the tilt of mean sea level along the east coast of north america the tilt of mean sea level along the north american east coast has been a subject of debate for many decades improvements in geoid and ocean circulation models and gps positioning of tide gauge benchmarks provide an opportunity to produce new tilt estimates tilts estimated using tide gauge measurements referenced to high resolution geoid models the geodetic approach and ocean circulation models the ocean approach are compared the geodetic estimates are broadly similar with tilts downward to the north through the florida straits and at cape hatteras estimates from the ocean approach show good agreement with the geodetic estimates indicating a convergence of the two approaches and resolving the long standing debate as to the sign of the tilt these tilts differ from those used by yin and goddard 2013 to support a link between changing ocean circulation and coastal sea level rise

magma sediment mingling in an ordovician rift basin the plouezec plourivo half graben armorican massif france the plouezec plourivo basin ppb armorican massif is an ordovician half graben filled with red bed deposits lying on a cadomian metamorphic basement peperites crop out along its northeast coastal sector in connection with diverse magmatic and hydrothermal products combining field structural observations and geochemical analyses of magmatic rocks leads us to propose a model of emplacement of peperites in an extensional setting the ppb peperites result from mingling between magma and initially wet sediment the main corresponding facies consist of rounded magmatic bodies corrugated lava sediment contacts and a remarkable thin sheet of fluidized sediment extending over about 100 m parallel and c 10 cm above the base of a porphyritic lava flow a few ppb peperites formed under a dominant brittle regime are autoclastic breccias at the base of a lava flow and polymict breccias including both fluidal and blocky volcanic clasts sediment fluidization formation of vapor films magma sediment density contrasts and non explosive fragmentation are the main mechanisms invoked to generate the ppb peperites the c 100 m extended sediment derived sheet lying near the base of a lava flow likely formed by diapiric rise of fluidized sediment through molten lava we show that silicic contamination accompanied these peperitic processes

tilt of mean sea level along the pacific coasts of north america and japan the tilt of coastal mean sea level with respect to an equipotential surface is estimated using two fundamentally different approaches the geodetic approach is based on tide gauge and gps observations and a model of the geoid the ocean approach uses a high resolution dynamically based ocean model to estimate mean dynamic topography along the pacific coast of north america the two approaches give similar large scale profiles with a minimum at about 40 n and a maximum in the northern part of the gulf of alaska along the pacific coast of japan the geodetically determined coastal sea levels indicate an eastward drop of about 20 cm along the south coast and a further northward drop across tsugaru strait both of these features are reproduced by the ocean models an analysis of the alongshore momentum balance suggests that alongshore wind stress acting over the inner shelf is the primary driver of the mean sea level profile along the coast of north america several large scale features are explained using arrested topographic wave theory a similar momentum analysis and an additional study of time variability of sea level and circulation suggests that the kuroshio is the main driver of the mean sea level tilt along the south coast of japan discrepancies in the alongshore tilt of sea level estimated by the geodetic and ocean approaches along both coasts are discussed in terms of errors in the ocean and geoid models

apparent welding textures in altered pumice rich rocks fiamme and eutaxitic texture are common in ancient non welded pumice breccias the fiamme are phyllosilicate rich lenses that define a bedding parallel foliation resembling eutaxitic texture in welded ignimbrites pumice breccias in the cambrian mount read volcanics australia are composed of tube pumice clasts bubble wall shards plagioclase crystal fragments and volcanic lithic clasts and contain dark green fiamme and stylolites these sericite or chlorite sericite fiamme are aligned roughly parallel to regional bedding and are enclosed in pale pink feldspar quartz altered domains of uncompacted randomly oriented tube pumice clasts and bubble wall shards similarly pumice breccias in the miocene green tuff belt in the hokuroku basin japan comprise tube pumice clasts fiamme bubble wall shards crystal fragments and non vesicular volcanic clasts the dark green wispy smectite or chlorite fiamme are aligned parallel to bedding and are enclosed in domains of variably clay zeolite and sericite altered uncompacted pumice clasts and shards the fiamme in these examples vary in length 0 5 mm to 1 m length to height ratio 3 1 to 40 1 shape e g flame like feathery branching bow tie wedge and internal texture porphyritic massive vesicular or stylolitic the fiamme define an anastomosing bedding parallel pre tectonic eutaxitic texture delicate feathery terminations and locally preserved vesicles indicate that the fiamme are altered compacted pumice clasts the presence of bedding parallel stylolites and solution seams undeformed shards and pumice clasts adjacent to the fiamme and the overprinting of fiamme by the regional cleavage suggest that the fiamme formed during diagenesis prior to tectonic deformation and that compaction did not involve welding fiamme and eutaxitic texture in these examples resulted from the alteration dissolution and mechanical compaction of cold tube pumice clasts during diagenesis and lithification

deep water facies processes and models a review and classification scheme for modern and ancient sediments abstract a review of previous work on modern and ancient deep water facies processes and models is presented with a new classification scheme involving 40 distinct facies related to 15 conceptually distinct facies groups these facies are fixed points in a spectrum of facies generated in a process continuum from resedimentation processes through semi permanent bottom currents to pelagic settling in essence the scheme is descriptive of the sedimentary attributes of sediments although it is designed to aid interpretation of possible sediment transport deposition processes the classification scheme is three tier with facies classes groups and constituent facies and is hierarchical to allow flexibility in its use there are seven facies classes with classes a e defined largely on the basis of grain size differences class f on the basis of internal organization and class g on composition the facies classes are class a gravels muddy gravels gravelly muds and pebbly sands with 5 gravel grade class b sands with 80 sand grade and 80 mud 40 silt and 0 20 sand class e muds and clays with 95 mud grade for the purpose of large scale mapping or reconnaissance fieldwork either the level of facies classes or groups may be appropriate whereas for more detailed sedimentology the more detailed facies level will be necessary

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

geochemical modeling of the zoned footwall alteration pipe hellyer volcanic hosted massive sulfide deposit western tasmania australia the mineralogy of hydrothermal alteration assemblages siliceous core chlorite zone sericite zone in the footwall pipe of the hellyer volcanic hosted massive sulfide vhms deposit is controlled mainly by the temperature ph and redox state of the hydrothermal fluids based on the results of our numerical modeling the zoned alteration system could have formed by a combination of water rock interaction and cooling with a siliceous core predicted to form at the center of the conduit passing outward to a chlorite dominated zone a sericite rich zone and finally grading out to unaltered andesite these mineralogical changes relate to a gradual evolution of fluid chemistry water rock ratio ph and temperature from the core to the margin of the system initial temperatures were probably close to 350 degrees c and the hydrothermal fluids were reduced h2s dominated at low temperatures 200 degrees c a peripheral alteration zone consisting mostly of k feldspar chlorite sericite and hematite is predicted to form this low temperature zone has not been recognized at hellyer but elevated k2o contents and local k feldspar development have been noted at other vhms deposits suggesting that this zone might form at low temperatures and low water rock ratios in the footwall of vhms deposits if the existence of barren outer k feldspar alteration zones is confirmed the findings could have important implications for exploration specifically with regards to distinguishing ore related alteration zones from barren alteration systems

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

fiamme textures in volcanic successions flaming issues of definition and interpretation abstract fiamme are aligned flame like lenses found in welded ignimbrite fiamme also occur in welded pyroclastic fall deposits secondary welded pumice rich facies diagenetically altered and compacted non welded pumiceous volcaniclastic facies and lavas fiamme can be formed in a variety of ways the common genetic use of the term fiamme for pumice clasts that have undergone welding compaction is too narrow fiamme is best used as a descriptive term for elongate lenses or domains of the same mineralogy texture and composition which define a pre tectonic foliation and are separated by domains of different mineralogy texture or composition this descriptive term can be used regardless of the origin of the texture and remains appropriate for flattened pumice clasts in welded ignimbrite

volcanic influences on hydrothermal and diagenetic alteration evidence from highway reward mount windsor subprovince australia synvolcanic sills and cryptodomes hosting the highway reward volcanic hosted massive sulfide deposit invaded wet poorly consolidated silt sand and pumice breccia margins of the porphyriric units display perlitic and quench fractures suggesting that they were formerly glassy interiors of the rhyolites rhyodacites and dacites were originally glassy partly glassy or comprised crystalline domains exhibiting spherulitic lithophysae and micropoikilitic textures no glass is preserved and the sills and cryptodomes are now completely crystalline primary devitrification structures crystallized early above the glass transition temperature and before the formarion of perlite or quench fractures crystallization of residual glass proceeded by diagenetic alteration volcanic associated hydrothermal alteration and ore associated hydrothermal alteration massive sulfide ore is enclosed in a discordant alteration envelope that extends at least 60 m above ore and is known to a depth of 150 m in the footwall in general there is a progression from central quartz sericite pyrite zones giving way to zones of chlorite n anhydrite n gypsum chlorite sericite quartz and finally chloritesericite distal to ore the outermost alteration grades into ithofacies that have altered to various background assemblages of feldspar hematite sericite chlorite quartz epidote and carbonate compared to least altered lithofacies the quartz sericite pyrite zones are enriched in sion k20 fe o3 s and ba and depleted in n o cao mgo and sr elevated concentrations of mgo fe203 and s coupled with low na o cao and k o values characterize chlorirized zones the pattern of low n o cao and mgo values and high k o values passing outward through the chlorite sericite n quartz zones is more erratic the ishikawa alteration index ai value and the chlorite carbonate pyrite index ccpi value become progressively larger passing from background altered facies ai 60 ccpi 20 55 into the footwall and hanging wall alteration zones ai 89 97 ccpi 41 99 at ai values greater than 90 cu bi and mo are elevated the s n o ratio increases toward ore whereas sr ba ratios are lowest at ai values above 90 the geochemical halo patterns reflect the composite response of lithofacies to mineralogical and textural chan es accompanying diagenetic alteration volcanic associated hydrothermal alteration and ore associated hydromermal alteration most alteration zones around ore display two or more overprinting alteration mineral assemblages within single alteration zones the distribution of alteration minerals and assemblages varies spatially in response to contrasring lithofacies character formerly glassy coherent and volcaniclastic facies display mineralogical and textural changes that reflect the influence of fracture perlitic quench and or matrix permeability and porosity on fluid migration crystalline domains of volcanic facies generally preserve their original texture although recrystallization has partly destroyed primary devitrification microstructures alteration minerals are localized along cooling joints hydraulic fractures and veins or form mottled patchy or wispy domains in contrast siltstone that separates intrusions and forms the matrix in peperite is relatively unaltered or was baked during magma sediment mixing in zones of intense quartz sericite n pyrite chlorite n anhydrite gypsum and sericite alteration high water rock ratios an extended history of fluid flow and elevated temperatures promoted large scale mobilization of elements in all facies relics of the early alteration mineral assemblages are locally preserved in these zones and imply a progression from initial volcanic determined

determining coastal mean dynamic topography by geodetic methods in geodesy coastal mean dynamic topography mdt was traditionally determined by spirit levelling technique advances in navigation satellite positioning e g gps and geoid determination enable space based levelling with an accuracy of about 3 cm at tide gauges recent cryosat 2 a satellite altimetry mission with synthetic aperture radar sar and sar interferometric measurements extends the space based levelling to the coastal ocean with the same accuracy however barriers remain in applying the two space based geodetic methods for mdt determination over the coastal ocean because current geoid modelling focuses primarily on land as a substitute to spirit levelling to realize the vertical datum

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

the gold content of volcanogenic massive sulfide deposits volcanogenic massive sulfide deposits contain variable amounts of gold both in terms of average grade and total gold content with some vms deposits hosting world class gold mines with more than 100 t au previous studies have identified gold rich vms as having an average gold grade expressed in g t exceeding the total abundance of base metals expressed in wt however statistically meaningful criteria for the identification of truly anomalous deposits have not been established this paper presents a more extensive analysis of gold grades and tonnages of 513 vms deposits worldwide revealing a number of important features in the distribution of the data a large proportion of deposits are characterized by a relatively low gold grade 2 g t with a gradual decrease in frequency towards maximum gold grades defining a log normal distribution in the analysis presented in this paper the geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of vms deposits based on gold grade especially when comparing deposits within individual belts and districts the geometric mean gold grade of 513 vms deposits worldwide is 0 76 g t the geometric standard deviation is 2 70 g t au in this analysis deposits with more than 3 46 g t au geometric mean plus one geometric standard deviation are considered auriferous the geometric mean gold content is 4 7 t au with a geometric standard deviation of 26 3 t au deposits containing 31 t au or more geometric mean plus one geometric standard deviation are also considered to be anomalous in terms of gold content irrespective of the gold grade deposits with more than 3 46 g t au and 31 t au are considered gold rich vms a large proportion of the total gold hosted in vms worldwide is found in a relatively small number of such deposits the identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in vms at the district scale the gold rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes the gold rich vms are commonly associated with transitional to calc alkaline intermediate to felsic volcanic rocks which may reflect a particularly fertile geodynamic setting and or timing e g early arc rifting or rifting front at the deposit scale uncommon alteration assemblages e g advanced argillic aluminous strongly siliceous or potassium feldspar alteration and trace element signatures may be recognized e g au ag as sb bi hg te suggesting a direct magmatic input in some systems

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

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

a comparative assessment of coastal mean dynamic topography in norway by geodetic and ocean approaches the ocean s mean dynamic topography mdt is the surface representation of ocean circulation it may be determined by the ocean approach using numerical ocean circulation models or by the geodetic approach where mdt is the height of the mean sea surface mss or mean sea level msl above the geoid using new geoid models geodetic mdt profiles based on tide gauges dedicated coastal altimetry products and conventional altimetry are compared with six ocean mdt estimates independent of geodetic data emphasis is put on the determination of high resolution geoid models combining esa s fifth release r5 of goce satellite only global gravity models ggms with a regional geoid model for norway by a filtering technique differences between mdt profiles along the norwegian coast together with taylor diagrams confirm that geodetic and ocean mdts agree on the 3 7 cm level at the tide gauges and on the 5 11 cm level at the altimetry sites some geodetic mdts correlate more with the best performing ocean mdt than do other ocean mdts suggesting a convergence of the methods while the goce r5 geoids are shown to be more accurate over land they do not necessarily show the best agreement over the ocean pointwise monomission altimetry products give results comparable with the multimission dtu13mss grid on the 5 cm level however dedicated coastal altimetry products generally do not offer an improvement over conventional altimetry along the norwegian coast

subaqueous rhyolitic dome top tuff cones a model based on the devonian bunga beds southeastern australia and a modern analogue the relics of two late devonian subaqueous rhyolitic dome top tuff and pumice cone successions are preserved in the bunga beds outlier of the boyd volcanic complex southeastern australia these cone successions and other rhyolitic volcanics of the bunga beds are associated with turbidite and other deep water massflow sedimentary rocks the two cone successions have a generally similar stratigraphy at the base flow banded variably autobrecciated and quench fragmented rhyolite representing an intrusive to extrusive dome is overlain by rhyolitesediment breccia representing extrusion of the dome through the deep water sediment pile and resedimentation down its flanks in the northern cone succession an overlying succession of bedded pumiceous crystal rich to crystal poor tuffs represents the onset of pyroclastic activity and growth of a tuff cone an overyling debris flow deposit represents degradation of part of the cone the topmost unit a stratified pumice succession is thought to represent another cone building eruptive phase and is separated from the underlying strata by a major slide surface the southern cone succession contains less tuff and abundant pumice and is also terminated by a debris flow deposit indicating cone degradation a modern analogue for the inferred eruptive style and sequence is the 1953 1957 rhyolite eruption that formed the tuluman island lava tuff cone complex in the bismarck sea the eruptions were often cyclical consisting of an initial inferred submarine lava forming stage passing into a pumicecone forming stage in some cases a subaeriallava forming stage and a final stage following the cessation of volcanism during which the cones collapsed gravitationally or were destroyed by wave erosion using observations from both the tuluman island eruptions and the preserved stratigraphies of the devonian tuff cones a dynamic model is proposed for the formation of subaqueous rhyolitic dome top tuff and pumice cones

relations between basalts and adakitic felsic intrusive bodies in a soft substrate environment the south ouessant visean basin in the variscan belt armorican massif france the metasedimentary and magmatic terranes in the southern part of the ouessant island western brittany france are the offshore prolongation of the leon variscan metamorphic domain they mainly c

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

evolution of the fossa cone vulcano abstract in decreasing order of abundance the principal emplacement mechanisms for deposits of the fossa edifice of vulcano include dry surge wet surge pyroclastic fall lahar lava flow pyroclastic flow and epiclastic processes most samples from pyroclastic beds on fossa contain two grain size populations the coarser mode at 0 5 1 5 resulted from modified ballistic transport whereas the finer mode at 2 5 3 5 is related to surge transport reconstruction of the entire stratigraphy of the cone permits the beds to be grouped into five principal eruptive cycles all of which postdate the lower pilato ash of lipari dated at 11 000 to 8 500 y b p pte nere cycle palizzi cycle commenda cycle pietre cotte cycle and the modern cycle additional cycles may be present but exposures on the cone are insufficient for their adequate definition all cycles follow a similar stochastic pattern starting with surge eruptions and ending with effusion of lava from the crater rim the frequency of pyroclastic fall events increases with time throughout each cycle this progressive decrease in the efficiency of water melt interaction through the duration of each cycle may be due to a gradual rise of each new magma column coupled with an increase in magmatic volatiles tectonism and magma mixing both play a role in triggering eruptions on fossa the present crater lies at the intersection of two prominent tectonic trends a nnw fracture system parallels the main eruptive centers and an ene set aligns with the migration of minor vents the silicic lavas of fossa contain a mixture of two components xenocrysts of plagioclase augite and olivine surrounded by a dark glass are intimately dispersed into an evolved rhyolitic matrix

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

the apparent british sea slope is caused by systematic errors in the levelling based vertical datum the spirit levelling based british vertical datum ordnance datum newlyn implies a south north apparent slope in mean sea level of up to 53 mm deg 1 latitude due to the datum falling on heading northwards although this apparent slope has been investigated since the 1960s explanations of its origin have remained inconclusive it has also been suggested that rather than a slope the british vertical datum includes a step of about 240 mm affecting all sites north of about 53 n in either case the british vertical datum may be of limited use for any study requiring accurate heights or changes in heights such as testing geoid models groundwater and hydrocarbon extraction the calibration and validation of satellite based digital terrain models and the unification of vertical datums internationally within the last decade however based on an apparent reduction in the slope to only 12 mm deg 1 latitude with respect to recent geoid models it has been claimed that the british vertical datum does provide a physically meaningful surface for use in scientific applications in this paper we reinvestigate the presence of apparent south north sea slopes around britain and reported slopes in the vertical datum using the egm2008 global gravitational model together with mean sea level and gps data from british tide gauges gps ellipsoidal heights of 178 fundamental benchmarks across mainland britain and vertical deflection observations at 192 stations we demonstrate a south north slope in the british vertical datum of 20 25 mm deg 1 latitude with respect to both mean sea level corrected for the ocean s mean dynamic topography and the inverse barometer response to atmospheric pressure loading and the egm2008 quasigeoid model while egm2008 is shown to exhibit a negligible slope of 2 4 mm deg 1 with respect to mean sea level it is clear therefore that the slope can only arise from systematic errors in the levelling although we are unable to isolate their exact origin using an offset detection method based on a penalized likelihood maximization using the schwarz information criterion we do not detect a step in the vertical datum affecting all sites north of 53 n but do identify regional distortions that we attribute to the inhomogeneity in both the levelling data used and the least squares adjustment procedures used to realize the datum we conclude that the british vertical datum remains unsuitable for scientific purposes

comparison of turbidite facies associations in modern passive margin mississippi fan with ancient active margin fans abstract our comparison of the modern passive margin mississippi fan dsdp leg 96 with ancient active margin fans e g eocene hecho group spain reveals major differences in turbidite facies associations mutti and ricci lucchi scheme and in seismic characteristics in the lower fan area the lower outer mississippi fan is composed of channel facies b and f and non channel facies c and d whereas ancient fans are characterized by non channelized thickening upward depositional lobe facies c and d an absence of depositional lobes in the lower mississippi fan is also suggested by a lack of convex upward mounded seismic reflections with bidirectional downlap continuous seismic reflections of the lower mississippi fan may represent sheet sands but not those of true depositional lobes with mounded character extensive channelization in modern passive margin fans appears to be a product of the lateral shifting of a major sinuous distributary system developed as a consequence of low gradients and the transport of sediment with a relatively low sand mud ratio in contrast channels in active margin fans are short and of low sinuosity as a result of high gradients and the transport of sediment with a relatively high sand mud ratio the turbidite facies association scheme which was developed exclusively from ancient active margin fans should be applied to mature passive margin fans with qualifications because of the differences in spatial distribution of turbidite facies and their associations

subaqueous cryptodome eruption hydrothermal activity and related seafloor morphologies on the andesitic north su volcano abstract north su is a double peaked active andesite submarine volcano located in the eastern manus basin of the bismarck sea that reaches a depth of 1154 m it hosts a vigorous and varied hydrothermal system with black and white smoker vents along with several areas of diffuse venting and deposits of native sulfur geologic mapping based on rov observations from 2006 and 2011 combined with morphologic features identified from repeated bathymetric surveys in 2002 and 2011 documents the emplacement of a volcanic cryptodome between 2006 and 2011 we use our observations and rock analyses to interpret an eruption scenario where highly viscous crystal rich andesitic magma erupted slowly into the water saturated gravel dominated slope of north su an intense fragmentation process produced abundant blocky clasts of a heterogeneous magma olivine crystals within a rhyolitic groundmass that only rarely breached through the clastic cover onto the seafloor phreatic and phreatomagmatic explosions beneath the seafloor cause mixing of juvenile and pre existing lithic clasts and produce a volcaniclastic deposit this volcaniclastic deposit consists of blocky non altered clasts next variably 1 100 altered clasts hydrothermal precipitates and crystal fragments the usually applied parameters to identify juvenile subaqueous lava fragments i e fluidal shape or chilled margin were not applicable to distinguish between pre existing non altered clasts and juvenile clasts this deposit is updomed during further injection of magma and mechanical disruption gas propelled turbulent clast recycling causes clasts to develop variably rounded shapes an abundance of blocky clasts and the lack of clasts typical for the contact of liquid lava with water is interpreted to be the result of a cooled high viscosity crystal rich magma that failed as a brittle solid upon stress the high viscosity allows the lava to form blocky and short lobes the pervasive volcaniclastic cover on north su is partly cemented by hydrothermal precipitates these hydrothermally cemented breccias crusts and single pillars show that hydrothermal circulation through a thick layer of volcaniclastic deposits can temporarily increase slope stability through precipitation and cementation

the changing face of the deep colonization of the early ordovician deep sea floor puna northwest argentina abstract an upper tremadocian deep sea ichnofauna from the chiquero formation of puna northwest argentina represents a link between ediacaran and cambrian microbial mat dominated ecosystems and younger ordovician deep marine trace fossil assemblages this ichnofauna is preserved at the base of thin bedded turbidites formed in the lobe fringe of a back arc deep sea fan while ediacaran cambrian deep marine trace fossils are typically linked to matground grazing and feeding microbial textures in the chiquero formation are rare and not associated with trace fossils morphologic patterns e g radial trace fossils and networks of the chiquero ichnofauna indicate the onset of novel trophic types recording trapping of microorganisms and bacterial farming however in comparison with younger ordovician deep sea ichnofaunas graphoglyptids are relatively rare poorly diverse and geometrically simpler this study indicates that the early ordovician was a pivotal point in the ecology of deep sea infaunal communities this upper tremadocian ichnofauna records the arrival of the agronomic revolution to the deep sea comparisons with slightly older and younger deep sea ichnofaunas demonstrate that the colonization of the deep sea was a protracted process spanning the early paleozoic lagging behind colonization of nearshore and offshore substrates

fluid geochemistry of a deep seated geothermal resource in the puna plateau jujuy province argentina abstract this study focused on the geochemical and isotopic features of thermal fluids discharged from five zones located in the high altitude puna plateau jujuy province between s 22 20 23 20 and w 66 67 i e granada vilama pairique coranzuli and olaroz partially mature waters with a na cl composition were recognized in all the investigated zones suggesting that a deep hydrothermal reservoir hosted within the paleozoic crystalline basement represents the main hydrothermal fluid source the hydrothermal reservoirs are mainly recharged by meteoric water although based on the 18 o h 2 o and d h 2 o values some contribution of andesitic water cannot be completely ruled out regional s oriented faulting systems which generated a horst and graben tectonics and ne nw and we oriented transverse structures likely act as preferentially uprising pathways for the deep originated fluids as also supported by the rc ra values up to 1 39 indicating the occurrence of significant amounts of mantle he up to 16 carbon dioxide the most abundant compound in the gas phase associated with the thermal waters mostly originated from a crustal source although the occurrence of co 2 from a mantle source contaminated by organic rich material due to the subduction process is also possible relatively small and cold na hco 3 type aquifers were produced by the interaction between meteoric water and cretaceous palaeogene to miocene sediments dissolution of evaporitic surficial deposits strongly affected the chemistry of the thermal springs in the peripheral zones of the study area geothermometry in the na k ca mg system suggested equilibrium temperatures up to 200 c for the deep aquifer whereas lower temperatures from 105 to 155 c were inferred by applying the h 2 geothermometer likely due to re equilibrium processes during the thermal fluid uprising within relatively shallow na hco 3 aquifers the great depth of the geothermal resource possibly 5000 m b g l is likely preventing further studies aimed to evaluate possible exploitation although the occurrence of li and ba rich deposits associated may attract financial investments giving a pulse for the development of this remote region

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

the north south tilt in the australian height datum is explained by the ocean s mean dynamic topography 1 using geodetic and oceanographic data we show that the apparent north south slope between the australian height datum ahd and the geoid is caused almost completely by the ocean s time mean dynamic topography mdt this is because the ahd was constrained to zero height at local mean sea level at multiple tide gauges around the australian continent using mdt models and corrected leveling data almost all of the apparent north south slope can be removed from the ahd an auxiliary observation is that a satellite only mdt model based on only around one year of goce data generates results commensurate with geodetic oceanographic and combined mdt models

stratigraphic volcanic setting of massive sulfide deposits in the cambrian mount read volcanics tasmania the cambrian mount read volcanics of western tasmania host the volcanic hosted massive sulfide vhms deposits at hellyer que river rosebery hercules and mount lyell the volcanics were erupted along and partly onto the western margin of a precambrian basement terrane now represented by the tyennan region the volcanic belt is asymmetrical in section with a main eastern zone of relatively massive lava rich sequences accompanied by abundant intrusions and a broader western zone of volcano sedimentary sequences rich in volcaniclastic mass flow sandstone and breccia the rocks have been strongly deformed regionally metamorphosed to lower greenschist facies and hydrothermally altered in many areas stratigraphic and facies relationships within the highly complex volcanic belt are critically reviewed and reassessed the main volcanic zone is considered to comprise two interfingering lava rich associations the quartz feldspar porphyritic eastern sequence and the largely feldspar porphyritic central volcanic complex this lava rich zone interfingers with the western volcano sedimentary sequences herein referred to as the yolande river sequence the dundas group and the mount charter group new term recent volcanologic studies indicate that the lava rich sequences and indeed the bulk of the preserved mount read volcanics are submarine in character despite the presence of abundant ignimbritelike pumiceous deposits the early volcanism was predominantly rhyolitic dacitic in composition but was followed by a period of active andesitic basaltic volcanism during which the massive sulfide deposits at hellyer and que river and some of those at mount lyell were formed this widespread andesitic basaltic volcanism appears to coincide with a period of active extension and rifting along the belt focused to some extent on the henty fault system the rifting episode is evidenced by abundant tholeiitic dikes along the henty fault and throughout the northern central volcanic complex and by tholeiitic pillow lavas within the henty fault wedge the andesitic basaltic volcanism appears to have culminated in distinctive p 2 o 5 and light rare earth element lree enriched basalts at hellyer and similar rocks at lynch creek and howards plains near queenstown may be correlates the hellyer basalts were buried by black shale and the final volcanic phase was marked by a return to active felsic volcanism which produced widespread crystal and pumice rich mass flow deposits of the southwell subgroup and tyndall group

geometrical control of subduction related magmatism the mesozoic and cenozoic plutonic history of western colombia radiometric age data from western colombia combined with geological evidence allow five main plutonic episodes ranging in age from triassic to tertiary to be recognized it is suggested that variation in the convergence angle of the oceanic plate relative to the continental edge was an important factor affecting the timing and spatial distribution of plutonic activity on a regional scale major breaks in activity are probably best attributed to either low angle parallel convergence or periods of accretion along the convergent margin

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

the coastal mean dynamic topography in norway observed by cryosat 2 and goce new generation synthetic aperture radar altimetry as implemented on cryosat 2 observes sea surface heights in coastal areas that were previously not monitored by conventional altimetry therefore cryosat 2 is expected to improve the coastal mean dynamic topography mdt however the mdt remains highly reliant on the geoid using new regional geoid models as well as cryosat 2 data we determine three geodetic coastal mdt models in norway and validate them against independent tide gauge observations and the operational coastal ocean model norkyst800 the cryosat 2 mdts agree on the 3 5 cm level with both tide gauge geodetic and ocean mdts along the norwegian coast in addition we compute geostrophic surface currents to help identifying errors in the geoid models we find that even though the regional geoid models are all based on the latest satellite gravity data as provided by goce the resulting circulation patterns differ we demonstrate that some of these differences are due to erroneous or lack of marine gravity data this suggests that there is significant mdt signal at spatial scales beyond goce and that the geodetic approach to mdt determination benefits from the additional terrestrial gravity information provided by a regional geoid model we also find that the border of the geographical mode mask of cryosat 2 coincides with the norwegian coastal current making it challenging to distinguish between artifacts in the cryosat 2 observations during mode switch and ocean signal

types of submarine fan lobes models and implications different lobe models imply significantly different reservoir geometries thus one must apply the proper lobe model to ancient fan sequences braided suprafan lobes are characterized by stacked channel sand bodies with good lateral and vertical communication and they constitute excellent reservoir facies depositional lobes composed of sheet like sand bodies with good lateral and moderate vertical communication exhibit properties of good reservoir facies fanlobes which refer to meandering channels and associated levee facies of large mud rich submarine fans such as the mississippi fan are characterized by offset stacked sand bodies with poor lateral and vertical communication these lenticular sands have the potential to be moderately good reservoir facies ponded obes which represent mud rich slump facies of slope environments comprise poor reservoir facies because of low sand content and poor sand body connectivity furthermore the presence of contorted mud layers in ponded lobes is expected to hinder fluid flow external mounded reflections in seismic profiles often are interpreted as lobes however there are no definite seismic criteria to delineate mud rich lobes from sand rich lobes

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

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

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

puncoviscana folded belt in northwestern argentina testimony of late proterozoic rodinia fragmentation and pre gondwana collisional episodes stratigraphic correlations and tectonic analysis suggest that the puncoviscana fold belt of northwestern argentina was an intracontinental basin with bimodal igneous suites that formed in connection with the breakup of the rodinia supercontinent at 800 ma several lines of evidences point to an initial lithosphere rupture possibly induced by a rising mantle plume the earliest synrift igneous products are represented by ultra potassic dykes and alkaline lava flows of high lree hree and low zr nb y nb ratios the dyke emplacements and the initiation of rifting were probably synchronous they pass laterally and upwards middle part of the puncoviscana succession into basalts of alkaline transitional character oib like source the distinctive chemical feature of these lavas are very similar to the source of oceanic island basalts thus they are thought to represent a magmatism associated with the rift and rift drift transition stage during this stage of rifting probably true oceanic crust was formed the upper part of the puncoviscana sequence late precambrian lower cambrian in age comprises a thick and monotonous sequence of pillow lavas massive basaltic flows and minor volcanic breccias and hyaloclastites these lavas exhibit morb trace element characteristics with high feot and tio2 low k2o and p2o5 flat light ree spectra little or no depletion in nb and ta this volcanism consists of the major and latest effusive episode from the puncoviscana basin which was slightly modified by subduction processes the geodynamical model proposed for the generation of these volcanic rocks could have been developed in two stages in the first stage the volcanic event is compatible with a progressive opening of a continental rift leading to formation of a mature oceanic basin in contrast the second stage shows the effects of a completed wilson cycle including a primitive volcanic arc which continued until the accreted cuyania arequipa belen antofalla caba terrane against the proto gondwana western borderland of the amazonian shield 535 ma

distinguishing lavas from intrusions in an early paleozoic submarine backarc sequence puna argentina abstract in ancient volcano sedimentary successions the reconstruction of the facies architecture may be difficult because of incomplete exposure deformation metamorphism and hydrothermal alteration the distinction of lavas or domes from shallow intrusions is critical for the ordering of volcanic intrusive sedimentary and hydrothermal events both lavas and shallow intrusions typically have porphyritic textures and may have breccia along their top contacts detailed study of these breccias and their contact relationships is a reliable means of distinguishing lavas or domes from shallow intrusions in this contribution we describe rhyolites in an early paleozoic submarine volcano sedimentary succession in northwestern argentina known as the chiquero formation formed in a rapidly subsiding backarc setting this succession is mainly composed of turbidite interbedded with porphyritic rhyolite dacite units many of the rhyolites have breccias along their upper contacts rhyolite clasts in the breccias match the underlying rhyolites in terms of phenocryst populations and texture the main breccia facies along upper contacts are monomictic rhyolite breccia mudstone matrix rhyolite breccia and siliceous mudstone matrix rhyolite breccia the monomictic rhyolite breccia is interpreted to be in situ hyaloclastite formed by quench fragmentation of the tops of rhyolite lavas extruded onto the sea floor the mudstone matrix rhyolite breccia and the siliceous mudstone matrix rhyolite breccia are also interpreted as hyaloclastite but the spaces between the rhyolite clasts have been infilled by the locally available sediment and hydrothermal silica respectively the mudstone matrix rhyolite breccia and the siliceous mudstone matrix rhyolite breccia superficially resemble peperite in being composed of igneous and sedimentary components however the infilling sediment is laminated and the laminae are conformable with bedding in the overlying turbidite sequence implying that the sediment passively infilled pore spaces in pre existing rhyolite breccia hence the studied rhyolites of the chiquero formation were submarine lavas emplaced on the sea floor those lavas were probably emplaced during the middle ordovician based on correlation with a dated rhyolite interpreted to be syn sedimentary however at some localities the turbidite sequence contains tremadocian arenigian early ordovician fossils and a discrepancy exists between the isotopic age of the rhyolites and the age of the host sedimentary sequence based on fossils it is likely that the chiquero formation spans a wider age range than previously thought from early ordovician to late ordovician and that at least four episodes of rhyolitic dacitic magmatism contributed to this backarc succession

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

zn pb cu massive sulfide deposits brine pool types occur in collisional orogens black smoker types occur in backarc and or arc basins volcanic hosted massive sulfide deposits of zn pb cu type were derived either from seawater dominated buoyant fluids that built mounds on the seafloor e g the ores of the hokuroku basin japan or from saline fluids that reversed buoyancy on mixing with seawater and filled basins on the seafloor e g several ores of the iberian pyrite belt and the mount read province in tasmania the hokuroku ores formed above subduction zones during protracted periods of regional extension but both the iberian pyrite belt and the mount read province formed under extensional stress during continent continent iberia or arc continent mount read collision and orogenesis in the iberian pyrite belt oblique convergence resulted in transcurrent faulting and this may also be the case for the mount read province transcurrent faulting may have allowed easy vertical access for the ore related magmas some of which were sourced in the asthenosphere as well as the blueschist and eclogitic facies emplaced in adjacent terrains and possibly also saline fluids exsolved from the magmas

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

submarine fan and channel levee deposits in the lower cretaceous bogota trough colombian andes abstract bogota trough in the cordillera oriental of colombia was an elongate ne sw oriented lower cretaceous basin it was one of the main depocentres in the northern andes during earliest cretaceous time six lithofacies and three facies associations are recognised based on four detailed stratigraphic sections situated in the western portion of the trough sedimentation in the basin comprised channel levee fan lobe and outer fan basin plain depositional environments channel levee complexes without a well developed fan growth pattern were more proximal to the sediment supply in more distal settings the migrating channels evolved into suprafan lobes their sediments were covered by outer fan basin plain deposits at a time of retrogradation of the fan system the evolution in the basin continued with progradation and development of depositional lobes and channel fill middle fan environments the western portion of the trough was situated near to the zone of convergence between the nazca and the south american plates and the main sediment supply derived from the paleo central cordillera which in early cretaceous time consisted of an uplifted jurassic plutonic arc this active margin defined the coexistence of small sand rich radial fans and channel levee complexes in the eastern portion of the basin main source area the stable guayana shield determined the existence of a larger fan system of a hybrid type between radial and elongate fans despite the differences between the two fan systems in eastern and western portions of the trough the observed retrogradational and progradational sequences are similar

amalgamation surfaces bed thicknesses and dish structures in sand rich submarine fans numeric differences in channelized and unchannelized deposits and their diagnostic value abstract hydraulic differences between channelized and unchannelized flows in sand rich submarine fans result in different distributions of amalgamation surfaces bed thicknesses and dish structures in successions of these two different environments distribution trends of these fabrics were quantified for the sand rich fans of the reiselsberger sandstein cenomanian turonian these trends can be used as criteria to distinguish channelized from unchannelized paleoenvironments of sand rich submarine fans amalgamation surfaces in the studied fans channelized regions are considerably more abundant than in the unchannelized fan areas in unchannelized deposits tabular amalgamation surfaces outnumber nontabular ones whereas the opposite occurs in channelized successions these results indicate a higher degree of erosive power of gravity driven sediment flows in channels as a result of a greater flow thickness higher flow velocity and turbulence the average turbidite layer thickness in channelized successions is markedly greater than in unchannelized deposits layer as defined herein this is mainly attributed to the combined effects of differences in sediment fall out rate and the inefficiency of sand rich suspensions to transport sand in the proximal and channelized fan areas more sediment is deposited from a flow in the form of a layer than in distal unchannelized fan regions despite a higher degree of erosion in channels the greater average bed thickness in channel fills is a function of layer thickness and more frequent amalgamations bed as defined herein dish structures seem to be considerably more common in midfan than in outer fan successions this may indicate a higher sedimentation rate from individual suspension currents in midfan areas

chilling and brecciation of a devonian rhyolite sill intruded into wet sediments northern sierra nevada california localized pockets of peperite breccia occur near the base of a well exposed hypabyssal rhyolite sill within the upper devonian volcanic sequence of the northern sierra nevada the peperites resulted from chilling fragmentation and commingling of rhyolite with wet poorly consolidated sediment zones of hyaloclastite breccia extend into the sill above the peperites and represent areas where chilled rhyolite underwent fragmentation but was not intermixed with sediment a dense spherulitic intergrowth developed rapidly within the chilled rhyolite immediately prior to its fragmentation formation of this quench texture probably reflects a reduction in viscosity of the magma due to retention of volatiles in the melt under conditions of relatively high confining pressure

processes of magma wet sediment interaction in a large scale jurassic andesitic peperite complex northern sierra nevada california the middle jurassic tuttle lake formation in the northern sierra nevada california comprises a thick volcaniclastic sequence deposited in a submarine island arc setting and penetrated by numerous related hypabyssal intrusions a composite andesite diorite intrusive complex 4 5 km long and 1 5 km thick was emplaced while the host tuttle lake sediments were still wet and unconsolidated large parts of the intrusive complex consist of peperite formed where andesitic magma intruded and intermixed with tuff lapilli tuff and tuff breccia the southern half of the complex consists of augite phyric andesite containing peperite in numerous small isolated pockets and in more extensive laterally continuous zones the peperites comprise three main types recognized previously in other peperite studies fluidal peperite consists of small 30 cm closely spaced at least partly interconnected globular to amoeboid andesite bodies enclosed by tuff this peperite type developed during intrusion of magma into fine grained wet sediment along unstable interfaces and fluidization of the sediment facilitated development of complex intrusive geometries blocky peperite and mixed blocky and fluidal peperite formed where magma intruded coarser sediment and underwent variable degrees of brittle fragmentation by quenching and dynamic stressing of rigid margins possibly aided by small steam explosions the northern half of the intrusive complex consists predominantly of a different type of peperite in which decimetre scale plagioclase phyric andesite clasts with ellipsoidal elongate or angular polyhedral shapes are closely packed to widely dispersed within disrupted host sediment textural features suggest the andesite clasts were derived from conduits through which magma was flowing and preserved remnants of the conduits are represented by elongate sinuous bodies up to 30 m or more in length disruption and dispersal of the andesite clasts are inferred to have occurred at least partly by steam explosions that ripped apart a network of interconnected feeder conduits penetrating the host sediments closely packed peperite is present adjacent to mappable intrusions of coherent andesite and along the margin of a large mass of coarse grained diorite these coherent intrusions are considered to be major feeders for this part of the complex examples of magma wet sediment interaction similar in scale to the extensive peperites described here occur elsewhere in ancient island arc strata in the northern sierra nevada based on these and other published examples large scale peperites probably are more common than generally realized and are likely to be important in settings where thick sediment sequences accumulate during active volcanism careful mapping in well exposed terrains may be required to recognize large scale peperite complexes of this type

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

peperitic textures of ordovician dacitic synsedimentary intrusions in argentina s puna highland clues to emplacement conditions abstract synsedimentary crystal rich dacitic sills laccoliths and cryptodomes emplaced in early ordovician submarine thin bedded silt sandstone sequences show a variety of magma water interaction features megapeperites occurring along the igneous contact contain angular dacitic megaclasts that are dispersed in dominantly structureless host sediment they result mainly from quench fragmentation of magma and dynamic stressing of cooling magma bodies on contact with wet sediments combined in some instances with fluidization of the sediments or minor explosive expansion of water incorporated by magma breaching the sediment water interface or stopping of water saturated roof sediments by shallowing intrusions globular peperites having bulbous to globular dacitic clasts immersed in the host sediment with evidence of fluidization along the contact zone are also recognized at the top and base of sills in this case a vapor film might have formed at the magma sediment interface insulating the magma from direct contact with the sediment and suppressing quench fragmentation and steam explosions the diversity of peperite textures observed in the same intrusive and sedimentary rocks appears to be mainly the result of different levels of emplacement of the synsedimentary dacitic intrusions scarcity of peperites related to mafic sills is attributed to their having been emplaced late during the evolution of the basin

the ages and tectonic setting of the faja eruptiva de la puna oriental ordovician nw argentina abstract the ordovician faja eruptiva de la puna oriental is a magmatic predominantly intrusive belt in the puna of northwestern argentina with a n s extension of ca 400 km scarce isotope geochemical ages and biostratigraphic data on some of the folded faja eruptiva country rocks assign the magmatism either to the lower and lower middle ordovician or to the latest ordovician interpretations of origin and tectonic framework of the faja eruptiva are controversial and vary between arc back arc and collisional orogenic settings we present high resolution la icp ms u pb age and hf isotope data on zircons from 10 plutonic samples covering the magmatic belt along a length of 200 km in the northern argentinian puna the xenocrystic and magmatic zircon age data have a wide spread between 2700 ma and 440 ma concordia and weighted mean age data document protracted magmatism in two phases between 480 and 460 ma and between 453 and 444 ma and constrain the time of the last intrusions at 444 3 ma and at 445 2 ma thus defining this last and main phase of intrusion at 444 ma ehf t values define a main vertical trend centered at 500 ma with ehf t values between 3 and 16 indicating significant mixing of juvenile early paleozoic melts with paleoproterozoic crustal components a second trend is formed by zircons with ages between 1 1 ga and c 500 ma and predominantly positive ehf values between 8 and 3 and originates in juvenile mantle compositions between 1 6 and 1 1 ga the spread of the zircon and hf data document that the faja eruptiva intrusives have experienced large scale contamination by the hosting crustal basement it follows that the basement of the puna is formed either by the upper proterozoic lower cambrian puncoviscana formation as an erosional product of the proterozoic orogenic belts of sw amazonia or that the puna including its puncoviscana basement is underlain by a crust shaped by these orogenies the main intrusive event at 444 ma has been linked to the ocloyic orogeny in the late ordovician the plutons intruded very likely in a sinistral strike slip regime after the main folding phase of the ocloyic orogeny had deformed the ordovician sedimentary country rocks

textural and chemical characteristics of diagenetic and hydrothermal alteration in glassy volcanic rocks examples from the mount read volcanics tasmania the mount black and sterling valley volcanics comprise a complex cambrian succession of originally glassy felsic to mafic submarine volcanic facies in western tasmania the mount black and sterling valley volcanics have been modified by the combined effects of diagenesis hydrothermal alteration and regional metamorphism metamorphosed diagenetic and hydrothermal alteration facies have been distinguished using a combination of alteration mineralogy overprinting relationships texture distribution intensity and whole rock geochemistry alteration facies that are interpreted to be the regionally metamorphosed equivalents of diagenetic clays and zeolites are regionally extensive and overprinted by the regional cleavage although widespread their distribution is patchy and their intensities are highly variable reflecting the complexity of the original textures in glassy volcanic rocks thin films of sericite carbonate and chlorite sericite hematite replace clays that coated original glassy surfaces at the onset of diagenesis prior to compaction feldspar quartz sericite chlorite sericite and chlorite sericite hematite alteration facies replace zeolites and clays that filled pore space and altered glass prior to and synchronous with compaction the final diagenetic alteration facies chlorite epidote began after compaction and continued during metamorphism diagenetic alteration involved significant mineralogical and textural changes but only minor changes in chemistry the chemical changes associated with diagenetic alteration facies are consistent with the interaction of rhyolitic and basaltic glass with seawater during burial alteration facies that are interpreted to be hydrothermal are local in distribution crosscut stratigraphic boundaries and involve significant changes in texture mineralogy and composition early hydrothermal alteration facies quartz sericite and calcite quartz hematite predated compaction and were synchronous with diagenesis chlorite calcite magnetite and chlorite pyrite alteration facies were synchronous with regional deformation and are associated with tectonic breccias faults and shear zones chlorite quartz calcite alteration facies postdated regional deformation