potential field inversion for a layer with uneven thickness the tyrrhenian sea density model abstract inversion of large scale potential field anomalies aimed at determining density or magnetization is usually made in the fourier domain the commonly adopted geometry is based on a layer of constant thickness characterized by a bottom surface at a fixed distance from the top surface we propose a new method to overcome this limiting geometry by inverting in the usual iterating scheme using top and bottom surfaces of differing but known shapes randomly generated synthetic models will be analyzed and finally performance of this method will be tested on real gravity data describing the isostatic residual anomaly of the southern tyrrhenian sea in italy the final result is a density model that shows the distribution of the oceanic crust in this region which is delimited by known structural elements and appears strongly correlated with the oceanized abyssal basins of vavilov and marsili

hydrothermal activity in the se tyrrhenian sea an overview of 30 years of research subduction related volcanic activity in the southeast tyrrhenian back arc basin has resulted in a large variety of calcalkaline rocks ranging from arc tholeiitic to shoshonitic and rhyolitic composition which were emplaced in both oceanic and continental crust hydrothermal systems in the se tyrrhenian sea have leached these magmatic rocks generating a wide range of oxyhydroxide and sulfide deposits all the hydrothermal occurrences formed at much shallower depths than those from the mid ocean ridges oxyhydroxide deposits metalliferous sediments crusts and nodules are almost pure hydrothermal formations with insignificant hydrogenetic and diagenetic contributions they exhibit strong separation of mn rich and fe rich end members with mn rich occurrences dominant their geochemistry suggests a relative enrichment of mn in the hydrothermal systems of the se tyrrhenian the sulfides are zn and pb rich but poor in cu and relatively poor in fe this suggests either deep seated magma chambers or boiling of the hydrothermal fluids beneath the seafloor as a consequence 1 cu and a large proportion of the fe are deposited as sulfides in the basement rocks and sediment cover 2 the hydrothermal fluids become relatively enriched in mn zn and pb a number of accessory sulfosalts and selenides not typical of mid ocean ridge massive sulfides are present

structure of the earth s inner core jacobs1 proposed that the earth s inner core is growing through the freezing of outer core material as the earth gradually cools2 recent studies have shown that compositional effects associated with this freezing process can release energy at a rate sufficient to power the geodynamo3 4 and may be crucial in determining the dynamic state of the outer core5 here we investigate the effects of composition on the freezing process itself drawing on metallurgical experience and speculate on the structure and state of the inner core we propose that the interface separating the inner and outer core is dendritic and argue that the region in which freezing takes place may extend throughout the entire inner core consequently the compositionally driven convective motions which stir the outer core and sustain the geodynamo also occur within the interdendritic spaces of the inner core the seismic evidence which corroborates this proposal is briefly reviewed

anthropogenic pb component in hydrothermal ochres from marsili seamount tyrrhenian sea abstract recent hydrothermal fe oxyhydroxide precipitates ochres were sampled during two submersible expeditions to the ne part of the marsili seamount summit se tyrrhenian sea the marsili ochres belong to type 1 primary sulfide poor fe oxyhydroxides according to the classification of hekinian et al hekinian r hoffert m larque p cheminee j l stoffers p bideau d 1993 hydrothermal fe and si oxyhydroxide deposits from south pacific intraplate volcanoes and east pacific rise axial and off axial regions econ geol 88 2099 2121 they are x ray amorphous highly metalliferous al al mn fe 0 4 low in si transition metals co ni cu zn pb and rare earth elements ree and enriched in b v and mo their chemical composition and ree distribution patterns indicate precipitation from low temperature hydrothermal fluid mixed with seawater measured pb isotope compositions in the ochres indicate that the pb is dominantly anthropogenic in origin by contrast the pb isotope ratios in the nearby higher temperature hydrothermal deposits from the panarea arc volcano show that the pb is derived mainly from local volcanic rocks the fact that the pb isotopic signature of the marsili ochres is controlled by recent anthropogenic input suggests that the fe oxyhydroxides precipitated from fluids depleted in transition metals the low 206pb 207pb ratios in the ochres reflect the contribution of pb from australian ores indicating precipitation of the ochres somewhere between present day and the beginning of australian pb import to europe the young age of the ochres and the presence of other hydrothermal deposits along the marsili crest suggest that the magmatic chamber beneath the seamount may still be alive this study represents the first observation of anthropogenic influence on submarine hydrothermal deposits

active hydrothermal discharge on the submarine aeolian arc 1 in november 2007 we conducted a water column and seafloor mapping study of the submarine volcanoes of the aeolian arc in the southern tyrrhenian sea aboard the r v urania on 26 conductivity temperature depth casts and tows we measured temperature conductivity pressure and light scattering and also collected discrete samples for helium isotopes methane and ph the 3he 4he isotope ratio an unambiguous indicator of hydrothermal input showed a clear excess above background at 6 of the 10 submarine volcanoes surveyed marsili seamount had the highest anomaly where the 3he 4he ratio reached a 3he value of 23 at 610 m depth compared with background values of 5 smaller but distinct 3he anomalies occurred over palinuro enarete eolo sisifo and secca del capo although hydrothermal emissions are known to occur offshore of some aeolian subaerial volcanoes and hydrothermal deposits have been sampled throughout the arc our results are the first to confirm active discharge on marsili enarete eolo sisifo and secca del capo samples collected over lametini filicudi north alicudi north and alcione had 3he near the regional background values suggesting either absence of or very weak hydrothermal activity on these seamounts hydrocasts between the volcanoes revealed a consistent 3he maximum between 11 and 13 at 2000 m depth throughout the se tyrrhenian sea the volcanoes of the aeolian arc and the marsili back arc all 1000 m deep cannot contribute directly to this maximum this deep 3he excess may be a remnant of tritium decay or may have been produced by an unknown deep hydrothermal source

recent volcanic events and the distribution of hydrothermal venting at the lucky strike hydrothermal field mid atlantic ridge 1 we present new high resolution bathymetry and backscatter data acquired in 2006 with the rov victor 6000 over the lucky strike hydrothermal field mid atlantic ridge as long term monitoring of the lucky strike area momar project is being implemented these new high resolution data offer an unprecedented view of the distribution of hydrothermal edifices eruptive facies and small scale tectonic features in the lucky strike vent field we show that vents located in the nw and ne correspond with wide expanses of lumpy seafloor which we interpret as primarily made of broken chimneys and sulfide edifices they are found above scarps with relief 50 m or on associated mass wasting deposits by contrast the se and sw vents correspond with small expanses of lumpy seafloor and are located near smaller scarps which we interpret as more recent faults hydrothermal edifices in the sw venting area appear very recent postdating the emplacement and faulting of the most recent lava we propose that this difference in the age of hydrothermal edifices does not mean that hydrothermal venting itself is more recent in the southern part of the lucky strike field because preexisting sulfide deposits there may have been buried by recent volcanic deposits instead the older edifices in the northern part of the hydrothermal field may have been allowed more time to grow because they are set above the level of recent lava flows the formation of a lava lake is the most recent eruptive event detected at lucky strike lava drainback is evidenced by benches and lava pillars suggesting a close connection with an underlying magma reservoir which probably corresponds to the melt body imaged by singh et al 2006 we have found no evidence that this lake was active for months to decades as lava lakes at terrestrial volcanoes it may instead have formed as a lava pond with successive lava flows covering the eruptive vents as proposed for similar features at the epr the horizontal surface of the lake is deformed only near its southwestern shore along a nne trending set of faults and fissures which appear to control the distribution of hydrothermal chimneys

mapping of seafloor hydrothermally altered rocks using geophysical methods marsili and palinuro seamounts southern tyrrhenian sea hydrothermal alteration processes involve mineralogical chemical and textural changes as a result of hot aqueous fluid rock interaction under evolving boundary conditions these changes affect the physico chemical properties of the rocks enabling high resolution geophysical prospecting to be an important tool in the detection of seafloor hydrothermal alteration here we present the results of recent geophysical investigations of the marsili and palinuro volcanic complexes southern tyrrhenian sea during the 2010 tir10 and 2011 mava2011 cruises by the r v urania the new dataset includes a dense grid of multibeam bathymetry seafloor reflectivity magnetic and gravity lines and high resolution single chirp and multichannel seismic profiles the surveys were focused on areas known to host intense hydrothermal alteration in order to provide a more detailed description of the marsili and palinuro hydrothermal systems ground truthing was based on earlier discoveries of hydrothermal vents and their associated deposits and on direct observations made by rov dives high resolution morpho bathymetry sonar reflectivity rock magnetization and density distribution together enabled us to assess the extent of seafloor hydrothermal alteration and its relationship to local volcanic and tectonic structures hydrothermal alteration associated with the marsili seamount is largely distributed along primary volcano tectonic structures at the ridge crest by contrast at palinuro hydrothermal alteration is mostly associated with secondary volcanic structures such as collapsed calderas and volcanism reactivation along ring faults in particular evidence for intense hydrothermal activity occurs at palinuro where volcanotectonic features interact with regional tectonic structures

on electric fields produced by inductive sources on the seafloor abstractthe transient electromagnetic tem method has recently been proposed as a tool for mineral exploration on the seafloor similar to airborne tem surveys conducted on land marine tem systems can use a concentric or coincident wire loop transmitter and receiver towed behind a ship such towed loop tem surveys can be further augmented by placing additional stationary receivers on the seafloor throughout the survey area we examine the electric fields measured by remote receivers from an inductive source transmitter within a 1d layered earth model at sea it is conceivable to deploy either a horizontal transmitter such as the analogous standard airborne configuration or a more exotic vertical transmitter therefore we study and compare the sensitivity of the vertical and horizontal towed loop systems with a variety of seafloor conductivity structures our results indicate that the horizontal loop system is more sensitive to the thickness of a buried conductive layer and would be advantageous over

a self potential investigation of submarine massive sulfides palinuro seamount tyrrhenian sea the self potential sp method detects naturally occurring electric fields which may be produced by electrically conductive mineral deposits such as massive sulfides recently there has been increasing interest in applying this method in a marine environment to explore for seafloor massive sulfide sms deposits which may contain economic resources of base and precious metals while sms sites that are associated with active venting and are not buried under sediment cover are known to produce an sp signal the effectiveness of the method at detecting inactive and sediment covered deposits remained an outstanding question we built an instrument capable of recording sp data in a marine setting we carried out a test of the instrument at the palinuro seamount in the tyrrhenian sea palinuro is one of only a few known sites containing an sms occurrence which is buried under sediment and not associated with active hydrothermal venting although diffuse seepage of hydrothermal fluids is known to occur at the site elevated electric field strengths recorded in and near the site of previously drilled massive sulfide samples are on the order of 1 3 mv m a second zone of high field strengths was detected by us to the north of the drilling area where gravity coring later confirmed the existence of massive sulfides our observations indicate that an sp signal can be observed at the site of sms mineralization even when the mineralized zone is shallowly buried and active hydrothermal venting is not present these observations could aid in the planning of future marine research expeditions which use the sp method in the exploration of seafloor massive sulfides

3 d focused inversion of near seafloor magnetic data with application to the brothers volcano hydrothermal system southern pacific ocean new zealand 1 we describe and apply a new inversion method for 3 d modeling of magnetic anomalies designed for general application but which is particularly useful for the interpretation of near seafloor magnetic anomalies the crust subsurface is modeled by a set of prismatic cells each with uniform magnetization that together reproduce the observed magnetic field this problem is linear with respect to the magnetization and the number of cells is normally greater than the amount of available data thus the solution is obtained by solving an under determined linear problem a focused solution exhibiting sharp boundaries between different magnetization domains is obtained by allowing the amplitudes of magnetization to vary between a pre determined range and by minimizing the region of the 3 d space where the source shows large variations i e large gradients a regularization functional based on a depth weighting function is also introduced in order to counter act the natural decay of the magnetic field intensity with depth the inversion method has been used to explore the characteristics of the submarine hydrothermal system of brothers volcano in the kermadec arc by inverting near bottom magnetic data acquired by autonomous underwater vehicles auvs different surface expressions of the hydrothermal vent fields show specific vertical structures in their underlying demagnetization regions that we interpret to represent hydrothermal upflow zones for example at focused vent sites the demagnetized conduits are vertical pipe like structures extending to depths of 1000 m below the seafloor whereas at diffuse vent sites the demagnetization regions are characterized by thin and inclined conduits

volcanic and hydrothermal processes in submarine calderas the kulo lasi example sw pacific abstract the study area is located at the transition between the northern end of the tonga trench and the north fiji fracture zone where tectonic movements are reputed to be the fastest in the world to the southeast of futuna island a broad area of volcanism occurs within a region characterized by a change in the tectonic fabric between a ne sw oriented volcanic graben and the n s oriented alofi ridge in 2010 the active volcano kulo lasi which represents the most recent volcanic episode in the futuna area was discovered in the center of this extensive volcanic zone kulo lasi is a 20 km diameter shield volcano that rises 400 m above the seafloor it is composed of basaltic to trachy andesitic lava with no obvious geochemical affinity with the tonga subduction that occurs 500 km to the east the central caldera is 5 km in diameter and 300 m deep and is located at a water depth of 1500 m diving operations with the submersible nautile and high resolution auv mapping have revealed the presence of numerous active and inactive hydrothermal fields on the floor and the walls of the caldera four tectono volcanic stages can be distinguished at kulo lasi caldera in stage 1 the shield volcano is built annular reverse faults develop at the summit and control circulation of water rock dominated hydrothermal fluids and high temperature alteration of rocks along the nascent normal faults mixing of hydrothermal fluids with seawater is favored along normal superficial faults leading to the formation of low temperature fe mn mineralization at the summit of the volcano during stage 2 the caldera collapse gradually revealing outcrops of the altered and mineralized zones formed during stage 1 as the magma chamber cools and collapses less heat is available as a result medium to low temperature

distribution des terres rares dans les depots hydrothermaux de la zone famous et des galapagos comparaison avec les sediments metalliferes abstract hydrothermal deposits sensu stricto have been recovered during the famous cruise and leg 54 of the deep sea drilling project near the galapagos spreading centre the studied sediments mainly composed of clay material have very poor ree concentrations below about ten ppm the shale normalized patterns are characterized by a significant enrichment in heavy rare earths and show a negative ce anomaly the magnitude of this anomaly fluctuates but is generally lower than the seawater ce anomaly the geochemical characteristics of these hydrothermal deposits are in contrast with those of metalliferous sediments which are more enriched in trace elements especially in ree

cross strata and bedforms of probable transitional dune to upper stage plane bed origin from a late precambrian fluvial sandstone northern norway a late precambrian fluvial sandstone sequence in northern norway is dominated by large scale cross sets that show either lenticular or tabular geometries in the streamwise sections the lenticular sets interdigitate and in places show nearly symmetrical formsets the tabular sets are in places solitary but are mainly grouped in cosets in both cross set types the cross strata range from concave up to sigmoidal in shape with the latter variety comprising subhorizontal to gently inclined topset strata with parting lineation that merge uninterruptedly downflow into the steeper 10 2 foresets within the cross sets the geometry and dip azimuths of the foresets are conspicuously consistent although the concave up and sigmoidal strata commonly alternate downcurrent the cross strata characteristics suggest flood stage deposition from relatively high velocity steady currents heavily laden with suspended sand both cross set types are interpreted as representing bedforms generated by flow in the dune to upper stage plane bed transition the lenticular cross sets probably represent periodic dunes but it is far less clear whether the long bedforms represented by the tabular sets should be classified as dunes or rather as solitary to quasi periodic bars

hydrothermal fluids associated with seafloor mineralization at two southern kermadec arc volcanoes offshore new zealand massive sulfide samples have been recovered from brothers and rumble ii west volcanoes of the southern kermadec frontal arc northeast of new zealand both are caldera forming volcanoes with brothers largely dacitic and rumble ii west basaltic to basaltic andesite in composition the sulfide samples are considered to be pieces of chimneys from near the base of the caldera walls and are dominated by cu fe ba pb chalcopyrite pyrite barite galena and to a lesser extent zn fe ba pb sphalerite pyrite barite galena mineralization gold is present in the samples up to 6 1 ppm paragenetic relationships suggest that the two hydrothermal systems have heated up and later cooled down oxidation of the sulfides is common and suggests that parts of the deposits are relatively old fluid inclusion microthermometric data show salinities fall predominantly in the range 3 0 to 3 4 wt nacl equivalent similar to seawater values 3 2 wt about 15 of the brothers salinity data range to both lower 2 2 wt and higher 3 9 wt than seawater values homogenization temperatures for type i inclusions in barite range between 175 and 322 c for the brothers samples and between 205 and 268 c for one rumble ii west sample a dramatic decrease in temperature and or change in the oxidation state of the hydrothermal fluid are considered the main mechanisms responsible for gold deposition at the kermadec vent sites this was achieved by mixing the hydrothermal fluid with ambient seawater within what are inferred to have been 300 c white smoker chimneys consistent with s isotope results fluid inclusion volatiles are dominated by h2o 99 81 99 98 mol followed by co2 0 03 0 17 and lesser amounts of n2 0 004 0 023 ch4 0 002 0 026 and trace cos and c2 c3 hydrocarbons fluid inclusions hosted by barite contain noticeably lesser amounts of gas than those within sulfides consistent with mixing the source of the relatively high concentrations of ch4 is enigmatic although may be related to the thermal degradation of organic rich sediments intercalated within the volcanic pile addition of a pressure correction and the effect of dissolved gases show that the hydrothermal fluids did not boil at the chimney depths however the range of measured salinities in the brothers field combined with slightly positive trends in fluid inclusion co2 ch4 versus co2 n2 plots suggest sub seafloor phase separation may have occurred in the hydrothermal system prior to venting

high resolution magnetics reveal the deep structure of a volcanic arc related basalt hosted hydrothermal site palinuro tyrrhenian sea high resolution magnetic surveys have been acquired over the partially sedimented palinuro massive sulfide deposits in the aeolian volcanic arc tyrrhenian sea surveys flown close to the seafloor using an autonomous underwater vehicle auv show that the volcanic arc related basalt hosted hydrothermal site is associated with zones of lower magnetization this observation reflects the alteration of basalt affected by hydrothermal circulation and or the progressive accumulation of a nonmagnetic deposit made of hydrothermal and volcaniclastic material and or a thermal demagnetization of titanomagnetite due to the upwelling of hot fluids to discriminate among these inferences estimate the shape of the nonmagnetic deposit and the characteristics of the underlying altered area the stockwork we use high resolution vector magnetic data acquired by the auv abyss geomar above a crater shaped depression hosting a weakly active hydrothermal site our study unveils a relatively small nonmagnetic deposit accumulated at the bottom of the depression and locked between the surrounding volcanic cones thermal demagnetization is unlikely but the stockwork extends beyond the limits of the nonmagnetic deposit forming lobe shaped zones believed to be a consequence of older volcanic episodes having contributed in generating the cones

geometry and kinematics of dunes during steady and unsteady flows in the calamus river nebraska usa the geometry and kinematics of river dunes were studied in a reach of the calamus river nebraska during day long surveys dune height length steepness migration rate creation and destruction were measured concurrently with bedload transport rate flow depth flow velocity and bed shear stress within a survey individual dune heights lengths and migration rates were highly variable associated with their three dimensional geometry and changes in their shape through time notwithstanding this variability there were discernible changes in mean dune height length and migration rate in response to changing discharge over several days changes in mean dune height and length lagged only slightly behind changes in discharge therefore during periods of both steady and unsteady flow mean dune lengths were quite close to equilibrium values predicted by theoretical models mean dune steepnesses were also similar to predicted equilibrium values except during high falling flows when the steepness was above that predicted variations in mean dune height and length with discharge are similar to those predicted by theory under conditions of low mean dune excursion and discharge variation with a short high water period and long low water period however the calculated rates of change of height of individual dunes vary considerably from those measured rates of dune creation and destruction were unrelated to discharge variations contrary to previous results instead creations and destructions were apparently the result of local variations in bed shear stress and sediment transport rate observed changes in dune height during unsteady flows agree with theory fairly well at low bed shear stresses but not at higher bed shear stresses when suspended sediment transport is significant

drilling shallow water massive sulfides at the palinuro volcanic complex aeolian island arc italy a subseafloor replacement style barite and sulfide occurrence was drilled in shallow waters at the palinuro volcanic complex the northernmost aeolian arc volcano in the tyrrhenian sea italy using a lander type drilling device 11 successful drill holes yielded a total of 13 5 m of core from a sediment filled depression located at a water depth of 630 to 650 m the longest continuous drill core recovered consists of 4 84 m of massive to semimassive barite and sulfides with abundant late native sulfur overprint seafloor observations suggest that the hydrothermal system associated with the formation of the subseafloor barite and sulfide ore zone is still active although black smoker activity does not occur on the seafloor the recovered drill core shows that the subseafloor deposit is zoned with depth the top of the mineralized zone is comprised of a variably silicified vuggy barite sulfide facies that shows notable polymetallic metal enrichment while the deeper portion of the mineralized zone is dominated by massive pyrite having distinctly lower base and precious metal grades metal zonation of the barite and sulfide deposit is related to the evolution of the hydrothermal fluids in space and time the barite cap and the massive pyrite present in the deeper portion of the mineralized zone appear to have formed early in the paragenesis during the main stage of the mineralization the barite cap was brecciated and cemented by a polymetallic assemblage of barite and pyrite with minor chalcopyrite and tetrahedrite trace famatinite and rare cinnabar lower temperature precipitates formed during the main stage of mineralization include sphalerite galena pyrite opal a and barite which are associated with traces of pb sb as sulfosalts such as bournonite seligmannite or semseyite a distinct mineral assemblage of fine grained anhedral enargite hypogene covellite chalcopyrite and galena is commonly associated with colloform sphalerite galena and pyrite as a late phase of this main stage colloform pyrite and marcasite are the last sulfides formed in the paragenetic sequence the deposit is interpreted to have formed from fluids having an intermediate sulfidation state although excursions to high and very high sulfidation states are indicated by the presence of abundant enargite and hypogene covellite laser ablation and conventional sulfur isotope analyses show that pyrite formed close to the seafloor within the zone of polymetallic metal enrichment has a variable sulfur isotope composition 34s 39 to 3 whereas a more narrow range is observed in the massive pyrite at depth 34s 10 to 0 similar variations were also documented for the late native sulfur overprint overall the negative sulfur isotope ratios at depth the intermediate to very high sulfidation conditions during mineralization and the abundance of native sulfur suggest contributions of magmatic volatiles to the mineralizing fluids from a degassing magma chamber at depth biological processes are interpreted to have played a major role during late stages of ore formation the combination of a subseafloor replacement deposit with a massive to semimassive barite cap rock overlying massive pyrite the intermediate to high sulfidation characteristics and the strong biological influence on the late stages of mineralization are distinct from other modern seafloor massive sulfide deposits and represents a style of submarine mineralization not previously recognized in a modern volcanic arc environment the barite and sulfide occurrence at palinuro shares many characteristics with porphyry related base metal veins and intermediate sulfidation epithermal deposits suggesting that metallogenic processes associated with arc related magmatic hydrothermal systems are not restricted to the subaerial environment

metalliferous sediments from eolo seamount tyrrhenian sea hydrothermal deposition and re deposition in a zone of oxygen depletion a sediment core taken from the south east slope of the eolo seamount is composed of alternating red brown and light brown to bluish grey layers with signs of re deposition in the middle upper section the red brown layers are fe rich metalliferous sediments formed as a result of low temperature 77 c hydrothermal discharge whereas the bluish grey layers most probably originated from background sedimentation of al rich detrital material the metalliferous layers are composed mainly of si rich goethite containing some al co precipitation of hydrothermally released sio44 and fe2 as amorphous or poorly crystalline fe si oxyhydroxides explains the high si concentration in goethite the elevated al content of the goethite is fairly unusual but reflects the extremely high background al content of the tyrrhenian seawater due to the high eolian terrigenous flux from the sahara desert the sr and nd isotope data suggest that the eolo metalliferous sediments are the product of a 3 component mixture hydrothermal fluid seawater and detrital material saharan dust and aeolian arc material the enrichment in fe p as mo cd be sb w y v depletion in ree and transition elements cu co ni zn and the ree distribution patterns support the low temperature hydrothermal deposition of the metalliferous layers the hydrothermal field is located in a seawater layer of relative o2 depletion which led to a significant fractionation of the hydrothermally emitted fe and mn fe oxyhydroxides precipitated immediately around the vents whereas mn stayed in solution longer and the mn oxides precipitated higher up on the seamount slope in seawater with relatively higher o2 levels high seismic activity led to sediment re deposition and slumping of the mn rich layers down slope and mixing with the fe rich layers

potential field modeling of collapse prone submarine volcanoes in the southern tyrrhenian sea italy 1 hydrothermal alteration may weaken volcanic rocks causing the gravitational instability of portions of active volcanoes with potentially hazardous collapses here we show high resolution multibeam magnetic and gravity surveys of the marsili seamount the largest active volcano of europe located in the southern tyrrhenian back arc basin these surveys reveal zones with exceptionally low densities and with vanishing magnetizations due probably to the comminution of basalts during hyaloclastic submarine eruptions and to their post eruptive hydrothermal alteration the location of these regions correlates with morphological data showing the occurrence of past collapses similar evidence has been obtained from pre existing data at vavilov seamount another older volcanic system in the tyrrhenian back arc basin here a large volume of at least 50 km3 may have collapsed in a single event from its 40 km long western flank given the similarities between these volcanoes a large collapse event may also be expected at marsili

multifrequency geoacoustic imaging of fluid escape structures offshore costa rica implications for the quantification of seep processes quantification of fluid fluxes from cold seeps depends on accurate estimates of the spatial validity of flux measurements these estimates are strongly influenced by the choice of geoacoustic mapping tools multibeam bathymetry side scan sonar and chirp subbottom profiler data of several mound shaped cold seeps offshore central costa rica show great variety in morphology and structure although the features are only a few kilometers apart mound 11 a 35 m high and 1000 m in diameter structure situated in the se of the study area has an irregular morphology but a smooth surface on side scan sonar data while mound 12 30 m high 600 m across is a cone of more regular outline but with a rough surface and mound grillo 5 m high 500 m across shows the same rough surface as mound 12 but without relief video observations and sediment cores indicate that the structures are formed by the precipitation of authigenic carbonates and indications for extensive mud extrusion are absent except for one possible mudflow at mound 11 different sonar frequencies result in variable estimates of the extent of these mounds with low frequencies suggesting much wider cold seeps consequently overestimating fluid fluxes the absence of mud volcanism compared to accretionary prisms where mud volcanism occurs is related to different tectonic styles strong sediment overpressure and thrust faulting in typical accretionary prisms can generate mud volcanism while subduction erosion and normal faulting extension of the overriding plate at the costa rican margin result in fluid venting driven by only slight fluid overpressures

caldera forming processes and the origin of submarine volcanogenic massive sulfide deposits certain volcanogenic massive sulfide vms ore deposits form in submarine calderas this association is well known but the link between caldera formation and the origins of the deposits remains poorly understood here we show that the size and location of a vms deposit within a submarine caldera may be determined by how and when the caldera formed these spatial temporal conditions control development of the hydrothermal system associated with the vms deposit we propose that caldera opening along outward dipping faults promotes magma degassing seawater influx and high temperature leaching resulting in a metal rich hydrothermal fluid these outward dipping faults are considered to provide critical pathways for ore forming fluids responsible for some caldera hosted vms deposits and may also be fundamentally important for the formation of many other caldera hosted ore deposit types

rapid 3 d forward model of potential fields with application to the palinuro seamount magnetic anomaly southern tyrrhenian sea italy 1 we show a set of forward model equations in the fourier domain for calculating the 3 d gravity and magnetic anomalies of a given 3 d distribution of density or magnetization one property of the potential field equations is that they are given by convolution products providing a very simple analytic expression in the fourier domain under this assumption the domain of the density or magnetization parameters is connected by a biunivoc relationship with the data space and potential field anomalies can be seen as filtered versions of the corresponding density or magnetization distributions a very fine spatial discretization can be obtained by using a large number of points within a unique 3 d grid where both the source distributions and field data are defined the main advantage of this formulation is that it dramatically reduces execution times providing a very fast forward model tool useful for modeling anomalies at different altitudes we use this method to evaluate an average magnetization of 8 a m for the palinuro seamount in the tyrrhenian sea southern italy thus performing a joint interpretation of morphological and newly acquired magnetic data

crustal magnetization of brothers volcano new zealand measured by autonomous underwater vehicles geophysical expression of a submarine hydrothermal system near bottom magnetic anomaly data have been acquired using autonomous underwater vehicles at brothers volcano southern kermadec arc new zealand crustal magnetization for the study area was obtained by inverting the magnetic data and shows a strong correlation between areas of low magnetization and four hydrothermal fields one of which was unknown prior to our surveys the magnetization pattern is consistent with a model of discrete individual zones of fluid upflow focused along caldera ring faults that provide preferred pathways for the ascent of the hydrothermal fluids differences in the amplitude of the magnetization over the vent fields appear to correlate with age and temperature variations of the hydrothermal fields

detailed morphology and structure of an active submarine arc caldera brothers volcano kermadec arc a survey of the brothers caldera volcano kermadec arc with the autonomous underwater vehicle abe has revealed new details of the morphology and structure of this submarine frontal arc caldera and the geologic setting of its hydrothermal activity brothers volcano has formed between major sw netrending faults within the extensional field of the havre trough brothers may be unique among known submarine calderas in that it has four active hydrothermal systems two high temperature sulfide depositing sites associated with faulting on the northwestern and western walls i e the nw caldera and w caldera hydrothermal sites respectively and gas rich sites on the summits of the constructional cones that fill most of the southern part of the caldera i e the upper and lower cone sites the 3 0 3 4 km caldera is well defined by a topographic rim encompassing 320 of its circumference and which lies between the bounds of two outer half grabenshaped faults in the northwest and southeast sectors there is not a morphologically well defined continuous ring fault at the map resolution although near vertical scarps are present discontinuously at the base of sections of the wall the width of the wall varies from 200 m at its southwest portion to 750 m on its northern section the widest part of the wall is its northwest sector which also has the largest documented area of hydrothermal alteration and where sea floor magnetization is lowest in addition to primary northwest southeast elongation and southwest northeast structures caused by faulting within the regional back arc strain field there are also less well developed west southwestnorth northeast regional structures intersecting the volcano that is appar ent on the abe bathymetry and at outcrop scale from submersible observations asymmetrical trap doorstyle caldera collapse is considered a possible mechanism for the formation of the brothers caldera

foredeep geometries at the front of the apennines in the ionian sea central mediterranean abstract a new regional seismic section in the ionian sea across the apennines belt and related foreland shows how the present foredeep geometry may be an example for interpreting discontinuous tilted and deformed earlier basins now incorporated in the internal parts of the accretionary wedge onlap stratal terminations of the foredeep sediments on the foreland monocline may simulate downlap geometries once involved and tilted by back thrusting the geometry of the ionian foredeep is controlled by the dip of the regional monocline and internally by the variable dip and length of the limb of the external fold which may be either foreland verging or hinterland verging the generation of a new fold within the foredeep splits the basin into a new foredeep toward the foreland and a thrust top basin toward the hinterland the thrust top basin dimension is primarily controlled by the distance between the two folds and related thrusts at its margins the foredeep in its overall history is composed by a series of concave heterogeneous lenses progressively displaced and piled up toward the foreland to the east the formation of each sedimentary lens is controlled by the development of a new fold and the contemporaneous retreat of the regional monocline which creates new accommodation space the complex 3d geometry of the apennines foredeep mainly results from lateral variations of the latter parameters as well as variations in sediment supply and eustasy

interactions between volcanism and tectonics in the western aeolian sector southern tyrrhenian sea summary new high resolution bathymetric and magnetic data from the western aeolian sector southern tyrrhenian sea provide insights into structural and volcanic development of the area suggesting a strong interaction between volcanism and tectonics the analysis of these data combined with relocated earthquake distribution focal plane solutions and strain rate evaluation indicates that the dextral strike slip sisifo alicudi shear zone is a complex and wide area of active deformation representing the superficial expression of the deep seated lithospheric tear fault separating the subduction slab below sicily and calabria most of the observed volcanic features are aligned along a nw se trend such as the filicudi island alicudi north seamount and eolo enarete alignments and are dissected by hundred metre high scarps along conjugate nne ssw trending fault systems the magnetic field pattern matches the main trends of volcanic features spectral analysis and euler deconvolution of magnetic anomalies show the existence of both deep and shallow sources high amplitude high frequency anomalies due to shallow sources are dominant close to the volcanic edifices of alicudi and filicudi while the main contribution on the surrounding eolo enarete alicudi north and filicudi north seamounts is given by low amplitude anomalies and or deeper magnetic sources this is probably related to different ages of the volcanic rocks although hydrothermal processes may have played an important role in blanketing magnetic anomalies in particular at enarete and eolo seamounts relative chronology of the eruptive centres and the inferred deformation pattern outline the quaternary evolution of the western aeolian arc sisifo alicudi north and filicudi north seamounts might have developed in an early stage following the late pliocene early pleistocene se ward migration of arc related volcanism due to the ionian subduction hinge retreat eolo enarete and filicudi represent later manifestations that led volcanoes to develop during mid late pleistocene when the stress regime in the area changed due to the sse ward propagation of the subduction slab tear fault and the consequent reorientation and decrease of trench migration velocity finally volcanic activity occurred in a very short time span at alicudi where an almost conical volcanic edifice emerged suggesting negligible interactions with regional fault systems

ultrafast oceanic spreading of the marsili basin southern tyrrhenian sea evidence from magnetic anomaly analysis spectral analysis of both shipborne and airborne magnetic maps of the southern tyrrhenian sea reveals seven subparallel positive negative magnetic anomaly stripes over the flat lying deep floor of the marsili oceanic basin this represents the first evidence of oceanic magnetic anomalies in the tyrrhenian sea the central positive stripe is along the marsili seamount a superinflated spreading ridge located at the basin axis the stratigraphy of ocean drilling program site 650 and k ar ages from the marsili seamount suggest that the marsili basin opened at the remarkable full spreading rate of 19 cm yr between ca 1 6 and 2 1 ma about the olduvai subchron this is the highest spreading rate ever documented including that observed at the cocos pacific plate boundary renewed but slow spreading during the brunhes chron after 0 78 ma coupled with huge magmatic inflation gave rise to the marsili volcano our new data and interpretation show that backarc spreading of the tyrrhenian sea was episodic with sudden rapid pulses punctuating relatively long periods of tectonic quiescence

the palinuro volcano and magmatism of the southeastern tyrrhenian sea mediterranean abstract the palinuro seamount is a complex volcano located along an e w trending possibly strike slip fault system extending seaward of the calabrian arc in the southeastern tyrrhenian sea the lavas from its top are pleistocene in age and display a marked calcalkaline affinity age and petrochemistry are almost identical to those of the aeolian island arc that have been interpreted as generated by subduction of the eastern mediterranean beneath the calabrian arc the bathyal plain between these volcanic areas is presently undergoing distension possibly with marginal oceanization here a third volcano the marsili seamount again displays in its topmost portions pleistocene lavas with calc alkaline affinity in the southeastern tyrrhenian sea calc alkaline magmas thus seem not to be confined to the island arc system but also characterize volcanics emplaced in apparently quite different structural settings

thermal constriction and slab tearing at the origin of a superinflated spreading ridge marsili volcano tyrrhenian sea 1 recently acquired swath bathymetry of the marsili basin has offered an unprecedented opportunity to study the processes of back arc ocean basin development in the tyrrhenian sea in particular the detailed morphology of marsili seamount a large strongly elongated volcano located in an axial position within the 2 ma ocean crust floored marsili basin is a key to understanding the mechanisms governing lithosphere formation in this young basin the basin is near circular in shape with diameter on the order of 120 km and is positioned in the southern tyrrhenian sea above the steeply dipping ionian oceanic slab of mesozoic age it is bounded southward by the aeolian volcanic arc and the calabrian accretionary wedge surface evidence of the northwesterly directed subduction the most outstanding feature of the basin is the elongated 3000 m high marsili volcano which reveals distinctive morphology strikingly akin to the high order segmentation and volcanic landforms described in mid ocean slow spreading ridges on the basis of its distinctive morphology and incremental growth relationship we propose that marsili volcano represents a superinflated spreading ridge resulting from a distinct thermal pulse of increased melt production occurring within the young and immature marsili basin surrounding cooler continental lithosphere thermally constricts ridge propagation and crust production in marsili basin to the finite scale of marsili volcano increased melt production to feed the superinflated marsili ridge is generated by deep lateral asthenospheric mantle flow produced at the edges of tears that bound the subducting ocean crust of the ionian plate slow spreading plate separation outpaced by the increase in magma generation results in vertical accretion to produce the superinflated ridge the existence of dip directed tears delimiting the narrow ionian slab is supported by the geological evolution of the surrounding foreland and apennine maghrebid mountain belt during early middle pleistocene i e the time of formation of the marsili volcano present day structure and volcanism furnish direct and indirect surface evidence of the presence and location of the slab tears

a proposal for the kinematic modelling of w dipping subductions possible applications to the tyrrhenian apennines system in w dipping subduction zones there is a general eastward progression of the back arc basin accretionary wedge foredeep complex with the forward progression early stages of the complex are revealed by slices of upper crust and sedimentary cover abandoned to the west left floating above a new section of mantle a major shear zone should form at the new moho separating upper crust slices of earlier accretionary stages and the eastward flowing mantle the mantle wedging at the top of the subduction plane could be responsible for the uplift of the central parts of the belt the retreating of the subduction hinge is interpreted as due to the push generated by the eastward mantle flow detected in the hot spot reference frame the foredeep depth is mainly a function of the radius of curvature of the subduction hinge the frontal wedge is constructed from the stacking of the upper layers of the subducting plate and the syntectonic clastics that fill the foredeep which are progressively involved in thrusting and later by extension in order to preserve volume balance the lithosphere of the eastern plate before subduction has to be the same size as that which has been subducted due to the longer length of the arc with respect to the original length of the linear margin between the two converging plates laterally stretched subducted lithosphere is predicted at depth w dipping subductions usually have a short life probably due to their inherent capability to produce new lateral heterogeneities of the lithosphere the thin back arc which are a key factor in controlling and generating new subductions both e and w dipping this model is applied to the apennines tyrrhenian sea system

origin of volcanism on the flanks of the pacific antarctic ridge between 41 30 s and 52 s 1 non hot spot intraplate volcanism is a common feature near the east pacific rise or pacific antarctic ridge volcanic ridges and seamount chains tens to hundreds of kilometers long are asymmetrically distributed about the ridge axis with most volcanic features occurring on the pacific plate their origins remain controversial we have analyzed off axis volcanic ridges near the pacific antarctic ridge from bathymetry backscatter gravity and geochemistry data of the pacantarctic 2 cruise k ar dating of samples dredged on these structures reveals a contrast of up to 3 ma between the volcanoes and the underlying crust the volcanic activity as suggested by the strong backscatter in sonar images appears to be limited to areas of seafloor younger than about 3 ma all surveyed ridges north of the menard transform fault tf show recent activity close to the ridge axis and are not affected by faults the off axis volcanic ridges south of the menard tf show recent volcanic flows in their center and are affected by n s extension two different types of volcanoes can be characterized conical flat topped ones and rough elongated ones associated with narrow e w trending volcanic ridges some of them showing strong backscattering on the em12 imagery from the morphology of the seamount chains and the ages of the lava samples we infer that the magma source for the volcanic ridges is related to the feeding of the ridge axis through three dimensional mantle convective circulation we suggest that a change in the relative plate motion since about 5 ma might have induced an offset of the mantle upwelling circulation under the ridge axis so that anomalously hot mantle rises under the pacific ridge flank the kinematic change is also likely responsible for the tectonic deformation in the young lithosphere south of menard tf

near bottom magnetic signatures of submarine hydrothermal systems at marsili and palinuro volcanoes southern tyrrhenian sea italy near bottom magnetic field data were collected using a towed magnetometer over selected parts of palinuro and marsili submarine volcanoes in the southern tyrrhenian sea italy we obtained equivalent magnetizations maps at these sites by inverting the corresponding magnetic anomalies highlighting the seafloor expression of hydrothermal alteration zones of reduced magnetization are interpreted as evidence for alteration related to hydrothermal processes they are associated with water column and seafloor observations of hydrothermal activity and altered host rocks at marsili volcano a large elliptical area of reduced magnetization is located south of the summit cone and perpendicular to the trend of marsili volcano itself this confirms the presence of a large hydrothermal system centered over the more recent eastern volcanic ridge and its associated magma chamber similarly areas of reduced magnetization over palinuro caldera are consistent with hydrothermal venting occurring along the caldera walls consistent with permeability structures related to caldera ring faults providing preferred pathways for the upflow of hydrothermal fluids

transfer zones in an oblique back arc basin setting insights from the latium campania segmented margin tyrrhenian sea new multichannel seismic reflection profiles were acquired to unravel the structure of a portion of the eastern margin of the tyrrhenian basin this extensional feature is part of an oligocene to present back arc basin in the hangingwall of the west directed apennines subduction system the basin provides excellent conditions to investigate the early stage processes leading to the development of rifted passive margins and to the emplacement of oceanic crust in an oblique setting the interpreted post stack migrated seismic profiles highlight the geometry and kinematics of the pontine escarpment that connects the latium campania continental margin to the vavilov basin the latter is the main feature of the area related to the early pliocene extension of the tyrrhenian sea several morphological variations are pointed out along strike mirroring different structural settings of the margin itself a steeper margin to the north corresponds to high angle possibly transtensional faults whereas a smooth slope in the southern portion corresponds to several more distributed listric faults this work contributes to the understanding of the interplay between extensional and transtensional tectonics along the margins of an oblique back arc basin

a first application of a marine inductive source electromagnetic configuration with remote electric dipole receivers palinuro seamount tyrrhenian sea we study a new marine electromagnetic configuration which consists of a ship towed inductive source transmitter and a series of remote electric dipole receivers placed on the seafloor the approach was tested at the palinuro seamount in the southern tyrrhenian sea at a site where massive sulfide mineralization has been previously identified by shallow drilling a 3d model of the palinuro study area was created using bathymetry data and forward modeling of the electric field diffusion was carried out using a finite volume method these numerical results suggest that the remote receivers can theoretically detect a block of shallowly buried conductive material at up to 100 m away when the transmitter is located directly above the target we also compared the sensitivity of the method using either a horizontal loop transmitter or a vertical loop transmitter and found that when either transmitter is located directly above the mineralized zone the vertical loop transmitter has sensitivity to the target at a farther distance than the horizontal loop transmitter in the broadside direction by a few 10s of meters furthermore the vertical loop transmitter is more effective at distinguishing the seafloor conductivity structure when the vertical separation between transmitter and receiver is large due to the bathymetry as a horizontal transmitter is logistically easier to deploy we conducted a first test of the method with a horizontal transmitter apparent conductivities are calculated from the electric field transients recorded at the remote receivers the analysis indicates higher apparent seafloor conductivities when the transmitter is located near the mineralized zone forward modeling suggests that the best match to the apparent conductivity data is obtained when the mineralized zone is extended southward by 40 m beyond the zone of previous drilling our results demonstrate that the method adds value to the exploration and characterization of seafloor massive sulfide deposits

hydrothermal nontronite formation at eolo seamount aeolian volcanic arc tyrrhenian sea abstract a sediment core containing a yellowish green clay bed was recovered from an area of extensive hydrothermal deposition at the se slope of the eolo seamount tyrrhenian sea the clay bed is composed of pure nontronite described for the first time in the tyrrhenian sea which appears to be the most aluminous nontronite ever found among the seafloor hydrothermal deposits the high al content suggests precipitation from al containing hydrothermal solutions the ree distribution of the eolo nontronite has a v shape pattern the heavy ree enrichment is in part due to their preferential partitioning in the nontronite structure this enrichment was possibly further enhanced by the hree preferential sorption on bacterial cell walls the light ree enrichment is the result of scavenging uptake by one of the nontronite precursors i e poorly ordered fe oxyhydroxides from the hydrothermal fluids oxygen isotopic composition of the nontronite yields a formation temperature of 30 c consistent with a low temperature hydrothermal origin the relatively radiogenic nd isotopic signature of the nontronite compared to the present day mediterranean seawater indicates that approximately half of nd and presumably the rest of the lree are derived from local volcanic sources on the other hand 87 sr 86 sr is dominated by present day seawater sr scanning electron microscopy investigation revealed that the nontronite is composed of aggregates of lepispheres and tube like filaments which are indicative of bacteria assisted precipitation bacteria inhabiting this hydrothermal site likely acted as reactive geochemical surfaces on which poorly ordered hydrothermal fe oxyhydroxides and silica precipitated upon aging the interactions of these primary hydrothermal precipitates coating bacterial filaments and cell walls likely led to the formation of nontronite finally the well balanced interlayer and layer charges of the crystal lattice of seafloor hydrothermal nontronite decrease its sorption capacity to zero thus the ubiquitous nontronite precipitation along the active plate boundaries and around the hot spots has no significant impact on oceanic trace element chemistry

copper ore grade hydrothermal mineralization discovered in a seamount in the tyrrhenian sea mediterranean is the mineralization related to porphyry coppers or to base metal lodes abstract a luzonite and tennantite tetrahedrite bearing massive sulfide mineralization was discovered when sampling the crater of the palinuro seamount located within a probable island arc or marginal basin tectonic setting the mineralization is made up of indurated sulfide crusts interpreted to have been deposited by a seawater sediment interface and mixed with ooze of organic and volcanic origin a preliminary investigation of the economic minerals showed besides luzonite and tennantite tetrahedrite native rare copper all associated with pyrite predominantly and baryte native silver bismuthinite and stibnite were also found a dust like white precipitate was observed by submersible close to the mineralized zone but no structures or edifices resembling black smokers have yet been identified massive pyrite deposits associated with such uncommon mineral assemblages are found in the high level volcanic parts of porphyry copper systems or associated with base metal lodes the massive sulfide discovery is suggested to have a volcanogenic exhalative origin and a genetic relationship with porphyry coppers or base metal sulfide lodes

hydrothermalism in the tyrrhenian sea inorganic and microbial sulfur cycling as revealed by geochemical and multiple sulfur isotope data abstract the palinuro volcanic complex and the panarea hydrothermal field both located in the tyrrhenian sea italy are associated with island arc magmatism and characterized by polymetallic sulfide mineralization dissolved sulfide concentrations ph and eh measured in porewaters at both sites reveal a variable hydrothermal influence on porewater chemistry multiple sulfur isotopic measurements for disseminated sulfides crs chromium reducible sulfur extracted from sediments at palinuro yielded a broad range in 34s range between 29 8 and 10 2 and 33s values between 0 015 and 0 134 in contrast sediments at panarea exhibit a much smaller range in 34scrs with less negative values between 11 3 and 1 8 the sulfur isotope signatures are interpreted to reflect a mixture between hydrothermal and biogenic sulfide with a more substantial biogenic contribution at panarea multiple sulfur isotope measurements were performed on sulfides and elemental sulfur from drill core material from the palinuro massive sulfide complex 34s and 33s values for pyrite between 32 8 and 1 1 and between 0 012 to 0 042 respectively as well as for elemental sulfur with 34s and 33s values between 26 7 and 2 1 and between 0 035 and 0 109 respectively point to a microbial origin for much of the sulfide and elemental sulfur studied moreover data suggest a coupling of bacterial sulfate reduction sulfide oxidation and sulfur disproportionation in addition 34s values for barite between 25 0 and 63 6 are also in agreement with high microbial turnover of sulfate at palinuro although a magmatic so2 contribution towards the formation of the palinuro massive sulfide complex is very likely the activity of different sulfur utilizing microorganisms played a fundamental role during its formation thus porewater and multiple sulfur isotope data reveal differences in the hydrothermal activity at palinuro and panarea drill sites and underline the importance of microbial communities for the origin of massive sulfide mineralizations in the hydrothermal subsurface

bed shear stress over subaqueous dunes and the transition to upper stage plane beds plane beds that replace small bedforms e g ripples on the backs of subaqueous dunes are dynamically similar to upper stage plane beds local bed shear stresses at the position on dunes where plane beds develop may be two to three times larger than on a completely plane bed under the same general hydraulic conditions these observations help explain the transition from dunes to a wholly upper stage plane bed

the marsili ridge southern tyrrhenian sea italy an island arc volcanic complex emplaced on a relict back arc basin marsili seamount 1 ma southern tyrrhenian sea italy is classically interpreted as the spreading ridge of the about 2 ma old marsili oceanic back arc associated to the southern tyrrhenian sea calabrian arc subduction setting high resolution bathymetric data show that the ridge extends along a nne ssw strike and consists of 4 sectors and 11 major segments seafloor failures and central type activity from an overpressurized sill like reservoir characterize the central sector whereas fissural volcanism and passive magma ascent take places at the edges cones indicative of high effusion rates concentrate in the axial zone whereas flat top shields associated to lower rates are located at the northern tip along axis lateral magma migration due to a local deepening of the elastic brittle thickness of the crust develops from the central sector toward the northern tip the opening of the marsili back arc basin vanished from about 1 ma and the marsili ridge formed by passive magma ascent along pre existing fractures inherited by early spreading activity the values of the long term output rate the ratio between magmatic pressure and tectonic stress and the morphological features of the lava flows and dikes are consistent with those found in volcanic arc subduction settings marsili ridge represents a volcanic arc edifice emplaced on an older relict back arc the formation of the marsili ridge marks the transition from an extensional subduction setting to a compressive one

evolution of the southern tyrrhenian slab tear and active tectonics along the western edge of the tyrrhenian subducted slab abstract the evolution of the southern tyrrhenian subduction has been possibly controlled by distinct episodes of slab break off as indicated by a critical review of the geological literature and by the analysis of purposely acquired multichannel seismic profiles within the proposed interpretation the first episode occurred from 8 5 to 4 0 ma and affected the segment of the slab located in the sardinia channel causing the abandonment of the adventure thrust front in western sicily the second episode occurred between 2 5 and 1 6 ma affecting the segment of slab located north of sicily and was preceeded by rifting in the strait of sicily the space and time location of these episodes appear controlled by discontinuities pre existing within the subducted african plate that trend at high angle to the advancing subduction front these discontinuities delimit segment of subducted slab that can be affected by slab break off and can act as wayouts for magma and mantle derived he the major of these discontinuities the malta escarpment has been reactivated in the quaternary as a trench perpendicular tear step faults ultimately the hierarchy in strength of these trench perpendicular features could have affected the timing and amount of trench retreat and backarc opening

chronology of the transition from a spreading ridge to an accretional seamount in the marsili backarc basin tyrrhenian sea inversion of new high resolution magnetic data from the marsili seamount and the surrounding basin in the tyrrhenian sea reveals nne ssw magnetization stripes ranging from the matuyama chron to the brunhes chron including the short positive jaramillo subchron the detailed magnetic chronology shows that from the late matuyama 1 77 ma the average half spreading rate was about 1 5 cm yr 1 with a slight decrease between the jaramillo and the brunhes events when the growth of the volcanic edifice overcame lateral spreading analysis of spreading rate and volume of erupted lava indicates that at the beginning of the jaramillo subchron 1 07 ma the marsili basin evolved from pure horizontal spreading to a superinflated seamount as a consequence of tearing of the ionian slab our data give us a snapshot of the geodynamic transition from an active backarc spreading phase to the vertical accretion of the seafloor because of a radical change in the subduction dynamics

crustal motion along the eurasia nubia plate boundary in the calabrian arc and sicily and active extension in the messina straits from gps measurements 1 we investigate crustal deformation along the eurasia nubia plate boundary in calabria and sicily revealed by the gps velocity field obtained by the combination of continuous site velocities with previous results from episodic campaigns we recognize two distinct crustal domains characterized by different motions and styles of deformation convergence in sicily is taken up by crustal shortening along the former tyrrhenian back arc passive margin in agreement with seismological data and geological evidence of recent cessation of deformation along the plio pleistocene subduction front the analysis of the gps data and the consistency between earthquake slip vectors and convergence direction suggest that eu nu convergence in sicily does not require intermediate crustal blocks significant eurasia 3 mm yr to nne and nubia fixed 5 mm yr to ese residual velocities in calabria suggest instead the presence of an intermediate crustal block which can be interpreted as a forearc sliver or as an independent ionian block according to the first hypothesis subduction is still active in the ionian wedge although we find no evidence for active back arc spreading in the tyrrhenian sea the n115 e oriented sicily calabria gps relative motion is consistent with the extension observed during the 1908 mw 7 1 messina earthquake we suggest that up to 3 mm yr 80 of this estimated relative motion between sicily and the calabrian arc may be taken up in the messina straits

odp leg 107 in the tyrrhenian sea insights into passive margin and back arc basin evolution leg 107 of the ocean drilling program drilled a west northwest east southeast transect of seven sites across the tyrrhenian sea the youngest of the sub basins of the mediterranean sea sites 654 653 652 and 656 document the rifting and subsidence of the sardinia passive continental margin on the upper margin site 654 we cored a classic transgressive sequence subaerial conglomerates overlain by oyster bearing sands overlain by marine marl comparison between the recovered lithologies and seismic reflection profiles suggests that the synrift sediments on the upper margin are tortonian late miocene to messinian latest miocene in age whereas synrift sediments on the lower margin are messinian to pliocene in age during the messinian desiccation of the mediterranean sites 654 and 653 now on the upper sardinian margin apparently occupied a basinal setting where they received nannoplankton bearing clays interbedded with laminated gypsum sites 656 and 652 now on the lower sardinia margin were apparently higher standing during the desiccation event their messinian facies are subaerial and lacustrine respectively we infer from these lines of evidence that tilting and subsidence occurred more than a million years earlier on the upper margin than on the lower margin such diachroneity can be interpreted in terms of migration of the zone of maximum extension above a rolling back subduction zone or in terms of extension of continental crust by shear along a deep detachment fault sites 655 651 and 650 were drilled into two small basalt floored basins of the central and eastern tyrrhenian emplacement of basaltic crust in the central tyrrhenian vavilov basin apparently began more than a million years before emplacement of basaltic crust in the eastern tyrrhenian marsili basin this observation is compatible with previous suggestions that the tyrrhenian has grown southeastward in response to rollback of the down going slab that currently dips northwestward under the toe of italy at the easternmost site high vesicularity of the basalt and benthic foram assemblages in the oldest sediments imply that the basalt erupted in water shallower than 2 500 m it has apparently subsequently subsided to its present depth of 4 100 m below sea level nearly three times as fast as normal subsidence of crust formed at a mid ocean ridge

submarine hydrothermal activity and gold rich mineralization at brothers volcano kermadec arc new zealand brothers volcano of the kermadec intraoceanic arc is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world it has two distinct vent fields known as the nw caldera and cone sites whose geology permeability vent fluid compositions mineralogy and ore forming conditions are in stark contrast to each other the nw caldera site strikes for 600 m in a sw ne direction with chimneys occurring over a 145 m depth interval between 1 690 and 1 545 m at least 100 dead and active sulfide chimney spires occur in this field and are typically 2 3 m in height with some reaching 6 7 m their ages at time of sampling fall broadly into three groups 4 23 and 35 years old the chimneys typically occur near the base of individual fault controlled benches on the caldera wall striking in lines orthogonal to the slopes rarer are massive sulfide crusts 2 3 m thick two main types of chimney predominate cu rich up to 28 5 wt cu and more commonly zn rich up to 43 8 wt zn geochemical results show that mo bi co se sn and au up to 91 ppm are correlated with the cu mineralization whereas cd hg sb ag and as are associated with the dominant zn rich mineralization the cone site comprises the upper cone site atop the summit of the recent main dacite cone and the lower cone site that straddles the summit of an older smaller more degraded dacite cone on the ne flank of the main cone huge volumes of diffuse venting are seen at the lower cone site in contrast to venting at both the upper cone and nw caldera sites individual vents are marked by low relief 0 5 m mounds comprising predominately native sulfur with bacterial mats vent fluids of the nw caldera field are focused hot 300 c acidic ph 2 8 metal rich and gas poor calculated end member fluids from nw caldera vents indicate that phase separation has occurred with cl values ranging from 93 to 137 of seawater values by contrast vent fluids at the cone site are diffuse noticeably cooler 122 c more acidic ph 1 9 metal poor and gas rich higher than seawater values of so4 and mg in the cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water rock interactions iron oxide crusts 3 years in age cover the main cone summit and appear to have formed from fe rich brines evidence for magmatic contributions to the hydrothermal system at brothers includes high concentrations of dissolved co2 e g 206 mm kg at the cone site high co2 3he negative d and 18oh2o for vent fluids negative 34s for sulfides to 4 6 sulfur to 10 2 and 15n2 to 3 5 vent fluid ph values to 1 9 and mineral assemblages common to high sulfidation systems changing physicochemical conditions at the brothers hydrothermal system and especially the cone site occur over periods of months to hundreds of years as shown by interlayered cu au and zn rich zones in chimneys variable fluid and isotopic compositions similar shifts in 3he 4he values for both cone and nw caldera sites and overprinting of magmatic mineral assemblages by water rock dominated assemblages metals especially cu and possibly au may be entering the hydrothermal system via the dissolution of metal rich glasses they are then transported rapidly up into the system via magmatic volatiles utilizing vertical 2 5 km long narrow 300 m diameter pipes consistent with evidence of vent fluids forming at relatively shallow depths the nw caldera and cone sites are considered to represent stages along a continuum between water rock and magmatic hydrothermal dominated end members

flexural behavior of the continental lithosphere in italy constraints imposed by gravity and deflection data a procedure is developed that systematically matches observations of plate flexure and gravity anomalies at simple convergent boundaries to the bestfitting two dimensional flexural geometry obtained by a thin elastic sheet of specified elastic strength the procedure allows analytical solution for three independent variables one of which is the initial preflexure elevation of the reference surface and two of which are related to the vertical forces and bending moments that act on the plate application to four profiles constructed across the apennine convergent system in italy shows that the observed depth of the basal pliocene surface which marks the base of the foredeep basin and the observed bouguer gravity anomalies can be fit by a two dimensional elastic plate model with an effective elastic thickness of about 20 km on three profiles and about 10 km on the fourth profile the initial elevation prior to flexure is determined to have been about 1000 m below sealevel on all profiles large bending moments and or vertical shear forces are required to act at the effective plate ends in order to maintain the observed deflection moments between 0 5 1017 and 3 1017 n and shear forces between 3 1012 and 3 1012 n m gravity modelling indicates that on the two northernmost profiles these terminal forces can not be supplied by a static mass at crustal depths and suggests that on all four profiles the terminal forces are supplied by anomalously dense material present at depths of 75 150 km beneath and west of the west coast of italy this dense material probably corresponds to westward subducted lithosphere of the adriatic plate extending from the northern apennines to the southern apennines and calabria this study suggests that in subduction systems like the apennines that are characterized by backarc extension forces acting on subducted lithosphere at depth can be expressed at the surface in the geometry of the foredeep basin that forms adjacent to the subduction zone

tectonic volcanic and hydrothermal features of a submarine portion of the aeolian arc tyrrhenian sea abstract multibeam side scan sonar remotely operated vehicle and bottom sampling data have been acquired over a sector of the aeolian arc to assess its volcano tectonic characteristics and hydrothermal mineralization potential in this paper we report a description of the areas where major tectonic volcanic and hydrothermal activity has been observed there areas are the basiluzzo area the secca dei pesci area the southwestern panarea platform the secca del capo highs the offshore area between salina and lipari and the eastern slope of vulcano the study region lies at the junction of two major e w and ne sw trending tectonic lineaments through which the extensional faulting of the calabrian and sicilian margins leading to the formation of the tyrrhenian back arc sea took place the recent tectonics of the study area dominated by ne sw and e w trending extensional structures appears to be still controlled by the processes which have originated the tyrrhenian back arc opening many newly discovered recent volcanic features have been observed e g 1 three pairs of volcanic cones aligned along ne sw tectonic lineaments in the offshore between salina and lipari 2 a field of fresh tube and pillow lavas in the eastern offshore of vulcano 3 outcrops of fresh volcanic rocks in the panarea platform in particular around basiluzzo islet suggesting recent volcanic activity two types of hydrothermal mineralization were sampled i e sediment hosted sulphide deposits and fe rich crusts and sediments the polymetallic sulphide deposits were sampled in a depression south of basiluzzo islet for which area a kuroko type hydrothermal system reaching high temperature black ore deposition is suggested in the other sectors of the study area however a lower temperature hydrothermal circulation is thought to have originated the fe rich tetsusekiei type samples

morphology sedimentology and palaeohydraulic significance of large gravel dunes altai mountains siberia coarse gravel bedforms which resulted from pleistocene glacial outburst floods are identified as subaqueous dunes comparison of the morphology of these fossil structures with modern dunes shows that the form of two dimensional 2 d transverse dunes and 3 d cuspate and lunate dunes developed in coarse gravels is comparable with sand dune morphology within lesser scale geophysical flows the similarity of the steepest gravel dunes with equilibrium dunes in sand indicates that grain size is not a major factor in constraining primary duneform internal structure indicates that flow over 2 d dunes was relatively uniform but over 3 d bedforms flow was locally variable flow separation and complex streaming of flow occurred over the steepest 3 d dunes cross beds are thin and few approach the angle of repose consequently most dunes did not migrate primarily by avalanching but by stoss entrained gravel transported over the crests rolling down and depositing on the lee slopes the lee formed when flood power was waning some dunes were siightly planed down during falling stage because lee side cross beds tend to be steeper than the angle of the preserved lee slope however silt rich caps indicate that any height reduction was contemporary with the final deposition of foresets post flood modification has been negligible although the modern topography is subdued by loess deposits within the dune troughs lee side sediments are often finer than the stoss slope sediments which indicates

quaternary still stand landforms and relations with flank instability events of the palinuro bank southeastern tyrrhenian sea a high resolution morphological and geological inspection was carried out on the palinuro bank 39 30 n 14 48 e a volcanic complex made by several coalescent volcanic features located on the campanian continental slope eastern tyrrhenian sea italy a shallow 84 m asl volcanic edifice characterized by a flat top modelled surface is present on its central sector the use of a very high resolution digital terrain model allowed recognition of the presence of relict morphologies perhaps notches inner margins related to the past sea level still stands three depth levels of paleo shorelines markers are located at 90 m 100 m and 123 m respectively in addiction the truncated shape of the cone itself located between 84 m and 130 m could be interpreted as a tilted marine terrace breaks in slope produced by terrace landforms caused oversteepening that could have triggered lateral collapses both on the northern and southern flanks of the bank as suggested by the presence of steep slopes 25 40 and indicated by acoustic facies on chirp high resolution mono channel seismic profiles the results allow further hypotheses on vertical displacement between the western sector of the palinuro bank where caldera shapes are present and the central sector made by shallower volcanic cones these two sectors also differ in terms of magnetic properties

styles of back arc extension in the central mediterranean in the central mediterranean two back arc basins the liguro provencal lpb and the tyrrhenian basin tb opened progressively and consecutively from the late eocene oligocene to the present evolution in space and time of rifting and drifting processes along three different transects across these basins shows differences in the style of extension lpb opened with the formation of a narrow single rift while in the tb deformation and magmatism is spread over a wide area moreover at the northern end of the tb the locus of extension progressively migrated towards the east whereas in the southern tb the locus of extension and magmatism migrated inside the basin inducing continental break up and drifting of the previously formed older conjugate basins we propose that these different styles of back arc extension depend upon internal conditions such as prerift rheology linked with its geological heritage and external conditions e g the style of subduction

the ventotene volcanic ridge a newly explored complex in the central tyrrhenian sea italy new high resolution geophysical data collected along the eastern margin of the tyrrhenian back arc basin in the pontine islands area reveal a nw se elongated morphological high the ventotene volcanic ridge vr located on the northern edge of the ventotene basin high resolution multibeam bathymetry combined with magnetic data multi and single channel seismic profiles and rov dives suggest that vr results from aggregation of a series of volcanic edifices the summit of these volcanoes is flat and occurs at about 170 m water depth given their depths we propose that flat morphologies were probably caused by surf erosion during quaternary glacial sea level lowstands seismic stratigraphy together with magnetic data suggest that the volcanic activity in this area is older than 190 130 ka age and may be coeval with that of ventotene island middle pleistocene the submarine volcanoes located 25 km north of ventotene are part of a e w regional volcanic alignment and extend the pontine volcanism landward toward the gaeta bay integration of structural data from multichannel seismic profiles in this sector of the eastern tyrrhenian margin indicates that several normal and or transtensional faults striking wnw ese nnw sse and ne sw offset the basement and form alternating structural highs and depressions filled by thick mostly undeformed sedimentary units arc related magmatism is widespread in the study area where the vr is placed at the hangingwall of the west directed apennines subduction zone which is undergoing tensional and transtensional tectonics bathymetric and topographic evidence shows that vr lies in between a major ne sw trending escarpment east of ponza and a ne sw trending graben southwest of the roccamonfina volcano a ne sw transfer zone that accommodate the extension along this segmented portion of the margin this suggests that the interaction between ne sw and nw se trending fault systems acts as a structural control on location of eruptive centers given that main volcanic edifices develop along the nw se direction compatible with the extensional setting of the tyrrhenian basin

potential mass movements on the palinuro volcanic chain southern tyrrhenian sea italy and consequent tsunami generation abstract the palinuro volcanic chain pvc is located about 80 km offshore the campania region italy in the southern sector of the tyrrhenian sea the chain consists of 15 volcanic edifices aligned in an e w direction with two distinct major seamounts palinuro and glabro they cover a 90 km long and 20 km wide area with a present day volume of 2700 km3 palinuro volcanism emplaced between 0 8 and 0 3 ma although shallow seismicity and hydrothermalism indicate an ongoing volcanic activity a geomorphological analysis of the volcanic chain and data from a multichannel seismic profile reveal large volumes of buried chaotic material suggesting gravity mass sliding from the volcano flanks and slide scars a stability analysis of the palinuro flanks has been carried out to determine the sectors potentially prone to sliding in case of shallow volcanic earthquakes landslides are simulated by adopting a scenario based approach tsunamis induced by these mass movements and their propagation across the tyrrhenian sea are modeled results suggest that shallow earthquakes m 4 6 4 8 are able to destabilize the flanks of the volcanic chain generating slope failures sliding volumes in the order of 1 5 km3 and 2 4 km3 may induce waves as high as 1 5 and 6 m respectively along the peri tyrrhenian coast our results underline the need for further investigations on the stability of the submarine volcanoes of the tyrrhenian basin these volcanoes are still poorly known although their instability could trigger large tsunamis along the southern italy coastal sectors our recommendation is that multiparamertic monitoring networks on pvc and periodic oceanic cruises should be put into action and further that a systematic evaluation of the tsunami hazard related to possible sliding phenomena on the flanks of the tyrrhenian seamounts should be performed