guided wave propagation in laterally varying media ii lg waves in north western europe summary lg wave observations at norsar from a sequence of explosions straddling the central graben in the north sea show that the phase is almost extinguished by passing through this structure for models of the graben structure based on seismic refraction experiments with crustal thinning beneath a zone of thickened sediments numerical modelling of lg propagation shows very poor transmission the inclusion of attenuation simulating the effects of scattering from faults and other complex structures further diminishes the transmittivity the theoretical effect of a crustal pinch is to redistribute s energy over a wide range of groups velocities a pattern that fits well with the observations three components recordings at norsar of explosive charges fired in water covering a wide range of azimuths show significant transverse components to the seismograms the transverse energy builds up with travel time and for lg is of the same order as the vertical component these results are consistent with the theoretical prediction of progressive net transfer of energy from rayleigh to love modes as the wavetrain propagates through a three dimensionally heterogeneous medium

upper mantle structure under western europe from fundamental and higher mode surface waves using the nars array summary a generalized inversion of a new data set consisting of surface wave phase velocities and sn traveltimes has resulted in a new shear velocity and density model for the west european platform wepl 2 the surface wave phase velocity data set consists of fundamental and higher mode mode 1 6 measurements from 25 to 70mhz using the network of autonomously recording stations nars array which was specifically designed for higher mode surface wave measurements the sn traveltime data set consists of isc readings for selected european events major features of wepl 2 are a high velocity lid of 80 140 km depth underlain by a pronounced low velocity zone between 160 and 220 km depth the transition zone 400 650 km depth is characterized by high shear velocities with respect to prem the density shows a positive gradient from 60 to 140 km depth followed by an approximately constant value down to 400 km depth a model for the baltic shield scsh 2 is obtained by combination of nolet s 1977 higher mode phase velocity data set for western europe including the baltic shield and the present phase velocities for the platform this shield model shows an absence of the low velocity layer and low shear velocities in the top of the transition layer with respect to wepl 2 density although less well resolved shows lower values for the shield structure between 200 and 350 km depth

theoretical study of the excitation spectral characteristics and geometrical attenuation of regional seismic phases abstract we present a theoretical study of the generation and geometrical attenuation of regional crustal phases we do this through the computation of seismograms in the epicentral distance range from 60 to 500 km the geometrical attenuation of lg waves with epicentral distance is of the form r 0 83 pg wave amplitudes display a much stronger decay of the form r 1 5 the spectral density of the crustal transfer function for pg waves is relatively flat for frequencies between 0 1 and 5 hz while lg wave spectra strongly fall off beyond 2 to 3 hz the excitation of pg wave is insensitive to the depth of the source within the crust while the lg amplitude is about 50 per cent higher for a source in the upper and middle crust than in the lower crust the amplitudes of these two phases drastically decrease when the source is below the moho these results illustrate the important role of wave guide played by the crust for the propagation of lg and pg we find that the geometrical attenuation of pg and lg waves is independent of source mechanisms in the case of an explosion the excitation of pg is insensitive to the source depth the lg wave amplitude is small in comparison to pg and rayleigh waves and depends on the closeness of the source to an interface or to the free surface

mapping of crustal heterogeneity in the north sea basin via the propagation of lg waves summary the propagation of lg waves within the continental area in and around the north sea basin shows strong dependence on the path between source and receiver paths lying within the british isles and norway show very clear lg phases but paths which cross the graben zone lying in the middle of the north sea basin have very weak lg over 150 paths have now been studied across the region and the character of the lg wave has been described by comparison with the size of the sn phase for shallow events this gives a stable measure of the efficiency of lg propagation the regions which appear to block the transmission of lg are quite localized in the middle of the north sea in the region with graben structures and extend on into the netherlands a weak zone of poor transmission appears to be associated with the oslo graben with the relatively dense areal coverage provided by paths crossing the basin with a wide range of azimuths it is possible to attempt to invert for the pattern of crustal heterogeneity which gives rise to the observed character of the lg propagation an interative scheme has been devised to find the propagation properties in cells of a 1 x 1 grid and a well defined map of the heterogeneity is obtained the strongest heterogeneities correlate very well with the major tectonic features of the viking and central grabens running north south through the basin where the path coverage is greatest the position of the heterogeneity can be tightly constrained and lies within a rather narrow zone around 100 km wide despite the number of paths employed it is not possible to obtain this level of resolution over the whole region seen in the light of theoretical studies of lg wave transmission the heterogeneity map gives an indication of the strength of horizontal gradients in seismic properties in the crust these are most likely to be associated with crustal thinning beneath the graben structures

the complete synthesis of seismic crustal phases at regional distances using a new method to evaluate green s functions for elastic layered media we compute complete synthetic seismograms at regional distances for an earthquake in the earth crust we choose as source parameters the ones inferred for an earthquake in central france and compare the computed seismograms to the ones recorded at several short period stations of the french seismic network the major features of the records including complexity and duration are well reproduced by the synthetics lg waves which are the prominant phase are shown to be guided waves made up of sh and sv waves incident on the moho at angles of incidence more grazing than the critical angle and multiply reflected within the crust the length of the computed lg wave coda extends between group velocities of 3 5 and 2 8 km s and is in good agreement with the data

density versus depth models from multimode surface waves multimode love and rayleigh wave data related to the pacific ocean and to north america are inverted using two sets of parameters 1 the isotropic p and s velocities plus the density and 2 five elastic parameters describing a transversely isotropic medium plus the density it is found that the assumption of isotropy leads to very unrealistic upper mantle models while much more realistic models are obtained under the assumption of transverse isotropy the lateral variations in density between the pacific ocean and north america are then less than 1 5 and in both regions a large density gradient is well resolved at a depth near 360 km

on regional s the character of regional s wave trains is quite complex and consists of two major elements sn waves which principally travel in the upper mantle and lg waves guided in the earth s crust the effect of lateral heterogeneity is to modify the signals for these phases compared with the predictions for horizontally stratified models however complete synthetic seismogram calculations for simple stratified crustal models for a suite of distances out to 950 km including both sn and lg provide a range of insights into the nature of the s wave train in particular late picks of sn arrivals are likely to arise because the actual s onset has been missed in the p coda and a higher amplitude surface multiple phase with an extra crustal delay has been picked instead such a effect was first recognized by lapwood 1955 in a study of the iss readings for a sequence of japanese events recorded at regional distances but has usually not been taken into consideration in studies using regional networks lateral heterogeneity along the propagation path has the effect of inducing interconversion between sn and lg energy and thus alters the character of the s wave train the lower attenuation for s in the uppermost mantle compared with the crust frequently leaves sn as the most prominent phase at ranges greater than 1000 km long range propagation of high frequency lg requires a relatively undisturbed crust

seismic wavefield calculation for laterally heterogeneous earth models ii the influence of upper mantle heterogeneity summary there is increasing evidence that the earth s mantle is laterally heterogeneous on a broad range of scales but the character of smaller scale heterogeneity has to be deduced indirectly the aim of the present paper is to examine the influence of a variety of stochastic representations of heterogeneity on seismic wave behaviour to help constrain the nature of the variations in seismic properties in the upper mantle for each of the models the seismic wavefield is simulated using a pseudospectral method in a 2 d cylindrical coordinate system the presence of stochastic heterogeneity is particularly important for those parts of the seismic wavefield where a significant portion of the propagation path in the upper mantle is close to horizontal such as the pp and ss phases and fundamental mode and higher mode surface waves the effects are noticeable traveltime anomalies and waveform changes for the body waves particularly associated with phase triplications and significant phase shifts for rayleigh waves a variety of styles of stochastic heterogeneity models are compared for the same source and station configurations using wavefield snapshots and the character of the calculated seismograms the influence of heterogeneity on body waves and on longer period rayleigh waves increases as the scale length increases compared to the wavelength of the seismic waves the aspect ratio of the heterogeneity has a pronounced effect on the coherence and amplitude of traveltime fluctuations and waveform changes across stations at the surface which depend on the structures encountered along the propagation paths to the specific receivers the effect of nearly isotropic heterogeneity is to induce small short scale variations in traveltime fluctuations and waveform changes as the heterogeneity becomes more plate like the fluctuations are on a broader scale and of larger amplitude because the individual patches of heterogeneity have a stronger influence the effects of broad scale and stochastic heterogeneity are compared for a model built from a slice through a tomographic model derived from delay time inversion for the himalayan region as would be expected the influence of the deterministic heterogeneity derived from the tomography study has the result of introducing systematic traveltime variations for body waves and noticeable phase shifts for surface waves when compared with the results for the background reference model the addition of a moderate level of small scale stochastic heterogeneity which could not be resolved in the tomography study has a limited effect on the seismic wavefield at longer periods but is much more significant for periods of less than 4 s when the heterogeneity scale is of the order of 40 km

pyrite framboid evidence for oxygen poor deposition during the permian triassic crisis in kashmir abstract the khunamuh formation of the guryul ravine section in kashmir provides one of the most detailed deep water records of the end permian mass extinction in perigondwanan palaeolatitudes examination of pyrite framboid size distributions and sediment microfabric reveals a distinct change in the uppermost permian strata from nonlaminated pyrite free silty mudstones to finely laminated silty shales rich in framboidal pyrite around 1 m above the base of the formation the size frequency distribution of the framboids is identical to populations from severely oxygen restricted modern depositional environments this change to dysoxic benthic conditions coincides with the rapid demise of diverse permian brachiopod and bryozoan assemblages thus the link between extinction and anoxia is clearly seen at guryul ravine and it provides an interesting contrast to other perigondwanan sections developed in shallower water where both the onset of anoxia and the extinction occurred somewhat later in the earliest triassic

time relationships between volcanism plutonism alteration mineralization in cu stratabound ore deposits from the michilla mining district northern chile a 40 ar 39 ar geochronological approach the michilla mining district comprises one of the most important stratabound and breccia style copper deposits of the coastal cordillera of northern chile hosted by the middle jurassic volcanic rocks of the la negra formation 40ar 39ar analyses carried out on igneous and alteration minerals from volcanic and plutonic rocks in the district allow a chronological sequence of several magmatic and alteration events of the district to be established the first event was the extrusion of a thick lava series of the la negra formation dated at 159 9 1 0 ma 2 from the upper part of the series a contemporaneous intrusion is dated at 159 6 1 1 ma and later intrusive events are dated at 145 5 2 8 and 137 4 1 1 ma respectively analyzed alteration minerals such as adularia sericite and actinolite apparently give valid 40ar 39ar plateau and miniplateau ages they indicate the occurrence of several alteration events at ca 160 163 154 157 143 148 and 135 137 ma the first alteration event being partly contemporaneous with volcanic and plutonic rocks was probably produced in a high thermal gradient environment the later events may be related either to a regional low grade hydrothermal alteration metamorphism process or to plutonic intrusions the cu mineralization of the michilla district is robustly bracketed between 163 6 1 9 and 137 4 1 1 ma corresponding to dating of actinolite coexisting with early stage chalcocite and a postmineralization barren dyke respectively more precisely the association of small intrusives a dated stock from the michilla district with cu mineralization in the region strongly suggests that the main michilla ore deposit is related to a magmatic hydrothermal event that occurred between 157 4 3 6 and 163 5 1 9 ma contemporaneous or shortly after the extrusion of the volcanic sequence this age is in agreement with the re os age of 159 16 ma obtained from the mineralization itself trista aguilera et al miner depos 41 99 105 2006

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

propagation of regional seismic phases in the indian shield constraints on crustal and upper mantle velocity models the regional seismic wave field in the central indian shield is studied including propagation characteristics of various prominent phases well recorded in the broadband seismograms of the 21 may 1997 jabalpur deep crustal focal depth 36 km earthquake m w 5 8 the seismograms covering a distance range out to about 1650 km although limited in number seem to well reveal the prominent phases including the p bar and lg as well as the high frequency pn and sn and their coda by detailed numerical simulations the generation and propagation characteristics of the p bar phase from earthquake sources at shallow and deep crustal depths are examined it is found that the p bar phase propagates efficiently at regional distances even for a deep crustal source depth the p bar phase is nevertheless very sensitive to the surface layer velocity structure extremely weak in the absence of a low velocity surface layer and also slightly weak in the presence of a relatively high velocity surface layer analyses of the jabalpur earthquake seismograms and the synthetics reveal that the p bar phase is well generated and propagates efficiently in the deccan traps v p 4 8 4 9 km sec covered regions i e even without a lower velocity surface layer surrounding the earthquake epicenter and the recording stations further the anatomy of the p bar phase is revealed by several computational models its time window composed of several multiple pmp reflections as well as pms conversions the principal boundaries being the moho and the free surface the first observations of high frequency pn and sn phases in the indian shield are recognized from the jabalpur earthquake seismograms by numerical simulations consistent with these observations including the coda a lamellae model with alternating high and low velocity layers for the structure of the indian continental uppermost mantle is inferred a complete synthesis of the regional seismograms is obtained based on the inferred models of the p and s wave velocity structure of the crust and upper mantle in the central indian shield comparison of the synthetics with the jabalpur earthquake seismograms reveals a consistent fit to various observations including the lg phase group velocity window 3 6 3 2 km sec the low pass filtered seismograms at the regional distances are further found to reveal coherent phases consistent with predicted reflection times from discontinuities in the upper mantle a plausible p velocity model inferred from these observations reveals velocity discontinuities at average depths of 230 320 430 and 680 km suggesting significant stratification of the upper mantle b region in the indian shield

the role of organic matter in the genesis of the el soldado volcanic hosted manto type cu deposit chile solid bitumen residual petroleum occurs intimately associated with sulfides in several manto type cu deposits of central chile el soldado 32 degrees 38 s 71 degrees 04 w is one of the largest manto type deposits 130 million metric tons1 5 cu and is hosted by rhyolites and andesites of the lower cretaceous lo prado formation as a result of basinal burial in the early cretaceous back arc basin petroleum was generated from organic rich shales in the underlying lower lo prado formation and migrated into primary and structural porosity in the upper lo prado formation migration was controlled by extensional basinal faults low temperature 90 degrees c biodegradation of petroleum developed an early stage i assemblage of mostly framboidal pyrite or sphalerite or chalcopyrite geopetal structures related to pressure degassing of semi solid petroleum suggest that migration occurred while the strata were horizontal at ca 130 ma continued basinal burial led to thermal degassing increased maturation and solidification of the petroleum low grade regional pumpellyite prehnite metamorphism of the sequence was followed at ca 110 to 103 ma by the influx of high temperature ca 300 degrees c cu rich fluids concurrently with emplacement of the cretaceous batholith into the basin basinal fluids were focused into a now tilted sequence by a brittle shear north south to north northwest fault system copper sulfides stage ii assemblage replaced preexisting pyrite and bitumen forming zoned orebodies with a central chalcocite hematite zone followed outward by bornite chalcocite chalcopyrite bornite and pyrite chalcopyrite zones the mineralizing fluids altered the bitumen thermally and chemically as follows 1 reflectance r o increased up to ca 5 percent in the core of the orebodies against a background of ca 3 percent 2 anisotropy nongranular microscale and domain developed and the bitumen was locally graphitized 3 chlorine or cu or fe was incorporated into the bitumen affecting its reflectance the source of cu was most likely the overlying oxidized volcanic pile the cu was transported as chloride cucl complexes precipitating where the cucl rich solutions reacted with bitumen adsorption reduction and pyrite from the stage i assemblage the study demonstrates that in the lower cretaceous basin of chile degraded petroleum reservoirs can be important controls for metallic mineralization derived from hydrothermal solutions of different sources particularly if biodegradation generated pyrite

sedimentary pyrite framboid size frequency distributions a meta analysis abstract framboids microscopic sub spheroidal aggregates of pyrite microcrystals are found in sediments of all ages and framboid size frequency distributions are widely used to determine the oxygenation states of paleo waters sedimentary framboid populations display unimodal log normal size distributions as a consequence of the multiplicative central limit theorem in probability theory the application of additive statistics to framboid populations and their consequent characterization in terms of arithmetic means and standard deviations is wrong because it predicts a subset of framboids with negative diameters a meta analysis of 377 sets of measurements of the diameters of 48 063 pyrite framboids from 104 sediment and sedimentary rock locations shows that the geometric mean diameter of sedimentary framboids is 6 2 m and the geometric standard deviation is 1 5 ninety five percent of all sedimentary framboids have geometric mean diameters between 2 9 and 13 9 m the geometric mean diameter of modern syngenetic framboids formed within euxinic water columns is 4 7 m and that of diagenetic framboids formed within sediments is 6 7 m the estimated measurement error is 10 framboid mean diameters can be used to help discriminate the oxygenation state of paleo waters a minimum number of 30 measurements is required and ideally 100 measurements are recommended the conflicting evidence reported in the literature for the application of framboid size frequency measurements results mainly from the intrinsic nature of statistical analyses there is always a finite chance that a particular framboid size frequency distribution is a result of either syngenetic or diagenetic processes including the systematic stereological error in framboid size measurements the geometric mean size range for syngenetic framboids is 2 9 10 9 m and that for diagenetic framboids 3 1 20 9 m this suggests a significant overlap in geometric mean diameters of framboids from euxinic and non euxinic environments between 3 and 11 m geometric mean framboid diameters within this size range are not robust proxies for paleo water oxygenation conditions the origin of the smaller sizes of syngenetic compared with diagenetic framboids appears to be related to the limited time available for framboid crystal growth within the water column the statistical uncertainty in assigning particular framboid size frequency distributions to defined oxygenation conditions results mainly from a some diagenetic framboids forming over a limited time thereby also producing smaller framboids and b mixtures of syngenetic and diagenetic framboid populations through unavoidable time averaging of samples the absence of any significant differences in the sizes of modern and ancient framboids indicates that framboids do not continue to grow over extended time periods once formed they remain the same over geologic time periods and only change through infilling overgrowth and recrystallization the result is that ancient framboids may sample the contemporary paleoenvironment in the sedimentary system in which they are found

spectral analysis of seismic waves in the northern indian ocean region abstract attenuation of ground motion amplitudes away from the seismic source is recognized as a significant issue by researchers of particular interest is the attenuation or propagation of seismic waves from long distance sources regions like sri lanka have experienced tremors from events as far as 1500 km a recently identified diffusing plate boundary just around 300 km away from the southern tip of sri lanka poses significant seismic risk however a comprehensive study of the region with respect to the propagation or attenuation of seismic waves has generally been lacking with the availability of new archival data of 71 events recorded at three digital broadband stations we have estimated q value for the northern indian ocean region surrounding sri lanka multiple linear regression analysis of recorded vertical component fourier acceleration amplitudes yields a relatively higher q 0 value of about 389 2 35 for the subject region furthermore the combined effect of upper crustal amplification and attenuation has been assessed using the standard horizontal to vertical ratio method the negligible upper crustal modifications obtained from the analysis imply the presence of an older crustal rock stratigraphy at near source depths around the subject region source spectra of recorded events have also been derived by correcting the observed amplitudes for geometric and anelastic attenuation the source spectra analysis resulted in a typical stress drop value of about 50 bars which is consistent with brune s source spectra models stochastic modeling of a recent m w 8 6 event that occurred in the region was undertaken based on the parameters derived from the analysis and compared with the real recorded spectra results show a reliable match between the simulations and the recorded spectra which supports the validity of the estimated parameters seismological parameters derived from this study can provide reliable estimates of seismic hazard of sri lanka

the andacollo strata bound gold deposit chile and its position in a porphyry copper gold system the andacollo mining district is in the coastal cordillera of central chile 400 km north northeast of santiago the andacollo deposits are the products of a complex hydrothermal system and consist of a porphyry copper gold deposit and peripheral strata bound manto gold deposits and veins with minor associated base metals the hydrothermal system was part of the pacific porphyry copper belt which was generated during development of an early cretaceous magmatic arc displaying shoshonitic petrochemical affiliations rocks that crop out in the area include a volcanic sequence the arqueros and quebrada marquesa formations consisting of andesitc and dacite flows volcanic breccias and pyroclastic rocks of early cretaceous age intrusive rocks range from diorite to granodiorite in composition and date between 87 and 130 ma the porphyry copper gold deposit is zoned vertically downward from a leached capping through a supergene enrichment blanket to a hypogene sulfide zone alteration is characterized by central potassic k feldspar biotite phyllic and peripheral propylitic zones abundant northwest trending tensional fractures were superimposed on the porphyry copper gold deposit and surrounding areas during the later stages of the evolving mineralized system the fractures channeled mineralizing fluids from the central parts of the porphyry copper deposit outward for up to 5 km replacement by adularia and sericite took place together with deposition of gold bearing pyrite and minor amounts of zinc and copper where these fluids encountered permeable dacite flows and andesite flow breccias the alteration process caused remobilization of aluminum and alkalies and addition of k 2 o which attains values of 12 to 13 wt percent the andacollo system is interpreted to be a porphyry copper gold deposit that is transitional outward to distal epithermal adularia sericite type contact metasomatic gold orebodies

geology and geochemistry of the sediment hosted cheshmeh konan redbed type copper deposit nw iran the several hundred m thick miocene upper red formation in northwestern iran hosts stratiform and fault controlled copper mineralization copper enrichment in the percent range occurs in dm thick carbonaceous sandstone and shale units within the clastic redbed sequence and consists of fine grained disseminated copper sulfides chalcopyrite bornite chalcocite and supergene alteration minerals covellite malachite and azurite the copper mineralization formed after calcite cementation of the primary rock permeability copper sulfides occur mainly as replacement of diagenetic pyrite which in turn replaced organic matter electron microprobe analysis on bornite chalcocite and covellite identifies elevated silver contents in these minerals up to 0 12 0 72 and 1 21 wt respectively whereas chalcopyrite and pyrite have only trace amounts of silver 0 26 and 0 06 wt respectively microthermometric data on fluid inclusions in authigenic quartz and calcite indicate that the cu mineralization is related to a diagenetic fluid of moderate to low temperature th 96 160 c but high salinity 25 38 wt cacl2 equiv the range of 34s in pyrite is 41 9 to 16 4 average 31 4 where framboidal pyrite shows the most negative values between 41 9 and 31 8 and fine grained pyrite has relatively heavier 34s values 29 2 to 16 4 consistent with a bacteriogenic derivation of the sulfur the cu sulfides chalcopyrite bornite and chalcocite show slightly heavier values from 14 6 to 9 0 and their sulfur sources may be both the precursor pyrite s and the bacterial reduction of sulfate bearing basinal brines carbonates related to the ore stage show isotopically light values of 13cv pdb from 8 2 to 5 1 and 18ov pdb from 10 3 to 7 2 indicating a mixed source of oxidation of organic carbon ca 20 and hco3 from seawater porewater ca 0 the copper mineralization is mainly controlled by organic matter content and paleopermeability intragranular space to large fracture patterns enhanced by feldspar and calcite dissolution the cheshmeh konan deposit can be classified as a redbed type sediment hosted stratiform copper ssc deposit

s wave attenuation in the marmara region northwestern turkey the frequency dependent attenuation of shear waves in the crust is estimated by using two different methods based on the rate of time decay of coda wave amplitude qc 1 and the rate of decay of the s wave to coda wave amplitude ratio with distance qs 1 the epicentral distances of selected earthquakes range between 20 and 110 km and magnitudes are around 3 the quality factors qc are calculated at frequencies of 1 5 3 6 12 and 24 hz and lapse times of 40 50 60 and 70 s estimated qc values show a dependence on frequency and lapse time we observed the similarity in the frequency dependency of qc 41 1 07 f1 08 0 03 and qs 50 1 7 f1 09 0 05 for a lapse time of 50 s indicating that the attenuation mechanism for coda waves is similar to that of the direct s waves

sulfide mineral chemistry investigation of sediment hosted stratiform copper deposits nahand ivand area nw iran abstract copper mineralization in nahand ivand area nw iran appears as disseminated copper sulfides along a redox boundary between gray sandstone and microconglomerate and hematitic sandstones siltstones and shaly marl geochemical analyses of the nahand ivand deposits show as much 35 wt cu and 730 ppm ag in the gray sandstone electron probe micro analysis epma was used to determine the mineralogical composition and distribution patterns of copper and silver bearing phases mainly in pyrite and cu bearing sulfides the epma data were essential for evaluating the distribution and partitioning of potential economically valuable components between co existing minerals furthermore they contribute to a better understanding of the genesis of the nahand ivand copper deposits and will guide further exploration in the region the epma results from different types of pyrite reveal cu contents as high as 0 32 wt 1 10 wt and 2 88 wt for framboidal pyrite pyi overgrowths on framboidal pyrite pyii and diagenetic pyrite pyiii respectively this successive increase of copper from pyi to pyiii is attributed to a continuous supply of copper that replaces framboidal pyrite in turn by the more copper rich digenetic pyrite because of hydrothermal overprinting pyrite has been replaced by djurleite roxbyite and other nonstoichiometric cu s minerals that include covellite the epma study indicates that covellite contains significant concentrations of ag locally 1 wt in contrast only trace amounts of silver have been detected in pyrite and other copper sulfides indicating that covellite is the major ag carrier in the ore according to textural relationships such open space filling impregnation and replacement textures and the epma results later stage copper bearing fluids were responsible for the silver enrichment in the nahand ivand deposits

size evolution of micropyrite from diagenesis to low grade metamorphism size distribution and evolution of framboidal and euhedral microscopic crystals of pyrite micropyrites mpy have been used for the last thirty years to deduce palaeo redox conditions the analysis of the mpy distributions can give valuable information about these palaeo redox conditions however other information can also be retrieved from this type of analysis in this work we propose that the formation of new populations of mpy is a proxy of the transition from the anchizone to the epizone high resolution x ray tomography micro ct was used to determine the size distributions of mpy hosted in pelitic rocks subjected to different grades of low temperature metamorphism these data were filtered and statistically analysed which allowed us to find a statistical representative size distribution of the mpy present in the samples the metamorphic grade was determined using the kubler index in combination with petrological and scanning electron microscopy sem examination the results show a relationship between metamorphic grade and mpy size distributions and that new populations of mpy formed due to the effects of metamorphism this new methodology for mpy size distribution has different potential applications in some fields of earth sciences such as palaeoenvironment reconstruction ore mining or metamorphic petrology

the early andean magmatic province eamp 40ar 39ar dating on mesozoic volcanic and plutonic rocks from the coastal cordillera northern chile abstract the early andean magmatic province eamp consists of about 150 000 km 3 of volcanic and plutonic units in the coastal cordillera of northern chile and southern peru and represents a major magmatic mesozoic event in the world for which the precise age of the thick volcanic series was unknown thirty 40 ar 39 ar analyses were carried out on primary mineral phases of volcanic and plutonic rocks from northern chile 18 30 24 s reliable plateau and mini plateau ages were obtained on plagioclase amphibole and biotite from volcanic and plutonic rocks despite widespread strong alteration degree in the arica tocopilla and antofagasta 700 km apart regions the ages obtained on lava flows constrain the volcanic activity between 164 and 150 ma and no n s migration of volcanism is observed the uppermost lava flows of the volcanic sequence at the type locality of the la negra formation extruded at ca 153 150 ma suggesting the end of the volcanic activity of the arc at that time the oldest volcanic activity occurred probably at ca 175 170 ma in the iquique area although no plateau age could be obtained the plutonic bodies of the same regions were dated between ca 160 and 142 ma indicating that they were partly contemporaneous with the volcanic activity at least one volcanic pulse around 160 ma is evidenced over the entire investigated reach of the eamp according to the ages found in arica tocopilla michilla and mantos blancos regions the episodic emplacement of huge amounts of subduction related volcanism is observed throughout the whole andean history and particularly during the jurassic southern peru northern chile and southern argentina these events probably correspond to periodic extensional geodynamic episodes as a consequence of particular subduction conditions such as change of obliquity of the convergence change in the subduction angle slab roll back effect or lower convergence rate that remain to be precisely defined

lg wave attenuation in the australian crust abstract we estimate the lg wave quality factor q across the australian continent from vertical component lg waveforms a tomographic inversion is performed to construct an lg attenuation model for 58 frequencies between 0 05 and 10 0 hz the available spatial resolution is approximately 1 5 1 5 for the 0 5 2 0 hz band at 1 0 hz the lg wave q over the whole island continent varies from 50 to 1250 with an average value of 850 significant regional variations in the lg wave q images tie well with many geological features and boundaries in australia the cratons in western northern and southern parts of australia usually have higher q values 700 1250 while the volcanic regions sedimentary basins and orogenic areas in eastern australia are characterized by increased attenuation lower q values 50 650 we determine the frequency dependent q of lg waves for different blocks across australia and find the frequency dependence of q is much more complex than the traditional single power law representation when combined with the assumed geometrical spreading relation the lg q maps provide a new way of assessing potential ground motion across the continent for any event location

amplitude tomography of lg waves in xinjiang and its adjacent regions amplitude tomography of lg waves at frequencies from 1 to 5 hz are investigated in this work to reveal the lateral attenuation heterogeneities of the study area the xinjiang uygur autonomous region of china and its adjacent regions by using a large set of broadband seismic waveform data first we inverted the average q lg at each of 10 frequencies from 0 5 to 5 hz then the study area was divided into evenly spaced 1 1 grid cells after conducting both a checkerboard test and a resolution test finally the high resolution q lg tomographic images at the 10 frequencies were obtained the moment magnitudes of the events and the site terms of the stations we used were obtained simultaneously the attenuation pattern of q lg at each frequency shows obvious lateral heterogeneities in xinjiang and its adjacent regions which are coincident with the geological features of the area the tarim basin and the middle and the eastern part of the southern tian shan belong to high q regions the northeastern margin of the pamir plateau the northwestern margin of the tibetan plateau the western part of the southern tian shan and northern tian shan are prominent low q areas the attenuation pattern of lg waves shows that large scale tectonic boundaries zones with rapid topographic or crustal thickness gradient are in good accordance with the boundaries of the high and low q lg most of the historical strong earthquakes occurred on the interior or edge of low q lg areas

on the nature of regional seismic phases i phase representations for pn pg sn lg summary an operator development of the seismic wavefield is used to generate descriptions of the propagation processes contributing to the main regional seismic phases pn pg sn lg these operator forms are valid for laterally heterogeneous crust and mantle models and include the major processes of interconversion between wavetypes these representations of the regional phases are used to examine the theoretical basis for discriminants between earthquakes and underground explosions based on the relative amplitudes of p and s phases the ratio of sn to pn amplitude looks promising as a high frequency discriminant however the ratio of lg to pn amplitudes is not as useful because of the complex nature of the propagation characteristics of lg

mass balance reconstruction of a modern vertisol implications for interpreting the geochemistry and burial alteration of paleo vertisols abstract utilizing identical sampling and analytical techniques the morphological and chemical characteristics of a modern vertisol houston black series central texas can be directly compared with an upper mississippian paleo vertisol from the appalachian basin pennington formation east central tennessee mass balance reconstructions suggest retention of primary pedochemical patterns in the paleo vertisol including patterns of soil volume change strain and transport functions translocations of many major and trace elements retention of primary pedochemical patterns suggests that vertisols constitute nearly closed systems during burial diagenesis chemical and mineralogical changes associated with burial diagenesis of the paleo vertisol include oxidation of organic carbon oc illitization of smectites dehydration and recrystallization of fe mn oxyhydroxides and dolomitization of pedogenic calcite significant differences in the chemical behavior of gilgai microhigh and microlow pedons in modern vertisols have implications for interpretation of geochemical data obtained from paleo vertisols overall wetter soil conditions and variable redox potential under gilgai microlows promote greater depths of leaching and mobility of redox sensitive trace elements including co cr cu mn ni and v gilgai microhighs behave as evaporative wicks that draw moisture and soluble phases towards the soil surface resulting in precipitation of metal hydrosylate complexes and sulfates gypsum at the capillary fringe and shallower depths of leaching and fixation of trace elements paleoprecipitation estimates from paleosols based on the depth to the top of the pedogenic carbonate horizon should therefore utilize field petrographic and geochemical data for characterizing maximum depths of leaching loss or gain of exchangeable bases and calcification rather than relying solely upon field data

the role of bitumen in strata bound copper deposit formation in the copiapo area northern chile in northern chile between 27 and 33 s there are numerous deposits where residual petroleum is associated with cu ag mineralisation the most famous being el soldado all of these deposits are hosted by lower cretaceous volcanic or volcanoclastic facies along the axis of a former backarc basin this close relationship suggests that the generation migration and emplacement of hydrocarbons in the cretaceous volcanic units is a regional process associated with the evolution of the cretaceous backarc basin and points to the importance of pyrobitumen as an exploration tool for similar cu ag deposits the present work analyses four small strata bound copper deposits located along a north south belt approximately 10 km east of copiapo in northern chile these deposits are typically hosted by pyrobitumen rich andesitic volcanic to volcanoclastic rocks intercalated with the marine carbonate pabellon formation the youngest formation within the chanarcillo group the strong genetic and spatial relationships between the pyrobitumen rich lavas and the mineral deposits allow us to define this volcanic belt as the ocoita pabellon metallotect two hydrothermal events can be distinguished based on the mineralogical textural fluid inclusion and isotope data of ore and gangue and on the optical properties of residual petroleum during the early event petroleum was mobilised from the source rocks into the primary and secondary porosity of the lavas by fe rich hydrothermal fluids which precipitated pyrite as an early sulphide phase the second event is characterised by cu rich hydrothermal fluids which induced three successive sub stages of cu sulphide precipitation the hydrothermal fluids chemically and thermally altered the first stage bitumen transforming it into pyrobitumen the present work documents similarities between the ocoita pabellon metallotect and the el soldado ore deposit and emphasises important differences in the el soldado host rocks a petroleum reservoir existed prior to the arrival of the mineralising hydrothermal fluids the framboidal pyrite was formed by assistance of bacteria the s of the cu sulphides was inherited from the pyrite and the fluid source was basin connate metamorphic brine in the ocoita pabellon metallotect the hydrocarbons were mobilised into the host rocks by hydrothermal fluids the pyrite is epigenetic the 34s values of pyrite and copper sulphides are very different with distinctive light 34s signature of cu sulphides 34s between 44 7 and 17 9 and the calculated 18o of hydrothermal fluids indicates the participation of meteoric water in the late phases of the hydrothermal system

palaeoenvironmental and palaeoclimatic reconstruction of the upper cretaceous late campanian early maastrichtian horseshoe canyon formation alberta canada abstract pedogenic features and geochemical signatures of paleosol profiles exposed in the horseshoe canyon formation hcfm were studied to reconstruct the ancient environments and climates that prevailed at high latitude 60 n in the north american western interior during the late campanian to early maastrichtian eight pedotypes representing hydromorphic moderately drained and well drained paleosols were recognized when considered within their stratigraphic context these paleosols show that palaeoenvironmental and palaeoclimatic changes occurred either gradually between major lithological subdivisions of the hcfm or relatively rapidly within subdivisions hydromorphic paleosols predominant in the coal bearing stratigraphic interval at the base of the hcfm were gradually replaced by well drained paleosols in the overlying coal poor interval while climate remained warm and humid during this change in soil drainage conditions mean annual temperature and precipitation dropped rapidly higher in section shortly prior to the campanian maastrichtian boundary without concomitant lithological or pedological changes a brief return of poorly drained paleosols in the middle of the hcfm coincides with a regional marine transgression drumheller marine tongue well drained palaeoenvironments associated with a warm and dry climate persisted through the upper part of the hcfm until a gradual return to poorly drained conditions and to a warm humid climate occurred at the top of the formation an important decline in turtle diversity through the hcfm previously attributed to climate is shown to coincide instead with changes in soil drainage conditions where aridity landscape instability and migratory barriers possibly acted as secondary limiting factors to faunal recovery

regional wave propagation in china and its surrounding regions a comprehensive study of the gross characteristics of high frequency seismic wave propagation in china and its surrounding regions was accomplished to learn more about how regional geology affects high frequency phases amplitudes of the regional seismic waves sn and lg relative to p coda were used to map lateral variations of shear wave attenuation in the crust and upper mantle over 7000 digital seismograms from 13 broadband stations of the chinese digital seismic network and global seismic network in the frequency range 0 5 to 5 0 hz were visually examined propagation efficiencies of sn and lg were qualitatively analyzed by ranking their amplitudes relative to the p wave coda efficient sn propagation is observed in the tien shan tarim platform southern tibet yangzi paraplatform and sino korean platform we have confirmed results of previous studies by finding a lack of sn transmission in north central tibet the ryukyu and japan arcs burma and the baikal rift an important observation which has not been previously reported is that sn does not propagate across mongolia the elimination of sn and the occurrence of recent volcanism in north central tibet and mongolia suggest that there is partial melt in the uppermost mantle beneath those regions high frequency lg waves propagate efficiently for most of china indochina and mongolia lg signals are attenuated within central tibet as well as along its southern boundary crustal structure variations along with an anomalously low q crust are primarily responsible for weakened lg amplitudes in tibet propagation paths across oceanic crust in the sea of japan and the andaman sea show blockage of the lg phase as well this investigation has relevance to comprehensive test ban treaty monitoring by showing where certain regional phases will or will not propagate efficiently

pyrite morphology in the first member of the late cretaceous qingshankou formation songliao basin northeast china abstract the study of sedimentary pyrite morphological characteristics provides useful information on depositional environments and early diagenic processes and can be used as an indicator of redox conditions in ancient lake bottom waters the results of this study in the songliao basin in northeastern china show that euhedral crystals and framboids are the dominant pyrite forms in the mudstones of the first member of the qingshankou formation k2qn1 the framboidal size distribution indicates that during the deposition of k2qn1 redox conditions in the bottom water fluctuated from oxic dysoxic to euxinic anoxic to oxic dysoxic the presence of euxinic anoxic bottom water suggests that an anoxic event developed in the songliao ancient lake and continued for 196 ka the development of an anoxic bottom environment was the most important factor in hydrocarbon source rock formation in the songliao basin

differences in attenuation of ground motion perpendicular to the mexican subduction zone between colima and guerrero an explanation based on numerical modeling abstract a recent article tejeda jacome and chavez garcia 2007 showed that significant differences in seismic ground motion attenuation perpendicular to the pacific coast exist between guerrero and colima in western mexico for hypocentral distances larger than 100 km larger ground motions are predicted using a model derived from local data in the northern section of the subduction zone colima relative to ground motion models derived using data from the southern section guerrero in this article we consider two possible explanations for the differences the first possible explanation is differences in the geometry of the subducting slab between colima and guerrero the second is the varying shallow structure of the overriding plate due to the presence of the trans mexican volcanic belt tmvb oblique to the middle american trench we use 2d numerical modeling for p sv waves to investigate which of the two factors can explain the differences in the observed attenuation our results show that it is the presence of the tmvb closer to the coast in colima that better explains the differences

mesozoic magmatic and tectonic events within the andean plate boundary zone 26 27 30 s north chile constraints from 40 ar 39 ar mineral ages in north chile jurassic cretaceous arc magmatism is represented by several narrow belts of plutons and two separate volcanic sequences new 40 ar 39 ar mineral ages confirm five distinct episodes of magma emplacement as plutonic complexes c 202 188 ma c 160 153 ma c 142 138 ma c 130 127 ma and c 106 103 ma conjugate dike sets were emplaced immediately before periods of plutonism and each distinct episode of magmatism prior to c 127 ma was located successively eastward inboard from the subduction boundary features interpreted to result from regional extension within the magmatic arc steeply dipping ductile mylonitic shear zones were developed in wall rocks along western contacts of late jurassic and early cretaceous plutons steeply plunging mineral stretching lineations and a variety of kinematic indicators record an east side down extension along eastern faults of the atacama fault system steeply dipping ductile mylonitic shear zones display subhorizontal mineral stretching lin

generation of the teleseismic p wave coda from aleutian earthquakes summary we investigate large amplitude phases arriving in the p wave coda of broad band seismograms from teleseisms recorded by the grafenberg array the german regional seismic network and the global seismic network the data set consists of all events mb 5 6 from the aleutian arc between 1977 and 1992 earthquakes with large amplitude coda waves correlate with the presence of oceanic crust in the source region the amplitudes sometimes approach those of the p wave much larger than predicted by theory modelling indicates that phases in the p wave coda cannot be p wave multiples beneath the source and receiver or underside reflections which precede pp from upper mantle discontinuities among the events seismograms are very similar where the arrival times of the unusual phases agree approximately with the predicted times of s to p conversions from the upper mantle discontinuities under the source because the large amplitude phases in the p wave coda have little if any dependence on event depth and have predominantly an sv wave radiation pattern towards the receiver we suggest that they originate as sv and or rayleigh waves and are enhanced by lateral heterogeneity and multipathing from the subducting aleutian slab

anatomy and evolution of a lower cretaceous alluvial plain sedimentology and palaeosols in the upper blairmore group south western alberta canada the lower cretaceous albian upper blairmore group is part of a thick clastic wedge that formed adjacent to the rising cordillera in south western alberta regional transgressive intervals are superimposed on the overall regressive succession alluvial conglomerates sandstones and mudstones were deposited in east north eastward draining fluvial systems orientated transverse to the basin axis five facies associations have been identified igneous pebble conglomerate thick sandstone interbedded lenticular sandstone and mudstone thick mudstone with thin sandstone interlayers and fossiliferous sandstone and mudstone the facies associations are interpreted as gravelly fluvial channels sandy fluvial channels sand dominated floodplains mud dominated floodplains and marine shoreline deposits respectively five types of palaeosols are recognized in the upper blairmore group based on lithology the presence of pedogenic features clay coatings root traces ferruginous nodules slickensides carbonate nodules and degree of horizonization the regional distribution of the various types of palaeosols enables a refinement of the palaeoenvironmental reconstruction permitting an assessment of the controls on floodplain evolution in source proximal areas palaeosol development was inhibited by high rates of sedimentation in source distal locations poor drainage resulting from high watertables low topography and lower rates of sedimentation also inhibited palaeosol development the best developed palaeosols containing bt horizons occur in intermediate alluvial plain positions tectonic hinge zone where the floodplains were most stable due to a balance between sedimentation erosion and subsidence rates extrapolating from the upper blairmore group suggests that the tectonic hinge zone of continental foreland basins can be established by palaeosol analysis at the hinge zone soil development is controlled primarily by climate and tectonics and their effect on sediment supply whereas closer to the palaeoshoreline relative sea level fluctuations resulting in poor drainage may have a more significant influence

iron framboids in the hydrocarbon related middle devonian hollard mound of the anti atlas mountain range in morocco evidence of potential microbial biosignatures iron framboids in the context of a middle devonian hydrocarbon seep conical mound anti atlas morocco have been thoroughly investigated through a combination of techniques including optical and high resolution scanning electron microscopy x ray diffraction energy dispersive x ray spectroscopy raman microscopy and time of flight secondary ion mass spectroscopy framboids occur embedded in laminated carbonates of the mound and are precipitated along the veins that crosscut it and served as the conduits for channeled reduced hydrocarbon rich fluids the morphology structure and composition of the framboids contribute to the reconstruction of the complex interplay between the advected fluids and the associated biological and or abiological processes a comparison of our dataset with that from modern framboids formed under similar conditions indicates that the fe rich framboids represent replaced primary pyrite framboids produced as a consequence of bacterial sulfate reduction and the anaerobic oxidation of methane

stochastic prediction of ground motion and spectral response parameters at hard rock sites in eastern north america empirical predictions of ground motions from large eastern north american earthquakes are hampered by a lack of data for such events for this reason most prediction techniques have been based at least in part on data from the seismically active and well instrumented western north america concentrating on the prediction of response spectra on hard rock sites we have used a relatively new theoretical technique that does not require western data to make ground motion predictions for eastern north america this method often referred to as the stochastic model has its origins in the work of hanks and mcguire who treat high frequency motions as filtered random gaussian noise for which the filter parameters are determined by a seismological model of both the source and the wave propagation the model has been successfully applied to the predictions of ground motions in the western united states and to short period magnitudes from large to great earthquakes worldwide for our application the essential parameters of the model are estimated by using existing data from small to moderate eastern north american earthquakes a crucial part of the model is the relation between seismic moment and corner frequency the relation proposed in 1983 by nuttli for mid plate earthquakes leads to predictions of ground motions that are lower than available data by a factor of about 4 on the other hand a constant stress parameter of 100 bars gives model predictions in good accord with the data to aid in applications the ground motion predictions are given in the form of regression equations for earthquakes of magnitude 4 5 to 7 5 at distances within 100 km of the source the explanatory variables are hypocentral distance and moment magnitude m because predictions are often required in terms of m g rather than m we have used the theoretical model to establish a relation between the two magnitudes the predicted relation agrees with the sparse data available although the large uncertainties in the observed magnitudes for the larger events as well as the sensitivity of the theoretical magnitude to the attenuation model make it difficult to discriminate between various source scaling models

lg and rg waves on the california regional networks from the december 23 1985 nahanni earthquake we investigate lg and rg propagation in california using the central and southern california regional networks approximately 550 stations constitute these two short period networks providing a dense coverage of almost the entire state the waveforms recorded from the december 23 1985 nahanni canada earthquake are used to construct three profiles along the propagation path almost n s and three perpendicular to the propagation path almost e w to look at the nature of propagation of these two types of surface waves groups of records from stations in various geological and tectonic provinces in california are also examined in order to establish regional characteristics of the surface waves we find that the propagation characteristics of lg differ from those of rg across california lg waves are apparently more sensitive to crustal heterogeneities the most striking observations are the similarity of coda for both the lg and the rg waves within geologic provinces and the marked difference in coda between regions these differences are seen in the amplitudes coda duration shape of the energy envelope frequency content and sharpness of the phase initiation in general a decrease in the moho depth near the pacific coast is correlated with a decrease in the surface wave amplitude especially at higher frequencies 0 15 0 2 hz most interesting is the association of the san andreas fault with abrupt changes in the wave train amplitudes the surface waves are amplified in the vicinity of the fault zone and then decrease in amplitude after the zone is crossed in the coast ranges amplitudes are low and waveform coherence is poor the rg phase dominates the record in the sierra nevada and both surface waves are amplified by the thick sedimentary sequence of the great valley

source parameters and scaling relationships of earthquakes in israel abstract determination of earthquake dynamic source parameters such as the seismic moment stress drop and rupture area are often based purely on theoretical considerations in reality however some of the corrected coefficients utilized in the computations should preferably be defined empirically in the present study 39 earthquakes of ml between 3 0 and 6 7 are used to define the correction coefficients associated with distance geometric and unelastic attenuation and ratios between zero frequency spectral amplitides of s waves recorded by vertical and horizontal seismographs these are used in turn to determine the seismic moment m0 and the empirical correlation between log m0 and ml magnitudes for that region the validity of using constant stress drop assumption and correlation between moment and corner frequency is also discussed

reconstruction of early triassic ocean redox conditions based on framboidal pyrite from the nanpanjiang basin south china abstract widespread oceanic anoxia has been implicated as an important factor in the ptb permian triassic boundary mass extinction and the delayed recovery of early triassic marine ecosystems an investigation of framboidal pyrite in the bianyang section nanpanjiang basin south china suggests that euxinia dysoxia peaked during the induan late smithian to earliest spathian and late spathian these anoxic episodes show a relationship albeit imperfect to major episodes of climatic warming during the early triassic that were associated with intensified oceanic stratification reduced marine productivity and organic carbon sinking fluxes as well as diminished burial fluxes of organic carbon and reduced sulfur in contrast intervals of better oxygenated marine conditions were associated with episodes of relative climatic cooling during the early to middle smithian and mid spathian the degree of ventilation of the thermocline region in particular had a profound effect on marine biotas with intervals of improved ventilation resulting in increased global diversity among ammonoids and conodonts and increased local abundance of foraminifera in the nanpanjiang basin these observations suggest that oceanic redox fluctuations played an important role in the delayed recovery of early triassic marine ecosystems and specifically that episodic expansion of oceanic oxygen minimum zones omzs resulted in repeated setbacks to the recovery process a pattern that persisted until the late spathian

characterization of micropyrite populations in low grade metamorphic slate a study using high resolution x ray tomography abstract measuring the abundance and size distribution of framboidal and euhedral microscopic crystals of pyrite has proven to be an effective method to determine the paleoenvironmental conditions in sedimentary rocks bearing these minerals however micropyrites can be found in other geological environments as well such as low grade metamorphic and hydrothermal in these cases their sizes and distributions are expected to be different from those deposited in a sedimentary environment due to the different genetic processes involved this paper analyzes the size and distribution of the micropyrite population in a low degree metamorphic slate originally formed under anoxic to low oxygen conditions the geological record of this rock suggests that micropyrite formation took place in different stages resulting in different population distributions traditionally sem has been used to characterize micropyrite populations however for this study a new technique in this field was applied namely high resolution x ray tomography micro ct which allows for 3d visualization and analysis of the stone s structure based on the differences in the x ray attenuation coefficient of the component minerals as complementary technique transmitted and reflected optical microscopy was used size and population distributions of the micropyrites were measured using sem and micro ct and then statistically analyzed sem was able to determine the morphology and size of micropyrites in 2d while micro ct provided statistically relevant information about the size histogram of the micropyrites the data obtained indicate the existence of three overlapping populations of micropyrites two of them have small sizes and a narrow range of distribution which can be attributed to sedimentary processes and the other have larger sizes and a broader range of distribution attributed to the effect of metamorphic processes in summary micro ct coupled with sem and accurate statistical analysis proved capable of differentiating between overlapping micropyrite populations in a sample of low grade metamorphic slate

hypocenter constraint with regional seismic data a theoretical analysis for the natural resources defense council network in kazakhstan ussr source depth and epicenter determination remains a simple but key method for discrimination between earthquakes and nuclear explosions at near regional distances a variety of secondary body wave arrivals can be observed that may be useful for constraining source depth and epicenter in this paper we study the source location problem using regional arrival time and arrival azimuth data from a sparse seismic network a theoretical analysis of the source location inverse problem provides estimates of the stability and uncertainty of the solution for a particular suite of data as a function of epicenter and depth as well as evaluating the importance of each datum to the solution an empirical analysis with actual data complements the theoretical analysis our approach is applied to the three station natural resources defense council soviet academy of sciences network in kazakhstan the theoretical analysis indicates that reasonable constraint on depth and epicenter is possible whenever three distinct phases p pn pg pzp and pmp or equivalent s phases are observed at two or three stations our theoretical analysis for two station locations shows that the epicenter constraints are extremely poor for sources along the line passing through the two observing stations the use of arrival azimuth in two station locations results in improvement in epicenter constraint for events occurring in the vicinity of the line connecting the two stations but there is no significant improvement elsewhere an empirical analysis of data from two of the september 1987 chemical explosions and data from an explosion in an active mining area supports the theoretical analysis showing that two station locations both epicenter and depth are quite reliable furthermore the theoretical analysis also indicates that even with data from a single observing station satisfactory results are obtained if three or more phases plus arrival azimuth are available

raman characterization of carbonaceous material in the macraes orogenic gold deposit and metasedimentary host rocks new zealand abstract raman spectroscopic and petrographic analyses were performed on samples collected from zones distal and proximal to the macraes gold deposit in the otago schist of new zealand to characterize the features and possible origins of carbonaceous material cm and to assess the potential role of cm in the formation of gold deposits cm is a common component in meta sedimentary orogenic gold deposits and it has been proposed that cm contributes to gold mineralization processes but the details of the mechanisms responsible are not fully understood documentation of the origins of the otago schist cm will improve our understanding of the role of cm in gold deposits this work has identified four types of cm of varying thermal maturity and origins from prehnite pumpellyite grade to lower greenschist grade samples in prehnite pumpellyite and pumpellyite actinolite grade rocks low maturity cm 1 coexists with framboidal pyrite indicating an in situ sedimentary origin with a potential association with the source of gold low crystallinity cm 2 is also found in low grade samples and is likely to have been deposited from fluids unrelated to gold mobilization cm 3 is the highest maturity cm recognized cm 3 is found in samples from the highest metamorphic grades studied lower greenschist facies where bands of cm 3 cross cut the foliation cm 3 is therefore thought to have been transported by fluids though possibly only at short length scales cm 4 is less mature than cm 3 and is found in mineralized rocks in association with sulfide minerals and gold cm 4 is likely to have a depositional origin but its precise role with respect to gold mineralization has not been identified

development of framboidal pyrite during diagenesis low grade regional metamorphism and hydrothermal alteration distribution patterns microstructural relationships and compositional variations for framboidal pyrite in the paleozoic sedimentary host rocks to gold deposits on the northern carlin trend nevada and at fosterville in central victoria collectively demonstrate that it is not all of synsedimentary early diagenetic origin framboidal pyrite also nucleated in hydrothermal veins formed at several kilometers depth and along dissolution surfaces stylolites and crenulation cleavages formed during metamorphism at up to anchizonal grade i e prehnitepumpellyite facies there are no obvious differences in either the size range or internal morphology of framboids formed in these various settings suggesting that a single relatively simple crystallization path may operate over a wide depth range in the upper crust at fosterville anomalously metal rich including au framboidal pyrite is most abundant adjacent to laminated shear veins that developed by slip along bedding surfaces during folding of the sedimentary host rocks microstructural relationships and pb isotope compositions for the framboidal pyrite and other similarly distributed early formed sulfides support development in response to the localized episodic influx of metal enriched h 2s bearing hydrothermal fluids during regional deformation between 440 and 400 ma these findings may have implications for other similarly deformed metasedimentary successions where the discovery of au bearing framboidal pyrite has recently been cited as evidence for significant au enrichment during sedimentation 2009 society of economic geologists inc

attenuation of high frequency shear waves in the crust measurements from new york state south africa and southern california we compare the attenuation of high frequency 3 30 hz shear waves for crustal paths in new york state south africa and southern california over source receiver distances of about 10 400 km the data consist of digital recordings of s waves 5 100 km and lg waves 100 400 km produced by earthquakes we use a coda normalization method to remove the effects of site amplification and source excitation from the amplitudes of the s and lg waves over the entire distance range studied 10 400 km the amplitude decay of 3 hz shear wave energy is considerably less for the tectonicaily stable areas of new york and south africa than for the tectonicaily active region of southern california high frequency 30 hz s wave attenuation is significantly less for new york and south africa than for southern california for distances between 15 and 90 km we parameterize the decay with distance r of coda normalized shear wave amplitudes with a frequency independent q and geometrical spreading exponent where geometrical spreading is proportional to r for new york state the s wave amplitude decay 3 30 hz is well described by a frequency independent q of 2100 330 490 and of 1 3 0 1 the decay of lg wave amplitudes from 3 to 15 hz in the new york state region is fit with a frequency independent q of 1600 280 330 of 0 70 0 2 the s wave amplitudes 3 30hz in south africa yield a q of 1500 190 380 and of 1 3 0 1 fixing the geometrical spreading at r 0 5 produces an lg wave q estimate at 3 hz in south africa of 360 50 80 this lg wave q is low considering that south africa is a cratonic tectonicaily stable area the s wave amplitudes from southern california are described with a frequency independent q of 800 150 240 and a large geometrical spreading exponent of of 1 9 0 2 we find an lg wave q at 3 hz of 260 30 for southern california after constraining the geometrical spreading at r 0 5

frequency dependent lg attenuation in the indian platform we use seismograms from regional earthquakes recorded on digital seismographs in peninsular india to determine the frequency dependent q of lg for the indian platform we measure lg attenuation by determining the decay of spectral amplitudes with distance the available data suggest some spatial variation in attenuation but a much denser ray path coverage would be required to validate such observations we therefore combine all the measurements of overlapping regions that span both the shield and intervening terranes to obtain an average value of attenuation for the indian platform lg q 665 10 with the frequency exponent n 0 67 0 03 this average value of lg attenuation for the indian platform is similar to the average for other stable regions of the globe

ore mineralogy fluid inclusion and stable isotopic characteristics of stratiform copper deposits in the coastal cordillera of northern chile late jurassic stratiform copper deposits in the coastal range of northern chile susana lince and buena vista of the carolina de michilla district and mantos de la luna are hosted in an andesite dominant volcanic pile of the jurassic la negra formation which is extensively intruded by gabbroic to granodioritic plutons and dikes primary copper mineralization is characterized by chalcocite cu1 90s digenite bornite chalcopyrite hematite supergene alteration of these minerals has produced chalcocite djurleite covellite atacamite chrysocolla and copper oxides copper wad fluid inclusion data indicate a variable temperature of formation 200 to 380 c and a wide range of fluid salinities 7 to 34 wt nacl carbon and oxygen isotopic compositions of calcite from the susana lince deposit 13c 2 6 to 3 6 18o 13 7 to 18 7 combined with the thermometric data suggest that the fluid responsible for the calcite mineralization derives from mixing of high temperature meteoric water with cooler basinal brines these data imply that the stratiform copper deposits of the coastal cordillera are epigenetic and formed from non magmatic moderately oxidized hydrothermal solutions

pyrite framboid study of marine permian triassic boundary sections a complex anoxic event and its relationship to contemporaneous mass extinction size analysis of pyrite framboids has been undertaken on epicontinental permian triassic boundary sections throughout the world in order to evaluate the intensity and duration of anoxia mid paleolatitude sections from the margins of the boreal spitsbergen greenland and neotethyan oceans western australia reveal intense anoxia throughout the permian triassic boundary interval with euxinic conditions frequently developing and dysoxia encountered even in relatively shallow water settings above storm wave base at equatorial paleolatitudes weakly oxygenated dysoxic conditions are widely developed in a broad range of water depths including those shallow enough to produce oolite deposition although euxinia was rare western and eastern tethyan locations re veal a complex and unstable redox history anoxia in the hindeodus praeparvus zone was replaced by oxygenated facies in the permian triassic boundary interval h changxingensis to h parvus zones oxygen poor deposition returned during the succeeding isarcicella isarcica zone the more persistent and intense development of oxygen restriction in cooler water mid paleolatitude sections argues against warming and dissolved oxygen decline as the key cause of permian triassic bound ary anoxia in higher paleolatitudes the ben thic invertebrate extinctions occurred during a prolonged phase of oxygen poor deposition while in equatorial tethyan locations benthic losses occurred at the end of the fi rst anoxic phase in the late h praeparvus zone

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

regional phases in continental and oceanic environments summary the very different crustal thicknesses between continental and oceanic crust lead to the establishment of distinct styles of regional seismic wavefield observations and numerical simulations of events near subduction zones in japan allow a direct comparison of seismic wave propagation in oceanic and continental structures the thick zone of lower seismic velocities in the continental crust acts to trap s wave energy in particular and generates crustally guided phases such as pg lg in the oceanic environment there is no efficient s wave trapping and crustal energy progressively leaks into the mantle reverberations in the crust and the water above help to sustain the amplitude of the mantle arrivals pn sn to large distances

regional wave propagation from mexican subduction zone earthquakes the attenuation functions for interplate and inslab events the seismic waves from subduction zone earthquakes are significantly affected by the presence of 3d variation in crust and upper mantle structure around the source area these heterogeneous structures also profoundly modify the character of seismic waves as they propagate from the source area to regional distances this is illustrated by studying shallow interplate earthquakes along the mexican subduction zone and deeper inslab normal faulting earthquakes in the subducted cocos plate beneath mexican mainland the strong motion recordings of these earthquakes are used to evaluate the character of wave propagation along the path between the source region and mexico city we compare the wavefield from two large earthquakes of different source type during the shallow h 17 km interplate 1995 guerrero earthquake m w 7 3 the lg phase is the most prominent feature at regional distances of about 150 to a few hundred kilometers from the source the presence of a lateral velocity gradient in the crust caused by the subduction of the cocos plate enhances the lg wave amplitude which is then amplified further in the mexican volcanic belt by amplification in the low velocity volcanic rocks both effects lead to very large ground motions along the path from the coast to the mexican inland in the frequency band from 0 2 to 4 hz however for the deeper h 40 km inslab normal faulting 1999 oaxaca earthquake m w 7 5 the amplitude of the lg phase is too small to produce the abnormal wave propagation and the direct s wave and its multiple sms reflections between the free surface and moho show a simple attenuation with increasing distance we compare these observations with numerical simulations of seismic wave propagation using the fourier spectral method the results provide a key to the understanding of seismic wave field generated by shallow interplate and deeper inslab earthquakes in a realistic 3d heterogeneous structure

regional pn body wave magnitude scale mb pn for earthquakes along the northern mid atlantic ridge we obtained a robust regional body wave magnitude scale mb pn for earthquakes along the northern mid atlantic ridge by using pn wave recorded at continental stations the new magnitude scale is mb pn log10 a nm 1 86 log10 100 km c 1 62 where a is the zero to peak amplitude of pn wave on the simulated vertical wood anderson seismogram in nanometers is the epicentral distance in kilometers 1 86 represents amplitude attenuation c is the station correction and 1 62 anchors the mb pn to the moment magnitude mw plus amplitude loss in the two crustal legs by using moment magnitude as reference we obtained the event magnitude adjustments ema which represent the difference between the known long period mw and the short period mb pn emas correlate with the source property where ridge events show strong long period waves but poor high frequency signals which lead to mb pn mw and negative adjustment of 0 20 0 24 m u almost all normal faulting events are along spreading ridges whereas strike slip events are along the fracture zones and transform faults hence we developed source specific magnitude adjustments ssma which range from 0 27 m u for earthquakes along the ridges to 0 26 m u for earthquakes along the transform faults using ssma we obtained a regional pn magnitude that is consistent with mw and mb p the regression relationship is mw 0 91 mb pn ssma 0 46 with a standard deviation of 0 15 m u

analysis of short period regional phase path effects associated with topography in eurasia propagation of regional seismic phases is highly dependent on path effects but we have a limited understanding of these effects and no general procedure for accounting for path variation influence on regional waveforms thus there is strong regional variability in the effectiveness of regional wave discriminants used to identify small earthquakes and nuclear explosions motivated by many observations of correlation between surface geology and regional phase behavior we empirically explore the relationship between short period regional and upper mantle distance signal energy and statistics of topography along different travel paths using data for underground nuclear explosions at semipalatinsk kazakhstan we find strong linear correlations of the logarithmic rms amplitude ratio sn lg and to a lesser extent p lg with mean altitude rms roughness rms slope and skewness of topography along the paths to receivers in eurasia this indicates that energy partitioning in the regional wave field is controlled by wave guide structure and attenuation variations that are manifested in surface topography this suggests that it is feasible in many cases to directly calibrate regional discriminants for path effects in terms of observable surface topography as a surrogate for overall path properties the relationships also help to understand the nature of regional phase propagation

seismic anisotropy the state of the art ii summary the theory causes observations and possible applications of seismic anisotropy in the earth have developed considerably since the previous state of the art paper was published in 1977 the behaviour of waves in layered anisotropic media is now much better understood and the evidence for seismic anisotropy indicates that anisotropy is likely to be present throughout much of the crust and upper mantle the top few hundred kilometres of the mantle appears to be anisotropic with the orientations aligned by the present or palaeo stress field the upper part of the crust is frequently anisotropic probably due to cracks differentially aligned by the non lithostatic stresses the possibility of being able to monitor crack geometry by seismic techniques opens a wide range of applications in currently important activities

contrasts in regional seismic wave propagation to station wmq in central asia summary the varying character of regional seismic phase propagation in central asia is well illustrated by the character of the seismograms at the urumqi station wmq in xinjiang china three different classes of behaviour are seen for propagation across the relatively stable platforms to the north along the tien shan chain and across the tarim basin from tibet these paths demonstrate the influences of the variation in crustal structure on the regional phases particularly the tibetan plateau and its north and south boundaries but also the influence of the pamirs on propagation along the tien shan as an interference phase lg is sensitive to changes in crustal structure and can be used to study crustal heterogeneity lg can propagate along the tien shan chain trapped by the gradients in structure on either side but with a progressive loss in amplitude and frequency however once the northern boundary of tibet is crossed the high frequencies in the lg train are lost and there is little recognizable arrival the amplitude ratios of the different crustal phases pn sn and lg can be used to characterize the behaviour and the different classes of propagation can be further separated when account is made of the frequency content in the lg window the influence of the transitions in crustal structure at the northern edge of the tibetan plateau on propagation to wmq is investigated using numerical modelling with the pseudospectral method for models of crustal variations this demonstrates how the crustal pinch at the northern boundary operates to modify the fairly efficient propagation inside tibet with substantial transfer of energy into the mantle

framboidal chalcopyrite and bornite constrain redox conditions during formation of their host rocks in the copper stratabound mineralization of picachos north central chile abstract the picachos project is a copper deposit that occurs in manto type orebodies in north central chile and it exhibits common features of chilean stratabound or manto type copper deposits 1 an increase of copper contents from the margins to the centre of the orebodies 2 sodic and potassic hydrothermal alteration of host rocks with subsequent chloritization and sericite alteration and 3 its occurrence in sequences of limestones that are intercalated with volcanic rocks the most salient characteristic of the picachos project is the presence of pervasive framboidal pyrite in both the non mineralized limestones and the host rocks of the copper mineralization these framboidal pyrites are well preserved probably due to their close relationship with organic matter and have no evident textures of overgrowth recrystallization or dissolution moreover framboidal chalcopyrite and bornite are formed in the external and internal areas respectively of the orebodies sharing common morphological characteristics with framboidal pyrite and are formed by the replacement of the original pyrite framboids without changing their shape and size distribution representative size distributions of framboidal pyrite chalcopyrite and bornite are determined using high resolution x ray tomography micro ct this study highlights the effectiveness of these analytical techniques to obtain the representative size distribution of framboids in mineralized rocks the preservation of the original framboidal texture of pyrite makes it possible to infer anoxic to near dysoxic conditions the size distributions of framboidal chalcopyrite and bornite are hypothesized to be additional potential paleo redox indicators referring to the same formation dynamic as typical framboidal pyrites

stochastic waveguide in the lithosphere indonesian subduction zone to australian craton summary earthquakes occurring in the indonesian subduction zone recorded in the cratonic regions of northern australia have long high frequency coda associated with both p and s waves similar behaviour is seen for earthquakes within australia on paths within the cratonic regions the complex character of the coda and its rapid spatial variation indicate that the high frequency waves have travelled within a zone of strong multiple scattering with very high intrinsic q there are subtle variations in the nature of the coda that can be described through a coda q the variations in coda are associated with the position along the arc and the nature of the transition from the subduction zone to the continental lithosphere the character of the coda observations can be captured with numerical simulations in models derived from seismic tomography for northern australia and the neighbouring subduction zone incorporating lower crustal and mantle heterogeneity with much longer horizontal than vertical correlation length high frequency calculations to high frequency 16 hz for long propagation distances up to 1500 km have been carried out using finite difference modelling on the earth simulator the variations in coda properties can be associated with the way in which the seismic energy gets ducted into the stochastic waveguide associated with the lithosphere the most efficient transfer occurs where continental lithospheric material is adjacent to the earthquake zone

mechanisms of seismic attenuation in the crust scattering and anelasticity in new york state south africa and southern california the envelopes of high frequency seismograms from earthquakes in new york state south africa and southern california are analyzed to determine how much of the observed attenuation of shear waves in the crust is caused by anelasticity and how much is produced by scattering from small scale heterogeneities for seismograms from new york and south africa there is a systematic enrichment of high frequency energy that develops in the coda relative to the direct s or l sub g waves the author uses the growth with source receiver distance of the high frequency energy in the coda relative to the direct wave to estimate the scattering attenuation of the crust and the relative time decay of high frequency energy in the coda to determine the anelastic attenuation using the estimate of l sub g wave q as a constraint he finds that the scattering q in the crust of new york is either independent of frequency or increases with frequency f slower than f sup 0 3 a similar analysis for south africa indicates that scattering is the major cause of the observed s wave attenuation of high frequency energy 30 hz at local distances 100 km for southern california the extent of the scattering attenuation is unclear from the data more although the relatively steep coda decay of southern california implies that anelastic attenuation is stronger there than in new york or south africa for southern california and new york state the 3 hz coda q taken from the late coda 50 110 s is comparable to the l sub g wave q however the 3 hz coda q for south africa over these lapse times is about 5 times the estimated l sub g wave q for all three areas the frequency dependence of the coda q does not match the frequency dependence of the s wave q and for new york and south africa it changes with lapse time less

framboidal pyrite evidence for persistent low oxygen levels in shallow marine facies of the nanpanjiang basin during the permian triassic transition abstract previous studies suggested that anoxia was a causal factor in the end permian mass extinction epme marked by abrupt enrichment of pyrite framboids in the post epme microbialites of the earliest triassic on shallow platforms and that this dysoxic anoxic phase followed a time of well oxygenated seafloors here we report persistent dysoxia throughout the latest permian and euxinia just before the epme based on a new redox history reconstruction study using framboidal pyrite size distribution as well as sulfur isotopic compositions of pyrites from the taiping section on the pingguo platform in the nanpanjiang basin in china further we show that the epme was followed here by rapid oxygenation not an anoxic incursion this revised redox history might be an unusual localized phenomenon when compared to other platforms or it could be solid sedimentary evidence for redox oscillations outside the bioclast enriched photic zone which broadens our understanding of terrestrial marine ecosystem interactions before and during the epme

lg wave propagation and crustal structure differences near denmark and the north sea summary recordings of regional earthquakes near denmark and the north sea have been collected in an attempt to find the lg wave propagation properties in the area propagation paths of lengths between 300 and 1100km are investigated the amplitudes of the lg waves and the other seismic phases in the seismograms are compared the propagation paths are classified according to whether the lg wave propagation compared to p and s wave propagation is good intermediate or poor it is noted that there is a distinct regional pattern in the lg wave attenuation the lg wave propagation is poor across the north sea the north sea is surrounded by areas of good continental lg wave propagation except towards the south east in the netherlands and western germany an area in skagerrak is characterized by good but slow propagation of a surface wave similar to lg since this is exactly the area of a cluster of earthquakes in skagerrak it is suggested that the two phenomena are caused by the same structural inhomogeneities in the area just off the coast of north western denmark the lg wave propagation is as good in the northern part of denmark as it is in the fennoscandian shield the extent to which the propagation is poor across the north sea is dependent on the frequency of the lg waves observed with different seismographs the lg waves are more attenuated relative to the other seismic phases the higher the frequency is between 0 25 and 2 hz as the structural differences between the fennoscandian bedrock area and the norwegian danish basin with 8 10 km of sediments has no effect on the lg wave propagation it is suggested that the structural anomalies causing the poor lg wave propagation across the north sea are deep crustal anomalies possibly significant variations in crustal thickness it is likely that such deep crustal differences are located along the most prominent upper crustal differences in the sedimentary grabens in the middle of the north sea the poor propagation across the north sea is similar to that observed across a sedimentary basin in eastern greenland which also developed mainly before seafloor spreading separated greenland from europe the frequency dependent propagation of the lg waves is explainable in terms of surface wave propagation across structural boundaries as well as in terms of anelastic attenuation

subduction zone guided waves and the heterogeneity structure of the subducted plate intensity anomalies in northern japan 1 the subducting pacific plate acts an efficient waveguide for high frequency signals and often produces anomalously large intensity on the eastern seaboard of northern japan during deep earthquakes the waveform records in the region of high intensity show a low frequency f 2 hz later arrivals with a long coda this behavior is not explained by a simple subduction zone model comprising a high velocity plate with low attenuation from the analysis of observed broadband waveforms and numerical simulation of seismic wave propagation in the pacific subduction zone we demonstrate that the high frequency guided waves traveling in the subducting plate arise from the scattering of seismic waves by heterogeneity in plate structure our preferred model of the heterogeneity has elongated scatterers parallel to the plate margin described by a von karmann function with a downdip correlation length of about 10 km and much shorter correlation length of about 0 5 km in thickness the standard deviation of wave speed fluctuations from the averaged background model is about 2 this new heterogeneous plate model generates significant scattering of seismic waves with wavelengths shorter than correlation distance in thickness but low frequency waves with long wavelengths can easy tunnel through such lamina structure the result is frequency selective propagation characteristics with a faster low frequency phase followed by large and high frequency signals with very long coda a low wave speed channel effect from the former oceanic crust at the top of the subducting slab is not necessary to explain the observed dispersed signals and the very long high frequency coda three dimensional simulations using the earth simulator supercomputer for modeling of high frequency seismic wave propagation in the pacific subduction zone including plate heterogeneity clearly demonstrate the scattering waveguide effects for high frequency seismic waves traveling in the plate the region of large intensity for the heterogeneous model migrates away from the hypocenter into northern japan with an elongated zone along the pacific coast almost comparable to the observations from deep events in the pacific plate

reciprocal stratigraphy of the campanian paleocene western interior of north america abstract the claggett bearpaw and cannonball successions campanian paleocene of the western interior foreland system were deposited during a series of regional second and third order transgressions and regressions locally modulated by fourth and lower order cycles the reciprocal flexural behaviour of the foreland lithosphere in response to orogenic cycles of loading and unloading results in out of phase sequences on opposite sides of the basin which defines the concept of reciprocal stratigraphies the proximal and distal regions of the basin are separated by a few kilometre wide hinge zone of proximal to distal facies change with the mid point taken as a stratigraphic hinge line which defines the boundary between coeval marine transgressive and regressive systems tracts or between nonmarine sequences and correlative sequence boundaries hinge lines have been mapped in alberta saskatchewan montana and wyoming for consecutive time slices during the campanian paleocene interval areally the hinge line traces a semielliptical pattern outlining the region of maximum foreland basin subsidence it migrated at 10 km ma to the north in response to late cretaceous paleocene orogenic dextral transpression the hinge line also migrated eastward during the campanian and maastrichtian in response to thrust sheet advance and westward during the paleocene in response to the redistribution of orogenic load associated with a transition from transpression to transtension possibly accompanied by a visco elastic deepening and narrowing of the foredeep

modelling short period crustal phases at regional distances for the seismic source parameter inversion abstract waveforms of short period crustal phases observed at regional distances are modelled in an attempt to retrieve the source parameters of small earthquakes for a simple shield type crustal structure the synthetic seismograms calculated for elementary source mechanisms show that the waveforms of crustal phases are quite distinct for different source mechanisms and suggest that these features can be used to constrain the source mechanisms waveforms of the crustal phases are also strongly affected even by small variations in the crustal thickness as well as in the focal depth a generalized linearized waveform inversion technique is used to invert the regional crustal phases for a deviatoric moment tensor source the inversion technique is applied to regional short period records from a small earthquake in central sweden for determining its source parameters the waveform inversion which mainly used lg waves produced a satisfactory fit between the observed and synthetic records suggesting that the source mechanism and focal depth estimates were reasonable the focal depth of 40 km obtained for the event studied suggests the occurrence of a deep crustal earthquake and demonstrates the usefulness of crustal phases in studying small intraplate earthquakes

extremely negative and inhomogeneous sulfur isotope signatures in cretaceous chilean manto type cu ag deposits coastal range of central chile abstract chilean manto type cmt cu ag hydrothermal deposits share a characteristic association of volcano sedimentary jurassic to lower cretaceous host rocks style of mineralization ore and associated mineralogy and geochemistry with ore grades typically 1 cu that make this family of deposits significant and interesting both academically and economically although often stratabound geological evidence supports an epigenetic origin for these deposits we present a detailed stable isotope study of la serena and melipilla naltahua lower cretaceous deposits central chile which reveals extremely negative 34 s values to 50 which are among the lowest values found in any ore deposit in addition the range of 34 s values from sulfides in the two areas is very wide 38 3 to 6 9 in la serena and 50 4 to 0 6 in melipilla naltahua these new data significantly extended the reported range of 34 s data for cmt deposits co existing sulfates range from 7 9 to 14 3 and are exclusive to la serena deposit the wide sulfide isotopic range occurs at deposit and hand specimen scale and suggests a polygenic sulfur source for these deposits where bacteriogenic sulfide dominates while sulfur isotope data for the bulk of jurassic cmt deposits northern chile suggests a predominant magmatic source in their origin mean 2 7 1 9 1 contributions of a magmatic component is only likely to be involved at melipilla naltahua deposit the 13 c values obtained for calcites associated with the mineralization range from 20 1 to 0 2 also suggesting polygenic carbon sources with the likely strong involvement of degradation of organic matter and leaching of limestone two different genetic models with involvement of hydrocarbon are proposed for both areas for melipilla naltahua a two step model can be developed as follows 1 framboidal pyrite growth with very low 34 s formed by bacterial sulfate reduction in an open system and with diagenetic degradation of oil related brines leaving pyrobitumen 2 cu bearing stage replacing of framboidal pyrite inheriting depleted sulfur as low as 50 4 together with sulfides directly precipitated from a hydrothermal fluid with 34 s close to 0 for la serena a single step model fits best without framboidal pyrite generation cu bearing sulfides were precipitated mainly in veins where cu plus base metal bearing hydrothermal fluids mixed with h 2 s generated by bacterial sulfate reduction in the host rocks isotopic evidence clearly illustrates that bacterial activity perhaps enhanced by hydrothermal activity was fed by hydrocarbon brines and sulfate remobilized from continental evaporites it is possible that variable ecological conditions led to different extents of isotopic fractionation adding to the typical sulfur isotopic heterogeneity of such bacterial systems for both areas the cu bearing stage occurred during the peak to waning stages of the very low grade metamorphism that affected the lower cretaceous sequence