geomagnetism and age study of tyrrhenian seamounts summary we discuss the results of measurements of the magnetic anomaly field of several seamounts located on the ocean floor and on the bordering continental slopes of the tyrrhenian sea this geomagnetic study of seamounts is based on joint 3 d analyses of the magnetic anomalies and the bathymetry on measurements of the magnetic properties of rock specimens and on geochronological data the 3 d analysis of the magnetic anomalies of large volcanoes emplaced in the small oceanic basins of vavilov and marsili serves to shed light on the spatial distribution of the magnetized bodies by eliminating the effect of topography a new magnetic anomaly map of the southern tyrrhenian sea is obtained by the merging of shipborne local data measured on topographic highs with data of regional type the study of the magnetic patterns and age of the oceanic seamounts indicates that the volcanic activity mainly developed prior to chron c2 2 02 ma bp on the vavilov and magnaghi edifices vavilov basin whereas the volcanism of a big oceanic seamount emplaced in the small basin of marsili took place mainly during the period of chron c1 0 0 78 ma bp

regional scale morphological pattern of the tyrrhenian sea new insights from emodnet bathymetry abstract a large body of literature exists on the morphology of the tyrrhenian sea the youngest back arc basin of the eastern mediterranean however most of these studies are focused on local areas without considering the broad regional setting in this paper we consider the morphology of the entire tyrrhenian sea at a regional scale based on a dem analysis of middle resolution bathymetry downloaded from the emodnet website based on these data a first morpholineaments map has been created identifying 500 features 10 km in length without considering their tectonic settings and age furthermore a tyrrhenian regional tectonic map has been digitized from literature and the faults divided in pre pliocene pliocene and plio quaternary morpholineaments and tectonic lineaments have been grouped in six tyrrhenian sea areas plotted in rose diagrams in order to obtain the main trends in each region and to detect relationships between morphology and tectonics rose diagrams show that most of the identified morpholineaments have a tectonic origin although they are not coeval as they developed during different phases of the opening of the tyrrhenian back arc basin moreover morpholineaments data suggest that some regions of the tyrrhenian sea may be dominated by a single main trend whereas in other regions the occurrence of more trends testifies a major tectonic complexity

crack formation on top of propagating reverse faults of the chuculay fault system northern chile insights from field data and numerical modelling abstract reverse faults in northern chile have formed 20 300 m high scarps that contain open fractures which occur in a zone of 20 1600 m wide two dimensional numerical models were used to explore the geometrical and mechanical parameters needed to produce extension within a bulk contractional regime all of the mechanical models show the same structure as the field a concentration of cracks predominantly at the top rather than on the forelimbs of the scarps in the field case extension begins as soon as a discrete scarp forms with progressive shortening the scarp height increases producing a broadening of the zone in extension the numerical models show that this broadening stabilizes when a maximum in the scarp height is reached to produce concentration of the extension on top of the scarps the reverse fault needs to be weak 10 the models suggest that distribution of this extensional zone depends on the cross sectional geometry of the fault and on the location of the detachment at depth the main mechanism that produces extension on the top of the reverse scarp is stretching of the topographic surface by folding of the hanging wall at the tip of the fault zone

the lithosphere asthenosphere system in the calabrian arc and surrounding seas southern italy a fairly detailed structural model of the lithosphere asthenosphere system thickness s and p wave velocities of the crust and of the uppermost mantle layers has been defined in the calabrian arc region southern tyrrhenian sea calabria and the northwestern part of the ionian sea in southern italy using seismic data from literature as a priori constraints of the nonlinear inversion of surface wave data

group velocity tomography and regionalization in italy and bordering areas abstract more than 200 group velocity dispersion curves 109 new dispersion data and 101 collected from literature of the fundamental mode of rayleigh waves in the period range from 10 to 35 s have been processed to obtain tomographic maps for the italian peninsula and bordering areas we compute average dispersion relations over a 1 1 grid and since the lateral resolving power of our data set is of about 200 km we group the cells of the grid according to their dispersion curves in this way and without any a priori geological constraints we define seven different regions each characterised by a distinctive mean group velocity dispersion curve the resulting regionalization can be easily correlated with the main tectonic features of the study area and mimics a recently proposed structural sketch average models of the shear wave velocity in the crust and in the upper mantle for a few selected regions are presented the very low s wave velocity values found in the uppermost upper mantle of the southern tyrrhenian basin are consistent with a large percentage of partial melting in agreement with the presence of the vavilov magnaghi and marsili huge volcanic bodies

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

p wave deep velocity structure of the southern tyrrhenian subduction zone from nonlinear teleseismic traveltime tomography a new 3 d model for the p wave velocity structure of the southern tyrrhenian subduction zone stsz is determined from nonlinear inversion of relative arrival times of teleseismic events the data used in the imaging are the travel time residuals of both direct p and pk p df and secondary pp sp pcp pkp bc phases computed with respect to the global 1 d velocity model ak135 2308 teleseismic waveforms were collected for this study from 109 events recorded by the italian national seismic network rsnc during 1988 1998 the velocity perturbation field is reconstructed gradually by means an iterative sequence of linearized inversions incorporating a 3 d minimum travel time ray tracing the tomographic images reveal a broad high velocity zone dominating the pattern of lateral variations beneath the southern tyrrhenian sea and calabria this fast structure extends laterally for a maximum of 350 km from northern sicily to southern campania and vertically for at least 400 km from the uppermost mantle down to 500 km depth below 350 km the geometry of the depicted slab is characterized by horizontal deflection of the subducting lithosphere towards the central tyrrhenian basin

mantle degassing on a near shore volcano se tyrrhenian sea the presence of a seamount like structure located a few nautical miles offshore the capo vaticano promontory western calabria s italy was revealed by combined geophysical and geochemical investigation the edifice covers 55 km2 with a top located at a depth of about 70 m below sea level and consists mainly of a nw trending structure orthogonally interrupted by minor ridges the largest of which is affected by extensional faults the top of the edifice hosts active vents injected fluids that have been investigated for dissolved volatiles gas analyses revealed high co2 and ch4 contents several orders of magnitude above the atmospheric type values expected for shallow coastal marine waters and a noteworthy enrichment in mantle derived 3he which is an unambiguous indicator of the mantle origin of the fluids our results combined with available data from the literature suggest that the edifice is a tectonically controlled volcanic system which presence near the calabria region changes the role played by faults in the frame of the subduction process

the opening processes in the deep tyrrhenian basins of marsili and vavilov as deduced from magnetic and chronological evidence of their igneous crust abstract shapes and chronology of magnetic anomalies of the mafic crust flooring the marsili and vavilov abyssal plains in the central tyrrhenian sea are discussed in the marsili deep basin the possible 3 phase evolution of a magmatic tectonic process of spreading is considered the early magmatic phase apparently took place at the time of the olduvai magnetic event 1 87 to 1 67 ma b p site 650 of the ocean drilling project leg 107 it appears to consist of spreading manifestations of a low magnetic intensity and a round shape forming the igneous basement around the marsili volcano the late phase was characterized by a spreading process exhibiting a linear configuration and high intensity of the magnetic anomalies organized spreading this phase of the brunhes epoch has given rise to the great marsili volcano emplaced in the basin s central part the intermediate phase shows reversed magnetic polarity and slightly elongated shapes it appears to have developed in late matuyama times from 1 67 to 0 73 ma ago the intensities of the magnetic anomalies in the basin of vavilov are on the whole lower than those present in the magnetic field of the marsili also in the vavilov deep basin the magnetic anomalies associated with the early volcanic manifestations which are of late miocene age about 7 5 ma are characterized by low intensity and a round shape whereas those associated with the effusions on the vavilov volcano whose age ranges from late pliocene to late quaternary from 2 4 to less than 0 12 ma exhibit a high intensity and a linear shape the two bathyal plains have inter arc structural settings from west to east the vavilov bathyal plain is bordered by the orogenic volcanic belt of the island of sardinia and maybe a central tyrrhenian arc the latter and the arc of the eolie which is active in the present time border the marsili plain the ages of the early spreading processes in the bathyal plains respectively from about 10 to 6 ma and from 1 9 to 1 3 ma appear to represent distinctive temporal markers in fact they may be coincident with the periods of quiescence of the volcanic activity that affected the adjoining arcs

first documented deep submarine explosive eruptions at the marsili seamount tyrrhenian sea italy a case of historical volcanism in the mediterranean sea abstract the marsili seamount ms is an about 3200 m high volcanic complex measuring 70 30 km with the top at 500 m b s l ms is interpreted as the ridge of the 2 ma old marsili back arc basin belonging to the calabrian arc ionian sea subduction system southern tyrrhenian sea italy previous studies indicate that the ms activity developed between 1 and 0 1 ma through effusions of lava flows here new stratigraphic textural geochemical and 14c geochronological data from a 95 cm long gravity core cor02 recovered at 839 m bsl in the ms central sector are presented cor02 contains mud and two tephras consisting of 98 to 100 area of volcanic ash the thickness of the upper tephra teph01 is 15 cm and that of the lower tephra teph02 is 60 cm the tephras have poor to moderate sorting loose to partly welded levels and erosive contacts which imply a short distance source of the pyroclastics 14c dating on fossils above and below teph01 gives an age of 3 ka bp calculations of the sedimentation rates from the mud sediments above and between the tephras suggest that a formation of teph02 at 5 ka bp ms ashes has a high k calcalkaline affinity with 53 wt

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

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

volcanological and petrological evolution of marsili seamount southern tyrrhenian sea abstract a swath bathymetric survey was conducted on marsili volcano the biggest seamount in the tyrrhenian sea it stands 3000 m above the surrounding oceanic crust of the 3500 m deep marsili back arc basin and is axially located within the basin the seamount has an elongated shape and presents distinctive morphology with narrow 2400 m on the edifice is governed by h2o and probably co2 exsolution and is not a feature indicative of shallow water depth eruption

geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex geodynamic settings the tyrrhenian sea and surroundings abstract information on the physical and chemical properties of the lithosphere asthenosphere system las can be obtained by geophysical investigation and by studies of petrology geochemistry of magmatic rocks and entrained xenoliths integration of petrological and geophysical studies is particularly useful in geodynamically complex areas characterised by abundant and compositionally variable young magmatism such as in the tyrrhenian sea and surroundings a thin crust less than 10 km overlying a soft mantle where partial melting can reach about 10 is observed for magnaghi vavilov and marsili which belong to the central tyrrhenian sea backarc volcanism where subalkaline rocks dominate similar characteristics are seen for the uppermost crust of ischia a crust about 20 km thick is observed for the majority of the continental volcanoes including amiata vulsini roccamonfina phlegraean fields vesuvius vulture stromboli vulcano lipari etna and ustica a thicker crust is present at albani about 25 km and at cimino vico sabatini about 30 km the structure of the upper mantle in contrast shows striking differences among various volcanic provinces volcanoes of the roman region vulsini sabatini alban hills sit over an upper mantle characterised by vs mostly ranging from about 4 2 to 4 4 km s at the alban hills however slightly lower vs values of about 4 1 km s are detected between 60 and 120 km of depth this parallels the similar and rather homogeneous compositional features of the roman volcanoes whereas the lower vs values detected at the alban hills may reflect the occurrence of small amounts of melts within the mantle in agreement with the younger age of this volcano the axial zone of the apennines where ultrapotassic kamafugitic volcanoes are present has a mantle structure with high velocity lid vs 4 5 km s occurring at the base of a 40 km thick crust beneath the campanian volcanoes of vesuvius and phlegraean fields the mantle structure shows a rigid body dipping westward a feature that continues southward up to the eastern aeolian arc in contrast at ischia the upper mantle contains a shallow low velocity layer vs 3 5 4 0 km s just beneath a thin but complex crust the western aeolian arc and ustica sit over an upper mantle with vs 4 2 4 4 km s although a rigid layer vs 4 55 km s from about 80 to 150 km occurs beneath the western aeolian arc in sardinia no significant differences in the las structure are detected from north to south the petrological geochemical signatures of italian volcanoes show strong variations that allow us to distinguish several magmatic provinces these often coincide with mantle sectors identified by vs tomography for instance the roman volcanoes show remarkable similar petrological and geochemical characteristics mirroring similar structure of the las the structure and geochemical isotopic composition of the upper mantle change significantly when we move to the stromboli campanian volcanoes the geochemical signatures of ischia and procida volcanoes are similar to other campanian centres but sr pb isotopic ratios are lower marking a transition to the backarc mantle of the central tyrrhenian sea the structural variations from stromboli to the central vulcano and lipari and western aeolian arc are accompanied by strong variations of geochemical signatures such as a decrease of sr isotope ratios and an increase of nd pb isotope and lile hfse ratios the dominance of mafic subalkaline magmatism in the tyrrhenian sea basin denotes large degrees of partial melting well in agreement with the soft characteristics of the uppermost mantle in this area in contrast striking isotopic differences of plio quaternary volcanic rocks from southern to northern sardinia does not find a match in the las geophysical characteristics the combination of petrological and geophysical constraints allows us to propose a 3d schematic geodynamic model of the tyrrhenian basin and bordering volcanic areas including the subduction of the ionian adria lithosphere in the southern tyrrhenian sea and to place constraints on the geodynamic evolution of the whole region

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

water co2 cl and f in melt inclusions in phenocrysts from three holocene explosive eruptions crater lake oregon rare melt inclusions 100 m in diameter trapped near the boundaries of corroded patchy zones in plagioclase phenocrysts from plinian pumice of three holocene eruptions were analyzed by ir spectroscopy for molecular h 2o oh groups and co 2 and by electron microprobe for cl and f the three rhyodacitic eruptions each of which began with aplinian phase occurred over 200 yr the llao rock and cleetwood eruptions ended with degassed lava flows and the subsequent climactic eruption with voluminous ignimbrite groundmass glass and melt inclusion compositions anhydrous are similar inclusions with total h 2o concentrations of 1 2 3 4 wt are adjacent to fractures or are hourglass inclusions suggesting partial degassing caused by depressurization melt inclusions in phenocrysts in climactic ignimbrite may have vesiculated for the same reason intact inclusions in plinian pumices have total h 2o concentrations believed to represent magmatic h 2o contents wt llao rock 5 3 5 3 cleetwood 3 8 4 7 climactic 3 9 0 2 l n 6 ratios of or molecular h 2o indicate closure temperatures of 200 500oc that reflect syn or posteruptive cooling co 2 concentrations are 25 ppm h 2o and co 2 concentrations indicate saturation pressures of 1 0 1 8 kbar or depths 5 km six inclusions from climactic pumice average 400 40 l ppm f 1880 70 ppm cl f and cl concentrations of the other samples are similar and not well correlated with each other or with total h 2o location of melt inclusions near boundaries of patchy zones which are mantled by oscillatory zoned overgrowths suggests that their h 2o concentrations represent magmatic values significantly before eruption although mean h 2o concentrations of analyzed melt inclusions decrease for the three successive eruptions it is not certain that this indicates a corresponding change in magmatic h 2o content during the interval between eruptions

geothermal structure of the tyrrhenian sea over 200 heat flow measurements have been carried out in the tyrrhenian sea mostly since 1977 as part of the heat flow map for italy and surrounding seas italian program as well as part of the french italian tyrrhenia program all data have been corrected for the influence of the plio quaternary sedimentation measured heat flow values were evaluated according to the sedimentary environment following criteria outlined by sclater et al 1980 in this way areas affected mainly by shallow thermal effects in the zones with maximum density of data have been displayed filtering out these shallow contributions the major regional geothermal trends were obtained the tyrrhenian basin can be divided in two distinct regions with different geothermal characteristics the northern part of the basin appears to be connected with the continental structures involved in the interaction between the corsica and tuscan margins the maximum heat flow area located offshore civitavecchia is related to the tensile structures of the tuscan geothermal province the most important thermal features of the central and southern part are located along the central belt trending nw se the lowest heat flow values are located in the peri tyrrhenian areas and are related to the continental margins of the basin while the maxima are connected with the stretched and thinned area localized in the bathyal plain taking into account the heat flow data as well as other geological and geophysical information an evolutionary model for the tyrrhenian sea is presented suggesting a generalized stretching of an initially continental crust accompanied by intensive rifting phases which may have favoured the onset of oceanic type crust

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

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

calc alkaline magmatism and rifting of the deep water volcano of marsili aeolian back arc tyrrhenian sea abstract geochemistry and mineral chemistry data indicate that new lava samples recovered from a large depth interval of marsili volcano southern tyrrhenian sea are calc alkaline the deep to intermediate portions of the volcano are made up by calc alkaline basalts whereas the summit consists of high potassium calc alkaline andesites the contents of mgo cao total iron cr ni and v decrease with increasing silica while k 2 o rb ba th nb and lree exhibit the opposite behavior the andesite lavas of the top at waterdepth shallower than about 800 m are younger than 0 2 ma composition of the basalts varies with the waterdepth overall the deepest products of marsili are geochemically more mafic than those erupted in the higher physiographic positions geochemical features suggest the existence of a mantle source that was modified by metasomatic acquirement of subduction derived incompatible elements the seamount lies on oceanic crust which formed above subducting lithosphere not earlier than about 2 ma ago it is currently undergoing extension along linear faults the major distensional fractures trend n s to n15 e paralleling the physiographic elongation of the volcano at the summit later faults have an oblique ne sw orientation which is associated with the eruption of high potassium andesites the transition from basalts to high potassium andesites is discussed as a possible response to the extension and rapid subsidence that dominate the volcano and surrounding region

seismicity and p wave velocity image of the southern tyrrhenian subduction zone summary this paper focuses on the deep earth structure and earthquake distribution within the southern tyrrhenian subduction zone we discuss seismological observations which provide insight into the mechanics of subduction processes for an unusual compressional margin the motivation for this work derives from the recognition that little is known about one of the most intriguing geodynamic features of the italian peninsula and the fact that a large amount of information can be extracted from data collected by the istituto nazionale di geofisica national seismic network we show that the hypocentres of intermediate and deep earthquakes that have occurred since 1988 image a nw dipping plane continuous from the ionian sea to the tyrrhenian down to 450 km depth we also present a 3 d model of the deep structure beneath southern italy derived using deep earthquake seismic tomography tomographic images reveal a high velocity body dipping from the apulian and iblean forelands towards the tyrrhenian basin in the crust and upper mantle at least down to 320 km depth this high velocity body may be related to the cold subducted ionian lithosphere earthquake hypocentres are confined within the high velocity body delineating the subduction beneath the calabrian arc

magma emplacement at anomalous spreading ridge constraints due to plagioclase crystals from basalts of marsili seamount southern tyrrhenian back arc abstract plagioclase crystals from four basalt samples dredged from different portions of the marsili seamount southern tyrrhenian italy provide a detailed record of the changes occurring in the surrounding magma during its ascent in the crust the textural features and chemical zoning i e an content and fe mg sr and ba concentrations of the plagioclases from each sample show that aggregation of various generations of crystals occurred in the host melt prior to eruption plagioclases resulting from crystallisation in small sill intrusions where local flotation of plagioclase may have occurred are ubiquitous instead large up to 1 mm homogeneous an rich plagioclases are rare and have only been found in two of the studied basalts recovered from the northern and southern portions of the volcano respectively these crystals record crystallisation events occurring long before eruption and probably derive from deep seated crystalline material at the highest an values the sr and ba concentrations of the studied plagioclases also indicate the existence of two distinct mafic magmas within the lower crustal plumbing system of the marsili volcano one with lower sr and ba contents than the other three of the four studied basalts came from magma with low sr and ba whereas the fourth which erupted from the southern portion of the volcano sampled magma richer in sr and ba the ascent of magma caused resorption of the previously formed plagioclase crystals and regrowth of normally or inversely zoned portions depending on the water saturated or water undersaturated conditions of the surrounding magma respectively small shallow magmatic reservoirs may be located under the southern part of the marsili volcano as testified by the resorbed sodic cores an52 57 found in the two basalt samples from this portion

unravelling the conundrum of river response to rising sea level from laboratory to field part i laboratory experiments the most recent deglaciation resulted in a global sea level rise of some 120 m over approximately 12 000 years in this part i of two parts a moving boundary numerical model is developed to predict the response of rivers to this rise the model was motivated by experiments at small scale which have identified two modes describing the transgression of a river mouth autoretreat without abandonment of the river delta no sediment starvation at the topset foreset break and sediment starved autoretreat with abandonment of the delta in the latter case transgression is far more rapid and its effects are felt much further upstream of the river mouth the moving boundary numerical model is checked against experiments the generally favourable results of the check motivate adaptation of the model to describe the response of the much larger fly strickland river system papua new guinea to holocene sea level rise this is done in the companion paper part ii

crystallization kinetics in continuous decompression experiments implications for interpreting natural magma ascent processes decompression experiments were performed to study the kinetics of plagioclase crystallization during ascent of hydrous rhyodacite magma these experiments differ from previous studies in that they employ a continuous rather than stepwise pressure time trajectory four series of experiments were performed at rates of 0 5 10mpa h corresponding to ascent rates of 0 007 0 14 m s experiments quenched along each decompression path allow snapshot style monitoring of progressive crystallization as expected rates of plagioclase nucleation and growth depend strongly on decompression rate regardless of decompression rate approximately equal volumes of feldspar crystallize during a given decompression interval even when the observed crystallinity is lower than the equilibrium crystallinity apparently a constant degree of solidification is maintained by a crystallization mechanism striking a shifting balance between nuclei formation and growth of existing crystals other key results pertain to the efficacy with which experimental results allow interpretation of the decompression histories of natural rocks feldspar microlites do not maintain chemical equilibrium with melt they are more anorthite rich than equilibrium plagioclase suggesting that interpretations of magma ascent processes in nature require comparisons with dynamic rather than static phase equilibrium experiments although decompression rate is an important element controlling final textures in volcanic rocks no single compositional or textural parameter uniquely records this rate of the criteria examined microlite number density and morphology are the best indicators of magma decompression rate based on a small number of comparisons between continuous and multi step decompression style at the same time integrated decompression rate 1mpa h decompression path evidently influences crystal texture with stepwise decompression yielding textures correlative with faster decompression than indicated by the time integrated decompression rate thus consideration of magma ascent style in addition to rate will undoubtedly strengthen the interpretive power of experimental studies for constraining natural magma ascent processes