chemistry of hydrothermal fluids from the 17 s active site on the north fiji basin ridge sw pacific abstract in june 1989 a diving cruise of the french submersible nautile was made along the north fiji basin spreading ridge the objective was the geological and geochemical study of the active spreading axis and of the hydrothermal processes discovered during the kaiyo cruise in 1988 active anhydrite chimneys associated with underlaying sulfide deposits were studied in the central spreading ridge the transparent venting fluid showed significant salinity depletion the extrapolated concentrations of all the chemical species in the pure end member showed a signature similar to that of the cl depleted hydrothermal fluid from the ashes vent site in the juan de fuca ridge these features suggest that the present hydrothermal end member resulted from subcritical phase separation which generated a low salinity vapor phase followed by condensation and mixing with normal seawater in the last part of the plumbing system of the vents

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

life history of an anticyclonic eddy 1 we use the trajectory of three buoys dragged below the surface mixed layer together with sea surface temperature imagery to examine the evolution of an anticyclonic warm core eddy since its generation by the canary islands two buoys remain within the eddy during some 100 days and the third one remains almost 200 days while drifting southwestward up to 500 km with the mean canary current the eddy merges with several younger anticyclonic and cyclonic eddies in each occasion suffering substantial changes the eddy core defined as a region with near solid body type rotation and radial convergence initially occupies the whole eddy after interacting with another vortex the inner core markedly slows down although it continues displaying radial convergence and relatively small radial oscillations and an uncoupled outer ring is formed or enhanced which revolves even more slowly and displays large radial fluctuations the vortex extensive life is consistent with its inertially stable character and observations of radial convergence a very simple model of vortex merging where cylinders fuse conserving mass and angular momentum gives fair results the observations suggest that the eddy changes as the result of its own slow evolution and sporadic mixing events from a young stage where the core retains its vorticity and occupies most of the eddy through a mature stage where the eddy has a reduced inner core and a slowly revolving outer ring to a decay stage where the vorticity maximum is substantially reduced

arc and intraplate volcanism in the spences bridge group implications for cretaceous tectonics in the canadian cordillera the spences bridge group a late albian 100 ma age volcanic succession built on the western margin of superterrane i comprises two stratigraphic units with contrasting geochemistry the lower unit the pimainus formation represents a set of stratovolcanoes with calcalkaline character lavas of the overlying spins formation deposited as a shield volcano are hybrids between pimainus arc magma and spins type melts of intraplate affinity integration of regional geology suggests that the pimainus formation was produced by short lived easterly dipping subduction beneath superterrane i that convergence closed a narrow oceanic basin now represented by the methow tyaughton trough bringing superterrane ii into collision with superterrane 1 accretion in the latest albian resulted in cessation of pimainus are volcanism the eruption of spins lavas and easterly directed deformation of methow tyaughton strata early to middle cretaceous are volcanism of the gambier group on superterrane ii was produced by a separate concurrently active subduction zone

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

geochronological constraints on magmatism and polyphase deformation and metamorphism in the southern omineca belt british columbia the omineca belt between nelson and creston in southeastern british columbia was affected by overlapping pulses of mesozoic magmatism metamorphism and deformation u pb geochronological data from zircon and monazite were collected by laser ablation inductively coupled plasma mass spectrometry la icp ms to constrain the timing of these events the porcupine creek stock 162 3 1 3 ma intruded across folds and fabrics associated with the earliest phase of regional deformation and metamorphism d1m1 restricting it to the early middle jurassic the jurassic structures are overprinted northwards by early cretaceous deformation and metamorphism d2m2 the baldy pluton 117 8 1 2 ma crosscuts the regional 144 134 ma m2 isograds yet was pervasively affected by the d2 deformation indicating that d2 deformation outlasted m2 metamorphism but had ceased by 111 ma the age of an undeformed pluton monazite dates from a kyanite bearing rock in the contact aureole of the middle jurassic wall stock over

eddy advective and diffusive transports of heat and salt in the southern ocean there are two distinct mechanisms by which eddies provide systematic transport of tracer on isopycnals the advective transport associated with the slumping of isopycnals and the diffusive transport associated with down gradient diffusion depending on the large scale tracer distribution eddy advective transport has either the same direction as or opposite direction to eddy diffusive transport as a consequence eddy advection and eddy diffusion can reinforce each other for some tracers but oppose each other for other tracers using scaling analysis it is argued that the relative directions of eddy advective and diffusive transports can be determined simply from the relative slopes of tracers and isopycnals an eddy resolving 1 12 global ocean model is used to illustrate the two eddy transport mechanisms for temperature and salinity in the southern ocean applications to other tracers such as oxygen are discussed the diagnosed eddy diffusivity for temperature and salinity is found to be considerably different from the eddy diffusivity for eddy advective transport velocity

volcanic episodicity and a non steady state rift valley along northeast pacific spreading centers evidence from sea marc i sea marc i side looking sonar images and sea beam bathymetry along a 400 km stretch of the juan de fuca ridge crest provide evidence that excessive extrusive volcanism periodically builds a crestal ridge along the axis of seafloor spreading an elongate summit depression esd or rift valley is commonly observed in the spine of this crestal ridge the crestal ridge volcanic landform has a distinctive shape that is recognized in bathymetric contours both along the spreading axis and at least up to 30 km away from the axis the landform has a plan form shape that resembles a side view of an archer s bow with the long dimension of the bow form parallel to the strike of the ridge in cross section the bow form is flat on top and has steep flanks these bow form shapes can be explained by magma that rises into the crust at a discrete center and flows laterally into belts of ridge parallel dikes similar to icelandic fissure eruptions both the variable dimensions of the esd along axis of the juan de fuca ridge and the relationship among volcanic flow morphologies within and beyond the esd suggest the four different segments of the juan de fuca ridge presented in detail here display different stages in a cycle of oceanic crust accretion this cycle includes episodes in which there is 1 extrusive volcanic construction which widen the crestal ridge prior to the collapse of the summit depression 2 collapse within the summit region of the crestal ridge to form an esd during a phase of volcanic inactivity and 3 renewed magmatism in the esd as its floor widens by extension and brittle fracture of the upper crust this episodic model implies that the width of the young seafloor affected by volcanic extrusion or dominated by tectonic stretching varies through time

a u pb zircon age from the kuskanax batholith southeastern british columbia u pb dates on three fractions of zircon from the foliated border zone of the southeast part of the kuskanax batholith are slightly discordant and indicate emplacement of the batholith ago assuming no subsequent zircon pb loss the analyses are slightly discordant and reflect the presence of inherited zircon pb 2060 300 ma old this interpretation of the data is consistent with geological relationships and available k ar dates a geologically derived maximum age for the batholith is about 185 ma this age determination has important implications for timing of deformation in the kootenay arc

chronology of warm core ring 82b a chronology constructed from satellite derived thermal imagery is presented to describe the formation and life history of warm core ring 82b this overview provides insight into a classification of features and discrete events associated with gulf stream warm core rings and allows these events as well as our limited shipboard observations to be placed in a broader spatial and temporal context than would otherwise be possible without the satellite data events influencing the evolution of 82b include environmental factors such as meteorological influences and gulf stream interactions as well as those stimulated by encounters with changes in bottom topography the interactions of the ring with surrounding waters are especially noteworthy and the existence of vortex vortex interactions is shown to be a significant cause of local water advection through streamer activity ring events are documented by following changes in ring size shape translation and surface thermal structure our satellite observations are supported by extensive contemporaneous shipboard observations including xbt ctd bops biooptical profiling system temperature profiles and along track sea surface temperature measurements in addition acoustic velocity profiling and drifter trajectories have been used to corroborate hydrographic features of the ring and environs these ship and satellite data form a coherent space time overview of the ring and its environment and show them to be closely related and continually interacting

seafloor spreading in the north fiji basin southwest pacific abstract the seapso leg 3 cruise december 1985 was carried out in the north fiji basin aboard the ifremer r v jean charcot the main purpose of the cruise was to carry out a geophysical and geological study of the central part of the basin between 16 s and 22 s to this end bathymetric profiles with the help of the seabeam multichannel echosounder single channel seismic reflection profiles and magnetic and gravimetric profiles were made moreover geological samples were taken by dredging and piston coring as well as water samples with the help of a multiprobe one of the aims of the cruise was to explore the present day spreading axis of the north fiji basin we were able to show that accretion the rate of which is about 7 cm yr in the north fiji basin has been constrained in a n s direction for 3 ma very recently between 0 6 and 0 7 ma ago the accretion process changed resulting in the creation of a ridge ridge trench triple junction centered at 173 30 e and 16 40 s water samples taken in the vicinity of this triple junction show significant anomalies of methane and manganese which are probably linked to hydrothermal events in its morphological characteristics transversal as well as longitudinal the ridge of the north fiji basin shows striking similarities to the east pacific rise it presents the same differences in level the same sizes of structures and the same particular features overlapping spreading centers offsets etc another aim of the seapso cruise was to study the complex deformation area located immediately to the west of the fiji islands which we interpret as a distensive type deformation in a strike slip system

nd sr isotopic constraints on the interactions of the intermontane superterrane with the western edge of north america in the southern canadian cordillera sr and nd isotopic compositions of the late paleozoic metavolcanics and late triassic to early tertiary granitoids from four magmatic episodes in the southern canadian cordillera from the kootenay arc to the fraser fault have been used to i identify the sources of these rocks ii constrain the compressive tectonic history from middle jurassic to paleocene and iii constrain the western boundary of the basement in this region the 215 190 ma old primitive granitoids end 3 1 to 8 7 87sr 86sr 0 7028 0 7043 of the late triassic and early jurassic magmatic episode were emplaced in the paleozoic oceanic crust of quesnellia end 2 9 to 9 3 prior to its obduction over the basement in contrast during the younger magmatic episodes middle late jurassic cretaceous and early tertiary the granitoids from western quesnellia show primitive isotopic compositions and those from eastern quesnellia show eastward increasing crust contaminated compositions the contaminated characters of the middle

tracking fluvial response to climate change in the pacific northwest a combined provenance approach using ar and nd isotopic systems on fine grained sediments traditional provenance techniques nd isotopes and clay mineralogy are combined with recently developed bulk sediment 40 ar 39 ar radiometric methods to determine how the terrestrial sources of sediment to the oregon continental margin have changed over the last 25 000 years both pacific northwest river borne detritus and sediment from piston coring site ew9504 17pc 2671 m water depth offshore southern oregon have been analyzed nd isotopic analyses of river silts show a range of 10 units in end north of the core site the columbia river has end 7 6 while the coos river has a value of end 10 8 rivers proximal to the core site have more radiogenic values from north to south of end 5 0 umpqua river end 1 3 rogue river end 0 6 klamath river and end 3 0 eel river measured end in core sediments show subtle downcore changes between end 0 9 and 2 5 the bulk sediment 40 ar 39 ar plateau ages show more notable downcore variation between 25 and 14 ka ranging from 113 5 to 124 0 ma but are still within the range of bulk ages previously measured on river mouth sediments the nd isotopic analyses are combined with bulk sediment 40 ar 39 ar plateau ages into a ternary mixing model to quantitatively assess the sources of terrigenous material mixtures are best described by three sources proximal to the core site the umpqua rogue klamath and eel rivers from 14 ka to present sediment deposited in the interval from 22 to 25 ka is not adequately described by the present day rivers and requires an additional source this additional source is best explained by an enhanced contribution from the interior cascade volcanic arc probably due to glaciation in the cascade range and the presence of pluvial lake modoc in the upper klamath basin at this time from 22 to 14 ka the influence of cascade range sediment at the core site was overprinted by contemporaneous glaciation and sediment production in the klamath mountains and possibly addition of sediment from the eel river region as well thus differential erosion appears to play a primary role in the provenance changes seen at the core site and is more significant than sediment transport changes due to ocean circulation during this time period overall the combined ar nd isotopic technique provides insight into the coupling of land surface processes and ocean circulation related to climate change and will be a useful provenance tool in a variety of geologic climatic settings r 2007 elsevier ltd all rights reserved

eocene structural development of the valhalla complex southeastern british columbia the valhalla complex a cordilleran metamorphic core complex is a 100 km by 30 km structural culmination within the omineca belt of southeastern british columbia it comprises sheets of granitic orthogneiss ranging in age from 100 to 59 ma with intervening paragneiss of uncertain age and stratigraphic correlation the complex is roofed by the ductile valkyr shear zone and the ductile brittle slocan lake fault zone the upper plate comprises lower grade metasedimentary rocks intruded by middle jurassic plutons the valkyr shear zone and the slocan lake fault zone deform 62 and 59 ma granitic sheets in their footwalls the easterly directed valkyr shear zone is a 2 to 3 km thick zone of distributed ductile strain which is arched over the complex and is exposed around the periphery on the northern western and southern margins the shear zone was active between 59 and 54 ma under amphibolite facies conditions the juxtaposition of upper and lower plates with different structural and metamorphic histories indicates that the valkyr shear zone is a significant structure with large displacement there is evidence to support an easterly rooting direction consistent with an extensional origin its surface breakaway is suggested to be west of the valhalla complex the slocan lake fault zone on the eastern side of the complex is a gently 30 easterly dipping ductile brittle normal fault which roots to the east it was active between 54 and approximately 45 ma and truncates the valkyr shear zone timing and structural relationships indicate that the valkyr shear zone and the slocan lake fault zone are genetically related movement on the ductile valkyr shear zone arching of the complex and displacement on the slocan lake fault zone occurred as a continuum in early to middle eocene time this paper documents the presence of significant eocene ductile strain in the valhalla complex and suggests that the role of extension in this region is more profound than had been previously recognized

mesozoic cenozoic deformation in the canadian cordillera the record of a continental bulldozer abstract a possible mesozoic cenozoic trajectory for the north american craton is outlined from latitude changes of the craton derived from a revised apparent polar wander path and from westward movement of the craton based on the assumption that africa has been the least mobile continent geographically since the latest paleozoic during each of five time intervals that span 220 million years the craton trajectory had a different vector each vector appears to be reflected in the canadian cordillera by the dominant style and orientation of structures formed during that interval for much of the past 220 million years the meridionally oriented western margin of the pangea laurasia north america plate has been the site of arc magmatism where weak arc back arc lithosphere sandwiched between strong ocean floor and craton lithospheres at times coupled across convergent or transform plate boundaries focused and recorded strain when the craton apparently moved due westward between 180 160 ma and 120 60 ma the dominant structures formed then record orogen normal compression and were accompanied by orogeny structures formed during the earlier episode are mainly in the eastern and interior cordillera and their formation shortly followed or coincided with accretion of most terranes to the craton margin in the later episode compressional structures span the entire cordillera which emerged as a tectonic and physiographic entity before and between these intervals when the craton apparently moved mostly northwestward mainly geological and paleomagnetic considerations indicate some terranes moved southward sinistrally relative to the craton after 60 ma southwestward movement of the craton was concurrent with large northward dextral strike slip faults that disrupted the newly established ancestral cordillera the coincidence between the age of structures that record dominant orogen normal compression at times when the craton apparently moved due westward and orogen parallel displacements when the craton had either northward or southward components of motion suggests the craton acting as a continental bulldozer was the primary driver of cordilleran deformation and orogenesis

intraseasonal variability of cross slope flow in the northern south china sea abstractcross slope flow plays an important role in the exchange of material heat and momentum between the continental shelf and the open sea in the northern south china sea scs long period ob

east pacific rise from siqueiros to orozco fracture zones along strike continuity of axial neovolcanic zone and structure and evolution of overlapping spreading centers we have used the sea beam multibeam echo sounding system to survey the east pacific rise epr from 8 20 n to 18 30 n obtaining complete coverage of the epr axial neovolcanic zone and all intervening transform faults here we focus on the epr neovolcanic zone and the definition of overlapping spreading centers ocs s between the orozco and siqueiros transform faults the neovolcanic zone is narrow 0 5 2 0 km and continuous along strike and occurs within and near a strike continuous axial summit graben the neovolcanic zone and summit graben reside along the crest of a volcanic axial high which is 2 10 km wide and which continues uninterrupted along strike for 40 140 km within 20 50 km of an intersection with a transform fault the axial neovolcanic zone narrows and deepens and within only 3 6 km of the intersection the neovolcanic zone turns sharply into the transform valley at seven locations between the siqueiros and orozco transform faults the axial neovolcanic zone is discontinuous and is laterally offset a short distance 1 15 km in contrast with a classic ridge transform ridge plate boundary however offset rise terminations overlap each other by a distance approximately 3 times greater than their offset they curve toward each other and often one merges into the other along strike separating the osc s is an elliptical overlap basin up to 600 m deep whose long axis is subparallel to the adjacent spreading centers the overlap basin is characterized by volcanic constructional edifices a key difference between these offsets and small transform faults in the atlantic is that there are no transform fault structures in the overlap basin which link the offset rise axes a continuous axial depth profile reveals a long wavelength 20 60 km undulation of the rise axis which may be associated with variations in the magmatic budget along strike the lowest points in the axial depth profile occur near transform faults and at osc s suggesting that these features are associated with along strike minima in the magmatic budget we suggest that major phases of volcanic activity propagate episodically along the axis away from centers of magmatic inflation and that osc s develop where magmatic pulses fail to meet due to misalignment of fracture systems sinuous bends in the rise axis or other heterogeneities transform faults fail to develop on fast spreading centers where the lateral offsets are small 15 km because the lithosphere is too thin and weak to maintain a classic rigid plate ridge transform fault pattern the osc geometry is unstable and evolves rapidly and the overlapping rises may propagate at rates faster than the local spreading rate one of the two osc s prevails while the other is abandoned while the locations of osc s may not be fixed relative to the rise axis they may tend to recur near the same place creating scars in older lithosphere which resemble fracture zones but whose fine scale structure is quite different there is excellent agreement between the observed structure of osc s and laboratory studies of osc s using wax models photoelastic studies of overlapping cracks and boundary element modeling of overlapping cracks seismic refraction and reflection near two osc s suggests that large offset osc s have separate magma chambers beneath the offset rise axes while small offset osc s may share a single axial magma chamber three dimensional inversion of magnetic anomalies suggests that significant petrologic anomalies may occur near some osc tips waxing and waning of overlapping magma chambers may give rise to the eruption of highly fractionated feti basalts and associated magnetic anomalies

interannual variability of the south china sea throughflow inferred from wind data and an ocean data assimilation product 1 the luzon strait transport as an index for the south china sea throughflow has attracted much attention recently in this study the interannual variability of luzon strait transport is examined using the island rule and results from ocean data assimilation transport variability obtained from these two approaches is consistent with each other assessment of contribution from each integral segment involved in the island rule indicates that wind stress in the western and central equatorial pacific is the key factor regulating the interannual variability of the luzon strait transport whereas the effect of local wind stress in the vicinity of the luzon strait is secondary analysis also shows that when the westerly easterly wind anomalies in the tropical pacific break out the luzon strait transport increases decreases associated with the variations in the

geochronology and geochemistry of the max porphyry mo deposit and its relationship to pb zn ag mineralization kootenay arc southeastern british columbia canada the max porphyry mo deposit is located at the northern end of the kootenay arc in southeastern british columbia canada molybdenum mineralization is genetically related to the variably altered trout lake granodiorite stock which has lithogeochemical affinities to the low fluorine calc alkaline granodiorite hosted porphyry mo deposit type three molybdenite samples from early and late mo bearing veins yield re os dates that overlap within analytical error with a weighted average age of 80 3 0 2 ma these dates are in close agreement with two 206pb 238u weighted average zircon ages for phases of the trout lake stock at 80 3 1 6 and 79 2 1 0 ma indicating that crystallization of the stock and hydrothermal molybdenite formation were coeval and likely cogenetic 40ar 39ar plateau ages for primary biotite in igneous dikes secondary biotite in early potassic alteration and muscovite in late phyllic alteration range from 80 to 76 ma the younger 40ar 39ar plateau ages may reflect unusually slow cooling of the magmatic hydrothermal system or a late thermal disturbance pb zn ag vein deposits are common throughout the kootenay arc and several such veins are located within and proximal to the max porphyry mo deposit the presence of rare molybdenite associated with sphalerite and argentiferous galena in some of these pb zn ag veins suggests that they represent a late stage event related to the max magmatic hydrothermal system fluid inclusions in quartz from mo and pb zn ag veins are similar and can be divided into two compositional groups type 1 aqueous liquid rich fluid inclusions and type 2 aqueous carbonic liquid rich fluid inclusions pressure corrected 1 4 1 7 kbar trapping temperatures of typical type 1 inclusions from mo bearing veins range from 430 to 460 c and for pb zn ag veins from 335 to 365 c the ranges of salinity 0 12 wt nacl equiv in fluid inclusions from both vein types are almost identical and type 2 inclusions from both vein types contain similar amounts of co2 avg xco2 0 08 with traces of ch4 the similarity of chemistry in the two vein types suggests a genetic link between porphyry mo mineralization and adjacent pb zn ag deposits however muscovite from the alteration halo around a pb zn ag vein within the max deposit yielded a 40ar 39ar plateau age of 72 2 0 5 ma this date is significantly younger than the 80 ma age of porphyry magmatism and mo mineralization suggesting either that this event is in fact unrelated to porphyry mo mineralization at 80 ma or that the k ar isotope system has been disturbed by a later thermal event

eocene melting of precambrian lithospheric mantle analcime bearing volcanic rocks from the challis kamloops belt of south central british columbia abstract potassic silica undersaturated mafic volcanic rocks form a minor portion of the predominantly calc alkaline eocene challis kamloops volcanic belt which extends from the northwestern united states into central british columbia canada their major occurrence is in the penticton group in south central british columbia where they reach a thickness of up to 500 m and form the northwestern edge of the montana alkaline province these analcime bearing rocks 53 52 ma old are typically rhomb porphyries of ternary feldspar an28ab52or20 additional phenocryst phases include clinopyroxene analcime phlogopite and rare olivine the rocks are characterized by high total alkalis particularly k2o 4 5 wt as well as by a distinct enrichment of large ion lithophile elements versus heavy rare earth elements and high field strength elements they have unusual isotopic compositions compared to most other rocks of the challis kamloops belt particularly high negative nd values and elevated but relatively uniform initial 87sr 86sr ratios 0 7065 the potassic silica undersaturated rocks overlie precambrian crust and lithosphere and were at least in part derived from ancient metasomatized subcontinental mantle lithosphere which was modified in a precambrian subduction setting the alkaline rocks of the challis kamloops belt are related to a slab window environment in particular they were formed above the southern edge of the kula plate adjacent to the kula farallon slab window whereas the montana alkaline province situated well to the southeast was formed directly above the kula farallon slab window upwelling of the hotter asthenospheric mantle may have been the thermal trigger necessary to induce melting of fertile and metasomatized lithospheric mantle

u pb zircon and monazite ages for the okanogan range batholith washington implications for the magmatic and tectonic evolution of the southern canadian and northern united states cordillera new u pb zircon and monazite dates for the okanogan range batholith a suite of trondhjemitic plutonic rocks in north central washington are interpreted to reflect minimum crystallization ages of 114 111 ma these new data suggest that the okanogan range batholith may represent an older southerly segment of the late albian spences bridge group which crops out in southern british columbia this would constitute a 300 km long north northwest trending belt of 130 100 ma volcanic and plutonic rocks along the western margin of the intermontane belt herein named the okanogan spences bridge arc the okanogan spences bridge arc and the gambier arc in the coast belt of british columbia were coeval widely separated early cretaceous magmatic belts in the southern canadian northern united states cordillera the cbronologic data require reevaluation of models proposing one versus two east dipping subduction zones to explain the origin of these two parallel magmatic belts neither model adequately reconciles all geologic observations

meridional overturning circulation in the south china sea envisioned from the high resolution global reanalysis data glba0 08 the pattern of meridional overturning circulation moc in the south china sea scs is studied using a numerical lagrangian tracing method with the hycom ncoda global 1 12 degrees analysis glba0 08 data the scs moc has a sandwich structure which consists of a layer of stronger clockwise circulation above 500 m depth a counterclockwise layer in the mid layer between 500 and 1000 m depth and a weaker clockwise layer below 1000 m the deep below 1000 m depth clockwise layer is divided into three cells namely the deep southern moc cell dsmoc the deep middle moc cell dmmoc and the unclosed deep northern moc cell dnmoc the inflow through the luzon strait is the main source for the scs mocs the upper layer luzon strait inflow dominates the upper scs moc structure but has relatively less contribution to the dnmoc whereas the deep layer luzon strait inflow mainly influences the dnmoc and it mostly rises near 18 degrees n the inflow through the taiwan strait mainly contributes to the upper layer moc moreover inflows from the mindoro and karimata straits contribute negatively to the upper moc but play a significant role on the dsmoc the backward integration of lagrangian trajectories further validates that the scs deep water comes not only from the deep inflow but also from the entrainment of the middle and upper layer inflow through the luzon strait in the scs basin there are three northwest southeast tilted zones where tracers upwell which correspond to the three deep moc cells one possible mechanism for these upwelling zones is the interaction between the continental slope trapped waves and the westward planetary rossby waves

geology and geochemistry of a 800 m section through young upper oceanic crust in the north fiji basin southwest pacific lagabrielle y auzende j m eissen j p janin m c and cotten j 1994 geology and geochemistry of a 800 m section through young upper oceanic crust in the north fiji basin southwest pacific in j m auzende and t urabe editors north fiji basin starmer french japanese program mar geol 116 113 132 we report the results of geological and structural observations made during one dive of the french submersible nautile during the starmer cruise in 1989 in the vicinity of the 16 40 s triple junction in the north fiji basin this dive provided a spectacular 800 m continuous section of oceanic crust exposed along the northern wall of a 3000 m deep basin at the eastern branch of the triple junction a number of volcanic facies have been encountered including massive and pillowed lavas sheeted dikes and spectacular columnar jointed massive lavas pillowed lavas have been observed only at the base and at the top of the section the ratio between massive and pillowed basalts is high suggesting that the crust in this area grew mostly during a stage of high eruptive rate dikes have been observed in the middle part of the section they probably do not represent the top of a classical dike complex but an isolated set of sheeted dikes possibly the feeders of overlying flows the abundance of vertical tectonic breccias observed during the first part of the dive confirms that the basal part of the wall can be regarded as a major tectonic boundary along which occurred significant vertical and strike slip motions micropaleontological data from sedimentary rocks collected during the dive bring new constraints to the evolution of the triple junction the oceanic crust in the surveyed area is at least as old as 1 9 1 3 ma based on the age of sedimentary rocks collected in talus at the base of the wall and observed at the summit of the section the collected basalts include 1 n type morbs 2 e type morbs and 3 babbs this emphasizes the heterogeneous nature of the mantle beneath the central nfb some portions of the depleted mantle underlying the central nfb triple junction area have recorded contamination from melts or fluids from an ancient subduction zone probably the new hebrides during the opening of the nfb whereas adjacent mantle areas show the influence from an alkali enriched source such alkali enriched characters are reported from recent basalts of the northern nfb south pandora ridge rotuma island

double saloon door tectonics in the north fiji basin abstract fiji platform rotated counter clockwise from at least 10 2 ma until 1 56 ma while vanuatu arc rotated clockwise from 12 10 ma until the present a revised model incorporating these opposite rotations explains the distribution of magnetic anomalies in the north fiji basin nfb the conjugate margin of southwest fiji platform is southeast vanuatu arc previous models which associate nw oriented anomalies off southwest fiji with similarly oriented anomalies northeast of vanuatu arc are therefore wrong secondly these models propose a nw oriented spreading ridge extending to 19 s 177 5 e almost 500 km southeast of the mapped extension of rifted island arc crust on vanuatu arc this creates an unacceptable overlap with fiji platform in pre rift reconstructions thirdly anomalies off sw fiji which are nw oriented in their present day position were oriented nne during initial breakup rather than aligning with nw oriented anomalies in the western nfb they are matched by nne oriented anomalies off se vanuatu arc with further rotation these conjugate anomaly sets form a fan shape in the southern nfb fourthly previous models which recognise a triple junction only from 3 ma do not explain early wnw ese separation of vanuatu arc and fiji platform required by well documented opposite rotations nfb characteristics which match the double saloon door tectonic model include opposite rotations of island arc terranes backarc seafloor spreading which is both arc parallel and arc perpendicular and rifts propagating north south northeast and northwest features which do not match the double saloon door model include the north fiji fracture zone and the west fiji spreading centre both initiated post 1 5 ma when fiji platform stopped rotating and only one terrane vanuatu arc continued to rotate the nfb developed via double saloon door tectonics from 12 10 ma until 1 5 ma whereas post 1 5 ma opening constitutes single saloon door rotation

southern ocean eddy phenomenology mesoscale eddies are ubiquitous features in the southern ocean yet their phenomenology is not well quantified to tackle this task we use satellite observations of sea level anomalies and sea surface temperature sst as well as in situ temperature and salinity measurements from profiling floats over the period 1997 2010 we identified over a million mesoscale eddy instances and were able to track about 105 of them over 1 month or more the antarctic circumpolar current acc the boundary current systems and the regions where they interact are hot spots of eddy presence representing also the birth places and graveyards of most eddies these hot spots contrast strongly to areas shallower than about 2000 m where mesoscale eddies are essentially absent likely due to topographical steering anticyclones tend to dominate the southern subtropical gyres and cyclones the northern flank of the acc major causes of regional polarity dominance are larger formation numbers and lifespans with a contribution of differential propagation pathways of long lived eddies areas of dominance of one polarity are generally congruent with the same polarity being longer lived bigger of larger amplitude and more intense eddies extend down to at least 2000 m in the acc eddies show near surface temperature and salinity maxima whereas eddies in the subtropical areas generally have deeper anomaly maxima presumably inherited from their origin in the boundary currents the temperature and salinity signatures of the average eddy suggest that their tracer anomalies are a result of both trapping in the eddy core and stirring

a census of eddy activities in the south china sea during 1993 2007 1 numerous mesoscale eddies occur each year in the south china sea scs but their statistical characteristics are still not well documented a pacific basin wide three dimensional physical biogeochemical model has been developed and the result in the scs subdomain is used to quantify the eddy activities during the period of 1993 2007 the modeled results are compared with a merged and gridded satellite product of sea level anomaly by using the same eddy identification and tracking method on average there are about 32 9 2 4 eddies predicted by the model and 32 8 3 4 eddies observed by satellite each year and about 52 of them are cyclonic eddies the radius of these eddies ranges from about 46 5 to 223 5 km with a mean value of 87 4 km more than 70 of the eddies have a radius smaller than 100 km the mean area covered by these eddies each year is around 160 170 km2 equivalent to 9 8 of the scs area with water depths greater than 1000 m linear relationships are found between eddy lifetime and eddy magnitude and between eddy vertical extent and eddy magnitude showing that strong eddies usually last longer and penetrate deeper than weak ones interannual variations in eddy numbers and the total eddy occupied area indicate that eddy activities in the scs do not directly correspond to the el nino southern oscillation events the wind stress curls are thought to be an important but not the only mechanism of eddy genesis in the scs

merging and migration of two meddies in this study a scenario is developed of two adjacent mediterranean water eddies meddies as they were observed merging and drifting through the iberian basin observations are based on four rafos floats at 850 1050 dbar two hydrographic surveys centered roughly at 38 n 24 w and trajectories of surface drifters drogued at 100 m in april 1991 the meddy a was identified and labeled by surface drifters during the revisit one month later two meddies were encountered b1 and b2 in the vicinity of the former meddy a the coalescence of b1 subsequently identified as a one month older and b2 is inferred from a simple kinematic model describing the observed movement of the rafos floats for up to three months after the second ctd survey the deduced vorticity front radius 15 km within b1 was of insufficient strength to keep the core waters of b1 isolated and prevent the absorption of b1 by b2 the resulting meddy b1 b2 showed a clear near surface dynamical signal its deep root 1800 m could explain the expulsion from the meddy of the remaining rafos float and surface drifter at the time of the meddy s collision with the josephine seamount for the first time a set of lagrangian and hydrographic observations give direct evidence that neighboring meddies can merge as predicted by theoretical considerations

geochemical mineralogical and isotopic data relating to the origin and tectonic setting of the rossland volcanic rocks southern british columbia bulk rock and mineral chemical and isotopic analyses of rossland volcanic rocks are used to infer the nature of the magma extruded in the nelson rossland area of southern british columbia during th

the nicola group late triassic and early jurassic subduction related volcanism in british columbia mafic lavas of the nicola group are divided into three distinct petrographic and geochemical types type 1 lavas are strongly augite porphyritic picrites basalts and andesites that belong to a high potassium to shoshonitic rock series type 2 lavas are augite and plagioclase porphyritic basalts and andesites that belong to a low potassium calc alkaline series and type 3 lavas are petrographically variable tholeiitic to transitional basalts and andesites low concentrations of ti zr y and nb and moderate to high concentrations of k rb ba and sr in type 1 and 2 lavas clearly indicate a subduction related tectonic setting of eruption type 3 lavas show chemical affinities intermediate between modern day island arc and intraplate volcanics type 1 shoshonitic lavas generally lie east of and are younger than type 2 calc alkaline lavas a relationship that implies an east dipping early mesozoic subduction zone beneath the nicola arc these interpretations resolve previous uncertainties regarding th

blocking and westward passage of eddies in the luzon strait satellite observations have shown the abundance of generally westward propagating eddies in the subtropical regions in the north pacific ocean especially north of 10 n eddies transport mass and can significantly impact the circulation as well as the heat salt and nutrient balances of the western pacific marginal seas this paper uses a numerical model to examine the conditions when eddies can or cannot freely propagate westward through the luzon strait into the south china sea scs composite analyses on the 10 year model data show that the fates of eddies depend on the strength and path of the kuroshio in one path that exists mostly during fall and winter the kuroshio loops westward into the scs the potential vorticity pv across the current is weak and eddies are likely to propagate freely through the luzon strait in another path which exists mostly during spring and summer the kuroshio tends to leap directly northward bypassing the scs the pv across it strengthens and eddies are then blocked and are constrained to also follow the northward path nonlinear eddy current interaction and the existence of a cyclone north of the luzon island during the looping phase explain why eddies of both signs can pass through the strait it is shown also that the upstream state of the kuroshio in the western tropical pacific plays an important role in dictating the different paths of the kuroshio the looping leaping path is caused by a weakened stronger kuroshio transport related to the northward southward shift of the north equatorial current in wintertime summertime

propagating rifts in the north fiji basin southwest pacific the accretion system in the north fiji marginal basin currently consists of four major differently oriented axes multibeam bathymetry recently acquired over the central north south axis between 18 and 21 s reveals a peculiar tectonic framework fanned patterns of the sea floor topography at the northern and southern tips of this segment are the general shape of a rugby ball these data and the interpretation of magnetic anomalies indicate that this central sector of the ridge has lengthened northward at the expense of the axis aligned n15 e both spreading and propagation rates are about 70 80 mm yr a southward propagation is also envisaged on the basis of the similar morphotectonic framework observed at the southern tip of the north south ridge

recent geodynamic evolution of the north fiji basin southwest pacific a cruise of the r v jean charcot seapso iii december 1985 in the north fiji basin between 16 and 22 s obtained new structural and magnetic data concerning the central part of the basin these have been used for the reinterpretation of the national oceanic and atmospheric administration and u s naval research project aeromagnetic survey 1979 the structural surface ship magnetic and aeromagnetic data allow us to present a sketch of the evolution in four stages of the north fiji basin for the past 10 m y

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

in situ geological and geochemical study of an active hydrothermal site on the north fiji basin ridge abstract in june 1989 a diving cruise by the submersiblenautile was carried out on the north fiji basin spreading ridge the objective of the cruise was a geological and geochemical study of the active spreading axis and associated hydrothermal processes this operation was the third cruise of the french japanese starmer project following the two cruises of the r v kaiyo in 1987 and 1988 six dives along the spreading axis between 16 58 s and 17 00s show that the axial graben consists of alternating n15 trending horsts and grabens extinct hydrothermal sites have been observed all along the graben these consist of fossil chimneys oxide staining and dead shells at 16 59 s an active chimney has been discovered and called the white lady because of its almost exclusively anhydrite composition this chimney expels a peculiar water characterized by low chlorinity and a 285 c maximum temperature in the northern extremity of the n15 axis a wide fossil hydrothermal site has been explored and sampled it is located in an area cut by n15 n140 and n60 trending faults and fissures

mesoscale eddies cases study at xisha waters in the south china sea in 2009 2010 analyzing the observed currents at xisha 110 3899 degrees e 17 1038 degrees n during may 2009 to may 2010 it is found that the kinetic energy has significant mesoscale variability and each peak responds to large positive negative ocean surface current curl caused by mesoscale eddies compared the kinetic energy with the wind stress work and the pressure work it is also found that the barotropic pressure work which is mainly contributed by the sea surface height ssh corresponding to the mesoscale eddies behaves like the kinetic energy the contribution of the mesoscale eddies to the kinetic energy can be up to 90 sometimes and reach deep level every time using the satellite altimeter data the paths of mesoscale eddies contributing to the kinetic energy variability are traced back in the winter half of the year the mesoscale eddies propagating along the northern south china sea shelf or across the basin from the west of the philippines toward xisha arrive at xisha influencing the kinetic energy in the summer half of the year the mesoscale eddies are mainly from the south which were shed from the vietnam coast current and the cause for eddy shedding may be related to the relaxation of the ekman transport anomalies

petrology and geochemistry of the kamloops group volcanics british columbia the kamloops group is an alkali rich calc alkaline volcanic suite of early to middle eocene age widespread in south central british columbia rock types in the suite range from high k basalt through andesite to rhyolite the suite is characterized by relatively high k2o sr and ba but low zr ti and ni concentrations only moderate ce enrichment and little or no fe enrichment initial ratios 87sr 86sr are about 0 7040 in the western half and about 0 7060 in the eastern half of the study area no difference in chemistry or mineralogy marks this sharp transition chemically similar suites include the absaroka gallatin suite in wyoming and the lower san juan summer coon suite in colorado the content of k2o at 60 sio2 increases regularly eastward across southern british columbia the chemical data support the subduction related continental arc origin of the kamloops group volcanics the volcanic rocks consist in the main of augite pigeonite andesites ranging from 52 to 62 silica with subordinate qu

kinematics of active spreading in the central north fiji basin southwest pacific abstract based on a synthesis of magnetic and bathymetric data we re evaluate the kinematics of the recent opening of the central part of the north fiji basin nfb the westward motion of the pacific plate along the left lateral north fiji fracture zone nffz results in the opening of two n s trending spreading ridges located at 173 30 e and 176 e both ridges show complex features such as propagating rifts ridge jumps and overlapping spreading centres their spreading rates are similar 7 6 to 4 cm yr 1 across the western ridge 5 5 cm yr 1 across the eastern one while the nffz is purely strike slip to the east of the eastern ridge it becomes more complex to the west it changes from transpressional to transtensional then to purely transform and finally joins the western n s ridge in a rrr type triple junction our kinematic analysis shows that most of the left lateral motion along the nffz is transferred to the eastern ridge at the rtf type 176 e triple junction it suggests that the western n s ridge is probably connected to the north with another left lateral transform possibly the south pandora ridge

eddy heat and salt transports in the south china sea and their seasonal modulations this study describes characteristics of eddy turbulent heat and salt transports in the basin scale circulation as well as in the embedded mesoscale eddy found in the south china sea scs we first showed the features of turbulent heat and salt transports in mesoscale eddies using sea level anomaly sla data in situ hydrographic data and 375 argo profiles we found that the transports were horizontally variable due to asymmetric distributions of temperature and salinity anomalies and that they were vertically correlated with the thermocline and halocline depths in the eddies an existing barrier layer caused the halocline and eddy salt transport to be relatively shallow we then analyzed the transports in the basin scale circulation using an eddy diffusivity method and the sea surface height data the argo profiles and the climatological hydrographic data we found that relatively large poleward eddy heat transports occurred to the east of vietnam eov in summer and to the west of the luzon islands wol in winter while a large equatorward heat transport was located to the west of the luzon strait wls in winter the eddy salt transports were mostly similar to the heat transports but in the equatorward direction due to the fact that the mean salinity in the upper layer in the scs tended to decrease toward the equator using a 21 2 layer reduced gravity model we conducted a baroclinic instability study and showed that the baroclinic instability was critical to the seasonal variation of eddy kinetic energy eke and thus the eddy transports eov wls and wol were regions with strong baroclinic instability and thus with intensified eddy transports in the scs the combined effects of vertical velocity shear latitude and stratification determined the intensity of the baroclinic instability which intensified the eddy transports eov during summer and wls and wol during winter

an example of a recent accretion on the mid atlantic ridge the snake pit neovolcanic ridge mark area 23 22 n abstract the inner rift vailey of the mark area mid atlantic ridge at the kane fracture zone was investigated with the submersible nautile at the latitude of the snake pit hydrothermal field 23 22 n a transect across the axial valley shows a stepwise increase in the sediment thickness away from the axis these steps probably reflect major magmatic and tectonic events in the evolution of the inner floor dives on the summit of the snake pit neovolcanic ridge constrain a generalized geological map and document relations between hydrothermal activity magmatism and faulting the neovolcanic ridge was constructed by the build up of several hundred metres of pillow lava flows its summit is intensely fissured and cut by an axial graben about 100 m wide three hydrothermal sites were recognized within the axial graben the eastern site the most active is structurally related to the eastern fault scarp the central site is located within the graben the western site associated with the western fault scarp is more complex and was constructed by two successive hydrothermal events the new data suggest a model of evolution for the inner floor of the rift valley involving alternating stages of magmatism and volcanism which produce ridges and troughs preserved outside of the axial domain these volcano tectonic cycles have an approximate duration of 100 000 years we discuss variations in the morphology of the mar along strike in the light of this model of evolution

three long lived anticyclonic eddies in the northern south china sea 1 in august 2007 three long lived anticyclonic eddies ace1 ace2 and ace3 were detected by both satellite sea level anomaly sla map and in situ measurements in the northern south china sea scs ace3 had a two core ace3 1 and ace3 2 structure in situ stations along 18 degrees n almost cut through the centers of ace2 and ace3 2 near the centers of ace2 and ace3 2 mean temperature and sound velocity are similar to 0 65 degrees c and similar to 2 m s 1 larger than those in their surrounding areas respectively while mean salinity and density are similar to 0 02 psu and similar to 0 15 m 3 s 1 smaller than those in their surrounding areas due to downwelling near the eddy cores the depths of maximum and minimum salinity near the eddy cores are similar to 65 m and similar to 35 m larger than those in their surrounding areas the vertical depth with current speed larger than 0 05 m s 1 can reach similar to 900 m their detailed evolutionary processes were depicted based on the variation of geostrophic currents and the trajectories of five drifting buoys ace1 lasted 147 days while ace2 and ace3 lasted 168 days and 210 days respectively ace1 had a smaller mean sla 18 8 cm in its lifetime than ace2 21 8 cm and ace3 25 3 cm but had a larger negative mean vorticity 7 7 x 10 6 s 1 than ace2 7 0 x 10 6 s 1 and ace3 7 0 x 10 6 s 1 one short lived anticyclonic eddy that split from ace2 and another one that merged with ace3 both had a smaller sla negative vorticity and diameter than ace2 and ace3 respectively

proterozoic mantle under quesnellia variably reset rb sr mineral isochrons in ultramafic nodules carried up in cenozoic volcanic vents of the southern omineca belt handpicked acid washed diopside orthopyroxene and olivine separates from 14 lherzolite nodules from four localities in southern british columbia have been analyzed for 87rb 86sr and 87sr 86sr the host lavas of late cenozoic to pleistocene age are nepheline normative alkali basalt and basanite with sr and nd isotopic ratios 0 7025 0 7029 0 51310 0 51326 close to those of mid ocean ridge basalt the present day sr isotopic compositions of nodule diopsides 9 239 ppm sr are 0 7021 0 7041 similar to those of the host rocks orthopyroxene and olivine however have 87rb 86sr ratios of 0 1 to 1 0 and much more radiogenic sr 87sr 86sr commonly 0 708 0 720 and in several cases the three minerals form linear arrays in 87rb 86sr versus 87sr 86sr plots if interpreted as mineral isochrons these give dates from 99 to 1989 ma many cluster around 440 770 ma four nodules from two localities west kettle river and big timothy mountain give dates of 1201 1989 ma maximum dates for the other localities

a middle jurassic to early tertiary andean sierran arc model for the coast belt of british columbia regional tectonic features of the western canadian cordillera can be interpreted in terms of middle jurassic accretion of a single composite superterrane stikinia wrangellia alexander to ancestral north america closure of the intervening cache creek bridge river ocean moved the continental edge to a new position west of the accreted superterrane the coast belt is primarily a succession of superimposed middle jurassic to early tertiary magmatic arcs related to prolonged subduction of pacific ocean lithosphere beneath the new north american margin discrete magmatic pulses separated by lulls or periods of relative quiescence successively overprinted the new margin the insular and intermontane superterranes previously viewed as widely separate entities prior to mid cretaceous time were already amalgamated before an initial middle jurassic overprint produced an ancestral coast belt late jurassic to early cretaceous rift related marine basins mid to late cretaceous compressional structures and early tertiary extensional features coincident with the coast belt are subsidiary intraplate attributes that reflect external adjustments in plate motions within a primary subduction related andean magmatic arc

neodymium isotopic evidence for decreasing crustal contributions to cenozoic ignimbrites of the western united states implications for the thermal evolution of the cordilleran crust numerous studies of large volume rhyolite systems from the western united states conclude that rhyolite is primarily generated by extensive fractional crystallization of basalt accompanied by assimilation of crustal wallrock relative crustal contributions to large volume rhyolite can be estimated by comparing the nd isotopic composition of the rhyolite with the nd isotopic characteristics of crust and mantle reservoirs associated with different continental basement age provinces we have estimated the crustal contributions to 12 early oligocene to pleistocene rhyolite systems located throughout the cordillera we have determined that 1 crustal contributions to large volume rhyolite systems decrease from the oligocene to the miocene and 2 rhyolite systems younger than 20 ma are dominated by mantle components the crustal contributions to rhyolite systems may be controlled by system size and duration crustal thickness tectonic setting crustal composition crustal density and crustal temperature we conclude that regional cooling of the lower crust which progressively limited the amount of crustal wallrock assimilated by rhyolite systems is the only parameter that is consistent with geologic and geochemical data for rhyolite systems and the geologic evolution of the cordillera a quantitative model that relates the amount of crustal contribution to assimilation recharge rates and the temperature of the crust indicates that lower crustal temperatures would have to decrease about 300 c between early oligocene and early miocene time to account for the decrease in crustal contributions

along axis variations in seafloor spreading in the mark area recent investigations with the manned submersible alvin and the angus deep towed camera sled greatly extended the known range of variations in the style of seafloor spreading along the axis of the mid atlantic ridge five transects of the spreading centre at intervals of10 20 km south of the kane fracture zone at 24 n latitude demonstrate dramatic changes in the style and magnitude of tectonic extension development of the neovolcanic zone expression of hydrothermal venting types oflithologic exposures and morphology of the median valley

anticyclonic eddy sheddings from kuroshio loop and the accompanying cyclonic eddy in the northeastern south china sea abstractsheddings of kuroshio loop current klc eddies in the northeastern south china sea scs are investigated using mooring arrays multiple satellite data and data assimilative hycom products based on altimeter sea surface heights between 1992 and 2014 a total of 19 prominent klc eddy shedding klces events were identified among which four events were confirmed by the concurrent moored and satellite observations compared to the leaping behavior of kuroshio klces is a relatively short duration phenomenon that primarily occurs in boreal autumn and winter the klc and its shedding anticyclonic eddy ae trap a large amount of pacific water with high temperature salinity and low chlorophyll concentration in the upper layer the corresponding annual mean transport caused by klces reaches 0 24 0 38 sv 1 sv 106 m3 s 1 accounting for 6 8 10 8 of the upper layer luzon strait transport altimeter based statistics show that among 90 of the historical klces events a cyclonic eddy ce is immedi

a possible triple junction at 14 50 s on the north fiji basin ridge southwest pacific auzende j m grficia mont e bendel v huchon p lafoy y lagabrielle y de alteriis g and tanahashi m 1994 a possible triple junction at 14 50 s on the north fiji basin ridge southwest pacific in j m auzende and t urabe editors north fiji basin sxarner french japanese program mar geol 116 25 35 recent full coverage bathymetric and geophysical surveys yokosuka 90 and 91 carried out in the framework of the starmer japanese french joint project reveal details of the structure of the n160 segment of the north fiji basin ridge despite its intermediate spreading rate this segment shows a slow spreading type morphology with steep 1000 m high walls reaching an axial depth of 4000 m its northern tip at 14 50 s is a complex area involving several plates boundaries this domain can be interpreted either as a complex boundary between two plates or as a new triple junction symmetrical with the 16 50 s triple junction characterizing its southern tip in either case the complexity of the spreading ridge geometry in this area illustrates the instability of the accretionary geometry due to the deformation of the whole north fiji basin between the much larger indo australian and pacific plates

decadal variation and trends in subsurface salinity from 1960 to 2012 in the northern south china sea observations suggest that subsurface waters in the northern south china sea nscs exhibited substantial low frequency variability with a striking decadal change in the southern limit of the 34 6 psu isohaline long term freshening of the subsurface waters started in 1960 was followed by salinification from 1975 and freshening occurred again from 1993 to 2012 the linear trends were 0 0076 0 0100 and 0 0078 psu yr respectively an analysis of the subsurface salinity budget reveals that the main underlying contributors to subsurface salinity are horizontal advection and vertical entrainment in particular advection driven by the luzon strait transport and vertical entrainment from the mixed layer are the key factors controlling variations on subsurface salinity diagnosis of the salinity budget further suggests that entrainment from the mixed layer played a more important role in the freshening periods than in the salinifying period

neodymium strontium lead isotopic study of vancouver island igneous rocks combined neodymium strontium and lead isotope measurements show that vancouver island is made up of phanerozoic crustal material accreted to north america in the mesozoic and early cenozoic but

anatexis and metamorphism in tectonically thickened continental crust exemplified by the sevier hinterland western north america the generation of granitoid magmas by partial melting of crustal rocks during continental thickening events is well documented in many geological provinces throughout the world including the late mesozoic sevier belt of western north america we present a thermal and petrologic model of anatexis and metamorphism in regions of crustal thickening where the only mantle contribution is the normal conductive supply of heat through the base of the lithosphere i e advection of mass and energy are excluded we distinguish between formation of migmatites and generation of mobile granitoid magmas and examine the temporal and spatial relationships between these two distinct anatectic processes between anatexis and regional deformation and between anatexis and metamorphism a fundamental conclusion is that if protoliths rich in hydrous minerals are present regional anatexis is the end product of classical barrovian metamorphism in thickened continental crust even in the absence of a free water rich fluid phase barrovian metamorphic facies series are predicted with thickening ratios maximum crustal thickness attained initial crustal thickness as low as 1 3 but mobile granitoid magmas are not formed if this ratio is less than approximately 1 5 above these lower bounds barrovian metamorphism and anatectic granitoid magmatism occur independently of the magnitude of thickening and of the way in which thickening is accomplished both processes are sensitive to a diminished heat supply lowering either moho heat flow or crustal radioactive heat production results in blueschist eclogite metamorphism and inhibits the formation of mobile granitoid magmas we model anatexis under fluid absent conditions and show that with such a constraint migmatization is always a syn kinematic process relative to the crustal thickening event whereas generation of mobile granitoid magmas is in most cases post kinematic relative to crustal thickening but can be syn kinematic if thickening takes more than approximately 50 myr the typical time intervals for melting are consistent with geological observations mobile granitoid magmas are predicted by most of our models within approximately 10 myr of the end of the crustal thickening event this incubation period results primarily from the temperature increase required for the dehydration melting reactions capable of producing large melt fractions to occur the energetic requirements of anatexis are relatively minor compared to conductive crustal thermal budgets as shown by the fact that once the necessary p t conditions are attained melting reactions are completed within time intervals on the order of 1 myr i e 1 2 orders of magnitude smaller than the characteristic time scales of the tectonic processes involved in crustal thickening

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

u pb geochronology of jurassic to early tertiary granitic intrusives from the nelson castlegar area southeastern british columbia canada eleven u pb zircon dates from seven intrusives in the nelson castlegar area provide new age constraints on the granitoid magmatism in southeastern british columbia four samples from the nelson batholith date three distinct intrusive phases spanning ca 10 ma one sample from the eastern porphyritic phase coffee creek yields the oldest age at 172 5 5 0 ma two samples from the central k feldspar megacrystic phase crescent bay give precise ages at 162 0 1 0 and 161 5 1 5 ma and possibly date the youngest phase of the batholith an intermediate age of emplacement at 166 0 3 0 ma is suggested for the southern tail of the batholith the new and published data suggest that the nelson batholith was emplaced in roughly concentric zones in contrast the southern quartz diorite phase and the northwestern granodiorite phase of the bonnington pluton were emplaced coevally during the middle jurassic at 167 4 2 0 and 165 0 3 0 ma respectively middle jurassic ages were also obtained for a sample of

morphostructure and magnetic fabric of the northwestern north fiji basin four successive spreading phases are distinguished in the northwestern part of the north fiji basin after an initial ne sw opening a n s spreading phase took place up to the northwesternmost tip of the basin along the south pandora tikopia and 9 30 ridges the n s spreading phase in the northern north fiji basin was followed by an e w opening phase along the central north fiji basin axis a triple junction was probably active during an intermediate stage between the two phases e w spreading underwent a reorganisation that induced the functioning of the 16 40 s triple junction and the development of the e w trending hazel holme extensional zone from the active central spreading axis to the southern tip of the new hebrides back arc troughs active extension also occurs along the e w santa cruz trough which crosscuts the arc platform at the northern end of the n s trending back arc troughs the existence of the back arc troughs is mainly due to the construction of the 400 km long volcanic duff ridge which trapped a piece of the old north fiji basin oceanic crust

on the stability of triple junctions and its relation to episodicity in spreading a convenient representation of triple junctions that involve only ridges r and transform faults f is proposed this representation combines in a simple way information from geographic and velocity spaces the velocity triangle provides the budget of lithospheric surface change which directly results from interactions of the three plates a discussion of the relative positions of the triple junction with respect to the velocity triangle demonstrates that in general there are several triple junction configurations that are compatible with a given triangle this discussion stresses the importance of oblique and asymmetric spreading pairs of triple junction configurations that are of particular interest are rrr rrf and rrr ffr when the triple junction lies outside of the triangle at least one of the ridges will shorten leading to yet another type of potentially unstable configuration the present configurations of the bouvet galapagos and indian ocean triple junctions are reviewed a method is proposed to reconstruct past configurations of the indian ocean junction at the time of anomalies 23 and 28 the main parameters that influence triple junction evolution are the lengths of transform faults the availability of magma and related connectivity of magma chambers and the also related spreading velocities this study confirms an earlier suggestion that activity at constructive plate boundaries occurs in two preferred modes the effusive and tectonic modes corresponding here to rrr and to rrf rff configurations respectively these modes apparently alternate in episodes of typically 1 ma duration the significance of this time constant and consequences for lithospheric mechanics are briefly discussed

the eocene oligocene magmatic hiatus in the south central canadian cordillera a capture of the kula plate by the pacific plate the tertiary paleogene and neogene geological record in south central canadian cordillera is dominated by the 350 400 km wide lower eocene volcanic arc and the overlying miocene recent back arc lavas that are separated by a hiatus in magmatic activity between 48 and 24 ma in the black dome area 240 km north of vancouver the eocene volcanic rocks are mainly continental margin calc alkaline andesite and dacite resulting from the melting of a juvenile mafic source at the base of the crust in contrast the miocene volcanic rocks resemble continental flood basalts both eocene and miocene rocks from the black dome volcanic complex have high positive end values 7 2 to 7 4 and 6 4 to 7 6 respectively and low initial sr isotopic ratios 0 702 516 0 703 528 and 0 703 376 0 703 392 respectively comparable to modern oceanic basalts the onset of the hiatus in magmatism at 48 ma coincides with capture of the kula plate by the pacific plate resulting in a change in convergence direction with the

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

diffuse back arc deformation in the southwestern pacific earthquake distribution and focal mechanisms from the lau and north fiji back arc basins indicate a diffuse and shear dominated system of deformation at odds with traditional plate tectonic models of lithospheric accretion in back arc basins the entire back arc region between the tonga and new hebrides arcs is more realistically modelled as a giant internally deformed pull apart basin formed along a left step in the transform boundary between the pacific and indo australian plates

mesoscale eddies in the south china sea mean properties spatiotemporal variability and impact on thermohaline structure we investigated mean properties and the spatiotemporal variability of eddies in the south china sea scs by analyzing more than 7000 eddies corresponding to 827 eddy tracks identified using the winding angle method and 17 years of satellite altimetry data eddies are mainly generated in a northeast southwest direction and southwest of luzon strait there is no significant difference between the numbers of two types of eddies anticyclonic and cyclonic in most regions the mean radius and lifetime of eddies are 132 km and 8 8 weeks respectively both depending on where the eddies are formed anticyclonic and cyclonic eddies tend to deform during their lifetimes in different ways furthermore eddy propagation and evolution characteristics are examined in the northern scs eddies mainly propagate southwestward along the continental slope with velocities of 5 0 9 0 cm s 1 while in the central scs eddies tend to move with slight divergence but still in a quasi westward direction with velocities of 2 0 6 4 cm s 1 eddy propagation in the western basin to the east of vietnam is quite random with no uniform propagate direction investigation of 38 long lived eddies shows that eddies have a swift growing phase during the first 12 weeks and then a slow decaying phase that affects the eddy radii and eddy energy densities nevertheless vorticity has less variability in addition the effect of eddies on the thermocline and halocline is analyzed using 763 argo temperature profile data cyclonic eddies drive the thermocline shallower and thinner and significantly strengthen the thermocline intensity whereas anticyclonic eddies cause the thermocline to deepen and thicken and weaken the thermocline intensity to a certain degree the halocline impacted by cyclonic eddies is also shallower and thinner than that impacted by anticyclonic eddies finally eddy temporal variations are examined at seasonal and interannual scales eddy activity is sensitive to the wind stress curl and in the northern scs it is also related with the strength of the background flows

u pb and k ar dates related to the timing of magmatism and deformation in the cache creek terrane and quesnellia southern british columbia u pb dating of zircon from the guichon creek batholith indicates an emplacement age of 210 3 ma comparison with previously published k ar 211 188 ma and rb sr 205 and 196 ma dates reveals that intrusion mineralization cooling and uplift of the batholith took some 20 ma spanning the triassic jurassic boundary on the decade of north american geology dnag time scale the mount martley pluton and tiffin creek stock yield late jurassic dates of 155 2 ma u pb zircon and 152 5 ma k ar hornblende respectively and provide a reliable minimum age kimmeridgian for penetrative deformation in the cache creek terrane k ar whole rock dates from cache creek terrane and ashcroft formation argillites range from early permian 266 8 ma and early jurassic 194 6 ma to late jurassic kimmeridgian 154 5 ma we interpret the younger dates as recording middle late jurassic tectonism and the older ones as possible relics from earlier deformation episodes an early cretaceous k ar date 129 5 ma for a lamprophyre dike that cuts the nicola group suggests that the early cretaceous magmatic arc of the coast plutonic complex had an eastern alkalic fringe in the intermontane belt

geochronometry of the eagle plutonic complex and the coquihalla area southwestern british columbia new u pb k ar and rb sr dates from the eagle plutonic complex and adjacent map units place timing constraints on intrusive and deformational events along the southwestern margin of the intermontane belt u pb zircon minimum dates for eagle tonalite and gneiss 148 6 156 4 and 157 4 ma document previously unrecognized middle to late jurassic magmatism and syn intrusive deformation along the eastern margin of the eagle plutonic complex and the southwestern margin of the intermontane terrane widespread mid cretaceous albian cenomanian resetting of k ar and rb sr isotopic systematics in jurassic and older rocks is coeval and cogenetic with emplacement of plutons of the fallslake plutonic suite 110 5 2 ma u pb which crosscut jurassic plutons and structures but were themselves ductilely deformed along the pasayten fault during sinistral east side up reverse displacement k ar and rb sr cooling dates for the fallslake suite of ca 100 ma including dates from mylonites along the pasayten fau

geochemical characterization of mid cretaceous granitoids of the kootenay arc in the southern canadian cordillera within southeast british columbia mid cretaceous granitoid batholiths are exposed in the omineca belt a north south trending metamorphic and plutonic orogenic belt the bugaboo horsethief creek and fry creek batholiths are post kinematic with respect to regional metamorphism that affected their host rocks and are composed of hornblende and biotite granodiorites and granites in all three batholiths and two mica granites in fry creek the biotite granites are weakly peraluminous have initial esr ranging from 36 to 56 and initial end ranging from 4 8 to 7 5 and overlap the range of nd sr isotopic compositions for precambrian basement gneisses and proterozoic metasediments found in southeast british columbia the initial 206pb 204pb versus 208pb 204pb and 207pb 204pb for these granitoids lie in bands between model lower and upper crustal pb isotopic compositions above the northern hemisphere reference line for oceanic basalts these granitoids have high nb and rb and low ba abundances relative t

mesoscale eddies in the south china sea observed with altimeter data 1 a composite time series 1993 2000 of sea surface height anomaly from several satellites is used to identify eddies in the south china sea scs the eddy lifetime radius strength and straight line travel distance are estimated altogether 58 anticyclonic eddies and 28 cyclonic eddies are identified for this period they are grouped into four geographical zones according to known eddy generation mechanisms and their statistics are discussed accordingly our geographical classification is a useful first step in gaining an overview of their generation

turbulent diapycnal mixing in the subtropical northwestern pacific spatial seasonal variations and role of eddies both spatial and seasonal variation of turbulent diapycnal mixing in the subtropical northwestern pacific are evaluated by employing a fine scale parameterization method based on profiles of potential density which are obtained from ctd measurements during our recent hydrographic surveys implemented by the china national key basic research project from 2008 to 2010 and the world ocean circulation experiment over smooth seafloor the value of diffusivity away from the boundary is comparable with the values observed in the stratified midlatitude ocean interior i e o 10 5 m 2 s 1 on the other hand enhanced diapycnal mixing i e o 10 4 m 2 s 1 or larger has been found over rough topography such as the central basin trough okidaito ridge the origin of the kuroshio current and especially luzon strait which might result from dissipation of baroclinic energy generated when barotropic tides rub over rough topography over flat bathymetry mixing is probably stirred by the wind work on near inertial motions in the upper 600 m and enhanced downward propagating energy has been found in the presence of anticyclonic eddies which points to the important role of anticyclonic eddies in enhancing the diapycnal mixing at greater depth the diffusivity also displays a distinct seasonal variation with strong weak mixing corresponding to strong weak wind input energy in winter summer which however is only confined to upper 600 m this is different from the midlatitude northwestern pacific where seasonality of diffusivity can be found at 1500 m depth

comparison of the selkirk fan structure with mechanical models implications for interpretation of the southern canadian cordillera sandbox and finite element models have demonstrated that a uniform coulomb layer that deforms under basal boundary conditions of asymmetric detachment and underthrusting of the underlying substrate develops as a structural fan the fan has a broad pro wedge of thrusts and folds that verge toward the subducting plate and a narrower retro wedge of thrusts and folds that develop above the stationary lithospheerec plate the selkirk fan of the canadian cordillera is similar in structure and we infer that it originated during jurassic accretion of terranes to the western boundary of cratonic north america by processes analogous to those of the models palinspastic restoration of the selkirk fan to the jurassic places it within the present coast belt by implication the north american plate must have extended this far west in early jurassic time previously published interpretations of lithoprobe seismic reflection profiles support this interpretation and suggest that lower crust underlying the intermontane belt and the eastern edge of the coast belt is the relict of the pre jurassic north american plate and that the accreted terranes that currently overlap this plate boundary by up to 300 km are crustal slivers that were detached from their subducting lithosphere deformed as in the models and obducted onto the north american plate this model satisfies geological and geophysical constraints it suggests a mechanism of crustal deformation involving only minor shortening of the north american plate across the width of the orogen

an exceptional anticyclonic eddy in the south china sea in 2010 the highest sea level near the xisha islands in recent 20 years occurred during august 2010 satellite altimeter data indicated that the extreme event was largely due to an anticyclonic eddy whose amplitude exceeded 20 cm and size exceeded 400 km on 11 august 2010 cruise observations showed the eddy raised the center temperature by 7 7 degrees c at 75 m and vertically extended to 500 m eddy tracking showed it had a life span of more than 8 months and propagated far from the south of xisha islands such strong and long lasting eddy that moved northward for such a long distance was observed for the first time in the south china sea scs observational data from ctd xbt and the reconstructed three dimensional temperature and salinity were used to explore the eddy s features and vertical structure our analyses show the 2010 summer monsoon and current in the western boundary of the scs were largely altered after the 09 10 el nino event from may onward the wind blew northward and strengthened over the northwestern scs such wind drove a strong northward current along the western boundary which carried the eddy northward by advection from may to july energy budget showed during the eddy northward propagation the boundary current passed energy to the eddy which led to the continuing growth of the eddy in both strength and size