliths are87Sr/86Sr: 0.703537–0.703647,143Nd/144Nd: 0.512732–0.512766,206Pb/204Pb: 18.097–19.106,207Pb/204Pb: 15.522–15.579, and208Pb/204Pb: 37.850–38.794. This range suggests the involvement of two mantle source components. One of these may be the low-velocity component recognized in Cenozoic magmatism in the eastern Atlantic Ocean to central Europe and western Mediterranean. The other component, which differs from those involved in other domains of Cenozoic volcanism in Europe and adjacent areas, may be located in the lithospheric mantle underlying NE Spain, which was metasomatized during late Variscan to early Alpine deformation.

Thermoremanence in red sandstone clasts and emplacement temperature of a quaternary pyroclastic deposit (Catalan Volcanic Zone, ne Spain)

The application of the progressive thermal demagnetization procedure of volcanic rock debris has been frequently used to determine the emplacement temperatures of pyroclastic deposits and thus to characterize the nature of these volcanic deposits. This debris consists of a mixture of juvenile fragments derived from the explosive fragmentation of erupting magma and an assortment of lithic clasts derived mainly from the walls of a volcanic conduit, as well as from the ground. The temperature at which the clasts were deposited can be estimated by analyzing its remanent magnetization. To do this, oriented samples of clasts are subjected to progressive thermal demagnetization and the directions of the resulting remanent vectors provide the necessary information. Clasts of basalt, andesite, limestone, pumice and homebricks have previously been used to estimate the emplacement temperatures of pyroclastic deposits. According to our data, clasts of red sandstones also seem to be good carriers of thermoremanent magnetization. We have carried out a paleomagnetic study on a Quaternary, lithic-rich, massive, pyroclastic deposit from the Puig d'Adri volcano (Catalan Volcanic Zone), which contains a large number of red sandstone clasts. It is concluded that the studied deposit cannot be considered as a lahar or as a pyroclastic surge deposit, considering both the emplacement temperature and the morphological features.

Cenozoic magmatism of the valencia trough (western mediterranean): Relationship between structural evolution and volcanism ∗

The Cenozoic magmatism of the Valencia trough is characterized by the existence of two volcanic cycles. The first cycle (Early Miocene-Middle Miocene) comprises calc-alkaline rocks which have been recognized in the central to eastern offshore areas and in Mallorca. The second cycle (Middle Miocene to Recent) is represented mainly by poorly differentiated alkaline rocks which are predominantly distributed along the Iberian margin of the Valencia trough. In accordance with the inferred structural evolution of the Valencia trough, petrological and geochemical data, as well as volcanological evidence, we suggest that two different geodynamic environments existed during these magmatic cycles. The Early to Middle Miocene calc-alkaline volcanism developed under compressive tectonic conditions and seems to be associated with the northwestern dipping subduction of the African plate. In contrast, the Middle Miocene to Recent alkaline volcanism is associated with extensional tectonics and can be explained within the framework of a low volcanicity rift model. Three zones—Catalan, Valencian and Columbretes—each located at different parts of the rift structure, can be distinguished in the Middle Miocene to Recent volcanism. This intraplate volcanism results from partial melting, due to extension-driven decompression, with the largest degrees of melting in the centre of the Valencia trough (Columbretes volcanic zone). In the Catalan volcanic zone a progressive increase in the extension rate from the first to the last volcanic episode has occurred, favouring the interaction of two mantle sources.