evidence for preservation of crustal root beneath the proterozoic lapland kola orogen northern fennoscandian shield derived from p and s wave velocity models of polar and hukka wide angle reflection and refraction profiles and fire4 reflection transect 1 we present an analysis of the crust and upper mantle in the northern fennoscandian shield based on new p and s wave 2 d velocity models of the polar and hukka wide angle reflection and refraction profiles and results of a new seismic reflection experiment in finland finnish reflection experiment the profiles are almost collocated and crossed the proterozoic lapland kola orogen a substantial difference of the depth of the wide angle moho 40 42 km and the reflection moho 47 50 km was found in order to explain this difference we compared the velocity models to published values of vp and vp vs for the main types of lower crustal and mantle rocks we found that the main reason for disagreement is that the wide angle moho and the reflection moho correspond to different petrological boundaries in the southwest and northeast portions of the profiles the wide angle moho marks contact of either anorthositic or granulitic lower crust with a reflective layer in the upper mantle composed of peridotites and pyroxenites the reflection moho represents the bottom of this lower layer in the center of the profile the wide angle moho marks the top of a large eclogitic body in the upper mantle representing a well preserved crustal root beneath the lapland kola orogen formed because of the collision of three former archaean crustal blocks terranes or microcontinents lack of postorogenic tectonic collapse suggests another mechanism for stabilization of the lithosphere in the area upper mantle reflectors at depth of 65 75 km may mark the upper boundary of the cold and mechanically strong archaean upper mantle wedge alternatively these reflectors may represent a top of uplifted asthenosphere that can explain preservation of crustal root

crust mantle boundary in the central fennoscandian shield constraints from wide angle p and s wave velocity models and new results of reflection profiling in finland 1 our paper presents analysis of the crust mantle boundary in the central fennoscandian shield based on new p and s wave two dimensional velocity models of the sveka 81 sveka 91 and fennia wide angle reflection and refraction profiles and on results of a new seismic reflection experiment in finland finnish reflection experiment fire in this area the crust is extremely thick 50 60 km and the moho boundary is difficult to detect using methods based on interpretation of p waves only near vertical profiling and wide angle experiments however the s wave reflections from the moho boundary sms are frequently more pronounced in wide angle data than the p wave reflections pmp in order to infer the crust mantle transition we developed new p and s wave velocity models using reprocessing of the old data and compared them to record sections of collocated reflection profiles and to published values of vp and vp vs for the main types of lower crustal and upper mantle rocks on the basis of the lateral variations of vp vp vs and reflectivity in the lower crust and upper mantle three main types of the crust mantle boundary were distinguished the first type corresponds to eclogitized lower crust that overlies peridotitic upper mantle in this case the moho coincides with the lithological crust mantle boundary the second type corresponds to lower crust composed of mafic garnet granulites overlying the peridotitic upper mantle for which the moho and the lithologic crust mantle boundary coincide as well the third type corresponds to the mafic garnet granulites underlain by a layer of eclogitic upper mantle in the latter case the lithological crust mantle boundary is deeper than the moho

mount logan ice core record of tropical and solar influences on aleutian low variability 500 1998 a d continuous high resolution paleoclimate records from the north pacific region spanning the past 1500 years are rare and the behavior of the aleutian low alow pressure center the dominant climatological feature in the gulf of alaska remains poorly constrained here we present a continuous 1500 year long calibrated proxy record for the strength of the wintertime december march alow from the mount logan summit pr col 5200 m asl ice core soluble sodium time series we show that ice core sodium concentrations are statistically correlated with north pacific sea level pressure and zonal wind speed our alow proxy record reveals a weak alow from circa 900 1300 a d and 1575 1675 a d and a comparatively stronger alow from circa 500 900 a d 1300 1575 a d and 1675 a d to present the mount logan alow proxy record shows strong similarities with tropical paleoclimate proxy records sensitive to the el nino southern oscillation and is consistent with the hypothesis that the medieval climate anomaly was characterized by more persistent la nina like conditions while the little ice age was characterized by at least two intervals of more persistent el nino like conditions the mount logan alow proxy record is significantly p 0 05 correlated and coherent with solar irradiance proxy records over various time scales with stronger solar irradiance generally associated with a weaker alow and la nina like tropical conditions however a step like increase in alow strength during the dalton solar minimum circa 1820 is associated with enhanced walker circulation furthermore rising co2 forcing or internal variability may be masking the twentieth century rise in solar irradiance

shear wave anisotropy of laminated lower crust beneath urach sw germany a comparison with xenoliths and with exposed lower crustal sections in order to investigate the laminated lower crust beneath urach sw germany we analysed 1 the anisotropy and reflectivity of seismic shear waves and 2 the composition of xenoliths samples we conclude that the directional dependence of shear waves of the lower crust is effectively transversely isotropic with a maximum velocity difference of 3 to 6 both seismic signature and petrological information are compared with reference profiles deduced from the exposed lower crustal sections of ivrea and calabria italy the comparison based on synthetic seismograms shows that the observed combination of shear wave anisotropy and reflectivity pattern corresponds to alternating layers containing a high amount of metapelites such as found in the calabria profile and in the val strona subsection of ivrea the main portion of the whole rock anisotropy is caused by the lattice preferred orientation of anisotropic minerals so called intrinsic anisotropy the effect of alternating rock layering so called layering anisotropy contributes only a minor portion to the whole rock anisotropy layered mafic intrusions such as found in the val sesia subsection of ivrea are nearly isotropic both seismic anisotropy and xenoliths indicate that mafic layers do not play a major role for the laminated lower crust at urach they may be restricted to a thin layer at the crust mantle boundary

large scale crustal heterogeneities and lithospheric strength in cratons abstract the rheology and thermal structure of the continental lithosphere are intimately linked in old cratons the effective elastic thickness of the lithosphere has been estimated by various spectral inverse methods based on the correlation between topography and gravity anomalies estimates vary within a very large range from 40 km to 120 km depending on the method used in this paper we use forward models to account for lateral variations in mechanical properties and their effect on the equivalent elastic thickness eet of the lithosphere from these models which allow brittle elastic ductile rheologies and mechanical discontinuities faults we have calculated the strain stress distributions and displacement fields vertical integration of the stress permits a local determination of the effective elastic thickness the computed displacements were used to calculate related bouguer and free air gravity anomalies and compare them with the observations the analysis is applied to the 2000 ma kapuskasing uplift in the superior province of the canadian shield where the presence of a high density block in the upper crust is due to the upthrusting of midcrustal rocks along a major thrust fault the study shows that the stability of this structure on geologic time scales requires a strong lower crustal rheology a cold geotherm and the fault to be healed this study also shows that because of stress dependence of the non linear rheology crustal heterogeneities may cause significant 40 local reductions of the lithospheric strength away from the kapuskasing structure the average strength of the lithosphere remains high eet 100 km conventional methods for estimating the elastic thickness would not resolve such local strength reductions in cratons but would predict depending on the method used highly overestimated or instead underestimated eet

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

a record of holocene summer climate from a canadian high arctic ice core melt layers in ice cores are formed by melting on the snow pack surface which produces water that percolates down and refreezes in the colder snow layers below melt layers are distinguished by their bubble texture because more ice forms in the snow pack in warm summers than in cool summers the changing concentration with depth of melt layers in snow pits1 2 and ice cores3 5 is an indicator of past summer climate here we report on studies of melt layers in two canadian high arctic surface to bedrock ice cores although changes in elevation of the drill site owing to isostatic depression and uplift may contribute up to 40 of the total climatic signal recorded in the melt layers we interpret their varying concentrations in terms of changing summer temperatures over the past 10 000 years the warmest summers occurred 8 10 kyr ago and the coldest only 150 years ago the summers over the past 100 years have been the warmest for more than 1 000 years but are still not as warm as those of the early holocene the melt layer record is in broad agreement with geological records of glacier retreat during the holocene6 8 indicating that these data also contain information of regional significance

tectonics of the kola collision suture and adjacent archaean and early proterozoic terrains in the northeastern region of the baltic shield as preparation for the deep seismic and other geophysical experiments along the polar profile which transects the granulite belt and the kola collision suture structural field work has been performed in northernmost finland and norway and published geological information including data from the neighbouring soviet territory of the kola peninsula have been compiled and reinterpreted based on these studies and a classification according to crustal and structural ages the northeastern region of the baltic shield is divided into six major tectonic units these units are separated and outlined by important low angle ductile shear or thrust zones of late archaean to early proterozoic age the lateral extension of these units into soviet territory and their involvement in large scale crustal deformation structures are described using the view down the plunge method a generalised tectonic cross section that predicts the crustal structures along the polar profile is compiled and the structures around the kola deep drill hole are reinterpreted the kola suture belt through parts of which the kola deep bore hole has been drilled is considered to represent a ca 1900 ma old arc continent and continent continent collision suture it divides the northeastern shield region into two major crustal compartments a northern compartment comprising the murmansk and sorvaranger units and a southern compartment including the inari unit the granulite belt and the tanaelv belt as well as the more southernly situated south lapland karelia craton of the karelian province of the svecokarelian fold belt the kola suture belt is outlined by a 2 40 km wide and ca 500 km long crustal belt composed of 1 1 early proterozoic ca 2400 2000 ma old metavolcanic and metasedimentary sequences which originally formed part of the attenuated margin of the northern archaean compartment and 2 2 the remains of a ca 2000 1900 ma old predominantly andesitic island arc terrain this island arc terrain was built up above a sw plunging subduction zone initiated ca 2000 ma ago in the southern part of a newly formed oceanic domain the kola ocean due to continued subduction and complete consumption of this ocean the northern passive margin deposits and the island arc terrain were brought into tectonic juxtaposition and during the final arc continent and continent continent collision they were overthrusted onto the northern archaean continent along its southern boundary the kola suture belt is tectonically overlain by the archaean rocks of the inari unit this unit was derived from a microcontinent split from the southern compartment the depositional basin of the protoliths of the granulite belt being formed to the south of the microcontinent the inari microcontinent appears to have wedged out towards the southeast as the continuation of the granulite belt north of the white sea is in direct tectonic contact with the kola suture belt the granulite belt is composed of high grade paragneisses and minor amounts of meta igneous rocks the paragneisses formed from thick turbidite and mass flow deposits lain down in a back arc basin south of the inari microcontinent a thermal anomaly beneath the partly oceanic basement of the back arc basin is believed to have contributed to the ca 2000 1900 ma old granulite facies metamorphism of the granulite assemblages granulite facies conditions still prevailed when the inari microcontinent overrode the granulites and when the granulite belt as such was formed and was overthrusted for at least 100 km towards the southwest in conjunction with the latter event the rocks of the basement of the basin also became involved in thrust movements these now form the tanaelv belt which shows gradational tectonic contacts towards underlying cover and basement rocks of the south lapland karelia craton although not all parts of this craton were affected by the svecokarelian deformation it is considered to belong to the karelian province of the svecokarelian fold belt a ca 1900 1800 ma old episode of wrench faulting and the intrusion of 1790 1770 ma old post kinematic granites concluded the svecokarelian evolution of the northeastern shield region

interhemispheric plasma flows in the equatorial topside ionosphere latitudinal longitudinal and seasonal variations in the field aligned and perpendicular flows measured at an altitude near 830 km by the defense meteorological satellite program f10 satellite are examined these profiles are studied during the nighttime 2100 magnetic local time for solstice periods in 1991 when the solar activity is high latitude and longitude variations show the influence of f region winds in modulating the observed field aligned flows at night large downward field aligned flows of the order 400 600 ms 1 are observed in the winter hemisphere and coincide in longitude with the location of previously identified adiabatic heating effects studied by venkatraman and heelis 1999a interhemispheric flows at 2100 hours local time are seen to extend up to apex heights of 1000 km during times of high solar activity perpendicular drifts however are relatively invariant with latitude as expected

synchronizing ice cores from the renland and agassiz ice caps to the greenland ice core chronology 1 four ice cores from the agassiz ice cap in the canadian high arctic and one ice core from the renland ice cap in eastern greenland have been synchronized to the greenland ice core chronology 2005 gicc05 which is based on annual layer counts in the dye 3 grip and ngrip ice cores volcanic reference horizons seen in electrical conductivity measurements ecm have been used to carry out the synchronization throughout the holocene the agassiz ice cores have been matched to the ngrip ice core ecm signal while the renland core has been matched to the grip ice core ecm signal thus tying the cores to gicc05 furthermore it has been possible to synchronize the renland ice core to ngrip gicc05 in the glacial period back to 60 000 years b2k years before a d 2000 on the basis of a matching of transitions between stadials and interstadials this work brings the total number of ice core records that have been rigorously tied to the gicc05 timescale up to nine renland annual layer thicknesses are increasing with depth during the period from 7 to 8 5 ka b2k a highly unusual observation only matched by a similar thickness increase in the glacial section of the renland core some 60 ka ago annual layer thicknesses in the agassiz ice cores point to a well developed raymond bump in the agassiz ice cap

characteristics of radiation and propagation of seismic waves in northern finland estimated based on records of local earthquakes the characteristics of radiation and propagation of seismic waves required in various seismological applications especially in seismic hazard assessment are estimated in northern finland based on records of local earthquakes 80 records from four stations mw 1 5 to 4 1 h 3 to 25 km northern finland possesses relatively low seismic activity however rather strong earthquakes occurred there in the past we applied coda normalization method to estimate the quality factor q f q0fn and then verified and corrected the q f estimates at low frequencies by stochastic simulations we obtained q0 80 to 100 n 1 1 to 1 2 for hypocentral distances of 20 to 150 km and q0 180 to 350 n 0 7 to 0 9 for hypocentral distances of 150 to 320 km other parameters were estimated by the empirical methods and stochastic simulation of local earthquakes ml 2 0 we estimated the stress drop 200 bars geometrical spreading as a two segment function 1 r for r 0 to 80 km and 1 80 for r 80 to 300 km the duration of seismic motion depending on the hypocentral distance kappa value 0 001 to 0 03 s and some other parameters the obtained high estimates of the stress drop along with rather high q values may result in noticeably increased compared to those that could be expected on average pga estimates in seismic hazard assessment in northern finland

climate changes in northeastern brazil from deglacial to meghalayan periods and related environmental impacts abstract changes in insolation driven by precession and obliquity are considered the major driver of tropical precipitation on orbital time scales and responsible for vegetation and physical landscape changes during the late holocene over tropical south america here we investigate the environmental changes in the karst region of chapada do apodi northeastern brazil neb using a multi proxy approach including carbon 13c oxygen 18o and strontium 87sr 86sr isotopic analyses on speleothems from different caves carbonate bedrock and clastic cave deposits this approach reveals that the balance between soil formation and erosion and their alternating impact on vegetation and precipitation changes occurred in response to variations in the position and intensity of the intertropical convergence zone itcz over the region the high 13c and 18o and low 87sr 86sr values at 4 200 yrs bp indicate a massive episode of soil erosion resulting in the exposure of carbonate bedrocks over a large area of the karst terrain this event marks the beginning of the meghalayan chronozone characterized as the aridification of this region decline in soil production drying out of underground drainages and increased dominance of dry adapted flora species characteristic of a more open vegetation caatinga we investigated if the holocene climatic changes affected human occupation in the neb and found that the overall demographic course is virtually identical to the well established curve characterized by population deflation during middle holocene

compositional and metamorphic controls on velocity and reflectivity in the continental crust an example from the grenville province of eastern quebec we present velocity and density data for a suite of gabbros and metagabbros over a range of metamorphic grades from subgreenschist to the eclogite facies most of these rocks have a mesocratic protolith with overlapping bulk chemistry ranges providing an opportunity to investigate the systematics of mineralogy and physical properties across a wide range of metamorphic grades with minimal compositional variation in addition more mafic gabbros in the eclogite facies were also investigated in order to take into account variations in the extent of transformation of gabbro to eclogite controlled by bulk chemistry the physical properties data are used as the basis for a first order crustal model composed of granitic anorthositic and gabbroic components the objective of constructing the crustal model is to evaluate the relative contribution of compositional variation and metamorphism to the velocity density and reflectivity structure of the continental crust the model suggests that in the upper crust if fracture porosity is neglected composition dominates the velocity and density structure while in the middle and lower crust composition and metamorphism play equally important roles simulations designed to predict potential reflection coefficient size distributions for the various bulk chemistries and mineralogies in the crustal model indicate step increases in the potential for large reflection coefficients that are dominantly controlled by metamorphic grade step increases in reflectivity are predicted between the lower and upper amphibolite facies and between incompletely and completely eclogitized metagabbros in the eclogite facies we also consider several alternative mixing models which account for the effects of one of the three lithologic components occurring as isolated bodies rather than perfectly mixed with the other two components these models indicate a reduction of the potential for large reflection coefficients by as much as 50 emphasizing the importance of the degree of mixing for crustal reflectivity

a log normal spectral analysis of inorganic grain size distributions from a canadian boreal lake core towards refining depositional process proxy data from high latitude lakes better methods for interpreting grain size spectra will enhance current understanding of past transport depositional processes a high resolution inorganic grain size dataset has been measured from a freeze core extracted from alberta lake e a boreal fresh water lake 40 km east of the athabasca oil sands in north eastern alberta canada the grain size spectra are remarkably consistent throughout the core exhibiting a structure comprising six persistent grain size distributions below ca 250 m plus a rare medium sand distribution automated deconvolution of the grain size spectra produced poor results constraining the modes of two of the distributions produced deconvolution solutions that were statistically excellent and consistent with the structure of each spectrum statistical analysis of the constrained solutions indicates that deconvolution successfully extracted independent grain size populations conversely the multimodal spectra generate traditional measures for example mean grain size that are inconsistent combinations of different individual populations and thus are poor proxies of transport depositional processes alberta lake e is situated in a boreal wetland landscape where sediment delivery is dominated by overland flow transport during spring melt this context means that the alberta lake e grain size spectra can be interpreted to reflect i a bedload component transported during short duration high discharge events that reflect the intensity of the melt and ii a finer suspended load component representing material whose magnitude is controlled by the volume of the spring melt stratigraphically bedload and suspended load populations demonstrate different short wavelength and long wavelength cyclicity suggesting that spring melt is likely to be driven by cyclic external forcing factors the links between the grain size spectra and spring melt have potential for generating proxy records that better capture the external controls over spring melt in boreal systems and the risks associated with these energetic hydrodynamics this is exemplified by the coarsest alberta lake e distributions which indicate that more intense spring melt dynamics occurred in pre historical times this article is protected by copyright all rights reserved

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

a gcm based analysis of circulation controls on δ18o in the southwest yukon canada implications for climate reconstructions in the region 1 to improve our understanding of paleoclimatic records in the southwest yukon we examined controls on precipitation 18o using an isotopically equipped atmospheric general circulation model gcm our results show that particularly during the cool season elevated 18o is associated with a deeper aleutian low and stronger southerly moisture flow while lower 18o is associated with the opposite meteorological conditions these results suggest that the large mid 19th century shift towards lower 18o values seen in paleoclimate records from the region was associated with a shift towards a weaker aleutian low while in disagreement with a previous interpretation of this shift it is consistent with records of glacial advance and tree ring growth during the same period and observational studies of aleutian low controls on temperature and precipitation in the region

statistical analysis of an ionospheric parameter as a base for earthquake prediction 1 this paper is related to the use of ionospheric density variations to tentatively predict earthquakes the results of this statistical analysis are presented as a function of various parameters the ion density was recorded by the low altitude satellite demeter during more than 6 years and a search for anomalies was automatically conducted with the complete data set in a second time a software checked if each anomaly could correspond to an earthquake the search was conducted at less than 1500 km from the anomaly positions and until 15 days after the anomaly time the earthquakes have been classified depending on their magnitude depth and position below the sea or inland this attempt to predict earthquakes of course generates a lot of false alarms and wrong detections nevertheless it is shown that the number of good detections increases with the magnitude of the earthquakes in average the number of perturbations is higher the day of the earthquake and then smoothly decreases for the days before earthquakes below the sea are better detected there are seismic areas close to the south atlantic magnetic anomaly and at high latitudes where the number of natural perturbations is too important to expect a high number of good detections finally when there are several perturbations corresponding to a single earthquake it is possible to combine their positions to have a better estimation of the location of the future epicenter however uncertainties about the time and the magnitude are large

lithospheric structure of the bohemian massif and adjacent variscan belt in central europe based on profile s01 from the sudetes 2003 experiment 1 the sudetes 2003 seismic experiment investigated the lithospheric structure of the eastern part of the variscan belt of central europe the key profile of this experiment s01 was 630 km long and extended southwestward from the margin of the east european craton across the trans european suture zone tesz and sudetes and across the bohemian massif that contains the active eger ohre rift which is an element of the european cenozoic rift system good quality first arrivals and later phases of refracted reflected p and s waves were interpreted using 2 d ray tracing techniques the derived seismic model shows large variations in the internal structure of the crust while the depth to the moho varies in the relatively narrow depth interval of 28 35 km except for the polish basin on the northeast end of the profile the sedimentary cover is thin the crystalline upper and middle crust with velocities of 5 9 6 4 km s 1 is about 20 km thick and the 7 10 km thick lower crust can be divided into three regions based on p wave velocities a low velocity region 6 5 6 6 km s 1 beneath eger rift and sudetes that is bounded on the southwest and northeast by regions of significantly higher velocity 6 8 7 1 km s 1 beneath the saxothuringian and moldanubian in the southwest and fore sudetic monocline and polish basin in the northeast high velocity bodies vp 6 5 km s 1 were delineated in the upper crust of the eger rift region the seismic structure along the s01 profile images a variscan orogenic wedge resting on the down warped margin of the plate margin containing the tesz this situation implies the northerly directed subduction of the rheic ocean that existed between the southern margin of the old red continent and the armorican terranes presently accreted into the variscan belt closure of this ocean produced the rheic suture between low velocity crust of the variscan orogenic wedge and higher velocity crust of the tesz

seismic wide angle constraints on the crust of the southern urals a wide angle seismic reflection refraction data set was acquired during spring 1995 across the southern urals to characterize the lithosphere beneath this paleozoic orogen the wide angle reflectivity features a strong frequency dependence while the lower crustal reflectivity is in the range of 6 15 hz the pmp is characterized by frequencies below 6 hz after detailed frequency filtering the seismic phases constrain a new average p wave velocity crustal model that consists of an upper layer of 5 0 6 0 km s which correlates with the surface geology 5 7 km depths at which the velocities increase to 6 2 6 3 km s 10 30 km depths at which on average the crust is characterized by velocities of 6 6 km s and finally the lower crust from 30 35 km down to the moho which has velocities ranging from 6 8 to 7 4 km s two different s wave velocity models one for the n s and one for the e w were derived from the analysis of the horizontal component recordings crustal sections of poisson s ratio and anisotropy were calculated from the velocity models the poisson s ratio increases in the lower crust at both sides of the root zone a localized 2 3 anisotropy zone is imaged within the lower crust beneath the terranes east of the root this feature is supported by time differences in the sms phase and by the particle motion diagrams which reveal two polarized directions of motion velocities are higher in the central part of the orogen than for the siberian and eastern plates these seismic recordings support a 50 56 km crustal thickness beneath the central part of the orogen in contrast to moho depths of 45 km documented at the edges of the transect the lateral variation of the pmp phase in frequency content and in waveform can be taken as evidence of different genetic origins of the moho in the southern urals

thermal decomposition of carbonates in fault zones slip weakening and temperature limiting effects 1 during an earthquake the heat generated by fault friction may be large enough to activate the devolatilization of minerals forming the fault rocks in this paper we model the mechanical effects of calcite thermal decomposition on the slip behavior of a fault zone during an earthquake to do so we introduce the coupled effects of calcite volume loss heat consumption and co2 production in the theoretical analysis of shear heating and thermal pressurization of pore fluids we consider a rapidly deforming shear band consisting of a fluid saturated carbonate rock the equations that govern the evolution of pore pressure and temperature inside the band and the mass of emitted co2 are deduced from the mass and energy balance of the multiphase saturated medium and from the kinetics of the chemical decomposition of calcite numerical simulation of seismic slip at depths of 5 to 8 km show that decarbonation has two critical consequences on fault slip first the endothermic reaction of calcite decomposition limits the coseismic temperature increase to less than 800 c corresponding to the initiation of the chemical reaction inside the shear band second the rapid emission of co2 by decarbonation significantly increases the slip weakening effect of thermal pressurization the pore pressure reaches a maximum and then decreases due to the reduction of solid volume causing a restrengthening of shear stress our theoretical study shows on the example of decarbonation that the thermal decomposition of minerals is an important slip weakening process and that a large part of the frictional heat of earthquakes may go into endothermic devolatilization reactions

lithoprobe reflection studies of archean and proterozoic crust in canada abstract lithoprobe canada s national collaborative earth science research project established to develop a comprehensive understanding of the evolution of the north american continent is a multidisciplinary program spearheaded by seismic reflection studies five recently recorded seismic lines discussed in this paper are located in precambrian regions the mesoproterozoic grenville province the paleoproterozoic trans hudson orogen tho the paleoproterozoic archean basement of alberta and the archean superior province data acquired across the grenville orogen in eastern quebec show strong reflectivity throughout the crust upper crustal reflections can be correlated with exposed structural elements including extensional shear zones and packages of deformed high pressure rocks eclogites in a marine survey across the grenville orogen off southeastern labrador seismic images show variably dipping reflections and a structural high associated with a major gravity anomaly data acquired across central alberta show crustal scale thrust stacking and imbrication of the archean hearne craton to the east across the trans hudson orogen images of similar collisional features are observed geochronologic constraints indicate contemporaneity of tectonic activity between the two regions at 1 8 ga suggesting that collisional tectonic activity was coeval over a broad crustal region ca 1000 km across strike in the superior province seismic data across a collision zone involving the northern abitibi greenstone belt and the arc related opatica plutonic belt show spectacular crustal reflectivity and dipping reflections that extend 8 s 30 km into the mantle the latter feature is interpreted as representing a relict 2 69 ga old suture associated with subduction providing the first direct evidence that plate tectonics was active in the late archean these five examples supported by other lithoprobe results refute a number of generalizations about crustal reflectivity that have been made in the past and illustrate how reflection studies combined with other geoscience studies can lead to a better understanding of precambrian tectonics reflectivity persists throughout the crust there is no general separation into a poorly reflective upper crust and a reflective lower crust crustal reflectivity in archean and proterozoic regions is as pervasive as that in areas of more recent tectonism the precambrian reflection moho is generally well defined but shows a range of characteristics relative ages of reflectors can be discerned and tectonic significance can be attached to characteristic features of the crustal reflectivity

holocene thinning of the greenland ice sheet the nature of the response of the greenland ice sheet gis to climate change is a fundamental question in climate science but the details remain unclear during the holocene climate optimum 6 000 to 9 000 years ago for example many locations in the northern hemisphere showed unusual warmth yet changes in greenland appeared inconsistent vinther et al now standardize the previously disparate seeming ice core records of climate history on the gis during the holocene and find consistent evidence for a stronger climate optimum than was previously recognized together with elevation reduction and marginal ice sheet thinning the response of the greenland ice sheet gis to changes in climate remains uncertain during the holocene climatic optimum an unusually warm period from about 9 000 to 6 000 years ago changes in greenland appear inconsistent with the rest of the northern hemisphere here the greenland holocene temperature history and the evolution of gis surface elevation are extracted from four gis locations the results may resolve this disparity on entering an era of global warming the stability of the greenland ice sheet gis is an important concern1 especially in the light of new evidence of rapidly changing flow and melt conditions at the gis margins2 studying the response of the gis to past climatic change may help to advance our understanding of gis dynamics the previous interpretation of evidence from stable isotopes 18o in water from gis ice cores was that holocene climate variability on the gis differed spatially3 and that a consistent holocene climate optimum the unusually warm period from about 9 000 to 6 000 years ago found in many northern latitude palaeoclimate records4 did not exist here we extract both the greenland holocene temperature history and the evolution of gis surface elevation at four gis locations we achieve this by comparing 18o from gis ice cores3 5 with 18o from ice cores from small marginal icecaps contrary to the earlier interpretation of 18o evidence from ice cores3 6 our new temperature history reveals a pronounced holocene climatic optimum in greenland coinciding with maximum thinning near the gis margins our 18o based results are corroborated by the air content of ice cores a proxy for surface elevation7 state of the art ice sheet models are generally found to be underestimating the extent and changes in gis elevation and area our findings may help to improve the ability of models to reproduce the gis response to holocene climate

the crustal structure along the polar profile from seismic refraction investigations abstract seismic refraction investigations along a 440 km long profije on the northern baltic shield have resolved the crustal structure in this area of archaean to early proterozoic lithosphere formation the profile called the polar profile extends approximately along a sw ne oriented line from the karelian province in northern finland across the lapland granulite belt and the kola peninsula province to the varanger peninsula in northeastern norway at six shotpoints large explosions 200 1680 kg and at three shotpoints small explosions 80 kg were detonated and recorded at an average station spacing of 2 km providing high quality record sections a two dimensional cross section of the crust was obtained by forward modelling using ray tracing techniques high velocity bodies are found in the upper crust related to the karasjok kittila greenstone belt and the lapland granulite belt they extend to a depth of 6 13 km in the karelian province in the southwest a low velocity zone was found between the depths of 8 and 14 km the middle crust shows a slight increase in the average velocities from the southwest to the northeast and a small velocity jump is found along a mid crustal boundary between 18 and 21 km the thickness of the middle crust varies between 16 and 18 km the lower crust and the crust mantle boundary moho show considerable lateral variation the top of the lower crust lies between 26 and 33 km while its thickness decreases from 21 km in the southwest to 10 14 km beneath the lapland granulite belt and the inari terrain reaching 20 km again in the extreme northeast the velocities also change laterally the thin lower crust is characterized by rather low velocities 6 8 6 9 km s whereas in the southwest and northeast the velocities 6 9 7 3 km s resemble more typical shield structures the moho is found at 47 km in the karelian province rises to 40 km beneath the lapland granulite belt and descends to 46 km in the northeastern part of the kola peninsula province the upper mantle velocities at the moho range from 8 1 km s in the region of the thin crust to 8 5 km s and more beneath the karelian province it is tempting to suggest that the anomalous lower crust underlying the lapland granulite belt and the inari terrain may represent the remnants of an early proterozoic back arc basin that was active prior to the 2 0 to 1 9 ga plate convergence event during which the lapland granulite belt was thrust onto the archaean basement of the karelian province another explanation is to assume that the velocity reduction in the anomalous lower crust was caused by a rather pronounced uplift of this region following the 1 9 ga collision event

geophysical constraints on the crustal structure of the east european platform margin and its foreland based on the polcrust 01 deep reflection seismic profile abstract a new 240 km long deep seismic reflection profile polcrust 01 was recently acquired in se poland crossing the east european platform eep margin south east of the north german polish caledonides ngpc here we document geophysical field work and subsequent data processing and modeling results obtained from reflection seismic data are augmented by results of the first arrival tomography applied to co located extended offset refraction data as well as potential field modeling and comparison with the available wide angle reflection refraction data our preferred model of the crustal structure derived by integrating seismic potential field and geological data is composed of crustal blocks terranes separated by nearly vertical faults these are i intact part of the eep ii ysogory terrane iii malopolska terrane and iv carpathian mts with their basement reflective lower crust of the eep can be an inherited feature of crustal extension rifting or compressional tectonics acting at the cratonic margin the teisseyre tornquist zone ttz is depicted as a caledonian transcurrent accretion zone corresponding with the near vertical tomaszow fault bounding the ysogory terrane to the east the crust of the ysogory terrane suggests eep affinity although its middle lower crust thickness is highly reduced the malopolska terrane seems to be internally subdivided into blocks of different magnetic properties of the lower crust the carpathian frontal thrust is associated with a change in the rock properties in the deep basement an unknown crustal block which is not visible in seismic data alone the interpreted structure of the caledonian terranes and their tectonic boundaries favors a transcurrent style of a crustal accretion along the central and se polish segments of the ttz implying a very complex nature of the caledonian accretionary belt of central europe from an array of terranes displaced along the ttz to an accretionary wedge of the collisional ngpc orogen between nw poland and southern north sea area

seismic model of the crust and upper mantle in the scythian platform the dobre 5 profile across the north western black sea and the crimean peninsula the scythian platform scp with a heterogeneous basement of baikalian variscan cimmerian age is located between the east european craton eec on the north and the crimean caucasus orogenic belt and the black sea bs basin on the south in order to get new constrains on the basin architecture and crustal structure of the scp and a better understanding of the tectonic processes and evolution of the southern margin of the eec during mesozoic and cenozoic time a 630 km long seismic wide angle refraction and reflection warr profile dobre 5 was acquired in 2011 october it crosses in a w e direction the fore dobrudja trough the odessa shelf of the bs and the crimean plain the field acquisition included eight chemical shot points located every 50 km and recorded by 215 stations placed every 2 0 km on the land in addition the offshore data from existing profile 26 placed in the odessa shelf were used the obtained seismic model shows clear lateral segmentation of the crust within the study region on four domains the fore dobrudja domain km 20 160 an offshore domain of the karkinit trough at the odessa shelf of the bs km 160 360 an onshore domain of the central crimean uplift crimean plain km 360 520 and the indolo kuban trough at the kerch peninsula km 520 620 that is the easternmost part of the crimea two contrasting domains of the scp within the central part of the dobre 5 profile the karkinit trough and the central crimean uplift may represent different stages of the scp formation a deep karkinit trough with an underlying high velocity 7 16 km s 1 lower crust body suggests its rifting related origin during early cretaceous time the central crimean uplift represents a thick up to 47 km crustal domain consisting of three layers with velocities 5 8 6 4 6 5 6 6 and 6 7 7 0 km s 1 which could be evidence of this part of the scp originating on the crust of precambrian craton eec the thick heterogeneous basement of the central crimean uplift shows inclusions of granitic bodies associated with magmatic activity related with variscan orogeny within the scp general bending and crustal scale buckling of the central crimean uplift with a wavelength of 230 km could be an effect of the alpine compressional tectonics in the adjacent crimean mountains the extended rifted continental margin of the scp eec at the odessa shelf and buckling uplifted domain of the central crimean uplift affected by compressional tectonics are separated by the n s oriented western crimean fault the crust of the southern margin of the eec is separated from the scp which originated on the eec crust tectonised and reworked during the palaeozoic mesozoic by the crustal fault of w e orientation which corresponds with the golitsyn fault observed at the surface between the eec and the scp the fore dobrudja domain with a thick 10 km heterogeneous basement and two subhorizontal layers in the crystalline crust with velocities 6 2 6 3 and 6 4 6 65 km s 1 differs from the scp crust and its origin could be very similar to that of the trans european suture zone and palaeozoic west european platform

the accretionary svecofennian orogen insight from the babel profiles abstract the babel profiles b c 1 7 form a 1200 km long nearly continuous cross section through the svecofennides the near vertical marine reflection profiles display a wide range of crustal structures that can be associated with both the accretionary svecofennian orogeny 1 96 1 75 ga and the following subjotnian and jotnian rift stages 1 65 1 11 ga the svecofennian accretionary orogeny took place when a number of micro plates with island arc affinities and surface expression of a large archipelago accreted to the continental karelian plate some of the accreting terranes seem to have had older cores that have acted as crustal indentors during the collision babel profiles 3 and 4 image a series of collisional terrane boundaries between karelian continental margin savo arc sa and central finland arc cfa in the north the karelian margin has been both over and underthrust by the savo arc cfa comprises a folded thrust package on top of a continental nucleus and the savo arc the associated subduction zone and accretionary prism are interpreted to lie to the south underneath the bothnian basin area where prominent ne dipping lower to middle crustal reflections are found along babel profiles 1 and 4 an oblique collision of the central finland arc and the continent resulted in the development of the strike slip fault on the young hot savo arc babel profiles 1 6 7 and c image the internal architecture of the southern and central finland arcs the unusually thick crust 55 60 km hosts unreflective high density mafic intrusions acting as a crustal indentor a highly reflective antiform structure developed on the southern side of it southern finland arc complex sfa is an imbrication structure comprising stacked slices of arc related crust on an older continental nucleus bergslagen nucleus prior to the collision the sfa suffered from gravitational collapse during which the crust was thinned profile b images the architecture of the central and southern swedish svecofennides the sormland terrane sob is interpreted as the accretionary prism of the southern finland arc squeezed between the svecofennian collage in the north and the advancing continent to the south the southern continent island arc is characterised by ne dipping crustal reflections and moho offsets as well as step wise increasing thickness of the crust after the final collision large volumes of mantle derived material intruded the crust as large mushroom shaped plutons they are interpreted as the heat source for the tib magmatism in southern and western scandinavia

el nino southern oscillation events recorded in the stratigraphy of the tropical quelccaya ice cap peru snow accumulation measured during 1982 1983 on the quelccaya ice cap peru was 70 percent of the average from 1975 through 1983 inspection of 19 years 1964 through 1983 of accumulation measured near the summit of quelccaya reveals a substantial decrease 30 percent in association with the last five el nino southern oscillation enso occurrences in the equatorial pacific the enso phenomenon is now recognized as a global event arising from large scale interactions between the ocean and the atmosphere understanding this extreme event with the goal of prediction requires a record of past occurrences the quelccaya ice cap which contains 1500 years of annually accumulated ice layers may provide a long and detailed record of the most extreme enso events

wide angle reflection migration technique with an example from the polar profile northern scandinavia abstract the 440 km long polar profile runs approximately sw to ne across the baltic shield from the karelian province through the lapland granulite belt and the kola peninsula province in northern finland and northern norway the migration method developed by v n pilipenko physics of the earth n1 1983 36 42 was applied to the wide angle reflection data obtained along the profile to prepare the data for the migration p and s waves were analysed with more attention to the distribution of real reflectors in the crust and on the relation between the p and s wave velocities depth migrated images of the crustal structure were obtained for both the p and s wave fields this new analysis revealed structural features of the crust which had not before been imaged the most impressive features are several inclined boundaries in the upper crust dipping northeast beneath the lapland granulite belt another newly found element is a lower crustal boundary at a depth of 35 km in the karelian province which is well traced in the p wave migration image but is not observed in the s wave image this boundary corresponds to a strong change in the v p v s ratio in the lower crust which may be interpreted in terms of mafic crustal composition we have found that this migration technique can be applied to deep seismic sounding data resulting in new opportunities for deep crustal seismic studies nevertheless more and denser observations are necessary to continue the improvement of the resolution and the reliability of the structure images

petrology and geochemistry of mafic granulite xenoliths from the lahtojoki kimberlite pipe eastern finland abstract the lahtojoki kimberlite pipe in kaavi eastern finland contains lower crustal mafic granulite xenoliths with a mineral assemblage cpx amph pl grt opx bt the tweequ thermobarometry indicates crystallization at ca 800 900 c and 0 75 1 25 gpa which corresponds with crustal depths of ca 22 38 km reaction textures and results of thermobarometry in some xenoliths indicate post peak decompression with cooling chemical composition of the xenoliths suggest that their protoliths crystallized from basaltic melts with some k enrichment their ree patterns are slightly lree enriched some xenoliths having small negative eu anomalies the u pb ion probe dating of zircons from two samples yielded variable ages for zircons even in the same xenolith between ca 2 6 and 1 7 ga these ages correspond with main late archaean and palaeoproterozoic orogenic events in the fennoscandian shield the sm nd garnet clinopyroxene isochron age from one dated sample is 1 6 ga which represents either a cooling or reheating of the lower crust by rapakivi magmatism because the petrology geochemistry and ages of xenoliths do not correlate well with the nearest exposed archaean mafic granulites it is evident that the present lower crust underlying the archaean rocks has a considerable palaeoproterozoic component

constraints on seismic velocity anomalies beneath the siberian craton from xenoliths and petrophysics high seismic vp velocity anomalies 8 7 9 0km s 1 have long been known about in regions of the uppermost mantle of the siberian craton often in association with kimberlite fields laboratory measurement of seismic properties of five xenoliths three peridotites and two eclogites from the udachnaya kimberlite under confining pressures up to 600 mpa were extrapolated to uppermost mantle p t conditions of 1500 mpa and 500 c however none of the velocities are high enough to explain the observations eclogites or peridotites are commonly considered to be the source of anomalous high velocities we prefer a peridotitic source to an eclogitic source due to the unusual chemistry and regional uniformity of eclogitic garnets required maximum velocity limitations on laboratory measurements of seismic properties of natural eclogites and purported abundance of eclogites in the lithosphere alternatively a highly depleted peridotite such as dunite or harzburgite can produce velocities high enough to match observations olivine petrofabrics in most peridotites including the three peridotites used in this study are great enough to produce the observed high velocities provided olivine petrofabrics are continuous enough and correctly oriented to be seismically detectable and the modal proportion of olivine is high there have been suggestions by other authors that the siberian upper mantle is highly depleted and that a lithosphere scale shear zone exists which may have acted to organize fabrics into segments large enough for detection anomalously high vp vs velocity ratios of greater than 1 8 are expected parallel to the olivine 100 maxima required to be present in a high velocity olivine dominated upper mantle vp vs velocity ratios can serve as a means of inferring large scale anisotropy when limited seismic data are available as in siberia 2006 elsevier b v all rights reserved

seismic velocities and anisotropy of the lower continental crust a review seismic anisotropy is often neglected in seismic studies of the earth s crust since anisotropy is a common property of many typically deep crustal rocks its potential contribution to solving questions of the deep crust is evaluated the anisotropic seismic velocities obtained from laboratory measurements can be verified by computations based on the elastic constants and on numerical data pertaining to the texture of rock forming minerals for typical lower crustal rocks the influence of layering is significantly less important than the influence of rock texture surprisingly most natural lower crustal rocks show a hexagonal type of anisotropy maximum anisotropy is observed for rocks with a high content of aligned mica it seems possible to distinguish between layered intrusives and metasediments on the basis of in situ measurements of anisotropy which can thus be used to validate different scenarios of crustal evolution

the diffusive ocean conveyor 1 we use a novel path density transport diagnostic to trace out the deep branch of the ocean conveyor in a global circulation model our results suggest that the majority of the world s deep water is not transported back to the surface along the current systems of the standard great ocean conveyor goc standard goc routes are evident only for waters with interior residence times less than about a thousand years accounting for less than a quarter of the ventilation to re exposure flux waters with longer are spread across the deep oceans by the diffusive conveyor and by 3000 years organized into a characteristic deep north pacific pattern that is dominated by eddy diffusion the observed depletion of oxygen and 14c in the deep n pacific is consistent with a diffusive conveyor and should not be interpreted as evidence of an advective terminus of the goc deep branch

seismic structural and petrological models of the subcrustal lithosphere in southern germany a quantitative revaluation anisotropy in the subcontinental lithosphere becomes increasingly important because it is observed in many seismic studies especially for p n waves typical rocks of the uppermost mantle are peridotites which predominantly exhibit a pronounced elastic anisotropy this anisotropy is mainly caused by the anisotropic elastic properties and the lattice preferred orientation here referred to as texture of olivine to evaluate the elastic anisotropy of peridotites from the subcontinental lithosphere specimens of the northern hessian depression germany and the balmuccia ultramafic massif northern italy have been used they comprise four olivine texture types which are characteristic for olivine textures observed worldwide the bulk rock elastic properties have been calculated using olivine and orthopyroxene textures their single crystal elastic constants at ambient pressure temperature conditions and their volume fraction clinopyroxene and spinel are assumed to be randomly distributed the effect of four different orientations of the foliation within the uppermost mantle has been evaluated since this orientation is usually unknown two of the olivine textures have a pronounced azimuthal dependence of compressional waves when a horizontal foliation within the uppermost mantle is presumed these variations cause significant azimuthal variations of the p wave reflections coefficients at the moho primarily we predict a significant azimuthal dependence of the critical points where the reflected amplitude increases from approximately 15 to 95 possibly these azimuthal variations can be detected by seismic reflection measurements carried out at earth surface the remaining two texture types only manifest a small directional dependence when anisotropy of compressional waves is observed in seismic studies these latter types can only be of subordinate importance however all of the peridotites investigated are able to explain the seismically observed azimuthal variations of compressional waves when a vertical foliation is proposed this ambiguity can be substantially reduced when shear waves s waves are considered the directional distribution of s wave velocities and of the s wave splitting exhibits characteristic patterns for the different olivine texture types this could be used to discriminate between different texture types and orientations of the foliation within the uppermost mantle a fundamental requirement for a more comprehensive interpretation is the availability of detailed s wave observations the maximum s wave splitting in the peridotites investigated coincides with the maximum of the faster leading s wave this may be of importance to detect s wave splitting in future seismic studies

anisotropy in multi offset deep crustal seismic experiments modelling of deep seismic wide angle data commonly assumes that the earth is heterogeneous and isotropic it is important to know the magnitudes of errors that may be introduced by isotropic based wide angle models when the earth is anisotropic it is equally important to find ways of detecting anisotropy and determining its properties this paper explores the errors introduced by interpreting anisotropic seismic data with isotropic models errors in p wave reflector depths are dependent on the magnitude of the velocity anisotropy and the direction of the fast axis the interpreted isotropic model velocity function is found to correspond closely to the horizontal velocity of the anisotropic medium an additional observed parameter is the time mismatch which we define to be the difference between the vertical two way traveltime to a reflector and the time converted wide angle position of the reflector the magnitude of the time mismatch is typically 1 0 s when the whole crust is anisotropic and is found to be closely related to the magnitude and sign of the anisotropic anellipticity the relationships are extendible to more complicated models including those with vertical velocity gradients crustal zonation and lower symmetry orders a time mismatch may be symptomatic of the presence of anisotropy we illustrate the observation of a time mismatch for a real multi offset seismic data set collected north of scotland and discuss the implications for crustal anisotropy in that region

velocity measurement bias of the ambient noise method due to source directivity a case study for the swedish national seismic network the bias of velocity measurements from ambient noise covariograms due to an anisotropic distribution of noise sources is studied assuming that the noise field consists of planar surface waves from

equatorial longitude and local time variations of topside magnetic field aligned ion drifts at solar minimum 1 in the topside ionosphere the high mobility of the plasma along the magnetic field allows field aligned ion drifts to occur readily as a result of field aligned gravitational forces collisional forces or pressure gradients therefore variations in the field aligned ion drifts can be used to explore the influence of thermospheric electrodynamic and chemical processes on the ionosphere longitude and local time variations in the field aligned ion drifts near the magnetic equator are presented using observations from the coupled ion neutral dynamics investigation on board the communications navigation outage forecast system satellite these observations were obtained during the period of extremely low solar activity present in 2008 and 2009 allowing the seasonal local time and longitudinal variations to reveal the relative importance of the processes responsible for topside field aligned plasma drifts during solar minimum this investigation found that the low altitude winds and tides the net ionization or loss and the meridional e b drift were all influential in creating longitudinal and local time variations in the field aligned drift though the strength of the influence seen by each driver was found to vary with season local time and longitude

connecting the atlantic sector and the north pacific mt logan ice core stable isotope records during the holocene the role of el nino the 18o holocene of the mt logan ice core is very different from those of eastern arctic canada and greenland the large changes seen in logan dwarf even the largest change the cooling event 8200 years ago in the atlantic sector cores large changes in logan s 18o and d are related to the state of el nino as reflected by the quelccaya 18o series it is found that the lagged auto difference series of the ice core records from the agassiz ice cap greenland and the 23 site stack of paleotemperature records of kaufman et al kaufman ds schneider dp mckay np ammann cm bradley rs briffa kr et al 2009 recent warming reverses long term arctic cooling science 325 1236 produce highly significant matches to the mt logan 18o series these correspondences suggest a lag of 1200 years this lag time is what some models of the diffusive great ocean conveyor d goc predict for the average travel time from the north atlantic to the tropical eastern pacific monte carlo testing of the correlation

crust and upper mantle structure along the dss baltic profile in se finland summary the 430 km long dss baltic profile in se finland runs through the rapakivi intrusion the svecokarelian geosynclinal complex including the ladoga bothnian bay zone and the archean basement complex a brief description of field operations in 1982 is presented record sections of p and s waves were used for the interpretations a starting model was constructed by inverse methods and improved by dynamic ray tracing modelling three blocks are indentified on the cross section from sw to ne these are the southern associated with the rapakivi massif depth to moho m about 40 km the central ladoga bothnian bay zone with m of approximately 55 60 km and the northern archean crystalline basement with m about 40 45 km the average crustal velocity is 6 6 6 7 kms the crustal structure along the baltic profile is compared with the surrounding dss profiles finnish sveka and soviet kern tulos and ladoga profiles the eastern border of the ladoga bothnian bay zone was located and specific features of the crust and uppermost mantle along the profile area are discussed

an array study of lithospheric structure across the protogine zone varmland south central sweden signs of a paleocontinental collision abstract a small seismological array was installed on both sides of the protogine zone pz in varmland south central sweden to study the structure of the mantle lithosphere and lateral variations of its anisotropy no distinct isotropic velocity anomalies were detected by tomography in the upper mantle around the pz the observed velocity variations depending on the direction of propagation can be explained by anisotropy within the subcrustal lithosphere on both sides of the suture the best solution of a joint analysis of anisotropic inferences from teleseismic p residual spheres and an inversion of shear wave splitting parameters resulted in 3d self consistent anisotropic models of blocks of the subcrustal lithosphere the anisotropic structures within the lithosphere are approximated by hexagonal models k p 5 with low velocity symmetry axes the high velocity planes dip to the e in a region westward of the pz and to the nw eastward of the pz the pz can be interpreted as a steep and narrow suture cutting the whole lithosphere and separating the two anisotropic blocks of different origin

evidence for early proterozoic plate tectonics from seismic reflection profiles in the baltic shield plate tectonics provides the linking framework for all tectonic and magmatic activity seen today but it is not known when plate tectonics first developed on earth new deep seismic reflection and

physical properties of ultrahigh pressure metamorphic rocks from the sulu terrain eastern central china implications for the seismic structure at the donghai ccsd drilling site about 30 samples representing major lithologies of sulu ultrahigh pressure uhp metamorphic rocks were collected from surface exposures and exploration wells and compressional vp and shear wave vs velocities and their directional dependence anisotropy were determined over a range of constant confining pressures up to 600 mpa and temperatures ranging from 20 to 600 degreesc samples range in composition from acidic to ultramafic p and s wave velocities measured at 600 mpa vary from 5 08 to 8 64 km s and 2 34 to 4 93 km s respectively densities are in the range from 2 60 to 3 68 g cm 3 to make a direct tie between seismic measurements refraction and reflection and subsurface lithologies the experimental velocity data corresponding to shallow depths were used to calculate velocity profiles for the different lithologies and profiles of reflection coefficients at possible lithologic interfaces across the projected 5000 m chinese continental scientific drilling program ccsd crustal segment comparison of calculated in situ velocities with respective intrinsic velocities suggests that the in situ velocities at shallow depths are lowered by an increased abundance of open microcracks the strongly reflective zone beneath the donghai drill site can be explained by the impedance contrasts between the different lithologies contacts between eclogite peridotite and felsic rocks gt gneiss granitic gneiss in particular may give rise to strong seismic reflections in addition shear induced lattice preferred orientation lpo related seismic anisotropy can increase reflectivity for the explanation of the high velocity bodies 6 4 km s around 1000 m and below 3200 m depth large proportions of eclogite peridotite about 40 and 30 vol respectively are needed c 2002 elsevier science b v all rights reserved

geochemical and tectono magmatic evolution of the volcano sedimentary rocks of pechenga and other greenstone fragments within the kola greenstone belt russia abstract the early proterozoic volcano sedimentary pechenga and imandra varzuga regions form the two larger fragments within the kola greenstone belt a prominent feature of the north eastern baltic shield this belt also contains three smaller fragments at polmak pasvik and ust ponoy the geology of the larger fragments consists of an older northern and a younger southern part separated by prominent conformable deformation zones accordingly the 2350 1850 ma lithological succession of the pechenga greenstone fragment is subdivided into the northern 2550 1905 ma and southern pechenga complexes 1905 1700 ma likewise the imandra varzuga fragment comprises the northern and southern imandra varzuga complexes the relatively better known northern pechenga complex is subdivided into four units which in turn are subdivided into 11 formations in contrast southern pechenga complex comprises only one unit subdivided into four volcano sedimentary and two volcanic formations both the volcanic and volcaniclastic components of these complexes are characterised by magmatic compositions ranging from basaltic andesite to trachybasalt trachyandesite basalt ferropicrite basalt picrite basalt andesite picrite basalt and andesite dacite rhyolite the gabbro wehrlite intrusions hosting the pechenga ni cu sulphide deposits lower down in the stratigraphy are petrogenetically related to ferropicritic volcanics volcanic rocks of the southern pechenga complex extruded from six autonomous contemporaneous volcanic centres the volcanic rocks belong to two geochemical cycles each starting with tholeiitic and ending with calc alkaline magmas these changes reflect magmatic responses to major tectonic phases of crustal rifting and closure changes in the sr and nd isotope ratios indicate that the magmatic melts originated in various deep mantle and mantle crustal source areas a systematic gradual geochemical change is observed between subsequent volcanic formations notwithstanding the fact that the deposition of such volcanic formations is commonly interrupted by sedimentary events changes in the magmatic source were therefore gradual and the magmatic processes were continuous the kola greenstone belt formed as an intracontinental rift kalevian rifting event that has undergone a complex tectono metamorphic evolution during the karelian orogenic megacycle 2550 1700 ma of the northern baltic shield the history of two complete tectono magmatic cycles the lapponian cycle and the svecofennian cycle within this megacycle is recorded in the volcano sedimentary successions of the pechenga fragment the complete lapponian cycle is embodied within the volcanic sequence of the imandra varzuga fragment where the composition of the volcanic and volcano sedimentary rocks range from tholeiitic and boninitic basalts to basaltic andesites calc alkaline rhyodacite boninitic picrite basalts and basaltic andesites subalkalic trachybasalts and trachyandesites here the subsequent svecofennian cycle is represented by tholeiitic basalts and ferropicrites followed al rich basalts and concluded by dacite rhyolites trachyandesites and trachytes during the final phases of the kalevian rifting event tholeiitic and ferropicritic magmas were generated from two distinct mantle sources the tholeiitic magma was derived from a subabyssal depleted mantle source in contrast the ferropicritic magma came from an abyssal metasomatically enriched mantle source the larger degree of mantle contamination in the latter was probably critical in the formation of the ni cu ores of the pechenga gabbro wehrlite intrusions

a minimum thermodynamic model for the bipolar seesaw 1 the simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of antarctic ice cores the model results from the classic bipolar seesaw by coupling it to a heat reservoir in this thermal bipolar seesaw the heat reservoir convolves northern time signals with a characteristic timescale applying the model to the data of grip and byrd we demonstrate that maximum correlation can be obtained using a timescale of about 1000 1500 years higher correlations are obtained by first filtering out the long term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw the model resolves the apparent confusion whether northern and southern climate records are in or out of phase synchronous or time lagged

formal subdivision of the holocene series epoch a discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommission on quaternary stratigraphy international commission on stratigraphy this discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommision on quaternary stratigraphy sqs of the international commission on stratigraphy ics considers the prospects for a formal subdivision of the holocene series epoch although previous attempts to subdivide the holocene have proved inconclusive recent developments in quaternary stratigraphy notably the definition of the pleistocene holocene boundary and the emergence of formal subdivisions of the pleistocene series epoch mean that it may be timely to revisit this matter the quaternary literature reveals a widespread but variable informal usage of a tripartite division of the holocene early middle or mid and late and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology we propose an early middle holocene boundary at 8200 a bp and a middle late holocene boundary at 4200 a bp each of which is linked to a global stratotype section and point gssp should the proposal find a broad measure of support from the quaternary community a submission will be made to the international union of geological sciences iugs via the sqs and the ics for formal ratification of this subdivision of the holocene series epoch copyright 2012 john wiley sons ltd

volcanic aerosol records and tephrochronology of the summit greenland ice cores the recently collected greenland ice sheet project 2 gisp2 and greenland ice core project ice cores from summit greenland provide lengthy and highly resolved records of the deposition of both the aerosol h2so4 and silicate tephra components of past volcanism both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism climate system the continuous time series of volcanic so42 for the last 110 000 years show a strong relationship between periods of increased volcanism and periods of climatic change the greatest number of volcanic so42 signals many of very high magnitude occur during and after the final stages of deglaciation 6000 17 000 years ago possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins sea level change the increase in the number of volcanic so42 signals at 27 000 36 000 and 79 000 85 000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation respectively a comparison of the electrical conductivity of the gisp2 core with that of the volcanic so42 record for the holocene indicates that only about half of the larger volcanic signals are coincident in the two records other volcanic acids besides h2so4 and other so42 sources can complicate the comparisons although the threshold level picked to make such comparisons is especially critical tephra has been found in both cores with a composition similar to that originating from the vatnaoldur eruption that produced the settlement layer in iceland mid a d 870s from the icelandic eruption that produced the saksunarvatn ash 10 300 years ago and from the icelandic eruption s that produced the z2 ash zone in north atlantic marine cores 52 700 years ago the presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras the presence of both rhyolitic and basaltic shards in the z2 ash in thegisp2 core and the composition of the basaltic grains lend support to multiple icelandic sources torfajokull area and katla for the z2 layer deposition of the z2 layer occurs at the beginning of a stadial event further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions

lithospheric structure beneath trans carpathian transect from precambrian platform to pannonian basin celebration 2000 seismic profile cel05 1 in 2000 a consortium of european and north american institutions completed a huge active source seismic experiment focused on central europe the central european lithospheric experiment based on refraction or celebration 2000 this experiment primarily consisted of a network of seismic refraction profiles that extended from the east european craton along and across the trans european suture zone region in poland to the bohemian massif and through the carpathians and eastern alps to the pannonian basin the longest profile cel05 1420 km is the focus of this paper the resulting two dimensional tomographic and ray tracing models show strong variations in crustal and lower lithospheric structure clear crustal thickening from the pannonian basin 24 25 km thick to the trans european suture zone region 50 km together with the configuration of the lower lithospheric reflectors suggests northward subduction of mantle underlying carpathian pannonian plate under the european plate this however conflicts with strong geological evidence for southward subduction and we present three tectonic models that are to not totally mutually exclusive to explain the lithospheric structure of the area 1 northward old subduction of the pannonian lithosphere under the east european craton in the jurassic lower cretaceous 2 a collisional zone containing a crocodile structure where carpatho pannonian upper crust is obducting over the crystalline crust of the east european craton and the carpathian pannonian mantle lithosphere is underthrusting cratonic lower crust and 3 lithosphere thinning due to the effects of neogene extension and heating with the slab associated with young subduction southward in the miocene having been either detached and or rolled back to the east in the last case the northwestward dipping in the lithosphere can be interpreted as being due to isotherms that could represent the lithosphere asthenosphere boundary in the pannonian region

seismic velocities and q factors in the uppermost crust beneath the sveka profile in finland the sveka deep seismic sounding profile in central finland was shot in 1981 to study the crustal structure of the fennoscandian shield in the contact zone between the archaean and svecokarelian provinces apart from p and s waves well developed rayleigh surface waves r waves with periods of 0 5 2 0 s were recorded from all the shot points in the frequency band 0 5 2 5 hz the r waves were clearly observed on the entire 325 km long profile amplitudes of p s and r waves corrected for charge size were used to study the attenuation of waves and q factors from the records of body and r waves the distributions of seismic velocities and quality factors were determined using the dynamic ray tracing method 2 d modelling and the reflectivity method 1 d modelling in the 2 d model of the uppermost crust the p wave velocities vary from 5 8 5 9 km s at the top to 6 2 6 3 km s at a depth of 6 km the velocity ratio solvpvs varies with depth and distance from 1 67 to 1 74 reaching its maximum value of 1 8 2 0 in the uppermost 200 500 m and values of 1 76 1 80 in the uppermost 1 km the quality factors qp and qs vary in the uppermost 1 km from 20 to 120 reaching a higher value of 140 in the marginal zone of the archaean basement in the depth range of 1 2 km q values of 80 400 were found in the depth range 2 6 km q values of 300 800 were found for the svecokarelian province and 200 400 for the archaean the low values of vs and q in the uppermost 1 km are thought to be the result of rock fracturing the crack density was estimated for the uppermost crust along the profile for the sveka profile we found values of 0 35 0 54 in the uppermost 200 m 0 10 0 32 at a depth of 0 2 1 0 km and 0 1 for depths of 1 4 km the comparison of our seismic data with results of theoretical and laboratory investigations implies that the uppermost crustal rocks are saturated the zones of strong attenuation of r waves coincide with faults and schist zones which are well known from surface geology

formal subdivision of the quaternary system period present status and future directions abstract the quaternary system period and pleistocene series epoch were defined in 2009 by the global boundary stratotype section and point gssp for the gelasian stage age 2 58 ma which aligns with marine isotope stage mis 103 and approximates the gauss matuyama chron boundary contrary to earlier reports the vrica gssp 1 80 ma was repurposed in 2011 to define the calabrian stage effectively completing the lower pleistocene subseries subepoch the candidate for the middle pleistocene subseries and proposed chibanian stage gssp 774 ka is the chiba section japan it aligns with mis 19 and approximates the matuyama brunhes chron boundary 773 ka the upper pleistocene subseries with a base traditionally marked by the onset of the last interglacial is not yet defined by gssp the holocene series epoch was formally defined in 2008 by a gssp in the ngrip2 greenland ice core with an age of 11 700 yr b2k before 2000 ce and in 2018 was subdivided using climatic events at 8 2 and 4 2 ka into the greenlandian northgrippian and meghalayan stages ages and their corresponding lower early middle upper late subseries subepochs the northgrippian gssp 8236 yr b2k is defined in the ngrip1 greenland ice core and the meghalayan gssp 4250 yr b2k in a speleothem from meghalaya india this subdivision formally introduces the rank of subseries subepoch and incorporates by far the briefest of all stages into the geological time scale using ice cores and a speleothem for gssps is unique to the holocene the presently undefined term anthropocene is already used extensively and like holocene subdivisional terms its functionality will be enhanced by formal definition the anthropocene should not be confused with anthropogenic it reflects a tipping point in the earth system response to the marked intensification of human impacts not simply the fact of human impact the geological anthropocene as currently envisioned would start in the mid twentieth century holding the rank of series and terminating the holocene but not interfering with its subdivision other than to terminate the meghalayan stage

the polar profile revisited combined p and s wave interpretation abstract the polar profile project studied the crustal structure in a 440 km long swath extending across the northern baltic shield in a southwest northeasterly direction the obtained seismic data comprise p waves and very clear s waves the results of forward modelling using the raytracing technique together with synthetic seismograms for the s waves necessitated slight modification of a previously published velocity model obtained from p waves only the profile crosses the lapland granulite belt with granulite facies rocks at the surface the lapland granulite belt and a part of the karasjok kittila greenstone belt are recognized as high velocity bodies in the upper crust both for p and s waves the v p v s ratio and poisson ratio respectively seems to be slightly lower than that in the surrounding archaean gneisses which also prevail in the middle crust down to a depth of about 30 km the lower crust 30 45 km is marked by a pronounced velocity contrast of the p waves in respect to the middle crust but only a small velocity contrast for the s waves is seen in the southwestern part of the profile unusually high velocities 8 6 8 7 km s are found in the upper mantle at depths of 46 to 50 km

coincident normal incidence and wide angle reflections from the moho evidence for crustal seismic anisotropy abstract we explore the consequences of interpreting wide angle crustal seismic data assuming isotropic models when the real crust may be anisotropic we have used a simple anisotropic model to generate synthetic travel times and have inverted these assuming an isotropic layered model for the crust we show that neglecting the effects of anisotropy can produce estimates of crustal thickness and crustal velocity structure that are significantly in error for realistic levels of anisotropy 10 the error in crustal thickness can be several kilometres and the error in average velocity can be 0 5 km s we show that isotropic inversion of anisotropic data can lead to an apparent mismatch between the position of the moho inferred from normal incidence and wide angle data as an example of such a mismatch we show data acquired over the continental crust offshore the north of scotland the dataset we have modelled includes a wide angle expanding spread profile a conventional ocean bottom seismometer profile a high resolution wide angle onshore offshore experiment a synthetic aperture 16 km offset cdp profile and a conventional deep reflection profile these data show unusually sharp bright and continuous reflections from the moho at all offsets the normal incidence reflection moho and the moho modelled from the wide angle data both show the same lateral structure however they are offset one from the other in normal incidence two way travel time this mismatch is considerably larger than the maximum error expected in the wide angle model and is much greater than the accuracy with which the moho can be picked on the reflection data if we assume that this mismatch is caused by crustal scale seismic anisotropy then the synthetic results indicate that anisotropy in the crust north of scotland is about 7

crustal architecture of the inverted central lapland rift along the hukka 2007 profile we have studied the lateral velocity variations along a partly buried inverted paleo rift in central lapland northern europe with a 2d wide angle reflection and refraction experiment hukka 2007 the experiment was designed to use seven chemical explosions from commercial and military sites as sources of seismic energy the shots were recorded by 102 stations with an average spacing of 3 45 km two dimensional crustal models of variations in p wave velocity and vp vs ratio were calculated using the ray tracing forward modeling technique the hukka 2007 experiment comprises a 455 km long profile that runs nnw sse parallel to the kittila shear zone a major deformation zone hosting gold deposits in the area the profile crosses paleoproterozoic and reactivated archean terranes of central lapland the velocity model shows a significant difference in crustal velocity structure between the northern distances 0 120 km and southern parts of the profile the difference in p wave velocities and vp vs ratio can be followed through the whole crust down to the moho boundary indicating major tectonic boundaries upper crustal velocities seem to vary with the terranes compositional differences mapped at the surface the lower layer of the upper crust displays velocities of 6 0 6 1 km s both paleoproterozoic and archean terranes are associated with high velocity bodies 6 30 6 35 km s at 100 and 200 350 km distances the central lapland greenstone belt and central lapland granitoid complex are associated with a 4 km thick zone of unusually low velocities 6 0 km s at distances between 120 and 220 km we interpret the hukka 2007 profile to image an old partly buried inverted continental rift zone that has been closed and modified by younger tectonic events it has structural features typical of rifts inward dipping rift shoulders undulating thickness of the middle crust high velocity lower crust and a rather uniform crustal thickness of 48 km

upper mantle reflectivity beneath the williston basin phase change moho and the origin of intracratonic basins cocorp consortium for continental reflection profiling deep reflection profiles crossing the northern williston basin show 1 dipping reflections within the crust of the underlying trans hudson orogen that extend downward into the upper mantle and 2 no clearly defined reflection moho in contrast lithoprobe canada9s national geoscience project profiles crossing the trans hudson orogen north of the basin show dipping reflections within the crust that terminate at a sharply defined subhorizontal reflection moho a reflection character typical of the interior of collapsed phanerozoic orogens we suggest that a crustal root produced during hudsonian collision was incompletely removed by normal postorogenic extension in the region now underlain by the williston basin this remnant crustal keel much later underwent eclogite facies metamorphism which overprinted a new nonreflective moho across the root and induced the subsidence of the williston basin

the mt logan holocene late wisconsinan isotope record tropical pacific yukon connections the ice core recovered from prospector russell col on mt logan 5 4 km a s l in the yukon spans over 20 000 years this unique record offers a pacific view of the stable isotope and chemical record from the lateglacial to the present the timescale is based on seasonal counted years the largest known volcanic acid signatures and the major shift in stable isotopes and chemistry at the end of the younger dryas there are large and sustained changes in the stable isotopic record that are anti correlated with marine and continental chemistry series the oxygen 18 in this area is not a proxy for palaeotemperature but rather for source region the last major isotope shift in ad 1840 in 18 o and chemistry is compared with the quinn s enso record during periods of more frequent la nina stronger tropical easterlies there is more zonal flow of water vapour transport to the pacific northwest 18 o values are larger and the deuterium excess d smaller these periods coincide with periods of lower accumulation precipitation in southern yukon the holocene 18 o record indicates many large shifts between the meridional strong el nino and zonal la nina comparison of the logan isotopic record and the moisture temperature sensitive time series of peat bog inception dates for the northwest shows a strong correlation 0 36 that points to high accumulation rates coincident with low 18 o and enhanced meridional flow major changes in the core at 4200 bp and 7000 8000 bp point to enhanced meridional flow which coincide with big changes in the pacific palaeorecords of the balance between el nino and la nina 4200 bp seems to have inaugurated the modern enso world

petrology of two diamondiferous eclogite xenoliths from the lahtojoki kimberlite pipe eastern finland abstract diamondiferous group a eclogites constitute a minor portion of the mantle derived xenoliths in the eastern finland kimberlites they have been derived from the depth interval 150 230 km where they are inferred to occur as thin layers or small pods within coarse grained garnet peridotites the chemical and isotopic composition of minerals suggest that they represent proterozoic mantle derived melts or cumulates rather than subducted oceanic lithosphere during magma ascent and emplacement of the kimberlites the eclogite xenoliths were mechanically and chemically rounded judging from the types of surface markings in addition those octahedral crystal faces of diamonds that were partially exposed from the rounded eclogite xenolith became covered by trigons and overlain by microlamination due to their reaction with the kimberlite magma the diamonds bear evidence of pervasive plastic deformation which is not however evident in the eclogite host this suggests that annealing at ambient lithospheric temperatures has effectively recrystallised the silicates while the diamond has retained its lattice imperfections and thus still has the potential to yield information about ancient mantle deformation one of our samples is estimated to contain approximately 90 000 ct ton diamond implying that some diamonds occur within very high grade pods or thin seams in the lithospheric mantle to our knowledge this is one of the most diamondiferous samples described

anisotropic lithosphere under the fennoscandian shield from p receiver functions and sks waveforms of the polenet lapnet array abstract seismic azimuthal anisotropy is the key evidence of the past and present strains in the upper mantle the standard analysis of shear wave splitting with the sks techniques is useful in mapping lateral variations but it is insensitive to depth of anisotropy and to variations of anisotropy with depth to retrieve the depth localized anisotropy under the fennoscandian shield we inverted p wave receiver functions of the polenet lapnet array in northern finland jointly with sks recordings shear wave anisotropy of 2 5 with the fast direction of 40 60 in a depth range from the moho to 110 km is a robust result of the inversion the obtained direction is nearly normal to the azimuth of the maximum horizontal compressional stress in the lithosphere but a recent origin of this anisotropy is in doubt this anisotropy may be frozen since the precambrian but it shows no clear relation with the trends of the precambrian tectonics the upper anisotropic layer accounts for 40 of shear wave splitting in sks and to explain the rest another anisotropic layer is required the top of the second layer with a practically similar fast direction is found at a depth of 200 240 km this direction is close to the current apm direction of the lithosphere with implication that the inferred anisotropy may be related with the current plate motion and the anisotropic layer belongs to the asthenosphere the bottom of this layer is uncertain but it is at least 320 km deep in a depth range from 160 km to 200 240 km the fast anisotropy direction is 110 150 origin of this direction is unclear

shear wave splitting as a diagnostic of variable anisotropic structure of the upper mantle beneath central fennoscandia abstract we analyze splitting of shear waves recorded during the svekalapko passive seismic experiment in south central finland to study fabrics of the mantle lithosphere of the precambrian region and thus to bring information into a debate on existence of plate tectonics or its forms in the early stage of continent formation geographical variations of the splitting parameters and their distinct dependence on direction of wave propagation through the upper mantle allow us to identify six domains of the central fennoscandian mantle lithosphere including the proterozoic archean transition and to model their fabrics by joint inversion of body wave anisotropic parameters fabrics of the archean mantle lithosphere can be approximated by a peridotite aggregate with lineation a dipping to the ne on the other hand anisotropy of the proterozoic mantle lithosphere is weaker and we model its fabric by the a c foliations dipping to the se we present a 3d self consistent anisotropic model of the proterozoic and archean upper mantle along the sw ne profile in the south central finland boundaries of inter growing wedges of the proterozoic and archean mantle lithospheres explain the longitudinal and shear wave propagation and polarization mantle xenolith ages surface wave tomography and location of the upper mantle reflectors we interpret the six anisotropic domains as fragments of mantle lithosphere retaining an old fossil olivine fabric which was created before these micro continents assembled

rupture creep lamellae and crocodiles happenings in the continental crust from the observation of certain seismic reflectivity patterns in phanerozoic continental crusts a relationship is suggested between 1 rupture and seismicity generally restricted to the upper crust 2 crocodile tectonics a kind of vertical indentation observed by diverging plane reflectors preferably in the middle crust 3 creep and the formation of reflecting lamellae in the lower crust based on these observations and on viscosity depth estimates a conceptual model for the above mentioned structures is presented which is also compatible with observations in older crusts boundary conditions are given for rupture as well as for lamellae forming creep

structure and composition of the precambrian crust along the polar profile in the northern baltic shield abstract along the 500 km long polar profile the continental crust of the northern baltic shield consists of several archaean and early proterozoic crustal segments in the south in the karelian province the upper crust consists of a 3 1 2 6 ga old archaean substratum with a 0 6 km thick low to medium grade volcanosedimentary cover here shallow basin facies rocks of the central lapland complex have been thrust northwards onto the karasjok kittila greenstone belt the repeatedly folded cover rocks form linear troughs between domes and culminations of granitoids the 47 48 km thick crust of the karelian province is of a shield type it is characterised by a low velocity layer interpreted as a horizon of decollement below the supracrustal and granitoid rocks in the lapland granulite belt early proterozoic high grade metapelites and metapsammites with minor metaigneous intercalations have been thrust to the southwest they are separated from the underlying karelian province by the tectonic mixture zone of the tanaelv belt in the interpretations two alternative models are given for the shape of the lapland granulite belt it is either a synformal nappe or a ne dipping body pinching out at depth and overthrust from the north by the archaean inari terrain both the lapland granulite belt and the inari terrain have a 42 44 km thick crust with a relatively thin lower crust marked by lower seismic velocities the early proterozoic polmak pasvik pechenga belt separates the archaean inari terrain from the archaean sorvaranger terrain in the north this belt is interpreted as a suture zone which continues to depth it may either dip steeply towards irregularities in the moho or form a sw dipping low angle plane below the lapland granulite belt the northernmost part of the baltic shield is concealed beneath a 0 7 km thick very low grade metamorphic late proterozoic cover this cover is divided into two parts by the trollfjord komagelv strike slip fault here the crust is again of a normal shield type with a thickness of 42 46 km

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

a revised geodynamic model for the lapland kola orogen abstract the paleoproterozoic lapland kola orogen in fennoscandia has been studied for decades and several plate tectonic models have been proposed including one sided subduction zone either towards sw or nw or two opposite verging subduction zones before the collision based on new structural and isotope data from finland and recently published data from russia we propose a revised tectonic model for the paleoproterozoic lapland kola orogen the main components are foreland in the ne followed by cryptic suture inari arc retro arc basin and retro arc foreland in the sw the latter three constitute the inari orocline subduction towards present sw and subsequent arc magmatism inari arc started at ca 1 98 ga followed by voluminous sedimentation in the deepening retro arc basin underplating of a mid ocean ridge caused flat subduction and magmatic flare at 1 92 ga over a broad distance in the retro arc basin rapid heating led to melting of the retro arc basin sediments and voluminous amounts of granulite facies diatexites formed during collision d1 at 1915 1910 ma large thrust nappes formed on the foreland deformation in the retro arc basin is seen as recumbent folding and shearing of diatexites in the lower parts of the basin and thrusting of metatextite diatexite packages in the upper parts a post collisional stage is seen as 1904 ma appinites and decompression derived granites at 1 90 1 89 ga renewed shortening d2 due to far field effects in sw at 1 88 1 87 ga led to thick skin shortening of the archean middle crust large scale crustal duplexing of already cooled granulites towards the retro arc foreland and inclined upright folding of granulites in the opposite direction towards the inari arc a switch in the stress field from ne sw to nw se led to orogen parallel contraction and buckling started along a dextral strike slip fault zone to form the inari orocline buckling is seen in the bending of pre orocline fabrics and formation of syn orocline fabrics radial conical folds d3 radial fractures a strike slip fault zone and thrusting at the hinge zone the end result is a mega scale parallel multi layer fold composed of the inari arc retro arc basin and possibly also the heated retro arc foreland

subdividing the holocene series epoch formalization of stages ages and subseries subepochs and designation of gssps and auxiliary stratotypes the holocene which currently spans 11 700 years is the shortest series epoch within the geological time scale gts yet it contains a rich archive of evidence in stratigraphical contexts that are frequently continuous and often preserved at high levels of resolution on 14 june 2018 the executive committee of the international union of geological sciences formally ratified a proposal to subdivide the holocene into three stages ages along with their equivalent subseries subepochs each anchored by a global boundary stratotype section and point gssp the new stages are the greenlandian lower early holocene subseries subepoch with its gssp in the greenland ngrip2 ice core and dated at 11 700 a b2k before 2000 ce the northgrippian middle holocene subseries subepoch with its gssp in the greenland ngrip1 ice core and dated at 8236 a b2k and the meghalayan upper late holocene subseries subepoch with its gssp in a speleothem from mawmluh cave north eastern india with a date of 4250 a b2k we explain the nomenclature of the new divisions describe the procedures involved in the ratification process designate auxiliary stratotypes to support the gssps and consider the implications of the subdivision for defining the anthropocene as a new unit within the gts less

deep seismic reflection characteristics of the continental crust four types of seismic reflection fabrics appear to characterize the continental crust 1 a cratonic fabric dominated by diffractions and dipping reflections but lacking a pronounced reflection moho 2 regions of thin skinned foreland deformation with abundant shallow but sparse deep reflections 3 a unidirectional fabric that dips toward the hinterland and may represent a crustal scale ramp zone and 4 zones of highly layered lower crust and high amplitude reflection moho the first three types are commonly observed in transects across single mountain belts but the fourth appears to correspond to regions of elevated lower crustal temperatures such as those encountered in rift provinces and perhaps elsewhere

holocene climatic records from agassiz ice cap ellesmere island nwt canada four ice cores from the top of the agassiz ice cap and down a flow line have been variously analysed for 8 18o ecm solid conductivity and ice melt layer stratigraphy stratigraphic correlation

nature of crustal reflectivity along the dekorp profiles in germany in comparison with reflection patterns from different tectonic units worldwide a review reflectivity of the continental crust displays many different patterns the dekorp lines are used as a basis for comparing and reviewing reflectivity in different tectonic units the brittle upper crust generally exhibits only two types of reflectivity it is either rather transparent preferably in some extensional provinces or and it shows traces of thrust and shear zones of former or present ruptures as these zones have a low impedance interior with few exceptions their first reflection onsets have a negative polarity and evince strong but short signals which sometimes can be correlated over several kilometers the generally ductile lower crust displays a completely different reflectivity in warm extensional and thin crusts the lower part is full of reflecting lamellae it is suggested that this type of reflectivity has a thermo rheological origin the creation of lamellae must take place in a ductile material with contrasting impedance under extensional stresses it can be associated with mineral alignment and corresponding seismic anisotropy destruction of lamellae may take place by a cooling process transforming parts of the lower crust into a brittle regime small stresses might deform or break the lamellae and leave a certain dispersed reflectivity like that in some old and cold shields there are no observations of reflecting lamellae in the upper crust or in the upper mantle in all areas the moho is the last reflecting band reflection moho which most often is identical with the classical refraction moho there are isolated mostly dipping reflections in the uppermost mantle in zones where the last tectonic event a delamination or subduction was not succeeded by a heating process the uppermost mantle is brittle again in most areas and may keep the memory of a cold collision over billions of years

crustal and upper mantle structure of the western carpathians from celebration 2000 profiles cel01 and cel04 seismic models and geological implications summary celebration 2000 was a large international experiment that focused on the lithospheric structure in central europe it consisted of several wide angle reflection and refraction seismic profiles profiles cel01 and cel04 are located in the transition from the precambrian and palaeozoic platforms to the carpathian orogen the data were modelled using 2 d tomographic and forward modelling techniques the profile cel01 about 900 km long extends from the southwestern margin of the east european craton to the pannonian basin system the depth of moho boundary varies along the profile from 27 33 km under the pannonian basin system area 30 39 under the carpathians and within the tesz to 40 45 km under the east european craton the cel04 profile 630 km long starts in the polish trough pt and reaches the pannonian basin system along the cel04 profile the moho interface shallows from 40 km beneath the pt to about 35 km in the maopolska unit the crustal thickness is 43 km beneath the carpathians and 25 km beneath the pannonian basin system the results obtained are consistent with a commonly accepted view of the carpathians thought to be formed largely due to the interplay between palaeogene to middle miocene subduction of oceanic or suboceanic crust and subsequent collision a feature that we interpret as the subduction related orogenic root is at least partially preserved in both profiles and is manifested by a crustal thicknesses of 39

interpreting h2o isotope variations in high altitude ice cores using a cyclone model 1 vertical profiles of isotope 18o or d values versus altitude z from sea level to high altitude provide a link to cyclones which impact most ice core sites cyclonic structure variations cause anomalous variations in ice core time series which may obscure the basic temperature signal only one site mount logan yukon provides a complete versus z profile generated solely from data at other sites such a profile has to be constructed by supplementing field data this requires using the so called isotopic or thermometer which relates to a reference temperature t the construction of gapped sections of versus z curves requires assuming a typical atmospheric lapse rate dt dz where t is air temperature and using the slope d dt of a site derived thermometer to calculate d dz using a three layer model of a cyclone examples are given to show geometrically how changes in the thickness of the middle mixed layer leads to the appearance of anomalous values in time series producing decalibration of the thermometer there the results indicate that restrictions apply to the use of the thermometer in ice core paleothermometry according to site altitude regional meteorology and climate state

shear wave modeling and poisson s ratio in the variscan belt of sw iberia in 2003 two wide angle reflection refraction seismic transects were acquired in the variscan belt of sw iberia the approximately 250 and 300 km long dense trace spacing transects revealed clear s wave arrivals in the shot gathers recorded by vertical component sensors in both transects first s wave arrivals sg and moho reflections sms are the most prominent phases that can be correlated from shot to shot sg is observed up to relatively large offsets and constrains the upper and middle crust s wave velocities the sms is seen from offset 0 18 s twtt to 150 km offset where it intercepts first s wave arrivals sg the upper mantle refracted phase sn is difficult to recognize although pms smp converted phases can be identified using a 2 d ray tracing approach two s wave velocity models for the crust of sw iberia were obtained these s wave velocity models complement the previous p wave velocity models and provide us with relatively well resolved poisson s ratio crustal sections for sw iberia the resulting poisson s ratio models present differences between tectonic zones at upper and middle crustal depths thus supporting the existence of different tectonic zones prior to the variscan collision the most noteworthy feature is the high poisson s ratio value over 0 28 coincident with high p wave velocity areas over 6 8 km s at midcrustal depths in order to constrain the possible crustal composition p wave velocities and poisson s ratios have been compared with published laboratory measurements on different crustal rock types this comparison indicates that the high p wave velocity and poisson s ratios are compatible with a mixture of mafic to ultramafic rock types alternating with felsic ones this result is consistent with the existence of mafic layered bodies in the middle crust in the same way that has been suggested by previous works in this area

crustal structure across the tesz along polonaise 97 seismic profile p2 in nw poland abstract the polonaise 97 po lish l ithospheric on set a n i nternational s eismic e xperiment 1997 seismic experiment in poland targeted the deep structure of the trans european suture zone tesz and the complex series of upper crustal features around the polish basin one of the seismic profiles was the 300 km long profile p2 in northwestern poland across the tesz results of 2d modelling show that the crustal thickness varies considerably along the profile 29 km below the palaeozoic platform 35 47 km at the crustal keel at the teisseyre tornquist zone ttz slightly displaced to the northeast of the geologic inversion zone and 42 km below the precambrian craton in the polish basin and further to the south the depth down to the consolidated basement is 6 14 km as characterised by a velocity of 5 8 5 9 km s the low basement velocities less than 6 0 km s extend to a depth of 16 22 km in the middle crust with a thickness of ca 4 14 km the velocity changes from 6 2 km s in the southwestern to 6 8 km s in the northeastern parts of the profile the lower crust also differs between the southwestern and northeastern parts of the profile from 8 km thickness with a velocity of 6 8 7 0 km s at a depth of 22 km to ca 12 km thickness with a velocity of 7 0 7 2 km s at a depth of 30 km in the lowermost crust a body with a velocity of 7 20 7 25 km s was found above moho at a depth of 33 45 km in the central part of the profile sub moho velocities are 8 2 8 3 km s beneath the palaeozoic platform and ttz and about 8 1 km s beneath the precambrian platform seismic reflectors in the upper mantle were interpreted at 45 km depth beneath the palaeozoic platform and 55 km depth beneath the ttz the polish basin is an up to 14 km thick asymmetric graben feature the basement beneath the palaeozoic platform in the southwest is similar to other areas that were subject to caledonian deformation avalonia such that the variscan basement has only been imaged at a shallow depth along the profile at northeastern end of the profile the velocity structure is comparable to the crustal structure found in other portions of the east european craton eec the crustal keel may be related to the geologic inversion processes or to magmatic underplating during the carboniferous permian extension and volcanic activity

crustal structure of the trans european suture zone region along polonaise 97 seismic profile p4 1 the large scale polonaise 97 seismic experiment investigated the velocity structure of the crust and upper mantle in the trans european suture zone tesz region between the precambrian east european craton eec and paleozoic platform that comprises terranes added during the caledonian and variscan orogenies 530 370 and 370 225 ma respectively this experiment included 64 shots recorded by 613 seismic stations during two deployments very good quality data were recorded along five profiles and the longest and most important one p4 is the focus of this paper clear first arrivals and later phases of waves reflected refracted in the crust and moho were interpreted using two dimensional 2 d tomographic inversion and ray tracing techniques the crustal thickness along the profile varies from 30 35 km in the paleozoic platform area to 40 km below and due northeast of the tesz to 43 km in the polish part of the eec and to 50 km in lithuania the paleozoic platform and eec are divided by the polish basin so the upper crustal structure varies considerably in the area of the polish basin the p wave velocity is very low vp 6 1 km s down to depths of 15 20 km indicating that a very thick sedimentary sequence is present we suggest two possible tectonic interpretations of the velocity models 1 baltica indented avalonia obducting its upper crust and underthrusting its lower crust in a tectonic flake structure and 2 a rifted margin of baltica underlies the polish basin this model is similar to other interpretations of seismic profiles recorded in the baltic sea the second model implies that the paleozoic platform solely consists of avalonian lithosphere and the eec of baltica lithosphere it offers a simple explanation of the difference in crustal thickness of the two platforms it also implies that the caledonian and variscan orogenies in this area were relatively soft collisions that left this continental margin largely intact

preserved collisional crustal structure of the southern urals revealed by vibroseis profiling the vibroseis reflection profiling component of the urseis 95 experiment provides a high resolution crustal scale image of the unextended southern uralide orogen a marked lateral and vertical variation of reflectivity throughout the entire crust differentiates the former margin of the east european craton to the west from accreted terranes to the east between these regions is a less reflective zone corresponding to the magnitogorsk volcanic arc and the crustal root zone continuous reflections and reflective domains that correlate at the surface with major tectonic features define a bivergent orogen in which the paleozoic collisional structure has been largely preserved