revisited relationship between tropical and north pacific sea surface temperature variations 1 the relationship between the tropical and north pacific sea surface temperature sst variations is reexamined following the results of deser and blackmon 1995 db95 based on a much longer period of data 1949 2010 as in db95 the two leading sst modes the el nino southern oscillation enso mode and the north pacific mode represent the sst variations in the pacific domain before 1992 considering the period after 1992 however one needs to consider a new mode of sst variation along with the two modes mentioned to understand the relationship between the tropical and north pacific sst variations a new sst mode known as the warm pool mode exhibits a strong variance in the warm pool region and undergoes a phase shift after the mid 1990s reflecting a warming in the warm pool region and a cooling in the central and eastern equatorial pacific it is found that the warm pool mode accompanies the north pacific oscillation like atmospheric variability over the north pacific through this teleconnection the warm pool mode mostly shows a relationship between the warm pool sst and the associated north pacific sst component and which has some similarities with the north pacific gyre oscillation

new geophysical data from the northern cordillera preliminary interpretations and implications for the tectonics and deep geology in this paper we analyze recently acquired geophysical data from the northern cordillera and their relation to the mapped geology a prominent gravity high 45 mgal 1 gal 1 cm s 2 coincides with a magnetic low and an aseismic region in west central yukon where the underlying geology is dominated by quartzo feldspathic rocks having moderate densities extension 15 magmatic underplating and accretion of the anomalous region onto oceanic crust are three possible explanations magnetic gravity and seismicity data all show significant differences in the physical state of the crust on either side of the tintina fault and together with geological data indicating large offset suggest it was once a major crustal scale strike slip fault the new gravity data also delineate an arcuate zone of steep gradients up to 1 4 mgal km in the miogeocline which may correlate with a west dipping proterozoic basement ramp mapped on deep seismic sections farther to the north and a transition from thin east to thick sediment cover west seismicity data show that current tectonic activity is concentrated along the pacific north america plate margin in southwestern yukon and adjacent alaska and although there is a marked decrease in activity inland of this margin notable concentrations occur along the denali fault system and in the eastern miogeocline there is a distinct absence of earthquakes in parts of the selwyn basin and in the northern yukon tanana terrane limited field studies suggest activity is confined to the upper 10 15 km of the crust

tectonic significance of potential field anomalies in western canada results from the lithoprobe snorcle transect potential field anomalies within the lithoprobe snorcle slave northern cordillera lithospheric evolution transect area provide geometrical constraints for regional crustal and lithospheric structures as well as for local anomalies when coupled with subsurface geometry visible on nearly 2500 km of deep seismic reflection and refraction profiles areal distribution of gravity and magnetic anomalies permit structures to be projected away from seismic cross sections and forward modelling provides tests of different interpretations of deep crustal and upper mantle density structures in a key result from modelling a paleoproterozoic subduction zone beneath the wopmay orogen probably consists of high density rocks such as eclogite within the upper mantle this result supports the concept of moderate to low angle intra lithospheric sutures on an even larger scale applications of bandpass and directional filters assist in detecting anomalies according to wavelength or azimuthal orientation and thus

an alternate method for estimating dynamic height from xbt profiles using empirical vertical modes abstract a technique is presented that applies modal decomposition to estimate dynamic height 0 450 db from xbt temperature profiles std data are used to establish empirical relationships between vertically integrated temperature profiles and empirical dynamic height modes these are then applied to xbt data to estimate dynamic height a standard error of 0 028 dynamic meters is obtained for the waters of the gulf of alaska an ocean region subject to substantial freshwater buoyancy forcing and with a t s relationship that has considerable scatter the residual error is a substantial improvement relative to the conventional t s correlation technique when applied to this region systematic errors between estimated and true dynamic height were evaluated the 20 year long time series at ocean station p 50 n 145 w indicated weak variations in the error interannually but not seasonally there were no evident systematic alongshore variations in the error in the ocean boundary current regime near the perim

seismic interpretation of crustal scale extension in the intermontane belt of the northern canadian cordillera the crustal thickness of the canadian cordillera which may have reached 50 65 km during the cretaceous is now only 32 38 km along its length in the south postorogenic extension during the eocene resulted in the formation of core complexes and crustal scale extensional shear zones whereas in the north evidence for postorogenic extension is either limited to relatively minor basin formation in a transtensional environment or has not been recognized using new images of lithoprobe seismic reflection line 2a in northern british columbia which has been previously interpreted in terms of terrane accretion i make an alternative interpretation of crustal scale postaccretion extension in the middle and upper crust as early as the late permian to early triassic the quesnellia and stikinia arc terranes were accreted to ancestral north america along a crustal ramp which is imaged in the lower crust an extensional shear zone which extends from close to the surface to 20 km depth is identified from the geometry of reflections in the overlying structural basin and a lateral change in seismic velocity the oceanic cache creek terrane which is 4 km thick in the vicinity of line 2a was preserved because it was imbricated with its overlap assemblage and dropped into the 10 km deep structural half graben which may correspond approximately to the combined extent of the whitehorse trough and the cache creek terrane in southern yukon and northern british columbia

imaging the lithospheric mantle in northwestern canada with seismic wide angle reflections normal moveout corrected and stacked sections of wide angle reflection data collected in the archean slave province and paleoproterozoic wopmay orogen in northwestern canada image the crust mantle boundary as a subhorizontal discontinuity at about 32 36 km depth along a 450 km lateral extent and for the first time from such data layering within the lithospheric mantle at depths between 75 and 90 km over a lateral distance of 750 km these images correspond to moho and mantle reflections observed on a co located multichannel seismic mcs reflection profile structural features and or the basalt eclogite phase change associated with subduction of oceanic and or delaminated lower crust are possible sources of the deep reflectivity one mantle reflection group lies west of the mcs data and east of the cordilleran deformation front it could have similar sources or result from the mesoproterozoic racklan orogen or meso neoproterozoic rifting of the ancient margin

lithospheric structure across the craton cordilleran transition of northeastern british columbia the lithospheric structure of the transition from the craton to the cordillera in northeastern british columbia is interpreted from inversion of seismic refraction wide angle reflection data along a 460 km profile and from 3 d 3 dimensional inversion and 2 5 d forward modelling of bouguer gravity data the seismic profile extends westward from the sediment covered edge of cratonic north america across the foreland and omineca morphogeological belts to the eastern boundary of accreted terranes beyond the tintina fault across the ancient cratonic margin the resultant models reveal a westward thickening package of low upper crustal velocities 6 2 km s and less and low densities to almost 20 km depth below the western canada sedimentary basin overlying a west facing ramp of higher velocities and densities in the middle and lower crust these features are inferred to represent passive margin sediments deposited on the ancient rifted margin during the mid to late proterozoic and early paleozoic a we

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

transpression between two warm mafic plates the queen charlotte fault revisited the queen charlotte fault is a transpressive transform plate boundary between the pacific and north american plates offshore western canada previous models for the accommodation of transpression include internal deformation of both plates adjacent to the plate boundary or oblique subduction of the oceanic plate the latter has been the preferred model both plates are warm and mafic and have similar mechanical structures new multichannel seismic reflection data show a near vertical queen charlotte fault down to the first water bottom multiple significant subsidence east of the queen charlotte fault a large melange where the fault is in a compressive left step and faulting which involves oceanic basement gravity modeling of profiles indicates that moho varies fairly smoothly across the plate boundary isostatic anomalies indicate that the pacific plate is flexed downward adjacent to the queen charlotte fault upward flexure of north america along with crust thickened relative to crust in the adjacent basin creates topography known as the queen charlotte islands combined with other regional studies these observations suggest that the plate boundary is a vertical strike slip fault and that transpression is taken up within each plate

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

a low velocity zone atop the transition zone in northwestern canada 1 seismic studies over the past decade have identified an s wave low velocity zone lvz above the transition zone at various locations around the globe this layer is hypothesized to be a lens of dense hydrous silicate melt ponding atop the 410 km discontinuity beneath the silicate melt density crossover predicted to exist within the upper mantle we have assembled a p and s receiver function data set to quantify the physical properties and geographical extent of the layer in northwestern canada geographic profiles formed from 1 d migration of receiver functions computed for the canadian northwest experiment canoe and portable observatories for lithospheric analysis and research investigating seismicity polaris slave arrays reveal an lvz beneath many stations at a nominal depth of 340 km to constrain layer thickness and poisson s ratio we performed a grid search over a suite of 1 d velocity profiles to model the relative delay times of direct conversions and reverberations from the top of the lvz and 410 km discontinuity as recorded at the yellowknife array in addition we performed linearized inversion of transmission coefficient amplitudes to estimate s velocity contrasts at the bounding interfaces the lvz is characterized by a thickness of 36 km with an s velocity contrast of 7 8 and poisson s ratio of 0 42 taken at face value the two latter results require an increase in p velocity into the lvz the poisson s ratio lies well above the iasp91 average of 0 29 0 3 for this depth range and favors the presence of high melt or fluid fractions

the mohorovicic discontinuity beneath the continental crust an overview of seismic constraints abstract the seismic signature of the moho from which geologic and tectonic evolution hypotheses are derived is to a large degree a result of the seismic methodology which has been used to obtain the image seismic data of different types passive source earthquake broad band recordings and controlled source seismic refraction densely recorded wide angle deep seismic reflection and normal incidence reflection using vibroseistm explosives or airguns have contributed to the description of the moho as a relatively complex transition zone of critical importance for the quality and resolution of the seismic image are the acquisition parameters used in the imaging experiments a variety of signatures have been obtained for the moho at different scales generally dependent upon bandwidth of the seismic source this variety prevents the development of a single universally applicable interpretation in this way source frequency content and source and sensor spacing determine the vertical and lateral resolution of the images respectively in most cases the different seismic probes provide complementary data that gives a fuller picture of the physical structure of the moho and its relationship to a petrologic crust mantle transition in regional seismic studies carried out using passive source recordings the moho is a relatively well defined structure with marked lateral continuity the characteristics of this boundary change depending on the geology and tectonic evolution of the targeted area refraction and wide angle studies suggest the moho to be often a relatively sharp velocity contrast whereas the moho in coincident high quality seismic reflection images is often seen as the abrupt downward decrease in seismic reflectivity the origin of the moho and its relation to the crust mantle boundary is probably better constrained by careful analysis of its internal details which can be complex and geographically varied unlike the oceanic moho which is formed in a relatively simple well understood process the continental moho can be subject to an extensive variety of tectonic processes making overarching conclusions about the continental moho difficult speaking very broadly 1 in orogenic belts still undergoing compression and active continental volcanic arcs the moho evolves with the mountain belt 2 in collapsed phanerozoic orogenic belts the moho under the collapse structure was formed during the collapse often by a combination of processes 3 in regions having experienced widespread basaltic volcanism the moho can result from underplated basalt and basaltic residuum in precambrian terranes the moho may be as ancient as the formation of the crust in others precambrian tectonic and magmatic processes have reset it we note that seismic reflection data in phanerosoic orogens as well as from precambrian cratonic terranes often show thrust type structures extending as deep as the moho and suggest that even where crust and mantle xenoliths provide similar age of formation dates the crust may be semi allochothonous

evidence for the existence of a north hawaiian ridge current abstract two different datasets are examined for information about the existence and characteristics of the north hawaiian ridge current nhrc the pan pacific drifter dataset shows a mean nhrc to be confined to within about 100 km of the northern side of the hawaiian ridge a close look at the distribution of the data shows that the current is mostly confined in time to a two month period in the fall of 1991 mbt data from the trade wind zone oceanography pilot study conducted in the mid 1960s were also examined of the 14 cruises with sections north of the hawaiian ridge 5 showed evidence of northwestward flow along the ridge of those 5 one was associated with northward meandering of the north equatorial current it is thus suggested that the nhrc is highly intermittent there are three related hypotheses for the formation of the nhrc 1 propagation of rossby waves westward into the ridge 2 forking of the north equatorial current and 3 as a western boundary current for the eastern pacific north

joint inversion of teleseismic receiver functions and magnetotelluric data using a genetic algorithm are seismic velocities and electrical conductivities compatible 1 joint inversion of different kinds of geophysical data has the potential to improve model resolution under the assumption that the different observations are sensitive to the same subsurface features here we examine the compatibility of p wave teleseismic receiver functions and long period magnetotelluric mt observations using joint inversion to infer one dimensional lithospheric structure we apply a genetic algorithm to invert teleseismic and mt data from the slave craton a region where previous independent analyses of these data have indicated correlated layering of the lithosphere examination of model resolution and parameter trade off suggests that the main features of this area the moho central slave mantle conductor and the lithosphere asthenosphere boundary are sensed to varying degrees by both methods thus joint inversion of these two complementary data sets can be used to construct improved models of the lithosphere further studies will be needed to assess whether the approach can be applied globally

characterization of the crust of the coast mountains batholith british columbia from p to s converted seismic waves and petrologic modeling abstract the late triassic to early tertiary coast mountains batholith cmb of british columbia provides an ideal locale to study the processes whereby accreted terranes and subduction related melts interact to form stable continental crust of intermediate to felsic composition and complementary ultramafic residuals seismic measurements combined with calculated elastic properties of various cmb rock compositions provide a window into the deep crustal lithologies that are key to understanding the processes of continental growth and evolution we use a combination of seismic observations and petrologic modeling to construct hypothetical crustal sections at representative locations across the cmb then test the viability of these sections via forward modeling with synthetic seismic data the compositions that make up our petrologic forward models are based on calculations using the free energy minimization program perple x to predict mineral assemblages at depth for the bulk compositions of exposed plutonic rocks collected in the study area seismic data were collected along two transects in west central british columbia a southern line that crossed the cmb near the town of bella coola near 52 n and a northern line centered on the towns of terrace and kitimat near 54 n along both transects seismic receiver functions reveal high vp vs ratios near the insular intermontane terrane boundary and crustal thickness increasing from 26 3 km to 34 3 km at the 1 sigma certainty level from west to east across the coast shear zone csz on the southern line we observe an anomalous region of complex receiver functions and diminished moho signals beneath the central portion of the cmb our petrologic and seismic profiles show that observed seismic data from much of the cmb can be well matched in terms of crustal thickness and structure average vp vs and amplitude of the moho converted phase without including ultramafic residual material in the lower crust

demographics of mesoscale eddies in the california current 1 demographics and variability of persistent mesoscale eddies in the california current have been investigated in a systematic manner using a decade 1995 2004 of merged satellite altimeter data the number of persistent eddies formed each year varied almost 3 fold 4 fold for cyclones anticyclones and was strongly modulated by the 1997 1998 el nino event over the 10 year period cyclone formation was maximum in both winter and summer while maximum anticyclone formation occurred only in winter the majority of long lived eddies 70 day lifespan originated seaward of the 1000 m isobath and with the exception of 2 anticyclones did not form between 45 and 50 n maximum westward propagation of long lived eddies was almost 800 km with similar mean propagation speeds for cyclones and anticyclones

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

variability of the north pacific current and its bifurcation abstract the north pacific current npc bifurcates approaching the west coast of north america into a subpolar branch that forms the alaska current and a subtropical branch that includes the california current the variability of this current system is discussed using numerical results from a wind driven reduced gravity model indices of the strength of the subpolar and subtropical components of the npc are examined based on output from multi decadal simulations with the numerical model this shows periods of both correlated and anti correlated variability of the subpolar and subtropical gyres a decomposition of the gyre transport time series indicates that the dominant mode of variability is a breathing mode in which the subpolar and subtropical gyres co vary in response to fluctuations in the strength of the npc this finding is consistent with an analysis of dynamic height data of limited duration from the array of argo drifting floats the variability of the npc is also examined using sea surface height ssh data from satellite altimetry over the period 1993 2005 the leading mode of ssh over the northeast pacific dominates the variability of the npc and is shown to be associated with in phase variations in the transport of the subtropical and subpolar gyres a strong correlation is found between time dependent fluctuations in ssh across the npc and variations in the strength of the transport of the npc in the model this agreement provides evidence for variability of the npc occuring in direct response to large scale atmospheric forcing

changes in the north pacific current divergence and california current transport based on hadgem2 es cmip5 projections to the end of the century abstract this study aims to evaluate the potential changes to the strength of the north pacific current npc and its position of divergence which would alter the variability of the alaska ac and california cc currents throughout the century for this the volume transports of these currents were evaluated using the historical cmip5 and rcp4 5 experimental results of the hadgem2 es model from 1985 to 2100 in general the npc will migrate to the north in accord to the northwestward expansion of north pacific high which would alter the positioning and the amount of flow entering the ac and cc systems by 2100 along with the bifurcation shift changes in the two main modes of variability i e the bifurcation and breathing modes are expected the bifurcation mode will become responsible for only 11 of the total variability while presenting a positive anomaly throughout the century these results indicate the role of npc migration on the southward transport of enriched waters and the possible impact on the primary productivity along the north american coast

analysis of longitudinal variations in north pacific alkalinity to improve predictive algorithms the causes of natural variation in alkalinity in the north pacific surface ocean need to be investigated to understand the carbon cycle and to improve predictive algorithms we used glodapv2 to test hypotheses on the causes of three longitudinal phenomena in alk a tracer of calcium carbonate cycling these phenomena are a an increase from east to west between 45 n and 55 n b an increase from west to east between 25 n and 40 n and c a minor increase from west to east in the equatorial upwelling region between 45 n and 55 n alk is higher on the western than on the eastern side and this is associated with denser isopycnals with higher alk lying at shallower depths between 25 n and 40 n upwelling along the north american continental shelf causes higher alk in the east along the equator a strong east west trend was not observed even though the upwelling on the eastern side of the basin is more intense because the water brought to the surface is not high in alk we created two algorithms to predict alkalinity one for the entire pacific ocean north of 30 s and one for the eastern margin the pacific ocean algorithm is more accurate than the commonly used algorithm published by lee et al 2006 of similar accuracy to the best previously published algorithm by sasse et al 2013 and is less biased with longitude than other algorithms in the subpolar north pacific our eastern margin algorithm is more accurate than previously published algorithms

surface wave images of western canada lithospheric variations across the cordillera craton boundary two station surface wave analysis was used to measure rayleigh wave phase velocities between 105 station pairs in western canada straddling the boundary between the tectonically active cordillera

accreted terranes of northwestern british columbia canada lithospheric velocity structure and tectonics 1 lithospheric structure beneath the accreted terranes of the northwestern canadian cordillera is interpreted from analyses of p wave refraction and wide angle reflection data the 535 km long profile extends from the deformed and displaced ancestral north american margin across the omineca belt suture zone and intermontane superterrane to the coast belt this region is interpreted to have grown westward through a progression from thin skinned to thick skinned accretionary tectonics large lateral variations of velocities 2 0 6 4 km s within the upper 15 km correlate with the mapped geological and terrane elements fault offsets and the imbricated base of an overlap basin are clearly identified inboard of the stikine accreted terrane a zone of slow upper crustal velocities thins to the east consistent with an interpretation of thin skinned accretion leaving slivers of terranes overlying a wedge of metamorphosed proterozoic continental margin sediments however in the lower crust the proposed underlying cratonic ramp is not distinguished from outboard or overlying accreted crust by lateral p velocity contrasts or wide angle reflections the moho remains nearly horizontal beneath the intermontane and omineca belts gradually thinning to the east from 36 5 to 35 km to the southwest below the coast belt and to the northeast beneath the tintina fault the crust thins to 32 km upper mantle velocities across the coast intermontane and omineca belts are 7 8 7 9 km s the slow upper mantle and lower crustal velocities are indicative of high temperatures that may permit the flat moho or weak lower crust to partially decouple the crust from the mantle reflections in the upper mantle between 50 70 km depth may be related to the base of the lithosphere or to heterogeneities introduced through melting or accretionary subduction events

lithospheric geometry of the wopmay orogen from a slave craton to bear province magnetotelluric transect 1 two dimensional inversions of lithospheric probing magnetotelluric mt data at a total of 20 sites acquired along an approximately east west 300 km long profile across the wopmay orogen in the northwest territories canada provide electrical resistivity models of the boundary between the archean slave craton and the adjacent proterozoic bear province an analysis of distortion effects and structural dimensionality indicates that the mt responses are primarily one dimensional or only weakly two dimensional with a depth independent geoelectric strike angle of n32 e consistent with regional structural geology the regional scale model generated from the longer period responses from all of the sites along the profile reveals significant lateral variations in the lithospheric mantle resistive cratonic roots are imaged to depths of 200 km beneath both the slave craton and the hottah terrane of the bear province these are separated by a less resistive region beneath the great bear magmatic zone which is speculatively interpreted as a consequence of a decrease in the grain size of olivine in the wopmay mantle caused by localized shearing compared to its neighboring cratonic roots focused two dimensional models from higher frequency responses at sites on specific sections of the profile reveal the resistivity structure at crustal depths beneath the region these suggest that the root of the slave craton crosses beneath the wopmay orogen and that the wopmay fault zone does not penetrate into the lower crust a comparison of these results with those obtained during the lithoprobe project farther south shows striking along strike variations in the conductivity structure associated with the wopmay orogen

continental collisions and seismic signature processes active during continental collisions and orogenic collapse create distinct structures which are imaged by reflection seismic profiling examples are shown and discussed

archean proterozoic collision boundary in central fennoscandia revisited abstract archean proterozoic ap collision boundary in central fennoscandia is a complex collage of archean basement rocks its paleoproterozoic supracrustal cover rocks and svecofennian 1 93 1 78 ga supracrustal and plutonic rocks the apparent steep nature and complexity of the ap boundary has led to contradictory tectonic models varying from arc continent collision via back arc closure to accretion of arc terranes along a strike slip shear zone we present new geochronology data from detrital zircons combined with whole rock geochemical and sm nd isotopic data on paleoproterozoic sedimentary and volcanic rocks across the boundary to revise its nature the 2 06 ga siilinjarvi volcanic complex and associated turbidites with an inferred deposition age at 2 1 2 06 ga are part of the cover sequence the siilinjarvi volcanic rocks derive from both plume oib and sub continental lithospheric mantle sclm magma sources and are often contaminated by the archean crust the sahara suite sedimentary cover rocks are derived from local 1 95 1 92 ga bimodal volcano plutonic source which source also explains the common age population found in younger sedimentary rocks the nalantojarvi suite psammites with maximum depositional ages of 1 97 1 93 ga are continental slope to deep water sediments deposited at the continental margin contemporaneous mafic magmatism seen as lavas and dykes show a change from sclm dominated present east to asthenospheric depleted mantle dm dominated present west melts the interpretation of the nalantojarvi suite as cover rocks of the lower plate indicates that the archean crust continues at least 50 km more to the west than thought earlier parautochthonous sedimentary rocks from salahmi eastern kansanneva and loutemaki with maximum depositional ages at 1 92 1 91 ga are inferred as collision related foredeep deposits from local sources both the lampaanjarvi suite and pyhajarvi suite sedimentary rocks have deposited at 1 89 1 88 ga or later whereas the lampaanjarvi suite rocks are dominated by a local source and the pyhajarvi suite rocks derive from a mixture of older sediments and 1 89 1 88 ga granitoids at least two tectono metamorphic stages separated with a major unconformity can be differentiated in the study area the early deformation and metamorphic stage in the nalantojarvi suite has occurred before the intrusion of the late to post collisional pyroxene granitoids at 1 88 ga the pyhajarvi suite sedimentary rocks have been deposited after the intrusion of these granitoids between 1880 and 1875 ma and then subsequently deformed and metamorphosed at 1875 ma we propose a tectonic model where the continental breakup occurred at 2 1 2 06 ga followed by a new spreading within the pre existing passive margin at 1 98 1 93 ga during initial continent arc collision the subducted slab steepened strongly at high angle subduction ceased rapidly and finally detached and shallow slab breakoff occurred at 1 92 1 91 ga followed subsequently by ophiolite obduction and a formation of a foreland fold and thrust belt mantle crust decoupling of the archean lithosphere occurred and a crocodile jaw formed where the arc rocks are partly buried beneath the bounding archean continent similar features have been recorded in other ap collision zones which could indicate that the buoyant nature of the archean lithosphere combined with denser paleoproterozoic lithosphere may be a general cause for decoupling of archean crust and mantle during arc continent collision in paleoproterozoic

retrieval of moho reflected shear wave arrivals from ambient seismic noise theoretical studies on ambient seismic noise asn predict that complete green s function between seismic stations can be retrieved from cross correlation however only fundamental mode surface waves emerge in most studies involving real data here we show that moho reflected body wave sms and its multiples can be identified with asn for station pairs near their critical distances in the short period band 1 5 s we also show that an uneven distribution of noise sources such as mining activity and wind topography interaction can cause surface wave precursors which mask weaker body wave phases

archean and proterozoic crustal evolution evidence from crustal seismology seismic velocity models for archean and proterozoic provinces throughout the world are analyzed the thickness of the crust in archean provinces is generally found to be about 35 km except at collisional boundaries whereas proterozoic crust has a significantly greater thickness of about 45 km and has a substantially thicker high velocity 7 0 km s layer at the base we consider two models that may explain these differences the first model attributes the difference to a change in the composition of the upper mantle the higher temperatures in the archean mantle led to the eruption of komatiitic lavas resulting in an ultradepleted lithosphere unable to produce significant volumes of basaltic melt proterozoic crust developed above fertile mantle and subsequent partial melting resulted in basaltic underplating and crustal inflation in the second model convection in the hot archean mantle is considered to have been too turbulent to sustain stable long lived subduction zones by the proterozoic the mantle had cooled sufficiently for substantial island and continental arcs to be constructed and the high velocity basal layer was formed by basaltic underplating

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

lithospheric structure in northwestern canada from lithoprobe seismic refraction and related studies a synthesis the snorcle refraction wide angle reflection r war experiment snore 97 included four individual lines along the three transect corridors a combination of snore 97 results with those from earlier studies permits generation of a 2000 km long lithospheric velocity model that extends from the archean slave craton to the present pacific basin using this model and coincident near vertical incidence nvi reflection data and geological information an interpreted cross section that exemplifies 4 ga of lithospheric development is generated the velocity structural models correlate well with the reflection sections and provide additional structural compositional and thermal constraints geological structures and some faults are defined in the upper crust at a larger scale the seismic data identify a variety of orogenic styles ranging from thin to thick skinned accretion in the cordillera and crustal scale tectonic wedging associated with both paleoproterozoic and mesozoic collisions models of poisson

identifying and quantifying natural co2 sequestration processes over geological timescales the jackson dome co2 deposit usa co2 sources sinks and migration mechanisms in natural co2 gas fields provide critical analogues for developing the safe application of anthropogenic co2 sequestration technologies here we use noble gas and carbon isotopes together with other gases to identify and quantify the origin transport and trapping mechanisms of co2 in the late cretaceous jackson dome co2 gas deposit 98 75 to 99 38 co2 located in central mississippi usa and producing from 5000 m it is one of the deepest commercial co2 gas fields in the world 10 gas samples from producing wells were determined for their noble gas chemical and stable carbon isotope composition he 3 he 4 ratios range between 4 27r a and 5 01r a where r a is the atmospheric value of 1 4 x 10 6 indicating a strong mantle signature similar to co2 deposits worldwide co2 he 3 decreases with increasing groundwater derived ne 20 and he 4 we model several different processes that could account for the jackson dome data and conclude that similar to other co2 dominated deposits a groundwater gas stripping and re dissolution ggs r process best accounts for observed ne 20 ar 36 kr 84 ar 36 co2 he 3 delta c 13 co2 he 4 ne 20 and ar 36 in this context crustal and magmatic co2 components contribute 57 and 43 respectively changes in co2 he 3 across the field show that groundwater contact is responsible for up to 75 loss of original emplaced co2 delta c 13 co2 variance limits the degree of precipitation to be less than 27 with the remaining co2 loss being accounted for by dissolution only a higher degree of dissolution gas loss and evidence for water contact at the reservoir crest compared to the reservoir flanks is used to argue that co2 in this system has not undergone subsequent loss to either dissolution or precipitation since shortly after reservoir filling at over 60 ma c 2012 elsevier ltd all rights reserved

major dextral transcurrent displacements along the northern rocky mountain trench and related lineaments in north central british columbia the northern rocky mountain trench and a number of other prominent lineaments along and east of the eastern margin of the intermontane belt mark faults along which dextral transcurrent movements have been dominant offsets of shelf to off shelf facies boundaries in lower paleozoic rocks indicate a cumulative displacement of at least 750 km and probably 900 km within the system of faults related to those in the northern rocky mountain and the tintina trenches farther west another system of faults appears to offset plutons and stratigraphic assemblages along the eastern margin of the intermontane belt by as much as 300 km these faults including the kutcho and the pinchi connect in part with the teslin suture zone in yukon territory and probably with the fraser river straight creek fault zone in southern british columbia although dextral transcurrent faulting may have taken place between the middle jurassic and early cenozoic the most convincing evidence points to middle cretaceous and particularly to early cenozoic eocene displacements the eocene movements were temporally related to plutonism volcanism lamprophyre dike emplacement high heat flow sedimentation in grabens and rapid uplift of northwesterly trending elongate ranges climactic episodes of granite emplacement particularly in and near the northern omineca crystalline belt at 100 m y 70 m y and 50 m y ago may have been facilitated by changes from dominantly compressional to dominantly transcurrent and related tensional strain

neodymium isotopic evidence for the tectonic assembly of late archean crust in the slave province northwest canada the ca 2 7 2 5 ga slave province is a granitegreenstone terrane comprising deformed sedimentary and subordinate volcanic belts extensively intruded by granitoid rocks the nd isotopic data are reported for 58 samples of supracrustal and granitoid rocks exposed along a 400 km east west transect at 65 n across the structural grain of the province initial nd values reveal distinctly different crustal sources in the eastern compared to the western parts of the province as expected from tectonic assembly of the province through accretion of juvenile crust to older continental crust supracrustal sequences ca 2 71 2 65 ga from the central and eastern parts of the province have positive nd 1 values 0 3 to 3 6 consistent with juvenile sources and formation remote from significantly older crust syn to late deformation ca 2 63 2 60 ga mantle derived diorites and related tonalites type i from the central and eastern parts of the province have similar initial nd values 0 1 to 2 7 in contrast samples from the westernmost plutons which intrude exposed pre 3 1 ga crust have much lower nd 1 values 1 0 to4 6 suggesting contamination of these magmas by older crust the nd 1 values of post deformation granites s s type ii also vary systematically across the province values for granites west of longitude 110 30 w range from 0 2 to 5 3 those to the east range from 0 6 to 3 7 these data suggest mixed crustal sources dominated by mid to early archean material nd 2 6 to 17 at 2 6 ga for the western granitoid rocks and juvenile sources for the eastern granites the nd isotopic data are consistent with the geology of the province in that exposures of mid to early archean crustal rocks predating the principal 2 7 2 5 ga orogenic event are restricted to the western part of the province the asymmetric pattern defined by the nd isotopic data indicates the presence of distinct crustal rocks beneath the slave province similar isotopic variations observed across phanerozoic collisional orogens have been interpreted to reflect tectonic assembly of crust by accretion of juvenile crustal terranes to an older continental margin this process may also have been an important mechanism in the cratonization of the slave province

moho reflectivity patterns a comparison of canadian lithoprobe transects abstract the complex nature of the continental moho may be strongly influenced by the tectonic and magmatic history of the lithosphere observations of moho variability from near vertical incidence seismic reflection surveys suggest that it may be possible to correlate moho reflectivity and lithospheric evolution as an initial step in attempting to determine such correlations we qualitatively compare seismic reflection data from canadian lithoprobe transects that sample regions of exceptionally diverse age and tectonic history the seven selected datasets were collected using consistent acquisition parameters facilitating effective and meaningful comparisons among transects the moho reflections exhibit considerable variability however in virtually all recent transects a distinct moho is observed even in regions where lower crust is considered to have stabilized in the early proterozoic or archean this suggests not only that relationships between moho reflectivity and tectonics can be extended into the archean but that tectonic age is poorly correlated with moho reflectivity the qualitative comparisons do not clearly link a specific tectonic process with a distinctive reflection pattern however well defined moho reflections are associated with lower crustal deformational processes including compression transpression and extension this indicates that ductile shear and the rheologies of the lower crust moho transition and upper mantle play important roles in influencing reflective character indistinct moho reflectivity may be associated with regions that have experienced little ductile deformation or with processes that have disrupted reflective laminations however the majority of incoherent moho reflections appear related to signal degradation associated with data acquisition the study demonstrates that the qualitative characteristics of moho reflectivity are difficult to correlate with tectonic history and thus use as an interpretive tool isolating quantitative reflection characteristics of the moho from distortions imposed by the overlying crust is a challenging problem but appears necessary to further understanding of the crust mantle transition

on folds and thrusts affecting the coppermine river group northwestern canadian shield examination of existing geological and aeromagnetic maps of the coppermine homocline reveals two periods of deformation which affect rocks of the coppermine river group but predate rocks of the rae group the oldest event generated easterly trending folds and southerly vergent thrust faults and is probably related to events along the northern margin of laurentia the younger event caused northerly trending folds possibly correlates with an east west compressional event seen in the subsurface of the interior plains and was likely a result of plate interactions along the western margin of laurentia both deformational events that affect the coppermine homocline are younger than 1267 ma and are not correlative with the pre 1268 ma racklan orogeny of the northern cordillera

why is the north america cordillera high hot backarcs thermal isostasy and mountain belts global mountain belts are commonly concluded to be a consequence of crustal thickening resulting from continental collision with high elevations supported by crustal roots however accumulating seismic structure data indicate that many mountain belts have no crustal root most of the north american cordillera has a 30 35 km crust in contrast to 40 45 km for the lower elevation craton and other stable areas it has been shown previously that most such mountain belts are in present or recent backarcs that are uniformly hot from thermal constraints we predict a uniform 1600 m elevation support of the cordillera by thermal expansion compared to stable areas over most of the cordillera relative to stable areas the elevations after correction for variable crustal thickness and density are in excellent agreement when subduction and shallow backarc convection stop the lithosphere may cool and the elevations of mountain belts subside over 300 m y

teleseismic studies of the canadian landmass lithoprobe and its legacy national research council of canada nrc research press http www nrc cnrc gc ca notices e html copyright permission to reproduce materials on this web site were produced and or compiled by the national research council for the purpose of providing canadians with direct access to information about the programs and services offered by the government of canada the material on this site is covered by the provisions of the copyright act by canadian laws policies regulations and international agreements such provisions serve to identify the information source and in specific instances to prohibit reproduction of materials without written permission

wave field tau p analysis for 2 d velocity models application to western north american lithosphere the international deep probe refraction experiment is a continental scale study of the crust and upper mantle in western north america to determine well constrained mantle velocity depth structures for the stable archean hearne and wyoming provinces and the tectonically modified proterozoic lithosphere of the southern rocky mountains and colorado plateau an initial 2 d velocity interpretation for deep probe has been accomplished by the application of the downward continued wave field p transform method this approach involves two linear transforms for each shot gather from the experiment a p transform or slant stack of the input data followed by a downward continuation to z p space using an appropriate velocity function the determination of this velocity function is an iterative process which converges when the downward continued wave field images a velocity function which is the same as that used to create it the resulting 1 d velocity function z from each gather is converted to a 2 d function x z using ray theory eleven profiles along the deep probe corridor have been analysed the resulting functions have been combined gridded and contoured to produce a velocity structure section for the project which provides an initial model for the application of more advanced interpretation procedures as a result the lithospheric structures of three major tectonic provinces have been identified in an efficient and effective manner that did not require picking of travel times

architecture and evolution of accretionary orogens in the altaids collage the early paleozoic west junggar nw china understanding the development and evolution of accretionary orogens is crucial for characterizing continental crust growth in time and space in the altaids tectonic collage of central asia conflicting geodynamic models have been proposed about the paleozoic evolution during which juvenile continental crust has been extensively formed this study focuses on west junggar nw china a key region that has not been extensively studied yet a multidisciplinary approach including detrital zircon provenance study geochemistry and field structural analysis provides new constraints on the evolution of three early paleozoic units of west junggar oceanic subduction predominates in early paleozoic time as indicated by ophiolitic melanges fore arc volcaniclastic turbidites and magmatic arc suites however the development of an olistostrome supplied by a sub contemporaneous carbonate platform the occurrence of continental molasse and the chronology and geochemistry of magmatic events reveal interruptions of subduction discrete collisions of volcanic arcs and micro continent are inferred from the tectonic structure of the belt which displays allochthonous units rooted in the suture zone early paleozoic magmatic and sedimentary rocks of west junggar bear some resemblance to contemporaneous analogues in eastern kazakhstan and suggest a lateral connection on the basis of these new results we propose a geodynamic evolution in four steps 1 early to middle ordovician intra oceanic subduction forming island arcs 2 late ordovician tectonic accretion of island arcs against the kazakhstan continental margin 3 early to middle silurian resumption of subduction and active continental margin magmatism and 4 late silurian early devonian micro continent collision this scenario consistent with the formation of the kazakhstan block supports a model of multiple episodic accretions for the altaids tectonic collage rather than a continuous continental margin evolution these results also suggest that in central asia continental crust growth results from alternating vertical and horizontal growth episodes throughout the paleozoic

deep seismic reflection constraints on paleogene crustal extension in the south central intermontane belt british columbia following growth of the canadian cordillera during the mesozoic the southern cordillera was subject to extension during the paleocene and eocene that correlated with widespread volcanic activity in south central british columbia including across much of the nechako chilcotin plateau in 2008 geoscience bc acquired 330 km of deep vibroseis reflection profiles on the plateau mostly over the stikinia arc terrane but also over its eastern contact with the oceanic cache creek terrane all seven seismic reflection lines reveal a strongly reflective lower crust that extends from 7 to 9 s down to the moho which is defined by the downward termination of reflectivity at 11 12 s in the uppermost crust extension occurred by block faulting with faults soling into subhorizontal to shallowly dipping detachments above 10 km depth extension in the deeper upper and middle crust which was partly controlled by antiforms likely related to earlier shortening was accommodated on a network of anastomosing shear zones

upper mantle stratigraphy of the slave craton canada insights into a new kimberlite province mantle xenoliths carried by kimberlite magma provide the only hard evidence of the rock types that constitute cratonic roots and the conditions under which they formed here we present the first such data for the slave craton northern canada based on samples of peridotite eclogite and pyroxenite collected from a middle jurassic kimberlite jericho pipe the petrology and thermobarometric analysis of these mantle xenoliths provide estimates of the thermal state and stratigraphy of the underlying mantle and constrain the evolution of this ancient craton the upper mantle beneath the north central slave is relatively cold as is typical of cratonic environments but it is also associated with relatively high values of surface heat flow 47 50 mw m 2 because of this craton9s highly radiogenic crust below 160 190 km the jericho p t array shows a significant high temperature disturbance caused by transient magmatic events the apparent source region for both porphyroclastic peridotite and other texturally unequilibrated magmatic rocks coincides with this thermal excursion and is taken to mark the base of the petrological lithosphere the depth of this petrological transition is also consistent with important geophysical discontinuities mapped below the slave craton

relationship of topex poseidon altimetric height to steric height and circulation in the north pacific topex poseidon altimetric height is compared with 20 transpacific eddy resolving realizations of steric height the latter are calculated from temperature expendable bathythermograph xbt and salinity expendable conductivity and temperature profiler xctd profiles along a precisely repeating ship track over a period of 5 years the overall difference between steric height and altimetric height is 5 2 cm rms on long wavelengths 500 km containing 17 of the steric height variance the 3 0 cm rms difference and lowered coherence are due to the sparse distribution of altimeter ground tracks along the xbt section the 2 4 cm rms difference in the basin wide spatial mean appears to be due to fluctuations in bottom pressure differences between steric height and altimetric height increase near the western boundary but data variance increases even more and so the signal to noise ratio is highest in the western quarter of the transect basin wide integrals of surface geostrophic transport from steric height and altimetric height are in reasonable agreement the 1 9 104 m2 s 1 rms difference is mainly because the interpolated altimetric height lacks spatial resolution across the narrow western boundary current a linear regression is used to demonstrate the estimation of subsurface temperature from altimetric data errors diminish from 0 8 c at 200 m to 0 3 c at 400 m geostrophic volume transport 0 800 m shows agreement that is similar to surface transport with 4 8 sverdrup sv 106 m3 s 1 rms difference the combination of altimetric height with subsurface temperature and salinity profiling is a powerful tool for observing variability in circulation and transport of the upper ocean the continuing need for appropriate subsurface data for verification and for statistical estimation is emphasized this includes salinity measurements which significantly reduce errors in specific volume and steric height

the california current system in relation to the northeast pacific ocean circulation abstract the california current system is described in its regional setting using two modern datasets argo provides a broadscale view of the entire eastern north pacific ocean for the period 2004 2010 and the high resolution xbt network includes transects from honolulu to san francisco 1991 2010 and to los angeles 2008 2010 together these datasets describe a california current of 500 800 km width extending along the coast from 43 n to 23 n the mean southward transport of the california current is about 5 sv off central and southern california with about 2 5 sv of northward flow on its inshore side interannual variations are 50 or more of the mean transports the salinity minimum in the core of the california current is supplied by the north pacific current and by freshwater from the northern continental shelf and modified by alongshore geostrophic and across shore ekman advection as well as eddy fluxes and air sea exchange the heat and freshwater content of the california current vary in response to the fluctuating strength of the alongshore geostrophic flow on its offshore side the california current is influenced by north pacific intermediate waters at its deepest levels and by eastern subtropical mode waters on shallower density surfaces in total the sources of the california current its alongshore advection and its strong interactions with the inshore upwelling region and the offshore gyre interior combine to make this a rich and diverse ecosystem the present work reviews previous contributions to the regional oceanography and uses the new datasets to paint a spatially and temporally more comprehensive description than was possible previously

the california current system as a transmitter of millennial scale climate change on the northeastern pacific margin from 10 to 50 ka a high resolution record of 18o and mg ca based temperatures spanning 10 50 ka has been reconstructed from the vancouver margin of the northeastern pacific ocean md02 2496 from two planktonic foraminiferal species neogloboquadrina pachyderma s and globigerina bulloides while 18ocalcite appears synchronous with dansgaard oeschger interstadials dois throughout the record millennial scale variability in sea surface temperatures ssts and reconstructed 18oseawater are frequently out of phase with greenland climate changes in water mass characteristics such as 18ocalcite and enriched 15n events apparently responded to millennial scale climate change during marine isotope stage 3 mis 3 such that negative 18ocalcite excursions coincided with heavier 15n these water mass characteristic shifts are suggestive of the presence of surface water advected from the eastern tropical north pacific etnp by relative strengthening of the california undercurrent cuc bringing warm salty tropical waters poleward the linkage between the strength of the cuc on the ne pacific margin and millennial scale climate change may be related to increased sea surface heights off central america as the intertropical convergence zone itcz shifted northward in response to changes in north atlantic ocean circulation poor correlations between proxies exist through late mis 3 into mis 2 ice sheet growth could have disrupted the linkage between cuc and the ne pacific margin as the laurentide ice sheet disrupted atmospheric circulation and the cordilleran ice sheet increasingly influenced regional paleoceanography

seasonal variations of the large scale geostrophic flow field and eddy kinetic energy inferred from the topex poseidon and jason 1 tandem mission data 1 geostrophic surface velocity anomalies are used to analyze the annual variations of the large scale geostrophic currents and of the eddy kinetic energy eke field of the ocean circulation the underlying geostrophic currents were estimated from the jason 1 topex poseidon jtp tandem altimetric sea surface height data using the parallel track approach with a 10 km along track resolution however because of the given separation of the tracks of the two satellites only large mesoscale eddies are resolved by the tandem measurements the analysis covers the entire 3 year period of the tandem mission 109 repeat cycles from september 2002 to september 2005 the analysis of the seasonal flow changes reveals annual changes of all major current systems but especially of the zonal flow field in low latitudes leading to zonal jets on the annual cycle in the southern pacific atlantic and indian oceans in middle and high latitudes indications of a seasonally modulated strength of the sverdrup circulation emerge from the analysis the eke field also shows changes in its amplitude on the annual period in low latitudes those can be rationalized as resulting from seasonally modulated currents in middle and high latitudes changes in the wind driven barotropic circulation loom large which are not represented in other altimetric velocity products results shown suggest that velocity time series of the jtp tandem mission should be continued through similar constellations e g of jason 1 and jason 2

crustal structure of nw british columbia and se alaska from seismic wide angle studies coast plutonic complex to stikinia crustal structure beneath the transition from the coast belt to the intermontane superterrane of the northern canadian cordillera is interpreted from the inversion of refraction and wide angle reflection seismic data the profile traverses an accretionary suture zone coast plutonic complex to continental crust deformed by the transpressive collision stikine terrane using data acquired by the accrete onshore offshore experiment and by a partially overlapping lithoprobe onshore experiment p wave travel time inversion and forward amplitude modeling are employed to determine crustal velocity structure the model exhibits a well defined transition throughout the crust that distinguishes the coast plutonic complex cpc from stikinia average crustal velocities beneath the cpc 6 45 km s are considerably faster than those beneath stikinia 6 25 km s crustal thickness also changes across the transition thin crust beneath the coast belt 30 32 km thickens beneath stikinia 35 37 km the observations within the coast belt are consistent with a tectonic history most recently dominated by extensional deformation primary structural control could be associated with either neogene extension and or the processes that are responsible for exhuming the coast belt during the early paleogene and have been inferred from geological studies slow mantle velocities 7 8 7 9 km s beneath the entire profile are indicative of high upper mantle temperatures comparison with the southern cordilleran coast belt reveals similar velocity structure within the massive plutonic complexes however substantial differences between the northern and southern coast belts emphasize along strike variations in terranes orogen geometry and postorogenic tectonics

early proterozoic magmatism in yukon canada constraints on the evolution of northwestern laurentia northwestern laurentia after cratonization at about 1 85 ga underwent a series of tectonic and magmatic events during the proterozoic that were followed by separation of laurentia from another landmass probably australia the oldest magmatic event produced the bonnet plume river intrusions bpri which intruded the wernecke supergroup as short dikes and small stocks the bpri are hydrothermally altered tholeiitic diorites gabbros and subordinate anorthositic and syenitic rocks with trace element signatures consistent with a rift origin depleted mantle model ages range from 2 29 to 2 57 ga and end values range from 0 7 to 1 7 an increasing crustal component is apparent in rocks with more evolved compositions four u pb zircon ages 1705 9 0 7 1709 4 1 4 1711 1 5 1 and 1713 6 12 7 ma indicate a paleoproterozoic age for the bpri these dates constrain the age of the wernecke supergroup to ca 1710 ma making it the oldest supracrustal succession in western laurentia e g 240 ma older than the belt supergroup of southeastern british columbia and the northwestern united states the wernecke supergroup was deposited in the first rift basin to open along the western margin of laurentia but was later inverted by the pre 1 6 ga racklan orogeny an event possibly influenced by transmission of compression from the yavapai and mazatzal orogenies in southern laurentia the neoproterozoic southwestern united states east antarctica sweat reconstruction which places australia next to northwestern laurentia is supported by linkages between paleoproterozoic and mesoproterozoic geological features in northwestern canada and australia

short lived 1 9 ga continental margin and its destruction wopmay orogen northwest canada a 1 9 ga continental margin in the northwest of the canadian shield evolved in less than 15 m y from a zone of crustal stretching through a phase of passive margin subsidence to attempted subduction beneath an exotic microcontinent reversal of subduction polarity and generation of a major episutural magmatic arc occurred within 15 m y following microcontinental accretion terminal collision occurred 90 m y at most after initial rifting certain differences in detail between this collided margin and those of phanerozoic age may be related to subduction of newly rifted lithosphere rapid evolution of the orogen the contracted passive margin phase in particular is consistent with but does not prove more rapid recycling of oceanic plates at that time

ambient seismic noise tomography of canada and adjacent regions part i crustal structures this paper presents the first continental scale study of the crust and upper mantle shear velocity v s structure of canada and adjacent regions using ambient noise tomography continuous waveform data recorded between 2003 and 2009 with 788 broadband seismograph stations in canada and adjacent regions were used in the analysis the higher primary frequency band of the ambient noise provides better resolution of crustal structures than previous tomographic models based on earthquake waveforms prominent low velocity anomalies are observed at shallow depths 20 km beneath the gulf of st lawrence in east canada the sedimentary basins of west canada and the cordillera in contrast the canadian shield exhibits high crustal velocities we characterize the crust mantle transition in terms of not only its depth and velocity but also its sharpness defined by its thickness and the amount of velocity increase considerable variations in the physical properties of the crust mantle transition are observed across canada positive correlations between the crustal thickness moho velocity and the thickness of the transition are evident throughout most of the craton except near hudson bay where the uppermost mantle v s is relatively low prominent vertical v s gradients are observed in the midcrust beneath the cordillera and beneath most of the canadian shield the midcrust velocity contrast beneath the cordillera may correspond to a detachment zone associated with high temperatures immediately beneath whereas the large midcrust velocity gradient beneath the canadian shield probably represents an ancient rheological boundary between the upper and lower crust

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

formation and variation of temperature inversions in the eastern subarctic north pacific 1 hydrographic data from profiling float observations for 2001 2005 and from expendable bathythermograph observations for 1993 2005 were analyzed to study the formation and variation of temperature inversions t inversions in the eastern subarctic north pacific snp the formation and variation of t inversions differed significantly between the northern and southern regions of the eastern snp in the northern region the temperature minimum t min at the top of t inversions outcropped to the sea surface and was cooled in the mixed layer nearly every winter this process caused a seasonal cycle in the magnitude of t inversions t with a maximum in winter in the southern region the winter t min outcropped relatively infrequently and the t did not exhibit a significant maximum in winter during most years the t min in the southern region was likely to outcrop upstream near the date line roughly one year earlier and was then advected to the southern region

interannual variability in northeast pacific circulation 1 interannual variability of the circulation in the northeast pacific ocean is explored through a joint analysis of expendable bathythermograph xbt and expendable conductivity temperature depth xctd data satellite altimetry and output from a model that was constrained by ocean data xbt temperature profiles with high spatial resolution are available in the eastern north pacific along two repeated transects these ship tracks along with the coast of north america define a closed box which is used to study the time mean circulation and its variability on interannual timescales geostrophic velocities from xbt data are compared with geostrophic velocities from model output as well as the full model velocity fields correlations in variability on interannual timescales between transport in the subpolar gyre and in the subtropical gyre are present in both model output and data the nature of the variability and its relation to the changes of the strength of the north pacific current npc which supplies the water for both gyres are explored interannual variability in gyre transport is found to be related to both the bifurcation of the npc resulting in an anticorrelation in transport between the two gyres and to variations in npc strength resulting in simultaneous changes in the two gyres the dominant signal is found to be a long term increase in the npc which results in a strengthening of the subtropical gyre possible connections with local scale wind stress changes and with the el nino southern oscillation phenomenon are also explored

seismic velocity structure of the queen charlotte basin beneath hecate strait seismic refraction data across hecate strait in the northern queen charlotte basin were collected in a coincident reflection and refraction survey crustal velocity models provide a framework to help understand the formation of the sedimentary basin and the processes occurring near the queen charlotte fault a major ocean continent transform fault beneath the sediments which have a maximum thickness of 6 km a velocity gradient extends from about 5 to 8 km depth within which velocities increase typically from 6 3 to 6 4 km s 1 a thick constant velocity region was found down to a depth varying from 14 to 22 km with the smallest depths located beneath the central basin the base of the constant velocity layer was marked by a distinct mid crustal interface across which velocities increased from 6 4 6 5 km s 1 to approximately 6 8 6 9 km s 1 moho was interpreted to be at a near uniform depth of 26 28 km beneath hecate strait and the eastern queen charlotte islands the associated variation in crustal t

accretion of the archean slave province continental rift models have long been applied to the archean slave province of northwestern canada a reassessment of these models shows them to be incompatible with observed geological relations and suggests that contractional tectonic models may be more appropriate than extensional ones regions composed of different rock suites e g orthogneisses vs mafic volcanics are separated by high strain zones recording large displacements it is proposed that the high strain zones separate four distinct terranes that have been juxtaposed during collisional orogenesis from west to east these include the anton terrane interpreted as an archean microcontinent the sleepy dragon terrane possibly an exhumed more eastern part of the anton terrane the contwoyto terrane a westward verging fold and thrust belt containing tectonic slivers of greenstone volcanics and the hackett river volcanic terrane interpreted as an archean island arc the contwoyto and hackett river terranes represent a paired accretionary prism and island arc system that formed above an east dipping subduction zone these collided with the anton microcontinent producing a basement nappe expressed as the sleepy dragon terrane during the main accretion event within the slave province the whole tectonic assemblage was intruded by late kinematic to postkinematic granitoids

how the crust meets the mantle lithoprobe perspectives on the mohorovicic discontinuity and crust mantle transition application of regional geophysical and geological methods throughout two decades of canada s lithoprobe project provides new opportunities to analyze the mohorovicic discontinuity moho and crust mantle transition the transect format employed during lithoprobe in which 10 specified regions of canada were targeted for approximately a decade each between 1984 and 2003 permitted teams of scientists to focus on geological geophysical and tectonic issues for each transect as a primary objective was to enhance knowledge of the structure of the crust and lithosphere an obvious target in each transect was the nature and origin of the moho and crust mantle transition accordingly the combined results provide new perspectives on the moho and the relationship of the moho to the crust mantle transition perhaps the most important result is that the continental geophysical moho is a deceptively simple feature it has a variety of signatures at different scales that preclude a single universally applicable interpretation in methods that provide large scale information such as regional seismic studies it is a relatively abrupt refraction velocity contrast that often displays a dramatic downward decrease in seismic reflectivity however its origin in a geological or tectonic sense is perhaps best determined by careful analyses of structural details near the geophysical moho which are complex and varied in some areas within canada it appears that the geophysical moho may be old and perhaps remains from the time the crust formed in other areas it appears to be a relatively young feature that was superimposed onto older crustal fabrics

wide angle seismic imaging across accreted terranes southeastern alaska and western british columbia abstract this study addresses the question of crustal moho and uppermost mantle structure across an accreted terrane continental arc and fold and thrust belt in southeastern alaska and western british columbia the 186 km long portland canal line of the accrete wide angle seismic dataset across the coast mountains is analyzed using a combination of travel time analysis techniques including delay time tomography turning ray tomography reciprocal time analysis intercept time inversion and forward ray tracing additional constraints on the model are obtained from a coincident vertical incidence seismic section and from correlation with the mapping of geologic structures plunging into the seismic section the study reveals moderately high crustal velocities low velocity gradient in the middle crust and decreasing average crustal velocity and a north deepening moho termination of crustal reflectivity across a vertical zone the coast shear zone csz indicates that the csz is most likely a strike slip fault associated with a transpressive tectonic regime a mid cretaceous thrust system mapped on the surface to the west of the csz is imaged by several groups of mid to lower crustal reflectors extending close to the moho indicating it was a thick skinned thrust system ne dipping fabric imaged within the coast mountains batholith cmb is associated with a ductile deformation during early eocene crustal extension the crustal section under the cmb which has an average velocity of 6 55 km s and shallower than average crustal thickness of 31 km can be considered as corresponding to the lower two thirds of an average crustal section which has been inflated by intrusions of high velocity tonalite to gabbro sills

lithospheric structure beneath the archaean slave province and proterozoic wopmay orogen northwestern canada from a lithoprobe refraction wide angle reflection survey the slave geological province a relatively small craton in nw canada that includes the oldest rocks in the world is one of five cratons that form the archaean continental core of north america the palaeoproterozoic wopmay orogen lying between the craton and the phanerozoic northern canadian cordillera represents crustal growth through addition of a series of north south oriented magmatic arcs and accreted terranes as part of lithoprobe s multidisciplinary studies line 11 of the snore 97 seismic refraction wide angle reflection survey investigated the structure of the lithosphere in this region interpretation of crustal and mantle arrivals from 13 record sections followed an iterative procedure of traveltime inversion and forward modelling results show that crustal thickness at 32 35 km remains relatively constant from the archaean regions in the east to proterozoic domains in the west contrary to average values of crustal thicknesses from global compilations that suggest thicker proterozoic crust at the westernmost end of the line where crustal extension and basin formation are inferred the crust thins to 30 km upper crustal velocities to about 12 km depth lie in the range of 5 8 6 2 km s 1 the middle crust of thickness 8 10 km has velocities between 6 2 and 6 6 km s 1 average velocities for the lower crust differentiated as a 10 km thick layer range between 6 6 and 6 9 km s 1 with a higher velocity region 7 1 km s 1 in the transition zone between the fort simpson magmatic arc and hottah accreted terrane in the wopmay orogen where a palaeoproterozoic subduction zone has been inferred from coincident multichannel reflection data in the same area anomalously low upper mantle velocities 7 5 km s 1 have been found indicating that the effects of collision subduction and accompanying physical changes in the rocks comprising the mantle lithospheric wedge above the underthrusting structure may have been retained for 1800 ma data from most record sections with offset distances greater than 250 km show continuous wide angle reflections from upper mantle depths of about 75 km and almost 100 km although poorly constrained velocities in this depth range vary from 8 4 to 8 8 km s 1 interpretation of these phases and mantle reflections from equivalent depths in coincident near vertical incidence multichannel data relates them to subduction and underthrusting of oceanic crust and subsequent phase changes that occurred during the assembly of the craton and the evolution of the palaeoproterozoic orogen

geophysical evidence for crustal thickness variations between the denali and tintina fault systems in west central yukon analyses of receiver functions recorded at two broadband seismic stations in the northern cordillera indicate that the crust is thinner beneath dawson 35 km than whitehorse 39 km a simple two dimensional gravity model constrained by the seismic results shows that this change in crustal thickness occurs at about 63 n in a zone approximately 35 km wide where the moho dips at 8 to the south the bouguer anomaly high associated with the thinner crust can be traced westward into east central alaska where crustal thinning and extension are well documented therefore we propose that west central yukon north of 63 n has been extended also on the basis of geological and other geophysical data we examine three likely time windows in the cretaceous early tertiary and present we discuss data which indicate that early tertiary and younger extension may be related to the transfer of motion from the denali fault system inboard to the tintina fault system earlier cretaceous extension has been variously attributed to collision related back arc extension syncollisional processes or gravitational collapse of an overthickened crustal section the relative importance of extension in these periods remains nebulus however the correspondence between the transition in crustal thickness determined in this study and a mapped boundary between lower plate and upper plate rocks suggests mid cretaceous extension exerted a significant influence on current moho depths

the moho of north america a brief review focused on recent studies abstract recent national programs in canada lithoprobe and the u s earthscope are providing vast quantities of data and many new scientific insights concerning crustal and lithospheric mantle structure and evolution more modest but significant results are also being produced in and about mexico this paper primarily focuses on results published since 2005 and presents an updated moho map of north america this overview of crustal structure does reveal a number of interesting observations for example two buried distinct crustal blocks have been discovered in the past 20 years one was caught in a precambrian suture zone in canada and the other is buried under the gulf coast region and is still of unknown origin the precambrian assembly of the continent has been documented by the mapping of numerous suture zones and shallow portions of subducted slabs have been preserved in several cases not surprisingly the internal structure of these suture zones is complex and highly variable isostatic adjustment has been shown to be a complex process involving the lithospheric mantle not just crustal structure variations specifically the correlation of crustal thickness with elevation is only approximate at best several crustal blocks that have been stable over very long periods of time possess unusually thick crust whose lower portion is usually fast vp 7 0 km s rifting has been shown to affect the crust in a variety of ways ranging from the massive magmatic modification that produced the mid continent rift system to the broad region of extension in the basin and range province crustal structure along the active modern western margin of north america is highly complex as would be expected as a result of transitions between subduction and transform faulting and variations in volcanism and intraplate magmatism we clearly still have a lot to learn about the structure and evolution of this continent

lithospheric structure in the southern canadian cordillera from a network of seismic refraction lines lithospheric velocity structure and its relationship to regional tectonics and development of the southern canadian cordillera are derived from a synthesis of interpretations from nine in line seismic refraction wide angle reflection profiles and broadside data recorded during the lithoprobe southern cordillera refraction experiment score and other refraction experiments across southern british columbia and one profile in northwestern washington consistency of the score two dimensional models at their intersection positions is achieved through application of a simultaneous inversion of all relevant traveltime data the cross sectional and map presentations demonstrate the strong degree of three dimensional heterogeneity within the crust and upper mantle a first order characteristic is the continuous increase in crustal velocities westward from the foreland belt to the insular belt the variations do not correlate with the morphogeological belts they do correspond with large scale geological and or

a tomographic crustal velocity model of the central fennoscandian shield summary in this paper local seismic tomographic method is used to find the terrane distribution within the central parts of the accretionary svecofennian orogen this study presents a crustal pwave velocity model and for the first time the s wave velocity and vp vs ratio model of svekalapko area that is 700 800 km 2 in southern and central finland the 3 d model is presented as p and s wave velocity as well as vp vs ratio depth slices and vertical sections the data set comprised of several subsets of crustal pg and sg wave traveltime data from local events recorded by the svekalapko seismic tomography array in 1998 1999 from older controlled source shots recorded at portable stations as well as at permanent stations and from non controlled chemical explosions recorded at permanent seismic stations from 300 local explosions a total of 10 404 pg wave and 9361 sg wave arrival times were inverted to create independent 3 d vp and vs tomographic models from which the vp vs ratio was calculated according to sensitivity tests the optimal horizontal resolution of recognizable velocity structures in the central study area is at least 60 km down to depths of 40 km in the final model the seismic velocities vary smoothly the lateral variations are larger for vp 5 9 6 6 km s 1 than for vs 3 5 3 8 km s 1 in the upper 20 km of the crust at depths of 20 40 km vp varies from 6 5 to 7 2 km s 1 and vs from 3 7 to 4 1 km s 1 the vp vs ratio varies spatially more distinct than p and s wave velocities usually from 1 70 to 1 74 in the upper crust and from 1 72 to 1 78 in the lower crust schist belts and their continuations at depth are associated with lower velocities and lower vp vs ratios vp 6 2 6 8 km s 1 vs 3 6 3 9 km s 1 vp vs 1 68 1 73 than the granitoid areas vp 6 3 7 4 km s 1 vs 3 6 4 2 km s 1 vp vs 1 72 1 78 the svecofennian orogen was accreted from crustal blocks ranging in size from 100 100 km 2 to 200 200 km 2 in cross sectional area the intervening sedimentary belts have ca 0 2 km s 1 lower p and s wave velocities and ca 0 04 lower vp vs ratios tomographic model supports the idea that the thick svecofennian crust was accreted from several crustal terranes some hidden and that the crust was later modified by intra and underplating

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

generation of new continental crust and terrane accretion in southeastern alaska and western british columbia constraints from p and s wave wide angle seismic data accrete abstract the accrete study addresses the question of continental assemblage in southeastern alaska and western british columbia through accretion of exotic terranes and generation of new crust by magmatic addition in a former continental arc we present results of wide angle p and s wave seismic interpretation of a 300 km long marine land seismic line across the contacts between accreted terranes and coast mountains additional constraints on the model are obtained from correlation with geologic mapping our results indicate that the coast shear zone csz is a nearly vertical fault zone probably related to a transpressive regime west of the csz the mid cretaceous 90 ma thrust belt is rooted in the deep crust and is truncated by the csz from the interpretation of the imaged sub vertical reflecting zones we infer the positions of the alexander wrangellia terrane boundary awb and of tertiary extensional grabens within dixon entrance near its intersection with the profile the observed values of vp and vp vs in the lower crust of the alexander terrane are similar to those of oceanic crust and distinctly different from the coast mountains batholith cmb to the northeast the crust under the cmb 32 km is thinner than the average continental crust and the moho is sharp 200 m and highly reflective the low velocity mantle 7 9 km s suggests high temperature consistent with the stability of garnet in mafic rocks in the lower crust the lower crustal velocity of 6 9 km s supports a lower crust composed of interlayered garnet pyroxene granulite and quartzofeldspathic restite related to batholith generation the crustal section under the cmb is seismically identical to the lower two thirds of normal crust heated and inflated by intrusions of tonalite and gabbro interlayered with restites from batholith generation and uplifted during exhumation

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

nacr14 a 3d model for the crustal structure of the north american continent abstract based on the large number of crustal seismic experiments carried out in the last decades we create nacr14 a 3d crustal model of the north american continent at a resolution of 1 1 we present maps of thickness and average velocities of the main layers that comprise the north american crystalline crust obtained from the most recent seismic crustal models within the usgs crustal structure database however the crustal data are unevenly distributed and in some cases discrepancies exist between published models in order to construct a consistent 3d crustal model with three layers in the crystalline crust we refrained from a direct interpolation of the crustal seismic parameters in the database instead we implemented the following sequence of steps 1 definition of the geometry of the main tectonic provinces of north america 2 selection and evaluation of the reliability of seismic crustal models in the database 3 estimation of the p wave seismic velocity and thickness of the upper middle and lower crust for each tectonic province 4 estimation of the interpolated pn velocity distribution the resulting average velocity of the crystalline crust is mostly consistent with that of the seismic points the main variations of the structure of the crystalline crust of north america displayed in the model can be related to its tectonic evolution the model available in a digital form can be used in various geophysical applications such as the correction for the crustal effects in gravity and seismic tomography and models of dynamic topography in order to detect heterogeneities characterizing the underlying upper mantle

constraints on the composition of the crust and uppermost mantle in northwestern canada vp vs variations along lithoprobe s snorcle transect shear wave seismic data recorded along four profiles during the snore 97 1997 slave northern cordillera refraction experiment refraction wide angle reflection experiment in northwestern canada are analyzed to provide s wave velocity vs models these are combined with previous p wave velocity vp models to produce cross sections of the ratio vp vs for the crust and upper mantle the vp vs values are related to rock types through comparisons with published laboratory data the slave craton has low vp vs values of 1 68 1 72 indicating a predominantly silicic crustal composition higher values 1 78 for the great bear and eastern hottah domains of the wopmay orogen imply a more mafic than average crustal composition in the western hottah and fort simpson arc values of vp vs drop to 1 69 these low values continue westward for 700 km into the foreland and omineca belts of the cordillera providing support for the interpretation from coincident seismic reflection studies that much of the crust fro

the 1991 1996 natmap slave province project introduction the 11 papers contributed to this issue on the geology of the slave province are summarized and where appropriate links between data from the various contributions are emphasized in the discussion we provide a synthesis of the present knowledge base on pre yellowknife supergroup basement rocks throughout the slave province all available age data on mesoarchean and paleoarchean basement rocks are compiled and in a first attempt to seek regional correlations 10 events of crustal growth and or reworking are recognized spanning well over 1 billion years of earth s history the spatial distributions of these events across the craton are discussed finally we pose a series of important questions that remain and that may help guide future research

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

the queen charlotte islands refraction project part i the queen charlotte fault zone the active margin between the continental north american plate and oceanic pacific plate west of the queen charlotte islands was the site of an extensive onshore offshore seismic refraction project

global ocean circulation during 1992 1997 estimated from ocean observations and a general circulation model 1 a three dimensional oceanic state is estimated for the period 1992 1997 as it results from combining large scale ocean data sets with a general circulation model at the cost of increased computational load the estimation assimilation method is chosen specifically so that the resulting state estimate is consistent with the model equations having no artificial sources or sinks to bring the model into close agreement with observations its initial temperature and salinity conditions are permitted to change as are the time dependent surface fluxes of momentum heat and freshwater resulting changes of these control vectors are largely consistent with accepted uncertainties in the hydrographic climatology and meteorological analyses the assimilation procedure is able to correct for many of the traditional shortcomings of the flow field by changing the surface boundary conditions changes in the resulting flow field are predominantly on the gyre scale and affect many features that are often poorly simulated in traditional numerical simulations such as the strengths of the gulf stream and its extension the azores current and the anticyclonic circulation associated with the labrador sea tests of the results and their consistency with prior error assumptions show that the constrained model has moved considerably closer to the observations imposed as constraints but has also moved closer to independent data from the world ocean circulation experiment not used in the assimilation procedure in some regions where the comparisons remain indeterminate not enough ocean observations are available and it is difficult to ascribe the residuals to either the model or the observations although problems remain a useful first solution to the global time dependent ocean state estimation problem has been found the estimates will continue to improve through the evolution of numerical models computer power increases more data and more efficient estimation methods

modeling wide angle seismic data for crustal structure southeastern grenville province a modeling methodology for obtaining two dimensional 2 d crustal structure from wide angle seismic data is applied to data from the southeastern grenville province pre modeling steps include 1 assignment of arrival pick uncertainties for appropriate data fitting and weighting using an empirical relationship based on signal to noise ratio 2 using a modified form of travel time reciprocity to avoid unreasonable levels of model heterogeneity and 3 identifying data unsuitable for 2 d modeling the goal of the travel time inversion amplitude modeling approach is to obtain a minimum structure and minimum parameter model that takes into account both horizontal and vertical variations in the resolution of typical wide angle data each step of a layer stripping procedure involves a series of inversions in which a one dimensional or simple starting model is improved with additional velocity and or interface nodes until a satisfactory trade off between travel time fit parameter resolution and complete ray coverage of all source receiver pairs is achieved using zero vertical velocity gradient layers and head waves during preliminary first arrival inversion can 1 decrease the number of intermediate models 2 allow greater lateral heterogeneity to be imaged and 3 simplify incorporation of amplitude modeling constraints into the final model using amplitude distance curves allows quantitative modeling of the relative amplitude and offset variations of phases discrepancies between observed and calculated reflection amplitudes are used to infer fundamental non step like velocity changes at layer boundaries later arrivals due to unresolved velocity anomalies are modeled using reflecting segments that float within the model without an associated velocity structure these reflectors provide a spatial image like that obtained from vertical incidence reflection data as opposed to a velocity image the model of grenville crustal structure is more detailed than a model obtained from a previous interpretation of the data and includes elements analogous to those imaged in nearby deep reflection data a crustal scale zone of wide angle reflectors with an average easterly apparent dip of 13 defines a major grenvillian terrane boundary

the structure and nature of the moho beneath central iberia abstract the moho is the most conspicuous feature in the alcudia deep normal incidence and wide angle seismic reflection datasets acquired across the central iberia zone this discontinuity appears to be sub horizontal with a slight dip toward the center of the iberian peninsula beneath the tajo basin densely spaced wide angle seismic reflection data reveal conspicuous pmp and sms reflections in the shot records these reflections arriving over a 1 5 s time window and characterized by a relatively low frequency content are used to infer the internal structure and characteristics of this crustal boundary in an effort to place constraints on its nature beneath the studied area the wide angle shot records were processed in order to generate low fold stacks that reveal gradual deepening of moho pmp phases from 10 2 s twt 31 km in the central iberian zone to 11 8 s twt 36 km beneath the tajo basin the moho seismic signature was the main objective of a series of 1 d and 2 d synthetic modeling simulations reflectivity modeling was used as the 1 d modeling approach and an elastic finite difference scheme was used for the 2 d modeling the moho can be considered to be a self similar fractal heterogeneous media with a bimodal velocity distribution alternating crustal and mantle values with horizontal correlation lengths that range between 1 and 4 km and vertical correlation lengths that range from 0 2 to 1 km the depth of this boundary is most probably the result of late to post variscan re equilibration processes affecting a previously deformed and laminated lower crust the mechanisms that took part in this process might have differed to the north and south of the sampled central iberian zone being more thermally induced to the north near the central system processes leading to the layered structure of the moho boundary either tectonic or magmatic should be further investigated

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

evolution of the slave craton greenstone belts in the slave craton represent the episodic accumulation of volcanic and sedimentary rocks over as much as 200 m y in the western craton volcanic and sedimentary rocks were deposited between 2 81 and 2 60 ga on 2 9 3 1 ga sialic basement not tectonically juxtaposed with it deposition of 2 6 ga turbidite and conglomerate sequences across the entire slave craton was synchronous with or followed by the main phase of regional deformation and metamorphism at 2 6 2 58 ga and final stabilization of the craton

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