sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

an 15 000 year record of el nino driven alluviation in southwestern ecuador debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the pacific ocean in ecuador these storm induced events were dated by radiocarbon and the age of laminae that are less than 200 years old matches the historic record of el nino events from about 15 000 to about 7000 calendar years before the present the periodicity of clastic deposition is greater than or equal to 15 years thereafter there is a progressive increase in frequency to periodicities of 2 to 8 5 years this is the modern el nino periodicity which was established about 5000 calendar years before the present this may reflect the onset of a steeper zonal sea surface temperature gradient which was driven by enhanced trade winds

minimum winter temperature reconstruction from average earlywood vessel area of european oak quercus robur in n poland abstract tree ring based temperature reconstructions form a substantial part of the international proxy data base used to examine and model global climate variations of the last millennium however most tree ring based reconstructions are derived from study sites in the high latitudes or high altitudes paying very little attention to low elevation sites thus a large gap in the geographical coverage of climate reconstructions from temperate low elevation sites in central europe still exists this motivated us to concentrate our efforts on the european oak quercus robur in n poland we developed a new robust tree ring width chronology trw as well as four wood anatomical chronologies e g average vessel area and number of vessels from q robur for the period 1810 to 2010 the chronologies were examined for their climatological responses while trw was found to have weak correlations with climate the earlywood vessel parameters evp especially average vessel area ava revealed significant positive correlations to minimum winter temperatures based on stable climate growth correlations a reconstruction of minimum winter temperatures 29th november to 20th january back to 1810 was performed for north poland the reconstruction indicates a promising potential to reveal low frequency climate information an additional extreme year analysis suggested that in cold winters a cold warm cold pattern in the minimum temperatures was responsible for the relatively small earlywood vessels spatial field correlations imply that our reconstruction is more related to temperature variations towards the east of europe the reconstructed temperature compared well with two existing temperature reconstructions especially during most of the 20th century even though the temperature reconstructions differ spatially and temporally based on these findings the relatively extensive resource of archeological oak material from this region may be useful to perform multicentennial climate reconstructions in the temperate climate zone

depositional environments in an arid closed basin and their implications for oil and gas exploration the lower permian fengcheng formation in the junggar basin china the fengcheng formation is a nonmarine carbonate dominated succession that formed under arid climatic conditions in a hydrologically closed basin two transects and two seismic profiles were examined the characteristics and environmental significance of different lithofacies were studied and a model of depositional environment divisions was proposed the sedimentary model involved an alkaline lake in which the depositional environments consisted of a shallow saline lake margin slope saline lake center and steep lake margin from northeast to southwest the perennial central salty lake was located in the southwestern part of the study area whereas there were widespread low gradient lake margins in the northeast east southeast and southern parts of the study area lake level fluctuations had a major influence on the shallow saline lake system and complicated the depositional environments in these areas the deposits are derived from bedrock reworking volcanic eruptions and authigenic minerals that precipitated from brine during the hypersaline phase fine grained terrigenous clastic sediments volcanic ashes and dusts and authigenic minerals mixed in the depocenter concentration center of the brine pool which was covered by high salinity brines and the depositional environment was anoxic as a result of salinity based brine stratification a thick sodium carbonate succession occurred in the depocenter of the ancient mahu lake where bedded sodium carbonate alternated with fine grained organic rich tuff or tuffaceous hydrocarbon source rocks microorganisms bloomed in the alkaline high salinity brine and the organic matter was well preserved which is similar to those modern alkaline saline lakes in eastern africa and western north america thus the permian fengcheng formation contains source rocks that formed in an alkaline saline lake

deep structure of the southern kerguelen plateau southern indian ocean from ocean bottom seismometer wide angle seismic data wide angle seismic data collected during the kerguelen ocean bottom seismometer experiment provide the first images of the deep structure of the southern kerguelen plateau and support a new interpretation of the origin of the plateau velocity models based on travel time inversions and reflectivity synthetic seismograms show a 22 km thick crust composed of 1 6 km of sedimentary cover 5 3 km of upper crust 11 0 km of lower crust and a 4 to 6 km thick reflective zone immediately above moho velocities in the upper crust from 3 8 4 5 km s at top to 6 0 6 5 km s at bottom are consistent with the basaltic nature of this layer the top of which was sampled during the ocean drilling program velocities in the lower crust increase continuously from 6 60 km s at the top to 6 90 km s at 19 5 km depth the reflective zone at the base of the crust identified by wide angle reflections is observed only along the nnw sse direction it consists of alternating high and low velocity layers with an average velocity of 6 70 km s in the nnw sse direction and 6 90 km s in the perpendicular direction strong azimuthal anisotropy is also observed in the upper mantle with velocities of 8 60 and 8 00 km s in the nnw sse and e w directions respectively the absence of high velocities at the base of the crust that characterizes many large volume mafic provinces the reflective lower crust and anisotropy in upper mantle suggest that the southern kerguelen plateau represents a stretched continental fragment overlain by basaltic flows isolated from the antarctic margin during the early opening of the indian ocean

scratching the surface estimating dimensions of large igneous provinces a study of five major basaltic provinces including oceanic plateaus volcanic passive margins and continental flood basalts shows that they are voluminous constructions of extrusive igneous rock underlain by intrusive rock crustal thickness ranges from 20 to 40 km and lower crust is characterized by high 7 0 7 6 km s seismic velocities volumes and emplacement rates derived for two oceanic plateaus the ontong java and kerguelen broken ridge reveal short lived pulses of increased global crustal production and suggest an origin involving the lower mantle the ontong java rate of emplacement may have exceeded the contemporaneous global production rate of the entire mid ocean ridge system despite the importance off large igneous provinces in studies of mantle dynamics and the global environment scarce age and deep crustal data necessitate intensified efforts in seismic imaging and scientific drilling in a range of such features

high precision 40ar 39ar age for the jehol biota abstract abundant fossils of the terrestrial jehol biota including plants insects dinosaurs birds mammals and freshwater invertebrates were discovered from the yixian formation and the overlying jiufotang formation in inner mongolia hebei province and liaoning province northeastern china because of the exceptional preservation of fossils the jehol biota is one of the most important mesozoic lagerstatten and is referred to as a mesozoic pompeii the jehol biota has provided a rare opportunity to address questions about the origin of birds the evolution of feathers and flight the early diversification of angiosperms and the timing of placental mammal radiation six tuff samples and two basalt samples collected from the tuchengzi the yixian and the jiufotang formations near the classic outcrops in western liaoning ne china yielded high precision 40 ar 39 ar ages we obtain an age of 129 7 0 5 ma for a basaltic lava from the bottom of the yixian formation and an age of 122 1 0 3 ma for a tuff from the lowermost part of the overlying jiufotang formation our age results provide an age calibration of the whole yixian formation and show that the whole formation was deposited entirely within early cretaceous time over an interval of 7 ma

1300 years of climatic history for western central asia inferred from tree rings more than 200 000 ring width measurements from 384 trees were obtained for 20 individual sites ranging from the lower to upper local timber lines in the northwest karakorum of pakistan and the southern tien shan of kirghizia samples were obtained predominantly from juniper species juniperus and were analysed to reconstruct regional climatic variation patterns in western central asia since ad 618 site distri bution represents diverse ecological conditions e g combinations of temperature and moisture stress within the karakorum and tien shan mountains permitting both intra montane and inter montane comparisons of chronologies three different types of chronologies ree ecting interannual decadal and centennial scale ring width variations were calculated a statistic skeleton plotting technique was used to identify ring width pointer years interannual a 101 year kernel e lter was used to identify decadal scale variations and for a subset of long lived trees the mean ring width of the entire single series was used to identify centennial trends after extracting and calibrating each of these three distinct wavelengths in ring width variation the results were combined into a comprehensive reconstruction ree ecting primarily temperature e uctuations in western central asia since ad 618 the nature and the temporally changing strength of the climatic signals of this reconstruction are discussed in detail a maximum latewood density record of pinus tienschanica from central tien shan was used as a predictor series to calibrate and validate tree ring width variation in so doing we link our results to the circumpolar maximum latewood density network briffa et al 1998a 1998b schweingruber and briffa 1996

paleomagnetic constraints on the geodynamic history of the major blocks of china from the permian to the present paleomagnetic study of china and its environs has been the center of a major international effort for the last 10 years in this paper we critically review all available paleomagnetic poles of upper permian to tertiary age from the main blocks of china with the goal of placing constraints on models of the formation and the subsequent deformation of the region after selecting reliable poles by applying objective criteria we divide our analysis into first order motions of blocks and second order deformation within blocks for first order analysis apparent polar wander paths are constructed for the major blocks we discuss the compatibilities and contradictions between the geological and paleomagnetic records a sequence of paleogeographic configurations taking into account geological constraints but remaining within paleomagnetic uncertainties is presented in general the major blocks were probably in contact throughout the permian and triassic but the jurassic was the key age during which most of the movement toward china s present configuration took place our reconstructions include certain details which are suggested by the paleomagnetic record but whose geological signatures seem to have been hidden by subsequent events during the cretaceous chinese poles agree with poles from other continents transferred onto eurasia at the second order we observe that for almost each period with sufficient data the paleomagnetic poles are streaked along a small circle centered on the sampling region indicating that much of china has been affected by small 20 differential rotations this we interpret as deformation caused in part by the extrusion of the chinese blocks away from the indian collision the complete annotated list of poles is given as an appendix

early cretaceous volcanism and its impact on fossil preservation in western liaoning ne china abstract the so called jehol biota an excellently preserved early cretaceous biota consisting of both lacustrine and terrestrial organisms is one of the most important mesozoic fossillagerstatten although there have been extensive palaeontological studies little work has been done on the volcanic settings under which the biota was preserved the sihetun area is the most famous fossil locality of the jehol biota in western liaoning and the volcanic succession in that area is the most representative and best studied we use a case study of the volcanic succession of the lower cretaceous yixian formation in the sihetun area to reconstruct the volcanic complexes and their history to propose a depositional model of the volcanic successions and to understand the relationship between volcanic activity and fossil preservation in western liaoning the volcanic succession comprises four volcanic complexes each with distinct products a shield volcano an intermediate multi vent center a volcanic lake in summit caldera and finally lava domes the presence of a caldera is postulated from exposures which suggest the presence of an inner topographic wall bounding faults and intra caldera fill frequent volcanic activities and widespread existence of volcanic lakes during the early cretaceous are thought to account for the exceptional preservation of invertebrates and vertebrates of the jehol biota in western liaoning

seasonal to sub seasonal palaeoenvironmental changes in lake sihetun lower cretaceous yixian formation ne china sedimentary properties of the fossil bearing deposits of lake sihetun yixian formation lower cretaceous were investigated on a high resolution sub millimetric scale data were obtained from three excavations and 50 thin sections lake evolution is subdivided into four phases of which phases 2 and 3 provided suitable conditions for excellent fossil preservation six microfacies are recognized within these two phases 1 allochthonous siliciclastic laminae 26 1 m thick on average 2 chrysophycean cyst accumulations 3 tuffaceous silt 4 lacustrine chemical precipitates 5 tuff and 6 normal graded sandy to silty siliciclastics phase 2 is characterized by microfacies 1 5 and phase 3 by microfacies 6 biofilms are common and mass occurrences of framboids pyrite pseudomorphs are occurring in sediments of phase 2 varves can be verified for microfacies 2 and 4 179 m thick thicknesses of microfacies 2 highly fluctuate depending on the occurrence of seasonal heavier rains which led to deposition of tuffaceous silt layers microfacies 3 meromictic conditions dominated phase 2 but recurrent mixing is demonstrated by short lived colonization events by a benthic invertebrate fauna the transition of phase 2 to holomictic phase 3 is marked by a dramatic increase in sediment yield associated with a change from dry to humid climates fossil preservation differs according to the diverse physical and chemical conditions during lake evolution phase 2 yields framboid replacement of organic tissue and excellent preservation of growth increments of clam shrimp carapaces which are poorly preserved in phase 3 conversely though exhibiting a different mode of preservation insect fossils are superbly preserved as dark stains sealed by silica coatings during phase 3

experimental study of a kiglapait marginal rock and implications for trace element partitioning in layered intrusions abstract experiments on a chilled marginal rock from the kiglapait intrusion labrador have been performed in order to constrain the partitioning behaviour of major and trace elements during formation of kiglapait lower zone lz cumulates at 0 1 mpa and f o 2 close to fmq the liquidus is bracketed between 1225 and 1212 c and the only liquidus phases are plagioclase an 73 74 and olivine fo 82 85 in contrast lz troctolites contain fo 67 5 olivine and an 63 4 plagioclase plagioclase melt partition coefficients d s for li ti rb sr y zr ba la and eu determined by ion microprobe analysis of run products are similar to those for other basaltic systems but differ systematically from apparent d s calculated from bulk analyses of lz plagioclases and modelled liquid compositions obtained by summation the discrepancies in d s and phase compositions are inconsistent with diffusion controlled boundary layer growth crystallisation of trapped intercumulus liquid is quantitatively plausible however a the volume of liquid required to reconcile experimental and model d s 20 1 is larger than that estimated from observed proportions of intercumulus phases 11 2 and b this mechanism alone cannot reduce x an in lz plagioclases due to very slow al si interdiffusion the discrepancy between experiment and model is best resolved if the parental melt to lz cumulates was more evolved higher fe mg na ca ree and alkalis lower sr than the summed bulk composition in accord with a recent revision of the kiglapait fe mg based on olivine compositions

late mesozoic stratigraphy in western liaoning china a review abstract based on progress in stratigraphic and paleontological studies we discuss the subdivision of late mesozoic strata in western liaoning focusing on the controversies surrounding the relationship of the jiufotang and shahai formations and whether or not the zhanglaogongtun and banlashan formations exist as distinct lithologic units we describe the late mesozoic strata at representative sections associated with the new discoveries we also discuss the correlation of late mesozoic strata between western liaoning and eastern heilongjiang and their implications for the ages of the strata in liaoning

diagenesis of bivalves from jurassic and lower cretaceous lacustrine deposits of northeastern china in contrast to the numerous excellently preserved arthropods vertebrates and plants from the mesozoic lacustrine fossil lagerstatten of northeastern china which have calcium phosphate or organic skeletons the preservation of taxa with a calcareous skeleton is fairly poor here we investigate using a scanning electron microscope and energy dispersive x ray spectrometer the preservational modes of bivalves from the jurassic daohugou fossil beds of inner mongolia and the lower cretaceous yixian formation of eastern liaoning the jurassic bivalve ferganoconcha sibirica is preserved as strongly compressed composite moulds which contain remains of the organic periostracum in the yixian formation the bivalves sphaerium anderssoni and arguniella ventricosa occur as compacted internal external or composite moulds or are preserved with a silicified shell and rarely with a shell consisting of iron hydroxides which had replaced pyrite during late diagenesis weathering silicification produced partly fabric replacive microcrystalline quartz and partly void filling megaquartz crystals after the carbonate shell had been dissolved films of authigenic aluminosilicate minerals partly secondarily silicified cover the exterior and interior shell surfaces occasionally early diagenetic pyrite crystals now oxidized to iron hydroxides filled shell cavities forming internal moulds and rarely replaced the bivalve shell the poor preservation of the bivalves reflects the environment and water chemistry of these lakes which were heavily influenced by volcanic processes frequent ash deposition and decomposition of volcanic glass particles created acidic and alkaline lake and interstitial waters which led to early diagenetic formation of authigenic aluminosilicate minerals ferruginous internal moulds dissolution of shell carbonate and silicification of shells

stratigraphy correlation depositional environments and cyclicity of the early cretaceous yixian and jurassic cretaceous tuchengzi formations in the sihetun area ne china based on three continuous cores abstract three continuous cores acquired in the sihetun area of liaoning province famous for feathered non avian dinosaurs of the jehol biota reveal the stratigraphic and facies relationships of the divisions of the early cretaceous yixian and underlying jurassic early cretaceous tuchengzi formations based on these cores we propose a modified lithostratigraphic nomenclature in the sihetun sub basin in which the yixian formation is divided into three members the lujiatun member a fluvial and alluvial volcaniclastic sandstone and conglomerate unconformably overlying the tuchengzi formation with articulated tetrapods plausibly preserved in burrows the xiatulaigou member an extrusive basaltic flow and breccia comprising the only true lavas in the area and the jianshangou member a cyclical lacustrine mudstone containing a taphocoenosis of articulated compression fossils with soft tissue preservation including non avian dinosaurs birds pterosaurs mammals fish crustaceans insects mollusks and plants the latter is divided into 4 units the basal dajianshanzi bed a shallow water lacustrine unit with abundant mollusks and rooted zones the anjiagou bed the main tetrapod bearing unit consisting of microlaminated dark gray mudstones with many interbedded airfall ashes deposited in a meromictic lake the hengdaozi bed comprised of thin and rhythmically to medium bedded light gray to tan mudstones and sandstones with few discrete ashes famous for its diverse insects and plants including early angiosperms deposited in alternating dysoxic and oxygenated bottom water and the huangbanjigou bed the most obviously cyclical of the units with dark gray microlaminated intervals with articulated vertebrates alternating with more massive lighter colored mudstones and volcaniclastic sandstones deposited in lakes that oscillated in depth cyclicity in the jianshangou member is dominated by meter scale cycles that may be paced by orbital variations unambiguous relatively rapid lateral facies changes within the yixian formation are suggestive of local relief not the bottom of a giant flat bottomed basin

modeling the three dimensional structure of macroscopic magma transport systems application to kilauea volcano hawaii we report the results of modeling the three dimensional internal structure of kilauea s magmatic passageways the approach uses a clear plexiglass model containing equally spaced levels upon which well located seismic hypocenters are plotted application of constraining geologic and geophysical criteria to this distributed volume of earthquakes permits the interpretation of seismic structures produced by fracturing in response to locally high fluid pressures four magma transport and storage structures have been identified within and beneath kilauea 1 primary conduit the conduit transporting magma into kilauea s summit storage reservoir rises from the model base 14 6 km to the 6 5 km depth level it is a zone of intense fracturing and inferred intrusion whose horizontal sections are elliptical in planform over its height the average major axis of the component horizontal sections is 3 3 km with an average minor axis of 1 7 km this yields an aspect ratio of 0 52 at the 14 6 km level the strike of the major axis is n67 e during passage from the upper mantle through the oceanic crust this axis rotates in a right handed sense until the strike is n41 w at the 6 5 km level 2 magma chamber complex floor the interval from 6 5 to 5 7 km immediately over the primary conduit is aseismic this suggests differentially high fluid to rock ratios and relatively weak pathways for further vertical transport into higher levels of the storage complex as well as lateral leakage eastward into the mauna ulu staging area for later vertical ascent beneath the upper east rift zone seismicity within the immediately subjacent rocks that form the top of the primary conduit at 6 5 km suggests that this inferred magma rich horizon forms the effective floor of the summit storage complex 3 magma chamber crown intense seismicity over the 1 1 1 9 km depth interval defines an elliptical region in plan view the top of this region has a broad apex with an average major axis of 1 5 km and an average minor axis of 1 1 km producing an aspect ratio of 0 73 this region coincides with the epicentral position of summit vertical displacement maxima during inflationary deformation and is interpreted as a region of intense diking crowning the summit storage complex 4 upper east rift zone pipe from a depth of 5 7 km a cylindrical region of seismicity rises beneath the upper east rift zone to the 1 9 km level where it merges with the subhorizontal upper east rift zone duct this pipe like zone has a mean diameter of 1 4 km and a vertical axis that pierces the surface of the volcano at the intersection of the koae fracture system and the upper east rift zone we suggest this pipe forms a principal connection between the base of the summit storage reservoir and near surface storage compartments and ducts in the upper east rift zone in this role the pipe is suggested to have contributed heavily to mauna ulu s magma supply during 1969 1974 the model of magma transport and storage thus constructed provides a context in which other types of data e g ground deformation and electrical conductivity may be interpreted as well as a means of refining petrological inferences based on lava chemistry

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

petrography and implications of continental rocks from the agulhas plateau southwest indian ocean seismic refraction and seismic reflection profiles reported elsewhere indicate that the agulhas plateau is a continental fragment that was rifted from the falkland plateau and intruded by basaltic magmas during the early opening of the south atlantic dredge hauls recovering a characteristic suite of low to high grade continental metamorphic rocks indurated sedimentary rocks and basaltic igneous samples support this origin and evolutionary history both the petrography of the gneiss specimens and k ar ages of 1 074 36 m y and 478 17 m y on fresh biotites from two of the rocks are compatible with petrography and ages of the formerly adjacent continental rocks of southern africa the falkland islands falkland plateau and antarctica

magma mixing recharge and eruption histories recorded in plagioclase phenocrysts from el chichon volcano mexico operative throughout the 200 ky history of the el chichon magma consistent core to rim decreases of sr sr ratios and coincident system increases in sr concentrations in plagioclase phenocrysts of varying size 1 cm to 2 mm are reported from samples of the 1982 and pre 1982 200 ka eruptions of el chichon volcano maximum sr sr ratios of 0 7054 significantly higher than the wholerock isotopic ratios 0 7040 0 7045 are found in the cores

relationship of pyroclastic volcanism and lake water acidification to jehol biota mass mortality events early cretaceous northeastern china abstract geochemical analysis of the 14 4 m thick lacustrine succession of the lower cretaceous yixian formation jehol group has yielded new insights concerning vertebrate mass mortality events in the lake sihetun volcanic caldera in western liaoning province northeastern china that produced the jehol biota fossil lagerstatten the long term evolution of the caldera system resulted in a shift from felsic to mafic magma chemistry accompanied by a reduced frequency of pyroclastic eruptions declining hydrothermal activity and lower lacustrine productivity the basal tetrapod beds exhibit strong hydrothermal influence as indicated by enrichments of boron b certain alkalis rb cs rare earth elements rees yttrium y and many metals e g co cr cu ge mo ni sb u v and w and by strongly negative molybdenum isotope compositions 98mo to 2 50 that may record large fractionations between molybdate and thiomolybdate species in the sihetun caldera hydrothermal system in contrast the overlying fish beds and non fossiliferous beds have an elemental and mo isotopic composition similar to calc alkaline basalts 98mo 0 29 0 04 in the surrounding watershed suggesting weathering of yixian formation volcanic rocks as the major source of sediment during its

the effect of pressure on dsr plag melt and dcr opx melt implications for anorthosite petrogenesis the crystal liquid partition coefficients for sr and cr dsr and dcr have been determined from electron microprobe analyses of plagioclase liquid and orthopyroxene liquid pairs produced in melting experiments run at pressures from 1 bar to 27 kbar on two compositions relevant to anorthosite petrogenesis one is a primitive jotunite hypersthene monzodiorite tj the other is a sample of an anorthositic dyke 500b results indicate that dsr plag liq remains nearly constant with increasing pressure tj 1 7 to 2 6 500b 0 9 to 1 4 this modest variation apparently results from the combined and opposing effects of crystal chemistry and pressure dsr increases with the albite content of plagioclase which itself increases with pressure along a composition s liquidus so pressure must have an intrinsic negative effect the two models for dsr j blundy b wood geochim cosmochim acta 55 1991 193 209 i bindeman a davis m drake geochim cosmochim acta 62 1998 1175 1193 that take into account the strong correlation between dsr and plagioclase composition overestimate dsr at high pressure whereas the two models that ignore plagioclase composition s morse geochim cosmochim acta 56 1992 1735 1738 r nielsen comput geosci 18 1992 773 788 underestimate it moreover since none of these models takes into account any pressure effect the discrepancies between predicted and observed dsr increase with pressure for all models the new results also show that dcr opx liq increases significantly with pressure dcr 2 at 1 atm and 14 2 at 10 kbar these new data confirm earlier less precise determinations of dcr that were used to infer a high pressure origin for al and cr rich orthopyroxene megacrysts the calculated sr and cr concentrations of liquids in equilibrium at 10 kbar with plagioclase and orthopyroxene megacrysts from anorthosite massifs sr 370 to 610 ppm and cr 20 to 130 ppm are in the range of what is observed in high al gabbros and primitive jotunites the inferred parent magmas of massive anorthosites fl 2000 published by elsevier science b v all rights reserved

mineral chemistry of mildly alkalic basalts from the 25 ma mont crozier section kerguelen archipelago constraints on phenocryst crystallization environments phenocryst compositions and mineral melt equilibria in the mildly alkalic basalts from the 25 ma mont crozier section on the kerguelen archipelago are used to estimate the depths at which magmas stalled and crystallized and to constrain the rule of crustal structure in the evolution of magmas produced by the kerguelen mantle plume the crozier section of nearly 1000m height consists of variably porphyritic flows up to 21 vol phenocrysts dominated by plagioclase clinopyroxene olivine fe ti oxides feldspars show an extreme range of compositions from high ca plagioclase an to sanidine and variable textures that are related to extensive fractionation degassing and mixing in relatively low pressure sub volcanic magma chambers although clinopyroxene is a minor phenocryst type 0 3 vol its non quadrilateral components principally al 1 9 8 6 wt al o vary widely the results of clinopyroxene liquid thermobarometry and clinopyroxene structural barometry indicate that the crozier magmas crystallized at pressures ranging from 1 kbar to 11 12 kbar with high al clinopyroxene recording the highest pressures of crystallization high al clinopyroxene rich cumulates may represent an important component of the seismic crust to mantle transition zone at 14 16 km depth high pressure high al clinopyroxene crystallization became important in the mildly alkalic basaltic magmas from the kerguelen archipelago as ascending magmas stalled and fractionated at or near the crust mantle interface which became deeper as a result of progressive crustal thickening as the archipelago moved from a ridge centered setting at 40 ma to an intraplate position by 25 ma

oxygen deficiency in lake sihetun formation of the lower cretaceous liaoning fossillagerstatte china the redox state of lake sihetun represented by the lower cretaceous yixian formation western liaoning china is evaluated to understand the formation of this konservat lagerstatte lake evolution is subdivided into four phases of which phases 2 and 3 exhibit excellent fossil preservation exceptional preservation and mass mortality events within phase 2 were previously attributed to synsedimentary volcanism and oxygen deficiency however the volcanic trigger for mass mortality events remains enigmatic and distinction between anoxia and dysoxia has not been put forward so far to resolve the redox state of the lake during phase 2 5394 diameters of pyrite framboid pseudomorphs in 29 thin sections from three localities have been measured framboid size distributions reveal that lake sihetun was governed by dysoxic bottom waters with spells of anoxia recording pronounced environmental stress hence holomictic eutrophic conditions were episodically replaced by meromictic interludes spatial variations in redox state were common and oxic conditions were detected in two of the three studied localities concentrated iron sulphide layers resulted from biofilms at the lake floor or the development of microenvironments around organic remains which preserved highly reactive organic compounds in contrast sediments of phase 3 record oxic conditions and an entirely holomictic lake

plagioclase residence times at two island arc volcanoes kameni islands santorini and soufriere st vincent determined by sr diffusion systematics the diffusive relaxation of trace element profiles in plagioclase phenocrysts may provide important constraints on magma residence times in crustal magma chambers initial trace element profiles in plagioclase phenocrysts are governed by variations in the concentration of a trace element in the melt and by the plagioclase melt partition coefficient trace element diffusion will subsequently act to modify this initial profile and given enough time produce a profile that is in equilibrium with the anorthite variations within the crystal we argue that the trace element partition coefficient da b between two parts a and b of a plagioclase crystal of variable anorthite content is equal to the ratio of their crystal liquid partition coefficients and that the equilibrium profile of the crystal can be calculated the time required to establish diffusive equilibrium is dependent on the wavelength and amplitude of the initial trace element concentration range and on the diffusivity of the trace element in plagioclase strontium plagioclase melt partition coefficients and diffusivities are calculated for a range of magmatic temperatures and plagioclase compositions a one dimensional diffusion model is developed that describes the diffusive destruction of oscillatory trace element zoning with time and allows the calculation of upper limits for plagioclase crystal residence times in a magma reservoir the model is tested using major and trace element concentrations measured along crystal traverses of plagioclase phenocrysts from the kameni island dacites santorini and from the 1979 soufriere andesite st vincent three out of eight plagioclase phenocrysts have sr concentration profiles that are not in diffusive equilibrium for these the diffusion model is employed to calculate maximum crystal residence times from incomplete diffusive equilibration of trace element zoning in plagioclase maximum crystal residence times range from 100 to 450 years this is in good agreement with estimates from crystal size distribution and from ra th disequilibrium studies for the kameni islands for soufriere however such short residence times are incompatible with u th mineral errorchron data that suggest residence times of 40 ka in a thermally buffered magma reservoir to reconcile these apparently different ages we invoke a more complicated magmatic history for soufriere where an initially buffered magma reservoir is disturbed by magma mixing and suffers limited additional crystal fractionation prior to eruption

high resolution palaeoecological and taphonomic analysis of early cretaceous lake biota western liaoning ne china abstract the faunal content of eighteen bedding planes within the jianshangou unit of the lower cretaceous yixian formation of western liaoning has been analysed in detail in order to understand the environmental and taphonomic framework of this famous lacustrine fossillagerstatte the bedding planes were excavated within a 3 m thick section which is composed of laminated mudstones graded sandstones and mudstones and horizontally stratified structureless sandstones and tuffs all investigated bedding planes occur within the laminated mudstone facies and contain elements of the so called jehol biota in particular the conchostracan eosestheria ovata the ephemerid nymph hexagenites trisetalis and the crustacean liaoningogriphus quadripartitus these three faunal elements occur in high abundance originally possessed chitinous skeletons and are preserved as compressed faintly mineralized coats or in the case of eosestheria still possess organic material the specimens do no represent exuviae but body fossils the fossils can be grouped into three low diversity associations each characterized by one of the three taxa the plan view orientation of the taxa is invariably random and size frequency histograms are bimodal or polymodal this indicates that the fauna is autochthonous and that the histograms reflect several recruitment phases apparently the faunal elements suffered seasonal mass mortality caused by anoxic conditions which became established in the lake during the summer months increased humidity during the winter led to mixing of the lake waters re establishment of oxic conditions and to deposition of a thin film of sediment such environmental conditions were episodically interrupted by flash floods and volcanic ash falls which may have been responsible for the preservation of the more spectacular elements of the jehol biota such as birds and feathered dinosaurs

boundary layer crystallization in a basaltic magma chamber evidence from rishiri volcano northern japan the evolution of basaltic magma by mushy boundary layer processes introduction in a magma chamber is documented for an alkali basalt kutsugata the evolution of magma chambers is of major petrologic lava from rishiri volcano northern japan on the basis of zoning interest and has been studied extensively experimental patterns of plagioclase phenocrysts and their spatial distribution in and theoretical studies that have investigated the cooling the lava plagioclase phenocrysts with complex zoning patterns can of magma chambers have demonstrated that a magma be divided into four types type 1 is characterized by an extremely chamber solidifies through formation of a mushy boundan rich core an71 90 which is commonly corroded and filled with ary layer composed of crystals and interstitial melt along sodic plagioclase type 2 has an ab rich core surrounded by a calcic the chamber walls e g brandeis jaupart 1986 turner mantle characteristic of partial dissolution type 3 is characterized by et al 1986 marsh 1988 tait jaupart 1992 layered igneous complexes e g morse 1969 shirley 1987 an ab rich core that is commonly surrounded by a reversely zoned mcbirney 1996 provide useful information on how slightly calcic mantle type 4 has an ab rich core without a calcic mafic magma chambers evolve and consolidate but they mantle the an rich cores of the type 1 plagioclase are too calcic do not offer much insight into the instantaneous state of to have crystallized from a liquid represented by any whole rock a chamber because those intrusions integrate processes composition at the estimated temperatures of the kutsugata magma that occurred over long solidification times mcbirney system the an rich cores are inferred to have been formed in a noyes 1979 tait 1988 volcanic products such as mushy boundary layer along the wall of a magma chamber where lava flows and tephra deposits can sample the inthe magma was relatively cool and rich in water because of significant stantaneous state of a magma chamber there are a few olivine fractionation and possibly because of addition of water studies along this line of approach tait 1988 de silva expelled from the chilled margin and or groundwater from the 1989 nakada et al 1994 these studies focused on surrounding crust the ab rich cores of types 2 4 plagioclase crystal aggregates in volcanic products and concluded phenocrysts are interpreted to have crystallized in the main magma that the crystal formation in a mushy boundary layer body of the reservoir the types 2 and 3 ab rich cores were brought plays a dominant role in magmatic evolution in a magma to the mushy layer by convection the temporal and spatial variations reservoir however these studies were mostly on silicic of zoning patterns of plagioclase phenocrysts in basaltic lava flows magmas and there are significant differences in physical give useful information on the evolution of mafic magma chambers and chemical features between silicic and mafic magma chambers in this paper the magmatic evolution of an alkali basalt kutsugata lava from rishiri volcano northern japan is studied the kutsugata lava is divided into three lava flows on the basis of whole rock chemical

continental rifting and initial sea floor spreading in the woodlark basin our understanding of the processes by which continents rift and sea floor spreading initiates is derived primarily from studies either of old passive margins and oceanic crust or of young regions of intra continental extension where spreading has not yet started it has been thought that continental rifting ceases when sea floor spreading begins1 2 that oceanic fracture zones develop from transfer or transform faults within continental rifts3 4 and that linear magnetic anomalies correlate with the onset of sea floor spreading during times of magnetic reversals5 6 here we present a marine geophysical survey of one of the few active examples of continental rifting and spreading initiation the western woodlark basin papuan peninsula region of new guinea which shows that in detail these assumptions do not hold the data confirm models of the rifting to spreading transition that invoke both ridge propagation and nucleation of discrete spreading cells7 10 and provide an unambiguous example of a spreading centre reorienting by synchronous jumping rather than propagation

hydroclimatic variation in far north queensland since 1860 inferred from tree rings abstract in tropical australia palaeoclimatic proxies derived from tree rings are sought after sources for reconstructing climate variations however dendroclimatology has not been widely applied in tropical forests and even less so in the australian tropics due to the extreme rarity of species producing anatomically distinct annual growth rings furthermore most australian tree species exhibit rather strong opportunistic growth with non annual growth zones that are less suitable for dendrochronology recent studies on the australian red cedar toona ciliata in the upper kangaroo valley near sydney revealed that tree ring based climate reconstructions are feasible with this species this study moved 2500 km further north and concentrated on the tropical stands of t ciliata because it is one of the few deciduous tree species in tropical australia likely characterised by a dormant period of the cambium and thus annual tree rings although dendroclimatological studies indicate that some australian tree species are suitable for reconstructing climate patterns a well replicated tree ring record from far north queensland has not been developed until now tree cores of t ciliata were developed into a 140 year tree ring widths index chronology the analyses showed that the ring widths indices correlate with march june precipitation as recorded at kairi research station march june precipitation was reconstructed using the tree ring data with 35 of the variance explained the reconstructed series contains both high and low frequency climate signals this suggests that growth of t ciliata is influenced by climate phenomena of different wave lengths which can be associated with el nino southern oscillation enso and interdecadal pacific oscillation ipo

crustal forensics in arc magmas abstract the geochemical characteristics of continental crust are present in nearly all arc magmas these characteristics may reflect a specific source process such as fluid fluxing common to both arc magmas and the continental crust and or may reflect the incorporation of continental crust into arc magmas either at source via subducted sediment or via contamination during differentiation resolving the relative mass contributions of juvenile mantle derived material versus that derived from pre existing crust of the upper plate and providing these estimates on an element by element basis is important because 1 we want to constrain crustal growth rates 2 we want to quantitatively track element cycling at convergent margins and 3 we want to determine the origin of economically important elements and compounds traditional geochemical approaches for determining the contributions of various components to arc magmas are particularly successful when applied on a comparative basis studies of suites from multiple magmatic systems along arcs for which differentiation effects can be individually constrained can be used to extrapolate to potential source compositions in the lesser antilles arc for example differentiation trends from individual volcanoes are consistent with open system evolution however such trends do not project back to a common primitive magma composition suggesting that differentiation modifies magmas that were derived from distinct mantle sources we propose that such approaches should now be complemented by petrographically constrained mineral scale isotope and trace element analysis to unravel the contributing components to arc magmas this innovative approach can 1 better constrain true end member compositions by returning wider ranges in geochemical compositions among constituent minerals than is found in whole rocks 2 better determine magmatic evolution processes from core rim isotopic or trace element profiles from the phases contained in magmas and 3 constrain rates of differentiation by applying diffusion controlled timescales to element profiles an example from nguaruhoe volcano new zealand underscores the importance of such a microsampling approach showing that mineral isotopic compositions encompass wide ranges that whole rock isotopic compositions are consequently simply element weighted averages of the heterogeneous crystal cargo and that open system evolution is proved by core rim variations in sr isotope ratios nguaruhoe is just one of many systems examined through microanalytical approaches the overwhelming conclusion of these studies is that crystal cargoes are not truly phenocrystic but are inherited from various sources the implication of this realization is that the interpretation of whole rock isotopic data including the currently popular u series needs careful evaluation in the context of petrographic observations

a new method for dating tree rings in trees with faint indeterminate ring boundaries using the itrax core scanner abstract eastern australia is known to experience multi decadal periods of flood and drought subtropical southeast queensland is one region where these devastating extreme events occur regularly yet a full understanding of their frequency and magnitude cannot be determined from the short duration 100 years proxy rainfall information but locating suitable forest stands is difficult due to extensive land clearing by european settlers another factor deterring the use of trees as proxy data sources is that longer lived species frequently contain anomalous rings particularly faint rings hindering their use for paleoclimate study here we present a method which overcomes the problems of identifying faint ring boundaries in trees by using x radiographs and density patterns developed on the itrax core scanner we analysed 39 tree cores from 20 trees at a site in d aguilar national park located just north of brisbane city in queensland australia each core had a 2 mm lath cut perpendicular to its rings which was then passed through an itrax core scanner the tree ring boundaries were identified on the image by both the visual features in the radiograph and the change in density observed between rings from this information we developed a tree ring chronology the chronology was checked using bomb pulse radiocarbon dating on five trees to confirm the annual nature of the rings and to correct dating errors in the chronology due to false rings which are common in this species climate response function analysis showed austral annual rainfall june may was the dominant environmental variable driving tree growth finally a 69 year statistically significant reconstruction of brisbane precipitation was produced showing that this non destructive itrax ring identification technique together with age validation by bomb pulse radiocarbon dating is useful for dendroclimatological studies of trees with faint ring boundaries

signals of barremian 116 ma or younger oceanic crust beneath the bay of bengal along 14 n latitude between 81 e and 93 e abstract the magnetic profile along 14 n in the bay of bengal collected on board r v samudra manthan of the geological survey of india was processed in the frequency domain from the energy spectrum the computed average thickness of sediment cover comes to 6 km and the average geothermal gradient to 20 c km analysis of the vertical magnetic structure by a singular point method yields a pseudosection marked by four clear domains the eighty five east ridge appears as a pair of strong magnetic features between 84 e and 86 e whereas the ninety east ridge shows up as a narrow well defined vertical magnetic feature at 92 e by match filtering technique we extracted a magnetic profile of the basement which displays a number of polarity reversals the reversals between 81 e and 84 e appear to be records of barremian or younger seafloor spreading instead of m series reversals between 132 and 119 ma this is based on the fact that neither the basic lavas nor the marine sediments so far obtained from the basin margin are older than barremian 116 ma given the uncertainty in apwp of the indian landmass between 200 and 117 ma the rajmahal hot spot might have powered the rifting of india from antartica from 117 ma onwards initiation of rifting at 132 ma as reconstructed by earlier workers is not proved

depositional evolution of the early cretaceous sihetun lake and implications for regional climatic and volcanic history in western liaoning ne china numerous well known fossils of the jehol biota including early birds feathered theropods primitive mammals and putative early angiosperms have been discovered in lacustrine deposits lake sihetun of the lower cretaceous yixian formation of western liaoning province ne china based on extensive field investigations and four high resolution excavations we document in detail the spatio temporal changes of sedimentary facies facies associations and limnic community relicts reconstruct the depositional history and discuss the significance of these deposits regarding the regional climatic and volcanic history four phases are recognized in the history of lake sihetun they are 1 a phase of fluctuating but gradually rising water level indicated by subaerial and shallow water lacustrine deposits 2 a lake with beach nearshore facies along the marginal areas and suspension dominated lake floor facies in central areas 3 a lake phase with a lake floor dominated by hyperpycnal flows and 4 progradation of a fan delta two distinct depositional conditions are observed stratified and unstratified lake intervals the former occurred mainly during the second phase and produced clay poor and clay rich laminae whereas the latter developed during the other three phases and were dominated by deposition of subaqueous sedimentary density flows these alternations of depositional conditions in offshore lacustrine deposits suggest that the yixian formation may have formed under a transitional climate regime fluctuating gradually from warm and dry to warm and humid conditions resurgent volcanism is inferred to have become stronger during the late phase of lake development based on distribution of deposits characterizing the unstratified lake interval and volcanic rocks of the overlying upper lava unit a higher content of primary pyroclastic fragments and evidence of strong syndepositional disturbance

late cretaceous magmatism in madagascar palaeomagnetic evidence for a stationary marion hotspot late cretaceous basaltic volcanics in the morondava basin sw madagascar possess high quality and pre fold palaeomagnetic data declination 353 5 inclination 54 8 95 2 4 the palaeomagnetic data are all of normal magnetic polarity and remanence acquisition is linked to the terminal stages of the cretaceous normal superchron 83 ma this is sustained by an 40ar 39ar age of 83 6 1 6 ma from one of the tested basaltic flows a precise u pb zircon baddeleyite age from northeast madagascar demonstrates magmatism at least back to 91 6 0 3 ma thus reliable isotope ages for the madagascar cretaceous igneous province span a range of 8 million years late cretaceous palaeomagnetic data obtained from volcanics and dolerites all over madagascar are directionally concordant and the combined palaeomagnetic pole latitude 68 5 n longitude 230 3 e a95 5 5 n 8 studies sampling age range ca 84 90 ma represents one of the best late cretaceous poles for the former gondwanan elements the collective palaeomagnetic data yield a palaeolatitude of 45 3 s 5 3 4 7 for the proposed focal point of the marion plume volcan de l androy southeast madagascar during the late cretaceous this is in perfect agreement with hotspot controlled reconstructions that place the marion hotspot 46 0 s beneath southeast madagascar during the late cretaceous setting true polar wander aside hotspot movements in the indian ocean do not appear to exceed ca 0 75 cm yr and the marion hotspot appears stationary within the resolution power of palaeomagnetic data

the stratigraphy and paleoenvironment of a lycoptera bed site in eastern inner mongolia china correlation with the fossiliferous lower cretaceous strata in western liaoning abstract the stratigraphy and the fossil assemblage of a lower cretaceous lycoptera bed of the xinganling group in naketa arongqi area inner mongolia china are described and the paleoenvironment is discussed as it relates to the jehol biota the naketa fossil bed belongs to the lower part of volcanic sedimentary jiufengshan formation and preserves a typical eel eosestheria ephemeropsis trisetalis lycoptera davidi faunal assemblage which indicates a strong affiliation to the jehol biota of western liaoning china the fossil bed was deposited in a shallow to semi deep lacustrine setting with occurrence of oil shale facies and this is different from the lycoptera bed of the yixian formation and more similar to the overlying jiufotang formation in western liaoning a layer of volcanic tuffite within the fossil bed is dated as 121 6 0 47 ma using the zircon u pb isotopic dating method this age is contemporary with the age of the base of jehol biota producing jiufotang formation in western liaoning thereby supporting the biostratigraphic correlation however the genus lycoptera is almost entirely absent in western liaoning with only one species in the jiufotang formation where the dominant fish genus is jinanichthys therefore lycoptera in the great xing an mountain areas appears to have a longer record than in western liaoning which likely indicates that the fish fauna changed earlier in western liaoning and this observation supports the hypothesis that the yanliao area was the diversification center of some cretaceous new groups in ne asia preliminary analysis of the taphonomy and the geology indicates that the mass mortality of fish at the naketa site may not be related to volcanism additional taphonomic investigations would allow a better understanding of the early cretaceous aquatic paleoecology and paleoenvironment in the volcanic rifting regions the great xing an mountain area is a new opportunity for expanding the research on the jehol biota beyond the core localities in western liaoning

pb loss patterns in zircons from a high grade metamorphic terrain as revealed by different dating methods upb and pbpb ages for igneous and metamorphic zircons from northern sri lanka abstract we report u pb and 207 pb 206 pb ages for multigrain fractions single grains and grain domains in zircons from highgrade igneous and sedimentary rocks of the vavuniya charnockite province vcp in northern sri lanka using the ionmicroprobe shrimp a new vapour digestion technique vdt and evaporation charnockitic enderbitic and mangeritic gneisses are derived from i type tonalitic syenitic granodioritic and granitic precursors for which the u pb systematics of zircons as determined by shrimp suggest crystallization ages between 1000 and 1100 ma many translucent round and multifacetted zircons in these rocks are not of metamorphic but of igneous origin and acquired their shape through partial zircon dissolution and recrystallization the large majority of zircons exhibit severe and variable pb loss some 540 580 ma ago which we ascribe to granulite grade metamorphism almost immediately followed by local retrogression most of the zircons lost pb from the entire grain with no domains remaining that reflect the original pb isotopic composition it was therefore impossible to obtain meaningful 207 pb 206 pb evaporation ages for such grains and this cautions against use of this method in zircons that experienced severe pb loss however zircons formed during high grade metamorphism apparently retain their primary pb isotopic composition and were dated successfully by the evaporation technique yielding ages between 553 26 and 560 30 ma conventional multigrain analysis and small fractions following vdt for two samples although much more precise than the shrimp data yielded only strongly discordant data points with patterns reflecting variable pb loss these data alone would not have made it possible to obtain reliable primary zircon crystallization ages 207 pb 206 pb evaporation ages for detrital zircons from two garnetiferous gneiss samples of sedimentary origin in the centre of the vcp revealed a maximum age of 1329 18 ma whereas a metaquartzite near the southern margin of the vcp contained zircons with 207 pb 206 pb ages between 1857 14 and 2543 14 ma we interpret the latter rock as belonging to the highland complex which occurs adjacent to the vcp our zircon data in combination with nd model ages milisenda et al 1994 suggest the vcp to be part of the wanni complex a distinct crustal domain in northern sri lanka characterized by relatively young ages in comparison with much older ages in the adjacent highland complex

the middle triassic evolution of the bangong nujiang tethyan ocean evidence from analyses of oib type basalts and oib derived phonolites in northern tibet in this paper we present new major and trace element chemical data for the basalts and phonolites of the nare ocean island fragment naoi as well as zircon u pb age data and hf isotope compositions for the naoi phonolites in the middle segment of the bangong nujiang suture zone northern tibet our aim is to assess the genesis of these rocks and to reconstruct the middle triassic evolution of the bangong nujiang tethyan ocean bnto the naoi retains an ocean island type double layered structure comprising a basaltic basement and an oceanic sedimentary cover sequence conglomerate and limestone the latter accompanied by layers of erupted phonolite near the top of the sequence the basalts in the naoi are enriched in light rare earth elements and high field strength elements nb ta zr hf and ti and they exhibit chondrite normalized ree patterns and primitive mantle normalized trace element patterns similar to those of ocean island basalts taking into consideration their high dy yb sm yb and la sm ratios we conclude that the naoi basalts were derived from the partial melting of garnet peridotite in the mantle the naoi phonolites have lree enriched chondrite normalized ree patterns with negative eu anomalies eu eu 0 41 0 43 and primitive mantle normalized trace element patterns with enrichments in nb ta zr and hf and depletions in ba u sr p and ti given the high contents of nb 172 256 ppm ta 11 8 16 0 ppm zr 927 1117 ppm and hf 20 8 26 9 ppm and the very low contents of mgo 0 11 0 25 wt the very low mg values 5 10 and the near zero contents of cr 1 27 7 59 ppm ni 0 43 7 19 ppm and co 0 11 0 38 ppm and the small and homogeneously positive e hf t values 4 9 to 9 5 we infer that the naoi phonolites were formed by the fractional crystallization of an oib derived mafic parent magma the phonolites of the naoi contain zircons that yielded u pb ages of 239 and 242 ma indicating that the naoi formed during the middle triassic these data combined with data from modern ocean islands e g canary islands cape verde fernando de noronha tristan da cunha and gough in the atlantic ocean and society and austral cook in the pacific ocean lead us to infer that the bnto was open for a long time before the middle triassic and that the ocean had already developed into a mature ocean with a thick oceanic lithosphere by at least the middle triassic

the dynamics of kerguelen plateau magma evolution new insights from major element trace element and sr isotope microanalysis of plagioclase hosted in elan bank basalts abstract the kerguelen plateau and broken ridge in the southern indian ocean together represent one of the most voluminous large igneous provinces lips ever emplaced on earth a scientific objective of ocean drilling program odp leg 183 was to constrain the post melting magma evolution of kerguelen plateau magmas in an effort to better understand this evolution isotopic and trace element analysis of individual plagioclase crystals hosted within two kerguelen plateau basalts recovered from elan bank were undertaken previous whole rock studies established that the two host basalts investigated in this study are samples of crustally contaminated lower group and relatively uncontaminated upper group basalt plagioclase phenocrysts from the uncontaminated basalt are dominantly normal zoned and exhibit a 87sr 86sri range of 0 704845 0 704985 which overlaps uncontaminated group whole rock values previously reported plagioclase crystals from the contaminated basalt are dominantly reverse zoned and exhibit a 87sr 86sri range of 0 705510 0 705735 which all lie within contaminated group whole rock values previously reported there are no systematic within crystal core to rim variations in 87sr 86sri from either group with the exception that contaminated group crystal rims have overall less radiogenic 87sr 86sri than other zones these observations indicate that crustal assimilation occurred before the formation of unit 10 plagioclase phenocrysts which is supported by parent magma trace element abundance data inverted using carefully calculated partition coefficients trace element diffusion modeling indicates that the upper group basalt unit 4 experienced a more vigorous eruptive flux than the lower group basalt unit 10 we suggest that plagioclase phenocrysts in both the upper and lower group basalts originated from the shallowest section of what was likely a complex magma chamber system we contend that the magmatic system contained regions of extensive plagioclase dominated crystal mush crustal assimilation was not a significant ongoing process in this portion of the elan bank magmatic system both basalts exhibit compelling evidence for remobilization and partial resorption of crystalline debris e g reverse zoned crystals glomerocrysts we suggest unit 4 and 10 magmas ascended different sections of the elan bank magma system where the unit 10 magmas ascended a section of the magma system that penetrated a stranded fragment of continental crust

effects of planetary thermal structure on the ascent and cooling of magma on venus magellan radar images of the surface of venus show a spatially broad distribution of volcanic features models of magmatic ascent processes to planetary surfaces indicate that the thermal structure of the interior significantly influences the rate of magmatic cooling and thus the amount of magma that can be transported to the surface before solidification in order to understand which aspects of planetary thermal structure have the greatest influence on the cooling of buoyantly ascending magma we have constructed magma cooling profiles for a plutonic ascent mechanism and evaluated the profiles for variations in the surface and mantle temperature surface temperature gradient and thermal gradient curvature results show that for a wide variety of thermal conditions smaller and slower magma bodies are capable of reaching the surface on venus compared to earth primarily due to the higher surface temperature of venus little to no effect on the cooling and transport of magma are found to result from elevated mantle temperatures elevation dependent surface temperature variations or details of the thermal gradient curvature the enhanced tendency of magma to reach the surface on venus may provide at least a partial explanation for the extensive spatial distribution of observed volcanism on the surface

magma evolution revealed by anorthite rich plagioclase cumulate xenoliths from the ontong java plateau insights into lip magma dynamics and melt evolution abstract petrologic studies of igneous rocks often rely on whole rock analyses alone to deduce source and melting histories whole rock compositions represent a mixture of the processes responsible for the final texture and composition of the rock but do not emphasize the evolutionary processes that the rock may have experienced we examine the major minor and trace element compositions of plagioclase phenocrysts and plagioclase rich cumulate xenoliths from a sequence of kwaimbaita pillow basalt and massive flows recovered from ocean drilling program odp site 1183 on the expansive 122 ma ontong java plateau ojp and from subaerial outcrops on the island of malaita solomon islands these data are used to reconstruct equilibrium liquid compositions to understand magma dynamics magma evolution and the distribution basalt types across the ojp results reveal that crystals frequently are out of equilibrium with their host basalt two distinct compositional zones are present in plagioclase phenocrysts and xenolith crystals an80 86 and an65 79 equilibrium magma compositions derived from each of these zones are distinct in relative terms the following distinctions are made an80 86 sr y and eu richer ba and lree depleted higher sr ti lower ba sr and la y an65 79 sr y and eu poorer ba and lree enriched lower sr ti higher ba sr and la y we observed several an65 79 parent magmas with higher la y lower sr and higher lree than the majority of an65 79 zones which suggests that they grew from highly fractionated magmas the an80 86 zones of both xenolith crystals and phenocrysts appear to have crystallized relatively early and are attributed to growth in magmas more primitive than parent magmas of an65 79 zones or the host magma using melts modeling we demonstrate a significant role for h2o is not necessary to form an rich crystals from known ojp magma types these types of zones can instead form when relatively primitive ojp magmas ascend and partially crystallize at low pressures crystal mush layers are rheological elements of multiply saturated solidification fronts and conditions for extreme fractionation are met deep with thermally and mechanically insulated mush solidification fronts conditions in a homogenous magma body alone cannot generate the range of magma compositions and textures recorded in ojp plagioclase crystals we suggest that the ojp magma chamber system consisted of crystal mush dominated regions and liquid dominated regions in a laterally and vertically extensive system of interconnected dikes and sills solidification front disruption was common during magma recharge and transport which freed debris to mix with ojp magmas the volume of crystalline debris from disrupted solidification fronts was small relative to the overall magma volume which leads to little change of bulk magma chemistry this can explain the dominance of the kwaimbaita basalt type across the ojp evidence of solidification front disruption is best preserved as allochthonous crystals both more and less primitive than bulk magma chemistry both of which were observed in ojp basalts coincident with a zone of neutral buoyancy the shallow ojp magma chamber system existed at a depth of 0 7 km the ojp magma chamber system was thinner near the plateau margins which provided less density filtration of magmas this allowed more diverse magma types to reach the surface along the margins it is envisaged that as the ojp formed the zone of neutral buoyancy slowly migrated upward leading to slow yet pervasive assimilation of overlying seawater altered basalt at the base of the lava pile

oxygen isotopes of east asian dinosaurs reveal exceptionally cold early cretaceous climates early cretaceous vertebrate assemblages from east asia and particularly the jehol biota of northeastern china flourished during a period of highly debated climatic history while the unique characters of these continental faunas have been the subject of various speculations about their biogeographic history little attention has been paid to their possible climatic causes here we address this question using the oxygen isotope composition of apatite phosphate from various reptile remains recovered from china thailand and japan values indicate that cold terrestrial climates prevailed at least in this part of asia during the barremian early albian interval estimated mean air temperatures of about 10 4 c at midlatitudes 42 n correspond to present day cool temperate climatic conditions such low temperatures are in agreement with previous reports of cold marine temperatures during this part of the early cretaceous as well as with the widespread occurrence of the temperate fossil wood genus xenoxylon and the absence of thermophilic reptiles such as crocodilians in northeastern china the unique character of the jehol biota is thus not only the result of its evolutionary and biogeographical history but is also due to rather cold local climatic conditions linked to the paleolatitudinal position of northeastern china and global icehouse climates that prevailed during this part of the early cretaceous

provenance of proterozoic garnet biotite gneiss recovered from elan bank kerguelen plateau southern indian ocean at elan bank of the kerguelen plateau in the southeast indian ocean leg 183 of the ocean drilling program recovered clasts of garnet biotite gneiss in a fluvial conglomerate intercalated with basalt flows u pb and pb pb dates of zircons and monazites in these clasts and an overlying sandstone range from 534 to 2547 ma which is much older than the surrounding indian ocean seafloor these dates show that old continental crust resides in the shallow crust of the oceanic kerguelen plateau and that the breakup of gondwana dispersed continental fragments into the nascent indian ocean lithosphere

lacustrine varve formation through time abstract studies using sediment traps in lakes reveal that the seasonal flux of sediment regulates both the composition and timing of deposition of materials that reach the bottoms of lakes if the bottom waters of a lake are partly or totally anoxic the seasonally deposited materials are preserved as annual groupings of laminae varves common components that form individual laminae consist of allochthonous clastic material derived from the drainage basin precipitated carbonate minerals diatom frustules iron rich and manganese rich flocs autochthonous organic detritus and autochthonous and allochthonous materials resuspended from the bottom the style of varving has changed over geologic time reflecting changes in biologic evolution and types of materials available precipitated iron rich laminations were common in the middle precambrian graded sets of clastic organic laminations persisted through the precambrian prior to the evolution of bioturbating benthic organisms glaciolacustrine varves appear to have retained their distinctive character through time carbonate rich varves occurred sporadically in the precambrian and phanerozoic with the exception of diatoms major components of modern lacustrine varves were present through the paleozoic and mesozoic and yet varves are rare in strata of these ages and may have accumulated in marine to brackish water environments diatoms were introduced into lacustrine systems in early tertiary time and are common components of varves from then on diatom laminae combined with a greater chance for geologic preservation of younger lake deposits have increased the number of geologically young occurrences of varved sediments however seasonal associations of modern varve components and the processes they represent are present in ancient deposits and provide clues to the interpretation of ancient environments

minor and trace element zoning in plagioclase implications for magma chamber processes at parinacota volcano northern chile textural and compositional zoning in plagioclase phenocrysts in a sample from parinacota volcano chile was investigated using backscattered electron images and electron microprobe analysis of major and trace elements large 2 mm oscillatory zoned crystals type i with resorption surfaces of moderate an discontinuities 10 an and decreasing trace element contents sr mg ti towards the rim reflect melt differentiation and turbulent convection in the main magma body early recharge with a low sr mafic magma is seen in the core small scale sr variations in the core indicate limited diffusion and thus residence and differentiation times of the magma shorter than a few thousand years smaller crystals type ii with low trace element an ratio reflect the influence of an h2o rich melt probably from a differentiated boundary layer closed system in situ crystallisation mafic magma recharge and the role of a water rich differentiated boundary layer can be distinguished from the an trace element relationships crystals apparently move relatively freely between different parts and regimes in the magma chamber evidence for convective crystal dispersion high sr type ii crystals indicate an earlier input of sr rich mafic magma recharge of two distinct mafic magma types is thus identified high sr and low sr which must have been present at increasing recharge rates with time in the plumbing system throughout the volcano s history

a new late quaternary palaeohydrological record from the humid tropics of northeastern australia abstract high resolution x ray fluorescence xrf is presented as a robust palaeoclimatic proxy suitable for use on late pleistocene to holocene sediments located in a volcanic crater on the atherton tableland in northeastern queensland australia the proxy allows identification of wet and dry shifts in a complex sedimentary sequence comprised of peat gyttja laminated organic rich muds and fine clastic silt rich sediments significant correlation is found between the xrf record and other proxies including magnetic susceptibility humification grain size macrocharcoal 13c and c n and pollen sixteen wetter periods are identified in the 37 ka sedimentary record for bromfield swamp three wetter periods commence in late marine isotope stage 3 nine in the early glacial one in the late de glacial and four in holocene nineteen drier periods are identified four in late mis 3 seven in the early glacial one during the lgm one in the late de glacial period and six in the holocene the xrf record for bromfield swamp is specifically used to identify periods of abrupt climate change marked changes in effective precipitation are detected at 32 690 30 080 24 660 21 870 11 880 10 020 9170 and 5120 cal yr bp the detection of these abrupt climate events may allow correlation with records from terrestrial sites across the southern hemisphere and potentially the northern hemisphere