lithospheric processes and products in the southern canadian cordillera a lithoprobe perspective analyses of lithoprobe and other data from southwestern canada provide new insights on how this portion of the cordillera formed during plate convergence along the western margin of north america crustal rocks are detached from their mantle lithosphere which must have been consumed during subduction detachment occurred at or near the base of the crust beneath the intermontane and or omineca belts probably along the tips of tectonic wedges while the rocks were still outboard of the relatively cool mechanically rigid north american craton during the late cretaceous and early tertiary rotation of detached rocks caught between the north american craton and the oceanic plates accounts for some apparently conflicting results between paleomagnetic data that indicate large northward translation of rocks in the western cordillera and regional geological features that appear to preclude comparable amounts of translation of rocks in the eastern cordillera during the same time interval transpression assoc

development of a chenier plain firth of thames new zealand abstract a chenier plain is a prograded coastal plain in which ridges composed of coarse material moved by longshore drift are stranded overlying finer grained marine or littoral sediments subsurface data from the miranda coastal plain firth of thames new zealand confirm that shell ridges between kaiaua and miranda are true cheniers surveys of a modern chenier indicate that coarse sediment and shell form sand bars on the foreshore and that these migrate landwards through swash action subsequently a shell ridge is built on the sand bar from shell derived from offshore and reworked from the north and storm events form a storm crest above high spring tide level deposition of fine grained sediment occurs in an embayed tidal flat behind the chenier and within this environment the bivalve mactra ovata is found these sediments can accrete to an elevation at which mangrove and salt marsh are able to colonise the chenier may continue to transgress landwards though at a slower rate retreating over the embayed tidal flat mangrove or marsh and compressing these sediments erosion of these compressed muds on the face of the beach leaves specimens of mactra in their growth position exposed on the modern chenier at an elevation of 0 62 0 80 m above msl stratigraphical observations along a west east profile across the coastal plain reveal that sandy muddy sediments are underlain by peat clayey tephra and older marine sediments and 4 radiometric dates of 30 000 yrs b p have been determined on these shell ridges on the plain are underlain by blue muds within which occurs a band of mactra ovata tristis in growth position these sediments are considered analogous to the embayed tidal flat sediments behind the modern chenier the continuity of the shell layer radiometrically dated to 3650 60 yrs b p to landward and 1260 50 yrs b p to seaward implies that there have not been oscillations of sea level during this regressive coastal phase while the shell ridges have developed mactra were also found in situ at the north and south of the coastal plain dated to 4510 70 and 200 60 yrs b p respectively from elevations on sub fossil mactra it is implied that sea level was 0 70 0 90 m above present 3600 years ago and that it fell gradually until 1200 years ago when it was close to present erosion deposition and migration of a chenier can occur simultaneously and long term variations in sea level or in sediment supply do not appear necessary to explain the episodic formation of chenier ridges

archean lamprophyre dikes of the superior province canada distribution petrology and geochemical characteristics shoshonitic lamprophyre dikes of late archean age are a volumetrically minor yet widespread component of magmatism in the superior province and preferentially occur along major structures that delineate subprovince boundaries lamprophyre swarms are most prominently developed in fault graben where they are associated with alkali gabbro and trachytes and molasse sediments mineralogically the dikes are characterized by zoned phlogopite or hornblende phenocrysts restriction of feldspar to the groundmass globular segregations of k feldspar and calcite panidiomorphic texture and the sporadic presence of crustal xenoliths compositionally fresh dikes have contents of sio2 47 51 wt tio2 0 55 0 60 and p2o5 0 36 1 58 and k2o na2o ratios 1 5 2 3 and mg numbers 78 80 comparable to phanerozoic shoshonitic lamprophyres unaltered dikes are characterized by extreme enrichments of the lithophile elements k rb ba cs th u and light rare earth elements lree and enhanced abundances of cr 650 920 ppm co 37 42 ni 264 355 and sc 22 28 mid ocean ridge basalt normalized plots display 1 consistent enrichments of k rb and ba relative to sr and lree 2 variable enrichments of rb and ba relative to k and 3 troughs at ta nb and ti compared with fresh rocks altered samples have systematically lower k rb ba and sr contents but similar ree distributions and profiles from th yb and sc ni on normalized diagrams suites of post archean ultramafic lamprophyres in the superior province are enriched in large ion lithophile elements lile lree and compatible elements relative to their archean counterparts and lack troughs at ta nb and ti emplacement of the lamprophyres was diachronous from north 2705 ma to south 2674 ma probably being related to localized extension during the successive accretion of individual subprovinces archean lamprophyre magmas were derived from a depleted mantle source variably enriched in lile and lree by sediments and altered oceanic crust with small variable degrees of crustal contamination whereas the post archean lamprophyres lacked a plate margin setting

crustal paleorheology of the southeastern canadian cordillera and its influence on the kinematics of jurassic convergence the kinematic evolution of the southeastern canadian cordillera 52 n 54 n during the jurassic is characterized by an eastward migration of the active boundary of convergence between north america and allochthonous terranes and by two reversals in regional structural vergence to investigate possible mechanical controls on the kinematics of convergence the thermal and geological structure of the jurassic continental margin at three stages in its history of shortening were palinspastically reconstructed and analyzed with the use of strength versus depth profiles the resulting models reproduce to a first order the observed distribution of brittle and ductile deformation and provide a mechanical basis for the localization and orientation of displacement zones during shortening of the continental margin the initial eastward migration of the active boundary of convergence between north america and allochthonous terranes from outboard of the continental margin sediment prism into the thick central part of the continental margin prism is attributed to thermal weakening of the continental margin lithosphere during obduction of the oceanic terrane the subsequent eastward migration of the convergence boundary into the inner part of the continental margin lithosphere is attributed to thermal weakening of the lithosphere during prograde regional metamorphism reversals in regional structural vergence accompanying each migration apparently occur because the push necessary to continue displacement on one displacement trajectory exceeds the failure strength of another displacement trajectory that dips in the opposite direction

northeast trending folds in the western skeena fold belt northern canadian cordillera a record of early cretaceous sinistral plate convergence abstract the western portion of the skeena fold belt northern canadian cordillera contains northeast trending folds that are highly oblique to northwest trending folds in the eastern portion of the fold belt and to most mesozoic contractional structures in the northern cordillera the northeast trending folds locally interfere with the northwest trending folds and one region includes transected folds geometric relationships within and between the two fold sets are not easily reconciled by notions of the northeast trending folds resulting from vertical axis rotation of blocks influence of basement features or lateral variations in magnitude of shortening the northeast trending folds are inferred to result from sinistral plate convergence early in the history of the fold belt early cretaceous northeast trending folds in the skeena fold belt are the most conspicuous elements of a seldom studied group of similarly oriented contractional structures which collectively define a belt at least 1700 km long within and bordering the coast belt the extent of early cretaceous structures potentially related to sinistral convergence supports them having originated in response to the relative plate motion rather than local controls e g indentors this agrees with relative plate motion studies based on ocean floor reconstructions which suggest a mid cretaceous change from sinistral to dextral convergence

paleomagnetism magnetic anisotropy and mid cretaceous paleolatitude of the duke island alaska ultramafic complex we report paleomagnetic results from layered igneous rocks that imply substantial post mid cretaceous poleward motion of the insular superterrane western canadian cordillera and southeast alaska relative to north america the samples studied are from the stratiform zoned ultramafic body at duke island which intruded rocks of the alexander terrane at the south end of the southeastern alaska archipelago at about 110 ma thermal and alternating field demagnetization experiments show that the characteristic remanence of the ultramafic rocks has high coercivity and a narrow unblocking temperature range just below the curie temperature of magnetite this remanence is likely carried by low ti titanomagnetite exsolved within clinopyroxene and perhaps other silicate hosts the duke island intrusion exhibits a well developed gravitational layering that was deformed during initial cooling but below 540 c into folds that plunge moderately to the west southwest the characteristic remanence clearly predates this early folding and is therefore primary the fisher parameter describing the concentration of the overall mean remanence direction improves from 3 to 32 when the site mean directions are corrected by restoring the layering to estimated paleohorizontal all samples exhibit a magnetic anisotropy that is strong but nonuniform in orientation across the intrusion and we show that it has no significant or systematic effect on the site mean directions of remanence at least some of the anisotropy derives from secondary magnetite formed during partial serpentinization the mean paleomagnetic inclination 56 10 corroborates paleomagnetic results from five coeval silicic plutons of the canadian coast plutonic complex to the south and southeast and implies 3000 km 1300 km of poleward transport relative to the north american craton between mid cretaceous and middle eocene time the insular superterrane and coast plutonic complex shared a common paleolatitude history with more poleward transport than coeval inboard terranes

seasonal and spatial variability of particulate matter of a muddy intertidal flood front the concentration and composition of suspended particulate matter spm were measured weekly for a period of one year in the flood front waters traversing a muddy tidal flat spm concentrations were lowest in the winter when portions of the tidal flat were covered with ice and biological activity was minimal in contrast the summer months had the highest spm concentrations which reflected increased bottom resuspension the two main sources of spm were suspended matter carried in from offshore on the flooding tide and resuspended in situ bottom sediments the offshore source was characterized by low spm concentrations coarse textures and a high content of protein and chlorophyll a samples taken during resuspension events storms showers had high spm concentrations finer textures and were enriched in dead detrital organic material phaeophytin at any one time the spm was primarily an admixture of these two sources the highest spm measurements were taken during storm events with rainfall seeming to play a dominant physical role in aiding resuspension spm concentrations textures and compositions collected during the storms closely approximated spm measurements made over newly dug clam flats

southern continuation of the coast shear zone and paleocene strain partitioning in british columbia southeast alaska this paper documents the newly recognized southern continuation of the early tertiary coast shear zone extending its known length by 350 km to more than 1200 km three sites along the shear zone in british columbia douglas channel bella coola and machmell river have similar histories during the period ca 65 55 ma the shear zone is 2 11 km thick and is defined by well developed mylonite zones that strike northwest and dip steeply northeast motion on the shear zone was predominantly reverse with the northeast side up synkinematic plutons are common in the shear zone lower plate rocks high grade gneiss derived from an ancient continental margin assemblage show little evidence of the extensive deformation and plutonism in the shear zone north of bella coola high grade gneiss forms the upper plate but to the south weakly metamorphosed rocks of stikinia compose the upper plate geochronologic data show that the shear zone was active between ca 60 and 55 ma at douglas channel ca 62 and 56 ma at bella coola and after 66 and before 56 ma near the machmell river these features match those of the coast shear zone in southeast alaska and adjacent british columbia together the shear zones formed a continental scale reverse ductile fault in paleocene time plate reconstructions show an oblique component to the dominantly dextral transcurrent paleocene margin partitioning of this motion across the continental margin produced a regional system of strike slip faults and contraction on the coast shear zone

deformation of stratiform znpb barite deposits in the northern canadian cordillera abstract the major stratiform sediment hosted zn pb barite deposits of the northern canadian cordillera occur in the palaeozoic selwyn basin kechika trough they formed in euxinic fine grained clastic dominated extensional basins that developed within the carbonate platform of the passive margin of ancestral north america during the late jurassic to mid cretaceous these basins and the stratiform ore deposits were subjected to low greenschist facies regional metamorphism and fold and thrust deformation as they were incorporated into the western part of the rocky mountains mackenzie mountains foreland fold and thrust belt this paper summarises the results of detailed field and microscopic studies on four of these deposits the tom deposit the howards pass deposit the cirque deposit and the driftpile creek deposit the dominant mineralogy of these deposits is sphalerite galena pyrite and in some cases significant barite is present low greenschist grade metamorphism and deformation is characterised by cataclastic flow and brecciation in coarse grained massive pyritic sulphides and by folding recrystallisation and cleavage development in fine grained sulphides and barite relict primary depositional diagenetic structures are found within the orebodies deformation is characterised by strong pressure solution fabrics in barite in fine grained laminated pyrite layers and in mixed sulphide carbonate beds marked local transposition is found with significant remobilisation of galena barite and pyrite the deformation mechanics of these sulphide barite deposits are illustrated using schematic deformation mechanism maps

paleoseismological evidence from lake sediments for recent movement on the denali and other faults yukon territory canada abstract most of the pacific north america plate motion in northwestern canada and southeastern alaska occurs along coastal faults that are the inland extension of the queen charlotte dextral transform fault more ancient faults farther east such as the denali and duke river faults exhibit moderate earthquake activity and may be accommodating part of the pacific plate motion paleoseismological results based on seismic resuspension of lake sediments covering a period of up to 3000 years show that the seismicity on the denali duke river fault system is remarkably recent spanning just the last three to five centuries there is a northerly trending zone of seismicity from the active fairweather contact fault system on the coast across to the part of the denali fault that is currently as well as prehistorically active this partial transfer eastward of pacific plate motion may be analogous to a similar proposed transfer of motion northward to the denali fault from the same fairweather contact fault system farther west in alaska

sediment distribution dispersal and budget in the yellow sea abstract information on the surface sediment distribution in the yellow sea is newly compiled based on all available data produced by chinese and korean workers and is used to refine the dispersal patterns and budget of sediments derived from the adjoining landmass the central yellow sea is largely covered with fine grained sediments originating from the huanghe river 2 2 10 8 t yr about 20 of the total discharge thick sediment accumulation exceeding 5 mm yr occurs in the gulf of bohai and around the shandong peninsula about two thirds of the total huanghe river discharge the old huanghe delta suffers from reworking by strong tides and waves and forms a mud patch southwest of cheju island accumulation rate 2 10 7 t yr more than half of the sediments derived from the changjiang river are deposited along the coast of the east china sea the remainder accumulate on the inner shelf off the river mouth in the southeastern yellow sea the keum river dominates sediment discharge forming a holocene mud belt along the southwestern coast of korea accumulation rate 5 10 6 t yr turbid water plumes occur nearshore throughout the year and their suspended sediments are transported along the tip of the peninsula to the western coastal embayments in the south sea the nakdong river discharge of 1 10 7 t yr is responsible for the eastern nearshore mud of the south sea relict sands occur in the northern part of the yellow sea in the northern east china sea and in the korea strait

double peak flood current asymmetry in a shallow water constituent dominated embayment with a macro tidal flat 1 tide and tidal current distortions were examined in hampyung embayment a shallow semidiurnal tide dominated bay with large tidal flats via in situ monitoring harmonic analyses reveal that the shallow water constituents of the tides and tidal currents are strong in this restricted setting relative to on the open coast in particular the amplitudes of the shallow water currents constituents m4 ms4 m6 2ms6 are three times greater than those of the diurnal constituents k1 o1 the quarter diurnal m4 ms4 and sexta diurnal m6 2ms6 current amplitudes account for 35 and 17 of the semi diurnal current m2 s2 amplitudes which account for 42 of total amplitude the ms4 current amplitude is as important as that of the m4 amplitude in the middle of the bay such strong generation of shallow water velocity constituents induced by non linear processes leads to an ebb dominated tidal regime with double flood current velocity peaks

an overview of the nature distribution and inferred tectonic setting of granitoids in the late archaean norseman wiluna belt abstract the highly mineralized late archaean norseman wiluna belt yilgarn block western australia has lithostratigraphic associations and a structural style and history that has recently been interpreted in terms of a subduction related tectonic setting it is important to investigate whether the geochemistry and petrology of the granitoids in the belt are compatible with such a model the granitoid suite within the belt can be subdivided into association 1 large composite batholiths of calc alkaline affinity spatially and temporally associated with calc alkaline volcanic centres association 2 plutons ranging from quartz diorite and tonalite to monzogranite and syenogranite spatially related to dike swarms of felsic to intermediate porphyries and calc alkaline lamprophyres and association 3 peralkaline to alkaline batholiths and stocks which are spatially and temporally associated with rhyolitic volcanic centres and major lineaments the calc alkaline associations 1 and 2 have characteristics comparable with suites of variable fractionated i type granitoids in phanerozoic continental margin are settings including 1 a wide range in sio 2 2 meta to peraluminous compositions 3 a progression from granodiorite to granite with plutons becoming more k 2 o rich and hornblende poor with time 4 lile enrichment and relative depletion of ta nb and ti in contrast to most phanerozoic granitoids the norseman wiluna belt granitoids have highly fractionated ree patterns and low contents of yb and y with respect to average post archaean equivalents ree data and trace element characteristics suggest derivation from a mafic source leaving hornblende and or garnet as residual phases peralkaline granitoids of association 3 exhibit enrichments on sio 2 na 2 o k 2 o zr y nb and ta with respect to the calc alkaline granitoids they post date associations 1 and 2 and are consistent with the concept that they represent a continuation of magmatism in a post orogenic environment thus the nature and distribution of the granitoids of the norseman wiluna belt are consistent with interpretations that the belt formed in a subduction related convergent margin setting

structural aspects of suspect terranes and accretionary tectonics in western north america abstract the regional structural relationships between the cordilleran suspect terranes and cratonic north america and within the suspect terranes themselves are reviewed for eastern alaska western canada and united states and northern mexico a distinctive characteristic of the relationships between the suspect terranes and the north american craton is that although much modified by post accretionary strike slip faulting thrust faulting and extensional detachment faults the generally more distal and or oceanic terranes are frequently found as rootless nappes or thin thrust sheets sitting upon more inboard terranes or upon the craton itself the amount of tectonic transport implied is large strike slip faulting has been a very significant aspect of the structural evolution of the north american cordillera with total distributed displacements of over 2000 km documented on geologic relationships alone and much more implied by paleomagnetic evidence at least since later mesozoic time to the present movements were such that the terranes moved northward post accretionary intraplate telescoping along thrust faults transpressional strike slip faulting and delamination at mid to upper crustal levels were important processes in cordilleran tectonic evolution

mesoscale and regional kinematics of the northwestern yalakom fault system major paleogene dextral faulting in british columbia canada the northwestern yalakom fault system yfs lies on the eastern margin of the coast belt in southwestern british columbia the yalakom fault is the most significant structure in the fault system with at least 115 km of dextral slip mostly of early tertiary age the nw yfs is up to 25 km wide and is bounded on the southwest by the tchaikazan fault zone which had 5 km or more of dextral slip kinematic and paleostress analysis of mesofaults and map scale structures shows that secondary faults within the nw yfs had both dextral and sinistral oblique slip three large synclines had increasing amounts of clockwise vertical axis rotation from southeast to northwest block rotation between two synthetic strike slip faults with large offset yalakom and moderate offset tchaikazan is similar to current kinematics between the san andreas and san jacinto faults in southern california the nw yfs was active from latest cretaceous to mainly eocene time and postdates early late cretaceous thrust faulting to the southwest early stage mesofaults are compatible with the thrust belt and suggest that open folds developed in the foreland of the thrust belt before strike slip faulting commenced the abrupt northwest termination of the yfs may be related to extension within the adjacent tatla lake metamorphic complex some dextral slip may have been transferred farther northwest through the coast belt but these structures have not been documented in west central british columbia most of the 120 km of dextral slip on the yfs was transferred to the north via a mosaic of normal and strike slip faults in central british columbia thus the yfs forms the southwestern margin of a broad zone of transtensional structures that extends to the tintina rocky mountain trench fault zone these structures accommodated northwestward displacement of the northwestern cordillera in paleogene time

distribution of suspended sediment in the korea strait and southeastern yellow sea onset of winter monsoons abstract high energy conditions in the yellow sea begin each year with the onset of monsoon winds in late october these transitional season surges of cold air initiate sediment resuspension vertical mixing of suspended sediments and a wind driven coastal current that flows to the south during the summer to winter transition suspended sediment concentrations in the southeastern yellow sea range from 5 100 mg l 1 at the surface and 5 500 mg l 1 at the bottom the highest concentrations occur off the southwest tip of the korean peninsula and the lowest occur in the central part of the korea strait the rate of transitional season destratification may depend on the timing and intensity of monsoonal surges whereas a late onset of monsoon winds allows waters to remain longer in their moderately stratified summer condition an early onset of monsoon winds tends to destratify the water column by mid november resulting in a nearly uniform high concentration of suspended sediments from surface to bottom the band of more turbid coastal water ends abruptly 25 50 km offshore as a turbidity front in waters 20 80 m deep a wind driven residual flow to the south appears to transport large volumes of this turbid water into the korea strait and perhaps as far as the sea of japan

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

tectonic implications of paleomagnetic poles from lower tertiary volcanic rocks south central alaska we have determined the paleolatitude of lower tertiary volcanic rocks in southern alaska to measure possible poleward translation of the wrangellia and the peninsular terranes after 50 m y ago previous paleomagnetic studies have shown that in triassic and jurassic time these terranes were located near the equator and have moved at least 3000 km poleward relative to the north american craton our sample localities are in the northern talkeetna mountains in mildly deformed andesite and dacite flows 50 4 51 3 53 9 and 56 3 m y by k ar that overlap lower cretaceous flysch lower permian volcanic rocks of wrangellia and upper triassic pillow basalt of the susitna terrane results from 26 cooling units 23 of reversed polarity and 3 of normal polarity give a mean paleomagnetic pole at 69 5 n 179 6 e 95 12 2 stratigraphic sections from opposite limbs of a syncline yield directional paths that pass the fold test satisfying a necessary condition for primary origin of the magnetization the corresponding mean paleolatitude 76 n of the northern talkeetna mountains is 8 10 higher than the latitude predicted from the eocene reference pole for north america therefore northward drift of the talkeetna superterrane which is the amalgamation of the wrangellia and peninsular terranes during and after middle jurassic time was probably complete by 50 m y ago our results are consistent with paleomagnetic poles from uppermost cretaceous and paleocene volcanic sequences in denali national park the lake clark region northern bristol bay region and near mcgrath these poles generally lie south of the cratonic poles suggesting that the region between the kaltag bruin bay and castle mountain faults has rotated counterclockwise relative to north america since the early eocene

dynamics governing the response of tidal current along the mouth of jiaozhou bay to land reclamation 7 abstract data collected from the previous studies show that the tidal current along the mouth of jiaoz 8 hou bay jzb appears to have weakened whereas the spatial asymmetry stronger flooding in the north 9 region and stronger ebbing in the south region has remained nearly unchanged during the past aq4 several 10 decades of large scale land reclamation this study is conducted to explain the underlying dynamics for this 11 phenomenon the analytic evaluation of the tidal motion indicates that the tidal current in a small coastal 12 bay such as the jzb is linearly proportional to its length l if l is far less than one quarter of the tidal wave 13 length this relation suggests that the decrease in tidal current speed in jzb mouth results from the land 14 reclamation within the bay also the relationship between bay areas and tidal current along the jzb mouth 15 can be derived the results of this simple theoretical method for predicting the change in mean tidal current 16 amplitude after the land reclamation largely agree with previous three dimensional 3 d modeling studies 17 it is also found that the spatial asymmetry of the tidal current along the jzb mouth is controlled by the 18 sharp headland the local factor the unchanged shoreline around the headland leads to the stable spatial 19 asymmetry of the tidal current the weaker tidal current can explain the weaker residual current and the 20 unchanged asymmetry of the tidal current explains the unaltered pattern of inflow over the north region

compaction corrected paleomagnetic paleolatitudes for late cretaceous rudists along the cretaceous california margin evidence for less than 1500 km of post late cretaceous offset for baja british columbia the paleolatitudinal distribution of bivalve rudists has important significance for the baja british columbia baja bc hypothesis that western canadian superterranes from british columbia have been displaced 3000 km since cretaceous time rudists are not observed in baja bc sedimentary rocks yet they are common in late cretaceous strata in california and baja california which have the same paleomagnetically determined paleolatitudes approximately 25 n as baja bc rocks of late cretaceous age in order to resolve this contradiction and to delimit more exactly the southern paleolatitudes of baja bc paleomagnetic inclinations corrected for the effects of burial compaction were used to determine the paleolatitudinal distribution of rudists along the california margin compaction corrected paleomagnetic data from the peninsular ranges and salinia terranes indicate that rudists were restricted to paleolatitudes between 34 and 40 n evidence of coastal upwelling in the latest cretaceous marca shale may explain the northern limit of the rudist distribution these data suggest that baja bc was no farther south than 40 n in the late cretaceous thus limiting its post cretaceous displacement to less than 1500 km and that burial compaction has also affected the paleomagnetism of nanaimo group sedimentary rocks from vancouver island this result also helps resolve the conflict between paleomagnetic results which show 1500 km of post late cretaceous offset between the insular coast plutonic complex superterrane and the intermontane superterrane and geologic observations which can allow only tens of kilometers of offset between these terranes in the methow tyaughton basin

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

paleomagnetism of the late paleozoic slide mountain terrane northern and central british columbia paleomagnetic samples were collected from mid pennsylvanian to lower permian red argillaceous cherts at two localities of the slide mountain terrane 18 sites from the sylvester allochthon in northern british columbia and 11 sites from sliding mountain in central british columbia a secondary component of natural remanent magnetization in the sylvester samples yields a paleomagnetic pole that can be brought into coincidence with the jurassic portion of the north american apparent polar wander path by inferring vertical axis rotation during obduction of the allochthon both localities yield a characteristic component chrm with unblocking temperatures from 650 to 680 c after structural correction for bedding tilt all inclinations of chrm are negative consistent with magnetization during a reversed polarity interval in the northern hemisphere site mean chrm directions show consistent inclinations but distinct stratigraphic groupings of declinations inclination only statistics indicate that the chrm p

the yukon tanana terrane part of north america at 215 ma from paleomagnetism of the taylor mountain batholith alaska abstract the massive unmetamorphosed 212 ma taylor mountain batholith underlies 648 km2 of the yukon tanana terrane ytt in east central alaska and intrudes klippen thrust sheets of the fortymile river assemblage and the chicken metamorphic complex structural evidence indicates that the batholith is neither tilted nor rotated about a vertical axis paleomagnetic analysis of 295 specimens from 24 sites in the batholith and cross cutting mafic dikes isolates a stable primary characteristic remanent magnetization in magnetite with unblocking temperatures of 500 to 585 c that places the batholith s paleopole at 61 4 n 102 2 e n 17 95 5 2 on the north american apparent polar wander path apwp at 215 5 ma 1 the taylor mountain paleopole alone and all ytt paleopoles together show that the ytt has been a para autochthonous part of the north american margin since the late triassic further the intermontane belt imb paleopoles are distinct from the north american and ytt paleopoles prior to the mid eocene and provide two apwp segments one imb segment includes the quesnel cache creek eastern coast belt and northern stikine terranes and the second more speculative imb segment includes the central and southwestern stikine and methow terranes this analysis supports tectonic models for the northern cordillera in which the imb terranes were obducted onto north america during the late cretaceous to mid eocene co eval with the laramide orogeny

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

syn accretionary multistage assembly of an early jurassic alaskan type intrusion in the canadian cordillera u pb and 40ar 39ar geochronology of the turnagain ultramafic mafic intrusive complex yukon tanana terrane the magmatic evolution of the early jurassic turnagain alaskan type intrusion is inextricably linked to terrane accretionary events at the north american continental margin we have calibrated the

paleomagnetic evidence for poleward transport of upper jurassic rocks in the decatur terrane san juan islands washington the san juan islands are underlain by a west vergent late cretaceous thrust and nappe system part of a larger thrust belt exposed in the northwest cascades of washington and the southwestern coast mountains of british columbia published paleomagnetic data from cretaceous plutons for example the coast plutonic complex intruding the thrust belt suggest that it has been displaced northward by as much as 2400 km since 90 100 ma this study focuses on the preintrusive travel history of the decatur terrane one of the units involved in the san juan thrusting the decatur terrane is of special interest because it may be correlative with the coast range ophiolite cro and great valley sequence of the southern california coast ranges we report new paleomagnetic data from the james island formation an upper jurassic preintrusive turbidite unit and from the obstruction formation a terrigenous sandstone unit deposited on the decatur terrane in the late cretaceous nine sites in the obstruction formation yield a single remanence direction grand mean d 90 7 i 67 9 that is clearly a postfolding overprint possibly of late cretaceous age the six site mean remanence directions from the james island formation cluster well only after restoring the beds to horizontal by a scheme that takes account of their complex structure this positive fold test and the presence of two polarities provide evidence that the remanence is primary the mean paleolatitude corresponding to the corrected remanence direction from the james island formation is 0 9 2 the data thus corroborate equatorial paleolatitudes derived from parts of the cro by others and suggest that the decatur terrane and cro represent fragments of a larger terrane originally located near the jurassic equator unlike the cro however the decatur terrane was still near the equator at 145 ma if the plutons intruding the san juan north cascades thrust belt formed 2400 km to the south then the paleomagnetism of the decatur terrane suggests it moved 20 farther poleward in the interval 145 ma to 97 ma than did an equivalent site on north america a much smaller amount of pre late cretaceous motion is allowed by error limits on the paleolatitudes but more is required if tilting is partly responsible for the shallow paleomagnetism of the cretaceous plutons

structure and tectonic development of the southern rocky mountain trench the rocky mountain trench is one of the youngest most prominent and most enigmatic structures of the canadian cordillera approximately 650 km of seismic reflection data providing regional three dimensional coverage over an area of 10 000 km include six crossings of the rocky mountain trench between 49 n and 50 15 n prominent reflections from mid proterozoic moyie sills outline thrust and fold structures of a late jurassic to early cretaceous fault system that was cut by the rocky mountain trench fault in the tertiary the near basement reflections outline a 10 km high west facing basement ramp the hinge line of which spatially coincides with the rocky mountain trench in this area this ramp is part of a mid proterozoic margin upon which the belt purcell supergroup was deposited and is preserved beneath the trench during mesozoic contraction the basal detachment of the foreland belt closely followed the craton cover contact across the basement ramp thrusting ceased and extension was initiated when a culmination of thick basinal strata was juxtaposed with the basement ramp in the eocene miocene the basement ramp and the culmination above it focused stress reactivating the basal detachment and causing extensional faulting in the southern rocky mountain trench the rocky mountain trench fault may be linked via the basal detachment to the flathead fault on the east and the eocene extensional faults that flank the omineca belt on the west

jurassic location of the yukon tanana terrane from palaeomagnetism of the folded mississippian tatlmain batholith and ragged stock

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

a conceptual model for the preservation of thick transgressive shoreline successions examples from the forearc nanaimo basin british columbia canada abstract sequence stratigraphic models derived from passive margins and foreland basins characterize transgressive shorelines excluding incised valleys as recording periods of sediment starvation and are commonly represented as thin 10 m are more likely to be developed in active tectonic settings e g forearc and rift basins which generally experience high sedimentation rates and relatively rapid changes in base level settings with high sedimentation rates and moderate base level rise lead to progradational trends despite overall transgression of the shoreline in settings where changes in eustatic sea level mainly control the resulting stratigraphic architecture e g passive margins thin transgressive successions 1 10 m are more likely to be produced finally in settings defined by relatively slow base level change e g foreland basins the resultant transgressive succession typically comprises a lag 1 m overlain by offshore mudstones this conceptual model highlights the importance of the interplay between sedimentation rates and base level rise and is intended as a guide for the predictive modeling of sedimentary basins

a temporal and spatial study of mudflat erosion and deposition sediment elevations were measured on an intertidal mudflat in maine to determine the temporal and spatial changes in sediment volume the winter and spring months were times of greatest sediment change with erosion in winter months followed by rapid accretion in the spring in some months erosion and deposition took place during the same time interval but on different parts of the mudflat the data suggest that areas of erosion quickly become sites of accretion indicating that an equilibrium surface level is being maintained mudflats may strongly influence the adjacent estuary by acting as sediment banks that can periodically lend sediments to the particulate pool offshore we conclude that mudflats should not be thought of as steady accretionary environments but rather as more variable environments that respond to seasonal changes

paleomagnetism of the methow region north central washington structural application of paleomagnetic data in a complexly deformed variably remagnetized terrane jurassic through paleocene rocks of the methow pasayten belt were studied in order to use paleomagnetic directions to resolve the question of cretaceous northward transport in the end circumstanc

deciphering shallow paleomagnetic inclinations 1 implications from correlation of albian volcanic rocks along the insular intermontane superterrane boundary in the southern canadian cordillera 1 geologic and paleomagnetic data lead to two contradictory hypotheses regarding the paleoposition of the insular and intermontane superterranes that presently constitute the western canadian cordillera paleomagnetic data from the insular and intermontane superterranes suggest a southerly origin coinciding with the latitude of mexico and the northwest united states respectively during the mid cretaceous geologic evidence points to a northerly origin for these same tectonic entities during this period both models cannot be correct geologic and paleomagnetic data from the empire valley churn creek area in south central british columbia 51 5 n 122 5 w are critical to resolving these contradictory hypotheses late cretaceous rocks correlated to the insular superterrane with large paleomagnetic displacements unconformably overlie mid cretaceous rocks correlative to the spences bridge group of the intermontane superterrane we provide paleomagnetic evidence of this correlation based on similar magnetic properties opaque mineral assemblages demagnetization behavior fold test results mean inclinations clockwise vertical axes rotations and statistically indistinguishable paleomagnetic poles and displacement estimates this correlation and the observed geologic relationships in the empire valley churn creek area indicate that the insular and intermontane superterranes were linked by the mid cretaceous sites from the two previous spences bridge group studies are combined with their correlatives in the empire valley churn creek area to give 81 sites that yield a paleomagnetic pole of 60 5 n 304 5 e dp 3 7 dm 5 5 which corresponds to 1050 450 km of displacement from the south this new displacement estimate suggests that the spences bridge arc formed at the latitude of southern oregon during the mid cretaceous

northward translation of baja british columbia along the late cretaceous to paleocene margin of western north america paleomagnetic data suggest that a large part of british columbia and southern alaska was at the latitude of baja california mexico in early late cretaceous time this allochthonous block baja bc includes the insular talkeetna in alaska and intermontane composite terranes the miniterranes between them and possibly part of the omineca metamorphic belt assuming that baja bc was adjacent to north america by middle cretaceous an analysis using plate kinematics of the pacific basin produces a model of northward movement of baja bc which is compatible with the known geology of the reconstructed margin of western north america baja bc moved north 2400 km as part of the kuia plate along a transform margin with north america from 85 to 66 ma this time interval is marked by the cessation of igneous activity in the sierra nevada development of wrench faults and basins along coastal california and initiation of laramide style tectonics to the east within baja bc diminished igneous activity to the west was coeval with possible wrench tectonic basins along its eastern margin by the end of the cretaceous baja bc was positioned from oregon to northern british columbia between 66 and 56 ma baja bc became attached to north america in a dextral transpressive stage during which the kula north america plate boundary expanded to encompass the whole block with a series of northwest trending strike slip faults a fold and thrust belt in the east and large scale uplifts and the formation of an incipient volcanic arc on the west southern alaska was the site of convergence during the whole of the period of northward translation of baja bc a late cretaceous subduction zone in alaska evolved into a major compressional belt as the basin and miniterranes on the northern margin of baja bc collided with interior alaska the collision culminated in the paleocene with formation of the mckinley granites and coeval dextral slip on the denali fault system

dispersal of fine grained sediments in the southeastern yellow sea a steady state model a large portion of the yellow sea is floored by fine grained clastics derived largely from the hwangho and yangtze rivers in the southeastern yellow sea however coarse grained sediments prevail derived probably from the short and steep korean rivers farther east the coarse grained sediments contain substantial amounts of fine fractions near the keum estuary detrital clays such as kaolinite and chlorite are abundant in the free fractions and this trend extends for about 120 km both toward the northwest and the southwest illite appears to be dominant in the rest of the yellow sea the data suggest that the bulk of fine grained sediments in the southeastern yellow sea originates from the keum river the sediments are subsequently transported by prevailing nearshore currents both northwestward during summer and southwestward in winter the tidal currents may also play a role the close correspondance between the oceanographic data and the mineralogic evidence suggests that the dispersal of fine grained sediments in the southeastern yellow sea occurs largely under the steady state conditions

paleomagnetic evidence for motions of parts of the canadian cordillera abstract paleomagnetic evidence from major terranes of the western cordillera in canada referred to collectively as baja british columbia indicates that they have moved as a whole about 2300 km from the south and rotated 60 clockwise relative to north america in the late cretaceous and earliest tertiary 85 50 ma sometime between the early jurassic and the mid cretaceous 190 100 ma these same terranes moved south over 1000 km and underwent irregular but where well constrained counter clockwise rotations the terranes amongst themselves seem to have shared much the same paleolatitude during and since the late triassic although they may have undergone relative rotations in the later jurassic and early cretaceous these motions are now known to be broadly consistent with the motions of oceanic plates to the west as calculated by independent procedures and indicate that the terranes of the western cordillera were for part of their existence coupled to oceanic plates first to the farallon plate during the late jurassic and early cretaceous and then to the kula plate during the late cretaceous and early tertiary it was this change of allegiance from farallon to kula that caused first the southerly and then the northerly motion the paleomagnetic evidence despite claims to the contrary is consistent with geologically inferred displacements along major faults in the canadian cordillera when due account is taken of the age constraints on those motions

crustal evolution of the eastern canadian cordillera the cordillera is not like the himalayas the himalayas are supported by the indian continent that was thrust under the asian continent the eastern cordillera is supported not by imbricated continents but by imbricated continental margin of the ancient western north america that ancient margin was compressed and imbricated as it was confined between the north american craton and the minicontinent of stikinia in the eastern canadian cordillera tectonic thickening is in the collision zone and not on either side of it as for example in the tibetan plateau where the underthrust indian continent has duplicated the thickness of the crust in the eastern canadian cordillera jurassic and early cretaceous thrusts and faults are directed away from the collision zone toward the converging blocks the oppositely directed thrust faults outline wedge shaped sheets of rock sedimentary and volcanic rocks cover the crystalline rocks on which they were deposited basement and the underlying upper mantle may have been detached from each other during the compression the basement therefore would have imbricated internally between the cover and the mantle as a duplex structure confinement of the ancient margin s basement between the colliding blocks requires that the volume of basement under the margin be the same as that presently between the colliding blocks the possibility of such an equality has been tested and confirmed in cross section the cross section of the ancient western margin from that test has many features comparable to cross sections recently drawn through the eastern continental margin of canada

paleomagnetism and geochronology of 23 ma gabbroic intrusions in the keku strait alaska and implications for the alexander terrane samples of tertiary gabbro from 24 sites in the keku strait alaska help constrain the displacement history of the alexander terrane step heating experiments on a plagioclase separate from these previously undated intrusions indicate a discordant 40ar 39ar age of 23 1 1 7 ma the characteristic magnetization resides in magnetite is easily isolated by thermal and alternating field demagnetization and has both normal and reversed polarities the mean paleomagnetic pole with no structural correction is latitude 87 1 n longitude 141 6 e a95 10 1 with n 20 sites this pole indicates insignificant tectonic displacement 0 5 8 2 southward and rotation 0 6 15 2 counterclockwise we therefore conclude that any northward displacement or vertical axis rotation of the alexander terrane and or tilting in the vicinity of the keku strait must have occurred before 23 ma

the 3d geophysical investigation of a middle cretaceous to paleocene regional decollement in the cordillera of northern canada and alaska

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

structural divergence and transpression in the teslin tectonic zone southern yukon territory the structural and tectonic evolution of the teslin tectonic zone a complex belt of ductilely deformed rocks forming the southern extension of the yukon tanana terrane in the northern canadian cordillera is elucidated with new field data and by the reinterpretation of existing data the zone includes greenschist to amphibolite facies metasedimentary and metaplutonic rocks of the nisutlin and anvil assemblages characterized by s and l s tectonite fabrics primary contact relationships and ages show that most rocks in the zone were contiguous by mississippian time mapping identified a number of strain domains which preserve s fabrics dipping northeasterly or southwesterly variable mineral lineation orientations and a variety of shear directions including easterly and westerly vergent thrust shear down to the east and down to the west normal shear and dextral strike slip shear regional constraints and microstructures suggest that latest ductile deformation was late triassic to early jurassic in age structural characteristics are explained most effectively by convergent dominated transpression in combination with tectonic wedging and associated back thrusting above a low angle west dipping detachment oblique eastward and upward movement of the rocks over the detachment which may have coincided with the top of thinned north american continental crust produced easterly vergent shear and localized or widespread tectonic wedging and back thrusting produced westerly vergent shear the transpressive deformation postdates formation of the nisutlin assemblage by mississippian time and subduction of the slide mountain ocean beneath the nisutlin assemblage in permian to early triassic time the western margin of the teslin tectonic zone was truncated by cretaceous strike slip faults and translated northward rocks of the peraluminous orthogneiss assemblage of the yukon tanana terrane in central yukon acted as the tectonic wedge and were overthrust by rocks of the nisutlin and anvil assemblages in early jurassic time before unroofing by local extension in cretaceous time

the origin and evolution of the klondike goldfields yukon canada abstract the world famous klondike goldfields are located in the unglaciated part of west central yukon canada since their discovery over 100 years ago they have produced an estimated 311 tonnes of gold primarily from bench and creek placers that are fluvial in origin and range from pliocene to holocene in age historically the placers are classified into three levels of gravel with four main units these include the high level white channel gravel pliocene presently the most important gold bearing unit which sits nonconformably on an erosional bedrock surface i e the white channel strath and is overlain and interbedded with the glaciofluvial klondike gravel pliocene the intermediate level gravel pleistocene the least important economically and the low level gravel pleistocene holocene historically the most important gold bearing unit but it has been mined three or four times now the goldfields originated from the weathering and erosion of early cretaceous discordant mesothermal quartz veins and the light grey color of the matrix of the white channel gravel is due mainly to weathering and diagenetic alteration by groundwater flow the concentration of placer gold is related to a hierarchy of physical scales at the lithofacies scale metres bed roughness determined sites of gold deposition at the element scale tens of metres gravel bars were preferentially enriched in gold at the reach scale hundreds of metres stream gradient was an important factor at the system scale hundreds of km braided river environments transported large amounts of gold and at the sequence scale thousands of km economic placers formed initially in the high level white channel gravel and later in the intermediate level and low level gravel the white channel strath is interpreted as an erosional tectonic terrace that formed during isostatic uplift and under conditions of dynamic equilibrium the high level white channel gravel and klondike gravel are interpreted as a depositional climatic terrace that formed during a reversal in the tectonically induced downcutting which is attributed to the initial and most extensive of the pre reid glaciations 3 ma in the yukon the intermediate level gravel is interpreted as minor erosional complex response terraces that formed during static equilibrium when there were pauses in valley floor degradation which are attributed to the subsequent and less extensive pre reid glaciations the low level gravel formed also during valley floor degradation and may represent a return to dynamic equilibrium conditions hence the dominant forcing mechanisms controlling the evolution of the goldfields were isostatically compensated exhumation and climatic change related to the repeated glaciation of the yukon in addition the lowering of baselevel from high level to intermediate level and finally to low level gravel was accompanied by a decrease in accommodation space as indicated by a decrease in gravel thickness which resulted in an increase in the concentration of the placer gold

response of continental magmatic arcs to regional tectonic changes recorded by synorogenic plutons in the middle crust an example from the coast mountains of british columbia abstract the coast mountains of british columbia record an increase in magmatic activity acceleration in exhumation rate and a change from transpression to extension between 60 and 52 ma structural analysis of fabrics in three mid crustal plutons and country rocks leads to conclusions about pluton emplacement mechanisms and strain partitioning during changing tectonic conditions the quottoon and kitlope plutons 60 ma have steep foliations and lineations consistent with partitioned transpressional deformation the chief matthew s pluton 57 55 ma intruded during the formation of a sub horizontal transposition foliation and has radially distributed lineations consistent with sub vertical flattening during extension the change in orientation of the foliation represents an almost orthogonal rotation of the shortening direction from sub horizontal to sub vertical the chief mathew s pluton is interpreted to intrude initially into gently dipping fractures perpendicular to the steeply dipping foliation these melt filled fractures acted as conduits for melt triggering horizontal flow and eventually formed kilometer scale sills the steeply dipping fabrics of the coast shear zone provided pathways for melt to ascended from lower to middle crustal depths partitioning deformation into three dimensional domains of flattening simple shear and constrictional strain created the space for plutons this pattern of deformation reflects the interaction of regional deformation with magma emplacement

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

late quaternary stratigraphy of the yeongsan estuary southwestern korea abstract the 18 820 m long sediment core mw 1 from the yeongsan estuary consists of five primary unconsolidated to semi consolidated units ranging in age from late pleistocene to holocene overlying a cretaceous aged basement from oldest to youngest these units include units 1 2 3 fluvial units unit 4 paleosol unit and unit 5 holocene estuarine deposits units 1 2 and 3 are interpreted as in channel or overbank deposits plant materials included within the units and the toc tn total organic carbon total nitrogen ratios 11 14 are also indicative of terrestrial origin unit 2 yields radiocarbon date of 37 700 14 c yrbp unit 4 the paleosol unit is estimated to be originally deposited in fluvial setting such as the area of floodplain or backswamp away from the main channel based on the sporadic distribution of the stagnant freshwater acritarch pseudoschizaea and algae spirogyra the timing of deposition of the original sediments of the paleosol unit is constrained by radiocarbon age of underlying fluvial sediments unit 2 the timing of pedogenesis is around the last glacial maximum when sea level of the yellow sea was lowered temperature was lowered rainfall was reduced and the inland was sparsely vegetated estuarine deposits unit 5 are interpreted to be deposited during the holocene marine transgression

physical processes and fine grained sediment dynamics coast of surinam south america abstract the prograding holocene mud wedge between the amazon and orinoco rivers in the trade wind belt of northeastern south america provides a modern day example of muds accumulating under moderate wave energy conditions gigantic shore attached mudbanks 10 km 20 km composed partly of thixotropic fluid mud gel front this coast every 30 60 km to form a buffer to wave attack and a temporary storage for fine grained sediments this mesotidal coast tide range 2 0 m with gentle offshore slope 0 0006 allows the exposure twice a day of extensive tidal flat deposits which are backed by mangrove swamps on a well developed chenier plain complex field experiments were conducted in surinam du ing 1975 and 1977 to provide new information on process form relationships in this interesting but unusual muddy environment simultaneous measurements of waves currents tide elevation suspended sediment concentration and variations in mud density show that soft intertidal and subtidal muds are suspended at both tide and wave frequency suspended sediment concentrations typically exceed 1 000 mg l at the surface as incoming solitary like waves partially disperse fluid mud into overlying water on a falling or rising tide redeposition of mud may occur near time of high tide the strong attenuation of shallow water waves by these muds provides conditions that are favorable for further sedimentation high concentrations of suspended fluid mud together with solitary like waves from the northeast throughout the year can lead to extraordinarily high net sediment transport rates in the nearshore zone calculations based on solitary wave theory and on data obtained from this study indicate that 15 65 106 m3 of mud can move along shore each year without involving breaking waves the concept of radiation stress and a nearshore circulation cell or bedload transport farther offshore outside the zone of wave dominance wind driven currents and the guiana current combine to transport muds to the northwest consistent with the observed direction of mudflat migration

evolution of late quaternary mud deposits and recent sediment budget in the southeastern yellow sea abstract analysis of high resolution seismic reflection profiles and sediment samples has revealed the evolution and sediment budget of the southeastern yellow sea mud belt seysm along the southwestern korean peninsula the seysm up to 50 m thick over 250 km long and 20 55 km wide can be divided into three stratigraphic units a1 a2 and b from oldest to youngest unit a1 overlying the acoustic basement comprises the northern part of the seysm unit a2 comprises the southern part of the seysm much of unit a2 is exposed at the seafloor unit b completely covers unit a1 and pinches out southward 14c data suggest that evolution of each unit is closely related to the postglacial sea level changes unit a1 consists of estuarine deltaic or shallow water muds deposited during the early to middle stage of postglacial sea level rise ca 14 000 7000 yr b p unit a2 corresponds to relict muds deposited during the last deceleration stage of sea level rise ca 7000 3 500 yr b p unit b consists of shelf muds deposited during the recent sea level highstand ca very low background activities of 210pb of the surface sediment of unit a2 suggest that the present day sediment accumulation is negligible in the southern seysm on the other hand 210pb excess activity profiles in unit b yield an average sediment accumulation rate of 3 9 mm yr indicating active sediment accumulation in the northern seysm the annual sink 3 0 10 7 tons yr of fine grained sediment in unit b is about an order of magnitude greater than can be explained by the sediment input from the korean rivers alone we propose that reworking of unit a2 has provided large volumes of muds to unit b resulting in excessive sediment accumulation in the northern seysm much of unit a2 in turn is likely to have originated from erosion of unit a1 in the north this rather unique erosional depositional regime of the seysm is probably owing to the tidal and regional currents characteristic in the southeastern yellow sea

geometry evolution and tectonic framework of the skeena fold belt north central british columbia the intermontane belt of the canadian cordillera has long been viewed as a passive relatively rigid block between two metamorphic plutonic belts the coast plutonic complex and the omineca belt however the skeena fold belt which spans most of the width of the northern intermontane belt exhibits shortening comparable with that in the rocky mountain fold and thrust belt the skeena fold belt has many features of thin skinned fold and thrust belts such as thrust faults which sole into a detachment a wide variety of structural styles which depend on rock type a foreland basin which was cannibalized by continued deformation a frontal triangle zone and a hinterland of metamorphic and plutonic rocks coast plutonic complex the skeena fold belt thus is comparable with the rocky mountain fold and thrust belt but rather than deforming a continental terrace wedge it developed in a terrane stikinia which had accreted to north america in the early mesozoic and in jurassic and cretaceous clastic successions bowser lake and sustut groups which overlie stikinia structural and stratigraphic relationships show that the earliest deformation occurred between oxfordian and albian time and that the last folds developed in latest cretaceous or early tertiary time as much as 160 km of northeastward shortening in the skeena fold belt was broadly contemporaneous with crustal thickening in the coast plutonic complex and omineca belt with dextral strike slip faulting east of the skeena fold belt and with shortening in the rocky mountain fold and thrust belt therefore between latest jurassic and early tertiary times horizontal shortening occured across most of the width of the northern canadian cordillera concurrent shortening across the cordillera suggests that a common detachment or detachments fed all of these zones as far east as the rocky mountain fold and thrust belt

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

estimation of seasonal topographic variation in tidal flats using waterline method a case study in gomso and hampyeong bay south korea abstract morphologic and topographic changes of tidal flats can be key indicators for monitoring environmental changes and sea level rise recently a number of studies have been performed to estimate temporal topographic changes in tidal flats based on the waterline method using a number of remote sensing data that were acquired at different tidal heights however the effect of seasonal variation has not been taken into consideration nor been understood so far in this study 18 scenes of landsat tm and etm data covering the period 2003 2004 and corresponding tidal gauge observation data were used to estimate seasonal topographic variations in two major tidal flats in gomso and hampyeong bay in the southern part of the west sea of south korea using the waterline method our results showed that the summer deposition was dominant in gomso bay with overall average seasonal topographic increase of approximately 18 6 cm in contrast hampyeong bay showed more dominant summer erosion with overall average seasonal topographic subsidence of about 5 0 cm in addition the net overall sedimentation budget was estimated as 6 308 047 m 3 and 2 210 986 m 3 in gomso and hampyeong bay respectively the results also indicates that although both bays of gomso and hampyeong are classified as semi enclosed tidal flat the sedimentary facies caused by formation geometry and sediment type led to different topographic changes the results demonstrate that the amount of seasonal topographic variations is not negligible and are expected to improve the accuracy of topographic change derived by the waterline method

large scale coast parallel displacements in the cordillera a granitic resolution to a paleomagnetic dilemma abstract resolution of the paleomagnetic dilemma the discrepancy between large paleomagnetically determined dextral displacement of outboard portions of the northern cordillera and much smaller offsets implied by mapping and stratigraphic correlations is fundamental to understanding the tectonic evolution of the cordillera this paper presents structural orientation data from the middle cretaceous dawson range batholith of west central yukon and its wallrocks and suggests that some of the missing displacement may be found in intrusions the elongate northwest trending batholith has a margin parallel foliation a sub horizontal stretching lineation and records syn intrusive dextral shearing in country rocks adjacent to the batholith north trending lineations are deflected clockwise into near parallelism with the batholith s margins lineations from wallrock screens within the batholith are all aligned parallel with the batholith s long axis the big creek strike slip fault forms the north margin of the batholith and accommodated a minimum of 20 km of dextral slip these observations imply that the batholith invaded an active dextral shear zone accommodated shearing while crystallizing and focused post crystallization fault development the batholith is conservatively estimated to have accommodated 45 km of syn intrusive shearing collectively middle cretaceous intrusions of the northern cordillera may account for 400 km of previously unrecognized dextral displacement

lower paleozoic stratigraphic and biostratigraphic correlations in the canadian cordillera implications for the tectonic evolution of the laurentian margin the ancient laurentian margin rifted in the latest neoproterozoic to early cambrian but appears not to have developed as a simple passive margin through a long post rift drift phase stratigraphic and conodont biostratigraphic information from four platform to basin transects across the margin has advanced our knowledge of the early paleozoic evolution of the margin in northeastern british columbia two northern transects span the macdonald platform to kechika trough and ospika embayment and a third transect spans the parautochthonous cassiar terrane in the southern rocky mountains new conodont biostratigraphic data for the ordovician succession of the bow platform is correlated to coeval basinal facies of the white river trough in total from 26 stratigraphic sections over 25 km of strata were measured and 1200 conodont samples were collected that yielded over 100 000 conodont elements key zonal species were used for regional correlation of uppermost cambrian to middle devonian strata along the cordillera the biostratigraphy temporally constrains at least two periods of renewed extension along the margin in the latest cambrian and late early ordovician alkalic volcanics associated with abrupt facies changes across the ancient shelf break intervals of slope debris breccia deposits and distal turbidite flows suggest the margin was characterized by intervals of volcanism basin foundering and platform flooding siliciclastics in the succession were sourced by a reactivation of tectonic highs such as the peace river arch prominent hiatuses punctuate the succession including unconformities of early late ordovician sub llandovery possibly early to middle silurian and early devonian ages

mid cretaceous thrusting in the southern coast belt british columbia and washington after strike slip fault reconstruction a major thrust system of mid cretaceous age is present along much of the coast belt of northwestern north america thrusting was concurrent and spatially coincided with emplacement of a great volume of arc intrusives and minor local strike slip faulting in the southern coast belt 52 to 47 n thrusting was followed by major dextral slip faulting which resulted in significant translational shuffling of the thrust system in this paper we restore the displacements on major dextral slip faults of the southern coast belt and then analyze the mid cretaceous thrust system two reconstructions were made that use dextral faulting on the yalakom fault 115 km castle pass and ross lake faults 10 km and fraser fault 100 km the reconstructions differ in the amount of dextral offset on the straight creek fault 160 and 100 km and how much the ne part of the cascades crystalline core expanded 30 km and 0 km during eocene extension reconstruction a produces the best match of lithotectonic units and thrust systems our synthesis shows that the southern coast belt thrust system was 250 180 km wide after thrusting the thrust system was mainly southwest vergent but had a belt of northeast vergent back thrusts on the northeast side associated with the tyaughton methow basin which may indicate large scale tectonic wedging thrust faults are commonly low to moderate angle but high angle faults also occur especially as late stage out of sequence structures involving plutons the amount of thrust displacement across the system is unknown but must be at least 100 km and may be many hundreds of kilometers most thrusting occurred from 100 to 80 ma and did not migrate systematically until after 90 ma when thrusting and magmatism shifted to the northeast for a few million years widespread thrusting occurred both near plutons and where there are no or small plutons which strongly suggests that thrust faulting was caused by regional to plate scale forces such as rapid plate convergence and or arc continent collision

superimposed quesnel late paleozoic jurassic and yukon tanana devonian mississippian arc assemblages cassiar mountains northern british columbia field u pb and igneous petrochemical evidence allochthons in the cassiar mountains of northern british columbia contain assemblages belonging to two distinct canadian cordilleran terranes yukon tanana ytt and quesnellia these assemblages of pre late devonian devonian mississippian pennsylvanian permian and early jurassic age occur in intrusive and depositional as well as structural contact with each other the allochthons are gently dipping thrust panels interrupted by the mid cretaceous cassiar batholith a key element for correlation across the batholith is the mississippian and older pericratonic dorsey complex new devonian mississippian u pb ages for deformed plutons within it document an igneous suite like those in type yukon tanana exposures farther north other characteristics of the dorsey complex that ally it with ytt are orthoquartzites and grits and amphibolite bodies with transitional mid ocean ridge basalt morb to ocean island basalt oib petrochemical signatures unconformities deformed clasts in the late paleozoic sequences and a shared mid permian intrusive suite show that later arcs onlapped the mid paleozoic and older ytt assemblage the early jurassic intrusive suite cuts all major contacts and fabrics except the terrane bounding fault between the slide mountain and combined ytt quesnel terranes it represents a northern continuation of a plutonic belt that extends the length of the mesozoic quesnel magmatic arc these relationships carry important implications for cordilleran terrane history and the tectonic evolution of the north american margin at least some of the major terranes were not unrelated entities prior to their accretion to the continent but a system of superimposed and interconnected arcs that developed over a protracted time interval with complex and evolving paleogeographic configurations much like the modern western pacific province

structural evolution of basement gneisses and hadrynian cover bulldog creek area rocky mountains british columbia two gneiss bodies are contained in thrust sheets on the west edge of the rocky mountain main ranges near valemount british columbia the bulldog gneiss comprises aphebian or older paragneiss and amphibolitic gneiss intruded by aphebian orthogneiss sheets the yellowjacket gneiss is granodioritic orthogneiss of unknown age both gneiss bodies are basement highs with thin hadrynian metasediment cover sequences the cover sequences are assigned to the lower miette group and are correlated with horsethief creek group internal shortening of gneiss thrust sheets is expressed by recumbent folding and stacking of thin thrust sheets of gneiss and cover the bulldog gneiss and its cover were carried on the postmetamorphic purcell thrust the yellowjacket gneiss and its cover were carried on the pre to synmetamorphic bear foot thrust northeast and northwest displacement is documented on the moderately southwest dipping bear foot thrust and a dextral oblique slip thrust model is proposed to explain the duality

seasonal variation of sedimentary processes in a semi enclosed bay hampyong bay korea abstract multi annual sedimentological observations on tidal flat sediments were carried out in hampyong bay southeastern yellow sea to infer the budget of modern muddy sediments in the bay sedimentation rates over a four year period show contrasting types of seasonal sedimentary cycles occurring in the tidal flats within the elongated bay both sides of the bay are largely sheltered from winter waves resulting in surface mud deposition during winter and erosion during summer in contrast tidal flats along the head of the bay are influenced by winter waves resulting in a reversed trend where erosion occurs during winter and deposition during summer tidal flats near the bay mouth however show a sedimentary cycle disrupted by the construction of sea walls undergoing consistent erosion throughout the observational period the shoreline artificially straightened seems to cause tidal currents to bypass the tidal flat and hence to be much stronger these differences in sedimentary cycles suggest the critical importance of the orientation of tidal flats relative to the propagating direction from n nw of the monsoon winter storm waves on the tidal flat sedimentation in the eastern coastal area of the yellow sea the preliminary budget estimation for the tidal flat mud suggests that the tidal flats in hampyong bay are subject to the slight but consistent erosion as a whole

seasonal variation of sediment deposition in the hudson river estuary abstract during and following the spring freshet rapid rates of sediment deposition were observed in the hudson river estuary side scan sonar surveys and sediment coring studies revealed a large amount of spatial variability in sedimentation within the estuary and a distinct seasonal progression during the freshet sediment was deposited in the seaward reaches of the estuary in the two month period after the freshet this sediment was eroded and sedimentation occurred 10 30 km further landward at the estuarine turbidity maximum etm zone the thickness of the new freshet deposit was as great as 40 cm in the etm indicating intense trapping and rapid deposition the location of this depocenter corresponded to a frontal zone where water column observations and modeling studies have indicated enhanced sediment trapping the mass of the new deposits was estimated at 300 000 metric tons during both 1998 and 1999 with similar spatial distributions in 1998 the estimated fluvial input was 560 000 metric tons significantly greater than the 120 000 metric tons estimated for 1999 thus the mass of the observed deposits appear to be more influenced by the redistribution of sediment within the estuary due to seasonal variations in erosion deposition conditions rather than by the direct input of sediment from the watershed

two stage exhumation of midcrustal arc rocks coast mountains british columbia 1 new geologic data from the central gneiss complex along douglas channel help delineate the burial and exhumation of the late cretaceous to eocene coast mountains magmatic arc arc plutonism was on going between 90 and 60 ma replaced by formation of dikes to 52 ma supracrustal rocks were buried to midcrustal levels by 90 ma and garnet and kyanite grew from 90 through 70 ma subsequent exhumation was nearly isothermal and took place in two stages the first occurred from 70 to 59 ma as the arc contracted obliquely and sillimanite replaced kyanite exhumation was slow 0 5 mm yr probably accomplished by erosion aided by coaxial crustal thinning exhumation rates about doubled in the second stage of exhumation after 59 ma and before 52 ma penetrative deformation ended prior to intrusion of the quottoon pluton at 59 ma and 6 5 kbar production of cordierite rims on garnet at 4 5 kbar and 700 c signaled the end of near isothermal decompression prior to 52 ma rapid cooling 100 c 106 years of the central gneiss complex followed cordierite growth temperatures dropped to 250 by 48 ma the increase in exhumation rate and the subsequent rapid cooling are attributed to excision of 6 km of crust on a detachment system on the northeastern side of the central gneiss complex comparison to other parts of the coast mountains arc the sierra nevada and fiordland new zealand shows that the amount and tempo of exhumation vary greatly within and between arcs suggesting that the processes accommodating exhumation vary significantly

north american apparent polar wander plate motion and left oblique convergence late jurassic early cretaceous orogenic consequences the north american apparent polar wander apw path indicates an episode of unusually rapid absolute northward motion of western north america between 150 and 135 ma during this time the northward component of absolute motion of points along the washington oregon california coast was in excess of 150 km m y and perhaps as high as 230 km m y we believe that such high absolute northward velocity for north america probably ensures that relative motions of oceanic plates and terranes influenced by them were to the south at this time the inception of rapid northward motion and left oblique convergence was abrupt and should be recorded in the geology of the western cordillera it is tempting to correlate this period of unusual pacific basin north american interaction with the nevadan orogeny in the klamath mountains as well as with left lateral strike slip structures such as the pine nut fault and bear mountains fault zone significant differences exist between north american plate motion recorded by the late jurassic cretaceous apw path and that predicted by a fixed hotspot model we believe that this discrepancy reflects uncertainty associated with pre late cretaceous hotspot tracks and poorly constrained relative plate motions during the cretaceous normal polarity superchron

sedimentary processes of fine grained material and the effect of seawall construction in the daeho macrotidal flat nearshore area northern west coast of korea abstract sedimentary processes on the lower tidal flat of the reclaimed seosan bay daeho tidal flat at the west coast of korea have undergone significant changes since 1984 when seawalls over 8 km long were constructed at the bay mouth comparison of pre and post construction tidal flow models indicates that in general tidal currents have increased considerably in front of the daeho tidal flat with tidal flow directions having changed from shore normal to shore parallel the 12 h measurements of currents and suspended sediment concentrations at four anchored hydrographic stations show nearshore suspended sediments drifting southward throughout the year bypassing the daeho tidal flat cyclic seasonal variations occur prominently in the grain texture of the tidal flat sediments and associated sedimentation rates in summer fine grained sediments deposit at a rate of 2 6 mm month particularly in sheltered places during the winter monsoon erosional processes are greatly enhanced by the interplay of tidal currents and waves up to 30 mm month this sedimentary seasonality is reflected in the variations in the concentration of nearshore suspended matter the concentration of suspended matter is much higher in winter 60 80 mg l because of vigorous resuspension activities compared with the summer concentration 10 30 mg l the direct effect of seawall construction coupled with strong natural seasonality can be seen from the continuous monitoring of sedimentation rates on the tidal flat the 2 year 1993 1995 measurements indicate that the entire daeho tidal flat was eroded during that period at the abnormally high average rate of 10 cm year the causal blocking of bayward sediment and water movements by any artificial structure might lead to similar erosional conditions to many other bays facing the yellow sea on the both chinese and korean coastlines subjected to energetic winter wave attack

pressure temperature and tectonic evolution of triassic lawsonite aragonite blueschists from pinchi lake british columbia a blueschist and eclogite terrane is associated with one of the largest faults in the canadian cordilleran orogen the pinchi fault blueschists in situ and retrogressed eclogite blocks occur along the pinchi fault zone near 54 30 n and 124 w critical blueschist facies mineral assemblages include lawsonite glaucophane jadeite lawsonite glaucophane quartz and aragonite white mica 40ar 39ar spectra on blueschist and eclogite yield ages in the range 221 8 1 9 to 223 5 1 7 ma establishing a direct link between the blueschists and eclogites preservation of aragonite sets rigid constraints on the pressure temperature fluid time conditions of unroofing k ar dates indicate that this is some of the oldest documented metamorphic aragonite comparison with computed petrogenetic grids suggests that metamorphic temperatures were in the range 200 300 c with pressures greater than 8 10 kbar 1 kbar 100 mpa unroofing likely occurred during collision of the cache creek terrane with quesnellia in the lat

lower crustal deformation during terrane dispersion along strike slip faults abstract after accretion terranes caught between obliquely converging plates are often displaced several hundreds of kilometers how this motion is accommodated at depth is not well known spurred by our trans alaskan crustal transect tact seismic studies of the yukon tanana terrane alaska i propose that the lower crust responds ductilely to accommodate differential movement between upper crust and upper mantle during margin parallel translation the locations of these ductile regions are dependent on temperature composition and strain rate for geotherms based on moderate surface heat flow 60 90 mwm 2 and reasonable geological strain rates 100 in 3 ma typical lower crustal rocks can deform ductilely the resultant subhorizontal layered fabric should be detectable with seismic techniques two terranes that have experienced hundreds of kilometers of margin parallel translation the yukon tanana terrane sampled by our seismic refraction wide angle reflection profiles and the salinian block california sampled by both seismic refraction and reflection have reflective lower crust both of these terranes have moderate to high surface heat flows have relatively thin crust and are interpreted seismically to be underlain by a quartzo feldspathic lower crust conditions favorable for ductile deformation in the lower crust interpretations of lower crustal layering for these two terranes is based on an increase in lower crustal reflectivity this layering is attributed to tectonic banding consistent with ductile deformation

reply to comment on paleomagnetism of the upper cretaceous strata of mount tatlow evidence for 3000 km of northward displacement of the eastern coast belt british columbia by p j wynne et al and on paleomagnetism of the spences bridge group and northward displacement of the intermontane belt british columbia a second look by e irving et al

paleomagnetism of the resurrection peninsula alaska implications for the tectonics of southern alaska and the kula farallon ridge the rocks of the resurrection peninsula compose an ophiolite 57 1 ma within the vast accretionary prism of the chugach prince william terrane paleomagnetic data from pillow basalt and sheeted dikes of the ophiolite yield a mean paleolatitude of 54 7 which implies 13 9 of poleward displacement the characteristic component of the remanence resides in a ti poor titanomagnetite with a blocking temperature close td 580 c a positive fold test and the petrology of the magnetic minerals lead us to conclude that the characteristic remanent magnetization chrm in the sheeted dikes originated as a primary thermoremanent magnetization trm we hypothesize that the chrm of the pillow basalt originated as a chemical remanent magnetization crm acquired soon after formation of the rocks during hydrothermal metamorphism structural data indicate polyphase deformation with folding about vertical and horizontal axes the paleomagnetic data pass a fold test only when we incorporate this interpretation in our structural correction geologic relationships lead us to interpret the resurrection peninsula ophiolite as a fragment of the extinct kula farallon ridge that accreted to the chugach prince william terrane soon after formation the paleomagnetic paleolatitude indicates that the ridge intersected the north american continental margin in the vicinity of northern washington in late paleocene time the paleostrike of the sheeted dikes n26 e 12 shows that the ridge trended nne according to current plate tectonic models if the chugach prince william terrane moved north with the full coastwise displacement of the kula plate the resurrection peninsula ophiolite would have arrived at its present position at 45 ma this age is perhaps slightly later than that of the terranes that lay immediately inboard peninsular and wrangellia terranes indicating some relative displacement between those terranes and the chugach prince william terrane such displacement in turn agrees with studies which imply a coast plutonicmetamorphic complex provenance for the chugach prince william terrane

rethinking yellowstone in yukon and baja british columbia paleomagnetism of the late cretaceous swede dome stock northern canadian cordillera 1 paleomagnetic results obtained from the 69 8 ma swede dome stock emplaced into the pericratonic yukon tanana terrane ytt west of dawson yukon indicate a minimal northward translation of 360 575 km and a clockwise rotation of 20 23 with respect to north america in accord with the displacement of 425 km along the nearby tintina fault coeval carmacks group volcanics in contrast have previously indicated 1900 km northward translation and minimal rotation and have been proposed to be a displaced manifestation of the fixed yellowstone hot spot thus providing an independent estimate of the late cretaceous paleoposition of the baja british columbia terranes of western north america a compilation of recent mid and late cretaceous paleomagnetic results from the ytt and intermontane belt imb terranes reveals that the carmacks group paleomagnetic result is anomalous the ytt and imb terranes which form the bulk of baja british columbia appear instead to have experienced 1000 km northward translation with respect to north america since 70 ma consistent with geological estimates of motion along plausible accommodating faults in addition past mobility of the hawaii emperor hot spot implies that the pacific hot spots may have experienced 1200 km of southward motion from 81 to 47 ma if so then the paleoposition of the yellowstone hot spot if it existed at 70 ma would likely have produced the carmacks magmatism 1000 km north of yellowstone s current latitude consistent with a moderate 1000 km post 70 ma northward translation of the ytt and imb terranes to their present position in north america

origin of inner shelf mud deposit in the southeastern yellow sea huksan mud belt abstract a variety of previous sedimentological results together with newly obtained hydrodynamic data are summarized and reinterpreted with respect to the most likely origin of the huksan mud belt hmb in the southeastern yellow sea the hmb consists of two mud units that have similar grain texture and clay mineralogy but can be differentiated on seismic profiles because the lower unit is generally harder than the watery upper unit the hydrographic measurements together with satellite imagery clearly indicate that the suspended plume covering the hmb originates from the west coast of korea the suspended plume becomes enhanced by winter monsoon winds beginning in late fall most of the studies of clay mineralogy geochemistry and isotherm distribution also suggest that the hmb has been derived from the west coast of korea particularly from the keum river an approximate evaluation of the depositional time for the hmb based on its dimensions and the discharge rate of the keum river suggests a time duration of the order of 14 000 years hydrodynamic measurements across two transects over the northernmost hmb reveal that suspended matter travels southwest toward the main body of the hmb in a well constrained corridor ultimately connected with the keum river time series 12 5 h hydrodynamic measurements at a site over the hmb suggest that the winter season suspended plume carries concentrations of suspended matter one to two orders of magnitude higher than those of the summer silt grains of 5 6 well sorted through numerous resuspension events settle out onto the hmb forming distinctive silt laminae alternating with clay rich laminae

paleomagnetic data from alaska reliability interpretation and terrane trajectories virtually the entire body of paleomagnetic data collected from southern alaska depicts a clear decrease in paleolatitude with increasing age strongly suggesting that southern alaska represents a displaced terrane in this paper paleomagnetic studies from southern alaska have been classified with respect to a quality index that is based on four criteria these criteria are the presence of both polarities of magnetic remanence stepwise thermal or alternating field demagnetization of specimens principal component analysis of demagnetization data and a successful fold test of the 51 studies compiled only four from southern alaska and one from western canada are demonstrated to satisfy all criteria and fall therefore in the category of group 3 highly reliable two studies from southern alaska satisfy three of the four criteria lacking both polarities of characteristic remanence and are judged to be of group 2 reliable two of these paleomagnetic studies constrain the accretion time of the southern alaska terrane to the relatively stationary region of central alaska north of the denali fault four paleomagnetic studies from the southern alaska terrane show a distinct paleolatitude anomaly when compared with their expected paleolatitudes from the north american apparent polar wander path using the model of engebretson et al 1984 a series of models are presented to best fit these highly reliable and reliable paleomagnetic studies the model preferred in this article assumes an accretion time with north america of 50 ma and documents pre 50 ma displacement of the southern alaska terrane on the kula plate if the ghost rocks paleomagnetic magnetizations plumley et al 1983 are assumed to be of earliest tertiary age this model fits all of the low paleolatitudes observed in southern alaska models incorporating coastwise translation of the southern alaska terrane along the western boundary of the north america plate and a 50 ma suturing age of this terrane to north america do not satisfy the paleomagnetic constraints four of the reliable studies can be modeled assuming strike slip motion of the southern alaska terrane along the western boundary of the north america plate if a 40 ma suturing age is assumed in this model however the paleomagnetic data must be presumed to represent the highest permissible paleolatitude and the ghost rocks formation paleolatitudes are problematically lower than is possible to model with coastwise translation

suspended sediment transport on a temperate microtidal mudflat the danish wadden sea abstract time series measurements of suspended sediment transport and bed level change on a microtidal mudflat of the danish wadden sea were carried out between february 1997 and september 2000 the data show that the mudflat is generally accreting except for periods with onshore winds when wave induced erosion takes place during periods of low water levels at the site in general a continuous net input of mud was recorded during periods of weak or offshore winds i e the import is not event controlled and this was interrupted by episodic loss of mud during a few tidal periods with onshore winds the net landward transport of suspended sediment during calm weather or periods of offshore wind is caused by settling and scour lag and tidal asymmetry a very large input of suspended material was observed in the period following a strong storm the landward directed net transport during the five tidal periods following the storm being equivalent to approximately 40 of the net annual accumulation in the area the typical depth of sediment reworking at the intertidal study site is 2 5 cm some seasonal variation can be deduced from the data set with a tendency for deposition during spring and summer and erosion in the winter period the seasonality was especially clear at the most landward station where accretion following periods of ice formation in the area is due to grounding of sediment transported by ice floes but otherwise deposition is mainly taking place in the warmer seasons net accretion over the three year measuring period along the transect varies between 0 6 and 1 9 cm a 1 deposition is largest at the most landward station and the accretion found on the basis of repeated bed level measurements compares well with 210 pb and 137 cs dating

timing and tectonic setting of stikine terrane magmatism babine takla lakes area central british columbia new bedrock mapping completed as part of the nechako natmap project indicates that the area between babine and takla lakes in central british columbia is underlain by rocks of the early permian asitka late triassic takla and early to middle jurassic hazelton volcanic arc assemblages of the stikine terrane these are cut by large composite stocks of quartz diorite granodiorite and quartz monzonite previously mapped as the late triassic to early jurassic topley intrusions new u pb n 6 and laser 40ar 39ar n 10 isotopic age dates reported in this paper suggest there are two distinct ages of plutons the topley intrusive suite with isotopic ages between 218 and 193 ma and east of babine lake the new spike peak intrusive suite with isotopic ages ranging from 179 to 166 ma west of the main plutonic belt is a thick volcanic succession of subaerial porphyritic andesite flows volcanic breccias and rhyolitic ash flow tuffs that have isotopic ages between 185 and 174 ma these rocks are assigned t

development of stratigraphy and sediment distribution in the northeastern yellow sea during holocene sea level rise abstract a succession of holocene deposits in the northeastern yellow sea were interpreted in a sequence stratigraphic context and sedimentology of each deposit was characterized based on analyses of high resolution seismic profiles and sediment cores taken along a transect thin 3 m transgressive sediments that accumulated through shoreface erosion during the rapid sea level rise in the early holocene overlie a subaerially eroded low gradient late pleistocene platform on the present day inner shelf region cores reveal marine sands over tidal estuarine sandy muds with an intervening rather indistinct ravinement surface in the deepest shelf area these early holocene tidal estuarine deposits remain exposed at the seabottom in the mid o late holocene two contrasting deposits of the highstand type deltaic clayey mud and tidal sand ridges began to accumulate in response to slower rates of sea level rise a series of tidal sand ridges in the nearshore area migrated offshore over the transgressive sand sheet and a deltaic watery mud prograded discordantly over consolidated tidal estuarine deposits in the central shelf the transgressive facies relationships present a model for macrotidal epicontinental sea settings subject to low wave energy and reduced sediment supply