metamorphic evidence for tilt of the spuzzum pluton diminished basis for the baja british columbia concept to address the question of tilt versus translation as the mechanism responsible for discordance between paleomagnetic directions of cretaceous plutons in the british columbia coast plutonic complex and the north american reference direction metamorphic pressures around the margin of the spuzzum pluton have been determined pressures are derived from microprobe analyses and evaluation of exchange equilibria in the assemblage garnet biotite plagioclase aluminum silicate quartz samples studied come from eight localities in the contact aureole around the pluton and encompass the area of a previous paleomagnetic study the analyzed samples are coarse grained and exhibit textural features indicative of equilibrium crystallization following emplacement of the spuzzum pluton results of this study indicate a complicated tilt history for the spuzzum pluton with tilt first to the northeast then to the southwest the southwest tilt can fully explain the discordance of the paleomagnetic direction in the spuzzum but does not preclude translation however in view of the tilt history of this pluton the paleomagnetic data derived from it should not be used in an analysis of north south translation

regional tilt of the mount stuart batholith washington determined using aluminum in hornblende barometry implications for northward translation of baja british columbia we have developed a new quantitative method to estimate paleohorizontal in granitic plutons using the aluminum in hornblende ah barometer the method is used to correct previously published paleomagnetic data from the 93 96 ma mount stuart batholith of the cascades mountains washington state for the effects of postemplacement tilting ah barometry was done on 46 samples from the batholith using the compositions of hornblende rims coexisting with the full mineral assemblage required for pressureestimation high contrastback scatteredelectronimagingwas usedtoensurethattheanalyzedhornblendeswerenotsignificantly affected by subsolidus alteration the success of the ah barometry is indicated by two observations first increases in the al content of the hornblendes are governed almost entirely by a pressure sensitive tschermak type substitution second amphibole plagioclase thermometry indicates that assemblage equilibration occurred at or very near magmatic conditions 650 c and that temperature has a negligible effect on our pressure estimates ah barometry results indicate that the depth of crystallization across the batholith decreases systematically from 0 3 gpa in the northwest to 0 15 gpa in the southeast consistentwithindependentbarometryforthecontactaureole ofthebatholithandregionalstructuralandstratigraphicrelations using a best fit planar tilt model and bootstrap analysis of uncertainties we estimate that the paleohorizontal plane has a strike of 43 630 4 and dip of 7 62 0 southeast 695 confidence our estimated paleohorizontal allows us to restore the paleomagnetic data of beck et al 1981 and to estimate the original paleolatitude of the mount stuart batholith beck et al found that the southern part of the batholith yielded a number of sites with a well defined high coercivity remanence the carrier of this remanence was not resolved but the following four lines of evidence stronglysuggestthatthepublisheddirectionswereacquiredshortly after emplacement of the batholith 1 the stable sites all came from the shallowest and most rapidly cooled portions of the batholith as indicated by our ah results and concordant k ar ages for hornblende biotite pairs 2 the high coercivity component was always normal in polarity which is consistent with emplacement of the mount stuart batholith at the end of the cretaceous long normal 3 sites from the batholith and the contact aureole gave similar directions 4 the directions show no indication of tilt related smearing after restoration the paleomagnetic data indicate 42 6 11 clockwise rotation and 3100 6 600 km of northward offset

upper limit of docking time for stikinia and terrane i paleomagnetic evidence from the eocene ootsa lake group british columbia the middle eocene ootsa lake group is exposed in the central portion of the stikine terrane where it was sampled along the shoreline of tahtsa reach and whitesail reach the group consists of dominantly subaerial flows which range in composition from basalt to rhyolite that unconformably overly the jurassic hazelton group detailed alternating field and thermal stepwise demagnetizations were done on all specimens from the 21 sites collected the presence of a normal and reversed polarity remanence a positive fold test and high coercivities and unblocking temperatures indicate that a prefolding primary remanence has been isolated the mean tilt corrected direction of d 002 2 i 69 2 95 7 4 from 13 sites for which paleohorizontal is well known yields a pole position at 354 6 e 88 0 n a95 11 5 which is statistically indistinguishable from published 50 ma reference poles for cratonic north america this evidence demonstrates that the proposed large scale northward displacement of stik

new geophysical data from the northern cordillera preliminary interpretations and implications for the tectonics and deep geology in this paper we analyze recently acquired geophysical data from the northern cordillera and their relation to the mapped geology a prominent gravity high 45 mgal 1 gal 1 cm s 2 coincides with a magnetic low and an aseismic region in west central yukon where the underlying geology is dominated by quartzo feldspathic rocks having moderate densities extension 15 magmatic underplating and accretion of the anomalous region onto oceanic crust are three possible explanations magnetic gravity and seismicity data all show significant differences in the physical state of the crust on either side of the tintina fault and together with geological data indicating large offset suggest it was once a major crustal scale strike slip fault the new gravity data also delineate an arcuate zone of steep gradients up to 1 4 mgal km in the miogeocline which may correlate with a west dipping proterozoic basement ramp mapped on deep seismic sections farther to the north and a transition from thin east to thick sediment cover west seismicity data show that current tectonic activity is concentrated along the pacific north america plate margin in southwestern yukon and adjacent alaska and although there is a marked decrease in activity inland of this margin notable concentrations occur along the denali fault system and in the eastern miogeocline there is a distinct absence of earthquakes in parts of the selwyn basin and in the northern yukon tanana terrane limited field studies suggest activity is confined to the upper 10 15 km of the crust

northward motion of the whitehorse trough paleomagnetic evidence from the upper cretaceous carmacks group reply the upper cretaceous carmacks group 70 4 2 4 ma comprises gently dipping basaltic and andesitic lava flows overlying volcaniclastic deposits of the intermontane belt in the whitehorse trough the sampling area is in southern yukon and northern british columbia it lies west of the tintina northern rocky mountain trench fault and teslin suture zone and east of the denali shakwak fault volcanic sections were sampled in three regions spread over 300 km providing the first paleomagnetic data from pre tertiary volcanic rocks in the northern canadian cordillera alternating field and thermal demagnetization revealed stable magnetization for 18 of the 27 sites collected the overall mean direction d 166 7 i 71 4 k 53 95 4 8 n 18 sites is pre folding and is most probably primary latest cretaceous this gives a paleopole at 109 4 e 82 1 n k 21 a95 7 8 a critical evaluation of north american cratonic data yields a reference paleopole for the latest cretaceous at 185 8 e 77

separating multidomain and single domain like remanences in pseudo single domain magnetites 215 540 nm by low temperature demagnetization it has long been hypothesized that the pseudo single domain properties of submicron magnetites are a result of coexisting multidomain and single domain like remanences we have separated these two types of remanence by low temperature demagnetization ltd in which samples are cooled through the low temperature magnetite isotropic point and rewarmed to room temperature all in zero field at the isotropic point the first crystalline anisotropy constant vanishes and multidomain remanence due to displaced domain walls will be unpinned we measured stepwise alternating field af and thermal demagnetization curves of weak field thermoremanent magnetization trm and anhysteretic remanent magnetization and of saturation isothermal remanent magnetization irms both with and without prior ltd for magnetites with mean particle sizes of 215 390 and 540 nm the memory fraction of remanence recovered after ltd which represents the single domain like component decreased from 44 for 215 nm grains to 23 for 540 nm grains in the case of irms memory of trm was approximately twice as large af decay curves were soft and multidomain like before ltd but became harder and single domain like in shape after ltd ltd removed most low unblocking temperature trm and irms distributed low unblocking temperatures are therefore a multidomain phenomenon probably resulting from successive adjustments of domain walls to changing internal fields and pinning strengths during heating

post triassic para autochthoneity of the yukon tanana terrane paleomagnetism of the early cretaceous quiet lake batholith

paleomagnetism of the spences bridge group and northward displacement of the intermontane belt british columbia a second look the spences bridge group is a mid cretaceous 104 ma volcanic succession in the southern intermontane belt of the canadian cordillera 50 5 n 121 w it comprises the pimainus formation mafic to felsic lava volcaniclastic and interbedded epiclastic rocks and the overlying spius formation andesitic lava flows including previous work we have 55 sites distributed among 15 localities representing most of the 3000 m thickness forty seven sites 286 oriented cores 457 specimens mainly andesites yielded acceptable data the beds are gently to moderately tilted partly due to synvolcanic deformation samples taken from a sequence of flows at any one locality have with one exception well grouped magnetization directions polarities are all normal as expected for rocks laid down in the cretaceous normal superchron declinations always are clockwise of that expected of cratonic north america indicating 60 rotation of the spences bridge group as a whole however declinations differ from locality to locality implying relative interlocality rotations about vertical axes hence inclination only analysis has been used to estimate dispersion mean inclination and paleolatitude minimum dispersion for the spius formation 27 sites was achieved after 80 untilting but the changes between 80 and 100 untilting are insignificant indicating that magnetization was acquired predominantly before tilting by contrast minimum dispersion for the pimainus formation 20 sites was achieved after 50 untilting indicating that magnetization was acquired after synvolcanic tilting when buried beneath the overlying spius formation polished thin section studies show that magnetite in the pimainus formation has undergone extensive low temperature hydrothermal alteration whereas magnetite in the spius formation shows little alteration throughout the range of tilt correction from 0 to 100 the mean inclinations of both formations were less than expected from observations obtained from mid cretaceous rocks of cratonic north america the best estimate of paleolatitude from the spius formation is 50 8 5 0 p 0 05 which is 9 5 5 7 less than would be expected had the rocks had been rigidly attached to north america this corresponds to displacement from the south of 1100 600 km displacement between the northern intermontane belt and craton probably was accommodated along major strike slip faults northern rocky mountain trench finlay pinchi etc in the south our results require a major dextral fault the intra quesnellia fault to be situated during late cretaceous or paleocene time within or marginal to the omineca belt along which about 1000 km of dextral motion occurred this could be a southern extension of the pinchi fault whose trace is now obscured by eocene extension and tectonic denudation the results also indicate that the largest tectonic discontinuity in the canadian cordillera occurs not to the east of the intermontane belt as commonly assumed but to the west because the displacements relative to cratonic north america observed from the intermontane belt are only about one third of those observed from the coast belt

角閃石中のアルミニウム圧力計を使って決定された ワシントン州 stuart山バソリスの広域的傾動 バハ ブリティシュコロンビアの北方への転移に関する意味

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

extraordinary sediment delivery and rapid geomorphic response following the 2008 2009 eruption of chaiten volcano chile u s geological survey volcano science center sernageomin s programa de riesgos volcanicos conicyt fondecyt grants 1110609 1141064 11130671 conicyt fondap 15090013 vamos research centre

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

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

the big flush paleomagnetic signature of a 70 ma regional hydrothermal event in displaced rocks of the northern canadian cordillera the 70 ma carmacks group a subaerial volcanic succession which once covered much of central southwest yukon has a paleomagnetic remanent direction which passes the fold test and the reversal test a new collection of 13 sites combined with 13 sites from a previous study renders a pole 088 6 e 78 4 n a95 7 8 which is far sided with respect to the pole for cratonic north america and implies a displacement from the south of 1900 700 km late triassic mandanna member red beds and early jurassic nordenskild formation tuffs deformed in the late jurassic fail the fold test and conglomerate test but pass a contact test with eocene dykes the postdeformational remanent direction is identical to that isolated from the carmacks group the magnetic signature contained in these older formations is probably an overprint produced by an extensive hydrothermal system active during carmacks extrusion geological work indicates that the carmacks group is plume related given its paleomagnetic latitude and geological nature we hypothesize that the carmacks group is a displaced segment of the yellowstone hot spot track and the hydrothermal system which remagnetized the older rocks was established by mantle upwelling below the region resume le groupe de carmacks go de 70 ma est une succession volcanique subaorienne qui couvrait jadis la majeure partie du centre sud ouest du yukon il possde une direction paloomagnotique romanente certifioe par le test du pli et le test des inversions une nouveau groupe de 13 sites combino 13 sites diune otude antorieure fournit un pule 088 6 e 78 4 n a95 7 8 qui est considorablement oloigno par rapport au pule du craton de liamorique du nord et qui implique un doplacement partir du sud de 1900 700 km les couches rouges du membre de mandanna du trias tardif et les tufs du formation de nordenskild du jurassique prococe qui subirent une doformation durant le jurassique tardif ont ochouo le test du pli et le test de conglomorat mais ils ont passo avec succs le test de contact avec les dykes de li ocne la direction romanente post tectonique est identique celle isoloe du groupe de carmacks la signature magnotique qui caractorise ces formations plus anciennes est probablement une roaimantation produite par un systme hydrothermal otendu qui fut actif durant liextrusion de carmacks liotude goologique rovle que le groupe de carmacks est apparento un panache tant donno sa latitude paloomagnotique et sa nature goologique nous avanaons lihypothse que le groupe de carmacks reprosente un segment doplaco du traco du point chaud de yellowstone et que le systme hydrothermal qui a roaimanto les roches les plus anciennes est ds liascension du manteau sous la rogion otudioe

major dextral transcurrent displacements along the northern rocky mountain trench and related lineaments in north central british columbia the northern rocky mountain trench and a number of other prominent lineaments along and east of the eastern margin of the intermontane belt mark faults along which dextral transcurrent movements have been dominant offsets of shelf to off shelf facies boundaries in lower paleozoic rocks indicate a cumulative displacement of at least 750 km and probably 900 km within the system of faults related to those in the northern rocky mountain and the tintina trenches farther west another system of faults appears to offset plutons and stratigraphic assemblages along the eastern margin of the intermontane belt by as much as 300 km these faults including the kutcho and the pinchi connect in part with the teslin suture zone in yukon territory and probably with the fraser river straight creek fault zone in southern british columbia although dextral transcurrent faulting may have taken place between the middle jurassic and early cenozoic the most convincing evidence points to middle cretaceous and particularly to early cenozoic eocene displacements the eocene movements were temporally related to plutonism volcanism lamprophyre dike emplacement high heat flow sedimentation in grabens and rapid uplift of northwesterly trending elongate ranges climactic episodes of granite emplacement particularly in and near the northern omineca crystalline belt at 100 m y 70 m y and 50 m y ago may have been facilitated by changes from dominantly compressional to dominantly transcurrent and related tensional strain

massive biomass flushing despite modest channel response in the rayas river following the 2008 eruption of chaiten volcano chile abstract the 2008 eruption of chaiten volcano in southern chile severely impacted several densely forested river catchments by supplying excess pyroclastic sediment to the channel networks our aim is to substantiate whether and how channel geometry and forest stands changed in the rayas river following the sudden input of pyroclastic sediment we measured the resulting changes to channel geometry and riparian forest stands along 17 6 km of the impacted gravel bed rayas river 294 km 2 from multiple high resolution satellite images aerial photographs and fieldwork to quantify yield volume characteristics of the forest stands limited channel changes during the last 60 years before the eruption reflect a dynamic equilibrium condition of the river corridor despite the high annual precipitation and the sediment supply from chaiten and michinmahuida volcanoes in the headwaters images taken in 1945 2004 and 2005 show that total size of the vegetated channel islands nearly doubled between 1945 and 2004 and remained unchanged between 2004 and 2005 pyroclastic sediment entering the rayas river after the 2008 eruption caused only minor average channel widening 7 but killed all island vegetation in the study reach substantial shifts in the size distribution of in channel vegetation patches reflect losses in total island area of 46 from 2005 to 2009 and an additional 34 from 2009 to 2012 the estimated pulsed release of organic carbon into the channel mainly in the form of large wood from obliterated island and floodplain forests was 78 400 tc km y and surpasses most documented yields from small mountainous catchments with similar rainfall forest cover and disturbance history while making up between 20 and 60 of the annual carbon burial rate of fluvial sediments in the northern patagonian fjords we conclude that the carbon footprint of the 2008 chaiten eruption on the rayas river was more significant than the measured geomorphic impacts on channel geometry for the first five years following disturbance the modest post eruptive geomorphic response in this river is a poor indicator of its biogeochemical response

sedimentology palynostratigraphy and palynofacies of the late oligocene makum coalfield assam india a window on lowland tropical vegetation during the most recent episode of significant global warmth abstract the sedimentology palynofacies and pollen and spore assemblages together with observations on the preserved megaflora from the tirap coal mine assam india 27 17 20 n 95 46 15 e provide important insights into the composition and distribution of plant communities in a late oligocene tropical delta palaeolatitude approximately 18 n these insights take on additional significance because the late oligocene included the last significantly warm interval in earth s history before progressive neogene cooling to the present day icehouse the lower two thirds of a 188 m studied section represents lower delta plain environments with only a small degree of brackish water marine influence raised mires autochthonous swamps and allochthonous organic matter accumulations comprise the vitrinite rich high volatile bituminous b coals the upper third of the section represents upper delta plain environments with high sediment pass through here standing fossil forests attest to frequent inundation and recovery of the arborescent interfluve vegetation throughout the period of deposition of the studied section several 100 kyr sediment supply exceeded increases in accommodation space afforded by basin subsidence relative sea level rise a dominance of spores attributed to cyatheaceous and other fern taxa indicates that tree ferns and other pteridophytes were a major component of the vegetation throughout the environments represented by the section despite the absence of ferns in the megafossil record nypa and mangrove megaremains together with mangrove pollen and acrostichum spores attest to the presence of a mangrove community similar in composition to those of modern southeast asia palms and megathermal tree taxa such as those belonging to the malvaceae meliaceae alangiaceae anacardiaceae and pellicieraceae inhabited the interfluve and swamp forests perennial herbs of the family gunneraceae occur throughout the section palynofacies analysis shows a dominance of anoxic dysoxic environments with a small part of the lower part of the section exhibiting more oxic conditions associated with circumstantial evidence for mild marine possibly tidal influence most palynodebris fluoresce only weakly consistent with the relatively high rank for coals of this age a small number of reworked gondwanic permian grains suggest sediment erosion from the highlands to the north the late oligocene tropical delta vegetation has much in common with modern lowland wet megathermal forests from southeast asia however tree ferns appear more prevalent in the late oligocene

discordant paleomagnetic poles from the canadian coast plutonic complex regional tilt rather than large scale displacement stratigraphic petrologic and isotopic data indicate that parts of the coast plutonic complex and the north cascade range have been tilted northeast side up by angles of approximately 30 degree about north northwest trending axes these tilts can account for discordant paleomagnetic directions observed in mid cretaceous plutons from these regions without large scale displacement relative to north america

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

deciphering shallow paleomagnetic inclinations 2 implications from late cretaceous strata overlapping the insular intermontane superterrane boundary in the southern canadian cordillera 1 significant discrepancies exist between paleomagnetic and geologic estimates of the timing and magnitude of terrane displacement in the southern canadian cordillera lithostratigraphic palynological geochronologic geochemical and structural data to which we add paleomagnetic data demonstrate that upper cretaceous strata in churn creek are laterally equivalent facies of the silverquick powell creek spc succession these rocks therefore comprise a single overlap sequence linking the insular and intermontane superterranes by late albian cenomanian time 95 ma contradicting previous assertions based solely on paleomagnetic interpretation that major 2000 km latitudinal displacement separated the two regions the churn creek succession retains primary magnetic remanence as demonstrated by positive fold conglomerate and contact tests the sediments do not hold the anisotropy signature of compaction shallowed inclinations the mean inclination of all spc sites from both mount tatlow and churn creek is 55 6 2 3 n 36 sites corresponding to a paleolatitude of 36 1 2 4 this reflects northward translation of the composite insular intermontane superterrane of 3050 450 km between 85 and 50 ma the silverquick powell creek succession at churn creek unconformably overlies the northern end of the spences bridge group a late early cretaceous volcanic arc assemblage on the intermontane superterrane paleomagnetic data in the companion paper place it 1050 450 km south of its current position between 100 and 105 ma integration of these new data sets require that the insular and intermontane superterranes formed a single enormous crustal block that underwent complex episodic south north translation between circa 105 and 50 ma the timing rate and vectors of translation are problematic in terms of geologic constraints along the continental margin

paleomagnetic results for eocene volcanic rocks from northeastern washington and the tertiary tectonics of the pacific northwest the direction of remanent magnetization for 102 sites in eocene volcanic and volcaniclastic rocks of the o brien creek formation sanpoil volcanics and klondike mountain formation suggests approximately 25 of clockwise rotation of a 100 by 200 km area in northeastern washington the volcanic rocks consist chiefly of rhyodacite and quartz latite flows with intercalated ash flow tuff and volcaniclastic layers these rocks have been sampled at 102 sites distributed among five volcanotectonic depressions the toroda creek republic keller and first thought grabens and the spokane enterprise lineament the volcanic rocks probably range in age from 55 m y to about 48 m y and the 50 to 48 m y old volcanic rocks within this suite appear to be rotated as much as the older rocks previous investigators have shown that 40 m y old and younger plutonic rocks of northwestern washington are not rotated hence we infer that the north central washington rocks were rotated to their present declination between 48 and 40 m y b p during the middle and or late eocene during early eocene time this region was extended in a westward direction through crustal necking gneiss doming diking and graben formation internal deformation of the region related to this crustal extension was extreme but most bedrock units that were formed concurrent with the crustal extension were probably in place prior to the rotation hence we infer that the rotation was chiefly accommodated by movement on faults peripheral to the sampled area faults active during paleogene time appear to define boundaries of a triangular crustal block the sanpoil block encompassing much of northeastern washington northern idaho northwestern montana and adjacent parts of british columbia the faults include the laramide thrusts of the rocky mountain thrust belt the strike slip faults of the lewis and clark line and strike slip faults of the straight creek fraser zone we suggest that during early eocene time the sanpoil block was extended westward through crustal necking and dilation and then during the middle eocene was rotated clockwise and thrust over the craton in a final stage of laramide thrusting the motor driving these deformations presumably was interaction of north america with oceanic lithosphere off its western margin such interaction probably involved right oblique underthrusting and dextral shear

yellowstone in yukon the late cretaceous carmacks group the late cretaceous carmacks group a thick subaerial volcanic succession that once covered much of southwest yukon was deposited on an uplifted terrane and is divisible into a lower fragmental unit and an upper flood basalt unit coeval hydrothermal activity resulted in widespread alteration and gold mineralization the lavas are shoshonites enriched in large ion lithophile and light rare earth elements but depleted in high field strength elements ankaramitic absarokite flows in the upper carmacks group range up to 15 wt mgo requiring a high liquidus temperature 1400 c at 1 bar dry high k 2 o contents 3 of these magnesian lavas indicate that the potassic character of the volcanic suite was established in the mantle although previously interpreted as subduction related the carmacks group was erupted during a cordilleran wide magmatic lull and lacks coeval calc alkalic batholiths the lavas are petrologically similar to plume related eocene to pliocene potassic lavas of the western united states new paleomagnetic collections combined with previous work place the carmacks group 17 2 6 5 1900 700 km south of its present position relative to the craton during deposition near the paleolocation of the yellowstone hotspot the spatial coincidence similarity of tectonic setting and lithologic similarity of the carmacks group and yellowstone volcanic successions suggest that the carmacks group is the 70 ma effusion of the yellowstone hotspot subsequent northward displacement of the carmacks group is attributed to coupling with the kula plate correlation of the carmacks group and the yellowstone hotspot fixes the paleolatitude and the paleolongitude of the terranes of the northern intermontane belt at 70 ma

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

stratigraphic and isotopic link between the northern stikine terrane and an ancient continental margin assemblage canadian cordillera geologic and isotopic data strongly imply a late triassic depositional link between a juvenile volcanic arc northern stikine terrane and an outboard ancient continental margin assemblage nisling terrane in the canadian cordillera two sandstone samples and a schist clast from a conglomerate layer at the base of the upper triassic stuhini group northern stikine terrane have nd depleted mantle model ages of 1400 1430 and 1600 ma respectively other stuhini group rocks have model ages of 390 660 and 690 ma three samples of nisling terrane schist and gneiss yield nd model ages of 910 1770 and 2450 ma and highly radiogenic 87 sr 86 sr ratios these isotopic data corroborate stratigraphic evidence that detritus at the base of northern stikine was shed from the nisling terrane and strengthen interpretations that these terranes became linked by late triassic time thus upper triassic strata of the northern stikine terrane may have accumulated on top of or adjacent to an exotic continental fragment a rifted fragment of the north american margin or the in situ north american margin

northward motion of the whitehorse trough paleomagnetic evidence from the upper cretaceous carmacks group discussion discordant paleomagnetic directions in mid cretaceous plutons of the coast plutonic complex and north cascades have been interpreted as indicating mid cretaceous paleolatitudes 2000 2500 km south relative to north america beck et al 1981 irving et al 1985 umhoefer 1987 but this magnitude of northward transport contradicts interpreted pre midcretaceous links between the north american miogeocline and westerly parts of the cordillera price and charmichael 1986 because paleohorizontal cannot be directly determined in plutonic rocks the discordant paleomagnetic directions may also be explained by tilting of the plutons about a horizontal axis primarily because of the consistent nature of the paleomagnetic discordance over a large region beck et al 1981 and irving et al 1985 have preferred the interpretation of northwards transport however butler et al 1989 recently pointed out geological evidence indicating that widespread northeast side up tilting may have affected the western portion of the coast plutonic complex and the north cascades resolution of this debate is of obvious importance to understanding the tectonic evolution of the canadian cordillera marquis and globerman reported results of a paleomagnetic study of the upper cretaceous carmacks group in the whitehorse trough the carmacks group is composed of gently dipping basaltic and andesitic lava flows that have been dated at 70 4 2 4 ma these rocks lie west of the tintina northern rocky mountain trench fault and the teslin suture zone because paleohorizontal can be unambiguously determined for these volcanic rocks the paleomagnetic data presented by marquis and globerman are potentially very important in resolving the tilt versus translation question marquis and globerman collected paleomagnetic samples in three regions spread over 300 km based on detailed laboratory studies they successfully isolated characteristic remanent magnetization chrm from 18 of 27 paleomagnetic sites flows the acquired paleomagnetic data pass a fold test of stability and contain sites of both normal and reversed polarity and magnetic properties indicate that the chrm is a primary thermoremanent magnetization the observed angular dispersion of virtual geomagnetic poles vgp s indicates some degree of required sampling of geomagnetic secular variation marquis and globerman determined a paleomagnetic pole from the carmacks group at 82 n 109 e with 95 confidence region ag5 of radius 7 8 using a 70 ma north american reference paleomagnetic pole of 77 7 n 185 8 e ag5 7 7 and the methods of beck 1980 as modified by demarest

paleomagnetism of the middle cretaceous iritono granite in the abukuma region northeast japan abstract we have studied the paleomagnetism of the middle cretaceous iritono granite of the abukuma massif in northeast japan together with 40 ar 39 ar dating paleomagnetic samples were collected from ten sites of the iritono granite 102 ma 40 ar 39 ar age and two sites of its associated gabbroic dikes the samples were carefully subjected to alternating field and thermal demagnetizations and to rock magnetic analyses most of natural remanent magnetizations show mixtures of two components 1 h component high coercivity b c 50 90 mt or high blocking temperature t b 350 560 c component and 2 l component relatively low b c or low t b component h component was obtained from all the 12 sites to give a mean direction of shallow inclination and northwesterly declination i 29 9 d 311 0 95 2 7 n 12 this direction is different from the geocentric axial dipole field at the present latitude i 56 5 and the typical direction of the cenozoic remagnetization in northeast japan since rock magnetic properties indicate that the h component of the iritono granite is carried mainly by magnetite inclusions in plagioclase this component probably retains a primary one thus the shallow inclination indicates that the abukuma massif was located at a low latitude 16 1 1 6 n about 100 ma and then drifted northward by about 20 in latitude the northwesterly deflection is attributed mostly to the counterclockwise rotation of northeast japan due to miocene opening of the japan sea according to this model the low pressure and high temperature low p high t metamorphism of the abukuma massif which has been well known as a typical location would have not occurred in the present location on the other hand the l component is carried mainly by pyrrhotite and its mean direction shows a moderate inclination and a northwesterly declination i 42 8 d 311 5 95 3 3 n 9 since this direction is intermediate between the h component and early cenozoic remagnetization in northeast japan some thermal event would have occurred at lower temperature than pyrrhotite curie point 320 c during the middle cretaceous to early cenozoic time to have resulted in partial remagnetization

paleomagnetism of the upper cretaceous strata of mount tatlow evidence for 3000 km of northward displacement of the eastern coast belt british columbia this study contributes the first paleomagnetic data from dated cretaceous units of the coast belt 51 3 n 123 8 w in which paleohorizontal bedding surfaces can be identified with certainty we sampled 38 sites through a 1 5 km stratigraphic interval of cenomanian silverquick sedimentary strata and cenomanian to campanian powell creek volcanics in the tatlow syncline in the tyaughton methow basin magnetizations at 21 sites have high unblocking temperatures tub and pass the tilt test precision k 5 before untilting maximum k 48 after 100 untilting magnetic minerals of volcanics show original textures mean declinations in volcanic and sedimentary rocks are statistically identical and polarity is consistently normal the mean inclination 55 4 3 4 probability p 0 05 of this pretilting magnetization is 20 1 4 0 shallower than that expected if the rocks were deposited in their present position relative to cratonic north america field and laboratory observations rule out other causes for these anomalous shallow inclinations these rocks therefore have been displaced northward by 3000 500 km relative to cratonic north america since mid cretaceous time this displacement is almost 3 times greater than that estimated from mid cretaceous volcanics in the now adjacent intermontane belt evidently the two belts were not amalgamated until latest cretaceous or early tertiary time these results are inconsistent with all previous geologically based tectonic reconstructions of the cordillera magnetizations at eight sites in silverquick and powell creek beds have low tub and directional characteristics similar to those in three younger diorite intrusions reversed and normal polarities occur the rocks are commonly highly altered and maximum precision occurs after 40 untilting the magnetizations therefore are interpreted as overprints of latest cretaceous age acquired during folding

paleomagnetic evidence for displacement from the south of the coast plutonic complex british columbia the mid cretaceous spuzzum and porteau plutons of the coast plutonic complex of british columbia have two magnetizations a and b the a magnetization eight sites 83 specimens d 30 3 i 56 7 95 4 9 paleolatitude 37 5 n paleopole 65 0 n 14 9 w a95 6 2 is considered to have been acquired in the age range 105 90 ma this result differs from the field established for cratonic north america in this time range the difference could be caused either by previously undetected tilting about a horizontal axis of the plutons or by their rotation about a vertical axis and lateral displacement relative to the craton previously observed mid cretaceous magnetizations from other rock units from the western canadian cordillera and the cascades of washington united states are similarly discordant with respect to the craton this similarity over such a large area indicates that although local undetected tilting could be partly responsible it is unlikely to be the prime cause and we argue ther

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

paleomagnetic and geobarometric study of the mid cretaceous whitehorse pluton yukon territory this is the first of several lithoprobe paleomagnetic studies underway to examine geotectonic motions in the northern canadian cordillera except for one controversial study estimates for terranes underlying the intermontane belt in the yukon have been extrapolated from studies in alaska southern british columbia and the northwestern united states the whitehorse pluton is a large unmetamorphosed and undeformed tonalitic body of mid cretaceous age 112 ma that was intruded into sedimentary units of the whitehorse trough in the stikinia terrane geothermobarometric estimates for eight sites around the pluton indicate that postmagnetization tilting has been negligible since cooling through the hornblende crystallization temperature and that the pluton is a high level intrusion paleomagnetic measurements for 22 of 24 sites in the pluton yield a well defined characteristic remanent magnetization chrm direction that is steeply down and northwards the chrm direction gives a paleopole of 285 5 e 81 7 n

paleomagnetism of the eocene kamloops group and the cratonization of terrane i of the canadian cordillera the lower middle eocene 49 4 2 4 ma kamloops group is exposed in the middle of the quesnellia subterrane of terrane i the group consists of the siliciclastic tranquille beds and the overlying dewdrop flats plateau basalts and andesites detailed alternating field af and thermal step demagnetization was carried out on 282 specimens from 26 flow sites and one conglomerate site and saturation isothermal remanent magnetization sirm tests were performed to examine the remanence carriers the petrology of the gently dipping flows the presence of antiparallel normal and reverse remanence the conglomerate test and the fold test all indicate that a primary remanence has been isolated it resides in both magnetite and hematite over a broad range of af coercivities blocking temperatures and domain sizes its mean direction of 355 0 73 4 95 6 9 gives a pole position of 138 4 w 81 4 n dp 11 0 dm 12 3 that is statistically indistinguishable from the 50 ma reference pole for the north a

paleomagnetism of eocene rocks of the kelowna and castlegar areas british columbia studies in determining paleohorizontal the middle eocene marron volcanics mean age 52 2 ma of the kelowna outlier form the upper part of the hanging wall of the westerly dipping okanagan valley fault ovf in south central british columbia they overlie quesnellia the ovf is currently interpreted as the westernmost member of a network of low angle extension faults in the southern omenica belt the ovf was active in the middle eocene at much the same time that the marron volcanics were cooling relative to present horizontal the magnetizations are widely scattered fisher s precision parameter k 8 and after correction for bedding attitudes there is no significant improvement k 9 evidently some magnetizations were acquired before referred to as category 1 and others after category 2 tilting that is the horizontal plane at the time of magnetization sometimes did and sometimes did not coincide with the bedding plane partial unfolding experiments carried out on the two categories separately yield a precision comparable to t

comment on paleomagnetism of the upper cretaceous strata of mount tatlow evidence for 3000 km of northward displacement of the eastern coast belt british columbia by p j wynne et al and on paleomagnetism of the spences bridge group and northward

where are the missing faults in translated terranes abstract a central dilemma in understanding terranes that have translated long distances is that modern plate tectonics and paleomagnetic studies indicate translations of thousands of kilometers while the faults along which the terranes moved these great distances are not found relations long known from geology and from recent studies of modern transform plate boundaries suggest that preserving strike slip faults that record 1000 km scale translations is unlikely and therefore in many cases paleomagnetism may be our only reliable indicator of how far terranes translated four reasons are explored here for why large offset strike slip faults are likely to be missing in translated terranes 1 strike slip faults in continents commonly are partially or wholly destroyed or reactivated only 400 500 km of over 1000 km of offset on cretaceous early tertiary strike slip faults in northern british columbia are accounted for in southern british columbia the missing strike slip faults probably continued south into the hinterland of the rocky mountain thrust belt as oblique thrust faults much like the modern alpine marlborough fault system of new zealand the major strike slip faults in southeastern british columbia were obliterated by eocene extensional faulting uplift and erosion 2 offsets of 1000 km scale are likely to occur on many anastomosing faults with offsets of 100 km scale many of which are left behind and not found in the translated terrane the greater san andreas plate boundary has accumulated 1200 km of transform motion that is distributed on numerous faults from the offshore borderland to eastern california there is a narrow terrane in the offshore borderland of california that has moved 1200 km relative to north america but no single fault has nearly that much offset 3 major faults in narrow oceans formed by oblique divergent plate boundaries have a low potential for preservation for example the deep dense oceanic crust of the gulf of california where the major transform faults of the oblique rift lie has a low potential for preservation in contrast baja california is currently a continental terrane that has translated 300 km relative to north america along the plate boundary in the gulf of california because of the relative buoyancy of continental crust baja california is likely to be preserved in any future accretion event 4 faults in the margins of oblique divergent plate boundaries are dominantly normal faults and not strike slip faults there is little strike slip faulting in central baja california even though the plate boundary has a rift angle of only 20 recent field data and modeling show that at 0 20 strike slip faults will dominate the secondary faults surprisingly at 20 to 35 there are both strike slip and normal faults and at 35 45 there are few or no strike slip faults even though the relative motion of these types of oblique rifts is dominated by transcurrent motion over extensional motion

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

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

new 42 ma cratonic north american paleomagnetic pole from the yukon underscores another cordilleran paleomagnetism geology conundrum eocene posttectonic plutons of the beaver river alkalic complex in southeastern yukon intruded devonian mississippian and triassic sandstones in the foothills of the canadian cordillera a paleomagnetic collection of 27 sites from three separate plutons produced 326 specimens that were analyzed using alternating field and thermal step demagnetization methods the a component characteristic remanent magnetization chrm resides in magnetite with normal polarity in the 42 6 0 8 ma beaver river pluton reversed polarity in the 42 1 0 7 ma larson creek east pluton and both polarities in the 41 3 0 4 ma larson creek west pluton corresponding with magnetic polarity chrons 20n 19r and the boundary between chron 19r and 18n respectively the chrms of the plutons are indistinguishable 2 with a mean for the 42 0 0 5 ma complex of d 158 8 i 73 1 n 21 sites 95 3 0 k 116 8 a positive paleomagnetic contact test shows the a component to be primary and the poorly isolated b component

paleomagnetic and geobarometric study of the late cretaceous mount lorne stock southern yukon territory the 75 ma mount lorne monzodiorite stock has been studied paleomagnetically to estimate the tectonic motion of the northern canadian cordillera since the late cretaceous the stock is one of sever

probabilistic analysis of rain triggered lahar initiation at tungurahua volcano semi continuous production of pyroclastic material by intermittent strombolian vulcanian and sub plinian eruptions at volcan tungurahua ecuador has created a persistent rain triggered lahar hazard during the 1999 present eruptive episode lahars threaten the city of banos which lies approximately 8 km from the crater as well as other villages and vital infrastructure situated in close proximity to the dense radial drainage network of the volcano this study analyses the initiation of rain triggered lahars and the influence of antecedent rainfall on this process in two northern instrumented drainages la pampa and the vazcun analysis of lahar triggering rainfall intensity and duration between march 2012 and june 2013 yields a power law relationship whilst receiver operating characteristic roc analysis indicates that peak rainfall intensity 10 30 and 60 min is the most effective single predictor of lahar occurrence the probability of a lahar exceeding a pre defined magnitude increases with peak rainfall intensity incorporation of antecedent rainfall 24 h and 3 5 and 7 days as a secondary variable significantly impacts lahar probabilities particularly during moderate high intensity rainfall events the resultant two and three dimensional lahar probability matrices are applied to rainfall data between 1st july and 31st december 2013 with the aim of predicting lahar occurrence composite lahar indicators comprised from the mean lahar probability estimates of individual matrices are shown to perform this task most effectively roc analysis indicates a probability 80 that these composite indicators will generate a higher estimated lahar probability for a randomly selected lahar event than a randomly selected non lahar event this method provides an average of 24 min of additional warning time compared with the current acoustic flow monitors afms used for lahar detection effectively doubling warning times for key downstream infrastructure in the two drainages ultimately this method of lahar analysis could be used to construct real time probabilistic rain triggered lahar forecasts as an aid to current lahar hazard mitigation techniques at any location with a significant rain triggered lahar hazard and a basic instrumental setup

testing terrane transport an inclusive approach to the baja b c controversy the baja british columbia hypothesis holds that a large segment of the western edge of northern north america baja b c was situated alongside california and northern mexico in middle cretaceous time was displaced northward in the late cretaceous and paleocene by north oblique convergence of the kula plate with north america and arrived near its present location by the early eocene a consistent body of paleomagnetic data supports this hypothesis however doubt persists and various crucial tests of a geologic nature have been proposed one such test concerns the provenance of zircons in cretaceous sedimentary basins of baja b c in this paper we use both paleomagnetic data and zircon occurrences to reconfirm the baja b c hypothesis we first argue that the only truly crucial tests yet performed have been paleomagnetic and that all such tests have been positive second we show that detrital zircon data from the upper cretaceous nanaimo group although not a crucial test provide valuable paleogeographic information available data demonstrate a change in detrital zircon provenance in the nanaimo group that closely matches the position of these rocks predicted by the baja b c hypothesis detrital zircons in the nanaimo group suggest a change from a southwestern north american source rich in grenville and 1 4 1 5 ga rocks to an increasing contribution from older parts of the craton such as the wyoming province together detrital zircons and paleomagnetic inclinations allow us to assemble a detailed schedule of northward tectonic transport of the baja b c terranes