alkali free tourmaline in the system mgo al2o3 b2o3 sio2 h2o abstract an end member of the tourmaline series with a structural formula mg 2 al al 6 bo 3 3 si 6 o 18 oh 4 has been synthesized in the system mgo al 2 o 3 b 2 o 3 sio 2 h 2 o where it represents the only phase with a tourmaline structure our experiments provide no evidence for the substitutions al mg h mg 2h b h si and alal mgsi and we were not able to synthesize a phase mg aluminobuergerite characterized by mg in the 3a site and a strong oh deficiency reported by rosenberg and foit 1975 the alkali free tourmaline has a vacant 3a site and is related to dravite by the al for na mg substitution it is stable from at least 300 c to about 800 c at low fluid pressures and 100 excess b 2 o 3 and can be synthesized up to a pressure of 20 kbars at higher temperatures the tourmaline decomposes into grandidierite or a boron bearing phase possibly related to mullite b mullite quartz and unidentified solid phases or the tourmaline melts incongruently into corundum liquid depending on pressure in the absence of excess b 2 o 3 tourmaline stability is lowered by about 60 c tourmaline may coexist with the other mgo al 2 o 3 b 2 o 3 sio 2 h 2 o phases forsterite enstatite chlorite talc quartz grandidierite corundum spinel b mullite cordierite and sinhalite depending on the prevailing ptx conditions the 3a vacant tourmaline has the space group r3m with a 15 90 a c 7 115 a and v 1557 0 a 3 however these values vary at room temperature with the pressure temperature conditions of synthesis by 0 015 a in a 0 010 a in c and 4 0 a 3 in v probably as a result of mgal order disorder relations in the octahedral positions despite these variations intensity calculations support the assumed structural formula refractive indices are n o 1 631 2 n e 1 610 2 n 0 021 the infrared spectrum is intermediate between those of dravite and elbaite the common alkali and calcium deficiencies of natural tourmalines may at least partly be explained by miscibilities towards 3a vacant end members the apparent absence of 3a vacant tourmaline in nature is probably due to the lack of fluids that carry boron but no na or ca

paleoseismology along the southern kuril trench inferred from diatom based sea level reconstructions 1 2 3 3 400 500 1

intersector element partitioning in tourmaline a potentially powerful single crystal thermometer hourglass sector zoning and related polar overgrowths are common features of metamorphic tourmaline developing as a result of variations in element preference on the different growth surfaces for sector zoned crystals three domains are present for each growth zone c c and a with compositional differences most distinct for ca and ti and among c and c sectors intersector differences vary commonly showing decreasing fractionation from core to rim attributed to increasing metamorphic grade here we show that intersector element partitioning is temperature dependent and derive empirical geothermometers based on c c and c a partitioning of ca and ti these thermometers are applicable over a range of temperatures and bulk rock compositions intersector partitioning is not affected by re equilibration and records and preserves complete t histories of individual tourmaline grains from prograde to peak and on to retrograde growth information on element mobility is preserved by tourmaline composition because intersector partitioning is independent of element concentration these factors make intersector partitioning an ideal tool to elucidate the thermal history of tourmaline grains and thus their host environment and tourmaline s refractory nature preserves these signatures even into the sedimentary record

coupling instrumental and geological records of sea level change evidence from southern new england of an increase in the rate of sea level rise in the late 19th century 1 we construct a high resolution relative sea level record for the past 700 years by dating basal salt marsh peat samples above a glacial erratic in an eastern connecticut salt marsh to test whether or not the apparent recent acceleration in the rate of sea level rise slr is coeval with climate warming the data reveal an average slr rate of 1 0 0 2 mm year from about 1300 to 1850 a d coupling of the regional tide gauge data 1856 to present with this marsh based record indicates that the nearly three fold increase in the regional rate of slr to modern levels likely occurred in the later half of the 19th century thus the timing of the observed slr rate increase is coincident with the onset of climate warming indicating a possible link between historic slr increases and recent temperature increases

syntectonic carbonate veins from the barbados accretionary prism odp leg 110 record of palaeohydrology syntectonic carbonate veins were found along the decollement zone between the atlantic and caribbean plates and in two sites 12 and 17 km landward of the deformation front of the barbados accretionary prism odp leg 110 both calcite and lesser amounts of rhodochrosite mnco3 occur in microcrystalline fibrous and blocky mosaic forms in veins deposited along scaly shear zones descriptions of the occurrences textures mineralogy and stable isotope geochemistry of these veins presented herein help trace the hydrological evolution of the barbados accretionary prism which has seen the impact of more deeply derived fluids on elevated sediment temperatures and altered geochemistry of interstitial fluids at one site for example vein forming fluids have been as much as 10 c warmer and 1 more enriched in 18o than expected carbon isotope ratios of veins indicate a mixture of carbon derived from seawater and from oxidized organic matter during sulphate reduction although dissolution of calcareous skeletons may be an additional component the presence of methane is recorded in one vein sample in the accretionary prism indicating that either the plumbing of the prism has changed with time allowing more fluid to leak into the prism in the past or that materials currently 1 km above the decollement zone were once deformed in the decollement using oxygen isotope analyses of rhodochrosite samples from two sites in conjunction with measurements of fluid temperature and 18o values of interstitial fluids it is proposed that the fractionation of oxygen isotopes between rhodochrosite and water 1000 1n 38 at 25 c 10 greater than the fractionation between calcite and water however it appears that substitution of 10 20 mol ca into rhodochrosite reduces the fractionation factor by 2 9 so impure diagenetic rhodochrosite samples from the deep ocean will rarely be this enriched in 18o

stability limits of hydrous minerals in sediment and mid ocean ridge basalt compositions implications for water transport in subduction zones phase relationships in hydrated natural sediment and mid ocean ridge basalt morb compositions were investigated experimentally from 6 to 15 gpa and 700 c to 1400 c in order to determine the stability of hydrous phases in subducting slabs and to constrain reactions resulting in the release of water from subduction zones to the mantle phengite and hydrous aluminum silicates topaz oh and phase egg are stable in the sediment composition at depths greater than 150 km and constitute h2o reservoirs similarly lawsonite is an h2o reservoir in morb composition at depths greater than 150 km according to mass balance calculations based on experimental run products the weight proportions of phengite and h2o at 6 gpa in the sediment are about 50 and 2 respectively at pressures from 8 to 12 gpa topaz oh al2sio4 oh 2 appears as the hydrous mineral and the sediment retains about 0 5 0 7 wt h2o at higher pressures phase egg alsio3 oh appears as the hydrous phase with a large stability field the h2o content in the sediment is about 0 5 wt at pressures greater than 12 gpa in natural morb compositions lawsonite is the hydrous phase at pressures lower than 10 gpa about 1 wt h2o in the morb composition is retained by lawsonite at 6 gpa and 800 c above 6 gpa a lawsonite out reaction is controlled by compositional changes of garnet and clinopyroxene if the oceanic crust descends with an overlying sediment layer water can be carried down into the transition zone by the sediment the amount of transported water is controlled by the chemical compositions of the subducting sediments water in the morb layer can be stored to 300 km in lawsonite for a cold subduction zone geotherm water release at depths greater than 200 km through progressive lawsonite breakdown can hydrate the overlying mantle causing the generation of a peridotite region including hydrous phases chondrodite clinohumite phase a and phase e if this hydrous peridotite is dragged down by the descending oceanic crust water can be transported into the transition zone by the subduction process the amount of transported water is controlled by the thermal state of the slab and the chemical composition of morb

evidence for a weak and overpressured decollement beneath sediment dominated accretionary prisms we present structural data from several underthrust sequences in southwest alaska that suggest that the deformation regime beneath accretionary prisms is characterized by a subvertical 1 and regionally extensive layer parallel shearing these results contrast markedly with the results obtained from the more shallow parts of accretionary prisms and fold and thrust belts where 1 plunges gently seaward or toward the deformation front on the basis of mohr circle diagrams we propose that these different stress directions are consistent only with a model in which the two regimes are separated by a very weak decollement and calculate coefficient of friction values that range from 0 25 to 0 08 these values are significantly lower than coefficient of friction values calculated for the basal decollement in the taiwan fold and thrust belt e g 0 2 barr and dahlen 1989a and they are also lower than laboratory friction measurements for most rocks e g 0 6 0 8 byerlee 1978 consequently these low values suggest the presence of rocks with unusual material properties e g montmorillonite logan and rauenzahn 1987 or anomalous fluid pressures along the decollement on the basis of the occurrence of shale diapirs the distribution of early veins and the absence of montmorillonite in the underthrust sequences we propose that there was an anomalously high fluid pressure along the decollement fault instead of there being such a low coefficient of friction these results emphasize the importance of dewatering and fluid flow in controlling the position of the decollement which in turn determines how the accretionary prism grows in essence it is the development of a weak overpressured decollement within a thick sediment pile that allows plate convergence to be partitioned into offscraping and underthrusting regimes

crust derived potassic fluid in metamorphic microdiamond abstract a highly potassic coh fluid with dissolved phosphate chloride and sulfate sulfide was identified as nanometer size inclusions in metamorphic microdiamonds of kokchetav dolomite marble and garnet quartz pyroxene rock using an analytical electron microscope aem coupled with an energy dispersive x ray edx spectrometer this provides a direct piece of evidence for the formation of metamorphic microdiamonds from such a fluid although this crust derived potassic fluid and the associated solid precipitates are in some respects similar to the fluid inclusions in fibrous cloudy mantle diamonds distinct chemical differences exist this potassic coh fluid in addition has the potential to trigger high to ultrahigh k magmatic and k metasomatic processes in mantle

boron isotope fractionation between tourmaline and fluid an experimental re investigation the fractionation of boron isotopes between synthetic dravitic tourmaline and fluid was determined by hydrothermal experiments between 400 and 700 c at 200 mpa and at 500 c 500 mpa tourmaline was crystallized from an oxide mix in presence of water that contained boron in excess in one series of experiments b fluid b tour was 9 after the run in another series it was 0 1 all experiments produced tourmaline as the sole boron bearing solid along with traces of quartz and talc powder xrd and rietveld refinements revealed no significant amounts of tetrahedrally coordinated boron in tourmaline 11b always preferentially fractionated into the fluid for experiments where b fluid b tour was 9 a consistent temperature dependent boron isotope fractionation curve resulted approximated by 11b tour fluid 4 20 1 000 t k 3 52 r2 0 77 and valid from 400 to 700 c no pressure dependence was observed the fractionation 2 7 0 5 at 400 c and 0 8 0 5 at 700 c is much lower than that previously presented by palmer et al 1992 experiments where b fluid b tour was 0 1 showed a significant larger apparent fractionation of up to 4 7 in one of these runs the isotopic composition of handpicked tourmaline crystals of different size varied by 1 3 this is interpreted as resulting from fractional crystallization of boron isotopes during tourmaline growth due to the small boron reservoir of the fluid relative to tourmaline thus indicating larger fractionation than observed at equilibrium the effect is eliminated or minimized in experiments with very high boron excess in the fluid we therefore suggest that values given by the above relation represent the true equilibrium fractionations

nappe geometry in the western swiss alps abstract detailed geological mapping during the last 20 years in the western swiss alps has shown clearly that most of the lower basement nappes are fold nappes possessing normal and inverted limbs moreover their cores are made of strongly deformed gneisses indicating that important ductile strain took place during the formation of the fold nappes it is therefore probably wrong to imagine deep basement nappes as rigid slices as often actually claimed especially when interpreting seismic profiles true brittle type thrust nappes involving basement rocks only occur in the internal and upper parts of the belt cover nappes on the contrary are in most parts of the alpine belt thrust sheets following more or less the rules of thin skinned tectonics many basement fold nappes lost part of their sedimentary cover during or just before their formation by decollement along ductile horizons the result is that many cover thrust nappes in the external part of the alps are directly related to their original basement fold nappes

elevation changes and the great 1960 chilean earthquake support for aseismic slip we reanalyse the near field vertical displacement data for the great chilean earthquake of 1960 to provide constraints on the down dip slip distribution a recent study of free oscillation data confirms earlier proposals of a slow precursor comparable in size to the main shock we seek evidence for this event in the displacement data spatial coverage of the data is inadequate to allow determination of a unique fault model but inversions show that thrust slip must extend over a width of about 300 km and to a depth between 60 km and 85 km well below the seismogenic zone for interplate events we propose that this deeper slip is the source of the slow event our preferred class of solutions has moments ranging from 1 6 1023 n m to 2 5 1023 n m only 30 to 45 of the free oscillation value underestimation of the near trench displacements by 50 together with a seismic overestimation of moment by 30 due to tradeoff with rise time would result in satisfactory agreement

the pyrope coesite rocks and their country rocks at parigi dora maira massif western alps detailed petrography mineral chemistry and pt path both the coarse and fine grained varieties of the partly coesite bearing pyrope quartzites their interlayered jadeite kyanite rocks and the biotite phengite gneiss country rock common to all of them were subjected to detailed petrographic and textural studies in order to determine the sequence of crystallisation of their mineral constituents which were also studied analytically by microprobe prior to pyrope and coesite growth the mg rich metapelites were talc kyanite chlorite rutile ellenbergerite schists which upon continued prograde metamorphism developed first pyrope megacrysts in silica deficient local environments at the expense of chlorite talc kyanite and subsequently the smaller pyrope crystals with coesite inclusions from reacting talc kyanite based on geobarometrically useful mineral inclusions as well as on experimentally determined phase relations a prograde pt path simplified for water activity 1 is constructed which passes through the approximate pt conditions 16 kbar and 560 c 29 kbar and 720 c and finally up to 37 kbar at about 800 c where the mg rich metapelite was a pyrope coesite rock with phengite kyanite and talc still present during the retrograde path pyrope was altered metasomatically either into phlogopite kyanite quartz or at a later stage to chlorite muscovite quartz both assemblages yield pt constraints the latter about 7 9 kbar 500 600 c the country rock gneisses have also endured high pressures of at least 15 kbar but they provide mostly constraints on the lowest portion of the uplift conditions within the greenschist facies about 5 kbar 450 c microprobe data are presented for the following minerals pyrope ellenbergerite dumortierite unusually mgti rich jadeite vermiculite formed after na phlogopite paragonite and for several generations of phengite chlorite talc phlogopite dravite and glaucophane in the high pressure rocks as well as for biotite chlorite phengites epidote garnet albite and k feldspar in the country rock gneisses an outstanding open problem identified in this study is the preservation of minerals as inclusions within kyanite and pyrope beyond their pt stability limits

boron cycling by subducted lithosphere insights from diamondiferous tourmaline from the kokchetav ultrahigh pressure metamorphic belt abstract subduction of lithosphere involving surficial materials into the deep mantle is fundamental to the chemical evolution of the earth however the chemical evolution of the lithosphere during subduction to depth remains equivocal in order to identify materials subjected to geological processes near the surface and at depths in subduction zones we examined b and li isotopes behavior in a unique diamondiferous k rich tourmaline k tourmaline from the kokchetav ultrahigh pressure metamorphic belt the k tourmaline which includes microdiamonds in its core is enriched in 11b relative to 10b 11b 1 2 to 7 7 and 7li relative to 6li 7li 1 1 to 3 1 it is suggested that the k tourmaline crystallized at high pressure in the diamond stability field from a silicate melt generated at high pressure and temperature conditions of the kokchetav peak metamorphism the heavy isotope signature of this k tourmaline differs from that of ordinary na tourmalines in crustal rocks enriched in the light b isotope 11b 16 6 to 2 3 which experienced isotope fractionation through metamorphic dehydration reactions a possible source of the heavy b isotope signature is serpentine in the subducted lithospheric mantle serpentinization of the lithospheric mantle with enrichment of heavy b isotope can be produced by normal faulting at trench outer rise or trench slope regions followed by penetration of seawater into the lithospheric mantle serpentine breakdown in the lithospheric mantle subducted in subarc regions likely provided fluids with the heavy b isotope signature which was acquired during the serpentinization prior to subduction the fluids could ascend and cause partial melting of the overlying crustal layer and the resultant silicate melt could inherit the heavy b isotope signature the subducting lithospheric mantle is a key repository for modeling the flux of fluids and associated elements acquired at a near the surface into the deep mantle

factors in the preservation of coesite the importance of fluid infiltration the survival of coesite in ultrahigh pressure uhp rocks is most commonly attributed to rapid exhumation continuous cooling during uplift and inclusion in strong phases that can sustain a high internal over pressure during decompression exceptions to all of these criteria exist perhaps less attention has been paid to the role of fluid infiltration in the preservation of coesite we used infrared spectroscopy to measure water contents of coesite and coesite pseudomorphs in a variety of uhp rocks in all cases oh concentrations in coesite are below the detection limit of 100 ppm h2o the silica phases surrounding coesite however show varying amounts of h2o this is most spectacularly observed in pyrope quartzites from the dora maira massif that contain at least three phases of silica replacing coesite also distinguished by varying color of cathodoluminescence cl palisade textured quartz 100 ppm h2o red violet cl mosaic quartz which is actually chalcedony up to 0 4 wt h2o yellow brown cl and a rare highly hydrated silica phase interpreted to be opal 7 wt h2o dark blue cl very similar signatures are observed in a grospydite xenolith from the roberts victor kimberlite the quartz replacing coesite in other uhp samples studied contains on the order of 500 ppm h2o or less and most measurements are under the detection limit of our technique we infer that palisade quartz forms under dry or nearly dry conditions and at high temperatures during dilation of the host phase the formation of hydrous silica phases such as chalcedony and opal however must take place at much lower temperatures after cracking of the host phase which allows external fluids to infiltrate delay of fluid infiltration to low temperatures where kinetics are slow even in the presence of water is the most critical factor in the preservation of coesite

structural and fluid evolution of a young accretionary complex the hoh rock assemblage of the western olympic peninsula washington the hoh rock assemblage of the western olympic peninsula washington was deposited in eocene to miocene time and accreted deformed uplifted and eroded by the late miocene northeast dipping fault zones within the hoh are characterized by intensely deformed mud matrix melange and they range from 200 m to 1 000 m thick kinematic indicators within the matrix indicate thrusting to the west southwest both hanging wall and footwall sections are strongly folded and faulted wall rock sections are lithostratigraphically distinct with hanging walls composed of massive coarse sandstone and conglomerate and footwall sections composed of thin to medium bedded sandstone and siltstone folds within the wall rock sections are oblique to and are truncated by the later fault zone melanges indicating that the fault zones postdate folding evidence of fluid involvement in the hoh rocks includes petroliferous outcrops carbonate and clay cement and veins of carbonate and laumontite the progressive evolution of veins and cements paragenetic sequence can be interpreted in terms of crystallization under conditions of increasing consolidation decreasing salinity and changing fluid composition suppressed carbonate luminescence may reflect crystallization under reducing conditions perhaps related to the sulfate reduction zone the presence of hydrocarbons or clay dehydration although deformational features may be associated with the earliest phase of veining most of the localized grain breakage and matrix shear zones formed after the early micritic veins and before the last phase of sparitic carbonate laumontite veins laumontite occurred syn deformationally and in equilibrium with carbonate and also post deformationally the paragenetic sequences observed in all samples from the hoh rock assemblage can be correlated suggesting that the sources and processes controlling the fluid emplacement were similar across a wide region in addition the paragenetic sequence in the hoh rocks is similar to that documented in autochthonous coeval basins of southwest washington this similarity suggests that the precipitates formed during the evolution of the hoh rocks involved fluids that originated within the matrix and did not involve exotic or far traveled fluids

diversity of potassium bearing tourmalines in diamondiferous kokchetav uhp metamorphic rocks a geochemical recorder from peak to retrograde metamorphic stages abstract chemical variations and inclusion mineralogy of tourmaline in diamond bearing ultrahigh pressure uhp gneisses and related siliceous rocks from the kokchetav massif kazakhstan are extensively investigated in conjunction with a review of previously discovered k bearing tourmaline with microdiamond inclusions tourmalines in these kokchetav uhp rocks have a wide compositional range dravite potassium oxy dravite schorl uvite feruvite foitite and some of their oxy variants with potassium content ranging from 0 to 0 576 atoms per formula unit apfu based on y z t cations 15 or 0 2 76 wt k 2 o and decreasing from core to rim the variation in potassium is spatially related to the inclusion mineralogy and is attributed to changes in metamorphic grade four stages of tourmaline growth in the kokchetav uhp rocks are recognized based on the potassium contents and occurrences in order of decreasing p and t 1 k dominant tourmaline k na ca and x vacancy with microdiamond and high si ti phengite inclusions and without quartz inclusions 2 k rich tourmaline k 0 2 0 05 apfu with graphite phengite kyanite and quartz inclusions 3 k poor tourmaline k 0 05 0 01 apfu with matrix quartz and biotite and 4 k free anhedral or overgrown tourmaline associated with low p t minerals such as amphibole or chlorite several lines of evidence also suggest that k dominant tourmaline crystallized in the diamond stability field tourmalines in the kokchetav uhp rocks recorded multi stage growth history from peak uhp conditions through a granulite facies overprint event including partial melting and ultimately to the latest retrograde metamorphism during exhumation

microfossil analysis of sediments representing the 1964 earthquake exposed at girdwood flats alaska usa abstract diatom pollen foraminifera and thecamoebian assemblages from an outcrop of peat and silt at girdwood flats in the upper turnagain arm of the cook inlet alaska record four phases of relative land and sea level changes the first phase is the development of freshwater swamp above high marsh sediments during relative land uplift caused by strain accumulation along the locked portion of the alaska aleutian subduction zone in second phase the top 2 cm of the peat all microfossil groups record pre seismic relative sea level rise relative land subsidence the third phase is rapid land subsidence 1 7 m during the earthquake of march 1964 that initiated intertidal silt accumulation above the peat the final phase is the colonisation of mudflat by salt marsh communities during post seismic land uplift the microfossil data compare favourably with sequences from washington oregon and british columbia that record late holocene submergence events caused by earthquakes the comparable changes in microfossil assemblages record the different phases of relative land and sea level changes and the magnitude of land subsidence caused by each earthquake expressed relative to the tidal range at the site these results raise the question whether preseismic sea level rise represents any kind of warning of large earthquakes

full interseismic locking of the nankai and japan west kurile subduction zones an analysis of uniform elastic strain accumulation in japan constrained by permanent gps we analyze permanent global positioning system gps data obtained over japan between 1995 and 1997 to estimate the instantaneous interseismic coupling ratio of the seismogenic zones due to the subduction of the pacific and philippine sea plates below the japanese islands we first derive the gps strain rate fields that characterize the crustal deformation of southern and northern japan and invert them to determine the effective subduction velocity along the central nankai trough on one side and the japan west kurile trench on the other these reference free velocities are close to those predicted by plate motion models with respect to eurasia we conclude that the eurasian reference frame gives a good approximation to the subduction motion and that to first order both subduction zones were fully locked during the period of measurements we then test whether the coupling ratio shows local variations within the seismogenic zones to do this we divide the subduction interface into 35 km 30 km elements that we model by point source groups and we invert the gps velocity field referenced to eurasia to derive the coupling ratio between 0 and 1 on each fault element the results are coherent over the 3 years and confirm that both the central nankai and the japan west kurile seismogenic zones are homogeneously fully locked most of the coupling ratios are close to 1 and a few are close to 0 intermediate values are rare the zones of decoupling correspond either to strong postseismic afterslip associated with the 1994 sanriku oki interplate earthquake japan trench or to a small overestimation of the actual lower limit of the locked zone we conclude that within the resolution of the gps data and the model 1 partial coupling did not exist during these 3 years along the nankai and japan west kurile trenches 2 the small seismic coupling ratio previously derived from earthquakes analysis for the japan and kurile trenches may indicate that a significant part of the elastic energy is dissipated silently through slow earthquakes and postseismic afterslip and 3 the heterogeneous coseismic slip pattern observed for the large and great earthquakes that rupture both subduction zones is in great contrast to the homogeneous loading finally we discuss the nonelastic residual deformation within the frame of the long term deformation of the japanese islands

the 1960 chile earthquake inversion for slip distribution from surface deformation summary a total of 166 observations of sea level change 130 measurements of elevation difference and 16 determinations of horizontal strain provide an excellent view of the quasi static source process of the great 1960 chilean earthquake these surface deformation data were employed in classical uniform slip fault models as well as more recently developed models that allow spatial variability of slip the best uniform slip planar usp model is 850km long 130km wide and dips 20 seventeen metres of fault displacement contributed to a usp moment of 9 4 times 1022 n m the variable slip planar vsp model concentrates slip on a 900 km long 150 km wide band parallel to the coast several peaks of slip with dimensions of 50 100 km appear in this band and are thought to represent major subduction zone asperities important fractures of the oceanic lithosphere bound the 1960 rupture and are offered as a potential source of fault segmentation within the chilean subduction zone the vsp moment for 1960 earthquake totals 9 5 times 1022 n m about one fifth of the value estimated for the foreshock mainshock sequence from seismic methods except for areas out to sea geodetic resolution on the fault is fairly uniform thus it is unlikely that slip missed by the network could increase the vsp moment much beyond 1 8 times 1023 n m several patches of moment isolated from the main body at 80 110 km depth are found down dip in the vsp model and are presumably indicative of aseismic slip one patch at the northern end of the rupture is probably associated with the initiation phase of the mainshock although the time sequence of the relationship is unknown tide gauge records suggest that another patch between 40 and 43 s responsible for the observed strain and uplifts inland at those latitudes is not of coseismic origin but derives from in place post seismic creep over several years apparently great 1960 type events are not typical members of the 128 yr earthquake cycle in south central chile the nazca south america boundary here is characterized by a variable rupture mode in which major asperities are completely broken by great earthquakes only once in four or five earthquake cycles the more frequent large earthquakes that geographically overlap the great events fill in between the locked zones

deformation of the japanese islands and seismic coupling an interpretation based on gsi permanent gps observations summary the entire area of the japanese islands has been covered by the permanent gps observation network of the geographical survey institute since 1994 in this paper we use a solution for the vectors of motion during 1995 for a selection of 116 stations to discuss the origin of the observed deformation field we refer the displacement field to eurasia using the vlbi determined motion of kashima and demonstrate that other choices such as the okhotsk or north american plates for north japan are not compatible with the data 1 yr gps velocities are much higher than geological constraints would allow because these short term measurements include transient elastic deformation however the good qualitative agreement between the observed geodetic deformation tensors and those inferred from active faults and earthquakes suggests that the quaternary permanent deformation is essentially the result of the transfer of part of the subduction induced elastic deformation into permanent plastic deformation we then compute the elastic deformation of the japanese islands caused by interseismic loading of the pacific and philippine subduction planes the geometry of the coupled zone and its downward extension are determined from the distribution of earthquakes for the pacific slab for the philippine slab we use the geometry proposed by hyndman et al 1995 these elastic models account for most of the observed velocity field if the subduction movement of the philippine sea plate is 100 per cent locked and if that of the pacific plate is 75 85 per cent locked we note that the boundaries of the areas where significant elastic deformation is predicted more than 10 mm yr 1 of motion with respect to eurasia coincide with the main zones of permanent deformation the eastern japan sea deformation zone for the pacific subduction elastic deformation field and the setouchi mtl deformation zone for the nankai field each zone probably accommodates 10 15 mm yr 1 of motion in the long term convergence in the eastern japan sea strike slip in the setouchi mtl zone to account for this deformation the evect of elastic loading from the trench must be combined with 5 10 mm yr 1 of motion of the amur plate with respect to eurasia because loading during the subduction earthquake cycle causes an increase in stress in the eastern japan sea and setouchi mtl deformation zones the probability of earthquake occurrence in these zones may be higher near the end of the cycle

crustal tilting derived from holocene sea level observations along the east coast of hokkaido in japan and upper mantle rheology late holocene sea level observations at sites along the east coast of hokkaido in japan indicate a gradual decrease of the altitude of relative sea level eastward toward the tip of nemuro peninsula these observations in seismically active areas can be explained by glaciohydroisostatic adjustment due to the last deglaciation for an earth model with a thin lithosphere of 30 40 km thickness and with no low viscosity layer or with a 25 km lithosphere overlying a low viscosity layer less than 50 km although more data as a function of time are needed to distinguish these models thus the vertical crustal displacement associated with the subduction of the pacific plate seems to has not been cumulated on a time scale of 103 104 years

tourmaline breakdown in a pelitic system implications for boron cycling through subduction zones pressure temperature conditions of tourmaline breakdown in a metapelite were determined by high pressure experiments at 700 900 c and 4 6 gpa these experiments produced an eclogite facies assemblage of garnet clinopyroxene phengite coesite kyanite and rare rutile the modal proportions of tourmaline clearly decreased between 4 5 and 5 gpa at 700 c between 4 and 4 5 gpa at 800 c and between 800 and 850 c at 4 gpa with tourmaline that survived the higher temperature conditions appearing corroded and thus metastable decreases in the modal abundance of tourmaline are accompanied by decreasing modal abundance of coesite and increasing that of clinopyroxene garnet and kyanite the boron content of phengite increases significantly these changes suggest that with increasing pressure and temperature tourmaline reacts with coesite to produce clinopyroxene garnet kyanite and boron bearing phengite and fluid our results suggest that 1 tourmaline breakdown occurs at lower pressures and temperatures in sio2 saturated systems than in sio2 undersaturated systems 2 in even cold subduction zones subducting sediments should release boron rich fluids by tourmaline breakdown before reaching depths of 150 km and 3 even after tourmaline breakdown a significant amount of boron partitioned into phengite could be stored in deeply subducted sediments

the kokchetav massif kazakhstan type locality of diamond bearing uhp metamorphic rocks abstract after the discovery of metamorphic coesite in crustal rocks from the western alps italy and the western gneiss region norway in the mid 1980s of the last century metamorphic diamond was observed only a few years later in situ in the kokchetav massif kazakhstan findings of such coesite and diamond bearing ultrahigh pressure metamorphic uhp rocks with protoliths formed or embedded in crustal levels and subsequently experienced pt conditions within or even higher than the coesite stability field have dramatically changed our geodynamic view of orogenetic processes these occurrences provide evidence that crustal rocks were subducted into mantle depths and exhumed to the surface recent studies even suggest continental subduction to depths exceeding 300 km these rocks have been extensively studied and many new and important observations have been made thus far more than 350 papers have been published on various aspects of kokchetav uhp rocks the kokchetav massif of northern kazakhstan is part of one of the largest suture zones in central asia and contains slices of hp and uhp metamorphic rocks classical uhp rocks mainly occur in the kumdy kol barchi kol and kulet areas and include a large variety of lithologies such as calcsilicate rocks eclogite gneisses schists marbles of various compositions garnet pyroxene quartz rocks and garnet peridotite most of them contain microdiamonds some of which reach a grain size of 200 m most diamond grains show cuboid shapes but in rare cases diamonds within clinozoisite gneiss from barchi kol occur as octahhedral form microdiamonds contain highly potassic fluid inclusions as well as solid inclusions like carbonates silicates and metal sulfides which favour the idea of diamond formation from a c o h bearing fluid nitrogen isotope data and negative 13c values of kokchetav diamonds indicate a metasedimentary origin pt estimates of kokchetav uhp rocks yield peak metamorphic conditions of at least 43 kbar at temperatures of about 950 1000 c some zircon separates show inherited proterozoic cores and 537 530 ma uhp metamorphic mantle zones several ar ar ages on micas scatter around 529 528 and 521 517 ma and reflect different stages of the exhumation history migmatization occurred during exhumation at about 526 520 ma isotopic studies on calcsilicate rocks confirm a metasedimentary origin 18o values of garnet and clinopyroxene of a layered calcsilicate rock rule out the possibility having a primitive mantle protolith similar studies on eclogites indicate their basaltic protolith having experienced water rock interaction prior to uhp metamorphism a number of unique mineralogical findings have been made on kokchetav uhp rocks k feldspar exsolutions in clinopyroxene demonstrate that potassium can be incorporated into the cpx structure under upper mantle pressures other significant observations are coesite exsolutions in titanite quartz rods in cpx the discovery of k tourmaline as well as new minerals like kokchetavite a hexagonal polymorph of k feldspar and kumdykolite an orthorhombic polymorph of albite the kokchetav uhp rocks represent a unique and challenging stomping ground for geoscientists of various disciplines from crystallography petrology and geochemistry to geophysics and geodynamics geotectonics it concerns all who are interested in the diverse metamorphic processes under upper mantle conditions

shearing of partially consolidated sediments in a lower trench slope setting shimanto belt sw japan abstract detailed mapping of a coastal platform in shikoku sw japan provides evidence for progressive deformation in partially lithified sediments the eocene sediments involved are interpreted as lower slope basin deposits an assemblage of listric normal faults sheath folds broken formations and late stage faulting has developed during the sediments burial and uplift history these structures are typical of many other areas in the shimanto belt of shikoku despite the soft sediment style of deformation the consistency of the fold orientations relative to the regional foliation suggests that they are valid kinematic indicators a sequence of extensional faulting overprinted by synchronous folding and shearing is recognized this is interpreted as the response of the sediments to shape changes in the accretionary basement induced by shortening a general model has been constructed for the evolution of the structures it is proposed that early listric normal faults are subsequently deformed either by shearing along planar surfaces or by motion over frontal and lateral ramps back rotation of sediments during progressive shortening near the front of the prism tightens the fold hinges and rotates the fold axes towards the local shear direction alternative sequences which could account for the observed geometries are also discussed

multiple zircon growth during fast exhumation of diamondiferous deeply subducted continental crust kokchetav massif kazakhstan diamondiferous rocks from the kokchetav massif kazakhstan represent deeply subducted continental crust in order to constrain the age of ultra high pressure uhp metamorphism and subsequent retrogression during exhumation zircons from diamondiferous gneisses and metacarbonates have been investigated by a combined petrological and isotopic study four different zircon domains were distinguished on the basis of transmitted light microscopy cathodoluminescence trace element contents and mineral inclusions mineral inclusions and trace element characteristics of the zircon domains permit us to relate zircon growth to metamorphic conditions domain 1 consists of rounded cores and lacks evidence of uhp metamorphism domain 2 contains diamond coesite omphacite and titanian phengite inclusions providing evidence that it formed at uhp metamorphic conditions p 43 kbar t 950 c domain 3 is characterised by low pressure mineral inclusions such as garnet biotite and plagioclase which are common minerals in the granulite facies overprint of the gneisses p 10 kbar t 800 c this multi stage zircon growth during cooling and exhumation of the diamondiferous rocks can be best explained by zircon growth from zr saturated partial melts present in the gneisses domain 4 forms idiomorphic overgrowths and the rare earth element pattern indicates that it formed without coexisting garnet most probably at amphibolite facies conditions p 5 kbar t 600 c the metamorphic zircon domains were dated by shrimp ion microprobe and yielded ages of 527 5 528 8 and 526 5 ma for domains 2 3 and 4 respectively these indistinguishable ages provide evidence for a fast exhumation beyond the resolution of shrimp dating the mean age of all zircons formed between uhp metamorphic conditions and granulite facies metamorphism is 528 3 ma indicating that decompression took place in less than 6 ma hence the deeply subducted continental crust was exhumed from mantle depth to the base of the crust at rates higher than 1 8 cm year we propose a two stage exhumation model to explain the obtained p t t path fast exhumation on top of the subducted slab from depth 140 to 35 km was driven by buoyancy and facilitated by the presence of partial melts a period of near isobaric cooling was followed by a second decompression event probably related to extension in a late stage of continental collision

tourmaline in a low grade clastic metasedimentary rock an example of the petrogenetic potential of tourmaline detrital tourmaline grains and their associated tourmaline overgrowths provide a means to unravel the provenance and petrogenetic history of low grade clastic metasedimentary rocks evidence derives from tourmaline grains found in a lithic wacke metamorphosed to chlorite zone conditions the detrital tourmaline cores are diagnostic indicators of the source rocks of the sediment whereas the overgrowths record both diagenetic and metamorphic reactions in the rock tourmaline grains consist of a detrital core surrounded by asymmetric overgrowths comprised of inner and outer rims abrupt chemical discontinuities between each of these zones implies that volume diffusion within tourmaline was minor under the conditions of formation compositions of the detrital cores vary widely yet can be correlated with source rock types that are consistent with lithic fragments recognizable in the metawacke at either the analogous or antilogous pole inner rim compositions proximal to the detrital cores converge despite the substrate tourmaline composition indicating an approach to chemical equilibrium however significant dufferences in al and x site vacancies at the expense of mg na and ti between the analogous and antilogous poles of the inner rims demonstrate the presence of significant amounts of compositional polarity outer rim compositions at either pole also converge but compositional polarity between the analogous and antilogous poles persists the presence of the inner and outer rims separated by a compositional discontinuity suggests punctuated evolution of the overgrowth this implies that boron was sporadically available during diagenesis and metamorphism based on boron contents of minerals this may correspond to a mechanism such as boron release due to polytypic change of illite or consumption of illite and or muscovite as such tourmaline growth stages may serve as a monitor of chemical reactions in low grade metamorphic rocks

the interaction of fluid processes and progressive deformation during shallow level accretion examples from the shimanto belt of sw japan the interaction of deformation and fluid flow is recorded in the mesostmcture and microstructure of the shimanto belt in the eastern hata peninsula of sw japan large areas of disrupted strata including the okitsu melange have been generated during the progressive deformation associated with shallow level accretion the resulting assemblage of structures and their crosscutting relations reflect the complex interplay between pore fluid pressures lithification states and strain rates evidence for the relative timing of structures diagenesis and modes of fluid migration has been used to constrain a generalized model for the nature of fluid outflow during the accretion and burial of trenchslope lithologies early outflow was diffuse but the flow direction was controlled mainly by a regionally pervasive structural anisotropy and the predominance of independent paniculate flow as the sediments became more lithified fluid flow was focused along faults in which transient microfractures controlled the permeability fractures released pore fluid pressure promoting further deformation by diffusive mass transfer this in turn resulted in the buildup of pore fluid pressures and tectonic stresses and a recurrence of fracturing in some fault zones and in the okitsu melange several such deformation mechanism cycles can be identified the development of a complex array of faults during the late stages of accretionary complex evolution resulted in fluid flow paths becoming multidirectional

synthesis of tourmaline solid solutions in the system na 2 o mgo al 2 o 3 sio 2 b 2 o 3 h 2 o hcl and the distribution of na between tourmaline and fluid at 300 to 700 c and 200 mpa tourmaline has been synthesized hydrothermally at 200 mpa between 300 and 700 c from oxide mixtures with mg al ratios for the end members dravite namg3al6 si6o18 bo3 3 oh 3 oh and mg foitite mg2al al6 si6o18 bo3 3 oh 3 oh six different na concentrations were investigated to determine the distribution of na between tourmaline and fluid in the sio2 saturated system na2o mgo al2o3 sio2 b2o3 h2o hcl synthetic tourmaline ranges from x site vacant tourmaline mg foitite to nearly ideal dravite with na 0 95 apfu there are small but significant amounts of proton deficiency and negligible tetrahedral al chemical variation is primarily caused by the substitutions al mg 1na 1 and minor almg 1h 1 varying amounts of na and determine the mg al ratios besides tourmaline and quartz additional mg al phases are chlorite and at 700 c cordierite albite is also present at high na concentrations in the bulk composition the c dimension of the tourmaline crystals increases with na in tourmaline the amount of na in the x site depends strongly on the bulk concentration of na in the system as well as on the temperature these factors in turn control the phase assemblage and the composition of the fluid phase for the assemblage tourmaline quartz chlorite cordierite fluid a linear relationship exists between na concentration in the fluid quenched after the run and tourmaline with temperature t c 25 c nafluid natur 558 878 14 692 r2 0 96

holocene relative sea level changes along the seattle fault at restoration point washington abstract at a marsh on the hanging wall of the seattle fault fossil brackish water diatom and plant seed assemblages show that the marsh lay near sea level between 7500 and 1000 cal yr b p this marsh is uniquely situated for recording environmental changes associated with past earthquakes on the seattle fault since 7500 cal yr b p changes in fossil diatoms and seeds record several rapid environmental changes in the earliest of these brackish conditions changed to freshwater 6900 cal yr b p possibly because of coseismic uplift or beach berm accretion if coseismic uplift produced the freshening 6900 cal yr b p that uplift probably did not exceed 2 m during another event about 1700 cal yr b p brackish plant and diatom assemblages changed rapidly to a tidal flat assemblage because of either tectonic subsidence or berm erosion the site then remained a tideflat until the most recent event when an abrupt shift from tideflat diatoms to freshwater taxa resulted from 7 m of uplift during an earthquake on the seattle fault 1000 cal yr b p regardless of the earlier events no seattle fault earthquake similar to the one 1000 cal yr b p occurred at any other time in the past 7500 years

initiation and development of the pennine basal thrust swiss alps a structural and geochronological study of an exhumed megathrust abstract the pennine basal thrust pbt is an exhumed megathrust developed during continental collision from late eocene to miocene to trace its evolution five samples with indications for up to three microstructurally diachronous white mica generations were investigated by laser in situ and step heating 40 ar 39 ar dating three deformation related crystallization ages can be distinguished 1 d 1 characterized in the pbt hanging wall by an s 1 foliation defined by white mica chloritoid began at or before 38 0 ma 2 d 2 formed a pervasive s 2 cleavage and synchronous white mica rich veins dated at 27 ma 3 d 3 produced an s 3 crenulation cleavage and chlorite white mica veins dated at 23 ma older ages of 96 ma footwall and 115 ma hanging wall are interpreted as minimum ages for the detrital component finally discrete faulting produced fault gouge with an illite k ar age of 19 ma a simplified back restored reconstruction provides a tectonic context for the dated structures in this framework d 1 occurred during middle to late eocene tectonic accretion after late eocene initiation of continental collision d 2 reflects oligocene top to nw shearing with both in and out of sequence thrusting d 3 then developed from 23 to 19 ma during the progressive deactivation of the pbt

from oceanic closure to continental collision a synthesis of the schistes lustres metamorphic complex of the western alps recent lithostratigraphic and structural studies made in the western alps along the valais savoy and queyras schistes lustres transects indicate that there are strong similarities in the nature of the sedimentary series and in the general structural edifice between these areas the main new conclusion is that a significant part of the schistes lustres complex is made up of syn orogenic upper cretaceous deposits a first type present in all three transects consists of lower upper cretaceous metasedimentary rocks containing oceanic and continental detrital materials which were deposited on the western edge of the northwest tethyan paleomargin and in the oceanic realm undergoing tectonization a second type is made up of upper cretaceous calcareous gritty metaflysch known only in the savoy transect which is interpreted as a sedimentary consequence of the complete or partial closure of the tethyan ocean

structural evolution of underthrusted sediments kodiak islands alaska the late cretaceous to early tertiary sediments of the kodiak accretionary complex preserve the earliest deformation associated with underthrusting along a thickly sedimented convergent margin because of the thick trench fill this early deformation resulted in the formation of two distinct structural terranes 1 coherent terranes of layered turbidites and 2 melange terranes the earliest deformation d1 in the coherent terranes is marked by normal faults mineralized layer perpendicular veins in sandstones and microfaults in shales these features suggest that 1 was vertical and that 3 was horizontal and nw trending during d1 we interpret d1 structures as hydrofractures that formed in flat lying sediments with high fluid pressures caused by rapid tectonic loading in contrast the melanges appear to record a more protracted and complex history that culminated in structures similar to the d1 structures above we have recognized three successive transitional stages in the melanges i breakup of sand beds along cataclastic shear zones with dispersal of sand inclusions within a relatively ductile shale matrix resulting in the blocks in matrix character of the melange ii development of ductile shear bands that crosscut the melange fabric at a low angle and iii hydrofracturing with the formation of calcite and quartz filled veins in sandstone inclusions and microfaults in the shales the sequence of microstructures associated with stages i iii records increased cohesion of the sediments during deformation dominated by layer parallel shear intense mineralization and microfaulting during stage iii suggest that the melanges are zones of concentrated fluid flow with a fracture dominated permeability stage iii structures are texturally indistinguishable and contemporaneous with the less pervasive d1 structures in the coherent terranes based on these observations we believe that the melanges are major shear zones that formed at the top of the subducting pile and immediately below a major decollement the coherent terranes represent the structurally and stratigraphically lowest sediments and they bypassed the stage i and ii deformations of the melanges because they were the greatest distance from the decollement when they were deformed moreover both the melange and coherent terranes appear to have bypassed the shallow zone of intense horizontal shortening that dominates the toe of the overriding accretionary prism

geochemistry and boron isotopic compositions of tourmaline from the paleoproterozoic amphibolites ne china implications for the origin of borate deposit abstract the paleoproterozoic metasediments and metavolcanics in the jiao liao ji belt northeastern china host a large number of borate deposits to trace the source of boron in these borate deposits we carried out in situ chemical and boron isotopic studies on tourmalines of amphibolites from the lieryu formation of the liaohe group in the jiao liao ji belt the petrology and the chemical compositions of tourmalines of amphibolites show that these tourmalines formed by influx of b rich fluids during different stages of metamorphism the 11b values of tourmaline continue to decline during the successive metamorphism tourmalines that formed during the prograde metamorphism show higher 11b values 9 52 10 18 than those formed during the peak metamorphism of amphibolite facies 7 22 9 43 subsequently tourmalines with lower 11b values formed during the retrograde metamorphism of greenschist facies which have slightly different boron isotopic compositions in cores 4 18 5 50 and rims 2 66 4 66 mainly due to the temperature effect the boron isotopic variations of tourmalines of amphibolites match well with our modeling study of boron isotope the results suggest that tourmalines may be precipitated from fluids released from dehydration of marine sediments with relative high 11b values 9 during prograde metamorphism in the same way the borate deposits formed from the liberated b rich fluids that interacted with the mg rich carbonates and or silicates

a 4500 year record of emergence events at onnetoh hokkaido northern japan reconstructed using plant macrofossils abstract plant macrofossils vascular plants and mosses document six episodic emergence events during the late holocene at onnetoh eastern hokkaido northern japan four events were dated by the ams radiocarbon method to 4240 3910 3640 3360 1520 1260 and 790 660 cal year bp and another was dated by liquid scintillation spectrometry of radiocarbon to 2750 2430 cal year bp we attribute the three most recent and the two oldest periods of emergence events identified in this study to uplift associated with unusually large interplate earthquakes along the southwestern part of the kuril subduction zone

non destructive analyses to determine appropriate stratigraphic level for dating of tsunami deposits abstract the upper boundary of a tsunami deposit often comprises a mud dominated layer called a mud cap resulting from the different settling times of various grain sizes in the suspended sediment this mud cap is often visibly indistinguishable from muds that can be deposited under normal circumstances following a tsunami in fact dating organic material immediately above the sandy tsunami deposit often produces significantly older ages than the actual age of the event because of the mud cap contains a wide variety of entrained material herein we present several analytical results related to mud caps our results indicate that mud caps are difficult to recognize visually whereas ct and xrf analyses enable us to recognize them in a non destructive way for the dating of tsunami deposits it is crucially important to conduct such non destructive analyses before sampling to recognize unfavorable stratigraphic components for dating such careful sampling is extremely important for accurate dating of tsunami deposit which is essential for reconstruction of paleotsunami size and its frequency therefore our finding will also contribute to tsunami hazard assessment

the original swiss flysch a reappraisal of the type deposits in the swiss prealps abstract the flysch sequences of the swiss prealps alpine front ranges are described and interpreted in the light of a decade of study by a group research project at fribourg the geographical and geological settings are illustrated the stratigraphy and sedimentology the sedimentary petrography and the geodynamic setting are discussed correlations within and outside the prealps as well as outstanding problems are treated the flysch units and sequences covered are the gurnigel flysch the medianes flysch helminthoid flysch fouyet manche and mocausa flysch hundsruck flysch niesen flysch and the ultrahelvetic flysch the data from clast framework grain and heavy mineral analysis from micropalaeontology from facies analysis palaeocurrent measurements and stratigraphy allow the interpretation of sedimentary environments source terranes and depositional models in all cases flysch deposits are deep marine detrital accumulations and source areas were undergoing active tectonics individual models are based on the deep sea fan concept but interpretations tend to show significant modifications with respect to simple fan characteristics these departures are to some extent due to available grain size to active structuring of basins or to minor controls such as eustatic variations or climatic influence the integration of sedimentological data with stratigraphy and regional structure furnishes palinspastic reconstructions in map view these provide insights on the palaeogeography of the western alps from mid cretaceous to oligocene and give a picture of the evolution of the western mediterranean tethys during the same period the relationship between flysch deposition and alpine mountain building is confirmed while constraints on basin evolution are established

an experimental study on k and na incorporation in dravitic tourmaline and insight into the origin of diamondiferous tourmaline from the kokchetav massif kazakhstan tourmaline was synthesized in the system mgo al2o3 b2o3 sio2 kcl nacl h2o from an oxide mixture and excess fluid at 500 700 c and 0 2 4 0 gpa to investigate the effect of pressure temperature and fluid composition on the relative incorporation of na and k in dravitic tourmaline incorporation of k at the x site increases with pressure temperature and kcl concentration a maximum of 0 71 k pfu leaving 0 29 x vacant sites pfu was incorporated into k dravite synthesized at 4 0 gpa 700 c from a 4 78 m kcl na free fluid in contrast na incorporation depends predominately on fluid composition rather than pressure or temperature dravite with the highest na content of 1 00 na pfu was synthesized at 0 4 gpa and 700 c from a 3 87 m nacl and 1 08 m kcl fluid all synthesized crystals are zoned and the dominant solid solution in the na and k bearing system is between magnesio foitite mg2al al6si6o18 bo3 3 oh 3oh and dravite namg3al6si6o18 bo3 3 oh 3 oh with the dravitic component increasing with the concentration of na in the fluid in the k bearing na free system the dominant solid solution is between magnesio foitite and k dravite kmg3al6si6o18 bo3 3 oh 3 oh with the k dravitic component increasing with pressure temperature and the concentration of k in the fluid the unit cell volume of tourmaline increases with k incorporation from 1555 1 3 to 1588 1 2 a3 reflecting the incorporation of the relatively large k ion comparison of our results to the compositional data for maruyamaite k dominant tourmaline from the ultrahigh pressure rocks of the kokchetav massif in kazakhstan suggests that the latter was formed in a k rich na poor environment at ultrahigh pressure conditions near the diamond stability field

dating tsunami deposits present knowledge and challenges abstract dating approaches for fine sediment tsunami deposits can be divided into two categories 1 dating directly using materials from within a tsunami deposit and 2 dating indirectly using materials from above and below it for the former optically stimulated luminescence osl dating has a possible advantage in that is can directly date the burial age of sediments laid down by a tsunami however because of methodological limitations osl dating cannot always provide a reliable age although 14c and u th dating of reworked material from within a tsunami deposit are possible means of determining the age of the event the results merely represent a maximum age of deposition for these reasons dating is commonly achieved indirectly from 14c dates taken from samples in sections immediately above and below a tsunami deposit however indirectly dated results do not provide a precise timing of the event therefore there are distinct limitations in the ability to obtain high precision dating of past tsunamis recent methodological developments including the application of bayesian statistical analysis to radiocarbon dating results and the selection of appropriate dating materials has significantly improved the accuracy of age determination by reducing errors this review presents several methodological improvements that have enhanced tsunami deposit age estimation the most important points for a more precise tsunami age estimation are the numbers of 14c samples dated coupled with the use of bayesian statistical analysis these points are applicable not only to tsunami deposits but also to many other past geohazard events

coesite inclusions and prograde compositional zonation of garnet in whiteschist of the hp uhpm kokchetav massif kazakhstan a record of progressive uhp metamorphism coarse grained whiteschist containing the assemblage garnet kyanite phengite talc quartz coesite is an abundant constituent of the ultrahigh pressure metamorphic uhpm belt in the kulet region of the kokchetav massif of kazakhstan garnet displays prograde compositional zonation with decreasing spessartine and increasing pyrope components from core to rim cores were recrystallized at t 380 c inner to 580 c outer at p 10 kbar garnet ilmenite geothermometry margarite quartz stability and mantles at t 720 760 c and ph20 34 36 kbar coesite graphite stability phengite geobarometer kfmash system reaction equilibria textural evidence indicates that rims grew during decompression and cooling within the qtz stability field silica inclusions quartz and or coesite of various textural types within garnets display a systematic zonal distribution cores contain abundant inclusions of euhedral quartz type 1 inclusions inner mantle regions contain inclusions of polycrystalline quartz pseudomorphs after coesite type 2 with minute dusty micro inclusions of chlorite and more rarely talc and kyanite in their cores intense radial and concentric fractures are well developed in the garnet intermediate mantle regions contain bimineralic inclusions with coesite cores and palisade quartz rims type 3 which are also surrounded by radial fractures subhedral inclusions of pure coesite without quartz overgrowths or radial fractures type 4 occur in the outer part of the mantle garnet rims are silica inclusion free type 1 inclusions in garnet cores represent the low p low t precursor stage to uhpm recrystallization and attest to the persistence of low p assemblages in the coesite stability field coesites in inclusion types 2 3 and 4 are interpreted to have sequentially crystallized by net transfer reaction kyanite talc garnet coesite h2o and were sequestered within the garnet with progressively decreasing amounts of intragranular aqueous fluid during the retrograde evolution of the rock all three inclusion types diverged from the host garnet p t path at the coesite quartz equilibrium and followed a trajectory parallel to the equilibrium boundary resulting in inclusion overpressure coesite in type 2 inclusions suffered rapid intragranular h2o catalysed transformation to quartz and ruptured the host garnet at about 600 c when inclusion p 27 kbar garnet host p 9 kbar instantaneous decompression to the host garnet p t path passed through the kyanite talc chlorite quartz reaction equilibrium resulting in the dusty micro assemblage in inclusion cores type 3 inclusions suffered a lower volumetric proportion transformation to quartz at the coesite quartz equilibrium and finally underwent rupture and decompression when t 400 c facilitating coesite preservation type 4 coesite inclusions are interpreted to have suffered minimal transformation to quartz and proceeded to surface temperature conditions along or near the coesite quartz equilibrium boundary

the development of a diatom based transfer function along the pacific coast of eastern hokkaido northern japan an aid in paleoseismic studies of the kuril subduction zone abstract this paper provides a dataset to develop a diatom based transfer function which is applicable to paleoseismic studies at southwestern kuril subduction zone northern japan modern diatom samples were collected from five transects from saltmarshes of lakes akkeshi and onnetoh along the pacific coast of eastern hokkaido the relationships between diatom species and environmental variables were elucidated by canonical correspondence analysis cca and partial ccas partial ccas associated with monte carlo permutation tests show that elevation accounts for a significant portion of the total variance in the diatom data therefore statistically significant transfer functions quantifying the relationship between modern diatom assemblages and elevation were developed using weighted averaging partial least squares and applied to fossil diatom assemblages from lake onnetoh the reconstructed curve of elevations contains five emergence and four submergence events and the transfer functions calculated the amplitude of four of the emergence events to be at least 1 m the results are consistent with paleoecological data produced by previous studies if these events represent uplift associated with interplate earthquake and subsidence during an interseismic period along the kuril subduction zone transfer functions of eastern hokkaido can contribute to reconstruction of the recurrence intervals and the amplitude of earthquakes

metasomatic flow of metacarbonate derived fluids carrying isotopically heavy boron in continental subduction zones insights from tourmaline bearing ultra high pressure eclogites and veins dabie terrane eastern china abstract tourmaline one of the most important hosts of boron b in crustal rocks has rarely been found in natural high pressure hp and ultra hp uhp eclogites here we report the first finding of tourmaline bearing uhp eclogites and veins in the dabie terrane china these distinctive samples occur exclusively in impure uhp marbles investigations on the eclogite vein marble system provide important insights into the origin flow and metasomatic effects of eclogite facies 11b rich fluids in continental subduction zones petrologic and geochemical evidence indicates that tourmaline in the eclogites tur e formed by metasomatism due to the infiltration of a b rich fluid under conditions of ca 2 2 2 6 gpa and 610 660 c the hp veins containing euhedral tourmaline tur v and occurring at the eclogite marble contacts or in the interiors of eclogite lenses represent the crystallized products of the infiltrating fluid systematic compositional variations along the profile from the interiors of the eclogite lenses to their margins and mass balance calculations indicate large inputs of b carbon large ion lithophile elements and light rare earth elements to the eclogites during fluid infiltration all types of tourmaline including the tur e and tur v as well as minor amounts of tourmaline in the marbles tur m have similar compositions dravitic with xmg values mg mg fe of 0 7 0 8 in situ analyses using laser ablation multicollector inductively coupled plasma mass spectrometry show that all of tourmaline has high 11b values ranging from 6 to 15 which suggest a 11b rich isotope signature for the infiltrating fluid the tourmaline b isotope data together with the detailed field observations and whole rock sr nd isotopes reveal that the infiltrating fluid was derived from the impure marbles influx of such fluid was highly channelized and was mainly achieved along lithologic boundaries between uhp marbles and eclogites or along fractures in the eclogites this study indicates that impure marbles are an important reservoir of isotopically heavy b in deeply subducted continental slabs this point may be of particular importance because most b reservoirs in subducted continental crust typically have light b isotopic compositions our results highlight that subducted metacarbonate rocks could liberate eclogite facies b rich high 11b fluids and thus might exert important effects on the cycle of b and its isotopes in subduction zones

origin of vein structures in the slope deposits of modern accretionary prisms vein structures that have been described from the slope apron sediments of modern accretionary prisms represent brittle failure caused by an effective tensile stress the effective stress arises from abnormal pore water pressure acting in opposition to the compressional stresses on the sediment thus even though 3 the minimum stress may be compressional if the pore water pressure is of greater magnitude than 3 the resultant effective stress will be tensional and failure opening of the veins will occur in the 1 2 plane as the veins open the pore water can escape into the veins and eventually out of the sediment along more permeable coarser beds the initial movement of pore water into the veins may entrain finer grains from the host rock near the vein walls resulting in the observed finer grained vein filling then as the veins close as pore water escapes the elongate and platy grains may be rotated into near parallelism with the vein walls the tributaries that are observed at the ends of some veins may be a result of continued dewatering after the veins have closed as the pore water is forced to diffuse back into the sediment after being concentrated into an efficient flow by the parallel preferred orientation of the platy mineral grains in the vein

evidence for 17th century tsunamis generated on the kuril kamchatka subduction zone lake tokotan hokkaido japan abstract in the seventeenth century two tsunamis that were generated by earthquakes on the kuril kamchatka subduction zone inundated the eastern coast of hokkaido northern japan stratigraphic evidence for these two tsunamis and related land level change in coastal hokkaido consists of two landward thinning sand layers in the sediments of lake tokotan a coastal lagoon on the hokkaido coast the marine origin of these sand layers is indicated by the presence of brackish marine diatoms the rarity and high degree of fragmentation of diatom valves suggests that the sands were transported in a short time over a considerable distance tsunamis at this site were probably generated by great earthquakes along the kuril kamchatka trench volcanic ash deposits lying just above the sands suggest that tsunamis occurred in the late 17th century tsunamis during the historic period are not recorded in lake tokotan which suggests that the sand layers were deposited by tsunamis substantially larger than historic tsunamis

episodic emergence in the past 3000 years at the akkeshi estuary hokkaido northern japan at the akkeshi estuary rapid emergence interrupted holocene submergence at least four times in the past 3000 years each emergence event produced an upward change from estuarine mud to freshwater peat while the estuarine mud abounds in brackish and marine diatoms freshwater taxa dominate the peat emergence events occurred from 1700 to 2300 1000 to 1300 and 500 to 700 cal yr b p an additional emergence event predated by several decades a volcanic ash that erupted in a d 1694 at least three of the events produced contacts abrupt enough to represent uplift during earthquakes such uplift may reconcile seemingly conflicting records of vertical crustal movement in eastern hokkaido this tectonically active area which is being subducted by the pacific plate at 8 cm yr contains marine terraces that imply 0 1 0 5 mm yr of net uplift in the late quaternary however these terraces adjoin tide gages that recorded 8 9 mm yr of steady submergence in the 20th century the terrace uplift need not conflict with the gaged submergence if the region is subject to occasional coseismic uplift as during the emergence events implied by holocene geology near akkeshi

a comparison of the evolution of diamondiferous quartz rich rocks from the saxonian erzgebirge and the kokchetav massif are so called diamondiferous gneisses magmatic rocks abstract the petrography and chemical composition of minerals of quartz rich diamondiferous rocks from the kokchetav massif especially the zonation of garnet were studied and compared with diamondiferous quartzofeldspathic rocks from the saxonian erzgebirge many compositional and textural features were found to be similar for instance microdiamonds are enclosed systematically in a specific intermediate growth zone of garnet in these rocks on the basis of experimental data a magmatic scenario was constructed to check if the quartz rich diamondiferous rocks are of magmatic origin by this the p t paths derived here for the kokchetav rocks and the textural observations it is concluded that the minerals of the diamondiferous rocks have crystallized from silicate melts these melts originated by anatexis of deeply submerged metasediments erzgebirge at t as high as 1200 c kokchetav massif at 50 100 c lower t and ascended from at least 200 km depth relics of the pre anatectic evolution are still present for instance as garnet cores after ascent and emplacement of the magma in deep portions of thickened continental crust kokchetav massif 45 50 km close to 800 c erzgebirge 55 60 km at 30 50 c lower t considerable quantities of white and or dark micas formed by peritectic reactions from melt for instance garnets could be resorbed at this stage and biotite grew instead after the magmatic stage retrogression took place much stronger in the kokchetav massif this was accompanied by deformation transforming broadly the magmatic texture of quartz rich diamondiferous rocks from the kokchetav massif to a gneissic texture

on the occurrence and boron isotopic composition of tourmaline in ultra high pressure metamorphic rocks abstract the extensive p t stability and the high chemical variability of tourmaline tur together with its common occurrence in metasediments proves its high potential for petrological and isotope geochemical studies on fluid rock interaction in subduction and collision related rocks this paper reviews the occurrence major element chemistry and boron isotopic composition of tur in high and ultrahigh pressure metamorphic uhpm rocks in addition it presents a new discovery of coesite bearing tur schorl from the erzgebirge germany as well as tur dravite related to the retrograde history of coesite and diamond bearing rocks from the erzgebirge and the kokchetav massif kazakhstan the scarce data on worldwide occurrences of u hpm tur reveal a high occupation of the crystallographic x site dominated by na and the possible presence of excess b with little further distinctiveness in its major element composition when compared with tur from medium grade rocks high k 2 o contents in tur are probably not related to uhp growth or equilibration the b isotopic composition of u hpm tur ranges in 11 b from 16 to 1 with many samples in or below the range of continental crust in contrast tur formed during retrograde fluid influx typically shows high 11 b values up to 28 suggesting heavy b fluids infiltrating the exhuming u hpm units coesite inclusions in tur characterized by raman spectroscopy are regarded as the best indicator for its uhp stability supplementary material analytical methods tourmaline compositions and boron isotope values are available at http www geolsoc org uk sup18354

identifying coseismic subsidence in tidal wetland stratigraphic sequences at the cascadia subduction zone of western north america tidal wetland stratigraphy reveals that great plate boundary earthquakes have caused hundreds of kilometers of coast to subside at the cascadia subduction zone however determining earthquake recurrence intervals and mapping the coastal extent of past great earthquake ruptures in this region are complicated by the effects of many sedimentologic hydrographic and oceanographic processes that occur on the coasts of tectonically passive as well as active continental margins tidal wetland stratigraphy at many cascadia estuaries differs little from that at similar sites on passive margin coasts where stratigraphic sequences form through nonseismic processes unrelated to coseismic land level changes methods developed through study of similar stratigraphic sequences in europe provide a framework for investigating the cascadia estuarine record five kinds of criteria must be evaluated when inferring regional coastal subsidence due to great plate boundary earthquakes the suddenness and amount of submergence the lateral extent of submerged tidal wetland soils the coincidence of submergence with tsunami deposits and the degree of synchroneity of submergence events at widely spaced sites evaluation of such criteria at the cascadia subduction zone indicates regional coastal subsidence during at least two great earthquakes evidence for a coseismic origin remains equivocal however for the many peat mud contacts in cascadia stratigraphic sequences that lack 1 contrasts in lithology or fossils indicative of more than half a meter of submergence 2 well studied tsunami deposits or 3 precise ages needed for regional correlation paleoecologic studies of fossil assemblages are particularly important in estimating the size of sudden sea level changes recorded by abrupt peat mud contacts and in helping to distinguish erosional and gradually formed contacts from coseismic contacts reconstruction of a history of great earthquakes for the cascadia subduction zone will require rigorous application of the above criteria and many detailed investigations

insight into diagenetic processes from authigenic tourmaline an example from carboniferous and permian siliciclastic rocks of western poland abstract authigenic tourmaline is a rare and minor component of siliciclastic rocks however once it occurs it can be used to interpret a number of subsurface parameters and processes such as fluid composition redox state salinity ph and fluid migration paths notwithstanding the conditions of tourmaline authigenesis still need to be recognize with greater clarity carboniferous and permian siliciclastic rocks in the subsurface of western poland in the vicinity of the dolsk fault show unusually high boron contents at places surpassing 1000 g g which are associated with the presence of authigenic tourmaline the mineral forms fine elongated crystals of nano to micrometer width grouped in radiating or semi parallel aggregates which are dispersed in the clay matrix of shales and graywackes coat grain surfaces and line secondary pores in porous sandstones replace some grains in volcaniclastic breccia and overgrow detrital tourmalines in quartzarenites regardless of host rock compositions the tourmaline is si deficient moderately al rich and shows significant x site vacancies and highly variable mg mg fetot ratios in rare zoned tourmaline the mg mg fetot ratios distinctly decrease and vacancies slightly increase towards the growth direction the results suggest that the tourmaline nucleated rapidly under a strong driving force at high boron concentration and high temperature the fluids which enabled the process were acidic reducing b and mg bearing and of low na and ca contents the tourmaline grew primarily at the expense of kaolinite possibly of other clay minerals and k feldspar in the temperature range 150 200 c its crystallization was a short episode in the diagenetic history of the host rocks tourmaline authigenesis across the carboniferous permian unconformity in the proximity of a prominent fault zone is evidence for fluid and heat migration along faults and for temporarily open geochemical system during late diagenesis the source of boron has been unproven yet the circulation of bitterns originated from upper permian evaporites was highly probable

aperiodic recurrence of geologically recorded tsunamis during the past 5500 years in eastern hokkaido japan 1 along hokkaido s pacific coast near the town of kiritappu sandy deposits in a muddy lagoon and on a nearby beach ridge plain provide evidence for 15 tsunamis between 200 and 6000 years ago additional sand beds at the lagoon probably represent the historical tsunamis of a d 1843 and 1894 we observed the sequences of sandy deposits in continuous slices 2 to 4 m deep some of the deposits consist of just a single sand bed whereas others contain multiple units of sand muddy sand or sandy mud and mud caps including plant detritus we also found at the lagoon a 17th century tsunami deposit that thickens and thins regardless of elevation or distance inland we bracketed the ages of most of the inferred tsunamis by radiocarbon dating of detritus mainly seeds and leaves at the lagoon and charcoal at the beach ridge plain from pretsunami and posttsunami beds tsunami dates computed from the bracketing ages commonly have uncertainties spanning 2 to 4 centuries within these uncertainties the inferred sequence of 15 prehistoric tsunamis at the lagoon beginning almost 6000 years ago can be matched tsunami by tsunami with the inferred history at the beach ridge plain 15 km away the sand sheet extents suggest that most of these tsunamis were larger than any generated at hokkaido in the last 200 years the intervals between these inferred outsized tsunamis average nearly 400 years but range widely from about 100 to about 800 years

the accretion of foreland basin sediments during early stages of continental collision in the european alps and similarities to accretionary wedge tectonics we present structural observations from foreland basin sediments that were incorporated into the orogenic wedge of the central european alps during early stages of continental collision our analysis focuses on the prograde evolution and considers the full history of the sediments ranging from their deposition in the basin to deep burial and metamorphism at temperatures of 320 c the tectonic evolution is matched with constraints on the diagenetic alteration of the sediments for this purpose we calculate the temperatures and depths of sediment compaction and illitization as well as the associated fluid liberation the data set highlights that the tectonic incorporation of the sediments into the orogenic wedge was strongly controlled by their diagenetic state earliest deformation took place during imbrication and frontal accretion of unconsolidated and fluid saturated sediments ductile folding of the sediments occurred already at this stage and was assisted by particulate flow with the progressive consolidation of the sediments the elastic strength increased which resulted in an overall embrittlement this rheological change is recorded by the onset of out of sequence thrusting brittle faulting and the formation of massive quartz calcite veins which took place in the approximate temperature range of the seismogenic zone i e 150 350 c moreover widespread pressure solution resulted in the formation of a penetrative cleavage and records slow but long lasting deformation at low background strain rates in summary the prograde tectonic evolution of the frontal alpine wedge exhibits many similarities with the structural and mechanical evolution of accretionary wedges at active subduction zones

a tectonically induced eocene sedimentary melange in the west ligurian alps italy abstract the southern alpine foreland basin succession late eocene early oligocene lies over the mesozoic condensed carbonate succession of the provencal dauphinois domain ends with a chaotic complex and is overthrust by more internal alpine units san remo monte saccarello ligurian unit emplaced in late oligocene early miocene times the chaotic complex consists of debris flow paraconglomerates breccias and megablocks up to km sized despite the post eocene alpine tectonics overprint particularly intense in its uppermost part the sedimentary origin of the chaotic complex is proved by the interbedding of paraconglomerates and breccias with fine grained turbidites megablocks consist both of formations buried below the chaotic deposits mesozoic provencal dauphinois succession eocene alpine foreland basin succession both of exotic units ligurian helminthoides flysch paraconglomerate and breccia clasts were sourced by the penecontemporaneous turbidite sands and muds as well as the same lithologies as megablocks all these features suggest the activity of early alpine eocene strike slip or transtensive fault systems that juxtaposed and exhumed the helminthoides flysch unit and the provencal dauphinois succession submarine ridges were generated and favored rock fall phenomena that involved both small mm to dm sized clasts and huge slabs detached from the main rock masses these morphostructural highs were flanked by oversteepened slopes affected by failures that gave rise to debris flows involving hemipelagic muds and turbidite sands and lithified fragments of older formations which resulted in strongly polygenic paraconglomerates the studied melange is thus fully due to sedimentary processes that were however completely controlled by early alpine tectonics

structural styles in mesozoic and cenozoic melanges in the western cordillera of north america the term melange is currently used to describe several different kinds of mudstone rich rocks that are broadly characterized by an obscure stratigraphy stratal disruption or a chaotic block in matrix fabric four types of melange which can be defined in outcrop on the basis of mesoscopic fabric and lithologic composition are particularly widespread and distinctive type i includes sequences of originally interbedded sandstone and mudstone that record incipient to thorough disruption and fragmentation of strata accomplished largely by layer parallel extension type ii consists of similarly deformed thin layers of green tuff radiolarian ribbon chert and minor sandstone originally interbedded with black mudstone disruption in both types i and ii which probably occurred while the sediments were incompletely consolidated has been ascribed to either imbricate faulting in accretionary wedges or gravitationally driven deformation type iii comprises inclusions of diverse shapes sizes and compositions enveloped in a locally scaly pelitic matrix the ultimate source of fragments is obscure because the majority were not derived by either the progressive disruption of interbedded sediments or in situ tectonic plucking and abrasion of adjacent rocks although some type iii melanges may have originated deep within accretionary prisms final emplacement as olistostromes muddy debris flow deposits or mud diapirs seems likely type iii melanges are mechanically analogous to scaly sheared serpentinites many probably have been tectonically remobilized or even intruded into shallow level fault zones type iv consists of lenticular inclusions bounded by an anastomosing network of subparallel faults their fabric records progressive slicing in brittle fault zones each of the four types of melange described here could in theory have formed in a variety of settings on or within an accretionary wedge at an active convergent margin none can yet be singled out as a uniquely diagnostic subduction melange

early deformation of ultrahelvetic melanges in the helvetic nappes western swiss alps abstract the ultrahelvetic melanges represent an important clue for understanding the tertiary alpine orogeny particularly in the external alps of western switzerland the remarkable architecture of the upper and lower ultrahelvetic units is classically explained by an important phase of gravity sliding and orogenic sliding accompanied by the formation of chaotic complexes and olistostromes wildflysch a phenomenon called diverticulation a structural analysis reveals evidence for early phases of deformation despite strong overprinting by late alpine deformation these early fabrics are observed in foliated pebbly mudstone a tectonic breccia part of the melange matrix in disrupted flysch sequences and in dark shales they attest to brecciation related to a complex pattern of veining with several generations of calcite cement and several stages of failure during lithification and they show the important role of fluids during the deformation they present numerous analogies with the fabrics described in association with thrusts in accretionary prisms considering the tectonic fabrics and the relations among the infra prealpine melanges a tectonic model to explain the emplacement of the ultrahelvetic units is proposed in which the decollements developed in three weak levels the early fabrics evolved within a basal thrust formed in a final stage of the valaisan subduction

use of pollen and vascular plants to estimate coseismic subsidence at a tidal marsh near tofino british columbia abstract we use botanical data to estimate coseismic subsidence produced by the 1700 cascadia earthquake at a tidal marsh near tofino british columbia association indices for cyperaceae 0 3 triglochin type 0 4 poaceae 0 7 potentilla type 0 6 achillea type 0 6 and ericales 0 6 pollen reveal that high marsh taxa have greater fidelity and therefore greater value as indicators of elevation than low marsh taxa pollen taxa that are abundant and have narrow elevation ranges include poaceae potentilla type achillea type and triglochin type vegetation and surface pollen define four marsh zones low middle high and forest edge transition deposits beneath the marsh include a buried peat capped by tsunami sand the sand is abruptly overlain by peaty mud which grades into peaty soil of the modern marsh the buried peat contains pollen indicative of a high to forest edge transition marsh pollen assemblages from the top of the buried peat and the overlying tsunami sand are similar probably because the tsunami entrained litter as it moved over the marsh surface sediments above the tsunami sand yielded pollen characteristic of a low to middle marsh environment including abundant cyperaceae triglochin type poaceae and chenopodiaceae we calibrated fossil pollen data to elevation using partial least squares weighted averaging partial least squares weighted averaging and weighted averaging with tolerance downweighting the last of these methods explains the largest amount of variance root mean square error of prediction 0 3 r 2 0 85 and yielded values of coseismic subsidence at three sites of 0 65 0 3 0 69 0 3 and 0 50 0 3 m average 0 6 0 3 m these values agree with previously published estimates of coseismic subsidence near tofino based on foraminifera

fluctuations in relative sea level during the past 3000 yr in the onnetoh estuary hokkaido northern japan this paper presents the results of a litho bio and chronostratigraphical study of the evidence for late holocene sea level change palaeoseismicity and coastal evolution at the onnetoh estuary northwest japan alternating peat and mud couplets record evidence for four falls in relative sea level since ca 2500 cal yr bp in the latest instance intertidal mud with a salt tolerant diatom and plant macrofossil flora is abruptly overlain by a freshwater peat containing abundant macrofossil remains of the conifer picea glehnii these stratigraphical changes record an abrupt change from tidal flat to upland with no intermediate transition through saltmarsh in the other three instances the stratigraphy records a more gradual fall in relative sea level as shown by gradational stratigraphical contacts and transitional diatom and plant macrofossil assemblages once established these freshwater peat communities are gradually submerged and become overlain by saltmarsh and then intertidal muds radiocarbon ages and tephra date the emergence events to 2700 1750 gradual 1350 950 gradual 650 300 gradual and ca 400 cal yr bp abrupt these ages are similar to a sequence of emergence events recorded at the akkeshi estuary 70 km to the west of the present study site the three falls in relative sea level may record coseismic or swift post seismic uplift caused by plate boundary subduction earthquakes on the kurile subduction zone the oldest relative sea level fall is correlated with the so called yayoi regression dated to 1500 3000 cal yr bp in other parts of japan copyright 2002 john wiley sons ltd

tectonic rotation and diverse remanence carriers revealed by the paleomagnetism of eo oligocene turbidites from two ultrahelvetic units western alps haute savoie france abstract our paleomagnetic study of two ultrahelvetic units from the western alps shows that 1 one unit has experienced an important vertical axis tectonic rotation and 2 in turbidite deposits the nature of the remanence carrier can differ between coarse grained and fine grained intervals samples were collected at close intervals from weakly deformed turbidites in two different areas derochoir and marais characteristic remanent magnetization chrm was measured with alternating field and thermal demagnetization whereas clues for identifying the main remanence carrier were provided by coercivity spectra analysis in the derochoir area the bulk of the section consists of fine grained rocks magnetic intensity values are small directions are scattered and no polarity reversals were detected remanence was probably acquired during late diagenesis or regional tectonic deformation in coarser lithologies depositional chrm has probably been preserved by an early phase of cementation in the marais turbidites remanent magnetization is mainly carried by magnetite although some samples show clustered directions several polarity inversions have been observed suggesting that remanence was acquired soon after sediment deposition magnetic directions values indicate a counterclockwise rotation of about 110 of the marais sediments with respect to the stable european craton this movement which partly affects the underlying subalpine chains is probably related to sinistral strike slip motion along a major regional accident during the late oligocene or miocene

aseismic faulting following the 1973 nemuro oki earthquake hokkaido japan a retrospective study tidal records at hanasaki southeastern hokkaido are analysed to clarify the post seismic crustal vertical movement in the 1973 nemuro oki japan earthquake the result shows that the post seismic uplift as speculated bykasahara 1975 terminated in late 1975 and reverted to the previous rate of rapid subsidence of about 1 cm yr ceasing of the post seismic uplift which occurred much earlier than previously speculated could be explained by supplementary mechanisms such as frictional resistance against creeping at the fault surface this unexpected mode of movement however raises a new question about the accumulation of tectonic movements in this district since the subsidence rate extrapolated from geomorphological data for the past several thousand years is almost one order of magnitude lower than the recent rate as mentioned above we have to provide some alternative explanation for the discrepancy between the two rates in other words simple repetition of co post and inter seismic movements in seismic cycles due to plate subduction must be modified in this district several possible modifications to the subduction process are suggested and a brief discussion of vertical movements expected in each case is given

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

distribution of living and dead diatoms in tidal wetlands of northern japan relations to taphonomy abstract this paper presents the results of a survey of the contemporary diatom distributions in four tidal marshes of eastern hokkaido northern japan distribution of living diatom cells as defined by cluster analysis have relations to vegetation and substratum and clearly to tide level comparison between living and dead diatoms in each cluster provides synecological information relating to diatom taphonomy in the tidal wetland environments four assemblages are recognized and they are summarized as follows 1 an upland assemblage consisting of autochthonous freshwater diatoms adapted to relatively dry conditions 2 a high marsh assemblage formed at or slightly above mean high tide level mhtl with only few allochthonous components 3 a low marsh assemblage formed below mhtl dead valves within this assemblage are repeated widely redistributed by tidal processes this assemblage is therefore a mixed assemblage comprising a combination of allochthonous and autochthonous diatoms 4 a tidal flat assemblage on death diatom valves in tidal flat are immediately redistributed by tidal currents and the dead diatom assemblage here has the characteristics of an autochthonous or residual assemblage autecological perspectives based on the distribution patterns can advance these interpretations dead valves of the epiphytic diatom cocconeis scutellum which possesses a raphid valve r valve and a rapheless valve p valve are common on two transects but only p valves are widely distributed beyond the seaweed zone which represents the actual habitat of this species such selective processes are related mainly to the life form characteristics of monoraphid species only r valves remain attached to their substratum on death the tychoplankton paralia sp is also a widely distributed species in the case of paralia their long chains float more readily than other specimens are transported easily by tidal currents and then trapped in entire tidal environments these observations suggest it is likely that concentrations of only p valves of c scutellum or paralia in the tidal marsh deposits should be treated as allochthonous components in the diatom assemblage

high pressure behaviour of selected boron minerals and the question of boron distribution between fluids and rocks abstract experimental results in the simplest possible systems up to generally 20 50 kbar in a few cases 100 kbar bearing on the pt stability limits of 17 end member borosilicates and borates are summarized except for the sillimanite structure type minerals grandidierite and werdingite which break down near 10 kbar the following phases are stable up to much higher pressures and no influence of boron coordination with oxygen three or fourfold can be recognized alkali free dravite b nepheline boromuscovite danburite dravite dumortierite jeremejevite oh kotoite magnesiodumortierite prismatine pseudosinhalite reedmergnerite szaibelyite sinhalite suanite the framework borosilicates reedmergnerite and danburite remain more stable towards higher pressures than their al analogues albite and anorthite respectively kornerupine stability decreases with decreasing boron content in the mineral from about 37 kbar for near end member prismatine to 12 kbar for the boron free end member with a maximum thermal stability of 1050 c at 30 kbar boron rich kornerupine prismatine is the thermally most stable borosilicate at high pressures thus all the above 15 phases can in principle occur as minerals of ultrahigh pressure metamorphic rocks boron initially enriched in crustal rocks may be subducted to depths exceeding 100 km in al rich systems b 2 o 3 generally behaves as an inert component and enters refractory minerals so that such rocks may act as sinks for boron even in the presence of h 2 o in other systems rich sio 2 na 2 o mgo however boron is more volatile and may fractionate into hydrous fluids that may cause metasomatism elsewhere altogether the behaviour of boron in natural petrogenetic systems is strongly dependent on the local chemical environment

subduction and accretion of the permanente terrane near san francisco california previous studies of the calera limestone permanente terrane franciscan complex of california have shown that deposition occurred at approximately 25 n paleolatitude atop an oceanic plateau or rise and that it was subsequently transported northeast and accreted to the north american continental margin in the early tertiary the permanente terrane in the study area along the pacific coast south of san francisco contains a suite of rock types present in north dipping imbricate thrust slices possibly related to the subduction and accretion of an oceanic crustal sequence geochemical studies of greenstones thought to represent fragments of the dismembered oceanic crust indicate affinities with mid ocean ridge basalts and within plate basalt these greenstones may represent fragments of the rise upon which the calera limestone was deposited metamorphic minerals in the greenstones indicate both sea floor metamorphism and locally high pressure low temperature metamorphism it is concluded tentatively that the entire permanente terrane in the study area underwent high pressure low temperature metamorphism but that temporal or geologic conditions prevented widespread recrystallization or development of blueschist facies minerals structures in the deformed rocks can be related to underthrusting beneath the continental margin and attachment to the overriding plate studies of veins indicate several stages of dewatering it is likely that dewatering was a major process in the attachment event as shown by veins associated with this phase of deformation structurally interleaved melanges and broken formation contain sedimentary rock clearly derived from a continental margin these rocks probably represent trench and trench slope facies that were underthrust with the accreting oceanic crustal sequence

tourmaline as a petrogenetic indicator in the pfitsch formation western tauern window eastern alps abstract tourmaline is a common accessory mineral in the metasedimentary pfitsch formation located in the pfitscher joch passo de vizze area in the tauern window of the eastern alps these post variscan metasedimentary units experienced peak metamorphic conditions of 550 c 1 0 gpa during the alpine orogeny tourmaline is most abundant in a 25 m thick unit of feldspathic gneiss 20 200 g g b where it occurs as idiomorphic crystals typically 10 mm in length the abundance and size of the tourmaline crystals increase near coarse grained quartzofeldspathic segregations 1200 g g b reflecting the mobilization and concentration of b by metamorphic fluids near segregations individual tourmaline crystals have up to three growth zones recording pro 350 500 c 0 7 1 0 gpa and retrograde 400 c 0 2 gpa growth as determined by combining textural information and sector zoning thermometry retrograde tourmaline occurs as individual crystals as well as overgrowths on prograde tourmaline crystals especially on the surface of extensional fractures formed by e w extension during regional decompression tourmaline in the pfitsch formation is dravitic with a variable fe content that correlates with the fe content of its respective host unit charge balance calculations suggest that a significant proportion of fe in tourmaline is ferric supporting the interpretation of a subaerial continental sedimentary protolith tourmaline near segregations has the highest inferred ferric iron content which decreases across growth zones potentially reflecting a reduction of the fluid during metamorphism the mg mg fe ratio increases with prograde tourmaline growth and decreases in retrograde overgrowths in contrast the ca ca na ratio increases gradually from 0 05 to 0 20 with prograde growth and continues to increase up to 0 25 in the retrograde overgrowths recording the maximum ca ca na ratio of the fluid during alpine metamorphism the metasediments of the pfitsch formation have very low and variable whole rock 11 b values 14 1 to 33 6 with the highest values 17 7 to 14 1 found in b rich samples 165 1200 g g b containing abundant tourmaline and the lowest values 24 2 to 33 6 in b depleted samples 21 40 g g which lack tourmaline this observation supports preferential loss of 11 b from the rocks during prograde metamorphism zoned tourmaline crystals in the pfitsch formation show successively decreasing b isotope ratios from 7 8 to 11 2 in their cores and 17 3 to 20 3 in their rims as supported by a rayleigh fractionation model the b isotope values of the host rocks and the tourmaline crystals are most easily explained by the internal redistribution of b from a b rich precursor mineral e g mica to the tourmaline during alpine metamorphism

subduction zone paleoseismology along the pacific coast of northeast japan progress and remaining problems abstract this paper reviews recent progress in tsunami geology and the history of coastal uplift subsidence along the pacific coasts of hokkaido and tohoku facing the kuril and japan trenches respectively in the last 20 years research by tsunami geologists in northeast japan has focused on extending the record of tsunamis beyond the range of historical documents in the region which span too little time to reveal much of the earthquake history over the last millennia along the coast of hokkaido recurrent sandy deposits are evidence of historical and prehistoric large tsunamis at kiritappu marsh for example at least 15 identified tsunami deposits occurred between 200 and 6 000 years ago the spatial distribution of the most recent prehistoric tsunami deposit that of the so called 17th century earthquake and tsunami exceeds historical and recent tsunami inundations in eastern hokkaido numerical simulations of this event require a multi segment fault model with variable slip mw 8 8 encompassing both the tokachi oki and nemuro oki regions to reproduce the observed deposit distribution in eastern hokkaido the recurrence interval of such multi segment earthquakes along the southern kuril trench is estimated to be 100 800 years based on tephrochronological and radiocarbon evidence tsunami deposits are also associated with historical earthquakes in 1843 and 1894 in eastern hokkaido and with the 1640 komagatake eruption in western hokkaido the 17th century earthquake probably triggered postseismic coastal deformation diatom based transfer functions suggest rapid subsidence before the event and gradual uplift afterward and historical volcanic ash layers indicate that gradual postseismic uplift occurred over decades a simple dislocation model can explain such gradual uplift as an aseismic fault extension after the 17th century event in the tohoku region a tsunami deposit associated with the 869 jogan earthquake has been identified and the inundation area of this event has been constrained based on the lateral extent of the tsunami deposit and its stratigraphic position beneath the historical to a tephra 915 ce land level changes at odaka fukushima prefecture associated with the jogan event have been estimated based on changes of fossil diatom assemblages below and above the tsunami deposit numerical simulations based on geological evidence and observations of the 2011 tohoku tsunami deposit suggest that the jogan event was a plate boundary rupture at least 200 km long along the japan trench mw 8 3 8 6 the 1454 kyotoku tsunami is also considered to have been generated by a rupture area including the miyagi oki region part of the jogan rupture it remains unclear whether the 869 1454 and 2011 tsunamis were similar in size and source if they were the recurrence intervals of such events near sendai are less than 600 years and more regular than those for multi segment earthquakes along the kuril trench

experimental constraints on phase relations in subducted continental crust synthesis piston cylinder experiments were carried out in the range 2 0 4 5 gpa and 680 1 050 c to investigate phase relations in subducted continental crust a model composition kcmash has been used because all major ultrahigh pressure uhp minerals of the whole range of rock types typical for continental crust can be reproduced within this system the combination of experimental results with phase petrologic constraints permits construction of a uhp petrogenetic grid the phase relations demonstrate that the most important uhp paragenesis consists of coesite kyanite phengite clinopyroxene and garnet in subducted continental crust below 700 c talc is stable instead of garnet as most of these minerals are also stable at much lower pressure and temperature conditions it is thus not easy to recognize uhp metamorphism in subducted crust a general feature however is the absence of feldspars at h2o saturated conditions plagioclase is never stable at uhp conditions but k feldspar can occur in h2o undersaturated rocks mineral compositions in the experiments are fully buffered by coexisting phases the si content of phengite and biotite increase with increasing pressure at 4 0 gpa 780 c biotite contains 3 28 si per formula unit which is most probably caused by solid solution of biotite with talc above 800 c the caal2sio6 component in clinopyroxene buffered with kyanite coesite and a mg phase increases with increasing temperature providing a tool to distinguish between cold and hot eclogites up to 10 ca eskolaite ca0 5 0 5alsi2o6 in clinopyroxene has been found at the highest temperature and pressure investigated 900 c 4 5 gpa garnet buffered with coesite kyanite and clinopyroxene displays an increase of grossular component with increasing pressure for a given temperature although the investigated system represents a simplification with respect to natural rocks it helps to constrain general features of subducted continental crust the observed phase relations and phase compositions demonstrate that at pressures 3 0 gpa and temperatures 800 c continental crust can retain significant amounts of h2o 1 wt whereas k free mafic or ultramafic rocks are dry at these conditions uhp parageneses are only preserved if the whole exhumation path is situated within the stability field of phengite i e if there is cooling during exhumation or if the whole exhumation occurred at t 700 c in contrast break down of phengite and concomitant partial melting in terranes that show isothermal decompression may lead to a complete recrystallization of the subducted crust during exhumation the density of uhp rocks can be estimated on the basis of the established phase relations pelitic rocks are likely to have a density close to mantle rocks 3 3 g cm3 because of significant amounts of dense garnet and kyanite whereas granitic rocks are less dense 3 0 g cm3 hence subducted average continental crust is most probably buoyant with respect to mantle rocks and tends to get exhumed as soon as it is detached from the down going slab electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00410 001 0336 3

the indicative meaning of diatoms pollen and botanical macro fossils for the reconstruction of palaeoenvironments and sea level fluctuations along the coast of lower saxony germany abstract interdisciplinary studies carried out on marine and terrestrial deposits such as tidal flats lagoonal deposits and salt marshes have provided the basis for interpreting holocene sea level fluctuations along the southern north sea coast radiocarbon dating provides the timeframe for the studies the employed palaeoecological techniques include analysis of pollen diatoms and botanical macro remains benefits and constraints of each technique are discussed using examples of sediment cores from around the southern north sea sea level index points have been defined using the results of these interdisciplinary studies and then employed to reconstruct the sea level oscillations of the last two millennia

p t x controls on ca and na distribution between mg al tourmaline and fluid ca na partitioning between tourmaline and a coexisting fluid is investigated in the system cao na2o b2o3 al2o3 mgo sio2 h2o cl between 0 2 4 0 gpa and 500 700 c the synthesis experiments produced a mineral assemblage of tourmaline coesite quartz and in some cases additional phases typically comprising 1 0 gpa ca partitions preferentially into the fluid resulting in na dominant tourmaline compositions temperature has a secondary effect on ca na partitioning with higher temperatures correlating with increased ca incorporation in tourmaline based on the experimental findings tourmaline is expected to have ca rich compositions when it forms in low pressure high temperature ca rich rocks consistent with the current record of tourmaline occurrence the bulk mg al ratio and the ph of the tourmaline forming system may also affect ca incorporation in tourmaline but remain to be investigated experimentally

an 40 ar 39 ar rb sr and stable isotope study of micas in low grade fold and thrust belt an example from the swiss helvetic alps white micas in carbonate rich tectonites and a few other rock types of large thrusts in the swiss helvetic fold and thrust belt have been analyzed by 40ar 39ar and rb sr techniques to better constrain the timing of alpine deformation for this region incremental 40ar 39ar heating experiments of 25 weakly metamorphosed anchizone to low greenschist samples yield plateau and staircase spectra we interpret most of the staircase release spectra result from variable mixtures of syntectonic neoformed and detrital micas the range in dates obtained within individual spectra depends primarily on the duration of mica nucleation and growth and relative proportions of neoformed and detrital mica rb sr analyses of 12 samples yield dates of ca 10 39 ma excluding one anomalously young sample these dates are slightly younger than the 40ar 39ar total gas dates obtained for the same samples the rb sr dates were calculated using initial 87sr 86sr ratios obtained from the carbonate dominated host rocks which are higher than normal mesozoic carbonate values due to exchange with fluids of higher 87sr 86sr ratios and lower 18o 16o ratios model dates calculated using 87sr 86sr values typical of mesozoic marine carbonates more closely approximate the 40ar 39ar total gas dates for most of the samples the similarities of rb sr and 40ar 39ar total gas dates are consistent with limited amounts of detrital mica in the samples the 18o values range from 24 15 vsmow for 2 6 m micas and 27 16 for the carbonate host rocks the carbonate values are significantly lower than their protolith values due to localized fluid rock interaction and fluid flow along most thrust surfaces although most calcite mica pairs are not in oxygen isotope equilibrium at temperatures of ca 200 400 c their isotopic fractionations are indicative of either 1 partial exchange between the minerals and a common external fluid or 2 growth or isotopic exchange of the mica with the carbonate after the carbonate had isotopically exchanged with an external fluid the geological significance of these results is not easily or uniquely determined and exemplifies the difficulties inherent in dating very fine grained micas of highly deformed tectonites in low grade metamorphic terranes two generalizations can be made regarding the dates obtained from the helvetic thrusts 1 samples from the two highest thrusts mt gond and sublage have all of their 40ar 39ar steps above 20 ma and 2 most samples from the deepest helvetic thrusts have steps often accounting for more than 80 of 39ar release between 15 and 25 ma these dates are consistent with the order of thrusting in the foreland imbricating system and increase proportions of neoformed to detrital mica in the more metamorphosed hinterland and deeply buried portions of the nappe pile individual thrusts accommodated the majority of their displacement during their initial incorporation into the foreland imbricating system and some thrusts remained active or were reactivated down to 15 ma

astronomical dating in the 19th century abstract today astronomical tuning is widely accepted as numerical dating method after having revolutionised the age calibration of the geological archive and time scale over the last decades however its origin is not well known and tracing its roots is important especially from a science historic perspective astronomical tuning developed in consequence of the astronomical theory of the ice ages and was repeatedly used in the second half of the 19th century before the invention of radio isotopic dating building upon earlier ideas of joseph adhemar james croll started to formulate his astronomical theory of the ice ages in 1864 according to which precession controlled ice ages occur alternatingly on both hemispheres at times of maximum eccentricity of the earth s orbit the publication of these ideas compelled charles lyell to revise his principles of geology and add croll s theory thus providing an alternative to his own geographical cause of the ice ages both croll and lyell initially tuned the last glacial epoch to the prominent eccentricity maximum 850 000 yr ago this age was used as starting point by lyell to calculate an age of 240 million years for the beginning of the cambrium but croll soon revised the tuning to a much younger less prominent eccentricity maximum between 240 000 and 80 000 yr ago in addition he tuned older glacial deposits of late miocene and eocene ages to eccentricity maxima around 800 000 and 2 800 000 yr ago archibald and james geikie were the first to recognize interglacials during the last glacial epoch as predicted by croll s theory and attempted to tune them to precession soon after frank taylor linked a series of 15 end moraines left behind by the retreating ice sheet to precession to arrive at a possible age of 300 000 yr for the maximum glaciation in a classic paper axel blytt 1876 explained the scattered distribution of plant groups in norway to precession induced alternating rainy and dry periods as recorded by the layering in holocene peat bogs he specifically linked the exceptionally wet atlantic period to the prolonged precession minimum at 33 300 yr ago and further related basic stratigraphic alternations to precession induced climate change in general such a linkage was also proposed by grove karl gilbert for cyclic alternations in the marine cretaceous of north america extrapolating sedimentation rates he arrived at an astronomical duration for part of the cretaceous that was roughly as long as the final estimate of william thomson for the age of the earth assuming that orbital parameters directly affect sea level karl mayer eymar and blytt correlated the well known succession of tertiary stages to precession and eccentricity respectively remarkably blytt like croll before him used very long period cycles in eccentricity to establish and validate his tuning understandably these studies in the second half of the 19th century were largely deductive in nature and proved partly incorrect later nevertheless this fascinating period marks a crucial phase in the development of the astronomical theory of the ice ages and climate and in astronomical dating it preceded the final inductive phase which started with the recovery of deep sea cores in 1947 and led to a spectacular revival of the astronomical theory by a century the first half of the 20th century can best be regarded as an intermediate phase despite the significant progress made in both theoretical aspects and tuning

coesite exsolution from supersilicic titanite in uhp marble from the kokchetav massif northern kazakhstan coesite exsolved from supersilicic titanite was discovered in an impure calcite marble at kumdy kol in the kokchetav uhp ultrahigh pressure metamorphic terrane northern kazakhstan this impure marble consists mainly of calcite k feldspar diopside and symplectites of diopside zoisite with minor amount of titanite phengite and garnet no diamond was found in the marble coesite and quartz which have needle or platy shapes measuring about 20 60 m in length occur as major exsolved phases in the cores and mantles of titanite crystals with minor calcite and apatite the strongest raman band for the coesite needles and plates was confirmed at about 524 cm 1 with a weak band at about 271 cm 1 to estimate the initial composition of the titanite before coesite exsolution exsolved phases were reintegrated by measuring their area fractions on digital images the highest excess si in titanite was thus determined to be 0 145 atoms per formula unit apfu this composition requires a pressure higher than 6 gpa on the basis of phase relations in the system catisio5 casi2o5 this pressure is consistent with other evidence of high pressure in the same marble such as 1 4 1 8 wt k2o and over 1000 ppm h2o in diopside supersilicic titanite and coesite exsolution also indicate that sio2 exsolution occurred in the coesite stability field during exhumation of the uhp metamorphic unit

microfossil evidence for land movements associated with the ad 1964 alaska earthquake microfossil diatom and pollen data from a number of cores at coastal marshes at girdwood flats and kenai flats in cook inlet alaska suggest that there was a phase of gradual land subsidence prior to the main shock of the ad 1964 earthquake this phase followed a long period of gradual land uplift since the last large earthquake which occurred about 730 900 years ago caesium 137cs records indicate that subsidence started approximately 15 years before the 1964 earthquake this pre seismic subsidence is evident in the coastal marsh sediment sequences in changes in diatom and pollen assemblages that indicate changes in tidal marsh environments or a change from raised bog to marsh conditions the microfossil evidence indicates 0 15 m pre seismic land subsidence at both girdwood flats and kenai flats and co seismic subsidence of 1 8 m and 0 2 m respectively

micropalaeontological evidence for the holocene earthquake history of the eastern bay of plenty new zealand and a new index for determining the land elevation record abstract fossil foraminifera and diatoms are used to identify sudden probably earthquake related elevational changes in three holocene sedimentary sequences from the high tidal fringes of ohiwa harbour eastern bay of plenty new zealand modern analogue calibration sets of faunal and floral census data are used to estimate palaeosalinities and palaeotidal elevations that help quantify seismic related vertical displacements age models for the three vibracored sequences are built on a combination of tephrostratigraphy and radiocarbon dating a new index the land elevation record ler is introduced to graphically portray earthquake related vertical land displacements on a time depth diagram also plotted are elements used to calculate ler such as the indicative depth estimated from microfossils inferred sediment compaction and the new zealand holocene palaeo sea level curve all three ohiwa cores spread over 3 km of coast contain both freshwater and intertidal sediments a prominent erosional contact between freshwater peat or soil and overlying intertidal mud records a major subsidence event in each core of c 2 m dated at ca 2600 cal years bp the deepest core 7 4 m indicates that this is the only substantial vertical displacement event to have occurred in the last 8 ka a small subsidence event ca 0 3 0 7 m is indicated close to the top of one core but is not present in the other two sites this may be the result of a local land subsidence during the poorly known taneatua earthquake of 1866 there is no historic human record of earthquake displacements around ohiwa but mid pleistocene interglacial marine sediments have been uplifted 10 60 m in several identified fault blocks our study provides conclusive evidence of at least 2 m of earthquake related subsidence during the holocene with a recurrence time of major earthquakes of ca 5 ka

tidal marsh stratigraphy sea level change and large earthquakes ii submergence events during the last 3500 years at netarts bay oregon usa abstract this is the second investigation where we apply the methods and scientific framework common to sea level investigations in northwest europe to test a model of coseismic land subsidence followed by land uplift during interseismic strain accumulation used to explain alternating peat mud couplets of late holocene age found in many of the estuaries of the pacific northwest of the usa and canada recent studies in this region interpret such couplets as the product of repeated large magnitude 8 or 9 earthquakes on the cascadia subduction zone stratigraphic investigations of the intertidal sediments at netarts bay oregon using lithological pollen and diatom analyses reveal different types of submergence associated with peat mud couplets during the last 3500 yr three peat mud couplets record gradual sedimentation changes within an infilling body of water four other couplets record rapid submergence burial of tidal marshes and their replacement by low marsh environments in three of the events rapid submergence is small 0 0 5 m the most recent marsh submergence event around ad 1700 was 0 4 0 3 m most of the buried peats contain microfossil evidence for a gradual increase in marine influence before the rapid change from organic to minerogenic sedimentation similar gradual changes are common in comparable palaeoenvironments on non seismic coasts and are strong evidence against a simple interseismic strain accumulation coseismic subsidence model one hypothesis is that the gradual increase in marine influence before each submergence represents pre seismic relative sea level rise caused by a reduction in the rate of land uplift the microfossil analyses provide evidence of three stages within an earthquake deformation cycle coseismic subsidence interseismic land uplift and pre seismic reduction in the rate of land uplift at present the microfossil data do not differentiate between rapid post seismic land uplift and rapid sedimentation

postseismic coastal uplift in southern chile tide gage records at puerto montt referenced to a mareograph in talcahuano indicate a large at least 75 cm postseismic uplift of the region following the 1960 mw 9 5 event field observations carried out in 1989 at the same locations of previous measurements in 1968 are consistent with tide gage records the postseismic elevation changes are modeled as the result of propagating creep on the downdip extension of the coseismic fault for a 30 e fault dip minimum square error indicates a fault creep velocity of 4 6 km yr and slip amplitude of 3 5 m