fluidization pipes in volcaniclastic mass flows volcan hudson southern chile the presence of fluidization pipes within pyroclastic sediments has been proposed as a criterion for differentiating these volcaniclastic deposits from those of epiclastic mass flows observations of pipe structures within low temperature epiclastic mudflows produced by the 1971 eruption of volcan hudson southern chile demonstrate that this assumption is invalid and that the presence of pipes may only be utilized to interpret the precise mechanics of the fluidization process itself

emplacement of pyroclastic density currents pdcs in a deep sea environment the val d aveto formation case northern apennines italy abstract the occurrence of pdc deposits in a foredeep basin sequence named val d aveto formation 32 29 ma northern apennines italy provides new information on the behavior of pyroclastic density currents entering the water in this work stratigraphic petrographic and mineralogical features that characterize three pyroclastic deposits have been described and analyzed in the field facies and lithological analysis on the blocky size fraction and in the laboratory image analyses on the blocky size detritus optical analyses of the microtextures mineralogical analyses through x ray powder diffraction xrpd and scanning electron microscope with energy dispersive x ray spectometry sem eds the deposits are lapilli to blocky size with a blocky size fraction constituted of accidental detritus in thin sections their groundmass texture varies from porphyritic to eutaxitic where coarser particles become close each others growth rims have been also detected around plagioclase crystals pyrite habits and oxidation and plagioclase albitization are consistent with hydrothermal temperature conditions of 200 c all these results have been compared with the information provided by modern examples of pdc deposits and laboratory experiments on the behavior of water hot particles mixing grain to grain collision has been considered as the main flow mechanism that sustained and avoided the disaggregation of the pdcs entering the water

fluidization of host sediments and its impacts on peperites forming processes the cretaceous buan volcanics korea abstract in the cretaceous buan volcanics sw korea blocky and fluidal peperites are developed in a bed of poorly sorted massive pumiceous lapilli tuff hot sediments as a result of the vertical to subvertical intrusion of the trachyandesitic dikes into the bed blocky peperites are composed of polyhedral or platy juvenile clasts with a jigsaw crack texture fluidal peperites are characterized by fluidal or globular juvenile clasts with irregular or ragged margins the blocky peperites are ubiquitous in the host sediments whereas the fluidal peperites only occur in fine grained zone well sorted fine to very fine ash that are aligned parallel to the dike margin the development of the fine grained zone within the poorly sorted host sediments is interpreted to form by grain size segregation caused by upward moving pore water fluidization that has resulted from heat transfer from intruding magma toward the waterlogged host sediments during intrusion with the release of pore water and the selective entrainment of fine grained ash the fine grained zone formed within the host sediments subsequent interactions between the fine grained zone and the intruding magma resulted in ductile deformation of the magma which generated fluidal peperites outside the fine grained zone because of the relative deficiency of both pore water and fine grained ash intruding magma fragmented in a brittle manner resulting in the formation of blocky peperites the results of this study suggest that redistribution of constituent particles ash and interstitial fluids during fluidization resulted in heterogeneous physical conditions of the host sediments which influenced peperite forming processes

experimental studies of the fluidization of layered sediments and the formation of fluid escape structures experiments demonstrate that fluid escape structures can be produced as a result of unstable fluidization behaviour where a lower base layer of granular material is inhibited from fluidizing by the presence of an overlying non fluidizing top layer before the base layer can fluidize the weight of the overlying material must be balanced and this is accomplished by base layer material pressing against the bottom surface of the confining top layer forming a static layer this static layer allows the top layer to lift away from the base layer which is then free to fluidize a water filled crack forms below the static layer and as this grows instability causes the static layer and top layer to bend and conical voids to form below the antiformal sections rupture occurs at the apex of the water void allowing the underlying water and fluidizing material to burst out through the top layer the fluidized base layer material then flows through the rupture until all of this material except that in the static layer is deposited above the previously overlying layer and a stable fluidization system results the top layer material is bent upwards around the rupture and the resulting pillar type escape structure is preserved if flow then ceases the vigour of the burst out is greatest when the base layer material has a grain size 15 of the top layer material if the base layer grain size is less than 8 of the top layer then base layer material will pass through the top layer pore spaces without forming an escape structure if cohesive material is present escape structures form when a layer of fine grained cohesive material overlies a layer of cohesionless material at low flow rates small pipes with scattered angular bends pierce the top layer and base layer material passes through them the base layer material is ejected on to the top layer and builds up around the mouth of each pipe to form constructional structures sand volcanoes this is in contrast to the cohesionless experiments where the weight of material being deposited on the top layer caused an ejecta filled depression to form around the rupture if flow then ceases both the pipes and the sand volcanoes are preserved at high flow rates where the base layer fluidizes the top cohesive layer becomes fragmented small fragments circulate within the fluidizing base layer and are preserved as floating clasts large fragments sink to the bottom of the fluidizing base layer erosion of the bottom surface of these larger fragments causes this surface to become convex downward the experimentally derived structures are similar to pillar type structures observed in the field and the processes described can be used to investigate the development of these structures fluidization experiments also demonstrate the genesis of dish structures and the cohesive behaviour can be applied to the deformation of these structures after initial formation

petrology geochemistry and geochronology of the post collisional triassic mangerite and syenite in the gwangcheon area hongseong belt south korea abstract the gwangcheon intrusive rocks occur in the hongseong collision belt of south korea which is thought to represent the eastern extension of the dabie sulu collision zone of china the central part of the gwangcheon intrusive complex consists of orthopyroxene bearing monzonite mangerite and the marginal part is composed of syenite north of the gwangcheon mangerite the post collisional 233 2 ma haemi biotite granite contains syenite enclaves shrimp u pb zircon analysis yields ages of 232 3 ma for the mangerite and 230 3 ma for a syenite enclave within the haemi biotite granite the mangerite syenite complex and syenite enclaves exhibit a shoshonitic affinity with a total alkalinity na2o k2o of 7 38 9 64 wt high k2o mg ba sr cr ni and lree contents and insignificant negative eu anomalies geochemical data indicate that the mangerite syenite intrusion and the syenite enclaves are post collisional igneous rocks formed by the partial melting of an enriched lithospheric mantle the heat for this melting was derived from asthenospheric upwelling following oceanic slab break off the shrimp age data suggest that both the gwangcheon intrusives and the syenite enclaves formed after the triassic continental collision of the north and south china blocks in korea

first finding of eclogite facies metamorphic event in south korea and its correlation with the dabie sulu collision belt in china abstract metabasite lenses occur within granitic gneiss at bibong in the southwestern part of the gyeonggi massif south korea bibong metabasites experienced an initial eclogite facies metamorphism 17 0 20 9 kbar 835 860 c which was succeeded by a granulite facies metamorphism 11 5 14 6 kbar 830 850 c and finally overprinted by an amphibolite facies metamorphism 6 7 11 0 kbar 570 740 c the metabasites have sm nd internal isochron ages at 225 258 ma and the major elements of the metabasites display an island arc affinity the petrochemical and geochronological data suggest the southwestern part of the gyeonggi massif as an extension of the triassic dabie sulu collision belt in china

physical modelling of sand injectites abstract sand injectites are structures that result from intrusion of fluidized sand into fractures we have studied them in the tampen spur area of the north sea and have reproduced them experimentally by driving compressed air through layers of sand glass microspheres and silica powder the silica powder was cohesive and capable of hydraulic fracturing whereas the sand and glass microspheres were almost non cohesive and therefore able to fluidize the models were dynamically similar to their natural counterparts for as long as equilibrium was static when the processes became dynamic so that inertial forces were significant the scaling was approximate and the corresponding reynolds numbers differed the experimental apparatus was a square box 1 m 1 m wide resting on a grid of fluid diffusers during the experiments the fluid pressure increased until it attained and surpassed the weight of overburden flat lying hydraulic fractures containing air formed within cohesive and least permeable layers heterogeneities in material properties and layer thicknesses were responsible for localizing fracture networks when any one network broke through to the surface rapid flow of air through the fractures fluidized the underlying mobile materials and even depleted some of the layers some of the fluidized material extruded at the surface through vents forming volcanoes and sheets the remainder lodged at depth forming sand injectites or laccoliths conical sand injectites formed preferentially where layers had high resistance to bending laccoliths formed nearer the surface where overlying layers had low resistance to bending the experimental sand injectites were broadly similar to those in the tampen spur area of the north sea as well as other areas

tracking source materials of phanerozoic granitoids in south korea by zircon hf isotopes phanerozoic granitoids in south korea are classified into four primary spatiotemporal groups showing geochemical and isotopic diversity this study presents the first in situ hf isotope data for zircons extracted from representative outcrops of each granitoid group the core to rim variation in ehf values observed in some zircon grains provides evidence for open system processes influenced by the input of more primitive melts or interactions with pre existing crustal materials a general core to rim decrease in lu hf and th u ratios indicates a progressive compositional change in the melts during magmatic differentiation contrasting evolutionary paths demonstrated by zircon ehf values suggest that the neoproterozoic to palaeozoic crust including the permian granitoids was recycled during the cretaceous to palaeogene magmatism in south eastern korea whereas the palaeoarchaean to palaeoproterozoic crust provided major source material for the triassic to jurassic granitoids in central korea

tectonic and sedimentary evolution of a cretaceous continental arc backarc system in the korean peninsula new view abstract this paper focuses on the tectonic and sedimentary evolution of the cretaceous volcanic rocks and nonmarine successions in the southeastern part of the korean peninsula which constitute an ancient continental arc system the arc system gyeongsang arc system comprising an arc platform gyeongsang volcanic arc and a backarc basin gyeongsang backarc basin was a southwestward extension of the japanese arc formed by oblique northward subduction of the proto pacific izanagi plate under the asian continent the backarc basin was initiated in the southeastern part of the korean peninsula in the early cretaceous as a narrow ns trending trough the basin was bounded by a major fault in the northern part of the basin from which sediments largely emanated sediments were deposited in streamflow dominated alluvial fans adjacent to the fault bounded basin margin in the north and low gradient fluvial systems of braided channels that extended southward and southeastward for tens of kilometers sediments were also derived from the western highland margin draining precambrian to jurassic basement rocks the initially narrow trough progressively expanded toward the east resulting in eastward migration of depocenters that eventually generated a broad fluvio lacustrine plain fringing the volcanic arc platform the arc platform played an important role for the derivation of volcanogenic materials and accreted sediments into the backarc basin via extensive fluvial network pyroclastic density currents and landslides which originated from the arc platform also entered the basin in addition extrusion of basaltic volcanic rocks was continual within the basin during basin expansion the resultant succession of mixed sedimentary and volcanogenic rocks is generally indicative of a temporal increase in volcanic activity in the arc platform and in subsidence rate of the basin in the late cretaceous andesitic to rhyolitic volcanism became climactic in the arc platform producing a number of calderas or volcanotectonic depressions volcaniclastic aprons fringing the arc platform encroached upon the basin fill intraarc basins produced by sinistral shearing of the arc platform received sediments from active volcanoes and footwalls of contemporaneous faults forming small scale streamflow dominated alluvial fans and floodplains with later development of a deep lake overall the gyeongsang arc system formed under an extensional or transtensional sinistral strike slip stress regime suggesting that the subducting and the overriding plates were not strongly coupled both the volcanic arc and the backarc basin ceased to develop as volcanic activities shifted progressively eastward in the paleogene accompanied with rollback of the subduction of the izanagi plate

soft sediment deformation structures in cambrian siliciclastic and carbonate storm deposits shandong province china differential liquefaction and fluidization triggered by storm wave loading abstract this paper focuses on soft sediment deformation structures ssds in both siliciclastic and carbonate storm deposits of the cambrian mantou and chaomidian formations shandong province china in order to understand their deformation mechanisms and possible triggers siliciclastic ssds e g sand volcanoes and pillows and carbonate ssds e g sedimentary dykes grainstone matrix breccias deformed cross beddings and marlstone matrix breccias occur exclusively in hummocky cross stratified fine sandstone and peloidal grainstone respectively the siliciclastic ssds formed in porous and permeable surface sediment whereas the carbonate ssds formed under shallow burial conditions when early marine cementation prevailed the various deformation structures resulted mainly from differences between siliciclastic and carbonate sediment conditions and resulting deformation mechanisms sand volcanoes formed by upward extrusion of over pressured fluidized sandy sediment whereas sand pillows resulted from upward injection of lower density muddy sediment into overlying liquefied sandy sediment sedimentary dykes and grainstone matrix limestone breccias formed as a result of differential liquefaction and fluidization of heterogeneously cemented carbonate sediment whereas deformed cross beddings and marlstone matrix limestone breccias developed by the thixotropic liquidization and injection of clayey sediment and further disruption of thin peloidal layers sedimentary facies analysis and analysis of the physical processes indicate that the ssds were most likely caused by cyclic loading of storm waves

termination of the permo triassic songrim indosinian orogeny in the ogcheon belt south korea occurrence of ca 220 ma post orogenic alkali granites and their tectonic implications abstract the indosinian orogeny is defined in a broad sense as encompassing all the late paleozoic to early mesozoic tectonic events associated with the closure of the eastern parts of the paleo tethys ocean it includes the permo triassic continent continent collision between the north china and south china blocks that generated the qinling dabie sulu orogen containing the largest ultrahigh pressure uhp terrane in the world the korean peninsula situated at the easternmost end of the tethyan tectonic regime was also tectonically influenced by the indosinian orogeny often known as the songrim orogeny in korea the songrim orogeny characterized by intense regional medium to high pressure metamorphism extends from the imjingang belt through the gyeonggi massif to the ogcheon belt it was initiated as early as the early permian period ca 290 ma and peaked in the triassic period ca 255 to 225 ma this paper presents new geochemical and shrimp u pb zircon ages for two alkali granites that postdated the songrim orogeny in the ogcheon belt both granites are contemporaneous 219 3 3 3 ma and 219 6 1 9 ma and are geochemically post orogenic a type granites intruded in an extensional setting subsequent to a major collision the data provide a critical time constraint on the termination of the indosinian orogeny in the korean peninsula despite the absence of an uhp terrane in the korean peninsula similarities in the duration metamorphic characteristics and post orogenic magmatism between the qinling dabie sulu and songrim orogens as parts of the broad indosinian orogenic regime are clearly alike suggesting a genetic linkage in their time space characteristics

sedimentology and event timing of a catastrophic volcaniclastic mass flow volcan hudson southern chile eruption of volcan hudson aisen region southern chile on 12 august 1971 melted up to 80 of ice within the 9 km wide hudson caldera rapid mobilisation of abundant fluvio glacial sediment within the adjacent huemules valley led to the generation of a catastrophic mass flow which swept westwards along the valley eventually entering the fjord some 40 km downstream the mass flow developing from one source and being unaffected by tributary input was characterised by three events within the flood hydrograph 1 a precessional flood possibly linked to breakage of an early formed dammed lake 2 a main mass flow which varied in its rheological behaviour from plug flow to hyperconcentrated flow and 3 a recessional flood at the tail of the main flow which diluted towards a concentrated streamflow the main debris flow displayed characteristics of pulsing internal segregation density stratification significant downstream sediment assimilation cohesive frictional freezing with ensuing fluidisation and development of an advancing runout phase consideration of these sedimentary characteristics and spatial temporal flow transformations are used to propose a schematic model of event timing within this catastrophic volcaniclastic flow

depositional environments and cyclicity of the early ordovician carbonate ramp in the western tarim basin nw china abstract during the early ordovician the tarim basin nw china was mainly occupied by an extensive shallow water carbonate platform on which a carbonate ramp system was developed in the bachu keping area of the western part of the basin three well exposed typical outcrop sections of the lower ordovician penglaiba formation were investigated in order to identify the depositional facies and to clarify origins of meter scale cycles and depositional sequences thereby the platform evolution thirteen lithofacies are identified and further grouped into three depositional facies associations peritidal restricted and open marine subtidal facies these lithofacies are vertically stacked into meter scale shallowing upward peritidal and subtidal cycles the peritidal cycles are mainly distributed in the lower and uppermost parts of the penglaiba formation deposited in the inner middle ramp and commonly start with shallow subtidal to intertidal facies followed by inter to supratidal facies in contrast the subtidal cycles occur throughout the formation mostly in the middle outer ramp and are dominated by shallow to relatively deep i e intermediate subtidal facies the dominance of asymmetrical and incomplete cycles suggests a dominant control of earth s orbital forcing on the cyclic deposition on the platform on the basis of vertical facies and cycle stacking patterns and accommodation changes illustrated by the fischer plots from all studied sections five third order depositional sequences are recognized in the penglaiba formation individual sequences comprise a lower transgressive part and an upper regressive one in shallow water depositional environments the transgressive packages are dominated by thicker than average subtidal cycles indicating an increase in accommodation space whereas regressive parts are mainly represented by thinner than average peritidal and subtidal cycles denoting a decrease in accommodation space in contrast in intermediate to deep subtidal environments transgressive and regressive packages display an opposite trend in accommodation space changes sequence boundaries except the basal and top boundaries of the penglaiba formation are usually represented by laterally traceable transitional boundary zones without apparent subaerial exposure features good correlation of the long term changes in accommodation space or sea level inferred from vertical stacking patterns of facies and cycles suggests an overriding eustatic control on the formation of meter scale cycles and third order depositional sequences as well as platform evolution superimposed with local and or regional tectonic influence during the early ordovician this study would help understand the controls on the tempo spatial facies distribution stratal cyclicity and carbonate platform evolution in the western tarim basin during the early ordovician facilitating prediction for favorable subsurface carbonate reservoirs and future hydrocarbon exploration and production in the penglaiba formation

resedimentation of cold pumiceous ignimbrite into water facies transformations simulated in flume experiments deposits and transport processes resulting from the resedimentation of cold unconsolidated ignimbrite into water were simulated by flume experiments the ignimbrite sample used was poorly sorted 2 4 3 fine ash rich 2000 kg m 3 and pumice 500 to ca 1300 kg m 3 as a result of the binding forces of the ash matrix the experiments involved resedimentation from a steep front onto the floor with or without an initial ramp of the water filled tank under both still and wave generated conditions larger discrete collapse events were induced by oversteepening the sample front and by undercutting from wave action the mass of the collapse and proportion of pore space water strongly influenced the style of resedimentation and the deposits initial collapse events were from the top of the steep front and fell onto the floor the largest densest clasts were deposited as a lithic lag in a proximal sediment wedge or rolled down to a break in slope fine ash was transported in dilute turbidity currents and coarse unsaturated pumice clasts floated off moderate collapse events generated high density turbidity currents trapping pumice in the flow causing them to saturate these low density pumice clasts were easily remobilized by wave activity and passing currents and accumulated on the gentle slope at the bottom of the resedimented deposit large collapse events slumped producing poorly sorted mounds similar in texture to the original starting material as the matrix of the ignimbrite sample became saturated with water moderate and large collapse events generated debrisflows and slurries that deposited massive poorly sorted deposits furthermore once more gentle slopes were established between the sample and deposit small cascading grainflows deposited lithic clasts on the upper slopes and levees of pumice at the terminus of low relief ash channels the experiments show that excluding large collapse events and debrisflows resedimenting ignimbrite in water is effective at segregating low density pumice clasts from dense lithic clasts and fine ash experiments using fine ash poor ignimbrite and well sorted quartz sand for comparison formed an inherently unstable initial steep front that immediately collapsed by continuous grain avalanches the grainflow deposits had textures similar to the fines poor starting material

re os dating of molybdenite from the pueblo viejo au ag cu and douvray cu au districts hispaniola re os dating of three samples of hydrothermal molybdenite collected from the pueblo viejo au ag cu district 5 5 moz gold past production 16 2 moz proven plus probable gold ore reserves yields ages of 112 1 0 4 112 0 0 4 and 111 5 0 4 ma these re os dates confirm an early cretaceous age for mineralization coeval with tholeiitic intraoceanic island arc volcanism and in particular with an episode of felsic magmatism and extension across the early cretaceous arc 110 118 ma re os dating of a sample of hydrothermal molybdenite collected from the douvray porphyry cu mo deposit with inferred resources of 1 257 mlb cu 0 276 moz au 6 84 moz ag and 4 367 tons mo yields an age of 93 3 0 3 ma coeval with calc alkaline magmatism along the greater antilles island arc

sediment deformation in miocene and post miocene strata northeastern brazil evidence for paleoseismicity in a passive margin abstract stratigraphic intervals characterized by varied and complex styles of soft sediment deformation structures are well preserved in miocene and late pleistocene to holocene deposits of a sedimentary basin located in northeastern brazil the miocene strata represented by the barreiras formation record only brittle structures including numerous faults and fractures with straight and high angle dipping planes that are often filled with sands derived from overlying beds folds consisting of broad anticlines and synclines are also present in this unit the late pleistocene to holocene deposits named post barreiras sediments contain an indurated sandy package with a large variety of ductile and brittle deformation structures i e massive sandstones with isolated sand fragments and breccias undulatory strata sand dykes and diapirs sinks and bowls pebbly pockets plunged sediment mixtures fitted sand masses cone shaped cracks fault grading and sedimentary enclaves these features confined to sharp based stratigraphic horizons that progressively grade downward into undisturbed deposits are related to seismic shocks of high surface wave magnitude i e ms 5 or 6 amalgamated seismites suggest that previously formed seismites were affected by subsequent seismic wave propagation seismic waves caused by activity along one or most likely several tectonic structures would have propagated throughout the depositional environment producing laterally extensive seismites the close proximity to earthquake epicenters would have promoted pervasive re sedimentation due to pore overpressure resulting high volumes of massive sandstones and breccia the similarity between deposits with correlatable strata from many other areas along the brazilian coast allows raise the hypothesis that the seismic episodes might have affected sedimentation patterns in a large i e extension of several hundreds of kilometers geographic area thus the modern seismicity recorded along northeastern brazil was recurrent during the quaternary and perhaps also in the pliocene the estimated high magnitude of the seismic events and the great regional extent of the affected area demonstrate that the brazilian coast experienced tectonic stress through the last geological episodes of its evolution which would have favored sediment accumulation and penecontemporaneous re sedimentation this geological context is unexpected in a passive margin inducing to revisit the debate on how active is a passive margin

mantle and slab contributions in arc magmas destructive plate margins are major sites of terrestrial magmatism that have long had a key role in models for the generation of continental crust and the development of chemical heterogeneities in the upper mantle in these models it is important to evaluate the nature and size of contributions from preexisting crust in the generation of magmas above subduction zones and to constrain the size of the fluxes of different elements from the subducted crust and the overlying mantle wedge in arc magmas kay 1 980 hawkesworth ellam 1 989 hawkesworth et al 1 99 1 a mcculloch gamble 1 99 1 the more mobile components of the subducted oceanic crust are the products of element fractionation processes in the upper continental crust the ocean basins and hydrothermal systems on the ocean floor they therefore have distinctive isotope and even trace element ratios that in principle should be readily distinguished from those in peridotite in the mantle wedge prior to subduction in practice however element ratios are almost certainly fractionated during shallow level dehydration of sub ducted material and at greater depths where material from the slab appears to contribute in the generation of arc magmas moreover the isotope signal of slab derived material may be heavily diluted by exchange with

evidence for late messinian seismites nijar basin south east spain the feos formation of the nijar basin comprises sediments deposited during the final stage of the messinian salinity crisis when the mediterranean was almost totally isolated levels of soft sediment deformation structures occur in both conglomeratic alluvial sediments deposited close to faults and the hyposaline lago mare facies a laminated and thin bedded succession of whitish chalky marls and intercalated sands alternating with non marine coastal plain deposits deformation structures in the coarse clastics include funnel shaped depressions filled with conglomerate liquefaction dykes terminating downwards in gravel pockets soft sediment mixing bodies chaotic intervals and flame structures evidence for soft sediment deformation in the fine grained lago mare facies comprises syndepositional faulting and fault grading sandstone dykes mixed layers slumping and sliding of sandstone beds convolute bedding and pillar and flame structures the soft sediment deformed intervals resemble those ascribed elsewhere to seismic shaking moreover the study area provides the appropriate conditions for the preservation of deformation structures induced by seismicity such as location in a tectonically active area variable sediment input to produce heterolithic deposits and an absence of bioturbation the vertical distribution of soft sediment deformation implies frequent seismic shocks underlining the importance of seismicity in the betic region during the late messinian when the nijar basin became separated from the sorbas basin to the north the presence of liquefied gravel injections in the marginal facies indicates strong earthquakes m 7 the identification of at least four separate fissured levels within a single lago mare interval suggests a recurrence interval for large magnitude earthquakes of the order of millennia assuming that the cyclicity of the alternating lago mare and continental intervals was precession controlled this suggestion is consistent with the present day seismic activity in se spain

paleomagnetic evidence for high temperature emplacement of the 1883 subaqueous pyroclastic flows from krakatau volcano indonesia the paroxysmal 1883 eruption of krakatau volcano in indonesia discharged at least 6 5 km3 dense rock equivalent of pyroclastic material into the shallow waters of the sunda straits within a 15 km radius of the volcano progressive thermal demagnetization studies of individually oriented pumice clasts from a core sample of the submarine pyroclastic deposits show that 41 out of 47 clasts exhibit single component remanence with mean inclination of 2 4 the partial thermoremanent magnetization components of both pumice and lithic clasts are well grouped in orientation indicating that substantial cooling of clasts must have occurred following deposition estimated subaqueous emplacement temperature for such clasts is greater than 500 c rare two component lithic fragments exhibit inflection points on vector endpoint diagrams that mark the temperature below which the fragments acquired magnetization of similar orientation these inflection points range from 350 to 550 c indicating a minimum subaqueous emplacement temperature of 350 c paleomagnetic evidence for high emplacement temperature supports the hypothesis that proximal 1883 submarine pyroclastic deposits resulted from entrance of hot subaerially generated pyroclastic flows into the sea similar deposits have been interpreted from the geologic record but this is the first documented example of submarine pyroclastic flows from a historic eruption the krakatau deposits thus serve as an important modern analog for the study of pyroclastic flow seawater interactions

permo triassic and paleoproterozoic metamorphism related to continental collision in yangpyeong south korea abstract gneisses and migmatites exposed in the yangpyeong area in the northern gyeonggi massif provide insight into the paleoproterozoic and triassic metamorphic events in south korea garnet biotite gneiss and sillimanite garnet biotite gneiss in the western part of the area reveal paleoproterozoic metamorphism 1888 1871 ma at p t conditions of 760 820 c and 8 10 kbar and 710 750 c and 5 7 kbar respectively these rocks were overprinted by low p t type metamorphism 590 650 c 3 4 kbar during the triassic ca 237 ma in contrast a cordierite rich migmatite near the post collisional triassic igneous complex in the eastern part of the area was strongly metamorphosed during the triassic ca 235 ma at 750 790 c and 7 8 kbar the similar triassic ages in the western and eastern areas suggest that low p t type metamorphism occurred as a second stage of regional metamorphism which is characterized by the production of cordierite with an irregularly shaped garnet the metamorphic grade of the triassic metamorphism decreases spatially towards the west from granulite facies to amphibolite facies metamorphic conditions and the paleoproterozoic metamorphism is well preserved in the western part with low grade triassic metamorphism the new discovery of the triassic metamorphic event in the yangpyeong area in addition to the previously reported triassic post collision igneous event supports the idea that the continental collision belt between the north and south china blocks extends from the hongseong area into the odesan area through the yangpyeong area in south korea

polygenetic sand volcanoes on the features of liquefaction processes generated by a single event 2012 emilia romagna 5 9 mw earthquake italy one of the most important geological effects generated by the seismic events of emilia romagna italy 2012 was the liquefaction the first earthquake took place on 20th may 5 9 mw and generated liquefaction in the locality of san carlo mainly recorded as large fissure sand volcanoes detailed stratigraphic and sedimentology analyses of these sand bodies indicated the assemblage of rhythmic normal graded beds of sand for many individual sand volcanoes this is interpreted as repeated individual sand extrusions generating polygenetic sand blows for a single earthquake this original analysis made for first time in a case of extensive seismic liquefaction indicates that the different pulses sand extrusion occurred after seismic shaking and therefore no related to the cyclic seismic shearing stimulated by surface seismic waves underground liquefaction of shallow sandy layers and ground cracking assisted by relevant lateral spreading promoted water and sand ejections e w direction localised and repeated ground subsidence and bulging supported by the ejection of the underlying fluidized sediments feedback transient ground undulations and repeated sand ejections the unstable undulating behaviour of the ground reinforced and sustained the liquefaction process through time after the seismic shaking leading the occurrence of polygenetic sand volcanoes in summary the seismic liquefaction is the starting point of the process although only if these sand ejections could promote the instability of the ground since underground sand depletions feedback the liquefaction process through time the process stops when the hydrostatic balance is recovered in the affected zone

experimentally derived high pressure cumulates from hydrous arc magmas and consequences for the seismic velocity structure of lower arc crust 1 this contribution explores the consequences of experimentally derived ultramafic plutonic rocks for estimates of continental crust composition the formation of high pressure cumulates from primitive to evolved hydrous arc magmas was investigated in the range 0 8 1 5 gpa and 1350 800 c to provide constraints on solid assemblages that form the roots of island arc crust at pressures exceeding 0 8 gpa 25km 40 60 of ultramafic cumulates are produced to obtain andesite to dacite compositions that are typical for evolved island arc volcanic and plutonic rocks calculated cumulate densities are comparable or higher than upper mantle values while seismic velocities vp vary continuously between 7 3 and 8 km s resulting in a broad crust mantle transition the moho represents a plagioclase saturation boundary our results are consistent with seismic imaging from continental margins and island arcs revealing that beneath an active volcanic front a sharp geophysical moho signature is sometimes absent

paleozoic to mesozoic micro block tectonics in the eastern central asian orogenic belt insights from magnetic and gravity anomalies abstract the ne china region involves a complex accretionary belt formed by multiple stages of assembly of micro blocks from the paleozoic to mesozoic the tectonics of which provides important clues on the evolution of the east asian continental margin with a view to evaluating the micro block evolution in ne china we used gravity and magnetic methods to analyze the geophysical characteristics of the micro blocks and their boundaries combining with regional geology paleomagnetism and paleontology we reconstructed the micro block assembly history in the eastern central asian orogenic belt five paleozoic to mesozoic micro blocks are recognized in ne china the erguna xing an songnen jiamusi and nadanhada and their boundaries show significant differences in gravity and magnetic fields the boundary between the erguna block eb and the xing an block xb shows as a continuous tectonic line in the gravity field whereas the one between the xb and the songnen block sb exhibits a rather discrete but strong magnetic anomaly belt the boundary between the sb and the jiamusi block jb is characterized by both distinct gravity and magnetic anomalies the nadanhada micro block nmb appears as an independent micro block in the fourth order detail field of the bouguer gravity anomaly where it shows as a short axis or circinate structure in this anomaly field the paleozoic to mesozoic tectonic evolution of these micro blocks in ne china is closely related to five sutures in the eastern central asian orogenic belt the xinlin xiguitu suture was first formed at 500 ma leading to the assembly of the eb and the xb the heihe hegenshan suture was formed at 320 290 ma marking the amalgamation of the xb and the sb the mudanjiang yilan suture was formed at 200 ma marking the collision of the jb and the sb the paleo asian ocean closed during 250 230 ma in a scissor style the subduction of the paleo pacific ocean was initiated at 200 ma based on the deep structural architecture imaged from gravity and magnetic anomalies we propose an evolutionary model of the micro blocks in the ne china which provides important insights into the tectonic evolution of the ne china region during the paleozoic to mesozoic

the september 16 2015 illapel tsunami chile sedimentology of tsunami deposits at the beaches of la serena and coquimbo abstract on september 16 2015 a mw 8 3 earthquake occurred off the coast of central chile 46 km west of the town of illapel the quake caused a tsunami impacting the coast mainly between the towns of caldera c 27 s and pichidangui c 32 s at coquimbo and la serena c 30 s the tsunami attained large wave heights on the order of 4 5 m leading to flooding and destruction of infrastructure including the coastal road we report the results of a post tsunami sedimentological field survey undertaken in october 2015 focussing on the beaches of coquimbo and la serena at playa changa a beach at coquimbo affected by the highest waves the tsunami destroyed large parts of the coastal road embankments on both the seaward and landward sides on the landward side the tsunami distributed triangular concrete construction elements of the embankment across the coastal plain on the seaward side granite boulders of up to 2 t were ripped out of the coastal road embankment and transported onto the beach sand used in construction of the embankment was redistributed across the beach as an outflow deposit at la serena we observed a laminated package of tsunami deposits along a 20 m long trench perpendicular to the coast the sediments have erosive basal surfaces with an amplitude of up to 50 cm the deposit thickness varies between 10 and 50 cm the sedimentary package consists of 6 mostly lenticular layers of variable thickness and spatial extent ranging between dark laminae a few millimeters thick and rich in heavy minerals and lighter colored sand layers up to 15 cm thick grain size distributions are moderately well to well sorted and unimodal with modes between 1 3 and 2 0 medium sand cross beds in the lower four layers indicate deposition from tsunami inflow cross bedding in the second layer from the top layer records outflow the abundance of cross beds and laminae suggests that deposition of sand from bed load traction currents was the prevailing mode of deposition water escape structures occur as small sand diapirs and volcanoes water escape through small volcanoes appears to have been coeval to formation of the overlying layer by traction deposition this synchroneity is indicated by sand sourced from the lower layer which has been preserved as a thin plume deformed in the downcurrent i e landward direction in the newly forming upper layer other sediment layers show sand diapirs intruding up to 15 cm into the overlying tsunami deposit the assemblage of sedimentary structures indicates rapid deposition from one or several waves associated with the tsunami event

mesoproterozoic magmatic suites from the central western korean peninsula imprints of columbia disruption in east asia abstract middle mesoproterozoic rift related magmatisms of mantle plume origin are of global interest in understanding the breakup of the columbia supercontinent here we investigate the age equivalent basement rocks along the western marginal areas of the northwestern gyeonggi massif in the central western korean peninsula the sensitive high resolution ion microprobe shrimp u pb zircon ages of the late middle mesoproterozoic mafic dykes and monzonitic intrusions from the dongman island and the early late mesoproterozoic syenites from the kimpo area show 1259 12 ma 1222 9 ma and 1197 5 ma 1194 6 ma respectively suggesting multiple magmatic pulses the late middle mesoproterozoic monzonitic intrusions and early late mesoproterozoic syenites are characterized by a1 type granite affinity formed in continental rifts the middle mesoproterozoic mafic dykes show characteristics of transitional composition between tholeiitic alkaline basalts to alkaline basalt having geochemical affinity of oib wpb derived from enriched mantle sources indicating a mantle plume origin the data presented in this work together with previous lithological geochemical and geochronological information on the magmatic suites from the western margin of the gyeonggi massif provide important insight into a mesoproterozoic continental margin rift setting at ca 1259 1194 ma and are broadly coeval with the mesoproterozoic hotspot track identified in the laurentia north china craton and baltica providing the imprints of the columbia disruption in northeast asia

water escape structures in coarse grained volcaniclastic fluvial deposits of the ellensburg formation south central washington abstract the miocene ellensburg formation of south central washington consists largely of volcaniclastic fluvial sediments deposited on a gentle eastward sloping surface off the cascade volcanic belt the ellensburg fluvial systems were periodically choked with texturally immature volcanic detritus and were probably characterized by rapid deposition and aggradation pillar structures and pocket structures of water escape origin are generally uncommon in coarse grained sediments but are common in conglomeratic deposits of the ellensburg development of water escape structures in the ellensburg and in other coarse grained units is probably dependent on a combination of variables that includes depositional slope rates of sediment deposition and aggradation textural maturity sediment density and regional seismicity

experimental aqueous fluidization of ignimbrite abstract experiments were carried out on the aqueous fluidization behaviour of ignimbrite and the associated formation of fluid escape pipes the starting material was an ignimbrite that had been saturated with water under vacuum until 80 15 of the vesicles were filled this aimed to reproduce water logging conditions of a hot pyroclastic flow in contact with water such as in the case of a lahar or of a pyroclastic flow entering the sea the ignimbrite sample was fluidized by water at vertical velocities from 0 005 to 7 mm s 1 for durations of 10 180 min channelling occurred almost immediately at even the lowest velocities and pipe channel size increased slightly with time the pipes had the form of elongated upwardly flared funnels and grew downwards and sideways with time even under decreasing flow conditions pipe nucleation and growth generated irregular pressure fluctuations in the sample showing that the standard p u plots commonly used in fluidization studies are not useful for coarse grained poorly sorted samples each pipe was stratified internally with a basal layer rich in dense lithic and crystals an intermediate layer rich in pumice and an upper layer rich in fine components as much as 30 of the initial sample mass was elutriated including platy mica crystals at the highest flow rates at velocities exceeding 2 mm s 1 duration of experiment 10 min single pipes grew and coalesced rapidly either forming a single large pipe or causing the entire sample to become segregation layered in natural water lain sediments pipes may form near the end of deposition and during compaction because during transport shear may reduce channelling by water we also measured the degree of crystal enrichment in pipes we conclude that the presence of fluid escape pipes in ignimbrite like sediment cannot be used to infer a gas fluidized origin of the deposit since the geometry granulometry and degree of crystal enrichment in water generated pipes are similar to those in pipes formed by gas under dry conditions

towards establishing criteria for identifying trigger mechanisms for soft sediment deformation a case study of late pleistocene lacustrine sands and clays onikobe and nakayamadaira basins northeastern japan five main deformation units discrete sheets of deformed sediments that lie between a significant thickness of undeformed sediment were selected for study within late pleistocene lacustrine sands and clays in the onikobe and nakayamadaira basins northeastern japan the deformed units show evidence of deformation by a variety of mechanisms including fluidization liquefaction brittle failure and cohesive flow driving forces are thought to be primarily reverse density gradient systems but also include gravitational body force shear stress and unequal loading the main trigger mechanisms are firstly earthquakes secondly overloading from volcanic sands and thirdly to a lesser extent subaqueous currents consideration is given to criteria that allow the trigger mechanism to be identified this study shows that the following criteria can be used to identify a seismic triggering agent i setting ii the extent of the deformation units iii absence of evidence relating to other potential trigger mechanisms and iv evidence relating to other potential trigger mechanisms is present but can be seen elsewhere in the stratigraphic section associated with undeformed sediment conversely the following criteria while they are important in interpreting the driving force and deformation mechanism have no relevance to the trigger mechanism i sediment composition ii deformation structures being restricted to a single stratigraphic interval 1 m thick not necessarily correlatable over large areas and iii similarity to structures in the literature

continental origin of the bibong eclogite southwestern gyeonggi massif south korea eclogite is a high pressure hp metamorphic rock that provides important information about the subduction of both continental and oceanic crusts in this study we present shrimp zircon u pb isotopic data for a suite of the basement gneisses to investigate the origin of the proterozoic bibong eclogite in the hongseong area south korea zircon grains from the basement felsic gneisses yielded paleoproterozoic protolith ages ranging from ca 2197 to 1880 ma and were intruded by syenite at ca 750 ma a hp regional metamorphic event of triassic age ca 255 227 ma is recorded in the zircon rims of the country rocks which is also observed in the zircons from the eclogite the contacts between the bibong eclogite and its host rocks support an origin for the proterozoic protoliths indicating continental intrusions the hongseong area thus preserves evidence for the triassic collision indicating a tectonic linkage among the northeast asian continents

geochronological and geochemical implications of early to middle jurassic continental adakitic arc magmatism in the korean peninsula abstract sensitive high resolution ion microprobe shrimp zircon u pb ages and whole rock chemical compositions of early to middle jurassic plutons from the central to southern korean peninsula are reported to investigate the effect of paleo pacific plate subduction preserved along the continental margin twenty one plutonic rocks from the yeongnam massif i e sunchang and namwon plutons the okcheon belt jeongup boeun and mungyeong plutons the northeast gangreung pluton and the gyeonggi massif gonam anheung and ganghwa plutons have age ranges from ca 189 186 ma to 177 ma 177 166 ma and 177 173 ma respectively most plutonic rocks have chemical compositions similar to adakites showing high sio 2 45 62 74 96 wt low mgo 0 01 2 84 wt high na 2 o 2 65 4 83 wt high sr y and la yb low y and yb as well as low hfses nb and ta but initial sr ratios 0 7048 0 7262 k 2 o 0 50 5 88 wt and k 2 o na 2 o 0 34 2 1 were unlikely to have been formed by melting of either a thickened and or delaminated lower continental crust or an altered oceanic crust these suggest that the adakitic plutonic rocks in this region resulted from partial melting of an enriched mantle source metasomatized by dewatering from a delaminated flat slab the spatial distributions of this continental adakitic plutonic belt based on the present study together with previously reported geochronological results indicate that magmatic pulses gradually migrated toward the continent across the korean peninsula as a result of slab shallowing caused by periodic slab buckling the similar geochronological and geochemical characteristics petrogenesis and tectonic setting of the plutonic belt spanning the korean peninsula japan eastern china and eastern russia indicate a possible link to an active subduction system that existed during the early to middle jurassic although the products of the plate subduction might differ in different locations along the east asian continental margin

the role of fluidization in the emplacement of pyroclastic flows 2 experimental results and their interpretation abstract although often quoted as being important in the emplacement of pyroclastic flows little relevant experimental fluidization work has been done fluidization processes are first reviewed for a simple system against which ignimbrite samples can be compared results from fluidization experiments on ignimbrite samples show that their behaviour differs radically from any simple system principally because of their extremely poor sorting at a certain gas velocity u ie whose value cannot be predicted some ignimbrite samples begin to expand whilst at a higher gas velocity u mp the samples begin to show segregation structures the minimum fluidization velocity u mf in simple systems is replaced by u mp the value of the latter in pyroclastic materials cannot be easily or reliably predicted from published u mf correlations and a new empirical method for determining u mp is presented from the experimental data during fluidization ignimbrite samples expand much less than more conventional materials due to the bypassing of gas through segregation channels the total amount of expansion is also limited e g a 100 m thick pyroclastic flow will from fairly high gas velocities deflate to form an ignimbrite which is not less than 70 85 m thick during fluidization the poor sorting causes only part of the weight of the ignimbrite samples to be supported by the gas flow the degree of support increasing with an improvement in sorting segregation structures and grain size and compositional variations within fluidized ignimbrite samples show varying behaviour depending on the sorting of the sample after subjecting a sample to high gas velocities the net result is a grain size and compositionally zoned bed which becomes richer upwards in pumice and fine material once formed these features cannot be destroyed under laboratory conditions implying that some segregation structures should be present in any ignimbrite where u mp was exceeded

possible eastward extension of chinese collision belt in south korea the imjingang belt structural petrological and geochronological data from the middle korean peninsula indicate that the qinling dabie sulu collisional belt of east central china crosses the yellow sea and extends into the imjingang belt the yeoncheon complex first identified as the western imjingang belt comprises primarily north dipping metamorphic sequences 1 the northern jingok unit consisting of barrovian type metapelites and 2 the southern samgot unit consisting of calc silicate and amphibolitic rocks south vergent structures with reverse sense shearing are dominant in the jingok unit whereas late normal sense shearing is pervasive in the samgot unit and the deformed granitoid to the south these structural patterns are interpreted to correspond to extensional deformation associated with uplift following compression in a collisional belt pressure temperature p t estimates from the amphibolites suggest a high p amphibolite facies metamorphism 8 13 kbar and 630 790 c possibly evolving from eclogite facies conditions along a clockwise p t path sm nd and rb sr geochronological data suggest that the amphibolites emplaced in late proterozoic time were metamorphosed during permian triassic time

funnel shaped breccia filled clastic dykes in the late cambrian chaomidian formation shandong province china abstract some examples of a funnel shaped structure filled with both angular and rounded clasts occur in a peloidal grainstone bed of the chaomidian formation late cambrian in the jiulongshan area shandong province china the clasts consist of peloidal grainstone which is the same as that of the walls of the funnels the structures are interpreted as dykes formed by upward escape of pore water and or fluidized sediment through a narrow conduit which was gradually widened by the force of the intruding fluid sediment the erosional capacity of the pressurized fluid sediment mixture consequently diminished upwards which explains the gradual decrease in intensity of fragmentation from the adjoining walls in this direction

fluid flow due to the advance of basin scale silica reaction zones the conversion of biogenic silica opal a to opal ct cristobalite and tridymite in biosiliceous sediment causes increased rates of water expulsion because of the reduction in sediment porosity and dehydration of the amorphous opal a phase this release of water occurs over large tracts of sedimentary basins during sediment burial within discrete diagenetic reaction zones analysis of two dimensional and three dimensional seismic data sets from basins in the northern hemisphere provides geophysical evidence for a variety of fluid conduits and roughly circular erosional depressions at the contemporaneous seabed we interpret these features as indicative of water expulsion and focused fluid flow emanating from opal a to opal ct reaction zones at burial depths within the range 200 800 m the rate at which water is expelled depends upon the degree of porosity reduction and the weight fraction of bound water at the reaction zone as well as the rate of advance of the reaction zone where the reaction is actively taking place within homogeneous biosiliceous sediment the rate of water expulsion is independent of the reaction rate this is because water is released across the entire reaction zone therefore slow reaction rates are compensated for by expulsion of water across wider reaction zones we calculate the rate and volume of water expulsion for the faeroe shetland basin where the sediment immediately below the reaction zone contains on average 30 opal ct by weight the estimated volumetric rate of water expulsion per unit surface area at the present day is 6 m3 my 1 per square meter which is greater than the vertical flux of water at the same depth from compaction of the deeper basin fill the average volumetric rate of water expulsion is 120 km3 my 1 across the whole basin biogenic silica is particularly rich in neogene successions in high latitude and equatorial regions and where silica reaction zones are identified they should be factored into sediment compaction and fluid flow histories

improvements of precision and accuracy in in situ hf isotope microanalysis of zircon using the laser ablation mc icpms technique abstract we have developed a new analytical technique for precise and accurate in situ hf isotope ratio measurements for zircons by means of laser ablation multiple collector inductively coupled plasma mass spectrometry la mc icpms newly designed sample cell and n 2 mixing technique provided higher elemental sensitivity with smoother signal intensity profiles in order to improve the accuracy of the hf isotope ratio analysis previously reported correction methods for isobaric interferences on 176 hf by 176 yb and 176 lu were rigorously evaluated and we found that the use of independent mass bias factors for hf and yb in the isobaric interference correction resulted in more reliable hf isotopic data in order to test the reliability of the hf isotopic data from 35 m diameter ablation pits that are smaller than the typical size of most zircon grains lu hf isotopes for three zircons harvard 91500 antarctic zircon pma7 and acasta zircon ay199 were measured the present 176 hf 177 hf isotope ratio of 0 282321 46 2 s d and initial 176 hf 177 hf isotope ratio of 0 282315 47 2 s d were obtained for zircon standard 91500 the resulting present 176 hf 177 hf isotope ratio shows an excellent agreement with the previously reported data our in situ isotopic data revealed that the lu hf ratio varied significantly within the 91500 grain 176 lu 177 hf 0 000130 0 000345 suggesting the existence of slight isotopic heterogeneity in present 176 hf 177 hf approximately 15 ppm for antarctic zircon pma7 despite the smaller size of the single grain 50 100 m wide 80 300 m long and the presence of various mineral inclusions resulting analytical precision for the initial 176 hf 177 hf ratio was 128 ppm 0 281208 36 2 s d for acasta zircon ay199 despite the high yb hf 0 05 and lu hf 0 01 isotope ratios with the early archean crystallization age 3 74 ga resulting analytical precision for the initial 176 hf 177 hf ratio was 187 ppm 0 280160 52 2 s d these results demonstrate clearly that in situ hf isotope ratio microanalysis developed here has the potential to become a significant tool for zircon lu hf isotopic study

the middle permian to triassic tectono magmatic system in the southern korean peninsula abstract the permo triassic adakitic magmatism in the southern korean peninsula preserves important tectonomagmatic records along the east asian continental margin in this study we present shrimp la mc icpms u pb zircon ages and hf isotope signature with whole rock geochemical compositions of the middle permian to middle triassic granitoid gneiss granitoid suites and the middle to late triassic plutonic rocks in the southeastern korean peninsula the former yields three age groups of ca 272 263 ma ca 258 251 ma and ca 243 240 ma respectively the latter group yields ca 237 216 ma ages indicating a long term magmatism that lasted from the middle permian to late triassic the granitoid gneiss granitoid suites have chemical compositions similar to high silica adakitic rocks showing high sio2 59 55 73 97 wt na2o 3 55 5 30 wt sr y 30 401 and la ybn 11 173 and low mgo 0 18 1 82 wt y 2 14 ppm and ybn 2 7 these rocks are peraluminous with high ba and sr and show relatively high k2o contents and k2o na2o ratios 0 7 with positive correlation between la ybn vs sr y ratios and high initial sr ratios these features reflect different contribution of the slab derived adakite melts that interacted with peridotitic mantle in the metasomatized mantle wedge and the middle paleoproterozoic lower crustal basement of the yeongnam massif on the contrary the triassic alkaline magmatism in the yeongnam massif is alternatively interpreted either by a tectonic switch to the extension dominated arc system or by a delamination of an overthickened arc the results from this study offer important evidence for a common subduction accretion system existed between the north and south china cratons and microcontinents between them along margins of the east asian continental blocks with different plate interaction in different locations generating distinct magmatic suites

geochronology and geochemical and nd sr isotopic characteristics of triassic plutonic rocks in the gyeonggi massif south korea constraints on triassic post collisional magmatism abstract sensitive high resolution ion microprobe shrimp zircon u pb ages and whole rock chemical and isotopic sr nd compositions have been measured on some middle triassic plutonic rocks associated with post collisional magmatism in the gyeonggi massif hongseong namyang and yangpyeong areas south korea plutonic rocks from the southwest hongseong and central yangpyeong gyeonggi massif and central okcheon belt cheongsan have ages of ca 227 226 231 and 225 ma respectively the plutonic rocks from hongseong are dominated by granite and quartz syenite from namyang by granite and from yangpyeong by quartz monzonite to quartz syenite and gabbro three rocks from the gyeonggi massif have the depletions in ta nb p and ti and enrichment in large ion lithophile elements lile characteristic of plutonic rocks that are subduction related or derived from an arc related crustal source the hongseong quartz syenite and yangpyeong quartz monzonite to quartz syenite have features of shoshonitic and high ba sr granitoids with lree enrichment and no significant eu anomaly the plutonic rocks from the gyeonggi massif have high initial 87 sr 86 sr ratios 0 7083 0 7144 and strongly negative e nd t 20 3 to 10 4 indicating derivation of the magmas from sources in the middle to upper crust these high k calc alkaline and shoshonitic plutonic rocks formed during periods of relaxation that separated the culminations of post orogenic uplift collapse in the transitions from orogenic to anorogenic events after the early middle triassic continent continent collision 249 229 ma between the north and south china blocks in south korea the plutonic rocks of the gyeonggi massif support therefore a possible eastern extension of the early middle triassic dabie sulu collision belt in china

geotectonic framework of permo triassic magmatism within the korean peninsula abstract this study presents sensitive high resolution ion microprobe shrimp u pb zircon ages and whole rock chemical and isotopic sr nd compositions of representative triassic plutons from south korea the plutons from the gyeonggi massif hongseong namyang yangpyeong and odesan the central okcheon belt baeknok and yongsan and the yeongnam massif sangju gimcheon hamyang and macheon yield zircon u pb ages of ca 232 226 ma 227 226 ma and 240 228 ma respectively among the triassic plutonic suite in south korea those within the gyeonggi massif are dominated by granite syenite monzonite monzodiorite and gabbro plutons within the okcheon belt are mainly by granite to quartz monzodiorite the yeongnam massif mainly incorporates granite to granodiorite and minor monzodiorite intrusions the geochemical signatures of the triassic plutons are characterized by ta nb troughs depletion of p and ti and enrichment of lile most plutons except macheon monzodioritic pluton show high initial 87 sr 86 sr ratios 0 708248 0 714678 and strongly negative e nd t 20 3 to 7 7 values suggesting contribution from middle to upper crust in contrast the macheon monzodioritic pluton in the yeongnam massif shows relatively low initial 87 sr 86 sr ratios 0 706547 0 706629 and negative e nd t 4 43 to 3 62 values the middle triassic syenite monzonite granite gabbro series in and around the gyeonggi massif possess high k calc alkaline and shoshonitic affinity suggesting a post collisional magmatic event following the permo triassic collision between the north and south china blocks the triassic plutons in the yeongnam massif and the okcheon belt together with a permian yeongdeok pluton in the gyeongsang basin show features typical of high to medium k calc alkaline magmatism with lree and lile enrichments this together with a depletion of y and hree suggests their formation in a subduction setting our results provide robust evidence to consider the gyeonggi massif as an extension of the qinling dabie sulu belt between the north and south china blocks in central china the okcheon belt and yeongnam massif in south korea together with the continental margin of south china are marked by a common permian to triassic magmatic episode probably related to the paleo pacific slab subduction

origin of the vertically orientated clasts in brecciated shallow marine limestones of the chaomidian formation furongian shandong province china numerous shallow marine limestone layers of the furongian late cambrian chaomidian formation in the jiulongshan section shandong province china are breccias some of these breccias show abundant vertical to subvertical clasts typically these clasts end abruptly at the contact plane with the overlying deposit either abutting the overlying sedimentary bed or via an erosional plane that truncates the clasts a few exposures show concentrations of clasts that must have been uplifted to the extent that they transgressed the then sedimentary surface or possibly penetrated the overlying sediment which in this case consists of muds or marls the clasts tend to show clusters with respect to the enclosing fabric all clasts are parallel to each other in a specific cluster while the various clusters may show different orientations of the clasts it is deduced that both the exceptional position and the exceptional orientation of the clasts must be ascribed to the upward movement of the clasts under the influence of pore water escaping under high pressure through fluidized sediment

the influence of palaeotopography on facies architecture and pyroclastic flow processes of a lithic rich ignimbrite in a high gradient setting the abrigo ignimbrite tenerife canary islands abstract the late pleistocene 188 19 ka abrigo ignimbrite represents the last major explosive caldera forming eruption on tenerife it consists almost entirely of a moderate volume 1 8 km 3 light grey phonolitic lithic rich ignimbrite deposit although a possible abrigo member thin fall deposit is locally preserved beneath the ignimbrite suggesting an initial short lived stable plinian eruption column the ignimbrite deposit is dispersed radially around the lower flanks of the las canadas edifice and correlates to a clast supported lithic breccia on the eastern and northern caldera wall much of the ignimbrite was probably deposited offshore or within the caldera now buried by more recent lavas two major depositional units separated by a co ignimbrite ash cloud deposit and which display dramatic variations in thickness pyroclastic flows were channelised along and deposited within the same valleys that exist today and were commonly continuous and sheet like across the interfluves the basal zones of pyroclastic flows are envisaged as a bed load of coarse lithic lapilli and blocks transported under their own momentum and with the support of the surrounding fine ash gas granular flow

characteristics of jurassic continental arc magmatism in south korea tectonic implications abstract study of whole rock geochemical and isotope sr nd characteristics of jurassic plutons from south korea shows differences in chemical compositions that might reflect the jurassic tectonic environments of east asia these plutons are dominated by granites and granodiorites with subordinate intermediate monzodiorite to diorite phases all analyzed samples show depletions in ta nb p and ti and enrichment in large ion lithophile elements characteristic of high k calc alkaline i type granitoids of the active continental margin early jurassic plutons fall into two groups documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontc

seismogenic deformation structures in microbialites and mudstones silurian lockport dolomite northwestern ohio u s a syndepositional deformation structures are present at two different stratigraphic levels in the silurian lockport dolomite at a quarry in maumee ohio such structures are absent in this unit at twelve other quarries in northwestern ohio the structures at maumee present within stromatolites thrombolites and variably bedded mudstones include convolute layers homogenization of bedding and breccia clasts clasts of stromatolites boudinage structures normal reverse and thrust faults and discordant and concordant breccias the distribution of deformation structures within beds suggests substantial control from substrate rheology possibly resulting from differences in degrees of lithification and from variations in water content the extensive variety of syndepositional deformation structures juxtaposed evidence for nearly synchronous compression and dilation proximity 4 5 km of the structures to the largest fault in northwestern ohio the bowling green fault and the restricted geographic distribution of the deformation structures suggest seismic shaking as a probable mode of genesis similarities between features produced by seismogenic deformation of siliciclastic sediments and deformation features in the lockport dolomite provide additional evidence that the latter features are seismogenic it is postulated that two earthquakes one with a magnitude 5 caused the formation of the syndepositional deformation structures present in the youngest facies in the lockport dolomite at maumee quarry the bowling green fault 4 5 km west of maumee was a growth fault during formation of the lockport dolomite and is considered to have been the source of earthquakes that created the syndepositonal deformation structures in this unit at maumee quarry evidence from the lockport dolomite in northwestern ohio suggests that seismogenic deformation structures created by two earthquakes along the bowling green fault with magnitudes of 5 did not form in this unit over large areas i e all of northwestern ohio this evidence challenges the suggestion that syndepositional seismogenic deformation structures are always formed over a large area

settling behaviour of concentrated dispersions and some volcanological applications abstract experiments have been carried out on the settling of non aggregating poorly sorted aqueous dispersions laced with lowdensity particles in order to gain insight into the sedimentation behaviour of volcaniclastic flows which contain pumice two poorly sorted dispersions of silicon carbide particles with continuous size distributions were studied plastic beads were added as a light component experiments were carried out at solids concentrations between 10 and 60 vol dispersions of low concentration generated normally graded deposits in which particles of different densities were in approximate hydraulic equivalence above a critical concentration 45 to 60 depending on the grain size distribution particle segregation was suppressed and the dispersion settled to form a virtually ungraded bed hindered settling at intermediate concentrations generated normally graded deposits with elutriation pipes floating rafts of plastic and capping layers of fines elutriated by escaping pore fluid buoyancy forces resulted in strong hydraulic inequivalence between light and dense components in the deposits from intermediate concentrations two mechanisms of elutriation pipe growth were observed at intermediate concentrations pipes grew progressively upwards in the deposit as the latter aggraded whereas at high concentrations they nucleated and grew uniformly throughout the whole dispersion elutriation pipes form readily during sedimentation of some poorly sorted aqueous dispersions the presence of elutriation pipes cannot be used alone to distinguish between deposits of epiclastic and pyroclastic flows reverse grading of pumice pumice rafts elutriation pipes and layers of elutriated fines should characterise deposits from pumice rich submarine mass flows despite differences in the fluid phase the experiments also have implications for fluidization mechanisms in pyroclastic flows hindered settling of a concentrated poorly sorted dispersion is a type of self fluidization in which the sedimentation of large particles causes a sufficiently strong vertical fluid flux to fluidize or elutriate smaller ones hindered settling is intrinsic to all pyroclastic flows as they spread out and deflate across the landscape and may reinforce other gas sources as an effective fluidization mechanism during emplacement of type 2 and type 3 ignimbrites and of coignimbrite lag breccias

age of the los ranchos formation dominican republic timing and tectonic setting of primitive island arc volcanism in the caribbean region this study reports u pb ages for zircons from the los ranchos formation which is part of the primitive island arc sequence the oldest volcanic rocks in the greater antilles zircons were analyzed from three samples quartz porphyry quartz keratophyre from the lower part of the formation quita sueno member fragmental quartz porphyry from the upper part of the formation pueblo viejo member and the cotui quartz diorite stock that intrudes the lower part of the formation the lower part of the los ranchos formation represented by the quita sueno sample formed at either 113 9 0 8 or 118 6 0 5 ma depending on interpretation of the data whereas the upper part represented by the pueblo viejo sample formed ca 110 9 0 8 ma the cotui stock rd 73 601 was emplaced ca 111 8 0 6 ma or 112 9 0 9 ma depending on whether eight grains reflect subtle inheritance these results show that the los ranchos formation was emplaced during the aptian albian transition that the cotui stock could have supplied magma to the volcanic sequence and fluids to the pueblo viejo gold silver deposit in the upper part of the formation and that carbonaceous sediments in the upper part of the formation formed at the same time as ocean anoxic event 1b paquier caribbean plate tectonic models involving invasion of anomalous pacific crust into the caribbean region appear to agree best with this age because they provide a mechanism for the change from primitive island arc pia to calcalkaline magmatism and account for the restricted ocean circulation necessary to generate regional anoxic conditions

periglacial paleosols and cryogenian paleoclimate near adelaide south australia abstract late cryogenian deformation of the reynella siltstone near hallett cove south australia has been interpreted as shallow marine methane seeps which were furthermore proposed to have played a role in deglaciation from snowball earth re examination and new analyses of these same outcrops confirms an earlier interpretation of this intrastratal deformation as periglacial paleosols which are evidence that even at maximum extent late cryogenian glaciers did not cover all continental lowlands let alone the world ocean known miocene and pliocene methane seeps of california examined for this study are very different in their gray color rounded nodules and clayey host rock compared with red highly deformed and silty to pebbly reynella siltstone of hallett cove stable isotopic composition of nodular carbonate in the reynella siltstone fails to show extreme carbon isotopic depletion or the meteoric oxygen lines characteristic of known methane seeps and sphaerosideritic waterlogged paleosols but instead shows covariance of carbon and oxygen isotopic composition comparable with that in pedogenic and subaerial carbonate of well drained soils mass balance geochemical analyses show modest weathering compatible with sand wedge structures and evaporitic pseudomorphs indicative of arid and frigid paleoclimate outcrops of reynella siltstone near hallett cove represent frigid low latitude floodplains not submarine methane seeps nor global glaciation

degassing structures in volcaniclastic kimberlite examples from southern african kimberlite pipes kimberlite pipes are commonly filled with a distinctive structureless facies termed volcaniclastic kimberlite previously also termed tuffisitic kimberlite breccia tkb which constitutes a thorough mix of both juvenile material and lithic clasts derived from all stratigraphic levels within this facies at several kimberlite pipes we have identified steeply inclined segregation structures developed on length scales ranging from several centimetres to decimetres the structures are pipe like in 2d and characterised by a concentration of coarse crystals and lithic clasts and depletion of the fine components that characterise the host matrix they are interpreted as degassing structures generated by the passing of fluids through particulate deposits during the earliest or latest stages of fluidisation in this paper we identify three circumstances in which degassing structures are generated in volcaniclastic kimberlite emplacement 1 pyroclastic density current deposits 2 local segregations caused by degassing through pipe fill and 3 fluidisation during channelling of deep sourced gas particle dispersions to our knowledge these structures have not been described in kimberlites before and provide important evidence for the occurrence of gas fluidisation during the waning stages of kimberlite eruptions using examples from southern african kimberlite pipes we describe general aspects of their structure combined with particle size distributions clast fabric studies and petrographic compositions

mesozoic episodic magmatism in south korea and its tectonic implication 1 ne trending granitoid batholiths in south korea are part of the huge phanerozoic granitoid belt in east asia the crystallization ages of granitoid plutons show three episodes of mesozoic magmatism in south korea triassic 248 210 ma jurassic 197 158 ma and late cretaceous early tertiary 110 50 ma with a late jurassic early cretaceous 50 m y hiatus the granitoid ages and kinematic analyses of the mesozoic structures in south korea suggest that the middle jurassic 180 170 ma dextral strike slip ductile shear zones formed by the northwest orthogonal subduction of the izanagi plate whereas the cretaceous sinistral faults formed by the northward oblique subduction of the same plate which generally agree with proposed reconstruction of plate motions albeit uncertain around east asia among the models proposed to explain magmatic lull in a continental arc shallow angle subduction associated with high convergence rate and subduction of oceanic plateaus might be the probable cause for the magmatic hiatus in south korea and japan the huge width 500 km of the east asian granitoid belt may be explained by oceanward retreat of subduction zone in the cretaceous in association with change in the movement direction of the subducting plate

cenozoic continental arc magmatism and associated mineralization in ecuador most of the economic ore deposits of ecuador are porphyry cu and epithermal style gold deposits associated with tertiary continental arc magmatism this study presents major and trace element geochemistry as well as radiogenic isotope pb sr signatures of continental arc magmatic rocks of ecuador of eocene to late miocene 50 9 ma elm and late miocene to recent 8 0 ma lmr ages the most primitive elm and lmr rocks analyzed consistently display similar trace element and isotopic signatures suggesting a common origin most likely an enriched morb type mantle in contrast major and trace element geochemistry as well as radiogenic isotope systematics of the whole sets of elm and lmr samples indicate strikingly different evolutions between elm and lmr rocks the elm rocks have consistently low sr y increasing rb sr and decreasing eu gd with sio2 suggesting an evolution through plagioclase dominated fractional crystallization at shallow crustal levels 20 km and most likely at sub crustal levels 40 50 km the change in geochemical signatures of tertiary magmatic rocks of ecuador from the elm to the lmr type coincides chronologically with the transition from a transpressional to a compressional regime that occurred at 9 ma and has been attributed by other investigations to the onset of subduction of the aseismic carnegie ridge

water upwelling pipes and soft sediment deformation structures in lower pleistocene calcarenites salento southern italy a thin sedimentary blanket consisting mostly of subtidal unconformity bounded calcarenite units was deposited in the small novoli graben apulian foreland southern italy in pliocene2pleistocene time in a limited part of the study area the lower pleistocene calcarenite di gravina forming the thicker part of this blanket is crossed by continuous to discontinuous cylindrical pipes as much as 12 m high most commonly consisting of stacked concaveupward laminae locally grading upward into soft sediment deformation features and large dishes the evidence favors an origin linked to upwelling of overpressured groundwater from a large karstic reservoir hosted in the mesozoic carbonate rocks the reservoir periodically developed a relatively high hydrostatic head due to tertiary to pleistocene cover acting as an aquitard or aquiclude as a result submarine springs were generated the activity of which was primarily controlled by relative sea level fluctuations it is suggested that the pipes were located in those points where the hydrostatic pressure was sufficient to fluidize the overlying sediment and could be released without notably affecting the surrounding sediments some pipes cross calcarenitic infills of karstic sinkholes developed in the underlying units whereas others follow the course of vertical to high angle extensional synsedimentary tectonic fractures generated when the calcarenites were still in an unconsolidated to semiconsolidated state the former relationships suggest that vertical routes of water upwelling during highstand of base level commonly coincided with axes of vadose solution during base level lowstand the latter suggest that opening of fractures enhanced the connection of the deep aquifer with the surface hence intensifying water upwelling we think that fluidization along the fractures was not hindered by the partially coherent state and that pipes with a cylindrical geometry could form in spite of the planarity of the fractures the formation of the pipes and their internal structure of stacked concave upward laminae is thought to be consistent with a process of fluidization due to through flowing waters we believe that essential in this process is the role of upward migrating transient water filled cavities akin to the voidage waves hassett s 1961a 1961b parvoids experimentally reproduced by several authors in liquid fluidized beds and regarded as true instability phenomena of a fluidized suspension occurring above minimum fluidization velocity it is suggested that the process is akin to the production of the dish structure it consists of the filling of transient upward migrating water filled cavities through steady fallout of particles from the cavity roof their redeposition in a more consolidated state and subsidence of the roof due to water seepage upward from the cavity the process was accompanied by segregation of grains according to their size and density as well by elutriation of finest particles and led to a new pattern of sediment texture packing and fabric with respect to the surrounding calcarenites

large scale liquefaction and fluidization in the cap chat melange quebec appalachians the cap chat melange crops out discontinuously for 200 km along the south shore of the st lawrence river in the gaspe peninsula it is located just south of logan s line the northern limit of the humber zone with the taconian foreland basin this melange is composed of dismembered rocks of the adjacent formations in particular the lower ordovician riviere ouelle and middle ordovician tourelle formations with lesser contributions by the middle ordovician des landes and the cambrian orignal formations blocks in the melange vary in size from a few centimetres to several kilometres with well preserved internal stratigraphy in the larger blocks the distribution of blocks is not uniform and the composition of the surrounding matrix changes with corresponding changes in block composition tectonic processes mostly extensional and compressional faulting are responsible for some of the chaotic aspects of the melange however the main mechanism was as follows i large scale liquefaction of the mudstone rich riviere ouelle formation ii sinking with consequent dismembering of the tourelle formation into this underlying weakened riviere ouelle formation and iii fluidization of the lowermost sand beds of the tourelle formation resulting in abundant sandstone sills and dikes in the riviere ouelle formation

mantle eduction tectonic fluidisation at depth abstract recent direct observations in trench environments demonstrate that massive volumes of wet sediments are subducted the gas phases in and near trench zones also show the evidence for subduction of organics and ocean fluids serpentine sea mounts also show that large quantities of serpentine are subducted thus in the upper layers of the subducting slab metamorphic processes must generate fluidized beds which may be extruded along the subduction faults or intruded by hydraulic fracture mechanisms into the overlying cover rocks this process which we term eduction may account for some of the exotic assemblages containing high pressure rocks found in subduction assemblages the equivalent of deep mud dykes and volcanoes the same process may be associated with seismic events

phanerozoic high pressure eclogite and intermediate pressure granulite facies metamorphism in the gyeonggi massif south korea implications for the eastward extension of the dabie sulu continental collision zone abstract petrological analysis zircon trace element analysis and shrimp zircon u pb dating of retrogressed eclogite and garnet granulite from bibong hongseong area sw gyeonggi massif south korea provide compelling evidence for triassic 231 4 3 3 ma high pressure hp eclogite facies m1 metamorphisms at a peak pressure temperature p t of ca 16 5 20 0 kb and 775 850 c this was followed by isothermal decompression itd with a sharp decrease in pressure from 20 to 10 kb and a slight temperature rise from eclogite facies m1 to granulite facies m2 followed by uplift and cooling granitic orthogneiss surrounding the baekdong garnet granulite and the ophiolite related ultramafic lenticular body near bibong records evidence for a later silurian 418 8 ma intermediate high pressure ihp granulite facies metamorphism and a prograde p t path with peak p t conditions of ca 13 5 kb and 800 c k ar ages of biotite from garnet granulites amphibolites and granitic orthogneisses in and around the bibong metabasite lenticular body are 208 219 ma recording cooling to about 310 c after the early triassic metamorphic peak neoproterozoic zircon cores in the retrogressed eclogite and granitic orthogneiss provide evidence that the protoliths of these rocks were 800 and 900 ma old respectively similar to the ages of tectonic episodes in the central orogenic belt of china this and the evidence for triassic hp uhp metamorphism in both china and korea is consistent with a regional tectonic link within northeast asia from the time of rodinia amalgamation to triassic continent continent collision between the north and south china blocks and with an eastward extension of the dabie sulu suture zone into the hongseong area of south korea

density driven deformation structures in glacigenic consolidated diamicts examples from traeth y mwnt cardiganshire wales u k abstract density driven deformation may occur when a sediment of higher bulk wet density is deposited on top of one of a lower bulk wet density and occurs commonly in glacigenic sediments by recognizing density driven deformation of gravels and sands embedded in diamicts it is possible to reconstruct relative preconsolidation states of the diamicts density driven structures indicate that during deformation the diamict behaved as a viscous fluid thus providing important evidence for the viscosity and physical state of diamicts after deposition which has implications for the depositional environment the density driven process and its implications for reconstructing depositional environments is discussed criteria are given for the recognition of density driven deformation stages of gravels and sands deposited on top of a viscous mud

clastic pipes and mud volcanism across mars terrestrial analog evidence of past martian groundwater and subsurface fluid mobilization abstract clastic pipes are cylindrical injection features that vertically crosscut bedding with sharp contacts terrestrial pipes have cylindrical morphologies massive or radially graded interiors and raised outer rims increased grain size and subsequent cementation along the more porous edges makes the rims more resistant to weathering pipes have crosscutting relationships with other pipes due to multiple formation events or migrating eruption centers and are associated with other soft sediment deformation features terrestrial clastic pipes form via liquefaction and fluidization which require a near surface groundwater system to initiate i e sand sized sediments must be saturated for pipes to form clastic pipes cm to 1000 m diameters occur on mars across multiple time periods and terrains and are recognized in both rover and orbital imagery a conical or cylindrical geometry and massive interior core characterize these features the pipes on mars show various geomorphic expressions and are classified into five types by the presence or absence of a raised outer rim or a central pit these types are interpreted to represent the erosional evolution of pipes at different stages from their initial surface eruptive structures to their weathered remnants eroded conical hills martian pipes formed via fluidization as evidenced by 1 raised outer rims possibly indicating textural differences along the pipe edges from traction interactions of fluid suspended sediment 2 crosscutting relationships with other pipes suggesting reactivated fluidization pathways or migrating eruptive vents and 3 close spatial association between pipes and other features thought to form by soft sediment deformation e g contorted bedding integration of terrestrial analog data with the mars observations provides evidence for past martian groundwater and subsurface fluid mobilization

aseismic controls on in situ soft sediment deformation processes and products in submarine slope deposits of the karoo basin south africa intervals of soft sediment deformation features including vertical fluid escape and load structures are common and well exposed in permian lower slope deposits of the tanqua depocentre karoo basin the structures mainly comprise elongated flames and load structures associated with ruptured sandstones and structureless siltstones observed over a range of scales the presence of an upper structureless siltstone layer linked to the flames interpreted as a product of the debouching of fine grained material transported through the flame onto the palaeo seabed together with the drag and upward folding of lower sandstone layers is evidence that the flames were formed in situ by upward movement of sediment rich fluids flames are oriented parallel to the deep water palaeoslope in lateral splay deposits between two major slope channel complexes statistical correlation and regression analyses of 180 flame structures from seven stratigraphic intervals suggest a common mechanism for the deformation and indicate the importance of fluidization as a deformation mechanism importantly deformation occurred in an instantaneous and synchronous manner liquefaction and fluidization were triggered by incremental movement of sediment over steeper local gradients that were generated by deposition of a lateral splay on an inherited local north west facing slope seismic activity is not invoked as a trigger mechanism because of the restricted spatial occurrence of these features and the lack of indications of earthquakes during the time of deposition of the deep water succession the driving mechanisms that resulted in the final configuration of the soft sediment deformation structures involved a combination of vertical shear stress caused by fluidization development of an inverse density gradient and a downslope component of force associated with the local slope ground penetrating radar profiles confirm the overall north east orientation of the flame structures and provide a basis for recognition of potential larger scale examples of flames in seismic reflection data sets

unusually large clastic dykes formed by elutriation of a poorly sorted coarser grained source tuff dykes of unusual size invade coarser grained volcaniclastic rocks of the jurassic mawson formation at coombs hills and allan hills antarctica we infer that the material for the largest dykes was elutriated from their host9s matrix to our knowledge this mode of genesis has not been invoked before in this volcanic setting elutriation was driven by magmatic heat but the production of relatively finer grained clastic dykes by elutriation of material from coarser ill sorted sources may be significant in many settings

subaqueous pyroclastic flows and ignimbrites an assessment an assessment of the literature on subaqueous pyroclastic flows and their deposits shows that the term pyroclastic flow is frequently used loosely to describe primary hot gas rich pyroclastic flows mass flows which resulted from the transformation of gassupported flows into water supported ones and secondary mass flows carrying redeposited pyroclastic debris based on subaerial pyroclastic flows the term pyroclastic flow should be restricted to demonstrably hot gas rich mass flows of pyroclastic debris using this definition very few examples of subaqueous pyroclastic deposits with evidence for hot emplacement and of having been wholly submerged have been described in the majority of these cases the evidence for a hot state of emplacement and for the subaqueous nature of the host depositional environment is inadequate the only unequivocal cases of hot pyroclastic flow deposits with adequate supporting evidence are the ordovician nearshore shallow marine ignimbrites of ireland and wales and miocene ignimbrites of southwest japan resulting from the passage of subaerially erupted pyroclastic flows into shallow water other possible examples are near vent dense clast deposits in the donzurobo formation of japan possible submarine intra caldera ponded ignimbrite successions in california and wales and near vent pumiceous deposits of ramsay island wales all other purported cases are either clearly the result of water supported mass flow transportation and deposition debris avalanches debris flows turbidity currents or lack adequate supporting evidence regarding the heat state or the palaeoenvironment only the shallow marine ignimbrites of ireland and wales show adequate evidence of welding but even these could have been nearly wholly exposed above sea level when welding occurred we conclude that when pyroclastic flows enter water they are generally disrupted explosively and or ingest water and transform into water supported mass flows and we suggest the various scenarios in which this occurs there is no evidence to suggest that welding in wholly subaqueous environments is common

complex plumbing systems in the near subsurface geometries of authigenic carbonates from dolgovskoy mound black sea constrained by analogue experiments targeted sampling on the dolgovskoy mound northern shatsky ridge revealed the presence of spectacular laterally extensive and differently shaped authigenic carbonates the sampling stations were selected based on sidescan sonar and profiler images that show patchy backscatter and irregular and discontinuous reflections in the near subsurface the interpretation of acoustic data from the top part of the mound supports the seafloor observations and the sampling that revealed the presence of a complex subsurface plumbing system characterized by carbonates and gas the crusts sampled consist of carbonate cemented layered hemipelagic sedimentary unit 1 associated with several centimetres thick microbial mats three different carbonate morphologies were observed a tabular slabs b subsurface cavernous carbonates consisting of void chambers up to 20 cm3 in size and c chimney and tubular conduits vertically oriented or forming a subhorizontal network in the subsurface the methanogenic origin of the carbonates is established based on visual observations of fluids seepage structures 13c depletion of the carbonates 13c varying between 36 7 and 27 4 and by thin carbonate layers present within the thick microbial mats laboratory experiments with a hele shaw cell were conducted in order to simulate the gas seepage through contrasting grain size media present on the seafloor combined petrography visual observations and sandbox simulations allowed a characterization of the dynamics and the structures of the plumbing system in the near subsurface based on sample observations and the experiments three observed morphologies of authigenic carbonates are interpreted respectively as a darcian porous flow through the finely laminated clayey coccolith rich layers b gas accumulation chambers at sites where significant fluid escape was impeded by thicker clayey layers forming the laminated unit1 and c focussed vertical fluid venting and subhorizontal migration of overpressured fluids released from b the hele shaw cell experiments represent a promising tool for investigating shallow fluid flow pathways in marine systems

the role of gas fluidisation in the formation of massive volcaniclastic kimberlite abstract massive volcaniclastic kimberlite mvk deposits are a volumetrically important constituent in most kimberlite diatremes mvks are typically characterised by their uniform texture and homogeneous composition and previous studies suggest that they exhibit little appreciable internal variation however new field results from the venetia k1 diatreme south africa show that mvk displays significant changes over metre scales the textural characteristics and large and small scale structure of the deposits are described and interpreted as being due to fluidisation laboratory experiments of tapered fluidised beds demonstrate how they are heterogeneous with fluidisation and mixing limited to the centre of the bed marginal wedge shaped regions remain unfluidised the unfluidised regions are internally laminated and slip downwards when a high proportion of the bed is fluidised the observations also demonstrate how fluctuations in gas velocity can produce steep internal boundaries between laminated and well mixed regions data consistent with gas fluidisation in mvk deposits includes the massive structure uniform distribution of lithic clasts presence of steep internal contacts dominantly sub vertical crystal fabrics across the vent occurrence of surface derived material along the tapered diatreme walls and the presence of degassing structures we propose that the overall structure of the venetia k1 diatreme fill is consistent with a multi stage fluidised emplacement which involved 1 strong initial fluidisation that caused thorough mixing of juvenile and lithic material 2 a gradual step wise decrease in gas flux that produced nested pipe like sequences and 3 migration of the narrow fluidised column towards the steep eastern diatreme wall the occurrence of 4 degassing structures in mvk deposits across the vent is consistent with an overall rapid transition from high to low degrees of fluidisation towards the end of the eruption

chronology of the pueblo viejo epithermal gold silver deposit dominican republic formation in an early cretaceous intra oceanic island arc and burial under ophiolite the pueblo viejo deposit production to 1996 166 t au 760 t ag is located in the dominican republic on the caribbean island of hispaniola and ranks as one of the largest high sulfidation acid sulfate epithermal deposits reserves in 2007 635 t au 3 648 t ag one of the advanced argillic ore bodies is cut by an inter mineral andesite porphyry dike which is altered to a retrograde chlorite illite assemblage but overprinted by late stage quartz pyrite sphalerite veins and associated low grade au ag zn cd hg in as se and te mineralization the precise tims u pb age 109 6 0 6 ma of the youngest zircon population in this dike confirms that the deposit is part of the early cretaceous los ranchos intra oceanic island arc intrusion related gold sulfide mineralization took place during late andesite dacite volcanism within a thick pile 200 m of carbonaceous sand and siltstones deposited in a restricted marine basin the high level deposit was shielded from erosion after burial under a late albian 109 100 ma ophiolite complex 8 km thick which was in turn covered by the volcano sedimentary successions 4 km of a late cretaceous early tertiary calc akaline magmatic arc estimates of stratigraphic thickness and published alunite illite and feldspar k ar ages and closure temperatures alunite 270 20 c illite 260 30 c k feldspar 150 c indicate a burial depth of about 12 km at 80 ma during peak burial metamorphism 300 c and 300 mpa the alteration assemblage kaolinite quartz in the deposit dehydrated to pyrophyllite temperature time relations imply that the los ranchos terrane then cooled at a rate of 3 4 c ma during slow uplift and erosion

elutriation pipes in ignimbrites an analysis of concepts based on the huichapan ignimbrite mexico abstract the upper portion of the huichapan ignimbrite uhi central mexico is a non welded massive ignimbrite characterized by large and well developed fines poor elutriation pipes we conclude that the most important pipe forming process in the huichapan ignimbrite was deposition triggered aggregative type segregation and this process is enhanced by positive pore pressure feedback during the rapid settling of the pyroclastic material in experiments pumice concentration zones and elutriation pipes have been formed in separated portions of the deposits contrary to the experimental results in the uhi both pumice concentration zones and elutriation pipes have been observed alongside one another within the deposit we interpret this association to have formed during time periods of unusually high deposition rate within a long lived sustained pyroclastic density current system elutriation pipes were formed because of low shearing and vertical channeling of gases and the pumice concentration zones formed because of pumice segregation during hindered settling nevertheless the deposition rate was so high that the segregated pumice was frozen before it could bypass within the deposit right next to the elutriation pipes we present a classification scheme of five types of elutriation pipes based on our field observations in the uhi and a review of field and experimental work from other authors 1 tubular pipes 2 irregular tubular pipes 3 anastomosing pipes 4 pinch out pipes 5 deflected pipes irregular tubular pipes are the most common in the volcanic geological record and they form because of deposition triggered aggregative type segregation and or post depositional upward fluid flow likely anastomosing elutriation pipes are a unique product of deposition triggered aggregative type segregation a comparison between the lower and upper portion of the huichapan ignimbrite leads to the conclusion that deposition triggered pipe formation is enhanced by poor sorting low shearing and presence of large clasts 5 32 mm pipe free ignimbrites in the volcanic geological record likely come from relatively better sorted dispersions with few coarse clasts but more importantly strong shearing during deposition may be the main processes that diminish pipe formation

rapid injection of particles and gas into non fluidized granular material and some volcanological implications in diatremes and other volcanic vents steep bodies of volcaniclastic material having differing properties particle size distribution proportion of lithic fragments etc from those of the surrounding vent filling volcaniclastic material are often found it has been proposed that cylindrical or cone shaped bodies result from the passage of debris jets generated after phreatomagmatic explosions or other discrete subterranean bursts to learn more about such phenomena we model experimentally the injection of gas particulate dispersions through other particles analogue materials glass beads or sand and a finite amount of compressed air are used in the laboratory the gas is made available by rapidly opening a valve therefore the injection of gas and coloured particles into a granular host is a brief 1 s discrete event comparable to what occurs in nature following subterranean explosions the injection assumes a bubble shape while expanding and propagating upwards in reaction the upper part of the clastic host moves upward and outward above the bubble forming a dome the doming effect is much more pronounced for shallow injection depths thin hosts with dome angles reaching more than 45 significant surface doming is also observed for some full scale subterranean blasts e g buried nuclear explosions so it is not an artefact of our setup what happens next in the experiments depends on the depth of injection and the nature of the host material with shallow injection into a permeable host glass beads the compressed air in the bubble is able to diffuse rapidly through the roof meanwhile the coloured beads sediment into the transient cavity which is also closing laterally because of inward directed granular flow of the host depending on the initial gas pressure in the reservoir the two phase flow can erupt or not non erupting injections produce cylindrical bodies of coloured beads whereas erupting runs produce flaring upward or conical deposits changing the particle size of the host glass beads does not have a large effect under the size range investigated 100 200 to 300 400 m doubling the host thickness injection depth requires a doubling of the initial gas pressure to produce similar phenomena such injections whether erupting or wholly subterranean provide a compelling explanation for the origin and characteristics of multiple cross cutting bodies that have been documented for diatreme and other vent deposits

some major problems with existing models and terminology associated with kimberlite pipes from a volcanological perspective and some suggestions five significant problems hinder advances in understanding of the volcanology of kimberlites 1 kimberlite geology is very model driven 2 a highly genetic terminology drives deposit or facies interpretation 3 the effects of alteration on preserved depositional textures have been grossly underestimated 4 the level of understanding of the physical process significance of preserved textures is limited and 5 some inferred processes and deposits are not based on actual modern volcanological processes these issues need to be addressed in order to advance understanding of kimberlite volcanological pipe forming processes and deposits the traditional steep sided southern african pipe model class i consists of a steep tapering pipe with a deep root zone a middle diatreme zone and an upper crater zone if preserved each zone is thought to be dominated by distinctive facies respectively hypabyssal kimberlite hk descriptively called here massive coherent porphyritic kimberlite tuffisitic kimberlite breccia tkb descriptively here called massive poorly sorted lapilli tuff and crater zone facies which include variably bedded pyroclastic kimberlite and resedimented and reworked volcaniclastic kimberlite rvk porphyritic coherent kimberlite may however also be emplaced at different levels in the pipe as later stage intrusions as well as dykes in the surrounding country rock the relationship between hk and tkb is not always clear sub terranean fluidisation as an emplacement process is a largely unsubstantiated hypothesis modern in vent volcanological processes should initially be considered to explain observed deposits crater zone volcaniclastic deposits can occur within the diatreme zone of some pipes indicating that the pipe was largely empty at the end of the eruption and subsequently began to fill in largely through resedimentation and sourcing of pyroclastic deposits from nearby vents classes ii and iii canadian kimberlite models have a more factual descriptive basis but are still inadequately documented given the recency of their discovery the diversity amongst kimberlite bodies suggests that a three model classification is an over simplification every kimberlite is altered to varying degrees which is an intrinsic consequence of the ultrabasic composition of kimberlite and the in vent context few preserve original textures the effects of syn to post emplacement alteration on original textures have not been adequately considered to date and should be back stripped to identify original textural elements and configurations applying sedimentological textural configurations as a guide to emplacement processes would be useful the traditional terminology has many connotations about spatial position in pipe and of process perhaps the traditional terminology can be retained in the industrial situation as a general lithofacies mining terminological scheme because it is so entrenched however for research purposes a more descriptive lithofacies terminology should be adopted to facilitate detailed understanding of deposit characteristics important variations in these and the process origins for example every deposit of tkb is different in componentry texture or depositional structure however because so many deposits in many different pipes are called tkb there is an implication that they are all similar and that similar processes were involved which is far from clear

sedimentology of the krakatau 1883 submarine pyroclastic deposits the majority of tephra generated during the paroxysmal 1883 eruption of krakatau volcano indonesia was deposited in the sea within a 15 km radius of the caldera two syneruptive pyroclastic facies have been recovered in scuba cores which sampled the 1883 subaqueous pyroclastic deposit the most commonly recovered facies is a massive textured poorly sorted mixture of pumice and lithic lapilli to block sized fragments set in a silty to sandy ash matrix this facies is indistinguishable from the 1883 subaerial pyroclastic flow deposits preserved on the krakatau islands on the basis of grain size and component abundances a less common facies consists of well sorted planarlaminated to low angle cross bedded vitric enriched silty ash entrance of subaerial pyroclastic flows into the sea resulted in subaqueous deposition of the massive facies primarily by deceleration and sinking of highly concentrated deflated components of pyroclastic flows as they traveled over water the basal component of the deposit suggests no mixing with seawater as inferred from retention of the fine ash fraction high temperature of emplacement and lack of traction structures and no significant hydraulic sorting of components the laminated facies was most likely deposited from low concentration pyroclastic density currents generated by shear along the boundary between the submarine pyroclastic flows and seawater the krakatau deposits are the first well documented example of true submarine pyroclastic flow deposition from a modern eruption and thus constitute an important analog for the interpretation of ancient sequences where subaqueous deposition has been inferred based on the facies characteristics of encapsulating sedimentary sequences

the origin of consolidation laminae and dish structures in some deep water sandstones abstract consolidation laminae and dish structures form high density zones that are interpreted to have formed by disruption of primary structures during gravitational collapse of the grain framework during water escape and consolidation they are not associated with higher contents of clay size material than adjacent units but the chloritic clay minerals associated with consolidation laminae and dish structures have a different microtexture than observed elsewhere clay mineral texture has a direct effect on petrophysical characteristics in particular water saturation and conductivity in hydrocarbon saturated intervals ct scans identify consolidation laminae and dish structures as zones of high density that correspond to tighter packing of sand grains and are unrelated to clay distribution dish structures may form independently of consolidation laminae or by further modification of fragmented consolidation laminae

a new concept on tectonic correlation between korea china and japan histories from the late proterozoic to cretaceous abstract the dabie sulu collision belt in china extends to the hongseong odesan belt in korea while the okcheon metamorphic belt in korea is considered as an extension of the nanhua rift within the south china block the hongseong odesan belt divides korea s gyeonggi massif into northern and southern portions the southern gyeonggi massif and the yeongnam massif are correlated with china s yangtze and cathaysia blocks respectively while the northern gyeonggi massif is part of the southern margin of the north china block the southern and northern gyeonggi massifs rifted from the rodinia supercontinent during the neoproterozoic to form the borders of the south china and north china blocks respectively subduction commenced along the southern and eastern borders of the north china block in the ordovician and continued until a triassic collision between the north china and south china blocks while subduction was occurring on the margin of the north china block high p t metamorphic belts and accretionary complexes developed along the inner zone of southwest japan from the ordovician to the permian during the subduction the hida belt in japan grew as a continental margin or continental arc collision between the north and south china blocks began in korea during the permian 290 260 ma and propagated westwards until the late triassic 230 210 ma creating the sinistral tanlu fault in china and the dextral fault in the hida and hida marginal belt in japan phanerozoic subduction and collision along the southern and western borders of the north china block led to formation of the qinling dabie sulu hongseong hida yanji belt

shrimp u pb dating and geochemistry of the cretaceous plutonic rocks in the korean peninsula a new tectonic model of the cretaceous korean peninsula abstract the cretaceous tectonomagmatism of the korean peninsula was examined based on geochemical and geochronological data of the cretaceous plutonic rocks along with distribution of volcano sedimentary nonmarine n to ne trending fault bounded sedimentary basins we conducted sensitive high resolution ion microprobe shrimp zircon u pb ages and whole rock geochemical compositions of 21 cretaceous plutonic rocks together with previously published data from the central to southern korean peninsula four age groups of plutonic rocks were identified group i ca 119 106 ma in the northern to central area group ii ca 99 87 ma in the central southern area group iii ca 85 82 ma in the central to southern area and group iv ca 76 67 ma in the southernmost area these results indicate a sporadic trenchward younging trend of the cretaceous magmatism in the korean peninsula the group i ii and iii rocks are dominated by high k calc alkaline i type rocks with rift related a type granitoids in contrast the group iv rocks are high k calc alkaline i type plutonic rocks with no a type rocks the geochemical signatures of the entire groups indicated lrees light rare earth elements enrichments and negative nb ta and ti anomalies indicating normal arc magmatism a new tectonic model of the cretaceous korean peninsula was proposed based on temporal and spatial distribution of the cretaceous plutons represented by four age groups 1 magmatic quiescence throughout the korean peninsula from ca 160 to 120 ma 2 intrusions of the i and a type granitoids in the northern and central korean peninsula group i plutonic rocks from ca 120 to 100 ma resulted from the partial melting of the lower continental crust due to the rollback of the izanagi plate expressed as the conversion from flat lying subduction to normal subduction the gyeongsang nonmarine sedimentary rift basin in the korean peninsula and adakite magmatism preserved in the present day japanese islands supported the slab rollback followed by steepening of the izanagi plate with an injection of upwelling of the hot asthenosphere into the mantle wedge 3 alternating shallow from 100 to 85 ma to steep from 85 to 65 ma subduction resulted in the migration of the normal arc magmatism in the southern korean peninsula expressed as the intruded i and a type group iii and i type granitoids group iv respectively the tectonomagmatism of the korean peninsula showed the unique style of evolution different from those of south china and japanese islands

seismically induced soft sediment deformation structures revealed by x ray computed tomography of boring cores abstract x ray computed tomography ct allows us to visualize three dimensional structures hidden in boring cores nondestructively we applied medical x ray ct to cores containing seismically induced soft sediment deformation structures ssdss obtained from the kanto region of japan where the 2011 off the pacific coast of tohoku earthquake occurred the ct images obtained clearly revealed various types of the seismically induced ssdss embedded in the cores a propagating sand dyke bent complexly by the preexisting geological structure deformed laminations of fluidized sandy layers and two types of downward mass movement ductile downward folding and brittle normal faulting as compensation for upward sand transport through sand dykes two advanced image analysis techniques were applied to the sand dyke ct images for the first time the growcut algorithm a specific digital image segmentation technique that uses cellular automata was used successfully to extract the three dimensional complex sand dyke structures embedded in the sandy sediments which would have been difficult to achieve using a conventional image processing technique local autocorrelation image analysis was performed to detect the flow pattern aligned along the sand dykes objectively the results demonstrate that x ray ct coupled with advanced digital image analysis techniques is a promising approach to studying the seismically induced ssdss in boring cores

adakites without slab melting high pressure differentiation of island arc magma mindanao the philippines abstract new geochemical data for pleistocene magmatic rocks from the surigao peninsula eastern mindanao the philippines demonstrate typical adakitic traits including elevation of sr y and depletion of the heavy rare earth elements 87sr 86sr and 143nd 144nd ratios of the adakites do not support melting of the subducted philippine sea plate but resemble pliocene arc lavas generated in the same subduction zone excepting the heavy rare earth elements the adakites and arc lavas also possess similar ratios of incompatible elements suggesting that the adakites were ultimately derived from melting of the mantle wedge the wide range of sio2 in the adakites and its strong correlation with trace element concentrations and ratios indicate two possible mechanisms for generating the adakitic signature 1 adakitic melt was produced from basaltic arc magma by fractional crystallisation of a garnet bearing assemblage 2 solidified basaltic rock containing garnet melted to yield adakitic magma in either case the basaltic precursor was generated from fluid modified mantle then differentiated within the garnet stability field in surigao this requires differentiation within mantle the surigao example suggests that any subduction zone has the potential to produce adakitic magma if basalt crystallises at sufficient depth this has important implications for the geodynamics of modern and ancient subduction zones that have generated similar rocks

anatomy of a water escape cusp in upper proterozoic torridon group sandstones scotland abstract evidence from recently published experiments is applied to the interpretation of a typical soft sediment deformation structure in coarse fluvial sandstones from the applecross formation of the upper proterozoic torridon group in northwest scotland the structure is an interfacial cusp formed at the contact between two cross bedded sandstone units in an upward coarsening sequence the characteristics of the structure suggest that deformation took place while the sediment was in a fluidized state during fluidization a water filled cavity developed near the top of the lower unit separating fluidized sediment beneath from a static couplet above the cavity became narrower and taller as fluidization continued focussing fluidization at a point primary stratification was destroyed in the fluidized zone but there is no evidence that fluidized sediment burst through the overlying zone a rupture may be out of the plane of the section or alternatively fluidization could have stopped before this stage was reached or fluid pressures could have been dissipated upwards the cavity closed leaving the lower part of the static couplet as a distinct unit estimates of the fluidization velocity and the duration of fluidization suggest the volume of water required for fluidization this could have been derived from packing changes following liquefaction of underlying sediment or from groundwater movements within the braided fluvial environment

discussion of c e 2000 volcanic domes and gold mineralization in the pueblo viejo district dominican republic mineralium deposita vol 35 pp 511 525