paleomagnetism of coastal california and baja california alternatives to large scale northward transport paleomagnetic data from the santa lucia orocopia sloa and baja borderland bba allochthons of coastal california and baja california have been interpreted to indicate up to 2500 km of post mid cretaceous northward transport of these regions with respect to interior north america however with neogene strike slip offsets taken into account geological interpretations correlate basement rocks of the coastal allochthons with continental basement rocks directly across the san andreas and related fault systems we have examined paleomagnetic data from sloa and bba and conclude that apparent discordances can be explained without large scale pre neogene tectonic transport three major observations are fundamental to this analysis 1 paleolatitudes derived from volcanic rocks of the jurassic eugenia formation of bba and coast range ophiolite of sloa are concordant when compared to revised jurassic reference paleomagnetic poles from interior north america 2 isotopic and paleobarometric data from the peninsula ranges batholith in southern california indicate that the batholith has been tilted northeast side up by an amount that can account for discordant paleomagnetic directions observed in plutonic rocks of the batholith without large scale northward transport 3 literal interpretation of the paleolatitudes determined from paleomagnetic directions in upper cretaceous and paleogene marine sedimentary rocks of sloa and bba requires north then south then north transport and a complex motion history between the two allochthons however concordant paleolatitudes are indicated by some sedimentary rocks while coeval or younger sedimentary rocks of the same allochthon have discordant paleolatitudes coupled with recent documentations of compaction shallowing of paleomagnetic inclination in other marine sedimentary rocks these inconsistencies suggest that paleolatitudes derived from most of the marine sedimentary rocks of sloa and bba are biased towards low paleolatitudes by compaction shallowing

paleomagnetism of the upper cretaceous nanaimo group southwestern canadian cordillera the baja b c model has the insular superterrane and related entities of the canadian cordillera subject to 3000 km of northward displacement with respect to cratonic north america from 90 to 50 ma the upper cretaceous nanaimo group on and about vancouver island british columbia is a prime target to test the model paleomagnetically because of its locality and age we have widely sampled the basin 67 sites from seven islands spread over 150 km santonian to maastrichtian age most samples have low unblocking temperatures 450 c and coercivities 10 mt and strong present field contamination forcing us to reject three quarters of the collection beds are insufficiently tilted to provide a conclusive fold test and we see evidence of relative vertical axis rotations however inclination only analysis indicates pretilting remanence is preserved for many samples both polarities are observed and reversals correlate well to paleontological data proving that primary remanence is observed the mea

pedogenic carbonate carbon isotopic constraints on paleoprecipitation evolution of desert in the pacific northwest usa in response to topographic development of the cascade range abstract the cascade range in the northwestern u s acts as an orographic barrier to the easterly movement of humid air masses from the pacific ocean producing a massive rain shadow with arid to semi arid climate conditions on the leeward side of the range pedogenic carbonates formed in the c3 dominated landscapes east of the range have 13ccarbonate that is enriched by approximately 4 relative to carbonates formed in sub tropical c3 dominated ecosystems we measured stable isotopic compositions of pedogenic carbonates preserved in the quaternary and neogene sedimentary rock units in the inland pacific northwest and examined the impact of long term aridification and paleohydrology on their isotopic compositions the determined 13ccarbonate record shows a gradual increase of 5 from approximately 10 in older pedogenic carbonates to 5 in younger ones whereas 18ocarbonate record indicates a decrease of approximately 4 in the late neogene in addition the quaternary 13ccarbonate and 18ocarbonate records indicate the highest 13c and 18o among the samples during the pleistocene and significant fluctuation over the time period the gradual increase in the 13ccarbonate and the decrease in the 18ocarbonate in the late neogene are interpreted by the development of the rain shadow as a result of topographic development of the cascade range changes in the quaternary isotope records suggest a decrease in regional precipitation and isotopically depleted winter precipitation resulting from changes in large scale atmospheric circulation patterns due to advance and retreat of northern hemisphere continental ice sheet the isotope record from pedogenic carbonates provides a direct record of climatic change suggesting that long term carbon isotope data can provide useful constraints on timing and intensity of regional desertification and its associated climate and topographic interaction

helium and neon isotopes in the imnaha basalt columbia river basalt group evidence for a yellowstone plume source abstract helium neon and argon isotopic compositions were measured in two flows of the columbia river flood basalt the imnaha basalt has a 3 he 4 he ratio of 11 4 times atmospheric and 20 ne 22 ne and 21 ne 22 ne ratios characteristic of a plume component the measured 3 he 4 he is a lower limit due to possible preferential 3 he loss and or addition of radiogenic 4 he a wanapum basalt flow erupted approximately 2 ma later in the waning stages of volcanism has more morb like noble gases the he nd and sr isotopic compositions of these lavas suggest that the columbia river basalts were derived from the yellowstone plume head which contained both high helium plume material and entrained depleted mantle as the eruptions progressed the plume component in the melting region was gradually diluted or replaced

continental flood basalts episodic magmatism above long lived hotspots abstract the eruption of continental flood basalt cfb may reflect episodic magmatism above long lived mantle plumes the iceland and yellowstone hotspots have generated successive cfb provinces large intrusive complexes anomalous uplift basin formation and rifting events and linear volcanic chains dating back 120 and 70 ma respectively amagmatic intervals occurred 1 when ascent of plumes to shallow levels was impeded by impenetrable lithosphere resulting in sub lithospheric ponding of plume mantle and 2 in response to dispersion by subducting oceanic lithosphere in convergent margin settings by comparison with the plume eruptive potential of typical oceanic hotspots it is apparent that preservation of only a small portion of plume mantle ponded during an amagmatic interval is necessary to account for large volume of cfbs thermal erosion lithospheric attenuation translation of ponded hotspot mantle to the base of thinner penetrable lithosphere and passage of plume mantle through slab windows in subducting oceanic lithosphere led to subsequent breakthrough and eruption of cfb since both mantle plume and plate tectonic processes have been operating since the archean it seems likely that the migration of continents over hotspots with attendant magmatic and tectonic consequences is a common occurrence in the geological record

palaeoclimate of the late jurassic of portugal comparison with the western united states investigation of the palaeoclimatic conditions associated with upper jurassic strata in portugal and comparison with published palaeoclimate reconstructions of the upper jurassic morrison formation in western north america provide important insights into the conditions that allowed two of the richest terrestrial faunas of this period to flourish geochemical analyses and observations of palaeosol morphology in the informally named upper jurassic lourinhaformation of western portugal indicate warm and wet palaeoclimatic conditions with strongly seasonal precipitation patterns palaeosol profiles are dominated by carbonate accumulations and abundant shrink swell vertic features that are both indicative of seasonal variation in moisture availability the d 18 osmow and ddsmow values of phyllosilicates sampled from palaeosol profiles range from 22ae4 to 22ae7 and 53ae0 to 37ae3 respectively these isotope values correspond to temperatures of formation between 32 c and 39 c 3 with an average of 36 c which suggest surface temperatures between 27 c and 34 c average 31 c on average these surface temperature estimates are 1 c higher than the highest summer temperatures modelled for late jurassic iberia using general circulation models elemental analysis of matrix material from palaeosol b horizons provides proxy chemical index of alteration minus potassium estimates of mean annual precipitation ranging from 766 to 1394 mm year with an average of approximately 1100 mm year palaeoclimatic conditions during deposition of the lourinhaformation are broadly similar to those inferred for the morrison formation except somewhat wetter seasonal variation in moisture availability does not seem to have negatively impacted the ability of these environments to support rich and relatively abundant faunas the similar climate between these two late jurassic terrestrial ecosystems is probably one of the factors which explains the similarity of their vertebrate faunas

investigations of newly formed sea ice in the cape bathurst polynya 1 structural physical and optical properties 1 the physical structural and optical properties of newly formed ice types were studied in the cape bathurst polynya 71 n 127 w during fall freezeup in october to early november 2003 variable meteorological conditions with occasional snowfall resulted in the formation of numerous ice types and surface conditions ice samples were collected from horizontally homogeneous surfaces representative of the area crystallographic analysis on 33 ice cores revealed highly variable growth conditions and formation mechanisms in the area the mean fraction of granular ice was 33 while intermediate granular columnar and columnar ice contributed 37 and 30 respectively salinity profiles in the ice were c shaped and as the ice grew thicker bulk salinities decreased according to 4 582 13 358 hi cm these conditions resulted in brine volumes ranging from 4 to 46 bare ice surfaces commonly formed a high salinity brine skim layer due to brine expulsion salinities up to 40 were observed in this layer under suitable conditions frost flowers formed on the ice and their presence was related to characteristic ice microstructure with crystals that appeared disc like in shape fine grained snow ice was formed when snow merged with surface brine to create a complex hypersaline surface at the snow ice interface the spectral reflectance for the thin ice types was most strongly related to surface conditions the presence of frost flowers significantly increased the reflectance independent of snow precipitation any increase in ice thickness was found to have little effect on the reflectance once a 20 30 mm thick snow layer was present

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

a paleoclimate interpretation derived from pedogenic clay minerals from the piedmont province virginia abstract oxygen isotope ratios of pedogenic kaolinites were measured to estimate the ambient climate conditions during the formation of a saprolite in the piedmont province woodbridge va kaolinite is the predominant pedogenic clay mineral in this saprolite it is formed mostly from weathering of muscovite and to a lesser extent from weathering of microcline a dioctahedral smectite vermiculite phase formed by weathering muscovite is present in minor amounts the 18o 16o ratios indicate that most if not all the kaolinite formed in a cooler climatic regime in which meteoric waters were more depleted in 18o than most present meteoric waters it is possible that the pedogenic kaolinite formed shortly after or during the pleistocene glacial stage in north america this interpretation is consistent with the age of this saprolite derived from 10be dating methods the oxygen isotopic signatures of these kaolinites are not consistent with an older middle or early miocene age for this saprolite

field observations and model calculations of dielectric properties of arctic sea ice in the microwave c band the complex dielectric constant of first year and multiyear sea ice was measured during the seasonal ice monitoring and modeling simms field experiments conducted in the arctic in the spring of 1992 1993 and 1995 the dielectric constant was also computed based on an established dielectric mixing model by using different assumptions about inclusion shape computations were based on detailed measurements and observations of ice physical properties and crystalline structure comparison between measurements and model results was conducted to identify working models for first year and multiyear ice for first year ice models that employ the assumption of vertically oriented brine pockets are applicable to columnar ice and those with the assumption of randomly oriented brine pockets are applicable to frazil ice the validity of the models are established only for ice temperatures less than 8 spl deg c for multiyear ice there is no need to account for air bubble shape the coexistence of brine and air inclusions in multiyear pond ice makes it characteristically different from hummock ice best results for pond ice were obtained from a simple model that accounts only for volume fractions of inclusions rather than their shape physical parameters that can be retrieved directly from the dielectric constant are salinity of first year ice at temperatures below 15 spl deg c and density of multiyear hummock ice detailed measurements of permittivity and loss of first year and multiyear ice are presented along with some insight into interactions between the dielectric constant and physical parameters

paleomagnetism and geobarometry of the big creek batholith suggests that the yukon tanana terrane has been a parautochthon since early jurassic abstract the 190 5 ma big creek hornblende syenite and monzogabbro batholith has an outcrop area of 400 km2 within the yukon tanana terrane ytt in the west central part of the yukon territory of canada paleomagnetic analysis of 245 specimens from 21 sites isolates a characteristic remanent magnetization residing principally in magnetite and subordinately in hematite the unit mean direction for the batholith from 16 normal polarity and two reverse polarity sites is d 305 6 i 72 1 95 3 9 al in hornblende geothermobarometry at six locations yields emplacement depths of 16 2 km three arguments suggest that the characteristic remanent magnetization was acquired on exhumation at 180 ma more significantly the pole position indicates no northward translation but counterclockwise rotation implying that the ytt formed close to its present position on the jurassic margin of the north american craton this implies in turn that the allochthonous terranes of the intermontane and coast belts of the western cordillera impacted onto and overrode the ytt upon accretion during late cretaceous to middle eocene time

age of emplacement and basement character of the cache creek terrane as constrained by new isotopic and geochemical data new u pb and rb sr isotopic and major and trace element geochemical data are reported for late triassic to eocene granite bodies that intrude the cache creek and stikine terranes in the atlin bennett area of northwestern british columbia the u pb isotopic age data help constrain closure of the cache creek ocean and obduction of the cache creek terrane to before 172 ma middle jurassic low 87sr 86sr initial ratios 0 7037 0 7046 and lack of evidence for inheritance in zircons suggest that rocks underlying the cache creek terrane are largely primitive in nature with derivation of intrusive rocks predominantly from unevolved sources a genetic link between late triassic granitic plutons and stuhini arc volcanics of stikinia is supported by trace and rare earth element data which indicate generation of magma in a volcanic arc setting geochemical patterns for postaccretion middle jurassic and late cretaceous to early tertiary age plutons are similar to those of the late triassic indicating that middle ju

remote sensing of sea ice thickness and salinity with 0 5 2 ghz microwave radiometry an ultrawideband radiometer was used to measure microwave brightness temperature spectra over arctic sea ice in the lincoln sea near the north coast of greenland spectra over the range of 0 5 2 ghz were compared to thermal infrared images collected during the airborne campaign and also compared to nearly concurrent sentinel 1 c band synthetic aperture radar sar data based on those comparisons spectral signatures were associated with thick multiyear ice and thin ice a radiative transfer rt model consisting of a homogeneous slab of sea ice bounded by sea water and air was then used to invert the spectra for sea ice thickness and salinity inferred thicknesses were consistent with ice thickness climatology for ice floes in the lincoln sea salinities are higher than expected which may be a consequence of neglecting surface and volume scattering contributions in the models

geometric test for late cretaceous paleogene intracontinental transform faulting in the canadian cordillera the tintina trench northern rocky mountain trench tt nrmt fault zone and the fraser river straight creek fr sc fault zone are separate en echelon concentric small circle fault segments of a composite intracontinental transform fault zone more than 2500 km long that cuts diagonally across the canadian cordillera from the outboard part of a tectonic collage of accreted foreign terranes in the south into the north american preaccretionary continental margin in the north most of the 450 km of right hand slip on the tt nrmt fault zone was transformed southward during the late cretaceous and paleocene into oblique convergence in the southern canadian rockies the remainder probably comprising less than 100 km was transformed southwestward during early and middle eocene time via a zone of distributed shear and east west crustal stretching into right hand slip on the en echelon fr sc fault zone these interpretations based on regional systematic mapping of geologic structures are in conflict with interpretations of paleomagnetic measurements that call for more than 1000 km of post mid cretaceous right hand displacement along the general locus of the tt nrmt fault zone involving foreign terranes and the parts of north america to which they had been accreted this paradox must be resolved

sea ice emissivity modeling at l band and application to 2007 pol ice campaign field data sea ice emissivity models for the l band frequency range are described and then tested on pol ice campaign field measurements pol ice was conducted in march 2007 in the northern baltic in preparation for the launch of the soil moisture and ocean salinity smos instrument a satellite microwave radiometer operating at 1 4 ghz the campaign comprised airborne measurements from the emirad l band radiometer and the e m bird ice thickness meter because of the translucency of sea ice at l band it is hoped that smos will render information on ice thickness three variations on radiative transfer are used to model emirad brightness temperatures from collocated e m bird measurements a single plane parallel model an ensemble of such models and a ridged monte carlo model based on geometric optics that includes both the top and bottom surface topography all three models accurately account for the instrument antenna pattern relevant to satellite mounted radiometers that sample a large and heterogeneous area because of ice growth processes salinity and by extension permittivity are partial functions of ice thickness thus the models are further refined so that permittivity varies with ice thickness which was necessary to correctly model the polarization difference other issues related to effective permittivities an intermediate quantity in the models are discussed analysis of partial correlations shows that ice ridging makes a significant contribution to the measured signal commending further study using scattering models that are more appropriate to the scale of the ridging relative to the wavelength

stable isotopic evidence for neogene surface downdrop in the central basin and range province authigenic calcite and smectite stable isotopic records were determined for five neogene terrestrial stratigraphic sections from the central basin and range province and surrounding regions we recognized a general pattern of increasing authigenic mineral 18 o values with decreasing age since the middle miocene throughout the region we suggest this pattern results from regional elevation decrease and associated changes in atmospheric circulation patterns an anomalous pattern of decreasing 18 o values with decreasing age is observed in the miocene horse spring formation exposed in the lake mead basin which is contemporaneous with local magmatic activity we suggest this pattern results from surficial uplift of local highlands feeding water into the horse spring depositional system the topographic histories suggested here provide insight into the response of the land surface to crustal processes neogene extensional deformation in the central basin and range province resulted in a net regional elevation decrease

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

18o 16o and d h ratios of pedogenic kaolinite in a north american cenomanian laterite paleoclimatic implications abstract kaolinite gibbsite and quartz are the dominant minerals in samples collected from two outcrops of a cenomanian 95 ma laterite in southwestern minnesota a combination of measured yields and isotope ratios permitted mass balance calculations of the d and 18 o values of the kaolinite in these samples these calculations yielded kaolinite d values of about 73 and 18 o values of about 18 7 the d and 18 o values appear to preserve information on the ancient weathering system if formed in hydrogen and oxygen isotope equilibrium with water characterized by the global meteoric water line gmwl the kaolinite d and 18 o values indicate a crystallization temperature of 22 5 c a nominal paleotemperature of 22 c implies a 18 o value for the corresponding water of 6 3 the combination of temperature and meteoric water 18 o values is consistent with relatively intense rainfall at that mid paleolatitude location 40 n on the eastern shore of the north american western interior seaway the inferred cenomanian paleosol temperature of 22 c is in general accord with published mid cretaceous continental mean annual temperatures mat estimated from leaf margin analyses of fossil plants when compared with results from a published gcm based cenomanian climate simulation which specifies a latitudinal sea surface temperature sst gradient that was either near modern or smaller than modern the kaolinite paleotemperature of 22 c is closer to the gcm predicted mat for a smaller equator to pole temperature difference in the mid cretaceous moreover the warm kaolinite derived mid paleolatitude temperature of 22 c is associated with proxy estimates of high concentrations of atmospheric co 2 in the cenomanian the overall similarity of proxy and model results suggests that the general features of cenomanian continental climate in that north american locale are probably being revealed

the cordilleran ribbon continent of north america the north american cordilleran orogen is the result of a two stage process a triassic jurassic accretion within panthalassa forming saybia a composite ribbon continent and b late cretaceous collision of saybia with north america this model requires that a large portion of the continental foreland of the orogen is exotic the exotic continental component of saybia cassiar platform is distinguished from the autochthon on the basis of its a triassic eurasian fauna b involvement in a major late triassic early jurassic orogenic event and c young in part grenvillian basement and mantle a mid cretaceous magmatic arc records west dipping subduction beneath the east margin of saybia the related accretionary prism consists of imbricated shale chert and deep water limestones the medial basin and overlies an isotopically juvenile mantle domain carbonatite complexes delineate the cryptic suture separating saybia and the autochthon paleomagnetic and paleobotanical data place saybia 2000 km to the south relative to the autochthon at 80 ma late cretaceous thrust belt development records transpression between the north moving ribbon continent and the autochthon pinning against the okhotsk chukotka arc in siberia buckled saybia giving rise to the alaskan promontory

lithospheric structure of the yukon northern canadian cordillera obtained from magnetotelluric data 1 two goals of lithoprobe s geoscientific studies in the phanerozoic accretionary cordillera of western north america were to define the subsurface geometries of the terranes and to infer the physical conditions of the crust these questions were addressed in canada s southern cordillera a decade ago and have more recently been addressed in the northern cordillera of which one component of the new studies is magnetotelluric mt profiling from ancestral north american rocks to the coast we present a resistivity cross section and its interpretation of the northern cordillera derived from modeling data from 42 mt sites along a 470 km long ne sw profile beneath the coast belt southwestern end of the profile a deep crustal low resistivity layer dips inland we interpret the crustal part of this conductor as being due to metasedimentary rocks emplaced and metamorphosed during paleocene kula plate subduction a strong lateral transition in lithospheric mantle resistivity exists below the intermontane belt that is spatially coincident with changes in chemical and isotopic characteristics of tertiary to recent alkaline lavas suggesting that isotopically enriched lithosphere related to the coast belt basalts extends partly beneath the intermontane belt the unusually high lower crustal resistivity in the intermontane and omineca belts similar in value to the resistivity found in the unextended part of central british columbia excludes the presence of fluids or conducting metasediments finally our resistivity model displays strong lateral variation of the middle and lower crust between different terranes within the same belt as a result of the complex structural evolution of the lithosphere index terms 0925 exploration geophysics magnetic and electrical methods 1515 geomagnetism and paleomagnetism geomagnetic induction 8110 tectonophysics continental tectonics general 0905 8120 tectonophysics dynamics of lithosphere and mantle general keywords magnetotelluric accreted terranes northern canadian cordillera

a paleomagnetic test for northward tectonic transport of the eastern selwyn basin northern canadian cordillera data from the mid cretaceous ragged pluton ragged pluton is a member of the tungsten plutonic suite in the eastern selwyn basin this circular massive 97 ma granitic pluton is 5 km in diameter it intrudes deformed and metamorphosed clastic strata of the neoproterozoic to lower cambrian vampire formation thermal and alternating field step demagnetization data for 216 specimens from 21 plutonic sites isolated a stable characteristic remanent magnetization chrm direction at 20 sites of declination d 325 9 inclination i 80 4 95 2 7 k 142 thermal demagnetization and saturation remanence analysis show that the chrm is carried by both single domain pyrrhotite and magnetite ragged pluton s paleopole at 73 9 n latitude 191 4 e longitude dp 5 0 dm 5 2 is concordant with its co eval 97 ma north american reference paleopole showing at 95 confidence that the pluton has not been significantly rotated or translated relative to north america this paleomagnetic result favours tectonic models in which the eastern selwyn basin is

terrane wrecks coupled oroclines and paleomagnetic inclination anomalies abstract three major orogenic belts that are host to coupled oroclines terrane wrecks are likewise characterized by or directly associated with paleomagnetic inclination anomalies 1 the north american cordillera 2 the western european variscan belt and 3 the eastern european alpine system implied paleolatitudinal discrepancies in each orogen are of similar magnitude to the translation required by orogen parallel shortening during oroclinal formation the alaskan coupled oroclines accommodated 3000 km of orogen parallel shortening in the north american cordillera where primary remanent paleomagnetic inclinations in late cretaceous rocks require the bulk of the belt to have been translated 2000 to 3000 km northward relative to cratonic north america the iberian coupled oroclines accommodated 1100 km of orogen parallel shortening in the western european variscan belt within which mid paleozoic paleomagnetic inclinations are shallow with respect to stable gondwana the implied existence of a 3500 km wide paleotethys ocean between the variscan autochthon and the north gondwana margin is seemingly at odds with paleontological constraints the carpathian balkan oroclines accommodated 1000 km of orogen parallel shortening in the eastern alpine system directly north northeast of an eastern mediterranean region where primary remanent inclinations in late oligocene to miocene rocks require northward translation between 500 and 1000 km palinspastic restoration of the alaskan and carpathian balkan oroclines fully accounts for the translations recorded by the cordilleran and eastern mediterranean inclination anomalies respectively restoration of the iberian coupled oroclines confirms the existence of paleotethys but only accounts for one third of the paleolatitudinal discrepancy recorded by the variscan inclination anomaly fully resolving the variscan inclination anomaly requires 1 a paleomagnetic data set of greater temporal and spatial extent 2 refinement of the geometric and geological continuity of the variscan belt across western europe

paleomagnetism and tectonic significance of albian and cenomanian turbidites ochoco basin mitchell inlier central oregon 1 understanding continental growth and convergent margin dynamics associated with terrane accretion and modification of the cordilleran margin of north america is prevented by conflicts in paleogeographic models for major terranes oceanic plates and the north american margin we present new paleomagnetic data suggesting that the blue mountains superterrane located at an inboard portion of the cordilleran margin has undergone substantial northward translation and clockwise rotation relative to north america since mid cretaceous time positive baked contact conglomerate and fold tests provide evidence that the magnetization of these rocks dates from their deposition these results yield a mean direction of d 10 8 i 58 5 k 127 95 4 1 and n 11 comparison of magnetic inclinations and magnetic fabrics shows no evidence for inclination error a paleolatitude of 39 2 4 8 4 3 n is obtained indicating a paleolatitude anomaly of 15 9 4 1 northward translation of 1760 460 km and cw rotation of 37 7 3 with respect to north america since circa 93 ma application of an ad hoc 5 inclination error yields translation of 1200 460 km through comparison with other units in the western cordillera we infer that the mitchell inlier was located adjacent to the sierra nevada arc during mid cretaceous time and that the blue mountains province may correlate with the intermontane superterrane in british columbia other interpretations such as large inclination errors or an independent displacement history for the mitchell inlier are possible but unlikely more work is needed to fully test these hypotheses and resolve major questions of cordilleran tectonics

stable isotopic evidence for a pre middle miocene rain shadow in the western basin and range implications for the paleotopography of the sierra nevada 1 a recently proposed method for approximating the paleorelief of mountain belts makes use of the predictable relationship between the isotopic depletion of precipitation and the net elevation of an orographic barrier over which an air mass rises this rain shadow effect often creates desert regions on the lee side of mountain belts in which precipitation is isotopically light changes in the isotopic composition of precipitation can be estimated from the isotopic composition of authigenic or pedogenic minerals which can then be used to infer both the development of relief during orogenesis as well as the stability of a rain shadow formed by developing mountains the 18o of smectites formed from the weathering of middle miocene to late pliocene volcanic ashes currently exposed in the rain shadow of the modern sierra nevada of california show no indication of large scale late cenozoic surface uplift of the sierra and corresponding regional rain shadow development rather smectite isotope data tentatively suggest that elevations may have decreased over this time by as much as 2000 m toward the southern end of the range and 700 m in regions farther north this suggests that the modern rain shadow cast over the western basin and range has been in existence since pre middle miocene and that the sierra nevada have been a prominent orographic barrier since before this time these interpretations are in accord with several recent studies also suggesting a possible cenozoic elevation loss of an already developed sierra nevada mountain range

evaluation of the baja controversy using paleomagnetic and faunal data plume magmatism and piercing points abstract the controversy over late cretaceous locations of baja alaska baja bc stikinia and western quesnellia centres around whether a they were within 1000 km of their present positions or b located 1000 5000 km south along the western coast of laurentia to be transported northwards by the kula plate during the late cretaceous and cenozoic the latter is supported by paleomagnetic data including data that pass a fold contact or reversal test whereas the former is based upon correlation of strata across faults although various critical tests have been proposed and tried interpretations are equivocal e g alternative interpretations for the source of detrital zircons in baja bc we propose that the presence of plume magmatism provides unique vertical piercing points thus correlation of the 70 ma plume magmatism in northern stikinia with the yellowstone hotspot locates stikinia 2000 km to the south and 1000 km off the western coast of laurentia on the other hand the absence of 90 70 ma yellowstone plume magmatism in the presently adjacent baja bc but the presence of 60 47 ma yellowstone plume spreading ridge magmatism in southern baja bc southern vancouver island and coast ranges of washington and oregon implies that it moved at least 1200 km northwards between 70 and 60 ma i e a rate of 12 cm year the spreading ridge may be correlated with the kula farallon ridge furthermore the presence of middle late triassic plume magmatism in wrangellia and the peninsula and alexander terranes suggests 2000 km of relative dextral movement between baja alaska and baja bc applying these conclusions to pre 90 ma paths of baja alaska bc across the pacific ocean suggests that it had three components 1 northeasterly between 230 and 180 ma 2 eastsoutheasterly between 180 and 140 ma and 3 northeasterly between 140 and 90 ma whereas the latter component is consistent with published terrane tracks the 180 140 ma component is at odds suggesting that this latter segment be reassessed the weight of evidence in favour of correlating geological piercing points across the gulf of california appears to outweigh paleomagnetic evidence for 1000 2500 km of apparent northward displacement of baja california in the cretaceous and early tertiary which may be explained by 15 20 tilting of fault blocks recorded by 40 ar 39 ar cooling ages thus we conclude that whereas baja alaska baja bc stikina and western quesnellia were transported between 1000 and 5000 km northwards along the western margin of laurentia during the late cretaceous and cenozoic baja california has not moved more than that required to open the gulf of california

anisotropy of magnetic susceptibility studies in tertiary ridge parallel dykes iceland tertiary margin normal aishihik dykes yukon and proterozoic kenora kabetogama composite dykes minnesota and ontario abstract mafic dykes of different ages were collected from three different tectonic settings and analyzed using anisotropy of magnetic susceptibility ams as a proxy for magmatic flow during intrusion in iceland ridge parallel basaltic dykes were sampled on each side of the active tectonic boundary the dykes are k max orientation indicating vertical emplacement the eocene aishihik dyke swarm intrudes the yukon tanana terrane in the yukon province canada over an area 200 by 60 km these dykes were intruded normal to the accretionary margin are porphyritic andesites and have an intermediate geochemical signature based on major and trace element analyses ten dykes were sampled and 111 cores analyzed using ams and the dykes preserve a vertical k max orientation indicating intrusion was vertical through 30 km of continental crust the 2 06 ga kenora kabetogama dykes in northern minnesota and western ontario crosscut a variety of archean terranes thickness 50 km in a radiating pattern the unmetamorphosed basaltic dykes are 1 120 m wide 10 110 km in length are vertical in orientation and can be grouped as either being single intrusion or multiple intrusion composite dykes ams data preserve a vertical k max orientation for the southerly locations 2 dykes n 53 and horizontal k max for the remainder to the northwest 15 dykes n 194 maximum magnetic susceptibility axes 4 dykes n 92 for composite dykes are scattered and yield inconsistent flow directions with regard to the dyke margin almost all of our results are normal in that the magnetic foliation the plane containing k max and k int normal to k min is parallel to the dyke planes which gives us confidence that the magnetic lineations i e k max orientations are parallel to magmatic flow

calculation of oxygen isotope fractionation in metal oxides abstract a theoretical model calculating the thermodynamic isotope factors of oxygen in metal oxides of geochemical interest is presented for temperatures between 0 and 1200 c on the basis of the modified increment method the following order of 18o enrichment is obtained cassiterite rutile magnetite ilmenite ulvospinel hematite uraninite chromite corundum spinel the results are expressed as 103 in a 106 t2 b 103 t c which compare well with existing theoretical experimental and empirical calibrations on quartz oxides and oxides water systems the present calculations enable not only estimation of the oxygen isotope composition of fluids from which the metal oxides were precipitated when independent temperature information is available but can also be applied as oxygen isotope geothermometers to igneous and metamorphic rocks

spatial variation in fluid flow and geochemical fluxes across the sediment seawater interface at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanism is an important pathway for transfer of deep sourced fluids enriched in hydrocarbons and other elements into the ocean numerous mud volcanoes mvs have been discovered along oceanic plate margins and integrated elemental fluxes are potentially significant for oceanic chemical budgets here we present the first detailed study of the spatial variation in fluid and chemical fluxes at the carlos ribeiro mv in the gulf of cadiz to this end we combine analyses of the chemical composition of pore fluids with a 1 d transport reaction model to quantify fluid fluxes and fluxes of boron lithium and methane across the sediment seawater interface the pore fluids are significantly depleted in chloride but enriched in lithium boron and hydrocarbons relative to seawater pore water profiles of sulphate hydrogen sulphide and total alkalinity indicate that anaerobic oxidation of methane occurs at 34 180 cm depth below seafloor clay mineral dehydration and in particular the transformation of smectite to illite produces pore fluids that are depleted in chloride and potassium profiles of boron lithium and potassium are closely related which suggests that lithium and boron are released from the sediments during this transformation pore fluids are expelled into the water column by advection fluid flow velocities are 4 cm yr 1 at the apex of the mv but they rapidly decrease to 0 4 cm yr 1 at the periphery the associated fluxes of boron lithium and methane vary between 7 301 0 5 6 and 0 806 mmol m 2 yr 1 respectively we demonstrate that fluxes of li and b due to mud volcanism may be important on a global scale however release of methane into the overlying water column is suppressed by microbial methanotrophy

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

paleomagnetism of the flores volcanics vancouver island in place by eocene time the eocene flores volcanics of the insular belt of southwestern vancouver island have u pb zircon ages of 51 50 ma and a mean direction of magnetization d i of 349 8 69 6 12 collecting sites

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

late cretaceous age of the hutshi mount nansen and carmacks groups southwestern yukon territory and northwestern british columbia volcanic rocks of the hutshi mount nansen and carmacks groups occur in the southwestern yukon where they unconformably overlie the yukon crystalline terrane and deformed strata of the whitehorse trough the volcanic rocks are faulted and tilted locally altered and largely postorogenic the more basic carmacks volcanics locally overlie intermediate to acid rocks of the mount nansen group but are mostly in isolated exposures northwest of the hutshi and mount nansen volcanics hutshi mount nansen volcanics of the miners range are porphyritic partly vesicular calc alkaline andesite flows and flow breccias intruded by calc alkaline alkali rich rhyolite and two feldspar andesite dikes a low greenschist metamorphic overprint affects most rocks carmacks volcanics near carmacks are flows epiclastic breccias and sintered tuffs interbedded with immature volcanic sandstone one analysed breccia clast is calc alkaline andesite but the flows are potassic basalt trachybasalt and tristanite recent assignme

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

climatic implications of surface domains in arrays of δd and δ18o from hydroxyl minerals goethite as an example abstract paired d h and 18o 16o analyses of natural goethites range from 224 to 93 for d and from 15 5 to 2 8 for 18o the isotopic systematics of these goethites seem to be most closely mimicked by the goethite water d h and 18o 16o fractionation curves of yapp 1987 yapp 1990 most of these goethites are of unknown age but the large range of their isotopic compositions illustrates the possible paleoenvironmental significance of surface domains calculated for hydroxyl minerals a modern surface domain msd for goethite in coordinates of d and 18o was calculated from the following information a scatter in the modern relationship between surface temperatures and 18o of meteoric water rozanski et al 1993 b average annual surface air temperatures from 0 c to 30 c for the meteoric water sample sites c the meteoric water line mwl of craig 1961 and d the goethite water isotopic fractionation factors of yapp 1987 yapp 1990 goethites that had formed in continental environments in approximate thermal equilibrium with the earth s modern atmosphere would be expected to lie within the msd and 16 of 31 goethites do so the remaining 15 are outliers of the 16 msd samples 12 including the three samples from active soil or bog environments are concordant the calculated isotopic temperatures of the concordant goethites range from 6 c to 27 c and are the same within analytical uncertainty as the modern average surface air temperatures at the respective sites calculated temperatures of the four discordant msd samples range from 7 c to 25 c and are higher than corresponding modern surface temperatures a warm earth surface domain wesd was calculated with an assumed temperature of 35 c for the tropics eight of the 15 outlier samples plot within the portion of the wesd that does not overlap the msd thus these eight goethites may have formed at times when the earth s global climate was warmer than at present temperatures calculated from the eight wesd samples range from 20 c to 33 c and suggest lower latitudinal temperature gradients as predicted by climate models of a warmer earth calculated temperatures of the seven samples that lie outside both the msd and the wesd non sd samples range from 19 c to 69 c the non sd status of these seven samples suggests that they formed in environments dominated by subsurface heat sources surface domains can be calculated for any hydroxyl mineral for which both the hydrogen and oxygen isotope mineral water fractionation factors are known the concept of surface domains provides a criterion for assessing the likelihood that a particular sample records information on ancient climatic temperature

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

intensification of monsoon microclimate and asynchronous c4 appearance isotopic evidence from the indian siwalik sediments article i nfo analysis of the d h ratio of pedogenic clay and the 18 o 16 o ratio of carbonate nodules collected from siwalik sediments in india indicates three episodes of monsoon intensification at 11 ma 6 ma and 3 ma these episodes coincide with major pulses of tectonic uplift in the himalayas suggesting causal link between monsoon intensity and uplift in addition variation in the carbon isotope ratio of carbonate nodules and residual organic matter indicates a change in vegetation regime from pure c3 type to a mix of c3 c4 type during this time span isotopic analysis of samples collected from different locations of the himalayan siwalik shows that the late miocene c4 appearance was locally asynchronous by 3 ma similar to what is seen on a global scale the lack of synchronous emergence of c4 plants in various parts of siwalik probably indicates a combined effect of microclimate e g varying monsoon intensity and habitat disturbance e g forest fire in contrast subsequent expansion of c4 plants during the late miocene pliocene time could be entirely due to monsoon intensification that favoured c4 respiration in a warm and seasonally variable rainfall regime 2010 elsevier b v all rights reserved

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

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

additional k ar isotopic dates for the carmacks group upper cretaceous west central yukon three whole rock k ar analyses on andesites from the indian river area west central yukon yielded dates of 69 0 1 7 65 2 1 7 and 64 8 1 7 ma these confirm earlier dates indicating the carmacks group is late cretaceous in age a single date of 51 4 3 9 ma was obtained from a tuff in the sixty mile river area west central yukon suggesting an eocene age for these deposits however this date is considered equivocal because it is anomalous when compared with the other dates from the area

aluminum dependent trace element partitioning in clinopyroxene as technical advances have dramatically increased our ability to analyze trace elements the need for more reliable data on the compositional dependence of trace element partitioning between minerals and melt has become increasingly important the late cretaceous carmacks group of south central yukon comprises a succession of primitive high mg ankaramitic lavas characterized by shoshonitic chemical affinities and containing large complexly zoned clinopyroxene phenocrysts the compositional zonation of the clinopyroxene phenocrysts is characterized by relatively fe rich mg mg mg fe 0 85 but mottled cores surrounded by mantles of cyclically zoned clinopyroxene whose mg varies repeatedly between 0 9 and 0 80 these cyclically zoned clinopyroxene mantles appear to record the repeated influx and mixing of batches of primitive with more evolved magma in a deep sub crustal 1 2 gpa magma chamber s laser ablation icp ms was used to analyze the trace element variation in these zoned clinopyroxenes the results indicate more than a threefold variation in the absolute concentrations of th zr rare earth elements ree and y within individual clinopyroxene phenocrysts with no apparent change in the degree of ree or high field strength element hfse fractionation the variation in absolute abundances of trace elements correlates closely with the major element composition of the clinopyroxene with the most enriched clinopyroxene having the lowest mg and highest al contents the problem is that the amount of crystal fractionation required to explain the major element variation 20 in these clinopyroxene phenocrysts cannot explain the increase in the abundance of the incompatible trace elements which would require more than 70 crystal fractionation if constant partition coefficients are assumed the anomalous increase in incompatible trace elements appears to reflect an increase in their partition coefficients with increasing aliv in the clinopyroxene with an increase in al2o3 from 1 5 to 4 0 wt during 20 crystal fractionation over a temperature decrease of 100 c being associated with more that a threefold increase in the partition coefficients of th zr ree and y the magnitude of these increases may indicate that the substitution of these trace elements into clinopyroxene is better modeled in some natural systems by a local charge balance model rather than the distributed charge model that better replicates the results of annealed experiments these findings indicate that the effect of al on the partition coefficients of incompatible trace elements in clinopyroxene may be under appreciated in natural magmatic systems and that the application of experimentally determined clinopyroxene partition coefficients to natural systems must be done with caution

oxygen and hydrogen isotope compositions of permian pedogenic phyllosilicates development of modern surface domain arrays and implications for paleotemperature reconstructions abstract mineralogic chemical and oxygen and hydrogen isotope compositions of 15 different phyllosilicate samples from permo pennsylvanian age paleosols of the eastern shelf of the midland basin of texas and the southern anadarko basin are presented mixtures of 2 1 phyllosilicates and kaolinite dominate most samples although some samples consist of relatively pure 2 1 phyllosilicates chemical and mineralogic data are used in conjunction with published thermodynamic data to calculate hydrogen and oxygen isotope fractionation factors for each sample in turn application of measured oxygen and hydrogen isotope compositions of the phyllosilicates to temperature dependent fractionation equations are used to calculate paleotemperatures of crystallization the d values of the phyllosilicates range from 69 to 55 the 18 o values range from 19 5 to 22 7 if these samples preserve a record of equilibrium with paleo meteoric waters the isotopic compositions of the phyllosilicates correspond to paleotemperatures of phyllosilicate crystallization ranging from 22 3 c to 35 3 c in particular the stratigraphic trend of calculated temperatures from midland basin samples suggests that early permian surface temperatures may have been up to 10 c warmer than those of the latest pennsylvanian

the hydrogen and oxygen isotope geochemistry of pedogenic clay minerals principles and theoretical background abstract the 18 o 16 o and d h ratios of the structural oxygen and hydrogen of naturally occurring clay minerals carry information about the conditions under which the minerals formed clays generally form in isotopic equilibrium with the environment and hence have isotopic compositions that reflect the temperature of formation and the 18 o 16 o and d h ratios of water in the micro environment the isotopic signature of water in the weathering environment is a reflection of the climate once formed clays are resistant to isotopic alteration under surface and near surface conditions except when they undergo subsequent mineralogical alteration in some instances this alteration may be subtle as in the case of conversion of kaolinite with a high degree of crystalline order as measured by the hinckley index to kaolinite of low crystalline order in a pedogenic profile isotopic studies of pedogenic clays may be expected to yield more information about pedogenesis and paleoclimate when both 18 o 16 o and d h ratios of the clays are measured however few studies have incorporated the use of the two isotope ratios

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

bounds on the complex permittivity of sea ice an analytic method for obtaining bounds on effective properties of composites is applied to the complex permittivity of sea ice the sea ice is assumed to be a two component random medium consisting of pure ice of permittivity 1 and brine of permittivity 2 the method exploits the properties of as an analytic function of the ratio 1 2 two types of bounds on are obtained the first bound r1 is a region in the complex plane which assumes only that the relative volume fractions p1 and p2 1 p1 of the ice and brine are known the region r1 is bounded by circular arcs and for any microgeometry with the given volume fractions must lie inside it in addition to the volume fractions the second bound r2 assumes that the sea ice is statistically isotropic within the horizontal plane the region r2 is again bounded by circular arcs and lies inside r1 built into the method is a systematic way of obtaining tighter bounds on by incorporating information about the correlation functions of the brine inclusions the bounding method developed here which does not assume any specific geometry for the brine inclusions offers an alternative to the classical mixing formula approach adopted previously in the study of sea ice in these mixing formulas specific assumptions are made about the inclusion geometry which are simply not satisfied by the sea ice under many conditions the bounds r1 and r2 are compared with experimental data obtained from artificially grown sea ice at the frequencies 4 8 and 9 5 ghz excellent agreement with the data is achieved

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

a stable isotope study of recharge processes in the english chalk the 2h and 18o values of water contained in unsaturated chalk have been measured in drillcore profiles taken over a period of 28 months on arable land in cambridgeshire eastern england the isotopic composition of rainfall and lysimeter drainage on the same site has also been monitored over a period of four years the distribution of isotope values in the upper few metres of soil and unsaturated chalk shows that the mechanism of infiltration is not simple piston like downward displacement since the scale of vertical fluctuations is incompatible with estimated annual infiltration and the apparent rates of movement of matrix water derived from thermonuclear tritium studies lysimeter drainage is not isotopically identical to matrix water at the same depth suggesting that different routes to water table are associated with consistently different isotopic content although there is an apparent difference between matrix water beneath arable and permanent grassland these differences appear to cancel out in the composition of bulk recharge beneath these land types the regional aquifer has a uniform isotopic composition similar in value to weighted average rainfall and lysimeter drainage suggesting that the recharge abstraction system has been in isotopic equilibrium for many years despite changes in pumping rates and land use two other chalk sites in southern england have been investigated in less detail but indicate clear difference in infiltration behaviour from that seen in cambridgeshire this seems to be related to a higher matrix conductivity and annual rainfall amount

large scale fractures related to inception of the yellowstone hotspot during middle miocene time western north america was subject to flood basalt volcanism dike swarm injection and broad scale fracturing and folding of the crust we propose a simple model to account for these events and for a regional pattern of geologic and geophysical features aeromagnetic maps reveal some of the most important elements of this pattern which are several narrow arcuate anomalies here referred to as the northern nevada rifts these rifts extend hundreds of kilometers across nevada and are likely caused by highly magnetic middle miocene mafic dikes with the aid of filtering techniques the anomalies can be traced into oregon together with other geologic features such as fold axes dike swarms and faults they produce a spoke like pattern fanning over 2208 of arc that converges toward a point near the oregon idaho border lat 448n a possible cause for this pattern is a point source of stress at the base of the crust related to the formation of the yellowstone hotspot the spoke like pattern however does not persist at large distances from the emerging hotspot several hundred kilometers to the south the northern nevada rifts deviate significantly 308 from a radial trend we show that a simple model imposing a point source of stress at the base of the crust and a regional stress field aligned with the presumed middle miocene stress direction fits the observed fracture pattern it thus accounts for both the radial pattern present near the nascent hotspot and the far field pattern due to regional stresses

intra oceanic subduction shaped the assembly of cordilleran north america the western quarter of north america consists of accreted terranes crustal blocks added over the past 200 million years but the reason for this is unclear the widely accepted explanation posits that the oceanic farallon plate acted as a conveyor belt sweeping terranes into the continental margin while subducting under it here we show that this hypothesis which fails to explain many terrane complexities is also inconsistent with new tomographic images of lower mantle slabs and with their locations relative to plate reconstructions we offer a reinterpretation of north american palaeogeography and test it quantitatively collision events are clearly recorded by slab geometry and can be time calibrated and reconciled with plate reconstructions and surface geology the seas west of cretaceous north america must have resembled today s western pacific strung with island arcs all proto pacific plates initially subducted into almost stationary intra oceanic trenches and accumulated below as massive vertical slab walls above the slabs long lived volcanic archipelagos and subduction complexes grew crustal accretion occurred when north america overrode the archipelagos causing major episodes of cordilleran mountain building a new explanation for the origin of the accreted terranes that form the mountainous cordillera of western north america is proposed and tested stationary intra oceanic subduction deposited massive slab walls in the mantle and grew volcanic archipelagos at the surface which were overridden by and accreted to north america during cretaceous times the generally accepted account of how the geology of western north america developed involves the oceanic farallon plate acting as a conveyor belt sweeping crustal terranes onto the continental margin as it moves beneath the north american plate this model fails to explain many aspects of this accreted terrane and here karin sigloch and mitchell mihalynuk present an alternative model based on new tomographic images of lower mantle slabs and modelling of deep mantle structure in the region they propose that during the cretaceous period there were a series of island arcs west of north america beneath which proto pacific plates subducted into almost stationary trenches long lived volcanic archipelagos and subduction complexes grew above the slabs and then accreted onto north america as it overrode the archipelagos causing episodes of cordilleran mountain building

the 3d geophysical investigation of a middle cretaceous to paleocene regional decollement in the cordillera of northern canada and alaska

late paleozoic continental warming of a cold tropical basin and floristic change in western pangea abstract an increase in mineral crystallization temperatures of 13 3 c is preserved in paleosol profiles ancient soils within a stratigraphic interval of cooler than soil temperatures observed in the modern lowland tropics to permian age soil mineral crystallization temperatures which are equivalent to or slightly exceed soil temperatures observed in modern lowland tropics this record of mineral crystallization temperatures occurs at a time when some sources indicate the onset of the largest single glaciation of the late paleozoic ice age the temperature change indicated by these paleosol minerals is accompanied by a unidirectional irreversible change in the composition of tropical lowland vegetation this transition delineates the magnitude and characteristics of vegetational changes in the modern tropics that might accompany continued atmospheric warming times of low surface temperatures coincide with a typical late pennsylvanian tropical pangean wet biome dominated by sigillaria macroneuropteris other pteridosperms and marattialean ferns this plant assemblage is replaced spatially by a xeromorphic biome dominated by conifers callipterids and other seed plants characteristic of the tropical permian across western and central pangea the fully xeromorphic flora appears initially in sub meter scale beds within outcrops otherwise characterized by wet flora and becomes predominant once peak surface temperatures were reached in the earliest permian a narrow stratigraphic interval 20 m separates these two biomes in the region marking what was to be a permanent floristic change in western pangea the lower diversity floras of seasonally dry habitats apparently migrated from drier extrabasinal areas into increasingly dry landscapes formerly dominated by the wet biome this study documents the regional disappearance of an entire tropical biome with a net reduction of biodiversity accompanying rapid environmental warming

oxygen isotope geochemistry of kaolinite in laterite forming processes manaus amazonas brazil abstract mineralogic crystallographic and oxygen isotopic analyses were made of kaolinites from a 20 m thick lateritic profile developed on the detrital sands and clays of the mid cretaceous to tertiary alter do chao formation central amazon basin brazil a detailed 18o profile of soil water from the upper 4 m of the same section was also measured kaolinite separates were prepared from different pedogenic facies of small hand specimens most of these kaolinite separates exhibit polymodal size distributions the separates were further divided into individual particle size modes for subsequent isotopic and crystallographic analysis in general hinckley index and 18o values of different size fractions of the same sample differ hinckley index values decrease strongly and fe content increases in the upward direction in the profile we conclude that 1 the kaolinite in the profile has progressively evolved in response to changing microenvironments as weathering fronts have moved progressively downward 2 different kaolinite fractions even within a single facies of a single sample a few cm3 in size typically formed under somewhat different conditions 3 the bulk of the fine grained kaolinite in the lateritic profile does not constitute a continuous inverted time record that is lower levels do not represent more recent kaolinite formation and higher levels do not represent older kaolinite formation and 4 isotopic compositions of kaolinites from lateritic paleosols should provide an indication of mean climatic conditions and some measure of seasonality during the interval preceding the removal of the laterite from the active weathering environment we speculate that the different conditions under which the different kaolinite fractions have formed may be related at least in part to variations in soil microenvironments that are ultimately derived from seasonal and year to year variations in the chemistry and isotopic composition of infiltrating rainfall

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

reconstructing the ancestral yellowstone plume from accreted seamounts and its relationship to flat slab subduction recent geodynamic analyses have emphasized the relationship between modern flat slab subduction zones and the overriding of buoyant oceanic crust although most models for the evolution of the late mesozoic cenozoic laramide orogeny in the southwestern united states involve flat slab subduction the mechanisms proposed are controversial an examination of the geological evolution of the 60 50 ma crescent terrane of the coast ranges indicates that it was formed in a shallowing upward loihi type oceanic setting culminating in the eruption of subaerial lavas plate reconstructions indicate that the crescent terrane was emplaced into ca 20 ma crust and the presence of subaerial lavas implies an uplift due to the plume of ca 4 2 km which we use to calculate a minimum buoyancy flux of 1 1 mg s 1 similar to that of the modern yellowstone plume published paleomagnetic data indicate that the crescent terrane was formed at a paleolatitude similar to that of the yellowstone plume the crescent seamount was accreted within 5 my of the cessation of plume magmatism plate reconstructions indicate that it would have originated about 750 km to the west of the north american plate margin if it developed above a fixed yellowstone plume and are therefore consistent with the recorded very short interval between its formation and tectonic emplacement we interpret the crescent terrane as due to the ancestral yellowstone plume such a plume would have generated an elongate swell and related plateau that would have been overridden by the north american margin taken together the relationship between flat slab and overriding of oceanic plateau in laramide times would have been analogous to the relationship between modern andean flat slab subduction zones and the juan fernandez and nazca oceanic plateaus d 2003 elsevier science b v all rights reserved

new u pb age constraints on latest cretaceous magmatism and associated mineralization in the fawnie range nechako plateau central british columbia new u pb ages and k ar dates primarily for rocks proximal to mineral occurrences in the fawnie range of central british columbia document latest cretaceous ca 74 66 ma continental arc igneous activity and date associated base and precious metal mineralization u pb ages of ca 73 69 ma for the capoose pluton and hypabyssal to extrusive garnet rhyolites at the capoose prospect demonstrate a latest cretaceous age for mineralization and a likely plutonic source for mineralizing fluids a u pb age of ca 67 ma for a late mineralized felsic dyke and two k ar dates ca 70 and 68 ma for hornfelsed jurassic volcanic rocks at the blackwater davidson prospect constrain a latest cretaceous age for mineralization a u pb age of ca 74 ma for a fine grained diorite sill that cuts a significant epithermal gold vein at the tsacha prospect places a minimum age on mineralization at this probable jura cretaceous deposit and documents latest cretaceous magmatism latest cretaceous k ar dates are reported for an andes

thermodynamics and lattice vibrations of minerals 5 applications to phase equilibria isotopic fractionation and high pressure thermodynamic properties in previous papers in this series a model that uses available elastic structural and spectroscopic data on minerals has been used to predict the thermodynamic functions cv heat capacity s entropy e internal energy and f helmholtz free energy in this paper four applications to problems of current geochemical and geophysical interest are presented 1 interpretation of complex trends of calorimetric data 2 calculation of phase equilibria 3 calculation of oxygen isotopic fractionation factors and 4 estimation of the effect of pressure on thermodynamic functions the model demonstrates that trends in high temperature thermodynamic properties of silicates are determined by the position and relative numbers of high frequency modes generally antisymmetric si al o stretching modes the position of these modes varies systematically with degree of polymerization of tetrahedra and therefore high temperature calorimetric behavior is relatively systematic as a function of crystal structure and mineral composition trends at low frequency are much more complex because the low frequency optic modes that most strongly influence the low temperature thermodynamic functions depend in a complex way on the size coordination and mass of cations and various polyhedra in the minerals the heat capacity curves of kyanite andalusite and sillimanite and of quartz coesite and stishovite show crossovers that cannot be explained by debye theory which accounts only for acoustic mode behavior but can be explained by the model spectra proposed because proper account is taken of the changing low and high frequency optic modes upon polymorphic transformations the proposed model is sufficiently accurate that phase equilibrium problems can be addressed the quartz coesite stishovite equilibrium curves the kyanite andalusite sillimanite triple point and the breakdown of albite to jadeite plus quartz are cited as specific examples for each example predicted slopes of equilibrium curves agree moderately well to excellently with slopes determined experimentally the calculated slopes are sensitive to spectroscopic parameters particularly to the distribution of optic modes in the far infrared this sensitivity is discussed in detail for the albite breakdown reaction the model can be used for prediction of isotopic fractionation factors if spectra of the isotopic forms of the mineral are known or postulated a simple set of rules for generating hypothetical spectra of 18o minerals from measured spectra of the 16o forms is given reduced partition functions are calculated for 13 minerals at 298 k the model values of reduced partition function 1000 ln of these minerals decrease in the order quartz calcite albite muscovite clinoenstatite anorthite diopside pyrope grossular zircon forsterite andradite rutile in good agreement with experimental data at 1000 k the first six minerals show small crossovers so that the order becomes calcite muscovite albite quartz anorthite and clinoenstatite the differences in 1000 ln at high temperature for these minerals are so small that the model probably cannot address the deviations from experimental trends the model clearly defines the region in which the fractionation factors do not follow a 1 t trend and should be useful for extrapolation of experimental data to low temperatures finally a modified gruneisen parameter model is proposed for shift of the lattice vibrational frequencies under compression and thermodynamic properties to 1000 kbar 1000 k are given for nine minerals at 1 mbar the predicted decrease in entropy at 298 k ranges from 54 of the 1 bar value for periclase to 25 for stishovite

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

paleoenvironmental and paleoclimatic reconstruction of cretaceous aptian cenomanian terrestrial formations of texas and oklahoma using phyllosilicates abstract clay mineralogy chemistry and stable oxygen and hydrogen isotope compositions of 11 phyllosilicate samples from cretaceous paleosol profiles were determined in order to evaluate early to late cretaceous paleoenvironments and paleoclimates around north central texas and southern oklahoma samples consist of mineralogical mixtures of illite smectite and kaolinite samples from the albian antlers formation in southern oklahoma and the cenomanian woodbine formation are dominated by kaolinite while the remaining samples are dominated by smectite and illite major element compositions of paleosol matrix materials are used to calculate calmag weathering values that range from 31 to 84 and correspond to cretaceous paleoprecipitation estimates ranging from 270 to 1490 mm yr paleosol phyllosilicate hydrogen and oxygen stable isotope values range from 50 to 67 to 18 5 to 21 7 respectively and in conjunction with their respective mineral and chemical compositions correspond to in situ soil crystallization temperatures ranging from 26 3 c to 31 c paleoprecipitation trends exhibit two marked increases in precipitation from the early to late cretaceous in the albian antlers formation and cenomanian woodbine formation stratigraphic intervals with phyllosilicates that yield cooler temperature estimates coincide with stratigraphic intervals with markedly higher precipitation estimates based on calmag values importantly cool high precipitation intervals correlate with periods of extensive shallow seas upon the north american craton comparison of cretaceous temperature precipitation and meteoric water estimates to modern analogs supports the presence of climates similar to modern tropical climates during the cretaceous at subtropical or temperate paleolatitudes in what is now texas and oklahoma consistent with general circulation models and energy balance models suggesting a pervading cretaceous greenhouse

low frequency passive microwave observations of sea ice in the weddell sea the microwave emission properties of first year sea ice were investigated from the r v polarstern during the antarctic winter weddell gyre project in 1989 radiometer measurements were made at 611 mhz and 10 ghz and were accompanied by video and visual observations using the theory of radiometric emission from a layered medium a method for deriving sea ice thickness from radiometer data is developed and tested the model is based on an incoherent reflection process and predicts that the emissivity of saline ice increases monotonically with increasing ice thickness until saturation occurs

application of environmental isotope tracers to modeling in hydrology advances in nuclear science and computer development have made practicable chemical transport models employing the environmental isotopes found in natural waters the heavy isotopes of hydrogen deuterium stable and tritium radioactive forming part of the water molecule are the most conservative tracers of water known the heavy stable oxygen isotope 18o circulates in tandem with deuterium in the hydrologic cycle tritium fallout varies seasonally and annually in a systematic fashion and due to its property of radioactive decay is highly useful for dating time of recharge of soil moisture and groundwater 14c is valuable for tracing old groundwater owing to its relatively long half life of 5568 yr but detailed knowledge of the hydrochemistry of the system is required for successful modeling deuterium and 18o are of principal value because they reflect the temperature at which precipitation condensed thus they show pronounced seasonal variability and also the effects of altitude latitude distance from the sea amount of precipitation history of evaporation and long period climatic cycles principal areas of application of environmental isotopes to hydrologic modeling have been in soil moisture transport modeling of mixing and evapotranspiration in large lakes and swamps glacial ice movement groundwater flow and transport of contaminants in groundwater

stable isotope paleoaltimetry a critical review stable isotope paleoaltimetry makes use of systematic trends in the distribution and isotopic composition of modern precipitation with climate and topography and of the potential to estimate the isotopic composition of paleoprecipitation from authigenic in situ formed minerals to illustrate the usefulness as well as potential limitations of this method we review 1 processes controlling the isotopic composition of modern precipitation 2 stable isotope data from modern precipitation across regions of high topography and 3 stable isotope data from authigenic minerals that have been used to infer paleotopography from this we conclude that stable isotope studies of authigenic minerals can permit useful inferences on paleotopography with uncertainties that critically depend on a detailed understanding of local to global scale paleoclimate during the time interval of interest

large scale coast parallel displacements in the cordillera a granitic resolution to a paleomagnetic dilemma abstract resolution of the paleomagnetic dilemma the discrepancy between large paleomagnetically determined dextral displacement of outboard portions of the northern cordillera and much smaller offsets implied by mapping and stratigraphic correlations is fundamental to understanding the tectonic evolution of the cordillera this paper presents structural orientation data from the middle cretaceous dawson range batholith of west central yukon and its wallrocks and suggests that some of the missing displacement may be found in intrusions the elongate northwest trending batholith has a margin parallel foliation a sub horizontal stretching lineation and records syn intrusive dextral shearing in country rocks adjacent to the batholith north trending lineations are deflected clockwise into near parallelism with the batholith s margins lineations from wallrock screens within the batholith are all aligned parallel with the batholith s long axis the big creek strike slip fault forms the north margin of the batholith and accommodated a minimum of 20 km of dextral slip these observations imply that the batholith invaded an active dextral shear zone accommodated shearing while crystallizing and focused post crystallization fault development the batholith is conservatively estimated to have accommodated 45 km of syn intrusive shearing collectively middle cretaceous intrusions of the northern cordillera may account for 400 km of previously unrecognized dextral displacement

the eocene southern vancouver island orocline a response to seamount accretion and the cause of fold and thrust belt and extensional basin formation abstract a deflection of the fault controlled southwestern coastline of vancouver island suggests the presence of a minor orocline with a southern crustal block south of barkley sound alberni inlet rotated 20 counterclockwise relative to a northern fixed crustal block about a pole of rotation located northeast of port alberni in this paper two models of orocline development one of pure block rotation and one of pure bending are proposed the predictions of these models are tested against available geological maps structural orientation data identified regions of extension and contraction and paleomagnetic data structural orientation and paleomagnetic data are consistent with 18 of post late cretaceous counter clockwise rotation of the southern crustal block relative to the northern fixed crustal block a southward increase in the magnitude of rotation evident in the structural orientation data argues for a model of bending both bending and block rotation models predict the development of a zone of contraction along the northeast margin of the southern crustal block coincident with the location of the eocene cowichan fold and thrust belt that diminishes northward toward the pole of rotation as predicted the fold and thrust belt is characterized by a northerly decrease in the amount of shortening from 30 at the south end of the thrust belt to 0 shortening north of port alberni the northerly decrease in shortening is complemented by a north to south change in structural style from cylindrical to conical folds and finally to planar undeformed strata the model of block rotation predicts the presence of a zone of extension extending southwest from the zone of rotation coincident with the location of eocene extensional structures within barkley sound and with horst and graben structures in the offshore eocene to miocene tofino basin extension is less than predicted by a model of pure block rotation and suggests that much of the oroclinal rotation was accommodated by bending timing constraints indicate that orocline development was coeval with and resulted from the eocene accretion of seamounts of the crescent terrane these findings demonstrate that oroclinal orogeny the buckling of a linear crustal beam about vertical axes of rotation can significantly impact the geometry structure and character of an orogenic belt even where the buckles are minor

stable isotope geochronology of the australian regolith australian regolith profiles can be assigned to one of three post palaeozoic age groups on the basis of the oxygen isotope composition of authigenic clay minerals developed in the profile systematic variations in the isotopic composition of meteoric waters and therefore of the authigenic regolith minerals that formed in equilibrium with them are a result of the continent s drift from high to low latitudes and changes in global climate residual clays collected in situ from regolith profiles of post mid tertiary age have 18o values between 17 5 and 21 3 with the exception of samples from northern australia north of approximately 20 s which have anomalously low values because meteoric waters in northern australia are largely derived from monsoonal rain the high 18o values of post mid tertiary residual clays are consistent with australia s northward drift to low warm latitudes during this time compared with the much higher latitudes it occupied for most of its post palaeozoic history late tertiary residual clays have 18o values that are indistinguishable from all other post mid tertiary clays indicating that further subdivision of the sample groups is not feasible on a continent wide scale comparison with hypothetical modern clays in equilibrium with modern meteoric waters confirms that there has been very little change in the isotopic composition of meteoric waters in australia since the mid tertiary pre mid tertiary clays have lower 18o values between 10 0 and 17 5 which are consistently lower than post mid tertiary clays 18o values of less than 14 to 15 are thought to reflect weathering events during much earlier geologic periods perhaps early or mid mesozoic when australia was at high latitude and the australian climate was humid and cool to cold several workers have documented the existence of very old regolith profiles and land surfaces in australia and support for the above hypothesis comes from three analyses of clays from profiles of stratigraphically demonstrable pre late mesozoic age which have 18o values between 10 2 and 12 3 regolith profiles composed of low 18o clays 15 are widespread in australia and it is possible that a much greater part of the modern landscape than previously recognized developed in the early or mid mesozoic the 18o values of transported i e sedimentary kaolinites reveals that the major source for many tertiary kaolinitic sediments was this postulated pre late mesozoic low 18o regolith the stableisotope evidence that much of the australian regolith formed in comparatively cold conditions suggests that contrary to some traditional interpretations lateritization and deep weathering phenomena are not solely the result of weathering in tropical or sub tropical climates the hydrogen isotope composition of the clays range from 115 to 50 however it is inferred that the majority of clays have undergone some post formational hydrogen isotope exchange which renders their d composition unsuitable for dating purposes

paleomagnetism and age of three canadian rocky mountain diatremes paleomagnetic results and age estimates derived from them arc presented for three diatremes using as a basis of comparison the combined apparent polar wander apw path for north america and europe of van der voo the cross diatreme of the front ranges of the canadian rocky mountains has yielded a radiometric age of 241 ma earliest triassic and is hosted by the flat lying pennsylvanian tunnel mountain formation it has normal polarity magnetization and yields a paleopole correctly placed according to its radiometric age on the apw path the blackpool diatreme for which no radiometric age is available which is located in the main ranges of the rocky mountains is known to be post late ordovician because it is hosted by rocks of that age it also has magnetization of normal polarity and yields a paleopole that when calculated with respect to present horizontal is coincident with the latest cretaceous to paleocene paleopole for north america the paleopole when calculated with respect to bedding

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

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

geophysical investigation and reconstruction of lithospheric structure and its control on geology structure and mineralization in the cordillera of northern canada and eastern alaska a reconstruction of the tintina fault is applied to regional geophysical and topographic data facilitating the definition of west trending lineaments within the lower crust and or mantle lithosphere oblique to the nw trending structure of the cordilleran terranes the lineaments which exhibit a range of geophysical and geological signatures are interpreted to be related to the liard transfer zone continuous to the denali fault that divided lower and upper plates during late proterozoic cambrian rifting of the laurentian margin three dimensional gravity models show a density increase in the lower crust and mantle lithosphere to the north the transfer zone also divides bimodal mantle xenolith suites to the south from unimodal suites to the north these conclusions suggest that extended north american basement related to laurentian margin rifting that would have brought mantle lithosphere rocks to a shallow depth continuously underlies a thin carapace of accreted terranes in western yukon and eastern alaska the interpreted continuity of north american basement reaffirms that if oroclinal bending of the intermontane terranes occurred then it was prior to its emplacement upon the rifted basement examination of the spatial relationships between mineral occurrences and postaccretionary cretaceous lithospheric lineaments from their manifestation in geophysical geological and topographic data suggest that the late proterozoic lineaments influenced mesozoic mineralization through influence on the development of the shallow crustal structure intrusion and exhumation and erosion

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

salinity profiles of antarctic sea ice field data and model results in order to describe and compare sea ice salinity distributions which are of interest in the study of physical and biological ice characteristics as well as ice ocean interaction we have computed composite profiles and fitted third degree polynomials to salinity data of 129 cores from the weddell sea four characteristic profile shapes have been recognized and described through the polynomial coefficients c s i and type profiles the field data have been compared with ideal salinity profiles generated by a simulation scheme based on thermodynamic growth under climatological conditions representative of the weddell sea composite salinity profiles agree well with simulations irrespective of the growth mechanism i e frazil or congelation suggesting that ice properties which depend on salinity or porosity may evolve independent of ice growth conditions analysis of salinity and 18o data in conjunction with the simulations demonstrates that apart from meteorological conditions controlling growth velocity and temperature distribution within the ice flooding and upward brine expulsion are important in raising top salinities as frequently observed low top salinities are typical of ice that has undergone retexturing and differential desalination salinity decreases towards the bottom of a floe are a result of high oceanic heat fluxes and snow cover effects as a consequence of these processes the bulk salinity of weddell sea ice cannot be described by a simple linear age thickness relationship as characteristic of arctic first year ice

formation of a rain shadow o and h stable isotope records in authigenic clays from the siwalik group in eastern bhutan we measure the oxygen and hydrogen stable isotope composition of authigenic clays from himalayan foreland sediments siwalik group and from present day small stream waters in eastern bhutan to explore the impact of uplift of the shillong plateau on rain shadow formation over the himalayan foothills stable isotope data from authigenic clay minerals 2 m suggest the presence of three paleoclimatic periods during deposition of the siwalik group between 7 and 1 ma the mean 18o value in paleometeoric waters which were in equilibrium with clay minerals is 2 5 lower than in modern meteoric and stream waters at the elevation of the foreland basin we discuss the factors that could have changed the isotopic composition of water over time and we conclude that a the most likely and significant cause for the increase in meteoric water 18o values over time is the amount effect specifically a decrease in mean annual precipitation b the change in mean annual precipitation over the foreland basin and foothills of the himalaya is the result of orographic effect caused by the shillong plateau s uplift the critical elevation of the shillong plateau required to induce significant orographic precipitation was attained after 1 2 ma c by applying scale analysis we estimate that the mean annual precipitation over the foreland basin of the eastern bhutan himalayas has decreased by a factor of 1 7 2 5 over the last 1 3 million years 2018 american geophysical union all rights reserved