Calatrava Volcanic Research Articles

Alkaline Silicate Metasomatism Recorded through Fe-Ti-Rich Mantle Xenoliths from the Calatrava Volcanic Field (Spain)

Much of the lithospheric subcontinental mantle (SCLM) sampled in the Calatrava Volcanic Field (CVF) shows refertilization by alkaline metasomatic agents. The Cerro Pelado and El Palo ultramafic xenolith suites record the best evidence of this type of metasomatism in this volcanic field. Several groups of peridotite (lherzolite, wehrlite, and dunite) and pyroxenite (clinopyroxenite and websterite) xenoliths have been distinguished. Despite having scarce phlogopites and amphiboles as modal metasomatic phases, all studied xenoliths present a variable cryptic metasomatism, highlighted by the strong Fe-Ti enrichment and fractionated REE patterns in the most evolved wehrlite and pyroxenite varieties. They show a common trend of an Fe-Ti-Ca increase, whereas the pyroxenites are more depleted in Fe compared to the lherzolites and wehrlites. Trace-element (REE and multi-trace) patterns are roughly similar among them, suggesting different interactions and refertilization degrees by alkaline silicate melts. The same Sr–Nd isotopic EAR composition, combined with trace-element chemistry of metasomatic xenolith phases and phenocrysts from the Calatrava volcanics, highlights the main role of this magmatism in percolation processes beneath Central Iberia. These mantle xenoliths also show variable amounts of interstitial glass that originated by in situ partial melting, favored by the enriched chemical nature of cryptically metasomatized clinopyroxene during their volcanic transport. This alkaline-refertilized mantle type represents the main domain within the SCLM beneath Central Iberia, as was also recorded in other Western European Cenozoic volcanic fields.

Nature and evolution of the lower crust under central Spain: Inferences from granulite xenoliths (Calatrava Volcanic Field-Spanish central system)

So far, the nature and evolution of the lower crust under central Spain have been constrained mainly on the basis of a heterogeneous suite of granulite xenoliths from the Spanish Central System (SCS). In recent years, ultramafic volcanics from the Calatrava Volcanic Field (CVF) have also provided deep-seated crustal xenoliths which have not been studied in detail. Our data, combining mineral, whole-rock and isotopic geochemistry with U–Pb–Hf isotope ratios in zircons from the CVF and SCS xenoliths, highlight the felsic composition of the lower crust under central Iberia. A number of the Calatrava xenoliths represents Variscan igneous protoliths, which are a minor population in the SCS, and were likely formed by crystallisation of intermediate and felsic melts in the lower crust during the Variscan orogeny (leucodiorite protolith age of 314 ± 3 Ma and leucogranite protolith age of 308 ± 2.5 Ma). U–Pb data of metamorphic zircons show that granulite-facies metamorphism mainly occurred from 299 to 285 Ma in both areas. These ages are slightly younger than those of granitic intrusions that could be genetically related to the granulitic residue, which points to a main role of U–Pb isotope resetting in lower crustal zircons during HT or UHT conditions. The zircon U–Pb–Hf isotopic ratios support the idea that the lower crust in central Iberia consists mainly of Ordovician–Neoproterozoic metaigneous and metasedimentary rocks associated with the Cadomian continental arc of northern Gondwana. These rocks provide evidence of mixing between juvenile magmas and an enriched crustal component, ultimately extracted from an Eburnean crust. Other more evolved components present in detrital zircons are likely related to recycling of Archean crust derived from North Africa cratonic terranes.

Morphometric Analysis of Scoria Cones to Define the ‘Volcano-Type’ of the Campo de Calatrava Volcanic Region (Central Spain)

The Campo de Calatrava Volcanic Region is the largest volcanic field in the Iberian Peninsula and presents a complex volcanic history, with more than 360 monogenetic basaltic volcanoes developed in effusive, Strombolian, and hydromagmatic eruptions. The large number of scoria cones, compared to the other existing types of volcanic morphologies, indicates that these landforms represent the most common eruptive events that occurred during Calatrava’s geological past. In this work, a morphometric analysis of the scoria cones was carried out, based on statistical analysis of the main morphological parameters of these volcanoes (height, cone width, crater width, crater depth, slope, area, etc.). The results were used to identify the most frequent scoria cone by means of statistical analysis of its main morphological features. To do this, a methodology based on statistical correlations of the morphological and morphometric parameters that best define the morphology of these volcanoes was applied. The number of cones and their distribution correspond to platform volcanic fields. The most frequent identified monogenetic volcano corresponds to a scoria cone developed in Strombolian dynamics with lava flows, with mean dimensions of 36.54 m height, 0.008113 km3 volume and an area of 0.454 km2.

The Calatrava paradox to decipher the origin of carbonatites: A petrological insight on Finca La Nava, Calatrava Province (central Spain)

The paper presents a detailed petrographic and geochemical study of the pyroclastites outcropping at La Nava maar (Calatrava Volcanic Province-CVP). Here, extrusive carbonatites mix with melilite nephelinite lapilli and bombs, crustal and mantle debris. Nephelinite and carbonatite are not characterised by a HFSE distribution typical of immiscible pairs. ΣREE and La/Lu ratios reflect primitive mantle carbonates and kimberlites. Igneous carbonates have δ13C and δ18O isotopic ratios in the range of extrusive carbonatites and differ from local sedimentary carbonates. Carbonatites have 87Sr/86Sr and 144Nd/143Nd isotopic ratios similar to Calatrava leucitites but different to melilite nephelinite. The difference indicates that melilite nephelinites and carbonatites are co-eruptive but not comagmatic. The mingled magmatic convoy, underwent decarbonation processes, releasing Ca and Mg that reacted with parental silicate melt. Consequently, the nephelinitic melt evolved towards a melilititic composition producing Ca-rich overgrowths on mafic phenocrysts and reacted to produce high Mg#, low Cr + Ni forsterite. Mass balance calculations indicats that the nephelinite magma assimilated up to 30% of the carbonatite magma. Mixing modelling based on the Sr and Nd isotopic composition of mantle xenoliths and carbonatites indicate that La Nava carbonatite may represent the mantle metasomatic agent.

Radiometric ages and time–space distribution of volcanism in the Campo de Calatrava Volcanic Field (Iberian Peninsula)

The volcanic region of Campo de Calatrava, which is located in the centre of the Iberian Peninsula, is characterized by monogenetic, strombolian and hydromagmatic volcanic activity. It is made up of more than two hundred volcanoes distributed over an area of about 4000 km2. They are mainly comprised of sodic alkaline and ultra-alkaline rocks, few evolved rocks (basalts, basanites, olivine nephelinites and olivine melilitites) and occasionally ultrapotassic rocks (olivine leucitites) and carbonatites. New radiometric ages (K/Ar and 40Ar/39Ar) allow a better understanding of the distribution and temporal evolution of volcanic activity in this region. The oldest volcanism is ultrapotassic and restricted to a single vent. The new 40Ar/39Ar ages date this centre between 7.4 Ma and 7.1 Ma, so it was contemporary with other ultrapotassic activity in the Iberian Peninsula (the lamproites of the SE of Spain). After a break of about 3 million years, the main volcanic activity in the region took place, without apparent major pauses, from about 4 Ma to less than 0.7 Ma, with most radiometric ages concentrated between 3.5 and 1.5 Ma. Except in the case of olivine leucitites, there are no significant compositional differences related to the ages of the volcanoes, although there may be minor variations. The mildly alkaline volcanoes (basalts and basanites) tend to be concentrated in the central areas of the region, while on the peripheral areas, the volcanoes are essentially ultra-alkaline. The spatial age distribution of the volcanoes seems to show a shift of the volcanic activity over time towards the northeast. The spatial age distribution of the volcanoes seems to show a displacement of volcanic activity over time towards the northeast, accompanied by an increase in its intensity.

Characterization and Geotourist Resources of the Campo de Calatrava Volcanic Region (Ciudad Real, Castilla-La Mancha, Spain) to Develop a UNESCO Global Geopark Project

The Campo de Calatrava Volcanic Region is located in Central Spain (Ciudad Real province, Castilla-La Mancha) where some eruptions of different intensity and spatial location took place throughout a period of more than 8 million years. As a result, more than 360 volcanic edifices spread over 5000 km2. Eruptions of this volcanic system were derived from alkaline magmas with events of low explosivity (Hawaiian and Strombolian). These events are characterized by three different manifestations: the emission of pyroclasts (cinder and spatter cones) and lava flows; some hydromagmatic events, which lead to the formation of wide craters (maars) and pyroclastic flows; and remnant volcanic activity related to gas emission (CO2), hot springs (hervideros) and carbonic water fountains (fuentes agrias). The methods used for this study are based on analytical studies of geography, geomorphology and geoheritage to identify volcanoes and their resources and attractions linked to the historical-cultural heritage. These volcanoes are a potential economic resource and attraction for the promotion of volcano tourism (geotourism), and they are the basis for achieving a UNESCO Global Geopark Project, as a sustainable territorial and economic management model, to be part of the international networks of conservation and protection of nature and, especially, that of volcanoes.

Depleted lherzolite xenoliths from the leucititic Morrón de Villamayor volcano (Calatrava volcanic field, Spain)

This work reports petrographical, mineralogical and geochemical data of a suite of mantle xenoliths from the Morrón de Villamayor volcanic centre (MVM), which belongs to the Calatrava Volcanic Field (CVF), a part of the Circum-Mediterranean Anorogenic Cenozoic Igneous Province. The MVM volcano is the only centre belonging to the first stage of the CVF magmatism, an ultrapotassic stage that provides a sampling of the subcontinental lithospheric mantle beneath central Spain. The MVM peridotites record a variable host melt interaction (spongy texture and reaction zones), more intense toward xenolith-host leucitite contacts that it was formed during transport within the volcanic melt. The studied mantle xenoliths are spinel lherzolites equilibrated at lower temperatures (618–942 °C) and similar pressure ranges (8.8–13.6 kbar) than other studied CVF mantle xenoliths, and record a lithospheric mantle before the main volcanic Calatrava event. The MVM lherzolites could be classified in two groups by their chondrite-normalized rare earth element (REE) clinopyroxene patterns: group-1 lherzolites show flat pattern, and group-2 lherzolites display a LREE-depleted (N-MORB like) pattern. Group-1 lherzolites represent a more residual lithospheric mantle (up to 9 partial melting %) than group-2 lherzolites (~ 5%), the latter with similar partial melting degrees than other mantle xenoliths from the CVF. Moreover, group-1 lherzolites have undergone a post partial melting refertilization by different metasomatic agents: silicate and alkaline silicate melts different in composition to host leucitite. A primary clinopyroxene concentrate from these MVM lherzolites provides high Sr (87Sr/86Sr = 0.706104) and intermediate Nd (143Nd/144Nd = 0.512830) initial radiogenic ratios, not previously recorded in this volcanic field. This sampling proves the presence of an enriched isotope mantle pole in xenolith suites of the Calatrava area, trending in composition to an intermediate DMM-EMII component.

Pyroxenites and Megacrysts From Alkaline Melts of the Calatrava Volcanic Field (Central Spain): Inferences From Trace Element Geochemistry and Sr-Nd Isotope Composition

Alkaline volcanic rocks from explosive monogenetic centers often carry an unusual cargo of crystals and rock fragments, which may provide valuable constraints on magma source, ascent and eruption. One of such examples is the Cenozoic Calatrava Volcanic Field in central Spain, a still poorly explored area to address these issues. Clinopyroxene, amphibole and phlogopite appear either as megacryst/phenocrysts or forming fine-grained cumulates (pyroxenite enclaves s.l.) in some eruptive centers of this volcanic field. They have previously been interpreted as cogenetic high-P minerals formed within the upper lithospheric mantle. The presence of Fe-Na-rich green and Mg-Cr-rich colorless clinopyroxene types as phenocryst cores or as oscillatory zoned crystals in pyroxenite enclaves points to a complex evolution of mineral fractionates from petrogenetically related magmas. In trace element chemistry all studied clinopyroxene types show parallel rare earth element patterns irrespective of whether they are megacrysts, colorless or green core phenocrysts, or zoned crystals within pyroxenite cumulates. This similarity indicates a genetic relationship between all the fractionated minerals. This is in agreement with the overlapping of initial 143Nd/144Nd and 87Sr/86Sr ratios of pyroxenite enclaves (0.512793–0.512885 and 0.703268–0.703778) that is within the chemical field of the host magmas and the Calatrava volcanics. The initial 143Nd/144Nd and 87Sr/86Sr ratios of megacrystic clinopyroxene, amphibole and phlogopite show a more restricted range (0.512832–0.512890 and 0.703217–0.703466), also falling within the isotopic composition of the Calatrava volcanic rocks. Deep magmatic systems beneath monogenetic volcanic fields involve several stages of melt accumulation, fractionation and contamination at variable depths. Trace element and isotope mineral chemistry are powerful tools to understand the history of ascent and stagnation of alkaline basaltic magmas and discriminate between magma mixing, wall-rock contamination and closed magmatic system evolution. In our study, we establish a cogenetic origin for green and colorless clinopyroxene as high-pressure precipitates from liquids of different fractionation degrees (up to 80%, for the highly evolved melts equilibrated with the green clinopyroxene), originated from a highly solidified front of silica-undersaturated alkaline magmas at mantle reservoirs.

Granulite-facies gneisses and meta-igneous xenoliths from the Campo de Calatrava volcanic field (Spain): Implications for the tectonics of the Variscan lower crust

The microstructural, petrofabric and geochronological study of deep-seated xenoliths from the La Encomienda volcano (Neogene Campo de Calatrava Volcanic Field) has helped to characterize the nature and dynamics of processes operative in the lower crust and subcontinental mantle domains of the Central Iberian Zone in the Iberian Massif (Spain). We present the finding of three new xenolith types: noritic andesine meta-anorthosites, aluminous granulites and felsic granulites. Plagioclase (andesine), hypersthene, ilmenite, apatite and zircon make up the mineral assemblage in equilibrium in the anorthosite xenoliths, whereas K-feldspar (sanidine), antiperthitic plagioclase (oligoclase-andesine), quartz, sillimanite, garnet, rutile and biotite conform the mineral assemblage in the aluminous granulites. Felsic granulites differ from the aluminous type in the smaller amount of garnet, the occurrence of perthitic microcline and the lack of sillimanite and biotite. The presence of significant fabrics in the constituent minerals indicates that they underwent high-temperature deformations representative of low crustal domains.U-Th-Pb analyses on anorthositic zircons provide a Variscan Late Carboniferous Concordia age of 309 ± 3 Ma, interpreted as the age of the igneous protolith of the granulitic anorthosite. Estimations for zircons in the felsic granulites yield three age groups at 288 ± 2 Ma, 398 ± 2 Ma and 490 ± 2 Ma. The first one would represent a late- to post-Variscan (Cimmerian) regional metamorphic event under granulite-facies conditions. The last two might be related to the age of an igneous component of the protolith at ca. 490 Ma and possibly that of a previous tectonothermal event at 400 Ma. 206Pb/238U results on the aluminous and felsic granulitic rutiles give ages of 5 ± 1 Ma that may correspond to resetting during Neogene volcanic events.A tentative scenario would contemplate the existence of Upper Carboniferous (late-Variscan) lithospheric shear zones along which mantle-derived components would have raised until the mantle-crust interface. The associated thermal budget would have acted as an important heat source responsible for heat conduction into the lower crust, along with eventual crustal melting. Removal of the mafic portions would have led to formation of low-density plagioclase-rich accumulations propagating upwards until its eventual incorporation in low crustal domains along with the formation of deep-seated granulites. The occurrence of these lithologies and the large volumes of hybrid monzogranites to granodiorites in the Central Iberian Zone might indicate, congruently, that, more than expected, mantle-derived magmas would have also played an important role during crustal growth processes related to the final stages of the Variscan orogeny in this part of the Iberian Massif.

Geomorphological evolution and chronology of the eruptive activity of the Columba and Cuevas volcanoes (Campo de Calatrava Volcanic Field, Ciudad Real, Central Spain)

In this study we analyze the geomorphological evolution and chronology of the eruptive phases of the Columba and Cuevas volcanoes (Campo de Calatrava Volcanic Field, Central Spain). These are two cinder cones located at the margins of the Jabalón River valley, between the localities of Granátula de Calatrava and Aldea del Rey (Ciudad Real). In order to generate geomorphological map, we conducted fieldwork and photointerpretation of aerial images, in addition to morphometric and volcanostratigraphic analyses aimed at correlating the volcanic deposits and fluvial terraces of the Jabalón River. Finally, we applied OSL (optically stimulated luminescence) dating to obtain the age of fluvial deposits affected by both volcanoes, plus radiocarbon dating to the organic matter of a paleosoil located between the Columba volcano deposits. The results provide a maximum age of 75.16 ± 4.9 ka for the formation of the Cuevas volcano. Moreover, the Columba volcano began its activity with a Strombolian phase around 33.9 ± 2.36 ka BP, followed by a long period of inactivity between 24.9 and 23.2 ka and 14–13.5 ka BP in which the aforementioned paleosoil formed. Subsequently, the eruptive activity resumed with a phreatomagmatic phase followed by another Strombolian phase, in which a lava flow was emplaced crossing and damming the Jabalón River, thus forcing the deposition of a 9 m thick fluvial terrace above it, at about 6.27 ± 4.28 ka. The Columba volcano is a good example of polycyclic eruptive behavior in a monogenetic volcanic field, whose last eruption occurred between 14 and 6.2 ka ago. The interaction between volcanic and fluvial processes was responsible for the morphological evolution of the area, the study of which has been crucial to determine the evolution of the eruptive activity, its morphological results, and the relative chronologies.

The Campo de Calatrava Volcanic Field (central Spain): Fluid geochemistry in a CO2-rich area

The Campo de Calatrava Volcanic Field (CCVF) located in central-southern Spain (along with Selva-Emporda in Catalonia, NE Spain) is regarded as one of the most important CO2 emitting zones in Peninsular Spain. Here, we report and evaluate new molecular and isotopic geochemistry of thermal waters and CO2-rich gas discharges from the CCVF. Locally, these CO2-rich fluid emissions represent the remnants of the past volcanic activity that affected this area from the late Miocene through the Quaternary, with the most recent events occurring in the Holocene. The locations of discharging fluids and previous volcanic centers appear to be aligned along well-defined NW-SE and NNW-SSE lineaments, with subordinate trends in the ENE-WSW direction. The chemical and isotopic composition of the thermal waters suggests a meteoric origin, dominated by three distinct geochemical facies: 1) HCO3-Mg(Ca) type waters, associated with a relatively shallow aquifer and related to the interaction of meteoric waters with CO2-rich gases, alkaline volcanic products, and sedimentary formations, 2) SO4(Cl)-Ca(Mg) type waters, which stems from the two rivers (Guadiana and Jabalón) that drain Triassic evaporitic rocks before entering the study area, and 3) HCO3-Na type waters, hosted in deep geopressurized CO2-rich reservoirs within the Ordovician basement rocks.The 87Sr/86Sr isotopic compositions (ranging between 0.70415 and 0.71623) and δ34S-SO4 values (+10.7 to +18.3‰ vs. CDT) of CO2-rich fluids are consistent with interactions between water and either the Paleozoic basement, Triassic evaporites, Quaternary volcanic rocks, or a combination thereof. Dissolution of a CO2-rich gas phase into the aquifer produces low pH values (down to 5.4) and enhances water-rock interactions causing relatively high salinity (Total Ionic Salinity: up to ∼185 meq/L). Carbon dioxide is by far the most abundant gas constituent (up to 992 mmol/mol) and is dominated by mantle-derived sources as indicated by the combination of relatively high helium isotopic ratios (up to 2.7 R/Ra), high isotopic ratios of carbon in CO2 (ranging between −6.8 and −3.2‰ V-PDB), and the carbon isotopic signature of TDIC (from −6.8 to +2.2‰ vs. VPDB).In the last two decades, numerous (CO2-rich) gas blowouts have occurred in the area during well drillings, suggesting the presence of a geopressurized gas reservoir at relatively shallow depth.

Intra-cone plumbing system and eruptive dynamics of small-volume basaltic volcanoes: A case study in the Calatrava Volcanic Field

The Manoteras volcano (Tortonian to Pleistocene, Calatrava Volcanic Field, Spain) is composed of a scoria and spatter cone surrounded by a field of pahoehoe lava. The volcanic cone is made essentially of vitreous lapilli-tuffs with intercalations of vitreous tuffs and spatter deposits, without any intercalations of lava flows. Erosion has uncovered an intra-cone plumbing system formed by coherent dykes and pyroclastic dykes (mixed-type dykes). This dyke swarm reflects processes of intrusion at the end of the eruption or even post-eruption. All the volcanic products are nephelinitic in composition. The main dyke is up to 3.4m thick and has an exposed length of ~1000m. It is composed mostly of coherent nephelinite with some pyroclastic sections at its northern extremity. This dyke is regarded as a feeder dyke of the volcano, although the upper parts of the dike have been eroded, which prevents the observation of the characteristics and nature of the possible overlying vent(s). Mixed-type dykes could also have acted as small linear vents and indicate that the magma fragmentation level during final waning stages of the eruption was located inside the volcanic cone. The pyroclastic deposits that make up the volcanic cone at the current exposure level were probably developed during a major phase of violent Strombolian style that formed the scoria cone, followed by a Hawaiian phase that formed the summital intracrater spatter deposit. Three central-type vents have been identified: one at the highest point of the remnant volcanic cone (summital vent), from where the earlier explosive eruptions took place, and the other two at the fringe of the cone base, from where emissions were only effusive. The lava flows were emitted from these boccas through the scoria cone feeding the lava field. The results obtained, based on careful field observations, add substantial complexity to the proposed eruptive models for small-volume basaltic volcanoes as it appears evident that there may exist and evolution through time from central conduit settings to fissure eruptions. Moreover, it is shown that intracone plumbing systems can integrate coherent and clastic dykes of variable thicknesses, which, in some cases could represent feeder dykes.

Landforms in the Campo de Calatrava Volcanic Field (Ciudad Real, Central Spain)

ABSTRACTA detailed geomorphological map of the Campo de Calatrava Volcanic Field (CCVF) is presented at a scale of 1:50,000. The Campo de Calatrava, located on the south-eastern edge of the Hercynian Massif, is one of the most unusual volcanic areas of the Iberian Peninsula. The volcanic activity develops chronologically from Upper Miocene to Holocene, with a wide range of styles and eruptive dynamics that have created a variety of forms and types of volcanoes, the abundance of maars being outstanding. Thus, this map represents both the landforms of volcanic origin and the interferences that volcanic activity has caused in other processes and forms, offering the reader the key to understanding the origin and fundamental features of the landscape of the territory. Also shown is the crucial role geomorphological mapping can play as a basic tool in the conservation of natural heritage and in territorial planning. The mapping system applied is the French CNRS RCP 77, although various local adaptations have been incorporated. The map legend consists of 80 elements arranged in 10 sections, in which a wide variety of morphostructures, forms and deposits produced under various types of both relict and active morphogenetic systems are identified.

Petrofabric and seismic properties of lithospheric mantle xenoliths from the Calatrava volcanic field (Central Spain)

The microstructural and petrofabric study of peridotite xenoliths from the El Aprisco (Neogene Calatrava Volcanic Field) has provided new information on deformation mechanisms, ambient conditions and seismic properties of the central Iberian subcontinental mantle. Olivine, orthopyroxene, clinopyroxene, amphibole and spinel constitute the mineral assemblage in equilibrium. Their microstructure indicates that they accommodated crystal-plastic deformation under high water fugacity conditions. Crystallographic preferred orientation patterns of key minerals were determined with the EBSD technique. The xenoliths exhibit B, C and A olivine fabrics. B-type fabrics, involving the (010)[001] slip system, may develop in domains where deformation occurs under comparatively lower temperature, higher water-content and faster strain rates. They are interpreted here as the result of deformation in a suprasubduction mantle setting triggered by changing conditions imposed by a cooler subducting slab that incorporated fluids into the system. Xenoliths with olivine C-type fabrics involve activation of the dominant (100)[001] slip system, denote intracrystalline slip at higher temperatures and water-contents. They are here interpreted to sample lithospheric mantle domains where the impact of those new conditions was not so strong. Finally, the A-type fabrics, characteristic of the (010)[100] slip system, are frequent in the mantle under moderate to high temperature. These fabrics are considered here as characteristic of the mantle prior to subduction. The olivine fabrics constrain heterogeneous seismic properties. Propagation orientation of P waves (8.27–8.51km/s) coincides with olivine [100] axis concentrations, whereas the fastest S1 waves (5.13–5.22km/s) propagate parallel to [010] axis minima. The maximum shear wave birefringence (VS1–VS2=0.17–0.37km/s) is close to the direction of the macroscopic lineation. Heterogeneity of calculated seismic properties would concur with preservation of fossil flow perturbations, reworking and metasomatism in the subcontinental lithospheric mantle of central Spain, likely related to changes in the ambient conditions close to paleosubductions.

Ca-rich carbonates associated with ultrabasic-ultramafic melts: Carbonatite or limestone xenoliths? A case study from the late Miocene Morron de Villamayor volcano (Calatrava Volcanic Field, central Spain)

The volcanic products of the late Miocene Morron de Villamayor volcano (Calatrava Volcanic Field, central Spain) are known for being one of the few outcrops of leucitites in the entire circum-Mediterranean area. These rocks are important because aragonite of mantle origin has been reported as inclusion in olivine macrocrysts. We use petrographic observations, mineral compositions, as well as oxygen and carbon isotope ratios coupled with experimental petrology to understand the origin of carbonate phase in these olivine-phyric rocks.Groundmass and macrocryst olivines range from δ18OVSMOW of +4.8‰, typical of mantle olivine values, to +7.4‰, indicating contamination by sedimentary carbonate. Carbonates are characterized by heavy oxygen isotope compositions (δ18OVSMOW >+24‰), and relatively light carbon isotopes (δ13CPDB <−11‰), resembling skarn values, and distinct from typical mantle carbonatite compositions.Petrography, mineral compositions such as low Mg# of clinopyroxene and biotite, low Ca# and low incompatible element abundance of the carbonate, and isotopic ratios of O and C, do not support a mantle origin for the carbonate. Rather, the carbonate inclusions found in the olivine macrocrysts are interpreted as basement limestone fragments entrapped by the rising crystallizing magma. Comparison with experimental carbonatitic and silicate-carbonatitic melts indicates that low-degree partial melts of a carbonated peridotite must have a dolomitic rather than the aragonitic/calcitic composition as those found trapped in the Morron de Villamayor olivine macrocrysts.

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.

From the North-Iberian Margin to the Alboran Basin: A lithosphere geo-transect across the Iberian Plate

A ~1000-km-long lithospheric transect running from the North-Iberian Margin to the Alboran Basin (W-Mediterranean) is investigated. The main goal is to image the changes in the crustal and upper mantle structure occurring in: i) the North-Iberian margin, whose deformation in Alpine times gave rise to the uplift of the Cantabrian Mountains related to Iberia–Eurasia incipient subduction; ii) the Spanish Meseta, characterized by the presence of Cenozoic basins on top of a Variscan basement with weak Alpine deformation in the Central System, and localized Neogene–Quaternary deep volcanism; and iii) the Betic–Alboran system related to Africa–Iberia collision and the roll-back of the Ligurian–Tethyan domain. The modeling approach, combines potential fields, elevation, thermal, seismic, and petrological data under a self-consistent scheme. The crustal structure is mainly constrained by seismic data whereas the upper mantle is constrained by tomographic models. The results highlight the lateral variations in the topography of the lithosphere–asthenosphere boundary (LAB), suggesting a strong lithospheric mantle strain below the Cantabrian and Betic mountain belts. The LAB depth ranges from 180km beneath the Cantabrian Mountains to 135–110km beneath Iberia Meseta deepening again to values of 160km beneath the Betic Cordillera. The Central System, with a mean elevation of 1300m, has a negligible signature on the LAB depth. We have considered four lithospheric mantle compositions: a predominantly average Phanerozoic in the continental mainland, two more fertile compositions in the Alboran Sea and in the Calatrava Volcanic Province, and a hydrated uppermost mantle in the North-Iberian Margin. These compositional differences allowed us to reproduce the main trends of the geophysical observables as well as the inferred P- and S-wave seismic velocities from tomography models and seismic experiments available in the study transect. The high mean topography of Iberia can be partly consistent with a low-velocity/high-temperature/low-density layer in the sublithospheric mantle.

A comparison of the Landsat image and LAHARZ-simulated lahar inundation hazard zone by the 2010 Merapi eruption

Located above the Java subduction zone, Merapi Volcano is an active stratovolcano with a volcanic activity cycle of 1–5 years. Most Merapi eruptions are relatively small with volcanic explosivity index (VEI) of 1–3. However, the most recent eruption, which occurred in 2010, was quite violent with a VEI of 4 and 386 people were killed. In this study, lahars and pyroclastic flow zones were detected using optical Landsat images and the lahar and pyroclastic flow zone simulated using the LAHARZ program. To detect areal extents of lahar and pyroclastic flows using Landsat images, supervised classification was performed after atmospheric correction by using a cosine of the solar zenith correction (COST) model. As a result, the extracted dimensions of pyroclastic flows are nearly identical to the Calatrava Volcanic Province (CVP) monthly reports. Then, areas of potential lahar and pyroclastic flow inundation based on flow volume using the LAHARZ program were simulated and mapped. Finally, the detected lahars and pyroclastic flow zones were compared with the simulated potential zones using LAHARZ program and verified. Results showed satisfactory similarity (55.63 %) between the detected and simulated zone. The simulated zones using the LAHARZ program can be used as an essential volcanic hazard map for preventing life and property damages for Merapi Volcano and other hazardous volcanic areas. Also, the LAHARZ program can be used to map volcano hazards in other hazardous volcanic areas.

CO2 and Rn degassing from the natural analog of Campo de Calatrava (Spain): Implications for monitoring of CO2 storage sites

Natural analogs offer a valuable opportunity to investigate the long-term impacts associated with the potential leakage in geological storage of CO2.Degassing of CO2 and radon isotopes (222Rn–220Rn) from soil, gas vents and thermal water discharges was investigated in the natural analog of Campo de Calatrava Volcanic Field (CCVF; Central Spain) to determine the CO2–Rn relationships and to assess the role of CO2 as carrier gas for radon. Furthermore, radon measurements to discriminate between shallow and deep gas sources were evaluated under the perspective of their applicability in monitoring programs of carbon storage projects.CO2 flux as high as 5000gm−2d−1 and 222Rn activities up to 430kBqm−3 were measured; 220Rn activities were one order of magnitude lower than those of 222Rn. The 222Rn/220Rn ratios were used to constrain the source of the Campo de Calatrava soil gases since a positive correlation between radon isotopic ratios and CO2 fluxes was observed. Thus, in agreement with previous studies, our results indicate a deep mantle-related origin of CO2 for both free and soil gases, suggesting that carbon dioxide is an efficient carrier for Rn. Furthermore, it was ascertained that the increase of 222Rn in the soil gases was likely produced by two main processes: (i) direct transport by a carrier gas, i.e., CO2 and (ii) generation at shallow level due to the presence of relatively high concentrations of dissolved U and Ra in the thermal aquifer of Campo de Calatrava.The diffuse CO2 soil flux and radon isotopic surveys carried out in the Campo de Calatrava Volcanic Fields can also be applicable to geochemical monitoring programs in CCS (Carbon Capture and Storage) areas as these parameters are useful to: (i) constrain CO2 leakages once detected and (ii) monitor both the evolution of the leakages and the effectiveness of subsequent remediation activities. These measurements can also conveniently be used to detect diffuse leakages.

Structures and geometries of the Tajo Basin crust, Spain: Results of a magnetotelluric investigation compared to seismic and thermal models

The Tajo Basin and Betic Mountain Chain in the south central region of the Iberian Peninsula were chosen for investigation in the first phase of the magnetotelluric (MT) component of the PICASSO (Program to Investigate the Convective Alboran Sea System Overturn) project. The MT results provide information about the electrical conductivity distribution in previously unprobed subsurface regions, as well as complimenting and enhancing results of prior geological and geophysical investigations thereby enabling the definition of a petrological subsurface model and a comprehensive understanding about the tectonic setting. Two-dimensional (2-D) inversion of the MT data provides enhanced insight into Iberian subsurface geology in the crust. The most striking features of the final model are (i) a distinct vertical interface within the Variscan basement beneath the center of the Tajo Basin that is spatially associated with the boundary between regions with and without substantial Alpine deformation, and (ii) a middle to lower crustal conductive anomaly that can be related to remnants of asthenospheric intrusion in connection with Pliocene volcanic events in the Calatrava Volcanic Province. For the latter, effects of hydrous phases are inferred that may originate from dehydration processes within the subducting slab beneath Alboran Domain and Betic Mountain Chain.