Caracausi, Antonio

Tectonically active areas of Central Italy are marked by intense CO 2 degassing, whose origin and role in earthquake processes are fundamental questions in geoscience. This study investigates the origin and geological controls on the geochemistry of light hydrocarbons from CO 2-dominated gas emissions located in the inner sector of the Umbria-Marche Apennines (Central Italy), aiming to better understand the sources and migration pathways of geogenic fluids in the region. Our findings indicate that light hydrocarbons are predominantly thermogenic, with negligible abiotic contributions. We demonstrate that Mesozoic carbonate rocks are the primary source across the study area, though conditions of hydrocarbon formation and migration vary. Specifically, higher temperatures and open-system conditions prevail in the southern regions, likely due to thermal stress associated with Quaternary magmatism. We propose that light hydrocarbons form at crustal depths (≤5-6 km) and are transported to the surface by ascending CO 2 from deeper sources. Finally, this work highlights that hydrocarbon geochemistry, combined with helium isotopes, can provide insights for reconstructing the circulation and origin of fluids in crustal reservoirs and assessing the thermal regime in tectonically active areas.

This study provides new mineral chemistry data together with micro-thermometric measurements on fluid inclusions hosted in ultramafic xenoliths (lherzolite, wehrlite, and dunite) brought to the surface by the last Mt. Vulture volcano activity (140 ka; southern Italy), and fed by melilitite-carbonatite magmas. Petrographic evidence and mineralogical compositions of Mt. Vulture xenoliths are consistent with an origin in the upper mantle. Fluid inclusions in rock-forming minerals of lherzolite and wehrlite xenoliths are CO2-dominated. The equilibrium temperature calculated by geothermometric estimates ranges from 1039 C (±36°C) to 1142°C (±15°C), and entrapment pressures of fluid inclusions with post-trapping re-equilibration correspond to the local crust–mantle boundary (32 km depth), and to a shallow reservoir located at 12–14 km depth. These results contribute to constrain the origin of these xenoliths and the depth of storage of magmas erupted from Mt. Vulture, where carbonatite-like metasomatism and mantle-derived CO2 degassing occur.

Fault slip is a complex natural phenomenon involving multiple spatiotemporal scales from seconds to days to weeks. To understand the physical and chemical processes responsible for the full fault slip spectrum, a multidisciplinary approach is highly recommended. The Near Fault Observatories (NFOs) aim at providing highprecision and spatiotemporally dense multidisciplinary near-fault data, enabling the generation of new original observations and innovative scientific products. The Alto Tiberina Near Fault Observatory is a permanent monitoring infrastructure established around the Alto Tiberina fault (ATF), a 60 km long low-angle normal fault (mean dip 20°), located along a sector of the Northern Apennines (central Italy) undergoing an extension at a rate of about 3 mm yr −1. The presence of repeating earthquakes on the ATF and a steep gradient in crustal velocities measured across the ATF by GNSS stations suggest large and deep (5-12 km) portions of the ATF undergoing aseismic creep. Both laboratory and theoretical studies indicate that any given patch of a fault can creep, nucleate slow earthquakes, and host large earthquakes, as also documented in nature for certain ruptures (e.g., Iquique in 2014, Tōhoku in 2011, and Parkfield in 2004). Nonetheless, how a fault patch switches from one mode of slip to another, as well as the interaction between creep, slow slip, and regular earthquakes, is still poorly documented by near-field observation. With the strainmeter array along the Alto Tiberina fault system (STAR) project, we build a series of six geophysical observatory sites consisting of 80-160 m deep vertical boreholes instrumented with strainmeters and seismometers as well as meteorological and GNSS antennas and additional seismometers at the surface. By covering the portions of the ATF that exhibits repeated earthquakes at shallow depth (above 4 km) with these new observatory sites, we aim to collect unique open-access data to answer fundamental questions about the relationship between creep, slow slip, dynamic earthquake rupture, and tectonic faulting.

In this study, we present scaling relationships between fault lengths, fault slip-rates and historical seismicity for an active normal fault system, seismically accommodating crustal extension within the upper plate of the Ionian subduction zone (southern Italy). This crustal extension is confirmed by historical seismicity and instrumental geodesy, with GNSS-derived values of horizonal deformation within a range of 2-3 mm/yr throughout Calabria and the Messina Strait region. We collated data for fault slip-rates, fault lengths and historical earthquakes for a given fault to explore whether fault slip-rates are correlated with fault size and their geometric moment.We present new results showing a robust correlation between fault lengths and fault slip-rates, which supports the idea of a relationship for a given fault between fault slip-rates and the geometric moment.We discuss our results in terms of how these correlations should be used if regional deformation is accommodated by localised strain on faults mostly arranged along strike rather than distributed strain on multiple faults across-strike. For instance, we compare our empirical correlation between fault lengths and fault throw-rates over the Middle-Late Pleistocene in Calabria and the Messina Strait with those from Central and Southern Apennines over the Holocene, characterized by strain distributed on multiple faults across-strike and strain localised on faults mostly arranged along-strike, respectively.Tectonic and seismic hazard implications are discussed for future investigations based on fault slip-rates, fault size and historical seismicity.

This study is focused on fluids characterization and circulations through the crust of the Irpinia region, an active seismic zone in Southern Italy, that has experienced several high-magnitude earthquakes, including a catastrophic one in 1980 (M = 6.9 Ms). Using isotopic geochemistry and the carbon‑helium system in free and dissolved volatiles in water, this study aims to explore the processes at depth that can alter pristine chemistry of these natural fluids. Gas-rock-water interactions and their impact on CO2 emissions and isotopic composition are evaluated using a multidisciplinary model that integrates geochemistry and regional geological data. By analyzing the He isotopic signature in the natural fluids, the release of mantle-derived He on a regional scale in Southern Italy is verified, along with significant emissions of deep-sourced CO2. The proposed model, supported by geological and geophysical constraints, is based on the interactions between gas, rock, and water within the crust and the degassing of deep-sourced CO2. Furthermore, this study reveals that the Total Dissolved Inorganic Carbon (TDIC) in cold waters results from mixing between a shallow and a deeper carbon endmember that is equilibrated with carbonate lithology. In addition, the geochemical signature of TDIC in thermal carbon-rich water is explained by supplementary secondary processes, including equilibrium fractionation between solid, gas, and aqueous phases, as well as sinks such as mineral precipitation and CO2 degassing. These findings have important implications for developing effective monitoring strategies for crustal fluids in different geological contexts and highlight the critical need to understand gas-water-rock interaction processes that control fluid chemistry at depths that can affect the assessment of the CO2 flux in atmosphere. Finally, this study highlights that the emissions of natural CO2 from the seismically active Irpinia area are up to 4.08·10+9 mol·y-1, which amounts is in the range of worldwide volcanic systems.

The redox state of the Earth’s upper mantle (i.e., oxygen fugacity, fO2 ) is a key variable that influences numerous processes occurring at depth like the mobility of volatile species, partial melting, and metasomatism. It is linked to the oxidation state of peridotite rocks, which is normally determined through the available oxythermobarometers after measuring the chemical composition of equilibrated rock-forming minerals and the Fe3C in redox-sensitive minerals like spinel or garnet. To date, accurate measurements of Fe3C = P Fe in peridotites have been limited to those peridotites (e.g., harzburgites and lherzolites) for which an oxythermobarometer exists and where spinel (or garnet) crystals can be easily separated and measured by conventional 57Fe Mössbauer spectroscopy. Wehrlitic rocks have been generally formed by the interaction of a lherzolite with carbonatitic melts and, therefore, have recorded the passage of (metasomatic) fluids at mantle conditions. However, no oxythermobarometer exists to determine their equilibrium fO2 . The aim of this study was to retrieve the fO2 of the mantle beneath Mt. Vulture volcano (Italy) through the study of a wehrlitic lapillus emitted during the last eruption ( 140 kyr ago) that contain olivines with multiple tiny spinel inclusions with sizes <40 μm. To our knowledge, the Fe oxidation state of these inclusions has been never determined with the Mössbauer technique due to their small sizes. Here, we present measurements of the Fe3C = P Fe using in situ synchrotron Mössbauer spectroscopy coupled with chemical and spectroscopic analysis of both host olivine and spinel inclusions. The results show Fe3C = P Fe ratios of 0.03–0.05 for olivine and 0.40–0.45 for the included spinels, the latter of which appear higher than those reported in literature for mantle spinel harzburgites and lherzolites. Given the evidence of the mantle origin of the trapped spinels, we propose that the high fO2 (between 0.81 and 1.00 log above the fayalite–magnetite–quartz buffer; FMQ) likely results from the interaction between the pristine spinel lherzolite and a CO2-rich metasomatic agent prior to the spinel entrapment in olivines at mantle depths.

Deeply-sourced fluids are released in volcanically and tectonically active regions through conduits such as fumaroles, natural springs, and permeable soils. The origin and transport of the fluids in volcanic and tectonic systems are a key research theme in Earth Sciences, which is of particular importance for geo-hazard mitigation and resource exploration. This Research Topic aims to present recent advances in fluid geochemistry and its application in volcanically and tectonically active regions. Under this context, 10 papers covering a series of research themes in fluid geochemistry were published in this Research Topic, as briefly summarized below. People living close to active fault zones are threatened by earthquake hazard and therefore monitoring the status of active faults is important to mitigate the damage caused by future earthquakes. Caracausi et al. reported data from a novel infrastructure designed for multidisciplinary and continuous monitoring of the Alto Tiberina fault, Italy. Monitoring results (including seismic, geodetic, and geochemical data) from The Alto Tiberina Near Fault Observatory (TABOO-NFO) would shed new light on earthquake prediction studies in other countries. Fidani et al. conducted a comprehensive statistical analysis of CO2 time series registered at the Gallicano test site, Italy, and identified the correlations between low- magnitude earthquakes and CO2 anomalies in spring waters. Li et al. studied the spatial variations in soil Rn and CO2 emissions in the Wuzhong-Lingwu region, NW China, as well as the possible controlling factors of earthquakes, stress state, and deep-to-shallow crustal structures. Their findings offer new insight into combining geochemical characteristics of soil gas and seismological methods to estimate regional seismic hazards. Under the context of continuous collision between Indian and Asian continents, the Tibetan Plateau and its surrounding regions have drawn increasing concern from the Earth science community because of intensive and frequent earthquake events. Liu et al. reported the first estimates of diffuse soil CO2 flux (~1.2 Mt yr–1) for the Anninghe-Zemuhe fault in the Southeast Tibetan Plateau and found close relationships between spatial variations in soil CO2 fluxes and that of regional seismic activity. Based on the geochemistry of hot spring waters, Liu et al. explored the controls of the Jinshajiang fault zone (SW China) on hydrothermal fluid circulation, water-rock interaction, and earthquakes, which highlighted the role of hot spring water discharging from fracture zones in receiving the hydrological information on seismic activity. Also published in this Research Topic, Liu et al. presented an example of post-earthquake hydrological changes based on carbon isotope data of spring waters collected after the 2021 Mw 7.4 Maduo earthquake in eastern Tibetan Plateau. They quantitatively identified enhanced mobilization of the shallow soil organic carbon following the 2021 Maduo earthquake and suggested that earthquakes could disturb the circulation of subsurface fluids and their interaction with the country rocks and sediments on short timescales. Wang et al. investigated origin and circulation of geothermal waters in the Karakoram strike-slip fault zone in western Tibet. Their results show that geothermal water is correlated with the epicenter and focal depth of earthquakes, especially for high-temperature spring water with deeper circulation and extremely high Li, B, Fe, and As concentrations. Three papers in this Research Topic focus on the degassing of historically active volcanoes. Gherardi et al. investigated helium isotopes on gas extracted by crushing from melt and fluid inclusions in minerals from Plinian and inter-Plinian tephra and lavas of Vesuvius, Italy. Their results show that i) 3He/4He values are buffered within an extended, deep-seated reservoir at about 10 km filled with magma rising from the mantle, and ii) magma ponding at crustal depth could be considered a key mechanism that might have the potential to homogenize the helium isotope signal. Located in the hinterland of Northeast Asia, the active Arxan volcanic field remains less studied for the characteristics of its present-day volcanic degassing. Pan et al. focused on diffuse soil CO2 fluxes and found that annual CO2 emission flux from the volcanic field to the atmosphere is ~0.63 × 105 t and is comparable to that of the Iwojima volcano in Japan. This is the first flux estimate for soil CO2 emissions of the Arxan volcanic field. Cui et al. presented a geochemical study on the hot spring water and gases from the Arxan volcanic field. They identified ~3%–23% mantle helium inputs and thus heat supply in the hydrothermal fluids, suggesting that the residual mantle-derived melts beneath the Arxan volcanic field are still releasing fluids/volatiles and heating the overlying hydrothermal systems.

Mantle-derived noble gases in volcanic gases are powerful tracers of terrestrial volatile evolution, as they contain mixtures of both primordial (from Earth's accretion) and secondary (e.g., radiogenic) isotope signals that characterize the composition of deep Earth. However, volcanic gases emitted through subaerial hydrothermal systems also contain contributions from shallow reservoirs (groundwater, crust, atmosphere). Deconvolving deep and shallow source signals is critical for robust interpretations of mantle-derived signals. Here, we use a novel dynamic mass spectrometry technique to measure argon, krypton, and xenon isotopes in volcanic gas with ultrahigh precision. Data from Iceland, Germany, United States (Yellowstone, Salton Sea), Costa Rica, and Chile show that subsurface isotope fractionation within hydrothermal systems is a globally pervasive and previously unrecognized process causing substantial nonradiogenic Ar-Kr-Xe isotope variations. Quantitatively accounting for this process is vital for accurately interpreting mantle-derived volatile (e.g., noble gas and nitrogen) signals, with profound implications for our understanding of terrestrial volatile evolution.

Volcanic activities have great implications on geological carbon cycle, and ascertaining the deep carbon contribution in earth surface that run along the volcanic edifices is important to understand the relationship between solid earth degassing and global climate change. This study reports analytical results of major dissolved ions concentrations, carbon isotopic compositions (δ13CDIC and Δ14CDIC) of dissolved inorganic carbon (DIC) of rivers, cold springs and hot springs from Changbaishan volcanic area, Northeast China. The hydrothermal fluids had a significant impact on solutes budgets, as well as carbon isotopes for the rivers. The changes in concentrations of major ions are mainly controlled by mixing of high-temperature water/rock interaction and low-temperature water/rock interaction, and low-temperature water/rock interaction can be explained by the change of chemical composition between volcanic cone (trachyte) and basaltic shield. We used Δ14CDIC to figure out the contributions of deep carbon and surface carbon. While δ13CDIC was sensitive to CO2 outgassing, and we thus estimated the minimum deep CO2 outgassing yield (1.24×104 t C yr1) based on DIC flux corrected for outgassing by a Rayleigh model. In the Changbaishan volcanic area, deep carbon release flux was higher than CO2 consumption flux by silicate weathering, while the deep CO2 outgassing flux was an underestimate, consistent with the theory that deep CO2 release regulate climate on geological timescales. This study calls for a better understanding of the effects of volcanic activities on earth surface’s carbon cycling, which has great implications on studying global climate change.

Static and dynamic stress, along with earthquakes, can trigger the emission and migration of crustal fluids, as frequently observed on the surface and within the upper crust of tectonically active areas such as the northern Apennines of Italy. To investigate the origin of these fluids and their interconnection with the seismogenic process, we complemented The Alto Tiberina Near Fault Observatory (TABOO-NFO), a multidisciplinary monitoring infrastructure composed of a dense array of seismic, geodetic, strain, and radon sensors, with a proper geochemical network grounded on four soil CO2 flux monitoring stations and weather sensors, placed near the main vents of the superficial manifestations. The TABOO-NFO is a state-of-the-art monitoring infrastructure, which allows for studying various geophysical parameters connected to the deformation processes active along a crustal fault system dominated by the Alto Tiberina fault (ATF), which is a 60 km long normal fault dipping at a low angle (<15°–20°). The region is favourable for conducting geochemical studies, as it is characterised by the presence of over-pressurised fluids trapped at certain depths and superficial manifestations associated with the emission of large quantities of fluids. After describing the theoretical framework and the technological aspects based on which we developed the geochemical monitoring network, we described the data recorded in the first months. Over the studied period, the results showed that soil CO2 flux was primarily influenced by environmental parameters, and that the selected sites received a regular supply of deep-origin CO2.