rhyolitic globular peperites from the aznalcollar mining district iberian pyrite belt spain physical and chemical controls abstract globular peperites are exposed along the aznalcollar mining district iberian pyrite belt ipb spain these rocks originated by mingling of a low viscosity rhyolitic sill with unlithified wet sediments highly amygdaloidal up to 80 vol millimeters to centimeters across rhyolite globules extend from the upper contact of the sill for several centimeters into fine grained volcaniclastic host rocks the sill is very similar to other rhyolites in the ipb in terms of petrography and chemistry it is aphyric to very sparsely quartz phyric with small quartz phenocrysts vesicularity has been measured in the sill as vesicle area fraction determined by point counting over a rectangular grid and number density per unit area determined by counting every vesicle within the grid area amygdale distribution measured within the sill indicates a process by which vesicles migrated vertically from the lower portions of the sill to the roof zone we suggest that this migration process caused local density changes large enough to allow the rhyolitic magma to become buoyant enough to move through the overlying sediments producing globular peperites globular structures are preserved when rhyolite globules entered the wet sediment

seep carbonates in a thrust related anticline at the leading edge of an orogenic wedge the case of the middle late miocene salsomaggiore ridge northern apennines italy abstract seep carbonates are important indicators of submarine fluid expulsion and dewatering of sediments along convergent margins and accretionary prisms in the northern apennine compressional wedge seep carbonates usually occur in pelitic successions from different settings of the middle late miocene foreland basin system in serravallian foredeep deposits of the salsomaggiore area seep carbonates cemented and or encrusted coarse grained sandstones and conglomerates fluid expulsion strictly related to variable intensities in tectonic stresses generated seep carbonate facies and sediment instabilities depending on the position of the fluid pathway feeders within the salsomaggiore ridge a middle late miocene intra basinal high at the leading edge of the apenninic orogenic wedge this site provides a unique opportunity for analyzing depositional characters and the three dimensional distribution and evolution of a seepage system in a thrust related anticline the resulting evolutionary model shares common features with recent ridges in other accretionary wedges in this model a strict relationship between tectonics seepage and sediment instability during a major tectonic phase is outlined

a miocene coarse volcaniclastic mass flow deposit in the shimane peninsula sw japan product of a deep submarine eruption a subaqueous volcaniclastic mass flow deposit in the miocene josoji formation shimane peninsula is 15 16 m thick and comprises mainly blocks and lapilli of rhyolite and andesite pumices and non to poorly vesiculated rhyolite it can be divided into four layers in ascending order layer 1 is an inversely to normally graded and poorly sorted lithic breccia 0 3 6 m thick layer 2 is an inversely to normally graded tuff breccia to lapilli tuff 6 11 m thick this layer bifurcates laterally into minor depositional units individually composed of a massive lithic rich lower part and a diffusely stratified pumice rich upper part with inverse to normal grading of both lithic and pumice clasts layer 3 is 2 5 3 m thick and consists of interbedded fines depleted pumice rich and pumice poor layers a few centimeters thick layer 4 is a well stratified and well sorted coarse ash bed 1 5 2 m thick the volcaniclastic deposit shows internal features of high density turbidites and contains no evidence for emplacement at a high temperature the mass flow deposit is extremely coarse grained dominated by traction structures and is interpreted as the product of a deep submarine explosive eruption of vesicular magma or explosive collapse of lava

structure and emplacement of a rhyolitic obsidian flow little glass mountain medicine lake highland northern california many rhyolitic obsidian flows show consistent stratigraphic relations among textural units exposed in the flow fronts of undissected flows and in cross sections of older flows the stratigraphy of the holocene little glass mountain rhyolitic obsidian flow consists of from bottom to top air fall tephra deposits basal breccia coarsely vesicular pumice obsidian finely vesicular pumice and surface breccia slightly crystalline rhyolite occurs near the vent areas a model of obsidian flow emplacement based on these textural relations is presented this stratigraphy may reflect the distribution of volatiles within the magma source region with the interlayered contact between coarsely vesicular pumice and overlying obsidian indicating stratification of volatiles in the magma body the distribution of pumiceous and glassy zones along with the orientations of flow banding can be used to map the surface structure of rhyolitic obsidian flows this complex structure as mapped on the little glass mountain flow reflects both the initial flow stratigraphy and subsequent deformational processes during emplacement of the lava three processes disrupt the initial flow configuration the rise of coarse pumice diapirs from the base of the flow the inward propagation of fractures in areas of extension and surface folding in sites of flow parallel compression subvertical flow banding in vent areas indicates that fracturing accompanies the emergence of lava most of the observed upper surface of a dome originates as a fracture plane the structure of domes that form over vent areas may reflect the orientation of dike like conduits as well as the local state of stress during extrusion

highly isotopically depleted isoprenoids molecular markers for ancient methane venting abstract we propose that organic compounds found in a miocene limestone from marmorito northern italy are source markers for organic matter present in ancient methane vent systems cold seeps the limestone contains high concentrations of the tail to tail linked acyclic c20 isoprenoid 2 6 11 15 tetramethylhexadecane crocetane a c25 homolog 2 6 10 15 19 pentamethylicosane pme and a distinctive glycerol ether lipid containing 3 7 11 15 tetramethylhexadecyl phytanyl moieties the chemical structures of these biomarkers indicate a common origin from archaea their extremely 13c depleted isotope compositions 13c 108 to 115 6 pdb suggest that the respective archaea have directly or indirectly introduced isotopically depleted methane derived carbon into their biomass we postulate that a second major cluster of biomarkers showing heavier isotope values 13c 88 is derived from sulfate reducing bacteria srb the observed biomarkers sustain the idea that methanogenic bacteria in a syntrophic community with srb are responsible for the anaerobic oxidation of methane in marine sediments marmorito may thus represent a conceivable ancient scenario for methane consumption performed by a defined two membered bacterial consortium 1 archaea that perform reversed methanogenesis by oxidizing methane and producing co2 and h2 and 2 srb that consume the resulting h2 furthermore the respective organic molecules are unlike other compounds tightly bound to the crystalline carbonate phase the marmorito carbonates can thus be regarded as cold seep microbialites rather than mere authigenic carbonates

subaqueous rhyolite block lavas in the miocene ushikiri formation shimane peninsula sw japan abstract a rhyolite mass of the miocene ushikiri formation in the western part of the shimane peninsula sw japan is a small subaqueous edifice about 600 m high and 4 km wide formed at water depths between 200 and 1000 m it consists mainly of three relatively flat lava flow units 50 300 m in maximum thickness each of which includes lobes and their polyhedral fragments the lava lobes are poorly to well vesiculated glassy to microcrystalline and flow banded and folded compared with mafic pillows they are large having thick quenched and brecciated glassy crusts because of their high viscosity surface tension and thermal conductivity their surfaces disintegrate into polyhedral fragments and grade into massive volcanic breccia the massive volcanic breccia composed of the lobe fragments is poorly sorted and covered with stratified volcanic breccia of the same rock type the rhyolite lavas commonly bifurcate in a manner similar to mafic pillow lavas however they are highly silicic with 1 5 vol phenocrysts and have elongated vesicles and flow folds implying that they were visco plastic during flowage their surface features are similar to those of subaerial block lava with respect to rheological and morphological features they are subaqueous equivalents of block lava

large scale rhyolite peperites jurassic southern chile development of a jurassic volcano tectonic rift basin in the southern andes created a setting in which thick rhyolitic volcaniclastic sequences accumulated in submarine environments and were penetrated by hypabyssal intrusions during or shortly after deposition in the ultima esperanza district of southern chile extensive masses of peperite were produced when rhyolite magma underwent quenching disruption and commingling with wet unconsolidated sediments during intrusion at shallow levels beneath the sea floor the peperite forms discordant intrusive masses with volumes of up to several cubic kilometers in which large widely spaced coherent rhyolite feeder pods are surrounded by and grade into closely packed and dispersed peperite closely packed peperite consists of tightly fitting clasts separated by sediment filled fractures in dispersed peperite the sediment forms a matrix surrounding large masses of fractured rhyolite and smaller more widely separated rhyolite clasts evidence of in situ quench fragmentation is well preserved on both outcrop and thin section scales thin sections show that clast margins and in some cases entire small clasts underwent cooling contraction granulation releasing shards of quenched rhyolite and fragments of phenocrysts into the adjacent sediment interaction between magma and wet sediment was non explosive and involved fluidization of the host sediments creating space for the intruding magma and causing pervasive injection of highly mobile sediment along thermal contraction cracks in quench fragmented rhyolite the ability of the magma to undergo complex intermixing with large volumes of sediment with widespread preservation of in situ fragmentation textures is interpreted to reflect a relatively low magma viscosity presumably caused by retention of volatiles in the magma at the ambient pressures involved beds of redeposited peperite within the rift basin fill indicate that some of the intrusive peperite masses reached the sea floor undergoing slumping and mass flow the peperites were thus an important local source of coarse grained debris during the evolution of the basin

a comparison of miocene and archean rhyolite hyaloclastites evidence for a hot and fluid rhyolite lava abstract in this paper we compare the geology and petrography of miocene and archean submarine rhyolite hyaloclastites the hyaloclastites are sparsely 10 or less plagioclase quartz and pyroxene phyric the hyaloclastites consist of a feeder dyke from which branch lava lobes and irregularly shaped lava pods the lava bodies consist of a holocrystalline core with microlitic texture grading outward into a flow layered rim zone and finally into obsidian the proportion of plagioclase and pyroxene microlites decreases outward some layers of the rim zone may be pumiceous vesicularity up to 50 vesicle size 1 mm or less but most of the lava has less than 5 vesicles one or a few cm long the obsidian shows perlitic fracture patterns the lava bodies grade through an in situ breccia into a hyaloclastite composed of angular obsidian granules and in many cases of fragments of lava lobes evidence for alteration at high temperature is as follows in the archean rhyolite hyaloclastites plagioclase microlites are overgrown by quartz albite spherulites furthermore parts of the miocene and archean hyaloclastite have been cemented and granules have been marginally replaced by quartz and albite hyaloclastite cemented at high temperature locally shows columnar joints at low temperatures obsidian has been hydrated and or has been replaced by clay minerals zeolites chlorite or prehnite chess board albite and fibroradial prehnite in archean hyaloclastite is possibly a pseudomorph after zeolites the sparsely porphyritic nature of the lava and the absence of microlites from the quenched glass suggests that the thyolite hyaloclastites extruded at high near liquidus temperature furthermore pumice is present only locally in the flow layered rim zone and in fragments derived from that zone these features suggest that vesiculation was inhibited by the weight of the water column high temperature and possibly the volatile h 2 o content explain the relatively low viscosity and shear strength of the lava and resulted in the flow morphology particular to this type of hyaloclastic rhyolite flows

melting of the glacier base during a small volume subglacial rhyolite eruption evidence from blahnukur iceland abstract although observations of recent volcanic eruptions beneath vatnajokull iceland have improved the understanding of ice deformation and meltwater drainage little is known about the processes that occur at the glacier base we present observations of the products of a small volume effusive subglacial rhyolite eruption at blahnukur torfajokull iceland lava bodies typically 7 m long have unusual conical morphologies and columnar joint orientations that suggest emplacement within cavities melted into the base of a glacier cavities appear to have been steep walled and randomly distributed these features can be explained by a simple model of conductive heat loss during the ascent of a lava body to the glacier base the released heat melts a cavity in the overlying ice the development of vapour escape pipes in the waterlogged permeable breccias surrounding the lava allows rapid heat transfer between lava and ice the formed meltwater percolates into the breccias recharging the cooling system and leaving a steam filled cavity the slow ascent rates of intrusive rhyolitic magma bodies provide ample time for a cavity to be melted in the ice above even during the final 10 m of ascent to the glacier base an equilibrium cavity size is calculated at which melting is balanced by creep closure this is dependent upon the heat input and the difference between glaciostatic and cavity pressure the cavity sizes inferred from blahnukur are consistent with a pressure differential of 2 4 mpa suggesting that the ice was at least 200 m thick this is consistent with the volcanic stratigraphy which indicates that the ice exceeded 350 m in thickness although this is the first time that a subglacial cavity system of this type has been reconstructed from an ancient volcanic sequence it shares many characteristics with the modern firn cave system formed by fumarolic melting within the summit crater of mount rainier washington at both localities it appears that localised heating at the glacier base has resulted in heterogeneous melting patterns despite the different rheological properties of ice and firn similar patterns of cavity roof deformation are inferred the development of low pressure subglacial cavities in regions of high heat flux may influence the trajectory of rising magma with manifold implications for eruptive mechanisms and resultant subglacial volcanic landforms

geothermometry geochronology and mass transfer associated with hydrothermal alteration of a rhyolitic hyaloclastite from ponza island italy abstract a rhyolitic hyaloclastite from ponza island italy was hydrothermally altered producing four distinct alteration zones based on x ray diffraction mineralogy and field textures 1 nonpervasive argillic zone 2 propylitic zone 3 silicic zone and 4 sericitic zone the unaltered hyaloclastite is volcanic breccia with clasts of vesiculated obsidian in a matrix of predominantly pumice lapilli incomplete alteration of the hyaloclastite resulted in the nonpervasive argillic zone characterized by smectite and disordered opal ct the other three zones exhibit more complete alteration of the hyaloclastite the propylitic zone is characterized by mixed layer illite smectite i s with 10 to 85 i mordenite opal c and authigenic k feldspar akspar the silicic zone is characterized by i s with 90 i pure illite quartz akspar and occasional albite the sericitic zone consists primarily of i s with 66 i pure illite quartz and minor akspar and pyrite k ar dates of i s indicate hydrothermal alteration occurred at 3 38 0 08 ma oxygen isotope compositions of i s systematically decrease from zones 1 to 4 in the argillic zone smectite has 18o values of 21 7 to 22 0 and i s from the propylitic silicic and sericitic zones ranges from 14 5 to 16 3 12 5 to 14 0 and 8 6 to 11 9 respectively 18o values for quartz from the silicic and sericitic zones range from 12 6 to 15 9 by use of isotope fractionation equations and data from authigenic quartz hosted primary fluid inclusions alteration temperatures ranged from 50 to 65 c for the argillic zone 85 to 125 c for the propylitic zone 110 to 210 c for the silicic zone and 145 to 225 c for the sericitic zone fluid inclusion data and calculated 18owater values indicate that hydrothermal fluids were seawater dominated mass transfer calculations indicate that hydrothermal alteration proceeded in a relatively open chemical system and alteration in the sericitic zone involved the most extensive loss of chemical species especially si systematic gains in mg occur in all alteration zones as a result of i s clay mineral formation and systematic losses of na ca and k occur in most zones with the exception of ca calculations of mass transfer associated with hydrothermal alteration on ponza agree with chemical fluxes observed in laboratory experiments involving hydrothermal reactions of rhyolite and seawater the anomalous ca loss at ponza may be due to hydrothermal formation of anhydrite and later low temperature dissolution on the basis of mg enrichments derived from circulating seawater we estimate the following minimum water rock ratios 9 3 6 and 9 for the argillic propylitic silicic and sericitic zones respectively hydrothermal fluid ph for the propylitic and silicic zones was neutral to slightly basic and relatively acidic for the sericitic zone as a result of condensation of carbonic and perhaps other acids

facies architecture of a silicic intrusion dominated volcanic centre at highway reward queensland australia abstract the highway reward massive sulphide deposit is hosted by a silicic volcanic succession in the cambro ordovician seventy mile range group northeastern australia three principal lithofacies associations have been identified in the host succession the volcanogenic sedimentary facies association the primary volcanic facies association and the resedimented syn eruptive facies association the volcanogenic sedimentary facies association comprises volcanic and non volcanic siltstone and sandstone turbidites that indicate submarine settings below storm wave base lithofacies of the primary volcanic facies association include coherent rhyolite rhyodacite and dacite and associated non stratified breccia facies autoclastic breccia and peperite the resedimented volcaniclastic facies association contains clasts that were initially formed and deposited by volcanic processes but then redeposited by mass flow processes resedimentation was more or less syn eruptive so that the deposits are essentially monomictic and clast shapes are unmodified this facies association includes monomictic rhyolitic to dacitic breccia resedimented autoclastic facies siltstone matrix rhyolitic to dacitic breccia resedimented intrusive hyaloclastite or resedimented peperite and graded lithic crystal pumice breccia and sandstone pumiceous and crystal rich turbidites the graded lithic crystal pumice breccia and sandstone facies is the submarine record of a volcanic centre s that is not preserved or is located outside the study area pumice shards and crystals are pyroclasts that reflect the importance of explosive magmatic and or phreatomagmatic eruptions and suggest that the source vents were in shallow water or subaerial settings the lithofacies associations at highway reward collectively define a submarine shallow intrusion dominated volcanic centre contact relationships and phenocryst populations indicate the presence of more than 13 distinct porphyritic units with a collective volume of 0 5 km 3 single porphyritic units vary from the size and shape of the lavas and intrusions reflect a restricted supply of magma during eruption intrusion the style of emplacement and the subaqueous emplacement environment due to rapid quenching and mixing with unconsolidated clastic facies the sills and cryptodomes did not spread far from their conduits the shape and distribution of the lavas and intrusions were further influenced by the positions of previously or concurrently emplaced units magma preferentially invaded the sediment avoiding the older units or conforming to their margins large intrusions and their dewatered envelope may have formed a barrier to the lateral progression and ascent of subsequent batches of magma

facies analyses and volcanic setting of the giant neves corvo massive sulfide deposit iberian pyrite belt portugal in the iberian pyrite belt volcanic rocks are relatively scarce accounting for approximately only 25 of the geologic record with the remaining 75 consisting of sedimentary units this association is very clear in the host succession to the neves corvo massive sulfide deposit in portugal the neves corvo host succession comprises the products of explosive and effusive rhyolitic eruptions intercalated with mudstone that records a submarine below wave base environment and provides precise biostratigraphic age constraints the first and second volcanic events involved eruptions at local intrabasinal vents the first event generated thick beds of fiamme breccia that are late famennian in age the fiamme were originally pumice clasts produced by explosive eruptions and were subsequently compacted the second event was the late strunian latest famennian effusion of rhyolitic lava that was pervasively quench fragmented the third and final event is younger than the massive sulfide deposits poorly represented in the mine area and minor compared with the two other events the integration of biostratigraphic data with the volcanic facies architecture indicates that the neves corvo ore deposits are similar in age to the late strunian rhyolitic lava although regionally the iberian pyrite belt is essentially a sedimentary succession ore formation at neves corvo can be closely linked to discrete volcanic events that produced a relatively narrow range of volcanic facies

an explosive intrusive subglacial rhyolite eruption at dalakvisl torfajokull iceland this paper describes unusual rhyolitic deposits at dalakvisl torfajokull iceland that were emplaced during a quaternary subglacial eruption despite its small volume 0 2 km3 the eruption mechanisms were highly variable and involved both explosive and intrusive phases the explosive phase involved vesiculation driven magma fragmentation at the glacier base and generated a pumiceous pyroclastic deposit containing deformed sheets of dense obsidian textures suggest that the obsidian was generated by the collapse of partly fragmented foam that was intruding the deposit and water contents indicate quenching at elevated pressures in contrast the intrusive phase of the eruption generated vesicle poor quench hyaloclastites associated with a variety of peperitic lava bodies the presence of juvenile rich fluvio lacustrine sediments is the first documented evidence that meltwater may pond close to the vent during subglacial rhyolite eruptions if the bedrock topography is favourable in order to explain the variable eruption mechanisms a conceptual model is presented in which the transition from an explosive to an intrusive eruption was controlled by the space available for fragmentation within the subglacial cavity melted above the vent when the cavity became completely filled by volcanic deposits the vent became blocked and rising magma was forced to intrude through poorly consolidated debris this led to arrested fragmentation and welding of foam domains to form vesicle poor obsidian lava the transition to an intrusive eruption has taken place although this vent blocking mechanism is particularly relevant to subglacial eruptions it may also apply to subaerial rhyolitic eruptions where patterns of explosive and effusive activity cannot be explained by shallow degassing processes alone meanwhile the variable style of a small volume subglacial rhyolite eruption further highlights the complex processes that mediate volcano ice interactions

an upper jurassic methane seep limestone from the fossil bluff group forearc basin of alexander island antarctica an anomalous upper jurassic limestone bed 3 m thick is present within the volcaniclastic infill of a forearc basin exposed on alexander island antarctica the limestone formally designated the gateway pass limestone bed contains laminated crusts and blocks including hardgrounds showing radial fibrous and botryoidal calcite cements carbon isotope values are very negative delta 13 c of 33 5 per thousand to 44 6 per thousand pdb indicating a methane oxidation origin for the carbonate the limestone bed formed around a submarine cold seep in the antarctic peninsula forearc basin adjacent to the accretionary prism in contrast to adjacent nearly barren sea floor the limestone also yields a benthic island assemblage containing abundant gastropods and bivalves the seep is directly comparable to certain jurassic seeps at the convergent margin of the northeast pacific and both are related to subduction at the eastern proto pacific margin

subaqueous paleoproterozoic metarhyolite dome flow cone complex flin flon greenstone belt manitoba canada abstract two sparsely plagioclase phyric rhyolite domes 50 100 m thick and 125 250 m long as observed in 2 dimensional vertically dipping exposures are partly mantled by a rhyolite volcaniclastic complex that on the south side of the domes also forms a half cone like mound at least 60 m thick and 500 m long the domes and mantling volcaniclastic complex are overlain by three aphyric to sparsely phyric rhyolite flows that are 70 120 m thick and 550 1200 m long domes and flows have a lower columnar jointed highly fractured locally brecciated subfacies that grades upward into 40 95 crackled and disaggregated breccia crackled breccia is a highly fractured subfacies in which clast like areas are bounded by closely spaced joints and minor matrix but there is only limited rotation of clasts crackled breccia was produced by quench fracturing combined with hydraulic action of water converted to steam or supercritical fluid within the fractures overlying disaggregated breccia comprises rotated particles and 25 50 matrix it is most abundant near flow margins and is a crumble breccia produced by flow advance or expansion the volcaniclastic mound comprises lenticular interlayered facies of 1 resedimented phreatomagmatically generated heterolithic rhyolitic tuff and lapilli tuff 2 isolated to close packed rhyolite lobes that are 0 5 5 m thick and 0 5 50 m long the lobes are at least in part pillows and 3 units comprising small

wave theoretical inversion of teleseismic surface waves in a regional network phase velocity maps and a three dimensional upper mantle shear wave velocity model for southern germany summary using teleseimic surface wave data from 110 selected earthquakes recorded at 10broad band stations in southern germany we construct phase velocity maps of rayleigh waves for southern germany in a further step these maps are inverted for a three dimensional model of the sv velocity of the upper 200 km of the mantle we attempt to take into account the effect of heterogeneous structure outside the study region by jointly inverting the data for heterogeneous phase velocity inside the study region and the distortion of the incoming wavefields by the surrounding structure the total wavefield in the study region is computed with a scattering formalism which includes multiple forward scattering and single backscattering since in principle the data can be perfectly fit by the incoming wavefields without any heterogeneous structure inside the study area we impose additional constraints on the incoming wavefields to reduce the non uniqueness the most important constraint is an energy criterion which states that the energy of the modelled wavefield in the study area averaged over many events should be equal to the energy sampled by the stations we demonstrate that enforcing this criterion generates phase velocity maps with heterogeneous structure nevertheless we are able to satisfy the energy criterion without any heterogeneous structure at the price of an only slightly increased data misfit hence it must be concluded that a seismic network of size and station density such as the one used in this study is still insufficient to demonstrate convincingly the existence of heterogeneities in the network area using teleseismic surface waves any reasonable structure combined with the appropriate incoming wavefields would allow an acceptable fit of our data this frustrating conclusion of course applies to all other comparable studies which use teleseismic surface waves although we cannot convincingly show that any phase velocity map we find should be preferred over others we are able to obtain good reconstructions of test structures from realistic synthetic data with the same station and event distribution as the real data moreover we find that the geometric pattern of the phase velocity maps obtained from real data depends only weakly on the constraints applied in the inversion while the amplitude of the phase velocity perturbations is almost completely determined by the constraints for all periods considered the fit to the data is extremely good the reduction of the quadratic misfit relative to the case of plane incoming waves and no structure is dramatic for the shorter periods the 3 d model of vertical shear wave velocity down to a depth of 200 km exhibits a basic division into four quadrants separated by a vertical plane intersecting the surface along a nearly west east line and a horizontal plane at about 130 km depth the northern rants show high velocities in the top 120 km and low velocities below 140 km the opposite is the case for the southern quadrants an exception to this general feature is a pronounced low velocity zone in the northwestern corner of the region

late jurassic early cretaceous hydrocarbon seep boulders from novaya zemlya and their faunas the paper describes late jurassic early cretaceous seep carbonate boulders from the russian arctic island of novaya zemlya collected in 1875 by a e nordenskiold during his expedition to siberia the carbonates are significantly depleted in heavy carbon isotopes 13c values as low as ca 40 and show textures typical for carbonates formed under the influence of hydrocarbons such as fibrous carbonate cements and corrosion cavities the rocks contain index fossils of late oxfordian early kimmeridgian late tithonian jurassic and latest berriasian early valanginian cretaceous age the fossil fauna is species rich and dominated by molluscs with subordinate brachiopods echinoderms foraminifera serpulids and ostracods most of the species including two chemosymbiotic bivalve species likely belong to the background fauna only a species of a hokkaidoconchid gastropod and a possible abyssochrysoid gastropod can be interpreted as restricted to the seep environment other seep faunas with similar taxonomic structure are suggestive of rather shallow water settings but in case of novaya zemlya seep faunas such structure might result also from high northern latitude

spherulites quench fractures and relict perlite in a late devonian rhyolite dyke queensland australia abstract a late devonian rhyolite dyke displays perlitic and other fracture sets as well as textures generated by crystallisation of the glass the dyke is less than a metre wide and has sharp contacts with ignimbrite although originally glassy no glass is preserved aligned magnetite after pyroxene microlites and trains of small 0 5 1 mm spherical spherulites crystallised early at temperatures above the glass transition temperature and before formation of the fracture sets long subplanar fractures oriented perpendicular to the dyke walls extend almost the full dyke width and end by merging with adjacent long fractures short subplanar cross fractures are perpendicular to and terminate at the long fractures well defined perlitic fractures are present within the volumes of rock generally

why did ancient chemosynthetic seep and vent assemblages occur in shallower water than they do today cold seep communities have relatively low diversity are dominated by one or two taxa present in high density and high biomass in comparison with the surrounding fauna and are restricted to aphotic habitats their associated heterotrophic fauna are usually distinctive from the fauna of their surroundings in contrast a more commonplace chemoautotrophically based community occurs in shallow photic habitats the associated heterotrophic fauna includes many of the species typical of the surrounding communities and typically dominates abundance whereas the species with chemoautotrophic symbionts dominate biomass all modern seep assemblages are deeper than 550 m many fossil seep assemblages occurred in water as shallow as the mid shelf 200 m in contrast communities where species with chemoautotrophic symbionts are biomass dominants but not numerical dominants are common in shallow waters at present but rarely reported in the geological record we suggest that the absence of cold seep communities on the continental shelf presently is due to a combination of predation and competitive exclusion by primary consumers limiting the presence of species dependent on chemoautotrophic symbionts we suggest that cold seep assemblages are more common at shelf depths in the fossil record for two reasons a the biases of preservation have accentuated their distribution by transforming communities where species with chemoautotrophic symbionts dominate by biomass but not numerically into cold seep appearing assemblages b the importance of predation pressure and oligotrophy has varied with decreased predation pressure accompanying increased oligotrophy favoring cold seep communities we suggest that the paucity of shallow water assemblages with species harboring chemoautotrophic symbionts as biomass dominants in the fossil record is based on the reliance of paleoecological analysis on numerical abundance data when energy flow analyses are required to identify these assemblages the distinctiveness of the fossil seep assemblage is intensified by taphonomic processes that bias the assemblage against small individuals and epifaunal species so that diversity declines the small heterotrophic component of the assemblage is significantly reduced and the epifaunal component is minimized the final assemblage is usually dominated by the better preserved large infaunal clams which perchance are also the species with chemoautotrophic symbionts in contrast preservation does not enhance the distinctiveness of these chemoautotroph harboring species in shallow water

facies architecture and palaeoenvironmental constraints of subaqueous felsic volcanism in the iberian pyrite belt the paymogo volcano sedimentary alignment abstract the paymogo volcano sedimentary alignment pvsa is an essentially igneous sequence associated with vhms deposits of the iberian pyrite belt unlike other areas of this iberian mining district where mafic igneous rocks are abundant in the pvsa these are essentially felsic two facies associations have been distinguished based on petrographic and chemical features a lower dacite facies association and an upper rhyolite facies association the main ore horizons appear related to volcanic breccias of the rhyolite facies association a detailed petrographic study of these breccias suggests they are resedimented hyaloclastite deposits the analysis of volcanic facies indicates that the volcanism developed at water depths deeper than 500 m consistent with the minimum depth at which vhms deposits can form we conclude that detailed volcanological studies provide effective constraints to palaeoenvironmental interpretations which are relevant in assessing regional stratigraphy and area selection for vhms exploration

distinguishing peperite from other sediment matrix igneous breccias lessons from the iberian pyrite belt abstract breccias composed of coarse monomictic porphyritic igneous clasts and fine grained matrix are common in subaqueous volcanic successions we use the descriptive name sediment matrix igneous breccia for this facies and have recognized at least five different origins among examples in the iberian pyrite belt 1 peperite 2 sediment infill volcanic breccia 3 mud matrix resedimented hyaloclastite 4 mud rich water settled fiamme breccia and 5 apparent sediment matrix igneous breccia because the components and textures are similar discriminating among the different origins can be very difficult both peperite and sediment infill volcanic breccia can occur along top contacts of thick intervals of felsic coherent and monomictic breccia facies the presence of peperite indicates that the contact is intrusive whereas the presence of sediment infill volcanic breccia indicates that the contact is depositional hence correct distinction between peperite and sediment infill volcanic breccia is an important means of discriminating felsic intrusions from felsic lavas and domes the distinction underpins the reconstruction of volcanic centers and facies architecture and the ordering of volcanic intrusive sedimentary and mineralizing events in ancient submarine volcanic successions in addition in volcanic hosted massive sulfide districts such as the iberian pyrite belt paleoseafloor positions are considered highly prospective for massive sulfide ore bodies correct interpretation of sediment matrix igneous breccias is also important in this context because sediment infill volcanic breccia mud matrix resedimented hyaloclastite and mud rich water settled fiamme breccia all form or are deposited at the seafloor and hence delineate paleoseafloor positions in contrast peperite and apparent sediment matrix igneous breccias form subsurface and do not delineate paleoseafloor positions

a gis based study of earthquake hazard as a tool for the microzonation of bucharest abstract bucharest the capital of romania is situated close to one of the most seismically active areas in europe the vrancea region in the eastern carpathians the necessity of a well documented microzonation of the city and its immediate surroundings is clearly evident due to this seismic risk in the absence of a sufficient dense network of ground motion recording stations in bucharest the only possible way to realise a comprehensive microzonation is to correlate detailed subsurface geological data at instrumented sites with the macroseismic intensities and to extrapolate the results to non instrumented areas in this regards the geology of bucharest is relatively well known based on a great number of geotechnical drillings about 1200 for the first time a digital geological model dgm of the subsurface of bucharest was obtained based on the integration of numerous borehole data with a geographic information system gis transfer functions and dynamic ground responses were calculated with the linear modelling software proshake using soil profiles taken from discrete locations in the developed model and shear wave velocities and densities characteristic for each quaternary unit the distribution of computed spectral amplifications and spectral accelerations were generated for the ground surface of bucharest by interpolation important insights were made concerning the primary geological influencing factors on the observed historical damages to buildings which resulted from earthquakes through statistical regression analyses between various geotechnical properties and parameters associated with the historical damages

the shear wave velocity underneath bucharest city romania from the analysis of love waves summary from the dispersion of love waves we infer models of shear wave velocity structure underneath bucharest romania at depths down to 2 km that can contribute to seismic hazard estimation waves from eight regional events recorded during 10 months with a network of 34 seismic broad band stations of the urban seismology urs experiment are used although these events provide poor azimuthal coverage the data reliably constrain a shear wave velocity model with an interface between the neogene and the cretaceous sediments that is dipping northwards towards the carpathian mountains array processing techniques that account for non uniform wave propagation are used to estimate the dispersion of structural phase velocity from this we infer subsurface structure at three different latitudes the neogene sediments are represented by a gradient layer with no significant lateral variation shear wave velocity increases from approximately 400 m s 1 near the surface to 1 km s 1 at 1 km depth and 5 km in the south and to 1 35 km s 1 at 1 5 km depth and 5 km in the north from the centre of bucharest respectively for the half space representing the cretaceous sediments we obtain shear wave velocities of 2 7 2 9 km s 1 the results are consistent with results from boreholes and shallow seismics for the near surface structure and results from receiver function studies and crustal refraction seismic studies for the deeper structure the details of the neogene layer comprising a vertical gradient fill a gap in existing models of the subsurface structure of bucharest and can contribute to modelling of seismic hazard for the city since the signalto noise ratio restricted useful data to the frequency range from 90 to 290 mhz the inversion could not constrain the near surface velocity independently due to strong trade off between near surface velocity and depth of half space the latter had to be introduced as ap rioridata from previous studies

subaqueous calderas in the archean abitibi greenstone belt an overview and new ideas abstract the 300 700 km abitibi greenstone belt in canada contains numerous world class archean volcanogenic massive sulfide vms deposits yet documentation of archean subaqueous calderas hosting such deposits is lacking the modern sunrise deposit in the myojin knoll caldera of the izu bonin arc shows that submarine calderas are first order sites for vms the hunter mine and normetal calderas as well as the blake river megacaldera complex are reviewed with respect to geometry regional geology physical volcanology dyke emplacement and hydrothermal carbonate alteration these subaqueous calderas are placed into the geodynamic context of the abitibi greenstone belt the abitibi belt displays a complex history of oceanic arc formation evolution collision and fragmentation with numerous types of volcanic edifices and sedimentary basins controlled by oblique subduction and mantle plumes analogue models yielding new insights into the sequence of caldera forming events and their synvolcanic fault patterns are applied to explain archean examples underpressure experiments develop a consistent sequence of fault patterns that compare favourably with natural caldera events during subsidence two sets of faults propagate from the magma chamber margin 1 early reverse outward dipping faults and 2 normal inward dipping faults the largest massive sulfide deposits form preferentially at the caldera margin based on experimental studies and detailed facies mapping the hunter mine caldera is of the segmented piecemeal variety and the normetal caldera is akin to a piston structure the blake river megacaldera contains 1 the e w trending misema 2 the nw trending new senator and 3 the ne trending noranda calderas with the latter two being nested graben type calderas consistent with oblique archean subduction the poorly documented hydrothermal carbonate alteration is discussed and a new exploration model for calderas is presented the alteration study was evaluated at three levels microprobe analysis geochemical staining of drill core and whole rock analyses there were two principal stages of alteration related to vms formation an early silicification phase developed either at depth and or at the seawater interface whereby silicification was bedding parallel in fine grained volcaniclastic deposits near the water surface a pervasive and extensive semi conformable carbonate alteration zone with a discordant focused root zone along faults evolved subsequently three distinct carbonate pairings were observed 1 proximal siderite sideroplesite fe ankerite next to the vms deposit 2 an intermediate ankerite fe dolomite zone and 3 a distal calcite dolomite zone the carbonate phase is associated with the mineralizing event transitions between carbonate species are subtle and changes are indicated by mineral assemblage overlap the silica carbonate hydrothermal alteration pattern is a replacement product and is far more widespread than has been documented this alteration can be easily confused with primary carbonates and chemical precipitation deposits e g banded iron formation if detailed volcano sedimentary facies mapping with alteration has not been conducted and if outcrop is insufficient

a felsic dyke swarm formed under the sea the archean hunter mine group south central abitibi belt quebec canada an extensive rhyolitic dyke swarm has intruded subaqueous pyroclastic deposits iron formations hyaloclastite breccias and lava flows of the 2730 ma hunter mine group hmg in the south central part of the archean abitibi belt quebec the dyke swarm has a minimum width of 500 m and can be traced perpendicular to the section for 2 4 km based on crosscutting relationships chilled margins quartz content and colour five distinct dyke generations have been established each dyke generation has several magmatic pulses as indicated by parallel rows of columnar joints absence of brecciation between parallel rows suggests extremely brief intervals between magma pulses the central parts of most dykes display inverted v shaped patterns of columnar joint convergence inferred to indicate differential cooling during the late stages of dyke propagation the dykes commonly display delicate spherulites suggesting rapid cooling solidification temperatures between 400 and 600 c and penecontemporaneous devitrification quartz feldspar aggregates in the groundmass have locally developed microgranophyric textures large spherulites near the chilled margins probably formed at temperatures below 400 c percolation of abundant water throughout the dyke complex is suggested by ubiquitous prominent chilled dyke margins development of a chilled margin 500 m along one dyke suggests that water percolated at least 500 m below the water rock interface because the dykes intruded subaqueous pyroclastic deposits of similar composition dyke emplacement below the sea floor is inferred interstratification of pillowed flows and brecciated pillowed flows containing rhyolite fragments at the top of the 4 5 km thick sequence indicates that the central felsic complex probably never emerged during its evolutionary history supporting the contention that the felsic dyke complex was emplaced beneath the archean sea floor

late miocene seep carbonates and fluid migration on top of the montepetra intrabasinal high northern apennines italy relations with synsedimentary folding abstract during the miocene hydrocarbon seep carbonates located atop intrabasinal highs and associated with sediment instability formed commonly at the deformation front of the northern apennine collisional orogen the parallelism between the structural trend and the distribution of seep carbonates suggests a close relationship between tectonics and gas fluid emission the montepetra intrabasinal high was formed during the closure stage of the foredeep being related to the synsedimentary growth of an anticline field geometry suggests that detachment folding was the leading mechanism of anticline growth and synsedimentary instability along the anticline flanks ten different bodies of seep carbonates occur in the tortonian early messinian sediments nine in the hinge zone and one in the southern backlimb of the anticline foraminiferal study geochemistry facies investigation and the three dimensional geometry of carbonate bodies with respect to the encasing terrigenous sediments indicate a protracted late tortonian early messinian activity of fluid migration with re mobilization and ascent of sediments from the core of the anticline stabilization of chemosynthesis related communities and in situ brecciation seepage atop the intrabasinal high was fed by different circuits one related to the compaction dewatering of shallow tortonian early messinian sediments and a deeper one related to the deformation of the anticline core and to the activity of detachment surfaces and of faults propagating through the sedimentary cover

reconstruction of the tectonic volcanic and sedimentary setting of strongly deformed zn cu massive sulfide deposits at benambra victoria the wilga and currawong massive sulfide deposits at benambra are hosted by a strongly deformed upper silurian rhyolite dacite andesite basalt sediment succession dominated by silicic volcanics and sedimentary rocks this host succession developed in an ensialic back arc or intra arc basin of limited extensional origin on the active gondwana continental margin strong deformation is related to compressional and transcurrent crustal movements during closing of the depositional basin at the end of the silurian and to subsequent steep faulting the massive sulfide deposits are essentially synvolcanic because 1 they have the same three generations of tectonic structures and the same intensity of deformation as their host rocks suggesting that the ores predate the earliest compressional deformation 2 the ores are constrained to a late silurian age similar to their host rocks because both the host rocks and this earliest deformation are late silurian in age 3 there is a tight stratigraphic control on the location of the massive sulfides and 4 the stratigraphy depositional setting and alteration are similar to many other less deformed volcanic associated massive sulfide districts deformation and alteration inhibit detailed stratigraphic correlation and modify rock textures but do not destroy facies relationships which allow sedimentological and volcanological interpretation sedimentary facies associations indicate that mineralization occurred in the basin center after fault controlled subsidence from a mixed subaerial and subaqueous environment with active rhyolitic volcanism through a marine shelf environment with mixed limestone volcaniclastic sedimentation to a moderate to deep water environment with mudstone and turbidite sedimentation and rhyolitic to basaltic volcanism juvenile elastic and nonelastic volcanic rocks are closely associated subequal in volume and comprise 50 to 70 percent of the volcano sedimentary sequence evaluation of fragmentation and emplacement processes indicates that the juvenile volcaniclastics are mainly in situ resedimented and intrusive hyaloclastites rather than pyroelastics classification of primary contact relationships of the volcanics into passive slightly disruptive and highly disruptive types and the internal facies organization of the volcanic units indicate that the volcanics form extrusive domes extrusive tabular flows partially emergent cryptodomes and sills and entirely intrusive sills shallow sills and cryptodomes emplaced into wet subsea floor sediments are texturally similar to but more abundant than lavas in the environment of mineralization these shallow intrusions are distinguished by disruptive upper contacts including sediment veined and sediment matrix hyaloclastite their recognition is critical because the mineralized stratigraphic interval can only be correlated using volcanics and sediments emplaced on the sea floor based on extrusive units the massive sulfides occur within 100 m above the last major extrusive rhyolites and within 50 m below the first major basalt lava integrating the tectonic structural sedimentological and volcanological data shows that the massive sulfides formed in siltstone in the proximal near vent facies association of a low profile mainly nonexplosive moderate to deep water submarine volcano composed of turbiditic sediments interleaved with numerous rhyolitic to basaltic sills lavas and associated hyaloclastites the ores can be related in space and time to the advanced stage of extension and subsidence in a continental margin incipient rift when relatively deep marine conditions were attained generation of voluminous rhyolitic crustal melts waned and basaltic magma started to penetrate up deep extensional faults to the sea floor the spatial association of the last rhyolite extrusions the massive sulfides and the first basalt extrusions suggests that these rocks are genetically related and that all were fed via the same extensional fault system this setting of silicic volcanic associated massive sulfides at benambra provides a model for the many deposits related to mainly nonexplosive volcanism and an alternative to the recently popular submarine pyroclastic caldera model

urban shakemap methodology for bucharest 1 we develop a methodology for a shakemap for the romanian capital bucharest that can be rapidly computed and delivered to the public once real time data access is available to a sufficient extent the methodology with which the californian shakemaps are generated cannot be transferred to bucharest due to a missing understanding of the relationship between the geological near surface structure and the ground motion amplification however a systematic incorporation of previous seismological observations using fourier amplitude spectra of weak and strong ground motion and a recent urban broadband experiment in bucharest allows us to interpolate computed seismic intensities from 11 sites where accelerometers measure the actual motion of a specific earthquake to 31 additional locations in the city so that a reasonably reliable distribution of ground motion in the city can be determined we demonstrate this methodology using the mw 6 0 intermediate depth earthquake of october 27 2004

non explosive magma water interaction in a continental setting miocene examples from the eastern cordillera central andes nw argentina the middle upper miocene las burras almagro el toro bat igneous complex within the eastern cordillera of the central andes 24 s nw argentina has revealed evidence of non explosive interaction of andesitic magma with water or wet clastic sediments in a continental setting including peperite generation we describe and interpret lithofacies and emplacement mechanisms in three case studies the las cuevas member 11 8 ma comprises facies related to i andesite extruded in a subaqueous setting and generating lobe hyaloclastite lava and ii marginal parts of subaerial andesite lava dome s in contact with surface water comprising fluidal lava lobes hyaloclastite and juvenile clasts with glassy rims the lampazar member 7 8 ma is represented by a syn volcanic andesite intrusion and related peperite that formed within unconsolidated water saturated coarse grained volcaniclastic conglomerate and breccia the andesite intrusion is finger shaped and grades into intrusive pillows pillows are up to 2 m wide tightly packed near the intrusion fingers and gradually become dispersed in the host sediment 50 m from the parent intrusion the almagro a member 7 2 ma shows evidence of mingling between water saturated coarse grained volcaniclastic alluvial breccia and intruding andesite magma the resulting intrusive pillows are characterized by ellipsoidal and tubular shape and concentric structure the high level penetration of magma in this coarse sediment was unconfined and irregular magma was detached in apophyses and lobes with sharp contacts and fluidal shapes and without quench fragmentation and formation of a hyaloclastite envelope the presence of peperite and magma water contact facies in the bat volcanic sequence indicates the possible availability of water in the system between 11 7 ma and suggests a depositional setting in this part of the foreland basin of the central andes characterized by an overall topographically low coastal floodplain that included extensive wetlands

endogenous growth of a miocene submarine dacite cryptodome rebun island hokkaido japan momo iwa rebun island hokkaido japan is a dacite cryptodome 200 300 m across and 190 m high the dome is inferred to have intruded wet poorly consolidated sediment in a shallow marine environment the internal structure of the dome is concentric with a massive core banded rim and narrow brecciated border all of which are composed of compositionally uniform feldspar phyric dacite boundaries between each of the zones are distinct but gradational the massive core consists of homogeneous coherent unfractured dacite and is characterized by radial columnar joints 60 200 cm across the banded rim encircles the massive core and is 40 m wide it is characterized by large scale flow banding parallel to the dome surface the flow banding comprises alternating partly crystalline and more glassy bands 80 150 cm thick the outermost brecciated border is up to 80 cm thick and consists of in situ breccia and blocky peperite the in situ breccia comprises polyhedral dacite clasts 5 20 cm across and a cogenetic granular matrix the blocky peperite consists of polyhedral dacite clasts 0 5 2 cm across separated by the host sediment mudstone the internal structures of the dome suggest endogenous growth involving a continuous magma supply during a single intrusive phase and simple expansion from the interior although much larger the internal structures of momo iwa closely resemble those of lobes in subaqueous felsic lobe hyaloclastite lavas

morphology and growth style of a miocene submarine dacite lava dome at atsumi northeast japan abstract a miocene submarine lava dome at tate iwa atsumi yamagata japan displays well preserved primary morphological features the dome currently rises above a wave cut coastal platform and is 55 m high and 90 180 m across it comprises a massive core and a lava lobe hyaloclastite rim both of which are composed of compositionally uniform feldspar phyric dacite sio2 64 wt the boundary between these two zones is distinct but gradational the massive core consists of homogeneous coherent dacite and is characterized by flow banding along the margin and by columnar joints radiating from the centre to the margin the lava lobe hyaloclastite rim encircles the massive core and consists of a complex of 80 90 dacitic lava lobes and 10 20 hyaloclastite the lava lobes are 1 6 m thick 3 12 m wide and more than 5 m long each lobe consists of a radially columnar jointed core and a glassy rim 10 30 cm thick the hyaloclastite comprises polyhedral dacite clasts 5 100 cm across in a matrix of dacite fragments up to 5 mm across the lava lobes and hyaloclastite have gradational contacts in places paleobathymetric studies based on foraminifera in sediment beneath the dome and the k ar age of the dome suggest that it was extruded in a middle bathyal environment 1500 2000 m below sea level at 12 9 0 6 ma the internal structures of the dome suggest that it formed by a combination of exogenous growth involving extrusions of small dacite lobes and endogenous growth involving a continuous magma supply and simple expansion from the interior the presence of small lava lobes along the rim suggests that the magma had relatively low viscosity at the time of extrusion in spite of its high silica content magma temperatures calculated by two pyroxene and fe ti oxide geothermometers were 999 1042 and 957 1005 c respectively the inferred low viscosity may be attributed to the high temperature of the magma and or a high confining pressure resulting from the deep sea environment

facies architecture of the upper oligocene submarine smrekovec stratovolcano northern slovenia abstract the upper oligocene smrekovec volcanic complex svc represents the remains of a submarine stratovolcano which underwent early miocene tectonic dissection and large scale displacement along the periadriatic line according to the lithofacies architecture abundance and spatial distribution central medial and distal zones of the former volcano edifice have been recognized the zones extend at a distance of 0 2 km 2 5 km and 5 20 km south of the periadriatic line respectively lavas shallow intrusive bodies autobreccia peperite and hyaloclastite deposits occur mainly in the central zone which is extensively altered under hydrothermal conditions characterised by the development of zeolites mainly laumontite prehnite chlorite albite and epidote explosive volcanic activity intensified with the evolution of magma from basaltic andesitic to dacitic gas and water supported eruption fed density flows are assumed their deposits show lithofacies organisation in pyroclastic depositional units pdus similar to either volcaniclastic turbidites type 1 or thin subaqueous ignimbrites type 2 volcaniclastic debris flow deposits are developed as volcaniclastic breccia and sandy debris flow deposits the former occurs in the central and medial zones and the latter occurs in the medial zone only the most widespread lithofacies in the svc are volcaniclastic turbidite deposits three types of sedimentary unit tsu have been distinguished type 1 is 2 5 m thick and dominated by the massive division it mainly occurs in the central zone type 2 is 0 7 3 5 m thick and occurs in the central and medial zones it comprises the massive division bedded fining and thinning upward division and a horizontally wavy and cross laminated division topped by massive fine grained tuff type 3 is 0 1 1 5 m thick and mainly occurs in the distal zone the massive division is absent and thinly bedded and laminated divisions are topped by massive fine grained tuff volcaniclastic turbidites were settled from low density turbidity currents and related suspension clouds mixed volcaniclastic siliciclastic deposits are subordinate in occurrence and restricted to the distal zone they are commonly reworked by bottom currents

facies architecture and origin of a submarine rhyolitic lava flow dome complex ponza italy the islands of ponza and gavi western pontine archipelago italy preserve parts of a subaqueously emplaced high silica 75 77 sio2 rhyolitic lava flow that overlies the margins of three older domes exposures of the lava alone cover 24 km2 and with a thickness of 150 m exposed in the cliffs the preserved volume of the lava flow is 3 6 km3 and the original volume is likely to have exceeded 7 km3 the lava flow consists of coherent obsidian and several hyaloclastite facies including in situ and clast rotated breccias and sandstones which all exhibit gradational relationships the coherent obsidian occurs as separate domains and is often flow banded although flow folds occur the banding is generally subhorizontal dipping gently to the nne the hyaloclastite representing 90 of the lava by volume has a diffuse layering varying from 0 5 to 2 m in thickness this layering also dips gently to the nne and is marked in places by alternation of some coherent horizons coarse and finely fragmented in situ hyaloclastite pumiceous hyaloclastite and clast rotated hyaloclastite the layering is laterally continuous and consistent in orientation over most of the 13 km length of ponza the subhorizontal orientation of the flow banding and presence of resedimented deposits in the upper parts of the sequence indicate that the unit is a lava flow the resedimented deposits comprise both proximal and distal deposits of debris flows and turbidity currents initiated by gravitational instability of the upper and marginal parts of the lava flow and include stratified monomictic obsidian breccias and bedded vitric siltstones and sandstones the lava flow has been intruded and crosscut by rhyolitic bodies of various ages including discordant coherent to internally fractured contemporaneous rhyolite bodies and late penecontemporaneous dikes with glassy margins and alteration haloes

morphological and sedimentological characteristics of the neogene submarine coherent lavas and hyaloclastites in southwest hokkaido japan abstract the neogene formations in southwest hokkaido japan are mostly composed of submarine volcanic products such as submarine coherent lavas and hyaloclastites associated with feeder dikes this paper presents criteria for recognition of submarine effusion products through description of the morphological and sedimentological characteristics of coherent lavas such as pillow lobes sheet flow lava lobes and pseudo pillow lavas and hyaloclastites and feeder dikes and a small amount of associate pyroclastic rocks

mid cretaceous hydrothermal vents and authigenic carbonates in a transform margin basque cantabrian basin western pyrenees a multidisciplinary study a comprehensive study of authigenic carbonates and associated fauna in late albian organic rich deep water deposits the black flysch group reveals that carbonate precipitation was a by product of the anaerobic oxidation of hydrocarbon rich hydrothermal fluids the authigenic carbonates are exposed along the kardala and alkolea sea cliffs in the western pyrenees the two vent carbonates occur 1 km apart adjacent to the synsedimentary right reverse mutriku fault but in contrasting structural domains the kardala carbonates occur on a structural ridge hangingwall and the alkolea carbonates are positioned at the base of an erosional scarp folded downward footwall the similarity in pattern of the carbonate phases and complex paragenetic events for both vent precipitates implies that hydrothermal fluid generation processes and pore water evolution during early and late diagenesis were similar nevertheless a comparison of the geochemistry fossil fauna and morphology of carbonate structures of both precipitates suggests that the vented hydrocarbon type flow intensity and temperature of hydrothermal fluids were different at the kardala vent intense focused flow of hot up to 109 c oil rich fluids were generated allowing the development of a relatively abundant chemosynthesis based fauna in contrast at the alkolea vent diffuse flows of warm thermogenic methane rich fluids were expelled to the sea floor and no chemosynthetic fauna developed these differences are related to the contrasting structural setting of each locality similar d 13 corg values for both pyrobitumen fills and host unit organic matter suggest that the hydrocarbon source was the black flysch group contact alteration of these organic rich sediments by syndepositional hydrothermal fluids generated hydrothermal petroleum oil and gas hydrocarbons which probably migrated updip to the sea floor by contemporary compression tectonics

three dimensional lithofacies variations in hyaloclastite deposits analysis of the spatial lithofacies variability within lava fed delta formations in southern iceland has revealed complex three dimensional volcanic architectures in hyaloclastite deposits in non glacial settings two depositional environments are studied a lava entering a marine embayment stori nupur and b lava advancing into a body of water of the flanks of a surtseyan cone hjorleifshof i interaction between environmental factors such as shoreline geomorphology water depth wave energy levels the nature of the lava transport system lava supply rate all affect the resulting lava deltas creating complex lithofacies arrangements and stacking patterns recognised here are two types of hyaloclastite deltas one of syn sedimentary origin hjorleifshof i and one derived from primary fragmentation processes stori nupur syn sedimentary systems are dominated by destabilisation of the hyaloclastite pile leading to reworking downslope and share similarities to alluvial delta systems conversely primary fragmented systems are controlled by waxing and waning cycles in volcanic effusivity whereby the hyaloclastite unit recorded is not the product of one lava flow rather than one eruptive event

exogenous and endogenous construction of the subaqueous glenwood felsic lava flow complex abitibi greenstone belt quebec canada abstract both intrusive and extrusive volcanic facies of a felsic lava flow complex are exposed as the outcrops of the glenwood rhyolite within the blake river group of the abitibi greenstone belt quebec canada sub vertically dipping volcanic facies allows for the identification of the internal architecture of an archean subaqueous felsic flow complex detailed facies analyses show volcanic facies and volcanic textures and structures atypical of subaqueous pyroclastic deposits or deposits of dome complexes additionally a complex network of mafic dykes cross cut the felsic facies when integrated with facies specific geochemical analyses a coherent model for all volcanic and intrusive facies and supplemental information regarding the host volcanic complex has been developed detailed mapping reveals extrusive or exogenous aphanitic felsic volcanic facies and intrusive or endogenous quartz and feldspar phyric felsic volcanic facies exogenous facies are comprised of massive lobate in situ brecciated flow breccia and flow front breccia facies whereas the only visible endogenous facies is a quartz and feldspar phyric unit that intrudes the brecciated facies on the eastern side of the complex all felsic facies demonstrate a west to east flow direction both exogenous and endogenous facies have similar chemical compositions ranging from dacite to rhyodacite with a transitional affinity mafic to intermediate dykes predominantly strike north south and east west with occasional east northeast trending units wispy terminations at some dyke margins and dismembered dykes indicate they were intruded into a still cooling viscoelastic medium geochemical analyses further defines that most east west trending dykes have a tholeiitic affinity whereas north south trending dykes are dominantly calc alkaline and east northeast trending dykes are transitional the subaqueous glenwood felsic flow complex was emplaced in a fault bounded depression and consists of stacked exogenous dacite rhyodacite lobes and intruded by a late quartz and feldspar phyric endogenous lobe the intrusion of mafic dykes occurred relatively soon after the cessation of felsic activity as evidenced by primary textures consistent with intrusion into a viscoelastic medium combined the extrusive and intrusive facies of the complex attests to the complexity of the host volcanic environment

late orogenic basins in the archaean superior province canada characteristics and inferences abstract the late orogenic archaean duparquet kirkland and stormy basins of the canadian superior province are characterized by bounding crustal scale faults and abundant porphyry stock emplacement lava flows and pyroclastic deposits are restricted to the kirkland and stormy basins and coarse clastic detritus characterizes the duparquet basin seven distinct lithofacies are identified 1 mafic volcanic 2 felsic volcanic 3 pyroclastic 4 volcaniclastic 5 conglomerate sandstone 6 sandstone argillite conglomerate and 7 argillite sandstone tuffaceous sandstone the mafic and felsic volcanic lithofacies represent effusive lava flows the pyroclastic lithofacies is formed of subaerial surge and airfall deposits and the volcaniclastic lithofacies is composed of reworked volcanic debris the conglomerate sandstone lithofacies is interpreted as alluvial fan fan delta or proximal braided stream deposits whereas the sandstone argillite lithofacies is consistent with sandy dominated flood or braidplain deposits a dominantly shallow water lacustrine setting is inferred for the argillite sandstone lithofacies these different lithofacies record the basin history and can be used to identify basin forming processes lithofacies stacking and rapid lateral changes of lithological units in conjunction with interformational unconformities and basin margin faults suggest tectonically induced sedimentation volcanism can also influence basin evolution and the delicate balance between erosion sedimentation and prevalent transport processes is affected by volcanic input catastrophic influx of pyroclastic material facilitated mass wasting processes and formation of non confined hyperconcentrated flood flow deposits account for local congestion of alluvial or fluvial dispersal patterns confined stream flow processes govern sedimentation during intravolcanic phases or prominent tectonic uplift in addition climate which controls the weathering processes and vegetation which stabilizes unconsolidated material affects the transport and depositional process a co 2 rich aggressive weathering humid archaean atmosphere favours traction current deposits and an absence of vegetation promotes rapid denudation although tectonism is the prevalent long term controlling factor in restricted basins the effects of volcanism climate and lack of vegetation can also be detected

felsic fire fountaining beneath archean seas pyroclastic deposits of the 2730 ma hunter mine group quebec canada abstract the lapilli tuff breccias ltb 1 and ltb 2 of the archean hunter mine group in the south central part of the abitibi greenstone belt are inferred to be the product of subaqueous lava fountaining intercalated sub wave base iron formations interstratified turbiditic tuffs the absence of wave induced sedimentary structures and the stratigraphic position of lapilli tuff breccias beneath basaltic komatiites support this contention a complete eruptive sequence shows a tripartite division into a massive breccia b stratified lapilli tuff and c turbiditic tuff lapilli tuff division the massive breccia division is characterized by clusters of isolated and compressed irregular shaped clasts inferred to be deposited directly from the hot magmatic lava fountain abundant vesicular pyroclasts with a vesicle content of up to 60 exhibit locally coalescing vesicles indicating bubble nucleation prior to eruption the prevalence of irregular to amoeboid clast shapes suggests transport from the vent in a steamy rich high density current to the site under a self generated steam cupola ubiquitous subequant lapilli size pyroclasts of the stratified lapilli tuff division suggest that significant ingress of water into the fountain changed the prevalent fragmentation process from magmatic to hydrovolcanic the turbiditic tuff lapilli tuff division composed of pumice lithic fragments and vitric ash is envisaged to have formed by gravitational collapse of a subaqueous turbulent eruptive plume this type of eruptive mechanism constituted a minor but important process of volcanic construction on the ocean floor during the archean and possibly during incipient arc and backarc formation in modern day settings

vrancea99 the crustal structure beneath the southeastern carpathians and the moesian platform from a seismic refraction profile in romania the vrancea99 seismic refraction experiment is part of an international and multidisciplinary project to study the intermediate depth earthquakes of the eastern carpathians in romania as part of the seismic experiment a 300 km long refraction profile was recorded between the cities of bacau and bucharest traversing the vrancea epicentral region in nne ssw direction the results deduced using forward and inverse ray trace modelling indicate a multi layered crust the sedimentary succession comprises two to four seismic layers of variable thickness and with velocities ranging from 2 0 to 5 8 km s the seismic basement coincides with a velocity step up to 5 9 km s velocities in the upper crystalline crust are 5 9 6 2 km s an intra crustal discontinuity at 18 31 km divides the crust into an upper and a lower layer velocities within the lower crust are 6 7 7 0 km s strong wide angle pmp reflections indicate the existence of a first order moho at a depth of 30 km near the southern end of the line and 41 km near the centre constraints on upper mantle seismic velocities 7 9 km s are provided by pn arrival times from two shot points only within the upper mantle a low velocity zone is interpreted travel times of a plp reflection define the bottom of this low velocity layer at a depth of 55 km the velocity beneath this interface must be at least 8 5 km s geologic interpretation of the seismic data suggests that the neogene tectonic convergence of the eastern carpathians resulted in thin skinned shortening of the sedimentary cover and in thick skinned shortening in the crystalline crust on the autochthonous cover of the moesian platform several blocks can be recognised which are characterised by different lithological compositions this could indicate a pre structuring of the platform at mesozoic and or palaeozoic times with a probable active involvement of the intramoesian and the capidava ovidiu faults especially the intramoesian fault is clearly recognisable on the refraction line no clear indications of the important trotus fault in the north of the profile could be found in the central part of the seismic line a thinned lower crust and the low velocity zone in the uppermost mantle point to the possibility of crustal delamination and partial melting in the upper mantle

water settling and resedimentation of submarine rhyolitic pumice at yali eastern aegean greece abstract the yali pumice breccia is a very thick 150 m quaternary succession of submarine pumice that has been uplifted and exposed in the southern part of yali island in the eastern aegean greece the pumice breccia comprises moderately to well sorted 0 03 3 m thick beds of loose pumice clasts that are poor in fine matrix predominantly the larger pumice clasts cobbles and boulders are prismatic with quenched margins and internal polyhedral joints in comparison the smaller pumice clasts are polyhedral angular to subrounded blocky pebbles and granules these smaller clasts lack quenched margins and have sharp curviplanar surfaces that cross cut vesicle boundaries we interpret the larger pumice clasts to be the products of spalling and explosive fragmentation of a small extrusion of submarine pumiceous lava the smaller pumice clasts were generated by a combination of 1 passive and explosive disintegration of the larger pumice clasts and 2 phreatomagmatic explosions phreatomagmatic explosions also generated a minor component of non or poorly vesicular juvenile and basement derived lithic clasts the yali pumice breccia includes four major facies cobble boulder pebble mixed cobble dominant and mixed pebble dominant the cobble boulder facies occurs in well sorted massive tabular beds of large 64 mm 1 5 m pumice up to 3 m thick that lack both lithic clasts and fine matrix this facies has textural and lithological features consistent with deposition of large pumice clasts by means of water settling from suspension the three remaining facies are comparatively less well sorted although still fines poor and include rare lithic clasts they exhibit massive or internally diffusely stratified wedging 0 1 2 m thick beds of coarser grained medium pebble to cobble pumice clasts that onlap or are separated by wedge shaped thinner

spherulitic aphyric pillow lobe metatholeiitic dacite lava of the timmins area ontario canada a new archean facies formed from superheated melts fragmental rocks of the v10 units of the vipond formation of the tisdale assemblage previously have been identified as pillow basalts but many samples are shown to be intermediate to felsic in character likely tholeiitic dacite in composition specifically the v10b unit is mapped as a pillow lobe dacite aside from being more geochemically evolved in terms of their immobile trace elements these rocks differ from typical pillow basalts in that they have more abundant primary breccia and hyaloclastite the pillow lobes are contorted having been folded in a plastic state and are zoned typically having a spherulite rich core moreover the flows are aphyric interpreted to mean that they were erupted in a superheated state this along with their pillow lobe nature demonstrates that they were erupted as relatively low viscosity melts for such silicic compositions interaction with water quenched the outer pillow lobe and contributed to the formation of the abundant breccia the fact that the melt was crystal and microlite free inhibited crystal growth such that the bulk of the lobes were quenched to crystal free glass nucleation occurred only in the cores where cooling rates were lower in comparison to the medial and exterior areas of the pillow lobes although in the cores crystal growth rates were high so that abundant spherulite formation took place the flows are exposed over a strike length of more than 10 km and are interpreted to be continuous and to have resulted from fissure eruptions the resulting porous permeable high fe mg high surface area glassy rocks may have been ideal for channeling and reacting with gold bearing hydrothermal solutions descriptions of most other archean subaqueous felsic lobes document that the lavas were phyric and that spherulites formed near the external lobe margin the distinctly different zoning of the v10b pillow lobes suggests that they constitute a new archean facies formed from superheated melts

on the potential generality of depth related ecologic structure in cold seep communities evidence from cenozoic and mesozoic examples faunal communities inhabiting hydrocarbon seeps in the deep sea today show a depth related change in their ecologic structure the proportion of obligate endemic taxa increases with depth while the abundance of predators and other background taxa decreases here the fossil record of seep communities is investigated for similar gradients the middle eocene to middle miocene deep water cold seep deposits in western washington state usa are from different depths those of the middle to late eocene humptulips bear river and whiskey creek sites lived in depths of 500 to 2000 m those of the late oligocene to middle miocene seep communities of the lincoln creek and astoria formations in depths of 16 to 900 m these seeps were inhabited by the same taxa that inhabit cold seeps today and like their modern analogs they show an increasing proportion of obligate taxa and a decreasing abundance of predators and other background taxa with depth also among late mesozoic seep sites a depth related change in the proportion of obligate taxa is apparent seep communities in shallow shelf settings harbor virtually no obligates while seep communities in outer shelf to slope settings show a high proportion of obligates although the constituting species have different taxonomic affinities than their cenozoic and extant counterparts unlike in modern examples differences between seep communities from outer shelf and slope depths were not seen it is hypothesized that due to the higher mesozoic sea levels many seep communities on the continental shelves were located below the photic zone where an obligate seep fauna could develop because an increase in the proportion of obligate taxa with depth can be seen both in the cenozoic and in the late mesozoic despite the different taxonomic affinities of the obligate taxa it is suggested here that this depth related structure is a general feature of seep faunas independent of the taxa that express this pattern

metamorphic and thermal history of a fore arc basin the fossil bluff group alexander island antarctica the himalia ridge formation fossil bluff group alexander island is a 2 2 km thick sequence of upper jurassic lower cretaceous conglomerates sandstones and mudstones derived from an andesitic volcanic arc and deposited in a fore arc basin the metamorphic and thermal history of the formation has been determined using authigenic mineral assemblages and vitrinite reflectance measurements metamorphic effects include compaction pore space reduction cementation and dissolution and replacement of detrital grains by clay minerals smectite illite smectite corrensite and kaolinite calcite chlorite laumontite prehnite pumpellyite albite and mica with less common quartz haematite pyrite and epidote the authigenic mineral assemblages exhibit a depth dependence and laumontite and calcite exhibit a strong antipathetic relationship detrital organic matter in the argillaceous layers has vitrinite reflectance values r o ranging from 2 3 to 3 7 this indicates considerable thermal maturation with a systematic increase in reflectivity with increasing depth there is good correlation of metamorphic mineral assemblages with chlorite crystallinity and vitrinite reflectance values all indicating temperatures in the range of 140 20degreesc at the top of the sequence to 250 10degreesc at the base of the sequence the temperatures suggest a geothermal gradient of 36 64degreesc km and a most likely gradient of 50degreesc km it is suggested that this higher than average gradient for a fore arc basin resulted either from rifting during basin formation or from a late stage arc migration event

sediment instability related to fluid venting in miocene authigenic carbonate deposits of the northern apennines italy chemosynthetic carbonates identified by isotopic palaeoecological and sedimentological features are concentrated in middle late miocene satellite and foredeep deposits of the northern apennines chemoherms in the foredeep are hosted in thick pelitic intervals probably deposited in intrabasinal structural highs which are entirely or partly involved in large slumps in many cases associated with extrabasinal slides sediment textures in carbonates and in the enclosing foredeep pelitic sediments indicate a link between hydrocarbon fluid venting sediment deformation and mobilisation and tectonics the intensity and style of fluid release phases directly influenced chemoherm typology and also determined overpressure conditions in low shear strength pelitic sediments favouring sediment mobilisation and influencing slope instability which widely affected the apennine foredeep chemosynthetic carbonates are associated with sites of tectonically fractured and compressed sediments in the apennine foredeep thrust belt system thus indicating a relation with the tectonic loading of the apennine thrust sheets which favoured fluid expulsion along forerunner faults possible gas hydrate contributions to fluid expulsion processes are discussed based on sediment textures compared with modern vent areas finally sediment instability may have facilitated a large amount of fluid escape thus stopping carbonate precipitation

crustal properties from s wave and gravity data along a seismic refraction profile in romania vrancea 99 is a seismic refraction line that was carried out in 1999 to investigate the deep structure and physical properties of the upper lithosphere of the southeastern carpathians and its foreland it runs from the city of bacau to the danube river traversing the vrancea epicentral area of strong intermediate depth seismicity and the city of bucharest interpretation of p wave arrivals led to a velocity model that displays a multi layered crust with velocities increasing with depth the range of p wave velocities in the sedimentary cover increases from n to s and a structuring of the autochthonous basement of the moesian platform is observed the crystalline crust displays thickness variations but at the same time the lateral velocity structure along the seismic line remains almost constant an intra crustal boundary separates an upper crust from the lower crust within the upper mantle a low velocity zone is detected at a depth of about 55 km the interpretation of observable s waves resulted in a velocity model that shows the same multi layered crust with s velocities increasing similarly with depth as the p waves the corresponding poisson s ratio is highly variable throughout the crust and ranges from 0 20 0 35 for the sedimentary cover to 0 22 0 25 for the crystalline crust the interpretation of the vp vs and poisson s ratio in petrological terms suggests a large variety of rocks from sand and clay to sandstone limestone and dolomite within the sedimentary cover within the crystalline crust the most probably rock types are granite granodiorite granite gneiss and or felsic amphibolite gneiss in the upper part and gneiss and or amphibolite in the lower part based on the 2 d seismic velocity model a density model is developed density values are assigned to each layer in agreement with the p wave velocity model and with values accepted for the geological units in the area after several iterations a good fit between the computed and observed bouguer anomalies was obtained along the seismic line

geologic setting of pacmanus hydrothermal area high resolution mapping and in situ observations abstract this study presents a systematic analysis and interpretation of autonomous underwater vehicle based microbathymetry combined with remotely operated vehicle rov video recordings rock analyses and temperature measurements within the pacmanus hydrothermal area located on pual ridge in the bismarck sea of eastern manus basin the data obtained during research cruise magellan 06 and so 216 provides a framework for understanding the relationship between the volcanism tectonism and hydrothermal activity pacmanus is a submarine felsic vocanically hosted hydrothermal area that hosts multiple vent fields located within several hundred meters of one another but with different fluid chemistries vent temperatures and morphologies the total area of hydrothermal activity is estimated to be 20 279 m2 the microbathymetry maps combined with the rov video observations allow for precise high resolution mapping estimates of the areal extents of hydrothermal activity we find the distribution of hydrothermal fields in the pacmanus area is primarily controlled by volcanic features that include lava domes thick and massive blocky lava flows breccias and feeder dykes spatial variation in the permeability of local volcanic facies appears to control the distribution of venting within a field we define a three stage chronological sequence for the volcanic evolution of the pacmanus based on lava flow morphology sediment cover and lava sio2 concentration in stage 1 sparsely to moderately porphyritic dacite lavas 68 69 8 wt sio2 erupted to form domes or cryptodomes in stage 2 aphyric lava with slightly lower sio2 concentrations 67 2 67 9 wt sio2 formed jumbled and pillowed lava flows in the most recent phase stage 3 massive blocky lavas with 69 to 72 5 wt sio2 were erupted through multiple vents constructing a volcanic ridge identified as the pacmanus neovolcanic zone the transition between these stages may be gradual and related to progressive heating of a silicic magma following a recharge event of hot mantle derived melts

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

distribution and significance of crystalline perlitic and vesicular textures in the ordovician garth tuff wales diverse spherulitic and granular crystalline fabrics perlitic textures and fabrics related to the growth and migration of vesicles occur in the garth tuff a largely welded ordovician ignimbrite defining the distribution of such textures helps to constrain the ignimbrite s cooling and degassing history suites of spherulitic and perlitic textures closely reflect variation in cooling rates seven facies are defined based on the style and intensity of crystallisation 1 a medium to coarsely crystalline equigranular facies 2 an intensely spherulitic facies 3 a sparsely spherulitic facies 4 a pectinate facies 5 a microcrystalline to cryptocrystalline equigranular facies 6 a lithophysal facies and 7 a transitional perlite pectinate facies textural changes from facies 1 to 5 reflect progressively higher cooling rates facies 1 occurs in proximal settings in the ignimbrite s core facies 2 to 5 successively envelop facies 1 with facies 2 becoming the dominant fabric in the ignimbrite s core in medial settings facies 5 is typically developed in the originally glassy perlitic zones at the ignimbrite s welded margins crystallisation under hydrous conditions is reflected by second boiling textures in the sporadically developed lithophysal facies the seventh facies reflects a subtle interplay between cooling hydration and crystallisation which locally prevented perlitic fracturing the distribution of amygdales reflects patterns of volatile migration and entrapment in the lower levels of the ignimbrite amygdales occur in irregular concentrations or rare subvertical pipe like structures pipe like structures attest to fumarolic activity while the ignimbrite was in a rheomorphic state amygdales are widespread and evenly distributed in the upper levels of the ignimbrite however the top of the welding profile is characterised by a thin poorly vesiculated originally vitrophyric horizon that abruptly caps an intense concentration of amygdales ductile and brittle fabrics developed during the upward migration of gas microscopic drag folds occur around some amygdales jigsaw fit to clast rotated breccias originated through both late stage pneumatic fracturing and autobrecciation vaporisation of water at the flow base provided a significant source of volatiles in addition to gas released during cooling and crystallisation secondary alteration has enhanced or modified some fabrics perlitic zones were susceptible to patchy chlorite sericite carbonate diagenetic alteration diagenesis and metamorphism have contributed to the infilling of vesicles

facies reconstruction of a hydrothermally altered dacite extrusive sequence evidence from geophysical downhole logging data odp leg 193 odp leg 193 drilled into the pacmanus hydrothermal field papua new guinea which is an activehydrothermal vent field associated with felsic magmatism in a convergent geodynamic setting thepacmanus hydrothermal field is part of the eastern manus basin and is located near the crest of pualridge a 500 to 700 meters high felsic neo volcanic ridge two sites snowcap site 1188 and romanruins site 1189 were drilled approximately 800 m apart although low core recovery limited theexamination of the subsurface geology geophysical downhole measurements provided continuous recordsof in situ physical properties with depth and were used to reconstruct lithostratigraphic profiles downholelogging operations included standard wire line logging and logging while drilling lwd measurements electrical resistivity images of the borehole wall were examined to find characteristic textures and threedifferent volcanic facies were distinguished coherent dacite volcaniclastic dacite and brecciated dacite inaddition intervals with sulfide mineralization were identified based on characteristic responses of thephotoelectric factor log a comparison of the reconstructed profiles from both sites shows considerabledifferences in the proportions of facies and the thickness of individual layers thick units of coherent faciesare predominant at snowcap and indicate a proximal position of the site within the volcanic system of pualridge at roman ruins thin individual layers with rapid changes in volcanic facies and a higherproportion of volcaniclastic and brecciated dacite suggest a medial position these differences in volcanicfacies show that the volcanic architecture at pual ridge is characterized by small scale facies changes emplacement of small volume individual lava flows and complex geometries of individual emplacementunits geophysical logging data suggest that subseafloor hydrothermal activity is focused to the areaaround one hole at roman ruins downhole logs from this hole show characteristic cyclic patterns in theelectrical resistivity and photoelectric factor logs indicating that hydrothermal sulfide mineralization isconcentrated at the tops of individual lava flows representing paleo seafloor positions

an early jurassic deep water stromatolitic bioherm related to possible methane seepage los molles formation neuquen argentina an assemblage of microbial stromatolites and worm tubes makes up a limestone bioherm 15 m thick and 60 m in diameter enclosed in marls and dark shales of the early jurassic los molles formation neuquen basin argentina the los molles formation is a basinal unit consisting primarily of shales silts and sandstone turbidites deposited after the first general marine transgression in the basin below storm wave base in relatively deep water poorly oxygenated conditions the bioherm is composed of stacked stromatolites 1 4 m in diameter and 1 2 m thick they initially grew horizontally tabular stromatolites or vertically columnar stromatolites and later became domal equidimensional to asymmetric structures they often display vertical and overturned flanks each stromatolite consists of micritic laminae alternating with early botryoidal cements which make up the bulk of the structure calcareous worm tubes are embedded in peloidal micrite associated with the stromatolites the growth of the assemblage was uninterrupted by terrigenous input the diagenetic sequence indicates evolution from marine phreatic to burial environments isotopic values for micrite worm tubes early botryoidal cements and spar cements yield very negative 13c values down to 33 and negative 16o values down to 11 these depleted values indicate precipitation in very anomalous conditions in the jurassic ocean under the influence of methane rich fluids these characteristics suggest that the stromatolitic bioherm formed in relation to methane seeps in the seafloor of the neuquen basin it is suggested that the structure grew within the photic zone although a chemosynthetic component cannot be excluded minimum depositional depth has been estimated at 50 m and could be up to 100 m the vent fluids would have migrated through shallowly buried early rift faults which bound underlying depocenters infilled with continental clastic and volcanic rocks the origin of these fluids could be related to magmatic activity which resulted in accumulation of the syn rift volcanics alternatively the structure could indicate seepage related to the presence of hydrocarbon accumulations in the syn rift succession during the jurassic the importance of which is being gradually acknowledged in the petroleum system of the neuquen basin

cretaceous methane seep deposits from new zealand and their fauna abstract six cretaceous methane seep deposits are reported from the raukumara peninsula eastern north island new zealand dinoflagellate dating indicates a late albian to mid cenomanian age for three deposits from port awanui and a mid campanian age for two deposits from waipiro bay and for one from owhena stream the dominant petrographic fabric of the carbonates is detrital micrite and the numerous fenestrae and vugs are filled with various cements including two types of non detrital micrite and botryoidal and banded fibrous calcites these petrographic features in combination with negative 13c values of early diagenetic micrites as low as 29 2 vs v pdb and 13c depleted molecular fossils such as the archaeal biomarkers pentamethylicosane 97 vs v pdb and biphytane 99 and the bacterial biomarker anteiso c15 fatty acid 47 reveal that sulfate dependent anaerobic oxidation of methane aom induced the formation of these deposits the carbonates preserve a typical mollusk dominated late mesozoic deep water seep fauna including the large modiomorphid bivalve caspiconcha the lucinid bivalve ezolucina and limpets hokkaidoconchids and a large abyssochrysoid among the gastropods with close biogeographic relationships to north pacific seep faunas of cretaceous age in contrast to the general marine mollusk fauna of new zealand which shows a high degree of endemism in both the cenozoic and recent new zealand s cretaceous to present day seep faunas consist largely of taxa known from coeval seeps around the world thus while deep water seeps in new zealand were repeatedly or continuously colonized by members of the global seep fauna the general mollusk fauna of the new zealand region developed a considerable degree of endemism during this time

drill core based facies reconstruction of a deep marine felsic volcano hosting an active hydrothermal system pual ridge papau new guinea odp leg 193 abstract pual ridge is a deep marine felsic volcanic edifice in the eastern manus back arc basin papua new guinea with an estimated volume of 6 to 9 km 3 it is 1 1 5 km wide 20 km long and rises 500 600 m above the surrounding ocean floor the active pacmanus hydrothermal field on the crest of pual ridge at 1640 1690 m below sea level was the target of ocean drilling program leg 193 variably altered dacite lavas have been recovered from the subsurface of a low t discharge site snowcap and a high t black smoker site roman ruins reaching a maximum depth of 380 m below seafloor mbsf volcanic facies interpretation of these cores is difficult due to incomplete recovery and widespread pseudoclastic textures generated by fracturing and multi phase incomplete fluid dacite interaction however distinction of genuine volcaniclastic facies and facies with alteration related clastic appearance is important in order to define paleo seafloor positions within the volcanic stratigraphy that may be prospective for massive sulfide mineralization this has been accomplished using remnant primary characteristics indicative of transportation such as polymictic composition grading or textural evidence for differential movement of individual clasts three phases of volcanic activity can be distinguished and a proximal facies association dominated by coherent facies of dacite lavas exists below snowcap at roman ruins a medial facies association consists of lava flows with about equal proportions of coherent and volcaniclastic facies endogenous growth was an important process during lava flow emplacement and groundmass textures such as perlite flow banding and spherulites indicate that cooling rates were variable locally allowing for high temperature devitrification a tube pumice breccia unit is interpreted as the resedimented facies of a quench fragmented highly vesicular dacite lava carapace sulfide accumulations in the subsurface are restricted to roman ruins suggesting that the abundance of volcaniclastic facies favored ascent of metal bearing fluids due to the inherent high permeability evidence for mineralization at paleo seafloor positions at 110 and 195 mbsf indicate a complex interrelationship between volcanic and hydrothermal activity a facies model has been developed which may help to locate subaqueous felsic lava dominated volcanic centers and associated sulfide deposits in ancient volcano sedimentary successions

controls of fluid chemistry and complexation on rare earth element contents of anhydrite from the pacmanus subseafloor hydrothermal system manus basin papua new guinea ocean drilling program odp leg 193 successfully drilled four deep holes 126 to 386 m into basement underlying the active dacite hosted pacmanus hydrothermal field in the eastern manus basin anhydrite is abundant in the drill core material filling veins and vesicles cementing breccias and occasionally replacing igneous material we report rare earth element ree contents of anhydrite from a site of diffuse venting site 1188 which show extreme variability in terms of both absolute concentrations e g 0 08 28 3 ppm nd and pattern shape lan smn 0 08 3 78 smn ybn 0 48 23 1 eu eu 0 59 6 1 the range of ree patterns in anhydrite includes enrichments in the middle and heavy rees and variable eu anomalies the patterns differ markedly from those of anhydrite recovered during odp leg 158 from the tag hydrothermal system at the mid atlantic ridge which display uniform lree enriched patterns with positive eu anomalies very similar to tag vent fluid patterns as the system is active the host rock composition is uniform and the anhydrite veins appear to relate to the same hydrothermal stage we can rule out predominant host rock and transport control instead we propose that the variation in ree content reflects waxing and waning input of magmatic volatiles hf so2 and variable complexation of rees in the fluids ree speciation calculations suggest that increased fluoride and possibly sulfate concentrations at pacmanus may affect ree complexation in fluids whereas at tag only chloride and hydroxide complexes play a significant role the majority of the anhydrites do not show positive eu anomalies suggesting that the fluids were more oxidizing than in typical mid ocean ridge hydrothermal systems we use other hydrothermal fluids from the manus basin vienna woods and desmos which bracket the pacmanus fluids in terms of acidity and ligand concentrations to examine the dependence of ree complexation on fluid composition geochemical modeling reveals that under the prevailing conditions at pacmanus ph 3 5 t 250 300 c eu oxidation state and the relative importance of fluoride versus chloride complexing are very sensitive to small variations in oxygen fugacity temperature and ph patterns with extreme mid ree enrichment may reflect speciation effects free ion abundance coupled with crystal chemical control we conclude that the great variability in ree concentrations and pattern shape is likely due to variable fluid composition and ree complexation in the fluids

giant rafted pumice blocks from the most recent eruption of taupo volcano new zealand insights from palaeomagnetic and textural data abstract giant blocks of pumice lie strewn along a former shoreline of intracaldera lake taupo new zealand and are the sole subaerial evidence of the most recent volcanism at the taupo supervolcano geochemically they are identical to material erupted during the complex and multiphase 1 8 ka taupo eruption which they post date by one to two decades the blocks some of which are 10 m long show complex jointing patterns indicative of both surface chilling and continued interior expansion as well as heterogeneous vesicularity with dense rims mean density 917 kg m3 grading via an intervening transition zone mean density 844 kg m3 into a more highly vesicular interior mean density 815 kg m3 analysis of thermal demagnetisation data indicates significant reorientation of the blocks as they cooled through a series of blocking temperatures some parts of block rims cooled to below 580 c well before emplacement on the shore whereas other parts in the interior and transition zones which cooled more slowly acquired different orientations before stranding some block interiors cooled after blocks were finally deposited and record the direction of the 1 8 ka field the blocks are believed to be derived from one or both of a pair of rhyolitic lava domes that developed on the bed of lake taupo several decades after the climactic taupo eruption over the inferred vent area these and similar giant rafted pumice blocks in other marine and lacustrine settings raise a number of questions about how volatile rich felsic magma can be erupted underwater with only limited thermal fragmentation furthermore the prolonged flotation of out sized fragments of vesiculated magma formed during subaqueous dome growth contrasts with the rapid sinking of smaller pieces of hot plinian pumice under laboratory conditions the genesis of pumice forming the blocks is not entirely clear most simply the blocks may represent part of a vesiculated carapace of a growing lava dome broken loose as the dome grew and deformed then rising buoyantly to the surface parts of the carapace could also be released by local magma water explosions some textures of the pumice however suggest fresher magma released from beneath the carapace this may suggest that silicic dikes and pillows pods intruded into a growing mound of silicic hyaloclastite itself formed by quench fragmentation and thermal granulation of the dike margins this fragmental cover would have inhibited cooling of a still hot and actively vesiculating interior which was then released to float to the surface by gravitational destabilisation and collapse of the growing pile following their formation the large fragments of pumice floated to the lake s surface where they were blown ashore to become embedded in accumulating transgressive shoreface sediments and continue cooling

explosive rhyolite tuya formation classic examples from kerlingarfjoll iceland rhyolite eruptions in iceland mostly take place at long lived central volcanoes examples of which are found associated with each of the present day rift zone ice caps subglacial eruptions at kerlingarfjoll central volcano produced rhyolite tuyas that are notable for their exposures of early erupted pyroclastic material observations from a number of these edifices are synthesised into a general model for explosive rhyolite tuya formation eruptions begin with violent phreatomagmatic explosions that generate massive tuff mt but the influence of water quickly declines leading to the formation of massive lapilli tuffs mlt containing magmatically fragmented vesicular pumice and ash these are deposited rapidly near the vent probably by moist pyroclastic density currents confined by ice but not within a meltwater lake the explosive effusive transition is controlled by the ascent rate and gas content of the magma an unusual obsidian rich massive lapilli tuff lithofacies omlt is identified and interpreted as pyroclastic material that was intruded into gas fluidised deposits at the explosive effusive transition the effusive phase of eruption involves the emplacement of intrusions and lava caps intrusions of lava into the early erupted phreatomagmatic deposits are characterised by peperitic margins and the formation of hyaloclastite intrusions into stratigraphically higher levels of the pyroclastic material show more limited interaction with the host tephra and have microcrystalline cores large lava bodies with columnar jointed margins cap the tuyas and have intrusive basal contacts with the tephras the main influence of the ice is to confine the rhyolite eruptive products to immediately above the vent region this is in contrast to subglacial basaltic tuya forming eruptions which are characterised by the formation of meltwater lakes phreatomagmatic fragmentation and subaqueous deposition the lack of meltwater storage may reduce the potential for large jokulhlaups

fluidization of wet sediments during the emplacement and cooling of various igneous bodies during the emplacement and cooling of igneous bodies fluidization of wet sediment by water vapour may occur by heating or by pressure relief during the opening of fractures momentary fluidization causes sediment reconstitution and local transport continuous fluidization can result in substantial sediment displacement theoretical considerations show that fluidization due to heating is not likely to occur at depths where pressure is much greater than 312 bars studies of the emplacement of sills of andesite ayrshire fluid rhyolite ramsey island and viscous rhyolite moelwyn hills recognize a wide range of phenomena attributable to wet sediment fluidization and in places modify existing interpretations the transgressive bases of the subaqueously welded ash flow tuffs of the capel curig volcanic formation are consistent with emplacement attended by fluidization of the subjacent sediment evidently fluidization is a means by which large volumes of wet sediment can be replaced by igneous material with minimal disturbance of the remaining host also fluidization can result in exceptionally complex contact relationships between sedimentary host and intrusive rocks and can cause fractures formed during cooling to be thoroughly pervaded by sediment fluidization is commonly associated with the formation of peperites

gamma ray spectrometric analysis of hydrothermally altered dacite samples from the pacmanus hydrothermal field implications for the interpretation of gamma ray wireline measurements abstract spectral gamma ray wireline logging derives the concentrations of potassium thorium and uranium of the formation by measuring the gamma ray spectrum under the assumption of secular equilibrium these measurements were carried out in a number of boreholes drilled by ocean drilling program leg 193 at the pacmanus hydrothermal field spectral gamma ray logs from several of these holes show intervals of increased radioactivity associated with high uranium values of up to 60 ppm snowcap hydrothermal field and 25 ppm roman ruins hydrothermal field nine samples of hydrothermally altered dacite were analyzed using gamma spectrometry to examine the origin of elevated radioactivity and to test for distortion of secular equilibrium core spectrometry indicates that secular equilibrium is distorted distortion can be explained by either an uptake of nuclides of the lower part of the 238u decay series or by removal of 238u or 234th from the rocks in all cases wireline uranium logs and core spectrometry do not reflect true uranium concentrations of the formation but uranium is overestimated by a factor of 3 4 at roman ruins uranium values from wireline logging show higher uranium concentrations over large intervals than uranium values from core spectrometry and from published core geochemistry even when a possible leaching of uranium is taken into account wireline logs indicate that depth intervals of increased radioactivity are related to the occurrence of stockwork mineralization in these depth intervals core recovery was extremely low in addition to the distortion of secular equilibrium low core recovery and preferential loss of softer and more altered material cause a sampling bias between core samples and wireline data and may explain the observed difference in uranium concentrations between core and wireline logs

a multidisciplinary study of middle miocene seep carbonates from the northern apennine foredeep italy several pelitic intervals are intercalated at various levels within the marly arenaceous turbiditic successions of the middle miocene northern apennine foredeep they range in thickness from 30 to 200 m and represent sedimentation on top of ephemeral structural highs related to blind faults sediments are made up of hemipelagites and fine grained turbidites and include 13c depleted carbonates related to the rising of methane rich fluids hydrocarbon seep carbonates large portions of pelitic intervals are involved in chaotic masses by soft sediment deformation slumps slides intraformational breccias revealing an intense sediment instability during middle miocene a stratigraphic mineralogic and geochemical study was conducted on two of these pelitic intervals castagno d andrea mt citerna in order to reconstruct carbonate development the composition of fluids and to document the connections between fluid seepage and syndepositional tectonics this multidisciplinary approach has allowed us to discriminate between the two examined pelitic intervals in terms of age depositional rates and conditions organic carbon and post depositional processes seep carbonates are characterized by chemosymbiotic fossil communities autoclastic fractures and brecciation carbonate bodies show complex facies relationships as indicative of different stages in chemoherm growth the compositional study evidences the peculiar chemistry of chemoherm carbonates calcite low in mg and sr compared with carbonates in associated enclosing pelites and with modern chemoherms in general the non carbonate components within the chemoherms are enriched in detrital minerals and depleted in phyllosilicates with respect to the enclosing pelites the mineralogical changes in the clay component within the brecciated unit of the castagno d andrea chemoherms suggest authigenic precipitation of the mg rich phases isotopic analyses show the distinct carbon signature in the chemoherms from the two examined intervals castagno d andrea chemoherms more depleted from 15 8 up to 41 3 pdb than mt citerna from 5 2 up to 16 7 and the transitional 13c depletion trend observed moving from chemoherms to the enclosing pelites moderately depleted and te bouma sequence turbidites in the range of marine carbonates a slight but significant enrichment in 18o up to 1 4 pdb is observed for all chemoherms when compared to values of carbonate phases present in enclosing pelites geochemical data indicate that the brecciated facies of seep carbonates are related to an explosive release of gaseous fluids probably associated with the rise of deep hypersaline fluids

submarine volcanism eruption styles products and relevance to understanding the host rock successions to volcanic hosted massive sulfide deposits the increasing hydrostatic pressure of the water column with increasing water depth in subaqueous environments limits the ability of superheated volatiles to expand instantaneously against the ambient pressure explosive submarine eruptions are only likely in water depths less than 1 km and generally less than 500 m thus refuting models of highly explosive very deep water calderas popularly proposed as the host volcanic centers for the kuroko volcanic hosted massive sulfide vhms deposits of japan large volumes of blocky breccias can be produced by quench fragmentation during submarine lava eruptions and such deposits may have been mistaken for pyroclastic deposits in many cases in the past pyroclastic debris may occur in the host rock successions of some vhms deposits and may even be very voluminous however facies characteristics and theoretical constraints indicate that these are usually the products of mass flow deposition from shallow water or basin margin volcanic centers the maximum water depths for submarine explosive eruptions coincide approximately with the minimum pressures and water depths required to prevent boiling of mineralizing hydrothermal fluids in the stockwork before the fluids reach the sea floor the key elements in evaluating the prospectivity of ancient volcanic successions for vhms deposits appear to be deep water sediments and lavas or shallow intrusions in an extensional basin setting pyroclastic debris in many cases at least appears to be an accidental externally introduced component there is little evidence that explosive submarine calderas are essential as host volcanic centers to vhms deposits

high pressure metamorphism and deep crustal seismicity evidence from contemporaneous formation of pseudotachylytes and eclogite facies coronas the metamorphic complex of the western gneiss region wgr norway constitutes the root of the caledonian mountain belt and experienced temperatures of 700 800 c and pressures in excess of 20 kbar during peak metamorphism mafic bodies surrounded by strongly banded felsic gneisses commonly exhibit variable reequilibration to granulite and eclogite facies conditions and locally preserve igneous minerals and textures the krakeneset gabbro located on the island of vagsoy in the mixed hp uhp zone of the western wgr display evidence for extensive metastability through the entire prograde and retrograde p t histories eclogite constitutes less than a few percent of the total volume of the body and high pressure assemblages typically form thin coronas around magmatic phases or occur along localized zones of brittle deformation and fluid infiltration the gabbro displays pseudotachylyte vein networks that define subparallel brittle fault zones 50 cm wide transecting the gabbro body the pseudotachylytes contain m to mm scale amoeboid and dendrite like textures of garnet and plagioclase with inclusions of the eclogite facies minerals orthopyroxene omphacite amphibole and dolomite suggesting rapid disequilibrium growth of minerals during high pressure conditions textural and petrological evidence from pseudotachylytes and corona structures show that the growth of these unusual textures occurred shortly after pseudotachylyte crystallization by a process of rapid solid state alteration of a microcrystalline pseudotachylyte matrix the pseudotachylyte lined fault zones are in close spatial association with numerous amphibole carbonate filled hydrofractures with conspicuous fracture parallel alteration zones defined by hydrous eclogite facies assemblages these eclogite facies hydrofractures testify to the existence of high fluid pressures and to fluid infiltration following brittle failure during high grade metamorphic conditions geothermobarometric estimates ca t 650 700 c p 20 kbar and petrological data imply that hydrofracturing pseudotachylyte crystallization and the subsequent pseudotachylyte alteration process must have occurred during high pressure metamorphism our observations are suggestive of a deep crustal earthquake scenario where a high pressurized fluid phase plays a double role by causing both seismic failure through the embrittlement effect and facilitating eclogitization of the metastable anhydrous gabbro metamorphic reaction along hydrofractures and fault planes led to the development of eclogite facies foliation fabrics and illustrate the rheological change from brittle to plastic behavior associated with the gabbro to eclogite transition the formation of weak deep crustal shear zones following brittle failure represents an arrested initiation of the physical breakup and metamorphic reequilibration of the krakeneset gabbro during its residence deep in the former caledonian collision zone

proterozoic deep marine volcanic eruptive product obsidian glass in chanda limestone penganga group india its implications for basin evolution and metallogenesis abstract subaqueous effusive to low explosive eruptive product composed of blocky and fluidal fragments of glass and sparsely crystalline glass of obsidian lava are present in fine grained volcaniclastic debris flow conglomerate and turbidite occurring in a deep marine sequence of thin and even bedded grey siliceous micritic limestone of the chanda limestone the siliceous limestone conformably encloses stratiform manganese deposit obsidian glass fragments consist of coherent and amorphous glassy groundmass containing patches of devitrified fibrous glass oriented microlites and microphenocrysts of quartz and k feldspars euhedral crystals resorbed rounded and embayed crystals spherical vesicles microlites and flow texture are distinctive volcanic features observed in these fragments chemically similar to obsidian lava the blocky fragments represent the products of hydroclastic fragmentation whereas the fludial one may indicate formation under steam explosion gravitational instability of the resulting slurry of glass fragments and the ambient sea water sediments at the site of eruption causes gravity flows that carries the fragments along with epiclasts away from vent to a distal site for final deposition this study records maiden evidence of volcanism in the chanda limestone of the neoproterozoic penganga group and infers rifting and partial melting of the sialic crust and silicic lava flow during deposition of limestone unusually rich in silica the inferred tectono sedimentary setting facies association and mode of occurrence of the manganese deposit suggest a hydrothermal source for the metal

anatomy of seep carbonates ancient examples from the miocene of the northern apennines italy ancient hydrocarbon seep carbonates of miocene age have been reported from marine sedimentary successions of the northern apennines in the form of irregularly shaped micritic masses containing abundant fossil remains of oligotypic assemblages they are recognized by their peculiar biological sedimentological and geochemical features and represent an excellent on land example of carbonate bodies interpreted as the remains of ancient cold seeps in the apenninic chain the abundance and the extent of the outcrops provide a rare opportunity to study the geometry facies distribution and internal structures of fossil methane derived carbonates the present study reports an integrated view of the sedimentology mineral paragenesis and geochemistry of these seep carbonates in two different tectono sedimentary settings foredeep and satellite basins the main result of this study is the recognition of 17 facies in the investigated seepcarbonates the detailed facies and microfacies analysis led to the identification of different structures which occur in welldefined parts of the carbonate masses the recurring and broadly similar stratigraphy and facies association from the two considered geological environments is diagnostic of the different stages of seep carbonate formation and evolution d 2005 elsevier b v all rights reserved

facies architecture emplacement mechanisms and eruption style of the submarine andesite el barronal complex cabo de gata se spain abstract el barronal complex consists of a succession of andesite lavas and andesite volcaniclastic facies interbedded with carbonate and siliciclastic sedimentary rocks carbonate and siliciclastic rocks were deposited in a shallow marine environment during periods of volcanic quiescence lavas consist of an inner coherent core grading outward into hyaloclastite breccia made of dense clasts that in turn grade into hyaloclastite breccia made of vesicular clasts in massive to layered zones volcaniclastic facies contain clasts produced during explosive eruptions and reworked clasts from sources above wave base volcaniclastic facies were deposited from cold granular flows with different grain size populations stratigraphy and facies architecture at el barronal suggest that a succession of several discrete eruptive events occurred with a similar cyclic pattern made of an initial explosive phase followed by effusive emplacement of lavas in turn followed by a period of quiescence of volcanic activity hyaloclastic fragmentation of magma took place in the final stages of lava emplacement allowing only for local disorganization of the jigsaw fit texture

determination of the volcanostratigraphy of oceanic crust formed at superfast spreading ridge electrofacies analyses of odp iodp hole 1256d 1 the objective of this study is to construct a representative volcanostratigraphy of ocean drilling program hole 1256d the first complete penetration of intact upper oceanic crust formed at a superfast spreading rate an accurate knowledge of the volcanostratigraphy is vital to understand processes of crustal construction and submarine magmatism and to estimate chemical exchange with seawater but this is rarely achieved due to very low recovery rates in most basement holes we used two approaches to determine the rock types that form the wall rocks in the basement sections of hole 1256d 1 user guided interpretations of electrofacies acquired by imaging tools combined with other wireline tools and 2 the use of an artificial neutral network to objectively classify the responses of all available logging information great availability of formation microscanner fms images provided superior coverage of the borehole wall compared to previous attempts at core log integration this has resulted in more confident and detailed lithologic classifications such as with the distinction between pillows and different styles of breciation ten lithology types are suggested for a volcanostratigraphy model massive flows ponded lava fractured massive flows fragmented flows thin flows or thick pillows pillows breccias dikes in dike complex isolated dikes and gabbros three major lithology types in the extrusive section are massive flows both massive and fragmented massive flow 22 fragmented flows 32 and breccias 19 pillow lavas make up only 1 9 of the volcanic section and are confined to a 100 m interval below the extrusive section subvertical contacts interpreted to be dike margins are typically observed every 1 to 2 m with brecciated zones along the contacts the dikes dip steeply to the northeast indicating slight rotation away from the ridge axis we used an artificial neural network ann approach to determine a quantitative lithostratigraphy the ann is most strongly influenced by porosity and alteration degrees and the resulting stratigraphy most closely resembles the above classifications when clustered by fms texture as opposed to lithologic interpretation the ann thus provides a porosity based stratigraphy of the basement rather than the traditional lithology based stratigraphy

evolution of the south central part of the archean abitibi belt quebec part i stratigraphy and paleogeographic model the region comprises parts of the southern zone of the abitibi greenstone belt and of the bellecombe gneiss belt and the belleterre angliers greenstone belt the stratigraphic sequence of the abitibi belt consists of 1 a lower ultramafic division 2 a middle tholeiitic division and 3 an upper diverse division these divisions lap onto an older volcanic sequence to the north and west in the bellecombe belt sediments overlie the lower ultramafic division these sediments coarsen toward the abitibi belt and toward the stratigraphic top the volcanic rocks of the belleterre angliers belt overlie the sediments of the bellecombe belt five paleogeographic phases have been recognized during phase i a deep marine ultramafic lava plain covered the south part of the abitibi belt and the bellecombe belt faulting took place at the duparquet destor break during phase ii tholeiitic basalts formed a deep marine lava plain in the west of the abitibi belt whereas flows erupted mainly from central volcanic c

architecture of the volcanic layer from the costa rica rift constraints from core log integration 1 an understanding of the architecture of the ocean crust s volcanic layer is critical since this records the variations in volcanic activity during formation and subsequently controls the movement of hydrothermal fluids through this layer unfortunately core recovery in the majority of ocean drilling program odp deep sea drilling program basement holes is generally low and biased toward more massive lithologies consequently the identification and estimation of lithological diversity within the volcanic layer is only possible through the integration of core and wire line logging results wire line logging provides nearly continuous records of both physical and chemical properties of the borehole wall which can be used to identify the various volcanic sedimentary lithologies which then can be calibrated in regions of enhanced core recovery using this approach the architecture of the volcanics from odp hole 896a has been reconstructed this new model illustrates a hiatus in volcanism marked by a thick breccia horizon which probably marks the transition from axis to off axis volcanism

subglacial intermediate volcanism at kerlingarfjoll iceland magma water interactions beneath thick ice the products of andesite and dacite glaciovolcanism at kerlingarfjoll are unlike others previously described in the literature three sequences of lithofacies are described and interpreted here the andesitic deposits at campsite gully are divided into massive vitriclastic lapilli tuff with intrusions fluidal clast bearing vitriclastic lapilli tuff and stratified pumice rich vitriclastic lapilli tuff at tindur andesitic eruptions produced contorted pillow fragment breccia and the clast supported lithic breccia finally pillow lava with intrusions and crudely bedded vitriclastic lapilli tuff of dacitic composition are described at haraldur abundant vitriclasts the presence of pillow lavas hackly fracturing of lava bodies and lack of oxidation of clasts demonstrate that each of these lithofacies formed in the presence of abundant water this contrasts with all other descriptions of subglacially erupted intermediate magmas which are characterised by jointed and glassy lava flows and domes with a marked scarcity of fragmental material the kerlingarfjoll sequences therefore demonstrate that it is possible for intermediate magmas to generate and interact with significant volumes of water at the base of a glacier preliminary estimates of volatile contents in glassy clasts correspond to quenching pressures equivalent to 500 m water or 550 m ice this is consistent with eruption beneath an ice sheet that was thick enough to overwhelm the underlying topography and where meltwater drainage was controlled by the morphology of the glacier surface it is argued that the drainage of water due to steep topography and or thin and fractured ice as opposed to thermodynamic considerations is the most likely explanation for the absence of evidence for significant magma water interaction in previously described instances of intermediate glaciovolcanism the apparent low viscosity of the kerlingarfjoll magmas may relate to relatively high eruption temperatures and or the inhibition of degassing of the magma due to high ambient pressures and the consequent limitation of groundmass crystallisation

textural and mineralogical changes associated with the incipient hydrothermal alteration of glassy dacite at the submarine pacmanus hydrothermal system eastern manus basin variably altered dacite from the pacmanus vent field in the eastern manus back arc basin papua new guinea was studied to determine the textural and mineralogical characteristics of hydrothermal alteration taking place in the immediate subsurface of this modern seafloor hydrothermal system detailed textural investigations show that fluid flow through the glassy dacite has been strongly controlled by the primary volcanic textures quench fractures and networks of interconnected perlitic cracks linking vesicles provided pathways for hydrothermal fluids flowing up to the seafloor hydrothermal alteration along these pathways resulted in the formation of pseudoclastic textures textural evidence suggests that alteration of the glassy dacite has not been sustained the samples have been affected by incipient hydrothermal alteration that is typically not preserved in ancient volcanic rock hosted massive sulfide deposits interaction of the glassy dacite with hydrothermal fluids primarily resulted in the conversion of volcanic glass to dioctahedral smectite only minor amounts of trioctahedral smectite were formed destruction of the volcanic glass and the formation of smectite caused pronounced changes in the chemistry of the dacite samples in particular a decrease in the sio2 whole rock content and the na2o k2o ratio the two alkali elements behaved differently during hydrothermal alteration due to preferential incorporation of k into the interlayer position of the newly formed dioctahedral smectite smectite formation occurred under rock dominated conditions although the addition of mg was required to form trioctahedral smectite from the silicic volcanic glass primary plagioclase was resistant to hydrothermal alteration highlighting the fact that the destruction of volcanic glass and feldspar are not necessarily contemporaneous in massive sulfide forming hydrothermal systems incipient alteration of the glassy dacite close to the seafloor occurred at temperatures below 150 c in an environment that allowed the development of steep temperature gradients comparison of the new data to the findings of deep drilling during odp leg 193 suggests that the smectite rich alteration in the immediate subsurface of the pacmanus hydrothermal vent field represents the low temperature equivalent of illite and chlorite rich alteration associations forming in the upflow zones of the hydrothermal fluids in the deeper portion of the volcanic sequence

an upper pliocene coarse pumice breccia generated by a shallow submarine explosive eruption milos greece the filakopi pumice breccia fpb is a very well exposed pliocene volcaniclastic unit on milos greece and has a minimum bulk volume of 1 km3 it consists of three main units a basal lithic breccia 4 8 m mainly composed of angular to subangular andesitic and dacitic clasts up to 2 6 m in diameter b very thickly bedded poorly sorted pumice breccia 16 17 m and c very thick reversely graded grain supported coarse pumice breccia 6 5 20 m at the top the depositional setting is well constrained as shallow marine up to a few hundred metres by overlying fossiliferous and bioturbated mudstone this large volume of fine pumice clasts is interpreted to be the product of an explosive eruption from a submarine vent because 1 pumice clasts are the dominant component 2 the coarse pumice clasts 64 mm have complete quenched margins 3 very large 1 m pumice clasts are common 4 overall the formation shows good hydraulic sorting and 5 a significant volume of ash was deposited together with the coarsest pyroclasts

morphological features of miocene submarine coherent lavas from the green tuff basins examples from basaltic and andesitic rocks from the shimokita peninsula northern japan basaltic and andesitic volcanic rocks of miocene age exposed in the shimokita peninsula northern japan illustrate morphological features of typical submarine coherent lavas of the green tuff basins in japan they are pillow lobes with surface structures such as ropey wrinkles corrugations spreading cracks and tensional cracks and lava lobes composed of a lithic core and glassy border zone or rim with an in situ breccia zone grading outward into surrounding hyaloclastite in addition they include massive lavas with columnar joints and jointed dykes the submarine coherent lavas and dykes are commonly associated with hyaloclastic breccias such as pillow fragment breccia and angular fragment breccia the descriptions of the miocene volcanic rocks in the shimokita peninsula provide good criteria for recognition of submarine coherent lavas of basalt and andesite

age constraints and characteristics of subaqueous volcanic construction the archean hunter mine group abitibi greenstone belt the archean hunter mine group hmg is a 6 7 km thick south facing volcanic sequence at the southern limit of the northern volcanic zone abitibi greenstone belt the hmg is composed of 1 felsic lava flows and endogenous and exogenous domes with autoclastic breccia deposits 2 pyroclastic fire fountain products and high to low concentration volcaniclastic sediment gravity flows of autoclastic and pyroclastic origin interstratified with iron formation 3 mafic pillowed and brecciated flows 4 a prominent felsic dyke swarm and 5 abundant mafic intrusions the stratigraphy is complex as inferred by detailed volcano sedimentary facies mapping a 5 7 km wide n trending felsic dyke swarm coupled with abundant synvolcanic and synsedimentary faults chaotic breccias and mineralization suggest a central volcanic depression which is consistent with a caldera structure voluminous effusive activity and explosive fire fountaining eruptions contributed to caldera development rifting of this arc edifice is supported by the presence of felsic dykes and mafic tholeiitic sills the lithofacies and overlying komatiites flows are consistent with a deep water marine setting u pb age determinations help constrain the hmg caldera formation to 6 million years the sampled quartz feldspar phyric dykes yielded u pb zircon ages of 2728 3 4 3 4 and 2728 9 0 8 ma and together with a previously published dyke age of 2729 6 1 4 ma from the same dyke swarm a case is made that the swarm evolved over 1 million years 2728 6 2729 6 ma a lobate flow and flow breccia revealed similar ages of 2724 6 4 6 1 7 and 2727 6 4 2 2 0 ma whereas the up to 1 km thick gabbro diorite roquemaure sill precedes both felsic dykes and flows as indicated by the 2731 8 2 2 2 0 ma age the 2706 4 5 7 4 3 ma feldspar quartz phyric dykes occurred late in the history of the hmg and were not associated with subaqueous volcanic construction the 207pb 206pb ages of analyzed zircon fractions have an inherited component within error of the oldest crystallization ages obtained for the hmg complex collectively these age determinations and inheritance as well as stratigraphy support a tripartite division into a 2734 2730 ma lower formational stage a 2732 ma middle formational stage and a 2730 2728 ma upper formational stage the study shows that age constraints without detailed facies mapping may lead to erroneous conclusions on volcanic construction and that felsic volcanic dykes and flows may inherit an earlier component of their own volcanic edifice

products of an effusive subglacial rhyolite eruption blahnukur torfajokull iceland we present field observations from blahnukur a small volume 400 m thick lithofacies associations attest to complex patterns of volcano ice interaction erosive channels at the base of the subglacial sequence are filled by both eruption derived material and subglacial till which show evidence for deposition by flowing meltwater this suggests that meltwater was able to drain away from the vent area during the eruption much of the subglacial volcanic deposits consist of conical to irregularly shaped lava lobes typically 5 10 m long set in poorly sorted breccias with an ash grade matrix a gradational lavabreccia contact at the base of lava lobes represents a fossilised fragmentation interface driven by magma water interaction as the lava flowed over poorly consolidated waterlogged debris sets of columnar joints on the upper surfaces of lobes are interpreted as ice contact features the morphology of the lobes suggests that they chilled within conically shaped subglacial cavities 2 5 m high avalanche deposits mantling the flanks of blahnukur appear to have been generated by the collapse of lava lobes and surrounding breccia a variety of deposit characteristics suggests that this occurred both prior to and after quenching of the lava lobes collapse events may have occurred when the supporting ice walls were melted back from around the cooling lava lobes and breccias much larger lava flows were emplaced in the latter stages of the eruption columnar joint patterns suggest that these flowed and chilled within subglacial cavities 20 m high and 100 200 m in length there is little evidence for magma water interaction at lava flow margins which suggests that these larger cavities were drained of meltwater as rhyolite magma rose to the base of the glacier the nature of the subglacial cavity system played an important role in governing the style of eruption and the volcanic facies generated we present evidence that the cavity system evolved during the eruption reflecting variations in both melting rate and edifice growth that are best explained by a fluctuating eruption rate

surface wave dispersion and upper mantle structure beneath southern germany from joint inversion of network recorded teleseismic events we have determined the dispersion of fundamental mode rayleigh waves in southern germany in the frequency range 4 50 mhz by simultaneously inverting data from 66 teleseismic events recorded at a network of up to 9 broadband stations three different inversion experiments were performed determination of 1 isotropic phase velocity of 2 azimuthally anisotropic phase velocity assuming a plane wave traveling across the network and 3 isotropic phase velocity but now allowing for non plane properties of the wavefield in experiments 1 and 2 for each event amplitude phase and deviation from the great circle azimuth were estimated as well we have obtained remarkably stable results for phase velocity over the whole frequency range between 7 and 25 mhz azimuthal anisotropy is definitely below 0 5 percent below 7 and above 25 mhz we found up to 3 percent anisotropy but with negligible variance reduction compared to the isotropic inversion experiment 1 admitting non plane wavefields in the inversion still yields nearly identical phase velocities on inversion of the phase velocity curve in terms of shear wave velocity we obtained a rather shallow asthenosphere with minimum s of 4 28 km s at about 130 km depth covered by a thin lid with s of 4 63 km s

extremely fast supercooling of water in the anti jovian hemisphere of europa a speculative model for the fracturing pattern and ascent of brines along cracks the anti jovian hemisphere of europa the hemisphere opposite the one facing jupiter displays a complex array of fractures including roughly concentric and arcuate ones the geometry of this intriguing pattern on the icy surface of europa resembles the textural features displayed by perlitic volcanic glass we argue that fast cooling of a rhyolitic magma may serve as an analogue for fast supercooling of water leading to formation of amorphous ice glassy water we envisage two possible scenarios for ice melting and subsequent extremely fast supercooling 1 massive subglacial volcanic activity or 2 a large impact on the anti jovian hemisphere we suggest that extremely fast formation of amorphous ice on europa would result in a fracture pattern geometrically equivalent to that observed in perlitic glass fast supercooling of water will initially lead to brine retention in the ice phase however after some time these brines would be laterally rejected toward fractures furthermore as solidification progresses downward a shrinking ocean would increase brine concentration these brines would eventually escape to the surface via the fracture network finally high pressure crystallization of salts within fractures may provide an efficient mechanism for differential plate separation horizontal movement and formation of new fractures