Mediterranean Ridge Research Articles

Source rock potential and spatial distribution of the stratigraphic formations in the central Mediterranean Ridge: Evidence from mud volcanic deposits and 2D seismic data

Due to the lack of deep wells in the broader region, the mud volcanic deposits (mud breccia) are the only source of direct information for the deep stratigraphic units of the Mediterranean Ridge (MR), in the eastern Mediterranean. The study of this material, combined with the available seismic data, can improve the geological understanding of this frontier exploration area.In this paper, biostratigraphic and geochemical studies are performed on mud breccia deposits from five Mud Volcanoes (MVs) in the central MR, aiming to define the sediments’ stratigraphic origin and assess the source rock potential of the individual formations. In addition, regional seismic data is used to reveal the spatial distribution of the major lithostratigraphic formations in the subsurface.Results indicate an Eocene-Miocene origin for the mud breccia of Gelendzhik, Nice, Moscow and Dublin MVs, whereas a Paleocene (?) and Cretaceous origin is suggested for the Toronto MV deposits. Most clasts represent hemipelagic mudstones/marlstones. Regarding the source rock potential of the area, it is considered that: (a) nine clasts of Miocene, Eocene and undetermined age, reflect the presence of immature and early mature, gas-prone source rocks of poor to moderate potential; (b) a small clast discovered in the matrix of Dublin MV originates from an excellent quality oil-prone source rock; and (c) the discovered solid hydrocarbons and oil droplets point to an active petroleum system in the region.Seismic interpretation defines the spatial distribution of the Post-Evaporite, Evaporite and Pre-Evaporite formations. The burial depth of the Pre-Evaporite formation (source layers of MV deposits) significantly varies from 20 to 4970 m inside the study area and is largely dependent on Evaporite thickness.

Pore water signatures and gas hydrates occurrence in and around the Olimpi mud volcano field, south of Crete

Mud volcanoes in the Mediterranean Sea have been subject of scientific research since the 1970s and contributed to the understanding of these seafloor features and their role in the subduction budgets worldwide. Recently, the need to better characterize the connection of these mud volcanoes with the deeper lithologies of the accretionary prism and its implications led to expedition POS410 (2011) and SO278 (2020). During these expeditions, mud volcanoes which had been investigated in ODP Leg 160 (1996) were resampled and complemented with new sites along the Mediterranean Ridge accretionary complex. We present pore water data from six mud volcanoes and two brine pools in and around the Olimpi Mud Volcano Field (OMVF). The data highlight strong depletion in Cl (<200 mM), Na (∼200 mM), Mg and K (with concentrations ∼0 mM) and striking water isotope ratios (δ18O of +9.79‰ V-SMOW and δD of −26.33‰ V-SMOW), indicating dehydration of clay minerals at depth. At five locations, the interstitial waters are characterized by extremely high salinities (Cl > 5000 mM and Na >6500 mM), therefore drastically expanding the previous reports of highly saline pore waters in the OMVF. The measurements further reveal that Gelendzhik mud volcano, located in the western part of the OMVF along a major strike-slip fault, shows an unusual pore water downcore profile and its water isotopes signature differ strongly from the other structures (δ18O of +13.63‰ and δD of +1.83‰). Upon further investigation through XRF scans and hydrates stability calculations we tied the anomalous low salinity values of the Gelendzhik MV pore waters results from the presence of gas hydrates in the sediments. This is the first, indirect evidence of gas hydrates in the OMVF, several years after this hypothesis was formulated by De Lange and Brumsack (1998) and then quickly discarded.

Marine Geophysical Data and Its Application to Assessment of Crustal Structure along the Northern Egyptian Passive Continental Margin

The Egyptian passive continental margin is considered a remarkable geologic setting, in addition to being an occupation and manufacturing locality in north Egypt. This work used accessible potential field data, such as marine gravity data, to provide a wider vision of the potential field of the area under investigation. The results of the two-dimensional (2D) gravity modelling revealed a good agreement between the modelled gravity and observed gravity fields, including known regional structures found in the investigated area. The findings revealed that crustal modelling was affected by the tectonic structure and the huge thickness of sedimentary layers, which act as barriers to the crystal crust. The results revealed that the crustal thickness and density are spread among the deposited layer and the inferior mantle in the Moho range. Furthermore, it was found that the basement extent lies nearly 6–9 km lower in the northern Egyptian coastline to approximately 13 km under the Herodotus abyssal plain. Moreover, it was shown that the thickness of the sedimentary layers deposit increases near the East Mediterranean Ridge.

Late Cenozoic Evolution and Present Tectonic Setting of the Aegean–Hellenic Arc

The Aegean–Hellenic arc is a deformed sector of a long heterogeneous orogenic system (Tethyan belt), constituted by an inner old metamorphic crystalline core flanked by younger chains of European and African affinity, running from the Anatolian to the Pelagonian zones. Due to the convergence between the Arabian promontory and the Eurasian continental domain, the Anatolian sector of that belt has undergone a westward extrusion, accommodated by oroclinal bending, at the expense of the surrounding low buoyancy domains. Since the late Miocene, when the Aegean Tethyan belt collided with the Adriatic continental promontory, the southward bowing of the Aegean–Hellenic sector accelerated, leading to the consumption of the Levantine and Ionian oceanic domains and to the formation of the Mediterranean Ridge accretionary complex. The peculiar distribution of extensional and compressional deformation in the Aegean zone has mainly been influenced by the different rheological behaviours of the mainly ductile inner core (Cyclades arc) and of the mainly brittle outer belt (Hellenic arc). The bowing of the inner belt developed without involving any major fragmentation, whereas the outer brittle belt underwent a major break in its most curved sector, which led to the separation of the eastern (Crete–Rhodes) and western (Peloponnesus) Hellenic sectors. After separation, these structures underwent different shortening patterns, respectively driven by the convergence between southwestern Anatolia and the Libyan continental promontory (Crete–Rhodes) and by the convergence between the Cycladic Arc and the Adriatic continental domain (Peloponnesus). A discussion is given about the compatibility of the observed deformation pattern with the main alternative geodynamic interpretations and with the Nubia–Eurasia relative motions so far proposed.

Combined qualitative and quantitative regional interpretation of the thermal results of magnetic data in the Eastern Mediterranean Region

The study presents thermal structure and active-passive tectonic parts of the Eastern Mediterranean Region. Curie point depth, heat flow map, Moho depth and sediment thickness are used for interpretation. The levelled magnetic data that obtained from the World Digital Magnetic Anomaly Map (WDMAM) is used. The magnetic anomaly is divided into 39 zones for Curie point depth estimation. The Curie point depth values are calculated into Fourier domain. Then heat flow map is generated. The estimated Curie point depth values are ranging from 4.5 km to 25 km. Furthermore, heat flow values are between 55 mW/m2 and 277 mW/m2. Moho depth, Moho depth-Curie depth and sediment thickness are used for constraining interpretation. Interpretation indicates that the northern and southern parts of the Mediterranean Ridge present different thermal characteristics.

Pre-Messinian Deposits of the Mediterranean Ridge: Biostratigraphic and Geochemical Evidence from the Olimpi Mud Volcano Field

This study presents the results derived from micropaleontological and organic geochemical analyses of mud breccia samples obtained (through gravity coring) from five mud volcanoes (Gelendzhik, Heraklion, Moscow, Milano, Leipzig) located at the Olimpi mud volcano field on the Mediterranean Ridge accretionary complex. A thorough calcareous nannofossil semi-quantitative analysis was performed to determine the biostratigraphic assignment of the deep-seated source strata. Mudstone/shale clasts of different stratigraphic levels were identified and assigned to the Miocene nannofossil biozones CNM10, CNM8–9, CNM7, CNM6–7, and Oligocene CNO4/CNO5. A single mudstone clast from the Gelendzhik plateau, assigned to the biozone CNM10, demonstrated unique micropaleontological and geochemical characteristics, suggesting a sapropelic origin. Subsequently, the total organic carbon (TOC) content and thermal maturity of the collected mud breccias was evaluated using the Rock-Eval pyrolysis technique, and their oil and gas potential was estimated. The pyrolyzed sediments were both organic rich and organic poor (TOC &gt;0.5% or &lt;0.5%, respectively), with their organic matter showing characteristics of the type III kerogen that consists of adequate hydrogen to be gas generative, but insufficient hydrogen to be oil prone. However, the organic matter of the late Serravallian (CNM10) sapropelic mudstone was found to consist of a mixed type II/III kerogen, implying an oil-prone source rock.

Analysis of Ocean Bottom Pressure Anomalies and Seismic Activities in the MedRidge Zone

The Mediterranean Ridge accretionary complex (MAC) is a product of the convergence of Africa–Europe–Aegean plates. As a result, the region exhibits a continuous mass change (horizontal/vertical movements) that generates earthquakes. Over the last 50 years, approximately 430 earthquakes with M ≥ 5, including 36 M ≥ 6 earthquakes, have been recorded in the region. This study aims to link the ocean bottom deformations manifested through ocean bottom pressure variations with the earthquakes’ time series. To this end, we investigated the time series of the ocean bottom pressure (OBP) anomalies derived from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) satellite missions. The OBP time series comprises a decreasing trend in addition to 1.02, 1.52, 4.27, and 10.66-year periodic components, which can be explained by atmosphere, oceans, and hydrosphere (AOH) processes, the Earth’s pole movement, solar activity, and core–mantle coupling. It can be inferred from the results that the OBP anomalies time series/mass change is linked to a rising trend and periods in the earthquakes’ energy time series. Based on this preliminary work, ocean-bottom pressure variation appears to be a promising lead for further research.

Utilisation of GNSS and seismicity for monitoring crustal deformation of the Northern part of the Nile Delta, Egypt

ABSTRACT Nile Delta is one of the most significant regions in Egypt. The offshore Nile Delta is located in a complex structural area of Mediterranean Ridge, which is an important wrench fault separating the Arabian plate to the African Plate. This study aims at monitoring the recent crustal deformation and velocity of the Northern delta beside its connection to the seismicity and tectonic activities of the African plate using the permanent GNNS stations distributed at the Egyptian Delta and Europe. The available GNNS data (2009-2019) were analysed utilising the Bernese 5.2 software, to identify the velocity vectors, and the principal segments of crustal strains along the investigated region. The results show that the average absolute velocity ranges between 14 and 22 mm/yr with an accuracy of 3 mm/yr, and the residual velocity is estimated at 0.51 to 4.98 mm/yr with an accuracy of 2.5 mm/yr. Furthermore, the rate of the gathered strains in the northern Nile Delta was recently changed from low to moderate. The outcomes show that the area under investigation suffers from irregular seismic activity related to the crustal movements, which occurred along with the major fault trends in the region.

Preliminary results based on geochemical sedimentary constraints on the hydrocarbon potential and depositional environment of a Messinian sub-salt mixed siliciclastic-carbonate succession onshore Crete (Plouti section, eastern Mediterranean)

This study details new geochemical analysis from an outcrop in Crete to improve understanding of the hydrocarbon potential of the southern margin of the Hellenic Arc along the continental convergent zone of the central Mediterranean Ridge. Seventeen samples were collected from the Late Miocene sub-salt sedimentary succession of Plouti section in central Crete and were studied in terms of their organic geochemical features using Rock-Eval VI pyrolysis. Results of this investigation revealed intervals with sufficient organic material of good enough quality and quantity to be considered as potential source rocks. The obtained data generally present poor to fair and/or good in some cases hydrocarbon generation potential. The TOC values range from 0.03 to 1.99%, with an average fair (2.1 mg HC/g rock) hydrocarbon potential. A Type III kerogen was identified, indicating a terrestrial origin organic matter. T max and Production Index values suggest that the most promising parts of the section (organic-rich sediments) are immature with respect to oil generation and have not experienced high temperature during burial. Overall, the present study offers the opportunity to advance our understanding on the hydrocarbon potential onshore Crete and further investigate hydrocarbon prospectivity in the adjoining area, and particularly, the Greek part of the Mediterranean Ridge, a region with crucial economic and strategic importance.

FORAMINIFERI PLANCTONICI ED OSCILLAZIONI CLIMATICHE NELLA CAROTA BAN 84-27 (MEDITERRANEO ORIENTALE)

Planktonic foraminifera from Core BAN 84-27, recovered from a Mediterranean Ridge site located north of the Katia Basin (Eastern Mediterranean) were quantitatively investigated. The sediments are Late Pleistocene to Holocene in age; the sequence of sapropels, from S-1 to S-9, is almost complete, except S-2 and S4, which are missing and provides the lithostratigraphic framework. One tephra layer (Y-5) was identified.&#x0D; Peaks of abundance of Neogloboquadrina eceri were recognized in sapropels S-6 and S-8; these findings, recorded also in the reference cores, support the peculiarity of S-6 and S-8, which were deposited during cold intervals.A climatic curve, based on the relative abundance of climatically significant planktonic foraminifera, was constructed; its warm and cold peaks are correlatable to the fluctuations recorded in other Eastern Mediterranean cores (Core EASTW 29, Cobblestone Area 3; Core EASTW 6 and 45, Cobblestone Area 4; Cores KS-09 and RC9-181). The maximum diameter of Orbulina universa increases in accordance with relative abundance of climatically warmer species. This simple parameter seems to be an useful tool for paleoclimatic interpretations of Quaternary sediments, with larger sizes correlatable to warm intervals.&#x0D; Peaks of abundance of Neogloboquadrina eggeri were recognized in sapropels S-6 and S-8; these findings, recorded also in the reference cores, support the peculiarity of S-6 and S-8, which were deposited during cold intervals.&#x0D; The distribution of planktonic gastropods (Thecosomata Euthecosomata and Heteropoda) was investigated and correlated with the foraminiferal curve. The paleoclimatic value of pteropods is also evident in Core BAN 84-27: well diversified assemblages, characterized by a great abundance of warm water species (Limacina inflata), were observed in sapropels S-1 and S-9 and in other warm episodes. Poor assemblages, with sparse specimens of cold water species (L. retroversa) are present in cold episodes and in sapropel S-8. Intervals correlative to isotopic stages 1 to 9, substages 5a, 5c, 5e and substages 7a, 7c, 7d could be recognized. Moreover, climatic zone Z, Y, X, W and V (subzones V" and V') were identified. Average sediment accumulation rate is approximately 1.5 cm/1000 yr. Core BAN 84-27 represents the sedimentary expression of the last 320,000 yr in a low sedimentation rate area.

Assessment of the eruptive activity and identification of the mud breccia's source in the Olimpi mud volcano field, Eastern Mediterranean

Even though the intensity and frequency of the eruptive episodes of deep-sea mud volcanoes (MVs) substantially regulate the methane fluxes into the hydrosphere and the development of the near-seafloor sulfate zone that affects the position of the gas hydrate stability zone, these factors are not yet adequately investigated. Moreover, the evaluation of the eruptive sediment's thermal maturity may provide solid documentation of the petroleum generation potential in high depths below seafloor (bsf). Hence, the present study, through the integration of sedimentary facies analysis with hydrocarbon biomarker analysis (based on the concentrations of long-chain (C25–C35) n-alkanes, hopanes and steranes), supported by swath bathymetry data, examined five sediment cores recovered from the Gelendzhik, Moscow, Milano, Leipzig and Heraklion MVs of the Olimpi mud volcano field (OMVF) on the central Mediterranean Ridge. The main objective of this investigation was to assess the ‘modern’ eruptive activity in the OMVF and identify the mud breccia's origin and mobilization depth (based on its maturity level), and the ages of the source beds. Among the studied MVs, Milano, Leipzig and Heraklion appear ‘recently’ active, while Moscow perhaps remains in dormancy for at least one century. The eruptive activity in the OMVF seems to be, generally, vigorous and persistent, while it is linked with several source beds of variable stratigraphy or environmental condition. The multiple eruptive episodes, occurring as uninterrupted events or via pulses, create conditions that perhaps favour high releases of methane into the water column as well as the growth of the gas hydrate phase near the seafloor. The identified ‘modern’ mudflows appear thermally immature for oil generation, while they most probably originate from terrestrial source beds located not deeper than 2 km bsf. A Messinian age could be suggested for the principal sources of the very soft to soft mud breccias of the OMVF, while stratigraphic horizons of Early-Middle Miocene might be proposed as the likely major sources for the firm to very stiff mud breccias of the area.

The discovery of Lake Hephaestus, the youngest athalassohaline deep-sea formation on Earth

Hydrated, magnesium-rich minerals and subglacial brines exist on the martian surface, so the habitability of high-Mg2+ environments on Earth has extraterrestrial (as well as terrestrial) implications. Here, we report the discovery of a MgCl2-dominated (4.72 M) brine lake on the floor of the Mediterranean Ridge that underlies a 3500-m water column, and name it Lake Hephaestus. Stable isotope analyses indicated that the Hephaestus brine is derived from interactions between ancient bishofite-enriched evaporites and subsurface fluids. Analyses of sediment pore waters indicated that the Hephaestus depression had contained the MgCl2 brine for a remarkably short period; only 700 years. Lake Hephaestus is, therefore, the youngest among currently known submarine athalassohaline brine lakes on Earth. Due to its biologically hostile properties (low water-activity and extreme chaotropicity), the Hephaestus brine is devoid of life. By contrast, the seawater-Hephaestus brine interface has been shown to act as refuge for extremely halophilic and magnesium-adapted stratified communities of microbes, even at MgCl2 concentrations that approach the water-activity limit for life (0.653).

Mode conversion noise attenuation, modelling and removal: case studies from Cyprus and Egypt

The wavefront from a source that strikes an acoustic impedance contrast separates into four variables: transmitted and reflected compressional waves (P-wave) and transmitted and reflected shear waves (S-wave). Converted waves are those whose mode changes at the interface and can be recorded in a marine environment in the presence of large velocity contrasts. The difference in acoustic velocities at the boundary means that in high contrast media the distinction between compressional and shear velocities across the boundary is small; shear waves are not as refracted as compressional waves and can be recorded as partially converted reflected energy. The eastern Mediterranean contains two major sedimentary basins, the Levantine and Herodotus (see Figure 1). They have shared depositional regimes and therefore contain similar sedimentary sequences. The Levantine Basin sits offshore Cyprus, Israel, Palestine and Lebanon, and was formed by prolonged phased rifting, with subsequent subsidence and loading by deltaic sediments (Gradmann et al., 2005; Gardosh and Druckman, 2006). It forms a northeast-oriented depression about 2 km deep and contains more than 14 km of Mesozoic and Cenozoic sequences that include up to 2 km of Messinian salt (Druckman et al., 1995; Ben-Avraham et al., 2002; Netzeband et al., 2006). The local reservoirs include both Cretaceous and Jurassic sandstones and limestones, with older potential reservoirs in the Triassic sandstones. Shales and marls of Paleogene, Neogene, Cretaceous and Jurassic, along with Messinian salt and Triassic evaporites all form local seals (Roberts and Peace, 2007) in plays of a both stratigraphic and structural nature. The Herodotus Basin is a northeast trending 3 km deep depression, and represents a slab of the Early Mesozoic Neo-Tethys Ocean (see Figures 1 and 2). The basin is bounded on the north by the Mediterranean Ridge; on the northeast by the west portion of the Cyprus Arc and on the south by the Nile Delta cone. The Eratosthenes Seamount (ESM), a fragment of continental crust (Robertson, 1998), forms the eastern limit of the Herodotus Basin, and additionally delineates the boundary between the cone of the Nile Delta, the Herodotus Basin, and the Levant Basin. The Herodotus Basin itself contains up to 7 km of Mesozoic–Cenozoic sediment (Voogd and Truffert, 1992; Garfunkel, 1998), and is overlain by up to 3 km of Messinian salt (Garfunkel, 1998; Aal et al., 2000; Loncke et al., 2006).

Deformation patterns in the southwestern part of the Mediterranean Ridge (South Matapan Trench, Western Greece)

Seismic reflection data and bathymetry analyses, together with geological information, are combined in the present work to identify seabed structural deformation and crustal structure in the Western Mediterranean Ridge (the backstop and the South Matapan Trench). As a first step, we apply bathymetric data and state of art methods of pattern recognition to automatically detect seabed lineaments, which are possibly related to the presence of tectonic structures (faults). The resulting pattern is tied to seismic reflection data, further assisting in the construction of a stratigraphic and structural model for this part of the Mediterranean Ridge. Structural elements and stratigraphic units in the final model are estimated based on: (a) the detected lineaments on the seabed, (b) the distribution of the interval velocities and the presence of velocity inversions, (c) the continuity and the amplitudes of the seismic reflections, the seismic structure of the units and (d) well and stratigraphic data as well as the main tectonic structures from the nearest onshore areas. Seabed morphology in the study area is probably related with the past and recent tectonics movements that result from African and European plates’ convergence. Backthrusts and reverse faults, flower structures and deep normal faults are among the most important extensional/compressional structures interpreted in the study area.

Gravity‐Driven Deposits in an Active Margin (Ionian Sea) Over the Last 330,000 Years

AbstractIn the Ionian Sea, the subduction of the Nubia plate underneath the Eurasia plate leads to an important sediment remobilization on the Calabrian Arc and the Mediterranean Ridge. These events are often associated with earthquakes and tsunamis. In this study, we analyze gravity‐driven deposits in order to establish their recurrence time on the Calabrian Arc and the western Mediterranean Ridge. Four gravity cores collected on ridges and slope basins of accretionary prisms record turbidites, megaturbidites, slumping and micro‐faults over the last 330,000 years. These turbidites were dated by correlation with a hemipelagic core with a multi‐proxy approach: radiometric dating, δ18O, b* colour curve, sapropels and tephrochronology. The origin of the gravity‐driven deposits was studied with a sedimentary approach: grain‐size, lithology, thin section, geochemistry of volcanic glass. The results suggest three periods of presence/absence of gravity‐driven deposits: a first on the western lobe of the Calabrian Arc between 330,000 and 250,000 years, a second between 120,000 years and present day on the eastern lobe of the Calabrian Arc and over the last 60,000 years on the western lobe, and a third on the Mediterranean Ridge over the last 37,000 years. Return times for gravity‐driven deposits are around 1,000 years during the most important record periods. The turbidite activity also highlights the presence of volcaniclastic turbidites that seems to be link to the Etna changing morphology over the last 320,000 years.

GEOPHYSICAL STUDIES AND TECTONISM OF THE HELLENIDES

By constraining gravity modelling by Deep Seismic Soundings (DSS) and the Bouguer gravity field of Greece a 3-D density-velocity model of the crust and upper mantle was developed. It was shown that in the north Aegean Trough and the Thermaikos Basins the sediments exceed 7 km in thickness. The basins along the western Hellenides and the coastal regions of western Greece are filled with sediments of up to 10 km thickness, including the Prepulia and Alpine metamorphic limestones. The thickest sedimentary series however, were mapped offshore southwest and southeast of Crete and are of the order of 12 to 14 km. The crust along western Greece and the Peloponnese ranges between 42 and 32 km thickness while the Aegean region is floored by a stretched continental crust varying between 24 to 26 km in the north and eastern parts and thins to only 16 km at the central Cretan Sea. The upper mantle below the Aegean Sea is occupied by a lithothermal system of low density (3.25 gr/cm³) and Vp velocity (7.7 km/s), which is associated with the subducted Ionian lithosphere below the Aegean Sea. Isostasy is generally maintained at crustal and subcrustal levels except for the compressional domain of western Greece and the transition between the Mediterranean Ridge and the continental backstop. The isotherms computed from the Heat Flow density data and the density model showed a significant uplift of the temperature field below the Aegean domain. The 400°C isotherm is encountered at less than 10 Km depth. Tectonic deformation is controlled by dextral wrench faulting in the Aegean domain, while western Greece is dominated by compression and crustal shortening. Strike-slip and normal faults accommodate the western Hellenic thrusts and the westwards sliding of the Alpine napes, using the Triassic evaporates as lubricants.

Active tectonics of the Calabrian subduction revealed by new multi-beam bathymetric data and high-resolution seismic profiles in the Ionian Sea (Central Mediterranean)

The detailed morphology and internal structure of the Calabrian accretionary wedge and adjacent Eastern Sicily margin are imaged in unprecedented detail by a combined dataset of multi-beam bathymetry and high-resolution seismic profiles. The bathymetric data represent the results of 6 recent marine geophysical surveys since 2010 as well as a compilation of earlier surveys presented as a 2 arc-sec (60 m) grid. Several distinct morpho-tectonic provinces are identified including: the deeply incised Malta–Hyblean Escarpment, numerous submarine canyons, broad regions of relatively flat seafloor dominated by fields of sediment waves, the gently undulating anticlinal fold-and-thrust belts of the external Calabrian accretionary wedge and the adjacent portion of the Western Mediterranean Ridge. The Calabrian arc can be divided into 4 domains (from SE to NW): 1) the undeformed Ionian abyssal plain, 2) the external evaporitic wedge, 3) the internal clastic wedge, 4) the Calabrian backstop (Variscan crystalline basement). The Calabrian accretionary wedge can also be divided laterally into two major lobes, the NE- and the SW lobes, and two minor lobes. The kinematics of the limit between the two major lobes is investigated and shown to be sinistral in the external (evaporitic) wedge. A network of radial slip lines within the southernmost external wedge unequivocally demonstrate ongoing dextral displacement of a rigid indenter (representing the corner of the clastic wedge) into the evaporitic wedge thereby confirming the geodynamic model of an active lateral slab tear fault here off eastern Sicily. The slab tear produces a series of major sub-parallel dextral strike-slip faults offshore Mt. Etna and south of the Straits of Messina consistent with the relative motions between Calabria and the Peloritan domain (NE Sicily). Abundant strike-slip faulting, and wide-spread folding and thrusting observed throughout the entire accretionary wedge, indicate regional shortening between the Ionian abyssal plain (foreland) and the Calabrian–Peloritan backstop caused by active subduction.

Boron desorption and fractionation in Subduction Zone Fore Arcs: Implications for the sources and transport of deep fluids

AbstractAt many subduction zones, pore water geochemical anomalies at seafloor seeps and in shallow boreholes indicate fluid flow and chemical transport from depths of several kilometers. Identifying the source regions for these fluids is essential toward quantifying flow pathways and volatile fluxes through fore arcs, and in understanding their connection to the loci of excess pore pressure at depth. Here we develop a model to track the coupled effects of boron desorption, smectite dehydration, and progressive consolidation within sediment at the top of the subducting slab, where such deep fluid signals likely originate. Our analysis demonstrates that the relative timing of heating and consolidation is a dominant control on pore water composition. For cold slabs, pore water freshening is maximized because dehydration releases bound water into low porosity sediment, whereas boron concentrations and isotopic signatures are modest because desorption is strongly sensitive to temperature and is only partially complete. For warmer slabs, freshening is smaller, because dehydration occurs earlier and into larger porosities, but the boron signatures are larger. The former scenario is typical of nonaccretionary margins where insulating sediment on the subducting plate is commonly thin. This result provides a quantitative explanation for the global observation that signatures of deeply sourced fluids are generally strongest at nonaccretionary margins. Application of our multitracer approach to the Costa Rica, N. Japan, N. Barbados, and Mediterranean Ridge subduction zones illustrates that desorption and dehydration are viable explanations for observed geochemical signals, and suggest updip fluid migration from these source regions over tens of km.

Slab segmentation controls the interplate slip motion in the SW Hellenic subduction: New insight from the 2008Mw 6.8 Methoni interplate earthquake

AbstractWe present an integrated approach of the seismic structure and activity along the offshore SW Hellenic subduction from combined observations of marine and land seismic stations. Our imaging of the slab top topography from teleseismic receiver function analysis at ocean bottom seismometers supports a trenchward continuation of the along‐dip slab faults beneath the Peloponnesus. We further show that their morphostructural control accounts for the backstepping of the thrust contact of the Mediterranean Ridge accretionary wedge over the upper plate. Local seismic activity offshore SW Peloponnesus constrained by ocean bottom seismometer observations reveals a correlation with specific features of the forearc: the Matapan Troughs. We study theMw 6.8 14.02.2008 interplate earthquake offshore SW Peloponnesus and show that its nucleation, rupture zone, and aftershocks sequence are confined to one slab panel between two adjacent along‐dip faults and are thus controlled by not only the offshore slab top segmentation but also the upper plate sea‐bottom morphology.

Did the A.D. 365 Crete earthquake/tsunami trigger synchronous giant turbidity currents in the Mediterranean Sea?

Research Article| March 01, 2016 Did the A.D. 365 Crete earthquake/tsunami trigger synchronous giant turbidity currents in the Mediterranean Sea? Alina Polonia; Alina Polonia 1ISMAR-CNR (Istituto di Scienze Marine, Consiglio Nazionale delle Ricerche), Via Gobetti 101, 40129 Bologna, Italy Search for other works by this author on: GSW Google Scholar Stefano Claudio Vaiani; Stefano Claudio Vaiani 2Dipartimento di Scienze Biologiche, Geologiche e Ambientali, University of Bologna, Via Zamboni 67, 40127 Bologna, Italy Search for other works by this author on: GSW Google Scholar Gert J. de Lange Gert J. de Lange 3Department of Earth Sciences–Geochemistry, Faculty of Geosciences, Utrecht University, Princetonplein 9, 3584 CD Utrecht, Netherlands Search for other works by this author on: GSW Google Scholar Author and Article Information Alina Polonia 1ISMAR-CNR (Istituto di Scienze Marine, Consiglio Nazionale delle Ricerche), Via Gobetti 101, 40129 Bologna, Italy Stefano Claudio Vaiani 2Dipartimento di Scienze Biologiche, Geologiche e Ambientali, University of Bologna, Via Zamboni 67, 40127 Bologna, Italy Gert J. de Lange 3Department of Earth Sciences–Geochemistry, Faculty of Geosciences, Utrecht University, Princetonplein 9, 3584 CD Utrecht, Netherlands *E-mails: alina.polonia@ismar.cnr.it; stefano.vaiani@unibo.it; g.j.delange@uu.nl Publisher: Geological Society of America Received: 06 Nov 2015 Revision Received: 08 Jan 2016 Accepted: 13 Jan 2016 First Online: 09 Mar 2017 Online Issn: 1943-2682 Print Issn: 0091-7613 © 2016 Geological Society of America Geology (2016) 44 (3): 191–194. https://doi.org/10.1130/G37486.1 Article history Received: 06 Nov 2015 Revision Received: 08 Jan 2016 Accepted: 13 Jan 2016 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Alina Polonia, Stefano Claudio Vaiani, Gert J. de Lange; Did the A.D. 365 Crete earthquake/tsunami trigger synchronous giant turbidity currents in the Mediterranean Sea?. Geology 2016;; 44 (3): 191–194. doi: https://doi.org/10.1130/G37486.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract In the Ionian Sea, one of the most seismically active regions in the Mediterranean, subduction is commonly associated with uplift of coastal mountains, enhanced erosion, and seismic activity along the Calabrian Arc and Hellenic Arc, thus potentially resulting in repetitive mass failures. Some of the turbidites observed in the deep basins are thick and prominent on seismic records because of the acoustic transparency of their upper structureless mud layer. Our high-resolution study of the most recent of these megabeds, the homogenite Augias turbidite (HAT), provides key proxies to identify pelagic sediments deposited following the catastrophic causative event. Radiometric dating in an area >150,000 km2 indicates that the different Mediterranean so-called homogenite deposits are in fact synchronous and were deposited during a single basin-wide event within the time window A.D. 364–415. Unlike interpretations that relate this turbidite to different triggering events, including the Santorini caldera collapse, the turbidite can be traced back to a large tsunami sourced from the A.D. 365 Crete megathrust earthquake. Correlation of the single-event HAT over a wide area of the Mediterranean, from the northern Ionian Sea to the Mediterranean Ridge and the anoxic Tyro Basin south of Crete, suggests that the A.D. 365 Crete earthquake and tsunami must have produced devastating effects, including widespread massive sediment remobilization in the eastern Mediterranean Sea. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.