empirical and theoretical comparisons of the chicxulub and sudbury impact structures chicxulub and sudbury are 2 of the largest impact structures on earth research at the buried but well preserved chicxulub crater in mexico has identified 6 concentric structural rings in an analysis of the preserved structural elements in the eroded and tectonically deformed sudbury structure in canada we identified ring like structures corresponding in both radius and nature to 5 out of the 6 rings at chicxulub at sudbury the inner topographic peak ring is missing which if it existed has been eroded reconstructions of the transient cavities for each crater produce the same range of possible diameters 80110 km the close correspondence of structural elements between chicxulub and sudbury suggests that these 2 impact structures are approximately the same size both having a main structural basin diameter of 150 km and outer ring diameters of 200 km and 260 km this similarity in size and structure allows us to combine information from the 2 structures to assess the production of shock melt melt produced directly upon decompression from high pressure impact and impact melt shock melt and melt derived from the digestion of entrained clasts and erosion of the crater wall in large impacts our empirical comparisons suggest that sudbury has 70 more impact melt than does chicxulub 31 000 versus 18 000 km3 and 85 more shock melt 27 000 km3 versus 14 500 km3 to examine possible causes for this difference we develop an empirical method for estimating the amount of shock melt at each crater and then model the formation of shock melt in both comet and asteroid impacts we use an analytical model that gives energy scaling of shock melt production in close agreement with more computationally intense numerical models the results demonstrate that the differences in melt volumes can be readily explained if chicxulub was an asteroid impact and sudbury was a comet impact the estimated 70 difference in melt volumes can be explained by crater size differences only if the extremes in the possible range of melt volumes and crater sizes are invoked preheating of the target rocks at sudbury by the penokean orogeny cannot explain the excess melt at sudbury the majority of which resides in the suevite the greater amount of suevite at sudbury compared to chicxulub may be due to the dispersal of shock melt by cometary volatiles at sudbury

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

significance of first order faults in folding mechanically isotropic layers evidence from the sudbury basin canada abstract the sudbury basin is a non cylindrical fold basin demarcated by the layered sudbury igneous complex sic the eastern part of which is transected by prominent curved faults folding of the sic and adjacent rock units occurred in the brittle field and is peculiar due to its petrographically distinct but initially mechanically similar layers overall the layers are characterized by low levels of solid state strain raising the question how the layer contacts acquired their curvature we addressed this question by developing a g i s based workflow to analyze the orientation and slip vectors of the faults slip vectors form clusters of normal and reverse slip along a given fault the clustering is best interpreted in terms of successive slip events during folding of the sic as the faults formed most likely as planar reverse faults prior to folding of the sic they subsequently served as mechanically anisotropic elements to fold the sic the results contribute to 1 better understand the folding mechanisms of thick melt sheets in the upper crust 2 explain apparently incompatible principal strain axes during progressive deformation and 3 efficiently analyze the orientation and kinematics of fault zones close to the earth s surface

tides in the sea of okhotsk eight major tidal constituents in the sea of okhotsk have been investigated using a numerical solution of tidal equations on a 59 space grid the tides are dominated by the diurnal constituents diurnal tidal currents are enhanced in shelikhov bay and penzhinskaya guba at kashevarov bank in proximity to the kuril islands and at a few smaller locations the major energy sink for diurnal tides over 60 of the total energy is shelikhov bay and penzhinskaya guba the major portion of semidiurnal tide energy is dissipated in the northwestern region of the sea of okhotsk and in shelikhov bay and penzhinskaya guba nonlinear interactions of diurnal currents are investigated through k1 and o1 constituent behavior over kashevarov bank these interactions generate residual circulation of the order of 10 cm s 21 major oscillations at semidiurnal and fortnightly periods 13 66 days and higher harmonics of basic tidal periods the m2 tidal current caused by the nonlinear interaction of the diurnal constituents over kashevarov bank constitutes approximately a half of the total m2 tide current there the fortnightly current through nonlinear interactions also influences basic diurnal tidal currents by inducing fortnightly variations in the amplitude of these currents

local displacement of diapir contacts and its importance to pluton emplacement study abstract the extent to which mid crustal plutons have grown by diapirism cannot be deduced from the horizontal shortening of ductilely deformed host rocks and associated displacement of lateral intrusive contacts by contrast the vertical shortening above plutons and upward displacement of their roof contacts may provide a good measure of the diapiric component of pluton emplacement this is related to the vertical bulk translation of buoyant material in immature diapirs and associated escape flow of overlying rocks the length change of a vertical material line situated above the crest of an immature upright diapir corresponds to the upward displacement of the local contact the length change of horizonal material lines situated at lateral contacts of model diapirs however differs markedly from the contact displacement this is related to the absence of horizontal symmetry planes in the finite strain field about upright diapirs of any shape and the importance of vertical shear at the lateral contacts the host rock strain held of a hypothetical pluton grown in situ by spherical expansion ballooning has an infinite number of symmetry planes the strain held is characterized by large volume losses but the length change of all radial lines corresponds to the local magnitude of contact displacement this precludes the possibility of differentiating in ductile host rocks above plutons between vertical diapirism and spherical expansion unless gauges of volume change are available

tectonic and sedimentary evolution of the gulf of suez and the northwestern red sea abstract the structural pattern of the gulf of suez and red sea rift is inherited from the basement tectonics n140 faults clysmic direction parallel to the regional elongation of the rift are associated with submeridian aqaba direction and sub e w faults duwi direction that also play an important role in the rifting processes the pre rift sedimentary cover includes cretaceous and eocene platform deposits it was slightly deformed prior to rifting the syn rift sedimentary sequence comprises four major units groups a to d delimited by unconformities group a oligocene to early burdigalian continental to restricted subaquatic deposits group b burdigalian to middle miocene open marine sediments group c middle to upper miocene major evaporitic episode and group d plio pleistocene which returns to an open marine environment four majors stages of structuration are recorded an initial stage of compressive deformation direction of shortening close to nw se characterized by strike slip movements and associated drag folds early group a a tilted block stage late group a corresponding to the period of highest extensional rate a horst and graben stage group b resulting in the cutting out of the tilted blocks by numerous synthetic faults group b corresponds to the period of highest subsidence rate when a flexuration stage of the margin expressed by a centripetal evolution of the subsidence is associated with major periferal uplift

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

tidal and residual currents around a norfolk sandbank currents on either side of well bank were recorded for 41 days in may june 1981 in order to distinguish locally tidally generated asymmetries pertinent to maintenance of the bank from larger scale and wind driven flows semi diurnal currents were dominant nearly rectilinear and slightly inclined to the bank axis fourth diurnal currents were consistent with previously observed and computed fourth diurnal tides for the area overall amplitudes varied as the square of the semi diurnal amplitude hence they appear to be generated by tides but only a small part locally residual currents average over a tidal cycle were always in the sense of clock wise circulation around the bank consistent with simple models and giving strong evidence of local generation by tides this circulation combines with the semidiurnal currents to maintain the bank the slow increase of the residuals with the semi diurnal amplitude is interpreted as an effect of strong semi diurnal currents a persistent component onto the bank 7 m above the bottom at one position may indicate distortion of the frictional layer by the sloping bottom or by bank curvature

tectonic evolution of the northwestern red sea margin as related to basement structure abstract at the northwestern egyptian margin of the red sea a crystalline basement of pan african late proterozoic age is exposed beneath a phanerozoic sedimentary cover this tectonic situation provided an opportunity to study the younger red sea tectonic evolution in relation to features that are inherited from or reactivated in an underlying basement two structural maps compiled from published sources and our data covering the eastern egyptian basement from hurghada to the south show the most important structural elements the major central and southern parts of the basement in eastern egypt ced and sed are dominated by low angle thrusts other fractures n s e w nw se are distinctly less frequent and of local importance nw se oriented strike slip faults najd system overprinted the low angle thrusts of the northern ced these fault are related to ne sw trending normal faults which characterize the northern part of the basement ned before discussing general relationships between basement structure and red sea evolution a detailed example of the post pan african phanerozoic evolution of the low angle thrust dominated domains of the ced and the sed from a traverse south of 25 n is presented there detailed structural mapping showed phanerozoic normal faults close to the red sea trending nnw sse and at the margin of the phanerozoic cover east of the nile trending nnw sse and nw se leading to a horst like position of the basement within this horst deformation is restricted to a local sinistral strike slip fault trending n s the normal faults frequently used and reactivated fractures parallel or normal to the axial surface of earlier pan african folds igneous activity is confined to the western part of the basement where mafic dykes mafic to trachytic volcanics the alkaline gabal abu khrug ring complex and trachyte plugs in that time sequence from 104 to 80 ma are exposed mafic dykes are dependent on host rock properties distributed mainly in relatively brittle granitoid rocks trachyte intrusions are generally not related to particular host rocks but may follow pre existing structures crosscutting relationships with the igneous rocks imply a late cretaceous age for the faults in the west of the traverse however in the east at the red sea coast faults cut middle miocene sediments and are thus younger tectonic activity in the traverse area is therefore confined to two distinct episodes a late cretaceous event of alkaline magmatism and normal faulting at the western margin of the basement and a miocene or younger event of normal faulting at the present red sea coast in contrast to earlier views neither transform faults nor large scale riedel shears related to red sea tectonics have been met in the area this holds also true for the ced and sed as a whole where only local faults remain for potential reactivation during red sea tectonics except perhaps the duwi shear zone at quseir the prevailing n s e w or nw se directions of these faults preclude an interpretation as possible transform faults normal to the spreading axis of the red sea therefore it is no longer possible to assume a continuation of red sea transform faults into the continental crust

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

an upper bound for the tidally rectified current at one location on the southern flank of georges bank abstract long term current observations at 45 and 75 m at one location on the southern flank of georges bank in water 85 m deep were examined for evidence of tidal rectification loder has shown analytically that rectification of the strong semidiurnal tidal current can cause a mean along bank flow and thus may partially drive the observed clockwise circulation around georges bank the amplitude of the tidally rectified along bank flow is proportional to the squared amplitude of the cross bank tidal current a simply extension of loder s model to include the weaker n2 and s2 tidal components suggests that fortnightly 354 h and monthly 661 h variations of the square of the cross bank tidal current should cause a modulation of the subtidal along bank flow the predicted ratio r of the fortnightly and monthly modulation of the along bank flow to the mean along bank flow on the southern flank was a function of position and ranged from 0 1 0 5 the amplitude of modulation of the along bank flow at 360

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

correlation of strain and the anisotropy of magnetic susceptibility in the onaping formation evidence for a near circular origin of the sudbury basin abstract measurements of finite strain the anisotropy of magnetic susceptibility the magnetic carrier of the susceptibility and fieldwork have been carried out in the onaping formation of the sudbury basin ontario the magnetic fabric indicates that changes in the magnitude and type of magnetic susceptibility ellipsoids closely mirror the changing pattern of deformation from northwest to southeast across the onaping formation outcrops a quantitative correlation has been established between finite strain measurements and the magnetic susceptibility results and this allows the number of available strain measurements to be extended by more than 500 samples the finite strain results suggest a deformation path in which the onaping formation was first affected by nw se directed horizontal layer parallel shortening which produced an upright tectonic cleavage subsequently components of overthrust nw directed simple shear were superimposed upon the already deformed rocks of the onaping formation the result of removing the strain according to the sequence of superimposed deformations revealed by the deformation path suggests that the sudbury basin was nearly circular in shape prior to its deformation consequently a major objection to the meteorite impact theory for origin of the sudbury structure is eliminated

erratum crude quantitative estimates of the original northwest southeast dimension of the sudbury structure south central canadian shield the sudbury structure central ontario is the remnant of a large cryptoexplosion structure whose oval map pattern diameter ratio 2 2 differs markedly from the circular outline of many meteorite impact craters finite element modelling shows that i the original northwest southeast dimension could have been 2 3 times larger than at present and ii the vertical dimension of the sudbury structure was 10 km before tectonic deformation although our structural analyses furnish data that govern the geometric modelling large uncertainties remain where the state of tectonic deformation is poorly constrained a series of two dimensional models was made to cope with kinematic uncertainties and to assess their effect on the estimates of the geometry of the original sudbury structure

restoring post impact deformation at sudbury a circular argument recent seismic reflection observations have shown a considerable shortening of the sudbury structure in a direction roughly perpendicular to its long axis using a kinematic reconstruction technique for gridded geophysical data which takes into account non uniformly distributed strain we reconstruct the pre deformation shape of the sudbury structure and show that it could have been circular at the time of its formation 1 85 ga this supports an impact origin

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

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

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

peak ring rim collapse accommodated by impact melt filled transfer faults sudbury impact structure canada quartz diorite dikes in the footwall of the 1 85 ga sudbury impact structure were emplaced within fractures formed during hypervelocity impact the anisotropy of magnetic susceptibility of the radial copper cliff dike reveals a steeply dipping foliation that is counterclockwise oblique along both the eastern and western sides of the dike and a steeply northwest plunging lineation the data suggest that the copper cliff dike acted as a melt filled dextral transfer fault during collapse of the inner rim of the central peak ring of the impact crater to accommodate ultrahigh strain rate displacements peak ring rim collapse may have caused sulfide rich melts to be injected into the copper cliff dike leading to the formation of large cu ni platinum group element deposits

synchronous degassing patterns of the neighbouring volcanoes llaima and villarrica in south central chile the influence of tidal forces the neighbouring volcanoes villarrica and llaima are two of the most active volcanoes in chile and both currently degas continuously we present a semi continuous time series of so2 fluxes for villarrica and llaima volcanoes the time series was obtained using five scanning mini differential optical absorption spectrometers mini doas uv spectrometers over 6 months 13 february to 31 july 2010 and is based on 6 829 scans for villarrica and 7 165 scans for llaima statistical analyses of the so2 flux time series reveal a periodicity of degassing maxima about every 7 days and further a conspicuous synchronicity of the degassing maxima and minima between the two volcanoes intra day variations in so2 fluxes also show a striking correlation between villarrica and llaima all these patterns correlate well with the trend of the modelled solid earth tide curves where the 7 day degassing maxima correspond with both the fortnightly tidal maxima and minima the intra day degassing peaks mostly correlate well with the periods of maximum deformation rates during the diurnal tidal cycle and further with semidiurnal minima in atmospheric pressure a phenomenon we refer to as the tidal pump as there is little time lag between the tidal action and the changes in degassing rates we infer that degassing at both volcanoes is controlled by conduit convection involving physical separation between gas and magma at comparatively shallow levels variations in daily degassing rates were up to a factor of ca 12 and 10 for villarrica and llaima respectively without any noticeable changes in the periodicity we thus suggest that the described cyclic variations must be taken into account for all comparable volcanoes when using gas monitoring as a tool for volcanic hazard mitigation

the chief lake complex revisited and the problem of correlation across the grenville front south of sudbury ontario abstract south of sudbury the boundary between the southern and grenville provinces the grenville front is placed along the faulted southeastern edge the ca 1 46 ga chief lake complex clc a southeast dipping thrust sense mylonite zone lies in the immediate hanging wall of the grenville front boundary fault gfbf separating the clc in the southern province from metasedimentary granitoid anorthositic and amphibolitic gneiss in the grenville province to the southeast the gfbf also coincides with an abrupt break in the continuity of southeast trending diabase dykes of the 1 24 ga sudbury swarm the northern clc is a composite intrusion whose units include and are separated by large rafts of the early paleoproterozoic huronian supergroup in which relict stratigraphy outlines engulfed folds mafic rocks along the northwest contact of the clc previously interpreted as metasomatized nipissing gabbro 2 22 ga are in fact a phase of the chief lake intrusive suite commingled with granite the northwest contact coincides in part with a steep southeast side down pre intrusion fault that was later reactivated with reverse sense of displacement the chief lake granitoid rocks become increasingly foliated southeast toward the grenville front but two features suggest that at least some of the deformation of the chief lake intrusive suite was syn emplacement 1 the granitoid component of commingled rocks may be strongly foliated in places where the mafic component is undeformed and 2 included huronian metasedimentary rocks in general lack the constrictional fabric of their enveloping plutonic rocks sudbury dykes cut across the fabric of the clc but the facts that they are themselves buckled locally metamorphosed to greenschist facies and are offset by faults marked by ultramylonite and cataclasite attest to tectonism of grenvillian age in the footwall for a limited distance northwest of the gfbf granitoid rocks dated at 1 74 and 1 47 ga southwest of the study area and archean tonalitic rocks and 2 47 ga anorthositic gabbro to the northeast occur on both sides of the grenville front in the study area units of paragneiss in the hanging wall of the gfbf cannot be assigned to specific huronian formations in the southern province footwall however although not proven it is reasonable to correlate other hanging wall rocks namely mylonitic gabbroic anorthosite amphibolite and granitic gneiss to the 2 47 ga east bull lake intrusive suite nipissing gabbro and chief lake granite respectively in the southern province whereas sudbury dykes do not intrude the mylonitic rocks immediately above the gfbf they do reappear to the southeast as dyke segments and pods within mylonite bounded panels where they cut earlier isoclinal folds and exhibit a progressive increase in metamorphic grade across a gradient shallower than that in the enclosing gneissic rocks they document that much of the tectonic history recorded by their host rocks is pre grenvillian even so there is no evidence that the grenville front was ever the locus of a suture

comment on extension of the najd shear system from saudi arabia to the central eastern desert of egypt based on integrated field and landsat observations by m sultan r e arvidson i j duncan r j stern and b el kaliouby

tidal and lower frequency currents above fieberling guyot an intensive yearlong deployment of current meter moorings was made over and around fieberling guyot 32 5 n 127 75 w in the north pacific the measurements are used to investigate tidal currents the mean flow and subinertial current fluctuations the k1 and o1 diurnal tides were greatly amplified over the seamount apparently through dynamics resembling nonlinear seamount trapped waves the diurnal tides interacted nonlinearly to induce constituents at the sum frequency m2 and difference frequency fortnightly above the summit diurnal amplification was strongest at about 450 m and it extended from the seamount center out over the flanks the s2 semidiurnal tide was not substantially amplified over the seamount the mean flow was primarily along isobaths and was strongest about 50 m above the seamount rim it was driven by tidal rectification so that mean along isobath velocity at a given location correlated well with the amplitude of the local fortnightly tide at that location accompanying the mean flow was a cold dome over the seamount that was presumably maintained by a balance of mean downward advection and eddy tidal radial heat transport lower frequency current fluctuations were enhanced near the seamount and were apparently driven by fluctuations in the ambient flow

a trishear model for the deformation of the sudbury igneous complex canada abstract the sudbury igneous complex sic canada is an impact induced layered sheet of crystalline rocks deformed into an asymmetrical fold basin the sudbury basin the basin geometry at depth is largely unknown as few attempts were made to quantify displacement and rotation of layer contacts we propose that the dip of layer contacts and foliation surfaces in the southern sic can be approximated by trishear fault propagation folding trishear deformation accounts for 1 angular discordances between upper and basal sic contacts 2 local overturning of the sic 3 progressive steepening of foliation surfaces from nw to se 4 strain gradient in the sudbury basin sedimentary rocks and 5 thickness variations in sic layers moreover the south range shear zone a zone of moderately strong metamorphic fabrics coincides with the surface manifestation of the proposed trishear zone we demonstrate the use of structural data together with forward kinematic modelling to identify the strain distribution within the sic rotation of sic contacts and thickness changes of sic layers backward kinematic modelling provides information on the initial geometry of the sic and is used to restore the shape of the igneous sheet showing that the sic was shortened by approximately 10 km in nw se diameter most of the shortening was accommodated by 40 reduction in the thickness of the upper sic layer

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

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

3 d kinematic restoration of the eastern sudbury igneous complex canada and its importance for cu ni pge sulphide exploration abstract kinematic restorations of deformed igneous terranes have rarely been attempted due to the general absence of 1 planar primary lithological contacts 2 tightly constrained deformation kinematics and 3 geometric constraints on lithologies and structures at depth because of the vast number of exploration drill holes the deformed and layered 1 85 ga sudbury igneous complex sic in ontario canada is reasonably well understood with respect to 1 and 3 we therefore explored the kinematics of folding and faulting in the eastern sic and use the subsurface geometry of faults extracted from a model integrating surface mapping and drill core logs in an attempt to restore the geometry of part of the sic specifically we identified rotation magnitudes and the tilt axis of a kilometer scale plunging fold the west bay anticline which appears to have folded the eastern part of the sic we combined a 3 d model of the faults and lithological contacts of the sic fault kinematics calculated from the inversion of brittle shear faults at surface and limb rotations of the west bay anticline to kinematically restore the eastern part of the sic results of restorations using simple shear and flexural slip algorithms highlight the importance of slip on prominent curved faults that displaced the sic and facilitated its folding flexural slip appears to be the more plausible mechanism of the two as it removed the curvature of and displacement on prominent faults flexural slip restoration helps to estimate primary thickness variations of the sic and the results show that thickened parts of the main mass of the sic correspond spatially with known cu ni pge sulfide deposits this result demonstrates that 3 d restoration can be an important tool for mineral exploration in igneous terranes

ocean currents at axial volcano a northeastern pacific seamount 1 axial volcano is a magmatically active seamount that straddles the juan de fuca ridge jdfr with a summit depth of 1400 m the volcano intercepts deep ocean flows at a height well above that of the linear ridge adjoining it to the north and south multiyear yearlong observations of currents at axial show that mean flow circles the seamount in an anticyclonic sense consistent with dynamical constraints with means as large as 6 6 cm s 1 spectra of currents indicate prominent tidal inertial and in some cases weather band period 3 to 7 day peaks as has been seen elsewhere along the jdfr ridge for k1 o1 and s2 tidal currents at the seamount amplitudes are several times larger than the corresponding background amplitudes and rotation around the tidal current ellipses is anticyclonic m2 tidal currents show none of the same properties energy at the inertial frequency decreases by more than an order of magnitude from 100 m above to 400 m below the volcano s summit in contrast weather band wb period energy increases tenfold over the same depth range with wb energy all but unobservable at summit depth the presence of wb oscillations makes axial unlike other seamounts where long observations have been made the current meter observations also provide a picture of seasonal trends as expected during the period summer 1996 to spring 1997 largest amounts of wb energy are found during autumn and winter in contrast wb motion at axial volcano during winter 2000 was summer like in intensity a linear baroclinic model of forced damped azimuthal mode one oscillatory flow around an idealized axisymmetric seamount shows that amplification of diurnal flow should occur principally at the seamount summit while amplification of the wb should occur as the observations show on the seamount flanks model and measured phase relationships for temperature and current time series pairs circumscribing axial support the view that azimuthal mode one oscillations are prominent over the 0 8 to 6 day range for forcing period tc the model indicates that the principal topographic resonance as indicated by kinetic energy ke amplification occurs for a tc greater than 1 and less than 2 days with only mild dependence in that range on background stratification and seamount shape additional but weaker topographic resonances can occur at longer periods in model results but as tc becomes slightly larger than the frictional timescale topographic resonances no longer appear high dissipation and thus short frictional timescales reported by others in regions of rough sloping topography make topographic resonances at axial at periods greater than a few days somewhat unlikely the relatively broad wb spectral peaks at some axial sites are consequently more likely the result of spectral peaks in forcing than of topographic resonance

the sudbury huronian heat flow anomaly ontario canada abstract new measurements of the surface heat flux and radiogenic heat production in deep boreholes at 8 different sites are added to 10 older data to determine the heat flow field around the sudbury basin ontario canada this structure straddles the boundary between the archean superior province to the north and the paleoproterozoic southern province to the south which terminates against the grenville front the structure that includes the sudbury igneous complex sic was created by a meteorite impact ca 1 85 ga the mean value of the heat flux 50 mw m 2 is higher than that for the superior province 40 mw m 2 heat flow values are hardly perturbed by the presence of the sic and require a regional enhancement of heat production in the upper crust with respect to the average superior due mostly to the enriched huronian metasediments of the southern province the average radiogenic heat production of sic lithologies 1 2 w m 3 is higher than that of the local archean basement indicating that the impact melt sheet was partly derived from huronian sediments local variations in heat flux can be related to heat production differences between the abitibi upper crust and the huronian metasediments as well as thrusting and tectonic thickening in the southern province the higher than average values of heat flux and crustal heat production in the southern province imply elevated crustal temperatures and a weak rheology in the lower crust at the time of the meteorite impact and of the contemporaneous penokean orogeny large variations of crustal thermal structure at the edge of the superior province may have led to along strike differences in the style and extent of thrusting during the grenville orogeny

geochronology of proterozoic metamorphism in the deformed southern province northern lake huron region canada abstract metamorphic geochronology and thermochronology of the deformed southern province north of lake huron in ontario canada reveals a complex and protracted tectonothermal history for the proterozoic southern laurentide margin that is distinct from that of the lake superior region to the west while penokean interval deformation is well constrained in the lake superior area a well defined geon 18 geochronometric signature is lacking in the huronian vicinity the oldest metamorphic ages revealed by in situ monazite u th total pb electron microprobe analyses are ca 1800 ma with a strong geon 17 yavapai interval and local geon 14 15 magmatic influences furthermore conventional 40 ar 39 ar incremental step heating of hornblende indicates paleoproterozoic heating through 500 c occurred only adjacent to geon 17 intrusions regional analysis of mica cooling ages suggests that mesoproterozoic thermal overprinting of primary geon 17 magmatism and metamorphism is limited to south of the murray fault the penokean orogeny long considered the dominant paleoproterozoic event in the great lakes region is now recognized as only the first of several accretionary events that impinged on the southern laurentide margin however the penokean orogen is restricted to the 2100 ma embayment of the superior province rifted margin moreover subsequent tectonothermal pulses yavapai mazatzal and ca 1450 ma recorded in the rocks of the southern province in ontario mimic that documented across much of the central and western united states based on the distinct lack of penokean interval ages and the strong geon 17 and geon 14 total pb and 40 ar 39 ar geochronometric signature the tectonothermal history of southern province more closely resembles that of the southwest united states than the lake superior region

geology and origin of meatiq dome egypt a precambrian metamorphic core complex meatiq dome a metamorphic complex in the precambrian basement of the eastern desert of egypt exhibits many of the essential features of cordilleran metamorphic core complexes it is an antiformal structure with low dipping foliation and unidirectional mineral slickenside lineation the core consists of granite gneiss and is conformably overlain by a heterogeneous isoclinally folded mylonitic carapace the carapace grades upward into a nonmylonitic cover of low grade ophiolitic rocks the mylonitic rocks are interpreted to have formed in a low angle ductile shear zone during a compressional tectonic event accompanied by syntectonic intrusion of tonalite doming postdated mylonitization the absence of a brittle detachment surface at meatiq dome is its primary distinction from the otherwise similar cordilleran complexes

extension of the najd shear system from saudi arabia to the central eastern desert of egypt based on integrated field and landsat observations the najd shear system in saudi arabia extends over 1200 km in a nw se direction and has a width of approximately 300 km a digital color mosaic compiled from seven landsat thematic mapper scenes was used to delineate characteristic structural features of the najd system in the midyan region of saudi arabia and to search for similar features in the egyptian eastern desert the digital mosaic was generated using ratios of landsat thematic mapper bands bands 5 4 3 4 5 1 5 7 that are sensitive to the rock content of fe bearing aluminosilicates spectrally opaque phases and hydroxyl bearing or carbonate minerals respectively the mosaic covers approximately 130 000 km of late proterozoic exposures of the arabian nubian shield and has the eastern desert and the midyan region placed in their approximate pre red sea locations the ajjaj shear zone ajz marks the termination of the najd system against the eastern margin of the red sea in the midyan region the ajz aligns with the central eastern desert based on analysis of pre red sea locations analyses of landsat data and field observations show that the ajjaj shear zone and the central eastern desert exhibit the following features in common 1 outcrops that are generally elongate in a nw se direction as a result of folding with fine scale lithologic heterogeneity at the outcrop scale related to deformation associated with faulting 2 nw trending left lateral faults and ductile shear zones 3 subhorizontal nw trending mineral lineations and variably dipping nw trending foliations with local changes in attitude around large competent e g granitic bodies and 4 lithologic contacts that are generally tectonic in nature and related to faulting these features are less common to the north and south of both the ajjaj shear zone and the central eastern desert results are consistent with the najd shear system extending into the eastern desert and dominating the structural patterns within the central part of the eastern desert

assessment of georges bank recirculation from eulerian current observations in the great south channel abstract twenty vector averaging current meters vacms were deployed at various depths in the vicinity of the great south channel during several experiments conducted between 1976 and 1986 average record length 5 months since little more than mean current vectors from some records has been reported previously a basic description of the flow field is presented here with at least one current record occurring in every month of the year the hypothesis of increased subtidal flow around georges bank during the stratified season is supported anemometer data obtained at nearby noaa environmental buoys and the nantucket lightship are used to estimate wind stress the primary forcing in the well mixed season empirical modes of current structure demonstrate the spatial structure and the seasonal variability of wind and density driven dynamics in this region when averaged over a few months the northward transport through the great south channel fall mean 0 095 sv is small compared to the westward transport along the southern flank of georges bank fall mean 0 421 sv but the subtidal variability of the great south channel transport is highly energetic with a standard deviation 0 11 sv greater than the mean indicating that large reversals in transport can occur over a few days

effect of the topographic stress on the tide and wind induced residual currents in the gulf of california because eddy topography interactions topographic stress are difficult to resolve by numerical models a parameterization has been proposed by holloway 1992 based on the statistical mechanical equilibria tendencies neptune effect a vertically integrated numerical model is used to study the influence of neptune effect upon the tide and wind induced residual circulation of the gulf of california the model is forced at the mouth of the gulf by the tides and at the sea surface by the wind it is found that the parameterization induces mean currents in areas where the residuals produced by tides and winds are small tide and wind induced residuals are large along the mainland coast and from the archipelago to the north where the neptune effect parameterization is less important observations give some support to this parameterization