isotopic test of a thermally driven intraplate orogenic model australia a recently proposed model for intraplate orogenesis couples long term self heating of basement rocks by radioactive decay with thermal blanketing by overlying sedimentary deposits this model has been tested in one of the type areas in central australia the proterozoic musgrave complex which was reworked in an early cambrian orogeny we have determined the source of the pre orogenic and postorogenic sediments in the amadeus basin immediately to the north of the reworked basement including the fan deposits associated with uplift comprising uluru ayers rock and kata tjuta olgas detrital zircon age populations indicate that all basin sediments were derived from the musgrave complex which was therefore emergent rather than covered by sediments as required by the model in the basement the preservation of mesoproterozoic mica ages during transpressive burial to depths of 40 km ca 550 ma indicates that the associated thermal pulse was short lived not long lived as envisaged in the model we conclude therefore that the thermal blanketing model is inconsistent with the isotopic data and that the localization of deformation in intracratonic settings is associated with regions of contrasting strengths in central australia these are along the margins of the amadeus basin with the musgrave complex and arunta inlier

on the interpretation of caribbean paleo temperature reconstructions during the younger dryas 1 a conundrum exists regarding whether the sea surface temperatures decreased or increased over the southern caribbean and the western tropical atlantic region during the younger dryas when the north atlantic cooled substantially and the atlantic thermohaline circulation was weakened significantly despite the proximity of core locations some proxy reconstructions record a surface cooling while others indicate a warming we suggest that this seemingly paradoxical finding may at least partially be attributed to the competing physical processes that result in opposing signs of temperature change in the region in response to weakened north atlantic meridional overturning circulation our coupled ocean atmosphere model experiments indicate that the temperature response over the southern caribbean and western tropical atlantic regions is complex and can vary considerably in small spatial scales depending on the nature of physical processes that dominate

the sensitivity of the climate response to the magnitude and location of freshwater forcing last glacial maximum experiments abstract proxy records indicate that the locations and magnitudes of freshwater forcing to the atlantic ocean basin as iceberg discharges into the high latitude north atlantic laurentide meltwater input to the gulf of mexico or meltwater diversion to the north atlantic via the st lawrence river and other eastern outlets may have influenced the north atlantic thermohaline circulation and global climate we have performed last glacial maximum lgm simulations with the ncar community climate system model ccsm3 in which the magnitude of the freshwater forcing has been varied from 0 1 to 1 sv and inserted either into the subpolar north atlantic ocean or the gulf of mexico in these glacial freshening experiments the less dense freshwater provides a lid on the ocean water below suppressing ocean convection and interaction with the atmosphere above and reducing the atlantic meridional overturning circulation amoc this is the case whether the freshwater is added directly to the area of convection south of greenland or transported there by the subtropical and subpolar gyres when added to the gulf of mexico the amoc reduction is less for the smaller freshwater forcings but is not linear with the size of the freshwater perturbation the recovery of the amoc from a slow state is 200 years for the 0 1 sv experiment and 500 years for the 1 sv experiment for glacial climates with large northern hemisphere ice sheets and reduced greenhouse gases the cold subpolar north atlantic is primed to respond rapidly and dramatically to freshwater that is either directly dumped into this region or after being advected from the gulf of mexico greenland temperatures cool by 6 8 c in all the experiments with little sensitivity to the magnitude location or duration of the freshwater forcing but exhibiting large seasonality sea ice is important for explaining the responses the northern hemisphere high latitudes are slow to recover antarctica and the southern ocean show a bipolar response with warming and reduced sea ice this warming continues after the cessation of the freshwater forcing and shows a dependence on the duration of the freshwater forcing equatorward of the expanded sea ice the simulated temperature and salinity anomalies are sensitive to the amount of colder and fresher waters that are advected out of the subpolar north atlantic in the tropical atlantic the recovery of the intertropical convergence zone itcz from its more southerly position during the freshwater forcing is much more rapid than the recovery of the amoc and is more related to the recovery of low latitude surface temperatures than greenland temperature or sea ice these results have implications for using proxy records as indirect measures of the amoc

links between salinity variation in the caribbean and north atlantic thermohaline circulation variations in the strength of the north atlantic ocean thermohaline circulation have been linked to rapid climate changes1 during the last glacial cycle through oscillations in north atlantic deep water formation and northward oceanic heat flux2 3 4 the strength of the thermohaline circulation depends on the supply of warm salty water to the north atlantic which after losing heat to the atmosphere produces the dense water masses that sink to great depths and circulate back south2 here we analyse two caribbean sea sediment cores combining mg ca palaeothermometry with measurements of oxygen isotopes in foraminiferal calcite in order to reconstruct tropical atlantic surface salinity5 6 during the last glacial cycle we find that caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2 4 and 6 and lower salinities during the warm stages 3 and 5 covarying with the strength of north atlantic deep water formation7 at the initiation of the bolling allerod warm interval caribbean surface salinity decreased abruptly suggesting that the advection of salty tropical waters into the north atlantic amplified thermohaline circulation and contributed to high latitude warming

the basil cu co deposit eastern arunta region northern territory australia a metamorphosed volcanic hosted massive sulphide deposit abstract the basil cu co deposit harts range central australia is hosted by the riddock amphibolite a sequence that has been metamorphosed at upper amphibolite to granulite facies conditions at 480 460 ma larapinta event and subsequently reworked at amphibolite facies conditions 450 300 ma as a result many of the primary mineralization textures and other features that could characterise ore genesis have been obliterated however preserved textures and mineral relationships in the mineralized zone allow some constraints to be placed on the genetic history of the deposit using mineralogical petrographic and geochemical studies of host rocks and sulphides results of this study permit at least two genetic models to be ruled out firstly whole rock geochemistry and garnet compositions suggest that the deposit is not a skarn system secondly the lack of any significant ni signature and the presence of abundant zircons in the host amphibolite indicating that not all host rocks are mafic in composition and or magmatic in character make an orthomagmatic ni cu pge system unlikely alternatively basil is assigned to a volcanic hosted massive sulphide vhms style of mineralization formed on the seafloor within basaltic and sedimentary host rocks typical of deposits occurring in such settings the lack of a recognisable hydrothermal alteration zone is consistent with either destruction of the alteration zone during metamorphism or detachment of the ore from alteration during later deformation the occurrence of sulphide inclusions within garnet and amphibole indicates that the sulphides must be syn metamorphic or earlier partitioning of trace elements between pyrite and co existing pyrrhotite suggests that re crystallization occurred under equilibrium conditions the composition of sphalerite coexisting with pyrite and pyrrhotite indicates crystallization at pressures of at least 10 kbar consistent with peak metamorphism during the early ordovician larapinta event zr in titanite geothermometry indicates peak temperatures of 730 745 c

banded amphibolites of the harts range meta igneous complex central australia an early proterozoic basalt tonalite suite abstract a multistage petrogenesis is proposed for banded metabasaltic amphibolite and tonalite tectonically interlayered on a fine centimetre scale within upper and lower amphibolite sequences of the harts range meta igneous complex eastern arunta block central australia the basaltic amphibolites exhibit only slight rare earth element ree fractionation ce n yb n 2 5 and can be related by plagioclase clinopyroxene dominated low pressure fractional crystallisation in the tholeiitic trend early olivine removal from a moderately aluminous trace element impoverished tholeiitic picrite parent magma caused significant ni depletion in the evolved residual liquids that gave rise to the basaltic amphibolites the primary picritic melt was generated by high degrees 30 of hydrous partial melting of a depleted mantle source selectively re enriched in large ion lithophile lil elements chondrite normalised ree patterns for low al 2 o 3 tonalitic layers within the basaltic amphibolite units are moderately fractionated ce n yb n 3 3 7 3 and show significant negative eu anomalies ree modelling indicates that the precursors to the tonalitic rocks could have been generated by small degrees 10 of partial melting of a light rare earth element lree enriched basaltic parent with plagioclase clinopyroxene and minor hornblende comprising coexisting residual phases melting at relatively low p h 2 o the amphibolite sequence is interpreted as a complexly folded and metamorphosed bimodal basalt tonalite suite formed at an early proterozoic rifted continental margin or intra cratonic rift

african monsoonal precipitation modulated by interhemispheric temperature gradients the deglacial pattern of a high resolution alkenone derived temperature record from the southeastern tropical atlantic was compared with one from the northeastern subtropical atlantic during termination 1b surface waters in the eastern tropical atlantic 6 s reached modern temperatures whereas those in the subtropical northeastern atlantic 21 n were still considerably colder than today this asymmetrical warming may reflect meltwater induced reductions in the northward heat transport and helps to explain rapid changes in monsoonal precipitation over africa during the early holocene

high strain deformation and fluid infiltration diachronism of the middle crust new devonian permian alice springs ages 365 290 ma of shear zones in the strangways metamorphic complex central australia abstract the proterozoic granulite facies strangways metamorphic complex smc in the arunta region of central australia was partially hydrated during the devonian carboniferous 380 320 ma alice springs orogeny by amphibolite greenschist facies high strain deformation stable and radiogenic isotope analyses on coeval muscovite and biotite from shear zone samples of the smc were performed to analyse the composition and date the timing of fluid circulation and cooling stable isotope data 18 o and d indicate that in the south of the smc the source of fluids appear to be the thick successions of neoproterozoic heavitree quartzite while another source in the north and central part of the smc may be related to meteoric fluids the heterogeneous 18 o fluid and homogenous d fluid values for muscovite reflect changes in water rock ratios with initial high values in the south and lower in the north possibly suggesting a migration of fluids from south to north as indicated by the evolving 18 o fluid and homogenous d fluid values rb sr muscovite ages of 365 340 ma approximate the time of crystallization and fluid infiltration they also indicate that the shear zones were active at different times during the alice springs orogeny and that some were active prior to the peak carboniferous amphibolite facies metamorphism 40 ar 39 ar muscovite ages of 350 325 ma are mostly interpreted as cooling ages rb sr biotite ages of 335 290 ma are interpreted as cooling ages at 300 c sr closure temperature for biotite and extend the activity of the alice springs orogeny until the permian cooling histories of the wallaby knob and harry creek shear zones which serve as the tectonic boundaries of the smc to the north and south respectively indicate slow cooling 1 for c 30 ma 360 330 ma at both boundaries continuing until 290 ma in the western portion of the harry creek shear zone this slow cooling is associated with passive exhumation i e erosion rapid cooling 20 10 c ma 1 then occurred over c 10 ma 330 320 ma in the wallaby knob shear zone and in the east portion of the harry creek shear zone this change in cooling rate is associated with the combined initiation in the carboniferous of dextral and thrusting deformation by the pinnacles bore and erontonga shear zones

sediment transport near the break point associated with cross shore gradients in vertical eddy diffusivity sediment clouds entrained and mixed vertically into the water column at the breakpoint were observed to advect offshore with the return current following wave breaking at a natural beach an advection diffusion model is applied to this phenomenon providing for cross shore gradients in vertical eddy diffusivity within and beyond the surf zone which result in differential entrainment and settlement near the break point results indicate that the horizontal gradient in turbulent vertical sediment mixing can provide a significant mechanism for bar generation even if the surface gravity and infra gravity waves remain uncoupled quantitative estimates of the rate of bar accretion are obtained after calibrating the sediment transport model using field measurements of currents and suspended sediment loads in the absence of other processes accretion rates of order 20 mm hour associated with the horizontal gradient in vertical diffusivity are predicted on the offshore bar

neoarchaean metamorphic evolution of the yilgarn craton a record of subduction accretion extension and lithospheric delamination abstract the greater part of the metamorphic record of the yilgarn craton formed during a protracted middle neoarchaean orogenic cycle spanning from about 2750 to 2620 ma at least six distinct metamorphic events are defined by parageneses in different tectono stratigraphic settings this review characterizes the middle neoarchaean metamorphic response of the entire craton using large databases rock descriptions from 60 000 sites in government databases and 1040 pt determinations from all sources are used to construct metamorphic map patterns for each of these metamorphic events p t paths and timing of each metamorphic event are characterized using petrology and the well constrained pt determinations from this study n 287 combined with metamorphic age determinations from all sources n 114 the spatial patterns and metamorphic conditions of each event provides critical constraints on tectonic settings and changes in tectonics over 130 million years the record of metamorphism in conjunction with stratigraphic kinematic and magmatic constraints shows that the neoarchaean craton evolved from an accretionary crustal growth phase ma and m1 to thermal reworking of the crust during massive influx of granitic intrusions m2 and lithospheric extension after the termination of subduction m3 these events were followed by lithospheric delamination resulting in a craton wide diffusion delayed thermal pulse that coincided with renewed contraction m4 m1 metamorphism at 2748 19 2727 8 and 2706 10 ma experienced high p moderate t hairpin clockwise p t paths during burial of magmatic arc margins during terrane accretion events m2 regional contact type metamorphism at 2671 6 ma tracked low p moderate t clockwise p t paths in back arc settings during voluminous felsic magmatism related to shallow subduction m3 metamorphism at 2656 5 ma experienced low p moderate t anticlockwise p t paths in post volcanic rift basins formed during lithospheric extension m4 metamorphic peaks at 2644 4 and 2629 7 ma experienced low p high t clockwise p t paths during regional scale thermal pulses resulting from lower crust and mantle lithosphere delamination at 2665 2668 ma

selective organic matter preservation in burn down turbidites on the madeira abyssal plain 1 oxidized intervals of five organic rich madeira abyssal plain map turbidites deposited during the miocene pliocene and pleistocene all displayed comparable major loss of total organic carbon toc 84 3 1 accompanied by a negative isotopic 13c shift ranging from 0 3 to 2 9 major but significantly lower loss of total nitrogen ntot 61 7 1 also occurred leading to a decrease in toc relative to ntot c ntot and a 1 3 to 2 7 ntot isotopic 15n shift compound specific isotopic measurements on plant wax n alkanes indicate the terrestrial organic component in the unoxidized deposits is 13c enriched owing to significant c4 contribution selective preservation of terrestrial relative to marine organic carbon could account for the 13c behavior of toc upon oxidation but only if a 13c depleted component of the bulk terrestrial signal is selectively preserved in the process although the c ntot decrease and positive 15n shift seems inconsistent with selective terrestrial organic preservation results from analysis of a modern eolian dust sample collected in the vicinity indicate these observations are compatible regardless of the specific explanation for these isotopic observations however our findings provide evidence that paleoreconstruction of properties such as pco2 using the 13c of toc is a goal fraught with uncertainty whether or not the marine sedimentary record considered is contaminated with significant terrestrial input nonetheless despite major and selective loss of both marine and terrestrial components as a consequence of postdepositional oxidation intensive organic geochemical proxies such as the alkenone unsaturation index u37k appear resistant to change and thereby retain their paleoceanographic promise

shrimp and electron microprobe chronology of uht metamorphism in the napier complex east antarctica implications for zircon growth at 1 000 c zircons in ultra high temperature uht metamorphosed paragneisses from mt riiser larsen in the napier complex east antarctica were dated by using ion microprobe shrimp and electron microprobe emp both shrimp and emp analyses yield consistent 2520 2460 ma age populations for garnet orthopyroxene bearing paragneiss and leucosomes enclosed within the peak uht event was dated at 2480 ma by shrimp analyses on metamorphic zircons from the garnet orthopyroxene paragneiss and those on magmatic zircons from the leucosomes which are interpreted to be formed at syn uht as obtained by shrimp the uht metamorphic event was terminated no later than 2460 ma minor 2520 ma shrimp age suggests either the onset of prograde metamorphism or another high grade metamorphic event unrelated to the uht emp analyses on metamorphic zircons from sapphirine quartz and osumilite bearing magnesian paragneisses give c 2500 2450 ma ages inherited igneous zircon cores of the magnesian paragneisses yield relatively scattered emp ages ranging over c 3000 2650 ma suggesting that igneous materials of these ages sourced the protoliths of the paragneisses and that they were deposited during the interval c 2650 2520 ma

rate of arunta inlier evolution at the eastern margin of the entia dome central australia abstract zircon dating in the entia dome of the arunta inlier helps to temporally define the multiphase successive strangways and harts range orogenies it appears that the entire activity of both orogenies took place between 1767 2 ma and 1731 1 ma with a major shearing and thrusting event associated with plutonic activity at 1747 2 3 ma these comparatively short time spans indicated are quite sufficient for the large horizontal movements required for the intra continental basin formation and deformation that has been postulated by james and ding the earlier of these events are later than those currently proposed for equivalent stages of other middle proterozoic inliers of the north australian orogenic province which raises difficulties with detailed correlations in grouping the inliers together monazite u pb muscovite rb sr and biotite rb sr isotopic systems had not closed until 360 ma 325 ma and 308 ma respectively indicating uplift and cover removal from 20 km to

timing relationships between pegmatite emplacement metamorphism and deformation during the intra plate alice springs orogeny central australia in the harts range central australia the upper amphibolite facies to lower granulite facies c 480 460 ma harts range metamorphic complex hrmc and the upper amphibolite facies c 340 320 ma entia gneiss complex are cut by numerous generally peraluminous pegmatites and their deformed equivalents the pegmatites have previously been interpreted as locally derived partial melts however shrimp u pb monazite and zircon dating of 29 pegmatites or their deformed equivalents predominantly from the hrmc reveal that they were emplaced episodically throughout almost the entire duration of the polyphase c 450 300 ma intra plate alice springs orogeny episodes of pegmatite intrusion correlate with the age of major alice springs age structures and with deposition of syn orogenic sedimentary rocks in the adjacent centralian superbasin similar alice springs ages have not been obtained from anatectic country rocks in the hrmc suggesting that the pegmatites were not locally derived instead they are interpreted as highly fractionated granites and imply that much larger parental alice springs age granites exist at depth the mechanism to allow repeated felsic magmatism in an intraplate setting where all exposed rock types had a previous high temperature history is enigmatic however we suggest that episodic underthrusting and dehydration of unmetamorphosed centralian superbasin sedimentary rocks allowed crustal fertility to maintained over a c 140 ma interval during the intra plate alice springs orogeny

recent changes in the greenland scotland overflow derived water transport inferred from hydrographic observations in the southern irminger sea recent decadal changes 1955 2007 in the baroclinic transport tbc of the deep western boundary current dwbc carrying the greenland scotland overflow derived waters along the east greenland slope are quantified from a set of hydrographic sections in vicinity of cape farewell the updated historical record of tbc shows clear decadal variability 2 2 5 sv with the transport minima in the 1950s and mid 1990s maximum in the early 1980s and moderate to high transport in the 2000s since the mid 1990s the dwbc tbc has increased by 2 sv significant at the 99 9 level which constitute 20 of the mean absolute transport 9 0 sv as obtained from three cruises in 2002 2006 the dwbc tbc anomalies negatively correlate r 0 80 with thickness anomalies of the labrador sea water lsw at its origin implying a close association albeit not necessarily causative between the dwbc transport east of greenland and the lsw production

155 000 years of west african monsoon and ocean thermal evolution a detailed reconstruction of west african monsoon hydrology over the past 155 000 years suggests a close linkage to northern high latitude climate oscillations ba ca ratio and oxygen isotope composition of planktonic foraminifera in a marine sediment core from the gulf of guinea in the eastern equatorial atlantic eea reveal centennial scale variations of riverine freshwater input that are synchronous with northern high latitude stadials and interstadials of the penultimate interglacial and the last deglaciation eea mg ca based sea surface temperatures ssts were decoupled from northern high latitude millennial scale fluctuation and primarily responded to changes in atmospheric greenhouse gases and low latitude solar insolation the onset of enhanced monsoon precipitation lags behind the changes in eea ssts by up to 7000 years during glacial interglacial transitions this study demonstrates that the stadial interstadial and deglacial climate instability of the northern high latitudes exerts dominant control on the west african monsoon dynamics through an atmospheric linkage

atmospheric 14c variations derived from tree rings during the early younger dryas abstract atmospheric radiocarbon variations over the younger dryas interval from 13 000 to 11 600 cal yr bp are of immense scientific interest because they reveal crucial information about the linkages between climate ocean circulation and the carbon cycle however no direct and reliable atmospheric 14c records based on tree rings for the entire younger dryas have been available in this paper we present 1 high precision 14c measurements on the extension of absolute tree ring chronology from 12 400 to 12 560 cal yr bp and 2 high precision high resolution atmospheric 14c record derived from a 617 yr long tree ring chronology of huon pine from tasmania australia spanning the early younger dryas the new tree ring 14c records bridge the current gap in european tree ring radiocarbon chronologies during the early younger dryas linking the floating lateglacial pine record to the absolute tree ring timescale a continuous and reliable atmospheric 14c record for the past 14 000 cal yr bp including the younger dryas is now available the new records indicate that the abrupt rise in atmospheric 14c associated with the younger dryas onset occurs at 12 760 cal yr bp 240 yrs later than that recorded in cariaco varves with a smaller magnitude of 40 followed by several centennial 14c variations of 20 25 comparing the tree ring 14c to marine derived 14c and modelled 14c based on ice core 10be fluxes we conclude that changes in ocean circulation were mainly responsible for the younger dryas onset while a combination of changes in ocean circulation and 14c production rate were responsible for atmospheric 14c variations for the remainder of the younger dryas

chemostratigraphy and palaeo environmental characterisation of the cambrian stratigraphy in the amadeus basin australia abstract the sedimentary succession of the central australian amadeus basin consists of neoproterozoic to carboniferous sedimentary rocks and contains shallow marine subtidal carbonates of middle to late series 2 to furongian cambrian age a combination of sequence stratigraphy geochemistry and mineralogy shows a transgressive 2nd order cyclicity deposited between 511 490 ma and a change from arid low energy to humid high energy depositional environments this is reflected in an initially evaporitic sequence with upward decreasing halite and anhydrite abundance and transition from oxygenated to anoxic conditions reflected by the fe mineral species change from hematite to pyrite during transgression sequence boundaries of several 3rd order cycles consisting of hst carbonate rocks and lst siltstones correlate with globally recognised sequence boundaries linked to the inferred eustatic sea level record for the upper two series of the cambrian system the carbon isotope record for this 1400 m thick succession in combination with biostratigraphic age correlation allowed the identification of the globally recognised steptoean positive carbon isotope excursion spice drumian carbon isotope excursion dice and redlichiid olenellid extinction carbon isotope excursion roece

development of the late proterozoic to mid paleozoic intracratonic amadeus basin in central australia a key to understanding tectonic forces in plate interiors the intracratonic amadeus basin in central australia is a complex composite basin covering 17 000 km with at least nine distinct episodes of evolution between 900 and 300 ma these have been identified in neighboring central australian basins and are characterized by intervals of renewed subsidence followed by intervals of erosion and changes in basin shape several unconformities separating the tectonostratigraphic sequences represent periods of mild regional uplifts and correlate with major episodes of compressive tectonism at the evolving margin of the early australian plate in the absence of direct geological evidence for thermal events in the amadeus basin after the initial period of subsidence ended possibly at about 800 ma the correlations found between events in the amadeus basin those in the neighboring interconnected basins and tectonic events at the continental or plate margins emphasize that regional horizontal stress fields contribute significantly to primary basin forming mechanisms this suggests that stresses generated at continental or plate margins may propagate to the plate interior with the lithosphere acting as a stress guide throughout the history of the amadeus basin both periods when compressional stresses were dominant and when extensional tectonics controlled subsidence can be identified there were also transitional periods when neither compression nor extension dominated so that other processes masked the effects of weak horizontal stresses the most recent compressional thrust belt concentrated at the northern margin between 300 and 400 ma and has partly obscured the record of earlier basin shape and size

transient simulation of last deglaciation with a new mechanism for bolling allerod warming we conducted the first synchronously coupled atmosphere ocean general circulation model simulation from the last glacial maximum to the bolling allerod ba warming our model reproduces several major features of the deglacial climate evolution suggesting a good agreement in climate sensitivity between the model and observations in particular our model simulates the abrupt ba warming as a transient response of the atlantic meridional overturning circulation amoc to a sudden termination of freshwater discharge to the north atlantic before the ba in contrast to previous mechanisms that invoke amoc multiple equilibrium and southern hemisphere climate forcing we propose that the ba transition is caused by the superposition of climatic responses to the transient co 2 forcing the amoc recovery from heinrich event 1 and an amoc overshoot

geochemistry of metatholeiites from the harts range central australia implications for mantle source heterogeneity in a proterozoic mobile belt metatholeiite series from early middle proterozoic basement and cover sequences in the harts range central australia display marked differences in trace element abundances and ratios that reflect the chemical heterogeneity of their mantle sources the trace element data reveal a multistage geochemical evolution for the attendant proterozoic sub continental mantle early formed supracrustal tholeiites from the oonagalabi and entia basement gneiss complexes display slight to moderate light rare earth element lree enrichment ce yb n 1 8 3 9 unfractionated heavy ree distributions and chondritic zr nb and zr y ratios they were generated by variable degrees 15 30 of partial melting of a relatively undepleted mantle source in an extensional ensialic rift environment later formed metabasites comprise numerous sills that intrude the supracrustal sequence within the entia gneiss complex primary basaltic liquids for these rocks possessed more strongly fractionated ree levels ce yb n 3 0 12 3 large ion lithophile lil element enrichment and pronounced depletions in high field strength elements their high la nb ba zr and cr y ratios resemble those of convergent plate margin basaltic magmas derived from mantle sources that have been metasomatised as a result of subduction related processes metatholeiites from the harts range meta igneous complex in the cover sequence display high zr nb ratios reflecting a mantle source that was strongly depleted in incompatible elements during a previous melting event tholeiites from the lower part of the cover sequence show distinct lil element and lree depletion ce yb n 0 8 1 0 features resembling depleted n type mid ocean ridge basalts and some continental tholeiites tholeiites from the upper part of the cover sequence show enrichment of highly incompatible lil elements especially ba and k relative to ree and pronounced decoupling between high field strength elements and ree resulting in high la nb ratios they represent melts derived from a mantle source which has been depleted in a basaltic component and subsequently re enriched in incompatible elements e g via introduction of a subduction related component the inferred mantle evolution is compatible with a tectonic model that involves successive extensional and compressional episodes during repeated ensialic orogenesis as proposed for the harts range basement and cover sequences

fast teleconnections to the tropical atlantic sector from atlantic thermohaline adjustment 1 we examine the first decade of adjustment of the north atlantic climate following an abrupt freshening of the high north atlantic and resulting slowdown of the atlantic meridional overturning circulation amoc in a coupled model with reference to previously proposed teleconnection mechanisms after an initial ocean driven cooling at the subtropical subpolar gyre boundary subsequent equatorward progression is dominated by an atmosphere surface ocean mechanism driving evaporative cooling in the tropical north atlantic and resulting in an anomalous southward itcz displacement by year 2 the tropical cooling is countered by fast ocean baroclinic adjustment to the reduced overturning that increases the volume of tropical surface waters as well as ocean circulation changes to the increased northeasterly trades however it is the atmosphere surface ocean teleconnection that explains the hemispheric asymmetric nature of the tropical atlantic surface climate impact to amoc slowdown underlining its crucial importance in high to low latitude teleconnections

assessing the geochemical and tectonic impacts of fluid rock interaction in mid crustal shear zones a case study from the intracontinental alice springs orogen central australia the reynolds anmatjira ranges central australia form part of a high grade basement terrane dissected by intensely metasomatized transpressional shear zones active during the ordovician carboniferous alice springs orogeny unlike typical retrograde structures associated with discrete fluid flow the mid crustal setting and intracontinental nature of these shear systems present significant problems for the source and ingress mechanism of the fluid involved in their rehydration to address these issues we describe two detailed traverses across deformed and metasomatized basement rocks in this region and interrogate their record of fluid rock interaction from various perspectives both traverses combine structural and petrological observations with zr in rutile and ti in quartz thermobarometry oxygen and hydrogen stable isotope analysis and major trace and rare earth element mobility trends each technique is critically evaluated for its utility in this study and its more widespread applicability to alternative field areas providing a strategic framework for the general investigation of fluid affected shear zones ultimately the integrated data sets specify pressure temperature conditions of 530 c and 4 5 kbar implying average apparent thermal gradients of 29 36 c km 1 and depths of 14 18 km other characteristic features to emerge include strongly variable element mobilities and pronounced isotopic depletion fronts consistent with the alteration effects of an externally derived non equilibrium fluid this is confirmed by calculated fluid compositions indicative of contributions from a fluid of meteoric origin with estimated 18o and d values as low as 2 3 and 59 8 respectively we propose that these surficial fluid signatures are imposed on the mid crust by the prograde burial and dehydration of hydrothermally altered fault panels produced during pre orogenic basin formation progressive fluid release with continued subsidence then leads to the accumulation of increasing fluid volumes in the vicinity of the brittle ductile transition promoting extensive hydration metasomatism and reaction softening at the locus of stress transmission from plate boundary sources the sustained injection of externally derived fluids into refractory crustal material may thus stimulate a critical reduction in the long term strength of the lithosphere providing strong impetus for the initiation and advancement of intracontinental orogenesis

detrital zircon provenance constraints on the evolution of the harts range metamorphic complex central australia links to the centralian superbasin until recently it has been widely accepted that protoliths to metasediments of the harts range metamorphic complex central australia were deposited prior to c 1 75 ga and form part of the palaeoproterozoic arunta inlier however new sensitive high resolution ion microprobe u pb analyses of detrital zircon together with recently published data suggest that they were deposited coeval with c 545 520 ma sediments from the adjacent little metamorphosed neoproterozoic to palaeozoic centralian superbasin protoliths of the harts range metamorphic complex were deposited in the irindina sub basin an early to mid cambrian rift located between the present day amadeus and georgina basin remnants of the centralian superbasin deposition occurred during a widespread and long lived interval of extension in parts of central australia associated with eruption of the voluminous kalkarinji continental flood basalts the harts range metamorphic complex was metamorphosed to upper amphibolite to granulite facies conditions within c 40 ma of deposition of its sedimentary protoliths

impact of abrupt deglacial climate change on tropical atlantic subsurface temperatures both instrumental data analyses and coupled ocean atmosphere models indicate that atlantic meridional overturning circulation amoc variability is tightly linked to abrupt tropical north atlantic tna climate change through both atmospheric and oceanic processes although a slowdown of amoc results in an atmospheric induced surface cooling in the entire tna the subsurface experiences an even larger warming because of rapid reorganizations of ocean circulation patterns at intermediate water depths here we reconstruct high resolution temperature records using oxygen isotope values and mg ca ratios in both surface and subthermocline dwelling planktonic foraminifera from a sediment core located in the tna over the last 22 ky our results show significant changes in the vertical thermal gradient of the upper water column with the warmest subsurface temperatures of the last deglacial transition corresponding to the onset of the younger dryas furthermore we present new analyses of a climate model simulation forced with freshwater discharge into the north atlantic under last glacial maximum forcings and boundary conditions that reveal a maximum subsurface warming in the vicinity of the core site and a vertical thermal gradient change at the onset of amoc weakening consistent with the reconstructed record together our proxy reconstructions and modeling results provide convincing evidence for a subsurface oceanic teleconnection linking high latitude north atlantic climate to the tropical atlantic during periods of reduced amoc across the last deglacial transition

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

stable isotopes of planktonic foraminifera from tropical atlantic caribbean core tops implications for reconstructing upper ocean stratification abstract 18o values of nine tropical subtropical planktonic foraminiferal species with different preferential habitat depths collected from 62 core top samples along an east west transect across the tropical atlantic caribbean were used to test the applicability of interspecific 18o gradients for reconstructions of tropical upper ocean stratification in general the 18o difference 18o between intermediate and shallow dwelling species decreases and 18o between deep and intermediate dwellers increases with increasing thermocline depth towards the west the statistical significance of regional differences in 18o highlights 18o between the intermediate dwellers in particular globorotalia scitula and globorotalia tumida and the shallow dweller globigerinoides ruber pink as well as 18o between the deep dwellers globorotalia crassaformis or globorotalia truncatulinoides dextral and intermediate dwellers as most sensitive to changes in tropical atlantic thermocline depth based on the observed regional variations in interspecific 18o we propose a multispecies stratification index stratrop 18ointermediate 18oshallow 18odeep 18oshallow for the tropical ocean statistically significant differences in stratrop values between the e atlantic and the caribbean suggest that this index may be a useful tool to monitor variations in tropical upper ocean stratification in the geological record

linking growth episodes of zircon and metamorphic textures to zircon chemistry an example from the ultrahigh temperature granulites of rogaland sw norway in situ u th pb analyses by ion microprobe on zircon in intact textural relationships are combined with backscatter and cathodoluminescence imaging and trace element analyses to provide evidence for growth episodes of zircon this approach helps a to unravel the polymetamorphic history of aluminous migmatitic and granitoid gneisses of the regional contact aureole around the rogaland anorthosite norite intrusive complex and b to constrain the age of m 2 ultrahigh temperature uht metamorphism and the subsequent retrograde m 3 event all samples yield magmatic inherited zircon of c 1035 ma some an additional group at c 1050 ma this suggests that loss of pb by volume diffusion in non metamict zircon is not an important factor even under extreme crustal conditions furthermore the identical inheritance patterns in aluminous garnet cordierite osumilite bearing migmatites and orthogneisses indicate a metasomatic igneous instead of a sedimentary protolith for the migmatite results for the m 1 metamorphic event at c 1000 ma bp are consistent in all samples including those from outside the orthopyroxene in isograd the latter do not show evidence for zircon growth during the m 2 metamorphic episode zircon intergrown with or included within m 2 metamorphic minerals magnetite spinel orthopyroxene give an age of 927 7 ma 2 n 20 the youngest observed results are found in zircon outside m 2 minerals some overgrown by m 3 mineral assemblages late garnet coronas garnet quartz and orthopyroxene garnet symplectites and yield a slightly younger pooled age of 908 9 ma 2 n 6 these textures are relative time markers for the crystallization of zircon overgrowths during discrete stages of the uht event these youngest age groups are consistent with the emplacement age of the rogaland intrusive complex and the last magmatic activity tellnes dyke intrusion respectively this is direct and conclusive evidence for uht metamorphism in the regional aureole being caused by the intrusions and corrects earlier notions that the events are not linked trace element behaviour of zircon tb u and y content has been tracked through time in the samples and shows variations both within and between samples this heterogeneous behaviour at all scales appears to be common in metamorphic rocks and precludes the use of rules of thumb in the interpretation of zircon chemistry but chemical tracers are useful for recognition of zircon growth or recrystallization during metamorphism

geodynamics of the eastern yilgarn craton abstract over the last decade there have been significant advances in our understanding of the stratigraphy magmatism deformation metamorphism and timing of mineralisation in the eastern yilgarn craton eyc of western australia the integration of these disciplines has enabled a holistic review of the tectonic history of the eyc which favours a paraautochthonous tectonic model a significant advance has been the recognition of a 2810 ma rifting event off the eastern margin of the youanmi terrane which set up the north northwest trending architecture of the eyc rifting was followed by a 100 myr long phase of tectonic activity initiated by the establishment of a convergent margin at 2715 ma characterised by a west dipping subduction zone to the east of the eyc subduction was associated with the deposition of 2715 2670 ma volcanic stratigraphy and the emplacement of voluminous tonalite trondhjemite granodiorite magmatism which resulted in magmatic thickening of the crust volcanism was terminated by a 5 myr pulse of east northeast contraction followed by mid orogenic extension possibly linked to lithospheric and lower crustal delamination the lack of ultra high pressure metamorphism and the presence of high geothermal gradients preclude this contractional event from recording continent continent collision mid orogenic extension at 2665 ma resulted in the introduction of metasomatised mantle melts mafic granites and syenites deposition of siliciclastic basins which record metamorphic anticlockwise ptt paths and the start of significant economic gold mineralisation in the eyc high stretching factors and or delamination associated with this extension event resulted in significant heat input into the base of the crust which eventually led to the emplacement of low ca crustal melt granites and cratonisation of the eyc major gold mineralisation postdates mid orogenic extension and was associated with renewed compression transpression 2650 ma and the development of steep predominantly north northwest striking sinistral and later north to north northeast striking dextral strike slip faults during low ca granite emplacement

euxinia and primary production in late cretaceous eastern equatorial atlantic surface waters fostered orbitally driven formation of marine black shales 1 oceanic anoxic events oae in the cretaceous represent major perturbations in the global climate and ocean system characterized by widespread deposition of organic carbon in the ocean the causes and effects of these events are poorly constrained mainly because of the lack of high resolution marine records here we report the distribution of molecular markers from a millennial scale record of coniacian santonian black shale oae 3 from ocean drilling program site 959 in the deep ivorian basin in the eastern equatorial atlantic highly branched isoprenoids and alkenone derived organic compounds indicate that diatoms and calcareous nanoplankton were important primary producers changes in redox sensitive trace metal accumulation and biomarkers of green sulfur bacteria provide evidence for extreme variations in redox conditions with intervals of lower photic zone euxinia pze accordingly oxygen in the coniacian santonian tropical atlantic was absent as during the cenomanian turonian boundary oae 2 but over more restricted geographic area and more limited time intervals we hypothesize that pze was a common phenomenon typical in large areas of tropical continental margins these conditions fostered sequestration of atmospheric co2 and thus helped cause the positive excursion in 13c of carbonate documented in higher latitude marine records

sm nd evidence for high grade ordovician metamorphism in the arunta block central australia sm nd ages from the harts range in the south eastern arunta inlier in central australia indicate that regional metamorphism up to granulite facies occurred in the early ordovician c 475 ma this represents a radical departure from previous tectonic models for the region and identifies a previously unrecognized intraplate event in central australia peak metamorphic assemblages 800 c and 10 5 kbar formed at around 476 14 ma and underwent approximately 4 kbar of near isothermal decompression at 475 4 ma a coarse grained unfoliated garnet clinopyroxene bearing marble inferred to have recrystallized late in the decompressional evolution gives an age of 469 7 ma two lines of evidence suggest the early ordovician tectonism occurred in an extensional setting first the timing of the high grade lower crustal deformation coincides with a period of marine sedimentation in the amadeus and georgina basins that was associated with a seaway that developed across central australia second isothermal decompression of lower crustal rocks was associated with the formation of a regional sub horizontal mid crustal foliation in the entia gneiss complex which forms the structurally lowest part of the harts range upper amphibolite facies metamorphism c 700 c 8 9 kbar occurred at 479 15 ma there is no evidence that p t conditions in the entia gneiss complex were as high as in the overlying units this implies that the extensional system was reworked during a later compressional event sm nd data from the mid amphibolite facies c 650 c and 6 kbar detachment zone that separates the irindina supracrustal assemblage and entia gneiss complex give an age of 449 10 ma this age corresponds to the timing of a change in the pattern and style of sedimentation in the amadeus and georgina basins and indicates that the change in basin dynamics was associated with mid crustal deformation it also suggests that compressional deformation culminating in the devonian to carboniferous 400 300 ma alice springs orogeny may have begun as early as c 450 ma at present the extent of early ordovician tectonism in central australia is unknown however granulite facies metamorphism and associated intense deformation imply an event of regional extent an implication of this work is that high grade lower crustal metamorphism and intense deformation occurred during the development of a broad shallow slowly subsiding intraplate basin

millennial scale sea surface temperature variability in the western tropical north atlantic from planktonic foraminiferal census counts planktonic foraminiferal census counts are used to construct high resolution sea surface temperature sst and subsurface thermocline temperature records at a core site in the tobago basin lesser antilles the record is used to document climatic variability at this tropical site in comparison to middle and high latitude sites and to test current concepts of cross equatorial heat transports as a major player in interhemispheric climate variability temperatures are estimated using transfer function and modern analog techniques glacial maximum cooling of 2 5 3 c is indicated maximum cooling by 4 c is inferred for isotope stage 3 the sst record displays millennial scale variability with temperature jumps of up to 3 c and closely tracks the structure of ice core dansgaard oeschger cycles sst variations in part of the record run opposite to the sst evolution at high northern latitude sites pointing to thermohaline circulation and marine heat transport as an important factor driving sst in the tropical and high latitude atlantic both on orbital and suborbital timescales

evidence for calcification depth change of globorotalia truncatulinoides between deglaciation and holocene in the western atlantic ocean abstract measurements of the 18o in tests of planktonic and benthic foraminifera in the florida straits are used to reconstruct the properties of the water column through time over the last 12 ka lynch stieglitz et al in press the isotopic composition of the foraminifera largely reflects the vertical density gradient we use this reconstruction and 18o measurements on globorotalia truncatulinoides in a nearby core to track the depth habitat of this species from the last deglaciation to 1 6 ka b p around 9 ka g truncatulinoides was calcifying in much shallower water than during the late holocene the downward migration toward its modern habitat is a regional phenomenon over the western tropical atlantic continental slope the cause is still unclear but we hypothesize that the shallower calcification depth may be a response to the presence of glacial melt water or to circulation changes this study points to the value of further study of the ecology life cycle and calcification depth for g truncatulinoides and other planktonic foraminifera that are used to reconstruct the history of the thermocline and upper water column structure

an extended episode of early mesoproterozoic metamorphic fluid flow in the reynolds range central australia the products of metamorphic fluid flow are preserved in zones within the marbles and metamorphosed semipelites of the upper calcsilicate unit in the granulite portion of the late palaeoproterozoic reynolds range group northern arunta block central australia the zones of retrogression characterized by minerals such as wollastonite grossular and clinohumite local resetting of oxygen isotopic compositions and local major element metasomatism were channelways for water rich fluids derived from granulite facies metapelites u th pb isotopic ages measured by the shrimp ion microprobe on zircon and monazite from a granulite facies semipelite an early semiconcordant aluminous quartz rich fluid flow segregation and a late discordant quartz rich segregation record some of the extended thermal history of the area zircon cores from the semipelite show its likely protolith to be an igneous rock 1812 11 ma old itself derived from a source containing zircon as old as 2 2 ga low th u overgrowths on the zircon grew during granulite facies metamorphism at 1594 6 ma monazite cooled to its blocking temperature at 1576 8 ma zircon cores from the semiconcordant segregation are dominantly 2 3 ga old indicating that the source of the fluids was not the particular metamorphosed semipelite studied two generations of low th u overgrowths on the zircon give indistinguishable ages for the older and younger of 1589 8 and 1582 8 ma respectively the monazite age is the same 1576 12 ma zircon from the late discordant segregation gave 1568 4 ma fluid flow occurred for at least 18 3 ma and ended 26 3 ma after the peak of metamorphism suggesting a very slow cooling rate of 3 c ma 1 the last regional high grade metamorphism in the reynolds range occurred at 1 6 ga not 1 78 ga as previously thought the high grade event at 1 78 ga is a separate event that affected only the basement to the reynolds range group

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

indian derived sediments deposited in australia during gondwana assembly abstract sedimentary exchanges across continents during the collisional assembly and lifespan of supercontinents provide a powerful way of testing the assembling process and configuration of supercontinents the ord basin in north western australia contains mid cambrian shallow marine and deltaic sedimentary successions that post date the ca 650 520 ma paterson petermann orogeny ppo but are synchronous with the ca 530 470 ma kurgiakh orogeny in north india we report new u pb ages and hf isotopes of detrital zircons from the mid cambrian ord basin that suggest indian derived sedimentary input to australian cambrian basins compilations of published ediacaran ordovician samples from the centralian superbasin indicate that during the ca 650 520 ma ppo the 1200 1100 ma musgrave province in central australia was exhumed and fed sediments to the syn ppo centralian superbasin soon after the ppo termination the musgrave province likely remained a topographic high and continued to supply detritus to the amadeus and officer basins that were fragmented from the centralian superbasin supplemented by the 630 ma granites of the paterson orogen conversely we conclude that the mid cambrian ord basin did not record similar sedimentary provenance from the musgrave province rather indian derived detritus travelled along the northeastern gondwanan continental margin via longshore currents and in turn incorporated paterson granitic detritus during the assembly of gondwana including the kurgiakh orogeny in north india a broad provenance comparison between potential eastern gondwanan source regions and relevant asian neighbours suggests that south china and south qiangtang are affiliated with northern india but lhasa appears to have had a mixed affiliation between india and australia

deglacial sea surface temperature and salinity increase in the western tropical atlantic in synchrony with high latitude climate instabilities a sediment core from the western tropical atlantic covering the last 21 000 yr has been analysed for centennial scale reconstruction of sea surface temperature sst and ice volume corrected oxygen isotopic composition of sea water delta 18 o ivc sw using mg ca and delta 18 o of the shallow dwelling planktonic foraminifer globigerinoides ruber white at a period between 15 5 and 17 5 kyrbp the mg ca sstand delta 18 o ivc sw a proxy for sea surface salinity sss reveals a warming of around 2 5 degrees c along with all increase in salinity a second period of pronounced warming and sss increase occurred between 11 6 and 13 5 kyr bp within age model uncertainties both warming intervals were synchronous with air temperature increase over antarctica and ice retreat in the southern south atlantic and terminated with abrupt centennial scale sss decrease and slight sst cooling in conjunction with interglacial reactivation of the meridional overturning circulation moc we suggest that during these warm intervals production of saline and warm water of the north brazil current resulted in pronounced heat and salt accumulation and was associated with warming in the southern atlantic southward displacement of the intertropical convergence zone and weakened moc at the termination of the younger dryas and heinrich event 1 intensification of cross equatorial heat and salt transport caused centennial scale cooling and freshening of the western tropical atlantic surface water this study shows that the western tropical atlantic served as a heat and salt reservoir during deglaciation the sudden release of accumulated heat and salt at the end of younger drays and heinrich event 1 may have contributed to the rapid reinvigoration of the atlantic moc c 2005 elsevier b v all rights reserved

euxinia linked to the cambrian drumian carbon isotope excursion dice in australia geochemical and chemostratigraphic evidence abstract the cambrian drumian carbon isotope excursion dice event is a negative carbon isotope 13 c excursion it is associated with the first appearance datum fad of the agnostoid arthropod ptychagnostus atavus whose first appearance in the global boundary stratotype section and point gssp defines the base of the cambrian series 3 drumian stage although this isotopic event has been clearly identified in the great basin usa it has not been consistently reported in other areas of the world here we report a study integrating isotopic and geochemical data from middle cambrian series 3 sections from the northeastern georgina basin australia to investigate the occurrence of the dice event in australia and the paleoenvironmental conditions associated with this event the similarity between the isotopic excursions observed in the georgina basin 2 to 3 2 13 c excursion and that observed in the great basin 2 to 3 6 13 c excursion highlighted the presence of the dice in australia and emphasized the potential use of this event for refining global isotopic correlations the multi proxy correlation used in this study also showed a pulse of euxinia in association with the dice suggesting strongly euxinic conditions near the base of the drumian stage

structural evolution of the harts range area and its implication for the development of the arunta block central australia abstract a division of the high grade metamorphics of the arunta block in the harts range area into two main groups on the basis of lithology structure metamorphism and igneous activity is suggested as a result of detailed mapping the lower group is regarded as a basement terrain and comprises major layered felsic or granitic gneiss minor amphibolite and mafic granulite while the structurally overlying group is regarded as a cover sequence irindina supracrustal assemblage and comprises predominantly metasediments pelitic and semi pelitic gneiss calc silicate and quartzite and amphibolite anorthosite and ultramafic rock of the harts range meta igneous complex the cover sequence might have been deposited in an aulacogen or adjacent to a continental margin which developed by rifting of a pre existing basement the two groups both show early major ductile tectonothermal stages with four major fold generations and a later discrete shear event in the basement and two major fold generations and a later series of stacked nappes developing in the cover the basement s early orogenic evolution with associated granulite facies metamorphism is typical of intensely reworked early precambrian terrains and developed spatially and or temporally separated from the cover cover deformation closely resembles continental margin cordillera type overthrusting and thus thin skinned tectonics associated with large scale crustal shortening during the later harts range remobilization the basement and cover were juxtaposed by displacement on a fundamental crustal dislocation recumbent contraction fault mylonites repeatedly developed along the dislocation which was also isoclinally folded intruded by a major megacrystic granitoid bruna gneiss sheet and repeatedly rejuvenated the history of development of the dislocation is documented and described as a process of underthrusting of basement beneath cover which led to the final termination of the orogenic activity

sm nd and u pb zircon isotopic constraints on the provenance of sediments from the amadeus basin central australia evidence for ree fractionation abstract the amadeus basin of central australia is a late proterozoic to late palaeozoic ensialic depositional basin located between two proterozoic basement blocks of different nd crustal formation ages the older arunta block t dm nd 2 0 to 2 2 ga u pb zircon ages 1 5 1 9 ga to the north and the younger musgrave block t dm nd 1 7 to 1 9 ga u pb zircon ages 1 0 1 7 ga to the south initial nd isotopic compositions of the amadeus basin sediments generally fall into the region defined by the evolutionary trajectories of these two basement blocks indicating that the sediments are dominated by essentially two source components the older arunta block 147 sm 144 nd 0 114 and nd 0 20 4 and younger musgrave block 147 sm 144 nd 0 118 and nd 0 14 7 and or their equivalents stratigraphically higher sediments plot more closely to the evolutionary trajectory of the musgrave block this result together with the average provenance ages indicates the proportion of material from the musgrave block increases as the sediments become younger the sm nd isotopic data preclude a substantial involvement of archaean sources u pb zircon ion probe analyses of the late proterozoic heavitree quartzite and the late cambrian goyder formation are consistent with the sm nd isotopic constraints most of the zircons from the basal heavitree quartzite give concordant u pb zircon ages of 1500 to 1900 ma consistent with derivation from an arunta type source whilst zircons from the younger goyder sandstone give six discrete u pb zircon age groups of 511 20 615 15 960 109 1190 54 1633 24 and 1878 48 ma indicative of a dominantly musgrave type source with a minor contribution from the arunta block or reworked preexisting amadeus basin sediments the two youngest u pb zircon ages probably indicate some contribution from late proterozoic cambrian volcanics in central australia or a previously unrecognised younger local source in the basement blocks the 511 20 ma constrains the maximum depositional age of the sediment the amadeus basin sediments have a surprisingly wide range of 147sm 144nd ratios 0 077 0 136 irrespective of grain size and rock types in addition the calculated t dm nd values for samples from the same stratigraphic unit are well correlated with 147sm 144nd ratios with samples of different stratigraphic units forming sub parallel arrays these phenomena are interpreted in terms of ree fractionation and preferential sorting of preexisting ree rich phases during sedimentary recycling and deposition this process can lead to either an increase or a decrease in 147sm 144nd ratio of a sediment relative to its source and therefore an erroneous estimate of its t dm nd provenance age a theoretical model is developed which accounts for the observed correlation between t dm nd and 147sm 144nd ratios for suites of stratigraphically related sediments and allows a reliable estimate to be made of the provenance age of individual stratigraphic units assuming the average 147sm 144nd ratio of the source is known or can be estimated the provenance age for each stratigraphic unit of the amadeus basin has been calculated using this method the sm nd isotopic systematics in the amadeus basin sediments suggest that 1 1 ree fractionation during sedimentary recycling can in some cases be an important factor and needs to be considered 2 2 the provenance of the amadeus basin sediments was controlled by local source regions and cannot be used to infer large scale continental averages hence some caution must be evoked in using sm nd isotopic constraints from restricted sampling for more generalised models of crustal evolution

intracontinental orogeny enhanced by far field extension and local weak crust the accommodation of intraplate stresses in preexisting weak regions of plate interiors is here investigated using thin viscous sheet numerical models the intraplate stresses are governed by multicomponent and multidirectional stresses originating at plate boundaries the modeled scenarios mimic plate boundary conditions during the intraplate alice springs orogeny aso central australia and include 1 a northwest southeast zone of weak lithosphere within strong continental blocks to the north and southand 2 a principal south directed stress condition at the northern boundary that causes minor clockwise rotation of the northern block alternative tectonic environments are investigated in additional models that include 1 secondary compressional or extensional stresses acting at the eastern boundary representing the temporally variable stress conditions during the tasmanides orogeny and 2 an eastern wedge shaped zone of rheologically weak lithosphere mirroring rift fill of the irindina subbasin our results highlight that a low angle between major crustal features e g orogenic elongation and preexisting regional structures and the principal transmitted stresses is highly relevant in the concentration of elevated levels of differential stress and subsequent localization of deformation in plate interiors secondary stresses orthogonal to the principal acting stresses may introduce effects that explain the episodic orogenic activity in the case of the aso the combination of secondary extensional stresses at the eastern boundary of australia and weak lithosphere of the preexisting irindina subbasin strongly influences the observed spatial strain intensity localization and kinematics of deformation during the aso

geochronological constraints on orogenic events in the arunta inlier a review early workers subdivided the arunta inlier central australia into three major tectonic provinces classified the principal tectonostratigraphic units into three divisions and separated the tectonomagmatic history into five discrete events ranging in age from 1800 ma to 300 ma a review of the evidence for tectonic boundaries within the arunta inlier suggests that no major structural discontinuity exists between the northern and central tectonic provinces but that the redbank thrust zone is at least in part a province boundary the tectonostratigraphic division concept also requires revision as division 3 rocks of the northern and southern arunta cannot be time equivalents division 1 rocks grade into division 2 in the northern region and division 3 of the northern region may be equivalent to division 1 in the central region rocks originally assigned to divisions are better grouped into a larger number of lithological assemblages until better stratigraphic and isotopic correlations can be made compilation of rb sr and 40ar39ar age determinations obtained before 1984 indicate an almost complete age spectrum from 1800 ma to 1000 ma but age clusters exist at 1400 ma 1100 ma and 400 300 ma which have geological significance subdivision of older ages into discrete tectonic events was not justified from this data alone but more recent u pb isotopic analysis of zircons in rocks designated to particular structural metamorphic events has revealed a complex tectonic history in the 1880 1600 ma interval the northern and central provinces underwent major tectonism between 1780 1730 ma but much of the southern province was not deformed until 1600 ma the revised tectonic history nomenclature is proposed for the arunta inlier following deposition of a widespread turbiditic unit at or before 1880 ma possibly on thinned archaean crust the northern and central provinces underwent localized tectonism magmatism at 1880 ma yuendumu tectonic event and 1820 ma stafford tectonic event prior to the widespread strangways orogeny which is subdivided into an early phase at 1780 1770 ma and late phase at 1745 1730 ma it is not clear whether the strangways orogeny is a single arunta wide event or a series of separate short lived smaller scale events although the major deformation in all areas appears to have involved w to sw directed thrusting in the southern province the major events occurred at 1680 ma argilke tectonic event and 1600 ma chewings orogeny the latter involving n directed thrusting that was penecontemporaneous with post tectonic pegmatite intrusion in the northern province suggesting linkage of both regions at this stage the younger history of the inlier is characterised by several stages of uplift and isolated thermal magmatic events major mesoproterozoic crustal exhumation anmatjira uplift phase has been interpreted from widespread 1500 1400 ma ages including regional scale closure of 40ar 39ar systems in hornblende from mafic granulite outcrop scale rb sr total rock isotopic systems in mylonitized granitoids and sm nd garnet hornblende pairs in mylonitized amphibolites a 1150 ma thermal event in the southern part of the inlier teapot magmatic event is recorded by intrusion of granite pegmatites and the alkaline mordor igneous complex and by isotopic resetting of rb sr mineral systems dolerite dyke injection at 1050 ma reflects limited extensional tectonism that may have related to formation of the amadeus basin the second major uplift event was the alice springs orogeny at 400 300 ma an unusual intracratonic thick and thin skinned thrust event that involved limited retrograde amphibolite facies but extensive greenschist facies metamorphism and restricted pegmatite intrusion

granulite facies metamorphism in the mallee bore area northern harts range implications for the thermal evolution of the eastern arunta inlier central australia abstract the mallee bore area in the northern harts range of central australia underwent high temperature medium to high pressure granulite facies metamorphism individual geothermometers and geobarometers and average p t calculations using the program thermocalc suggest that peak metamorphic conditions were 705 810c and 8 12 kbar partial melting of both metasedimentary and meta igneous rocks forming garnet bearing restites occurred under peak metamorphic conditions comparison with partial melting experiments suggests that vapour absent melting in metabasic and metapelitic rocks with compositions close to those of rocks in the mallee bore area occurs at 800 875c and 9 10 kbar the lower temperatures obtained from geothermometry imply that mineral compositions were reset during cooling following the metamorphic peak the rocks underwent local mylonitization at 680 730c and 5 8 7 7 kbar after mylonitization ceased garnet retrogressed locally to biotite which was probably caused by fluids exsolving from crystallizing melts these three events are interpreted as different stages of a single continuous clockwise p t path the metamorphism at mallee bore probably occurred during the 1745 1730 ma late strangways orogeny and the area escaped significant crustal reworking during the anmatjira and alice springs events that locally reached amphibolite facies conditions elsewhere in the harts ranges

tree rings and ice cores reveal c 14 calibration uncertainties during the younger dryas the younger dryas interval during the last glacial termination was an abrupt return to glacial like conditions punctuating the transition to a warmer interglacial climate despite recent advances in the layer counting of ice core records of the termination the timing and length of the younger dryas remain controversial also a steep rise in the concentration of atmospheric radiocarbon at the onset of the interval recorded primarily in the cariaco basin has been difficult to reconcile with simulations of the younger dryas carbon cycle here we discuss a radiocarbon chronology from a tree ring record covering the late glacial period that has not been absolutely dated we correlate the chronology to ice core timescales using the common cosmic production signal in tree ring 14c and ice core 10be concentrations the results of this correlation suggest that the cariaco record may be biased by changes in the concentration of radiocarbon in the upper ocean during the early phase of the younger dryas climate reversal in the cariaco basin this bias in the marine record may also affect the accuracy of a widely used radiocarbon calibration curve over this interval our tree ring based radiocarbon record is easily reconciled with simulated production rates and carbon cycle changes associated with reduced ocean ventilation during the younger dryas attaching a floating tree ring chronology to ice core records that cover the abrupt younger dryas cold interval during the last glacial termination provides a better estimate of the onset and duration of the radiocarbon anomaly the chronology suggests that marine records may be biased by changes in the concentration of radiocarbon in the ocean which may affect the accuracy of a popular radiocarbon calibration program during this interval

caterpillar tectonics in the harts range area a kinship between two sequential proterozoic extension collision orogenic belts within the eastern arunta inlier of central australia abstract we propose that in the harts range area of the arunta inlier of central australia a basement and cover relationship previously described by us represents a thick complexly deformed contact zone between an early middle proterozoic fold belt the strangways orogenic belt sob and a younger middle proterozoic orogenic belt the harts range orogenic belt both of which contain their own supracrustal sequences rocks of the sob were deposited and possibly metamorphosed to a maximum grade of granulite facies at 1800 ma during an early phase of crustal extension they were subsequently intruded by a significant proportion of acidic magmas at 1767 ma and compressed to form a distinctively nne ssw trending orogenic belt a wnw ese trending shallowly north dipping zone of intense and repeated deformation termed the harts range detachment zone hrdz formed initially during a period of nne ssw crustal extension as a major low angle normal shear detachment zone within and crosses at a high angle to the trend of the basement rocks of the sob the hrdz has been intermittently active as a zone of crustal weakness since its initiation the first extensional movement on this zone began the formation of the harts range mobile belt hrmb which displays many of the characteristics of modern tectonic zones activated by plate movement a supracrustal cover sequence the harts range cover hrc formed in the major geosynclinal basin which developed on the subsiding upper plate of the hrdz continued crustal extension juxtaposed the cover sequence which was then metamorphosed to a maximum grade of amphibolite facies and granulite facies basement of the hrdz before a fundamental change in movement sense led to crustal contraction and a collision related thrusting phase the hrmb which includes the hrdz and the hrc was then internally deformed over a relatively very short time span 15 20 ma before voluminous granitic magma intruded mainly along the hrdz during the harts range orogeny hro the intrusion of this major granitoid at 1747 ma precisely fixes the time scale of evolution for the earlier phases of the hro the hro is documented in detail as a peculiar orogenic style of crustal contraction which was largely taken up by reverse sense discrete thrusting and shearing on faults and shear zones associated with the hrdz displacement on the hrdz was a stick slip process with repeated punctuation of thrust slip movement by pinning at points located progressively to the south each period of cessation of thrust slip movement was followed by folding of discrete thrusts of captured basement lobes within the hrdz and of the overlying supracrustal sequence the individual discrete movement phases and folding episodes are each named and described as is a model of this unusual type of proterozoic tectonic activity

timing and exhumation of eclogite facies shear zones musgrave block central australia timing constraints on shear zones can provide an insight into the kinematic and exhumation evolution of metamorphic belts in the musgrave block central australia granulite facies gneisses have been affected to varying degrees by mylonitic deformation some of which attained eclogite facies the davenport shear zone is a dominant strike slip system that formed at eclogite facies conditions t 650 c and p 12 0 kbar sm nd mineral isochrons obtained from equilibrated high pressure assemblages as well as 40ar 39ar data show that the eclogite and greenschist facies high strain overprints were coeval at c 550 ma mylonitic processes do not appear to have reset the u pb system in zircon but may have partially disturbed it the thermal gradient in the musgrave block crust at c 550 ma was c 16 c km 1 and at c 535 ma was c 18 c km 1 based on p t estimates of eclogite and greenschist facies shear zones respectively these estimates are similar to present day geothermal gradients in many stable continental shield areas suggesting that the region did not undergo a significant transient perturbation of the geotherm therefore in the musgrave block cooling subsequent to eclogite facies metamorphism appears to have been controlled by exhumation rather than by the removal of a heat source estimated exhumation rates in the range 0 2 to 1 5 mm year 1 are comparable with other orogenic belts rather than cratonic areas elsewhere

intermediate depth warming in the tropical atlantic related to weakened thermohaline circulation combining paleoclimate data and modeling results for the last deglaciation 1 benthic foraminiferal oxygen isotope ratios from two sediment cores recovered at 426 and 1299 m water depth in the eastern and western tropical atlantic show that a slowdown of the thermohaline circulation thc during heinrich event h1 and the younger dryas was accompanied by rapid and intense warming of intermediate depth waters millennial scale covariations of low paleosalinities in the subpolar north atlantic with decreased benthic oxygen isotope ratios in the eastern tropical atlantic throughout the past 10 000 years suggest that thc weakening might be related to middepth warming during the holocene period as well climate model experiments simulating a strong reduction of the thc in the atlantic ocean under present day and glacial conditions reveal that the increase of temperature in the middepth tropical and south atlantic is a common feature for both climatic states caused by a reduced ventilation of cold intermediate and deep waters in conjunction with downward mixing of heat from the thermocline from the similarity of the paleoclimatic records with the model simulations we infer that the characteristic pattern of temperature change in the atlantic ocean related to weakened thermohaline circulation can serve as an indicator of present day and future thc slowdown

ordovician high grade metamorphism of a newly recognised late neoproterozoic terrane in the northern harts range central australia granulite facies rocks from the northernmost harts range complex arunta inlier central australia have previously been interpreted as recording a single clockwise cycle of presumed palaeoproterozoic metamorphism 800 875 c and 9 10 kbar and subsequent decompression in a kilometre scale e w striking zone of noncoaxial high grade c 700 735 c and 5 8 6 4 kbar deformation however new shrimp u pb age determinations of zircon monazite and titanite from partially melted metabasites and metapelites indicate that granulite facies metamorphism occurred not in the proterozoic but in the ordovician c 470 ma the youngest metamorphic zircon overgrowths from two metabasites probably meta volcaniclastics yield 206pb 238u ages of 478 4 ma and 471 7 ma whereas those from two metapelites yield ages of 463 5 ma and 461 4 ma monazite from the two metapelites gave ages equal within error to those from metamorphic zircon rims in the same rock 457 5 ma and 462 5 ma respectively zircon and possibly monazite ages are interpreted as dating precipitation of these minerals from crystallizing melt within leucosomes in contrast titanite from the two metabasites yield 206pb 238u ages that are much younger 411 5 ma 417 7 ma respectively than those of coexisting zircon which might indicate that the terrane cooled slowly following final melt crystallization one metabasite has a second titanite population with an age of 384 7 ma which reflects titanite growth and or recrystallization during the 400 300 ma alice springs orogeny the c 380 ma titanite age is indistinguishable from the age of magmatic zircon from a small late and weakly deformed plug of biotite granite that intruded the granulites at 387 4 ma these data suggest that the northern harts range has been subject to at least two periods of reworking 475 460 ma 400 300 ma during the palaeozoic detrital zircon from the metapelites and metabasites and inherited zircon from the granite yield similar ranges of proterozoic ages with distinct age clusters at c 1300 1000 and c 650 ma these data imply that the deposition ages of the protoliths to the harts range complex are late neoproterozoic or early palaeozoic not palaeoproterozoic as previously assumed

synchroneity of tropical and high latitude atlantic temperatures over the last glacial termination a high resolution western tropical atlantic sea surface temperature sst record from the cariaco basin on the northern venezuelan shelf based on mg ca values in surface dwelling planktonic foraminifera reveals that changes in sst over the last glacial termination are synchronous within 30 to 90 years with the greenland ice sheet project 2 air temperature proxy record and atmospheric methane record the most prominent deglacial event in the cariaco record occurred during the younger dryas time interval when ssts dropped by 3 to 4 c a rapid southward shift in the atmospheric intertropical convergence zone could account for the synchroneity of tropical temperature atmospheric methane and high latitude changes during the younger dryas