Hyblean Plateau Research Articles

Extensive oxidizing events recorded by peridotite mantle xenoliths from the Hyblean Plateau: Evidence from combined measurements of ferric iron in spinel with noble gases and fluid inclusions chemistry in olivine

The study of the oxidation state of lithospheric mantle-derived rocks allows modelling the deep cycle of volatiles (e.g., C, H, O, N and S) in the Earth's interior, which in turn plays a role in magma genesis, metasomatism and volcanic degassing. At the oxygen fugacity (i.e., fO2) recorded by residual abyssal peridotites, volatile elements like carbon are predicted to be in the immobile form of graphite. However, the compilation of the redox state of worldwide-distributed continental xenoliths shows evidence of their oxidation and refertilization through time by deeply formed subduction-related metasomatic fluids. The analyses of fluid inclusions in mantle-derived minerals like olivine (or pyroxenes) represent a snapshot of the volatile circulation in depth, whose noble gases signature (He, Ar, Ne) is used to identify their possible source. This study aims to reconstruct the origin of mantle metasomatism underneath the Hyblean Plateau (Sicily, Italy) and its redox history through the investigation of spinel-peridotite nodules, combining fO2 estimates with noble gases and fluid inclusions chemistry from hand-picked olivine grains. We analyzed eight mantle xenoliths classified as spinel lherzolites and spinel harzburgites from the Valle Guffari (Hyblean Plateau, Sicily). The calculated logfO2 is higher than that of most cratonic xenoliths worldwide ranging between 0.28 and 1.27 log units above to the fayalite-magnetite-quartz (FMQ) reference buffer. Micro-Raman measurements on olivine grains with dendritic trails of (metasomatic) fluid inclusions reveal an assemblage made of Mg-Ca carbonates ± sulfide ± elemental sulfur ± CO2 in the most reduced sample, and Mg-Ca carbonates ± sulfates ± CO2 in the most oxidized sample, the latter associated with a silicate glass and (secondary) hydrous phases. Both assemblages are taken as evidence of the product of crystallization of deeply originated volatile-bearing silicate melts. Analyses of He, Ar, and Ne in olivine grains confirm the evidence of a mantle source reworked by metasomatic processes. Our data suggest that an initially residual Hyblean lithospheric mantle was affected by extensive oxidizing events at several depths caused by the interaction with slab-derived CO2-rich silicate metasomatic liquids.

Hydrogeochemical characterization of the alluvial aquifer of Catania Plain, Sicily (South Italy)

A hydrogeochemical study was carried out on the shallow Catania Plain alluvial aquifer, in eastern Sicily to reconstruct its hydrogeological structure, the meteoric recharge and to assess the influence of human activities on groundwater. To characterize the geochemistry of the shallow aquifer, two sampling campaigns were carried out, August–October 2004 and April–May 2005 in 47 sites distributed throughout the plain. The samples were collected and analyzed for physical–chemical parameters and major ions, as well as stable isotopes (δ18O and δ2H). Alluvial deposits with heterogeneous grain sizes constitute the aquifer. Varying conditions of vertical and horizontal permeability lead to the presence of a multilayered aquifer with different conditions of confinement and partial interconnection among layers. The sampled waters were separated into four groups of different compositions due to the water–rock interaction with the different lithologies present in and around the study area. Maps of electrical conductivity and sulfate show a systematic control of land use, in correspondence with the biggest farms. High sulfate concentration is due to both the natural interaction between local meteoric waters and Etna’s plume and the mixing with groundwater coming from the area where evaporitic rocks of the Gessoso Solfifera formation are present. In addition, anthropogenic contamination cannot be ruled out. A rain gauge network, consisting of 3 sites located at different altitudes, was installed to collect rain waters to determine isotopic data (δ2H and δ18O) and to measure the monthly rainfall amount. Based on the isotopic composition of sampled waters, it has been established that beyond the direct meteoric recharge, the recharging areas are in the North (Mt. Etna) and the South (Hyblean Plateau).

Petrographic, microstructural and petrophysical study of asphaltic limestone employed in the Late Baroque towns of the Val di Noto UNESCO site (south-eastern Sicily)

Pitchstone is one of the building materials used in the monumental architecture of the late Baroque towns of the Val di Noto (UNESCO World Heritage Site) in the Hyblean Plateau (SE Sicily). Our research goal is to define the relationships between microstructural properties and bitumen impregnation, which confer the distinctive shades and excellent physical–mechanical properties to this valuable geomaterial. The study has been conducted by optical microscopy, synchrotron X-ray microtomography, ultrasonic testing, gas chromatographic analysis, differential scanning calorimetry and thermogravimetry investigation on two differently impregnated samples, representative of the main exploited and marketed pitchstone lithotypes. It revealed a close relationship between petrofabric and petrophysical properties, and impregnation amount.

The Porosity in Heterogeneous Carbonate Reservoir Rocks: Tectonic versus Diagenetic Imprint—A Multi-Scale Study from the Hyblean Plateau (SE Sicily, Italy)

The petroleum industry has always been pursuing highly exploitable gas fields, which are often hosted in carbonate rocks. However, carbonates are highly heterogeneous and show different fabrics and structures as the result of sedimentation in various environments, and subsequent diagenesis and deformation. In this study, a multi-scale and multidisciplinary approach has been performed on classical reservoir rocks from the subsurface of the Hyblean Plateau (Sicily, Italy). We aim at unravelling the important and debated role of tectonic and diagenetic structures (mainly fractures as well as stylolites) in enhancing or reducing the porosity. Black shales, limestones, and laminites of intertidal environment represent the main lithologies. Structure cross-cutting relationships record different stages of the basin geological history, which are related to the tectonic evolution of the area. Our results show that porosity is uncommonly lightly affected by fractures and faults, because of their mineralization, whereas stylolites, which are often considered as barriers to fluid flow, show a certain porosity. Therefore, we want to highlight the importance of a multi-scale and multidisciplinary approach in the analysis of heterogeneously porous, fractured- and stylolite-rich carbonate rocks, and our study aspires to boost other similar gas reservoir studies in energy transition times.

Age attribution to a karst system using river long profile analysis (Hyblean Plateau, Sicily, Italy)

In steady-state tectonic-climate systems, the fluvio-karst processes attain a stable base level, whether it be local or global. In contrast, in an uplifting region, relative base-level changes force river incision processes and a concurrent lowering of the karst water-table. Even at local scales (e.g., single fault-controlled valley), combined tectonically- and climatically-driven base-level drops induce geomorphic and hydrogeological disequilibrium. Thus, the karst system develops vertically and the water-table lowers trying to attain the new local base level. Conversely, the paleo-karst network dries, and becomes abandoned as a hanging relic with aligned karst morphologies. They are exhumed by the entrenchment of the fluvial network, as base-level fall related knickpoints migrate upstream. We propose a geomorphic approach to build fluvio-karst age models, based upon the analysis of river long-profiles. This approach is complementary to altimetric correlation between karst horizons and coastal paleo-sea level markers. Our approach is useful for an inland study area that is far from the marine terraced coast or where active faulting cuts off the coastal area from the inland landscape. We tested the approach in the eastern sector of the Hyblean Plateau (Sicily, Italy), where a carbonate sequence experienced Middle-Late Pleistocene tectonic uplift combined with active faulting. Specifically, we investigated the Cassibile River basin, at the footwall of the active Cassibile-Noto Fault. By reconstructing river paleo-long profiles we fixed time-space reference lines, connecting the abandoned and hanging fluvio-karst levels to the correlative marine strandlines carved along the fault-controlled coastal landscape.

A hydrogeochemical approach to the characterization of low-enthalpy geothermal systems: the Scordia – Lentini graben (Sicily, Italy)

We describe the geochemical characteristics of groundwater samples collected in 23 water wells located on the northern margin of the Hyblean plateau (East Sicily). This area, mostly made of highly permeable carbonate rocks, is rich in low temperature (T < 50° C) hydrothermal groundwaters, distributed in an active sismogenetic zone, with several ENE-WSW-directed tectonic structures that drove magma to the surface during Upper Pliocene and Pleistocene. The chemical features suggest complex mixing between rainwater, CO2-rich groundwater, steam-heated groundwater and geothermal brines, as highlighted by Principal Component Analysis (PCA). Some parameters, however, indicate widespread pollution of the aquifers from human activities. Stable isotopes analysis confirms the meteoric origin of groundwater and supports the origin of dissolved CO2 mostly from mantle degassing through deep tectonic faults. Geothermometric estimates, mostly based on quartz and Saturation Indexes geothermometers, suggest minimum reservoir temperature between 100 and 120° C.

Deformation Pattern of the Northern Sector of the Malta Escarpment (Offshore SE Sicily, Italy): Fault Dimension, Slip Prediction, and Seismotectonic Implications

Marine seismic reflection data coupled with on-land structural measurements improve our knowledge about the active deformation pattern of the northern sector of the Malta Escarpment, a bathymetric and structural discontinuity in the near-offshore of Eastern Sicily. As favourably oriented to be reactivated within the Neogene Africa–Europe convergence, it is believed that the Malta Escarpment has a significant role in the recent seismotectonic framework of the Western Ionian Basin and the Hyblean foreland domain of SE Sicily, where some of the largest and most destructive Mediterranean earthquakes are located according to available historical catalogs. Offshore seismic data along with bathymetric grids illuminate the shallow subseafloor setting and allow more accurate mapping of the seafloor expression of previously identified faults in the area. The seismic interpretation and the near-fault sediment pattern analysis provide constraints on fault 3D geometries as well as on their through-time tectonic activity, suggesting also that part of the observed deformation may have been caused by nontectonic processes. Identified faults form currently an E-dipping, roughly N–S trending, and 60 km-long extensional belt deforming the seafloor with a significant displacement amount in the Ionian offshore between Catania and Siracusa. 3-dimensional parameters of faults were then used to derive expected magnitudes and their reactivation propensity. Empirical scaling relationships and forward methods point to a high seismic potential for the detected fault as well as predict the fault slip behavior according to the field-derived differential stress. This combined analysis along with faults displacement measurements pointed out how the longest and most continuous fault could be capable of generating M > 7 seismic events, putting forward strong seismotectonic implications for the adjacent and densely populated Hyblean Plateau. The expected magnitude and the estimated recurrence time interval are compatible with those inferred for large historical earthquakes in the area even if other offshore seismic sources cannot be ruled out.

Regional Deformation and Offshore Crustal Local Faulting as Combined Processes to Explain Uplift Through Time Constrained by Investigating Differentially Uplifted Late Quaternary Paleoshorelines: The Foreland Hyblean Plateau, SE Sicily

AbstractQuaternary uplift is well documented in SE Sicily, a region prone to damaging seismic events, such as the 1693 “Val di Noto” earthquake (Mw7.4), the largest seismic event reported within the Italian Earthquake Catalogue, whose seismogenic source is still debated and, consequently, the long‐term seismic hazard is poorly understood. However, the spatial variation in the timing and rates of uplift are still debated, so it is difficult to link the dominant tectonic process(es) responsible for the uplift and the location of seismogenic sources. To better constrain the uplift rate, we have refined the dating of Late Quaternary marine terraces, using a synchronous correlation approach, driven by both published and newly obtained numerical age controls (234U/230Th dating on corals). This has allowed recalculation of uplift rates along a N‐S oriented transect within the Hyblean Plateau (HP) foreland region. Consequently, we have mapped the geometry of paleoshorelines along a coastline‐parallel transect and hence the rates of uplift. The results suggest increasing uplift rate from south to north across the HP and that uplift rates have remained constant through the Late Quaternary. This spatially changing but temporally constant uplift places constraints on the proportion of uplift produced by regional geodynamic processes versus produced by local faults, such as an offshore east dipping active normal fault. We discuss these new findings in terms of the long‐term seismic hazard for one of the most seismically active regions in the Mediterranean Basin.

New Macroseismic and Morphotectonic Constraints to Infer a Fault Model for the 9 (Mw6.1) and 11 January (Mw7.3) 1693 Earthquakes (Southeastern Sicily)

This study deals with the earthquakes which occurred in southeastern Sicily in 1693 (January 9 and 11, Mw ≈ 6.1 and 7.3, respectively). Although they have been largely studied, robust and commonly accepted seismic sources are still missing. We performed a revision of the 1693 macroseismic data and, for the fore and main-shocks, modeled new NNE-SSW trending seismic sources. In the Hyblean Plateau area, we carried out an analysis of DEM and aerial photos to map tectonic features. Then, we performed field surveys on the main faults, and a morphotectonic study with the aim of characterizing the activity of mapped faults. The study revealed the presence of three main fault systems. The first is the Palazzolo-Villasmundo Fault System, composed of NNE-SSW and NE-SW trending north-west-dipping normal faults. Some of these faults could be reactivated as reverse faults. The second is the Augusta-Floridia Fault System, made of NNW-SSE and NW-SE normal faults. The third is composed of faults which have never been mapped before: the Canicattini-Villasmundo Fault System that shows both a segmented and stepping pattern, almost N-S trending and west-dipping normal faults; some of these faults show a left-lateral movement. The morphotectonic study demonstrated that the fault systems are active. Furthermore, both strike and kinematics of the studied faults well match with the regional stress field characterized by a NW-SE σ1, which in the study area is probably both affecting some pre-existing faults, the Palazzolo-Villasmundo and the Augusta-Floridia Fault Systems, and causing the formation of new faults, the Canicattini-Villasmundo Fault System. The latter system lies across the Hyblean Plateau with a total length of 35 km and, due to its aligned segmented pattern, it can be the surface expression of a master fault that seems dividing the Hyblean Plateau in two blocks. Moreover, the Canicattini-Villasmundo Fault System well fits the southern part of the 1693 revaluated seismic sources and matches with a current alignment of shocks mainly characterized by left-lateral focal mechanisms on almost N-S fault planes. Considering the possible rupture length in depth, it could manage to release Mw ≈ 7.1 earthquakes, representing a valuable candidate source for the 1693 earthquakes.

Geological Evidence does not Support a Shallow Origin for Diamonds in Ophiolite

Geological Evidence does not Support a Shallow Origin for Diamonds in Ophiolite

Crustal structure of Sicily from modelling of gravity and magnetic anomalies

We aim at modeling the main crustal and thermal interfaces of Sicily (Italy), a key area for understanding the geological complexity at the collisional boundary between the African and European plates. To this end, we analyze the gravity and magnetic fields, integrated with information from well logs, geology, heat flow, and seismic data. In order to make the most accurate description of the crustal structure of the area, we modeled with different methodologies the carbonate and crystalline top surfaces, as well as the Moho and the Curie isotherm surface. The reconstruction of the carbonate platform is achieved using a nonlinear 3D method constrained by the available seismic and borehole data. The crystalline top, the Curie, and the Moho are instead estimated by spectral analysis of both gravity and magnetic data. The results show a complex carbonate basement and a deep crystalline crust in central Sicily, with a prominent uplift beneath the Hyblean Plateau. Maps of the Moho and the Curie isotherm surface define a variable thermal and structural setting of Sicily, with very thin crust in the southern and eastern sectors, where high heat flow is found, and deep and cold crust below the Caltanissetta Basin.

Convective Instability in Intraplate Oceanic Mantle Caused by Amphibolite-Derived Garnet-Pyroxenites—A Xenolith Perspective (Hyblean Plateau, Sicily)

Geochemical characteristics of middle ocean ridge basalts (MORBs) testify partial melting of spinel-peridotite mixed with a few amounts of garnet-pyroxenite. The latter can be considered either autochthonous products of the crystallization of partial melts in the sub-oceanic mantle or allocthonous recycled crustal materials originated in subduction contexts. Here we suggest the “autocthnous recycled” origin for garnet-pyroxenites. Such a hypothesis derives from the study of garnet-bearing pyroxenite xenoliths from the Hyblean Plateau (Sicily). These consist of Al-diopside, pyralspite-series garnet, Al-spinel and Al-rich orthopyroxene. Trace element distribution resembles an enriched MORB but lower chromium. Major-element abundances closely fit in a tschermakitic-horneblende composition. Assuming that a high-Al amphibolite was formed by hydrothermal metasomatism of a troctolitic gabbro in a slow-spreading ridge segment, a transient temperature increasing induced dehydroxilization reaction in amphiboles, giving Al-spinel-pyroxenite and vapor as products. Garnet partially replaced spinel during an isobaric cooling stage. Density measurements at room conditions on representative samples gave values in the range 3290–3380 kg m−3. In general, a density contrast ≥300 kg m−3 can give rise to convective instability, provided a sufficient large size of the heavy masses and adequate rheological conditions of the system. Garnet-pyroxenite lumps can therefore sink in the underlying mantle, imparting the “garnet geochemical signature” to newly forming basaltic magma.

A new Vs30 map for Italy based on the seismic microzonation dataset

In this study, we derive a large-scale Vs30 map for Italy starting from the global terrain geomorphological classification based on normalized slope, local convexity, and surface texture (after Iwahashi et al., 2018). The novelty of the present work is the integration of a large amount of data from the Italian seismic microzonation dataset, consisting in about 35,000 borehole logs and 11,300 Vs profiles. The results of our analysis suggest that the geomorphological classes are correlated to subsoil lithologies and Vs30 values more than surface lithological types (after Amanti et al., 2008). As already done in Japan (Matsuoka and Wakamatsu, 2006), Greece (Stewart et al., 2014), Central and Eastern North America (Parker et al., 2017), and Pacific Northwest Region of North America (Ahdi et al., 2017), we found a proxy dependence of Vs30 from slope gradient and elevation through a lognormal linear regression model for each geomorphological class. A stepwise method allowed us to give meaning and statistical robustness to the regression model dependencies. The polygons inconsistent with the Iwahashi et al. (2018) approach (e.g., Meso-Cenozoic carbonate units of Apulian block and Hyblean Plateau related to the foreland domain) were replaced with the polygons of the lithological map (Amanti et al., 2008) and the associated Vs30 lognormal average values. Therefore, a hybrid raster Vs30 map was created with a spatial resolution of 50 × 50 m. The comparison with other previous maps shows how the forecast improves in terms of both accuracy and precision. For these reasons, the new Vs30 proxy-based map for Italy based on the seismic microzonation dataset represents a useful tool for improving several applications: ShakeMaps, stochastic event based hazard map, total hazard map, assessment of coseismic instabilities, seismic risk assessment for spatially distributed emergency and resilience systems. Vs30 raster maps and supplementary material are available in the Research Data (doi:10.17632/8458tgzc73.1).

Sicilian serpentinite xenoliths containing abiotic organics with nanodiamond clusters as key model for prebiotic processes

Rock fragments from the deepest parts of a buried hydrothermal system belonging to the Mesozoic Tethys Ocean entered as xenoliths in a Miocenic diatreme, hence brought to the surface, in the Hyblean Plateau (Sicily). Some xenoliths consist of strongly serpentinized ultramafic rocks bearing blebs of abiotic organic matter, where clusters of amorphous carbon nanoparticles, including nanodiamonds, are immersed. Such an occurrence conjures up established hypotheses that diamond surfaces are suitable catalytic platforms stimulating the assemblage of complex bio-organic molecules relevant to the emergence of life on Earth. The appearance of bio-organic molecules under primitive Earth conditions is one of the major unsolved questions on the origin of life. Here we report new micro-Raman spectra on blebs of abiotic organic matter from a selected xenolith. Diamond bands were related to hydrogenated nanocrystalline diamonds, with size of nearly 1–1.6 ​nm, formed from organics at low pressures and temperatures. In particular, diamond surfaces can give rise to crystalline interfacial water layers that may have played a fundamental role in the early biosphere evolution as a good medium for rapidly transporting positive charges in the form of hydrated protons. Nowadays, proton gradients in alkaline hydrothermal vents along oceanic ridges are generally viewed as key pre-biotic factors. In general, serpentinites span the entire geological record, including prebiotic times. These hydrous ultramafic rocks often display evidence of abiotic carbon species, both organic and inorganic, including nanodiamonds, being also capable to give rise to chemiosmotic processes and proton gradients necessary to the organisms, such as the “Last Universal Common Ancestor” (LUCA), in the prebiotic Earth.

Deep Origin of the Dome‐Shaped Hyblean Plateau, Southeastern Sicily: A New Tectono‐Magmatic Model

AbstractSoutheastern Sicily is characterized by a prominent topography known as the Hyblean Plateau. It is commonly considered as a flexural bulge formed by the northwest plunging of the Hyblean‐Malta platform beneath the Sicilian Fold and Thrust Belt. However its noncylindrical shape and multiphase uplift history correlated to the Late Miocene and Plio‐Pleistocene volcanism outline a possible magmatic control on the Hyblean Plateau topographic expression. We argue, using 2‐D flexural models, that the flexural bending alone is unlikely to explain the high anomalous elevation of the Hyblean Plateau. Moreover, topographic analysis show that the Hyblean Plateau has a dome shape composed of radially tilted preserved surfaces defining individual blocks. The block edges seem to be related to deep‐seated inherited faults. Using an analogue modeling approach, we show that magmatic intrusions beneath the thick Meso‐Cenozoic sedimentary cover can reproduce the first‐order morphology of the Hyblean Plateau when a structural inheritance is imposed. Accordingly, we propose a tectono‐magmatic model that favors mafic sill intrusions as the major uplift source for the topographic anomaly. However, to explain the strong positive Bouguer anomaly, a deeper high‐density intracrustal body is needed. Moho uprising related to Mesozoic rifting or mafic lower crust underplating/intraplating since the Late Cretaceous can be evoked. The small wavelength of the topography and the deep intracrustal mass anomaly makes the lithospheric elastic stresses sufficiently high to maintain a nonisostatic state over the geological time scales.

Stratigraphic and structural reconstruction of an offshore sector of the Hyblean Foreland ramp (southern Italy)

Through the seismo-stratigraphic analysis of new high- resolution seismic data acquired along the southwestern offshore of the Hyblean Plateau, this work aims to improve the knowledge about the stratigraphic and structural setting in the marine area connecting the Hyblean Plateau Foreland to the Gela-Catania Foredeep.Two main goals have motivated the acquisition of new seismic profiles along the southern coastline of Sicily, in the Marina di Ragusa offshore:(i) to obtain a better comprehension of the Cenozoic stratigraphic and structural setting of the area, with a particular attention to the characterization of the Pliocene-Holocene sedimentary deposits and their areal distribution;(ii) to identify, in the offshore area, the possible prolongation of the main structural lineaments outcropping in the hinterland (Scicli-Ragusa-Irminio Line), and verify the presence of structures, responsible for the tectonic activity affecting the area.Our model shows that an extensional fault system, characterized by a main NE-SW orientation, affects the highly deformed Oligo-Miocene, or older, substratum, originating structural highs and down-faulted sectors. These faults are inferred to record the early history of the Scicli Line and of the polyphase kinematic evolution of the N50° oriented regional fault systems.The Gessoso-Solfifera deposits (Messinian, Late Miocene) have been recognized in several sectors of the study area, showing a very peculiar seismic facies, and occupying deep erosional channels probably resting within down-faulted sectors. This feature is in good agreement with isolated onshore areas of the Hyblean Plateau (Licodia Eubea and south Vittoria villages) where the Gessoso-Solfifera deposits are associated to normal faults, thus documenting that Messinian evaporites are not restricted to compressive tectonic setting, such as the marginal sub-basins and the thrust top mini-basins of the Appennine-Maghrebian belt.A peculiar seismic facies has been associated to the Trubi Fm., unconformably lying upon the older succession.The undeformed seismic units, onlapping the older substratum, has been associated to the post-Trubi-Holocene deposits, arranged into seven seismic units that reflect the youngest depositional evolution of the nearby Catania-Gela Foredeep. These deposits, generally represented by plane-parallel seismic facies, are in turn separated by an unconformity highlighted by an onlap termination of the yougermost terms upon the older. In some cases they are interrupted by gas rising from the deeper succession that reaches, at times, also the seafloor.

Pyrite and Organic Compounds Coexisting in Intrusive Mafic Xenoliths (Hyblean Plateau, Sicily): Implications for Subsurface Abiogenesis.

Pyrite and organic matter closely coexist in some hydrothermally-altered gabbroic xenoliths from the Hyblean Plateau, Sicily. The representative sample consists of plagioclase, Fe-oxides, clinopyroxene, pyrite and minor amounts of many other minerals. Plagioclase displays incipient albitization, clinopyroxene is deeply corroded. Pyrite grains are widely replaced by spongy-textured magnetite, which locally hosts Ca-(and Fe-)sulfate micrograins and blebs of condensed organic matter. Whole-rock trace element distribution evidences that incompatible elements, particularly the fluid-mobile Ba, U and Pb, are significantly enriched with respect to N-MORB values. The mineralogical and geochemical characteristics of the sample, and its U-Pb zircon age of 216.9 ± 6.7 MA, conform to the xenolith-based viewpoint that the unexposed Hyblean basement is a relict of the Ionian Tethys lithospheric domain, mostly consisting of abyssal-type serpentinized peridotites with small gabbroic intrusions. Circulating hydrothermal fluids there favored the formation of hydrocarbons trough Fischer-Tropsch-type organic synthesis, giving also rise to sulfidization episodes. Subsequent variations in temperature and redox conditions of the system induced partial de-sulfidization, Fe-oxides precipitation and sulfate-forming reactions, also promoting poly-condensation and aromatization of the already-formed hydrocarbons. Here we show organic matter adhering to a crystal face of a microscopic pyrite grain. Pyrite surfaces, as abiotic analogues of enzymes, can adsorb and concentrate organic molecules, also acting as catalysts for a broad range of proto-biochemical reactions. The present data therefore may support established abiogenesis models suggesting that pyrite surfaces carried out primitive metabolic cycles in suitable environments of the early Earth, such as endolithic recesses in mafic rocks permeated by hydrothermal fluids.

Morphometric evidences of recent tectonic deformation along the southeastern margin of the Hyblean Plateau (SE-Sicily, Italy)

The present work focuses on the tectonic characterization of the southeastern portion of the Hyblean Plateau (SE-Sicily, Italy). Along the southeastern margin of this raised crustal block, a clear recent antiformal deformation, coupled with diffuse landscape rejuvenation, affects the summit surface. Many studies, using merely qualitative geomorphological approach, refer the recent morphotectonic evolution of this region to motion along an active border fault, located at the base of the well-developed, arc-shaped Avola mountain front. This paper provides new insights resulting from the morphometric analysis across the Avola region, in order to detail on the relationships between the landscape geomorphic unsteadiness and the long-term tectonic deformation. We perform both drainage system and relief investigations, consisting of the exploration of different geomorphic indices (e.g. hypsometric integral, topographic relief and dissection, SL index, ksn), long-profile analysis, marine terraces age model definition, field-based geomorphological and structural surveys. The results and the spatial distribution of morphometric indexes evidence the occurrence of two incipient NNE trending en-échelon fault segments, here named Cassibile-Noto Fault, responsible for the relief building along the southeastern border of the Hyblean Plateau. The northern fault segment directly controls the northern portion of the Avola mountain front, whereas the southern segment diverges from the main scarp, cutting through the low-standing areas of the coastal plain. In addition, the centrifugal arrangement of fluvial captures and the half-elliptical envelope of the downstream projections of coeval paleo-long profiles, as well as the distribution of Pleistocene marine terraces, well evidence the long-term WNW-ESE-trending low-amplitude bow-shaped deformation affecting the footwall of the Cassibile-Noto normal fault. We relate this convex-upward trend to the Late Pleistocene (<125 ka) tectonic deformation cumulated, at rate of ~0.80 ± 0.05 mm/a, along the active fault. This incipient tectonic structure represents an extensional tectonic boundary that accommodates, together with the Ispica Fault, the active NW-ward motion of the entire eastern sector of the Hyblean Plateau. Overall, the proposed updating of the tectonic setting of the study area, framed in the regional geodynamic picture of the eastern Sicily, would contribute to define a more suitable geological risk assessment of the region.

The evolution of the mantle source beneath Mt. Etna (Sicily, Italy): from the 600 ka tholeiites to the recent trachybasaltic magmas

ABSTRACTThe spatial/temporal proximity of Mt. Etna to the Hyblean Plateau and the Aeolian slab makes the discussion on the nature of its mantle source/s extremely controversial. In this study, a detailed geochemical overview of the entire Mt. Etna evolutionary sequence and a comparison with the magmatism of the Hyblean Plateau was proposed to: (i) simulate the composition of Mt. Etna tholeiitic to alkaline primitive magmas in equilibrium with a fertile mantle source; (ii) model the nature, composition and evolution of the mantle source from the tholeiitic stage (600 ka) to present magmatism. According to our simulations, two amphibole + phlogopite-bearing spinel lherzolite sources are able to explain the wide range of Etnean primary magmas. The enrichment in LILE, 87Sr/86Sr, Rb and H2O of the magmas emitted after 1971 (but also discontinuously generated in both historic and prehistoric times) are caused by different melting proportions of amphibole and phlogopite in a modally and compositionally homogeneous mantle domain, with melting degrees analogous to those required to produce magmas erupted prior to 1971. The behaviour of the hydrous phases during melting could be ascribed to a variable H2O/CO2 activity in the mantle source, in turn related to the heat/fluxes supply from the asthenospheric upwelling beneath Mt. Etna. All these considerations, strengthened by numerical models, are then merged to review the complex Pliocene/Lower Pleistocene to present day’s geodynamic evolution of eastern Sicily.

Assessment of the Geochemical Potential in a Complex Tectonic Environment of South-East Sicily: New Insights From Hydrochemical Data

We analyzed a large dataset (143 water sampling sites, 22 variables) of chemical parameters in local groundwaters from the south-east sector of Sicily, namely the Hyblean plateau, in order to set an original evaluation of its geothermal potential using applied geochemistry. The area was affected by volcanism until about 1.4 Ma. Today, though no active volcanism occurs, it is site of surface gas manifestations of focused degassing to which a mantle source has been attributed. We identified and thence selected the most promising sites (water springs and wells) based both on their main geochemical characteristics and on their calculated equilibrium temperature (resulting in the range between 50 and 140 °C). We then applied Principal Component Analysis (PCA) to this restricted dataset and we were able to discriminate between different sources of solutes, both natural and anthropogenic. Finally, we mapped the factor scores obtained from PCA and we focused on those likely related with geothermal conditions in order to highlight the areas with the highest geothermal potential.