a physical basis for the frictional melting of some rock forming minerals abstract under conditions of coseismic slip 0 1 2 0 m s 1 within the upper crust differences in the shear yield strengths fracture toughnesses melting points and to a lesser extent thermal conductivities of rock forming minerals result in a hierarchy of friction melting susceptibilities in many so called pseudotachylytes it is observed that phyllosilicates and amphiboles are preferentially consumed to form the melt phase whilst quartz and feldspar tend to survive as clasts this can be explained in terms of the disequilibrium flash melting of those mineral phases possessing the lower shear yield strengths fracture toughnesses and thermal conductivities rather than by eutectic melting that would otherwise generate equilibrium minimum melts indicative of igneous processes at high strain rates typical of coseismic faulting the mechanical behaviour of minerals is primarily controlled by their fracture toughnesses with progressive comminution during slip leading to fusion the friction melting dependence on the mechanical properties of minerals indicates that there may be an important relationship between wall rock lithology and earthquake magnitude if frictional melting results in fault lubrication

u pb evidence for polymetamorphic history of huronian rocks within the grenville front tectonic zone east of sudbury ontario canada abstract this paper presents u pb geochronological data for zircon titanite monazite apatite allanite and rutile from street township east of sudbury that help unravel two main facets of the geology of the grenville front tectonic zone gftz they document the presence of extensive huronian supergroup magmatic ca 2480 2460 ma and sedimentary rocks inside the gftz and highlight the significance of bimodal magmatism in the genesis of the huronian supergroup the data also provide further insights into the complex orogenic evolution of the gftz showing in particular that amphibolite facies metamorphism migmatization and deformation during grenvillian compression at 995 980 ma overprinted but did not totally erase the memory of earlier metamorphic events at ca 1720 and 1470 ma from the point of view of u pb systematics the results emphasize the nearly ubiquitous state of isotopic disequilibrium in these rocks most of the minerals investigated comprise two or more generations and are generally in a state of partial resetting because of the superimposed effects of younger events the preservation of pre grenvillian ages in titanite and allanite demonstrates that processes related to final grenvillian collision and exhumation occurred at great speed only apatite and to some degree rutile yield ages that are clearly post tectonic thereby reflecting the final stages of exhumation and cooling of the region

th u disequilibrium dating of middle and late pleistocene wood and shells from banks and victoria islands arctic canada an attempt has been made at dating middle and late pleistocene deposits from banks and victoria islands using the th u disequilibrium method geological correlations are difficult to establish because of the discontinuous nature of the terrestrial units and the relative absence of datable fossil wood and shells the th u geochemical system likely remained closed for extended periods because of the presence of permafrost which implies very limited or absent water circulation the th u age determinations obtained confirmed the previously established stratigraphic framework and provide chronological information in that samples of sangamonian age are differentiated from those that are younger wisconsinan and holocene or older middle pleistocene the th u disequilibrium method carefully used in areas where water circulation is limited can thus provide chronological control for sediments older than those that can be dated by the radiocarbon method

ore metal redistribution by hydrocarbon brine and hydrocarbon halide melt phases north range footwall of the sudbury igneous complex ontario canada we report methane dominant hydrocarbon fluid inclusions ch4 c2h6 c2h2 c3h8 coexisting with primary brine inclusions and secondary halide melt solid nacl inclusions in au pt rich quartz sulfide epidote alteration veins associated with the footwall style cu pge platinum group element au deposits at the fraser mine north range of the sudbury igneous complex evidence for coentrapment of immiscible hydrocarbon brine and hydrocarbon halide melt mixtures is demonstrated a primary ch4 brine assemblage was trapped during quartz growth at relatively low t min ttrapping 145 315 c and p max ptrapping 500 bar prior to the crystallization of sulfide minerals in the veins secondary inclusions contain solid halite and a mixture of ch4 c2h6 c2h2 and c3h8 and were trapped at a minimum t of 710 c the halite inclusions may represent halide melt that exsolved from crystallizing sulfide ores that texturally postdate by replacement early alteration quartz hosting the primary lower t brine ch4 assemblage laser ablation icp ms analyses show that the brine hydrocarbon and halide melt inclusions contain significant concentrations of cu 0 1 1 wt range au bi ag and pt all 0 1 10 ppm range cu pt and cu au ratios in the inclusions are significantly up to 4 log units lower than in the host alteration veins and adjacent massive sulfide ore veins suggesting either 1 early cu loss from the volatiles by chalcopyrite precipitation or 2 enhanced au and pt solubilities relative to cu at the temperatures of entrapment concentration ratios between coexisting brine and ch4 inclusions c rm elem rm brine c rm elem rm ch 4 are lower for cu au bi and ag than for other elements na ca fe mn zn pb indicating that during interaction with the brine the hydrocarbon phase was enriched in ore metals the high concentrations of ore metals in hydrocarbon brine and halide melt phases confirm that both aqueous and non aqueous volatiles were carriers of precious metals in the sudbury environment over a wide range of temperatures volatile evolution and magmatic sulfide differentiation were clearly part of a single continuous process in the sudbury footwall the exsolution of h2o poor volatiles from fractionated sulfide liquid may have been a principal mechanism controlling the final distribution of pge and au in the footwall ore systems the study reports the first measurements of precious metal concentrations in fluid inclusions from a magmatic ni cu pge environment the sudbury district

fractional crystallization of sulfide ore liquids at high temperature tie line compositions of fe ni cu sub 1 x s monosulfide solid solution mss and fe ni cu s liquid in the presence of sulfur vapor have been quenched from temperatures between 1 050 degrees and 1 180 degrees c more than 80 bulk compositions on both sulfur rich and sulfur poor sides of the mss field were investigated by sealed silica tube techniques qualitative observations of wetting behavior suggest increasing mobility in a silicate host rock as sulfide liquids become more cu rich partition coefficients for copper or 0 25 d super mss hq cu are obtained from ni bearing experiments with approximately 2 wt percent cu and no quench phases the equation d super mss hq cu 0 0003 x t degrees c 0 0310 x wt s 0 0069 x wt cu 1 3450 describes partitioning observed in ni free experiments above 1 000 degrees c above 1 000 degrees c the ni distribution coefficient d super mss hq cu decreases with increasing temperature and or sulfur content of the liquid these results yield improved models describing the fractional crystallization of natural sulfide liquids major element fe ni cu s compositions of ores from the sudbury district are shown to be entirely consistent with fractional crystallization at temperatures above 1 000 degrees c with the possible exception of rare samples enriched in both ni and cu sulfide liquids fractionating ni fe rich hanging wall ores at sudbury ontario must have been less cu rich than previously thought at temperatures above 950 degrees c reduced sulfur activity in residual liquids can result in massive late stage bornite rich ores

the nature age and petrogenesis of the cartier batholith northern flank of the sudbury structure ontario canada abstract the cartier batholith exposed about 50 km northwest of sudbury ontario canada is a late archean k rich granitic batholith along with the levack gneiss complex it forms the footwall of the north range of the sudbury igneous complex the cartier batholith dominantly monzogranitic to granodioritic is relatively homogeneous unfoliated and contains k feldspar megacrysts it shows several distinctive chemical features including high concentrations of zr th u and lree and low concentrations of nb ti and hree several discriminants suggest a post orogenic tectonic environment for the batholith this inference is consistent with a u pb age of 2642 1 ma obtained on zircon only slightly younger than the inferred timing of high grade metamorphism of the levack gneiss complex the cartier batholith could have formed as a result of approximately 33 partial melting of the levack gneiss complex

footwall type cu ni pge mineralization in the broken hammer area wisner township north range sudbury structure footwall type cu ni pge platinum group element deposits are a major focus of recent exploration in the sudbury mining camp owing to their higher cu and precious metal contents compared to orebodies situated along the lower contact of the sudbury igneous complex the most important footwall type orebodies occur in the onaping levack area of the north range but economic deposits are found along the east range of the structure as well recently promising occurrences were also discovered in wisner township of the north range in this paper we report results from two main footwall type cu ni pge occurrences the broken hammer zone and the south zone of wisner township both discoveries are situated in intensely brecciated zones of the footwall sudbury breccia 1 300 and 500 m respectively north of the present sudbury igneous complex footwall contact the mineralization consists of 1 massive sulfide veins 2 disseminated replacement sulfides and 3 silicate quartz dominated veins although massive sulfide veins account for the major part of the resource sulfide poor disseminations may have similarly high precious metal contents ore assemblages are dominated by chalcopyrite millerite magnetite and or pyrite quartz and hydrous silicates these are accompanied by platinum group minerals pgm and other trace minerals which commonly occur as composite grains within sulfides and hydrous silicates these include minerals typical of footwall type deposits e g merenskyite michenerite hessite but also minerals found only in a few sudbury deposits e g clausthalite sopcheite naumannite bohdanowiczite an unnamed cupdbis 3 mineral is one of the most abundant pgm at broken hammer and might be a pd equivalent of muckeite cunibis 3 statistical investigation of metal distribution patterns using grab sample and drilling data sets from both localities indicate important differences between the two occurrences and the various mineralization styles e g increasing cu cu ni and decreasing pt pt pd ratio with increasing sulfide content metal concentrations recalculated to 100 sulfides decrease by up to two orders of magnitude for all metals from the disseminated to the massive sulfides fluid inclusion studies revealed three fluid generations which are very similar to those described from well known footwall type deposits of the onaping levack area primary polyphase fluid inclusions in cu ni pge bearing assemblages represent a highly saline 30 40 wt nacl equiv magmatic hydrothermal system with a high temperature min 450 500 c and a lower temperature min 300 350 c stage a later low temperature ca rich fluid min 100 200 c is most probably part of a post sudbury igneous complex regional fluid flow in which temperature was controlled by the geothermal gradient and not related to ore forming processes the fluid inclusion data indicate that mobilization of highly saline and relatively high temperature 400 500 c sudbury igneous complex related magmatic hydrothermal fluids similar to those described from the onaping levack embayment also occurred in the wisner footwall although our studies do not rule out the possibility of an initial magmatic sulfide melt emplacement they prove that magmatic hydrothermal fluids played a significant role in the transport and deposition of metals

sudbury breccia canada a product of the 1850 ma sudbury event and host to footwall cu ni pge deposits abstract the sudbury structure formed by meteorite impact at 1850 ma consists of three major components 1 the sudbury basin 2 the sudbury igneous complex which surrounds the basin as an elliptical collar and 3 breccia bodies in the footwall known as sudbury breccia in general the breccia consists of subrounded fragments set in a dark fine grained to aphanitic matrix a comparison of the chemical composition of host rocks clasts and matrices indicates that brecciation was essentially an in situ process sudbury breccia forms irregular shaped bodies or dikes that range in size from mm to km scale contacts with the host rocks are commonly sharp the aspect ratio of most clasts is approximately 2 with the long axes parallel to dike walls the fractal dimension dr 1 55 although there appears to be some concentration of brecciation within concentric zones small sudbury breccia bodies within and outside these zones have more or less random strikes and steep dips sudbury breccia bodies near an embayment structure tend to be subparallel to the base of the sudbury igneous complex sudbury breccia occurs as much as 80 km from the outer margin of the sudbury igneous complex in an inner zone 5 to 15 km wide breccia comprises 5 of exposed bedrock with an increase in brecciation intensity in embayment structures sudbury breccia may be classified into three types based on the nature of the matrix clastic pseudotachylite and microcrystalline clastic sudbury breccia the dominant type in the southern province is characterized by flow surface structures possibly a sudden rise in pore pressure caused explosive dilation and fragmentation followed by fluidization and flowage into extension fractures pseudotachylite sudbury breccia mainly confined to archean rocks apparently formed by comminution and frictional melting microcrystalline sudbury breccia formed as a result of the thermal metamorphism of the north range footwall by the sudbury igneous complex this produced a zone approximately 1 2 km wide wherein the matrix of the breccia either recrystallized or locally melted an overprint of regional metamorphism obliterated contact effects in the south range footwall the ni cu pge magmatic sulphide deposits may be classified into four types based on structural setting sudbury igneous complex footwall contact footwall offset and sheared deposits sudbury breccia is the main host for footwall deposits e g mccreedy east victor lindsley sudbury breccia locally hosts mineralization in radial e g parkin and copper cliff and concentric e g frood stobie offset dikes

geochemical relationships in the sudbury igneous complex origin of the main mass and offset dikes petrological models relating the different rock types constituting the 1 85 ga sudbury igneous complex are constrained with extensive new geochemical data we show that the main mass felsic norite transition zone quartz gabbro and granophyre have similar ratios of the highly incompatible trace elements e g la sm 4 5 7 la nb 2 8 4 2 th zr 0 04 0 05 and that these variations are consistent with the crystallization and differentiation of magma types largely 80 derived from the upper crust with a smaller contribution from a mantle source although there is presently no conclusive proof that magma was generated in situ as a melt sheet produced by meteorite impact we find no principal reason why this model should be rejected however we propose that a small contribution of mantle derived picritic magma is required to explain the abundant ni cu and platinum group elements pge in the sudbury deposits as well as the compositions of the ultramafic inclusions mgo 12 36 wt fo sub 68 87 olivines with 450 3 700 ppm ni and abundant chrome rich spinel and the magnesian composition of the mafic norite 8 14 wt mgo and the sublayer 6 12 wt mgo we believe that the main mass of the sudbury complex achieved its present composition through incorporation of up to 20 percent mantle derived picritic magma emplaced along crustal fractures produced by the impact event these picritic magmas entered the melt sheet as a dense plume vigorously mixing with it and due to the marked compositional shift the mixed magma formed magmatic sulfides which sank through the magma column depleting the melt in ni cu and pge since both the felsic norite and granophyre have indistinguishable ratios of the incompatible trace elements we see no requirement to derive these units of rock by the crystallization of magmas derived from different sources rather the compositional difference between the felsic norite and granophyre is attributed to the in situ differentiation of the magma we show that the main mass has many compositional traits similar to those of most of the offset dike quartz diorites e g the parkin offset dike la sm 6 3 la nb 4 5 th zr 0 05 and of embayment related leucocratic norites from the whistle mine la sm 6 2 la nb 5 0 th zr 0 02 these rocks have compositions intermediate between the felsic norite and the granophyre and therefore crystallized from the same magma type arguably the unmineralized quartz diorites provide the best possible estimate of the original magma from which the sudbury complex crystallized in detail there are subtle variations in composition within and between offset dikes with the largest difference being between the north and south range offsets the north range offset dikes cut archean granitoids and gneisses and have elevated sr la yb la sm and gd yb and low tio 2 whereas the south range dikes cut early proterozoic sediments mafic volcanics and intrusions and have low sr la yb gd yb la sm and high tio 2 these differences may be caused by the assimilation of different country rocks during emplacement of the dike a strongly mineralized offset dike at the creighton mine has geochemical variations that are different when compared to the main mass and in the case of creighton are more similar to the local mineralized sublayer these data suggest that mineralized and barren quartz diorites have different geochemical compositions and that these traits may be of value in mineral exploration

microstructural and chemical changes associated with cataclasis and frictional melting at shallow crustal levels the cataclasite pseudotachylyte connection in pelitic schists of the nason terrane of washington state pseudotachylyte can be demonstrated to have developed subsequent to the formation of foliation parallel cataclasite zones numerous microstructural lines of evidence point to a genetic link between pseudotachylyte and cataclasite and chemical evidence indicates that cataclasis played an important role in controlling pseudotachylyte chemistry besides optical and textural differences between the cataclasite and pseudotachylyte which may occur together there is unambiguous evidence of a melt origin for the pseudotachylyte while such evidence within the cataclasite is absent tem evidence indicates that glass is present in at least some of the veins as demonstrated by a lack of electron diffraction microlites present in the glass lack dislocations high temperature microlites of a mineralogy and composition not present in the host schist occur in various habits which depend on the distance from the vein margin also present are assimilation textures apparently quenched sulfide droplets and vesicles and amygdules in a pseudotachylyte vein studied in detail five microstructural domains occur these include vein margin cataclasite a transitional dark pseudotachylyte vein interior glass opaque and sulfide rich blebs and translucent haloes surrounding some of the blebs the cryptocrystalline cataclasite matrix grades into the dark pseudotachylyte which optically grades into the glass after adjustment for silica the host schist and cataclasite matrix are chemically very similar the dark pseudotachylyte and glass with the exception of na2o and cao are chemically quite similar to the cataclasite matrix the main difference may be the result of the segregation of the opaque plagioclase blebs thus the pseudotachylyte chemistry is strongly dependent upon the chemistry of the material comprising the cataclasite matrix which in turn is dependent on mineral susceptibility to incorporation into the cataclasite matrix fluids infiltrated along the cataclasite zones prior to pseudotachylyte generation as recorded by hydration reactions sulfide veining na2o loss and fluid inclusions this demonstrates that pseudotachylytes can form under fluid rich conditions as opposed to the commonly assumed dry conditions

structural characteristics of the sudbury impact structure canada impact induced versus orogenic deformation a review orogenic deformation both preceding and following the impact event at sudbury strongly hinders a straightforward assessment of impact induced geological processes that generated the sudbury impact structure central to understanding these processes is the state of strain of the sudbury igneous complex the solidified impact melt sheet its underlying target rocks overlying impact breccias and post impact sedimentary rocks this review addresses 1 major structural metamorphic and magmatic characteristics of the impact melt sheet and associated dikes 2 attempts that have been made to constrain the primary geometry of the igneous complex 3 modes of impact induced deformation as well as 4 mechanisms of pre and post impact orogenic deformation the latter have important consequences for estimating parameters such as magnitude of structural uplift tilting of pre impact huronian strata and displacement on major discontinuities which collectively have not yet been considered in impact models in this regard a mechanism for the emplacement of offset dikes is suggested that accounts for the geometry of the dikes and magmatic characteristics as well as the occurrence of sulfides in the dikes moreover re interpretation of published paleomagnetic data suggests that orogenic folding of the solidified melt sheet commenced shortly after the impact uncertainties still exist as to whether the sudbury impact structure was a peak ring or a multi ring basin and the deformation mechanisms of rock flow during transient cavity formation and crater modification

frictional melting of sedimentary rock during high speed diamond drilling an analytical sem and tem investigation abstract high speed drilling at 900 rpm with a downhole motor driven natural diamond drag bit has resulted in the extreme alteration of sedimentary rock in an offshore canadian wildcat well these effects as revealed in the rock cuttings retrieved from the drilling fluid at surface include discolouration darkening cataclasis slickensiding and partial fusion calcareous siltstones are the most susceptible to alteration especially melting whereas sandstone and limestone cuttings mainly exhibit fracturing and surface glazing analytical scanning electron microscopy reveals that the calcareous siltstones have undergone decalcification via decarbonation and the loss of cao to the drilling fluid decarbonation combined with dehydration resulted in the vesiculation and explosive fragmentation of certain cuttings analytical transmission electron microscopy shows that glass is present in the calcareous siltstone cuttings most of the modifications exhibited by the sedimentary rocks can be attributed to the effects of high strain rate deformation and frictional heating at the bit rock interface that melting took place is supported by thermal calculations which indicate that for a coefficient of friction of 0 5 temperatures of approximately 1200 c were realized at diamond rock contacts such high temperatures can accelerate the wear of diamond and its substrate and hence shorten bit life as well as obliterate potentially important geological information in the rock cuttings

u pb baddeleyite ages of the kerns and triangle mountain intrusions nipissing diabase ontario u pb ages have been determined for two diabase intrusions from kerns and hudson townships that are part of the nipissing diabase suite from the proterozoic southern province canada the ages of the kerns and triangle mountain intrusions are 2217 2 4 and 2209 6 3 5 ma respectively based on analysis of primary baddeleyite from both intrusions together with a published u pb age for the castle mine intrusion these data indicate that the nipissing sills were emplaced separately over a time span of 2 8 1 6 ma given by the maximum and minimum overlap of errors on the u pb ages

fault rheology beyond frictional melting during earthquakes comminution and frictional heating both contribute to the dissipation of stored energy with sufficient dissipative heating melting processes can ensue yielding the production of frictional melts or pseudotachylytes it is commonly assumed that the newtonian viscosities of such melts control subsequent fault slip resistance rock melts however are viscoelastic bodies and at high strain rates they exhibit evidence of a glass transition here we present the results of high velocity friction experiments on a well characterized melt that demonstrate how slip in melt bearing faults can be governed by brittle fragmentation phenomena encountered at the glass transition slip analysis using models that incorporate viscoelastic responses indicates that even in the presence of melt slip persists in the solid state until sufficient heat is generated to reduce the viscosity and allow remobilization in the liquid state where a rock is present next to the melt we note that wear of the crystalline wall rock by liquid fragmentation and agglutination also contributes to the brittle component of these experimentally generated pseudotachylytes we conclude that in the case of pseudotachylyte generation during an earthquake slip even beyond the onset of frictional melting is not controlled merely by viscosity but rather by an interplay of viscoelastic forces around the glass transition which involves a response in the brittle solid regime of these rock melts we warn of the inadequacy of simple newtonian viscous analyses and call for the application of more realistic rheological interpretation of pseudotachylyte bearing fault systems in the evaluation and prediction of their slip dynamics

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

new insights on the runout of large landslides in the valles marineris canyons mars 1 analogy with lab scale dry granular flow experiments demonstrates that runouts and deposits heights of valles marineris vm landslides can be scaled on a curve varying primarily with the initial aspect ratio of the mobilized rock mass before slope failure this results suggests both that any interstitial fluid played a negligible part in the vm landslides dynamics and that mobility is not an appropriate tool to characterize their dynamics

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

structural analysis of the central and southwestern sudbury structure southern province canadian shield the sudbury structure ss is an unusual crater structure which acquired its present oval surface shape during northwest directed ductile thrusting lower amphibolite facies metamorphism accompanied the thrusting which generated a major reverse shear zone at least 50 km long the south range shear zone srsz transects the south range of the sudbury structure and exhumes a low level of the sudbury igneous complex sic assuming heterogeneous simple shear in the northwest southeast vertical plane on northeasterly striking glide surfaces minimal estimates of net displacement across the srsz exceed 8 km this displacement magnitude and the map pattern of the sic require the southwest closure of the ss to be steeply plunging in accord with a hypothetical funnel shape of the sic the rocks of the metasedimentary core of the ss are deformed into a family of second order buckle folds the tangent surface of which forms an upright open flexure within the first order structure of the sudbury synclinorium the

sudbury breccia at whitefish falls ontario evidence for an impact origin sudbury breccias are unusual clast matrix rock bodies formed in abundance around the sudbury igneous complex the most obvious manifestation of a major impact event at sudbury at whitefish falls 70 km southwest of sudbury similar breccias consisting of clasts of argillite and amphibolite dyke enclosed in a fine grained matrix of host rock are developed in metamorphosed argillites of the huronian supergroup pre brecciation brittle textures in the host argillite and breccia clasts such as layer parallel foliation offset by cataclastic fractures suggest that the host rock was entirely competent prior to brecciation one composite penetrative foliation and its associated ductile folding were also formed in the argillite host prior to brecciation post brecciation ductile deformation produced a regionally dominant east west trending foliation and two late stage folding events and indicate a syn penokean age of brecciation the breccias at whitefish falls are enriched in ferromagnesian minerals compare

microcrystalline textures resulting from rapid crystallization in a pseudotachylite melt in a meta anorthosite the very fine grained 1 m polygonal microcrystalline texture occurring in the groundmass of pseudotachylite veins in the harris meta anorthosite and its variation with position are described and an origin by crystallization from a melt at very large undercooling suggested the intrusive nature of the veins is shown by their geometry and internal structures clasts which are almost always only plagioclase are generally concentrated towards the centres of veins flow of tens of millimetres can account for this concentration in millimetre thick veins as a result of the bagnold effect the veins are generally thin 5 m to 5 mm or more are frequently zoned and always contain transparent granules of high relief probably al rich pyroxene and opaque granules of magnetite up to a few micrometres in size the granules are either uniformly distributed in microcrystalline textures or concentrated locally giving cellular textures in some veins spherulitic or bow tie textures occur the coarsest textures are found in the centres of the thickest veins the groundmass of the pseudotachylite is never completely isotropic but consists of a mosaic of transparent plagioclase crystals decreasing in size from the centres of thick veins to less than 1 m in thin veins or in the margins of thicker veins this fine microcrystalline texture was studied by both scanning and transmission electron microscopy and consists of polyhedral crystals of regular size in the range 0 2 1 5 m which show little sign of deformation the local composition of the pseudotachylites varies little from the average compositions of the rocks in optically homogeneous veins the variation being within the compositional space defined by the minerals of the host rock this shows that homogenization of the pseudotachylite has occurred in cellular veinsdifferentiation has occurred as the compositions of the cell centres lie outside those of the minerals of the host rock this was produced by segregation of the granules pyroxene being absent from the host rock the plagioclase in the pseudotachylite is more disordered than that in the host rock all the microtextures described are absent from the associated cataclasites and cannot be due to recrystallization of a fine grained and intensely strained rock powder the physical state on and after intrusion was that of a melt and injection was followed by crystallization the melt was produced by more or less total fusion of the host rock minerals at shallow depth by heat produced during local faulting and perhaps during crack propagation the fine microcrystalline texture very closely resembles that produced during hypercooling of molten metals and alloys it thus possibly formed not by devitrification but from a melt at much greater degrees of undercooling than the spherulitic and bow tie textures

laser probe argon 40 argon 39 dating of pseudotachylyte from the sudbury structure evidence for postimpact thermal overprinting in the north range ten pseudotachylyte samples from the north range of the 1850 ma sudbury impact structure have been analyzed by the 40ar 39ar laser spot fusion method field and petrological evidence indicate that the pseudotachylytes were formed at 1850 ma by comminution and frictional melting due to impact induced faulting the cryptocrystalline to microcrystalline grain size 30 m of the pseudotachylyte matrices and the predominance of orthoclase as the main k bearing phase have rendered the rocks particularly susceptible to ar loss the age determinations range from 1850 to 1000 ma with some samples yielding multiple ages that cannot be correlated with known geological events in the area however if the finite difference algorithm of wheeler 1996 is used to calculate combined ar loss and the accumulation of radiogenic ar for the k bearing phases it is possible to reproduce the range of observed ages the model infers that the long term volume diffusion of ar has occurred and that as a result the ar system cannot be treated with a conventional closure temperature approach the algorithm requires burial of the impact structure to 5 6 km depth and 160 180 c at 1850 ma followed by exhumation at 1000 ma these ages may be equated with two events penokean thin skinned overthrusting in the north range immediately following impact and exhumation 850 ma later coincident with the grenville orogeny to the southeast the results suggest that contrary to previously accepted paradigms the north range has been affected by a protracted period of postimpact low grade thermal metamorphism if these events also involved tectonic shortening within the north range as has been documented for the south range then the original size of the sudbury impact structure has been underestimated

multi stage hydrothermal processes involved in low sulfide cu ni pge mineralization in the footwall of the sudbury igneous complex canada amy lake pge zone east range the amy lake pge zone is a low sulfide type cu ni pge mineralization in the east range footwall of the 1 85 ga sudbury igneous complex occurring in a 100 m wide sudbury breccia belt that coincides with an impact related major fracture zone bay fault zone detailed hydrothermal alteration mapping fluid inclusion trace element and stable isotope studies revealed a complex alteration and mineralization history in a multi source multi stage sudbury related hydrothermal system the two major stages of syn sudbury hydrothermal activity are characterized by similarly high salinity high temperature fluids that are 1 locally derived from footwall granophyre bodies and typified with high ni cu and pge s ratios and high ree contents magmatic hydrothermal stage and 2 a more voluminous cu ni pge rich fluid flux probably originated from the sudbury igneous complex footwall contact hydrothermal stage the second hydrothermal flux was introduced by brittle fractures in the area and resulted in a complex zonation of alteration assemblages and mineralization governed by local footwall composition the sudbury related hydrothermal event was overprinted by shear related epidote veining and calcite chlorite replacement both regionally present in the sudbury structure based on analogies the most important factors involved in the formation of hydrothermal low sulfide mineralization are proposed to be 1 accumulation of pge enriched fluids 2 large scale brittle structures as conduits to these fluids and 3 adequate host rock composition as a chemical trap resulting in sulfide and pgm precipitation in environments meeting these criteria hydrothermal pge mineralization is known to have formed not only in the sudbury footwall but also from mafic ultramafic intrusions associated with primary magmatic pge from several locations around the world

sub million year age resolution of precambrian igneous events by thermal extraction thermal ionization mass spectrometer pb dating of zircon application to crystallization of the sudbury impact melt sheet a new approach to zircon dating is described that potentially offers a considerable improvement in the accuracy of 207 pb 206 pb ages on a wider variety of samples and at less cost than that generally available from conventional techniques zircon is first preheated in a vacuum to evaporate pb from altered domains leaving predominantly pb with isotopes that preserve the primary age of the sample refractory pb is removed from the zircon by thermal extraction at higher temperature directly into a silica melt ionization activator within a thermal ionization mass spectrometer this produces strong ion beams that allow 207 pb 206 pb isotope ratios to be measured to high precision 10 4 with almost negligible contamination from common pb isotope fractionation appears to be more reproducible than with conventional solution analysis allowing routine age determinations with precision of 0 2 m y for the precambrian as a test application zircon from a noritic boundary phase of the sudbury impact melt gives 1849 53 0 21 ma while a phase from several hundred meters higher in the noritic layer is resolvably younger at 1849 11 0 19 ma 95 confidence errors the enhanced precision and ease of application of this method should greatly increase the scientific power and availability of zircon dating

disappearing ink how pseudotachylytes are lost from the rock record abstract melt origin pseudotachylytes are the most widely accepted feature recording earthquake slip in the fault rock record however reports of pseudotachylytes are rare compared to the frequency and distribution of earthquakes in active faults suggesting melting occurs only under exceptional circumstances and therefore that pseudotachylytes are rarely formed in this paper we document the processes whereby pseudotachylytes are overprinted destroyed and otherwise removed from the rock record we present examples of recrystallized altered and cataclastically and crystal plastically deformed pseudotachylytes from a variety of ancient faults based on these observations we identify characteristics of pseudotachylytes that are resistant to change over geologic time and develop criteria to allow recognition of relict pseudotachylytes our results imply that pseudotachylytes are vastly under reported due to their vulnerability to destruction and the resulting difficulty in identification as a consequence the significance of frictional melting is underestimated the criteria we propose to distinguish relict pseudotachylytes can help to reconcile the observed frequency of earthquakes with the difficulty of demonstrating ancient seismic slip in the rock record

pseudotachylyte in muscovite bearing quartzite coseismic friction induced melting and plastic deformation of quartz abstract thin 0 5 2 mm thick pseudotachylyte veins occur within muscovite bearing 10 volume amphibolite facies quartzites of the schneeberg normal fault zone austroalpine southern tyrol italy pseudotachylytes are associated with precursor localized plastic microshear zones 50 150 m thick developed sub parallel to the host rock foliation and with conjugate sets oriented at a high angle to the foliation such microshear zones are characterized by recrystallization to ultrafine grained 1 2 m grain size mosaic aggregates of quartz showing a transition from a host controlled to a random crystallographic preferred orientation towards the shear zone interior subsequent coseismic slip mainly exploited these microshear zones microstructural analysis provides evidence of extensive friction induced melting of the muscovite bearing quartzite producing a bimodal melt composition first the host rock muscovite was completely melted and subsequently crystallized mainly as k feldspar then about 60 volume of the ultrafine grained quartz underwent melting and crystallized as spherulitic rims mostly consisting of quartz ti fe around melt corroded quartz clasts the two melts show immiscibility structures in the major injection veins exploiting microshear zones at high angles to the quartzite foliation in contrast they were mechanically mixed during flow along the main fault veins

a methodology for the semi automatic digital image analysis of fragmental impactites a semi automated digital image analysis method is developed for the comparative textural study of impact melt bearing breccias this method uses the freeware software imagej developed by the national institute of health nih digital image analysis is performed on scans of hand samples 10 15 cm across based on macroscopic interpretations of the rock components all image processing and segmentation are done semi automatically with the least possible manual intervention the areal fraction of components is estimated and modal abundances can be deduced where the physical optical properties e g contrast color of the samples allow it other parameters that can be measured include for example clast size clast preferred orientations average box counting dimension or fragment shape complexity and nearest neighbor distances nnd this semi automated method allows the analysis of a larger number of samples in a relatively short time textures granulometry and shape descriptors are of considerable importance in rock characterization the methodology is used to determine the variations of the physical characteristics of some examples of fragmental impactites

roundness of clasts in pseudotachylytes and cataclastic rocks as an indicator of frictional melting abstract we examine the roundness rd of clasts derived from fault rocks and discuss its possible application as an indicator for fracturing and chipping or frictional melting the roundness of quartz and feldspathic clasts derived from four frictional melting originated pseudotachylytes and one crushing without melting originated pseudotachylyte as well as three cataclastic rocks was measured between 230 and 270 clasts 10 m in size were measured for each sample the analyses show that rd is lower than 0 4 in all the clasts included in the cataclastic rocks and crushing originated pseudotachylyte whereas it varies from 0 1 to 1 0 and 35 90 of clasts have a roundness 0 4 in the melting originated pseudotachylyte it is suggested that the clasts having a roundness 0 4 were rounded by frictional melting rather than by fracturing or chipping in pseudotachylytes and that the roundness of clasts may be used as a special index of disintegration attributed to attrition and melting

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

pseudotachylite from the vredefort ring south africa and the origins of some lunar breccias pseudotachylite veins in the vredefort impact structure occur in rocks of widely varying composition and in stratigraphic units as thin as 10 m the compositions of the pseudotachylites however are the same as those of the rocks in which they occur with some systematic variations thus indicating in situ formation the textures of the pseudotachylites indicate that they formed predominantly by mechanical processes but temperatures were locally high enough to cause thermal metamorphism and possibly fusion the host rocks of the pseudotachylites are extensively mylonitized and show selective crushing of different mineral species greater resistance of quartz and feldspar to crushing partly but not entirely explains the systematic differences in composition between host rock and pseudotachylite shock features in the host rocks are generally of a low order but indicate pressures far in excess of those reasonably to be expected in crustal rocks deformed by terrestrial processes characteristics of the pseudotachylites breccias formed by one impact provide simple models for lunar breccias that may have undergone more than one cycle of brecciation

reconstructing the geochemical signature of sudbury breccia ontario canada implications for its formation and trace metal content the sudbury breccia is an impact generated pseudotachylitic breccia formed in the footwall of the 1 85 ga sudbury igneous complex in ontario canada the breccia is commonly developed in areas of contrasting country rock types and it represents a common host to footwall style cu ni platinum group element sulfide mineralization developed in the immediate footwall of large contact type ni cu rich ore deposits at the base of the sudbury igneous complex three models have been proposed for the genesis of the sudbury breccia 1 in situ frictional or shock melting of target rocks 2 cataclasis of the target rocks and or 3 injection of allochthonous impact melt from the sudbury igneous complex into the brecciated crater floor this study reports new mineralogical and geochemical data for samples of sudbury breccia and associated host rocks both proximal and distal to mineralization from six different locations around the sudbury structure a mixing model was used to construct the composition of the sudbury breccia matrix using a combination of country rock and quartz diorite from the offset dikes which are believed to provide an estimate of the composition of the early melt sheet we demonstrate that the breccia matrix can be successfully modeled from footwall lithologies with no requirement for a contribution from the impact melt sheet instead we propose a dynamic parautochthonous in situ melt model where the matrix of the breccia was derived in part by high temperature melting of footwall lithologies these inclusion and crystal laden melts were mixed and transported into tensile fracture zones that developed adjacent to weaknesses in the country rocks principal component analysis of sudbury breccia indicates that the trace metal content within the breccia that developed distal from mineralization is associated with assimilation of mafic units in the footwall in contrast the matrix of sudbury breccia developed closer to mineral zones has a contribution of metal derived from the fractionated sulfide melt and or a contribution of hydrothermally remobilized metal thus by comparing the trace metal content in sudbury breccia with local footwall lithologies baselines can be established that can help to identify anomalous metal contributions that may be derived from the periphery of a footwall mineral system

multiple hydrothermal processes in footwall units of the north range sudbury igneous complex canada and implications for the genesis of vein type cu ni pge deposits systematic regional sampling along the contact zone of the 1 85 ga age sudbury igneous complex with the archean levack gneiss footwall in the north range of the sudbury structure revealed textural mineralogical and fluid inclusion systematics of post sudbury igneous complex hydrothermal processes that affected the various lithologies at late stages of emplacement of the sudbury igneous complex and formation of magmatic fe ni cu sulfide deposits a partial melt from the levack gneiss invaded the contact zone this partial melt is revealed by small microdikes and irregular bodies of granophyric quartz plagioclase with megacrysts of hornblende clinopyroxene and titanite plagioclase hornblende equilibrium was established at 750 to 800 c and 1 10 to 1 55 kbars pressure corresponding to about a 4 to 6 km depth under lithostatic conditions f cl wt percent ratios around 15 for accessory apatite and hornblende indicate that a cl rich fluid phase separated during the crystallization of the footwall granophyre this is expressed as miarolites the cl rich fluid 50 wt nacl equiv salinity was trapped as primary fluid inclusions in quartz at around 480 c minimum temperature and around 1 1 kbars minimum pressure during supercooling these inclusions are rich in ca fe mn and k as well as na chloride this fluid may have interacted with earlier primary magmatic sulfide causing remobilization and reprecipitation of cu ni platinum group elements pge in veins and disseminations in the footwall these veins are parallel to the sudbury igneous complex footwall contact and are characterized by chalcopyrite pentlandite millerite magnetite stilpnomelane ferropyrosmalite epidote and chlorite michenerite moncheite merenskyite froodite insizwaite sobolevskite gold and bi ni sulfides are associated with sulfides epidote quartz actinolite and chlorite are common in the alteration selvages of the veins compositions and assemblages of platinum group minerals pgm indicate their precipitation below 575 to 485 c primary highly saline fluid inclusions about 40 wt nacl equiv in quartz indicate crystallization at 400 to 480 c and around 1 6 kbars minimum t and p respectively late carbonate epidote actinolite chlorite veins and alteration overprinted the earlier assemblages at about 300 to 400 c with some bornite millerite native silver and other bi sulfides the second stage of hydrothermal activity is characterized by regional carbonic aqueous nacl co 2 ch 4 h 2 o type immiscible fluids that were trapped as secondary inclusions in quartz from various lithologies no mineralization is related to this stage along the north range boiling of these fluids took place during a pressure drop from lithostatic to hydrostatic conditions during uplift from about a 5 to 6 to a 3 to 4 km depth at 300 to 350 c high 20 26 wt nacl equiv and low salinity 6 12 wt nacl equiv fluids coexisted with different carbonic species contents the predominant north south and northwest southeast orientations of fluid inclusion planes reveal that mobilization of carbonic aqueous solutions may be related to the northwesterly oriented thrusting in the sudbury structure during the late stages 1 8 1 7 ga of the penokean orogeny and to predominantly north south faulting in the north range the third stage of fluid mobilization also took place mostly along northerly and northwesterly oriented fractures aqueous fluids were ca rich brines 20 40 wt salinity with temperatures between 150 and 250 c some of these fluids also circulated in fractures parallel to the sudbury igneous complex footwall contact ne sw thus they locally may have interacted with the earlier sulfide assemblages and are also responsible for formation of late veinlets with chalcopyrite epidote quartz chlorite assemblages mobilization of these fluids took place under litho and hydrostatic conditions at about a 4 to 6 km depth this hydrothermal activity is related to a regional tectonothermal event during emplacement of northwesterly oriented sudbury dikes 1 24 ga regional scale fluid inclusion studies along the north range highlight the role of multiple hydrothermal processes in the metallogenic evolution of the sudbury igneous complex and especially in the distribution of copper and precious metals in the footwall units

generation of fragment rich pseudotachylite bodies during central uplift formation in the vredefort impact structure south africa abstract target rocks underlying the central portions of large terrestrial impact structures are characterized by the pervasive presence of fragment rich pseudotachylite bodies debates regarding the formation of these bodies include the origin of pseudotachylitic melts i e friction versus shock induced melting melt mobility causes of target rock fragmentation and timing of fragmentation and melt emplacement with respect to stages of cratering comprehensive structural analysis of pre impact mineral fabrics and properties of fragment rich pseudotachylite in the vredefort dome suggests that melt is allochthonous and was emplaced at an advanced stage of cratering into tensional fracture zones within the crater floor both concentration of bending strains imparted on target rocks during central uplift formation and thermal stresses induced by the emplacement of allochthonous melt led to fragmentation of target rock tensional fracture zones formed in an overall dilational strain field towards the end of cratering likely during collapse of the central uplift and constitute low pressure zones into which melt was forcefully drawn melt may have been drained from the overlying impact melt sheet or from sites within the crater floor and transported into fragment rich dilation zones our field based analysis failed to identify the presence of bona fide shear faults that could potentially have generated in situ frictional melts and fragments rather target rock fragmentation and melt generation that resulted in fragment rich pseudotachylite bodies are processes separated in space and time during cratering

normal fault control on bedrock channel incision and sediment supply insights from numerical modeling 1 the evolution of footwall drainage basins sediment supply and hanging wall stratigraphy in rift basins is investigated using a coupled numerical model of detachment limited stream network evolution and coarse grained fan delta deposition the response of bedrock channel networks to repeated footwall uplift events leads to increasing sediment supply over tens of thousands of years as the networks initiate and then expand followed by relatively constant sediment supply as the stream networks reach their maximum spatial extent the distinct time lag between the onset of tectonic activity and attainment of maximum sediment supply leads to stratigraphies that are initially aggradational and then progradational much of the variation in sediment supply is the product of the complex response and reorganization of the stream networks to faulting related perturbations and is not directly related to specific faulting events increasing fault displacement drives the system toward a new steady state with a higher sediment supply but is initially expressed as a retrogradation as sediment supply lags behind increased displacement the converse is true for a decrease in fault displacement which is initially expressed as progradation continual stochastic variation in recurrence interval leads to a system that does not achieve a steady state and as a result exhibits continual variation in sediment supply the model results emphasize the local tectonic controls on stratigraphic architectures developed within extensional basins and the complex manner in which stream network growth and response to tectonic activity can be expressed in the stratigraphic record

geology mineralization and emplacement of the foy offset dike sudbury impact structure the foy offset dike is the longest of the known radial dikes associated with the 1 85 ga sudbury igneous complex the foy dike extends for at least 30 km from the complex into the north range archean and proterozoic footwall rocks of the sudbury impact structure the dike ranges in width from 400 m where it connects to the sudbury igneous complex to 50 m at its most distal known exposure we divide the dike into a proximal segment and a distal segment based on where it intersects the concentric hess offset dike three main dike lithologies are distinguished all referred to as varieties of quartz diorite inclusion rich pyroxene quartz diorite occurs in the embayment adjacent to the base of the main mass of the sudbury igneous complex this constitutes the sublayer northward the sublayer gives way to amphibole biotite inclusion bearing quartz diorite and amphibole biotite inclusion poor quartz diorite the dike is mineralized and deposits in the proximal segment have been mined mineralization is associated with the inclusion rich dike phase at the nickel offset mine the dike contains inclusion bearing massive ni cu sulfides that also host platinum group minerals the orebodies occurred as strike parallel sheets within the central parts of the dike in association with inclusion bearing quartz diorite the geochemistry of the dike lithologies indicates that both the inclusion poor and inclusion bearing quartz diorite varieties are close in composition to the postulated bulk composition of the sudbury igneous complex this implies that the dike was emplaced prior to any significant fractionation of the main melt body and hence very early in the evolution of the sudbury complex we envisage dike emplacement rapidly following rebound and central uplift formation as part of the impact process early dike emplacement implies that the ore was also introduced early in the evolution of the melt sheet when the inclusion poor quartz diorite phases were still unconsolidated uplift would have caused extension in the target rocks and so dilated the footwall fractures and faults that then became hosts primarily via gravitationally driven intrusion to the primitive polymict impact melt breccias and sulfide ores the chilled margin compositions of the foy inclusion poor quartz diorite are considered good indicators of the original bulk composition of the sudbury igneous complex this idea is supported by comparison with calculated estimations of the bulk composition a shift in geochemical trends a grain size increase and a decrease in inclusion content occurs 22 km along the length of the dike which we believe corresponds to a fault system that downfaults to the north given that the dense ore would have preferentially settled toward the base of the foy dike fracture system postimpact downfaulting of the distal segment of the dike may have displaced any mineralized zones present to deeper levels relative to the proximal segment

geology of the giant sudbury polymetallic mining camp ontario canada a new 1 100 000 scale compilation bedrock geology map provided with this issue presents a geologic synthesis of canada s most prolific mining camp the world class sudbury structure with total past production and current reserves of over 1 7 billion tonnes of ni cu co pt pd au ag ore lydon 2007 the polymetallic ore is hosted within one of earth s largest preserved impact craters the new map of the ni cu pge sudbury district after ames et al 2005 is included in a pocket at the back of this issue map 1 and is linked to mineral deposit commodity and geochronology data in tables 1 and 2 of this paper view this table table 1 list of mineral deposits and occurrences of the sudbury map area map 1 view this table table 2 u pb isotope data across the map area since 1891 six compilation maps of the geology of sudbury have been published bell 1891 collins 1937 cooke 1946 card 1969 dressler 1984 ames et al 2005 fig 1 some of the ni cu pge mines have operated for over a century whereas new ore deposits discovered as recently as 2004 are already in production or are in the process of being developed i e advanced prospects in the last 15 years sudbury has been the training ground for 60 postgraduate geoscience students in north america fig 1 from 1903 to 1990 only 23 graduate theses were completed on sudbury related topics eight of them in the 1970s after the discovery of shatter cones dietz 1964 fig 1 number of graduate theses of north american geoscientists trained on sudbury geology per decade showing the minor peak in training after the discovery of shatter cones and the recent education boom with over 50 geoscience graduate theses completed since 1990 the dashed lines represent the regional geologic maps of the sudbury area

the trace metal content of amphibole as a proximity indicator for cu ni pge mineralization in the footwall of the sudbury igneous complex ontario canada alteration veins containing cl poor actinolite and actinolitic hornblende are a common feature throughout the archean aged gneisses and granitoids along the northern margin of the sudbury igneous complex ontario canada crosscutting relations and structural measurements show that the veins postdate the sudbury impact event but predate the emplacement of footwall style cu ni pge platinum group element sulfide ores the veins are four to five times more abundant in brecciated mineralized outcrop than in unbrecciated barren outcrop analyses of vein hosted amphibole by electron microprobe emp and laser ablation icp ms la icp ms show elevated concentrations of ni up to 100 times background increasing from 100 ppm to 1 0 wt cu up to 4 times background and sn up to 2 5 times background in proximity to sulfide veins copper and sn contents in amphibole are only anomalous within 10 to 20 m of mineralization and require quantification by la icp ms however anomalous ni concentrations in vein hosted amphibole may be detected with a high level of confidence solely by emp up to 700 m from mineralization in rocks that contain no visible sulfides in hand sample or thin section and show no bulk rock ni or cu anomalies the relationship between the ni content in amphibole in ppm and mineralization proximity distance d in meters is given by the following equation batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document ni amp 5100 d 0 45 end document the data indicate wide scale ni mobility in hydrothermal solutions in the sudbury footwall the formation of ni rich amphibole in the fracture networks by either the growth of primary ni rich amphibole or metasomatic ni enrichment of preexisting ni poor amphibole was associated with circulation of a sodium and halogen rich fluid between 390o and 550oc nickel may have been released into the footwall environment by extensive hydrothermal alteration of ni rich contact style sulfide ores that lie in the hanging wall of the cu rich footwall style ores in the footwall rocks pre existing fracture networks now amphibole bearing veins acted as common structural pathways first for the circulation of early ni rich fluids associated with leaching in the contact region and the onset of footwall mineralization and second for the emplacement of cu rich footwall style sulfide veins other metal concentrations in amphibole pb zn co show no relationship to mineralization proximity these metals may have been derived locally from country rocks during alteration reactions that promoted amphibole growth in the fractures identification of fracture hosted amphibole with anomalous ni contents in thin section or ni cu sn anomalous amphibole grains liberated from surface weathered rocks hosting sulfide veins may serve as useful proximity indicators for hidden footwall style sulfide deposits at sudbury

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

origin and emplacement of offset dykes in the sudbury impact structure constraints from hess the hess offset is a steeply dipping dyke located 12 15 km north of the 1 85 ga sudbury igneous complex sic within the 200 250 km diameter sudbury impact structure it is up to 60 m wide and strikes subconcentrically to the sic for at least 23 km the main phase of the dyke is granodioritic but it conforms with what is locally referred to as quartz diorite a term used for all the offset dykes of the sudbury impact structure rare earth element data shows that the hess offset is genetically related to the sic hess is most closely affiliated with an evolved felsic norite component of sic and not bulk impact melt this indicates that hess was emplaced during fractionation of the impact melt sheet rather than immediately following impact the main quartz diorite phase of the dyke comprises a quartz plagioclase hornblende biotite clinopyroxene orthopyroxene assemblage critically the hess offset occupies a concentric fault system that marks the northern limit of a pseudotachylyte rich shatter cone bearing annulus about the sic this fault system was active during the modification stage of the impact process

isotopic evidence for distinct crustal sources of north and south range ores sudbury igneous complex lead isotope ratios were measured on fe cu ni sulphide ores and associated silicate phases from nine mines on the north and south ranges of the sudbury igneous complex sic these data are compared with the lead isotope signatures of country rocks and shock melted sudbury breccias around the complex both ore and feldspar data from the south range fall along a 1 85 ga reference line the age of the igneous complex and indicate a magmatic origin for lead in the ore data from the north range are also consistent with a magmatic origin but are displaced to lower 206pb 204pb and 207pb 204pb ratios these two suites fall close to the lead isotope composition of country rocks adjacent to the south and north ranges respectively furthermore there is a close correspondence between lead signatures of the sic and sudbury breccia on each side of the complex the evidence suggests an origin for the sic by shock melting of different crustal units on the two sides of the complex this is consistent with the impact of a meteorite on the southward thickening apron of huronian strata which overlay the margin of the superior craton at 1 85 ga

origins of outliers of the huronian supergroup within the sudbury structure abstract the spatial relations between outliers of huronian metasediment and the current outline of the sudbury igneous complex sic have been used previously to constrain the original size of the meteorite impact crater despite uncertainty regarding their structure and origin the outliers are tight to isoclinal gently plunging synclines with northeast southwest trending axes slightly overturned to the northwest major deformation of the huronian supergroup preceded the 1849 ma sudbury meteorite impact event by sufficient time to permit peneplanation of the region impact occurred in a foredeep related to the subduction of the laurentia plate under the wisconson magmatic terranes faults truncate the northwest margins of most of the outliers where examined at several localities the northwest margin bounding faults are invariably occupied by pseudotachylite structural considerations provide evidence for thousands of meters of slip along these surfaces each of which was apparently accomplished in

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

petrographic and geochemical evidence for an allochthonous possibly impact melt origin of pseudotachylite from the vredefort dome south africa abstract hypotheses proposed to explain the origin of pseudotachylite bodies formed during impact cratering include 1 frictional heating 2 shock loading 3 decompression or 4 drainage of impact melt into target rocks in order to differentiate among these processes we conducted detailed geochemical and petrographic analysis of the matrices in pseudotachylitic veins and dikes and of their respective wall rocks our analyses indicate that the chemical compositions of matrices locally deviate significantly from their immediate wall rocks and that assimilation of wall rock has substantially modified the pseudotachylite matrix compositions in places variable magnitudes of assimilation can be explained by the surface area of wall rock or its fragments in contact with melt as well as the initial temperature and cooling rate of the pseudotachylitic melt chemical trends observed can be explained either by admixture of an exotic melt component with immediate wall rock or by mixing of melts derived from local lithologies trends in the compositional deviation of centimetre to metre wide pseudotachylite dikes from their immediate wall rocks are consistent with the presence of a primary melt component having granitoid composition akin to the average composition of vredefort granophyre dikes within veins melt transport can be geochemically and petrographically traced for distances of centimetres to metres with the direction of melt transport from larger pseudotachylite veins toward smaller ones and into apophyses sulphide and silicate mineralogy indicates that the initial temperature of pseudotachylitic melt must have been at least 1200 1700 c collectively these characteristics point to an allochthonous origin of pseudotachylitic melt we advocate the possibility that impact melt from the initially superheated impact melt sheet contributed to the formation of pseudotachylite bodies at vredefort

origin of large volume pseudotachylite in terrestrial impact structures large volume pseudotachylite bodies in impact structures are dike like and consist of angular and rounded wall rock fragments enveloped by a microcrystalline and sporadically glassy matrix that crystallized from a melt knowledge of the formation of pseudotachylite bodies is important for understanding mechanics of complex crater formation most current hypotheses of pseudotachylite formation inherently assume that fragmentation and melt generation occur during a single process based on the structure of pseudotachylite bodies at sudbury canada and vredefort south africa we show that these processes differ in time and space we demonstrate that the centimeter to kilometer scale bodies are effectively fragment and melt fi lled tension fractures that formed by differential rotation of target rock during cratering highly variable pseudotachylite characteristics can be accounted for by a single process i e drainage of initially superheated impact melt into tension fractures of the crater fl oor

melt origin of fault generated pseudotachylytes demonstrated by textures a petrographic and electron microprobe study of fault generated pseudotachylytes from the outer hebrides thrust zone scotland demonstrates that the textures have resulted from the primary crystallization of a clast laden melt rather than the devitrification of a glass or by crushing and cataclasis the observations are consistent with these pseudotachylytes having formed by frictional fusion followed by rapid quenching implying faulting at shallow crustal depths

thermal evolution and interaction between impact melt sheet and footwall a genetic model for the contact sublayer of the sudbury igneous complex canada 1 the sudbury igneous complex sic and associated ni cu pge mineralization has been interpreted in terms of a large meteorite impact event in this study the thermal relationship between the large cooling melt sheet and the surrounding country rock is examined in terms of its role in an evolving thermal gradient rather than as a passive receptacle for the melt sheet above thermal modeling of this environment is undertaken using physical and thermal constraints appropriate to the sic and assuming heat dissipation from the 2 5 km thick superheated melt sheet 1800 c by either diffusion with zero convection or by rapid convection within the melt sheet with zero convection basal cooling produces a solid base which lowers conductivity such that the immediate footwall rocks reach 1000 c producing partial melting that extends 200 m into the footwall in a rapidly convecting melt sheet the initial footwall chill is remelted and high temperatures maintained within the sheet close to the contact this results in higher temperatures being attained in the immediate footwall 1100 1200 c inducing complete melting of proximal footwall and partial melting to depths of 500 m below the melt sheet proximal footwall consists of paleoproterozoic huronian basalts granitoids and sediments exposed in the south range overlying archaean gneisses and granitoids total and partial melting of this material early in the cooling history of the melt sheet and the subsequent gravitational accommodation of these melts according to density would produce a basalt dominated basal liquid corresponding to the so called contact sublayer the thermal aureole predicted by our models is consistent with that preserved around the north range of the sic assuming 800 m of thermally induced erosion at the contact

pseudotachylyte petrogenesis constraints from the sudbury impact structure pseudotachylytes and their host rocks from the north range of the 1 85 ga sudbury impact structure have been investigated using analytical scanning electron microscopy electron microprobe analysis and xrf spectrometry the results show that the pseudotachylytes were produced in high speed slip zones by the frictional comminution and selective melting of wall rock lithologies the preferential assimilation of hydrous ferromagnesian phases during frictional melting produced relatively basic melts leaving the more mechanically resistant quartz and to a lesser extent plagioclase as included mineral clasts three distinct assemblages are identified within the pseudotachylytes a pre impact 1 85 ga rock and mineral clasts derived from host lithologies b a syn to immediately post impact 1 85 ga rapidly cooled quartz sanidine labradorite phlogopitic biotite matrix assemblage formed due to crystallization from a melt at 800 900 c and c a post impact 1 85 ga retrograde assemblage which overprints both clasts and matrices field evidence indicates that most pseudotachylyte formed in large displacement fault systems during gravitational collapse of the impact generated transient cavity the sudbury pseudotachylytes like endogenic pseudotachylytes were generated by frictional melting on fault surfaces the difference is primarily one of scale large km displacements occurring on impact induced ring faults can generate immense volumes of friction melt resulting in spectacular pseudotachylyte bodies up to 0 5 km thick and more than 10 km long

the formation of the sudbury breccia in the north range of the sudbury impact structure abstract in the north range of the ca 1 85 ga sudbury impact structure massive bodies of sudbury breccia cut across the archean levack gneiss complex and early proterozoic matachewan diabase dykes the complex underlies the sudbury igneous complex sic which represents an impact melt sheet that lined the floor of the impact crater the breccia occurs as 1 100 m wide irregular bodies that contain rounded clasts of diabase and tonalitic and dioritic levack gneiss within a fine grained to aphanitic black to dark grey matrix mineral chemical analyses and rietveld analyses based on x ray diffraction patterns show that the breccia matrix contains microclasts of magnesiohornblende oligoclase and quartz surrounded by metamorphic andesine laths actinolite kfeldspar albite and chlorite which crystallized during cooling of the sic on binary oxide sio2 diagrams breccia values plot on a compositional mixing line between those of the more felsic tonalitic gneiss and the more mafic dioritic gneiss and diabase the breccia has concentrations in rare earth elements rees intermediate between those of the dioritic and tonalitic gneisses and a ree pattern with a negative slope that is less pronounced than those of the gneisses this is due to the addition of a minor diabase component that has a slightly negative ree slope suggesting that the breccia is a mix of comminuted tonalitic gneiss dioritic gneiss and minor diabase comminution and cataclasis of these source rocks occurred along pre existing anisotropies and fractures that formed and were reactivated during the growth and collapse of the transient crater the comminuted materials mixed together as large bodies of breccia that were injected in dilational sites that opened during the upward expansion and collapse of the crater

chemical heterogeneities of caledonian pseudotachylites in the eidsfjord anorthosite north norway the 1 8 1 7 ga eidsfjord anorthosite complex on langoy vesteralen north norway is thrust over monzonitic gneisses in a 100 m wide fault zone the anorthosite contains abundant pseudotachylite which also overprint ductilely formed ultra mylonites in the monzonitic gneisses 40ar 39ar dating of the pseudotachylites indicates that this deformational event took place during the end of the caledonian orogeny pseudotachylite formation by in situ melting is corroborated by a detailed petrological investigation of chemical and textural criteria identity of host rock mineral compositions and modes with pseudotachylite clasts and calculated modes confirm the common notion that transport over more than a few cm did not occur during pseudotachylite formation because the characteristics of the host rocks are inherited by the pseudotachylite pseudotachylite compositions lie in the range of xrf whole rock analyses of deformed and undeformed host rocks demonstrating that no material was added or lost during pseudotachylitisation the pseudotachylites show strong chemical heterogeneity on a scale of tens of micrometers this compositional variation can be described by an approximately binary mixture of plagioclase with a homogenised mafic component comprising orthopyroxene clinopyroxene and fe ti oxides although the pseudotachylite matrix is not homogenised and locally shows schlieren textures the mafic phase in the anorthositic rocks must have homogenised very well before incorporation into the pseudotachylite different viscosities and mixing properties for the al and the fe rich parts of the pseudotachylite melt are inferred

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