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

refraction and shoaling of nonlinear internal waves at the malin shelf break abstract this paper applies a numerical model to explain the refraction and shoaling of nonlinear internal waves observed at the malin slope for a sequence of tidal cycles in the summer of 1995 the model is first order in dispersion and second order in nonlinearity and is based on the extended korteweg de vries ekdv equation the ekdv model is applied along a set of rays and includes the effect of variable depth the model predicts that an initial long wavelength wave which lies in water of depths between 500 and 900 m develops into a set of internal solitary waves as it passes across the shelf break and onto the continental shelf in agreement with observations the extent of refraction is small because the internal waves are high frequency and in this case the refraction is not strongly dependent on the nonlinear adjustment to phase speed in the observations the internal wave amplitude measured in terms of near surface currents or thermocline displacement initially grows as the wave crosses th

intra oceanic subduction related hydrothermal venting kermadec volcanic arc new zealand intra oceanic volcanic arcs mark the boundaries between converging lithospheric plates where subduction produces volcanic and tectonic activity that ensures a steady supply of magmatic heat and hydrothermal fluids to the seafloor here we report on the first broad and systematic survey of hydrothermal emissions generated along a submarine arc front more than half seven of 13 of the volcanoes surveyed along 260 km of the southern kermadec arc ne of new zealand are hydrothermally active our results indicate that volcanic arcs represent a previously unheeded but potentially extensive source of shallow 2 km water depth vent fields expelling fluids of a unique and heterogeneous composition into the oceans

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

volcanism associated with extension in an oligocene miocene arc southwestern viti levu fiji the wainimala group rocks of southwestern viti levu fiji represent part of an oligocene miocene island arc some of the early volcanism in this arc took place on a substrate of eocene oligocene frontal arc crust mainly andesitic transitional calcalkaline lavas were erupted from major subaerial volcanic edifices while elsewhere tholeiitic magmas formed low lying basaltic lava fields and small felsic volcanic centres on the seafloor the intrusion of a dense bimodal basalt dacite dyke swarm into the underlying frontal arc crust indicates that significant crustal extension accompanied the eruption of the inter edifice lavas geochemical variations within the wainimala volcanic suite are thought to have been generated through fractional crystallisation processes while relatively slow ascent and mixing of magmas took place beneath the major edifices efficient shallow level fractionation and rapid ascent of magmas occurred in the areas between them the contrasting styles of volcanism may reflect the interaction of ascending magmas with pre existing heterogeneities in the frontal arc substrate

surface uplift history of the incipient banda arc continent collision geology and synorogenic foraminifera of rote and savu islands indonesia abstract field mapping and analysis of foraminifera from synorogenic pelagic units of rote and savu islands indonesia reveals high rates of surface uplift of the incipient banda arc continent collision during the past 1 8 myr new geological maps of these islands document accretion to the banda forearc of triassic through tertiary sedimentary cover units from the down going australian continental margin foraminifera rich synorogenic deposits of the batu putih formation unconformably overlie these accreted units we use paleodepth versus time estimates from benthic and planktic foraminifera s to measure long term surface uplift rates for the accretionary wedge although strong currents in the region cause some problems with reworking several distinctive species have been found synorogenic deposits in savu and rote yield foraminifer s of biozone neogene n 18 to n22 5 6 1 0 myr that were deposited at estimated depths of around 3000 m these deposits are unconfomrably overlain by uplifted coral terraces the highest coral terraces in savu are 300 m above sea level and perhaps as old as 0 8 myr in rote the highest coral terrace is 200 above sea level and 0 2 myr old these data indicate that collision of the australian continental margin with the banda arc which initiated much earlier in timor has propagated westward towards rote where it is in the initial stages of accretionary wedge emergence collision of the scott plateau propagated se from sumba 2 3 ma to savu 1 0 0 5 ma and then to rote 0 2 ma average rates of surface uplift of the batu putih formation pelagic deposits during the past 2 myr in rote and savu are 1 5 and 2 3 mm a respectively the rise of these islands is clogging the indo pacific seaway

formation of high grade ignimbrites part ii a pyroclastic suspension current model with implications also for low grade ignimbrites analogue experiments in part i led to the conclusion that pyroclastic flows depositing very high grade ignimbrite move as dilute suspension currents in the thermo fluid dynamical model developed the degree of cooling of expanded turbulent pyroclastic flows dynamically evolves in response to entrainment of air and mass loss to sedimentation initial conditions of the currents are derived from column collapse modeling for magmas with an initial h2o content of 1 3 wt erupting through circular vents and caldera ring fissures the flows spread either longitudinally or radially from source up to a runout distance that increases with higher mass flux but decreases with higher gas content temperature bottom slope and coarser initial grain size progressive dilution by entrainment and sedimentation causes pyroclastic currents to transform into buoyant ash plumes at the runout distance the ash plumes reach stratospheric heights and distribute 30 80 of the erupted material as widespread co ignimbrite ash pyroclastic suspension currents with initial mass fluxes of 107 1012 kg s can spread for tens of kilometers with only limited cooling although they move as supercritical strongly entraining currents for the eruption conditions considered here with increasing eruption mass flux cooling during passage through the fountain diminishes while cooling during flow transport increases the net effect is that eruption temperature exerts the prime control on emplacement temperature pyroclastic suspension currents can form welded ignimbrite across their entire extent if eruption temperature is to 1 3 tmw the minimum welding temperature high eruption rates a large fraction of fine ash and a ring fissure vent favor the formation of extensive high grade ignimbrite for very hot eruptions producing sticky partially molten pyroclasts analysis of particle aggregation systematics shows that factors favoring longer runout also favor more efficient aggregation which reduces runout as a result very high grade ignimbrites cannot spread more than a few tens of kilometers from their source in cooler pyroclastic currents particles do not aggregate and the sedimentation process may involve re entrainment of particles which potentially leads to more extensive cooling and longer runout such effects however are only significant when net erosion of substrate occurs model results can be employed to estimate mass flux and duration of ignimbrite eruptions from measured ignimbrite masses and aspect ratios the model also provides an alternative explanation of the observed decrease in h lratios with ignimbrite mass

tectonics of short lived intra arc basins in the arc continent collision terrane of the coastal range eastern taiwan the coastal range in eastern taiwan was originated from an oblique collision between the luzon volcanic arc and asian continent since the late neogene in this collision terrane two intra arc basins the pliocene chingpu and pleistocene chengkung basins were developed on the eastern part of the neogene chimei and chengkuangao volcanic islands respectively prior to their accretion to eastern taiwan the tectonic evolution of these neogene volcanic islands and associated intra arc basins is reconstructed by stratigraphic and sedimentological analysis igneous rock geochemistry and comparison with observations in modern collision zone in the regions off southeastern taiwan in the coastal range the intra arc basin sequences are 1 5 10 km wide and 40 km long comparable in size to their modern analogues in the active collision zone the basin axis trends subparallel to the volcanic ridge in both basins deepwater flysch overlies shallow marine reef carbonates which in turn rest on volcanic basement indicating rapid arc collapse minimum rate of 1 km m y soon after the arc continent collision the arc collapse occurred earlier in the north chimei between 5 1 and 3 5 ma and later in the south chengkuangao between 2 9 and 1 8 ma in concert with a southward propagation of the oblique collision sedimentation ended about 2 ma and 1 ma in the chingpu and chengkung basins respectively coeval with rotation of the neogene volcanic islands this suggests that the rotation inverted the intra arc basin into thrusting uplifting and final emergence thus the duration of sedimentation for the intra arc basins spanned only about 0 8 3 1 m y on the basis of land geology offshore observations and a clay model experiment simulating oblique arc continent collision a model for the intra arc basin evolution in eastern taiwan is proposed during the collision strike slip faults would have been developed in the eastern part of volcanic islands to induce transtension movements thus forming pull apart intra arc basins on the collapsed volcanic island this mechanism is believed to be responsible for the formation of the pliocene chingpu and pleistocene chengkung basins as well as the present day offshore intra arc basins found on the lutao and lanhsu volcanic islands the two intra arc basins on lutao and lanhsu are predicted to be short lived as collision continues these two basins together with their underlying northern part of the luzon arc will be rotated thrust and uplifted in the next 1 m y and finally will become part of the southern extension of the coastal range

the eruptive history of morne jacob volcano martinique island french west indies geochronology geomorphology and geochemistry of the earliest volcanism in the recent lesser antilles arc martinique is the lesser antilles island where the most complete volcanic history of the arc can be found from the oligocene to the present time in this study we focused on the construction of morne jacob shield volcano in martinique which is the largest volcano of the lesser antilles we have dated twenty representative samples from the morne jacob by k ar based on the cassignol gillot technique used geochemical data and obtained morphological constraints that have helped us to reconstruct better the volcanic history of this shield volcano our results and the lack of reliable ages on other plio pleistocene islands show that the morne jacob is the oldest volcano of the aerial recent arc that has been dated so far it has a longer history than previously inferred with different stages ranging between 5 2 and 1 5 ma a large basaltic to andesitic shield volcano was first built between 5 2 and 4 0 ma j1 with tholeiitic lavas characterized by an increase of sio2 content through time after 800 kyr of repose calc alkaline andesites erupted over the first shield from 3 2 to 2 2 ma j2a the accumulation of lavas over a hyaloclastitic basement provoked spreading and northeast creeping of the northern flank of the volcano the mass movement induced regressive erosion particularly at the centre of the edifice then between 2 1 and 1 5 ma j2b calc alkaline lavas which show a decrease of the sio2 content through time erupted at the central vent and from peripheral fissures over the previous shield and down to the caribbean coast eruptive volumes were reconstructed permitting estimates of minimum output rates for the volcano s history minimum volume erupted during the first stage is 112 20 km3 and 33 25 km3 during the whole second stage yielding rates of about 0 107 km3 kyr and 0 019 km3 kyr respectively considering the entire history of morne jacob shield volcano between 5 14 0 07 and 1 54 0 03 ma we obtain a total volume of 145 32 km3 above the sea level and a time averaged construction rate of 0 040 0 008 km3 kyr with comparison between the reconstructed paleotopographies and the dem of present topography we have calculated an eroded volume of 18 km3 over the outcropping 210 km2 that have occurred during the last 1 5 myr finally our set of twenty k ar ages obtained on groundmass separates allow us to revise the eruptive chronology of morne jacob volcano and to date the earliest subaerial volcanic activity so far identified for the recent lesser antilles arc

kinematic setting and structural control of arc volcanism abstract the evaluation of the kinematic setting and the structural control of volcanic arcs are important in defining the tectono magmatic processes along convergent plate boundaries however our knowledge is fragmented and the available data highlight different behaviours this study analyzes the kinematic setting the structural control and the volcanic productivity of 16 arcs these arcs are characterized by predominant extensional compressional strike slip or oblique motions there is an overall coupling between the normal vs parallel motions along the arc and those of the underlying slab therefore the higher the trench normal or parallel component of the subduction rate the higher is the amount of arc normal or parallel motion this relation confirms that strain partitioning is in general feasible at many convergent settings involving also the volcanic arc portion the arc normal motion may be characterized by extension or compression as a function of the increase in the trench normal convergence or subduction velocity the lack of an evident relation between the subduction rate or convergence rate and the volcanic productivity of the arc is partly inconsistent with previous studies which highlight a relation between the subduction rate and melt production below arcs this discrepancy mainly suggests that different processes control the generation rise and eruption of magma at different depths varying the intrusive extrusive ratio along arcs the structure of the arc does not control the distribution of the volcanoes however it does control the volcanic output through different processes even though regional or local extension associated with strike slip or compressive structures is the ultimate requisite in any setting in general the higher the amount of extension the higher is the output rate along the arc

how do you grade peperites a spectacular graded peperite of volcanic origin from the palaeogene mull lava field of nw scotland the carraig mhor bed cmb consists of a basal facies of pale sub horizontally aligned fluidal shaped clasts of hydrothermally altered basalt set in a brown complexly laminated silt to clay grade host siliciclastic sediment the basal facies of the cmb grades upwards over an interval of 10 m into an upper facies dominated by smaller and more angular clasts of identical composition set in a subordinate proportion of the same sediment matrix the distinctive textural characteristics of the cmb together with its remarkably uniform grading motif may be explained in terms of the mingling of basaltic magma and fluidised siliciclastic sediment resulting in the ductile fragmentation of magma and production of the fluidal clasts which dominate the basal facies cooling of the system led to limited brittle fragmentation yielding the finer grained sediment poor upper facies of the cmb during cooling the larger fluidal shaped clasts settled to the base of the unit through the saturated sediment producing the vertical stratigraphic grading now preserved grading occurred essentially in situ during peperite formation and cannot be attributed to remobilisation mass flow or pyroclastic phenomena

upwelling rebound ephemeral secondary pycnoclines and the creation of a near bottom wave guide over the monterey bay continental shelf several sequential upwelling events were observed in fall 2012 using measurements from the outer half of the continental shelf in monterey bay during which the infiltration of dense water onto the shelf created a secondary near bottom pycnocline this deep pycnocline existed in concert with the near surface pycnocline and enabled the propagation of near bottom cold semidiurnal internal tidal bores as well as energetic high frequency nonlinear internal waves of elevation iwoe the iwoe occurred within 20 m of the bottom had amplitudes of 8 24 m periods of 6 45 min and depth integrated energy fluxes up to 200 w m 1 iribarren numbers 0 03 indicate that these iwoe were nonbreaking in this region of the shelf these observations further demonstrate how regional upwelling dynamics and the resulting bulk cross margin hydrography is a first order control on the ability of internal waves at tidal and higher frequencies to propagate through continental shelf waters

the taiwan ryukyu subduction collision complex folding of a viscoelastic slab and the double seismic zone 1 the termination of the ryukyu trench against eurasia and the oblique subduction of the philippine sea plate create a subduction collision complex offshore taiwan which has not previously been elucidated in detail we combine traveltime data from the seismic networks in taiwan and japan to better illuminate how the subducting ryukyu slab deforms in this subduction collision zone more than 5000 events recorded by both networks were relocated with the double difference method using an optimal regional one dimensional velocity model the offshore seismicity indicates that the double seismic zone with a gap of 15 20 km exists in the subducting slab in the depth range of 40 80 km focal mechanisms suggest that the double seismic zone is caused by east west compression resulting from oblique convergence the improved hypocentral locations for the first time reveal folding of the slab into a horizontal curvature larger in magnitude than and opposite in sign to that of the ryukyu trench in the depth range 50 100 km the anomalous curvature together with the focal mechanisms suggests that the slab folds against the eurasian lithosphere and that this deformation cannot be fully elastic we model this deformation mode as the developing instability of a viscoelastic maxwell layer embedded in a viscous medium the characteristic wavelength of the instability i e 250 km is consistent with folding of a slab whose viscosity is 100 times higher than that of the surrounding mantle for an along strike elastic membrane strain as small as 0 01 or more than 3 orders of magnitude higher if 5 elastic strain is allowed

nonlinear internal waves in the south china sea observation of the conversion of depression internal waves to elevation internal waves 1 the conversion of depression nonlinear internal solitons to elevation internal waves has been observed twice at the south china sea continental shelf break shipboard x band radar tow yo ctd adcp and high frequency acoustic flow visualization of the process are presented the data focuses on up slope propagation of depression internal solitons from a water depth of 264 m to a water depth of 110 m dissipation by large amplitude shear instabilities was observed the kinetic energy density was found to be a decreasing monotonic function of range with an energy dissipation rate coefficient of 0 063 km 1 the rate of energy dissipation over the 16 5 km soliton propagation path was 0 17 w m m simple numerical models of the waveform evolution are qualitatively compared to the observations the observations extracted scale parameters and dissipation rates should be useful for testing a variety of evolution equation representations of internal soliton propagation

mechanisms of hydrovolcanic pyroclast formation grain size scanning electron microscopy and experimental studies pyroclasts produced by explosive magma water interactions are of various sizes and shapes data from analysis of over 200 samples of hydrovolcanic ash are interpreted by comparison with experimentally produced ash grain size and scanning electron microscopy sem reveal information on the formation of hydrovolcanic pyroclasts strombolian explosions result from limited water interaction with magma and the pyroclasts produced are dominantly centimeter sized with increasing water interaction hydrovolcanism increases in explosivity to surtseyan and vulcanian activity these eruptions produce millimeter to micron sized pyroclasts the abundance of fine ash 63 m diameter increases from 5 to over 30 percent as water interaction reaches an explosive maximum this maximum occurs with interactions of virtually equal volumes of melt and water five dominant pyroclast shape types determined by sem result from hydrovolcanic fragmentation 1 blocky and equant 2 vesicular and irregular with smooth surfaces 3 moss like and convoluted 4 spherical or drop like and 5 plate like types 1 and 2 dominate pyroclasts greater than 100 m in diameter types 3 and 4 are typical of fine ash type 5 pyroclasts characterize ash less than 100 m in diameter resulting from hydrovolcanic fragmentation after strong vesiculation fragmentation mechanisms observed in experimental melt water interactions result from vapor film generation expansion and collapse fragments of congealed melt are products of several alternative mechanisms including stress wave cavitation detonation waves and fluid instability mixing all result in rapid heat transfer these mechanisms can explain the five observed pyroclast shapes stress wave fracturing cavitation of the melt results from high pressure and temperature gradients at the melt water interface simultaneous brittle fracture and quenching produces type 1 pyroclasts type 2 develops smooth fused surfaces due to turbulent mixing with water after fracture and before quenching fluid instabilities promote turbulent mixing of melt and water and produce fine ash this kind of fragmentation occurs during high energy explosions the increased melt surface area due to fine fragmentation promotes high efficiency heat exchange between the melt and water shapes of resulting pyroclasts are determined by maximum surface area type 3 and surface tension effects type 4 type 5 pyroclasts result from nearly simultaneous vesicle burst and melt water fragmentation

observation of very large and steep internal waves of elevation near the massachusetts coast 1 we report on near bottom waves of elevation with amplitude nearly half the 25 m water column very steep and propagating into a sheared turbulent wave guide the waves contained trapped cores transporting parcels of water shoreward these large waves depart strongly from weakly nonlinear and weakly nonhydrostatic conditions and challenge established paradigms they can also represent an important factor in the across shore transport of plankton and contaminants

high frequency internal waves on the oregon continental shelf abstract measurements of vertical velocity by isopycnal following neutrally buoyant floats deployed on the oregon shelf during the summers of 2000 and 2001 were used to characterize internal gravity waves on the shelf using measurements of vertical velocity the average spectrum of wentzel kramers brillouin wkb scaled vertical kinetic energy has the level predicted by the garrett munk model gm79 plus a narrow m2 tidal peak and a broad high frequency peak extending from about 0 1n to n and rising a decade above gm79 the high frequency peak varies in energy coherently with time across its entire bandwidth its energy is independent of the tidal energy the energy in the continuum region between the peaks is weakly correlated with the level of the high frequency peak energy and is independent of the tidal peak energy the vertical velocity is not gaussian but is highly intermittent with a calculated kurtosis of 19 the vertical kinetic energy varies geographically low energy is found offshore and

circulation and larval distribution in internal tidal bore warm fronts internal tidal bore warm fronts were observed during the summer of 1996 off the coast of southern california warm bore fronts had concentrating currents resulting from high frequency internal motions and from a larger two way flow the two way flow featured surface currents onshore and bottom currents offshore a sharp thermocline depression and high frequency large amplitude internal motions followed the leading edge of the bore with downwelling currents on the trailing side of the crest of the nonlinear internal waves and upwelling currents in front of the crest warm bores propagated onshore with a propagation speed c that ranged from 10 6 to 19 6 cm s 1 while time averaged frontal currents varied from 11 2 to 17 6 cm s 1 in the shallowest bin in one out of three cases c which implied that there were faster currents than the rate of advance of the front and which implied that the origin of surface frontal material is behind the front not in front of it three invertebrate larval taxa were found at all sites across fronts but only two intertidal barnacles pollicipes polymerus and chthamalus spp were concentrated at the front s surface while the subtidal bryozoan membranipora spp was not frontal pollicipes were more concentrated than were chthamalus the frontal downwelling currents observed suggested that concentrated larvae would have to swim upward in order to maintain depth pollicipes were abundant on the offshore warm side of the fronts but were absent or rare on the onshore colder side suggesting that the origin of frontal pollicipes was behind the front although an alternative cannot be ruled out conclusively chthamalus were more abundant at depth than at the surface at all sites except at the front where this pattern was reversed the origin of frontal chthamalus is uncertain membranipora were more abundant on the onshore colder side of the fronts and abundances were usually higher at depth than at surface lack of accumulation in this species may be due to its limited swimming capability

depositional and post depositional geochemistry and its correlation with the geotechnical properties of marine clays in ariake bay japan the mineralogy geochemistry and geotechnical properties of clay samples in ariake bay japan are presented the mineralogy and geochemistry are discussed in terms of depositional and post depositional processes and the correlations of the clay mineralogy and geochemistry with the geotechnical properties were examined by multiple regression analysis the most predominant clay mineral in the deposits was found to be smectite the vertical distribution of trace elements in the deposits was indicative of the periodical changes in the parent materials involved in the depositional processes the chloride concentration in the pore water varied according to a change in the sea level from brackish to marine and then brackish towards the surface the higher iron oxide contents near the surface and in the deepest zones were the results of pyrite oxidation in the deposits due to weathering under subaerial conditions smectite content was the most predominant governing factor for the consistency limits and activi

a nonlinear model of the shoaling and refraction of interfacial solitary waves in the ocean part i development of the model and investigations of the shoaling effect abstract oceanic internal waves are frequently observed to be of large amplitude and to exhibit significant wave front curvature as seen in synthetic aperture radar images the aim of this paper is to present a refraction model in two horizontal dimensions including moderate amplitude effects to model these common properties of internal waves the model incorporates second order nonlinearity and uses a ray method to allow arbitrary refraction for these preliminary investigations with the model a two layer ocean is assumed with an upper layer thickness of 50 m and a density difference across the layers of 0 5 kg m 3 an important aspect affecting the refraction of nonlinear waves is shoaling as the phase speed of a nonlinear wave depends on its amplitude in part i of this paper the development of the model is described and the shoaling phenomenon is investigated in detail the shoaling of interfacial internal solitary waves over both slowly varying and rapidly varying bathymetry is studied a wedg

marine geology in the arc continent collision zone off southeastern taiwan implications for late neogene evolution of the coastal range abstract marine geology in the region between taiwan and luzon is characterized by a convergent tectonics in the south and an oblique arc continent collision in the north in the collision zone six geologic provinces are recognized they are the manila trench the accretionary prism of the hengchun ridge the sutural basin of the southern longitudinal trough the subduction melange of the huatung ridge the forearc basins of the taitung and the north luzon troughs and the volcanic arc of the north luzon ridge the oceanic crust of the south china sea is subducting eastward beneath the philippine sea plate along the manila trench south of 20 n further to the north the trench has changed progressively its axis toward the west from the subduction melanges off southeastern taiwan at 3 ma to the hengchun peninsula of southern taiwan at 2 1 ma and then to the present day location off southwestern taiwan because of the continuing collision and the westward shifting of the manila trench sediments deposited in the region are passively incorporated into the accretionary prism and deformed to the hengchun ridge after the collision the southern longitudinal trough consisting of a 2 km thick of orogenic sediments represents a sutural basin superposed on the plate boundary between the accretionary prism of the hengchun ridge asian continent and the subduction melange of the huatung ridge philippine sea plate the huatung ridge is a bathymetric high connected to the southern coastal range and is characteristic of low negative free air gravity and magnetic anomalies the ridge contains deeply weathered sedimentary blocks with abraded deep water late pliocene foraminifera and identical clay mineral compositions as those in the onshore lichi melange this implies that at least a portion of the huatung ridge is composed of melange materials and represents a former subduction zone extending from the lichi melange of the southern coastal range the north luzon trough and the taitung trough are the constructed foreac basins with 2 km of orogenic sediments unconformably overlying the volcanic islands and the subduction melange the taitung trough is southward connected to the north luzon trough through a bathymetric passage which was formed by narrowing the north luzon trough as a consequence of clockwise rotation of the lutao volcanic island during the late pleistocene a detailed study of the four neogene tectonostratigraphic units in the coastal range shows that the overall history of the formation of the range can be related to the present day geologic provinces and the on going collision processes in the region off southeastern taiwan the range had evolved from a southward accretion of the shuilien loho remnant forearc basin and the chimei volcanic pair at 2 ma followed by the chengkung taiyuan remnant forearc basin and the chengkuangao volcanic island pair at 1 ma and the taitung trough and the lutao volcanic island pair presently in process by analogy the northern part of the north luzon trough and the lanhsu volcanic island will be accreted to the coastal range in the next million years the paired forearc basin volcanic island accretion model proposed in this study may thus have implications for mountain ranges that evolved from similar tectonics of oblique arc continent collision

mechanisms of contamination in lesser antilles island arc magmas from radiogenic and oxygen isotope relationships abstract oxygen sr and nd isotopic compositions for 29 volcanic samples from the lesser antilles are reported these span a considerable range in 18o from values similar to those of mantle derived lavas 18o 6 6 to 18o 14 0 although the highest 18o results are obtained from evolved andesites and dacites there is no clear correlation between 18o and sio2 an attempt is made to eliminate the effects of varying magma chemistry on 18o through differentiation by normalising to the chemical index of garlick 1 this enables the effects on 18o of processes other than magmatic fractionation to be more clearly assessed it is concluded that the range in 18o values measured cannot result from hydrothermal interaction or weathering alone although limited alteration of a few samples may be responsible for some scatter in the oxygen isotope data when 18o is plotted against radiogenic isotopic compositions well correlated trends are observed 18o increases with increasing87sr 86sr and decreasing143nd 144nd such behaviour is consistent with the contamination of mantle derived magmas by variable amounts of an ancient crustal component the shapes of mixing curves defining this process suggest that contamination occurs largely within the arc crust constraints from geochemical and geophysical data suggest that a terrigenous sediment intercalated within the arc crust is assimilated however subsequent fractional crystallisation at more shallow levels in the crust has obscured any chemical trends which might have resulted from combined assimilation fractional crystallisation furthermore it is suggested that the mantle derived magma has already undergone source contamination by the introduction of a slab derived fluid into the overlying mantle wedge

observations of nonlinear internal waves on the outer new england continental shelf during the summer shelfbreak primer study observations are presented of nonlinear internal waves on the outer new england continental shelf during the summer shelfbreak primer study conducted between july 26 and august 5 1996 current and temperature measurements were made with an upward looking acoustic doppler current profiler adcp located on the 147 m isobath near the shelfbreak and three vertical thermistor moorings located upshelf data from the adcp and two nearby thermistor chains show energetic internal tides propagating at roughly 0 9 m s 21 to the north northwest nearly perpendicular to the local topography with 10 15 cm s 21 horizontal currents and 15 30 m vertical displacements these waves evolve rapidly within a 5 8 km range into an undular internal tidal bore cross isobath barotropic tidal currents responsible for generating the internal tides are in the 5 12 cm s 21 range the bore formation is highly variable there is evidence of a correlation between internal tide steepening and a shelfbreak front jet orientation that is oppositely directed to the internal tide propagation there is no correlation between steepening and the jet s vertical shear statistics of the undular bores show rms travel time fluctuations from 0 8 to 1 7 hours and average tidal bore durations from 12 to 9 hours the average undular bore speed is 0 9 m s 21 with an rms fluctuation of 0 4 m s 21 the number of high frequency waves in the bore varies from 0 to 8 near the shelfbreak and increases to 30 waves 26 7 km upshelf the observed distribution function of temporal spacing between high frequency internal waves is spread between 4 and 20 min

sea surface temperature signatures of oceanic internal waves in low winds 1 in aerial surveys conducted during the tropical ocean global atmosphere coupled ocean atmosphere response experiment and the low wind component of the coupled boundary layer air sea transfer cblast low oceanographic field programs sea surface temperature sst variability at relatively short spatial scales o 50 m to o 1 km was observed to increase with decreasing wind speed a unique set of coincident surface and subsurface oceanic temperature measurements from cblast low is used to investigate the subsurface expression of this spatially organized sst variability and the sst variability is linked to internal waves the data are used to test two previously hypothesized mechanisms for sst signatures of oceanic internal waves a modulation of the cool skin effect and a modulation of vertical mixing within the diurnal warm layer under conditions of weak winds and strong insolation which favor formation of a diurnal warm layer the data reveal a link between the spatially periodic sst fluctuations and subsurface temperature and velocity fluctuations associated with oceanic internal waves suggesting that some mechanism involving the diurnal warm layer is responsible for the observed signal internal wave signals in skin temperature very closely resemble temperature signals measured at a depth of about 20 cm indicating that the observed internal wave sst signal is not a result of modulation of the cool skin effect numerical experiments using a one dimensional upper ocean model support the notion that internal wave heaving of the warm layer base can produce alternating bands of relatively warm and cool sst through the combined effects of surface heating and modulation of wind driven vertical shear

volcanic facies analysis of a subaqueous basalt lava flow complex at hruskovec nw croatia evidence of advanced rifting in the tethyan domain abstract the hruskovec quarry of basaltoid rocks is situated on the northwestern slopes of mt kalnik within the zagorje mid transdanubian zone a part of the north western dinarides the basaltoids are inter bedded with radiolarites of the middle and upper triassic age langobardian carnian norian spilites altered diabases and meta basalts form part of triassic volcanic sedimentary sequence made of sandstones shales micritic limestone altered vitric tuffs and radiolarian cherts incorporated tectonically into the jurassic cretaceous melange the architecture of the 2 km long and 100 m high pile of the extrusive basaltoid rocks is interpreted as a subaqueous basaltic lava flow the presented research deals with a variety of volcanic facies of the subaqueous basaltic lava flow which consists of several facial units 1 coherent pillow lavas with massive core the bending rims around the massive core 30 50 cm thick are dissected by polygonal columnar joints radiating from the pillow centres 2 closely packed pillows densely packed and contorted pillows due to emplacement accommodation clearly younging upward 3 pillow fragment breccia clast supported matrix poor monomict breccia formed proximal to the axis of the extrusion 4 isolated pillow breccia matrix supported clast poor breccia made of lava pipes and tubes within a matrix of fine grained sideromelan granules and shards 5 pyjama style pillows spherical decimetre to meter size pillow lava balls grown and chilled in isostatic state i e in a state of diminished density contrast within water soaked sediments named after peculiar alternating basaltic shelves inside the sphere which are encrusted with white secondary minerals 6 peperite and peperitic hyaloclastites blocky and globular peperites developed at the contact of soft wet sediment and hot intruding magma discovery of peperite and peperitic hyaloclastites within the triassic radiolarian cherts shales and micritic limestone with registration of conodonts index microfossils links their origin to magmatism during advanced rifting in a progressively subsiding basin during the triassic it precludes an affiliation of the subaqueous basaltic lava flow with the dismembered ophiolite formation a product of oceanization created in jurassic cretaceous times which is a commonly stated alternative explanation the basaltic rocks and their sedimentary hosts may be correlated with advanced triassic rifting and related volcanic sedimentary successions in the dinarides albanides helenides and further along the tethyan orogenic belt

internal solitary waves in the warm pool of the western equatorial pacific abstract during the spring tides of late november 1992 early january and early february 1993 solitary internal wave packets were observed at 2 s 156 15 e in the western equatorial pacific apparently generated in the nuguria island group 3 s 153 e the waves propagate northeastward at 2 4 2 8 m s 1 appearing in fixed phase with the underlying semidiurnal baroclinic tide the initial solitary wave crests have downward displacements in excess of 60 m and peak velocities greater than 80 cm s 1 groups of 1 3 crests are observed with vertical structure resembling a first mode internal wave and horizontal variability consistent with third order comb kdv solitons many of the packets exhibit an overall organization reminiscent of undular bores this borelike behavior is confined primarily to the upper 70 m not sharing the mode one dependency of the crests the solitons displace the ambient equatorial currents including the equatorial undercurrent both vertically 80 m and laterally 1 2 km with l

submarine hydrothermal mineralization in the okinawa trough sw of japan an overview abstract the okinawa trough is a heavily sedimented rifted back arc basin formed in an intracontinental rift zone submarine hydrothermal activity is located within the six back arc rifts located in the middle and southern okinawa trough and its distribution is controlled principally by tectonic factors subduction of the daito and gagua ridges beneath the ryukyu arc has resulted in fracturing of the brittle lithosphere beneath the okinawa trough hydrothermal activity is strongest in the volcanic arc rift migration phenomenon vamp area plus the jade site and southernmost part of the okinawa trough spot area which form the prolongation of these two ridges these areas are characterized by extremely high heat flow locally submarine hydrothermal fluids from the okinawa trough tend to be strongly influenced by interaction of the hydrothermal fluids with organic matter in the sediment resulting in high alkalinity and nh 4 concentrations of the fluids the fluids also contain high concentrations of co 2 of magmatic origin submarine hydrothermal mineralization in the trough is diverse the clam site consists principally of carbonate chimneys interaction of the hydrothermal fluid with organic matter in the sediment is particularly strong at this site this is most probably a sediment hosted deposit in which sulphide minerals have deposited within the sediment column leaving spent ore fluids to emerge at the seafloor the jade site consists of active and inactive sulphide sulphate chimneys and mounds the zn pb rich sulphides at this site contain the highest concentrations of pb ag and au so far recorded in submarine hydrothermal sulphide deposits at minami ensei knoll and hatoma knoll active and inactive chimneys consist principally of anhydrite and barite as a result of phase separation of the hydrothermal fluids beneath the seafloor an intense black smoker has recently been discovered at yonaguni knoll in the spot area if it is confirmed that sulphide mineralization is dominant at this site this could be a highly prospective area the most prospective areas for economic grade minerals in the okinawa trough appear to be the jade site and the spot area

analyzing yengisogat glacier surface velocities with alos palsar data feature tracking karakoram china little is known about the detailed behavior of glaciers in the karakoram mountains advanced land observing satellite alos phased array type l band synthetic aperture radar palsar data were used to obtain the surface velocity of the yengisogat glacier in the karakoram mountains four alos palsar data sets with 46 days temporal baseline acquired from 2007 to 2009 covered all four seasons and were used to extract the offset fields and estimate annual average surface velocity based on seasonal velocities for the alos palsar data the synthetic aperture radar sar feature tracking procedures within the gamma software were utilized instead of sar interferometry because of low coherence in case of fast moving glaciers or large time intervals between the image acquisitions the accuracy of the measurements is discussed and the measurements were consistent with previous results from optical imagery feature tracking it was revealed that the south tributaries contributed to the main flow of the glacier with the glacier surface velocities of the south tributaries moving more rapidly than the north tributaries this was mainly attributed to the effect of the glacier s aspect in the glacier long term development point of view seasonal and spatial variations of the glacier surface velocity imply that the tributary south skamri glacier is probably surging this has previously been mentioned by some researchers such as copland et al the equilibrium line altitude was found to be at about 5 000 m a s l for south tributaries estimated from the surface velocity distribution along the glacier centerline

effects of moist froude number and cape on a conditionally unstable flow over a mesoscale mountain ridge abstract in this study idealized simulations are performed for a conditionally unstable flow over a two dimensional mountain ridge in order to investigate the propagation and types of cloud precipitation systems controlled by the unsaturated moist froude number fw and the convective available potential energy cape a two dimensional moist flow regime diagram based on fw and cape is proposed for a conditionally unstable flow passing over a two dimensional mesoscale mountain ridge the characteristics of these flow regimes are 1 regime i flow with an upstream propagating convective system and an early slowly moving convective system over the mountain 2 regime ii flow with a long lasting orographic convective system over the mountain peak upslope or lee slope 3 regime iii flow with an orographic convective or mixed convective and stratiform precipitation system over the mountain and a downstream propagating convective system and 4 regime iv flow with an orographic stratiform precipitatio

kurile island arc volcanism structural and petrological aspects abstract this study discusses the structural and spatial characteristics of all known kurile island arc quaternary volcanoes which include 105 that are subaerial and 96 submarine volcanic activity in the island arc is distributed in two zones parallel to the kurile kamchatka deep sea trench the depth to the seismo focal zone in the frontal zone is 110 140 km and in the rear zone 160 190 km these frontal and rear volcanic zones show distinct variations in geochemical petrologic and mineralogic characteristics concentrations of k rb ba sr f be la ce nb zr u th ni and cr in similar volcanic rocks of the rear zone are typically more than twice as high as those in rocks of the frontal zone whereas concentrations of fe and v are half as high in the rear zone lavas as in those of the frontal zone variations in concentration along the strike of the arc are less pronounced the average 87 sr 86 sr ratios for the frontal and rear zones are northern kuriles 0 70322 and 0 70304 middle kuriles 0 70302 and 0 70295 and southern kuriles 0 70347 and 0 70306 respectively 143 nd 144nd values in lavas from the frontal and rear zones are 9 10 and 7 8 respectively be abundances in the kurile island arc lavas range from 2 2 10 6 at g to 7 9 10 6 at g no differences in 10 be abundances corresponding to the frontal and rear arc zones have been found acid and intermediate lavas from the volcanic front are characterized by a two pyroxene phenocryst association while similar lavas from the rear arc have amphibole and biotite bearing associations mineral compositions plagioclase pyroxene amphibole olivine in the two zones also show distinct differences plagioclase in the rear arc lavas is less calcic with higher k sr ba and lower fe than in the frontal lavas ferromagnesian minerals in the rear arc lavas contain less fe and more mg than in frontal lavas these data are used to develop a model for magma generation related to two levels of volatile separation from the subducting lithospheric plate

tectonics basin subsidence mechanisms and paleogeography of the caribbean south american plate boundary zone abstract using a mega regional dataset that includes over 20 000 km of on and offshore 2d seismic lines and 12 wells we illustrate three different stages of fault formation and basin evolution in the caribbean arc south american continent collisional zone transpressional deformation associated with oblique collision of the caribbean arc migrates diachronously over a distance of 1500 km from western venezuela in paleogene time 57 ma to a zone of active deformation in the eastern offshore trinidad area each diachronous stage of pre syn and post collisional basin formation is accompanied by distinct patterns of fault families we use subsidence histories from wells to link patterns of long term basinal subsidence to periods of activity of the fault families stage one of arc continent collision initial collision is characterized by overthrusting of the south and southeastward facing caribbean arc and forearc terranes onto the northward subducting mesozoic passive margin of northern south america northward flexure of the south american craton produces a foreland basin between the thrust front and the downward flexed continental crust that is initially filled by clastic sediments shed both from the colliding arc and cratonic areas to the south as the collision extends eastward towards trinidad this same process continues with progressively younger foreland basins formed to the east on the overthrusting caribbean arc and forearc terranes north south rifting adjacent to the collision zone initiates and is controlled by forward momentum of southward thrusting arc terranes combined with slab pull of the underlying and subducting north dipping south american slab uplift of fold thrust belts arc continent suture induces rerouting of large continental drainages parallel to the collisional zone and to the axis of the foreland basins stage two this late stage of arc continent collision is characterized by termination of deformation in one segment of the fold thrust belt as convergent deformation shifts eastward rebound of the collisional belt is produced as the north dipping subducted oceanic crust breaks off from the passive margin inducing inversion of preexisting normal faults as arc continent convergence reaches a maximum strain partitioning also begins to play an important role as oblique convergence continues accommodating deformation by the formation of parallel strike slip fault zones and backthrusting southward subduction of the caribbean plate beneath the south caribbean deformed belt as subsidence slows in the foreland basins sedimentation transitions from a marine underfilled basin to an overfilled continental basin offshore sedimentation is mostly marine sourced by the collided caribbean terranes localized islands and carbonate deposition stage three this final stage of arc continent collision is characterized by 1 complete slab breakoff of the northward dipping south american slab 2 east west extension of the caribbean arc as it elongates parallel to its strike forming oblique normal faults that produce deep rift and half grabens 3 continued strain partitioning strike slip faulting and folding the subsidence pattern in the caribbean basins is more complex than interpreted before showing a succession of extensional and inversion events the three tectonic stages closely control the structural styles and traps source rock distribution and stratigraphic traps for the abundant hydrocarbon resources of the on and offshore areas of venezuela and trinidad

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

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

seismic structure of the upper mantle beneath the philippine sea from seafloor and land observation implications for mantle convection and magma genesis in the izu bonin mariana subduction zone abstract we have determined the three dimensional shear wave speed structure of the upper mantle in and around the philippine sea region using seismograms recorded by dense land based and long term broadband ocean bottom seismographic stations we used a surface wave tomography technique in which multimode phase speeds are measured and inverted for a 3 d shear wave speed structure by incorporating the effects of a finite frequency and ray bending the new ocean bottom data provided us with improved spatial resolution 300 km in the philippine sea region in the upper 120 km the shear wave speed structure is well correlated with seafloor age at depths greater than 160 km fast anomalies of the subducting pacific plate are clearly defined we also found slow speed anomalies beneath the kyushu palau ridge at depths greater than 120 km along the izu bonin ogasawara mariana arc we have detected three separate slow anomalies in the mantle wedge at depths shallower than 100 km beneath the back arc each anomaly has a width of 500 km moreover these three anomalies have a close relationship with the three groups of frontal and rear arc volcanoes having distinct sr nd and pb isotope ratios we suggest that each of the anomalies is a site of large scale flow of upper mantle into the mantle wedge and that each already contains a component from the adjacent subducting slab

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

magma mingling in the tungho area coastal range of eastern taiwan article i nfo complex rocks consisting of different lithologic breccias and sediments in the tungho area of the southern coastal range eastern taiwan were formed by magmas and magma sediment mingling based on field occurrences petrography and mineral and rock compositions three components including mafic magma felsic magma and sediments can be identified the black breccias and white breccias were consolidated from mafic and felsic magma respectively isotopic composition shows these two magmas may be from the same source compared to the white breccias the black breccias show clast supported structures higher an values in plagioclase higher contents of mgo cao and fe2o3 and lower sio2 greater enrichment in the light rare earth elements lree and depletion in the heavy rare earth elements hree the white breccias show matrix supported blocks and mingling with tuffaceous sediments to form peperite physical and chemical evidence shows that the characteristics of these two components mafic and felsic magmas are still apparent in the mingled zone according to their petrography mafic and felsic magmas did not have much time for mingling white intrusive structures and black flow structures show that mingling occurred before they solidified finally the occurrence of mingling between magmas and sediments suggests that the mingling has taken place at the surface and not in the magma chamber

observations of internal bores and waves of elevation on the new england inner continental shelf during summer 2001 1 during july august 2001 oceanographic variability on the new england inner continental shelf was investigated with an emphasis on temporal scales shorter than tidal periods mooring and ship survey data showed that subtidal variation of inner shelf stratification was in response to regional ekman upwelling and downwelling wind driven dynamics high frequency variability in the vertical structure of the water column at an offshore mooring site was linked to the baroclinic internal tide and the onshore propagation of nonlinear solitary waves of depression temperature salinity and velocity data measured at an inshore mooring detected a bottom bore that formed on the flood phase of the tide during the ebb tide a second bottom discontinuity and series of nonlinear internal waves of elevation iwoe formed when the water column became for a time under hydraulic control a surface manifestation of these internal wave crests was also observed in aircraft remote sensing imagery the coupling of iwoe formation to the offshore solitary waves packets was investigated through internal wave breaking criterion derived in earlier laboratory studies results suggested that the offshore solitons shoaled on the sloping shelf and transformed from waves of depression to waves of elevation the coupling of inshore bore formation to the offshore solitary waves and the possible impact of these periodic features on mixing on the inner shelf region are discussed

miocene to recent calc alkalic volcanism in eastern taiwan k ar ages and petrography abstract k ar radiometric datings are presented for volcanic rocks from the coastal range of taiwan and from lanhsu and lutao islands the samples involved are basalts andesites and dacites which show the main petrological and geochemical characteristics of island arc magmas the k ar data show that volcanic activity occurred from early miocene to early pliocene times in the coastal range and in lanhsu island and during pliocene times ca 1 3 4 3 ma in lutao island the geological significance of early and middle miocene ages is discussed with respect to hydrothermal metasomatic alterations which have affected most of the samples a significant increase in incompatible elements e g k and sr is shown to have occurred during pliocene to recent times and is exemplified by the compositions of the lanhsu and lutao volcanic rocks the origin of these chemical variations is related to the magmatic effects of crustal thickening linked to the transition from subduction to collision regimes

internal wave breaking at concave and convex continental slopes abstract internal wave reflection from a sloping topographic boundary may lead to enhanced shear if the topographic angle to the horizontal is close to that of the internal wave group velocity vector previous analytic studies have suggested that shear enhancement is reduced at concave slopes as compared with convex and planar slopes near the critical angle here the internal wave reflection from concave and convex slopes that pass through the critical angle is investigated numerically using the nonhydrostatic massachusetts institute of technology general circulation model mitgcm overturning shear instability and resultant mixing are examined results are compared with simulations of wave reflection from planar slopes with angles greater than less than and equal to the critical angle in contrast to the analytic predictions no reduction in mixing is found for the concave slope as compared with the other slopes in all cases stratification is eroded in a band above the slope bounded at its outer

shoaling of nonlinear internal waves in massachusetts bay 1 the shoaling of the nonlinear internal tide in massachusetts bay is studied with a fully nonlinear and nonhydrostatic model the results are compared with current and temperature observations obtained during the august 1998 massachusetts bay internal wave experiment and observations from a shorter experiment which took place in september 2001 the model shows how the approaching nonlinear undular bore interacts strongly with a shoaling bottom offshore of where kdv theory predicts polarity switching should occur it is shown that the shoaling process is dominated by nonlinearity and the model results are interpreted with the aid of a two layer nonlinear but hydrostatic model after interacting with the shoaling bottom the undular bore emerges on the shallow shelf inshore of the 30 m isobath as a nonlinear internal tide with a range of possible shapes all of which are found in the available observational record

constraints on backstop geometry of the southwest ryukyu subduction based on reflection seismic data abstract based on the analysis of 45 seismic reflection profiles the top of the ryukyu arc basement is mapped in the forearc region east of taiwan the ryukyu arc slope dips 10 trenchward while beneath the forearc basins the arc basement shows a series of morphologic along arc highs and lows one of the basement highs the nanao basement rise has been described as an area uplifted by the subduction of the gagua ridge the other one the hoping basement rise is suggested in this study to be an uplifted feature caused by the subduction or the underplating of some local asperity the nature of this asperity could either be a detached block of the luzon arc an isolated seamount or some material removed from the frontal part southernmost extremity of the ryukyu margin from seismic reflection profiles we infer that the right lateral transcurrent fault system located at the rear of the accretionary wedge defines the surface projection of the southern termination of the ryukyu arc basement two crustal sections across the ryukyu subduction system demonstrate that the backstop terminates in the form of a near vertical wall with its height over 5 km such an unusual geometry could be produced by crustal truncation at the toe of the backstop

geodynamic processes of taiwan arc continent collision and comparison with analogs in timor papua new guinea urals and corsica abstract the taiwan arc continent collision involves four geodynamic processes intra oceanic subduction initial arc continent collision advanced arc continent collision and arc collapse subduction these processes now occur simultaneously in 19 24 30 n but have operated sequentially southward since the late miocene although the geological and geophysical features appear to change progressively from north to south across the island they are distinct within individual tectonic regimes using the present scenario as a basis for comparison it is suggested that timor is at the initial arc continent collision stage while papua new guinea and urals proceeded to the advanced arc continent collision stage however corsica represents an even more advanced stage than in taiwan where a previously accreted arc has collapsed and been totally removed

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

submarine volcaniclastic rocks in this chapter we are concerned with underwater volcaniclastic eruptions and products as well as pyroclastic flows and debris generated on land and transported by mass flowage into the sea submarine fallout deposits derived from land based eruptions are treated in chapter 7 clastic materials redistributed as mass flows or turbidity currents originating from the rapid build up of tephra and epiclastic volcanic debris along coastal parts of volcanoes are also discussed in various places throughout the text e g chap 13

facies variation of eruption units produced by the passage of single pyroclastic surge currents hopi buttes volcanic field usa abstract base surges are a significant volcanic hazard associated with phreatomagmatism but their transport and depositional dynamics are incompletely understood stratigraphic analysis and lateral tracing of surge eruption units produced by the passage of single base surges from haskie tuff ring hopi buttes volcanic field usa extend to 1 km from the vent and show similar downcurrent changes in lithofacies within 200 m of the vent eruption units are primarily disorganized lapilli tuff that is rich in juvenile pyroclasts at distances 200 m from the vent eruption units transform into a couplet of juvenile rich lapilli that grades upward into bedform bearing ash tuff at distances 900 m upper and lower beds of the eruption unit couplet transform into planar stratified beds at distances 1100 m couplets composing different eruption units are almost entirely composed of planar beds and amalgamate to form almost identical planar bedded ash tuff the collapse of dense eruption columns following explosive magma wet sediment interaction generated turbulent surge currents as the surges traveled away from the haskie vent they expanded and partitioned into a basal juvenile rich traction carpet and overlying accidental rich ash cloud surge near the limit of their runout the surges cooled and lost their pyroclastic load leaving planar beds of accidental rich ash the deposition of multiple surge eruption units with similar lateral and vertical facies transitions and a paucity of interbedded fallout suggests an eruption characterized by recurring phreatomagmatic explosions of similar size and the generation of surges with similar flow characteristics

flow separation and resuspension beneath shoaling nonlinear internal waves 1 laboratory observations are presented showing the structure and dynamics of the turbulent bottom boundary layer beneath nonlinear internal waves nliws of depression shoaling upon sloping topography the adverse pressure gradient beneath the shoaling waves causes the rear face to steepen flow separation to occur and wave induced near bottom vortices to suspend bed material the resuspension is directly attributed to the near bed viscous stress and to near bed patches of elevated positive reynolds stress generated by the vortical structures these results are consistent with published field observations of resuspension events beneath shoaling nliws elevated near bed viscous stresses are found throughout the domain at locations that are not correlated to the resuspension events near bed viscous stress is thus required for incipient sediment motion but is not necessarily a precursor for resuspension resuspension is dependent on the vertical velocity field associated with positive reynolds stress and is also found to occur where the mean wave averaged vertical velocity is directed away from the bed the results are interpreted by analogy to the eddy stress and turbulent bursting resuspension models developed for turbulent channel flows

contrasting timescales of crystallization and magma storage beneath the aleutian island arc abstract geologic chronologic and u th isotope data from pleistocene recent basaltic to rhyolitic lavas and their phenocrysts constrain the long term evolution of magmatic processes at seguam island aleutian island arc and suggest a model in which erupted magmas were derived from a single deep seated reservoir for 130 kyrs of its eruptive history the monotonic evolution in 230 th 232 th 0 ratios is consistent with radiogenic ingrowth of 230 th in a long lived magma reservoir between 142 and 9 ka internal u th mineral isochrons from seven lavas and one ignimbrite are indistinguishable from their eruption ages as constrained by 40 ar 39 ar dating which implies a short period i e 10 3 yrs or less of crystal residence in the magma prior to eruption these results can be reconciled if small batches of magma are repeatedly extracted from a deep thermally buffered basaltic reservoir followed by decompression driven crystallization and differentiation in small chambers or conduits in the upper crust immediately prior to eruption stratovolcano collapse at 9 ka produced a 4 km diameter caldera and a 70 m thick dacitic ignimbrite covering 12 km 2 the ignimbrite as well as subsequent rhyolitic and basaltic lava flows signal a decrease in 230 th 232 th 0 and 87 sr 86 sr ratios the abrupt change in magma composition at 9 ka most likely reflects disruption of the long lived reservoir by rapid ascent of basaltic magma with low 230 th 232 th and 87 sr 86 sr ratios and excess 226 ra while the physiochemical connection between cone collapse and rise of new magma into the shallow crust remains to be explored the shift in isotopic composition and evidence for a protracted 100 kyr period of magma storage would have been missed had the focus been on only the most recent historical eruptions our results suggest that not all arc basalt produced in the mantle wedge separates and ascends rapidly magma ascent rates and storage times may vary significantly over periods of 10 4 to 10 5 yrs at a single arc volcano and u th isotopes offer a means of better understanding relationships between explosive eruptions and changes in magma reservoir dynamics in island arcs provided a sufficiently long period of volcanic activity is examined

lava sediment interaction in desert settings are all peperite like textures the result of magma water interaction abstract this study reports on lava sediment interaction in dry depositional settings focusing on the early cretaceous volcano sedimentary sequence in the huab basin nw namibia as a detailed example here an active aeolian sand sea erg system was progressively engulfed by lavas of the etendeka flood basalt province 133 ma bp this volcanic flooding resulted in 1 the unprecedented preservation of large parts of the active dune system 2 the development of a variety of sediment interlayers and 3 a record of excellent examples of the dynamic interaction between lava and aeolian sand the lava sediment interaction happens on a variety of scales from simple sediment interbeds within the lavas at a large scale down to complex breccia horizons and bulbous lava sediment contacts at small scales peperite like textures are found where hot lava has dynamically interacted with unconsolidated aeolian sands such interaction could involve lava cascading down the front of dune faces or active aa style flow fronts bulldozing into and oversteepening dune faces causing rapid influx of sand into the active flow front resulting breccia horizons have been found up to 5 m thick locally the aeolian sand is baked to a quartzite by the hot lava in contrast on other surfaces the lava leaves striations in the sand as it flows across it indicating local flow directions and less pronounced interaction in places wind ripples and topset beds are preserved on the stoss side of the dune indicating the passive nature of emplacement for some of the lava flows peperites are often thought to form due to the presence of water within the unconsolidated sediments that the juvenile magma comes into contact with however examples from arid environments demonstrate that peperite forming processes are diverse and may not always require water therefore it is suggested that the term peperite should be used to describe deposits consisting of sediments mixed with juvenile magmatic components where it is clear that there has been a dynamic interaction between the two this leaves the presence or lack of water as an issue for interpreting the processes by which the peperite formed

giant tuff cone and 12 km wide associated caldera at ambrym volcano vanuatu new hebrides arc abstract ambrym in the new hebrides arc has been considered as an effusive basaltic volcano the present paper discusses the general structure of this edifice which consists of a basal shield volcano topped by an exceptionally large tuff cone surrounding a 12 km wide summit caldera dacitic pyroclastic flow deposits are exposed in the lower part of the tuff series they grade upward into composite sequences of bedded surtseyan type hyaloclastites ash flow deposits and fallout tephra which are essentially basaltic in composition in such a way that the tuff cone may be considered as mainly basaltic the relationship between the eruption of pyroclastics and the collapse event precludes a classical model of caldera formation at a basaltic volcano in which quiet subsidence i e kilauea type is the dominant mechanism interpretation of the tuff series implies intervention of external water and suggests both explosive and collapse mechanisms a model of caldera formation which assumes an enlargement of the ring fracture during a first plinian and dacitic then essentially hydrobasaltic eruption is proposed

evolution and petroleum geology of amlia and amukta intra arc summit basins aleutian ridge abstract amlia and amukta basins are the largest of many intra arc basins formed in late cenozoic time along the crest of the aleutian arc both basins are grabens filled with 2 5 km of arc derived sediment a complex system of normal faults deformed the basinal strata although initial deposits of late micocene age may be non marine in origin by early pliocene time most of the basinfill consisted of pelagic and hemipelagic debris and terrigenous turbidite deposits derived from wavebase and subaerial erosion of the arc s crestal areas late cenozoic volcanism along the arc commenced during or shortly after initial subsidence and greatly contributed to active deposition in amlia and amukta basins two groups of normal faults occur major boundary faults common to both basins and intra basin faults that arise primarily from arc parallel extension of the arc the most significant boundary fault amlia amukta fault is a south dipping growth fault striking parallel to the trend of the arc displacement across this fault forms a large half graben that is separated into the two depocentres of amlia and amukta basins by the formation of a late cenozoic volcanic centre seguam island faults of the second group reflect regional deformation of the arc and offset the basement floor as well as the overlying basinal section intra basin faults in amlia basin are predominantly aligned normal to the trend of the arc thereby indicating arc parallel extension those in amukta basin are aligned in multiple orientations and probably indicate a more complex mechanism of faulting displacement across intra basin faults is attributed to tectonic subsidence of the massif aided by depositional loading within the basins in addition most intra basin faults are listric and are associated with high growth rates although the hydrocarbon potential of amlia and amukta basins is difficult to assess based on existing data regional considerations imply that an adequate thermal history conducive to hydrocarbon generation has prevailed during the past 6 5 my the possibility for source rocks existing in the lower sections of the basins is suggested by exposures of middle and upper miocene carbonaceous mudstone on nearby atka island and the implication that euxinic conditions may have prevailed during the initial formation of the basins large structures have evolved to trap migrating hydrocarbons but questions remain concerning the preservation of primary porosity in a sedimentary section rich in reactive volcaniclastic debris

diking young volcanism and diffuse hydrothermal activity on the southern mid atlantic ridge the lilliput field at 9 33 s detailed exploration with remotely operated and autonomous deep submergence vehicles has revealed at 9 degrees 33 s the presence of the southernmost active hydrothermal field known so far on the mid atlantic ridge the size of the hydrothermal field which we have named lilliput is about 1000 m x 250 m it lies in a water depth of 1500 m on a ridge segment segment a3 with considerably thickened crust of 11 km four relatively small diffuse vent sites occur on a large young estimated 100 years old lava flow partly covering the flow with hydrothermal fe oxide hydroxide sediments based on homogeneous major element compositions of ca 25 lava samples this flow covers an area of at least 5 km x 0 6 km the lava flow erupted from a series of parallel fissures at the western edge of the flow and a volcanic ridge consisting of up to 30 m high pillow mounds the volcanic ridge probably represents the surface expression of an underlying dike which fed the flow several drained lava pond structures were observed within the flow but only one shows hydrothermal activity the hydrothermal venting and precipitation of abundant fe oxyhydroxides appear to be related to the young diking and eruption event and the four different hydrothermally active sites of the lilliput field lie along and almost equidistant from the eastern flank of the supposed dike although a hydrothermal plume some 500 m above the seafloor was found in two consecutive years 2005 and 2006 no high temperature venting associated with lilliput has been found in agreement with findings at other ridges with thick crust such as reykjanes high magma supply rate and frequent diking and eruption events may lead to hot hydrothermal vents being rare in slow spreading segments with thick crust whereas diffuse venting is abundant interestingly the fauna at the lilliput vents largely consists of small and apparently juvenile mussels bathymodiolus sp and did not show any signs of growth during the four years of continuing observations possibly reflecting pulsing hydrothermal activity

an assessment of 40ar39ar dating for the whole rock volcanic samples from the luzon arc near taiwan from electron microprobe petrographic and image analyses of samples from the northern tip of the luzon arc the effects of various alteration reactions phenocryst and groundmass assemblages on the whole rock 40ar39ar step heating spectra have been delineated the alteration of primary hornblende to an assemblage of zoisite chlorite sphene the palagonitization of glass and the crystallization of phillipsite tends to cause discordant 40ar39ar dates in the low temperature steps of the age spectra discordant 40ar39ar dates in the high temperature steps appear to result from degassing of inherited or trapped 40ar from coarse grained phenocrysts samples in which most of the k resides in groundmass plagioclase tend to yield meaningful plateau dates whereas samples in which most of the k resides primarily in palagonitized glass tend to yield meaningless plateau and isochron dates substantial loss of 39ar 13 40 occurred from irradiated samples prior to 40ar39ar step heating analysis which appears to be correlated with the abundance of groundmass and the degree of alteration this argon loss is attributed to thermally induced argon diffusion from the fine grained groundmass plagioclase glass and alteration phases during the pre step heating bakeout

age geochemical and isotopic variations in volcanic rocks from the coastal range of taiwan implications for magma generation in the northern luzon arc abstract this paper reports the first systematic analysis of age and geochemical variations in volcanic rocks from the coastal range of taiwan the northern luzon arc the rocks recovered from four main volcanoes vary from low k tholeiitic to medium k calc alkaline basalts to dacites the rocks are typical of arc magmatic products exhibiting enrichment in the large ion lithophile elements and depletion in the high field strength elements our new 40ar 39ar age data constrain the youngest eruption time in each of the four volcanoes i e from north to south at 7 2 ma yuemei 4 2 ma chimei 6 2 ma chengkuang ao and 8 5 ma tuluanshan respectively these data indicate that volcanism in the northern luzon arc did not cease progressively from north to south as previously alleged the high and broadly uniform nd isotope ratios end 10 1 to 8 8 and trace element characteristics of the rocks suggest a principal magma source from the depleted mantle wedge their overall geochemical variations are ascribed to magma chamber processes the effects of magmatic differentiation and crustal contamination differ among each volcano most likely owing to the discrepancy of residence time in individual magma chambers consequently we propose a binary mixing model for the magma generation that involves arc magmas sourced from the depleted mantle wedge and up to 5 crustal contamination with a continental fragment split off from the eurasian margin

observations of highly nonlinear internal solitons over the continental shelf surface disturbances caused by strong near surface internal waves are widely seen in coastal regions as bands of slick and rough water propagating shoreward these surface slicks are typically manifestations of optical and radar backscatter properties above internal solitons and have strong surface current pulses associated with them during a recent experiment studying coastal internal waves extremely strong solitary internal wave packets were observed over a three week period on a very shallow and strongly stratified pycnocline off northern oregon during periods of strongest tidal forcing solitons were consistently observed on the leading edge of a semidiurnal internal tide bore with pycnocline displacements up to 25m downward from a 7m initial depth in the first few solitons the extreme nonlinearity of these internal waves is believed to be unique in ocean observations this note characterizes these highly nonlinear solitary internal waves siw and presents a second order kdv model which reproduces the form of the displacements and the small change in soliton width with amplitude predicted by this model

observations of the internal tide and associated mixing across the malin shelf 1 an energetic internal tide was observed at two contrasting shelf continental sites to the west of scotland the first site was 5 km shoreward of the continental shelf break and the second was 45 km directly to the east of the first site each site was instrumented with a seabed mounted acoustic doppler current profiler and thermistor chain for a 2 week period in july 1996 when thermal stratification was well developed in addition to the measurements of the evolution of the water column structure and flow field two series of measurements of the rate of dissipation of turbulent kinetic energy were made at each of the sites the barotropic tide was found to contain an unusually strong diurnal component thought to be due to a coastally trapped wave as a result there is a significant diurnal component to the baroclinic energy spectra significant peaks are also present in the baroclinic energy spectra at interaction frequencies between the main semidiurnal m2 and diurnal k1 tidal constituents at both sites observations of profiles of the rate of dissipation of turbulent kinetic energy show a significant proportion of the measured rate of dissipation took place within the thermocline close to the shelf edge detailed observations of a hydraulic jump and nonlinear internal waves are analyzed to show significantly stronger mixing at this site characterized by diffusion coefficients of 1 6 and 6 1 10 4 m2 s 1 than at the site farther onshore where the diffusion coefficient is estimated to be 0 7 10 4 m2 s 1

effects of ambient velocity shear on nonlinear internal wave associated mixing at the columbia river plume front 1 large amplitude nonlinear internal waves nliws are frequently observed propagating away from columbia river tidal plume fronts they are generated because of the deceleration of the frontal bulge during the river influences on shelf ecosystems project cruises the velocity density structure and acoustic backscatter of the plume fronts and frontal nliws were observed using a towed vehicle vessel mounted instrumentation and a vessel x band radar these observations indicate that in the presence of strong ambient velocity shear the nliws with maximum amplitudes occur well below the density interface and at a depth deeper than in the absence of shear this deepening of the nliw shear is associated with intensified vertical mixing below the interface this is consistent with a dynamic analysis of nliws under the influence of sheared ambient flow obtained from a high order kdv model there are two mechanisms responsible for the vertical turbulent mixing intensification the nonlinear interaction between ambient shear and the nliws increases total velocity shear and causes the gradient richardson number rig to decrease below a critical value in certain depth ranges also because of the presence of the ambient shear the maximum nliw velocity shear occurs at a depth below the density interface where there is less stratification

internal waves and mixing near the kerguelen plateau abstractin the stratified ocean turbulent mixing is primarily attributed to the breaking of internal waves as such internal waves provide a link between large scale forcing and small scale mixing the internal wave field north of the kerguelen plateau is characterized using 914 high resolution hydrographic profiles from novel electromagnetic autonomous profiling explorer em apex floats altogether 46 coherent features are identified in the em apex velocity profiles and interpreted in terms of internal wave kinematics the large number of internal waves analyzed provides a quantitative framework for characterizing spatial variations in the internal wave field and for resolving generation versus propagation dynamics internal waves observed near the kerguelen plateau have a mean vertical wavelength of 200 m a mean horizontal wavelength of 15 km a mean period of 16 h and a mean horizontal group velocity of 3 cm s 1 the internal wave characteristics are dependent on regional dynamics suggesting tha

a mass wasting dominated quaternary mountain range the coastal range in eastern taiwan abstract fluvial bedrock incision which creates topographic relief and controls hillslope development has been considered the key medium linking denudation and tectonic uplift of unglaciated mountains this article however shows a different scenario from the coastal range in eastern taiwan this range with the steepness inherited from pre orogenic volcanoes has been subject to mass wasting even before its emergence above sea level no earlier than middle pleistocene numerous terraced alluvial fans fan deltas record the ancient mass movements of the range including rock avalanches multiple radiocarbon dates 1 km 2 alluvial terraces are typically exhibited close to the source ridges of mass movements and strath terraces along the downstream parts of rivers both were created when enormous sediment supply had exceeded or matched the prevailing river transport capacity this process along with the protection by giant boulders from mass movement disturbed the long term incision trend of rivers in response to tectonic uplift as a result the observed holocene bedrock incision at most sites has not kept pace with the tectonic uplift the spatial contrast in mass wasting histories further accounts for the great diversity of the terrace sequences even in areas with similar tectonic and base level conditions

the volcanoes of an oceanic arc from origin to destruction a case from the northern luzon arc abstract volcanoes were created grew uplifted became dormant or extinct and were accreted as part of continents during continuous arc continent collision volcanic rocks in eastern taiwan s coastal range cr are part of the northern luzon arc an oceanic island arc produced by the subduction of the south china sea plate beneath the philippine sea plate igneous rocks are characterized by intrusive bodies lava and pyroclastic flows and volcaniclastic rocks with minor tephra deposits based on volcanic facies associations sr nd isotopic geochemistry and the geography of the region four volcanoes were identified in the cr yuemei chimei chengkuangao and tuluanshan near vent facies associations show different degrees of erosion in the volcanic edifices for chimei chengkuangao and tuluanshan yuemei lacks near vent rocks implying that yuemei s main volcanic body may have been subducted at the ryukyu trench with the northward motion of the philippine sea plate these data suggest a hypothesis for the evolution of volcanism and geomorphology during arc growth and ensuing arc continent collision in the northern luzon arc which suggests that these volcanoes were formed from the seafloor emerging as islands during arc volcanism they then became dormant or extinct during collision and finally were uplifted and accreted by additional collision the oldest volcano yuemei may have already been subducted into the ryukyu trench

geochemistry and tectonic setting of the luzon arc philippines miocene 10 ma to recent volcanism is associated with eastward subduction along the manila trench for some 1 200 km from the coastal range in taiwan south to min doro we suggest calling this the luzon arc there are five distinct segments along this arc mindoro bataan northern luzon babuyan and taiwan the bataan and mindoro segments in the south are separated by a northeast southwest zone of volcanoes the northern luzon segment consists of pliocene to pleistocene necks and plugs that run along the entire western section of northern luzon the babuyan segment 10 ma to recent is made up of a larger number of active volcanoes than are other segments of the luzon arc the taiwan segment is composed entirely of extinct volcanoes in the coastal range and on the islands of lanhsu and lutao late miocene to 1 8 ma the nature of volcanism throughout the luzon are is clearly subduction related with calc alkaline affinities high th la ratios and negative nb ta and ti anomalies the earliest phase of volcanism so far recorded 10 ma however is tholeiitic island of calayan in the babuyan segment with mid oceanic ridge basalt like morb like tight rare earth element and large ion lithophile element concentrations and low th u ratios there are clear differences in sr and nd isotopic ratios among the samples from the luzon are samples from the southern segments mindoro through bataan fall within the mantle array with higher sr and lower nd isotopic values than those of morb pb isotope data indicate sediment involvement the isotopic values have been interpreted to result from source contamination by slab derived fluids bataan segment and by subducted crustal material from collision of the mindoro palawan terrane mindoro segment with the manila trench in contrast babuyan segment samples north have unusual island arc nd and sr isotopic ratios that fall below the mantle array they appear to be the result of sediment source contaminants or a unique mantle composition incorporation of sediments analyzed from eastern china and taiwan into a morb type mantle can explain the nd and sr isotopic ratios of the babuyan segment

simulation of the transformation of internal solitary waves on oceanic shelves abstract internal solitary waves transform as they propagate shoreward over the continental shelf into the coastal zone from a combination of the horizontal variability of the oceanic hydrology density and current stratification and the variable depth if this background environment varies sufficiently slowly in comparison with an individual solitary wave then that wave possesses a soliton like form with varying amplitude and phase this stage is studied in detail in the framework of the variable coefficient extended korteweg de vries equation where the variation of the solitary wave parameters can be described analytically through an asymptotic description as a slowly varying solitary wave direct numerical simulation of the variable coefficient extended korteweg de vries equation is performed for several oceanic shelves north west shelf of australia malin shelf edge and arctic shelf to demonstrate the applicability of the asymptotic theory it is shown that the solitary wave may maintain its sol

isotopic characteristics of subduction fluids in an intra oceanic setting izu bonin arc japan new radiogenic isotope and trace element data are presented for the volcanic sequences along 600 km of the active izu bonin arc the oligocene izu arc and their associated rift basins as with many intra oceanic island arcs the pliocene recent izu bonin frontal arc lavas are highly depleted in zr nb and the rare earth elements relative to typical mid ocean ridge basalt morb indicating that the mantle wedge source has undergone a previous episode of melting ratios between these elements such as nb zr and la sm as well as 143nd 144nd do not vary significantly along the length of the frontal arc these parameters suggest that each of the arc volcanoes is derived from similar melt fractions of the mantle wedge however ba zr ba rb and 87sr 86sr increase along the frontal arc to the north this leads us to propose that a variable enrichment in ba and radiogenic sr is superimposed on the mantle wedge sr nd and pb nd isotope variation indicate that both sr and pb become more radiogenic after fluid addition however pb isotope ratios do not correlate with increases in pb concentration or ratios such as ba zr and nb pb in other words the pb isotopic composition of the arc lavas appears to be independent of the amount of pb introduced by subduction fluids into the mantle source this buffering of pb isotopes along the frontal arc means that the isotopic composition of the lavas is indistinguishable from that of the fluid isotopic mixing models presented for the arc are only illustrative of the many plausible combinations of components and quantities despite this we are able to determine that the mantle wedge has isotopic characteristics similar to indian ocean morb and that the subduction fluid solute is primarily derived from subducted oceanic basalt with a 2 contribution from subducted sediment lavas in the oligocene izu arc and fore arc basin were derived from a mantle wedge of similar composition to the active arc despite levels of pb enrichment comparable to those of the modern arc the pb isotopes of the oligocene volcanics indicate a lower sediment input into the melting region

extensional collapse of the northern taiwan mountain belt as an active collision zone between the luzon arc and the china continental margin the taiwan mountain belt particularly its south central part is undergoing crustal shortening and rapid uplift the northern part of the orogen is however subjected to crustal stretching and rifting as a result of flipping of subduction from the northwest facing luzon arc system to the south facing ryukyu arc system taiwan and its neighboring southern ryukyu used to be part of the rifted china continental margin before the collision started in late miocene time engineered by the northwest movement of the philippine sea plate in the past 5 m y the north south trending luzon arc obliquely overrode the northeast southwest trending continental margin and tectonized it into a collision orogen that progressively enlarged and migrated from northeast to southwest following the southwest propagating collision the north dipping philippine sea plate which was subducting beneath the ryukyu arc also extended westward and caused flipping of subduction in the northern part of the collision orogen in consequence the orogen lost the compressive support by the colliding plates and became subjected to lithospheric stretching induced by the trench suction the collision orogen collapsed as a result of crustal thinning and its central part foundered into a deep submerged basin a whole spectrum of active tectonic scenarios ranging from orogenic buildup by collision to orogenic collapse by rifting and subsidence can be readily observed in the taiwan ryukyu area and provides a vivid example for the process of orogenic collapse

a double island arc between taiwan and luzon consequence of ridge subduction analysis of geomorphological geochronological geochemical and geophysical features in the segment of the taiwan luzon arc between taiwan and luzon the bashi segment allows the recognition of a double arc structure the two volcanic chains are separated by 50 km just north of luzon 18 n and converge near 20 n islets in the western chain are older and largely composed of volcanic rocks of miocene to pliocene age they all show low relief lateritic platforms and wave cut terraces and are covered by massive recrystallized limestone in contrast all active volcanoes in this segment of the taiwan luzon arc belong to the eastern chain where most islets are quaternary in age the volcanoes have well developed cone shapes and well preserved deposits of near vent facies magmas of the eastern chain have higher ksi la n la yb n and lowerend than their counterparts at the same latitude in the western chain therefore the magmas erupted in the eastern chain were derived from more enriched mantle sources than the magmas erupted in the western chain moreover the available seismological data seem to suggest an abrupt increase of the dip angle from 30 at 18 n to 80 at 20 n thus the double arc structure is located in the region where the benioff zone suddenly changes in analogy with the lesser antilles arc we propose a geodynamic model in which the double arc in the bashi strait is the tectonic manifestation of the subduction of the aseismic scarborough seamount chain the extinct mid ocean ridge of the south china sea before that ridge reached the manila trench the western chain was the volcanic front when the ridge reached the subduction zone at 5 4 ma its buoyancy temporarily interrupted the subduction thus causing a time gap in magmatic activity furthermore this ridge arc collision was probably also responsible for regional uplift causing extensive sub aerial weathering and erosion as well as massive reef formation in the western chain when subduction started again the dip angle became shallower in response to the extra buoyancy of the downgoing ridge if the depth of magma generation remained constant the shallower dip angle would have naturally led to an eastward shift of the volcanic front thus producing the younger eastern chain moreover we speculate that the abrupt change of the dip angle may have torn the downgoing slab thus allowing more enriched continental lithospheric material to invade the mantle wedge from the northwest thus imprinting a geochemically more enriched signature on the magmas of the eastern chain

the geochemistry and tectonic setting of the northern section of the luzon arc the philippines and taiwan abstract the luzon arc consists of a 1200 km chain of stratovolcanoes and volcanic necks stretching from mindoro 13 n to the coastal range of taiwan 24 n this study is concerned with three of the five major segments along the arc the northern luzon babuyan and taiwan segments the late tertiary to quaternary volcanics of these segments are primarily andesitic but range in composition from basalt to rhyolite and are typical arc volcanics porphyritic plagioclase textures primarily calc alkaline with a few tholeiitic volcanic centers low tio 2 concentrations and low high field strength element hfse to large ion lithophile element lile ratios there is a large range in k 2 o and other liles from low k tholeiites to high k calc alkaline suites calayan island and mt tabungon volcanic substratum of mt cagua volcanics in the babuyan segment and most rocks from the taiwan coastal range are low k tholeiites e g nearly flat ree patterns low lree and lile concentrations and low th u ratios the dominant calc alkaline series ranges from medium k to high k rocks the high k calc alkaline rocks are mainly young and are found on batan and lutao islands when the low k tholeiitic and medium and high k calc alkaline rocks are associated in the same region the low k rocks are usually older there is a general relationship between k 2 o and other lile concentrations and k ar radiometric dates to some extent 87 sr 86 sr ratios also increase with time throughout the arc there is a correlation between latitude and 87 sr 86 sr and a positive correlation between 87 sr 86 sr and la sm cn an increase in both these geochemical parameters has been associated with an increase in the input of continental crustal material in other arc regions the lowest 87 sr 86 sr ratios found along the entire luzon arc the samples from baguio are equivalent to those found in samples from mid tertiary plutons from northern luzon and the bicol arc both groups of rocks are associated with westward subduction along the philippine trench where presumably deep oceanic sediments with little or no continental crustal component have been subducted the absence of continental crust below the arc in the northern luzon and babuyan segments has been suggested by several groups of researchers this together with the fact that metasomatized ultramafic nodules probably of mantle origin in disequilibrium with their batan host lavas but with similar 87 sr 86 sr and la sm cn ratios to the host rocks suggests that upper level assimilation afc processes does not appear to be the major influence on the geochemical signatures a collision zone between the upper crustal block of eastern china and taiwan and the manila trench has been recorded in the northern section of the arc taiwan sediments have also been shown to decrease in thickness along the south china sea basin nearly parallel to the manila trench from north to south the sediment source region is most probably taiwan and perhaps eastern china this latitudinal in variation sediment thickness may explain the crustal signature related to both geochemical and age parameters we suggest that this crustal input has taken place via subduction of sediment rich in a crustal component

geological tectonic framework of solomon islands sw pacific crustal accretion and growth within an intra oceanic setting the solomon islands are a complex collage of crustal units or terrains herein termed the solomon block which have formed and accreted within an intra oceanic environment since cretaceous times predominantly cretaceous basaltic basement sequences are divided into 1 a plume related ontong java plateau terrain ojpt which includes malaita ulawa and northern santa isabel 2 a normal ocean ridge related south solomon morb terrain ssmt which includes choiseul and guadalcanal and 3 a hybrid makira terrain which has both morb and plume plateau affinities the ojpt formed as an integral part of the massive ontong java plateau ojp at c 122 ma and 90 ma respectively was subsequently affected by eocene oligocene alkaline and alnoitic magmatism and was unaffected by subsequent arc development the ssmt initially formed within a normal ocean ridge environment which produced a morb like basaltic basement through which two stages of arc crustal growth subsequently developed from the eocene onwards the makira terrain records the intermingling of basalts with plume plateau and morb affinities from c 90 ma to c 30 ma and a contribution from late miocene present day arc growth two distinct stages of arc growth occurred within the solomon block from the eocene to the early miocene stage 1 and from the late miocene to the present day stage 2 stage 1 arc growth created the basement of the central part of the solomon block the central solomon terrain cst which includes the shortland florida and south isabel islands stage 2 arc growth led to crustal growth in the west and south the new georgia terrain or ngt which includes savo and the new georgia and russell islands both stages of arc growth also added new material to pre existing crustal units within other terrains the solomon block terrane collage records the collision between the alaska sized ojp and the solomon arc initial contact possibly first occurred some 25 20 ma but it is only since around 4 ma that the ojp has more forcefully collided with the solomon arc and has been actively accreting since that time continuing to the present day we present a number of tectonic models in an attempt to understand the mechanism of plateau accretion one model depicts the ojp as splitting in two with the upper 4 10 km forming an imbricate stack verging to the northeast over which the solomon arc is overthrust whilst deeper portions of the ojp beneath a critical detachment surface are subducted the subduction of young 5 ma hot oceanic lithosphere belonging to the woodlark basin at the ssts has resulted in a sequence of tectonic phenomena including the production of unusual magma compositions e g na ti rich basalts and an abundance of picrites an anomalously small

excess pore pressure resulting from methane hydrate dissociation in marine sediments a theoretical approach 1 this study quantifies the excess pore pressure resulting from gas hydrate dissociation in marine sediments the excess pore pressure in confined pore spaces can be up to several tens of megapascals due to the tendency for volume expansion associated with gas hydrate dissociation on the other hand the magnitude of excess pore pressure in well connected sediment pores is generally smaller depending primarily on the hydrate dissociation rate and the sediment permeability volume expansion due to gas hydrate dissociation in well connected pore spaces is related via darcy s law to an increase in pore pressure and its gradient in sediment which drives an additional upward fluid flow through the sediment layer overlying the gas hydrate dissociation area the magnitude of this excess pore pressure is found to be proportional to the rate of gas hydrate dissociation and the depth below seafloor and inversely proportional to sediment permeability and the depth below sea level the excess pore pressure is the greatest at low initial pressures and decreases rapidly with increasing initial pressure excess pore pressure may be the result of gas hydrate dissociation due to continuous sedimentation tectonic uplift sea level fall heating or inhibitor injection the excess pore pressure is found to be potentially able 1 to facilitate or trigger submarine landslides in shallow water environments 2 to result in the formation of vertical columns of focused fluid flow and gas migration and 3 to cause the failure of a sediment layer confined by low permeability barriers in relatively deep water environments

scotia sea regional tectonic evolution implications for mantle flow and palaeocirculation abstract the scotia sea and surrounding scotia arc have evolved over the past 40 ma by extension behind an east migrating subduction zone at the boundary between the south american sam and antarctic ant plates the considerable data set now available regional geology and geophysics earthquake seismology satellite altimetry global plate analyses suggest why east migrating subduction began what has been the driving force that has sustained it and what other processes have controlled the mode of back arc extension in the scotia sea a suite of six reconstructions has been developed based on this data set the reconstruction to 40 ma creates a compact cuspate continental connection between south america and the antarctic peninsula at the subducting pacific margin with fragments now dispersed around the scotia arc occupying positions within it compatible with their known geology the driving force has been subduction of south american ocean floor which began as a result of southward migration of the pole of south american antarctic plate rotation and a key modulator of back arc extension has been collision of ridge crest sections of the south american antarctic plate boundary with the east advancing trench cenozoic regional tectonic evolution has two other likely consequences which greatly increase its importance firstly this region saw the tectonic disruption of the final barrier to complete circum antarctic deep water flow that may have had a profound effect on palaeoclimate secondly it is possible that the rapid roll back of the hinge of subduction is related to shallow eastward flow in the sub lithospheric mantle both of these consequences are explored the reconstructions show that rapid roll back of the subduction hinge averaging 50 mm a over the last 40 ma with respect to the south american plate has been a feature of all of scotia sea evolution and provide a history of motion of several oceanic microplates most of which are now welded together within the scotia sea this will guide the location of seismometers and or dredge hauls to test the hypothesis of shallow mantle flow and help interpret the results the reconstructions also allow an assessment of the creation of deep water pathways that would have permitted the development of the present day antarctic circumpolar current acc an early miocene onset within the period 22 17 ma seems likely for the acc depending on the structure and palaeo elevation of davis bank and aurora bank sections of the north scotia ridge however the study shows there was a delay of one or more million years between initial provision of a deep water pathway and the major mid miocene change in global climate involving the general level of antarctic glaciation that may have been related if these changes were related then the delay suggests that other factors possibly rough elevated ocean floor but also non tectonic factors such as atmospheric co2 were important in determining palaeoclimate

structure and generation of turbulence at interfaces strained by internal solitary waves propagating shoreward over the continental shelf abstract detailed observations of the structure within internal solitary waves propagating shoreward over oregon s continental shelf reveal the evolving nature of interfaces as they become unstable and break creating turbulent flow a persistent feature is high acoustic backscatter beginning in the vicinity of the wave trough and continuing through its trailing edge and wake this is demonstrated to be due to enhanced density microstructure increased small scale strain ahead of the wave trough compresses select density interfaces thereby locally increasing stratification this is followed by a sequence of overturning high density microstructure and turbulence at the interface which is coincident with the high acoustic backscatter the richardson number estimated from observations is larger than 1 4 indicating that the interface is stable however density profiles reveal these preturbulent interfaces to be o 10 cm thick much thinner than can be resolved with shipboard velocity measurements by as

the degeneration of internal waves in lakes with sloping topography in a laboratory study we quantified the temporal energy flux associated with the degeneration of basin scale internal waves in closed basins the system is two layer stratified and subjected to a single forcing event creating available potential energy at time zero a downscale energy transfer was observed from the wind forced basin scale motions to the turbulent motions where energy was lost due to high frequency internal wave breaking along sloping topography under moderate forcing conditions steepening of nonlinear basin scale wave components was found to produce a high frequency solitary wave packet that contained as much as 20 of the available potential energy introduced by the initial condition the characteristic lengthscale of a particular solitary wave was less than the characteristic slope length leading to wave breaking along the sloping boundary the ratio of the steepening timescale required for the evolution of the solitary waves to the travel time until the waves shoaled controlled their development and degeneration within the domain the energy loss along the slope the mixing efficiency and the breaker type were modeled using appropriate forms of an internal iribarren number defined as the ratio of the boundary slope to the wave slope amplitude wavelength this parameter allows generalization to the oceanographic context analysis of field data shows the portion of the internal wave spectrum for lakes between motions at the basin and buoyancy scales to be composed of progressive waves both weakly nonlinear waves sinusoidal profile with frequencies near 10 24 hz and strongly nonlinear waves hyperbolic secant squared profile with frequencies near 10 23 hz the results suggest that a periodically forced system may sustain a quasi steady flux of 20 of the potential energy introduced by the surface wind stress to the benthic boundary layer at the depth of the pycnocline

speculative tectonic model for the early mesozoic arc of the southwest cordilleran united states the early mesozoic continental arc of arizona california and western nevada is here interpreted to have occupied a continuous graben depression more than 1000 km long similar to the modern extensional are of central america high calculated rates of subsidence the presence of syndepositional normal faults and fault talus breccias the abundance of calderas and high level intrusions and interstratification of cale alkalic and alkalic volcanic rocks provide support for this model the arc graben depression acted as a long lived more than 40 m y trap for craton derived quartz sands which were funneled along the length and across the width of the depression

experimental study on the deterioration and natural remediation of the ariake sea tidal mud caused by the sea laver treatment acid practice and the upward seepage of pore water liquid this study presents a laboratory study of the following two aspects 1 the influence of sea laver treatment acid on the geoenvironmental properties of ariake sea tidal mud and 2 the natural remediation effect on the sea laver treatment acid contaminated ariake sea tidal mud caused by the upward seepage of pore water liquid in the mud firstly the mechanisms of the transport of sea laver treatment acid in the ariake sea tidal mud and the generation mechanisms of the upward seepage flow in the ariake sea tidal mud are discussed secondly a series of one dimensional laboratory infiltration tests were carried out to investigate the deterioration of the ariake sea tidal mud caused by the sea laver acid treatment practice test results reveal that the acid treatment practice caused considerable change in the geochemical properties of the mud in terms of increase in sulfide content and decrease in ph value after the treatment by the sea laver treatment acid the sulfide content of the mud even exceeded the safe limit value for the benthos which represents undesirable living condition for benthos thirdly series of laboratory fresh seawater infiltration tests for the deteriorated iida site mud were conducted to illustrate this natural remediation efficiency it is found that with the infiltration of the fresh seawater the sulfide content of the iida site mud was considerably reduced and ph value increased to an acceptable range for benthos living in the tidal flat mud with the increase in the infiltration time and the hydraulic gradient the remediation efficiency could be increased

observation of internal wave polarity conversion generated by a rising tide the observations reported here are based on time series of in situ observation data in laoshan bay off the qingdao coast a chain of thermistors t chain at a fixed location recorded a sequence of elevation internal waves followed by depression internal waves passing by over an elapsed time of about 1 h this observed polarity conversion at a fixed location is caused by the vertical stratification variation mainly induced by the rising tide which is believed to be the first reported observation of this kind the process of an elevation internal wave train converting to a depression wave train is simulated using the variable coefficient extended korteweg de vries vekdv equation which also provides a further comparison between theory and the reported observations

observations of shoaling nonlinear internal bores across the central california inner shelf abstractwe present observations of shoaling nonlinear internal bores off the coast of central california the dataset includes 15 moorings deployed during september october 2017 and cross shore shi