gcm analysis of local influences on ice core δ signals a high resolution gcm is used to examine the effect of changes in local surface climate parameters on the ice sheets that can influence the interpretation of the isotopic signal of the ice from deep cores the model suggests that the 10 c difference between the lgm surface temperature deduced from borehole thermometry and that deduced from the water isotope analysis to a great extent may be due to a modification of the precipitation seasonality in central greenland for central east antarctica the model tends to suggest a weak opposite bias

tectonic significance of holocene marine terraces in the coastal range eastern taiwan abstract well developed marine terraces on the coast of eastern taiwan between chengkung and hualien can be divided into three morphotectonic sectors 1 i chengkung kueian 2 ii shuilien and its vicinity 3 iii north of shuilien sector i displays at least five terrace levels and has undergone northward tilting and uplift the available 234 u 230 th and 14 c ages suggest that one of its holocene terraces rises to about 40 m and locally to 70 m above msl the average uplift rate for the holocene in this sector decreases northward from 9 10 mm yr to about 2 3 mm yr few traces of former shorelines or marine terraces higher than 5 m are found in sector ii north of shuilien in sector iii terrace elevation increases gradually and indicates an uplift rate of about 2 3 mm yr the uplift pattern agrees with geodetic data obtained between 1985 and 1988 the high uplift rates in sector i may represent compression and shortening of the northwestern corner of the philippine sea plate the low rates in sector ii may correlate with the region where the ryukyu trench meets the eastern coast of taiwan

a geophysical study of the manila trench luzon philippines 1 crustal structure gravity and regional tectonic evolution the manila trench subduction zone is an active convergent plate margin between the south china sea and the northern philippines the trench trends northerly and is associated with a volcanic arc an east dipping benioff zone beneath luzon and a well developed fore arc basin system the luzon trough fore arc basins lie landward of the manila trench and contain up to 4 5 km of cenozoic sediments offscraping and accretion of turbidite sediments deposited in the manila trench have resulted in the upbuilding and outbuilding of an accretionary prism which forms the seaward margin of the fore arc basin system the uplifted zambales ophiolite and its offshore extension form the landward side of the fore arc basin multichannel seismic reflection profiles reveal that folding and thrust faulting of trench strata occur at the base of the trench slope the major structural decollement at the manila trench usually forms near the unconformity separating the hemipelagic sediments from the turbidite sediments subduction and perhaps underplating of the basal hemipelagic trench sediments accompany the deformation and accretion of the overlying clastic deposits faulting and uplift occur within a narrow zone of the fore arc where seamounts associated with the relict spreading center of the south china sea basin have presumably been subducted north of lingayan gulf the fore arc is disrupted by active fault systems that trend north and northwest offshore from the luzon central valley and from the southern cordillera central based on regional geological and tectonic observations we infer that subduction probably began at the manila trench in late oligocene to middle miocene time the long term average convergence rate at the manila trench is estimated to be between 10 and 20 mm yr and may be slowing in the north owing to the collision of taiwan with eurasia

paleomagnetic results from luzon and the central philippines samples were collected from 86 paleomagnetic sites from the islands of luzon marinduque mindoro panay negros cebu and mindanao in the philippine arc the sampling sites range in age from pleistocene to jurassic characteristic directions of magnetization of the samples were determined by the use of vector plots curie temperature determinations thin section studies and hysteresis studies showed that remanence of these samples is carried by fine grained pseudo single domain magnetite positive fold tests from miocene data from panay jurassic data from mindoro and cretaceous data from cebu suggest that the magnetization of these regions was acquired prior to folding rotations reported below are measured with respect to the axial goecentric dipole field the plio pleistocene data set shows no resolvable rotation for the 22 sites this data set suggests that the various terranes that make up the philippine arc have behaved as a single unit during the past 5 m y or that deformation has been below the limits of resolution the inclination data from the plio pleistocene sites have anomalously shallow inclination and are consistent with other plio pleistocene data from vietnam taiwan and the marianas these data support earlier suggestions for a late neogene offset dipole effect the late miocene sites fall into two separate groups ten sites from western luzon show evidence for around 20 of clockwise rotation in contrast to this late miocene samples from the bicol region negros marinduque and mindanao are not rotated the cause of the postlate miocene clockwise rotation of luzon is unknown but a pliocene collision of the north luzon arc with taiwan is suggested early neogene results also separate into two different populations the population from marinduque shows evidence for a large counterclockwise rotation the second early neogene population comes from panay cebu and mindanao and clearly shows evidence for a clockwise rotation the validity of this rotation is further supported by a fold test and a reversal test these early neogene data sets are consistent with a middle to late miocene collision of the palawan continental terrane and the central philippine arc data from six dikes of possible oligocene age from the zambales ophiolite are highly discordant from the present field being rotated approximately 60 clockwise the directions from these dikes are similar to a direction reported earlier from late oligocene sediments also from the zambales region these two data sets support the interpretation that the eocene direction from zambales is recording a large clockwise rotation of the region data from the mesozoic sites are from two regions data from the cretaceous pandan formation of cebu are discordant with data from the upper jurassic from mindoro the presence of a fold test from each region and a reversal test from mindoro supports the interpretation that each of these data sets is reliable the vgp of mindoro is displaced southward from the late jurassic vgp of south china suggesting a post jurassic southward migration of mindoro

plate convergence and deformation north luzon ridge philippines abstract marine geophysical and earthquake seismology data indicate that the north luzon ridge a volcano capped bathymetrie ridge system that extends between luzon and taiwan is presently undergoing deformation in response to the relative motion between the asian and philippine sea plates plate motion models predict convergence along the western side of the philippine sea plate from japan in the north to indonesia in the south and most of this plate margin is defined by active subduction zones however the western boundary of the philippine sea plate adjacent to the north luzon ridge shows no evidence of an active wnw dipping subduction zone this is in marked contrast to the presence of both the philippine trench east luzon trough subduction zones to the south and the ryukyu trench subduction zone to the north crustal shortening in response to ongoing plate convergence in the north luzon ridge region apparently takes place through a complex pattern of strike slip and thrust faulting rather than by the typical subduction of oceanic lithosphere along a discreet zone the curvilinear bathymetrie trends within the north luzon ridge represent the traces of active faults the distribution of these faults mapped by both multichannel and single channel seismic reflection methods and earthquake seismicity patterns and focal mechanism solutions suggest that right lateral oblique slip faulting occurs along ne trending faults and left lateral oblique slip faulting takes place on n and nnw trending faults the relative plate convergence accommodated by the deformation of the north luzon ridge will probably be taken up in the future by the northward propagating east luzon trough subduction zone

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

estimates of sand transport in the oosterschelde tidal basin using current velocity measurements abstract estimates of sand transport have been made from mid depth velocity measurements in the oosterschelde tidal basin southwestern netherlands this involves 1 the use of a two region composite boundary layer model in deriving the local spatially averaged bed shear stress from velocity distributions over large bedforms megaripples and sandwaves the two regions are divided at 100 cm above the bed with an outer region roughness length of 1 5 cm and an inner region roughness length of 0 15 cm 2 the application of a modified bagnold s transport equation with the transport coefficient k depending on dimensionless excess shear stress in the form of a power law the calculations indicate very active sand movement in the present day oosterschelde tidal basin local sediment circulation may develop around shoals channel floor erosion may occur in parting areas of sediment transport the net sediment transport is mainly in the ebb direction estimates of sediment budget for the last 20 years show that large amounts of sand have been eroded from the oosterschelde tidal basin and transported to the ebb delta area these results are comparable with other estimates from echo sounding data reflecting the rapid adjustment of the basin to the increased tidal prism such active sediment redistribution and major morphological evolution processes would have important influence on the structural organization and sequential development of estuary ebb delta deposits information about the sedimentary processes in present day estuary tidal basins is valuable for a better understanding of ancient examples

spatial and temporal variability of snow accumulation in east antarctica from traverse data recent snow accumulation rate is a key quantity for ice core and mass balance studies several accumulation measurement methods stake farm fin core snow radar profiling surface morphology remote sensing were used compared and integrated at eight sites along a transect from terra nova bay to dome c east antarctica to provide information about the spatial and temporal variability of snow accumulation thirty nine cores were dated by identifying tritium b marker levels 1965 66 and non sea salt nss so4 2 spikes of the tambora indonesia volcanic event 1816 in order to provide information on temporal variability cores were linked by snow radar and global positioning system surveys to provide detailed information on spatial variability in snow accumulation stake farm and ice core accumulation rates are observed to differ significantly but isochrones snow radar correlate well with ice core derived accumulation the accumulation ablation pattern from stake measurements suggests that the annual local noise metre scale in snow accumulation can approach 2 years of ablation and more than four times the average annual accumulation with no accumulation or ablation for a 5 year period in up to 40 of cases the spatial variability of snow accumulation at the kilometre scale is one order of magnitude higher than temporal variability at the multi decadal secular scale stake measurements and firn cores at dome c confirm an approximate 30 increase in accumulation over the last two centuries with respect to the average over the last 5000 years

a climatology of southern hemisphere extratropical cyclones a climatology of extratropical cyclones determined by an objective automatic scheme applied to 15 years 1975 89 of once daily australian bureau of meteorology hemispheric analyses is presented contour maps of the positions of formation cyclogenesis dissipation cyclolysis together with other cyclone statistics are presented the distribution of cyclones through the hemisphere was found to be dominated by a permanent high latitude core coincident with the circumpolar trough during the winter and intermediate seasons two mid latitude branches are evident in the cyclone density originating in the tasman sea and south american sectors both spiraling poleward and merging with the circumpolar core in the southern oceans systems were observed to move in an castsouth east direction away from their location of formation exhibiting peak speeds of migration in the mid latitudes little seasonality was evident in the densitiy distribution of cyclones through the southern oceans but a considerable amount was found in their central pressure

subduction of aseismic ridges beneath the caribbean plate implications for the tectonics and seismic potential of the northeastern caribbean normal seafloor entering the puerto rico and northern lesser antillean trenches in the northeastern caribbean is interrupted by a series of aseismic ridges on the north and south american plates these topographic features lie close to the expected trend of fracture zones created about 80 110 m y ago when this seafloor was formed at the mid atlantic ridge the northernmost of the ridges that interact with the lesser antillean subduction zone the barracuda ridge intersects the arc in a region of high seismic activity some of this seismicity including a large shock in 1974 occurs within the overthrust plate and may be related to the deformation of the caribbean plate as it overrides the ridge a large bathymetric high the main ridge is oriented obliquely to the puerto rico trench and intersects the subduction zone north of the virgin islands in another cluster of seismic activity along the inner wall of the trench data from a seismic network in the northeastern caribbean indicate that this intersection is also characterized by both interpolate and intraplate seismic activity magnetic anomalies bathymetric trends and the pattern of deformed sediments on the inner wall of the trench strongly suggest that the main and barracuda ridges are parts of a formerly continuous aseismic ridge a segment of which has recently been overridden by the caribbean plate reconstruction of mid miocene to recent plate motions also suggest that at least two aseismic ridges and possibly fragments of the bahama platform have interacted with the subduction zone in the northeastern caribbean the introduction of these narrow segments of anomalous seafloor into the subduction zone has segmented the arc into elements about 200 km long these ridges may act as tectonic barriers or asperities during the rupture processes involved in large earthquakes they also leave a geologic imprint on segments of the arc with which they have interacted a 50 km landward jump of the locus of island arc volcanism occurred in late miocene time along the northern half of the lesser antilles we postulate that the subduction of a segment of seafloor of anomolously thick crust being more buoyant than adjacent seafloor resulted in a marked shoaling in the dip of the descending slab and therefore a shift of the locus of volcanism in the region near western puerto rico and eastern hispanolia plio pleistocene interaction with a similar feature in this case a part of the bahama platform about 3 4 m y ago led to a jump in the locus of subduction as evidenced by a gap in the downgoing seismic zone that segment of the bahama platform interferred with the subduction process and was subsequently sutured onto the caribbean plate when the boundary jumped about 60 km to the northeast the maximum size of historic shallow earthquakes along the lesser antillean arc varies from about 7 0 7 5 in the center of the arc where the dip of the shallow part of the plate boundary is steep to 8 0 8 5 along the northern part of the arc where the dip is shallow the interaction of anomalous seafloor as along the northern lesser antilles can lead to the development of a wider than normal zone of interplate contact and hence to earthquakes that are larger than those associated with more typical seafloor entering subduction zones major seismic gaps and regions of high seismic potential currently exist along the northern lesser antilles and to the north of puerto rico both gaps are bounded by anomalous features on the downgoing plate the intersection of these features with the plate boundary created large asperities that may be good places to search for precursors to future large earthquakes a great shock in 1787 may have ruptured an existing seismic gap north of puerto rico between 65 and 67 w thus that gap can be expected to eventually rupture again in a great shock and not to accommodate plate motion by totally aseismic processes

geodynamic evolution of the taiwan luzon mindoro belt since the late eocene abstract the structural framework of the taiwan luzon mindoro belt or festoon is described following three major transects the luzon transect with active subduction and active island arc the taiwan transect with active collision the mindoro transect with active subduction and inactive collision based on this geological study and on available geophysical data a model for the geodynamic evolution of this portion of the philippine sea and eurasia plates boundary is proposed in a succession of reconstructions between the late eocene and the present the major geodynamic events are 1 1 beginning of the opening of the south china sea s c s in lower oligocene times contemporaneous with obduction of the zambales and angat ophiolites on luzon 2 2 subduction of a mesozoic oceanic basin along the proto manila trench from the upper oligocene to the lower miocene 3 3 obduction of the south china sea oceanic crust onto the chinese and reed bank calamian passive margins in middle miocene time 14 15 ma related to a major kinematic reorganization end of opening of the s c s 4 4 beginning of collision between the luzon microblock and the two margins of the s c s in the upper miocene 7 ma collision is still active in taiwan whereas it stopped in mindoro during the pliocene

atmospheric influence on the deuterium excess signal in polar firn implications for ice core interpretation the seasonal deuterium excess signal of fresh snow samples from neumayer station coastal dronning maud land antarctica was studied to investigate the relationship between deuterium excess and precipitation origin an isotope model was combined with a trajectory model to determine the relative influence of different moisture sources on the mean annual course of the deuterium excess focusing on the phase lag between d 18 o and excess d whereas the annual course of d 18 o always shows an austral summer maximum which clearly depends on local temperature and the annual course of moisture source area parameters the deuterium excess of the fresh snow samples shows maximum values already in spring there can be many different reasons for the time lag between d 18 o and deuterium excess in an ice core including post depositional processes and changes in the moisture source of precipitation the use of fresh snow samples enabled us to exclude post depositional processes and study solely the influence of precipitation origin changes in the moisture source connected to systematic changes in the general atmospheric circulation can have a strong influence on the phase lag between deuterium excess and d 18 o which has to be taken into account for climatic interpretation of stable isotope profiles from ice cores

vertical crustal movements in eastern taiwan and their tectonic implications abstract leveling surveys along several routes and tidal observations at various points in eastern taiwan demonstrate rapid vertical crustal movements and they provide an effective means for monitoring the effects of collision between the philippine sea plate and the eurasian plate rapid elevation changes were detected in the southern section of the longitudinal valley repeated releveling along three routes since 1984 reveals that the coastal range was uplifted with respect to the longitudinal valley floor at a rate of about 3 0 cm yr this deformation is found to be confined within a very narrow zone along the east coast of taiwan two surveys 1984 and 1987 revealed that the coast is also undergoing uplift but at different rates from 0 cm yr to 3 5 cm yr the point of the most rapid uplift is located near 23 n and the rate generally diminishes towards the north the changes in rates may be controlled by the movements across faults tidal observations while providing a local datum show that uplift of the tidal station has occurred significant horizontal creep has been observed across many faults but rapid vertical creep as observed in the longitudinal valley is not very common

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

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

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

volcanic gaps due to oblique consumption of aseismic ridges abstract the present day consumption of oceanic ridges and other buoyant rises and fragments at circum pacific subduction zones and presumably elsewhere are closely related to existing gaps in volcanism examples are the gaps associated with the nazca juan fernandez cocos marcus necker and louisville ridges the buoyancy of these ridges breaks the continuity of the subducted plate which may lead to reduced water supply required for melting of magma and therefore create temporary volcanic gaps the oblique consumption of these ridges causes the gap to migrate with time this mechanism may be useful in interpreting time space patterns of past volcanic chains associated with subduction in terms of the consumption of the disruptive oceanic plateaus and ridges

paleomagnetic evidence for a diachronic clockwise rotation of the coastal range eastern taiwan abstract paleomagnetic results obtained from over 2100 cores sampled at 132 early pliocene to late pleistocene sites in the coastal range of eastern taiwan indicate that since the late pliocene the margin of the philippine sea plate has undergone a clockwise rotation of about 30 as a direct consequence of the plio pleistocene collision of this plate with the chinese continental plate the rotation is diachronic and started between 3 and 4 ma ago in the northern coastal range then propagated southward at an average speed of the order of 70 10 km ma this value is in very good agreement with estimates of the southward propagation of the collision between the philippine sea plate and the eurasian margin in taiwan it is suggested that the rotation reflects the deformation of the philippine sea plate at depth and does not results from the shallow deformations involved in the building of the coastal range orogen

the origin of present day antarctic precipitation from surface snow deuterium excess data the deuterium excess d is defined as a linear combination of the d h and 18 o 16 o ratios in natural waters we present an interpretation of deuterium excess data in surface antarctic snow using an isotopic model to derive information on the origin of present day antarctic precipitation the data come from near the coast d47 adelie land and from inland south pole 1000 km from the sea the one dimensional isotopic model belongs to the rayleigh family but fully accounts for mixed cloud processes between 0 c and 30 c modeling d in polar snowfalls meets the problem of a large sensitivity to the saturation conditions prevailing at snow formation therefore we decided to tune the saturation in the model in order to yield realistic mean d values but we use the seasonal phase of d versus which is less sensitive to the saturation conditions as an independent validation of the model predictions both inland and near the coast our model can simulate the observed phase between d and in snow with moisture of subtropical origin 40 20 s although we do not treat specifically storm precipitation near the coast this study indicates that the observed phase between d and brings up a new validation of isotopic models it supports a distant vapor source for large scale precipitation delivered to the antarctic continent

ice core age dating and paleothermometer calibration based on isotope and temperature profiles from deep boreholes at vostok station east antarctica an interpretation of the deuterium profile measured along the vostok east antarctica ice core down to 2755 m has been attempted on the basis of the borehole temperature analysis an inverse problem is solved to infer a local geophysical metronome the orbital signal in the surface temperature oscillations expressed as a sum of harmonics of milankovich periods by correlating the smoothed isotopic temperature record to the metronome a chronostratigraphy of the vostok ice core is derived with an accuracy of 3 0 4 5 kyr the developed timescale predicts an age of 241 kyr at a depth of 2760 m the ratio 13d 13t i between deuterium content and cloud temperature fluctuations at the top of the inversion layer is examined by fitting simulated and measured borehole temperature profiles the conventional estimate of the deuterium temperature slope corresponding to the present day spatial ratio 9 per mil oc is confirmed in general however the mismatch between modeled and measured borehole temperatures decreases noticeably if we allow surface temperature responsible for the thermal state of the ice sheet to undergo more intensive precession oscillations than those of the inversion temperature traced by isotope record with this assumption we obtain the long term temporal deuterium temperature slope to be 5 8 6 5 per mil oc which implies that the glacial interglacial temperature increase over central antarctica was about 15oc in the surface temperature and 10oc in the inversion temperature past variations of the accumulation rate and the corresponding changes in the ice sheet surface elevation are simultaneously simulated

four climate cycles in vostok ice core author s petit jr basile i leruyuet a raynaud d lorius c jouzel j stievenard m lipenkov vy barkov ni kudryashov bb davis m saltzman e kotlyakov v