the tectonothermal evolution of the cadomian belt of northern brittany france a neoproterozoic volcanic arc abstract the neoproterozoic cadomian belt northern brittany france results from the accretion of crustal blocks that record distinctive p t deformation paths in addition abundant gabbro dioritic to granitic intrusions during and after deformation influence the thermal pattern and are used as time markers as a whole the deformation history of the cadomian belt is characterised by a migration in time of the active zones which become younger towards the southeast relics of eocadomian rocks reveal that arc development took place at about 660 640 ma abundant calc alkaline magmatism intruding strongly deformed palaeoproterozoic orthogneisses characterise the northernmost unit of the cadomian belt i e the tregor unit which cooled before 600 ma the lanvollon basin a short lived intra arc rift containing abundant mafic and felsic volcanics followed by greywackes opened at about 600 580 ma the subsequent tectonothermal history of the cadomian belt is divided into two major episodes the first episode is related to the shortening of the intra arc rift and its southwestward thrusting over the guingamp unit this led to crustal thickening inducing partial melting in the guingamp unit exhumation of the latter rocks is accommodated by late extensional shearing along the boundary between the saint brieuc and guingamp units cooling of the saint brieuc unit is dated at about 570 560 ma the second episode is dominated by sinistral wrenching mainly localised in the eastern part of the cadomian belt at the boundary between the domnonean i e the arc domain and mancellian possibly a fore arc basin domains several shear zones developed during this episode some of them being associated with minor granitic intrusions dated around 550 ma the sinistral shear located southeast of the arc domain is reworking or crosscutting earlier high temperature fabrics within the saint brieuc unit in addition the vertical component of this shearing episode contributes significantly to the exhumation of the saint malo migmatites near the proterozoic cambrian boundary cordierite biotite granitoids intruded at shallow depths the fougeres unit their emplacement outlasting deformation of the sedimentary sequences minor stocks of muscovite leucogranites of cambrian age are possible equivalents of the abundant volcanism in an adjacent nw se trending rift this marks a major change in the kinematic framework with predominance of extension finally minor reactivation of the cadomian structures occurred during the carboniferous associated with the variscan orogeny

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

the 8 2 ka event from greenland ice cores we present a collection of high resolution chemistry and stable isotope records from the plateau of the greenland ice cap during the cold event 8200 yr ago using a composite of four records the cold event is observed as a 160 5 yr period during which decadal mean isotopic values were below average within which there is a central event of 69 yr during which values were consistently more than one standard deviation below the average for the preceding period four cores in north south and central greenland show differences at decadal and shorter timescales it is not yet clear if this represents significant spatial differences in response the results show clear evidence for colder temperatures and a decrease in snow accumulation rate however the changes in chemical concentrations for the ions looked at here are small suggesting only minor changes in atmospheric circulation for this event apart from the decrease in methane concentration greenland ice cores give only weak evidence for effects outside the north atlantic region

central european vegetation response to abrupt climate change at 8 2 ka oxygen isotope records show a major climatic reversal at 8 2 ka in greenland and europe annually laminated sediments from two lakes in switzerland and germany were sampled contiguously to assess the response of european vegetation to climate change ca 8 2 ka with time resolution and precision comparable to those of the greenland ice cores the pollen assemblages show pronounced and immediate responses 0 20 yr of terrestrial vegetation to the climatic change at 8 2 ka a sudden collapse of corylus avellana hazel was accompanied by the rapid expansion of pinus pine betula birch and tilia linden and by the invasion of fagus silvatica beech and abies alba fir vegetational changes suggest that climatic cooling reduced drought stress allowing more drought sensitive and taller growing species to out compete corylus avellana by forming denser forest canopies climate cooling at 8 2 ka and the immediate reorganization of terrestrial ecosystems has gone unrecognized by previous pollen studies on the basis of our data we conclude that the early holocene high abundance of c avellana in europe was climatically caused and we question the conventional opinion that postglacial expansions of f silvatica and a alba were controlled by low migration rates rather than by climate the close connection between climatic change and vegetational response at a subcontinental scale implies that forecasted global warming may trigger rapid collapses expansions and invasions of tree species

reflection and transmission of surface waves at a vertical discontinuity and imaging of lateral heterogeneity using reflected fundamental rayleigh waves we present a technique for the determination of approximate reflection and transmission coefficients of surface wave modes for a vertical plane discontinuity that is simple to use it is applied to different models of lateral heterogeneity furthermore a method for the localization of lateral heterogeneity using the coda of the fundamental rayleigh mode is proposed in particular the frequency content of surface waves enables the investigation of the lower crust and the uppermost mantle lateral changes of the s wave velocity density and p wave velocity lead to the formation of the coda of the fundamental rayleigh mode that contains delayed surface waves that reach the recording station indirectly the complicated structure of the coda makes it impossible to identify reflected surface waves visually using a small number of recordings only coda waveforms of a large number of source station pairs are inverted simultaneously for experimental reflection coefficients the method is successfully tested using an ultrasonic model experiment finally it is applied to central europe and especially to the tornquist zone tz mainly using records of the german regional seismological network grsn the resulting reflection coefficients depend on frequency and give an image of the location of reflectors

conventional and ion microprobe u pb dating of detrital zircons of the tentudia group serie negra sw spain implications for zircon systematics stratigraphy tectonics and the precambrian cambrian boundary conventional multi grain and ion microprobe dating of detrital zircons from a very low grade metagraywacke of the tentudia group upper part of the serie negra ossa morena zone sw spain reveals an uppermost vendian age for the deposition of the metagraywacke the youngest detrital zircon grain provides a maximum depositional age of about 565 ma thus these data contradict earlier middle to upper riphean ca 1350 850 ma estimates on the age of the tentudia group and favour a precambrian cambrian boundary falling into the range of 540 to 530 ma the presence of about 20 of pan african detrital zircons ranging from about 700 to 550 ma indicates the derivation from gondwana from the upper intercept ages of the fan shaped data field defined by conventionally determined zircon fractions it can be deduced that 2 1 ga old zircons as well as archean zircons existed in the provenance s of the serie negra sediments this mixing of crustal components of different ages is in line with the nd crustal residence age of 1 9 ga the latter value as well as other model ages of the iberian massif indicates unusually high amounts of ancient crust to be present in the strata this is different to other meta sediments of the european hercynides and suggests that the iberian strata of uppermost precambrian age may contain the detritus of more internal older parts of gondwana than other european strata of comparable ages geochemical data on the analysed sample and further metagraywackes of the tentudia group argue for a deposition in an arc environment such a scenario would conform with the syn to post orogenic shallow marine deposition of the studied sediments furthermore an upper time limit for the pre lower cambrian deformational history including two phases of regional deformation is given by the maximum age of deposition implying a very short time interval for deposition and deformation of the tentudia group concerning the u pb systematics of detrital zircon fractions it is probable that numerous previously published conventional multi grain zircon data on meta sedimentary rocks of the european hercynides readily can be explained by the presence of up to 20 of pan african detrital zircons and later phanerozoic lead loss during metamorphic transformation of the sedimentary protoliths moreover this implies that such metasediments originated from post pan african sedimentary precursors

age and impacts of the caldera forming aniakchak ii eruption in western alaska the mid holocene eruption of aniakchak volcano aniakchak ii in southwest alaska was among the largest eruptions globally in the last 10 000 years vei 6 despite evidence for possible impacts on global climate the precise age of the eruption is not well constrained and little is known about regional environmental impacts a closely spaced sequence of radiocarbon dates at a peatland site over 1000 km from the volcano show that peat accumulation was greatly reduced with a hiatus of approximately 90 120 yr following tephra deposition during this inferred hiatus no paleoenvironmental data are available but once vegetation returned the flora changed from a cyperaceae dominated assemblage to a poaceae dominated vegetation cover suggesting a drier and or more nutrient rich ecosystem oribatid mites are extremely abundant in the peat at the depth of the ash and show a longer term increasingly wet peat surface across the tephra layer the radiocarbon sample immediately below the tephra gave a date of 1636 1446 cal yr bc suggesting that the eruption might be younger than previously thought our findings suggest that the eruption may have led to a widespread reduction in peatland carbon sequestration and that the impacts on ecosystem functioning were profound and long lasting

sandstone petrography and geochemistry of late proterozoic sediments of the armorican massif france a key to basin development during the cadomian orogeny abstract brioverian late proterozoic sediments of the armorican massif in northwest france are contained within isolated basins whose development is linked to cadomian orogenesis these basins were formed between c 650 and 530 ma ago mainly by gravitational flow processes petrographical study and geochemical analysis of major and trace elements show that the sandstone formations of north brittany are characterized by great immaturity 10 20 feldspar 10 20 lithic fragments and high concentrations of na2o ba sr v and cr the formations from western and central brittany as well as the southern part of normandy are compositionally more mature 1 petrographical and geochemical data for north brittany formations yield plots which suggest a mixed source region composed of a continental active margin island arc and ancient basement material sedimentation of the brioverian group was influenced by a distensive tectonic regime towards the south sedimentary formations are characterized by continental source areas and were laid down in a passive tectonic environment however ree distribution patterns for sediments of this southern domain preserve evidence for the contribution of magmatic arc material such formations could have been deposited in a marginal basin

transition from island arc to passive setting on the continental margin of gondwana u pb zircon dating of neoproterozoic metaconglomerates from the se margin of the tepla barrandian unit bohemian massif abstract sedimentological petrological and geochemical data combined with shrimp and la icp ms u pb ages of pebbles of granitic rocks and detrital zircons from neoproterozoic vletice metaconglomerates of the se margin of the tepla barrandian unit were used to characterize the regional geotectonic setting at the proterozoic paleozoic boundary the metaconglomerates form several metres thick intercalations in metasediments of the svrchnice formation roof pendants of central bohemian plutonic complex which is considered to have been deposited in neoproterozoic cambrian times a sedimentological study indicates that the metaconglomerates are products of debris flows deposited in submarine canyons or proximal parts of submarine fans geochemistry of metaconglomerate matrix and petrography of pebbles revealed an obvious difference from the western and central part of the tepla barrandian unit proterozoic where pebbles eroded from uplifted parts of the basin and island arc sources are most common the abundance of quartz quartzite granite and crystalline limestone in pebbles together with the more mature composition of host metagreywackes indicate the presence of relatively evolved continental crust in the source area for the vletice metaconglomerates and shallowing of the neoproterozoic basin to the se in the present geographic co ordinate system the neoproterozoic to lowermost cambrian age of the svrchnice formation suggested by its comparison with similar rocks in the central part of the tepla barrandian unit was confirmed by u pb dating ages of detrital zircons from the metaconglomerate matrix cluster around two values archaean to paleoproterozoic u pb ages between ca 2580 and 1780 ma and neoproterozoic to early cambrian ages between 660 and 520 ma with a significant peaks at 600 and 544 ma suggesting local volcanic activity extending shortly beyond the proterozoic paleozoic boundary zircons separated from two trondhjemite pebbles from the metaconglomerate yielded a mean u pb age of 610 17 ma arguing for active arc magmatism during the latest neoproterozoic the overall age distribution of detrital zircons and the absence of grenvillian zircon ages favour a location of the tepla barrandian unit close to the west african craton at the neoproterozoic paleozoic boundary the rapid onset of a transtensional geotectonic regime and maturing of sediments is evidenced by the overlying cambrian shallow water clastics alternating with predominantly felsic calc alkaline to alkaline volcanics during the cambrian oblique plate convergence the active continental margin was transformed into belts of horsts and narrow pull apart or small rift basins after the ordovician break off of armorican terrane assemblage blocks from gondwana the extensional regime in the tepla barrandian unit continued until the beginning of variscan orogeny in the middle devonian

out of tune the dangers of aligning proxy archives abstract tuning is a widespread technique to combine date and interpret multiple fossil proxy archives through aligning supposedly synchronous events between the archives the approach will be reviewed by discussing a number of literature examples ranging from peat and tephra layers to orbital tuning and 18o series from marine and ice deposits potential problems will be highlighted such as the dangers of circular reasoning and unrecognised chronological uncertainties and some solutions suggested fossil proxy research could become enhanced if tuning were approached in a more quantitative reliable and objective way and especially if individual proxy archives were non tuned and kept on independent time scales

contrasting geochemical features of the central iberian zone shales iberian massif spain implications for the evolution of neoproterozoic lower cambrian sediments and their sources in other peri gondwanan areas abstract more than 90 samples of shales have been collected for geochemical purposes from neoproterozoic and lower cambrian sedimentary series in an extensive area of the central iberian zone ciz for similar sio2 and al2o3 abundances the neoproterozoic shales ns are characterized by relatively higher tio2 and zr abundances and by higher cr th and ti nb ratios by contrast the lower cambrian shales lcs have higher al2o3 tio2 rb zr la yb cn and th yb ratios diagrams such as al2o3 tio2 al2o3 tio2 ti nb tio2 zr tio2 zr nb and ti nb rb zr are useful to define two distinct fields that discriminate the neoproterozoic from the lower cambrian compositions these and other geochemical features suggest that these rocks were derived from different source compositions and that the lower cambrian shales lcs were chemically more fractionated than those of the neoproterozoic these distinctive chemical features are also recorded by neoproterozoic and cambrian fine grained rocks in other areas in the central iberian zone and in other zones within iberia published neodymium isotopic results consistently distinguish both compositions and together with the geochemical data support a relatively fractionated nature for the lower cambrian sediments compared to the neoproterozoic ones it is proposed that continental deposits derived from the interior orogens in north gondwana would have been the sources for neoproterozoic sediments in the iberian zones whereas the lower cambrian sediments in these zones would have been derived from older crust beneath those continental deposits thus the neoproterozoic lower cambrian stratigraphic succession in iberia reflects an inverse stratigraphy of the source area and contrasts with zones of central and western europe where equivalent sedimentary series record important coeval igneous contributions and show less fractionated geochemical characteristics finally the possible connection between the central iberian zone and the meguma zone mz in canada is discussed on the basis of certain sedimentological and geochemical features it is proposed that the sedimentary series of the central iberian zone and of the meguma zone represent respectively proximal and distal north gondwana derived sediments

imaging lateral heterogeneity in the northern apennines from time reversal of reflected surface waves summary prominent arrivals in the coda of seismograms from the wider alpine area can be associated with lateral reflections of love waves at the northern apennines mountain chain italy where structural heterogeneity causes an abrupt contrast in phase velocity we discuss an approach to image lateral heterogeneity from reflected surface waves using intermediate period threecomponent coda waveforms as sources for an adjoint wavefield that propagates the reflections backward in time we numerically compute three dimensional sensitivity kernels for the dependence of coda waveforms on p velocity s velocity and density based upon correlations between the adjoint and the regular forward wavefields we consider synthetic coda waveforms for a simplified model of the northern apennines as well as real coda observations from five moderate magnitude earthquakes m w 4 6 5 6 in the southern alps wave propagation is simulated using the spectral element method for which a 3 d regional earth model is used in the case of real data single and combined event sensitivity kernels provide clear images of the reflectivity associated with the northern apennines in kernels for density and s wave speed the kernels show that surface wave reflections occur near the axial zone of the mountain chain apart from the apennines the approach is able to image other smaller reflectivity patches from the coda waveforms like the ivrea zone in the southern alps our coda misfit kernels can be integrated in a gradient based waveform tomography where they could enhance the sharpness of the model at lateral discontinuities

cambrian ensialic rift related magmatism in the ossa morena zone evora aracena metamorphic belt sw iberian massif sm nd isotopes and shrimp zircon u th pb geochronology abstract the late ediacaran c 560 550 ma serie negra sediments of the evora aracena metamorphic belt ossa morena zone sw iberian massif preserve a record of the erosion of an avalonian cadomian magmatic arc and subsequent related turbiditic sedimentation detrital zircon from the serie negra is characterized by predominantly ediacaran and cryogenian ages with few paleoproterozoic and archean cores and a marked lack of grenvillian ages these features when combined with the metasediments enrichment in lree la yb 14 negative eu anomalies low 147 sm 144 nd values 0 121 and negative e nd 550 5 5 indicate that the protolith serie negra sediments were derived from a continental magmatic arc a period of late cadomian ca 560 540 ma tectonism was followed by an extended episode of widespread bimodal magmatism related to cambrian ca 540 500 ma rifting this tectonic inversion is expressed in the geological record by a regional early cambrian unconformity shrimp zircon u th pb ages from four felsic orthogneisses from the evora massif record cambrian 527 10 ma 522 5 ma 517 6 ma and 505 5 ma crystallization ages for their igneous protoliths this confirms the existence of widespread lower paleozoic igneous activity in the ossa morena zone i a lower cambrian ca 535 515 ma igneous felsic dominated sedimentary complex with calc alkaline signature and associated carbonate and siliciclastic deposition and ii a middle cambrian ordovician ca 515 490 ma igneous bimodal sedimentary complex with calc alkaline and tholeiitic signatures and associated dominant siliciclastic deposition but also carbonate sediments the cambrian felsic magmatism was characterized by negative eu anomalies la lu n 0 8 11 147 sm 144 nd 0 1289 0 1447 and e nd 500 ranging from 1 5 to 0 8 a tendency towards peraluminous compositions suggests late fractionation low degrees of partial melting or the mixing of crustal and mantle derived material in the magma source region some felsic rocks possibly represent the last residual melts of high temperature zircon undersaturated mafic magmas later affected by crustal contamination while others indicate partial melting of crustal metasediments variably contaminated by basaltic liquids the transition from early felsic dominated to later more mafic magmatism suggests the gradual opening of the system to tholeiitic n e morb products th n ta n 147 sm 144 nd 0 1478 0 1797 and e nd 500 values ranging from 6 4 to 7 3 while the n morb amphibolites have 147 sm 144 nd 0 1818 0 1979 and e nd 500 values of 5 8 and 7 0 reaching a maximum of 9 1 in contrast other amphibolites have a negative ta anomaly 1 35 n ta n 147 sm 144 nd values ranging from 0 1639 to 0 1946 and e nd 500 values of 3 5 to 5 2 suggesting derivation by crustal assimilation processes the sub alkaline igneous precursors of the amphibolites were most likely generated in a rift setting by asthenospheric upwelling these results strengthen the proposed geodynamic scenarios for the sw iberian massif by which cadomian accretion gave rise to an ensialic rift that developed into a proto oceanic basin and incipient spreading opening of the rheic ocean a similar transition from a convergent to a divergent plate boundary during the ediacaran to cambrian ordovician has also been reported in other segments of the northern gondwana margin

upper neoproterozoic lower cambrian sedimentary successions in the central iberian zone spain sequence stratigraphy petrology and chemostratigraphy implications for other european zones o3 tio2 zr and nb abundances in shales from all the units strongly suggest a gradual compositional change within this sedimentary succession together with the petrological data the chemical results do not reveal any obvious coeval volcanic contribution to the sediments on the basis of the chemical data a comparison is made with other european zones containing detrital sediments composed of reworked crustal components

proterozoic and cambrian successions in upper silesia an avalonian terrane in southern poland all cambrian series and several cambrian biozones have been recognized using acritarch biochronology within the siliciclastic successions underlying upper silesia in southern poland the entire cambrian succession is around 580 m thick and contains rare l

holocene peatland development and hydrological variability inferred from bog pine dendrochronology and peat stratigraphy a case study from southern sweden dendrochronological analysis was applied to subfossil remains of scots pine pinus sylvestris l buried in a south swedish peat deposit in combination with peat stratigraphy this approach was explored for its potential to provide information on the local hydrological and depositional history at the site forming the basis for a regional palaeohydrological analysis a 726 year ring width chronology was developed and assigned an absolute age of 7233 6508cal a bp 5284 4559 bc through cross dating with german bog pine chronologies whereas two short additional records of older ages were radiocarbon dated registration of growth positions of individual trees allowed assessment of the spatial dynamics of the pine population in response to hydrological changes and peatland ontogeny annually resolved growth variability patterns in the pine population reveal several establishment and degeneration phases probably reflecting fluctuations in bog surface wetness a major establishment phase at 7200 6900 cal a bp reflects the onset of a period of lowered groundwater level also indicated by increased peat humification and a development consistent with regional temperature and lake level reconstructions revealed from other proxies this study demonstrates that subfossil bog pine populations may provide annually to decadally resolved reconstructions of local groundwater variability which are highly relevant in a long term palaeoclimatic context copyright c 2012 john wiley sons ltd

geochemistry and tectonic setting of lewisian clastic metasediments from the early proterozoic loch maree group of gairloch nw scotland abstract the early proterozoic 2 0 ga loch maree group lmg of the lewisian complex consists of a supracrustal sequence of metasedimentary schists and associated tholeiitic metavolcanic amphibolites within the archaean basement the metasediments comprise three main mapped units the flowerdale schists kerrysdale schists and charlestown schists together with numerous narrower bands the dominant clastic metasediments within the schist units semipelites and psammites are chemically distinguished as a series of greywackes and lithic sandstones with variable lil and transition element abundances fractionated ree patterns and overall compositions similar to paas three chemical groups are recognized whose range of composition largely reflects the mixing between two main source components lewisian gneissose basement with an intermediate acid continental crust composition and local rift related amphibolites with a primitive tholeiitic composition which also incorporates components not preserved within the lmg the geochemistry of the clastic metasediments confirms a previous tectonic model for the lmg as an intracontinental extensional rift receiving clastic detritus from the adjacent uplifted basement as well as from internal volcanogenic sources

precadomian relicts in the armorican massif their age and role in the evolution of the western and central european cadomian hercynian belt abstract well dated precambrian is mostly developed in the north of the armorican massif in which area voluminous cadomian magmatism is dated at between 650 and 550 ma much older relicts occur at cap de la hague in guernsey and in the tregor and are also found in the northern continental margin of the iberian peninsula in all these occurrences whole rock systems have been opened so that the true ages cannot be determined by the rb sr whole rock isochron method four u pb zircon ages are between 1 8 and 2 ga in guernsey icart orthogneisses in tregor port beni trebeurden morguignen orthogneisses there is no evidence from strontium isotopes that these isolated and scattered relicts have a wide extension or that such ancient continental crust played an important role in magma genesis from 650 ma to 270 ma ago on the contrary the evolution of initial 87sr 86sr ratios with time shows that the observed mid and west european continental crust is probably not older than 700 ma the increase of the initial 87sr 86sr ratios of the magmas with time suggests that after its formation in cadomian times this segment of continental crust evolved virtually as a closed system and hercynian magmatism arose principally from re melting of relatively young sialic components

causes and timing of the 8200 yr bp event inferred from the comparison of the grip be 10 and the tree ring delta c 14 record we analyse the 8200 yr bp cold event by comparing the high resolution be 10 record from the grip ice core from central greenland with the well known tree ring delta 14 c record by transferring the absolute dated tree ring chronology to the ice core time scale we show that the coldest phase in the grip record occurred around 8150 yr bp furthermore this method allows us to disentangle production and climate effects on be 10 and c 14 with important implications for the reconstruction of past solar activity and changes in the carbon cycle and be 10 transport we show that in principle it is possible to infer changes in ocean circulation by comparing be 10 and c 14 records however the duration of the 8200 yr bp event is too short to assign unambiguously a significant change in atmospheric c 14 concentration to changes in the global ocean circulation based on the comparison of be 10 with climate records one could argue that the 8200 yr bp cold event is triggered by a change towards lower solar activity however this link is questioned by the fact that around this period there are other similar and even stronger changes in solar activity that have no apparent connection to climate changes c 2004 elsevier ltd all rights reserved less

the importance of along margin terrane transport in northern gondwana insights from detrital zircon parentage in neoproterozoic rocks from iberia and brittany abstract detrital zircons from late neoproterozoic rocks of the peri gondwanan cadomian belt of sw iberia and north armorican domain of brittany record neoproterozoic ca 860 550 ma palaeoproterozoic ca 2300 1800 and archaean ca 3300 2600 ma u pb ages the absence of mesoproterozoic zircons suggests that these terranes evolved in a peri w african realm this is in contrast to other western european terranes that preserve mesoproterozoic zircons and are likely to have evolved in a peri amazonian realm such a contrast in detrital zircon populations coupled with the presence of mesoproterozoic zircons in the ordovician armorican quartzite deposited in a peri african platform is interpreted to record along margin terrane transport the change in provenance suggests that subduction was replaced by transform faults that juxtaposed amazonia derived terranes against w africa derived terranes to form the avalonia and armorica microcontinents subsequent extension along the margin resulted in the birth of the rheic ocean and the outboard drift of avalonia

petrogenesis of graphitic cherts in the armorican segment of the cadomian orogenic belt nw france graphitic cherts are interbedded within terrigenous sediments in the cadomian orogenic belt of end proterozoic age in the armorican massif nw france the graphitic cherts are of two types massive cherts essentially composed of quartz sio2 96 and with rare sedimentary structures laminated cherts containing up to 3ae4 al2o3 and 92 98 sio2 sedimentary structures observed in the laminated cherts are indicative of a restricted hypersaline tidal or supratidal environment the origins of both types of chert are to be found in the diagenetic processes of silification of terrigenous and mixed terrigenousevaporitic facies these processes which could be mediated by the presence of organic matter were controlled by the migration of the freshwater saltwater mixing zone during periods of relative sea level change the proposed diagenetic origin for the cherts places a number of constraints on their use in the establishment of stratigraphic correlations

response to comment on abrupt warming events drove late pleistocene holarctic megafaunal turnover rasmussen and svensson correctly point out that there is currently no satisfactory method to fully align the greenland and cariaco basin records of climate change however our approach using interstadial onsets as tie points allows direct comparison between radiocarbon dates and greenland climate records crucially both the standard greenland and the merged greenland cariaco time scales show that interstadial warming was associated with megafaunal genetic transitions

the cadomian orogeny in saxo thuringia germany geochemical and nd sr pb isotopic characterization of marginal basins with constraints to geotectonic setting and provenance abstract the cadomian basement and the cambro ordovician overstep sequence in saxo thuringia is characterized by clastic sedimentation from the late neoproterozoic to the ordovician magmatism in the avalonian cadomian arc preserved in saxo thuringia occurred between ca 570 and 540 ma peri gondwanan basin remnants with cadomian to early palaeozoic rocks are exposed as very low grade metamorphosed rocks in six areas schwarzburg anticline berga anticline doberlug syncline north saxon anticline lausitz anticline and elbe zone a hiatus in sedimentation between 540 and 530 ma cadomian unconformity is related to the cadomian orogeny a second gap in sedimentation occurred during the upper cambrian 500 to 490 ma and is documented by a disconformity between lower to middle cambrian rocks and overlying tremadocian sediments major and trace element signatures of the cadomian sediments reflect an active margin continental arc those of the ordovician sediments a passive margin the cambrian sediments have inherited the arc signature through the input of relatively unaltered cadomian detritus initial nd and pb isotope data from the six saxo thuringian areas demonstrate that there is no change in source area with time for each location but that there are minor contrasts among the locations 1 cadomian sediments from the lausitz anticline the doberlug syncline and the elbe zone have lower 207pb 204pb than all other areas 2 the core of the schwarzburg anticline which is overprinted by greenschist facies conditions and detached is isotopically heterogeneous one part of its metasedimentary units has less radiogenic nd than sediments from other low grade units of similar age in the same area 3 cadomian sediments from the schwarzburg anticline show an input of younger felsic crust 4 the rothstein group shows distinct input of young volcanic material also 5 cadomian sediments from the lausitz anticline the elbe zone and parts of the north saxon anticline are characterized by input from an old mafic crust nd isotope data of the remaining areas yield average crustal residence ages of the sediment source of 1 5 1 9 ga which suggests derivation from an old craton as found for other parts of the iberian armorican terrane collage similarly the pb isotope data of all areas indicate sediment provenance from an old craton the rapid change of lithologies from greywacke to quartzite from the late neoproterozoic cadomian basement to the ordovician does not reflect changes in sediment provenance but is essentially due to increased reworking of older sediments and old weathering crusts that formed during various hiatus of sedimentation this change in sediment maturity takes its chemical expression in lower overall trace element contents in the quartzite dilution effect by quartz and relative enrichment of some trace elements zr mree hree due to detrital zircon and garnet the rb sr systematics of the quartzites and one ordovician tuffite was disturbed most likely during the variscan orogeny which suggests a lithology controlled mobility of alkali and calc alkali elements by comparison with available data it seems unlikely that only nd tdm model ages are useful to distinguish between west african and amazonian provenance nd tdm model ages of 1 5 to 1 9 ga in combination with paleobiogeographic aspects age data from detrital zircon and palaeogeographic constraints especially through tillites of the saharan glaciation in the hirnantian strongly indicate a provenance of saxo thuringia from the west african craton

dating raised bogs new aspects of ams 14c wiggle matching a reservoir effect and climatic change abstract high resolution ams dating of holocene raised bog deposits engbertsdijksvenen the netherlands shows natural 14c variations wiggles which can be matched with the dendrochronological calibration curve comparison of our results with other conventionally dated peat cores and the 14c record shows an unexpected and as yet unreported reservoir effect and a marked and sudden wetting of the bog surfaces coinciding with the advent of a sporer type solar minimum the homeric minimum the potential of ams dating to vastly improve the accuracy of holocene chronologies is demonstrated

superposed hercynian and cadomian orogenic cycles in the ossa morena zone and related areas of the iberian massif polyphase ductile deformation and metamorphism in the ossa morena zone of the iberian massif are related to a complex evolution including two major tectonothermal episodes of cadomian late proterozoic to early cambrian and hercynian age middle to late paleozoic petrological structural and geochronological data attest to a number of tectonic episodes in the 620 480 ma interval the model presented for this orogeny comprises stages of volcanic arc generation backarc extension tectonic inversion crustal thickening and cratonization in an andean type continental margin the hercynian cycle began in the early paleozoic with episodes of continental rifting orogenic events occurred in the 390 300 ma interval and affected both the cadomian basement which was heterogeneously reworked and overprinted and the paleozoic cover hercynian regional metamorphism was generally of low grade high pressure assemblages and thermal domes developed locally and were related to subduction and late extensional events the geodynamic model proposed for the cadomian and hercynian orogenies and the correlation with comparable areas from pre mesozoic massifs elsewhere in western europe account for the geodynamic scenarios that drove the fate of cadomian terranes

the upper neoproterozoic lower cambrian of the central iberian zone spain chemical and isotopic sm nd evidence that the sedimentary succession records an inverted stratigraphy of its source the upper neoproterozoic lower cambrian sedimentary succession in the central iberian zone has recently been divided into 12 sedimentary units i to xii units i to iv are of late neoproterozoic age and units v to xii are early cambrian throughout the stratigraphic section shales with similar ranges of sio2 and al2o3 have tio2 and zr contents that are coupled and vary gradually from the bottom unit i tio2 1 0 1 1 zr 245 287 ppm to the top unit xii tio2 0 74 0 86 zr 141 192 ppm these two parameters clearly distinguish upper neoproterozoic from lower cambrian compositions as do certain elemental ratios al2o3 tio2 rb zr nb ti which vary from low values at the bottom of the section to high at the top however other elements the rare earth elements rees y do not fit this general trend with heavy rees and y showing extreme concentrations in some lower cambrian units which also have negative ce anomalies units i to iii and units xi to xii have uniform tdm neodymium model ages 1 1 and 1 7 ga respectively but the units between these two groups have erratic values between 1 4 ga unit vii and 3 4 ga unit viii thus the bottom and top units have neodymium isotope ratios that indicate the presence of two source compositions a composition that records a juvenile contribution younger than 1 1 ga and a composition mainly derived from an old basement some samples from lower cambrian units have disturbed ree abundances and neodymium isotope ratios that are attributed to extensive chemical alteration that resulted in ree and y redistribution this alteration probably affected the material now preserved as unit iv during a period of relative sea level fall at the end of the late neoproterozoic both elemental and isotopic results support the suggestion that the upper neoproterozoic lower cambrian stratigraphic section records an inverse stratigraphy of a source hinterland composed of a cover sequence of relatively juvenile crustal materials underlain by an older basement through time the deeper crust gradually increased its contribution to the sediments in the basin from late neoproterozoic to lower cambrian times these results are compatible with data from many other european zones

imaging lateral heterogeneity using reflected surface waves surface waves that reflect or backscatter from sharp lateral changes in the near surface provide information about the location depth and amount of these variations we developed a 2d semianalytic forward model for surface wave propagation and used it to design a processing flow for determining surface wave reflection coefficients as a function of spatial location along a survey line and frequency or depth using these reflection coefficients we updated surface wave phase velocities determined by picking dispersion curves across the survey line the result was a sharply defined phase velocity model in the lateral direction which can be inverted for an s wave velocity model two synthetic examples of blind faults with data simulated by the spectral element method were developed for our processing flow buried faults were properly located and the s wave velocity model was improved in the lateral direction in addition our method effectively identified faults for seismic data acquired across the hockley fault system near houston texas

neoproterozoic cambrian synsedimentary magmatism in the central iberian zone spain geology petrology and geodynamic significance petrographic geochemical and field studies in low grade metamorphic areas ciudad rodrigo hurdes sierra de gata domain crhsg central western spain show that neoproterozoic lowermost cambrian series in the central iberian zone ciz record two kinds of provenance sources including 1 detrital material derived from recycled orogens and 2 a cadomian coeval juvenile contribution that governs their isotopic signature evidence of magmatism contemporaneous with neoproterozoic cambrian sedimentation is provided by the presence of coherent massive volcanic rocks metabasalts metaandesites and metarhyolites volcaniclastic shales sandstones conglomerates and breccias the appearance of volcanogenic lithic fragments and crystals mixed in different proportions with siliciclastic constituents and also present within calcareous components in the sedimentary succession reinforces this evidence although most of the selected volcanic and volcaniclastic samples appear to show tholeiitic affinity some of them display calc alkaline affinity different trace element ratios such as sm nd nb yb and ta yb suggest a magmatic evolution in the same tectonic setting the geochemical results reported here support the existence of an active geodynamic setting as a direct contributor to the synsedimentary and magmatic content of the neoproterozoic lowermost cambrian successions in the ciz in particular the relatively high end t values and the high range of f sm nd ratios are consistent with an active margin during the neoproterozoic early cambrian the existence of tectonic activity is also confirmed by the presence of synsedimentary deformation and volcanic rocks all of these traits favour a geodynamic model in which the iberian cadomian segment represented in the ciz would have been part of an active northern margin of gondwana with an associated magmatic arc and related basins during neoproterozoic lower cambrian times a proposed link between the ossa morena and the central iberian zones might account for late cadomian pull apart basins developed on both sides of the magmatic arc sharing the same scenario and involving similar magmatic activity during the neoproterozoic cambrian transition

holocene tephras highlight complexity of volcanic signals in greenland ice cores 1 acidity peaks in greenland ice cores have been used as critical reference horizons for synchronizing ice core records aiding the construction of a single greenland ice core chronology gicc05 for the holocene guided by gicc05 we examined sub sections of three greenland cores in the search for tephra from specific eruptions that might facilitate the linkage of ice core records the dating of prehistoric tephras and the understanding of the eruptions here we report the identification of 14 horizons with tephra particles including 11 that have not previously been reported from the north atlantic region and that have the potential to be valuable isochrons the positions of tephras whose major element data are consistent with ash from the katmai ad 1912 and oraefajokull ad 1362 eruptions confirm the annually resolved ice core chronology for the last 700 years we provide a more refined date for the so called ad860b tephra a widespread isochron found across nw europe and present new evidence relating to the 17th century bc thera aniakchak debate that shows n american eruptions likely contributed to the acid signals at this time our results emphasize the variable spatial and temporal distributions of volcanic products in greenland ice that call for a more cautious approach in the attribution of acid signals to specific eruptive events

lower brioverian formations upper proterozoic of the armorican massif france geodynamic evolution of source areas revealed by sandstone petrography and geochemistry abstract formations with interbedded cherts constitute an important part of the lower brioverian succession upper proterozoic age in the armorican massif northwest france these formations are composed of shale sandstone alternations with interbedded siliceous carbonaceous members petrographic and geochemical study of the detrital facies shows that these rocks are compositionally immature the wackes are rich in lithic fragments volcanic fragments 3 20 modal sedimentary and metamorphic fragments 0 7 modal and in feldspar 5 16 from the geochemical point of view they are relatively enriched in fe2 mgo about 5 5 and in alkalis with na 2 o k 2 o ratios greater than 1 the cao contents are low about 0 3 slightly negative eu anomalies are observed eu eu 0 8 their chemical compositions are in agreement with a dominantly acidic source area with deposition in a continental active margin setting compared with other upper proterozoic deposits of the armorican massif the interbedded chert formations appear rather similar to other deposits in north brittany which accumulated in an intra arc or back arc basin environment the formations with interbedded cherts are interpreted as having been deposited during an early stage of magmatic arc activity around 640 630 ma ago in an immature marginal basin the clastic supply to these formations is derived in part from early volcanic products acidic to intermediate which are linked to subduction beneath the north armorican domain another component is inherited from the reworking of 2000 ma old basement relics the opening of the back arc domain with associated basaltic volcanism would bring about a progressive displacement of the interbedded chert depositional basin towards the continental margin

two receiver measurements of phase velocity cross validation of ambient noise and earthquake based observations phase velocities derived from ambient noise cross correlation are compared with phase velocities calculated from cross correlations of waveform recordings of teleseismic earthquakes whose epicentres are approximately on the station station great circle the comparison is conducted both for rayleigh and love waves using over 1000 station pairs in central europe we describe in detail our signal processing method which allows for automated processing of large amounts of data ambient noise data are collected in the 5 80 s period range whereas teleseismic data are available between about 8 and 250 s resulting in a broad common period range between 8 and 80 s at intermediate periods around 30 s and for shorter interstation distances phase velocities measured from ambient noise are on average between 0 5 per cent and 1 5 per cent lower than those observed via the earthquake based method this discrepancy is small compared to typical phase velocity heterogeneities 10 per cent peak to peak or more observed in this period range we nevertheless conduct a suite of synthetic tests to evaluate whether known biases in ambient noise cross correlation measurements could account for this discrepancy we specifically evaluate the effects of heterogeneities in source distribution of azimuthal anisotropy in surface wave velocity and of the presence of near field rather than far field only sources of seismic noise we find that these effects can be quite important comparing individual station pairs the systematic discrepancy is presumably due to a combination of factors related to differences in sensitivity of earthquake versus noise data to lateral heterogeneity the data sets from both methods are used to create some preliminary tomographic maps that are characterized by velocity heterogeneities of similar amplitude and pattern confirming the overall agreement between the two measurement methods

graphite and quartz petrofabrics examples from the ediacaran black quartzites of the ossa morena zone sw iberia abstract we study with the electron back scattered diffraction ebsd technique the fabric of metamorphosed and ductilely deformed phtanites or graphitic cherts a common lithotype in ediacaran supracrustals of the west european cadomian orogen currently they are black quartzites with a planolinear tectonite structure microscopically they present a sub mm scale alternation of coarse and fine grained dynamically recrystallized quartz bands we attribute intracrystalline plasticity partitioning to variations in graphite inclusion concentration constraining quartz grain boundary mobility during dynamic recrystallization under non coaxial strain regimes and moderate to elevated temperatures 400 650 c lattice preferred orientations of quartz c and axes are geometrically related to the external reference frame provided by foliations and lineations we also identify the involvement of 0001 r m and m c quartz intracrystalline slip systems deformation modes operated simultaneously and under identical temperatures in interleaved parallel domains mm to cm thick in adjacent coarse and fine grained bands medium to high t plasticity is congruent with the syntectonic temperature gradients associated with the amphibolite facies metamorphism of the country rocks we also present the first specific study published so far on natural deformation graphite lattice preferred orientation graphite inclusions as well as those of mica exhibit mineral shape fabrics that suggest operation of 0001 slip however ebsd measurements also record fabrics suggestive of m slip in spite of a rather small volumetric proportion graphite spatial organization at increased shear strains facilitated ductile deformation if a graphite network is established in the rock it can potentially increase rock electrical conductivity thus accounting for mid and lower crust anomalous electric conductivity

reflection of seismic surface waves at the northern apennines abstract seismic surface waves with periods of 15 to 20 s are reflected laterally at the northern apennines for earthquakes originated and recorded in the wider alpine area a few hundred kilometres north of the apennines we can directly observe late arrivals of reflected regional surface waves these have a characteristic polarization of particle motion and often dominate the intermediate period surface wave coda love waves are the most prominent coda arrivals while reflected rayleigh waves show smaller amplitudes and become clear only after rotation of the recordings to the reflection incidence direction we can track the development of the love wave reflection along a temporary broad band transect across the northern apennines indicating the location of the reflector near to the highest topography from spectral element simulations of three dimensional wave propagation we attribute the reflection to a continuous 270 km long offset in the crust mantle boundary under the mountain belt with vertical throw of 20 km thus supporting a deep crustal root under the outer side of the apennines fold and thrust belt and significant crustal thinning on the inner side amplitude reflection coefficients for near normal incidence can be estimated as 7 for both love and rayleigh waves

british late glacial and holocene climatic history reconstructed from land snail assemblages gations have enabled refinement of the stratigraphic scheme as shells of land snails occur in quantity throughout the sequence preece 1998 they provide a detailed mollusk succession from the beginning of the late glacial until the present day the late glacial assemblages are dominated by species of open country and marsh but shadeintolerant species are replaced by a succession of woodland species during the early part of the holocene following forest clearances during the neolithic and bronze age 5000 3000 yr b p these closed forest communities show a reversion to grassland assemblages with only minor indications of scrub fig 2 a detailed chronology for this succession is provided by a series of

precise 14c ages of the vedde and saksunarvatn ashes and the younger dryas boundaries from western norway and their comparison with the greenland ice core gicc05 chronology the greenland ice cores with the gicc05 chronology represent a standard for late quaternary climate events and their ages whereas many other palaeoclimatic archives are dependent on 14 c dates it is therefore critical to know if the ice core and the calibrated 14 c chronologies are identical and if not to quantify the offset between them we present bayesian age depth modelling of 118 accelerator mass spectrometry 14 c dates from kraukenes lake calibrated using intcal09 that provide high precision ages of 12 066 42 and 10 210 35 cal a bp for the vedde and saksunarvatn ashes respectively the lower and upper younger dryas boundaries have ages of 12 710 52 and 11 546 59 cal a bp respectively the four dated levels coincide with correlative levels in gicc05 within the dating uncertainties but are all consistently younger at kraukenes the ages of the tephra chronostratigraphic markers suggest a mean offset of 70 years to older ages in the gicc05 compared with the intcal09 time scale responses to small climate changes 30 years before the younger dryas boundaries at kraukenes are suggested to correspond to the defined greenland stadial 1 boundaries this suggested difference in timing 30 years and time scale offset 70 years mean that the greenland stadial 1 boundaries appear 100 years older than the younger dryas boundaries copyright 2013 john wiley sons ltd

zircon u pb geochronology of paragneisses and biotite granites from the sw iberian massif portugal evidence for a palaeogeographical link between the ossa morena ediacaran basins and the west african craton

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

tectonic setting of cadomian low pressure metamorphism in the central ossa morena zone iberian massif sw spain abstract the upper proterozoic serie negra a monotonous pre and syntectonic slate greywacke series including volcanic episodes crops out widely in the central area of the ossa morena zone sw iberian massif iberian peninsula this unit was affected by complex late precambrian tectonothermal events the cadomian orogeny during which two phases of deformation d1 and d2 are recognized in the 610 585 ma time span the second deformational episode d2 was the most prominent and was related to progressive low pressure high temperature metamorphism lp ht reaching the highest grade in the lower structural levels where thermal evolution led to extensive migmatization and gave rise to the generation of different kinds of anatectic granitoids in this work we present field petrographic and analytical data dealing with the metamorphic evolution of a cadomian lp ht terrane from the central ossa morena zone iberian massif sw spain whose tectonic setting is unclear so far the tectonic setting proposed herein for cadomian d2 lp ht events is discussed in terms of its relationship to plate convergence or to extensional tectonic regimes modelling of the p t t trajectories undergone by a crust moderately overthickened by the thrusting of thinned sialic crust slices reproduces well the observed p t t aths if moderate or low uplift rate and high geothermal gradients are assumed for the uplift history numerical simulations combined with structural and metamorphic evidence support a compressional tectonic setting as responsible for the observed facies series distribution and deformation metamorphism relationships furthermore the regional geodynamic context coeval high pressure metamorphism in neighboring areas of the ossa morena zone and extensive calc alkaline magmatism is consistent with such a tectonic setting a correlation is tentatively proposed here between compressional cadomian deformations in the ossa morena zone upper proterozoic docking of avalonian terranes in ne america and cadomian orogenesis in the northern armorican massif

ediacaran palaeozoic tectonic evolution of the ossa morena and central iberian zones sw iberia as revealed by sm nd isotope systematics abstract sm nd isotopic analyses of palaeozoic sedimentary and igneous rocks in the southwest iberian massif western end of the european variscan belt are presented in order to unravel its complex poly orogenic evolution during the closure of the rheic ocean and the amalgamation of pangea the gondwanan margin in southwest iberia sw iberia is subdivided into the ossa morena and central iberian zones separated by the badajoz cordoba shear zone which represents a cryptic suture zone between these terranes the relationships between these terranes and between units preserved within the suture zone e g the sierra albarrana group during the palaeozoic and neoproterozoic are controversial sm nd isotopic studies of representative sedimentary sequences covering the entire pre variscan record of the ossa morena and central iberian zones show very similar characteristics from the uppermost ediacaran onwards these data indicate that their accretion to one another must have been completed by the late neoproterozoic ediacarin that time an event assigned to cadomian orogeny and that they never separated substantially from each other since that time the sm nd isotopic composition of the sierra albarrana group metasedimentary rocks is similar to that of the pre cadomian sequences of the ossa morena zone serie negra suggesting derivation from a common source the common provenance of the palaeozoic sequences in the two zones is identical to that of the pre cadomian serie negra of the ossa morena zone which in accordance with the data presented herein and published u pb zircon data indicates a west african affinity

deep seismic expression of an ancient plate boundary in europe seismological results on the structure of the upper mantle below europe reveal a marked contrast in seismic properties between precambrian and younger parts of europe the precambrian craton in eastern europe is characterized by high shear wave velocities which can be explained by low temperatures the transition to low seismic velocities below phanerozoic europe coincides with the crustal boundary zone of the craton and exists to depths of at least 140 kilometers despite the long and complex tectonic history of the plate boundary zone the transition is remarkably sharp which rules out any significant lateral transport of asthenospheric material across the suture zone

holocene mg ca alkenones and light stable isotope measurements on the outer north iceland shelf md99 2269 a comparison with other multi proxy data and sub division of the holocene to evaluate whether proxies that record surface near surface and bottom water conditions from the north iceland shelf have similar trends and periodicities we examine holocene century scale pale

structure of the 8200 year cold event revealed by a speleothem trace element record abrupt first order shifts in strontium and phosphorus concentrations in stalagmite calcite deposited in western ireland during the 8200 year event the major cooling episode 8200 years before the present are interpreted as responses to a drier climate lasting about 37 years both shifts are centered on 8330 80 years before the present coinciding with a large oxygen isotope anomaly and a change in the calcite petrography in this very high resolution monthly record antipathetic second order oscillations in phosphorus and strontium reveal decreased growth rates and increased rainfall seasonality growth rate variations within the event reveal a two pronged structure consistent with recent model simulations

large scale waveform inversions of surface waves for lateral heterogeneity 2 application to surface waves in europe and the mediterranean linear surface wave scattering theory is used to reconstruct the lateral heterogeneity under europe and the mediterranean using surface wave data recorded with the network of autonomously recording seismographs nars the waveform inversion of the phase and the amplitude of the direct surface wave leads to a variance reduction of approximately 40 and results in phase velocity maps in the period ranges 30 40 s 40 60 s and 60 100 s a resolution analysis is performed in order to establish the lateral resolution of these inversions using the phase velocity perturbations of the three period bands a two layer model for the s velocity under europe and the mediterranean is constructed the s velocity perturbations in the deepest layer 100 200 km are much more pronounced than in the top layer 0 100 km which confirms that the low velocity zone exhibits pronounced lateral variations in both layers the s velocity is low under the western mediterranean while the s velocity is high under the scandinavian shield in the deepest layer a high s velocity region extends from greece under the adriatic to northern italy several interesting smaller features such as the massif central are reconstructed one of the spectacular features of the reconstructed models is a sharp transition in the layer between 100 and 200 km near the tornquist tesseyre zone this would indicate that there is a sharp transition at depth between central europe and the east european platform the waveform inversion of the surface wave coda leads to good waveform fits but the reconstructed models are chaotic this is due both to a lack of sufficient data for a good imaging of the surface wave energy on the heterogeneities and to an appreciable noise component in the surface wave coda

transcurrent continental tectonics model for the ossa morena zone neoproterozoic paleozoic evolution sw iberian massif portugal the ossa morena zone sw iberian massif was affected by continuous orogen parallel transcurrent continental tectonics from the neoproterozoic to the carboniferous times involving transtension tt and transpression tp processes that co existed together occurred separately in neighbouring regions by the means of strain partitioning or even worked diachronically a first stage of transpression tp1 took place during the late neoproterozoic lower cambrian as a result of cadomian arc continent collisional processes structures generated by transtension tt1 from cambrian to lower devonian were related to strong lithosphere stretching responsible for the development of basins controlled by major detachments tilting rifting and important tectono thermal diachronic processes denudation phenomena and inhibition of sedimentation related with thermal uplift asthenosphere upwelling and consequent subsidence caused by isostatic equilibrium involving generalized transgressions were processes responsible for major unconformities the variscan tp2 tt2 episodes that followed diachronically tp1 tt1 by maintaining the orogen parallel transport direction were concomitant with syntectonic deposition of continental basins in the omz and foreland basins in the spz tt2 local transtension and tectonic exhumation of deep crustal rocks along major shear zones favoured the opening of tectonic troughs filled up by sediments and volcanism tp2 shortening have generated fold axes parallel to the orogen strike and composite dissymmetric flower structures

extension of the basin rayleigh wave amplification theory to include basin edge effects the presence of sediments near the earth s surface can significantly amplify the strength of shaking during earthquakes such basin or site amplification effects have been well documented in numerous regions yet the complex and often situational dependence of competing reasons for this amplification makes it hard to quantify in a general sense or to determine the most significant contributions simple 1d seismic profiles can be used to estimate the amplitude differences between a basin site and a hard rock reference site but this ignores any reflections or conversions at the basin edge or a resonance effect depending on the basin s geometry in this article we explore an analytic model based on coupling coefficients for surface rayleigh waves to account for the lateral discontinuities at a basin s edge datta 2018 we use this simple tool to explore the relationship between the basin s rayleigh wave amplification spectrum and various parameters such as basin depth edge slope angle and impedance contrast the step by step construction of the model allows us to quantify the contributions from various wave propagation effects with the goal of identifying situations under which various basin edge effects must be considered in addition to purely 1d estimates for the most velocity contrasts less than a factor of 5 the error made by the 1d theory in predicting maximum rayleigh wave basin amplification is under 35 for both the horizontal and the vertical components for simple basins the vertical amplification dominates at larger high frequencies and the horizontal at lower frequencies finally we demonstrate from comparisons with spectral element wavefield simulations that realistic velocity structures can be reduced to a simpler box shape for the semi analytic formulation used here with reasonable results for the purposes of estimating site amplification or microzonation an improved model that accounts for basin edge effects can be implemented without high computational cost

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

upper mantle and lithospheric heterogeneities in central and eastern europe as observed by teleseismic receiver functions summary data from 90 permanent broad band stations spread over central and eastern europe were analysed using ps receiver functions to study the crustal and upper mantle structure down to the mantle transition zone receiver functions provide valuable information on structural features which are important for the resolution of european lithospheric dynamics moho depths vary from less than 25 km in extensional areas in central europe to more than 50 km at stations in eastern europe craton and beneath the alpine carpathian belt a very shallow moho depth can be observed at stations in the upper rhine graben area ca 25 km whereas for example stations in the sw bohemian massif show a significantly deeper moho interface at a depth of 38 km vp vs ratios vary between 1 60 and 1 96 and show no clear correlation to the major tectonic units thus probably representing local variations in crustal composition delayed arrivals of converted phases from the mantle transition zone are observed at many stations in central europe whereas stations in the cratonic area show earlier arrivals compared with those calculated from the iasp91 earth reference model differential delay times between the p410s and p660s phases indicate a thickened mantle transition zone beneath the eastern alps the carpathians and the northern balkan peninsula whereas the transition zone thickness in eastern and central europe agrees with the iasp91 value the thickening of the mantle transition zone beneath the eastern alps and the carpathians could be caused by cold deeply subducted oceanic slabs

from cadomian subduction to early palaeozoic rifting the evolution of saxo thuringia at the margin of gondwana in the light of single zircon geochronology and basin development central european variscides germany

simulation of the cold climate event 8200 years ago by meltwater outburst from lake agassiz meltwater pulse is assumed to have a volume of 1 6 10 14 m 3 and a period of discharge of 2 years on the basis of glaciological modeling of the decay of the laurentide ice sheet lis we present a possible mechanism which can explain the centennial duration of the 8 2 ka cold event the mechanism is related to the existence of an additional equilibrium climate state with reduced north atlantic deep water nadw formation and a southward shift of the nadw formation area hints at the additional climate state were obtained from the largely varying duration of the pulse induced cold episode in response to overlaid random freshwater fluctuations in monte carlo simulations the model equilibrium state was attained by releasing a weak multicentury freshwater flux through the st lawrence pathway completed by the meltwater pulse the existence of such a climate mode appears essential for reproducing climate anomalies in close agreement with paleoclimatic reconstructions of the 8 2 ka event the results furthermore suggest that the temporal evolution of the cold event was partly a matter of chance index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4255 oceanography general numerical modeling 4532 oceanography physical general circulation 4215 oceanography general climate and interannual variability 3309 9325 information related to geographic region atlantic ocean

geodynamic evolution of a cadomian arc region the northern ossa morena zone iberian massif abstract ductile deformation and polyphase metamorphism in the ossa morena zone of the iberian massif are related to two major tectonothermal episodes of cadomian late neoproterozoic to early cambrian and variscan age middle to late paleozoic the available petrological structural and geochronological data suggest that a number of tectono metamorphic and magmatic episodes occurred during the 620 480 ma interval that would comprise a complete cadomian wilson cycle the geodynamic scenario was that of an andean type continental margin an evolutionary model is presented for this orogeny comprising stages of volcanic arc generation crustal thickening back arc extension tectonic inversion and cratonization a correlation with comparable areas from pre mesozoic massifs elsewhere in europe is proposed in particular with the armorican massif of northern france

geochemistry and petrology of recycled orogen derived sediments a case study from upper precambrian siliciclastic rocks of the central iberian zone iberian massif spain abstract two areas of upper precambrian siliciclastic rocks separated from each other by 150 km were selected in the central iberian zone ciz for a petrological and geochemical study the petrology of the coarser grained rocks indicates the absence or scarcity of igneous clasts the presence of extrabasinal and intrabasinal clasts and homogeneous features of sandstones ranging from very fine to fine grained the modal data of these rocks plot close to the qt l and qm lt sides of qtfl and qmflt triangular diagrams suggesting provenance from a recycled orogen the geochemical data on the shales and sandstones from the two areas studied are very uniform both groups of rock show similar ranges of relevant major element ratios such as al 2 o 3 tio 2 17 46 21 51 17 46 21 34 for shale and sandstone respectively al 2 o 3 feo t 2 40 3 79 2 18 3 33 and feo t feo t mgo 0 71 0 77 0 68 0 76 together with parallel average rare earth element ree patterns and similar values for some key trace element ratios la th th yb th u zr hf sm nd and cr sc other trace element ratios la sc th sc cr th and cr zr are uniform in the shales group and also in the sandstones group although minor differences become apparent when both groups are compared these differences are probably related to the quartz dilution effect affecting the relative abundance of phyllosilicates in these rocks and indirectly the sc and cr contents given their covariations with al2o3 the zr yb zr y and zr th ratios of the shales are uniform the sandstones show higher and more variable values and there is no correlation between zr abundance and any of these ratios in the shales or sandstones together with the parallel ree patterns shown by both groups of rock these results suggest the absence of heavy mineral fractionation during the transport of detrital material and or the relative importance of other minerals probably phyllosilicates in the control of yb y and th abundances apparently all the groups of rocks show a remarkable geochemical homogeneity despite the distance between the sampling areas thus the petrological and chemical data are consistent and point to a very extensive homogeneous and stable source region as the most plausible contributor to the upper precambrian siliciclastic rocks in the ciz the possible relationship between this zone and n gondwana is also discussed

asynchrony in key holocene chronologies evidence from irish bog pines the greenland ice core chronology 2005 gicc05 and the radiocarbon calibration curve intcal are the foremost time scales used in paleoclimatic and paleoenvironmental studies of the most recent 10 k y due to varying and often insufficient dating resolution opportunities to test the synchrony of these two influential chronologies are rare here we present evidence for a phase of major pine recruitment on irish bogs at ca 8160 yr b p dendrochronological dating of subfossil trees from three sites reveals synchronicity in germination across the study area indicative of a regional forcing the concurrent colonization of pine on peatland is interpreted in terms of drier surface conditions and provides the first substantive proxy data in support of a significant hydroclimatic change in the north of ireland accompanying the 8 2 ka climate cooling event the date of pine establishment does not overlap with the gicc05 age range for the event and possible lags between responses are unlikely to explain the full difference in light of recent studies highlighting a possible offset in gicc05 and intcal dates the irish pine record supports the notion of ice core dates being too early during the period of study if the suggested discrepancy in timing is an artifact of chronological error it is likely to have affected interpretations of previous proxy comparisons and alignments

waveform inversion for lateral heterogeneities using multimode surface waves summary we propose a waveform inversion scheme that can be used to invert strong structural heterogeneities the method is based on a ray approximation for surface waves strong structural lateral variations are modelled by vertical discontinuities therefore a geologically heterogeneous region is partitioned into a number of lateral homogeneous subregions synthetic seismograms are calculated by modal summation over incident and transmitted modes with this method the complete waveforms of surface waves including mode cross branch coupling multipathing and scattering are considered in the inversion we test the method with several geophysically realistic structural models an example of waveform inversion for real data a wave path across the iberian peninsula and the oceanic structure off the french coast owing to the gibraltar earthquake ms 5 7 is presented the method allows us to obtain the information represented by different set of structures along the same source receiver minor arc through which the waves have propagated the method is applicable to different models of lateral heterogeneity in its present development it is most appropriate for inverting structures around tectonic scenarios such as continental margins grabens and discontinuities between major plates

assessing the differences between the intcal and greenland ice core time scales for the last 14 000 years via the common cosmogenic radionuclide variations variations in galactic cosmic rays reaching the earth s atmosphere produce globally synchronous variations in the production rates of cosmogenic radionuclides in consequence they leave their imprint in tree ring 14c and ice core 10be records by identifying this signal and correcting for the known geochemical influences on the radionuclides it is possible to compare and synchronize the tree ring chronology and the greenland ice core time scale here we compare the intcal13 and the gicc05 time scales for the last 14 000 years via identification and synchronization of the common short term variations in the ice core 10be and tree ring 14c records most likely induced by variations in the solar modulation of galactic cosmic rays we conclude that systematic time scale differences have to be accounted for if ice core and 14c dated records are compared on decadal time scales these are mostly within the uncertainties of the time scales and the method proposed here however for large parts of the mid to late holocene i e after 7000 yrs bp the best agreement between ice core 10be and tree ring 14c records is obtained for time shifts outside the stated errors of the respective time scales a transfer function is proposed that can be applied to synchronize the gicc05 ice core time scale to the radiocarbon time scale

a synchronized dating of three greenland ice cores throughout the holocene as part of the effort to create the new greenland ice core chronology 2005 gicc05 a synchronized stratigraphical timescale for the holocene parts of the dye 3 grip and ngrip ice cores is made by using volcanic reference horizons in electri cal conductivity measurements to match the cores the main annual layer counting is carried out on the most suited records only exploit ing that the three ice cores have been drilled at locations with different climatic con ditions and differences in ice flow however supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid ity of the match after the verification the main dating is transferred to all records us ing the volcanic reference horizons as tie points an assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores the data used for the main annual layer counting of the past 7900 years are the dye 3 grip and ngrip stable isotope records as the high accumulation rate at the dye 3 drill site makes the seasonal cycle in the dye 3 stable isotopes very resistant to firn diffusion an effort has been made to extend the dye 3 holocene record the new syn chronized dating relies heavily on this record of 75 000 stable isotope samples the dat ing of the early holocene consists of an already established part of gicc05 for grip and ngrip which has now been transferred to the dye 3 core gicc05 dates the younger dryas termination as defined from deuterium excess to 11 703 b2k 130 years earlier than the previous grip dating

inherited arc signature in ediacaran and early cambrian basins of the ossa morena zone iberian massif portugal paleogeographic link with european and north african cadomian correlatives abstract geochemical data from clastic rocks of the ossa morena zone iberian massif show that the main source for the ediacaran and the early cambrian sediments was a recycled cadomian magmatic arc along the northern gondwana margin the geodynamic scenario for this segment of the avalonian cadomian active margin is considered in terms of three main stages 1 the 570 540 ma evolution of an active continental margin evolving oblique collision with accretion of oceanic crust a continental magmatic arc and the development of related marginal basins 2 the ediacaran early cambrian transition 540 520 ma coeval with important orogenic magmatism and the formation of transtensional basins with detritus derived from remnants of the magmatic arc and 3 gondwana fragmentation with the formation of early cambrian 520 510 ma shallow water platforms in transtensional grabens accompanied by rift related magmatism these processes are comparable to similar cadomian successions in other regions of gondwanan europe and northwest africa ediacaran and early cambrian basins preserved in the ossa morena zone portugal and spain the north armorican cadomian belt france the saxo thuringian zone germany the western meseta and the western high atlas morocco share a similar geotectonic evolution probably situated in the same paleogeographic west african peri gondwanan region of the avalonian cadomian active margin

rift related volcanism predating the birth of the rheic ocean ossa morena zone sw iberia abstract two very different periods of magma emplacement in the crust of the ossa morena zone early and main events in sw iberia have been previously interpreted to record a cambrian early ordovician rifting event that is thought to have culminated in the opening of the rheic ocean during the early ordovician new stratigraphic petrographic geochemical and sm nd isotope data from cambrian volcanic rocks included in six key low grade sections in both portugal and spain considerably improve our understanding of these events these data 1 confirm the existence of two rift related magmatic events in the cambrian of the ossa morena zone 2 demonstrate that the early rift related event was associated with migmatite and core complex formation in the mid upper crust and is represented by felsic peraluminous rocks the parent magmas of which were derived mainly from crustal sources and 3 show the main rift related event to be represented by a bimodal association of felsic and mafic rocks with minor amounts of intermediate rocks some of the mafic rocks show n morb affinity whereas others have oib or e morb affinities suggesting different heterogeneous mantle sources depleted and enriched asthenospheric and lithospheric plume like and non plume like the acid and intermediate rocks appear to represent hybrid mixtures of crust and mantle derived magmas this new data supports the hypothesis that the onset of rifting was associated with a process of oblique ridge trench collision we interpret the significant differences between the early and main events as reflecting the evolution from a wide rift stage with passive extension mainly accommodated by lower crust flow in a high heat flow setting to a narrow rift stage with active extension characterized by extension rates that outpaced thermal diffusion rates

approximation of surface wave mode conversion at a passive continental margin by a mode matching technique summary at a continental margin sharp structural changes cause strong lateral heterogeneity in s wave velocity p wave velocity and density therefore mode conversion of surface wave modes is expected passive continental margins may be modelled by vertical discontinuities mode conversion is then expressed in terms of re ection and transmission coe cients long period seismograms are calculated by mode summation over incident re ected and transmitted modes re ection and transmission coe cients for surface waves are approximated by a mode matching technique that is adapted to a spherical earth model an orthogonality relation for surface wave eigenfunctions on a spherical earth is given that allows one to simplify the linear system of equations for the determination of re ection and transmission coe cients transmission of fundamental love and rayleigh modes is strongly in uenced by upper crustal heterogeneity for frequencies larger than 40 hz for fundamental love modes and larger than 60 hz for fundamental rayleigh modes mode conversion to neighbouring modes can be strong but mode conversion is not necessarily con ned to neighbouring modes fundamental modes in particular can couple with more distant higher modes in synthetic seismograms calculated for epicentral distances up to 40 0 mode conversion between higher modes and fundamental modes results in shear coupled rayleigh waves

the moroccan anti atlas the west african craton passive margin with limited pan african activity implications for the northern limit of the craton abstract the moroccan anti atlas region located south of the south atlas fault has been viewed traditionally as containing two segments separated by the anti atlas major fault these two segments are said to consist of a 600 700 ma pan african segment located in the northeast and b 2 ga eburnian segment situated to the southwest on the basis of observations in the zenaga and saghro inliers and of a recent literature review we suggest that this subdivision is inappropriate in that eburnian and pan african materials occur throughout the anti atlas region the entire anti atlas is underlain by eburnian crust unconformably overlain by a lower neoproterozoic passive margin allochthonous pan african ocean crustal slices were thrust onto the west african craton wac passive margin sequence 685 ma ago as a result of pan african accretion tectonics high level high k calc alkaline and alkaline granitoids locally intruded the anti atlas sequence as a whole at the end of the pan african orogeny at 585 560 ma the intervening 100 m y interval was marked by quiescence this succession of events can be related to the behaviour of one single rigid cratonic passive margin during an orogeny and correlated to the pan african events that occurred to the east in the tuareg shield and to the north in avalonian terranes this model implies that the actual northern limit of the wac is located at the south atlas fault saf and not at the anti atlas major fault aamf we propose that the aamf corresponds to the southwestern boundary of an aulacogen that formed along the northern margin of the wac during early neoproterozoic times this is consistent with the development of the gourma aulacogen on the eastern side of the wac this model further suggests that the northeastern boundary of the wac occurs north and not south of ougarta algeria support for this model is provided by geological and geophysical evidence

late pleistocene and holocene tephrostratigraphy of interior alaska and yukon key beds and chronologies over the past 30 000 years abstract the aleutian arc alaska peninsula and wrangell volcanic field are the main source areas for tephra deposits found across alaska and northern canada and increasingly tephra from these eruptions have been found further afield in north america greenland and europe however there have been no broad scale reviews of the late pleistocene and holocene tephrostratigraphy for this region since the 1980s and this lack of data is hindering progress in identifying these tephra both locally and regionally to address this gap and the variable quality of associated geochemical and chronological data we undertake a detailed review of the latest pleistocene to holocene tephra found in interior alaska and yukon this paper discusses nineteen tephra that have distributions beyond southwest alaska and that have the potential to become or already are important regional markers this includes three modern events from the 20th century ten with limited data availability but potentially broad distributions and six that are widely reported in interior alaska and yukon each tephra is assessed in terms of chronology geochemistry and distribution with new bayesian age estimates and geochemical data when possible this includes new major element geochemical data for crater peak 1992 redoubt 1989 90 and two andesitic tephra from st michael island tephra d as well as revised age estimates for dawson tephra oshetna hayes set h aniakchak cfe ii and the white river ashes northern and eastern lobes

adakitic like magmatism in western ossa morena zone portugal geochemical and isotopic constraints of the pavia pluton abstract granitic rocks are a major component of the earth s continental crust and occur in a wide variety of tectonic settings their chemical and isotopic characterization is crucial to the recognition of the potential sources and mechanisms involved in their generation in this study we present the first whole rock chemical and isotopic sr nd o data for the pavia pluton 328 317 ma located near the western border of the ossa morena zone evora massif portugal major and trace element geochemistry suggests that the different granitic phases composing this intrusive body enclaves granites s l and crosscutting dikes represent independent magma pulses and the majority is similar to ttgs and adakites the little sr nd o isotopic variation with 87 sr 86 sr 328 0 70428 0 70560 end 328 ranging between 3 4 and 0 4 and 18 o varying from 5 6 to 8 4 implies an isotopically similar protolith for all phases the most viable mechanism for the generation of the pavia pluton adakitic like magmatism is assimilation fractional crystallization of a mantle derived magma this mechanism was also invoked to explain the genesis of other plutons within the evora massif but they have a distinct chemistry typical arc calc alkaline rocks the chemical differences between them and the pavia pluton granitic rocks are interpreted as the result of lower degrees of crustal assimilation and higher degrees of contamination of mantle derived magmas by the sinking slab after subduction blocking and subsequent slab break off

the cadomian active margin north armorican massif france a segment of the north atlantic panafrican belt abstract within the european variscan belt the armorican massif northwestern france contains an isolated fragment of the north atlantic panafrican belt the cadomian block mostly unaffected by variscan deformation this block is composed of neoproterozoic rocks ranging in age from 620 to 540 ma brioverian locally overlying a composite basement of icartian 2000 ma or pentevrian 750 ma age the cadomian tectonics the last magmatic manifestations of which are dated at around 540 ma were sealed by a cover of early cambrian rocks in normandy and early ordovician rocks in brittany five units are distinguished in this cadomian block tregor saint brieuc guingamp saint malo and fougeres although the units are bound by major faults the overall coherence of their different protolithic characteristics suggests that they can be fitted into a simple geodynamic model the tregor unit represented by the north tregor batholith of crustal affinity and its icartian host rock probably reflects an early cadomian evolution the saint brieuc unit essentially made up of magmatic rocks of juvenile affinity includes two assemblages juxtaposed by the cadomian tectonics 1 a volcanosedimentary succession formed in a typical island arc setting reflecting subduction around 610 ma and 2 a volcanic plutonic complex emplaced around 590 ma in an extensional active continental margin of pentevrian age the guingamp unit predominantly migmatitic includes a tectonic slice of deep origin the extrusion of which accompanied the exhumation of the migmatites it may represent the trace of a possible suture the saint malo unit is composed of brioverian detrital rocks the significance of which is uncertain passive continental margin or accretionary prism it is structured around a late migmatitic dome 540 ma the fougeres unit corresponds to the outer domain of the cadomian orogeny it was only weakly deformed by cadomian tectonics and is intruded by the large mancellian batholith of crustal origin dated at 540 ma together the structural units are interpreted in the framework of an evolving active margin juxtaposing continental margin marginal basin and volcanic arc before being shortened during the cadomian convergent tectonics

deep structure of the earth s crust in the contact zone of the palaeozoic and precambrian platforms in poland tornquist teisseyre zone abstract one of the major tectonic problems in europe concerns the southwest margin of the east european platform in the region of the so called polish danish trough in general this margin is assumed to be the tornquist teisseyre t t line running approximately from northwest to southeast in this part of europe determination of deep crustal structure of the contact zone between the precambrian platform and the palaeozoic platform was the main aim of the deep seismic sounding dss programme in poland in 1965 1982 deep seismic soundings of the earth s crust have been made in the t t line zone along nine profiles with a total length of about 2600 km the results of deep seismic soundings have shown that the crust in the marginal zone of the east european platform has highly anomalous properties the width of this zone ranges from 50 km in northwest poland to about 90 km in southeast poland the crustal thickness of the palaeozoic platform in poland is 30 35 km and of the precambrian platform 42 47 km while in the t t tectonic zone it varies from 50 to 55 km above the moho boundary in the t t zone at a depth of 40 45 km there is a seismic discontinuity with p wave velocities of 7 5 7 7 km s boundary velocities mean velocities and stratification of the earth s crust vary distinctly along the t t zone there are also observed high gravimetric and magnetic anomalies in the t t zone the t t tectonic zone determined in this manner is a deep tectonic trough with rift properties the deep fractures delineating the t t tectonic zone are of fundamental importance for the localization of the plate edge of the precambrian platform of eastern europe in the light of dss results the northeastern margin of the t t tectonic zone is a former plate boundary of the east european platform