evolution of the south central segment of the archean abitibi belt quebec part iii plutonic and metamorphic evolution and geotectonic model textural criteria permit distinction between the pre kenoran and kenoran phases of plutonism and metamorphism the pre kenoran plutons and pre kenoran metamorphic phases are directly related to the volcanic evolution synvolcanic tonalite trondhjemite plutons and swarms of mafic and felsic dykes core central volcanic complexes the volcanic rocks underwent three types of pre kenoran metamorphism namely a pervasive alteration a thermal contact metamorphism that affected narrow aureoles around synvolcanic plutons and a high intensity hydrothermal alteration that affected cross cutting pipes in central volcanic complexes synkinematic kenoran metamorphism resulted in the growth of minerals chlorite actinolite etc parallel to schistosities synkinematic metamorphic grade ranges form the pumpellyite prehnite facies to the amphibolite facies late to post kinematic metamorphic phases resulted in the growth of minerals across schistosities syn to post kinematic plutons are not voluminous in the part o

syenite associated disseminated gold deposits in the abitibi greenstone belt canada a distinct group of gold deposits in the abitibi greenstone belt is spatially associated with quartz monzonite to syenite stocks and dikes the deposits occur mainly along major fault zones in association with preserved slivers of alluvial fluvial timiskaming type sedimentary rocks the deposits consist of disseminated sulfide replacement zones with variably developed stockworks of quartz carbonate k feldspar veinlets within zones of carbonate albite k feldspar and sericite alteration the syenitic intrusions are broadly contemporaneous with deposition of timiskaming sedimentary rocks and together with disseminated gold mineralization they have been overprinted by subsequent regional folding and related penetrative cleavage disseminated gold orebodies occur within composite syenitic stocks or along their margins along satellite dikes and sills and along faults and lithologic contacts away from intrusions orebodies in these different positions are interpreted to represent proximal to distal components of large magmatic hydrothermal systems centered on and possibly genetically related to composite syenitic stocks

facies mosaics across the persian gulf and around antigua stochastic and deterministic products of shallow water sediment accumulation abstract among broadly different types of sedimentary successions those that accumulate in nearshore settings are perhaps unique in that a very wide range of rock types recurs with high frequency over relatively short stratigraphic intervals this vertical lithofacies heterogeneity suggests that deposition of any sedimentary unit at any site was short lived that many different sediment types existed within a complex mosaic over the depositional surface and that this facies montage repeatedly moved across surfaces of accumulation in response to eustatic sedimentologic and or tectonic forcing data on numbers and thicknesses of lithofacies units from several dozen such sequences define the size frequency distribution expected if horizons of lithologic change occur randomly within sedimentary successions walther s law suggests that the amount of vertical lithologic heterogeneity manifest in a sedimentary sequence should reflect the degree of lateral heterogeneity in sediment composition that existed across depositional surfaces if so this repetition should also be manifest in sizes and areal distributions of sediment patches constituting the depositional mosaic in order to examine size frequency relations of sediment bodies across surfaces of sediment accumulation we tabulated numbers and areal extents of lithotopes across two rather dissimilar settings across the persian gulf and around the caribbean island of antigua although compositions and lateral extents of different sediment types exhibit broad lateral variation across interior to margin transects in either area lithotope abundances and areal extents define frequency distributions that are in excellent agreement with those anticipated for a facies mosaic of elements whose mean linear widths constitute an exponential frequency distribution these are the size frequency distributions one would expect if mosaic element boundaries occur randomly across regions of sediment accumulation and suggest that distributions of lithotope areas from holocene surfaces are directly analogous to lithofacies thickness frequencies from ancient successions in addition to the fact that both of the size frequency distributions attest to the importance of stochastic processes during sediment deposition they also afford numerical descriptors of abundances and areal extents of holocene lithosomes that can then be used as controlling parameters in computational models of sediment accumulation importantly results derived from such simulations are based not on inference of water depth varying in response to change in subsidence sea level and rate of sediment accumulation but on statistical attributes intrinsic to modern and ancient marginal marine successions

the collapse of megafaunal populations in southeastern brazil whether humans or climate change caused the extinction of megafaunal populations is actively debated caves in the lagoa santa provide mixed assemblages of megafauna and human remains however it remains uncertain the extent to which humans and megafauna interacted or overlapped temporally here we present the first paleoecological record from lowland south america that tracks the decline of megafauna and its ecological implications we provide a data set for pollen charcoal and sporormiella from two lakes in southeastern brazil that span the last 23 000 yr the data showed reduced abundances of sporormiella and an inferred megafaunal population decline that began 18 000 yr ago with the functional extinction occurring between 12 000 and 11 500 yr ago population declines coincided with wet events the age of the final megafaunal decline is within the range of the first human occupation of the region our data are consistent with climate causing the population collapse with humans preventing population recovery and inducing extinction we did not observe some of the ecological repercussions documented at other sites and attributed to the megafaunal extinction habitat specific ecological consequences of the extinction add to the heterogeneity of late pleistocene and early holocene landscapes

oxygen isotopic composition of fossil horse tooth phosphate as a record of continental paleoclimate abstract oxygen isotopic elemental and x ray data are presented for a suite of 24 fossil horse teeth from nebraska ranging in age from 18 2 to 8 5 ma to test the use of 18o of enamel phosphate 18op04 as a quantitative record of continental climate modern equid teeth were analyzed to estimate a relationship between 8op04 and environment water multiple samples of seven different fossil species from burge quarry a 12 ma attritional fossil deposit indicate the diagenetic overprints exist but can be detected by decreased p concentration and increased crystallinity relative to modern enamel isotopic variation for the pristine samples from burge quarry is 1 5 1 n 9 which may represent the resolution of the procedure within a stratigraphic horizon there are no apparent correlations with body size hypsodonty or phylogeny a range of 7 0 in 18op04 occurs over the 10 m y interval a trend towards depleted 18op04 of about 4 corresponds to a depletion of up to 6 0 in 18o of precipitation between 18 2 and 8 5 ma but the range of variation of burge is large relative to the climate signal our results demonstrate that 18op04 should be useful in quantitatively reconstructing cenozoic continental paleoclimate on 106 year timescales isotopic variation due to taphonomic bias and the terrestrial rock record will likely obscure higher order climate signals

the timing of prograde metamorphism in the pontiac subprovince superior craton implications for archean geodynamics and gold mineralization abstract the pontiac subprovince is located in the superior province south of the abitibi subprovince the metasedimentary rocks of the pontiac group are characterized by a barrovian metamorphic gradient increasing from north to south from biotite through garnet to staurolite zone conditions the pontiac subprovince has been interpreted as an accretionary wedge or alternatively as an exotic terrane that was tectonically docked to the abitibi subprovince during archean subduction however few studies have attempted to characterize its pressure temperature time path to test this hypothesis and little is known about the timing relationship between regional metamorphism and the gold mineralization an e w lepidoblastic ductile micaceous foliation defines the regional fabric related to the second episode of deformation garnet and staurolite porphyroblasts are interpreted to be late to post kinematic to the regional fabric locally cordierite or andalusite porphyroblasts fully pseudomorphed by a polymineralic assemblage of muscovite feldspar and quartz are wrapped by the main foliation indicating that a potential low pressure high temperature metamorphism m1 preceded the main episode of deformation and barrovian metamorphism m2 pressure and temperature p t forward thermodynamic modelling on a water saturated pseudosection yielded peak conditions of 550 600 c and 5 6 kbar during a prograde clockwise p t path for m2 lu hf dating of garnet from three different locations within the staurolite zone yielded a weighted average age of 2657 5 4 4 ma 95 confidence level that is inferred to be representative of these conditions the age of garnet growth calls into question the previous tectonic interpretation of the abitibi and pontiac subprovinces and is coherent with the new rafted ribbon continent model of bedard 2018 because the canadian malartic gold mineralization is older or synchronous with the garnet growth episode in the staurolite zone south of the ore body this garnet age also provides an estimate of the minimum age of the mineralization event previously dated at 2664 11 ma with re os on molybdenite

a review of the superior province of the canadian shield a product of archean accretion abstract the superior province consists of northern and southern high grade gneiss subprovinces and a central region of alternating granite greenstone and metasedimentary belts subprovinces are commonly fault bounded and display contrasting lithological assemblages metamorphic and structural styles geophysical characteristics and ages they are comparable to phanerozoic suspect terranes the middle and late archean rocks of the superior province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca 3 1 ga high grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal rich belts but one minnesota river valley is part of an older ca 3 6 ga terrane that was juxtaposed late in the tectonic history granite greenstone terranes are characterized by low grade volcano sedimentary sequences tholeiitic komatiitic submarine lava plain tholeiitic calc alkalic submarine to subaerial central complexes early platform type quartz arenite stromatolitic carbonate late timiskaming type shoshonitic alkalic volcanic fluvial sediment that range in age from ca 3 0 ga to 2 7 ga the volcanics represent oceanic island arc and continental arc volcanism the quartz arenite carbonate sequences deposition on relatively stable early formed ca 3 0 ga crust and the timiskaming type sequences deposition in pull apart basins developed along strike slip faults late archean ca 2 75 2 70 ga greenstone sequences occur throughout the superior province middle archean ca 3 0 2 8 ga sequences are common in northern and central superior province rare or absent in the south volcanism was accompanied by mafic to trondhjemitic plutonism the metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca 3 0 ga to 2 7 ga the metasediments were deposited after major volcanism and probably represent accretionary prisms late archean orogenesis accompanied and followed by calc alkalic plutonism youngs southward from about 2 73 2 72 ga to 2 70 2 68 ga it involved large scale north south compression and dextral transpression and displays thin to thick skinned transitions the contemporaneity of events along the lengths of the belts and their southward younging coupled with the evidence of major compression are consistent with subduction driven oblique accretion of oceanic and continental volcanic arcs accretionary sedimentary wedges older microcontinental fragments etc in a convergent margin setting analogous to parts of the pacific rim differences eg abundance of komatiites and tonalitic plutonic suites are attributable to a hotter archean mantle

using hyperspectral imaging to vector towards mineralization at the canadian malartic gold deposit quebec canada abstract canadian malartic is a large tonnage low grade archean gold deposit 16 3 moz 1 08 g t au located in the abitibi region of quebec canada a large part of the mineralization is hosted in the pontiac group metasedimentary rocks which consist of mudstones to greywackes at upper greenschist to amphibolite facies in exploration and production environments these lithologies are challenging to characterize by conventional core logging methods while in a research setting thin section sized samples 2 cm 4 cm do not capture the full extent of mineralogical variability which can extend from centimeters to meters away from mineralized zones here high resolution hyperspectral imagery 0 2 1 0 mm pixel in both shortwave infrared swir 1000 2500 nm and longwave infrared lwir 8000 12000 nm is acquired for over two thousand meters of drill core and is used to visualize changes in mineralogy and mineral chemistry related to metamorphism and hydrothermal alteration unaltered metasedimentary rocks contain metamorphic white mica with alvi contents varying between 1 90 and 1 75 apfu 2195 to 2203 nm depending on metamorphic grade hydrothermal alteration is characterized by white mica which becomes progressively more phengitic with increasing alteration intensity with alvi contents ranging from 1 70 to 1 50 apfu 2204 to 2212 nm phengitic white mica extends from meters to tens of meters away from major mineralized zones and can be used as a vector towards mineralization in an exploration setting white mica composition is correlated to au content and can be used to discriminate between unmineralized 0 3 g t au 2205 2208 nm and highly mineralized 1 0 g t au 2208 nm samples which is a simple metric that can directly be applied to sort ore in a production environment the mg molar mg mg fe of biotite on the other hand is unaffected by metamorphic grade and consistently is mg 55 60 2251 2250 nm in unaltered samples in mineralized samples biotite is mg rich mg 65

using species distribution models in paleobiogeography a matter of data predictors and concepts article i nfo the increasing interest in the effects of climate changes on species distributions has been followed by the development of species distribution models sdms although these techniques are starting to be used to study the location and dynamics of past species distributions a sound theoretical framework for their use in paleoecology is still lacking in this paper we are reviewing the main challenges for constructing paleo species distribution models to describe and project the past distribution of species namely data limitations selection of predictors and choice of a biologically relevant modeling procedure we also review and discuss the current state of the art in paleo sdms providing a series of recommendations for their use and proposing future research lines to improve the use of these techniques in paleobiogeography

effects of diffusional modification of garnet growth zoning on p t path calculations the effect of intragranular diffusion on chemical zoning in garnet and on p t paths calculated from that zoning was evaluated using a numerical model of multicomponent diffusion in combination with simulations of garnet growth syn and post growth diffusion of mg fe mn ca species in garnet was calculated for a model pelitic assemblage over a range of temperatures from 485 to 635 c compositions from zoned garnet as modified by diffusion hypothetical inclusions of plagioclase within garnet and matrix phases were used to reconstruct pressure temperature p t paths from isobaric and polybaric model histories p t path calculations based on numerical simulations conducted over an input isobaric heating path that reached peak temperatures between 585 and 635 c show that relaxation of garnet compositional gradients by diffusion can induce modest to appreciable curvature in the inferred paths retrieved paths also indicated somewhat smaller overall temperature changes relative to the actual temperature difference of the input path the magnitude of these distortions is shown to depend upon the heating and cooling rate and garnet crystal size as well as the actual peak temperature condition the effect of diffusion on path trajectories in simulations with thermal histories that also included cooling were comparable to heating only models that reached peak temperatures approximately 15 30 c higher compositions of garnets with radii less than 1 mm that reached actual peak temperatures of 605 c along temperature time histories characteristic of regional metamorphism experienced sufficient diffusional relaxation to introduce errors of hundreds of bars to in excess of one kilobar in path trajectories path distortions were significant at heating cooling rates less than 10 c ma but rapidly diminished for rates faster than this in polybaric simulations diffusion effects were least noticeable when the actual pressure temperature conditions changed in a clockwise sense i e convex to higher p and higher t but apprecciable modification was seen in path models that underwent counterclockwise changes in p and t reequilibration of garnet rim compositions occurred during cooling on all paths and temperature maxima obtained from garnet biotite geothermometry underestimated actual peak conditions by 40 to 70 c calculations suggest that p t path trajectories calculated from garnets of at least 1 mm size and that experienced actual thermal maxima below 585 c are not likely to be distorted by diffusional effects during regional metamorphism however p t path reconstructions based on garnet zonation with smaller grains or higher temperatures may lead to misinterpretation of crystallization history the partitioning record of peak metamorphic temperatures may be destroyed by diffusional reequilibration of garnet rim compositions during cooling seriously complicating the task of quantitatively estimating diffusion effects on path calculations

biological mediation of stochastic peritidal carbonate accumulation exponential thickness frequencies of peritidal carbonate units in the lower ordovician kindblade and west spring creek formations at ardmore oklahoma are readily interpreted in a context of probabilities of upsection transition from one lithology to another these largely reflect poisson random processes of deposition from suspended load traction load and microbialitic accumulation although grainy to muddy particulate and cyanobacterial elements exhibit nearly equal ranges of unit thickness carbonate generation and or entrapment via algally mediated processes was less likely to lapse and therefore led to lower probability of transition to some other sediment type the mean thickness of microbially bound units is roughly double those from the physical transport and deposition of particulate material greater persistence of algal accumulation probably related to intrinsically higher biologically induced rates of carbonate precipitation and or binding by cyanobacteria stratigraphic intervals between successive occurrences of suspended load traction load and microbial units are also closely approximated by exponential frequency distributions for which regression slopes define probabilities of upsection recurrence of a particular sediment type values for grainy and algal carbonates are similar and are nearly twice that of muddy suspended load units although biological processes resulted in significantly lower transition probabilities for thrombolitic bioherms and cryptalgal laminites spatial dominance of carbonate mud across the region led to higher rates of stratigraphic recurrence and a volumetric dominance of muddy lithologies in the ardmore sequence poissonian distributions of unit stratigraphic duration and recurrence suggest a significant component of haphazard variation in the type and amount of accumulated carbonate sediment if deposition was influenced by extrabasinal forcing such control must have been nearly random in both secular and spatial dimensions of water depth change stratigraphic durations and recurrences in this sequence more closely reflect the inherently stochastic nature of carbonate accumulation in epicratonic platformal settings than any influence of rhythmic eustatic forcing

analyzing spatial patterns in modern carbonate sand bodies from great bahama bank abstract three carbonate sand bodies on great bahama bank which show a range of depositional facies patterns typifying modern deposits as well as their ancient counterparts are quantitatively interrogated to broaden our perspective of the types of information that can be derived from studies of modern environments rimming the southern end of tongue of the ocean toto is the broadest expanse of high energy sands found in the bahamas characterized by narrow sandbars separated by wide deep channels and a lack of islands a variation of the tidal bar motif with broader and more irregular sandbars relatively narrow channels and few small islands occurs at the northern end of exuma sound schooners sands associated with tidal channels and the numerous islands of the exumas chain along the western edge of exuma sound occur primarily as flood tidal deltas the geometry of sandbars that inhabit the three sand bodies is quantified using landsat remote sensing and assembled along with optically derived bathymetric surfaces into a gis this database is quantitatively examined using a suite of morphometric tools to compare and contrast geometric character of sandbars within and between the three sand bodies considered are properties such as the size shape complexity distribution orientation and topography of the individual sandbars profiles and spatial analysis tools enable sandbar and channel spacing position relative to the platform margin connectedness separation distances and density to be characterized as has been previously reported for reef dominated environments certain aspects of the geometry of the three systems are found to behave in a systematic and hence predictable manner though important mathematical differences are revealed between the scaling of reefal landscapes and the grainy geobodies considered by this study because the three sand bodies are disparate in their overall extent and depositional settings e g orientation prevalence of islands this predictable behavior has the potential to impart considerable insight to the characterization of grainstone systems

late pliocene pleistocene high resolution pollen sequence of colombia an overview of climatic change two long continental pollen records funza i 357 m and funza ii 586 m from the high plain of bogota colombia at 2550 m elevation have been studied palynologically fission track dates on zircon from intercalated volcanic ashes provided a chronological framework and showed the pollen records which correlate with high precision to be continuous over the interval from ca 3 2 ma to ca 27 ka the late pliocene pleistocene history of the montane forests and open alpine paramo vegetation is documented with a temporal resolution of ca 6 5 ka and for the upper 1 1 ma with a resolution of ca 1 2 ka the immigration of the northern hemisphere elements alnus at ca 1 ma and quercus at ca 0 33 ma which travelled along the panamanian landbridge caused significant changes in the composition of the andean montane forests the successive pleistocene glaciations forced the andean vegetation belts to an almost continuous altitudinal movement the upper forest line at present at ca 3200 m shifted between 1800 m glacials and ca 3500 m interglacials corresponding to a variation in temperature between ca 5 and 15 c at 2550 m altitude a provisional land sea correlation funza pollen odp site 677 18o is shown for the upper 1 2 ma stages 3 35 frequency analysis of several time series showed significant periods of the eccentricity 100 ka and precession 23 and 19 ka bands showing orbital forcing and a strong change in climatic variability around 800 ka at ca 2 7 ma a significant cooling of ca 5 c is documented reflecting the classical terrestrial pliocene pleistocene boundary which correlates to the reuverian praetiglian boundary of the nw european stratigraphical climatic subdivision

40ar 39ar geochronological evidence for multiple postmetamorphic hydrothermal events focused along faults in the southern abitibi greenstone belt thermal histories in the abitibi and pontiac subprovinces vary for three general domains 1 zones of impermeable rock with cooling rates of 8 c ma 2 zones of impermeable rock that are spatially associated with monzogranite plutons with apparent cooling rates of 1 2 cima and 3 permeable high strain zones with apparent cooling rates of 2594 ma from the volcanogenic massive sulphide related sericite alteration with the coarser mica yielding the younger date based on radiometric dating impermeable rocks were affected weakly by postmetamorphic hydrothermal events minerals in zones of higher permeability were reset during the intrusion of monzogranite plutons highly permeable zones such as the larder lake cadillac and porcupine destor faults were overprinted repeatedly this produces a drawn out series of dates from minerals with varying closure temperatures radiometric ages from fault zones or ore deposits cannot be used to interpret the cooling history and evolution of the abitibi belt as a whole

diet reconstruction for an extinct deer cervidae cetartiodactyla from the quaternary of south america abstract among the extinct cervids of the pleistocene in south america morenelaphus has the most abundant fossil record and the broadest geographic distribution however the paleoecology of morenelaphus is poorly known especially its dietary patterns thus this study aims to recognize the feeding habits of this extinct cervid through analysis of microwear the microwear analysis indicated a mixed feeder diet for morenelaphus both high pit values and frequency of individuals with low number of fine scratches indicated the consumption of grasses possibly including grit siliciclastic sediment ingested during feeding also our results suggest that morenelaphus possibly went extinct at the pleistocene holocene transition as a result of climate environmental changes and or a physiological nutritional crisis

the ti saturation surface for low to medium pressure metapelitic biotites implications for geothermometry and ti substitution mechanisms the ti content of biotite can serve as a geothermometer for graphitic peraluminous metapelites that contain ilmenite or rutile and have equilibrated at roughly 4 6 kbar the relationship between ti content temperature and mg mg fe value was calibrated empirically using an extensive natural biotite data set 529 samples from western maine and south central massachusetts in combination with the petrogenetic grid of spear et al 1999 the calculated ti saturation surface is curved such that for a given mg mg fe value ti concentration increases as a function of temperature in a nonlinear fashion and for a given temperature ti concentrations decrease with an increase in mg mg fe the fit to the ti saturation surface can be reformulated as the geothermometric expression t ln ti a c x mg 3 b 0 333 in which t is temperature in degrees celsius ti is the number of atoms per formula unit apfu normalized on the basis of 22 o atoms x mg is mg mg fe a 2 3594 b 4 6482 10 9 and c 1 7283 the calibration range for this expression is x mg 0 275 1 000 ti 0 04 0 60 apfu and t 480 800 c precision of the ti in biotite geothermometer is estimated to be 24 c at the lower temperature range and improves to 12 c at higher temperatures application of the ti in biotite geothermometer to ilmenite or rutile bearing graphitic peraluminous metapelites equilibrated at 3 6 kbar is generally consistent with independent temperature determinations but with some deviations that represent local reequilibration consequently the ti systematics in biotite can also serve as the basis of a very sensitive indicator of chemical equilibrium or lack thereof application of the geothermometer to metapelites not containing the requisite mineral assemblages can lead to minor to significant errors in estimated temperatures biotite ti substitution mechanisms are controlled by several factors based on the biotite calibration data set magnesian biotites x mg 0 65 incorporate ti in accordance with the exchange vector tial2r 1si 2 where r is the sum of the divalent cations mg fe mn this substitution mechanism is primarily a response to misfit of the octahedral and tetrahedral layers in magnesian biotites intermediate biotites x mg 0 65 particularly at higher temperatures exhibit enhanced ti concentrations most consistent with the ti deprotonation tio2r 1 oh 2 exchange vector dominance of ti deprotonation substitution is largely a function of reduction of h2o activity at higher metamorphic grades supplementary biotite data from metaluminous amphibolites and mafic granulites metamorphosed isothermally with variable h2o activities reveal that low al biotite incorporates significantly higher concentrations of ti relative to peraluminous biotite as a result of a combination of the exchange vectors tio2r 1 oh 2 and rsial 2 substituting in roughly an 8 1 ratio

geobarometry differential block movements and crustal structure of the southwestern abitibi greenstone belt canada the southern volcanic zone of the archean abitibi greenstone belt comprises several fault bounded tectonic blocks with distinct volcanic sedimentary sequences pressure temperature time p t t histories granite compositions and metallogenic provinces pressure distributions have been mapped out from an extensive new database derived from al in hornblende and other geobarometers in the composite crustal structure of the southern volcanic zone determined from the pressure time data the lacorne block and pontiac subprovince represent deeper crustal levels overlain by rocks exposed at the surface in the round lake or lac abitibi type blocks which are in turn capped by those exposed at the surface in a blake river rouyn type block exposure of the deeper crustal levels and juxtaposition of these distinct tectonic blocks are interpreted to have occurred by differential block uplift caused by strike slip faulting which was related to oblique collisional tectonics during late tectonic development of the superior province in late archean time

a model of ocean crust accretion for the superior province canada abstract one of the keys to understanding the origin of archaean greenstone belts lies in the geological relationships between mafic and ultramafic greenstones felsic to intermediate volcanic rocks and terrigenous sediments traditional models for greenstone belt evolution have been based on in situ stratigraphic relationships most of these models for example an oceanic island arc developed on oceanic basement back arc basins and the recently popular plume model predict concordant stratigraphic relationships among the various greenstone belt lithologies however rather than being depositional in nature several authors have indicated that many of the relationships between the different lithologies in greenstone belts are in fact tectonic suggesting an allochthonous origin for most greenstone sequences all of these latter models make analogies to phanerozoic tectonic processes involving accretion of oceanic materials with volcanism related to both plate subduction and rifting in this paper we have evaluated the geological relationships between volcanic rocks and sediments in three regions in the superior province where the accretion of oceanic material can be documented and direct comparisons are made to geological processes in phanerozoic accretionary complexes in the malartic area in the southeastern abitibi subprovince 3 to 4 km thick slices of komatiite and tholeiite with intercalated terrigenous sediment are tectonically imbricated and are overlain by calc alkaline volcanics which postdate tectonic stacking in both the larder lake region of the southwestern abitibi belt and in the beardmore geraldton belt at the south eastern limit of the wabigoon belt slices of iron rich tholeiite and chemical sediments of an oceanic origin are tectonically imbricated with terrigenous sediment the malartic val d or area is considered to be an example of accretion of an archaean oceanic plateau while the larder lake and the beardmore geraldton regions are potentially typical of accretion of normal oceanic crust in an arc environment phanerozoic accretion of oceanic crust is accompanied by a step back in subduction and in this paper we suggest that oceanic crust accretion may have been the principal mechanism by which the locus of subduction migrated towards the south of the superior province asthenospheric upwelling associated with the isolated sinking plate may have been responsible for widespread late magmatism this scenario requires that magmas be erupted through previously accreted volcanic plutonic and sedimentary material furthermore later ridge subduction will result in transpressional tectonics and eruption of mafic sequences over mature and immature volcano plutonic sequences the combined result of the plate tectonic scenario envisaged would result in the well described cyclic stratigraphy of many granite greenstone sequences

conditions and timing of metamorphism in the southern abitibi greenstone belt quebec regional metamorphism ranging in grade from the subgreenschist facies to the greenschist amphibolite facies transition affects all archean supracrustal rocks 2677 ma in the rouyn noranda area contact metamorphic minerals associated with the posttectonic preissac lacorne batholith 2643 ma show no evidence of a regional retrograde event accordingly the age of regional metamorphism can be bracketed between 2677 and 2643 ma three reaction isograds were mapped in subgreenschist facies metabasites dividing the low grade rocks into three metamorphic zones the pumpellyite actinolite zone the prehnite pumpellyite zone and the prehnite epidote zone in addition the pumpellyite actinolite epidote quartz bathograd corresponding to a pressure of approximately 200 mpa occurs on both sides of the porcupine destor fault low pressure regional metamorphism is also indicated both by the occurrence of an actinolite oligoclase zone and the persistence of pre regional metamorphic andalusite the coincidence

sedimentology of archean greenstone belts signatures of tectonic evolution abstract stratigraphic styles in archean greenstone belts are compared to those of modern and phanerozoic depositional basins in order to test the conformity of tectonic style through time six lithological associations in greenstone belts are recognized 1 mafic ultramafic volcanic 2 calc alkaline volcanic 3 bimodal volcanic 4 quartz arenite iron formation or carbonate 5 conglomerate wacke and 6 conglomerate arenite examples of the associations are described from the kaapvaal superior and zimbabwe provinces and the pilbara block each association differs only slightly between the four regions thereby emphasizing a common tectonostratigraphic theme sedimentary rocks are a minor component of the mafic ultramafic volcanic association they were deposited in two types of volcanic basin environments one similar to barred lagoons and bays around oceanic volcanic islands and the other similar to sediment starved platforms adjacent to coalesced volcanoes in inter arc intra arc and back are basins in contrast sedimentary rocks in the calc alkaline volcanic association comprise thick wedges of epiclastic and volcaniclastic detritus deposited in elongate sedimentary basins and thick wedges of pyroclastic and volcaniclastic detritus deposited adjacent to volcanic centers sedimentary facies were identical to those of forearc trench and marine volcanoplutonic arc settings chemogenic lithofacies in both volcanic associations were deposited in shallow to deep marine waters although shallow water profiles were selectively preserved in some terrains sedimentary rocks of the bimodal volcanic association are thick wedges of siliciclastic and volcaniclastic deposits interbedded with subaerial to submarine erupted flows of komatiite basalt and rhyolite depositional environments ranged from braid plain and braid delta to coastal marine and submarine fan starved basin deposits include banded iron formation and sulfidic black shale the association is identical to that of cratonic extensional basins in arc continent and intracontinental rifts sedimentary rocks of the quartz arenite iron formation or carbonate association onlap weathered basement or bimodal volcanic association rocks depositional environments were either transitional from fluvial to siliciclastic and carbonate marginal marine to offshore pelagic hemipelagic or from inshore intrabasinal clastic and volcaniclastic to offshore pelagic hemipelagic siliciclastic deposits are supermature two tectonic sites are represented those with siliciclastic facies represent continent adjacent syn to post rift stable shelves and those dominated by banded iron formation with volcaniclastic deposits represent arc adjacent post rift stable shelves sedimentary rocks of the conglomerate wacke association are represented by thick wedges of siliciclastic or volcaniclastic sandstone with minor volcanic components these were deposited in braid plain braid delta and submarine fan environments within elongate sedimentary basins coastal plain and pelagic basin facies are also present siliciclastic detritus was derived from syndepositional magmatic and metasedimentary thrust belts two stratigraphic styles are preserved one that records a flysch like stage of deep to marginal marine environments and the other that records a molasse like stage of marginal marine to fluvial environments the association is identical to that of compressional foreland basins of arc continent collisional and compressional arc tectonic affinities the conglomerate arenite association is preserved in elongate structural basins that transgress crustal components and all other supracrustal units it is dominated by thick wedges of siliciclastic sandstone although bimodal volcanic and volcaniclastic rocks can also be present depositional environments ranged from talus and alluvial fan and braid plain to either lacustrine or coastal marine local basin margins often show lateral offsets from source terrains and vertically skewed facies patterns longitudinal facies geometries are typical the association is similar to that of strike slip collisional graben in hinterland tectonic escape and terrane accretion orogens the examples show that despite all the ramifications of secular geophysical geothermal and geochemical global change the stratigraphic style of sedimentary rocks in archean greenstone belts can be matched with modern tectonic analogues thereby emphasizing the conformity of stratigraphic style through time the inseparable link between stratigraphic and tectonic styles implies that the tectonic style of greenstone belts was not temporally unique major differences exist with regards to the chemical composition of certain magmatic and sedimentary products but these are compensated for by their constant stratigraphic function in terms of depositional processes depositional environments and tectonic sites

geochemistry of fine grained clastic sediments in the archean abitibi greenstone belt canada implications for provenance and tectonic setting abstract archean sandstone and shale samples from turbiditic tf and alluvial facies af in the southern volcanic zone of the abitibi greenstone belt canada have been analyzed for major and trace elements the sandstones from tf are mainly greywackes whereas those from af are lithic arenite sio 2 ranges from 51 to 68 geochemically the clastic sediments cluster into mafic element mep and low mafic element lmep populations the mep sediments which include turbiditic facies sediment samples from the larder lake group in the kirkland lake area are characterized by elevated abundances of mgo 5 ni 200 ppm cr 400 ppm sc 22 ppm and feo 7 5 abundances lower contents of incompatible elements such as th u ta hf zr and total rees n ratios are 4 5 with eu eu 1 the lmep sediments which include samples from the beatty dome and three nations lake formations in timmins the kewagama group noranda area and timiskaming group in the kirkland lake area however show reverse abundance distributions the geochemical gaps shown by the major and trace elements define two populations of sediments suggesting contrasting provenances for them the mep sediments require a dominantly mafic and ultramafic 90 source with 10 felsic contribution whereas the lmep sediments require a mixture of felsic 75 and mafic 25 rocks this compositional distribution of the sediments is closely related to their tectonic environments the mep was formed in basins proximal to or within an active oceanic rift consequently having ultramafic and mafic rocks as the major source for the lmep calc alkaline volcanic sequences formed in an island arc like setting were the major source these two contrasting volcanic plutonic terranes were tectonically juxtaposed during late archean collisional tectonics

oblique archean subduction accretion and exhumation of an oceanic arc during dextral transpression southern volcanic zone abitibi subprovince canada abstract the archean abitibi subprovince divided into northern nvz and southern svz volcanic zones is characterized by the crustal scale destor porcupine manneville fault zone dpmfz which links the svz and nvz and the cadillac larder lake fault zone cllfz which separates the abitibi and pontiac subprovinces the dpmfz and cllfz represent major deformation zones that record over 60 million years of archean deformation the dextral transpressional phase in the nvz which represents incipient svz deformation occurred between 2700 and 2692 ma and is characterized by southeast se trending dextral faults e g macamic fault synorogenic flysch sedimentation is focussed at the interface between the svz nvz and pontiac abitibi subprovinces the se trending parfouru fault linking the two major trench fault systems is interpreted as a reactivated leaky transform fault and is associated with synorogenic flysch sedimentation the early monzodioritic suite of the preissac lacorne batholith was related to dpmfz thrusting ca 2692 2690 ma the change from early thrusting to transcurrent motion is recorded in the duparquet strike slip basin which formed between 2690 and 2680 ma along the dpmfz and the granada pull apart basin which evolved between 2680 and 2670 ma along the cllfz the timing of these basins indicates a diachronous evolution renewed thrusting affected the granada basin but not the northern duparquet strike slip basin so that a southward migrating deformation front is inferred late exhumation resulted in extension along both fault zones and was responsible for the juxtaposition of medium and low grade metamorphic rocks the monzogranitic suite of the lamotte pluton which occurred between 2660 and 2642 ma is linked to exhumation final dextral transpression post dating exhumation produced shearing and folding the svz of the abitibi subprovince shows the salient attributes of modern oblique orogenic collisions with alternating phases of thrusting and strike slip movement along crustal scale faults during dextral transpression

the pontiac problem quebec ontario in the light of gravity data a belt of archean quartzose metasedimentary gneisses with minor mafic volcanic rocks the pontiac group lies south of the blake river and older archean mafic volcanic rocks of the abitibi greenstone belt and is separated from them by the larder lake cadillac break to the west of the pontiac group on strike is the archean larder lake group of turbidite conglomerate argillite limestone and iron formation with abundant mafic flows and intrusions these strata also lie south of the larder lake cadillac break and south of the blake river and older archean mafic volcanic rocks the western contact between the pontiac and larder lake groups is covered by a narrow north south strip of proterozoic cobalt sedimentary rocks on the basis of gravity work that compares the bouguer gravity anomaly gradient across the cadillac break with that across the west margin of the pontiac group it is proposed that the larder lake and pontiac groups are separated by a north south fault and that the pontiac group repr

u pb age constraints for the magmatic and tectonic evolution of the pontiac subprovince quebec new u pb zircon titanite and monazite ages help constrain the history of magmatism and tectonism within the pontiac subprovince of western quebec the pontiac subprovince resembles other metasedimentary belts of the superior province however the stratigraphic relationships between the dominantly sedimentary rocks of the pontiac and the adjacent volcanic dominated abitibi belt to the north and west remain controversial volcanic rocks of the belleterre volcanic zone in the southern part of the pontiac subprovince have been interpreted by other workers as klippen of abitibi strata that were thrust southward onto the pontiac subprovince however volcanic rocks in the belleterre zone give crystallization ages of 2689 2682 ma which are younger than any extrusive rocks dated thus far from the abitibi belt single detrital zircon grains from pontiac sedimentary rocks give ages as young as 2683 ma indicating that the sediments are similar in age or younger than the volcanic units the volcanic rocks pro

a proposed integrated multi signature model for peritidal cycles in carbonates abstract a new integrated multi signature model for meter scale peritidal carbonate cycles presented here is relevant to the interpretation of these cycles in the stratigraphic record meter scale shallowing upward micro facies cycles are the most common type of peritidal parasequence peritidal parasequences are a fundamental component of carbonate sequence stratigraphic models however the existence of meter scale cycles in the geological record has been questioned owing to the failure to prove statistically the existence of these cycles using data on micro facies and stacking pattern taken from previous studies nevertheless the shallowing upwards micro facies interpretive template remains widely used to identify these cycles and parasequences we propose that the sedimentary signatures of meter scale peritidal cycles vary systematically during the various phases of an underlying 3rd order relative sea level cycle although during specific phases of a 3rd order relative sea level cycle meter scale peritidal cycles may be characterized by shallowing upward units e g early transgressive systems tract during other periods the stratigraphic signal of cyclicity may be more cryptic and complex causing them to be overlooked e g late transgressive systems tract and highstand systems tract we also propose that there is a half cycle phase shift in periods of deposition and the formation of drowning surfaces relative to 4th to 5th order relative sea level cycles over the course of a 3rd order relative sea level cycle these points have ramifications for defining parasequences and using stacking patterns to determine peritidal cycle periodicity specifically parasequences defined using flooding surfaces identify sedimentary units that inconsistently partition 4th to 5th order relative sea level cycles at different stages of a 3rd order relative sea level cycle we propose testable new physical stratigraphic signatures for identifying meter scale cycles that have consistent genetic significance each cycle recording a relative sea level cycle characterized by a 4th to 5th order relative sea level rise and fall meter scale peritidal cycles are recorded by an ordered pattern of systematically varying micro facies signatures related to their position within a 3rd order relative sea level cycle the integrated multi signature model of meter scale peritidal carbonate cycles we propose here may assist in explaining the apparently contradictory evidence both for and against their existence in the geological record as a result of the detailed consideration in this paper of the nature of parasequences and their variations with 3rd order relative sea level changes a redefinition of parasequence is required and one is presented here

middle pleistocene climate change recorded in fossil mammal teeth from tarija bolivia and upper limit of the ensenadan land mammal age fossiliferous middle pleistocene sediments of the tarija basin of southern bolivia contain a classic ensenadan land mammal fauna new carbon isotopic data reported here for 50 specimens of the grazing mammals equus horse and cuvieronius mastodon documented from eight stratigraphic levels at tarija vary significantly in the 13c values of their teeth the pattern of variation appears to reflect the proportion of c3 and c4 grasses eaten during colder more c3 and warmer more c4 times within age limits set by associated magnetostratigraphy the cold periods can be correlated with particular even numbered stages in the marine oxygen isotope record and the warm periods can be correlated with odd numbered stages the oldest fossil teeth analyzed from the tarija section can thereby be assigned to stage 29 and the youngest to stages 17 or 15 that is the teeth range in age from about 1 1 myr to as young as 0 7 myr based on correlation of the upper part of the tarija beds to the isotopic stages the upper limit of the ensenadan land mammal age is between 0 7 and 0 6 myr which is younger than stated in most previous studies

u pb geochronology of archean metasedimentary rocks in the pontiac and abitibi subprovinces quebec constraints on timing provenance and regional tectonics abstract u pb isotopic ages of single detrital zircons have been obtained from metasandstones in the northern part of the pontiac subprovince and from the cadillac kewagama and lac caste groups within the southern abitibi subprovince youngest detrital zircon ages from these sequences are 2685 2686 2687 and 2693 ma respectively the lac fourniere pluton which intrudes pontiac group metasedimentary rocks is dated at 2682 1 ma a similar age was previously measured from a pluton that cuts the kewagama group these data bracket deposition of greywacke in the pontiac and abitibi subprovinces to 2685 3 ma in contrast the youngest zircon found in a volcaniclastic unit interbedded with timiskaming group metawacke is 2673 2 ma while the age of a pluton that intrudes the timiskaming is 2672 1 ma thus the timiskaming group is distinctly younger than the other metasedimentary rocks the normalized probability distributions of detrital zircon ages from the pontiac and the abitibi metasedimentary rocks as well as of dated igneous rocks from the southern abitibi subprovince all show that their major zircon populations formed in the age range 2685 2710 ma the distributions for the abitibi metaturbidites and dated igneous rocks are very similar suggesting that metasedimentary rocks in the abitibi belt were mostly derived from the surrounding granite greenstone terrain the largest peak of the pontiac distribution is a few million years younger than that from the abitibi metasedimentary rocks but there is a correlation between major peaks and both groups show similar age ranges for older pre abitibi components 2750 2850 and 3020 3030 ma deposition of the ca 2685 ma sediments was virtually syn deformational based on previous field geochemical and isotopic studies as well as the detrital zircon age data the pontiac group may represent a foreland basin that may have developed from an accretionary prism the source of much of the sediment may have been an uplifted extinct continental arc to the north the arc was mostly eroded into the sediment basin and perhaps tectonically overridden by a southward advancing nappe complex comprised of its back arc basin now partly preserved in the southern volcanic zone of the abitibi subprovince metaturbidites exposed between metavolcanic assemblages within the greenstone belt may represent overturned unconformities at the structural base of the greenstones these were brought up by high angle faults which also localized deposition of non marine timiskaming type sediments it is tentatively suggested that pontiac type metasedimentary rocks extend most of the way beneath the abitibi subprovince the oldest part of the basin emerging as the quetico group in the western superior province

intergranular diffusion kinetics of fe and mg during retrograde metamorphism of a pelitic gneiss from the adirondack mountains abstract pelitic granulite gneiss from the irving pond formation in the southern adirondack highlands new york contains chemical zoning in fe and mg in both individual mineral grains and over a distance of millimeters in the polycrystalline matrix garnet porphyroblasts are zoned with increasing xalm and decreasing xprp towards crystal rims compositions of individual biotite grains in the matrix vary systematically with distance from the garnet porphyroblasts up to about 1 mm with the highest mg concentrations in grains adjacent to the garnet and progressive fe enrichment in grains further away we have constructed numerical models of the distribution of fe and mg components obtained during the retrograde reaction and diffusion history of this rock based on the mineral assemblage modes textural information and the preserved zoning trends these simulations indicate that the effective rate of intergranular transport of fe and mg components through the polycrystalline matrix was only one order of magnitude faster than the rate of volume diffusion in garnet the relatively slow intergranular kinetics indicate that grain boundaries did not provide rapid diffusion pathways absence of an interconnected fluid phase along grain edges and grain boundary annealing likely inhibited intergranular diffusivities during cooling our models also suggest that the mineral assemblage experienced metamorphic temperatures in excess of 700 c followed by rapid cooling this t t evolution is quite different than determined for the ca 1060 1000 ma regional granulite facies metamorphism in the adirondack highlands fe mg distribution in the gneiss likely reflects and earlier metamorphic episode

high latitude climate sensitivity to ice sheet forcing over the last 120 kyr abstract interpretation of ice core records is currently limited by paucity of modelling at adequate temporal and spatial resolutions several key questions relate to mechanisms of polar amplification and inter hemispheric coupling on glacial interglacial timescales here we present the first results from a large set of global ocean atmosphere climate model snap shot simulations covering the last 120 000 years using the hadley centre climate model hadcm3 at up to 1 kyr temporal resolution two sets of simulations were performed in order to examine the roles of orbit and greenhouse gases versus ice sheet forcing of orbital scale climate change a series of idealised heinrich events were also simulated but no changes to aerosols or vegetation were prescribed this paper focuses on high latitudes and inter hemispheric linkages the simulations reproduce polar temperature trends well compared to ice core reconstructions although the magnitude is underestimated polar amplification varies with obliquity but this variability is dampened by including variations in land ice coverage while the overall amplification factor increases the relatively constant amplification of antarctic temperatures with ice sheet forcing included suggests it is possible to use antarctic temperature reconstructions to estimate global changes which are roughly half the magnitude atlantic ocean overturning circulation varies considerably only with the introduction of northern hemisphere ice sheets but only weakens in the north atlantic in the deep glacial when ocean sea ice feedbacks result in the movement of the region of deep convection to lower latitudes and with the introduction of freshwater to the surface north atlantic in order to simulate heinrich events

stable carbon and oxygen isotope analysis of fossil tooth enamel using laser ablation abstract a technique is described whereby the 13c and 18o values of fossil tooth enamel can be measured in situ using laser ablation techniques the laser heats the sample and forms co2 from structural carbonate apatite the 18o values obtained with this method are equal to those of the phosphate oxygen due to the high temperature of reaction during ablation analytical precision is approximately 0 5 for both 13c and 18o the spatial resolution is 200 m or less which may be reduced as the technical modifications are made this method allows the analysis of samples that previously could not be analyzed due to difficulty with sample preparation size or rare nature the apparent oxygen isotope fractionation between the carbonate and laser derived oxygen co3 laser is 1 0071 for biogenic apatite at 38 c determined using the in situ laser comparison of 18o co3 and 18o laser analyses with 18o laser and 18o po4 results suggest a fractionation factor co3 po4 of 1 0083 variations in the 18o and 13c values of single teeth can be easily determined with the in situ technique this will allow the study of changes in diets or water sources during the period of tooth growth which for larger mammals can be several years for the tooth row the 13c and 18o values are important in paleodiet and paleoecology studies they can be used to study resource partitioning within an ecosystem and can shed light on the life history strategies within living and extinct species

constraints on the geodynamic evolution of the southern superior province u pb la icp ms analysis of detrital zircon in successor basins of the archean abitibi and pontiac subprovinces of ontario and quebec canada abstract to investigate the tectonic development of the southern superior province new u pb laser ablation inductively coupled mass spectrometry analysis of detrital zircon was conducted on graywacke samples from successor basins of the abitibi and pontiac subprovinces the three successor basin successions investigated are the 2690 2685 ma porcupine assemblage and the 2679 2669 ma timiskaming assemblage of the abitibi subprovince and the 2682 ma sedimentary rocks of the pontiac subprovince predominately neoarchean zircon grains 80 95 of the total zircon population reflect local sources in the abitibi and pontiac subprovinces the successor basins were deposited within 100 ma of the majority of the detrital zircon grains primary crystallization ages which is consistent with patterns observed at modern convergent margin settings porcupine assemblage samples contain 5 mesoarchean zircon while pontiac subprovince and timiskaming assemblage samples contain 18 and 13 respectively no local mesoarchean sources exist in the abitibi or pontiac subprovinces suggesting input from an adjacent hinterland the higher proportion of mesoarchean zircon in the timiskaming assemblage relative to the porcupine assemblage suggests that detritus from the hinterland was more prevalent during the later stages of collision probably as a result of progressive uplift and denudation of the hinterland the high proportion of mesoarchean zircon in the pontiac subprovince sedimentary rocks may reflect an additional mesoarchean source comparison to previously published geochronology data for the superior province indicates that the hinterland was to the northwest and is in part composed of the winnipeg river marmion and opatica subprovinces patterns of contractional deformation successor basin formation and felsic plutonism progressively young to the south in the southern superior province and are interpreted in terms of accretionary processes detrital transport across subprovince or terrane boundaries progressive hinterland emergence and foreland directed propagation of the deformational front recorded by successor basins is similar to that observed in modern style collisional or accretionary orogens

formation exposure and evolution of a high latitude beachrock in the intertidal zone of the corrubedo complex ria de arousa galicia nw spain abstract the presence of beachrocks is noted on the galician shoreline at 41 n a latitude at which this phenomenon is rarely found the present study focuses on the petrological characterization and sedimentological evolution of a beachrock that was exhumed during an exceptional storm in the winter of 2001 in the intertidal zone of a high energy beach the cemented material comprises medium to coarse mixed siliciclastic carbonate sands unlike tropical beachrocks the cement consists of epitaxial low mg calcite presenting varied morphologies and textures acicular and bladed coatings and pore linings pore fillings of sparitic calcite and meniscus style cements seawater dominantly wave action plus marine and meteoric mixed waters are invoked as the main generative fluids beachrock formation and evolution are approached from a morphodynamic viewpoint considering four progressive stages 1 initial cementation in the intertidal zone 2 exposure and modelling by wave action 3 colonization and hardening and 4 disintegration preservation and burial finally the morphodynamic significance climatic implications and occurrence of this type of cementation along the north and northwest shoreline of spain are discussed

constraint envelope analyses of macroecological patterns reveal climatic effects on pleistocene mammal extinctions abstract quantitative analysis of macroecological patterns for late pleistocene assemblages can be useful for disentangling the causes of late quaternary extinctions lqe however previous analyses have usually assumed linear relationships between macroecological traits such as body size and range size range shift that may have led to erroneous interpretations here we analyzed mammalian datasets to show how macroecological patterns support climate change as an important driver of the lqe which is contrary to previous analyses that did not account for more complex relationships among traits we employed quantile regression methods that allow a detailed and fine tuned quantitative analysis of complex macroecological patterns revealed as polygonal relationships i e constraint envelopes we showed that these triangular shaped envelopes that describe the macroecological relationship between body size and geographical range shift reflect nonrandom extinction processes under which the large bodied species are more prone to extinction during events of severe habitat loss such as glacial interglacial transitions hence we provide both a theoretical background and methodological framework to better understand how climate change induces body size biased species sorting and shapes complex macroecological patterns

outcrop analog for an oolitic carbonate ramp reservoir a scale dependent geologic modeling approach based on stratigraphic hierarchy considerable effort has been devoted to the development of simulation algorithms for facies modeling whereas a discussion of how to combine those techniques has not existed the integration of multiple geologic data into a three dimensional model which requires the combination of simulation techniques is yet a current challenge for reservoir modeling this article presents a thought process that guides the acquisition and modeling of geologic data at various scales our work is based on outcrop data collected from a jurassic carbonate ramp located in the high atlas mountain range of morocco the study window is 1 km 0 6 mi wide and 100 m 328 1 ft thick we describe and model the spatial and hierarchical arrangement of carbonate bodies spanning from largest to smallest 1 stacking pattern of high frequency depositional sequences 2 facies association and 3 lithofacies five sequence boundaries were modeled using differential global position system mapping and light detection and ranging data the surface based model shows a low angle profile with modest paleotopographic relief at the inner to middle ramp transition facies associations were populated using truncated gaussian simulation to preserve ordered trends between the inner middle and outer ramps at the lithofacies scale field observations and statistical analysis show a mosaiclike distribution that was simulated using a fully stochastic approach with sequential indicator simulation this study observes that the use of one single simulation technique is unlikely to correctly model the natural patterns and variability of carbonate rocks the selection and implementation of different techniques customized for each level of the stratigraphic hierarchy will provide the essential computing flexibility to model carbonate settings this study demonstrates that a scale dependent modeling approach should be a common procedure when building subsurface and outcrop models

geodynamic evolution of the southern abitibi and pontiac terranes evidence from geochemistry of granitoid magma series 2700 2630 ma four distinct granitic series developed during the evolution of the archean abitibi southern volcanic zone svz 1 a minor synvolcanic tonalite trondhjemite granodiorite ttg series was emplaced at 2700 ma which has extremely low k2o 1 5 wt rb 50 ppm and sr 200 ppm higher nb y and sc flat rare earth element ree patterns and negative eu anomalies 2 a voluminous tonalite granodiorite granite quartz monzonite tggm series developed syntectonically at 2695 2685 ma and displays low k2o 1 3 wt rb 10 50 ppm ba 1000 ppm and u enhanced sr depletion of ta nb and ti and strongly fractionated ree patterns la ybn 49 21 3 a late tectonic quartz syenite quartz monzonite granite smg series was emplaced from 2685 to 2675 ma and is grossly similar to the tggm but has lower cao k2o na2o and greater concentrations of rb ba th and u 4 a late tectonic to posttectonic alkali feldspar syenite alkali feldspar quartz syenite ss series was emplaced

a two stage model for the formation of the granite greenstone terrains of the kalgoorlie norseman area western australia abstract accurate dating of granites and greenstones from the kalgoorlie norseman area shows that there is considerable overlap in time between the formation of granites and greenstones however within any given area the oldest granites are always younger than the oldest greenstones it is suggested that the long lived 100 ma thermal anomaly in the uppermost asthenosphere that gave rise to the greenstones is also responsible for regional metamorphism and widespread crustal melting leading to the production of granites the time lag between greenstone and granite formation reflects the time taken to conduct heat from the mantle to the lower crust anatexis of the lower crust produces a layer of light granitic magma that may temporarily stop the ascent of basaltic magma where this happens the basaltic magma ponds at the base of the crust supplying additional heat and accelerating the melting process eventually the granitic melt layer becomes unstable and rises within the crust areas intruded by granite become topographic highs with topographic lows forming above areas where light melt has been withdrawn from the lower crust when the topographic highs protrude above sea level they are eroded to shed sediments into the topographic lows which contain the basaltic greenstones thus the change from a basalt dominated lower greenstone succession to a sediment and felsic volcanic dominated upper whitestone sequence seen in many granite greenstone terrains results from the intrusion of granitic magma into the upper crust the crust of the kalgoorlie norseman area formed in two distinct stages separated by a time break of up to 700 ma the first stage involved the formation of primitive crust probably above subduction zones this primitive crust was characterized by low rb sr and high sm nd ratios the second stage resulted from a major change in mantle convection that produced thermal upwellings in the mantle below the continents this led to the eruption of basaltic magmas and to metamorphism and anatexis of the lower crust to produce granitic magmas melting reset the rb sr sm nd and u pb systems giving the impression that the second event which occurred at 2 7 ga was a major crust forming event it was in fact a crustal reworking process although some basalt was added to the crust at this time although the two stage history of the kalgoorlie norseman area is clearly seen in the lead isotopes and in zircons it is not readily discernible from the rb sr and sm nd systematics due to mantle like ratios of those elements in the primitive crust

evolution of the south central segment of the archean abitibi belt quebec part ii tectonic evolution and geomechanical model in this paper we describe the relations between the paleogeographic and tectonic evolution of the southwestern part of the archean abitibi and bellecombe belts volcanism in the abitibi belt created a very thick anisotropic plate composed of competent volcanic rocks and broken by the duparquet destor break the depocenters of the upper division of diverse volcanic rocks subsided about 10 km relative to their surroundings and some central volcanic complexes within this division were consolidated by synvolcanic plutons and their thermal metamorphic aureole the cadillac break a normal fault separated the abitibi and bellecombe belts the latter consisted of comparatively incompetent sedimentary rocks on top of a basement composed of ultramafic mafic flows north south compression of the volcanic terrain during the kenoran orogeny produced a set of flexure folds f1 that curve around the consolidated cores of central volcanic complexes generally in an easterly direction synclinoria nucleated at the dee

structural setting textures and timing of hydrothermal vein systems in the val d or camp abitibi canada implications for the evolution of transcrustal second and third order fault zones and gold mineralization in the val d or camp archean abitibi greenstone belt canada numerous gold mineralized second and third order fault zones are spatially associated with the transcrustal cadillac tectonic zone ctz this situation is used to test whether fluid systems in the ctz have a similar structural timing to those in the gold hosting structures and hence the ctz could represent the main fluid conduit in the camp the transcrustal ctz at orenada no 2 contains structurally complex vein systems with mineralized quartz tourmaline veins related to both d2 oblique reverse faulting and f3 dextral asymmetric folding both of which have been overprinted by unmineralized subhorizontal and subvertical quartz veins quartz tourmaline veins within second and third order shear zones at paramaque and riviere heva also formed during d2 deformation and have been at least at riviere heva deformed by f3 asymmetric folding in contrast mineralized quartz vein systems at cartier malartic are controlled by f3 folding and over

147 sm 143 nd and 176 lu 176 hf systematics of eucrite and angrite meteorites comparative planetary geochemistry provides insight into the origin and evolutionary paths of planetary bodies in the inner solar system the eucrite and angrite achondrite groups are particularly interesting because they show evidence of early planetary differentiation we present 147sm 143nd and 176lu 176hf analyses of eight noncumulate basaltic eucrites two cumulate eucrites and three angrites which together place new constraints on the evolution and differentiation histories of the crusts of the eucrite and angrite parent bodies and their mantle mineralogies the chemical compositions of both eucrites and angrites indicate similar evolutionary paths and petrogenetic models with formation and isolation of differentiated crustal reservoirs associated with segregation of ilmenite we report a 147sm 143nd mineral isochron age for the moama cumulate eucrite of 4519 34 ma mswd 1 3 this age indicates protracted magmatism within deep crustal layers of the eucrite parent body lasting up to about 50 ma after the formation of the solar system we further demonstrate that the isotopic compositions of constituent minerals are compromised by secondary processes hindering precise determination of mineral isochron ages of basaltic eucrites and angrites we interpret the changes in geochemistry and consequently the erroneous 147sm 143nd and 176lu 176hf internal mineral isochron ages of basaltic eucrites and angrites as the result of metamorphic events such as impacts effects from pressure temperature and peak shock duration on the surfaces of the eucrite and angrite parent bodies

structural setting for canadian malartic style of gold mineralization in the pontiac subprovince south of the cadillac larder lake deformation zone quebec canada abstract the structural setting of the pontiac subprovince in the vicinity of the world class canadian malartic gold deposit has been revisited by combining and reinterpreting airborne geophysical surveys together with a century of structural observations felsic intermediate intrusive bodies are a key component of this deposit defining the regional and local favorable structural setting for intrusive rock emplacement within the clastic meta sedimentary rocks of the pontiac group south of the cadillac larder lake deformation zone may further assist gold exploration in similar tectonic environment three structural domains are interpreted in the area based on the geometry of the bedding folds and structural fabrics related to the three major phases of deformation during these events four phases of magmatism and one metamorphic episode occurred the north domain which hosts the canadian malartic deposit is characterized by highly variable bedding orientations produced by the interference patterns of isoclinal f 1 folds overprinted by open to tight steeply dipping f 2 folds the bedding in this domain is cut by a penetrative s 2 biotite foliation which possibly built on rheological changes enhanced by metasomatism in the footprint of the canadian malartic deposit by contrast the central and south domains display homogeneous bedding orientations cross cut by a discrete s 2 biotite foliation and syn to late d 2 metamorphic porphyroblasts in all domains the l 2 stretching lineation consistently plunges at about 60 degrees toward the east d 3 is a minor deformation event in the pontiac subprovince which possibly correlates with late dextral transcurrent movement along the cadillac larder lake deformation zone intrusive bodies were emplaced throughout the first and second deformation events phase 1 monzonite quartz monzodiorite and granodiorite plutons ca 2683 2680 ma intruded into consolidated pontiac sedimentary rocks during d 1 phase 2 quartz monzodiorite bodies ca 2679 2676 ma predominantly formed in the north domain along f 1 fold axial surfaces prior to or at the onset of d 2 phase 3 basic dykes ca 2675 2673 ma cross cut earlier felsic intermediate intrusions across all domains and subsequently developed an s 2 metamorphic hornblende foliation phase 4 magmatism ca 2672 2662 ma is related to the decelles batholith s type granite and pegmatite which is interpreted to be contemporaneous with the peak of regional metamorphism the decelles batholith may project at depth underneath the canadian malartic deposit and could be associated with magmatic hydrothermal mineralizing fluids in the canadian malartic deposit gold mineralization at canadian malartic is spatially located on the contact of phase 2 quartz monzodiorite bodies the proximity to the cadillac larder lake deformation zone combined with the rheological contrast between steeply dipping clastic meta sedimentary rocks and quartz monzodiorite intrusions favored the protracted failure of the contacts between these two rock masses thus forming favorable conduits for hydrothermal fluids e g the sladen fault zone such specific rheological behavior is demonstrated by domains of structural complexity emphasized by the variance of the bedding dip these structurally complex zones systematically host gold mineralization in the canadian malartic district of the pontiac subprovince proximal to the cadillac larder lake deformation zone

archean geodynamics and the abitibi pontiac collision implications for advection of fluids at transpressive collisional boundaries and the origin of giant quartz vein systems abstract giant quartz vein systems of all ages from the archean to cenozoic are characterised by similarities of geodynamic setting local structure paragenesis metal budget p t t paths and chemical fluid dynamic and isotopic properties that collectively imply a singular hydrothermal process such quartz vein provinces form in regional brittle ductile shear zones that define terrane boundaries including closure of back arc basins and arc continent or continent continent collisions examples include the svz of the archean abitibi belt the norseman wiluna belt yilgarn block kolar schist belt india foothills metamorphic belt california and coast ranges megalineament in the cordillera and the cenozoic monte rosa district insubric line evidence for an archean collisional environment comes from the abitibi and pontiac subprovince tectonic boundary which hosts giant quartz vein systems in this region the amphibolite facies lacorne tectonic block in the archean abitibi greenstone belt is anomalous with respect to the prevalent low grade supracrustal sequences in neighbouring blocks the lacorne block has mature clastic sediments with a zircon provenance age spectrum from 3040 2691 ma and two granitic magma series a late syntectonic monzodiorite monzonite granodiorite syenite series formed over 2685 2670 ma similar to phanerozoic volcanic arc granites and post tectonic garnet muscovite granites emplaced at 2650 2630 ma which compositionally resemble phanerozic collisional s type granites the pontiac subprovince to the south of the abitibi greenstone belt shares all the above features with the lacorne block and collided with and was locally thrust under the abitibi belt with differential uplift of the lacorne block following collision to generate a tectonic window following collision of allochthonous terranes the conjuction of large volumes of subcreted oceanic crust and sediments between accreted terranes displaced isotherms rise and metamorphic dehydration are all necessary conditions for forming giant quartz vein systems metamorphic fluids are expelled along the terrane boundary structures at deep levels and focussed into second and higher order splays at mid crustal levels where quartz and au precipitation occurs hydrothermal fluids that formed the giant quartz veins are remarkably uniform in h o c and sr isotopic compositions albeit with small provincial variations the veins and gold precipitated at 270 360 c from fluids with low salinity and moderate co2 at 2 3 kbar in the brittle ductile transition

late archaean thrusting in the northwestern pontiac subprovince canadian shield abstract in the northwestern archaean pontiac subprovince south verging structures such as drag folds with subhorizontal axes stretched objects down dip mineral lineations low angle thrusts and allochthonous metavolcanic slabs were mainly produced by thrusting in response to n s regional compression deformation of the dominantly metasedimentary sequences occurred under barrovian type metamorphism and the horizontal shortening was accompanied by downdip stretching in the regional foliation s1 two nappes are assumed to be present their boundary being marked by an abrupt change in structural style and metamorphic facies two phases of close to isoclinal folding are evident in the upper nappe but are absent from the lower nappe in the upper nappe d2 gives and e w tectonic trend to the rock units f2 folds range from upright to recumbent but are most typically moderately southward inclined folds that plunge gently towards the east or west besides mostly retrograde recrystallization within d2 fault zones s2 is a crenulation cleavage that did not develop sufficiently to obliterate the regional schistosity s1 and its associated stretching and mineral lineations this contrasts with the regionally penetrative nature of the main deformation event d1 and suggests a narrowing or partitioning of high strain zones with time possibly due to a decrease in the regional temperature syn orogenic sedimentation in the northwestern pontiac subprovince was probably enhanced by tectonically controlled uplift resulting from early regional kenoran compression the sedimentary basin was subsequently deformed by further n s compression which led to internal stacking nappe type displacements barrovian metamorphism and thrusting of the southern abitibi over the pontiac subprovince the common style of folding and the same orientation of various structural elements such as cleavage and lineation in the transition zone between the abitibi and pontiac subprovinces indicate continuity in deformation style regional scale transcurrent displacement along the northern subprovince boundary appears as a late localized response to regional compression

neoarchean disaggregation and reassembly of the superior craton the southern and western superior craton of canada swsc is widely considered to be a tectonic collage accreted from north to south by multiple coeval subduction zones we propose an alternative non plate tectonic scenario where swsc continental fragments are not exotic but derived by partial disaggregation of a heterogeneous older superior i craton in response to a mantle overturn event that started at ca 2780 ma during overturn radial mantle outflow stretched and disaggregated the lithosphere to create the concentric neoarchean fabric of the superior craton the southern part of which swsc broke up into ribbon continents separated by oceanic tracts neoarchean calc alkaline magmas record interaction between plume related magma and older crust a change in the mantle flow field at ca 2720 ma caused southward drift of the northern superior cratonic block as a result of mantle traction on its lithospheric keel and swsc terranes accreted to its leading edge

megafauna extinction in south america a new chronology for the argentine pampas abstract the megafauna extinction in south america was one of the most profound events with the loss of 50 genera 83 three orders disappeared notoungulata proboscidea litopterna as did all large xenarthrans but how this fits into global extinction is uncertain mainly due to the lack of chronological resolution in recent years there has been an increase in the number of radiocarbon dating at archeological and paleontological sites but this information varies greatly from area to area in south america and few data can be considered to constitute a taxon date the timing of the late pleistocene extinction in the pampas is poorly established most taxa only appear in the biostratigraphic context and many reported 14 c dates do not meet rigorous criteria for accepting dates including reports suggesting survival of megafauna into the holocene in the present paper we evaluate the published radiocarbon dates in the pampas and present 20 new radiocarbon dates for paleontological sites in order to establish a more accurate extinction window for the key taxa these new dates are sufficiently robust to assess correspondences among last appearance records of megafauna first appearance records of humans and the younger dryas to holocene climatic transition in the argentine pampas these results highlight the need for greater effort in taxa selection for dating

hydrothermal alteration mineralogy and geochemistry of the archean world class canadian malartic disseminated stockwork gold deposit southern abitibi greenstone belt quebec canada

single zircon age constraints on the tectonic juxtaposition of the archean abitibi greenstone belt and pontiac subprovince quebec canada abstract zircons from metasediments and granitoids in the high grade lacorne block within the low grade archean abitibi greenstone belt have been dated by the single zircon pb evaporation technique yielding 207pb 206pb minimum ages detrital zircons in the mature clastic metasediments of the lacorne block display a range of ages from 2691 8 ma to 3042 6 ma the younger zircon ages 2691 8 2695 4 2715 16 and 2719 4 ma thus impose an upper limit for deposition and indicate that the high grade lacorne block is not basement to the abitibi supracrustal sequence 2747 2680 ma existence of abundant 69 older detrital zircons 2750 ma suggests in turn that the abitibi supracrustal rocks are not the source of the lacorne sediments two generations of granitoids occur in the lacorne block an early monzodiorite monzonite granodiorite syenite series mmgs 2671 4 to 2675 24 ma and a younger s type garnet muscovite granite series gmg 2630 20 to 2655 8 ma this contrasts with granitoid magmatism in the abitibi greenstone belt which ended at 2675 ma the pontiac subprovince to the south of the abitibi greenstone belt shares all of the above features of the lacorne block including detrital zircon ages as well as the composition and timing of granitoid magmatism this is interpreted to indicate that the lacorne block was originally part of the same tectonic terrane as the pontiac subprovince after development of the mmgs magmatism 21670 2680 ma the pontiac subprovince locally underthrust the abitibi greenstone belt and crustal thickening promoted partial melting of underthrust pontiac metasediments to form the 2644 13 ma s type granites later differential uplift exposed the lacorne block as a high grade tectonic window in the abitibi greenstone belt

magnetic polarity stratigraphy of the middle pleistocene ensenadan tarija formation of southern bolivia abstract the tarija formation of southern bolivia which is well known for its classic vertebrate faunas is of prime importance in understanding of the chronology of the ensenadan land mammal age this formation consists of well exposed and relatively fossiliferous sections of clays clayey silts sands gravels and tuffs which were deposited in a predominately fluviatile regime in a pleistocene structural basin four stratigraphic sections each measuring 110 m or less were studied to establish a magnetic polarity stratigraphy paleomagnetic samples were collected from the finer grained sediments at 100 sites spaced at stratigraphic intervals of 5 m or less all paleomagnetic specimens were demagnetized in alternating fields of least 250 oersteds oe some specimens were also thermally demagnetized at 200 c or more of the 100 sites 77 were ultimately used to determine the magnetic polarity zonation based on the four sections sampled the tarija formation spans a time interval from about 1 my to about 0 7 my b p or perhaps younger the lower half of the composite section is of reversed polarity punctuated by a short normal event this sequence probably represents the late matuyama chron with the jaramillo subchron the upper part of the section is of normal polarity and represents early brunhes time a tuffaceous unit 43 m above the brunhes matuyama boundary yielded a fission track zircon age of 0 7 0 2 by b p these data indicate that the classic tarija fauna is middle pleistocene ensendan in age

synthesis of the structural evolution and associated gold mineralization of the cadillac fault abitibi canada abstract the cadillac fault zone cfz is a 250 km long east trending crustal discontinuity associated with numerous world class gold deposits in the archean abitibi subprovince in quebec the fault follows the boundary between the abitibi and the pontiac subprovinces and can be divided into four segments 1 rouyn 2 joannes 3 malartic and 4 val d or each displays different attitudes and structural styles the malartic segment strikes se whereas the other segments are e trending abrupt changes in strike or smaller scale faults represent limits between the segments structural styles include four generations of foliation with numerous shear sense indicators and folding specifically related to each foliation structural features can be correlated from one segment to another but display clear variations in attitude or expression a stretching lineation signature is definitely associated with each segment in the malartic segment the predominant e trending schistosity displays an angular relationship with the contact between groups and bedding suggesting that the se trending architecture of this segment was already emplaced prior to ductile deformation the evidence suggests a model where the cfz originates from several independent structures inherited from volcanism prior to timiskaming deformation and abitibi pontiac accretion the proto cfz was then linked up during the timiskaming deposition forming high strain zones inherited structures form the frame on which each deformation event was overprinted with different responses depending on segmentation the structural styles of each segment can be integrated in a structural evolution model for the cfz the n s shortening led to the development of a dominantly e striking penetrative foliation and folding during the subsequent extensional stage the cfz was reactivated with normal kinematics during the pontiac uplift a third deformation event is represented by the local development of nw trending cleavage axial planar to the s shaped minor folds finally a late nw se shortening event produced a dextral strike slip movement with ne striking vertical foliation and development of z shaped folds on bedding surfaces and anterior fabrics linkage of the cfz had a major impact on hydrothermal activity in the southern abitibi as it channeled fluids along large scale pathways distribution of gold bearing intrusions can also be related to segmentation and inherited structures of the cfz this association is expressed by gold mineralization styles present in several longitudinal fields reflecting fault segmentation

climate and humans set the place and time of proboscidean extinction in late quaternary of south america abstract the late quaternary extinctions have been widely debated for a long time but the varying magnitude of human vs climate change impacts across time and space is still an unresolved question here we assess the geographic range shifts in response to climate change based on ecological niche models enms and modeled the timing for extinction under human hunting scenario and both variables were used to explain the extinction dynamics of proboscideans during a full interglacial glacial cycle from 126 ka to 6 ka in south america we found a large contraction in the geographic range size of two proboscidean species studied cuvieronius hyodon and notiomastodon platensis across time the largest contractions of their geographical ranges occurred in the northern part of south america where we previously reported no evidence of coexistence among earliest humans and non sloth megafauna including proboscideans our results herein support a strong effect of climatic changes on geographical range dynamics of proboscideans throughout late quaternary although this does not fully support climate change as the single cause of their extinctions we show that both proboscideans were narrowly distributed on scattered patches of suitable habitats i e refugia around 11 ka period in which the earliest humans potentially arrived in south america increasing the population density thereafter under this overall unsuitable climatic condition at 11 ka both proboscideans would be extinct after around 550 years of human hunting but if climatic conditions were suitable like in last glacial maximum lgm the time for extinction would be at least 3 times longer under the same human hunting pressures thus our findings support the broken zig zag model and show that south american proboscideans might have been completely extinct due to human impacts during periods of climate crisis we conclude in agreement with an increasing body of evidence in the recent literature that the late quaternary megafaunal extinction event was the result of additive effects from different stressors and that the relative magnitude of these impacts vary across space and time indeed climate changes set the place where the proboscideans were extinct in south america whereas the humans set the time of these extinctions

crustal structure and kinematic framework of the northwestern pontiac subprovince quebec an integrated structural and geophysical study structural mapping gravity and magnetic modelling and interpretation of a deep seismic profile in the northwestern pontiac subprovince outline the crustal structure and early structural developme

40ar 39ar age constraints on the thermal history of the archean abitibi greenstone belt and the pontiac subprovince implications for terrane collision differential uplift and overprinting of gold deposits 40ar 39ar mineral age spectra of granitic and metamorphic rocks in conjunction with existing conventional zircon geochronology indicate that at least two major late archean thermal events affected tectonic blocks of the abitibi southern volcanic zone svz and the juxtaposed pontiac subprovince the earlier thermal activity 2690 2670 ma was accompanied by the intrusion of voluminous syntectonic plutons and caused low pressure greenschist facies metamorphism in the svz and intermediate pressure metamorphism in the pontiac subprovince the second thermal event 2660 2630 ma was coeval with the emplacement of syncollisional s type garnet muscovite granites in the pontiac subprovince and the higher grade lacorne block of the abitibi svz and reset the k ar systems in preexisting rocks magmatic amphibole from the syntectonic round lake batholith 2695 ma u pb zircon age of the abitibi svz has a slightly disturbed ar release spectrum with an upper plateau age of 2669 6 ma signifying that the low gra

the use of lithogeochemistry in delineating hydrothermal fluid pathways and vectoring towards gold mineralization in the malartic district quebec abstract the world class oxidized intrusion related canadian malartic gold deposit with reserves estimated at 5 56 moz au grading 1 10 g t au and a total geological endowment of 16 3 moz au is one of the largest gold deposits in the archean superior province of canada the gold mineralization is hosted predominantly by pontiac group metasedimentary rocks piche group metavolcanic rocks and quartz monzodiorite to granodiorite porphyritic intrusions the ore takes the form of a low grade envelope of disseminated pyrite 0 35 to 1 g t au grading inwards into higher grade 1 g t au stockwork and breccia zones hydrothermal alteration in the metasedimentary rocks is zonally distributed around the fluid pathways proximal alteration is characterized by a microcline albite quartz replacement type assemblage with lesser phlogopite calcite fe dolomite pyrite and rutile the distal alteration assemblage comprises biotite microcline albite phengite quartz calcite pyrite and rutile in this study we assess the magnitude and distribution of fluid rock interaction in the metasedimentary rocks of the malartic district the metaturbidites are separated into four lithotypes based on grain size to reduce the effects of primary depositional processes on mass change calculations despite the variability in protolith composition the metasedimentary rocks define a geochemically consistent cogenetic sequence the results of the mass transfer calculations indicate progressive gains in co2 s k2o and loi as well as au te w ag as be sb bi mo and pb from background to distal and proximal alteration zones relative to the least altered samples molar element ratio analysis alkali aluminum indicates an increase in alkali metasomatism k and na adjacent to the main hydrothermal fluid pathways which is manifested by the progressive stabilization of microcline and albite at the expense of oligoclase biotite and white mica ore associated pathfinder elements delineate broad enrichment patterns around the deposit and are used to understand hydrothermal fluid circulation in the malartic district a statistical approach based on a comparison of the mass change results with the background composition provides robust constraints on the magnitude and extent of the lithogeochemical haloes generally the alteration forms envelopes that extend along the s2 fabric with the largest lithogeochemical anomalies e g au w te and ag reaching up to 10 km in length and 2 km in width the results of this study demonstrate that whole rock lithogeochemistry can provide a valuable tool with which to define vectors toward gold mineralization in a regional exploration context

u pb systemstics in single zircons from the pontiac sediments abitibi greenstone belt twenty six detrital zircon grains from the late archaean pontiac sediments of the abitibi greenstone belt were dated individually by the u pb method in order to identify possible elements of an ancient pre 2 7 ga shield the results show that at least two components were present at the source areas of these sediments 1 materials of about 2700 2725 ma which were most likely derived from contemporaneous acid igneous rocks and 2 significantly older materials parts of which are at least 2940 ma old which were either part of an uplifted sedimentary basin or a sialic basement complex these results can be used to suggest a close link between igneous activity and basin subsidence and that the development of the abitibi volcanic belt was closely associated with the presence of some older sialic blocks

palaeomagnetism of late cenozoic fossiliferous sediments from barranca de los lobos buenos aires province argentina the magnetic age of the south american land mammal ages abstract palaeomagnetic data for a sequence of late cenozoic sediments exposed at bajada martinez de hoz and el muelle barranca de los lobos atlantic coastal area buenos aires province are reported the sequence comprises sediments assigned to the chapadmalal formation montehermosense land mammal age barranca de los lobos vorohue and san andres formations uquiense land mammal age miramar formation ensenadense land mammal age and arroyo seco and arroyo loberia formations lujanense land mammal age the magnetostratigraphy recorded in the sequence suggests a brunhes magnetic age 3 15 ma for the chapadmalal formation it also suggests a brunhes to late matuyama magnetic age for the lujanense land mammal age a matuyama magnetic age for the ensenadense land mammal age a gauss magnetic age for the uquiense land mammal age and an early gauss to gilbert magnetic age for the montehermosense land mammal age finally the results obtained suggest that the panama isthmus was formed at an age earlier than 3 0 ma possibly 4 0 3 5 ma ago

sequence organization and growth patterns of late mesoproterozoic stromatolite reefs an example from the burovaya formation turukhansk uplift siberia abstract the latest mesoproterozoic burovaya formation is a 600 1000 m thick stromatolite mud dominated carbonate unit demarcated by an erosional unconformity into two subformations containing stromatolite reefs of variable size and geometry the lower subformation consists of two distinct stratigraphic sequences the lower sequence records shelf to ramp evolution and includes small scale stromatolite reefs developed within an upper subtidal shelf settings at the transgressive systems tract and overlying mud dominated highstand deposits accumulated in lower subtidal to peritidal environments the second sequence of muddy and fine grained sediments makes up a lowstand systems tract and documents a progressive structural and environmental differentiation of the burovaya platform the upper subformation records a third stratigraphic sequence containing transgressive and highstand systems tracts represented by reef bearing and reef cap facies complexes the reef bearing complex characteristic of the transgressive and the bulk of the highstand systems tracts contains a giant 20 25 km wide 10 km long up to 550 m thick stromatolite reef and surrounding deep water carbonate mudstones containing sporadic slump block deposits the reef was located on the distally steepened part of the ramp and contains distinct internal facies organization defined by particular stromatolite microstructure and morphology and prevailing environments late highstand development of the burovaya platform was marked by the termination of reef accretion infilling of basinal relief by shallow water carbonate and shale sediments of the cap complex and subsequent subaerial exposure the history of the burovaya reef is indicative of the interplay between reef growth potential and platform geometry defined by regional tectonic and sea level dynamics

the isotopic composition of yb and the precise and accurate determination of lu concentrations and lu hf ratios by isotope dilution using mc icpms 1 we report yb isotopic data for the purpose of accurately correcting measurements of lu and lu hf ratios during multicollector inductively coupled plasma mass spectrometer mc icpms analysis the yb isotopic ratios agree with recent results of chu et al 2002 and amelin and davis 2004 when corrected for mass fractionation to the same reference values protocols for lu measurement involving simultaneous subtraction of yb interference and application of a fractionation correction based on yb are described it is shown that lu concentrations and lu hf ratios determined by mc icpms using this methodology are more precise and potentially more accurate than results based on analysis of lu by thermal ionization mass spectrometry tims a number of mc icpms lu hf isotopic analyses of standard rocks and other geological samples previously analyzed by tims are presented these document reproducibility of lu hf within 0 2 where most discrepancies can be assigned to the unknown lu mass fractionation during tims analysis

constraints on the genesis of the archean oxidized intrusion related canadian malartic gold deposit quebec canada a discussion sir in their paper entitled constraints on the genesis of the archean oxidized intrusion related canadian malartic gold deposit quebec canada helt et al 2014 present oxygen and hydrogen isotope data and discuss the origin of the hydrothermal fluids that formed the canadian malartic gold deposit on the basis of the calculated hydrogen 53 to 46 and oxygen 5 2 8 5 isotope compositions helt et al 2014 p 731 argued that the hydrothermal fluid that formed the canadian malartic gold mineralization and associated potassic alteration falls within the relatively small field of typical magmatic hydrothermal fluids the quartz and biotite 18o values from four late ore stage veins suggest that two pairs are in equilibrium at 531 c using bottinga and javoy 1975 whereas the other two have high 18obiotite values that are either caused by oxygen isotope disequilibrium as suggested by helt et al 2014 and or by contamination of the biotite concentrate by intergrown quartz fig 1 the contamination hypothesis may be supported by the relatively lower variance

archaean metasedimentary rocks from the northwestern pontiac subprovince of the canadian shield chemical characterization weathering and modelling of the source areas abstract the northwestern pontiac subprovince is dominated by a monotonous greywacke sequence metamorphosed and deformed during the late archaean kenoran orogeny limited chemical weathering of the source rocks is suggested by 1 low values of the chemical index of alteration 2 no preferential leaching of ca sr and ba 3 well defined correlations among mgo k2o and al2o3 and 4 small variations of cr ni the source was dominantly felsic as indicated by high th sc average 0 39 la co 1 06 zr cr 0 7 zr y 11 2 and sio2 mgo 19 4 the composition of these metasedimentary rocks can be modelled by mixing of three end member components 1 tonalites trondhjemites 65 in order to explain the sio2 al2o3 th u zr sr and ba abundances na k ratios strong depletion in hree and hfse relative to lree and lile low th y and k2o and fractionated la yb 19 4 2 komatiites 5 in order to explain the high cr 220 ppm and ni 66 ppm contents and 3 tholeiitic basalts 30 accounting for the observed tio2 0 62 wt v 144 ppm and sc 17 ppm concentrations the source region may be considered as a deeply eroded greenstone belt intruded by abundant tonalite trondhjemite plutons possibly now located to the south and east in the grenville province or possibly to the north underlying the dominantly volcanic abitibi subprovince