climatology of short period gravity waves observed over northern australia during the darwin area wave experiment dawex and their dominant source regions 1 the darwin area wave experiment dawex was designed to investigate the generation and propagation of gravity waves from intense regions of localized convection that occur regularly over northern australia in the vicinity of darwin during the premonsoon period this multinational program was conducted during the austral spring 2001 using a range of coordinated optical radar and in situ balloon measurements as part of this program all sky image observations of short period gravity wave events in the near infrared oh nightglow emission altitude 87 km were made from two well separated sites in northern australia wyndham 15 5 s 128 1 e and katherine 14 5 s 132 3 e over a 10 day period during november 2001 a total of 25 extensive wave events were observed during this period from which the dominant horizontal wave characteristics were determined to be wavelength 25 35 km and observed phase speed 27 75 m s yielding observed periods from 7 to 14 min consistent with previous measurements at other low latitude sites a key finding of this study was a marked anisotropy in the wave propagation headings with over 3 4 of the events exhibiting a strong southward component of motion and a clear preference for wave progression over the azimuthal range se to ssw although this range encompasses gravity waves originating locally from the darwin area the majority of the wave events exhibited propagation headings consistent with more distant sources located to the north and northwest of australia assuming deep convection was the dominant mechanism for the waves the strong asymmetry in their velocity distribution appears to result from a combination of nonuniformity in the geographic occurrence of thunderstorms coupled together with significant wind filtering effects at the source altitude and within the middle atmosphere these results are consistent with long range short period wave propagation most probably in the form of ducted waves possibly from intense convective regions located 1000 km to the north over the indonesian island chain

buried but preserved the proterozoic arubiddy ophiolite madura province western australia abstract we describe a previously unidentified proterozoic ophiolite complex situated in the madura province in southeastern western australia the madura province is almost entirely covered by mesozoic to cenozoic basin rocks but new basement drillcores have revealed oceanic crustal assemblages that record continental marginal basin formation followed by oceanic subduction and basin closure the pinto basalt has e morb oib chemical affinity and nd 1600 ma from 2 54 to 3 3 it formed by mantle upwelling beneath extending crust in an ocean continent transition zone and must be considerably older than c 1389 ma adakite that intrudes it the sleeper camp formation comprises mafic metavolcaniclastic schist intruded by metadolerite and plagiogranite veins zircon crystals from the metavolcaniclastic schist yield a dominant age component and maximum depositional age of 1536 13 ma the metadolerite and plagiogranite veins have zircon crystallization ages of 1479 8 ma and 1471 5 ma respectively interlayered basalt and sediments of the malcolm metamorphics have a maximum depositional age of c 1470 ma and were metamorphosed at 1315 11 ma the mafic rocks from both units are tholeiitic with morb like hfse ratios that point to a depleted mantle source similar to n morb but with trace element patterns that indicate subduction enrichment v ti ratio trends suggest the sleeper camp formation marks oceanic subduction initiation at c 1479 ma the progression to oceanic arc formation is recorded by the malcolm metamorphics after c 1470 ma and the haig cave supersuite from 1415 to 1389 ma the majority of these rocks occur within the hanging wall of the rodona shear zone and were structurally emplaced above the continental margin of the west australian craton between 1389 and 1330 ma during oceanic arc continent collision forming the arubiddy ophiolite complex the occurrence of oceanic crustal assemblages behind the accreted ophiolite complex frozen by the emplacement of voluminous 1192 1125 ma moodini supersuite ferrogabbros and granites demonstrates that continental collision did not occur between the west australian and south australian cratons the preservation of rocks of oceanic affinity behind ophiolites could be a hallmark of other proterozoic terranes that have escaped full continent continent collision

a 130 ka reconstruction of rainfall on the bolivian altiplano new efforts to link climate reconstructions from shoreline deposits and sediment cores yield an improved and more detailed lake history from the bolivian altiplano on the southern altiplano 10 lake oscillations have been identified from this new unified chronology each coincident with north atlantic cold events such as heinrich events h5 h2 h1 and the younger dryas by coupling this new lake history to a hydrologic budget model we are able to evaluate precipitation variability on the southern bolivian altiplano over the last 130 ka these modeling efforts underscore the relative aridity of the altiplano during the rare and small lake cycles occurring between 80 and 20 ka when colder temperatures combined with little or no change in rainfall produced smaller paleolakes relative aridity between 80 and 20 ka contrasts with the immense tauca lake cycle 18 1 14 1 ka which was six times larger than modern lake titicaca and coincided with heinrich event 1 this improved paleolake record from the southern altiplano reveals a strong link between central andean climate and atlantic sea surface temperature gradients during the late pleistocene even though today rainfall variability is driven mostly by pacific sea surface temperature anomalies associated with el nino southern oscillation however not all heinrich events appear to result in lake expansions most conspicuously during the global cold interval between 80 and 20 ka when the altiplano and amazon basin were relatively arid

transformation of an archean craton margin during proterozoic basin formation and magmatism the albany fraser orogen western australia abstract the albany fraser orogen is a well preserved example of proterozoic modification of an archean craton margin the formation of two successive basin systems accompanied by magmatism along the southern and southeastern yilgarn craton margin in western australia reflect distinct changes in tectonic regimes resulting in significant transformations of the archean craton crust provenance analysis from detrital zircons indicates that the first basin system the c 1815 1600 ma barren basin was dominantly filled with neoarchean detritus derived from the yilgarn craton and paleoproterozoic detritus derived from coeval voluminous mostly felsic magmatism the abundance of locally derived sediment deposited onto a reworked archean yilgarn craton substrate coupled with the progressively more juvenile isotopic signature of magmas indicates a largely extensional tectonic setting consistent with either a continental rift basin or a long lived backarc basin system this extensional regime led to the formation of a passive margin and oceanic basin along the craton edge the c 1600 1305 ma arid basin and formation of an ocean continent transition in the most heavily modified outboard region of the craton margin the eastern nornalup zone a change in tectonic regime is denoted by the formation of an oceanic arc the c 1410 ma loongana arc preserved in the adjoining madura province oceanic subduction led to accretion of the loongana arc onto the craton edge recorded by the presence of exotic detritus derived from this arc deposited into a foreland basin uppermost arid basin this accretion event triggered crustal thickening and the earliest phase of magmatism of stage i of the albany fraser orogeny at c 1330 ma a change to west dipping subduction beneath the accreted portion of the loongana arc placed the orogen into a backarc setting into which the remainder of the recherche supersuite mafic and felsic magmas were intruded thus the albany fraser orogen is regarded as an archean craton margin that preserves a long history of proterozoic transformation dominated by extensional processes that resulted in the formation of orogen wide basin systems accompanied by magmatism the recognition that the albany fraser orogen has always been part of the west australia craton and the tectonic regimes that have affected it provide important constraints on reconstructions of the nuna and rodinia supercontinents

scratching the surface a marine sediment provenance record from the continental slope of central wilkes land east antarctica the geology of wilkes land east antarctica is masked by kilometers of ice and remains largely unexplored defining the sediment provenance adjacent to this hidden region is important for distinguishing the proximal subglacial basement terranes and refining the dynamic regional glaciological history this study presents a detrital sediment provenance record spanning c 23 5 ka from the continental slope of central wilkes land sediment provenance was characterized using u pb geochronology and trace element geochemistry from detrital zircon titanite and apatite and pb isotopic signatures from detrital feldspar these data were compared with new feldspar pb isotopic signatures and existing u pb zircon datasets from rare nearby coastal outcrop a principally igneous source was revealed with dominant age populations between c 1360 1100 ma and c 1620 1490 ma characteristic of rocks of the proximal wilkes and banzare provinces respectively minor detritus was additionally sourced from the proximal nuyina province c 1450 1390 ma temporal variation in the climate and ice sheet configuration are likely responsible for subtle downcore changes observed in detrital sediment provenance high sedimentation rates during the glacial period suggest reworking of continental shelf sediments and downslope transport in debris flows during ice sheet advance glacial meltwater fluxes fed largely by the totten glacier were responsible for supplying detritus during deglaciation during interglacials detritus was derived from a broad coastal region and delivered to the slope via multiple glacial outlets these results present the first substantial offshore evidence to support recent interpretations that the subglacial crust of central wilkes land has a dominantly mesoproterozoic history

constraints and deception in the isotopic record the crustal evolution of the west musgrave province central australia abstract the hf and nd isotopic evolution of the musgrave province central australia is used to constrain the timing of crust formation and lithospheric organisation of proterozoic australia the dataset from this region challenges two widely held tenets of hf and nd isotope systematics namely that crust formation events can only be identified as periods when crystallisation ages correspond to model ages and that linear hf evolution arrays away from depleted mantle along crustal lu hf or sm nd slopes reflect reworking of the same source hf isotopes in musgrave province zircon crystals indicate two major crust formation events at c 1900 ma and at 1600 1550 ma although no juvenile rocks or crystals are known from c 1900 ma radiogenic addition into the crust at this time is required to account for consistent nd and hf evolution patterns which show no indication of an initially heterogeneous source oxygen isotopes in zircon grains confirm that much of the c 1900 ma hf isotopic signal is not compromised by mixtures furthermore the correspondence between mantle extraction and the commencement of reworking of archean material supports new crust generation at c 1900 ma and a coupling between lower and upper crustal processes the c 1900 ma timing of juvenile addition is dissimilar to that in the albany fraser and arunta orogens and may reflect continental arc development on the margin of a southern continent the general hf isotopic evolution trend of the musgrave province apparently reflects reworking from a dominant c 1900 ma source with some additional unradiogenic and radiogenic input through time however in the 1220 1050 ma interval this apparent isotopic evolution contrasts with geological observations that indicate input of voluminous mantle derived material intracontinental rifts and other regions with sustained very high temperature crustal recycling processes generate magmatic provinces with extreme hfse enrichment this can have a profound influence on isotopic evolution trends suppressing typical juvenile addition patterns isotopic mixture modelling indicates that a significant volume of mantle derived material can be accommodated within hfse enriched magmas without diverging isotopic signatures from apparent reworking trends in the musgrave province the crust had become so hfse enriched during the prolonged musgrave orogeny 1220 1150 ma that it was insensitive to mantle input which is estimated to have been as much as 85 during this event

isotopic insight into the proterozoic crustal evolution of the rudall province western australia abstract the proterozoic assembly of australia involved the convergence of three main archean cratonic entities the north west and south australian cratons and is recorded in the proterozoic orogenic belts surrounding these continental nuclei the rudall province of northern western australia is the sole exposure of a paleo to mesoproterozoic orogen lying between the north and west australian cratons and may record the effects of their amalgamation we present new zircon o u pb and lu hf isotope data from magmatic rocks across the rudall province to which we add existing isotope data to yield a crustal evolution overview hf evolution trends for the ca 1804 1762 ma kalkan supersuite the ca 1589 1549 ma krackatinny supersuite and the ca 1310 1286 ma camel suite indicate a significant input of archean east pilbara basement material albeit as a mix with more juvenile material including a possible ca 1900 ma component zircon 18o data suggest a contribution from supracrustal material into the magmatic source of the kalkan supersuite which may have been emplaced in an extensional setting in contrast the krackatinny supersuite and camel suite have mantle like 18o which may reflect partial melting of deeper archean sources geochemical data for the krackatinny supersuite shows geochemical trends implying that melting of thickened mafic crust progressed from deeper to shallower levels possibly in a rift setting camel suite k rich leucogranites may also have been emplaced in an extensional setting towards the end of high p metamorphism all terranes of the rudall province are para autochthonous with respect to the pilbara craton with no requirement for arc related magmatism we outline two potential scenarios for the paleo to mesoproterozoic geodynamic evolution of the rudall province an early cratonic amalgamation between the west and north australian cratons ca 1680 ma followed by mesoproterozoic intraplate events or a later assembly ca 1377 1275 ma we lean towards this later amalgamation scenario

crustal formation in the grenville province nd isotope evidence ninety eight new nd isotope analyses are presented for gneissic rocks from the grenville province when combined with over 250 published nd analyses and some unpublished analyses these data can be used to establish a first order crustal formation age map for most of the grenville parautochthon and allochthonous polycyclic belt in particular the geographic extents of a juvenile labradorian arc labradoria and a juvenile 1 5 ga arc quebecia are defined each with an area probably in excess of 100 000 km2 in addition pre 1 75 ga arcs are identified in ontario barilia and labrador makkovikia this work largely fills the last major gap in the continent wide crustal formation age map of the precambrian shield of north america

proterozoic crustal evolution of the eucla basement australia implications for destruction of oceanic crust during emergence of nuna abstract the crystalline basement beneath the cretaceous to cenozoic bight and eucla basins in western australia has received comparatively little attention even though it lies on the eastern margin of one of the most mineral resource endowed regions on the planet this basement is characterized by a complex geological evolution spanning c 2 billion years but paucity of outcrop and younger basin cover present a daunting challenge to understand the basement geology in this work the composition of the unexposed proterozoic crystalline basement to the bight and eucla basins is investigated through zircon hf isotopes and whole rock geochemistry from new drillcore samples this region includes two geophysically defined basement entities the madura province containing 1 c 1478 ma sleeper camp formation which has variable isotopic signatures including evolved values interpreted to reflect reworking of rare slivers of hyperextended archean crust 2 1415 1389 ma haig cave supersuite with mantle like isotope values interpreted as melting of subduction modified n morb source and 3 1181 1125 ma moodini supersuite with juvenile isotopic signatures interpreted to reflect mixed mafic lower crustal and asthenospheric melts produced at the base of thinned crust the coompana province to the east of the madura province has three major magmatic components 1 c 1610 ma toolgana supersuite with chemical and isotopic characteristics of primitive arc rock 2 c 1490 ma undawidgi supersuite with juvenile isotope values consistent with extensional processes involving asthenospheric input and 3 1192 1140 ma moodini supersuite with strong isotopic similarity to moodini supersuite rocks in the madura province this new isotopic and geochemical data shows that the madura and coompana regions together represent a huge tract of predominantly juvenile material magma sources recognised include 1 depleted mantle producing morb like crust at c 1950 ma but also contributing to younger magmatism 2 recycled c 1950 ma crust reworked in primitive arcs and in intra plate settings and 3 minor evolved material representing fragments of hyperextended continent the observed isotopic evolution pattern is comparable to that of other central australian proterozoic provinces including the musgrave province the northern margin of the gawler craton and components within the rudall province linking these isotopic signatures defines the mirning ocean and its subducted and underplated equivalents in a global context we suggest c 1950 ma crust production reflects the onset of ordered oceanic spreading centres which swept juvenile crustal fragments into nuna

revisiting the chronology and environmental conditions for the accretion of late pleistocene early holocene pampean loess argentina abstract the present research work reviews the age models of three previously studied loess sections across 700 km in the loess belt of the pampean region in central argentina the loess sections were investigated for the first time through high resolution luminescence dating in order to determine the chronology of the loess deposits and its temporal correlation with important palaeoclimatic records of the southern hemisphere reliable estimations of mass accumulation rates mars for loess were used to infer the temporal dust flux variation during the last glacial interglacial transition in southern south america the new age models have significant differences compared to the previously published ones of likely last glacial maximum lgm ages the three studied sections showed general bimodal grain size distributions consistent with multiple sources contributing dust to the pampas it is observed that higher mars values are associated with an increased presence of finer loess increases in loess accumulation are coeval with climatic transitions from wetter to drier periods in the puna altiplano plateau and high mars are related to synchronous climatic shifts to humid conditions in the pampean plain contrasting with dust fluxes observed in the more distal palaeoarchives i e the south atlantic ocean and the antarctic ice sheet the new data suggest increased dust accumulation in the pampas during the antarctic cold reversal acr and the holocene this supports the idea that changes related to atmospheric transport efficiency can better explain dust flux variations observed over glacial interglacial periods in distant palaeoarchives

are granites and granulites consanguineous an important question in petrology is whether the production of granite magma in orogens is a closed system process with respect to mass input from the mantle this is commonly addressed by inversion of geochemical data from upper crustal granites but a complementary approach is to assess the kinship of residual granulites and associated granites in exhumed orogenic crust here we report geochemical data for a suite of contemporaneous metasedimentary granulites and granites from the eastern ghats province india part of a grenville age orogen the prograde metamorphic evolution involved increasing temperature t and pressure p to a metamorphic peak at 1000 c at 0 7 gpa followed by slow close to isobaric cooling variations in the composition of granites are interpreted to be due to local processes including fractionation during melting or crystallization and or peritectic mineral entrainment the nd and sr isotope compositions of the granites can be matched by mixing between different granulites suggesting that they may have been derived solely from sedimentary protoliths leaving behind granulite facies residues however by including geochemical data from an adjacent area to the north it becomes clear that an increasingly important mass input from the mantle was involved in granite genesis from southwest to northeast in the eastern ghats province as confirmed by modeling assimilation fractional crystallization between an exemplar mantle derived melt at 1000 ma and the residual granulites the extreme peak metamorphic temperature and p t evolution suggest extended lithosphere that relaxed thermally to its former thickness during slow cooling we postulate that the spatial variation in mantle input to the granites was related to changing feedback between the rates of extension and flux of mantle melt

modern and holocene aeolian dust variability from talos dome northern victoria land to the interior of the antarctic ice sheet abstract high elevation sites from the inner part of the east antarctic plateau sample windborne dust representative of large portions of the southern hemisphere and are sensitive to long range atmospheric transport conditions to polar areas on the periphery of the ice sheet conversely the aeolian transport of particles from high elevation ice free areas can locally represent a relatively important additional input of dust to the atmosphere and the interplay of atmospheric dynamics dust transport and deposition is strictly related to the regional atmospheric circulation behaviour both at present day and in the past the understanding of the spatial extent where local sources can influence the mineral dust budget on the ice sheet is fundamental for understanding the atmospheric dust cycle in antarctica and for the interpretation of the dust history in marginal glaciological settings in this work we investigate the spatial variability of dust flux and provenance during modern pre industrial and holocene times along a transect connecting talos dome to the internal sites of the antarctic plateau and we extend the existing documentation of the isotopic sr nd fingerprint of dust sized sediments from victoria land source areas dust flux grain size and isotopic composition show a marked variability between talos dome mid point d4 and dome c vostok suggesting that local sources play an important role on the periphery of the ice sheet microscope observations reveal that background mineral aerosol in the taldice core is composed by a mixture of dust volcanic particles and micrometric sized fragments of diatoms these latter representing a small but pervasive component of antarctic sediments a set of samples from victoria land mostly consisting of regolith and glacial deposits from high elevation areas was collected specially for this work and the isotopic composition of the dust sized fraction of samples was analyzed results reveal a close relationship with the parent lithologies but direct comparison between source samples and firn ice core dust is problematical because of the ubiquitous volcanic contribution to the environmental particulate input in the talos dome area the frequency of events potentially suitable for peripheral dust transport to talos dome appears relatively high for present day conditions according to back trajectories calculations and the related air flow pattern well defined from a seasonal and spatial perspective also as expected from palaeo data these events appear extremely uncommon for internal sites

sediment routing and basin evolution in proterozoic to mesozoic east gondwana a case study from southern australia abstract sedimentary rocks along the southern margin of australia host an important record of the break up history of east gondwana as well as fragments of a deeper geological history which collectively help inform the geological evolution of a vast and largely underexplored region new drilling through cenozoic cover has allowed examination of the cretaceous rift related madura shelf sequence bight basin and identification of two new stratigraphic units beneath the shelf the possibly proterozoic shanes dam conglomerate and the interpreted palaeozoic southern officer basin unit the decoration sandstone recognition of these new units indicates an earlier basinal history than previously known lithostratigraphy of the new drillcore has been integrated with that published from onshore and offshore cores to present isopach maps of sedimentary cover on the madura shelf new palynological data demonstrate progression from more localised freshwater brackish fluvio lacustrine clastics in the early cretaceous foraminisporis wonthaggiensis valanginian to barremian to widespread topography blanketing fully marine glauconitic mudrocks in the mid cretaceous endoceratium ludbrookiae albian geochronology and hf isotope geochemistry show detrital zircon populations from the madura shelf are comparable to those from the southern officer basin as well as cenozoic shoreline and palaeovalley sediments in the region the detrital zircon population from the shanes dam conglomerate is defined by a unimodal 1400 ma peak which correlates with directly underlying crystalline basement of the madura province peak ages of 1150 ma and 1650 ma dominate the age spectra of all other samples indicating a stable sediment reservoir through much of the phanerozoic with sediments largely sourced from the albany fraser orogen and musgrave province directly and via multiple recycling events the madura shelf detrital zircon population differs from published data for the upper cretaceous ceduna delta to the east indicating significant differences in sediment provenance and routing between the ceduna sub basin and central bight basin

foreign contemporaries unravelling disparate isotopic signatures from mesoproterozoic central and western australia abstract extensive time constrained isotopic sm nd lu hf datasets on samples with well studied geological context demonstrates that the musgrave province of central australia and the albany fraser orogen of south western australia evolved through temporally similar mesoproterozoic orogenies at 1345 1260 and 1215 1140 ma but on completely different basement the west and north australian cratons amalgamated before the 1345 1260 ma event which saw the convergence and final amalgamation of those combined cratons with the south australian craton well defined nd and hf isotopic evolution arrays for the musgrave province reflect a juvenile basement with distinct 1950 1900 1600 1550 ma crust formation events rare non radiogenic material is seen only in detritus and in magmas that assimilated this material this evolved detritus was derived from non yilgarn archean sources and reworked archean sources which were added to sedimentary basins developed over the musgrave province basement during and after c 1400 ma to the south of the musgrave province the madura province has a similarly radiogenic signature to the musgrave province and is likely contiguous with it beneath younger cover sequences it shows 2 0 1 4 ma mantle extraction ages and is dominated by juvenile rocks reflecting oceanic crust consumed to the north of the south australian craton and east of the west australian craton available data support the suggestion that the musgrave province is simply modified madura province crust situated along the edge of the north australian craton together the musgrave province and the madura province represent proterozoic australia s most juvenile crustal remnant in stark contrast to this juvenile remnant the isotopic evolution array for the albany fraser orogen reveals a much more evolved signature charting progressive juvenile input into an archean source with strong isotopic and age similarity to the yilgarn craton of the west australian craton

a novel application of image analysis to interpret trace element distributions in magmatic sulphides abstract the albany fraser orogen in western australia hosts significant magmatic sulphide mineralisation but the impacts of its extensive metamorphic history on this mineralisation are poorly understood post formation modification including fluid facilitated alteration can upgrade or destroy mineralisation with significant consequences for economic ore deposits we present laser ablation trace element data from samples of variably altered sulphide breccia from the mineralised octagonal prospect located in the fraser zone of the albany fraser orogen mineral compositions are combined with laser ablation mapping and novel co localisation analysis to characterise the magmatic and post magmatic processes that modified element distributions within magmatic sulphide ore higher concentrations of re co ni os ir and lower concentrations of cu zn and ag in pyrrhotite and pentlandite relative to chalcopyrite record sulphide crystallisation from a sulphide liquid textural evidence and the compositions of pyrrhotite and pyrite are consistent with replacement of pyrrhotite by pyrite and associated magnetite element maps reveal intergranular variations in pentlandite ag content that are systematically linked to the sulphide distribution co localisation analysis shows that the associations among mn pb ag and the sample fracture networks are statistically significant the association is interpreted as a consequence of fluid assisted element remobilisation post formation alteration processes at octagonal were accompanied by variable remobilisation and depletion of metal concentrations associated with mineralisation the co localisation analysis provides an invaluable tool that enabled quantitative assessments of these relationships

metamorphic growth and recrystallization of zircon distinction by simultaneous in situ analyses of trace elements u th pb and lu hf isotopes in zircons from eclogite facies rocks in the sulu orogen simultaneous in situ analyses of trace elements u th pb and lu hf isotopes were carried out on distinct domains of zircons in ultrahigh pressure uhp eclogite facies metamorphic rocks from the main hole of the chinese continental scientific drilling ccsd in the sulu orogen for the first time trace elements are directly linked to lu hf isotopes in metamorphic zircons with reference to their u pb dates this enables methodological integration to distinguish four types of metamorphic zircon solid state replacement and dissolution recrystallizations of protolith zircons and new growth from the aqueous fluid metamorphically grown zircons are characterized by concordant u pb ages for the metamorphism flat hree patterns typical of the garnet effect low contents of ree especially hree y nb ta and th u high contents of hf low lu gd n lu hf and th u 0 1 ratios and elevated 176hf 177hf ratios relative to solid state recrystallized zircons this suggests the effects of both garnet and fluid on the growth of metamorphic zircons in contrast metamorphic recrystallization has reset the u th pb isotope system of protolith zircons to different extents depending on the extents of fluid action during metamorphism solid state recrystallized zircons exhibit the lowest degrees of resetting and thus almost inherit all geochemical features from the protolith zircons which are characterized by discordant u pb ages close to or below the protolith age steep mree hree patterns typical of magmatic origin high contents of trace elements and their ratios and low 176hf 177hf ratios on the other hand dissolution recrystallized zircons show the highest degrees of reworking and thus have concordant or nearly concordant u pb ages for the metamorphism steep mree hree patterns lowered contents of trace elements such as ree th u y nb ta and ti relative to the protolith zircons and almost unchanged hf isotope ratios replacement recrystallized zircons display intermediate degrees of reworking and thus have their many features of elements and isotopes in between while the metamorphic growth in the presence of both garnet and fluid is characterized by both depletion of hree with flat pattern and the low contents of trace elements the metamorphic recrystallization in the presence of aqueous fluid is indicated by gradual decreases of mree to hree without the flat hree pattern therefore the simultaneous in situ analyses of metamorphic zircons have the advantage over single term analyses in making distinction between the new growth and the different types of recrystallization

periodic paleoproterozoic calc alkaline magmatism at the south eastern margin of the yilgarn craton implications for nuna configuration abstract the age and composition of magmas provide fundamental information to chart the tectonic setting of crustal development through time and hence refine paleogeographic reconstructions the biranup zone of the albany fraser orogen in southwestern australia preserves a protracted record of magmatism associated with the formation and subsequent break up of the paleoproterozoic supercontinent nuna yet the configuration of proterozoic australia within nuna is not well constrained new u pb zircon geochronology on four samples of mafic intrusions in the north eastern biranup zone yield u pb crystallisation ages of 1809 17 ma 1798 12 ma 1796 12 ma and 1755 12 ma coeval with known pulses of felsic magmatism elsewhere in the orogen the lu hf isotope composition of zircon crystals from these mafic intrusions and the metasedimentary rocks they intrude reveal juvenile magmatic input into the archean yilgarn craton with this magmatism commencing as early as c 1 90 ga following this juvenile magmatism the margin of the craton was affected by at least three pulses of calcic to calc alkaline magmatism between 1 81 and 1 65 ga secular changes in zircon hf isotope composition are comparable in both duration and periodicity to 50 100 ma changes in magma composition and zircon chemistry observed in modern volcanic arcs of the american cordillera and in cambrian to carboniferous accretionary complexes of eastern australia isotopic patterns and whole rock chemistry are apparently consistent with the 1 81 1 70 ga paleoproterozoic igneous rocks of the albany fraser orogen forming in a magmatic arc above a pacific type subduction zone which extended along the south eastern margin of the yilgarn craton this interpretation is consistent with paleomagnetic data which places the yilgarn craton on the periphery of the supercontinent nuna at 1 90 1 60 ga

tracking mineralisation with in situ multiple sulphur isotopes a case study from the fraser zone western australia abstract sulphur isotopes have become a widely deployed tool to address the sources of fluids in ore systems given the widespread interaction of h2s hs and s 2 with metals however the sensitivity of sulphur isotopes to magma source composition relative to other radiogenic isotopes and the nature of processes differentially affecting isotopic systems have not been extensively explored in magmatic mineral systems in this work we present a case study of sulphide bearing magmas within the fraser zone of the albany fraser orogen in western australia that seeks to evaluate the sensitivity of sulphur isotopes to track magma source composition in space and time new 34 s data from mineralised nrm plato and octagonal localities of the fraser zone indicate variable degrees of assimilation of local sediments of the snowys dam formation despite an archean heritage in the fraser zone magmas being indicated by radiogenic isotopes sparse xenocrystic zircon and whole rock geochemical modelling 33 s data from these localities reveal archean sulphur is absent implying decoupling of the sulphur component from other geochemical and isotopic systems this is consistent with a mechanism by which archean sulphur was removed from detrital material incorporated in the fraser zone we conclude that sulphides were stripped from sediments during uplift erosion and transport to the fraser zone with these archean sulphur depleted sediments then assimilated by the fraser zone parental magmas our results indicate a coupling between variable assimilation of external sulphur by fraser zone magmas and the mineralisation present at the prospects studied however assimilated sulphur cannot account for all of the sulphur within mineralised samples indicating the involvement of additional processes such as tenor upgrading

cenozoic eucla basin and associated palaeovalleys southern australia climatic and tectonic influences on landscape evolution sedimentation and heavy mineral accumulation abstract the eucla basin including the vast nullarbor plain lies on the margins of the yilgarn musgrave and gawler cratons in southern australia and owes its distinctive landscape to a unique set of interactions between eustatic climatic and tectonic processes over the last 50 ma understanding of the history of the basin and the palaeovalleys that drained from the surrounding cratons are important because they contain major mineral deposits and the sediments derived from them contain remobilised gold uranium and heavy minerals in particular a remarkably preserved palaeoshoreline sequence along the north eastern margin of the eucla basin is highly prospective for heavy mineral placer deposits the record of marine marginal marine estuarine fluvial and lacustrine environments as constrained mainly by an extensive borehole dataset reflects major depositional events during the palaeocene early eocene middle late eocene oligocene early miocene middle miocene early pliocene and pliocene quaternary these events reflect the key role of eustatic sea level variation which during highstands inundated the craton margins flooding palaeovalleys to up to 400 km inboard of the present coastline however a systematic eastward migration of the depocentre across the eucla basin during the neogene together with apparent flow reversals in a number of palaeovalley systems draining the gawler craton suggest that the eucla basin has also been subject to differential vertical movements expressed as a west side up east side down tilting of 100 200 m this differential movement forms part of a broader north down southwest up dynamic topographic tilting of the australian continent associated with relatively fast 6 7 cm yr northward plate motion since fast spreading commenced in the southern ocean at 43 ma we suggest that the evolving dynamic topography field has played a key role in facilitating development of placer deposits largely through multistage eastward reworking of near shore sequences during highstand transgressive cycles on a progressively tilting platform under the influence of persistent westerly weather systems

strengths and limitations of zircon lu hf and o isotopes in modelling crustal growth abstract the robust nature of the mineral zircon combined with our analytical ability to readily acquire in situ uranium lead u pb lutetium hafnium lu hf and oxygen o isotopic data has resulted in a rapid rise in the use of zircon isotopic datasets for studying both the generation of continental crust and its growth through earth history in such studies there has been a strong focus on developing methods to determine the timing and or proportion of juvenile magmatic addition to the continental crust one widespread approach to determine the timing of crustal growth has been the construction or fitting of reworking arrays to regional hf isotopic datasets simple stochastic models are presented which highlight that in many cases apparent reworking arrays are much more likely to represent a process of on going dilution and refertilisation of ancient crust consistent with hot zone models of granitoid generation and the need to refertilise lower crustal reservoirs to maintain magmatism a new compilation of magmatic rock zircon lu hf and o isotope data is used to demonstrate that the use of mantle like o isotope data as a screening tool for meaningful hf model ages is also unlikely to be reliable with independently constrained data indicating that as few as 14 of hf model ages provide a meaningful indicator of the timing of crustal growth the limitations of hf model ages are discussed with regard to existing approaches for continental growth and we demonstrate that popular inverse modelling approaches suffer from a bias created by both the use of model ages and numerical artefacts in an effort to address some of the limitations within existing models we develop stochastic models based on joint calibration of multiple datasets which allow for more unique solutions

temperature effect over garnet effect on uptake of trace elements in zircon of ttg like rocks abstract to assess the garnet effect on uptake of rare earth elements in ttg petrogenesis zircon trace elements were analyzed for ttg like rocks in a neoproterozoic composite batholith at huangling in the yangtze gorge south china a ttg like suite has higher whole rock la yb and sr y ratios lower whole rock nb la ratios and e nd t values and lower zircon e hf t values than the other three non ttg suites zircons from this suite have higher hf nb and ta contents than those from the other three non ttg suites however ree profiles and ratios cannot be unambiguously distinguished between residued cores and co magmatic domains despite significant differences in their u pb ages and lu hf isotopes all zircons from the four suites are enriched in hree but depleted in lree with positive ce anomalies they display no to very weak eu anomalies contrasting to the typical zircon of magmatic origin this suggests that plagioclase was neither a stable phase during partial melting nor a removed phase during fractional crystallization most of the zircons from the ttg like rocks have ti contents lower than 30 ppm yielding a range of ti in zircon temperatures from 600 to 880 c while a part of zircons from all granitoids show various degrees of lree enrichment the absence of flat hree patterns is evident for all zircons including both residued cores and co magmatic domains in the ttg like rocks this suggests that there is no preferential uptake of hree in garnet relative to zircon even if garnet could exist as a stable phase during partial melting to form the ttg and their source rocks because partition coefficients for garnet melt zircon melt and zircon garnet decrease with increasing temperature during partial melting comparison of calculated apparent d hree values with experimental d hree values between zircon and melt allows estimate of temperatures for zircon crystallization this yields a range of 750 to 800 c for the ttg like rocks which is consistent with whole rock zircon saturation temperatures of 756 to 793 c however they are significantly lower than the crossover temperatures of 900 to 950 c for preferential partition of hree in the zircon garnet melt system thus the temperature is suggested as a key cause for the lack of garnet effect on the uptake of hree in zircons from the ttg like rocks therefore the temperature effect can play a critical role in dictating the partition of hree in the zircon garnet melt system of adakitic and ttg type rocks

earliest paleoproterozoic high grade metamorphism and orogenesis in the gawler craton south australia the southern cousin in the rae family neoarchean earliest paleoproterozoic rocks of the gawler craton preserved within the mulgathing complex south australia record metamorphism and deformation during an earliest paleoproterozoic tectonothermal event known as the sleafordian orogeny we present metamorphic data from pelitic gneisses of the mulgathing complex from three locations challenger mt christie and blackfellow hill in order to constrain the pressure temperature time p t t evolution of this orogeny in situ u pb dating via laser ablation inductively coupled plasma mass spectrometry shows that monazites within garnet porphyroblasts have ages ca 2470 ma providing an estimate of the timing peak p t conditions monazite crystallisation from melt occurred at ca 2460 ma in the presence of peritectic garnet either late on the prograde path during biotite dehydration melting or immediately following peak t lobate and patchy rims in leucosome hosted monazite suggest a dissolution reprecipitation process occurred during cooling across the elevated dry solidus at ca 2440 ma monazite younger than ca 2430 2420 ma that is located at grain boundaries between matrix minerals likely reflects monazite crystallisation during cooling across the dry solidus and or subsolidus mineral breakdown during the waning stages of the thermal event phase diagram modelling of pelitic gneisses suggests peak metamorphic conditions at the three localities overlap at 7 kbar and 850 c with apparent thermal gradients in the order of 125 135 c kbar 35 45 c km metamorphism involved a tight anticlockwise p t t path based on mineral assemblage paragenesis and indicates a slow shallow decompressive cooling path sub parallel to the apparent thermal gradient in the order of few degrees per myr a protracted magmatic history involving bimodal magmatism associated with a thinned and underplated extensional basin in the mulgathing complex was likely a thermal precursor to the high thermal gradient metamorphism and convergent transpressive deformation a significant period of post 2 4 ga quiescence in the gawler craton subsequent to basin inversion suggests that this orogenesis may have occurred interior to a plate margin the similarity in timing and style between the sleafordian orogeny in the gawler craton and the 2 5 2 28 ga arrowsmith orogeny of the rae craton supports the notion that these terranes together with the broader gawler adelie craton of the mawson continent the north australia craton elements of the north china sino korean and dharwar cratons formed part of a family of neoarchean terranes described as the rae family of cratons with a distinctive tectono metamorphic record as compared with other archean cratons we suggest the mawson continent is the southern member of this family dominated as it is by terranes now present in the northern hemisphere

pb isotope mapping of differentially uplifted archean basement a case study from the grenville province ontario abstract uranium mobility during regional metamorphism typically causes the continental crust to become stratified in the u pb ratio and hence over time pb isotope ratio this means that pb isotope analysis of old gneiss terranes might be used as a means of estimating the original burial depth of the crust and its subsequent uplift history the approach would be useful if other measures of burial depth such as mineral chemistry have been erased by younger metamorphic events a situation found in the nw grenville province to test the usefulness of this approach whole rock pb isotope data were collected for grenville gneisses in order to investigate their burial uplift history results were compared with levack gneiss data from sudbury immediately north of the study area several grenville gneisses have pb isotope ratios close to the least radiogenic levack gneiss signature believed to be exhumed from 20 km depth hence it is concluded that gneisses immediately se of the grenville front tectonic zone represent deeply eroded archean basement exhumed in the grenville orogeny on the other hand high pb isotope ratios near the archean proterozoic suture suggest the preservation of archean upper crustal rocks in this vicinity consistent with the burial of the craton margin under an accreted paleoproterozoic arc it is concluded that pb isotope mapping is a useful tool to study the exhumation of archean crust in highly metamorphosed orogenic belts such as the grenville province

a study of rare earth element ree sio 2 variations in felsic liquids generated by basalt fractionation and amphibolite melting a potential test for discriminating between the two different processes the origin of felsic magmas 63 sio2 in intra oceanic arc settings is still a matter of debate two very different processes are currently invoked to explain their origin these include fractional crystallization of basaltic magma and partial melting of lower crustal amphibolite because both fractionation and melting can lead to similar major element trace element and isotopic characteristics in felsic magmas such lines of evidence have been generally unsuccessful in discriminating between the two processes a commonly under appreciated aspect of rare earth element ree solid liquid partitioning behavior is that d ree for most common igneous minerals especially hornblende increase significantly with increasing liquid sio2 contents for some minerals e g hornblende and augite ree partitioning can change from incomptatible d 1 at high liquid sio2 when this behavior is incorporated into carefully constrained mass balance models for mafic basaltic amphibolite melting intermediate andesitic amphibolite melting lower or mid to upper crustal hornblende present basalt fractionation and mid to upper crustal hornblende absent basalt fractionation the following general predictions emerge for felsic magmas e g 63 to 76 sio2 partial melting of either mafic or intermediate amphibolite should regardless of the type of melting equilibrium fractional accumulated fractional yield ree abundances that remain essentially constant and then decrease or steadily decrease with increasing liquid sio2 content at high liquid sio2 contents lree abundances should be slightly enriched to slightly depleted i e c l c o 2 to 0 2 while hree abundances should be slightly depleted c l c o 1 to 0 2 lower crustal hornblende bearing basalt fractionation should yield roughly constant ree abundances with increasing liquid sio2 and exhibit only slight enrichment c l c o 1 2 mid to upper crustal hornblende bearing basalt fractionation should yield steadily increasing lree abundances but constant and then decreasing hree abundances at high liquid sio2 contents lree abundances may range from non enriched to highly enriched c l c o 1 to 5 while hree abundances are generally non enriched to only slightly enriched c l c o 1 to 2 hornblende absent basalt fractionation should yield steadily increasing ree abundances with increasing liquid sio2 contents at high sio2 contents both lree and hree are highly enriched c l c o 3 to 4 it is proposed that these model predictions constitute a viable test for determining a fractionation or amphibolite melting origin for felsic magmas in intra oceanic arc environments where continental crust is absent

a window into an ancient backarc the magmatic and metamorphic history of the fraser zone western australia abstract the fraser zone is a major lithotectonic domain of the albany fraser orogen western australia which records proterozoic modification of the margin of the archean yilgarn craton the fraser zone is volumetrically dominated by gabbroic rocks and their metamorphosed equivalents however little is known of the pressure temperature time p t t history or the geodynamic setting of these mafic rocks when considered within the context of existing p t constraints from spatially associated metapelitic rocks modelled phase equilibria suggest that both the unmetamorphosed gabbros and the granulite facies metagabbroic rocks equilibrated at 950 900 c and 7 kbar interpreted to record the conditions of magmatic crystallisation and peak metamorphism respectively these data support the view that mafic magmatism was the thermal driver for high t low p granulite facies metamorphism the absence of garnet from the metagabbroic rocks and the lack of evidence for its former presence i e as inclusions argues that during metamorphism the rocks never reached pressures above those they attained at the thermal peak coronae of zircon around ilmenite in the magmatic rocks reflect a local supply of zr as it exsolved from ilmenite permitting earlier growth of zircon around ilmenite than elsewhere during melt crystallisation u pb dating of coronal zircon 1315 5 ma and a discrete magmatic zircon grain isolated from ilmenite 1296 5 ma constrain the duration of magmatic crystallisation between ca 10 and 30 ma zircon in a metamorphosed gabbro constrains the timing of granulite facies metamorphism to 1293 6 ma synchronous with final crystallisation of the mafic magmas based on the implied metamorphic evolution of these rocks and that of the surrounding supracrustal package along with existing isotopic and geochemical data we suggest the fraser zone probably formed in a backarc or perhaps an intracontinental rift setting and records successive emplacement of gabbroic rocks into a thick sediment filled basin the older gabbroic rocks record hydration and reaction with the devolatilising and or partially molten metasedimentary rocks into which they were emplaced subsequent granulite facies metamorphism of these hydrated rocks was driven by the heat provided by the intrusion of younger mafic magmas

heat flow in southern australia and connections with east antarctica viscosity and melt generation at the base of ice sheets are critically dependent upon heat flow yet subglacial heat flow is poorly constrained due to the logistical challenges of obtaining boreholes that intersect the bedrock beneath thick ice cover currently continental estimates of antarctic heat flow are derived from geophysical methods that provide ambiguous constraints of crustal heat sources despite their demonstrated importance for accurate predictions of future ice sheet behavior this study pursues an alternative approach by using heat flow measurements from rock units in the coompana province of southern australia which represent the geological counterparts of those beneath wilkes land in east antarctica we present nine new surface heat flow estimates from this previously uncharacterized region ranging from 40 to 70 mw m2 with an average of 57 3 mw m2 these values compare favorably to recent geophysically derived estimates of 50 75 mw m2 for the totten glacier catchment of east antarctica and to the single in situ measurement of 75 mw m2 from the law dome deep ice borehole however they are appreciably lower than the range of 56 120 mw m2 83 13 mw m2 average for the abnormally enriched proterozoic terranes of the central australian heat flow province this study provides the first regional heat flow map of geological provinces formerly contiguous with east antarctica through the application of continent scale heat flow data sets tied to a jurassic plate tectonic reconstruction for gondwana our approach reveals several discrepancies with current heat flow models derived from geophysical methods and provides a more robust analysis of subglacial heat flow using this plate tectonic synthesis as a proxy for east antarctica

titanite petrochronology linked to phase equilibrium modelling constrains tectono thermal events in the akia terrane west greenland abstract the mesoarchean akia terrane in west greenland contains a detailed magmatic and metamorphic mineral growth record from 3 2 ga to at least c 2 5 ga this time span makes this region an important case study in the quest to track secular changes in geodynamic style which may ultimately inform on the development of plate tectonics as a globally linked system of lateral rigid plate motions the common accessory mineral titanite has recently become recognised as a powerful high temperature geochronometer whose chemistry may chart the thermal conditions of its growth furthermore titanite offers the potential to record the time temperature history of mafic lithologies which may lack zircon although titanite suffers from higher levels of common pb than many other u pb chronometers we show how measurement of 207pb 206pb in texturally coeval biotite may assist in the characterization of the appropriate common pb composition in titanite titanite extracted from two samples of mafic gneisses from the akia terrane both yield u pb ages of c 2 54 ga although coeval their chemistry implies growth under two distinctly different processes in one case the titanite has elevated total ree high th u and grew from an in situ partial melt consistent with an identical date to granite dyke zircon in contrast the second titanite sample contains greater common pb lower total ree lower th u and grew from dominantly hydrothermal fluids zr in titanite thermometry for partial melt derived titanite with activities constrained by phase equilibrium modelling indicates maxima of c 690 c elsewhere in the akia terrane coeval metamorphism linked to growth of hydrothermal titanite is estimated at temperatures of c 670 c these new results when coupled with existing findings indicate punctuated repeated metamorphic events in the akia terrane in which high temperature conditions re occurred at least three times between 3 0 and 2 5 ga but crucially changed in style across a c 3 0 ga change point we interpret this change in metamorphism as reflecting a fundamental shift in geodynamic style in west greenland at 3 0 ga consistent with other estimates for the onset of widespread plate tectonic type processes

a mesoproterozoic supercontinent evidence from the indian shield abstract geophysical signatures of late paleoproterozoic collisional sutures fold belts between the deccan protocontinent and bundelkhand craton and between the bundelkhand and mewar cratons of the north indian shield are presented the aravalli and satpura orogenies evolved during these continent continent collision episodes both the orogenic episodes are associated with granulite facies metamorphism and metallogeny serpentinised ultramafic breccia in ophiolitic melange is present in both regions structural discontinuities and oppositely dipping reflection fabrics with high conductivity anomalies are the characteristic features of these collision zones a major gravity high is also observed all along the strike of these fold belts to a distance of 700 1000 km paleoproterozoic 1 8 2 1 ma ages corresponding to compressional activity have also been observed in the southern granulite terrain and other gondwana fragments extensive granites and gneisses of 1900 ma age are observed in the lower himalayas and nanga parbat ranges late paleoproterozoic orogenic activity is also observed in all of the earth s shields intense orogenic activity of this period observed in various widely separated cratonic blocks is related to global plate tectonic processes and supercontinental episodes the available geophysical evidences in various parts of the globe suggest the presence of a supercontinent referred to as columbia during the early mesoproterozoic period

archean komatiite volcanism controlled by the evolution of early continents the generation and evolution of earth s continental crust has played a fundamental role in the development of the planet its formation modified the composition of the mantle contributed to the establishment of the atmosphere and led to the creation of ecological niches important for early life here we show that in the archean the formation and stabilization of continents also controlled the location geochemistry and volcanology of the hottest preserved lavas on earth komatiites these magmas typically represent 50 30 partial melting of the mantle and subsequently record important information on the thermal and chemical evolution of the archean proterozoic earth as a result it is vital to constrain and understand the processes that govern their localization and emplacement here we combined lu hf isotopes and u pb geochronology to map the four dimensional evolution of the yilgarn craton western australia and reveal the progressive development of an archean microcontinent our results show that in the early earth relatively small crustal blocks analogous to modern microplates progressively amalgamated to form larger continental masses and eventually the first cratons this cratonization process drove the hottest and most voluminous komatiite eruptions to the edge of established continental blocks the dynamic evolution of the early continents thus directly influenced the addition of deep mantle material to the archean crust oceans and atmosphere while also providing a fundamental control on the distribution of major magmatic ore deposits

magma mixing and the production of compositional variation within granite suites evidence from the granites of southeastern australia granite suites are groups of plutons possessing characteristic features that are a result of their derivation from source material of a specific composition variation within suites has been ascribed to a variety of processes magma mixing or mingling is a popular hypothesis generally proposed in terms of blending between a crustal melt and mafic material from the mantle that caused that melting when the compositions of pain of suites from the bega batholith of southeastern australia are compared any differences seen at either end of the range in composition are also seen at the other limit so that both the most mafic and mostfelsic rocks show similar relative abundances of particular elements similar relationships are seen for other granites in the region these observations are not consistent with largescale magma mixing or mingling and although those processes may operate on a small scale they cannot have been responsible for the major compositional variations likewise assimilation of country rocks had no significant role in producing variation in the granites of southeastern australia the production of variation by differential separation of melt from residual solid source material or restite must be favoured for many of the granite suites of this region

tropical climate changes at millennial and orbital timescales on the bolivian altiplano tropical south america is one of the three main centres of the global zonal overturning circulation of the equatorial atmosphere generally termed the walker circulation1 although this area plays a key role in global climate cycles little is known about south american climate history here we describe sediment cores and down hole logging results of deep drilling in the salar de uyuni on the bolivian altiplano located in the tropical andes we demonstrate that during the past 50 000 years the altiplano underwent important changes in effective moisture at both orbital 20 000 year and millennial timescales long duration wet periods such as the last glacial maximum marked in the drill core by continuous deposition of lacustrine sediments appear to have occurred in phase with summer insolation maxima produced by the earth s precessional cycle short duration millennial events correlate well with north atlantic cold events including heinrich events 1 and 2 as well as the younger dryas episode at both millennial and orbital timescales cold sea surface temperatures in the high latitude north atlantic were coeval with wet conditions in tropical south america suggesting a common forcing

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

the mesoproterozoic thermal evolution of the musgrave province in central australia plume vs the geological record abstract the 1090 to 2 of western and central australia it also included one of the most voluminous additions of juvenile felsic material to earth s crust with the development of one of the world s longest lived rhyolitic centres including the talbot supervolcano previous suggestions that the event was the result of a deep mantle plume cannot adequately account for the 50 m y duration of mantle derived magmatism or the fact that isolated localities such as the talbot sub basin preserve the entire magmatic record with no discernible regional age progressive spatial trend for at least 100 m y before the giles event the musgrave region experienced high to ultra high crustal temperatures possibly as an ultra hot orogen born from a c 1300 ma back arc granitic magmatism prior to the giles event also involved a significant mantle derived component and was accompanied by mid crustal ultra high temperature 1000 c metamorphism reflecting a thin and weak lithosphere this magmatism also resulted in a mid crustal 25 km deep layer greatly enriched in radiogenic heat producing elements that strongly augmented the already extreme crustal geotherms over a prolonged period the giles event may have been triggered when this regional musgrave thermal anomaly was displaced and again significantly destabilised along the mundrabilla shear zone a continent scale structure that juxtaposed the musgrave province against the easterly extension of the capricorn orogen where pre existing orogen scale structures were in extension these orogen scale structures funnelled the magmas that produced the warakurna large igneous province and the intersection of the musgrave thermal anomaly and the mundrabilla shear zone was the site of the talbot supervolcano although previously thought to be a result of a deep mantle plume the giles event was more likely the product of intra plate tectonic processes involving an anomalous and prolonged thermal pre history a magma focussing lithospheric architecture and large scale tectonic movements

provenance of rifted continental crust at the nexus of east gondwana breakup the bruce rise a prominent bathymetric feature offshore the bunger hills east antarctica has basement of unknown crustal affinity and age in east gondwana the bruce rise is reconstructed near the naturaliste plateau offshore sw australia and microcontinents now submerged in the eastern indian ocean new zircon u pb hf data from two c 1150 ma granite samples dredged from the eastern escarpment of the bruce rise demonstrate that these rocks are dominated by xenocrystic cargo mesoproterozoic xenocrystic cores show textural evidence of melt mediated coupled dissolution precipitation to form rim domains with apparent ages that skew towards c 1150 ma the zircon u pb hf signatures from the xenocrysts in the bruce rise granites and from c 1230 to 1180 ma felsic intermediate granites and orthogneisses from the conjugate naturaliste plateau basement suggest late mesoproterozoic magmatism occurred at a transition in the regional tectonic architecture between a reworked archean cratonic margin and proterozoic juvenile crust on the basis of plate reconstructions exhumation and thinning of the basement to the bruce rise naturaliste plateau occurred predominantly during rifting of india prior to c 120 ma minor further thinning likely occurred leading up to the onset of seafloor spreading between australia naturaliste plateau and antarctica bruce rise from c 90 to 84 ma

late quaternary paleoenvironments and paleoclimatic conditions in the distal andean piedmont southern mendoza argentina abstract the andean piedmont of mendoza is a semiarid region covered by extensive and partially vegetated dune fields consisting of mostly inactive aeolian landforms of diverse size and morphology this paper is focused on the san rafael plain srp environment situated in the distal andean piedmont of mendoza 34 30 s and reports the sedimentology and osl chronology of two representative exposures of late quaternary deposits including their paleoenvironmental and paleoclimatic significance eleven facies including channel floodplain fluvio aeolian interaction and reworked pyroclastic and aeolian deposits were described and grouped into two facies associations fa1 and fa2 fa1 was formed by unconfined sheet flows minor channelized streams and fluvial aeolian interaction processes fa2 was interpreted as aeolian dune and sand sheet deposits osl chronology from the srp sedimentary record indicates that between ca 58 39 ka and ca 36 24 ka mis 3 aggradation was governed by ephemeral fluvial processes fa1 under generally semiarid conditions during mis 2 the last glacial maximum ca 24 12 ka a major climatic shift to more arid conditions is documented by significant aeolian activity fa2 that became the dominant sedimentation process north of the diamante atuel fluvial system the inferred paleoenvironmental conditions from the srp sections are in broad agreement with regional evidence

tectonic framework and evolution of the gawler craton southern australia the gawler craton is the major crustal province in the southern australian proterozoic and is pivotal in models seeking to describe the evolution of proterozoic australia the craton is host to the olympic dam iron oxide cu au u ree deposit as well as a number of other iron oxide copper gold iocg au and iron ore deposits the evolution of the gawler craton is dominated by two major phases of tectonic activity late archean and late paleoproterozoic early mesoproterozoic in total spanning ca 1 billion years the late archean 2560 2500 ma basin development was coeval with arclike felsic magmatism and mafic ultramafic magmas including komatiites collisional deformation between 2480 and 2420 ma led to ca 400 m y of tectonic quiescence conceivably within an early paleoproterozoic continental interior the second major phase of tectonic activity was in the middle to late paleoproterozoic and early mesoproterozoic 2000 1450 ma paleoproterozoic tectonism was initially dominated by rift related events which produced a series of basins over the interval ca 1900 to 1730 ma some of which contain significant iron ore reserves transient contractional deformation at ca 1850 ma led to batholith scale granitic magmatism in part derived from melting of the late archean basement major basin development was finally terminated by the 1730 to 1690 ma kimban orogeny the effects of which are widespread and include the formation of crustal scale shear systems granitic magmatism and low to high grade metamorphism the kimban orogeny was followed by a renewed period of extension between ca 1680 and 1640 ma leading to local magmatism and sedimentation which appears in part to have been coeval with the high grade ca 1650 ma ooldean event in the western gawler craton at ca 1620 to 1615 ma the generation of the arc related st peter suite in the southern gawler craton implies that craton components were located at an active plate margin the arc environment was superseded by a transition to a continental interior regime which coincided with the voluminous gawler range volcanics 1595 1590 ma and hiltaba suite granitoids 1595 1575 ma the hiltaba suite is dominated by high t fractionated felsic rocks with coeval mafic magmatism confirming a mantle involvement emplacement of the hiltaba suite coincided with the major mineralizing interval in the gawler craton regionally two distinct mineral systems have been recognized the olympic iocg province in the eastern part of the craton and the gold dominated systems within the central gawler gold province the spatial distribution of iocg versus au dominated mineral systems appears to reflect regional variations in crustal composition and hiltaba suite petrogeneses hiltaba aged granites in the olympic iocg province are isotopically more evolved richer in u and th and oxidized compared to similar aged granites in the au dominated province modern day heat flow in the iocg province is significantly higher 90 10 mwm 2 compared to the au dominated province 54 5 mwm 2 suggesting there are important lithospheric compositional differences between the two metallogenic provinces which may reflect an older phase of craton assembly widespread northwest southeast contractional deformation coeval with the emplacement of the hiltaba suite is expressed by the formation and or reactivation of shear zones ranging up to crustal scale within this regime northwest trending structures such as those in the vicinity of the olympic dam deposit are likely to have accommodated dilation associated with strike slip movements intersection between these structures and northeast trending contractional faults may have formed suitable structural traps for 1590 to 1580 ma mineralization the timing of syn hiltaba deformation overlaps with transpression and medium to high grade metamorphism associated with the ca 1570 to 1540 ma kararan orogeny which dominates the geophysical architecture of the central northern part of the craton the youngest phase of deformation in the craton is expressed by reactivation of shear zones between ca 1470 and 1450 ma and regional cooling

isotopic evidence for rapid continental growth in an extensional accretionary orogen the tasmanides eastern australia the trace element signature of earth s continental crust resembles that of arc lavas but the continents may have formed during ancient igneous pulses that are hard to reconcile with supra subduction zone magmatism we explore the role of coupled arc back arc accretionary processes in crust generation by considering the tectonic context of whole rock nd isotope and zircon hf o isotope data from igneous rocks of the australian tasmanides 515 230 ma which is thought to have evolved by the repeated opening and closure of sediment filled back arc basins behind a long lived subduction zone the significance of this process for continental crust formation has yet to be evaluated from an isotopic perspective granitic rocks in this area define striking secular end ehf 18o trends that correlate with the pattern of deformational events and register changes in magma source during tectonic activity these trends reveal that juvenile magmatic input was enhanced during extensional back arc rifting episodes that immediately followed crustal thickening suggesting a relationship between slab rollback and continental growth interaction between juvenile magma and sedimentary units deposited during a preceding back arc rifting cycle was integral to the formation of stable continental material this highlights the importance of back arc environments for both the generation and differentiation of continental crust the juvenile component within the tasmanide igneous rocks increased from the cambrian to the triassic consistent with a diminished input from cratonderived metasedimentary material as the subduction zone migrated outboard of the gondwana margin subduction zone retreat formed large tracts of new crust in eastern australia at comparable rates to crust generation at modern island arcs providing a mechanism for rapid continental growth at convergent margins using isotopic tracers to link tectonic evolution and crust generation in modern and ancient orogens can lead to a better understanding of the geodynamic controls on planetary differentiation