glacial interglacial variablity in the benguela upwelling system spatial distribution and budgets of organic carbon accumulation 1 modern sedimentary total organic carbon toc content as a proxy for surface water export production was mapped on the shelf and on the upper continental slope of the benguela upwelling system using 137 core tops shelf maxima in toc can be correlated with maxima in surface water productivity on the slope high toc contents are observed offshore from sites of strong modern upwelling estimates of modern toc mass accumulation rates mar show that approximately 85 of the total is accumulating on the shelf toc mar were calculated mapped and budgeted for the holocene and for the last glacial maximum lgm using 19 sediment cores from the continental slope during the lgm centers of deposition and production have migrated offshore with respect to their holocene positions toc accumulation on the continental slope was approximately 84 higher during the lgm than during the holocene possibly reflecting enhanced productivity the toc distribution patterns and sediment echo sounding data suggest that undercurrents strongly influence the sedimentation off namibia winnowing and focusing result in great lateral heterogeneity of sedimentation rates and sediment properties individual cores therefore do not necessarily reflect general changes in export production these results highlight the need for detailed regional studies based on a large number of sediment cores for highly heterogeneous high productivity areas in order to derive general statements on total fluxes

geographic and seasonal distributions of brunt vaisala frequency and rossby radii in the north pacific and north atlantic abstract long term mean temperature and salinity profiles computed from an edited set of historical hydrographic data have been used to calculate mean profiles of density and brunt vaisala seasonal variations in internal rossby radii are everywhere surprisingly small

ekman transport along the galician coast northwest spain calculated from forecasted winds 1 ekman transport is studied close to the galician coast by means of forecasted winds provided by meteogalicia from november 2001 to october 2004 three different coastal zones are identified western coast from mino river to cape finisterre middle coast from cape finisterre to cape ortegal and northern coast from cape ortegal to cape penas in addition to existence of long term variations the periodicity of the transport signal is characterized by an annual component 365 days a seasonal fluctuation 50 to 80 days and a timescale related to passing storms 15 20 days although the periodicity of the signal is similar at the three zones owing to external meteorological forcing the ekman transport is modulated by the presence of the coast in such a way that seasonal patterns vary in intensity and direction along the coast thus the autumn winter pattern is characterized by high transport at the northern and middle coast pointing landward perpendicular to the shoreline and moderate values at the western coast pointing landward and oblique to the shoreline on the other hand the spring summer pattern is characterized by high transport at the western coast pointing seaward perpendicular to the shoreline the same orientation is observed at the middle coast although with a lower magnitude finally ekman transport at the northern coast points landward and oblique to the shoreline the different transport orientations are shown to be responsible for the upwelling probability variation along the coast

uranium lead dates from the central gneiss complex and ecstall pluton prince rupert map area british columbia uranium lead dates for nine zircon fractions from six rock samples of central gneiss complex cgc are concordant between 65 and 85 ma two fractions from a sample near the eastern edge of the cgc give discordant u pb dates between 108 and 171 ma but analytical uncertainties and geological complexities prohibit meaningful interpretation two fractions from two samples from the ecstall pluton give concordant u pb dates of about 98 4 ma and date the emplacement of the ecstall pluton the concordant cgc dates indicate late cretaceous to early tertiary peak metamorphism granulite and amphibolite facies of the cgc east of work channel lineament this contrasts with a slightly older mid cretaceous peak metamorphism west of work channel lineament inferred from the synmetamorphic nature of the ecstall pluton

variability in upwelling intensity and nutrient regime in the coastal upwelling system offshore namibia results from sediment archives the coastal upwelling system offshore namibia is ideally suited to address a focal question of the integrated marine biogeochemistry and ecosystem research programme what are the mechanisms that drive long term changes in ecosystems considerable interannual variability in climatic forcing is indicated by long time series of meteorological and remote sensing observation these accompany considerable interannual to interdecadal changes in the upwelling intensity over the last 100 years as well as a centennial trend on longer time scales the only archives available are sediment records spanning the late holocene to decipher the sediment record we mapped surface sediment patterns of proxies for physical sea surface temperature sst from alkenone unsaturation indexes and nutrient 15n on bulk sedimentary n variables their present day surface sediment patterns outline the coastal upwelling cells and filaments and associated high productivity area analysed in an array of dated sediment cores the spatial patterns of sst suggest long term 100 years variability in the location and intensity of individual upwelling cells the patterns of 15n outline an area of intense denitrification near the coast and advection of water with low oxygen concentrations in the undercurrent from the north 15n exhibits considerable downcore variability in particular over the last 50 years the variability appears to be governed by differences in extent of denitrification and thus of the shelf oxygen balance which appears to have deteriorated in the last 50 years together the data suggest that sst and denitrification conditions have remained in the narrow bounds outlined by today s patterns in surface sediments but that spatially small variability in upwelling intensity and make up of upwelling feed waters induced considerable changes in the lower trophic levels of the coastal upwelling ecosystem over the last 6 000 years attempts to correlate proxy records from sediments with observational time series and regional climate reconstructions were not successful possibly because annual to interannual environmental signals are erased in the process of sediment formation

a linear stratified ocean model of the coastal undercurrent the linear stratified ocean model of mccreary 1981 is used to study the wind driven response of the ocean near an eastern coast the model can be regarded as an extension of the inviscid models of lighthill 1969 and of gill clarke 1974 that allows the vertical diffusion of heat and momentum into the deep ocean solutions are still found as expansions of vertical normal modes vertical mixing affects each mode as a linear drag with a drag coefficient that increases rapidly with mode number n a zonally uniform band of steady equatorward winds forces the ocean and the resulting flow field has many features in common with observations at eastern boundaries there is a surface equatorward jet and a poleward coastal undercurrent confined within 10 20 km of the coast both currents extend well poleward of the wind band upwelling does not reach great depths but occurs only above the core of the undercurrent weak downwelling occurs at greater depths there is offshore ekman drift in the surface mixed layer and return flow at a depth slightly above the core of the undercurrent the baroclinic alongshore pressure gradient field and the vertical mixing of heat and momentum are essential elements of the model dynamics but the beta and horizontal mixing are not low order vertical modes n 6 tend toward a two dimensional balance they generate the transverse circulation pattern associated with coastal ekman pumping

coastal trapped wave propagation along the southwest african shelf as revealed by moored observations abstractcoastal trapped waves ctws that propagate poleward along the southwest african shelf potentially leak energy from lower latitudes into the benguela upwelling system bus thus in additi

paleomagnetism and geochronology of the ecstall pluton in the coast mountains of british columbia evidence for local deformation rather than large scale transport 1 samples for geochronologic geobarometric and paleomagnetic analyses were collected across the northern portion of the ecstall pluton southeast of prince rupert british columbia al in hornblende geobarometry indicates pressures from 740 10 to 840 30 mpa corresponding to crystallization depths of 25 to 30 km u pb analyses of zircons from western central and eastern localities within the pluton yield crystallization ages of 91 5 1 0 ma 90 8 1 0 ma and 90 5 1 0 ma respectively rock magnetic experiments reflected light microscopy and thermal demagnetization behavior suggest that natural remanent magnetism is carried by low ti titanohematite unblocking temperatures of the characteristic remanent magnetization chrm are dominantly in the 560 c to 630 c range with age of magnetization approximated by the 40ar 39ar hornblende ages of 84 2 0 10 ma on the western margin and 76 4 0 6 ma in the center of the pluton site mean chrm directions were isolated for paleomagnetic samples from 23 sites and are distributed along a small circle with subhorizontal axis at 340 azimuth chrm directions from the central portion of the pluton are concordant with the expected cretaceous magnetic field direction while chrm directions from the western margin are discordant by 70 folding of the ecstall pluton either during late cretaceous west directed thrust transport above the convex upward prince rupert shear zone or during younger deformation of the pluton and underlying shear zone can account for the paleomagnetic data and is consistent with the geochronologic geobarometric and structural geologic observations

oxygen 18 oxygen 16 and d h studies of plutonic granitic and metamorphic rocks across the cordilleran batholiths of southern british columbia hydrogen and oxygen isotope ratios of 500 samples mainly from granitic plutons were measured along a 700 km e w traverse across the accreted terranes of southern british columbia latitudes 49 52 n despite the geological complexity and range of intrusive ages late triassic to tertiary and although there are steps in the isotopic values at some geologic boundaries e g across the strait of georgia two clear patterns emerge 1 the 18 o 16 o and d h ratios of the waters involved in hydrothermal interactions with the granitic rocks show a regular eastward trend of depletion in d and 18 o enormous areas were affected by the hydrothermal processes but the most intense alteration is localized along major north trending lineaments e g okanagan lake 2 independent of the hydrothermal effects the primary 18 o values of the granitic rocks also change systematically eastward from 7 0 to 8 5 in vancouver island reaching a minimum of 5 5 to 7 0 in the western and central coast plutonic complex then increasing progressively from the eastern coast batholith to the okanagan batholith and attaining a maximum of 10 0 to 12 0 in the nelson batholith two groups of samples are unique in their high d values the first group is represented by two geographically isolated batholiths guichon and thuya that were not affected by the tertiary meteoric hydrothermal systems and that have therefore preserved their early jurassic to triassic k ar ages the second group is represented by the jurassic plutons of vancouver island there the hydrothermal fluids were both d rich and 18 o rich 18 o 0 as evidenced by the fact that feldspars in the altered granites are enriched in 18 o relative to coexisting quartz both anomalies can be explained if these terranes were located closer to the equator and or in a maritime environment at the time of intrusive and hydrothermal activity in agreement with available paleomagnetic data excluding these anomalous areas two distinct ages of meteoric hydrothermal activity can be identified cretaceous in the west and early to mid tertiary in the east the isotopic trends in the rocks are similar to the present day patterns of meteoric waters in the region with one primary difference the paleowaters are enriched in d by about 20 compatible with a northward translation of these terranes a climatic change or both the similarities of the patterns suggest a topography similar to that of the present day a mountain chain along the coast during the early tertiary the whole rock 18 o values of the granitic rocks determined by extrapolation of the trends of 18 o quartz versus 18 o feldspar to correct for hydrothermal alteration effects suggest that the main part of the coast plutonic complex formed from magmas similar to those in oceanic island arcs derived from basaltic crust or from an upper mantle source toward the east an increasingly larger component of sedimentary rocks must be present in the source regions of the granitic magmas it may be significant that right at the edge of the north american craton there is a drop in the 18 o of the plutons from 11 down to 9 5 suggesting involvement of old granitic crust instead of sedimentary rocks these new data from southern british columbia confirm and amplify previous studies that have documented 1 the existence of widespread and pervasive hydrothermal effects throughout the north american cordillera and 2 regular west to east asymmetries in the amounts of different kinds of parent rocks in the source regions from which these mesozoic and cenozoic granitic magmas were derived

land atmosphere ocean interactions in the southeastern atlantic interannual variability land atmosphere ocean interactions in the southeastern south atlantic and their connections to interannual variability are examined using a regional climate model coupled with an intermediate level ocean model in austral summer zonal displacements of the south atlantic subtropical high sash can induce variations of mixed layer currents in the benguela upwelling region through surface wind stress curl anomalies near the namibian coast and an eastward shifted sash is related to the first pacific south american mode when the sash is meridionally displaced mixed layer vertically integrated ekman transport anomalies are mainly a response to the change of alongshore surface wind stress the latitudinal shift of the sash tends to dampen the anomalous alongshore wind by modulating the land sea thermal contrast while opposed by oceanic diffusion although the position of the sash is closely linked to the phase of el nino southern oscillation enso and the southern annular mode sam in austral summer an overall relationship between benguela upwelling strength and enso or sam is absent during austral winter variations of the mixed layer ekman transport in the benguela upwelling region are connected to the strength of the sash through its impact on both coastal wind stress curl and alongshore surface wind stress compared with austral summer low level cloud cover change plays a more important role although wintertime sea surface temperature fluctuations in the equatorial atlantic are strong and may act to influence variability over the northern benguela area the surface heat budget analysis suggests that local air sea interactions dominate

kinematics and tectonic significance of transpressive structures within the coast plutonic complex british columbia abstract structural data from the coast plutonic complex near prince rupert british columbia are consistent with a deformational history dominated by dextral transpression from campanian to paleocene time penetrative east side up southwest directed ductile shearing produced moderately northeast plunging overturned kilometer scale isoclinal folds these folds are dextrally sheared and refolded into kilometer scale upright northwest plunging folds and steeply dipping transposed foliations with moderate to shallow northwest plunging lineations along their western side an east side up component to the transcurrent shearing is kinematically compatible with east side up shearing found within the great tonalite sill kinematic and geometric gradients and the spatial distribution of the finite stretching direction are interpreted to result from partitioning of transpression the location of these structures and overprinting relationships suggest the great tonalite sill intruded late kinematically into a crustal scale dextral transpressive shear zone these results indicate this shear zone could form part of the baja b c fault system that would have accommodated large northward displacements of the terranes making up western british columbia and southeast alaska this conclusion is based on 1 it is favorably located to accommodate the proposed displacements 2 deformation occurred during the time period of proposed large displacement 83 59 ma 3 the 15 km thickness of the shear zone indicates it records large displacements

high grade reworking of central australian granulites part 1 structural evolution abstract four distinct deformational events d2 d5 accompanying a granulite facies metamorphic cycle m2 m5 are shown to structurally overprint rework pre existing granulites m1 of the northeast strangways range in the central arunta block the first metamorphic cycle m1 at 1800 ma involved an anticlockwise p t path peaking at 850 950 c at 8 9 kbar m1 metamorphism involved widespread partial melting that produced stromitic migmatites and map scale concordant granitic gneisses isobaric cooling after the peak and accompanying hydration gave rise to a wide variety of coronitic and symplectitic reaction textures that enclose and replace m1 mineral parageneses no kinematic structuring is associated with m1 and the period encompassing the thermal peak and immediately subsequent are thought to have been absent of deviatoric stress the second metamorphic cycle m2 m5 possibly at 1400 1500 ma involved a clockwise p t path with a maximum p of 9 10 kbar and a thermal peak of approximately 800 c this metamorphic cycle accompanied the major ductile deformations recognized d2 d5 and has been labelled the proterozoic reworking the proterozoic reworking has been divided into two thermo barometric and structurally distinct periods d2 d3 involved regionally inclined ene wsw non coaxial shear of high bulk shear strains giving rise to an intense often mylonitic pervasive fabric s2 l2 and isoclinal and sheath folds on all scales f2 f3 s2 l2 is the first recognized kinematic fabric and does enclose and partially recrystallize m1 mineral parageneses including late m1 metamorphic reaction textures d2 d3 deformation was due to crustal shortening and gave rise to crustal over thickening loading accompanying prograde metamorphism m2 d4 d5 involved upright open and asymmetrical folding f4 and e w trending shear zone development s5 within a regionally extensive system of inclined oblique sinistral transpression both d2 d3 and d4 d5 episodes occurred under the same approximately e w directed compressive stress and are considered sequential episodes in the one tectonothermal cycle f4 folding accompanied significant melt formation and the peak of metamorphism of the m2 m5 metamorphic cycle s5 shear zones accompanied 3 4 kbar of decompression with cooling presumably during uplift in isostatic response to crustal over thickening in d2 d3 progression from inclined non coaxial shear to transpression occurred in response to an increase in the relative buoyancy forces limiting crustal thickening as is typical of many compressional orogens however the proterozoic reworking is atypical of simple linear or arcuate mountain belts because late stage shearing s5 is aligned sub parallel not at a high angle to the transport vector of the earlier ductile deformations d2 d3 consequently this region is modelled in terms of crustal shortening directed along the length of an e w trending orogen confined to the north and south by relatively stable crustal blocks when e w shortening could no longer be accommodated by crustal thickening strain was partitioned by sinistral transpression between the north and south bounding crustal blocks

origins and variability of the benguela current a subset of the benguela sources and transports best 1992 1993 data is analyzed to study the magnitude and variability of the large scale transports in the area the data consist of inverted echo sounder series and conductivity temperature depth stations the mean 16 month transport values for the upper 1000 m indicate that of the 13 sv northward transport within the benguela current 50 is derived from the central atlantic which from geometry may be chiefly south atlantic water 25 comes from the indian ocean which may be chiefly agulhas water and the remaining 25 may be a blend of agulhas and tropical atlantic water a simple schematic of the transport pattern with a somewhat restricted corridor for agulhas eddies translation is envisioned to the west of the eddy corridor flows the south atlantic source for the benguela current to the east is the agulhas indian ocean source the corridor is breached by south atlantic and indian water as the transient eddy field stirs these water masses

deep crystal response to continental collision the limpopo belt of southern africa the limpopo belt is an example of an archean 2700 ma continental collisional zone in which the thickened crust 70 km has virtually attained equilibrium with the adjacent non thickened plates by a process of upward movement and lateral spreading of the underthrust high grade metamorphosed plates

theory of the benguela upwelling system the paper gives a theoretical study of the benguela upwelling system by means of a relatively simple conceptual model that allows an analytical treatment the model consists of a stratified flat bottomed coastal ocean the coast is idealized by a straight wall the model ocean is forced by an alongshore wind band extending from the area near cape town to the border of angola and namibia the wind varies alongshore and cross shore wind stress curl and changes periodically in time the response of the coastal ocean is governed by coastal jets upwelling and kelvin waves as well as by a current system driven by the wind stress curl the model is able to reproduce several observed features such as the poleward undercurrent the northward coastal currents in most of the wind band and a southward coastal current near the northern edge of the wind band export of coastal jets out of the forcing area by coastal kelvin waves provide a mechanism to guide energy into the area off cape town the southward propagating kelvin waves may bend around the southern tip of africa and provide a dynamic linkage between the benguela coastal current and the agulhas current

simulation of the tropical thermal domes in the atlantic a seasonal cycle abstract a general ocean circulation model is used to analyze seasonal variations in the guinea dome and angola dome regions the cold guinea dome develops from june through september due to active divergence of heat transport the cooling is related to upwelling generated by the local wind stress curl associated with the northeast trade winds the guinea dome thus provides an active mechanism of absorbing heat from the atmosphere the coastal guinea region experiences semiannual warming in april july and november december due to intrusion of coastal downwelling kelvin waves from the equatorial region the angola dome in the southern hemisphere is found to be cooled from march through august the surface flux plays a major role in the seasonal variation of the heat budget in contrast to the situation of the guinea dome in the northern hemisphere the angola front located at the northern border of the cold angola dome becomes distinguishable particularly during the boreal fall because of the intrusion of w

offshore ekman transport and ekman pumping off peru during the 1997 1998 el nino 1 satellite ocean vector wind measurements are used to describe onshore offshore ekman transport and ekman pumping suction i e downward upward velocity in the coastal ocean at 15 s off peru where upwelling is the dominant physical process normal and el nino conditions are defined for may 1992 april 1997 and may 1997 may 1998 respectively during normal conditions both ekman suction and offshore ekman transport produced upwelling during the el nino the may august speed of ekman pumping 9 10 6 m s 1 was nearly 4 times larger than the normal speed of ekman suction and offshore ekman transport nearly doubled the strong ekman pumping may be the source for the deepened coastal thermocline during el nino although the evidence is not conclusive because of the absence of in situ observations

silica undersaturated sapphirine spinel and kornerupine granulite facies rocks ne strangways range central australia small pods of silica undersaturated al rich and mg rich granulite facies rocks containing sapphirine pleonastic spinel kornerupine cordierite orthopyroxene corundum sillimanite and gedrite are scattered throughout the ne strangways range central australia these are divided into four distinct rock types namely orthopyroxene rich aluminous granofels and metapelitic gneisses containing sapphirine spinel or kornerupine two granulite facies metamorphic events are recognized of which only the first m1 is considered in this paper peak metamorphic mineral parageneses indicate that the m1 thermal maximum occurred at approximately 900 950 c and 8 9 kbar all samples are characterized by profuse and diverse coronitic and symplectic reaction textures these are interpreted as evidence for the sequential crossing of the following reactions in the system fmas cordierite spinel corundum sapphirine sillimanite cordierite spinel orthopyroxene sapphirine sillimanite sapphirine spinel sillimanite orthopyroxene corundum sapphirine sillimanite cordierite orthopyroxene corundum phase stability relationships in fmas and mash indicate an anticlockwise p t path terminated by isobaric cooling such a path is exemplified by early low p mineral parageneses containing spinel corundum and gedrite and the occurrence of both prograde and retrograde corundum reaction textures preserve evidence for an increase in ah2o and ab2o3 with progressive isobaric cooling this hydrous retrogression resulted from crystallization of intimately associated m1 partial melt segregations there is no evidence for voluminous magmatic accretion giving rise to the high m1 thermal gradient the m1 p t path may be the result of either lithospheric thinning after both crustal thickening and burial of the supracrustal terrane or concomitant crustal thickening and mantle lithosphere thinning

correction to contrast of metamorphic and structural histories across the work channel lineament coast plutonic complex british columbia by maria luisa crawford and lincoln s hollister

the benguela upwelling system quantifying the sensitivity to resolution and coastal wind representation in a global climate model abstractof all the major coastal upwelling systems in the world s oceans the benguela located off southwest africa is the one that climate models find hardest to simulate well this paper investigates the sensitivity of upwelling processes and of sea surface temperature sst in this region to resolution of the climate model and to the offshore wind structure the community climate system model version 4 is used here together with the regional ocean modeling system the main result is that a realistic wind stress curl at the eastern boundary and a high resolution ocean model are required to well simulate the benguela upwelling system when the wind stress curl is too broad as with a 1 atmosphere model or coarser a sverdrup balance prevails at the eastern boundary implying southward ocean transport extending as far as 30 s and warm advection higher atmosphere resolution up to 0 5 does bring the atmospheric jet closer to the coast but there can be too strong a wind stress curl the most

deformational history of an outlier of metasedimentary rocks coast plutonic complex british columbia canada the khutzeymateen assemblage records a portion of the polyphase deformation experienced by rocks within the core of the coast plutonic complex this series of deformational events probably took place during late cretaceous to early eocene regional orogenic activity the khutzeymateen assemblage is dominated by metamorphosed graywackes and volcaniclastic material the earliest recognizable deformation involves thrust faulting that juxtaposed rocks of the khutzeymateen assemblage and central gneiss complex the next deformational event produced isoclinal folds f1 a penetrative foliation s1 and a strong mineral lineation l1 both f1 and l1 have a 340 15 orientation peak metamorphism p 450 50 mpa t 650 50 c was synchronous with this isoclinal folding event f1 folding was followed by a brittle chevron folding event f2 with a 335 20 orientation there is a strong lithologic control on the development of f2 minor folds which are developed predominantly within regularly layered qua

sediment underthrusting within a continental magmatic arc coast mountains batholith british columbia nsf ear 0309885 ear 1338583 idaho state university romanian national science funding agency uefiscdi grant pn iii p4 id pce 2016 0127

seasonal variability of the mauritania current and hydrography at 18 n extensive field campaigns in the mauritanian upwelling region between 2005 and 2016 provide the database for analyzing the seasonal variability of the eastern boundary circulation ebc and associated water mass distribution at 18 n the data set includes shipboard upper ocean current hydrographic and oxygen measurements from nine research cruises conducted during upwelling december to april and relaxation may to july seasons during the upwelling season the ebc closely resembles a classical eastern boundary current regime with a poleward undercurrent flowing beneath an equatorward coastal jet in contrast elevated poleward flow exceeding 30 cm s and extending from the surface down to 250 m depth is observed during the relaxation season the pronounced seasonal variability of the across shore structure of the ebc can be related to local wind forcing and is in general agreement with sverdrup balance the ebc transport is correlated to the wind stress curl leading the transport by 7 days the short lead time suggests a fast response of locally forced waves adjusting the ebc to wind forcing the seasonal and vertical water mass distribution is presented based on hydrographic observations the meridional oxygen distribution and corresponding water mass partitioning into south and north atlantic central water masses reveal a possible northerly ventilation pathway in the deeper layers of the central water stratum our results suggest that the poleward surface flow and the poleward undercurrent both are a consequence of the cyclonic wind stress curl forcing and thus propose to name it the mauritania current

the role of melt in the uplift and exhumation of orogenic belts abstract in some orogenic belts rapid pulses of uplift occur when melt is present detailed work on the relation of melt to structural and metamorphic features in several localities shows that hot metamorphic rocks and especially anatectic migmatite can be physically transported from the lower to middle crust on decollements the decollements form in the lower crust because even though the lower crust is structurally weak throughout due to thermally activated crystal plastic deformation mechanisms the crust is substantially weakened where melt forms or is intruded melt in the lower crust is present long enough to accomodate strain whereas in the upper crust it crystallizes too fast to be a factor in strain localization following crustal loading due to thrusting exhumation results in the formation of additional melt in the migmatites due to decompression melting support of this sequence of events includes 1 evidence for near isothermal decompression of high temperature metamorphic rocks with early high pressure minerals having formed pre or synchronous with penetrative deformation and with lower pressure minerals having formed after the deformation 2 the occurrence of magma sheets that occur along decollements between high temperature metamorphic rocks and lower temperature metamorphic rocks in either thrust or normal configurations 3 nearly concordant k ar cooling dates for biotite and hornblende suggesting rapid cooling rates and 4 post tectonic intrusions of leucogranite or leucotonalite that may represent the products of decompression melting the crystalline slabs of the high himalaya the compressional surges of the coast orogen of british columbia and alaska the cordillera of southern british columbia and the southern belt of the hercynian chain are examples where melt assisted rapid pulses of uplift appear to have occurred during the terminal phases of uplift and following uplift these orogenic belts were exhumed during extension while melt was still present

the scotia quaal metamorphic belt a distinct assemblage with pre early late cretaceous deformational and metamorphic history coast plutonic complex british columbia the scotia quaal metamorphic belt extends from hawkesbury island to work channel between the early late cretaceous ecstall and the paleogene quottoon plutons the belt consists of a proterozoic paleozoic metasedimentary and metavolcanic sequence the middle devonian big falls orthogneiss early jurassic orthogneiss and jurassic or cretaceous mafic and ultramafic intrusive rocks the assemblage may be correlative with nisling terrane lithologies and may have shared a common history at least from early jurassic time on with rocks of stikine terrane strong planar and linear fabrics abundant folds and scarcity of kinematic indicators characterize the belt s deformational style development of a strong foliation followed by three episodes of folding occurred between emplacement of the middle devonian big falls orthogneiss and early late cretaceous ecstall intrusion paleogene fabrics occur in the quottoon pluton and in the easternmost 1 5 km of the scotia quaal belt if a major paleogene shear zone is po

regionally extensive mid cretaceous west vergent thrust system in the northwestern cordillera implications for continent margin tectonism the intermontane insular superterrane boundary zone represents a fundamental crustal boundary separating the two largest allochthonous crustal fragments in the north american cordillera structural stratigraphic and geochronologic relations along this boundary indicate that substantial west vergent compression and concomitant crustal thickening occurred there in mid cretaceous time this orogenic zone extends for more than 1200 km along strike length between southern southeast alaska and northern washington in southern southeast alaska and northwest british columbia rocks of the insular superterrane were imbricated along a series of west to southwest vergent thrust faults in northern washington and southwestern british columbia a wide zone encompassing the margins of the two superterranes as well as numerous intervening smaller fragments was shortened principally along west vergent thrusts known geologic relations do not discriminate among existing tectonic models that explain the origin of the mid cretaceous thrust system