multiphase u pb geochronology of sintered breccias from the steen river impact structure canada mixed target considerations for a jurassic cretaceous boundary event abstract in situ u pb geochronology has been conducted using laser ablation inductively coupled mass spectrometry la icp ms on shocked and thermally metamorphosed apatite titanite and zircon grains from the steen river impact structure canada the dated relict mineral phases occur within impact melt bearing breccias that underwent post deposition sintering at 450 c t

recrystallization and chemical changes in apatite in response to hypervelocity impact despite the wide utility of apatite ca5 po4 3 f cl oh in the geosciences including tracing volatile abundances on the moon and mars little is known about how the mineral responds to the extrem

the application of reflection seismology to the investigation of the geometry of near surface units and faults in the blake river group abitibi belt quebec reprocessing of part of a lithoprobe high resolution seismic reflection line across the southern part of the abitibi belt has improved the imaging of shallow reflections and allowed correlation of the data with surface geology enhancement of early reflections was accomplished by focusing on the high frequency content of the data this improved resolution of reflections at two way traveltime as early as 0 3 s and attenuated noise such as shear waves the shallow reflections are interpreted as impedance contrasts at the contact between a metadiabase diorite body and metavolcanics rocks offsets of the reflectors correlate with faults mapped at the surface and indicate a downdropped block which may be of interest for mineral exploration

imaging and interpreting the shallow crystalline crust abstract in the past many tests of high resolution seismic imaging methods utilizing off the shelf technology from hydrocarbon exploration have had only limited success some problems associated with the application of seismic profiling in the shallow crystalline crust differ from those encountered in sedimentary basins perhaps the most fundamental distinction stems from differences in statistical properties of the reflection coefficient time series analysis of power spectra derived from borehole data indicates that the reflection coefficients in the crystalline crust are depleted in the seismic bandwidth relative to sedimentary basins this fundamental difference must be considered in the design of shallow crustal seismic surveys in order to achieve success to a first approximation acoustic impedance variations in sedimentary basins are controlled by velocity changes whereas velocity and density can vary independently in the crystalline crust and changes in density may be relatively more important in controlling reflectivity in certain instances density fluctuations outweigh velocity fluctuations for example physical rock property data from mining districts in the canadian shield suggest that massive fe oxide or sulphide bodies will generate strong seismic reflections

crustal geometry of the abitibi subprovince in light of three dimensional seismic reflector orientations we provide precise estimates of reflector orientations beneath the archean abitibi subprovince using two distinct approaches based on lithoprobe seismic reflection data in the first we use the dip of reflections observed on intersecting profiles to establish the three dimensional orientation of reflective structures in the second the strikes and dips of reflectors are estimated in the crooked parts of seismic reflection profiles by calculating a measure of coherency along the traveltime trajectories defined by a particular azimuth dip depth and medium velocity mid crustal reflectors define two areas with distinctive geometry reflectors beneath the southern abitibi belt are oppositely dipping and convergent at depth providing a v shape aspect to the greenstone rocks other reflectors beneath the northern abitibi belt are in general subparallel dipping at an average of 30 toward the north these north dipping reflectors are partly disrupted by a low reflectivity zone which is attributed to

new zircon shock phenomena and their use for dating and reconstruction of large impact structures revealed by electron nanobeam ebsd cl eds and isotopic u pb and u th he analysis of the vredefort domethis article is one of a series of papers published in this special issue on the theme of geochronology in honour of tom krogh integrated electron nanobeam ebsd cl eds and isotopic measurements u pb u th he of zircon from the collar and centre of the 80 km wide central uplift of the 2020 3 ma vredefort impact structure reveal new shock features in a microstructural progression related to impact basin formation and degree of u pb age resetting 1 planar fractures in 1k0 and 1k2 orientation during initial shock wave compression 2 curviplanar fractures in 1k1 orientation now annealed which host glassy inclusions of partial melt of the host rock 3 microtwin lamellae in an orientation of 65 about 110 attributed to shock wave rarefaction 4 nucleation of impact age crystallites possibly on microtwins during post shock heating by impact melt and 5 crystal plastic deformation linked to crater modification of the core of the central uplift planar fracturing and microtwinning 20 gpa in cold shock zircon in granitoid at a radial distance of 25 km failed to reset zircon age single grain id tims data

self induced fracture generation in zircon the mineral zircon has particular geological significance because of its use in the age determination of rocks and as a structural analogue phase for radioactive waste forms despite its widespread utility however radiation damage of the crystal structure metamictization causes a volume expansion of the crystal lattice and the generation of internal stresses which can induce fractures in the crystal a model has been developed which describes the state of stress in n concentric spherical shells each of which may have different material properties the case of a three shelled composite sphere has been examined explicitly in combination with fracture mechanics theory the model predicts that spatially distinct radial and or concentric fracture sets can be produced and such fracture patterns accurately describe the distribution and types of self induced fractures observed in natural zircons in general the formation of such microfractures in zircon is a function of the degree of metamictization shell thickness and the confining pressure the model predicts that the maximum depths in the earth s crust at which radial versus concentric fractures can form in a crystal are different suggesting that the types of fractures found in a suite of zircons from a particular rock might be potential indicators of the depth of burial because metamictization induced fractures may serve as potential pathways for the rapid leaching of various elements from the zircon crystal this may also have important implications in interpreting the u pb ages of fractured zircons or in evaluating the suitability of related crystalline phases as hosts for nuclear waste

crooked line 2d seismic reflection imaging in crystalline terrains part 2 migration seismic reflection surveys are frequently conducted over very complicated geological structure but surveying often must be confined to existing crooked roads or tracks typically data from such 2d crooked line surveys are processed using standard common midpoint cmp stacking techniques to obtain a 2d time section which is then 2d migrated in part i we show that a reflector dip component across the processing line can cause serious problems for standard cmp stacking we also propose a supplementary processing step in which cross dip is determined locally and cross dip moveout cdmo is removed from data to form an optimum cross dip stack however a crooked line survey is really a swath 3d survey and ideally we would like to obtain a 3d image of reflectivity surrounding the profile here we investigate the potential of 3d prestack kirchhoff migration to directly image all observed reflections i e we attempt to construct a 3d image volume of all reflectors viewed by the survey because reflectors t

a review of high resolution seismic profiling across the sudbury selbaie noranda and matagami mining camps lithoprobe high resolution seismic surveys have provided the first systematic images of the deep stratigraphy in four major canadian mining camps noranda matagami sudbury and selbaie systematic compressional wave velocity and density measurements in deep boreholes have established that lithological contacts were the main impedance contrast imaged although reflections from faults and deformation zones have also been observed the strongest reflections are attributed to mafic intrusions and some sulphides and oxides integrating seismic physical rock property measurements and geological data has resulted in the revision of several geological models with direct impact on local strategies for deep mineral exploration mining companies have shown an interest in seismic reflection methods and this has led to several follow up studies the application of seismic methods to the direct detection of massive sulphides based on physical rock property measurements has been studied through two dimensional an

shallow high resolution seismic imaging at the ansil mining camp in the abitibi greenstone belt volcanic rocks in and around the ansil mining camp host a large number of massive sulfide mineral deposits a high resolution seismic reflection profile was shot across the camp with the objective of mapping the contacts between the different volcanic units at which most of the ore bodies have been found numerous exploration boreholes define the geology to a depth of 1600 m and allow a precise comparison with the recorded reflections geophysical logs obtained in one deep borehole suggest that reflection coefficients between the andesite rhyolite units of the volcanic stratigraphy are around 0 05 but few corresponding reflections can be identified in the seismic data those reflections in the surface seismic profile that can be correlated with the subsurface geology originate from diorite sills at which reflection coefficients are between 0 05 and 0 11 we suggest that reflections are observed from the diorite sills because the sills were intruded as sheets some along fault planes resulting in inte

a pressure temperature phase diagram for zircon at extreme conditions abstract hypervelocity impact processes are uniquely capable of generating shock metamorphism which causes mineralogical transformations and deformation that register pressure p and temperature t conditions far beyond even the most extreme conditions created by terrestrial tectonics the mineral zircon zrsio4 responds to shock deformation in various ways including crystal plasticity twinning polymorphism e g transformation to the isochemical mineral reidite formation of granular texture and dissociation to zro2 sio2 which provide robust thermobarometers that record different extreme conditions the importance of understanding these material processes is two fold first these processes can mobilize and redistribute trace elements and thus be accompanied by variable degrees of resetting of the u pb system which is significant for the use of zircon as a geochronometer second some features described herein form exclusively during shock events and are diagnostic criteria that can be used to confirm the hypervelocity origin of suspected impact structures we present new p t diagrams showing the phase relations of zrsio4 polymorphs and associated dissociation products under extreme conditions using available empirical and theoretical constraints we present case studies to illustrate zircon microstructures formed in extreme environments and present electron backscatter diffraction data for grains from three impact structures mistastin lake of canada ries of germany and acraman of australia that preserve different minerals and microstructures associated with different shock conditions for each locality we demonstrate how systematic crystallographic orientation relationships within and between minerals can be used in conjunction with the new phase diagrams to constrain the p t history we outline a conceptual framework for a zircon based approach to extreme thermobarometry that incorporates both direct observation of high p and high t phases as well as inferences for the former existence of phases from orientation relationships in recrystallised products a concept we refer to here as phase heritage this new approach can be used to unravel the pressure temperature history of zircon bearing samples that have experienced extreme conditions such as rocks that originated in the earth s mantle and those shocked during impact events on earth and other planetary bodies

imaging of fracture zones in the finnsjon area central sweden using the seismic reflection method in 1987 the swedish nuclear fuel and waste management co skb funded the shooting of a 1 7 km long high resolution seismic profile over the finnsjon study site using a 60 channel acquisition system with a shotpoint and geophone spacing of 10 m the site is located about 140 km north of stockholm and the host rocks are mainly granodioritic the main objective of the profile was to image a known fracture zone with high hydraulic conductivity dipping gently to the west at depths of 100 to 400 m the initial processing of the data failed to image this fracture zone however a steeply dipping reflector was imaged indicating the field data were of adequate quality and that the problem lay in the processing these data have now been reprocessed and a clear image of the gently dipping zone has been obtained in addition several other reflectors were imaged in the reprocessed section both gently and steeply dipping ones correlations with borehole data indicate that the origin of these reflections are also fracture zones the improvement over the previous processing is caused mainly by 1 refraction statics 2 choice of frequency band 3 f k filtering and 4 velocity analyses in addition to reprocessing the data some further analyses were done including simulation of acquisition using only the near offset channels channels 1 30 and the far offset channels channels 31 60 and determining the damping factor q in the upper few hundred meters based upon the amplitude decay of the first arrivals the data acquisition simulation shows the far offset contribution to be significant even for shallow reflectors in this area contrary to what may be expected a q value of 10 determined from observed amplitude decay rates agrees well with theoretical ones assuming plane wave propagation in an attenuating medium

potential pitfalls of crooked line seismic reflection surveys during the last few years the geological survey of canada has pioneered the application of seismic reflection profiling to mineral exploration in close collaboration with canadian mining companies and with the lithoprobe project e g spencer et al 1993 milkereit et al 1994 because of the rugged terrain in crystalline rock environments dahle et al 1985 spencer et al 1993 vibroseis seismic surveys are frequently conducted along existing roads resulting in extremely crooked survey profiles crooked profiling geometry coupled with the complex nature of the geological targets pose special challenges for seismic data processing and interpretation many common midpoint seismic processing techniques are based on an implicit assumption of a straight line survey and are most effective with uniform fold and even offset distribution within common midpoint cmp gathers however with crooked line acquisition the cmp gathers are characterized by variable fold and uneven offset distribution based

impact shocked zircons discovery of shock induced textures reflecting increasing degrees of shock metamorphism abstract textural effects specifically characteristic of shock metamorphism in zircons from impact environments have not been reported previously however planar deformation features pdf due to shock metamorphism are well documented in quartz and other mineral grains from these same environments an etching technique was developed that allows sem visualization of pdf and other probable shock induced textural features such as granular polycrystalline texture in zircons from a variety of impact shock environments these textural features in shocked zircons from k t boundary distal ejecta form a series related to increasing degrees of shock that should correlate with proportionate resetting of the u pb isotopic system

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

southern abitibi greenstone belt archean crustal structure from seismic reflection profiles lithoprobe seismic reflection profiles from the 2 75 2 68 ga southern abitibi greenstone belt reveal subhorizontal reflection zones of regional extent in the upper 15 km of crust that contrast with the steep dips of rock units and structures at the surface the shallowest 6 12 km regional subhorizontal reflection zone is interpreted to be the base of the abitibi greenstone belt supracrustal assemblage which may be an intrusive and or tectonic contact shallowly dipping subparallel reflectors in the upper crust are interpreted as low angle faults consistent with out of sequence stratigraphy revealed by u pb geochronology truncations of reflectors suggest that regional steeply dipping gold mineralized fault zones penetrate to depths of 15 km the profiles are consistent with the kapuskasing crustal model of the central superior province wherein greenstone belts are underlain by middle crustal felsic intrusions and gneiss and a lower crustal zone of mafic gneiss and intrusions the profiles support tectonic models of deformation of the abitibi greenstone belt that invoke either folding and thrusting followed by regional steep faulting or folding and thrusting linked to the steep faults

seismic reflection and borehole geophysical investigations in the matagami mining camp a high frequency vibroseis seismic survey was conducted by lithoprobe across a well known section of the matagami mining camp to assess the usefulness of seismic methods in lithological mapping the data have been reprocessed to enhance shallow reflections critical processing steps for the preservation of the shallow features include refraction static corrections cross dip corrections and first break mutes the seismic data were calibrated using geophysical logs from two boreholes adjacent to the profile physical rock property measurements suggest that strong reflectivity within the volcanic sequence occurs at rhyolite gabbro contacts the lower wabassee group a sequence of gabbros and basalts with interlayered rhyolite horizons has been identified as a seismic marker this reflective package overlays the horizon where most sulphide deposits are known to be located in the matagami mining camp seismic reflection methods can be used to map the deep volcanic stratigraphy and structures

in situ la icp ms trace elements analysis of magnetite the fenghuangshan cu fe au deposit tongling eastern china abstract the fenghuangshan deposit is a typical cu fe au skarn deposit in the tongling area anhui province eastern china the deposit has a paragenetic sequence of a prograde skarn stage followed by a retrograde skarn stage and a final quartz sulfide and carbonate stages magnetite in the fenghuangshan deposit mainly formed in the retrograde and carbonate stages according to the morphology of magnetite and mineral assemblage of ores we divided magnetite bearing ores into three groups group 1 early retrograde skarn stage is represented by a mineral assemblage of magnetite and chalcopyrite group 2 late retrograde skarn stage has a mineral assemblage of magnetite chalcopyrite and wollastonite with characteristic ring like magnetite group 3 carbonate stage is characterized by large amounts of calcite veins crosscut or associated with magnetite and intensive hematization of magnetite crosscut by the veins laser ablation la icp ms was used to determine trace element concentrations of magnetite from the three mineralization stages positive correlations among mg al ca and si in magnetite indicate that these lithophile elements have similar behavior during the skarn formation process calcium is an important discriminant element for magnetite in skarn deposits positive correlations are also evident for pb sn and w in magnetite which also indicates their similar behavior in general magnetite grains of different stages have similar normalized trace element patterns indicating that they share a common source however some elements such as co and mn in magnetite decrease from early retrograde skarn stage late retrograde skarn stage to carbonate stage which may be attributed to the precipitation of coexisting minerals sulfides and carbonates or the decreasing temperature magnetite grains of the retrograde stage have higher mg mn and si al contents than those of the carbonate stage indicating a decreasing degree of fluid rock interaction during the skarn formation process trace element data of skarn magnetite indicate a more widely compositional variation than previously suggested magnetite from the fenghuangshan cu fe au deposit has similar composition to those from other cu cu fe or cu polymetallic skarn deposits but different from those from fe skarn deposits such that magnetite composition is very powerful in establishing the origin of skarn deposits

zircons from the acraman impact melt rock south australia shock metamorphism u pb and 40ar 39ar systematics and implications for the isotopic dating of impact events abstract this study presents the first optical and scanning electron microscopic characterization and u pb shrimp dating results for zircon grains separated from the most likely autochthonous impact melt rock in the central domain of the large 40 90 km eroded ediacaran acraman impact structure in south australia microtextural characteristics define five zircon subtypes corresponding to different levels of progressive shock metamorphism from virtually unshocked monocrystalline zircon grains that exhibit original magmatic zoning in cathodoluminescence images to fully granular zircons that have completely lost their primary zoning pattern and locally contain neocrystallized submicrometer sized spots of zro 2 probably baddeleyite that pseudomorph pre impact zircon the granular zircons correspond to the highest observed level of shock metamorphism and impact induced recrystallization zro 2 bearing granular zircons indicate shock pressures in excess of 65 70 gpa which are considerably higher than previous shock pressure estimates for the acraman impactites u pb systematics of untreated and chemically abraded melt rock zircons indicate that u pb ratios of the acraman zircons were variably reset during impact weakly shocked crystalline grains yield ages on concordia at 1 59 1 60 ga reflecting the magmatic age of the gawler range volcanics only the entirely granular zircon population was apparently impact reset but based on an ediacaran age from stratigraphic constraints on the ejecta layer experienced significant post impact pb loss the microcrystalline nature of granular zircons could have promoted pb diffusion and recoil in post impact time as suggested by grain size dependent diffusion and recoil modeling a positive correlation of u concentration and shock level suggests that granularization might have preferentially occurred in initially u rich probably metamict zircons 40 ar 39 ar dating of a melted yardea dacite clast from the acraman melt rock as well as k feldspar separated from shocked yardea dacite resulted in post impact alteration plateau ages suggestive of hydrothermal events at 500 ma and 450 ma that selectively affected the impactites exposed in the central domain of the acraman impact structure our study demonstrates that the acraman impact is particularly difficult to date in the absence of accurate and precise isotopic ages for acraman the ediacaran ejecta stratigraphic age of 635 541 ma is considered the most reliable age constraint currently available for the timing of the large acraman impact

thermal anomalies beneath the australian antarctic discordance abstract significant variations in shear wave velocity along the southeast indian ridge are delineated by ss s differential travel times the australian antarctic discordance shows ss s residuals that are 3 8 s faster than the adjoining segments 1500 2000 km away the large variability suggests that thermal structure in the upper mantle as opposed to crustal structure is the major cause of the velocity anomaly to quantify this inference we invert both geoid and topography into temperature perturbations beneath the ridge within specific depth extents assuming that the thermal sources and the geophysical observations are dynamically related in a viscous earth the joint inversion of these two sets of data is robust demanding a negative temperature anomaly of 80 and 250 c beneath the discordance for layers extending from the surface to depths of 300 and 100 km respectively in a forward sense the temperature so constrained predicts well the trend of the along axis variations in ss s residuals but with a smaller amplitude especially for the 8 s contrast between the discordance and the eastern end of the ridge where unusually high residuals sample a broad shallow region of ridge segments considering the proximity of the ss bounce points to the ridge axis and the possibility of sampling a partial melt zone the discrepancy in magnitude may be partially reconciled by deducting a presumed 2 3 s melt effect from the high residuals in the eastern end the resolved thermal perturbations drive asthenospheric flow along the ridge the flow converging and descending in the vicinity of the discordance this simple thermal viscous flow fmodel is consistent with the idea of pipe flow for the southeast indian ridge the source of the pipe flow may be the mantle plumes at the two ends of the ridge

application of multivariate statistical methods to indicate the origin and geochemical behavior of potentially hazardous elements in sediment around the sarcheshmeh copper mine se iran multivariate statistical techniques i e correlation coefficient analysis principal components analysis pca and hierarchical cluster analysis ca were applied to the total and water soluble concentrations of potentially hazardous metals in sediments associated with the sarcheshmeh mine one of the largest oligo miocene porphyry copper deposits in the world the samples were analyzed for hazardous metal concentration levels by inductively coupled plasma mass spectrometry method results indicate that the contaminant metals as cd cu mo s sb sn se pb and zn were positively correlated with the total concentrations these hazardous metals also have strong association in the pca and ca results different anthropic versus natural sources of contaminant metals were distinguished by using ca method water soluble fraction of hazardous metals showed that the hydro geochemical behavior of these metals in sediments is different considerably elements such as cd co cr cu fe mn ni s and zn are readily water soluble from contaminated samples especially from evaporative mineral phases while the release of as mo sb and pb into the water is limited by adsorption processes results obtained from the application of multivariate techniques on the water soluble fraction data set show that the hazardous metals are categorized into three groups including 1 ni s co cu cr and fe 2 se mn cd and zn and 3 sb as mo and sn this classification describes the hydro geochemical behavior of hazardous metals in water sediment environments of the sarcheshmeh porphyry copper mine and can be used as a basis in remedial and treatment strategies

deep structure of an archaean greenstone terrane more than half of the continental crust was formed before about 2 500 million years ago1 yet there is still considerable uncertainty regarding the structure and evolution of the ancient archaean cratons2 7 modern analogues proposed for the setting of archaean greenstone belts include aborted intra cratonic rifts continental margins and various oceanic settings2 7 alternatively archaean tectonics may have been quite different from the plate tectonics we see today2 4 6 the abitibi belt in canada is the largest archaean greenstone ternane3 and has been a touchstone for many models because its surface geology is relatively well known8 10 it contains significant gold and base metal deposits10 and it is less deformed and has suffered less erosion than most archaean ter ranes here we present deep seismic reflection data from part of the abitibi belt which reveal extensive subhorizontal and gently dipping reflection zones truncated by steeply inclined discontinuities which project to major fault zones at the surface our preliminary model of the abitibi belt comprises a mostly juvenile magmatic crust similar to that exposed in the nearby kapuskasing uplift11 12 dissected and imbricated by deep penetrating discontinuities associated with thrust and strike slipe faulting in view of the similarity of greenstone belts worldwide2 7 13 our seismic sections provide new constraints on the general processes that have affected archaean metavolcanic terranes

dating the cooling of exhumed central uplifts of impact structures by the u th he method a case study at manicouagan abstract forty titanite grain fragments from 9 central uplift samples of metamorphosed anorthosite from the manicouagan impact structure were dated by the u th he technique a u th he central age of 207 1 6 4 ma 2 standard error se n 40 has been determined with 4 outlier ages removed the central age is refined to 208 9 5 1 ma 2 se both of these ages are within error of the previously determined u pb zircon age of 214 1 ma 2 derived from the impact melt manicouagan s central uplift formed due to rapid elevation from 7 10 km depth as part of the modification stage of the impact process which has facilitated the dating of its emplacement due to resulting rapid exhumation and cooling and closure of the u th he system in titanite correlation with the previous u pb zircon 214 1 ma impact melt crystallization age indicates that the u th he titanite dating technique offers a new approach to dating complex impact structures in the absence of viable melt sheets or other melt products the youngest ca 195 ma u th he dates preserved in some titanite fragments are synchronous with early jurassic rift induced lithospheric thinning and associated igneous activity that defines the central atlantic magmatic province camp the u th he titanite data from manicouagan indicate that the influence of this regional event may extend west of the previously proposed limit of camp activity

tectonic and metallogenic implications of regional seismic profiles in the timmins mining camp four regional seismic reflection profiles totalling 153 line km were acquired near timmins ontario within the southern abitibi greenstone belt five additional high resolution lines targeted specific metallogenically important features such as the porcupine destor deformation zone interpretation of these profiles individually and in a composite north south transect reveals a number of prominent bands of reflectors within the upper 15 km of the crust that define a series of folds or antiformal stacks of thrust nappes structures and stratigraphy mapped at the surface confirm structural culminations in these locations at depths greater than 10 km the reflectors have generally shallower dips implying broad folding major ore deposits such as those at the kidd creek hollinger mcintyre and dome mines are located on the northern steeply dipping limbs of these antiformal stacks implying that the fold structures focused post tectonic mineralizing fluids within the upper crust into the near surface the porcupine destor deformation zone is proximal to the large gold deposits near timmins and is revealed by the new seismic data to be a composite of early fold structures and late transpressive fault arrays

mapping of crustal scale tectonic boundaries in the ossa morena zone using reprocessed iberseis reflection seismic data the iberseis deep seismic reflection profile imaged crustal scale structures in the sw iberian variscan belt crossing the south portuguese zone the ossa morena zone and the central iberian zone in spain two subsets of the profile corresponding to the south portuguese zone ossa morena zone and the ossa morena zone central iberian zone tectonic contacts have been reprocessed with the aim of investigating the influence of cross dip and to better image steeply dipping features alternative strategies for binning midpoints into common depth point cdp bins using different azimuths were examined for synthetic data we show that the choice of the cdp processing line and the bin azimuth orientation has a significant impact on the normal moveout and dip moveout velocities and is crucial to optimizing the quality of the stacked seismic image along the crooked profile multi azimuth binning normal moveout dip moveout and migration velocity analysis on synthetic and real data show the presence of clear sub vertical upper crustal structures near the south portuguese zone ossa morena zone suture the aroche fault this sub vertical reflectivity that was not imaged earlier projects into a location in the lower crust with low reflectivity

high resolution reflection seismic imaging of the ullared deformation zone southern sweden the ullared deformation zone udz is one of a few structures worldwide known to contain decompressed eclogite facies rocks of precambrian age given the unique nature of the ullared eclogites a 1

high temperature 350 c thermochronology and mechanisms of pb loss in apatite abstract natural processes driven by heat flow can be understood using quantitative reconstruction of the thermal history of accessory and common minerals that were formed or modified in these processes thermochronology assumes that isotopes are lost from minerals by thermally activated volume diffusion and forms the basis of many studies of the thermal evolution of the crust however some studies challenge this assumption and suggest that the mechanisms controlling isotope transport in minerals over geological time scales are dominated by aqueous fluid flow within mineral pathways here we test these contrasting hypotheses by inverse modelling apatite uranium lead u pb dates to produce theoretical t t solutions assuming pb was lost by volume diffusion these solutions are compared with independent geological constraints and intra grain apatite u pb dates which demonstrate that volume diffusion governed the displacement of pb this confirmation combined with an inverse modeling procedure that permits reheating and cooling paths to be distinguished between 375 and 570 c provides geologists with a unique tool for investigating the high temperature thermal evolution of accessory minerals using the u pb method

high resolution 2d seismic imaging and forward modeling of a polymetallic sulfide deposit at garpenberg central sweden we acquired a high resolution 2d seismic profile to test the capability of the seismic method in imaging a sulfide ore body at garpenberg central sweden delineation of the geologic structures wh

integrated geological and geophysical studies in the sg4 borehole area tagil volcanic arc middle urals location of seismic reflectors and source of the reflectivity near vertical incidence reflection seismic data acquired in the tagil volcanic arc middle urals show the upper crust to be highly reflective two intersecting seismic lines located near the ongoing 5400 m deep sg4 borehole show that the main reflectivity strikes approximately n s and dips 35 55 to the east prominent reflections intercept the borehole at 1000 1500 2800 2900 3400 and between 4000 and 5400 m which correspond to intervals of low velocity low density low resistivity the surface projections of these reflections lie parallel to the strike of magnetic anomaly trends multioffset vertical seismic profile vsp data acquired in the sg4 borehole show a seismic response dominated by p to s reflected converted waves from the moderately east dipping reflectivity and from a set of very steep east dipping reflectors not imaged by the surface data modeling of the vsp data constrains the depth at which reflectors intercept the borehole and suggests that the p to s conversions are best explained by low velocity porous intervals rather than higher velocity mafic material the most prominent east dipping reflection on the surface seismic data is only imaged on vsp shots that sample the crust closer to the e w seismic line this discrepancy between the vsp and the surface seismic data is attributed to rapid lateral changes in the physical properties of the reflector surface and borehole data suggest that the low velocity low density low resistivity intervals are the most important source of reflectivity in the sg4 borehole area although lithological contrasts may also play a role drill cores from the these zones contain hydrothermal alteration minerals indicating interaction with fluids tectonic criteria suggest that they might represent imbricated fracture zones often bounding different lithologies and or intrusions some of them might also represent high porosity lava flows or pyroclastic units common in island arc environments

reflection seismic investigations in the dannemora area central sweden insights into the geometry of polyphase deformation zones and magnetite skarn deposits the bergslagen region is one of the most ore prospective districts in sweden presented here are results from two nearly 25 km long reflection seismic profiles crossing this region in the dannemora

experimental hydrothermal alteration of partially metamict zircon we present the results of a series of hydrothermal experiments on grains from two partially metamict zircon samples from sri lanka in the temperature range 350 to 650 c and with different solutions 2 m alcl 3 2 m cacl 2 pure h 2 o and a multi cation solution under these conditions sharply bounded reaction fronts penetrated into the zircon grains and developed complex lobate and rim structures that resemble structures found in natural zircon systems the reaction zones are characterized by a marked increase in the cathodoluminescence intensity a decrease of the back scattered electron emission and an increased degree of structural order as revealed by micro raman and infrared spectroscopy sensitive high resolution ion microprobe and electron microprobe measurements revealed that the altered areas gained solvent cations e g ca 2 ba 2 mg 2 al 3 from the solution and lost variable amounts of zr si hf the ree u th as well as radiogenic pb a comparison between dry and hydrothermal annealing trends shows that the kinetics of structural recovery including recrystallization of the amorphous phase in metamict zircon is strongly enhanced under hydrothermal conditions this finding suggests that water catalyzes structural recovery processes in metamict zircon we found that the structure of the reacted areas does not resemble that of crystalline zircon i e is still characterized by a temperature dependent degree of disorder which would not be expected if the reaction is controlled by a coupled dissolution and re precipitation process instead the alteration process can be described best by a diffusion reaction recrystallization model in this model it is postulated that the diffusion of water into the metamict structure is the driving force for moving recrystallization fronts we found that the rate and the extent of solid state recrystallization of the amorphous phase is an important factor in determining the mobility of trace elements this interpretation is indicated by the observation that trace elements including u and th were preferentially lost during the reaction with a fluid at low temperatures where recrystallization of the amorphous material was slow or not activated at all the observed chemical alteration patterns are believed to reflect a competition between the kinetics of long range diffusion and ion exchange and the kinetics of the short range diffusion necessary for the recrystallization process

spatial modelling of hazardous elements at waste dumps using geostatistical approach a case study sarcheshmeh copper mine iran mining activities and resulting wastes can be considered as one of the most important sources of hazardous elements in the environment knowledge of the spatial distribution of toxic elements in waste dump systems is necessary to assess environmental hazard and strategy to achieve this goal this paper investigates spatial distribution of toxic elements using statistical and geostatistical analysis a total of 58 soil samples were collected and the amount of as cd co cr cu mn mo ni pb and zn was then determined at sarcheshmeh copper mine waste dumps in order to evaluate the presence of multivariate outliers mahalanobis distance technique d 2 was applied and the multivariate outlier samples were removed this resulted in an increase in correlation coefficient to reduce dimension of data set principal component analysis was applied and four principal components were determined which indicate 83 463 of the total variance of data set estimated pcs together with the toxic elements maps based on the ordinary kriging display aggregation of toxic elements in some parts and validity of predictions was evaluated using the leave one out cross validation method the regression coefficients of estimated and observed values presented the reliability of the kriging estimates sequential gaussian simulation method was applied for principal components due to similar results of estimated principal components and toxic elements the results of simulation maps are almost identical to estimated outcomes

in situ multiphase u pb geochronology and shock analysis of apatite titanite and zircon from the lac la moinerie impact structure canada in situ u pb geochronology has been performed via laser ablation inductively coupled mass spectrometry on shocked apatite titanite and zircon from the 8 km diameter lac la moinerie impact structure canada the three analyzed phases are inherited from target rocks that were transformed to impact melt bearing breccias and clast laden impact melts apatite yields an array of u pb ratios populating a region between a younger regression with a refined age of 453 5 ma and an older regression with a lower intercept age of 1708 10 ma titanite defines a younger regression with an age of 444 15 ma and an older array with a lower intercept at 1844 24 ma zircon yields an upper intercept age of 1810 13 ma and a lower intercept age of 433 21 ma within error of apatite and titanite the oldest ages from all three phases define paleoproterozoic igneous metamorphic events in granitoid target rocks of the de pas suite isotopic resetting in apatite and titanite with relatively high pb diffusion rates was controlled by a combination of proximity to impact generated superheated melt and the formation of fast diffusion pathways facilitated by shock effects and dynamic recrystallization zircon resetting was controlled by shock effects and metamictization which resulted in significant pb loss we outline an approach for discriminating true impact ages from metamict zircons with high common pb that have experienced post impact pb loss lower intercept ages of all phases constrain the age of formation for the lac la moinerie impact structure with apatite yielding the most precise age of 453 5 ma with an age of 453 ma lac la moinerie joins a growing cluster of more than 12 terrestrial impact structures formed in the middle to late ordovician with potential connection to the l chondrite parent body breakup event and a period of enhanced bombardment on earth

prestack and poststack migration of crooked line seismic reflection data a case study from the south portuguese zone fold belt southwestern iberia crooked line 2d seismic reflection survey geometries violate underlying assumptions of 2d imaging routines affecting our ability to resolve the subsurface reliably we compare three crooked line

3d seismic imaging of volcanogenic massive sulfide deposits in the flin flon mining camp canada part 1 seismic results abstracta 17 km2 3d 3c seismic survey was conducted within the active flin flon mining camp located in manitoba canada the results for the vertical component data as obtained by conventional dip moveout and prestack time migration processing sequences and comparison of images from the 3d seismic volume with the subsurface location of known ore zones and the mine horizon generally showed a very good correlation a well defined diffraction response from the shallowest ore zone was observed in the unmigrated data with a corresponding phase reversal in the migrated data at the transition from intact ore to backfilled ore zone the geometry of unmined and backfilled ore zones compared well with strong reflection amplitudes on corresponding cross sections to depths of 1000 m at greater depths the ore zone had a weaker seismic signature due to a combination of effects including imaging conditions ore composition and the increased presence of rhyolite within the mine horizon in the case of the deeper or

initiation development and benefits of lithoprobe shaping the direction of earth science research in canada and beyondthis article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent lithoprobe contribution 1480 lithoprobe is canada s national collaborative multidisciplinary earth science research project established to develop a comprehensive understanding of the evolution of northern north america it is regarded internationally as one of the most successful national geoscience projects ever undertaken part of lithoprobe s success derives from its history and organizational structure a one year phase i program 1984 1985 was highly successful phases ii to v carried the project forward until 2005 when funding terminated lithoprobe was organized as a decentralized research network of multidisciplinary scientific studies and collaborating scientists about 1500 scientific publications were generated lithoprobe s legacy also includes economic and social benefits new and improved understanding of earth history provides petroleum and mining companies with an enhanced knowledge base lithoprobe demonstrated the applicability of high resolution seismic reflection studies to mineral exploration development of a portable seismic refraction recorder and a long period magnetotelluric system led to technology transfer to canadian companies very high resolution seismic reflection studies applied first by lithoprobe are proving effective for exploration for uranium deposits in saskatchewan in the cratonic areas of canada lithoprobe seismic and magnetotelluric studies have provided significant new information relevant to exploration for diamonds on the west coast of canada lithoprobe studies provided data and a framework for better understanding the mega thrust earthquake hazard in the region lithoprobe established a highly effective public outreach strategy that involved the print and electronic media as well as material for educational purposes unequivocally lithoprobe has enhanced the already strong reputation of the earth sciences in canada

enhancing base metal exploration with seismic imaging commencing in 1988 and continuing for 5 years lithoprobe acquired a series of high resolution seismic experiments within and near base metal mining camps in canada including the abitibi subprovince of quebec and ontario the world class sudbury ni cu mining district the buchans mine in newfoundland and the thompson ni belt in manitoba this work undertaken in close cooperation with the geological survey of canada and major canadian mining companies stimulated an intensive and broadened series of followup studies with the common objective of assessing potential applications of multichannel seismic mcs imaging for deep mineral exploration and mine development this research was motivated by a widely recognized disparity between the depths from which ores can be profitably mined up to 2 km or more and the resolving depths typically 500 m of commonly used geophysical methods for mineral exploration initial rock property studies established that the expected contrast in acoustic impedance between

mineralogical and geochemical spatial analyses of a waste rock dump at the libiola fe cu sulphide mine eastern liguria italy in this work we investigated a 3 ha sulphide bearing waste rock dump libiola mine italy using mineralogical geochemical and geostatistical analyses the dumped materials were highly heterogeneous in grain size and lithology and varied both laterally and vertically other than the host rock of the ore basalts and serpentinites the dumped materials contained high amounts of low grade chalcopyrite and pyrite rich mineralisations due to these characteristics and to the absence of minerals able to neutralise acidity this waste rock dump can be classified as an acid mine drainage amd producer the study confirms that amd is still active and in the best scenario can persist for up to 6 17 103 years the consequences of this process are of serious environmental concern as it involves strong acidification of the circulating waters the release of potentially toxic metals into the soil streams and rivers and the precipitation of huge quantities of secondary fe oxides and fe oxyhydroxides

routine low damage apatite u pb dating using laser ablation multicollector icpms 1 apatite is a common u bearing accessory mineral with a u pb closure temperature of 500 c making u pb dating of apatite a potentially valuable thermochronometer however its low u concentration and tendency to incorporate common lead has limited widespread application to destructive isotope dilution methods we overcome previous limitations by using a nu plasma multicollector icpms with an attached short pulse excimer laser and by identifying two new matrix matched reference apatites to correct for elemental fractionation gem quality 485 myr old apatite from madagascar which we independently characterized by id tims analysis and 523 5 ma apatite from the mcclure mountain syenite source of the40ar 39ar reference mmhb common pb is corrected using measured 204pb isobarically corrected for hg interference and a five step iterative process using stacey and kramers common pb model we accurately reproduce ages of numerous independently characterized apatites regularly achieving precision of 2 2 by pooling as few as five 30 m spot analyses data quality in apatite with low u concentrations low 206pb 204pb values 30 and young ages 75 ma is compromised by the goal of avoiding significant grain damage such limitations can be overcome by using spot sizes 65 m or greater but at the expense of substantial grain damage for single detrital apatite grains with ages of 500 ma precision of 4 2 was achieved by pooling 2 to 3 spots per grain the accuracy of our detrital results is supported by a good age match with similar closure temperature 40ar 39ar detrital hornblende ages from the same sediment

transformations to granular zircon revealed twinning reidite and zro2 in shocked zircon from meteor crater arizona usa granular zircon in impact environments has long been recognized but remains poorly understood due to lack of experimental data to identify mechanisms involved in its genesis meteor crater in arizona usa contains abundant evidence of shock metamorphism including shocked quartz the high pressure polymorphs coesite and stishovite diaplectic sio2 glass and lechatelierite fused sio2 here we report the presence of granular zircon a new shocked mineral discovery at meteor crater that preserve critical orientation evidence of specific transformations that occurred during formation at extreme impact conditions the zircon grains occur as aggregates of sub micrometer neoblasts in highly shocked coconino sandstone cs comprised of lechatelierite electron backscatter diffraction shows that each grain consists of multiple domains some with boundaries disoriented by 65 around a known 112 shock twin orientation other domains have 001 in alignment with 110 of neighboring domains consistent with the former presence of the high pressure zrsio4 polymorph reidite additionally nearly all zircon preserve zro2 sio2 providing evidence of partial dissociation the genesis of cs granular zircon started with detrital zircon that experienced shock twinning and reidite formation at pressures from 20 to 30 gpa ultimately yielding a phase that retained crystallographic memory this phase subsequently recrystallized to systematically oriented zircon neoblasts and in some areas partially dissociated to zro2 the lechatelierite matrix experimentally constrained to form at 2000 c provided the ultrahigh temperature environment for zircon dissociation 1670 c and neoblast formation the capacity of granular zircon to preserve a cumulative pressure temperature record has not been recognized previously and provides a new method for investigating histories of impact related mineral transformations in the crust at conditions far beyond those at which most rocks melt

u pb geochronology of apatite and zircon from the brent impact structure canada a late ordovician sandbian katian boundary event associated with l chondrite parent body disruption in situ la icp ms u pb geochronology has been performed on apatite and zircon within thermally recrystallized clast laden and clast poor impact melt rocks from the brent impact structure a total of 377 laser analyses on 120 impact melt grown n 9 and impact recrystallized zircon grains n 111 were obtained from which a concordia age of 452 8 2 7 ma mswd 0 57 n 11 and a weighted average mean 206pb 238u age of 453 2 2 9 ma mswd 0 60 n 11 are calculated a total of 300 laser analyses from 100 relict apatite grains were obtained with an unanchored regression through all data yielding a lower intercept age of 453 2 6 0 ma mswd 5 8 n 300 that overlaps within error of zircon 207pb 206pb ratios obtained from feldspar clasts within clast laden impact melt retain the same initial pb composition as the target rocks from which they are derived while feldspars that crystallized from impact melt have 207pb 206pb ratios indicative of isotopic re equilibration between basement lithologies of two different ages a similar variability in 207pb 206pb is recorded by apatite this provides evidence for the involvement of neoproterozoic lake nipissing alkaline suite as well as mesoproterozoic grenville gneisses in the production of impact melt at brent recrystallized apatite grains exhibit enrichments in light rare earth elements lrees along neoblast grain boundaries indicative of trace element substitution and phase precipitation during impact induced recrystallization an age of 452 8 2 7 ma from zircon and 453 2 6 0 ma from apatite places the impact event in the late ordovician at or near the sandbian katian boundary confirming brent s involvement in the middle to late ordovician crater cluster event a period of enhanced impactor flux to earth related to the l chondrite parent body disruption

3d imaging challenges in steeply dipping mining structures new lights on acquisition geometry and processing from the brunswick no 6 seismic data canada we have analyzed and processed a 38 km 2 nonorthogonal 3d surface reflection seismic data in the brunswick no 6 area to better understand the effect of acquisition geometry on the resultant image

in situ la icp ms apatite and zircon u pb geochronology of the nicholson lake impact structure canada shock and related thermal effects abstract in situ laser ablation inductively coupled plasma mass spectrometry la icp ms has been deployed to determine the u pb ages of impact metamorphosed apatite and zircon associated with the 12 5 km diameter nicholson lake impact structure northwest territories canada the dated phases occur within both impact melt bearing breccias and clast laden impact melts a total of 84 laser ablation analyses from 57 apatite grains within seven rock samples yield a minimum refined lower intercept at 387 5 ma mswd 0 87 2 n 26 and maximum age with lower intercept of 1740 ma a total of 90 laser ablation analyses on 52 zircon grains from two rock samples yield a minimum intercept age of 384 8 ma mswd 1 3 2 n 22 with a maximum upper intercept age of 2679 14 ma and a second discordia with a 1740 ma upper intercept age the results are consistent with the target rocks comprising archean snow island suite 2 7 ga and paleoproterozoic nueltin plutonic suite 1 74 ga with the impact event occurring at approximately 385 ma the degree of resetting of inherited apatite can be related to its proximity to impact melt now partly devitrified glass within the host impact melt bearing breccias and clast laden impact melt rocks those grains in direct contact with melt bodies are reset while those occurring as inclusions in lithic or mineral clasts partly or wholly retain their original isotopic compositions the youngest impact reset apatite ages are most closely associated with the highest shock levels i e granular textured and thermally dissociated zircons which we relate to juxtaposition of apatite with superheated melt due to accumulated radiation damage prior to impact many of the relic zircons are metamict which facilitated enhanced pb diffusion and their resetting to the impact age granular zircons record impact ages while those exhibiting planar fractures or experiencing negligible shock record basement ages we link apatite and zircon geochronology to the textural and structural states of zrsio4 and its associated shock levels via field emission scanning electron microscopy and micro raman spectrometry

seismic reflection imaging over a massive sulfide deposit at the matagami mining camp quebec a 2 d seismic reflection profile was shot across the southern flank of the matagami mining camp almost directly above the recently discovered bell allard massive sulfide deposit now estimated at more than 6 million metric tons all orebodies found in the southern part of the mining camp including bell allard are located at the contact between the primarily basaltic wabassee group and the underlying rhyolitic watson lake group seismic reflections were recorded from the basalt rhyolite contacts of the lower wabassee group as well as from gabbro sills that intrude much of the volcanic stratigraphy a strong reflection from the top of the bell allard orebody was also detected but the reflection does not extend over the full width of the deposit as defined by drilling appearing to correlate with the lower pyrite rich zone faulting which can be interpreted from discontinuities in the observed reflections probably controlled the formation of the bell allard deposit if the interpreted gabbro sills are accepted as isotime markers then faulting of the deeper sill complex defines a series of half grabens within the rhyolitic watson lake group the bell allard deposit is found at the intersection of one of these apparently low angle normal faults with the top of the watson lake group indicating that sulfide mineralization may have been associated with fluid flow along the fault which likely penetrates to the underlying mafic intrusion although the precise geometry of subsurface faulting cannot be estimated from a single 2 d seismic profile these results indicate that a full 3 d seismic survey should allow the mapping of many of the subsurface fault systems and the verification of hypotheses of fault controlled deposit formation

seismic imaging of massive sulfide deposits part ii reflection seismic profiling seismic reflection profiling the dominant geophysical method for hydrocarbon exploration has the potential to provide images of regional structure for mineral exploration in the crystalline crust and direct detection of large massive sulfide orebodies previous tests of traditional seismic methods in hard rock environments have had mixed success based on these earlier results we have tailored acquisition and processing strategies to conditions in the canadian shield we illustrate these methods using an example from the sudbury basin a rich mineral producing region because of structural complexity that complicates interpretation of the seismic images the seismic data are integrated with detailed three dimensional forward modeling based on physical properties studies mine geology and well logging through this integrated approach we show that massive sulfides can produce a characteristic seismic reflection response and that surface seismic reflection profiling may be used to detect and delineate deep large massive sulfide deposits accurately in a complex geologic setting characterized by moderate dips

petrology and geochronology of paleoproterozoic intrusive rocks kiggavik uranium camp nunavut we investigated the age and petrology of paleoproterozoic granitic intrusions in the area of the kiggavik uranium exploration camp near the southeast margin of the aberdeen subbasin of the thelon basin a subset of these intrusions e g the lone gull stock is spatially associated with and mineralized by basement hosted unconformity related uranium deposits surface outcrop samples have field relations textures and compositions consistent with hudson suite granitoids and mixtures of monzogranite with minette we obtained u pb zircon ages ranging from ca 1818 to 1840 ma within the known range of the hudson suite and cogenetic minettes of the baker lake group 1 80 1 84 ga core samples of granitic rocks adjacent to mineralized zones are more complex and indicate an influence from the younger nueltin granite kivalliq igneous suite ca 1 77 1 73 ga one sample from the lone gull stock contains two zircon populations in texturally distinctive domains one at 1806 41 ma and the other at 1748

seismic methods in mineral exploration and mine planning a general overview of past and present case histories and a look into the future abstractdue to high metal prices and increased difficulties in finding shallower deposits the exploration for and exploitation of mineral resources is expected to move to greater depths consequently seismic methods will become a more important tool to help unravel structures hosting mineral deposits at great depth for mine planning and exploration these methods also can be used with varying degrees of success to directly target mineral deposits at depth we review important contributions that have been made in developing these techniques for the mining industry with focus on four main regions australia europe canada and south africa a wide range of case studies are covered including some that are published in the special issue accompanying this article from surface to borehole seismic methods as well as petrophysical data and seismic modeling of mineral deposits at present high resolution 2d surveys mostly are performed in mining areas but there is a general increasing trend in the use of 3

shocked monazite chronometry integrating microstructural and in situ isotopic age data for determining precise impact ages monazite is a robust geochronometer and occurs in a wide range of rock types monazite also records shock deformation from meteorite impact but the effects of impact related microstructures on the u th pb systematics remain poorly constrained we have therefore analyzed shock deformed monazite grains from the central uplift of the vredefort impact structure south africa and impact melt from the araguainha impact structure brazil using electron backscatter diffraction electron microprobe elemental mapping and secondary ion mass spectrometry sims crystallographic orientation mapping of monazite grains from both impact structures reveals a similar combination of crystal plastic deformation features including shock twins planar deformation bands and neoblasts shock twins were documented in up to four different orientations within individual monazite grains occurring as compound and or type one twins in 001 100 left 10 bar 1 right 110 left 212 right and type two irrational twin planes with rational shear directions in 0 bar 1 bar 1 and bar 1 bar 1 0 sims u th pb analyses of the plastically deformed parent domains reveal discordant age arrays where discordance scales with increasing plastic strain the correlation between discordance and strain is likely a result of the formation of fast diffusion pathways during the shock event neoblasts in granular monazite domains are strain free having grown during the impact events via consumption of strained parent grains neoblastic monazite from the inlandsee leucogranofels at vredefort records a 207pb 206pb age of 2010 15 ma 2 n 9 consistent with previous impact age estimates of 2020 ma neoblastic monazite from araguainha impact melt yield a concordia age of 259 5 ma 2 n 7 which is consistent with previous impact age estimates of 255 3 ma our results demonstrate that targeting discrete microstructural domains in shocked monazite as identified through orientation mapping for in situ u th pb analysis can date impact related deformation monazite is therefore one of the few high temperature geochronometers that can be used for accurate and precise dating of meteorite impacts

3d reflection seismic imaging at the 2 5 km deep cosc 1 scientific borehole central scandinavian caledonides the 2 5 km deep scientific cosc 1 borehole icdp 5054 1 a was successfully drilled with nearly complete core recovery during spring and summer of 2014 downhole and on core measurements through th

deep geometry of the sudbury structure from seismic reflection profiling seismic reflection data show the deep geometry of the sudbury structure to be markedly asymmetric the sudbury north range comprises shallowly south dipping sedimentary strata overlying a thick unit of heterolithic breccia and melt bodies layered rocks of the sudbury igneous complex and footwall gneiss reflections from the upper layers are interrupted by faults near the center of the sudbury basin whereas the basal mafic units and footwall gneiss continue dipping southward and appear to be tightly folded or truncated near the creighton fault in contrast the seismic image of the south range is dominated by a distinctive series of moderately south dipping reflections interpreted as thrust faults or shear zones on which severe telescoping and imbrication of lithological units and considerable northwest southeast shortening of the sudbury structure have occurred such shortening explains the noncircular shape of the structure and thus removes a critical objection to the sudbury impact crater hypothesis the new structural model is shown to be consistent with regional magnetic and gravity fields a large hidden ultramfic mafic mass is no longer required to explain the potential field data

resolution of impact related microstructures in lunar zircon a shock deformation mechanism map abstract the microstructures of lunar zircon grains from breccia samples 72215 73215 73235 and 76295 collected during the apollo 17 mission have been characterized via optical microscopy cathodoluminescence imaging and electron backscatter diffraction mapping these zircon grains preserve deformation microstructures that show a wide range in style and complexity planar deformation features pdfs are documented in lunar zircon for the first time and occur along 001 110 and 112 typically with 0 1 25 m spacing the widest pdfs associated with 112 contain microtwin lamellae with 65 misorientation relationships deformation bands parallel to 100 planes and irregular low angle misorientation axes this geometry is consistent with a dislocation glide system with 010 during dislocation creep nonplanar fractures recrystallized domains with sharp irregular interfaces and localized annealing textures along fractures are also observed no occurrences of reidite were detected shock deformation microstructures in zircon are explained in terms of elastic anisotropy of zircon pdfs form along a limited number of specific hkl planes that are perpendicular to directions of high young s modulus suggesting that pdfs are likely to be planes of longitudinal lattice damage twinned 112 pdfs also contain directions of high shear modulus a conceptual model is proposed for the development of different deformation microstructures during an impact event this shock deformation mechanism map is used to explain the relative timing conditions and complexity relationships between impact related deformation microstructures in zircon

seismic reflection profiles across the mine series in the noranda camp of the abitibi belt eastern canada the abitibi grenville lithoprobe project completed a regional line 21 and a high resolution line 21 1 seismic survey in the noranda central volcanic complex of the blake river group abitibi quebec line 21 provides a regional framework in which the archean crust is divided into three layers two of which are discussed here the uppermost layer which corresponds to the blake river group is the least reflective and lies above 4 s 12 km and the mid crustal layer which is composed of a complex pattern of generally east northeast dipping reflectors and lies between 4 and 8 s within the regional data the mine series of the central volcanic complex is imaged as a semitransparent series of reflectors overlying a highly reflective east facing structure interpreted as the subvolcanic flavrian pluton the high resolution data line 21 1 were collected in the vicinity of the ansil mine the seismic images in this region can be controlled by surface geology and extensive drill hole data and the projec

lead diffusion in apatite and zircon using ion implantation and rutherford backscattering techniques abstract ion implantation was used to introduce pb into the minerals zircon and apatite diffusion profiles were obtained using rutherford backscattering and the results were fitted with a model to determine the diffusion coefficients this approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times results for apatite over the temperature range 600 900 c are in good agreement with earlier results obtained for higher temperatures watson et al 1985 and are described by the following arrhenius law d 1 27 10 4 cm 2 s 1 exp 54 6 1 7 kcl mol 1 rt this suggests that radiation damage induced by ion implantation has little effect on pb diffusion in this case due to rapid annealing of induced damage at low temperatures the activation energy stated above is somewhat smaller than that previously determined 70 kcal mol 1 reflecting the larger range in 1 t sampled by the present results closure temperatures calculated with these diffusion parameters are in good agreement with those inferred from geochronologic data diffusion coefficients for pb in zircon determined in this study are greater than those obtained from a single experimental measurement and estimates of pb diffusion based on geochronologic data and u pb zoning in natural zircons the differing results for zircon and apatite obtained in this study appear to be related to each mineral s ability to anneal the radiation damage induced by ion implantation

shock metamorphosed zircon in terrestrial impact craters to ascertain the progressive stages of shock metamorphism of zircon samples from three well studied impact craters were analyzed by optical microscopy scanning electron microscopy sem and raman spectroscopy in thin section and grain separates these samples are comprised of well preserved rapidly quenched impactites from the ries crater germany strongly annealed impactites from the popigai crater siberia and altered variably quenched impactites from the chicxulub crater mexico the natural samples were compared with samples of experimentally shock metamorphosed zircon below 20 gpa zircon exhibits no distinct shock features above 20 gpa optically resolvable planar microstructures occur together with the high pressure polymorph reidite which was only retained in the ries samples decomposition of zircon to zro2 only occurs in shock stage iv melt fragments that were rapidly quenched this is not only a result of post shock temperatures in excess of 1700 c but could also be shock pressure induced which is indicated by possible relics of a high pressure polymorph of zro2 however zro2 was found to revert to zircon with a granular texture during devitrification of impact melts other granular textures represent recrystallized amorphous zrsio4 and reidite that reverted to zircon this requires annealing temperatures 1100 c a systematic study of zircons from a continuous impactite sequence of the chicxulub impact structure yields implications for the post shock temperature history of suevite like rocks until cooling below 600 c

evolution of the southern abitibi greenstone belt based on u pb geochronology autochthonous volcanic construction followed by plutonism regional deformation and sedimentation abstract new mapping and u pb zircon geochronological results in the southern abitibi greenstone belt sagb support an autochthonous regional stratigraphy comprised of nine supracrustal assemblages rather than the collage of allochthonous terranes proposed in recent publications based on lithological and geochronological criteria these supracrustal assemblages also encompass the swayze shining tree and montcalm greenstone belts indicating that despite separation by large granitic intrusions they are in fact part of one extensive greenstone belt in conjunction with the mapping the geochronological results support coherent upward facing stratigraphic sections with about 20 of the samples containing inherited zircons with ages similar to those found in underlying assemblages the seven oldest assemblages represent semi continuous volcanism from 2750 to 2697 ma the volcanism is compositionally diverse ranging from komatiite and tholeiitic basalt to calc alkaline mafic to felsic lavas intimate intermingling of the different magma clans occurs throughout much of the stratigraphic section regional fault control on the distribution of the volcanic assemblages provides evidence for early dip slip movement associated with volcanic extension dating back to at least 2725 ma the two youngest assemblages are dominantly sedimentary and were unconformably deposited on the volcanic assemblages in close proximity to regional faults the earlier sedimentary assemblage consists of turbidites and minor iron formation deposited from 2696 to 2692 ma and the youngest one of subaerial conglomerates fluvial sandstones and alkalic to shoshonitic volcanic rocks ranging in age from 2687 to 2675 ma the sedimentary assemblages are broadly contemporaneous with the emplacement of syntectonic granitic plutons regional folding and reactivated movement on the regional faults probably related to accretion of the abitibi to the superior province craton autochthonous repetition of different geodynamic environments over the 50 million years of volcanic activity with five dominantly tholeiitic komatiitic assemblages and two dominantly calc alkaline assemblages as well as the extensive intermingling of these different magma clans in a number of the assemblages appears to be unique to the archean it suggests complex large scale and long lived interaction between mantle plumes and subduction zone magmas the nd isotope data indicate a derivation of the diverse volcanic magmas from homogeneously depleted sources with end 2 5 0 5 demonstrating a lack of contamination by ancient enriched components

crooked line 2d seismic reflection imaging in crystalline terrains part 1 data processing for cost and access reasons most of the seismic reflection data collected in crystalline terrains have been acquired by 2d crooked line profiling when the survey geometry is significantly irregular and the geologic structures have cross profile dip several standard 2d imaging procedures severely underperform as a result reflection signal is poorly aligned across individual common midpoint cmp gathers and much is lost during the cmp stack to improve imaging either the methods used to align signal before stack need to be modified or more tolerant methods of combining trace signals than the standard cmp stack need to be applied because a high fold 2d crooked line profile is really a 3d survey of a swath of terrain around the processing line better signal alignment before cmp stacking may be achieved by revisiting the traveltime equation and including the cross dip terms into the moveout calculations therefore in addition to the correction of nmo and in line dip moveout dmo we also locally com

experimental shock deformation in zircon a transmission electron microscopic study abstract in recent years apparently shock induced and thus impact characteristic microdeformations in the form of planar microdeformation features and so called strawberry granular texture have been observed in zircons in rocks from confirmed impact structures and from the k t boundary the nature of the planar microdeformations in this mineral is however still unknown and critical information is needed regarding the shock pressure range in which these deformation effects are produced we experimentally shock deformed two series of thin zircon zrsio 4 target plates cut perpendicular to the c axis at shock pressures of 20 40 and 60 gpa the recovered samples were characterized by optical and scanning electron microscopy in addition one sample series was studied by transmission electron microscopy tem microdeformation effects observed at 20 gpa include pervasive micro cleavage and dislocation patterns plastic deformation is indicated by a high density of straight dislocations in glide configuration the dominant glide systems are 010 micro cleavages induced by shear stresses during the compression stage occur mostly in the 100 planes the large density of dislocations at crack tips shows that plastic deformation was initiated by the micro cracking processs at 40 gpa the sample was partly transformed from the zircon z to a scheelite cawo 4 type s structure planar deformation features pdfs containing an amorphous phase of zircon composition are present in the not yet transformed zircon relics the phase with scheelite structure initiated in the 100 planes of zircon consists of thin 0 1 to several m bands that crosscut the zircon matrix the phase transformation is displacive martensitic and can be related by 100 z 112 s and 001 z s the scheelite structure phase is densely twinned with twins in the 112 plane the 60 gpa sample consists completely of the scheelite structure phase crosscutting and displacing relationships between twins and pdfs demonstrate that pdfs are formed in the zircon structure i e before the phase transformation to the scheelite structure occurred most likely at the shock front crystallographic orientations of optically visible planar features in zircon in comparison with orientations of planar defects at the tem scale suggest that the optically visible features are more likely planar microfractures than pdfs

gently dipping fracture zones in paleoproterozoic metagranite sweden evidence from reflection seismic and cored borehole data and implications for the disposal of nuclear waste 1 the svecokarelian orogen in the coastal area north of stockholm central sweden is characterized by a complex deformation belt in this belt bedrock domains strike wnw nw dip steeply and are affected by high ductile strain these domains anastomose around tectonic lenses that are up to a few tens of kilometers in length and are a few kilometers wide the bedrock within the lenses is folded and in general affected by lower ductile strain site investigations for the disposal of highly radioactive nuclear waste are presently in progress within one of these lenses approximately 16 km of high resolution 10 m source and receiver spacing 100 channels seismic data were acquired in 2002 along five separate profiles 2 to 5 km in length within this lens in the southeast reflection orientations are well determined where profiles cross one another here there is a nearly one to one correlation of distinct reflections on the seismic sections with hydraulically conductive fracture zones in cored boreholes indicating that these fracture zones control the reflectivity however smaller lenses of amphibolite within the fracture zones may enhance the reflectivity the reflections dip gently to the sse and se and the zones in the boreholes are dominated by fractures that show the same dip direction or are subhorizontal a working hypothesis for the gently dipping fracture zones suggests that these structures formed as minor thrust faults during the later stages of the svecokarelian orogeny mineral fillings and coatings along fractures in these zones indicate later reactivation the current stress field a high intensity of fractures in the zones at a high angle to 3 high in situ stresses in the bedrock and rapid glacial unloading with the development of high differential stresses may explain the large volume of groundwater in these zones the reflection seismic data in combination with the verifying work presented in the cored borehole data have steered the subsequent focus in geoscientific studies to the northwestern part of the candidate area

fingerprinting the k t impact site and determining the time of impact by upb dating of single shocked zircons from distal ejecta abstract u pb isotopic dating of single 1 3 g zircons from k t distal ejecta from a site in the raton basin colorado provides a powerful new tool with which to determine both the time of the impact event and the age of the basement at the impact site data for the least shocked zircons are slightly displaced from the 544 5 ma primary age for a component of the target site white those for highly shocked and granular grains are strongly displaced towards the time of impact at 65 5 3 0 ma such shocked and granular zircons have never been reported from any source including explosive volcanic rocks zircon is refractory and has one of the highest thermal blocking temperatures hence it can record both shock features and primary and secondary ages without modification by post crystallization processes unlike shocked quartz which can come from almost anywhere on the earth s crust shocked zircons can be shown to come from a specific site because basement ages vary on the scale of meters to kilometers with u pb zircon dating it is now possible to correlate ejecta layers derived from the same target site test the single versus multiple impact hypothesis and identify the target source of impact ejecta the ages obtained in this study indicate that the manson impact site iowa which has basement rocks that are mid proterozoic in age cannot be the source of k t distal ejecta the k t distal ejecta probably originated from a single impact site because most grains have the same primary age