combining seismic noise techniques for landslide characterization a strong topographic relief and the presence of weakly consolidated sediments create favorable conditions for the development of landslides around the eastern rim of the fergana basin central asia in summer 2012 a field experiment employing small aperture seismic arrays was carried out on an unstable slope using ambient vibration recordings the aim of the study was to constrain the seismic response of a potential future landslide and to map lateral and vertical changes in the shear wave velocity of the surficial soil layers strong variations of horizontal to vertical spectral ratios in terms of amplitude and directionality indicated clear differences in local site effects probably reflecting the stability of different sections of the slope results further showed resonant frequencies of both the entire unstable block as well as for smaller individual parts the use of an ad hoc passive seismic tomography approach based on noise correlograms allowed for the mapping of the shear wave velocities of the sliding material even in cases of significant topography relief based on the recording of seismic noise only we clearly identified a low velocity body of weakly consolidated claystone and limestone material which can be interpreted as the landslide body with laterally varying thickness

self excitation process due to local seismic amplification responsible for the reactivation of the salcito landslide italy on 31 october 2002 1 an integrated numerical and geophysical approach was used to investigate the role of local seismic amplification in the reactivation of the salcito landslide italy after the molise earthquake of 31 october 2002 numerical stress strain analysis with flac 5 0 fdm software performed in dynamic configuration showed that the 1 hz frequency was consistent with landslide instability conditions the fourier spectrum of the triggering earthquake showed two main peaks occurring at 1 and 2 hz respectively which could be related to local effects the analysis of h v spectral ratios of ambient noise records obtained in the landslide area evidenced amplification effects in the 1 3 hz range on the basis of an engineering geology model numerical modeling of both 1 d and 2 d seismic wave propagation was conducted using linear and nonlinear solutions the simulation outputs showed 1 a 1 hz amplification ascribable to 2 d effects due to a landslide mass lying within a basin like geological structure 2 a double peak amplification at about 2 and 3 hz respectively ascribable to 1 d resonance of the landslide mass and 3 1 d plus lateral wave effects within the landslide mass in the 2 5 3 5 hz frequency range these findings suggest that local amplification of ground motion by the salcito landslide mass may generate a self excitation process responsible for its reactivation

geological and geochronological constraints on the formation of the jurassic maozaishan sn deposit dayishan orefield south china abstract the dayishan orefield in the central nanling belt is one of the most important sn districts in south china within this district there are more than seven medium to large sn sn cu and pb zn sn deposits the mineralization is associated with altered granites and greisen quartz veins both of which occur in the inner part of the dayishan granite batholith cassiterite is the principal ore mineral accompanied by subordinate molybdenite cassiterite separates from altered and mineralized granite and greisen quartz veins have concordia ages of 156 5 2 8 ma mswd 3 1 and 158 0 1 8 ma mswd 1 4 respectively molybdenite separates from molybdenite quartz veins that crosscut the greisen alteration have a re os isochron age of 157 9 7 7 ma mswd 26 whereas zircon separates from the porphyry monzogranite have a u pb age of 156 3 1 2 ma these ages are identical within the analytical error and together with the field relationships provide tight constraints on the sn mineralization at around 156 ma rhenium contents of the molybdenite suggests that the ore forming materials were derived from a crustal source whereas s and pb isotopic data point to mixed sources we suggest that the maozaishan deposit was formed by intrusion of the related pluton and occurred in the late jurassic during a period of lithospheric thinning and crustal extension of the south china block

ambient vibration analysis of an unstable mountain slope summary a field experiment with small aperture seismic arrays was performed on the unstable rock slope above the village of randa in the southern swiss alps the aim of this experiment was to constrain the seismic response of a potential future rockslide using ambient vibration recordings weak seismic events were identified on the recordings and site to reference spectral ratios were calculated using a reference site located on the stable part of the slope spectral ratios of up to 30 were observed at sites located within the unstable portion of the slope a strong variation of spectral ratios with azimuth indicates a directional site effect neither amplification nor directionality were observed at sites located in the stable part of the slope furthermore time frequency polarization analysis of the ambient noise was performed to provide robust estimates of frequency dependent directions of the maximum polarization it was found that the unstable part of the slope vibrates within a narrow range of directions 130 10 for the frequency range centred around 5 hz the polarization directions estimated from ambient seismic vibrations are in good agreement with the deformation directions obtained by geodetic and in situ measurements no directionality of ambient vibrations was observed at sites within the stable part of the slope

hydraulic control of flow over the sill in observatory inlet observations of density velocity and acoustic backscatter obtained over the sill in observatory inlet british columbia during the ebb tide illustrate several features of internal hydraulic control in a tidally forced stratified flow following high water slack the flow field was initially determined by critical control of the second internal mode at the sill crest as the flow speed increased a transition occurred and control changed to an approach control of the second internal mode located upstream of the sill crest whereas the critical control represents a minimum energy condition at the crest the approach control corresponds to a maximum energy condition upstream of the sill crest later when the ebb currents were just past their maximum values the control condition changed to critical control of the first internal mode the concept of approach control of flow over topography has not previously been discussed in the literature the data described here are believed to represent the first field observations of this phenomenon the changing hydraulic conditions are analyzed in terms of two and three layer hydraulic models model results are consistent with the evolution of the flow patterns although the model cannot reproduce the apparent hysteresis in the response after maximum ebb the concept of an approach control is demonstrated with a simple two layer laboratory model

the distribution of gold in rocks and minerals of the meguma group of nova scotia canada abstract rocks and constituent minerals of the meguma group from southeastern nova scotia were analyzed for gold by far the highest levels 4311 ng g ppb whole rocks 1 0 ppb and other minerals

differences between site characteristics obtained from microtremors s waves p waves and codas we examine differences of empirical site characteristics among s waves p waves coda and microtremors using records at 20 sites in and around the sendai basin japan and interpret the differences theoretically at soft soil sites the horizontal to vertical spectral ratios hvrs for early p coda become different from hvrs for a p wave with increasing time and eventually converge on hvrs for microtremors the hvrs for an s coda become similar to hvrs for microtremors with increasing time in the frequency range lower than 3 hz at soft soil sites by contrast at a rock site and two hard soil sites hvrs for s coda agree well with hvrs for an s wave the soil to rock spectral ratios for horizontal hhrs and vertical vvrs components for early s coda are larger than those for an s wave at soft soil sites when we use the deep sedimentary structures above the bedrock before tertiary age theoretical hvr for the fundamental mode of rayleigh waves is consistent with observed hvr for microtremors and theoretical hvr for an obliquely incident sv wave is consistent with observed hvr for an s wave theoretical s wave site amplification factor explains well observed hhr for s wave but does not coincide with hvr for microtremors in general the frequencies of maximum peaks of hvrs for microtremors do not coincide with those of hvrs and hhrs for s wave however if we select hvrs with peak frequencies lower than 1 hz and peak amplitudes larger than three the peak frequencies of hvrs for microtremors roughly coincide with those of hvrs and hhrs for s wave even under these constraints their amplitudes do not coincide with each other concerning coda we conclude that the rayleigh wave contamination in coda is significant in the frequency range lower than 3 hz at soft soil sites

semidiurnal internal tides in a patagonian fjord abstract the fjords of central chilean patagonia 47 s receive fresh water from both precipitation and the baker river this buoyancy input generates a two layer hydrographic system characterized by strong salinity stratification 30 g kg 1 over a depth range of 7 15 m which favors baroclinic conditions in the fjord hourly current velocity profiles were collected with an acoustic doppler current profiler adcp moored at a depth of 40 m during march april 2009 and complemented by 11 ctd profiles and hourly sea level time series these data allowed the detection of semidiurnal internal tidal waves for the first time in this region wavelength and horizontal phase speeds were determined by the dynamical mode 1 for internal waves maximum wavelength was 52 km travelling at a horizontal phase speed of 1 16 m s 1 wavelet spectral and empirical orthogonal function eof analysis techniques applied to the echo anomaly signal and to the baroclinic velocity showed largest semidiurnal amplitudes near the pycnocline out of three modes obtained from the eof analysis two modes displayed a two or three layer flow structure with flow direction reversing at the pycnocline the semidiurnal internal waves were found as fluctuations near the pycnocline in sporadic packets correlated to high discharge pulses of the baker river r2 0 77 additionally internal froude number calculations at the mouth of the baker river indicated critical flow conditions which allowed for generation of internal waves at the plume front these waves are separated from the river plume after internal wave phase speeds surpassed frontal speeds this suggests that the internal waves were modulated by pulses in high river discharge rather than the interaction of barotropic tide with bathymetry a sill an implication of these internal waves would be to increase vertical mixing of nutrients toward the surface through shear instabilities which would favor primary production

sm nd isotopic investigation of the age and origin of the meguma zone metasedimentary rocks the meguma zone of southern nova scotia is a suspect terrane in the eastern appalachians sm nd isotopic data on six samples from the thick sequence of flyschoid metasediments of the meguma group show that these rocks have a mean crustal residence age of tdm 1773 95 ma considerably older than their cambro ordovician depositional age this information should be useful in locating the matching terrane for the meguma and ultimately in determining whether it was derived from one or more precambrian sources with different crustal residence times

seismic instrumentation of landslides building a better model of dynamic landslide behavior although the geologic topographic and threshold shaking con ditions required to trigger landslides in earthquakes are probabilistically pre dictable models used to estimate the behavior of slopes under dynamic shaking conditions are overly simplistic because of the lack of direct measurement of landslide behavior during seismic shaking two permanent instrument arrays have been installed on seismically active landslides to simultaneously record acceleration pore pressure and permanent landslide displacement which will permit more accurate modeling of seismic landslide response

geochemical behavior of sulfur in granitoids during intrusion of the south mountain batholith nova scotia canada abstract a detailed stable isotope s o and elemental major trace s content study of peraluminous s type granites and granodiorites of the south mountain batholith and the meguma group metasediments into which the batholith was intruded has been conducted on a regional and local scale near mt uniacke sulfur contents of the metasediments range from 5 to 2440 ppm and 34 s ranges from 3 7 to 26 3 sulfur contents of the igneous rocks range from 6 to 570 ppm with the granites 20 ppm having lower sulfur contents than the granodiorites 300 ppm approximately 30 to 60 of the sulfur in the granodiorites is present as pyrrhotite a late phase with most of the remainder being present as sulfur substituted into biotite an early phase 18 oq quartz values of the mt uniacke granodiorites are heavy a 12 2 indicating formation of the magmas by partial melting of sedimentary rocks major element variations suggest that the granites are related to the granodiorites by fractional crystallization of plagioclase quartz and biotite comparison of the sulfur contents of the granodiorites with experimental determinations of sulfur solubility suggest that the distribution coefficient of sulfur d s between the cumulate and the magma during fractional crystallization 4 the regional granodiorites have a relatively restricted range of 34 s values 5 4 to 8 4 while the regional granites have a wide range of 34 s values 1 6 to 15 0 granodiorites at mt uniacke with normal magmatic values 0 76 to 1 42 for 18 o quartz feldspar have 34 s values between 6 6 and 12 3 and show good negative correlations between 34 s and s feo and mgo contents some granodiorites at mt uniacke have anomalously low sulfur contents for their major element composition and 18 o quartz feldspar values 0 45 to 0 67 indicate that these samples have undergone hydrothermal alteration and this alteration event is probably responsible for the low sulfur contents a number of processes have been considered in order to understand the variations of 34 s partial melting of inhomogeneous source rocks may be responsible for some of the regional 34 s variations but this implies that the granites are not genetically related to the granodiorites inhomogeneous source rocks are an unlikely explanation for the systematic variations of 34 s observed over only a few kilometres at mt uniacke rayleigh fractionation accompanying the fractional crystallization of biotite 34 s pyrrhotites silicate s 0 5 to 1 0 can account for only a small component of the observed 34 s variations the assimilation of isotopically variable sulfur derived from the meguma group metasediments during fractional crystallization combined assimilation fractional crystallization or afc provides the best explanation for the 34 s variations transfer of sulfur from the country rock may have been possible by either bulk afc where all of the country rock material is incorporated into the magma or by selective afc where sulfur and other volatile elements only are transferred from the country rock into the magma selective afc could have been effected by a sloping mechanism of intrusion followed by the heating of country rock xenoliths to the point where extensive desulfidation reactions took place with sulfur being transferred from the country rock to the magma by a fluid phase

chemical and isotopic pb sr zonation in a peraluminous granite pluton role of fluid fractionation the davis lake pluton dlp 800 km2 of southwestern nova scotia canada part of the large peraluminous south mountain batholith of ca 380 ma u pb zircon ar ar mica consists of granite and subordinate topaz muscovite leucogranite that hosts greisen tin base metal mineralization a new pb pb isochron age for leucogranite from the most evolved part of the dlp indicates a crystallization age of 378 3 6 ma coincident with other radiometric ages of the dlp rb sr re os pb pb the intrusion displays a compositional zonation defined by lead and strontium isotopic ratios as well as some major elements e g si f incompatible trace elements e g li rb ta u sn and elemental ratios e g k rb and nb ta the greisens and the leucogranites that host them are characterized by extreme radiogenic compositions for pb and sr and their chemical isotopic trends are extensions of the trends displayed by the less evolved granites the covariations of the isotopic ratios with several major and trace elements and elemental ratios as well as the pb pb and rb sr isochrones indicate that all phases of the intrusion originated from a homogeneous parental magma the granitoid magma underwent extensive fractional crystallization of feldspars minor biotite and accessory minerals monazite apatite and zircon in a compositionally zoned magma chamber that was subsequently accompanied by fluid fractionation during which time the internally derived fluorine rich fluids modified the rb sr u pb and th pb ratios leading to distinct variations of 87sr 86sr 206pb 204pb 238u 204pb and 232th 204pb isotopic ratios these data therefore document the evolution of a granitic magma through magmatic i e crystal fractionation orthomagmatic i e crystal fluid fractionation and hydrothermal i e fluid fractionation stages that culminated in the formation of a tin base metal deposit the pb isotope data also constrain the source region for the dlp as being avalonian basement that by inference must underlie much of the meguma terrane

use of nonparametric ranking statistics to characterize magmatic and post magmatic processes in the eastern south mountain batholith nova scotia canada abstract the south mountain batholith is a large post tectonic peraluminous granitoid complex consisting of many coalesced plutons compositions range from biotite granodiorite through two mica monzogranite to muscovite leucogranite application of the non parametric spearman rank correlation coefficient srcc statistic to major and trace element chemical data from one large pluton the halifax pluton and to two different groups of much smaller leucogranitoid bodies shows strongly different correlation coefficients in the three groups the halifax pluton shows strong srccs between compatible elements ba sr zr sc v la and weak srccs for the incompatible elements rb ta nb li f sn the leucogranites generally show correlations opposite to the halifax pluton and also show some strong correlations between elements that were poorly correlated in it na k li p non geological controls such as closure dissimilar compositional ranges dissimilar groupings and differing analytical precisions cannot account for the observed differences between the magnitudes and signs of the correlation coefficients in the three groups on the other hand geological controls principally magmatic vs hydrothermal do explain most of the differences in the correlation coefficients and the transition between magmatic and hydrothermal control is apparent spearman rank correlation coefficients can be used with compositional data drawn from populations with non normal distributions to provide a comprehensive and rapid nongraphical assessment of inter element correlations to quantify these inter element relationships and to both identify processes and to gauge their relative contributions to the observed compositions

baroclinic annular variability of internal motions in a patagonian fjord time series of horizontal velocities echo intensity wind velocity and atmospheric pressure were collected for 200 days in a patagonian fjord to explore pycnocline motions produced by the southern hemisphere s baroclinic annular mode bam the bam variability occurs between 20 and 30 days and is associated with fluctuations in atmospheric kinetic energy and in turbulent fluxes of heat spectra of horizontal velocities and normalized echo intensity in the fjord s water showed highest energy between 25 and 30 days this was explained by sustained westerly winds associated with extreme low pressure systems 900 hpa that had periodicity related to the bam wind forcing produced 40 cm s 1 along channel and cross channel currents in the surface layer which in turn created a wind induced setup toward the head of the fjord the setup was accompanied by a deepening of the pycnocline from 5 to 15 m depth with 25 to 30 day periodicity as derived from the normalized echo intensity the dominant empirical orthogonal function mode of the normalized echo intensity profiles explained 70 8 of the variance and also exhibited a 25 30 day periodicity further a wavelet and spectral analysis of 10 years of atmospheric pressure indicated peaks between 25 and 30 days each year indicating that the bam consistently influences weather patterns in chilean patagonia this is the first documented case of baroclinic annular variability in a specific region of the southern hemisphere and of its effects on fjord systems

post paleocene cooling in the southern canadian atlantic region evidence from apatite fission track models the traditional view of the geomorphic evolution of the southern canadian atlantic margin is one of gradual exhumation and peneplanation following triassic jurassic rifting thermal modelling of apatite fission track data from pre carboniferous granitic basement in nova scotia and from permian and triassic sandstones from nova scotia new brunswick and prince edward island suggest a more complex thermal evolution of the onshore part of the margin models clearly indicate significantly elevated regional paleotemperatures during jurassic time and as much as 30 c of post paleocene cooling model predicted paleogeothermal gradients for granitic samples from the digby d 1 well are normal ranging from 15 to 20 c km post paleocene cooling may be attributable to the combined effects of 13 c of exhumational cooling from erosion of approximately 700 m of post aptian sediments caused by decreased eustatic sea levels and 8 17 c of cooling from the propagation to depth of a 10 20 c decrease in paleo mean ann

earthquake induced chains of geologic hazards patterns mechanisms and impacts large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking most moderate and large magnitude earthquakes trigger landslides ranging from small failures in the soil cover to massive devastating rock avalanches some landslides dam rivers and impound lakes which can collapse days to centuries later and flood mountain valleys for hundreds of kilometers downstream landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows cracks and fractures can form and widen on mountain crests and flanks promoting increased frequency of landslides that lasts for decades more gradual impacts involve the flushing of excess debris downstream by rivers which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency settlements ecosystems and infrastructure ultimately earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales two recent events have attracted intense research into earthquake induced landslides and their consequences the magnitude m 7 6 chi chi taiwan earthquake of 1999 and the m 7 9 wenchuan china earthquake of 2008 using data and insights from these and several other earthquakes we analyze how such events initiate processes that change mountain landscapes highlight research gaps and suggest pathways toward a more complete understanding of the seismic effects on the earth s surface

directivity of slope dynamic response to seismic shaking 1 a four year long accelerometric monitoring of a landslide prone slope area in italy provided evidence of amplifications with systematic directional differences in shaking energy by a factor of 2 3 apparently correlated with the directions of local topographic features the examination of regional scale data revealed similar site response directivity phenomena also on some steep rock slopes not affected by amplification the spectral properties of the site responses were investigated using hvsr analysis and a new approach based on the multiplication of spectra from several events the results suggest that such phenomena are caused by a directional redistribution of spectral energy controlled by a combination of interrelated topographic and geologic factors acting in similar directions

reproduction of microseism h v spectral features using a three dimensional complex topographical model of the sediment bedrock interface in the osaka sedimentary basin summary estimating the velocity structure of microseisms based on the horizontal to vertical spectral ratio hvsr is an extremely practical means of modelling the subsurface structure necessary for strong ground motion predictions thus beyond the traditional framework of the 1 d velocity structure the hvsr derived from observation records of microseisms microtremors with a frequency of about 1 hz or lower originating from ocean waves in areas where the sediment bedrock interface has irregular topographies was reproduced by finite differential method fdm based simulation this study was conducted for the osaka sedimentary basin the sediment bedrock interface of which is three dimensionally complicated and contains grabens steps and ramps because high precision models for this basin have been constructed based on a wide range of existing exploration information the hvsrs of two components the east west direction and the north south direction to the vertical direction derived from the fdm simulations were both well reproduced in terms of not only the peak frequency hvfp but also the spectral curves for a number of observation sites above the sediment bedrock interface with complex geological features these results suggest that with a sufficient number of observation sites for microtremors and highly accurate a priori information on geophysical constants in the sedimentary layer that spatially serves as the reference the irregular shaped sediment bedrock interface may be estimated based on how well the hvsr curves and the hvfp agree between the observations and simulations furthermore the fdm simulations confirmed observed phenomena such as the polarization of the amplitude of horizontal motions and broad or plateau like hvsr peaks of microseisms in grabens and step structures it was determined that the hvfps in areas with these strong irregularities are higher than the peak frequency of rayleigh wave ellipticity for the fundamental mode rhvfp based on the 1 d velocity structure in addition there was a difference of about 20 per cent at most between the hvfp derived from fdm simulations and the rhvfp in areas where the depth of the sediment bedrock interface varies only slightly

dating transcurrent terrane accretion an example from the meguma and avalon composite terranes in the northern appalachians the polygenetic minas geofracture separates the meguma and avalon composite terranes of the maritime appalachians dynamically recrystallized muscovite and biotite occur within d3 shear zones which developed during dextral movement along the geofracture these record 40ar 39ar plateau ages between circa 360 and 370 ma comparable plateau ages are recorded by micas within undeformed portions of granitic plutons and their low pressure contact metamorphic aureoles these are similar to u pb ages previously reported for igneous monazite therefore indicating relatively rapid postmagmatic cooling at shallow crustal levels the d3 fabrics were superimposed on earlier s1 structures which formed during initial amalgamation of the meguma and avalon composite terranes whole rock slate phyllite samples collected outside high temperature portions of the plutonic contact aureoles yield 40ar 39ar plateau ages which correspond to groupings of circa 400 395 ma 390 385 ma and 380 375 ma these are interpreted to date diachronous formation of the s1 fabrics and concomitant low grade regional metamorphism in the circa 25 ma between initial amalgamation and granitic plutonism it is inferred that there was a slow rise of isotherms through the crust as a result of overthrust tectonic thickening this led to crustal melting and the production of widespread granitic magmas which were emplaced immediately prior to d3 dextral shearing

40ar 39ar dating of micas from the east kemptville tin deposit yarmouth county nova scotia the east kemptville tin deposit in nova scotia the largest known tin deposit in north america lies in a greisen zone within the davis lake pluton generally considered to be part of the devonian south mountain batholith our dating of micas from within the deposit suggests that the greisenization process that accompanied mineralization took place about 295 5 ma ago that is ca 60 ma after the emplacement of the batholith hydrothermal alteration mineralization activity in southern nova scotia coincided with extensive shearing and tectonism throughout the hercynian orogen the east kemptville deposit appears to be approximately coeval with similar mineralization in southwest england the iberian peninsula and northwest africa and much younger than the devonian acadian orogeny

ground motion in the presence of complex topography ii earthquake sources and 3d simulations abstract eight seismic stations were placed in a linear array with a topographic relief of 222 m over mission peak in the east san francisco bay region for a period of one year to study topographic effects seventy two well recorded local earthquakes are used to calculate spectral amplitude ratios relative to a reference site a well defined fundamental resonance peak is observed with individual station amplitudes following the theoretically predicted progression of larger amplitudes in the upslope direction favored directions of vibration are also seen that are related to the trapping of shear waves within the primary ridge dimensions spectral peaks above the fundamental one are also related to topographic effects but follow a more complex pattern theoretical predictions using a 3d velocity model and accurate topography reproduce many of the general frequency and time domain features of the data shifts in spectral frequencies and amplitude differences however are related to deficiencies of the model and point out the importance of contributing factors including the shear wave velocity under the topographic feature near surface velocity gradients and source parameters electronic supplement figures of recorded and simulated acceleration response spectra and earthquake ground motion directional response

seismically induced rock slope failures resulting from topographic amplification of strong ground motions the case of pacoima canyon california abstract the 1994 northridge earthquake mw 6 7 triggered extensive rock slope failures in pacoima canyon immediately north of los angeles california pacoima canyon is a narrow and steep canyon incised in gneissic and granitic rocks peak accelerations of nearly 1 6 g were recorded at a ridge that forms the left abutment of pacoima dam peak accelerations at the bottom of the canyon were less than 0 5 g suggesting the occurrence of topographic amplification topographic effects have been previously suggested to explain similarly high ground motions at the site during the 1971 mw 6 7 san fernando earthquake furthermore high landslide concentrations observed in the area have been attributed to unusually strong ground motions rather than higher susceptibility to sliding compared with nearby zones we conducted field investigations and slope stability back analyses to confirm the impact of topographic amplification on the triggering of landslides during the 1994 earthquake our results suggest that the observed extensive rock sliding and falling would have not been possible under unamplified seismic conditions which would have generated a significantly lower number of areas affected by landslides in contrast modelling slope stability using amplified ground shaking predicts slope failure distributions matching what occurred in 1994 this observation confirms a significant role for topographic amplification on the triggering of landslides at the site and emphasises the need to select carefully the inputs for seismic slope stability analyses

a geochemical study of the concentration process of tungsten and tin in the taourirts granites of central ahaggar algeria abstract the here presented geochemical study of the granite of three intrusions in the central ahaggar algeria was carried out in an effort to discriminate between w and sn bearing intrusions in the nahada intrusion w is not correlated with the other elements as this intrusion is linked to a large w deposit the correlation of w should be made with the elements of the fluid phase however this has not been taken into account in the present study although the tamazaror intrusion was also affected by a strong fluid phase only a minor w deposit was observed due to the fact that the w remained partially absorbed in a ferruginous phase caused by an extensive crustal contamination in the el bema intrusion accompanied by intrabatholitic sn veins w is correlated with a lithophile factor characterizing a fractional crystallization process which is recognized as an indicator of granite specialization for sn the chemical features of the intrusive granites allow a lithogeochemical approach to the prospection problems for w and sn in the central ahaggar

thermal history of the southwestern meguma zone nova scotia from an 40ar 39ar and fission track dating study of intrusive rocks two geologically distinct regions within the meguma terrane have been studied in detail and are shown to have contrasting thermal histories this conclusion is based on 31 new 40ar 39ar age spectra on micas k feldspars and hornblendes from several of the plutons in southern nova scotia which are satellites to the much larger south mountain batholith smb in addition we report four k feldspar age spectra from a locality in the northeastern part of the smb and seven fission track ages from both the southern and northern areas the complex age spectrum of hornblende from a mafic phase associated with the bamngton passage pluton suggests a minimum intrusive age of 385 ma a result consistent with geologic evidence that this pluton represents an early less evolved magmatic pulse later intrusive activity appears to have been coeval with the intrusion of the smb at ca 370 ma ago in the southern region argon clocks in feldspars were completely reset and mica clocks variably reset by a later thermal event the cumulative geochronologic and geologic evidence constrains this event to 300 320 ma ago in the smb this alleghanianl hercynian thermal disturbance is much less pronounced and appears to be localized to small areas that are often associated with economic mineralization k feldspars from the southern plutons record an episode of argon loss 220 230 ma ago which is less evident in the smb to the north upper triassic dike injection in the southern region associated with the initial rifting phase of the canadian atlantic margin accompanied this milder thermal pulse apatites in the two regions record a mean fission track age of ca 180 ma which we attribute to the final cooling of the terrane below about 100 c the timing of this event coincides with regional uplift recorded in sedimentary sequences along much of the maritime continental shelf deux kgions gtologiques distinctes inttgkes au terrane de meguma ont ctt ctudites en dctai1 et leurs histoires thermales

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

extrapolation of irregular subsurface structures using the horizontal to vertical spectral ratio of long period microtremors one of the key problems in modeling the 3d subsurface structure of sedimentary basins is extrapolation and or interpolation from 2d models constructed from reflection and refraction surveys the use of microtremor horizontal to vertical h v spectral ratios allowing simple and quick microtremor measurements may be suitable for this purpose the validity and usefulness of long period microtremor h v spectral ratios are investigated as a possible tool for extrapolation in 3d basin structure modeling three component microtremor observations were conducted at 51 stations in the northern section of the osaka basin which encompasses the most complex geological structures in the basin the microtremor h v spectral ratios were measured in the range 1 to 5 sec to reproduce these observations three 2d finite element models have been developed that account for the irregular shape of subsurface structures deduced from seismic reflection studies microtremor array studies and deep drilling data the 3d model obtained by combining the 2d models is consistent with geological information for the area such as surface geology and the location of active faults furthermore compared with the basement structure derived from the gravity prospecting this 3d model is more detailed and offers higher resolution than the gravitational method therefore the microtremor h v spectral ratio represents a useful technique of extrapolation and interpolation for modeling 3d basin structures

geologic fluid inclusion and stable isotope studies of the gays river lead zinc deposit nova scotia canada the gays river deposit is the largest carbonate hosted lead zinc deposit known in the mississippian windsor group of atlantic canada the orebody mainly occupies one flank of a porous dolomitized carbonate bank that unconformably overlies a basement ridge of the metasedimentary lower paleozoic megurea group the orebody consists of stratiform disseminated sulfides as open space fillings in primary and secondary pores of the dolomite and fault controlled veinlike bodies of high grade massive sphalerite and galena the carbonate bank is overlain by evaporite deposits of mississippian age underground mapping and laboratory studies suggest four main stages of evolution for gays river 1 deposition of the visean carbonate bank preore evaporite deposition pervasive dolomitization and growth of diagenetic marcasite 2 deposition of sphalerite galena chalcopyrite and calcite as a result of influx of hydrothermal metal rich saline brines into fractures and porous dolomite 3 postore deposition of calcite fluorite barite marcasite pyrite and selenite and 4 uplift localized dedolomitization of the mineralized carbonates and exposure by erosion in cretaceous times microthermometry of fluid inclusions yields the following mean homogenization temperatures sphalerite 215oc ore stage calcite 173oc postore calcite 142oc fluorite 142oc and barite 137oc pressure corrections should be minimal for these temperatures no evidence of boiling was observed in the inclusions salinity determinations from the ice melting temperatures of inclusions in postore fluorite and calcite yield a value of ca 20 4 equivalent wt percent naci for the hydrothermal fluid during the waning stages of mineralization isotopic analyses indicate that anhydrite and gypsum in the overlying evaporites and barite within the orebody are enriched in heavy sulfur t 34s 13 1 16 5 0 suggesting a mississippian seawater source ore stage sphalerite galena and chalcopyrite probably derived their sulfur b34s 8 0 13 65 0 from sulfates or possibly a homogenized basement source postore marcasite and pyrite are characterized by light probably biogenic sulfur ba4s 9 7 to 46 0 mineralized carbonates are significantly depleted in the heavier isotopes of oxygen and carbon with respect to their unmineralized equivalents preliminary lead isotope data for galena suggest that the metasedimentary basement was a source of lead this study disputes an earlier interpretation that the stratiform lead zinc ores are an early low temperature diagenetic cement of the carbonate bank the high grade zones are not residual concentrations related to sinkholes as originally thought instead both disseminated and massive ores are probably the result of the same mineralizing episode involving deeply convecting brines or brines expelled during basin dewatering under high geothermal gradients in the late paleozoic

thermochronologic constraints on ore formation at the gays river pb zn deposit nova scotia canada from apatite fission track analysis fission tracks in detrital apatites from the cambro ordovician metasedimentary basement in the vicinity of the carboniferous hosted gays river pb zn deposit nova scotia provide a record of final

the cassiterite polymetallic sulfide deposits of dachang guangxi people s republic of china the dachang mining district is the second largest producer of sn in china and an important source of other metals the known mineralizations can be divided into four groups 1 cassiterite cu fe pb zn sulfides and sulfosalts 2 zn cu skarn 3 sb w veins and 4 residual and placer concentrations of sn and fe oxides most orebodies are hosted by upper devonian calcareous marly and quartzitic formations in spatial association with cretaceous yanshanian magmatites a characteristic feature is the occurrence of stratiform lens shaped orebodies which appear to represent the root zone of overlying stockwork mineralizations the metallogeny of the district may be interpreted in terms of an upper devonian sn and polymetallic concentration with subsequent remobilization and possibly the introduction of additional elements during the late stages of the yanshanian magmatism

k ar and 40ar 39ar geochronology of granitoid rocks from southern nova scotia its bearing on the geological evolution of the meguma zone of the appalachians k ar and or 40ar 39ar apparent ages are reported for 28 samples of biotite and muscovite from nova scotia s south mountain batholith and associated northern satellite stocks in addition 14 mica samples from the southern satellite stocks were dated previous workers using primarily k ar and rb sr techniques have reported a spread of apparent ages ranging from 240 420 ma for these intrusive rocks the present data set is internally consistent and has been calibrated against accepted interlaboratory standards a mean age of 367 ma was obtained for the south mountain batholith and the northern stocks a value consistent with results recently obtained in an rb sr study by clarke and halliday no differences in apparent age among the various phases or clear geographic age distribution patterns were evident satellite stocks in the southern part of the province have in general younger apparent ages clustered in the range 300 320 ma we suggest that in southern areas mica argon systems record the effect

dating mineralization using several isotopic methods an example from the south mountain batholith nova scotia canada abstract granitic plutons in the meguma terrane may be broadly divided into two suites 1 an areally predominant cogenetic suite of peraluminous granitoid rocks tonalite leucogranite and 2 an areally subordinate paraintrusive suite specialized in sn w mo cu f u p zn as which appears to have been produced by fluid interaction with either residual magma or crystallized rock granite related mineralization is generally considered to have developed during terminal stages of magmatic crystallization that lead to metasomatism and hydrothermal alteration previous geochronological data have suggested that the main cogenetic suite was emplaced at 350 375 ma whereas some of the paraintrusive suite is markedly younger 250 350 ma the apparently large time interval between the intrusion of the cogenetic suite and some of the mineralization suggests that they are not coeval and has led to the conclusions that the younger mineralization may be related to later magmatism and or tectonothermal events rocks associated with two mineral occurrences in the south mountain batholith that had previously yielded anomalously young isotopic ages millet brook and westfield have been analyzed for u pb and ar isotopes in an attempt to resolve this dilemma new geochronological data from the millet brook area indicate that intrusion of granodiorite at 377 5 3 ma nearly concordant monazite age was closely followed by intrusion of most other phases all of which had cooled through 375 c closure temperature for ar in muscovite by 377 373 6 ma 40 ar 39 ar plateau ages new data from westfield indicate that a paraintrusive porphyry was intruded at 385 2 ma upper intercept of a chord through four nearly concordant zircon fractions and that greisen muscovite cooled through the closure temperature by 368 2 6 ma 40 ar 39 ar plateau age these data indicate that a previously reported rb sr whole rock isochron age of 270 ma at westfield reflect isotopic resetting that occurred below the blocking temperature for 40 ar 39 ar in muscovite 375 c clearly further rb sr analysis is required to document this process other 250 300 ma ages in the meguma terrane are recorded along the tobeatic fault zone away from the fault ages increase upto 370 ma suggesting that the fault may have acted as an important pathway for fluids and heat that facilitated isotopic resetting rb sr whole rock and mineral systems may be affected after formation of an alteration assemblage associated with mineralization by the migration of rb and its concentration in secondary minerals

the generation and trapping of solitary waves over topography observations of tidal flow over a sill show that upstream solitary wave generation occurred in conjunction with the downstream movement of a streamline bifurcation over the obstacle crest solitary waves appeared upstream of the bifurcation riding on the surface stratification shear flow instabilities on the plunging interface were also evident and may contribute to wave generation through subharmonic interaction nonlinear waves generated downstream of an internal control became trapped in the supercritical flow

the effect of lateral heterogeneity on horizontal to vertical spectral ratio of microtremors inferred from observation and synthetics abstract horizontal to vertical h v spectral ratios of microtremors hvrm have been traditionally interpreted as representing either the s wave amplification directly or the rayleigh wave ellipticity for a horizontally layered structure however based on the diffuse field theory we have derived an alternative theoretical basis that hvrm corresponds to the square root of the ratio between the imaginary part of the horizontal green s function and that of the vertical one under that condition the 1d horizontal layering assumption is not needed to interpret hvrm as observational evidence of such non 1d hvrm we discovered significant directional dependency at a site on the uji campus kyoto university japan the observed microtremor north south vertical spectral ratios are quite stable and have only one peak around 0 5 hz on the other hand the east west vertical spectral ratios are smaller in amplitude and have higher peak frequencies and sometimes two separated peaks the directional dependency of observed hvrm is aligned to the axis of the 2d basin structure we performed numerical analyses by spectral element method using a unit load on the surface to examine the effect of the 2d basin structure on the imaginary parts of the green s functions we found that the 2d basin structure clearly changes the characteristics of the h v spectral ratios in both perpendicular and parallel directions relative to the basin axis thus we succeeded in theoretically simulating the qualitative difference between the h v spectral ratios for two orthogonal horizontal components of the hvrm observed on the uji campus online material snapshots and animations of wave propagation

barotropic and baroclinic annular variability in the southern hemisphere abstractthe leading patterns of large scale climate variability in the southern hemisphere are examined in the context of extratropical kinetic energy it is argued that variability in the southern hemisphere extratropical flow can be viewed in the context of two distinct and largely independent structures both of which exhibit a high degree of annularity 1 a barotropic structure that dominates the variance in the zonal mean kinetic energy and 2 a baroclinic structure that dominates the variance in the eddy kinetic energy the former structure corresponds to the southern annular mode sam and has been extensively examined in the literature the latter structure emerges as the leading principal component time series of eddy kinetic energy and has received seemingly little attention in previous work the two structures play very different roles in cycling energy through the extratropical troposphere the sam is associated primarily with variability in the meridional propagation of wave activity has a s

the petrology geochemistry and economic potential of the musquodoboit batholith nova scotia the musquodoboit batholith of southwestern nova scotia is a massive post tectonic granitoid intrusion that was emplaced into the regionally deformed and metamorphosed meguma group metasedimentary rocks the batholith is composed primarily of medium to coarse grained monzogranites into which two small 1 km2 porphyries and numerous dykes have been injected all rocks contain quartz alkali feldspar plagioclase muscovite and biotite with the exception of some leucocratic dykes cordierite is a major constituent in most monzogranitic rocks and also occurs in some leucocratic dykes andalusite and garnet 0are also present as accessory phases in some rocks major element chemical analyses indicate that all rock types in the musquodoboit batholith are peraluminous compositions resemble those of the eastern part south mountain batholith however slightly higher concentrations of al2o3 and p2o5 distinguish the musquodoboit batholith from the central part of the south mountain batholith major and trace

s type granites in the western superior province a marker of archean collision zones detailed field observations indicate that neoarchean s type granites were emplaced along and or proximal to some terrane tectonic boundary zones in the western superior province southeastern m

metallogeny of tin magmatic differentiation versus geochemical heritage tio 2 sn and rb sr sn variation diagrams for granitic fractionation series from various tin and non tin provinces do not support the concept of geochemical heredity of tin i e the assumption of a primary crustal sn anomaly in tin provinces the controlling factor for the generation of tin granites is a special bulk distribution coefficient of sn probably dependent on the oxygen fugacity of the melt

some comments about stratiform tin deposits in the stara kamienica chain southwestern poland the origin of the stratiform tin deposits in the schist belt of the stara kamienica chain southwestern poland is re examined based upon new data which has become available it is the author s opinion that no genetic implications should be attached to the stratiform character of the deposits hydrothermal metasomatism associated with acid intrusives of the variscan karkonosze massif introduced mineralizing fluids along tectonic lineaments

diurnal signals in vertical motions on the hebridean shelf in this paper we consider the interpretation of measurements of vertical velocity and backscatter signal intensity made using an acoustic doppler current profiler adcp mounted on the seabed at a position on the hebridean continental shelf the existence of vertically migrating scatterers is inferred from both the backscatter signal intensity and vertical velocity data which indicate migration rates of 2 3 cm s 1 and shows consistency between the displacement deduced from the vertical velocity and the observed movement of scatterers from the near bed to the near surface regions evident in temporal variations in the backscatter signal intensity independent evidence that the observed vertical velocities are largely due to movements of the acoustic scatterers relative to the water is obtained through comparison of the adcp vertical velocity data with vertical velocities inferred from the movement of the thermocline the close phase locking between the motion and sunset and sunrise times has led us to interpret the signal in terms of the diel vertical migration of zooplankton although no biological samples were collected during this study previous surveys of the area have identified species of copepod and euphausiid that are known to migrate the 12 d of data available show an initial period when there was a strong vertical migration signal and a later period during which the signal was not clear by combining the observed vertical and horizontal velocity components in a particle tracking model it is demonstrated that the change in the migration signal may be a result of the advection of the patch of migrating zooplankton away from the adcp during the later part of the observational period

precise u pb dating of meguma basement xenoliths new evidence for avalonian underthrusting u pb zircon and monazite dates for granulite facies basement xenoliths from the popes harbour dyke on the eastern shore of nova scotia provide strong evidence that the meguma terrane overlies avalo

plutonic and hydrothermal events in the ackley granite southeast newfoundland as indicated by total fusion 40ar 39ar geochronology results of total fusion 40ar 39ar dating eight biotites four muscovites and one hornblende of magmatic and hydrothermal stages of the high silica chemically zoned ackley granite indicate three distinct episodes of magmatic activity viz 410 378 374 and 355 ma and that the metallogenic system w sn mo evolved synchronously with only one of the magmatic phases the oldest suite is indicated by two biotite dates at 410 4 4 4 and 392 5 7 6 ma which are themselves considered as representing partial resetting related to a tectonothermal event of acadian age thus the 410 ma age offers the best estimate of intrusion although it must be considered a minimum the main magmatic pulse for the ackley granite is indicated by dates between 378 and 374 ma with most of these phases occurring in the southern part of the complex concordant hornblende biotite ages 374 8 3 8 and 372 3 4 8 ma respectively for one of the southern phases rencontre lake granite suggests rapid cooling for this part o

possible feedback path for low frequency atmospheric oscillations abstract equatorial low frequency oscillations with periods of 1 2 months are being intensively studied by many investigators a strong equatorial dipole pattern is observed in which atmospheric variables such as temperate wind and pressure are out of phase between the indian ocean indonesia region and the western pacific while it is generally thought that the oscillations make a complete circuit around the earth from their excitation region in the equatorial indian ocean western pacific the signal is more difficult to observe over the south america atlantic africa sector using analyses of four year of satellite derived microwave radiance data evidence is presented here for the possibility of a feedback route in the southern hemisphere the observed propagation path extends from the central equatorial pacific across lower south america and heads equatorward after passing south of africa the response route finally reenters the equatorial indian ocean with the correct phase to enhance the primary e

observations of intratidal variability of flows over a sill contraction combination in a chilean fjord underway velocity measurements were carried out for the first time in a chilean fjord using an acoustic doppler velocimeter with the purpose of elucidating the intratidal variability of flows through a pass paso galvarino the pass included a sill where the bottom sloped by roughly 30 and a coastline contraction of 90 the relatively small dimensions of the pass allowed for rapid sampling of the flow evolution throughout the tidal cycle the backscattered sound signal from the velocimeter and from an echo sounder were used to describe the vertical excursions of the pycnocline throughout the domain and to identify regions of enhanced vertical mixing within the pass the spatial variability of the flow in the pass was consistent with uniform two layer flow at the narrowest section of the contraction the pycnocline dropped sharply around both maximum flood and maximum ebb while the flow accelerated downstream relative to the tidal flow the slope of the pycnocline changed sign from flood to ebb which was atypical of other fjord observations but could be explained by the transitions from subcritical to supercritical flow these transitions switched location at either side of the narrowest section of the contraction leeward of this section increased sound backscatter suggested intensified turbulence that extended over a greater area during ebb than during flood because the distance between the point of pycnocline drop and the end of the pass was longer during ebb enhanced vertical mixing within the pass was reflected in the tidally averaged fields by a three layer flow that consisted of near surface and near bottom flow converging toward the pass and flow around the pycnocline diverging away from the pass

amplification of seismic response of a large deep seated landslide in tokushima japan abstract to better understand seismic site responses of deep seated landslides we carried out long term seismic monitoring of a target landslide reactivated by a rainstorm in 2004 accompanying typhoon namtheun in naka town tokushima prefecture japan five seismometers with high sensitivity were installed at different locations on landslide areas with different elevations by examining numerous records of earthquake events we distinguished the effects of material contrast and topography on these localized amplifications for different areas and summarized their features with help of detailed geological and geophysical surveys to analyze differences in amplification the hvsr method calculating the horizontal to vertical spectral ratio of ground motion was applied the amplification on a landslide block with an hvsr peak amplitude smaller than 5 and resulting from topography is predominantly perpendicular to the direction of elongation of the mountain ridge however the amplification revealed by hvsr peak amplitude of 3 to 5 resulting from material contrasts in multiple strata showed differing amplification directions by examining the relationship between the hvsr peak amplitude and shear velocity profiles we found that the amplifications at different frequencies are greatly affected by the extent of material contrasts this may explain why the toe part of the slope with ancient landslide deposits generally shows the greatest ground motion characterized by hvsr peak amplitude normally 10 this type of strong amplification due to material contrasts may result in severe damage to residential areas in mountainous areas during an earthquake and should be considered for the construction of buildings on landslide areas

dynamic response of the chamousset rock column western alps france 1 this paper investigates the variation of the first resonance frequency of the chamousset limestone column 21 000 m3 vercors french alps before its collapse in november 2007 the site was instrumented with seismometers and extensometers during a 4 month period with some gaps in the measurements experimental results and numerical modeling showed that the resonance frequency of a prone to fall column can be derived from the spectra of continuous seismic noise records at the chamousset site the evolution of the resonance frequency appeared to be strongly controlled by the temperature when temperatures were positive slight resonance frequency variations correlated well with thermal fluctuations irreversible damage can occur during freeze thaw cycles and to a lesser extent during strong wind it coincided with a significant drop in resonance frequency which was interpreted as the result of rock bridge breakage this hypothesis is supported by fresh rupture observations after the collapse seismic event records and numerical modeling this study suggests that seismic noise recording could be used for assessing the potential failure of unstable columns in rigid rocks

origin of the granites and related sn and pb zn polymetallic ore deposits in the pengshan district jiangxi province south china constraints from geochronology geochemistry mineral chemistry and sr nd hf pb s isotopes the pengshan sn and pb zn polymetallic deposits are located in the south margin of the jiujiang ruichang jiurui district of the middle lower yangtze river metallogenic belt in south china four large deposits include huangjinwa zengjialong jianfengpo and zhangshiba the former three are sn dominant deposits which occur as stratiform orebodies in the contact zones of the pengshan granites and within the country rock strata whereas zhangshiba consists of stratiform pb zn orebodies within the precambrian metasedimentary strata in this study we present results on zircon u pb ages major and trace elements and mineral chemistry as well as sr nd hf isotope data of the granites pb and s isotopes of both the sn dominant and pb zn dominant deposits and u pb dating of cassiterite from the pengshan district shrimp and la icp ms zircon u pb dating shows that the pengshan granites were emplaced in the early cretaceous 129 128 ma which is in good agreement with the u pb dating 130 128 ma of cassiterite from the jianfengpo sn deposit the pengshan granites consist mainly of weakly peraluminous highly fractionated i type affinity granitic rocks detailed elemental and isotopic data suggest that the granites formed by partial melting of mesoproterozoic metamorphic basement materials with minor input of mantle derived melts the mineral chemistry of biotite demonstrates that the pengshan granitic magma had a low oxygen fugacity thereby precluding the tin dominantly partitioning into the rock forming silicate minerals and favoring accumulation in the exsolved residual liquid during magma crystallization stages sulfur isotopes show a relatively heavy sulfur isotopic composition from 5 8 to 17 6 and no difference for sulfur isotopes between the sn deposits 5 8 13 4 huangjinwa zengjialong jianfengpo and the pb zn deposit mostly 7 1 13 0 except for one 17 6 zhangshiba the sulfur isotope data of pyrite from the host sedimentary rocks show relatively higher 34s values of 22 7 28 7 lead isotopes indicate that the granites have higher 206pb 204pb 207pb 204pb and 208pb 204pb ratios than the host precambrian metasedimentary rocks and the sulfide minerals from the orebodies fall in between them again there is no difference for pb isotopes between the sn deposits huangjinwa zengjialong jianfengpo and the zhangshiba pb zn deposit the coincidence in s and pb isotope compositions for sn and pb zn deposits suggests that similar sources for these mineralization possibly derived from a mixed source of the granitic magmas and the precambrian metasedimentary rocks these data therefore favor of a magmatic hydrothermal origin for both the sn and pb zn polymetallic mineralization in the pengshan district

geophysical and structural signatures of syntectonic batholith construction the south mountain batholith meguma terrane nova scotia summary the late devonian south mountain batholith is a very large 7000 km2 composite peraluminous granitoid complex situated within the meguma terrane of the northern appalachians it is made up of two suites of granodioritic to leucogranitic plutons emplaced at approximately 380 370 ma during the acadian orogeny i e during the collision of gondwana with the eastern margin of north america a significant geophysical and geological database makes the south mountain batholith a type example of a very large syntectonic batholith emplaced within a collisional orogen gravity models reveal the plutons have flat or gently dipping floors at approximately 7 0 km depth and aspect ratios 651 they are underlain by deeper 10 km elongate northeast southwest trending roots that may indicate magma feeder zones dyke transport of granitic magma and the progressive construction of plutons by sheet injections are supported by field observations and by mapping of the anisotropy of magnetic susceptibility at the pluton scale the very narrow deformation aureole within the country rocks suggests lateral spreading of the plutons was not the main space creation mechanism during emplacement space was mostly created by vertical displacements of country rocks the data are consistent with a laccolithic model for syntectonic batholith assembly the laccolithic plutons may have been emplaced at the base of the meguma supergroup metasedimentary rocks suggesting a maximum thickness of approximately 7 0 km for the supracrustal rocks in the meguma terrane

the east kemptville tin deposit yarmouth county nova scotia a pb isotope study of the leucogranite and mineralized greisens evidence for a 366 ma metallogenic event pb isotopic data for whole rock leucogranite and mineral separates variably mineralized greisen and galena from the east kemptville sn cu zn ag deposit yarmouth county southwestern nova scoti

anomalous concentrations of seismically triggered rock falls in pacoima canyon are they caused by highly susceptible slopes or local amplification of seismic shaking anomalously high concentrations of rock falls were triggered in pacoima canyon los angeles california during the 1994 northridge earthquake similar concentrations were also documented from the 1971 san fernando earthquake using an engineering rock mass classification that evaluates the susceptibility of rock slopes to seismic failure based on the fracture properties of a rock mass in terms of a numerical q value that describes rock quality the rock slopes in pacoima canyon were compared with rock slopes in surrounding areas where topography and lithology are similar but rock fall concentrations from the earthquakes were much lower a statistical comparison of q values from five sites surrounding pacoima canyon indicates that seismic susceptibilities are similar to those within pacoima canyon differences in the characteristics of rock slopes between these sites are not sufficient to account for the relatively high concentrations of rock falls within pacoima canyon as compared to low concentrations elsewhere by eliminating susceptibility differences as a cause the most likely explanation for the differences in rock fall concentrations is anomalously high shaking levels in pacoima canyon possibly resulting from topographic amplification within the canyon manuscript received 21 may 2001

a multivariate approach to geochemical distinction between tin specialized and uranium specialized granites of southern nova scotia like most granitoid bodies that host significant granophile deposits the south mountain batholith smb of nova scotia consists of an earlier suite intruded by a later suite of smaller plutons that are more silicic and peraluminous the latter generally show a range of other geochemical features that readily identify them as specialized and allow for their separation from the earlier non specialized granites in the case of mineralization associated with the smb we can go one step further and clearly separate the specialized granites into stanniferous and uraniferous series which can be identified even where no sn or u enrichment is present although this can be done successfully using simple histograms of a number of elements li p sn and f we show that combining all elements in discriminant analysis guarantees 100 success in separating the two groups r mode factor analysis aids in accounting for the variance within each group the most important effect being a biotite factor because of bo

late devonian lamprophyric dykes in the meguma zone of nova scotia hornblende rich lamprophyric dykes from southeastern nova scotia are contemporaneous with the large peraluminous granitic batholiths ca 370 ma of the meguma zone and may be closely associated with their origin

the scotian basin offshore nova scotia thermal history and provenance of sandstones from apatite fission track and 40ar 39ar data apatite fission track and 40ar 39ar age spectrum data from sandstone drill core minerals taken from depths of 2 5 km in nine wells from the scotian basin are presented and interpreted in terms of the thermal history of the basin and the provenance of its sediments the focus of the study is a comparison of the data from these thermochronometers with each other and with previously published vitrinite reflectance and aromatization isomerization a i reactions in biomarker compounds from the same or nearby wells apatite fission track ages are generally in agreement with expectations in that they trend to zero at a depth of 4 km corrected bottom hole temperature 120 c shallower lower present temperature samples are partially annealed the degree of partial annealing correlates closely with the degree of a i reactions both thermal indicators are activated over the temperature range 60 120 c samples from two wells mic mac j 77 and erie d 26 are anomalous they are more annealed than present formati

characteristics of ree and other trace elements in response to successive and superimposed metasomatism within a portion of the south mountain batholith nova scotia canada abstract successive and superimposed periods of late to post magmatic metasomatism have resulted in mineralogical and textural modification within leuco monzogranitic rocks of the big indian lake polyphase intrusive suite bipis the alteration and associated mineralization exhibit a transition from an early pervasive style to a later fracture controlled style and can be defined by diagnostic ree and other trace element behavior while the anomalous behavior of some elements mno ta u k rb hree is attributed to metasomatic hydrothermal activity the compatible behavior of b f li w and rb appears to have been governed by predominately magmatic processes all elements including al can be mobilized during repeated fluid rock interaction the behavior of ree during evolution of the bipis indicates that they also were affected by both magmatic lree depletion eu depletion and metasomatic hree lree enrichment eu enrichment depletion processes the remobilization and subsequent redeposition of trace elements is dependent upon the nature and stability of the metasomatic mineral assemblages in this respect a metasomatized granitic rock could reflect a ree pattern similar to that of an unaltered equivalent

geochemical trends in the ackley granite southeast newfoundland their relevance to magmatic metallogenic processes in high silica granitoid systems the ackley granite occupying an area of approximately 2700 km2 was intruded at about 355 ma across the boundary between the avalon and gander tectonic terranes of southeast newfoundland it is dominated by k feldspar megacristic and equigranular biotite bearing granite with subordinate granodiorite but 10 separate phases have been recognized also including hornblende and muscovite bearing varieties small aplite pegmatite type molybdenite deposits occur in a southwest lobe and cassiterite wolframite bearing quartz topaz greisens are found as steeply dipping veins and pods within a south central lobe of the pluton a geochemical study of 357 rock samples randomly distributed on a grid of 2 km spacing shows systematic geographic variation in the concentrations of a range of elements the concentrations of silica and some other elements show a relatively abrupt change approximately 10 15 km west of the projected boundary between the avalon and gander terranes indicating that the different terranes ha

1 d and 2 d resonances in an alpine valley identified from ambient noise measurements and 3 d modelling summary h v spectral ratios are regularly used for estimating the bedrock depth in 1 d like basins exhibiting smooth lateral variations in the case of 2 d or 3 d pronounced geometries observational and numerical studies have shown that h v curves exhibit peculiar shapes and that the h v frequency generally overestimates 1 d theoretical resonance frequency to investigate the capabilities of the h v method in complex structures a detailed comparison between measured and 3 d simulated ambient vibrations was performed in the small size lower romanche valley french alps which shows significant variations in geometry downstream and upstream the sechilienne basin analysing the h v curve characteristics two different wave propagation modes were identified along the valley relying on previous geophysical investigation a power law relationship was derived between the bedrock depth and the h v peak frequency which was used for building a 3 d model of the valley geometry simulated and experimental h v curves were found to exhibit quite similar features in terms of curve shape and peak frequency values validating the 3 d structure this good agreement also evidenced two different propagation modes in the valley 2 d resonance in the sechilienne basin and 1 d resonance in the external parts this study underlines the interest of h v curves for investigating complex basin structures

paleomagnetism of the gays river zinc lead deposit nova scotia pennsylvanian ore genesis the gays river zinc lead deposit is the largest known mississippi valley type deposit in the mississippian windsor group of atlantic canada thermal and af demagnetization show that both ore and host rock have very similar magnetic characteristics stability tests constrain the magnetization to be mid mississippian to late pennsylvanian the pole position from the ore and host rock sites falls next to the pennsylvanian apw path suggesting an 8 clockwise rotation of the meguma platform relative to the craton regional thermal history and geochemical evidence suggest that the zinc lead ore magnetization and host rock remagnetization are coeval

ground motion in the presence of complex topography earthquake and ambient noise sources to study the influence of topography on ground motion eight seismic recorders were deployed for a period of one year over poverty ridge on the east side of the san francisco bay area california this location is desirable because of its proximity to local earthquake sources and the significant topographic relief of the array 439 m topographic amplification is evaluated as a function offrequency using a variety of methods including reference site based spectral ratios and single station horizontal to vertical spectral ratios using both shear waves from earthquakes and ambient noise field observations are compared with the predicted ground motion from an accurate digital model of the topography and a 3d local velocity model amplification factors from the theoretical calculations are consistent with observa tions the fundamental resonance of the ridge is prominently observed in the spectra of data and synthetics however higher frequency peaks are also seen primarily for sources in line with the major axis of the ridge perhaps indicating higher resonant modes excitations of lateral ribs off of the main ridge are also seen at frequencies consistent with their dimensions the favored directions of resonance are shown to be transverse to the major axes of the topographic features

metallogenic provinces geochemical provinces and regional geology what causes large scale patterns in low density geochemical maps of the c horizon of podzols in arctic europe the 2 mm fraction of 605 samples of the c horizon of podzols collected from an area of 188 000 km2 in the european arctic was analysed for more than 40 chemical elements the results were used to construct geochemical maps which showed clear regional distribution patterns notwithstanding the very low sample density of 1 site per 300 km2 some of these patterns fit established lithological boundaries others fit lineament structures in the area and underline the relative importance of certain tectonic directions some of which have not yet been delineated on existing geological maps some mark large scale hydrothermal events and related alteration finally some are connected with prominent known ore deposits occurring in the area however several large deposits and even famous metallogenic provinces fe ni cu are hardly or not at all reflected in the regional geochemical maps in their present definitions geochemical provinces and metallogenic provinces are thus not necessarily related special geochemical features can occur at very different scales the term geochemical province is so imprecise in terms of processes leading to regional scale geochemical features that it should be avoided low density geochemistry can be used to aid the interpretation of the geological evolution of large regions it can also be used to find prospective areas within such regions

geochemistry of tin bearing granitic rocks abstract the use of rb ba and rb sr ratios as guides to tin mineralization has only local interest because each of the correlations log rb ba log sn and log rb sr log sn of granitic series has a different slope in every area the ternary relation between rb ba and cs is useful to distinguish between sn bearing granitic rocks and non mineralized granitic rocks the sn bearing granitic rocks are late differentiates of anatectic melts s type with primary albite and muscovite and greisenized granites with metasomatic albite and muscovite they have high sn rb contents rb ba and rb sr ratios and low ba and sr contents the portuguese sn bearing muscovite granites aplites pegmatites and hypothermal quartz veins have muscovites richer in sn than those of greisenized granites f and sn of muscovites from portuguese sn bearing granitic rocks are positively correlated cassiterite crystallization seems to be independent of f h 2 o f in hf and favoured by a decrease in fo2

late paleozoic collision delamination short lived magmatism and rapid denudation in the meguma terrane nova scotia canada constraints from 40ar 39ar isotopic data the meguma terrane consists of 8 15 km of early paleozoic stratified rocks deposited on a continental basement that were deformed and metamorphosed during the late paleozoic as a result of lithospheric plate collision the oldest cleavage previously published whole rock 40ar 39ar plateau ages of 415 395 ma dates the onset of crustal thickening which was followed by voluminous but short lived late devonian granitic and minor mafic magmatism 380 370 ma this magmatism may have been the product of delamination of the lower lithosphere and upwelling of asthenosphere which effected melting above the new moho and resulted in intrusion at depths of 5 12 km 40ar 39ar plateau ages of hornblende muscovite and biotite indicate that at the present erosion level most of the meguma terrane cooled through 300 c by 368 360 ma slightly earlier than for the southwestern meguma terrane ca 345 ma the present erosion level was exhumed by the latest devonian early carboniferous visean the age of the

investigation of 3 d basin structures in the izmit bay area turkey by single station microtremor and gravimetric methods summary we investigate 3 d basin structures and site resonance frequencies in the izmit bay area of turkey by new geophysical surveys based on 239 single station microtremor and 405 point gravity measurements a fundamental resonance frequency map of the izmit bay was produced from the main peak in the horizontal to vertical component spectral ratio hvsr of microtremors the hvsr analysis of the microtremor data reveals single double broad peaked or no peak type hvsr curves varying in accordance with the surface geology and spatial extent of the three basins present in the izmit bay area in the deepest sections of the izmit golcuk and derince basins of the izmit bay the fundamental resonance frequencies are dominantly 0 24 0 30 hz these resonance frequencies should be taken into consideration along with higher mode frequencies to construct earthquake resistant structures in the izmit bay area the 3 d gravimetric bedrock depth map of the izmit basin shows that the basin has an asymmetric shape with its deepest section coinciding with the surface trace of the north anatolian fault the northern shoulder of the basin has a gentle dip on the kocaeli peneplain side and the southern shoulder is much steeper and it is bounded by the samanli mountains we derive a power law relationship that correlates the fundamental site resonance frequencies with the sedimentary cover thickness obtained from the gravity and shear wave velocity data in the izmit bay we use this relationship to estimate bedrock depths beneath golcuk and derince basins our estimation of maximum basin depths is 1400 m for the izmit and is 800 m for the golcuk and derince basins finally we have analysed a converted sp phase from a local earthquake recording made at site cmp to calculate and verify the sediment thickness estimations obtained from our gravimetric and microtremor analyses this calculation shows close agreement with that of the gravimetric and microtremor results our results show that the basins in the izmit bay area have a very thick sedimentary cover with very low shear velocities underlined by hard bedrock forming a sharp impedance contrast we anticipate that these results will be a key contribution to the quantitative assessment of seismic hazard for the izmit bay area before the occurrence of strong earthquakes in the marmara region

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

geochronological evidence for multiple tectono thermal overprinting events in the east kemptville muscovite topaz leucogranite yarmouth county nova scotia canada the east kemptville muscovite topaz leucogranite located in yarmouth county nova scotia canada is host rock to the only producing primary tin deposit in north america 56 mt 0 165 sn previous geochronological studies include i rb sr whole rock analyses of the quartz topaz greisens which indicated a date of 337 5 ma and ii 40ar 39ar analyses of greisen muscovite which indicated apparent plateau dates of ca 300 ma however the pervasive development of deformational fabrics at east kemptville suggests that both the rb sr whole rock and 40ar 39ar muscovite ages are at best minimum estimates for the inferred time of mineralization in the present study rb sr whole rock and mineral muscovite plagioclase k feldspar analyses and 40ar 39ar incremental step heating of a muscovite separate indicate the following i diffusion of sr on the whole rock scale terminated at 344 5 ma 11 point isochron date coincident with closure of muscovite to intracrystalline diffusion of ar apparent plat

origin of topaz bearing and related peraluminous granites of the late devonian davis lake pluton nova scotia canada crystal versus fluid fractionation abstract the davis lake pluton in the late devonian south mountain batholith in southwestern nova scotia canada is composed of peraluminous leucomonzogranites and subordinate topaz bearing leucogranites that host greisens and a primary tin deposit the concentrations of incompatible trace elements e g rb li u f ta and sn and element e g k rb nb ta and la sm and isotopic ratios e g 206 pb 204 pb and 87 sr 86 sr display a spatial zonation the granitic rocks were generated by extensive fractional crystallization of major phases feldspars and biotite and accessory minerals monazite apatite and zircon in a compositionally zoned magma chamber fractional crystallization of the evolving f rich peraluminous granitic magma was accompanied particularly in later stages by fluid fractionation involving fluorine complexing fluid fractionation was a major differentiation process during the terminal stages of the pluton s evolution it played an important role in the genesis of the evolved rocks which are characterized by low k rb 24 150 nb ta 1 6 la sm 1 5 4 and eu eu 0 01 0 3 ratios these ratios as well as the enhanced concentrations of li rb u ta and sn in these rocks correlate with f fluorine rich fluids modified the rb sr and u pb ratios which produced the distinct variations of 87 sr 86 sr and 206 pb 204 pb isotopic ratios the parent magma was formed by dehydration melting of lower crustal metasedimentary rocks the melting was related to crustal thickening in association with terrane and collision along the eastern margin of the appalachians

site effects modelling applied to the slope affected by the suusamyr earthquake kyrgyzstan 1992 abstract in 1992 a large magnitude earthquake ms 7 3 hit the northern part of the kyrgyz tien shan range where it triggered rockslides and many debris slides or flows one of these mass movements occurred on the chet korumdy ridge located in the suusamyr basin it consists of a multi rotational debris slump in its upper part that turned into a debris flow in its lower part involving arenitic material overlying silty clays it has a volume of about 0 5 to 1 10 6 m 3 a maximum thickness of 40 m and a run out of 200 m the field observations and measurements carried out on this slope suggest that local amplification effects could have contributed to the initiation of the seismic failure to test this hypothesis in the lack of instrumental evidence of local ground motion recordings we conducted a sensitivity study of site effects based on a numerical analysis in the visco elastic domain with a two dimensional finite difference code varying the topography and the geology of the investigated slope topographic site effects are found to be less important than geological site effects which are controlled by the contrast of impedance between the surface materials and the bedrock the geometry of the low velocity surface layer has also an influence on site effects which is often difficult to be distinguished from pure topographic effects considering all modelling results we conclude that site amplifications alone cannot have triggered the suusamyr landslide during the 1992 earthquake the static slope stability analyses done in previous studies revealed that the suusamyr failure neither can have a purely static origin even if the water table is very high within the arenite layer only a minor failure develops in the lower part of the slope therefore we believe that the triggering of the suusamyr landslide is a consequence of pore pressure build up in areas characterized by significant ground motion amplifications

compressional and shear wave velocity versus depth relations for common rock types in northern california abstract this article presents new empirical compressional and shear wave velocity vp and vs versus depth relationships for the most common rock types in northern california vp versus depth relations were developed from borehole laboratory seismic refraction and tomography and density measurements and were converted to vs versus depth relations using new empirical relations between vp and vs the relations proposed here account for increasing overburden pressure but not for variations in other factors that can influence velocity over short distance scales such as lithology consolidation induration porosity and stratigraphic age standard deviations of the misfits predicted by these relations thus provide a measure of the importance of the variability in vp and vs caused by these other factors because gabbros greenstones basalts and other mafic rocks have a different vp and vs relationship than sedimentary and granitic rocks the differences in vs between these rock types at depths below 6 or 7 km are generally small the new relations were used to derive the 2005 u s geological survey seismic velocity model for northern california employed in the broadband strong motion simulations of the 1989 loma prieta and 1906 san francisco earthquakes initial tests of the model indicate that the vp model generally compares favorably to regional seismic tomography models but that the vp and vs values proposed for the franciscan complex may be about 5 too high

the role of collisional tectonics in the metallogeny of the central andean tin belt abstract the inner arc of the central andes broadly corresponding to the eastern cordillera is the location of a rich tertiary and triassic sn w ag base metal metallogenic province commonly referred to as the bolivian tin belt we propose that the tertiary metallogeny which generated most of the tin ores was a direct consequence of discrete collisions between the south american plate and the nazca slab and sub slab mantle during the ongoing andean orogeny evidence supporting this proposal include 1 the coincidence of the tin province and the inner arc in a marked hump in the andean orogen which may represent tectonic indentation 2 the symmetry of the tin province with respect to the bolivian orocline the axis of which corresponds to the direction of highest compression 3 the relative symmetry of the magmatism and tin mineralization with respect to this axis 4 the concurrent timing of mineralization and compressional pulses 5 the similar host rock geochemistry and ore lead isotope data testifying to a common crustal reservoir and 6 the striking similarity of the igneous suites associated with the ore deposits to those from typical collisional orogens a number of studies have called upon a persistent tin anomaly to explain the metallogeny of the region we propose instead that the latter is better explained by periodic compressional interaction between the farallon nazca oceanic plate and the south american continent this led to the generation of peraluminous magmas which during fractional crystallization exsolved the fluids responsible for the voluminous sn w mineralization

u pb zircon geochronology of early permian to late triassic rocks from singapore and johor a plate tectonic reinterpretation article i nfo the results of u pb zircon geochronology of permian to middle triassic granitoids from singapore and neighbouring johor are presented rhyolite from pulau sibu is 276 5 ma gabbros from singapore give ages of 260 2 to 249 2 ma granites from singapore give ages from 249 2 to 230 6 ma and rhyolite from telkuma gives an age of 238 2 ma u pb detrital zircon age spectra from a late triassic conglomerate from singapore show carboniferous mid dle triassic and late triassic spikes at 350 245 and 217 ma respectively these new data when combined with published u pb zircon ages allow a revision of the plate tectonic evolution of the malaysian peninsula region a tin bearing magmatic arc evolved in the eastern malaysian peninsula part of indochina from the early permian to the middle triassic when the palaeo tethys ocean was subducted and sibumasu continental lithosphere was rifted from pangea this opened up the neo tethys ocean that the granitoid ages show a progressive decrease in age from pulau sibu 276 5 ma to singapore 230 6 ma suggests that during this andean type orogenic phase the subduction zone rolled back and steepened causing the locus of mainly i type magmatism to migrate from east to west in present day coordinates across the eastern and central belts and stretch the lithosphere as it did so in the late triassic sibumasu collided with indochina causing the western belt sibumasu to over thrust the central belt indochina along the bentong raub suture the lower half of the thickened crust formally the tin bearing indochina plate was partially melted and pre dominantly s type tin bearing granites were intruded into the upper crust formally sibumasu this late triassic collisional phase is the indosinian orogeny in peninsular malaysia

site effects in unstable rock slopes dynamic behavior of the randa instability switzerland we evaluate the dynamic response of the large around five million cubic meters unstable rock slope at randa switzerland based on ground motion recordings during small earthquakes seismic measurements revealed strong polarization of the wavefield in the direction of maximum slope displacement with spectral amplification factors 5 within the unstable area results further highlighted resonant frequencies of both the large unstable rock mass and individual blocks within it block vibration was confirmed by phase analysis of in situ displacement measurements from two bounding tension fractures during a small earthquake numerical simulation using a discontinuous elastic model showed that the presence of steeply dipping compliant fractures is crucial for recreating the observed site response such fractures are common in rock slope instabilities and are here shown to contribute to polarization and amplification of seismic shaking site effects that are rarely considered for hard rock slopes and which may influence the potential for earthquake triggered failure

40ar 39ar dating of hydrothermal biotite from high grade gold ore tangier gold deposit nova scotia further evidence for 370 ma gold metallogeny in the meguma terrane a hydrothermal biotite carbonate alteration zone adjacent to a high grade multi ounce gold vein in the tangier gold deposit meguma terrane nova scotia has given an 40 ar 39 ar plateau age of 374 ma the alteration halo is part of a vein package in the hinge zone of the tangier anticline which contains abundant auriferous quartz veins formed during flexural slip folding during a late stage reactivation of the regional fold belt the 374 ma age is similar to 40 ar 39 ar ages determined for hydrothermal vein minerals at seven other meguma gold districts thereby suggesting a terrane wide metallogenic event a similar age of vein formation and by inference gold mineralization and granite emplacement across the meguma terrane suggest that the cospatial and cotemporal nature of the two geological events may be related an integrated model including anatexis and devolitization of the lower crust possibly as a consequence of overriding a mantle plume in concert with late stage reactivation of the fold belt owing to continued transpression along a terrane bounding fault is proposed