the role of magma mixing in the petrogenesis of mafic alkaline lavas rockeskyllerkopf volcanic complex west eifel germany the quaternary rockeskyllerkopf volcanic complex rvc comprises three spatially and temporally distinct volcanic centers that can also be distinguished on the basis of their geochemical signatures all the volcanic products in the complex are olivine basanites whose major and trace element compositions span almost the entire range defined for the west eifel field as a whole the rvc lavas have lower al2o3 na2o and y contents and higher tio2 cao k2o sc v co rb and ba than the tertiary lavas in nearby hocheifel volcanic field within the complex the oldest south east lammersdorf center sel comprises primitive lavas with an average mgo content of 11 wt and lan ybn of 29 2 the second center mauseberg has similar mgo to sel but is distinct in its much higher lan ybn of 42 2 the rockeskyllerkopf center which was erupted after a break in activity comprises lavas similar in composition to the sel center but with distinctly higher al2o3 and lower mgo contents given the lack of evidence for significant fractionation or assimilation in the rvc lavas we attribute the compositional variations within and between the centers of the rvc to be due to variations in the composition of the source region in combination with magma mixing our preferred model involves 1 5 partial melting of lree enriched mantle in the garnet stability field likely within the thermal boundary layer at the base of the lithospheric mantle these melts mixed to variable degrees with 2 4 partial melts of phlogopite spinel peridotite formed at higher levels in the modally metasomatised lithospheric mantle

structure of the wollaston lake reflector trans hudson orogen canada from reflection avo analysis fractured diabase intrusion fluids or silicified shear zone abstract a nearly 160 km long wollaston lake reflector wlr observed in seismic reflection profile s2b of the 1994 lithoprobe trans hudson orogen transect thot in northern saskatchewan canada is among the most spectacular and well recorded features imaged within the crystalline crust based on modeling of its normal incidence reflectivity the observed bright spot reflector was originally interpreted as a series of tabular diabase intrusions in order to further elucidate its structure we reprocessed line s2b and analysed the wlr for the amplitude variations with offset avo by contrast to conventional approximate avo analysis we used the exact zoeppritz equations and considered a thin layer mixed positive and negative polarities reflectivity the results suggest two possible interpretations of the wlr 1 the reflector caused by a massive mafic intrusion as suggested earlier in which case the intruded rocks should have anomalous poisson s ratios of 0 33 and 2 the wlr represents a silicified shear zone with only moderate e g 5 10 alteration of the host rock and 0 2 although both of these models may to some extent co exist within the wlr its brightness sharpness great lateral extent and smooth shape favour the second interpretation in both models a fractured fluid filled zone within a major crustal detachment should have played a key role in the formation of the wlr the association of the reflector with laterally and depth migrating fluids is also supported by magneto telluric measurements of crustal conductivity beneath the wlr analogies from the studies of the kola superdeep borehole russia where free or metamorphic fluids were found at comparable depths also suggest that fluids may contribute to wlr structure and formation

thermokarst lake basin sediments tuktoyaktuk coastlands western arctic canada three stages of deposition are distinguished in thermokarst lake basin sequences in ice rich permafrost of the tuktoyaktuk coastlands western arctic canada 1 widespread retrogressive thaw slumping around lake margins that rapidly transports upland sediments into thermokarst lakes forming a distinctive basal unit of impure sand and or diamicton 2 a reduction or cessation of slumping because of the pinching out of adjacent ground ice slump stabilization or climatic cooling that reduces the input of clastic sediment permitting reworking of sediment around lake margins and suspension settling principally in basin centres 3 lakes drain and deposition may continue by gelifluction and accumulation of in situ peat or aeolian sand radiocarbon dating of detrital peat and wood from a progradational sequence basal unit defines a lateral younging trend in the direction of progradation a progradation rate is calculated to be 4 cm yr 1 consistent with rapid deposition during stage 1 above the nonuniform nature of the trend is attributed to episodic influxes of old organic material by slumping and reworking by waves and currents in comparison with thermokarst lake basin sequences previously described in alaska canada and siberia the middle unit of those in the tuktoyaktuk coastlands is similar whereas the basal unit is generally thicker and by contrast often contains diamicton these differences are attributed respectively to larger scale resedimentation of upland sediments by retrogressive thaw slumping and debris flow deposition in thermokarst lakes in the tuktoyaktuk coastlands compared with the sediments within supraglacial lakes in areas of moderate to high relief the middle unit of thermokarst lake basin sequences in the tuktoyaktuk coastlands lacks clastic varves and the basal unit is much thinner and texturally less variable these differences are attributed to higher relief and larger volumes of meltwater and glacigenic sediment in supraglacial lakes which promote more suspension settling and resedimentation of glacigenic sediment than in thermokarst lakes in the tuktoyaktuk coastlands it may be impossible to distinguish glacial and periglacial thermokarst lake basin sediments in permafrost areas of incomplete deglaciation not only is it often difficult to distinguish intrasedimental and buried glacier ice but the depositional processes associated with thaw of both ice types are presumably the same and the host sediments very similar

wave scattering theory in analysis of p wave anomalies at norsar and lasa summary observed travel time and amplitude anomalies at the norsar and lasa arrays are significantly larger than the measurement errors and cannot be explained in terms of deterministic crust and upper mantle structural models for the respective siting areas in this paper the chernov theory is used in modelling the crust and upper mantle as a random medium and also to estimate to what extent such models can account for the observed anomalies we find that the random medium modelling can explain 50 60 per cent of the variance of the time and amplitude anomalies at norsar the corresponding results for lasa are 50 60 per cent and 25 per cent respectively in contrast reasonable deterministic models cannot account for even 25 per cent of this variance while the random medium model can provide a satisfactory explanation of the observational data extensive tests have revealed that the parameters characterizing the random medium cannot be uniquely determined from the data the reasons underlying this limitation are discussed

late holocene diatom biostratigraphy and sea level changes in the southeastern beaufort sea late holocene sediments from the atkinson point area were analysed to provide quantitative reconstructions of recent sea level changes in the southeastern beaufort sea the succession of diatom assemblages in five cores revealed paleoenvironmental changes induced by the transgression of the beaufort sea during successive periods of lacustrine conditions breaching and flooding of thermokarst lakes by the sea and the landward migration of sandy spits based on radiocarbon dates and quantitative paleodepth determinations a relative sea level curve for the late holocene has been developed despite a loss of temporal precision due to old carbon contamination an envelope of sea level change has been defined for the last 2 ka bp suggesting a sea level rise in the order of 1 1 mm a 1 for the last millennium this paper presents the first sea level reconstruction inferred from a diatom based transfer function it represents an improvement over traditional methods which were limited to qualitative estimates of

compositional variation and the origin of deep crustal reflections abstract identifying the sources of crustal reflections is essential for deriving more geological information from deep crustal reflection profiles theoretical and model studies help place constraints on the role of compositional variation in producing deep crustal reflections analysis of laboratory derived velocities and densities of rock types typical for the continental crust indicates that reflection coefficients are generally small but significantly 17 of the possible reflection coefficients have magnitudes between 0 1 and 0 2 comparison between reflection coefficients derived from well logs and reflections observed in associated seismic profiles indicates that constructive interference associated with geological layering is at least as important as the magnitude of the reflection coefficients for producing detectable reflections constructive interference can increase reflection amplitude by two to three times but is limited to a relatively narrow range of layer thickness for a typical 10 40 hz seismic wavelet and typical crustal velocities of about 6 km s constructive interference occurs for layer thickness ranging between about 35 and 80 m layers thinner than 35 m interfere destructively if reflections result from compositional variation seismic models of hypothetical and observed geologic relations provide analogs for interpreting complex reflection patterns observed in deep crustal reflection profiles such models show reflection patterns similar to those observed in the reflection profiles the models indicate that the reflections could originate in the complexly deformed and intruded terranes that are common in the crystalline crust and it may not be necessary to appeal to unobserved phenomena such as special lamellae or fluid filled fractures to explain the reflections

evidence and implications of an extensive early mesozoic rift basin and basalt diabase sequence beneath the southeast coastal plain regional seismic reflection profiles across the georgia and south carolina coastal plain provide a detailed view into the internal structure and stratigraphy of the buried triassic jurassic south georgia basin reflection data indicate that the basin is a complex composite of smaller individual basins which vary drastically along strike these basins are relatively wide along north south profile maximum 100 km but appear to be more restricted along strike in cross section the basins are asymmetric being typically bounded on their south sides by an interpreted north dipping master normal falult the thickness of interpreted basin fill below the cretaceous tertiary overlap also varies drastically locally reaching 6 km analysis and correlation of the reflection profiles when integrated with drill hole and offshore reflection data suggest the presence of an areally extensive basalt flow and or diabase sill sequence of probable early middle jurassic age covering a large part of the triassic jurassic south georgia basin the sequence is traceable on seismic reflection profiles across much of the south georgia basin and may extend as far as from western georgia to offshore south carolina the implied areal extent of this sequence would be more than 100 000 km 2 ranking it among the great basalt flows and or sills of the world on seismic reflection profiles over the south georgia basin the basalt diabase sequence is also important in marking a post rift unconformity which separates tilted and apparently faulted lower mesozoic rift related strata below from a thinner more widespread and generally unfaulted sequence above this configuration is interpreted to mean that basalt extrusion and or hypabyssal intrusion occurred after the main episode of late triassic early jurassic normal faulting and associated localized subsidence syn rift phase and prior to a later jurassic episode of more widespread uniform subsidence post rift phase accompanied by relatively minor normal faulting this two stage evolutionary sequence is analogous to that of many rift basins throughout the world and suggests a hypothesis that the south georgia basin was an area of incipient crustal spreading associated with the early formation of the central atlantic ocean

high resolution stable water isotopes as tracers of thaw unconformities in permafrost a case study from western arctic canada abstract the knowledge of past permafrost conditions is of importance to assess the potential magnitude of changes that periglacial environments may experience as a result of climate warming or disturbance to assess if past thaw unconformities may be preserved from isotopic and geochemical discontinuities within permafrost this study investigates the distribution of ground ice stable water isotopes and major cations in two permafrost cores collected in a hummocky terrain site near inuvik northwest territories canada a site where the evolution of the active layer during a recent period of permafrost degradation and subsequent aggradation was documented based on the high resolution isotope geochemistry profiles closed system rayleigh type ionic segregation and isotope fractionation occurred during thermally induced water migration into shallow permafrost and its freezing along a negative soil temperature gradient due to thermally induced water migration into permafrost 18 o may not always be able to identify thaw unconformities however the calculation of the 18 o enrichment factors between ice and water e 18 o i w may be used to determine position of thaw unconformities in permafrost if thaw events are followed by permafrost aggradation the approach of using e 18 o i w provides additional information regarding past permafrost conditions that can complement change in cryostructures observed along natural exposures

a study of two mid crustal bright spots from southeast georgia usa summary two high amplitude reflections or bright spots occur on cocorp consortium for continental reflection profiling line georgia 16 at a record time of 5 9s corresponding to nearly 16 km depth they are significant because bright spots often mark great contrasts in subsurface physical properties the first is the surrency bright spot sbs an exceptionally bright antiformal reflection and the second is the reedy creek reflection rcr which lies 5 km to the south and resembles the south half of a diffraction the rcr is also imaged on a crossline georgia 18 as a relatively symmetric antiformal reflection these reflections coincide with the brunswick magnetic anomaly thought to mark the late palaeozoic alleghanian suture the sbs and the rcr are reflections from bodies that lie within the plane of georgia 16 migration and 2 d seismic modelling show the aniformal sbs is from a synformal reflector with a buried focus while the rcr is from a relatively small body the inferred geometry of the sbs reflector with its flat portion corresponding to the deepest part of the reflector argues that it does not represent fluids these results combined with recent evidence that the sbs is a reflection from a high velocity thin layer suggest that the sbs and the rcr might be reflections from ultramafic slices emplaced within the alleghanian suture zone during collision or from mafic sheets intruded into the suture zone during subsequent rifting the brightness of the sbs is attributed to a large impedance contrast constructive interference good data quality and a relatively large reflector size with respect to the fresnel zone and neighbouring reflectors

scattering parameters of the lithosphere below the massif central france from teleseismic wavefield records summary teleseismic p wave recordings are analysed in the frequency range 0 3 6 hz to derive structural statistical parameters of the lithosphere underneath the french massif central for this we analyse diverences in frequency dependent intensities of the mean wavefield and the fluctuation wavefield it is possible to discriminate a weak fluctuation regime of the wavefield in the frequency range below 1 hz and a strong fluctuation regime starting above 1 hz and continuing to higher frequencies the observed wavefield fluctuations in the frequency range 0 3 3 hz can be explained by scattering of the teleseismic p wave front at elastic inhomogeneities in the lithosphere a statistical distribution of the inhomogeneities is assumed and the concept of random media is applied the lithospheric structure under the massif central can be described as a 70 km thick heterogeneous layer with velocity fluctuations of 3 7 per cent and correlation lengths of the heterogeneities of 1 16 km

integrated seismic studies of the baltic shield using data in the gulf of bothnia region in the autumn of 1989 a co operative experiment involving 12 research institutions in northwestern europe collected 2268 km of deep seismic reflection profiles in the gulf of bothnia and the baltic

contrasts of seismic velocity density and strength across the moho abstract we provide an overview of contrast of elastomechanical parameters across the moho basically contrasts in seismic wave velocities density and yield strength these can be regarded as dynamic and quasi static endmembers of elastomechanical parameters of the crust mantle transition with respect to practical applications they are closely related because seismic investigations play the role of exploring the earth structure and physical state forming the boundary conditions for determining density and rheological models we address both average global moho models and petrophysical and structural factors that cause deviations from the global averages such as variations in moho depth temperature and rock composition fabric anisotropy and macro scale heterogeneity besides principle considerations these factors are put in a regional context in order to demonstrate how they are related to past and present tectonic processes seismic velocity and density contrasts are found between 0 and 25 whereas strength or viscosity contrasts may be orders of magnitude higher but may vanish as well or show a discontinuity of higher order only especially oceanic and old cratonic crust and near moho mantle may appear as a rheological unit although they are seismically well distinguishable in terms of seismic velocities the moho may vanish mainly under the influence of serpentinization or eclogitization originally defined as a first order discontinuity in seismic velocity the moho has turned out to be an interface across which other seismic properties such as seismic velocity gradients anisotropy and heterogeneity scale parameters can change strongly too however knowledge of these parameters as well as their relation to the rheology of the crust mantle transition is still restricted to local or regional examples so no global conclusions can be drawn

reflection polarity of the midcrustal surrency bright spot beneath southeastern georgia testing the fluid hypothesis a small reflection seismic experiment with an explosive source was conducted in southeastern georgia to determine the polarity of an unusually strong midcrustal reflector the surrency bright spot sbs which was found at a depth of approximately 16 km during earlier cocorp profiling in the region in addition to being very bright the sbs is notable for being unusually flat and horizontal for about half of its 4 km length as these characteristics are similar to those of fluid caused reflections at shallow depths it has been suggested that the sbs may be caused by in situ midcrustal fluids if caused by fluid enclosed in fracture porosity in solid rock the reflection would be expected to exhibit a negative polarity from the top of the porous zone the vibroseis data however gave ambiguous results with regard to polarity due to the limited bandwidth and inherent uncertainties about the phase of the source signal the new experiment consisted of four dynamite shots each recorded at three receiver stations by seismic group recorders sgr borrowed from amoco production company comparison of the dynamite records with geophone polarity tests indicate that the sbs is characterized by a positive reflection coefficient at its top this result itself does not negate the fluid hypothesis a fluid fluid interface could cause the positive reflection as well as the flat spot nature of the reflector waveform modeling shows that the sbs is caused by two or more thinly spaced reflectors a relatively high impedance layer about 120 m thick provided a good match to the observed dynamite data but requires a lower boundary having a slightly smaller reflection coefficient than the upper boundary 0 7 versus 1 0 a 150 m thick porous zone model also provided a relatively good fit to the observed dynamite data but in this model the polarity test requires that the initial sbs reflection of positive polarity be caused by a fluid fluid interface within the porous zone and that the top of the porous zone be relatively non reflective though these observations do not preclude the fluid hypothesis they certainly make the high impedance model the simpler of the two alternatives presented here the additional constraints imposed by the modeling also suggest that the sbs is more complex than these simple two interface models in either of these cases wavelet tuning contributes in part to the unusually large amplitude of the sbs reflection

direct hydrocarbon detection using comparative p wave and s wave seismic sections two field experiments in the sacramento basin and one in the green river basin demonstrate that comparative p wave and s wave cdp seismic sections can be used to detect gas directly in sandstone reservoirs the lines in the sacramento basin were shot over producing gas fields known to correlate with amplitude anomalies on p wave sections reflections of comparable strength are present on the p wave and s wave sections at lithologic boundaries but gas saturated zones correlating with p wave bright spots show no equivalent s wave amplitude anomalies the responses are consistent with laboratory observations that p wave velocity is more sensitive to the introduction of gas into liquid saturated pore space than s wave velocity the line in the green river basin was shot over a relatively deep gas field producing from an overpressured reservoir not associated with a conventional p wave bright spot the p wave reflection strength of the reservoir is about 50 percent greater than the s wave reflection strength

the hsi bright reflector further evidence for extensive magmatism in the precambrian of western canada abstract seismic reflection lines acquired in 1995 as part of lithoprobe canada s national geoscientific research program revealed unusually bright reflectors of extensive lateral scale in the archaean medicine hat block of southern alberta the herein named head smashed in hsi reflector is imaged over an area of at least 6000 km 2 in the upper half of the crust the reflector appears as a mostly horizontal to subhorizontal feature although continuous it has a complex and laterally variable internal structure comparison with a reflector of known impedance contrast in the overlying western canadian sedimentary basin indicates a high impedance structure to cause the reflections dense one dimensional modelling is consistent with the reflector being a multilayered structure with layer thicknesses in the range of tens to hundreds of metres and lateral scales of discrete reflecting elements between tens of metres and hundreds of metres polarity constraints overall geometry and reflection character strongly suggest that mafic ultramafic horizontal sheets are the cause of hsi reflectivity the hsi is the third major sequence of strong crustal reflectivity imaged by lithoprobe deep seismic data in the precambrian crust of western canada all three features are very similar in overall geometry reflector strength and character and have been interpreted as horizontal sheetlike intrusions small scale variations of the reflectivity signatures suggest a pronounced rheological heterogeneity in the upper crustal rocks within the host tectonic domains

isotopic and geochemical composition of marl lake waters and implications for radiocarbon dating of marl lake sediments radiocarbon dates on organic and calcareous fractions of sediment cores from marl lakes may yield anomalous ages due to the assumption of a constant hardwater correction factor along the sediment sequence a study of eight marl lakes in southern ontario that are actively precipitating calcium carbonate was conducted in order to assess those isotopic and aqueous geochemical parameters in modern lakes that may be utilized to estimate the history and extent of variations in the hardwater effect along such sediment sequences results show an increase in the 13c composition of lake dic dissolved inorganic carbon as approach to isotopic equilibrium with atmospheric co2 occurs differences in the extent to which this equilibrium is established also appear responsible for observed differences in the 14c activity of dic between lakes of as much as 20 pmc percent modern carbon these variations have been related to the relative residence times of water in each lake by examination of their corresponding seasona

enriched 13c composition of interstitial waters in sediments of a freshwater lake the dic dissolved inorganic carbon of interstitial waters from sediments of a small carbonate precipitating lake in southern ontario has highly enriched 13c values of up to 13 relative to pdb peedee belemnite this post depositional isotopic enrichment is attributed to the metabolism of methanogenic bacteria the 13c values of marl in the sediment profile are also enriched by an average of 3 to 4 relative to the associated molluscs photosynthetically induced carbonate precipitation and post depositional recrystallization are among the processes that are considered to contribute to the isotopically enriched marls evidence for the latter process is drawn from geochemical analyses on interstitial waters which show them to be at or very close to saturation with respect to calcite indicating that net calcite dissolution has occurred probably under the influence of high pco2 s generated by methanogenic bacteria such freshwater carbonate sediments with interstitial waters enriched in 13c provide

thaw lake expansion in a two dimensional coupled model of heat transfer thaw subsidence and mass movement 1 thaw lakes widespread in permafrost lowlands expand their basins by conduction of heat from warm lake water into adjacent permafrost subsidence of icy permafrost on thawing and movement of thawed sediment from lake margins into basins by diffusive and advective mass wasting we describe a cross sectional numerical model with thermal processes and mass wasting to test the model and provide an initial investigation of its utility the model is driven using historical daily temperatures and permafrost conditions for the northern seward peninsula alaska nsp thick syngenetic ice mean annual air temperature maat 6 c and yukon coastal plain ycp thin epigenetic ice maat 10 c in the model lakes develop dynamic equilibrium profiles that are independent of initial morphology these profiles migrate outward episodically and match the morphology of profiles from lakes that were measured at each site modeled nsp lakes expand more rapidly than ycp lakes 0 26 versus 0 10 m a 1 under respective modern climates when identical climates are imposed nsp lakes still grow more rapidly because their deeper basins and steeper bathymetric slopes move thawed insulating sediment away from the lake margin in sensitivity tests an increase of 3 c in maat causes 2 5 nsp and 1 6 ycp faster expansion of lakes an 8 c decrease essentially halts expansion for both sites consistent with paleostudies which attribute basins to postglacial warming in the model basins expand monotonically but lakes do not the 1 interannual variability of lake expansion is 0 51 nsp and 0 44 m a 1 ycp with single year rates of up to 8 m occurring because of instabilities from thermal mass movement coupling even under a stationary climate this variability is likely a minimum estimate compared to natural variability and suggests that long measurement time series of basins not lake surfaces would best detect thermokarst acceleration resulting from a climate change

massif central france new constraints on the geodynamical evolution from teleseismic tomography the massif central the most significant geomorphological unit of the hercynian belt in france is characterized by graben structures which are part of the european cenozoic rift system ecris and also by distinct volcanic episodes the most recent dated at 20 ma to 4000 years bp in order to study the lithosphere asthenosphere system beneath this volcanic area we performed a teleseismic field experiment during a six month period a joint french german team operated a network of 79 mobile short period seismic stations in addition to the 14 permanent stations inversion of p wave traveltime residuals of teleseismic events recorded by this dense array yielded a detailed image of the 3 d velocity structure beneath the massif central down to 180 km depth the upper 60 km of the lithosphere displays strong lateral heterogeneities and shows a remarkable correlation between the volcanic provinces and the negative velocity perturbations the 3 d model reveals two channels of low velocities interpreted as the remaining thermal signature of magma ascent following large lithospheric fractures inherited from hercynian time and reactivated during oligocene times the teleseismic inversion model yields no indication of a low velocity zone in the mantle associated with the graben structures proper the observation of smaller velocity perturbations and a change in the shape of the velocity pattern in the 60 100 km depth range indicates a smooth transition from the lithosphere to the asthenosphere thus giving an idea of the lithosphere thickness a broad volume of low velocities having a diameter of about 200 km from 100 km depth to the bottom of the model is present beneath the massif central this body is likely to be the source responsible for the volcanism it could be interpreted as the top of a plume type structure which is now in its cooling phase

a full scale field experiment 1978 1995 on the growth of permafrost by means of lake drainage western arctic coast a discussion of the method and some results on 13 august 1978 a lake on the western arctic coast was artificially drained in a multidisciplinary experiment on the growth of permafrost on the unfrozen bottom of the drained lake a bowl shaped talik unfrozen basin with a maximum depth of about 32 m underlay the lake bottom prior to drainage in the first winter after drainage downward freezing started on the exposed lake bottom and upward freezing from permafrost beneath the talik after drainage the soft lake bottom sediments hardened from water loss and freeze thaw consolidation gradual thinning of the active layer at many sites was accompanied by ground uplift and the growth of aggradational ice downward and upward freezing has resulted in solute rejection freezing point depressions pore water expulsion from the freezing of the saturated lake bottom sands and convective heat transfer from groundwater flow in an open hydrologie system the increasingly saline intrapermafrost groundwater flowing at an increasingly negative temperature be

reflectivity and seismic properties of the deep continental crust the recovery of drill core from a section of upper amphibolite facies terrane located in the inner piedmont of south carolina provides a rare opportunity to study in detail the seismic character of rocks which were once part of the deep continental crust seismic reflection profiles over the inner piedmont in the vicinity of the drill hole reveal subhorizontal high amplitude reflections the origin of these reflections has been investigated by measuring compressional wave velocities as a function of confining pressure and densities in 150 samples obtained from 305 m of drill core synthetic seismograms generated from the velocity and density measurements demonstrate that reflections originate from subhorizontal metamotphic layering probably originating from lower crustal ductile flow fine tuning of the metamotphic layering which is temperature and pressure related can produce bright spots in the deep crust anisotropy resulting from preferred mineral orientation is another important propeny of this sectim velocities are low for vertical wave propagatim whereas horizontal velocities are relatively high horizontal velocities show mly a slight variatim with azimuth which is unlikely to be detected using standard refractim techniques reflectivity decreases with increasing anisotropy critical to this study has been the continuous coring of a major section of high grade metamotphic terrane which has provided the necessary stratigraphic and lithologic cmtrol for the generation of accurate synthetic seismograms

evaluation of strength of heterogeneity in the lithosphere from peak amplitude analyses of teleseismic short period vector p waves summary we quantitatively characterize the regional variations in the strength of heterogeneity in the lithosphere of the globe by analysing the observed seismogram envelopes of teleseismic p waves in the frequency band of 0 5 4 hz we apply a theoretical scattering model based on the markov approximation for a plane p wave propagating through the random medium characterized by a gaussian autocorrelation function since this model presumes the vertical incidence of an impulsive plane wavelet we first analyse teleseismic p waves from deep earthquakes occurring along the western pacific regions we measure the ratios of peak intensity of transverse components to that of the sum of the three components and determine the quantity of randomness e 2 z a where e a and z are fractional fluctuation correlation distance and thickness of a heterogeneous structure respectively although source time functions of shallow earthquakes are too complex to directly apply the scattering model a good correlation between the ratios of peak amplitude and the normalized transverse amplitude which is the square root of the energy partition of the p coda waves into the transverse component enables us to use the shallow earthquakes that occur widely around the world as a result the quantity e 2 z a extends from 1 15 10 4 to 6 34 10 2 at 0 5 1 hz 2 02 10 3 to 1 89 10 1 at 1 2 hz and 1 49 10 4 to 1 89 10 1 at 2 4 hz which are in agreement with the results of previous studies using different methods the spatial distribution of randomness almost agrees with various tectonic settings and roughly correlates with lateral variations of lg coda q and shear wave velocity perturbations at 80 km depth suggesting that lateral heterogeneity extends from the shallow crust to uppermost mantle

seismic reflection investigations of the mount cayley bright spot a midcrustal reflector beneath the coast mountains british columbia an unusually high amplitude midcrustal reflector was discovered by a lithoprobe seismic reflection survey crossing a predominantly plutonic region in southwestern british columbia canada the bright spot was observed adjacent to mount cayley a large quaternary volcanic center associated with the cascadia subduction zone magmatic arc characterization of the bright spot may advance our understanding of either the midcrustal structure of magmatic supply systems or the presence and storage of saline fluids in the midcrust the location and three dimensional geometry of the reflector were determined using travel time inversion the resulting suite of models consistently describe a northwest dipping reflector that lies 12 5 to 13 km beneath the mount cayley volcanic complex the areal extent of the reflective surface is 3 km by 1 km and the structure is less than 1 6 km thick the transition between the body and the country rock must be rapid 200 m and exhibit a large impedance contrast in order to generate reflections of such high frequencies 30 hz and relative amplitudes 8 0 db our preferred interpretation for the reflector is a fossil sill complex associated with the volcanic development of mount cayley however the data do not rule out the possibility that the reflective structure represents melt lenses or saline fluid produced by the dewatering of the subducted slab the mount cayley bright spot lies just below the brittle upper crust as do the midcrustal reflectors detected beneath japanese subduction arc volcanoes this correlation suggests that thermal and rheological properties just below the brittle ductile crustal transition may be favorable for reflector formation

new cocorp profiling in the southeastern united states part ii brunswick and east coast magnetic anomalies opening of the north central atlantic ocean new cocorp profiles on the coastal plain of georgia and northern florida support the hypothesis that the brunswick anomaly marks a late paleozoic suture they do not support the alternate view that this anomaly is caused by a mesozoic rift basin the trend of the brunswick anomaly relative to the appalachian gravity gradient indicates that in westernmost georgia and adjacent alabama african basement suwannee terrane is in proximity to autochthonous north american basement grenville farther east one or more paleozoic accreted terranes intervene between the north american and african sides of the orogen offshore the brunswick anomaly closely parallels the east coast magnetic anomaly this relationship implies that the east coast magnetic anomaly marks not only the present continental oceanic crustal transition but also the northward continuation of the late paleozoic suture between north america and africa transitional crust beneath the carolina trough baltimore canyon trough and correlative parts of the african atlantic margin is thus likely to have formed within a preexisting suture zone the dramatic change in character of the u s atlantic margin southward from the carolina trough to the blake plateau probably reflects the fact that two different types of prerift crust are juxtaposed in this region

comparison of p and s wave seismic data a new method for detecting gas reservoirs compressional waves are sensitive to the type of pore fluid within rocks but shear waves are only slightly affected by changes in fluid type this suggests that a comparison of compressional and shear wave seismic data recorded over a prospect may allow an interpreter to discriminate between gas related anomalies and those related to lithology this case study documents that where a compressional wave bright spot or other direct hydrocarbon indicator is present such a comparison can be used to verify the presence of gas in practice the technique can only be used for a qualitative evaluation however future improvement of shear wave data quality may enable the use of more quantitative methods as well

introduction seismic wave scattering in three dimensionally heterogeneous earth the classical earth model of spherical symmetry or layered structure is undergoing a revolution the earth has been revealed to be laterally heterogeneous everywhere from the crust mantle to the core with scale from the grain size of rocks to the lowest orders of global spherical harmonics figure 1 shows the strength and scale length of heterogeneities in the crust and mantle of the earth in terms of v the perturbation index of seismic p or s wave speed defined as the r m s fractional variations of wave speed over the measured region the scale length of heterogeneities revealed by seismic waves not including the laboratory measurements of rock samples spans 8 orders of magnitude these heterogeneities with different scales have different effects to seismic waves the velocity and density heterogeneities can cause the change in waveform phase or travel time and amplitude fluctuation as well as apparent attenuation of the direct arrivals they can also generate coda waves such as the p coda s coda and lg coda caused by the lithospheric heterogeneities and precursory waves such as the scattered pkp waves as the precursors to pkikp caused by the heterogeneities near the core mantle boundary the near source or near receiver structures can modify the seismic waveforms by resonance and other effect rough topography or rough interface can cause the coupling between body wave and surface wave aligned cracks in the crust can produce the effective anisotrophy a great complexity arises when heterogeneities have interaction with anisotrophy and nonlinearity

cryostratigraphy paleogeography and climate change during the early holocene warm interval western arctic coast canada botanical and cryostratigraphic records from northwest canada indicate that the climate of the early holocene was considerably warmer than today tree line was over 100 km farther north and a thaw unconformity dating from 8000 14c years bp formed at the base of an active layer 2 5 times thicker than at present numerous thermokarst lake basins formed in the preceding millennia both the botanical and cryostratigraphic indices described are products of summer conditions previous reconstructions of early holocene climate have not assessed the significance of paleocoastal location on the seasonality and extent of apparent climate warming at present there is a steep gradient in growing season conditions between cooler sites on the beaufort sea coast and warmer inland locations winter conditions are more uniform because both sea and land are snow covered coastal retreat in the region has been rapid due to sea level rising over a gently sloping shelf containing readily erodible sediments the coastlin

reflection seismic imaging of the lujiang zongyang volcanic basin yangtze metallogenic belt an insight into the crustal structure and geodynamics of an ore district abstract five intersecting reflection seismic profiles were shot over the lu zong volcanic basin one of the seven ore districts in the middle and lower yangtze river metallogenic belt in east china the seismic data reveal diversified reflective patterns in the upper crust which are interpreted as horsts and grabens in general the middle crust presents both thrust related structures and boudinage and pinch and well structure on different profiles suggesting a strong structural heterogeneity which developed due to a change from compressional to extensional movement below the central part of a volcanic basin the lower crust shows an obvious reflective anisotropy both at the crust mantle and the brittle ductile transition in the crust this feature may be explained by magma system emplaced along a ne trending fault or weak zone at different depths the tan lu fault zone is present as a northwest dipping fault extending to the middle crust the lower crust beneath the tan lu fault and peripheries is possibly of dabie affinities the lu zong volcanic basin is clearly defined as an asymmetric graben with master faults on both the east and north flanks a contrasting reflection character suggests a division of the basin into northern and southern parts separated by a concealed fault the relatively thin volcanic sequences inferred to be 800 1000 m in thickness cover triassic and paleozoic sequences at depth that provide an exploration target in the northern part for deep porphyry and skarn deposits the dominant deformation reflects nw se oriented compression and extension formed during the yanshanian orogenic episode the contraction deformation is characterized by thrust faults with imbrication of crustal slices whereas the extension deformation is featured by normal faults regional detachments and basins underplating of mantle derived magma and a multi layer magma intrusion model are proposed to explain both seismic features and the ne striking lu zong volcanism and igneous intrusions in the region

evidence of climatic change from oxygen and carbon isotope variations in sediments of a small arctic lake canada radiocarbon dating of the organic rich sediments of lake illisarvik in the outer mackenzie delta indicates that formation of the lake occurred approximately 9500yr bp with maximum expansion around 6000 yr bp sedimentation rates have remained relatively constant at an average of 0 3mm yr 13c results on biogenic and inorganic carbonates and organics indicate a change from dominantly terrestrial organics 27 to 28 0 to submerged aquatic vegetation or plankton 18 to 23 0 upon formation of the lake 9500yr bp and a dramatic return to dominantly terrestrial organics at 5800yr bp 13c 27 to 30 0 this latter shift is accompanied by a drastic reduction in the macroflora and fauna populations 18o results suggest that a warmer climate than today existed prior to the shift at 5800yr bp

refraction seismic investigations of the northern massif central france abstract new refraction seismic data have been obtained in the northern french massif central seven shots were recorded simultaneously on two parallel nnw sse i e perpendicular to the surface structures oriented profiles allowing for inline and fan interpretations the results of a 2d interpretation reveal a large scale updoming of the moho of about 2 km compared to average western europe corresponding to the cenozoic uplift of the massif central local crustal thinning of up to 20 is restricted to the cenozoic grabens as seen at the surface beneath the volcanic area of cantal one of the largest cenozoic european shield volcanoes which was active in miocene to recent times significant crustal thickening of 2 3 km is observed velocities in the upper mantle are generally in the range of 7 9 8 1 km s beneath the limagne graben and surrounding undisturbed areas underneath the volcanic area of cezallier however velocity is reduced to about 7 7 km s corresponding to the area of crustal thickening therefore the low velocity in this zone is explained by the remainders of cooling magma chambers and heating by ascending hot plume material the cenozoic tectonic evolution of the massif central has affected crust and upper mantle in different ways oligocene rifting corresponds well to local crustal thinning but no correlation is detected to velocities of the upper mantle in contrast the volanic event occurring since miocene times is related to upper mantle velocity reduction and crustal thickening due to underplating

variations of the lithospheric seismic scattering strength below the massif central france and the frankonian jura se germany abstract small scale heterogeneities in the lithosphere below the frankonian jura se germany and the massif central france are studied using scattered teleseismic wavefields to compare both regions wavefields of earthquakes are analysed which were simultaneously recorded at permanent local networks because the average wavelets of the first p arrivals are nearly identical in the frankonian jura and the massif central it is possible to compare directly the scattering characteristics of the lithospheric environments although the overall form of the mean wavefields and the p codas are quite similar in both areas the intensity of the scattered seismic arrivals is increased in the massif central compared to the frankonian jura the same result is obtained using waveform data from mobile stations the increased seismic scattering strength in the massif central is interpreted as interaction of the incoming wavefield with solidified magmatic intrusions the lithospheric heterogeneities are most likely related to the known upwelling of the asthenosphere and the tertiary and quaternary volcanism in contrast the lithosphere beneath the frankonian jura seems to be less heterogeneous perhaps due to less structural alterations since its formation

physical and temporal factors controlling the development of near surface ground ice at illisarvik western arctic coast canada near surface permafrost was sampled in summer 2010 at 26 sites in the illisarvik drained lake basin and nine sites in the surrounding tundra on richards island nwt to investigate the growth of segregated near surface ground ice permafrost and ground ice have developed in the lake basin since drainage in 1978 the lake bed soils are predominantly silts of varying moisture and organic matter contents with sandier soils near the lake margins excess ice contents in the basin were also variable and ice enrichment was observed to a maximum depth of 60 cm below the 2010 permafrost table shrub covered wet areas had the highest mean excess ice content in the top 50 cm of permafrost 10 while grassy dryer areas 4 and poorly vegetated marginal areas 1 were less enriched with ice site wetness was the most important variable associated with near surface excess ice content in the lake basin silt content was a secondary variable mean excess ice content in the top 50 cm of permafrost at tundra sites

ice wedges on hillslopes and landform evolution in the late quaternary western arctic coast canada in rolling to hilly areas of the western arctic coast of canada anti syngenetic wedges which by definition are those that grow on denudational slopes are the most abundant type of ice wedge through prolonged slope denudation hilltop epigenetic wedges can evolve into hillslope anti syngenetic wedges and some bottom slope anti syngenetic wedges by means of deposition from upslope can evolve into bottom slope syngenetic wedges the axis of a hillslope wedge is oriented perpendicular to the slope so the wedge foliation varies according to the trend of the wedge with respect to the slope because the tops of hillslope wedges are truncated by slope recession the mean chronological age of anti syngenetic wedge ice decreases with time so the growth record for an old wedge is incomplete summer and winter measurements show that a thermally induced net movement of the active layer of hillslope polygons tends to transport material from their centres towards their troughs independent of the trends of the t

mapping random lithospheric heterogeneities in northern and central europe summary an energy flux model efm and a teleseismic fluctuation wavefield method tfwm have been applied to interpret the teleseismic p coda observed at three temporary and two permanent networks in northern and central europe the aim is to determine the small scale random structure of the lithosphere below the receivers various subsets of these data have been exploited previously with one of the two methods the main objectives here are to compare the performance of both methods with synthetic data sets to map the random structure of the lithosphere in terms of inverse scattering q q 1s correlation length a rms velocity fluctuation thickness l of the scattering layer and autocorrelation function acf using a combination of both methods with tfwm the product a 2 can be reliably determined if l is known l can be roughly estimated with efm although efm can in principle resolve a and separately a is recovered with a rather large uncertainty tfwm does not distinguish much between the acf type whereas with efm determination of the acf type is sometimes possible by combining the results of both methods we determine improved random medium parameters of the lithosphere for eleven subregions in northern and central europe in the baltic shield rhenohercynian belt ardenne and brabant mountains eastern rhenish massif eifel hunsruck mountains lorraine frankonian jura and massif central scattering predominantly occurs in the crust for the frequency range from 0 5 to 5 hz correlation lengths of 1 7 km and rms velocity fluctuations of 3 7 per cent are obtained for the rhenohercynian belt rh and the n german basin rms velocity fluctuations and correlation lengths could not be resolved the data from the n german basin nb cannot be explained by scattering within the crust only smallest scattering q was found in the n german basin qs 100 at 1 hz and largest scattering q in the baltic shield qs 450 at 2 3 hz for the frankonian jura only a gaussian acf can fit the q 1s values the data from the eastern rhenish massif also indicate a random medium with gaussian acf for all other subregions we cannot distinguish between exponential or gaussian acf for the random medium structure

time dependent morphology of thaw lakes and taliks in deep and shallow ground ice 1 the shape and depth of thaw lake basins depends on lake age on whether the talik thaw bulb is at steady state and on the distribution of ice in the ground to investigate implications of this broad hypothesis we use a numerical model of conductive heat transfer phase change and thaw subsidence of ice rich sediment beneath a lake in cross section for ground thermal properties with lake temperatures and dimensions consistent with measurements modeled talik depth approximately increases with except in lakes in deep ground ice which deepen more rapidly because of consolidation on thawing in deep ground ice environments basins achieve depths of 20 m in 5 ka expanding lakes with disequilibrium taliks have deep basins with broad 100 m wide inclined margins in shallow ground ice settings either original epigenetic ice or in permafrost that has reformed in drained basins lakes are 3 m deep and flat bottomed unaffected by preexisting topography and ground ice variations first generation lakes in deep ground ice are rounder and grow larger in area than later generation lakes these predictions are consistent with gps sonar and remote sensing measurements of bathymetry and plan view shape of first and later generation lakes in substrates with deep syngenetic ground ice pleistocene loess northern seward peninsula alaska and shallow epigenetic ice yukon arctic coastal plain

small scale heterogeneities below the grafenberg array germany from seismic wavefield fluctuations of hindu kush events summary small scale elastic heterogeneities 5 km are found in the upper lithosphere under neath the grafenberg array southeast germany the results are based on the analysis of broadband recordings of 17 intermediate depth 201 272 km events from the hindu kush region the wavefront of the first p arrival and the following 40 s coda are separated into coherent and incoherent scattered parts in the frequency range from 0 05 to 5 hz the frequency dependent intensities of the mean and fluctuation wavefields are used to describe the scattering characteristics of the lithosphere underneath the receivers it is possible to discriminate a weak fluctuation regime of the wavefield in the frequency range below approximately 1 5 2 5 hz and a strong fluctuation regime starting at 2 0 2 5 hz and continuing to higher frequencies in order to explain the observed wavefield fluctuations an approach with seismic scattering at random media type structures is proposed the preferred model contains heterogeneities with 3 7 per cent perturbations in seismic velocity and correlation lengths of 0 6 4 8 km in the crust this is compatible with models from active seismic experiments scattering in the lithospheric mantle is not required but cannot be excluded at weak velocity contrasts 3 per cent

random heterogeneity of the lithosphere across the trans european suture zone summary data from the passive teleseismic experiment tor across the trans european suture zone tesz which took place in 1996 1997 are used to study the random structure of the lithosphere ne of the tesz the baltic shield beneath southern sweden and beneath the north german danish basin p coda waves from deep teleseismic events give information on the small scale heterogeneity of the near receiver lithosphere on scales of one wavelength using an energy ux model the time and frequency behaviour of the p coda has been interpreted in terms of scattering qs and anelastic attenuation qi estimates of qs were obtained for the frequency range 0 5 3 hz for the north german danish basin and 0 5 7 hz for the baltic shield the two areas show a diierent scattering behaviour in denmark northern germany the scattering qs 125 200 is stronger than in southern sweden qs 275 500 and the peak of q 1 s occurs at higher frequencies ne of the tesz anelastic attenuation is negligible for the baltic shield whereas for the north german danish basin anelastic attenuation is present but still much weaker than scattering attenuation with a modi ed energy ux model for depth dependent scattering and assuming an exponential autocorrelation function the depth variation of correlation length a and rms velocity uctuation e can in principle be resolved for the baltic shield the scattering is mostly con ned to the crust with a 1k m ande 4 per cent the subcrustal lithosphere only shows weak uctuations the data from the north german danish basin cannot be explained by strong scattering within the crust only crustal parameters are a 5 10 km and e 8 per cent for the subcrustal lithosphere correlation lengths of 10 20 km and rms velocity uctuations of 6 8 per cent are found additional tests con rmed that the thick sedimentary cover in this area has no signi cant eiect on these results for the deeper structure correlation lengths for the sediments are smaller than 5 km and rms velocity uctuations e are 7 8 per cent

the s reflector west of galicia the seismic signature of a detachment fault the so called s reflector is a group of bright continuous reflections underlying the landward tilted fault blocks of the west galicia rifted margin s has been interpreted as the brittle ductile transition the lop of an intrusion a detachment fault and the crust mantle boundary to constrain the internal structure of the reflector we have carried out detailed analyses of these reflections we compare the waveforms of the seafloor reflection and its first multiple both to determine the amplitude of the seafloor reflection and to show hat the seafloor is in effect a spike in the reflectivity series so that the seafloor reflection can be used as the far field wavelet including both source and receiver ghosts we compare he waveform of the seafloor and 5 and show that within the resolution of our data s is a reflection from a step increase in acoustic impedance this result is confirmed through complex trace analysis and in particular the determination of the apparent polarity of s and the examination of the instantaneous frequency function s is consistently positive polarity and shows no significant frequency anomaly simple modelling shows that s is very unlikely to be a reflection from a thin layer we thus conclude that s is probably a single steplike interface from the varying frequency content of the data we determine a value for the effective q between s and the seafloor and use this to assess the amplitude loss due to attenuation and scattering we use a comparison between the seafloor and the s reflection to constrain the amplitude of s and estimate a reflection coefficient for s of at least 0 2 in places decreasing landwards by analogy with structures developed in the highly extended regions of the western united states we consider that the most likely interpretation of s is as a sharp west dipping detachment fault separating a granitic upper plate from a higher velocity lower plate locally probably serpentinized mantle

evidence from north west canada for an early holocene milankovitch thermal maximum according to the milankovitch theory of global climatic change maximum summer solar radiation at high latitudes of the northern hemisphere occurred at 10 000 yr bp refs 1 2 in particular it predicts summer solstice radiation greater by 9 10 preliminary climate simulation experiments with these increased values of radiation confirm that high latitude land surfaces received maximal insolation at 10 000 yr refs 3 4 paradoxically however the large volume of fossil pollen and other evidence from north america indicates a maximum of holocene warmth at 7 000 6 000 yr ref 5 and a recent review of the evidence from new england suggests that the warming began at 9 000 and ended at 5 000 yr but also stresses the difficulties of interpretation in terms of climate change6 we summarize here data from sites in the north west corner of mainland canada fig 1 that directly support the milankovitch hypothesis

crustal structure and deep reflector properties wide angle shear and compressional wave studies of the midcrustal surrency bright spot beneath southeastern georgia three component p sh and sv expanding spread profiles esp common midpoint profiles and sparse three dimensional p wave data were collected over an unusually strong midcrustal reflector the surrency bright spot sbs in southeastern georgia shear wave reflections from the sbs at 10 9 s 16 km depth and possibly from the lower crust at 18 3 s 29 km depth were recorded but required substantial source effort stacking and were too weak for reliable reflectivity measurements reflections on the esps delineate a 1 5 km thick atlantic coastal plain section whose seismic properties vp 2 53 km s vs 1 51 km s vp vs 1 67 are consistent with quartz rich sandstones and siltstones sitting atop a 15 km thick upper crust vp 6 38 km s vs 3 25 km s vp vs 1 96 which in turn overlies a 15 km thick lower crust of slower material vp 6 02 km s vs 3 26 km s vp vs 1 84 the velocity inversion may result from underthrusting of upper crustal rocks during suturing of florida to north america amplitude versus offset analyses combined with an earlier reflection polarity test and waveform modeling indicate that the sbs originates from a thin 80 120 m high impedance layer most likely a mafic dike or tectonically emplaced ultramafic body

exposed cross sections through the continental crust implications for crustal structure petrology and evolution abstract the continental crust is exposed in cross section at numerous sites on the earth s surface these exposures which appear to have formed by obduction along great faults during continental collision may be recognized by exposures of deep crustal rocks exhibiting asymmetric patterns of metamorphic grade and age across the faults and by distinctive bouguer anomaly patterns reflecting dipping basement structure and an anomalously deep mantle from an examination of five complexes which meet these criteria it is concluded that the most prominent layering in the crust is not compositional but metamorphic the lower crust consists of granulite facies rocks of mafic to intermediate composition while the intermediate and shallow levels consist predominantly of amphibolite facies gneisses and greenschist facies supracrustal rocks respectively post metamorphic granitic intrusions are common at intermediate to shallow levels position of discontinuities in refraction velocity where present commonly correspond to changes in composition or metamorphic grade with depth the continental crust is characterized by lateral and vertical heterogeneities of varying scale which are the apparent cause of the complex seismic reflections recorded by cocorp field observations coupled with geochemical data indicate a complex evolution of the lower crust which can include anatexis multiple deformation polymetamorphism and reworking of older crustal material the complexity of the crust is thus the result of continuous evolution by recycling and metamorphism through time in a variety of tectonic environments

energy flux model of seismic coda separation of scattering and intrinsic attenuation a new model of seismic coda is presented based on the balance between the energy scattered from the direct wave and the energy in the seismic coda this energy flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic anelastic attenuation of the medium this formula is valid for both weak and strong scattering and implicitly includes multiple scattering the model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity some of the simulations also included intrinsic dissipation the energy flux model explains the coda decay and amplitude observed in the synthetics for random media with a wide range of scattering q in contrast the single scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation scattering q less than or equal to 150 the simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate as predicted by the energy flux model the coda decay rate is sensitive however more to the intrinsic q of the medium the ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation thus analysis of the decay rate and amplitude of the coda can in principle produce separate estimates for the scattering and intrinsic q values of the crust we analyze the coda from two earthquakes near anza california intrinsic q values determined from these seismograms using the energy flux model are comparable to coda q values found from the single scattering theory the results demonstrate that coda q values are at best measures of the intrinsic attenuation of the lithosphere and are unrelated to the scatteing q less

integration of cocorp deep reflection and magnetic anomaly analysis in the southeastern united states implications for origin of the brunswick and east coast magnetic anomalies integration of magnetic anomaly analysis with cocorp deep reflection data from the southeastern united states provides three new constraints on the interpretation of the brunswick and east coast magnetic anomalies as well as on the reflection data these are as follows 1 the source of the brunswick anomaly lies within the deep crust this anomaly is not caused by a mesozoic rift basin as proposed by some workers 2 a simple seaward dipping high susceptibility slab model can explain both the brunswick and east coast magnetic anomalies the along strike change in character of the two anomalies results largely from a change in azimuth of the source body 3 beneath the southeastern united states this source body dips south lies immediately on the south flank of the prominent southward dipping reflective zone revealed on cocorp surveys and was previously associated with the alleghanian suture between north america and africa these results imply that a dipping highly magnetized zone in the upper plate of the alleghanian suture is responsible for both the brunswick and east coast magnetic anomalies the high susceptibility material responsible for these anomalies might be mafic lower continental or oceanic crust thrust upward during alleghanian continental collision or mafic igneous material intruded into the upper plate of the suture zone during subsequent mesozoic rifting or both the latter hypothesis implies that the alleghanian suture acted as a zone of weakness a repository which was reactivated to control the site of ultimate atlantic rifting and possibly initial sea floor spreading

deep 3 d seismic reflection imaging of precambrian sills in southwestern alberta canada abstract a number of bright reflector sequences within the crystalline basement were imaged on 2 d multichannel crustal seismic reflection profiles collected by lithoprobe from 1991 to 1995 one such sequence in southern alberta the head smashed in hsi reflector spans a depth range of 6 21 km with an aerial extent of at least 6000 km2 this series of reflectors and similar sequences in central alberta and northern saskatchewan have been interpreted as packages of horizontal sheet like mafic sills that intruded the precambrian basement hundreds of millions of years after crustal formation in 1999 through our request to extend an exploration survey to longer travel times a partnership group from the canadian petroleum industry recorded a 9 by 6 km 3 d reflection dataset to 8 s two way traveltime twtt at a location southwest of the hsi reflector following processing which included a special procedure to remove strong ground roll that persisted at travel times of interest we identified a sequence of reflections between 4 and 5 s that we correlate with those associated with the hsi reflector however the reflections are not as bright or as continuous as those on the 2 d profiles based on these results and the characteristics of the sills on the lithoprobe data we infer that we imaged the feathering ends of the sill intrusions such sills represent a net addition of crustal material and may provide insight into the ancient stress field during emplacement and clues as to how cratons achieve their thickness and stability although the survey area is small this study represents the first attempt in north america and only the second in the world to examine upper middle crustal structure to depths of approximately 20 km using industry style 3 d seismic reflection data the results indicate that industry 3 d data with extended recording times could provide useful information for studying the crystalline crust below sedimentary basins

crustal structure of the fennoscandian shield a traveltime interpretation of the long range fennolora seismic refraction profile abstract the 1979 fennoscandian long range project fennolora was aimed at the determination of the detailed structure in the earth s mantle down to a depth of about 400 km observation distances reached almost 2000 km within scandinavia between shotpoints off the north cape and the southern coast of sweden to achieve an unbiased regarding the upper mantle structure a careful crustal survey was carried out along the entire profile at the same time beneath the fennoscandian shield i e the central section of the profile the crust is characterized by quite a smooth increase in p wave velocity down to the moho which lies at a depth of about 50 km in the southern half of the shield and at about 45 km further north the mean crustal velocity is 6 6 6 7 km s at the base of the crust the velocity increases gradually from about 7 km s to 8 0 8 4 km s in a 5 10 km thick crust mantle transition zone both in the south and in the north the relatively homogeneous crust of the baltic shield borders on areas with a more differentiated velocity structure first order discontinuities at shallower depth characterize the crust mantle boundary near the southeastern tip of sweden 38 km and under the caledonides in the north 43 km

crustal structure and geodynamics of the middle and lower reaches of yangtze metallogenic belt and neighboring areas insights from deep seismic reflection profiling abstract a 300 km long seismic reflection profile was acquired across the middle and lower reaches of the yangtze river mly metallogenic belt and its adjacent areas the objective of the survey was to establish the deep architecture and geodynamic framework of the region results based on the interpretation of the deep seismic data include 1 tan lu fault appears as a subvertical thrust fault or transpression fault with its deep portion dipping toward the southeast 2 the zhangbaling uplift is squeezed out along this fault 3 complex upper crustal deformation structures beneath the chuquan depression include both kink bands thrusts imbrication and fold structures reflecting contraction deformation and detachment fault and normal fault structures reflecting extensional deformation 4 the crocodile reflection structure emerging beneath the tan lu fault and ningwu lishui volcanic basin which represents the decoupled deformation process of the upper and lower crust associated with intra continental subduction 5 further to the southeast the upper crust deformation shows a large scale wave form pattern making crustal scale syncline and anticline 6 the entire section of the reflection moho is clearly discernible at depth of 30 0 34 5 km and the moho beneath the middle and lower reaches of yangtze river metallogenic belt is shallowest while the moho beneath the north china block is deeper than that beneath the yangtze block the moho offsets could be seen beneath the ningwu volcanic basin the seismic reflection data suggest that lithosphere delamination and asthenosphere upwelling that may result from the mesozoic intra continental orogenesis is responsible for the formation of large scale magmatism and mineralization in the mly metallogenic belt

imaging a mantle plume beneath the french massif central abstract teleseismic tomography is now widely recognised as a very powerful tool for studying the velocity structure of the lithosphere asthenosphere system on both local and regional scales a prime objective is to identify velocity perturbations and to constrain their location and intensity here we use the arrival times of p waves from teleseismic events recorded by a dense network of mobile and permanent stations within the french massif central to derive a 3d p velocity model for an area of 425 km 300 km combined with knowledge of the basement geology of the area and the timing and geochemical characteristics of tertiary quaternary volcanic activity we consider that the velocity model provides unequivocal evidence for the ascent of a thermally and chemically anomalous mantle plume beneath the massif central during tertiary times our model is consistent with regional bouger gravity anomalies documented patterns of neogene recent uplift and deformation fabrics within lithosphere derived mantle xenoliths exhumed by the volcanics

tundra lakes and permafrost richards island western arctic coast canada lakes of average size 33 ha occupy a quarter of the surface area of richards island northwest territories most of the lakes have a central pool deeper than the thickness of winter ice and many have prominent shallow littoral terraces the relatively warm lake bottoms cause considerable disturbance to the surrounding continuous permafrost water and lake bottom temperatures the configuration of permafrost and active layer thickness were measured at a tundra lake between 1992 and 1997 the lake is oval 1 6 km long 800 m wide and as deep as 13 m sandy terraces covered by less than 1 m of water extend over 100 m from the shore the terraces are underlain by permafrost which terminates almost vertically at their edge the annual mean temperature measured at lake bottom in the central pool ranged between 1 5 c and 4 8 c depending on depth and between 0 2 c and 5 c on the terraces due to differences in snow cover and proximity to the central pool in consequence the temperature of permafrost at 7 m depth in the terraces also varied from 2 c near shore to 5 c in mid terrace the active layer in the terraces was uniformly 1 4 m deep geothermal modelling of talik configuration indicates that there is no permafrost beneath the central pool of the lake the modelling indicates that under equilibrium conditions about one quarter of the lakes on richards island have taliks that penetrate permafrost and at least 10 15 of the island is underlain by talik short term climatic changes predicted for the region imply a small increase in summer lake water temperature and an extension of the open water season accompanied by thicker snow cover in winter following such changes with longer freeze up and warmer terrace temperatures in winter permafrost may not be sustainable in the lake terraces

geochemistry and extractable fe and al in cold temperature soils of northwestern siberia the concentrations of major minor and trace elements in three cryosols from north western siberia were analysed to determine profiles of geochemical uniformity element mobility and the release and build up of extractable fe and al the scope of this study involves weathering processes over all or part of the lateglacial to the holocene epoch 10 ka bp q1 in a cold environment the variability of hf content in the horizons is likely silica induced and accounts for much of the concentration variation in the other elements the slight increases of mobile to immobile elements in the b horizons indicate trivial downward movement within the profiles iron and al extracts were investigated to elicit information regarding profile age and palaeoclimate extractable fe and al show slight increases relative to the total concentrations in the soil sola ah bw horizons lattice fe decreases in the ah bw horizons as a result of weathering and production of sesquioxides over time increases of ferrihydrite in the ah horizons and in the parent material of some profiles may indicate perched water tables at some time in the past possibly as sustained yearly water levels in the active layer free iron fed relative to total fe increases in the ah bw horizons compared with the lower horizons where the oxidation potential is weaker low total fe reflects reworked felsic rich deltaic and shallow marine deposits from the permian to the early tertiary thereafter emplaced by episodic flooding of glacial meltwater from the arctic urals and or the kara sea ice sheet organically complexed al alp uniformly low in all soils nevertheless shows trends indicating some downward movement a rather unique occurrence in arctic tundra soils as indicated by the slow increase of oxihydrites it may not be realistic to estimate the age of a profile by its physical characteristics however it appears possible to determine broad age ranges from the isotopic composition of water in soils organic carbon concentrations between and within soil profiles indicate it may be more prevalent in tundra soil than previously thought and may also play a significant role in uploading co2 to the atmosphere as warming and microbial activity q2 progresses copyright 2009 john wiley sons ltd

holocene climate effects on the development of a peatland on the tuktoyaktuk peninsula northwest territories abstract six cores were collected from a small peatland on the tuktoyaktuk peninsula yielding up to 1 8 m of organic material and 1 2 m of ice rich material stratigraphic relationships radiocarbon dating and pollen plant macrofossil and isotopic analyses are used to reconstruct the developmental history of the peatland organic matter began to accumulate in the basin about 7200 yr b p during a period when the climate is thought to have been warmer than present initially the permafrost table was probably below the bottom of the basin and an open water mineral wetland with emergent and submergent aquatic vegetation occupied the site enriched 18 o values from ice samples confirm the existence of an open water body with a water balance strongly affected by evaporation transformation to a graminoid fen peatland was underway by 6300 yr b p permafrost and ice began to form in the peatland at this time low centered polygons probably began to develop by 4700 yr b p and subsequently evolved into the high centered polygons which characterise the southwestern part of the peatland today peat accumulation in the polygons has been extremely slow for the last 4000 years the eastern wetter part of the basin has largely remained unchanged since its inception about 7000 yr b p development of the peatland may be linked to permafrost formation that was controlled by regional climate changes during the holocene

the first 20 years 1978 1979 to 1998 1999 of active layer development illisarvik experimental drained lake site western arctic coast canada active layer thickness snow depth minimum soil temperatures near surface ground ice soil heave and permafrost temperatures have been measured for over 20 years following the 1978 artificial drainage of lake illisarvik measurements of active layer thickness and other variables have been made at 25 m intervals along the major and minor axes of the oval shaped drained lake bed permafrost aggradation commenced in the lake bottom during the first winter following drainage before the establishment of vegetation there was little snow cover minimum ground temperatures were low and the active layer was relatively thin however both snow depth and minimum ground temperatures have risen where vegetation has grown the active layer has thickened and in response the temperature in permafrost has gradually increased in the lake bottom the change in snow depth associated with vegetation growth has been the dominant control on variation in active layer thickness and not summer weather conditions which ar

new cocorp profiling in the southeastern united states part i late paleozoic suture and mesozoic rift basin new cocorp profiling in the southeastern united states has revealed a broad zone of dipping reflections that extends downward through the crust beneath the coastal plain in western georgia the zone is over 50 km wide and most of the reflections dip moderately steeply toward the south regional considerations suggest that this feature marks the late paleozoic suture between north america and africa where crossed by the cocorp survey the suture occurs beneath the north flank of the triassic early jurassic south georgia basin the main depocenter of the south georgia basin occurs about 90 km to the south and is formed by a large half graben containing more than 5 km of rift basin fill farther south the paleozoic suwannee basin sequence beneath northern florida is poorly imaged on the cocorp profiles however weak reflections suggest that these strata including basal felsic volcanics may have an aggregate thickness of about 6 km in north central florida at the northwest end of the cocorp traverse a prominent horizon imaged in the upper crust beneath the inner piedmont probably marks the southern appalachian detachment the detachment appears to be cut off by the towaliga fault implying that the towaliga fault is in part a down to the north normal fault intermittent moho reflections occur at 11 12 s two way time along the length of the cocorp survey indicating that the crust in the region has a roughly uniform thickness of about 33 36 km assuming an average crustal velocity of 6 km s

measuring the seismic properties of tibetan bright spots evidence for free aqueous fluids in the tibetan middle crust seismic bright spots are commonly interpreted to mark fluid concentrations but their nature melt or aqueous is usually inferred only from circumstantial evidence of the geologic setting a band of bright spot reflections has been imaged by project indepth international deep profiling of tibet and the himalayas at about 15 km depth along 150 km of the northern yadong gulu rift southern tibet we use indepth three component wide angle seismic data to measure seismic velocities at the bright spot reflector and theoretical rock physics bounds to constrain the nature of the fluids merging of data from multiple bright spots allows us to use a one dimensional approximation travel time modeling yields average p and s velocities for the upper crust above the bright spots of 5 3 0 2 and 3 2 0 2 km s 1 respectively reflection amplitude variation with offset avo modeling constrains the p and s velocities of the bright spots to 3 0 0 8 and 1 6 0 8 km s 1 respectively multiple modeling procedures suggest these velocities are not model dependent our results imply that of the order of 10 volume of free aqueous fluids in the tibetan middle crust produces the observed bright spot reflections the presence of relatively large quantities of free aqueous fluids presumably mostly saline supercritical h2o does not preclude the presence of melt but does constrain the maximum temperature at the bright spots to the wet granite solidus about 650 c and thus the maximum surface heat flow to 110 mw m 2 the observed bright spots can alternatively be explained as a result of transient flow of aqueous fluids through a lower temperature and lower heat flow southern tibetan crust

modelling the teleseismic p coda envelope depth dependent scattering and deterministic structure abstract the p coda of teleseismic events contains information on the small scale random structure of the near receiver lithosphere various scattering theories have been suggested to model the time and frequency dependence of the coda envelopes for a given random structure a specially simple model is the energy flux model that describes p coda excitation in terms of scattering attenuation of the direct p wave front without dealing with the details of the scattering process it is based on energy conservation and is valid for both weak and strong scattering cases here the energy flux model is extended to include a depth dependence of the scattering structure a variation of the depth range of the random medium manifests itself mainly in different decay rates of the coda whereas the coda amplitudes at small lapse times behind the direct arrival are sensitive to the scattering strength of the shallow structure strongly heterogeneous layers at greater depths yield more complicated coda shapes which cannot be fully described by parameters like decay rate or coda q full waveform simulations in random structures superimposed onto a deterministic layered model show that 1 the energy flux model yields reliable results and 2 the effects of deterministic layering on the coda envelopes are relatively small for waves with small incidence angles and realistic scattering strength and therefore may be neglected in coda inversions for teleseismic waves

crustal structure of central japan and its petrological implications the crustal structure of central honshu japan has been influenced by several tectonic events a series of collision processes during the late tertiary extensive faulting highly compressive deformation and quaternary volcanism the southern part of the study area is covered by various granitic rocks which intrude into old palaeozoic formations quaternary volcanoes occupy the northern part and cover the basement which is mainly composed of granitic rocks and tertiary formations a traveltime inversion for velocity and interface depth was applied to the seismic data together with constraints from amplitude forward modelling to produce a seismic velocity model of the crust in central honshu in this experiment both refracted p and s waves are clearly recorded along a 110 km profile these provide constraints on the 2 d p and s wave velocity structure down to a depth of about 10 km moreover clear p wave reflections from intracrustal interfaces provide constraints on deeper parts of the crust down to about 25 km for the p wave velocity model the velocities of near surface layers show large lateral variations from 3 7 to 4 4 km s 1 increasing towards the south underlying layers have velocities ranging from 4 85 to 5 6 km s 1 velocities in the range 5 85 6 2 km s 1 characterize the upper crust that extends to a depth of about 15 km for the s wave velocity model the near surface layer velocities change from 1 7 to 2 55 km s 1 showing remarkable lateral heterogeneity whilst the upper crust is characterized by velocities of 3 4 3 6 km s 1 the deeper parts are modelled by two prominent reflectors in the mid crust the shallower one which delineates the bottom of the upper crust dips southwards from 14 to 16 km the deeper reflector lies between 20 and 24 km depth and dips northwards the velocity in this mid crustal layer is 6 35 km s 1 at the top and 6 7 km s 1 at the bottom the crustal thickness under the profile could not be determined because of a lack of pn and or pm p phases this study also presents the vp vs ratio and the poisson s ratio distribution and gives the probable composition of the upper crust poisson s ratio varies from 0 29 to 0 34 which can be ascribed to a porous and water saturated structure for the near surface layers in the northern part of the region poisson s ratios of about 0 24 0 25 in the southern part and 0 22 0 24 in the upper crust together with the geological data show that the upper crust has a felsic content and is formed by granite granodioritic rocks with a high quartz content the changes in the quartz content explain the lateral variations of vp vs and poisson s ratio in the model the higher velocities in the middle crust suggest a more mafic structure probably composed of diorites

cocorp new perspectives on the deep crust summary relict sutures from colliding continents regions characterized by a young mono layering and faulting throughout the crust mid crustal magma traps and seismic bright spots which suggest deep crustal fluids are among recent cocorp findings in addition new studies of signal penetration noise mitigation recording geometry and coherency filtering have yielded better understanding of and substantial improvements in data quality amplitude anomalies or bright spots in the basin and range may be due to magma at mid crustal levels in one case a normal fault appears to link the deep magma with young surface volcanics another bright spot 15 km deep in southeastern georgia has a flat geometry that suggests a gas liquid interface perhaps within fluids underthrust along an appalachian suture the mono continues to appear relatively undisturbed in many regions of past deformation suggesting that its formation post dates these major tectonic episodes the diversity of reflection patterns from the u s cordillera casts further doubt on the generality of the common model of a reflective layered lower crust underlying a transparent upper crust

absolute reflection coefficients from deep seismic reflections abstract many deep seismic reflection profiles show bright sub horizontal layered reflections in the lower continental crust accurate estimates are obtained for normal incidence reflection coefficients for the brightest of these reflections by using a marine seismic acquisition system that has been calibrated using deep water sea bottom multiples minimum bounds are placed upon these reflection coefficients by assuming minimum losses due to scattering anelastic attenuation and geometric spreading reflection coefficients of around 0 1 are obtained from the layered lower crust and around 0 15 from the moho it is argued that constructive interference between successive reflections from a layered sequence of reflectors is often unimportant consequently these coefficients can be used to place useful limits on the absolute acoustic impedance contrasts present at depth