the major ion composition of carboniferous seawater abstract the major ion chemistry na mg 2 ca 2 k so 4 2 and cl of carboniferous seawater was determined from chemical analyses of fluid inclusions in marine halites using the cryo scanning electron microscopy cryo sem x ray energy dispersive spectrometry eds technique fluid inclusions in halite from the mississippian windsor and mabou groups shubenacadie basin nova scotia canada asbian and pendleian substages 335 5 330 ma and from the pennsylvanian paradox formation utah usa desmoinesian stage 309 305 ma contain na mg 2 k ca 2 cl brines with no measurable so 4 2 which shows that the carboniferous ocean was a cacl 2 sea relatively enriched in ca 2 and low in so 4 2 with equivalents ca 2 so 4 2 hco 3 34 s values from anhydrite in the mississippian shubenacadie basin 13 2 14 0 and the pennsylvanian paradox formation 11 2 12 6 support seawater sources br in halite from the shubenacadie basin 53 111 ppm and the paradox basin 68 147 ppm also indicate seawater parentages carboniferous seawater modeled from fluid inclusions contained 22 mmol ca 2 kg h 2 o mississippian and 24 mmol ca 2 kg h 2 o pennsylvanian estimated sulfate concentrations are 14 mmol so 4 2 kg h 2 o mississippian and 12 mmol so 4 2 kg h 2 o pennsylvanian calculated mg 2 ca 2 ratios are 2 5 mississippian and 2 3 pennsylvanian with an estimated range of 2 0 3 2 the fluid inclusion record of seawater chemistry shows a long period of cacl 2 seas in the paleozoic from the early cambrian through the carboniferous when seawater was enriched in ca 2 and relatively depleted in so 4 2 during this 200 myr interval ca 2 decreased and so 4 2 increased but did not cross the ca 2 so 4 2 chemical divide to become a mgso 4 sea when so 4 2 in seawater became greater than ca 2 until the latest pennsylvanian or earliest permian 309 295 ma seawater remained a mgso 4 sea during the permian and triassic for 100 myr fluid inclusions also record a long interval from the early cambrian to the middle devonian when seawater had low mg 2 ca 2 ratios 2 ca 2 ratio of seawater rose from 0 9 in the middle devonian to 2 5 in the middle late mississippian 2 3 in the middle pennsylvanian and 3 5 in the early permian the transition from calcite seas to aragonite seas established from the mineralogy of oolites and early marine cements occurred in the late mississippian fluid inclusions show that seawater mg 2 ca 2 ratios rose above 2 by the middle to late mississippian coinciding exactly with the shift to aragonite seas aragonite seas existed for 100 myr from the late mississippian until the late triassic early jurassic

tropical zonal momentum balance in the ncep reanalyses the seasonal cycle of the zonal mean zonal momentum balance in the tropics is investigated using ncep reanalysis data it is found that the climatological stationary waves in the tropical upper troposphere which are dominated by the equatorial rossby wave response to tropical heating produce an equatorward eddy flux of westerly momentum in the equatorial belt the resulting westerly acceleration in the tropical upper troposphere is balanced by the advection of easterly momentum associated with the cross equatorial mean meridional circulation the eddy momentum fluxes and the cross equatorial flow both tend to be strongest during the monsoon seasons when the maximum diabatic heating is off the equator and weakest during april may the season of strongest equatorial symmetry of the heating the upper level rossby wave pattern exhibits a surprising degree of equatorial symmetry and follows a similar seasonal progression solutions of the nonlinear shallow water wave equation also show a predominantly equatorially symmetric response to a heat source centered off the equator

x ray microanalysis of fluid inclusions and its application to the geochemical modeling of evaporite basins direct access to brines trapped in halite is possible by freezing and breaking halite crystals on a cooling stage inside a scanning electron microscope quantitative analyses of major solutes na mg k ca cl and so4 in natural brines were obtained by means of x ray microanalysis of the frozen fluid inclusions using frozen droplets of brines with known composition as standards precision errors were estimated to be lower than 10 and detection limits vary from below 0 02 mol l for ca k and so4 to 0 55 mol l for na analyses of several inclusions of sizes larger than 20 m were performed for each cross section of halite the composition of primary fluid inclusions in halites from a drill core in the messinian basin of lorca se spain were used to constrain the parameters of a geochemical model of the evolution of the basin a computer program to simulate evaporation paths was developed using thermodynamic equilibrium and mass balance as constraints the halite sequence was interpreted as resulting from the evaporation of initial seawater in a hydrologically open basin with seawater replacing the evaporated water and a small fraction of basinal brine leaking out in the middle of the sampled sequence the basin was closed to the sea and only continental water flowed into the basin reworking part of the halite deposited in the margins in contrast with these results only very poor information would have been obtained from the mineralogical record alone consisting mainly of halite and minor gypsum

active deformation to the north of the altyn tagh fault constraints on the northward growth of the northern tibetan plateau abstract sinistral transpressive deformation occurs in the region north of the altyn tagh fault due to the indo eurasian collision in this region several late cenozoic faults have developed and the sanweishan fault is the key feature with clear landforms in this study slip rate measurements combined with several dating methods imply that the sanweishan fault has been active with sinistral strike slip rates of 0 33 0 04 mm a since 14 ka bp and 0 28 0 03 mm a since 20 ka bp which are more than an order of magnitude smaller than that of the atf to the south the horizontal displacements are 1 7 5 5 m in the eastern segment and 25 0 76 0 m in the middle and western segments of the sanweishan fault the increment of horizontal displacement along the main sanweishan fault is 3 0 4 0 m between paleoearthquakes and the magnitude of the latest paleoearthquake on the middle and eastern segments of the fault is up to m 7 2 7 5 the whole length of the sanweishan fault is 360 km or longer which include active faults in the yangguan and danghe reservoirs in the west more components of thrusting occur on the western and eastern segments of the sanweishan fault the growth of the sanweishan fault is similar to that of the atf but the former fault is younger and its slip rate is much smaller the differential slip rates on the sanweishan fault and atf may result in the clockwise rotation and eastward movement of the intervening block which compresses regions to the northeast

a review of magmatism and deformation history along the ne asian margin from ca 95 to 30 ma transition from the izanagi to pacific plate subduction in the early cenozoic abstract previous plate reconstruction in the paleo pacific domain indicates that the izanagi and pacific plates influenced the ne asian continental margin during the mesozoic and cenozoic respectively however it remains unclear how and when the transition from izanagi to pacific plate subduction occurred because most evidence came from the oceanic crust however the onshore geological records are poorly understood so in order to solve this problem we review recently published data and identify three magmatic episodes a magma gap and four deformation stages from ca 95 to 30 ma margin parallel izanagi pacific ridge subduction is proposed to explain the changing magmatic and deformation signatures and other regional events in the early cenozoic from ca 95 to 65 ma the n or nnw directed subduction of the izanagi plate triggered sinistral shearing along the nne striking faults arc magmas at that time incorporated older crustal materials from ca 65 to 55 ma the nww striking transform faults and ridge segments were subducted developing small slab windows and facilitating the input of juvenile magmas local extension was active above these windows during ca 55 to 45 ma the ridge was totally subducted and a margin wide slab window was opened resulting in an arc magma gap and extension massive asthenosphere upwelling caused the extensive accretion of juvenile materials from ca 45 30 ma the dextral nne trending faults resulted from the w directed subduction of the pacific plate new arc magmas were generated from juvenile materials and thus are isotopically depleted

retrograde net transfer reaction insurance for pressure temperature estimates retrograde net transfer reactions significantly affect compositions of metamorphic minerals yet are rarely considered when determining pressure temperature p t conditions two natural amphibolite facies metapelites from the central himalaya of nepal exhibit extremely common compositional patterns including increases in mn and fe fe mg at the rims of garnets which are the result of retrograde garnet dissolution and fe mg exchange with biotite however typical thermobarometric approaches for these rocks result in errors of hundreds of degrees and 3 6 kbar compared with thermobarometry of nearby rocks and petrogenetic grids these large errors result because dissolution of high fe garnet has strongly affected the fe mg ratio of matrix biotite x ray maps help evaluate the extent and chemical effects of retrograde reactions in these samples by identifying mineral regions that retain highest t compositions or through a new data processing approach by permitting correction of mineral compositions to original high t values these approaches ensure against retrograde net transfer reactions and should be applied routinely in thermobarometric studies they ultimately yield p t estimates that are more petrologically reasonable and permit rapid screening of samples for those least affected by retrograde reactions reconsideration of thermobarometry in the central and eastern himalaya indicates that retrograde net transfer reactions are extremely common therefore previous thermobarometric studies based on garnet major element compositions from that region should be reevaluated

evidence of potash salt formation in the pliocene sedom lagoon dead sea rift israel abstract the dead sea is a ca chloride evaporitic lake close to halite saturation carnallite kmgcl3 6h2o is the next mineral predicted to precipitate and is currently produced in solar ponds on the shores in israel and jordan the particular composition of the dead sea has been attributed to the contribution of pliocene residual brines formed during the deposition of the sedom formation that currently reappear as hydrothermal flows the chemical composition of these returning flows suggests that sedom brines reached the potash forming sylvite and or carnallite stage the sedom formation is a thick more than 2000 m evaporite succession made up of bedded salt rock accumulated during the pliocene when an arm of the mediterranean sea seeped through the dead sea rift forming the sedom lagoon the present study is focused on the upper part of the sedom formation mearat sedom member where detailed petrology bromine contents in salt cryo sem eds microanalysis of fluid inclusions in halite and isotopic compositions 34s and 18o in sulfates and 37cl in salt were investigated although halite is the main evaporite mineral minor sylvite and carnallite occurrences in the form of early diagenetic nodules cements and or authigenic crystals are commonly present the geochemical modeling of the primary fluid inclusion composition in halite points to the evaporation of seawater or mixtures of seawater and continental water with a very minor a cyclic evolution of the basinal brines can be deduced from the composition of fluid inclusions together with the bromine contents in halite and the sulfate isotopes thus stages of dilution involving fresh marine and or continental waters alternated with stages of high concentration when the saturation of the lagoon brine with respect to the potash salts was reached potash minerals could crystallize on the shores or in the marginal zones of the lagoon and could be dissolved and recycled during the subsequent dilution stages

the dynamics of intraseasonal atmospheric angular momentum oscillations abstract the global and zonal atmospheric angular momentum aam budget is computed from seven years of national centers for environmental prediction data and a composite budget of intraseasonal 30 70 day variations during northern winter is constructed regressions on the global aam tendency are used to produce maps of outgoing longwave radiation 200 hpa wind surface stress and sea level pressure during the composite aam cycle the primary synoptic features and surface torques that contribute to the aam changes are described in the global budget the friction and mountain torques contribute about equally to the aam tendency the friction torque peaks in phase with subtropical surface easterly wind anomalies in both hemispheres the mountain torque peaks when anomalies in the midlatitude northern hemisphere and subtropical southern hemisphere are weak but of the same sign the picture is different for the zonal mean budget in which the meridional convergence of the northward relative angular moment

mineralogy geochemistry and zircon u pb hf isotopes of the paleoproterozoic granulite facies metamorphic rocks from the aketashitage area southeastern tarim craton abstract the key to understanding the generation of mantle derived magma and the formation of new continental crust is the recognition of the granulite facies metamorphism associated partial melting and coeval magmatism that are documented in active continental margins we firstly present a combined analysis of petrography mineral chemistry zircon u pb ages and hafnium hf isotopes in addition to whole rock geochemistry on the garnet biotite gneisses grt bi gneisses and mafic granulites from the aketashitage area southeastern tarim craton the implications of this analysis are discussed with respect to the thermal and tectonic evolution of the tarim craton the grt bi gneisses and mafic granulites are strongly peraluminous in composition and have flat ree patterns with negative eu anomalies that are identical to those from the middle crust but higher than lower continental crust both the grt bi gneisses and the mafic granulites have negative nb ta anomalies slightly positive zr hf anomalies and pronounced positive spikes in u and pb the characteristics in whole rock geochemistry and mineral compositions indicate that the grt bi gneisses and mafic granulites have the same source locality which is most likely the garnet bearing middle crust the retrograde metamorphic p t estimates for the grt bi gneisses and mafic granulites are t 574 c p 7 0 kbar and t 715 c p 7 0 kbar respectively sims zircon u pb dating results reveal a large spread in metamorphic ages 2036 1962 ma for these granulite facies rocks interpreted to be the consequence of a large amount of magmas being added to the crust in an uninterrupted manner zircon hf isotopes are characterized by variable but mostly negative ehf t values 18 2 to 0 6 reasonably uniform hf isotopic compositions and highly variable tdmc model ages between 2628 and 3599 ma representing a long lived reworking of the preexisting crust our data along with available geological evidences lead us to propose a model for the evolution of the dunhuang block in the paleoproterozoic that is the southeastern margin of the tarim craton the dunhuang block was possibly an active continental margin during the paleoproterozoic the steep subduction of oceanic slab resulted in the thickening of the continental crust which in turn caused the crust anatexis the increase in asthenosphere high heat flow and the intrusion of mantle derived magma induced extensive heating which preceded the granulite facies metamorphism and coeval magmatism in the middle crust of the southern tarim craton

metamorphic p t path and sims zircon u pb dating of amphibolite of the namche barwa complex southeast tibet china abstract amphibolite from the core and the outer part of the namche barwa complex nbc southeast tibet experienced upper amphibolite facies metamorphism and records clockwise metamorphic p t paths prograde m1 peak m2 and retrograde m3 metamorphic mineral assemblages were identified in both amphibolite types the m2 p t conditions in the core and outer part of the nbc are similar zhibai amphibolite zba from the core 750 c 10 kbar paixiang amphibolite pxa from the outer part 670 750 c 8 5 10 5 kbar sims zircon u pb dating suggests that the protolith of pxa the outer part of the nbc formed at 90 80 ma similar to the mafic dykes within the tethyan himalaya this magmatism is probably related to tectonic events on the northern indian passive margin before its collision with the eurasian plate furthermore zircon records metamorphism from oligocene to late miocene 30 ma to 10 ma in the zba while pxa only documents a miocene metamorphic event 9 ma it is inferred that from oligocene to late miocene semi continuous advection of relatively hot material from the depth might have operated only in nbc core thus exhuming the zba to a shallower level while this material did not efficiently reach affect the pxa at late miocene 10 ma rapid exhumation started to propagate to the outer part of nbc and both units were amalgamated as a coherent block

atmospheric gas in modern and ancient halite fluid inclusions a screening protocol abstract halite possesses great potential for hosting and storing information vital to the reconstruction of earth s ancient climate seawater chemistry and evolving atmosphere here we propose a screening protocol that not only distinguishes between primary and secondary halite but also identifies fluid inclusions that carry original gas trapped during the primary crystallization process an integrated multi analytical protocol is presented for sample preparation petrographic evaluation analytical measurements and distinguishing original gases and contents from contaminants the screening protocol starts with the visual inspection of halite for primary chevron and hopper features and or milky appearance then petrography is used to distinguish between primary and secondary diagenetic crystal fabrics and inclusions the trace element and isotope geochemistry speak directly to the composition of the depositional and or diagenetic fluids and to the formation in marine non marine or diagenetic settings furthermore rare earth elements and redox sensitive elements may address the redox conditions of the salt pan flat brines whereas microthermometry helps characterize the depositional diagenetic environment s temperature finally gas extracted by quadrupole mass spectrometer from gas bubbles in fluid inclusions is screened with concomitant ch4 co2 and ar contents to distinguish and quantify organic matter decomposition contributions and with 40ar 36ar to monitor modern atmospheric gas diffusion leakage issues and thus contamination of the primary gas contents our test case shows that halite collected from cores is well suited in maintaining its original mineralogical texture chemistry and gas content our integrated screening protocol suggests that the 815 myr old halite from the tonian browne formation of the officer basin australia formed under atmospheric conditions of about 10 9 po2 back calculation or 9 6 po2 mean calculation the coeval neoproterozoic gypsum collected in outcrop from minto inlet victoria island canada underwent some mineralogical alteration however experiments suggest that depositional gypsum from outcrop core may have potential of retaining vestiges of original gas in fluid inclusions

the role of the divergent circulation for large scale eddy momentum transport in the tropics part i observations abstractthis work investigates the role played by the divergent circulation for meridional eddy momentum transport in the tropical atmosphere it is shown that the eddy momentum flux in the deep tr

glauberite halite association of the zaragoza gypsum formation lower miocene ebro basin ne spain glauberite is the most common mineral in the ancient sodium sulphate deposits in the mediterranean region although its origin primary or diagenetic continues to be a matter of debate a number of glauberite deposits of oligocene miocene age in spain display facies characteristics of sedimentologic significance in particular those in which a glauberite halite association is predominant in this context a log study of four boreholes in the zaragoza gypsum formation lower miocene ebro basin ne spain was carried out two glauberite halite lithofacies associations a and b are distinguished association a is composed of bedded cloudy halite and minor amounts of massive and clastic glauberite association b is made up of laminated to thin bedded clear macrocrystalline massive clastic and contorted lithofacies of glauberite and small amounts of bedded cloudy halite transparent glauberite cemented by clear halite as well as normal graded and reverse graded glauberite textures are common this type of transparent glauberite is interpreted as a primary subaqueous precipitate gypsum thenardite or mirabilite are absent in the two associations the depositional environment is interpreted as a shallow perennial saline lake system in which chloride brines association a and sulphate chloride brines association b are developed the geochemical study of halite crystals bromine contents and fluid inclusion compositions demonstrates that conditions for co precipitation of halite and glauberite or for precipitation of na sulphates mirabilite thenardite were never fulfilled in the saline lake system

juxtaposition of diverse subduction related tectonic blocks with contrasting metamorphic features and ages in the paleoproterozoic aketashitage orogen nw china implications for precambrian orogeny

a composite study of onset of the australian summer monsoon abstract onset of the australian summer monsoon is identified each year 1957 87 using the wind and rainfall record at darwin onset is defined as the first occurrence of wet 850 mb westerly winds composites of atmospheric fields at stations in and about the australian tropics are constructed relative to the onset date at darwin the composite onset is accompanied by the development of a convectively driven baroclinic circulation over northern australia upper tropospheric easterlies expand about the equator and the subtropical jet shifts poleward at onset this behavior is interpreted as a transient southerly shift of the local hadley circulation concurrent with the development of an upper level anticyclone over northern australia the composite onset coincides with the arrival of an eastward propagating convective anomaly the anomaly originates in the southern indian ocean propagates eastward at 5 m s 1 and is detectable as far east as the date line an eastward propagating zonal wind anomaly also

observations on the incorporation of trace elements in halite of oligocene salt beds bourg en bresse basin france abstract it is common practice to employ trace elements found in chloride salts as indicators of the conditions of deposition because some halite contains abundant fluid inclusions it is necessary to separate the salt from the inclusions before analysis this study presents the data derived from the use of a simple preparative technique which permits analysis of the trace elements in solid halite and provides a guide to test the success in elimination of the contaminants contained in the fluid inclusions the differentiation is accomplished simply by crushing the salt in alcohol followed by separate analysis of the fluid and solid components thus yielding accurate trace element concentrations in the solids crystal lattice dislocations and grain boundaries and the fluids br and k are present both in the solid and liquid phases of the halite but mg is exclusively in the fluid inclusions the elimination of the mg from the analysis of the solid phase may thus be employed as a monitor to indicate the degree of purification of the samples being analysed

recognition of ocean plate stratigraphy in accretionary orogens through earth history a record of 3 8billion years of sea floor spreading subduction and accretion abstract ocean plate stratigraphy ops is a term used to describe the sequence of sedimentary and volcanic rocks deposited on oceanic crust substratum from the time it forms at a spreading center to the time it is incorporated into an accretionary prism at a convergent margin in this study we review the major geological characteristics of relict cenozoic to early archean oceanic crust and ops persevered in alaska japan california franciscan complex central asia british isles canada slave province australia pilbara craton and greenland isua and ivisaartoq belts an assessment of ops in accretionary orogens spanning the duration of earth s rock record shows remarkable similarities between ops of all ages in terms of structural style major rock components sequence of accretion and trace element geochemical signatures volcanic rocks preserved in the orogenic belts are characterized predominantly by oceanic island arc basalts island arc picrites mid ocean ridge basalts back arc basalts oceanic plateau basalts ocean island basalts and boninites with extremely rare komatiites this demonstrates that sea floor spreading lateral movement of oceanic plates with accompanying sedimentation over the oceanic substratum and accretion at convergent margins have been major earth processes since at least 3 8 ga ago there have been some secular changes in the rock types in ops such as changes in carbonates and radiolarian cherts whose sources were in the biota in existence in phanerozoic times but absent in the precambrian but overall there have been few changes in the style of ops accretion with time komatiites and banded iron formations occur predominantly in archean orogenic belts reflecting higher mantle temperatures and less oxic seawater composition respectively before 2 5 ga this is clear documentation that plate tectonics including the lateral movement of oceanic lithosphere has been a major heat loss mechanism on earth since the early precambrian

the intraseasonal 30 50 day oscillation of the australian summer monsoon abstract the tropical intraseasonal 30 50 day oscillation manifests itself in the australian summer monsoon by a pronounced modulation of the monsoonal westerlies these 30 50 day fluctuations of the monsoonal westerlies are coherent with rainfall and olr across northern australia the olr fluctuation originates in the indian ocean and systematically propagates eastward at 5 m s 1 consistent with previous studies of the intraseasonal oscillation the detailed evolution of the intraseasonal oscillation of the monsoon is studied via composites of upper air data in and about the australian tropics during the summer periods 1957 87 91 events were identified at darwin australia the composite oscillation at darwin has a very deep baroclinic structure with westerlies extending up to 300 mb the westerly phase lasts about ten days and lags a similar duration rainfall event by about four days during the westerly phase the upper troposphere is warm and the extreme lower troposphere is cool this structure

observed relationships between the el nino southern oscillation and the extratropical zonal mean circulation abstract there is increasing evidence indicating that the climate response to variations in the el nino southern oscillation enso includes not only thermally forced zonal wind anomalies in the subtropics but also eddy driven zonal wind anomalies that extend into the mid high latitudes of both hemispheres in this study new insights into the observed seasonally varying signature of enso in the extratropical zonal mean circulation are provided and the associated linkages with the dominant patterns of extratropical variability are examined the zonal mean extratropical atmospheric response to enso is characterized by two principal features an equivalent barotropic dipole in the southern hemisphere sh zonal mean zonal flow with centers of action located near 40 and 60 during austral summer and a weaker but analogous dipole in the northern hemisphere nh with centers of action located near 25 and 45 during early and late boreal winter both structures are accompanied by eddy momentum flux ano

evaporitic sedimentation in the southeastern anatolian foreland basin new insights on the neotethys closure abstract we integrate stratigraphic petrographic and geochemical analysis of subsurface data wells together with field surveys to study the sedimentation of a marginal miocene sub basin of the southeastern anatolian foreland basin seafb se turkey this sub basin located in the batman siirt region is characterized by the existence of evaporites carbonates sulphates and chlorides and alluvial detritus which were divided in the following five lithostratigraphic members from older to younger lower and upper yapilar and lower middle and upper sulha these members deposited in an epicontinental mudflat during the early miocene both the bromine content and the sulphur and oxygen isotope composition 34 s v cdt and 18 o v smow of halite and sulphates samples respectively also suggest a marine origin of the precipitation brines however influence of geothermal fluids and dissolution and re precipitation of evaporites from uplifted areas in these brines such as the early miocene members and or triassic units is interpreted comparing and integrating our results with data documented in previous works it is here recognized that the depositional model of the studied sub basin differs from that which explain the coeval sedimentation of units situated in the western part of the seafb moreover our model shows some depositional and paleoenvironmental similarities with miocene evaporites located in the mesopotamian foreland basin this work provides valuable insights on the middle miocene salinity crisis which is related to the evolution of the neotethys closure

structure of the annual mean equatorial planetary waves in the era 40 reanalyses abstract the three dimensional structure of the annual mean equatorial planetary waves in the 40 yr ecmwf re analysis era 40 is documented the features in the free atmosphere are predominantly equatorially symmetric driven by east west heating gradients the geopotential height and wind perturbations are strongest at or just below the 150 hpa level below the level of maximum amplitude the circulations in the waves are thermally direct with latent heat release in deep convective clouds and radiative cooling in the intervening cloud free regions within the overlying capping layer the wave related circulations are thermally indirect with rising of the coldest air and sinking of air that is less cold at the cold point just above the 100 hpa 17 km level the era 40 annual mean vertical velocity in the equatorial belt ranges up to 3 mm s 1 over the equatorial western pacific during the boreal winter implying diabatic heating rates of up to 3 c day 1 an order of magnitude larger than typical clear

paleozoic multiple accretionary and collisional processes of the beishan orogenic collage in the paper by xiao and others american journal of science v 310 p 1553 1594 1 please substitute figure 16 reproduced here for figure 16 that appears between pages 1573 and 1574 the original figure 16 2 was printed at an improper size figure 3 1 lookup volpage 310

the celestite problem in gypsum sr geochemistry an evaluation of purifying methods of gypsiferous samples abstract celestite srso 4 is a very common mineral in gypsiferous rocks in order to evaluate the possible influence of celestite occurrence in gypsum strontium analysis sr content different fine grained lithofacies with a high content of enclosed minerals ranging from 5 to 35 of the bulk rock were studied and a series of experiments with artificial reagents were carried out the results showed that even very low concentrations the recommended methodology to prevent celestite contamination in sr content analysis of fine grained gypsum lithofacies involves three basic steps 1 celestite identification 2 celestite elimination and 3 geochemical analyses we found that back scattered electron microscopy is the best method to identify celestite over a wide range of celestite concentrations in the case of celestite occurrence microprobe analysis provided reliable results as the obtained sr values corresponded to the gypsum lattice if a bulk sample analysis is performed celestite must be eliminated or partially separated from the pure gypsiferous sample in order to reduce contamination for this different methods were modified and tested including a heavy liquid dibromomethane separation procedure however because none of these methods were completely satisfactory a new method based on a hcl 2n leaching was developed and tested nevertheless although the celestite content diminished considerably it was not totally eliminated in conclusion the presence of celestite must always be taken into account when gypsiferous samples are analyzed for their sr content or their 87 sr 86 sr ratio in order to avoid seriously biased results and non reliable geochemical and paleoenvironmental interpretations in celestite rich samples it is convenient to separate the celestite before carrying out the analysis

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

middle cambrian granites in the dunhuang block nw china mark the early subduction of the southernmost paleo asian ocean abstract the formation and evolution of the central asian orogenic belt caob were closely associated with the opening and closure of the so called paleo asian ocean pao the subduction of the southern pao is expected to have resulted in widespread paleozoic arc magmatism in the southernmost caob however the precise location and timing of such subduction remain uncertain the dunhuang block dhb in the southernmost caob is thought to have recorded such subduction in this contribution we report the results of the zircon u pb ages hf isotopes and whole rock geochemical data for the lianghu dapokouzi and xiaowan plutons in the northeastern dhb nw china zircon u pb dating reveals that these plutons formed at ca 510 ma the middle cambrian and may represent the oldest arc related magmatism in the dhb geochemically the dapokouzi pluton is characterized by high sio2 70 7 71 2 wt na2o 5 11 5 26 wt al2o3 15 5 15 6 wt and sr 730 733 ppm contents high sr y 380 398 ratios moderate mg 49 50 values low mgo 0 61 wt k2o 2 00 2 01 wt and y 1 84 1 93 ppm contents and weakly positive eu 1 39 1 44 anomalies indicating geochemical affinities of adakitic rocks they have positive ehf t values 11 2 to 13 9 close to the depleted mantle line and young two stage model ages tdm2 571 742 ma all the geochemical characteristics show that the dapokouzi pluton was derived from the remelting of juvenile crust with addition of minor metasomatized mantle derived materials and a residue phase dominated by garnet bearing amphibolite similarly the lianghu and xiaowan plutons have high sio2 70 2 74 4 wt and al2o3 12 8 14 3 wt low mgo 0 61 1 01 wt with mg values of 35 43 and k2o 0 43 1 55 wt contents compared to the dapokouzi pluton they exhibit low sr 121 155 ppm and y 15 3 23 1 ppm contents low sr y 5 25 9 54 ratios and cr ni co concentrations and pronouncedly positive ehf t values 11 0 to 14 7 indicating that the magmas originated from the remelting of juvenile lower crust followed by significant fractional crystallization at relatively shallow crustal depths data from this and previous studies convincingly suggest the dhb was located in a thickened continental arc setting during the early paleozoic probably related to the early subduction of the pao lithosphere crustal thickening as indicated by the geochemical signature of the dapokouzi pluton was most likely associated with the underplating of mantle derived mafic magmas during the slab subduction this study therefore highlights that the subduction of the southern pao might have initiated prior to 510 ma possibly dating back to the early cambrian

metamorphic evolution and sims zircon u pb geochronology of mafic granulite and amphibolite enclaves of the pingyang trondhjemitic pluton fuping terrane north china abstract the discrete mafic granulite and amphibolite enclaves within the pingyang trondhjemitic pluton fuping metamorphic terrane middle trans north china orogen ubiquitously record three stages of metamorphic assemblages for the mafic granulite enclaves the prograde metamorphic assemblage m1 is represented by mineral inclusions clinopyroxene hornblende plagioclase quartz apatite preserved in the garnet porphyroblast the metamorphic peak m2 assemblage consists of garnet and matrix minerals of clinopyroxene orthopyroxene hornblende plagioclase quartz magnetite ilmenite zircon and the retrograde m3 stage is represented by symplectite assemblage of orthopyroxene plagioclase clinopyroxene hornblende quartz rimming the garnet porphyroblast the metamorphic p t paths of the mafic granulite enclaves are defined to pass from 560 750 c 6 9 kbar m1 through 740 880 c 11 14 kbar m2 to 720 800 c 6 8 m3 indicative of a collisional orogenic process the metamorphic p t path of the amphibolite enclave experienced from 670 730 c 9 3 11 8 kbar to 710 730 c 3 9 5 5 kbar further certify such metamorphic feature of an orogenic belt sims u pb dating of zircons of the trondhjemitic gneiss yields the magmatic crystallization age of 2 52 ga and both the trondhjemitic gneiss and the mafic granulite enclaves yield the metamorphic age of 1 89 1 86 ga therefore it can be concluded that the fuping terrane was involved in the late palaeoproterozoic subduction collision uplifting tectonic process caused by amalgamation of the eastern and western blocks of the north china craton along the trans north china orogen

two high pressure low temperature serpentinite matrix melange belts motagua fault zone guatemala a record of aptian and maastrichtian collisions left lateral motion along the north american caribbean plate boundary has juxta posed two high pressure low temperature hp lt belts from separate cretaceous colli sions these two belts have quite different ages and different suites of high pressure as semblages yet they both contain jadeitite a relatively rare rock type this part of the plate boundary zone follows the motagua river valley in guatemala where it separates the maya block north american plate from the chortis block caribbean plate on both sides of the bounding motagua fault tectonic slices of serpentinite matrix melange host the hp lt rocks south of the fault the melange slices contain eclogite lawsonite eclogite glaucophane eclogite and blueschist blocks north of the fault the melange slices contain omphacite metabasite albitite and garnet amphibolite blocks but lack intact eclogite in addition to the dissimilar rock assemblages 40 ar 39 ar geochronology of phen gitic micas yields 77 65 ma for northern and 125 113 ma for southern blocks these data suggest that the southern belt formed during early cretaceous aptian northeastward dipping subduction of the farallon plate and collision of the chortis block with western mexico the block was then displaced southeastward along this suture in contrast the northern belt records subduction related to the maastrichtian collision of an extension of the chortis block perhaps the nicaraguan rise with the maya block

composition of fluid inclusions in permian salt beds palo duro basin texas u s a abstract several methods have been developed and used to extract and chemically analyze the two major types of fluid inclusions in bedded salt from the palo duro basin texas data on the ratio k ca mg were obtained on a few of the clouds of tiny inclusions in chevron salt representing the brines from which the salt originally crystallized much more complete quantitative data na k ca mg sr cl so 4 and br were obtained on 120 individual large mostly 500 m on an edge i e 1 6 10 4 g inclusions in recrystallized salt these latter fluids have a wide range of compositions even in a given piece of core indicating that fluids of grossly different composition were present in these salt beds during the several stages of recrystallization the analytical results indicating very large inter and intra sample chemical variation verify the conclusion reached earlier from petrography and microthermometry that the inclusion fluids in salt and their solutes are generally polygenetic the diversity in composition stems from the combination of a variety of sources for the fluids permian sea meteoric and groundwater as well as later migrating ground formation or meteoric waters of unknown age and a variety of subsequent geochemical processes of dissolution precipitation and rock water interaction the compositional data are frequently ambiguous but do provide constraints and may eventually yield a coherent history of the events that produced these beds such an understanding of the past history of the evaporite sequence of the palo duro basin should help in predicting the future role of the fluids in the salt if a nuclear waste repository is sited there

global view of the intraseasonal oscillation during northern winter abstract in this study svd analysis is applied to a normalized 200 mb streamfunction olr covariance matrix to extract the most recurrent coupled pattern in the northern winter after the removal of the climatological seasonal cycle and seasonal means for each winter the first two singular vectors are on an intraseasonal timescale and the combination of the two forms an oscillation it is characterized by eastward propagation in the indian ocean and the western pacific standing oscillations in both the tropics and the extratropics and the poleward propagation of a zonally symmetric structure although there exists an eastwardly propagating pattern the phase relationship between geopotential wind and streamfunction fields is inconsistent with that of equatorial kelvin waves eastward propagation is most evident in the tropics of the southern hemisphere while the signals in the northern hemisphere are characterized by standing oscillations the distinct characteristics of the northern and southern he

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

dunhuang tectonic belt in northwestern china as a part of the central asian orogenic belt structural and u pb geochronological evidence abstract the dunhuang tectonic belt dtb is located about 100 km south of the beishan tianshan orogen in the central asian orogenic belt in nw china it was previously considered as a part of the tarim or north china craton detailed structural analyses reveal two episodes of deformation in the central dtb d1 and d2 d1 is a north side up reverse shear and d2 a dextral strike slip mineral assemblages microstructures and quartz c axis patterns indicate that d1 deformation took place under amphibolite facies conditions 500 to 600 c and d2 mostly under greenschist facies conditions 300 450 c u pb zircon dating of eight granitoid intermediate intrusions mostly dikes with well constrained cross cutting relationships with the d1 and d2 structures and an amphibolite gneiss indicates that d1 deformation took place before ca 349 ma and most likely at ca 406 ma and d2 between ca 249 ma and ca 241 ma the dtb has a structural metamorphic and magmatic signature in the paleozoic mesozoic that is typical of an orogenic belt it shares a similar geological history with the beishan tianshan orogen and is likely a part of the central asian orogenic belt the dtb and the beishan tianshan orogen might represent two separate paleozoic mountain belts that developed more or less synchronously on the south and north sides respectively of the last vestige of the paleo asian ocean before its terminal closure in the permian the d1 reverse shearing in the dtb is interpreted to be related to a silurian devonian terrane accretion collision and the d2 dextral strike slip to post accretional collisional movement among terranes in late permian middle triassic time

the signature of enso in global temperature and precipitation fields derived from the microwave sounding unit abstract global temperature anomalies associated with enso are investigated making use of a 13 year record of gridded temperature and precipitation data from the microwave sounding unit msu the warm phase of the enso cycle during this period was characterized by an overall warming of the tropical troposphere superimposed upon a distinctive equatorially symmetric dumbbell shaped pattern straddling the equator near 140 w accompanied by negative anomalies along the equator over the western pacific by means of singular value decomposition svd analysis it is shown that this pattern fluctuated in phase with the displacements of convective activity over the equatorial pacific as reflected in the anomalies in outgoing longwave radiation olr and msu precipitation fields fluctuations in mean tropical tropospheric temperature lagged the olr anomalies and the related temperature pattern by about 3 months the same dumbbell shaped pattern was evident with reversed polarity in the lower stratosphere tog

a warming tropical central pacific dries the lower stratosphere the amount of water vapor in the tropical lower stratosphere tls which has an important influence on the radiative energy budget of the climate system is modulated by the temperature variability of the tropical tropopause layer ttl the ttl temperature variability is caused by a complex combination of the stratospheric quasi biennial oscillation qbo tropospheric convective processes in the tropics and the brewer dobson circulation bdc driven by mid latitude and subtropical atmospheric waves in 2000 the tls water vapor amount exhibited a stepwise transition to a dry phase apparently caused by a change in the bdc in this study we present observational and modeling evidence that the epochal change of water vapor between the periods of 1992 2000 and 2001 2005 was also partly caused by a concurrent sea surface temperature sst warming in the tropical central pacific this sst warming cools the ttl above by enhancing the equatorial wave induced upward motion near the tropopause which consequently reduces the amount of water vapor entering the stratosphere the qbo affects the tls water vapor primarily on inter annual timescales whereas a classical el nino southern oscillation enso event has small effect on tropical mean tls water vapor because its responses are longitudinally out of phase this study suggests that the tropical central pacific sst is another driver of tls water vapor variability on inter decadal timescales and the tropical sst changes could contribute to about 30 of the step wise drop of the lower stratospheric water vapor from 1992 2000 to 2001 2005

metamorphic evolution and geochronology of the dunhuang orogenic belt in the hongliuxia area northwestern china abstract garnet bearing mafic granulites and amphibolites from the hongliuxia area of the southern dunhuang orogenic belt northwestern china commonly occur as lenses or boudinages enclosed within metapelite or marble which represent the block in matrix feature typical of orogenic melange three to four generations of metamorphic mineral assemblages are preserved in these rocks in the high pressure amphibolites prograde mineral assemblages m1 occur as inclusions hornblende plagioclase quartz chlorite epidote ilmenite preserved within garnet porphyroblasts and formed at 550 590 c and 7 7 9 2 kbar based on geothermobarometry the metamorphic peak mineral assemblages m2 are composed of garnet hornblende plagioclase quartz clinopyroxene as well as titanite zircon rutile apatite as accessory minerals in the matrix and are estimated to have formed at 640 720 c and 14 1 16 0 kbar the first retrograde assemblages m3 are characterized by white eye socket symplectites hornblende plagioclase quartz biotite epidote magnetite rimming garnet porphyroblasts which formed at the expense of the garnet rims and adjacent matrix minerals during the decompression stage under p t conditions of 610 630 c and 5 6 11 8 kbar the second retrograde assemblages m4 are intergrowths of actinolite and worm like quartz produced by the breakdown of the matrix hornblendes and formed under p t conditions of 490 c and 2 8 kbar for the high pressure mafic granulites the prograde assemblages m1 are represented by plagioclase quartz preserved within the garnet porphyroblasts the metamorphic peak assemblages m2 are garnet matrix minerals clinopyroxene plagioclase quartz hornblende rutile zircon and were estimated to have formed at 680 c and 15 4 kbar the retrograde assemblages m3 are characterized by fine grained patches of hornblende plagioclase quartz rimming the garnet porphyroblasts as well as hornblende rimming clinopyroxene in the matrix and were inferred to have formed at 620 c and 4 2 kbar for the metapelitic gneiss the metamorphic peak assemblages are the garnet porphyroblasts plus the matrix minerals biotite plagioclase quartz ilmenite zircon which were estimated to have formed at 630 c and 8 9 kbar the mafic granulites and amphibolites record fairly similar clockwise p t paths that include nearly isothermal decompression processes which suggest that they experienced subduction and subsequent rapid tectonic exhumation sims and la icp ms u pb dating of zircons and 40ar 39ar dating of hornblende suggest that the metamorphism occurred at 430 390 ma field occurrences different protolith ages of the mafic granulites and amphibolites and the considerable gap in peak p t conditions between the amphibolite and mafic granulite boudinages and their country rock may suggest a melange accumulation process during the paleozoic caused by the silurian devonian orogeny which is possibly associated with the closure of the liuyuan ocean a branch of the paleo asian ocean near the southern central asian orogenic belt

possible imprints of late paleoproterozoic orogeny in the dunhuang terrane nw china constraints from igneous and metapelitic rocks abstract the dunhuang terrane is a nee trending tectonic belt confined by the tarim craton beishan orogen alxa block and altyn tagh fault to constrain the late paleoproterozoic geotectonic background of this terrane a synthetic research on petrology geochemistry zircon and monazite geochronology and zircon lu hf and whole rock nd isotopes of late paleoproterozoic ca 1 9 1 8 ga igneous rocks and metapelites was conducted the sanweishan dongshuigou na rich rhyolite and granite formed at ca 1 84 1 82 ga exhibit enriched light rare earth elements lrees depleted heavy rare earth elements hrees and insignificant eu anomalies with low y 3 44 6 39 ppm and yb 0 29 0 53 ppm but relatively high mg 54 5 58 5 and sr 368 643 ppm and variable cr 5 58 29 7 ppm and ni 2 82 15 6 ppm contents as well as negative to positive ehf t 6 1 to 6 4 values indicating subduction related arc magmatism accompanied by crustal mantle interaction the shuwozi granitic gneiss crystallized at ca 1 81 ga displays s type granite affinity a cnk 1 1 and has low sr y 1 0 1 3 and gd yb n 1 50 1 98 ratios and negative ehf t 20 3 to 5 1 and end t 4 3 values suggesting partial melting of crustal rocks at shallow crustal depth the hanxia amphibolite with protolith age of ca 1 86 1 84 ga is featured by depleted lree and flat hree patterns insignificant eu anomalies low nb ta 11 0 12 0 ta yb 0 02 0 04 th yb 0 01 0 04 and th ta 0 7 1 3 but high ti v 22 9 26 7 ratios and positive end t 2 7 4 0 values resembling depleted mantle derived n morb or babb back arc basin basalt geochemical affinities the metapelite characterized by mineral assemblage of garnet biotite sillimanite plagioclase k feldspar quartz and rutile documented ca 1 81 ga upper amphibolite facies metamorphism with peak metamorphic p t conditions being restricted to 690 810 c and 5 3 6 4 kbar based on conventional geothermobarometry these magmatic and metamorphic rocks were variously altered and deformed during paleozoic ca 430 360 ma tectonothermal event integrated with published data it can be inferred that the dunhuang terrane underwent ca 1 89 1 81 ga subduction collisional orogeny related to late paleoproterozoic ca 2 0 1 8 ga global assembly of the columbia supercontinent similar as those recorded in the northern tarim craton alxa block and quanji massif and then overprinted paleozoic ca 440 360 ma orogenic process corresponding to the previously proposed composite orogeny in the dunhuang terrane

the implications of tropical rossby waves for tropical tropopause cirrus formation and for the equatorial upwelling of the brewer dobson circulation this study puts forward a mechanism for the observed upwelling in the tropical upper troposphere and lower stratosphere in this hypothesis the tropical upwelling is driven by momentum transport by rossby waves that are generated by tropical convection to test this hypothesis model runs are conducted using an axisymmetric global primitive equation model in these runs the effect of rossby waves is included by driving the model with observed fields of large scale eddy momentum flux convergence the resulting overturning circulation includes both meridional flow from the intertropical convergence zone itcz to the equator and rising motion in the tropical tropopause transition layer ttl this circulation therefore helps to explain the transport of moisture from the lower portion of the ttl in the itcz to the equatorial cold point tropopause where tropopause cirrus layers frequently occur

why are the climatological zonal winds easterly in the equatorialupper troposphere abstract using 16 years of ncep ncar reanalysis data on the 200 mb surface it is shown that in the deep tropics the horizontal transient eddy momentum flux accelerates the zonal mean zonal wind this acceleration is mainly due to transient eddies of intraannual and interannual timescales and to those associated with the madden julian oscillation mjo the interannual timescale eddy fluxes are dominated by eastward propagating disturbances with zonal wavenumber 2 and a period of 2 4 yr suggesting that these eddy fluxes may be tied to the el nino southern oscillation in the deep tropics the single most important factor that decelerates the zonal mean zonal wind is the horizontal momentum flux divergence due to the transient meridional circulation associated with seasonal cycle of the hadley cells the deceleration by the transient meridional circulation is much greater than the acceleration due to the transient eddies this result indicates that a nonzero obliquity of the earth is crucial for maintai

tropical wave driving of the annual cycle in tropical tropopause temperatures part ii model results abstract the atmospheric response to a localized distribution of tropical heating is examined in terms of the stationary waves excited and how these impact the mean flow near the tropical tropopause this is done by examining nonlinear simulations of the gill model with a primitive equation model that extends from the surface up into the stratosphere the model produces strong cooling of zonal mean temperatures near the tropical tropopause when the heating is on the equator but weaker cooling with the heating at 15 n the model shows that equatorial rossby waves that penetrate the lower stratosphere and changes in ep flux divergence that correspond to the observed changes between december and august it is suggested that ascent in the upper tropical troposphere is driven by vorticity advection or equivalently potential vorticity fluxes due to these equatorial rossby waves particularly when the heating is close to the equator the model results provide support to the hypothesis that the annual cycle in tr

evidence of meridional motion in the summer lower stratosphere adjacent to monsoon regions twenty one years of rawinsonde data were used together with 8 years of uninitialized european centre for medium range weather forecasts ecmwf analyses to describe the climatological structure of large scale circulations adjacent to monsoon regions in northern and southern hemisphere summers in the upper troposphere and lower stratosphere equatorward and poleward motions occur on the eastern and western sides of monsoon regions respectively it is shown that significant meridional velocities 1 ms 1 penetrate the lower stratosphere up to a maximum height of 50 30 mbar largest meridional velocities are observed in connection with the asian monsoon in northern summer although evanescent in height these motions are relatively important for horizontal transport of constituents in the summer lower stratosphere when planetary waves are otherwise small asian and mexican monsoons in this season are displaced sufficiently far from the equator in close proximity to the tropopause break to have a significant role in stratosphere troposphere s t exchange the companion paper by chen 1995 provides evidence of irreversible s t exchange in the upper middle world during northern summer

on the role of planetary scale waves in the abrupt seasonal transition of the northern hemisphere general circulation the role of planetary scale waves in the abrupt seasonal transition of the northern hemisphere nh general circulation is studied in reanalysis data the winter to summer transition involves the growth of planetary scale wave latent heat and momentum transports in the region of monsoons and anticyclones that dominate over the zonal mean transport beginning in midspring the wave dominated regime coincides with an abrupt northward expansion of the cross equatorial circulation and reversal of the trade winds in the upper troposphere the transition coincides with the growth of cross equatorial planetary scale wave momentum transport and a poleward shift of subplanetary scale wave transport and jet stream the dynamics of the seasonal transition are captured by idealized aquaplanet model simulations with a prescribed subtropical planetary scale wave sea surface temperature sst perturbation the sst perturbation generates subtropical planetary scale wave streamfunction variance and transport in the lower and uppertroposphereconsistentwithquasigeostrophictheory beyondathresholdsst atransitionofthezonalmean circulation occurs which coincides with a localized reversal of absolute vorticity in the nh tropical upper troposphere the transition is abrupt in the lower troposphere because of the quadratic dependence of the wave transport on the sst perturbation and involves seasonal time scale feedbacks between the wave and zonal meanflow in theupper troposphere including cross equatorial wave propagation thezonal mean vertical and meridional flows associated with the circulation response are in balance with the planetary scale wave momentumand latentheat meridionalflux divergences the resultshighlightthe leading order roleofmonsoon anticyclone transport in the seasonal transition including its impact on the meridional extent of the hadley and ferrel cells they can also be used to explain why the transition is less abrupt in the southern hemisphere

tectonic history of subduction zones inferred from retrograde blueschist p t paths many phanerozoic convergent plate junctions are marked by discontinuous blueschist belts reflecting relatively high pressure p prograde trajectories common blueschist paragneisses such as those of the western alps exhibit widespread overprinting by greenschist and or epidote amphibolite facies assemblages for this type of high p belt retrograde metamorphism involved fairly rapid nearly isothermal decompression some terranes underwent continued heating during early stages of pressure release uplift probably occurred as a consequence of the entrance of an island arc oceanic plateau or segment of continental crust into the subduction zone collision resulting in marked deceleration or cessation of underflow and buoyant approximately adiabatic rise of the stranded recrystallized subduction complex other high p belts such as the franciscan of western california preserve metamorphic aragonite and lack a low p overprint retrogression approximately retraced the prograde p t temperature path or for early formed high grade blocks occurred at even higher p t ratios parts of this type of metamorphic belt evidently migrated slowly back up the subduction zone in response to isostatic forces during continued plate descent and refrigeration upward motion took place as tectonically imbricated slices as laminar return flow in melange zones and perhaps partly a lateral spreading extension of the underplated accretionary prism retrograde p t trajectories of high pmore belts therefore provide important constraints on the tectonic evolution of convergent plate junctions less

a depositional model for the terminal neoproterozoic early cambrian ara group evaporites in south oman six evaporite carbonate sequences are recognized in the terminal neoproterozoic early cambrian ara group in the subsurface of oman individual sequences consist of a lower evaporitic part that formed mainly during a lowstand systems tract overlying platform carbonates contain minor amounts of evaporites and represent transgressive and highstand systems tracts detailed sedimentological and geochemical investigation of the evaporites allowed reconstruction of the depositional environment source of brines and basin evolution at the beginning of the evaporative phase prograding succession a shallow water carbonate ramp gradually evolved into a series of shallow sulphate and halite salinas minor amounts of highly soluble salts locally record the last stage of basin desiccation this gradual increase in salinity contrasts sharply with the ensuing retrograding succession in which two corrosion surfaces separate shallow water halite from shallow water sulphate and shallow water sulphate from relatively deeper water carbonate respectively these surfaces record repeated flooding of the basin dissolution of evaporites and stepwise reduction in salinity final flooding led to submergence of the basin and the establishment of an open water carbonate ramp marine fossils in carbonates and bromine geochemistry of halite indicate a dominantly marine origin for the brines the ara group sequences represent a time of relatively stable arid climate in a tectonically active basin strong subsidence allowed accommodation of evaporites with a cumulative thickness of several kilometres while tectonic barriers simultaneously provided the required restricted conditions subsidence allowed evaporites to blanket basinal and platform areas the study suggests a deep basin shallow water model for the evaporites

the use of environmental markers to distinguish marine vs continental deposition and to quantify the significance of recycling in evaporite basins abstract environmental markers namely the bromine content of halite samples the electrolyte content of primary fluid inclusions in halite and the isotopic composition of sulphates from two tertiary evaporite sequences provide complementary information on the depositional environment marine vs continental the use of these markers together with lithofacies and thicknesses of precipitated evaporites enable the detection and quantification of evaporite recycling within evaporite basins the information provided by the isolated use of each of these geochemical markers should be used with caution as this could lead to erroneous interpretations of the depositional environment or may not detect significant evaporite recycling processes the complementary information provided by geochemical markers enable quantification of solute input from recycling of previous precipitates within the basins themselves or from older evaporites the input of recycled evaporites increases progressively together with evaporite basin restriction to the open ocean

diverse subduction and exhumation of tectono metamorphic slices in the kalatashitage area western paleozoic dunhuang orogenic belt northwestern china abstract high pressure mafic granulite and garnet amphibolite are identified as small scale tectonic slices within pelitic or semi pelitic gneiss in the kalatashitage area which is located in the western paleozoic dunhuang orogenic belt northwestern china these rocks retain three generations of metamorphic mineral assemblages prograde assemblage m1 preserved as inclusions within garnet porphyroblasts metamorphic peak assemblage m2 consisting of matrix minerals and garnet porphyroblasts and retrograde assemblage m3 mainly represented by the symplectic minerals surrounding the embayed garnet and the retrograded hornblende rimming matrix type clinopyroxene metamorphic pressure and temperature p t paths of high pressure mafic granulite amphibolite and metapelite retrieved by thermobarometry are all clockwise passing from 640 to 720 c 6 2 12 6 kbar m1 through 840 920 c 14 6 16 2 kbar m2 to 750 815 c 5 5 7 9 kbar m3 for high pressure mafic granulite from 650 c 5 7 kbar m1 through 750 c 9 2 kbar m2 to 780 c 8 1 kbar m3 for amphibolite and from 615 c 7 9 kbar m1 through 730 820 c 8 6 11 7 kbar m2 to 675 740 c 5 4 8 7 kbar m3 for pelitic and semi pelitic gneiss furthermore pseudosection modeling of high pressure mafic granulite indicates that the growth zonation of garnet porphyroblast exhibits prograde metamorphism in a p t range of 510 800 c 8 5 13 kbar and demonstrates peak metamorphic p t conditions of 850 c 16 kbar which are consistent with the thermobarometric estimates the significant pressure differences in peak metamorphism observed in different rocks indicate that the rocks initially subducted to remarkably different depths and were subsequently juxtaposed at shallower crustal levels during exhumation sensitive high resolution ion microprobe shrimp analysis and laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dating of metamorphic zircon indicates that the metamorphic events occurred at ca 430 420 ma m2 and ca 400 390 ma m3 respectively metamorphism was followed by the intrusion of granitic dykes at ca 244 ma moreover the metamorphic evolution indicates that the kalatashitage area was involved in the subduction collision and subsequent tectonic exhumation in the paleozoic combined with previous literature it is inferred that the discrepant subduction and exhumation of high grade metamorphic rocks is a universal phenomenon in the paleozoic dunhuang orogenic belt supporting the ubiquitous existence of subduction collision complexes in this orogenic belt

equatorial superrotation and the factors controlling the zonal mean zonal winds in the tropical upper troposphere the response of the zonal mean zonal winds in the tropical upper troposphere to thermal forcing in the tropics is studied using an idealized general circulation model with 18 vertical levels and simplified atmospheric physics the model produces a conventional general circulation with deep easterly flow over the equator when integrated using zonally invariant and hemispherically symmetric boundary conditions but persistent equatorial superrotation westerly zonal mean flow over the equator is obtained when steady longitudinal variations in diabatic heating are imposed at low latitudes the superrotation is driven by horizontal eddy momentum fluxes associated with the stationary planetary wave response to the applied tropical heating the strength of the equatorial westerlies is ultimately limited by vertical steady eddy momentum fluxes which are downward in the tropical upper troposphere and by the zonally averaged circulation in the meridional plane which erodes the mean westerly shear via vertical advection the transition to superrotation can be prevented by specifying offsetting zonally invariant heating and cooling anomalies on either side of the equator to create a solstitial basic state with a single dominant hadley cell straddling the equator superrotation is restricted in the solstitial climate because the strength of the mean meridional overturning is enhanced which increases the efficiency of vertical advection and because the cross equatorial flow in the upper troposphere provides an easterly zonal acceleration that offsets some of the momentum flux convergence associated with tropical eddy heating the cross equatorial flow aloft also reduces the stationary planetary wave response in the summer hemisphere these results suggest that hemispheric asymmetry in the mean meridional circulation is responsible for maintaining the observed mean easterly flow in the tropical upper troposphere against the westerly torques associated with tropical wave sources

the geochemical evolution of the catalan potash subbasin south pyrenean foreland basin spain over the last decade our studies in ancient evaporitic basins have been based on a detailed study of a single borehole record the detailed findings in medium to large sized evaporitic basins were shadowed with a relevant question can interpretations from a representative evaporitic record in a single borehole be extended to the whole evaporitic basin this paper addresses that question the results obtained are compared with results from another distant point within the basin the general methodology not only proves its reliability in interpreting the evolution of evaporitic basins from a single borehole but reveals its capability to obtain detailed palaeoenvironmental interpretations the chemical evolution of an upper eocene evaporitic sequence from the south pyrenean foreland basin spain has been investigated along the suria 19 borehole record detailed petrographic and mineralogical study x ray microanalysis of frozen primary inclusions trapped in halite cryo sem eds systematic isotopic analysis d 34 s and d 18 o in sulphates and computer based evaporation models have been integrated in a multi proxy methodology this study revealed that a variable amount of ca excess is required throughout different parts of the marine lower halite unit lhu for sylvite instead of k mg sulphates to form this ca excess is in turn different from that required for the western sector of the same evaporitic basin navarrese subbasin quick and variable changes in ca rich brines or equivalent dolomitization required are explained as internal processes within the basin rather than secular variations in seawater chemistry the general hydrological evolution of the catalan subbasin is explained as a restricted subbasin with a first marine stage in which continental input up to 50 of total input had an important control on the geochemistry of the subbasin a second stage was determined during potash precipitation in which the subbasin was cut from any seawater input to end up in its last stage as a purely continental evaporitic basin coupling evaporation models and analytical results we have obtained the proportions of recycling and their sources estimated to change from a 100 total mass of sulphate eocene source to 20 eocene and 80 triassic keuper towards the latest stage of potash precipitation the results obtained have been compared with results from the navarrese subbasin allowing an integrated interpretation of the hydrological evolution of the whole upper eocene south

a late archean tectonic melange in the central orogenic belt north china craton abstract laterally extensive belts of melange characterize phanerozoic convergent plate margins but are rare in archean terranes we document a late archean melange in the zanhuang massif of the north china craton ncc the zanhuang melange separates a passive margin to foreland basin sequence developed on the western edge of the eastern block of the ncc from an arc terrane consisting of trondhjemitic tonalitic and granodioritic ttg gneisses in the central orogenic belt cob of the ncc the melange belt contains a structurally complex tectonic mixture of metapelites metapsammites marbles and quartzites mixed with exotic tectonic blocks of ultramafic and metagabbroic rocks metabasalts that locally include relict pillow structures and ttg gneisses all units in the melange have been intruded by mafic dikes that were subsequently deformed and are now preserved as garnet amphibolite boudins we interpret the melange to mark the suture zone between the eastern block and the arc terrane in the cob field relationships and geochemistry suggest that the exotic ultramafic metagabbroic metabasaltic blocks are possible slivers of an intra oceanic arc or fore arc ophiolite incorporated into the melange during the arc continent collision process a circa 2 5 ga granitic pluton intrudes the melange and undeformed circa 2 5 ga pegmatites cut the melange tectonic models for the evolution of the cob are varied but include models that favor collision at 2 5 ga 2 1 ga and 1 8 ga this work shows clearly from field structural relationships and geochronology that the first collision must have occurred prior to 2 5 ga consistent with late archean suturing of the western margin of the eastern block with an arc terrane fuping terrane during an arc continent collision the presence of an archean melange with exotic blocks in a suture zone between an archean arc and continental margin is clear evidence for the operation of plate tectonics at circa 2 5 ga

on the tropical atmospheric signature of el nino abstractthe linear atmospheric signature of enso obtained by regressing fields of geopotential height z wind vertical velocity and rainfall upon the nino 3 4 sea surface temperature sst index is partitioned into zonally symmetric and eddy components the zonally symmetric component is thermally forced by the narrowing and intensification of the zonally averaged equatorial rain belt during el nino and mechanically forced by the weakening of the upper tropospheric equatorial stationary waves and their associated flux of wave activity the eddy component of the enso signature is decomposed into barotropic bt and baroclinic bc contributions the latter into first and second modal structures bc1 and bc2 separable functions of space x y and pressure p using eigenvector analysis bc1 exhibits a nearly equatorially symmetric planetary wave structure comprising three dumbbell shaped features suggestive of equatorial rossby waves with out of phase wind and geopotential height perturbations in the

metamorphic evolution and u pb geochronology of metapelite northeastern wutai complex implications for paleoproterozoic tectonic evolution of the trans north china orogen abstract the wutai complex lies in the middle part of the trans north china orogen mainly consisting of metamorphosed volcanic sedimentary rocks named as wutai group and late archean ttg gneisses garnet biotite schist from the northeastern part of the wutai group lower shizui subgroup mainly consists of garnet porphyroblast plus biotite staurolite kyanite sillimanite fibrolite plagioclase quartz as well as accessory minerals including ilmenite magnetite hematite apatite monazite and zircon petrographic observation and mineral chemistry indicate that these metapelites underwent the sequential prograde m1 peak m2 and retrograde m3 metamorphic stages geothermobarometry computation and phase equilibrium modelling show that the representative samples record clockwise p t paths passing from 3 7 kbar 570 630 c m1 through 9 10 kbar 615 660 c m2p to 6 9 kbar 655 680 c m2t and finally to a speculated exhumation stage m3 indicative of orogenic metamorphism srhimp and la icp ms u pb dating on inherited detrital zircons yielded three age peaks of 2 7 ga 2 5 ga and 2 1 ga the youngest 207pb 206pb age of 2064 21 ma of detrital zircon possibly constrains the maximum depositional age of the shizui subgroup sims and shrimp u pb dating of metamorphic monazite and zircon constrain the metamorphic age of the garnet bearing mica schist to be 1853 1823 ma combined with previous data the wutai complex was demonstrated to have been involved in a prolonged subduction collision process 1 97 1 82 ga between the western and eastern blocks in the paleoproterozoic

evaporites marine or non marine division of evaporites into those types that retain information about primary mineralogy textures and structures primary evaporites and those types so extensively altered that few or no primary features remain secondary evaporites only primary evaporites can give unequivocal data bout their marine or non marine origin to help evaluate such primary deposits they have been further divided using the following attributes 1 whether the depositional setting was marine or non marine 2 whether the source water was a seawater b meteoric c hydrothermal d diagenetic e volcanogenic or f mixed specific criteria for making distinctions are 1 kinds of fossils 2 sedimentology of the associated non saline facies 3 kinds of primary saline minerals 4 association of such saline minerals both in qualitative and quantitative terms 5 trace element isotope and fluid inclusion geochemistry of such saline minerals modified journal abstract

equatorial planetary waves and their signature in atmospheric variability abstractequatorial planetary waves are a fundamental component of the tropical climate system previous studies have examined their structure in the climatological mean circulation their role in the climatological mean momentum balance of the tropics and their contribution to the climatological mean upwelling across the tropical tropopause in this study the authors focus on the contribution of the equatorial planetary waves to variability in the tropical circulation about its climatological mean state the equatorial planetary waves that dominate the climatological mean exhibit considerable variability on intraseasonal and interannual time scales variability in the amplitude of the equatorial planetary waves is associated with a distinct pattern of equatorially symmetric climate variability that also emerges from empirical orthogonal function analysis of various tropical dynamical fields variability in the equatorial planetary waves is characterized by variations in 1 convection in the deep tropics

paleozoic tectonothermal event in mt dongbatu dunhuang terrane southernmost central asian orogenic belt caob implications for petrogenesis and geological evolution abstract in this contribution systematic petrographical whole rock geochemical geochronological and zircon lu hf isotopic investigations were conducted on paleozoic ca 410 400 ma metamorphic magmatic rocks from mt dongbatu in the central dunhuang terrane the metamorphic rocks in the shangkouzi area are of meta calcsilicate rocks and granitoid rocks occurring within these rocks are geochemically of trondhjemite whereas metamorphic rocks in the gangou area are metabasaltic rocks la icp ms zircon u pb dating results reveal that these metamorphic magmatic rocks recorded ca 1 6 ga magmatic event and metamorphic events of ca 410 400 ma and ca 370 ma field occurrence whole rock geochemistry mineral composition and zircon hf isotopes suggest that the 1 6 ga mantle derived basaltic magma together with iron rich and ca rich components and mica quartz schist of paleoproterozoic supracrustal rocks probably contributed to protolith of meta calcsilicate rocks in the shangkouzi area and granitoid rocks within meta calcsilicate rocks were possibly generated by partial melting of calcsilicate rocks combined with previously published data it is suggested that the protoliths of paleozoic high grade metamafic rocks in the dunhuang terrane are predominantly composed at least of basaltic rocks produced by magmatic events of 2 5 1 8 ga ca 1 8 ga and ca 1 6 ga the paleozoic granitoid rocks in the dunhuang terrane might have been derived from different magma sources as partial melting of subducted plate or thickened lower continental crust or pre existing basaltic rocks produced by 1 6 ga and 1 8 ga magmatic activities and calcsilicate rocks genetically associated basaltic magmatism at ca 1 6 ga considering regional tectonic evolution it can be concluded that the dunhuang terrane was probably in a post collisional extension setting at ca 1 6 ga producing certain amount of basaltic and calcsilicate rocks from the beginning of silurian ca 440 ma the dunhuang terrane was involved in the orogenic processes related to the closure of the southern paleo asian ocean becoming the active continental margin of the southernmost caob

amphibolite facies metamorphism and geochronology of the paleoproterozoic aketashitage orogenic belt northwestern china abstract garnet amphibolite and semi pelitic gneiss preserving three stages of metamorphic mineral assemblages i e the prograde metamorphic inclusion assemblage m1 preserved in the garnet porphyroblast metamorphic peak assemblage m2 and retrograde symplectic assemblage m3 have been recognized in the aketashitage area northwestern china geothermobarometric computation shows that the m1 m2 and m3 assemblages record the metamorphic p t conditions of 600 700 c 4 2 5 3 kbar 730 790 c 6 3 7 1 kbar and 770 c 5 6 kbar respectively these three metamorphic stages define clockwise p t paths including nearly isothermal decompression itd process indicating typical orogenic metamorphism the peak metamorphic p t conditions reach the transition zone between the high amphibolite facies and granulite facies and belong to intermediate p t facies series the shrimp and la icp ms u pb dating of metamorphic zircon implies that the subduction might occur as early as 1 97 ga and last as late as 1 84 ga combined with literature data it is concluded that the aketashitage area was a paleoproterozoic orogenic belt which is possibly related to the assembly of the basements of the columbia supercontinent

effect of tropical waves on the tropical tropopause transition layer upwelling abstract an initial value problem is employed with a gcm to investigate the role of the convectively driven rossby and kelvin waves for tropopause transition layer ttl upwelling in the tropics the convective heating is mimicked with a prescribed heating field and the lagrangian upwelling is identified by examining the evolution of passive tracer fields whose initial distribution is identical to the initial heating field this study shows that an overturning circulation induced by the tropical rossby waves is capable of generating the ttl upwelling even when the heating is placed in the eastern pacific the ttl upwelling occurs only over the western tropical pacific indicating that the background flow plays a crucial role the results from a rossby wave source analysis suggest that a key feature of the background flow is the strong absolute vorticity gradient associated with the asian subtropical jet in addition static stability is relatively weak over the western pacific suggesting that this ma

high pressure granulites formation recovery of peak conditions and implications for tectonics high pressure granulites are characterised by the key associations garnet clinopyroxene plagioclase quartz in basic rocks and kyanite k feldspar metapelites and felsic rocks and are typically orthopyroxene free in both basic and felsic bulk compositions in regional metamorphic areas two essential varieties exist a high to ultrahigh temperature group and a group representing overprinted eclogites the high to ultrahigh temperature type formerly contained high temperature ternary feldspar now mesoperthite coexisting with kyanite is associated with garnet peridotites and formed at conditions above 900 c and 1 5 gpa clinopyroxene in subordinate basic rocks is al rich and textural evidence points to a high pressure high temperature melting history the second variety contains symplectite like or poikilitic clinopyroxene plagioclase intergrowths indicating former plagioclase free i e eclogite facies assemblages this type of rock formed at conditions straddling the high pressure amphibolite high pressure granulite field at around 700 850 c 1 0 1 4 gpa importantly in the majority of high pressure granulites orthopyroxene is secondary and is a product of reactions at pressures lower than the peak recorded pressure in contrast to low and medium pressure granulites which form at conditions attainable in the mid to lower levels of normal continental crust high pressure granulites of nonxenolith origin mostly represent rocks formed as a result of short lived tectonic events that led to crustal thickening or subduction of the crust into the mantle short times at high temperature conditions are reflected in the preservation of prograde zoning in garnet and pyroxene high pressure granulites of both regional types although rare are known from both old and young metamorphic terranes e g c 45 ma namche barwa e himalaya 400 340 ma european variscides 1 8 ga hengshan china 1 9 ga snowbird saskatchewan and 2 5 ga jianping china this spread of ages supports proposals suggesting that thermal and tectonic processes in the lithosphere have not changed significantly since at least the end of the archean

tectonic melange records the silurian devonian subduction metamorphic process of the southern dunhuang terrane southernmost central asian orogenic belt the hongliuxia tectonic melange of the southern dunhuang terrane northwestern china southernmost central asian orogenic belt caob consists of eclogite mafic granulite and amphibolite as puddingstones within a matrix of metapelitic gneiss and marble these rocks are interpreted to be part of an ancient subduction zone setting secondary ion mass spectrometry u pb dating of metamorphic zircons obtained from the puddingstones and matrix metapelite suggests that the metamorphism occurred at ca 428 391 ma the metamorphic rocks all record similar clockwise metamorphic pressure temperature time p t t paths of the western alpine type however remarkable differences between metamorphic peak p t conditions ranging from 830 c and 24 2 kbar for the eclogite puddingstone to 700 c and 10 2 kbar for the metapelite matrix were found in the melange rocks this indicates the mixing of rocks from significantly different depths to create a tectonic melange in a subduction channel possibly juxtaposed during the uplift stage these data suggest that the southernmost caob underwent subduction and subsequent exhumation caused by subduction of the paleozoic hongliuxia ocean during the middle silurian to middle devonian

neoarchean metamorphic evolution and geochronology of the miyun metamorphic complex north china craton abstract mafic and felsic granulite from the miyun metamorphic complex northeast beijing north china craton occur as either interlayers or lenses within the late archean ttg gneiss in the mafic granulite the metamorphic peak assemblages m1 are represented by porphyroblast minerals plus matrix minerals orthopyroxene clinopyroxene plagioclase quartz k feldspar hornblende biotite as well as accessory minerals of zircon apatite ilmenite magnetite the post peak assemblages m2 are characterized by red eye socket symplectites garnet clinopyroxene plagioclase quartz rimming the orthopyroxene or clinopyroxene porphyroblast as well as accessory minerals of rutile and the final retrograde assemblages m3 are marked by the hornblende biotite intergrowth as for the felsic granulite the peak assemblages m1 are represented by the porphyroblast and matrix minerals garnet orthopyroxene biotite plagioclase quartz k feldspar as well as accessory minerals in the matrix zircon monazite apatite pyrite the post peak assemblages m2 are characterized by red eye socket symplectites garnet plagioclase quartz rimming the orthopyroxene porphyroblast and the final retrograde assemblages m3 are marked by the biotite calcite intergrowth geothermobarometric computation suggests that the m1 m2 and m3 assemblages of the mafic granulite were formed under p t conditions of 800 to 860 c 6 to 10 kbar 620 to 700 c 11 to 12 kbar and 590 to 660 c 4 to 6 kbar respectively suggesting that these granulites record anticlockwise p t paths including final nearly isothermal decompression itd segments indicative of orogenic process for the felsic granulite metamorphic p t conditions of the m1 and m3 assemblages were estimated to be 680 to 750 c 6 8 kbar and 670 to 680 c 5 kbar respectively also including itd process the widely penetrative gneissosity of the granulite and these p t paths suggest a collisional event of cold nappes overthrusting on hot ones or hot nappes being buried subducted into cold ones and finally experienced fast tectonic exhumation high precision sims and la icp ms u pb dating of metamorphic zircon of the granulite suggest that the metamorphism occurred at 2 5 ga these data confirm that the miyun metamorphic complex experienced a neoarchean collisional event within the eastern block of the north china craton

mechanisms of hemispherically symmetric climate variability inspired by paleoclimate evidence that much past climate change has been symmetric about the equator the causes of hemispherically symmetric variability in the recent observational record are examined using the national centers for environmental prediction national center for atmospheric research reanalysis dataset and numerical models it was found that the dominant cause of hemispherically symmetric variability is the el nino southern oscillation during an el nino event the tropics warm at all longitudes and the subtropical jets in both hemi spheres strengthen on their equatorward flanks poleward of the tropical warming there are latitude belts of marked cooling extending from the surface to the tropopause in both hemispheres at all longitudes and in all seasons the midlatitude cooling is caused by changes in the eddy driven mean meridional circulation changes in the transient eddy momentum fluxes during an el nino event force upper tropospheric ascent in midlatitudes through a balance between the eddy fluxes and the coriolis torque the eddy driven ascent causes anomalous adiabatic cooling which is primarily balanced by anomalous diabatic heating using a quasigeostrophic spherical model forced by an imposed surface eddy disturbance of chosen wave number and frequency it is shown that the anomalous eddy momentum fluxes are caused by the impact that the changes in the tropically forced subtropical jets have on the propagation in the latitude height plane of transient eddies changes in zonal winds and associated changes in the meridional gradient of potential vorticity create an anomalous region of low meridional wavenumber in the midlatitudes that refracts waves away both poleward and equatorward tropical forcing of variability in the eddy driven mean meridional circulation is another way in addition to rossby wave teleconnections whereby the tropics can influence extratropical climate unlike teleconnections this mechanism causes climate variability that has strong zonally and hemispherically symmetric components and operates throughout the seasonal cycle

paleozoic sanweishan arc in the northern dunhuang region nw china the dunhuang block is a phanerozoic orogen not a precambrian block abstract the dunhuang region is located to the south of the central asian orogenic belt and connecting the tarim craton westerly and north china craton easterly respectively it is an important position for understanding the geodynamics and tectonic framework of central asia however the issue about whether it is a phanerozoic orogen or a precambrian block is still controversial magmatic arcs are the most prominent and laterally persistent structural elements of orogenic belts and used to reconstruct now disrupted orogenic belts this paper concerns the petrogenesis and tectonic setting of andesitic dacitic rhyolitic volcaniclastic rocks and dacitic porphyries in the sanweishan area northern dunhuang region volcaniclastic rocks overlie the metasedimentary rocks by fault and dacitic porphyries intrude into the metasedimentary rocks the calc alkaline signature and relative enrichment of large ion lithophile elements of volcaniclastic rocks and dacitic porphyries seemingly favor a subduction setting zircon u pb dating results reveal the deposition at 424 414 ma for volcaniclastic rocks and emplacement at ca 364 ma for dacitic porphyries the coeval granitoid plutons in the sanweishan area show arc geochemical signature and are originated from partial melting of the subducted sediments based on the available data paleozoic volcanic subvolcanic rocks and plutons in this area probably represent a magmatic arc developed on the accretionary complex resembling the arc magmatic rocks formed in the nankai complex sw japanese island arc our results provide constraints on the existence of the paleozoic magmatic arc in the northern dunhuang region and suggest the so called dunhuang block is virtually a phanerozoic orogen rather than a precambrian block

propagating and standing components of the intraseasonal oscillation in tropical convection abstract two questions related to the intraseasonal variability of tropical convection and circulation remain controversial 1 to what degree is the convective component of the madden julian oscillation mjo a standing oscillation 2 is the eastward propagating circulation anomaly of the mjo coherent with a standing oscillation in convection in an attempt to settle these issues the authors undertake a series of statistical analyses of gridded outgoing longwave radiation and winds to quantify the magnitudes of the propagating and standing components of convection and their coherence with the propagating component of the circulation they demonstrate that no dominant standing oscillation in convection can be identified instead intraseasonal variability of convection is dominated by an eastward propagating mode which the authors interpret as the convective signal of the mjo this propagating component accounts for almost all of the convective variance that is coherent with the eastward propagating di

first report of coupled early permian paleomagnetic and geochronologic data from the dunhuang block nw china and implications for the tectonic evolution of the paleo asian ocean abstract in order to better understand the tectonic relationship between the dunhuang block dhb and its adjacent blocks and to constrain the timing of the closure of the paleo asian ocean a combined geochronologic and paleomagnetic investigation has been undertaken on early permian tuff basalt flows and sandstones from the shuangbaotang formation in the northwestern part of the dhb u pb zircon dating indicates that the age of the strata is between 280 6 2 9 ma and 291 4 2 6 ma thermal demagnetization of a three component isothermal remanent magnetization irm and curie point experiment suggest that magnetite dominates in the rock samples analyzed in addition there is a minor amount of hematite in some sandstones stepwise thermal demagnetization successfully isolated stable characteristic remanent magnetization chrm from 11 tuff layers two lava flows and nine sandstone beds two components were isolated from all samples a lower temperature component ltc and a higher temperature component htc the ltc is near the direction of the present day geomagnetic field and produced a negative fold test indicating it is a viscous remanent magnetization in the present day geomagnetic field most of the htc are reverse polarity normal 4 reverse 158 which is in accordance with the kiaman reversed superchron that spans the late carboniferous permian interval in addition the htc of all studied sites passed the fold and reverse tests suggesting that they likely represent primary remanent magnetization the tilt corrected mean direction from all sites tuff basalts and sandstones is ds 1 7 is 43 1 ks 403 95 1 5 n 22 the mean paleopole of the site mean direction corresponded vgps lies at 74 5 n 268 5 e with a95 1 6 considering the consistent inclination values recorded among the studied tuff basalts and sandstones and the low degrees of anisotropy within all samples we suggest that there is no significant inclination shallowing caused by depositional compaction in the sedimentary layers of the studied section taking into account the results from this study as well as previous late paleozoic paleomagentic studies from adjacent tectonic blocks we conclude that the dhb formed part of the amalgamated dunhuang north china alxa qaidam mega block during the early permian but was separated from the tarim block by a small ocean here named the qiemo xingxingxia paleo ocean at this time a comparison of the early permian paleolatitudes of these and other adjacent blocks suggest that the paleo asian ocean sensu lato was still open at this time combined with other geological evidence a paleogeographic reconstruction of the paleo asian ocean has been reconstructed for the early permian

neogene evaporites in desert volcanic environments atacama desert northern chile the upper miocene and pliocene evaporite deposits of the atacama desert of northern chile hilaricos and soledad formations are among the few nonmarine evaporites in which aridity not only formed the deposits but has also preserved them almost unaltered under near surface conditions these deposits are largely composed of displacive ca sulphate and halite together with minor amounts of glauberite thenardite and polyhalite however at the base and top of these deposits there are also beds of gypsum crystal pseudomorphs that originally formed as free growth forms within shallow brine bodies rather than as displacive sediments the halite is present as interstitial cement displacive cubes and shallow water bottom growth chevron crusts most of the calcium sulphate is presently anhydrite pseudomorphous after gypsum that was the primary depositional sulphate mineral the secondary anhydrite formed under early diagenetic conditions after slight burial some metres resulting from the effect of strongly evolved pore brines the anhydrite has been preserved without rehydration during late diagenetic and exhumation stages on account of the arid environment of the atacama desert both the hilaricos and the soledad formations contain geochemical markers indicating that these neogene evaporites had a largely non marine origin bromine content in the halite is very low few p p m indicating neither a sedimentological relation with sea water nor the likelihood of direct recycling of prior marine halites moreover the d 34 s of sulphates 4ae5 to 9 also reflects a non marine origin with a strong volcanic influence although some recycling of mesozoic marine sulphates cannot be ruled out d 34 s of dissolved sulphate from hot springs and streams in the area commonly displays positive values 2 to 10 leaching of oxidized sulphur and chlorine compounds from volcanoes and epithermal ore bodies very common in the associated drainage areas have been the main contribution to the accumulation of evaporites the sedimentary and diagenetic evolution of the hilaricos and soledad evaporites based on lithofacies analysis provides information about the palaeohydrological conditions in the central depression of northern chile during the neogene in addition the diagenesis and exhumation history of these evaporites confirms the persistence of strongly arid conditions from late miocene until the present a final phase of tectonism took place permitting the internal drainage to change and open to the sea resulting in dissolution and removal of a significant portion of these deposits despite the extensive dissolution the remaining evaporites have undergone little late exhumational hydration

on the signatures of equatorial and extratropical wave forcing in tropical tropopause layer temperatures abstracttemperatures in the tropical tropopause layer ttl play an important role in stratosphere troposphere exchange and in the formation and maintenance of thin cirrus clouds many previous studies have examined the contributions of extratropical and equatorial waves to the ttl using coarse vertical resolution satellite and reanalysis data in this study the authors provide new insight into the role of extratropical and equatorial waves in the ttl using high vertical resolution gps radio occultation data the results examine the influence of four different wave forcings on the ttl extratropical waves that propagate vertically into the stratosphere extratropical waves that propagate meridionally into the subtropical stratosphere extratropical waves that propagate meridionally into the subtropical troposphere and the equatorial planetary waves the vertically and meridionally propagating extratropical stratospheric waves are associated with deep zonally symmetric temperature anomalies that extend a

bromine geochemistry of salar de uyuni and deeper salt crusts central altiplano bolivia abstract the salar of uyuni in the central bolivian altiplano is probably the largest salt pan in the world 10 000 km 2 a 121 m deep well drilled in the central salar disclosed a complex evaporitic sequence of 12 salt crusts separated by 11 mud layers in the lower half of the profile thick halite beds alternate with thin mud layers the mud layers thicken upwards and show clear lacustrine features the thickness of the salt beds decreases markedly from the base upward the bromine content of the halite ranges from 1 3 to 10 4 mg kg the halite does not originate from the evaporation of the dilute inflow waters of the altiplano which would lead to br content of tens of mg kg the presence of halite of very low br content 2 mg kg in a gypsum diapir strongly suggests that most of the halite deposited at uyuni originated from the leaching of ancient salt formations associated with the numerous gypsum diapirs of the altiplano the deep and thick halite beds were probably deposited in a playa lake as suggested by their very low and fairly constant br content 1 6 2 3 mg kg and by the abundance of detrital minerals thereafter perennial salt lakes of increasing duration flooded the central altiplano increasing amounts of dilute inflow waters of low cl br ratio and the exhaustion of diapiric halite lead to an increase of both the thickness of the lacustrine layers and of the bromine content of the salt crusts 5 10 mg kg deposited as the lakes dried up paleolake levels in the central altiplano rose as those in the northern altiplano the titicaca basin were simultaneously falling the progressive fluvial erosion of the threshold between the northern and the central altiplano lowered the levels of the northern lakes and allowed more dilute waters of low cl br ratio to flood the central altiplano therefore both the thickness of lacustrine sediments and the bromine content of the salt crust increased to the present the three upper crusts show a decrease in bromine content which may reflect a recent modification of the inflow regime to the last lakes the salt crust deposited by the last salt lake 10 000 years ago shows a bromine distribution that unexpectedly increases with depth as the lake dried the salt crust was probably initialy distributed over a wider area than the present flat crust covering the topographic surface up to the level of the lake where halite reached saturation the dissolution of the initial salt of low br content from the margins of the lake to the center is probably responsible for the observed br distribution in the surface salt as in a playa during the holocene a severe drought hit the altiplano and drastically lowered the intracrustal brine table within the salt crust leaving a thin layer of high concentrated residual brine at the bottom of the crust bromine rich halite replaced primary halite by a temperature activated mechanism in the lower crust further increasing the br gradient with depth