melting and mingling of phonolitic pumice deposits with intruding dykes an example from the otago peninsula new zealand abstract a mound of bedded phonolitic pumice lapilli ash was deposited on the marine shelf modern otago peninsula new zealand during a shallow subaqueous eruption in the miocene basaltic dykes subsequently intruded the unconsolidated pumice deposit and formed an unusual peperite dyke sediment interaction began with weak steam driven mixing accompanied by fluidisation at the contact zone that produced a metres broad zone in which bulbous tongues up to 3 m of the dykes extended into and locally engulfed host sediment irregular sinuous contacts of dykes with the pumice are marked by black glass that formed by partial melting shearing and remoulding of the glassy pumice such melting and remoulding of host sediment is not a typical peperite feature temperature evolution volume of water vapour load pressure and time as well as initial contact temperature control the welding and remoulding of pumice and glass shards a slow cooling rate of the dykes at the dyke contacts is inferred from remoulding textures and is attributed to continuous feeding of the dyke seawater may have promoted softening and remoulding of the pumice because na and k if partially taken into the glass structure can decrease the melting point of glass dramatically and reduce the viscosity of the shards remoulding may have occurred by continuous conversion of seawater in the peperite to steam which is inferred to have enhanced transfer of na and k from seawater to pumice glass

scattering and anelastic attenuation of seismic energy in central and south central alaska abstract the characteristics of seismic energy attenuation in central and south central alaska are described the data analyzed are short period seismograms of local earthquakes recorded digitally in 12 bit at 120 hz sampling rate by permanent stations of the regional network in the study area first the coda amplitude decay rate was compared for two depth ranges 0 22 km and 63 133 km using the single scattering model the results show dependence of qc 1 on earthquake focal depth in the frequency f interval of 1

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

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

seismic wave attenuation in carbonates 1 the effect of pore fluids on seismic wave attenuation in carbonate rocks is important for interpreting remote sensing observations of carbonate reservoirs undergoing enhanced oil recovery here we measure the elastic moduli and attenuation in the laboratory for five carbonate samples with 20 to 30 porosity and permeability between 0 03 and 58 1 mdarcy contrary to most observations in sandstones bulk compressibility losses dominate over shear wave losses for dry samples and samples fully saturated with either liquid butane or brine this observation holds for four out of five samples at seismic 10 1000 hz and ultrasonic frequencies 0 8 mhz and reservoir pressures attenuation modeled from the modulus data using cole cole relations agrees in that the bulk losses are greater than the shear losses on average attenuation increases by 250 when brine substitutes a light hydrocarbon in these carbonate rocks for some of our samples attenuation is frequency dependent but in the typical exploration frequency range 10 100 hz attenuation is practically constant for the measured samples

seismic attenuation and pore fluid viscosity in clay rich reservoir sandstones the frequency dependence of seismic attenuation in a suite of clay rich reservoir sandstones was investigated in the laboratory compressional and shear wave velocities vp and vs and quality factors qp and qs were measured as functions of pore fluid viscosity at an effective pressure of 50 mpa and at an experimental frequency of about 0 8 mhz using the pulse echo technique the experimental viscosity ranged from 0 3 to 1000 centipoise which gives equivalent frequencies for a water saturated sandstone of 2 6 mhz to 780 hz assuming a global flow loss mechanism two types of behavior were observed high permeability greater than 100 millidarcies sandstones tend to show variable qp and qs which are similar in magnitude to those predicted by the biot theory over the viscosity range 0 3 to about 20 centipoise equivalent frequency range 2 6 mhz to about 39 khz low permeability less than 50 millidarcies sandstones tend to show almost constant qp and qs over the experimental viscosity range that are

the measurement of velocity dispersion and frequency dependent intrinsic attenuation in sedimentary rocks a series of experiments to determine the elastic properties of a sequence of saturated sedimentary rocks over as wide a frequency range as possible was carried out at the imperial college borehole test site these experiments fall into four categories vertical seismic profiles vsps within the frequency range 30 280 hz crosshole surveys 0 2 2 3 khz sonic logging 8 24 khz and laboratory measurements 300 900 khz the intrinsic attenuation and velocity of compressional and shear waves were measured whenever possible velocity dispersion is observed for both compressional and shear waves the intrinsic attenuation of compressional waves is frequency dependent with a peak in the attenuation in the sonic frequency band the data were modeled assuming the attenuation is caused by local fluid flow in pores of small aspect ratio the modeling indicates that the intrinsic attenuation may be dominated by cracks with aspect ratios of around 10 super 3 to 10 super 4

interactions between andesitic magma and poorly consolidated sediments examples in the neogene shirahama group south izu japan abstract the upper miocene lower pliocene shirahama group of south izu japan is a sequence of volcanielastic shallow sea sediments and subaqueous lava flows it is gently warped with indistinct preferred orientation and is cross cut by many andesitic intrusive bodies which range in size from less than a meter to several hundred meters the intrusive bodies exhibit various shapes and weak preferred orientation and often have hyaloclastic and peperitic textures along their peripheries hydrothermally altered and chaotically disturbed zones of host rocks also occur along the contacts the areas where the intrusive bodies are abundant are almost coincident with the areas where the more inclined beds and synsedimentary faults are developed the intrusive bodies dragged the surrounding beds with or without synsedimentary faults some intrusions occurred along the faults conjugate sets of the faults indicate that they were produced under unstable stress conditions these relationships between the beds and the intrusive bodies are assumed to have originated mostly by interaction between hot magma and poorly consolidated wet sediments at a shallow depth beneath the sea floor when the intrusions took place the stress conditions in the beds were irregular and unstable judging from the shapes and orientation of the intrusive bodies and also from the deformation characteristics of the enclosing beds some of the intrusive bodies are probably feeder dikes which supplied lave to the shirahama group

a direct comparison between vibrational resonance and pulse transmission data for assessment of seismic attenuation in rock for the same volume of rock i compare the attenuation obtained by seismic pulse transmission over the frequency range 1 150 khz with that obtained by vibrational resonance techniques over the frequency range 1 50 khz the initial studies were performed on a rectangular block of medium grained granite which was large enough to permit the installation of a seismic pulse transmission array over a 1 8 m path length yet small enough to permit whole body resonance a q of 82 for the p wave was derived from the vibrational resonance results whereas a q of 15 was derived from the pulse transmission results in light of models proposed for the viscoelastic geometric and elastic scattering attenuation mechanisms the experimental results suggest that this large discrepancy in q values is due to elastic scattering by grain clusters rather than individual grains within the granite scattering is significant in the high frequency pulse transmission tests but is considered insignificant in the lower frequency

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

zircon u pb and trace element data from rocks of the huai an complex new insights into the late paleoproterozoic collision between the eastern and western blocks of the north china craton abstract the trans north china orogen tnco is interpreted as a continent continent collisional belt along which the discrete archean eastern and western blocks amalgamated to form the basement of the north china craton the timing of its formation has not been precisely constrained yet six samples including five high grade metamorphic rocks and a pegmatite dike from the huai an complex in the northern segment of the tnco were selected for zircon u pb dating and trace element analysis a tonalite trondhjemite granodiorite ttg gneiss sample and a high pressure hp mafic granulite sample contain magmatic zircon cores yielding protolith formation ages of 2503 17 and 1964 38 ma respectively detrital zircons of magmatic origin in two metasedimentary rocks show concordant or moderately discordant u pb ages of 2683 22 to 1964 13 ma indicating that they were mainly derived from the tnco with some possibly derived from the archean continental rocks of the north china craton metamorphic zircons in the ttg gneiss and two metasedimentary rocks exhibit low hree contents flat hree patterns and negative eu anomalies implying their formation coeval with garnet and feldspar under grannulite facies conditions metamorphic zircons in an hp mafic granulite and a sample of leucosome from a ttg gneiss also have depleted hree contents flat hree patterns but only weak negative eu anomalies which may also indicate formation under granulite facies conditions whereas the weak eu anomalies may be due to the whole rock composition all these metamorphic zircons have formation temperatures of 702 749 c approaching the peak metamorphic temperatures of hp granulite rocks in this area they have identical ages of ca 1845 ma within analytical errors which is the best estimate age for hp granulite facies metamorphism of the huai an complex these results confirm previous models proposing late paleoproterozoic collision between the eastern and western blocks of the north china craton along the tnco on the other hand some metamorphic zircons in the leucosome sample show planar or polygonal zoning high th u contents and high th u ratios high ree contents and steep hree patterns indicating that they crystallized during partial melting with abundant garnet decomposition they yielded a weighted mean age of 1819 13 ma which we interpret to register the time of retrograde metamorphism combined with previously published data there are three age peaks at 1876 6 1849 2 and 1814 4 ma for metamorphic zircons from high grade metamorphic rocks in the tnco these may indicate either a protracted event or at least three peaks of metamorphism a pegmatite dike cutting the foliation of a mafic granulite boudin was dated at 1806 15 ma which signifies termination of collision between the eastern and western blocks in the huai an area

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

blocky versus fluidal peperite textures developed in volcanic conduits vents and crater lakes of phreatomagmatic volcanoes in mio pliocene volcanic fields of western hungary abstract volcanic fields in the pannonian basin western hungary comprise several mio pliocene volcaniclastic successions that are penetrated by numerous mafic intrusions peperite formed where intrusive and extrusive basaltic magma mingled with tuff lapilli tuff and non volcanic siliciclastic sediments within vent zones peperite is more common in the pannonian basin than generally realised and may be also important in other settings where sediment sequences accumulate during active volcanism hajagos hegy an erosional remnant of a maar volcano was subsequently occupied by a lava lake that interacted with unconsolidated sediments in the maar basin and formed both blocky and globular peperite similar peperite developed in kissomlyo a small tuff ring remnant where dykes invaded lake sediments that formed within a tuff ring lava foot peperite from both hajagos hegy and kissomlyo were formed when small lava flows travelled over wet sediments in craters of phreatomagmatic volcanoes at sag hegy a large phreatomagmatic volcanic complex peperite formed along the margin of a coherent intrusion all peperite in this study could be described as globular or blocky peperite globular and blocky types in the studied fields occur together regardless of the host sediment

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

introduction seismic wave scattering in three dimensionally heterogeneous earth the classical earth model of spherical symmetry or layered structure is undergoing a revolution the earth has been revealed to be laterally heterogeneous everywhere from the crust mantle to the core with scale from the grain size of rocks to the lowest orders of global spherical harmonics figure 1 shows the strength and scale length of heterogeneities in the crust and mantle of the earth in terms of v the perturbation index of seismic p or s wave speed defined as the r m s fractional variations of wave speed over the measured region the scale length of heterogeneities revealed by seismic waves not including the laboratory measurements of rock samples spans 8 orders of magnitude these heterogeneities with different scales have different effects to seismic waves the velocity and density heterogeneities can cause the change in waveform phase or travel time and amplitude fluctuation as well as apparent attenuation of the direct arrivals they can also generate coda waves such as the p coda s coda and lg coda caused by the lithospheric heterogeneities and precursory waves such as the scattered pkp waves as the precursors to pkikp caused by the heterogeneities near the core mantle boundary the near source or near receiver structures can modify the seismic waveforms by resonance and other effect rough topography or rough interface can cause the coupling between body wave and surface wave aligned cracks in the crust can produce the effective anisotrophy a great complexity arises when heterogeneities have interaction with anisotrophy and nonlinearity

intra vent peperites related to the phreatomagmatic 71 gulch volcano western snake river plain volcanic field idaho usa abstract the western snake river plain volcanic field in sw idaho contains up to 400 basaltic vents and centers that produced lava shields pahoehoe lava fields scoria cones and a great variety of phreatomagmatic volcanoes between late miocene and middle pleistocene time tephra deposits produced by phreatomagmatic eruptions are particularly well exposed in the walls of the snake river canyon where thick accumulations of pyroclastic rocks indicate widespread phreatomagmatic eruptive events throughout most of the volcanic history of the region previously many of the phreatomagmatic deposits were considered to be the products of subaqueous eruptions that took place on the floor of one or more large freshwater intra continental lakes recent field based observations confirm the presence of widespread phreatomagmatic pyroclastic rocks however some that had been interpreted as being subaqueous exhibit textural features that are more consistent with subaerial depositional environments intrusive and extrusive magmatic bodies with features associated with peperite formation have also been identified most of these peperites can be attributed to magma sediment mixing in intra crater conduit or vent settings and therefore they can only be used as widespread paleoenvironmental indicators with limitations to demonstrate magma and surface water e g lake non explosive interaction one of the studied sites 71 gulch volcano was previously used to indicate the presence of a shallow lake at this site there is clear field evidence that peperitic feeder dykes contacted muddy sandy siliciclastic sediments forming globular peperite the peperitic feeder dykes transition to pillowed ponded lava up section the ponded lavas are partially surrounded by a 5 m thick unit composed of gently dipping dune bedded volcanic glass shard rich unsorted tuff and lapilli tuff containing abundant impact sags caused by volcanic lithics we suggest that the 3d architecture of the erosional remnant of 71 gulch volcano does not require the presence of a lake at the time of its formation it is equally possible that that it represents a subaerial phreatomagmatic upper conduit crater filling succession this interpretation opens up many questions about the mio pliocene evolution of sw idaho the timing of the volcanism and its association with the evolution of the lacustrine systems in the region in addition re evaluations of the volcanic features in sw idaho have some general implications for the usage of phreatomagmatic pyroclastic rocks for paleoenvironmental reconstruction

thermodynamics and fluid dynamics of effusive subglacial eruptions we consider the thermodynamic and fluid dynamic processes that occur during subglacial effusive eruptions subglacial eruptions typically generate catastrophic floods jokulhlaups due to melting of ice by lava and generation of a large water cavity we consider the heat transfer from basaltic and rhyolitic lava eruptions to the ice for typical ranges of magma discharge and geometry of subglacial lavas in iceland our analysis shows that the heat flux out of cooling lava is large enough to sustain vigorous natural convection in the surrounding meltwater in subglacial eruptions the temperature difference driving convection is in the range 10 100 c average temperature of the meltwater must exceed 4 c and is usually substantially greater we calculate melting rates of the walls of the ice cavity in the range 1 40 m day indicating that large subglacial lakes can form rapidly as observed in the 1918 eruption of katla and the 1996 eruption of gjalp fissure in vatnajokull the volume changes associated with subglacial eruptions can cause large pressure changes in the developing ice cavity these pressure changes can be much larger than those associated with variation of bedrock and glacier surface topography previous models of water cavity stability based on hydrostatic and equilibrium conditions may not be applicable to water cavities produced rapidly in volcanic eruptions energy released by cooling of basaltic lava at the temperature of 1200 c results in a volume deficiency due to volume difference between ice and water provided that heat exchange efficiency is greater than approximately 80 a negative pressure change inhibits escape of water allowing large cavities to build up rhyolitic eruptions and basaltic eruptions with less than approximately 80 heat exchange efficiency cause positive pressure changes promoting continual escape of meltwater the pressure changes in the water cavity can cause surface deformation of the ice laboratory experiments were carried out to investigate the development of a water cavity by melting ice from a finite source area at its base the results confirm that the water cavity develops by convective heat transfer

a submarine welded ignimbrite crystal rich sandstone facies association in the cambrian tyndall group western tasmania australia three occurrences of rhyolitic welded ignimbrite are intercalated within a submarine below storm wave base sedimentary succession in the cambrian tyndall group mount read volcanics western tasmania these occurrences are closely associated with very thick crystal rich sandstone facies that is present at this stratigraphic level throughout the tyndall group this facies is interpreted to comprise deposits from syn eruptive crystal rich submarine sediment gravity flows that were generated by interaction of subaerial pyroclastic flows with seawater removal of fine ash and pumice from the submarine flows by hydraulic sorting and flotation resulted in marked crystal enrichment in the deposits rapid essentially syn eruptive aggradation of crystal rich sand led to temporary shoaling so that in some cases subsequent pyroclastic flows deposited welded ignimbrite in shallow marine or possibly subaerial settings e g zig zag hill welded ignimbrite breccia units composed of welded ignimbrite clasts and crystal rich matrix e g comstock and anthony road ignimbrite breccias imply that some welded ignimbrite was submerged providing clasts to syn eruptive submarine crystal rich sediment gravity flows one example of welded ignimbrite cradle mountain link road may have been deposited in an entirely below storm wave base environment the distinctive facies association of welded ignimbrite crystal rich sandstone and ignimbrite clast breccia in the tyndall group exemplifies the submarine record of a major rhyolitic explosive eruption in the source volcanic terrane

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

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

energy flux model of seismic coda separation of scattering and intrinsic attenuation a new model of seismic coda is presented based on the balance between the energy scattered from the direct wave and the energy in the seismic coda this energy flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic anelastic attenuation of the medium this formula is valid for both weak and strong scattering and implicitly includes multiple scattering the model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity some of the simulations also included intrinsic dissipation the energy flux model explains the coda decay and amplitude observed in the synthetics for random media with a wide range of scattering q in contrast the single scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation scattering q less than or equal to 150 the simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate as predicted by the energy flux model the coda decay rate is sensitive however more to the intrinsic q of the medium the ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation thus analysis of the decay rate and amplitude of the coda can in principle produce separate estimates for the scattering and intrinsic q values of the crust we analyze the coda from two earthquakes near anza california intrinsic q values determined from these seismograms using the energy flux model are comparable to coda q values found from the single scattering theory the results demonstrate that coda q values are at best measures of the intrinsic attenuation of the lithosphere and are unrelated to the scatteing q less

temporal change in scattering and attenuation associated with the earthquake occurrence a review of recent studies on coda waves the study of coda waves has recently attracted increasing attention from seismologists this is due to the fact that it is viewed as a new means by which the stress accumulation stage preceding a large earthquake can be measured since the scattering paths nearly uniformly cover a fairly large region around the focus and observation stations compared with the direct ray paths to date we have had many reports on the temporal variation of the relation between coda duration and amplitude magnitude and that of the coda attenuationq 1 which is estimated from coda amplitude decay some of these have shown a precursor like behavior however others seem to have shown a coseismic change we have critically reviewed these reports and discussed what these observational facts tell us about the change in the heterogeneous crust we found significant temporal variations not only in the mean but also in the scatter ofq 1 associated with the mainshock occurrence the formation of new cracks the reopening and growing of existing cracks the interaction of these cracks and the pore water movement through these cracks might correspond to such variations in addition we may expect an inhomogeneous distribution of crack clusters in a fairly large region compared with the aftershock region the gradual appearance of such crack clusters seems to be the most plausible mechanism by which coda decay gradients are caused to largely scatter in the stress accumulation stage

one dimensional random patchy saturation model for velocity and attenuation in porous rocks porous rocks encountered in hydrocarbon reservoirs are often saturated with a mixture of two or more fluids generation of synthetic seismograms as well as interpretation of in situ attenuation measurements require a theoretical understanding of the relation between the heterogeneous distribution of fluid patches and the acoustic properties of rocks thus the problem of calculating acoustic properties of rocks saturated with a mixture of two fluids has attracted considerable interest white 1975 murphy 1982 gist 1994 mavko and mukerji 1998 pride et al 2004 at the same time this problem is also interesting from the theoretical point of view because partially saturated rocks represent a particularly interesting situation when the effects of dynamic poroelasticity may be significant at seismic or sonic frequencies indeed it is a radical departure from the situation with a porous material fully saturated with a single fluid such a fully saturated material exhibits frequency dependent effects only at frequencies comparable with biot9s characteristic frequency bourbie et al 1987 c f where f is the fluid density is fluid viscosity is permeability and is porosity for frequencies much lower than c the dynamic effects can be ignored and gassmann theory applies

dike intrusion into unconsolidated sandstone and the development of quartzite contact zones abstract shallow near surface magma emplacement into a porous unlithified sandstone occurred by forceful dike dilation and was accompanied by a localized hydrothermal event petrographic fabric authigenic mineralogy and petrophysical data grade smoothly through the quartzite contact zone outward into the friable inmar sandstone of makhtesh ramon israel quartz grain deformation fracturing and rehealing of grains and pressure solution constitute overwhelming evidence of a compressive environment adjacent to dike margins albeit with temperatures and pressures insufficient to fully recrystallize detrital grains dikes were accommodated primarily by the repacking of the sandstone with both brittle and elastic grain interaction post emplacement heating together with elastic compressive stress dissipation lead to fracture healing and pressure solution the occasional columnar jointing must be related to thermal contraction of the quartzite during later cooling and resulting mode i cracks the alteration of both contact zone and dike material occurred via a transitory and confined hydrothermal seepage up dike margins elsewhere around the world highly altered intrusions bordered by indurated sometimes uniformly jointed sediments may also be the result of forceful magma emplacement and hydrothermal alteration at near surface levels

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

the determination of the seismic quality factor q from vsp data a comparison of different computational methods1 ten methods for the computation of attenuation have been investigated namely amplitude decay analytical signal wavelet modelling phase modelling frequency modelling rise time pulse amplitude matching technique spectral modelling and spectral ratio in particular we have studied the reliability of each of these methods in estimating correct values of q using three synthetic vsp seismograms for plane p waves with different noise contents the investigations proved that no single method is generally superior rather some methods are more suitable than others in specific situations depending on recording noise or geology the analytical signal method has been demonstrated to be superior if true amplitude recordings are available otherwise spectral modelling or in the noise free case the spectral ratio method is optimal finally two field vsps in sediments are investigated only in the case of the highest quality vsp can significant information be deduced from the computed attenuation

origin and metamorphism of peperite and associated rocks in the devonian elwell formation northern sierra nevada california the late devonian elwell formation is part of a late paleozoic island arc assemblage exposed in the northern sierra nevada california in the 10 km interval from mount elwell plumas county to packer lake sierra county it consists largely of numerous andesitic sills interleaved with phosphatic radiolarian chert and turbidity current and debris flow deposits peperite formed by interaction of intrusive andesitic magma and still moist incompletely lithified chert not far beneath the sea floor occurs sparingly the whole assemblage was thoroughly recrystallized greenschist facies regional metamorphism during the late jurassic nevadan orogeny the phosphatic chert is composed of white fluorapatite rich lenses and nodules enclosed in a black matrix consisting of microgranular quartz and carbonaceous material probably graphite radiolaria family entactiniidae are so abundant that the chert is thought to have originated as radiolarian ooze the phosphatic lenses and nodules probably formed by direct inorganic precipitation of fluorapatite from pore water within decaying radiolarians at the sediment water interface the andesitic sills are generally aphyric and aphanitic original textures varied from hyalopilitic in sill interiors to pilotaxitic at sill margins the andesite was charged with plagioclase now albite microlites and quench morphologies occur where sills intruded the wettest chert relatively thick sills commonly display columnar structure whereas a few originally more viscous sills are flow laminated the top of a sill emplaced essentially at the sediment water interface is pillowed many sills bear xenoliths of phosphatic chert and scarce quartz megacrysts evidently derived from the underlying dacitic sierra buttes formation appear nearly everywhere concentrations of major element oxides and immobile trace elements indicate that the andesite originated as part of the tholeiitic rock association of island arcs rare earth abundance patterns are particularly diagnostic of this paleotectonic setting most peperite has poorly sorted coarse ash to coarse block andesitic fragments uniformly distributed through a voluminous black chert matrix where invaded chert retained the most pore water quenched andesitic magma formed irregularly shaped lapilli and small pillows that initially exhibited ductile behavior rapid cooling below the softening point of glass resulted in brittle fracture of the lapilli during dispersal through the chert by steam explosions steam explosions also incorporated into the peperite rigid clasts of locally dewatered chert and shattered already formed phosphatic nodules where the invaded chert was better lithified freezing sill margins simply granulated quietly in situ by thermal contraction cracking of microlitic glass fluid chert injected widely spaced contraction joints deep within the sills in all cases there was sufficient heated connate water to cause palagonitization and chloritization of andesitic fragments greenschist facies metamorphism produced two mineral assemblages in the interiors of andesitic sills the second perhaps reflecting locally higher pco 2 ph 2 o during metamorphism 1 albite quartz epidote actinolite chlorite ti rich mineral calcite stilpnomelane white mica and 2 albite quartz chlorite ti rich mineral calcite stilpnomelane white mica epidote rich specks occurring sporadically in the sills represent metasomatism on a scale of millimetres to centimetres such specks are mineralogically zoned in andesitic fragments in intensely recrystallized peperite additional examples of local meta somatic activity include syntectonic crystallization of calcite rhombohedra across original vesicle walls in a sill cleavage developed locally during regional metamorphism is parallel to axial planes of closely appressed folds that deformed andesitic fragments in peperite and flow laminae in sills

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

correlation of 1 to 10 hz earthquake resonances with surface measurements of s wave reflections and refractions in the upper 50 m resonances observed in earthquake seismograms recorded in seattle washington the central united states and sherman oaks california are correlated with each site s respective near surface seismic velocity profile and reflectivity determined from shallow seismic reflection refraction surveys in all of these cases the resonance accounts for the highest amplitude shaking at the site above 1 hz these results show that imaging near surface reflections from the ground surface can locate impedance structures that are important contributors to earthquake ground shaking a high amplitude s wave reflection recorded 250 m northeast and 300 m east of the seattle kingdome earthquake recording station with a two way travel time of about 0 23 to 0 27 sec about 18 to 22 m depth marks the boundary between overlying alluvium v s 180 m sec and a higher velocity material v s about 400 m sec this reflector probably causes a strong 2 hz resonance that is observed in the earthquake data for the site near the kingdome in the central united states s wave reflections from a high impedance boundary an s wave velocity increase from about 200 m sec to 2000 m sec at about 40 m depth corresponds to a strong fundamental resonance at about 1 5 hz in sherman oaks strong resonances at about 1 0 and 4 hz are consistently observed on earthquake seismograms a strong s wave reflector at about 40 m depth may cause the 1 0 hz resonance the 4 0 hz resonance is possibly explained by constructive interference between the first overtone of the 1 0 hz resonance and a 3 25 to 3 9 hz resonance calculated from an areally consistent impedance boundary at about 10 m depth as determined by s wave refraction data