deep marine arc apron deposits and syndepositional magmatism in the alisitos group at punta cono baja california mexico rocks exposed at punta cono include very fine grained to coarse grained tuffs lapilli tuffs and tuff breccias deposited in a deep marine environment syndepositional basaltic intrusive activity was common in one locality a hyaloclastite peperite complex formed slumped sections with fluidal basalt clasts derived from intrusions that entered the sediment pile from below are present elsewhere abundant soft sediment folds in fine grained laminated subaqueous fall out tuff suggest steep gradients these are cut by shallow channels filled with coarse grained tuff lapilli tuff and rare tuff breccia the combination of marine fossils extreme textural immaturity abundant slump features and syndepositional magmatism indicates deposition upon the submarine flanks of an active volcano recognition of magma wet sediment interaction is hampered in volcaniclastic rocks because of the similarity between host and intrusive fragments products of magma water sediment interactions at punta maria include 1 jigsaw puzzle hyaloclastite formed by non explosive hydroclastic fragmentation of magma upon contact with water and water bearing sediment 2 peperites produced by mixing of magma with sediment and 3 an unusual tuff breccia unit the result of non explosive mixing of wisps of lava with sediment during remobilization of an unconsolidated section low explosivity magma water sediment interactions are favoured by relatively high hydrostatic pressures in sub wave base settings

nonexplosive and explosive magma wet sediment interaction during emplacement of eocene intrusions into cretaceous to eocene strata trans pecos igneous province west texas abstract eocene intrusion of alkaline basaltic to trachyandesitic magmas into unlithified upper cretaceous maastrichtian to eocene fluvial strata in part of the trans pecos igneous province in west texas produced an array of features recording both nonexplosive and explosive magma wet sediment interaction intrusive complexes with 40 ar 39 ar dates of 47 46 ma consist of coherent basalt peperite and disrupted sediment two of the complexes cutting cretaceous strata contain masses of conglomerate derived from eocene fluvial deposits that at the onset of intrusive activity would have been 400 500 m above the present level of exposure these intrusive complexes are inferred to be remnants of diatremes that fed maar volcanoes during an early stage of magmatism in this part of the trans pecos province disrupted cretaceous strata along diatreme margins record collapse of conduit walls during and after subsurface phreatomagmatic explosions eocene conglomerate slumped downward from higher levels during vent excavation coherent to pillowed basaltic intrusions emplaced at the close of explosive activity formed peperite within the conglomerate within disrupted cretaceous strata in the conduit walls and within inferred remnants of the phreatomagmatic slurry that filled the vents during explosive volcanism a younger series of intrusions with 40 ar 39 ar dates of 42 ma underwent nonexplosive interaction with upper cretaceous to paleocene mud and sand dikes and sills show fluidal billowed quenched margins against the host strata recording development of surface instabilities between magma and groundwater rich sediment accentuation of billowed margins resulted in propagation of intrusive pillows into the adjacent sediment more intense disruption and mingling of quenched magma with sediment locally produced fluidal and blocky peperite but sufficient volumes of pore fluid were not heated rapidly enough to generate phreatomagmatic explosions this work suggests that trans pecos texas may be an important locale for the study of subvolcanic phreatomagmatic processes and associated phenomena eocene intrusions in the study area underwent complex interactions with wet sediment at shallow levels beneath the surface in strata as old as maastrichtian which must have remained unlithified and rich in pore water for 20 25 ma

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

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

volcaniclastic dykes tell on fracturing explosive eruption and lateral collapse at stromboli volcano italy abstract in the upper part of the stromboli volcano in the le croci and bastimento areas two dyke like bodies of volcanic breccia up to two metre thick crosscut and intrude the products of vancori and neostromboli volcanoes we describe the lithofacies association of these unusual volcaniclastic dykes interpret the setting of dyke forming fractures and the emplacement mechanism of internal deposits and discuss their probable relationships with the explosive eruption and major lateral collapse events that occurred at the end of the neostromboli period the dyke volcaniclastic deposits contain juvenile magmatic fragments pyroclasts suggesting a primary volcanic origin their petrographic characteristics are coincident with the neostromboli products the architecture of the infilling deposits comprises symmetrically nested volcaniclastic units separated by sub vertical boundaries which are parallel to the dyke margins the volcanic units are composed of distinctive lithofacies the more external facies is composed of fine and coarse ash showing sub vertical laminations parallel to the contact wall the central facies comprises stratified lithic rich breccia and lapilli tuff whose stratification is sub horizontal and convolute discordant to the dyke margins only at le croci dyke the final unit shows a massive tuff breccia facies the volcaniclastic dykes experienced a polyphasic geological evolution comprising three stages the first phase consisted in fracturing explosive intrusion related to magma rising and upward injection of magmatic fluids and pyroclasts the second phase recorded the dilation of fractures and their role as pyroclastic conduits in an explosive eruption possibly coeval with the lateral collapse of the neostromboli lava cone finally in the third phase the immediately post eruption mass flow remobilization of pyroclastic deposits took place on the volcano slopes

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

miocene pillowed sills in the shimane peninsula sw japan abstract two miocene basaltic andesite pillowed sills in the shimane peninsula sw japan were intruded into wet marine sediments plastically deforming them the pillows are elongated constricted interconnected and relatively closely packed individual pillows have a poorly to moderately vesiculated somewhat crystalline rind thinner than a few centimeters and a moderately to well vesiculated more crystalline core contraction cracks and spreading cracks are poorly developed the pillows in the sills morphologically resemble pillow lava flows and during sill intrusion the magma bifurcated into pillow lobes in a manner similar to pillow lavas formation of pillows in sill probably occurs when the magma is intruded into wet sediments and protrudes fingers by the instability of the magma sediment interface with little turbulence of magma flow

volcano sedimentary characteristics in the abu treifiya basin cairo suez district egypt example of dynamics and fluidization over sedimentary and volcaniclastic beds by emplacement of syn volcanic basaltic rocks abstract this paper describes the neogene lava sediment mingling from the abu treifiya basin cairo suez district egypt the lava sediment interactions as peperites have been identified for the first time at the study area and can be used as paleoenvironmental indicators the identification of peperite reflects contemporaneous time relationship between volcanism and sedimentation and this finding is of primary importance to address the evolutional reconstruction of the abu treifiya basin characterization of the facies architecture and textural framework of peperites was carried out through detailed description and interpretation of their outcrops the peperites and sedimentary rocks are up to 350 m thick and form a distinct stratigraphic framework of diverse lithology that is widespread over several kilometers at the study area lateral and vertical facies of the peperites vary from sediment intercalated with the extrusive intrusive basaltic rocks forming peperitic breccias to lava sediment contacts at a large to small scales respectively peperites encompass five main facies types ascribed to i carbonate sediments hosted fluidal and blocky peperites ii lava flow hosted blocky peperites iii volcaniclastics hosted fluidal and blocky peperites iv sandstone siltstone rocks hosted blocky peperites and iv debris flows hosted blocky peperites soft sediment deformation structures vesiculated sediments sediments filled vesicles and fractures in lava flows indicate that lava flows mingled with unconsolidated wet sediments all the peperites in this study could be described as blocky or fluidal but mixtures of different clast shapes occur regardless of the host sediment the presence of fluidal and blocky juvenile clasts elucidates different eruptive styles reflecting a ductile and brittle fragmentation the gradual variation from fluidal to blocky peperite texture producing the vertical grading is affected by influencing factors e g the viscosity magma temperature confining pressure sediment fluidization and vapor film at the magma sediment interactions peperites in the study area record deposition within a shallow marine and fluvio lacustrine environment accumulated in a rift related basin developed during pre to syn rift phase respectively the facies transitions peperites in this area resulted from the explosive and sediment depositional processes which were mingled separately by volcanism under contrast geological conditions the development of such contrast in the depositional sequences reflects variation in the accommodation to sediment supply in the same accumulation space inside the depocenters during the rifting of the abu treifiya basin hydrothermal mineralizations comprising quartz and carbonate are restricted to peperites and lava flows

middle miocene volcaniclastic dikes at kukedo shimane peninsula sw japan fluidization of volcaniclastic beds by emplacement of syn volcanic andesitic dikes abstract at kukedo northern shimane peninsula sw japan volcaniclastic peperite dikes extend parallel to andesitic dikes in volcaniclastic turbidites of the middle miocene takashibiyama formation they mainly comprise a poorly sorted mixture of volcaniclasts derived from the host volcaniclastic turbidites andesitic dikes in direct contact with the volcaniclastic turbidites have fluidal contacts locally protruding into the volcaniclastic turbidites volcaniclastic beds are disorganized in a zone up to 1 m wide and are partly welded within 1 30 cm from the contacts one major volcaniclastic dike 0 5 1 5 m wide extends upwards from the lower segment to the upper segment of a laterally offset andesitic dike 1 5 3 m wide coarse lithic clasts are locally concentrated along the wall of the dike and juvenile clasts derived from the andesitic dike are sparsely set in the poorly sorted volcaniclastic mixture juvenile clasts are poorly vesicular and microcrystalline and mainly polyhedral in shape sparse fluidal juvenile clasts are fractured in situ into small clasts by quench cracks fluidization of host volcaniclastic turbidites occurred to form volcaniclastic dikes during emplacement of andesitic dikes driven by the excess pore fluid pressure imparted from the stress concentration at the advancing magma head and heating of pore water in the host volcaniclastic beds the volcaniclastic dike extending directly from the andesitic dike was produced by small scale dynamic mixing of magma and watery volcaniclastic beds upon offsetting of the andesitic dike welding was favored by the increased water vapor pressures and high temperatures in direct contact with andesitic dikes

quantitative experiments on phreatomagmatic explosions abstract an experimental set up for controlled generation of thermal explosions fuel coolant interactions has been built by an interdisciplinary research group of volcanologists physicists and engineering scientists the tee haus thermal explosion experiment during the last 3 years more than 500 experimental runs were performed aim of the project was not to build a mini volcano but to produce igniteable mixtures of water and hot melt on a small scale in order to investigate basic physical aspects such small scale mixtures however most probably also occur during phreatomagmatic events in nature mixtures of water and magma on a large scale may be modelled by combination of small elements earlier experimental studies of thermal explosions were carried out with the use of metal melts nearly exclusively therefore a carbonate melt approx 0 3 kg of 1 1 mass ratio na2co3 k2co3 was used for initial experimental series because of easy handling and more magma similarity by injection of water into this melt explosive mixtures were produced and ignited self triggering explosive interactions occurred in a wide melt temperature range 720 to 1040 c at melt temperatures exceeding 1000 c co2 increasingly degassed presence of non condensible gas bubbles in the melt strongly reduced the explosivity the intensity of explosions only slightly increased with higher melt temperatures but strongly increased with higher water injection velocities because of more intensive mixing a minimum injection velocity was found to be approx 0 7 m s 1 experiments with silicate melts derived from diverse remelted volcanic rocks were carried out with a slightly modified set up explosions were ignited by an additional trigger a shock wave of approx 8 j in volcanic systems shock waves of this magnitude are abundant volcanic tremor etc strong explosions with silicate melts were produced at melt temperatures between 1350 and 1750 c the produced explosions exerted repulsion forces of up to 24 000 n with a typical pulse duration of 1 ms carbonate melt resp 1 5 ms silicate melts the ejection velocity was found to be in a range between 200 and 400 m s 1 explosion energy values up to 500 j were calculated the maximum explosion pressure was calculated to be in the range between 10 and 100 mpa only part of the melt so called interactive melt reacts explosively with injected water most of the melt is passively ejected by and after the thermal explosion different fragmentation processes result in specific grain size and grain shape populations that can be distinguished from each other particles resulting from the fine fragmentation process that precedes and causes the thermal explosion are characterized by angular to subrounded shapes and grain sizes ranging from 20 m to 180 m the amount of interactive melt is proportional to the intensity of the explosion the maximum amount of water vapourized at the explosive interaction so called interactive water was estimated thus the water melt mass ratio for explosive interactions could be calculated the values range between 1 25 and 1 35 carbonate melt resp between 1 6 and 1 25 silicate melts

a miocene island arc volcanic seamount the takashibiyama formation shimane peninsula sw japan abstract the miocene volcanic complex of the takashibiyama formation consists largely of subalkali subaqueous basalt to andesite lavas and andesite to dacite subaqueous volcaniclastic flow deposits most of subaqueous lavas are moderately to intensely brecciated with rugged rough surfaces and ramp structures similar to subaerial block lava volcaniclastic flow deposits commonly include basalt to andesite lava fragments and or pyroclastic materials and are similar in internal features to debris flow and turbidite deposits subaqueous block lavas and minor pillow lavas form volcanic piles above the vents being flanked or covered with volcaniclastic flow deposits each volcanic pile is several kilometers wide and several hundred meters thick and overlaps one after another as the major eruptive center migrates from time to time thus the volcanic complex comprises three or more superimposed volcanic piles which are intruded by basalt to andesite dikes and sills and are underlain by mafic to intermediate large hypabyssal to plutonic bodies hydrothermal alteration occurs in places but especially concentrates in the lower part of the volcanic complex after the cessation of opening of the japan sea the volcanic complex started to erupt in a middle bathyal environment on the japan sea side and became emergent as it grew to a thickness over 1500 m during 4 m y under a n s trending horizontal compressional stress it is a volcanic seamount probably in a typical island arc setting

the use of pollen floras as a tool to estimate palaeoaltitude of mountains the eastern pyrenees in the late neogene a case study northern hemisphere vegetation is generally zoned as a consequence of latitudinal and altitudinal gradients temperature reconstruction from three successive pollen floral assemblages of tortonian messinian and zanclean age from the eastern pyrenees has been used to estimate the altitudinal evolution of the uplifted cerdanya basin and its surrounding massifs a new method has been developed for the uplifted basins which completes that already applied to pollen floras from coastal marine deposits close to mountains in contrast to previous hypotheses it seems that the eastern pyrenees occurred at a lower altitude in the late miocene before continuous uplift began 10 ma ago the rate of this uplift ranged between 0 06 and 0 12 mm yr

peperites and associated pillow lavas subjacent to the oman ophiolite abstract peperites are breccias consisting of a mix of cooled magma and sediment they result from the intrusion of molten rock into water saturated sediments we report an occurrence of peperite in the oman united arab emirates uae border region of khattm al shiklah and characterize samples that have been collected from 6 locations east of al ain uae at jabal um bak jabal hamra and jabal dai in oman geochemical analysis indicates that the magmas represented in these samples are related in addition field relations of the pillow lavas surrounded by limestone with deformed bedding and peperite boundaries between the pillows and the limestone are consistent with the pillow lavas forming directly within carbonate sediments it is likely that the ambient pressure was great enough and cooling of the magma rapid enough to prevent large explosions the fact that the magma also formed pillows is evidence of this the rapid quenching of the magma by water saturated fine unconsolidated sediments likely produced conditions similar to those attending pillow lava formation directly into water

variation in peperite textures associated with differing host sediment properties peperites formed by mixing of magma and wet sediment are well exposed along punta china baja california mexico where two sills intrude a section of lava flows limestones and volcaniclastic rocks irregular lobes and dikes extend from the sills several meters into host sediments including highly comminuted flow top breccias lithic lapilli tuff breccias and shelly micrites whereas intrusive contacts with lava flows are sharp and planar where one sill intruded both coarse grained volcaniclastic rock and fine grained limestone textural differences between the hosts produced strikingly different styles of peperite blocky masses of the basaltic intrusions up to 1 m in size were dispersed for distances up to 3 m into host lithic lapilli tuff breccias the blocks consequently underwent in situ fragmentation as they were rapidly quenched the high degree of dispersion resulted from steam explosions as the magma enveloped pockets of water in the coarse grained permeable host elutriation of fine grained material from vertical pipes in tuff breccia above the lower sill provides evidence for meter scale fluidization of the host the contact zone between the basaltic magma and the shelly micrite host resembles a mixture of two viscous immiscible fluids fluidal peperite intrusion occurred behind a stable vapor film which entrained lime mud particles and carried them off grain by grain as magma advanced into the host thin section scale elutriation pipes formed microglobular peperite represents a frozen example of a fuel coolant interaction fci between basaltic magma and fluidized micrite host the intimate intermixing of magma and host at the submillimeter level is attributed to fluid instabilities developed along the magma vapor host interface such intimate intermixing of magma and water bearing fragmental debris is commonly a precursory step toward explosive hydrovolcanism

secondary welding of submarine pumice lithic breccia at mount chalmers queensland australia very thick units of massive pumice and lithic clast rich breccia in the early permian berserker beds at mount chalmers queensland are deposits from cold water supported volcaniclastic mass flows emplaced in a below wave base submarine setting adjacent to syn volcanic andesitic and rhyolitic sills and dykes the pumice lithic breccia shows a well developed eutaxitic texture the eutaxitic foliation is parallel to intrusive contacts and extends as far as a few metres away from the contact at these sites pumice clasts are strongly flattened and tube vesicles within the pumice clasts are compacted and aligned parallel to the direction of flattening some lenticular pumice clasts contain small 2 mm round quartz filled amygdales and spherulites further away from the sills and dykes the pumice clasts have randomly oriented delicate tube vesicle structure and are blocky or lensoid in shape round amygdales were generated by re vesiculation of the glass and the spherulites indicate devitrification of the glass at relatively high temperatures the eutaxitic texture is therefore attributed to re heating and welding compaction of glassy pumice lithic breccia close to contacts with intrusions in cases involving sills secondary welding along the contacts formed extensive conformable eutaxitic zones in the pumice lithic breccia that could be mistaken for primary welding compaction in a hot primary pyroclastic deposit

the 1989 submarine eruption off eastern izu peninsula japan ejecta and eruption mechanisms the submarine eruption of a new small knoll which was named teishi knoll off eastern izu peninsula behind the izu mariana arc occurred in the evening of 13 july 1989 this is the first historic eruption of the higashi izu monogenetic volcano group the eruption of 13 july followed an earthquake swarm near ito city starting on 30 june there were subsequent volcanic tremors on 11 and 12 july and the formation of the teishi knoll on the 100 m deep insular shelf 4 km northeast of ito city there were five submarine explosions which were characterized by intermittent domelike bulges of water and black tephra jets which occurred within 10 min on 13 july ejecta of the eruption was small in volume and composed of highly crystalline basalt scoria highly vesiculated pumice and lithic material petrographical features suggest that the pumice was produced by vesiculation of reheated wet felsic tuff of an older formation the teishi knoll before the eruption was a circular dome 450 m across and 25 m high with steep sides and a flat summit considerations of submarine topographic change indicate the knoll was raised by sill like intrusion of 106 m3 of magma beneath a 30 m thick sediment blanket this shallow intrusion is assumed to have started on 11 july when volcanic tremors were observed for the first time but there was no indications of violent interaction between wet host sediments and intruding magma the submarine eruption of 13 july appears to have been friggered by a major lowering of the magma column the basalt scoria having crystal contents of more than 60 is assumed to be derived from the cooled plastic margin of the shallow intrusive body however glassy scoria which would indicate the interaction between hot fluidal magma and external water was not observed a scenario for the 1989 submarine eruption is as follows when rapid subsidence of the hot interior of the intrusive magma occurred reduced pressure caused the implosion of cooled plastic magma adjacent pressurized hot host material and wet sediment the mixing of these materials triggered the vigorous vapor explosions

the fracture behaviour of volcanic glass and relevance to quench fragmentation during formation of hyaloclastite and phreatomagmatism quench fragmentation is a non explosive process that occurs when molten magma is super cooled to glass upon contact with ambient water this occurs when coherent lavas are erupted subaqueously when they flow into water when magma intrudes into water saturated sediments and when magma and water interact explosively during phreatomagmatism quench fragmentation also occurs alongside explosive phreatomagmatic activity although products of quench fragmentation hyaloclastite sensu stricto have been discussed qualitatively in the volcanological literature compared to explosive fragmentation processes very little is known about the exact dynamics of quench fragmentation of magma and how this relates to the rheology and physical properties of volcanic glass based on literature from materials engineering we present a detailed review of the processes by which glass forms the properties of glass and the fracture mechanics that cause it to fragment non explosively we also consider how this can be applied to understanding the dynamics behind the volcanological processes of in situ glass fragmentation during quenching in wet environments and phreatomagmatism important parameters for the occurrence of quench fragmentation are the temperature difference between the magma and the ambient water and how much the ambient water is superheated above its leidenfrost temperature the geometry of the lava or magma intrusion the thermal conductivity and the thermal expansion are also of great importance the resistance of the magma against fragmentation can be increased with the presence of crystals provided the thermal expansion of the crystals does not greatly exceed that of the glass vesicles have the opposite effect unless the magma is highly vesicular this overview then provides a solid basis for further quantitative study of quench fragmentation and hyaloclastite formation

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

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

a hot miocene subaqueous scoria flow deposit in the shimane peninsula sw japan abstract a subaqueous scoria flow deposit occurs in the miocene takashibiyama formation in sw japan faunal assemblages in associated sediments suggest an outer shelf to upper bathyal environment with water depth likely between 200 and 1500 m the deposit 5 7 m thick is similar to subaerial scoria flow deposits containing mainly non to moderately vesiculated hyalopilitic basaltic andesite lapilli and coarse ash the essential basaltic andesite clasts are variably vesiculated even within single clasts and are commonly cracked with curviplanar surfaces whereas the inner parts are cracked in a pattern similar to perlitic cracks the clasts are blocky with curviplanar surfaces if non to poorly vesiculated and are fibrous with irregular shapes and flattened by compaction if more vesiculated at one proximal location fines depleted rootless pipes 5 90 cm wide and 1 3 m long occur and spherical to amoebic vesicles 0 01 0 3 mm in diameter and filled with stilbite quartz or greenish brown clay are common in the fine ash matrix and in siltstone clasts contained in the deposit the vesicles represent open spaces once supported by gas and the rootless pipes are interpreted as gas escape pipes magnetization vectors of essential clasts are dispersed not at random but around a single direction suggesting that the clasts gained thermoremanent magnetism mainly during cooling in the flow or during post emplacement cooling and then rotated to some extent by differential movement of the flow or by gas escape in the deposit the vesicularity shape and texture of essential clasts suggest a phreatomagmatic eruption involving magmatic vesiculation and dynamic interaction of magma and ambient water the perlitic cracks in the inside of the essential clasts and the paleomagnetic vectors of the essential clasts indicate that the flow was initially hot and that the deposit cooled slowly internal depositional features change rapidly over only 500 m rootless pipes and vesicles in the fine ash matrix and siltstone clasts are therefore absent at distal locations indicating that an initially cohesionless debris flow quickly became sufficiently turbulent to mix with ambient seawater

hyaloclastites peperites and soft sediment deformation textures of a shallow subaqueous miocene rhyolitic dome cryptodome complex palhaza hungary abstract the ne tokaj mountains at palhaza in ne hungary are made up of a complex association of miocene rhyolitic shallow intrusions cryptodomes and endogenous lava domes emplaced into and onto soft wet pelitic sediment in a shallow submarine environment the intrusive extrusive complex shows a range of interaction textures with the host muddy sediment ranging from blocky peperites formed on a 0 1 m scale through to irregular contacts closely resembling globular mega peperites on a 10 m scale the over 200 m thick igneous succession is interpreted to result from the pulsatory growth of shallow cryptodomes through muddy saturated host sediment the intrusions eventually breached the sedimentary cover to build up thick in situ hyaloclastite piles in the shallow subaqueous environment the coherent rhyolitic cryptodome facies is surrounded by intrusive hyaloclastite in the contact zone to the pelitic host sediment in the upper level of the complex rhyolitic dome rock is capped and surrounded by hyaloclastite formed due to quench fragmentation upon contact of the lava surface with sea water

a miocene basanite peperitic dyke at stanley northwestern tasmania australia abstract a miocene basanite dyke at stanley northwestern tasmania australia displays well preserved peperite texture the dyke is 2 m wide and has intruded basaltic breccia host sediment one contact of the dyke is fluidally shaped and amoeboid apophyses 10 25 cm long extend into the host sediment whereas the other contact is characterized by blocky peperite texture comprising tabular to wedge shaped clasts up to 30 cm across separated by host sediment the clasts have internal spherical fractures and some show splinter texture vesicles are common in the clasts and those intersected by clast margins have been filled with sediment the interior of the dyke comprises close packed blocky peperite consisting of tabular wedge shaped and polyhedral clasts tens of centimetres across separated by host sediment these clasts show well developed jigsaw fit texture the textures and structures in the basanite dyke are inferred to have formed in two stages an earlier hotter apophysis forming stage and a later cooler angular clast forming stage both of which occurred during the intrusion of magma into wet poorly consolidated sediment in a shallow marine environment during the apophysis forming stage the magma had relatively low viscosity and progressively displaced wet sediment the wet sediment around the dyke was partly fluidized by vaporization of pore water the angular clast forming stage reflects a change in the rheological behaviour of the magma from ductile to brittle most likely in response to decreasing temperature the chilled parts of the dyke were subject to stress arising from cooling contraction and also from continued pulsatory movement of hotter still ductile magma in the interior of the dyke resulting in brittle fragmentation brittle fragmentation was accompanied by movement of host sediment into the newly created open spaces forming blocky peperite spherical fractures splinter texture and sediment filled vesicles formed during the angular clast forming stage because the host sediment is texturally identical either side of the dyke increasing magma viscosity as temperature decreased combined with pulsatory intrusion were evidently important in the production of the blocky peperite

peperite a review of magma sediment mingling the study of peperite is important for understanding magma water interaction and explosive hydrovolcanic hazards this paper reviews the processes and products of peperite genesis peperite is common in arc related and other volcano sedimentary sequences where it can be voluminous and dispersed widely from the parent intrusions it also occurs in phreatomagmatic vent filling deposits and along contacts between sediment and intrusions lavas and hot volcaniclastic deposits in many environments peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal but other shapes occur and mixtures of different clast shapes are also found magma is dominantly fragmented by quenching hydromagmatic explosions magma sediment density contrasts and mechanical stress as a consequence of inflation or movement of magma or lava magma fragmentation by fluid fluid shearing and surface tension effects is probably also important in fluidal peperite fluidisation of host sediment hydromagmatic explosions forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed factors which could influence fragmentation and mingling processes include magma host sediment and peperite rheologies magma injection velocity volatile content of magma total volumes of magma and sediment involved total volume of pore water heated presence or absence of shock waves confining pressure and the nature of local and regional stress fields sediment rheology may be affected by dewatering compaction cementation vesiculation fracturing fragmentation fluidisation liquefaction shear liquification and melting during magma intrusion and peperite formation the presence of peperite intraclasts within peperite and single juvenile clasts with both sub planar and fluidal margins imply that peperite formation can be a multi stage process that varies both spatially and temporally mingling of juvenile clast populations formed under different thermal and mechanical conditions complicates the interpretation of magma fragmentation and mingling mechanisms

late paleozoic peperites in west junggar china and how they constrain regional tectonic and palaeoenvironmental setting abstract late paleozoic peperites have been identified for the first time at the bottom of tailegula formation in west junggar china this finding is significant for the reconstruction of late paleozoic evolution in the junggar region the peperites form successions up to 500 m thick interbedded with basaltic lava and sedimentary rocks four types of peperites are described and interpreted as resulting from basaltic lava bulldozed into wet unconsolidated sediments at their basal contacts zircon la icp ms u pb dating of a tuff lens enclosed by lava showed that the peperites formed in the late devonian ca 364 ma the peperite bearing units probably formed at a water depth of less than 3 km and are generally undeformed occurring in continuous stratigraphic sections distributed regionally over a distance of 100 km on either side of the darbut and baijiantan ophiolitic belts in contrast to the highly deformed slices of ophiolite they demonstrate that the darbut and baijiantan ophiolitic belts should not be interpreted as significant plate boundaries and represent the underlying ocean crust uplifted along tectonic lineaments within a continuous shallow remnant ocean basin the peperites formed during the spreading phase of the remnant ocean basin and represent the final stages of creation of oceanic crust

sedimentary signatures of the entrance of coarse grained volcaniclastic flows into the sea the example of the breccia units of the las palmas detritic formation mio pliocene gran canaria eastern atlantic spain abstract the transformations of volcaniclastic gravity flows entering the sea remain poorly understood they are recorded by sedimentary signatures in the volcaniclastic sedimentation of the mio pliocene las palmas detritic formation lpdf of the volcanic island of gran canaria these gravity flows are contemporaneous with an erosive period on the island succeeding the emplacement of the fataga volcanic group and the beginning of the evolution of the roque nublo stratovolcano the sedimentary section that crops out at the mouth of a paleobarranco at las cuevas del guincho comprises subtidal calcareous and clastic sediments affected by wave and storm action units 1 and 3 beach gravels unit 4 volcaniclastic deposits represented by reworked phonolitic pyroclastic deposits unit 1 breccia deposits that contain juvenile and phonolitic gravels and blocks mainly incorporated at the shoreline unit 2 and a debris avalanche deposit at the top unit 5 the breccia deposits display a reversely graded base which disappears distally as a result of seawater incorporation and liquidization of the volcaniclastic mass and mixing with marine sediment this breccia unit is interpreted as having been emplaced by a granular mass flow after transformation of a block and ash flow deposit that entered the sea in the debris avalanche deposits thermal quenching of juvenile basaltic lava clasts and large inclined clastic intrusions of underlying marine sediments suggest that the debris avalanche entered the sea rapid subaqueous emplacement of the granular mass flow and of the debris avalanche deformed the sedimentary substratum water incorporation reduced the influence of the volcaniclastic flows on the substratum ams data confirm the effect of water ingestion and correlative loss of cohesion and allow also reconstruction of paleoflow directions that were normal to the paleoshoreline of the northern coast of gran canaria all these volcaniclastic gravity flow deposits and their textural characteristics are particularly useful in the reconstruction of processes that occur at the subaerial submarine transition and for the location of ancient shorelines

miocene rhyolitic welded tuff infilling a funnel shaped eruption conduit shiotani southeast of matsue sw japan at shiotani sw japan rhyolitic welded tuff forms a steep sided funnel shaped body confined by paleogene granitic rocks to an elliptical area 1 1 5 km across the shiotani welded tuff is pervasively welded and foliated concordantly with the contact that dips inward at angles of 70 90 in contrast nearby contemporary volcaniclastic deposits are non welded and gently inclined near the contact with the granite the tuff is plastically deformed and shows lineations that plunge inward at angles of 40 65 lithic and crystal clasts in the rheomorphic outer part are rotated in a plane normal to the foliations and parallel to the lineations indicating downward flow of the welded tuff the geometry and internal structures suggest that the shiotani welded tuff was emplaced and welded in a funnel shaped eruption conduit upon collapse of a plinian or phreatoplinian eruption column the majority of the conduit filling pyroclasts probably fell back en masse into the conduit heat and steam from underlying magma and diffusion of interstitial volatiles into the glass perhaps reduced the viscosity of juvenile pyroclasts and facilitated welding in the conduit especially at deep levels the hot welded pyroclasts then flowed down the conduit wall during welding compaction and retreat of the magma these processes resulted in increased welding toward the contacts and welding foliations concordant with the steep wall emplacement of nearby correlative volcaniclastic mass flow deposits in a shelf to upper bathyal environment suggests a possibility that when active the shiotani conduit was under the sea welding compaction would occur even under the sea provided that the steam generated in the upper part of the conduit fill prevented water access

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

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

quenching and hydroclastic disruption of andesitic to rhyolitic intrusions in a submarine island arc sequence northern sierra nevada california devonian submarine island arc deposits of the sierra buttes formation in the northern sierra nevada are penetrated by numerous penecontemporaneous hypabyssal intrusions but related extrusive lavas are absent significant parts of the arc succession are occupied by andesitic to rhyolitic intrusive complexes that record the quenching and disruption of large volumes of magma injected into wet sediments at shallow levels beneath the sea floor extensive masses of intrusive hydroclastic breccia are characterized by in situ fragmentation textures and developed by progressive brittle disintegration of quenched magma pillows dispersed within the breccia formed as a series of interconnected tubes that supplied magma to the growing intrusive masses beds of redeposited hydroclastic breccia indicate that the intrusions locally reached the sea floor to undergo slumping and debris flow large scale steam explosions did not occur during magma wet sediment interaction probably due at least in part to the lithostatic and hydrostatic pressure acting on the intrusions low viscosity rhyolitic magma developed intrusive pillows and in situ hydroclastic breccia in the same fashion as quenched andesitic magma this fluid behavior was favored by retention of volatiles in the rhyolitic magma under relatively deep marine conditions quenched and disrupted hypabyssal complexes of the type described herein may be common elements of the submarine parts of island arcs and other volcanic environments where uprise of magma through thick sequences of wet sediment is impeded due to buoyancy constraints and rapid chilling

carson pass kirkwood paleocanyon system paleogeography of the ancestral cascades arc and implications for landscape evolution of the sierra nevada california tertiary strata of the central sierra nevada are dominated by widespread voluminous volcanic breccias that are largely undivided and undated the origin of which is poorly understood these dominantly andesitic strata are interpreted to be eruptive products of the ancestral cascades arc deposited and preserved within paleocanyons that crossed the present day sierra nevada before basin and range faulting began there these strata are thus important not only for understanding the paleogeography of the ancestral cascades arc but also for reconstructing the evolution of the sierra nevada landscape our regional scale mapping shows that paleocanyon fills of the central sierra nevada are dominated by intrusions and vent proximal facies along the present day sierran crest with more distal facies extending westward down the paleocanyons vent proximal facies consist of lava domes that collapsed to generate block and ash flow tuffs which in turn were remobilized down canyon to produce coarse grained volcanic mudflow and dilute flow fluvial deposits lava flows are rare instead magmas invaded wet volcaniclastic sediment to form in situ peperite piles that were partly remobilized to form debris flows or block and ash flows with peperite domains detailed mapping and dating of previously undifferentiated tertiary strata in the carson pass kirkwood area of the central sierra nevada has allowed us to identify 6 unconformity bounded sequences preserved within a paleocanyon as deep as 650 m cut into mesozoic granitic basement the carson pass kirkwood paleocanyon trends ne sw with a paleo transport direction roughly parallel to the modern mokelumne river drainage toward the sw sequence 1 consists of oligocene silicic ignimbrites sourced from nevada sequences 2 through 6 consist of dominantly andesitic rocks of the miocene ancestral cascades arc with 40 ar 39 ar ages ranging from 14 69 0 06 ma to 6 05 0 12 ma these new dates provide constraints on the ages of unconformities vertical relief on the unconformities within the paleocanyon ranges from 12 to 303 meters with paleoslope gradients range from 3 to 48 no evidence exists for widening or deepening of the paleocanyon into mesozoic basement during tertiary time so we infer that unconformity 1 the paleocanyon floor and walls was inherited from cretaceous time the deepest unconformities within the paleocanyon fill reincised into granitic basement in the early miocene unconformity 2 between 14 and 10 ma unconformity 5 and between 10 and 6 ma unconformity 6 the paleocanyon was also beheaded cut off from sources to the east by ca 10 ma we suggest that the early miocene reincision records tectonism related to the onset of arc magmatism in the sierra nevada the middle miocene reincision may record the onset of basin and range faulting in the central sierra the late miocene reincision may correspond to uplift attendant with the northward sweep of the triple junction through the latitude of the central sierra paleocanyons of the central sierra differ from those of the northern and southern sierra by showing steeper local paleorelief and the bouldery stream deposits attest to higher axial gradients than envisioned for other parts of the range this may indicate that the uplift history of the range is not uniform from segment to segment

basaltic phreatomagmatic fissure at 71 gulch part 2 unusual pyroclasts from sediment magma mingling and melting the behavior of magma as it encounters unconsolidated sediment can be studied in fortuitous exposures of incised volcanic systems to help determine the conditions that control the transport arrest or mingling of that magma in the sediment the pliocene subaqueous basaltic fissure at 71 gulch idaho usa contains unusual light colored glassy mingled clasts that were produced through the incorporation of domains of siliciclastic sands and silts into basalt these clasts contain textures reflective of melting and mechanical mixing of these sediments with the rising basalt along intrusions at depths 30 m beneath the pre eruptive surface and transport into and through a shallow subsurface debris filled vent mingled clasts comprised colorless glass with locally high silica contents and visible swirls of sideromelane along with crystals derived from both the host sediment and the 71 gulch basalt the unique combination of textures minerals plus major and trace element geochemistry within the geologic context of 71 gulch points to a two phase mixing that did not contribute directly to nor impede the phreatomagmatic explosions that erupted the mingled clasts