breccia dikes and crater related faults in impact craters on mars erosion and exposure on the floor of a crater 75 km in diameter at the dichotomy boundary environmental conditions on mars are conducive to the modification and erosion of impact craters potentially revealing the nature of their substructure on earth postimpact erosion of complex craters in a wide range of target rocks has revealed the nature and distribution of crater related fault structures and a complex array of breccia and pseudotachylyte dikes which range up to tens of meters in width and tens of kilometers in length we review the characteristics of fault structures breccia dikes and pseudotachylyte dikes on earth showing that they occur in complex network like patterns and are often offset along late stage crater related faults individual faults and dikes can undulate in width and can branch and bifurcate along strike detailed geological analyses of terrestrial craters show that faults and breccia dikes form during each of the major stages of the impact cratering process compression excavation and modification we report here on the discovery of prominent lattice like ridge networks occurring on the floor of a highly modified impact crater 75 km in diameter near the dichotomy boundary of the northern lowland and southern upland interior fill and crater floor units have been exhumed by fluvial and eolian processes to reveal a unit below the crater floor containing a distinctive set of linear ridges of broadly similar width and forming a lattice like pattern ridge exposures range from 1 4 km in length and 65 120 m in width are broadly parallel straight to slightly curving and are cross cut by near orthogonal ridges forming a box or lattice like pattern ridges are exposed on the exhumed crater floor extending from the base of the wall toward the center on the basis of the strong similarities of these features to terrestrial crater related fault structures and breccia dikes we interpret these ridges to be faults and breccia dikes formed below the floor of the crater during the excavation and modification stages of the impact event and subsequently exhumed by erosion the recognition of such features on mars will help in documenting the nature of impact cratering processes and aid in assessment of crustal structure faults and breccia dikes can also be used as data for the assessment of post cratering depths and degrees of landform exhumation

superimposition of a thrust transfer fault system on a large impact structure implications for ni cu pge exploration at sudbury a 2 0 km wide metamorphic aureole has been mapped beneath the northern margin of the 2 5 km thick sudbury igneous complex of the 1 85 ga sudbury impact structure the aureole is difficult to observe in the field because it overprints archean granitoids and high grade polydeformed gneisses which do not yield diagnostic thermal minerals at the macroscopic scale however detailed petrography and electron microscopy reveal four zones albite epidote 1 000 m wide hornblende 900 m and pyroxene 200 m hornfels facies and an innermost zone of partial melting 25 m using metamorphic isograds as markers we have revealed previously undetected thrust faults between the sudbury igneous complex and the archean footwall we demonstrate that in places all or part of the aureole has been overthrust and obscured at surface thrust units are segmented by northwest trending strike slip faults which together form thrust transfer fault systems that were active after the impact melt sheet had solidified this post impact deformation is attributed to late penokean 1 85 ga and possibly grenvillian 1 ga compression overthrusting of the footwall by the sudbury igneous complex may conceal sublayer footwall breccia and embayment units that are traditionally the hosts of massive ni cu sulfides and related platinum group element deposits an example is provided by the ministic offset dike located in the west of the sudbury basin which as an intrusion derived from the impact melt is atypical in not being associated with an exposed embayment structure

effects of multipropped excavation on an adjacent floating pile abstractdeep excavations inevitably induce stress relief and soil movement which may affect the safety and serviceability of nearby existing pile foundations although the effects of excavation on

vredefort sudbury chicxulub three of a kind vredefort sudbury and chicxulub are the largest known terrestrial impact structures all have been cited as multi ring basins the available data indicate that all have some form of multiple ring attributes most commonly structural features chicxulub however is the only example with morphological ring features there are also commonalities in the structural and lithological features of vredefort and sudbury and it is possible to construct a generalized compilation of the character of 200 300 km diameter impact basins on earth it is not clear however that any of these structures had the original morphological characteristics of large lunar multi ring basins additional data and synthesis are required to fully characterize these structures in order to realize their potential to constrain large scale cratering processes if this is not sufficient incentive for further studies the environmental effects of chicxulub aside the vredefort sudbury and chicxulub impact events are also the reason for

compaction permeability evolution and stress path effects in unconsolidated sand and weakly consolidated sandstone abstract the influence of stress paths on the mechanical behavior and coupled permeability evolution of quartz sand packings and soft sandstone have been investigated the proposed approach is mainly based on the performing drained compression tests keeping constant a stress path parameter k defined as the ratio of the horizontal to vertical effective stress increments macroscopic mechanical data and the stress path dependency of permeability have been measured in the elastic brittle and compaction regimes the micro structural characteristics of unconsolidated materials coarse rounded grains glass beads gb and angular grains durance sand ds and a weakly consolidated sandstone otter sherwood sandstone oss have been quantified in intact and deformed states combining petrophysical core analysis and multi scale imaging according to the feasibility of sub sampling of the different materials two different types of hydro mechanical behavior were evidenced for each material the weakly consolidated oss presents a mechanical behavior similar to the consolidated rocks with two distinct regimes of deformation the transition between these two regimes is a function of the stress path on the other hand the sand shows a gradual transition regime requiring the use of a curvature criterion to pick yield stresses this criterion has been validated on the basis of acoustic emissions analysis the modified cam clay model and the elliptical cap model allow capturing efficiently the yield envelopes the permeability measurements were performed with intermediate pressure ports to measure accurately the high permeable sand and to avoid end effects for oss permeability evolutions follow closely the volumetric strain evolutions in both the elastic and plastic regimes and are mainly controlled by the mean pressure before yield at these critical stresses the permeability drops drastically under the influence of deviatoric stress conversely for ds the correlation between strain and permeability is not obvious as permeability reduction is pronounced at an early stage of loading

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

4 d constrained depth conversion for reservoir compaction estimation application to ekofisk field ekofisk field in the norweigian sector of the north sea is a remarkable example of a strongly compacted chalk reservoir since the start of production in 1971 the water bottom has subsided by over 8 m as a result of reservoir compaction hermansen et al the field wide waterflood begun in 1989 was expected to halt pressure depletion and reservoir compaction after a few years of waterflooding ekofisk reservoir pressure began increasing but compaction and subsidence continued laboratory studies on chalk cores indicated that high porosity oil filled chalk compacts strongly when flushed with seawater these studies along with reservoir flow simulation and geomechanic modeling led to a model of a water weakening compaction sylte et al ongoing efforts deployed to monitor the reservoir compaction and seabed subsidence include twice a year compaction logging in a monitoring well daily gps measurements at the platforms and periodic bathymetry surveys nine surveys from 1970 to 1999

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

natural fractures in a united kingdom shale reservoir analog cleveland basin northeast england faults and fractures within the well exposed lower jurassic cleveland ironstone and whitby mudstone formations may provide insights into the tectonic history of gas prospective mississippian shale in northern england subvertical opening mode fractures occur throughout the cleveland basin bed parallel fractures some of which contain blocky calcite fills occur preferentially within well bedded clay rich mudstones of the cleveland ironstone and whitby mudstone formations at jet wyke and port mulgrave subvertical fractures display abutting or curving parallel relationships with under and overlying bed parallel fractures together these observations suggest that bed parallel fractures at times acted as free surfaces some bed parallel fractures curve toward and branch from calcite filled fault slip surfaces indicating that bed parallel fracturing and normal faulting were synchronous occurring within a regional stress field with vertical maximum principal stress this apparent paradox can be explained by normal compaction followed by cementation and coupling between pore pressure and minimum horizontal stress driven by poroelastic deformation or incipient slip along critically stressed normal faults causing elevation of horizontal stress in excess of the vertical stress within clay rich units propagation of bed parallel fractures was enhanced by dilatational strains adjacent to normal fault planes bed parallel fractures have not been observed within more rich units at the top of the whitby mudstone formation at whitby east cliff or within well bedded clay rich shale at saltwick nab this observation is consistent with the lack of normal faulting at saltwick nab and the whitby mudstone formation having been drained by structural and or stratigraphical juxtaposition against permeable middle jurassic sandstones at both these localities

anelasticity and dispersion in dry unconsolidated sands laboratory measurements reveal frame modulus dispersion and creeping behavior in room dry samples of unconsolidated quartzo feldspathic upper miocene turbidites from the wilmington field ca a single standard linear solid model predicts both the dispersion and the creep response similar behavior is observed in ottawa sand samples when mixed with wetted montmorillonite in this case the magnitude of dispersion and creep increase with increasing clay content we suggest that the anelastic behavior of the wilmington sands is due to the presence of micas and a small amount of clay the transition frequency of 2 10 4hz i e between high and low frequency behavior suggests that seismic sonic and ultrasonic measurements of rock moduli are quite similar in the absence of fluids the static frame modulus should be used to model tectonic processes and long term production related changes in oil field environments

early fracturing and impact residue emplacement can modelling help to predict their location in major craters understanding the nature and composition of larger extraterrestrial bodies that may collide with the earth is important one source of information lies in the record of ancient impact craters some of which have yielded chemical information as to the impacting body many deeply eroded craters have no remaining melt sheet or ejecta yet may contain impactor residue within basement fractures the emplacement mechanism for fractionated siderophile residues is likely to be gaseous although melt droplets and some solid materials may survive for breccia and melt filled fractures to contain extraterrestrial material they must form very early in the impact process most current numerical models do not dwell on the formation and location of early major fractures although fractures in and around small craters on brittle glass exposed to hypervelocity impact in low earth orbit have been successfully simulated modelling of fracture development associated with larger craters may help locate impact residues and test the models themselves

emplacement of metabreccia along the whistle offset dike sudbury implications for post impact modification of the sudbury impact structure the whistle offset dike is a radial dike linked to the ca 1850 ma sudbury igneous complex sic in sudbury ontario it is linked through the funnel shaped whistle embayment which formed as a depression along the floor of a superheated impact melt sheet represented by the present day sic the dike consists of metabreccia quartz diorite and inclusion bearing quartz diorite emplaced in older archean gneisses and intrusions metabreccia has a fine grained igneous textured matrix surrounding archean basement clasts it overlaps in major element compositions mgo cao sio 2 with the two quartz diorites the three have similar chondrite normalized rare earth element patterns characterized by pronounced negative slopes i e la yb n 17 29 and a weak negative eu anomaly this suggests that they originated from the same source melts metabreccia has higher high field strength element hfse ratios i e gd yb ce yb zr y and lower model initial 207 pb 204 pb isotopic ratios than the two quartz diorites suggesting that it assimilated more archean rocks with higher hfse ratios and lower 207 pb 204 pb ratios it formed as sic melts mixed with melted basement rocks at the sic basement contact this produced a strongly contaminated inclusion bearing melt which drained downward into an offset structure or fault entrained more fragments plucked from the walls of the fault and crystallized as metabreccia less contaminated quartz diorite was then emplaced in the still viscous metabreccia during reactivation of the fault caused by isostatic readjustment of the gravitationally unstable crater more melting assimilation of clasts and mixing of sic melts at the sic basement contact produced inclusion bearing quartz dioritic melts that were emplaced last along the whistle offset fault

emplacement of the whistle dike the whistle embayment and hosted sulfides sudbury impact structure based on anisotropies of magnetic susceptibility and magnetic remanence the sudbury impact structure is one of the few multi ring meteorite impact structures recognized on earth the meteorite impact occurred ca 1850 ma resulting in the production of impact melts derived from the crust possibly with a mantle component the impact melts formed the sudbury igneous complex and also were emplaced as radial and concentric dikes within the target rocks the whistle dike one of the radial offset dikes in the sudbury impact structure is connected to the sudbury igneous complex by the whistle embayment structure which is composed of noritic cumulates we present a study of the emplacement flow patterns in the whistle dike and the embayment using magnetic anisotropy methods to measure the petrofabrics that record emplacement petrographic and scanning electron microscope observations combined with thermal demagnetization measurements and tests of the acquisition and demagnetization of anhysteretic magnetic remanence indicate that the primary sources of the magnetic signals in the sample suite are coarse grained soft coercivity magnetite and pyrrhotite that are interpreted to be primary igneous phases some samples also contain hard coercivity phases of possible metamorphic origin the anisotropy of magnetic susceptibility ams the anisotropy of an hysteretic remanent magnetization aarm and the anisotropy of partial anhysteretic remanent magnetization aparm were measured for the samples collected at 20 sites within the whistle dike and the embayment structure including an exposed chalcopyrite rich massive sulfide body the ams method provided well defined interpretable fabrics for many of the sample sites however the ams and aarm methods were unsuccessful in providing interpretable fabric measurements at some sample sites due to contributions from the hard coercivity ferromagnetic minerals for those samples the aparm method was successful in isolating the sub fabric defined by the primary magnetite pyrrhotite crystals the fabric maps are consistent with lateral horizontal injection of the whistle offset dike and subsequent sinking of molten massive sulfides within the still ductile dike sinking of the massive sulfides is recorded by steeply plunging magnetic lineations the magnetic fabrics in the cumulate norites of the embayment structure show that the norites were deposited in a dynamic environment that resulted in a well oriented lineation which may record flow of gravity or thermal currents channelled along the embayment axis in the embayment the lineations plunge toward a massive sulfide body suggesting the flow that led to the formation of the lineation may also have led to emplacement of the massive sulfide ore it is suggested that steeply plunging lineations elsewhere in the whistle offset dike and possibly in other sudbury offset dikes might indicate the trails of sunken massive sulfides in the subsurface it is also suggested that magnetic fabrics might be useful to locate massive sulfide bodies hosted in embayment structures

predicting and monitoring long term compaction in unconsolidated reservoir sands using a dual power law model we propose a model for predicting the long term creep compaction of unconsolidated sand reservoirs prior to significant depletion the model is based upon linear viscoelasticity theory whereby deformation is decoupled into instantaneous and time dependent components the instantaneous component of deformation is modeled using a power law function of effective pressure model parameters are solved by conducting a constant strain rate laboratory experiment the time dependent deformation is modeled using a power law function of time associated model parameters are solved by conducting a creep strain test at the anticipated in situ effective pressure in total application of the model involves measurement of three model parameters obtained by conducting two different laboratory experiments we illustrate the model utilizing samples from unconsolidated sand reservoirs in the wilmington field in california and an offshore field in the gulf of mexico we show that the stiffness change associated with the porosity reduction predicted by the model is large and could be monitored using p wave velocity this should make compaction observable with 4d seismic surveys of the example fields

independence of geostatic stress from overconsolidation in some beaufort sea clays reply since 1982 extensive use has been made of the self bored pressuremeter in arctic offshore site investigations one finding of this work is that the in situ geostatic stress ratio k0 of beaufort sea clays is apparently unrelated to the overconsolidation ratio ocr the procedures and data to support this finding are documented and the finding is discussed in light of the present geological understanding for the area it is concluded that the independence of k0 from ocr may be quite widespread a finding that contradicts the widely held tenet regarding the existence of a single valued function relating k0 and ocr if k0 is regarded as important then it should be measured in situ key words self bored pressuremeter geostatic stress ratio k0 beaufort shelf geologic history overconsolidation ratio

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

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

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

discrimination between pressure and fluid saturation changes from time lapse seismic data explicit expressions for computing saturation and pressure related changes from time lapse seismic data have been derived and tested on a real time lapse seismic data set necessary input is near and far offset stacks for the baseline seismic survey and the repeat survey the method has been tested successfully in a segment where pressure measurements in two wells verify a pore pressure increase of 5 to 6 mpa between the baseline survey and the monitor survey estimated pressure changes using the proposed relationships fit very well with observations between the baseline and monitor seismic surveys 27 of the estimated recoverable hydrocarbon reserves were produced from this segment the estimated saturation changes also agree well with observed changes apart from some areas in the water zone that are mapped as being exposed to saturation changes which is unlikely saturation changes in other segments close to the original oil water contact and the top reservoir interface are also estimated and conf

geology mineralization and emplacement of the whistle parkin offset dike sudbury the whistle parkin dike is a 12 km long radial offset dike located in the northeast sector of the 1 85 ga sudbury impact structure the dike is connected to the sudbury igneous complex via a 0 5 km long 250 m wide embayment the whistle segment of the dike narrows to a width of approximately 30 m and extends for about 1 5 km from the complex where it is cut by the post creek fault zone this fault displaces the dike 2 km to the northwest beyond which it continues as the parkin portion of the dike the parkin segment extends a further 10 km north northeast the dike and genetically associated embayment are comprised of numerous rock types these include the sublayer radial breccia mafic sulfide bearing breccia inclusion rich quartz diorite and inclusion poor quartz diorite economic ni cu pge mineralization is found in association with the sublayer mafic sulfide bearing breccia and inclusion bearing quartz diorite phases rare earth element ree data reveal that the dike lithologies are representative of bulk sudbury igneous complex melt we propose a multistage emplacement mechanism for the dike the breccia units including the inclusion bearing quartz diorite phase were forcefully injected laterally into an impact generated radial crack during the excavation stage of crater formation subsequent early modification processes facilitated the intrusion of inclusion poor quartz diorite particularly along the dike margins inclusion poor quartz diorite emplacement may have been gravitationally driven from the overlying impact melt sheet later stage modification i e final transient cavity collapse caused decoupling of the whistle and parkin dike segments via faulting this occurred concurrently with the settling of the sublayer unit and associated economic sulfides into the embayment and main dike segments

application of hyperbolic stress strain models for sandstone and shale to fold wavelength in the mexican ridges foldbelt abstract the mexican ridges foldbelt on the continental slope east of mexico has major folds with wavelengths averaging 7 km locally there are also small amplitude near surface folds with wavelengths of 2 km initial dominant wavelength is modelled by the finite element method using the hyperbolic stress strain relationship originally derived for soils hyperbolic stress strain models for sandstone and shale are calibrated using field porosity depth relationships for shale and laboratory one dimensional consolidation data for sand and clay effective tangent young s modulus calculated from hyperbolic stress strain models is generally higher for sandstones than for shales and for both rock types modulus increases substantially with depth the finite element models of dominant wavelength duplicate the two orders of folds observed in the mexican ridges and match their wavelengths in the models fold wavelength is nearly constant for large variations in both sandstone fraction in the folded section and pore pressure magnitude in the overpressured basal shale below the folded section but fold amplification is increased by high pore pressure in the basal shale and by high sandstone fraction in the folded section fold wavelength is affected more by depth distribution of high pore pressure than by pressure magnitude and on the lower continental slope where grain size may be smaller a thicker zone of high pressure would partly explain the modest downslope increase in fold wavelength

chemical variations and genetic relationships between the hess and foy offset dikes at the sudbury impact structure offset dikes are found concentrically around and extending radially outward from the sudbury igneous complex sic which represents an 3 km thick differentiated impact melt sheet the dikes are typically composed of an inclusion rich so called quartz diorite iqd in the center of the dike and an inclusion poor quartz diorite qd along the margins of the dike new exposures of the intersection between the concentric hess and radial foy offset dikes provide an excellent opportunity to understand the relationship between the radial and concentric offset dikes and their internal phases the goal was to constrain the timing of the dike emplacements relative to the impact and formation of the sic results herein suggest that 1 the timing between the emplacement of the qd and iqd melts was geologically short 2 the hess and foy dikes coexisted as melts at the same time and the intersection between them represents a mixture of the two 3 the foy dike has a slightly more evolved chemical composition than the hess dike and 4 the iqd melt from the foy dike underwent some degree of chemical fractionation after its initial emplacement

rocks under strain strain induced time lapse time shifts are observed for depleting reservoirs pressure depletion as a result of oil and gas production creates changes in the stress and strain fields of the rock material both inside and outside the reservoir seismic waves propagating through these rocks have different traveltimes before and after depletion because the layer thicknesses change and the seismic velocity is altered by the changes in the stress and strain fields the cumulative change in two way traveltimes with depth is referred to as time lapse time shift

time dependent deformation of shale gas reservoir rocks and its long term effect on the in situ state of stress abstract laboratory testing of shale gas reservoir rocks reveal varying amounts of time dependent viscous deformation in response to applied differential stress the time dependent deformation is an inherent property of the dry rock as it occurs in the absence of pore fluid the contribution of the time dependent deformation is generally larger for rocks with more clay and organic content the time dependent behavior can be modeled as a power law function of time its magnitude is approximately linear with the magnitude of the applied differential stress and nearly insensitive to the confining pressure by applying linear viscoelastic theory and using laboratory constrained constitutive parameters we evaluated the effect of the time dependent deformation in modifying the in situ differential stress over time modeling suggests that a significant proportion of a differential stress change would be relaxed over time scales on the order of days because of this short time scale the composition of the rock as it influences the time dependent behavior may influence the in situ differential stress magnitudes stronger than the formation s geological loading history for these reservoirs

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

is the ancestral yellowstone hotspot responsible for the tertiary carlin mineralization in the great basin of nevada we propose a genetic relationship between the 43 34 ma magmatism extensional tectonics and gold mineralization event centered in the great basin of nevada and the development of the ancestral yellowstone hotspot the model is compatible with cenozoic regional tectonics and provides a plausible explanation of the spatial coincidence of the eocene oligocene magmatic events and the carlin type gold deposits these features are centered in the battle mountain region of the great basin coincident with the inferred ca 40 30 ma position of the yellowstone hotspot the yellowstone hotspot is probably a plume that ascended from the core mantle boundary a region thought to be anomalously rich in gold and in the moderately siderophile elements associated with gold deposits as the hotspot was progressively overridden by the north american plate after ca 60 ma a magmatically quiescent period related to subhorizontal subduction gave way to the generation of ca 43 34 ma voluminous intracrustal melts and metamorphic devolatization as the hotspot broke though the subducted farallon plate coeval crustal extension and convective circulation of hydrothermal fluids in the upper crust facilitated the exploitation of the structural and lithologic traps that characterize the classic carlin type deposits

searching for giant ancient impact structures on earth the mesoarchaean maniitsoq structure west greenland a 100km scale circular region in the archaean north atlantic craton centred at 651150n 511500w near maniitsoq town in west greenland comprises a set of highly unusual geological features that were created during a single event involving intense crushing and heating and are incompatible with crustal orogenic processes th presently exposed features of the maniitsoq structure were buried 20 25 km below the surface when this event occurred at c 3ga during waning convergent orogeny these features include a large aeromagnetic anomaly a central 35x50 km2 large area of comminuted quartzo feldspathic material regional scale circular deformation widespread random fractures with feather like textures intense fracture cleavage amphibolite granite matrix breccias unrelated to faulting or intrusions formation and common fluidisation of microbreccias abundant evidence of direct k feldspar and plagioclase melting superimposed on already migmatised rocks deformation of quartz by oc4 slip formation of planar elements in quartz and plagioclase and emplacement of crustally contaminated ultramafic intrusions and regional scale hydrothermal alteration under amphibolite facies conditions the diagnostic tools employed to identify impacting in the upper crust are inadequate for structures preserved deep within the continental crust nevertheless the inferred scale strain rates and temperatures necessary to create the maniitsoq structure rule out a terrestrial origin of the structure

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

monitoring primary depletion reservoirs using amplitudes and time shifts from high repeat seismic surveys in the high porosity poorly consolidated turbidites of the deepwater gulf of mexico production induced compaction is the main production drive mechanism when aquifer support is weak and prior to pressure support by secondary recovery water injection time lapse 4d seismic monitoring of this class of reservoirs has provided several new learning opportunities the time lapse amplitude response of these fields can be complicated due to saturation changes water replacing oil inside the reservoir rock compaction causing density and velocity changes inside the reservoir stress relief and associated deformation of the rock outside the reservoir and changes in reservoir fluid pressures due to pore pressure decrease methods that rely on time lapse amplitude changes with offset to discriminate pressure and saturation changes can help separate and thus simplify the interpretation of some of these effects tura and lumley 1999 landro 2001

contraction driven shear failure in compacting uncemented sediments shear failure in sediments is universally linked with active boundary conditions such as those imposed by tectonic stresses under conditions of no lateral strain and in the absence of tectonic stress soil mechanics theories predict a simple one dimensional compaction in which sediment particles displace vertically without shear failure during pressure diffusion conflicting with this theory shear failure planes are often found in sediments that formed under near horizontal burial conditions we investigated the effect of particle scale volume contraction as a potential cause of shear failure in uncemented particulate materials and found that loss of particle volume under confined conditions no external loading resulted in pronounced lateral stress reduction often reaching coulomb frictional failure conditions shear strain localization was analytically predicted and modeled numerically due entirely to volume loss at the grain scale we define this mode of internally driven shear failure as contractile to distinguish it from that caused by external loading and show that it can explain many natural fracture systems without invoking regional tectonics

the pele offset dykes sudbury impact structure canada the offset dykes are impact melt bearing dykes related to the 1 85 ga sudbury impact structure currently the dykes extend radially outward from or occur concentrically around the sudbury igneous complex which is the remnant of a differentiated impact melt sheet and the source of the dykes the recently identified three pele offset dykes intrude into the archean rocks north of the sudbury igneous complex in this study the pele dykes are characterized for the first time by a combination of fieldwork optical microscopy electron microprobe analyses and bulk geochemical analyses the pele offset dykes stand out from the other offset dykes at sudbury in two significant ways i all other known offset dykes consist of an inclusion rich lithology in the center of the dyke and an inclusion poor lithology along the margins the pele dykes however are only composed of the inclusion poor phase ii the pele dykes particularly the central and eastern dykes have a more evolved chemical composition relative

deformation modulus of heavily jointed sheared and blocky greywackes by pressuremeter tests numerical experimental and empirical assessments deformability of rock masses influencing their behavior is an important geomechanical property for the design of rock structures due to the difficulties in determining the deformability of jointed rock masses at the laboratory scale various in situ test methods such as pressuremeter dilatometer plate loading tests etc have been developed although these techniques are currently the best and direct methods they are time consuming and expensive and present operational difficulties in addition the influence of the test volume on deformation modulus depending on the method employed is also important for these reasons empirical equations to indirectly estimate the deformation modulus have also been recommended by several investigators as an alternative approach in this study the geomechanical quality of weak heavily jointed sheared and or blocky greywacke rock masses on which very concentrated civil works are continuing at the southern and southwestern parts of ankara turkey was assessed the deformation modulus was determined by pressuremeter tests the possible effects of variables on the derived deformation modulus from the pressuremeter test were evaluated by numerical methods and the comparisons between the deformation modulus of the greywackes obtained from the pressuremeter tests and their geomechanical quality gsi and rmr were made numerical simulations revealed that the presence of a disturbed annulus around the borehole causes underestimation of the deformation modulus while the effect of length to diameter ratio of the pressuremeter probe on the deformation modulus is minor based on the geo engineering characterization assessments mainly two greywacke rock masses with different geomechanical qualities were identified geotechnical quality of one of these rock masses was verified by the back analysis of two slope failures the empirical equations to indirectly estimate the deformation modulus of the greywackes using their gsi and rmr values yielded high coefficients of correlation

effective stress vane shear strength correction factor correlations a recent effective stress model of vane shear strength testing in soils can relate measured torques to vane shear strengths using theoretical analysis in terms of effective stress parameters the strength estimates are based on known in situ stresses and soil parameters derived from laboratory testing the model may be applied for example in obtaining theoretical estimates of conventional undrained vane shear strengths for comparison with field data and for use in stability analyses however the model incorporates a correction factor v analogous to bjerrum s field vane shear strength correction factor intended to compensate for pore pressure and shearing rate effects this correction factor must be evaluated before reliable torque or shear strength estimates can be made in any given case to facilitate this the paper presents correlations of v with both liquid limit and plasticity index based on world wide data from clays and silts the correlations are compared with independent data from norwegian clays

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

tectonic influences on the morphometry of the sudbury impact structure implications for terrestrial cratering and modeling impact structures developed on active terrestrial planets earth and venus are susceptible to pre impact tectonic influences on their formation this means that we cannot expect them to conform to ideal cratering models which are commonly based on the response of a homogeneous target devoid of pre existing flaws in the case of the 1 85 ga sudbury impact structure of ontario canada considerable influence has been exerted on modification stage processes by late archean to early proterozoic basement faults two trends are dominant 1 the nnw striking onaping fault system which is parallel to the 2 47 ga matachewan dyke swarm and 2 the ene striking murray fault system which acted as a major paleoproterozoic suture zone that contributed to the development of the huronian sedimentary basin between 2 45 2 2 ga sudbury has also been affected by syn to post impact regional deformation and metamorphism the 1 9 1 8 ga penokean orogeny which involved nnw directed reverse faulting uplift and transpression at mainly greenschist facies grade and the 1 16 0 99 ga grenville orogeny which overprinted the se sector of the impact structure to yield a polydeformed upper amphibolite facies terrain the pre syn and post impact tectonics of the region have rendered the sudbury structure a complicated feature careful reconstruction is required before its original morphometry can be established this is likely to be true for many impact structures developed on active terrestrial planets based on extensive field work combined with remote sensing and geophysical data four ring systems have been identified at sudbury the inner three rings broadly correlate with pseudotachylyte friction melt rich fault systems the first ring has a diameter of 90 km and defines what is interpreted to be the remains of the central uplift the second ring delimits the collapsed transient cavity diameter at 130 km and broadly corresponds to the original melt sheet diameter the third ring has a diameter of 180 km the fourth ring defines the suggested apparent crater diameter at 260 km this approximates the final rim diameter given that erosion in the north range is 6 km and the ring faults are steeply dipping impact damage beyond ring 4 may occur but has not yet been identified in the field one or more rings within the central uplift ring 1 may also exist this form and concentric structure indicates that sudbury is a peak ring or more probably a multi ring basin these parameters provide the foundation for modeling the formation of thisrelatively large terrestrial impact structure

comparison of the measured and finite element predicted ground deformations of a stiff lodgement till the use of the finite element method to model excavations and tunnels in dublin black boulder clay has in the past had limited success owing to the failure of the available constitutive models in commercially available software programs to adequately represent the essential features of a stiff soil a stiff soil lodgement till underlies much of the city of dublin ireland consequently the successful prediction of deformations in this soil arising from structural and infrastructural projects is of considerable importance research has shown that the stress strain response of a stiff soil is complex and depends on many factors including stress history stress level and strain direction these important features are included in the hardening plasticity small strain stiffness hss soil model that is incorporated in the plaxis v8 4 finite element code this paper describes the field and laboratory methods that were used to determine the parameters for incorporation in this soil model and the validati

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

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

magnetic fabric constraints on friction melt flow regimes and ore emplacement direction within the south range breccia belt sudbury impact structure abstract magnetic fabric analysis and petrography have been carried out on 1100 samples from the south range breccia belt srbb a 45 km long arc of huronian supergroup breccia fragments and crystallized friction melt pseudotachylyte sub concentric to the 1 85 ga sudbury impact structure optical petrography and analytical sem analyses show the pseudotachylyte to consist of fine grained quartz biotite and ilmenite with minor plagioclase apatite zircon pyrite and pyrrhotite alternating field and thermal demagnetization spectra indicate that the principal magnetic carrier in the matrix is pyrrhotite while clasts can contain either pyrrhotite or magnetite mean magnetic susceptibilities in the matrix are generally on the order of 10 4 si two ams anisotropy of magnetic susceptibility fabrics have been determined in the matrix the most common is an oblate sub vertical foliation sub parallel to the local strike of the srbb with anisotropies p ranging from 1 08 to 1 20 the second ams fabric is a weakly to strongly prolate sub vertical lineation with generally higher p values of 1 2 to 1 55 both fabrics are coaxial to the petrofabric in the matrix huronian clasts exhibit scattered heterogeneous ams fabrics distinct from those found in the srbb matrix the strongly prolate t 0 73 and anisotropic p 1 55 ams fabric found directly over the giant frood stobie ni cu pge deposit hosted within the srbb suggests that sulfide droplets were injected and or squeezed into the matrix above the deposit samples containing pyrrhotite from the edges of the deposit do not exhibit this magnetic signature similar prolate moderately anisotropic lineations are also found further to the east of the frood stobie mine and appear to be associated with a magnetotelluric conductor at depth it is suggested that these lineations are due to injection of material from depth into the srbb during failure of the inner rim of the sudbury impact structure during the crater modification stage the oblate magnetic fabric found within the srbb is consistent with frictional comminution and melting of the wall rock lithologies during collapse of the transient cavity and subsequent slumping of the crater walls however subsequent deformation of the sudbury structure by late penokean folding and thrusting to the nw could produce a similar oblate fabric tight clustering of the maximum principal axes of the magnetic susceptibility could be interpreted as being consistent with tectonometamorphic transposition of the matrix petrofabric as well as generation by slumping and friction melt flow during failure of the hanging wall further work is needed on undeformed impact structures of similar size to sudbury in order to constrain the petro and magnetic fabrics produced during rim collapse additional work in the westerly trending srbb along the edge of the creighton pluton would help to determine if the dominant ne sw trending matrix fabric is regional in origin or is controlled by the current orientation of portions of the srbb

determination of deformation modulus in a weak rock mass by using menard pressuremeter abstract the deformation modulus of heavily jointed andesitic rock mass was investigated by using 41 menard pressuremeter test results and geotechnical information obtained from seven geotechnical boreholes the geotechnical borehole logs and laboratory test results provided by a mining company were used for the assessment of rock mass characterization the log and the test results were taken into account in the rock mass classification work the well known empirical equations were employed to predict the deformation modulus of the rock mass the predictions and the pressuremeter test results were compared and their performance indicators were presented non linear multiple regression methods were used for predictive modelling of the deformation modulus of the rock mass by considering the available data rock quality designation rqd discontinuity condition rating dc of the rock mass rating rmr system and uniaxial compressive strength of the intact rock ci were taken into consideration as input parameters in four new prediction equations to be used for determination of deformation modulus one more equation was proposed by the addition of the depth as a predictive parameter the influence of the depth and vertical to horizontal stress ratio k on the deformation modulus was preliminarily examined by using finite element modelling initially the rock mass was assumed to be an isotropic elastic brittle plastic medium later on the rock mass was modelled as a discontinuum by imposing a discrete fracture network dfn keeping all of the mechanical properties constant different depth and k parameters were applied to the pressuremeter models no influence of the depth and k on the deformation modulus was observed for the isotropic medium while the depth contributed to an increase in the modulus in the anisotropic discontinuum analysis the numerical modelling findings constituted a basis for the inclusion of the depth parameter into the new predictions

emplacement of sulfide deposits in the copper cliff offset dike during collapse of the sudbury crater rim evidence from magnetic fabric studies quartz diorite offset dikes in the country rocks surrounding the 1 85 ga sudbury impact structure were emplaced within fractures formed during hypervelocity impact providing conduits for the injection of quartz diorite impact melts the offset dikes host major ni cu pge deposits with the radial copper cliff dike hosting 15 percent of the known sudbury ore the anisotropy of magnetic susceptibility of the copper cliff dike was studied to determine the nature of the fabrics that developed during emplacement of the quartz diorite and the associated sulfide bodies the anisotropy of magnetic susceptibility reveals a predominantly northwest southeast striking steeply dipping foliation and a steeply northwest to vertically plunging lineation the foliation along both the eastern and western sides of the dike is counterclockwise oblique to the north south to north northwest south southeast striking vertically dipping dike margins the magnetic fabrics in the dike are consistent with a component of strike slip displacement during emplacement of the quartz diorite melt the data are interpreted to indicate that the copper cliff dike acted as a melt lubricated dextral transfer fault during collapse of the inferred inner rim of the central peak ring to accommodate ultra high strain rate displacements on previously documented pseudotachylite rich normal fault zones collapse may have caused injection of sulfide rich melts into the copper cliff dike leading to the formation of cu ni pge deposits collapse of the inner rim of the central peak ring is thought to have occurred too soon after the impact to allow for fractionation of the sulfides from the impact melt sheet therefore it is suggested the sulfide rich impact melts were derived principally from the target rocks

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

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

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

differentiation and emplacement of the worthington offset dike of the sudbury impact structure ontario the offset dikes of the 1 85 ga sudbury igneous complex sic constitute a key topic in understanding the chemical evolution of the impact melt its mineralization and the interplay between melt migration and impact induced deformation the origin of the melt rocks in offset dikes as well as mode and timing of their emplacement are still a matter of debate like many other offset dikes the worthington is composed of an early emplaced texturally rather homogeneous quartz diorite qd phase at the dike margin and an inclusion and sulfide rich quartz diorite iqd phase emplaced later and mostly in the centre of the dike the chemical heterogeneity within and between qd and iqd is mainly attributed to variable assimilation of host rocks at the base of the sic prior to emplacement of the melt into the dike petrological data suggest that the parental magma of the worthington dike mainly developed during the pre liquidus temperature interval of the thermal evolution of the impact melt sheet 1200 c based on thermal models of the cooling history of the sic the two stage emplacement of the worthington dike occurred likely thousands to about ten thousand years after impact structural analysis indicates that an alignment of minerals and host rock fragments within the worthington dike was caused by ductile deformation under greenschist facies metamorphic conditions rather than flow during melt emplacement it is concluded that the worthington offset dike resulted from crater floor fracturing possibly driven by late stage isostatic readjustment of crust underlying the impact structure

a u pb age for mineralized nipissing diabase gowganda ontario concordant baddeleyite and rutile analyses from mineralized nipissing diabase at gowganda s castle mine yield a u pb age of baddeleyite is a primary phase of the diabase therefore the age dates the magmatic emplacement the genesis of rutile is less certain rutile could have formed during an episode of alteration veining and ag mineralization in which case the u pb age would also date the secondary event and demonstrate that ag mineralization was related to the nipissing magmatism however a primary magmatic origin of the rutile cannot be completely excluded for now thus the u pb age may not constrain the time of ag mineralization further research is needed to clarify this point

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

the south range breccia belt of the sudbury impact structure a possible terrace collapse feature the south range breccia belt srbb is an arcuate 45 km long zone of sudbury breccia in the south range of the 1 85 ga sudbury impact structure the belt varies in thickness between tens of meters to hundreds of meters and is composed of a polymict assemblage of huronian supergroup 2 49 2 20 ga nipissing diabase 2 2 ga and proterozoic granitoid breccia fragments ranging in size from a few millimeters to tens of meters the srbb matrix is composed of a fine grained 100 m assemblage of biotite quartz and ilmenite with trace amounts of plagioclase zircon titanite epidote pyrite chalcopyrite pyrrhotite and occasionally chlorite the srbb hosts the frood stobie vermilion and kirkwood quartz diorite offset dykes the former being associated with one of the largest ni cu pge sulphide deposits in the world optical petrography and whole rock geochemistry concur with previous studies that have suggested that the matrix of the srbb is derived from comminution and at least partial frictional melting of the wall rock huronian supergroup lithologies rare earth element ree data from all sampled lithologies associated with the srbb exhibit crustal signatures when normalized to c1 chondrite values additionally ree data from the quartz diorites disseminated sulphides in sudbury breccia and a sample of an aphanitic biotite hornblende tonalite dyke exhibit flat slopes when compared to the mafic and felsic norites quartz gabbro and granophyre units of the sudbury igneous complex sic which suggests that these lithologies are representative of bulk sic melt we suggest that the srbb was formed by high strain rate 1 m s gravity driven seismogenic slip of the inner ring of the sudbury impact structure during postimpact crustal readjustment crater modification stage failure of the hanging wall may have facilitated the injection of bulk sic melt into the srbb along with the ni cu pge sulphides of the frood stobie deposit postimpact penokean 1 9 1 7 ga tectonism particularly northwest directed shearing along the south range shear zone and associated thrust faulting could account for the present subvertical orientation of the srbb and the apparent lack of a connection at depth with the sic

determination of the deformation modulus of dispersible intercalated jointed cherts using the menard pressuremeter test abstract due to the difficulties encountered during the preparation of representative cores from fragile intercalated weathered jointed rock masses for laboratory scale testing various in situ test methods such as pressuremeter dilatometer plate loading plate jacking goodman jacking flat jack cable jacking tests etc have been developed for determining the deformation modulus of rock masses however almost all of these in situ tests require time consuming procedures have operational difficulties and have high costs therefore rock mass classification systems and empirical equations have been developed for estimation of parameters such as the deformation modulus in this study dispersible fragile intercalated and heavily jointed chert rock mass supporting several large scale structures under construction in manisa turkey was classified based on rmr gsi and ucs as input parameters for estimation of deformation modulus using some of well known empirical equations three chert rock masses with different geomechanical qualities were identified point load tests were performed to determine the ucs of the cherts to characterize the rock masses the deformation modulus obtained from the menard pressuremeter tests was compared to the modulus estimated using empirical equations in addition an attempt also was made to examine the dependency of the deformation modulus of the studied chert rock masses to the confining stress empirical relationships and equations with high correlation were obtained for predicting the deformation modulus by using input parameters such as rmr gsi ucs and confining stress

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

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

differentiation and source of the nipissing diabase intrusions ontario canada major and trace element data are presented for 2 2 ga proterozoic diabase sills from across the nipissing magmatic province of ontario in situ differentiation of the magma coupled with assimilation of huronian supergroup roof sediments is responsible for the variation in composition between quartz diabase and granophyric diabase seen within many of the differentiated intrusions uniform trace element and isotope ratio signatures such as la sm 2 8 3 7 and endchur 2 7 to 5 9 characterize chilled margins and undifferentiated quartz diabases these chemical signatures suggest the existence of a single magma source that was parental to intrusions throughout the magmatic province this magma has higher la sm and lower ti y than primitive mantle and is displaced towards the composition of shales most chilled diabases and quartz diabases have a similar mg 0 64 and 0 60 and ni content 98 and 127 ppm and it is argued that the magma differentiated at depth and was emplaced as a uniform low mg magma

gravity and magnetic field modeling and structure of the chicxulub crater mexico the chicxulub crater is an 180 km diameter peak ring crater based on drill hole logs and samples potential fields seismic reflection profiles and surface fracture patterns a structural cross section produced based on these constraints has the features expected for a large complex impact crater the bouguer gravity anomaly consists of a broad 90 km radius 30 mgal low with a central 20 km radius 20 mgal high and two 5 mgal concentric lows at 35 and 60 km radius the gravity anomaly is disrupted by large scale basement anomalies and possibly by large scale slumping and backwash erosion effects the magnetic field anomaly over the crater consists of three zones an outer zone from 45 to 90 km radius of low amplitude short wavelength anomalies with an irregular perimeter a middle zone from 20 to 45 km radius of high amplitude short wavelength anomalies slightly elongated nnw sse and an inner 20 km radius single large amplitude anomaly magnetic field modeling indicates that the melt pool averages 90 km in diameter and the melt volume in the crater is estimated at 20 000 km3 the melt pool size constrains the collapsed transient cavity diameter to 90 km gravity and magnetic field modeling indicate that the structural uplift is irregular in shape but 40 km in diameter and underlies or protrudes into the melt pool the preliminary structural cross section indicates that the inferred peak ring is decoupled from the structural uplift the geometry and bouguer gravity signature of the crater indicate that no significant uplift of the moho or relaxation of the crater has occurred

in situ lateral stress measurement in glaciolacustrine seattle clay using the pressuremeter pressuremeter testing was conducted for the state route sr 99 bored tunnel project in seattle washington to estimate in situ soil stress deformation parameters along the tunnel alignment many of the tests were conducted in a very stiff to hard glaciolacustrine clay known as seattle clay this unit is historically known for deep seated slope failures and many of these failures have been attributed to the release of high locked in lateral stresses estimation in situ lateral stresses along the tunnel alignment was a primary focus of the exploration program due to the hard consistency of this unit and the potential for cobbles neither self boring pressuremeter nor dilatometer testing was feasible therefore prebored pressuremeter testing was used using several lateral stress estimation techniques including a novel in situ creep testing approach the in situ lateral stresses in the seattle clay were estimated to be significantly higher than what would be expected by assuming a simple laterally constrained vertical loading and unloading stress path due to glaciation deformational features commonly encountered in seattle clay indicate its stress history also has included significant lateral shearing the memory of this shearing within the fabric of the clay may influence the in situ stress state and response to lateral unloading

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

evaluating the in situ lateral stress coefficient k0 of soils via paired shear wave velocity modes abstractthe utilization of shear wave velocities toward the evaluation of the in situ geostatic horizontal stress state in soils is validated specifically the lateral stress coefficient k0 field shear wave velocities from paired sets of different directional and polarization modes are compiled from 16 well documented test sites involving a variety of geomaterials focus is particularly placed on shear wave velocities measured by downhole tests vsvh crosshole tests vshv and special rotary type crosshole tests vshh at these sites field k0 stress states have been quantified using one or more direct assessment techniques including self boring pressuremeter total stress cells and hydrofracture in field testing as well as suction measurements special consolidometers and or triaxial arrangements on undisturbed samples in the laboratory although the specific delineation of stress induced versus inherent or fabric anisotropy may be difficult it is shown that the ratio of horizontally polarized