an interpretation of martian thermospheric waves based on analysis of a general circulation model planetary scale longitudinal variations in density observed by the mars global surveyor accelerometer in the 125 km region can be qualitatively reproduced by the nasa ames mars general circulation model in the 80 km altitude region but only when locations having specific local times are used in the analysis if the model results are averaged over all local times the high altitude longitudinal variations nearly disappear leaving only a small stationary wave 1 pattern consistent with theory and previous modeling studies this analysis suggests that the observed wavelike structures are a result of sampling tidal modes at a limited range of local times rather than by topographically forced rossby waves as previously suggested

thermal tides in the dusty martian atmosphere a verification of theory major features of the daily surface pressure oscillations observed by the viking landers during the two great dust storms on mars in 1977 can be explained in terms of the classical atmospheric tidal theory developed for the earth s atmosphere the most dramatic exception is the virtual disappearance of only the diurnal tide at viking lander 1 just before the second storm this disappearance is attributed to destructive interference between the usually westward traveling tide and an eastward traveling diurnal kelvin mode generated by orographically induced differential heating the continuing viking lander 1 pressure measurements can be used with the model to monitor future great dust storms

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

the stratigraphy of the nicola group in the hedley district british columbia and the chemistry of its intrusions and au skarns the nieola group at hedley british columbia is a late carnian to late norian late triassic sequence of calcareous sedimentary and arc related volcaniclastic rocks it was deposited on a tectonically active paleoslope that marked either the rifted eastern margin of the shallow marine nicola basin or the faulted edge of an intrabasinal platform the lower part of the nicola group comprises a succession of four essentially coeval sedimentary facies from east to west across the district these are informally named the thin approx 200 in shallow marine limestone dominant french mine formation the thicker calcareous siltstone dominant hedley and chuchuwayha formations in the central part of the district and the thick up to 2208 m deeper water and argillite dominant stemwinder formation these facies are all blanketed by the whistle formation a 1200 m thick unit of basaltic tuff and tuffaceous sediment whose base is marked by a gravity slide megabreccia the copperfield breccia the nicola arc at hedley was associated with two plutonic episodes oldest are the hdey intrusions which are related to economic au skarns including the nickel plate deposit which has produced over 71 t of gold from 13 4 mt of ore the hedley intrusions are similar in composition quartz gabbro to quartz diorite and overall metaluminous chemistry to other island arc generated plutons related to many cu and fe skarns in british columbia although they are less evolved they also differ in having lower fe28 fe8 ratios avg 0 23 indicating a reduced oxidation state and higher baila and scinb ratios a slightly younger plutonic episode produced the 193 ma early jurassic brodey batholith and the 194 ma mount riordan stock the latter is associated with the mount riordan crystal peak industrial garnet skarn gold skarns are preferentially developed in areas where the hedley intrusions cut the hedley and french mine formations the aka skarn ore is marked by anomlous as bi te and co values and by high pyrrhotitelpyrite and pyroxeneigarnet ratios it is distinct from the ore of fe cu mo bb zn w and sn skarns by its very low cuiau zniau and aglau ratios avg 97 18 and 12 respectively

regional stratigraphy and structural setting of the kamloops group south central british columbia the kamloops group is redefined as an assemblage of lower to middle eocene volcanic and sedimentary rocks widespread in south central british columbia in the type area west of kamloops the basal

distribution of paleogene and cretaceous rocks around the nazko river belt of central british columbia from 3 d long offset first arrival seismic tomography across the nechako chilcotin plateau of british columbia the distribution of cretaceous sedimentary rocks which are considered prospective for hydrocarbon exploration is poorly known due to the surface cover of glacial deposits and tertiary volcanic rocks to constrain the subsurface distribution of these cretaceous rocks in 2008 geoscience bc acquired seven long up to 14 4 km offset vibroseis seismic reflection lines across a north northwest trending belt of exhumed sedimentary rocks inferred to be part of the taylor creek group p wave velocity models which are consistent with sonic logs from nearby wells have been estimated using three dimensional first arrival tomography to depths ranging from 1 to 4 km igneous basement can be identified on most lines using the 5 5 km s isovelocity contour which locates the top of the basement to an accuracy of 400 m where its depth is known in exploration wells there is no general distinction on the basis of seismic velocity between cretaceous sedimentary

revised stratigraphic nomenclature and age determinations for mid cretaceous volcanic rocks in southwestern british columbia mid cretaceous volcanic and volcaniclastic rocks in southwestern british columbia east of the fraser fault system constitute two principal lithostratigraphic units the lower unit a composite succession of basaltic to rhyolitic lavas and various clastic rocks is exposed in a 215 km linear belt from near pavilion to south of princeton the upper unit mostly amygdaloidal andesite is restricted to the centre of the belt between spences bridge and kingsvale where it overlies the lower unit and contiguous basement rocks both units were deposited subaerially concurrent with folding and faulting and share a contact that varies from gradational near kingsvale to unconformable near spences bridge the names spences bridge group and kingsvale group were used by several authors for various parts of the volcanic stratigraphy we suggest revision of nomenclature whereby the lower and upper units are named pimainus formation and spius formation respectively together they constitute the spences bridge group the term kingsvale group is

lithostratigraphic and tectonic framework of jurassic and cretaceous intermontane sedimentary basins of south central british columbia1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia the south central intermontane belt of british columbia has a complex architecture comprising late paleozoic to mesozoic volcanic and plutonic arc magmatic suites marine and nonmarine clastic basins high grade metamorphic complexes and accretionary rocks jurassic and cretaceous clastic basins within this framework contain stratigraphy with hydrocarbon potential the geology is complicated by cretaceous to eocene deformation dismemberment and dislocation the eocene to neogene history of the southern intermontane belt is dominated by non arc volcanism followed by pleistocene to recent glaciation the volcanic and glacial cover makes this a difficult region to explore for resources much recent work has involved re evaluating the challenges that the overlying volcanic cover has historically presented to geophysical imaging of the sedimentary rocks in this region in light of technological advances in geophysical data collection and analysis this paper summarizes the lithological and stratigraphic fra

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

deep seismic reflection constraints on paleogene crustal extension in the south central intermontane belt british columbia following growth of the canadian cordillera during the mesozoic the southern cordillera was subject to extension during the paleocene and eocene that correlated with widespread volcanic activity in south central british columbia including across much of the nechako chilcotin plateau in 2008 geoscience bc acquired 330 km of deep vibroseis reflection profiles on the plateau mostly over the stikinia arc terrane but also over its eastern contact with the oceanic cache creek terrane all seven seismic reflection lines reveal a strongly reflective lower crust that extends from 7 to 9 s down to the moho which is defined by the downward termination of reflectivity at 11 12 s in the uppermost crust extension occurred by block faulting with faults soling into subhorizontal to shallowly dipping detachments above 10 km depth extension in the deeper upper and middle crust which was partly controlled by antiforms likely related to earlier shortening was accommodated on a network of anastomosing shear zones

the rock physical property database of british columbia and the distinct petrophysical signature of the chilcotin basalts rock physical properties provide the link between geophysical surveys and their geological interpretation the british columbia rock physical properties database compiled by the geological survey of canada now comprises 3876 values of density 930 values of electric resistivity 12 356 values of magnetic susceptibility and 2576 values of magnetic remanence and koenigsberger ratio the measurements are linked to sample locations lithologies and geological formation or unit maps histograms and biplots are used to demonstrate useful links between lithology and physical properties and serve as a background for future rock physical properties studies as expected density and resistivity are controlled mostly by porosity and mineralogy magnetic susceptibility has a bimodal distribution maxima at 4 10 4 and 2 10 2 si controlled by magnetite concentration magnetic remanence is shown to be more important than usually considered in magnetic survey analysis with koenigsberger ratios greater than u

erosion of bedrock by subglacial meltwater georgian bay ontario a regional view a spectacular series of sculpted erosional forms s forms is mapped and described from a 70 km wide area along the shore of georgian bay ontario which except for a scattered boulder lag has been swept clean of sediment a great variety of sculpted forms is described and illustrated and grouped into three classes transverse longitudinal and nondirectional forms transverse forms comprise transverse troughs muschelbruche sichelwannen and comma forms longitudinal forms comprise spindle flutes cavettos and furrows and nondirectional forms consist of undulating surfaces and potholes transverse forms are preferentially located on stoss slopes and longitudinal forms on lee slopes of rock rises undulating nondirectional forms are found on distal slopes and potholes at major breaks in slope this correlation of form and bed topography suggests that relief exerts considerable control on both form and location form geometry is also inferred to be related to coherent flow structures and their int

forced waves in the martian atmosphere from mgs tes nadir data abstract we have analyzed the temperature retrievals from mars global surveyor mgs thermal emission spectrometer tes nadir spectra to yield latitude height resolved maps of various atmospheric forced wave modes as a function of season for a full mars year among the isolated wave modes is the zonal mean time mean temperature which we used to derive zonal mean zonal winds and stationary wave quasi geostrophic indices of refraction diagnostic of their propagation the diurnal kelvin wave was isolated in the data with results roughly consistent with models wilson and hamilton 1996 j atmos sci 33 1290 1326 the s 1 and s 2 stationary waves were found to have significant amplitude in ducts extending up the winter polar jets while the s 3 stationary wave was found to be confined to near the surface the s 1 stationary wave was found to have little phase tilt with height during northern winter but significant westward phase tilt with height in the southern winter this indicates that the wave carries heat poleward slightly more than that found in barnes et al 1996 j geophys res 101 12 753 12 776 the s 1 stationary wave is likely the dominant mechanism for eddy meridional heat transport for the southern winter we noted that the phase of the s 2 stationary wave is nearly constant with time but that the s 1 stationary wave moved 90 of longitude from fall to winter and back in spring in the north while interannual variability is not yet addressed overall these results provide the first comprehensive benchmark for forced waves in mars s atmosphere against which future atmospheric models of mars can be compared

on determining paleohorizontal and latitudinal shifts paleomagnetism of spences bridge group british columbia the spences bridge group of late albian age palynology and u pb zircon date of 104 5 ma is situated in the intermontane belt of the southern canadian cordillera zeolite grade andesite lavas and interbedded volcaniclastic rocks have been sampled through a thickness of about 2900 m sampling has been confined to localities whose bedding attitudes are well defined and to rocks that have not undergone internal deformation of the 27 sites studied 25 gave single component magnetizations with well grouped directions high coercivities and high unblocking temperatures applying corrections for geological tilt to all 25 sites yielded minimum dispersion after 65 untilting analysis indicates that this is a consequence of the interaction of two modes of behavior one exhibited by y magnetizations at 8 sites in which minimum dispersion occurs after 35 untilting and one x magnetizations at 17 sites in which minimum dispersion occurs after 100 correction actually the dispersion is essentially constant in the range 88 to 100 correction the y magnetizations are uninterpretable in terms of the paleofield because no estimate of paleohorizontal can be made because of their positive response to the tilt test the x magnetizations were acquired before tilting and it is argued that geologically determined bedding planes are good estimators of paleohorizontal at the time of remanence aquisition there may be errors because of paleoslope but arguments are presented for believing that these are small on this basis the best estimate of the mean direction of the paleofield in spences bridge time is estimated to be d i declination inclination 38 7 63 9 17 sites k 44 compared with k 11 in situ 95 5 4 with a paleopole at 64 4 n 321 0 e k 24 compared with k 5 in situ a95 7 5 when compared with the cratonic reference field for mid cretaceous time this pretilting magnetization indicates a clockwise rotation of the study area of 66 3 11 8 p 0 05 and an apparent displacement from the south of 15 5 7 1 1725 790 km when these and other data previously obtained from cretaceous rocks of the pacific northwest are compiled they show an increase in apparent displacement from east to west across the cordillera this result is discussed in terms of three hypotheses 1 no translation but systematic tilts of about 30 to the southwest 2 translation of a substantial part of the pacific northwest referred to as baja british columbia and is defined more exactly in the text by variable amounts up to more than 2000 km from the south together with clockwise rotations and 3 lesser translation of baja british columbia by about 1500 km combined with variable tilting predominantly to the south it is concluded that paleomagnetic data as they are presently known are consistent with hypotheses 2 and 3 but unless serious sources of error are present are not consistent with hypothesis 1 the most likely candidate for such errors is the uncertainty in estimating initial dip of beds paleoslope in volcanic rock units

the structure of the upper atmosphere of mars in situ accelerometer measurements from mars global surveyor the mars global surveyor mgs z axis accelerometer has obtained over 200 vertical structures of thermospheric density temperature and pressure ranging from 110 to 170 kilometers compared to only three previous such vertical structures in november 1997 a regional dust storm in the southern hemisphere triggered an unexpectedly large thermospheric response at mid northern latitudes increasing the altitude of thermospheric pressure surfaces there by as much as 8 kilometers and indicating a strong global thermospheric response to a regional dust storm throughout the mgs mission thermospheric density bulges have been detected on opposite sides of the planet near 90 degreese and 90 degreesw in the vicinity of maximum terrain heights this wave 2 pattern may be caused by topographically forced planetary waves propagating up from the lower atmosphere

the gang ranch big bar area south central british columbia stratigraphy geochronology and palynology of the tertiary beds and their relationship to the fraser fault tertiary rocks in the gang ranch big bar area south central british columbia consist of 1 early or middle eocene 50 ma lavas breccias and tuffs capped by a mappable unit of conglomerate a

mars global surveyor radio science electron density profiles neutral atmosphere implications the mars global surveyor mgs radio sci ence rs experiment permits retrieval of electron density prof iles versus height 90 200 km from occultation mea surements an initial set of electron profiles is examined spanning high northern latitudes early morning solar local times and high solar zenith angles 78 to 81 near aphelion sampling for these 32 profiles is well distributed over longi tude the height of the photochemically driven ionospheric peak is observed to respond to the background neutral den sity structure with a mean height during this season at this location of 134 4 km strong wave 3 oscillations about this mean are clearly observed as a function of longitude and correspond to neutral density variations measured by the mgs accelerometer acc experiment the wave 3 tidal pattern implicated by both the rs and acc datasets is consistent with a semi diurnal wave frequency clearly the height of the martian dayside ionospheric peak is a sensitive indicator of the state of the underlying mars atmosphere this ionospheric peak height can be used as a proxy of the longitude specific non migrating tidal variations present in the mars lower thermosphere

nonmigrating tides inferred from the mars odyssey and mars global surveyor aerobraking data 1 we analyzed mars odyssey ody and mars global surveyor mgs accelerometer density retrievals in narrow local time lt bands during their respective aerobraking phases to study the large scale longitudinal density variations in the martian upper atmosphere the ody data and three seasons of mgs data fall winter and spring all displayed large zonal variations in density especially wave 2 and 3 with little vertical phase variation consistent with previous studies using mgs aerobraking data the large scale density structures were most likely nonmigrating tides sampled at specific lts the wave 2 modes observed in the ody and mgs data were approximately out of phase and their respective lt samplings were approximately 12 hours apart this reinforces the conclusion from previous studies that this mode is most likely an eastward propagating diurnal kelvin wave of zonal wave 1 which is produced by the interaction of the diurnal thermal forcing and the wave 2 component of the martian topography we also note a close association of enhanced gravity wave variances with the strong longitudinal variations in the large scale densities suggesting the possibility of tidal filtering of the gravity wave gw field

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

observations of martian tides over two annual cycles abstract the first four diurnal surface pressure harmonics have been analysed over major portions of two martian annual cycles mars years at the two viking lander sites the diurnal harmonies of surface wind have also been analysed at one of the sites since the atmospheric tides have previously been shown to provide a good indication of martian global dust storms these results provide a basis for comparing dust storm activity in the two years two global dust storms occurred during the first year during the second year there was only one major storm and it closely followed the pattern of the first storm of the first year a significant feature of the results is the brief but nearly complete vanishing of the diurnal pressure tide at the onset of one of the global dust storms it is proposed that this may have been due to interference between the normal westward propagating diurnal tide and a topographically forced eastward propagating tide and that the latter may have helped initiate the global s

initiation and flow behavior of the 1980 pine creek and muddy river lahars mount st helens washington two large high velocity lahars volcanic debris flows were triggered by a pyroclastic surge during the first few minutes of the may 18 1980 eruption of mount st helens the initial surge cloud evolved progressively by gravity segregation from a gas mobilized highly inflated density flow to a dense water mobilized basal debris flow lahar and accompanying ash cloud as it flowed down the east flank of the volcano the main source of the water for the lahars was probably from eroded snow and ice incorporated into the flow by turbulent mixing but ground water expelled together with the rock debris by the initiating volcanic explosions also may have contributed peak lahar discharge from the pine muddy fan upper smith creek and ape canyon probably exceeded 250 000 m 3 s initially but decreased exponentially in the downstream direction total volume of the lahars was in excess of 1 4 10 7 m 3 initial peak flow velocities in excess of 30 m s also decreased markedly downstream where flow was not impeded velocity was strongly related to the depth slope term r 2 3 s 1 2 from the manning uniform flow equation as a power law function during much of the route traveled lahar flow appears to have been supercritical deposits left in channels were generally thin relative to flow depth 0 to 2 5 m particles up to small boulder size were randomly distributed in the poorly sorted nonstratified matrix indicating complete suspension in a fully developed debris flow slurry however much larger clasts were transported as bed load computed sediment concentrations of matrix slurry samples ranged from 84 to 91 solids by weight and were similar for the two lahars two indirect methods for computing peak flow velocity previously only tentatively applied to debris flows were tested for accuracy by comparing computed lahar arrival times with recorded arrival times at swift reservoir the computed velocities appear to be 15 slower than the recorded velocities which is consistent with the restriction that the velocity formulas produce only minimum values

upper atmosphere of mars up to 120 km mars global surveyor accelerometer data analysis with the lmd general circulation model 1 mars global surveyor mgs aerobraking accelerometer density measurements are analyzed with the use of the general circulation model gcm at the laboratoire de meteorologie dynamique lmd mgs constant altitude density data are used obtaining longitudinal wavelike structures at fixed local times which appear to be dominated by low zonal wave number harmonics comparisons with simulated data for different seasons and latitudinal bands at constant altitude are performed excellent agreement is obtained between the simulated and observational data for low latitudes with accuracy in both mean and zonal structure higher latitudes show a reduction in agreement between gcm results and mgs data comparisons that result in good agreement with the observational data allow for the study of wave composition in the mgs data in particular the excellent agreement between the simulations and the data obtained at 115 km during areocentric longitude ls 65 allows the extraction of the major contributors to the signature with the eastward propagating diurnal waves of wave numbers one to three being the major players significant contributions are also obtained for eastward propagating semidiurnal waves of wave numbers two three and five and diurnal wave number five a sensitivity study is performed to delineate the effects of the near ir tidal forcing of the upper atmosphere on the wave content at those heights simulations without this forcing yield reduced amplitudes for diurnal eastward propagating waves two and three along with a more latitudinally symmetric response for these two components as well as for diurnal eastward propagating wave number one

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

cretaceous sedimentation and tectonics tyaughton methow basin southwestern british columbia the mesozoic tyaughton methow basin straddles the fraser yalakom pasayten straight creek fypsc strike slip fault zone between six tectono stratigraphic terranes in southwestern british columbia data from hauterivian cenomanian basin fill provide constraints for reconstruction of fault displacement and paleogeography the early cretaceous eastern margin of the basin was a region of uplifted jurassic plutons and active intermediate volcanism detritus shed southwestward from that margin was deposited as the marine jackass mountain group albian inner to mid fan facies of the jackass mountain group can be correlated across the yalakom fault suggesting 150 25 km of post albian dextral offset deposits of the jackass mountain group overlap the major strike slip zone fypsc if that zone represents the eastern boundary of the tectono stratigraphic terrane wrangellia then accretion of wrangellia to terranes to the east occurred before late early cretaceous time the western margin of the basin first b

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