multiple sources of quaternary tephra layers in the mariana trough abstract tephra layers in quaternary sediments stolper and newman 1994 model of binary mixing of source components with one endmember being the nmorb source of stolper and newman 1994 and the other one being a compositionally variable slab derived h2o rich component similar to the h2o component of stolper and newman 1994 this interpretation implies that the variation in k2o content in the arc derived glasses about a factor of 3 at 60 wt sio2 reflects a magmatic diversity that is inherent to the central mariana arc and is not necessarily reflective of temporal changes of the composition of arc magma sources

contrasting arc and morb like assemblages in the paleoproterozoic flin flon belt manitoba and the role of intra arc extension in localizing volcanic hosted massive sulphide deposits the flin flon belt trans hudson orogen manitoba and saskatchewan is the largest paleoproterozoic volcanic hosted massive sulphide vms district in the world with 118 7 million tonnes mt of z

mg ca ratios of single planktonic foraminifer shells and the potential to reconstruct the thermal seasonality of the water column mg ca ratios of surface and subsurface dwelling foraminifera provide valuable information about the past temperature of the water column planktonic foraminifera calcify over a period of weeks to months therefore the range of mg ca temperatures obtained from single specimens potentially records seasonal temperature changes we present solution derived mg ca ratios for single specimens of the planktonic foraminifera species globigerinoides ruber pink globigerinoides ruber white and globorotalia inflata from a sediment trap off northwest africa 20 45 6 n 18 41 9 w cleaning of single specimens was achieved using a flow through system in order to prevent sample loss mg ca ratios of surface dwelling g ruber pink show strong seasonality linked to sea surface temperature mg ca ratios of g ruber white do not show such seasonality subsurface dwelling g inflata flux is largest during the main upwelling season but mg ca ratios reflect annual temperatures at intermediate water depths the sediment trap time series suggests that changes in the range of mg ca ratios exhibited by single specimens of g ruber pink and g inflata from the sedimentary record should provide information on the past temperature range under which these species calcified statistical analysis suggests detectable changes in the mg ca range are 0 80 mmol mol g ruber pink and 0 34 mmol mol g inflata for g ruber pink such changes would indicate changes in the seasonal sea surface temperature range 4 c or a shift in the main calcification and reproductive period for g inflata such changes would indicate 1 7 c changes in the thermocline temperature or a change in the depth habitat

modeling of damage permeability changes and pressure responses during excavation of the tsx tunnel in granitic rock at url canada this paper presents numerical modeling of excavation induced damage permeability changes and fluid pressure responses during excavation of a test tunnel associated with the tunnel sealing experiment tsx at the underground research laboratory url in canada four different numerical models were applied using a wide range of approaches to model damage and permeability changes in the excavation disturbed zone edz around the tunnel using in situ calibration of model parameters the modeling could reproduce observed spatial distribution of damage and permeability changes around the tunnel as a combination of disturbance induced by stress redistribution around the tunnel and by the drill and blast operation the modeling showed that stress induced permeability increase above the tunnel is a result of micro and macrofracturing under high deviatoric shear stress whereas permeability increase alongside the tunnel is a result of opening of existing microfractures under decreased mean stress the remaining observed fracturing and permeability changes around the periphery of the tunnel were attributed to damage from the drill and blast operation moreover a reasonably good agreement was achieved between simulated and observed excavation induced pressure responses around the tsx tunnel for 1 year following its excavation the simulations showed that these pressure responses are caused by poroelastic effects as a result of increasing or decreasing mean stress with corresponding contraction or expansion of the pore volume the simulation results for pressure evolution were consistent with previous studies indicating that the observed pressure responses could be captured in a biot model using a relatively low biot willis coefficient 0 2 a porosity of n 0 007 and a relatively low permeability of k 2 10 22 m2 which is consistent with the very tight unfractured granite at the site

forty million years of magmatic evolution in the mariana arc the tephra glass record tephra glasses retrieved from 10 deep sea drilling project dsdp cores around the mariana arc system make up a remarkable record of explosive volcanism in the marianas over the past 40 m y major element compositions for approximately 1800 tephra glasses from basalt through rhyolite are reported and used to examine the nature and history of this activity three maxima of volcanic explosivity presumably related to especially vigorous volcanism in the mariana arc are identified with the biggest maximum at around 18 11 ma and two other maxima at 35 24 and 6 0 ma the two younger maxima are contemporaneous with peaks in explosive volcanism observed for other western pacific arcs explosive arc volcanism has been predominantly tholeiitic since shortly after arc inception no boninitic glasses were found the tephra glasses belong to the low to medium k suite except during an enigmatic phase of medium to high k explosive volcanism during the late miocene 11 7 ma even though mariana tephra glasses are largely similar in composition to mariana arc lavas the tephra show a much larger compositional range than that found for subaerial mariana arc lavas which totally lack dacitic to rhyolitic volcanic products the tephra glasses define a bimodal population in terms of silica content with a pronounced minimum or daly gap around 65 66 sio2 mariana tephra glasses are fractionated with the least evolved glass being fe rich and having a magnesium number mg 100mg mg fe 2 of 55 basaltic tephra glasses contain 16 a1203 average 14 3 a1203 and are not high alumina basalts this contrasts with the observation that modern mariana arc lavas contain 15 21 average 17 4 a1203 the high alumina basalt lavas of the mariana arc probably reflect plagioclase accumulation and not liquid compositions all tephra glasses plot near low pressure cotectics and reaction curves on the subprojection olivine clinopyroxene quartz mafic and felsic samples define distinct trends the mafic trend reflects fractional crystallization of mantle derived basaltic magma whereas the felsic trend may be due either to anatexis of mariana arc crust or to fractionation of mafic melts the tephra glass data reinforce the model that the magmatic evolution of the mariana arc has been dominated by low pressure fractionation perhaps accompanied by anatexis episodic changes in melting regime to generate miocene potassic tephra may be related to changing mantle sources and processes related to episodes of back arc basin spreading these episodic changes are superimposed on a long term increase in potassium that reflects progressive metasomatism of the mantle source long term increases in k20 contents for mariana arc magmas inferred from the tephra glass record are 0 004 wt m y mafic 0 011 wt m y intermediate and 0 023 wt m y felsic

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

late holocene expansion of istorvet ice cap liverpool land east greenland abstract the greenland ice sheet is undergoing dynamic changes that will have global implications if they continue into the future in this regard an understanding of how the ice sheet responded to past climate changes affords a baseline for anticipating future behavior small independent ice caps adjacent to the greenland ice sheet hereinafter called local ice caps are sensitive indicators of the response of greenland ice marginal zones to climate change therefore we reconstructed late holocene ice marginal fluctuations of the local istorvet ice cap in east greenland using radiocarbon dates of subfossil plants 10 be dates of surface boulders and analyses of sediment cores from both threshold and control lakes during the last termination the istorvet ice cap had retreated close to its maximum holocene position by 11 730 cal yr bp radiocarbon dates of subfossil plants exposed by recent recession of the ice margin indicate that the istorvet cap was smaller than at present from ad 200 to ad 1025 sediments from a threshold lake show no glacial input until the ice cap advanced to within 365 m of its holocene maximum position by ad 1150 thereafter the ice cap remained at or close to this position until at least ad 1660 the timing of this the most extensive of the holocene expansion is similar to that recorded at some glaciers in the alps and in southern alaska however in contrast to these other regions the expansion in east greenland at ad 1150 appears to have been very close to if not at a maximum holocene value comparison of the istorvet ice cap fluctuations with holocene glacier extents in southern hemisphere middle to high latitude locations on the antarctic peninsula and in the andes and the southern alps suggests an out of phase relationship if correct this pattern supports the hypothesis that a bipolar see saw of oceanic and or atmospheric circulation during the holocene produced asynchronous glacier response at some localities in the two polar hemispheres

nd and sr isotopic compositions of lavas from the northern mariana and southern volcano arcs implications for the origin of island arc melts nd and sr isotopic data are reported for lavas from 23 submarine and 3 subaerial volcanoes in the northern mariana and southern volcano arcs values of end range from 2 4 to 9 5 whereas 87sr 86sr ranges from 0 70319 to 0 70392 these vary systematically between and sometimes within arc segments the nd and sr isotopic compositions fall in the field of ocean island basalt oib and extend along the mantle array lavas from the volcano arc mariana central island province and the southern part of the northern seamount province have end to 10 and 87sr 86sr 0 7032 to 0 7039 these are often slightly displaced toward higher 87sr 86sr at similar end in contrast those lavas from the northern part of the mariana northern seamount province as far north as iwo jima show oib isotopic characteristics with end and 87sr 86sr 0 7035 to 0 7039 plots of 87sr 86sr and end versus ba la and la yb n support a model in which melts from the mariana and volcano arcs are derived by mixing of oib type mantle or melts therefrom and a metasomatized morb type mantle or melts therefrom an alternate interpretation is that anomalous trends on the plots of nd and sr isotopic composition versus incompatible element ratios found in some s nsp lavas suggest that the addition of a sedimentary component may be locally superimposed on the two component mixing of mantle end members

onset of neoglaciation in the southern hemisphere a review of evidence documenting an early neoglacial mid holocene advance of mountain glaciers in south america and new zealand reveals that of 16 glaciers for which radiocarbon age control exists only two have associated dates that may approximate the culmination of an advance advances of the remaining glaciers are controlled only by minimum or maximum limiting ages additional dates for several new zealand glaciers are based on weathering rind measurements having large potential errors twelve of the glaciers now terminate or have terminated in lakes or in tidewater and are subject to instabilities associated with calving termini an extensive debris cover in the ablation zone of nearly half of the glaciers makes their moraine succession potentially suspect as a record of detailed climatic variation the two glaciers with seemingly reliable age control are located in valleys where large rock avalanches could affect glacier mass balance and lead to random advances or where rock avalanche deposits might easily be mistaken for moraines and tills the early neoglacial interval has been defined primarily based on this set of data the ages taken at face value suggest that the early neoglacial advance culminated between ca 5400 and 4900 cal yr ago ca 4600 4400 14c yr bp this chronology however should remain provisional until improved age control is obtained for a large population of glaciers based on closely bracketing radiocarbon dates and or an adequate number of cosmogenic isotope ages data from calving glaciers and those subject to rock avalanche activity should be avoided or assessed critically copyright 2000 john wiley sons ltd

shoshonitic magmas in nascent arcs new evidence from submarine volcanoes in the northern marianas volcanoes in the northern mariana arc between uracas lat 20 n and minami iwo jima 24 n are very active yet entirely submarine in contrast to the predominantly low k basaltic magmas of the central mariana arc the northern mariana arc is dominated by more siliceous melts in the south and by shoshonites in the north the northern arc melts have enrichments in ba 800 ppm rb 70 ppm sr 1000 ppm ce 50 ppm and ce yb n 24 which increase to the north as far as iwo jima lavas from volcanoes north of iwo jima lack these enrichments and are indistinguishable from those of the central maranas the shoshonites are unusual in occurring along the magmatic front of a primitive intra oceanic arc we hypothesize that they represent the reconstruction of a magmatic arc following melting of enriched mantle due to the propagation of the mariana trough spreading center northward through the volcano arc shoshonites thus may characterize the initial stages of arc construction after an episode of back arc rifting and need not be restricted to the mature stages of arc evolution this situation contrasts with subduction zone initiation where first melts may be boninites or low k tholeiites these differing initial melts converge toward tholeiitic and calc alkaline compositions as arcs evolve

a laurentian grenville age oceanic arc back arc terrane in the sierra de pie de palo western sierras pampeanas argentina

mg ca and sr ca ratios in planktonic foraminifera proxies for upper water column temperature reconstruction reliable temperature estimates from both surface and subsurface ocean waters are needed to reconstructpast upper water column temperature gradients and past oceanic heat content this work examines therelationships between trace element ratios in fossil shells and seawater temperature for surface dwellingforaminifera species globigerinoides ruber white and globigerina bulloides and deep dwelling species globorotalia inflata globorotalia truncatulinoides dextral and sinistral and pulleniatina obliquiloculata mg ca and sr ca ratios in shells picked in 29 modern core tops from the north atlantic ocean are calibratedusing calculated isotopic temperatures mg ca ratios on g ruber and g bulloides agree with published dataand relationships for deep dwelling species mg ca calibration follows the equation mg ca 0 78 0 04 exp 0 051 0 003 t with a significant correlation coefficient of r

the holonda porphyrites norwegian caledonides geochemistry and tectonic setting of early mid ordovician shoshonitic volcanism petrological and geochemical data denote that the late arenig early llanvirn holonda porphyrites belong to the subduction related shoshonite association original compositions ranged from absarokite through shoshonite to latite and their very evolved nature signifies a mature arc aynity in an active continental margin setting much of the geochemical variation can be interpreted in terms of fractional crystallization followed by a varying admixture of cumulus phases to the ascending melt and accumulation of phenocrysts within the magmatic feeder system their eruptive products covered an area which was at least 20 25 km across forming local islands with carbonate rich shelves in a shallow to deeper marine environment the immediate substrate to the volcanosedimentary holonda basin is the lokken ophiolite which formed in a primitive oceanic arc marginal basin setting some 10 20 ma prior to the shoshonitic magmatic event arc continent collision led to emplacement of the oceanic arc and marginal basin crust onto the continental margin in pre late arenig times strong uplift of the obducted oceanic plate occurred in response to the buoyancy effect of the underthrusting less dense continental margin this is interpreted to have been followed by a reversal of subduction polarity and formation of a steeply dipping subduction zone against the continental margin lithosphere and was succeeded by the very evolved holonda porphyrite shoshonitic magmatism in volcanic islands along this submerged continental margin

ecological and temperature controls on mg ca ratios of globigerina bulloides from the southwest pacific ocean we present mg ca data for globigerina bulloides from 10 core top sites in the southwest pacific ocean analyzed by laser ablation inductively coupled plasma mass spectrometry la icpms mg ca values in g bulloides correlate with observed ocean temperatures 7 degrees c 19 degrees c and when combined with previously published data an integrated mg ca temperature calibration for 7 degrees c 31 degrees c is derived where mg ca mmol mol 0 955 x e 0 068 x t r 2 0 95 significant variability of mg ca values 20 30 was found for the four visible chambers of g bulloides with the final chamber consistently recording the lowest mg ca and is interpreted in part to reflect changes in the depth habitat with ontogeny incipient and variable dissolution of the thin and fragile final chamber and outermost layer concomitantly added to all chambers caused by different cleaning techniques prior to solution based icpms analyses may explain the minor differences in previously published mg ca temperature calibrations for this species if the lower mg ca of the final chamber reflects changes in depth habitat then la icpms of the penultimate or older chambers will most sensitively record past changes in near surface ocean temperatures mean size normalized g bulloides test weights correlate negatively with ocean temperature t 31 8 x e 30 5xwtn r 2 0 90 suggesting that in the southwest pacific ocean temperature is a prominent control on shell weight in addition to carbonate ion levels

techniques for gis modeling of coastal dunes coastal dunes present a unique problem to coastal scientists because of the dynamic nature of most coastal dune systems coastal dunes can change shape quickly and frequently due to storm generated winds and waves prevailing winds can transport significant amounts of sand throughout the dune system topographic and volumetric changes in a 150 40 m site on the outer banks of north carolina were assessed through a series of monthly field surveys conducted over a 1 year period from may 1997 to may 1998 this paper discusses the geographic information system gis methodology used for data acquisition and analysis and presents one methodology developed to measure 3 d dune morphodynamics using a 2 d and 3 d gis it serves as a guide for other coastal researchers who may have limited surveying or gis experience issues concerning sampling routine data density and grid cell size are discussed the methodology followed results in the production of a grid of interpolated elevation values that can be represented in a variety of ways including as topographic maps digital elevation models dem or two dimensional cross sections of the dune system the grid from the may 1998 survey is subtracted from the may 1997 grid to obtain elevation change information that in turn can be represented graphically the results of the analysis show that volumetric change over the 1 year period was dominated by erosion along the seaward face of the dune the monthly surveys show that this erosion was the result of two northeasters in january and february 1998 the loss of volume is partially compensated for by accumulation to the rear of the foredune ridge primarily in locations where blowouts facilitate aeolian transport of sediment from the beach the implication is that the dune system is eroding rapidly due to storm activity it also suggests that there is a mechanism for offsetting some of the volumetric loss through aeolian transport into the dune system

vistulian loess deposits in western poland and their palaeoenvironmental implications the loess deposits of western poland are a periglacial facies having been deposited in the plenivistulian so far western poland is the onlypart of the countryin which vistulian loess deposits occurring as small patches on di erent glacial and glacio uvial landfoms have been found the diagnostic features of these sediments provide a tool for the sub division of the main lithofacies loess deposits occur in two main lithofacies massive loess lm and laminated loess ll there are three sub lithofacies within the laminated loess cryptolaminated sl laminated loess sensu stricto ll and banded loess sm loess lithofacies are associated with a varied topographyand are distributed in the end moraines till plains and outwash plains there is a signi cant correlation with the periglacial zone and aeolian processes active during the vistulian in western poland 2001 elsevier science ltd and inqua all rights reserved

plagioclase nucleation and growth kinetics in a hydrous basaltic melt by decompression experiments isothermal single step decompression experiments at temperature of 1075 c and pressure between 5 and 50 mpa were used to study the crystallization kinetics of plagioclase in hydrous high k basaltic melts as a function of pressure effective undercooling teff and time single step decompression causes water exsolution and a consequent increase in the plagioclase liquidus thus imposing an effective undercooling teff accompanied by increased melt viscosity here we show that the decompression process acts directly on viscosity and thermodynamic energy barriers such as interfacial free energy controlling the nucleation process and favoring the formation of homogeneous nuclei also at high pressure low effective undercoolings in fact this study shows that similar crystal number densities na can be obtained both at low and high pressure between 5 and 50 mpa whereas crystal growth processes are favored at low pressures 5 10 mpa the main evidence of this study is that the crystallization of plagioclase in decompressed high k basalts is more rapid than that in rhyolitic melts on similar timescales the onset of the crystallization process during experiments was characterized by an initial nucleation event within the first hour of the experiment which produced the largest amount of plagioclase this nucleation event at short experimental duration can produce a dramatic change in crystal number density na and crystal fraction triggering a significant textural evolution in only 1 h in natural systems this may affect the magma rheology and eruptive dynamics on very short time scales

geological characteristics of strata in chongqing china and mitigation of the environmental impacts of tunneling induced geo hazards this study investigated the geological characteristics of strata in chongqing and the tunneling induced geo hazards therein the urban area of chongqing contains six syncline anticline pairs and is bounded by the huayingshan basement fault to the west and by the changshou zunyi basement fault to the east the bedrock containing sandstone and mudstone of the upper shaximiao formation resulting from middle triassic strata is occasionally outcropped during urbanization many valleys in chongqing require to be backfilled to create more flat ground thus the extent and thickness of the loose backfill layer varied from place to place while tunneling in chongqing the following geological characteristics may cause geo hazards 1 backfill with a loose structure poor gradation high permeability and large void ratio 2 highly or moderately weathered mudstone and sandstone that can easily become softened once subjected to groundwater seepage and 3 syncline folding containing perched water or confined fissure water the potential geo hazards include groundwater ingress ground surface settlement and strata collapse while tunneling within backfill synclines sandstone synclines or weak fractured rock significant amount of groundwater may be encountered thus leading to a high risk of groundwater ingress ground surface settlement can be triggered due to the disturbances of tunnel construction to the backfill or consolidation effect after groundwater ingress strata collapse can be caused by the blasting induced disturbances to poor surrounding geology or by inadequate overburden thickness or by an increase in the effective stress resulting from groundwater loss caused by leakage to mitigate the environmental impacts of the tunneling induced geo hazards a series of countermeasures that is advance geological drilling advance ground improvement including full face grouting and grouting of the surrounding geologic media and advance pipe umbrella use are proposed in this paper the results from a case study indicate that the proposed countermeasures can greatly decrease the ground surface settlement and amount of groundwater ingress during tunneling in chongqing verifying the effectiveness of the proposed countermeasures

petrology and tectonic significance of gabbros tonalites shoshonites and anorthosites in a late paleozoic arc root complex in the wrangellia terrane southern alaska plutonic rocks intrusive into the late paleozoic tetelna formation of southern alaska are the underpinnings of the late paleozoic skolai arc of the wrangellia terrane there are four groups of intrusive rocks within the skolai arc 1 gabbro diorite plutons that contain gabbroic to anorthositic cumulates along with a differentiated series of gabbros and diorites of basaltic to andesitic composition 2 silicic intrusions including tonalite granodiorite and granite 3 monzonitic to syenitic plutonic rocks of the ahtell complex and related dikes and sills 4 fault bounded bytownite anorthosite of uncertain age and association these anorthosites may be related to post skolai nikolai greenstone magmatism the silicic rocks yield discordant u pb zircon ages of 290 320 ma early to late pennsylvanian relative age relations suggest that the oldest intrusive rocks are the gabbro diorite plutons the youngest are the monzonitic rocks and that the silicic rocks span this range the gabbro diorite pluto

evolution of backarc rifting mariana trough 20 24 n the mariana trough is an actively opening backarc basin in the western pacific the trough formed by extension which longitudinally split an earlier arc massif creating a crescent shaped basin between the remnant west mariana ridge and eastern active volcanoes of the mariana arc opening increases southward from the volcano islands near 24 n where the two arcs join at 18 n in the central mariana trough the basin is widest and may be opening primarily by seafloor spreading we present a synthesis of closely spaced shipboard gravity magnetic and bathymetry measurements from the northern basin 20 24 n an area that undergoes a significant progressive southward increase in extension we have identified three stages in the evolution of rifting in this area 1 asymmetric rifting from 24 n to 22 15 n where faulting and magmatism have migrated laterally to remain near the active volcanic arc side of the basin 2 a localization of rifting from 22 15 n to 21 n where the primary zone of rifting separates from the active volcanic arc and 3 a further concentration of rifting from 21 n to 20 n leading to the formation of deep tectonic grabens near the center of the basin this last stage may be a precursor to or incipient seafloor spreading we describe a new type of magnetic lineation resolved in a three dimensional seafloor magnetization inversion of the trough between 20 and 24 n the detailed character of these lineations their association with tectonic structures and other geophysical observations indicate that they are not seafloor spreading lineations but rather result from magnetic intrusions and volcanism emplaced within preexisting less magnetic rifted arc crust the development of these well defined magnetization bands indicates that the zone of magmatism remains relatively narrow at any one time throughout the opening of the trough although tectonic deformation appears to be more widely distributed in addition the geometry of the magnetization bands with respect to the remnant arc border faults indicates that rifting propagated rapidly northward

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

seamarc ii evidence for the locus of seafloor spreading in the southern mariana trough abstract two surveys near 13 45 n across the mariana trough identify the axis of backarc seafloor spreading at 143 53 e the spreading center is identified on the basis of its high acoustic backscatter in seamarc ii side scan images and by the presence of young volcanic features neither asymmetric spreading nor discrete jumps in the spreading center location are required to explain the observed morphology and backscatter characteristics changes in the orientation of the seafloor spreading fabric suggest that an early phase of arc rifting may have been followed by northward propagation of the backarc spreading center to widen this portion of the basin this could have produced the current situation with the rift axis offset about 35 km east of the center of the mariana trough the off center position of the spreading axis may also the result of overgrowth of backarc crust by the volcanic arc

slope deposits as an indicator of anthropopressure in the light of research in central poland abstract results of research on neo holocene slope covers uncovered at archaeological sites in central poland are described in this paper geoarchaeological investigations have been undertaken in the ner river basin distinctive archaeological relicts of human activity document periods of intensive activity of human societies artefacts included within deposits play a very important role in correct recognition of the chronology of covers and ecofacts for reconstructions of environmental evolution the origin and development of slope covers have been correlated with anthropogenic changes of the natural environment two main phases of acceleration of slope processes have been recognised dated to the middle bronze age and to the late roman period slope deposits have been classified as deluvia deluvial slope wash deposits or colluvial deposits their features are most typical for deluvial sands and if they contain more humic matter for soil deluvia the deluvial covers have been deposited as an effect of moderately intensive slope wash processes accumulation of slope deposits has resulted from natural processes initiated by human impact during periods of intensive settlement and economic activity the slope cover sediments are the source for recognition of intensity of human impact and of economic activity of ancient societies and for distinct phases of hiatuses of settlement development the possibility of archaeological and palaeogeographical interpretations based on research on slope covers at archaeological sites is presented

modes of eastern equatorial pacific thermocline variability implications for enso dynamics over the last glacial period 1 changes in el nino southern oscillation enso variability are difficult to extract from paleoceanographic reconstructions because they are superimposed on changes in seasonal variability that modulate the first order climate signal here we address this problem by reconstructing thermocline structure from a marine sediment core retrieved from the eastern equatorial pacific at the core location changes in hydrologic parameters within the thermocline are linked to enso activity with a reduced influence of seasonal variability compared to surface waters we performed repeated isotopic analyses 18o on single specimens of the thermocline dwelling planktonic foraminifera neogloboquadrina dutertrei at several targeted time periods over the last 50 ka to extract the total thermocline variance a parameter supposed to reveal changes in enso no fundamental changes in amplitude and frequency of the events were detected despite differences in climatic background however our data suggest that long term variations in the thermocline variability occurred over the last 50 ka with the highest and lowest enso activities occurring during the last glacial period and the last glacial maximum respectively

short term beach dune sand budgets on the north sea coast of france sand supply from shoreface to dunes and the role of wind and fetch abstract three experimental plots covering the transition from the upper beach to the dune on the north sea coast of france were monitored at various intervals over a period of 18 24 months via high resolution terrain surveys in order to determine inter site sand budget variability as well as patterns and processes involved in sand exchanges between the upper beach and dune the wind regime consists of a fairly balanced mix of moderate 80 of winds are below 8 m s onshore offshore and shore parallel winds sustained dune accretion over several years depends on the periodic local onshore welding of shoreface tidal banks that have developed in the storm and tide dominated setting of the southern north sea the only site where this has occurred in the recent past is calais where bank welding has created a wide accreting upper beach sand flat at this site significant sand supply from the subtidal sand bank reservoir to the upper beach flat occurred only once over the 18 month survey following a major storm the bulk of the sand deposited over this large flat is not directly integrated into the adjacent embryo dunes by onshore winds but is progressively reworked in situ into developing dunes or transported alongshore by the balanced wind regime thus resulting in alongshore stretching of the embryo dune system the leffrinckoucke site near belgium shows moderate beach dune mobility and accretion while the wissant site exhibits significant upper beach bedform mobility controlled by strong longshore currents that result in large beach budget fluctuations with little net budget change to the detriment of the adjacent dunes accretion at these two sites which are representative of the rest of the north sea coast of france is presently constrained by the absence of a shore attached sand bank supply reservoir while upper beach dune sand exchanges are further limited by the narrow wave affected upper beach the intertidal morphology of bars and troughs which segments the aeolian fetch and the moderate wind energy conditions the balanced wind regime limits net sand mobilisation in favour of either the beach or the dune and may explain the relatively narrow longshore morphology of the dune ridges bounding this coast

geohydromechanical processes in the excavation damaged zone in crystalline rock rock salt and indurated and plastic clays in the context of radioactive waste disposal abstract the creation of an excavation disturbed zone edz or excavation damaged zone edz is expected around all man made openings in geologic formations macro and micro fracturing and in general a redistribution of in situ stresses and rearrangement of rock structures will occur in this zone resulting in drastic changes of permeability to flow mainly through the fractures and cracks induced by excavation the edz may have significant implications for the operation and long term performance of an underground nuclear waste repository various issues of concern need to be evaluated such as processes creating fractures in the edz the degree of permeability increase and the potential for sealing or healing with permeability reduction in the zone in recent years efforts along these lines have been made for a potential repository in four rock types crystalline rock salt indurated clay and plastic clay and these efforts have involved field laboratory and theoretical studies the present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on edz in these four rock types at a cluster conference and workshop held in luxembourg in november 2003 first definitions of excavation disturbed and edzs that may be applicable to all four rock types are proposed then an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the edz for crystalline rock salt indurated clay and plastic clay comparison tables of relevant processes associated factors and modelling and testing techniques are developed a discussion of the general state of the art and outstanding issues is also presented a substantial bibliography of relevant papers on the subject is supplied at the end of the paper

accuracy of interpolation techniques for the derivation of digital elevation models in relation to landform types and data density one of the most important scientific challenges of digital elevation modeling is the development of numerical representations of large areas with a high resolution although there have been many studies on the accuracy of interpolation techniques for the generation of digital elevation models dems in relation to landform types and data quantity or density there is still a need to evaluate the performance of these techniques on natural landscapes of differing morphologies and over a large range of scales to perform such an evaluation we investigated a total of six sites three in the mountainous region of northern laos and three in the more gentle landscape of western france with various surface areas from micro plots hillslopes and catchments the techniques used for the interpolation of point height data with density values from 4 to 109 points km2 include inverse distance weighting idw ordinary kriging ok universal kriging uk multiquadratic radial basis function mrbf and regularized spline with tension rst the study sites exhibited coefficients of variation cv of altitude between 12 and 78 and isotropic to anisotropic spatial structures with strengths from weak with a nugget sill ratio of 0 8 to strong 0 01 irrespective of the spatial scales or the variability and spatial structure of altitude few differences existed between the interpolation methods if the sampling density was high although mrbf performed slightly better however at lower sampling densities kriging yielded the best estimations for landscapes with strong spatial structure low cv and low anisotropy while rst yielded the best estimations for landscapes with low cv and weak spatial structure under conditions of high cv strong spatial structure and strong anisotropy idw performed slightly better than the other method the prediction errors in height estimation are discussed in relation to the possible interactions with spatial scale landform types and data density these results indicate that the accuracy of interpolation techniques for dem generation should be tested not only in relation to landform types and data density but also to their applicability to multi scales

dirt road a geomorphological and geochemical record of late holocene human activity in the catchment of lake radacz central pomerania poland abstract the paper offers a discussion of the record of human activity in the relief and sediments of a selected lake catchment in central pomerania in poland one of the basic markers of human activity here is a change in the lake water level the dropping level on average 1 m 100 years made it possible for people to develop successively exposed stretches of land along the shore an analysis of the polish national archeological records and archival maps showed that human development and impact appeared in the lakeshore zone as early as the neolithic in central pomerania the changes were especially intensive in the late holocene in the catchment of the lake under study they included a 100 increase in the length of nearby roads in the archives of its paleoenvironmental data most traces have been left on farming terraces while a poorly studied form of record of human activity is a dirt road running parallel to the shoreline geodetic and geochemical examination has revealed that the road is a stimulant of change its wheeled traffic mixes the accumulated and eroded material and this causes changes in the shoreline section the road cutting which is 2 m wide deepened while material accumulates in the form of 0 5 m wide lateral bars the compaction of the material brings about changes in the structure of the ground or soil its density porosity compactness moisture which affects its level of oxygenation and waterlogging and consequently its iron content to establish this a speciation analysis was carried out using the fe iii fe ii ratio it was determined that the lower the ratio the higher the susceptibility of land to deformation owing to an increase in soil density a drop in its water capacity reduction conditions and the predominance of fe ii the research discussed here is only a pilot study but the authors see extensive opportunities for using speciation analysis in geoarcheology

coeval potassic and sodic calc alkaline series in the post collisional hercynian tanncherfi intrusive complex northeastern morocco geochemical isotopic and geochronological evidence abstract the post collisional late hercynian tanncherfi intrusive complex tic is part of a widespread intrusive episode in the moroccan meseta the complex contains a wide range of rock types from monzogabbros to monzogranites two distinct magmatic series are recognized 1 a potassic shoshonitic series consisting of monzogabbros quartz monzonites and monzogranites and 2 a sodic granodioritic series represented by quartz monzodiorites and granodiorites all the tanncherfi plutonic rocks display similar spider diagram profiles with lile and lree enrichment and nb ta ti depletion which are typical of subduction related magmas combined major trace element compositions and sr nd isotopic results indicate that the two series have been derived from a lile and lree enriched continental lithospheric mantle source under different partial melting and or depth conditions intrusion of the tanncherfi rocks was not temporally related to subduction and the enrichment of their source is likely to be linked to preceding subduction events the two series evolved by fractional crystallization of clinopyroxene plagioclase hornblende biotite k feldspar and accessories fe ti oxide minerals titanite apatite and zircon for the potassic series while the sodic series combined fractional crystallization with assimilation of felsic magmas with lower sr isotopic ratio than the more mafic term of the series the quartz monzodiorite the intrusion of the potassic magmas 344 6 ma marks a major change in the tectonic regime of eastern meseta these magmas intruded during post thickening uplift and extension both probably favored by convective thinning of the lithosphere this model provides a reasonable mechanism for the genesis of other hercynian intrusive complexes in morocco

volcanism in nascent back arc basins behind the shichito ridge and adjacent areas in the izu ogasawara arc northwest pacific evidence for mixing between e type morb and island arc magmas at the initiation of back arc rifting mineral chemistry major and trace elements and 87sr 86sr ratios are presented for 29 igneous rocks dredged from the northern portion of the izu ogasawara arc these rocks are compositionally bimodal basement gabbro and trondhjemite from the arc are extremely poor in k2o 0 05 0 19 and rb 0 48 0 62 ppm and their ree patterns and sr isotope ratios indicate that there are island arc tholeiites quaternary volcanic rocks from the present volcanic front shichito ridge active arc back arc seamounts east side inactive arc and torishima knoll between the two back arc depressions incipient back arc basins behind the active arc have the same geochemical characteristics as the above plutonic rocks though they are not as depleted in k and rb rhyolite pumice from the backarc depression is also the depleted island arc tholeiite whereas basalts from the depression have compositions that are transitional between morb and island arc tholeiites in trace element ti ni cr v y and zr and mineral chemistries the back arc depression basalts have relatively high ban cen 0 66 1 24 cen ybn 1 1 1 9 and k ba 45 105 and low 87sr 86sr 0 70302 0 70332 and ba sr 0 1 0 2 which are similar to other back arc basin basalts and e type morb but are quite unlike the depleted island arc tholeiites the diverse trace element and sr isotope compositions of basalt andesite from the back arc depressions imply the interplay between e type morb and island arc tholeiite these chemical characteristics and the relationships of ce yb n vs ba ce n and ce yb n vs 87sr 86sr suggest that the back arc depression magmas are generated by mixing of e type morb and depleted island arc tholeiite magmas geochemical characters of the associated rhyolite from the depression are compatible with partial melting of lower crust

climatic versus human impact on the holocene sedimentation in river valleys of different order examples from the upper dnieper basin belarus records from floodplain deposits in selected river valleys of the dnieper river basin belarus were studied to reconstruct the phases of natural and anthropogenic environmental changes in the holocene sediment archives in the main valley and its four tributaries of different orders were studied by means of lithological and geochemical methods including grain size analysis x ray fluorescence analysis spectral analysis spore and pollen analyses and radiocarbon dating some differences in the response of different order fluvial systems to climate changes and human impact have been revealed fluvial deposits in the dnieper valley and in first order valleys contain records on the regional scale natural environmental changes while human impact is clearly pronounced only in deposits of the last millenium fluvial deposits in the valleys of second order record river evolution only since the neoholocene at the same time the lacustrine or carbonate freshwater deposits in these valleys contain the records of environmental changes in the entire holocene changes in the sequence and composition of fluvial deposits due to human impact occurred in high order valleys almost 2000 years later since 500 years bp as compared with pollen data

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

triassic plutonism in southern california southward younging of arc initiation along a truncated continental margin earliest cordilleran magnatism in the southwestern united states is recorded by a belt of triassic plutons that inme protemzoic basemint of the mojave crustal province and its cratona miogeoclinal cover the belt extends from the western mojave desert through the trausverse ranges to the colorado river trough triassic plutons are predominantly alkali calcic fe and sr mriched quartz mzrdior tes and monzonites the northern part of the belt is comlx sed of two older plutonic mites 241 231 ma which are high k to shoshonitic the southern part of the belt is a younger 218 213 ma sodic alkalic suite the plutonic record in southern california suggests a short lived southward younging continental margin arc sang for eraplacement of triassic plutons sulim on a continental margin modified by s mistral tranqform faulting triassic plutonism in this region was followed by a magmatic lull prior to the onset of voluminous middle to late jurassic cordilleran arc magmatism

analysis of flow path around the sealing section hg a experiment in the mont terri rock laboratory as part of the hg a experiment in the mont terri rock laboratory large scale in situ water gas injection experiments was conducted in a microtunnel this research work focuses on the numerical analysis of the experimental data and the in situ observations concerning a temporary change of the hydromechanical properties of opalinus clay during experimental operations three phases were numerically interpreted these included the generation of excavation damaged zone during tunnel excavation in which highly permeable flow paths around the tunnel have been formed the self sealing effect during water tests and the pressure evolution during a long term gas injection test a coupled two phase flow and mechanics model taking into account the strong anisotropic properties of opalinus clay was developed to interpret the measured data the hydraulic anisotropy was described by a transversely isotropic permeability tensor an elasto plastic model was established to consider both stiffness anisotropy and strength anisotropy anisotropic plasticity was studied using the microstructure tensor method

the tectonic significance of ordovician magmatism in the eastern lachlan fold belt abstract the shoshonitic rock series is a suite of igneous rocks derived from the mantle and containing high potassium plus low abundances of high field strength elements it is commonly associated with calcalkaline igneous rocks but in most modern examples a contemporary active subduction zone is not present mantle derived shoshonitic magmatism in the lachlan fold belt commenced in the early ordovician and terminated at the end of the ordovician when it was replaced by tholeiitic magmatism and the onset of wholesale melting of the lower to middle crust associated calcalkaline igneous rocks are insignificant the shoshonites are widely distributed across the eastern part of the fold belt in a series of discontinuous belts and volcanic centres the largest of which is the orange wellington belt extending from east of cowra to dubbo the broad geographical distribution is not typical of the curvilinear belts of volcanics associated with subduction zones and would be even greater if the intervening basins or troughs were unfolded all rocks analyzed to date are either clearly shoshonitic or show chemical features that indicate shoshonitic affinities prior to alteration and metamorphism in some areas lavas rich in olivine and clinopyroxene potassic trachybasalts dominate in others the more evolved plagioclase rich shoshonites are most abundant it is suggested that the ordovician magmatism was not accompanied by coeval subduction as has been generally assumed more likely the lithospheric mantle beneath the lachlan fold belt was modified during an earlier subduction event associated with the assembling of the basement blocks recognized from granite studies the cause of melting in the ordovician may be related to lithospheric heating or overturning prior to the upwelling of unmodified asthenosphere the hot 1200 c asthenosphere was the source for the silurian tholeiites and provided conductive heat for the melting of the lower to middle crust

geology of mankind for the past three centuries the effects of humans on the global environment have escalated because of these anthro pogenic emissions of carbon dioxide global climate may depart significantly from natural behaviour for many millennia to come it seems appropriate to assign the term anthropocene to the present in many ways human dominated geological epoch supplementing the holocene the warm period of the past 10 12 millennia

damage induced permeability changes in granite a case example at the url in canada abstract this paper concerns both in situ measurements of permeability and numerical modelling of changes in permeability induced by microcrack growth hydraulic experiments including pulse tests with the seppi probe are in progress these tests are a part of the tunnel sealing experiment tsx at the 420 m level of canada s underground research laboratory whose aim is to estimate the in situ hydraulic properties of lac du bonnet granite based on laboratory investigations the anisotropic damage model developed by homand et al comput geotech 22 1998 135 and recently reviewed by shao et al int j rock mech min sci 36 1999 1001 has been extended in order to account for changes in permeability induced by microcrack growth we have implemented this extension in the three dimensional code flac 3 d triaxial compression tests with permeability measurements carried out on two different granites provide a verification of the numerical implementation with a good agreement between experiments and predictions comparison between in situ measurements of permeability and predictions indicates that both the results of numerical modelling and observations are globally in agreement finally numerical modelling as well as the in situ measurements indicate that a depth of 50 70 cm is a good estimation of the extent of excavation disturbed zone in the tsx tunnel

structural evolution of auriferous veins at the endeavour 42 gold deposit cowal mining district nsw australia polyphase veins at the low grade structurally controlled epithermal gold deposit endeavour 42 in the junee narromine volcanic belt of the ordovician to silurian macquarie arc central new south wales australia record multiple tectonically driven fluid flow events during the mid paleozoic ordovician host rocks consist of a volcano sedimentary succession intruded by trachyandesite and andesitic lavas and intrusions as well as a volumetrically significant ordovician diorite sill the entire succession was tilted and faulted prior to the emplacement of multiple mafic to intermediate dike phases commonly localized along faults gold bearing veins cut all lithologic units at the endeavour 42 deposit with the exception of rare late stage intrusions economic gold is restricted to faults fault hosted breccias and veins with two distinct populations 1 an older steeply dipping conjugate vein set cut by 2 two younger moderately dipping vein sets both steep and inclined moderately dipping vein sets contain a similar mineral assemblage implying formation during a single epithermal system veins are generally 1 to 10 mm thick commonly straight walled but locally form overlapping veins with hard linkages the steep veins reactivated two sets of older faults fault parallel fractures and dike contacts and accommodated subhorizontal extension high gold grade hydrothermally cemented breccias are associated with early gold bearing veins and localized along deposit scale faults crosscutting the early steep gold bearing vein sets are inclined gold bearing veins with moderate dips to the southwest and west these opened as a new vein set and as veins localized along and at a slight angle to westward dipping bedding planes respectively the geometry of the inclined moderately dipping veins either represents a sudden change in the far field stress state to near vertical minimum compressive stress thereby suggesting a change from an extensional to a contractional environment or it may reflect local changes in the differential stress state with subhorizontal northeast southwest tension late veins and thrust faults in the deposit indicate a postmineral contractional environment the endeavour 42 deposit underwent tectonic burial until it was exhumed in the early carboniferous as indicated by 40ar 39ar plateau ages of 362 7 2 1 356 3 1 8 and 344 5 2 1 ma toward the end of the kanimblan cycle

development of a constitutive model for a bedded argillaceous rock from triaxial and true triaxial tests1 in this work a constitutive model that predicts the mechanical behaviour of opalinus clay is developed the model is based on the theory of plasticity and takes into consideration the inherent anisotropy due to the existence of bedding planes hardening behaviour before the peak strength softening behaviour after the peak and creep effects the model was implemented into the equations of pseudostatic equilibrium to simulate the mechanical response of opalinus clay during conventional triaxial tests using cylindrical samples and true triaxial tests using cubic samples the model satisfactorily reproduces the main physical processes that prevailed during those tests

on the hydro mechanical behaviour of remoulded and natural opalinus clay shale the geo energy sector makes use of advanced technologies such as shale gas extraction co2 sequestration and nuclear waste geological disposal that rely on the exploitation of shale formations due to the great depths involved in these applications and the difficulties in retrieving intact samples remoulded shale specimens are often adopted for hydro mechanical testing remoulded and intact shales may substantially differ in their hydro mechanical behaviour due to the particular structure of the natural material which is the result of diagenesis and burial history this paper presents an experimental campaign aimed at i characterizing the role of diagenesis and depth for opalinus clay shale and their impact on the hydro mechanical behaviour of the material and ii understanding how representative the behaviour of the remoulded material is with respect to that of the natural shale in this paper the hydro mechanical behaviour of remoulded and intact specimens from the opalinus clay shale formation is investigated by means of a comprehensive oedometric testing campaign the effects of depth and diagenesis on the material behaviour are analysed by testing intact specimens that come from two different sites and depths of the considered shale formation the results highlight a considerably greater stiffness for the natural opalinus clay with respect to the remoulded specimens when the same vertical effective stress is considered together with a significantly lower porosity for the former which is shown to be the result of diagenetic processes rather than solely mechanical compaction a lower swelling sensitivity is also manifested by the natural material with respect to the remoulded specimens as a result of the formation of bonding on the other hand the diagenetic processes do not seem to have a strong impact on the permeability of the material finally creep effects are reduced when diagenesis occurs while they become more relevant when the material is disturbed or remoulded the obtained results provide significant insight into the roles of depth diagenesis and structural disturbance on the hydro mechanical behaviour of the opalinus clay shale

using foraminiferal mg ca ratios to detect an ocean warming trend in the twentieth century from coastal shelf sediments in the bungo channel southwest japan to assess abnormal warming of temperature in southwest japan s coastal seas during the twentieth century we developed a 200 yr interannually resolved record of planktonic and benthic foraminiferal mg ca based temperature using neritic coastal sediment cores the winter to late spring bottom temperature 50 m record based on benthic foraminiferal nonion japonicum mg ca ratios in the bungo channel bc showed consistent variation with observed temperatures on a five year average basis the bc bottom temperature record showed a significant increasing trend of 1 5 c 100 yr during the twentieth century which was never apparent in nineteenth century that result suggests that our mg ca based thermometry approach using coastal benthic foraminifera can detect abnormally rising temperatures in neritic coastal seas in southwest japan the abnormal warming of winter to late spring bottom temperature in the bc contrasts with the lack of an increasing trend in the globigerinoides ruber based summer to autumn t

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

evolution of the mariana convergent plate margin system the mariana convergent plate margin system of the western pacific provides opportunities for studying the tectonic and geochemical processes of intraoceanic plate subduction without the added complexities of continental geology the system s relative geologic simplicity and the well exposed sections of lithosphere in each of its tectonic provinces permit in situ examination of processes critical to understanding subduction tectonics its general history provides analogs to ancient convergent margin terranes exposed on land and helps to explain the chemical mass balance in convergent plate margins the mariana convergent margin s long history of sequential formation of volcanic arcs and extensional back arc basins has created a series of volcanic arcs at the eastern edge of the philippine sea plate the trenchward edge of the overriding plate has a relatively sparse sediment cover rocks outcropping on the trench s inner slope are typical of the early formed suprasubduction zone s lithosphere and have been subjected to various processes related to its tectonic history pervasive forearc faulting has exposed crust and upper mantle lithosphere many large serpentinized peridotite seamounts are within 100 km of the trench axis from these we can learn the history of regional metamorphism and observe and sample active venting of slab fluids ocean drilling recovered suprasubduction zone lava sequences erupted since the eocene that suggest that the forearc region remains volcanologically dynamic seismic studies and seafloor mapping show evidence of deformation throughout forearc evolution large portions of uplifted southern forearc are exposed at the larger islands active volcanoes at the base of the eastern boundary fault of the mariana trough vary in size and composition along strike and record regional differences in source composition their locations along strike of the arc are controlled in part by cross arc structures that also facilitate formation of submarine volcano chains extending from the base of the fault westward into the back arc basin the western boundary is the west mariana ridge the western portion of the volcanic arc active prior to formation of the mariana trough the trough evolved in a two stage extension process of rifting and subsequent seafloor spreading the back arc basin varies along strike from rifted arc lithosphere with scattered volcanoes but no real spreading center in the north to a complex mid ocean type spreading center south of 20 n the change from initial rifting to true seafloor spreading is also evident across the mariana trough from rifted topography near the west mariana ridge to spreading ridges in the central to eastern basin south of 20 n this morphologic change indicates an early stage of extension with basin and range type topography predominant and volcanism restricted to fissure eruptions along fault block boundaries the spreading ridges and abyssal hill morphology evolved later as new lithosphere was generated at elongate volcanic ridges located in the center of rift valleys the center of extension intersects the active volcanic front differently at either end of the mariana trough in the north extension is by rifting of arc lithosphere where it intersects the arc in the south a major strike slip fault extends from the trench axis across the forearc through the volcanic arc and into the back arc basin arc magmas apparently leak along this fault zone into the forearc and the back arc spreading center the complexity of interrelated tectonism and magmatism in this convergent margin is daunting but studies of arc systems such as this provide the best hope of interpreting many of the exposed terranes accreted to continents comparison of subaerial terranes with recent studies of intraoceanic convergent margins will add to our understanding of plate interactions and of the evolution of the volcanic arcs and extensional back arc basins generated within such environments

geochemistry of 1 9 ga morb and oib like basalts from the amisk collage flin flon belt canada evidence for an intra oceanic origin subaqueously erupted basalts that occur in kilometre scale allochthons within the 1 9 ga flin flon belt canada appear to have been generated at oceanic ridges and possibly oceanic plateaus remote from archean cratons the ocean floor basalts fall into two categories 1 n type resembling n morbs and mariana type back arc basin basalts depleted to flat ree patterns high zrnb variable thnb and initial nd 3 3 to 5 4 2 e type resembling transitional and plume morbs slightly enriched ree patterns lower zrnb initial nd 3 1 to 4 5 in the largest and best studied allochthon the elbow athapapuskow assemblage mixing between depleted n morb and enriched oib sources or melts coupled with variable addition of a subduction lile component can explain the chemical variations in the basalts zircon u pb dates of 1904 ma for a syn volcanic diabase sill and 1901 6 5 ma for a gabbro peridotite cumulate complex demonstrate that crystallization of the ocean floor basalts overlapped with in part eruption of the tectonically juxtaposed 1 90 1 88 ga arc volcanic rocks the elbow athapapuskow allochthon is interpreted as back arc basin crust that developed simultaneously with flin flon arc magmatism subaerially erupted basalts that chemically resemble tholeiitic oibs 8 14 mgo relative hree depletion initial nd 2 2 to 3 4 occur in tectonic contact with the elbow athapapuskow assemblage the oibs may have been generated by deeper garnet residue melting of enriched mantle tapped during extension in the elbow athapapuskow back arc basin and were possibly erupted onto a remnant arc deeper mantle melting is also indicated by the presence of the lree enriched oceanic plateau like basalts of the sandy bay assemblage the back arc 01b and plateau volcanic assemblages were jux taposed against ca 1 9 ga arc assemblages in a philippines like intraoceanic accretionary complex by 1 87 ga

shoshonitic volcanism in the northern mariana arc 1 mineralogic and major and trace element characteristics petrographic and geochemical characteristics of samples dredged from 23 submarine volcanic edifices in the northern mariana and southern volcano arcs define two distinct rock series the central and northern mariana arc to 23 n and the northern volcano arc north of iwo jima are characterized by plagioclase clinopyroxene orthopyroxene titantomagnetite bearing subalkaline rocks including both low k and medium k series the northern mariana arc and southern volcano arc from 23 n to iwo jima are erupting rocks of a shoshonitic series with phenocrysts of plagioclase clinopyroxene olivine and biotite these rocks are less saturated than those of the subalkaline provinces and are substantially enriched in ba 400 900 ppm sr 600 1000 ppm k2o 1 4 5 and k2o na2o 0 4 1 2 relative to the subalkaline lavas ba y and ba zr increase by a factor of 3 to 4 in the shoshonitic rocks but k rb ba sr and k ba are relatively constant throughout the arc there is no relationship between degree of enrichment and volcano volume or degree of fractionation seamounts and islands within each province have the same range of compositions much of the intra edifice variation in lava composition can be modeled by 10 70 crystallization of plagioclase and clinopyroxene with smaller amounts of olivine orthopyroxene and titanomagnetite or by accumulation of 10 40 phenocrysts dominantly plagioclase the differences between parental lavas in the alkalic and subalkalic provinces require melting of two distinct mantle sources the occurrence of this enriched mantle in the northern marianas may be a consequence of the propagation of the mariana trough spreading center into the volcano arc

characterising and modelling the excavation damaged zone in crystalline rock in the context of radioactive waste disposal this paper describes current knowledge about the nature of and potential for thermo hydro mechanical chemical modelling of the excavation damaged zone edz around the excavations for an underground radioactive waste repository in the first part of the paper the disturbances associated with excavation are explained together with reviews of workshops that have been held on the subject in the second part of the paper the results of a decovalex demonstration of coupled models and their validation against experiment research funded by an international consortium of radioactive waste regulators and implementers http www decovalex com research programme on modelling the edz are presented four research teams used four different models to simulate the complete stress strain curve for avro granite from the swedish aspo hard rock laboratory subsequent research extended the work to computer simulation of the evolution of the repository using a wall block model and a near field model this included assessing the evolution of stress failure and permeability and time dependent effects during repository evolution as discussed all the computer models are well suited to sensitivity studies for evaluating the influence of their respective supporting parameters on the complete stress strain curve for rock and for modelling the edz

geophysical characterization of areas prone to quick clay landslides using radio magnetotelluric and seismic methods landslides attributed to quick clays have not only considerable influences on surface geomorphology they have caused delays in transportation systems environmental problems and human fatalities

shoshonites in southern tibet record late jurassic rifting of a tethyan intraoceanic island arc abstract detailed field mapping combined with a petrologic and geochemical investigation of the zedong terrane within the yarlung tsangpo suture zone provides insights to the evolution of now mostly subducted portions of tethys during the late jurassic the terrane is dominated by volcanic rocks of shoshonitic affinity which were erupted in a submarine oceanic island arc setting the volcanic island arc was built on a basement of oceanic crust and the shoshonites locally overlie a thin section of pillowed island arc tholeiites and red ribbon bedded radiolarian cherts geochemistry of the shoshonites suggests that their development occurred in a setting analogous to that of late miocene to early pliocene fiji and was associated with an arc rifting we speculate that this event may have been a far field response to developments associated with gondwana breakup

a 5 million year comparison of mg ca and alkenone paleothermometers geochemical sea surface temperature sst proxies such as the magnesium to calcium ratio mg ca in foraminifera and the alkenone unsaturation index uk 37 are becoming widely used in pre pleistocene climate records this study quantitatively compares previously published mg ca and uk 37 data from ocean drilling program odp site 847 in the eastern equatorial pacific to assess the utility of these proxies to reconstruct tropical sst over the last 5 ma foraminiferal mg ca sst calibrations that include a dissolution correction are most appropriate at this location because they provide sst estimates for the youngest sample that are close to modern mean annual sst the long term trends in the two records are remarkably similar and confirm a 3 5 c cooling trend from the early pliocene warm period to the late pleistocene noted in previous work absolute temperature estimates are similar for both proxies when errors in the dissolution correction used to estimate sst from mg ca are taken into account comparing the two sst records at odp site 847 to other records in the region shows that the eastern equatorial pacific was 2 4 c warmer during the early pliocene compared to today

timing and genesis of the adakitic and shoshonitic intrusions in the laoniushan complex southern margin of the north china craton implications for post collisional magmatism associated with the qinling orogen abstract the nww striking qinling orogen formed in the triassic by collision between the north china and yangtze cratons triassic granitoid intrusions mostly middle to high k calc alkaline are widespread in this orogen but contemporaneous intrusions are rare in the southern margin of the north china craton an area commonly considered as the hinterland belt of the orogen in this paper we report zircon u pb ages elemental geochemistry and sr nd hf isotope data for the laoniushan granitoid complex that was emplaced in the southern margin of the north china craton zircon u pb dating shows that the complex was emplaced in the late triassic 228 1 to 215 4 ma indicating that it is part of the post collisional magmatism in the qinling orogen the complex consists of from early to late biotite monzogranite quartz diorite quartz monzonite and hornblende monzonite which span a wide compositional range e g sio2 55 9 70 6 wt k2o na2o 6 6 10 2 wt and mg of 24 to 54 the biotite monzogranite has high al2o3 15 5 17 4 wt sr 396 1398 ppm and ba 1284 3993 ppm contents and relatively high la yb mostly 14 30 and sr y mostly 40 97 ratios but low yb mostly 1 3 1 6 ppm and y mostly14 19 ppm contents features typical of adakitic rocks the quartz monzonite hornblende monzonite and quartz diorite have a shoshonitic affinity with k2o up to 5 58 wt and k2o na2o ratios averaging 1 4 the rocks are characterized by strong lree hree fractionation in chondrite normalized ree pattern without obvious eu anomalies and show enrichment in large ion lithophile elements but depletion in high field strength elements nb ta ti the biotite monzogranite 228 ma has initial 87sr 86sr ratios of 0 7061 to 0 7067 end t values of 9 2 to 12 6 and ehf t values of 9 0 to 15 1 whereas the shoshonitic granitoids mainly 217 215 ma have similar initial 87sr 86sr ratios 0 7065 to 0 7075 but more radiogenic end t 12 4 to 17 0 and ehf t 14 1 to 17 0 the sr nd hf isotope data indicate that the rocks were likely generated by partial melting of an ancient lower continental crust with heterogeneous compositions as partly confirmed by the widespread presence of early paleoproterozoic inherited zircons mafic microgranular enclaves mmes characterized by fine grained igneous textures and an abundance of acicular apatites are common in the laoniushan complex compared with the host rocks they have lower sio2 48 6 53 7 wt and higher mg 51 56 cr 122 393 ppm and ni 24 79 ppm but equivalent sr nd isotope compositions indicating that the mmes likely originated from an ancient enriched lithospheric mantle the abundance of mmes in the granitoid intrusions suggest that magma mixing plays an important role in the generation of the laoniushan complex collectively it is suggested that the laoniushan complex was a product of post collisional magmatism related to lithospheric extension following slab break off formation of the adakitic and shoshonitic intrusions in the laoniushan complex indicates that the qinling orogen had evolved into a post collisional setting by about 230 210 ma