an overview of experimental models to understand a complex volcanic instability application to mount etna italy abstract volcanic edifices are often unable to support their own load triggering the instability of their flanks many analogue models have been aimed especially in the last decade at understanding the processes leading to volcano flank instability general behaviors were defined and the experimental results were compared to nature however available data at well studied unstable volcanoes may allow a deeper understanding of the specific processes leading to instability providing insights also at the local scale etna italy constitutes a suitable example for such a possibility because of its well monitored flank instability for which different triggering factors have been proposed in the last two decades among these factors recent insar data highlight the role played by magmatic intrusions and a weak basement under a differential unbuttressing at the volcano base this study considers original and recently published experimental data to test these factors possibly responsible for flank instability with the final aim to better understand and summarize the conditions leading to flank instability at etna in particular we simulate the following processes a the long term activity of a lithospheric boundary as the malta escarpment separating the ionian oceanic lithosphere from the continental sicilian lithosphere below the most unstable east flank of the volcano b spreading due to a weak basement with different boundary conditions c the pressurization of a magmatic reservoir as that active during the 1994 2001 inflation period d dike emplacement as observed during the major 2001 and 2002 2003 eruptions the experimental results suggest that 1 the long term activity of a lithospheric tectonic boundary may create a topographic slope which provides a differential buttressing at the volcano base a preparing factor to drive longer term 10 5 years instability on the east flank of the volcano 2 volcano spreading 4 years has limited effect on flank instability at etna 3 magmatic intrusions 1 years both in the form of mogi like sources or dikes provide the most important conditions to trigger flank instability on the shorter term

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

magmatic evolution of a volcano studied by 230th 238u disequilibrium and trace elements systematics the etna case age determinations of several lava flows from etna through 230th 238u disequilibrium internal isochrons yield a precise chronology of the volcano s history for the last 200 000 years and emphasize the main episodes in the formation of this huge complex strato volcano study of 230th232th 0 initial ratios of lavas together with their trace element compositions yields a consistent model of magmatic evolution implying the existence for 200 000 years of a deep reservoir of alkalic magma periodically mixed with magmas of tholeiitic affinity these short periods of mixing appear to be related to the formation of the large calderas of etna in addition to these processes affecting the deep reservoir fractional crystallization also occurred in more superficial levels of the volcanic edifice thereby yielding several series of differentiation of relatively short duration as for its geochemistry etna s volcanism is of oceanic type but with its own characteristics and in a peculiar geodynamic context at the edge of the african plate

effects of the 1989 fracture system in the dynamics of the upper se flank of etna revealed by volcanic tremor data the missing link 1 fracture reactivation is a widespread process in nature even though evidence of magma induced reactivation is less documented here we provide evidence of the reactivation of a fracture system on the upper flank of the mt etna volcano and consider its possible implications in understanding the recent volcanic and tectonic activity a nnw sse trending fracture partly accompanied by magma emplacement in the form of a laterally propagating dike formed in 1989 on the upper se flank of etna lava effusions in 1991 1993 2001 and 2006 were associated with volcano tectonic vt seismicity and ground deformations on the upper part of the volcano which document the seismogenetic involvement of the 1989 fractures although without eruptive phenomena along the discontinuity in addition to the aforementioned episodes of vt seismicity differences in the characteristics of the background seismic radiation volcanic tremor were measured at stations close to these fractures during the eruptive activity on 24 november 2006 for which more detailed volcanological and seismological time histories are available moving on from these findings we analyze volcanic tremor data recorded close to the summit and along the s flank of the volcano to highlight the interactions between seismic radiation and the 1989 fracture system centroid location of volcanic tremor and wave field characteristics at stations of the permanent local seismic network of etna highlight the guidance role played by the 1989 fractures during the eruptive activity on 24 november 2006 in addition the collected data shed light on hitherto unknown structural features which appear to connect the volcano summit to the lower se slope and also play an important role in controlling the instability of the e flank more generally this study shows how 1 using an integrated approach it is possible to link apparently different features to a common structure showing uniform and distinct dynamics relevant at the volcano scale and 2 fracture reactivation can also occur by means of magma intrusion playing an important role in the transfer of magma within a volcanic edifice

the deformation offshore of mount etna as imaged by multichannel seismic reflection profiles abstract despite the clear evidence of active flank dynamics that is affecting the eastern side of mount etna the contribution of tectonic processes has not been yet understood so far the various models proposed to explain the observed flank deformation have been based on onshore structural data coming from the volcanic edifice the ionian offshore of mount etna has been only recently investigated using multichannel seismic profiles and offers the opportunity to image the structural features of the substrate of the unstable flank of the volcano this contribution aims at describing the deformation located offshore mount etna using multichannel seismic profiles recently acquired during three seismic surveys the onshore flank deformation of mount etna appears to be laterally confined by two tectonic guidelines trending roughly e w located to the north and south of the deforming flank the northern guideline in particular takes the surface expression of a sharp fault pernicana fault though often assumed that these boundary structures continue offshore as linear features connected to a frontal thrust ramp the occurrence of this simple offshore structural system has not been imaged in fact seismic data show a remarkable degree of structural complexity offshore mount etna the pernicana fault for instance is not continuing offshore as a sharp feature rather the deformation is expressed as ene wsw folds located very close to the coastline it is possible that these tectonic structures might have affected the offshore of mount etna before the pernicana fault system was developed less than 15 ka ago the southern guideline of the collapsing eastern flank of the volcano is poorly expressed onshore and does not show up offshore in fact seismic data indicate that the catania canyon a remarkable e w trending feature does not reflect a tectonic control seismic interpretation also shows the occurrence of a structural high located just offshore the edifice of mount etna whereas a complex deformation affects the boundary of this offshore bulge it shows only limited internal deformation part of the topography of the offshore bulge pre existed the constructional phase of mount etna being an extension of the hyblean plateau only in the northern part the bulge is a recent tectonic feature being composed by plio quaternary strata that were folded before and during the building of mount etna the offshore bulge is bounded by a thrust fault that can be related to the intrusion of the large scale magmatic body below mount etna

evolution of volcanism around the eastern sector of mt etna inland and offshore in the structural framework of eastern sicily abstract the authors highlight a new perspective to understanding the volcanism in the mt etna eastern sector inland and offshore based on original studies of the sea floor off the ionian coast of etna by means of various direct surveying methods underwater explorations and indirect ones bathymetric reconstructions using echosounders they also propose a new interpretation of geophysical geochemical and structural surveys carried out over the last two decades results show that eastern etnean sector s volcanism extends as far as the ionian sea to a maximum distance from the coast of probably about 20 km in their opinion the absence of outcropping apparatuses in the lower eastern flank of etna is due to these apparatuses being buried by a large detritic formation chiancone due to the dismantling of the ancient alkaline centres aac localised to the west the authors consider the structures highlighted by the study of the digital elevation model dem of the ionian sea floor and by the multibeam analysis marani et al 2004 from seafloor to deep mantle architecture of the tyrrhenian backarc basin vol 44 mem descr carta geol ital pp 1 2 to be of a volcanic nature this hypothesis opens up a new field of study within the evolution of the eastern etnean edge s volcanism inland and offshore in the last 500 ky and would further confirm the eruptive axes migration from east to west

dissolution kinetics of plagioclase in the melt of the system diopside albite anorthite and origin of dusty plagioclase in andesites the textures and kinetics of reaction between plagioclase and melts have been investigated experimentally and origin of dusty plagioclase in andesites has been discussed in the experiments plagioclase of different compositions an96 an61 an54 an23 and an22 surrounded by glasses of six different compositions in the system diopside albite anorthite was heated at temperatures ranging from 1 200 to 1 410 c for 30 min to 88 h textures were closely related to temperature and chemical compositions a crystal became smaller and rounded above the plagioclase liquidus temperature of the starting melt glass and remained its original euhedral shape below the liquidus whatever the temperature the crystal melt interface became rough and often more complicated sieve like texture composed of plagioclase melt mixture in the scale of a few m was developed from the surface of the crystal inward formation of mantled plagioclase if the crystal is less calcic than the plagioclase in equilibrium with the surrounding melt and the interface remained smooth if the crystal is more calcic than the equilibrium plagioclase from these results the following two types of dissolution have been recognized 1 a crystal simply dissolves in the melt which is undersaturated with respect to the phase simple dissolution and a crystal is partially dissolved to form mantled plagioclase by reaction between sodic plagioclase and calcic melt partial dissolution the amount of a crystal dissolved and reacted increased proportional to the square root of time this suggests that these processes are controlled by diffusion probably in the crystal mantled plagioclase produced in the experiments were very similar both texturally and chemically to some of the so called resorbed plagioclase in igneous rocks chemical compositions and textures of plagioclase phenocrysts in island arc andesites of magma mixing origin have been examined cores of clear and dusty plagioclase were clacic about an90 and sodic about an50 respectively this result indicates that dusty plagioclases were formed by the partial melting due to reaction between sodic plagioclase already precipitated in a dacitic magma and a melt of intermediate composition in a mixed magma during the magma mixing

very shallow earthquakes and brittle deformation in active volcanic areas the eatnean region as an example abstract some aspects of the stress field acting in active volcanic areas were investigated by studying the relationship between surficial seismicity h 1 2 km and the brittle deformation pattern of the etna volcano the magmatic composition and structural character of mt etna are described together with its geodynamic regional context after a discussion of the problem of the state of stress in active volcanoes and a definition of very shallow seismicity the high level of surficial seismicity the morphology of the sedimentary basement and the kinematic behaviour of the faults suggest that the eastern flank of mt etna is a shallow seismotectonic domain structurally decoupled from the rest of the volcanic body this flank shows a tendency to slide in an eastern direction and is bound to the north by a left lateral oblique slip normal fault trending e w and in the south by an arcuate fault system with right lateral features right lateral oblique slip normal faults

origin of sector trilling in cordierite in daimonji hornfels kyoto japan sector trilling of cordierite in hornfels in the inner part of a contact aureole at daimonji japan is a new type which consists not only of six 100 sectors a sectors forming trilling but also of 001 sectors c sectors and high index sectors h sectors complex twins within and among these sectors were studied from a viewpoint of a pseudo twin the complex texture originated from both growth and transformation processes the c sector consists of three groups of domains which are related by a pseudo twin this intrasector pseudo twin indicates that the initial phase of the c sector was hexagonal cordierite indialite which later transformed to orthorhombic the a sector is related to adjacent sectors by a rotation of 120 around the c axis resulting in an intersector pseudo twin the a sector is interpreted to have formed by overgrowth of orthorhombic cordierite on prism faces of indialite the h sector with the dendritic texture is also interpreted to have grown as orthorhombic cordierite in hornfels in the middle part of the aureole cordierites with sector trilling often coexist with single crystals of cordierite and the sector trilling has no c and h sectors this trilling type suggests that nucleation of indialite was subsequently followed by growth of orthorhombic cordierite in its stable field

response of shallow marine carbonate facies to third order and high frequency sea level fluctuations hauptrogenstein formation northern switzerland abstract facies patterns in shallow marine carbonates of the hauptrogenstein formation of northern switzerland middle bajocian to early bathonian reflect small changes in sea level third order sea level fluctuations calculated from large scale facies patterns alternations of marl and carbonate dominated sedimentary units on the level of members and subsidence show two phases of sea level rise and fall in the late bajocian and a relative sea level rise in the early bathonian most of the sedimentary rocks were produced during phases of relative rise and highstand of sea level no periods of emergence during lowstands are preserved sea level changes of a higher order have been analyzed by facies changes at the outcrop scale thin shallowing up parasequences 0 5 6 m thick have been correlated across platform ramp and offshore sedimentary environments in each of these environments carbonates react differently to sea level fluctuations relative rises in sea level are represented by non deposition and biogenic sediments periods of stable or slightly falling sea level are dominated by oolitic sediments 1 in the offshoal environment marl layers at the base of thin shallowing up units are covered by increasingly proximal tempestites 2 in the ramp environment oblique stratified oolitic and bioclastic grainstones are bounded by marine flooding surfaces 3 on the platform marine flooding surfaces are overlain by beds deposited under moderate energy conditions coral beds oncoid beds platform tempestites which are in turn covered by high energy oblique stratified oolitic grainstones such parasequences deposited in response to small scale high frequency sea level changes can be correlated over distances of more than 100 km a model for evolution and response of carbonate facies to sea level changes is presented

tholeiitic and calc alkaline magma series at adatara volcano northeast japan 1 geochemical constraints on their origin abstract low alkali island arc by jakes and gill 1970 or low k by gill 1978 tholeiitic rocks are closely associated with calc alkaline rocks in the outer volcanic zone called the nasu volcanic zone of northeast japan major element trace element ni cr co sc v zr nb zn rb cs ba sr ce and y and sr isotope compositions are presented for 9 low alkali tholeiitic and 16 calc alkaline samples of adatara volcano belonging to the nasu volcanic zone in the trace elements vs sio 2 diagram the tholeiitic series and calc alkaline series show different trends to each other for co sc v zr rb sc ba and sr as expected from k 2 o contents the calc alkaline samples are enriched in incompatible elements such as rb cs ba ce and zr compared with the tholeiitic samples on the other hand contents of nb in the calc alkaline samples are somewhat lower than those in the tholeiitic samples plots of ni and cr contents vs sio 2 for the tholeiitic samples come near smooth trend lines whereas those for the calc alkaline samples are scattered sr isotopic ratios in the tholeiitic series lie within the range between 0 7056 and 0 7058 and between 0 7048 and 0 7052 in the calc alkaline series smooth major and trace element compositional trends in the tholeiitic series are successfully modelled by simple fractional crystallization of plagioclase hypersthene augite titanomagnetite and minor olivine similarly crystal fractionation models can closely reproduce major and most of the trace element variations in the calc alkaline series but failed to account for irregular variations of ni and cr the scattering of ni and cr probably reflects simultaneous crystal fractionation and subordinate magma mixing in the subvolcanic chamber the inferred fractionated phases for the calc alkaline series are richer in augite and titanomagnetite and slightly poorer in plagioclase than those for the tholeiitic series the tholeiitic magma and calc alkaline magma are not derived from a common parental tholeiitic magma and the calc alkaline parental magma is richer in sio 2 and incompatible elements in particular rb and zr poorer in radiogenic sr and possibly more oxidized than the tholeiitic parental magma

late quaternary slip rates on the acireale piedimonte normal faults and tectonic origin of mt etna sicily abstract mt etna is located along the east coast of sicily near the boundary between the continental crust of the hyblean plateau and the mesozoic oceanic crust of the ionian basin the main active faults near mt etna cut the base of its eastern flank forming a 30 km long system of nne and nnw trending ene chelon fault segments the acireale piedimonte system showing dip slip and oblique right lateral motion most segments are associated with shallow depth seismicity and all have late pleistocene to holocene vertical slip rates ranging between 1 and 2 mm yr typical of major active normal faults worldwide eruptive fissures arranged in nne to ne trending zones cut the highest slopes of the volcano on the footwall of the normal fault system structural analysis suggests that current motions along both the active faults and eruptive fissures are kinematically compatible and simply linked with ongoing wnw ese directed regional extension such extension characterizes at a greater scale the active tectonics of southern italy where all large shallow historical earthquakes have remained confined within a narrow normal fault belt or rift zone stretching from the northern calabrian arc to southeastern sicily the southernmost west dipping faults of that rift zone in calabria aspromonte cut across the calabro peloritan thrust belt to join the mostly east dipping acireale piedimonte faults along the western boundary of ionian oceanic lithosphere which continues southwards as the malta escarpment we thus relate magmatism at etna to dilational strain on the footwall of an east facing crustal scale normal fault at the bend where the siculo calabrian rift zone veers 60 eastwards as it begins to cross the calabrian arc leaving the east facing margin of the ionian sea to catch up with the west facing margin of the tyrrhenian sea farther north

platform drowning leading to cool water carbonate deposition evolution of a late ordovician turinian chatfieldian mixed sediment platform within the taconic orogen long point group newfoundland appalachians late ordovician turinian chatfieldian drowning of a mixed carbonate siliciclastic platform within the taconic orogen newfoundland appalachians is recorded by net deepening of an initial warm shallow water platform succession lourdes formation culminating in a metre scale thick condensed interval that characterizes a drowning succession punctuated by storm deposits composition of transported material suggests that seaward drowning was coupled with back stepping of a high energy carbonate factory related to hinterland uplift and erosion that would eventually lead to drowning of the outer platform beneath marine transported siliciclastic sediments winterhouse formation in the new offshore shelf setting a sparse reciprocal stratigraphy of fine to very coarse grained phosphatic carbonate and mixed sediment is interpreted to document gravity flow deposition downgradient from either a sustained or episodically developed high energy cool water carbonate source along the inner shelf transported carbo

geological evolution of mount etna volcano italy from earliest products until the first central volcanism between 500 and 100 ka ago inferred from geochronological and stratigraphic data we present an updated geological evolution of mount etna volcano based on new 40ar 39ar age determinations and stratigraphic data integrating the previous k ar ages volcanism began at about 500 ka ago through submarine eruptions on the gela catania foredeep basin about 300 ka ago fissure type eruptions occurred on the ancient alluvial plain of the simeto river forming a lava plateau from about 220 ka ago the eruptive activity was localised mainly along the ionian coast where fissure type eruptions built a shield volcano between 129 and 126 ka ago volcanism shifted westward toward the central portion of the present volcano val calanna moscarello area furthermore scattered effusive eruptions on the southern periphery of etna edifice occurred until about 121 ka ago the stabilization of the plumbing system on the valle del bove area is marked by the building of two small polygenic edifices tarderia and rocche volcanoes their eruptive activity was rather coeval ending 106 and 102 ka ago respectively during the investigated time span volcanism in etna region was controlled by a main e w extensional tectonic related to the reactivation of malta escarpment fault system in eastern sicily

remobilization of andesite magma by intrusion of mafic magma at the soufriere hills volcano montserrat west indies the 1995 1999 eruption of the soufriere hills volcano montintroduction serrat has produced a crystal rich andesite containing quenchthe soufriere hills volcano montserrat located in the textured mafic inclusions which show evidence of having been molten lesser antilles island arc in the west indies began to when incorporated into the host magma individual crystals in the erupt on 18 july 1995 after about 350 years of dormancy andesite record diverse histories amphibole phenocrysts vary from young et al 1998b the eruption was preceded by a pristine and unaltered to strongly oxidized and pseudomorphed by period of seismic swarms which began in january 1992 anhydrous reaction products plagioclase phenocrysts are commonly previous earthquake crises have occurred on montserrat reverse zoned often with dusty sieve textures reverse zoned rims are in 1896 1897 1932 1935 and 1966 1967 powell 1938 also common on orthopyroxene phenocrysts pyroxene geothermometry shepherd et al 1971 initial phreatic and phregives an average temperature of 858 20 c for orthopyroxene atomagmatic activity was followed by extrusion of an phenocryst cores whereas reverse zoned rims record temperatures andesitic lava dome in november 1995 pyroclastic flows from about 880 to 1050 c the heterogeneity in mineral rim generated by gravitational collapse of the unstable dome compositions zoning patterns and textures is interpreted as reflecting have been the dominant form of activity throughout the non uniform reheating and remobilization of the resident magma eruption but periods of explosive activity producing body by intrusion of hotter mafic magma convective remobilization pumice flows and falls have also occurred robertson et results in mixing together of phenocrysts that have experienced al 1998 young et al 1998b dome growth ceased different thermal histories depending on proximity to the intruding suddenly in march 1998 and further activity up to may mafic magma the low temperature and high crystallinity are 1999 has mainly involved gravitational collapses of the interpreted as reflecting the presence of a cool highly crystalline dome and periods of ash venting with some small scale magma body beneath the soufriere hills volcano the petrological vulcanian explosive events observations in combination with data on seismicity extrusion rate the soufriere hills volcano is the only active centre and so2 fluxes indicate that the current eruption was triggered by on montserrat the volcano is a composite of at least recent influx of hot mafic magma five andesitic lava domes flanked by pyroclastic deposits rea 1974 identified four other volcanic centres all

digital reconstruction and stratigraphic evolution of a microbial dominated isolated carbonate platform terminal proterozoic nama group namibia abstract a terminal proterozoic ca 550 ma isolated carbonate platform developed downdip on a carbonate ramp of the nama group of southern namibia the stratigraphic evolution of the platform was reconstructed from an extensive dataset that was compiled by using digital surveying technologies and traditional outcrop observations digital field geology techniques enabled rapid and accurate mapping over the 10 km outcrop belt with spatial and geological information captured at scales ranging from centimeters to kilometers furthermore these digital geology techniques made the reconstruction and interpretation of the development of the carbonate platform considerably more efficient and quantitative the carbonate platform deposits encompass three accommodation cycles in which each subsequent cycle experienced progressively greater influence of a long term accommodation increase aggradation and progradation during the first cycle produced a flat topped sheet like platform deposits of the first cycle show a coarsening upward motif grading from dominantly columnar stromatolitic thrombolites and interbedded mudstone grainstone at the base to dominantly massive and cross bedded dolostones toward the top the second cycle features aggradation and is typified by the formation of a distinct margin and development of a bucket shaped geometry the margin contained thrombolite mounds and domes whereas columnar stromatolitic thrombolites dominated the platform interior the third and last cycle records a gradual deepening trend with initial aggradation and formation of well bedded thin deposits in the interior and microbial mounds at the margins while the interior drowned the platform margins kept up with rising sea level and complex pinnacle reefs formed which contained fused and coalesced thrombolite mounds flanked by bioclastic grainstones and collapse breccias the top of the unit consists of a set of isolated large thrombolite mounds flanked by shale and is interpreted to indicate the final stage of the carbonate platform before drowning the overall geometric evolution and spatial scale of this platform from flat topped to bucket shaped with elevated margins is recorded in many proterozoic and phanerozoic isolated carbonate platforms this study clearly illustrates that accommodation changes are a fundamental control on the development of carbonate platforms regardless of whether they are formed from microbial or metazoan components or are of precambrian or phanerozoic age significantly the architectural elements and spatial dimensions are comparable throughout earth history

shelf geometry response to changes in relative sea level on a mixed carbonate siliciclastic shelf in the guyana basin abstract differences in the shelf margin geometry for various depositional regimes show how siliciclastic and carbonate margins respond differently to changes in accommodation space during the cenozoic sequences of carbonate and siliciclastic sediment were deposited in the guyana basin on the passive continental margin of ne south america study of the sequence geometries reveal significantly different geometric responses to changes in relative sea level of intervals dominated by carbonates to intervals dominated by siliciclastics using the geometrical shelf break as a reference point aggradation and progradation rates for the carbonate and siliciclastic depositional systems were measured in siliciclastics the lateral position of the margin remains roughly stationary with relative sea level rises in the order of 30 m my at higher rates the margin retreats at lower rates it progrades carbonate margins remain stationary or slightly progradational even with relative sea level rises of up to 100 m my the fastest rates observed in this study this illustrates the strong tendency of carbonate platforms to stack their margins and keep up with relative rises in sea level rather than gradually retreat landward as do siliciclastics this observation may explain why carbonate platforms preferentially try to defend a margin prior to ultimate backstepping the high aggradation potential of carbonate margins also gives onlap and downlap termination patterns on seismic profiles where carbonate platforms develop on sloping siliciclastic shelves the resulting unconformities are a result of differences in sediment dispersal between the two systems and not necessarily from changes of relative sea level

analogue modeling of flank instability at mount etna understanding the driving factors 1 mount etna is characterized by significant flank instability whose triggering factors are still a matter of debate we use analog models to investigate the role of different factors in the models a cone and base of granular material simulate the volcanic edifice and its basement the asymmetric geometry of the basement simulates the topographic gradient around the volcano injections of silicone sets a and b and low viscosity vegetable oil set c simulate the pressurization of plutonic complex deep reservoirs and the emplacement of dikes respectively other experiments set d reproduce regional extensional tectonics in the last 105 years within layers with different cohesion simulating strength differences in the basement laser scanner and control points allow the tracking of surface deformation with submillimeter precision the asymmetric topography enhances flank instability on the side with the weakest confinement i e seaside providing the preparing factor for instability in sets a and b any type of pressurized reservoir enhances up to 10 times the amount of flank instability toward the seaside with respect to the other flanks of the volcano in set c dike emplacement enhances seaside flank instability up to 8 times regional tectonics and crustal layering in set d enhance flank instability up to 2 and 1 3 times respectively considering the duration and frequency of the simulated processes in nature we propose a semiquantitative evaluation and hierarchy of the factors controlling flank instability at etna magmatic activity point like source inflation and dike emplacement provides the most important triggering factor extensional tectonics in the last 105 years and crustal layering are more than 10 times less effective this study shows the importance of differential buttressing at the volcano base for flank instability this condition is an important indication to expect asymmetric activity in any volcano flank eruptions and deformation

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

growth mode of middle triassic carbonate platforms in the western dolomites southern alps italy abstract the correlation of carbonate platform and slope sediments with biostratigraphically and radiometrically dated basinal successions in the western dolomites allows the reconstruction of the growth of a middle triassic carbonate platform schlern rosengarten over a time interval of approximately five ammonoid zones reitzi secedensis curionii gredleri archelaus zones the whole platform evolution had a total duration of

island arc carbonates characterization and recognition in the ancient geologic record abstract carbonates of island arc origin that are preserved in paleozoic mesozoic terranes of the north american cordillera exhibit a distinctive suite of paleontologic and lithologic features and share a fundamental similarity with limestones forming in modern volcanic arcs this study provides the first detailed synthesis of carbonate depositional systems in island arcs and documents primary sedimentary constituents based on facies relationships and faunal communities models are developed that show patterns in the long term evolution of shallow marine organisms and the construction evolution and demise of carbonate platforms in island arcs a suite of criteria is identified that may be used to differentiate island arc carbonates from limestones that accumulated in other platform settings biogeographic isolation prolonged subsidence steep submarine slopes and tectonic instability of volcanic edifices contribute to the development of relatively high levels of species endemism impoverished normal marine faunas complex provincial affinities and relict biotas in limestones that are characterized by exceptionally thick platform and periplatform sequences fringing and barrier reefs at the shelf margin extensive lagoonal deposits and rapid lateral and vertical facies changes although destructive tectonic and geologic processes in island arcs may hinder determining the original size and extent of the carbonate platform and particular facies types may not be represented e g fringing and barrier reefs may be replaced by sand shoals at the platform margin many characteristics have potential value for identifying carbonates of island arc origin in the ancient rock record apart from being associated with calc alkaline volcanic and volcaniclastic assemblages the most valuable suite of features for recognizing island arc carbonates is marine biotas that exhibit elevated levels of endemism and mixed paleobiogeographic affinities extraordinary thicknesses of platform shallow marine and periplatform carbonates and rapid facies changes between volcanic and carbonate rocks and between shallow and deep water limestones recognizing that an ensemble of features is distinctive within island arc carbonates considerably enhances identification of volcanic arcs in the ancient geologic record and thus improves the likelihood of successfully unraveling the complex geologic history of ocean basins

marine biodiversity through the late cenomanian early turonian palaeoceanographic controls and sequence stratigraphic biases changes in the marine macro and microfauna sedimentary geochemistry and surface water palaeoproductivity through the last 500 000 years of the cenomanian and first 300 000 years of the turonian are documented these are based on the succession at eastbourne the thickest and most complete section through the late cenomanian and early turonian in the anglo paris basin two levels of rapid faunal and geochemical change are identified one coincident with a significant increase in siliciclastic input at the base of the plenus marls member and the other with a marked drop in surface water productivity near the top of the same unit faunal change is demonstrated to be largely a pattern of immigration emigration rather than true extinction and our sequence stratigraphical analysis shows that it was coincident with major sea level changes no evidence is found to support the hypothesis that reduced bottom water oxygenation developed and was responsible for extinctions amongst the benthos in mid shelf environments the onset of pure chalk facies is interpreted to mark the breakdown of shelf break fronts and the spread of oligotrophic oceanic waters over much of the continental shelf initiated by rising sea level the cenomanian turonian event far from recording a mass extinction of shelf fauna is most probably an artifact caused by a significant switch in the nature of the surviving sedimentary record as a result of a major but perfectly ordinary oceanographic change

melt mineral fluid interactions in ultramafic nodules from alkaline lavas of mount etna sicily italy melt and fluid inclusion evidence abstract clinopyroxene phenocrysts and ultramafic nodules in the ancient alkaline lavas of mount etna contain melt and fluid inclusions which represent immiscible trapping of basaltic melt and co2 inclusions consist of glass vapor co2 hosted by clinopyroxene with kaersutite magnetite spinel and apatite daughter minerals type i and liquid co2 vapor co2 glass secondary inclusions type ii with highly variable fluid glass ratios electron microprobe investigations on type i melt inclusions indicate a glass of trachitic composition with extremely high chlorine contents 0 5 1 wt which we believe evolved from an initial melt composition of an alkali basalt homogenization temperatures th n 128 of type ii co2 glass inclusions display a bimodal fluid density distribution with high density 0 61 0 75 g cm3 co2 fluids in the nodules and low density 0 23 0 61 g cm3 co2 fluids in the phenocrysts a two step degassing process is proposed with high density immiscible co2 fluids formed at pressures of about 4 3 kbar the density distribution suggests interaction events between nodules ascending lavas and fluid phases with a peak around 3 5 kbar a second generation of lower density co2 is recorded around 2 8 kbar most likely prior to eruption

large submarine landslides offshore mt etna 1 high resolution seismic data we collected in the ionian sea reveal large submarine landslide deposits offshore from mt etna italy spatially consistent with the eastern flank collapse of this volcano a large debris avalanche deposit we relate to the valle del bove scar displays long offshore run outs till 20 km and a volume of a few tens of cubic kilometres 16 21 km 3 other landslide deposits are also imaged in particular a striking unique record of the relative timing of multiple submarine large slump events

hot fingers in the mantle wedge new insights into magma genesis in subduction zones abstract quaternary volcanoes in the northeast japan arc can be grouped into 10 volcanic clusters striking transverse to the arc these have an average width of 50 km and are separated by parallel gaps 30 75 km wide this clustering of volcanic centres topographic profiles low velocity regions in the mantle wedge and local negative bouguer gravity anomalies along the japan sea side of the volcanic arc are closely correlated all these observations may be related to locally developed hot regions within the mantle wedge that have the form of inclined 50 km wide fingers each of the 10 fingers recognised extends from deep mantle 150 km below the back arc region towards the shallower mantle 50 km beneath the volcanic front quaternary volcanoes are built immediately above the hot mantle fingers the volcanic basement along the fingers has been uplifted by repeated injection of magmas into the crust accompanied by quaternary volcanic activity at the surface although volcanic activity is rare along the japan sea coast tomographic results show that hot low velocity mantle fingers exist within the mantle wedge the negative bouguer anomalies at the rear of the volcanic arc could be caused by magmas supplied from the hot mantle fingers these have not yet been erupted but have accumulated at the moho discontinuity

chlorine isotope composition of volcanic gases and rocks at mount etna italy and inferences on the local mantle source abstract we present the first chlorine isotope compositional data for gases and lavas from mount etna italy and to our knowledge of active mediterranean volcanism we investigated lavas erupted and gases discharged during 2008 2011 from a high temperature fumarole ht 300 c and plume gases from both north east and central craters most of the samples vary in a narrow range of chlorine isotope composition 37 cl values 0 0 7 with gases partially overlapping with rocks only ht gases sampled in 2009 have been clearly affected by secondary processes 37 cl values 15 9 resulting in partial removal of chlorine and isotopic fractionation producing a 37 cl enrichment in the residual gaseous hcl these secondary processes also affect although to a lesser extent plume gases from north east crater nec although post magmatic processes are able to modify the chlorine isotope composition 37 cl values are not affected by magma degassing for residual fractions 0 3 in the melt or any effect is within our data variability finally 37 cl values and cl k ratios of magmatic chlorine constrain the etnean source to be compatible with depleted mantle dmm contaminated by altered oceanic crust aoc in agreement with indications from more common isotopic tracers of mantle processes

the extent and patterns of sediment filling of accommodation space on great bahama bank abstract great bahama bank gbb is the modern example of a flat topped isolated carbonate platform it is a major modern location of carbonate deposition that stands behind much of the understanding of modern processes of carbonate sedimentation serves as a training venue for academia and industry is the basis for numerous geological models and is commonly used as a reservoir analog gbb also provides valuable insight into the extent and patterns of sediment fill of accommodation space atop an isolated carbonate platform satellite imagery landsat tm and etm and an extensive set of water depth measurements n 5 723 were used to map bathymetry across gbb and derive a digital terrain model dtm analyzing the extent patterns and nature of sediment fill of accommodation space was facilitated by partitioning a depositional facies map on the basis of the dtm to show that 18 of accommodation on the gbb is overfilled and filled emergent to 1 5 m water depth 52 is underfilled 1 5 to 6 0 m and 30 is unfilled 1 5 m water depth and therefore the greater part of available accommodation 88 000 km2 remains incompletely filled with sediment areas of filled accommodation mostly extend platformward from the western coastlines of islands which in turn are preferentially distributed along the eastern windward margin of the gbb seventy percent of sediment in the areas of filled accommodation is rudstone high energy grainstone grainstone and mud poor packstone although dominated by grainstones 45 since it occupies so much space 55 000 km2 the underfilled sector also contains the most heterogeneous facies mosaic and by definition therefore the greatest and most complex lateral facies variations although islands are numerous n 1 430 they occupy only 8 or 8 700 km2 of the platform top despite their small proportional occupancy of the platform islands play a direct role in the accumulation of muddy fabrics and exert a sphere of influence over the character of sedimentation for many tens of kilometers from their coastlines further since islands represent the portion of the bank where accommodation has been overfilled their rarity emphasizes the challenges that such a large platform faces in filling accommodation space even given the diverse grain factories producing carbonate sediment mud precipitation through whitings ooids and reefs along the platform margins skeletal sediments and nonskeletal grains such as fecal pellets peloids and pelletoids two factors can be evoked to explain the inability of gbb to fill accommodation space first falling sea level during the pleistocene appears to have repeatedly aborted the filling process by analogy it will not be able to do so in the holocene either a situation exasperated by the second factor which is that most of the holocene gbb particularly areas away from islands presently lack any appreciable filling instead facies analysis suggest reduced sedimentation and enhanced cementation through regional mapping the work delivers a platform wide assessment of how accommodation is filled and the facies responsible for the filling amongst other trends by highlighting how the thickest accumulations of holocene sediment are skewed to the windward margin of the gbb and related to the presence of islands whereas the thinner accumulations which dominate the platform interior and are more grainy but also more heterogeneous than the thicker deposits these data might contain useful guidelines as to how depositional cycles might vary laterally in ancient systems

empirical evidence of orthogonal relationship between directional site effects and fracture azimuths in an active fault zone the case of the mt etna lower eastern flank abstract mt etna in eastern sicily is a composite active volcano whose eastern flank is affected by several normal and strike slip active faults in this study geological structural field survey and ambient vibration measurements are performed in the lower eastern flank of mt etna in order to define the role of the tectono stratigraphic setting in the seismic site response the sites of measurements are mainly distributed inside the few hundreds of meters long s caterina graben which is located between two main seismogenic active faults of this volcano sector the acireale and the fiandaca faults our study aims at defining the contribution of the fault related active deformation in determining the local ground motion amplification also providing a subsoil geological model based on the integration of geological and geophysical investigation therefore structural measurements were made in seven sites revealing coseismic and aseismic extensional fractures mainly striking nnw the seismic site response was studied processing the ambient vibration measurements through horizontal to vertical spectral ratio the measured fundamental frequency falls in the range 1 0 4 0 hz that we linked to the presence of a velocity contrast at depth of 80 200 m by calibrating a frequency depth function moreover the seismic site effect is due to the stratigraphic setting and is markedly directional showing maximum amplification along the direction orthogonal to the strike of the observed isooriented extensional fracture field produced by the activity of the s caterina graben it is noteworthy that far from the graben on sites of measurements located near the fiandaca fault we observed directional effects parallel to the direction of maximum extension inferred for this tectonic lineament our results suggest a linkage between directional site effects and local stress tensors and fractures field orientation

biosedimentology of the early jurassic post extinction carbonate depositional system central high atlas rift basin morocco this study documents a liassic example of the long ranging effects of mass extinction on carbonate systems biohistoric constraints inherent in the liassic carbonate depositional system are deciphered from normal marine sub tidal deposits of the central high atlas rift basin morocco through hettangian sinemurian to early toarcian times the integration of results from the analysis of lithofacies depositional geometries microfacies macrobenthos carbonate build ups carbon and oxygen stable isotopes and rare earth element yttrium distribution patterns allows the intrinsic or biohistoric control on the central high atlas deposits to be separated from extrinsic factors such as basin development and palaeoclimate the survival interval in the aftermath of the end triassic mass extinction persisted until the early sinemurian indicated by a severely depleted carbonate system impoverished in skeletal organisms a tectonic pulse at the early to late sinemurian boundary interval caused a basin widening with immigration of a marine fauna however until the latest sinemurian macdonelli subzone of the raricostatum zone the deposits were dominated by filter feeding benthic heterotrophs sponges brachiopods polychaetes and crinoids during this stage primary production within the enlarged basin must have been largely planktonic and there was a net flux of organic matter to the sea floor oxygen minimum zone a regional radiation of organic walled phytoplankton is inferred to explain the selective success of the filter feeding community and the occurrence of sponge mounds thus significant effects of the end triassic mass extinction are still present during the late sinemurian through almost the entire pliensbachian a highly productive shoal rimmed carbonate platform existed it developed subsequent to tectonic reorganization and a marine recirculation event radiolarian facies 13c 1 1 strongly negative ce anomaly photosymbiotic sediment producers mainly large bivalves now state the success of specialists and environmental equilibrium conditions in the latest pliensbachian the climax stage was reached with the development of a coralgal reef rimmed carbonate platform the liassic carbonate depositional system experienced a terminal multicausal early toarcian drowning event during which most of the large bivalves became extinct

dike emplacement and flank instability at mount etna constraints from a poro elastic model of flank collapse this work was funded by istituto nazionale di geofisica e vulcanologia ingv and the italian dipartimento per la protezione civile dpc dpc ingv project v4 flank

petrology of aoso volcano northeast japan arc temporal variation of the magma feeding system and nature of low k amphibole andesite in the aoso osore volcanic zone the aoso volcano is a member of the newly defined volcanic front of northeast japan characterized by the occurrence of low k and hornblende andesites its activity can be divided into three stages the early caldera forming and late stages while petrographic and geochemical data show all products underwent magma mixing or co mingling sr and nd isotopic ratios indicate that all are consanguineous the end member magmas are basaltic and andesitic in the early stage but basaltic and dacitic in the late stage in the caldera forming stage hornblende free and hornblende rich andesites co mingled which triggered an explosive eruption leading to caldera formation hornblende occurs also in the dacite from the early part of the late stage these hornblende andesites and dacites are lower in magmatic temperature compared to hornblende free andesites the estimated basaltic end member is low k and high in magmatic temperature and can be derived by a high degree of partial melting of mantle under the volcanic front the estimated andesitic and dacitic end members cannot be derived from the basaltic end member magma through fractional crystallization but can be derived from partial re melting of the solidified low k basalt leaving amphibolitic and gabbroic residues respectively

importance of gravitational spreading in the tectonic and volcanic evolution of mount etna the interaction between gravity and thermal effects largely determines the structural and magmatic evolution of volcanic constructs at scales spanning several orders of magnitude from small cones to the oceanic crust1 3 although gravitational spreading is a direct consequence of this interaction and a fundamental process in volcano growth it is rarely recognized as such here we describe a striking example of this process at etna volcano in italy the volcano and its clay rich substratum are slowly spreading towards the east and south driven by gravity spreading produces extensional structures in the summit region and contpressional structures at the base of the volcano eastward movement of the volcanic edifice over a stationary magma supply may be the cause of an apparent westward migration of volcanic activity as gravitational spreading seems to control the location and magnitude of shallow seismicity and flank eruptions an appreciation of its effects could become an essential element of future volcanic hazard evaluation our model proposed here for etna may also be relevant to a reinterpretation of the geological history of a number of other volcanoes

tholeiitic and calc alkaline magma series at adatara volcano northeast japan 2 mineralogy and phase relations abstract low alkali low k by gill 1978 or island arc by jakes and gill 1970 tholeiitic magma suites are closely associated with medium k by gill 1978 calc alkaline suites in the outer volcanic zone called nasu volcanic zone nvz of northeast japan chemistry and phase relations of phenocrysts are studied for representative 5 low alkali tholeiitic and 8 calc alkaline rock samples of adatara volcano in nvz in order to examine the mineralogical evolutionary mechanisms of the two series of magmas also clarified are differences in the magmatic temperature and oxygen fugacity between the two magma series the correlations between whole rock chemical compositions and mineralogy in the tholeiitic suite at this volcano are well documented supporting the argument that the members of this suite are related through fractional crystallization of observed phenycrystic phases part 1 fujinawa 1988 mineralogical observations in the calc alkaline suite are compatible with the views based on their whole rock chemical compositions although fractional crystallization process is dominant in the evolution of the calc alkaline magma intermittent mixing of small amounts of magnesian high temperature magmas operates concurrently temperature estimates with the two pyroxenes geothermometer range from 1080 c to 970 c in the tholeiitic suite whereas from 990 to 850 c in the calc alkaline suite temperature oxygen fugacity trends indicate that the low alkali tholeiitic magma evolves under conditions of higher temperature and lower oxygen fugacity than the calc alkaline magma in view of the fact that the hyperstene and augite phenocryst cores in the calc alkaline samples are compositionally distinguishable from the relevant phases in the tholeiitic samples it is unlikely that magma mixing played an essential role in the generation of the calc alkaline suite at adatara volcano

understanding the origin of magmatic necks insights from mt etna volcano italy and analogue models magmatic necks are commonly found in volcanic areas and they often exhibit a homogeneous structure with a cylindrical shape and a diameter of up to several hundreds of metres their massive and uniform structure poses a space problem for their emplacement in the brittle crust here we use field data and analogue models to investigate how necks may emplace at shallow levels field analysis focuses on characterising the geometric structural and magmatic features of two necks outcropping in the eroded portions of mt etna italy these are homogeneous and massive intrusive bodies related to a single episode of emplacement at 400 600 m below the paleosurface we further investigated their possible emplacement mechanism through analogue models injecting vegetable oil within a a flat sand pack and b a sand cone dikes form with both configurations erupting to the surface through vents however dikes injected within the cone are characterised by a larger thickening at shallow levels in correspondence with the vent where a neck like structure forms this suggests that the gravitational load imposed by a volcanic edifice provides the most suitable conditions for the development of magmatic neck as the downslope shear stresses enhance the deformation of the cone slope during shallow dike emplacement promoting shallow dilation and thickening of the dike therefore topography should be a further factor enhancing the development of necks in addition to those mechanisms previously proposed our results are consistent with natural examples of feeder dikes thickening towards the surface and dikes transitioning to necks supporting the reliability of the proposed conceptual model

possible role of amphibole in the origin of andesite some experimental and natural evidence experiments in the system high a1 basalt hab water have been conducted in the melting range at pressures between 1 atm and 10 kbar defining the amphibole stability field and the composition of liquids which coexist with this amphibole plagioclase is the anhydrous liquidus phase between 1 atm and 10 kbar but in the hydrous runs this role is taken by olivine at 7 kbar and then by clinopyroxene at higher pressures because amphibole is never on the high a1 basalt liquidus it is not likely that andesite is derived from primary basalt by pure fractional crystallisation although as we discuss other mechanisms including equilibrium crystallisation might implicate amphibole if primary basaltic magma undergoes closed system equilibrium crystallisation then the amphibole field will be intersected at between 50 and 100 c below the liquidus the compositions of melts coexisting with amphibole alone do not match those of any of the natural andesite or dacitic lavas associated with the particular high a1 basalt investigated like natural andesites they become rapidly silica enriched but they also become far more depleted in tio2 and mgo however the compositions of liquids lying directly on the divariant amphibole out reaction zone where amphibole liquid coexist with clinopyroxene or olivine plagioclase do resemble those of naturally occurring low silica andesites with increasing temperature pargasitic amphibole breaks down via incongruent melting reactions over a narrow temperature range to form a large volume of relatively low silica basaltic andesite liquid and a crystalline assemblage dominated by either clinopyroxene or olivine our important conclusion is that basaltic andesite liquid will be the product of reaction between cooling hydrous mafic liquid and anhydrous ferromagnesian phases the solid reactants could represent earlier cumulates from the same or different magma batches or they could be peridotite wall rock material because the amphibole out boundary coexisting with liquid is one of reaction it will not be traversed so long as the phases on the high temperature side remain thus the assemblage amphibole clinopyroxene olivine plagioclase liquid is one in which the liquid is buffered within limits and results reported here indicate that this buffering generates melts of low silica andesite composition when tapped to lower pressures these liquids will rise eventually to fractionate plagioclase rich assemblages yielding silicarich andesite and dacite melts conversely the partial melting of hornblende pyroxenite hornblende peridotite or hornblende gabbro can also yield basaltic andesite liquids the phase relationships suggested by these experiments are discussed in the light of naturally occurring phenocryst and xenolith assemblages from the east sunda arc primary magmatic additions to the lithosphere of volcanic arcs are basaltic and voluminous upper crustal andesite in these terranes complemented by mafic and ultramafic crystalline deposits emplaced in the lower crust or close to the moho together these components constitute total arc growth with a basaltic composition and represent the net accreted contribution to continental growth

active tectonic features and structural dynamics of the summit area of mt etna italy revealed by soil co2 and soil temperature surveying project cgl2005 07509 cli ministry of education and science of spain dpc ingv project flank istituto nazionale di geofisica e vulcanologia osservatorio etneo sezione di catania

use and abuse of the terms calcalkaline and calcalkalic the terms calcalkaline and calcalkalic are currently defined and used in multiple and non equivalent ways generally the variation of total fe as feo mgo within evolving subalkaline rock suites is regarded as the most distinctive character of calcalkaline compared with tholeiitic suites reflecting the relative timing of phase saturation with fe ti oxides plagioclase and ferromagnesian silicates other classification schemes are widely used including a minority of adherents to the original formalized definition of calcalkalic by peacock 1931 journal of geology 39 54 67 given the prevailing contradictory and confusing usage of these terms which leads to miscommunication it is proposed that the spectrum of subalkaline rocks be divided into high medium and low fe suites complementing divisions made on the basis of k contents the terms calcalkaline and calcalkalic should be restricted to rock suites that conform to peacock s definition

impact of tectonic and volcanism on the neogene evolution of isolated carbonate platforms sw indian ocean understanding the impact of tectonic activity and volcanism on long term i e millions years evolution of shallow water carbonate platforms represents a major issue for both industrial and academic perspectives the southern central mozambique channel is characterized by a 100 km long volcanic ridge hosting two guyots the hall and jaguar banks and a modern atoll bassas da india fringed by a large terrace dredge sampling geo physical acquisitions and submarines videos carried out during recent oceanographic cruises revealed that sub marine fl at top seamounts correspond to karsti fi ed and drowned shallow water carbonate platforms largely covered by volcanic material and structured by a dense network of normal faults microfacies and well constrained stratigraphic data indicate that these carbonate platforms developed in shallow water tropical envi ronments during miocene times and were characterized by biological assemblages dominated by corals larger benthic foraminifera red and green algae the drowning of these isolated carbonate platforms is revealed by the deposition of outer shelf sediments during the early pliocene and seems closely linked to 1 volcanic activity typi fi ed by the establishment of wide lava fl ow complexes and 2 to extensional tectonic deformation associat ed with high offset normal faults dividing the fl at top seamounts into distinctive structural blocks explosive vol canic activity also affected platform carbonates and was responsible for the formation of crater s and the deposition of tuff layers including carbonate fragments shallow water carbonate sedimentation resumed during late neogene time with the colonization of topographic highs inherited from tectonic deformation and volcanic accretion latest carbonate developments ultimately led to the formation of the bassas da india modern atoll the geological history of isolated carbonate platforms from the southern mozambique channel represents a new case illustrating the major impact of tectonic and volcanic activity on the long term evolution of shallow water car bonate platforms

petrological study of nasu chausudake volcano ca 16 ka to present northeastern japan chausudake volcano is representative of the active volcanoes in northeastern japan and has a record of many historical eruptions because its 16 ky eruptive history is well documented chausudake is well suited for examining the temporal change of magma chamber processes and for assessing potential hazards the activity of the chausudake volcano can be divided into six magmatic units ch1 ch6 most of its products have similar characteristics but those from unit ch1 show wider variation most rocks are andesite and have plagioclase clinopyroxene orthopyroxene and fe ti oxides as phenocrysts with or without olivine or quartz mafic inclusions which are observed in most products are basaltic andesites that have various combinations of the same phenocryst species petrographic features observed in host rocks and mafic inclusions such as disequilibrium phenocrysts and resorbed textures suggest magma mixing co mingling whole rock compositions of both host rocks and mafic inclusions show linear trends in variation diagrams which suggest that the rocks are derived from the mixing co mingling between mafic and felsic end members bulk silica content of the mafic end member magma is estimated to be ca 52 and contains mg rich olivine and an rich plagioclase the temperature of this end member is estimated to have been higher than 1 100 c bulk silica content of the felsic end member magma is estimated to be 66 and contains mg poor pyroxenes an poor plagioclase and quartz phenocrysts with a temperature of between 800 and 900 c trace element compositions show that the end members have different origins but have changed little over the entire 16 ky of activity the mafic end member magmas might come from a lower crustal homogeneous large magma chamber whereas the felsic end member magmas may be partial melts of crustal materials produced by the heat of the mafic end member felsic end member magma may have accumulated in the middle crust before ch1 activity the mixing ratio of the felsic to mafic end members was 0 5 0 5 to 0 4 0 6 for the ch1 unit and ca 0 4 0 6 for the other units considering that ca 75 of the total volume of the eruptive products form the first unit its wider compositional variation is attributed to more heterogeneous mixing ratios

a multidisciplinary study of the volcanoclastic deposit named chiancone inland and offshore in the frame of the evolution of volcanism in the etna area abstract in this work a detailed study about the volcanoclastic deposit pyroclastic cone called chiancone is carried out by 98 vertical electrical soundings vess and by analysis of the surface morphology made by two digital elevation model dem with high resolution the results seem to confirm what has been suggested by other researchers and shed some light on some dark aspects of this volcanoclastic deposit in particular it was found that the chiancone is quite a complex geologic formation whose deposition took place in several steps filling in depressions of various conductive substrate to depths of at least 300 m below the sea level the conductive substrate generally shows a higher resistivity than a clay one and is strongly tectonized and eroded the multibeam surveys carried out offshore in the ionian sea allow us to identify the geolithological nature of the substrate never before detected in the past they show the existence of an outcrop of a large cone shaped submarine pyroclastic body about 600 m deep covered near the coast by chiancone deposits the authors believe therefore that this pyroclastic body may form inland the conductive substrate of the formations outcropping in the studied area lava and chiancone and representing the product of the demolition of one or more existing volcanic apparatuses prior to the trifoglietto and mongibello which was given in the past the name of ancient etna

etnean and hyblean volcanism shifted away from the malta escarpment by crustal stresses abstract a fraction of the volcanic activity occurs intraplate challenging our models of melting and magma transfer to the earth s surface a prominent example is mt etna eastern sicily offset from the asthenospheric tear below the malta escarpment proposed as its melt source the nearby hyblean volcanism to the south and the overall northward migration of the eastern sicilian volcanism are also unexplained here we simulate crustal magma pathways beneath eastern sicily accounting for regional stresses and decompression due to the increase in the depth of the malta escarpment we find non vertical magma pathways with the competition of tectonic and loading stresses controlling the trajectories curvature and its change in time causing the observed migration of volcanism this suggests that the hyblean and etnean volcanism have been fed laterally from a melt pooling region below the malta escarpment the case of eastern sicily shows how the reconstruction of the evolution of magmatic provinces may require not only an assessment of the paleostresses but also of the contribution of surface loads and their variations at times the latter may even prevail accounting for these competing stresses may help shed light on the distribution and wandering of intraplate volcanism

the darwin point of pacific ocean atolls and guyots a reappraisal abstract the darwin point where atolls drown has been redefined as a function of climate sea level history paleolatitude seawater temperature and light during the last 34 ma in the hawaiian emperor chain the darwin point has been shown to shift at least between 24 and 30 n latitude atoll drowning there is correlated with decreased seawater temperature and light and depends on sea level history as well as the elevation of atoll summits at the time of sea level transgressions if the atoll top falls below 30 m with respect to sea level and the rate of sea level rise is more than 15 mm yr the atoll will drown results of the ocean drilling program legs 143 and 144 which investigated the histories of several nw pacific guyots indicate that the demise of the shallow water carbonate platforms there was related to either a temporal 110 100 ma eustatic sea level event the paleolatitude location 0 10 s of nutrient rich water and or increased seawater temperature greenhouse effect unconducive to the production of calcium carbonate by shallow water organisms hence the darwin point phenomena of atolls and guyots cannot be viewed as a manifestation of any single factor rather it results from a combination of factors including decreased water temperature and light related to higher latitude the amplitude and rate of sea level changes presence of nutrient rich waters and or elevated seawater temperatures it is indeed dynamic both in time space and cause

cumulate xenolith in oahu hawaii implications for deep magma chambers and hawaiian volcanism the maximum depth at which large 1000 km3 terrestrial mafic magma chambers can form has generally been thought to be the moho which occurs at a mean depth of about 35 kilometers beneath the continents and 8 kilometers beneath ocean basins however the presence of layers of cumulus magnesium rich spinel and olivine and intercumulus garnet in an unusual mantle xenolith from oahu hawaii suggests that this rock is a fragment of a large magma chamber that formed at a depth of about 90 kilometers hawaiian shield building magmas may pond and fractionate in such magma chambers before continuing their ascent this depth is at or near the base of the 90 million year old lithosphere beneath oahu thus rejuvenated stage alkalic magmas containing mantle xenoliths evidently also originate below the lithosphere

the tholeiite to alkalic basalt transition at haleakala volcano maui hawaii previous studies of alkalic lavas erupted during the waning growth stages 0 9 ma to present of haleakala volcano identified systematic temporal changes in isotopic and incompatible element abundance ratios these geochemical trends reflect a mantle mixing process with a systematic change in the proportions of mixing components we studied lavas from a 250 m thick stratigraphic sequence in honomanu gulch that includes the oldest 1 1 ma subaerial basalts exposed at haleakaka the lower 200 m of section is intercalated tholeiitic and alkalic basalt with similar isotopic sr nd pb and incompatible element abundance ratios e g nb la la ce la sr hf sm ti eu these lava compositions are consistent with derivation of alkalic and tholeiitic basalt by partial melting of a compositionally homogeneous clinopyroxene rich garnet lherzolite source the intercalated tholeiitic and alkalic honomanu lavas may reflect a process which tapped melts generated in different portions of a rising plume and we infer that the tholeiitic lavas reflect a melting range of 10 to 15 while the intercalated alkalic lavas reflect a range of 6 5 to 8 melting however within the uppermost 50 m of section 87sr 86sr decreases from 0 70371 to 0 70328 as eruption age decreased from 0 97 ma to 0 78 ma we infer that as lava compositions changed from intercalated tholeiitic and alkalic lavas to only alkalic lavas at 0 93 ma the mixing proportions of source components changed with a morb related mantle component becoming increasingly important as eruption age decreased

flank instability structure of mt etna inferred by a magnetotelluric survey this paper presents a magnetotelluric mt survey of the unstable eastern flank of mt etna we take thirty soundings along two profiles oriented in the n s and nw se directions and from these data recover two 2d resistivity models of the subsurface both models reveal three major layers in a resistive conductive resistive sequence the deepest extending to 14 km bsl the shallow layer corresponds to the volcanic cover and the intermediate conductive layer corresponds to underlying sediments segmented by faults these two electrical units are cut by e w striking faults the third layer basement is interpreted as mainly pertinent to the apennine maghrebian chain associated with sw ne striking regional faults the detailed shapes of the resistivity profiles clearly show that the ne rift is shallow rooted 0 1 km bsl thus presumably fed by lateral dikes from the central volcano conduit the nw se profile suggests by a series of listric faults reaching up to 3 km bsl then becoming almost horizontal toward the se the resistive basement dramatically dips from 3 km to 10 km bsl in correspondence with the timpe fault system several high conductivity zones close to the main faults suggest the presence of hydrothermal activity and fluid circulation that could enhance flank instability our results provide new findings about the geometry of the unstable etna flank and its relation to faults and subsurface structures

stratigraphic completeness of carbonate dominated records from continental interiors versus continental margins stratigraphic thinning occurs via condensation and omission at multiple scales abstract over phanerozoic time scales stratigraphic records from continental interiors or cratons are dramatically thinner and are generally assumed to be relatively incomplete with more numerous and longer duration hiatuses compared to records from more rapidly subsiding continental margins however this assumption need not be true for the shorter time scales i e several 106 years and shorter over which accumulation of the preserved stratigraphic record on the continental interior actually takes place this study compares carbonate dominated sedimentary records from the devonian continental interior iowa and continental margin nevada to evaluate whether the continental interior record is 1 miniaturized i e thinner but equally complete 2 comparable in thickness and quality where the sedimentary record is preserved but certain portions of the record are notably absent i e omitted or truncated or 3 so invariably preserved that equivalent stratigraphic packages cannot be recognized compared to the continental margin record this study finds that fourth to fifth order cycles in iowa are on average approximately half as thick and half as numerous compared to the continental margin of nevada moreover the stratigraphic record on the continental margin of nevada is dominated by cycles that are composed of tidal flat and shallow subtidal lithofacies capped by simple flooding surfaces and exhibit catch up or keep up depositional styles the continental interior record in iowa is dominated by cycles that are composed of subtidal lithofacies capped by a range of bounding surfaces and exhibit catch down or give up depositional styles these findings suggest that the thin record in iowa is largely a result of low sedimentation rates associated with suppressed carbonate production in this epeiric sea setting rather than minimal subsidence rates and an increased potential for subaerial exposure and associated loss of record

stratigraphic constraints for explosive activity in the past 100 ka at etna volcano italy the pyroclastic deposits of etna have been correlated over the whole volcanic edifice for the first time allowing the construction of a continuous record of tephra producing events which extends from approximately 100 ka to the present in this interval five main periods of explosive activity have been identified a 100 ka strombolian to subplinian activity b 80 to 100 ka plinian benmoreitic activity c 16 to 80 ka strombolian to subplinian from basaltic to mugearitic activity d 15 5 to 15 ka plinian benmoreitic activity accompanying the caldera forming eruptions of the ellittico volcano and e the most recent 13 ka basaltic explosive activity of strombolian and subplinian type of the present edifice that also includes the 122 b c plinian eruption this study results in a semi quantitative and in some cases quantitative definition of the intensity and chronology of the explosive activity at etna moreover this work gives a new significance to the volcanic hazards of etna a volcano generally considered to be the site of gentle effusive eruptions

structural features of the july august 2001 mount etna eruption evidence for a complex magma supply system we describe the evolution of the volcanic activity and deformation patterns observed at mount etna during the july august 2001 eruption seismicity started at 3000 m below sea level on 13 july accompanied by moderate ground swelling ground deformation culminated on 16 july with the development of a ne sw graben c 500 m wide and c 1 m deep in the cisternazza area at 2600 2500 m above sea level on the southern slope of the volcano on 17 july the eruption started at the summit of mount etna from the se crater central lateral eruptive system from which two radial c 30 m wide c 3000 m long fracture zones associated with eruptive fissures propagated both southward 17 july and northeastward 20 july on 18 july a new vent formed at 2100 m elevation at the southern base of the montagnola followed on the next day by the opening of a vent further upslope at 2550 m eccentric eruptive system the eruption lasted for 3 weeks approximately 80 of the total lava volume was erupted from the 2100 m and the 2550 m vents the collected structural data suggest that the cisternazza graben developed as a passive local response of the volcanic edifice to the ascent of a north south eccentric dyke which eventually reached the ground surface in the montagnola area 18 19 july in contrast the two narrow fracture zones radiating from the summit are interpreted as the lateral propagation from the conduit of the se crater of north south and ne sw oriented shallow dykes 2 3 m wide the evolution of the fracture pattern together with other volcanological data magma ascent and effusion rate eruptive style petrochemical characteristics of the erupted products and petrology of xenoliths within magma suggest that the eccentric and central lateral eruptions were fed by two distinct magmatic systems examples of eccentric activity accompanied by central lateral events have never been described before at etna

origin of a cool water oligo miocene deep shelf limestone eucla platform southern australia the abrakurrie limestone is an areally extensive bryozoan rich unit within the eucla platform a tertiary carbonate shelf which caps the central part of the southern australian continental margin the onshore portion the topic of this study has been exposed since middle miocene time and lies beneath the nullarbor plain the rocks are fine sand to granule sized calcarenites composed of bryozoans bivalves benthic foraminifera and echinoids with lesser numbers of brachiopods solitary corals and serpulids they conspicuously lack significant numbers of planktonic foraminifera and coralline algae most bryozoan remains are from delicate branching cyclostomes although delicate branching robust branching foliose fenestrate multilaminar encrusting and free living cheilostomes are variably abundant in specific units the poorly lithified sequence is punctuated by well cemented layers with erosional tops which are interpreted as hardgrounds the limestone is interpreted as a cool water deep shelf deposit which accumulated in water depths generally greater than 50 m on the inner part of the eucla platform a model which involves deposition and cementation on a carbonate shelf swept by open ocean swells is proposed to explain the style of sedimentation the shelf is envisaged as partitioned by the depth of the zone of wave abrasion sediments were produced throughout but accumulated only below this depth when the seafloor was above this depth it was an environment of cementation and erosion the vertical sequence correlates in a general way with the global sea level model for the mid cenozoic while accumulation rates for southern australian carbonates are similar to rates of cool water carbonate deposition elsewhere c 2 5 cm kyr 1 the rate of abrakurrie accumulation is much less suggesting that significant time periods are represented by the hardgrounds

earlier alkaline and transitional magmatic pulsation of mt etna volcano abstract the observation of glass inclusions with alkalic and transitional compositions in single olivine crystals from aci castello hyaloclastites indicates that small volumes of alkalic melts preceded tholeiite eruptions during the onset of mt etna volcanism the gradual shift in composition from alkalic to transitional melts is explained by simple partial melting of a compositionally uniform source with the degree of melting increasing by a factor of 3 4 during this early melting process such variation controls both the chemical and mineralogical signatures of emitted lavas the source shows trace element and isotopic signatures which may be representative of a himu type plume for etnean lavas

paleo environmental and volcano tectonic evolution of the southeastern flank of mt etna during the last 225 ka inferred from the volcanic succession of the timpe acireale sicily abstract the tectonic escarpments locally known as timpe cut a large sector of the eastern flank of etna and allow an ancient volcanic succession dating back to 225 ka to be exposed geological and volcanological investigations carried out on this succession have allowed us to recognize relevant angular unconformities and volcanic features which are the remnants of eruptive fissures as well as important changes in the nature composition and magmatic affinity of the exposed volcanics in particular the recognition in the lower part of the succession of important and unequivocal evidence of ancient eruptive fissures led us to propose a local origin for these volcanics and to revise previous interpretations which attributed their westward dipping to the progressive tectonic tilting of strata these elements led us to reinterpret the main features of the volcanic activity occurring since 250 ka bp and their relationship with tectonic structures active in the eastern flank of etna we propose a complex paleo environmental and volcano tectonic evolution of the southeastern flank of mt etna in which the timpe fault system played the role of the crustal structure that allowed the rise and eruption of magmas in the above considered time span

seismo tectonic behavior of the pernicana fault system mt etna a gauge for volcano flank instability 1 flank instability at basaltic volcanoes is often related to repeated dike intrusions along rift zones and accompanied by surface fracturing and seismicity these processes have been mostly studied during specific events and the lack of longer term observations hinders their better understanding here we analyze 20 years of deformation of the pernicana fault system pfs the key structure controlling the instability of the eastern flank of mt etna we exploit east west and vertical components of mean deformation velocity as well as corresponding time series computed from ers envisat 1992 2010 and cosmo skymed 2009 2011 satellite radar sensors via synthetic aperture radar interferometry techniques we then integrate and compare this information with field seismic and leveling data collected between 1980 and 2012 we observe transient displacements accompanied by seismicity overprinted on a long term background eastward motion 2 cm yr in the last decades these transient events were preceded by a constant amount of accumulated strain near the pfs the time of strain accumulation varies between a few years and a few decades also depending on magma emplacement within the nearby north east rift which may increase the strain along the pfs these results suggest that the amount of deformation near the pfs may be used as a gauge to forecast the occurrence of instability transients on the eastern flank of etna in this context the pfs may provide an ideal small scale structure to test the relations between strain accumulation stress loading and seismic energy release

new dating of rapid vertical deformation of santa tecla fault scarps mt etna volcano sicily by lichenometry method abstract the eastern slope of mt etna is characterised by shallow seismicity originating from normal oblique faulting timpe fault system related to wnw ese regional extension recent research has demonstrated that in the fault population of mt etna s eastern flank the minimum earthquake magnitude that will have a ground rupture effect is ca 2 5 this system is characterised by high frequency seismic activity due to thinned seismogenic crustal layer this characteristic together with the high density of the fault segments does not always for identification of the segments responsible for the earthquake the earthquakes affecting the medium lower eastern flank have been historically reconstructed by macroseismic analysis and reported in a macroseismic database and in recent decades by instrumental seismic registration which provide the seismological parameters capable of evaluating focal mechanism hypocentre and relative algorithms related to geometric parameters which control the growth of fault segments in this paper we present a methodology to evaluate the age of the rapid exhumation of the free face fault plane of the nnw sse oriented normal fault segment named s tecla timpe fault system it consists of the measurement of the thalli species lichenometry method in order to evaluate the parameters which characterise their growth the seismic history of the s tecla fault indicates eight certain events from 1865 to 2005 with 3 4 4 7 magnitude de guidi et al 2012 and reference therein we found evidence of two different recent rapid vertical deformation events at the base of the s tecla fault escarpment the oldest 20 m long and 0 25 m in height and the youngest with a 0 02 m high nude surface exposed we have observed that there are thalli of xanthoparmelia conspersa ehrh ex ach hale colonizing part of the nude surface on the escarpment the results highlight that the oldest thalli was dated at 43 7 years old showing that rapid vertical deformation generated the surface where the thalli after 4 years took root the displacement of this surface could be related to the seismic events occurring on 3rd august 1973 3 8 m in s m ammalati area probably accompanied by intense post seismic deformation the second and last event could be attributable to a 3 1 m seismic event occurring on 25th september 2014 iside 2016

third order depositional sequences controlled by synsedimentary extensional tectonics evidence from upper triassic carbonates of the carnian prealps ne italy the upper triassic platform margin deposits of the carnian prealps fail to show the succession of the two global sea level lowerings predicted for the norian and rhaetian by the haq global sea level curve in both cases a relative sea level rise occurs a discrepancy that can be explained by an increase in tectonically controlled subsidence a consequence of the plate scale rifting in the nw tethys gulf preceding oceanic spreading in the jurassic pulses of tectonic subsidence followed by relative quiescence are capable of generating depositional sequences similar in gross geometry and duration to the third order eustatic cycles of haq et al the late triassic part of the exxon global sea level curve partly derived from correlatable strata within the same palaeogeographical domain is likely to reflect pulses of tectonically induced subsidence rather than eustatic sea level changes

crustal structure of the ionian margin of sicily etna volcano in the frame of regional evolution abstract crustal imaging could be achieved on normal incidence reflection profiles offshore eastern sicily by using industrial grade reflection seismic with improved marine sources thick recent sediments a reflective pile including the mesozoic deposits a transparent upper crust and a band of low frequency reflections attributed to the lower crust are imaged in the seismic sections the structure of the crust and its thickness show features inherited from the mesozoic evolution as a passive margin by which ionian basin crust was formed around the hyblean continental promontory of africa to constitute the southern plate in the later convergence with europe the seismic images are also marked by the lithospheric deformation due to the neogene overriding of the northern part of this paleomargin by the calabro peloritan block of european continental crust this transpressive motion may have been guided along the northern part of this paleomargin where the seismic profiles evidence a hinge line between the northward upslope of the moho of that old passive margin and its downslope to the present slab under the tyrrhenian sea etna volcano is located at the intersection of this mantle upwarp by a zone of active sea bottom normal faults which cut across the formerly constructed compressional belt the onset of its volcanic activity is roughly coeval with that of the cessation of interplate thrusting and could hence be related to a change of the coupling of the ionian slab this slab is now probably disconnected from the overriding plate and rolled back in front of the expanding hot tyrrhenian asthenospheric dome with the mobilisation of a viscous mantle material at depth an active lithospheric fault is here imaged which cuts over more than 100 km into the ionian basin the fault runs from the tyrrhenian margin in the sse direction of etna updip of the southwestern lateral edge of this slab leaving north eastward the extruded calabrian block and on its south westward edge the uplifted crust and mantle structures of etna along it the crust including the mesozoic and deeper layers has sagged vertically in the segment in front of the slab with a finite throw across the fault increasing from the basin towards etna

tectonic control on the eruptive dynamics at mt etna volcano sicily during the 2001 and 2002 2003 eruptions abstract the eruptive events of the july august 2001 and october 2002 january 2003 at mt etna provide new insights for reconstructing the complex geometry of the feeding system and their relationship to regional tectonics the 2001 eruption took place mainly on the upper southern sector of the volcano the eruption was preceded by a large earthquake swarm for a few days before its onset and accompanied by ground deformation and fracturing the development of surface cracking along with the seismic pattern has allowed us to recognize three distinct eruptive systems the sw ne nnw sse and n s systems which have been simultaneously active such eruptive systems are only the upper portions of a complex feeding system that was fed at the same time by two distinct magmas the sw ne and nnw sse systems connected with the se crater conduit were fed by magma coming from depth whereas the n s system served instead as an ascending pathway for an amphibole bearing magma residing in a shallow reservoir the eruptive activity started again on october 2002 on the ne rift zone where about 20 eruptive vents were aligned between 2500 and 1900 m a s l and on the southern flank from the central crater to the montagnola the onset of eruptive activity was accompanied by a seismic swarm as in the 2001 eruptive event two independent feeding systems formed characterized by distinct magmas the sw ne system controlled the feeding of the northeast rift and was accommodated by left lateral displacement along the wnw ese trending pernicana fault the n s system fed the eruptions on the southern flank moreover the associated crustal deformation triggered seismic reactivation of tectonic structures in the eastern flank of the volcano and offshore these two last eruptions indicate that at mt etna the ascent of magma as well as the accommodation of deformation is strongly dominated by local extensional structures that are connected to a regional tectonic regime

the leaking bucket of a maldives atoll implications for the understanding of carbonate platform drowning abstract seismic and multibeam data as well as sediment samples were acquired in the south male atoll in the maldives archipelago in 2011 to unravel the stratigraphy and facies of the lagoonal deposits multichannel seismic lines show that the sedimentary succession locally reaches a maximum thickness of 15 20 m above an unconformity interpreted as the emersion surface which developed during the last glacial sea level lowstand such depocenters are located in current protected areas flanking the reef rim of the atoll or in infillings of karst dolinas much of the 50 m deep sea floor in the lagoon interior is current swept and has no or very minor sediment cover erosive current moats line drowned patch reefs whereas other areas are characterized by nondeposition karst sink holes blue holes and karst valleys occur throughout the lagoon from its rim to its center lagoonal sediments are mostly carbonate rubble and coarse grained carbonate sands with frequent large benthic foraminifers halimeda flakes red algal nodules mollusks bioclasts and intraclasts some of them glauconitic as well as very minor ooids finer grained deposits locally are deposited in current protected areas behind elongated faros i e small atolls which are part of the rim of south male atoll the south male atoll is a current flushed atoll where water and sediment export with the open sea is facilitated by the multiple passes dissecting the atoll rim with an elevated reef rim and tower like reefs in the atoll interior it is an example of a leaky bucket atoll which shares characteristics of incipiently drowned carbonate banks or drowning sequences as known from the geological record

origin of silicic magma and magma feeding system of the shirataka volcano ne japan abstract stratovolcanoes in ne japan produce mixed andesites dacites with a silicic end member the petrologic features of this end member remained uncertain and its origin has long been debated here we suggest how the silicic magma is generated and interpret the magma feeding system for one such stratovolcano the shirataka 0 9 0 7 ma the rocks of the shirataka are divided into six petrologic groups g1 6 mafic inclusions are observed in g1 g2 g5 and g6 silica poor inclusions have tschermakitic hornblende in the groundmass while the others are hornblende free the detailed petrologic study revealed that all products were formed by magma mixing mingling between mafic and silicic end members mafic end members 1150 c 47 52 wt sio2 have magnesian olivine magnesian clinopyroxene and an rich plagioclase phenocrysts whereas silicic end members 750 900 c 63 68 wt sio2 have an poor plagioclase low mg pyroxenes hornblende and quartz the phenocryst compositions an mg and temperature of silicic end members have changed among the groups over time the trends defined by such mafic and silicic end members of each group are systematically parallel except for g3 and g4 which have distinct specific bulk compositions suggesting that the two end members for each group have co genetic relationships the trace element model calculations indicate that each estimated silicic end member can be produced through partial remelting of the corresponding solidified mafic end member leaving a gabbroic residue the presence of groundmass hornblende in silica poor mafic inclusions suggests that volatile rich mafic magmas ascended settled and solidified as gabbroic bodies in the lower or middle crust silicic magmas were then produced by partial remelting of these bodies and ascended to the shallower part of the crust to form chambers leaving the gabbro finally wet mafic magmas newly supplied along the marginal part of the gabbroic bodies and injected into the chambers triggered the eruption and the mixing mingling took place during ascent to the surface two distinct silicic magmas were simultaneously formed by this mechanism and they mixed with corresponding mafic magmas in g3 and g4 giving rise to two discrete mixed magmas finally these magmas erupted contemporaneously mingling with each other and forming pyroclastic flows

modeling the effects of eruptive and seismic activities on flank instability at mount etna italy 1 the identification and evaluation of trigger mechanisms for volcano flank instabilities and or collapse represent a key issue for risk assessment in densely populated volcanic areas as well as in long distance settings particularly in case of island or coastal volcanoes here we address quantitatively the effects of external seismic and inner magmatic forcing on the stress strain state associated to flank instabilities at mount etna sicily southern italy by means of a 2 d finite difference method numerical modeling modeled seismic actions include strong near field strong far field and low magnitude near field earthquakes magmatic actions consider the inner pressure changes induced by energetic lava fountains in the summit crater area and subvertical and oblique dike ascent below the summit area model results are validated in light of available monitoring data and recent eruptive activity numerical results show that the main strain effects are produced by high magnitude near field earthquakes expected return time of 103 yrs and by vertical uprise of a magma dike below the volcano summit area maximum displacements in the order of tens of centimeters may involve the summit area up to some 106 m3 m over some kilometers laterally stress releases up to 107 pa may affect a limited portion of the magmatic conduit thus favoring major effusive flank eruptions major catastrophic events such as volcano flank collapse should not be expected by applying either individually or combined the aforementioned actions

high spatial resolution radon measurements reveal hidden active faults on mt etna radon emissions are frequently monitored in volcanically and tectonically active areas in order to reveal changes in soil degassing as radon acts a tracer for the more abundant co2 degassing commonly observed in such areas between july 2002 and may 2003 a series of discrete measurements of radon concentrations in soil were made with high spatial resolution similar to5 100 m in the santa venerina area on mt etna these measurements revealed well defined linear anomalies that we interpret as being caused by active faults whose higher porosity than surrounding soils allows an increased co2 flux carrying radon from beneath these faults were not visible at the surface and were therefore revealed at high spatial resolution by our radon survey our hypothesis that the positive anomalies are attributable to active faults was strengthened by the observation of concentrated damage along this geometry during the earthquakes that struck this area in late october 2003

discovery of a submerged relic reef and shoreline off grand cayman further support for an early holocene jump in sea level abstract drilling close to the base of a submerged sea cliff on the terraced eastern shelf of grand cayman has revealed a relic acropora palmata reef at a depth of 21 m below msl ten cores from its crest are principally composed of cobble sized clasts of a palmata set in a matrix of cemented skeletal grainstone the clasts have a distinctive succession of encrusters that indicate rapid burial a photophilic association of crustose coralline algae foraminifera and vermetid gastropods superimposed by a cryptic association of sclerosponges foraminifera and serpulids in addition to rapid burial u th thermal ionization mass spectrometer tims dating of coral clasts within 1 m of the relic reef surface indicates minor temporal mixing with ages between 8 9 and 8 1 ka such mixing and rapid burial is consistent with a hurricane deposit and is identical to deposits found on the crests of modern reefs in relation to its age the preservation of a 18 5 m intertidal notch cut into the submerged sea cliff on the western shelf of grand cayman implies that the crest of the relic reef has been lowered 1 5 2 m by marine abrasion bioerosion at a rate of 0 25 mm yr 1 reconstructing this eroded section using average holocene accretion rates indicates that the reef likely ceased accreting at 7 6 ka at a depth of 19 m comparing these data with other relic reefs in the caribbean indicates that the relic reef on grand cayman died within 160 years of relic reefs on barbados st croix st thomas and north florida this narrow interval of reef demise also coincides with the time when modern reefs were establishing themselves some 4 9 m higher upslope a fact that can only be resolved by invoking a rapid 6 m jump in sea level 7 5 ka ago such a jump would also account for two unexplained events around this time the restricted interval of global delta initiation and the catastrophic flooding of the glacially lowered black sea

directional resonance variations across the pernicana fault mt etna in relation to brittle deformation fields summary the pernicana fault pf is the main structural element of mt etna and the northern boundary of a section sliding to the southeast observed ground motion records in the damage zone of the pf show strong variations of directional resonance in the horizontal plane the observed resonance directions exhibit an abrupt rotation of azimuth by about 30 across the fault varying from n166 on the north side to n139 on the south we interpret the directional resonance observations in terms of changes in the kinematics and deformation fields on the opposite sides of the fault the northern side is affected primarily by the left lateral strike slip movement whereas the southern side that is subjected also to sliding is under a dominant extensional stress regime brittle deformation models based on the observed kinematic field predict different sets of fractures on the opposite sides of the fault synthetic cleavages and extensional fractures are expected to dominate in the northern and southern sides respectively these two fracture fields have different orientations n74 and n42 respectively and both show a near orthogonal relation 88 in the northern sector and 83 to the south with the azimuth of the observed directional resonance we conclude that the direction of the largest resonance motions is sensitive to and has transversal relationship with the dominant fracture orientation the directional amplification is inferred to be produced by stiffness anisotropy of the fault damage zone with larger seismic motions normal to the fractures

phase relations of a high mg basalt from the aleutian island arc implications for primary island arc basalts and high al basalts many volcanic centers in the aleutian islands have erupted lavas that range in composition from high mg basalt mgo 9 wt to more fractionated and voluminous high al basalts and basaltic andesites the petrogenetic relationships between these rock types and the composition of primary magmas has been vigorously debated the phase relations of a typical high mg basalt from the makushin volcanic field on unalaska island provide important constraints on petrogenetic models results of one atmosphere and moderate to high pressure 5 20 kb anhydrous experiments are similar to results obtained from primitive morb at low pressures olivine is the liquidus phase joined by plagioclase and clinopyroxene at progressively lower temperatures clinopyroxene is the second phase to crystallize at pressures greater than 5 kb and replaces olivine on the liquidus at approximately 10 kb above 10 kb the liquidus pyroxene is aluminous augite and orthopyroxene is the second phase to crystallize glasses in equilibrium with olivine and clinopyroxene at intermediate pressure 5 to 10 kb are similar in composition to high al basalt plagioclase is not involved and most likely does not become a liquidus phase until the liquid has evolved significantly although our studies do not confirm the primary nature of high mg basalts they do support a model in which high al basalts are generated by moderate amounts of crystal fractionation from more primitive high mg mg fe lower al2o3 basaltic magmas near the arc crust mantle boundary

continental margin large scale instability controlling the flank sliding of etna volcano abstract etna volcano is affected by a downward sliding of its eastern flank as rapid as a few cm year whose nature is highly debated recently collected marine geological and geophysical data allows a detailed image of the morphostructural setting of the continental margin facing the volcano here a large bulge offsets the margin that is deeply affected by widespread semicircular steps interpreted as evidence of large scale gravitational instability such features permeate the whole margin and extend inshore to the volcano sector where the larger ground deformations are measured both submarine instability and subaerial flank sliding are bounded by two regional tectonic lineaments interpreted as weakness lines these cross the coastline to accommodate the basinward movement of this large sector of the continental margin topped by the etna volcanic pile the new data allows re interpreting the tectonic setting of the coastal belt and proposing a novel structural model highlighting the active role of the continental margin instability to drive the seaward sliding of the volcano s eastern flank this model may suggest why a very active basaltic volcano has so unusually developed in front of an active thrust belt

mafic enclaves record syn eruptive basalt intrusion and mixing mafic enclaves hosted by andesite erupted at the soufriere hills volcano between 1995 and 2010 yield insights into syn eruptive mafic underplating of an andesite magma reservoir magma mixing and its role in sustaining eruptions that may be widely applicable in volcanic arc settings the mafic enclaves range in composition from basalt to andesite and are generated from a hybrid thermal boundary layer at the interface between the two magmas where the basalt quenches against the cooler andesite and the two magmas mix we show using an analytical model that the enclaves are generated when the hybrid layer just a few tens of centimetres thick becomes buoyant and forms plumes which rise up into the andesite mafic enclave geochemistry suggests that vapour saturated basalt was underplated quasi continuously throughout the first three eruptive phases of the eruption the end member basalt became more mg and v rich over time the andesite erupted during the final phases of the eruption contained more abundant and larger enclaves and the enclaves were more extensively hybridised with the andesite suggesting that at some time during the final few years of the eruption the intrusion of mafic magma at depth ceased allowing the hybrid layer to reach a greater thickness generating larger mafic enclaves the temporal trends in mafic enclave composition and abundance suggests that basalt recharge and underplating sustained the eruption by the transfer of heat and volatiles across the interface and when the recharge ceased the eruption waned our study has important implications for the petrological monitoring of long lived arc eruptions

anatomy of an unstable volcano from insar multiple processes affecting flank instability at mt etna 1994 2008 1 volcano deformation may occur under different conditions to understand how a volcano deforms as well as relations with magmatic activity we studied mt etna in detail using interferometric synthetic aperture radar insar data from 1994 to 2008 from 1994 to 2000 the volcano inflated with a linear behavior the inflation was accompanied by eastward and westward slip on the eastern and western flanks respectively the portions proximal to the summit showed higher inflation rates whereas the distal portions showed several sectors bounded by faults in some cases behaving as rigid blocks from 2000 to 2003 the deformation became nonlinear especially on the proximal eastern and western flanks showing marked eastward and westward displacements respectively this behavior resulted from the deformation induced by the emplacement of feeder dikes during the 2001 and 2002 2003 eruptions from 2003 to 2008 the deformation approached linearity again even though the overall pattern continued to be influenced by the emplacement of the dikes from 2001 to 2002 the eastward velocity on the eastern flank showed a marked asymmetry between the faster sectors to the north and those largely inactive to the south in addition from 1994 to 2008 part of the volcano base south west and north lower slopes experienced a consistent trend of uplift on the order of 0 5 cm yr this study reveals that the flanks of etna have undergone a complex instability resulting from three main processes in the long term 103 104 years the load of the volcano is responsible for the development of a peripheral bulge in the intermediate term 101 years observed from 1994 to 2000 inflation due to the accumulation of magma induces a moderate and linear uplift and outward slip of the flanks in the short term 1 year observed from 2001 to 2002 the emplacement of feeder dikes along the ne and south rifts results in a nonlinear focused and asymmetric deformation on the eastern and western flanks deformation due to flank instability is widespread at mt etna regardless of volcanic activity and remains by far the predominant type of deformation on the volcano

orbitally forced sedimentary rhythms in the stratigraphic record is there room for tidal forcing the imprint of orbital cycles which result from the varying eccentricity of the earth s orbit and changes in the orientation of its axis have been recognised throughout the phanerozoic rock record variations in insolation and their effect on climate are generally considered to be the sole transfer mechanism between the orbital variables and cyclic sedimentary successions common oceanographic principles however show that the ocean tide also responds to variations in the orbital parameters the ocean tide has not yet been considered to be a valid additional transfer mechanism for the orbital variations in geological studies of milankovitch cycles in sedimentary successions the insolation paradigm offers satisfying explanations and the role of long term variations of the ocean tide has not yet been appreciated variations in the ocean tide related to changing eccentricity at present 0 0165 theoretical maximum 0 0728 affect a variety of oceanographic and sedimentary processes in addition to the widely accepted paradigm of orbitally forced insolation changes the tidal transfer of orbital signals may explain certain less well understood aspects of orbitally induced cycles in the stratigraphic record related to ocean mixing organic productivity and tidal processes in shallow seas and deep water variations of the ocean tide in relation to the 18 6 year lunar nodal cycle which has no insolation counterpart by which they may be obscured indeed show that these relatively small variations can produce significant effects in sedimentary environments that are sensitive to variations in the strength of the ocean tide in analogy with the 18 6 year lunar nodal cycle orbital variations of the tide on milankovitch time scales are likely to have affected sedimentary systems in the past

a pilot gis database of active faults of mt etna sicily a tool for integrated hazard evaluation abstract a pilot gis based system has been implemented for the assessment and analysis of hazard related to active faults affecting the eastern and southern flanks of mt etna the system structure was developed in arcgis environment and consists of different thematic datasets that include spatially referenced arc features and associated database arc type features georeferenced into wgs84 ellipsoid utm zone 33 projection represent the five main fault systems that develop in the analysed region the backbone of the gis based system is constituted by the large amount of information which was collected from the literature and then stored and properly geocoded in a digital database this consists of thirty five alpha numeric fields which include all fault parameters available from literature such us location kinematics landform slip rate etc although the system has been implemented according to the most common procedures used by gis developer the architecture and content of the database represent a pilot backbone for digital storing of fault parameters providing a powerful tool in modelling hazard related to the active tectonics of mt etna the database collects organises and shares all scientific currently available information about the active faults of the volcano furthermore thanks to the strong effort spent on defining the fields of the database the structure proposed in this paper is open to the collection of further data coming from future improvements in the knowledge of the fault systems by layering additional user specific geographic information and managing the proposed database topological querying a great diversity of hazard and vulnerability maps can be produced by the user this is a proposal of a backbone for a comprehensive geographical database of fault systems universally applicable to other sites

buoyancy controlled eruption of magmas at mt etna buoyancy controls the ability of magma to rise its ascent rate and the style of the eruptions geophysical geological and petrological data have been integrated to evaluate the buoyancy of magmas at mt etna the density difference between host rocks and magmas is mainly related to the amount of h2o dissolved in the magma and to the bubble liquid separation processes in the depth interval 22 2 km b s l highly hydrated h2o 3 basaltic magmas or mixtures of bubbles liquid have positive buoyancy and rise rapidly conversely bubble depleted liquids with an intermediate h2o content 1 5 having neutral buoyancy will spread out and form magmatic reservoirs at different depths until cooling crystallization further modify composition and density these different processes account for the magma compositions location of magmatic reservoirs as determined by geophysical methods and the complex eruptive cycles slow effusions fire fountains and plinian eruptions that have been observed in the history of the volcano