assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures though many studies on the mg contents in the calcitic tests of foraminifers exist the processes controlling its uptake are still a matter of debate laboratory cultures offer an excellent opportunity to reveal these mechanisms the mg concentrations within single chambers of the planktic foraminifer globigerinoides sacculifer brady maintained under controlled laboratory conditions were measured 1 at variable temperatures 19 5 29 5 c and constant salinity and 2 at variable salinity 22 45 and constant temperature the experimental results suggest that under natural conditions temperature is the leading mechanism controlling the mg ca ratio temperature and magnesium are related proportionally a temperature increase of ca 10 c gives rise to an increase of the magnesium concentrations of ca 130 drastic unnatural salinity changes dominate the effects of temperature a 110 change in the mg ca ratio was observed when salinity was elevated or reduced by more than ca 10 specimens which underwent gametogenesis reveal significantly higher mg concentrations than specimens that did not release gametes partition coefficients for mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite when comparing observed mg ca ratios of foraminiferal tests with predicted mg ca ratios calculated according to empirical equations it becomes evident that foraminiferal tests are undersaturated with respect to mg for the water temperature they have experienced apparently foraminifers are capable of controlling their mg concentration the physiological processes presumably responsible for such depressed mg ca ratios appear to be temperature controlled as deduced from the close relationship of the observed mg ca ratios and water temperature this study demonstrates that variations in temperature and salinity are definitely reflected in the mg content of foraminiferal tests magnesium may thus serve as a paleo proxy for past surface water temperatures as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded

seismicity of the aegean and surrounding area abstract seismicity parameters based on instrumental and historical data are given for 36 seismic sources of shallow earthquakes and for 6 seismic sources of intermediate depth earthquakes in the aegean and surrounding area 34 n 43 n 18 e 30 e these parameters are of two categories parameters of the first category are useful for seismic hazard evaluation a and b values of the frequency magnitude relation maximum earthquake magnitude number of shocks larger than certain magnitude per year while parameters of the second category are proper for describing the spatial distribution of seismicity mean return period most probable magnitude in a certain time period moment rate shallow seismicity is highest along the convex side of the hellenic arc but close to the coast ionian islands south peloponnesus south of crete south of karpathos and rhodos in central greece patraikos corinthiakos evoikos gulfs thessalia and along a seismic belt which includes the northwestern anatolia fault zone the northernmost part of the aegean sea and the serbomacedonia zone the intermediate depth seismic activity is distributed in two parts of the benioff zone which dips from the convex side eastern mediterranean to the concave side aegean sea of the hellenic arc the one part shows a low dip angle and includes earthquakes with focal depths between 70 km and 100 km this part has a high seismicity earthquake magnitudes up to 8 0 and is situated below the inner slope of the sedimentary part of the hellenic arc eastern peloponnesus north of crete rhodos based on the fact that this part of the benioff zone is a continuation of the seismic zone of shallow earthquakes along the hellenic arc and that both zones have the same seismicity it is concluded that they constitute a continuous seismic belt on which coupling occurs between the subducted eastern mediterranean lithosphere and the overthrusted aegean lithosphere the other inner part of the benioff zone shows low seismicity maximum earthquake magnitude up to 7 1 with earthquakes of focal depths between 100 km and 180 km it dips at a mean angle of 38 below the volcanic arc of the southern aegean sea and is the result of the subduction of the front part of the eastern mediterranean lithosphere without coupling with the aegean lithosphere

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

thermal history of the ecstall pluton from 40ar 39ar geochronology and thermal modeling abstract new 40ar 39ar thermochronology results and thermal modeling support the hypothesis of hollister et al 2004 that reheating of the mid cretaceous ecstall pluton by intrusion of the coast mountains batholith cmb was responsible for spatially variable remagnetization of the ecstall pluton 40ar 39ar ages from hornblende and biotite from 12 locations along the skeena river across the northern part of the ecstall pluton decrease with proximity to the quottoon plutonic complex the nearest member of the cmb to the ecstall pluton the oldest 40ar 39ar ages are found farthest from the quottoon plutonic complex and are 90 3 ma for hornblende and 77 9 1 2 ma for biotite the youngest 40ar 39ar ages are found closest to the quottoon plutonic complex and are 51 6 1 2 ma for hornblende and 45 3 1 7 ma for biotite no obvious relationship between grain size and age is seen in the ecstall pluton biotites spatial trends in 40ar 39ar ages are consistent with model results for reheating by a thermal wall at the location of the quottoon plutonic complex although no unique solution is suggested our results indicate that the most appropriate thermal history for the ecstall pluton includes both reheating and northeast side up tilting of the ecstall pluton associated with intrusion of the quottoon plutonic complex estimates of northward translation from shallow paleomagnetic inclinations in the western part of the ecstall pluton are reduced to 3000 km consistent with the baja bc hypothesis when northeast side up tilting is accounted for

a bayesian multivariate calibration for globigerinoides ruber mg ca the use of mg ca in marine carbonates as a paleothermometer has been challenged by observations that implicate salinity as a contributing influence on mg incorporation into biotic calcite and that dissolution at the sea floor alters the original mg ca yet these factors have not yet been incorporated into a single calibration model we introduce a new bayesian calibration for globigerinoides ruber mg ca based on 186 globally distributed core top samples which explicitly takes into account the effect of temperature salinity and dissolution on this proxy our reported temperature salinity and dissolution here expressed as deep water co32 sensitivities are 2 8 7 0 9 c 3 9 1 2 psu and 3 3 1 3 mol kg 1 below a critical threshold of 21 mol kg in good agreement with previous culturing and core top studies we then perform a sensitivity experiment on a published record from the western tropical pacific to investigate the bias introduced by these secondary influences on the interpretation of past temperature variability this experiment highlights the potential for misinterpretations of past oceanographic changes when the secondary influences of salinity and dissolution are not accounted for multiproxy approaches could potentially help deconvolve the contributing influences but this awaits better characterization of the spatio temporal relationship between salinity and 18osw over millennial and orbital timescales

structural evolution of the alaska juneau lode gold deposit southeastern alaska the alaska juneau lode gold deposit is hosted by a series of polydeformed permian to late triassic volcanic pelitic volcaniclastic and mafic intrusive rocks rocks in the mine area have been sheared and metamorphosed to greenschist grade interpretation of rock fabrics indicates several generations of ductile and brittle deformation prior to mineralization reverse shear occurred along northwest striking and northeast dipping ductile shear zones mineralization consists of eocene auriferous quartz carbonate veins which cut the regional metamorphic fabrics mineralization was followed by reverse right lateral shear along northwest trending ductile brittle shear zones two northwest striking and steeply dipping vein sets host the bulk of the ore orientation of carbonate fibers within the quartz veins were used to determine the deformation regime that existed during mineralization plunge of the fibers indicate that down to the northeast extension occurred synchronous with mineralization structural da

cleaning method impact on the mg ca of three planktonic foraminifer species a downcore study along a depth transect abstract we performed a downcore comparison of mg ca ratios obtained using reductive and non reductive cleaning methods applied to globigerinoides ruber pulleniatina obliquiloculata and globorotalia menardii picked along two nearby sediment cores retrieved at 2100 m and 3875 m in the eastern equatorial indian ocean at the shallower site our results show statistically significant discrepancies in averaged relative mg ca loss induced by the reductive cleaning compared to non reductive cleaning g menardii 8 5 g ruber 6 2 p obliquiloculata 4 4 suggesting that reductive cleaning impact on relative mg ca loss is species specific at the deeper site differences between the relative mg ca losses for the three species are smaller g menardii 3 7 g ruber 4 1 and p obliquiloculata 6 3 suggesting the clear impact of in situ preservation state on the cleaning related mg ca loss the mg ca loss in both relative and absolute mmol mol value of species g ruber and g menardii are significantly smaller at the deeper site than the shallower site implying that these two species which have experienced intense dissolution on the sea floor are less prone to lose further mg during the reductive cleaning p obliquiloculata however show non significant difference in mg ca loss between the two sites indicating that the cleaning related mg ca loss in this species is somewhat insensitive to the preservation state at our two sites our data reveal that mg ca loss results from partial dissolution induced by the reductive step we conclude that the non reductive cleaning approach should be preferred for building inter laboratory homogeneous datasets of mg ca derived temperatures whereas the reductive step should be only included when severe oxide coating is observed

tectonic history of the eastern edge of the alexander terrane southeast alaska rocks exposed west of the coast plutonic complex in southern southeast alaska form an imbricate thrust belt that overprints the tectonic boundary between two of the largest allochthonous crustal fragments in the north american cordillera the insular and intermontane composite terranes in the alexander terrane insular composite terrane lower paleozoic metavolcanic and metasedimentary rocks descon formation and dioritic plutons are unconformably overlain by lower devonian clastic strata karheen formation these rocks are overlain locally by upper triassic basalt rhyolite and marine clastic strata hyd group upper jurassic and lower cretaceous metavolcanic and metasedimentary strata of the gravina sequence unconformably overlie the alexander terrane the gravina sequence forms a structural package over 15 km thick and records intermittent arc volcanism along the eastern edge of the alexander terrane the gravina sequence is structurally overlain by upper paleozoic and lower mesozoic metamorphosed basaltic strata marble and argillite alava sequence and locally by lower paleozoic supracrustal rocks and orthogneiss kah shakes sequence together these constitute the taku terrane which we correlate with the intermontane composite terrane local unconformity of gravina sequence strata over the alava sequence demonstrates that the gravina sequence overlapped an earlier structural boundary between the intermontane and insular composite terranes the rocks were deformed in the mid cretaceous by west vergent thrusting that was was broadly coeval with arc magmatism deformation involved emplacement of west directed thrust nappes over the structurally intact and relatively unmetamorphosed alexander terrane basement mid cretaceous tonalite granodiorite and quartz diorite intrude rocks of the thrust belt and are locally affected by the deformation mid cretaceous deformation occurred during two episodes that were contemporaneous with the emplacement of large sill like plutons older structures record ductile southwest vergent folding and faulting regional metamorphism and development of axial planar foliation the second generation structures developed during the later stages of southwest directed thrust faulting which juxtaposed rocks of contrasting metamorphic pressures and temperatures structural stratigraphic and geochronologic data indicate that the two phases of regional thrusting in southeast alaska occurred between 113 ma and 89 ma rocks in the western part of the thrust belt were uplifted regionally by 70 ma deformation involved the collapse of a marginal basin s and a magmatic arc and overprinted the older tectonic boundary between the insular composite terrane and the late mesozoic western margin of north america at that time the intermontane composite terrane contractional deformation along the length of the thrust belt was broadly coeval with arc magmatism and thus records intra arc tectonism late paleocene to early eocene igneous activity and extensional deformation subsequently affected the thrust belt

improving temperature estimates derived from mg ca of planktonic foraminifera using x ray computed tomography based dissolution index xdx 1 temperatures derived from mg ca ratios of the calcite tests of planktonic foraminifera are distorted when samples are partially dissolved and methods are required to quantify this source of inaccuracy here we compare a dissolution index xdx based on x ray computed tomography scans to mg ca of four species of foraminifera g ruber white g sacculifer without sac n dutertrei and p obliquiloculata from core top sediments from the tropical pacific atlantic and western indian ocean deepwater calcite saturation values co32 at the sites ranged from 55 to 23 mol kg an estimate of mg ca reduction in mg ca due to dissolution was made for each sample mg ca decreased linearly from deepwater co32 values of between 10 4 and 15 5 mol kg these values are minimum estimates of the threshold below which mg ca is affected by dissolution as they are limited by assumptions made in calculating mg ca sensitivity of mg ca to co32 was greatest for g ruber where mg ca decreased by 0 102 0 036 mmol mol per mol kg sensitivity was similar for g sacculifer 0 047 0 015 mmol mol per mol kg n dutertrei 0 037 0 010 mmol mol per mol kg and p obliquiloculata 0 040 0 008 mmol mol per mol kg sensitivity was similar at all sites for each species excepting an apparently greater response for n dutertrei from the caribbean compared to other sites calibrations between xdx and mg ca provide a means to estimate dissolution bias on mg ca poor correlation between xdx and 18o suggests that for the small sample size typical for analysis variability in initial 18o overwhelms dissolution effects

high temperature arc parallel normal faulting and transtension at the roots of an obliquely convergent orogen structural and kinematic data from northern coastal british columbia 54 5 n document intra arc deformation patterns at mid crustal levels during and after emplacement of the coast mountains batholith major arc parallel displacements occurred along high temperature 700 c ductile normal faults and steep sinistral transtensional shear zones within an obliquely convergent margin strain patterns and pluton emplacement were controlled by 1 structural anisotropies in host rocks that predate batholith emplacement and 2 kinematic compatibility requirements created by simultaneous motion on curved pluton bounding shear zones these controls superseded a partitioning of the arc parallel and arc normal components of oblique plate convergence onto strike slip and thrust faults respectively

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

a bimodal volcanic plutonic system the zarembo island extrusive suite and the burnett inlet intrusive complex the zarembo island volcanic rocks and the burnett inlet plutonic complex in central southeastern alaska were investigated to determine if they are genetically related the zarembo island volcanic suite consists of basalt andesite and rhyolite lava flows which exhibit features that suggest simultaneous eruptions of mafic and felsic lavas five kilometres to the southeast the broadly layered burnett inlet plutonic complex consists of gabbro diorite and granite plutons that also show characteristics of contemporaneous mafic and felsic magmatism these bimodal volcanic and plutonic rocks are similar in age ranging from 18 5 to 21 5 ma both suites show a gap in silica concentration between 60 and 65 wt and have similar major trace and rare earth element composition both suites also show igneous layering either as interlayered basalt and rhyolite flows or as alternating gabbro and granite sheets additionally both groups contain magma mingling and mixing textures including mafic enclaves in felsic members and quartz xenocrysts rimmed by clinopyroxene in enclaves these characteristics suggest that the burnett inlet intrusive complex and the zarembo island volcanic suite represent an eroded shallow level plutonic center and its eruptive cover the style of volcanism and the bimodal nature of magmatism suggest that igneous activity occurred during crustal extension and thinning that accompanied strike slip tectonic motion in southeastern alaska during the tertiary the volcanic plutonic rock associations now exposed at the surface indicate that at least 7 of post 20 ma crustal tilting has affected the region and can help to explain aberrant paleomagnetic poles in mid cretaceous intrusions of the cordillera coast belt

salinity bias on the foraminifera mg ca thermometry correction procedure and implications for past ocean hydrographic reconstructions 1 mg ca in foraminiferal calcite has recently been extensively used to estimate past oceanic temperatures here we show however that the mg ca temperature relationship of the planktonic species globigerinoides ruber is significantly affected by seawater salinity with a 1 psu change in salinity resulting in a 1 6 c bias in mg ca temperature calculations if not accounted for such a bias could lead for instance to systematic overestimations of mg ca temperatures during glacial periods when global ocean salinity had significantly increased compared to today we present here a correction procedure to derive unbiased sea surface temperatures sst and 18osw from g ruber tmg ca and 18of measurements this correction procedure was applied to a sedimentary record to reconstruct hydrographic changes since the last glacial maximum lgm in the western pacific warm pool while uncorrected tmg ca data indicate a 3 c warming of the western pacific warm pool since the lgm the salinity corrected sst result in a stronger warming of 4 c

adaptation of a flow through leaching procedure for mg ca paleothermometry 1 mg ca ratios in planktonic foraminifera reflect calcification temperatures and are thus useful for sea surface temperature sst reconstructions despite the obvious utility of this paleoceanographic tracer problems of dissolution gametogenic calcification and contaminant phases have thus far limited confidence in mg ca based reconstructions here we show strong evidence of mg heterogeneity in foraminiferal calcite by sequentially measuring the composition of different forms of calcite ontogenetic gametogenic diagenetic in the same shells while monitoring and removing contaminant phases a new flow through method combines chromatographic technology and inductively coupled plasma mass spectrometry icp ms in a series of cleaning and dissolution reactions monitored continuously with time resolved analysis tra this combination of slow controlled dissolution and tra provides a complete elemental description of contaminant phases and sorts the cleaned calcium carbonate based on dissolution sensitivity examination of partially dissolved shells with electron microscopy suggests that the flow through method simulates the natural dissolution sequence and effectively separates the different calcite domains within a single foraminiferal shell heterogeneity of mg ca in foraminiferal calcite is clearly demonstrated in flow through analysis foraminiferal shells have initially high mg levels that decrease steadily throughout dissolution later dissolution yields lower mg ca which is likely due to a combination of subsurface calcification and biomineralization effects mg ca ratios from the most dissolution sensitive high mg portions of surface dwelling species in core tops are used to calculate calcification temperatures a comparison of late holocene core top data with world ocean atlas sst data indicates that the flow through method does yield viable sst estimates furthermore a depth transect in the eastern tropical pacific suggests that this approach provides the opportunity to extract initial calcification temperatures despite partial dissolution of foraminiferal shells

distinct responses of planktonic foraminiferal b ca to dissolution on seafloor we have measured b ca in four core top planktonic foraminiferal species globigerinoides ruber white globigerinoides sacculifer without final sac like chamber neogloboquadrina dutertrei and pulleniatina obliquiloculata from three depth transects the caribbean sea the southwestern indian ocean and the ontong java plateau to evaluate the effect of dissolution on planktonic foraminiferal b ca at each transect g ruber w and g sacculifer w o sac show decreasing b ca with increasing water depth this decrease in b ca is accompanied with decreases in shell weights mg ca and bottom water calcite saturation state this indicates a postdepositional dissolution effect on b ca in these two species the strong correlation observed between changes in b ca and bottom water calcite saturation state offers an approach to correcting for the dissolution bias by contrast b ca in n dutertrei and p obliquiloculata remains unchanged along depth transects although shell weights and mg ca display significant declines overall our core top results suggest species specific dissolution effects on b ca in different planktonic foraminiferal species

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

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

an intensity ratio calibration method for the accurate determination of mg ca and sr ca of marine carbonates by icp aes an inductively coupled plasma atomic emission spectroscopy icp aes method for the accurate and precise simultaneous measurement of the mg ca and sr ca content of carbonates was established while a precision of 0 3 1 standard deviation sd is easily obtainable for both mg ca and sr ca analysis a ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures an alternative ratio calibration procedure is proposed which overcomes the ca matrix effects and ensures the accuracy of the mg ca and sr ca analysis of marine carbonates to 0 3 almost an order of magnitude better than conventional calibration methods the longer term precision is 0 1 if the batch run average values are corrected for longer term drift the method is suitable for analysis of foraminiferal calcite and coral aragonite and can easily be adjusted for the analysis of other carbonates or microsamples

further constraints on the diagenetic influences and salinity effect on globigerinoides ruber white mg ca thermometry implications in the mediterranean sea we analyzed mg ca ratios of the planktonic species globigerinoides ruber white picked from 49 box core samples covering the whole mediterranean sea and 2 core tops from the atlantic ocean over the entire data set we found no significant correlation between mg ca and 18o derived calcification temperatures this lack of correlation is chiefly due to the presence of an early diagenetic mg rich calcite coating which can constitute up to 20 of the total shell calcite in the central and eastern mediterranean basin and result in anomalously high mg ca values and a high scattering in the western mediterranean sea however g ruber mg ca scattering shows smaller amplitude and mg rich calcite remains under the xrd detection limit sem observations indicate that only a few samples are affected by trace amounts of post mortem calcite overgrowths most of this calcite being likely removed during the chemical cleaning for mg ca analyses using core top sediments from the western mediterranean sea we performed an empirical calibration exercise which confirms that g ruber mg ca is not only related to temperature but it is also significantly affected by sea surface salinity this salinity effect is not specific to high salinity environments such as the mediterranean sea since it appears to be coherent with recent results obtained on indo pacific and atlantic surface sediments which suggest that a 1 psu change in sss results in a 1 7 c mg ca temperature bias this sensitivity to salinity is significantly higher than those deduced from culture experiments

contrast of metamorphic and structural histories across the work channel lineament coast plutonic complex british columbia a prominent topographic lineament along the western margin of the coast plutonic complex of southeast alaska and adjacent parts of british columbia separates terranes of contrasting metamorphic histories where it enters british columbia near prince rupert as the work channel lineament the western terrane preserves a regional medium high pressure metamorphic facies series increasing from chlorite grade in the west to kyanite muscovite migmatite near the lineament the metamorphic structural and age relations of the western terrane are consistent with a model of crustal thickening accompanied by westward transport of higher over lower grade metamorphic units during the jurassic this terrane was uplifted and cooled by cretaceous time 85 ma east of work channel lineament high temperature relatively low pressure assemblages are overprinted onto high pressure assemblages the low pressure metamorphic assemblages developed in the eocene during rapid uplift 2 mm yr of rocks which initially may have been metamorphosed at the same time and along the same pt gradient as those of the western terrane structures along the work channel lineament suggest vertical motion during uplift of the eastern terrane and after metamorphism of the western terrane because the metamorphic discontinuity across the lineament is 3 5 kbar at about 700 the lineament in the prince rupert area marks a major crustal break

u pb geochronology of detrital zircons from a continental margin assemblage in the northern coast mountains southeastern alaska metamorphic rocks within and west of the northern coast mountains in southeastern alaska consist of an upper proterozoic to upper paleozoic continental margin assemblage that we interpret to belong to the yukon tanana terrane u pb geochronologic analyses of single detrital zircon grains from four samples of quartzite suggest that the zircons were shed from source regions containing rocks of 495 ma 750 ma 1 05 1 40 ga 1 75 2 00 ga 2 3 ga 2 5 2 7 ga and 3 0 ga multigrain fractions from two samples yield upper intercepts between 2 0 and 2 3 ga but the scarcity of single grains of similar age suggests that these fractions comprise a mixture of 2 3 ga grains zircons in these rocks generally overlap in age with i detrital zircons in metasedimentary rocks of the yukon tanana terrane in eastern alaska and yukon ii detrital zircons in strata of the cordilleran miogeocline and iii plutonic and gneissic rocks that intrude or are overlain by miogeoclinal strata in addition the p

incorporation and preservation of mg in globigerinoides sacculifer implications for reconstructing the temperature and 18o 16o of seawater using bathymetric transects of surface sediments underlying similar sea surface temperatures but exposed to increasing dissolution we examined the processes which affect the relationship between foraminiferal mg ca and 18o we found that globigerinoides saccculifer calcifies over a relatively large range of water depth and that this is apparent in their mg content on the seafloor foraminiferal mg ca is substantially altered by dissolution with the degree of alteration increasing with water depth selective dissolution of the chamber calcite formed in surface waters shifts the shell s bulk mg ca and 18o toward the chemistries of the secondary crust acquired in colder thermocline waters the magnitude of this shift depends on both the range of temperatures over which the shell calcified and the degree to which it is subsequently dissolved in spite of this shift the initial relationship between mg ca and 18o determined by their temperature dependence is maintained we conclude that paired measurements of 18o and mg ca can be used for reconstructing 18owater though care must be taken to determine where in the water column the reconstruction applies

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

mg ca variation in planktonic foraminifera tests implications for reconstructing palaeo seawater temperature and habitat migration the nature of compositional variability within the tiny calcitic shells tests that are precipitated by planktonic foraminifera has been investigated using laser ablation inductively coupled plasma mass spectrometry la icp ms systematic large and correlated variation of mg ca mn ca ba ca and zn ca but relatively uniform sr ca are observed through the test walls of analysed species globigerinoides sacculifer globigerinoides ruber neogloboquadrina pachyderma and neogloboquadrina dutertrei distinct chamber and chamber wall layer compositions can be resolved within individual tests and mg ca compositional differences observed in sequentially precipitated test components of the different species analysed are consistent with seawater temperature changes occurring with habitat migration during their adult life cycle stages estimated test calcification temperatures are in keeping with available seawater temperature constraints indicating the potential for accurate seawater temperature reconstruction using la icp ms mg rich 1 6 mol mg surface veneers that are also enriched in mn ba and zn have been found on all species and all fossil tests as well as on live sampled tests of g ruber with the latter suggesting a possible biogenic origin these mg rich surfaces bias bulk test compositions toward higher mg ca values by between 5 and 35

variations in mg ca and sr ca ratios of planktonic foraminifera caused by postdepositional dissolution evidence of shallow mg dependent dissolution a comparative study has been made of two species of planktonic foraminifera g tumida and g sacculifer in a depth transect on the ontong java plateau western equatorial pacific g tumida tests from core top sediments showed decreasing mg ca 2 65 1 25 mmol mol and sr ca 1 50 1 16 mmol mol ratios with increasing water depth 1600 4400 m while no such variation was found in g sacculifer tests in excess of 355 m average mg ca 3 6 mmol mol sr ca 1 4 mmol mol artificial dissolution of g tumida tests led to a decrease in both mg ca and sr ca but in g sacculifer there was no significant change in the ratios analyses by electron microprobe revealed that mg ca of the inner chamber calcite in g tumida tests was much higher than that of the calcite crust keel whereas sr ca was only slightly elevated there were no consistent spatial differences in either mg ca or sr ca for g sacculifer tests dissolution in the oceans gives rise to the removal of the chamber calcite in g tumida about 30 of the total calcite leaving the keel calcite although g tumida is thought of as a dissolution resistant form the majority of mg ca and sr ca depletion and chamber loss occurs above the lysocline it is also possible that much of the mg enriched gametogenic calcite has been lost by dissolution from g sacculifer above 1600 m mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera calculations show that the saturation horizon for mg rich parts of tests may be elevated by several hundred meters compared with normal calcite

inside story an x ray computed tomography method for assessing dissolution in the tests of planktonic foraminifera x ray computed tomography ct provides an insight into the progression of dissolution in the tests of planktonic foraminifera four species of foraminifera g ruber white g sacculifer n dutertrei and p obliquiloculata from pacific atlantic and indian ocean core top samples were examined by ct and sem inner chamber walls began to dissolve at co32 values of 12 14 mol kg close to the calcite saturation horizon dissolution and precipitation of calcite may occur simultaneously inner calcite of g sacculifer n dutertrei and p obliquiloculata from such sites appeared altered or replaced whereas outer crust calcite was dense with no pores unlike the other species there was no distinction between inner and outer calcite in ct scans of g ruber empty calcite crusts of n dutertrei and p obliquiloculata were most resistant to dissolution and were present in samples where co32 20 mol kg five stages of preservation were identified in ct scans and an empirical dissolution index xdx was established xdx appears to be insensitive to initial test mass mass loss in response to dissolution was similar between species and sites at 0 4 g mol kg we provide calibrations to estimate co32 and initial test mass from xdx

the tatshenshini shear zone new in southwestern yukon canada comparison with the coast shear zone in british columbia and southeastern alaska and implications regarding the shakwak suture the tatshenshini shear zone extends from klukshu lake in southwestern yukon southward to the yukon british columbia border deformation in the shear zone ranges from hundreds of meters to a few kilometers in width and is characterized by protomylonitic and mylonitic turbidites belonging to the dezadeash formation jurassic cretaceous that are overlain by protomylonitic granodiorite of the ruby range batholith late cretaceous tertiary the dezadeash formation ruby range batholith contact bedding and deformation and magmatic fabrics within the tatshenshini shear zone are all coplanar striking northwest southeast and dipping moderately to the northeast kinematic indicators from the dezadeash formation and ruby range batholith record a top to the southwest sense of shear collision of the insular superterrane with the intermontane superterrane by the mid cretaceous resulted in the eastward directed underplating of yukon tanana terrane equivalent rocks by the dezadeash formation and the formation of the tatshenshini shear zone the tatshenshini shear zone preceded and controlled emplacement of the ruby range batholith but magmatism ending 58 56 myr ago outlasted deformation the results of this work support the correlation of the ruby range batholith with the adjacent great tonalite sill in southeastern alaska it also suggests a linkage between the tatshenshini shear zone and the coast shear zone in southeastern alaska and along which the great tonalite sill was emplaced the tatshenshini shear zone and the coast shear zone represent the coda of long lived tectonism along the shakwak suture the accretionary boundary between the insular and intermontane superterranes

the source of ions for biomineralization in foraminifera and their implications for paleoceanographic proxies the global carbon cycle is strongly perturbed by fossil fuel burning leading to atmospheric co2 increase climatic warming followed by polar ice melting and global sea level rise are predicted due to the greenhouse effect of increasing co2 in the atmosphere houghton et al 1995 the ocean plays a major role in neutralizing the excess co2 because the amount of inorganic carbon available for exchange with the atmosphere in the ocean is approximately 50 60 times larger than in the atmosphere e g siegenthaler and sarmiento 1993 the bulk of the atmospheric co2 excess will eventually be neutralized by caco3 dissolution in the deep marine environment this is however is a relatively slow process that operates on the time scale of ocean circulation 1000 yrs and is therefore causing an accumulation of co2 in the atmosphere this phenomenon will result in potentially severe consequences to the well being of global ecological systems obviously the scientific attention of many biogeochemists is focused on processes controlling the response of the marine system to changes in atmospheric co2 concentrations e g archer and maier reimer 1994 broecker 1997 sigman and boyle 2000 berger 2002 foraminifera corals and coccolithophores in the global carbon cycle there are four dominant processes involved in neutralizing the excess atmospheric co2 in the ocean these are 1 gas exchange at the air sea interface and reaction with the carbonate ion to form bicarbonate 2 net primary productivity 3 caco3 production and dissolution and 4 ocean circulation most of these processes are biologically mediated and may have special importance in shallow tropical environments where the exchange with the atmosphere is more direct in this review we address the mechanism of biomineralization in one of the major groups that precipitates caco3 in the ocean the foraminifera as we will show this group

stresses and plate boundary forces associated with subduction plate margins primary tectonic stress in the lithosphere is predominantly caused by lateral density variations within the earth and associated topographical loading when such a stress system caused by major sublithospheric density anomalies is intersected by a weak zone which cuts across the lithosphere plate boundary forces develop and modify the plate interior stresses in this paper unite element analysis is used to model the stresses and plate boundary forces associated with subduction plate boundaries with dipping and vertical slabs extending to about 270 and 400 km depths having the subduction fault both locked and unlocked in such regions several types of horizontal deviatoric stress may occur including 1 local compression in the trench arc region caused by the dense sinking slab and the associated surface downflexure 2 plate interior tension which occurs when this compression is intersected by a weak subduction fault 3 local tension associated with thickening of the crust at the arc and elsewhere 4 local tension in the back arc region produced by the underlying low density upper mantle and 5 downbending stresses in the subducting slab thermal stresses and transmitted ridge push which are not included in the modelling here a gradient from compression in the forearc to tension in the back arc can be modelled in terms of these stresses when the fault is partially locked it is however the intersection of the local compression 1 by an unlocked or partially locked subduction fault that modifies the plate interior stresses and gives rise to the slab pull and trench suction plate boundary forces the state of stress in the interior of the overriding plate is also crucially influenced by back arc spreading where this occurs plate boundary forces have been evaluated for each of the models it is shown that slab pull and trench suction may be of comparable magnitude

crystallinity of foraminifera shells a proxy to reconstruct past bottom water co3 changes 1 the reconstruction of past changes in bottom water co3 is central to evaluating competing oceanic scenarios that deal with long term variations in atmospheric pco2 in search of a quantitative bottom water co3 proxy we analyzed the variations of calcite crystallinity of planktonic foraminifera globigerinoides ruber shells picked from core top samples along three depth transects ontong java plateau and the northeast margin of irian jaya in the western equatorial pacific and the sierra leone rise in the eastern tropical atlantic the strong empirical relationship between calcite crystallinity inferred from the full width at half maximum fwhm of calcite 104 x ray diffraction peak and bottom water saturation relative to calcite co3 shows that foraminifera calcite crystallinity could be a promising proxy for the reconstruction of upper pleistocene bottom water carbonate ion concentration

protolith relations of the gravina belt and yukon tanana terrane in central southeastern alaska metamorphic rocks west of the coast mountains batholith in central southeastern alaska are divided into the gravina belt taku terrane and newly defined ruth assemblage the ruth assemblage comprises metapelite quartzose metaclastic strata quartzite marble felsic metatuff mafic metavolcanic rocks and orthogneiss depositional and emplacement ages of 367 pm 10 ma and 345 pm 13 ma inferred from discordant u pb zircon analyses on felsic metatuff and granodioritic orthogneiss respectively require that at least portions of the ruth assemblage be late devonian and early mississippian in age the assemblage is similar in age and protolith to and thus correlated with the yukon tanana terrane the gravina belt is characterized by upper jurassic and lower cretaceous mafic volcanic rocks and tuffaceous turbiditic clastic strata that unconformably overlie the alexander terrane metamorphic rocks that structurally underlie the taku terrane and ruth assemblage are included in this assemblage trace

u pb zircon geochronology of lower jurassic and paleozoic stikinian strata and tertiary intrusions northwestern british columbia new u pb zircon ages are reported from western stikinia devonian and pennsylvanian ages of volcanic rocks at oweegee dome confirm the presence of pre permian strata and with paleozoic and triassic detrital zircons from lower jurassic sandstone they help to demonstrate pre lower jurassic deformation and uplift the absence of pre paleozoic inherited zircon from all samples is consistent with nd sr isotopic data which suggest that stikinia consists mainly of juvenile crust u pb ages for posttectonic intrusions suggest that structures in skeena fold belt in the kinskuch area formed prior to eocene time five ages for felsic volcanic rocks from stratigraphically well constrained upper parts of the hazelton arc are approximately 196 199 ma and suggest near contemporaneity for cessation of volcanism in the areas studied the sinemurian or late sinemurian early pliensbachian ages are older than previously reported u pb and biostratigraphic ages for presumed correlative rocks to the west and westward migra

thermochronology in southeast alaska and southwest yukon implications for north american plate response to terrane accretion abstract this study presents the first comprehensive dataset of low temperature thermochronology from 43 bedrock samples collected north of the active yakutat north american plate boundary our apatite and zircon u th he and fission track data reveal the cooling history of the inboard wrangellia composite terrane that is dominated by rapid cooling after late jurassic to early cretaceous arc magmatism followed by very little cooling and exhumation until today deformation resulting in rock exhumation due to the collision of the yakutat microplate is spatially very limited 20 30 km and is concentrated mainly in the chugach prince william terrane and rocks near the border ranges fault focused exhumation from greater depths of ca 10 km with very high rates 5 km myr is localized at the syntaxis region starting ca 10 ma and shifted south through time the rapid exhumation rates are explained by the development of strong feedbacks between tectonically driven surface uplift and erosion which started already before glaciation of the area the shift in the location towards the south is a consequence of continuous readjusting between tectonics and climate which is changing on local and global scales since the late miocene

thermobarometric constraints on the structural evolution of the coast mountains batholith central southeastern alaska thermobarometric data from amphibolite facies metamorphic rocks west of the coast mountains batholith provide important constraints on the structural evolution of the mid cretaceous sumdum fanshaw

ancient continental margin assemblage in the northern coast mountains southeast alaska and northwest canada geologic relations indicate that quartz rich metasedimentary rocks in the northern coast mountains separate strata to the east that belong to the stikine terrane from strata to the west of the alexander wrangellia and taku terranes the quartz rich rocks structurally overlie western terranes along a mid cretaceous thrust fault and are overlain structurally originally stratigraphically by strata of the stikine terrace these rocks are interpreted to be a continental margin assemblage that belongs to the yukon crystalline terrane u pb and nd isotopic data indicate that the metasedimentary rocks were shed from a source terrane consisting at least in part of proterozoic rocks

strain partitioning and batholith emplacement at the root of a transpressive magmatic arc abstract an integrative study of the high pressure ecstall batholith and its country rocks prince rupert area british columbia reveals the interplay of deformation and plutonism produced in the largest cordilleran magmatic arc i e the coast plutonic complex during mid cretaceous convergence between the farallon oceanic plate and north america the results emphasize the interference between three strain fields 1 an early 92 ma crustal wedge produced by orogen perpendicular sw vergent thrusting 2 an orogen parallel sinistral strike slip shear zone active until 87 ma and 3 the lateral expansion of the batholith 93 91 ma against the shear zone the batholith expanded in a direction oblique with respect to the shear zone trend 20 by extruding country rocks against its head in a direction normal to its expansion direction during sinistral strike slip partitioned transpression the batholith s emplacement combined far field batholith boundary normal translation extrusion related rotation and radial and concentric elongation in its structural aureole this case study may typify the process by which a modern magmatic arc grows longitudinally at depth during transpression the direction and sense of growth being determined by the direction of plate motion relative to the magmatic arc and the degree of strike slip partitioning of transpression

105 million years of igneous activity wrangell alaska to prince rupert british columbia the coast mountains orogen which lies along coastal british columbia and southeastern alaska records extensive mesozoic and cenozoic igneous activity here we focus on the two youngest periods 105 50 ma and 30 ma present the history of subduction orogen uplift and finally extension associated with this magmatic activity can be related to plate motion since the mid cretaceous the 105 50 ma period is related to terrane accretion and subduction the northwest southeast trending coast shear zone divides the resulting coast mountains calc alkaline continental margin batholith into a western 105 90 ma and an eastern 80 50 ma arc melting of hydrous mantle overlying a dehydrating slab generated the plutons of the western arc the plutons of the eastern arc show a wider range of compositions their origin consists of mantle melts modified by melts from lower crustal rocks of continental affinity and possibly amphibolitic hydrated basalt in both parts of the arc igneous bodies also resulted from crustal melting these are very abundant in the eastern arc during the younger period bi modal igneous suites consisting of mantle derived mafic magmas and coeval crustal melts are associated with crustal extension and block faulting

a numerical model of the hellenic subduction zone active stress field and sea level changes a 2 d viscoelastic finite element model for subduction in the southern aegean sea allows us to study the distribution of stress and surface velocities in a vertical cross section through the island of crete recent tomographic results constrain the geometry of the slab and the structure of the crust lithosphere and mantle two models are considered the first for passive subduction driven solely by slab pull and the second one where active convergence between the african and aegean plates is also included both models predict subsidence of the hellenic trench and of cretan trough uplift of crete and of the aegean volcanic arc the island of crete is subject to differential uplift highest in the southern part with maximum rates of 1 5 and of 3 2 mm yr for the two models respectively these results agree with the tectonic uplift inferred from holocene sea level changes in the island the style of stress within the modeled african and aegean plates is in general agreement with the focal mechanisms of the largest earthquakes along the subduction zone

structural development of the western metamorphic belt adjacent to the coast plutonic complex southeastern alaska evidence from holkham bay the coast plutonic complex in southeastern alaska and british columbia is bordered on the west by low to medium grade metamorphic rocks of the western metamorphic belt this belt includes intensely deformed rocks underlying a prominent topographic low the coast range megalineament structural data from the northern part of the belt near holkham bay southeastern alaska constrain the shear sense during polyphase deformation tectonite fabrics within the western metamorphic belt record at least three deformational events variation in foliation development fold geometry and metamorphism indicate that deformation was heterogeneously partitioned four tectonic zones can be defined the peninsular coast range megalineament coherent and straight zones the earliest recognized deformation resulted in folding that transposed bedding into a tectonite layering s1 throughout the western metamorphic belt these structures are inferred to have developed during late cretaceous crustal thickening that resulted in moderate to high pressure metamorphism later deformation probably early tertiary resulted in abundant mesoscopic and macroscopic f2 folds of s1 and development of shear bands in the coast range megalineament zone the vergence and variation in plunge of f2 folds are compatible with subvertical east side up displacement across the coast range megalineament zone uplift of the coast plutonic complex shear bands indicate right lateral strike slip motion occurred during the waning stages of metamorphism probably following development of f2 folds brittle faults parallel to the coast range megalineament contain subhorizontal slickensides suggesting additional strike slip movement

strain partitioning in an obliquely convergent orogen plutonism and synorogenic collapse coast mountains batholith british columbia canada 1 we describe the crustal structure of the coast mountains batholith between 54 and 55 n within the canadian cordillera with emphasis on emplacement of the 7 km thick kasiks sill complex ksc kinematic patterns that developed during emplacement of the ksc are the result of interactions between magma transport magma accumulation and regional deformation the sills were emplaced during nw directed normal shearing and flattening of country rocks that host the ksc a 2 km thick shallowly ne dipping mylonite zone cuts the eastern side of the ksc kinematic indicators within the mylonite zone record top to the east normal displacements structural analysis shows that mylonite formation occurred during subvertical shortening and east northeast subhorizontal extension u pb zircon age dates show that ene directed normal shearing along the eastern side of the ksc and wnw directed normal shearing within the ksc occurred contemporaneously between 54 and 51 ma indicating strong strain partitioning between the mylonite and the ksc this pattern of strain partitioning is interpreted to have been driven by return flow of melt laden crust in response to tectonic denudation of the upper crust seismic profiling shows that many of these structures extend to mid and lower crustal depths comparison of our results with other regions within the canadian cordillera indicates that orogen scale right lateral strike slip faults deformed synchronously with wide spread magmatism and formation of extensional gneiss domes thus the crustal structure of the coast mountains batholith was the result of early tertiary batholith construction during dextral oblique convergence and synorogenic collapse

phase transformations in a harzburgite composition to 26 gpa implications for dynamical behaviour of the subducting slab abstract the mineralogy adopted by a depleted harzburgite composition has been studied over the pressure interval 5 26 gpa at temperatures of 1300 1400 c the pyroxene garnet component of the harzburgite composition harzburgite minus 82 wt olivine transforms to majorite garnet by 18 19 gpa and further disproportionates to the assemblage of garnet stishovite mg 2 sio 4 spinel above 20 gpa at still higher pressures first ilmenite 22 24 gpa and then perovskite mgsio 3 24 26 gpa are found to coexist with garnet garnet disappears at 26 gpa and almost complete transition to perovskite is achieved at this pressure the mineral proportions and density profiles in the subducting oceanic lithosphere modelled by a combination of 80 harzburgite 20 primitive morb compositions are calculated as a function of depth under conditions isothermal with surrounding pyrolite mantle and also for a temperature distribution in which the slab is substantially cooler than surrounding mantle to below 700 km under isothermal conditions the slab has a density similar to surrounding mantle to a depth of 600 km however between 600 and 700 km the slab is up to 0 08 g cm 3 denser than surrounding mantle this is caused primarily by the higher alumina content in pyrolite as compared to harzburgite which causes the transition to perovskite in pyrolite to occur at substantially higher pressures than in harzburgite the presence of alumina also smears out the garnet perovskite transition in pyrolite over a depth interval of 50 km whereas this transformation is much sharper in the harzburgite composition calculations based on the observed phase equilibria also show that a subducted cool slab remains much denser by 0 1 0 3 g cm 3 than surrounding mantle to a depth of 700 km but possesses a density similar to surrounding mantle below this depth these results have important implications for the dynamical behaviour of slabs possessing different thermal regimes when they encounter the 670 km discontinuity and also for the nature of this discontinuity

application of lu hf garnet dating to unravel the relationships between deformation metamorphism and plutonism an example from the prince rupert area british columbia abstract the tectonic history of the prince rupert area is marked by profound crustal thickening from thrusting that produced inverted metamorphic field gradients and transpression in crustal scale shear zones syn tectonic garnet in the prince rupert area has lu hf ages of 102 6 3 7 ma and 108 3 4 1 ma 2 porphyroblast matrix relationships in these samples and samples from the same outcrops indicate syn tectonic garnet growth these relationships imply that the garnet ages directly date the development of the metamorphic foliations a third sample of migmatitic garnet amphibolite from the contact aureole of the 94 90 ma ecstall pluton had complex isotope systematics interpreted to indicate a garnet growth episode 105 ma similar to the ages obtained from the other samples and a growth or equilibration event at 94 ma during pluton emplacement the data show that the older lu hf garnet ages date prograde metamorphism during foliation development and modification during pluton emplacement the ecstall pluton was emplaced 10 to 15 m y after regional metamorphism and thrust stacking in the prince rupert area in order to place our samples in a regional tectonic context we compare our results to patterns of regional deformation metamorphism and plutonism throughout the north american cordillera in the time period between 110 and 85 ma contractional and transpressional deformation occurred throughout much of the north american cordillera at this time from southeastern alaska to the baja peninsula in mexico left lateral transpression dominated the canadian cordillera whereas right lateral transpression affected areas south of the idaho salmon river suture zone including the sierra nevada batholith this reversal in kinematics in the northern and southern cordillera within coeval magmatic belts appears to be a first order feature of the geology of the north american cordillera during the cretaceous

u pb geochronology of late cretaceous and early tertiary plutons in the northern coast mountains batholith u pb geochronologic studies demonstrate that steeply dipping sheetlike tonalitic plutons along the western margin of the northern coast mountains batholith were emplaced between 83 and 57 perhaps 55 ma less elongate tonalitic granodioritic bodies in central portions of the batholith yield ages of 59 58 ma coeval with younger phases of the tonalitic sheets large granite granodiorite bodies in central and eastern portions of the batholith were emplaced at 51 48 ma trends in ages suggest that the tonalitic bodies generally become younger southeastward and that at the latitude of juneau plutonism migrated northeastward across the batholith at 0 9 km ma variations in the age shape location and degree of fabric development among the various plutons indicate that late cretaceous paleocene tonalitic bodies were emplaced into a steeply dipping dip slip shear zone that was active along the western margin of the batholith postkinematic eocene plutons were emplaced at shallow crustal levels inhe

structural and geochronologic relations along the western flank of the coast mountains batholith stikine river to cape fanshaw central southeastern alaska abstract geologic and u pb geochronologic studies in central southeastern alaska provide constraints on the mid cretaceous to mid tertiary deformation west of the coast mountains batholith the ne dipping sumdum and fanshaw faults record the w directed emplacement of the ruth assemblage yukon tanana terrane and taku terrane over the subjacent gravina belt and alexander terrane ductile fabrics of the sumdum fanshaw fault system truncate early formed foliation and thrust faults in albian and older gravina belt strata u pb age data from syn and post tectonic plutons suggest that deformation was ongoing at 92 9 3 0 ma but had mostly ceased by 90 ma the sumdum fanshaw fault system marks the tectonic boundary between the alexander wrangellia terrane and inboard yukon tanana and stikine terranes and lies within a thrust belt that extends from southern alaska to northern washington mid cretaceous structures are truncated to the east by ne dipping ductile fabrics of the coast shear zone sheet like paleocene tonalites were emplaced into and deformed within the shear zone undeformed mid eocene dikes cross cut the tonalites kinematic relations in the coast shear zone suggest a complex displacement history that includes both east side up reverse and west side up normal shear the shear zone probably accommodated the collapse of overthickened crust developed during mid cretaceous shortening

influence of test size water depth and ecology on mg ca sr ca δ18o and δ13c in nine modern species of planktic foraminifers abstract mg ca palaeothermometry in foraminiferal calcite is a widely applied tool in palaeoceanography however our understanding of the effects of planktic foraminiferal ecology and early diagenesis on test calcite mg ca is limited here we report results of a study designed to shed new light on ecological size related and very early water column diagenetic controls on mg ca in planktic foraminiferal calcite we analysed mg ca and stable isotopes of nine modern planktic foraminiferal species across fourteen mostly 50 m window sieve fractions in a core top sample from the north atlantic ocean we also analysed mg ca in four of these nine species from plankton tow samples collected from 0 to 2500 m water depth in the north atlantic ocean and arabian sea our core top study confirms that sensitivity of mg ca to change in test size is species specific but reveals an overall decrease in mg ca with increasing test size in all but one species orbulina universa for which mg ca increases with size these findings are broadly consistent with known ecological behaviour suggesting that the size related signal is largely environmentally rather than calcification rate controlled our results underscore the need to undertake mg ca palaeothermometry on narrow size fractions of planktic foraminifers particularly for shallow dwelling species such as g bulloides and g ruber where mg ca is most sensitive to test size across the size range of 200 350 m our plankton tow data from the arabian sea are in agreement with in situ temperatures in contrast our data from the north atlantic ocean reveal large variability and marked offsets to warmer values from in situ temperatures that are interpreted to reflect lateral advection from the south storm induced vertical mixing of the water column and or the influence of surface water salinity on the mg ca signal none of our plankton tow mg ca data shows any evidence of test dissolution in the water column our study provides important verification that the mg ca signal recorded during calcification does not undergo diagenetic degradation during test transport to the sea floor thereby satisfying an important precondition of its palaeo proxy utility

geology of the western flank of the coast mountains between cape fanshaw and taku inlet southeastern alaska the western flank of the coast mountains batholith between cape fanshaw and taku inlet is underlain primarily by jura cretaceous strata of the gravina belt pre permian permian and triassic strata of the taku terrane and mid proterozoic to upper paleozoic rocks of continental margin affinity the continental margin rocks include mid proterozoic to lower paleozoic quartzite and marble of the tracy arm assemblage mid paleozoic metavolcanic and subordinate metasedimentary rocks of the endicott arm assemblage and upper paleozoic quartz rich metaturbidites and metaconglomerate of the port houghton assemblage we suggest that these three assemblages are correlative with components of the yukon tanana terrane which underlies a large region of yukon and eastern alaska rocks of the gravina belt taku terrane and yukon tanana terrane are juxtaposed along west vergent thrust faults of mid cretaceous age and are internally deformed and disrupted along latest cretaceous to early eocene dip slip and possibly strike slip shear zones these rocks and structures together with mid cretaceous to eocene plutons of the coast mountains batholith separate rocks of the alexander wrangellia terrane to the west from rocks of the stikine terrane to the east mid cretaceous thrust faults in the area belong to a system of thrusts that form the inboard margin of the alexander wrangellia terrane from central alaska to northwestern washington the continental margin rocks in the northern coast mountains may be part of the in situ north american margin that has been overthrust by the stikine and adjacent terranes alternatively these rocks may have 1 rifted from and then returned to the north american margin 2 moved 800 km along left lateral or right lateral faults from elsewhere along the north american margin or 3 originated near a continent other than north america

eocene 51 ma end to northward translation of the coast plutonic complex paleomagnetism and k ar dating of the white pass dikes abstract the white pass mafic dikes are located in the coast belt inboard of the coast shear zone denali fault system east of skagway alaska astride the alaska british columbia border the dikes intrude eocene felsic plutons in the coast plutonic complex three k ar analyses date the dikes at 51 9 0 8 ma biotite 50 1 1 0 ma and 45 0 0 8 ma both whole rock structural analysis on these vertical dikes indicates that the study area has not been tilted significantly since dike emplacement conventional alternating field and thermal step demagnetization and saturation remanence paleomagnetic methods were used to analyse 407 specimens from 27 dike and five host rock sites three contact tests show that the specimens retain a primary thermoremanent magnetization trm carried in pseudosingle to multidomain magnetite although some magnetization in a few dikes is carried by pyrrhotite the dual polarity trm is mostly reversed and the 24 accepted dike sites give a pole position of 245 7 e 76 3 n dp 4 2 dm 4 4 indicating a paleolatitude discordance of 8 4 south and a clockwise rotation of 40 9 with respect to the north american craton these data along with other paleomagnetic data on eocene rocks indicate that the allochthonous eastern coast and intermontane belt terranes had halted their northward translation by about 51 ma but continued to be rotated clockwise by an average of 24 10 thereafter probably on underlying sole faults

reply to comment by m e beck and b a housen on paleomagnetism and geochronology of the ecstall pluton in the coast mountains of british columbia evidence for local deformation rather than large scale transport

field geochemical and isotopic evidence for magma mixing and assimilation and fractional crystallization processes in the quottoon igneous complex northwestern british columbia and southeastern alaska the quartz dioritic quottoon igneous complex qic is a major paleogene 65 56 ma magmatic body in northwestern british columbia and southeastern alaska that was emplaced along the coast shear zon

resolving high precision u pb ages from tertiary plutons with complex zircon systematics success in establishing high precision crystallization ages with the u pb zircon method is highly dependent on the ability to isolate or remove the effects of inherited xenocrystic components or secondary lead loss or the combined effects of both current conventional single crystal and ion probe shrimp methods are successfully applied to paleozoic and older samples but typically suffer from imprecision when applied to younger mesozoic cenozoic samples due to generally reduced radiogenic lead concentrations here we apply a series of intense partial dissolution steps to multigrain zircon fractions from a series of paleocene tonalitic to granodioritic intrusive rocks from southeastern alaska the zircon systematics are complicated by both minor inheritance and postcrystallization lead loss physical and isotopic evidence demonstrate that the partial dissolution steps preferentially remove outer layers susceptible to lead loss as well as core regions containing inherited components the final residues are often hollow shells of low u primary igneous zircon that yield highly precise reproducible and concordant ages the resulting age determinations commonly statistically differ at the 95 confidence level from ages based on apparently concordant but less precise conventional isotope dilution analyses the uncertainties of which masked minor subtle isotopic complexities this observation strongly cautions against basing age assignments of samples yielding slightly discordant data on 1 single concordant analyses accompanied by an array of discordant data or 2 the mean of several 206pb 238u or 207pb 206pb ages the step wise dissolution technique allows age determinations on young relatively low u and pb zircons at a resolution not currently possible with techniques such as single grain conventional or spot ion probe analyses widespread application of the technique will likely prove instrumental in resolving detailed magmatic histories of igneous complexes where zircon systematics are typically complex

two phase evolution of accretionary margins examples from the north american cordillera abstract the coast mountains orogen southeastern alaska and the salmon river suture zone western idaho record the accretion of oceanic crustal fragments to the north american cordilleran margin structural elements associated with these boundaries include a western accretion related thrust belt and steeply dipping post accretionary shear zone the shear zones the coast shear zone southeastern alaska and western idaho shear zone idaho are steeply dipping crustal scale structures characterized by steep isotopic and geophysical gradients the presence of syndeformational tabular calc alkaline tonalitic plutons concordant with shear zone fabrics locally preserved dextral strike slip indicators and pervasive down dip mineral and elongation lineations are consistent with an intra arc transpressional origin for both structures in addition to strike slip translation the structures accommodated exhumation of high pressure moderate temperature metamorphic rocks within the thrust belt to the west and moderate pressure high temperature batholithic rocks to the east similarities between the structures in alaska and idaho suggest that the observed two stage history of underthrusting of accreting crustal fragments followed by modification by intra arc transpressional shear zones is a common tectonic process our analysis implies that recognition of processes active during the accretion of crustal fragments to continental or cratonal margins is commonly inhibited by post accretion deformation and provides insight into lower crustal processes presently operative under modern strike slip accretionary boundaries in addition the intra arc transpressional shear zones e g the coast and western idaho shear zones are structures that could have accommodated paleomagnetically determined large magnitude transcurrent displacements

diagenetic mg rich calcite in mediterranean sediments quantification and impact on foraminiferal mg ca thermometry abstract mg ca ratios in planktonic foraminifera have been developed into a powerful tool in paleoceanography to reconstruct past sea surface temperatures sst however additional factors that might have an influence on mg ca like dissolution salinity diagenesis and carbonate ion effects have come into focus in this paper the occurrence of diagenetic calcification and its potential effects on mg ca have been studied using 20 well preserved core tops recovered from the mediterranean sea analyses were performed on two planktonic foraminifer species globigerinoides ruber and globigerina bulloides using icp aes mg ca measurements sem observations and x ray diffractometry analyses foraminiferal mg ca values are higher than those obtained in the open sea the highest values were found in the eastern mediterranean basin these anomalies cannot be simply explained by a salinity effect because mg ca ratios when corrected for temperature influence do not display any significant correlation with salinity our results seem to indicate that diagenesis can account for anomalously high mg ca values indeed sem observations show aggregates of rhombohedral crystals that could be interpreted as secondary calcite overgrowths we note also the occurrence of numerous coccoliths trapped in foraminifer walls and covered with a secondary mineral phase x ray diffraction diagrams of numerous foraminiferal samples exhibit peak of mg rich calcite 10 12 associated with the usual foraminifer calcite peak it has been demonstrated that this calcite highly rich in mg is compatible with an inorganic calcite precipitated directly from seawater the deconvolution of the main xrd peak 104 shows that the percentage of mg rich calcite can reach up to 21 of the total foraminiferal calcite in the eastern basin whereas in the western mediterranean sea proportions do not exceed 5 in addition we demonstrate that the diagenetic process is very heterogeneous even at the sample scale and is not simply a reflection of co 3 at the sea bottom thus the high mg ca ratios measured from mediterranean sea planktonic foraminifera does not appear to be caused by increased mg uptake in a high salinity setting but instead result chiefly from the presence of mg rich calcite 10 12 deposited during early diagenetic processes

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

the role of subduction on the horizontal motions in the tyrrhenian basin a numerical model the horizontal motions in the tyrrhenian basin and surrounding chains induced by subduction along the calabrian arc and northern apennines are analyzed by means of numerical models based on finite element techniques the driving mechanism in 2 dimensional vertical cross sections perpendicular to the trench is the slab pull due to the negative buoyancy of a stratified viscoelastic plate that models the ionic oceanic lithosphere or adriatic plate sinking in the upper mantle for the modern tectonic setting of the area we test the sensitivity of extension in the back arc and of roll back of the overriding plate to variations in the viscosity structure and in the geometry of subduction our results are compared with extensional velocities inferred from geology and slr vlbi data

dissolution effects on the crystallography and mg ca content of planktonic foraminifera globorotalia tumida rotaliina revealed by x ray diffractometry several authors suggested that the thinning with increasing depth of deposition of calcite x ray diffractometry xrd peaks obtained on planktonic foraminifera tests resulted from the preferential removal of their poorly crystallized parts as dissolution increases by deconvolving xrd peak 104 from globorotalia tumida surface sediments sierra leone rise depth transect we show that the full width at midheight does not depend only upon crystallinity but reflects also the chemical and structural heterogeneity of foraminifera tests which results in closely spaced individual 104 diffraction peaks corresponding to phases with slightly different mg contents g tumida contains two calcite phases a well crystallized mg poor calcite and a poorly crystallized mg richer calcite increasing dissolution results in the preferential removal of the mg richer calcite and the improvement of its crystallinity whereas the mg poor calcite does not seem to be affected by dissolution between 2750 m and 4950 m of water depth on sierra leone rise

exhumation and tilting of the western metamorphic belt of the coast orogen in southern southeastern alaska the uplift history of the western metamorphic belt in southern southeastern alaska can be traced using emplacement depths and cooling ages of mid cretaceous plutons which intruded the metamorphic belt during the period 101 ma to 89 ma during the period 101 ma to 94 ma the rocks of the metamorphic belt now at the surface were buried to a depth of approximately 30 km pressure data indicate that by 89 ma the western portion of the metamorphic belt was at a shallower crustal level 23 km within the study area while the eastern side remained at a depth of approximately 30 km cooling curves constructed from minerals in mid cretaceous plutonic rocks indicate that the western side of the metamorphic belt cooled earlier than the eastern side an observation consistent with the inferred uplift history southwestward transport of metamorphic belt rocks within the hanging walls of thrust and high angle faults may have provided one mechanism for uplift during mid to late cretaceous time the eastern portion of the western metamorphic belt cooled rapidly at 55 ma probably in response to a period of rapid uplift the coast shear zone an early tertiary high angle fault with west side up displacement bounds the east side of the metamorphic belt we suggest tertiary uplift occurred by tilting of the metamorphic belt due to movement along this fault

eocene rotation of the coast plutonic complex and intermontane belt paleomagnetism of eocene plutons along the klondike highway paleomagnetic results are reported for the 59 ma skagway 54 ma fraser 53 ma summit lake and 48 ma clifton felsic plutons of the eastern coast plutonic complex cpc that outcrop along the south klondike highway in alaska and british columbia thermal and alternating field step demagnetizing methods yielded stable characteristic remanent magnetization chrm directions for all 29 sites of normal reversed and mixed polarity the chrm resides in single or pseudosingle domain magnetite and or pyrrhotite that is shown to be primary by contact tests with the 47 ma vertical white pass mafic dikes paleopoles from six 56 to 50 ma mean 52 2 ma intermontane belt yukon tanana terrane imb ytt units that cannot be explained by tectonic tilt are compared with nine clustered 59 to 46 ma mean 52 4 ma eastern cpc paleopoles both paleopole populations show nonsignificant poleward northward translation relative to north america imb ytt 3 7 5 3 n cpc 4 3 6 4 s overall 1 2 4 9 s ind

batholith emplacement at mid crustal levels and its exhumation within an obliquely convergent margin abstract emplacement of the central part of the coast mountains batholith of northern coastal british columbia occurred within a regime characterized by oblique convergence between the farallon kula and north american plates we use new structural kinematic and u pb isotopic data to show that the locations geometry and mechanisms of pluton emplacement within this batholith were controlled by displacements within a network of normal faults and transtensional shear zones these data also show that the most active period of pluton emplacement from 67 to 51 ma coincided with a change in style of deformation within the batholith prior to 67 ma plutons were emplaced within an arc dominated by regional scale contractional shear zones in contrast emplacement of 67 51 ma plutons occurred in an arc increasingly dominated by normal faults with arc parallel to oblique displacement and by sinistral transtensional shear zones we have identified and mapped the structure of three plutonic complexes composed of 67 to 51 ma plutons the khyex sill complex arden lake plutonic complex and quottoon plutonic complex shear zone controlled emplacement of plutons within the batholith accounts for the widely different orientations and structural features that characterize plutons within these three complexes during and after this latest cretaceous paleogene period of intense plutonic activity and accompanying deformation the deep roots of the batholith were rapidly unroofed by ductile normal faulting prior to 50 ma

40ar 39ar constraints on the emplacement uplift and cooling of the coast plutonic complex sill southeastern alaska a 700 km long and 5 to 15 km wide aggregation of sill like tertiary plutons separates low to medium grade greenschist to amphibolite facies metamorphic rocks to the west from medium to high grade upper amphibolite to granulite facies gneisses and granitic plutons to the east along the western boundary of the coast plutonic complex in southeastern alaska and british columbia 40ar 39ar analyses of hornblende biotite and plagioclase samples from a sea level traverse and a 1 to 2 km elevation traverse across one of the sills near holkham bay southeastern alaska yield dates that vary systematically with position samples collected on the eastern margin of the sill are 3 to 6 m y younger than samples of the same mineral collected at the same elevation from the western margin of the sill indicating that the western margin cooled earlier samples collected at sea level yield 40ar 39ar dates on hornblende biotite and plagioclase that are consistently younger than those collected at 1 and 2 km elevation dates from the center and eastern margin of the sill define isotherm migration rates km m y of 0 8 1 3 at 60 56 ma hornblende 0 8 0 6 at 56 53 ma biotite and 0 4 at 54 50 ma plagioclase 40ar 39ar dates from a single sea level sample collected 15 km farther south indicate no significant variation in dates parallel to the southeasterly strike of the sill for at least 30 km the younger dates calculated for the east side relative to the west side and metamorphic temperatures suggest that the country rock was hotter to the east than to the west when the pluton cooled through mineral blocking temperatures the rapid isotherm migration rates calculated from the vertically distributed samples and the suggestion of hotter country rock to the east during cooling is consistent with an interpretation that the pluton intruded during uplift of the rocks to the east because the relative precision of the 40ar 39ar technique is sufficient to detect subtle difference in the cooling ages its application to spatially distributed samples within a homogeneous plutonic body as in this study may yield new insights into the timing of metamorphism magmatism and tectonism of young mountain belts

large scale transpressive shear zone patterns and displacements within magmatic arcs the coast plutonic complex british columbia the coast plutonic complex is the largest magmatic arc of the north american cordillera extending from northwestern washington state to eastern alaska it forms the transition between two tectonic domains that are suspected to have undergone several phases of large several thousands of kilometers orogen parallel displacement during the mesozoic and early cenozoic a compilation of fabric data published isotopic ages and new structural observations shows that the western coast plutonic complex was affected by subvertical orogen parallel crustal scale shear zones these shear zones mainly reflect sinistral transpression and were sequentially active from 110 to 87 ma during the intrusion of voluminous batholiths sinistral shearing was roughly coeval with the development of the thrust belts flanking the coast plutonic complex between 101 and 85 ma suggesting plate scale transpression was a first order process in the construction of the coast mountains orogen these shear zones separate panels with distinct plutonic and cooling histories suggesting the sinistral displacements between crustal blocks were large greater than tens to hundreds of kilometers this transpressive shear system likely reflects the jurassic to early late cretaceous migration of outboard cordilleran terranes to the south suggested by paleomagnetic evidence and plate reconstruction models this example from the coast orogen shows how transpression is partitioned between a thermally weakened magmatic arc and outwardly vergent fold and thrust belts our analysis further shows that the 2000 km long late cretaceous to early tertiary coast shear zone has a minimum extent toward the south to at least 51 30 n

nd isotopic characterization of metamorphic rocks in the coast mountains alaskan and canadian cordillera ancient crust bounded by juvenile terranes nd isotopic data are reported for 52 samples from the crustal region between the alexander wrangellia terrane and the stikine terrane of the alaskan and canadian cordillera this region is composed of the gravina belt a jurassic cretaceous assemblage of volcanic and clastic sedimentary rocks the taku terrane a terrane of probable early permian to late triassic age and four assemblages of metamorphic rocks that occur to the west of and within the coast mountains batholith the gravina belt has end t values that range from 1 1 to 8 3 similar to values of the underlying alexander terrane and consistent with the interpretation that it is a juvenile belt that formed in a back arc or intra arc basin within the alexander terrane mid cretaceous plutons that were emplaced into the gravina belt have end t values of 4 4 to 5 7 and were probably produced by mantle derived melts that incorporated some alexander terrane crust the taku terrane has end 0 values that range from 5 5 to 3 3 with corresponding depleted mantle model tdm ages of 440 to 1430 ma a mid cretaceous pluton intruding the taku terrane has an end t value of 5 1 a value indistinguishable from those determined for cretaceous plutons intruding the gravina belt metamorphic rocks east of and structurally overlying the taku terrane are divided into the tracy arm assemblage end 0 26 to 0 tdm 800 2450 ma the endicott arm assemblage end 0 10 to 1 3 tdm 950 1500 ma the port houghton assemblage end 0 9 4 to 1 1 tdm 550 1500 ma and the ruth assemblage end 0 9 4 to 2 0 tdm 650 1300 ma these isotopic signatures indicate that a substantial component of each metamorphic assemblage was derived from precambrian continental crust the metamorphic rocks from these assemblages are lithologically very similar to rocks of the yukon tanana ytt terrane of eastern alaska and yukon territory and have such similar u pb detrital zircon ages and nd isotopic compositions to ytt rocks that they are considered part of that terrane possible tectonic scenarios that can explain the present geometry of the ytt with respect to the alexander wrangellia and stikine terranes include 1 the ytt is the upturned stratigraphic basement of the stikine terrane 2 part of the ytt was structurally emplaced beside the stikine terrane in a transpressive tectonic regime 3 the stikine terrane and other inboard terranes are huge sheets that were thrust over the margin of the ytt before the final accretion of the alexander wrangellia terrane