anisotropy of magnetic susceptibility and paleomagnetic studies in relation to the tectonic evolution of the miocene pleistocene accretionary sequence in the boso and miura peninsulas central japan abstract anisotropy of magnetic susceptibility ams and paleomagnetic methods have been applied on the middle miocene pleistocene sedimentary sequence in the boso and miura peninsulas of central japan in order to identify the invisible regional deformation sense as well as the intensity of deformation of sediments the southern sequences of the two peninsulas were subjected to syn sedimentary deformation of folding and faulting generated in compressional tectonics a previous result of the ams experiment on the sequences shows a development of a strong magnetic lineation thus it is conceivable that the lineation had to be generated during the process of deformation and in a direction perpendicular to the shortening however the orientation of the magnetic lineations is inconsistent among the different tectonic domains in the southern sequence the paleomagnetic declination in each domain reveals a clockwise rotation in various degrees reconstructed directions of the magnetic lineations show a consistent pattern in the east west direction suggesting that the sedimentary sequence was subjected to a north southward compression in contrast the compressive direction of the sediment cover on the pliocene pleistocene sequence reveals a northwest direction our results suggest that the philippine sea plate had been subducting northward during the middle miocene pliocene and changed its direction during the pliocene

decadal variability in the kuroshio oyashio extension simulated in an eddy resolving ogcm abstract through analysis of a hindcast integration of an eddy resolving quasi global ocean general circulation model decadal variability in the kuroshio oyashio extension region is investigated with particular emphasis on that of the subarctic oyashio and the kuroshio extension ke fronts the ke front is deep and is accompanied by a sharp sea surface height ssh gradient with modest sea surface temperature sst gradient in contrast the subarctic front is shallow and is recognized as a zone of tight gradient in sst but not ssh as a decadal scale change from a warm period around 1970 to a cool period in the mid 1980s those fronts in the model migrate southward as observed and the associated pronounced cooling is confined mainly to those frontal zones reflecting the distinctive vertical structure of the fronts the mixed layer cooling is the strongest along the subarctic front whereas the subsurface cooling and the associated salinity changes are most pronounced along the ke front concomitan

anatomy of north pacific decadal variability abstract a systematic analysis of north pacific decadal variability in a full physics coupled ocean atmosphere model is executed the model is an updated and improved version of the coupled model studied by latif and barnett evidence is sought for determining the details of the mechanism responsible for the enhanced variance of some variables at 20 30 yr timescales the possible mechanisms include a midlatitude gyre ocean atmosphere feedback loop stochastic forcing remote forcing or sampling error decadal variability in the model is expressed most prominently in anomalies of upper ocean streamfunction sea surface temperature sst and latent surface heat flux in the kuroshio oyashio extension koe region off japan the decadal signal off japan is initiated by changes in strength and position of the aleutian low the atmospheric perturbations excite sst anomalies in the central and eastern north pacific with opposing signs and canonical structure the atmospheric perturbations also change the ekm

mesozoic aseismic ridges on the farallon plate and southward migration of shallow subduction during the laramide orogeny we propose that an aseismic ridge of late jurassic and early cretaceous age on the farallon plate was subducted beneath the unites states cordillera during the laramide orogeny the relative buoyancy of the aseismic ridge caused shallow subduction which resulted in a magmatic lull 70 40 ma in the existing near trench magmatic arc and laramide uplift and faulting of crystalline basement 1000 1500 km inland from the trench the timing and latitudinal limits of the subduction of the aseismic ridge are similar to the timing and latitudinal limits of both the laramide orogeny and the magmatic lull in the western cordillera because the north northeast trending aseismic ridge was moving northeast relative to the north american plate the point of collision of the aseismic ridge with north america and therefore the locus of shallow subduction migrated southward with time causing the well documented southward migration of the magmatic lull

a varve based calibration of the bridge river tephra fall a 1 cm thick layer of bridge river tephra is preserved in a core of varved lake sediments recovered from hector lake alberta the varve sequence extends from the core top to well below the tephra layer and has bseen calibrated to calendar years a varve count yields a calendar age of 2332 bp for the ash layer with a potential error of about 50 years this age is about 30 years younger than the current best radiocarbon based estimate of the time of the eruption however in light of the potential errors in both the varve count and the radiocarbon age the two ages are not inconsistent the tephra contains no biotite in the past biotite free bridge river tephra has been associated with a possible late ca 2000 bp tephra fall but the tephra from hector lake is clearly associated with the main 2300 2400 bp eruptive event

evidence for catastrophic volcanic debris flows in pemberton valley british columbia the mount meager volcanic complex in southern british columbia is snow and ice covered and has steep glaciated and unstable slopes of hydrothermally altered volcanic deposits three large volume 108 m3 volcanic debris flow deposits derived from the mount meager volcanic complex have been identified the volcanic debris flows travelled at least 30 km downstream from the volcanic complex and inundated now populated areas of pemberton valley clay content and mineralogy of the deposits indicate that the volcanic debris flows were clay rich 5 7 clay in the matrix and derived from hydrothermally altered volcanic material the youngest volcanic debris flow deposit is interpreted to be associated with the last known volcanic eruption 2360 calendar cal years bp the other two debris flows may not have been directly associated with eruptions volcanic debris flow hazard inundation maps have been produced using the geographic information system gis based modelling program laharz the maps provide esti

origin of high magnesian andesites in the setouchi volcanic belt southwest japan ii melting phase relations at high pressures melting phase relations of an augite olivine high magnesian andesite and an augite olivine basalt from the miocene setouchi volcanic belt in southwest japan have been studied under water saturated water undersaturated and under anhydrous conditions both the andesite and the basalt are characterized by low feo mgo ratios 0 86 and 0 76 in weight respectively and qualify as primary magmas derived from the upper mantle the andesite melt coexists with olivine orthopyroxene and clinopyroxene at 15 kbar and 1030 c under water saturated conditions and at 10 kbar and 1070 c under water undersaturated conditions 7 wt h2o in the melt the basalt melt also coexists with the above three phases at 11 kbar and 1305 c under anhydrous conditions and at 15 kbar and 1205 c in the presence of 4 wt water present studies indicate that high magnesian andesite magmas may be produced even under water undersaturated conditions by partial melting of mantle peridotite it is suggested that two types of high magnesian andesites in the setouchi volcanic belt augite olivine and bronzite olivine andesites were produced by different degrees of partial melting augite olivine andesite magmas whose mantle residual is lherzolite were formed by lower degrees of partial melting than bronzite olivine andesite magmas which coexist with harzburgite the basalt magmas which were often extruded in close proximity to the high magnesian andesite magmas are not partial melting products of a mantle peridotite which had previously melted to yield high magnesian andesite magmas

progress of illitization along an imbricate frontal thrust at shallow depths in an accretionary prism abstract fossil imbricate thrusts branching from a decollement in an ancient accretionary prism the miura boso accretionary prism are exposed in the southern parts of the miura and boso peninsulas in central japan an analysis of the clay mineralogy of fault rocks along one of the imbricate thrust faults the shirako fault revealed local illitization of mixed layer illite smectite i s and the partial breakdown of kaolinite the shape of the i 001 s 001 reflection in the x ray diffraction pattern suggests that the illite fraction in i s crystallites within the fault gouge is 9 more than in the surrounding rocks these results imply that there has been a local temperature anomaly within the slip zone attributable to frictional heating induced by high velocity slip a thermal model coupled with a kinetic simulation of illitization in i s suggests that the reaction was probably facilitated by multiple high velocity slips at a peak temperature of 450 c suggesting repeated seismic rupture propagations to the prism toe as also inferred from the modern accretionary prism in the nankai trough

plate tectonics and the evolution of the british isles this paper is an essay on the rationalism and difficulties of the geological corollaries of plate tectonics with illustrations particularly from the geological history of the british isles there is special emphasis on the mechanics of continental lithosphere in extension when basins are formed and in convergence whereby continental lithosphere thinned in extension is shortened and restacked to form orogenic belts an upper lithosphere stress concentrating elastic lid suffers extremely complex inhomogeneous deformations above a simpler viscoelastic lower lithosphere whose deformation drives strain and displacement in the elastic lid the very nature of plate tectonics as relative motion among a multi plate mosaic of plates provides a rational semi quantitative framework for large scale geological complexity in space and time the caledonian and hercynian history of the british isles may be explained semi quantitatively in terms of plate boundary evolution but it is not possible to define unequivocal solutions the rationalism of plate tectonics is exhibited on a smaller more direct field scale by many of the complexities of ophiolite complexes such as ballantrae scotland that can be explained as the effects of the evolution of ridge ridge transforms and by diachronous deformation and sedimentation in subduction accretion prisms such as the southern uplands deformational and sedimentary patterns in nw europe from triassic times to the present day resulted from a complex interaction of extensional events related to diachronous atlantic opening and compressional events related to sequential alpine shortening phases those widespread events are typical of intracontinental plate boundary systems and create great difficulties for the geologist wishing to decipher relative plate motion from geological sequences because huge areas much larger than the british isles must be analysed and synthesized before much sense can be extracted further difficulties arise from the palinspastic and preservation problems of convergent boundaries orogenic shortening telescopes and partially subducts facies belts most orogenic belts were assembled as a collage of displaced and rotated terrain elements that were subsequently flattened elongated and straightened to an apparent but deceiving simplicity therefore while plate tectonics provides a rational geological framework against which for example british basin evolution can be tested and explained we cannot yet use the geological effects of plate boundary evolution to reconstruct relative plate motion quantitatively

intra arc deformations with vertical rotation axes the case of the pre middle miocene terranes of southwest japan abstract various folds bends with vertical or subvertical rotation axes occur in the pre middle miocene terranes of southwest japan they are variable in shape conical folds accordion folds megakink bands and so on and some are accompanied with strike slip faults they range from several kilometers to more than 100 km in width and some of their hinge surfaces are traceable more than a few tens of kilometers their shapes which resemble megakink band or buckle folds indicate that they were produced by horizontal compression with vertical or subvertical 2 axes in a shallow level of the crust they were superimposed on the pre middle miocene fold and thrust structures or nappe melange complexes and are regarded to have been formed mostly during the middle miocene contemporaneous with the clockwise rotation of southwest japan related to the fan shaped opening of the sea of japan geometrical analysis clearly suggests that the drifting southwest japan behaved as a non rigid body and the formation of these structures resulted from the differential rotation of the terranes and the collision of the izu bonin arc with eastern southwest japan

role of the tectonic facies concept in orogenic analysis and its application to tethys in the eastern mediterranean region abstract the purpose of this paper is to advocate the use of a tectonic facies concept which aids systematic and objective analysis of orogenic belts the tectonic facies concept as discussed here focuses on the recognition of discrete tectonic settings mainly those exposed at high crustal levels in orogenic belts application of the tectonic facies concept can help field geologists to relate plate scale processes to outcrop geology tectonic facies are recognised based on knowledge of the modern oceans and margins and well constrained land settings tectonic facies analogous to sedimentary facies can be identified from integrated sets of field data and related laboratory studies a number of tectonic facies models can be recognised in this way their identification aids interpretation and comparisons of orogenic belts palinspastic reconstructions require additional information particularly age kinematic and palaeomagnetic data in this paper the tectonic facies concept is tested by application to a well documented mainly high level orogenic segment tethys in the eastern mediterranean area and is found to be an effective way both of the describing and interpreting this region other methods of tectonic analysis e g recognition of tectono stratigraphic terranes may also be found useful in certain settings and can be used in conjunction with the tectonic facies concept

kuroshio extension variability and forcing of the pacific decadal oscillations responses and potential feedback abstract a forcing mechanism is sought for the large scale circulation changes in the kuroshio extension region of the western north pacific ocean as inferred by topex poseidon sea surface height ssh data the low frequency signal of the kuroshio extension over the last decade was characterized by a modulation in its zonal mean flow intensity the mean kuroshio extension jet weakened progressively from 1993 to 1996 and this trend reversed after 1997 the ability to simulate the major trends in the observed ssh signals with linear vorticity dynamics leads the authors to conclude that the modulation in the zonal mean jet was remotely forced by wind stress curl anomalies in the eastern north pacific ocean related to the pacific decadal oscillations pdos to be specific the weakening strengthening trend in 1993 96 1997 2001 was caused by westward expansions of negative positive ssh anomalies south of the kuroshio extension and positive negative ssh anomalies north of the kuroshio extension emerg

basin evolution in the arc arc izu collision zone mio pliocene miura group central japan a comparative study of the present collision zone between the izu bonin ridge island arc with mainland japan honshu arc and the mio pliocene of onshore se japan suggests that arc arc collision processes and the resulting stratigraphic successions may be repetitious and predictable arc arc collision has led to the incremental accretion of segments of delaminated izu bonin arc crust onto the honshu arc associated with the sequential southward migration in jumps of the plate boundary and trench prior to accretion of a segment of izu bonin arc crust the leading edge underwent uplift to generate an approximately trench parallel topographic high the zenisu ridge being the present example with the hayama mineoka uplift zone as a mio pliocene example the ridge separated a northern trench or trough from a southern intra oceanic arc basin during collision accretion the trench received both honshu arc derived terrigenous and izu bonin arc derived volcaniclastic sediments whereas the arc basin tended to receive only arc deposits during the final stages of accretion the arc basin began to receive ever increasing volumes of terrigenous honshu arc derived detritus fed through basement controlled canyons the accretionary process was accompanied by intense deformation and the residual deep marine basin was then infilled above an angular unconformity

low frequency variability of the north pacific ocean the roles of boundary and wind driven baroclinic rossby waves 1 the effects of the sea level variability along the eastern boundary of the north pacific ocean including those associated with el nino southern oscillation have been considered an important factor in determining the low frequency large scale variability of the ocean interior through rossby waves generated at the eastern boundary this hypothesis is examined in this study using 8 years worth of the sea surface height observations made by the topex poseidon satellite the timescales of interest are longer than 90 days with the annual cycle removed the results indicate that the influence of the eastern boundary of the north pacific ocean has limited offshore extent varying from 3000 4000 km at 10 n to 200 300 km at 50 n the variability in the ocean interior is primarily driven by wind with only a minor influence from the boundary simulations of a linear two layer model of the ocean driven by wind stress curl are correlated with the observations the effects of wind forcing accumulate along the characteristics of long nondispersive rossby waves in the time longitude domain these wind driven rossby waves overwhelm the boundary driven waves in the ocean interior where there are only some small residual effects of the boundary driven waves however these small effects become clearer after the simulated wind driven variability is removed from the observations index terms 4556 oceanography physical sea level variations 4504 oceanography physical air sea interactions 0312 4215 oceanography general climate and interannual variability 3309 keywords rossby waves satellite altimetry el nino north pacific eastern boundary

timing of rotational motion of southwest japan inferred from paleomagnetism abstract paleomagnetic field directions for the period younger than 35 ma are obtained from igneous rocks distributed in the san in district inner zone of southwest japan the remanent magnetization of samples between 30 and 35 ma old are fairly well grouped with a mean direction of d 65 9 i 48 6 and 95 6 5 this result establishes that southwest japan rotated clockwise 56 12 during the past 30 m y a declination value of about 60 is observed in the rocks of 28 ma d 52 2 i 33 5 and 21 ma d 69 9 i 49 5 comparing this with results from dacitic rocks with an age of 15 ma in other areas of southwest japan suggests that rotational motion did not occur possibly until 15 ma these results require that the rotation of southwest japan occurred just after the shikoku basin had been created

tidal rhythmites in a deep sea environment an example from mio pliocene misaki formation miura peninsula japan abstract the mio pliocene misaki formation miura peninsula japan is characterized by alternation of mafic scoriaceous pebbly sandstone pumiceous sandstone and siltstone and mudstone formed in a fore arc basin in an arc arc collisional zone the qualitative as well as quantitative evidences of tide during the misaki sedimentation in the jogashima area miura peninsula are presented here the lunar synodic period of 28 days lunar month extracted from the misaki tidal rhythmite agrees well with the published miocene tidal rhythmite data the couplet series of the misaki tidal rhythmite however is often interrupted by downslope resedimentation via turbidity currents intense penecontemporaneous deformation and bioturbation association of deep sea turbidites mass flow deposits and tidal rhythmite suggest misaki sedimentation in the miura peninsula took place in a submarine canyon setting

impact of a quaternary volcano on holocene sedimentation in lillooet river valley british columbia lillooet river drains 3850 km 2 of the rugged coast mountains in southwestern british columbia including the slopes of a dormant quaternary volcano at mount meager a drilling program was conducted 32 65 km downstream from the volcano to search for evidence of anomalous sedimentation caused by volcanism or large landslides at mount meager drilling revealed an alluvial sequence consisting of river channel bar and overbank sediments interlayered with volcaniclastic units deposited by debris flows and hyperconcentrated flows the sediments constitute the upper part of a prograded delta that filled a late pleistocene lake calibrated radiocarbon ages obtained from drill core at 13 sites show that the average long term floodplain aggradation rate is 4 4 mm a 1 and the average delta progradation rate is 6 0 m a 1 aggradation and progradation rates however varied markedly over time large volumes of sediment were deposited in the valley following edifice collapse events and the eruption of mount meager volcano about 2360 years ago causing pulses in delta progradation with estimated rates to 150 m a 1 over 50 yr intervals two of the volcaniclastic units identified in drill core correlate with previously documented strong acoustic reflectors in lillooet lake at the downstream end of the basin the mount meager massif constitutes only 2 of the lillooet river drainage but lithology counts of lillooet river channel gravels indicate that a disproportionate percentage of the sediment is derived from the volcano the data indicate that deposits of large debris flows are important elements of the sedimentary sequence and that mount meager dominates the sediment supply to lillooet river d 2005 elsevier b v all rights reserved

provenance and magmatic tectonic setting of campanian aged volcaniclastic sandstones of the kannaviou formation in western cyprus evidence for a south neotethyan continental margin volcanic arc abstract regionally developed late cretaceous subduction related magmatism in the eastern mediterranean records progressive closure of the southern neotethys in western cyprus the late cretaceous c 90 ma troodos ophiolite is depositionally overlain by volcaniclastic sandstones up to 750 m thick that are dominated by redeposited pyroclastic fallout interbedded with both non calcareous and calcareous radiolarian bearing mudstones the sands were mainly deposited by channelised mass flow processes and to a lesser extent by turbidity currents in a deep water forearc basin the succession was folded and locally thrust deformed related to latest cretaceous emplacement of adjacent mesozoic continental margin and oceanic units mamonia complex sims u pb analysis of euhedral to subhedral magmatic zircon crystals yielded a weighted mean 206pb 238u age of 80 1 1 1 ma campanian sandstone petrography including compositional framework q12f21l67 suggests sediment supply from a volcanic arc subordinate continentally derived detritus suggests a continental margin arc setting for the mafic to felsic fallout ash sims analysis of little altered volcanic glass indicates high th nb and th la ratios that suggest the involvement of continental crust and or subducted terrigenous sediments in magma genesis whole rock chondrite normalised ree patterns have comparable trends to modern and ancient forearc basin volcaniclastic sands and sandstones e g northwest pacific region trace element chemistry although scattered towards the continental island arc fields on some geochemical diagrams e g th sc zr mainly suggests an oceanic island arc source for the kannaviou formation sandstones with variable enrichments in v cr ni sc depletion in nb ta and relatively low trace element ratios e g la co th co la sc th sc an explanation for this apparent discrepancy is that the volcaniclastic sandstones were derived from a relatively primitive arc constructed on previously depleted rifted thinned neotethyan continental crust the inferred continental margin arc developed during early stage northward subduction of the southern neotethys beneath a tauride microcontinent to the north large volumes of volcanic ash were derived from continental margin arc volcanism probably in the vicinity of the kyrenia range in northern cyprus

downstream dilution of a lahar transition from debris flow to hyperconcentrated streamflow nearly instantaneous melting of snow and ice by the march 19 1982 eruption of mount st helens released a 4 106 m3 flood of water from the crater that was converted to a lahar volcanic debris flow through erosion and incorporation of sediment by the time it reached the base of the volcano over the next 81 km that it traveled down the toutle river the flood wave was progressively diluted through several mechanisms a transformation from debris flow to hyperconcentrated streamflow began to occur about 27 km downstream from the crater when the total sediment concentration had decreased to about 78 by weight 57 by volume the hyperconcentrated lahar runout flood wave transporting immense quantities of sand in suspension continued to experience progressive downstream dilution although turbulence was significantly dampened by the extremely high suspended load very large standing waves and antidune waves were observed the hyperconcentrated lahar runout flow deposited an unusual faintly stratified coarse sand which locally contained small isolated gravel lenses very similar deposits in the quaternary stratigraphy of mount st helens and other cascades volcanoes suggest that lahars may be more frequent than previously recognized

geohazards in coastal areas near the northernmost sagami trough central japan review of neotectonic activity in onshore and offshore areas of the izu island arc collision subduction zone

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

the july 29 1998 debris flow and landslide dam at capricorn creek mount meager volcanic complex southern coast mountains british columbia a very large debris flow was triggered during a period of record breaking high temperatures in upper capricorn creek within the mount meager volcanic complex a part of the garibaldi volcanic belt of the southern coast mountains the debris flow deposit impounded meager creek creating an 800 m long landslide dammed lake the total event volume was 1 2 106 m3 the debris flow was followed by three days of almost continuous hyperconcentrated flow surges which caused significant fluvial aggradation in the meager creek flood plain below the capricorn creek confluence within a few days of the formation of the landslide dam a spillway notch had been cut through the deposit thereby preventing the occurrence of a catastrophic dam break the landslide which triggered the debris flow originated in deep volcanic colluvium having a previous history of progressive slope deformation a consequence of glacial downwasting since the neoglacial maximum this paper highlights an important landslide response to rec

decadal changes in the north pacific oceanic frontal zones as revealed in ship and satellite observations 1 influence of decadal climate changes upon the north pacific subarctic and subtropical oceanic frontal zones np safz and np stfz respectively is documented both satellite and ship measured sea surface temperature sst data reveal the strong confinement of wintertime decadal sst anomalies to those frontal zones the satellite data indicate that the wintertime np safz tended to be narrow and shift northward under the weakened surface westerlies during a warm event in the early 1990s the opposite was the case under the enhanced westerlies during a cool event in the mid 1980s decadal scale modulations in the frontal intensity are also evident in the satellite data a diagnosis based on a simple linearized mixed layer model suggests that the observed anomalous frontal intensity was contributed by the sign reversal of anomalous wind stress curl through the ekman processes and by an anomaly dipole of the net heat flux around the safz these decadal scale modulations in the np safz and their relationships with decadal fluctuations in the local surface westerlies are confirmed in the ship measured data over the 4 recent decades it is found that the safz happens to be a region where the decadal variability in the surface westerlies are unlikely to be masked by the higher frequency fluctuations as it almost coincides with the ridge trough line of the remote atmospheric response to the el nino southern oscillation

significance of the remarkable unconformity in the plio pleistocene of the japanese islands abstract the kurotaki unconformity is located in the boso peninsula between the subduction zone in the pacific plate and the philippine sea plate the underlying stratum miura group and overlying stratum kazusa group bordering the kurotaki unconformity are greatly different with respect to geologic structure and age the influence of the pacific plate is reflected in the kazusa group and that of the philippine sea plate in the miura group thus the kurotaki unconformity gives a geological constraint on tectonic conditions around the japanese islands this study has clarified of the formation age of the kurotaki unconformity based on tephrochronology the age of the unconformity is ca 3 0 2 8 ma the formation age of the unconformity is specified based on tephrochronology common and widespread tephra layers were found in strata bordering the unconformity the formation of the regional kurotaki unconformity indicates a widespread event in the vicinity of the newly designated pliocene pleistocene boundary in the japanese islands

large holocene landslides from pylon peak southwestern british columbia mount meager massif the northernmost volcano of the cascade volcanic belt has been the site of very large 10 7 m 3 landslides in the holocene epoch we document two complex landslides at pylon peak one of the peaks of the mount meager massif about 7900 14 c and 3900 14 c years ago about 8700 and 4400 calendar years ago together the two landslides displaced 6 1 0 8 m 3 of volcanic rock from the south flank of pylon peak into nearby meager creek valley each landslide consisted of at least two phases an early debris flow resulting from failure of hydrothermally altered pyroclastic rock at mid levels on the mountain and a later rock avalanche from a higher source both debris flows likely traveled down meager creek and preliminary evidence from drilling indicates the 4400 year old event traveled down lillooet river into areas that are now settled and where population density is increasing rapidly the mobility of the debris flows was due to the high content of fine weathered volcanic sediment and the availability of sufficient water the causes of the landslides are a wet climate and the presence of weak hydrothermally altered volcanic rock containing abundant phreatic water on glacially oversteepened slopes the landslides may have been triggered by earthquakes or by upwelling of magma to shallow depths within the volcano however they may also have occurred without specific triggers following extended periods of progressive weakening of the volcanic rocks

collision of the izu arc with honshu and the effects of oblique subduction in the miura boso peninsulas abstract collision of the izu arc in central japan is discussed with a focus on its tectonic effects to the east of the arc in the miura boso peninsulas of honshu the tectonics are the combination of the following events philippine sea plate spreading in the late oligocene to early miocene opening of the sea of japan in the middle miocene obduction of ophiolitic rocks in the northeasternmost corner of the philippine sea plate and forearc sedimentation between the honshu and izu arcs oblique subduction has shifted the plate boundary from northeast to southwest from the present mineoka tectonic belt through the miura fold belt to the sagami trough since the miocene remarkable right lateral transpressional deformation occurred throughout this period of the oblique collision and subduction

the history and dynamics of a welded pyroclastic dam and its failure the 2 360 bp eruption of mount meager british columbia began as an explosive dacitic sub plinian eruption that waned rapidly to a sustained period of vulcanian eruption triggered dome collapse events producing voluminous block and ash flow baf deposits the earliest baf deposits accumulated rapidly enough immediately downslope of the vent to retain heat and weld using the deposit as a paleoviscometer determines an effective viscosity of 109 1010 pa s during welding this prolific production of hot lava and block and ash flows in a steep mountainous terrain created a 110 m high largely impermeable dam capped by permeable non welded baf deposits and unconsolidated avalanche deposits that blocked the flow of the lillooet river and created a temporary lake the welded pyroclastic dam was compromised and overtopped at least once before the peak dam height was reached renewed eruption caused buildup of the dam to a maximum of 780 m above sea level asl and grew the temporary lake to an elevation of 740 m asl and a minimum volume of 0 55 km3 the rise of lake level led to catastrophic failure of the top of the dam generating an outburst flood that carved a canyon through most of the dam and resulted in a voluminous lahar that is traced at least 65 km downstream based on current flow rates of the lillooet river the lake would have overtopped the final dam at a minimum of 39 65 days after its formation the peak deluge lasted approximately 8 h and eroded a 2 5 km long canyon into the still hot dam core before returning to background flow rates

distribution and origin of igneous rocks from the landward slopes of the mariana trench implications for its structure and evolution the landward slope of the mariana trench is composed largely of igneous rocks serpentinites and serpentinized ultramafic rocks occur at nearly all structural levels on the slope from depths of 8000 to 1200 m seamountlike features on the trench slope break are the surface expression of serpentinite diapirs cumulate and massive gabbros are found several varieties of volcanic rocks are common including boninites altered and metamorphosed basalts andesites and dacites the chemical characteristics of the volcanic rocks indicate that nearly all are products of island arc volcanism together with the gabbros these volcanic rocks represent what is probably a late eocene arc complex these rocks were probably the first volcanic products to result from the subduction of the pacific plate beneath the phillippine sea plate their exposure on the trench slope today implies a significant amount of tectonic erosion of the landward slope since eocene time most of this removal of material appears to have occurred during the early stages of subduction there are isolated occurrences on the landward slope of rock assemblages including alkalic basalts chert hyaloclastites upper cretaceous siliceous sediments and shallow water limestones these assemblages are very similar to rocks dredged from seamounts on the offshore flankmore of the trench and their presence on the landward slope suggests that since the cessation of vigorous tectonic erosion there has been episodic accretion of seamount fragments to the landward slope less

structure and development of the sagami trough and the boso triple junction abstract the sagami trough is located at the particular plate margin where the izu forearc is subducted underneath the honshu forearc at its southeastern end the world s only known ttt type triple junction boso triple junction has developed several different kinds of basins occur in different segments along the sagami trough and at the triple junction the bathymetric geologic and geophysical data obtained during the kaiko project and from additional studies are summarized together with our onland studies we suggest that the right lateral oblique plate motion formed an eduction margin in the sagami basin while a normal subduction margin and an oblique subduction margin have been formed in the middle sagami trough basin these tectonic phenomena resulted from the long lasting compressional covergence between the philippine sea plate and eurasian plate since the early or middle miocene the north basin on the northeasternmost margin of the philippine sea plate near the boso triple junction has developed as a stretched basin due to the westward motion of the philippine sea plate with respect to the eurasian plate

a simple model of the decadal response of the ocean to stochastic wind forcing abstract a simple linear model is used to estimate the decadal response of the extratropical ocean to wind stress forcing assuming a flat bottom a mean state at rest and no dissipation the barotropic fields are governed by a time dependent sverdrup balance the baroclinic ones by the long rossby wave equation the ocean is bounded by a coast in the east and a radiation condition is used in the west at each frequency the baroclinic response consists of a forced response plus a rossby wave generated at the eastern boundary for zonally independent forcing the response propagates westward at twice the rossby phase speed the wind stress is assumed to be stochastic with a white frequency spectrum so the model represents the continuous excitation of the ocean interior by the weather fluctuations the model predicts the shape and level of the frequency spectra of the oceanic pressure field and their variation with longitude and latitude the baroclinic response is spread over a continuum of frequencies

origin of high magnesian andesites in the setouchi volcanic belt southwest japan i petrographical and chemical characteristics high magnesian andesites of middle miocene age occur in southwest japan forming an obvious volcanic belt these andesites have low feo mgo ratios 0 546 0 931 and are rich in ni 101 312 ppm co 30 0 45 1 ppm and cr 208 756 ppm they are relatively aphyric phenocrysts 10 vol and the phenocrysts of magnesian olivine fo88 are in equilibrium with the host high magnesian andesite magmas on the basis of the fe mg exchange partitioning these features suggest that the high magnesian andesites are not differentiated or accumulative they appear to represent primary andesites generated in the upper mantle these southwest japanese high magnesian andesites are rich in incompatible elements and show light rare earth enrichment relative to boninites suggesting that the former is derived from a less depleted mantle source than the latter

structural features of the bonin arc implications for its tectonic history abstract the bonin arc from the shikoku basin to the trench axis is broken into four crustal blocks each separated by major right lateral strike slip faults from north to south they are termed the sumisu jima the sofu gan and the central bonin dislocations these dislocations are delineated by 1 1 changes in trends of en echelon ridge and trough structures of the main arc 2 2 right lateral offsets of the bathymetry and structure of the arc s outer ridge 3 3 right lateral offsets in the free air gravity contours the most likely time of formation of the en echelon structures and fracturing of the arc into the four crustal blocks is between 27 and 17 m y b p miocene during this time japan was moving southeastward relative to asia and the philippine sea plate including the bonin arc was moving northward subducting beneath southwest japan also convergence and subduction of the pacific plate was taking place along the east side of the bonin arc which involved the collision of thick buoyant crustal blocks of the marcus necker ridge near the south end of the arc these movements resulted in compressive forces acting on the bonin arc from the northwest and produced a clockwise torque within the arc the response to these forces included development of ne nne structural trends within the arc and fracturing of the arc into four crustal blocks offset from each other by ne nne right lateral displacements

soft sediment deformation structures in the mio pliocene misaki formation within alternating deep sea clays and volcanic ashes miura peninsula japan abstract the mio pliocene misaki formation of the miura group miura peninsula japan shows an extremely wide variety of soft sediment deformation structures the most common deformation structures are load casts and associated flame structures dish and pillar structures synsedimentary faults multilobated convolutions chaotic deformation structures sedimentary veins and dykes and large scale slides and slump scars the formation which accumulated in a deep sea environment 2000 3000 m is well exposed in and around jogashima it consists of relative thin commonly dm scale alternations of deep marine fine grained sediments and volcanic ejecta that are as a rule coarse grained since the formation represents fore arc deposits of the izu bonin and the honsu arc collision zone it might be expected that tectonic activity also played a role as a trigger of the soft sediment deformation structures that abound in these sediments this is indicated indeed by the abundance of soft sediment deformations over large lateral distances that occur in numerous beds that are sandwiched between undeformed beds on the basis of their characteristics and the geological context these layers can be explained satisfactorily only by assuming deformation triggered by seismicity which must be related to the izu bonin and honsu arc collision the layers thus form deep marine seismites

proglacial sediment trapping in recently formed silt lake upper lillooet valley coast mountains british columbia the sedimentology of proglacial silt lake was assessed by lake sediment coring and monitoring of lacustrine processes during a late summer period of high glacier melt to characterize sediment delivery from the heavily glacierized catchment and investigate the sediment trapping dynamics of this upland lake a complete varve chronology was established for a distal basin of the lake which was exposed by lillooet glacier retreat between 1947 and 1962 the varve record showed decreasing sedimentation rates in the basin while the glacier retreated and as the lake became free of ice contact in the early 1970s although recession has continued over recent decades and glacier proximity to the lake has therefore continued decreasing lacustrine sedimentation rates are now accelerating due to changing basin morphometry caused by delta progradation over shorter time scales lake sedimentation patterns respond to changing runoff conditions including late summer glacier melt intensity intra annual flooding events diumal runoff fluctuations and within lake turbidity currents turbidity currents included quasi regular flows during high diurnal discharges and an episodic flushing of temporarily stored sediment from the sandur or delta at a time of low stage suspended sediment yield to silt lake is estimated to exceed 103 mg km 2 a 1 a magnitude that surpasses previous local and regional yield estimates for the glacierized headwaters of the lillooet river valley since silt lake currently traps a significant prooportion of that upland sediment supply and the trapping efficiency of the basin has been variable at decadal time scales the formation and continued development of lilt lake has likely had a significant influence on downstream sediment delivery lacustrine sediment based proxies of long term hydroclimatic variability being developed in glacially distal settings should include provisions for dynamic sediment trapping effects in upstream water bodies that often form in the active proglacial environment copyright 2008 john wiley sons ltd

on the relationship between tropical and north pacific sea surface temperature variations abstract empirical orthogonal function analysis of winter sea surface temperature sst anomalies over the pacific domain 60 n 20 s reveals an el nino southern oscillation enso mode that is linked to the eastern north pacific and a north pacific mode that is linearly independent of enso the north pacific mode exhibits maximum amplitude and variance explained along 40 n west of 170 w ssts in this region have decreased by 1 5 c from 1950 to 1987 the cooling in winter has been associated with a strengthening of the overlying westerly winds

petrology of serpentine sandstone as a key to tectonic development of serpentine belts abstract the petrology of serpentine sandstone which is ubiquitous in the serpentine belt could provide some constraints on petrological characteristics for lost or eroded serpentinite masses the chemistry of detrital chrome spinel and chrome diopside in particular is a useful indicator of the equilibrium temperature and lithology of the source peridotite combined with the petrology of the associated serpentinite masses this could provide the difference in the petrological characteristics if any between the lost serpentine and that now exposed in a serpentine belt and consequently some constraints could be placed on the tectonic history of the serpentine belt itself in the mineoka belt a narrow serpentine belt in central japan the serpentinite mass exposed during the miocene has experienced a lower pyroxene temperature and wider lithology than the serpentinite masses now exposed in the same area this fact possibly indicates that a vertical slice of the upper mantle peridotite has been uplifted and intermittently protruded since the miocene the mineoka belt is probably placed on part of a fossil transcurrent fault which had worked in the opening of the shikoku basin of the northern end of the philippine sea plate along the transcurrent fault the mantle peridotite slices with various petrologic characteristics could have been continuously emplaced in the same way as in the present day oceanic fracture zone on the other hand in the kamuikotan belt of hokkaido northern japan the source of a miocene serpentine sandstone at furenai has the same petrologic characteristics as the now associated sarugawa peridotite mass the sarugawa mass is a dismembered part of an ophiolite suite uplifted during the collision between the eurasia plate and the okhotsk north america plate in miocene times the furenai serpentine sandstone was produced in a small sedimentary basin within the sarugawa peridotite mass during the middle miocene contrary to the mineoka belt large vertical uplift movements of the peridotite mass did not occur in the kamuikotan zone after the miocene

differential preservation in the geologic record of intraoceanic arc sedimentary and tectonic processes abstract records of ancient intraoceanic arc activity now preserved in continental suture zones are commonly used to reconstruct paleogeography and plate motion and to understand how continental crust is formed recycled and maintained through time however interpreting tectonic and sedimentary records from ancient terranes after arc continent collision is complicated by preferential preservation of evidence for some arc processes and loss of evidence for others in this synthesis we examine what is lost and what is preserved in the translation from modern processes to the ancient record of intraoceanic arcs composition of accreted arc terranes differs as a function of arc continent collision geometry forward facing collision can accrete an oceanic arc on to either a passive or an active continental margin with the arc facing the continent and colliding trench and forearc side first in a backward facing collision involving two subduction zones with similar polarity the arc collides backarc first with an active continental margin the preservation of evidence for contemporary sedimentary and tectonic arc processes in the geologic record depends greatly on how well the various parts of the arc survive collision and orogeny in each case preservation of arc terranes likely is biased towards those that were in a state of tectonic accretion for tens of millions of years before collision rather than tectonic erosion the prevalence of tectonic erosion in modern intraoceanic arcs implies that valuable records of arc processes are commonly destroyed even before the arc collides with a continent arc systems are most likely to undergo tectonic accretion shortly before forward facing collision with a continent and thus most forearc and accretionary prism material in ancient arc terranes likely is temporally biased toward the final stages of arc activity when sediment flux to the trench was greatest and tectonic accretion prevailed collision geometry and tectonic erosion vs accretion are important controls on the ultimate survival of material from the trench forearc arc massif intra arc basins and backarc basins and thus on how well an ancient arc terrane preserves evidence for tectonic processes such as subduction of aseismic ridges and seamounts oblique plate convergence and arc rifting forward facing collision involves substantial recycling melting and fractionation of continent derived material during and after collision and so produces melts rich in silica and incompatible trace elements as a result forward facing collision can drive the composition of accreted arc crust toward that of average continental crust

implication for the two stage layer parallel faults in the context of the izu forearc collision zone examples from the miura accretionary prism central japan abstract the southern tip of the miura peninsula central japan exposes nice outcrops of forearc sediment accreted to another forearc which occurred during a series of izu arc collision with the honshu arc neogene deep marine volcaniclastic sedimentary sequences the misaki formation show many types of faulting and folding associated with layer parallel faults besides many imbricate thrusts of the main deformation stage the layer parallel faults are divided into two stages one is related to northwestward gravity driven slump deposits the other is southeastward thrust faulting and the both are associated with many layer duplications with liquefaction of sediments the slumping is commonly developed in the upper part of the sequence in the surface of the down going slab before accretion whereas the thrusting is dominant in the lower part within the toe of the accretionary prism probably along the decollement zones in the prism thus the misaki formation represents a good example of deformation just before and after shallow forearc accretion in the arc collision zone

sedimentological consequences of arc arc collision an example from mio pliocene miura group japan abstract this paper presents brief sedimentological inventory of the misaki and the overlying hasse formation constituting the miura group based on observations made at jogashima island miura peninsula and infers the nature of the stratigraphic transition from tectonic viewpoint the lower part of the misaki formation is made of very coarse to coarse grained scoriaceous normally graded sandstones fine grained sandstones siltstones and mudstones and indicates a deep sea submarine canyon depositional setting there is no evidence of storm reworking shallow marine processes in the lower parts of the misaki formation at least in the jogashima island as suggested by stow et al 1998 however the upper part of the misaki succession formed in a shallow marine depositional setting the overlying hasse formation characterized by brownish coloured very coarse to coarse grained large scale trough cross stratified very poorly sorted sandstones very poorly sorted polymictic and matrix dominated mass flow conglomerates with siltstone fine grained sandstone clasts derived from the underlying misaki formation and occasional reverse grading in significant contrast to the underlying misaki formation the hasse formation lacks very fine grained sandstone siltstone mudstone facies unlike the tholeiitic basalt composition of the lapilli and pebbles of the misaki sandstone beds the scoriaceous lapilli and pumiceous beds of the hasse formation are of calc alkaline composition the hasse sedimentation probably took place in much shallower paleogeography compared to the underlying misaki formation most probably in an alluvial fan braided fluvial setting the misaki hasse stratigraphic contact is very sharp and erosional and represents a subaerial unconformity i e depositional sequence boundary our sedimentological data from the jogashima island clearly indicate progressive shallowing of the depositional setting during the terminal phase of the misaki sedimentation and much abrupt shallowing across the misaki hasse transition possibly as a consequence of ongoing collision between the izu bonin and honshu arcs

paleogeographic reconstruction and origin of the philippine sea abstract our reconstruction of the philippine sea suggests that it formed by two distinct episodes of back arc spreading each of which resulted from seaward retreat of the trench in the first episode the protoizu bonin trench retreated northward and the west philippine basin formed behind the northern half of the palau kyushu ridge in the second episode the izu mariana trench retreated eastward and the shikoku and parece vela basins formed behind it during the last 17 ma the philippine sea basin has been moving northwestward with respect to eurasia shifting the ttt triple junction off central japan westward by about 50 km the motion of the philippine sea with respect to eurasia at the triple junction changed from north northwestward to west northwestward 10 5 ma ago for the period before 17 ma ago we construct two models retreating trench model and anchored slab model the izu bonin trench migrated from south to northeast rotating in a clock wise sense since 48 ma ago in the retreating trench model in the anchored slab model the trench has been fixed with respect to eurasian margin since 43 ma ago we prefer the retreating trench model because the deformation of the plate boundary along the eastern margin of eurasia during 30 17 ma ago is much simpler for this model than for the anchored slab model furthermore rotations of the bonin mariana islands are consistent with those predicted from the retreating trench model the 48 ma ages of the northern part of the palau kyushu ridge and of chichi jima of the bonin islands indicate that there was subduction beneath the northern half of the ridge beginning at least 48 ma ago from this and the subparallelism in trend between the northern part of the palau kyushu ridge and the central basin ridge we propose that the major part of the west philippine basin formed by back arc spreading in a n s direction behind the northern part of the palau kyushu ridge the pacific plate was moving northward with respect to hot spots from 48 to 43 ma ago which implies that the pacific plate is not likely to have been subducting beneath the west philippine basin during this time we speculate that another plate existed south of the pacific plate and thai it was subducting beneath both tile west philippine basin and australia the annihilation of this plate might he a cause for the sudden change of the pacific plate motion at 43 ma ago

volcanology of the 2350 b p eruption of mount meager volcanic complex british columbia canada implications for hazards from eruptions in topographically complex terrain the pebble creek formation previously known as the bridge river assemblage comprises the eruptive products of a 2350 calendar year b p eruption of the mount meager volcanic complex and two rock avalanche deposits volcanic rocks of the pebble creek formation are the youngest known volcanic rocks of this complex they are dacitic in composition and con tain phenocrysts of plagioclase orthopyroxene amphi bole biotite and minor oxides in a glassy groundmass the eruption was episodic and the formation com prises fallout pumice bridge river tephra pyroclastic flows lahars and a lava flow it also includes a unique form of welded block and ash breccia derived from col lapsing fronts of the lava flow this merapi type brec cia dammed the lillooet river collapse of the dam triggered a flood that flowed down the lillooet valley the flood had an estimated total volume of 10 9 m 3 and inundated the lillooet valley to a depth of at least 30 m above the paleo valley floor 5 5 km downstream of the blockage rock avalanches comprising mainly blocks of plinth assemblage volcanic rocks an older formation making up part of the mount meager vol canic complex underlie and overlie the primary vol canic units of the formation both rock avalanches are unrelated to the 2350 b p eruption although the post eruption avalanche may have its origins in the over steepened slopes created by the explosive phase of the eruption much of the stratigraphic complexity evident in the pebble creek formation results from deposition in a narrow steep sided mountain valley containing a major river

island arc elements and arc related ophiolites abstract all major structural elements in island arc systems fore arc magmatic arc back arc basins and remnant arcs are potential ophiolite sources and those features that allegedly characterise ophiolites of ocean ridge origin sheeted dyke complexes mantling pelagic rocks hydrothermal metamorphism and associated mineralization can also arise within arc settings age relations are critical in the interpretation of arc related ophiolites remnants of oceanic lithosphere identified by a pre arc initiation age are restricted to fore arc magmatic arc and remnant arc elements as are ophiolite masses generated at the inception of underthrusting the latter apparently common in ancient fore arc terrains form in nascent arc systems in which the rate of role back of the subduction hinge exceeds the rate of convergence spreading occurs above a foundering slab resulting in some arc like compositional features in simple arc systems later ophiolitic rocks have formed either in the active back arc basin or the magmatic arc only those ophiolites that have resided within or very close behind magmatic arcs should show calcalkaline or arc tholeiite magmatic affinities or be intruded or overlain by these rocks volcanic derived sediment or pelagic material may mantle ophiolites from all arc settings but pelagic rocks will generally dominate in stratigraphic sequences above remnant arcs and on back arc basin floors except adjacent to the magmatic arc ophiolites generated at major ocean ridges are unlikely to be immediately overlain by sediment with a significant volcanic component whereas such detritus may lie directly on arc inception arc and back arc ophiolites some arc derived ophiolites are preserved in their original tectonic position others can be identified from their internal features their relationship to other tectonic elements and the nature of associated rocks

variety of subduction and accretion processes in cretaceous to recent plate boundaries around southwest and central japan abstract the shimanto and miura boso terranes in southwest and central japan are analyzed for the understanding of variation of the subduction accretion process in convergent plate boundaries the shimanto is a cretaceous to recent honshu accretionary prism of 200 km width in the honshu arc side and is made up of melange flysch and olistostrome units these are repeated by many thrust faults and local broad and tight folds to make schuppen structures shallow marine and olistostromal bodies overlie part of the schuppen structures unconformably or are included within the structures normal subduction tectonics prevail for the formation of the accretionary prism but the effects of probable transform tectonics during late oligocene to early miocene are considerable the miura boso region is a terrane newly accreted from the izu arc to the honshu arc this terrane is made up of miocene and younger volcaniclastic sedimentary rocks dismembered ophiolitic materials and some of the rocks from the shimanto supergroup the miura boso terrane is characterized by transpressional tectonics associated with eduction during the sedimentation on the highly oblique subduction zone between the eurasia later north america and philippine sea plates several cases for the emplacement of the basaltic and other oceanic rocks to the landward side of the accretionary prism are discussed to account for the basic problem of the subduction accretion tectonics

paleoposition of southwest japan at 16 ma implication from paleomagnetism of the miocene ichishi group abstract new paleomagnetic data from shallow marine sediments of the ichishi group suggest a clockwise tectonic rotation of southwest japan in the middle miocene samples have been collected from mud or tuff layers at 17 sites stability of remanent magnetization has been examined by using alternating field and thermal demagnetization the polarity sequence composed of four normal and seven reversed polarity sites is correlated to polarity epoch 16 15 2 17 6 ma based on micropaleontological assignment of the upper ichishi group to blow s zone n8 the mean paleomagnetic direction of the 11 sites shows an anomalous declination toward the northeast this result suggests that southwest japan was subjected to a clockwise rotation through 45 since 16 ma the clockwise rotation can be explained by the drift of southwest japan associated with the spreading of the japan sea during the middle miocene

objective delineation of lahar inundation hazard zones a new method of delineating lahar hazard zones in valleys that head on volcano flanks provides a rapid objective reproducible alternative to traditional methods the rationale for the method derives from scaling analyses of generic lahar paths and statistical analyses of 27 lahar paths documented at nine volcanoes together these analyses yield semiempirical equations that predict inundated valley cross sectional areas a and planimetric areas b as functions of lahar volume v the predictive equations a 0 05v 2 3 and b 200v 2 3 provide all information necessary to calculate and plot in

palaeoceanography and tectonic setting of the jurassic coast range ophiolite central california evidence from the extrusive rocks and the volcaniclastic sediment cover abstract the primary thesis of this paper is that the character of sedimentary rocks within or directly on top of an ophiolite complex can be used to constrain tectonic models of oceanic crustal genesis late jurassic c 169 161 ma coast range ophiolite remnants are exposed e and w of the san andreas fault in central california ophiolite volcanic rocks are mainly sub alkaline tholeiitic basalts but include subordinate intermediate and silicic flows and breccias available immobile major and trace element data indicate that the coast range ophiolite formed above a subduction zone possibly in a fore arc setting as suggested by the presence of high magnesian andesites and boninites the ophiolite extrusives mainly comprise pillow lava and lava breccia formed on a rugged fault controlled ocean floor interlava pelagic sediment is restricted to very small amounts of interstitial red chert and nannoplankton limestone widespread occurrence of vesicular lavas probably reflects high primary volatile contents rather than eruption in shallow water local interbeds of arc derived silicic tephra in the uppermost extrusives suggest that the ophiolite and cover sediments formed together in a single tectonic setting depositionally overlying deep water successions up to 600 m thick comprise radiolarian rich tuffaceous and volcaniclastic sediments of callovian mid tithonian age 165 148 ma depositional processes included airfall turbidity currents mass flow and current reworking small si fe mn lenses along the lava sediment contact formed by hydrothermal replacement of basal siliceous tuffaceous sediments or by direct chemical precipitation at one locality llanada the ophiolite is overlain by up to 1 8 km of younger tithonian basic intermed and acid lava flows submarine lahars and mainly silicic pyroclastic sediments of inferred volcanic arc origin the volcaniclastic cover passes conformably upwards into late tithonian and younger terrigenous deep water clastic sediments of the great valley group deposited in a fore arc setting the coast range ophiolite and its cover are interpreted as an incipient intraoceanic volcanic arc possibly developed above an eastward continent ward dipping subduction zone within the equatorial pacific ocean in this scenario short lived 5 8 ma supra subduction zone spreading to form the ophiolite was followed by callovian tithonian arc volcanism shedding tuffaceous debris onto the adjacent fore arc subduction was active separately along the western american continental margin with the result that the coast range arc ophiolite complex eventually collided with north america triggering the late jurassic nevadan orogeny and initiating franciscan subduction accretion the coast range ophiolite remnants at least those west of the san andreas fault were apparently translated northwards to their present positions after late cretaceous

interdecadal variability of the pacific ocean model response to observed heat flux and wind stress anomalies variability of the pacific ocean is examined in numerical simulations with an ocean general circulation model forced by observed anomalies of surface heat flux wind stress and turbulent kinetic energy tke over the period 1970 88 the model captures the 1976 77 winter time climate shift in sea surface temperature as well as its monthly seasonal and longer term variability as evidenced in regional time series and empirical orthogonal function analyses examination of the surface mixed layer heat budget reveals that the 1976 77 shift was caused by a unique concurrance of sustained heat flux input anomalies and very strong horizontal advection anomalies during a multi month period preceding the shift in both the central pacific region where cooling occurred and the california coastal region where warming occurred in the central pacific the warm conditions preceding and the cold conditions following the shift tend to be maintained by anomalous vertical mixing due to increases in the atmospheric momentum flux tke input into the mixed layer which deepens in the model after the shift from the early 1970s to the late 1970s and 1980s since the ocean model does not contain feedback to the atmosphere and it succeeds in capturing the major features of the 1976 77 shift it appears that the midlatitude part of the shift was driven by the atmosphere although effects of midlatitude ocean atmosphere feedback are still possible the surface mixed layer heat budget also reveals that in the central pacific the effects of heat flux input and vertical mixing anomalies are comparable in amplitude while horizontal advection anomalies are roughly half that size in the california coastal region in contrast where wind variability is much weaker than in the central pacific horizontal advection and vertical mixing effects on the mixed layer heat budget are only one quarter the size of typical heat flux input anomalies

north pacific decadal variability in the community climate system model version 2 abstract north pacific decadal oceanic and atmospheric variability is examined from a 650 yr control integration of the community climate system model version 2 the dominant pattern of winter sea surface temperature sst variability is similar to the observed pacific decadal oscillation with maximum amplitude along the kuroshio extension sst anomalies in this region exhibit significant spectral peaks at approximately 16 and 40 yr lateral geostrophic heat flux divergence caused by a meridional shift of the kuroshio extension forced by basin scale wind stress curl anomalies 3 5 yr earlier is responsible for the decadal sst variability local surface heat flux and ekman heat flux divergence act as a damping and positive feedback respectively a simple linear rossby wave model is invoked to explicitly demonstrate the link between the wind stress curl forcing and decadal variability in the kuroshio extension the rossby wave model not only successfully reproduces the two decadal spectral peaks but a

stratigraphy of the kazusa group boso peninsula an expanded and highly resolved marine sedimentary record from the lower and middle pleistocene of central japan major climatic reorganizations including changes in the nature of glacial interglacial cycles through the pleistocene are a key issue for improving the understanding of earth s climate system highly resolved marine sedimentary records are essential to reconstruct the details of these past climatic changes and investigate the mechanisms responsible for them the kazusa group located in the central part of the japanese island chain is well exposed and contains a remarkably continuous and thick deep and shallow water marine sedimentary succession this group also contains well preserved marine microfossils pollen paleomagnetic reversal events geochemical signatures and a large number of tephra beds these features allow us to establish a robust chronological and stratigraphic framework for the kazusa group and provide a rare opportunity to study oceanic and terrestrial climatic and environmental changes at high resolution especially through the lower and lower middle pleistocene in the boso peninsula chiba prefecture the kazusa group is deeply incised yielding spectacular river cut exposures the matuyama brunhes paleomagnetic reversal is observed immediately above the widespread byakubi e byk e tephra in the chiba composite section within the kokumoto formation kazusa group because the matuyama brunhes boundary customarily serves as the primary guide for the lower middle pleistocene subseries boundary the chiba composite section is considered an excellent candidate for its global boundary stratotype section and point gssp this study reviews the published data for the kazusa group hitherto almost exclusively in japanese in order to place the chiba composite section within its broader depositional and chronostratigraphic context

depositional architecture provenance and tectonic eustatic modulation of miocene submarine fans in the shikoku basin results from nankai trough seismogenic zone experiment seismostratigraphy coring and logging while drilling during integrated ocean drilling program expeditions 319 322 and 333 sites c0011 c0012 show three miocene submarine fans in the ne shikoku basin with broadly coeval deposits at ocean drilling program site 1177 and deep sea drilling project site 297 nw shikoku basin the sediment dispersal patterns have major implications for paleogeographies at that time the oldest finer grained kyushu fan has sheet like geometry quartz rich flows were fed mostly from an ancestral landmass in the east china sea during prolonged hemipelagic mud deposition at c0011 c0012 similar to 12 2 to 9 1 ma sand supply continued at sites 1177 and 297 sand delivery to much of the shikoku basin halted during a phase of sinistral strike slip to oblique plate motion after which the daiichi zenisu fan similar to 9 1 to 8 0 ma was fed by submarine channels the youngest fan daini zenisu similar to 8 0 to 7 6 ma has sheet like geometry with thick bedded coarse grained pumiceous sandstones the pumice fragments were fed from a mixed provenance that included the collision zone of the izu bonin and honshu arcs the shift from channelized to sheet like flows was favored by renewal of relatively rapid northward subduction which accentuated the trench as a bathymetric depression increased sand supply appears to correlate with long term eustatic lowstands of sea level the stratigraphic position and 3 d geometry of the sandbodies have important implications for subduction related processes including the potential for focused fluid flow and fluid overpressures above and below the plate boundary fault in sheet like sands pathways for fluid flow have greater horizontal permeability compared with those in channel sands

volcanic ash layers facilitate high resolution sequence stratigraphy at convergent plate margins an example from the plio pleistocene forearc basin fill in the boso peninsula japan abstract in this paper a method is presented for the definition of high resolution siliciclastic depositional sequences in onshore outcrop belts in a forearc basin setting and the development of high frequency depositional sequences in the infill of the plio pleistocene kazusa forearc basin in the boso peninsula of japan in terms of the interaction between forearc tectonics and glacio eustasy is discussed volcanic ash layers are commonly intercalated in siliciclastic successions at convergent plate margins and provide physically defined chronostratigraphic markers the mapping of lateral termination of volcanic ash layers together with the interpretation of depositional facies discontinuities permits the identification of onlap offlap and downlap stratal termination patterns in onshore outcrop belts in particular this type of analysis is useful to identify bounding surfaces in offshore muddy sediments the relative abundance of intercalated volcanic ash layers and their associated pyroclastic volcaniclastic fragments in marine siliciclastic successions is interpreted to correspond to temporal variation in the relative rate of supply of coarse grained terrigenous sediments to a marine environment during a relative sea level cycle in particular transgressive stages are characterized by the reduction of active supply of coarse grained terrigenous sediments to a marine elastic environment and this results in the increase of relative abundance of intercalated volcanic ash layers and their associated volcanogenic lithofacies this kind of sediment is hierarchically identified in response to the development of marine flooding surfaces transgressive systems tracts and transgressive sequence sets in general boundaries of depositional sequences and their component building blocks are interpreted to provide a chronostratigraphic framework for local and regional correlations of siliciclastic successions the mapping of volcanic ash layers can identify diachronous evolution of bounding surfaces and component building blocks of a high frequency depositional sequence in relation to spatial variations in sedimentation rates and basin subsidence which are superimposed by eustatic sea level changes

paleomagnetic evidence for the clockwise rotation of southwest japan abstract over 500 oriented samples of felsic rocks of cretaceous to middle miocene age were collected along the go river in the central part of southwest japan in an attempt to detect the process of tectonic rotation of southwest japan from the paleomagnetic view point thermal demagnetization was successful in isolating characteristic directions from the remanent magnetization of samples reliability of the paleomagnetic direction is ascertained through the agreement of directions from different kinds of rocks as well as the presence of both normal and reversed polarities the paleomagnetic results establish that southwest japan began to rotate clockwise through58 14 later than 28 ma and ceased its motion by about 12 ma southwest japan has undergone no detectable north south translation since 28 ma these results imply that southwest japan was rotated about the pivot around 34 n 129 e between 28 ma and 12 ma in association with the opening of the japan sea

an 825 year long varve record from lillooet lake british columbia and its potential as a flood proxy abstract lillooet river in southwest british columbia has produced damaging floods many times during the past century the floods are recorded in lillooet lake into which the river flows as anomalously thick clastic varves in order to determine whether an 825 year long varve record obtained from 12 percussion and vibracores can be used as flood proxy we compare river discharge records dating back to 1914 to the thickness of the varves deposited during the same time period correlations between varve thickness and a variety of historical discharge measures are low to moderate for the periods 1914 2004 r 2 0 37 and 1914 1945 r 2 0 40 but higher for the period 1946 2004 r 2 0 55 the best correlation r 2 0 55 is between maximum fall discharge and varve thickness during the most recent period 1946 2004 varve thickness for the earlier period of hydrometric data 1914 1946 which is a time of rapid glacier retreat and warmer temperatures in british columbia is best explained with a discharge proxy combining nival runoff glacier runoff and maximum fall discharge landslides glacier fluctuations river dyking artificial lowering of lillooet lake as well as lag effects of storms are responsible for the considerable unexplained variance in the relation between discharge measures and varve thickness over the historic period the cores contain many anomalously thick varves some of which we attribute to previously dated prehistoric landslides in the watershed or to local landslides into the lake we conclude that many historic and prehistoric floods are faithfully recorded as anomalously thick clastic varves but that other processes operating in the watershed preclude using this record as a reliable paleo flood proxy

magnetic fabric development in the tertiary accretionary complex in the boso and miura peninsulas of central japan it has been demonstrated that the anisotropy of magnetic susceptibility ams is a sensitive indicator for distinguishing various processes that had acted during and after the deposition of sediments recently much attention has been focused on proving its usefulness in distinguishing early deformation signatures in sediments which show no visible grain scale deformation here we present the ams results of the neogene miura group of central japan which was formed by arc arc collision tectonics with subdivisions of two contrasting tectonic provinces the southern province a highly deformed accretionary prism and slope basin and the northern province a gently deformed forearc basin samples were collected from 21 sites in both tectonic settings we obtained from axes orientations three typical fabric domains considered to represent sedimentary tectonically deformed and their intermediate types the shape parameters of ams also revealed distinctions clearly sedimentary fabrics are more foliated and anisotropic deformed fabrics show a more prolate shape and are closer to being isotropic the sedimentary fabrics predominate in the northern forearc basin sequence whereas the intermediate and deformed fabrics occur predominantly in the southern province the general trend of the shape of the magnetic fabric in studied sediments reveals a clear evolution in the pattern of the isotropic tectonic fabric constructed from foliated sedimentary fabric

varied responses to subduction in nankai trough and japan trench forearcs responses of sediment entering trenches range from accretion at the foot of the inner slope to subduction into the mantle with inner trench slopes variously displaying uplift subsidence growth and retreat leg 87 is the latest of the dsdp voyages which have provided many clues to the behaviour of subduction zones and was devoted to the study of subduction processes in two trenches off japan the nankai trough fig 1 on the basis of very high quality reflection profiles1 2 is accreting most or all its trench fill which is being stripped off the underlying shikoku basin haemipelagites along a decollement near their contact fig 2a because these seismic profiles define the large scale geometry so clearly the objective of the leg 87 drilling programme was to investigate the structural fabric and physical properties of sediments as they enter the subduction zone using these data which we now report we hoped to deduce or constrain the stress conditions accompanying deformation

improved age estimates for the white river and bridge river tephras western canada new 14c ages date the eruptions that produced the white river and bridge river tephras two important holocene marker beds in western canada the 14c ages were obtained on trees in growth position buried in coarse tephra and a pyroclastic flow near the source vents the mean calendric age of the white river eruption based on four 14c ages is 1147 cal years bp calibrated years approximately equivalent to calendric years or ad 803 the 2 age range obtained from the two most precise 14c ages is 1014 1256 cal years bp or ad 694 936 the mean age of the bridge river eruption determined both from i the single most precise outer ring 14c age and ii the weighted mean of six outer ring 14c ages is 2360 cal years bp or 411 bc 2 age range 2349 2704 cal years bp or 755 400 bc