interaction of magmatic fluids and silicate melt residues with saline groundwater in the footwall of the sudbury igneous complex ontario canada new evidence from bulk rock geochemistry fluid inclusions and stable isotopes abstract along the northern margin of the 1 85 ga sudbury igneous complex sic canada a volumetrically minor rock type known as the footwall granophyre fwgp preserves evidence of the interaction of magmatic fluid and groundwater the fwgp comprises veins dikes and irregular bodies of a quartz alkali feldspar plagioclase intergrowth that are most abundant near footwall style cu ni platinum group element mineralization textures and cross cutting relations show that the emplacement of the fwgp created favourable sites for the later deposition of sulfides geochemical and physical evidence show that the fwgp did not form by in situ partial melting of the archean country rocks in the footwall beneath the sic it represents a mobilized injected silicate residue from either the contact between partially melted country rocks and the sic or from the crystallizing sic itself its bulk composition can be modeled as the product of fractional crystallization of a liquid with an initial composition equivalent to granophyric matrix trapped liquid in the lowermost units of the sic norite and sublayer primary fluid saline h 2 o poor and melt silicate h 2 o rich inclusions hosted in quartz from the fwgp have bulk and trace element compositions consistent with those hosted in quartz from the granophyric matrix of the lower units of the sic norite sublayer fluid inclusions contain mixtures of a high salinity 44 70 wt nacl equivalent n 39 na fe rich aqueous magmatic fluid and a lower salinity ca and sr rich groundwater the magmatic end member is thought to be an sic derived volatile phase estimates of the mixing proportions show that primary and secondary inclusions in the fwgp contain 60 100 and 30 80 of the magmatic end member by mass respectively fluids responsible for the remobilization of ore metals represent mixtures containing a much higher proportion of the groundwater end member not less than 70 by mass compared to the fluids trapped in the fwgp at considerable distance 400 m from the sic the chlorine isotope composition of biotite in the fwgp is enriched in 37 cl 37 cl 0 98 to 1 61 scapolite from the high temperature veins and the interstices of rock types in the main mass of the sic shows similar enrichment in 37 cl up to 1 34 whereas biotite from the archean country rocks 37 cl 0 88 to 0 53 and associated groundwater are 37 cl depleted the results of this study lead to two important conclusions concerning genetic and exploration models for the footwall ore zones first magmatic end member fluid introduced into the footwall with the melt from which the fwgp crystallized contained very little cu rarely 100 ppm the main ore metal in the footwall ores this result questions hydrothermal models for footwall ore formation that hypothesize that cu and other ore metals were remobilized from sulfide deposits along the sic contact by magmatic hydrothermal fluids and redeposited in the footwall it is more likely that ore metals were only locally remobilized in the footwall ore zones when metal poor hybrid fluids interacted with pre existing sulfide veins of magmatic origin second inclusions containing the hybrid fluid occur in the fwgp rock type throughout the footwall in both mineralized and unmineralized areas therefore although the fwgp preserves stable cl isotope and fluid inclusion evidence that magmatic fluid was introduced into the footwall detection of this magmatic component alone will not serve as a useful exploration method in contrast mapping the distribution and abundance of fwgp may be ore predictive since fwgp emplacement and its higher abundance in mineralized areas appears to have been a structural and textural prerequisite for footwall ore emplacement

large scale dynamics of the mesosphere and lower thermosphere an analysis using the extended canadian middle atmosphere model the extended canadian middle atmosphere model is used to investigate the large scale dynamics of the mesosphere and lower thermosphere mlt it is shown that the 4 day wave is substantially amplified in southern polar winter in the presence of instabilities arising from strong vertical shears in the mlt zonal mean zonal winds brought about by parameterized nonorographic gravity wave drag a weaker 4 day wave in northern polar winter is attributed to the weaker wind shears that result from weaker parameterized wave drag the 2 day wave also exhibits a strong dependence on zonal wind shears in agreement with previous modeling studies in the equatorial upper mesosphere the migrating diurnal tide provides most of the resolved westward wave forcing which varies semiannually in conjunction with the tide itself resolved forcing by eastward traveling disturbances is dominated by smaller scales nonmigrating tides and other planetary scale waves play only a minor role in the zonal mean zonal momentum budget in the tropics at these heights resolved waves are shown to play a significant role in the zonal mean meridional momentum budget in the mlt impacting significantly on gradient wind balance balance fails at low latitudes as a result of a strong reynolds stress associated with the migrating diurnal tide an effect which is most pronounced at equinox when the tide is strongest resolved and parameterized waves account for most of the imbalance at higher latitudes in summer this results in the gradient wind underestimating the actual eastward wind reversal by up to 40

instability at the winter stratopause a mechanism for the 4 day wave abstract studies using climatological fields in a three dimensional stability model show unstable modes near the polar winter stratopause with periods neat 4 days the calculated modes exhibit equatorward momentum and heat fluxes near the stratopause similar to characteristics of observed 4 day wave events demonstrating that both baroclinic and barotropic processes are important for this instability the baroclinic and baratropic components are considered separately by selectively removing either horizontal or vertical shear from the background flow although both situations reveal instability growth rates are very slow realistic growth rates occur only for climatological flows including both horizontal and vertical shears similar unstable fast moving waves are found near the polar stratopause for several winter months in both hemispheres

the sudbury structure as a terrestrial mare basin this paper reviews the origin development and present status of the hypothesis that the sudbury structure of ontario canada is a deformed precambrian impact crater analogous to the circular lunar maria the petrologic similarity of the maria and terrestrial lopoliths such as the bushveld duluth and sudbury igneous complexes was suggested in 1961 assuming these to be extrusive features roofed by their own silicic differentiates this led to the proposal by r s dietz in 1962 that the sudbury structure was a tectonically deformed impact basin occupied by an extrusive lopolith and analogous to the small lunar maria he then searched for and found shatter cones at sudbury discovery of shock metamorphic features in the onaping formation by b m french in 1967 showed that this formation was a fallback breccia detailed studies since the 1970s have further strengthened the impact theory isotopic and impact modeling investigations have shown that the sudbury igneous complex may be largely impact melt rather than internally generated magma the shape and size of the original impact crater are not well known the absence of compressional deformation of the north range supports an originally elliptical shape which has been shown to be similar to those of impact craters on the moon and mars however field mapping and reflection profiling suggest that much of the present ellipticity may have been produced by northwest directed ductile thrusting concentrated on the south range and interior of the complex the size of the original structure is also uncertain recent investigations indicate that the present igneous complex is only the central part of a much larger and perhaps multiring structure the analogy between the sudbury structure and lunar maria though petrologically wrong is valid to the extent that both classes of structure were initially formed by impact however the size and shape of the original crater and the degree to which the sudbury intrusive complex and its ore deposits are impact generated are still open to debate

origin and formation of metabreccia in the parkin offset dike sudbury impact structure canada the 1 85 ga sudbury impact structure is considered a remnant of a peak ring or multi ring basin with an estimated original diameter of 150 to 200 km the offset dikes are radial and concentric dike

the 4 day wave in the antarctic mesosphere a zonal wave number one eastward propagating planetary wave observed in the high latitude winter stratosphere with a period near 4 days has been studied by a number of previous authors radar observations coupled with stratospheric analyses are here used to demonstrate that this wave known as the 4 day wave extends into the antarctic upper mesosphere previous workers have asserted that the wave is a manifestation of the observation of warm pools rotating in the polar vortex and that the pool seems to behave in a quasi nondispersive manner the observation of the 4 day wave in the upper mesosophere presented here appears to validate previous claims that the warm pools are being maintained by wavelike dynamics rather than simple advection

vitric compositions in the onaping formation and their relationship to the sudbury igneous complex sudbury structure the 1 85 ga sudbury structure is the largest well preserved exposed example of a terrestrial impact crater it contains world class ni cu platinum group element pge ores associated with the igneous component a new understanding of the geology and geochemistry of the vitric crater fill sequence the onaping formation provides constraints on the evolution of 1 85 ga igneous rocks in the sudbury structure the onaping formation has a well defined mappable stratigraphy composed of three members seven stratigraphic units and two types of intraformational dikes that are overprinted by an impact generated hydrothermal system stratigraphic and alteration mapping provided a basis for well constrained sampling and allowed the definition of the geochemical characteristics of the less altered rocks from each unit including vitric bombs and blocks and intraformational vitric dikes significantly the identification of a least altered composition of the vitric onaping formation enabled an investigation of the link between the early formed vitric melt phase in the impact crater fill sequence and the sudbury igneous complex and offset dikes the least altered vitric onaping formation represented by the massive xenolith poor cores of vitric bombs blocks and intraformational dikes is andesitic in composition consistent with a crustally derived melt the melt composition 61 6 wt sio 2 4 28 mgo 60 ppm ni is remarkably uniform throughout the onaping formation with a typical enrichment of large ion lithophile and light rare earth elements and pronounced negative nb and ti anomalies incompatible trace element ratios and bulk concentrations of the onaping formation coincide with the main mass norite and offset quartz diorite compositions of the underlying sudbury igneous complex but differ distinctly from the granophyre and quartz gabbro root mean squared differences in composition of the vitric onaping formation with the units of the sudbury igneous complex and quartz diorite offset dikes show that the vitric onaping formation does not directly match any of these igneous units but more closely resembles the composition of the ministic and manchester offset dikes the quartz diorite offset dikes have been proposed as representative of the bulk composition of the original melt of the sudbury igneous complex in detail there are small compositional differences between north and south range offset dikes and between these offset dikes and the concentric manchester offset dike however such differences are lacking in the onaping formation we propose that the least altered vitric composition of the onaping formation represents the best estimate of the bulk composition of an initial quenched melt or shock melt formed early in the evolution of the sudbury structure and is a logical starting liquid to model the evolution of the sudbury main mass and offset dikes the offset dike compositions can be derived from onaping formation vitric shock melt by assimilation of progressively greater amounts of mafic material at deeper levels in the crater this mafic contaminated melt or impact melt developed at the base of the melt sheet and was injected into the offset dikes both prior to and contemporaneously with the earliest stages of sulfide precipitation from the sudbury complex fractionation of the mafic contaminated melt by plagioclase and pyroxene accumulation produced the north range felsic and mafic norite and the south range norites the chalcophile metal content of the onaping formation vitric phase closely reflects the overall metal ratios of the magmatic sulfide ores the vitric onaping formation and unmineralized offset dikes have low liquidus temperatures 1 115 1 125 c and if these units represent the source of metals in the sulfide deposits unusually high mass distribution coefficients for cu and ni and high r factors are necessary to account for the metal endowment

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

chemical and dynamical discontinuity at the extratropical tropopause based on start08 and waccm analyses 1 using isentropic trace gas gradients of o3 and co the discontinuity in the chemical composition of the upper troposphere ut and lower stratosphere ls is examined on middle world isentropes from 300 to 380 k the analysis is a follow up study of the dynamical discontinuity as represented by the potential vorticity pv gradient based tropopause which is based on the product of isentropic pv gradients and wind speed overall there is fairly good consistency between the chemical discontinuity in trace gas distributions and the pv gradient based tropopause trace gas gradients at the pv gradient based tropopause are stronger in winter than in summer revealing the seasonal cycle of the tropopause transport barrier the analysis of the trace gas gradients also identifies atmospheric transport pathways in the upper troposphere lower stratosphere utls several regions where trace gas gradients are found to be decoupled from the dynamical field indicate preferred transport pathways between the ut and ls in particular anomalous co and o3 gradients above eastern africa eastern asia and the west pacific are likely related to convective transport and anomalous o3 gradients over the north atlantic and north pacific are related to isentropic transport connected to frequent wave breaking the results indicate that the pv gradient based tropopause definition provides a good identification of the dynamical and chemical discontinuity and is therefore effective in locating the physical boundary in the utls

eastward propagating planetary waves with periods of 1 5 days in the winter antarctic stratosphere as revealed by merra and lidar 1 this study presents the first report of planetary wave pw influences on significant temperature perturbations 10 20 k within a course of one day detected by an fe lidar from 35 to 51 km in the austral winter of 2011 at mcmurdo 77 8 s 166 7 e antarctica such large temperature perturbations are captured in the modern era retrospective analysis for research and applications merra data and correspond to various phases of eastward propagating pws with periods of 1 5 days as revealed in merra the strongest pw dominating the temperature perturbations has a period of 4 5 days with wavenumber 1 a 2 day wave with wavenumber 2 and a 1 25 day wave with wavenumber 3 also have significant influences we find that these eastward propagating pws are highly confined to winter high latitudes likely because negative refractive indices equatorward of 45 s result in evanescent wave characteristics and prevent the pws from propagating to lower latitudes the eliassen palm flux divergence and instability analyses suggest that barotropic baroclinic instability at 50 s 60 s induced by the stratospheric polar night jet and or the double jet structure is the most likely wave source such instability in the region poleward of 70 s is a complementary source for the 4 day wave where we find that the heat flux of the 4 day wave is large and transported from 70 s toward the pole above 40 km this transport direction is likely linked to the meridional gradient of background temperature the migrating diurnal tide near 78 s in the upper stratosphere is discernable but significantly smaller than that of the dominant 4 day wave

world class ni cu pge deposits key factors in their genesis magmatic ni cu sulfide deposits form as the result of segregation and concentration of droplets of liquid sulfide from mafic or ultramafic magma and the partitioning of chalcophile elements into these from the silicate melt sulfide saturation of a magma is not enough in itself to produce an ore deposit the appropriate physical environment is required so that the sulfide liquid mixes with enough magma to become adequately enriched in chalcophile metals and then is concentrated in a restricted locality so that the resulting concentration is of ore grade the deposits of the noril sk region have developed within flat elongate bodies 15 2 0 2 km that intrude argillites evaporites and coal measures adjacent to a major trans crustal fault and immediately below the centre of a 3 5 km thick volcanic basin studies of the overlying basalts have shown that lavas forming a 500 m thick sequence within these have lost 75 of their cu and ni and more than 90 of their pge overlying basalts show a gradual recovery in their chalcophile element concentrations to reach normal values 500 m above the top of the highly depleted zone the ore bearing noril sk type intrusions correlate with those basalts above the depleted zone that contain normal levels of chalcophile elements the high proportion of sulfide 2 10 wt associated with the noril sk type intrusions the high pge content of the ores the extensive metamorphic aureole 100 400 m around the bodies and the heavy sulfur isotopic composition of the ores 8 12 34s are explicable if the ore bearing bodies are exit conduits from high level intrusions along which magma has flowed en route to extrude at surface the first magma to enter these intrusions reacted with much evaporitic sulfur at a low r value and thus gave rise to sulfides with low metal tenors successive flow of magma through the system progressively enriched the sulfides in the conduits losing progressively less of their chalcophile metals and thus accounting for the upward increase in metals in successive lava flows above the highly depleted flows the voisey s bay deposit lies partly within a 30 100 m thick sheet of troctolite interpreted as a feeder for the 1 334 ga voisey s bay intrusion and partly at the base of this intrusion where the feeder adjoins it studies of olivine compositions indicate that an early pulse of magma through the feeder and into the intrusion was ni depleted but that subsequent pulses were much less depleted trace element re os and s and o isotope data and mineralogical studies indicate that the magma pulses interacted with country gneiss probably principally in a deeper level intrusion extracting sio2 na2o k2o and possibly sulfur form the gneiss which accounts for the magma becoming sulfide saturated the jinchuan deposit of north central china occurs within a 6 km long dyke like body of peridotite the compositions of olivine within the dyke the igneous rocks themselves and the ore are all inconsistent with derivation of the body from ultramafic magma as originally supposed and indicate that the structure forms the keel of a much larger intrusion of magnesian basalt magma flow of magma into the intrusion has resulted in olivine and sulfide being retained where the keel was widening out into the intrusion the west australian komatiite related deposits occur in thermal erosional troughs which have developed due to the channelisation of magma flow and the resulting thermal erosion of underlying sediments and basalt by the hot komatiite magma the sediments are sulfide rich and may have contributed substantially to the sulfide of the ores the mineralisation in the duluth complex occurs in troctolitic intrusions along the western margin of the complex as a result of magma interacting with and extracting sulfur from the underlying graphite and sulfide bearing sediments no magma flow channels have been identified so far and the lack of magma flow subsequent to the development of sulfide immiscibility is regarded as the reason why these deposits are not of economic grade when most major ni cu sulfide deposits are compared they prove to have a number of features in common olivine rich magma proximity to a major crustal fault sulfide bearing country rocks chalcophile element depletion in related intrusive or extrusive rocks field and or geochemical evidence of interaction between the magma and the country rocks and the presence of or proximity to a magma conduit the features are thought to explain the three key requirements sulfide immiscibilty adequate mixing between sulfides and magma and localisation of the sulfides discussed and have important implications with respect to exploration

evolution of palaeoproterozoic mafic intrusions located within the thermal aureole of the sudbury igneous complex canada isotopic geochronological and geochemical evidence abstract impact cratering and their resultant geological phenomena are recognised as significant factors in the lithological and biologic evolution of the earth age dating of impact events is critical in correlating cause and effects for these catastrophic processes the falconbridge and drury township twp intrusions were emplaced at the contact between neoarchaean basement and palaeoproterozoic volcanosedimentary rocks and also lie at the southeast and southwest edges of the sudbury igneous complex sic within its thermal contact aureole the falconbridge twp intrusion is dated at 2441 3 ma by u pb zircon with evidence of archaean inheritance from its host granitoids granitoids from the southernmost abitibi subprovince are dated here between 2670 11 ma for an undeformed algoman granite and 2696 18 ma for a foliated granitoid consistent with existing data from the abitibi greenstone belt and from the wawa subprovince major and trace element geochemical evidence common pb isotopic compositions and end2440 values between 0 and 1 are all consistent with a palaeoproterozoic origin for the falconbridge twp intrusion and support inclusion in the east bull lake type suite of leucogabbroic plutons and sills in contrast the drury twp intrusion gives a u pb zircon age of 1859 13 ma coincident with the date of sic emplacement while the major and trace element compositions are comparable to the falconbridge data the drury displays significant heterogeneity in end2440 with values ranging from 3 7 to 0 1 and contains more radiogenic pb isotopic compositions field geochemical and isotopic evidence clearly distinguishes this intrusion from constituents of the sic itself and indicates that the drury too is a palaeoproterozoic intrusion this requires that apparently unshocked undeformed magmatic looking zircon has been grown or reset in a postmagmatic setting this has significant implications for the identification of mantle derived magmas and crustal remelts associated with large impact craters a resetting mechanism involving aggressive hydrothermal alteration of zircon facilitated by halogen complexing is proposed inducing rapid postshock lead loss and subsequent annealing

shallow impact isotopic insights into crustal contributions to the sudbury impact melt sheet abstract the largest known terrestrial impact melt sheet occurs within the 1850 ma sudbury structure ontario in order to evaluate the relative contributions of different target lithologies to the melt sheet we have investigated the pb isotope compositions of feldspar separates from early formed quartz diorite magmas within offset dykes from around the impact structure the samples define a linear array on plots of age corrected 206 pb 204 pb versus 207 pb 204 pb samples from offset dykes hosted by the huronian supergroup south range have a range of 206 pb 204 pb 1850 from 15 424 to 17 255 and 207 pb 204 pb 1850 from 15 390 to 15 801 whilst those hosted by archean gneisses of the superior province north range cluster around 206 pb 204 pb 1850 14 8 and 206 pb 204 pb 1850 15 1 these values can be approximated by binary mixing between the two major groups of target lithologies a mix of 60 70 of superior province gneisses with 30 40 of huronian metasedimentary material closely matches the pb isotope compositions of north range offset dyke samples whereas in the south range the required huronian component is up to ca 80 these mixing proportions are consistent with sr nd and os isotope and trace element constraints a third minor component either locally exposed paleoproterozoic mafic rocks or the lower crust is also required however the isotopic trace element and ni cu platinum group element characteristics of the melt sheet can be accommodated without the involvement of an average lower crustal or meteoritic component a major contribution of huronian supracrustal material which had a pre impact thickness of up to 12 km is required to explain the chemical characteristics of the impact melts which also have a strong upper crustal affinity e g eu sm 0 22 rb sr 0 2 0 35 as such a shallower level of melting is apparent than that predicted by many previous impact models for the sudbury event this can be accommodated by considering approach trajectories for the impactor oblique to the earth s surface in addition the isotopic and trace element variability identified indicates that the melt sheet was heterogeneous at an early stage and may not have been completely homogenised during crater formation our findings have significant implications for the nature of the sudbury impact event the evolution of the melt sheet and the crustal sources of metals contained in sudbury s world class ni cu pge sulphide ores

rare earth element characteristics and origin of the sudbury igneous complex ontario canada abstract systematic geochemical studies have been carried out on the sudbury igneous complex sic and its country rocks the two main rock types of the sic norite and granophyre show contrasting chemical features the norite contains 54 58 wt sio2 whereas the granophyre has a sio2 content of 65 71 wt all rocks are characterized by high absolute rare earth element contents ree 63 314 ppm the granophyre having more than twice the ree contents of the norite and by lree enriched chondrite normalized distribution patterns huronian volcanic rocks and huronian plutonic granites have the highest ree contents and hree enrichment among the country rocks archean rocks are characterized by very steep ree patterns and positive eu anomalies nipissing diabase contains the lowest ree contents and has a flat ree pattern within the sic the ree values are more or less constant through the norite but the abundances of some elements such as ce and yb decrease slightly upward with stratigraphy ree contents increase sharply in passing from norite to granophyre and the eu eu ratio decreases from around unity to 0 66 the contrasting ree contents of the norite and granophyre combined with their distinctive major and trace element contents are considered to indicate that they resulted from two separate batches of magma probably emplaced at about the same time the previous models in which the sic was considered to originate from a single magma either contaminated mantle magma or crustal melt are not adequate a new hypothesis is developed based on the chemical features observed in this study the sic is considered to have comprised two independent intrusions the norite was derived from a heavily contaminated mantle magma 30 60 the main contaminant being archean granulite facies rocks of the lower crust the granophyre represents a crustal melt 75 archean rocks and 25 huronian granite induced by meteorite impact the new hypothesis better accounts for the large proportion of granophyre in relation to norite and for the ni cu sulfide mineralization associated with the sic it is also favored by the rb sr isotopic data

gravity wave induced anomalous potential vorticity gradient generating planetary waves in the winter mesosphere abstractthis study shows that gravity wave gw forcing gwf plays a crucial role in the barotropic baroclinic instability that is frequently observed in the mesosphere and considered an origin of planetary waves pws such as quasi 2 day and quasi 4 day waves simulation data from a gw resolving general circulation model were analyzed focusing on the winter northern hemisphere where pws are active the unstable field is characterized by a significant potential vorticity pv maximum with an anomalous latitudinal gradient at higher latitudes that suddenly appears in the midlatitudes of the upper mesosphere this pv maximum is attributed to an enhanced static stability that develops through the following two processes 1 strong pws from the troposphere break in the middle stratosphere causing a poleward and downward shift of the westerly jet to higher latitudes and 2 strong gwf located above the jet simultaneously shifts and forms an upwelling in the midlatitudes causing a significant increase in

simulation of the eastward 4 day wave in the antarctic winter mesosphere using a gravity wave resolving general circulation model 1 the eastward moving 4 day wave in the antarctic winter mesosphere is investigated using a high resolution middle atmosphere general circulation model that directly simulates the spontaneous generation propagation and dissipation of gravity waves the results are also compared with the simulated seasonal march of the meridional structures of the westerly jet streams in the southern hemisphere upper stratosphere and mesosphere in order to investigate baroclinic barotropic instability as a possible excitation mechanism for the 4 day wave the model successfully reproduces the dynamically unstable double jet structure of the mesospheric westerly winds the simulated 4 day wave develops in association with the baroclinic and barotropic instability of the mesospheric mean flows and has similar characteristics to those observed at 50 60 s near the stratopause the 4 day wave has strong equatorward heat flux associated with strong baroclinicity in the antarctic winter mesosphere mainly attributable to poleward overturning circulation driven by gravity wave forcing eastward forcing due to the 4 day wave occurs within the double jet structure and offsets part of the westward forcing due to gravity waves such an effect partially acts to stabilize the unstable mean flow structure in the antarctic winter mesosphere

evolution of the sublayer of the sudbury igneous complex geochemical sm nd isotopic and petrologic evidence abstract the mineralized sublayer at the base of the sudbury igneous complex sic consists of two variants the noritic contact sublayer and radial and concentric quartz dioritic offset dykes both are characterized by the presence of significant quantities of ni cu pge sulphides and by a prominent population of recrystallized diabasic textured and melanocratic to ultramafic fragments the two variants of the sublayer contain compositionally distinct inclusion populations and inclusion bearing matrices contact sublayer and offset dykes hosted by north range granitoid footwall can be distinguished from those hosted by south range basaltic and metasedimentary footwall environments the compositional variation in sic rocks can be described in terms of contributions from exposed crustal rocks and differentiation of the resultant melt s the basaltic inclusion population is characterized by hornfels recrystallization of the plagioclase and is geochemically and isotopically identified with huronian basalts which comprise the south range footwall with ce yb n ratios of around 2 5 and e nd 1850 between 2 to 5 the melanocratic inclusions in the sublayer are typically coarse grained and undeformed with incompatible element contents and radiogenic isotopic compositions intermediate between those of the basaltic inclusions and those of the melt sheet which has ce yb n ratios of around 10 and e nd 1850 around 9 calculated crystallization models are consistent with derivation of the ultramafic inclusions by crystallization from a magma produced by mixing of molten basaltic footwall with basal melt sheet it is proposed that the sublayer appeared as the marginal facies of a meteorite impact melt sheet as a result of footwall melting following the impact this basal layer was progressively enriched in sulphides and mafic cumulates from above through differentiation during cooling offset dykes were emplaced and the magmas effectively removed from the system subsequently continued evolution of the marginal facies produced the more mafic inclusions in the contact sublayer no extracrustal e g mantle component is envisioned in this model to explain the silicate compositional distributions in the sic and mafic crustal rocks in the target zone are implicated as the metal source for the sic deposits

lidar observations of stratospheric gravity waves from 2011 to 2015 at mcmurdo 77 84 s 166 69 e antarctica 1 vertical wavelengths periods and frequency and vertical wave number spectra five years of atmospheric temperature data collected with an fe boltzmann lidar by the university of colorado group from 2011 to 2015 at arrival heights are used to characterize the vertical wavelengths periods vertical phase speeds frequency spectra and vertical wave number spectra of stratospheric gravity waves from 30 to 50 km altitudes over 1000 dominant gravity wave events are identified from the data the seasonal spectral distributions of vertical wavelengths periods and vertical phase speeds in summer winter and spring fall are found obeying a lognormal distribution both the downward and upward phase progression gravity waves are observed by the lidar and the fractions of gravity waves with downward phase progression increase from summer 59 to winter 70

the sudbury structure controversial or misunderstood the origins of the sudbury structure and associated igneous complex have been controversial most models call for a major impact event followed by impact induced igneous activity although totally igneous models are still being proposed much of the controversy is due in our opinion to a misunderstanding of the size of the original sudbury structure by analogy with other terrestrial impact structures the spatial distribution of shock features and huronian cover rocks at the sudbury structure suggest that the transient cavity was 100 km in diameter which places the original final structural rim diameter in the range of 150 200 km theoretical calculations and empirical relationships indicate that the formation of an impact structure of this size will result in 104 km3 of impact melt more than sufficient to produce a melt body the size of the igneous complex present volume 4 8 103 km3 for the igneous complex to be an impact melt sheet it must have a composition similar to that of the target rocks evidence for this has been presented previously for sr and nd isotopic data which suggest a crustal origin here we also present new evidence from least squares mixing models that the average composition of the igneous complex corresponds to a mix of archean granite greenstone terrain with possibly a small component of huronian cover rocks this is a geologically reasonable mix based on the interpreted target rock geology and the geometry of melt formation in an impact event of this size the igneous complex is differentiated which is not a characteristic of previously studied terrestrial impact melt sheets this can be ascribed however to its great thickness and slower cooling that large impact melt sheets can differentiate has important implications for how the lunar samples and the early geologic history of the lunar highlands are interpreted if this working hypothesis is accepted namely that both the sudbury structure and the igneous complex are impact in origin then previous hybrid impact igneous hypotheses can be discarded and the sudbury structure can be studied specifically for the constraints it provides to large scale cratering and the formation of basin sized multiring impact structures

isotopic heterogeneity in the sudbury impact melt sheet abstract a unique terrestrial large impact melt sheet is preserved in the 1850 ma sudbury structure ontario we have undertaken a pb isotope investigation of the southern limb of the melt sheet termed the south range main mass the model initial pb isotope ratios 207 pb 204 pb m vary stratigraphically through the predominantly quartz monzogabbroic lower unit varying from 15 40 to 15 45 at the base to ca 15 35 at the top of the sequence lateral variations of similar range occur in basal lower unit samples over scales of less than 5 km the range of these variations is similar to those of locally exposed upper crustal target rocks and it is evident that the melt sheet has efficiently preserved inherited variability during the violent phases of crater formation superheated impact melts are expected to be well mixed mechanically therefore significant post impact melting of target rocks fallback material and entrained clasts is required to explain such heterogeneity the sudbury structure hosts world class ni cu pge sulphide ore deposits systematic variation in 207 pb 204 pb m occurs throughout sulphide ores within the creighton embayment from massive 15 42 15 45 to interstitial ca 15 40 15 41 and disseminated ca 15 39 sulphide linking the pb isotope composition of these ores to the immediately overlying lower unit stratigraphy a protracted sulphide segregation history is apparent massive sulphides segregated early prior to or during initial silicate crystallisation although the total time involved in sulphide accumulation spanned much of the crystallisation of the lower unit it is also shown that lateral variations in ni depletion throughout the main mass correlate with pb isotopes those segments with the strongest chalcophile element depletion signatures reflecting the accumulation of significant basal sulphides have high initial pb isotope values consistent with early sulphide segregation the characterisation of pb isotopic heterogeneity has therefore provided insights into the evolution and scales of mixing of the melt sheet with the identified chemical variability between melt cells having a significant influence on ore forming processes

seismic imaging of the enigmatic sudbury structure the sudbury structure on the southern margin of the superior craton was created by a catastrophic explosion in 1 85 ga and hosts one of the world s largest ni cu reserves as a unique terrestrial geological feature its genesis has been vigorously debated for more than a century in an effort to optimize the image from seismic reflection data acquired across the center of the sudbury structure we have developed a straight line common midpoint binning strategy and employed cross dip corrections these pseudo three dimensional seismic processing techniques coupled with standard processing methods have overcome limitations associated with conventional two dimensional seismic data processing and have substantially enhanced the seismic image warranting a more detailed and reliable structural interpretation the new image has revealed a major previously unrecognized zone of imbricated nw thrusts interpretation of these thrusts provides critical timing constraints relating the sudbury tectonic deformation to deposition of the sudbury basin sediments the onwatin argillites are penetrated by blind thrust faults whereas the overlying chelmsford turbidites are undeformed and most likely postdate the thrusting thus the uniform paleocurrent trends observed in the chelmsford reflect subsequent deformation history and may be dismissed as evidence against an impact origin based on our interpretation of the seismic image the original volume of the sudbury igneous complex likely an impact melt sheet is 1 104 km3 supporting the claim that the sudbury structure represents the eroded and tectonized remanent of one of the largest known impact structure 200 km on earth

quasi biennial oscillation of short period planetary waves and polar night jet in winter antarctica observed in saber and merra 2 and mechanism study with a quasi geostrophic model

osmium isotope evidence for a crustal origin of platinum group elements in the sudbury nickel ore ontario canada abstract sulphide ores from the international nickel company s inco creighton mine sudbury were analysed for osmium isotope ratios by icp ms rhenium and osmium abundances were determined by isotope dilution using a mixed spike in solid solution in a nickel sulphide matrix calculated initial 187 os 188 os ratios at 1 85 ga the emplacement age of the sudbury complex cluster around 0 60 the occurrence of less radiogenic compositions is attributed to post emplacement open system behaviour of the re os system the creighton results strongly overlap the initial ratios of published osmium data from two other sudbury mines suggesting a narrow range of isotope ratio in the original ore within the range of estimated osmium isotope compositions in the country rock at 1 85 ga using published and new data therefore the sulphide ores of the sudbury complex can have an entirely crustal source without a mantle derived contribution this conclusion is consistent with published neodymium isotope data for the complex and supports the meteorite impact hypothesis since this is the most effective means of fusing the large quantity of crustal rocks necessary to generate the complex the extraction of platinum group elements pge from this silicate melt by a nickel sulphide liquid was probably analogous to the laboratory fire assay procedure

a fundamental dispute a discussion of on some fundamentals of igneous petrology by bruce d marsh contributions to mineralogy and petrology 2013 166 665 690 marsh contrib miner petrol 166 665 690 2013 again claims that crystal free basalt magmas are unable to differentiate in crustal magma chambers and regards layered intrusions as primarily due to the repeated emplacement of crystal suspensions he ignores an earlier critique of his unconventional inferences latypov j petrol 50 1047 1069 2009 as well as a wealth of petrographic geochemical and experimental evidence supporting the dominant role of fractional crystallization in the solidification of layered intrusions most tellingly the cryptic variations preserved in the skaergaard and many other basaltic layered intrusions would require an exceedingly implausible sequence of phenocrystic magmas but are wholly consistent with in situ fractional crystallization a major flaw in marsh s hypothesis is that it dismisses progressive fractional crystallization within any magma chamber and hence prohibits the formation of crystal slurries with phenocrysts and melts that change systematically in composition in any feeder system this inherent attribute of the hypothesis excludes the formation of layered intrusions anywhere

inertia gravity waves in antarctica a case study using simultaneous lidar and radar measurements at mcmurdo scott base 77 8 s 166 7 e 1 this study presents the first coincident observation of inertia gravity waves igws by lidar and radar in the antarctic mesopause region this is also the first known observation of two simultaneous igws at the same location an fe boltzmann lidar at arrival heights 77 8 s 166 7 e provides high resolution temperature data and a co located mf radar provides wind data on 29 june 2011 coherent wave structures are observed in both the fe lidar temperature and mf radar winds two dominant waves are determined from the temperature data with apparent periods of 7 7 0 2 and 5 0 0 1 h and vertical wavelengths of 22 2 and 23 2 km respectively the simultaneous measurements of temperature and wind allow the intrinsic wave properties to be derived from hodograph analyses unambiguously the analysis shows that the longer period wave propagates northward with an azimuth of 11 5 clockwise from north this wave has a horizontal wavelength of h 2 2 0 2 103 km and an intrinsic period of i 7 9 0 3 h the intrinsic horizontal phase speed cih for this wave is 80 4 m s while the horizontal and vertical group velocities cgh and cgz are 48 3 m s and 0 5 0 1 m s respectively the shorter period wave has i 4 5 0 3 h and 100 4 with h 1 1 0 1 103 km and cih 68 5 m s its group velocities are cgh 58 5 m s and cgz 1 1 0 1 m s therefore both waves propagate with very shallow elevation angles from the horizon 0 6 0 1 and 1 1 0 1 for the longer and shorter period waves respectively but originate from different sources our analysis suggests that the longer period igw most likely originates from the stratosphere in a region of unbalanced flow

two high precision u pb zircon ages for the sudbury nickel irruptive two independent u pb zircon ages were measured using norite samples from the north and south ranges of the sudbury nickel irruptive ages of and ma were obtained with a probability of fit within experimental error of 51 and 57 respectively previous determinations by the rb sr whole rock method gave ages between about 1700 and 2000 ma with errors of the order of 100 ma the difference in precision is inherent in the two methods zircons from the norite are highly radiogenic and almost concordant whereas rb sr whole rock ages are determined by very small increments in radiogenic 87sr the two zircon ages have completely different discordia so that all simple models for lead loss by continuous diffusion can be excluded

the basal onaping intrusion in the north range roof rocks of the sudbury igneous complex the 1 85 ga sudbury impact structure is one of the largest impact structures on earth igneous bodies the so called basal onaping intrusion occur at the contact between the sudbury igneous complex sic and the overlying onaping formation and occupy 50 of this contact zone the basal onaping intrusion is presently considered part of the onaping formation which is a complex series of breccias here we present petrological and geochemical data from two drill cores and field data from the north range of the sudbury structure which suggests that the basal onaping intrusion is not part of the onaping formation our observations indicate that the basal onaping intrusion crystallized from a melt and has a groundmass comprising a skeletal intergrowth of feldspar and quartz that points to simultaneous cooling of both components increasing grain size and decreasing amounts of clasts with increasing depth are general features of roof rocks of coherent impact melt rocks at other impact structures and the basal onaping intrusion planar deformation features within quartz clasts of the basal onaping intrusion are indicators for shock metamorphism and together with the melt matrix point to the basal onaping intrusion as being an impact melt rock by definition importantly the contact between granophyre of the sic and basal onaping intrusion is transitional and we suggest that the basal onaping intrusion is what remains of the roof rocks of the sic and thus is a unit of the sic and not the onaping formation we suggest henceforth that this unit be referred to as the upper contact unit of the sic

the sudbury igneous complex viscous emulsion differentiation of a superheated impact melt sheet the sudbury igneous complex of ontario canada is the remnant of a voluminous melt sheet produced in a few minutes by impact of a massive meteorite into continental crust 1 85 ga ago the transient cavity and melting zone reached the moho and instantly 2 min relaxed to form a more familiar large shallow crater holding a thick superheated 1700 c melt sheet covered by 2 km of breccia there is little about the resulting bimodal igneous complex that resembles crystallization of well known sheet like bodies of similar composition yet the norite and granophyre exhibit a remarkable similarity in isotopic and trace element compositions suggesting an intimate common parentage from the surrounding crust this petrogenetic enigma is explained here as a natural unavoidable consequence of the impact process in the rapid formation of a superheated magmatic emulsion which we take as the high temperature equivalent of breccia a wide spectrum of viscously discrete interdispersed parcels of mafic and felsic liquids reflecting the compositional heterogeneity of the target crustal materials formed the emulsion within days to months the emulsion components separated according to their relative densities into a bimodal norite granophyre assemblage that formed the basic structure of the present sudbury igneous complex there is clear evidence of this emulsion in the earliest dikes i e offsets which likely give the earliest state of the nascent melt sheet immediately following emulsion separation the strongly superheated bimodal melt sheet underwent vigorous thermal convection in each layer these convective motions homogenized and rapidly cooled the magma to the liquidus temperatures whereupon convection ceased the pattern of convection was pinned in place by the embayment topography of the crater floor which in turn played a pivotal role in directing sulfide deposition into the embayments all further cooling was by conduction of heat through the upper and lower boundaries during which time solidification fronts were established and propagated inward from the upper and lower margins there is clear evidence of solidification from the floor upward and the roof downward minimal differentiation and compositional modification took place throughout cooling and solidification nevertheless during the solidification stage granitic rock fragments on the crater floor and rafts of fallback breccia from the thick overlying onaping formation became unstable and entered the melt sheet and the partially melted remnants collected at the interface between the norite and granophyre some interstitial melt from the norite also percolated upward and altogether the blocks and melt produced the distinctive chemical and physical characteristics of the unusual transition zone the sudbury melt sheet is in essence a full scale magmatic experiment the conditions of formation relative to any other large terrestrial magma are precisely known thus the clear lack of any significant modal layering the overall homogeneous nature of each unit and the lack of any significant chemical differentiation through crystal fractionation establish sudbury as a valuable example of what does not happen under the initial conditions long assumed to prevail at the formation of most large magma chambers

the sudbury structure constraints on its genesis from lithoprobe results results of the lithoprobe transect provide additional corroboration of the impact model for the origin of the sudbury structure high resolution seismic reflection data indicate that the sudbury igneous complex sic is indeed continuous under the sudbury basin there is no indication of a feeder dike system or a previously assumed hidden mafic mass all these observations strongly support the interpretation of the sic as a coherent impact melt sheet in addition the seismic and to a lesser extent magnetic and gravity results point to a highly assymmetric structure to the sic at depth with significant tectonic disruption in the south range the present non circularity of the sic is caused by post impact ductile deformation and thrusting due to northwest directed compression decompressing this strain pattern leads to an original diameter of the sic between 60 and 80 km which in consequence would extend the original diameter of the final crater up to a maximum of 280 km

the sudbury structure ontario canada a tectonically deformed multi ring impact basin the occurrence of shock metamorphic features substantiates an impact origin for the 1 85 ga old sudbury structure but this has not been universally accepted recent improvements in knowledge of large scale impact processes combined with new petrographic geochemical geophysical lithoprobe and structural data allow the sudbury structure to be interpreted as a multi ring impact structure the structure consists of the following lithologies sudbury breccia dike breccias occurring up to 80 km from the sudbury igneous complex sic footwall rocks and footwall breccia brecciated shocked crater floor materials in part thermally metamorphosed by the overlying sic sublayer and offset dikes main mass of the sic and basal member of the onaping formation of geochemically heterogeneous coherent impact melt complex ranging from inclusion rich basal unit through a dominantly inclusion free to a capping inclusion rich impact melt rock grey member of of melt rich impact breccia suevite green member of of thin layer of fall back ejecta black member of of reworked and redeposited breccia material onwatin and chelmsford formations post impact sediments observational and analytical data support an integrated step by step impact model for the genesis of these units analysis of the present spatial distribution of various impact related lithologies and shock metamorphic effects result in an estimated original rim to rim diameter of the final crater of 200 or even 280 km for the sudbury structure prior to tectonic thrusting and deformation during the penokean orogeny

absence of shock metamorphic effects in the bushveld complex south africa results of an intensive search abstract an extensive search was made for distinctive shock metamorphic effects in order to test the theory that the bushveld complex bc was formed by the impact of large extraterrestrial objects field and petrographie studies concentrated on two geological environments in which current impact cratering theories predict the formation and preservation of such shock metamorphic effects as shatter cones unusual fragmental or melt breccias and shock lamellae in quartz these are 1 pre bc quartzite xenoliths in the rooiberg group a thick sequence of acid lavas rhyolites and rhyodacites and related rocks proposed by earlier workers as a possible crater filling impact melt and 2 the locally observable contact between the rooiberg group and the underlying pre bc basement pretoria group a contact possibly corresponding to the original crater floor in established impact structures more than 320 samples of pre bc quartzite were collected and examined petrographically for shock metamorphic effects no megascopic shock metamorphic effects shatter cones or unusual breccias were observed in any outcrop in thin section no petrographic shock effects e g shock lamellae hi quartz and kink bands in biotite were observed in any sample the quartzites from both the basement 80 samples and the rooiberg xenoliths 245 samples are virtually undeformed cataclastic textures are rare and individual quartz grains show only normal metamorphic deformation lamellae bohm lamellae and single or multiple sets of fluid inclusions arranged along irregular planes which appear to be healed fractures although some of these parallel sets superficially resemble so called decorated shock lamellae universal stage measurements of their orientation demonstrate that they are totally different the absence of both megascopic and microscopic shock metamorphic effects in a large suite of carefully selected samples strongly indicates that impact models for the bc are not correct and that the bc is not an impact structure this conclusion also agrees with 1 the complex stratigraphy now recognized in the lower rooiberg group which is not consistent with an impact melt origin 2 the absence in the rooiberg group of any of the distinctive melt rich fragmentai breccias which dominate the crater filling deposits in established large impact structures and 3 the undeformed character of the basement rocks below the rooiberg group and the apparently concordant contact between them

stationary planetary waves in upper mesospheric winds abstract quasi stationary planetary scale longitudinal variations are found in the upper mesospheric winds measured during winter by the hrdi satellite instrument these are negatively correlated with eddy winds in the stratosphere two different mechanisms are proposed to explain the mesospheric perturbation winds and their anticorrelation with stratospheric winds 1 planetary waves propagate through the stratosphere and into the mesosphere with a phase shift of one half cycle and 2 mesospheric perturbations are forced in situ by gravity waves whose spectrum has longitudinal asymmetries due to filtering by planetary waves in the stratosphere the first mechanism is more consistent with the observations during southern hemisphere late winter august and also may explain the observations during northern hemisphere early winter december the second mechanism gives a more consistent explanation for the northern hemisphere late winter observations as previously shown by the author the hemispheric diff

the sudbury impact layer in the paleoproterozoic iron ranges of northern michigan usa a layer of breccia that contains fragments of impact ejecta has been found at 10 sites in the paleoproterozoic iron ranges of northern michigan in the lake superior region of the united states radiometric age constraints from events predating and postdating depo si tion of the breccia are ca 1875 ma and 1830 ma the major bolide impact that occurred at 1850 ma at sudbury ontario 500 700 km east of these sites is the likely causative event the michigan sites described here along with previously described sites in minnesota and ontario defi ne an extensive ejecta bearing deposit throughout the paleoproterozoic iron ranges of the lake superior region that we refer to as the sudbury impact layer the layer at the sites in michigan exhibits a range of thicknesses lithologic characters and sedimentary settings the diversity of rock types and internal stratigraphic details of the layer imply that several different processes of transport and deposition are represented but the detailed investigations needed to document them are incomplete many of the sites had been described and interpreted previously as products of common terrestrial processes but the presence of relict shock induced planar deformation features in quartz indicates that the breccia layer is in fact the product of an extra terrestrial impact at most localities this layer also contains relict fragments of altered devitrifi ed glass and or accretionary lapilli one immediate use of the impact layer is as an ultraprecise time line that ties together the well known stratigraphic sequences of the various geographically separated iron ranges the correlation of which has remained controversial for many decades the sudbury impact layer most commonly lies at a horizon that records a signifi cant change in the character of sediments across the region the impact layer marks the end of a major period of banded iron formation deposition that was succeeded by deposition of ficlastic rocks commonly black shales the impact may have produced regional if not global changes in the environment that resulted in this widespread synchronous change in sedimentation style

first lidar observations of quasi biennial oscillation induced interannual variations of gravity wave potential energy density at mcmurdo via a modulation of the antarctic polar vortex

deformation of the sudbury structure paleomagnetic evidence from the sudbury breccia abstract paleomagnetic results from fine grained samples of sudbury breccia collected from 28 sites around the northern half of the 1 85 ga sudbury igneous complex sic reveal the existence of two major components of magnetization a and b a carried by magnetite was formed close to the time of the sic and has a direction that is related to the dip of the norite unit within the different ranges of the sic component b mainly carried by pyrrhotite is a younger secondary magnetization of more problematical origin in part related to heating during the 1 24 ga sudbury magmatic event in the northwest part of the sic a is found in breccia clasts intermediate norite sublayer levack gneiss and matachewan diabase indicating that it is due to baking by the sic tilt correcting the west range by 36 the north range by 22 and the northern east range by 36 about axes parallel to local strike of the norite minimises the dispersion of the paleomagnetic data to give a pre folding direction of 199 4 78 8 the paleomagnetic data are similar to those obtained by morris morris w a 1984 paleomagnetic constraints on the magmatic tectonic and metamorphic history of the sudbury basin region in pye e g naldrett a j giblin p e eds the geology and ore deposits of the sudbury structure special vol 1 ontario geological survey pp 411 427 on the sic suggesting for the first time that the sic and the surrounding basement were deformed probably during the 1 9 1 7 ga penokean orogen as a single unit the un folding of the paleomagnetic directions indicates that sic limbs were already inclined a result of the original intrusion configuration or a syn folding remanence it is possible that the sic was originally flatter if the distribution of paleomagnetic directions is the result of flexural flow folding this explanation could also produce a similar distribution of paleomagnetic directions across the basin but cannot be quantified due to the lack of measurable fold related strain in breccia and sic units around the northern half of the basin

the manicouagan impact melt sheet evidence for isotopic homogenization with limited assimilation abstract the rb sr pb pb and sm nd isotope chemistry of impact generated melt and target rocks has been determined from the 214 ma 90 km rim diameter manicouagan impact structure of canada fifty seven samples were obtained from 8 field sites and 11 drill core sites across the impact melt sheet located on the 55 km diameter central island ile rene levasseur the results reveal that the impact melt though locally differentiated via fractional crystallization was isotopically homogenized during its formation following its derivation primarily from charnockites and mesocratic gneisses the isotopic signatures of the target rocks indicate that the protolith for the melt was the proterozoic manicouagan imbricate zone and that the underlying archean gagnon terrane was not involved in melt production or its subsequent modification via assimilation despite impact melt resting on archean lithologies in the southwest sector of the melt sheet limited assimilation of the footwall in this sector is attributed to the relatively rapid cooling of a thinner peripheral melt body

numerical modeling of the excitation propagation and dissipation of primary and secondary gravity waves during wintertime at mcmurdo station in the antarctic

large scale waves in the mesosphere and lower thermosphere observed by saber observations made by the sounding of the atmosphere using broadband emission radiometry saber instrument on board nasa s thermosphere ionosphere mesosphere energetics and dynamics timed satellite have been processed using salby s fast fourier synoptic mapping ffsm algorithm the mapped data provide a first synoptic look at the mean structure and traveling waves of the mesosphere and lower thermosphere mlt since the launch of the timed satellite in december 2001 the results show the presence of various wave modes in the mlt which reach largest amplitude above the mesopause and include kelvin and rossby gravity waves eastward propagating diurnal oscillations non sunsynchronous tides and a set of quasi normal modes associated with the so called 2 day wave the latter exhibits marked seasonal variability attaining large amplitudes during the solstices and all but disappearing at the equinoxes saber data also show a strong quasi stationary rossby wave signal throughout the middle atmosphere of the winter hemisphere the signal extends into the tropics and even into the summer hemisphere in the mlt suggesting ducting by westerly background zonal winds at certain times of the year the 5 day rossby normal mode and the 4 day wave associated with instability of the polar night jet are also prominent in saber data

first lidar observations of polar mesospheric clouds and fe temperatures at mcmurdo 77 8 s 166 7 e antarctica 1 we report the first lidar observations of polar mesospheric clouds pmcs and temperatures made with an fe boltzmann lidar at mcmurdo antarctica in summer 2010 2011 eighty five hours of pmcs were observed between 21 dec 2010 and 15 feb 2011 giving an overall occurrence frequency of 29 9 the mean pmc centroid altitude is 84 59 0 17 km confirming previous reports that clouds in the southern hemisphere are 1 km higher than in the north by combining the mcmurdo 77 8 s observations with those obtained at the south pole 90 s and rothera 67 5 s we find that the mean pmc altitude increases with increasing latitude with a statistically significant ascending rate of 40 3 m deg a negative correlation is found between the daily mean temperatures at 90 km and pmc brightness the observations provide direct evidence that the cold phase of wave induced temperature oscillations facilitates pmc formation and fe depletion supporting previous modeling results

the origin of stationary planetary waves in the upper mesosphere abstract satellite observations indicate that quasi stationary planetary waves often exist to at least 100 km in the winter mesosphere waves are also seen in the summer upper mesosphere a three dimensional numerical model was used to simulate these waves and to diagnose the physical processes involved the waves simulated in the model closely resemble observed waves several model runs that isolate specific processes are used to determine the relative importance of two forcing mechanisms in the model planetary waves that propagate from below are significantly damped at the altitude where gravity wave drag becomes large about 75 km in the winter midlatitudes or below if a reversal in the mean wind is encountered momentum forcing associated with breaking gravity waves that have been filtered by planetary scale wind variations below acts to generate planetary waves in the middle and upper mesosphere the amplitude from in situ forcing by gravity wave breaking exceeds the amplitude from the upward prop

two day wave traveling westward with wave number 1 during the sudden stratospheric warming in january 2017 quasi two day wave qtdw propagating westward with wavenumber number 1 w1 in january 2017 is studied using global temperature observed by saber and wind observed by a meteor radar at fuke china 19 0on 109 8oe the amplitude of w1 significantly enhances during january 2017 when two stratospheric warming events occur the temperature perturbation of w1 reaches maximum amplitude of more than 6k at latitude 15o around 84 km and 95 km the structure of temperature w1 is symmetric with regard to the equator the temporal variation of w1 is consistent with the stationary planetary wave with wavenumber 2 spw2 but contrary to the qtdw propagating westward with wavenumber 3 w3 when spw2 is large during two sudden stratospheric warming events energy transfers from w3 to w1 two bursts of the two day wave in meridional wind observed by the meteor radar are just corresponding to the local maxima of w3 and w1 respectively we conclude that during january 2017 w1 is generated by the nonlinear interaction between spw2 and w3 spw2 which is modulated by the quasi 16 day perturbation in the stratosphere plays a key role in the energy transmission from w3 to w1 and it is responsible for the 16 day variation of w1

dynamics of the 4 day wave in the southern hemisphere polar stratosphere abstract dynamics of the 4 day wave in the southern hemisphere polar stratosphere is investigated using horizontal wind and temperature data these were derived from synoptic maps of satellite measured brightness temperatures which were generated using the fast fourier synoptic mapping technique of salby circulation statistics from these data are compared to those from the national meteorological center nmc operational stratospheric analyses demonstrating improvements afforded by detailed treatment of asynoptic sampling effects the 4 day wave is isolated using temporally filtered data several events of wave growth and decay are observed in the upper stratosphere during august 1980 derived zonal mean and eddy statistics suggest that the 4 day wave results from an instability of the zonal mean flow near 55 60 s at and above 1 mb inspection of climatological data suggests the source of the instability to be the double jet structure in the upper stratosphere and mesosphere the subtropical mesosp

re os isotope systematics of ni cu sulfide ores sudbury igneous complex ontario evidence for a major crustal component sudbury igneous complex sublayer ores from the levack west falconbridge and strathcona mines were analyzed for their re and os concentrations and os isotopic compositions the re os isotope systematics of three ores from the different mines give isochron ages of1 840 60 ma 1770 60 ma and 1780 110 ma suggesting that the re os system became closed at the time of or soon after the 1850 1 ma crystallization age of the complex the os isotopic compositions of different portions of the complex at the time of crystallization varied considerably with initial187os 186os1850 ranging from 4 64 at levack west to 7 55 at strathcona these heterogeneities require that the os and probably also the other platinum group elements contained in the ores were derived from at least two sources in addition the high initial187os 186os ratios indicate that the os was derived predominantly from ancient crust previous studies have suggested that the complex either crystallized from a mixture of mantle derived basaltic melt and ancient continental crust or was derived exclusively from the fusion of ancient continental crust resulting from a meteorite impact results of modelling suggest that if a contemporaneous mantle derived basaltic melt was involved in the origin of the sic it likely contributed 50 of the os to all three ores the large percentage of ancient crust involved in the production of the ores is most consistent with an interpretation of substantial crustal fusion resulting from meteorite impact

igneous rocks formed by hypervelocity impact abstract igneous rocks are the primary building blocks of planetary crusts most igneous rocks originate via decompression melting and or wet melting of protolith lithologies within planetary interiors and their classification and compositional petrographic and textural characteristics are well studied as our exploration of the solar system continues so too does the inventory of intrusive and extrusive igneous rocks settings and processes the results of planetary exploration have also clearly demonstrated that impact cratering is a ubiquitous geological process that has affected and will continue to affect all planetary objects with a solid surface whether that be rock or ice it is now recognized that the production of igneous rocks is a fundamental outcome of hypervelocity impact the goal of this review is to provide an up to date synthesis of our knowledge and understanding of igneous rocks formed by hypervelocity impact following a brief overview of the basics of the impact process we describe how and why melts are generated during impact events and how impact melting differs from endogenic igneous processes while the process may differ we show that the products of hypervelocity impact can share close similarities with volcanic and shallow intrusive igneous rocks of endogenic origin such impact melt rocks as they are termed can display lobate margins and cooling cracks columnar joints and at the hand specimen and microscopic scale such rocks can display mineral textures that are typical of volcanic rocks such as quench crystallites ophitic porphyritic as well as features such as vesicles flow textures and so on historically these similarities led to the misidentification of some igneous rocks now known to be impact melt rocks as being of endogenic origin this raises the question as to how to distinguish between an impact versus an endogenic origin for igneous like rocks on other planetary bodies where fieldwork and sample analysis may not be possible and all that may be available is remote sensing data while the interpretation of some impact melt rocks may be relatively straightforward e g for clast rich varieties and those with clear projectile contamination we conclude that distinguishing between impact and endogenic igneous rocks is a non trivial task that ultimately may require sample investigation and analysis to be conducted caution is therefore urged in the interpretation of igneous rocks on planetary surfaces

strontium and neodymium isotopic characteristics of a heterolithic breccia in the basement of the sudbury impact structure canada abstract rb sr and sm nd measurements were undertaken on footwall breccia samples originating from levack township in the north range of the sudbury structure the granitic to quartzdioritic matrix of this heterolithic breccia which contains shocked rock and mineral fragments yields a rb sr isochron age of 1 825 0 021 ga isr 0 70356 0 00005 2 errors based on the analysis of 3 6 mm thick adjacent whole rock slabs from a large hand specimen this age is interpreted as a cooling age after the thermal metamorphism of the footwall breccia by the 1 85 ga old sudbury igneous complex which had caused temperatures in excess of 1000 c in the matrix near the contact mafic rock fragments in this breccia were excluded from the sr isotope exchange at that time the sm nd system of the identical small whole rock samples was only partly disturbed by the sudbury igneous complex the data points scatter around a 2 05 0 49 ga regression line without age significance plagioclase k feldspar and mafic mineral phases of the breccia matrix combined with the corresponding whole rocks display a range in rb sr ages from 1 67 0 08 ga to 1 430 0 015 ga obviously associated with metasomatic processes in the footwall breccia during the declining penokean metamorphism strontium and neodymium model parameters of the footwall breccia matrix near levack show little variation esrt 16 33 to 18 07 endt 10 69 to 11 79 t 1 86 ga and mean tnddm 2 74 0 04 ga based on these results bedrocks exposed in the south range and rocks now forming the sedimentary filling of the sudbury basin can be excluded as major components in the matrix of the analyzed footwall breccia the convergence of neodymium model ages with u pb ages on zircons from the levack gneiss which forms the crystalline basement adjacent to the footwall breccia in the levack area support an exclusively local origin for matrix and fragments of this breccia it is proposed that the footwall breccia is part of the uplifted floor of the sudbury crater

short term variability in the migrating diurnal tide caused by interactions with the quasi 2 day wave 1 the migrating diurnal tide is one of the dominant dynamical features in the low latitudes of the earth s mesosphere and lower thermosphere mlt region representing the atmospheric response to the largest component of solar forcing ground based observations of the tide have resolved short term variations attributed to nonlinear interactions between the tide and planetary waves that are also in the region using the ncar thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm we simulate a quasi 2 day wave qtdw event under late january conditions in this case sideband sum and difference child waves are resolved indicating that a nonlinear interaction is occurring between the qtdw and the tide the migrating diurnal tide in the mlt displays local amplitude decreases of 20 40 as well as a shortening of vertical wavelength by roughly 4 km examining the physical mechanisms driving the interaction nonlinear advection is found to result in amplification of the tide in some regions and damping in others manifesting as increased smoothing of the tidal structure when the qtdw is present in the mlt additionally the qtdw also enhances the easterly summer mean wind jet that can also account for changes in tidal amplitude and vertical wavelength we find that qtdw induced background atmosphere changes in time gcm can drive tidal variability at levels greater than nonlinear advection a possibility not previously considered

friction melt distribution in a multi ring impact basin it is generally accepted that multi ring basins are the consequence of very large impacts but the mechanism by which they form is still a matter of contention1 2 most of what is currently known about multi ring basins is based on remote studies of the moon3 5 and to a lesser extent mars and mercury4 6 but at least two multi ring impact basins have been recognized on earth7 the sudbury8 canada and vredefort9 south africa impact structures providing an opportunity to study their properties directly here we describe the distribution of friction melt pseudotachylyte in the floor of the sudbury impact basin although the veins and dykes of pseudotachylyte decrease in both thickness and frequency of occurrence towards the basin periphery the greatest volumes of friction melt appear to define four rings around the central impact melt sheet field evidence indicates that the rings originated as zones of large displacement which facilitated localized frictional melting of the basin floor during the modification collapse stage of the cratering process by analogy we argue that the rings of other multi ring impact basins are also likely to be the remnants of such large displacement fault zones

testing the validity of the petrological hypothesis no phenocrysts no post emplacement differentiation an extravagant hypothesis no phenocrysts no post emplacement differentiation has been put forward by marsh in a series of papers for the development of mafic ultramafic intrusions this hypothesis is based on an assertion that the majority of these intrusions are structureless and undifferentiated because they lack residual granitic rocks to explain this the hypothesis postulates that phenocryst free magmas are not able to differentiate in crustal chambers because all evolved interstitial liquid is locked in solidification fronts producing compositionally uniform magmatic bodies layered well differentiated intrusions are attributed to the successive emplacement of magma pulses with phenocrysts of different phase and chemical compositions rather than to slow magma cooling and fractional crystallization as conventional models imply such phenocryst laden magma pulses are supposed to be derived from an underlying magmatic mush column however structureless undifferentiated mafic ultramafic bodies simply do not exist in nature all wellstudied mafic ultramafic bodies with or without residual granitic rocks that crystallized from parental magmas of non eutectic composition tend to reveal clear evidence of internal compositional differentiation in terms of crystallization sequences e g ol opx opx pl opx pl cpx mineral compositions e g an in plag en in cpx and compatible incompatible major and trace element geochemistry e g mg number cr rare earth elements this is especially evident in layered intrusions that represent the key evidence against the hypothesis essentially by denying the ability of magma to differentiate in intrusive bodies the hypothesis forbids magmatic differentiation in any sub chamber related to the entire magmatic mush column as a result magma pulses in which phenocrysts progressively change in composition cannot be derived from the column to form layered intrusions the hypothesis is thus contradictory baseless and fundamentally flawed it should be abandoned in favour of a classical fractional crystallization model based on the pioneering experiments of bowen and amply confirmed over almost a century by subsequent studies of layered intrusions the classical model was is and will most probably remain the best explanation for the origin of differentiated magmatic bodies

winter temperature tides from 30 to 110 km at mcmurdo 77 8 s 166 7 e antarctica lidar observations and comparisons with wam we provide the first characterization of diurnal and semidiurnal thermal tides in temperature from 30 to 110 km in the winter season may through august at mcmurdo 77 8 s 166 7 e antarctica the observations were made with an fe boltzmann temperature lidar in 2011 and 2012 over 330 h of winter data are compiled into a composite day of temperature perturbations that significantly reduce the incoherent wave effects while preserving the coherent tidal signatures both diurnal and semidiurnal tides have small amplitudes less than 3 k below 100 km with vertical wavelengths of 29 and 23 km respectively a new finding of this study is the fast growth of diurnal and semidiurnal tidal amplitudes above 100 km to at least 15 k near 110 km exceeding that of the freely propagating tides originating from the lower atmosphere such fast growth exists for all kp index cases and diurnal amplitude increases to 15 30 k at 110 km with larger kp indices corresponding to larger tidal amplitudes and faster growth rates the slopes of diurnal tidal phases become steeper above 100 km and the tidal phases barely change with altitude from 100 to 106 km the tidal growth behavior is reproduced in the whole atmosphere model wam with phases comparable to the observations but magnitudes significantly underestimated wam compares reasonably well with the observations below 100 km the observed significant amplitude increases and phase structure changes suggest additional tidal sources near or above 100 km which deserve future investigation

eastward moving 2 4 day waves in the winter antarctic mesosphere the structure of short period 2 4 days planetary waves in the antarctic mesosphere has been determined from ground based wind measurements at the south pole observations are made with a fabry perot spectrometer fps to determine the meridional wind component of oh tracer molecules azimuth scanning of the fps shows that the observed modes are of zonal wavenumber one as expected at the rotation pole in the neutral atmosphere at scott base 78 s observations are made with an mf spaced antenna mode mesospheric wind profiler radar the vertical structure of the waves at altitudes of 80 100 km shows a phase variation corresponding to a vertical wavelength of more than 100 km the observed periods support previous interpretations based on satellite observations and barotropic instability models of modes associated with the 4 day wave

the terrestrial impact cratering record approximately 130 terrestrial hypervelocity impact craters are currently known due to variations in preservation and in geologic knowledge this sample is biased towards young x 20 km craters on the cratons of australia europe including the former u s s r and north america the rate of discovery of new craters is 3 5 craters per year although modified by erosion terrestrial impact craters exhibit the range of morphologies observed for craters on other terrestrial planetary bodies such as the moon terrestrial craters provide essential ground truth data on the geologic effects of impact and the subsurface structure of impact craters which can be used to constrain interpretations of lunar samples and models of crater formation due to erosion and its effects on form terrestrial craters are recognized primarily by the occurrence of shock metamorphic effects these include shatter cones microscopic planar deformation features solid state and fusion glasses high pressure polymorphs and whole rock melting and vaporization shock recovery experiments indicate that these features occur over shock pressures of 5 gpa to x 100 gpa terrestrial craters have a set of geophysical characteristics which are largely the result of the passage of a shock wave and impact induced fracturing they include gravity and magnetic lows and reductions in seismic velocity the gravity anomalies are seldom greater than 30 mgal due to the limiting effects of lithostatic pressure on fracturing at large complex craters the gravity signature may include a central relative gravity high due to uplift and short wavelength central magnetic anomalies due to a variety of processes much current work is focused on the effects of impact on earth evolution previous work on shock metamorphism and the contamination of impact melt rocks by meteoritic siderophile elements provides a basis for the interpretation of the physical and chemical evidence from cretaceous tertiary boundary sites as resulting from a major impact suggestions that other biological boundaries in the stratigraphie record are due to periodic impacts are not supported by time series analysis of the terrestrial cratering record by analogy with the lunar record and modelling of the effects of very large impacts it has been proposed that biological and atmospheric evolution of the earth could not stabilize before the end of the late heavy bombardment 3 8 ga ago the present terrestrial cratering rate is 5 4 2 7 10 15 km 2a 1 for a diameter 20 km this represents a local threat on historic time scales on a global scale a major impact sufficient to cripple human civilization severely will occur on time scales of 106 a

magnetic fabric constraints on the initial geometry of the sudbury igneous complex a folded sheet or a basin shaped igneous body abstract interpreted either as a folded igneous sheet or a basin shaped intrusion the origin of the palaeoproterozoic sudbury igneous complex sic ontario canada has been debated by geologists for over a century most recent proposals view the sic to have been emplaced as a horizontal impact melt and subsequently folded after solidification this requires the sic to have folded from an originally horizontal sheet to the present basinal geometry with dips of 30 in the north range and 70 in the east range the fold scenario would require the sharply curved juncture between the north and east ranges north lobe to be deformed in the solid state due to folding in order to test the fold model the rock fabric was investigated in the east and north ranges and the north lobe of sic at 256 sites with the aid of anisotropy of magnetic susceptibility ams a sampling transect through an undeformed portion of the sic in the western north range reveals that the gabbro norite exhibits sic contact parallel magnetic foliation and down dip magnetic lineation both of which respectively correlate to an igneous foliation and lineation the granophyre in contrast features spatially consistent magnetic lineation that is oriented orthogonal to the sic contact this magnetic lineation can be correlated to a mineral fabric characterised by aligned acicular crystals of plagioclase and is interpreted to be a wall orthogonal crystallisation texture the east and north ranges in the eastern sic reveal similar patterns of ams fabrics the magnetic lineation of the granophyre is orthogonal to the basal contact of the sic in the east and north ranges and in the fold like north lobe between the two ranges an axial planar magnetic foliation is developed in the granophyre as the north lobe is approached but the magnetic lineation is nevertheless contact orthogonal and well defined this ams fabric is interpreted to be a combination of an original igneous contact orthogonal lineation and a foliation resulting from tectonic overprint the preservation of the contact orthogonal magnetic lineation implies low levels of tectonic overprint conservative shortening strains estimated from ams numerical modelling suggest

oxygen isotopic and chemical compositions of rocks of the sudbury basin ontario the whole rock oxygen isotopic composition of the main units of the sudbury irruptive and surrounding rocks has been studied using samples from two traverses of the north range and one of the south range norite has an average 18o of 6 7 about 1 greater than that of fresh oceanic basalts and similar to that of some continental basalts granophyre is slightly richer in 18o 18o 7 3 in neither unit is there significant correlation between 18o and sio2 content or degree of alteration as estimated by water content or microscopic appearance the pervasive hydrous alteration of norite and granophyre apparently occurred in the presence of a small volume of water whose isotopic composition was buffered by the igneous rocks inclusion free devitrified glass melt rock and matrix from the onaping formation have 18o values in the range 6 2 12 1 its average 18o is 8 2 comparable to that of archean gneiss as required by the model for the origin of the formation as a fallback breccia from a me

hf isotope evidence for effective impact melt homogenisation at the sudbury impact crater ontario canada abstract we report on the first zircon hafnium oxygen isotope and trace element study of a transect through one of the largest terrestrial impact melt sheets the differentiated melt sheet at the 1 85 ga originally ca 200 km in diameter sudbury impact crater ontario canada yields a tight range of uniform zircon hf isotope compositions e hf 1850 of ca 9 to 12 this is consistent with its well established crustal origin and indicates differentiation from a single melt that was initially efficiently homogenised we propose that the heterogeneity in other isotopic systems such as pb in early emplaced impact melt at sudbury is associated with volatility related depletion during the impact cratering process this depletion leaves the isotopic systems of more volatile elements more susceptible to contamination during post impact assimilation of country rock whereas the systems of more refractory elements preserve initial homogeneities zircon oxygen isotope compositions in the melt sheet are also restricted in range relative to those in the impacted target rocks however they display a marked offset approximately one third up the melt sheet stratigraphy that is interpreted to be a result of post impact assimilation of 18 o enirched rocks into the base of the cooling impact melt given that impact cratering was a more dominant process in the early history of the inner solar system than it is today and the possibility that impact melt sheets were sources of ex situ hadean zircon grains these findings may have significance for the interpretation of the early zircon hf record we speculate that apparent e hf time arrays observed in the oldest terrestrial and lunar zircon datasets may be related to impact melting homogenising previously more diverse crust we also show that spatially restricted partial melting of rocks buried beneath the superheated impact melt at sudbury provided a zircon crystallising environment distinct to the impact melt sheet itself

origin of the sudbury complex by meteoritic impact neodymium isotopic evidence samarium neodymium isotopic data on whole rocks and minerals of the sudbury complex in canada gave an igneous crystallization age of 1840 21 x 10 6 years the initial epsilon neodymium values for 15 whole rocks are similar to those for average upper continental crust falling on the crustal trend of neodymium isotopic evolution as defined by shales the rare earth element concentration patterns of sudbury rocks are also similar to upper crustal averages these data suggest that the sudbury complex formed from melts generated in the upper crust and are consistent with a meteoritic impact

the evolution of the onaping formation at the sudbury impact structure the 1 4 1 6 km thick onaping formation consists of a complex series of breccias and melt bodies lying above the sudbury igneous complex sic at the sudbury impact structure based on the presence of shocked lithic clasts and various glassy phases the onaping has been described as a suevitic breccia with an origin at least in part as fallback material recent mapping and a redefined stratigraphy have emphasized similarities and differences in its various vitric phases both as clast types and discrete intrusive bodies the nature of the onaping and that of other suevitic breccias overlying impact melt sheets is reviewed the relative thickness internal stratigraphic and lithological character and the relative chronology of depositional units indicate multiple processes were involved over some time in the formation of the onaping the sudbury structure formed in a foreland basin and water played an essential role in the evolution of the onaping as indicated by a major hydrothermal system generated during its formation taken together observations and interpretations of the onaping suggest a working hypothesis for the origin of the onaping that includes not only impact but also the interaction of sea water with the impact melt resulting in repeated explosive interactions involving proto sic materials and mixing with pre existing lithologies this is complicated by additional brecciation events due to the intrusion of proto sic materials into the evolving and thickening onaping fragmentation mechanisms changed as the system evolved and involved vesiculation in the formation of the upper two thirds of the onaping

uranium lead zircon systematics in the sudbury impact crater fill implications for target lithologies and crater evolution the sudbury impact structure is one of only a few terrestrial impact craters capable of providing insight into large impact processes however despite more than a century of study no consensus exists regarding its depths of excavation and melting this study presents 3920 u pb zircon dates for target lithologies and the crater fill as well as new pb isotope data for target lithologies in an attempt to further constrain these depths and understand the behaviour of zircon in large impacts only 1 5 of the crater fill zircons have dates within uncertainty of the 1 85 ga impact event with most seeming to preserve their pre impact u pb systematics the preponderance of undisturbed zircon in the crater fill suggests that this mineral is an effective means of tracing target lithologies in impact basins a significant fraction of crater fill zircon was dated between 2 50 and 2 61 ga which is negligible amongst known target lithologies and therefore identifies previously unrecognized target rocks the pb isotope systematics are compatible with the proposal that the 2 6 ga rock represents typical mid to lower crustal basement and could have been an important contributor to the melt sheet the combined data argue against a shallow melting scenario with regard to hadean terrestrial zircon the lesson from sudbury is that zircon can be recycled through multiple large impact events and still preserve the age of the original crust supplementary materials sample information trace element and pb isotope data for granitoid and gneiss feldspar pb modelling parameters u pb zircon data concordia diagrams and airborne radiometric images are available at http www geolsoc org uk sup18881

trace element and isotopic evidence for archean basement in the lonar crater impact breccia deccan volcanic province abstract the lonar impact crater in the deccan traps of the indian peninsula provides unique opportunities to study physical and chemical processes of impact cratering on basaltic targets because terrestrial impact craters on basalts are extremely rare such studies are needed for determining provenance and other parameters of the excavated rocks and the cratering phenomenon that may have implications for similar crater formations in lunar martian and other basaltic targets in the solar system considering some of these objectives we analyzed trace elements and nd sr pb isotopes of impact breccia rocks and target basalts collected from the lonar crater chondrite normalized rare earth element ree patterns in the target basalts and breccia rocks show similar light ree enriched patterns although in detail the impact breccia are more fractionated in la sm compared to the target basalts the target basalts also show much lower concentrations of rb ba th u and pb compared to the breccia and are characterized by rb ba and pb depletions with respect to the primitive mantle normalized th u nb ta and the ree contents the breccia rocks are significantly enriched in rb ba and pb and to a lesser extent in th and u compared to the target rocks the nd sr and pb isotopic compositions of the lonar target basalts can be correlated with those of the poladpur suite one of the mid section volcano stratigraphic units of the deccan traps in contrast to the host basalts the impact breccia rocks show more radiogenic sr less radiogenic nd and higher rb sr and lower sm nd ratios indicating an additional component other than the target basalt that must have been derived from beneath the basaltic target rocks at the impact site the deccan traps in western india are underlain by archean to mid proterozoic cratonic rocks the overall geochemical signatures of the impact breccia rocks specifically the trace element concentrations negative end values radiogenic sr isotopic composition as well as the high 207pb 204pb at low 206pb 204pb indicate that a major component of the lonar impact breccia was derived from melting of archean basement rocks we argue that the archean component in the breccia cannot be from the incorporation of paleosols that are weathering products of the target basalts or from the inter trappean sediments that are most commonly cherts and limestones of mesozoic age similarly the possible role of eolian sediments in causing the archean pb isotopic signature identical to those of the deccan basement in the breccia rocks can be excluded the basement beneath the lonar region is believed to be similar to the dharwar craton of peninsular india based on their similar pb isotopic compositions with the breccia rocks we suggest the archean chitradurga group of rocks of this craton to be present in the basement beneath the deccan lavas of the lonar region the thickness of the basaltic target rocks at the crater site 400 m and the inferred crater depth 350 m 610 m based on depth to diameter ratios in simple planetary craters 0 2 0 33 are consistent with our conclusion regarding melting and incorporation of these ancient basement rocks in the impact breccia of the lonar crater using pi group scaling relations the observed crater diameter and density of the basaltic target rocks we have estimated with reasonable approximation the diameter of the lonar impactor to be either 70 m 86 m or 120 m assuming the bolide to be an iron meteorite stony iron meteorite or an ordinary chondrite respectively

pre emplacement re os ages from ultramafic inclusions in the sublayer of the sudbury igneous complex ontario abstract re os isotope analyses have been performed on a suite of 14 melanorite inclusions from the sublayer of the sudbury igneous complex sic at whistle mine 30 km nne of sudbury ontario canada six s poor olivine melanorites have relatively unradiogenic present day 187 os 188 os ratios of 0 16 1 2 and define an imprecise age of 1 97 ga their 187 os 188 os 1 85 ratios of 0 107 0 237 are compatible with derivation either from the mantle at the time of sic formation 1 85 ga ago or from pre existing crustal rocks with low re os ratios and unradiogenic os isotope compositions in contrast the relatively s rich inclusions define much older ages of 2 46 ga melanorites and 2 67 ga olivine melanorites while 187 os 188 os 1 85 ratios of 0 41 1 80 unequivocally demonstrate that their os was largely derived from pre existing crustal lithologies the os isotope compositions and s abundances of the inclusions are consistent with mixing at 1 85 ga between an unradiogenic silicate fraction defined by the s poor suite and a radiogenic sulphide rich component with re os ratios similar to those of pre existing crustal lithologies attempts to evaluate the source of the ni cu s and pge in the sic through mass balance calculations are not definitive because of the difficulties in estimating accurately both present day and pre sic crustal abundances however crude estimates suggest that the overall levels of ni and cu in the pre impact crust were probably sufficient to account for the budget of these elements in the present day sic but do not rule out the possibility of significant late archaean early proterozoic sulphide mineralisation in the pre existing sic target rocks

geoscience impact a synthesis of studies of the sudbury structure geophysical probing results are synthesized into a three dimensional framework necessary for understanding the genesis of the sudbury structure based primarily on seismic reflection results centred on the sudbury igneous complex remnants of crustal melting from a catastrophic meteorite impact are superimposed on the juxtaposition of mid crustal rocks exhumed during the archean against deformed paleoproterozoic sedimentary rocks sedimentation metamorphism deformation and metasomatic overprints are all part of the post impact history of sudbury and tend to dominate the geophysical response of the structure pre impact deformation although certainly preserved in some aspects of sudbury geology is not clearly expressed in the geophysical data nor are any elements of impact induced deformation geophysical views of the sudbury igneous complex are thus somewhat biased in representing mostly the post impact but pre grenvillian history of the region with the exception of igneous events establishing th

lidar observations of persistent gravity waves with periods of 3 10 h in the antarctic middle and upper atmosphere at mcmurdo 77 83 s 166 67 e persistent dominant and large amplitude gravity waves with 3 10 h periods and vertical wavelengths 20 30 km are observed in temperatures from the stratosphere to lower thermosphere with an fe boltzmann lidar at mcmurdo antarctica these waves exhibit characteristics of inertia gravity waves in case studies yet they are extremely persistent and have been present during every lidar observation we characterize these 3 10 h waves in the mesosphere and lower thermosphere using lidar temperature data in june from 2011 to 2015 a new method is applied to identify the major wave events from every lidar run longer than 12 h a continuous 65 h lidar run on 28 30 june 2014 exhibits a 7 5 h wave spanning 60 h and 6 5 h and 3 4 h waves spanning 40 and 45 h respectively over the course of 5 years 323 h of data in june reveal that the major wave periods occur in several groups centered from 3 5 to 7 5 h with vertical phase speeds of 0 8 2 m s these 3 10 h waves possess more than half of the spectral energy for 93 of the time a rigorous prewhitening postcoloring technique is introduced for frequency power spectra investigation the resulting spectral slopes are unusually steep 2 7 below 100 km but gradually become shallower with increasing altitude reaching about 1 6 at 110 km two dimensional fast fourier transform spectra confirm that these waves have a uniform dominant vertical wavelength of 20 30 km across periods of 3 5 10 h these statistical features shed light on the wave source and pave the way for future research

fluid sources and hydrothermal architecture of the sudbury structure constraints from femtosecond la mc icp ms sr isotopic analysis of hydrothermal epidote and calcite abstract this study presents new sr isotopic data on hydrothermal mineral assemblages from different stratigraphic levels within the sudbury impact structure determined using femtosecond la mc icp ms these data provide new insights into the origin of the hydrothermal fluids that have circulated through and around the sudbury igneous complex sic and further define the overall hydrothermal architecture of the structure early blocky miarolitic epidote from the sic has a narrow range of initial 87 sr 86 sr 0 70710 to 0 70742 similar to the sic 0 70648 to 0 70736 that is consistent with the precipitation from orthomagmatic fluids derived from the sic the 87 sr 86 sr values of later replacement miarolitic and vein epidote from different stratigraphic levels of the sic and of replacement and amygdule epidote from the overlying onaping formation are distinctly higher up to 0 71753 than those of the blocky miarolitic epidote these data suggest that the fluids responsible for this late epidote were not derived from the sic and more likely represent basement derived fluids that passed through the sic and onaping formation the sr isotopic composition of syngenetic laminated calcite in the post impact vermillion formation suggests precipitation from proterozoic seawater 87 sr 86 sr 0 70295 whereas some vermilion formation related syngenetic laminated calcite and epigenetic discordant and replacement mineralized calcite with more radiogenic values suggest precipitation from seawater modified through interaction with the vitric and lithic fragments present in the onaping formation the formation of some replacement and amygdule carbonate in the onaping formation also involved mixing between seawater and basement derived fluids of similar chemical and isotopic composition to those responsible for the replacement epidote hosted by the sic and onaping formation the sr isotopic composition of hydrothermal epidote from throughout the sudbury structure indicates a fluid connection between the footwall and hanging wall of the sudbury igneous complex

recognition of eroded astroblemes abstract the morphology of lunar craters degrades only slowly by the formation of new impacts and their ejecta it is not the same on earth because of weathering and tectonism generally the typical crater topography has disappeared and the term impact structure or astrobleme is applied on planetary surfaces as on the moon two classes of craters are recognized based on their depth to diameter ratio simple bowl shaped and complex readjusted flat bottomed craters with a sharp transition from simple to complex pike 1977 1980 on earth small simple craters retain some of their typical rimmed pit morphology because they are generally recent many are associated with meteorite fragments large impact structures or astroblemes in addition to their specific circular features are recognized as such only by the presence of shock metamorphism criteria such as dense minerals coesite stishovite diaplectic minerals and glass maskelynite planar deformation features in minerals principaly in quartz and feldspars and shattercones which are commonly used these criteria are abundant in allochthonous breccia particularly in fall back breccia among which there are glass fragments such as tectite or microtectite glass spherules shards droplets rods etc but on the floor of the astroblemes the criteria of shock metamorphism are restricted to the central part which is often covered or eroded using the measurements of nine astroblemes visited a scaling model is presented for two types of craters readjusted along listric slip surfaces a well readjusted model based on data from charlevoix and manicouagan canada and a partly readjusted model based on data from the ries germany both possess a central uplift and a ring graben there is also on the floor of the astrobleme a specific type of breccia mylolisthenite and pseudotachylite associated with the displacement along the autochthonous masses of rocks in very large impact structures the shock metamorphism is able to melt a part of the floor grieve and cintala 1992 the heat resulting from the superheated impact melt destroys a part of the shock metamorphism criteria

the shabogamo intrusive suite labrador sr and nd isotopic evidence for contaminated mafic magmas in the proterozoic abstract the shabogamo intrusive suite comprises numerous bodies of variably metamorphosed gabbro which intrude archean and proterozoic sequences at the junction of the superior churchill and grenville structural provinces in western labrador combined sm nd and rb sr systematics in two bodies ranging from unmetamorphosed to lightly metamorphosed document a crystallization age of about 1375 m y and suggest that both bodies crystallized from magmas with similar nd and sr isotopic compositions this age is in accordance with the existence of a regional magmatic event in the churchill province at approximately 1400 m y rb sr systematics in two bodies of amphibolite grade gabbro suggest a regional metamorphic event at about 950 m y corresponding to the waning stages of grenville activity sm nd systematics in these high grade bodies are affected to a much lesser degree than rb sr initial ratios for143nd 144nd and87sr 86sr are lower and higher respectively than bulk earth values at 1375 m y both these displacements are in the direction of older crustal material at 1375 m y and a model is proposed to produce the shabogamo magma by mixing a mantle derived magma with a partial melt of crustal rocks approximately 4 1 by volume young volcanic rocks with anomalous nd and sr isotopic ratios which have previously been taken as evidence for enriched mantle may be interpreted similarly

terrestrial impact melt rocks and glasses abstract the effects of meteorite and comet impact on earth are rock brecciation the formation of shock metamorphic features rock melting and the formation of impact structures i e simple craters complex craters and multi ring basins large events such as the 65 ma chicxulub impact are believed to have had catastrophic environmental effects that profoundly influenced the development of life on earth in this review an attempt is made to summarize some of the voluminous literature on impact melting one important aspect of planetary impact provide some comments on this process and to make suggestions for future research the products of impact melting are glasses impact melt rocks and pseudotachylites our treatise deals mainly with the geological setting petrography and major element chemistry of melt rocks and glasses impact glasses in several petrographic aspects are similar to volcanic glasses but they are associated with shock metamorphosed mineral and rock fragments and in places with siderophile element anomalies suggestive of meteoritic contamination they are found in allogenic breccia deposits within fall back suevite and outside fall out suevite impact craters and as spherules in distal ejecta large events such as the k t boundary chicxulub impact are responsible for the formation of worldwide ejecta horizons which are associated with siderophile element anomalies and shock metamorphosed mineral and rock debris impact glasses have a bulk chemical composition that is homogeneous but exemptions to this rule are common on a microscopic scale however impact glasses are commonly strikingly heterogeneous tektites are glasses ejected from craters over large distances they are characterized by very low water and volatile contents and element abundances and ratios that are evidence that tektites formed by melting of upper crustal sedimentary rocks four tektite strewn fields are known three of which can be tied to specific impact craters impact melt rocks form sheets lenses and dike like bodies within or beneath allogenic fallback breccia deposits in the impact crater and possibly on crater terraces and flanks dikes of impact melt rocks also intrude the rocks of the crater floor they commonly contain shock metamorphosed target rock and mineral fragments in various stages of assimilation and are glassy or fine to coarse grained chemically they are strikingly homogeneous but as with impact glasses exemptions to this rule do exist large and thick melt bodies such as the sudbury igneous complex sic are differentiated or may represent a combination of impact melt rocks sensu strictu and impact triggered deep crustal melts a concerted multidisciplinary approach to future research on impact melting and on other aspects of meteorite and comet impact is advocated impact models are models only and uncritical reliance on their validity will not lead to a better understanding of impact processes especially of melting excavation and deposition of allogenic breccias and the spatial position of breccias in relation to sheets and lenses of melt rocks within the crater impact triggered pressure release melting of target rocks beneath the excavation cavity may be responsible for the existence of melt rocks beneath the impact melt rocks sensu strictu this controversial idea needs to be tested by a re evaluation of existing data and models be they based on field or laboratory research only a relatively small number of terrestrial impact structures has been investigated in sufficient detail as it relates to geological and geophysical mapping in this review we summarize observations made on impact melt rocks and impact glasses in a number of north american brent haughton manicouagan new quebec sudbury wanapitei all in canada asian popigai russia zhamanshin kazakhstan two south african structures morokweng and vredefort the henbury crater field of australia and one european crater ries germany our tables listing major element chemical compositions of impact glasses and melt rocks however include also data from structures not dealt with in further detail

introduction to the special section on the lithoprobe sudbury project integrated geophysical and rock property studies of the sudbury structure have revealed it is highly deformed with substantial ns shortening in the sudbury igneous complex understanding the nature and extent of deformation is essential to determining the original shape of the structure and the results of these studies are sufficient to discount many of the objections to an impact origin

on the nature of buttressing in margin parallel strike slip fault systems margin parallel strike slip faults commonly develop along convergent plate margins where an oceanic plate subducts obliquely beneath a continental plate such faults detach a sliver of continental crust from the leading edge of the overriding plate fault motion then causes the sliver to move parallel to the continental margin in the direction of the transverse component of relative plate motion however few slivers move as rapidly as predicted by simple analyses of the forces acting on them this discrepancy must be due principally to the buttress effect resistance to displacement of the sliver arising from a space problem at its leading edge more simply a sliver can move only if it has somewhere to go buttresses can be geometrical as when the continental margin changes trend abruptly or they can arise from changes in the physical properties of the overriding plate or in other factors such as subduction angle and angle of obliquity that help determine whether sliver motion will occur a strongly buttressed sliver will move only insofar as the buttress can be overcome obvious ways in which a buttress can be overcome are by thickening the crust or widening the sliver examples of both are known crustal thickening entails elevation increase sliver motion is opposed by both gravity and friction widening the sliver is a more complex process that results in areas of extension and compression forming within the sliver as well as a characteristic pattern of overlapping curved fault segments this latter response may be the cause of curvature in many strike slip fault systems

first observations of short period eastward propagating planetary waves from the stratosphere to the lower thermosphere 110 km in winter antarctica unique fe lidar observations in may 2014 at mcmurdo combined with aura microwave limb sounder mls measurements lead to a new discovery that the amplitudes of 4 day and 2 5 day planetary waves pws grow rapidly from 1 2 k at 100 km to over 10 k at 110 km this report is also the first observation of short period 1 5 days eastward propagating pws from 30 km all the way to 110 km the specified dynamics whole atmosphere community climate model reproduces the observed three dominant peaks of amplitudes in temperature and coherent vertical phase structures the data model comparison indicates a possible mechanism after pws originated from the stratosphere dissipate along the critical level the surviving waves are amplified by in situ instability in the mesosphere and lower thermosphere resulting in the second third peak in geopotential temperature this third peak in temperature explains the pw amplitude growth from 100 to 110 km

on the significance of crater ages new ages for dellen sweden and araguainha brazil samples of a few grams in weight from the impact melt at the dellen crater sweden and the araguainha dome brazil were analyzed by rb sr and sm nd techniques for dellen pure labradorite orthopyroxene and glass separates from a clast free impact melt rock with holohyaline ground mass yield an internal rb sr isochron with 89 0 2 7 ma isr 0 83571 0 00007 2 compared to ar ar plateau ages of 102 3 2 ma and 109 6 2 0 ma published for total melt rocks various whole rock values not plotting on this rb sr isochron indicate primary variations in 87sr86sr over the melt sheet the age of the araguainha dome brazil is bracketed by the rb sr model age of 243 19 ma isr 0 7226 0 0005 for altered cordierite in the impact melt and by the internal rb sr isochron age of 449 9 ma isr 0 7140 0 0007 for an uplifted granite shock stage ib in melt rocks from both impact structures 143nd144nd was not homogenized during total rock melting sm nd data either scatter around the primary isochron araguainha or point to a partial resetting dellen this data array may be caused by tiny refractory ree rich inclusions in the main mineral phases which dominate the sm nd system of the impact melt rocks the significant difference between the new isochron age for dellen and ar ar ages show that the data base for analysis of periodicity in cratering record most probably lack precision and accuracy

recrystallized impact glasses of the onaping formation and the sudbury igneous complex sudbury structure ontario canada abstract the origin of the sudbury structure and of the associated heterolithic breccias of the onaping formation and the sudbury igneous complex have been controversial while an impact origin of the structure has gained wide acceptance over the last 15 years the origin of the recrystallized onaping formation glasses and of the igneous complex is still being debated recently the interpretation of the breccias of the onaping formation as suevitic fall back impact breccias has been challenged the igneous complex is interpreted either as a differentiated impact melt sheet or as a combination of an upper impact melt represented by the granophyre and a lower impact triggered magmatic body consisting of the norite sublayer formations the onaping formation contains glasses as fluidal and nonfluidal fragments of various shapes and sizes they are recrystallized and our research indicates that they are petrographically heterogeneous and span a wide range of chemical compositions these characteristics are not known from glasses of volcanic deposits this suggests an origin by shock vitrification an interpretation consistent with their association with numerous and varied country rock clasts that exhibit microscopic shock metamorphic features the recrystallized glass fragments represent individual solid state and liquid state vitrified rocks or relatively small melt pods the basal member lies beneath the gray and black members of the onaping formation and where not metamorphic has an igneous matrix igneous textured melt bodies occur in the upper two members and above the basal member a comparison of the chemical compositions of recrystallized glasses and of the matrices of the basal member and the melt bodies with the components and the bulk composition of the igneous complex is inconclusive as to the origin of the igneous complex basal member matrix and melt bodies on average are chemically similar to the granophyre of the sudbury igneous complex suggesting that they are genetically related our chemical results allow interpretation of the entire igneous complex as a differentiated impact melt however they are also consistent with the granophyre alone being the impact melt and the norite and quartz gabbro beneath it representing an impact triggered magmatic body this interpretation is preferred as it is consistent with a number of field observations a re evaluation and extension of structural field studies and of geochemical data as well as a systematic study of the contact relationships of the various igneous phases of the igneous complex are needed to establish a sudbury impact model consistent with all data and observations

variation in trace element content of magnetite crystallized from a fractionating sulfide liquid sudbury canada implications for provenance discrimination abstract laser ablation icp ms analysis has been applied to many accessory minerals in order to understand better the process by which the rock formed and for provenance discrimination we have determined trace element concentrations of fe oxides in massive sulfides that form ni cu pge deposits at the base of the sudbury igneous complex in canada the samples represent the crystallization products of fractionating sulfide liquids and consist of early forming fe rich monosulfide solution mss cumulates and residual cu rich intermediate solid solution iss this study shows that fe oxide geochemistry is a sensitive petrogenetic indicator for the degree of fractionation of the sulfide liquid and provides an insight into the partitioning of elements between sulfide and fe oxide phases in addition it is useful in determining the provenance of detrital fe oxide in a sulfide melt all lithophile elements cr ti v al mn sc nb ga ge ta hf w and zr are compatible into fe oxide the concentrations of these elements are highest in the early forming fe oxide titanomagnetite which crystallized with fe rich mss upon the continual crystallization of fe oxide from the sulfide liquid the lithophile elements gradually decrease so that late forming fe oxide magnetite which crystallized from the residual cu rich liquid is depleted in these elements this behavior is in contrast with fe oxides that crystallized from a fractionating silicate melt whereby the concentration of incompatible elements such as ti increases rather than decreases the behavior of the chalcophile elements in magnetite is largely controlled by the crystallization of the sulfide minerals with only ni co zn mo sn and pb present above detection limit in magnetite nickel mo and co are compatible in fe rich mss and thus the co crystallizing fe oxide is depleted in these elements in contrast magnetite that crystallized later from the fractionated liquid with cu rich iss is enriched in ni mo and co because fe rich mss is absent the concentrations of sn and pb which are incompatible with fe rich mss are highest in magnetite that formed from the fractionated cu rich liquid at subsolidus temperatures ilmenite exsolved from titanomagnetite whereas al spinel exsolved from the cores of some magnetite locally redistributing the trace elements however during laser ablation icp ms analysis of these fe oxides both the magnetite and its exsolution products are ablated so that the analysis represents the original magmatic composition of the fe oxide that crystallized from the sulfide melt

lidar observations of neutral fe layers and fast gravity waves in the thermosphere 110 155 km at mcmurdo 77 8 s 166 7 e antarctica 1 we report the first lidar observations of neutral fe layers with gravity wave signatures in the thermosphere from 110 155 km at mcmurdo antarctica in may 2011 the thermospheric fe densities are low ranging from 200 cm 3 at 120 km to 20 cm 3 at 150 km the measured temperatures from 115 135 km are considerably warmer than msis and appear to be related to joule heating enhanced by aurora the observed waves originate in the lower atmosphere and show periods of 1 5 2 h through 77 155 km the vertical wavelength increases from 13 km at 115 km to 70 km at 150 km altitude these wave characteristics are strikingly similar to the traveling ionospheric disturbances caused by internal gravity waves the thermospheric fe layers are likely formed through the neutralization of vertically converged fe layers that descend in height following the gravity wave downward phase progression

the growth of the continent through geological time studied by nd isotope analysis of shales abstract we determined the nd isotopic composition and the sm nd ratios in a series of australian shales ranging from 0 2 gy to 3 3 gy the first result of this study is the constancy of the sm nd ratio in these shales as in granitoids secondly the initial 143nd 144nd ratio gives a regular curve decreasing through geological time both results confirm that shales are representative samples of the continental crust when insoluble elements like ree are studied we calculated their nd model ages of crustal differentiation the model ages regularly decrease with the stratigraphic ages and after 2 gy the curve flattens and tends to an asymptotic value at around 1 8 gy the significance of the shales is that they represent a mixture of continental materials and we consider the model age of such a mixture directly linked with the mean age of the continental portion feeding the sedimentary basin from these results we deduce a quantitative model of the growth curve of the continental source of the shales taking into account the effects of erosion which selectively sample recent mountains relative to shield areas we propose that the results obtained here are representative of the whole gondwana continent having studied the case of the australian shales we try to extend our study first we applied our quantitative approach to the recent results obtained by o nions et al on north atlantic provinces the continental growth curves obtained by our inversion procedure are quite distinct from the australian shales showing the regional character of shales with these two cases studied we try to compare our results with the already developed model for continental growth the consideration of the surface conservative versus surface non conservative models clearly show the non uniqueness of the geological interpretation of the growth curve on the other hand we have calculated for each case the recycling rate versus geological time by comparing the growth curve with the hurley rand province age curve such recycling increases with time in agreement with the data obtained on nd and sr initial ratios on granitoids

resetting of neodymium isotopes and redistribution of rees during sedimentary processes the early proterozoic chelmsford formation sudbury basin ontario canada abstract the rees abundances and neodymium isotope compositions of sandstones and siltstones from the early proterozoic chelmsford formation reveal that the rees in some samples were redistributed during the early proterozoic by surficial processes and that prior to redistribution the nd isotope system was partially reset the chelmsford formation is a coarse grained turbidite sequence the youngest of three clastic units that fill the sudbury basin in ontario it is constrained to have been derived from nearby late archean superior province rocks by petrography major and trace element chemistry and pb isotopic compositions of whole rocks and feldspar although ree patterns and nd model ages for samples from around the base of the formation reflect their derivation from undisturbed superior province rocks tdm 2800 ma five samples from higher in the stratigraphic section show evidence that up to 60 of their la has been removed and sm nd has increased by up to 60 these samples also have anomalously high nd model ages tdm 3400 to 4400 ma the presence of pronounced positive ce anomalies in the samples with anomalous tdm indicates the influence of surficial processes on the ree composition the data scatter about a vertical array on a plot of f sm nd vs ndt 1800 nd calculated at 1800 ma approximately the depositional age with values of f sm nd between 0 45 and 0 14 mixing of nd from other sources is difficult to reconcile with the petrography major and trace element geochemistry and nd and pb isotopes removal of an lree enriched phase from the sedimentary system provides a viable mechanism to produce the ree and nd isotopic characteristics of the chelmsford formation samples neodymium isotopes require that this phase was partially isotopically equilibrated with the matrix sediment near the time of sedimentation this study shows the dangers of indiscriminate use of nd model ages in provenance studies and demonstrates that the simultaneous examination of sm nd and nd isotopes on f sm nd vs nd or isochron plots is required for the recognition of sedimentary redistribution of the ree

the sudbury igneous complex a differentiated impact melt sheet the sudbury structure ontario is the remnant of a 1 85 ga old impact crater which originally had a diameter of 200 to 250 km the sudbury igneous complex occurs within the sudbury structure the sudbury igneous complex is a 2 5 to 3 0 km thick 60 27 km elliptical igneous rock body which consists of four major lithologies from top to bottom traditionally termed granophyre quartz gabbro norite and contact sublayer sulfide and inclusion bearing noritic rock with the exception of the latter all these lithologies are continuous across the structure modal analyses reveal that following the iugs system of nomenclature quartz gabbro samples are in fact quartz monzogabbros a few of the norite samples are quartz gabbros and most norite samples are quartz monzogabbros in view of these observations and in order to clarify the nomenclature an updated terminology is proposed from top to bottom upper unit middle unit lower unit and contact sublayer the bulk composition of the sudbury igneous complex from north range data is granodioritic continuous and gradational mineralogical and geochemical variations between the lithological units are evidence that the complex behaved as a single melt system all the sudbury igneous complex lithologies have the same light to heavy rare earth element ree ratio and an overall pattern of increased light ree and depleted heavy ree the occurrence of primary hydrous minerals hornblende and biotite deuteric alteration and abundant micrographic and granophyric intergrowths demonstrate that the melt was rich in h2o moreover the granophyric and other far from equilibrium textures are most likely due to rapid crystallization triggered by exsolution of a volatile phase the sudbury igneous complex differs from traditional layered mafic complexes in the following aspects it has an overall intermediate composition a hydrous nature a crustal isotopic signature normative corundum and an unusually large volume of granophyre the sudbury complex differs from known terrestrial impact melt sheets only by its great thickness and the presence of chemical and therefore mineralogical layering reported here for the first time and similar to those found in impact melt rocks elsewhere are the occurrences of plagioclase xenocrysts with complex twinning and zoning patterns and planar deformation features in quartz xenocrysts the well known ore deposits of the sudbury region are directly related to the genesis of the sudbury igneous complex some ores precipitated from the sudbury melt whereas others were concentrated by hydrothermal fluids that percolated through the crystallized complex it is concluded that the sudbury igneous complex is the best exposed and only well documented to date terrestrial impact melt sheet to have differentiated

190pt 186os and 187re 187os systematics of the sudbury igneous complex ontario abstract we measured by negative thermal ionization mass spectrometry ntims re os and 186 os 188 os and 187 os 188 os in 26 samples of 18 ni cu sulfide ores from the falconbridge mccreedy west and strathcona mines at sudbury ontario at mccreedy west and falconbridge the isochron re os ages are 1835 70 ma and 1827 340 ma and the initial 187 os 188 os ratios 0 514 0 019 and 0 550 0 024 respectively the ages agree with the canonical value of 1850 1 ma for the sudbury igneous complex sic for hangingwall and deep zone ores at strathcona the age of 1780 7 ma may reflect resetting by dyke activity the high initial 187 os 188 os of 0 934 0 005 in these ores is distinct from those at mccreedy west and falconbridge strathcona deep copper zone ores have highly radiogenic os giving a mean model age of 1883 54 ma that is similar to ages at mccreedy west and falconbridge but distinct from other strathcona sulfides initial 186 os 188 os in two strathcona ores with low 190 pt 188 os average 0 119 826 0 000 009 n 3 and 0 119 827 0 000 004 n 3 respectively with a grand mean of 0 119 827 0 000 003 this ratio may be slightly lower than the chondritic value at that time similar ores at falconbridge and mccreedy west show more scatter averaging 0 119 855 0 000 008 n 6 and 0 119 867 0 000 020 n 3 respectively these values are substantially suprachondritic the re os isotope systematics of sudbury ores are clearly of crustal origin and may be derived from a binary mixture of superior province and huronian metasedimentary rocks with strathcona falconbridge and mccreedy west ores containing respectively 55 16 and 12 of os from superior sediments the suprachondritic 186 os 188 os at mccreedy west and falconbridge may be due to admixture of archean or paleozoic mafic rocks with 190 pt 188 os 0 1 no trace of the asteroid that produced the sudbury structure has been reported at the whistle mine s poor olivine melanorite inclusions with high ni and os and low 187 os 188 os may contain the signature of a magmatically fractionated asteroidal core contributing 1 to 2 5 metal the s poor melanorite ni and os data are equally well explained by admixture of 40 mantle peridotite however