an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

subduction collision and exhumation in the ultrahigh pressure qinling dabie orogen c abstract high pressure metamorphism and ophiolite emplacement songshugou ophiolite attended suturing of the yangtze craton to rodinia during the c l o ga grenvillian oro geny the qinling microcontinent then rifted from the yangtze craton at c 750ma the erlangping intraoceanic arc formed in the early ordovician was emplaced onto the qinling microcontinent in the ordovician silurian and then both units were accreted to the sino

formation and evolution of the tancheng lujiang wrench fault system a major shear system to the northwest of the pacific ocean abstract in the northwestern peri pacific tectonic belt on the continental margin of east asia there is a series of major faults trending ne nne i e the tancheng lujiang wrench fault system this fault system extends more than 5000 km with a width of 800 1000 km in the continent and a general strike of n30 e on the basis of the results of special research on the major faults and a lot of new information about the fault system the authors discuss early mesozoic triassic jurassic period sinistral transcurrent faulting in the different regions it is suggested that in the eastern continent of east asia the e w trending tectonic pattern of the paleozoic and beginning of the mesozoic appear in the nuclei of the sino korean continent massif and the yangtze continent massif these ancient continent massifs accreted both southwards and northwards which finally led to their collision and suturing to the angura continent massif later this tectonic framework was changed greatly by the tancheng lujiang wrench fault system along which left lateral horizontal displacement of 1000 1500 km took place since the mesozoic the dislocation and deformation of horizontal displacement of the tancheng lujiang fault system produced a series of structures trending ne nne in the continental margin which have greatly transformed the ancient structures of the preceding mesozoic this is an important diktyogenese in the continent of east asia during the horizontal displacement motion of these faults the folds nappes and decollement structures pull apart basins and subductions within the continent occurred in the continent at the same time some large sinistral ductile shear zones of horizontal displacement appeared the depth of the deformed horizon of ductile shear which belongs to simple shear was controlled by the tectonic element and distance away from the continental margin whilst the ductile shear deformation occurred the fault dynamo thermal metamorphism and the fault remelting took place and magma activity appeared within the continent in the mesozoic the fault zones used to be high energy zones and recently became the seismic belts within the continent formation of the tan lu fault system was due to the collision between the southern and northern blocks its large sinistral horizontal displacement in the mesozoic was closely related to the kula plate moving northwards therefore the continent disintegrated by shearing which produced some new terranes the shear edge belt was formed between the continent and ocean the change of relative motion between the continent and pacific ocean plate transformed the tan lu fault system into first extension and then compression clarifying the characteristics of the tan lu fault system is an important key in understanding the evolution of the east asia continent since the mesozoic

tectono stratigraphy of the orhaniye basin turkey implications for collision chronology and paleogene biogeography of central anatolia abstract located along the izmir ankara erzincan suture iaes the maastrichtian paleogene orhaniye basin has yielded a highly enigmatic yet poorly dated paleogene mammal fauna the endemic character of which has suggested high faunal provincialism associated with paleogeographic isolation of the anatolian landmass during the early cenozoic despite its biogeographic significance the tectono stratigraphic history of the orhaniye basin has been poorly documented here we combine sedimentary magnetostratigraphic and geochronological data to infer the chronology and depositional history of the orhaniye basin we then assess how our new data and interpretations for the orhaniye basin impact 1 the timing and mechanisms of seaway closure along the iaes and 2 the biogeographic evolution of anatolia our results show that the orhaniye basin initially developed as a forearc basin during the maastrichtian before shifting to a retroarc foreland basin setting sometime between the early paleocene and 44 ma this chronology supports a two step scenario for the assemblage of the central anatolian landmass with incipient collision during the paleocene early eocene and final seaway retreat along the iaes during the earliest late eocene after the last marine incursion into the foreland basin our dating for the orhaniye mammal fauna 44 43 ma indicates the persistence of faunal endemism in northern anatolia until at least the late lutetian despite the advanced stage of iaes closure the tectonic evolution of dispersal corridors linking northern anatolia with adjacent parts of eurasia was not directly associated with iaes closure and consecutive uplifts but rather with the build up of continental bridges on the margins of anatolia in the alpine and tibetan himalayan orogens

variation in peak p t conditions across the upper contact of the uhp terrane dabieshan china gradational or abrupt the southern dabieshan terrane sdt has previously been divided into high pressure hp and ultrahigh pressure uhp terranes and its regional extent and the tectonic nature of its boundaries are hotly debated topics in this study an eclogite bearing area of 100 km2 near taihu is mapped in detail and divided into northern middle and southern zones on the basis of lithological characteristics the northern zone consists of epidote biotite gneiss and eclogite blocks the middle zone includes granitic gneiss biotite gneiss eclogites and amphibolite and the southern zone is composed mainly of garnet bearing mica schist the eclogites occur mainly as lens or blocks in the northern and middle zones the peak p t conditions for 61 eclogite samples across the area are estimated using the grt cpx fe2 mg thermometers and the grt cpx phe barometers the results indicate three different p t regions 2 82 4 09 gpa 759 942 c in the northern zone and 2 00 3 54 gpa 641 839 c in the granitic gneiss and 1 38 2 36 gpa 535 768 c in the biotite gneiss from the middle zone combined with the spatial distribution of eclogites across the area the p t values for eclogites increase continuously from the south to the north defining a reference geotherm of 5 c km 1 however some unreasonable apparent gradients can be established along two south north profiles across the area and display a p t difference between the northern and middle zones on the basis of the average p t data for eclogites across the area a gap of at least 0 3 gpa 20 c exists between the northern and middle zones by contrast the p t values of eclogites from the middle zone show a coherent pattern with transitional characteristics from hp in the south to uhp in the north we suggest that the sdt was a coherent slab during subduction and was broken up by a major fault during exhumation which was formed under uhp metamorphic conditions

the oldest uhp eclogites of the world age of uhp metamorphism nature of protoliths and tectonic implications coesite bearing eclogitic rocks from the pan african belt in northern mali were dated by multichronological methods rb sr sm nd and ar ar rb sr and sm nd isotope analyses on whole rock and mineral separates of an omphacite kyanite micaschist and a mafic eclogite yielded concordant ages of about 620 ma this is interpreted as the time of the eclogitisation which represents the oldest ultrahigh pressure uhp metamorphic event so far recorded in the continental crust the nearly identical rb sr and sm nd ages suggest very rapid exhumation as observed in many phanerozoic uhp rocks 40ar 39ar dating of phengites from two uhp micaschists gave much older ages of 1045 and 760 ma phengite from a quartzite collected from the same site yielded a plateau date of 623 3 ma which is in agreement with the rb sr and sm nd dates the two 40ar 39ar ages older than 625 ma testify once more the recurrent problem of excess ar in ultrahigh pressure phengites the occurrence of the mali uhp eclogites indicates that by the late precambrian the earth has cooled enough to sustain the formation and preservation of deeply subducted uhp metamorphic rocks the new ages of ca 620 ma also constrain the amalgamation in nw gondwana to have occurred in the latest proterozoic but not in the middle cambrian this is supported by several recent chronological data for the southern segment of the major suture zone in the dahomeyide orogenic belt

fluid evolution during hp and uhp metamorphism in dabie shan china constraints from mineral chemistry fluid inclusions and stable isotopes the dabie shan ultrahigh pressure uhp metamorphic terrane is introduction located in the eastern part of the east west striking qinling dabie the discovery of coesite and micro diamond as phases orogenic belt in china a major mylonitized contact zone of produced by deep metamorphism of continental crust 200 300 m width divides dabie shan into the south dabie revolutionized our understanding of continental collision terrane sdt and the north dabie complex ndc combined zones and mantle dynamics attending subduction of investigation of major and trace element geochemistry fluid inclusions continental lithosphere in general we define metaand oxygen and hydrogen isotopes constrains the fluid history during morphic rocks with coesite and micro diamond as ultrathe metamorphic evolution of the two metamorphic belts which high pressure uhp rocks which have been increasingly differ in their fluid and metamorphic evolution fluid inclusions in recognized so far more than a dozen uhp terranes rocks from the sdt are mainly aqueous with varying salinities have been documented within the major continental whereas those from the ndc are dominated by co2 low o collision belts in the eurasian plate values in the sdt rocks 2 8 to 8 6 indicate meteoric the dabie sulu belt in east central china is the water rock interactions before uhp metamorphism whereas rocks largest among the uhp metamorphic terranes found from the ndc show normal o values 6 7 9 0 with no worldwide research activities over the past decade have obvious meteoric water rock signature whole rock rare earth element documented a number of characteristic features of this ree contents correlate with oxygen isotope compositions samples area including rapid subduction followed by rapid initial from the sdt have higher ree contents and lower o values uplift e g li et al 1993 xiao li 1993 eide et al whereas samples from the ndc have lower ree contents and 1994 the abundance of hydroxyl bearing uhp mineral higher o values during retrograde metamorphism fluids with phases okay 1994 zhang et al 1995 very low o different hydrogen isotope compositions interacted with the rocks from values ranging from 15 to 10 yui et al 1995 1997 the sdt zheng et al 1996 1998 1999 xiao et al 1997 rumble yui 1998 and the world record highest nd 0 values ever measured for eclogite jahn et al 1996 the nature and mobility of fluids in high pressure hp

a red corundum bearing vein in the rai iz ultramafic rocks polar urals russia the product of fluid activity in a subduction zone abstract the veins in the mantle wedge peridotite can record the activity of slab derived melt fluid which is the reflection of the material circulation between crust and mantle a red corundum bearing vein is present in the rai iz ultramafic rocks in the polar urals russia the ultramafic rocks are harzburgite and dunite and the red corundum bearing rocks consist of phlogopite paragonite oligoclase red corundum and chromian spinel red corundum occurs as prophyroblasts or fine grains that contain 92 98 wt al2o3 and 2 7 wt cr2o3 chromian spinel has cr values 100cr cr al atomic ratio of 46 78 oligoclase is characterized by an values of 20 30 phlogopite is ba rich bao 0 8 2 7 wt and paragonite is sr rich sro 0 8 2 3 wt zircons from the oligoclasite show oscillatory zoning and th u values of

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

solute sources and chemical weathering in the owens lake watershed eastern california 1 chemical and strontium isotope analyses of solutes in a series of streams representing the bulk of the water reaching the 8500 km2 owens lake watershed provide a unique opportunity to evaluate factors that control stream chemistry on a regional scale the streams drain terrain that is dominated by mesozoic granitoids of the sierra nevada batholith but that also contains irregularly distributed roof pendants of paleozoic metasedimentary sequences mass balance modeling indicates that plagioclase feldspar weathering is the dominant contributor to stream chemistry and that carbonate dissolution is also a significant source of solutes for most streams the calculated ratio of plagioclase to carbonate is highly sensitive to the assumed weathering product of plagioclase kaolinite versus smectite and we suggest that the importance of carbonate could be exaggerated in cases where only the plagioclase to kaolinite reaction is considered strontium isotope 87sr 86sr ratios range from 0 70685 to 0 71958 with a flow weighted mean of 0 70911 to the extent that this value represents the water that would be flowing into owens lake were it not diverted by the los angeles aqueduct system the flow weighted mean 87sr 86sr ratio is consistent with ratios measured in owens lake core carbonates ranging in age up to 25 kyr the overall sr budget of the watershed is determined by the relative contributions of carbonate dissolution and plagioclase feldspar weathering and is dominated by reactions related to pyrite oxidation and hydrothermal fluid input from just two subbasins the impact of these processes needs to be considered when modeling regional and global riverine sr budgets climate related shifts in the relative importance of silicate mineral weathering reactions appear to be only second order effects on a regional scale

ultra high pressure metamorphism of carbonate rocks in the dabie mountains central china abstract widespread ultra high p assemblages including coesite quartz pseudomorphs after coesite aragonite and calcite pseudomorphs after aragonite in marble gneiss and phengite schist are present in the dabie mountains eclogite terrane these assemblages indicate that the ultra high p metamorphic event occurred on a regional scale during triassic collision between the sino korean and yangtze cratons marble in the dabie mountains is interlayered with coesite bearing eclogite and gneiss and as blocks of various size within gneiss discontinuous boudins of eclogite occur within marble layers marble contains an ultra high p assemblage of calcite aragonite dolomite clinopyroxene garnet phengite epidote rutile and quartz coesite coesite quartz pseudomorphs after coesite aragonite and calcite pseudomorphs after aragonite occur as fine grained inclusions in garnet and omphacite phengites contain about 3 6 si atoms per formula unit based on 11 oxygens similar to the coesite bearing eclogite marble exhibits retrograde recrystallization under amphibolite greenschist facies conditions generated during uplift of the ultra high p metamorphic terrane retrograde minerals are fine grained and replace coarse grained peak metamorphic phases the most typical replacements are symplectic pargasitic hornblende epidote after garnet diopside plagioclase an18 after omphacite and fibrous phlogopite after phengite ferroan pargasite plagioclase and actinolite formed along grain boundaries between garnet and calcite and calcite and quartz respectively the estimated peak p t conditions for marble are comparable to those for eclogite garnet clinopyroxene geothermometry yields temperatures of 630 760 c the garnet phengite thermometer gives somewhat lower temperatures the minimum pressure of peak metamorphism is 27 kbar based on the occurrence of coesite such estimates of ultra high p conditions are consistent with the coexistence of grossular rich garnet rutile and the high jadeite content of omphacite in marble the fluid for the peak metamorphism was calculated to have a very low xco2 0 03 the p t conditions for retrograde metamorphism were estimated to be 475 550 c at 7 kbar

diamond from the dabie shan metamorphic rocks and its implication for tectonic setting diamond occurs in ultrahigh pressure metamorphic rocks from dabie shan anhui province eastern china diamond bearing rocks include eclogite gamet pyroxenite and jadeitite diamond occurs in a mineral assemblage with coesite and jadeite the diamonds and diamondiferous rocks of dabie shan are interpreted to be the products of ultrahigh pressure metamorphism in the underthrust basement of the yangtze continental plate during the early mesozoic at greater than 4 0 gigapascals and 900 c this interpretation is based on the distribution of rock units the stability field of diamond and isotopic data indicating a crustal origin for the rocks most diamonds occur as euhedral inclusions in garnets and are 10 to 60 micrometers across although some are up to 700 micrometers across

ultradeep metamorphic rocks the retrospective viewpoint ultradeep or ultra high pressure uhp metamorphic rocks formed from crustal protoliths within the stability field of coesite at pressures 2 5 3 0 gpa corresponding to depths 80 120 km occur locally though regionally distributed in at least five continental areas their recognition is solely based on characteristic minerals and mineral assemblages calibrated by experimental high pressure studies detailed petrographic and microprobe work especially on mineral inclusions in favorable cases allows the derivation of prograde pt paths during subduction and of retrograde ones during exhumation commonly the gneisses adjacent to the uhp rocks do not exhibit signs of ultradeep metamorphism apparently because the kinetics of their mineral reactions are sufficiently fast to allow complete reequilibration to shallower pt conditions during the retrograde path it is also possible however that uhp equilibria were not attained throughout the rock volumes subducted but only along zones of shearing and fluid introduction if it is true that not all uhp metamorphic rocks return to the crustal orogenic belts but some continue to be subducted to greater mantle depths the classical geochemical pattern of a one way mass transfer from mantle to crust throughout the earth s history is at stake the assumed gradual growth of continents may have had a counterpart of continent destruction during collision events most recent experimental studies at high pressures and relatively low temperatures show that at least three new hydrous mg a1 silicates exist that were not found in nature thus far but may be characteristic minerals in the cold portions of old subduction zones thus extending the water retentivity of subducting slabs to greater and hitherto unexpected depths

precambrian blueschist terranes of the world blueschists are most common in post paleozoic orogenic belts higher geothermal gradients and a thinner lithosphere in the precambrian are widely thought to have disfavored blueschist formation however several precambrian blueschist belts have been reported from eurasia on the basis of established geologic and geochronologic constraints these belts are grouped as suspect possible and definite precambrian blueschists suspect ones include those in alaska in anglesey u k in the scandinavian caledonides and in yunnan china possible precambrian blueschist belts are those in delhi india in central china in heilongjiang china and in the urals and altai sayan tien shan u s s r definite precambrian blueschist terranes are those in western africa and in aksu china these blueschist belts are described with emphasis on the age constraints the recently investigated aksu blueschist terrane is presented as an example this high p t coherent blueschist greenschist terrane at aksu is unconformably overlain by a thick unmetamorphosed sedimentary sequence ranging in age from late sinian ca 600 800 ma through eocambrian to paleozoic the basal sinian conglomerates contain subrounded to rounded clasts of the underlying schist clearly demonstrating the pre sinian age of blueschist facies metamorphism characteristic features of the above mentioned blueschist belts include 1 1 the blueschist terranes are coherent and primary compositional lithological layers are well preserved melange belts are not common 2 2 protoliths include pelite sandstone bimodal volcanics limestone and small quantities of pillow basalt and pelagic sediment ultramafics are rare 3 3 the protoliths were subjected to multiple deformation and transitional blueschist greenschist facies metamorphism typical precambrian blueschist contains the assemblage crossitic amphibole epidote chlorite albite quartz actinolite rare lawsonite jadeitic pyroxene and aragonite have been described in few belts 4 4 the metamorphic facies series belongs to the high pressure intermediate type of miyashiro 1961 the precambrian blueschist and other pre mesozoic intracontinental blueschist of eurasia formed before rather than during final closure of intervening ocean basins between pairs of continents they do not usually mark the location of terminal sutures but are the result of earlier accretion and continental growth by subduction underplating and imbrication of accretionary wedges including both oceanic and continent derived elastics the rare preservation of precambrian blueschist is due to greenschist overprinting when the heat flow and geothermal gradient was high rather than reflecting lack of production their existence in china and africa demonstrates that requisite conditions for blueschist facies metamorphism existed at least 700 ma ago

effect of grossular content in garnet on the partitioning of fe and mg between garnet and biotite in contrast to ferry 1980 x ca values in garnet even lower than 0 1 have a significant effect on the calculated equilibrium temperature using the experimental calibration of the fe and mg paritioning between garnet and biotite garnet compositions and mg fe distribution coefficients from samples of the eoalpine staurolite in zone in the southern otztal are related by the quadratic regression equation ink d 1 7500 0 0226 2 978 0 5317 x ca gt 5 906 2 359 x ca gt 2 temperatures derived by the ferry and spear 1978 calibration using chemistry corrected k d values are petrologically realistic analysis of our data supports non ideal mixing of grossular with almandine pyrope solid solution the derived excess mixing energies are quite small for the almandine pyrope solution w femg 133 cal mole and about 2775 cal mole for the difference between pyrope grossular and almandine grossular solutions w mgca w feca at metamorphic conditions of 570 c and 5 000 bar the mixing parameters proposed by ganguly and saxena 1984 are not confirmed by our data as they would result in significantly lower temperatures

degassing of mantle derived co2 and he from springs in the southern colorado plateau region neotectonic connections and implications for groundwater systems groundwaters of the southern colorado plateau arizona transition zone region are a heterogeneous mixture of chemically diverse waters including meteoric epigenic fluids karst aquifer waters and deeply sourced endogenic fluids we investigate the composition of travertine depositing co 2 rich springs to determine the origin transport and mixing of these various components the san francisco mountain recharge area has little surface flow instead waters discharge through major springs hundreds of kilometers away about 70 9340 l s of the total recharge 13 500 l s discharges 100 km to the north in the incised aquifer system at grand canyon most of this water 85 8070 l s emerges through two travertine depositing karst spring systems blue springs 6230 l s and havasu springs 1840 l s about 30 of recharge 4150 l s flows to the south and discharges along nw striking faults in the arizona transition zone forming the base flow for the verde river geochemical data define regional mixing trends between meteoric recharge and different endogenic end members that range from bicarbonate waters to sulfate waters water quality in the region is dictated by the percentage and character of the endogenic inputs that cause a measurable degradation of groundwater quality for water supply sources for the high co 2 include dissolution of limestone and dolostone c carb and external carbon c external c external is computed as the bicarbonate alkalinity dissolved inorganic carbon dic minus the c carb c external dic c carb c external is deconvolved using carbon isotopes into biogenically derived sedimentary carbon c organic and deep co 2 inputs c endogenic measured 13 c values are 17 to 3 versus pee dee belemnite pdb assuming 13 c carb 2 13 c organic 28 and 13 c endogenic 5 water chemistry mixing models indicate that an average of 42 of the total dic comes from dissolution of carbonate rocks 25 from organic carbon including soil respired co 2 and 33 from deep endogenic sources helium isotope values 3 he 4 he in gases dissolved in spring waters in the southern colorado plateau region range from 0 10 to 1 16 r a relative to air indicating that a significant component of the deeply derived fluid is from the mantle mean of 5 asthenospheric or 10 subcontinental lithospheric mantle source measured co 2 3 he ratios of 2 10 9 to 1 4 10 13 are adjusted by removing the proportion of co 2 from c carb and c organic to give values 10 for all but four samples various mixing models using co 2 3 he suggest that the mantle derived components of the co 2 load are highly variable from spring to spring and may make up an average of 10 of the total co 2 load of the regional springs fluid rock interactions involving endogenic fluids are suggested by 87 sr 86 sr 18 o and other tracers the endogenic co 2 component multiplied by discharge for each spring yields an integrated annual flux of deeply derived co 2 to the groundwater system of 1 4 10 9 mol yr this co 2 emission from the colorado plateau region reflects a complex tectonic evolution involving laramide hydration of the lithosphere above the farallon slab addition of fluids from mid tertiary mantle tectonism during slab removal and ongoing fluid movement induced by neotectonic small scale asthenospheric convection

stable isotope characteristics of eclogites from the ultra high pressure metamorphic terrain east central china abstract a stable isotope study was made for the ultra high pressure uhp metamorphic rocks in the dabie and sulu terrains east central china 18 o values of minerals in eclogites cover a wide range from 4 to 6 the o isotope fractionations between minerals i e omphacite phengite and or amphibole and garnet in eclogites are mostly not in isotopic equilibrium the large range of o isotope composition of garnet may approximate the 18 o variations of eclogites during uhp metamorphism and must have been largely inherited from their pre subduction basaltic precursors which might have interacted with meteoric waters under variable temperature conditions and water rock ratios before uhp metamorphism the o isotope disequilibrium between minerals and garnet in eclogites was caused by retrograde hydration reactions the fluids required for these hydration reactions must have low or even negative o isotope compositions it is postulated that such fluids were either originated from meteoric deep infiltration or were derived from low 18 o para gneisses

skilful predictions of the winter north atlantic oscillation one year ahead the north atlantic oscillation profoundly influences european and north american winter weather dynamical model predictions now exhibit skill in prediction of the winter north atlantic oscillation more than one year in advance

evaporitic carbonates in the pre salt of santos basin genesis and tectonic implications abstract since the first discoveries of oil accumulations in the carbonate reservoirs of the lower cretaceous barra velha formation of the santos basin their genesis has been the subject of intense discussion different depositional models have been proposed with some authors advocating a microbial origin while others an abiotic origin as travertines or travertine like rocks this search for a modern carbonate analogue for these unusual rocks may have disregarded an intriguing alternative an evaporative model supported by our petrographical and geochemical data evaporitic sediment patterns in endorheic basins in a depositional framework of brine drawdown are dominated by ephemeral salt pan hydrology bedded salt crusts form a stack of subaqueous aligned crystal beds at the sediment water interface salt grows diagenetically within saline and mud layers beneath the dry pan surface finally laminated sediments are deposited we observe a similar cyclic pattern in the pre salt core we described beds of shrub like crystals and diagenetic spherulites growing in magnesium clay matrix are followed by laminites the model we propose attempts to contribute solving the puzzle of pre salt carbonate deposition by integrating sedimentology and geochemistry with basin tectonics our observations and basin tectonics point to the exciting possibility that the sag phase carbonates of the santos campos basin were deposited as the initial transitional stage of a closed sub sea level evaporite basin whose rising salinities culminated in the deposition of halite and bittern salts carnallite sylvite tachyhydrite basinwide evaporites are singular events in the geological record they form when a giant sub sea level basin becomes a sump of continental marine and hydrothermal fluids producing unexpected brine compositions in unusual depositional settings present in ancient evaporitic basins but absent from most modern ones the novelty in this paper is that we apply to pre salt carbonate deposition the sedimentology hydrology and geochemistry of ancient evaporitic basins with this concept in mind we propose a geochemical model for the unusual pre salt carbonate precipitation of the santos basin regarding the walvis rio grande volcanic high as a topographic barrier during the aptian we suggest that the main sources of calcium to the barra velha paleolake were hydrothermal brines mostly from infiltrating seawater that reacted at depth with the basalts of the volcanic barrier hyperextension of the lithosphere with a shallow moho increased geothermal gradients to levels favorable for the generation of hydrothermal cacl2 brines a process facilitated by the already elevated ca ion and low sulfate concentration of the cretaceous ocean these cacl2 rich fluids would pass through the volcanic barrier into a sub sea level paleolake in the rift basin the high salinity paleolake would become saturated in calcium bicarbonate carbonate as internally drained nahco3 bearing alkaline waters formed by physical chemical weathering of penecontemporaneous basaltic rocks mix with the cacl2 bearing hot brines percolating through the barrier producing a hybrid brine 2nahco3 cacl2 ca hco3 2 2nacl such a depositional system integrating the geochemical depositional controls of sag phase carbonates with those of the south atlantic evaporites has important implications for unravelling the genesis of these exotic deposits

a 36cl chronology of lacustrine sedimentation in the pleistocene owens river system we have used 36 cl to date climatically sensitive saline lake sediments from hydrologically closed basins in southeastern california primarily sediments from searles and panamint basins during wet periods of the past 2 0 m y lakes that formed in the closed basins fluctuated in size in direct response to the balance between runoff and evaporation we have compiled a chronology for the km 3 core from searles lake based on ages determined by 36 cl for the evaporites together with those determined by 14 c and u th series for younger sediments and by magnetostratigraphy for older sediments this chronology along with other criteria such as correlations between searles and panamint basins the chloride budget and sedimentology is used to reconstruct the history of lake fluctuations in the paleo owens river system we infer that searles lake desiccated at most twice since 600 ka during the interval around 290 ka and from 10 ka to the present the lake history curve shows that the holocene epoch is anomalously arid major overflows from searles to panamint occurred during the intervals between 1 3 ma and 1 0 ma 750 ka and 600 ka 500 ka and 400 ka and 150 ka and 120 ka comparing the lake fluctuation chronology to the 18 o record of marine foraminifera we infer that the strongest similarity is in the periodicities of the cycles 40 to 50 kyr before the matuyama brunhes magnetic reversal 730 ka and 100 kyr thereafter we find however that at searles lake this fluctuation in the lake chronology is modulated by longer term cycles of aridity and humidity thus although the mid latitude quaternary climate record reflects the mid to high latitude ice volume fluctuations that dominate the marine 18 o record it also contains evidence for climatic forcing of a different type

ar ar geochronology of ultrahigh pressure metamorphism in central china the dabie shan of china contain the largest areal exposure of ultrahigh pressure regional metamorphic rock known on earth the thermal history of these unusual rocks is central to understanding the tectonic processes responsible for their creation preservation and exhumation published ages of ultrahigh pressure metamorphism and subsequent cooling range from archean to jurassic by analyzing 21 dabie hornblende phengite and biotite samples by the 40ar 39ar method we find that 1 cooling from peak metamorphic temperatures to 300 c occurred between about 206 and 178 ma 2 widespread cretaceous ages reflect reheating by a postultrahigh pressure magmatic extensional episode 3 40ar 39ar and k ar ages older than 230 ma and perhaps 210 ma are geologically meaningless due to the incorporation of excess 40ar and 4 dabie ultrahigh pressure metamorphic rocks are temporally related to blueschist facies rocks farther west in the suture zone

decadal evolution of ocean thermal anomalies in the north atlantic the effects of ekman overturning and horizontal transport basin scale thermal anomalies in the north atlantic extending to depths of 1 2km are more pronounced thanthebackgroundwarmingover thelast 60years a dynamicalanalysis basedonreanalyses ofhistorical data from1965to2000suggeststhat thesethermalanomaliesare formedbyocean heat convergences augmented by the poorly known air sea fluxes the heat convergence is separated into contributions from the horizontal circulation and the meridional overturning circulation moc the latter further separated into ekman and moc transport minus ekman transport moc ekman cells the subtropical thermal anomalies are mainly controlled by wind induced changes in the ekman heat convergence while the subpolar thermal anomalies are controlled by the moc ekman heat convergence the horizontal heat convergence is generally weaker only becoming significant within the subpolar gyre these thermal anomalies often have an opposing sign between thesubtropicalandsubpolargyres associatedwithopposingchangesinthemeridionalvolumetransportdriving the ekman and moc ekman heat convergences these changes in gyre scale convergences in heat transport are probably induced by the winds as they correlate with the zonal wind stress at gyre boundaries

studies of labrador sea water formation and variability in the subpolar north atlantic in the light of international partnership and collaboration abstract labrador sea water lsw the lightest contribution to north atlantic deep water nadw and one of the most prominent water masses of the subpolar north atlantic has seen remarkable changes over the past century lsw originates in the labrador sea where it is formed through wintertime ocean convection of varying intensity depth and spatial extent formation of lsw followed by its respective injection into the mid depth circulation system is mandatory for ventilating and renewing water layers of the interior ocean indispensably important for unraveling the history of variability in formation and properties of lsw as well as for mapping its large scale spreading and export are sustained physical and chemical observations from the deep ocean these observations started at the beginning of the 20th century from occasional mostly national surveys and today constitute large scale multi national collaborative efforts including a vast arsenal of sophisticated instrumentation in a historical context we revisit major milestones over the past 100 years which have established and are constantly adding to shaping today s knowledge on lsw and present first details on the latest vintage of lsw generated during the strong winter of 2013 2014 respective argo data reveal mixed layer depths greater than 1700 m marking formation of a new cold and fresh anomaly that has spread since then over the subpolar north atlantic we further summarize the on going observational efforts in the subpolar north atlantic and present a compilation of hydrographic standard lines that serve to provide top to bottom information on nadw components

geochronology and isotopic character of ultrahigh pressure metamorphism with implications for collision of the sino korean and yangtze cratons central china the collision zone between the sino korean and yangtze cratons in central china is marked by subduction related metamorphic rocks composed of crustal protoliths these range in metamorphic grade from ultrahigh pressure eclogite to low greenschist facies the paragenesis of the ultrahigh pressure rocks coesite and diamond bearing indicates subduction to depths greater than 120 km as a result of continental collision despite extreme metamorphic conditions zircons have not undergone pb loss but rather illustrate two periods of growth crystallization between 700 and 800 ma and ultrahigh pressure metamorphism at 218 2 5 ma previous studies have predicted a time transgressive collision but age data presented in this study indicate that the collision was approximately coeval along the length of the suture u pb zircon ages of these ultrahigh pressure metamorphic rocks are 218 4 2 5 ma and 217 1 8 7 ma for the dabie mountains and shandong peninsula respectively the similar ages imply that the tan lu fault which offsets the ultrahigh pressure metamorphic rocks is a secondary feature not related to collision or subduction whole rock isotopic data show that both rb sr and u pb were open systems during metamorphism but that sm nd probably remained closed nd initial isotopes display crustal signatures indicating that the crust subducted as a coherent slab rather than becoming intercalated with mantle material at depth sm nd data in conjunction with u pb zircon dating indicate that the ultrahigh pressure rocks are not typical yangtze craton basement 2 9 ga but that they originally crystallized in a rift environment between 700 and 800 ma discrepancies between 40ar 39ar plateaus sm nd isochrons and u pb zircon ages render calculation of a p t t path unrealistic

changes in arctic melt season and implications for sea ice loss the arctic wide melt season has lengthened at a rate of 5 days decade 1 from 1979 to 2013 dominated by later autumn freezeup within the kara laptev east siberian chukchi and beaufort seas between 6 and 11 days decade 1 while melt onset trends are generally smaller the timing of melt onset has a large influence on the total amount of solar energy absorbed during summer the additional heat stored in the upper ocean of approximately 752 mj m 2 during the last decade increases sea surface temperatures by 0 5 to 1 5 c and largely explains the observed delays in autumn freezeup within the arctic ocean s adjacent seas cumulative anomalies in total absorbed solar radiation from may through september for the most recent pentad locally exceed 300 400 mj m 2 in the beaufort chukchi and east siberian seas this extra solar energy is equivalent to melting 0 97 to 1 3 m of ice during the summer

high pressure ultrahigh pressure eclogites from the hong an block east central china geochemical characterization isotope disequilibrium and geochronological controversy the hong an block western dabieshan exposes a series of hp uhp metamorphic rocks with a s to n distribution from blueschist greenschist kyanite free to kyanite and coesite bearing eclogites the available age data are inconclusive that hinder our understanding of the tectonic evolution of the block the metamorphic temperatures in the hong an block tmeta 700 to 500 c are lower by 50 150 c than that of the dabie and sulu terranes in this work we undertook new trace element and sr nd o isotopic analyses on minerals in order to gain more insight into the geochronological problems the results are as follows 1 trace element distribution patterns suggest that garnet and omphacite in many cases are out of chemical equilibrium and the presence of high temperature lree rich mineral inclusions e g epidote in garnet and omphacite has contributed to isotope disequilibrium 2 sm nd isotope analyses yielded no isochron ages for the hong an eclogites 3 rb sr isotope analyses gave mixed results in some cases coexisting minerals are completely out of isotope equilibrium and in others isochron relationship is established yielding ages from 210 ma to 225 ma the pattern of rb sr isotope disequilibrium appears to be independent of the petrological and o isotope temperatures 4 in contrast to the unequilibrated sm nd isotopic systems oxygen isotopes of the eclogite minerals seem to have attained isotope equilibrium or near equilibrium oxygen isotope temperatures are comparable with petrological temperatures however this is an apparent feature due to mass balance constraints 5 whole rock 18o values show a large variation from 10 to 8 suggesting that their protoliths have undergone very different processes of water rock interaction in view of the overall geochronological information we conclude that the hp uhp metamorphism in the hong an block took place in the triassic at about 220 230 ma as observed in the dabie and sulu terranes the significance of published paleozoic dates 450 300 ma for the xiongdian eclogite is not clear however any hypotheses advocating two periods of uhp metamorphic events for the same tectonic unit or in the same locality are not constrained by the geochronological data

mineralogic controls on the composition of natural waters dominated by silicate hydrolysis a detailed mineral solute mass balance spreadsheet model has been developed to improve understanding of mineralogic controls on water composition in surface waters and groundwater systems dominated by silicate lithologies the spreadsheet based approach is used to investigate mass balance solutions over a range of mineral compositions for predominant multi element phases such as plagioclase biotite chlorite amphibole and dioctahedral smectite the mass balance technique has been applied to a variety of hydrogeologic environments including calibrated watersheds springs and groundwater systems lithologic settings include plutonic metamorphic minor volcanic and sedimentary alluvial and glacial deposits materials sites investigated most of which allowed comparison with earlier work include ephemeral and perennial springs of the central sierra nevada mountains california the loch vale colorado high altitude watershed four catchments in the inyo mountains california and nevada watersheds in the catoctin mountain maryland area and ground water flow systems in vekol valley arizona and in the trout lake area wisconsin analytical mass balances were derived with a novel approach that permits graphic analysis of the functional dependency of mineral mass transfer coefficients on variations in major silicate composition a 10 x 10 matrix of mineral solute reaction equations was used to solve for the best mass balances alternative methods were developed to investigate cases where the number of mineral phases exceeds the number of solute constraints 10 that are commonly found in clastic silicate dominated systems with diverse sources and or phase mixtures of variable chemistry such as an assortment of plagioclase compositions techniques were also developed to allow for important structurally controlled compositional variation in clay minerals final mass balance choices were tempered by thermodynamic stability calculations for various minerals under near surface weathering conditions mineral mass transfer ratios were also found to be useful in restricting mass balances additional constraints were provided by establishing consistent sets of similar mineral assemblages and mineral compositions for a series of wells along a ground water flow path or through comparison of multiple nearby watersheds subject to similar climatic and vegetative conditions whereas unique analytical solutions from spreadsheet mass balances were not always possible a surprisingly limited range was obtained for mineral assemblages and compositions satisfying observed mineral occurrences and thermodynamic stability conditions our results demonstrate the importance of having well characterized mineral compositions for both reactant and product phases the mass balance results are particularly sensitive to the compositions of plagioclase dioctahedral smectite and a few primary mafic mineral groups trioctahedral mica amphibole and pyroxene in addition to mineral controls the specific examples studied demonstrate effects of dolomite and calcite overprints on silicate weathering biomass fluctuations road salt contamination and on buried evaporite salts a comparison of the mass balance results from surface and groundwater systems indicates strong similarities suggesting that similar processes dominate the mineral controls in both settings and that under soil weathering conditions ion exchange might have been overemphasized except under conditions where pre existing waters are displaced by solutions of significantly different composition

the impact of labrador sea temperature and salinity variability on density and the subpolar amoc in a decadal prediction system labrador sea density variability is important for atlantic meridional overturning circulation amoc dynamics and hence decadal variability in the atlantic we investigate whether temperature or salinity dominate top 500m interannual labrador sea density variability in gridded observations an assimilation of the observations and a set of multi annual hindcasts we find that salinity dominates in the observations and assimilation in the hindcasts salinity remains dominant for the first year but from year three these revert to the same temperature dominance seen in the underlying climate model this is due to damping of the interannual salinity variability possibly caused by unrealistically large convection that develops crucially the hindcasts have high correlation skill in temperature salinity throughout but no skill in density dynamic sea level or the subpolar amoc due to the incorrect drivers this highlights the importance of correctly simulating both the sign and magnitude of temperature salinity variability in a prediction system

coesite bearing eclogite from the dabie mountains in central china coesite and coesite pseudomorphs are recognized in eclogite from the dabie mountains a collision zone between the sino korean and yangtze cratons in central china this third known occurrence of coesite in deep crustal rocks is within an archean gneiss terrane and is the first locality where coesite has been identified as an inclusion in both omphacite and garnet crystals at the same location coesite bearing eclogite is estimated to form at pressures of 28 kbar and temperatures from 600 to 710 c the dabie mountains eclogite underwent retrograde metamorphism to amphibolite facies after its formation the preservation of coesite in eclogite is found to be strongly controlled by the pressure temperature time path that coesite bearing eclogite followed during its uplift and retrograde metamorphism

the timing of crustal extension and the eruption of continental flood basalts the association between mantle plumes continental flood basalt eruption and the extension and rifting of the crust is well recognized1 3 but there has always been controversy as to whether the plume or the rifting was the initiating factor4 5 was rifting triggered by doming above the thermal plume2 3 6 or was rifting the driving force preceding the associated volcanicity7 8 here i show that recent flow by flow mapping of two continental flood basalt provinces the columbia river basalt group and the deccan basalt group allows one to infer the relative timing of volcanicity and crustal extension in both provinces eruption of the main tholeiitic phase preceded significant extension and crustal thinning this suggests that the primary event in the formation of these provinces was the upwelling of a mantle plume and that the subsequent crustal extension rifting and decompression was in part a consequence of the initiation of that plume

interdecadal variations of the thermohaline circulation in a coupled ocean atmosphere model abstract a fully coupled ocean atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the north atlantic ocean with a time scale of approximately 50 years the irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation approximately 52 n to 72 n combined with much smaller density anomalies of opposite sign in the broad rising region the spatial pattern of see surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the north atlantic the anomalies of sea surface temperature induce model surface air temperature anomalies over the northern north atlantic arctic and northwestern europe

fluid rock interactions during ultra high pressure metamorphism dabie shan china oxygen isotope analyses of garnet separates and whole rock samples of gneiss and marble hosted eclogites from the ultra high pressure uhp dabie shan terrain fall in the range 6 76 to 10 76 comparison of the isotopic compositions of the eclogites with those of their host rocks leads to the following conclusions 1 the basaltic protolith of the eclogites had isotopic compositions in the range 2 15 to 4 99 it is proposed that this is the result of contamination of the parent basaltic magma with hydrothermally altered18o depleted source materials 2 18o enriched eclogite compositions resulted from local scale 3 m interaction between this basaltic eclogite protolith and fluids produced by decarbonation of impure marble lithologies during uhp metamorphism 3 18o depleted eclogite and gneiss compositions resulted from regional scale meteoric hydrothermal alteration of the basalts and their host rocks prior to uhp metamorphism epidote separates and whole rocks from the cores and rims of mineralogically zoned eclogite boudins within amphibolite grade biotite gneisses show no distinct isotopic differences this suggests that the preferential recrystallisation of the gneisses and the associated amphibolite grade overprint of the rims of eclogite bodies could not have resulted from regional scale infiltration of significant volumes of fluid during the exhumation of the dabie shan terrain

coesite in clinopyroxene in the caledonides and its implications for geodynamics coesite is reported for the first time from the caledonide orogen it occurs as inclusions in clinopyroxene in the dolomite eclogite at grytting norway and provides valuable new evidence to support the hypothesis of extremely high pressure 30 kbar in certain norwegian eclogites this finding has implications for the geodynamics and kinetics of the concepts of microscale intracrystalline tectonic overpressure and of macroscale local or regional tectonic overpressure and for the hypotheses of subduction and obduction involving a more than 100km vertical component of transport

discovery of clinoenstatite in garnet pyroxenites from the dabie sulu ultrahigh pressure terrane east central china transmission electron microscopy tem reveals that some enstatites from garnet pyroxenites in the chinese dabie sulu ultrahigh pressure uhp terrane consist of intimate intergrowths of orthoenstatite oren and clinoenstatite clen and some grains of pyroxene mgfe 2 si 2 o 6 exhibit inclined extinction these garnet pyroxenites are enclosed in coesite bearing eclogite or interlayered with harzburgite and omphacitite they contain garnet prp 54 to prp 73 enstatite en 85 to en 92 magnesite and titanomagnetite sulu sample or clinohumite dabie sample and recrystallized at about 4 0 6 5 0 2 gpa 750 50 c all clinoenstatite lamellae in the host orthoenstatite have even numbers of 9 a 100 fringes without twins and are oriented parallel to 100 of the host the lamellae and host phases have nearly identical mgfe 2 si 2 o 6 compositions the thickest observed clen lamellae are 0 4 m clinoenstatites from sulu have cell parameters a 9 67 7 a b 8 88 6 a c 5 22 3 a 107 7 2 and v 427 8 a 3 and those from dabie a 9 53 6 a b 8 88 6 a c 5 24 3 a 107 0 2 and v 424 8 a 3 the tem electron diffraction patterns indicate that both clinoenstatites possess p 2 1 c structures and are the low p polymorph of clinoenstatite the host orthoenstatites have cell dimension a 18 32 12 a b 8 88 6 a c 5 20 3 a for the sulu sample and a 18 24 12 a b 8 88 6 a c 5 18 3 a for the dabie sample clinoenstatites in garnet pyroxenites from the dabie sulu uhp terrane may have formed either by inversion from oren or by the displacive transformation from high p clinoenstatite during decompression

high pressure blueschists and eclogites in hong an a framework for addressing the evolution of high and ultrahigh pressure rocks in central china the hong an region in the qinling dabie collisional zone in eastern china hosts a series of metamorphic rocks exposing a south to north distribution from blueschist blueschist greenschist amphibolite eclogite kyanite free and kyanite eclogite to coesite eclogite facies rocks that represent progressively deeper levels of the mesozoic subduction collision complex the hong an area is interesting for three reasons 1 it escaped the thermal and structural overprint imparted on much of the dabie mountains during early cretaceous intrusion of voluminous granites and granodiorites 2 the high pressure hp hong an eclogites are widely distributed often preserve prograde crystallization histories and can be directly linked in time and space to the blueschist blueschist greenschist rocks exposed to the south 3 the blueschist blueschist greenschist facies rocks are generally better exposed than their equivalents in the southeastern dabie mountains and offer some opportunity for simultaneous structural and metamorphic analysis the hong an area hp rocks offer perhaps the closest approximation to a preserved snapshot of mesozoic pressure temperature p t conditions attending early subduction exhumation in the region and are thus essential to generating a coherent picture of the dynamics attending both metamorphism and exposure of the coeval ultrahigh pressure uhp rocks the purpose of this contribution is twofold 1 to document previously unpublished metamorphic and structural data characterizing these hp sequences and their relative continuity in hong an 2 to incorporate these data with recent geochronologic structural and paleomagnetic information in the context of protracted late paleozoic through mesozoic subduction collision and exhumation metamorphism and exhumation of some of the southern hong an hp sequences appear to have occurred concomitant with oceanic subduction immediately to the west and thus may have preceded widespread continental subduction collision moreover all of the hp uhp sequences in the region were exhumed before the end of collision between the sino korean and yangtze cratons at ca 160 ma exhumation of hp uhp rocks both before and during continental plate collision is neither novel for central china nor for other hp uhp zones but is important to take into account when reconstructing the evolution of such orogens

stable isotope geochemistry of marbles from the coesite uhp terrains of dabieshan and sulu china abstract marbles from dabieshan and sulu china suffered ultra high pressure uhp metamorphism in the coesite eclogite facies at approximately 700 c and 30 kbars during triassic continental collision and subduction the marbles range in isotopic composition from 7 to 25 18 o vsmow and from 0 to 6 13 c vpdb high 13 c values are representative of unmodified protoliths and are similar to those of 13 c enriched sinian carbonate rocks from the yangtze craton high oxygen isotope ratios reflect pristine protoliths but the low values may have been caused by infiltration of low 18 o meteoric water during diagenesis and dolomitization by fracture controlled infiltration of water during subduction by metamorphic mineral reactions or by a combination of these processes no evidence of regional isotopic transport during uhp metamorphism has been found sampling on scales of 1 to 100 m shows marbles to be inhomogeneous in both carbon and oxygen isotopes only samples separated by less than 10 cm have equilibrated oxygen and carbon isotope compositions limited isotopic equilibration between adjacent rocks is consistent with the preservation of unaltered uhp minerals and indicates that the metamorphic fluid rock system was rock dominated during and following peak metamorphism a freely flowing pervasive fluid phase was not present during uhp metamorphism there is no evidence of isotopic exchange between marble and the upper mantle into which it was subducted correlation of geochemical similarities of uhp marbles with sinian limestones implies that the subducted edge of the yangtze craton extends at least as far north as the coesite eclogite facies rocks of dabieshan deposition of protolith carbonates may have taken place in a cold climate either preceding or following but not coincident with neoproterozoic glaciation

magnetite lamellae in olivine and clinohumite from dabie uhp ultramafic rocks central china ultrahigh pressure uhp minerals of the maowu mafic ultramafic complex in the dabieshan east central china exhibit many exsolution textures magnetite lamellae are common in olivines and ti clinohumites from harzburgite and garnet pyroxenite monazite ce lamellae occur in apatites from the garnet pyroxenite independent p t estimates suggest that these ultramafic rocks formed at p 5 gpa and t 700 50 c the lamellae bearing minerals are believed to preserve an earlier higher p t record prior to exsolution compositions and unit cell parameters of the magnetite and host olivine and intergrowth relations were determined using a newly developed x ray diffraction microprobe technique employing synchrotron radiation the host olivine and magnetite lamellae bear a topotaxial relation with 220 mag 200 ol 111 mag 3 3 1 ol 11 1 mag 331 ol 242 mag 2 2 0 ol the recalculated composition of primary olivine may contain up to 1 5 wt fe 2o3 four hypotheses may explain the observed intergrowths of oriented magnetite lamellae in olivine 1 oxidation of olivine 2 decomposition of fe 3 bearing olivine formed at 6 gpa 3 exsolution of a spinel wadsleyite solid solution fe 3o4 fe mg 2sio4 during decompression and 4 breakdown of phase a mg7si2 oh 6 enstatite the third hypothesis appears to be the most likely inasmuch as no additional silicate phase occurs as associated inclusions in the olivine host however the actual mechanism for exsolution of magnetite from olivine remains to be studied experimentally

tectonics of an ultrahigh pressure metamorphic terrane the dabie shan tongbai shan orogen china ultrahigh pressure metamorphic rocks with coesite and diamond form a tectonic slice over 20 km thick called the eclogite zone within the dabie shan complex in the qinling orogen in central china the orogen separates the sino korean block in the north from the yangtze block in the south the dabie shan complex is a composite terrane made up of eclogite facies and amphibolite facies gneiss slices and represents fragments of the lower continental crust of the yangtze block the dabie shan complex is bounded in the south by a triassic foreland fold thrust belt and in the north by a greenschist facies metaclastic unit the foziling group which probably represents the passive continental apron deposits of the yangtze block farther north is a granulite facies gneiss complex the qinling group which has ultramafic slivers and includes the remnants of an island arc with two bounding suture zones north of the qinling group are early paleozoic active margin deposits of the sino korean block the eclogite zone in the dabie shan complex is sandwiched between amphibolite facies gneiss slices dating by sm nd rb sr and ar ar of two eclogite samples from the eclogite zone gives early to middle triassic ages 236 246 ma the initial end values indicate reworking of a 2 11 and 1 55 ga continental crust a himalayan type tectonic evolution is envisaged for the qinling orogen with the creation of a 100 km thick crustal thrust wedge through continuous underplating during the subduction of the yangtze continental lithosphere exhumation of the ultrahigh pressure metamorphic rocks was chiefly achieved by the southward propagation of the thrust planes thereby isostatically uplifting and eroding the earlier deeply subducted parts of the orogen a total of 680 km of southward thrusting in front of dabie shan is inferred based on the abrupt termination of the tanlu fault normal faulting possibly caused by gravitational collapse probably also had a role in the exhumation process

an anatomy of the cooling of the north atlantic ocean in the 1960s and 1970s abstractin the 1960s and early 1970s sea surface temperatures in the north atlantic ocean cooled rapidly there is still considerable uncertainty about the causes of this event although various mechanisms have been proposed in this observational study it is demonstrated that the cooling proceeded in several distinct stages cool anomalies initially appeared in the mid 1960s in the nordic seas and gulf stream extension before spreading to cover most of the subpolar gyre subsequently cool anomalies spread into the tropical north atlantic before retreating in the late 1970s back to the subpolar gyre there is strong evidence that changes in atmospheric circulation linked to a southward shift of the atlantic itcz played an important role in the event particularly in the period 1972 76 theories for the cooling event must account for its distinctive space time evolution the authors analysis suggests that the most likely drivers were 1 the great salinity anomaly of the late 1960s 2 an earlier

ultrahigh pressure uhp low al titanites from carbonate bearing rocks in dabieshan sulu uhp terrane eastern china titanites previously reported from high pressure rocks commonly contain high al and f contents this finding has led previous workers to conclude that high al and f in titanite can expand its stability field to high pressure and ultrahigh pressure uhp conditions in this study a coesite inclusion was identified in titanite of aragonite and jadeite bearing gneiss from the dabieshan uhp metamorphic terrane of eastern china we also found uhp titanite in carbonate bearing garnet clinopyroxenite from the sulu uhp terrane interestingly both types of the uhp titanite mentioned above contain low al and f contents therefore our data indicate that the high al and f contents are not necessary criteria for stabilizing titanite to uhp conditions it is inferred that the uhp titanite formed via the reaction tio 2 caco 3 sio 2 catisio 5 co 2 and that the presence of the uhp assemblage aragonite rutile clinopyroxene coesite in the host rock and a very low x co 2 value in the coexisting fluid are crucial conditions for the formation of these uhp titanites

field occurrences and petrology of eclogites from the dabie mountains anhui central china four distinct types of eclogites are recognized according to their field occurrences and mineral parageneses in a gneiss terrane of the dabie mountains a collision zone between the sino korean and yangtze cratons in central china some eclogites contain coesite and its quartz pseudomorphs enclosed in garnet and omphacite type i eclogites occur as layers in serpentinites and contain garnet clinopyroxene orthopyroxene phengite rutile and coesite pseudomorph type ii eclogites occur as lenticular bodies inside serpentinites and contain garnet clinopyroxene quartz rutile and edenitic hornblende type iii eclogites occur as blocks of 2 cm to 20 m in size in a matrix of hornblende gneiss and biotite gneiss and type iv eclogites occur as thin layers interbedded with amphibolites p t estimates for these different eclogites indicate that they were formed under different physical conditions all the eclogites were affected by later regional metamorphism for which the p t conditions are estimated this paper provides an introduction to the abundant eclogites from central china which have not been reported previously in western literature specifically the mode of field occurrence petrography mineral chemistry and formation conditions of the four types of eclogites are described the paper is thus designed to establish a petrological framework for future detailed studies of the eclogites and their country rocks in an ancient zone of collision

the al 2 o 3 contents of enstatite in equilibrium with garnet in the system mgo al 2 o 3 sio 2 at 15 40 kbar and 900 1 600 c forty six reversed determinations of the al2o3content of enstatite in equilibrium with garnet were made in the p t range 15 40 kbar 900 1 600 c in the mgo al2o3 sio2 system starting materials were mixtures of synthetic pyrope al free enstatite and pyrope enstatite 5 12 al2o3 al2o3 contents in reversal run pairs closely approached common values from both the high and low al sides most experiments were done in a piston cylinder device using a nacl medium some runs at very high temperatures were made in pyrex nacl or pyrex talc assemblies the measured enstatite compositions expressed as mole fractions of mg2 mgal alsi3 o12 x opy en were fitted by a monte carlo method to the equilibrium condition begin gathered delta h 970 0 970 delta s 970 0 hfill mathop smallint limits 1 p delta v 970 0 dp mathop smallint limits 970 t delta s t 0 dt rt ln x opy en 0 hfill end gathered where the best fit parameters of h s and v 1 bar 970 k for the reaction pyrope opy are 2 040 cal mol 2 12 eu and 9 55 cc mol in addition to the determination of al2o3 contents of enstatite the univariant reaction pyrope forsterite enstatite spinel was reversibly located in the range 1 100 1 400 c a best fit line passes through 22 22 5 and 25 kbar at 1 040 1 255 and 1 415 c respectively our results for the univariant reaction are in agreement with previous studies of macgregor 1974 and haselton 1979 however comparison of the experimentally determined curve with thermochemical calculations suggests that there may be a small error in the tabulated h f 970 1 0 value for enstatite a value of 8 32 rather than 8 81 kcal mole charlu et al 1975 is consistent with the present data application of garnet enstatite spinel forsterite equilibria to natural materials is fraught with difficulties the effects of nonternary components are poorly understood and the low solubilities of al2o3 in enstatite under most geologically reasonable conditions make barometric or thermometric calculations highly sensitive more detailed studies including reversed determinations in low friction assemblies are sorely needed before the effects of important diluents such as fe ca and cr can be fully understood

propagation pathways of classical labrador sea water from its source region to 26 n 1 more than two decades of hydrography on the abaco line east of the bahamas at 26 n reveals decadal variability in the salinity of classical labrador sea water clsw despite the long distance from its source region in the north atlantic ocean hydrographic time series from the labrador sea and from the abaco line show a pronounced step like decrease in salinity between 1985 and 1995 in the labrador sea and between 1995 and 2010 at the abaco line suggesting a time lag between the two locations of approximately 9 years the amplitude of the anomaly at the abaco line is 50 of the amplitude in the labrador sea a similar time lag and reduction of amplitude is found in the high resolution ofes model in which salinity anomalies can be observed propagating through the deep western boundary current as well as through a broad interior pathway on its way south to the abaco line the clsw becomes 8 standard deviations saltier due to isopycnal mixing with mediterranean outflow water mow climatological data in the north atlantic suggests that the mixing ratio of mow to clsw at the abaco line is 1 4 and that no variability in mow is required to explain the observed variability at the abaco line the data studied here suggest that decadal clsw anomalies stay relatively coherent while getting advected despite the important role of interior pathways

the paleozoic metamorphic history of the central orogenic belt of china from 40ar 39ar geochronology of eclogite garnet fluid inclusions abstract the pressure temperature time evolution of the uhp eclogites of dabie sulu in the eastern sector of the central orogenic belt of china shows a complex pattern of predominantly triassic and to a lesser extent early paleozoic ages 40 ar 39 ar stepwise crushing analysis of eclogitic garnets yielded consistently paleozoic ages because our initial results from the bixiling eclogite were of limited areal extent their significance required further testing data for garnet bearing gneiss and eclogites from new locations in northern and southern dabieshan shuanghe ganghe and hongmiao confirm the paleozoic garnet results obtained from bixiling eclogite we also tested the technique on a garnet sample of known paleozoic age from altyn tagh in the western central orogenic belt these new results indicate that light colored garnets from dabieshan and altyn tagh yield concordant 40 ar 39 ar ages ranging from 445 465 ma by in vacuo crushing and confirm that a paleozoic u hp metamorphic event took place in the central orogenic belt from altyn tagh in western china to dabieshan in eastern china in contrast dark colored garnets from mafic metavolcanics do not yield 40 ar 39 ar plateaux or isochrons ages

a multimodel study of sea surface temperature and subsurface density fingerprints of the atlantic meridional overturning circulation abstractthe atlantic meridional overturning circulation amoc is an important component of the north atlantic climate system here simulations from 10 coupled climate models are used to calculate patterns of sea surface temperature sst and subsurface density change associated with decadal amoc variability the models are evaluated using observational constraints and it is shown that all 10 models suffer from north atlantic deep water transports that are too shallow although the biases are least severe in the community climate system model version 4 ccsm4 in the models that best compare with observations positive amoc anomalies are associated with reduced labrador sea stratification and increased midocean 800 1800 m densities in the subpolar gyre maximum correlations occur when amoc anomalies lag labrador sea stratification and subsurface density anomalies by 2 6 yr and 0 3 yr respectively in all 10 models north atlantic warming follows positive amoc anomalies but the patterns and magnitud

ultra high pressure uhp marble and eclogite in the su lu uhp terrane eastern china a large mass of dolomitic marble including many eclogite blocks occurs in orthogneisses of the rongcheng area of the su lu province eastern china the marble consists mainly of dolomite calcite formerly aragonite graphite forsterite diopside talc tremolite and phlogopite aggregates of talc and calcite occur at the boundary between dolomite and diopside tremolite is a reaction product between talc and calcite eclogite blocks are rimmed by dark green amphibolite the primary mineral assemblage in the core of eclogite is na bearing garnet up to 0 2 wt na2o omphacitic pyroxene clintonite and rutile secondary minerals are pargasitic edenitic amphibole plagioclase sodic diopside chlorite zoisite and titanite the peak metamorphic conditions based on stability of the dolomite forsterite aragonite now calcite graphite assemblage under conditions where tremolite is unstable are estimated at t 610 660 c and p 2 5 3 5 gpa for xco 0 001 a reaction between dolomite and diopside to form talc under tremolite unstable conditions indicates a temperature decrease under ultra high pressure conditions p 2 4 gpa xco 0 0013 the formation of secondary tremolite is consistent with a nearly adiabatic pressure decrease post dating the ultra high pressure metamorphism the temperature decrease under ultra high pressure conditions preceding decompression may reflect the underplating of a cold slab and the rapid decompression probably corresponds to the upwelling stage promoted by the delamination of a downwelling lithospheric root the p t conditions of the amphibolitization stage are estimated at 0 9 gpa and 460 c and are similar to conditions recorded by the surrounding orthogneisses

a decadal prediction case study late twentieth century north atlantic ocean heat content an ensemble of initialized decadal prediction dp experiments using the community climate system model version 4 ccsm4 shows considerable skill at forecasting changes in north atlantic upper ocean heat content and surface temperature up to a decade in advance coupled model ensembles were integrated forward from each of 10 different start dates spanning from 1961 to 2006 with ocean and sea ice initial conditions obtained from a forced historical experiment a coordinated ocean ice reference experiment with interannual forcing core ia which exhibits good correspondence with late twentieth century ocean observations from the north atlantic subpolar gyre spg region north atlantic heat content anomalies from the dp ensemble correlate highly with those from the core ia simulation after correcting for a drift bias in particular theobservedlarge rapid rise in spgheatcontentin themid 1990sis successfullypredicted in the ensemble initialized in january of 1991 a budget of spg heat content from the core ia experiment sheds light on the origins of the 1990s regime shift and it demonstrates the extent to which low frequency changes in ocean heat advection related to the atlantic meridional overturning circulation dominate temperature tendencies in this region similar budgets from the dp ensembles reveal varying degrees of predictive skill in the individual heat budget terms with large advective heat flux anomalies from the south exhibiting the highest correlation with core ia the skill of the dp in this region is thus tied to correct initialization of ocean circulation anomalies while external forcing is found to contribute negligibly and for incorrect reasons to predictive skill in this region over this time period

occurrence and field relationships of ultrahigh pressure metagranitoid and coesite eclogite in the su lu terrane eastern china coesite eclogite is associated with metagranitoid in a 50 100 m 2 outcrop within the regionally developed amphibolite facies su lu orthogneiss primary intrusive relationships between the metagranitoid and basic rocks and bulk chemistry analyses show that together they represent a composite igneous body that has subsequently been strongly deformed and metamorphosed the presence of rutile sodie pyroxene corona garnet and possible pseudomorphs after coesite all suggest very high pressures of metamorphism in the metagranitoid this is the first documented occurrence of ultrahigh pressure uhp metagranitoid outside of the european alps the existence of uhp metagranitoid shows that low density of rocks does not necessarily prevent subduction to mantle depths even at peak metamorphic conditions the uhp composite igneous body reported here would have a bulk density less than the mantle buoyancy forces may therefore have been important in the early exhumation of this unit other outcrops of coesite eclogite in the su lu region may also have been originally metamorphosed along with low density granitoid rocks

influence of magmatic hydrothermal activity on brine evolution in closed basins searles lake california evaporites in a 700 m long core km 3 from searles lake california preserve a record of the chemical evolution of inflow waters chemical analyses of fluid inclusions in halite and evaporite minerals show that the major ion composition of inflow waters to searles lake was changed by distant hydrothermal activity associated with magmatism at long valley caldera between 1 27 and 1 0 m y ago below core depths of 291 m the evaporites consist of ca bearing sulfates anhydrite glauberite and halite fluid inclusions in the halite show that parent waters were na cl so42 rich waters above 291 m the evaporites include sodium carbonates pirssonite trona and halite and fluid inclusion brines are na k hco3 co32 cl so42 rich these fluctuations in mineralogy and brine chemistry document an alkalinity spike beginning between 1 27 and 1 0 ma when inflow waters to searles lake crossed the caco3 chemical divide and began to produce alkaline brines that precipitated trona upon evaporation the owens river is a modern chemical analog for inflow water into searles lake beginning between 1 27 ma and 1 0 ma a major contributor of solutes to the owens river is hot creek in long valley caldera which is fed by hydrothermal springs with high alkalinity from magmatically derived co2 the timing of magmatism in owens valley and the appearance of sodium carbonate minerals in core km 3 suggest a causal relationship volcanism and hydrothermal activity provided co2 and elevated alkalinity to searles lake inflow waters 0 5 0 2 m y before the eruptions that formed the bishop tuff and long valley caldera

paleoenvironmental setting mechanism and consequence of massive organic carbon burial in the permian junggar basin nw china abstract the junggar basin in northwestern china is a typical walled sedimentary basin that has a prolonged basin evolution history from the paleozoic to cenozoic and is rich in petroleum resources permian strata reach thousands of meters in thickness and have been intensively studied for their record of regional tectonics and paleoenvironments they have also been exploited for oil and gas for the past several decades in this paper we summarize perspectives on tectonic evolution stratigraphic framework sedimentary environments and the paleoclimate of the permian junggar basin and the adjacent turpan basin further we discuss the mechanism and consequences of massive organic carbon burial based on a compilation of published radiometric dating datasets an updated chronostratigraphic framework was proposed for the junggar basin this framework constrains the ages of two main petroleum source intervals the fengcheng formation and the lucaogou and equivalent formations as early permian and middle permian respectively although a global warming and drying trend was present throughout the permian period the regional climate over the junggar basin was drier in early permian and more humid in the middle late permian with short term climatic fluctuations during the deposition of the two petroleum source intervals dry and temperate climate prevailed and evaporative lacustrine environment dominated organic matter enrichment was promoted by stable salinity stratification and limited dilution by inorganic sediments leading to one of the richest lacustrine source rock deposits in the world the average organic carbon burial rates were 11 2 gc m2 yr for the lucaogou formation and 3 5 gc m2 yr for the fengcheng formation lower than the average organic carbon burial rate in modern lakes however considering the large areas of global tectonic lakes in the permian period organic carbon burial in lacustrine environments could act as a significant carbon sink and impact the global carbon cycle and climate evolution

the role of attenuation in the formation of the railroad valley structural basin east central nevada detachment control of petroleum reservoirs the eastern boundary of railroad valley has long been considered a large displacement steep normal fault by mapping a low angle fault called the white pine detachment wpd from the ranges into the valley we show that steep normal faulting was not a significant process in the formation of railroad valley the wpd or its equivalent extends throughout the white pine and grant ranges as shown by mapping of previous authors well data show that it is also present in railroad valley our structure contour map of the wpd based on surface and subsurface data shows that the wpd dips uniformly from the ranges into railroad valley and is not displaced significantly by high angle faulting even if high angle faulting were assumed the maximum displacement consistent with the data would be 2000 ft 610 m much smaller than the total structural relief of at least 16 000 ft 4880 m between the grant range and the adjacent valley structural elevations in the valley are low because the paleozoic section has been greatly attenuated a related contribution to structural relief is uplifting of the ranges caused by diapiric emplacement of plutons in response to tectonic unloading the wpd is only one of many detachments in railroad valley we propose that most or all of the oil reservoirs are in attenuated brittle blocks between detachments seals are provided by detachments or by the discontinuous nature of associated fracturing attenuation by juxtaposing hot infrastructure rocks with rocks that normally occur thousands of feet above the granitic and metamorphic basement may have contributed to maturation of source rocks begin page 1154

petroleum geology of cretaceous tertiary rift basins in niger chad and central african republic this overview of the petroleum geology of rift basins in niger chad and central african republic car is based on exploration work by exxon and partners in the years 1969 1991 the work included 50 000 km of modern reflection seismic 53 exploration wells 1 000 000 km2 of aeromagnetic coverage and about 10 500 km of gravity profiles the results outline ten cretaceous and tertiary rift basins which constitute a major part of the west and central african rift system wcars the rift basins derive from a multiphased geologic history dating from the pan african approximately 750 550 ma to the holocene main rifting was probably caused by the stretching and subsidence of african crustal blocks during the breakup of gondwana in the early cretaceous and by r activated plate movements in the early tertiary wcars in the study area is divided into the west african rift subsystem was and the central african rift subsystem cas was basins in niger and chad are chiefly extensional and are filled by up to 13 000 m of lower cretaceous to holocene continental and marine clastics the basins contain five oil 19 43 api and two oil and gas accumulations in upper cretaceous and eocene sandstone reservoirs the hydrocarbons are sourced and sealed by upper cretaceous and eocene marine and lacustrine shales the most common structural styles and hydrocarbon traps usually are associated with normal fault blocks cas rift basins in chad and car are extensional and transtensional and are filled by up to 7500 m of chiefly lower cretaceous continental clastics the basins contain eight oil 15 39 api and one oil and gas discovery in lower and upper cretaceous sandstone reservoirs the hydrocarbons are sourced by lower cretaceous shales and sealed by interbedded lacustrine and flood plain shales structural styles range from simple fault blocks through complex flower structures the main hydrocarbon traps are in contractional anticlines geological conditions favor the discovery of potentially commercial volumes of oil in wcars basins of niger chad and car

a genetic model for na carbonate mineral precipitation in the miocene beypazari trona deposit ankara province turkey abstract the miocene beypazari trona deposit in central anatolia turkey with estimated reserves of 250 million of tons of soda ash sodium carbonate is the second largest na carbonate deposit in the world petrographic observations of sodium carbonate evaporites from basin center cores show that the evaporites and associated minerals underwent significant early diagenetic mineral transformations in the beypazari basin trona pirssonite and nahcolite are the major evaporite minerals with subordinate bradleyite shortite and thenardite pirssonite occurs in organic rich muds oil shales pirssonite is not a primary mineral but rather appears to have formed diagenetically from displacive gaylussite trona precipitated subaqueously in lake waters and as interstitial phase in playa muds nahcolite is a later diagenetic mineral replacing both trona and pirssonite beds evaporite minerals are closely related to pyrite in oil shales and are also associated with diagenetic silicates mg rich smectites zeolites k feldspar searlesite and idiomorphic quartz formed by reaction of alkaline brines with pyroclastic deposits the proposed sedimentary model involves an alkaline lake in which water depth fluctuated from deep perennial meromictic stratified stages to shallow ephemeral playa lake stages lake margin clastic deposits are absent in the center of the basin wherein na carbonate minerals were formed suggesting the prevalence of a groundwater regime during drawdown events

sapphirine and ti clinohumite in ultra high pressure garnet pyroxenite and eclogite from dabie shan china sapphirine occurs as inclusions along with clinochlore enstatite talc corundum gedrite hornblende and phlogopite in millimetre size garnets from the orthopyroxenites in a 50 m thick mafic ultramafic lens in dabie shan in china the lens enclosed by felsic gneiss is made up of metre scale intercalation of garnet or thopyroxenite garnet clinopyroxenite eclogite and gneiss the equilibrium conditions of the matrix minerals as determined from the fe mg exchange equilibria between garnet and orthopyroxene and al solubility in orthopyroxene were 740 50 c temperature and over 40 kbar pressure pressures of over 28 kbar are also indicated by inclusions of quartz pseudomorphs after coesite in garnet from the eclogites phase relations among the inclusion minerals on the other hand indicate similar temperatures of 730 30 c but much lower pressures of 4 2 kbar the mafic ultramafic lens was therefore not a direct mantle fragment but was probably a low pressure cumulate in the upper crust the early granulite facies metamorphism was most likely part of a precambrian event genetically unrelated to the triassic ultra highpressure metamorphism ti clinohumite occurs in garnet orthopyroxenites as a matrix mineral and appears to have been stable during the ultra high pressure metamorphism its stability was controlled by the fluorine fugacity as documented by its reaction textures with olivine

fe2 mg partitioning experiments between orthopyroxene and spinel using ultrahigh temperature granulite from the napier complex east antarctica

immiscibility in ca amphiboles the literature data of nine different occurrences of coexisting mineral pairs of ca amphibole have been studied and the bulk vectors spanning the miscibiuty gap derived the additive component is always impure mg tremolite accompanied by some glaucophane and cummingtonite component the four major exchange components required to describe the compositional variation in coexisting mineral pairs are the edenite ed tschermaki ts femg j and f tschermaks fets vector trivalent iron is postulated on the basis of excess charges in the bulk vector the size of which coincides with residuals in al si fe and mg the four cations have equal sizes forming the vector ft al mg jsi j this distribution scheme is consistent for all the different occurrences and sets the basis for a comparison deviations from the scheme would radically complicate the proposed exchange pattern the ratio t ed in most mineral samples fluctuates between one and two projection of the data points in the vector space ts ed onto the line 1ed 2ts tr hbl or 1ed 1ts tr prg provides the projected tremolite content x y 7 x w or 1x j this parameter applied to coexisting pairs and plotted against the ratio mg mg fe shows some characteristic features about the miscibiuty gap in the mg pure system the solvus is almost symmetric and located in the temperature range between 800 and 870 c small amounts 0 10pfu offe in the m 4 sites and replacing ca have a dramatic effect forcing the solvus to much lower temperatures of 650 c an increase in the ratio fe fc mg causes a shift of the solvus towards more tremolitic compositions with temperatures 500 650 c the maximum asymmetry of the solvus is reached where the al poor member tremolite has a composition of x y 10 and mg mg fe 0 6 the corresponding al rich member has x 0 5 and mg mg fe 0 4 an anomaly of the solvus is observed at mg mg fe 0 8 it manifests as a kind of highly asymmetric sub gap in the tremolite rich composition range this is explained by the partitioning of fe into the single m 3 site and is characterized by a thermal hump to 650 700 c

preliminary phanerozoic polar wander paths for the north and south china blocks polar wander paths for the north and south china blocks suggest that 1 both were parts of gondwana in the palaeozoic 2 the north china block accreted to siberia in the late permian and 3 the south china block accreted to the north china block in the middle triassic to the early jurassic comparison of the polar wander path for the south china block with that for northern eurasia suggests that relative motion of over 4 000 km has occurred between them

a model of palaeozoic obduction and exhumation of high pressure low temperature rocks in the southern urals abstract a new evolutionary geodynamic model of devonian continental subduction and exhumation of high pressure low temperature metamorphic rocks in the southern urals is proposed based on the results of physical modelling geological and geophysical data and on the comparison of this belt with other orogens the model includes the following principal phases 1 closure of the western uralian ocean by eastward intraoceanic subduction associated with the magnitogorsk volcanic arc 2 subduction of the european continental margin causing failure of the overriding plate in the arc area along a fault dipping eastward under the arc 3 subduction into the mantle of the fore arc block together with the underlying continental crust and sedimentary layer the sedimentary cover as well as the crustal and mantle fragments of this block are scraped off and accreted in front of and under the arc the continental crust shielded from the hot mantle by the fore arc block subducts to depths of more than 150 km remaining at a relatively low temperature the crust then fails at depths of several tens of kilometres 4 the subducted crustal slice starts to rapidly rise and intrude the interplate zone scraping and pushing up the sediments and slivers of the oceanic fore arc block previously dragged down to different depths 5 exhumation of the rising high pressure low temperature rocks within the uraltau dome separating the subduction accretionary complex from the magnitogorsk arc the eastern border of the uraltau dome coincides with the main uralian fault this fault represents a complex suture zone which at the stage of deep crustal subduction was associated with a major thrust subduction fault and at the exhumation stage with a major normal fault corresponding to the upper surface of the rising crustal sedimentary body

tectonics of the qinling belt build up and evolution of eastern asia the structure and history of the qinling range which separates the north and south china cratons are a key to the tectonic evolution of eastern asia the mountain range is composed of a northern palaeozoic belt and a southern mesozoic belt the palaeozoic orogeny probably involved the closure of an oceanic basin along a north dipping subduction zone followed by south vergent obduction of ophiolites and intracontinental thrusting during the devonian the mesozoic belt appears to be the product of purely intracontinental shallow crustal deformation over a large decollement with at least 100 km of horizontal transport since the devonian both belts have been sliced by huge east west sinistral strike slip faults

locally and remotely forced subtropical amoc variability a matter of time scales mechanisms driving the north atlantic meridional overturning circulation amoc variability at low frequency are of central interest for accurate climate predictions although the subpolar gyre region has been identified as a preferred place for generating climate timescale signals their southward propagation remains under consideration complicating the interpretation of the observed time series provided by the rapid climate change meridional overturning circulation and heatflux array western boundary time series rapid mocha wbts program in this study we aim at disentangling the respective contribution of the local atmospheric forcing from signals of remote origin for the subtropical low frequency amoc variability we analyze for this a set of four ensembles of a regional 208s 558n eddy resolving 1 128 north atlantic oceanic configuration where surface forcing and open boundary conditions are alternatively permuted from fully varying realistic to yearly repeating signals their analysis reveals the predominance of local atmospherically forced signal at interannual time scales 2 10 years whereas signals imposed by the boundaries are responsible for the decadal 10 30 years part of the spectrum due to this marked timescale separation we show that although the intergyre region exhibits peculiarities most of the subtropical amoc variability can be understood as a linear superposition of these two signals finally we find that the decadal scale boundary forced amoc variability has both northern and southern origins although the former dominates over the latter including at the site of the rapid array 26 58n

a role of the atlantic ocean in predicting summer surface air temperature over north east asia we assess the ability of the depresys3 prediction system to predict the summer jjas surface air temperature over north east asia depresys3 is based on a high resolution ocean atmosphere coupled climate prediction system 60 km in the atmosphere and 25 km in the ocean which is full field initialized from 1960 to 2014 26 start dates we find skill in predicting surface air temperature relative to a long term trend for 1 and 2 5 year lead times over north east asia the north atlantic ocean and eastern europe depresys3 also reproduces the interdecadal evolution of surface air temperature over the north atlantic subpolar gyre and north east asia for both lead times along with the strong warming that occurred in the mid 1990s over both areas composite analysis reveals that the skill at capturing interdecadal changes in north east asia is associated with the propagation of an atmospheric rossby wave which follows the subtropical jet and modulates surface air temperature from europe to eastern asia we hypothesise that this circumglobal teleconnection pattern is excited over the atlantic ocean and is related to atlantic multi decadal variability and the associated changes in precipitation over the sahel and the subtropical atlantic ocean this mechanism is robust for the 2 5 year lead time for the 1 year lead time the pacific ocean also plays an important role in leading to skill in predicting sat over northeast asia increased temperatures and precipitation over the western pacific ocean was found to be associated with a pacific japan like pattern which can affect east asia s climate

a multimodel comparison of centennial atlantic meridional overturning circulation variability a mechanism contributing to centennial variability of the atlantic meridional overturning circulation amoc is tested with multi millennial control simulations of several coupled general circulation models cgcms these are a substantially extended integration of the 3rd hadley centre coupled climate model hadcm3 the kiel climate model kcm and the max plank institute earth system model mpi esm significant amoc variability on time scales of around 100 years is simulated in these models the centennial mechanism links changes in the strength of the amoc with oceanic salinities and surface temperatures and atmospheric phenomena such as the intertropical convergence zone itcz 2 of the 3 models reproduce all aspects of the mechanism with the third mpi esm reproducing most of them a comparison with a high resolution paleo proxy for sea surface temperatures ssts north of iceland over the last 4 000 years also linked to the itcz suggests that elements of this mechanism may also be detectable in the real world

the role of excess co2 in the formation of trona deposits abstract the prevailing theory for the formation of trona na3 co3 hco3 2 h2o relies on evaporative concentration of na hco 3 water produced by silicate hydrolysis of volcanic rock or volcaniclastic sediments given the abundance of closed drainage basins dominated by volcanics it is puzzling that there are so few trona deposits and present day lakes that would yield dominantly na co3 minerals upon evaporation groundwater in the san bernardino basin southeastern arizona usa and northeastern sonora mexico would yield mainly na co3 minerals upon evaporation but waters in the surrounding basins would not analysis of the chemical evolution of this groundwater shows that the critical difference from the surrounding basins is not lithology but the injection of magmatic co2 many major deposits of trona and na co3 type lakes appear to have had excess co2 input either from magmatic sources or from the decay of organic matter it is proposed that along with the presence of volcanics addition of excess co2 is an important pre condition for the formation of trona deposits

into the forbidden zone very low temperatures at high pressures have long been believed to constitute a forbidden zone not realized in earth however recent studies of ultrahigh pressure uhp terranes indicate that these rocks have experienced such forbidden zone conditions liou et al discuss the implications of these observations for plate tectonics

spatial and temporal variability of the chemistry of the shallow groundwater in the alluvial fan area of the luanhe river north china groundwater in the alluvial fan area of the luanhe river north china was monitored every 2 months for a year subsequently the temporal and spatial variability in the hydrochemical characteristics of the water was investigated using hierarchical cluster analysis hca and a trilinear piper diagram it is found that the spatial variability in the groundwater composition from different monitoring wells has obvious differences even if the distance between many of the wells is small also the difference in the ion concentration was found to be up to fivefold for the same monitored well research has indicated that the groundwater s chemical characteristics are mainly controlled by soil type the amount of precipitation the luanhe river the groundwater and human factors the thickness and continuous distribution of clay influences the velocity and ion exchange rate of the groundwater flow this results in the amount of total dissolved solids in the groundwater increasing from upstream to downstream in the flood season june july and august ion concentration gradually decreases as a result of the increased recharging of the groundwater due to precipitation classification using hca indicates that the samples can be clustered into different groups according to correlation coefficients also the chemical composition of the water from monitoring wells near the luanhe river is approximately consistent with that from the luanhe river this implies that the samples have some compositions resulted from the mixing of groundwater and river water the piper diagram indicates that ca2 mg2 and hco3 ions are the predominant ones present i e the type of groundwater is of the ca mg hco3 type

eclogites preserved as pebbles in jurassic conglomerate dabie mountains china abstract two types of eclogite pebbles were discovered in middle to upper jurassic conglomerates from the hefei basin north of the dabie ultrahigh pressure uhp terrain china type a eclogite pebbles are characterized by idioblastic garnet with well preserved chemical zonation si content in phengite is lower than 3 5 per formula unit pfu the maximum metamorphic pressure is lower than 2 5 gpa and the temperature is below 600 c type b eclogite pebbles contain coesite pseudomorphs in xenoblastic garnet si content in phengite is higher than 3 5 pfu the maximum metamorphic pressure is 2 8 4 0 gpa at 700 c indicating uhp metamorphism types a and b eclogite pebbles are comparable with eclogites occurring in the southern portion of the dabie uhp terrain based on the petrologic similarities and northeastwards directed paleocurrents we infer that the eclogite pebbles were eroded from the dabie uhp terrain sandstones containing detrital phengite with si content higher than 3 5 pfu are also derived from uhp rocks these petrologic and stratigraphic data place time constraints on exhumation and erosion history of the dabie uhp terrain

hydrogeochemistry of the middle rio grande aquifer system fluid mixing and salinization of the rio grande due to fault inputs abstract deeply derived fluids influence river and groundwater hydrochemistry at the socorro constriction in the central new mexico rio grande rift new hydrochemical transects in the rio grande rift provide three dimensional perspectives on sources contributing to surface and groundwaters in addition to abrupt salinity increases in the rio grande major and trace ion chemistry 18o d 13c 87sr 86sr 3h and 3he 4he variations in springs and wells across the rift are best explained by mixing of deeply derived endogenic fluids containing both mantle and crustal inputs with shallow groundwater endogenic fluids ascend along rift bounding and intra rift faults and can cause increased salinity accompanied by an increase in metals and overall degradation of water quality our data reinforce models that attribute a downstream increase in salinity to geological not agricultural influences hydrochemical mixing of endogenic waters along faults in shallow aquifers has a major influence on groundwater and surface water quality and variability in arid tectonically active regions with important ramifications for water management

empirical calibration of the clinopyroxene garnet magnesium isotope geothermometer and implications the large equilibrium mg isotope fractionation between clinopyroxene and garnet observed in eclogites makes it a potential high precision geothermometer but calibration of this thermometer by natural samples is still limited here we report mg isotopic compositions of eclogite whole rocks as well as mg and o isotopic compositions of clinopyroxene and garnet separates from 16 eclogites that formed at different temperatures from the dabie orogen china the whole rock 26mg values vary from 1 20 to 0 10 among them 11 samples display limited 26mg variations from 0 36 to 0 17 similar to those of their protoliths the mineral separates exhibit very different 26mg values from 0 39 to 0 39 for clinopyroxenes and from 1 94 to 0 81 for garnets the clinopyroxene garnet mg isotope fractionation 26mgclinopyroxene garnet 26mgclinopyroxene 26mggarnet varies from 1 05 to 2 15 the clinopyroxene garnet o isotope fractionation 18oclinopyroxene garnet 18oclinopyroxene 18ogarnet varies from 1 01 to 0 98 equilibrium mg isotope fractionation between clinopyroxene and garnet in the investigated samples is selected based on both the 26mgclinopyroxene versus 26mggarnet plot and the state of o isotope equilibrium between clinopyroxene and garnet the equilibrium 26mgclinopyroxene garnet and corresponding temperature data obtained in this study together with those available so far in literatures for natural eclogites are used to calibrate the clinopyroxene garnet mg isotope thermometer this yields a function of 26mgclinopyroxene garnet 0 99 0 06 106 t2 where t is temperature in kelvin the refined function not only provides the best empirically calibrated clinopyroxene garnet mg isotope thermometer for precise constraints of temperatures of clinopyroxene and garnet bearing rocks but also has potential applications in high temperature mg isotope geochemistry

quaternary history of the lake magadi basin southern kenya rift tectonic and climatic controls abstract sediments from the magadi basin south kenya rift preserve a one million year palaeoenvironmental record that reflects interactions between climatic volcanic and tectonic controls climate changes that impacted sedimentation include wet dry cycles on variable timescales and an overall progressive trend towards greater aridity volcanic influences involved inputs of tephra to the basin significant inflow of geothermal fluids and the effects of weathering erosion and transportation of clastics from trachyte and basalt terrains tectonic controls which were often step like reflect the influence of faults that provided pathways for fluids and which controlled accommodation space and drainage directions intensified aridity and evaporative concentration resulted in salinity and ph increasing with time which led to a change from calcite deposition in mildly saline lakes before 380 ka to the later formation of zeolites from reactions of volcaniclastic debris with highly alkaline lake and pore water after 105 ka hyperalkaline conditions led to trona accumulation and increasingly variable rare earth elements rees the presence of mixed saline and freshwater diatom taxa between 545 and 16 ka indicates climate variability and episodic inputs of fresh water to saline lakes calcrete formed in lake marginal settings during semi arid periods tectonic controls operated independently of climate but they interacted together to determine environmental conditions aquatic deposition was maintained during periods of increasing aridity because fault controlled ambient and geothermal springs continued to flow lakewards this recharge in turn limited pedogenesis palaeosols are common in other rift floor sequences trona formed when aridity and evapoconcentration increased but its precipitation also reflects increased magmatic co2 that ascended along faults basin fragmentation and north south fractures caused loss of cross rift east west drainage from rift marginal basalts resulting in reduced transition metals after 545 ka the magadi basin demonstrates how a careful reconstruction of these complex tectono climatic interactions is essential for accurate palaeoenvironmental reconstruction in continental rifts and in other tectonic settings

the green river salt mystery what was the source of the hyperalkaline lake waters abstract bicarbonate rich source waters were needed to form the largest sodium carbonate evaporite deposits in the geologic record the early and middle eocene green river trona nahco 3 na 2 co 3 2h 2 o in the bridger basin wyoming and nahcolite nahco 3 in the piceance creek basin colorado large modern and pleistocene trona deposits are associated with magmatic activity and na hco 3 rich hydrothermal inflow waters either within the depositional basin lake magadi kenya or at great distances searles lake california no evidence exists for magmatic sources of co 2 near the green river formation several regional volcanic centers were active 300 km or more to the north but drainage reconstructions show that waters from these areas did not discharge into the green river formation lakes during evaporite deposition alternatively na hco 3 rich waters could have drained northwestward from the colorado mineral belt to the bridger basin via the proposed aspen river a river originating in the colorado mineral belt sawatch uplift could also have provided source waters to the piceance creek basin field evidence however has not yet documented these flow paths and specific eocene volcanic centers and hydrothermal source areas have yet to be identified other explanations for the elevated alkalinities needed to form thick sodium carbonate evaporites include accelerated silicate mineral weathering rates during a period of high atmospheric p co 2 and eocene warmth amplified chemical weathering may explain the cluster of sodium carbonate evaporites in the usa and china that are eocene in age another possible source of alkalinity to the green river lakes is fault controlled upward migration of a deep sedimentary source of co 2 the large amount of organic matter preserved in the evaporitic wilkins peak and parachute creek members raises the possibility that decay of organic matter in green river lakes could have added sufficient co 2 and alkalinity to produce waters capable of precipitating trona and nahcolite although such degradation of organic matter has not created hyperalkalinity in modern lakes

integrated geophysical geochemical and hydrogeological investigation of shallow groundwater resources in parts of the ikom mamfe embayment and the adjoining areas in cross river state nigeria information generated from geophysical geochemical and hydrogeological data has been used in assessing the groundwater resource potential quality and usability and in mapping flow directions within the shallow subsurface of the mamfe embayment cross river state nigeria the electrical resistivity technique in which the schlumberger s vertical electrical sounding field procedure has been adopted was the geophysical method employed lithology logs from drilling records discharge rates static water level information were the hydrogeological information utilized while the geochemical techniques involve analyses of water samples apparent resistances were measured using different resistivity meters including oyo mcohm model 2115 abem terrameter sas300b and sas1000 models and igis ssp ats mrp model with maximum current electrode separation reaching 1 km in some communities geological information was used as control in the modelling and interpretation of all geophysical data the physico chemical parameters of the water samples from the different water sources in the area were determined using different analytical techniques and in some cases by in situ direct measurement of some parameters measured values of electrical conductivity static water level available aquifer discharge information and calculated sar and na were integrated into the geophysical and hydrogeological results the shallow subsurface of the area is segmented into four hydrogeological provinces crystalline basement province cbp cross river plain province crpp nkporo afikpo shales province nasp and alluvial buried river province abrp with localized groundwater flow patterns results indicated that the alluvial discharge rate of 3 83 l s fractured sandstone discharge rate of 2 43 l s and basement discharge rate of 1 80 l s aquifers are more yielding than the aquifers in areas covered with deformed shales discharge rate of 0 62 l s and siltstone aquifers discharge rate of 0 97 l s the aquifer horizons are inhomogeneous and anisotropic with topography and lithology exerting significant influence on groundwater flow direction however there appears to be some high yielding aquifers at depths greater than 100 m in the crpp areas although researches on their distribution are still ongoing precipitation is the major source of recharge and the water is enriched with na k ca2 mg2 text hco 3 cl text so 4 2 and text no 3 throughout the year graphical analyses of hydrochemical data using piper and stiff diagrams show that ca mg co3 hco3 is the dominant water facies results from ec sar and na show that the water is fresh and belongs to the good to excellent class and is therefore suitable for domestic agricultural and industrial use

ultrahigh ϵnd eclogites from an ultrahigh pressure metamorphic terrane of china the su lu ultrahigh pressure uhp metamorphic terrane is part of the qinling dabie suture zone formed by the collision between the sino korean and yangtze cratonic blocks geochemical and isotopic investigation of the uhp metamorphic rocks has revealed a spectacular history for some eclogitic rocks retrograded coesite bearing eclogites from the weihai area in the eastern end of the su lu terrane have recorded an extraordinary nd isotopic growth with a world record high nd value of 264 range 170 to 264 such isotopic characteristics are consistent with the observed extreme lree fractionation and very high sm nd ratios the sm nd isotopic data allow us to calculate the minimum age of protolith formation at 1 7 ga assuming their evolution from a depleted or a chondritic mantle geochemical data indicate that the eclogite protoliths were of basaltic compositions originally but underwent metasomatism water rock interaction at high pressures and temperatures leading to the present apparent andesitic composition and extreme lree depletion this process took place in the proterozoic 1 7 ga and was not related to the mesozoic continental collision and ultrahigh pressure metamorphism at 210 220 ma ago because of a protracted retrograde metamorphism garnet sm nd systems were not closed until 160 ma ago 50 ma after the peak eclogite metamorphism this implies that the exhumation history is significantly different in different parts of the dabie and su lu uhp metamorphic terranes from geochemical analyses and isotopic age determinations we argue that at least two ancient tectonic events in the middle and late proterozoic can be identified prior to the last mesozoic continental collision and accompanying uhp metamorphism in the su lu and dabie terrane