chemistry of hydrothermal fluids from the 17 s active site on the north fiji basin ridge sw pacific abstract in june 1989 a diving cruise of the french submersible nautile was made along the north fiji basin spreading ridge the objective was the geological and geochemical study of the active spreading axis and of the hydrothermal processes discovered during the kaiyo cruise in 1988 active anhydrite chimneys associated with underlaying sulfide deposits were studied in the central spreading ridge the transparent venting fluid showed significant salinity depletion the extrapolated concentrations of all the chemical species in the pure end member showed a signature similar to that of the cl depleted hydrothermal fluid from the ashes vent site in the juan de fuca ridge these features suggest that the present hydrothermal end member resulted from subcritical phase separation which generated a low salinity vapor phase followed by condensation and mixing with normal seawater in the last part of the plumbing system of the vents

late cenozoic river system reorganization and its origin within the qilian shan ne tibet abstract the northward growth of the tibetan plateau has reshaped the qilian shan orogen with prolonged history along two large strike slip faults the altyn tagh fault on the west and the haiyuan fault on the east this orogen with its high elevation is referred to as the water tower of the northeastern margin of the tibetan plateau shedding many rivers into the surrounding arid areas in a way different from all other orogens within the plateau the factors that control the evolution of these rivers in this highly active region particularly their relative contribution through time are not well known our study presents evidence that the left lateral movement of the haiyuan fault one of the largest active strike slip faults within the tibetan plateau since 13 8 ma created a series of nw trending linear thrust fold belts aligned in an en echelon pattern along the trace of the fault this completely reconfigured the flow direction of the rivers within the qilian shan range from n s rivers that flowed into the hexi corridor and qaidam basin to today s w e rivers flowing into the tarim basin and longxi basin along a series of nw trending linear thrust folds belt aligned in an en echelon pattern along the trace of the haiyuan fault on the north and south this river system reorganization event is corroborated by sedimentary and geochronologic evidence within the intermountain basins where these rivers flow the longxi basin the largest intermountain basin surrounding the qilian shan on the east was drained by rivers flowing east which were dammed by the uplift of the liupan shan since 10 8 ma to form a large lake the second river system reorganization again occurred through climate change in 1 8 ma it included the incision of the yellow river capturing major rivers and halting their flow to the southeast it is concluded that the haiyuan fault plays a crucial role not only in the lateral growth of the tibetan plateau but also in the uplift of the qilian shan which led to the river system reorganization

climate change and tectonic activity during the early pliocene warm period from the ostracod record at lake qinghai northeastern tibetan plateau abstract the early pliocene warm period epwp 5 3 ma is sometimes thought to be a useful analogue for a future warmer world and thus the boundary conditions and drivers of climate in the epwp may provide valuable lessons for understanding how a future warmer world might unfold lake qinghai is located on the northeastern margin of the tibetan plateau tp and is affected by both monsoon climate and westerlies circulation it is sensitive to the climate drivers of these systems its sediments accumulated over the cenozoic period are a rich source of information for climate tectonics and environmental changes of the period we present a high resolution ostracod record from a lake qinghai sediment core with a record of the period 5 10 2 60 ma thus covering the epwp ostracods appear at 4 63 ma and are most abundant until 3 58 ma while a body of water was present at the core site this suggests a phase of humid climate and an intensified asian summer monsoon asm which is consistent with a warmer and wetter climate in the early pliocene within this period the ostracod record shows some variabilities in lake level with deeper periods suggesting more intense asm compared to those with shallower water the disappearance of ostracods at 3 58 ma may provide evidence for the uplift of qinghai nanshan south of qinghai lake since this is when the asm intensified

downwind aeolian sediment accumulations associated with lake level variations of the qinghai lake during the holocene northeastern qinghai tibetan plateau many lakes in the qinghai tibetan plateau qtp have aeolian sands distributed in their downwind shores however it has been rarely systemically investigated on whether the downwind dune sand and lake evolved in association with each other or they evolved independently here we take the well known qinghai lake and its downwind sand area as a case study to investigate the issue of water sand interaction grain size magnetic susceptibility and geochemical data along with optically stimulated luminescence osl ages suggest that the downwind eastern shore sandy lands co varied with the lake level fluctuations or lake extension changes of the qinghai lake during the holocene epoch during the early holocene lake lowstands 11 9 ka ka is 1000 years vast areas of exposed lacustrine sediments were eroded by prevailing westerly winds therefore causing sand to accumulate at the eastern shore bajada areas along the west piedmonts of the riyue mount and to expand along the daotang river valley in contrast during the mid to late holocene lake highstands 7 1 2 ka eastern shore dune sands were largely stabilized and loess accumulated and even paleosol developed leading to substantial shrinkage of the eastern shore sandy lands in addition using gis tool we reconstructed the spatial extensions of the lake during highstand mid holocene and lowstand early holocene and eastern shore desert range of early holocene as a result this study indicates a close connection between the lakes in qtp and the aeolian sands downwind

microbial populations of hydrothermal fluid and plumes in the north fiji basin with reference to chemosynthesis abstract bacterioplankton abundance of the hydrothermal plumes in the north fiji basin nfb was anomalously high in bottom waters at several sampling stations good correlation between the manganese concentration and the bacterial viable counts was found for the bottommost waters sulfur bacterial strains supposedly major chemosynthetic microorganisms associated with hydrothermal activity were isolated from the bottommost water the bacterial population growth and the co2 uptake by the sulfur bacterial strains suggested the sulfur bacteria in the plumes were facultatively autotrophic also a sulfur bacterial strain from the hydrothermal fluid was shown to be thermophilic eurybaric biogeochemical roles of the planktonic sulfur bacteria in the hydrothermal area were pointed out as 1 a food source to filter feeders of the vent fauna and 2 a possible first settler of the hydrothermal ecosystems

use of ground probing radar and resistivity surveys for archaeological investigations in japan geophysical methods are normally used to estimate the distribution of cultural relics before digging objects of archaeological interest are usually located within a few meters of the surface therefore geophysical methods suitable for archaeological exploration are those which provide high resolution at shallow depths the most commonly used geophysical methods are ground probing radar resistivity and magnetometry of these methods we used mainly ground probing radar and resistivity surveys in archaeological investigations at four sites three of the sites were in gumma prefecture japan they were covered with volcanic deposits loam or pumice using ground probing radar we were able to locate ancient dwellings burial mounds and a distribution of archaeologically significant culture layers at the other site in nara prefecture we located part of the remains of an ancient city in this investigation the resistivity method and ground probing radar were combined to determine the loc

multi scale morphologic variability of the north fiji basin ridge southwest pacific abstract two cruises of the french japanese starmer joint project carried out with the submersibles nautile 1989 and shinkai 6500 1991 have been devoted to the in situ exploration of the north fiji basin ridge four areas located near 16 20 17 18 50 and 19 s have been explored during 42 dives at 16 20 s the axial zone trending n160 corresponds to a prominent graben with walls 1000 m high tectonic features and recent screes are present and the hydrothermal activity is characterized by sporadic fluid discharge at 17 s present accretion is confined to a high dome less than 1900 m deep and cut in its axial part by a wide graben trending n15 at this site hydrothermal features of two types are observed fossil chimneys of sulfides and active vents made of anhydrite and expelling water at 285 c the site at 18 50 s is located on top of an axial dome very similar to those of the east pacific rise small fissures and very fresh volcanic flows argue for a present day activity with weak evidence of tectonics hydrothermal emanations with animal colonies are found scattered over the whole area the fourth site at 19 s shows old and viscous lavas and a very mature tectonic activity compared to the preceding station which is located only 20 km northward large scale variations have been detected between three segments different thermal regimes can explain the distinct morphologies observed decakilometric scale variations do occur between stations 14 with volcanic predominance and 19 s where tectonic activity is dominating finally small scale variations are observed on sites 4 and 14 where volcanic features gradually give way to tectonic structures the north fiji basin ridge with an intermediate average spreading rate shows tectonic volcanic and hydrothermal variability ranging from 1 km to tens of kilometres and related to a temporary fine scale organisation of the accretionary processes

pleistocene drainage reorganization driven by the isostatic response to deep incision into the northeastern tibetan plateau pleistocene drainage basin integration led to progressive excavation of tertiary quaternary sedimentary basins along the yellow river in the northeastern tibetan plateau cosmogenic burial dating of ancestral river deposits and basin fi ll from two key watershed divides confi rms a fl uvial connection between basins at 0 5 1 2 ma prior to excavation by the yellow river pres ervation of the relict depositional surface that represents the maximum height of basin fi ll allows reconstruction of the volume of eroded material across a broad region we quantify the iso static response to this erosional unloading using a two dimensional fl exural model calculated maximum vertical displacements for different effective elastic thicknesses vary from 160 m to 260 m near the pleistocene spillway from the qinghai paleo lake we suggest that the isostatic response to fl excavation along the yellow river defeated local tributaries isolated lake qinghai and led to the development of an internally drained basin in the past 0 5 1 2 m y

the north fiji basin basalts and their magma sources part ii sr nd isotopic and trace element constraints abstract sr nd isotope and trace element data are reported for basalts from the north fiji basin nfb nfb basalts are characterized by extreme variations in isotopic ratios and trace element abundances which are related to mantle heterogeneities values of 87 sr 86 sr for basalts from the northern segments n160 and triple junction range from 0 7029 to 0 7041 whereas 143 nd 144 nd values vary from 0 51281 to 0 51313 most of the basalts from these segments are characterized by strong relative enrichments in rb ba sr k nb ta la ce and ti that are comparable to oib components the central segments n15 and n s have 143 nd 144 nd ratios between 0 51298 and 0 51363 and 87 sr 86 sr ratios between 0 7029 and 0 7033 and are depleted in large ion lithophile light rare earth and high field strength elements similar to n morb covariation between trace element and isotopic ratios among nfb basalts supports a model in which melts from the nfb rift system are derived by mixing of oib type and depleted n morb mantle components the sr nd isotopic and trace element variability indicates that the nfb basalt source is heterogeneous on the scale of individual melt batches

revisiting clay sized mineral and elemental records of the silicate weathering history in the northern tibetan plateau during the late cenozoic the role of aeolian dust

seafloor spreading in the north fiji basin southwest pacific abstract the seapso leg 3 cruise december 1985 was carried out in the north fiji basin aboard the ifremer r v jean charcot the main purpose of the cruise was to carry out a geophysical and geological study of the central part of the basin between 16 s and 22 s to this end bathymetric profiles with the help of the seabeam multichannel echosounder single channel seismic reflection profiles and magnetic and gravimetric profiles were made moreover geological samples were taken by dredging and piston coring as well as water samples with the help of a multiprobe one of the aims of the cruise was to explore the present day spreading axis of the north fiji basin we were able to show that accretion the rate of which is about 7 cm yr in the north fiji basin has been constrained in a n s direction for 3 ma very recently between 0 6 and 0 7 ma ago the accretion process changed resulting in the creation of a ridge ridge trench triple junction centered at 173 30 e and 16 40 s water samples taken in the vicinity of this triple junction show significant anomalies of methane and manganese which are probably linked to hydrothermal events in its morphological characteristics transversal as well as longitudinal the ridge of the north fiji basin shows striking similarities to the east pacific rise it presents the same differences in level the same sizes of structures and the same particular features overlapping spreading centers offsets etc another aim of the seapso cruise was to study the complex deformation area located immediately to the west of the fiji islands which we interpret as a distensive type deformation in a strike slip system

helium and carbon geochemistry of hydrothermal fluids from the north fiji basin spreading ridge southwest pacific the north fiji basin is one of the active marginal basins in the southwestern pacific hydrothermal fluid emanations were located at two sites on the central ridge of the basin high temperature fluids 230 290 c venting from anhydrite chimneys at a 17 s site have end member compositions of 11 0 14 5 mmol kg of co2 30 4 43 5 mol kg of ch4 and 2 3 4 5 10 5 cm3stp g of he taking phase separation processes into account the gas abundances are not enriched compared with the mid oceanic ridge hydrothermal systems isotopic compositions of co2 13c 6 2 to 5 7 pdb ch4 13c 20 to 18 pdb and helium rra 9 0 10 0 are comparable to the mid oceanic ridge signature together with basalt helium data the helium isotopic signature may be attributed to the incorporation of a hotspot like primitive component low temperature shimmering fluids the highest measured temperature was 5 2 c associated with biological communities at a site at 18 50 s show slight chemical anomalies in some species in sio2 mn li ph and ch4 and helium isotope ratios distinct from ambient seawater evaluated helium isotopic compositions prior to dilution fall between rra 8 4 and 8 9 supporting the suggestion of high temperature hydrothermal activity at this site although this was not observed by dive expeditions the gas geochemistry of these two different types of fluids show several similar characteristics to the mid oceanic ridge hydrothermal systems this result is in accordance with previous petrological studies which demonstrated a dominant n morb source signature and a co existing oib source influence of the north fiji basin magmatism

late pliocene establishment of exorheic drainage in the northeastern tibetan plateau as evidenced by the wuquan formation in the lanzhou basin abstract the fluvial archives in the upper reach yellow river basins provide important information about drainage history of the northeastern tibetan plateau tp associated with geomorphologic evolution and climate change however the pliocene fluvial strata within this region have not been studied in detail hence limiting the understanding of the late cenozoic development of regional fluvial systems in this paper we present the results of a study of the geochronology sedimentology and provenance of the fluvial sequence of the wuquan formation in the lanzhou basin in the northeastern tp magnetostratigraphic and cosmogenic nuclide burial ages indicate that the wuquan formation was deposited during 3 6 2 2 ma furthermore sedimentary facies gravel composition paleocurrent data and detrital zircon u pb age spectra reveal that the fluvial sequence resembles the terraces of the yellow river in terms of source area flow direction and depositional environment our results indicate that a paleo drainage system flowing out of the northeastern tp was established by ca 3 6 ma and that the upstream parts of the yellow river must have developed subsequently from this paleo drainage system the late pliocene drainage system fits well with the dramatic uplift of the northeastern tp an intensified asian summer monsoon and global increase in erosion rates which may reflect interactions between geomorphic evolution tectonic deformation and climate change

fault plane solutions of earthquakes and active tectonics of the tibetan plateau and its margins summary fault plane solutions of earthquakes within and on the margins of the tibetan plateau show diverse styles of faulting and deformation with thrust faulting and crustal shortening normal to the margins of the plateau and with normal and strike slip faulting resulting in roughly east west crustal extension within the plateau the direction of overthrusting of the himalaya onto the indian shield is radially outward varying from southwest in the western himalaya to south southeast in the east assuming that the indian shield behaves rigidly this requires a west northwest divergence of western tibet from southeastern tibet at a rate of 18 9 mm yr 1 comparable with the rate of convergence at the himalaya fault plane solutions of earthquakes in the southern portion of the tibet plateau consistently show large components of normal faulting on roughly north striking planes and corroborate such extension within the high plateau where elevations exceed 5000 m normal and strike slip faulting occur so that an overall east southeast west northwest extension of the region at about 10 mm yr 1 is partitioned into roughly equal parts of crustal thinning and north northeast south southwest crustal shortening about 5 mm yr 1 in general strike slip faulting characterizes solutions for earthquakes within eastern tibet where mean elevations drop below 4500 5000 m but the orientations of the strike slip faults vary across the region in central tibet left lateral slip occurs on planes trending roughly northeast but for earthquakes farther east the orientations of that plane become progressively east west and then southeast this variation in orientation implies a rotation of material along curved left lateral shear zones thus the eastward extrusion of tibet appears to be facilitated not only by rapid left lateral shear but also by large clockwise rotations of the material in eastern tibet the rate of eastward extrusion of material in eastern tibet relative to the tarim basin to its north is roughly 30 40 mm yr 1 fault plane solutions of earthquakes in the northern and eastern margins of tibet show large components of thrust faulting with the p axes oriented radially outward from the plateau and approximately perpendicular to the regional topographic contours of the plateau the orientation of this crustal shortening is northeast southwest on the northeastern margin east west on the eastern margin and northwest southeast in the longmenshan on the southeastern margin thus at least some of the extrusion of eastern tibet out of india s northward path into asia is absorbed by crustal shortening on the margins of the plateau the variation from normal faulting in the high tibetan plateau where elevations exceed 5000 m to dominantly strike slip faulting farther east where elevations are lower and then to thrust faulting on the margins of the plateau where elevations drop below 3000 m surely results at least in part from a decrease in the value of the vertical stress the magnitude of the east west compressive stress need not vary across the plateau

800 km long n s spreading system of the north fiji basin abstract the 800 km long n s spreading system in the north fiji basin consists of six contiguous fan shaped rift segments each 100 200 km long with various structural styles such as structural overprinting triple junction rift propagation voluminous magmatism and transform or strike slip fault influence deformation of the plate boundary system within the young hot weak lithosphere occurred under local stress conditions resulting in a unique rift segmentation distinct from that of midoceanic ridges spreading across a series of short and variably oriented segments produces series of fanning spreading centers whose rotation pole is located at the end of each segment the surrounding seafloor basement has adjusted to this setting with non rigid deformation or with fragmentation furthermore the changing tectonic framework caused by the arc rotation probably makes it difficult to keep the same stress condition for a long period small scale fan shaped sea floor spreading is short lived and results in a rapidly evolving plate boundary geometry this suggests a more complicated tectonic style for marginal basins than mid ocean ridge spreading centers

late quaternary lake level changes of lake el gygytgyn ne siberia abstract lake el gygytgyn is situated in a 3 6 ma old impact crater in northeastern siberia presented here is a reconstruction of the quaternary lake level history as derived from sediment cores from the southern lake shelf there a cliff like bench 10 m below the modern water level has been investigated deep water sediments on the shelf indicate high lake levels during a warm mid pleistocene period one period with low lake level prior to marine oxygen isotope stage mis 3 has been identified followed by a period of high lake level 10 m above present in the course of mis 2 the lake level dropped to 10 m at the end of mis 2 the bench was formed and coarse beach sedimentation occurred subsequently the lake level rose rapidly to the holocene level changes in water level are likely linked to climate variability during relatively temperate periods the lake becomes free of ice in summer strong wave actions transport sediment parallel to the coast and towards the outlet where the material tends to accumulate resulting in lake level rise during cold periods the perennial lake ice cover hampers any wave activity and pebble transport keeping the outlet open and causing the lake level to drop

geology and geochemistry of a 800 m section through young upper oceanic crust in the north fiji basin southwest pacific lagabrielle y auzende j m eissen j p janin m c and cotten j 1994 geology and geochemistry of a 800 m section through young upper oceanic crust in the north fiji basin southwest pacific in j m auzende and t urabe editors north fiji basin starmer french japanese program mar geol 116 113 132 we report the results of geological and structural observations made during one dive of the french submersible nautile during the starmer cruise in 1989 in the vicinity of the 16 40 s triple junction in the north fiji basin this dive provided a spectacular 800 m continuous section of oceanic crust exposed along the northern wall of a 3000 m deep basin at the eastern branch of the triple junction a number of volcanic facies have been encountered including massive and pillowed lavas sheeted dikes and spectacular columnar jointed massive lavas pillowed lavas have been observed only at the base and at the top of the section the ratio between massive and pillowed basalts is high suggesting that the crust in this area grew mostly during a stage of high eruptive rate dikes have been observed in the middle part of the section they probably do not represent the top of a classical dike complex but an isolated set of sheeted dikes possibly the feeders of overlying flows the abundance of vertical tectonic breccias observed during the first part of the dive confirms that the basal part of the wall can be regarded as a major tectonic boundary along which occurred significant vertical and strike slip motions micropaleontological data from sedimentary rocks collected during the dive bring new constraints to the evolution of the triple junction the oceanic crust in the surveyed area is at least as old as 1 9 1 3 ma based on the age of sedimentary rocks collected in talus at the base of the wall and observed at the summit of the section the collected basalts include 1 n type morbs 2 e type morbs and 3 babbs this emphasizes the heterogeneous nature of the mantle beneath the central nfb some portions of the depleted mantle underlying the central nfb triple junction area have recorded contamination from melts or fluids from an ancient subduction zone probably the new hebrides during the opening of the nfb whereas adjacent mantle areas show the influence from an alkali enriched source such alkali enriched characters are reported from recent basalts of the northern nfb south pandora ridge rotuma island

lake qinghai sediment geochemistry linked to hydroclimate variability since the last glacial abstract geochemistry of basin sediments from semi arid regions is valuable to understand past hydroclimatic changes here we investigate the links of sedimentary geochemistry rb sr ca zr toc and caco 3 carbonate mineralogy and ostracod shell 18 o of lake qinghai a basin proximal to major dust production centers at mid latitudes of the northern hemisphere to changes in depositional conditions and hydroclimate during the past 32 ka surface lacustrine sediments are characterized by low rb high sr low rb sr high caco 3 and high ca zr values in contrast to the chemical compositions of eolian loess high rb low sr high rb sr low caco 3 and low ca zr a direct comparison of soluble ca and sr in two short cores with instrumental water discharge data suggests that lacustrine precipitates in lake qinghai are dominated by authigenic aragonite formed under ca 2 limited water conditions and that the accumulation rate of aragonite dominantly depends on solute fluxes into the lake during the rainy seasons late may to september our high resolution down core records show that sediments during the last glacial 32 19 8 ka had high rb low sr low caco 3 and low ca zr indicating eolian dust loess accumulation in a desiccated basin under dry glacial conditions further supported by grain size and pollen results this type of sedimentation was maintained during the last deglacial 19 8 11 5 ka but interrupted by episodic lacustrine precipitates with high sr high caco 3 high ca zr and low rb at 11 5 ka sedimentary rb sr ca zr caco 3 and toc show dramatic and permanent changes implying an abrupt shift in the atmospheric circulation at the onset of the holocene in the lake qinghai region lacustrine precipitates have persisted throughout the holocene with a maximum during the early to mid holocene 10 5 8 0 ka since 8 0 ka the gradual and significant decreases in aragonite and sr accumulations in tandem with increasing dust deposit and more positive ostracod 18 o may be linked to a weakening of asian summer monsoons during the mid to late holocene overall our records appear to show a high sensitivity of sediment development and geochemistry in lake qinghai to the regional hydroclimate changes since the last glacial

sr nd and pb isotope constraints on the formation of the metalliferous sediments in the nereus deep red sea previous chemical analyses of sediments from nereus deep core 412 located in the northern part of the red sea at about 23 20 n have demonstrated the occurrence of v rich authigenic magnetites associated with fe zn and cu sulphides mostly located at the bottom of the core the evolutionary stage of nereus deep is intermediate between that of the immature shaban deep and the more evolved atlantis ii deep previous studies have proposed either morb basalts by analogy with east pacific rise sulphide deposits or sediments as possible sources of the metals in the red sea metalliferous sediments sr nd and pb isotope systematics observed at ten levels in nereus core 412 lead us to distinguish three types of sediments 1 with predominantly basaltic fragments associated with loose titanomagnetite crystals 0 70413 87sr86sr 0 70622 0 51271 143nd144nd 0 51300 18 618 206pb204pb 18 673 2 detrital or biogenic sediments with a continental isotopic imprint 0 70938 87sr86sr 0 71323 0 51242 143nd144nd 0 51262 18 848 206pb204pb 18 890 and 3 v rich metalliferous sediments 0 70872 87sr86sr 0 70895 0 51260 143nd144nd 0 51274 18 717 206pb204pb 18 851 on sr nd and pb pb isotope diagrams this last group of sediments defines a field located between the fields of the first two groups our data suggest that the sr nd and pb in the studied metalliferous sediments were derived from overlying sedimentary beds in which the two main constituent detrital components show very distinct origins red sea morb and continental arabo nubian shield these data clearly support a model of convective circulation within the nereus deep sedimentary pile this model involves leaching two main components from the upper sedimentary layers of the core and a downward circulation of a hot fluid promoting the growth of v rich magnetites and fe zn and cu sulphides when the fluid cooled by mixing with the pore water of sediments from the lower part of the core a driving force represented by magmatic activity located near the 412 core in the nereus deep is required to explain the presence of hot convective fluids these data also suggest that for sedimented ridges the isotopic imprint of a basaltic source in metalliferous sediments or a hydrothermal ore deposit may result by interaction of a hot fluid with detrital sediments that are enriched in basaltic clasts and loose magmatic crystals

deglacial and holocene archaeal lipid inferred paleohydrology and paleotemperature history of lake qinghai northeastern qinghai tibetan plateau abstract we investigate the distribution of archaeal lipids in a 5 8 m long sedimentary core recovered from lake qinghai to extract regional hydroclimate and temperature signals since the last deglaciation for this important region the paleohydrology was reconstructed from the relative abundance of thaumarchaeol thaum and the archaeol and caldarchaeol ecometric ace index the thaum inferred lake level record was extended to deglaciation showing three periods 11 9 13 0 14 1 14 7 and 15 1 17 2 cal ka bp with relatively higher lake levels than those during the early holocene the ace record demonstrates three periods 10 6 11 2 13 2 13 4 and 17 4 17 6 cal ka bp of elevated salinity when the lake was shallow filtered tex86 record based on archaeal lipid distributions corresponded to relatively higher lake levels implying that a certain lake size is required for using the tex86 paleothermometer at 1 4 cal ka bp the reconstructed temperature fluctuated significantly and correlated negatively with inferred lake level indicating that lake temperature and hydrological change might be coupled during this period we attribute this co variance to the importance of summer temperature in controlling evaporation for this arid semi arid region moreover our results indicate that archaeal lipids have potential in reconstructing paleoclimate patterns from lacustrine sedimentary cores but the data should be interpreted with care

recent geodynamic evolution of the north fiji basin southwest pacific a cruise of the r v jean charcot seapso iii december 1985 in the north fiji basin between 16 and 22 s obtained new structural and magnetic data concerning the central part of the basin these have been used for the reinterpretation of the national oceanic and atmospheric administration and u s naval research project aeromagnetic survey 1979 the structural surface ship magnetic and aeromagnetic data allow us to present a sketch of the evolution in four stages of the north fiji basin for the past 10 m y

active tectonism within the fiji platform southwest pacific new observational data on the velocity structure seismicity and state of stress of the large submarine platform that includes the fiji islands demonstrate that the platform is an active participant in the pervasive regional deformation of the pacific indian australian plate boundary refraction data collected within the fiji platform demonstrate that its crustal thickness 15 25 km and seismic velocity structure are comparable to those of active island arcs uppermost mantle velocity beneath the platform is anomalously low 7 55 km s in the same range as that observed beneath the neighboring marginal basins and island arcs shallow seismicity is observed both within and along the boundaries of the fiji platform moderate to large earthquakes within the platform occur more sporadically than those along its margins these intraplate events are separated by long periods of quiescence earthquake depths within the platform are concentrated in the upper 13 16 km as in other areas of extensional strike slip tectonics both the large 1953 suva earthquake m s 6 75 and microearthquakes within and around the island of viti levu occur by strike slip faulting under the same stress field that is deforming the north fiji and lau basins the low upper mantle velocities presence of widespread seismicity and neogene volcanism and state of stress of the fiji platform contradict the notion of a stable land mass surrounded by zones of deformation in the neighboring back arc basins

wind blown origin of the pliocene red clay formation in the central loess plateau china abstract in order to determine the depositional processes of the pliocene red clay formation deposited directly beneath the plio pleistocene loess in the chinese loess plateau four red clay sections spanning over 400 km are studied grain size analysis of closely spaced samples in the sections shows that the particles of the red clay are very fine with the sand fraction 63 m being negligible and that all the curves indicating changes in different grain size parameters have a similar pattern the grain size records in the upper part of the four sections are almost identical with the median grain size centered at 4 8 m the ree patterns of 28 samples from the jiaxian red clay section are all characterized by lree enrichments relatively flat hree and slight negative eu anomaly being similar to those of eolian loess and the average upper continental crust these lines of evidence point to a wind blown origin of the red clay deposits accumulation of the loess soil sequences in the chinese loess plateau during the past 2 6 ma can be therefore regarded as the continuation of the pliocene atmospheric dust deposition observations of spatial grain size changes in the loess plateau suggest that the eolian red clay might be transported mainly by the westerlies differing significantly from the overlying loess that was transported essentially by the east asia winter monsoonal winds

in situ geological and geochemical study of an active hydrothermal site on the north fiji basin ridge abstract in june 1989 a diving cruise by the submersiblenautile was carried out on the north fiji basin spreading ridge the objective of the cruise was a geological and geochemical study of the active spreading axis and associated hydrothermal processes this operation was the third cruise of the french japanese starmer project following the two cruises of the r v kaiyo in 1987 and 1988 six dives along the spreading axis between 16 58 s and 17 00s show that the axial graben consists of alternating n15 trending horsts and grabens extinct hydrothermal sites have been observed all along the graben these consist of fossil chimneys oxide staining and dead shells at 16 59 s an active chimney has been discovered and called the white lady because of its almost exclusively anhydrite composition this chimney expels a peculiar water characterized by low chlorinity and a 285 c maximum temperature in the northern extremity of the n15 axis a wide fossil hydrothermal site has been explored and sampled it is located in an area cut by n15 n140 and n60 trending faults and fissures

ground penetrating radar survey finalized to the recovery of the s agata alla badia church in catania eastern sicily italy numerous archaeological sites dating to the greek roman period have been found in the underground of the city of catania eastern sicily italy their presence is a testimony of the several settlements that have followed in this area over time in this work we have conducted electromagnetic surveys consisting of ten georadar profiles inside the church of s agata alla badia damaged during the earthquake occurred in eastern sicily on 13 december 1990 the aim was to investigate the area where the church is located to obtain information useful for its structural recovery mechanical drillings were also carried out to reconstruct the local stratigraphy which could be complicated by the presence of underground cavities and artefacts as evidenced by recent excavations beneath the catania cathedral in the nearby piazza duomo from the interpretation of the gpr data the presence of ancient masonry structures underlying the recent foundations was highlighted in addition the gpr survey allowed us to identify and locate reflective horizons in the subsurface probably due to the presence of materials with different state of aggregation and or to buried structures

sedimentary evolution of the foreland basin in the ne tibetan plateau and the growth of the qilian shan since 7 ma we studied the magnetostratigraphy and sedimentary facies of a 550 m long drill core from the jiudong basin in the ne tibetan plateau our aims were to reconstruct the late cenozoic sedimentary evolution of this foreland basin and to determine the spatiotemporal pattern of growth of the qilian shan the magnetostratigraphy indicates that the sedimentary sequence was deposited during ca 7 0 ma from ca 6 7 3 0 ma the sediment accumulation rate increased gradually from similar to 30 mm k y to 120 mm k y which was associated with the gradual evolution of sedimentary facies from a shallow lake delta front to braided rivers the progradation of the depositional system from 7 ma to 3 ma probably reflects the growth of the relief of the qilian shan caused by tectonic uplift the occurrence of a continuous braided river environment from 3 ma to the present suggests that the high relief of the qilian shan developed before 3 ma an abrupt decrease of the sedimentation rate to similar to 46 mm k y during 3 0 1 8 ma and the deposition of coarse grained sediments indicates the uplift of the basin center we interpret this to reflect the propagation of the thrust system of the qilian shan into the basin along a southward dipping decollement from ca 3 ma climatic changes may have influenced the sedimentary sequence by introducing long distancetransported thin coarse sand gravel layers which are sandwiched within the sequence and likely were a response to cooling events or climatic transitions the widespread occurrence of deformation within the basin region in the ne tibetan plateau at ca 3 ma indicates that this date marks the basinward growth of the deformation system

northeastward growth of the tibet plateau deduced from balanced reconstruction of two depositional areas the qaidam and hexi corridor basins china we address the problem of late cenozoic uplift erosion and growth of northeastern tibet by reconstructing from isopach maps and drill holes the volumes and masses of sediments deposited in the qaidam and hexi corridor basins since 35 myr ago the mass budget is based on simple geometrical assumptions such as regional similarity of the thickness ratios between strata of different ages in the qaidam where our record extends back to the oligocene the budget shows a huge rise of the accumulation rates after the beginning of the pliocene 5 3 ma the early pliocene seems to be the period of maximum deposition with accumulation rates in excess of 1 mm yr 1 2 7 kg m 2 yr 1 of compacted rocks throughout the basin there also seems to be a southeastward shift of the largest depocenters between the upper pliocene 3 4 1 6 ma and the quaternary in the hexi corridor sedimentation is confined to small foreland flexural depressions associated with the frontal thrusts of the qilian shan and occurs at an average rate one order of magnitude smaller than in the qaidam basin the accumulation rate is maximum in the quaternary the sedimentation history appears to support a plateau building mechanism resulting from the combination of two geologicallly common processes crustal scale thrusting and sedimentary basin infilling the time needed to completely fill the qaidam basin and make its catchment a plateau closely resembling that of the highest part of tibet qangtang is of the order of 9 myr the mechanism now at work north of the kunlun which involves rapid infilling of broad flat areas separated by relatively narrow mountain ranges has thus probably been important in producing the high smooth topography that characterizes much of central tibet

mid pliocene asian monsoon intensification and the onset of northern hemisphere glaciation the late pliocene onset of major northern hemisphere glaciation nhg is one of the most important steps in the cenozoic global cooling although most attempts have been focused on high latitude climate feedbacks no consensus has been reached in explaining the forcing mechanism of this dramatic climate change here we present a key low latitude climate record the high resolution asian monsoon precipitation variability for the past fi ve million years reconstructed from south china sea sediments our results with supporting evidence from other records indicate signifi cant mid pliocene asian monsoon intensifi cation preceding the initiation of nhg at ca 2 7 ma ago this 1 4 million year long monsoon intensifi cation probably enhanced monsoon induced asian continental erosion and chemical weathering and in the process left fi ngerprints in marine calcium isotopes furthermore increased rock weathering and or organic carbon burial probably lowered the contemporary atmospheric co 2 and may have triggered the nhg onset

seven million years of wind and precipitation variability on the chinese loess plateau abstract recent studies of the eolian deposits in northern china have extended the east asian monsoon history back to the early miocene however the relative intensities of monsoonal winds and precipitation and the extent of their coupling prior to the pleistocene epoch remain poorly constrained mainly due to uncertainties in the interpretation of proxy indices generated from the mio pliocene red clay sequences here we reconstruct east asian monsoon oscillations over the past 7 ma using magnetic susceptibility and carbonate content as summer monsoon precipitation proxies and quartz grain size as a winter monsoon wind intensity index our results suggest that precipitation and wind intensity exhibited significant orbital scale variations prior to 4 2 ma followed by slightly damped variability between 4 2 and 2 75 ma subsequently east asian monsoon circulation experienced two large shifts at about 2 75 and 1 25 ma characterized by stepwise strengthening of glacial wind and interglacial precipitation a remarkable change in east asian monsoon seasonality occurred around 3 15 2 75 ma prior to 3 15 ma strong winds were positively correlated with high effective precipitation whereas after 2 75 ma strong winds were negatively correlated with heavy precipitation this shift was probably induced by a change from an insolation forced system to one strongly influenced by the combined effects of the phased uplift of the himalaya tibetan plateau and the simultaneous development of the northern hemisphere ice sheets

kinematics of active spreading in the central north fiji basin southwest pacific abstract based on a synthesis of magnetic and bathymetric data we re evaluate the kinematics of the recent opening of the central part of the north fiji basin nfb the westward motion of the pacific plate along the left lateral north fiji fracture zone nffz results in the opening of two n s trending spreading ridges located at 173 30 e and 176 e both ridges show complex features such as propagating rifts ridge jumps and overlapping spreading centres their spreading rates are similar 7 6 to 4 cm yr 1 across the western ridge 5 5 cm yr 1 across the eastern one while the nffz is purely strike slip to the east of the eastern ridge it becomes more complex to the west it changes from transpressional to transtensional then to purely transform and finally joins the western n s ridge in a rrr type triple junction our kinematic analysis shows that most of the left lateral motion along the nffz is transferred to the eastern ridge at the rtf type 176 e triple junction it suggests that the western n s ridge is probably connected to the north with another left lateral transform possibly the south pandora ridge

late cenozoic climate changes in china s western interior a review of research on lake qinghai and comparison with other records abstract we review late cenozoic climate and environment changes in the western interior of china with an emphasis on lacustrine records from lake qinghai widespread deposition of red clay in the marginal basins of the tibetan plateau indicates that the asian monsoon system was initially established by 8 ma when the plateau reached a threshold altitude subsequent strengthening of the winter monsoon along with the establishment of the northern hemisphere ice sheets reflects a long term trend of global cooling the few cores from the tibetan plateau that reach back a million years suggest that they record the mid pleistocene transition from glacial cycles dominated by 41 ka cycles to those dominated by 100 ka cycles during terminations i and ii strengthening of the summer monsoon in china s interior was delayed compared with sea level and insolation records and it did not reach the western tibetan plateau and the tarim basin lacustrine carbonate 18 o records reveal no climatic anomaly during mis3 so that high terraces interpreted as evidence for extremely high lake levels during mis3 remain an enigma following the last glacial maximum lsm several lines of evidence from lake qinghai and elsewhere point to an initial warming of regional climate about 14 500 cal yr bp which was followed by a brief cold reversal possibly corresponding to the younger dryas event in the north atlantic region maximum warming occurred about 10 000 cal yr bp accompanied by increased monsoon precipitation in the eastern tibetan plateau superimposed on this general pattern are small amplitude centennial scale oscillations during the holocene warmer than present climate conditions terminated about 4000 cal yr bp progressive lowering of the water level in lake qinghai during the last half century is mainly a result of negative precipitation evaporation balance within the context of global warming

geological evidence bearing on the miocene to recent structural evolution of the new hebrides arc abstract the new hebrides archipelago is a complex reversed arc system that can be divided into four major volcanic provinces the western belt is an early to middle miocene extinct volcanic arc that as a result of polarity reversal is now incorporated into the frontal arc of the present day configuration the eastern belt initially received detritus in the early middle miocene from a tholeiitic arc complex but in the mio pliocene became the locus of a more calc alkaline arc volcanism volcanic activity then ceased in the eastern belt but is well represented as a third and largely submerged marginal province through the pliocene into the early pleistocene the present volcanic line the central chain is essentially a continuation of the marginal province volcanism into recent times initial tectonic events in the new hebrides arc were associated with the regional disruption in the middle miocene of an east facing system with consequent termination of western belt arc volcanism the western belt remained as a landmass during the lowermost late miocene but subsided following a late miocene renewal of island arc volcanism to the east this latest phase was coeval with initial expansion of the north fiji basin and marked the advent of the new hebrides as a westwards migrating reversed arc system during arc migration there were apparent hiatuses in island arc volcanism the most notable being a middle pliocene to late pleistocene period of quiescence in the central sector tectonism in the early pleistocene recent raised the fore arc brought about rifting and extension to the rear and concentrated volcanism along the presently active central chain

mid pliocene global land monsoon from pliomip1 simulations abstract the mid piacenzian pliocene warm period approximately 3 3 3 0 ma monsoon not only provides us with a useful insight into the future monsoon under a warming scenario with high atmospheric co2 concentration but is also hypothesized to play a key role in climate feedback through impact on the carbon cycle on a geological timescale the monsoon evolution over time is one key to test this hypothesis in this sense we examine the mid piacenzian global land monsoon area glma precipitation glmp and glmp intensity glmpi using all available model data from the pliocene model intercomparison project phase 1 pliomip1 relative to the pre industrial period both the glma and glmp increase in the mid piacenzian and by an average of 7 3 and 5 8 respectively on a large scale the increased glmp comes mainly from northern africa asia and northern australia quantitatively it is the variation of glma not of glmpi that makes a major contribution to the glmp change further analysis reveals that anomalous inland water vapor transportation due to the reduced large scale meridional thermal contrast in the mid to upper troposphere together with the variation of vertical moisture advection and evaporation explains most of the global land monsoon changes a model data comparison shows that the simulated monsoon precipitation variations are roughly consistent with the reconstructions in northern africa asia northern australia central america and eastern south america moreover the intensified mid piacenzian asian monsoon which is supported by both simulations and reconstructions or an overall intensified global land monsoon is hypothesized to contribute to the lowering of atmospheric co2 concentration and the subsequent onset of the sustained major northern hemisphere glaciation

systematics of and postulated controls on submarine hydrothermal solution chemistry the chemical compositions of seafloor hydrothermal solutions from the galapagos spreading center 21 n and 13 n on the east pacific rise the southern juan de fuca ridge and the guaymas basin gulf of california are examined for systematic variations several elemental ratios elemental products and empirical geothermometers show much consistency among the various areas in spite of large absolute differences in elemental concentrations the results suggest that most of the major cations in these solutions are solubility controlled with respect to a similar phase assemblage at all of the sites examination of the solution chemistry in conjunction with experimental results and seafloor rock alteration data permits identification of phases which may be important in controlling the solution chemistry as potassium appears to be solubility controlled its use to calculate water rock ratios is inappropriate lithium appears to be a better element to use in these calculations a model to explain the observed solution chemistries as a result of three component mixing is discussed all of the solutions are postulated to be either the result of mixing between a seawater hydrothermal solution which has not undergone a phase separation and is hence gas containing a gas rich vapor phase and a gas poor brine phase or any one of these individual components alone the vapor and brine phases are the result of phase separation which may have occurred at some time in the past essentially all of the reported data fall within the field defined by these three components the solutions apparently have had sufficient time after the mixing event s to reequilibrate with the rock this is true for quartz as well as other chemical components the best test of this model is chloride together with gas and isotropic data as the model predicts that solutions with elevated chlorinities will be depleted in gases and enriched in 18 o and low chlorinity solutions will have elevated gas contents and lower 18 o

late miocene early pleistocene paleoclimate history of the chinese loess plateau revealed by remanence unmixing previous studies show that the quaternary loess sequence and the late miocene pliocene red clay sequence on the chinese loess plateau clp share similar magnetic properties despite their being deposited under different climate conditions to solve this paradox we apply a novel remanence unmixing technique and demonstrate that loess and red clay on the central clp contain a similar low coercivity pedogenic component but their high coercivity components differ dramatically reflecting different oxidation and temperature conditions we infer that temperatures on the chinese loess plateau cooled from the late miocene to the quaternary in a manner similar to sea surface temperature records for the same time interval this coherency between marine and terrestrial records argues for a co2 forcing on long term paleoclimatic variations key points backfield remanence data of chinese loess and red clay consist of two components loess and red clay have similar pedogenic but different detrital components the loess plateau experienced a cooling trend from the late miocene to the quaternary

modeling the late pliocene global monsoon response to individual boundary conditions the late pliocene is a pre quaternary warming period compared to the preindustrial period here based on the updated prism4 pliocene research interpretation and synoptic mapping version 4 boundary conditions from the pliocene model intercomparison project phase 2 pliomip2 seven experiments are conducted to simulate the global monsoon in the late pliocene interglacial period and further investigate the impacts from changes in the individual boundary conditions by using the community earth system model cesm 1 0 4 the simulated late pliocene interglacial climate is generally warmer and wetter than the preindustrial period climate with an expanded monsoon domain particularly in north africa asia and australia the differences in topography vegetation and lakes outside of greenland and antarctica account for the greatest contribution to monsoon changes moreover orbital parameter variations further significantly affect monsoon domains and lead to significant fluctuations in monsoon precipitation and winds on the orbital scale and the changed magnitude is even larger than that between the late pliocene and preindustrial period when orbital forcing is not considered

holocene aeolian activity and climatic change in qinghai lake basin northeastern qinghai tibetan plateau abstract aeolian deposits in the qinghai lake basin on the northeastern qinghai tibetan plateau netp were studied in order to reconstruct changes in aeolian activity related to climatic changes over the last 12 5 ka we used 20 optically stimulated luminescence and conventional radiocarbon dates to construct chronological frameworks for four aeolian sections the results indicate that aeolian activity occurred episodically at 12 5 ka 11 2 ka 9 0 ka 8 5 ka 5 5 ka 2 6 2 4 ka and 1 0 9 ka paleosols developed mainly during 9 5 4 ka the field stratigraphy of the sections together with measurements of grain size magnetic susceptibility ms and total organic carbon toc indicate that aeolian activity was strong during the last glacial period following the younger dryas yd holocene interglacial conditions began to develop in the qinghai lake basin at 12 ka with the strengthened asian summer monsoon asm and the decrease in insolation the climate became warm and humid according to the record of aeolian activity the early holocene can be divided into two intervals before and after 9 5 ka aeolian activity remained strong from 12 ka 9 5 ka although the climate was more humid than that of the last glacial period between 9 5 ka and 8 5 ka the aeolian activity weakened and the climate became warm and wet but variable following the mid holocene climatic optimum the climate became significantly drier at 4 ka and aeolian activity strengthened again overall the asm dominated aeolian activity in the qinghai lake basin during the holocene with enhanced aeolian activity corresponding to a weakened asm paleosol development exhibited a lagged response to the strengthened asm and therefore aeolian sand layers in the section do not always indicate a cold and dry climate

late cenozoic deformation and uplift of the ne tibetan plateau evidence from high resolution magnetostratigraphy of the guide basin qinghai province china the cenozoic intramontane gonghe guide basin in qinghai province china is tectonically controlled by the sinistral strike slip framework of the kunlun and altyn tagh south qilian faults in the northeastern tibetan plateau the basin is filled with thick cenozoic clastic sedimentary formations which provide important evidence of the deformation of this part of the plateau although they have long lacked good age constraints detailed magnetostratigraphic and paleontologic investigations of five sections in the guide basin and their lithologic and sedimentary characteristics allow us to divide a formerly undifferentiated unit the guide group into six formations where ages are now magnetostratigraphically well established they are given in parentheses the amigang 1 8 2 6 ma ganjia 2 6 3 6 ma and herjia formations 3 6 to ca 7 0 7 8 ma and the older miocene ashigong garang and guidemen formations these rocks document a generally upward coarsening sequence characterized by increasing accumulation rates increasing gravel content and sizes of its components changes of bedding dips and source rock types and marginal growth faults collectively reflect accelerated deformation and uplift of the ne tibetan plateau after 8 ma punctuated by a sharp increase in sedimentation rate at ca 3 2 ma that reflects the boulder conglomerates of the ganjia formation interestingly much of the vergence of the compressional deformation in the basin is to the south accommodated by a sequence of six thrusts f1 f6 which become active one by one progressively later toward the south undoubtedly contributing to the uplift of this part of the plateau f1 likely initiated the guide basin due to crustal flexure in the oligocene f2 was active in the early miocene f4 and f5 at ca 3 6 ma and f6 was active in the early pleistocene the detailed late miocene and younger magnetostratigraphy allows us to place much improved time constraints on the deformation and hence uplift of northeastern tibet which when compared with ages for events on other parts of the plateau provides important boundary conditions for the geodynamical evolution of tibet

palaeoclimatic changes in the qinghai lake area during the last 18 000 years abstract multi proxy analysis of a sediment core from qinghai lake including pollen carbonate toc tn and 13 c of organic matter was used to document regional climatic changes during the last 18 000 years climate was very cold and dry before 16 9 cal kyr bp the warm and wet period which began at about 14 1 cal kyr bp culminated at 6 5 cal kyr bp and came to its end at about 4 5 cal kyr bp after that the climate gradually became colder and drier during the transitional period from the late glacial to the holocene the climate fluctuated frequently the short term climatic oscillations including the bolling allerod younger dryas and the cooling event at ca 8 2 cal kyr bp appear to be recorded in the qinghai lake sedimentary record the climatic evolution in the qinghai lake area during the past 18 000 years indicates that solar insolation changes on the ten thousand year scale are the likely driving force of the east asia monsoon

a high resolution holocene record of the east asian summer monsoon variability in sediments from mountain ganhai lake north china abstract a high resolution environmental magnetic records from a sediment profile in mountain ganhai lake has provided new insights into modulation of the east asian summer monsoon easm on climatic changes in north china from the final period of last deglacial stage to holocene large pseudo single domain psd to multidomain md detrital magnetite grains are identified in the lake samples the upwards decreasing magnetic susceptibility and anhysteretic remanent magnetic susceptibility arm are consistent with the dominant vegetation changes grassland 13 0 10 5 ka under dry and cold conditions shrub forest grassland 10 5 5 8 ka in a warm and humid climate and forest where the pinus trees increase rapidly to be the dominant taxa indicating the climate changes from warm and humid to cooler but drier between 5 8 ka and 4 0 ka the lower s 100mt and s 300mt ratios coincide with the higher degree of soil stability and a stable lake stage at 11 8 6 5 ka changes in magnetic anisotropy are also linked to environmental and climatic changes with t parameters showing higher values during warm interglacial periods the anisotropy patterns indicate three different stages of the lake evolution 1 an early stage of the lake accompanied by a disturbed high energy flow a coarse average mineral particle diameter mpd distribution 16 28 m and scattered subvertical minimum direction k3 at 13 0 11 8 ka 2 a fairly stable lake environment between 11 8 ka and 6 5 ka indicated by a low energy flow finer mpd 9 69 m and subvertical k3 axes 3 an unstable high energy flow and coarse mpd 20 03 m with tilted k3 axes thus indicating a transition from lake center to lakeside 6 5 4 0 ka these multi proxy records reveal a weak easm activity in the final period of the last deglaciation 13 0 11 8 ka a high easm intensity in the early mid holocene 11 8 4 8 ka an easm maxima in the mid holocene 8 0 5 8 ka which then generally weakens at 4 3 4 2 ka overall this study suggests the anisotropy and climatic changes in the alpine lake are significantly affected by the insolation driven easm

submarine venting of phase separated hydrothermal fluids at axial volcano juan de fuca ridge since the discovery of high temperature venting on the east pacific rise in 19791 it has been expected2 3 because of the physical properties of sea water at pressures and temperatures encountered during submarine hydrothermal circulation4 5 that phase separated fluids would discharge from ridgecrest vents although this notion is supported by the reported large deviations in vent fluid chlorinity relative to that of sea water 40 200 6 7 by observations of venting at p t conditions clearly within the two phase region 220 bar and 420 c 8 and by fluid inclusion data9 10 unequivocal identification11 of phase separated venting fluids has remained elusive here we report observations of chloride and metal depleted gas enriched fluids from a shallow vent field on the juan de fuca ridge which confirm the expectation that phase separated effluents are delivered to the deep ocean from some sea floor venting systems

late mio pliocene landscape evolution around the chaka basin in the ne tibetan plateau insights from geochemical perspectives abstract the present ne tibetan plateau is characterized by a rugged mountain range and basin landforms knowledge of the landscape evolution as recorded by basin sediments will help to understand the growth history of the ne tibetan plateau our present contribution targeted the neogene chaka basin south of the qinghai nan shan and reports 40 geochemical sr nd trace element and rare earth element ree results of the sediments values of end vary from 15 6 to 11 6 for all samples but end is higher for samples younger than 5 5 ma 87sr 86sr ratios are all between 0 71441 and 0 71844 with the variation becoming less after 4 5 ma little variation in the sr nd isotopes and in the ree trend indicates that the source regions have very similar geochemical features the contribution of aeolian loess into the basin sediments after 3 5 ma is also speculated from the trace element and ree results these geochemical results reveal a change in the source region to the qinghai nan shan around 4 5 5 5 ma which is consistent with previous lithoface evidence since 3 5 ma landscape and topographic relief were further developed thus aeolian loess was deposited onto the fluvial fans south of the qinghai nan shan while global cooling and aridification began to dominate collectively our present geochemical study of the chaka basin sediments reveals stages of landscape evolution in ne tibet since the late miocene

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

magnetostratigraphic determination of the age of ancient lake qinghai and record of the east asian monsoon since 4 63 ma lake qinghai in north china is the largest interior plateau lake in central asia and is sensitive to climate change and the environmental effects of tibetan plateau uplift we have obtained an almost continuous 626 m long sediment core from an in filled part of the southern lake basin which documents both the age of the origin of the lake and the evolution of the east asian monsoon during the late cenozoic high resolution magnetostratigraphy provides a chronology back to ca 5 1 ma analysis of lithofacies and depositional environments reveal that the change from eolian to lacustrine facies occurred at ca 4 63 ma corresponding to a shift from an arid or semi arid to a more humid climate which resulted in the origin of lake qinghai changes in sediment lithology and mean grain size indicate that the lake level fluctuated considerably superimposed on a long term trend from higher to lower levels in response to variations in the east asian monsoon this archive is a significant additional source of information on regional and global environmental change complementing the existing records from north china which are mainly based on analysis of loess deposits

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

holocene moisture and east asian summer monsoon evolution in the northeastern tibetan plateau recorded by lake qinghai and its environs a review of conflicting proxies abstract climatic and environmental changes in the northeastern tibetan plateau are controlled by the asian summer monsoon asm and the westerlies two key circulation components of the global climate system which directly affect a large human population and associated ecosystems in eastern asia during the past few decades a series of holocene palaeoclimatic records have been obtained from sediment cores from lake qinghai and from various other geological archives in the surrounding area of the northeastern tibetan plateau however because of uncertainties regarding the sediment chronologies and the climatic significance of the proxies used the nature of holocene climatic changes in the region remains unclear and even controversial here we review all major classes of the published data from drilled cores from lake qinghai as well as other evidence from lakes and aeolian deposits from surrounding areas in order to reconstruct changes in moisture patterns and possible summer monsoon evolution in the area during the holocene combining the results of moisture and precipitation proxies such as vegetation history pollen based precipitation reconstruction aeolian activity lake water depth lake level changes salinity and sediment redness we conclude that moisture and precipitation began to increase in the early holocene reached their maximum during the middle holocene and decreased during the late holocene similar to the pattern of the east asian summer monsoon easm in northern china it is clear that the region experienced a relatively dry climate and weak easm during the early holocene as indicated by relatively low tree pollen percentages and fluctuating pollen concentrations generally low lake levels of lake qinghai and the adjacent lake hurleg and lake toson in the qaidam basin and widely distributed aeolian sand deposition in the lake qinghai basin and the nearby gonghe basin to the south and in the eastern qaidam basin to the west we argue that the ostracod 18o record which is widely used as a proxy of effective moisture and summer monsoon intensity in lake sediments at least in lake qinghai and which exhibits light values in the early holocene and heavier values thereafter cannot be used to reflect the strength of the easm or the intensity of monsoon precipitation as is also the case for leaf wax 2h records rather we argue that as is the case of the chinese speleothem 18o record which also is often interpreted as an easm proxy it reflects variation in the 18o of precipitation overall we suggest that the easm significantly affected precipitation in the northeastern tibetan plateau during the holocene and that it increased in strength during the early holocene reached a maximum during the middle holocene and decreased during the late holocene

a possible triple junction at 14 50 s on the north fiji basin ridge southwest pacific auzende j m grficia mont e bendel v huchon p lafoy y lagabrielle y de alteriis g and tanahashi m 1994 a possible triple junction at 14 50 s on the north fiji basin ridge southwest pacific in j m auzende and t urabe editors north fiji basin sxarner french japanese program mar geol 116 25 35 recent full coverage bathymetric and geophysical surveys yokosuka 90 and 91 carried out in the framework of the starmer japanese french joint project reveal details of the structure of the n160 segment of the north fiji basin ridge despite its intermediate spreading rate this segment shows a slow spreading type morphology with steep 1000 m high walls reaching an axial depth of 4000 m its northern tip at 14 50 s is a complex area involving several plates boundaries this domain can be interpreted either as a complex boundary between two plates or as a new triple junction symmetrical with the 16 50 s triple junction characterizing its southern tip in either case the complexity of the spreading ridge geometry in this area illustrates the instability of the accretionary geometry due to the deformation of the whole north fiji basin between the much larger indo australian and pacific plates

active thrusting and folding in the qilian shan and decoupling between upper crust and mantle in northeastern tibet fieldwork south of the city of gaotai gansu province china shows that active shortening of surface sediments in the foothills of the yumu shan a large fore mountain of the qilian shan at the northeastern edge of tibet involves both overthrusting and flexural slip folding north of this mountain we found and mapped a prominent north facing thrust scarp that offsets a holocene fan sloping gently 3 4 to the north part of this scarp appears to be related to the m 7 5 180 a d earthquake that may have led to the demise of the han dynasty city of luo tuo chen in the hexi corridor a set of 10 100 150 m long profiles measured across this scarp 3 2 m high on the average can be made to fit the diffusion degraded morphology of a surface break related to the 180 a d event using a value of about 3 3 m 2 10 3 yr for the mass diffusivity of fanglomerates in this part of gansu province smaller mountain facing scarps on a terrace capped foothill result from bedding slip concurrent with active folding of underlying steeply northdipping plioquaternary sandstone and conglomerate beds holocene uplift rates along the yumu shan which is only one of the qilian shan ranges are estimated to be between 0 4 and 1 9 mm yr which implies that much of the mountain formed in the quaternary the periclinal structure of the plioquaternary envelope under which the paleozoic core of the yumu shan plunges towards the west suggests that the whole 3200 m high mountain is a basement ramp anticline mountains striking parallel to the yumu shan with similar structure and comparable or greater sizes north and south of the hexi corridor probably also correspond to recent crustal ramp anticlines this implies that the wide mountainous upper crustal wedge making the northeastern edge of the tibet qinghai plateau is detached from the underlying lower crust and upper mantle

origin of desert loess from some experimental observations a longstanding problem of quaternary geology has been the origin of the silty deposit known as loess of the many explanations for its formation and distribution1 2 the most commonly accepted is that the silt is produced by subglacial grinding processes1 3 4 followed by redistribution and deposition by the wind the large expanses of loess in central europe are therefore considered to be the consequence of quaternary glaciation5 there is however a view6 7 that loessic silt may also originate as the product of processes in hot deserts some proponents of the desert loess hypothesis consider that silt size material is the product of weathering processes7 which may include salt weathering8 or weathering down incipient cracks9 an alternative mechanism is aeolian attrition of sand grains although probably as a result of the experimental work of kuenen10 smalley and krinsley11 consider that only fine silt 2 6 m is produced in large quantities by the abrasion of quartz grains we have simulated aeolian attrition of angular quartz grains previously produced by weathering in deserts the products of abrasion show that both coarse and fine silt sizes are produced these findings suggest that desert aeolian processes can produce loess we also suggest that much of this material from many deserts has been deposited in the sea but that the chinese loess could have been produced in the gobi desert the finest particles produced by such attrition may be a source of silica for silcrete formation

magnetostratigraphy of deep drilling core 15yzk01 in the northwestern qaidam basin ne tibetan plateau tectonic movement salt deposits and their link to quaternary glaciation abstract the thick cenozoic sediments in the qaidam basin contain considerable information about the uplift of tibetan plateau climate change and salt deposits in this paper a palaeomagnetic study was performed on the 1400 m long drilling core 15yzk01 from the yiliping playa in the northwestern qaidam basin to obtain a timescale documenting this information the polarity sequence consisted of 17 pairs of normal and reversed zones and can be correlated well with subchrons c2ar c1n of the geomagnetic polarity timescale gpts 2012 from ca 4 1 to 0 002 ma three periods of high sedimentation rates occurred at ca 4 1 3 207 ma 2 581 1 945 ma and 0 781 0 002 ma these 3 periods correspond to 4 episodes of tectonic activity on the tibetan plateau the qingzang movement 3 6 ma the b phase of the qingzang movement 2 6 ma the kunlun huanghe movement 1 1 0 7 ma and the gonghe movement 0 15 ma the dips of the formations in the drilling core indicate that the yiliping area was uplifted at ca 3 236 ma after this uplift the sedimentation rate sharply decreased from 39 1 cm ka to 19 2 cm ka in the pliocene the yiliping area mainly featured a freshwater environment and the earliest gypsum sediment formed at ca 3 530 ma after the qingzang movement after the b phase of the qingzang movement the yiliping area alternated between freshwater and semi saline lake environments and 20 layers of gypsum bearing strata began to appear since 2 103 ma after the kunlun huanghe movement the yiliping area alternated between semi saline and saline lake environments and salt deposits began to form at 0 733 ma or 0 746 ma in the middle pleistocene four salt forming periods in the yiliping area can be correlated with quaternary glaciations on the tibetan plateau the s1 deposit corresponds to the wangkun glaciation the s3 and s4 deposits and the mirabilite bearing stratum between them correspond to the penultimate glaciation and s5 began to form in the last glaciation the calculated formation age of s2 has to be considered with caution and it is very close to the timing of the wangkun glaciation a reduction in the water supply of the salt lakes during the quaternary glaciations was an important driving factor in the formation of salt deposits in the qaidam basin and the quaternary glaciations were closely related to the tectonic activity of the tibetan plateau

quaternary normal faulting in southeastern sicily italy a seismic source for the 1693 large earthquake summary we present geological and morphological data combined with an analysis of seismic reflection lines across the ionian ovshore zone and information on historical earthquakes in order to yield new constraints on active faulting in southeastern sicily this region one of the most seismically active of the mediterranean is avected by wnw ese regional extension producing normal faulting of the southern edge of the siculo calabrian rift zone our data describe two systems of quaternary normal faults characterized by diverent ages and related to distinct tectonic processes the older nw se trending normal fault segments developed up to 400 kyr ago and striking perpendicular to the main front of the maghrebian thrust belt bound the small basins occurring along the eastern coast of the hyblean plateau the younger fault system is represented by prominent nnw sse trending normal fault segments and extends along the ionian ovshore zone following the ne sw trending avola and rosolini ispica normal faults these faults are characterized by vertical slip rates of 0 7 3 3 mm yr 1 and might be associated with the large seismic events of january 1693 we suggest that the main shock of the january 1693 earthquakes m 7 could be related to a 45 km long normal fault with a right lateral component of motion a long term net slip rate of about 3 7 mm yr 1 is calculated and a recurrence interval of about 550 50 yr is proposed for large events similar to that of january 1693

magnetostratigraphy and paleoclimatic interpretation of a continuous 7 2 ma late cenozoic eolian sediments from the chinese loess plateau an almost 300m thick eolian sequence of late cenozoic sediments which includes 162 5m of quaternary loess paleosols and 126m of late tertiary eolian red clay from the central part of the chinese loess plateau was investigated to determine the magnetostratigraphy the results show that eolian dust accumulation and by inference the related east asia paleomonsoon had begun by 7 2ma as paleomonsoon are largely controlled by the tibetan plateau this implies that the plateau had reached some critical elevation by 7 2ma the section also documents a rapid increase in eolian dust accumulation in the late cenozoic at 3 2ma that is probably due to the influence of global ice volume on the east asian monsoon

lake qinghai china closed basin like levels and the oxygen isotope record for ostracoda since the latest pleistocene abstract in 1985 a sino swiss limnogeological expedition to china s largest inland lake recovered seismic profiles and piston cores to help calibrate palaeoclimatic models of monsoon and insolation fluctuations over the northern tibet qinghai plateau since the last glacial maximum lake qinghai a perennial lake with an area of 4278 km2 1985 at 3194 m above sea level receives drainage from 30 000 km2 of catchment near the northwest corner of the plateau the 26 5 m deep terminal lake 1985 with brackish alkaline magnesium sulphate rich waters 14 g 1 1 tds has not overflowed since the last glacial but its levels have responded to climatic and hydrologic changes seismic reflection profiles for the sub bottom sediment structures revealed a complex topography with channels relict terraces tectonic tilting and deformation in deposits buried under a 4 6 m packet of mainly flat bedded sediments from which core samples were recovered the lowermost cored material 14 500 yr b p comprises mainly water lain loess deposited in a smaller flood plain lake of up a few metres depth under cold arid climatic conditions ams radiocarbon dating indicates average sedimentation rates for latest pleistocene and holocene deposits in central basin regions of 0 3 0 5 mm yr 1 the 18o values of fossil ostracod valves provide a record of changes in the isotopic chemistry of the lake waters that can be related to the precipitation evaporation budgets which have controlled the palaeo levels for lake qinghai the precipitation evaporation budget for the lake qinghai region is largely determined by the asian monsoon system the lake qinghai sediment record shows that there was no large influx of glacoer melt waters into the lake basin during the post glacial the regional climate remained arid until at least 12 500 yr b p when an incipient monsoon was possibly initiated river transported silts first reached the basin centre at 11 800 yr b p when the lake depth may have increased to 5 m possibly a monsoonal weakening for several centuries after 10 800 yr b p europe younger dryas caused a further period of aridity at 10 200 yr b p the basin began filling towards modern lake dimensions in response to a permanent strengthening of the asian monsoon substantial lake level rises probably characterised the periods 10 200 9800 9500 8500 8300 7200 yr b p and through perhaps a century at about 6800 yr b p decreasing levels probably characterised the intervening intervals short term lake level fluctuations through the mid holocene climatic optimum were minimal indicating a very stable climatic hydrologic regime an isotopic steady state for the lake waters since 3000 500 yr b p obscures the climatic hydrologic regime dependent 18o gradient but there is little stratigraphic evidence to suggest that the lake level has been significantly below its present level since that time three negative 18o excursions for the lake waters may correspond to known glacier advances on the plateau at 3000 2000 and 1500 yr b p during china s neoglacial

occurrence of greigite in the pliocene sediments of lake qinghai china and its paleoenvironmental and paleomagnetic implications lake qinghai in north china is the largest interior plateau lake in central asia and is climatically sensitive an almost continuous 626 m long sediment core was drilled in an infilled part of the southern lake basin of lake qinghai the magnetic susceptibility record reveals the presence of two distinct peaks within an interval of fine grained lacustrine sediments of lower pliocene age we selected a depth interval of approximately 40 m spanning the magnetic susceptibility peaks for detailed rock magnetic and geochemical analyses in order to identify the magnetic mineralogy responsible and to assess its possible paleoenvironmental and paleomagnetic implications rock magnetic x ray diffraction analysis scanning electron microscopy sem and energy dispersive analysis of x ray edax analyses reveal that the main magnetic carrier is greigite fe3s4 the greigite is of early diagenetic origin and formed in an inerval of high lake level and inferred relatively warm humid climate the greigite enriched zones are separated by an interval of relatively high total sulfur and organic carbon content and we infer that in the adjacent greigite bearing zones the lower concentrations of sulfur and organic carbon and high levels of reactive iron arrested the process of pyritization resulting in the preservation of the greigite on a time scale of several million years the greigite zones contain narrow intervals of normally magnetized sediments which may be previously unrecognized cryptochrons within the gilbert chron or alternatively they may reflect the continued formation of greigite long after the age of deposition of the surrounding sediment matrix

geodynamics of an arc ridge junction the case of the new hebrides arc north fiji basin abstract detailed surveys bathymetry magnetism seismicity and focal mechanism solutions recorded on the junction between the southern new hebrides arc and the north fiji basin enlighten the geodynamic complexity of the area the presently active c n s oriented spreading structures of the north fiji basin are superimposed on ancient ones which appeared during a n135 e spreading episode active before 3 ma a recent southward extension of the new hebrides arc occurred c 2 ma ago structural and geophysical consequences of both events partly obscure the present arc ridge junction for example back arc troughs do not exist to the south of the former arc termination n45 e structural directions present all over the studied area are interpreted as older transform faults related to the n135 e spreading axis which also left recognizable nw se magnetic anomalies however the new hebrides arc north fiji basin junction remains geodynamically unstable due to the concomitance of convergent strike slip and divergent movements their respective crustal expressions i e arc volcanism lateral displacements and seafloor spreading are examined and considered in their regional environment a provisional model of the arc ridge junction that accounts for most of the parameters analysed above is presented

formation and re orientation of the suerkuli basin within the altyn tagh in northeastern tibetan plateau since late miocene abstract the altyn tagh fault atf had formed in eocene time however the temporal evolution of slip along the fault remains elusive despite its important role in governing growth of the tibetan plateau tp and evaluating models of continental lithosphere deformation here we perform a high resolution magnetostratigraphic study on neogene sediments from the suerkuli basin a small basin located between two active strands of the atf results show that both depositional environment and the sedimentation rate changed at about 5 4 and 6 ma respectively lithofacies shift from conglomerates and sandstones with parallel and cross beddings to mudstones with horizontal bedding suggesting a sedimentary fluvial to lacustrine depositional environment shift even aridification increased over northern china from the tarim basin to the qaidam basin during late miocene to early pliocene times lacustrine deposition had started in the suerkuli basin still we argue that an increase in slip rate along the atf triggered concurrently forming of the intermontane basin the inferred timing of increased slip rate on the atf coincides with a variation in movement of the indian plate relative to eurasian plate since late miocene early pliocene time our work suggests that a re orientation of crustal shortening and deformation in the northern tp began since late miocene and supports the idea that the modern boundary of the tp orogen had rejuvenated to adjust deformation in plate boundary conditions

seismotectonics and present day relative plate motions in the new hebrides north fiji basin region abstract relative motions between the pacific plate p indo australian plate ia new hebrides nh arc microplate and the north fiji basin nfb microplate are estimated using shallow seismicity 276 focal mechanism solutions bathymetry magnetism and the rm 2 plate model of minster and jordan 1978 within the nfb we define the western nfb wnfb eastern nfb enfb and southern nfb snfb microplates a 8 cm y spreading in a n72 e direction occurs along the n s trending spreading ridge of nfb wnfb enfb boundary along the enfb ia boundary located at 176 e a 3 cm y extension in a n108 e direction is proposed the wnfb p boundary which includes the hazel holme extensional zone hhez is complex and a general n25 e extension 2 cm y is inferred the fiji fracture zone ffz is composed of two segments along the eastern zone p ia boundary trending n80 e a left lateral strike slip motion occurs 9 6 cm y accommodated by minor n109 e extension pull apart while along the western zone enfb p boundary a n84 e trending left lateral strike slip motion 7 cm y is inferred the wnfb snfb boundary corresponds to a n70 e broad fracture zone along which an e w left lateral strike slip motion is proposed the snfb microplate moves rapidly eastwards 10 5 cm y at 172 e and is almost attached to the ia plate within the nfb an improved model is discussed which includes deformations within the ia and p plates and rotations with euler poles close to the nfb along the new hebrides trench the consumption rates are respectively 16 15 9 and 12 cm y at 11 12 5 15 5 and 20 s the minimum rate occurs where the d entrecasteaux ridge collides with the new hebrides arc rates of extension at the rear of the nh arc are 7 5 5 and 2 cm y at 11 12 5 and 20 s respectively back arc compression occurs between 13 30 s and 17 s the western end of the hazel holme extension zone coincides with the 13 30 s boundary separating the nh back arc compressive belt and the northern nh back arc troughs south of 21 22 s the trend of the slip vector changes along the nh trench from n70 e to n20 w this implies a n s motion of convergence along the e w trending southern part of the nh trench motion snfb ia of 1 5 cm y at 172 e and the existence of a n70 e trending left lateral fracture zone crossing the southern part of the nfb this fracture should be considered as a major plate boundary

along strike topographic variation of qinghai nanshan and its significance for landscape evolution in the northeastern tibetan plateau abstract cenozoic basins and ranges constitute the high topography of the northeastern tibetan plateau which is derived from the indo asian collision the geomorphological characteristics of the ranges provide direct insight into the uplift processes which are responsible for the patterns of the ranges and the growth of the northeastern tibetan plateau this study analyzed the geomorphological features of qinghai nanshan one of the youngest ranges within the northeastern tibetan plateau including elevation slope distribution and the channel steepness index topographic analysis revealed that elevations and slopes in western and central portions of qinghai nanshan were higher than those in the eastern portion whereas the channel steepness index revealed a step growth mode from west to east considering the topographic features the lateral gradient of precipitation increasing from west to east and the lithology distribution it is concluded that the geomorphological features of qinghai nanshan are influenced mainly by tectonic activities and reflect the growth pattern and or the tectonic setting of the range comparing with previous studies it is shown that the formation mechanism of qinghai nanshan follows a middle to sides growth pattern furthermore the degree of inclination of the erosion surface distributed on the northern flank of the range suggests that qinghai nanshan is controlled jointly by the listric qinghai nanshan thrust fault and the influences from the elashan and riyueshan dextral strike slip faults in addition the northeastern tibetan plateau exhibits an outside in growth process which might reflect the northeastward growth of the entire northeastern tibetan plateau