Geociencias Barcelona

The 2021 Tajogaite eruption on La Palma was the most destructive volcanic event in recent Canary Islands history, lasting 85 days and producing extensive lava flows and tephra deposits. Beyond its immediate impacts on infrastructure and air quality, the eruption raised critical questions about how tephra properties influence environmental hazards and public health. Fine ash particles (

Reconstructing the eruptive history of active volcanic complexes is essential for carrying out a proper long-term volcanic hazard assessment. This reconstruction relies on the accurate correlation of volcanic deposits (e.g. tephra layers), which is often hampered by compositional overlaps between units. Traditional methods (e.g. comparison of samples using harker diagrams of two elements) often struggle with the high-dimensional nature of geochemical data. On the other hand, data-driven approaches (e.g. cluster analysis) offer a robust solution by using statistical algorithms to objectively identify subtle geochemical signatures.The lack of extensive and homogeneous datasets prevents using data-driven approaches for tephra correlation studies, as it is the case of the Teide-Pico Viejo (T-PV) volcanic complex (Tenerife, Canary Islands). Despite posing a significant threat to a densely populated island, T-PV's eruptive dynamics remain only partially constrained: current models attribute high-explosivity (sub-plinian) events primarily to satellite felsic domes (e.g., Montaña Blanca, Pico Cabras), whereas activity at the main Teide stratocone is widely assumed to be limited to moderate-intensity, violent Strombolian eruptions. However, stratigraphic constraints on Teide’s northern flank remain limited, as the source vents for a significant number of tephra deposits have not been identified yet.To link these unidentified deposits to their source vent, we constructed a geochemical dataset of 74 samples that integrates reference material (lavas and tephras with source vents confirmed by geological mapping) with the target unidentified tephra layers. We analyzed the complete suite for whole-rock geochemistry and micro-analytical phases (phenocrysts and glasses) in some selected samples. We then developed a two-stage data-driven workflow: first, we performed an agglomerative Hierarchical Cluster Analysis (HCA) on whole-rock major and trace elements to group the unknown tephras with chemically affine reference lava and/or tephra samples. Second, these potential correlations were validated through petrographic assessment and a second HCA on the electron probe microanalyses (EPMA) of glass and minerals. The accuracy of our methodology is evidenced by the correct attribution of reference lava-tephra pairs from known eruptions (e.g. Montaña Blanca and Montaña Majúa).When applied to the unidentified deposits, this method enabled the correlation of three previously unidentified tephra deposits: one with Montaña Reventada eruption, and two with the central Teide vent. Both Teide-sourced eruptions, dated to

Transfer fault zones are commonly associated with volcanic activity. While geochronological methods such as the U Pb and Ar Ar dating have been traditionally used to establish the absolute timing of volcanism, recent advances allow us the dating of fracture-filling minerals. However, integrated tectono-volcanic and geochronological studies of fault zones are scarce, limiting our ability to constrain accurately the evolution of fault-controlled volcanic zones. This paper reviews the tectono-volcanic history of northeastern Iberia through the geochronological and kinematic analysis of well-known examples of Neogene to Quaternary fault zones with associated volcanism along the Transverse Ranges. These fault zones are located at the northwestern tip of a NW-SE transfer zone that segmented the Liguro-Provençal Rift. We integrate available geological and geophysical data with new structural analysis of meter scale fractures across three fault zones and U Pb dating of fracture-filling carbonates. The U Pb dating of fracture-filling calcite reveals early Eocene strike-slip faulting at ~49 Ma, during the Alpine compression, and synchronous strike-slip and extensional dip-slip faulting from ~22 to ~2 Ma, coinciding with the Liguro-Provençal rifting. We propose a new lithospheric-scale model in which faults acted as sub-vertical conduits for the ascent of magmas sourced from the lithosphere-asthenosphere boundary, based on the composition of recovered xenoliths. Our geochronological dataset supports the hypothesis that fault reactivation governs the timing, location and migration of volcanism in the Neogene to Quaternary Catalan Volcanic Zone, which was additionally influenced by lithospheric thinning and the development of transfer fault zones that potentially reflect the reactivation of Mesozoic structures. These processes share striking similarities with those observed in the western Mediterranean Region, the European Cenozoic Rift System, and other extensional systems worldwide, highlighting the role of inherited transfer fault zones in the evolution of volcanism.

The family of transition metal phosphorus trichalcogenides (MPX3, where M is a transition metal and X = S or Se) has recently attracted considerable attention due to their tunable band gaps and synergistic effects among electronic, magnetic, structural, and optical properties. We examine the influence of hydrostatic pressure on the optical, structural and vibrational properties of layered HgPSe3 through spectroscopic and diffraction techniques combined with first-principles calculations. Optical absorption measurements reveal a phase transition at 3.6 GPa, evidenced by a decrease in the band gap energy of approximately 200 meV, resulting in a change in sample color from bright to dark red. The same phase transition was confirmed by structural methods: powder X-ray diffraction and Raman spectroscopy. We propose that the compound undergoes a structural transition from its ambient pressure monoclinic phase to a high-pressure triclinic phase. Birch-Murnaghan fits give an experimental bulk modulus of B0 = 29.7 GPa, in very good agreement with the theoretical value of B0 = 28.1 GPa. Experimental pressure coefficients are obtained and compared with theoretical predictions. Our findings unveil a complex interplay between the structural and optical properties of HgPSe3 under pressure, which could be exploited to fabricate novel applications based on the tunable properties of van der Waals materials.

Upper Jurassic and Lower Cretaceous limestones and dolostones serve as hydrocarbon reservoirs in the offshore area of NE Spain. Since similar dolomitized rocks crop out in the adjacent onshore Maestrat Basin in the SE Iberian Range, understanding the dolomitization and other diagenetic processes is key to assessing reservoir properties. The Maestrat Basin dolostones crop out as elongated, asymmetric bodies, ranging from tens of centimetres to kilometres in length and up to 150m thick, with a wedge-shaped geometry closely associated with fractures. These dolostones are calcium-rich with low concentrations of Mn, Sr, and Na, but variable Fe, indicating that the replacement of the host limestone was followed by dolomite cement precipitation. Fluid inclusion data suggestthat dolomitization took place at temperatures ranging between 70 and 120ºC. Such temperatures, together with the high 87Sr/86Sr ratio and fluid salinity (16 to 23% wt. NaCl equivalent), reveal that the dolomitization process took place in burial conditions, from fluids that were infiltrated and likely interacted with Triassic, Liassic, and basement rocks. Although the exact age of dolomitization is not fully constrained, it is thought to coincide with fault-related dolomitization events of the same type previously described in the Maestrat Basin, likely during the latest Early Cretaceous and/or during the Late Cretaceous, in relation to the post-rift basin stage. Geochemical differences between the depocenters and structural highs may reflect the controls of the Maestrat Basin basinarchitecture on the composition and distribution of fluids.

Abstract Syn‐to late‐orogenic extension caused by gravitational collapse is a process that has been documented in most orogens. In this paper, we investigate the contemporaneous stress field in Taiwan to examine syn‐orogenic extensional faulting and the possible gravitational collapse modes by which it is taking place. We use a new, large, well‐constrained, clustered earthquake focal mechanism data set from which we calculate the stress field ( σ 1 , σ 2 , σ 3 ), the direction of the maximum compressive horizontal stress ( S H ), and determine the most likely fault plane orientations and kinematics. Our results show that, in the upper 21 km of the crust, shearing, with lesser compression are the dominant stress regimes in the Western Foothills and Hsuehshan Range, resulting in a complex interaction of strike‐slip (with transpression and transtension) and thrust faulting. Extension is predominately localized in the upper 14 km of the crust in the Central Range (CR), where it is roughly orogen‐parallel. S H and the best‐fit fault planes in the CR strike roughly NW‐SE, at a high angle to the structural and topographic grain. At depths greater than 21 km, compression and shear, with transpression and minor extension are the dominant stress regimes throughout Taiwan. Along the eastern flank of the mountain belt, mixed compression and shear stress regimes at depths greater than 50 km are related to the Manila and Ryukyu subduction zones. Our new results allow, for the first time, to characterize an ongoing, large‐scale, orogen‐parallel extension in Taiwan related to lateral extrusion with free‐boundary gravitational collapse.

Below the central nave of the Gothic Cathedral of Palencia (14th to 16th centuries) lies the Crypt of San Antolín, which represents the remains of a Visigothic building from the mid-7th century. The crypt itself has suffered recurrent episodes of flooding over the centuries. However, the latest flooding, which began in mid-2021 and ended in mid-2023, is one of the most long-lasting episodes on the historical record. To establish the origin of these flooding episodes, the geological and hydrological properties of the subsoil have been determined by direct prospecting techniques (drilling) and indirect geophysical techniques (Electrical Resistivity Tomography). The prospecting has determined that the aquifer in the area has a basin-like geometry, which favors the accumulation of water below the crypt. This work has shown that the recurrent floods suffered by the crypt prior to 2021 are related to episodes of intense rainfall. However, after 2021, there is a direct relationship between the persistent flooding and the onset of landscaping at the Plaza de San Antolín, one of the squares near the cathedral. In addition, previous archaeological excavations carried out in 1965 in that same square had disrupted the stratigraphic column, easing the percolation of water. We conclude that the increase in landscaped areas in archaeological environments may modify the hydrogeological dynamics of the subsoil and affect the surrounding buildings.

Abstract A structural analysis of intra‐montane basins establishes the deformation field of the southwestern Tian Shan, that part of the Tian Shan that faces the Pamir and thus the deformation that the Indian mantle‐lithosphere indenter beneath the Pamir imposes—northward indentation and westward crustal collapse. Tight‐isoclinal footwall synclines in the basins accompany major ∼E‐striking Cenozoic reverse faults that reactivate Paleozoic ones, separate basement blocks, and accommodated ∼N‒S shortening and dextral strike‐slip faulting. They connect with ∼WNW‐striking dextral strike‐slip faults, and ∼ENE‐striking thrusts; the latter are confined to the western southwestern Tian Shan. The deformation field resembles that of the Afghan‐Tajik Basin fold‐thrust belt and mimics in shape the geometry of the intermediate‐depth earthquake zone beneath the Pamir that traces the lithospheric delamination zone separating the Indian mantle indenter from Asian lithosphere. The basement‐rooted Cenozoic faults require a detachment underlying the southwestern Tian Shan, likely along the brittle‐ductile transition, consistent with the regular spacing of the intra‐montane basins. This mid‐crustal detachment and the shallow evaporite detachment below the Afghan‐Tajik Basin may root in a common deeper one, likely along the Moho. As the southwestern Tian Shan is involved in the northward motion and westward collapse of the Pamir, the deep detachment must root in the lithospheric delamination zone of the Pamir. The deep structure of the eastern Tian Shan is different; thus, the detachment underlying the southwestern Tian Shan and Afghan‐Tajik Basin must terminate along the eastern margin of the Pamir delamination zone, that is, along the western margin of the Tarim craton.

The Schofield groundwater body on the island of Oʻahu is one of the most important freshwater reservoirs yet has enigmatically high hydraulic head as compared to the adjacent basal water bodies. Various hypotheses have been proposed to explain this so-called North Schofield Dam, yet for the most part the Schofield aquifer’s high head remains unexplained. For this study we collected extensive self-potential and seismic ambient noise datasets in an effort to better understand the geologic and fluid flow conditions across the North Schofield Dam boundary.  We collected 40 km of interconnected self-potential profiles and seismic ambient noise data recorded by 53 stations (Magseis Fairfield) over 18 consecutive days. As a complementary approach, we performed a basic clustering analysis of our self-potential dataset. Our results revealed two distinct domains with different geophysical signatures, demarcated by a NE-SW-striking boundary. The southeastern area exhibits higher self-potential values and seismic velocities, while the northwestern area has lower values for both data types. This sharp boundary, oriented N25°, separates two hydrogeological domains and precisely highlights the North Schofield dam. We interpret that the NW domain contains buried valley-fill material with low permeability, while lava flows from the Wai‘anae and Koʻolau volcanoes dominate the SE zone. We interpret that the mostly impervious valley-fill material acts as a water flow boundary that may explain the abnormally high groundwater levels observed in the Schofield groundwater unit. We thus provide for the first time, the orientation, underground geometry, and geological nature of the North Schofield Dam. This study helps in understanding the mechanisms associated with forming a large aquifer in the elevated central part of the island of Oʻahu. It also emphasizes the importance of geological complexity of volcanic environments in influencing groundwater storage and flow. Our findings will be key to improving hydrogeological models, and thus fresh groundwater resources management on O‘ahu, and it opens perspectives for further comparative studies on other volcanic islands.

Passive seismic methods have gained significant attention in recent decades due to their cost-effective and non-invasive nature, making them ideal for continuous monitoring of subsurface dynamics. Among these methods, ambient noise coda-wave interferometry is widely used for detecting time-lapse changes in seismic velocities and has been successfully applied in diverse geological settings. However, its effectiveness might be limited by the complexity of coda wave composition, which complicates the estimation of the depth sensitivity of velocity changes, and by the instability of noise sources, which can introduce artificial velocity changes. These limitations highlight the need for alternative methodologies. In this study, we evaluate the potential of Rayleigh wave ellipticity as a non-interferometric tool for detecting near-surface variations. Using the degree of polarization method, combined with time-frequency analysis to isolate Rayleigh waves, we analyze time-lapse variations in ellipticity from multiple field case studies. To quantify these variations, we employ normalized cross-correlation and cross-covariance metrics. Unlike other widely used noise-based methods, such as spectral analysis or horizontal-to-vertical spectral ratios, our approach examines the full ellipticity function. This allows for the detection of velocity changes over a broader depth range without being limited to specific features of the curve.Our results demonstrate the robustness of Rayleigh wave ellipticity in detecting shallow subsurface changes, which is source-unbiased. This approach addresses key limitations of existing geophysical methods and expands the toolbox for seismic monitoring, enabling a more comprehensive analysis of subsurface dynamics. Potential applications include monitoring groundwater variations, assessing infrastructure stability, and contributing to the understanding of subsurface dynamics in complex environments, making it a versatile and powerful tool for environmental and geological studies. Rayleigh wave ellipticity emerges as a robust, independent alternative, offering a refined approach for monitoring subsurface changes and addressing the challenges faced by other noise-based methods.This work has received funding from the AGEMERA project, financed by the European Union’s Horizon Europe research and innovation programme under grant agreement N° 101058178.  As well, this work has benefited from partial support of the STONE project (CPP2021-0090072), financed with funds from the Ministry of Science and Innovation through the State Agency for Innovation (MCIN/AEI/10.13039/501100011033) and the European Union-Next Generation through the Recovery, Transformation and Resilience Plan (PRTR).