analysis of bar morphology using multi temporal and multi sensor satellite images example from the han estuary korea abstract in the present paper we report a new powerful technique of studying bar morphology using multi sensor and multi temporal satellite images with examples from the inaccessible field sites of the han estuary in korea the technique utilizes the ability of multi spectral optical sensors for classifying the types of land cover and the ability of synthetic aperture radar sar for acquiring radar imagery during day and night irrespective of cloud cover combining the data acquired by both types of sensors at different times the bar morphology of the han estuary is analyzed in this study the han estuary is situated on the north limit line nnl dividing north and south korea and considered to have retained its rich ecological value however because of the limited access to the estuary little information is available on the morphology of the han estuary and the technique based on satellite remote sensing described in this paper is the most suitable and only approach to obtaining information on such inaccessible areas in the present paper the bar morphology of the han estuary from the years 2000 to 2009 is investigated using multi temporal spaceborne optical sensors including those on board of spot 5 landsat 7 quickbird kompsat 2 and orbview 3 and also c band synthetic aperture radar sar on board of radarsat 1 and envisat with limited field survey data sixteen sets of optical data and twelve sets of sar data were used to study the spatial and temporal variations of bar morphology and the effects of tide and precipitation the results show that there was some variation in shape and size of bars depending on the location the tidal effect is large on the bars closer to the open yellow sea and the effect of precipitation was observed on the bars located in the mouths of rivers based on the changes of the bar water boundary a topographical map was produced showing the relative height of bars using the technique of satellite remote sensing this paper has shown for the first time the long term bar morphological characteristics of the restricted han estuary on the nll and the authors anticipate that the results together with the relative height map of bars will constitute the basis of future morphological and ecological studies in this important estuary

ndsr isotopic study of proterozoic to triassic sediments from southeastern british columbia abstract sedimentary rocks from the southeastern canadian cordillera varying in age from mid proterozoic to triassic have been analysed for their nd isotopic composition e nd t values range from 1 5 to 17 2 and nd model ages t dm nd vary from 1 00 to 2 32 ga much in excess over their stratigraphic ages the difference between the two ages ranges from 0 43 to 1 93 ga decreasing as the sediments become stratigraphically older nd isotopic compositions of sediments suggest that there are two distinct continental sources of sediments in the cordilleran miogeocline a an older source e nd 0 from 20 3 to 23 8 with apparent crustal residence ages of 2 26 2 32 ga and b a younger source average e nd 0 14 0 with the crustal residence age of about 1 8 ga the older residence ages are interpreted to be due to mixtures of materials from the archean and proterozoic crusts sediments belonging to the laib formation lower cambrian and lower clastic part of the milford group namurian appear to have derived from an archean continental segment with some admixture of sediments from the early proterozoic source the younger crustal source which seems to be the principal supplier of sediments for most of the stratigraphic units aldridge formation middle proterozoic horsethief creek group upper proterozoic hamill and lardeau groups lower cambrian nelway formation middle cambrian active formation ordovician and part of milford group is not the archean canadian shield immediately to the east recent subsurface mapping of the alberta basement beneath the phanerozoic sedimentary cover using u pb zircon dating of igneous lithologies 1 has established the extensive archean and early proterozoic crustal provinces it is proposed here that the early proterozoic province of west central alberta is the most likely source of the easterly derived sedimentary rocks of the cordilleran miogeocline with t cr ages from 1 94 to 1 50 ga on the basis of sedimentologic tectonic and isotopic evidence we suggest that the younger sediments could be to some extent recycled older sediments for the triassic slocan and ymir groups eastern part of quesnel terrane sedimentologic lithologic tectonic and isotopic evidence suggest the source was a western one with about 1 8 ga crustal residence age comparison of the crustal residence ages with stratigraphic ages shows the best fit nd evolution curve for the cordilleran miogeocline approximately coincides with the continental growth curve deduced for the north atlantic province and similar to the growth curve for gondwana during the phanerozoic this curve also passes through the north american composite the levelling off of crustal residence ages for the mid proterozoic to triassic sediments at about 1 8 ga supports the idea of negligible crustal growth since at least 1 7 ga the average crustal residence age of the modern miogeoclinal and cratonic sediments

the hsi bright reflector further evidence for extensive magmatism in the precambrian of western canada abstract seismic reflection lines acquired in 1995 as part of lithoprobe canada s national geoscientific research program revealed unusually bright reflectors of extensive lateral scale in the archaean medicine hat block of southern alberta the herein named head smashed in hsi reflector is imaged over an area of at least 6000 km 2 in the upper half of the crust the reflector appears as a mostly horizontal to subhorizontal feature although continuous it has a complex and laterally variable internal structure comparison with a reflector of known impedance contrast in the overlying western canadian sedimentary basin indicates a high impedance structure to cause the reflections dense one dimensional modelling is consistent with the reflector being a multilayered structure with layer thicknesses in the range of tens to hundreds of metres and lateral scales of discrete reflecting elements between tens of metres and hundreds of metres polarity constraints overall geometry and reflection character strongly suggest that mafic ultramafic horizontal sheets are the cause of hsi reflectivity the hsi is the third major sequence of strong crustal reflectivity imaged by lithoprobe deep seismic data in the precambrian crust of western canada all three features are very similar in overall geometry reflector strength and character and have been interpreted as horizontal sheetlike intrusions small scale variations of the reflectivity signatures suggest a pronounced rheological heterogeneity in the upper crustal rocks within the host tectonic domains

introduction to special issue of canadian journal of earth sciences the alberta basement transect of lithoprobe from outcrops in northeastern alberta to exposures within structural culminations in the canadian cordillera the crystalline basement that lies buried beneath the phanerozoic alberta basin of western canada represents a significant part of the canadian shield ca 750 000 km2 the advent of modern high resolution aeromagnetic data and u pb geochronology have opened the doors for the next era of investigation of the crystalline basement of the alberta basin aeromagnetic data and geochronology provided important physical and temporal links to the exposed canadian shield which allowed its structural framework to be extrapolated into the subsurface the most recent chapter in this evolving story has been the alberta basement transects of lithoprobe a 12 year program which has used multi disciplinary geoscience studies to further elucidate the nature history and geometric characteristics of basement domains beneath the alberta basin this special issue is the second in a three issue set of publications

tectonic significance of gravity and magnetic variations along the lithoprobe southern canadian cordillera transect correlation of potential field data to regional geological features within the lithoprobe southern canadian cordillera transect corridor allows characterization of anomaly patterns according to their likely sources long wavelength bouguer gravity anomalies are attributed to isostatic effects of topography which in most areas is compensated two notable exceptions occur in the foreland belt a large positive isostatic anomaly is likely due to mechanical support of topography formed as cordilleran thrust sheets were emplaced over the thick craton and on the west coast isostatic anomalies are related to active subduction long wavelength magnetic anomalies in the foreland belt are associated with cratonal basement beneath the thrust sheets and these can be followed westward to near the omineca belt a prominent positive magnetic anomaly along the western coast belt is probably associated with mafic rocks generated during subduction elsewhere relatively short wavelength gravity and magnetic anomalies c

a relic proterozoic subduction zone in western canada new evidence from seismic reflection and receiver function data lithoprobe seismic reflection profiles in the western canada sedimentary basin reveal a prominent band of dipping reflections that appear to extend into the upper mantle the nne strike of these reflections determined from intersecting profiles is parallel to the trend of the ca 1 8 ga rimbey domain an overlying magmatic belt receiver function analysis of teleseismic data recorded at a nearby site shows evidence for a low velocity zone lvz beneath the rimbey domain between 13 and 16 km depth the unusually low s wave velocity of the lvz 2 9 0 2 km s suggests a composition similar to serpentinized peridotites that occur in ophiolites taken together our data support a model of proterozoic subduction beneath the hearne province we interpret the dipping reflections observed on the seismic profiles as a shear zone that developed during subduction of a se dipping slab and the lvz as a fragment of oceanic lithosphere that was obducted to the overriding plate

toroidal flow in the outer core and the thermal regime below the core mantle boundary numerical calculations of fluid dynamos are used to constrain the probable origin of toroidal flows in the outer core azimuthal drift of the core fluid relative to the mantle is the sum of three components 1 uniform differential rotation of the core relative to the mantle produced by electromagnetic torques on the mantle 2 cylindrical flow driven by electromagnetic torques in the core and 3 buoyantly driven thermal wind flow produced by lateral variations of temperature and composition dynamo calculations indicate that electromagnetic torques on the mantle contribute to long term drift but are not likely to be its primary cause zonal flow driven by electromagnetic torques in the core and thermal wind flows driven by zonal temperature gradients are both sufficiently energetic to account for azimuthal flows with angular velocities of 0 1 0 5 yr 1 as inferred from frozen flux analyses of secular variation

cordilleria revisited with a three dimensional model for cretaceous tectonics in british columbia the cordilleria microcontinent theory for the tectonics of british columbia in the cretaceous and early tertiary and for the origin of the canadian rocky mountains and related features is reviewed new isotopic geological and paleomagnetic data support the hypothesis that the amalgamated superterranes of british columbia and alaska were not attached to the mainland of north america in the early cretaceous and were probably well south of their present relative position consideration of that evidence together with sedimentological evidence from the albian leads to a slightly earlier best estimate 115 ma for the time of initial collision in the yukon new geophysical data for southeastern british columbia and idaho lead to a comparison with the iapetus suture in northern england it is suggested that the cordilleria suture dips west from the present purcell thrust and related structures and should cut the moho a new model for regional deformation in se british columbia is proposed involving a flake

simulations of crustal anatexis implications for the growth and differentiation of continental crust there is overwhelming and incontrovertible petrological and geophysical evidence for the significant role played by mantle derived mafic magma in the generation and growth of continental crust likewise intrusion of mafic magmas beneath or into continental crust is very likely the major source of enthalpy that drives intracrustal differentiation a simple dynamical model has been constructed to examine the critical factors that govern the evolution and time scale of crustal anatexic events when driven by basaltic magma underplating or injection into crust critical factors include the intensity of the enthalpy input i e the power dissipated and the rheological properties bulk composition and compositional structure of the source rocks undergoing partial fusion we have performed numerical simulations to evaluate these factors using phase equilibria and thermochemical and transport property data applicable to the binary eutectic system caal2si2o8 camgsi2o6 as a rough analog to study anatexis of mafic lower crust the role of enthalpy power is tested by varying the enthalpy or temperature along the base of the crustal block while maintaining a fixed temperature at the top as ratio tbot ttop increases modestly from 1 05 to 1 15 the average fraction of melt at steady state in the anatexic region increases from 50 to 75 time to attain steady state scales inversely with tbot ttop with an increase by a factor of 2 for a 10 decrease in tbot ttop typical anatexic timescales are in the range 103 to 105 years for length scales in range 102 to 103 m the consequences of different rheological models especially the importance of darcy percolative flow relative to en masse flow within the partial melt region was also investigated a value of the solid fraction called the critical value scrit is set such that for 0 0 5 relatively large volumes of nearly homogeneous melt are rapidly generated in distinction for scrit small more enthalpy is stored in the solid and less melt is produced however the compositional spectrum of liquids generated within the anatexic region is significantly larger for small scrit because of the sensitive dependence of solidi and liquidi on bulk composition melt productivity is related to bulk composition given a particular enthalpy power input and rheological model there is a factor of 2 difference in volume of melt generated when the bulk composition of the source is 10 modal percent less refractory compositionally zoned melts form by melting of either homogeneous or layered sources although composition frequency relations are sensitive to the initial subsolidus compositional structure the effects of anatexic events are to fundamentally reorganize the pattern of compositional structure within the crust intracrustal differentiation is a long term inevitable process associated with the underplating or injection of mafic magma into preexisting crust

lithoprobe crustal reflection cross section of the southern canadian cordillera 1 foreland thrust and fold belt to fraser river fault seismic reflection data from the south central canadian cordillera covering the interval from the easternmost metamorphic core complexes near arrow lakes to the fraser river fault system along the fraser river reveal a highly reflective and complex crust the base of the crustal reflectivity interpreted as the reflection moho is clearly delineated by a continuous sharp boundary that is essentially planar and slopes uniformly over a distance of 250 km from about 12 0 s in the east to about 10 5 s in the west this virtual lack of relief at the base of the crust contrasts sharply with surface structures that involve 25 km or more of structural relief some of these surface structures can be readily correlated to structures that are outlined by the reflection data and that can be followed into the middle and lower crust even though part of this area was subjected to large amounts of eocene extension the crust is not divisible into transparent upper and reflective lower layers as it is in parts of the u s cordillera three structural culminations the monashee complex the vernon antiform and the central nicola horst are interpreted on the basis of the reflection configuration and the surface geological relationships to have formed initially during jurassic to eocene compression and then to have been modified and exposed during early and middle eocene extension an example of a compressional structure observed on the profiles is the monashee decollement which can be traced from the surface westward into the lower crust extension is manifested along a variety of normal faults including the regionally extensive low angle okanagan valley eagle river fault system moderately dipping faults such as the columbia river and slocan lake faults and high angle faults such as the quilchena creek and coldwater faults both jurassic to eocene compressional shear zones and early to middle eocene extensional shear zones are listric into the lower crust or moho under the intermontane belt

heat flow and structure of the lithosphere in the eastern canadian shield twenty two new determinations of heat flow and radiogenic heat production in the superior and grenville provinces of the canadian shield are presented the new data and previously published measurements strongly constrain the thermal structure of the eastern canadian shield in the abitibi greenstone belt heat flow gradually increases from 29 mw m 2 near the grenville front to 44 mw m 2 east of the kapuskasing uplift this heat flow variation is interpreted in terms of crustal thickening and increased thickness of a tonalitic layer with average heat production of about 1 1 w m 3 this interpretation based on estimated heat production of major rock types in the region is consistent with crustal models derived from recent seismic reflection and refraction studies it also leads to an estimate of about 12 mw m 2 for the mantle heat flow beneath the area the average heat flow in the grenville province 41 10 mw m 2 is the same as that of the superior province this similarity and the lack of significant variation of heat flow across the grenville front indicate that the crust on both sides of the front has similar heat production and thus composition in the western part of the grenville province heat flow reaches high values in the vicinity of the boundary between the allochtonous polycyclic and monocyclic belts where enriched granitic plutons are found in the crystalline terranes in the central part of the grenville province heat flow and heat production are related to each other the parameters of the linear heat flow heat production relationship qr 30 2 in mw m 2 and d 7 1 1 7 km are close to those of the much younger appalachian province implying that the higher appalachian heat flow is due solely to higher heat production in the upper crust the data provide no evidence for variation of mantle heat flow between the superior grenville and appalachian provinces whose tectonic ages range between 2700 and 400 ma the small value of the mantle heat flow about 12 mw m 2 implies that the depth to the 450 c isotherm which controls the effective elastic thickness of the lithosphere is very sensitive to crustal heat production

north american central plains conductivity anomaly goes east the north american central plains electrical conductivity nacp anomaly has been known for almost two decades and its influence on palaeotectonic models of the north american continent has been significant magnetometer array studies have located the structure in a gross sense but there has not been until now a comprehensive magnetotelluric mt survey of it in this letter we report on the preliminary interpretation of data from thirty five mt sites recorded along a 400 km east west profile just north of the us canadian border we show that the anomaly at this latitude is 75 km farther east of the location previously mapped by the array studies modelling indicates that the conductive body has its top surface at about 10 km depth and appears to be anticlinal in shape the profile also extends sufficiently east that it traverses another previously known electrical structure referred to herein as the tobe anomaly we consider briefly other geophysical and geological data for the region and tentatively infer that the nacp structure is terminated to the east by the interpreted southern extension of the tabbernor fault fold system and that the tobe anomaly is an expression of the known southern extension of the thompson nickel belt both beneath phanerozoic sediments of the williston basin

mechanism for geomagnetic polarity reversals recent studies of old magnetic observations1 and the seismic velocity of the lower mantle2 suggest that at least part of the geomagnetic secular variation is driven by temperature anomalies in the solid mantle3 in particular a patch of flux of opposite sign to that expected for a dipole field occurs beneath southern africa it has intensified throughout the twentieth century by a process that is believed to be flux expulsion associated with a particularly hot part of the lowermost mantle and is drifting westwards a similar patch lies beneath south america here i show that the present fall in the dipole moment is directly related to the intensification and southward movement of these patches and suggest the fall occasionally leads to polarity reversal the almost linear increase in the frequency of polarity reversals that has occurred since the cretaceous quiet interval is attributed to the growth of the hot patch of mantle presently under southern africa

nd isotopic evidence for the antiquity of the wyoming province sm nd isotopic data on late archean age metasedimentary rocks from around the wyoming province yield nd values at 2 6 ga from 12 9 to 3 3 which correspond to depleted mantle model ages of 2 7 to 3 8 ga these results indicate that crust of a wide variety of ages was exposed and eroding in late archean time the predominance of middle archean model ages suggests that continental crust was extensive in the wyoming province by this time no resolvable correlation exists between initial nd value and geographic location or depositional environment of the metasedimentary rock samples thus there is no indication that any part of the province was established at a time different from the rest the nd isotopic characteristics of archean rocks from the wyoming province contrast with those of the superior province confirming that although their proterozoic evolution has been parallel the two cratons did not share a common archean history

smnd upb and rbsr geochronology and lithostructural relationships in the southwestern rae province constraints on crustal assembly in the western canadian shield the rae province is an area of archean crust bounded by the early proterozoic thelon orogen to the northwest and mylonites of the snowbird tectonic zone to the southeast the southern part of the province in saskatchewan is a highgrade complex of ultramafic mafic and felsic orthogneisses with interlayered supracrustal units the oldest rocks in the area were derived from layered mafic plutonic complexes and supracrustal units the earliest deformation d1 resulted in development of a layer parallel foliation preserved in small lensoid pods of anorthosite gabbro and pyroxenite a pyroxenite yields a sm nd tdm age of 3 5 ga and is isotopically similar to a mafic granulite metabasalt associated with early supracrustal units these rocks were intruded by a sequence of mafic and tonalitic orthogneisses that yield a sm nd isochron age of 3 32 2 87 and tdm ages of 3 2 3 1 ga the mafic tonalitic gneisses were subsequently migmatized producing anatectic net veins of tonalitic to granitic pegmatite these were deformed during d2 deformation the terrane was then intruded by minor granodioritic to tonalitic plutonic sheets and a swarm of mafic dikes that were deformed by the last major period of inhomogeneous deformation d3 which ended at 2 0 ga the clearwater complex a large 24 8 km long anorthosite massif intruded the gneiss complex following d3 and yields a sm nd mineral wholerock isochron age of 1 85 ga sm nd rb sr and u pb shrimp data record multiple thermotectonic events and provide constraints on crustal evolution of the rae province u pb shrimp data for metamorphic zircons separated from an early anorthosite associated with units that give pre 3 2 ga nd model ages show considerable variation in th u ratio zircons yield virtually concordant data that record archean 2 9 ga and several early proterozoic between 2 3 and 1 85 thermotectonic events sm nd data are generally poorly correlated possibly as a result either of slight remobilization of ree s during granulite facies metamorphism or that rocks with distinct origins were compared rb sr whole rock and mineral data show substantial re equilibration in mafic tonalitic gneisses at 2 8 ga and in supracrustal units at 2 3 ga also a discordant granitic dike and biotite separated from a metapelite yield rb sr tdm ages of 1 9 ga these metamorphic ages are interpreted to reflect thermotectonism associated with formation and assembly of juvenile early proterozoic crust in the talston thelon plutonic zone to the west and with terminal collision in the trans hudson orogen to the east

knowledge based land cover classification using ers 1 jers 1 sar composites land cover classification of an ers 1 jers 1 composite is explored in the context of regional to global scale applicability each of these orbiting synthetic aperture radars provide somewhat complementary information since data is collected using significantly different frequencies polarizations and look angles ers 1 c band vv polarization 23 spl deg jers 1 l band hh polarization 35 spl deg this results in a classification procedure for the composite image a co registered pair from the same season that is superior to that obtained from either of the two sensors alone a conceptual model is presented to show how simple structural attributes of terrain surfaces and vegetation cover relate to the data from these two sensors the conceptual model is knowledge based and it is supported by both theoretical considerations and experimental observations the knowledge based conceptual model is incorporated into a classifier that uses hierarchical decision rules to differentiate land cover classes the land cover classes are defined on the basis of generalized structural properties of widespread applicability the classifier operates sequentially and produces two levels of classification at level 2 terrain is structurally differentiated into man made features urban surfaces short vegetation and tall vegetation at level 2 the tall vegetation class is differentiated on the basis of plant architectural properties of the woody stems and foliage growth forms of woody stems include excurrent i e pines decurrent i e oaks and columnar i e palm architecture two classes of leaves are considered broadleaf and needle leaf the composite classifier yields overall accuracies in excess of 90 for a test site in northern michigan located along the southern ecotone of the boreal forest for the area examined the sar based classification is superior to unsupervised classification of multitemporal avhrr data supplemented with a priori information on elevation climate and ecoregion

kinematic evolution of the lower plate during intracontinental subduction an example from the scandinavian caledonides geophysical data combined with pressure temperature time data form the basis for a reconstruction of the kinematic evolution of the scandinavian caledonides collisional orogenic belt the reconstruction suggests that the early stages of collision between baltica and laurentia involved intracontinental subduction of a minimum of 150 km of baltic continental crust to a depth of at least 100 km the subduction juxtaposed strong laurentian upper mantle rocks in the upper plate against weak baltic crustal rocks in the lower plate continued plate convergence coupled with the buoyancy of the baltic rocks resulted in thrust imbrication of a substantial portion of the lower plate and extrusion of the crustal rocks from the subduction zone thrusting also resulted in incorporation of fragments of the laurentian upper mantle into the baltic crust the reconstruction also suggests that direct interaction between the laurentian and baltic crustal rocks and the time of greatest crustal thickness in the orogen occurred after extrusion of the baltic crust from the subduction zone one implication of this suggestion is that the eclogite coesite assemblage presently exposed at the surface in the hinterland of the caledonides probably formed early in the collision sequence during subduction rather than during the time of greatest crustal thickness the reconstruction also suggests that exposure of the high pressure mineral assemblage was a two phase process involving extrusion from the subduction zone by thrusting during convergence and unroofing by a combination of extension on low angle normal faults and erosion the kinematic model derived for the scandinavian caledonides provides a possible scenario for the evolution of other collisional orogenic belts containing very high pressure mineral assemblages formed in situ in continental rocks and associated ultamafic rocks of mantle origin

seismic reflection and potential field studies of the vulcan structure western canada a paleoproterozoic pyrenees the vulcan structure is a major tectonic boundary between the medicine hat and loverna blocks archean crustal domains that are buried beneath the western canada sedimentary basin it is characterized by prominent east trending gravity and magnetic anomalies more than 350 km in length which cut across the potential field fabric of southern alberta at a high angle three decades ago the vulcan structure was the target of one of the first deep crustal seismic profiles and it has since been variously interpreted as a failed proterozoic rift an intraplate collisional zone and or a largely amagmatic proterozoic suture several recent lithoprobe seismic reflection profiles coupled with new coincident high resolution gravity data regional gravity data and updated aeromag netic coverage provide the basis for a revised model of the crustal architecture in this region we interpret the vulcan structure to be a relatively narrow 40 70 km axial zone of a continental collisional belt the seismic images imply crustal delamination and south directed subduction of the lower crust of the loverna block the axial gravity low and corresponding magnetic anomaly are interpreted to originate from a large granitic pluton while prominent gravity highs on the flanks of the structure are modeled as thrust slices of lower crustal and or mantle material brought up during the collision cross cutting relationships inferred from aeromagnetic data indicate that the timing of collision postdated formation of archean fabrics in the medicine hat block but predated terminal collision in the adjacent transhudson orogen the geographic extent inferred net shortening and tectonic setting of the vulcan structure appear to resemble the modern pyrenees belt although the deep structure appears to be more akin to the scandinavian caledonides either scenario is consistent with an interpretation of the vulcan structure as the proterozoic collisional suture between the wyoming and hearne provinces of the laurentian craton

basement heat flow in the western canada sedimentary basin abstract the effective thermal conductivity of the entire sedimentary succession is calculated at 487 locations in the western canada sedimentary basin based on net rock analyses and thermal conductivity values corrected for temperature and porosity effects an easterly trend of increasing values is caused by shallower burial depth and by a reduced proportion of low conductivity shales geothermal gradients calculated previously and corrected for pleistocene glaciations are used in estimating the basement heat flow after subtracting the heat generated by radioactive decay in the sedimentary strata the distribution of basement heat flow with values between 30 and 80 mw m 2 is linked with the complex structure of the basement which is comprised of archean blocks accreted terranes orogenic belts and magmatic arcs heat flow heat generation relations in alberta show that the reduced heat flow and the characteristic length scale for the uppercrust thermal layer are of the order of 35 mw m 2 and 6 km respectively

mantle heterogeneities and their significance results from lithoprobe seismic reflection and refraction wide angle reflection studiesthis article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent lithoprobe contribution 1486 within lithoprobe s 10 transects data from more than 20 000 km of multichannel seismic mcs reflection profiling and 12 refraction wide angle reflection r war surveys were acquired while the

gravity patterns and precambrian structure in the north american central plains bouguer gravity patterns revealed in horizontal gradient images are used to locate and examine the tectonic nature of precambrian structural boundaries buried beneath the north american central plains the southern boundary of the superior province west of the midcontinent gravity high mgh interpreted as a collisional suture is relocated as much as 200 km south of previous geophysically defined positions close to a position defined recently by using drill hole information east of the high this boundary is thought to trace a 900 km arc subparallel to the mgh the western boundary of the superior province is regarded as a suture containing significant components of transcurrent faulting the eastern boundary of the wyoming province another suture is traced northward into the churchill province near the northwestern margin of a 1900 1600 ma magmatic belt this boundary and proterozoic terrane to the east are transected by previously unrecognized faults hundreds of kilometres long gravity patterns also suggest that the north american central plains conductivity anomaly may not be a continuous suture related conductor

an early proterozoic vgp from an oriented drillcore into the precambrian basement of southern alberta summary we report paleomagnetic results for 25 samples from a fully oriented pancanadian petroleum drillcore which penetrated the precambrian basement of southern alberta at a depth of 2550 m samples were taken at approximately 1 m intervals over a 7 m section of core intensities of natural remanent magnetization nrm were 0 5 14 a m over the section which consists mainly of granodiorite with one short granite interval x ray and curie temperature data indicated magnetite as the only important nrm carrier most of the nrm was an intense steeply inclined drilling remanence with coercivities 20 mt and distributed low to intermediate unblocking temperatures after magnetic cleaning a weak but stable primary nrm with high coercivities and high unblocking temperatures was isolated with d 157 i 52 k 118 mg5 3 n 20 the corresponding virtual geomagnetic pole vgp is 4 s 93 w dp 3 dm 4 which falls on the north american apparent polar wander path around 1850 ma the basement of this part of alberta is probably an extension of the churchill structural province of the laurentian shield

lithospheric flexure and gravity anomalies at proterozoic plate boundaries in the canadian shield abstract proposed proterozoic sutures in the canadian shield show paired positive and negative gravity anomalies previous interpretations ascribe the negative anomaly to an increase in crustal thickness of the older province towards the suture and the positive to increased density and thickness of the younger province here the asymmetrical negative anomaly is interpreted to be the result of flexure of the older lithosphere as it is thrust under the younger more buoyant plate the absence of any visual correlation between topography and observed gravity over suture zones suggests the presence of subsurface loads which are thought to be the primary sources for the related positive gravity anomalies two dimensional modelling of suture anomalies has resulted in the following estimates for elastic plate thicknesses in the canadian shield 60 km for the slave plate and 75 120 125 km for the cape smith labrador and grenville areas of the superior province flexural rigidities at sutures increase with the age of the lithosphere when loaded supporting previous results obtained in oceans and mountain ranges

source terranes for proterozoic sedimentary rocks in southern british columbia nd isotopic and petrographic evidence quartz arenites of the fort steele formation the lowest exposed stratigraphic unit of the purcell supergroup have nd crustal residence times tcr of 2 61 2 63 ga these overlap the low end of the tcr range of the polymetamorphic kenoran hudsonian basement of southern alberta and southwestern saskatchewan the tcr values of overlying fine grained purcell rocks average 2 0 ga near lake windermere the basal toby conglomerates of the windermere supergroup apparently derived from underlying purcell strata have tcr values of 1 98 and 2 03 ga stratigraphically higher argillite and arkoses range from 2 35 to 2 54 ga this higher range indicates contributions from a source terrane different from the main body of the purcell supergroup our interpretation of events in the east kootenay area is that early purcell sedimentation fort steele formation was derived from reworking of the crystalline basement of the alberta shelf as the beltian sea transgressed as the basin deepened it was filled by fine grained

deep probe imaging the roots of western north america analysis of the lithoprobe deep probe and southern alberta refraction experiment data sets focusing on the region between deep probe shots 43 and 55 has resulted in a continental scale velocity structural model of the lithosphere of platformal western laurentia reaching depths of 150 km three major lithospheric blocks were investigated i the hearne province a typical continental archean cratonic province lying beneath the western canada sedimentary basin ii the wyoming province an even older block of phanerozoic modified archean crust with an enigmatic lower lithosphere and iii the yavapai mazatzal province proterozoic terranes underlying the colorado plateau and southern rocky mountains in this study the northern two of these regions are investigated with a modified ray theoretical traveltime inversion routine that respects the spherical geometry of the earth the resulting crustal velocity structure combined with supporting geological and geophysical data reveals that the medicine hat block mhb lying between the hearne and wyoming provinces is a third independent archean crustal block the subcrustal lithosphere along the profile is homogeneous in velocity structure but two significant northward dipping reflectors are apparent and interpreted as relic subduction zones associated with sutures between the three archean blocks the hearne crust is typical of an archean shield or platform both in its thickness of 34 50 km and its seismic velocity structure the crust of the archean mhb and wyoming province which ranges in thickness from 49 to 60 km includes a 10 30 km thick high velocity layer interpreted to be proterozoic in age such a feature is unexpected beneath archean crustal provinces but if the region is considered to be the remanent marginal portion of a larger archean continent then the interpreted proterozoic underplating and lack of an archean lithospheric root can be explained the variable topography along the reflective upper and lower boundaries of this layer especially within the mhb suggests considerable variability in its emplacement and subsequent tectonic history

the s type ladybird leucogranite suite of southeastern british columbia geochemical and isotopic evidence for a genetic link with migmatite formation in the north american basement gneisses of the monashee complex abstract the 62 52 ma ladybird granite lbg suite is a peraluminous leucocratic s type quartz monzonitic to granitic suite which occurs as batholiths stocks dikes sills and pegmatite veins predominantly in the high grade rocks of the shuswap complex in southeastern british columbia the emplacement of the lbg was synchronous with the production of abundant migmatites within thor odin dome of the monashee complex an exposure of north american basement exhumed from depths of ca 26 33 km by eocene extensional faults the lbg and the leucosome in migmatites from thor odin dome have similar major and trace element patterns and are both characterized by zircons which have inherited precambrian cores whole rock nd isotope compositions show a range of values for the lbg with end 55 ma values from 5 0 to 17 2 the end 55 ma for the leucosome samples range from 9 5 to 23 6 overlapping with those of the granitic suite these data support the interpretation of a genetic link between formation of the lbg suite and melting of north american basement rocks such as those exposed in the core of thor odin dome the leucosome samples have lower high field strength element hfse concentrations and positive eu anomalies whereas the lbg samples have higher hfse concentrations and negative eu anomalies the similar trace element characteristics suggest that the leucosome from the migmatites and the lbg are related whereby most of the leucosome samples are cumulates and the lbg samples represent evolved or residual melts the initial 87sr 86sr isotope values for both the lbg and leucosome samples have a large range however the initial sr isotopic ratios for the lbg suite are lower than those of the leucosome samples with 87sr 86sr 55 ma ranging from 0 70603 to 0 73688 and 0 74256 to 0 76593 respectively this isotopic discrepancy suggests either a isotopic disequilibrium during partial melting in the mid to lower crust where the leucosome formed b the distribution of sr during partial melting was controlled by different melt producing reactions and or c isotopic heterogeneity in the source rocks at least part of the lbg suite likely formed via melting of north american basement rocks that were dominantly of sedimentary origin melting of the proterozoic supracrustal metasedimentary rocks overlying north american basement may also have contributed to the formation of the different phases of the suite found at the regional scale however the abundant leucosomes in the basement rocks of thor odin dome may mark the paths along which anatectic melt migrated in the structurally overlying ladybird granites of the south fosthall pluton

multi genetic origin of the continental moho insights from lithoprobe this paper reviews four hypotheses for the origin of the continental crust mantle boundary and discusses seismic parameters with which these hypotheses might be tested the relict moho hypothesis posits that the oceanic moho is preserved during continental assembly the magmatic underplating hypothesis posits formation of a new moho by episodic emplacement of sill like intrusive bodies the metamorphic or metasomatic front hypothesis posits that the moho is overprinted by a phase transformation and the regional decollement hypothesis posits that the moho behaves as a structural detachment these hypotheses are not mutually exclusive and examples from the canadian lithoprobe program suggest that all four may be applicable in different regions of north america comparison of seismic images from a fossil subduction zone with modern subduction at cascadia suggests that serpentinization of the forearc mantle a previously unrecognized mechanism for overprinting and erasing the reflection moho may have occurred in the proterozoic

control on sediment and organic carbon delivery to the arctic ocean revealed with space borne synthetic aperture radar ob river siberia an important control on river biogeochemistry and sediment load is the process of water exchange between primary channels and the flood plain particularly in low r elief areas containing lakes ephemeral channels and other aquatic ecosystems flood plain exchange may be a dominant process on the lowland rivers of arctic russia which are among the world s largest in water discharge yet are strikingly deficient in their delivery of sediment to the arctic shelf temporal synthetic aperture radar sar amplitude and interferometric images of the ob river siberia reveal a time varying limnological network controlling water sediment and nutrient exchange between flood plain wetlands and the main channel the amount of hydrologic exchange decreases by one order of magnitude from june to september enhancing sedimentation over as much as 90 of the flood plain and enriching channel waters with colloidal organic carbon this observation combined with russian field measurements of water discharge and sediment load indicates that a major sediment sink on the lower ob flood plain may be responsible for the low amount of sediment delivery by the ob river to its estuary and the kara sea

striding athabasca mylonite zone implications for the archean and early proterozoic tectonics of the western canadian shield study of the northern saskatchewan district of mackenzie segment of the snowbird tectonic zone suggests that fragments of relatively stiff mid archean crust possibly arc related have controlled the localization shape and complex kinematics of the multistage striding athabasca mylonite zone during the archean as well as the geometry of the early proterozoic rifted margin of the western churchill continent by the late archean the striding athabasca mylonite zone was located in the interior of the western churchill continent well removed from the contemporaneous plate margins except for the alberta segment the snowbird tectonic zone was not the site of an early proterozoic plate margin we suggest that the geometry of the archean early proterozoic boundary in the western canadian shield represents a jagged continental margin composed of a pair of reentrants defined by rifted and transform segments these segments were inherited from early proterozoic breakup and controlled by the archean structure

nd evidence for extensive archean basement in the western churchill province canada to determine the extent of reworked archean crust in the western churchill province we have examined sm nd crustal residence ages of basement cores in southern alberta and southwestern saskatchewan along with crustal residence ages calculated for other sm nd data available from the churchill province the deep drill hole samples from the interior platform give sm nd crustal residence ages that average 2 8 ga granulites from northeastern alberta and composite gneisses from northern saskatchewan also provide archean crustal residence ages these data demonstrate that the presence of reworked archean crust in the western churchill province is more widespread than has been confirmed previously we suggest that sm nd crustal residence ages are valuable estimates of crust formation times especially in orogenic areas where other isotope systems have been disturbed

steady flows at the top of earth s core derived from geomagnetic field models select models of the main geomagnetic field and its secular variation are extrapolated to the base of an insulating mantle and used to estimate the adjacent fluid motion of a perfectly conducting outer core the assumption of steady motion provides formally unique solutions and is tested along with that of no upwelling the hypothesis of no upwelling is found to be substantially worse than that of steady motion although the actual motion is not thought to be steady the large scale secular variation at the top of the core can be adequately described by a large scale combined toroidal poloidal circulation which is steady for intervals of at least a decade or two the derived flows include a bulk westward drift but are complicated by superimposed jets gyres and surface divergence indicative of vigorous vertical motion at depth the circulation pattern and key global properties including rms speed upwelling and westward drift are found to be fairly insensitive to variations in modeling parameters

buried proterozoic foredeep under the western canada sedimentary basin electromagnetic studies of the precambrian basement beneath the western canada sedimentary basin in alberta indicate a narrow linear conductivity anomaly spatially correlated with a strong positive magnetic feature the red deer high the conductor is located below sedimentary cover near the top of the crystalline basement and has limited depth extent we propose that this anomalous feature represents graphitic metasedimentary rocks in the euxinic flysch facies of a proterozoic foredeep sequence the strong magneticanomalyresultsfromanassociatedironformationdepositedontheouterrampofthe foredeep this model explains the geophysical anomalies has analogues on the exposed shield and is consistent with the timing deformation history and known geology of the precambrian basement

the secular variation of earth s magnetic field models of the magnetic field at the core mantle boundary at selected epochs from 1715 0 to 1980 0 reveal novel features in the field at the core these suggest that the flow of core fluid is coupled to the mantle and that magnetic diffusion is significant

comment on linking the mesoproterozoic belt purcell and udzha basins across the west laurentia siberia connection abstract paleogeographic reconstruction of the northern siberian craton against southwestern laurentia in accordance with paleomagnetic data basement piercing points and the best fit of the rift margins aligns mesoproterozoic dike and sill swarms in northeast siberia with correlative ones in montana and wyoming it also juxtaposes the mesoproterozoic belt purcell basin of west laurentia against the mesoproterozoic udzha basin of the northern siberian craton we review the veracity of this hypothetical belt purcell udzha basin as a test of our siberia west laurentia reconstruction various elements of the structural framework of the basins are closely aligned in the reconstruction the udzha trough is aligned with the st mary moyie fault zone and vulcan basement structure of southwestern canada the khastakh trough is aligned with the helena embayment of central montana parts of the belt purcell supergroup appear to correlate with parts of the riphean section in northeastern siberia however the siberian section appears to be much thinner than the belt purcell section and precise correlation is not possible with present stratigraphic and geochronological data the reconstruction leads to the prediction that the udzha rift channeled sediment from a cratonic pediment into the delta and alluvial fan complex in the deep belt purcell rift basin distributary channels may have shifted within the udzha basin to feed shifting depocenters in the belt purcell basin details of age and tectonic evolution for the udzha basin are less clear than for the belt purcell basin but we outline specific geological relationships predicted by the reconstruction model and suggest tests for future research

paleoproterozoic collisional orogen beneath the western canada sedimentary basin imaged by lithoprobe crustal seismic reflection data exceptionally clear images of crustal structure of the canadian shield that underlies the western canada sedimentary basin beneath 3 5 2 2 km of phanerozoic sedimentary strata have been obtained on a seismic reflection profile acquired by lithoprobe the profile crosses tectonic domains of central alberta and delineates a major buried orogenic belt of paleoproterozoic 1 8 ga age associated with crustal scale thrust imbrication and deflections in the crust mantle boundary available geochronologic data suggest that crustal imbrication observed in the alberta basement was coeval with that documented in the trans hudson orogen to the east 1 80 1 83 ga and implies that a large region of continental crust extending 1000 km from the western superior province to the snowbird tectonic zone underwent considerable shortening during assembly of this part of the canadian shield

gravity anomaly map of the pyrenean region and a comparison of the deep geological structure of the western and eastern pyrenees abstract a gravity anomaly map based on over 13 000 observations accurately delineates the major features of the pyrenean region an extensive gravity anomaly low in the south of the region appears to result from crustal thickening associated with the pyrenean mountain building episode several large positive gravity anomalies are apparent in the north pyrenean zone in the centre and west of the mountain chain but are absent in the east the interpretation of a series of gravity anomaly profiles along the pyrenees has been controlled by existing geophysical data the interpretations confirm the cause of the southern gravity anomaly low as thickened iberian crust and demonstrate as shown by previous seismic investigations that the transition to much thinner european crust is quite abrupt the sources of the positive anomalies in the north pyrenean zone are bodies in the upper crust with densities too high to be explained in terms of crustal materials these are interpreted as segments of upper mantle that originated in transtensional n s separation across the north pyrenean fault and were emplaced at shallow levels by thrusting during pyrenean orogenesis this is the first time that evidence has been presented for the presence of such mantle bodies in the pyrenees it is suggested that their absence in the east is caused by less extension between iberia and europe in this region during the transform motion between them prior to orogenesis allowing only limited ascent of deep material the greater extension in the west would have allowed the ascent of upper mantle into the space between iberia and europe which would have been further elevated during the thrusting associated with pyrenean orogenesis

wyoming on the run toward final paleoproterozoic assembly of laurentia paleoproterozoic suture zones mark the formation of supercontinent nuna and provide a record of north america s assembly conspicuously young ages ca 1 715 ga associated with deformation in southeast wyoming craton argue for a more protracted consolidation of laurentia long after peak metamorphism in the trans hudson orogen using paleomagnetic data from the newly dated 1899 5 ma sourdough mafic dike swarm wyoming craton we compare the relative positions of wyoming superior and slave cratons before during and after peak metamorphism in the trans hudson orogen with these constraints we refine a collisional model for laurentia that incorporates wyoming craton after superior and slave cratons united redefining the paleoproterozoic sutures that bind southern laurentia

tectonothermics of the north american great plains basement abstract heat flow and heat generation data from the superior churchill and wyoming provinces of western north america contribute to our understanding of the nature of the crust beneath the sedimentary cover of the great plains a major structural boundary defined by gravity gradient data thomas et al 1987 splits the terrains between the cratons into two distinct geothermal provinces the wyoming and churchill provinces are characterised by higher heat flow than the superior province and the eastern part of the intervening hudsonian terrain the proterozoic mobile belt pmb heat flow in the pmb is typical of that of the superior craton this suggests on the basis of a model by ballard and pollack 1987 that the pmb is underlain by archaean cratonic lithosphere the similarity in heat flow between the pmb and the superior craton suggests that the crust of the pmb is akin to that of the superior craton rather than to that of the more radiogenic wyoming and churchill cratons geochronologic gravity aeromagnetic and geothermal data suggest that the structural boundary defining the western boundary of the pmb is also the eastern boundary of the wyoming craton geothermal data alone suggest that the wyoming craton might extend as far north as the cratonic segment of the churchill province or that the wyoming and churchill provinces may gradually merge together

crustal velocity structure from sarex the southern alberta refraction experiment lithoprobe s southern alberta refraction experiment sarex extends 800 km from east central alberta to central montana it was designed to investigate crustal velocity structure of the archean domains underlying the western canada sedimentary basin from north to south sarex crosses the loverna domain of the hearne province the vulcan structure the medicine hat block previously considered part of the hearne province the great falls tectonic zone and the northern wyoming province ten shot points along the profile in canada were recorded on 521 seismographs deployed at 1 km intervals to extend the line an additional 140 seismographs were deployed at intervals of 1 25 2 50 km in montana data interpretation used an iterative application of damped least squares inversion of traveltime picks and forward modeling results show different velocity structures for the major blocks loverna medicine hat and wyoming indicating that each is distinct wavy undulations in the velocity structure of the lov

crustal structure beneath the western canada sedimentary basin constraints from gravity and magnetic modelling regional gravity and magnetic anomalies that originate from crystalline basement rocks extend over many parts of the western canada sedimentary basin although these potential field anomalies provide a basis for tectonic subdivisions of the basement crust most previous interpretations of these features have been largely qualitative in nature this study focuses on numerical simulation and quantitative interpretation of five regional potential field anomalies in alberta canada for which independent constraints on crustal structure are available from lithoprobe seismic and electromagnetic studies the kimiwan high 55 n 116 w is a roughly 250 km long linear magnetic high seismic profiles across this anomaly provide evidence for a crustal scale extensional fault system that offsets the winagami reflection sequence a series of mid crustal sills we find that the magnetic anomaly can be modelled as either a 15 40 km wide zone of moderate positive susceptibility 4 5 10 3 si units in the hanging wall

the ecors deep reflection seismic survey across the pyrenees the pyrenees are an alpine age mountain belt located on the boundary between the iberian and european plates using the same geological and geophysical data earth scientists studying the structure of the pyrenees during the past ten years have not reached a consensus here we report the first results from a nearly continuous 255 km long reflection seismic survey across the pyrenean chain this first deep reflection profile of an entire erogenic belt will help to constrain possible models for the structure and formation of the pyrenean chain

relict subduction zones in canada 1 relict subduction zones that are interpreted on 10 lithoprobe deep seismic reflection profiles in canada provide key observational evidence that lithosphere plate interactions have operated with essentially the same resultant geometry for at least 2 7 gyr subduction zone reflections are generally found beneath known collisional belts and their orientations are often consistent with the locations of exposed arcs sutures and subduction complexes they project from the lower crust into the upper mantle and provide key geometric relationships between the crust moho and upper mantle the interpretation of subduction zone reflections as being syntectonic establishes a minimum age for the overlying lower crust and mantle wedge and precludes inferred formation of the moho and upper mantle by postorogenic delamination in these areas the orientation of subduction zone reflections may be synthetic or antithetic to exposed sutures indicating juxtaposition by subcretion or by delamination respectively the mantle wedge above the subduction zone reflections may exhibit sparse reflectivity subduction zone reflections commonly dip toward the craton indicating a preferred dip of subduction during the last stages of convergence within an orogen or else a higher likelihood of preservation beneath older domains interpreted ages of the canadian examples range from recent to neoarchean 2 7 ga providing observational evidence that plate tectonics or similar processes have been active since at least the neoarchean the locations and geometries of these relict subduction zones provide a snapshot of accretion boundaries in the mantle and establish a framework for the neoarchean recent accretionary architecture of the north american lithosphere