the metagabbros orthogneisses and paragneisses of the connemara complex western ireland although now largely disappeared within the 400 ma old galway granite the syntectonic connemara metagabbro gneiss complex which crystallized at 490 ma arenig is the largest intrusion into the dalradian rocks it is part of widespread cambro ordovician volcanism and plutonic injection into continental crust in the appalachian caledonide orogenic belt being synchronous in crystallization with the widely obducted 490 ma ophiolites within the orogeny the peridotites and hornblende gabbros were injected broken up and shouldered aside by quartz diorite granodiorite granite and trondhjemite gneisses and it is shown that these orthogneisses are not the in situ differentiation products of the gabbro magma the hornblende in the metagabbros is mainly igneous but is partly metamorphic and replaces olivine fo 75 92 orthopyroxene en 65 92 clinopyroxene wo 48 5 en 50 39 fs 5 14 and plagioclase typically an 80 92 range an 50 96 an aureole at least 10 km wide in the sillimanite zone was imposed and cordierite garnet sillimanite dalradian hornfelses were partially melted at temperatures up to 1000 o c near to the gabbros at 4 5 1 kbar corresponding to c 18 km depth this suggests that the complex forms part of the root of a now eroded batholith of calc alkaline affinities the gabbros corresponding to the transition zone to a basic bottom which is often supposed to underlie many batholiths within the orthogneisses are sheets of paragneiss formed from dalradian metasediments which have been folded up from the floor and down into sides of the magma chamber which process could be illustrative of the means by which basic magma can intimately interact with crustal material the 18 o 16 o d h nd and sr isotope evidence and the existence of inherited zircons in the gneisses indicate that the gabbro and gneiss magmas were significantly contaminated with crustal possibly dalradian material both before and after intrusion with the lowest initial 87 sr 86 sr at 490 ma being 0 708 even in samples far removed from metasediment the metagabbros are tholeiitic to high alumina basalt in character but the gneisses have distinct calc alkaline geochemistry the chemistry igneous hornblende and highly calcic plagioclase match many arc plutons in the western usa the syntectonic nature and the ubiquitous gneissic fabric in the quartz diorites trondhjemites and granites is a consequence of early movements which were probably in part connected with the separation of the connemara massif and which culminated in slicing off the largely inverted complex and carrying it southwards on the mannin thrust which underlies the whole of connemara the complex is thus a fragment of a now disrupted cambro ordovician continental magmatic arc or continent island arc environment which can be traced along the se edge of the laurentian continent

seismic tomography a window into deep earth abstract the goal of this paper is to provide an overview of the current state of the art in seismic tomography and trace its origins from pioneering work in the early 1970s to its present status as the pre eminent tool for imaging the earth s interior at a variety of scales due to length limitations we cannot hope to cover every aspect of this diverse topic or include mathematical derivations of the underlying principles rather we will provide a largely descriptive coverage of the methodology that is targeted at readers not intimately familiar with the topic the relative merits of local versus global parameterization ray tracing versus wavefront tracking backprojection versus gradient based inversion and synthetic testing versus model covariance are explored a variety of key application areas are also discussed including body wave traveltime tomography surface wave tomography attenuation tomography and ambient noise tomography established and emerging trends many of which are driven by the ongoing rapid increases in available computing power will also be examined including finite frequency tomography full waveform tomography and joint tomography using multiple datasets several practical applications of seismic tomography including body wave traveltime attenuation and surface waveform are presented in order to reinforce prior discussion of theory

improving global shear wave traveltime tomography usingthree dimensional ray tracing and iterative inversion a fully non linear approach to global tomography using s wave arrival times has been implemented using 3 d ray tracing with an iterative linearized inversion scheme the starting model for the 3 d inversion was the long wavelength saw12d model derived from inversion of global waveforms the traveltime tomography leads to the introduction of smaller scale structure and a final model in which small scale detail exists and can be resolved with a smooth interconnection through long wavelength structure the two point ray tracing was implemented using a pseudo bending approach for a full spherical 3 d model of the mantle generally the ray paths in the full 3 d model and 1 d reference model are quite close but the inclusion of a more accurate treatment of the rays improves the resolution of wave speed gradients and the positioning of heterogeneity particularly near strong variations in wave speed for example in subduction zones a further advantage of the use of 3 d ray tracing is that it is possible to undertake resolution tests with fewer approximations with the aid of the non linear inversion a number of global s models have been constructed using different assumptions about the character of the model for example solutions can be produced that are designed to introduce minimum differences from a 1 d reference model a variance reduction of 48 per cent was achieved in the inversions with considerable benefit from the inclusion of iterative inversion with 3 d ray tracing and the improved quality of the data set used in this study resolution in the lower part of the mantle has been improved by supplementing the s arrival time data with sks times for the distance range from 84 to 118 the new global s models retain the general features of models derived by one pass linearized inversion with 1 d ray tracing but provide more focused images with a higher perturbation level for the same damping parameters the new models are able to provide a good definition of features revealed by regional tomography using arrival time and waveform data for example the complex slab morphology beneath the tonga and kermadec regions and the sharp boundary between slow and fast uppermost mantle regions beneath western and eastern europe

ray tracing directly in a 3 d ellipsoidal earth model for multiphase global arrivals seismic ray tracing methods are widely used in seismology with most such algorithms being executed in cartesian or spherical coordinate systems however the actual earth is not a perfect sphere but rather an ellipsoid meaning that results calculated in spherical coordinates may be different from the actual situation the general approach is to first calculate traveltimes in a spherical earth model then apply ellipsoidal time corrections to obtain more accurate traveltime data alternatively one may directly conduct the ray tracing in the ellipsoidal earth model without any time corrections in this paper we extend the functional of the multistage irregular shortest path method previously formulated for a spherical earth model to an ellipsoidal earth model in order to trace multiphase global seismic arrivals the results of two models indicate that the proposed algorithm has high computational accuracy which can be further tuned by decreasing the secondary node spacing comparison tests indicate that the traveltime differences between the ellipsoidal and spherical coordinate ray tracing methods cannot be ignored for direct p and s arrivals reflected pcp and scs arrivals and reflected and converted pcs and scp arrivals the traveltime differences te ts computed by the ellipsoidal and spherical ray tracing methods have different distribution patterns being dependent on the source locations however in general these traveltime differences te ts have relatively large negative values near the polar region and positive values near the equatorial region except for sources located near the polar region for ellipsoidal time correction in a specific case the maximum differences between the traveltimes computed by the ellipsoidal coordinate ray tracing method and the ak135 traveltime table after application of ellipsoidal time corrections are less than 0 1 s meanwhile the maximum differences between the traveltimes predicted by the ellipsoidal coordinate ray tracing method and by the spherical coordinate ray tracing method after application of ellipsoidal time corrections are only 0 075 s for the six stated phases these results indicating that ray tracing could be conducted directly in the ellipsoidal earth model

on recent seismic tomography for the western united states 1 in recent years a number of relatively high resolution seismic tomography models for the uppermost mantle underneath the western united states have been published and vigorous debate has ensued about their tectonic interpretation i present a straightforward yet quantitative comparison between models in order to help establish a framework for geodynamic interpretation and to help judge the role of tomographic theory vs data selection mapped s and p wave anomalies are found to be remarkably consistent between models which implies that seismologists are beginning to narrow down the structure underneath active continental margins to scales of 200 km large discrepancies between published anomaly amplitudes exist however and the models on the high end of the spectrum raise questions as to how they are to be interpreted in terms of temperature composition and melting

a low seismic wavespeed anomaly beneath northwestern india a seismic signature of the deccan plume abstract seismic tomography of the indian region using p wave arrival times reveals an approximately cylindrical region of lowered seismic velocities in the upper mantle to the north of the gulf of cambay and the present exposure of the deccan flood basalts this anomaly with low velocities interrupts the characteristically high seismic velocities in the lithosphere beneath peninsular india and extends from shallow depth down to a more extensive low velocity zone beneath 200 km the centre of the low velocity anomaly lies just below the earliest alkaline magmatism which has been directly associated with the deccan plume in the northern portion of the cambay graben these magmatic events precede the main deccan flood eruptions by at least 3 myr the lowered seismic wavespeeds link into the ancient narmada lineament and to some extent to the south but here unfortunately the tomographic image runs out of resolution synthetic tests indicate that such a zone of lowered wavespeeds can be recovered with some loss of amplitude towards the south the association of the current seismic anomaly with the deccan traps is intriguing since the cambay graben remains a place of raised heat flow one explanation would be that the seismic anomaly represents the signature of the initial conduit through which plume material forced its way through the lithosphere beneath the cambay rift the zone of lowered seismic velocities beneath the indian lithosphere might then represent the remains of the initial plume head which would need to have moved with india over the 65 myr since the deccan eruptions

silurian deformation in eastern notre dame bay newfoundland eastern notre dame bay newfoundland is divided into five fault bounded terranes they are from north to south the twillingate terrane the chanceport terrane the new world island terrane the dildo run terrane and the port albert terrane the new world island terrane is characterized by fault repeated sequences of middle ordovician to early silurian turbiditic sandstones sansom formation and conglomerates goldson formation the chanceport terrane has a lower volcanic unit and an upper sedimentary unit consisting of red and green siltstones shales overlain by turdiditic sandstones this sequence is structurally overlain by a mafic and felsic volcanic unit the clastic sedimentary rocks of the chanceport new world island and port albert terranes best record the silurian deformation in the area silurian deformation is divided into two deformation events an early silurian d1 thrusting event and a late silurian d2 dextral ductile faulting event the early silurian joey s cove melange constrains th

sharpening the tomographic image of the subducting slab below sumatra the andaman islands and burma summary taking advantage of the increased ray coverage due to seismicity following the 2004 december and 2005 march great earthquakes an improved iterative regional global tomographic method was applied to the sumatra andaman and adjacent regions to better constrain the 3 d mantle velocity heterogeneity in the region velocity and hypocentral parameters were iteratively perturbed to sharpen the image of the subducted slab several iterations were performed and the effects of source mislocation were considered in the iterative process an issue usually neglected in global tomography we find that source relocation between iterations increases the amplitudes of slab anomalies and sharpens the definition of slab geometry beyond what can be achieved by a fixed source iterative inversion alone in addition extensive restoration tests of synthetic data were conducted that emphasize enhancements obtained by our iterative process these tests show significant increases in amplitude and decreased smearing of synthetic slab features thus when applied to the real data similar enhancements are inferred in the resulting model which better illustrates the complex slab geometry in the upper mantle and transition zone regions along the sumatra andaman and burma subduction zones

the nutrient salinity and stable oxygen isotope composition of bering and chukchi seas waters in and near the bering strait seawater nutrient salinity and oxygen 18 data collected from 1990 to 1993 in the bering and chukchi seas were used to identify potential sources of nutrients and water masses that result in formation of the arctic ocean upper halocline and its associated nutrient maximum water matching the delta sup 18 o values of the arctic ocean upper halocline and containing sufficient or a nearly sufficient nutrient and salinity concentration was collected in subsurface waters in the summer in portions of the bering sea particularly the gulf of anadyr however nutrient concentrations significantly declined in this north flowing water over the shallow continental shelf before it reached the bering strait as a consequence of biological utilization and dilution with nutrient poor and oxygen 18 depleted fresh water therefore it does not appear likely that the flow of unaltered water through the bering strait in the summer plays a critical role in the formation of the arctic ocean upper halocline the role of other mechanisms for contributing pacific derived waters to the arctic ocean nutrient maximum is considered copyright 1997 american geophysical union

melange development in the boones point complex north central newfoundland the boones point complex in north central newfoundland is a narrow melange belt separating roberts arm terrain volcanic and volcaniclastic rocks to the north from upper ordovician westerly derived

seismic evidence for a chemical heterogeneity in the midmantle a strong and slightly dipping seismic reflector beneath the mariana subduction zone 1 a clear later phase 80 s after the direct p wave is observed in most of individual seismograms recorded by a short period seismometer network in japan j array from a cluster of deep earthquakes that occurred at the northern mariana subduction zone this phase 1 shows a p wave particle motion 2 arrives later from earthquakes with shallower focal depths 3 has a steeper incident angle than that of p wave and 4 shows a deviation of a few degrees in the arrival azimuth from that of p wave we interpret it as an s to p converted wave which takes off downward from the source and is reflected at a velocity discontinuity reflector below the earthquakes travel time inversion shows that the seismic reflector dips southwest by 20 at 24 25 n 144 75 e and at a depth of 1115 km with a lateral extension at least 100 100 km the location corresponds to the lower edge of a high velocity anomaly in global tomographic models amplitude and waveform analyses suggest a decrease of s wave velocity by 2 6 and an increase of density by 2 9 within the reflector there is almost no difference in p wave velocity 1 between the reflector and the surrounding mantle the estimated thickness of the reflector is 12 km these observations indicate that the observed seismic structure is more likely to be a chemical reservoir rather than a purely thermal anomaly the seismic reflector might be a piece of subducted oceanic crust as suggested by a previous study it also could be related to the break down of the d phase of dense hydrous magnesium silicates at midmantle pressure condition reported by recent mineral physics studies both scenarios imply that mechanical chemical segregation might occur within the subducted slab at midmantle condition

seismic evidence for a mantle plume oceanwards of the kamchatka aleutian trench junction summary a non linear iterative p wave traveltime tomography has revealed a mantle plume originating at a depth of nearly 1000 km rising across the 600 km discontinuity and deflecting subhorizontally in the uppermost mantle presumably by shear flow due to the overlying moving plate data from the geophysical survey of russia 1955 1997 were inverted jointly with the catalogues of international seismological centre and usgs national earthquake information centre 1964 1998 the result shows a 300 500 kmwide cylindrical low velocity anomaly yx2 per cent that extends from a depth of greater than 900 km to shallower than 200 km the anomaly is almost vertical at depths up to y400 km and rises obliquely to the north up to y200 km under the ocean floor near the northern end of emperor seamounts above y300 km depth a subsidiary anomaly extends subhorizontally to the nw in fair agreement with the direction of movement of the pacific plate the overlying seafloor is characterized by anomalously high heat flow which may be attributed to the thermal effect of the mantle plume

brunswick subduction complex in the canadian appalachians record of the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick subduction complex in the new brunswick part of the canadian appalachians records the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick complex is anomalously well preserved compared with equivalent rocks and structures elsewhere owing to its unique position in the deepest part of the quebec reentrant of the laurentian margin this part of the margin experienced less underthrusting and exhumation and overprinting by orogen parallel faulting than the adjacent promontories where collision started earlier the early southeast to east vergent thrust related structures represent a progressive d1 deformation that formed in response to northwestward subduction of the previously extended gander margin and subsequent tectonic unroofing of the subduction complex the original shallow northwestward dipping envelope to s1 was deformed in the late silurian by d2 upright folds and associated shear zones into a steep belt during terminal collision the d2 structures probably formed in response to sinistral transpression together d1 and d2 indicate that convergence was oblique and sinistral most rocks incorporated in the subduction complex formed in the tetagouche back arc basin that evolved from rifting of an arenig magmatic arc built on the gander margin into a wide marginal basin subduction was initiated in the late ordovician 455 ma in the back arc basin following collision of the middle ordovician popelogan arc with laurentia in the caradoc shortly after its opening in the late arenig 473 ma the closure history of the iapetus ocean involved more than one subduction zone and arc continent collision and rivals the southwestern pacific ocean in its complexities

upper mantle structure beneath the siberian craton and surrounding areas based on regional tomographic inversion of p and pp travel times abstract we present a model of 3d seismic anomalies in the upper mantle beneath a part of northern asia that includes the siberian craton the west siberian plate the mountains framing siberia altai sayan and baikal and mongolia we used the differential travel times of pp and p phases to investigate the deep seismic structure beneath a large part of the siberian region where neither stations nor earthquake distributions are sufficient to apply other body wave tomographic schemes to show the reliability of the results based on inversion if the pp p residuals we performed various tests including 1 tests with odd even data 2 synthetic tests with checkerboard and realistic patterns and 3 inversions in other areas with clear structures furthermore for the southern part of the study area we present another model based on the inverse tomographic scheme its which uses travel times recorded by worldwide stations from events located in the study area in the overlapping areas these two independent models are generally consistent the main model of this study is obtained by merging the results of the pp p and its schemes this model shows a clear differentiation between the high velocity siberian craton and low velocity structures beneath the mountains framing siberia the area of cenozoic magmatism in western sayan is clearly associated with a low velocity anomaly at a depth of 600 700 km this low velocity pattern is located beneath the cratonic area while at shallower depths it seems to flow around the bottom of the thick craton lithosphere to the sw margin of the craton

fossil evidence for fault derived stratigraphic repetition in the northeastern newfoundland appalachians two types of bedding parallel faults are common in the dunnage zone of eastern notre dame bay they are i early thrusts which together with bedding were rotated by later folding into steep attitudes and ii postfolding transcurrent faults both types of faults occur at all scales and give rise to repetitions in the stratigraphic sequence a compilation of the ages of various rock types based on fossil evidence indicates a relatively simple stratigraphy for the dunnage zone this interpretation appears to be at variance with many reported stratigraphic successions until repetitions by bedding parallel faulting are taken into account examples are given of sequences in which the repetition of various rock types dated by means of fossils is due to bedding parallel faulting we believe that the simple lithostratigraphy is a reliable aid for structural interpretations in areas where fossils are scarce or absent

air sea co2 fluxes and the continental shelf pump of carbon in the chukchi sea adjacent to the arctic ocean the chukchi sea a shallow sea ice covered coastal sea adjacent to the arctic ocean exhibits an intense bloom of phytoplankton each year due to the exposure of nutrient laden surface waters during the brief summertime retreat and melting of sea ice the impact of phytoplankton production and other factors on the seasonal dynamics of carbon and air sea co2 fluxes were investigated during two survey cruises 5 may 15 june 2002 and 17 july 26 august 2002 as part of the western arctic shelf basins interactions sbi project in springtime most of the chukchi sea was sea ice covered 95 and remnant winter water was present across the shelf surface layer seawater partial pressure of co2 pco2 ranged from 200 320 atm indicative of undersaturation with respect to atmospheric pco2 although sea ice cover kept rates of air to sea co2 flux generally low 80 air to sea co2 fluxes remained generally low 2 mmoles co2 m 2 d 1 seasonal i e may to september and annual net air to sea co2 fluxes from the chukchi sea shelf were estimated at 27 7 tg c yr 1 and 38 7 tg c yr 1 respectively the chukchi sea represents the largest oceanic co2 sink in the marginal coastal seas adjacent to the arctic ocean an active continental shelf pump of carbon driven by the northward transport of nutrient rich water of pacific ocean origin high rates of primary and net community production during the sea ice free period and lateral export of organic carbon maintains the chukchi sea shelf and slope as a perennial ocean co2 sink

early silurian palaeolatitude of the springdale group redbeds of central newfoundland a palaeomagnetic determination with a remanence anisotropy test for inclination error we studied the palaeomagnetism of red fine grained sandstones and coarse siltstones of the early silurian springdale group of central newfoundland at 10 sites a high blocking temperature characteristic remanence carried by haematite was isolated this remanence is shown to predate probable early devonian folding anti parallel north and south directed remanences through a 100 m section of redbeds and a positive conglomerate test on haematite bearing volcanic clasts suggest absence of remagnetization inverting the south directed sites and unfolding yields a characteristic remanence with a mean declination of 23 6 and a mean inclination of 14 2 myg5 7 3 k 45 4 the inclination corresponds to a probable early silurian palaeolatitude of 7 s f 4 we find no significant difference between early silurian palaeolatitudes for central newfoundland north and south of the red indian line suture and conclude that the part of the iapetus ocean across the suture had narrowed to less than about 5 by the early silurian this is consistent with palaeomagnetic results from britain and ireland that suggest no more than a narrow iapetus at low palaeolatitude by the early silurian we also tested whether we have underestimated palaeolatitude because of sediment compaction reducing remanence inclination from that of the early silurian field we measured anisotropy of the isothermal remanence irm acquisition for one specimen from each stable site finding that a field of 200 to 800 rnt applied at 45 to bedding produced an isothermal remanence oriented on average at 42 to bedding theory then predicts that sediment compaction caused less than 2 average inclination shallowing in the springdale group redbeds and less than a 1 underestimation of palaeolatitude

density and bulk sound velocity jumps across the 660 km seismic discontinuity abstract molecular dynamics md simulation with realistic and accurate potential models previously obtained for mg2sio4 polymorphs mgo periclase and mgsio3 polymorphs is used to predict the density and bulk sound velocity jumps in the phase transformation from mg2sio4 spinel to mgsio3 perovskite plus mgo periclase at high temperature and high pressure conditions corresponding to the 660 km seismic discontinuity in the mantle the simulated density and bulk sound velocity jumps are then compared with seismological models reported for the 660 km discontinuity the md simulation for a pyrolite composition 60 vol spinel is found to be compatible with a recent model sf99 shearer and flanagan science 285 1999 1545 within nearly 1 limit for both density and bulk sound velocity jumps the md simulated bulk sound velocity jump for a piclogite composition 40 vol spinel is also consistent with sf99 within 1 while the md density jump for the piclogite lies outside the sf99 data our md computed density and bulk sound velocity jumps either for the pyrolite or the piclogite composition differ substantially from the values by the prem or the ak135 model

joint seismic tomography for bulk sound and shear wave speed in the earth s mantle high quality p and s travel times are now available from careful reprocessing of data reported to international agencies a restricted data set has been extracted for which comparable ray coverage is achieved for p and s and used for a joint inversion to produce a three dimensional model for shear and bulk sound velocities represented in terms of 2 2 cells and 18 layers in depth through the mantle about 106 times for each of p and s are combined to produce 312 549 summary rays for each wave type linearizing about the ak135 reference model 583 200 coupled tomographic equations are solved using an iterative partitioned scheme clear high resolution images are obtained for both bulk sound speed and shear wavespeed the bulk and shear moduli have differing sensitivity to temperature and mineral composition and so the images of the two velocity distributions help to constrain the nature of the processes which produce the variations different heterogeneity regimes can be recognised in the upper mantle the transition zone most of the lower mantle and the lowermost mantle in the upper mantle many features can be explained by thermal effects but in some orogenic zones e g western north america the opposite sense of the bulk sound and shear wave speed variation requires compositional effects or volatiles to outweigh any thermal effects in the lower mantle pronounced narrow structures which may represent remnant subduction are most marked in shear the level of large scale variations in bulk sound speed compared to shear diminishes with depth in the lower mantle reaching a minimum near 2000 km below this depth the variability of both wave speeds increases near the core mantle boundary the variations of the two wave speeds show little concordance suggesting the presence of widespread chemical heterogeneity

freshwater balance and the sources of deep and bottom waters in the arctic ocean inferred from the distribution of h218o data from sections across the eurasian basin of the arctic ocean occupied in 1987 and 1991 are used to derive information on the freshwater balance of the arctic ocean and on sources of the deep waters of the nansen amundsen and makarov basins using salinity h218o and mass balances we estimate the river runoff and the sea ice melt water fractions contained in the upper waters of the arctic ocean and infer pathways of the river runoff signal from the shelf seas across the central arctic ocean to fram strait the average mean residence time of the river runoff fraction contained in the arctic ocean halocline is determined to be about 11 to 14 years pacific water entering through bering strait is traced using silicate and its influence on the halocline waters of the canadian basin is estimated water column inventories of river runoff and sea ice melt water are calculated for a section just north of fram strait and implications of these inventories for sea ice export through fram strait are discussed comparison of the 18o 16o ratios of shelf water atlantic water and the deep waters of the arctic ocean indicate that the sources of the deep and bottom waters of the eurasian basin are located in the barents and kara seas

seismic rays and traveltime tomography of strongly heterogeneous mantle structure application to the central mediterranean summary the structure of the earth s upper mantle near convergent plate margins such as along the nubia eurasia collision zone in the mediterranean involves strong seismic wave speed contrasts associated with subducting lithospheric slabs and opening backarc basins in this environment seismic wave propagation is strongly influenced by heterogeneity and requires appropriate modelling practice although accurate numerical methods are often used to model seismic traveltimes in the crust only approximate techniques have been used for the mantle on the assumption that speed contrasts are weaker we devise optimize and test a method aimed at recovering strongly heterogeneous mantle structures using a finite difference scheme to calculate first arrival traveltimes and trace seismic rays with high accuracy even in the presence of strong gradients we adapt this forward scheme successfully used in local scale tomography to spherical geometry through source specific earth flattening approximations and we split calculations in meshes with different step size to model optimally the crust with a 2 km step and the mantle 6 km step we then use an iterative non linear inversion approach starting from a simple 1 d prior model we test the ability of this procedure to reconstruct sample structures devised to be illustrative for the mediterranean region using synthetic data calculated on the real distribution of sources and stations reported by the bulletins of the international seismological centre isc besides regular checkerboard patterns we also reconstruct a more representative model different strategies are used and compared in linear and non linear inversion we find that a linear approach by which rays are only traced once in the background model may result in an illusory fit to data realistic upper mantle structures strongly deflect seismic rays and correct paths can only be found after a few iterations although linear inversion seems able to identify the main features quite well we verify how non linear inversion and 3 d ray tracing significantly improve the results especially when we attempt to reconstruct a realistic structure we also apply the finite difference non linear traveltime tomography to data from the isc to retrieve upper mantle structure in the central mediterranean we verify that the non linear inversion is able to reveal sharpened velocity contrasts and thinner bodies than linear inversion clear differentiation found in the nonlinear result between signatures of northern and southern dinarides showing lithosphere subducting only beneath the southern sector is more coherent with the regional geodynamic framework such improvements due to non linear mantle tomography may contribute to the general picture of slab detachment and small scale mantle convection in the mediterranean region and therefore significantly impact on geodynamic implications of resulting models

physical and geochemical properties across the atlantic pacific water mass front in the southern canadian basin temperature salinity nutrients oxygen and halocarbon data collected in the arctic ocean reveal a frontal structure previously unrecognized in the hydrography of the canadian basin samples were collected on a 1300 km section extending from the beaufort sea in the canada basin to the east siberian sea in the makarov basin these data collected in 1993 aboard the ccgs henry larsen reveal a lateral boundary between water masses of atlantic and pacific origin the term water mass assembly is introduced to describe the basic arrangement or vertical stacking of water masses found in the arctic ocean recognizing that water mass components within each assembly may differ from basin to basin using historical data two primary water mass assemblies are defined each consisting of three layers an upper layer an atlantic layer and a deep layer these two assemblies are marked by important differences one assembly here defined as the western arctic wa assembly is characterized by an upper layer of relatively fresh high nutrient water of pacific origin below this by an atlantic layer with a core temperature generally below 0 5 c and finally by a deep layer of higher salinities and colder temperatures about 0 5 c than found in the overlying atlantic layer the second assembly here defined as eastern arctic ea assembly is characterized by the absence of pacific water in the upper layer below this by an atlantic layer core as warm as 2 to 3 c and by a colder about 0 9 c deep layer because the presence or absence of pacific origin water is a key characteristic distinguishing the two assemblies we will refer to the water mass boundary between the two assemblies as the atlantic pacific front earlier research indicated that water masses in the arctic ocean were separated by a front above the lomonosov ridge into the canadian and eurasian basins although all larsen 93 stations from the canada basin a1 d1 display classic wa assembly characteristics the makarov basin station e1 shows ea assembly characteristics in the upper and atlantic layers and a wa assembly deep layer this suggests a relocation in the position of the atlantic pacific boundary away from the lomonosov ridge further larsen 93 data show the transition region between the atlantic and deep layers is fresher in the makarov basin than corresponding water in either the canada or eurasian basins implying a source of cold low salinity water perhaps from the laptev and east siberian shelves the front separating these two assemblies lies above the mendeleyev ridge and is marked by large lateral gradients in all measured properties in particular the penetration of anthropogenic halocarbons is 2 to 3 times deeper in the makarov basin than in the canada basin implying enhanced rates of ventilation this suggests that direct exchange between the canadian and eurasian basins has occurred recently near the perimeter and that physical and chemical properties including contaminants may have been transported by boundary currents more quickly from one basin to the other

behaviour of dissolved organic matter and inorganic nutrients during experimental sea ice formation it is well established that during sea ice formation crystals aggregate into a solid matrix and dissolved seawater constituents including inorganic nutrients are rejected from the ice matrix however the behaviour of dissolved organic matter dom during ice formation and growth has not been studied to date dom is the primary energetic substrate for microbial heterotrophic activity in seawater and sea ice and therefore it is at the base of the trophic fluxes within the microbial food web the aim of our study was to compare the behaviour of dom and inorganic nutrients during formation and growth of sea ice experiments were conducted in an indoor basin at 15 c three 1 m3 tanks to which synthetic seawater nutrients and dissolved organic compounds diatom extracted dom had been added were sampled over a period of 5 days during sea ice formation samples were collected throughout the experiment from water underlying the ice and at the end from the ice as well brine was obtained from the ice by centrifuging ice cores inorganic nutrients nitrate and phosphate were substantially enriched in brine in comparison to water and ice phases consistent with the processes of ice formation and brine rejection dissolved organic carbon doc was also enriched in brine but was more variable and enriched in comparison to the dilution line no difference in bacteria numbers was observed between water ice and brine no bacteria growth was measured and therefore had no influence on the doc levels we conclude that the incorporation of dissolved organic compounds in newly forming ice is conservative however since the proportions of doc in the brine were partially higher than those of the inorganic nutrients concentrating effects of doc in brine might be different compared to salts

synthesis of palaeozoic deformational events and terrane accretion in the canadian appalachians plate tectonic theory predicts that most deformation is associated with subduction and terrane accretion with some deformation associated with transform transcurrent movements deformation associated with subduction varies between two end members 1 where the tectonic regime is dominated by subduction of oceanic lithosphere containing small terranes a narrow surface zone of accretionary deformation along the subduction zone starts diachronously on the subducting plate at the trench as material is transferred from the subducting plate to the over riding plate and 2 where continent continent collision is occurring a wide surface zone of accretionary deformation starts synchronously or with limited diachronism palaeozoic deformational events in the canadian appalachians correspond to narrow diachronous events in the ordovician and silurian whereas devonian carboniferous and permian deformational events are widespread and broadly synchronous along the western side of the canadian appalachians the taconian deformational event starts diachronously throughout the ordovician and corresponds to the north north west accretion of the notre dame ascot weedon st victor and various ophiolitic massifs volcanic arc and peri arc terranes over cratonic north america within the eastern half of the central mobile belt the late cambrian early ordovician penobscotian deformational event corresponds to the south easterly accretion of the exploits subzone various volcanic are and peri arc terranes over the gander zone continental rise in the centre of the orogen the late ordovician silurian beothukan deformational event corresponds to the south easterly accretion of the notre dame over the exploits gander subzones along the south eastern side of the central mobile belt the silurian ganderian deformational event corresponds to the north north east sinistral transcurrent accretion of the avalon composite terrane microcontinent over the gander exploits zones along the south eastern half of the orogen the late silurian middle devonian acadian deformation event corresponds to the westerly accretion of the meguma terrane intradeep or continental rise over the avalon composite terrane affecting the entire orogen the late devonian carboniferous and permian acadian alleghanian deformational events correspond to the east west convergence between laurentia and gondwana continent continent collision

radiocarbon in dissolved organic and inorganic carbon of the arctic ocean publications geophysical research letters research letter 10 1002 2016gl072138 key points doc in the deep eurasian basin appears to contain at least 8 bomb c modern doc appears to be selectively lost in the beaufort sea and slope water a relationship between doc c and total hydrolysable amino acids in the beaufort suggests that chemical composition controls doc cycling supporting information supporting information s1 correspondence to e r m druffel edruffel uci edu citation druffel e r m s grif n c s glynn r benner and b d walker 2017 radiocarbon in dissolved organic and inorganic carbon of the arctic ocean geophys res lett 44 doi 10 1002 2016gl072138 received 28 nov 2016 accepted 13 feb 2017 accepted article online 15 feb 2017 radiocarbon in dissolved organic and inorganic carbon of the arctic ocean e r m druffel 1 s grif n 1 c s glynn 1 r benner 2 and b d walker 1 department of earth system science university of california irvine california usa 2 marine science program university of south carolina columbia south carolina usa abstract dissolved organic carbon doc in the ocean is thousands of 14 c years old yet a portion of the doc cycles on much shorter time scales days to decades we present 14 c measurements of doc in the arctic ocean and estimate that 8 of the doc in the deep eurasian basin contains bomb 14 c while this is a limited data set there appears to be selective loss of modern doc in the surface and halocline waters of the open beaufort sea versus the beaufort slope at one of the beaufort sea stations there is a linear relationship between doc 14 c values and previously measured total hydrolysable amino acid concentrations as reported by shen et al 2012 indicating that deep doc contains small amounts of bioavailable doc the 14 c data show that not all of the deep doc is recalcitrant 1 introduction the arctic ocean has a large continental shelf region and the largest input of freshwater per unit volume of any ocean dissolved organic carbon doc in surface waters of the arctic is the highest of any ocean due to the large ux of terrigenous doc from arctic rivers amon et al 2012 benner et al 2005 hansell et al 2004 this ux of doc is expected to increase as the earth continues to warm caus ing release of organic c from expansive arctic permafrost watersheds anderson and amon 2015 benner et al 2004 there are four main water masses in the arctic ocean 1 polar surface water 2 halocline water 30 200 m 3 atlantic derived water 200 800 m and 4 deep atlantic water polar surface water is cold and fresh having been derived from arctic rivers and sea ice melt the halocline water is formed on the continental shelves from freezing and brine release and is laterally advected into the arctic basin aagaard et al 1981 water from the paci c ocean ows into the beaufort sea between 75 and 100 m depth upper halocline water while water from the atlantic ocean enters from the fram strait and barents sea lower halocline water the beaufort sea in the southern canadian basin and eurasian basin are separated by the lomonosov ridge whose sill depth is about 1500 m keeping the deep waters of the canada basin and beaufort sea relatively isolated ostlund et al 1987 figure 1 radiocarbon provides quantitative information on the time scale of doc cycling in the global ocean though the existing data are sparse the available 14 c ages of doc reveal that the difference between the average prebomb 1000 m depth and slope bottom depth from 100 to 1000 m and the eurasian basin to evaluate the distribution and cycling of doc in the arctic ocean we estimate that 8 of the doc in the eurasian basin is of postbomb origin we nd that doc concentrations and 14 c values in the upper beaufort sea and slope are linearly correlated with salinity samples from one station in the beaufort sea has total hydrolysable amino acid measurements shen et al 2012 that are strongly correlated with doc 14 c values which indicates that deep doc contains little bioavailable doc radiocarbon in the arctic ocean

ocean acidification and biologically induced seasonality of carbonate mineral saturation states in the western arctic ocean calcium carbonate caco3 mineral saturation states for aragonite aragonite and calcite calcite are calculated for waters of the chukchi sea shelf and canada basin of the western arctic ocean during the shelf basin interactions project from 2002 to 2004 on the chukchi sea shelf a strong seasonality and vertical differentiation of aragonite and calcite saturation states was observed during the summertime sea ice retreat period high rates of phytoplankton primary production and net community production act to increase the aragonite and calcite of surface waters while subsurface waters become undersaturated with respect to aragonite due primarily to remineralization of organic matter to co2 this seasonal phytoplankton carbonate saturation state interaction induces strong undersaturation of aragonite aragonite 10 the seasonal aragonite undersaturation of waters observed on the chukchi sea shelf is likely a recent phenomenon that results from the uptake of anthropogenic co2 and subsequent ocean acidification with seasonality of saturation states superimposed by biological processes these undersaturated waters are potentially highly corrosive to calcifying benthic fauna e g bivalves and echinoderms found on the shelf with implications for the food sources of large benthic feeding mammals e g walrus gray whales and bearded seals the benthic ecosystem of the chukchi sea and other arctic ocean shelves is thus potentially vulnerable to future ocean acidification and suppression of caco3 saturation states

lithostratigraphy and geochemistry of the cottrells cove group buchans roberts arm volcanic belt new constraints for the paleotectonic setting of the notre dame subzone newfoundland appalachians new sedimentological geochemical and geochronological data from the cottrells cove group in central newfoundland provide important constraints on the nature of the notre dame subzone its tectonic setting and the history of the laurentian margin during the early ordovician the cottrells cove group forms the eastern extension of the roberts arm group and correlates with the chanceport group on new world island it is represented by two volcano sedimentary formations that occur in a complex thrust stack the fortune harbour formation consists of calc alkalic island arc lavas followed by a 1250 m thick succession of volcaniclastic deposits radiolarian cherts and calc alkalic mafic flows which were deposited in a back arc basin plain setting the volcaniclastic deposits include felsic tuff which has a u pb zircon age of 484 f 2 ma and an inheritance component of 2517 f 26 ma these new u pb and nd isotope data suggest that the island arc back arc volcanism and sedimentation in the notre dame subzone developed in the vicinity of continental margin and approximately 10 ma earlier than has previously been established the moores cove formation is undated but contains boulders of calc alkalic basalt and is presumed to be at least in part younger than the fortune harbour formation tholeiitic lavas together with associated radiolarian cherts and volcaniclastic deposits constitute the basal part of the moores cove formation and may have been deposited in a back arc environment synchronously with some parts of the fortune harbour formation they are conformably followed by an over 1200 m thick coarsening upward succession of lower slope and submarine fan deposits the polymictic flysch containing clasts of island arc basalt accompanied by other volcanic plutonic ultramafic and sedimentary detritus may record middle or upper ordovician uplift and erosion of obducted arc back arc volcano sedimentary sequences and their ophiolitic substrate

application of a three dimensional ray tracing technique to global p pp and pdiff traveltime tomography summary a 3 d ray path tracing algorithm was successfully applied to global p wave traveltime tomography the inversion was conducted iteratively using the resultant p wave velocity model as the initial model for the subsequent iteration the lsqr method was adopted to solve a large and sparse system of equations this iteratively linearized inversion with 3 d ray tracing increased wave speed anomalies located heterogeneities better and reduced smearing as compared to those derived from a conventional one step inversion using 1 d ray tracing although the general pattern of velocity anomalies was similar a major difference was found in the lowermost mantle where the departure of a ray path from the great circle path tends to be in general greatest in particular a pronounced high velocity anomaly develops beneath the indian ocean a feature not obvious in the result of 1 d inversion the final p wave velocity model was obtained by including reported pp and pdiff traveltime data the addition of the pp data sharpened the images and enhanced velocity anomalies in the upper mantle especially at latitudes above 45 of the northern hemisphere the addition of the pdiff data sharpened and amplified velocity anomalies in the lowermost mantle in general

southwest new world island stratigraphy new fossil data new implications for the history of the central mobile belt newfoundland the identification of fossils from 16 new localities on southwestern new world island has resulted in the refinement and simplification of local stratigraphy and in the correlation of rock units across an intensely deformed area complex stratigraphic classifications of earlier workers are replaced by a simpler scheme consisting of four formations the summerford formation oldest rogers cove formation sansom formation and goldson formation mclange units are fault related and cannot be included in the stratigraphy fossil and lithological data provided here confirm previous indications that the rocks of the summerford formation are the remains of a long lived volcanic island complex this complex is overlain by a markedly diachronous coarsening upwards sequence of marine clastic sediments now represented by the rogers cove sansom and goldson formations the new stratigraphic data combined with structural evidence indicate that the stratigraphy is repeated across several bedding parallel faults significant diachroneity of formation boundaries and the absence of syndepositional high angle faults suggest deposition in one large rnid paleozoic basin rather than in a number of small dynamic basins

mid 1980s distribution of tritium 3he 14c and 39ar in the greenland norwegian seas and the nansen basin of the arctic ocean abstract the distributions of tritium 3 he 14c and 39ar observed in the period between 1985 and 1987 in the greenland norwegian seas and the nansen basin of the arctic ocean are presented the data are used to outline aspects of the large scale circulation and the exchange of deep water between the greenland norwegian seas and the nansen basin additionally semi quantitative estimates of mean ages of the main water masses found in these regions are obtained apparent tritium 3 he ages of the upper waters depth 1 500m depth of the greenland norwegian seas show apparent tritium 3 he ages between about 17 years in the greenland sea and 30 years in the norwegian sea 39ar based estimates of the nansen basin intermediate deep and bottom water ages are 91 26 23 161 50 44 and 277 33 31 years for arctic intermediate water aiw eurasian basin deep water ebdw and eurasian basin bottom water ebbw respectively within the errors age estimates of ebdw and ebbw based on 14 c tritium correlations are consistent with those derived from 39ar 163 to 287 years for ebdw and 244 to 368 years for ebbw a quantitative evaluation of the data in terms of deep water formation and exchange rates based on box model calculations is presented in an accompanying paper

delay time tomography of the upper mantle below europe the mediterranean and asia minor summary the method of linearized delay time tomography is applied to retrieve the p velocity heterogeneity of the upper mantle in central europe the mediterranean and asia minor the upper mantle is parametrized in slowness cell functions with lateral dimensions of 1 the model parametrization includes event mislocation vectors and station delay time corrections in all 20 000 parameters describe the model delay time data selected from the isc data base 1964 1982 from regional events and from stations up to 90 of epicentral distance are used about 18 000 events and 937 stations contributed nearly 500 000 delay times we discuss the tomographic method the data processing the cell model employed the computation of the ray geometry the use of composite rays in tomography and the cell hit count the inversions are performed with two different iterative row action methods lsqr and sirt results obtained with the lsqr method will be shown only the spatial resolution is investigated with sensitivity analyses using two different synthetic velocity models a spike model and a model with harmonically varying velocity anomalies the spatial resolution is estimated to be high on the order of the cell size in the mantle below central and southeastern europe the mapped velocity heterogeneity exhibits primarily low velocities around a depth of 200 km and just above the transition from upper to lower mantle this indicates a systematic deviation of the reference model jeffreys bullen from the radially averaged earth structure which may violate the basic assumptions underlying the linearized approach a posteriori investigation of the data also indicates the presence of a low velocity zone and the existence of strong velocity depth gradients

joint bulk sound and shear tomography for western pacific subduction zones abstract detailed regional body wave tomographic inversion of the western pacific region has been performed using p and s travel times from common sources and receivers with a joint inversion in terms of bulk sound and shear wave speed variations in the mantle this technique allows the separation of the influence of bulk and shear moduli and hence a more direct comparison with mineral physics information the study region is parameterized with cells of side 0 5 to 2 and 19 layers to a depth of 1500 km while the rest of the mantle was parameterized with 5 5 cells with 16 layers between the surface and the core mantle boundary a simultaneous inversion is made for regional and global structures to minimize the influence of surrounding structures on the regional image a nested iterative inversion scheme is employed with local linearization and three dimensional ray tracing through the successive model updates the results of the regional tomographic inversion reveal the penetration of a subducted slab below the 660 km discontinuity at the kurile kamchatka trench while flattening of slabs above this depth is observed in the japan and izu bonin subduction zones on both the bulk sound and shear wave speed images the penetration of a subducted slab down to a depth of at least 1200 km is seen below the southern part of the bonin trench mariana philippine and java subduction zones fast shear wave speed perturbations associated with the subducted slabs down to the 410 km transition zone are larger than the comparable bulk sound perturbations for all these subduction zones except the philippines the bulk sound signature for the subducted slab is more pronounced than for shear in the philippines talaud new guinea solomon and tonga subduction zones where penetration of the slab into the middle mantle is observed variation in the amplitude ratio between bulk sound and shear wave speed anomalies correlates well with the subduction parameters of the descending slab slabs younger than 90 ma at the trench show bulk sound dominance in the upper mantle while older slabs have a stronger shear wave speed signature spreading of the fast shear wave speed zone between 800 and 1000 km is observed in the areas of deep subducted slab penetration but has no comparable expression in the bulk sound images this high velocity feature may reflect physical or chemical disequilibria introduced to the lower mantle by subducted slabs

structure and evolution of lithospheric slab beneath the sunda arc indonesia tomographic imaging reveals seismic anomalies beneath the sunda island arc indonesia that suggest that the lithospheric slab penetrates to a depth of at least 1500 kilometers the sunda slab forms the eastern end of a deep anomaly associated with the past subduction of the plate underlying the mesozoic tethys ocean in accord with previous studies the lithospheric slab was imaged as a continuous feature from the surface to the lower mantle below java with a local deflection where the slab continues into the lower mantle the deep slab seems to be detached from the upper mantle slab beneath sumatra this complex slab structure is related to the tertiary evolution of southeastern asia and the indian ocean region

signature of remnant slabs in the north pacific from p wave tomography summary a 3 d ray tracing technique was used in a global tomographic inversion in order to obtaintomographicimagesofthenorthpacific thedatareportedbythegeophysical surveyofrussia 1955 1997 wereusedtogetherwiththecataloguesoftheinternational seismologicalcenter 1964 1991 andtheusgeologicalsurveynationalearthquake information center 1991 1998 and the recompiled catalogue was reprocessed the final data set used for following the inversion contained 523430 summary ray paths the whole of the earth s mantle was parametrized by cells of 2 2 and 19 layers the large and sparse system of observation equations was solved using an iterative lsqr algorithm asubhorizontalhigh velocityanomalyisrevealedjustabovethe660kmdiscontinuity beneaththealeutiansubductionzone thishigh velocityfeatureisobservedatlatitudes of up to 70 n and is interpreted as a remnant of the subducted kula plate which disappeared through ridge subduction at about 48ma a further positive velocity perturbation feature can be identified beneath the chukotka peninsula and okhotsk sea extending from 300 to 660km depth and then either extending further down to 800km chukotka or deflecting along the 660km discontinuity okhotsk sea this high velocity anomaly is interpreted as a remnant slab of the okhotsk plate accreted to siberia at 55ma

river runoff sea ice meltwater and pacific water distribution and mean residence times in the arctic ocean hydrographic and tracer data collected during ark iv 3 fs polarstern in 1987 arctic91 ib oden and aos94 ccgs louis s st laurent expeditions reveal the evolution of the near surface waters in the arctic ocean during the late 1980s and early 1990s salinity nutrients dissolved oxygen and 18 o data are used to quantify the components of arctic freshwater river runoff sea ice meltwater and pacific water the calculated river runoff fractions suggest that in 1994 a large portion of water from the pechora ob yenisey kotuy and lena rivers did not flow off the shelf closest to their river deltas but remained on the shelf and traveled via cyclonic circulation into the laptev and east siberian seas river runoff flowed off the shelf at the lomonosov ridge and most left the shelf at the mendeleyev ridge arctic91 and aos94 pacific water fraction estimates of upper halocline water the traditionally defined core of the pacific water mass document a decrease in extent compared to historical data the front between atlantic water and pacific water shifted from the lomonosov ridge location in 1991 to the mendeleyev ridge in 1994 the relative age structure of the upper waters is described by using the 3 h 3 he age the mean 3 h 3 he age measured in the halocline within the salinity surface of 33 1 0 3 is 4 3 1 7 years and that for the 34 2 0 2 salinity surface is 9 6 4 6 years lateral variations in the relative age structure within the halocline and atlantic water support the well known cyclonic boundary current circulation

tomographic inversion for three dimensional anisotropy of earth s inner core abstract seismological studies generally suggest that the earth s inner core is anisotropic and the anisotropic structure changes significantly both laterally and with depth previous body wave studies of the inner core have relied on ray tracing or waveform modeling using one dimensional 1d models here we present non linear tomographic inversions of the inner core anisotropy using three dimensional 3d ray tracing spline parameterization and a large collection of pkp differential travel times we adapt a pseudo bending ray tracing pbr method in spherical coordinates for seismic rays that traverse the inner core pkp df phase the method iteratively perturbs each discontinuity point and continuous segment of the ray through 3d earth structure so that its travel time is minimum the 3d anisotropic structure of the inner core is approximated to the first order as 3d heterogeneous but isotropic structure for a given ray the data are corrected using a scaled mantle tomographic model the inner core anisotropy model obtained has the following major features 1 the model has strong hemispherical and depth variation the isotropic velocity in the topmost inner core is greater in quasi eastern hemisphere qeh 40 160 e than in quasi western hemisphere qwh other longitudes the anisotropy is weak in qeh to the depth of 600 700 km below the inner core boundary icb while in qwh the anisotropy increases at much shallower depth about 100 200 km below the icb to about 3 4 then remains at about 2 4 throughout the rest of the inner core 2 the anisotropy form changes abruptly over a depth range of about 150 km at the radius of about 600 km slightly less than half of the inner core radius forming a distinct inner inner core iic the velocity in the iic has maximums at equatorial and polar directions and minimum at an angle of about 40 from the equatorial plane the velocity in the outer inner core oic however changes little for ray directions 0 40 from the equatorial plane 3 despite large variation of the anisotropy the isotropic velocity voigt average throughout the inner core is nearly uniform the results suggest that the oic is likely composed of the same type of iron crystals with uniform chemistry but the iic may be composed of a different type of crystal alignment a different iron phase or a different chemical composition our tests on model parameterization mantle correction and linear and non linear inversion suggest the main features of our model are very robust however fine scale structures are likely to differ particularly in the major transition zones e g in the topmost qwh isotropy to anisotropy between oic and iic change in the form of anisotropy and between qeh and qwh in oic difference in anisotropy strength searches for possible waveform complications from these boundaries need to be aware of the directional dependence and geographical variation to be successful

late middle ordovician olistostrome formation and magmatism along the red indian line the laurentian arc gondwanan arc boundary at sops head newfoundland the sops head complex of badger bay central newfoundland includes olistostromal and tectonized melanges and marks the red indian line the boundary between the peri gondwanan exploits and peri laurentian notre dame subzones of the oceanic dunnage zone basalts in the olistostromal melange preserve peperitic contacts with mudstone and limestone within slumped sedimentary units demonstrating that magmatism was coeval with olistostrome formation conodonts from the limestones date these events as late darriwilian llandeilian middle ordovician in age the conodont fauna consists entirely of north atlantic faunal realm elements suggesting a peri gondwanan or mid iapetan provenance for limestone of the sops head complex basalt geochemistry suggests magmatism in a mature volcanic arc to back arc setting the sops head complex shows similarities in age provenance and stratigraphic setting to the dunnage melange suggesting that the two units are correlative

multiscale seismic tomography and earthquake relocation incorporating differential time data application to the maule subduction zone chile abstract we present a multiscale seismic tomography method incorporating differential time data this is an extension of the double difference tomography method to teleseismic distances using a nested regional global model parameterization it allows inclusion of absolute and differential time data observed at any distance potentially improving resolution of structure in areas where local or regional data are sparse the algorithm named teletomodd is quite flexible and is applicable to a variety of relocation and tomography problems including simultaneously solving for global velocity structure to illustrate the technique we apply it to the maule region of chile where an m w 8 8 earthquake occurred in 2010

adaptive whole earth tomography 1 an approach for seismic tomography is presented which allows the parameterization to be refined during the inversion the objective is to use the data to refine the mesh and the velocity model together and hence both are considered part of the solution some simple rules are used to identify the volumes of a three dimensional model in need of refinement the self adaptive parameterization is applied to an initial mesh built from uniformly distributed spherical triangles and delaunay tetrahedra application of the technique to a typical summary ray p wave arrival time data set shows it to be both feasible and practical for large scale whole earth tomography a noticeable trend in the resulting models as the parameterization is refined is the thinning of the farallon and tethys subduction features imaged in the mid mantle together with an increase in amplitude of the velocity perturbation

middle ordovician conodonts from the buchans group central newfoundland and their significance for regional stratigraphy of the central volcanic belt reply conodonts have been recovered from carbonate clasts within breccia units in the buchans group of central newfoundland the assemblage is characterized by specimens of cordylodus horridus barnes and poplawski and histiodella holodentata ethington and clark these and other species recovered suggest a whiterockian latest arenig early llanvirn age for the clasts this is somewhat older than the whole rock rb sr age of 447 18 ma on volcanics of the buchans group the carbonate clasts are considered to be derived from the area of deposition of the buchans group rather than from some exotic source this interpretation is based on knowledge of local tectonics inferred paleogeogaphy and geographic distribution of the conodont assemblage all other clasts in the breccia units are considered of local origin if the conodonts are of local buchans group origin then they indicate a whiterockian age for the unit in view of this current regional models for the central volcanic belt may require substantial revi

major flux of terrigenous dissolved organic matter through the arctic ocean high latitude rivers supply the arctic ocean with a disproportionately large share of global riverine discharge and terrigenous dissolved organic matter dom we used the abundance of lignin a macromolecule unique to vascular plants and stable carbon isotope ratios 13c to trace the high molecular weight fraction of terrigenous dom in major water masses of the arctic ocean lignin oxidation products in ultrafiltered dom udom 1 000 da from arctic rivers were depleted in syringyl relative to vanillyl phenols s v 0 3 0 5 compared to udom in temperate and tropical rivers s v 0 5 1 2 indicating that gymnosperm vegetation is a major source of terrigenous udom to the arctic ocean high concentrations of lignin oxidation products 83 320 ng l 1 and a depletion of 13c 13c 23 0 to 21 9 in udom throughout the surface arctic ocean indicate that terrigenous udom accounts for a much greater fraction of the udom in the surface arctic 5 33 than in the pacific and atlantic oceans 0 7 2 4 in contrast udom in deep water from the arctic ocean as well as waters from throughout the greenland gyre had relatively low concentrations of lignin oxidation products 24 45 ng l 1 and was enriched in 13c 13c 21 0 to 20 8 terrigenous udom has a relatively short residence 1 6 yr in surface polar waters prior to export to the north atlantic ocean assuming that the bulk of arctic derived dom is compositionally similar to the udom fraction we estimate that 12 41 of terrigenous dom 2 9 10 3 tg c yr 1 discharged by rivers to the arctic ocean is exported to the north atlantic via surface waters of the east greenland current it appears very little terrigenous dom from the arctic is incorporated into north atlantic deep water and distributed globally via deep thermohaline circulation

the palaeogeography of early ordovician iapetus terranes an integration of faunal and palaeomagnetic constraints abstract new and existing fossil data from ireland britain newfoundland and scandinavia emphasize a significant degree of latitudinal variation in biogeographic patterns across the ordovician iapetus ocean platform provinces together with marginal belts and island complexes can be recognised with increasing clarity on the basis of palaeontological information statistical analysis of the distribution patterns of about 70 early ordovician brachiopod genera across some 25 sites using both cladistic and phenetic methods together with a critical analysis of their geological settings combined with current palaeogeographic and palaeomagnetic data reaffirm the existence of the celtic brachiopod province during the early ordovician the majority of sites assigned to the celtic province define a high latitude peri gondwanan belt shadowing the distribution of the low latitude circum laurentian toquima table head faunas rapidly changing ordovician faunal signals across the baltic province and exploits zone of central newfoundland track the cross latitude movement of these terranes from high temperate to near tropical belts during the period new fossil information together with continuing statistical appraisal of an expanding database are providing more accurate and sophisticated models for the dynamics of the iapetus ocean system

biostratigraphy and biofacies of the middle darriwilian ordovician conodonts from the laoshidan section in the western margin of the north china craton abstract middle ordovician conodonts from the sandaokan and zhuozishan formations of the laoshidan section at the western margin of the north china craton consist of 39 identified and six indeterminate species belonging to 21 genera and three taxa left in open nomenclature at both genus and species levels of particular biostratigraphic importance is the presence of morphologically advanced species of histiodella associated with several age diagnostic endemic taxa making it possible to recognize international conodont biozones in the main part of the sequence three histiodella based zones are recognized in the studied section including the histiodella cf holodentata histiodella kristinae and histiodella bellburnensis zones in ascending order they can be directly correlated with the conodont zonations established in western newfoundland canada and tarim western china and compared well with the conodont biozones of baltoscandia and yangtze central china however the same stratigraphic interval on the north china platform is barren of conodonts multivariate statistical studies on these conodonts allow recognition of four conodont biofacies scalpellodus biofacies panderodus biofacies drepanoistodus biofacies and phragmodus biofacies turnovers of the conodont biofacies are related to either sea level changes or mixing of shallow water conodonts due to down slope transportation excluding the effect of the allochthonous conodonts the transgressive regressive patterns demonstrated by the conodont biofacies compare closely to the published sea level curves for the western margin of the north china craton

seismic tomography with p and s data reveals lateral variations in the rigidity of deep slabs abstract regional seismic tomography of the northwest pacific island arcs using p and s wave arrival time data with similar path coverage reveals an oceanic lithospheric slab deflected in the mantle transition zone beneath the izu bonin region in good agreement with the results of earlier tomographic and other seismic studies in the region the s wave images however do not show clearly the deflection of the slab this implies that the stagnant lithospheric slab in the transition zone is more likely a bulk sound structure which is strongly supported by our results from joint inversions for bulk sound and shear wavespeeds for the izu bonin region where trench migration has been reported the properties of the deflected slab lying on top of the 660 km discontinuity show strong bulk sound and weak shear signatures in contrast to the descending slab itself there is an indication in the shear images that a component of the former oceanic lithosphere is penetrating into the top of the lower mantle suggesting that a slab split has occurred

heterogeneity within the subducting pacific slab beneath the izu bonin mariana arc evidence from tomography using 3d ray tracing inversion techniques distinct zones of seismic heterogeneity along the izu bonin mariana arc have been investigated using complimenting regional bulk sound shear wave speed and p wave tomographic images the distribution of seismic anomalies and the inferred geometry of the subducting pacific plate have been modelled in unprecedented detail using joint tomography and new p wave model using a 3d inversion algorithm the use of 3d ray tracing techniques and smaller cell parameterizations have greatly enhanced the resolution of gradients therefore the models show much more detail about the structure and physical properties of the subduction zone the well defined features from the multiple wave speed images are used to elucidate the distinct morphology change between slab beneath the izu bonin horizontal slab and mariana vertical arcs and the distribution of physical properties in the mantle and the subducting oceanic lithosphere changes in physical properties within the slab tear at the southern end of the izu bonin arc identified as a bgap or thinningq in the tomographic images could be the result of the distortion of the pacific plate as its shape transforms between near horizontal to near vertical a decrease in the rigidity and strength of the lithosphere the subduction of the marcus necker ridge change in subduction velocity or a combination of all these factors strong slow anomalies exist both in the mantle wedge above and below the slab beneath the izu bonin arc but are not present beneath the mariana arc at the junction between the izu bonin and mariana arcs it appears that the there are two separate pieces of the pacific plate the torn slab north of 268 n and a buckled near vertically dipping slab south of the tear the transition between the two distinct slab morphologies coincides with the location of the ogasawara plateau and the trench d 2005 elsevier b v all rights reserved

stagnant slab a review a stagnant slab is a subducted slab of oceanic lithosphere subhorizontally deflected above across or below the 660 km discontinuity this phenomenon has now been widely recognized beneath subduction zones around the circum pacific and in the mediterranean collaboration of seismic and electromagnetic observations mineral physics measurements and geodynamic modeling has begun to provide a consistent picture of stagnant slab

seismic heterogeneity in the mantle strong shear wave signature of slabs from joint tomography abstract the primary source of information on heterogeneity within the earth comes from seismic tomography a powerful tool for examining the character of heterogeneity comes from the comparison of images of bulk sound and shear wavespeed extracted in a single inversion since this isolates the dependencies on the elastic moduli however particularly in such multi parameter inversions there are many hidden facets which can have a strong influence on the results such as the weightings between parameters and in the misfit functions joint inversion with restricted data sets giving comparable cover for p and s waves provides useful checks on more inclusive studies and can provide relatively high resolution in some areas the relative behaviour of bulk sound and shear wavespeed can provide a useful guide to the definition of heterogeneity regimes for subduction zones a large part of the tomographic signal comes from s wavespeed variations in the upper mantle and transition there can be significant bulk sound speed contributions for younger slabs and in stagnant slabs associated with slab roll back for subducted oceanic lithosphere older than about 90 ma shear wavespeed variations nearly always are dominant and so the p wave images are controlled by shear modulus variations the narrow segments of fast wavespeeds in the depth range 900 1500 km in the lower mantle are dominated by s variations with very little bulk sound contribution deep in the mantle there are many fast features without obvious association with subduction in the last 100 ma which suggests long lived preservation of components of the geodynamic cycle

lower to middle ordovician evolution of peri laurentian arc and backarc complexes in iapetus constraints from the annieopsquotch accretionary tract central newfoundland the annieopsquotch accretionary tract in newfoundland is composed of a series of west dipping structural panels each containing remnants of ophiolitic and arc backarc complexes of laurentian affinity formed during the ordovician closure of iapetus panels were transferred from an upper plate to a lower plate setting during their middle to late ordovician accretion to the laurentian margin and become progressively younger eastward geochronological data indicate a complex and rapid history of generation and accretion of peri laurentian suprasubduction zone rocks the rapid changes in tectonic environments and the complexity of the relationships are analogous to the complex arc backarc relationships observed in the western pacific today the recognition of the peri laurentian provenance of these units based on stratigraphy geochronology isotopes and geochemistry defines the position of the red indian line the fundamental suture zone in the northern appalachians but more importantly enables the development of a realistic tectonic model for the annieopsquotch accretionary tract involving both thrust and sinistral transcurrent displacements the oldest and most inboard unit in the annieopsquotch accretionary tract is the annieopsquotch ophiolite belt ca 480 ma which marks the initiation of subduction outboard of the laurentian margin the lloyds river ophiolite complex ca 473 ma preserves a fragment of younger more mid ocean ridge like backarc oceanic crust than the adjacent structurally overlying annieopsquotch ophiolite belt the lloyds river ophiolite complex originated as a backarc to the buchans group ca 473 ma ensialic bimodal calc alkaline arc the panels containing the annieopsquotch ophiolite belt and lloyds river ophiolite complex were stitched and overlain by ensialic arc rocks of the otter pond complex ca 468 ma immediately after their accretion to composite laurentia together with the structurally underlying buchans group the youngest structurally lowest two panels comprise the elements of the red indian lake group 465 460 ma which record the opening of a backarc basin and the subsequent establishment of a bimodal ensialic calc alkaline arc sequence the observed relationships indicate that the annieopsquotch accretionary tract was generated above a single west dipping subduction zone outboard of the laurentian margin over 20 m y accretion mainly took place in two stages at ca 468 and 450 ma which correspond with the collision between laurentia and the dashwoods ribbon continent and the collision with the peri gondwanan victoria arc along the red indian line respectively both collisions form part of the taconic orogeny the latter late ordovician collision terminated the relatively rapid closure of the main iapetan tract the proposed model is similar to the correlative tracts in the british and irish caledonides and may encourage a new look at the new england appalachians

linkages among runoff dissolved organic carbon and the stable oxygen isotope composition of seawater and other water mass indicators in the arctic ocean 1 flow weighted dissolved organic carbon doc concentrations and 18o values were determined from major arctic rivers specifically the ob yenisey lena kolyma mackenzie and yukon during 2003 2004 these data were considered in conjunction with marine data for doc 18o values nutrients salinity and fluorometric indicators of doc obtained during sampling at the shelf basin boundary of the chukchi and beaufort seas on the basis of these data freshwater in the sampled marine waters is likely derived from regional sources such as the mackenzie the bering strait inflow and possibly eastern siberian rivers including the kolyma or the lena but not rivers farther west in the eurasian arctic freshwater from melted sea ice is insignificant over annual cycles although melted sea ice was a locally dominant freshwater component following summer sea ice retreat in 2002 doc concentrations were correlated with the runoff fraction with an apparent meteoric water doc concentration of 174 1 m this is lower than the flow weighted concentrations measured at river mouths of the five largest arctic rivers 358 to 917 m indicating removal of doc during transport through estuaries shelves and in the deep basin flow weighted doc concentrations in the two largest north american arctic rivers the yukon 625 m and the mackenzie 358 m are lower than in the three largest eurasian arctic rivers the ob 825 m the yenesey 858 m and the lena 917 m a fluorometer responding to chromophoric dissolved organic matter cdom was not correlated with doc concentrations in pacific influenced surface waters unlike previous observations in the atlantic layer nutrient distributions concentrations and derived ratios suggest the cdom fluorometer may be responding to the release of chromophoric materials from shelf sediments shipboard incubations of undisturbed sediment cores indicate that sediments on the bering and chukchi sea shelves are a net source of doc to the arctic ocean

on the possibility of a folded crustal layer stored in the hydrous mantle transition zone abstract previous numerical studies of mantle convection focusing on subduction dynamics have indicated that viscosity rheological heterogeneity in the subducting plates and the surrounding mantle may have a primary effect on the behavior of subducting plates meanwhile the existence of a low viscosity layer lvl beneath the mantle transition zone mtz has been suggested by several geodynamic studies we investigated the effects of a rheologically weaker crustal layer in a hydrous wet mtz with an underlying lvl on the behavior of subducting plates and determined the trace of crustal material using a numerical simulation model of subduction dynamics in three dimensional regional spherical geometry the combined effect of a rheologically weaker crustal layer and an lvl beneath the mtz produces characteristic transient behavior of the crustal layer whose trace shows a folded loop like feature in the wet mtz along with a folded subducting slab in the lvl this phenomenon is caused by mechanical interaction of the crustal layer with an upward positive bending force due to the main body of the subducting slab folding in the lvl and an enhanced downward negative buoyancy force due to an increase in density from the garnet to the post garnet phase of crustal material the transiently folded crustal layer behind the root of the stagnant slab is also observed this result is consistent with seismological evidence suggesting a piece of subducted oceanic crust in the uppermost lower mantle beneath the subducting slab in the mariana trench over half of the subducted crust is temporarily stored in the mtz however this stored crustal material begins to penetrate into the lower mantle within 10 myr a relatively short timeframe relative to the overturn time of mantle convection eventually most of the crustal material is entrained into the lower mantle but a non negligible portion remains stored in the mtz for 50 myr after the beginning of the accumulation of subducted crust in the mtz

spatial and temporal evolution of the subducting pacific plate structure along the western pacific margin 1 tomographic images of the subducting pacific plate beneath the izu bonin mariana arc illustrate a progression of geometries from shallow dipping to vertical from north to south along the arc recent advances in technology and inversion techniques have improved resolution of slab structure beneath the western pacific island arcs but reasons for the variation in geometry and morphology are still poorly understood by comparing high resolution tomographic images of the western pacific and updated paleogeographic reconstructions we are able to link the spatiotemporal evolution of the subducting pacific plate back to the mid miocene we have reconstructed tectonic motions along the kurile japan izu bonin mariana arc system and the ryukyu arc to provide an independent additional interpretation of the subducting pacific plate using the most current plate motion data we then investigate the plausibility of our model and three other proposed models based on the interpreted slab structure from tomographic images the new reconstruction agrees with the basic characteristics of former trench retreat models but illustrates the importance of the collision of the ogasawara plateau with the trench in the mid miocene and its subsequent effect on the slab structure at depth and the impact of other aseismic ridge collisions along the plate boundary the combination of evidence in changed physical properties imaged with tomography and the current interpreted slab morphology can be analyzed with the past plate motions to understand subduction zone processes

hydrographic changes in the canada basin of the arctic ocean 1979 1996 hydrographic surveys of the southern canada basin have been conducted in winter almost annually since 1979 coverage has extended 100 200 km beyond the shelf to water depths of 2000 3000 m water properties in the upper 1500 m have fluctuated over intervals of a few years and progressive changes have taken place during the 17 years of this study at depths below the warm core of the atlantic layer water is warmer and fresher now than in the early 1980s these changes reflect a thickening of the warm core at its lower boundary by more than 100 m the maximum temperature of the atlantic water has decreased by 0 06 c and the salinity at the maximum has decreased by 0 027 above the atlantic layer the lower halocline 34 5 isohaline has cooled by 0 12 c a change which may indicate that ventilation of this level on the european side of the arctic has been more effective in recent years a good correlation between temperature fluctuations on the 34 5 isohaline and depth fluctuations of the lower 0 c isotherm suggests common forcing of both parameters variation in the flow through the barents sea into the arctic is proposed as that common influence the upper halocine has warmed by 0 15 c on the 33 5 isohaline this trend could be a consequence of decreasing ventilation of the upper halocline over the broad shallow shelves on the pacific side of the arctic ocean and may be related to the decrease in the strength of the siberian high during the same time the net result of changes in the hydrography of the canada basin has been an increase of 0 2 gj m 2 in stored sensible heat an amount sufficient to melt about 0 7 m of sea ice the bulk of the increase results from the thickening of the atlantic layer below 500 m

subducting slabs stagnant in the mantle transition zone the p wave velocity structure beneath the western pacific is found from the international seismological center first arrival data special attention was paid to the deep structure beneath the wadati benioff zone we discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks this way of discretization minimizes a problem with tomographic studies of regional scale difficulty in making corrections for the effects outside the region of interest our solution is iterative with the alternate step of the relocation of earthquakes using the whole mantle model of inoue et al 1990 as a starting model a first order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model the essential result depends little on whether the reference spherical model is smooth or discontinuous near 400 and 670 km depths we examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere the resolution is depth dependent but in general good enough to see the slab configuration beneath the southern kurile japan izu bonin arcs and the java arc it is relatively poor beneath the northern kurile and mariana arcs the seismic image of subducting slab beneath the southern kurile to bonin arcs bends to subhorizontal near the leading edge of the wadati benioff zone and extends continentward over a distance of more than 1000 km the subhorizontal portion of the slab connects a high velocity blob to the bottom that reaches a depth of at least 800 km across the 670 km discontinuity under the japan arc although the image of the java slab directly penetrates the 670 km discontinuity it then bends to a shallow dip with a considerable spread reaching a depth of about 1200 km these results suggest that descending slabs of lithosphere in the western pacific tend to be stagnant in the transition zone under a subtle control of the 670 km discontinuity although stagnant slab materials eventually descend into the lower mantle they no longer maintain their original configuration below the 670 km discontinuity

synoptic flow and density observations near an arctic shelf break analyses of data from three shipborne surveys describe the quasi synoptic density and velocity fields near barrow canyon alaska the canyon parallels the northwestern coast of alaska and contains three different water masses these are 1 warm and fresh alaskan coastal waters that originate from the bering strait 2 cold and moderately salty waters that originate from the chukchi shelf and 3 warm and salty waters that originate from the atlantic layer of the arctic ocean a halocline separates the chukchi shelf and atlantic layer waters the halocline slopes upward into the canyon where it is then twisted to slope across the wide canyon an intensification of the beaufort gyre near the shelf break just seaward of barrow canyon raises the halocline more than 100 m toward the surface locally upwelling favorable winds raise the arctic halocline which thus is ventilated within barrow canyon adjacent to the coast in the absence of winds the halocline slopes acrosscanyon in the thermal wind sense due to a northward flowing coastal current velocity measurements from a towed acoustic doppler current profiler reveal a northward flowing jet that transports about 0 3 sv sv 106 kg m23 of bering sea summer water into the arctic ocean at speeds that exceed 0 7 m s21 total northward transports through the canyon exceed 1 0 sv the warm waters of this coastal current supply more than 100 w m22 of heat to the atmosphere the jet separates both from the bottom and from the coast hence a laterally and vertically sheared jet forms which breaks into three branches at about 71 88n latitude

on seismological reference models and the perceived nature of heterogeneity a key ingredient in understanding earth structure is the integration of seismological information with results from mineral physics for both the dominant radial dependence of material properties and the 3d structure revealed by seismic tomography in each case an important role is played by reference models for the internal structure of the earth originally constructed to meet seismological needs representations of the travel times of seismic phases are required for the location of seismic events and these have been supplemented by models that match the frequencies of the free oscillation of the earth which have played a major role in characterising seismic sources through the centroid moment tensor derived from long period records parameterised models were introduced to combat the computational demands of inversion and have been extensively used however in such models e g prem the form of the seismic parameters is prescribed to have a functional behaviour such as a cubic based on mathematical convenience rather than physical requirements any 1d models face the challenge of the significant lateral heterogeneity at the top and bottom of the mantle as well as the more subtle variations in between it may well be possible to capture the long wavelength components of 3d heterogeneity but the nature of available data sources means that it will be difficult to achieve comparable p and s definition for the whole mantle in many circumstances reference models are used for comparison with models constructed for different data sets it is then best that e g a cratonic reference model is used to judge results from cratons regionalisation of travel time observations provides a means of constructing such reference models for a broad range of tectonic environments when coupled with suitable path corrections it is possible to make a good account of regional 2d variations it is desirable that reference models used for interpretation of seismic tomography are tied as clearly as possible to mineral physics results with a representation based on the bulk modulus k shear modulus g and density rather than just the p and s wavespeeds comparator models for different mineral compositions and temperature regimes have the potential to aid the interpretation of tomographic images particularly in the separation of the influences of temperature and composition

structural evolution of a transpression zone in north central newfoundland abstract a dextral transpression zone in notre dame bay north central newfoundland was active in middle to late silurian times following the closure of a marginal basin the deformation in the transpression zone was complex and involved several generations of structures deformation was initially distributed over wide low strain zones through the formation of a penetrative regional cleavage with steepening and overturning of the strata the orientation of the sequence was favorable for strike slip bedding parallel movement and the deformation became more efficiently accommodated by shear within the incompetent lithologic horizons forming localized shear zones in high strain zones the sheared incompetent horizons define a belt of melange the boones point complex centered on the contact between a volcanic island arc terrane to the north and a marginal basin terrane to the south two cleavages with similar orientation and morphology were generated at different times during the structural evolution of the transpression zone one of the cleavages is regional in distribution and is transposed by the shear zones folds with no axial planar cleavage but a cleavage cutting obliquely across their hinges are reported they have the geometry of transected folds but are clearly the result of overprinting by a younger generation of cleavage

the conodont paroistodus horridus barnes and poplawski as a new biostratigraphical tool for the middle darriwilian ordovician abstract this contribution develops an analysis on the conodont paroistodus horridus barnes and poplawski from several argentine precordilleran sections from these collections we have established that p horridus occurs from the lenodus crassus zone to the amorphognathus tvaerensis zone darriwilian to early sandbian this study recognizes several primary morphological features of p horridus which vary through the darriwilian and three evolutionary morphological types can be identified early form middle form with two stages and late form the co occurrence of index conodonts with the successive stages of this evolutionary development allowed a significant biostratigraphical value to be assigned for each different morphological type of p horridus based on this information we propose a detailed biostratigraphical control and correlation with equivalent strata from canada china australia united states norway and western central asia

improving depth resolution of teleseismic tomography by simultaneous inversion of teleseismic and global p wave traveltime data application to the vrancea region in southeastern europe summary over the years teleseismic tomography has developed to be a sophisticated method to study the earth s upper mantle on a regional scale using data from tomographic experiments with temporary station networks one faces some inherent problems which include limited resolution at depth and artefacts due to a plane wave approximation at the bottom of the model volume simultaneous inversion of dense regionally recorded teleseismic and global p wave traveltime data provides an opportunity to overcome these specific problems the calculation of the entire ray path using a 3 d ray tracing algorithm and a non linear iterative inversion scheme allow to localize heterogeneities in the earth s mantle and to improve resolution at depth application of a variable parametrization scheme provides not only a regional high resolution model but additionally allows to include a priori constrained structures such as a crustal model derived from independent studies we investigated the effect of different inversion strategies for a priori constrained model parameters and found that for upper mantle studies one must allow further perturbation of the known velocity structure during inversion to avoid artefacts down to the mantle transition zone we apply this approach to the romanian vrancea region in southeastern europe the results show a near vertical narrow high velocity body underneath that region extending down to 280 km depth approximately outlining the narrowly spaced seismogenic volume and a deeper differently oriented positive anomaly coupled to the shallower segment at the latter s southwestern edge at north northwest and west of the vrancea region we find an extended region of decreased seismic p wave velocity down to 200 km depth being interpreted as a shallow lithosphere asthenosphere boundary and asthenospheric mantle flow due to lateral migration of the high velocity body from synthetic reconstruction tests we found that inversion of the combined data set of regionally recorded teleseismic and global traveltime data enhances resolution up to depths greater than could be resolved by the teleseismic data alone

the origin and significance of the delaney dome formation connemara ireland dalradian meta sediments of the laurentian margin and mafic intrusions thereof in sw connemara ireland tectonically overlie meta rhyolites of the delaney dome formation the two units are separated by the mannin thrust a new u pb age of 474 6 5 5 ma shows that the delaney dome formation is a temporal equivalent of arc volcanic rocks preserved in the adjacent south mayo trough the tourmakeady volcanic group erupted during the collision of an oceanic island arc with the laurentian margin in the grampian orogeny new rare earth and high field strength element data show that the delaney dome formation and tourmakeady volcanic group are chemically similar and arc like in character this suggests that the delaney dome formation is an along strike equivalent of the tourmakeady group strike slip faulted south of the south mayo trough during or after the grampian orogeny further correlation of these units with northern appalachian rhyolites is also possible the delaney dome formation is an extrusive temporal equivalent of intrusions that penetrate the connemara dalradian thus movement along the mannin thrust brought mid crustal plutons and dalradian country rocks tectonically above the extrusive volcanic sequence the mannin thrust is identified as a major imbricating structure within a continental arc but not a terrane boundary

geochemistry u pb geochronology and genesis of granitoid clasts in transported volcanogenic massive sulfide ore deposits buchans newfoundland1 the buchans group central newfoundland represents an ordovician continental bimodal calc alkaline arc sequence that hosts numerous volcanogenic massive sulfide vms occurrences including both i

interconnection of ferro periclase controls subducted slab morphology at the top of the lower mantle abstract the electrical conductivity of mantle rocks during phase transformation from ringwoodite to silicate perovskite and ferro periclase was measured at 25 gpa and various temperatures ranging from 1300 to 1900 k the electrical conductivity was high at the initial stage of annealing suggesting that ferro periclase forms interconnected layers in aggregates of silicate perovskite and ferro periclase that are representative of lower mantle rock at 1900 k the electrical conductivity quickly decreased and reached that of silicate perovskite suggesting the cut off of the interconnected ferro periclase because of rounding of crystals below 1700 k the high conductivity values were maintained for experimental duration the interconnection of ferro periclase which has a lower viscosity than silicate perovskite can be maintained in a cold descending slab over geological time scales 1 my indicating that a colder slab is less viscous than the warmer mantle surrounding it the low viscosity slab can be prevented from penetrating into the deeper part of the lower mantle by the high viscosities encountered at a depth of 1000 km referred to as the viscosity hill that cause stagnation at this depth as observed by seismic tomography

mantle structure beneath indonesia inferred from high resolution tomographic imaging we investigated mantle structure beneath the indonesian region by means of tomographic inversions of traveltime residuals of direct p and the surface reflected depth phases pp and pwp the hypocentres and phase data used in the inversions were derived from the reprocessing of data reported to international data centres which include data from the australian skippy project we used more than 6 0 10 data from more than 50 000 globally distributed earthquakes recorded at a subset of nearly 3000 seismological stations worldwide the use of depth phases improved the sampling of the upper mantle structure in particular beneath the back arc regions the mapping of distant aspherical mantle structure into the study region was minimized by combining a high resolution regional with a low resolution global inversion the inversion was linearized around the ak135 reference velocity model and a combination of minimum norm and gradient damping was applied to constrain the solution inversion of different subsets of the data and test inversions of synthetic data indicate that resolution is sufficient to substantiate the conclusions pertinent to the complex large scale structure of the subducted slab beneath the indonesian archipelago the tomographic images confirm previous evidence for regional slab penetration into the upper part of the lower mantle but suggest a more complex trajectory of mantle flow beneath indonesia the implied lateral variation in the shape of the upper mantle slab is generally in good agreement with inferences from seismicity the data reveal a seismic anomaly beneath the sunda arc which is detected to at least 1500 km in depth and forms the eastern end of a deep anomaly associated with the past subduction of lithosphere of the mesozoic tethys ocean below java the lithospheric slab is probably continuous from the earth s surface to the lower mantle but beneath sumatra the deep slab seems to be detached from the seismogenic slab the high resolution images suggest that the subducted slab is deflected in the transition zone beneath the banda arc and that the descending slabs form a spoon shaped structure north of the banda sea we detect the two opposing subducted slabs of the molucca sea plate this is consistent with previous studies but our images suggest that the westward subduction has a significantly steeper dip than the eastward subduction slab structure beneath the banda and molucca seas is explained in the context of the continent arc collision between australia and the southeast indonesian island arc and the arc arc collision between sangihe and halmahera inversion of traveltime residuals of direct s phases a novelty for this region largely confirms the inferences from the p wave data even though less detail is resolved

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

evolution of mantle structure beneath the northwest pacific evidence from seismic tomography and paleogeographic reconstructions 1 plate motions and subducting slab morphology are intricately connected and through the integration of seismicity tomographic images and relative plate motions the evolution of mantle structure can be interpreted tomographic images of p wave shear wave speed and bulk sound speed perturbations of the northwest pacific region have been interpreted to define the extent and geometry of the subducting pacific plate we have found that the subducted pacific plate beneath the japan and kurile arcs is coherent but is very complex at the junction of the two arcs near the hokkaido corner as the slab subduction angle decreases from north to south while the slab thickens the pacific slab beneath the japan arc is slightly thinner and subducting through the upper mantle at a less steep angle than the slab beneath the kurile arc as the slab reaches the 660 km discontinuity it becomes stagnant and lies in a horizontal position on top of the transition zone both beneath the izu and japan arcs in contrast the slab beneath the kurile arc is subducting at a steeper angle and penetrates through the transition zone into the lower mantle the difference in slab morphology appears to be due to a combination of change in dip of the subducting plate and the convergence velocity of the pacific plate along the margin a new paleogeographic reconstruction of northeast asia was assembled to evaluate the plate motions that could explain the foundation of the current slab morphology the plate reconstruction was based on euler pole motions of the pacific philippine amurian okhotsk and north american plates relative to stable eurasia plate the new tectonic model illustrates the collision of the japan and kurile arcs the opening of the kurile basin disparity in pacific plate velocities along the arc and different rates of trench retreat along the izu japan and kurile segments of the western pacific margin the plate motion model was interpreted in conjunction with the physical properties of the mantle imaged with the p wave and joint tomography to assess the evolution of the pacific plate morphology since the mid miocene and to provide constraints on the plausible plate motions in the region

strong hydrographic controls on spatial and seasonal variability of dissolved organic carbon in the chukchi sea abstract a detailed analysis of dissolved organic carbon doc distribution in the western arctic ocean was performed during the spring and summer of 2002 and the summer of 2003 doc concentrations were compared between the three cruises and with previously reported arctic work concentrations of doc were highest in the surface water where they also showed the highest degree of variability spatially seasonally and annually over the canada basin doc concentrations in the main water masses were 1 surface layer 71 4 m ranging from 50 to 90 m 2 bering sea winter water 66 2 m ranging from 58 to 75 m 3 halocline layer 63 3 m ranging from 59 to 68 m 4 atlantic layer 53 2 m ranging from 48 to 57 m and 5 deep arctic layer 47 1 m ranging from 45 to 50 m in the upper 200 m doc concentrations were correlated with salinity with higher doc concentrations present in less saline waters this correlation indicates the strong influence that fluvial input from the mackenzie and yukon rivers had on the doc system in the upper layer of the chukchi sea and bering strait over the deep basin there appeared to be a relationship between doc in the upper 10 m and the degree of sea ice melt water present we found that sea ice melt water dilutes the doc signal in the surface waters which is contrary to studies conducted in the central arctic ocean

toward quantifying uncertainty in travel time tomography using the null space shuttle 1 the solution of large linear tomographic inverse problems is fundamentally non unique we suggest to explore the non uniqueness explicitly by examining the null space of the forward operator we show that with the null space shuttle it is possible to assess robustness in tomographic models and we illustrate the concept for the global p wave model mit p08 we found a broad range of acceptable solutions compatible with the travel time data the root mean square rms velocity perturbations vary from 0 2 to 0 6 in the lowermost mantle and from 0 3 to 1 3 in the upper mantle such large variations in average amplitudes prohibit meaningful inferences on temperature or chemical variations in the earth from tomographic models alone on a global scale much short wavelength structure resides in the null space of the forward operator suggesting that the data do not everywhere resolve structure on the smallest length scale 200 km allowed by the block parameterization used in mit p08 and similar models this indicates that great care should be taken when interpreting such structure as a practical measure we suggest that only those structures for which the wave speed perturbations do not change sign within the range of models permitted by the data should be considered robust with this criterion the model null space analysis shows that the high velocity anomalies in the lower mantle which are often interpreted as remnants of slabs of subducted lithosphere are required by the seismic data low velocity anomalies underneath for instance hawaii iceland and africa show varying degrees of robustness

silurian llandovery graptolites from the bay of exploits north central newfoundland and their geological significance only one specimen of a silurian graptolite has ever been recorded from newfoundland and it was not identifiable below generic level the graptolite assemblage discussed and figured here from a sequence of turbidites on upper black island north central newfoundland includes the first positively identified silurian taxa from the province and provides the first unequivocal evidence of silurian oceanic sedimentation in the dunnage zone the graptolite taxa include rastrites peregrinus barrande coronograptus sp cf c gregarius lapworth monograptus austerus sequens hutt orthograptus insectiformis nicholson monograptus spp indet climacograptus sp and glyptograptus sp this assemblage demonstrates that the strata previously assigned to the middle ordovician lawrence harbour formation are actually aeronian middle llandovery in age and that the turbidites considerably postdate both the lawrence harbour and point leamington formations of the exploits subzone furthermore the graptoli