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

structural analysis and metamorphism of the barlow fault zone chibougamau area neoarchean abitibi subprovince implications for gold mineralization faults and deformation zones are important features of archean terranes because of their significance for structural evolution and the formation of large gold districts in the chibougamau area no

the southern westerlies during the last glacial maximum in pmip2 simulations the southern hemisphere westerly winds are an important component of the climate system at hemispheric and global scales variations in their intensity and latitudinal position through an ice age cycle have been proposed as important drivers of global climate change due to their influence on deep ocean circulation and changes in atmospheric co2 the position intensity and associated climatology of the southern westerlies during the last glacial maximum lgm however is still poorly understood from empirical and modelling standpoints here we analyse the behaviour of the southern westerlies during the lgm using four coupled ocean atmosphere simulations carried out by the palaeoclimate modelling intercomparison project phase 2 pmip2 we analysed the atmospheric circulation by direct inspection of the winds and by using a cyclone tracking software to indicate storm tracks the models suggest that changes were most significant during winter and over the pacific ocean for this season and region three out four models indicate decreased wind intensities at the near surface as well as in the upper troposphere although the lgm atmosphere is colder and the equator to pole surface temperature gradient generally increases the tropospheric temperature gradients actually decrease explaining the weaker circulation we evaluated the atmospheric influence on the southern ocean by examining the effect of wind stress on the ekman pumping again three of the models indicate decreased upwelling in a latitudinal band over the southern ocean all models indicate a drier lgm than at present with a clear decrease in precipitation south of 40 s over the oceans we identify important differences in precipitation anomalies over the land masses at regional scale including a drier climate over new zealand and wetter over nw patagonia

gold mineralization patterns in relation to the lithologic and tectonic evolution of the chibougamau mining district quebec canada the chibougamau mining camp a major gold producer has so far produced a total of 1 050 mt of gold at an average grade of 1 85 g tonne in contrast to a general tendency to group the deposits as vein type with varying compositions this paper demonstrates the strong influence of regional lithologic and tectonic evolution of the area on the gold mineralization patterns a syn volcanic period of mineralization comprises both the volcanogenic massive sulphide and disseminated mineralization and the subsequent epithermal mineralization the latter is also associated with evolving volcanic landforms and syn volcanic intrusions the emplacement of the typical archean lode gold deposits and later cu au deposits of uncertain origin coincides with the syn deformational kenoran period the spatial relationship between the east west trending shear zones and a north east trending fault system is shown to be a possible mechanism for generating added dilatancy during the gold mineralizing phase a late to post kenoran shear system controlled the emplacement of the last major phase of gold mineralization within a stratiform intrusion

northern westerlies during the last glacial maximum results from cmip5 simulations abstractbased upon simulations from phase 5 of the coupled model intercomparison project cmip5 the vertical and regional characteristics of the northern westerlies during the last glacial maximum lgm are investigated in this study at the northern hemispheric scale all nine available models simulate a poleward shift of the 200 hpa jet and eight models simulate an equatorward shift of the 850 hpa jet compared to the preindustrial period these shifts are of approximately 2 3 latitude for the arithmetic multimodel mean the upper tropospheric cooling in the tropics possibly due to reduced latent heat release is expected to account for the poleward shift of the 200 hpa jet through the thermal wind relationship changes in the midlatitude baroclinic instability in response to the amplified polar cooling are associated with the jet stream in the lower troposphere through anomalous eddy activity in particular the types of predominant baroclinic eddies are regionally dependent the behavior of the 8

climate and marine carbon cycle response to changes in the strength of the southern hemispheric westerlies 1 it has been previously suggested that changes in the strength and position of the southern hemisphere westerlies could be a key contributor to glacial interglacial atmospheric co2 variations to test this hypothesis we perform a series of sensitivity experiments using an earth system model of intermediate complexity a strengthening of the climatological mean surface winds over the southern ocean induces stronger upwelling and increases the formation of antarctic bottom water enhanced ekman pumping brings more dissolved inorganic carbon dic rich waters to the surface however the stronger upwelling also supplies more nutrients to the surface thereby enhancing marine export production in the southern hemisphere and decreasing the dic content in the euphotic zone the net response is a small atmospheric co2 increase 5 ppmv compared to the full glacial interglacial co2 amplitude of 90 ppmv roughly the opposite results are obtained for a weakening of the southern hemisphere westerly winds

sensitivity of southern hemisphere circulation to lgm and 4 co2 climates 1 this paper investigates the effect of last glacial maximum lgm versus high co2 world boundary condition on the southern hemisphere atmospheric circulation in particular on the strength and latitudinal position of the near surface southern westerly winds sww pmip2 and pmip3 experiments as well as the abrupt 4 co2 simulations from cmip5 were analyzed robust findings include poleward expansion of the mean meridional circulation mmc and intensified and poleward shifted sww in the 4 co2 simulations consistent with recent observations and 21st century climate change projections and for the lgm stronger and southward shifted northern hemisphere mmc and weakened southern hadley cell however six of the eight lgm simulations show a decrease in the sww the other two models simulate the opposite a critical difference between the models is strong coupling between sea ice extent surface temperature gradients sww and ferrel cell in the two models with stronger and poleward shifted sww

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

connecting antarctic sea ice to deep ocean circulation in modern and glacial climate simulations antarctic sea ice formation plays a key role in shaping the abyssal overturning circulation and stratification in all ocean basins by driving surface buoyancy loss through the associated brine rejection changes in antarctic sea ice have therefore been suggested as drivers of major glacial interglacial ocean circulation rearrangements here the relationship between antarctic sea ice buoyancy loss deep ocean stratification and overturning circulation is investigated in last glacial maximum and preindustrial simulations from the paleoclimate modelling intercomparison project pmip the simulations show substantial inter model differences in their representation of the glacial deep ocean state and circulation which is often at odds with the geological evidence we argue that these apparent inconsistencies can largely be attributed to differing and likely insufficient antarctic sea ice formation discrepancies can be further amplified by short integration times deep ocean equilibration and sea ice representation should therefore be carefully evaluated in the forthcoming pmip4 simulations

significance of a midlatitude sst frontal zone in the formation of a storm track and an eddy driven westerly jet abstract in a set of idealized aquaplanet experiments with an atmospheric general circulation model to which zonally uniform sea surface temperature sst is prescribed globally as the lower boundary condition an assessment is made of the potential influence of the frontal sst gradient upon the formation of a storm track and an eddy driven midlatitude polar front jet pfj and on its robustness against changes in the intensity of a subtropical jet stj in experiments with the frontal midlatitude sst gradient as that observed in the southwestern indian ocean transient eddy activity in each of the winter and summer hemispheres is organized into a deep storm track along the sst front with an enhanced low level baroclinic growth of eddies in the winter hemisphere another storm track forms just below the intense stj core but it is confined to the upper troposphere with no significant baroclinic eddy growth underneath the near surface westerlies are strongest near the midlatitude sst front as observe

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

southern ocean wind response to north atlantic cooling and the rise in atmospheric co2 modeling perspective and paleoceanographic implications 1 a recent study found enhanced upwelling rates in the southern ocean during the last glacial termination that coincided with the deglacial warming in antarctica and the rise in atmospheric co2 they hypothesized that the intensification of southern hemisphere midlatitude westerlies the presumed cause of the increased wind driven upwelling was triggered by an initial cooling within the glacial north atlantic whose influence was then communicated to the southern midlatitudes through an atmospheric teleconnection in this study we explore the viability of the above hypothesis using a modeling strategy focusing on the atmospheric teleconnection in simulations where north atlantic cooling was applied the model intertropical convergence zone shifted southward and westerlies and wind stress over southern ocean increased by as much as 25 while the perennial westerly anomalies occur over the entire southern ocean they are strongest over the south pacific during the austral winter when the wind stress anomalies were applied to an earth system model incorporating interactive marine biogeochemistry atmospheric co2 rises between 20 and 60 ppm depending on the biological response we thus confirm the viability of the proposed atmospheric teleconnection hypothesis the teleconnection appears to involves two distinct steps first the north atlantic cooling shifts the intertropical convergence zone southward weakening the southern branch of the hadley circulation and second how the altered hadley circulation in turn modifies the structure of midlatitude westerlies in the south pacific via the former s influence on the southern hemisphere subtropical jet this study underscores the control of the northern hemisphere has on southern midlatitude westerlies mediating by tropical circulation in contrast to past paleoclimate hypotheses that the magnitude and position of the southern midlatitude westerlies was controlled by global mean temperature our results do not preclude other potential mechanisms for affecting southern ocean ventilation in particular through oceanic pathways

diapirism during regional compression the structural pattern in the chibougamau region of the archean abitibi belt quebec the major fold pattern of the chibougamau region in the archean abitibi belt quebec is the result of two fold phases the principal f1 synclines first formed as subsiding fault troughs and were shortened in ns direction and molded around volcanic centers that had been consolidated by large synvolcanic plutons they have a general easterly direction but curve locally to the ne or se n trending f1 folds are locally present in the anticlinoria and are thought to have been produced by the upwelling of basement gneiss and or synvolcanic plutons the f2 folds have rather regular easterly trends their axial plane schistosity s2 is the predominant planar fabric element basin margin faults were transformed into east trending thrust faults during the f1 and f2 folding

evolution of the meridional shift of the subtropical and subpolar westerly jet over the southern hemisphere during the past 21 000 years abstract deciphering the variations in the subtropical westerly jet stj and the subpolar westerly jet spj over the southern hemisphere in earth s history will help us to better understand how the westerlies may respond to various external forcings in the future using simulation of transient climate evolution over the past 21 000 years simulations we demonstrate that the stj migrated equatorward in the last glacial maximum relative to the present which followed by abrupt poleward equatorward and poleward shifts during the heinrich stadial i antarctic cold reversal and younger dryas respectively these large amplitude fluctuations are controlled by changes in meltwater fluxes and polar ice sheet topography during the holocene the stj shows no obvious long term trend due to the offsetting effect between increased orbital insolation in austral summer and decreased antarctic ice sheet topography the meridional shift of the spj shows an in phase change with the stj during the past 21 kyr in terms of the dynamic mechanisms the meridional shift of the stj and spj is induced by changes in the meridional temperature gradient and the maximum eddy growth rate respectively and is also linked to changes in the mean meridional circulations that is the hadley and ferrel cells the modeled meridional shift of the southern westerlies is supported by the results from the paleoclimate modelling intercomparison project phase and is consistent with several reconstructions but it is difficult to constrain robustly by geological evidence as the reconstructed westerlies vary across sites and proxies nevertheless our study provides a possible scenario for the evolution of the southern westerlies during the past 21 kyr and identifies the dominant forcing and the associated mechanisms which may advance our knowledge on the future behavior of the southern westerlies

a consistent poleward shift of the storm tracks in simulations of 21st century climate 1 a consistent poleward and upward shift and intensification of the storm tracks is found in an ensemble of 21st century climate simulations performed by 15 coupled climate models the shift of the storm tracks is accompanied by a poleward shift and upward expansion of the midlatitude baroclinic regions associated with enhanced warming in the tropical upper troposphere and increased tropopause height the poleward shift in baroclinicity is augmented in the southern hemisphere and partially offset in the northern hemisphere by changes in the surface meridional temperature gradient the poleward shift of the storm tracks also tends to be accompanied by poleward shifts in surface wind stress and precipitation and a shift towards the high index state of the annular modes these results highlight the integral role that the storm tracks play in the climate system and the importance of understanding how and why they will change in the future

geology alteration and origin of archean au ag cu mineralization associated with the synvolcanic chibougamau pluton the brosman prospect abitibi greenstone belt canada the au ag cu brosman prospect is located in the line lake area on the northern limb of the chibougamau anticline in the northeast part of the archean abitibi greenstone belt this prospect comprises a broad n s subvertical mineralized envelope formed in a synvolcanic fault related environment this envelope is at least 300 m long up to 30 m wide and is known to a depth of 950 m where it remains open it exhibits two contrasting mineralized zones that are representative of the varying styles of mineralization in the area the auriferous zone consists of both ubiquitous pyrite disseminations and au bearing silicate sulfide veins in strongly fractured intrusive effusive and volcaniclastic rocks showing propylitic and chloritic alteration assemblages the polymetallic zone on the other hand is characterized by discrete cu ag au rich magnetite sulfide veins and lesser pyrite disseminations within distal propylitic and proximal potassic to sodic alteration zones the polymetallic zone is hosted by a chaotic assemblage of gabbro and tuff bodies interpreted as a talus megabreccia several lines of evidence including the spatial distribution pattern and nature of the alteration and mineralization assemblages metal associations mass balance calculations pyrite composition and crosscutting relationships are indicative of a preregional deformation synvolcanic origin for the hydrothermal activity crosscutting relationships alteration characteristics as well as whole rock and la icp ms pyrite analyses reveal two stages of hydrothermal alteration and mineralization stage i consists of both ubiquitous disseminated pyrite found in the polymetallic and auriferous zones and contemporaneous magnetite sulfide veins restricted to the polymetallic zone stage ii is restricted to the auriferous zone and corresponds to au bearing silicate sulfide veins with characteristic vein halo chloritic alteration overprinting stage i alteration and mineralization this hydrothermal activity is interpreted to have occurred concurrently with the development of the fertile deeper magmatic hydrothermal system related to the chibougamau pluton stage i hydrothermal activity related to the early build up of the volcanic sequence formed a continuum of mineralization from discrete massive magnetite sulfide veins to ubiquitous pyrite disseminations in a submarine talus megabreccia generated along synvolcanic faults afterward a late au rich contribution to the hydrothermal fluids possibly related to intermediate to felsic magmatism the 2707 6 1 4 ma line lake stock produced stage ii silicate sulfide veins overprinting mineralization and alteration in favorably oriented and sustainably permeable fracture zones of the auriferous zone overall this study suggests that the brosman prospect is a rare example of archean polymetallic mineralization produced by a shallow subaqueous epithermal style subsystem developed in a broader fertile magmatic hydrothermal arc setting

what have we learnt from palaeoclimate simulations there has been a gradual evolution in the way that palaeoclimate modelling and palaeoenvironmental data are used together to understand how the earth system works from an initial and largely descriptive phase through explicit hypothesis testing to diagnosis of underlying mechanisms analyses of past climate states are now regarded as integral to the evaluation of climate models and have become part of the toolkit used to assess the likely realism of future projections palaeoclimate assessment has demonstrated that changes in large scale features of climate that are governed by the energy and water balance show consistent responses to changes in forcing in different climate states and these consistent responses are reproduced by climate models however state of the art models are still largely unable to reproduce observed changes in climate at a regional scale reliably while palaeoclimate analyses of state of the art climate models suggest an urgent need for model improvement much work is also needed on extending and improving palaeoclimate reconstructions and quantifying and reducing both numerical and interpretative uncertainties

volcanism and related slope to shallow marine volcaniclastic sedimentation an archean example near chibougamau quebec canada abstract volcaniclastic sedimentary rocks and k rich lava flows of the archean hauy formation are discontinuously exposed in a 850 m thick sequence in the waconichi synclinorium northwest of chibougamau quebec the interstratified sedimentary rocks comprise two major sedimentary facies associations the graded bedded facies association wbfa indicative of deposition by sediment gravity flows and the wavy bedded facies association wbfa defined by wave induced structures the gbfa is near the base of the stratigraphic section and is interstratified up section with the wbfa in the gbfa the abundance of synsedimentary folding truncated slump folds load casts and low angle erosional surfaces as well as sediments deposited by turbidity currents and debris flows support designation as a volcanic slope deposit in the wbfa trough crossbeds wavy bedded gravels and plane bedded volcaniclastic sandstones are indicative of a nearshore setting the abundance of angular to subangular lithic volcanic fragments and broken and euhedral pyroxene crystals in the sediments is suggestive of a pyroclastic origin some beds may represent primary pyroclastic material but unequivocal petrographic recognition of pumice or glass shards is not possible because of metamorphic overprint composition suggests an initial magmatic or phreatomagmatic eruption subsequently reworked along the shoreline and transported downslope lava flows comprising massive to lobate andesites and massive to blocky basalts constitute most of the stratigraphic sequence pillowed flows are strikingly absent from the section both compositional types have an increase in vesicularity and change in flow form up section from massive to lobate or blocky suggesting progressively shallower water depths the composite character represented by hauy lava flows and associated volcaniclastic sediments in characteristic of stratovolcanoes the studied section is an integral part of an evolved arc with an adjacent backarc basin the volcano sedimentary facies indicate the development of a volcanic island in one of these basins

a precambrian upper basin slope and prodelta in northeast finnmark north northway a possible ancient upper continental slope abstract the 60 m to 540 m thick lower naeringselva member of the basnaering formation crops out on varanger peninsula north norway and is part of the 9 km thick late precambrian barents sea group it is underlain by at least 3 2 km of submarine fan deposits and is the oldest part of a 2 5 km to 3 5 km thick fluvio deltaic succession basnaering formation the upper part of the member is delta front deposits the lower naeringselva member mainly comprises fine grained thin bedded deposits divided into four facies 1 facies i parallel laminated mudstone 2 facies ii current rippled siltstone interpreted with facies i as low density low velocity turbidity current deposits 3 facies iii structureless mudstone interpreted as possible hemipelagic deposits and 4 facies iv wave rippled fine very fine grained sandstone interpreted as due to wave action soft sediment deformation is abundant as various styles of slide slump and in situ disturbed layers up to tens of meters thick erosional depositional discordances are evident between packets of beds the stratigraphic position and sedimentology of the lower naeringselva member suggest that it is part of an ancient upper basin slope and prodelta with submarine fan deposits on the lower basin slope paleocurrent data with a limited number of slide fold readings imply that deposits from downs lope flowing sediment laden currents prograded the slope towards the east north east apart from sporadic storm events the slope was below wave base modern analogues for the lower naeringselva member appear to be the upper part of continental slopes separating submarine fan from delta deposits as in the mississippi delta slope fan system

a transitional alluvial to marine sequence the eocene llajas formation southern california abstract the early to middle eocene llajas formation of the southwestern santa susana mountains transverse ranges in southern california forms a retrogradational system followed by a progradational system the retrogradational system grades vertically upward from coastal alluvial fan to shallow marine to outer shelf to slope with incised channels these channels and associated outer shelf to slope facies were subsequently covered by progradational shallow marine facies the progradational cycle is incomplete due to erosional truncation by the nonmarine early late eocene sespe formation

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

how important are southern hemisphere wind changes for low glacial carbon dioxide a model study 1 the response of atmospheric co2 to modifications in the strength and position of southern hemisphere westerlies is examined with the bern3d ocean model the model responds more sensitively to changes in the wind amplitude than to variations in latitudinal position depending on the model setup a 50 reduction in wind strength leads to a co2 drawdown of 3 34 ppm while a 50 increase results in a rise of 10 24 ppm a poleward shift of 5 lowers co2 by 2 16 ppm whereas an equatorward shift of 5 induces a co2 increase of 2 14 ppm physical and biological mechanisms equally contribute to the modeled changes in atmospheric co2 our results are in conflict with the hypothesis that southern hemisphere wind changes are responsible for the low atmospheric co2 concentrations during glacial periods

storm generated sedimentary structures in subtidal marine facies with examples from the middle and upper ordovician of southwestern virginia abstract the role of storms is of major importance in forming stratification in open shelf facies though storm processes on modern shelves are not fully understood enough is known to see how sediments are influenced storms transport sand away from coastal areas and suspend and transport sand and mud on the open shelf when wave base is lowered storms generate winnowed lag deposits of shells or gravel but coarser sediment and shells of megafauna are little transported except in very near shore environments the martinsburg formation middle and upper ordovician of southwestern virginia was deposited on a storm influenced open marine platform in contrast to the classic turbidite flysch basin of the martinsburg in the great valley of virginia to the northeast deposition of most martinsburg sediments was due to storms sediments deposited during single storm events occur in characteristic fining upward sequences 1 to 80 cm thick in both carbonate and terrigenous clastic dominated areas of the platform individual storm deposits consist of a sharp erosional base overlain by a couplet of whole fossil packstone and laminated calcarenite siltite or quartzose siltstone to very fine sandstone which is gradational to shale packstones are typically intraclastic have shells aligned parallel o bedding and convex up often with adhering or contained mud and have abundant infiltration textures such as cement filled shelter voids packstones grade abruptly to a laminated bed with horizontal plane lamination large and small scale in phase undulatory lamination and wave ripple cross lamination commonly occurring in ordered vertical sequences laminated beds contain escape burrows are weekly graded and have irregularly mounded upper bed surfaces laminated beds grade upward to shale containing horizontal branching burrows and marine fossils the faunal content of the fining upward sequences matches that of the interbedded shale storm generated beds vary greatly in thickness laterally and frequently pinch out completely fining upward sequences formed by scouring winnowing and suspension of the sand and mud during the height of the storm to form the erosional base and autochthonous lag of whole fossils storms preferentially preserve whole fossils rather than fragmenting them infiltration of finer sediment into the lag deposit and deposition of the laminated bed occurred as the storm waned laminated beds are molded into a distinctive suite of sedimentary structures by wave generated currents the shale represents deposition of finest storm suspended material and continued hemipelagic sedimentation similar sequences are widely distributed in the geologic record variability of storm generated sequences can be related to changing water depth thus storm deposits may be useful in basin analysis to estimate relative water depths and trace transgressive and regressive events

petrogenetic and geodynamic origin of the neoarchean dore lake complex abitibi subprovince superior province canada the neoarchean ca 2728 ma anorthosite bearing dore lake complex in the northeastern abitibi subprovince quebec was emplaced into an association of intra oceanic tholeiitic basalts and gabbros known as the obatogamau formation the obatogamau formation constitutes the lower part of the roy group which is composed of two cycles of tholeiitic to calc alkaline volcanic and volcaniclastic rocks siliciclastic and chemical sedimentary rocks and layered mafic to ultramafic sills in this study we report major and trace element results and nd sr pb and o isotope data for anorthosites leucogabbros gabbros and mafic dykes from the dore lake complex and spatially associated basalts and gabbros of the obatogamau formation to assess their petrogenetic origin and geodynamic setting field and petrographic observations indicate that the dore lake complex and associated volcanic rocks underwent extensive metamorphic alteration under greenschist facies conditions resulting in widespread epidotization 20 40 and chloritization 10 40 of many rock types plagioclase recrystallized mainly to anorthite and albite endmembers erasing intermediate compositions metamorphic alteration also led to the mobilization of many elements e g lile and transition metals and to significant disturbance of the rb sr and u pb isotope systems resulting in 1935 150 and 3326 270 ma errorchron ages respectively the sm nd isotope system was less disturbed yielding an errorchron age of 2624 160 ma on many binary major and trace element diagrams the least altered anorthosites and leucogabbros and the gabbros and mafic dykes of the dore lake complex plot in separate fields signifying the presence of two distinct magma types in the complex the gabbros and mafic dykes in the dore lake complex share the geochemical characteristics of tholeiitic basalts and gabbros in the obatogamau formation suggesting a possible genetic link between the two rock associations initial end 2 6 to 5 0 and 18o 6 1 to 7 9 values for the dore lake complex and gabbros of the obatogamau formation end 2 8 to 4 0 18o 7 3 to 8 0 are consistent with depleted mantle sources all rock types in the dore lake complex and the roy group share the trace element characteristics of modern arc magmas suggesting a suprasubduction zone setting for these two lithological associations on the basis of regional geology and geochemical data we suggest that the dore lake complex and the obatogamau formation represent a dismembered fragment of a suture zone like many phanerozoic ophiolites resulting from closure of a back arc basin between 2703 and 2690 ma

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

the de correlation of westerly winds and westerly wind stress over the southern ocean during the last glacial maximum motivated by indications from paleo evidence this paper investigates the changes of the southern westerly winds sww and westerly wind stress between the last glacial maximum lgm and pre industrial in the pmip3 cmip5 simulations highlighting the role of antarctic sea ice in modulating the wind effect on ocean particularly a de correlation occurs between the changes in sww and westerly wind stress caused primarily by an equatorward expansion of winter antarctic sea ice that undermines the efficacy of wind in generating stress over the liquid ocean such de correlation may reflect the lgm condition in reality in view of the fact that the model which simulates this condition has most fidelity in simulating modern sww and antarctic sea ice therein two models stand out for their agreements with paleo evidence regarding the change of sww and the westerly wind stress they simulate strengthened and poleward migrated lgm sww in the atmosphere consistent with the indications from dust records whilst in the ocean they well capture an equatorward shifted pattern of the observed oceanic front shift with most pronounced equatorward shifted westerly wind stress during the lgm

breakdown of the linear relationship between the southern hemisphere hadley cell edge and jet latitude changes in the last glacial maximum abstracta poleward displacement of the hadley cell hc edge and the eddy driven jet latitude has been observed in the southern hemisphere sh during the last few decades this change is further p

paleogeographic and paleotectonic response to magmatic processes a case history from the archean sequence in the chibougamau area quebec the chibougamau area quebec is characteristic of the internal zone of the archean abitibi orogenic belt the paleogeographic paleotectonic and magmatic history of the archean sequence in the chibougamau area is subdivided into three stages in the first stage a submarine volcanic chain formed mainly by the effusion of submarine lava flows composed of primitive potash poor tholeiitic basalt the volcanic chain gradually grew to sea level in the second stage volcanic islands emerged and grew mainly pyroclastic eruptions of strongly differentiated calc alkaline andesite and dacite concentrated on the volcanic islands whereas effusion of basalt continued at first in the surrounding basin a felsic volcaniclastic apron was deposited around the volcanic islands in the third stage the volcanic islands were uplifted and were eroded to the level of their subvolcanic plutons the debris derived from this volcanic plutonic terrain was deposited in downfaulted marine and continental basins the contemporaneous volcanism was shoshonitic the first paleogeographic stage is interpreted as the growth of an immature island arc during the second stage the island arc became mature and its crust was thickened by accretion of plutonic material the third stage is a period of back arc extension

modeling obliquity and co2effects on southern hemisphere climate during the past 408 ka abstractthe effect of obliquity and co2 changes on southern hemispheric climate is studied with a series of numerical modeling experiments using the earth system model of intermediate complexity loch vecode ecbilt clio agism model loveclim and a coupled general circulation model model for interdisciplinary research on climate miroc it is shown in time slice simulations that phases of low obliquity enhance the meridional extratropical temperature gradient increase the atmospheric baroclinicity and intensify the lower and middle troposphere southern hemisphere westerlies and storm tracks furthermore a transient model simulation is conducted with loveclim that covers the greenhouse gas ice sheet and orbital forcing history of the past 408 ka this simulation reproduces reconstructed glacial interglacial variations in temperature and sea ice qualitatively well and shows that the meridional heat transport associated with the orbitally paced modulation of middle troposphere westerlies and storm tr

synvolcanic gold mineralization within a deformation zone the chevrier deposit chibougamau abitibi subprovince canada the chevrier gold deposit is located in the northeastern part of the abitibi subprovince within the chevrier volcanic centre cvc this calc alkaline volcanic centre evolved from mafic to felsic in a submarine environment and the chevrier deposit is spatially associated with the uppermost unit composed mostly of massive dacite to rhyolite dated at 2730 ma the chevrier deposit is divided in two zones the north zone is composed of high grade discordant quartz carbonate veins and disseminated pyrite mostly within melanocratic gabbro dykes whereas the south zone is within a low grade concordant pyrite envelope associated with quartz carbonate pyrite veinlets both zones are highly deformed and show strong carbonate sericite and chlorite alterations although these zones share many characteristics with orogenic deposits the crosscutting of the chevrier deposit by structures associated with the major deformation events suggests that mineralization was prior to these events furthermore felsic dykes associated with the formation of the cvc crosscut auriferous veins and zones therefore suggesting a synvolcanic timing for the gold mineralization characteristics of the zones such as similar vein composition and alteration mineral assemblages and location within the volcanic pile suggest that they are part of a single hydrothermal event where the south zone represents the shallower part of the deposit the chevrier deposit is classified as a noncarbonate hosted stockwork and disseminated deposit and shows many similarities with strata bound gold deposits of the andacollo mining district of chile dating of mineralization at the chevrier deposit indicates that the emplacement of gold occurred more than 25 ma before the onset of the orogeny affecting this part of the abitibi subprovince it also illustrates how synvolcanic mineralization can be misinterpreted as an orogenic deposit without the presence of crosscutting relationships with dykes faults or other structures

the interconnected global climate system a review of tropical polar teleconnections abstractthis paper summarizes advances in research on tropical polar teleconnections made roughly over the last decade elucidating el nino southern oscillation enso impacts on high latitudes has remained an important focus along different lines of inquiry tropical to polar connections have also been discovered at the intra seasonal timescale associated with madden julian oscillations mjo on the timescale of decades changes in mjo phases can result in temperature and sea ice changes in the polar regions of both hemispheres moreover the long term changes in sst of the western tropical pacific tropical atlantic and north atlantic ocean have been linked to the rapid winter warming around the antarctic peninsula while sst changes in the central tropical pacific have been linked to the warming in west antarctica rossby wave trains emanating from the tropics remain the key mechanism for tropical and polar teleconnections from intraseasonal to decadal timescales enso related tropical sst anomal

uncorking the southern ocean s vintage co2 antarctic ice cores provide a well documented link between earth s climate and the co2 content of the atmosphere over the past 800 000 years 1 many hypotheses to explain this relationship envision releases of co2 to the atmosphere from the deep waters of the southern ocean around antarctica 2 but there has been limited evidence on page 1147 of this issue skinner et al 3 use the radiocarbon 14c content in the shells of surface and bottom dwelling organisms foraminifera recovered from the southern ocean to track how co2 moved from the deep sea to the atmosphere during the warming transition out of the last ice age deglaciation first bottom dwelling foraminifera record the buildup of 14c depleted co2 in the deep ocean during the last glacial period more than 21 000 years ago second the shells of surface dwellers record the transfer of 14c depleted co2 to the surface between 17 000 and 21 000 years ago

southern hemisphere westerly wind influence on southern new zealand hydrology during the lateglacial and holocene southern hemisphere westerly wind influence on new zealand hydrology

deglacial changes of the southern margin of the southern westerly winds revealed by terrestrial records from sw patagonia 52 s much of the ongoing discussion regarding synchrony or bipolar asynchrony of paleoclimate events has centered on the timing and structure of the last glacial termination in the southern mid latitudes in particular the southwestern patagonian region 50 e55 s its location adjacent to the drake passage and near the southern margin of the southern westerly winds sww allows examining the postulated links between the southern oceanesww coupled system and atmospheric co2 variations through the last glacial termination results from two sites located in the ultima esperanza area 52

bimodal volcanism in archean greenstone belts exemplified by greywacke composition lake superior park ontario in the archean gamitagama lake greenstone belt a metagreywacke metasiltstone formation at least 3 6 km thick largely had an easily eroded unconsolidated subaerial pyroclastic felsic volcanic provenance the remains of this provenance are now represented by a 0 600 m thick felsic formation sandwiched between mafic flow formations in an adjacent and laterally equivalent 4 5 km thick metavolcanic sequence the felsic formation includes flows plus various pyroclastic units including crystal rich ash flow tuff volcanism erosion transportation and sedimentation appear to have been essentially contemporaneous with subaerially erupted ash that was being transported rapidly by rivers to the sedimentary basin where it was deposited in a submarine fan angular to rounded framework sand grains form 39 of the greywacke in the proportion 49 plagioclase 36 quartz and 15 lithic clasts dominantly felsic volcanic despite the moderately high quartz content a felsic pyroclastic volcanic provenance can be sho

evolution of the south central part of the archean abitibi belt quebec part i stratigraphy and paleogeographic model the region comprises parts of the southern zone of the abitibi greenstone belt and of the bellecombe gneiss belt and the belleterre angliers greenstone belt the stratigraphic sequence of the abitibi belt consists of 1 a lower ultramafic division 2 a middle tholeiitic division and 3 an upper diverse division these divisions lap onto an older volcanic sequence to the north and west in the bellecombe belt sediments overlie the lower ultramafic division these sediments coarsen toward the abitibi belt and toward the stratigraphic top the volcanic rocks of the belleterre angliers belt overlie the sediments of the bellecombe belt five paleogeographic phases have been recognized during phase i a deep marine ultramafic lava plain covered the south part of the abitibi belt and the bellecombe belt faulting took place at the duparquet destor break during phase ii tholeiitic basalts formed a deep marine lava plain in the west of the abitibi belt whereas flows erupted mainly from central volcanic c

accretion of japanese island arcs and implications for the origin of archean greenstone belts the present day region of arc arc collision between the izu bonin arc and mainland japan honshu arc in the western pacific called the izu collision zone or icz provides a useful kinematic model for the development of many archean greenstone belts the compositional assemblage thermal structure and structural style of the crust in the icz are very similar to those inferred for many archean greenstone belts in both cases thick young and flaky arc crust with a high heat flux is in collision with another crustal block the icz has resulted in the imbrication of very thick slices of crust and associated sediments juxtaposed against older accretionary prisms many archean greenstone belts show similar geological features and we suggest that the incremental imbrication of the crust was a common tectonic style in some archean convergent margins

a mass balance between archean and phanerozoic rates of magma emplacement crustal growth and erosion implications for recycling of the continental crust abstract the rate of magma emplacement into the archean abitibi belt calculated from stratigraphic and paleogeographic data and from published age determinations is similar to the rate of magma emplacement into mesozoic cenozoic island arcs both rates exceed estimated growth rate of the continental crust by at least a factor 2 the imbalance between the rates of magma emplacement and crustal growth proves recycling the data suggest that a mass equivalent of the total continental crust is recycled through the mantle in roughly 1 ga

a mechanical analysis of the late archean gwillim lake shear belt chibougamau area quebec deflection of older structures stratification schistosities fold axes and thrust faults defines a major left lateral transcurrent shear belt associated with the gwillim lake fault in the chibougamau area stratigraphic and sedimentological work in the waconichi syncline permitted determination of vertical and lateral movement components of the gwillim lake fault and its associated second order faults comparison with experimental and theoretical studies suggests an interpretation as follows north to east northeast trending minor faults are riedel r shears northwest trending minor faults are conjugate riedel r shears and east trending minor faults are thrust or restraint shears p the gwillim lake fault is the principal displacement d shear the main regional compressive stress had a n10 e direction the shear belt formed during late archean time and has been slightly reactivated after the deposition of the early proterozoic chibougamau formation

ventilation of the deep southern ocean and deglacial co2 rise past glacial interglacial increases in the concentration of atmospheric carbon dioxide co2 are thought to arise from the rapid release of co2 sequestered in the deep sea primarily via the southern ocean here we present radiocarbon evidence from the atlantic sector of the southern ocean that strongly supports this hypothesis we show that during the last glacial period deep water circulating around antarctica was more than two times older than today relative to the atmosphere during deglaciation the dissipation of this old and presumably co2 enriched deep water played an important role in the pulsed rise of atmospheric co2 through its variable influence on the upwelling branch of the antarctic overturning circulation

sensitivity of southern hemisphere westerly wind to boundary conditions for the last glacial maximum abstract the southern hemisphere sh westerly wind change in the lgm is critical in understanding the glacial interglacial carbon cycle since its strength and position influence the upwelling of the carbon rich deep water to the surface to examine the change in sh westerly wind in the lgm we adopted cam5 atmosphere general circulation model gcm and performed lgm simulation with sensitivity experiments by specifying the lgm sea ice in the southern ocean so ice sheet over antarctica and tropical pacific sea surface temperature the sh westerly response to lgm boundary conditions in the cam5 was compared with those from cmip5 lgm simulations in the cam5 lgm simulation the sh westerly wind substantially increases between 40 s and 65 s while the zonal mean zonal wind decreases at latitudes higher than 65 s the position of the sh maximum westerly wind moves poleward by about 8 in the lgm simulation sensitivity experiments suggest that the increase in sh westerly winds is mainly due to the increase in sea ice in the so that accounts for 60 of total wind change in the cmip5 pmip3 lgm experiments most of the models show the slight increase and poleward shift of the sh westerly wind as in the cam5 experiment the increased and poleward shifted westerly wind in the lgm obtained in the current model result is consistent with previous model results and some lines of proxy evidence though opposite model responses and proxy evidence exist for the sh westerly wind change

defining an appropriate steady state line for merriespruit gold tailings failure of the merriespruit gold tailings dam in 1994 in south africa was unusual in that never before had a gold tailings dam in south africa failed in such a catastrophic fashion conventional thinking was that gold tailings would always exhibit dilative characteristics upon loading primarily because of the method of deposition which allows significant consolidation to occur due to sun drying this paper demonstrates that the concept of a steady state line which separates dilative from contractive behaviour upon undrained loading is applicable to merriespruit tailings four particle size distributions of merriespruit tailings were tested to determine the influence of the percent finer than 75 m on the position of the steady state line the tailings with the greater percentage of fines gave a steady state line that plotted above all the others which translated to the requirement that a greater relative density was necessary to produce noncontractive behaviour than for the low fines tailings samples

a terrestrial shallow marine transition in the archean opemisca group east of chapais quebec abstract the stella and hauy formations of the archean opemisca group in the eastern chapais syncline feature numerous fluvial to shallow marine transitions throughout the stratigraphic sequence during the first depositional phase stella formation relatively high gradient alluvial fans prograde into a shallow marine environment the coarse clastic sediments reflect a scott type depositional environment the initial depositional environment is envisaged to be a high energy wave and storm flood dominated coastline bordered by coastal alluvial fans shallow marine deposits consist of coarse to very coarse grained sandstones and intraclast and pebble to cobble conglomerates the prevalent shallow marine sediments are related to storm and or flood deposition terrigenous sediments of the donjek type depositional environment prevail during the second depositional phase hauy formation the shallow marine sediments although still wave and storm flood dominated are finergrained and when correlated with the terrigenous sediments imply a lower gradient and a maturing of the coastline furthermore contemporaneous volcanism of andesitic shoshonitic to basaltic composition occurs during this evolutionary stage the sedimentary basin gradually evolved during the two depositional phases the repetition of terrigenous and shallow marine sediments throughout the stratigraphic sequence coarsening and fining sequences in the conglomerates and the alluvial fan setting strongly suggest a fault bounded basin margin tectonic uplift of the hinterland initiates alluvial fan progradation onto the shelf whereas quiescent periods are documented by marine transgression the clast composition of the conglomerates and the alluvial fan environment suggest local derivation of clasts the synvolcanic chibougamau pluton and the lake dore complex acted as a stable basement during deposition of the opemisca group the small landmass served as a stable platform for shallow marine deposition even when tectonically influenced a late phase intraplutonic cratonic development of an initial backarc basin system internal zone of the abitibi greenstone belt is proposed as the overall depositional setting of the chapais basin