unexpected tunnelling volume losses in the westminster area london during construction of the running tunnels for the jubilee line extension london large variations in tunnelling volume loss were measured over about a 2 km distance between waterloo south of the thames and the area north of st james s park at the design stage a value of volume loss of 2 was adopted which was thought to be conservative in practice volume losses of greater than 3 were measured in westminster and in st james s park south of the lake north of the st james s park lake volume losses were less than 2 as expected reliable estimates of volume loss are required for the planning and approval of future tunnelling projects in london and so a detailed investigation was undertaken to establish the reasons for the observed differences two primary and interlinked causes for the large volume losses are identified first the method of tunnelling and construction control south of the lake up to 1 9 m of unsupported tunnel heading was often advanced ahead of the shield and as a result abo

a 15 000 year paleoenvironmental record from meiji seamount far northwestern pacific late glacial and holocene hemipelagic sediments from meiji seamount in the far northwest pacific contain common to abundant planktonic and benthic foraminifera for ams 14c dating for stable isotope analysis and for interpreting paleoclimate change we present here chronostratigraphic faunal and geochemical results from a piston core which indicate that during glacial times as young as 14 000 yrs bp the northwest pacific sea surface salinity was at least as low as today effectively inhibiting convective overturn between 12 000 and 13 000 yrs ago after a major flux of ice rafting there is faunal and 18o evidence of an abrupt decrease in surface ocean salinity coincident with this event was an increase in biological productivity shown by higher fluxes of calcium carbonate organic carbon opal and greater abundances and lower 13o of the benthic foraminifera uvigerina oxygen isotope ratios in uvigerina and cibicidoides show step like decreases at about 13 000 14 000 11 000 10 000 and 6000 8000 yrs bp these events may be analogous to steps in the north atlantic 18o record during meltwater events if this interpretation is correct then the temperature and salinity history of the deep pacific lags that of the north atlantic by about 1000 yrs consistent with the transport time of deep water from the north atlantic to the north pacific

quantitative resolution of eolian continental crustal material and volcanic detritus in north pacific surface sediment proxy records of continental climate and atmospheric circulation provided by analyses of eolian continental material extracted from marine sediment have resulted in significant new information concerning the behavior of these climate systems on various timescales these studies however currently are limited to certain geographic areas because no chemical or physical extraction procedure provides an unambiguous separation of eolian continental crustal material from other contaminants like volcanic detritus we employ a combined analytical and statistical procedure in an effort to extract a more refined eolian signal from areas that may be affected by volcanic detritus bulk surface sediment samples from 33 locations in the north pacific were treated using a conventional sequential extraction procedure to remove the carbonate silica and oxyhydroxide components and the residue was analyzed by instrumental neutron activation analysis inaa for la ce sm eu yb lu hf sc and th q mode factor analysis of these data shows that 99 of the variance is explained by two end members which we interpret to be continental crustal material and volcanic detritus five least squares normative analysis models were evaluated to estimate the relative amount of these end members in each sample the continental crustal component was approximated using a fine grained fraction of china loess and bulk loess the volcanic component was approximated using the compositions of average kurile kamchatka volcanic material a median ocean drilling program odp leg 145 ash and a median kurile basalt the model based on average kurile kamchatka volcanic material and the fine loess fraction gives the most accurate results central and east pacific samples typically contain up to 100 of the eolian continental crustal component while samples near japan kamchatka and the aleutians contain a majority of volcanic detritus however the highly variable composition of volcanic material can result in systematic errors up to 25 in samples dominated by volcanic detritus the geographic distribution of the compositional end members is consistent with a continental dust source originating in asia and being diluted by ash from the volcanic arcs of the pacific rim this improved identification and resolution of the eolian continental component realized in this approach should permit paleoclimatic reconstructions to be developed from sediments in significant portions of the world that were previously precluded from analysis because of limitations with chemical or physical extraction procedures

causes and implications of the middle rare earth element depletion in the eolian component of north pacific sediment abstract previous studies clearly demonstrate that the detrital fraction of central north pacific sediment is derived almost exclusively from wind born particles from the arid and semi arid regions in asia these conclusions are based in part on trajectories observed for westerly wind systems and on a grainsize distribution for central north pacific sediment which can only be explained by eolian transport these observations have been verified by comparing the mineralogy neodymium isotopic composition and trace element geochemistry of the sediment with its asian source region however recent geochemical investigations consistently highlight compositional differences exemplified by a mree middle rare earth element depletion and a lower th sc ratio in eolian material extracted from north pacific sediment when compared to bulk china loess the continental analog of the eolian material these geochemical differences persist even when the bulk loess is subjected to the same extraction procedure here we present experiments demonstrating that these compositional differences are caused by a combination of grainsize fractionation during transport and partial dissolution of ree and th bearing phosphatic phases during the extraction procedure two bulk loess samples from china were separated into several different grain size fractions and a split of each fraction was subjected to the extraction procedure commonly used to isolate terrigenous material from marine sediment all extracted and unextracted sample pairs were analyzed for p th sc fe la ce sm eu yb and lu the amount of p removed by the extraction procedure correlates well with both the observed mree depletion and the decrease in th sc and is most pronounced in the finest grained samples these correlations strongly suggest that the extraction procedure dissolves inorganic phosphate phases which are rich in mrees and th a comparison of the compositions of the 2 3 mm loess size fractions with central north pacific sediment shows that both of these materials are identical

tonnage cutoff model and average grade cutoff model for a single ore deposit abstract ore reserve estimation and resource prediction are important aspects of deposit exploration and mining the cutoff has great influence on the reserve and resource calculation despite this the study on the mathematical relationships of the tonnage average grade and cutoff is still scant according to the fractal distribution of element concentrations which are obtained from analysis of channel samples of constant length along exploration or mining works the tonnage cutoff and average grade cutoff models are constructed which are applicable in both exploration and operating mine environments via these models the relationships between ore tonnage metal tonnage and cutoff are obtained in terms of the fractal model of element concentrations moreover the thickness of the mineralized zone in each exploration or mining work follows a fractal model and assuming that the thickness is a continuous variable a model for calculating the mass of the mineralized zone in a single deposit is established given the mineralized zone mass the tonnage cutoff and average grade cutoff models can be utilized to calculate ore reserve and average grade especially when the cutoff changes a fault controlled disseminated and veinlet gold deposit in jiaodong gold province china is selected as a case study the estimates of the ore reserves obtained from these models are found to be consistent with the results obtained by the traditional geometric block method

zircon u pb and hf isotopic constraints on the onset time of india asia collision the time of initial collision between india and asia has been extremely controversial despite the fact that it is vital to constraining the orogenesis and subsequent evolution of the himalayas and tibetan plateau here we report u pb and hf isotope analysis of detrital zircons from two principal foreland basins that is the sangdanlin and gyangze basins respectively in the western and central parts of southern tibet our data suggest that asian derived clastic sediments started contributing to sedimentation on the indian continental margin earlier than generally thought at 60 ma in both basins near the yarlung zangbo suture zone in southern tibet no evidence for the existence of an intra oceanic arc within the neotethys is observed we conclude that 60 ma can be used to constrain the onset time of the india asia collision at least in central tibet after this initial collision closure of the neotethys propagated both westward and eastward with the final closure occurring at 50 and 45 ma in northwestern and eastern himalayas respectively our conclusion differs significantly from the previous view that the india asia collision may have started in northwestern himalaya and propagated eastward with diachronous suturing

analysis of tunnel excavation in london clay incorporating soil structure recent studies on london clay have identified a number of different units in the geological profile and have highlighted the role of soil structure in mechanical behaviour in fact structure is the dominant factor determining the differences in the mechanical response of different units in the paper numerical analyses simulating the undrained excavation of a tunnel in st james s park are presented london clay behaviour is characterised by a kinematic hardening structured soil model incorporating structure and stiffness degradation the parameters and initial conditions are based on a careful calibration that takes into account the presence of different units within the london clay formation and the different degrees of soil structure the analyses performed result in a very satisfactory reproduction of the magnitude and patterns of short term surface and subsurface displacements as well as pore pressures the paper concludes with a discussion of the results in the context of other analyses performed

correction to conjugate strike slip faulting along the bangong nujiang suture zone accommodates coeval east west extension and north south shortening in the interior of the tibetan plateau correction

asian dustfall in the st elias mountains yukon canada in april 2001 a major atmospheric dustfall event occurred in the st elias mountains yukon territory canada field samples were collected and analyzed for particle size mineralogy chemical composition and sr nd and pb isotopes dusts found above 3000 m had their source in the gobi desert region of northern china and inner mongolia and were transported to the yukon following a series of major dust storms that took place in early april dusts found below 3000 m had local yukon or mixed source s the asian dusts had a modal volume diameter of 4 m typical of far traveled mineral aerosols however larger 10 m particles were also found at 5000 m suggesting a very rapid trans pacific transport in the mid troposphere we estimate that the april 2001 event deposited from 5500 to 6335 tons of dust over an area of 21 000 km2 in the southwestern yukon most of which probably fell within a week our findings are consistent with instrumental observations and model simulations of the april 2001 event while the dust cloud was reportedly mixed with volatile pollutants from asia we found no evidence of metal pollution associated with the dustfall in the yukon our findings contribute to clarify the dynamics and the geochemical impact of asian dust long range transport events and to better estimate eolian fluxes of dustborne elements e g fe to the ocean associated with such events they may also assist in identifying past asian dust events in ice cores drilled from the st elias mountains icefields to develop a long term record of their frequency magnitude and source s

correlation between mineralization intensity and fluid rock reaction in the xinli gold deposit jiaodong peninsula china constraints from petrographic and statistical approaches abstract the jiaodong peninsula the most productive gold province in china is dominated by jiaojia type gold deposits that formed at ca 120 ma the deposits are characterized by widespread alteration and mineralization resulted from fluid rock reactions in the footwall of regional faults it is known that the interrupted appearance of continuous mineralization zones and barren zones along regional faults is controlled by changes in the dip direction and dip angle of these faults which can cause local dilational sense in the continuous mineralization zone intensive fluid rock reactions occurred yet whether and how the fluid rock reaction impacted on the mineralization intensity are not well constrained in this study we selected the xinli jiaojia type gold deposit associated sanshandao cangshang fault located on the northwest margin of the jiaodong peninsula to examine in detail the distribution of orebody parameters and to observe the mineralization occurrences we applied the number size fractal model and the lacunarity method to quantify the distribution of gold concentration along drifts with the goal of clarifying the ambiguities noted above the drifts in continuous mineralization zones can be divided into stable and unstable types according to lateral changes in the dip direction and dip angle of the sanshandao cangshang fault stable and unstable drifts share several common features 1 statistical results show that changes in the dip direction and dip angle of this fault bear almost no relationship to the thickness or grade thickness of the orebody 2 mineralization along drifts is most intense at some distance from the fault plane rather than at locations immediately adjacent to the fault plane where fracturing is most extensive and according to fluid infiltration theory would be the most likely regions of intense mineralization 3 gold bearing sulfide pods and veinlets in the alteration zone commonly possess irregular and corroded boundaries that are considered to be an indicator of fluid rock reactions 4 the threshold the gold concentration that divides a segment with a lower fractal dimension in a lower concentration range from one with a higher fractal dimension in a higher concentration range and the lacunarity the parameter that evaluates the evenness of high gold concentration distribution show positive and negative relationships respectively to the thickness and grade thickness of a drift we thereby argue on the basis of these features that fluid rock reactions were an important factor responsible for the mineralization upgrade in continuous mineralization zones an increase in the threshold and a decrease in the lacunarity indicate that fluid rock reactions causing gold precipitation are more intensive and more evenly distributed throughout the footwall for better mineralization these phenomena suggest that fluid rock reactions responsible for the gold precipitation possibly own the characteristics of spatial self organization mechanism which is widely developed in various geological fluid rock reaction processes

dust transport from non east asian sources to the north pacific 1 it is generally thought that east asia dominates the supply of eolian dust to the north pacific here we show the first data based evidence of dust primarily from non east asian sources even during march 2010 when a super dust storm from east asia struck the western pacific chemical characteristics of aerosol samples collected at a high mountain site in taiwan show variable inputs from eolian dust and biomass burning from backward trajectory analyses satellite observation and model simulation dust origins can be traced to the middle east and north africa suggesting an integrated source from the global dust belt our global model results demonstrate that dust deposition in the north pacific is primarily contributed by non east asian sources with an eastward decrease along the westerlies

neodymium isotopic variations in north pacific modern silicate sediment and the insignificance of detrital ree contributions to seawater the neodymium isotopic composition of the silicate fraction of holocene pelagic sediments from the north pacific define two provinces a central north pacific province characterized by unradiogenic and remarkably homogeneous end 10 2 0 5 and a narrow circum pacific marginal province characterized by more radiogenic and variable end 4 2 3 8 the silicate fraction in the central north pacific is exclusively eolian based on prevailing wind patterns meteorological data and neodymium isotopic data the only significant sediment source is chinese loess leaching experiments on chinese loess confirm that leachable nd is isotopically indistinguishable from bulk and residual silicate nd silicates in the circum north pacific marginal province comprise eolian loess volcanic ash and hemipelagic sediments derived from volcanic arcs a compilation of pacific seawater and mn nodule end data shows no clear spatial variation except for a general decrease from surface to deep waters from 3 to 4 and slightly lower end in bottom waters along the western north pacific due to the incursion of antarctic bottom water the relative homogeneity of bottom water end which contrasts sharply with the distinctive variation in sediment end plus the large difference between the average end of bottom waters and the central north pacific eolian silicates 4 vs 10 suggests that any contribution of ree to seawater from eolian materials is insignificant furthermore leaching of ree from eolian particles as they sink though the water column must be insignificant because nd in shallow waters is more radiogenic than nd in deeper waters that there is no contrast in the nd isotopic composition of bottom waters that overlie the central and marginal sediment provinces suggests that the ash and hemipelagic sediments derived from pacific rim volcanic arcs also contribute minimal ree to seawater the elimination of eolian ash and hemipelagic sediments leaves only near shore riverine particulates as a possibly significant particulate source of ree to seawater

geotechnical variation of london clay across central london the paper presents classification and stress path test results from various sites across central london and focuses on interpreting the observed behaviour within the context of the geology and geo

4he as a tracer of continental dust a 1 9 million year record of aeolian flux to the west equatorial pacific ocean the mass accumulation rates mars of aeolian dust in the ocean basins provide an important record of climate in the continental source regions of atmospheric dust and of the prevailing wind patterns responsible for dust transport in the geologic past the incorporation of other terrigenous components such as volcanic ashes in seafloor sediments however often obscures the aeolian dust record we describe a new approach which uses the delivery rate of crustal 4he to seafloor sediments as a proxy for the mass accumulation rate of old continental dust which is unaffected by the addition of other terrigenous components we have determined the flux of crustal 4he delivered to the seafloor of the ontong java plateau ojp in the western equatorial pacific over the last 1 9 myrs crustal 4he fluxes vary between 7 7 and 30 ncc cm 2 kyr 1 and show excellent correlation with global climate as recorded by oxygen isotopes with high crustal 4he fluxes associated with glacial periods over the entire interval studied furthermore the onset of strong 100 kyr glacial interglacial climate cycling is clearly seen in the 4he flux record about 700 kyrs ago these data record variations in the supply of asian dust in response to climate driven changes in the aridity of the asian dust sources consistent with earlier work on asian dust flux to the northern pacific ocean however in contrast to previous studies of sites in the central and eastern equatorial pacific ocean there is no evidence that the inter tropical convergence zone an effective rainfall barrier to the southward transport of northern hemisphere dust across the equator in the central and eastern pacific has influenced the delivery of asian dust to the ojp the most likely carrier phase for crustal helium in these sediments is zircon which can reasonably account for all the 4he observed in the samples as a first order estimate these results suggest that the mass accumulation rate of asian dust on the ojp over the last 1 9 myrs varied from about 4 to 15 mg cm 2 kyr 1 in contrast previous studies show that over the same interval the total mar of terrigenous dust i e asian dust plus local volcanics on ojp varied between about 34 and 90 mg cm 2 kyr 1

genesis of the bangbu gold deposit in the southern tibet evidenced from in situ sulfur isotopes and trace element compositions of pyrite abstract the bangbu orogenic gold deposit in the north himalaya of the southern tibet contains more than 40 t au at an average grade of 7 0 g t in this deposits gold bearing quartz veins were controlled by nearly e trending qusong cuogu zhemulang shear zone and occurred within the secondary faults which crosscut late triassic greenschist facies rocks to further understand the sulfur source and ore forming process we have conducted a compressive study of in situ sims sulfur isotopes and la icp ms trace element compositions of two stages of pyrite at bangbu early stage pyrite py1 is coarse grained mostly 0 2 2 mm and euhedral and has gold concentrations of less than 0 3 54 ppm mean of 20 ppm and 34s values of 1 6 5 1 mean of 3 2 late stage pyrite py2 is generally fine grained mostly

mid eocene high sr y granites in the northern himalayan gneiss domes melting thickened lower continental crust abstract within the himalayan collisional belt granotoids occur along two sub parallel belts the northern himalayan gneiss domes nhgd and the high himalayan crystalline series hhcs in the yardoi area of nhgd two mica granite a new type granite occurs in the core of the yardoi gneiss dome ygd dala and quedang from north to south and extends at least 50 km long these granites have similar mineral composition elemental and radiogenic isotope geochemistry and age of formation shrimp zircon u pb dating indicates that the yardoi and the quedang two mica granites formed at 42 6 1 1 ma and 42 8 0 6 ma respectively similar to the dala pluton these two mica granites have 1 high sio2 68 wt al2o3 15 wt and a cnk 1 0 2 relatively high sr and lree but low y 40 and up to 250 and la yb 30 4 very weak or no eu anomalies and 5 as compared with those in the himalayan leucogranites low initial sr 87sr 86sr i

a comparison study of the c a and s a models with singularity analysis to identify geochemical anomalies in covered areas abstract fractal multifractal modeling of geochemical data is an interesting topic in the field of applied geochemistry identification of weak anomalies for mineral exploration in covered areas is one of the most challenging tasks for utilization of geochemical data in this study three fractal models consisting of the concentration area c a spectrum area s a and singularity index models were applied to identify geochemical anomalies in the covered area located in the chaobuleng fe polymetallic district inner mongolia china the results show that 1 the grassland cover weakens the concentrations of geochemical elements 2 the c a model has a limitation to identify weak anomalies in covered areas 3 the s a model is a powerful tool to decompose mixed geochemical patterns into a geochemical anomaly map and a varied geochemical background map but suffers edge effects in an irregular shaped study area and 4 the singularity index is a useful tool to identify weak geochemical anomalies

asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean rea d k and leinen m 1988 asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean palaeogeogr palaeoclimatol palaeoecol 66 1 8 a 30 000 year record of eolian deposition in the northwestern pacific ocean provides a history of the aridity of the asian source region and information on the changing latitude and intensity of the zonal westerlies the position of the maximum in eolian flux to the deep sea remained unchanged at 38 to 40 n during this entire time period but the dust flux record of aridity is greatest 6000 years ago at the holocene climatic optimum eolian grainsize data indicate that the northern margin of the westerly jet stream retreated northward during the holocene to a poleward extreme at about 6000 years ago and then moved back toward the equator the change in wind intensity across this margin was continually reduced throughout the holocene these sorts of data enhance our understanding of the behavior of the atmosphere during times of climate change and can be used to test computer generated models of past climatic conditions

a multifractal analysis of mineralization characteristics of the dayingezhuang disseminated veinlet gold deposit in the jiaodong gold province of china abstract the gold concentration distributions along drifts in the dayingezhuang fault controlled disseminated veinlet gold deposit in the jiaodong gold province eastern china has been analyzed using a multifractal technique with the aim of better understanding the ore forming processes some intensely mineralized areas show small gold singularities representing compact concentration distributions which is resulted from intense stress release and development of abundant microfractures with various sizes several intensely and moderately mineralized areas are characterized by isolated distributions of lower concentrations suggesting that only relatively large microfractures locally develop resulted from less intense stress release some barely and moderately mineralized areas show isolated distributions of higher concentrations due to occurrences of only a few fractures or large microfracture most barely mineralized areas are characterized by dense concentrations distributions because the widespread development of relatively small microfractures caused by weak stress release thus making the areas unsuitable for gold deposition these characteristics reflect that variable development of the structures is responsible for different gold mineralization within the deposit the ratios between the singularity a q and its fractal dimension f a q for the different drifts vary similarly as q 0 8 or q 0 8 thus from the multifractal viewpoint it is suggested that gold enrichment processes are consistent in both mineralized and barely mineralized areas despite their differing mineral intensities

quantifying lithogenic inputs to the north pacific ocean using the long lived thorium isotopes abstract dissolved 232th is added to the ocean though the partial dissolution of lithogenic materials such as aerosol dust in the same way as other lithogenically sourced and more biologically important trace metals such as fe oceanic 230th on the other hand is sourced primarily from the highly predictable decay of dissolved 234u the rate at which dissolved 232th is released by mineral dissolution can be constrained by a th removal rate derived from 230th 234u disequilibria assuming steady state calculated fluxes of dissolved 232th can in turn be used to estimate fluxes of other lithogenically sourced dissolved metals as well as the original lithogenic supplies such as aerosol dust deposition given the concentration and fractional solubility of th or other metals in the lithogenic material this method is applied to 7 water column profiles from the innovative north pacific experiment inopex cruise of 2009 and 2 sites from the subtropical north pacific the structure of shallow depth profiles suggests rapid scavenging at the surface and at least partial regeneration of dissolved 232th at 100 200 m depth this rapid cycling could involve colloidal th generated during mineral dissolution which may not be subject to the same removal rates as the more truly dissolved 230th an additional deep source of 232th was revealed in deep waters most likely dissolution of seafloor sediments and offers a constraint on dissolved trace element supply due to boundary exchange

equatorial pacific productivity and dust flux during the mid pleistocene climate transition received 6 may 2005 revised 30 august 2005 accepted 19 september 2005 published 17 december 2005 1 we present a helium isotope record for core tt013 114pc from the central equatorial pacific 140 w 4 n 4432 m water depth spanning a period of 1 million years we focus on the time interval from 560 to 800 kyr largely coinciding with the mid pleistocene climate transition mpt when the dominant period of the earth s climate variability shifted from 41 kyr to 100 kyr the terrigenous 4 he concentrations from our study correlate very well with published titanium concentrations in this core strongly supporting the use of terrigenous 4 he as a monitor of continental dust normalizing titanium and terrigenous 4 he concentrations to 3 he suggests that the dust supply during the mpt was approximately 30 lower compared to the subsequent period 560 100 kyr the 3 he normalized barium aluminum and phosphorus concentrations trace elements with a predominantly biogenic source in these sediments are relatively constant this is in contrast to previous studies that reported an apparent rise of titanium normalized productivity proxies rather than a significant increase in productivity during the mpt we conclude that the dust flux to the central equatorial pacific was reduced and that the export productivity was approximately constant during this period of climate reorganization

improved provenance tracing of asian dust sources using rare earth elements and selected trace elements for palaeomonsoon studies on the eastern tibetan plateau abstract the asian monsoon forms an important part of the earth s climate system yet our understanding of the past interactions between its different sub systems the east asian and indian monsoons and between monsoonal winds and other prevailing wind currents such as the westerly jet is limited particularly in central asia this in turn affects our ability to develop climate models capable of accurately predicting future changes in atmospheric circulation patterns and monsoon intensities in asia provenance studies of mineral dust deposited in terrestrial settings such as peat bogs can address this problem directly by offering the possibility to examine past deposition rates and wind direction and hence reconstruct past atmospheric circulation patterns however such studies are challenged by several issues most importantly the identification of proxies that unambiguously distinguish between the different potential dust sources and that are independent of particle size in addition a single analytical method that is suitable for sample preparation of both dust source i e desert sand soil and receptor i e dust archive such as peat or soil profiles material is desirable in order to minimize error propagation derived from the experimental and analytical work here an improved geochemical framework of provenance tracers to study atmospheric circulation patterns and palaeomonsoon variability in central asia is provided by combining for the first time mineralogical as well as major and trace elemental sc y th and the rare earth elements information on chinese central chinese loess plateau northern qaidam basin and taklamakan badain juran and tengger deserts indian thar desert and tibetan eastern qinghai tibetan plateau dust sources quartz feldspars and clay minerals are the major constituents of all studied sources with highly variable calcite contents reflected in the cao concentrations chinese and tibetan dust sources are enriched in middle ree relative to the upper continental crust and average shale but the thar desert has a ree signature distinctly different from all other dust sources there are significant differences in major trace and ree compositions between the coarse and fine fractions of the surface sands with the finest 2 o 3 fe 2 o 3 mno mgo and k 2 o and the all ree normalized to post archean australian shale paas are particle size independent tracers of which combinations of y ree la yb y tb y la and eu eu can be used to distinguish the thar desert the chinese deserts the chinese loess plateau and the tibetan soils their independence upon grain size means that these tracers can be applied to the long range provenance tracing of asian dust even when only bulk samples are available in the source region combinations of la th y tb y ree sc la and y er distinguish the tibetan soils from the chinese loess plateau and the chinese deserts la th and notably th ree isolate the signature of the badain juran desert and the combination of sc la and y er that of the taklamakan desert the similarity in all trace and ree based provenance tracers between the northern qaidam basin and tengger desert suggests that these two deposits may have a common aeolian source

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

regional patterns of pleistocene ice rafted debris flux in the north pacific ird mass accumulation rate mar records are presented for deep sea drilling project site 580 and ocean drilling program sites 882 and 887 and are combined with results from previous ird mar studies to provide a synthesis of north pacific pleistocene ice rafting important regional differences in the ice rafting histories of the nw and ne pacific are highlighted by this synthesis and include 1 significant variations in ird fluxes across the north pacific which identify two major ird sources coastal alaska and coastal siberia kamchatka peninsula and 2 significant variations in the timing of ird supply across the north pacific particularly in response to global scale climatic forcing these regional differences indicate that local and regional controls on iceberg input transport and melting exert a major influence on ice rafting throughout the north pacific this suggests that a single generalized ice rafting record for the north pacific does not adequately describe the complexity of this basin s pleistocene history data used to calculate lsrs and ird mars for sites 380 882 and 887 are available on diskette or via anonymous ftp from kosmos agu org directory apend usemame anonymous password guest diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 or by phone at 800 966 2481 15 00 payment must accompany order

sedimentary history of the tethyan basin in the tibetan himalayas after an epicontinental phase the sedimentary rocks in the tibetan himalayas document a complete wilson cycle of the neo tethyan tethys ill evolution between the gondwana supercontinent and its northward drifting margin lhasa block from the late permian to the eocene during the triassic rift stage the basin was filled with a huge clastic dominated sediment wedge with up to 5 000 m of flysch in the northern zone widespread deltaic clastics and shallow water carbonates of late norian to earliest jurassic age in the southern zone mark in conjunction with decreasing tectonic subsidence the transition to the drift stage some 4 500 m of jurassic and early cretaceous shallow water carbonates and siliciclastics accumulated on the tethyan indian passive margin deepening upward sequences with condensed beds at their tops alternate with repeated progradational packages of shelf sediments extensive abyssal sediments with basaltic volcanics in the northern deep water zone reflect continued ocean spreading and thermal subsidence paleomagnetic data gained separately for the northern indian plate and the lhasa block indicate that the neo tethys reached its maximum width about 110 ma ago with a spreading rate of 4 8 cm year before it commenced to close again during the remnant basin stage in the late cretaceous and paleogene a shallowing upward megasequence capped by a carbonate platform developed in the southern inner shelf realm in the northern slope basin plain zone turbidites and chaotic sediments derived from both the acretionary wedge and the steepening slope of the passive margin accumulated the depositional center of the remnant basin shifted southward as a result of flexural subsidence and southward overthrusting the sediments from the triassic to the paleogene are tentatively subdivided into five mega sequences which are controlled mainly by regional tectonics climatic influence e g carbonate deposition due to northward plate motion is partially subdued by terrigenous input and or increased water depth during the oligocene and miocene crustal shortening led to rapid uplift and the deposition of fluvial molasse in limited basins

a kinematic hardening constitutive model for natural clays with loss of structure a rate independent constitutive model for natural clays is presented formulated within the framework of kinematic hardening with elements of bounding surface plasticity the modelling framework is intended to include effects of damage to structure caused by irrecoverable plastic strains caused by sampling laboratory testing or geotechnical loading the incorporation of a structure measure allows the size of the bounding surface to decay with plastic deformations this model can be seen as a logical extension from the cam clay model the steady fall of stiffness with strain towards the cam clay value is controlled by a particular interpolation function this ensures a smooth degree of approach between a kinematically hardening bubble which is the boundary of the elastic region and the bounding surface during their relative translation with stress history the model describes the essential phenomena of pre failure behaviour of natural clays stiffness variation with strain volumetric change accompanyi

quaternary extension in southern tibet field observations and tectonic implications we summarize evidence for quaternary and active faulting collected in the field during three sino french expeditions to southeastern tibet 1980 1982 detailed mapping of quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the himalayas in the last 2 0 5 m y the maximum horizontal principal stress in south tibet appears to be only the intermediate principal stress 2 1 being vertical south of the chord joining the eastern and western syntaxes of the himalayan arc extensional strains are principally localized within seven regularly spaced rift zones three of which have been studied in some detail the extension direction is determined to be n96 e 7 mainly from statistical averaging of strikes of newly formed normal faults throw rates on normal faults are evaluated for different time spans 2 0 5 m y 60 40 kyr and 10 2 kyr b p using structural and topographic reliefs as well as synglacial and postglacial vertical offsets the rate of quaternary extension is about 1 m y 1 along an 1100 km long ese traverse across south tibet this corresponds to a spreading rate of 1 0 6 cm yr this rate and the divergent horizontal projections of slip vectors of earthquakes along the himalayan front constrain the rate at which rigid india underthrusts southern tibet to be 2 1 cm yr although most of the normal faults appear to be independent of and nearly orthogonal to the e w mesozoic tertiary tectonic fabric the yadong gulu rift appears to be guided for over 130 km by the older oblique ne sw nyainqentanglha range and fault zones along it this reactivated zone is the most prominent left lateral strike slip fault system in se tibet excepting this zone and the vicinity of the se extremity of the karakorum fault quaternary strike slip faulting is rare in south tibet i e south of the chord between the syntaxes of the himalayan arc north of the chord the tectonic style is different there minor conjugate strike slip faulting is widespread and appears to control quaternary normal faulting which is more diffuse and subdued than in south tibet along the chord the presence of a major zone of active right lateral en echelon strike slip faults karakorum jiali fault zone probably reflects the greater facility of eastward extrusion in north central tibet in response to the northward push of india the eastern himalayan syntaxis may be an obstacle to such extrusion movements south of the chord

dust deposition to the surface waters of the western and central north pacific inferred from surface water dissolved aluminum concentrations 1 dissolved al was determined on similar to 3500 surface water samples collected in the nw pacific during the 2002 intergovernmental oceanographic commission ioc contaminant baseline survey in addition dissolved al was determined on samples collected at 9 vertical stations occupied along the cruise track surface water al distributions when converted to annual mineral dust deposition measures and brown 1996 imply extremely low depositions mean values 0 3 g m 2 yr 1 to surface waters of the subarctic gyre despite the atmospheric transport of large amounts of mineral dust across this region from the desert regions of china the calculated deposition values are also much lower than the 1 10 g m 2 yr 1 predicted for this region by the gesamp model duce et al 1991 the lowest mineral dust depositions correspond to the high nutrient low chlorophyll hnlc region of the nw pacific which implies that the biogeochemical status of this region is the result of low atmospheric micronutrient input similar to other hnlc regions in the subtropical gyre the al derived dust deposition mean values 0 1 0 6 g m 2 yr 1 agrees well with the 1 g m 2 yr 1 predictions of the gesamp model enriched concentrations of dissolved al in the coastal waters near kauai from fluvial sources indicate the potential role of remote high islands in adding reactive trace elements to the nearby surface waters in the vertical profiles elevated dissolved al concentrations 4 8 nm were found to correspond to the potential density of the western pacific subtropical mode waters which form in the recirculation zone of the kuroshio

the stiffness of natural london clay an investigation of natural london clay is reported involving advanced triaxial hollow cylinder apparatus hca and dynamic testing techniques significant anisotropy was revealed at all scales of deformation and the framework of cross anisotropic elasticity was found to apply broadly to the initial elastic behaviour the stiffness parameters obtained by independent techniques generally exhibited good agreement with the greatest deviation being seen in the poisson s ratios which fell far from the values usually assumed in conventional foundation analysis probing tests established the limits to the elastic domain over a range of depths showing that these scaled in proportion to the mean effective stress level as did those of a second kinematic surface that surrounded the elastic domain once engaged this second surface signified a new pattern of strain increment directions faster elastic plastic stiffness decay with strain and also a greater dependence of behaviour on recent stress history howev

geochronology and petrogenesis of miocene granitic intrusions related to the zhibula cu skarn deposit in the gangdese belt southern tibet abstract the zhibula cu skarn deposit 19 5 mt ore 1 64 near the qulong porphyry cu mo deposit is located in the gangdese porphyry copper belt in southern tibet the deposit is a typical metasomatic skarn that is related to the interaction of magmatic hydrothermal fluids and calcareous host rocks stratiform skarn orebodies are mainly distributed in the contact between tuff and marble in the lower part of the jurassic yeba formation endoskarn zonations for an outward trend are observed in the granodiorite which grade from a fresh granodiorite to a weakly chlorite altered granodiorite a green diopside bearing granodiorite and a dark red brown garnet bearing granodiorite the zhibula granodiorite and monzogranite have similar secondary ion mass spectrometry sims zircon u pb ages of 16 9 0 3 ma and 17 0 0 2 ma respectively they exhibit different fractional crystallization from granodiorite sio 2 64 8 69 3 wt to monzogranite sio 2 72 3 76 8 wt both the granodiorite and monzogranite are characterized by high al 2 o 3 12 6 16 7 wt and k 2 o 1 5 5 5 wt contents high sr y 35 151 and la yb 19 48 ratios and variable mgo 0 16 3 91 and mg 31 61 values they display features of enrichment in large ion lithophile elements liles e g rb ba sr and k depletion in high field strength elements hfses e g nb ta ti and p and moderate negative eu anomalies eu 0 58 0 98 they show restricted in situ zircon hf isotopic compositions 6 7 to 8 8 only one sample is 4 5 and consistent 18 o values 6 0 to 6 6 the geochemical data indicated that the miocene zhibula granitic intrusions formed by the magma that were characterized by high sr y ratios and were derived from the partial melting of the thickened juvenile lower crust which may have been metasomatized by the slab melts during subduction of the neo tethyan oceanic crust and were induced by the convective removal of the thickened lithosphere in addition the zhibula cu skarn deposit and the qulong cu mo deposit form a significant porphyry skarn ore system

the identification of the guqiong orogenic ag au polymetallic deposit in southern tibet evidences from mineralogy geochronology and fluid evolution abstract guqiong is an ag au polymetallic deposit located in the eastern part of the au sb ore belt along the indus yarlung zangbo suture in the north himalaya in this study we have identified three major alteration mineralization stages for guqiong based on the mineral assemblages and their paragenetic relationships namely the i pre ore alteration forming mainly ore barren thick quartz veins and vuggy quartz ii main ore stage that comprises quartz veins with sulfide mineralization including ag au bearing minerals in this stage sericite occurs closely associated with sulfides iii the post ore stage characterized by the formation of calcite and quartz with trace sulfides fluid inclusion assemblage fia microthermometry was conducted on barren and mineralized quartz and sphalerite three types of inclusions are identified based on their petrographic features and laser raman spectra i e the pure carbonic pc aqueous carbonic three phase c1 and two phase c2 and aqueous w types the fias in stage i ore barren quartz are mainly pc type and c1 type which are characterized by being high temperatures 260 to 300 c low salinities 0 8 to 3 5 wt nacl eqv and with abundant co2 sphalerite of main ore stage contains mainly w type with limited c2 type of low temperatures 158 to 180 c and medium salinities 5 6 to 6 7 wt nacl eqv meanwhile the fia in mineralized quartz is featured by the general coexistence of c2 type and w type with local pc type and c1 type inclusions the fluid system may have been a mixture of the two aforementioned fluids in barren quartz and sphalerite as indicated by two significantly different fias c type and w type with contrasting homogenization temperatures 260 to 290 c and 180 to 220 c respectively but comparable salinities 0 2 to 8 2 and 0 2 to 8 1 wt nacl eqv respectively the fluid d 18o and 13c values of the main ore stage quartz are 172 to 114 8 8 to 13 1 and 13 4 to 7 7 respectively the negative 13c values are interpreted as devolatilization products of biogenic carbon with a metamorphic origin while the d and 18o values likely reflect meteoric water involvement into metamorphic fluids we propose that fluid mixing had occurred and caused sulfide precipitation at the main ore stage additionally the estimated fluid trapping depth of 5 to 6 km obtained using 3 d phase diagram is consistent with the formation depth of many orogenic type deposits worldwide 40ar 39ar dating on sericite yielded a well defined plateau age of 42 03 0 42 ma with normal and inverse isochron ages of 42 8 1 6 ma and 42 9 1 9 ma respectively these ages bracket the ag au mineralization at guqiong place it in the main stage india asia collision and further support its orogenic type origin

glacial interglacial sediment transport to the meiji drift northwest pacific ocean evidence for timing of beringian outwashing abstract a large sediment deposit known as the meiji drift located in the northwestern pacific ocean is thought to have formed from deep water exiting the bering sea although no notable deep water forms there presently we determine the terrigenous sources since 140 ka to the drift using bulk sediment 40ar 39ar and nd isotopic analyses on the silt sized 20 63 m terrigenous fraction from ocean drilling program odp site 884 to reconstruct paleo circulation patterns there are large changes in both isotopic tracers varying on glacial interglacial cycles during glacial intervals bulk sediment 40ar 39ar ages range between 40 and 80 ma while nd isotopic values range from end 1 to 2 during interglacial intervals sediments become much younger and more radiogenic with bulk sediment ages falling to 2 15 ma and nd isotopic values ranging between end 5 and 9 these data and quantitative comparison to potential source rocks indicate that the young kamchatkan and aleutian arcs lying nw and ne of the meiji drift contribute the majority of sediment during interglacials conversely older source rocks such as those drained by the yukon river and northeast russia are the dominant origin of sediments during glacials mixing model calculations suggest that as much as 35 45 of the sediment deposited in the meiji drift during glacials is from the bering sea it remains unclear whether thermohaline type circulation or focussing of bering sea flow lead to the glacial interglacial sediment source changes observed here

tectonics of the northern himalaya since the india asia collision abstract the india asia collision resulted in the construction of the vast himalayan orogen the northern himalayan domain began to experience extensional tectonics since eocene oligocene transition eot when the himalayan orogeny was still in progress major structures generated by the extension in the northern himalaya include the south tibet detachment system stds the north himalayan gneiss domes nhgd and the north south trending rifts nstr the earliest emplacement of syn deformational leucogranite at 36 32 ma along the stds marks the initial transformation from thickening to thinning in the northern himalayan domain at eot the thickening before eot caused crustal partial melting which formed the weak root of the thickened orogen or the so called channel flow this channel flow triggered the collapse of the orogen extrusion of the greater himalayan crystalline complex ghc and the onset of extensional tectonics of the stds the similarities in tectono thermal history and geochemistry of rocks between the stds and nhgd suggest that the formation of the nhgd has a direct relationship to the activity of the stds the extension of stds and the resultant thinning caused further partial melting of the crust leading to the larger scale emplacement of leucogranite during miocene 27 13 ma diapirism of these plutons shaped the domes in nhgd exposing the ghc and the shear zones of the stds in the northern himalaya in gyirong another tectonic transform from extension to shortening occurred after 18 7 ma in dinggye region the stds was offset by the nstr culminating the deformation at 13 ma when the nstr began to be active this indicates another tectonic transform in the northern himalaya at 13 ma when the n s extension of the stds ceased and gave way to e w extension of the nstr marking the end of the peak granitic magmatism in northern himalaya multiple episodes of deformation in the major structures such as the stds mct and nstr and superposition of different structures indicate a multiphase orogenic process in the himalayas in which mountain building and collapse occurred alternately with the formation of nstr and conjugate shear zones in tibet this tectonic scenario was possibly controlled by the india asia convergent rate we propose that the extension was an integral part of the orogenic process rather than a simple marker of the culmination of the orogeny

paleonutrient and productivity records from the subarctic north pacific for pleistocene glacial terminations i to v our study addresses fundamental questions of the mode and timing of orbital and millennial scale changes in the meridional overturning circulation moc of the subarctic north pacific particular concerns are the vertical mixing the present and past abundance of nutrients in surface waters despite strong stratification and the north pacific north atlantic seesaw of oscillations in sea surface temperature sst we do this by generating and interpreting multiple records for glacial terminations i v down two long piston cores one each from the western and eastern subarctic pacific chlorins and biogenic opal are proxies for surface water productivity delta 13 c of epibenthic foraminifera is a record of deepwater ventilation and the delta 13 c of n pachyderma sin is a tracer of nutrients in subsurface waters that extend up to the sea surface during times of vertical mixing the degree of mixing is traced by pairing sst and delta 18 o records of planktic surface and subsurface pycnocline dwellers tight age control is deduced from a suite of age calibrated 14 c plateau boundaries for termination i and benthic delta 18 o and geomagnetic events for the last 800 ka carbon 14 paleoreservoir ages record the ages of surface and deep waters to uncover short term changes in moc over termination i we have defined a standard sequence of short term productivity events for termination i also evident during terminations ii to v and subsequent interglacials over the last 450 ka the peak glacial regime of stable stratification and low productivity terminated together with the end of ice rafting and melting near 17 ka similar to 2000 years after the onset of termination i pulses of vertical mixing and incursion of warm surface waters from the subtropics followed convected young water masses finally penetrated down to 3600 m water depth at 17 0 to less than 14 5 ka significantly improving bottom water ventilation through the late deglacial and earliest interglacial mixing with upwelled nutrients from the pycnocline induced short term maxima in algal production of chlorins and biogenic opal near 17 15 and 15 12 ka respectively deglacial meltwater incursions in the aleutian current and silica input from north american rivers also promoted east pacific productivity after 15 5 ka productivity decreased during the late deglacial and early interglacial coeval with an exceptional peak in caco 3 preservation caused by both low organic flux and well ventilated deepwater subsequently low salinity and cool surface waters and in turn stratification were gradually restored a second opal dominated productivity maximum marked the ends of interglacials the deglacial pulses of vertical mixing around 17 11 ka imply an important contribution of the north pacific to the coeval release of oceanic co 2 into the atmosphere and support the east west seesaw model of climate change

the use of kinematic hardening models for predicting tunnelling induced ground movements in london clay the use of a kinematic hardening soil model for predicting short and long term ground movements due to tunnelling in london clay is investigated the model is calibrated against oedometer and triaxial tests on intact samples from different units of the london clay the calibrated model is then used in finite element analysis to simulate the field response at st james s park during excavation of the jubilee line extension tunnels the finite element predictions compare well with the available field monitoring data the importance of using consistent initial conditions for this complex boundary value problem in conjunction with the model parameters selected is highlighted the stiffness response of different regions of the finite element mesh indicates that the rate at which the stiffness degrades and the stiffness response further away from the tunnel boundary affect the short term predictions significantly the long term predictions confirm that the compression characteristics of the soil control the mag

grain size distribution and depositional processes of the mineral component of abyssal sediments lessons from the north pacific grain size analyses of the mineral component of abyssal pacific surface sediments show two distinctly different size distributions that can be associated with sediments that are dominantly eolian and dominantly hemipelagic respectively in the range of 1 to 30 m eolian grains show a distinct size mode at about 2 m 9 and little material coarser than about 16 m 6 hemipelagic grains are characterized by a much flatter size distribution that has a broad size mode near 2 m 9 and important amounts of material coarser than 16 m 6 this ability to distinguish between hemipelagic and eolian grains will obviate some long standing concerns in the interpretation of deep sea sediments examples of the utility of this technique are given for the north pacific and south atlantic

statistical analysis of lake sediment geochemical data for understanding surface geological factors and processes an example from amazonian upland lakes brazil abstract statistical evaluation applied to geochemical data of upland lake sediments and their catchment basins rocks from serra dos carajas was used to identify geochemical signatures associated with underlying processes sediment provenances and source sink relationship the lakes are violao amendoim and tres irmas ti1 ti2 and ti3 a centred log ratio transformation clr was used prior to multivariate analyses in order to eliminate closure issues in compositional data due to the similarity between 15n values and organic sources mainly from c3 plants the three lakes were clustered together violao lake receives largest organic contribution from autochthonous sources such as siliceous sponge spicules and algae except for it shallower portion wnw extension which is more similar to ti2 having low 15n values that are similar to the isotopic signature of upland swamps the upper continental crust ucc normalization pattern shows that sediments are mainly enriched in fe p and se which is closely related to the catchment lithology the distribution of elements in ti2 is significantly different from the other lakes because it is dominated by organic carbon while the other lakes are a mix of detritus and organic carbon factor analysis fa using clr transformed data distinguishes several geochemical assemblages in the sediments with the major detritic groups being similar to catchment basin laterites the ti zr hf nb y hrees group corresponds to resistant minerals which remained stable during lateritization the lrees group reflects mobilization and reprecipitation by ree bearing minerals and the al v cr sc association reflects metavolcanic rock the fe p mo as zn cluster in the sediments is attributed to fe oxyhydroxide precipitation while toc so3 hg se group is controlled by organic matter principal component analysis pca further indicates that detritic lake sediments are not directly derived from the parent rocks but from weathered crusts mainly ferruginous laterites and soils which is consistent with their elements ratios

variability in modern sea surface temperature sea ice and terrigenous input in the sub polar north pacific and bering sea reconstruction from biomarker data in order to study the modern sea surface characteristics of the sub polar north pacific and the bering sea i e sea surface temperature sst and sea ice cover surface sediments recovered during the rv sonne expedition 202 in 2009 were analysed to distinguish between marine and terrestrial organic carbon hydrogen index values long chain n alkanes and specific sterols have been determined the results show that in the bering sea especially on the sea slope the organic carbon source is mainly caused by high primary production in the north pacific on the other hand the organic material originates predominantly from terrestrial higher plants probably related to dust input from asia sst has been reconstructed using the modified alkenone unsaturation index calibration from muller et al 1998 offers the most reliable estimate of mean annual temperature in the central north pacific but does not correlate with mean annual temperature throughout the study area in the eastern north pacific and the bering sea the sikes et al 1997 calibration seems to be more accurate and matches summer sst the distribution of the novel sea ice proxy ip25 highly branched c25 isoprenoid alkene in surface sediments is in accord with the modern spring sea ice edge and shows the potential of this proxy to track past variation in sea ice cover in the study area

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

fluctuations of eolian flux and ocean productivity in the mid latitude north pacific during the last 200 kyr abstract in order to understand fluctuations in terrestrial and marine environments a sedimentary core h3571 was investigated from the hess rise located in the mid latitude north pacific under the north westerly wind system the 18 o grain size and grain shape of type 1 quartz suggest that this quartz is of aerosol origin good correlation between al and aerosol quartz in content and mass accumulation rate mar indicates that the alumino silicate minerals in the sediments are mainly transported by wind mar of mineral aerosol maraerosol varies from 156 to 732 mg cm 2 kyr 1 during the last 200 kyr the maraerosol maxima occur in oxygen isotope stage ois 4 to latest ois 5 middle ois 6 moderate maxima occur in early ois 1 2 late ois 3 and middle ois 3 these maxima are ascribed to reduced precipitation during the summer monsoon and to strengthened wind speed during the winter monsoon the mean organic carbon total nitrogen atomic ratio is 7 2 suggesting that the organic matter in the core h3571 is also mainly of marine origin the mar of organic carbon marorganic exhibits two prominent maxima in ois 2 and 4 and relatively high values in middle and late ois 6 enhanced primary productivity is most likely to be responsible for the high burial rate of organic carbon in the sediments carbonate and phosphorus inputs with aerosol into sea surface have played a minor role through dissolution in diminishing pco2 in surface water during glacial times on the other hand the aerosol silica supply to the ocean may have some potential to affect the burial of biogenic silica into sediments the effect of mineral aerosol on the ocean carbon cycle would be greater in the coastal and hemipelagic regions of the western pacific and equatorial atlantic as compared with that in the hess rise regime

stream sediment geochemical data analysis for district scale mineral exploration targeting measuring the performance of the spatial u statistic and c a fractal modeling abstract recognition of mineralization related geochemical footprints and modeling their multi element dispersion patterns are important aspects to consider when vectoring toward undiscovered ore deposits the collection analysis and interpretation of stream sediment geochemical data together make an exploration method that has proven to be successful at the district scale mineral exploration targeting identifying the possible sources of stream sediment geochemical anomalies and mapping evidence i e footprints of the underlying ore forming processes however are not trivial tasks this is because stream sediment samples represent transported material reflecting the entire geology upstream from the sample locations furthermore indicator element distribution patterns are commonly strongly affected by local factors such as regolith topographic gradient vegetation density and or climate therefore there is a need for finding a better geochemical anomaly separation method regarding the nature of geochemical data obtained from the area sampled the main objectives of this study were 1 evaluating and comparing the spatial u statistic and concentration area fractal modeling methods of anomaly identification both amenable to spatial analysis for recognizing geochemical footprints of porphyry copper mineralization and 2 measuring their performance in the context of district scale exploration targeting in an area located in southeast iran subsequently the methods were first evaluated on a dataset of element contents to decompose anomalous populations finally the geochemical model that proved more efficient with respect to predicting the known mineral deposits was integrated with additional evidence maps to delineate exploration targets our evaluation of the resulting geochemical targeting model demonstrated that the targets derived from this method are robust and worthy of follow up exploration

aeolian dust dynamics in central asia during the pleistocene driven by the long term migration seasonality and permanency of the asiatic polar front loess paleosol sequences preserve detailed archives of climate change reflecting the dynamics of aeolian dust sedimentation and the paleodust content of the atmosphere the detailed investigation of particle size distributions psds of windblown sediments is an increasingly used approach to assess the paleorecord of aeolian dust dynamics the central asian loess belt offers the potential to reconstruct pleistocene atmospheric circulation patterns along an adjacent west east transect within interior eurasia through granulometric studies in this study we present the aeolian dust record of the loess sequence at remisowka se kazakhstan which reflects a detailed signal of glacial interglacial climate and atmospheric dynamics in central asia on the basis of radiocarbon and amino acid geochronologic data long term semicontinuous trends in the aeolian dust record of the last glacial cycle are observed and interpreted to reveal their paleoclimate signal in consideration of the modern synoptical atmospheric circulation patterns and aeolian dust transport in central asia it is likely that the observed trends reflect the long term migration seasonal duration and permanency of the polar front during the late pleistocene previously published models which focused on the reciprocal glacial interglacial influence of the zonal westerlies and the asiatic high on the aeolian dust transport in central asia were overly simplified and should be modified to include the major influence of the asiatic polar front as the polar front activity is intimately connected with the development and position of the interhemispherically active high level planetary frontal zone hpfz the presented data give insight to long term aeolian dust dynamics and climate variability of interior eurasia which are linked with interhemispheric climates

the magnitude timing and abruptness of changes in north african dust deposition over the last 20 000 yr reconstructions of eolian dust accumulation in northwest african margin sediments provide important continuous records of past changes in atmospheric circulation and aridity in the region existing records indicate dramatic changes in north african dust emissions over the last 20 ka but the limited spatial extent of these records and the lack of high resolution flux data do not allow us to determine whether changes in dust deposition occurred with similar timing magnitude and abruptness throughout northwest africa here we present new records from a meridional transect of cores stretching from 311 nt o 191n along the northwest african margin by combining grain size endmember modeling with 230 th normalized fluxes for the first time we are able to document spatial and temporal changes in dust deposition under the north african dust plume throughout the last 20 ka our results provide quantitative estimates of the magnitude of dust flux changes associated with heinrich stadial 1 the younger dryas and the african humid period ahp 11 7 5 ka offering robust targets for model based estimates of the climatic and biogeochemical impacts of past changes in north african dust emissions our data suggest that dust fluxes between 8 and 6 ka were a factor of 5 lower than average fluxes during the last 2 ka using a simple model to estimate the effects of bioturbation on dust input signals we find that our data are consistent with abrupt synchronous changes in dust fluxes in all cores at the beginning and end of the ahp the mean ages of these transitions are 11 870 2 ka 1s and 4 970 2 ka respectively

glacial flour dust storms in the gulf of alaska hydrologic and meteorological controls and their importance as a source of bioavailable iron 1 iron is an essential micronutrient that limits primary productivity in much of the ocean including the gulf of alaska goa however the processes that transport iron to the ocean surface are poorly quantified we combine satellite and meteorological data to provide the first description of widespread dust transport from coastal alaska into the goa dust is frequently transported from glacially derived sediment at the mouths of several rivers the most prominent of which is the copper river these dust events occur most frequently in autumn when coastal river levels are low and riverbed sediments are exposed the dust plumes are transported several hundred kilometers beyond the continental shelf into iron limited waters we estimate the mass of dust transported from the copper river valley during one 2006 dust event to be between 25 80 ktons based on conservative estimates this equates to a soluble iron loading of 30 200 tons we suggest the soluble fe flux from dust originating in glaciofluvial sediment deposits from the entire goa coastline is two to three times larger and is comparable to the annual fe flux to goa surface waters from eddies of coastal origin given that glaciers are retreating in the coastal goa region and in other locations it is important to examine whether fluxes of dust are increasing from glacierized landscapes to the ocean and to assess the impact of associated fe on marine ecosystems

miocene sn polymetallic mineralization in the tethyan himalaya southeastern tibet a case study of the cuonadong deposit abstract the cuonadong deposit is located in the cuonadong gneiss dome of the eastern tethyan himalaya and is characterized as a large to superlarge scale sn polymetallic deposit in the himalaya orogen the mineralization pattern includes skarn w sn mineralization in the strong shear zone of the dome mantle hydrothermal sn w veins controlled by north south trending rifts nstrs and be rb mineralization in pegmatitic leucogranite the results of this study show that the zircon u pb age of undeformed postkinematic leucogranites is 15 5 0 1 ma n 28 mswd 1 4 the cassiterite u pb age of the vein type sn w orebody is 14 3 0 5 ma n 40 mswd 3 2 and the muscovite ar ar age of beryl bearing pegmatitic leucogranite is 15 2 0 2 ma mswd 1 5 the isotopic dating results demonstrate that the cuonadong sn w be rb mineralization has a close genetic relationship with the miocene ca 16 14 ma leucogranite magmatic hydrothermal activity in the cuonadong dome the deformed synkinematic two mica granite 18 ma was cut by the sn w ore veins 14 ma faulted by nstrs indicating that the e w trending extension of the nstrs initiated at ca 18 14 ma the himalaya leucogranite belongs to a highly fractionated granite with high sn content 15 ppm in conclusion the himalaya leucogranite is considered to be tin granite in this study and therefore the himalaya presents high potential for sn polymetallic mineralization prospecting

the influence of soil anisotropy and k0 on ground surface movements resulting from tunnel excavation finite element fe analysis is now often used in engineering practice to model tunnel induced ground surface settlement for initial stress regimes with a high coefficient of lateral earth pressure at rest k0 it has been shown by several studies that the transverse settlement trough predicted by two dimensional 2d fe analysis is too wide when compared with field data it has been suggested that 3d effects and or soil anisotropy could account for this discrepancy this paper presents a suite of both 2d and 3d fe analyses of tunnel construction in london clay both isotropic and anisotropic non linear elastic pre yield models are employed and it is shown that even for a high degree of soil anisotropy the transverse settlement trough remains too shallow by comparing longitudinal settlement profiles obtained from 3d analyses with field data it is demonstrated that the longitudinal trough extends too far in the longitudinal direction and that consequently it is difficult to establish steady state set

eolian dust input to the subarctic north pacific eolian dust is a significant source of iron and other nutrients that are essential for the health of marine ecosystems and potentially a controlling factor of the high nutrient low chlorophyll status of the subarctic north pacific we map the spatial distribution of dust input using three different geochemical tracers of eolian dust 4he 232th and rare earth elements in combination with grain size distribution data from a set of core top sediments covering the entire subarctic north pacific using the suite of geochemical proxies to fingerprint different lithogenic components we deconvolve eolian dust input from other lithogenic inputs such as volcanic ash ice rafted debris riverine and hemipelagic input while the open ocean sites far away from the volcanic arcs are dominantly composed of pure eolian dust lithogenic components other than eolian dust play a more crucial role along the arcs in sites dominated by dust eolian dust input appears to be characterized by a nearly uniform grain size mode at 4 m applying the 230th normalization technique our proxies yield a consistent pattern of uniform dust fluxes of 1 2 g m2 yr across the subarctic north pacific elevated eolian dust fluxes of 2 4 g m2 yr characterize the westernmost region off japan and the southern kurile islands south of 45 n and west of 165 e along the main pathway of the westerly winds the core top based dust flux reconstruction is consistent with recent estimates based on dissolved thorium isotope concentrations in seawater from the subarctic north pacific the dust flux pattern compares well with state of the art dust model predictions in the western and central subarctic north pacific but we find that dust fluxes are higher than modeled fluxes by 0 5 1 g m2 yr in the northwest northeast and eastern subarctic north pacific our results provide an important benchmark for biogeochemical models and a robust approach for downcore studies testing dust induced iron fertilization of past changes in biological productivity in the subarctic north pacific

dust transport and the question of desert loess formation although contemporary dust storms are frequent in arid and semi arid areas desert loess deposits are poorly developed much of the world s loess occurs in mid latitude areas which experienced glaciation during the pleistocene ocean core evidence indicates that dust transport from sub tropical deserts increased during cold stages of the pleistocene but loess formed only on certain desert margins for reasons which have not been fully explained this paper re examines the mechanisms of dust transport and deposition and the circumstances leading to the accumulation of thick loess typical loess is composed mainly of medium silt grains which are transported in short term suspension a few metres above the ground significant thicknesses of loess form only when dust is trapped within a limited area often relatively close to the source dust particles finer than 20 m are transported mainly in long term suspension over a greater height range and may be widely dispersed the availability of silt and the frequency magnitude and direction of dust transporting winds are important factors governing the potential for loess formation but the existence of a suitable dust trap is particularly important traps may be formed by topographic obstacles areas of moist ground or vegetated surfaces vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid latitudes during the pleistocene dust blown during glacial periods from certain deserts notably in sinai soviet central asia and china accumulated as loess in neighbouring semi arid regions on the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps during most of the holocene net dust deposition rates in all desert marginal areas have been too low for significant loess accumulation this is mainly due to a reduction in silt availability and a tendency towards landscape stability reported dust storm frequencies during the past 50 years over estimate the longer term holocene dust flux due to the effects of human activities much modern dust owes its origin to erosion of cultivated soils in semi arid areas and is finer than typical loess

geochemistry of eolian dust in pacific pelagic sediments implications for paleoclimatic interpretations geochemical data rees th sc were determined for the operationally defined eolian dust oded fraction 63 m of late quaternary sediment samples n 57 from the north and equatorial pacific ocean paleoclimate studies commonly have assumed that this sediment fraction represents eolian materials from continental source regions this study shows on the basis of geochemical data published mineralogical data and mixing models that the oded fraction actually is a mixture of materials from two endmember sources the continental crust eolian transported weathering products and the oceanic crust primarily volcanogenic material mixing model results show that the average ash content is significant in the oded fraction equatorial pacific 43 north pacific 24 we have used this information to reconsider and refine the results of previous paleoclimate studies in the northwest pacific the flux of the eolian fraction is greater during glacial stages and shows a latitudinal maximum between 35 n and 42 n eolian fluxes are greatest during interglacial periods in the equatorial pacific these results are consistent with previous interpretations in contrast to previous assumptions eolian mass accumulation rates may not be a valid indicator of paleo aridity because they are correlated with grain size furthermore the relative abundance of the two endmembers is correlated with the average grain size of the dust fraction the continental crust component is associated with larger grains this compositional effect should be considered in future studies which commonly utilize grain size as a proxy indicator of paleo wind intensity

atmospheric transport of iron and its deposition in the ocean the atmospheric transport of continental weathering products is responsible for much of the mineral material and fe entering the open ocean and is probably the dominant source of nutrient fe in the photic zone in regions where other nutrients are present in high concentrations the flux of fe from the atmosphere may be a limiting factor in primary productivity due to the larger source regions for dust north of the equator 8 times more atmospheric fe is deposited in the northern hemisphere than in the southern hemisphere the mineral aerosol and fe transport and deposition are highly variable due to the episodic nature of dust generation and its transport and deposition processes between 10 and 50 of the total atmospheric fe entering the world ocean appears to dissolve i e it will pass through a 0 4 m pore size filter rapidly when the mineral matter enters the ocean much of the atmospheric fe is present as fe ii apparently produced as a result of photochemical reduction reactions taking place during atmospheric transport this readily soluble fe ii should be available immediately for use as a nutrient by phytoplankton atmospheric transport from the continents is estimated to supply 3 times as much dissolved fe to the oceans as that delivered via rivers

genesis of luobuzhen pb zn veins implications for porphyry cu systems and exploration targeting at luobuzhen dongshibu in western gangdese belt southern tibet abstract porphyry systems are known to form in magmatic arc environment and commonly include porphyry cu epithermal pb zn au ag skarn polymetallic mineralization etc the systems are rarely reported in collisional zones such as the gangdese belt in southern tibet where many postcollisional porphyry copper deposits occurred in addition other types of mineral systems are rarely present except porphyry copper mineralization in the gangdese belt in this study we present pb zn bearing quartz veins at luobuzhen in the western gangdese belt the luobuzhen pb zn veins cross cut dacite of the linzizong group with zircon u pb age of 50 1 0 2 ma and monzogranite with zircon u pb age of 17 1 0 1 ma ore minerals include sphalerite galena chalcopyrite and pyrite gangue minerals are quartz with minor chlorite and sericite primary fluid inclusions of quartz are liquid rich aqueous and two phase inclusions the homogenization temperatures of these primary inclusions are moderate to high 267 400 c and salinities range from 8 9 to 18 4 wt nacl equiv quartz has 18 o smow values of 6 2 9 3 while sulfides have 34 s v cdt values of 5 1 to 0 1 206 pb 204 pb of 18 722 18 849 207 pb 204 pb of 15 640 15 785 and 208 pb 204 pb of 39 068 39 560 these data suggest that magmatic fluids with contribution from meteoric water magmatic sulfur and lead derived from upper crust and metasomatized mantle by indian continental materials would be critical for the luobuzhen base metal mineralization the dongshibu area located at 2 km east of the luobuzhen is characterized by high concentrations of cu up to 1450 ppm and mo up to 130 ppm of stream sediments which is quite different from high concentrations in pb zn ag and au shown in the luobuzhen area in addition porphyry copper mineralization related alteration and veins veinlets occur in the miocene monzogranite at dongshibu the monzogranite is characterized by high sr y ratios which are also shown on ore forming intrusions in the gangdese postcollisional porphyry copper deposits and shows similar zircon hf isotopes to the ore related high sr y intrusions from the zhunuo porphyry copper deposit which is located 20 km northeast of the luobuzhen dongshibu a comprehensive analysis allows us to infer that the base metal veins at luobuzhen are components of a porphyry cu system with porphyry cu mineralization likely present at dongshibu and epithermal au ag veins possibly occurring at luobuzhen which are indicative of the existence of porphyry copper systems in collisional zones the potential porphyry cu mineralization and epithermal au ag veins should be targeted in future exploration at luobuzhen dongshibu

tethys tectonic evolution and its bearing on the distribution of important mineral deposits in the sanjiang region sw china abstract the sanjiang region in se tibet plateau and nw yunnan is known to have formed by amalgamation of gondwana derived continental blocks and arc terranes as a result of oceanic subduction followed by continental collision from paleozoic to mesozoic in this paper we provide a synthesis of tectonic evolution magmatism and metallogeny in the region based on data from literatures early paleozoic ophiolites 473 439 ma in the changning menglian belt indicate the existence of a proto tethys ocean in this region two episodes of subduction related magmatism in the early paleozoic one occurred in the baoshan and tengchong blocks at 502 455 ma and the other occurred in the simao block at 421 401 ma are regarded as evidence for two different events of subduction of the proto tethys ocean at different locations the proto tethys was succeeded in early devonian by the paleo tethys which comprised the main ocean and three branches ailaoshan jinshajiang and garze litang the changning menglian main ocean existed from middle devonian to middle triassic the remnants of the oceanic crust are preserved in a few places in the longmu tso shuanghu suture as well as in the changning menglian ophiolite belt the eastward subduction of the main oceanic plate from early permian to early triassic formed a prominent arc terrane stretching 1500 km from yunnan to eastern tibet from the waning stage of subduction to post subduction numerous s type granite plutons with ages varying between 230 and 219 ma such as the lincang batholith in yunnan were emplaced at or close to the suture this event produced several hydrothermal w sn deposits in the region the tectonic evolution and associated magmatism of the jinshajiang and ailaoshan branch oceans are generally comparable to those of the main ocean however the branch oceans were subducted westward instead the garze litang branch ocean also underwent westward subduction from middle devonian to late triassic arc related high sr y porphyry intrusions and associated porphyry skarn cu mo au deposits are common in the jinshajiang ailaoshan region especially in the yidun arc which formed prior to jurassic the vms deposits in the sanjiang region formed in diverse tectonic settings including middle silurian back arc basins carboniferous oceanic islands paleozoic subduction zones and triassic post subduction rifting environments the mesozoic and early cenozoic evolution of the baoshan and tengchong blocks was largely influenced by eastward oceanic subduction of the meso and neo tethys from late permian to middle cretaceous and from late cretaceous to 50 ma respectively abundant early cretaceous granitoids and associated skarn type pb zn and sn fe deposits in the baoshan and tengchong blocks were produced in the background of the shan boundary oceanic slab subduction to the west and the break off of the nujiang bitu oceanic slab to the north the subduction of the neo tethys oceanic plate beneath the tengchong block from late cretaceous to paleogene formed abundant s type granitoids and many skarn type and greisen type sn w deposits granitoids formed at 105 to 81 ma and contemporaneous hydrothermal w mo ag and au deposits which temporally coincided with the subduction of the neo tethys are common in the yidun arc terrane

evidence for early 44 ma himalayan crustal thickening tethyan himalaya southeastern tibet abstract comprehensive understanding of himalayan orogenesis is limited in part by a poor knowledge of the eohimalayan episode a phase of tectonic activity predating the better understood neohimalayan crustal thickening associated with coaxial deformation along the main central thrust the cambo ordovician to tertiary metasedimentary sequences outcropping within the tethyan himalaya are the structurally highest units of the himalayan fold and thrust belt they and are inferred to have been the first to have accreted to asia a compilation of data from transects along the length of the main himalayan arc shows that the tethyan sequences have experienced at least five deformation events although the timing of these episodes is poorly constrained emplacement of a series of undeformed granitoid bodies following the second of these events which accounts for the majority of crustal thickening in the tethyan himalayan units is constrained by u pb zircon dating to be older than 44 1 1 2 ma thus significant crustal thickening had occurred along the length of the proto himalayan arc by the mid eocene or within 10 to 20 myr of the initiation of himalayan orogenesis

lead isotopes in north pacific deep water implications for past changes in input sources and circulation patterns the sources of non anthropogenic pb in seawater have been the subject of debate here we present pb isotope time series that indicate that the non anthropogenic pb budget of the northernmost pacific ocean has been governed by ocean circulation and riverine inputs which in turn have ultimately been controlled by tectonic processes despite the fact that the investigated locations are situated within the asian dust plume and proximal to extensive arc volcanism eolian contributions have had little impact we have obtained the first high resolution and high precision pb isotope time series of north pacific deep water from two ferromanganese crusts from the gulf of alaska in the ne pacific ocean and from the detroit seamount in the nw pacific ocean both crusts were dated applying 10be 9be ratios and yield continuous time series for the past 13 5 and 9 6 myr respectively lead isotopes show a monotonic evolution in 206pb 204pb from low values in the miocene 18 57 to high values at present day 18 84 in both crusts even though they are separated by more than 3000 km along the aleutian arc the variation exceeds the amplitude found in equatorial pacific deep water records by about three fold there also is a striking similarity in 207pb 204pb and 208pb 204pb ratios of the two crusts indicating the existence of a local circulation cell in the sub polar north pacific where efficient lateral mixing has taken place but only limited exchange in terms of pb with deep water from the equatorial pacific has occurred both crusts display well defined trends with age in pb pb isotope mixing plots which require the involvement of at least four distinct pb sources for north pacific deep water the pb isotope time series reveal that eolian supplies volcanic ash and continent derived loess have only been of minor importance for the dissolved pb budget of marginal sites in the deep north pacific over the past 6 myr the two predominant sources have been young volcanic arcs one located in the northeastern part and one located in the northwestern part of the pacific margin from where material has been eroded and delivered to the ocean most likely via riverine pathways

millennial scale oscillations of the westerly jet path during the last glacial period abstract it has been established that east asian summer monsoon intensity varies with dansgaard oeschger cycles suggesting a connection between the climates of east asia and the north atlantic on a millennial timescale however the dynamics of such a connection are still unsolved here we demonstrate that temporal changes in the provenance of aeolian dust in japan sea sediments which we interpret to reflect changes in the westerly jet path over east asia exhibit variations in harmony with dansgaard oeschger cycles the dominance of dust with a mongolian gobi provenance during stadials suggests a westerly jet axis located to the south of the himalaya tibetan plateau throughout most of the year whereas the co dominance of dust from both the taklimakan desert and the mongolian gobi during interstadials suggests that the westerly jet axis jumped to the north of the tibetan plateau at latest in summer as the shift of the westerly jet axis to the north of the tibetan plateau is closely related to the onset of the east asian summer monsoon changes of the westerly jet path apparently critically affect the teleconnection between the climates of asia and north atlantic on a millennial timescale

orbital and millennial scale variations in asian dust transport path to the japan sea abstract orbital and millennial scale variations in the asian monsoon and its probable association with the dansgaard oeschger d o cycles have been demonstrated by previous studies however the origin and nature of such variations are poorly understood the japan sea is located down wind of the arid areas of the eurasian continent and thus receives significant amounts of aeolian dust consequently the hemipelagic sediments of the japan sea are expected to record a continuous aeolian dust accumulation which may provide information about the past variations in asian monsoon grain size flux and provenance of aeolian dust in the sediments were examined using two sediment cores obtained from the northern and southern parts of the japan sea in order to understand the spatial variability of asian monsoon since the silt fraction of the detrital materials in hemipelagic sediments of the japan sea is composed predominantly of aeolian dust the grain size flux and provenance of the silt fraction were examined the taklimakan desert loess plateau and siberia northeast china areas were identified as possible source areas of aeolian dust in the sediments of the japan sea based on the electron spin resonance esr signal intensity and crystallinity of quartz moreover the relative contribution of aeolian dust from each source area was estimated based on the esr signal intensity and crystallinity of quartz aeolian dust fluxes from the two source areas at the southern site were then estimated grain size and flux of eolian dust at the northern site and fluxes of aeolian dust from two source areas at the southern site show orbital scale variations in harmony with the insolation change at 30 n in june these results indicate orbital scale changes in the extent of the arid area and or frequency of dust storms in the taklimakan desert loess plateau and siberia northeast china areas and suggest that southward northward shifts of the westerly jet axis occurred together with either intensified weakened winter monsoon decreased increased winter precipitation in the siberia northeast china area or southeastward northwestward shifts of summer monsoon limit during periods of smaller larger insolation at 30 n in june in addition to these orbital scale variations millennial scale variations possibly associated with the d o cycles are observed in the grain size record of aeolian dust at the two sites based on analogy with orbital scale variations these millennial scale variations are considered to reflect millennial scale changes in the position of the westerly jet axis together with the changes either in winter monsoon intensity winter precipitation or position of summer monsoon limit our results suggest n s oscillations in the westerly jet and summer monsoon limit and changes in the intensity of the winter monsoon on orbital and millennial timescales

eolian inputs of lead to the north pacific we evaluate the importance of natural eolian pb to the dissolved oceanic pb budget by measuring the isotopic composition of pb in 35 holocene and late quaternary sediment samples from the north pacific and in 10 samples of chinese loess when the pacific is divided into sediments provinces based on published end and sedimentological data pb from the central north pacific tends to be the most radiogenic and homogeneous due to the dominance of eolian chinese loess lead from the marginal north pacific and the sparsely sampled regions south of 5 n are less radiogenic and more variable owing to hemipelagic inputs from various volcanic arcs and older continental crust located around the pacific rim 208pb 204pb ratios provide the most distinctive provenance information due to the relatively high ratios in chinese loess the chinese loess samples come from 3 localities and span up to 2 myr of time acetic acid leachate bulk loess and loess silicate fractions were analyzed separately leachate pb is considerably less radiogenic than silicate pb the isotopic composition of the silicate component closely matches the sediment data from the central north pacific confirming the dominance of eolian loess in this region we divided up a suite of published hydrogenous pb isotope data from the pacific ocean according to their locations within the three independently defined sediment provinces these data define three distinct fields differentiated primarily by their 206pb 204pb ratios which increase going from the central to southern to marginal provinces this relationship with sediment province strongly suggests that natural eolian and probably hemipelagic inputs significantly impact the seawater pb budget direct support for the dominance of eolian chinese loess in the central north pacific dissolved pb budget comes from the close match between loess leachate pb and the central province hydrogenous pb data eolian inputs are likely to dominate local seawater pb budgets only where eolian pb fluxes are high relative to hemipelagic pb fluxes and where the flux of pb carried by deep water advection is low

global deep sea burial rate of calcium carbonate during the last glacial maximum global databases concentrations rates in holocene and last glacial of calcium carbonate and mass accumulation maximum sediments were used to estimate the deep sea sedimentary calcium carbonate burial rate during these two time intervals sparse calcite mass accumulation rate data were extrapolated across regions of varying calcium carbonate concentration using a gridded map of calcium carbonate concentrations and the assumption that accumulation of noncarbonate material is uncorrelated with calcite concentration within some geographical region mean noncarbonate accumulation rates were estimated within each of nine regions determined by the distribution and nature of the accumulation rate data for core top sediments data coverage 67 of the high calcite the regions of reasonable encompass 75 sediments globally and within these regions we estimate an accumulation rate of 55 9 3 6x1011 mol yr 1 the same regions cover 48 of glacial high caco3 sediments the smaller fraction is due to a shift of calcite deposition to the poorly sampled south pacific and total 44 1 6 0x1011 mol yr 1 projecting to 100 coverage south and total 44 1 6 0x1011 both estimates yields accumulation estimates of 8 3x1012 mol yr 1 today and 9 2x1012 mol yr 1 during glacial time this is little better than a guess given the incomplete data coverage but it suggests that glacial deep sea calcite burial rate was probably not considerably faster than today in spite of a presumed decreasein shallow water burial during glacial time

controls on deglacial changes in biogenic fluxes in the north pacific ocean the subarctic north pacific ocean holds a large co2 reservoir that is currently isolated from the atmosphere by a low salinity layer it has recently been hypothesized that the reorganization of these high co2 waters may have played a crucial role in the degassing of carbon dioxide to the atmosphere during the last deglaciation this reorganization would leave some imprint on paleo productivity records here we present 230th normalized biogenic fluxes from an intermediate depth sediment core in the northwest pacific rc10 196 54 7 n 177 1 e 1007 m and place them within the context of a synthesis of previously published biogenic flux data from 49 deep sea cores north of 20 n ranging from 420 to 3968 m water depth the 230th normalized opal carbonate and organic carbon fluxes from rc10 196 peak approximately 13 000 calendar years bp during the bolling allerod b a period our data synthesis suggests that biogenic fluxes were in general lowest during the last glacial period increased somewhat in the northwest pacific during heinrich event 1 and reached a maximum across the entire north pacific during the b a period we evaluate several mechanisms as possible drivers of deglacial change in biogenic fluxes in the north pacific including changes in preservation sediment focusing sea ice extent iron inputs stratification and circulation shifts initiated in the north atlantic and north pacific our analysis suggests that while micronutrient sources likely contributed to some of the observed changes the heterogeneity in timing of glaciogenic retreat and sea level make these mechanisms unlikely causes of region wide contemporaneous peaks in export production we argue that paleoobservations are most consistent with ventilation increases in both the north pacific during h1 and north atlantic during b a being the primary drivers of increases in biogenic flux during the deglaciation as respectively they were likely to bring nutrients to the surface via increased vertical mixing and shoaling of the global thermocline

identifying geochemical anomalies associated with sb au pb zn ag mineralization in north himalaya southern tibet abstract the north himalaya is a prospective area for sb sb au au pb zn ag and sb pb zn ag mineralization geochemical anomalies for mineralizing elements and element associations were identified using concentration area c a fractal model together with statistical analyses including the mean 2 standard deviation mean 2std and the median 2 median absolute deviation median 2mad the results show that the mean 2std for log transformed data and c a model could well identify the geochemical anomalies associated with mineralization in the north himalaya sb au anomalies show a better spatial association with sb sb au and sb pb zn ag deposits than those of single sb element au anomalies are associated with all deposits and pb zn ag anomalies are associated with pb zn and sb pb zn ag deposits in addition weak anomalies associated with sb mineralization can be identified by the singularity method with the utilization of the sb au sb au and pb zn ag anomalies identified by c a fractal model and mean 2std for log transformed data as well as the singularity method we can facilitate the exploration targeting of various deposits in the north himalaya in addition our results also show that principal component analysis pca of centered logratio clr transformed data can accurately recognize three different geochemical assemblage compositions representing three different types of mineralization i e au pb zn ag and sb in the north himalaya

copper prospectivity in tibet china based on the identification of geochemical anomalies abstract the qinghai tibet plateau is an important mineral rich region and is well known for its copper resources this study investigates stream sediment geochemistry in assessing the potential for cu resources in the region a spectrum area model is used to process large volumes of data with multifractal and power spectrum analysis the model can be used to separate geochemical anomalies from geochemical background levels thus eliminating the influence of different geomorphological landscapes it is recognised from this study that geochemical anomalies are closely related to deep seated faults forming terrane boundaries that are multiply deformed and intruded by granites second order structures related to these tectonic zones are commonly mineralised and are considered highly prospective for mineral resources the results of this study indicate that geochemical anomalies are useful for identifying potential cu mineral resources

characterization of late glacial continental dust in the greenland ice core project ice core twelve glacial dust samples extracted from the greenland ice core project ice core have been characterized in terms of mineralogy sr and nd isotopic composition and rare earth element concentrations the ice samples are taken from the younger dryas the bolling the last glacial maximum and both cold and mild glacial periods back to 44 kyr b p a comparison with samples from possible dust source areas determines eastern asia as being the main source area at all times hereby confirming and extending earlier results biscaye et al 1997 this finding is partly in agreement with recent atmospheric general circulation model simulations of glacial atmospheric dust transport andersen et al 1998 mahowald et al 1999 a low intersample variability in tracer characteristics is discussed in the context of a volcanogenic influence grain size dependence and variability in the conti nental dust source areas the clay mineralogy of the ice core dust shows a weak climatic de pendence while the isotopic composition of sr and nd does not correlate with climate this is interpreted as a geographical variation of source areas on a regional scale within asia two ice dust samples were size fractionated at 2 gm and the grain size dependence on tracer characteristics is in accordance with the literature

modelling of long term ground response to tunnelling under st james s park london following a tunnel excavation in low permeability soil it is commonly observed that the ground surface continues to settle and ground loading on the tunnel lining changes as the pore pressures in the ground approach a new equilibrium condition the monitored ground response following the tunnelling under st james s park london shows that the mechanism of subsurface deformation is composed of three different zones swelling consolidation and rigid body movement the swelling took place in a confined zone above the tunnel crown extending vertically to approximately 5 m above it on the sides of the tunnel the consolidation of the soil occurred in the zone primarily within the tunnel horizon from the shoulder to just beneath the invert and extending laterally to a large offset from the tunnel centreline above these swelling and consolidation zones the soil moved downward as a rigid body in this study soil fluid coupled three dimensional finite element analyses were performed to simulate the mechanism of long term ground response monitored at st james s park an advanced critical state soil model which can simulate the behaviour of london clay in both drained and undrained conditions was adopted for the analyses the analysis results are discussed and compared with the field monitoring data it is found that the observed mechanism of long term subsurface ground and tunnel lining response at st james s park can be simulated accurately only when stiffness anisotropy the variation of permeability between different units within the london clay and non uniform drainage conditions for the tunnel lining are considered this has important implications for future prediction of the long term behaviour of tunnels in clays

alteration and mineralization at the zhibula cu skarn deposit gangdese belt tibet abstract the zhibula cu skarn deposit contains 0 32 mt cu metal with an average grade of 1 64 and is located in the gangdese porphyry copper belt in southern tibet the deposit is a typical metasomatic skarn that is related to the interaction of magmatic hydrothermal fluids and calcareous host rock stratiform skarn orebodies occur at the contact between tuff and marble in the lower jurassic yeba formation alteration zones generally grade from a fresh tuff to a garnet bearing tuff a garnet pyroxene skarn and finally to a wollastonite marble minor endoskarn alteration zonations are also observed in the causative intrusion which grade from a fresh granodiorite to a weakly chlorite altered granodiorite a green diopside bearing granodiorite and to a dark red brown garnet bearing granodiorite prograde minerals which were identified by electron probe microanalysis include andradite grossularite of various colors e g red green and yellow and green diopside retrograde metamorphic minerals overprint the prograde skarn and are mainly composed of epidote quartz and chlorite the ore minerals consist of chalcopyrite and bornite followed by magnetite molybdenite pyrite pyrrhotite galena and sphalerite three types of fluid inclusions are recognized in the zhibula deposit including liquid rich two phase inclusions type l vapor rich two phase inclusions type v and daughter mineral bearing three phase inclusions type s as the skarn formation evolved from prograde stage i to early retrograde stage ii and later retrograde stage iii the ore forming fluids correspondingly evolved from high temperature 405 667 c high salinity up to 44 0 wt nacl equiv and high pressure 500 600 bar to low moderate temperature 194 420 c moderate high salinity 10 1 18 3 and 30 0 44 2 wt nacl equiv and low moderate pressure 250 350 bar isotopic data of 34 s 0 1 to 6 8 estimated 34 s fluids 0 7 d h2o 91 to 159 and 18 o h2o 1 5 to 9 2 suggest that the ore forming fluid and material came from magmatic hydrothermal fluids that were associated with miocene zhibula intrusions fluid immiscibility likely occurred at the stage i and stage ii during the formation of the skarn and mineralization fluid boiling occurred during the stage iii which is the most important cu deposition mechanism for the zhibula deposit

characteristics of the london clay from the terminal 5 site at heathrow airport the innovative engineering approach adopted for the new terminal 5 at heathrow airport called for an advanced investigation of the london clay strata including detailed in situ profiling and stress path laboratory testing on high quality rotary cored samples although the scope of the investigations exceeded that normally specified for conventional design questions relating to the structure and anisotropy of stiffness and strength of the clay remained that could not be answered further research was required and the deep excavations at the site provided the opportunity for a team from imperial college to take multiple block samples from three depths supplemented by two additional dedicated rotary cored boreholes intensive research was performed at imperial college on these samples as described in three companion papers by gasparre et al and nishimura et al this overview paper integrates the findings from the recent research with those from the commercial investigation and with earlier studies to e

the influence of structure on the behaviour of london clay an intensive investigation is described into the london clay units from heathrow terminal 5 intrinsic properties and composition were established and relating the behaviour of intact and reconsti

a biostratigraphy for the london clay in london biostratigraphy enables specific layers of strata to be given a unique stratigraphic address that can be used to identify the horizons in which in situ tests are conducted and from which samples for testing are collected this is particularly valuable when working in fine grained deposits where stratigraphic position is not easily recognised by lithology alone and permits any data bank of geotechnical values and performance to be used without fear of confusing one stratigraphic layer with another construction in the london clay formation and its supporting research has necessitated an accurate and speedy method for identifying with a precision of centimetres the stratigraphic layer from which geotechnical data have been obtained the principles that enable biostratigraphy to be used for this purpose are explained and illustrated with reference to the london clay formation in london this approach can be used in most sedimentary strata an example of biostratigraphic data used in london is presented

mapping singularities with stream sediment geochemical data for prediction of undiscovered mineral deposits in gejiu yunnan province china abstract this paper proposes the concept of singularity for characterizing hydrothermal mineralization processes a singular physical process may result in anomalous amounts of energy release or material accumulation within a narrow spatial temporal interval mineralization can be considered as a type of singular process due to large amounts of material accumulation and element enrichment a spatial singularity mapping technique is developed based on the local singularity involved in the context of multifractal theory it assembles geochemical map at different scales and calculates an index indicating the scaling characteristics of enrichment and depletion of geochemical concentration at multiple scales this index was used for quantifying spatial singularity of mineralization associated geochemical anomalies a case study for the gejiu tin polymetallic mineral district yunnan province china demonstrates that the concepts of singularity and the singularity mapping technique are applicable and useful for delineating anomalies caused by mineralization and for predicting the locations of undiscovered mineral deposits

identification and mapping of geochemical patterns and their significance for regional metallogeny in the southern sanjiang china abstract the southern sanjiang region southwestern china comprises various continental blocks tectonic sutures and arcs this complex structural area is a proper place for the recognition of geochemical patterns and understanding of regional metallogenesis considering each individual tectonic unit i e western south china block ailaoshan suture simao block changning menglian suture baoshan block and tengchong block as a statistical unit this study identifies the distribution patterns of geochemical elements distinguishes elemental associations for different geological backgrounds controlled by the regional lithology and diverse mineralizations and thereby delineates the mineralized anomalies to achieve the goals the kriging interpolation staged factor analysis and local singularity technology were utilized after the centered logratio clr transformation of stream sediment geochemical data the spatial distributions of metallogenic elements au ag cu pb zn and sn show that not all the areas with high concentrations of elements contain ore deposits it means that the formation of ore deposits is an independent anomalous geological event not necessarily related to the original regional abundance of geochemical elements the different element associations obtained by staged factor analysis of 28 elements are able to reveal the geological backgrounds and metallogenic signatures for different tectonic units for example the element associations for the first second and third factors fs in the western south china block are groups of ti co v sb ag as and th u be see text for the detailed element associations which represent the emeishan flood basalts ag pb mineralization and felsic rocks respectively similarly the element associations co v cu be u th and sb ag au for f1 f2 and f3 in the ailaoshan suture respectively represent the ophiolite complex and mafic rocks felsic rocks and au mineralization the associations from f1 to f4 in the simao block are th u sn v co cr cd ag pb and au sb which represent the linchang batholith mafic rocks ag pb zn mineralization and au mineralization respectively the distribution patterns of their factor scores can roughly distinguish the anomalies caused by regional backgrounds and mineralizations the local singularity of factor scores for mineralization can further identify mineralized areas in most of the tectonic units nevertheless an exception occurs in the western south china block where the background element association ti co v cu ni cr p mn nb zn f1 obscures the au signature therefore we substituted the single element au for mineralized element association f1 to perform singularity mapping and obtained better result it was concluded that the combination of staged factor analysis local singularity and tectonic setting is effective in regional metallogenic potential analysis

fractal models for ore reserve estimation abstract traditional geometric and geostatistic methods for reserve estimation in a single deposit are difficult to use with skewed distribution mineralization variables including grade orebody thickness and grade thickness a common characteristic of most deposits and require complex data processing it has been shown that the skewed mineralization variables can be described by the number size model in a fractal domain based on the number size model assuming that orebody thickness and grade thickness are continuous variables the fractal model for reserve estimation fmre in a single deposit can be established in the fmre ore tonnage can be estimated given the orebody area and the fractal parameters of orebody thickness distribution and metal tonnage can be estimated based on the orebody area and the fractal parameters of grade thickness distribution the reserve estimated by the fmre can denote actual ore tonnage and metal tonnage that can be mined out of the deposit the frme was applied to the dayingezhuang gold deposit in the jiaodong gold province in china the gold reserves via the fmre and the traditional geometric block method are similar with relative errors of 3 11 in ore tonnage and 0 29 in metal tonnage compared to traditional reserve estimation the fmre is much easier in calculation process and is more reasonable in dealing with the skewed distribution however this new method fails to calculate local reserve which can be derived via any of the traditional estimation methods

provenance of dust in the pacific ocean eolian dust preserved in deep sea sediment cores provides a valuable indicator of past atmospheric circulation and continental paleoclimate in order to identify the provenance of eolian dust nd and sr isotopic compositions and rb sr and rare earth element ree concentrations have been determined for the silicate fractions of deep sea sediments from the north and central pacific ocean different regions of the pacific ocean are characterized by distinct air borne inputs producing a large range in end 10 to 1 stsr 86sr 0 705 0 721 la yb 5 15 eun eu 0 6 1 0 and sr nd 4 33 the average nd isotopic composition of pacific deep sea sediments eno 6 is more radiogenic than the average from the atlantic ena 8 in contrast the average 1475m 14and ratio for pacific sediments 0 114 is identical to that of atlantic sediments and to that of global average riverine suspended material the values of ena and 147sm 144nd are positively correlated for the pacific samples but negatively correlated for atlantic samples reflecting a fundamental difference between the dominant components in the end members with radiogenic nd island arc components in the pacific and lree enriched intraplate ocean island components in the atlantic samples from the north central pacific have distinctive unradiogenic end values of 10 87sr 86sr 0 715 high la yb 12 and low eun eu 0 6 and sr nd 3 6 these data are virtually identical to the values for loess from asia and endorse the use of these sediments as indicators of asian paleoclimate and paleowind directions island arc contributions appear to dominate in the northwest pacific resulting in higher end 1 to 1 and lower 87sr 86sr 0 705 and la yb 5 sediments from the eastern pacific tend to have intermediate sr and nd isotopic compositions but regionally variable sr nd and ree patterns they appear to be derived from the west margin of the north and south american continents rather than from asia our results confirm that dust provenance can be constrained by isotopic and geochemical analyses which will facilitate reconstructions of past atmospheric circulation and continental paleoclimate

the lhasa terrane record of a microcontinent and its histories of drift and growth article i nfo the lhasa terrane in southern tibet has long been accepted as the last geological block accreted to eurasia before its collision with the northward drifting indian continent in the cenozoic but its lithospheric architecture drift and growth histories and the nature of its northern suture with eurasia via the qiangtang terrane remain enigmatic using zircon in situ u pb and lu hf isotopic and bulk rock geochemical data of mesozoic early tertiary magmatic rocks sampled along four north south traverses across the lhasa terrane we show that the lhasa terrane has ancient basement rocks of proterozoic and archean ages up to 2870 ma in its centre with younger and juvenile crust phanerozoic accreted towards its both northern and southern edges this finding proves that the central lhasa subterrane was once a microcontinent this continent has survived from its long journey across the paleo tethyan ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the qiangtang terrane to the north and with the indian continent to the south zircon hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks e g 50 90 0 70 and 30 100 to the mesozoic magmatism in the southern central and northern lhasa subterranes respectively we suggest that much of the mesozoic magmatism in the lhasa terrane may be associated with the southward bangong nujiang tethyan seafloor subduction beneath the lhasa terrane which likely began in the middle permian or earlier and ceased in the late early cretaceous and that the significant changes of zircon ehf t at 113 and 52 ma record tectonomagmatic activities as a result of slab break off and related mantle melting events following the qiangtang lhasa amalgamation and india lhasa amalgamation respectively these results manifest the efficacy of zircons as a chronometer u pb dating and a geochemical tracer hf isotopes in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics

age and thermal history of eo and neohimalayan granitoids eastern himalaya abstract four distinct granitoid suites outcrop across a n s transect in the eastern himalaya between the main central thrust mct and the indus tsangpo suture the arunachal and tsona leucogranites outcrop respectively in the mct hanging wall and adjacent the south tibetan detachment both crystallized at about 19 ma and appear to be lateral equivalents of the high himalayan leucogranites in the central tethyan himalaya the dala granitoids form a suite of undeformed plutons emplaced into deformed tethyan himalayan sequence metasediments in the northern tethyan himalaya the yala xiangbo granitoids are part of an igneous complex in the core of the yala xiangbo dome both the dala and yala xiangbo granitoids have eocene magmatic ages 44 1 1 2 ma and 42 5 ma respectively that are notably older than the vast majority of post collisional granitoids along the main himalayan arc pelitic units from the core of the yala xiangbo dome record two episodes of amphibolite grade metamorphism and monazite growth coinciding with well documented episodes of eohimalayan and neohimalayan metamorphism the thermochronological histories of the dala and yala xiangbo units suggest that the eastern tethyan himalaya was tectonically quiescent from ca 40 ma until ca 15 ma miocene exhumation of the dala and yala xiangbo units and all north himalayan domes studied to date appears best explained by a structural control such as concurrent north directed motion on the great counter thrust we hypothesize that an extension of the ninety east ridge may have been responsible for eocene high heat flow beneath the eastern himalaya and explain the localization of magmatism there

predicting the stand up time of temporary london clay slopes at terminal 5 heathrow airport the paper describes the results of finite element analyses of the temporary slope geometries in london clay at london heathrow airport s terminal 5 the aims of the analyses were to examine the times before failures developed and to identify the failure mechanisms involved the brittle behaviour of the london clay was modelled and the effects of progressive failure were taken into account the possible presence of tectonic shears with their strength close to residual was considered by comparing analyses with and without a tectonic shear zone the predicted time to failure of the slopes and the form of the failure whether shallow or deep seated were determined by a combination of the assumed permeability profile and whether or not allowances were made for increases in permeability as the clay swelled the average surface suction the in situ k0 profile the depth of excavation and whether or not a low strength tectonic shear surface was present in the slope the analyses fall into the category of clas

asian provenance of glacial dust stage 2 in the greenland ice sheet project 2 ice core summit greenland samples of dust from the greenland ice sheet project 2 gisp2 ice core summit greenland dated within marine isotope stage 2 between 23 340 and 26 180 calendar years b p around the time of the coldest local last glacial temperatures have been analyzed to determine their provenance to accomplish this we have compared them with approximately coeval aeolian sediments mostly loesses sampled in possible source areas psas from around the northern hemisphere the 5 m grain size fraction of these samples was analyzed on the basis that it corresponds to the atmospheric dust component of that time and locale which was sufficiently fine grained to be transported over long distances on the basis of comparison of the clay mineralogy and sr nd and pb isotope composition with ice dust and psas and assuming that we have sampled the most important psas we have determined that the probable source area of these gisp2 dusts was in eastern asia the dust was not derived from either the midcontinental united states or the sahara two more proximal areas that have been suggested as potential sources based on atmospheric circulation modeling except for a brief period during an interstadial when dust transport was exceptionally low for glacial times and had a mineralogical composition indicative of a slightly more southern provenance the source area of the dust did not change significantly during times of variably higher fluxes of dust with larger mean grain size or lower fluxes of dust with smaller mean grain size this includes the high dust period that correlates with the heinrich 2 period of major iceberg discharge into the north atlantic variable wind strengths must therefore be invoked to account for these abrupt and significant changes in dust flux and grain size

tunnelling induced deformation and damage on historical masonry structures the analysis of deformation and damage mechanisms induced by shallow tunnelling on masonry structures is carried out using an integrated geotechnical and structural numerical approach based on two dimensional finite element analyses the masonry construction schematised as a block structure with periodic texture is regarded at a macroscopic scale as a homogenised anisotropic medium the overall mechanical properties display anisotropy and singularities in the yield surface arising from the discrete nature of the block structure and the geometrical arrangement of the blocks the soil is modelled by means of a linear elastic perfectly plastic model the numerical analyses are performed assuming plane strain and plane stress conditions for the soil and the masonry structure respectively a displacement controlled technique is adopted to simulate the tunnel construction which produces settlement troughs in agreement with the empirical gaussian predictions at different volume losses under free field con

conjugate strike slip faulting along the bangong nujiang suture zone accommodates coeval east west extension and north south shortening in the interior of the tibetan plateau this is the published version copyright 2002 american geophysical union all rights reserved

geology s pb isotopes and 40 ar 39 ar geochronology of the zhaxikang sb pb zn ag deposit in southern tibet implications for multiple mineralization events at zhaxikang several au sb sb au pb zn and sb pb zn ag deposits are present throughout the north himalaya in southern tibet china the largest sb pb zn ag deposit is zhaxikang 18 mt at 0 6 wt sb 2 0 wt pb 3 5 wt zn and 78 g t ag zhaxikang veins are hosted within n s trending faults which crosscut the early middle jurassic ridang formation consisting of shale interbedded with sandstone and limestone deposited on a passive continental margin ore paragenesis indicates that zhaxikang mineralization occurred in two main phases composed of six total stages the initial phase was characterized by assemblages of fine grained mn fe carbonate arsenopyrite pyrite sphalerite stage 1 followed by relatively coarse grained mn fe carbonate fe rich sphalerite galena pyrite stage 2 the second phase was marked by assemblages of quartz pyrite fe poor sphalerite and ag rich galena tetrahedrite sericite stage 3 quartz sb pb sulfosalt minerals mainly composed of boulangerite and jamesonite stage 4 quartz stibnite cinnabar stage 5 and quartz calcite stage 6 sulfides of stage 2 have 34sv cdt of 8 4 12 0 206pb 204pb ratios of 19 648 to 19 659 207pb 204pb ratios of 15 788 to 15 812 and 208pb 204pb ratios of 40 035 to 40 153 sulfides of stage 3 have similar 34sv cdt of 6 1 11 2 and relatively more radiogenic lead isotopes 206pb 204pb 19 683 19 792 stage 4 sb pb sulfosalt minerals have 34sv cdt of 5 0 7 2 and even more radiogenic lead 206pb 204pb 19 811 19 981 by contrast stibnite of stage 5 has 34sv cdt of 4 5 7 8 and less radiogenic lead 206pb 204pb 18 880 18 974 taken together with the geological observations that the pb zn bearing mn fe carbonate veins were crosscut by various types of quartz veins sphalerite and galena of stage 2 underwent dissolution and remobilization and that sb pb fe sulfosalts formed at the expense of pb from stage 2 galena and of fe from stage 2 sphalerite we argue that the early pb zn veins were overprinted by later sb rich fluids stage 2 fluids were likely acidic and oxidized and leached lead from high grade metamorphic rocks of the greater himalayan crystalline complex ghc and sulfur from reduced rocks such as slate of the ridang formation along n s trending faults leading to precipitation of pb zn sulfides and mn fe carbonate and formation of solution collapse breccias later sb rich fluids leached pb from the ghc and the pre existing sulfides and deposited fe poor sphalerite ag rich galena tetrahedrite sb pb sulfosalts and stibnite in quartz veins that cut pre existing pb zn bearing mn fe carbonate veins the sb rich fluids also likely leached pb from early cretaceous gabbro and formed stibnite at shallow levels where early pb zn bearing mn fe carbonate veins are absent a sericite 40ar 39ar plateau age of 17 9 0 5 ma from stage 3 veins represents the timing of the onset of stage 3 mineralization

quantitative estimates of asian dust input to the western philippine sea in the mid late quaternary and its potential significance for paleoenvironment we present a new high resolution multiproxy data set of sr nd isotopes rare earth element soluble iron and total organic carbon data from international marine global change study core md06 3047 located in the western philippine sea we integrate our new data with published clay mineralogy rare earth element chemistry thermocline depth and delta c 13 differences between benthic and planktonic foraminifera in order to quantitatively constrain asian dust input to the basin we explore the relationship between philippine sea and high latitude pacific eolian fluxes as well as its significance for marine productivity and atmospheric co2 during the mid late quaternary three different indices indicate that asian dust contributes between similar to 15 and similar to 50 to the detrital fraction of the sediments eolian dust flux in core md06 3047 is similar to that in the polar southern pacific sediment coherent changes for most dust flux maximum minimum indicate that dust generation in interhemispheric source areas might have a common response to climatic variation over the mid late quaternary furthermore we note relatively good coherence between asian dust input soluble iron concentration local marine productivity and even global atmospheric co2 concentration over the entire study interval this suggests that dust borne iron fertilization of marine phytoplankton might have been a periodic process operating at glacial interglacial time scales over the past 700 ka we suggest that strengthening of the biological pump in the philippine sea and elsewhere in the tropical western pacific during the mid late quaternary glacial periods may contribute to the lowering of atmospheric co2 concentrations during ice ages