temporal geomagnetic and related attributes of kimberlite magmatism at ekati northwest territories canada abstract this paper outlines the development of a multi disciplinary strategy to focus exploration for economic kimberlites on the ekati property high resolution aeromagnetic data provide an over arching spatial and magnetostratigraphic framework for exploration and kimberlite discovery at ekati and hence also for this investigation the temporal geomagnetic spatial and related attributes of kimberlites with variable diamond content have been constrained by judiciously augmenting the information gathered during routine exploration with detailed laboratory based or field based investigations the natural remanent magnetisation of 36 ekati kimberlites has been correlated with their age as determined by isotopic dating techniques and placed in the context of a well constrained geomagnetic polarity timescale kimberlite magmatism occurred over the period 75 to 45 ma in at least five temporally discrete intrusive episodes based on current evidence the older kimberlites 75 to 59 ma have low diamond contents and are distributed throughout the property younger kimberlites 56 to 45 ma have moderate to high diamond contents and occur in three distinct intrusive corridors with nne to ne orientations economic kimberlite pipes erupted at 55 4 0 4 ma along the a154 lynx intrusive corridor which is 7 km wide and oriented at 015 and at 53 2 0 3 ma along the panda intrusive corridor which is 1 km wide and oriented at 038 the intrusion ages straddle a paleopole reversal at chron c24n consistent with the observation that the older economic kimberlites present as aeromagnetic low anomalies while the younger economic pipes are characterised as aeromagnetic highs the aeromagnetic responses for these kimberlites are generally muted because they contain volcaniclastic rock types with low magnetic susceptibility kimberlites throughout the ekati property carry a primary natural magnetic remanence nrm vector in ti bearing groundmass magnetite and it dominates over vectors related to induced magnetisation magnetostratigraphic correlation of ekati kimberlites may therefore present a powerful adjunct to existing exploration techniques mainly because the diamond content of ekati kimberlites apparently is related more to the age of eruption than to any other parameter investigated in this work

an active deep marine strike slip basin along the north anatolian fault in turkey the tekirdag depression within the marmara sea in the mediterranean region is an active rhomb shaped strike slip basin along the north anatolian fault with a basin floor at a water depth of 1150 m new multichannel seismic reflection data and on land geological studies indicate that the basin is forming along a releasing bend of the strike slip fault and is filled with syntransform sediments of pliocene quaternary age the basin is bounded on one side by the north anatolian fault and on the other side by a subparallel normal fault which forms the steep submarine slope in cross section the basin is strongly asymmetric with the thickness of the syntransform strata increasing from a few tens of meters on the submarine slope to over 2 5 km adjacent to the north anatolian fault seismic sections also show that the slope forming normal fault connects at depth to the north anatolian fault implying that the basin is completely detached from its substratum the whole structure can be envisaged as a huge rather flat negative flower structure the releasing bend of the north anatolian fault responsible for the formation of the basin is flanked by a constraining bend along the constraining bend the syntransform strata are being underthrust implying a recent change in the direction of the regional displacement vector this thrusting is responsible for the uplift of the submarine slope to a height of 924 m possibly by a mechanism of elastic rebound regional geology suggests that most of the syntransform strata are lacustrine with only the topmost few hundred meters consisting of deep marine clays the anomalous present depth of the tekirdag depression is due to reduced quaternary sedimentation coupled with high rates of displacement along the north anatolian fault which amounts to 20 mm yr in the marmara sea region

upper mantle structure of the northern cascadia subduction zone previous knowledge of the structure of the cascadia subduction zone north of the canada united states border has been derived from a variety of geophysical studies that accurately delineated the downgoing juan de fuca plate from the offshore deformation front to depths of 50 60 km beneath south central vancouver island and the georgia strait little is known however of the structure of the cascadia subduction zone farther westward and to greater depths in the upper mantle we have assembled a set of some 1100 teleseismic traveltimes from events recorded on the western canadian telemetered network to augment a previously existing data set recorded on the washington regional seismograph network the composite data set is inverted for upper mantle structure below washington oregon and southwestern british columbia we analyze the new northern portion of the model between 48 5 50 n and 118 127 w which provides the first images of the deep slab structure in this region the model is parameterized using s

s velocity variations beneath north america 1 we investigate s velocity variation in the upper mantle beneath north american to better understand the effects of data heterogeneity model parameterization and regularization to this end we analyzed and fit regional s and rayleigh wave trains generated by earthquakes around north america that occurred between the years 2000 through 2006 including waveforms from the transportable array stations of earthscope s usarray these new data were combined with constraints used for the 3 d s velocity model na04 in order to create a new model na07 another model was created from a suite of good fit models to provide a useful guide for model velocities and uncertainties by estimating ranges of probable velocity variations throughout the upper mantle we find that the southern and eastern edges of the north american craton appear to be defined by paleozoic orogens rather than proterozoic ones on average the archean portion of the craton is 200 km thick while the paleozoic part averages 175 km thick with an 80 m s lower s velocity the horizontal gradients in velocity are over 1 0 100 km at the western margin of the craton 0 5 100 km in the south and 1 100 km at the eastern margin

the last reconnection of the marmara sea turkey to the world ocean a paleoceanographic and paleoclimatic perspective during the late glacial marine isotope stage 2 the marmara sea transformed into a brackish lake as global sea level fell below the sill in the dardanelles strait a record of the basin s reconnection to the global ocean is preserved in its sediments permitting the extraction of the paleoceanographic and paleoclimatic history of the region the goal of this study is to develop a high resolution record of the lacustrine to marine transition of marmara sea in order to reconstruct regional and global climatic events at a millennial scale for this purpose we mapped the paleoshorelines of marmara sea along the northern eastern and southern shelves at cekmece prince islands and imrali using data from multibeam bathymetry high resolution subbottom profiling chirp and ten sediment cores detailed sedimentologic biostratigraphic foraminifers mollusk diatoms x ray fluorescence geochemical scanning and oxygen and carbon stable isotope analyses correlated to a calibrated radiocarbon chronology provided evidence for cold and dry conditions prior to 15 ka bp warm conditions of the bolling allerod from 15 to 13 ka bp a rapid marine incursion at 12 ka bp still stand of marmara sea and sediment reworking of the paleoshorelines during the younger dryas at 11 5 to 10 5 ka bp and development of strong stratification and influx of nutrients as black sea waters spilled into marmara sea at 9 2 ka bp stable environmental conditions developed in marmara sea after 6 0 ka bp as sea level reached its present shoreline and the basin floors filled with sediments achieving their present configuration

late pleistocene holocene evolution of the northern shelf of the sea of marmara abstract chirp sub bottom profiling multibeam bathymetric mapping and a combination of faunal and isotopic analysis of molluscs and foraminifera in sediment cores on the northern shelf of the sea of marmara som provide evidence of sea level excursions water exchanges between the adjacent mediterranean and black seas and oscillating salinity over the last 160 ka bp during the marine isotope stages mis 2 mis 3 mis 4 and mis 6 the som disconnected from the mediterranean sea and evolved into a lake during mis 1 mis 5 and mis 7 the som reconnected and became salty once again sapropels formed shortly after each invasion of mediterranean saltwater observed in our cores concurrent suboxic dysoxic conditions prevailed over quite shallow substrates on the shelf ancient shorelines are pervasive at 85 m on the northern shelf and in the region of prince islands coincident with the elevation of the modern bedrock sill in the canakkale dardanelles strait at times when global eustatic sea level dropped below this sill the surface of the som stabilized at its outlet and freshened thus this particular shoreline is interpreted as the edge of the most recent som lake that existed from about 75 ka bp to 12 ka bp the freshening is observed in very light 6 values of 18 o measured on freshwater molluscs and the complete absence of foraminifera two brief lacustrine episodes during mis 5 suggest that the level of the canakkale outlet might have been as shallow as 50 m in the past a likelihood supported by submerged terraces along its margins bounding the modern central channel and the presence of an euryhaline biofacies in unit l4 1 corresponding to mis 5b 18 o profiles and carbon 14 dating show that salinification of the som and the blossoming of bioherms evolved rapidly after the latest connection with the mediterranean at 12 ka bp however freshening proceeded more slowly once the connection was severed

pleistocene holocene calcareous nannofossil biostratigraphy of core samples from the northeastern sea of marmara fenerbahce pendik nw turkey abstract pseudoemiliana lacunosa gephyrocapsa oceanica and emiliania huxleyi ionian pleistocene holocene calcareous nannoplankton zones were identified from 82 samples of 14 cores taken from 8 locations in the northeastern sea of marmara the investigation indicates that the identified biozones have been alternated by tectonic activity in the 1 5 and 6 core locations the study area has been affected three times by tectonic activity during the pleistocene holocene time interval the first activity occured during the early pleistocene and the others during holocene

s wave velocity structure of the canadian upper mantle abstract we investigate mantle structure beneath the canadian landmass using 500 surface wave waveforms recorded at stations of the canadian national seismic network and global seismic network the data are processed using the method of partitioned waveform inversion and afford a comprehensive sampling of s velocity structure beneath the north american craton and adjacent orogenic belts our study thereby extends results from previous regional s wave studies north of the coterminous us and provides a characterization of mantle structure beneath canada which is complementary to the body wave model of grand j geophys res 99 1994 11591 the resulting 3d velocity model is well resolved to a depth of 400 km over most of the region and displays two prominent large scale anomalies a high velocity structure beneath the canadian shield and platform associated with the cratonic keel and pronounced low velocities beneath the cordillera the contrast between these features is strong up to 10 and at more southerly latitudes is sharp with the transition occurring over distances of 600 km or less laterally coherent high velocities persist to depths of ca 250 km beneath the north american craton which we interpret to represent the base of the continental keel smaller scale variations are observed within the cratonic mantle but in general show little correlation with surface geological provinces moderately low velocities beneath the st lawrence valley region and labrador may be related to intracontinental volcanism and rifting respectively

distribution of surficial shelf sediments in the northeastern and southwestern parts of the sea of marmara strait and canyon regimes of the dardanelles and bosporus surficial sediment samples collected from the northeastern and southwestern shelf regions of the sea of marmara together with data available from other sources indicate marked variations in sediment compositions resulting from differences in topographical hydrological and biological conditions in the strait channels of the dardanelles and bosporus where strong undercurrents prevail the floor was covered mostly by coarse grained sediments rich in sand and gravel however in areas of relatively low energy conditions sediments contained appreciable amounts of mud with a tendency towards an increase in the amount of clay towards the open sea the effects of the strong undercurrents on the bedforms was also apparent in the southern strait of bosporus where sidescan sonar surveys revealed the presence of asymmetrical sand ripples although terrigenous mud is the principal sediment type in the two canyons dardanelles and south bosporus the sediments in particular on the floor of south bosporus canyon show a distinct contrast between the inner n s and outer e w trending parts along its axis where depths are greatest the outer part of the canyon appears to contain much more coarse sediment in part derived from the benthic communities than the inner canyon in general both the topography related current regimes and the biological activities in the study areas mostly determine the types and modes of sediment distribution among the biogenic components the calcareous corraline algae rhodophycae chiefly lithothamnium calcareum and l fruticolusum and the molusc families galeommatacae and cerithiospidae are associated with the prevailing mediterranean undercurrents especially in the shallower waters of the junction of the sea of marmara and strait of bosporus the relatively abundant mollusc species mytilus galloprovincialis and modiolus barbatus and the trochidae in the strait of bosporus are largely affected by black sea waters the wide range of carbonate concentrations in the sediments generally reflects the relative abundances of biogenic admixtures in the samples high carbonate percentages in the sediments are usually associated with low mud contents and vice versa interestingly the organic carbon contents of the sediments generally increase with proximity to the black sea suggesting influxes of appreciable amounts of organic matter from the black sea

mechanical controls on the deformation of continents at convergent margins abstract spatial variations in the rigidity of continental plates expressed in terms of an effective elastic thickness t e can have a profound influence on the style of deformation of ocean continent convergent margins depending on the spatial distribution of t e strains related to plate boundary forces can become concentrated where t e is small we calculate t e and t e anisotropy in western canada by using and comparing the wavelet and multitaper coherence methods in addition to a nearly stepwise change in t e from the cordillera to the craton we show that weak axes of t e anisotropy are parallel with most compressive directions of horizontal stress components and fast axes of upper mantle seismic anisotropy maxima in the magnitude of t e anisotropy are spatially correlated with the locations of most earthquakes and the locations and directions of maxima in electrical anisotropy and conductivity the pattern of brittle failure and seismicity is explained as a response to plate boundary forces acting on a plate of variable rigidity and is expected to induce the observed mechanical anisotropy and enhance the flow of crustal fluids resulting in locally high electrical conductivities our combined results thus suggest for the first time that the elastic properties of continental lithosphere have a leading order influence on the deformation and evolution of convergent plate boundaries

deformation rates estimated from earthquakes in the northern cordillera of canada and eastern alaska 1 we estimate deformation rates from earthquake catalog statistics to investigate current strain distribution resulting from the collision of the yakutat block with north america the collision is accommodated over a broad region of alaska and nw canada in a variety of tectonic regimes our estimates have significant uncertainties but the results are generally in agreement with other deformation rate estimates gps and geological data and provide useful first order constraints on local long term tectonic deformation and seismic hazard we estimate that 50 75 of relative plate motion is taken up by earthquakes on the yakutat north america boundaries with lateral crustal extrusion other far field strain and possibly aseismic creep accommodating the remainder we calculate dextral strike slip of 4 5 10 2 mm a on the denali fault system in alaska remarkably similar to late pleistocene holocene rates from geomorphic offsets right lateral motion essentially bypasses the denali fault in easternmost alaska and westernmost yukon passing instead along the totschunda and duke river fault systems right lateral transpression of 5 10 mm a suggests that the alaskan fore arc does not have fully block like behavior between the denali and tintina kaltag faults in alaska 10 20 mm a of dextral shear is accommodated by several ne trending bookshelf faults significant seismic deformation in cases higher than expected from gps data is indicated in the ne cordillera where preexisting faults have a strong control on the pattern and mechanisms of current deformation

seismic stratigraphy of the fault controlled submarine canyon valley system on the shelf and upper slope of anamur bay northeastern mediterranean sea abstract high resolution shallow seismic reflection uniboom and echosounding profiles obtained on the shelf and upper slope areas of anamur bay turkey northeastern mediterranean were studied together with previous data on the onshore geology of the area to investigate the origin and related seismic stratigraphy of the submarine anamur canyon it was found that the main axial trend of the submarine anamur canyon is aligned with the offshore projection of the n s orientated onshore anamur thrust fault of late cretaceous senonian to early tertiary age interpretation of the distinct reflection configurations observed on the seismic profiles reveals the presence of various seismic facies comparable with the depositional sequences resulting from the relative sea level changes during the late quaternary the acoustic basement probably miocene in age is overlain by a sedimentary column mainly plio quaternary which in turn can be divided into two major seismic sequences and 12 seismic facies that show considerable variations in both their lateral and horizontal extent a palaeo deltaic environment sequence i with its typical topset and foreset facies was recognized and the corresponding deposits are interpreted to be indications of coastal deltaic progradation during late pleistocene sea level highstands or during the early phases of the last major eustatic lowering reflections of sequence ii which includes nine distinct facies are marked by onlap configuration and are believed to be marine deposits of the flandrian transgression at least four transgressive cycles are evident from the seismic profiles at 70 90 60 45 and 40 m water depths the two sequences i and ii are now covered with the most recent facies

three dimensional structure across the tintina strike slip fault northern canadian cordillera from seismic refraction and reflection tomography accepted 2006 june 5 received 2006 june 3 in original form 2005 september 4 summary the development of the northern canadian cordillera involved major strike slip displacement of accreted terranes relative to north america along faults such as the tintina which has experienced 425 km of dextral motion since the palaeocene the snore seismic refraction wideangle reflection experiment was carried out in 1997 as one component of lithoprobe s slavenorthern cordillera lithospheric evolution snorcle transect in addition to four 2 d profiles two sets of broadside recordings were acquired to image the 3 d structure across the tintina fault tf in areas centred at about 59 5 n and 62 n simultaneous and independent refraction and reflection traveltime tomography were applied to the combined inline and broadside data set for each region to establish the range of lower crustal velocity moho depth and upper mantle velocity structure consistent with the data our preferred models are the average of the simultaneous and independent models since they represent the robust features required by the data the preferred 3 d models are generally consistent with the 2 d models obtained from the inline data in previous independent studies there are along strike variations across the tf perhaps due to the change in strike direction or the amount of motion along the fault in the north compared to the south in the lower crust the only correlation with the tf that is required by the data is a 0 1 km s 1 drop in velocity to the southwest of the fault in the northern study area the absence of a strong correlation with the tf in the lower crust is consistent with the interpreted continuity of lower crustal units across the fault in the snorcle reflection data the moho is relatively flat throughout the study area 34 35 km depth but there is broad crustal thickening of a few kilometres centred 50 km southwest of the tf in the northern and southern study areas this thickening may be the result of a period when there was a component of compression along the tf there is strong evidence for a 0 3 0 4 km s 1 drop in upper mantle velocity to the west of the tf in the south and weak evidence for 0 1 km s 1 drop to the southwest in the north the upper mantle variations in the south indicate that the tf is the boundary between cooler and or more refractory ancestral north american mantle to the east and warmer and or more fertile mantle beneath accreted north america to the west in the north the mantle appears to be more intermediate in its properties on both sides of the tf

global shear speed structure of the upper mantle and transition zone s u m m a r y the rapid expansion of broad band seismic networks over the last decade has paved the way for a new generation of global tomographic models significantly improved resolution of global upper mantle and crustal structure can now be achieved provided that structural information is extracted effectively from both surface and body waves and that the effects of errors in the data are controlled and minimized here we present a new global vertically polarized shear speed model that yields considerable improvements in resolution compared to previous ones for a variety of features in the upper mantle and crust the model sl2013sv is constrained by an unprecedentedly large set of waveform fits 3 4 of a million broad band seismograms computed in seismogram dependent frequency bands up to a maximum period range of 11 450 s automated multimode inversion of surface and s wave forms was used to extract a set of linear equations with uncorrelated uncertainties from each seismogram the equations described perturbations in elastic structure within approximate sensitivity volumes between sources and receivers going beyond ray theory we calculated the phase of every mode at every frequency and its derivative with respect to sand p velocity perturbations by integration over a sensitivity area in a 3 d reference model the normally small perturbations of the 3 d model required to fit the waveforms were then linearized using these accurate derivatives the equations yielded by the waveform inversion of all the seismograms were simultaneously inverted for a 3 d model of shear and compressional speeds and azimuthal anisotropy within the crust and upper mantle elaborate outlier analysis was used to control the propagation of errors in the data source parameters timing at the stations etc the selection of only the most mutually consistent equations exploited the data redundancy provided by our data set and strongly reduced the effect of the errors increasing the resolution of the imaging our new shear speed model is parametrized on a triangular grid with a 280 km spacing in well sampled continental domains lateral resolution approaches or exceeds that of regionalscale studies the close match of known surface expressions of deep structure with the distribution of anomalies in the model provides a useful benchmark in oceanic regions spreading ridges are very well resolved with narrow anomalies in the shallow mantle closely confined near the ridge axis and those deeper down to 100 120 km showing variability in their width and location with respect to the ridge major subduction zones worldwide are well captured extending from shallow depths down to the transition zone the large size of our waveform fit data set also provides a strong statistical foundation to re examine the validity field of the jwkb approximation and surface wave ray theory our analysis shows that the approximations are likely to be valid within certain time frequency portions of most seismograms with high signal to noise ratios and these portions can be identified using a set of consistent criteria that we apply in the course of waveform fitting

seismic evidence for a fossil mantle plume beneath south america and implications for plate driving forces a teleseismic travel time study reveals the presence of a fossil plume in the deep upper mantle beneath brazil which has apparently remained geographically fixed with respect to the overly ing continent despite thousands of kilometres of plate motion this result implies that the upper mantle and lithosphere beneath south america have remained coupled since the breakup of gondwanaland and may provide an answer to the long standing question of what forces drive continental plates

current deformation in the northern canadian cordillera inferred from gps measurements 1 continuous and campaign style global positioning system gps measurements provide new constraints on the first order current deformation pattern of the northern cordillera of nw canada and eastern alaska the yakutat block is currently colliding with north america in the corner of the gulf of alaska our data infer that relative yakutat north america motion is accommodated across the eastern boundary by right lateral motion 40 mm a mainly on the fairweather fault and minor shortening 6 mm a to the north collision is taken up by shortening 31 mm a mainly on the chugach st elias fault system with westward extrusion and possible counterclockwise rotation of the yakutat block and alaskan fore arc facilitated by 23 mm a right lateral motion that is shared by several faults the seismicity pattern indicates that plate boundary deformation is far reaching producing strain throughout eastern alaska yukon and western northwest territories our gps data confirm the transfer of strain from the yakutat collision zone and enable the extent of plate boundary deformation to be mapped thereby defining the western edge of stable north america gps sites in sw yukon show motion of 3 10 mm a to the ne confirming that strain is transferred at least 400 km from the yakutat collision continued transfer north toward the mackenzie delta and ne to the mackenzie mountains indicated by current seismicity is not yet well resolved by the campaign gps data which are hampered by coseismic and postseismic effects of the 2002 mw 7 9 earthquake on the denali fault in eastern alaska

the electrical resistivity structure of archean to tertiary lithosphere along 3200 km of snorcle profiles northwestern canada magnetotelluric mt measurements to image the three dimensional resistivity structure of the north american continent from an archean core to a region of tertiary assembly were recorded at almost 300 sites along 3200 km of profiles on the lithoprobe slave northern cordillera lithospheric evolution snorcle transect in northwestern canada at the largest scale the mt results indicate significant lithospheric thickness variation from 260 km at the southwest margin of the slave craton to significantly 100 km at the southwestern end of the snorcle transect in the cordillera at intermediate scale the resistivity results allow broad terrane subdivisions to be made several anomalously conductive zones along the snorcle transect in rocks ranging in age from archean to tertiary are attributed to the introduction of either water or carbon into the crust and mantle during subduction processes at the local scale the mt data image two major faults crossing the study area the great slave lake shear zone and the tintina fault the resistivity images show that both the tintina fault and great slave lake shear zone form crustal scale features and that the tintina fault has a remarkably uniform resistivity signature over a 400 km strike length in the study area arguably the most controversial conclusion reached is that the mt data do not support the western extension of north american autochthonous basement suggested from interpretation of the seismic reflection data

architecture of the crust and uppermost mantle in the northern canadian cordillera from receiver functions the northern canadian cordillera ncc is an active orogenic belt in northwestern canada characterized by deformed autochtonous and allochtonous structures that were emplaced in successive episodes of convergence since the late cretaceous seismicity and crustal deformation are concentrated along corridors located far 200 to 800 km from the convergent plate margin proposed geodynamic models require information on crust and mantle structure and strain history which are poorly constrained we calculate receiver functions using 66 broadband seismic stations within and around the ncc and process them to estimate moho depth and p to s velocity ratio vp vs of the cordilleran crust we also perform a harmonic decomposition to determine the anisotropy of the subsurface layers from these results we construct simple seismic velocity models at selected stations and simulate receiver function data to constrain crust and uppermost mantle structure and anisotropy our results indicate a relatively flat and sharp moho at 32 2 km depth and crustal vp vs of 1 75 0 05 seismic anisotropy is pervasive in the upper crust and within a thin 10 15 km thick sub moho layer the modeled plunging slow axis of hexagonal symmetry of the upper crustal anisotropic layer may reflect the presence of fractures or mica rich mylonites the subhorizontal fast axis of hexagonal anisotropy within the sub moho layer is generally consistent with the se nw orientation of large scale tectonic structures these results allow us to revise the geodynamic models proposed to explain active deformation within the ncc

heat flow heat generation and crustal temperatures in the northern canadian cordillera thermal control of tectonics 1 the heat flow in the northern canadian cordillera between 59 and 64 n is very high 105 22 mw m2 the average upper crust heat generation is 4 6 2 4 microw m3 giving a reduced deep heat flow of 59 mw m2 similar to the southern canadian cordillera 49 53 n estimated moho temperatures of 800 1000 c and lithosphere only 50 60 km thick are substantiated by slow upper mantle seismic velocities and by high elevations associated with crust only 32 35 km thick the new data support the conclusion that all of the north and south america cordilleras are hot the paleoproterozoic wopmay orogen to the east has a remarkably high heat flow of 90 15 mw m2 for such an old and stable region however basement samples indicate high heat generation and estimated deep temperatures are intermediate between the cordillera and the slave craton further to the east heat flow from the yellowknife area of the slave craton 53 mw m2 implies low lithosphere temperatures in agreement with kimberlite xenolith p t data the high temperatures in the cordillera result in a very thin and weak lithosphere and may allow a lower crust detachment the north and central cordillera have been inland of the coastal queen charlotte transform fault since subduction stopped in the eocene thus some process has maintained high temperatures in the former back arc for more than 40 ma

seismic structure of the upper mantle beneath the northern canadian cordillera from teleseismic travel time inversion abstract teleseismic tomography is used to image upper mantle structure beneath the northern canadian cordillera with the objective of determining the physical state of the upper mantle along the western half of the snorcle lithoprobe transect the resulting three dimensional p wave velocity model resolves structure beneath the southern yukon and northernmost british columbia between 100 and 600 km depth two significant anomalies are identified the first a relatively shallow high velocity feature located at the western edge of the model is interpreted as being the edge of the pacific slab from the southern alaska subduction zone the second is a large tabular low velocity anomaly centred at 60 n by 136 w elongate northwest southeast dipping southwest and reaching a depth of 450 500 km this low velocity anomaly is judged to reflect a thermal anomaly of 100 200 c with a possible compositional component its northeastern boundary is particularly sharp and is interpreted to represent the boundary between thin cordilleran lithosphere and a colder cratonic mantle root our preferred explanation for the low velocity feature is a thermal anomaly resulting from the advective upflow produced by the opening of a slab window beneath the northern cordillera a possible alternative is dense downward percolating partial melt generated by sub orogenic heating as past work e g stolper et al j geophys res 86 1981 6261 6271 suggests that basic partial melts may be denser than peridotite below 200 km depth

palynology of sapropelic layers from the marmara sea palynological records of the sediments from the deep basins of the marmara sea revealed four palynological zones indicating the changing climatic conditions during late glacial to holocene the lower two zones were defined by the high abundance of artemisia and chenopodiaceae that suggest the climate of the source area was cold and arid however the establishment of mediterranean warm and wet climate and corresponding regression of continental aridity were shown by the decreasing chenopodiaceae and increasing pollen grains of humid type vegetation in zone c the highest total pollen with the dominance of quercus identifies the deglaciation and coincides with the formation of sapropelic layers in the marmara sea the warmer and humid condition of deglaciation was indicated with diversified moisture demanding deciduous and coniferous pollen grains in zone b these pollen assemblages and their distribution pattern indicate that the source area was warm and wet during the deposition of sapropelic layers in the marmara sea and also reflect signals of black sea origin

the cordilleran ribbon continent of north america the north american cordilleran orogen is the result of a two stage process a triassic jurassic accretion within panthalassa forming saybia a composite ribbon continent and b late cretaceous collision of saybia with north america this model requires that a large portion of the continental foreland of the orogen is exotic the exotic continental component of saybia cassiar platform is distinguished from the autochthon on the basis of its a triassic eurasian fauna b involvement in a major late triassic early jurassic orogenic event and c young in part grenvillian basement and mantle a mid cretaceous magmatic arc records west dipping subduction beneath the east margin of saybia the related accretionary prism consists of imbricated shale chert and deep water limestones the medial basin and overlies an isotopically juvenile mantle domain carbonatite complexes delineate the cryptic suture separating saybia and the autochthon paleomagnetic and paleobotanical data place saybia 2000 km to the south relative to the autochthon at 80 ma late cretaceous thrust belt development records transpression between the north moving ribbon continent and the autochthon pinning against the okhotsk chukotka arc in siberia buckled saybia giving rise to the alaskan promontory

lithospheric structure of the yukon northern canadian cordillera obtained from magnetotelluric data 1 two goals of lithoprobe s geoscientific studies in the phanerozoic accretionary cordillera of western north america were to define the subsurface geometries of the terranes and to infer the physical conditions of the crust these questions were addressed in canada s southern cordillera a decade ago and have more recently been addressed in the northern cordillera of which one component of the new studies is magnetotelluric mt profiling from ancestral north american rocks to the coast we present a resistivity cross section and its interpretation of the northern cordillera derived from modeling data from 42 mt sites along a 470 km long ne sw profile beneath the coast belt southwestern end of the profile a deep crustal low resistivity layer dips inland we interpret the crustal part of this conductor as being due to metasedimentary rocks emplaced and metamorphosed during paleocene kula plate subduction a strong lateral transition in lithospheric mantle resistivity exists below the intermontane belt that is spatially coincident with changes in chemical and isotopic characteristics of tertiary to recent alkaline lavas suggesting that isotopically enriched lithosphere related to the coast belt basalts extends partly beneath the intermontane belt the unusually high lower crustal resistivity in the intermontane and omineca belts similar in value to the resistivity found in the unextended part of central british columbia excludes the presence of fluids or conducting metasediments finally our resistivity model displays strong lateral variation of the middle and lower crust between different terranes within the same belt as a result of the complex structural evolution of the lithosphere index terms 0925 exploration geophysics magnetic and electrical methods 1515 geomagnetism and paleomagnetism geomagnetic induction 8110 tectonophysics continental tectonics general 0905 8120 tectonophysics dynamics of lithosphere and mantle general keywords magnetotelluric accreted terranes northern canadian cordillera

subduction geometry beneath south central alaska and its relationship to volcanism the southern alaskan margin captures a transition between compression and strike slip dominated deformation accretion of the over thickened yakutat terrane termination of aleutian arc magmatism and the enigmatic wrangell volcanic field the extent of subduction and mantle structure below this region is uncertain with important implications for volcanism we present compressional and shear wave mantle velocity models below south central alaska that leverage a new seismometer deployment to produce the most complete image of the subducting pacific yakutat plate to date we image a steeply dipping slab extending below central alaska to 400 km depth which abruptly terminates east of 145 w there is no significant slab anomaly beneath the nearby wrangell volcanoes a paucity of volcanism is observed above the subducting yakutat terrane but the slab structure below 150 km depth and wadati benioff zone here are similar to those along the aleutian alaska arc features of the mantle wedge or overlying lithosphere are thus responsible for the volcanic gap

seismic anisotropy of the slave craton nw canada from joint interpretation of sks and rayleigh waves summary teleseismic events recorded at a 25 element array in nw canada between 2001 and 2006 provided sufficient distribution in back azimuth to demonstrate birefringence in sks and skks waves as well as directional dependence of rayleigh wave phase velocities typical delays between orthogonally polarized sks waves are 0 8 1 2 s and modelling of azimuthal dependence indicates two nearly horizontal layers of anisotropy within the mantle anisotropy of rayleigh waves is generally consistent with models of layered vs anisotropies that increase with depth from 1 per cent at the moho to 9 per cent at 200 km but vary between subarrays consistency between the sks and rayleigh wave anisotropies in one subarray suggests that the assumption of symmetry about a horizontal axis is valid there but is not fully valid in other parts of the craton the upper layer of anisotropy occupies approximately the uppermost 120 km in which the fast polarization direction strikes generally north south coinciding with regional scale fold axes mapped at the surface the fast polarization direction of the deeper layer aligns with current north america plate motion but its correlation with trends of coeval kimberlite eruptions within the lac de gras field suggests it can be at least partly attributed to structural preferred orientation of vertical dykes inferred to exist to depths of 200 km

early holocene age and provenance of a mid shelf delta lobe south of the strait of bosphorus turkey and its link to vigorous black sea outflow abstract the chronology of an abandoned holocene delta lobe present water depth 40 70 m on the northeastern shelf of the marmara sea south of the strait of bosphorus was revised from the early holocene 11 0 9 7 cal ka to the middle holocene 6 65 3 75 cal ka by eris et al eris k k ryan w b f cagatay m n sancar u lericolais g menot g bard e 2007 the timing and evolution of the post glacial transgression across the sea of marmara shelf south of istanbul marine geology 243 57 76 three independent seismic and multibeam surveys and replotting of navigational fixes for the 1992 1993 vintage survey lines which eris et al correlated to their md04 2750 giant piston core confirm that they misplotted the location of the md04 2750 core site on seismic profiles by a minimum of 200 m because of rapid convergence of seismic reflections in this critical area the assessment of the age of the holocene delta proposed by eris et al is incorrect instead existing and new data allow the age of this delta lobe to be refined to 11 1 10 2 cal ka 200 300 years each using several dated cores and the md04 2750 chronology itself a dense grid of previously unpublished seismic data shows that the lobe emanates from the strait of bosphorus and not from any of the local small streams mineralogy of the very fine sand fraction of the delta excludes the kurbagalidere stream as a source of the detritus as does the composition of detrital hornblendes it is concluded that the early holocene delta lobe indeed records a period of strong black sea outflow as advocated by co authors rnh and aea in 2002 re examination of multibeam imagery from the strait itself provides support for strong southward flow that potentially coincided with accumulation of the delta lobe at the southern exit of the strait

geochemical characteristics of the recent sediments from the sea of marmara abstract six box cores one boomerang core and one hundred sixty six surface sediment samples recovered in the sea of marmara were analyzed in an attempt to establish the main controls on distribution and origin of trace metals within the oxic to suboxic basin of this sea surface and downcore data indicate that the abundance and distribution of the total metal concentrations for fe ni zn cr co cu and pb can largely be explained by the variable admixtures of terrigenous components in response to textural variations and biogenic calcareous components poor in metal contents the distribution of cr and ni seems to be controlled in part by a contribution from the weathering of basic ultrabasic sources on the coastal hinterland a small but significant amount of cu zn and pb in sediments from the northeastern sea of marmara probably suggests a pollution effect from the northerly located golden horn estuary that is known as one of the most polluted coastal regions of turkey looking at the data it seems that the mn concentrations are unusually high in the deep water sediments 4498 9127 ppm carbonate free along the east west trending marmara trough but low in sediments from the adjacent shallow waters 307 2059 ppm carbonate free the mn enrichment in deep water relative to shallow water marmara sediments is further indicated by the fe mn ratios being on average 11 23 in deep waters and 34 69 in shallow waters the contents of other metals fe ni zn cr co cu pb in both shallow and deep water sediments fall nearly within the same range as those found in average crustal and sedimentary rocks suggesting no significant enrichment of these metals in the deep marmara basins the downcore changes in the color from reddish brown at the surface top 2 5 cm to greenish gray in the subsurface 5 cm together with the occurrence of high mn concentrations in the surface sediment layers in cores can be attributed at least in part to the diagenetic mn enrichment within the sediment column the usually low organic carbon contents and biogenic components present in sediments reflect that the well known biogenic mechanism for the enrichment of mn seems to be of minor importance in the deep marmara waters the generally low mn concentrations contained in the surface grab and core sediments from the black sea and aegean sea approaching those of the sea of marmara do not provide any conclusion to support significant mn contribution from these two adjacent seas particularly from the so called manganese pump zones in the shallow black sea waters comparison with other deep sea sediments which have been deposited under the influences of hydrothermal activities worldwide suggests mn enrichment in deep water relative to shallow water sediments of the sea of marmara mainly as a result of hydrothermal contributions from this seismically active marine region based on the average fe mn ratios obtained in cores which tend to increase gradually from 11 in the deep central basin to 67 69 in the northeastern and southwestern shelves the central basin of marmara trough can be considered as a possible potential source for hydrothermal solutions leading to the enrichment of mn in the deep marmara waters however this remains to be further investigated

high resolution seismic profiling in the sea of marmara northwest turkey late quaternary sedimentation and sea level changes high resolution sparker seismic profiling was carried out in the sea of marmara northwest turkey to study the late quaternary tectonics and sedimentation of this important active basin at the western end of the north anatolian fault zone a sedimentary unit interpreted as the clinoforms of a prograding delta was observed in places along the outer part of the southern shelf the topset foreset transitions of the latest clinoforms cluster around 100 m below present sea level they were probably deposited during the last glacial maximum and early phase of deglaciation between 25 and 13 k y b p when the level of the aegean was below that of the dardanelles sill 60 70 m below sea level at present therefore the sea of marmara was isolated from the aegean during the last glacial maximum but it is possible that a fluvial overflow existed across the dardanelles during this time stabilizing the level of the marmara lake and allowing the delta progradation rivers that drain into the sea of marmara from the south have a much greater combined drainage basin area and sediment flux than those draining the region to the north this may explain the much broader shelf to the south half graben bounded by north dipping normal faults observed within the southern shelf would tend to trap sediment sourced from the south and subdue any sea bed morphology on the shelf

quaternary paleoclimatic paleoceanographic and tectonic evolution of the marmara sea and environs strabo 63 bc 21 ad book 1 3 4 jones 1954 themarmarasea fig 1 hasalwaysattractedinterestasagreatgatewaylinkingtheblackseato the eastern mediterranean sea through a net work of narrow straits with shallow sills straitsof bosphorus istanbul and dardanelles c anakkale forthepast2500 3000yr informa tion about surface and bottom currents depthsoundings and sea level variation were crucialforsafenavigationacrossthesestraitsbysea far ingpeopleandexplorers thusconstitutingama jorstrategicassetandyieldingenormouseconom icandpoliticaladvantages throughoutantiquity sailors knew that the bottom waters across thestraits of dardanelles and bosphorus owednorthward and utilized this knowledge to sailintothemarmaraseaandblackseabyloweringlargebasketswithweightsintothenorth owingmediterranean water to counteract the strongsouth directed surface out ow from the blacksea systematic scienti c investigations in the mar marasearegionstartedinthelate19thcentury the rstbathymetricsurveyrevealedthepresenceof three deep basins and their intervening ridges andrussow 1901 p nar 1943 subsequentlyproposedthatasinglefaulttransectedthesethreebasins extending from the izmit bay in the eastto the gulf of saros in the west pfannensteil 1944 noted the rhombohedric shape of thedeepmarmaraseabasinsandproposedthattheridgesseparatingthebasinsrepresenthorstblocksbounded by normal faults healsosuggested inadditiontothestraitofbosphorus thepresenceofasecondchannel thesakaryabosphorus fig 1 which connected the black sea to the mar mara sea during the quaternary in 1948 ketinpublished his renowned paper revealing the truenatureofthenorthanatolianfaultasoneoftheworld slargest active intra continental strike slipfaults ketin 1948 pavoni 1961 and kopp etal 1969 proposedthataseriesofsyntheticand

circulation and water mass transformation in a model of the chukchi sea 1 the circulation and water mass transformation in a regional ocean ice model of the chukchi sea are discussed the model has horizontal resolution of o 4 km is forced by fluxes derived from daily ncep reanalysis fields and has seasonally varying transport temperature and salinity imposed at bering strait many of the observed characteristics of the mean circulation and seasonal cycle in the chukchi sea are reproduced the discussion focuses on the branching of the inflow transport into pathways following herald canyon central channel and the alaskan coast the pattern of ice melt and the water mass transformation and formation of winter water and hypersaline water the ice melt pattern and timing is strongly influenced by advection through bering strait high frequency forcing results in a larger region of ice melt particularly over the shoals and in the northern chukchi sea compared to monthly mean forcing in the model the seasonal cycle of salinity in the southern and central chukchi sea is dominated by advection through bering strait while local atmospheric forcing and brine rejection are more important north of herald and hanna shoals and in barrow canyon however since the residence time in the chukchi sea is generally less than 1 year interannual variability in the bering strait salinity will be reflected in the salinity across the chukchi sea and at barrow canyon

plateau uplift in western canada caused by lithospheric delamination along a craton edge mantle convection helps create continental plateaux seismic imaging of the mantle beneath the canadian cordillera an ancient plateau suggests the plateau formed when upwelling mantle caused a block of lithosphere to detach

contrasting seismic characteristics of three major faults in northwestern canada the lithoprobe slave northern cordillera lithospheric evolution snorcle profiles crossed three major tectonic zones of the northwestern canadian shield and northern canadian cordillera that are diverse in age and in depth of penetration the oldest 2630 2590 ma the yellowknife river fault zone formed as a strike slip fault in a tensional strain regime reflector attenuation or truncations align vertically beneath the fault trace through much of the crust implying a near vertical fault plane the youngest 60 10 ma the tintina fault zone produced cumulative dextral strike slip displacements of 425 km perhaps 800 km tomographic velocity and ray trace models of reflection data indicate that several fault splays form a tectonic zone 30 km wide at the surface but truncations of deeper crustal reflections suggest that the zone thins in the mid crust and widens near the moho this apparent variable width versus depth of the tintina fault is atypical of major strike slip faults worldwide the teslin fault was an active terrane boundary during accretion of terranes onto north america observed reflection geometries indicate that the juxtapositions of highly contrasting metamorphic grades across the teslin fault are confined to the upper crust along snorcle line 3 implying that the fault soles eastward into a mid crustal detachment at the interpreted top of north american crust the limited depth extent of the teslin fault zone is similar to some models of the san andreas fault and may result from their similar histories as convergent margin structures

present day geodynamics of the northern north american cordillera abstract diffuse continental deformation results from interactions at plate boundaries buoyancy forces generated by gradients in gravitational potential energy and loads applied to the base of the lithosphere using finite element models we calculate a deviatoric stress field associated with buoyancy forces and then perform an iterative inversion to calculate deviatoric stress fields associated with boundary forces in the northern north american cordillera our results reveal the presence of two distinct geodynamic domains in the outboard domain approximately equal magnitudes of boundary and buoyancy forces can account for the observed deformation along the aleutian megathrust in contrast large boundary forces related to subduction of the pacific and yakutat slabs dominate the force balance in south central alaska and combine with relatively small buoyancy forces to reproduce the observed kinematic indicators in the inboard domain encompassed by interior and northern alaska and western canada boundary and buoyancy forces alone cannot reproduce the observed deformation therefore we infer that deviatoric stresses due to basal tractions from a deeper mantle convection cell contribute to surface deformation in the inboard domain low effective lithospheric viscosity in south central alaska and the balancing effect of an independent geodynamic system driven by basal tractions in northern alaska combine to confine the anomalously large yakutat related boundary deviatoric stresses to south central alaska deviatoric stresses associated with flat slab subduction of the yakutat microplate are a factor of two greater than boundary force estimates for the andean and indian eurasian convergent margins where buoyancy and boundary forces are roughly equal in magnitude and dominate the force balance

lateral mixing across ice meltwater fronts of the chukchi sea shelf summer and fall hydrographic sections in the northeastern chukchi sea frequently capture 5 20 m thick intrapycnocline lenses or horizontal plumes of warm moderately salty summer bering sea water flowing northward from bering strait these features occur within the shallow 20 m depth pycnocline separating cold dilute surface meltwater from near freezing salty winter formed waters beneath the pycnocline an idealized numerical model suggests that the features arise from eddies and meanders generated by instability of the surface front separating meltwater from bering sea water warm bering sea water is transported across the front and into the pycnocline by the cross frontal velocities associated with the instabilities the accompanying lateral eddy heat fluxes may be important both in summer for promoting ice melt and in fall by delaying the onset of ice formation over portions of this shelf lateral heat flux magnitudes depend upon the stratification of the bering sea water

observed increases in bering strait oceanic fluxes from the pacific to the arctic from 2001 to 2011 and their impacts on the arctic ocean water column 1 mooring data indicate the bering strait throughflow increases 50 from 2001 0 7 sv to 2011 1 1 sv driving heat and freshwater flux increases increase in the pacific arctic pressure head explains two thirds of the change the rest being attributable to weaker local winds the 2011 heat flux 5 1020j approaches the previous record high 2007 due to transport increases and warmer lower layer ll temperatures despite surface temperature sst cooling in the last decade warmer ll waters arrive earlier 1 6 1 1 days yr though winds and sst are typical for recent decades maximum summer salinities likely set in the bering sea remain remarkably constant 33 1 psu over the decade elucidating the stable salinity of the western arctic cold halocline despite this freshwater flux variability strongly driven by transport exceeds variability in other arctic freshwater sources remote data winds sst prove insufficient for quantifying variability indicating interannual change can still only be assessed by in situ year round measurements

the mackenzie river magnetic anomaly yukon and northwest territories canada evidence for early proterozoic magmatic arc crust at the edge of the north american craton abstract we characterize the nature of the source of the high amplitude long wavelength mackenzie river magnetic anomaly mra yukon and northwest territories canada based on magnetic field data collected at three different altitudes 300 m 3 5 km and 400 km the mra is the largest amplitude 13 nt satellite magnetic anomaly over canada within the extent of the mra source depth estimates 8 12 km from euler deconvolution of low altitude aeromagnetic data show coincidence with basement depths interpreted from reflection seismic data inversion of high altitude 3 5 km aeromagnetic data produces an average magnetization of 2 5 a m within a 15 to 35 km deep layer a value typical of magmatic arc complexes early proterozoic magmatic arc rocks have been sampled to the southeast of the mra within the fort simpson magnetic anomaly the mra is one of several broad scale magnetic highs that occur along the inboard margin of the cordillera in canada and alaska which are coincident with geometric changes in the thrust front transition from the mobile belt to stable cratonic north america the inferred early proterozoic magmatic arc complex along the western edge of the north american craton likely influenced later tectonic evolution by acting as a buttress along the inboard margin of the cordilleran fold and thrust belt

organized patches of bioherm growth where the strait of dardanelles enters the marmara sea turkey abstract high resolution multibeam mosaics show that the seafloor across the southwestern marmara sea is host to remarkably organized near circular bioherm mounds which commonly are arranged into large tightly packed clusters grab samples and gravity cores reveal that the bioherms are predominantly composed of very fine grained calcareous silty mud with abundant bioclasts including centimetre scale masses of coralline red algae and intact disarticulated mollusc shells mainly the genera modiolus and mytilus geometric analysis of multibeam images reveals that the average bioherm is 15 6 m in diameter occupies 190 m2 of seabed stands 113 cm above the adjacent seafloor and its crest is 20 6 m from the crests of neighbouring bioherms in regions of tightly packed bioherm clusters referred to as bioherm colonies the inter mound depressions are on average 4 4 m wide and 33 cm deep although each bioherm mound is nearly circular the surrounding inter mound channels form a more rectilinear mesh of linked pentagonal and hexagonal polygons suggesting densest possible spatial packing of the mounds near neighbour statistics of r 2 11 2 14 indicate an essentially uniform spacing between the bioherms which is the expected result for close packing on a plane and full utilization of the available space the bioherms occur at depths between 30 m and 60 m they are absent above and below these depths in this part of the southwestern marmara sea at the eastern exit of the strait of dardanelles water depth controls important water mass properties such as salinity nutrient supply and availability of light other inferred critical controls are the availability of a suitable hard substrate where holocene muds are thin or absent and nutrient supply potentially including a component from escaping methane rich pore fluids evidence here and elsewhere in the marmara sea provisionally dates the onset of bioherm growth and development to the latest pleistocene earliest holocene after global sealevel rose to the breach depth of the strait of dardanelles at 13 8 cal ka

the summer hydrographic structure of the hanna shoal region on the northeastern chukchi sea shelf 2011 2013 abstract we used shipboard and towed ctd current meter and satellite tracked drifter data to examine the hydrographic structure in the northeastern chukchi sea in august september of 2011 2012 and 2013 in all years the densest winter water was around and east of hanna shoal in 2012 and 2013 a 15 m deep layer of cold dilute meltwater overlaid the dense water north of the shelf region between 71 2 and 71 5 n a front extends from the southwest side of hanna shoal toward the head of barrow canyon separated meltwaters from warmer saltier bering sea summer waters to the south stratification was stronger and the surface density variances in the meso and sub mesoscale range were higher north of the front than to the south no meltwater or surface fronts were present in 2011 due to a very early ice retreat differences in summer ice cover may be due to differences in the amount of grounded ice atop hanna shoal associated with the previous winter s regional ice drift along the north side of hanna shoal the model predicted clockwise barotropic flow carrying waters from the western side of the shoal appears to converge with a counterclockwise baroclinic flow on the northeast side the baroclinic tendency is confined to the upper 30 m and can include waters transported from the shelfbreak the inferred zonal convergence implies that north of the shoal a near surface waters are a mixture of waters from the western and eastern chukchi sea and b the cross isobath pressure gradient collapses thereby facilitating leakage of upper layer waters northward across the shelf

dense water formation around islands 1 basic constraints on the dense water formation rate and circulation resulting from cooling around an island are discussed the domain under consideration consists of an island surrounded by a shelf a continental slope and a stratified ocean atmospheric cooling over the shelf forms a dense water that penetrates down the sloping bottom into the stratified basin strong azimuthal flows are generated over the sloping bottom as a result of thermal wind thermally direct and indirect mean overturning cells are also forced over the slope as a result of bands of convergent and divergent reynolds stresses associated with the jets the coriolis force associated with the net mass flux into the downwelling region over the slope is balanced by these nonlinear terms giving rise to a fundamentally different momentum budget than arises in semienclosed marginal seas subject to cooling a similar momentum balance is found for cases with canyons and ridges around the island provided that the terms are considered in a coordinate system that follows the topography both eddy fluxes and the mean overturning cells are important for the radial heat flux although the eddy fluxes typically dominate the properties of the dense water formed over the shelf temperature diapycnal mass flux are predicted well by application of baroclinic instability theory and simple heat and mass budgets it is shown that each of these quantities depends only on a nondimensional number derived from environmental parameters such as the shelf depth coriolis parameter offshore temperature field and atmospheric forcing

seismic velocity structure and anisotropy of the alaska subduction zone based on surface wave tomography southcentral alaska is a complex tectonic region that transitions from subduction of pacific crust to flat slab subduction and collision of overthickened yakutat crust because much of the yakutat crust has been subducted seismic imaging is needed in order to understand the crustal and upper mantle structural framework for this active tectonic setting here we use teleseismic rayleigh waves to image large scale variations in shear wave structure our imaging technique employs a two plane wave representation with finite frequency sensitivity kernels our 3 d isotropic model reveals several features the subducting pacific yakutat slab slow wave speeds characterizing the onshore yakutat collision zone slow wave speeds of the wrangell subduction zone and a deep tomographic contrast at the eastern edge of the pacific yakutat slab we produce anisotropic phase velocity maps that exhibit variations in the fast direction of azimuthal anisotropy these maps show the dominance of the yakutat slab on the observed pattern of anisotropy west of the yakutat slab the fast directions are approximately aligned with the plate convergence direction in the region of the yakutat slab the pattern is more complicated along the margins of the slab the fast directions are roughly parallel to the margins we identify notable differences and similarities with published sks splitting measurements integrative modeling using 3 d anisotropy models and different seismic measurements will be needed in order to establish a detailed 3 d anisotropic velocity model for alaska this study provides a large scale starting point for such an effort

body wave tomography of western canada abstract in this study we have produced p and s wave velocity models for western canada using 23 420 delay times measured on vertical component seismograms and 15 805 delay times measured on transverse component seismograms respectively from a range of permanent and temporary networks resolution is best in southwestern british columbia and along the canoe northwestern alberta southern yukon and northwest territories and batholiths northwestern bc arrays where the station density is the highest and fair elsewhere we focus our attention on two distinct features 1 the transition from phanerozoic to cratonic mantle in northwestern canada and 2 the complex tectonic environment at the northern terminus of the cascadia subduction zone where the plate boundary changes from convergent to transform we find that the main transition from phanerozoic to cratonic mantle in northwestern canada occurs at the cordilleran deformation front and represents a sharp jump in seismic velocity from 2 to 2 over a distance of 50 km in northern cascadia we have imaged and characterized the signature of the subducting juan de fuca plate and observed evidence of subduction beyond the northern edge of the slab we also demonstrate that the anahim hotspot track is underlain by a 2 low velocity zone possibly extending to 400 km beneath nazko cone that appears to be the source of volcanism in this area consequently we associate the source of magmatism in this area to a mantle scale rather than lithospheric scale process

control of lithospheric inheritance on neotectonic activity in northwestern canada lithospheric inheritance is thought to affect the location and reactivation of tectonic structures through successive cycles of supercontinent formation and dispersal however its relation to neotectonic activity remains unclear in northwestern canada abundant seismicity throughout the northern canadian cordillera ncc is geographically confined by several crustal scale boundaries yet its southern extent terminates abruptly along the inferred westward extension of a late cretaceous rifted margin boundary called the liard transfer zone ltz we use seismic data to show that the uppermost mantle beneath the cordillera exhibits a sharp north south contrast in fabric across the ltz south of the ltz fast axes of seismic wave propagation align closely with the lithospheric mantle fabric orientation of the adjacent canadian shield north of the ltz fast axes are reoriented subparallel to the motion of the pacific plate and follow the strike of the large dextral strike slip tintina and denali faults we attribute changes in anisotropic delay times across the tintina and denali faults to localized shear within the lithosphere this implies that the crust and lithospheric mantle remained mechanically coupled during shearing we propose that the contrast in uppermost mantle structure across the ltz reflects a change in the nature and origin of the lithospheric mantle from inherited rifted margin structures which affects the stability of the lithosphere and limits the extent of seismic activity within the ncc these results indicate that neotectonic activity in modern cordilleras is controlled in part by inherited upper mantle structures

upper mantle structure beneath southern african cratons from seismic finite frequency p and s body wave tomography abstract we present a 3d high resolution seismic model of the southern african cratonic region from teleseismic tomographic inversion of the p and s body wave dataset recorded by the southern african seismic experiment sase utilizing 3d sensitivity kernels we invert traveltime residuals of teleseismic body waves to calculate velocity anomalies in the upper mantle down to a 700 km depth with respect to the ak135 reference model various resolution tests allow evaluation of the extent of smearing effects and help defining the optimum inversion parameters i e damping and smoothness for regularizing the inversion calculations the fast lithospheric keels of the kaapvaal and zimbabwe cratons reach depths of 300 350 km and 200 250 km respectively the paleo orogenic limpopo belt is represented by negative velocity perturbations down to a depth of 250 km implying the presence of chemically fertile material with anomalously low wave speeds the bushveld complex has low velocity down to 150 km which is attributed to chemical modification of the cratonic mantle in the present model the finite frequency sensitivity kernels allow to resolve relatively small scale anomalies such as the colesberg magnetic lineament in the suture zone between the eastern and western blocks of the kaapvaal craton and a small northern block of the kaapvaal craton located between the limpopo belt and the bushveld complex

holocene sedimentation in the tectonically active tekirdag basin western marmara sea turkey abstract the effects of various depositional conditions and active tectonics on the late holocene sedimentation in the tekirdag basin west of the marmara sea were investigated in 11 gravity cores and on 3 seismic profiles representing shelf to slope to deep basin floor environments except for the two coarser grained avg 60 sand and gravel and calcareous avg 25 caco 3 shelf cores sediments in the slope and basin floor cores constitute low calcareous avg 12 caco 3 and terrigenous mud 90 silt and clay the occurrences of relatively higher total organic carbon contents in sediments from the southern slope 1 14 1 38 compared to that from the northern slope 0 37 1 2 indicate significant input from the southern rivers the presence of silty sandy laminations within the mud matrix of the cores and chaotic and mounded reflection configurations on the seismic profiles from the slope and basin floor environments all suggest the effects of gravity mass movements of sediments slides slumps turbidites most likely due to seismotectonic events earthquakes however it was difficult to establish a basin wide correlation between the historical earthquake events in the region and the positions of silty sandy laminations in dated deep sea sediment cores due to complicated other events such as repeated river run off and floods increased sediment load and slope failure the water contents of sediments from the basin floor avg 10 30 are significantly lower than those from the slope sediments avg 32 46 the former can be explained by the influences of synsedimentation with tectonics and compaction between the north and south boundary sub faults of the naf system whereas the latter shows fluidization of slope sediments during sliding and slumping radiocarbon dated base sections from three cores revealed that sediment deposition at these sites commenced about 4700 bp when the late holocene depositional conditions changed from the formation of upper sapropels to the present state the increases of organic carbon contents at or near the base sections of the cores support this contention

recent sedimentation on the shelf and upper slope in the bay of anamur southern coast of turkey abstract sedimentological studies supported by uniboom profiles and sonographs of surface sediments from a part of the narrow southern shelf of anatolia indented by the head of a submarine canyon and partly covered by meadows of macrophytobenthos revealed abrupt lateral and vertical variations in the holocene sedimentary facies these variations have essentially been controlled by the migration of depocentres palaeo topography of the shelf and an overall decrease in the rate of fluviatile sediment supply in the late holocene as sea level reached approximately its present position nearly 5 ka b p the bulk of the siliciclastic input began to be trapped in the inner shelf zone most of the terrigenous mud bypasses the shelf to be trapped in the canyon head but transport of modern detrital sand and gravel does not take place across the shelf this is because of the relative weakness of the onshore offshore currents the prevailing microtidal conditions and a belt of phytobenthos between 10 and 30 m which traps the sediments the plants also create the ecological conditions favourable for biological carbonate production however some gravel and sand size relict sediments have been transported from the outer shelf into the canyon head by gravity induced or cross canyon currents the mudline occurs at about the 100 m isobath marking the deepest limit of effective bottom turbulence for the resuspension of silt and clay on the shelf

indentor corner tectonics in the yakutat st elias collision constrained by gps the yakutat st elias collision in se alaska and adjacent canada represents a prime example of present day tectonics associated with an indentor corner its eastern syntaxis is marked by high exhumation a sharp structural bend and strain concentration at the transition from shortening to oblique transpression here we present gps velocity and strain rate fields that cover the syntaxis including 11 new stations in the core of the st elias mountains these data are corrected for transient deformation glacial isostatic adjustment and postseismic and interseismic loading to produce residual velocities and strain rates representative of long term tectonics the main features of these velocity and strain rate fields are a peak in strain rates strain knot in the syntaxis at the junction between the main fault systems and a rapid rotation from convergence parallel to convergence normal orientations of the velocities and shortening axes around the syntaxis leading to shortening across the southern denali fault these features are consistent with the strain and tectonic patterns expected near an indentor corner at the transition from shortening to transpression with a combination of diffuse and localized deformation the gps velocities and strain rates show diffuse deformation around the syntaxis from pure convergence parallel shortening in the orogenic wedge to oblique extension that accommodates the strain rotation at the front of the syntaxis this indentor corner model also results in a near zero strike slip rate on the southern denali fault and shows no clear evidence for a throughgoing fault hypothesized to link the fairweather and totschunda faults

precambrian crust beneath the mesozoic northern canadian cordillera discovered by lithoprobe seismic reflection profiling 1 the cordillera in northern canada is underlain by westward tapering layers that can be followed from outcrops of proterozoic strata in the foreland belt to the lowermost crust of the orogenic interior a distance of as much as 500 km across strike they are interpreted as stratified proterozoic rocks including 1 8 0 7 ga supracrustal rocks and their basement the layering was discovered on two new deep seismic reflection profiles in the yukon line 3 650 km and northern british columbia line 2 1245 km in two segments that were acquired as part of the lithoprobe slave northern cordillera lithospheric evolution snorcle transect in the mackenzie mountains of the eastern yukon the layering in line 3 is visible between 5 0 and 12 0 s 15 to 36 km depth it is followed southwestward for nearly 650 km 500 km across strike and thins to less than 1 0 s 3 0 3 5 km thickness near the moho at the yukon alaska international boundary in the northern rocky mountains of british columbia the upper part of the layering on line 2 correlates with outcrops of proterozoic 1 76 1 0 ga strata in the muskwa anticlinorium at this location the layering is at least 15 km thick and is followed westward then southward into the middle and lower crust for 700 km 300 km across strike it disappears as a thin taper at the base of the crust 150 km east of the coast of the alaskan panhandle the only significant disruption in the layering occurs at the tintina fault zone a late to postorogenic strike slip fault with up to 800 km of displacement which appears as a vertical zone of little reflectivity that disrupts the continuity of the deep layering on both profiles 300 km apart the base of the layered reflection zone coincides with the moho which exhibits variable character and undulates in a series of broad arches with widths of 150 km in general the mantle appears to have few reflections however at the southwest end of line 3 near the alaska british columbia border a reflection dips eastward from 14 0 s to 21 0 s 45 to 73 km depth beneath exposed eocene magmatic rocks it is interpreted as a relict subduction surface of the kula plate our interpretation of proterozoic layered rocks beneath most of the northern cordillera suggests a much different crustal structure than previously considered 1 ancient north american crust comprising up to 25 km of metamorphosed proterozoic to paleozoic sediments plus 5 10 km of pre 1 8 ga crystalline basement projects westward beneath most of the northern canadian cordillera 2 the lateral 500 km by at least 1000 km and vertical up to 25 km extent of the proterozoic layers and their internal deformation are consistent with a long lived margin for northwestern north america with alternating episodes of extension and contraction 3 the detachments that carry deformed rocks of the mackenzie mountains and northern rocky mountains are largely confined to the upper crustal region above the layering 4 accreted terranes include thin klippen that were thrust over north american pericratonic strata e g yukon tanana and terranes such as nisling and stikinia that thicken westward as the underlying proterozoic layers taper and disappear 5 the ages of exposed rocks are not necessarily indicative of the ages of underlying crust a frequent observation in lithoprobe interpretations so that estimates of crustal growth based on surface geology may not be representative

precambrian plate tectonics in northern hudson bay evidence from p and s wave seismic tomography and analysis of source side effects in relative arrival time data sets the geology of northern hudson bay canada documents more than 2 billion years of history including the assembly of precambrian and archean terranes during several paleoproterozoic orogenies culminating in the trans hudson orogen tho 1 8 ga the tho has been hypothesized to be similar in scale and nature to the ongoing himalaya karakoram tibetan orogen but the nature of lithospheric terrane boundaries including potential plate scale underthrusting is poorly understood to address this problem we present new p and s wave tomographic models of the mantle seismic structure using data from recent seismograph networks stretching from northern ontario to nunavut 60 100 w and 50 80 n the large size of our network requires careful mitigation of the influence of source side structure that contaminates our relative arrival time residuals our tomographic models reveal a complicated internal structure in the archean churchill plate however no seismic wave speed distinction is observed across the snowbird tectonic zone which bisects the churchill the mantle lithosphere in the central region of hudson bay is distinct from the tho indicating potential boundaries of microcontinents and lithospheric blocks between the principal colliders slow wave speeds underlie southern baffin island the leading edge of the generally high wave speed churchill plate this is interpreted to be paleoproterozoic material underthrust beneath baffin island in a modern style subduction zone setting

evolution and dynamics of the flow through herald canyon in the western chukchi sea abstract the flow of summer and winter pacific water masses through herald canyon is investigated using data from a high resolution hydrographic velocity survey conducted in summer 2004 the survey was part of the russian american long term census of the arctic rusalca program and consisted of four cross canyon transects occupied over a 2 day period at the time of the survey dense winter water was entering the western side of the canyon from the chukchi sea flowing alongside a poleward jet of summer water on the canyon s eastern flank as the dense water progressed northward it switched sides of the canyon and underwent a sudden increase in layer thickness this coincided with vertical mixing near the interface of the winter and summer water producing a new water mass mode exiting the canyon all of these features are consistent with the notion of hydraulic activity occurring in the canyon a three layer hydraulic theory is applied to the flow which suggests that it is supercritical and that hydraulic control is likely a lock exchange formulation accurately predicts the northward transport of the winter water the origin of the winter water and the manner in which it drains into the canyon is investigated using satellite ice concentration data atmospheric re analysis fields historical in situ data and a simple circulation model finally the fate of the pacific water exiting the canyon and its connection to the chukchi shelfbreak current is discussed

the geology of kimberlite pipes of the ekati property northwest territories canada abstract this paper reviews key characteristics of kimberlites on the ekati property nwt canada to date 150 kimberlites have been discovered on the property five of which are mined for diamonds the kimberlites intrude archean basement of the central slave craton numerous proterozoic diabase dykes intrude the area the precambrian rocks are overlain by quaternary glacial sediments no phanerozoic rocks are present however mudstone xenoliths and disaggregated sediment within the kimberlites indicate that late cretaceous and tertiary cover likely

pathways of pacific water across the chukchi sea a numerical model study 1 pathways of pacific water flowing from the north pacific ocean through bering strait and across the chukchi sea are investigated using a two dimensional barotropic model in the no wind case the flow is driven only by a prescribed steady northward flow of 0 8 sv through bering strait the resulting steady state circulation consists of a broad northeasterly flow basically following the topography with a few areas of intensified currents about half of the inflow travels northwest through hope valley while the other half turns somewhat toward the northeast along the alaskan coast the flow through hope valley is intensified as it passes through herald canyon but much of this flow escapes the canyon to move eastward joining the flow in the broad valley between herald and hanna shoals another area of slightly intensified currents there is a confluence of nearly all of the flow along the alaskan coast west of pt barrow to create a very strong and narrow coastal jet that follows the shelf topography eastward onto the beaufort shelf thus in this no wind case nearly all of the pacific water entering the chukchi sea eventually ends up flowing eastward along the narrow beaufort shelf with no discernable flow across the shelf edge toward the interior canada basin travel times for water parcels to move from bering strait to pt barrow vary tremendously according to the path taken e g less than 6 months along the alaskan coast but about 30 months along the westernmost path through herald canyon this flow field is relatively insensitive to idealized wind forcing when the winds are from the south west or north in which cases the shelf transports tend to be intensified however strong northeasterly to easterly winds are able to completely reverse the flows along the beaufort shelf and the alaskan coast and force most of the throughflow in a more northerly direction across the chukchi sea shelf edge potentially supplying the surface waters of the interior canada basin with pacific water the entire shelf circulation reacts promptly to changing wind conditions with a response time of 2 3 days the intense coastal jet between icy cape and pt barrow implies that dense water formed here from winter coastal polynyas may be quickly swept away along the coast in contrast there is a relatively quiet nearshore region to the west between cape lisburne and icy cape where dense water may accumulate much longer and continue to become denser before it is carried across the shelf

distribution of clay minerals in surface sediments of the aegean sea a compilation extensive published data sets and some new data on the clay mineral composition of surface sediments in the aegean sea northeastern mediterranean sea have been compiled in order to map the distribution patterns of clay mineral assemblages and to decipher source areas and transport paths we distinguished six provinces a northwest aegean province a marmara dardanelles province a west turkey province a southeast aegean province a kithira province and a central aegean province the clay mineral assemblages in the coastal and shelf areas carry the signature of the riverine sediment discharge from southeast europe and turkey respectively the southern aegean sea is probably influenced by the river nile discharge and transport of clay minerals by surface currents the clay minerals in the central aegean sea form a mixed assemblage comprising components of the other assemblages a dispersion and dilution of clay minerals by surface currents is obvious

on the origin of the bosphorus abstract the palaeozoic upper cretaceous basement palaeomorphology of the bosphorus the strait of istanbul bears the evidence of a valley of a palaeostream running to the black sea in the north a palaeobasin deeper than 160 m opening to the sea of marmara in the south and a barrier between these two features this suggest that the northern part of the bosphorus was formed mainly by fluvial activity whereas the southern part developed as a basin by faulting the recent sediment thickness exceeds 130 m in the basin indicating that the southern part of the bosphorus was once essentially depositional rather than an erosional the present form of the bosphorus was established in holocene time by the connection of the basin in the south with the stream in the north the barrier and the stream valley in the north have been deepened by erosion and faulting to form a strait connecting the black sea and the mediterranean

structure and fabric of the crust and uppermost mantle in the northern canadian cordillera from rayleigh wave tomography abstract the seismic structure and fabric of the lithosphere and underlying mantle beneath the northern canadian cordillera provides important constraints on its evolution and current tectonics however it is poorly characterized due to historically sparse networks of seismic instruments we use data from past and recently deployed networks of broadband seismic stations in northwestern canada and measure rayleigh waves propagating between all available pairs of seismic stations using two complementary techniques ambient noise and teleseismic two station interferometry the rayleigh wave data are processed to obtain phase velocity dispersion curves that are inverted for phase velocity maps at periods between 8 and 80 s to first order these maps show high velocity anomalies within the canadian shield and low velocity anomalies within the cordillera at all periods at short periods 30 s mostly sensitive to uppermost mantle depths high velocity anomalies of the canadian shield extend west past the cordilleran deformation front and suggest the presence of cratonic lithosphere beneath the cordillera whereas the lowest velocities underlie the allochtonous terranes anisotropy within the crust and uppermost mantle exhibits fast axis orientations aligned with the major faults and fabric of the cordillera and show evidence for vertical changes in anisotropy these results provide new constraints on geodynamic models proposed to explain neotectonic deformation in this area

late quaternary co seismic sedimentation in the sea of marmara s deep basins the deep northern part of the sea of marmara northwestern turkey is composed of several aligned actively subsiding basins which are the direct structural and morphological expression of the north anatolian fault s northern branch the last 20 kyr of their sedimentary fill lacustrine before 12 kyr bp have been investigated through giant piston coring onboard r v marion dufresne marmacore cruise 2001 and chirp subbottom profiler onboard r v atalante during marmarascarps cruise 2002 especially during the lacustrine stage the infilling of the deep basins tekirda central kumburgaz and cinarcic basins up to 1250 m depth was dominated by turbidites with coarse mixed siliciclastic and bioclastic basal part intercalated in hemipelagic type finegrained calcareous and slightly siliceous clays often especially in the thickest ones the turbidites show strong segregation and a sharp boundary between coarse part and suspendedload part in the central basin 8 m of a unique sedimentary event include a 5 to 8m thick homogenite well imaged on seismic profiles the latter is interpreted as related to a major possibly triggered tsunami effect as described in the eastern mediterranean by kastens and cita 1981 in the marine holocene upper part of the sedimentary fill repeated to and from structures affecting silt or fine sand are evidencing seiche like effects and thus earthquake triggering detailed correlations between two deep coring sites 1250 and 1200 m indicate more than 100 overthickening in the deepest one this implies specific processes of distribution of terrigenous input by dense hyperpycnal currents high kinetic energy seiche effect complex reflections on steep slopes the peculiar sedimentary infilling of the sea of marmara s central basin and by extrapolation of the whole set is tentatively interpreted as a direct consequence of the strong seismic activity the imprint of the latter is more obvious prior to the base of the holocene as environmental conditions favoured marginal accumulation especially on the southern shelf of large amounts of erosion products available for mass wasting

seismic anisotropy associated with continental lithosphere accretion beneath the canoe array northwestern canada we examine upper mantle seismic anisotropy beneath the cordillera and craton of northwestern canada using the multi event station averages of shear wave splitting of sks skks and ssks phases recorded during the canadian northwest experiment canoe splitting times derived from multi event averaging at each station range from 0 to 1 4 s with an array average of 0 65 s over broad portions of the array fast directions are coherent and roughly consistent with the direction of absolute plate motion in a hotspot reference frame suggesting that coherent asthenospheric fabric underlies the plate in much of the region within this broad framework fast directions and splitting times show marked variability over length scales of 50 200km and are generally correlated with surface and or crustal tectonics anomalous splitting is observed across an ancient suture within the cratonic lithosphere apparently associated with complex dipping fabric produced during continental assembly the deformation front of the canadian rockies correlates with a significant change in splitting behavior consistent with the front range demarking the craton cordillera transition within the mantle splitting times are small across much of the cordillera indicating that lithospheric and or asthenospheric fabric is weaker or less coherent than beneath the craton in the western cordillera fast directions rotate abruptly to parallel the plate boundary implying that fabric associated with plate boundary deformation extends 200km into the north american continent

electromagnetic images of a strike slip fault the tintina fault northern canadian 1 wideband magnetotelluric mt data were acquired along three profiles crossing the strike slip tintina fault in northwestern canada the mt responses obtained exhibit remarkable similarity from all three profiles implying similar two dimensional 2 d electromagnetic behavior of the fault zone over a strike length of at least 350 km analyses of the mt responses for dimensionality corroborate the validity of assuming regional 2 d structures in interpretation several high conductivity anomalies at different depth scales are present in the models obtained and we suggest that both the shallow structures and the deep crustal scale anomalies are caused by electronic conduction mechanisms in interconnected mineralized zones intriguingly the middle and lower crust beneath the surface expression of the tintina fault is highly resistive in contrast to some other large scale strike slip faults this implies that fault zone processes that result in interconnected conducting phases are not generic in nature but are controlled by local conditions

late quaternary sedimentation in the strait of bosporus high resolution seismic profiling abstract uniboom profiling supported by borehole data in the southern part of the bosporus revealed that close to its banks holocene sediments are underlain by the faulted slopes of a valley cut in many places into the palaeozoic bedrock away from the banks the sediments thicken and their boundary with the underlying pleistocene deposits is defined by an erosional surface at about the 80 ms twt this surface marks the initiation of marine currents in the valley as its deeper parts began to be submerged in the late pleistocene to early holocene marine spillway phase the upward coarsening holocene sequence records the subsequent evolution of the present two way marine strait the sequence is divided into three seismostratigraphic units the lowest one constitutes an onlapping fill deposited under salt wedge estuarine conditions when sediment input and runoff discharge were high and sealevel was still rising but the flow of mediterranean waters into the black sea was not continuous it fills low areas and is well developed under a sill close to the southern entrance of the strait as sealevel rose closer to its present level and the rate of terrigenous input decreased in the middle holocene this unit began to be eroded and reworked by strong bottom currents the second unit records the transitional stage between the estuarine phase and the present two layered current system its seismic facies and sedimentary features indicate deposition under high energy conditions and shifting loci of accumulation the third surficial unit is a thin depositional lag rich in shell fragments blanketing the other two units it records deposition under fully marine conditions and flow of powerful bottom currents during the last few millenia

p wave teleseismic traveltime tomography of the north american midcontinent the remains of the 1 1 ga midcontinent rift mcr lie in the middle of the tectonically stable portion of north america previous and ongoing studies have imaged strong heterogeneity associated with the mcr in the crust but have not imaged such within the mantle it is unclear whether this is due to the absence of rift related mantle structures or these studies had insufficient resolution to image them to address this issue we measured 46 374 teleseismic p wave delay times from seismograms recorded by the usarray transportable array superior province rifting earthscope experiment and surrounding permanent stations we included these and 54 866 delay times from prior studies in our tomographic inversion we find that high velocity anomalies are widespread in our study area but there are also prominent low velocity anomalies two of these are coincident with high bouguer gravity anomalies associated with the mcr in iowa and the minnesota wisconsin border at 50 to 150 km depth extensive resolution testing shows that these anomalies could be the result of downward vertical smearing of relatively low velocities from rift related material that underplated the crust although we cannot exclude that the subcrustal mantle lithosphere beneath the mcr is anomalously enriched hydrated or warm other anomalies occur at syntaxes of the penokean orogen one with the superior province and marshfield terrane in southern minnesota and another with the yavapai and mazatzal terranes both at 100 to 250 km depth in the midmantle we image two linear high velocity anomalies interpreted as subducted fragments of the farallon and kula plates

heavy metal geochemistry of surface sediments from the southern black sea shelf and upper slope abstract a wide variety of sediment types mud to sandy gravel was obtained at fourty seven stations on the southern black sea shelf and upper slope and analyzed for their heavy metal geochemistry distribution of grain size carbonates organic carbon and heavy metals show marked changes in the topography biological activity and land geology of the region studied sediments constitued up to 39 caco3 mainly of biogenic origin from the shell remains of benthic organisms organic carbon contents of the sediments 0 13 3 09 usually reflect the prevailing primary productivities in the black sea although significant terrigenous influences are also inferred the heavy metal concentrations largely indicate the influences from the geochemical weathering of terrigenous sources on land in comparison with the average sedimentary rocks and other modern sediments from the adjacent regions the concentrations of cr ni cu zn and pb are somehow higher in the surface sediments from the southern black sea in particular cr ni and cu are found in high abundances in the eastern parts of the study area this is thought to reflect not only the well mixed fine grained nature of the sediments but also the possible contribution from metal rich rocks mafic and ultramafic sources and associated economic mineral deposits in the catchment areas of rivers which drain this part of the coast the presence of significant positive correlations between the concentrations of cr and ni and zn and pb strongly suggest common sources and or similar enrichment mechanisms for these metals the relationships among the geochemical variables revealed that fe and mn oxides hydrates and sulfides and organic phases together with the clay and silt sized grain fractions are the important associations of the studied heavy metals

sedimentology and mineralogy of surficial bottom deposits from the aegean canakkale marmara transition eastern mediterranean effects of marine and terrestrial factors abstract grain size carbonate and xrd mineral data of surficial shelf sediments from 113 stations in the aegean marmara transition revealed the presence of three distinctive sectors which were controlled by the changing morphologic hydrodynamic benthic and terrigenous conditions that lasted during the late quaternary the northeastern aegean sea forms the western sector of the study area this region shows several bank and ridge like bottom features at 60 70 m water depths which are widely capped with sand and gravel up to 93 of both biogenic 30 caco 3 and terrigenous 3 origin the low abundances of fine grained materials 1 24 mud in this biogenic belt are probably in response to higher current velocities in the sea and to low fluvial discharges from the adjacent land masses biogenic materials consist of a large variety of calcareous remains of benthic organisms which are partly cemented by carbonate it is hypothesized that this biogenic belt at least in part is a relict feature canakkale strait is the central sector of the study area and its bottom is covered largely by terrigenous sand and gravel 3 the coarse grained nature of the sea floor of canakkale strait can be explained by the prevailing high current velocities western marmara sea is the eastern sector of the study area where the local major rivers supply a great part of the terrigenous materials and the prevailing low current velocities favour fine grained materials deposition here 3 up to 99 mud calcite mainly mg calcite 5 92 quartz 3 72 feldspars mainly plagioclase 7 56 and micas are the major bulk minerals in the sediments except for mg calcite which is mainly derived from calcareous biogenic components bulk minerals reflect a terrigenous source from the adjacent land masses in particular the overall lower qtz fsp ratios in the study area 0 4 1 2 showed significant increases i e enrichment of quartz relative to feldspars qtz fsp 1 2 2 4 in the inner biogenic belt of the northern aegean sea where older or relic early holocene sediments are suspected to occur if so these values can be used as an indicator for long duration of lowstands of sea level and associated intense current and wave activities 17 a expandable smectite 23 84 illite 12 43 and kaolinite 6 38 determined in the less than 2 m of the sediment are the major clay minerals higher abundances of smectite relative to illite and kaolinite found in sediments particularly off the mouths of rivers karamenderes gonen and biga and off the gokceada and bozcaada islands reflect mainly local sources for the clay minerals studied the higher smectite illite ratios of abundances are largely attributed to the weathered volcanic rocks which are widely distributed on the surrounding land masses however the prevailing current and wind patterns seem to be important factors controlling clay mineral distribution in marine sediments of this study

geophysical investigation and reconstruction of lithospheric structure and its control on geology structure and mineralization in the cordillera of northern canada and eastern alaska a reconstruction of the tintina fault is applied to regional geophysical and topographic data facilitating the definition of west trending lineaments within the lower crust and or mantle lithosphere oblique to the nw trending structure of the cordilleran terranes the lineaments which exhibit a range of geophysical and geological signatures are interpreted to be related to the liard transfer zone continuous to the denali fault that divided lower and upper plates during late proterozoic cambrian rifting of the laurentian margin three dimensional gravity models show a density increase in the lower crust and mantle lithosphere to the north the transfer zone also divides bimodal mantle xenolith suites to the south from unimodal suites to the north these conclusions suggest that extended north american basement related to laurentian margin rifting that would have brought mantle lithosphere rocks to a shallow depth continuously underlies a thin carapace of accreted terranes in western yukon and eastern alaska the interpreted continuity of north american basement reaffirms that if oroclinal bending of the intermontane terranes occurred then it was prior to its emplacement upon the rifted basement examination of the spatial relationships between mineral occurrences and postaccretionary cretaceous lithospheric lineaments from their manifestation in geophysical geological and topographic data suggest that the late proterozoic lineaments influenced mesozoic mineralization through influence on the development of the shallow crustal structure intrusion and exhumation and erosion

an 1800 km cross section of the lithosphere through the northwestern north american plate lessons from 4 0 billion years of earth s history the lithoprobe slave northern cordillera lithospheric evolution snorcle study across northwestern north america in combination with related crustal studies has been synthesized into an 1800 km long cross section of the lithosphere that is constrained by high resolution geophysical data seismic reflection refraction electromagnetic potential fields and detailed bedrock geology the cross section offers one of the longest continuous profiles of the continental lithosphere anywhere in the world that is constrained by combined geophysical measurements and electromagnetic properties and exposed bedrock geological relationships the primary conclusion of the study is that during all major orogenic episodes recorded from archean to present in that part of earth s lithosphere the crust and perhaps much of the mantle was reorganized and redistributed rather than being differentiated from the mantle at the time of orogenesis the observed subsurface geometries of relict subduction zones accretion

sea level changes and related depositional environments on the southern marmara shelf abstract petrographic data obtained from 182 surface sediment samples together with the available bathymetric data are used to investigate the effects of the last major sea level changes on shelf evolution in the southern sea of marmara grain size analysis reveals the presence of at least three belts or zones which are rich in coarse grained sand and gravel sediments these coarse grained belts which are up to 45 km long 15 km wide show up to 20 m of relief and are presently found at 40 80 m average 60 m water depths based on microscopic examination and residual analysis the sediments from these belts are interpreted as indicators of high energy shallow waters where detrital siliciclastics with some benthic contribution accumulated the presence of a 62 65 m deep sill in the canakkale strait and the consideration of sea level curves would suggest that the marmara shelves must have been subaerially exposed down to 65 m water depths for about 10 000 yrs 22 000 12 000 yrs b p sufficient time to modify former shelf topographies and form such bottom relief while difficult to date we believe that coarse grained belts found on the southern marmara shelf must be relict i e former shorelines beaches and their formation is largely related to low stands of sea level during the late pleistocene regression and early holocene transgression however the available high resolution seismic profiling data suggest that the neotectonism in this seismically active sea of marmara plays an important role to explain the raise of these older shorelines to their present levels on the sea floor

lithospheric variations across the superior province ontario canada evidence from tomography and shear wave splitting 1 the superior province of the canadian shield is the largest contiguous region of the archean crust a combination of data from multiple experiments is used to obtain shear wave splitting parameters and a three dimensional tomographic velocity model beneath a large portion of the superior corresponding approximately to the province of ontario shear wave splits are obtained at 24 sites across the superior displaying strong averaging 1 34 s ene wsw splitting at stations west of 86 w and weaker 0 67 s e w splitting in the east the fast direction is subparallel to both absolute plate motion and tectonic belt boundaries the recovered tomographic velocity model shows a major boundary oriented nnw sse separating high velocities in the western superior ws from low velocities in the east and coinciding with the divide between weak and strong shear wave splits other features include a 200 km thick low velocity anomaly corresponding to the nipigon embayment a 1 0 ga failed rift branch and a linear low velocity anomaly in the east attributed to the great meteor hot spot track the nipigon anomaly in the western portion of the model is probably in situ while the great meteor track is displaced from crustal features associated with the hot spot we interpret this displacement as evidence that the eastern lithosphere has been deformed by basal drag while the western lithosphere has remained stable and propose that the east west lithospheric boundary we have detected represents a change in mechanical properties between stronger higher velocity western material with consistent anisotropic fabric and weaker eastern material with more variable fabric

crustal and upper mantle anisotropy related to fossilized transpression fabric along the denali fault northern canadian cordillera we analyze crustal and upper mantle structure near the denali fault northern canadian cordillera using 11 broadband seismic stations receiver functions at five stations within 5 30 km of the fault trace display a strong p to s conversion within the midcrust 10 25 km depth that systematically varies with back azimuth stacking and velocity inversion along complementary northwest southeast and northeast southwest back azimuth ranges yield a strong anisotropy 10 in the midcrust with complex crustal anisotropic behavior at least two layers close to the denali and duke river faults junction anisotropy occurs in a low velocity zone with the fast axis parallel to the denali fault trend three additional stations close to the denali fault 15 30 km as well as two stations further away 100 km show no significant crustal anisotropy shear wave sks splitting analysis indicates similar upper mantle anisotropy with a fast axis parallel to the trend of the denali fault for all stations except for station why located 125 km away we relate this crustal and upper mantle anisotropy to fossilized structural and mineral fabrics due to eocene transpression on the denali fault these results suggest the main transpression phase 400 km displacement was accommodated in a shear zone at least 50 60 km less than 125 km wide in the midcrust and upper mantle lack of clear anisotropy in the lowermost crust may relate to complex deformation within a detachment layer orogenic float model online material table of sks splitting information and figures of receiver function analysis

clay mineral distribution in last glacial holocene sediment cores from the eastern marmara sea cinarcik basin izmit gulf transition nw turkey multisources and transport paths in a two way flow system abstract the regional variations in grain size xrd bulk and clay mineral distribution in 97 sediment samples from 6 gravity cores obtained from 20 to 300 m water depths have been investigated to reveal source and transportation patterns as well as the effects of climatic and sea level changes during the last 25 000 14 c bp in the eastern marmara sea ems nw turkey the major proportions of sediments in the ems consist of silt 20 83 and clay 17 90 whereas sand and gravel abundances rarely exceed 10 of the bulk minerals 10 a micas 23 55 and feldspars 17 55 dominate over quartz 10 21 and calcite 10 26 smectites 23 62 illite 18 36 chlorites 6 21 kaolinite 2 20 and 14s 14c mixed layer minerals 0 27 constitute the principal clay mineral assemblages both bulk and clay mineral assemblages in the ems are similar to those found in the izmit gulf on the southern marmara shelf at the marmara aegean approaches and the southern black sea this would suggest that there is no distinct source for mineral assemblages of the study area outside the marmara basin the concentrations of clay fractions and clay mineral assemblages tend to increase or decrease with depth in the cores but this is limited to some intervals and not to entire sections in the cores this distribution pattern therefore represents rather local sources of provenance and surrounding fluvial drainage basins together with dilution and distribution effects by current transport processes rather than the expected paleoclimatic features and sedimentary input by inflowing black sea and aegean sea water masses throughout the last glacial to holocene

tectonics of the northern canadian cordillera imaged using modern magnetotelluric analysis abstract magnetotelluric data from lithoprobe snorcle corridor 2 in western canada crossing the rocky mountain trench tintina fault between 56 and 60 n have been analyzed using modern mt methods to provide new insights into the tectonics of the north american cordillera and ancestral north america resistivity images of the crust were obtained using two independent sets of unconstrained 2 d inversions and constrained 2 d inversions incorporating seismic constraints structure to the west of the tintina fault includes uniform moderate mid to lower crustal resistivity in a seismically defined westward tapering wedge of ancestral north american rocks to the east between the tintina fault and the liard line a transfer zone in asymmetric neoproterozoic rifting the wedge includes a major synformal conductor that parallels seismic reflections the large lateral changes in resistivity can be explained by transition between different blocks of asymmetric rifting the synformal conductor is attributed to graphitic rocks from the aida formation of the mesoproterozoic muskwa assemblage that were re distributed in a sag basin on the lower plate margin in the blackwater block spatially complex upper crustal resistivity in the cordillera can be interpreted in terms of lithological variations and alteration processes an east dipping conductor in stikinia is attributed to east dipping jurassic and relatively high conductivity beneath the eskay rift may be explained by crustal fertilization a conductor in the cache creek terrane is attributed to listwanite alteration of ultramafic bodies on the king salmon fault and high conductivity in the slide mountain terrane within the sylvester allochthon to localized carbonaceous alteration a series of conductors above north american basement is attributed to deformation and metamorphic processes associated with mesozoic thrust faulting to the west of the tintina fault the source material for these conductors is likely from the stikinia terrane and to the east it is likely from the muskwa assemblage