late proterozoic high pressure granulite facies meta morphism in the north east ox inlier north west ireland high pressure granulite facies gneisses in the ne ox inlier in nw ireland have undergone extensive caledonian retrogression in the local area of slishwood however reworking was negligible and the gneisses psammites semipelites pelites metabasites and ultramafites preserve evidence of p t changes at high grade which mainly post date pre caledonian polyphase deformation temperatures reached 850 900 c based on garnet clinopyroxene geothermometry and the presence of mesoperthite during and after decompression from earlier eclogite facies conditions inferred from textural evidence of plagioclase release in sieve textured augite subsequent cooling at high pressure is inferred from the unequivocal replacement of sillimanite by kyanite a sm nd mineral isochron gt cpx plag wr of 605 37 ma is taken to date a point on the cooling path and confirms the hitherto suspected pre caledonian age of the high grade metamorphism geochemical and sm nd isotopic data indicate that the protoliths were probably late proterozoic arkosic sediments and tholeiites following metamorphism they apparently came to reside near the base of the crust where they slowly cooled the eventual exhumation of these gneisses is attributed to caledonian crustal imbrication followed by rapid isostatic recovery

the computation of body wave synthetic seismograms in laterally homogeneous media synthetic seismograms computed for realistic horizontally stratified media are now routinely used as an aid to seismic interpretation this paper reviews the theoretical background to these methods and presents comparisons of the two popular algorithms reflectivity and wkbj seismograms for a variety of earth models the transformed wave equations are developed from the equations for a spherical gravitating medium in a symmetric form suitable for body wave calculations four methods of solving these equations in general inhomogeneous layers are described the wkbj and langer asymptotic expansions and the wkbj and langer iterative solutions together with the earth flattening transformation and the ray expansion transformed solutions for body waves can then be obtained for realistic layered media four methods of inverting the frequency and wave number transformations are also described the real and complex spectral and slowness methods although realistic seismic models are normally sufficiently complicated that numerical calculations are essential before proceeding with numerical comparisons we have included a review of the canonical signals included in body wave seismograms these analytic results for direct rays partial and total reflections turning rays on forward and reversed branches head waves interface waves airy caustics and fresnel and interface shadows are useful to anticipate and understand numerical problems and results finally a comparison of green s functions for crustal mantle and whole earth models calculated using the wkbj and reflectivity algorithms is included

love mode dispersion across subduction zones by finite element modelling summary phase velocity and mode conversion of love waves with normal incidence across a subduction zone have been studied with the use of the finite element algorithm previously developed for seismic waves through anomalous earth structures two rather different models are considered representing subduction slabs under japan and the north island of new zealand fundamental mode love wave dispersion curves have been calculated for wave periods between 5 and 60s comparison with phase velocity curves for the adjacent ocean and island regions shows that the phase velocity for the subduction zones is in general slightly less than the mean of the phase velocities of the adjacent regions for example at a period of 20 s the phase velocity in the model of the subduction zone of japan is 4 1 57 km s and the mean of the phase velocities in the regions at the ends of the model is 4 245 km sc1 at the same period the phase velocity in the new zealand subduction model is 3 895 km s and the mean of the phase velocities at the ends of the model is 4 150 km s at a period of 10 s only 5 per cent of the energy of the incident fundamental love mode is transmitted in the fundamental mode across the model of the subduction zone of japan at a period of 15 s 18 per cent of the energy of the incident fundamental love mode is transmitted in the fundamental mode across the new zealand subduction zone at these periods a subduction zone significantly scatters the energy of the fundamental love mode in the same way as a continental margin scatters it the relevance of these results for the inversion of dispersion measurements of surface waves with circumglobal paths is that subduction zones have a negligible effect on the phase velocity of the fundamental love mode and that scattering of the fundamental love mode at subduction zones and at continental margins is important only at periods less than approximately 40 s

synthetic sh seismograms in a laterally varying medium by the discrete wavenumber method summary we present a new method to calculate the sh wavefield produced by a seismic source in a half space with an irregular buried interface the diffractiog interface is represented by a distribution of body forces the green s functions needed to solve the boundary conditions are evaluated using the discrete wavenumber method our approach relies on the introduction of a periodicity in the source medium configuration and on the discretization of the interface at regular spacing the technique developed is applicable to boundaries of arbitrary shapes and is valid at all frequencies some examples of calculation in simple configurations are presented showing the capabilities of the method

decompressed eclogites in the sveconorwegian grenvillian orogen of sw sweden petrology and tectonic implications relict eclogites and associated high pressure rocks are present in the eastern segment of the sw swedish gneiss region the tectonic counterpart of the parautochthonous belt of the canadian grenville these rocks give evidence of sveconorwegian eclogite facies metamorphism and subsequent pervasive reworking and deformation at granulite and amphibolite facies conditions the best preserved eclogite relics suggest a clockwise p t t history beginning in the amphibolite facies progressing through the eclogite facies decompressing and partially reequilibrating through the high and medium pressure granulite facies before cooling through the amphibolite facies textures demonstrate the former coexistence of the plagioclase free assemblages garnet clinopyroxene quartz rutile ilmenite garnet clinopyroxene kyanite rutile and garnet kyanite quartz rutile the former existence of omphacite is evidenced by up to 45 vol plagioclase expelled as small grains within large clinopyroxene matrix plagioclase is secondary and occurs expelled from clinopyroxene or in fine grained granulite facies reaction domains formed during resorption of garnet and kyanite garnet shows preserved prograde growth zoning with rimward increasing pyrope content decreasing spessartine content and decreasing fe fe mg ratio but is partly resorbed and reequilibrated at the rims p t estimates from microdomains with clinopyroxene plagioclase quartz garnet indicate pressures of 9 5 12 kbar and temperatures of 705 795 c for a stage of the granulite facies decompression the preservation of the prograde zoning suggests that the rocks did not reside at these high temperatures for more than a few million years and chemical disequilibrium and frozen reaction textures indicate heterogeneous reaction progress and overstepping of reactions during the decompression through the granulite facies together these features suggest a rapid tectonic exhumation the eclogite relics occur within a high grade deformation zone with wnw ese stretching and associated oblique normal sense top to the east sensu lato displacement suggesting that extension was a main cause for the decompression and exhumation probable tectonic scenarios for this deformation are sveconorwegian late orogenic gravitational collapse or overall wnw ese extension

40ar 39ar geochronological constraints on the tectonothermal evolution of the eastern segment of the sveconorwegian orogen south central sweden

petrology and ion microprobe u pb chronology applied to a metabasic intrusion in southern sweden a study on zircon formation during metamorphism and deformation the aker metabasite occupies a key position in a major tectonic lineament in southernmost sweden the protogine zone which coincides closely with the eastern boundary of the late mesoproterozoic sveconorwegian orogen of southwest scandinavia metamorphic reactions associated with the transformation from isotropic gabbro to foliated garnet amphibolite were identified from disequilibrium textures of which some involved release of zirconium zr and growth of metamorphic zircon ion microprobe dating of igneous zircon gave 1562 6 ma whereas metamorphic zircons yielded ages of 1437 21 1217 75 and 1006 68 ma the presence of baddeleyite pseudomorphs made up of saccharoidal zircon and a higher abundance of older rather than younger metamorphic zircons suggest redistribution of zr into new zircon first by the breakdown of baddeleyite zro2 and later by the consumption of igneous phases containing trace amounts of zr several generations of metamorphic zircon and the presence of 1 56 and 1 22 ga mafic intrusions along the protogine zone call for a complex tectonic history probably reaching back to at least similar to1 56 ga growth of metamorphic zircon at similar to1 44 ga may relate to a regional compressional event the wnw trending deformational structures on both sides of the protogine zone may possibly relate to that event the similar to1 22 ga metamorphic zircons are coeval with the emplacement of numerous granitic syenitic and mafic intrusions along and parallel to the protogine zone the age around 1 0 ga finally marks sveconorwegian metamorphism for which thermobarometry of the aker garnet amphibolite suggests 1000 1200 mpa at 600degreesc 630degreesc thereafter significant relative uplift of the rocks to the west of the protogine zone occurred on nearly vertical north south trending deformation zones less

tracking the prograde p t path of precambrian eclogite using ti in quartz and zr in rutile geothermobarometry a fe ti rich garnet clinopyroxene and quartz eclogite sample from the 1 0 ga sveconorwegian orogen sw sweden contains abundant quartz rutile and zircon in distinct micro textural sites garnet core garnet rim and matrix constituting an ideal case for investigation of the behavior of zr in rutile and ti in quartz at high pressure and temperature a p t path peaking at 16 5 19 kbar and 850 900 c has been constrained independently for the same rock by pseudosection modelling input pressures from this model were used for trace element geothermometry of each garnet micro textural domain trace element thermo baro metry based on in situ secondary ion mass spectrometry analyses of ti contents in quartz and zr contents in rutile yields p t estimates of progressive crystallization of quartz and rutile along the prograde metamorphic path for inclusions in the garnet cores zr in rutile geothermometry yields 700 715 c and ti in quartz 620 640 c at 7 kbar for inclusions in the garnet rims temperature estimates are 760 790 c zr in rutile and 740 920 c ti in quartz at 12 18 kbar finally matrix rutile records 775 800 c and locally 900 c and quartz records temperatures up to 900 c at 18 kbar ti in quartz estimates for the metamorphic peak inclusions in the garnet rims and matrix conform to the pseudosection but appear too low for the early prograde stage garnet cores possibly due to lack of equilibrium at t 700 c the pseudosection shows that rutile was produced by continuous ilmenite breakdown during the early stages of prograde metamorphism a reaction that was completed at 730 c rutile grains in the garnet rims and the matrix grew subsequently larger by recrystallization of previously produced rutile however recrystallized rutile does not predominantly record peak temperatures but instead yield 745 840 c between 12 and 18 kbar in the pseudosection this temperature range broadly coincides with a stage during which ti bearing hornblende was consumed and clinopyroxene produced i e dehydration the zr contents thus appear to reflect the last stage of efficient rutile recrystallization catalysed by fluids released by the dehydration of hornblende preceding the metamorphic peak concurrently combination of the isopleths for ti content in quartz and zr content in rutile i e independent from pseudosection modelling yields pressure and temperature conditions in almost perfect agreement with the p t path as deduced from the pseudosection the variation in ti concentration in quartz is small regardless of crystal size and the ti in quartz geothermometer provides both precise and accurate peak temperatures of 875 920 c without a significant diffusional reequilibration the lack of significant ti diffusion in quartz is consistent with an inferred short residence time at high temperature this study illustrates that zr in rutile and ti in quartz geothermobarometry can robustly constrain prograde p t conditions and yield further insights into recrystallization processes at high temperature the combination of these methods and integration of the results with pseudosection modelling is a versatile tool for investigating the petrologic history of high grade rocks less

modified topographic amplification factors for a single faced slope due to kinematic soil structure interaction in this paper we evaluate the additive effects of topography soil nonlinearity and soil structure interaction ssi along the crest of an idealized 40 m high cliff type topographic feature with slope inclination 300 where excessive damage was observed during the athens 1999 earthquake the objective of this paper is to investigate the relative contribution of topographic amplification and kinematic ssi as a function of the incident motion frequency content and geotechnical site conditions for a surface and an embedded structure located at the cliff crest for this purpose we perform elastic parametric and nonlinear site specific two dimensional finite element simulations using three profiles and six input motions we illustrate the role of ssi in altering the response at the location of peak topographic amplification potential behind the crest the effects of incident motion incoherency on the transient structural response and the beneficial contribution of structural embedment we finally suggest that empirical models for base slab averaging of shallow foundations developed as a function of site conditions structural dimensions and center line location could be combined with topographic amplification factors to predict realistic design spectra for structures located on irregular topographic features

an example of two dimensional synthetic seismogram modeling abstract synthetic seismograms for laterally inhomogeneous velocity and q structures can be calculated by the disk ray theory drt method ray tracing through the model provides travel time distance slowness and ray amplitude data which are combined to synthesize seismic record sections by drt the amplitude factors include geometrical spreading attenuation due to q 1 reflection and transmission coefficients and the free surface conversion coefficient comparison of drt synthetic seismograms with those calculated by the reflectivity method for a layer over a half space model shows excellent agreement in both amplitude and waveform character of all arrivals direct reflected p to s converted multiply reflected and head waves may be synthesized by the drt method in an application of two dimensional synthetic seismogram modeling using the drt method synthetic seismogram record sections were calculated for a complicated geological model of the crust in the eastern snake river plain idaho and compared with observed seismic data in this application we find that a small modification of the snake river plain velocity model which was interpreted from travel time data produces drt synthetic seismograms which compare well with the amplitude and waveform character of the observed seismograms

hybrid modeling of p sv seismic motion at inhomogeneous viscoelastic topographic structures a new hybrid two step method for computation of p sv seismic motion at inhomogeneous viscoelastic topographic structure is presented the method is based on a combination of the discrete wavenumber dw finite difference fd and finite element fe methods in the first step the dw method is used to calculate the source radiation and wave propagation in the background 1d medium in the second step the fd fe algorithm is used to compute the wave propagation along the topographic structure the accuracy of the method has been separately tested for inclusion of the attenuation and for inclusion of the free surface topography through numerical comparisons with analytical and independent numerical methods the method is a generalization of the hybrid dw fd method of zahradnik and moczo 1996 for localized structures with a flat free surface numerical computations for a ridge sediment valley and the ridge neighboring the sediment valley show that a ridge can considerably influence the response of the neighboring sediment valley this means that the neighboring topographic feature should be taken into account even when we are only interested in the valley response

calculation of synthetic seismograms in a laterally varying medium by the boundary element discrete wavenumber method abstract we investigate the propagation of lg waves in laterally varying crustal structures by numerical simulation the method of calculation is formulated in terms of boundary integral equations where the green9s functions are evaluated by wavenumber summation the approach is well suited to study the propagation of seismic waves in a layered medium where the interfaces are flat in some regions and irregular in others we investigate the effect of a crustal fault with vertical offset and study the case of a lateral change in crustal thickness the results show that the lg wave amplitude is only slightly affected by the presence of these heterogeneities they confirm the robustness of lg wave propagation in presence of lateral heterogeneities observed in other numerical simulations they show that large scale geometric features of the crust cannot account alone for the strong attenuation of lg waves observed in many regions the results also suggest a possible relation between the level of lg wave coda and the degree of roughness of the moho they further indicate the importance of backscattering and suggest a possible use of the backscattered wave field to map strong crustal heterogeneities

high pressure metamorphism during the llano orogeny inferred from proterozoic eclogite remnants mineral chemistries and textures in mafic garnet pyroxene rock within the lost creek gneiss in the purdy hill quadrangle mason county texas record three distinct p t events two of them at pressures higher than any previously documented for these grenville age rocks the earliest metamorphic episode produced an eclogitic assemblage of pyrope rich almandine sodian augite orthopyroxene pargasitic amphibole some orthopyroxene cores record pressures greater than 15 kbar even for the most conservative estimated temperature of 500 c garnet and orthopyroxene rims and matrix clinopyroxene and amphibole record a second event at 750 c and 8 kbar symplectites of clinopyroxene plagioclase and coronas around garnet of plagioclase amphibole magnetite formed in response to reheating and hydration associated with postkinematic intrusion at the amphibolite facies conditions 600 650 c 3 5 5 kbar commonly recorded in the region recognition of early high pressure metamorphic episodes markedly strengthens the correlation between these rocks and other grenville age exposures along the continental margin and provides petrologic support for models invoking proterozoic subduction accompanying the llano orogeny

a review of numerical experiments on seismic wave scattering this paper reviews applications of the finite difference and finite element methods to the study of seismic wave scattering in both simple and complex velocity models these numerical simulations have improved our understanding of seismic scattering in portions of the earth where there is significant lateral heterogeneity such as the crust the methods propagate complete seismic wavefields through highly complex media and include multiply scattered waves and converted phases e g p tosv sv top body wave to surface wave the numerical methods have been especially useful in cases of moderate and strong scattering in complex media where multiple scattering becomes important progress has been made with numerical methods in understanding how near surface low velocity basin structures scatter surface waves and vertically incident body waves the numerical methods have proven useful in evaluating scattering of surface waves and body waves from topography of both the free surface and interfaces buried at depth numerical studies have demonstrated the importance of conversions from body waves to surface waves andvice versa when lateral heterogeneities and topographic relief are present in the uppermost crust recently several investigations have applied numerical methods to study seismic wave propagation in velocity models which vary randomly in space this stochastic approach seeks to understand the effects of small scale complexity in the earth which cannot be resolved deterministically these experiments have quantified the relationships between the statistical properties of the random heterogeneity and the measurable properties of high frequency 1 hz seismograms these simulations have been applied to the study of many features observed in actual high frequency seismic waves including the amplitude and time decay of seismic coda the apparent attenuation from scattering the dispersion of waveforms and the travel time and waveform variations across arrays of receivers

petrology and u pb geochronology of mafic high pressure metamorphic coronites from the tshenukutish domain eastern grenville province abstract a suite of mafic and ultramafic rocks from the tshenukutish domain eastern grenville province have been the subject of a detailed petrographic and geochemical study combined with u pb geochronology the tshenukutish domain is the highest tectonic level in the recently discovered eclogite bearing manicouagan imbricate zone the mafic and ultramafic rocks are characteristic of two of the lithotectonic segments in the domain the lac espadon segment and the baie du nord segment in the lac espadon segment cumulate textures and geochemical characteristics suggest that the units represent a layered mafic and ultramafic complex and an unrelated apatite rich fe ti mafic pegmatite nelsonite body in contrast the samples from the baie du nord segment represent fairly homogeneous fe ti gabbros and anorthosites the samples studied show abundant petrographic evidence for high pressure metamorphism for instance the widespread development of garnet clinopyroxene and kyanite bearing metamorphic assemblages estimates of the conditions of high pressure metamorphism in previous studies and melting textures in deformed and hydrated gabbro margins are in the range 750 900 c and 1600 1800 mpa the gabbroic end members from both segments suggest within plate tholeiite petrotectonic signatures ree patterns of gabbros and cumulates in both segments suggest fractionation from a tholeiitic source cumulate textures fractionation and inherited zircons suggest high crustal level emplacement of the magmatic protoliths in the tshenukutish domain in the lac espadon segment u pb ages of igneous zircon and baddeleyite give an age range of 1643 1629 ma for the emplacement of the layered complex the nelsonite in the les gives a poorly constrained igneous zircon age of 1596 126 99 ma in the baie du nord segment baddeleyite gives an age of 1170 5 ma for emplacement of the fe ti gabbros this is the youngest intrusion in the td and thus gives a maximum limit for the onset of grenvillian metamorphism ages of high p metamorphism are further constrained by zircon formed during partial melting of deformed and hydrated fe ti gabbro margins 1046 3 ma overgrowth of igneous zircon 1042 22 28 ma in the nelsonite saccharoidal zircon replacing baddeleyite 1030 10 7 ma and 1030 12 ma and new growth of equant zircon 1012 12 ma from the undeformed interior of the gabbros these ages indicate that the high p metamorphism of the tshenukutish domain was late grenvillian ottawan retrogression to amphibolite facies is constrained by the ages of titanite 1006 997 ma in deformed gabbro margins rutile ages range between 960 and 929 ma and are interpreted as cooling ages the difference between the ages of titanite and rutile suggest slow cooling of the tshenukutish domain after initial high pressure and temperature metamorphism and exhumation

kinematics of a major fan like structure in the eastern part of the sveconorwegian orogen baltic shield south central sweden abstract the n s trending so called protogine zone in the baltic shield of south central sweden is usually considered to mark a tectonic boundary between the rocks of the transscandinavian igneous belt tib in the east and the sveconorwegian orogen in the west detailed structural mapping in the karlskoga kristinehamn area has shown that an anastomosing network of ductile deformation zones with generally n s strike extends ca 40 km east of the traditional protogine zone furthermore the western boundary of this ductile deformation and the tib is not constrained in the kristinehamn area reconnaissance studies indicate that they both extend westwards towards the so called mylonite zone it is suggested that the eastern limit of the sveconorwegian orogen is located some 40 km east of the present boundary and that the protogine zone concept is obsolete the term sveconorwegian frontal deformation zone sfdz is proposed as a more appropriate alternative in southern sweden south of lake vattern and to correspond to a younger set of oblique ductile deformation zones with reverse and right lateral components of movement in the easternmost part of the orogen farther to the north ductile deformation zones older than the sfdz in the karlskoga kristinehamn area display a fan like geometry in an e w cross section with steep westerly dips in the eastern part of the section vertical dips farther west and moderate easterly dips in the western part of the section kinematic analysis indicates that dip slip movements predominate with a consistent top to the east sense of movement across the entire fan like structure in their present orientation deformation zones are characterized by reverse movements in the eastern part and normal movements in the western part of the structure between kristinehamn and the mylonite zone the main foliation is gently dipping to subhorizontal indicating that the regional structure is strongly asymmetric and that the fan like structure occurs close to the foreland of the orogen deformation zones are spaced to semi penetrative in the eastern part of the fan like structure whereas the deformation is more or less penetrative and the tib rocks are transformed to orthogneisses west of kristinehamn this east to west increase in bulk strain is in accordance with an increase in syn deformational metamorphic grade across the structure younger ductile deformation zones belonging to the sfdz are responsible for a major change in orientation of the older deformation zones in the easternmost part of the structure the fan like structure is best explained by models involving the interference of two separate tectonic events deformation occurred after 1 57 ga and prior to deposition of neoproterozoic and younger cover sedimentary rocks it is not yet clear whether the initial phase of deformation early sveconorwegian or older was related to the build up of an imbricate thrust stack in a compressional regime as favoured here or to regional e w extension the younger deformation phase was related to rotation of these older structures into the compressional late sveconorwegian sfdz

sveconorwegian massif type anorthosites and related granitoids result from post collisional melting of a continental arc root article i nfo two magmatic suites were emplaced during the post collisional evolution of the sveconorwegian orogeny an anorthosite mangerite charnockite suite amc suite and an hornblende and biotite bearing granitoids suite hbg suite the amc suite is exclusively located in the westernmost and warmest part of the orogen in granulite facies gneisses whereas the hbg suite intruded in the rest of the orogen but not in the granulite domain new u pb zircon geochronological data confirm previous age determinations 970 932 ma hbg suite and 933 916 ma amc suite the mafic facies of the two post collisional magmatic suites have similar geochemical compositions but the hbg differentiation trend displays higher cao sr u and th as well as lower k2o and feot mgo than the amc differentiation trend the hbg suite is hydrous and has a broadly higher fo2 whereas the amc suite is anhydrous the inferred parent magmas of both suites have overlapping initial sr nd and pb isotopic compositions with increasing differentiation the two trends point towards two different crustal contaminants together with the recent recognition of a major crustal shear zone located just east of the amc suite this difference suggests that the suites were emplaced in two different lithotectonic units using published experimental constraints and geochemical modeling we suggest that the mafic facies of both suites were produced by partial melting of lower crustal sources which were previously underplated probably during the evolution of a long lasting convergent margin later these lower crustal sources were modified by the regional granulite facies metamorphism 1 035 to 0 97 ga prevailing in the westernmost part of the orogen thus producing an anhydrous lower crustal source for the amc suite accordingly we conclude that the sveconorwegian massif type anorthosites result from partial melting of the continental arc root this process if accepted for other amcg anorthosite mangerite charnockite granite complexes was possible in the proterozoic because of a sufficiently high temperature but not in the archean because in subduction zones the main transfer to the crust was then felsic tonalites granodiorites and not basaltic we thus further suggest that the onset of massif type anorthosites at the beginning of the proterozoic may mark the time when plate tectonics began to operate in a similar way as today

linking deformation migmatite formation and zircon u pb geochronology in polymetamorphic orthogneisses sveconorwegian province sweden absolute ages of migmatization in the polymetamorphic parautochthonous basement of the sveconorwegian province sweden have been determined using u pb ion probe analysis of zircon domains that formed in leucosome of migmatitic orthogneisses migmatite zircon was formed by recrystallization whereas dissolution reprecipitation and neocrystallization were subordinate the recrystallized migmatite zircon was identified by comparison of zircon in mesosomes and leucosomes it is backscatter electron bright u rich 800 4400 ppm with low th u ratios generally 0 01 0 1 unzoned or oscillatory ghost zoned and occurs as up to 100 m thick rims with transitional contacts to cores of protolith zircon protolith ages of 1686 12 and 1668 11 ma were obtained from moderately resorbed igneous zircon crystals generally th u 0 5 1 5 u 300 ppm in mesosomes protolith zircon is also present as resorbed cores in the leucosomes linkage of folding synchronous migmatization and formation of recrystallized zircon rims allowed direct dating of south vergent folding at 976 7 ma at a second locality similar recrystallized zircon rims in leucosome date pre sveconorwegian migmatization at 1425 7 ma an upper age bracket of 1394 12 ma for two overprinting phases of deformation upright folding along gently ssw plunging axes and stretching in ese was set by zircon in a folded metagranitic dyke lower age brackets for these events were set at 952 7 and 946 8 ma by zircon in two crosscutting and undeformed granite pegmatite dykes together with previously published data the present results demonstrate i tectonometamorphic reworking during the hallandian orogenesis at 1 44 1 42 ga resulting in migmatization and formation of a coarse gneissic layering ii sveconorwegian continent continent collision at 0 98 0 96 ga involving a emplacement of an eclogite unit b regional high pressure granulite facies metamorphism c southvergent folding subhorizontal east west stretching and migmatization all of which caused overprint or transposition of older mesoproterozoic and sveconorwegian structures the sveconorwegian migmatization and folding took place during or shortly after the emplacement of sveconorwegian eclogite and is interpreted as a result of north south shortening synchronous with east west extension and unroofing during late stages of the continent continent collision

effects of topographic amplification induced by a u shaped canyon on seismic waves abstract the series solution of wave functions for 2d scattering and diffraction of plane sh shear horizontal waves induced by a u shaped canyon is proposed herein to account for the topographic effect of such a canyon the wave function expansion method has been frequently employed to study the topographic effect because it can reveal the physics of the wave scattering and can test the accuracy of other methods through a new domain decomposition strategy the half space having a u shaped canyon is divided into three subregions hence we defined three cylindrical coordinate systems in each coordinate system the wave field satisfying the helmholtz equation was represented by means of the separation of variables method in terms of the series of both bessel functions and hankel functions with unknown complex coefficients then three wave fields are all represented in the same coordinate system using the graf addition theorem the unknown coefficients are solved by satisfying the continuity conditions of the auxiliary boundary and the traction free boundary conditions on the bottom of the canyon to show the effects of symmetrical and nonsymmetrical u shaped canyons on the surface ground motion a parametric analysis is carried out in the frequency domain surface and subsurface transient responses in the time domain demonstrate the phenomenon of wave propagating and scattering it is found that a zone of amplification can obviously take place at the bottom of a u shaped canyon with nearly vertical walls

topographic effects on the seismic response of steep slopes a frequency domain parametric study using generalized consistent transmitting boundaries has been performed to evaluate the significance of topographic effects on the seismic response of steep slopes the results show that the peak amplification of motion at the crest of a slope occurs at a normalized frequency h 0 2 where h is the slope height and is the wavelength of the motion the importance of the natural site frequency is illustrated by the analysis of a stepped layer over a half space it was found that the natural frequency of the region behind the crest can dominate the response relative to the topographic effect for the conditions studied moreover the effect of topography can be handled separately from the amplification due to the natural frequency of the deposit behind the crest of the slope this concept of separating the amplification caused by topography from that caused by the natural frequency is advantageous to the development of a simplified method to estimate topographic effects

elastic finite difference modeling of cross hole seismic data cross hole seismic data exhibit unique characteristics not seen in surface survey data or even in vertical seismic profile data these are to a large extent due to the near horizontal propagation involved transmitted reflected evanescent guided and converted waves are all prominent these require an elastic algorithm for realistic simulation elastic finite differences are used to synthesize responses both fixed time snapshots and seismogram profiles for a series of two dimensional models of increasing complexity special emphasis is given to guided waves in continuous and segmented low velocity zones

40ar 39ar geochronology across the mylonite zone and the southwester granulite province in the sveconorwegian orogen of s sweden abstract the crustal segment between the mylonite zone mz and the protogine zone in southern sweden the southwestern granulite province sgp is characterized by numerous occurrences of granulite and upper amphibolite facies rocks including migmatitic gneisses mafic granulites garnet amphibolites and charnockites the southwest part of the mylonite zone north of varberg marks a tectonic upper boundary of the sgp a 40 ar 39 ar study was initiated across the mylonite zone and within the sgp in order to constrain and compare the ages obtained from within the sgp with those obtained north of and within the mylonite zone 23 homblendes and one muscovite have been analyzed the results of these analyses indicate the following 1 hornblendes from within and near the mz yield 40 ar 39 ar hornblende ages of 915 ma these ages are interpreted to date the dynamic crystallization or cooling below 500 c of the deformation associated with the mz 2 away from the mz there is a distribution of ages between those which yield younger sveconorwegian ages of 931 934 ma and those which yield older sveconorwegian ages generally between 960 and 1007 ma the younger age may be associated with orogenic uplift while the older one may be associated with an earlier sveconorwegian crustal thickening event 3 the one muscovite age of 904 ma would indicate a late cooling rate of at least 6 15 c ma cooling rates of this magnitude may suggest that the final uplift of the sveconorwegian orogen was related to large scale crustal extension

mineral and fluid inclusions in zircon of uhp metamorphic rocks from the ccsd main drill hole a record of metamorphism and fluid activity abstract the chinese continental scientific drilling ccsd main drill hole 0 3000 m in donghai southern sulu orogen consists of eclogite paragneiss orthogneiss schist and garnet peridotite detailed investigations of raman cathodoluminescence and microprobe analyses show that zircons from most eclogites gneisses and schists have oscillatory zoned magmatic cores with low pressure mineral inclusions of qtz pl kf and ap and a metamorphic rim with relatively uniform luminescence and eclogite facies mineral inclusions of grt omp phn coe and rt the chemical compositions of the uhp metamorphic mineral inclusions in zircon are similar to those from the matrix of the host rocks similar uhp metamorphic p t conditions of about 770 c and 32 kbar were estimated from coexisting minerals in zircon and in the matrix these observations suggest that all investigated lithologies experienced a joint in situ uhp metamorphism during continental deep subduction in rare cases magmatic cores of zircon contain coesite and omphacite inclusions and show patchy and irregular luminescence implying that the cores have been largely altered possibly by fluid mineral interaction during uhp metamorphism abundant h 2 o co 2 h 2 o or co 2 dominated fluid inclusions with low to medium salinities occur isolated or clustered in the magmatic cores of some zircons coexisting with low p mineral inclusions these fluid inclusions should have been trapped during magmatic crystallization and thus as primary only few h 2 o and or co 2 dominated fluid inclusions were found to occur together with uhp mineral inclusions in zircons of metamorphic origin indicating that uhp metamorphism occurred under relatively dry conditions the diversity in fluid inclusion populations in uhp rocks from different depths suggests a closed fluid system without large scale fluid migration during subduction and exhumation

the application of finite element analysis to body wave propagation problems summary the finite element method is shown to be a powerful tool for the numerical modelling of seismic body wave propagation problems applications extend to both problems on a scale of interest to engineers and also to large scale seismological problems solutions are sought in the time domain efficient programs have been written to accomplish this the scope of numerical solutions has been greatly enhanced by the use of a previously reported scheme for exactly cancelling reflections at the boundaries of the model the finite difference results of boore and the analytical results of trifunac for the amplification due to a mountain and an alluvial valley respectively are compared with new finite element results the new results agree well although there are some difficulties with resonance in the alluvial valley problem boore s sh results have been extended to vertical p and sv incidence a deep earthquake zone has been modelled realistically in two dimensions and earthquakes simulated at depth it is suggested that the variation in observed amplitude across the top of the zone due to refraction away from the slab may be used to provide an estimate of the thickness of the slab from long period observations of local earthquakes

1 05 1 01 ga sveconorwegian metamorphism and deformation of the supracrustal sequence at saesvatn south norway re os dating of cu mo mineral occurrences

2 dreflectivity method and synthetic seismograms for irregularly layered structures i sh wave generation summary the reflectivity method for complete sh seismograms has been extended to two dimensionally layered structures the aki larner technique is generalized to solve the integral equations for 2 d boundary conditions and propagator matrices are enlarged to express a total sh wavefield synthetic seismograms in a soft basin are calculated for an incident plane wave they compare favourably with the results of the finiteeiement and finitedifference methods even in the later portion where asymptotic ray and beam theories break down synthetic seismograms due to a line force and a point dislocation are also presented

eclogitized gabbros from the eastern grenville province textures metamorphic context and implications undeformed lenses of olivine orthopyroxene gabbro belonging to the 1429 ma shabogamo intrusive suite parautochthonous belt of the eastern grenville province host the first occurrence of eclogite mineral assemblages reported from the grenville province these rocks preserve igneous textures overprinted by eclogite mineralogy and by textures related to subsequent unloading high pressure signatures include omphacite pseudomorphs after augite plagioclase replacement by garnet kyanite corundum and orthopyroxene omphacite garnet coronas between olivine and plagioclase transformations related to decompression include replacement of garnet kyanite corundum by spinel plagioclase growth of plagioclase collars between clinopyroxene and garnet and de jadeitization of omphacite clinopyroxenes with numerous plagioclase inclusions and garnets surrounded by clinopyroxene plagioclase symplectites in granoblastic mafic rocks from the same area are also evidence of decompression from high pressures these

seismic radiation from an sh line source in a laterally heterogeneous planar fault zone a solution to the class of problems in which an sh line source is operating in a medium consisting of two quarter spaces with an arbitrary number of semi infinite vertical layers in between is given in a frequency wavenumber domain the general result is applied to a model with a single vertical layer and synthetic seismograms are calculated for a source specified as an sh line dislocation at the interface between the vertical layer and the faster quarter space the numerical examples demonstrate that moderate fault normal material heterogeneity can have significant effects on the seismic response of a medium the overall distribution of travel times amplitudes and motion polarities in the presence of fault zone material heterogeneity is different from a corresponding distribution in a homogeneous half space the effects are most prominent near the fault zone where head waves surface waves and trapped modes result in waveform complexities large amplifications over an order of magnitude in the fault zone itself and first motion polarities which are reversed from homogeneous medium predictions the results imply that material heterogeneity should be included in fault zone models which are used for the interpretation of observed seismic data and theoretical calculations of near fault responses such models can be utilized to obtain important fault zone and earthquake source parameters

prograde metamorphic zircon formation in gabbroic rocks the tale of microtextures u pb zircon dates of metagabbroic rocks such as eclogite mafic granulite and garnet amphibolite are used to constrain the timing of tectonometamorphic evolution in orogens worldwide for such interpretation however it is imperative to define at which stage of the p t evolution that zircon crystallization took place the prograde peak or retrograde stage in order to accurately interpret metamorphic zircon ages it is necessary to assess how the zircon crystallized or recrystallized as zircon can dissolve or grow under different metamorphic conditions zircon is robust to retrograde isotopic resetting under most crustal conditions but equilibrium zr mass balance models have suggested that zircon is largely produced during retrograde metamorphism this study takes a textural approach and identifies and reviews zircon forming textures and reactions in gabbro and metagabbro at different metamorphic grades ranging from subgreenschist to upper amphibolite and eclogite facies and at different stages of metamorphic recrystallization the textural relationships demonstrate that in metagabbro metamorphic zircon grows during the early stage of metamorphic recrystallization independent of pressure and temperature the mode of zircon formation is remarkably similar throughout different stages of metamorphic recrystallization and the most significant source of zr is igneous baddeleyite hence in contrast to the equilibrium mass balance model most zircon in metagabbro forms by prograde metamorphic reactions that consume igneous phases and not by late retrograde reactions and the onset of zircon forming reactions is governed primarily by the introduction of a hydrous fluid commonly accompanied by ductile deformation less

ground motion observations at hotel montana during the m 7 0 2010 haiti earthquake topography or soil amplification unusually severe structural damage was reported during the 2010 m 7 0 haiti earthquake in the vicinity of hotel montana located on top of a ridge in the district of petionville prompted by the observations u s geological survey seismic stations were deployed and aftershock recordings indicated ground motion amplification on the top of the hill compared to adjacent stations on reference site conditions the presence of topographic relief has been shown to significantly aggravate the consequences of strong ground motion during past events and topographic effects were brought forward to explain the observations in this paper we test the hypothesis of topographic amplification as the dominant factor that contributed to the damage concentration in the vicinity of hotel montana we initially conduct numerical simulations of the ridge seismic response assuming elastic homogeneous site conditions and show that numerical predictions of topographic amplification disagree with the field data both in amplitude and in frequency conversely while 1d ground response analyses for the site conditions at the hilltop predict amplification in the same frequency range as the field data they significantly underestimate the recorded amplitude we then conduct numerical simulations of the foothill ridge response to seismic motion while accounting for soil layering and qualitatively demonstrate that the recorded amplification is most likely attributed to coupled site topographic amplification effects namely to seismic waves trapped in the soft soil layers of the near surface amplified as a consequence of reverberations and further modified due to diffraction and scattering upon incidence on the irregular ground surface parametric investigations of the topography soil amplification coupling effects are then conducted and our results show that when accounting for a hypothetical soil bedrock interface at 100 m depth predictions are in excellent agreement with the observed motion

effect of a simple mountain range on underground seismic motion summary the influence of a simple mountain range on seismic ground motion is studied a two dimensional model of the medium and vertically incident plane sh waves are considered attention is devoted not only lo the wavefield along the earth s surface but also within the medium the wavefield is computed in two steps i the computation of the impulse response by the finite difference method 2 the computation of the response to a time variation of the incident wave approximately corresponding to a hundred yeai local earthquake a the sitc numerical results the impulse 1 esponse the transfer function the accelerograms and their spectra indicate strong spatial variability of the wavefield due to the topographical anomaly the differences as large as 100 per cent in the peak amplitudes of the accelerograms and of the order of 5 hz in their predominant frequencies at closely 200 m spaccd internal points of the medium have been found attention is focused also on the effect of causal absorption even unrealistically strong absorption seems to be unable to reduce significantly the spatial variability of the ground niotion caused by the topography a variability like this implying the occurrence of underground differential strains might be of engineering inipoi lance in the antiseismic desigti of underground structures tunnels for example in mountainous seismic i egions the groundmotion variability along the surface of the mountain is considerably smaller than within the medium

the effect of underground structure on seismic motions of the ground surface summary two dimensional finite element modelling of underground structural anomalies at shallow depths has been done to obtain the response at the ground surface to damped vertically incident sh waves power spectral ratios are examined to determine what effects the position shape depth and size of the anomaly have on the surface seismograms based on the results gathered from a number of models inferences are made with respect to the inverse problem given the seismic motion of the ground surface what can be said about the underground structure

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

high temperature deformation in the basal shear zone of an eclogite bearing fold nappe sveconorwegian orogen sweden ductile shear zones associated with emplacement of high pressure nappes are key features to resolve exhumation mechanisms the eastern segment of the sveconorwegian orogen hosts an eclogite bearing fold nappe whose basal shear zone shows structures associated with emplacement of the eclogite bearing nappe and decompression under high to intermediate pressure granulite and upper amphibolite fades conditions based on detailed structural mapping of a 4 km well exposed section of the basal shear zone we describe two major phases of deformation an early deformation stage d1 formed a penetrative gneissic foliation and tectonic layering including isoclinal folds f1 the sequence was subsequently affected by up to km scale tight south vergent folds f2 with sheared out limbs at the outcrop scale asymmetric f2 folds are commonly s vergent but symmetric folds with different degrees of tightness are also present melt was present at all stages of deformation and the structural relations demonstrate mutual feedback between melt localization and fold formation f2 folds have shallowly e plunging fold axis parallel to a stretching lineation defined by high grade mineral aggregates both constitute prominent structures of the basal shear zone f2 folds are associated with an axial planar fabric s2 defined by upper amphibolite and locally granulite facies mineral assemblages d2 shear structures are associated with top to the east kinematic indicators throughout the section the d1 episode was responsible for emplacement of the eclogite nappe into its present structural position the subsequently developed lineation parallel folds are interpreted to form by general shear where the structures reflect the regional e directed flow of the entire eclogite nappe c 2015 elsevier b v all rights reserved less

ground motion at mountains and sedimentary basins with vertical seismic velocity gradient summary the boundary integral gaussian beam method benites aki 1989 is applied to study the ground motion in 2 d structures that exhibit irregular topography and interface and whose shear wave velocity varies linearly with depth for incident plane sh waves in our first example of application the model is a half space whose free surface topography is a ridge of cosine shape with vertical shear wave velocity gradient in the second the model is a semi cylindrical sedimentary basin in a homogeneous half space in which the shear wave velocity of the sediments increases with depth our results for the case of the mountain show that the amplification on its top predicted by the 2 d modelling when the velocity is constant is enhanced when the velocity gradient is present for all frequencies and by a factor up to 3 in the case of the basin results show that the velocity gradient 1 enhances the amplification at the edges of the valley 2 makes the reverberations due to 2 d resonance have larger amplitudes and shorter intervals between arrivals 3 shortens the total duration of the seismograms at all stations within the basin

u pb and sm nd dating of high pressure granulite and upper amphibolite facies rocks from sw sweden abstract geochronological data from different radiometric systems on high grade metamorphic rocks in the southwest swedish granulite region southwestern sweden are generally analytically precise but sometimes in conflict with each other age data from seven samples on which a variety of radiometric methods have been applied are presented the age of peak metamorphism is determined by metamorphic zircons from two garnet amphibolites at c 975 ma using the conventional u pb isotope and pb pb evaporation methods titanites from the same type of rocks give ages of c 923 3 ma and 945 2 ma the sm nd data on mafic granulites and garnet amphibolites yield surprisingly young ages between 945 and 900 ma similar to previous sm nd ages these ages are comparable to or even younger than the 40 ar 39 ar hornblende ages that range between 1030 and 930 ma assuming that the sm nd systematics are entirely controlled by volume diffusion the closure temperature of the sm nd system in minerals from these rocks would be comparable to or lower than that of ar diffusion in hornblende i e around 500 c

localized solid state dehydration associated with the varberg charnockite intrusion sw sweden the mineralogy petrology and fluid inclusion chemistry of two charnockite patches within a distance of 4 5 km of the varberg magmatic charnockite intrusion sw sweden are investigated and described utilizing sem empa and fluid inclusion microthermometry garnet clinopyroxene 890 930 degrees c garnet amphibole 600 800 degrees c and garnet biotite 670 860 degrees c fe mg exchange thermometry indicates high temperatures for charnockite patch i compared to relatively lower garnet orthopyroxene garnet amphibole and garnet biotite temperatures of 500 to 600 degrees c for charnockite patch ii plagioclase in the charnockitic patches tends to be more anorthitic and less albitic x an 0 20 x ab 0 76 than in the surrounding regional granitic gneiss x an 0 13 x ab 0 84 replacement antiperthite is commonly found in unrelated plagioclase grains from either patch compared to the regional granitic gneiss where it is relatively rare in either patch k feldspar is considerably less albitic x kfs 0 90 0 92 x ab 0 05 0 10 compared to k feldspar from the regional granitic gneiss it can also be found as micro veins along quartz grain rims both patches are dominated by clinopyroxene as opposed to orthopyroxene garnet biotite and amphibole and in both charnockite patches tend to have lower fe and correspondingly higher mg values compared with garnet biotite and amphibole from the surrounding regional granitic gneiss fluorapatite tends to be relatively enriched in cl and depleted in y ree compared with fluorapatite from the regional granitic gneiss fluid inclusions in charnockite patches i and ii are dominantly carbonic similar to what is seen for the varberg charnockite in addition to quartz relatively high density carbonic inclusions are also preserved in garnet and in fluorapatite it is presumed that pure carbonic fluids must have once coexisted with relic magmatic h2o co2 nacl fluids at peak metamorphic conditions the most likely scenario suggests that charnockite patches i and ii were formed during the later stages of crystallization of the varberg charnockite magmatic body during which copious amounts of co2 rich fluids with a brine cacl2 dominated component were expelled into the country rock via pegmatoid segregations both within and in the immediate surroundings of the charnockite body patch i appears to represent the extension of a pegmatoid segregation whereas patch ii appears to represent fluid induced lower temperature solid state dehydration transport was facilitated via a system of tectonic fissures and fractures generated in the regional migmatized granitic gneiss during its emplacement within the scope of what is known these two charnockite patches fall into the generally observed parameters for localized dehydration zones in general c 2014 elsevier b v all rights reserved less

inherited pb components in magmatic titanite and their consequence for the interpretation of upb ages abstract the occurrence of inherited radiogenic pb components in 35 ma old magmatic titanite is reported here for the first time the about 810 ma age of the inherited components is identical to that contained in zircon from the same amphibole bearing syenite sample in both minerals the precambrian components were not totally reset during magmatic new growth at 35 ma this age pattern substantiates that the u pb chronometer in titanite is resistant to temperatures in excess of 712 c as is already known for zircon and monazite in consequence u pb ages from crystalline titanites have to be interpreted as the age of mineral formation or re crystallization rather than the time of u pb system closure during cooling of the rock

new tectonic divisions of the grenville province southeast canadian shield on the basis of geological geophysical and geochronological data the grenville province has been divided into three first order longitudinal belts the parautochthonous belt pb allochthonous polycyclic belt apb and allochthonous monocyclic belt amb these are set apart by three first order tectonic boundaries the grenville front gf allochthon boundary thrust abt and monocyclic belt boundary zone mbbz the belts are subdivided into terranes based on internal lithological character the gf separates the archean to proterozoic foreland northwest of the orogen from reworked equivalents to the southeast continuous at the scale of the orogen its main characteristic is that of a crustal scale contraction fault the pb although less clearly identified along the length of the orogen in most places represents upgraded and tectonically reworked rocks of the adjacent foreland the boundary between the pb and the apb to the southeast the abt is most clearly delineated in the eastern half of the province it is the locus of major crustal delamination along which high grade mostly middle proterozoic polycyclic terranes were tectonically transported northwest toward and onto the pb the amb comprises two separate areas underlain by the wakeham supergroup and what is currently known as the grenville supergroup respectively its basal contact the mbbz is a decollement zone of variable kinematic significance between older polycyclic rocks and tectonically overlying monocyclic rocks this first order zonation implies a tectonic polarity to the grenville province superimposed on which are second order features evident from contrasting tectonic styles and radiometric ages these characteristics are consistent with a diachronous or oblique collisional model for the grenville orogen

geochronology of eclogite facies metamorphism in the sveconorwegian province of sw sweden abstract decompressed eclogites in the sveconorwegian province sw sweden have been dated using u pb geochronology zircons are common as inclusions in garnet and kyanite and other minerals in the decompressed eclogites titanite inclusions are found exclusively in the core of garnets the mineral inclusions and the chemical zoning of the garnets suggest inital growth under prograde amphibolite facies conditions followed by eclogite facies metamorphism and subsequent decompression through the high pressure granulite and upper amphibolite facies the zircon and titanite thus formed prior to the eclogite stage of the p t path the age of the eclogite forming event was determined by ion probe dating of zircon inclusions in garnets the obtained age of 972 14 ma is the maximum age of the eclogitisation the age of the titanite inclusions in garnet is 945 4 ma this age is similar to other u pb ages of titanite in the region which suggest that the titanite has been isotopically reset and that the age reflects cooling the mode of occurrence textural relationships and the chemical homogeneity suggest that the zircons formed from zr released from magmatitic fe ti oxides and possibly amphiboles during breakdown of magmatic minerals at the onset of the sveconorwegian metamorphism spot analyses of complex zircons from a granitic dyke in the eclogite yielded an age of 1403 15 ma for magmatic cores and an age of 963 22 ma for metamorphic rims the older age is a minimum age of the eclogite protolith and correspond to the age of a generation of granites in the region the rim age is within error identical to the age of eclogite metamorphism the eclogite metamorphism in sw sweden is younger than its grenvillian counterparts in scotland canada and usa

numerical modeling of fault zone trapped waves acoustic case abstract we have obtained numerical results for an acoustic wave propagating in a 3d medium with mixed boundary conditions the specific model involves a vertical low velocity fault zone of varying thickness embedded in an otherwise homogeneous half space at the fault zone boundary the stress and displacement are continuous on the free surface the stress is zero a pseudo spectrum method is employed to achieve sufficient resolution with reasonable computation time on a cray results show the development of guided waves trapped in the fault zone these guided waves display large amplitudes and lengthening waveforms they propagate at lower velocity with amplitudes that drop off mainly due to energy leakage out of the fault zone as the width of the fault zone varies the wave energy tends to funnel into the new low velocity wave guide at large distance these guided waves become the dominant arrivals on seismograms the waveforms are useful to recover the geometry and properties of the fault zone

geochronology of high pressure mafic granulite dykes in sw sweden tracking the p t t path of metamorphism using hf isotopes in zircon and baddeleyite although the u pb zircon chronometer has been widely used for dating metamorphism in moderate to high grade rocks it is generally difficult to link the u pb age of zircon to specific metamorphic reactions in this study the initial hf isotopic composition of secondary zircon is compared with the evolution of hf isotopic composition of the bulk sample back projected from the measured value through time this approach may enhance the interpretation of radiometric ages performed on metamorphic mineral assemblages here u pb sm nd and lu hf geochronology and thermobarometry have been integrated and applied to two metamorphosed diabase dykes in the sveconorwegian orogen sw sweden the dykes are located 5 km east of the nne trending gota alv deformation zone in the idefjorden terrane and trend parallel to this zone the lunden dyke is recrystallized into a coronitic granulite facies assemblage u pb isotopic analyses of baddeleyite in this dyke indicate an emplacement age of 1300 ma thermobarometric techniques applied to garnet and omphacitic clinopyroxene coronas indicate high pressure metamorphism at c 15 kbar and c 740 c growth of polycrystalline zircon at the expense of baddeleyite occurred at 1046 6 ma identical hf isotopic composition of polycrystalline zircon and baddeleyite shows that the baddeleyite to zircon transition took place before hf equilibration among the other metamorphic minerals and hence the c 1046 ma age of polycrystalline zircon sets an upper age limit of metamorphism of this sample the haregarden dyke is recrystallized into a granoblastic transitional upper amphibolite to granulite facies assemblage the estimated p t conditions are c 10 kbar and c 700 c analyses of small 30 m clear and round zircon in this sample yield a concordia u pb age of 1026 4 ma which is indistinguishable from the lu hf and sm nd mineral isochron ages of 1027 9 ma and 1022 34 ma this type of secondary zircon plots at the lower end of the lu hf isochron and indicates simultaneous growth with garnet at c 1026 ma a time when hf isotopic equilibrium among minerals must have been reached

polyphasal foreland vergent deformation in a deep section of the 1 ga sveconorwegian orogen metamorphic belts in precambrian shields expose deep interiors of orogens and are often challenging to interpret in tectonic terms the eastern segment of the 1 1 0 9 ga sveconorwegian orogen is a metamorphic belt which was metamorphosed at high pressure granulite and upper amphibolite facies at 35 40 km depth and shows highly complex fold patterns we use detailed structural analysis in combination with u pb sims dating of complex zircon to identify the structural and tectonic evolution in a composite migmatitic orthogneiss complex of the eastern segment we link four fold phases to late orogenic foreland vergent flow and date d 2 and d 3 at 0 97 0 95 ga leucosome and mesosome of felsic metasupracrustal migmatitic gneiss contain igneous zircon that dates the crystallization of the source rock or protolith at 1695 8 ma and 1690 8 ma respectively demonstrating a temporal link to unmetamorphosed or little metamorphosed igneous rocks east of the sveconorwegian orogen the transscandinavian igneous belt early migmatization attributed to hallandian orogenesis is dated by formation of secondary zircon in two leucosome samples at 1402 12 and 1386 7 ma the pre sveconorwegian structure s c which is strongly overprinted by sveconorwegian deformation and migmatization is a composite coarse gneissic layering made up of a primary compositional layering and variably present hallandian leucosome veins the dominant foliation a pervasive gneissic banding s 1 is axial planar to intrafolial f 1 folds and developed as a result of tectonic overprint of s c s 1 is associated with a strong ese trending aggregate stretching lineation l 1 s 1 and l 1 were folded by asymmetric se vergent f 2 folds during foreland vergent flow crystallization of sveconorwegian zircon in syn f 2 leucosome dates this phase at 970 5 ma the sequence was subsequently deformed by symmetric and asymmetric f 3 folds that are s to se vergent syn f 3 leucosome mineral parageneses and microtextures associated with d 3 show that this deformation occurred under still high temperatures the last ductile phase d 4 also involved the generation of leucosome synkinematic with n s trending folds that deformed all previous structures under amphibolite fades conditions k feldspar rich originally coarse grained and strongly deformed metapegmatite contain two generations of zircon texturally old 1414 5 ma cores and fragments and voluminous sveconorwegian envelopes and new grains that demonstrate the presence of melt as late as 958 7 ma ductile structures are similar in metasupracrustal and metaplutonic orthogneiss complexes likely these units were tectonically juxtaposed during d 1 while d2 d4 structures reflect a common tectonic evolution after their emplacement we interpret d1 4 structures as recording wnw ese convergence d 1 and ese vergent flow d 2 and d 3 followed by e w gentle upright folding d 4 sveconorwegian 0 98 0 96 ga foreland vergent deformation accompanied by migmatization at all four stages was responsible for formation of the polyphasal deformation pattern in this part of the orogen published by elsevier b v less

two dimensional analysis of the effect of subsurface anomalies on the free surface response to incident sh waves summary two dimensional finite element modelling of subsurface anomalies at shallow depth has been done to obtain the response to incident sh waves vertically incident sh and obliquely incident sh have been examined power spectral ratios were studied to determine the effect on the surface seismograms of the position shape depth size and material composition of the anomaly a number of relationships between the surface response and the anomaly has been identified these relationships may be used in solving the inverse problem given the seismic motion of the ground surface determine the physical properties of the underground structure

molybdenite re os dating constrains gravitational collapse of the sveconorwegian orogen sw scandinavia abstract re os dating of molybdenite from small deposits is used to define crustal domains exhibiting ductile versus brittle behaviour during gravitational collapse of the sveconorwegian orogen in sw scandinavia a 1019 3 ma planar quartz vein defines a minimum age for brittle behaviour in central telemark in rogaland vest agder molybdenite associated with deformed quartz and pegmatite veins formed between 982 3 and 947 3 ma in the amphibolite facies domain three deposits and between 953 3 and 931 3 ma west of the clinopyroxene in isograd two deposits in the vicinity of the 0 93 0 92 ga rogaland anorthosite complex the data constrain the last increment of ductile deformation to be younger than 0 95 and 0 93 ga in these two metamorphic zones respectively molybdenite is the product of an equilibrium between biotite oxide and sulfide minerals and a fluid or hydrated melt phase after the peak of 1 03 0 97 ga regional metamorphism molybdenite precipitation is locally episodic a model for gravitational collapse of the sveconorwegian orogen controlled by lithospheric extension after 0 97 ga is proposed in the west of the orogen the rogaland vest agder sector is interpreted as a large shallow gneiss dome formed slowly in two stages in a warm and structurally weak crust the first stage at 0 96 0 93 ga was associated with intrusion of the post collisional hornblende biotite granite suite the second stage at 0 93 0 92 ga restricted to the southwesternmost area was associated with intrusion of the anorthosite mangerite charnockite suite most of the central part of the orogen was already situated in the brittle upper crust well before 0 97 ga and did not undergo significant exhumation during collapse in the east of the orogen situated against the colder cratonic foreland exhumation of high grade rocks of the eastern segment occurred between 0 97 and 0 95 ga and included preservation of high pressure rocks but no plutonism

zirconium abundance in granulite facies minerals with implications for zircon geochronology in high grade rocks zircon growth in high grade metamorphic rocks may be triggered by net transfer reactions involving the breakdown of a phase bearing zirconium zr we have measured the concentration of zr in the major minerals in granulite facies rocks of differing bulk composition both garnet and hornblende contain tens of parts per million zr and no other major phase contains significant zr simple calculations show that reaction of either garnet or hornblende to form non zr bearing phases will release sufficient zr to account for at least some new zircon growth u pb ages from new zircon grown as a result of either hornblende or garnet breakdown are not expected to record the time of peak metamorphism but rather will record the time of particular metamorphic reactions allowing direct correlation of zircon ages with petrologically derived pressure temperature time paths this approach offers the potential for more rigorous interpretation of the metamorphic significance of zircon ages than has previously been possible

copper lead and zinc trapping in mediterranean deep sea sediments probable coprecipitation with mn and fe abstract in the deepest area of the western mediterranean sea between sardinia and minorca sediments are relatively rich in zn and fe on the periphery of this area the sediments are rather rich in cu pb and mn and to a lesser extent in zn in this last case the vertical profile of mn in the sediment suggests that the mn enrichment in the top level with an mn concentration of 1500 g g 1 is due to an ascending mn flux from deeper levels reducing for mn oxyhydroxides to the surficial 0 4 cm thick oxidizing sediment the concentrations of cu pb and zn dissolved in the surficial sediment pore waters are too low to allow direct precipitation of mere oxides or hydroxides of these metals but enrichment in the mn rich deep sea zone can be explained by a coprecipitation process during the precipitation of mn oxides or hydroxides since mn dissolved in surficial sediment pore water is present in an apparent slight oversaturation with respect to the solubility product in the deepest areas where zn seems to precipitate with fe hydroxides the surficial sediments appear to be too reducing to allow mn oxides to precipitate cu and pb are trapped not so well there calculations of chemical equilibria of the species concerned are consistent with these considerations since mn seems to be released from sediments in the deepest zone with total mn concentrations g g 1 it can be assumed that there the surficial sediments correspond nearly to a reducing medium for the mn oxides therefore the bottom seawaters of these deepest area of the western mediterranean sea seem to have rather low o 2 concentrations and to be only rarely renewed

three dimensional geometrical ray theory and modelling of transmitted seismic energy of data from the nevada test site this paper presents a geometrically based algorithm for computing synthetic seismograms for energy transmitted through a 3 d velocity distribution 3 d ray tracing is performed to compute the traveltimes and geometrical spreading amplitude the formulations of both kinematic and dynamic ray tracing systems are presented the two point ray tracing problem is solved by systematically updating the initial conditions and adjusting the ray direction until the ray intersects the specified endpoint the amount of adjustment required depends on the derivatives of the position with respect to the given starting angles between consecutive rays the algorithm uses derivatives to define the steepest descent direction and to update the initial directions the convergence rate depends on the complexity of the model test seismograms compare favourably with those from a 2 d asymptotic ray theory algorithm and a 3 d gaussian beam algorithm the algorithm is flexible in modelling arbitrary source and recorder geometries for various smoothly varying 3 d velocity distributions the algorithm is further tested by simulating surface to tunnel vibroseis field data shear waves as well as compressional waves may be approximately included application of the algorithm to a data set from the rainier mesa of the nevada test site produced a good fit to the transmitted first arrival traveltimes and amplitudes with approximately 15 per cent variation in the local 3 d velocity

late sveconorwegian metamorphism and deformation in southwestern sweden abstract the precambrian of southwestern sweden is divided into eastern and western crustal segments separated by a major tectonic boundary the mylonite zone the southern part of the eastern segment is characterized by numerous occurrences of mafic granulites and charnockites the western segment comprising greenschist to amphibolite facies gneisses of supracrustal and plutonic origin sm nd mineral ages of the granulite facies metamorphism in the eastern segment range from 920 to 880 ma garnet pyroxene feldspar whole rock sm nd isochrons of the varberg charnockite and the traslovslage mafic granulite yield ages of 893 5 ma and 881 4 ma respectively this late sveconorwegian late grenvillian granulite facies metamorphism in southern sweden appears to be confined to the eastern segment while the last high grade metamorphic event in the western segment is contemporaneous with the 1100 ma old granulite facies metamorphism in the bamble area of se norway at least three phases of regionally important deformation postdate the late sveconorwegian metamorphism in southwestern sweden deformation related to movements within the mylonite zone was contemporaneous with or later than the granulite facies metamorphism in the varberg area and took place mainly under retrograde metamorphic conditions leading to almost complete replacement of garnet and pyroxene by amphibole biotite and plagioclase extensional tectonics were presumably important during the uplift of the granulite terrain east of the mylonite zone peak p t conditions during the late sveconorwegian metamorphic event were considerably higher than those required for the melting of granitoid rocks the sm nd ages of granulite facies parageneses within the eastern segment are approximately the same as those of numerous late sveconorwegian granite intrusions in southwestern scandinavia suggesting a genetic relationship between high grade metamorphism at depth and the emplacement of granites at higher crustal levels the nd model ages of the varberg charnockite agree reasonably well with the nd model ages of 1700 1600 ma old granites within the same crustal domain while the model age of the mafic granulite originally a mafic dyke corresponds roughly to the model ages of 930 ma old mafic dykes in se sweden

partial melting in amphibolites in a deep section of the sveconorwegian orogen sw sweden garnet amphibolite metataxites at the steningekusten nature reserve in southwestern sweden contain tonalitic patches and veins whole rock chemistry suggests that the protoliths were mafic igneous rocks with alkaline affinities orthopyroxene megacrysts are present in leucosome in parts of these garnet amphibolites but absent in others orthopyroxene megacrysts were formed by vapor absent melting initiated by incongruent melting of biotite followed by the breakdown of hornblende the net reaction was bt hbl pi qtz opx melt cpx gt melting occurred at pressures of approximately 1 gpa and temperatures which probably exceeded 800 degrees c pyroxenes are surrounded by hornblende quartz symplectites and hornblende in these coronas has distinctly lower concentrations of na k and ti than that in adjacent mesosorne the hornblende rims formed upon cooling and reaction with crystallizing melt this created a barrier to further reaction thus preserving the orthopyroxene megacrysts garnet amphibolite metatexites lacking pyroxene megacrysts have features characteristic of vapor present melting including lack of peritectic phases predicted by vapor absent melting reactions larger amounts of leucosome 14 versus 7 and less distinct melanosomes the variation in these migmatites reflects open system behavior either on a regional scale with the migration of aqueous fluids into the amphibolites or on a local scale with the migration of melt within the amphibolites zircons from all units have cl dark core domains that are dated at 1415 1390 ma the core zones are cut and overgrown by cl dark and cl bright rims that are dated at 975 965 ma the zircon rims are thin in the mesosome but are thicker in the leucosome suggesting that they formed during migmatization new growth of zircon associated with migmatization at ca 970 ma corresponds to the timing of crustal scale partial melting in the deep regions of the sveconorwegian orogen synchronous with east west extension and the intrusion of mafic dykes if partial melting was driven by an influx of aqueous fluids they were probably derived from a relatively cool source region which would indicate tectonic juxtaposition of hotter and cooler terranes c 2015 elsevier b v all rights reserved less

determination of magnetic properties of rocks by analysis of demagnetization curves hematite ilmenite bearing rocks from sw sweden granulites from the high grade sveconorwegian corresponding to grenvillian gneiss terrane of sw sweden were investigated in order to relate magnetic properties to the granulite facies mineralogy and the amphibolite facies retrograde mineralogy we used standard paleomagnetic techniques susceptibility measurements electron and optical microscopy and a new way to analyze demagnetization curves based on vector difference sums the new technique allowed quantitation of the relative contributions of partial natural remanent magnetization nrm components as well as numerical extraction of thermal and coercive force alternating field af unblocking data two major components were identified one stable which is carried by hematite ilmenite and one less stable carried by multidomain md magnetite the age of the hematite ilmenite component is circa 930 ma and it has steep negative inclination coercivities in excess of 150 mt and unblocking temperatures between 540 degrees c and 640 degrees c two corresponding poles are reported 1 paleolatitude paleolongitude plat plong 218 degrees 24 3 with dp dm 9 4 degrees 9 9 degrees paleopole and 2 plat plong 203 degrees 51 degrees with d p d m 4 4 degrees 5 6 degrees vgp the md magnetite component is a recent or cretaceous paleogene steeply positive inclined nrm component associated with strong induced magnetization plat plong 2 degrees 74 degrees and d p d m 11 degrees 14 degrees vgp the md magnetite was unblocked at conditions of 6 40 mt and 60 400 degrees c our new analysis method was successful in showing that retrograde amphibole formation strongly decreases the importance of the hematite ilmenite component on behalf of the md magnetite it has a diminishing effect on a negative aeromagnetic anomaly in the area the 930 ma components constitute 80 0 of the vector difference sums depending on rock composition however as this fraction goes down to 60 the induced magnetization seems to outweigh the hematite ilmenite influence on aeromagnetic anomalies due to its opposite direction these rocks still have a strong and stable hematite ilmenite dominated nrm less

elastic wave propagation and site amplification in the salt lake valley utah from simulated normal faulting earthquakes the two dimensional seismic response of the salt lake valley to near and far field earthquakes has been investigated from simulations of vertically incident plane waves and from normal faulting earthquakes generated on the basin bounding wasatch fault the response to normal faulting earthquakes was simulated using a two dimensional finite element method and the plane wave response was calculated from two dimensional finite difference simulations the plane wave simulations were then compared with observed site amplifications in the salt lake valley based on seismic recordings from nuclear explosions in southern nevada that show 10 times greater amplification within the basin than measured values on hard rock sites while previous studies attribute this increased site amplification to the near surface unconsolidated consolidated alluvial fill contact our synthetic seismograms suggest that in the frequency band 0 3 to 1 5 hz at least one half the site amplification can be attributed to the impedance contrast between the basin sediments and higher velocity basement rocks synthetic seismograms from vertically incident plane wave sources and buried double couple sources predict large amplitude rayleigh wave propagation from the edges of the basin and in general uniform site amplification in contrast near field simulations of basin bounding normal faulting earthquakes predict large amplitude rayleigh waves propagating westward from the fault across the basin spectra of synthetic accelerograms computed from the normal faulting earthquakes shows that spectral amplification within the basin is primarily due to source directivity with a maxima near the surface projection of the fault that decays rapidly away from the fault importantly the synthetic modeling of near field earthquake sources show that near field directivity effects are important and should be considered in an earthquake hazard assessment of the salt lake valley and similar geologic settings along the wasatch front

earthquake ground motion and structural response in alluvial valleys this paper is concerned with the problem of soil amplification and structural damage due to local site conditions in sedimentary valleys during earthquakes it focuses on a small valley in kirovakan for which 1d wave propagation analyses have failed to provide adequate answers for the large extent and spatial distribution of damage during the 1988 armenia earthquake a more realistic 2d finite element analysis is performed herein in search of an explanation of the observed behavior using as input an inferred rock accelerogram the response of the valley is calculated for a vertically incident sh wave synthetic accelerograms of the surface ground motion are presented for different sites these accelerograms are then used to determine the amplification ratios of the surface response with respect to that of the free field motion of the rock outcrop for different frequencies and for a continuous set of sites in addition response spectra are evaluated for simple oscillators representing structures located at various sites results of the 2d simulations show striking differences with respect to those from 1d analyses in particular 1 while the resonant frequencies exhibited by a 1d model for a given site also appear in the 2d model the peak ground response and structural response are almost twice as large for the 2d as for the 1d model 2 the 2d model exhibits in addition a new set of resonant frequencies and concomitant mode shapes across the valley which are directly related to its finite width and 3 due to these additional resonances the ground amplification ratio tends to oscillate very rapidly both spatially and with frequency leading to the observation that two identical structures located in the same vicinity or two slightly different structures located essentially on the same site can be subjected to significantly different seismic forces even if the underlying soils have very similar characteristics these results provide a meaningful explanation for the observed damage and thus serve to exemplify a situation in which site effects caused by the finite lateral extent of a valley must be taken into consideration in order to model satisfactorily seismic behavior

the effect of topography on earthquake ground motion a review and new results a brief review of experimental and theoretical results about the effect of topography on seismic motion shows that they are consistent only on a qualitative basis amplification at mountain tops for wavelengths comparable with mountain widths is predicted and observed but the numerical simulations often underestimate the actual observed effects we propose that this disagreement is because current models are not complex enough we therefore computed the response to incident sh waves of a set of different complex configurations that include two dimensional surface topography with or without periodic ridges and subsurface layering the results show that 1 the topographic effect in itself is difficult to isolate from other effects like surface layering and therefore the amplification on top of geomorphologically complex sites cannot be predicted by a priori estimations based solely on topography and 2 the high crest base amplification ratio observed in the field cannot usually be matched even with complex two dimensional structures with incident plane sh waves which suggests that more complex models are needed to incorporate more complex wave fields e g sv surface and three dimensional geologic configurations

protolith ages and timing of deformation in the eastern marginal part of the sveconorwegian orogen southwestern sweden abstract u pb zircon and titanite ages from variably metamorphosed igneous rocks in the eastern marginal part of the sveconorwegian orogen eastern segment north of lake vanern sweden suggest that these rocks belong to the younger c 1 71 1 65 ga igneous suite of the c 1 85 1 65 ga transscandinavian igneous belt tib two porphyritic meta granites and one isotropic monzonite yield u pb zircon ages of 1661 27 1674 7 and 1674 7 ma respectively these ages support earlier interpretations that the eastern segment north of lake vanern contains tectonically reworked tib rocks and that there is no major lithological discontinuity either across the sveconorwegian frontal deformation zone or within the eastern segment igneous brown coloured titanites from five samples yield similar u pb ages as the zircons in contrast colourless and oblate shaped titanites from the western penetratively deformed parts of the eastern segment give concordant ages of 976 4 and 956 6 ma further to the east similar titanite from both a penetratively deformed meta granite and a ductile shear zone within a porphyritic quartz monzonite are strongly discordant close to late sveconorwegian lower intercept ages this type of titanite is interpreted to be syntectonic and formed during the upper greenschist east to amphibolite west facies fabric forming event in the eastern segment since the brown igneous titanites and the zircons share a common igneous origin and the single type of metamorphic titanites are either concordant or strongly discordant towards late sveconorwegian intercept ages it is inferred that no major tectonothermal event occurred between the time of tib emplacement and the late sveconorwegian tectonothermal reworking pre sveconorwegian palaeo to mesoproterozoic deformational and metamorphic events gothian which have been inferred west of and further south within the eastern segment appear to be absent in the northern part of this crustal unit

effects of local soil conditions on the topographic aggravation of seismic motion parametric investigation and recorded field evidence from the 1999 athens earthquake during the 1999 athens earthquake the town of adames located on the eastern side of the kifissos river canyon experienced unexpectedly heavy damage despite the particular geometry of the slope that caused significant motion amplification topography effects alone cannot explain the uneven damage distribution within a 300 m zone parallel to the canyon s crest which is characterized by a rather uniform structural quality in this article we illustrate the important role of soil stratigraphy and material heterogeneity on the topographic aggravation of surface ground motion for this purpose we first conduct an extensive time domain parametric study using idealized stratified profiles and gaussian stochastic fields to characterize the spatial distribution of soil properties and using ricker wavelets to describe the seismic input motion the results show that both topography and local soil conditions significantly affect the spatial variability of seismic motion we next perform elastic two dimensional wave propagation analyses based on available local geotechnical and seismological data and validate our results by comparison with aftershock recordings

coronitic metagabbro and eclogite from the grenville province of western quebec interpretation of u pb geochronology and metamorphism we present new u pb and metamorphic data on high pressure coronitic metagabbros from three distinct structural settings in the parautochthonous belt of the grenville province in western quebec intrusive ages are i for metagabbro close to the grenville front correlative with the sudbury dykes defined in ontario ii for an eclogitized lens at the base of the highest structural level sl4 a new age for mafic magmatism in the western grenville and iii for metagabbro from sl4 interpreted as correlative with metagabbros from the algonquin and shawanaga domains in ontario metamorphism in all cases is grenvillian with the best constrained age of 1069 3 ma for the metagabbro of sl4 metamorphic grade increases from the grenville front to the south the mafic rocks preserve relict igneous textures overprinted by garnet clinopyroxene that developed as coronas and or pseudomorphs after igneous phases the highest grade metagabbros contain omphacite and some lack primary plagioclase therefore b

late orogenic sveconorwegian massif anorthosite in the jotun nappe complex sw norway and causes of repeated amcg magmatism along the baltoscandian margin the age and tectonometamorphic history of massif anorthosite in the jotun nappe complex sw norway were investigated by zircon and titanite u pb id tims the anorthosite contains sparse zircons showing complex u pb systematics reflecting events dated at 965 4 and 913 2 ma and a pronounced caledonian metamorphic overprint the oldest age is interpreted as the protolith age of the massif anorthosite we propose that the jotun anorthosite is related to 970 960 ma magmatism in the western gneiss region and coeval orogen perpendicular extension conversely a 930 ma high grade metamorphic event in the jotun nappe complex and the related lindas nappe is likely related to formation of the autochthonous ca 930 ma rogaland anorthosite complex we suggest that the two late to post orogenic amcg events reflect two instances of lithospheric foundering below the orogen separated by ca 20 30 my the 913 2 ma metamorphic episode appears to date a heating event restricted to the outermost edge of the western gneiss region leucosome formation in high grade gneisses geographically close to the jotun anorthosite is dated at 892 4 ma and suggested to reflect co2 rich fluid flux along shear zones

conventional u pb dating versus single grain pb evaporation dating of complex zircons from a pegmatite in the high grade gneisses of southwestern sweden u pb multi grain dating of zircons from a pegmatite dyke in southwestern sweden yield analyses which define a discordia with upper and lower intercept ages of 1510 32 ma and 631 64 ma respectively dating by the single zircon evaporation method on prismatic zircons from the same dyke indicates a primary crystallization age of 1409 20 ma in addition four oval zircon grains yield a 207pb206pb age of 969 27 ma the older single zircon evaporation age is interpreted as representative of pegmatite emplacement whereas the younger age is suggested to correspond to isotopic disturbance and new zircon growth during a late sveconorwegian metamorphic event to explain the false intercept ages in the u pb concordia diagram this study suggests a three stage model including 1 crystallization of zircons during pegmatite intrusion 2 episodic lead loss and new zircon growth during high grade metamorphism and 3 a recent lead loss event as the dykes are strongly deformed the protolith age of the pegmatite provides an upper age limit for the gneiss forming event the single zircon age of 969 27 ma is interpreted to be associated with this event which took place during high grade metamorphic conditions

the seismic response of a steep slope high resolution observations with a dense three component seismic array we deployed an array of 35 three component seismographs to measure site effects associated with a 50 m high slope that is the highwall of an abandoned surface coal mine near sullivan indiana the strip mine pit had filled with water to within 10 m of the top of the highwall our array was deployed over this slope and recorded 10 underwater explosions detonated in the lake 800 m away the raw data show a site resonance revealed by ringy waveforms observed at stations near the slope crest the ringing is seen on the vertical component immediately following the p arrival and on the horizontal components immediately following what we interpret as a secondary p arrival formed by a direct wave propagating through the water three dimensional particle motion analysis demonstrates that the p wave signal is linearly polarized on the flat ground behind the slope but becomes strongly elliptical for stations on the slope the direct wave through the water is nearly horizontally polarized and shows a pronounced amplification of about a factor of 2 for stations at the top of the slope we quantify the variations in the site resonance by using spectral ratios we observe a factor of 2 amplification at about 9 hz that we interpret as a fundamental mode of the slope face online material animations of 3d and 4d visualizations manuscript received 8 june 2001