collisional snowbird tectonic zone resurrected growth of laurentia during the 1 9 ga accretionary phase of the hudsonian orogeny the 2800 km long snowbird tectonic zone is one of the most controversial tectonic features of the canadian shield metamorphic and in situ geochronologic data reported here reveal that a 1 9 ga medium to high pressure belt extends along most of this tectonic zone in contrast to recent interpretations a collisional origin is indicated by the length of this metamorphic belt tectonic thickening documented in parts of it geological contrasts across it and subduction type microdiamonds within it this collisional event marks a pre 1 865 ga phase of the hudsonian orogeny involving microcontinent accretion that was fundamental to the growth of laurentia

quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation abstract a new method of analysing isothermal remanent magnetisation irm acquisition curves based on cumulative log gaussian analysis robertson and france phys earth planet inter 82 1994 223 234 is proposed it is based on the curve fitting of the irm acquisition curve versus the logarithm of the applied field with i the acquisition curve on a linear scale ii the acquisition curve expressed as a gradient and iii the acquisition curve on a probability scale even when a sample is not saturated its magnetic properties can be defined although with less certainty the number of magnetic components required for an optimal fit to a measured irm acquisition curve is evaluated statistically the method discriminates on the basis of different mineral coercivity therefore additional rock magnetic tests are still required to separate minerals with similar coercivities

optimal excitation of interannual atlantic meridional overturning circulation variability the optimal excitation of atlantic meridional overturning circulation moc anomalies is investigated in an ocean general circulation model with an idealized configuration the optimal three dimensional spatial structure of temperature and salinity perturbations defined as the leading singular vector and generating the maximum amplification of moc anomalies is evaluated by solving a generalized eigenvalue problem using tangent linear and adjoint models despite the stable linearized dynamics a large amplification of moc anomalies mostly due to the interference of nonnormal modes is initiated by the optimal perturbations the largest amplification of moc anomalies found to be excited by high latitude deep density perturbations in the northern part of the basin is achieved after about 7 5 years the anomalies grow as a result of a conversion of mean available potential energy into potential and kinetic energy of the perturbations reminiscent of baroclinic instability the time scale of growth of moc anomalies can be understood by examining the time evolution of deep zonal density gradients which are related to the moc via the thermal wind relation the velocity of propagation of the density anomalies found to depend on the horizontal component of the mean flow velocity and the mean density gradient determines the growth time scale of the moc anomalies and therefore provides an upper bound on the moc predictability time the results suggest that the nonnormal linearized ocean dynamics can give rise to enhanced moc variability if for instance overflows eddies and or deep convection can excite high latitude density anomalies in the ocean interior with a structure resembling that of the optimal perturbations found in this study the findings also indicate that errors in ocean initial conditions or in model parameterizations or processes particularly at depth may significantly reduce the atlantic moc predictability time to less than a decade

triaxial strength and deformability of intact and increasingly jointed granite samples abstract triaxial strength tests were performed on artificially jointed standard size granite specimens with two sub vertical and three sub horizontal 2 3 joints a fully servo controlled press was used to load the samples and attain residual strength these tests add to an existing test database for intact and artificially jointed 1 2 joints samples of the same rock the main parameters from each test were used to analyse tendencies in particular changes in elasticity and peak and residual strength in line with increased jointing peak strength and apparent young s modulus decreased from the intact to the jointed specimens reflecting a tendency analogous to that deriving from the use of classification systems to characterize rock masses mohr coulomb and hoek brown failure criteria were fit to peak and residual strength tests results in the case of the hoek brown criterion it seems that an equivalent of the geological strength index gsi which reflects structure at the specimen scale could be of use in estimating the decrease in strength of increasingly jointed samples residual strength envelopes were practically the same for the intact and jointed specimens our results for granite would suggest that the so called rock mechanics scale effect at large i e the relevant change in material properties from rock samples at lab scale to that of the rock mass including the occurrence of natural discontinuities at the engineering work scale is more due to structure number orientation spacing and features of occurring joints than to sample scale effect i e the variation in properties when testing different size from a few mm to some decimetres unjointed intact rock samples at the laboratory

post failure behaviour of a rock mass under the influence of triaxial and true triaxial confinement in this paper results of triaxial and true triaxial testing conducted on physical models of a rock mass are used to describe its post failure behaviour the specimens comprised of three continuous joint sets and were prepared from blocks of sand lime model material the testing was performed using a true triaxial system tts developed by the authors the results show strain hardening strain softening and plastic behaviour in the simulated rock mass specimens depending upon joint geometry and stress state expressions are suggested to estimate post peak modulus in triaxial and true triaxial stress conditions finally a zonation table is proposed to assess the strain hardening softening and plasticity behaviour of a rock mass material with the help of joint geometry and confining stress conditions at site

seventeenth canadian geotechnical colloquium the effect of cohesion loss and stress path on brittle rock strength stress strain curves for brittle rocks show three characteristic stress levels crack initiation long term strength and peak strength damage controlled testing at low confining stresses has shown that the long term and peak strengths are sensitive to the amount of induced damage i e the greater the amount of damage the lower the long term and peak strengths these tests also showed that the brittle failure process is characterized by a loss of cohesion as friction is mobilized excavation of a circular test tunnel in massive brittle rock resulted in failure around the tunnel the back calculated strength for the failed rock around the tunnel is approximately one half of that measured in laboratory tests crack induced damage of lac du bonnet granite both in the laboratory and in situ begins when the load exceeds approximately one third of the unconfined compressive strength however the stress level associated with failure is a function of loading path in the laboratory where the loading path monotonically increases the ultimate strength of an unconfined sample is 225 mpa numerical studies suggest that in situ the loading path around the tunnel is more complex involving stress increase and decrease and stress rotation for this loading path failure initiates at a stress between 100 and 120 mpa conventional frictional failure criteria did not adequately predict the extent of brittle failure measured around the circular tunnel the results from the damage controlled laboratory tests and the microseismic monitoring carried out during tunnel construction indicate a constant deviatoric stress criterion is a reliable indicator for predicting the onset of damage this criterion was also found to give a reasonable prediction for the maximum depth of failure around the test tunnel the fundamental assumption in the constant deviatoric stress criterion is that at low confining stresses such as those which occur around underground openings the brittle failure process is dominated by cohesion loss

the moho as a magnetic boundary revisited we have re examined the question of whether it is generally true that in continental regions a relatively magnetic crust overlies a relatively non magnetic mantle whereas the original conclusion was based on limited data the present study is based on about 400 globally distributed xenolith samples while it is now clear that the moho represents a maximum velocity gradient in a complex transition from crust to mantle and while crustal magnetization is highly variable the original concept of a magnetic crust overlying a non magnetic mantle is strongly supported by the new data a large upper mantle xenolith suite of ultramafic composition is characterized by non magnetic chrome spinels and magnesian ilmenites such rocks are magnetic only where demonstrably altered the most significantly magnetic rocks within the crust are mafic types prograded to granulite grade or mafic melts of basaltic composition which crystallized deep in the crust at high pressure and temperature prograded rocks have characteristic magnetite curie points and are strongly magnetic especially the more mafic compositions while the mafic rocks formed by crystallization at depth have curie points between 400 570 c and are strongly magnetic induced magnetizations are commonly several a m and can readily account for long wavelength magnetic anomalies measured by satellite and aircraft thus there is no need to search for exotic sources for missing crustal magnetization no metal or other peculiar magnetic species have been observed by us in any of our unaltered samples mineral assemblages including magnetic components are consistent with oxidizing conditions close to the fmq buffer

petrophysical constraints on magnetic anomalies associated with metamorphic reactions in northern saskatchewan canada1 the western chipman domain of the east athabasca mylonite triangle in northern saskatchewan canada displays a large positive aeromagnetic anomaly that is the result of retrograde magnetite produc

multistage exhumation and juxtaposition of lower continental crust in the western canadian shield linking high resolution u pb and 40ar 39ar thermochronometry with pressure temperature deformation paths 1 new u pb titanite apatite rutile and 40ar 39ar hornblende muscovite biotite data are linked with existing pressure temperature deformation paths to impose detailed temporal constraints on the juxtaposition and unroofing of domains in an extensive 20 000 km2 region of exhumed lower crust in the east lake athabasca region of the western canadian shield in the 200 m y between circa 1 9 ga high pressure granulite facies metamorphism and circa 1 7 ga unconformable deposition of athabasca basin sediments on the exhumed rocks our analysis reveals at least three distinct phases of unroofing at different rates specifically we distinguish 1 an early phase of extensional unroofing in the chipman domain at rates of 1 5 2 0 km m y from 1 0 gpa to 0 8 gpa associated with mafic magmatism and metamorphism 2 an episode of regional contractional uplift and associated unroofing along the legs lake shear zone at circa 1850 ma from 0 7 0 8 gpa to 0 4 0 5 gpa and 3 a final period of extensional unroofing at rates of 0 2 0 3 km m y from 0 4 to 0 5 gpa that culminated in transport of current exposures to near surface conditions the cooling patterns and retrograde assemblages are consistent with pauses between exhumational phases the apparent convergence of disparate higher temperature histories in several deep crustal domains at circa 1 89 1 88 ga implies their juxtaposition at 0 7 0 8 gpa conditions regional east directed thrusting of the deep crustal domains as a coherent unit at 1 85 ga juxtaposed the granulites with middle crustal hearne domain rocks at 0 4 0 5 gpa conditions the detailed exhumational history allows correlation with changing regional tectonic regimes associated with the amalgamation of laurentia the temporal and spatial heterogeneity of exhumation patterns in the east lake athabasca region may be a common feature of the unroofing histories of lower crustal rocks

variations of sea surface temperature wind stress and rainfall over the tropical atlantic and south america abstract empirical orthogonal functions e0fs and composite analyses are used to investigate the development of sea surface temperature sst anomaly patterns over the tropical atlantic the evolution of large scale rainfall anomaly patterns over the equatorial atlantic and south america are also investigated the eof analyses revealed that a pattern of anomalous sst and wind stress asymmetric relative to the equator is the dominant mode of interannual and longer variability over the tropical atlantic the most important findings of this study are as follows atmospheric circulation anomalies precede the development of basinwide anomalous sst patterns over the tropical atlantic anomalous sst originate off the african coast simultaneously with atmospheric circulation anomalies and expand westward afterward the time lag between wind stress relaxation strengthening and maximum sst warming cooling is about two months anomalous atmospheric circulation patterns over northern tropical atlantic are phase

an anatomy of the cooling of the north atlantic ocean in the 1960s and 1970s abstractin the 1960s and early 1970s sea surface temperatures in the north atlantic ocean cooled rapidly there is still considerable uncertainty about the causes of this event although various mechanisms have been proposed in this observational study it is demonstrated that the cooling proceeded in several distinct stages cool anomalies initially appeared in the mid 1960s in the nordic seas and gulf stream extension before spreading to cover most of the subpolar gyre subsequently cool anomalies spread into the tropical north atlantic before retreating in the late 1970s back to the subpolar gyre there is strong evidence that changes in atmospheric circulation linked to a southward shift of the atlantic itcz played an important role in the event particularly in the period 1972 76 theories for the cooling event must account for its distinctive space time evolution the authors analysis suggests that the most likely drivers were 1 the great salinity anomaly of the late 1960s 2 an earlier

engineering properties of rock salt and simplified closed form deformation solution for circular opening in rock salt under the true triaxial stress state abstract underground structures and storage caverns are increasingly being constructed in rock salt due to its unique self healing ability and impervious nature rock salts are likely to experience and develop time dependent behavior deformation hence the characterization of rock salt for its properties including viscosity are pertinent for design of these structures in addition the material in underground openings experiences true triaxial stresses and hence it is vital to study the behaviour of such structures under true triaxial loading conditions this paper presents results of extensive laboratory testing carried out on specimens of khewra rock salt for its physico mechanical properties physical and engineering properties such as mineralogy density sonic wave velocity resistivity point load index and shear strength properties were measured a simplified closed form solution which deploys three dimensional strength criterion mogi coulomb with maxwell viscoelastic behaviour is developed to assess the stress and deformation behaviour of circular opening in plane strain condition the closed form solution assumes that the material exhibits the maxwell behavior when the stresses are lower than the yield stress and the material behavior is the combination of maxwell and mogi coulomb elastoplastic material when the stresses are equal to the yield stress in addition a cylindrical wellbore problem is solved with the proposed closed form solution and the deformation of the wellbore was estimated for the different time intervals

pb diffusion in monazite a combined rbs sims study abstract we report measurements of pb diffusion in both synthetic cepo4 and natural monazites run under dry 1 atm conditions powdered mixtures of prereacted cepo4 and pbzro3 were used as the source of pb diffusant for in diffusion experiments conducted in sealed pt capsules for durations ranging from a few hours to several weeks following the diffusion anneals pb concentration profiles were measured with rutherford backscattering spectroscopy rbs and supplemented by measurements with secondary ion mass spectrometry sims in order to evaluate potential compositional effects upon pb diffusivity and simulate diffusional pb loss that might occur in natural systems we also conducted out diffusion experiments on pb bearing natural monazites in these experiments monazite grains were surrounded by a synthetic zircon powder to act as a sink monazites from these experiments were analyzed with sims over the temperature range 1100 to 1350 c the arrhenius relation determined for in diffusion experiments on synthetic monazite is given by d 0 94 exp 592 39 kj mol 1 rt m 2 s 1 diffusivities for synthetic and natural monazites are similar as are results of measurements made on the same samples using both rbs and sims the activation energy for pb diffusion we determined is more than three times that for natural monazite reported previously with pb diffusivities at

atlantic sst gradient and the influence of enso 1 the relationship between the boreal winter el nino sst anomaly and boreal spring tropical atlantic sst gradient north atlantic minus south atlantic is investigated using a long detrended sst record for both el nino and la nina concordant cases same sign for nino3 index and atlantic sst gradient slightly dominate over discordant ones reflecting the fact that the nino3 index correlates more strongly with the north atlantic than the south atlantic sst anomaly the ratio of the numbers of concordant and discordant cases is 4 3 overall indicating strong non enso influences on the atlantic sst gradient the composite of the concordant cases shows an sst anomaly in the north atlantic with the same sign as nino3 and an opposite signed anomaly off the southwest coast of africa resembling benguela nino that of the discordant cases is dominated by a pre existing sst anomaly with the same sign as nino3 in the south central south atlantic

post yield plastic frictional parameters of a rock salt using the concept of mobilized strength abstract salt slabbing spalling and fallout surrounding underground salt storage cavern are closely associated with the nonlinear deformability and post yield property of rock salt a better understanding of the pre and post yield behavior of rock salt helps the designer in predicting displacements and failure zones around the salt cavity more accurately as well as in the optimizing design and operation in the present study an approach to determine young s modulus and poisson s ratio from triaxial test plots has been discussed a series of compression tests was performed to explore the nonlinear deformability and post yield strength properties of a rock salt the rock salt specimens were prepared from jintan salt deposit china it is found that the error in modulus obtained by directly computing the gradient of stress strain curve is relatively small and can be used in analysis however error in poisson s ratio is large the post yield strength characteristics were described by nonlinear empirical evolution law of mobilized strength components with maximum principal strain during the process of strain softening hardening the proposed generalized mohr coulomb strength criterion with cohesion weakening and frictional strengthening was proved effective to capture the post yield behavior of rock salt

optimal growth of central and east pacific enso events central pacific cp type and eastern pacific ep type el ni no and the southern oscillation enso events are investigated using linear inverse modeling optimal initial conditions and growth rates for cp or ep enso events are identified explicitly using a cp or ep enso norm the dominant difference in initial conditions that lead to cp and ep enso events is the role of the second empirical orthogonal function of tropical sea surface temperature which represents the pacific meridional mode pmm optimal initial conditions for cp type enso events include warm sst anomalies in the central subtropical pacific a characteristic of the pmm while optimal initial conditions for ep type enso events are focused in the eastern equatorial pacific and southern hemisphere subtropics along about 25 s thermocline anomalies differ in initial structures and in their influence on sst for cp and ep events results point to different roles of the pmm and thermocline variations in the evolution of cp and ep enso events

magnetism at depth a view from an ancient continental subduction and collision zone recent sophisticated global data compilations and magnetic surveys have been used to investigate the nature of magnetization in the lower crust and upper mantle two approaches to constraining magnetizations are developed providing minimum 0 01 si and maximum 0 04 si susceptibility estimates given some assumed thickness 15 km here these values are higher than are found in many continental rocks are there rocks deeper in the crust or upper mantle that are more magnetic than expected or are the model assumptions incomplete what is the magnetic behavior of deep crustal and upper mantle rocks when slightly cooler than the curie or neel temperatures of their magnetic minerals after being exhumed from locations of high grade metamorphism at greater depth different sets of equilibrium metamorphic minerals can be considered that would form under different conditions results on 1501 samples from the western gneiss region wgr norway mainly from mafic and ultramafic bodies subducted to depths of 60 200 km and temperatures of 750 up to 950 c at the very highest pressures show that rocks did not fully equilibrate to the dominant metamorphic facies conditions there is a large variation in petrophysical properties oxide minerals and mineral assemblages in wgr samples though they cannot explain the broad high amplitude deep seated anomalies measured in this region the presence of magnetite and exsolved titanohematite and hemo ilmenite in samples shows those magnetic phases are preserved even at eclogite facies conditions in part because complete eclogite facies equilibrium was rarely achieved

circulation mechanisms related to northeast brazil rainfall anomalies this study explores the role of the upper ocean for circulation anomalies in the overlying atmosphere with focus on the late boreal winter and extreme climatic events in northeast brazil data sources comprise rainfall records in the nordeste surface ship observations of the sea surface temperature sst pressure and wind fields coads period 1948 1990 satellite observations of tropical convection hrc 1971 1988 and upper air analyses of the european centre for medium range weather forecasts ecmwf 1980 1991 all for the tropical atlantic sector interhemispheric sst gradients are most strongly associated with north south contrasts in pressure and the meridional wind component whereas the inverse sst pressure relations in situ are less close enhanced northward temperature increase in the tropical atlantic is accompanied by steeper meridional pressure gradient and accelerated southerly wind component which is representative of a northward displaced intertropical convergence zone itcz with the latter in turn leading to drought in northeast brazil interhemispheric contrasts in the 850 1000 mbar layer mean temperature are similar to those of sst and account for most of the meridional surface pressure gradient during wet as compared to dry years in northeast brazil the tropical north atlantic is cooler and the south atlantic warmer and accordingly the lower tropospheric thickness is reduced to the north but inflated to the south of the equator resulting in increased reduced surface pressure over the north south atlantic as well as reduced southerly surface wind stronger subsidence over the outer tropics of the northern hemisphere and intensified ascending motion and convective activity over the nordeste related to a southward displaced near equatorial convection belt the surface and upper air evidence thus indicates the ways in which the interhemispheric sst gradients exert a hydrostatic control on the lower tropospheric thickness pattern and thus force the south north surface pressure gradients and the surface meridional wind component and hence modulate the latitude position of the itcz and nordeste rainfall

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

causes of enhanced sst variability over the equatorial atlantic and its relationship to the atlantic zonal mode in cmip5 abstracta spurious band of enhanced sea surface temperature sst variance sbev is identified over the northern equatorial atlantic in the geophysical fluid dynamics laboratory gfdl climate model version 2 1 the sbev is especially pronounced in boreal spring owing to the combined effect of both anomalous atmospheric thermal forcing and oceanic vertical upwelling the sbev is a common bias in phase 5 of the coupled model intercomparison project cmip5 found in 14 out of 23 models the sbev in cmip5 is associated with the atmospheric thermal forcing and the oceanic vertical upwelling similar to gfdl cm2 1 while the tropical north atlantic variability is only weakly correlated with the atlantic zonal mode azm in observations the sbev in cmip5 produces conditions that drive and intensify the azm variability via triggering the bjerknes feedback this partially explains why azm is strong in some cmip5 models even though the equatorial cold tongue and easterly trades are biased low

relationship between the equatorial and meridional modes of climatic variability in the tropical atlantic the tropical atlantic ocean exhibits two primary modes of interannual climate variability an equatorial mode analogous to but weaker than the pacific el nino phenomenon and a meridional mode that does not have a pacific counterpart the equatorial mode is responsible for warm and cold sea surface temperature sst events mainly in the gulf of guinea and is identifiable by abnormal changes in the equatorial thermocline slope resulting from zonal wind anomalies in the western tropical atlantic the meridional mode is characterized by a north south interhemispheric gradient of sst anomalies here it is shown using observed surface and subsurface oceanic temperatures that the meridional mode is linked to the equatorial mode at both decadal and short interannual 1 2 years time scales both modes involve north south displacements of the itcz as in the annual response

thermochronology of isotopically zoned micas insights from the southwestern usa proterozoic orogen abstract we have used three different 40 ar 39 ar laser microprobe methods to explore the distribution of radiogenic 40 ar in 1 0 1 5 mm biotite crystals from the ca 1680 ma horse mountain monzogranite of central arizona incremental heating of two single crystals with a defocused laser beam produced flat age spectra with near plateau ages of 1190 ma showing no indication of intracrystalline 40 ar inhomogeneity in contrast total fusion of twenty five biotite fragments 100 pm yielded apparent ages ranging from 1006 7 to 1212 0 ma detailed age mapping in the 001 plane of two crystals with the laser focused to a minimum spot size confirms that the age dispersion in the fragment data reflects the existence of 200 m y age gradients in single crystals the two mapped crystals display very different age distribution patterns that suggest radiogenic 40 ar loss through two mechanisms volume diffusion on a scale comparable to that of the grain radius and more rapid diffusion along discrete zones of high crystal defect density simple inverse modeling of the overall age dispersion in the two mapped crystals and the fragment population is consistent with the development of the observed age gradients by slow cooling at an average rate of 0 5 k m y the horse mountain results as well as previously published studies indicate that conventional incremental heating of hydrous phases can homogenize intracrystalline gradients in 40 ar thereby masking important details of the thermal history of analyzed samples in contrast detailed isotopic mapping studies offer a wealth of information and will become more powerful with continued improvement in the spatial resolution of 40 ar 39 ar laser microprobes total fusion studies of crystal fragment populations can be readily automated making them less labor intensive than mapping studies our preliminary experiment on a limited horse mountain fragment population suggests that this procedure has great potential as a reconnaissance tool for thermal history research

geochronological constraints on the legs lake shear zone with implications for regional exhumation of lower continental crust western churchill province canadian shield the legs lake shear zone marks the southeastern boundary of an extensive region 20 000 km2 of high pressure 0 8 1 5 gpa granulite facies rocks in the western churchill province canada the shear zone is one of the largest exhumation related structures in the canadian shield and coincides with the central segment of the 2 800 km long snowbird tectonic zone the movement history of this shear zone is critical for the development of models for the exhumation history of the high pressure region we used electron microprobe u th pb dating of monazite with supplemental id tims u pb geochronology to place constraints on the timing of shear zone activity combining these and other data we suggest that regional exhumation occurred during at least three distinct phases over an 150 million year period the first phase involved high temperature decompression from 1 0 to 0 8 0 7 gpa shortly following 1 9 ga peak metamorphism possibly under an extensional regime the second phase involved rock uplift and decompression of the hanging wall to 0 5 0 4 gpa during east vergent thrusting across the legs lake shear zone at ca 1 85 ga this phase was likely driven by early collision related convergence in the trans hudson orogen the final phase of regional exhumation involving the removal of 15 20 km of overburden from both footwall and hanging wall likely occurred after 1 78 ga and may have been related to regional extensional faulting

interpretation of aeromagnetic data in the jameson land basin central east greenland structures and related mineralized systems this paper provides a detailed interpretation of several aeromagnetic datasets over the jameson land basin in central east greenland the interpretation is based on texture and lineament analysis o

effects of finite size joints on the deformability of jointed rock at the two dimensional level a numerical decomposition technique which has resulted from a linking between joint geometry modeling and generation schemes and a distinct element code udec is used to study the effect of joint geometry parameters of finite size joints on the deformability properties of jointed rock at the two dimensional 2d level the influence of joint geometry parameters such as joint density ratio of joint size to block size and joint orientation on the deformability of jointed rock is shown relations are established between deformability properties of jointed rock and fracture tensor parameters an incrementally linear elastic anisotropic constitutive model is developed to represent the prefailure mechanical behaivour of jointed rock at the 2d level this constitutive model has captured the anisotropic scale dependent behaviour of jointed rock in this model the effect of the joint geometry network in the rock mass is incorporated in terms of fracture tensor components some insight is given related to estimation of representative elementary volumes for deformability properties of jointed rock a

the cora lake shear zone athabasca granulite terrane an intraplate response to far field orogenic processes during the amalgamation of laurentia the cora lake shear zone clsz is a 4 6 km wide localized high strain zone that bisects the polydeformed athabasca granulite terrane northern saskatchewan it also coincides with the geophysical trace of the snowbird tectonic zone the clsz represents a major lithotectonic and thermobarometric discontinuity within the exposure of 20 000 km2 of high pressure granulites most rocks have a strong mineral lineation plunging moderately to the southwest the northwestern subdomain hangingwall is characterized by ca 2 6 ga plutonic rocks that contain an early subhorizontal gneissic layering ca 2 57 ga that was overprinted by large amplitude folds and a partitioned but pervasive axial planar dextral shear fabric at ca 1 9 ga thermobarometry suggests metamorphic conditions of 0 9 gpa and 750 c during both of the phases of tectonism the footwall is predominantly underlain by the ca 3 3 3 0 ga chipman tonalite layers of intercalated mafic and felsic granulite and the widespread 1 9 ga chipman

magnetization of lower crust and interpretation of regional magnetic anomalies example from lofoten and vesteralen norway the interpretation of regional magnetic anomalies commonly observed over continental crust in both satellite and near surface magnetic data has remained enigmatic in its requirement for laterally extensive thick highly magnetic and deep seated sources presented here are the results of a detailed field analytical and experimental study of the magnetic mineralogy and magnetic properties of rocks from lofoten and vesteralen norway a province of deep seated origin with associated regional magnetic and gravity anomalies these rocks have a bulk magnetic character of surprising uniformity with susceptibilities hysteresis and curie temperatures defined solely by coarse grained magnetite stable remanence is observed in samples from sw lofoten but is not of significant magnitude the thermal enhancement of magnetic susceptibility the hopkinson effect is not important rocks from the deepest part of the section have the largest average susceptibilities 6 10 2 si and magnitudes of natural remanent magnetization nrm 5 10 4 a m2 kg these values of susceptibility together with the oft observed viscous character of the nrm suggest that these granulite facies lithologies particularly those of sw lofoten are perfect examples of lower crustal sources of typical regional magnetic anomalies furthermore these intermediate pressure granulites define a unique magnetic petrology especially for mafic compositions at higher grades of metamorphism high pressure granulites and eclogites or lower grades greenschist and amphibolite facies such magnetite bearing assemblages will be unstable and their high or low grade equivalents will be only weakly magnetic this evidence and these conclusions may be used to constrain models of lower crustal sources of regional magnetic anomalies over stable cratons it portrays the lower crust as a highly magnetic unit defined by metamorphic grade with a curie isotherm of 575 c magnetite and magnetization parallel to the ambient geomagnetic field induced and viscous components

hoek brown parameters for predicting the depth of brittle failure around tunnels a review of underground openings excavated in varying rock masstypes and conditions indicates that the initiation of brittlefailure occurs when the damage index di expressed as theratio of the maximum tangential boundary stress to the laboratoryunconfined compressive strength exceeds approx0 4 when thedamage index exceeds this value the depth of brittle failure around a tunnel can be estimated by using a strengthenvelope based solely on cohesion which in terms of thehoek brown parameters implies that m 0 it is proposed that inthe brittle failure process peak cohesion and friction are notmobilized together and that around underground openings thebrittle failure process is dominated by a loss of the intrinsiccohesion of the rock mass such that the frictional strengthcomponent can be ignored for estimating the depth of brittlefailure an essential component in designing support for theopening case histories were analyzed using the hoek brownfailure criterion with traditional frictional parameter

investigation of mechanical properties of jointed granite under compression using lattice spring based synthetic rock mass modeling approach abstract joint waviness is one of the important parameters of joint that need to be considered in civil and mining engineering design of structures built in or on jointed rock masses however this parameter is often overlooked by designers in this study the mechanical properties of laboratory scale jointed granite with both planar and non planar joints of different joint configurations are investigated using the lattice spring based synthetic rock mass ls srm modeling approach jointed granite models are calibrated using the laboratory test results and the calibrated lattice model parameters are used to perform both conventional triaxial and true triaxial compression tests in addition the influences of joint orientation intensity and persistence on the strength and deformability of jointed granite with both planar and non planar joints are investigated the simulation results show that the strength and deformation modulus of the jointed rock decrease with the increase of joint intensity and persistence the strength and deformation modulus of the jointed rock are higher for the ones with non planar joints under the true triaxial loading condition the strength and deformation modulus of the jointed granite depend strongly on the magnitude and orientation of the intermediate principal stress

magnetic properties of ultrahigh pressure eclogites controlled by retrograde metamorphism a case study from the zk703 drillhole in donghai eastern china parallel studies on rock magnetic properties petrology and mineralogy were conducted on 16 eclogite samples from the zk703 hole and magnetic susceptibilities and densities of 41 eclogite samples with different degree of retrograde metamorphism from fresh eclogite to fully retrograded eclogite from the chinese continental scientific drilling ccsd near the zk703 hole located at donghai southern sulu ultrahigh pressure metamorphic belt eastern china results show 1 that the high field slopes obtained from the hysteresis loops the paramagnetic fraction para and density have a positive correlation with the volume concentration of garnet omphacite a typical mineral assemblage used to semi quantify the degree of retrograde metamorphism the low field slopes obtained from hysteresis loops the ferrimagnetic susceptibility fraction ferri saturation isothermal remanent magnetization mrs and saturation magnetization ms have a positive correlation with the volume concentration of symplectite a mineral related to retrograded metamorphism therefore they could be potential indicators for quickly semi quantifying the degree of retrograde metamorphism of the eclogite units 2 the dominant magnetic carriers in retrograded eclogites are magnetite particles in pseudo single domain grain size region 3 the p t conditions during the retrograde decompressional process could first increase the concentration of magnetite which can reach up to 3 for extensively retrograded eclogite and then was dissolved for fully retrograded eclogite therefore change in the magnetite contents during the retrograde process is the major factor controlling the magnetism of retrograde eclogites

using calculated chemical potential relationships to account for replacement of kyanite by symplectite in high pressure granulites calculated mineral equilibria are used to account for the formation of sapphirine plagioclase spinel plagioclase and corundum plagioclase symplectites replacing kyanite in quartz plagioclase garnet kyanite granulite facies gneisses from the southern domain of the athabasca granulite terrane a segment of the snowbird tectonic zone in northern saskatchewan canada metamorphic conditions of 14 kbar and 800 c are established for the high pressure garnet kyanite assemblage using constraints from p t pseudosections and zr in rutile thermometry replacement of kyanite by symplectites reflects the reaction of kyanite with the matrix following near isothermal decompression to 10 kbar the chemical potential gradients developed between the kyanite and the matrix led to diffusion that attempted to flatten the gradients kyanite persisting as a stable phase while it is consumed by symplectite from its edge in this local equilibrium model the mineral and mineral compositional spatial relationships are shown to correspond to paths in na2o cao k2o feo mgo in the model chemical system na2o cao k2o feo mgo al2o3 sio2 nckfmas with sio2 and al2o3 taken to be completely immobile the values of na2o and cao are constrained by fixing p t conditions and choosing appropriate na2o and cao values that correspond to the observed plagioclase compositions feo mgo diagrams show the corresponding spatial relationships with kyanite and the symplectite phases these results demonstrate that the replacement of kyanite by sapphirine plagioclase and spinel plagioclase appears to be metastable with respect to replacement by corundum plagioclase replacement by corundum plagioclase does also occur apparently overprinting pre existing symplectite and also kyanite ignoring corundum the resulting diagrams account for the spatial relationships and compositions observed in the spinel plagioclase and sapphirine plagioclase symplectites they are predicted to occur over both a wide range of p t conditions 6 11 kbar 650 850 c and plagioclase compositions xan 0 5 0 9 the wide range of p t conditions that may result in identical spatial and compositional relationships suggests that such reaction textures may be of limited use in accurately quantifying the p t conditions of retrograde metamorphism

multi peak deformation behavior of jointed rock mass under uniaxial compression insight from particle flow modeling abstract evaluation of mechanical properties of jointed rock mass is very important for geological engineering problems related to underground opening slope stability dam foundation and hydraulic fracturing etc it is generally known that both strength and deformability of rock mass may change with joint geometry and arrangement by pfc particle flow code modeling this paper aims at understanding the damage mechanism of the multi peak deformation behavior of jointed rock mass with different joint orientations and continuity factors under uniaxial compression observed in the physical model tests with the smooth joint contact model not only has the inherent roughness in conventional joint model been avoided but also we can monitor the joint aperture number of closed joints and forces acting on the joints during the damage process it is shown that mobilization of joint strength plays an important role in the multi peak deformation behavior of rock mass if the joint strength is slightly mobilized or immobilized i e most joints keep open during the test strain softening occurs however if the joint strength is significantly or fully mobilized yielding platform or strain hardening may happen

statistical meso damage model for quasi brittle rocks to account for damage tolerance principle damage evolution in quasi brittle rocks is a complicated procedure in which both the post peak strain softening behavior and the immobile residual strength play key roles the post peak behavior observed from existing experiments is critical for the determination of the complete constitutive relation of quasi brittle rocks based on the test observation on the post peak immobile residual strength of quasi brittle rock specimens a proper damage tolerance is defined in this study following this theme a damage tolerance principle is presented by adopting an alternative methodology which incorporates a loading function to represent the reaction to the stress state and a condition of damage tolerance based on the mohr coulomb criterion without cohesive strength then an iterative solution is proposed to identify the parameters of the proposed model the identified constitutive law is employed to determine the load deformation behavior of quasi brittle rocks including sandstone and quartzite and the calculated results are compared with the test results under different confinement stress levels results show that the developed constitutive law for quasi brittle rocks with damage tolerance principle can be used to predict the post peak behavior including the strain softening behavior and the immobile residual strength with acceptable accuracy finally a parametric study is conducted to essentially investigate the effect of parameters of the proposed model on the observed characteristics of quasi brittle rocks

the critical role of non normality in partitioning tropical and extratropical contributions to pna growth abstractthe pacific north american pna teleconnection pattern has been linked both to tropical phenomena including the madden julian oscillation mjo and el nino southern oscillation enso an

analysis of the atlantic meridional mode using linear inverse modeling seasonality and regional influences abstractpredictability and variability of the tropical atlantic meridional mode amm is investigated using linear inverse modeling lim analysis of the lim using an energy norm identifies two optimal structures that experience some transient growth one related to el nino southern oscillation enso and the other to the atlantic multidecadal oscillation amo amm patterns analysis of the lim using an amm norm identifies an amm optimal with similar structure to the second energy optima opt2 both the amm optimal and opt2 exhibit two bands of sst anomalies in the mid to high latitude atlantic the amm optimal also contains some elements of the first energy optimal enso indicating that the lim captures the well known relationship between enso and the amm seasonal correlations of lim predictions with the observed amm show enhanced amm predictability during boreal spring and for long lead around 11 15 months forecasts initialized around september regional lims were constructed to determine the

global teleconnections of meridional overturning circulation anomalies there is a wide range of evidence from both models and palaeoclimatic data that indicates the possibility of abrupt changes in the oceanic meridional overturning circulation moc however much of our dynamical understanding of the moc comes from steady state models that rely upon the assumption of thermodynamic equilibrium and are therefore only valid on millennial time scales here a dynamical model for the global teleconnections of moc anomalies on annual to multidecadal time scales is developed it is based on a linear theory for the propagation of zonally integrated meridional transport anomalies in a reduced gravity ocean and allows for multiple ocean basins connected by a circumpolar channel to the south the theory demonstrates that the equator acts as a low pass filter to moc anomalies as a consequence moc anomalies on decadal and shorter time scales are confined to the hemispheric basin in which they are generated and have little impact on the remainder of the global ocean the linear theory is compared with the results of a global nonlinear numerical integration which it reproduces to a good approximation

global scale modes of surface temperature variability on interannual to century timescales using 100 years of global temperature anomaly data we have performed a singular value decomposition of temperature variations in narrow frequency bands to isolate coherent spatio temporal modes of global climate variability statistical significance is determined from confidence limits obtained by monte carlo simulations secular variance is dominated by a globally coherent trend with nearly all grid points warming in phase at varying amplitude a smaller but significant share of the secular variance corresponds to a pattern dominated by warming and subsequent cooling in the high latitude north atlantic with a roughly centennial timescale spatial patterns associated with significant peaks in variance within a broad period range from 2 8 to 5 7 years exhibit characteristic el nino southern oscillation enso patterns a recent transition to a regime of higher enso frequency is suggested by our analysis an interdecadal mode in the 15 to 18 years period range appears to represent long term enso variability this mode has a sizeable projection onto global average temperature and accounts for much of the anomalous global warmth of the 1980s a quasi biennial mode centered near 2 2 years period and a mode centered at 7 to 8 years period both exhibit predominantly a north atlantic oscillation nao temperature pattern a potentially significant decadal mode centered on 11 to 12 years period also exhibits an nao temperature pattern and may be modulated by the century scale north atlantic variability

syntectonic generation and segregation of tonalitic melts from amphibolite dikes in the lower crust striding athabasca mylonite zone northern saskatchewan vapor absent melting in a swarm of amphibolite dikes in the lower crust has produced segregations of tonalitic and trondhjemitic composition in a variety of textures and structures that dramatically illustrate the mechanisms of melt segregation during deformation the 3 2 ga chipman dikes intrude the mylonitized chipman tonalite within the striding athabasca mylonite zone of northern saskatchewan dike emplacement spans a major sinistral transpressive ductile deformation and granulite facies metamorphic event older dikes are intensely folded and sheared younger dikes are undeformed major and trace element analyses indicate that the dikes are tholeiitic basalts similar in composition to midocean ridge basalt thermobarometry finds conditions of 750 850 c 1 0 gpa the youngest most pristine dikes contain hornblende and plagioclase with minor clinopyroxene and garnet older migmatitic dikes have tonalitic to trondhjemitic segregations spatially associated with garnet crystals where small the segregations occupy tails or strain shadows on every garnet crystal where garnets and segregations are large leucosomes form an interconnected network that extends into the host tonalite tonalitic pools probably of dike origin collect in boudin necks and fold hinges the chipman dikes are interpreted to have been emplaced solidified and partially melted during ductile shearing in the lowermost crust perhaps near the base of an archean island arc they appear to offer an exceptional view of magma genesis where underplated mantle derived mafic magmas provide not only heat but also a component of material to new felsic magmas deformation is essential to the process allowing access of mafic magma into the lower crust and facilitating the segregation of the new felsic melts from their source rocks

nonnormal thermohaline circulation dynamics in a coupled ocean atmosphere gcm abstract using the gfdl coupled atmosphere ocean general circulation model cm2 1 the transient amplification of thermohaline circulation thc anomalies due to its nonnormal dynamics is studied a reduced space based on empirical orthogonal functions eofs of temperature and salinity anomaly fields in the north atlantic is constructed under the assumption that the dynamics of this reduced space is linear the propagator of the system is then evaluated and the transient growth of thc anomalies analyzed although the linear dynamics are stable such that any initial perturbation eventually decays nonnormal effects are found to result in a significant transient growth of temperature salinity and thc anomalies the growth time scale for these anomalies is between 5 and 10 yr providing an estimate of the predictability time of the north atlantic thc in this model there are indications that these results are merely a lower bound on the nonnormality of thc dynamics in the present coupled gcm this seems

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined

the ivrea zone and lower crustal magnetization abstract the ivrea zone in northern italy is an arcuate belt of rocks whose geological and geophysical properties indicate that they were once deep in the crust it is one of several presumed lower crustal cross sections whose magnetic properties have been well studied in a systematic way the others are the lofoten vesteralen terrane in norway the pikwitonei cross lake subprovince in manitoba the kapuskasing uplift in ontario and to a lesser extent the lewisian terrane in scotland rocks from the ivrea zone have highly variable magnetic properties consistently strong magnetization is associated with serpentinized ultramafics and the main metagabbro sequence many amphibolites and a few metapelites are also strongly magnetic natural remanent magnetization generally with a strong present field overprint has intensities comparable to induced magnetization in the more highly magnetic rocks although the strongly magnetic units have magnetizations high enough about 4 a m to account for the magnetic anomaly associated with the zone they would be required to make up a considerably larger proportion of the subsurface body than they represent in the surface outcrop a common observation in the other crustal cross sections as well like the other cross sections magnetization in the ivrea zone is carried by magnetite with some pyrrhotite in less magnetic metapelitic samples the ivrea zone contains more ultramafic rocks than most of the other sections but shows no direct correlation between magnetization and composition degree of serpentinization has a far greater influence on the magnetization of the ultramafic rocks

ultimate bearing capacity of rock masses based on modified mohr coulomb strength criterion a method for calculating the bearing capacity of spread foundations in rock is presented bearing capacity of spread foundations on rock masses based on modified mohr coulomb strength criterion charts and figures are presented for a quick obtaining of bearing capacity for shallow foundations comparison of the ultimate bearing capacity using the hoek and brown criterion and the modified mohr coulomb strength criterion

timescales and significance of high pressure high temperature metamorphism and mafic dike anatexis snowbird tectonic zone canada new geochronological isotopic and geochemical data for a spectacular swarm of deep crustal migmatitic mafic dikes offer important insight into processes operative during 1 9 ga high pressure high temperature metamorphism along the snowbird tectonic zone in northern saskatchewan high precision u pb zircon dates reveal anatexis of chipman mafic dikes at 1 896 2 0 3 ma during syntectonic and synmetamorphic intrusion at conditions of 1 0 1 2 gpa 750 c u pb zircon dates of 1 894 1 891 ma for cross cutting pegmatites place a lower bound on major metamorphism and deformation at the currently exposed crustal levels the persistence of elevated temperatures for 14 m y following peak conditions is implied by younger u pb titanite dates and by sm nd whole rock isotopic data that suggest the derivation of the pegmatites by melting of a mafic source limited melting of the host felsic gneiss at 1 9 ga despite high temperature is consistent with evidence for their previous dehydration by granulite facies metamorphism in the archean spatial heterogeneity in patterns of mafic dike and tonalitic gneiss anatexis can be attributed to lateral peak temperature and compositional variability we correlate 1 896 ma chipman mafic dike emplacement and metamorphism with substantial 1 9 ga mafic magmatism over a minimum along strike extent of 1 200 km of the snowbird tectonic zone this suggests a significant continent wide period of asthenospheric upwelling that induced incipient continental rifting extension was subsequently terminated by hinterland contraction associated with trans hudson accretion and orogenesis little activity in the lower crust for ca 650 m y prior to proterozoic metamorphism and mafic magmatism implies an extended interval of cratonic stability that was disrupted at 1 9 ga this episode of destabilization contrasts with the record of long term stability in most preserved cratons and is important for understanding the lithospheric characteristics and tectonic circumstances that control the destruction or survival of continents

a constitutive model for the deformation of a rock mass containing sets of ubiquitous joints abstract as part of the rock mass the discontinuities inherently affect the strength and the deformational behavior of rock mass existing models can either handle the pre or post peak deformation of intact rock or joints alone however a model which can determine the failure mode and simulate the complete pre and post deformation of rock mass with multi sets of joints is not yet available this study focusses on rock mass with multi sets of ubiquitous joints and establishes a mathematic model and an associated numerical implementation accounting for the anisotropy in strength and deformation induced by the existence of joints accordingly an approach incorporating the existing models or methods to enable simulation of the complete deformation of rock mass is proposed in addition to the pre and post peak deformation characteristics for intact rock the pre peak deformation of joint such as the closure shear and dilatancy effect as well as its post peak deformation such as the reduction on roughness have also been taken into account a series of comparisons validates that the proposed model is capable of presenting the joint induced anisotropy in strength and deformation of rock mass determining the possible failure modes and reasonably simulating the complete stress strain relationship as well

location structure and seismicity of the seattle fault zone washington evidence from aeromagnetic anomalies geologic mapping and seismic reflection data a high resolution aeromagnetic survey of the puget lowland shows details of the seattle fault zone an active but largely concealed east trending zone of reverse faulting at the southern margin of the seattle basin three elongate east trending magnetic anomalies are associated with north dipping tertiary strata exposed in the hanging wall the magnetic anomalies indicate where these strata continue beneath glacial deposits the northernmost anomaly a narrow elongate magnetic high precisely correlates with magnetic miocene volcanic conglomerate the middle anomaly a broad magnetic low correlates with thick nonmagnetic eocene and oligocene marine and fluvial strata the southern anomaly a broad complex magnetic high correlates with eocene volcanic and sedimentary rocks this tripartite package of anomalies is especially clear over bainbridge island west of seattle and over the region east of lake washington although attenuated in the intervening region the pattern can be correlated with the mapped strike of beds following a northwest striking anticline beneath seattle the aeromagnetic and geologic data define three main strands of the seattle fault zone identified in marine seismic reflection profiles to be subparallel to mapped bedrock trends over a distance of 50 km the locus of faulting coincides with a diffuse zone of shallow crustal seismicity and the region of uplift produced by the m 7 seattle earthquake of a d 900 930

prediction of tropical atlantic sea surface temperatures using linear inverse modeling the predictability of tropical atlantic sea surface temperature on seasonal to interannual timescales by linear inverse modeling is quantified the authors find that predictability of caribbean sea and north tropical atlantic sea surface temperature anomalies sstas is enhanced when one uses global tropical sstas as predictors compared with using only tropical atlantic predictors this predictability advantage does not carry over into the equatorial and south tropical atlantic indeed persistence is a competitive predictor in those regions to help resolve the issue of whether or not the dipole structure found by applying empirical orthogonal function analysis to tropical atlantic ssts is an artifact of the technique or a physically real structure the authors combine empirically derived normal modes and their adjoints to form influence functions maps highlighting the geographical areas to which the north tropical atlantic and the south tropical atlantic ssts are most sensitive at specified lead times when the analysis is confined to the atlantic basin the 6 month influence functions in the north and south tropical atlantic tend to be of the opposite sign and evolve into clear dipoles within 6 months when the analysis is performed on global tropical ssts the 6 month influence functions are connected

forcing of anomalous sea surface temperature evolution in the tropical atlantic during pacific warm events the seasonal evolution of anomalous interhemispheric sea surface temperature sst gradients in the tropical atlantic from january to april is studied by composites of the 10 warmest warm and 10 coldest cold januaries during 1948 1993 in the equatorial pacific using comprehensive ocean atmosphere data set ship observations in the warm as compared with the cold years an anomalous weakening of the northward sst gradient develops mainly due to anomalous warming in the tropical north atlantic this stems from the combination of three forcings all related to the weakened north atlantic trade winds during pacific warm events most important are the reduced latent heat flux in much of the tropical north atlantic and anomalous downwelling equatorward of 20 n with a further contribution from increased net radiation resulting from the reduced cloudiness due to the diminished convergence in the downstream portion of the north atlantic trades in response to the development of warm anomalies in the tropical north atlantic during january march the cross equatorial northward winds accelerate to april and this leads south of the equator not only to ekman downwelling enhanced divergence reduced cloudiness and increased net radiation but also to enhanced wind speed and evaporation the result is a modest anomalous warming in the western tropical south atlantic increased air temperature over the entire basin presumably due to atmospheric advection from the pacific has little effect on the atlantic sst pattern the anomalous interhemispheric sst gradient controlled primarily by the warm anomaly in the north atlantic has a pivotal role to play in steering the late boreal winter atmospheric circulation in the tropical atlantic sector and thus regional climate anomalies

horizontal gravity gradient an aid to the definition of crustal structure in north america a map of the magnitude of the horizontal bouguer gravity gradient over the north american continent is used to delineate lateral discontinuities in upper crustal density and or thickness associated with such processes as suturing and rifting the usefulness of gradient trends in mapping major structural boundaries which are sometimes poorly exposed or completely buried is demonstrated by examples such as the buried southward extension of the grenville front and buried boundaries of the superior province gradient trends also draw attention to poorly known structures which may have major tectonic significance and to a continent wide structural fabric which may provide a record of the tectonic growth of the north american continent

the athabasca granulite terrane and evidence for dynamic behavior of lower continental crust deeply exhumed granulite terranes have long been considered nonrepresentative of lower continental crust largely because their bulk compositions do not match the lower crustal xenolith record a pa

analysis of atlantic sst variability factoring interbasin links and the secular trend clarified structure of the atlantic multidecadal oscillation abstract atlantic sst variability in the twentieth century is analyzed factoring the influence of natural sst variability in the pacific basin and the secular change in global ssts the tropical and northern extratropical basins are analyzed together using the extended eof technique which permits extraction of the interannual and multidecadal modes in the pan atlantic basin in a single step the leading mode of pacific uninfluenced sst variability is a multidecadal oscillation focused in the extratropical basin with a period of 70 yr the mode differs from the conventional atlantic multidecadal oscillation amo in the near quiescence of the tropical subtropical basin highlighting the significant influence of the pacific basin on this region in conventional analysis as much as 45 of the regional variance resulting from the conventional amo is due to this influence the second and third modes capture the growth east to west development and decay near simultaneous loss of amplitudes of interannual

a linear inverse model of tropical and south pacific seasonal predictability a multivariate linear inverse model lim is developed to demonstrate the mechanisms and seasonal predictability of the dominant modes of variability from the tropical and south pacific oceans we construct a lim whose covariance matrix is a combination of principal components derived from tropical and extratropical sea surface temperature and south pacific ocean vertically averaged temperature anomalies eigen decomposition of the linear deterministic system yields stationary and or propagating eigenmodes of which the least damped modes resemble el nino southern oscillation enso and the south pacific decadal oscillation spdo we show that although the oscillatory periods of enso and spdo are distinct they have very close damping time scales indicating that the predictive skill of the surface enso and spdo is comparable the most damped noise modes occur in the midlatitude south pacific ocean reflecting atmospheric eastward propagating rossby wave train variability we argue that these ocean wave trains occur due to the high frequency atmospheric variability of the pacific south american pattern imprinting onto the surface ocean the enso spring predictability barrier is apparent in lim predictions initialized in march may mam but displays a significant correlation skill of up to 3 months for the spdo the predictability barrier tends to appear in june september jas indicating remote but delayed influences from the tropics we demonstrate that subsurface processes in the south pacific ocean are the main source of decadal variability and further that by characterizing the upper ocean temperature contribution in the lim the seasonal predictability of both enso and the spdo variability is increased

contrasts in sillimanite deformation in felsic tectonites from anhydrous granulite and hydrous amphibolite facies shear zones western canadian shield abstract the deformation behavior of crustal materials in variably hydrated metamorphic environments can significantly influence the rheological and seismic properties of continental crust optical observations and electron backscatter diffraction ebsd analyses are used to characterize sillimanite deformation behavior in felsic tectonites from two deformation settings in the athabasca granulite terrane western canadian shield under estimated conditions of 0 8 1 0 gpa 725 850 c in the cora lake shear zone the data suggest that sillimanite deformed by dislocation creep with slip in the 001 direction accompanied by subgrain rotation recrystallization where sillimanite locally remained undeformed strain was concentrated in surrounding weaker phases under hydrated conditions of 0 4 0 6 gpa 550 650 c in the grease river shear zone textures and cathodoluminescence imaging point to dissolution precipitation creep as the major deformation mechanism for sillimanite resulting in synkinematic growth of foliation parallel euhedral sillimanite in a preferred orientation with 001 parallel to the lineation the results suggest that temperature fluid content and modal mineralogy of the surrounding phases may all have significant influence on sillimanite deformation but that preferential alignment of sillimanite 001 parallel to the lineation persists regardless of contrasts in the conditions or mechanisms of deformation

modified mohr coulomb criterion for non linear triaxial and polyaxial strength of jointed rocks abstract rocks encountered in civil and mining engineering fields are invariably jointed and act under triaxial or polyaxial stress conditions the mohr coulomb shear strength criterion is the most widely used criterion for jointed rocks in its present form there are two major limitations of this criterion firstly it considers the strength response to be linear and secondly the effect of the intermediate principal stress on the strength behaviour is ignored a modified non linear form of mohr coulomb strength criterion has been suggested in this study to overcome these limitations barton s concept of critical state for rocks has been imbibed in the linear mohr coulomb criterion to deduce a semi empirical expression for non linear criterion however the shear strength parameters of the conventional mohr coulomb criterion are used in the proposed criterion the proposed criterion is a simple and rational nonlinear polyaxial strength criterion for anisotropic jointed rocks in an earlier publication 1 the applicability of the criterion was evaluated for intact rocks in present paper the criterion is extended to jointed rocks which are anisotropic in nature the applicability of the proposed criterion has been verified by applying it to extensive experimental data on triaxial and polyaxial test results on jointed rocks available from literature applicability of the criterion to explain rock burst conditions for some indian rocks is also demonstrated

shape and microstructure of microgranitoid enclaves indicators of magma mingling and flow abstract at tarandore point 328 km south of sydney new south wales australia two tonalite phases are in contact with a gabbroic diorite all belonging to the moruya batholith lobate to crenulate contacts pillowing of the more mafic phase in the more felsic phase net veining of the more mafic phase by the more felsic local chilling of the more mafic phase against the more felsic and an abundance of rounded to elongate microgranitoid enclaves all suggest mingling of magmas at the site of emplacement therefore all phases were emplaced before the others solidified and an order of intrusion cannot be determined the variety of microgranitoid enclaves suggests that repeated magma mingling has occurred linear geochemical trends indicate either magma mixing or restite unmixing as a prime cause of variation in the members of the moruya suite of granitoids direct evidence of mixing is not present but evidence that the magmas were substantially liquid at the time of emplacement sugests that mixing is possible restite unmixing is unlikely to be the prime process because near minimum melts which would occur in all granitoid phases according to that model should mix easily rather than mingling in fact mingling has occurred between tonalite phases of very similar composition which would not be expected if the liquid parts of enclaves were minimum melts available experimental and theoretical data on mixing in both magma chambers and conduits cannot be applied directly to the occurrence at tarandore point owing to inadequately constrained parameters but mixing generally should be favoured by higher temperatures which is consistent with our inference that relatively high proportions of melt were present in the granitoid phases at the time of emplacement conduit mixing may be reflected in a local zone of strong to extreme elongation of enclaves in which the distortion has been accomplished by magmatic flow without solid state deformation as evidenced by strong dimensional preferred orientations coupled with a lack of microstructural evidence of intragranular plastic strain this suggests that elongate enclaves should not be used as indicators of solid state deformation or as tectonic strain markers without microstructural evidence that suitably strong intracrystalline plastic deformation has taken place

lizardite versus antigorite serpentinite magnetite hydrogen and life the serpentinization of peridotite operates according to one or the other or a combination of two end member mechanisms in low temperature environments 50 300 c where lizardite is the predominant serpentine mineral olivine is consumed by reaction with h2o but its composition mg remains unchanged mg rich lizardite magnetite and dihydrogen gas brucite are products of the reaction at higher temperatures 400 600 c rates of mgfe diffusion in olivine are orders of magnitude faster with the result that the growth of mg rich antigorite can be accommodated by a compositional adjustment of olivine eliminating the need to precipitate magnetite and evolve hydrogen this latter end member mechanism probably best reflects the situation in the forearc mantle wedge

magnetic mineralogy in an archean crustal cross section implications for crustal magnetization a traverse across precambrian rocks from the kapuskasing uplift in ontario provided 31 samples from a crustal cross section that is now exposed at the surface about half the samples are dominantly paramagnetic magnetite accompanied in a few samples by minor amounts of pyrrhotite is the only significant magnetic mineral in the other half magnetic susceptibilities of these samples are constant between room temperature and about 540 c above which temperature they drop rapidly to zero magnetic susceptibility does not depend on rock type apparent original depth in the crust or degree of metamorphism the average induced magnetization of the most magnetic units in this section is less than 1 a m which is much lower than the source requirements for the deep crust deduced from aeromagnetic and satellite magnetometer surveys

a pan atlantic decadal climate oscillation sea surface temperature sst variabilities on time scales of 10 14 years have been documented in various parts of the atlantic ocean here we present observational evidence that these regional variabilities are part of a coherent pan atlantic decadal oscillation pado characterized by zonal bands of sst and wind anomalies stacked in the meridional direction with alternate polarities from the south atlantic all the way to greenland we propose that the interaction of wind evaporation and sst is key to establishing this interhemispherical pado based on results from a new ocean atmosphere coupling model forced by extratropical wind forcing the model successfully reproduces the observed decadal oscillation in both sst and wind velocity over the tropics this decadal extratropical forcing of the tropics is in sharp contrast to the well known tropics to extratropics teleconnection that operates on interannual time scales in association with el nino southern oscillation enso

a teleconnection between atlantic sea surface temperature and eastern and central north pacific tropical cyclones the el nino southern oscillation enso is a major source of seasonal tropical cyclone tc predictability in both local and remote ocean basins unusually warm eastern central equatorial pacific sea surface temperature sst during el nino tends to enhance eastern and central north pacific ecnp tcs and suppress atlantic tcs here we demonstrate that atlantic sst variability likewise influences remote tc activity in the eastern central pacific through a walker circulation type response analogous to the enso atlantic tc teleconnection using observations and 27 km resolution tropical channel model tcm simulations observed and simulated ecnp tc activity is reduced during the positive atlantic meridional mode amm which is characterized by warm northern and cool southern tropical atlantic sst anomalies and vice versa during the negative amm large ensembles of tcm simulations indicate that sst variability rather than internal atmospheric variability drives extreme ecnp hurricane seasons

petrological and geochronological constraints on high pressure high temperature metamorphism in the snowbird tectonic zone canada the upper deck of the east athabasca mylonite triangle eamt northern saskatchewan canada contains mafic granulites that have undergone high p t metamorphism at conditions ranging from 1 3 to 1 9 gpa 890 960 c coronitic textures in these mafic granulites indicate a near isothermal decompression path to 0 9 gpa 800 c the godfrey granite occurs to the north adjacent to the upper deck high p t domain well preserved corona textures in the godfrey granite constrain igneous crystallization and early metamorphism in the intermediate pressure granulite field opx pl at 1 0 gpa 775 c followed by metamorphism in the high pressure granulite field grt cpx pl at 1 2 gpa 860 c u pb geochronology of zircon in upper deck mafic granulite yields evidence for events at both c 2 5 ga and c 1 9 ga the oldest zircon dates are interpreted to constrain a minimum age for crystallization or early metamorphism of the protolith a population of 1 9 ga zircon in one mafic granulite is interpreted to constrain the timing of high p t metamorphism titanite from the mafic granulites yields dates ranging from 1900 to 1894 ma and is interpreted to have grown along the decompression path but still above its closure temperature indicating cooling following the high p t metamorphism from c 960 650 c in 4 10 myr zircon dates from the godfrey granite indicate a minimum crystallization age of 2 61ga without any evidence for 1 9 ga overgrowths the data indicate that an early granulite facies event occurred at c 2 55 2 52 ga in the lower crust c 1 0 gpa but at 1 9 ga the upper deck underwent high p t metamorphism then decompressed to 0 9 1 0 gpa juxtaposition of the upper deck and godfrey granite would have occurred after or been related to this decompression in this model the high p t rocks are exhumed quickly following the high pressure metamorphism this type of metamorphism is typically associated with collisional orogenesis which has important implications for the snowbird tectonic zone as a fundamental boundary in the canadian shield

an empirical model of tropical ocean dynamics to extend the linear stochastically forced paradigm of tropical sea surface temperature sst variability to the subsurface ocean a linear inverse model lim is constructed from the simultaneous and 3 month lag covariances of observed 3 month running mean anomalies of sst thermocline depth and zonal wind stress this lim is then used to identify the empirically determined linear dynamics with physical processes to gauge their relative importance to enso evolution optimal growth of sst anomalies over several months is triggered by both an initial sst anomaly and a central equatorial pacific thermocline anomaly that propagates slowly eastward while leading the amplifying sst anomaly the initial sst and thermocline anomalies each produce roughly half the sst amplification if interactions between the sea surface and the thermocline are removed in the linear dynamical operator the sst anomaly undergoes less optimal growth but is also more persistent and its location shifts from the eastern to central pacific optimal growth is also found to be essentially the result of two stable eigenmodes with similar structure but differing 2 and 4 year periods evolving from initial destructive to constructive interference variations among enso events could then be a consequence not of changing stability characteristics but of random excitation of these two eigenmodes which represent different balances between surface and subsurface coupled dynamics as found in previous studies the impact of the additional variables on lim sst forecasts is relatively small for short time scales over time intervals greater than about 9 months however the additional variables both significantly enhance forecast skill and predict lag covariances and associated power spectra whose closer agreement with observations enhances the validation of the linear model moreover a secondary type of optimal growth exists that is not present in a lim constructed from sst alone in which initial sst anomalies in the southwest tropical pacific and indian ocean play a larger role than on shorter time scales apparently driving sustained off equatorial wind stress anomalies in the eastern pacific that result in a more persistent equatorial thermocline anomaly and a more protracted and predictable enso event

continental transform tectonics great slave lake shear zone ca 1 9 ga northwest canada great slave lake shear zone gslsz is a northeast trending dextral mylonite zone across which the coeval north trending thelon and taltson magmatic zones on the west margin of the churchill province are offset 300 700 km it is proposed that the gslsz is a continental transform structure related to oblique collisional indentation of the active margin of the churchill province by the microcontinental slave province this accounts for geologic and geophysical differences between the thelon and taltson zones and explains the localization of a tibetan type queen maud uplift north of the gslsz and the abrupt loss of slip on the gslsz east of the uplift it also provides a new model for the athapuscow aulacogen analogous to the modern bay of bengal indo burman ranges sagaing transform andaman sea situation

modest movements spectacular fabrics in an intracontinental deep crustal strike slip fault striding athabasca mylonite zone nw canadian shield geometry and strain partitioning within lower crustal intraplate strike slip shear zones can be extremely complex compared with analogous structural levels of interplate strike slip shear zones sited at plate margins striding athabasca mylonite zone canadian shield is a spectacular ca 500 km long granulite facies continental intraplate shear zone the shear zone is composed of middle archean granulite facies annealed mylonites ca 3 13 ga and late archean ca 2 62 2 60 ga granulite facies ribbon mylonite belts which thread a sinuous course along a chain of crustal scale lozenges cored by relatively stiff rocks of mafic to intermediate composition to the northeast the mylonites form a n s trending 5 10 km thick dextral strike slip belt to the southwest this bifurcates into a pair of conjugate strike slip shear zones overlain by a contemporaneous dip slip shear zone striding athabasca mylonite zone was kinematically inefficient as a strike slip fault and cannot have accommodated large wallrock displacements nevertheless spectacular granulite facies ribbon mylonites were formed throughout the shear zone reflecting the very high temperatures ca 850 1000 c high recrystallization rate strain rate ratios and the transpressive nature of the deformation wk 1 possibly accommodated by significant volume loss by magma migration

sequence stratigraphy and evolution of the paleoproterozoic intracontinental baker lake and thelon basins western churchill province nunavut canada abstract the baker lake and thelon basins lie along the border between the rae and hearne domains of the western churchill province basin fill comprises the dubawnt supergroup a ca 1 85 1 70 ga succession of predominantly continental clastic and intercalated volcanic rocks that nonconformably and unconformably overlies granitic and supracrustal rocks most of late archean age the dubawnt supergroup comprises three second order sedimentary sequences that record deposition within a rift basin a modified rift basin and a thermal sag basin respectively the baker sequence is inferred to represent the principal phase in the development of baker lake basin a series of generally elongate northeast striking half graben and fault bounded troughs filled with continental redbeds and coeval voluminous ultrapotassic volcanic rocks faults parallel to the basin margin exhibit evidence for strike slip ca 1 83 1 81 ga the nature and timing of basin development and associated magmatism allows that it may be a transtensional basin that formed by lateral escape in response to crustal thickening during the trans hudson orogeny similar to the formation of mesozoic and cenozoic strike slip and associated rift basins on the margins of the tibetan plateau the overlying whart sequence was deposited in small basins formed by block faulting and tilting of the baker sequence basin fill comprises eolian and alluvial redbeds with intercalated rhyolite flows and epiclastic rocks distribution of facies and stratigraphy suggest that faulting occurred throughout deposition of the whart sequence but ceased before deposition of the overlying barrens sequence ca 1 72 ga deformation and basin formation can be linked to a regional episode of granite emplacement and associated thermal metamorphism ca 1 76 1 75 ga the barrens sequence represents deposition over a broader area primarily in thelon basin strata generally are thinner and flatter than underlying sequences and display lateral continuity indicating minimal influence from syndepositional faulting the depositional record reflects progressive upward fining and eventually the first record of marine transgression within the dubawnt supergroup these features suggest that the barrens sequence was deposited over a broad region of thermal subsidence likely related to cooling of previously attenuated continental lithosphere the barrens sequence may be a remnant of a huge cratonic sand sheet that included the thelon athabasca amundsen and elu basins a regional subsidence mechanism to account for these basins may be mantle downwelling linked to the late stage amalgamation of laurentia the tripartite sequence evolution of the baker lake and thelon basins represents a framework for future sequence correlation among late paleoproterozoic basins in laurentia and shares characteristics with the evolution of contemporaneous intracontinental basins from north central australia and southeastern brazil

argon composition of metamorphic fluids implications for 40ar 39ar geochronology the concentration and isotopic composition of argon trapped in fluid inclusions within a mylonitic amphibolite were determined by combining electron microprobe sup 40 ar sup 39 ar laser microprobe and fluid inclusion analyses on the same samples in our study fluid in inclusions formed during ductile deformation was probably derived locally from the paleozoic caledonian sequences whereas brines emplaced in cross cutting fractures were derived from proterozoic footwall rocks several kilometers from the mylonite by utilizing sup 38 ar sub cl to correct for open quotes excess sup 40 ar close quotes we estimate a 370 ma closure age for the amphibole which is distinctly younger than the 440 480 ma plateau ages indicated by step heating spectra the open quotes excess sup 40 ar close quotes responsible for the anomalous plateaus probably resulted from diffusive re equilibration of the amphibole with the fluids present during ductile deformation of the mylonite the significantly younger cooling age determined by our method is concordant with ages determined from more recent geochronological studies in the region these ages indicate that the western gneiss terrain in our study area records deformation and cooling associated with siluro devonian tectonothermal metamorphism rather than an earlier caledonian tectonism as proposed in previous sup 40 ar sup 39 ar investigators 46 refs 8 figs

paleomagnetism and structural history of the ghost range intrusive complex central abitibi belt ontario further evidence for the late archean geomagnetic field of north america on the basis of their remanence properties the lithologies of the late archean 2710 2703 ma ghost range complex an east west trending layered mafic ultramafic extrusive sequence in the central

contractional uplift of deep crustal rocks along the legs lake shear zone western churchill province canadian shield the legs lake shear zone juxtaposes high pressure 1 0 gpa granulite and eclogite facies rocks with low pressure 0 5 gpa amphibolite to granulite facies rocks and thus may represent an important crustal scale exhumation related structure in the western canadian shield field mapping and structural and petrologic analysis document the deformation and metamorphic history of rocks within and adjacent to the shear zone at least two important phases of deformation are recorded 1 early oblique thrusting d2 that placed high grade rocks over lower grade rocks and 2 more discrete and lower grade brittle ductile normal faulting d3 that may represent the later part of the exhumation history the northwest dipping shear zone consists of 5 8 km of mylonite in map view which bounds the southeast margin of the east athabasca mylonite triangle high pressure granulite facies metamorphism 750 850 c 1 0 1 2 gpa occurred in the east athabasca mylonite triangle at ca 1900 ma prior to d2 juxtaposit

reconstruction of a large deep crustal terrane implications for the snowbird tectonic zone and early growth of laurentia the 2800 km long snowbird tectonic zone is a well recognized but still enigmatic feature in the western canadian shield it has been interpreted as a paleoproterozoic continental suture or an archean strike slip fault system but here we suggest that the distinctive geometry of the central snowbird tectonic zone is primarily due to the interaction of crosscutting paleoproterozoic intracontinental thrust and strike slip shear zones having a length of hundreds of kilometers first a major zone of thrust sense shearing coeval with early continent continent collision between the superior and western churchill provinces accommodated uplift of a large exposure of granulite facies lower continental crust younger strike slip shear zones perhaps analogous to asian fault systems behind the himalayan orogen offset the thrust zone thus the current geometry and distribution of deep crustal rocks in this region represent a relatively late stage in the tectonic evolution of the western churchill province rather than an accretionary one earlier structures oriented at a high angle to the snowbird tectonic zone may record the fundamental accretionary history in this part of laurentia

interdecadal variations in north atlantic sea surface temperature and associated atmospheric conditions abstract evidence is presented for a distinct pattern of ocean atmosphere relationship associated with interdecadal variability in the north atlantic region using a century of surface marine observations it is shown that middle and high latitude sea surface temperature sst display a long term fluctuation with negative anomalies before 1920 and during the 1970s and 1980s positive sst conditions prevailed from about 1930 to 1960 the pattern of interdecadal sst variability is constructed by subtracting the average field during 15 cold years from that during a similar interval of warm years the early century warming and the more recent cooling display a similar spatial pattern in both cases the pattern is basin scale and largely of one polarity with maxima in the vicinity of iceland in the labrador sea and northeast of bermuda the corresponding differences in surface atmospheric conditions are determined by averaging and subtracting in the same manner fields of sea level pressure slp and surf

aeromagnetic interpretation of the kirkland lake larder lake portion of the abitibi greenstone belt ontario high resolution aeromagnetic data from the larder lake kirkland lake region have been analyzed to develop optimum maps for geologic interpretation the use of the apparent susceptibility technique has led to a map that shows clearly the major lithologies in a major synclinorium in the abitibi greenstone belt calc alkaline volcanics of the blake river group are weakly magnetic but show ring like anomalies associated with intrusives where magnetite has been generated in the country rock alternating bands of mg rich and fe rich tholeiites of the kinojevis group show a strong magnetization associated with the fe rich phases gabbroic intrusions underlain by serpentine and peridotite give strong levels of magnetization these various units have been sampled and it is shown that the susceptibility is not high enough to account for the anomalies rather the anomalies are associated with the mean natural remanent magnetization in the formations sampled these studies have led to a revised geological map of this region

magnetic properties of exposed deep crustal rocks from the superior province of manitoba abstract a traverse across precambrian rocks of the superior province in central manitoba provided 56 samples for magnetic study from the pikwitonei granulite domain and the adjacent cross lake subprovince these rocks represent a cross section of the continental crust presently exposed at the surface thirty one samples are dominantly paramagnetic and three contain pyrrhotite twenty two samples from silicic plutonic rocks which make up about 80 of the section by volume contain nearly pure magnetite and have susceptibilities that are almost constant between room temperature and 540 c averaging about 1 10 2 si units the mafic supracrustal rocks with much higher iron content are about an order of magnitude less magnetic because they contain little or no magnetite susceptibility is generally independent of metamorphic grade or apparent depth in the crust the discrepancy between induced magnetizations of measured lower crustal rocks and the source requirements of long wavelength magnetic anomalies may be due to a high temperature viscous magnetization in the deep crust

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

geology and thermotectonic evolution of the western margin of the trans hudson orogen evidence from the eastern sub athabasca basement saskatchewan in the cree lake zone of northern saskatchewan reworked archean orthogneisses are overlain by a highly deformed supracrustal sequence the paleoproterozoic wollaston group this package of rocks was deformed and metamorphosed during the ca 1 8 ga continent continent collision of the trans hudson orogen tho forming the wollaston fold thrust belt that underlies the eastern athabasca basin the hudsonian structural metamorphic and magmatic evolution of the wollaston fold thrust belt in the eastern athabasca area involved six major stages 1 early collisional stage dp1 at 1860 1835 ma involved burial of wollaston group metasediments from surface to depths equivalent to 3 5vkbar 1 kbar 100 mpa by thrust pile stacking or imbrication tectonics prograde metamorphism with garnet growth and development of early leucosomes and emplacement of ca 1840 ma grey granite suite 2 collisional stage dp2a at 1835 1820 ma involved continued deeper burial of wollaston group metasediments along a prograde

extratropical forcing of tropical atlantic variability during boreal summer and fall abstractthe connection between midlatitude atlantic sea surface temperature sst anomalies and tropical sst variations during boreal summer and fall are investigated using a coupled general circulation model gcm this research follows on an observational study that finds that using linear inverse modeling lim predictions of boreal summer tropical atlantic meridional mode amm variations can be made with skill exceeding persistence with lead times of about one year the lim framework identified extratropical atlantic sst anomalies as important precursors to the amm variations the authors have corroborated this finding using a general circulation model coupled to a slab ocean which represents a completely different physical basis from the lim initializing the gcm with the lim derived optimal sst anomaly in november results in a steady equatorward propagation of sst anomalies into the subtropics during the following boreal spring thereafter the gcm suggests that two possible feedbacks propagate

decadal predictability of the atlantic ocean in a coupled gcm forecast skill and optimal perturbations using linear inverse modeling abstract the decadal predictability of three dimensional atlantic ocean anomalies is examined in a coupled global climate model the third climate configuration of the met office unified model hadcm3 using a linear inverse modeling lim approach it is found that the evolution of temperature and salinity in the atlantic and the strength of the meridional overturning circulation moc can be effectively described by a linear dynamical system forced by white noise the forecasts produced using this linear model are more skillful than other reference forecasts for several decades furthermore significant nonnormal amplification is found under several different norms the regions from which this growth occurs are found to be fairly shallow and located in the far north atlantic initially anomalies in the nordic seas impact the moc and the anomalies then grow to fill the entire atlantic basin especially at depth over one to three decades it is found that the structure of the optimal initial conditio

unstable transition of the tropical climate to an equatorially asymmetric statein a coupled ocean atmosphere model abstract over a large zonal extent of the central and eastern pacific the intertropical convergence zone itcz is located to the north of the equator collocated with this itcz is a zonal band of warm sea surface where the highest sea surface temperatures sst along a meridian are found a one dimensional coupled ocean atmosphere model that neglects zonal variations is used to investigate this problem of latitudinal asymmetry in the tropical climate the equatorially symmetric model solution is found to be unstable to infinitesimal disturbances and equatorial asymmetries develop spontaneously a linear instability that is stationary in space and antisymmetric about the equator is responsible for the unstable transition of the model from the symmetric state the destabilizing mechanism involves a positive feedback between the scalar wind speed and sst through surface evaporation which is illustrated with a simple low order model that contains only two sst grid points one in each hemisphere the exist

eclogites of the snowbird tectonic zone petrological and u pb geochronological evidence for paleoproterozoic high pressure metamorphism in the western canadian shield eclogite occurs within the southern domain of the east athabasca mylonite triangle in northern saskatchewan situated at the boundary between the archean rae and hearne provinces of the western canadian shield the east athabasca mylonite triangle is a fundamental exposure of the 3 000 km long snowbird tectonic zone the eclogite occurs in association with a variety of lower crustal high pressure granulites that record a complex metamorphic history from 2 6 to 1 9 ga temperatures of the eclogite facies metamorphism are constrained by garnet clinopyroxene exchange thermometry at 920 1 000 c minimum pressure conditions are recorded by the jadeite quartz albite geobarometer at 1 8 2 0 gpa a near isothermal decompression path to granulite facies conditions is inferred from retrograde reaction textures involving the formation of granulite facies assemblages such as orthopyroxene plagioclase and pargasite plagioclase u pb idtims zircon geochronology of the eclogite yields a weighted mean 207pb 206pb date of 1 904 0 0 3 ma which we interpret as the time of peak eclogite facies metamorphism shrimp in situ analyses of metamorphic zircons included within omphacitic clinopyroxene support this interpretation with a weighted mean 207pb 206pb date of 1 905 19 ma inclusion suites of high pressure phases and the petrographic setting of zircon are a direct link between zircon growth and eclogite facies metamorphism zircon from one eclogite sample has older cores that are 2 54 ga which is a minimum age for the emplacement or earliest metamorphism of the gabbroic protolith u pb rutile data indicate slow cooling at 1 c ma below 500 c from 1 88 to 1 85 ga the formation and exhumation of the eclogites at ca 1 9 ga has important implications for the tectonic significance of the snowbird tectonic zone during the paleoproterozoic the eclogites described here are consistent with transport of continental crust to mantle depths during the paleoproterozoic followed by rapid buoyancy driven exhumation to normal lower crustal depths

can remanent magnetization in the deep crust contribute to long wavelength magnetic anomalies long wavelength aeromagnetic anomalies require sources in the deep crust that are far more magnetic than the measured induced magnetization of lower crustal rocks several scientists have suggested that remanence in the deep crust may provide the missing magnetization this is not likely either through stable and or viscous remanence bodies large enough to contribute to surface anomalies and carrying stable remanence probably cooled slowly enough that they are subdivided into zones of alternating polarity this subdivision sharply reduces the power in the long wavelength portion of the anomaly spectrum on the other hand if such a body carries a viscous remanence the viscous component will be acquired in such a way as to bring the total magnetization of the body into equilibrium with the earth s field this equilibrium total magnetization is only about 25 greater than the induced magnetization not enough to explain the discrepancy

magnetism of the lower crust observations from the chipman domain athabasca granulite terrain northern canada abstract magnetic properties of lower crustal rocks produce anomalies seen in satellite aeromagnetic and ground studies and are assumed to be responsible for observed long wave length anomalies lwa of 20 nt the soon to be launched swarm satellites will provide extensive data on the magnetization of the lower to middle crust in anticipation of this event we are investigating magnetic properties in a superbly exposed section of lower crust in northern saskatchewan the athabasca granulite terrain agt is a complex region of felsic and mafic lower crustal rocks part of the snowbird tectonic zone stretching ne sw across the canadian shield the agt is composed of a sequence of rocks identified as lower crustal in origin by their high pressure 1 0 gpa and high temperature 800 c metamorphism dated at 2 6 ga and 1 9 ga with uplift and exhumation at 1 85 1 80 ga the agt is characterized by low negative aeromagnetic anomalies with distinct large positive anomalies in the southern and central regions the chipman domain on the east side consists of tonalites mafic granulites and granite intruded by the chipman dike swarm at 1 9 ga where anomalies cut across mapped lithologic boundaries susceptibility measurements from both field and lab readings range over several orders of magnitude from 1 10 5 to 3 10 1 si with higher values related to both mafic granulite and some tonalite samples remanence values also show considerable variability from 0 1 ma m to 90 a m with the weakest magnetization found in the chipman dikes and the fehr granite forty samples out of 89 have koenigsberger ratios greater than 1 but low initial remanence limits its influence on anomalies hysteresis and low temperature measurements identify magnetite as the predominant iron oxide this section of lower crustal rocks has paramagnetic granites and dikes with ferromagnetic mafic granulites and bimodal tonalites defined by geographic location

analysis of the field dependence of remanent magnetization curves 1 a new method to calculate and analyze coercivity distributions of measured acquisition demagnetization curves of remanent magnetization is presented the acquisition demagnetization curves are linearized by rescaling both the field and the magnetization axes an appropriate filtering of the linearized curves efficiently removes measurement errors prior to evaluating the coercivity distributions the filtered coercivity distributions are modeled using a set of generalized probability density functions in order to estimate the contributions of different magnetic components an error estimation is calculated for these functions with analytical and numerical methods in order to evaluate whether the model is significantly different from the measured data three sediment samples from baldeggersee switzerland and three samples of urban atmospheric particulate matter pm have been analyzed using this method it is found that the coercivity distributions of some of the magnetic components show significant and consistent deviations from a logarithmic gaussian function large deviations are found also in the coercivity distributions of theoretical af demagnetization curves of single domain and multidomain particles constraints in the shape of model functions affect the identification and quantification of magnetic components from remanent magnetization curves and should be avoided as far as possible the generalized probability density function presented in this paper is suitable for appropriate modeling of gaussian and a large number of non gaussian coercivity distributions