low heat flux and large variations of lithospheric thickness in the canadian shield 1 ten new heat flux determinations have been made using measurements in 22 mining exploration boreholes located at latitudes higher than 51 n in the canadian shield they provide data in poorly sampled regions near the core of the north american craton where one expects the lithosphere to be thickest the new heat flux values are all smaller than 34 mw m 2 and are among the lowest recorded so far in the shield for all the new sites there is no relationship between heat flux and heat production in surface rocks in the canadian shield heat flux variations occur at wavelengths 100 km and are mostly of crustal origin local averages in two 250 250 km windows located on archean areas at high latitudes on either side of james bay are 29 mw m 2 and 31 mw m 2 the lowest values found so far at this scale in the canadian shield s wave traveltime delays derived from tomographic models provide the additional constraints needed to resolve differences of deep lithospheric thermal structure there is no significant correlation between average surface heat flux and traveltime delays within the canadian shield confirming that variations of the surface heat flux are mostly of crustal origin traveltime delays cannot be explained by variations in crustal heat production only and require variations of heat supply to the lithosphere and or radiogenic heat production in the lithospheric mantle these variations are associated with changes of lithospheric thickness that may be as large as 80 km the heat flux at the base of the superior lithosphere is constrained to be 11 2 mw m 2

moho signature from wide angle reflections preliminary results of the 1993 trans hudson orogen refraction experiment abstract in 1993 a combined crustal seismic refraction and wide angle reflection experiment was conducted over the northern saskatchewan and manitoba portion of the trans hudson orogen by lithoprobe the program included three seismic lines extending over 1900 km in length the exceptionally high quality data collected during the field experiment included seismic reflections and refraction events from the moho and upper lithospheric mantle the relatively high seismic fold and signal to noise ratio of the field observations made it possible to process the wide angle portion of the data set with standard reflection signal enhancement techniques the moho is revealed as a complex interface with significant structural relief 40 52 km that correlates in first order fashion with crustal geology and structure the moho topography is interpreted as a result of variable ductile reworking and eclogitization of the lower crust

the adiabatic pole to pole overturning circulation abstractthe adiabatic pole to pole cell of the residual overturning circulation roc is studied in a two hemisphere semienclosed basin with a zonally reentrant channel occupying the southernmost eighth of the domain three different models of increasing complexity are used a simple analytically tractable zonally averaged model a coarse resolution numerical model with parameterized eddies and an eddy resolving general circulation model two elements are found to be necessary for the existence of an adiabatic pole to pole cell 1 a thermally indirect wind driven overturning circulation in the zonally reentrant channel analogous to the deacon cell in the antarctic circumpolar current acc region and 2 a set of outcropping isopycnals shared between the channel and the semienclosed region of the northern hemisphere these points are supported by several computations varying the domain geometry the surface buoyancy distribution and the wind forcing all three models give results that are qualitat

on the hemispheric origins of meltwater pulse 1a abstract during the glacial interglacial transition that began subsequent to the last glacial maximum approximately 21 000 calendar years ago globally averaged eustatic sea level rose by approximately 120 m as climate warmed to its current holocene state this rise of relative sea level rsl did not occur smoothly however but was characterized by the occurrence of one or more episodes of extremely rapid increase the most extreme of these events has come to be referred to as meltwater pulse 1a and was initially identified in the coral based record of rsl history from the island of barbados in the caribbean sea although it has usually been assumed that this episode of rapid rsl rise was derivative of a partial collapse of the northern hemisphere ice sheets it has recently been suggested that this pulse could have originated in a dramatic melt back of the antarctic ice sheet in this paper the arguments presented in favour of the southern hemisphere source are revisited in order to assess the plausibility of this alternative scenario based upon the analyses presented it is concluded that the evidence previously provided in support of the southern hemisphere scenario is in fact unable to rule out an entirely northern hemisphere source for the meltwater pulse 1a since explicit evidence does exist that both the laurentide and fennoscandian ice sheets contributed to this event and that antarctic ice sheet melting occurred significantly later the southern hemisphere appears not to have been a prime mover of northern hemisphere events

abyssal connections of antarctic bottom water in a southern ocean state estimate antarctic bottom water aabw is formed in a few locations around the antarctic continent each source with distinct temperature and salinity after formation the different aabw varieties cross the southern ocean and flow into the subtropical abyssal basins it is shown here using the analysis of lagrangian trajectories within the southern ocean state estimate sose model that the pathways of the different sources of aabw have to a large extent amalgamated into one pathway by the time it reaches 31 s in the deep subtropical basins the antarctic circumpolar current appears to play an important role in the amalgamation as 70 of the aabw completes at least one circumpolar loop before reaching the subtropical basins this amalgamation of aabw pathways suggests that on decadal to centennial time scales changes to properties and formation rates in any of the aabw source regions will be conveyed to all three subtropical abyssal basins 2013 american geophysical union all rights reserved

contribution of topographically generated submesoscale turbulence to southern ocean overturning the ocean s global overturning circulation regulates the transport and storage of heat carbon and nutrients upwelling across the southern ocean s antarctic circumpolar current and into the mixed layer coupled to water mass modification by surface buoyancy forcing has been highlighted as a key process in the closure of the overturning circulation here using twelve high resolution hydrographic sections in southern drake passage collected with autonomous ocean gliders we show that circumpolar deep water originating from the north atlantic known as lower circumpolar deep water intersects sloping topography in narrow and strong boundary currents observations of strong lateral buoyancy gradients enhanced bottom turbulence thick bottom mixed layers and modified water masses are consistent with growing evidence that topographically generated submesoscale flows over continental slopes enhance near bottom mixing and that cross density upwelling occurs preferentially over sloping topography interactions between narrow frontal currents and topography occur elsewhere along the path of the antarctic circumpolar current which leads us to propose that such interactions contribute significantly to the closure of the overturning in the southern ocean

mapping ocean observations in a dynamical framework a 2004 06 ocean atlas abstract this paper exploits a new observational atlas for the near global ocean for the best observed 3 yr period from december 2003 through november 2006 the atlas consists of mapped observations and derived quantities together they form a full representation of the ocean state and its seasonal cycle the mapped observations are primarily altimeter data satellite sst and argo profiles gcm interpolation is used to synthesize these datasets and the resulting atlas is a fairly close fit to each one of them for observed quantities especially the atlas is a practical means to evaluate free running gcm simulations and to put field experiments into a broader context the atlas derived quantities include the middepth dynamic topography as well as ocean fluxes of heat and salt freshwater the atlas is publicly available online www ecco group org this paper provides insight into two oceanographic problems that are the subject of vigorous ongoing research first regarding ocean circulation estimates

transformation of deep water masses along lagrangian upwelling pathways in the southern ocean upwelling of northern deep waters in the southern ocean is fundamentally important for the closure of the global meridional overturning circulation and delivers carbon and nutrient rich deep waters to the sea surface we quantify water mass transformation along upwelling pathways originating in the atlantic indian and pacific and ending at the surface of the southern ocean using lagrangian trajectories in an eddy permitting ocean state estimate recent related work shows that upwelling in the interior below about 400 m depth is localized at hot spots associated with major topographic features in the path of the antarctic circumpolar current while upwelling through the surface layer is more broadly distributed in the ocean interior upwelling is largely isopycnal atlantic and to a lesser extent indian deep waters cool and freshen while pacific deep waters are more stable leading to a homogenization of water mass properties as upwelling water approaches the mixed layer there is net strong transformation toward lighter densities due to mixing of freshwater but there is a divergence in the density distribution as upper circumpolar deep water tends become lighter and dense lower circumpolar deep water tends to become denser the spatial distribution of transformation shows more rapid transformation at eddy hot spots associated with major topography where density gradients are enhanced however the majority of cumulative density change along trajectories is achieved by background mixing we compare the lagrangian analysis to diagnosed eulerian water mass transformation to attribute the mechanisms leading to the observed transformation

geophysics of proposed proterozoic sutures in canada abstract sutures have been identified or proposed at several sites in the canadian shield although many authors have suggested that some form of primitive plate tectonic processes have played a major role in the formation of the archean crust of the superior structural province proterozoic sutures resembling phanerozoic examples have been proposed only within the younger churchill and grenville provinces and at or near the boundaries between the older superior and slave provinces and the younger provinces gravity magnetic seismic and paleomagnetic data related to three proposed sutures in the latter category have been interpreted and generally support the view that the shield comprises a mosaic of once separated but now joined cratonic blocks the sutures vary in complexity from wide zones containing distinctive rocks formed at ancient accreting and consuming plate margins to cryptic sutures marked only by abrupt changes in metamorphism and zones of cataclasis paired negative and positive gravity anomalies associated with these sutures have been interpreted in terms of juxtaposed crustal blocks of different density and thickness magnetic anomaly patterns change abruptly at structural province boundaries available seismic results support the concept of thickened crust in the younger province as derived from gravity modelling most authors prefer interpretation of proterozoic pole positions in terms of one plate models but in some cases the interpretation of paleomagnetic data is equivocal and two plate models have been proposed

global ocean meridional overturning abstract a decade mean global ocean circulation is estimated using inverse techniques incorporating air sea fluxes of heat and freshwater recent hydrographic sections and direct current measurements this information is used to determine mass heat freshwater and other chemical transports and to constrain boundary currents and dense overflows the 18 boxes defined by these sections are divided into 45 isopycnal neutral density layers diapycnal transfers within the boxes are allowed representing advective fluxes and mixing processes air sea fluxes at the surface produce transfers between outcropping layers the model obtains a global overturning circulation consistent with the various observations revealing two global scale meridional circulation cells an upper cell with sinking in the arctic and subarctic regions and upwelling in the southern ocean and a lower cell with sinking around the antarctic continent and abyssal upwelling mainly below the crests of the major bathymetric ridges

interior water mass variability in the southern hemisphere oceans during the last decade abstractusing an argo dataset and the eccov4 reanalysis a volume budget was performed to address the main mechanisms driving the volume change of the interior water masses in the southern hemisphe

thermobaricity in the transition zones between alpha and beta oceans abstractthe role of the ocean in earth s climate is fundamentally influenced by the locally dominant stratifying property heat or salt which in turn can be used to categorize the ocean into three classes alpha beta and transition zone oceans alpha and beta oceans are regions where the stratification is permanently set by heat and salt respectively transition zone oceans exist between alpha and beta oceans and are regions where the stratification is seasonally or intermittently set by heat or salt despite their large ranges of temperature and salinity transition zone oceans are the most weakly stratified regions of the upper oceans making them ideal locations for thermobaric effects arising from the nonlinear equation of state of seawater here a novel definition and quantification of alpha beta and transition zone oceans is presented and used to analyze 4 years 2010 13 of hydrographic data developed from the argo profiling float array two types of thermobaric instabilities are defined and

heat flow gravity and structure of the abitibi belt superior province canada implications for mantle heat flow the results of new heat flow measurements are presented for eleven sites located in the abitibi greenstone belt of the archean superior province these new and previously published heat flow data are used with gravity and seismic data to constrain the crustal structure and composition of the abitibi subprovince and to determine the mantle heat flow beneath the canadian shield in order to analyze the long wavelength variations in heat flow and bouguer gravity anomaly the crust was divided into three layers with distinctive composition and physical properties average density heat production and thickness for each layer were varied within a range compatible with measurements and yielded crustal models consistent with gravity and heat flow data the dominant contribution to crustal heat production is that of a tonalitic type layer which has the lowest density the models require mantle heat flow to range between 10 and 14 mw m 2 the westward increase in heat flow requires the tonalitic layer to thicken from the grenville front toward the kapuskasing uplift at the expense of the greenstone supracrustals long wavelength gravity data are more affected by changes in crustal thickness than by composition and the low bouguer anomaly near the eastern grenville front is caused by 5 6 km of crustal thickening in greenstone terranes the long wavelength variations in heat flow are more useful for determining average crustal composition and the thickness of supracrustals than the gravity data

turbulence and diapycnal mixing in drake passage abstractdirect measurements of turbulence levels in the drake passage region of the southern ocean show a marked enhancement over the phoenix ridge at this site the antarctic circumpolar current acc is constricted in its flow between the southern tip of south america and the northern tip of the antarctic peninsula observed turbulent kinetic energy dissipation rates are enhanced in the regions corresponding to the acc frontal zones where strong flow reaches the bottom in these areas turbulent dissipation levels reach 10 8 w kg 1 at abyssal and middepths the mixing enhancement in the frontal regions is sufficient to elevate the diapycnal turbulent diffusivity acting in the deep water above the axis of the ridge to 1 10 4 m2 s 1 this level is an order of magnitude larger than the mixing levels observed upstream in the acc above smoother bathymetry outside of the frontal regions dissipation rates are o 10 10 w kg 1 comparable to the background levels of turbulence found throughout most mid and

overturning circulation driven by breaking internal waves in the deep ocean a global estimate of the water mass transformation by internal wave driven mixing in the deep ocean is presented the estimate is based on the energy conversion from tidal and geostrophic motions into internal waves combined with a turbulent mixing parameterization we show that internal wave driven mixing in the deep ocean can sustain 20 30 sv of water mass transformation one third or more of this transformation is attributed to lee waves generated by geostrophic motions flowing over rough topography primarily in the southern ocean while these results are uncertain due to many assumptions poorly constrained parameters and data noise that enter in the calculation the result that lee wave driven mixing plays an important role in the abyssal ocean circulation is likely robust the implication is that lee wave driven mixing should be represented in ocean and climate models but currently it is not citation nikurashin m and r ferrari 2013 overturning circulation driven by breaking internal waves in the deep ocean geophys res lett 40 doi 10 1002 grl 50542

thermal state under the tohoko arc with consideration of crustal heat generation abstract the thermal structure beneath subduction zones plays a key role in aiding understanding of tectonic activities such as seismicity volcanism arc formation and genesis of back arc basins around subduction zones many simulations have been made to estimate the thermal process in the mantle wedge which causes the surface activities in the tohoku arc many heat flow measurements have been made and the heat flow profile from the trench to the back arc has been constructed in this study the thermal structure in the crust of northeast japan is investigated to account for the surface heat flow data to estimate the contribution of the heat generation in the crust to the surface heat flow the heat production rate was obtained on granitic and metamorphic rocks collected from the hidaka metamorphic zone hokkaido japan where the vertical crustal section of an island arc is understood to be exposed at the surface instrumentation neutron activation analysis and gamma ray spectrometry were adopted to analyze the concentration of heat producing elements the obtained rate of heat generation and its decrease with increasing depth for the upper part of the crust were found to be similar to those estimated for stable continental areas but the heat generation rate was almost constant in the lower part of the crust the vertical distribution of the heat production rate in the crust of the northeastern japan arc was estimated from the present results and previous estimates of heat production rates in various rocks using the crustal structure determined by explosion seismology the total heat generation in the crust thus estimated is about 30 mw m 2 with the surface heat flow data and estimated heat generation distribution in the crust the thermal structure in the crust was simulated numerically modeling calculations were made on a cross section along the line from the japan trench to the japan sea a direction parallel to the direction of convergence of the pacific and eurasian plates the models were two dimensional and included frictional heating at the upper surface of the slab the calculated thermal structure in the crust shows that the temperature at the moho is about 850 c and almost about 250 c lower than previous estimates the magnitude of the interplate stress was derived by considering the rate of frictional heating at the interface between the plates in order to explain the surface heat flow between the trench and aseismic front the interplate stress should be less than 20 mpa at depth in the crust

the global influence of localized dynamics in the southern ocean the circulation of the southern ocean connects ocean basins links the deep and shallow layers of the ocean and has a strong influence on global ocean circulation climate biogeochemical cycles and the antarctic ice sheet processes that act on local and regional scales which are often mediated by the interaction of the flow with topography are fundamental in shaping the large scale three dimensional circulation of the southern ocean recent advances provide insight into the response of the southern ocean to future change and the implications for climate the carbon cycle and sea level rise

ocean forcing of glacier retreat in the western antarctic peninsula in recent decades hundreds of glaciers draining the antarctic peninsula 63 to 70 s have undergone systematic and progressive change these changes are widely attributed to rapid increases in regional surface air temperature but it is now clear that this cannot be the sole driver here we identify a strong correspondence between mid depth ocean temperatures and glacier front changes along the 1000 kilometer western coastline in the south glaciers that terminate in warm circumpolar deep water have undergone considerable retreat whereas those in the far northwest which terminate in cooler waters have not furthermore a mid ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat we conclude that changes in ocean induced melting are the primary cause of retreat for glaciers in this region

water mass transformation by cabbeling and thermobaricity water mass transformation is an important process for the global ocean circulation nonlinearities in the equation of state of seawater lead to water mass transformation due to cabbeling and thermobaricity here the contribution of cabbeling and thermobaricity to water mass transformation is calculated in a neutral density framework using temperature gradients derived from observationally based gridded climatologies and observationally based estimates of the spatially varying eddy diffusivities it is shown that cabbeling and thermobaricity play a significant role in the water mass transformation budget with cabbeling having a particularly important role in the formation of antarctic intermediate water and antarctic bottom water a physical hypothesis is presented which explains why cabbeling is important for antarctic intermediate water formation it is shown that spatially varying estimates of eddy diffusivities are essential to correctly quantify the role of cabbeling to the formation of antarctic intermediate water

the plume head continental lithosphere interaction using a tectonically realistic formulation for the lithosphere summary current debates on the existence of mantle plumes largely originate from interpretations of supposed signatures of plume induced surface topography that are compared with predictions of geodynamic models of plume lithosphere interactions these models often inaccurately predict surface evolution in general they assume a fixed upper surface and consider the lithosphere as a single viscous layer in nature the surface evolution is affected by the elastic brittle ductile deformation by a free upper surface and by the layered structure of the lithosphere we make a step towards reconciling mantle and tectonic scale studies by introducing a tectonically realistic continental plate model in large scale plume lithosphere interaction this model includes i a natural free surface boundary condition ii an explicit elastic viscous ductile plastic brittle rheology and iii a stratified structure of continental lithosphere the numerical experiments demonstrate a number of important differences from predictions of conventional models in particular this relates to plate bending mechanical decoupling of crustal and mantle layers and tension compression instabilities which produce transient topographic signatures such as uplift and subsidence at large 500 km and small scale 300 400 200 300 and 50 100 km the mantle plumes do not necessarily produce detectable large scale topographic highs but often generate only alternating small scale surface features that could otherwise be attributed to regional tectonics a single large wavelength deformation predicted by conventional models develops only for a very cold and thick lithosphere distinct topographic wavelengths or temporarily spaced events observed in the east african rift system as well as over french massif central can be explained by a single plume impinging at the base of the continental lithosphere without evoking complex asthenospheric upwelling

elastic thickness of the lithosphere in the central canadian shield we have used the coherence between bouguer gravity and topography to determine the elastic thickness t e of the lithosphere in central canada in order to improve the resolution we have estimated the spectra with the maximum entropy method the variations in elastic thickness delineate three main regions 1 the interior platform where t e varies between 25 and 50 km 2 the shield includes several high rigidity cores in particular in the trans hudson orogen and in the hearne province where t e 80km 3 the hudson bay basin has an elastic thickness between 50 and 70 km with higher values in the eastern part the results suggest that t e is controlled by the thermal regime in the platform there is no difference in t e between the proterozoic and archean provinces of the shield in the platform the elastic thickness is lowest where sediments are thickest indicating that low rigidity has amplified the subsidence of the basin

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

secular variation of the geocenter the degree 1 deformations of earth induced by a surface load are computed in a reference frame related to the center of mass of the planet using a theoretical approach love number formalism at secular timescale where earth has a viscoelastic behavior the temporal variation of the coordinates of the geocenter induced by the pleistocenic deglaciation is investigated for two loading histories three ice sheets with the same time dependence or ice 3g model testing different viscosity profiles within the mantle the present day secular variation of earth s geocenter induced by postglacial rebound is found to be from 0 2 up to 0 5 mm yr and consequently we suggest that observations from space geodesy of this rate could be used to constrain the viscosity contrast between upper and lower mantle

intraoceanic tectonics and the development of continental crust 1 92 1 84 ga evolution of the flin flon belt canada the flin flon belt is a complex amisk collage of distinct tectono stratigraphic assemblages that was brought together at a relatively early stage in the tectonic evolution of the paleoproterozoic trans hudson orogen four main tectono stratigraphic assemblage types are recognized isotopically juvenile oceanic arc 1 90 1 88 ga ocean floor ca 1 90 ga oceanic plateau ocean island and isotopically evolved arc 1 92 1 90 ga oceanic arc assemblages include tholeiitic calc alkaline and lesser shoshonitic volcanic and volcaniclastic rocks as well as turbidites and arc rift volcanic rocks the tectono stratigraphic assemblages were juxtaposed in an accretionary complex amisk collage at ca 1 88 1 87 ga probably as a result of arc arc collision collisions accretionary collage structures are largely obliterated by subsequent deformation and metamorphic events but can be inferred where cut by calc alkaline plutons related to a 1 866 1 838 ga arc coeval subaerial volcanism is recorded in ca 1 87 1 85 ga calc alkaline to shoshonitic volcaniclastic sequences unroofing of the accretionary collage development of a paleosol and deposition of continental alluvial fluvial sedimentary rocks occurred ca 1 85 1 84 ga coeval with the waning stages of post accretion arc magmatism stabilization of the flin flon belt by 1 85 1 84 ga as part of a philippines or japan like microcontinent is attributed to both tectonic and magmatic thickening of the lithosphere

heat flow and heat generation in the churchill province of the canadian shield and their palaeotectonic significance six new heat flow determinations are presented for proterozoic mobile belts of the churchill province of the canadian shield an area that was affected by several stages of the hudsonian orogenic sequence 1 9 1 6 ga ago with other previously published values the mean of eight determinations considered reliable and representative and corrected for the effects of pleistocene glaciation is 44 7 mw m 2 heat generation measurements have also been made values range from 0 1 1 04 w m 3 a linear relation between heat flow and heat production is apparent the heat flow axis intercept is 37 mw m 2 and the scale depth is 11 km compared with 28 mw m 2 and 13 6 km for the archaean superior province approximately 20 of the churchill heat flow appears to be derived from radioactive decay in the upper crust compared with 30 for the superior province and shields as a whole the observations imply that the heat flow heat production relation for the churchill province should be written as q qc qe a0b where qc is equivalent to the reduced heat flow for the archaean terrain b is similar for the two and qe is an additional component of heat flow in the proterozoic mobile belts of the churchill province a speculative tectonic model is presented it is suggested that rifting along two axes of an original craton which had lateral variations in near surface radiogenic element concentration followed by erosion of the radiogenic layer and subsequent reconvergence of the cratonic segments led to widespread redistribution of radioactive elements into the reactivated inter rift crustal block one result would be that crustal temperatures are higher in that part of the churchill province than in the superior

heat flow and structure of the lithosphere in the eastern canadian shield twenty two new determinations of heat flow and radiogenic heat production in the superior and grenville provinces of the canadian shield are presented the new data and previously published measurements strongly constrain the thermal structure of the eastern canadian shield in the abitibi greenstone belt heat flow gradually increases from 29 mw m 2 near the grenville front to 44 mw m 2 east of the kapuskasing uplift this heat flow variation is interpreted in terms of crustal thickening and increased thickness of a tonalitic layer with average heat production of about 1 1 w m 3 this interpretation based on estimated heat production of major rock types in the region is consistent with crustal models derived from recent seismic reflection and refraction studies it also leads to an estimate of about 12 mw m 2 for the mantle heat flow beneath the area the average heat flow in the grenville province 41 10 mw m 2 is the same as that of the superior province this similarity and the lack of significant variation of heat flow across the grenville front indicate that the crust on both sides of the front has similar heat production and thus composition in the western part of the grenville province heat flow reaches high values in the vicinity of the boundary between the allochtonous polycyclic and monocyclic belts where enriched granitic plutons are found in the crystalline terranes in the central part of the grenville province heat flow and heat production are related to each other the parameters of the linear heat flow heat production relationship qr 30 2 in mw m 2 and d 7 1 1 7 km are close to those of the much younger appalachian province implying that the higher appalachian heat flow is due solely to higher heat production in the upper crust the data provide no evidence for variation of mantle heat flow between the superior grenville and appalachian provinces whose tectonic ages range between 2700 and 400 ma the small value of the mantle heat flow about 12 mw m 2 implies that the depth to the 450 c isotherm which controls the effective elastic thickness of the lithosphere is very sensitive to crustal heat production

lake water geochemistry on the western kola peninsula north west russia abstract water samples were taken from 120 lakes spread over the western half of the kola peninsula nw russia the samples were analysed for 37 elements ph and electrical conductivity lake water chemistry appears in most cases to be dominated by a ca na hco3 signature characteristic of natural carbonate silicate weathering input of elements from marine derived salts and from the ni industry roasting plant at zapoljarnij smelter at nikel and smelter refinery at monchegorsk emissions are restricted to limited regions considering that 3 of the world s largest point source emitters of so2 are located within the area the median lake water ph is surprisingly close to neutral 6 6 range 4 2 7 4 indeed some of the apparently so4 contaminated lakes nearest to the smelters yield the highest ph values changes in climate and vegetation from north to south within the survey area probably have an influence on element concentrations and ph as observed in the lake waters proton displacement by sea salt cation input provides an explanation of low ph lakes in coastal areas

widespread intense turbulent mixing in the southern ocean observations of internal wave velocity fluctuations show that enhanced turbulent mixing over rough topography in the southern ocean is remarkably intense and widespread mixing rates exceeding background values by a factor of 10 to 1000 are common above complex bathymetry over a distance of 2000 to 3000 kilometers at depths greater than 500 to 1000 meters this suggests that turbulent mixing in the southern ocean may contribute crucially to driving the upward transport of water closing the ocean s meridional overturning circulation and thus needs to be represented in numerical simulations of the global ocean circulation and the spreading of biogeochemical tracers

the diffusive ocean conveyor 1 we use a novel path density transport diagnostic to trace out the deep branch of the ocean conveyor in a global circulation model our results suggest that the majority of the world s deep water is not transported back to the surface along the current systems of the standard great ocean conveyor goc standard goc routes are evident only for waters with interior residence times less than about a thousand years accounting for less than a quarter of the ventilation to re exposure flux waters with longer are spread across the deep oceans by the diffusive conveyor and by 3000 years organized into a characteristic deep north pacific pattern that is dominated by eddy diffusion the observed depletion of oxygen and 14c in the deep n pacific is consistent with a diffusive conveyor and should not be interpreted as evidence of an advective terminus of the goc deep branch

distribution of radiogenic heat generation in the arc s crust of the hokkaido island japan radiogenic heat generation was measured for rocks collected in the vertical section of the crust of the arc exposed in the hokkaido island japan measured heat generation value of metasediments is nearly constant of 1 0 w m and independent of the metamorphic grade using the measured heat generation value together with the published heat generation data of a granitic body emplaced in this section vertical profile of heat generation in the crust is constructed the estimated heat generation profile shows steep decrease with depth but is not lower than a value of 1 0 w m in the upper crust in the lower crust metabasites are dominant and heat generation value is one order of magnitude lower than that in the upper crust surface heat flow derived from the crustal heat generation is estimated to be 25 mw m when the crustal heat generation is considered temperature at the bottom of the crust estimated from surface heat flow becomes 300 c lower this temperature difference corresponds to the viscosity variation of more than three orders of magnitude which is important for understanding lithosphere dynamics

the diabatic deacon cell abstract southern ocean air sea fluxes from the coads dataset are examined for compatibility between buoyancy gain and northward ekman transport an analysis in density classes points to an upwelling of upper circumpolar deep water and subsequent buoyancy gain from air sea exchange as water flows northward in the ekman layer the upper circumpolar deep water layer is too shallow to admit southward geostrophic flow along topography and an eddy mass flux mechanism for southward transport in this layer to replenish the upwelling is advanced based on observed large scale potential vorticity gradients estimates of the strength and vertical structure of the meridional flow are given using repeated hydrographic sections and a new climatology

geothermics of the williston basin in canada in relation to hydrodynamics and hydrocarbon occurrences over 8 400 bottom hole temperature bht values from the canadian part of the williston basin were analyzed and a temperature high was discovered in the weyburn area of southeastern saskatchewan geothermal gradients thermal conductivities and heat flow have been investigated for most of the mesozoic cenozoic clastic unit as well as the upper paleozoic carbonate evaporite unit regional heat flow variations with depth occur which are closely related to the hydrodynamics governed by the topography and geology the blanketing effect of low conductivity shaly formations may cause a temperature anomaly in the south where the thickest phanerozoic cover exists however the weyburn high can be explained only partially in this way hydrodynamics has also contributed to formation of the temperature anomaly there the process of forming the anomaly by the blanketing effect and hydrodynamics also contributed to oil deposition there is a correlation between mississippian oil occurrences in the southeastern part o

new heat flow density and radiogenic heat production data in the canadian shield and the quebec appalachians new heat flow density hfd measurements were performed at 10 sites in quebec for five of the sites located in the superior province the heat flow density varies between 24 and 35 mw m2 26 and 37 mw m2 after adjustment for pleistocene climatic variations in the grenville province the values obtained range between 25 and 28 mw m2 29 and 31 mw m2 after adjustment for two nearby sites in the gaspe region appalachians the heat flow density is 47 mw m2 48 mw m2 after adjustment radiogenic heat production was also measured at the sites located in the meta volcano sedimentary sequences of the superior province the heat production is low 0 1 0 6 w m3 and it does not always correlate with the surface heat flow in the grenville province the hfd is close to slightly higher than the reduced heat flow of the superior the higher hfd in the appalachians is partly explained by the higher crustal heat production and partly by higher deep heat flow

heat flow variations in a deep borehole near sept iles quebec canada paleoclimatic interpretation and implications for regional heat flow estimates a deep 2000m borehole in the sept iles intrusion on the north shore of the saint lawrence river in quebec canada was repeatedly logged for temperature systematic variations of the temperature gradient with depth are not correlated with the thermal conductivity we interpreted the temperature profile as follows 1 during the last glacial maximum the temperature at the base of the ice sheet was cold 5 c 2 when the region was below sea level between 10 and 5ky b p the ground surface temperature was warm 6 c 3 the average ground surface temperature dropped to 2 c at 5ky b p when the region rebounded above sea level 4 the long time averaged ground surface temperature before the last glacial maximum was 0 1 c 5 the reference heat flow 36 37mw m 2 is 4 5mw m 2 higher than estimated from the upper 1000m of the heat flow profile this interpretation can not be extrapolated to the entire region covered by the laurentide ice sheet except for extremely deep 1500m boreholes the small uncertainty 15 affecting heat flow estimates can not be eliminated

water mass transformation by sea ice in the upper branch of the southern ocean overturning sea ice formation is a key factor in the lower branch of the southern ocean overturning circulation observation based data in conjunction with a water mass transformation framework reveal that sea ice plays a central role in the upper branch too

an eddy permitting southern ocean state estimate abstract an eddy permitting general circulation model of the southern ocean is fit by constrained least squares to a large observational dataset during 2005 06 data used include argo float profiles ctd synoptic sections southern elephant seals as oceanographic samplers seaos instrument mounted seal profiles xbts altimetric observations envisat geosat jason 1 and ocean topography experiment topex poseidon and infrared and microwave radiometer observed sea surface temperature an adjoint model is used to determine descent directions in minimizing a misfit function each of whose elements has been weighted by an estimate of the observational plus model error the model is brought into near agreement with the data by adjusting its control vector here consisting of initial and meteorological boundary conditions although total consistency has not yet been achieved the existing solution is in good agreement with the great majority of the 2005 and 2006 southern ocean observations and better repr

subpolar mode water in the northeastern atlantic 2 origin and transformation 1 the processes that lead to the transformation and origin of the eastern north atlantic subpolar mode waters spmw are investigated from observational data using an extended walin framework air sea flux data from the national oceanography center southampton nocs and hydrographic data from the a24 cruise collected during the world ocean circulation experiment woce are used to estimate the contribution of diapycnal and isopycnal fluxes to the density classes that include spmw surface diapycnal volume flux is the dominant source of waters in the spmw density in the north atlantic subpolar gyre the diapycnal volume flux occurs along the main branches of the north atlantic current nac and it has an average transport of 14 6 5 sv with a maximum of 21 5 sv across the 27 35sq isopycnal the regional distribution of the diapycnal flux on isopycnal surfaces is computed to identify the areas with the largest diapycnal flux these regions coincide with the location of spmw based on potential vorticity the surface diapycnal flux is associated with obduction and subduction through the permanent pycnocline therefore the water involved in the transformation of spmws is continuously exchanged with the ocean interior in addition we suggest that subduction is not associated with smooth advection from the mixed layer to the ocean interior but is water mass loss entrainment into the deep overflows of the subpolar gyre the isopycnal component of the spmw throughput is estimated from the geostrophic transport across the a24 section from greenland to scotland and is 10 to 40 of the diapycnal flux

a detailed study of the distribution of heat flow and radioactivity in new hampshire u s a abstract we present a set of 39 new determinations of heat flow and radiogenic heat production for several different geological environments in the state of new hampshire u s a with the extensive data set now available for the state the linear relation of heat flow and heat production appears as a very useful generalization for the study of the heat flow field of a geological province our measurements indicate that the vertical distribution of radiogenic heat production is similar in plutonic and metasedimentary rocks our data are compatible with the linear relationship established earlier by f birch and his co workers in 1968 young granites are markedly enriched in radioactive elements and those which do not outcrop are revealed by anomalies in the general relation of heat flow versus radioactivity heat flow is high for plutons by low elsewhere the mean heat flow through metasedimentary formations is 1 15 cal cm2 s 48 mw m2 a value near the mean heat flow for old cratons the lowest heat flow measured is 0 76 cal cm2 s 32 mw m2 for a unit poor in radioactivity the heat flow field grades smoothly into the low heat flow regions of the canadian shield the new hampshire region is in thermal equilibrium its heat flow is in secular equilibrium with the heat generated by crustal sources and that supplied from the mantle in this area the thermal perturbations due to orogenic events decrease below the detection level in less than 200 275 ma the thickness of the layer which is thermally affected during continent continent collision type orogenies cannot be greater than about 190 km

rapid cross density ocean mixing at mid depths in the drake passage measured by tracer release diapycnal mixing across density surfaces is an important process in the global ocean overturning circulation1 2 3 mixing in the interior of most of the ocean however is thought to have a magnitude just one tenth of that required to close the global circulation by the downward mixing of less dense waters4 some of this deficit is made up by intense near bottom mixing occurring in restricted hot spots associated with rough ocean floor topography5 6 but it is not clear whether the waters at mid depth 1 000 to 3 000 metres are returned to the surface by cross density mixing or by along density flows7 here we show that diapycnal mixing of mid depth 1 500 metres waters undergoes a sustained 20 fold increase as the antarctic circumpolar current flows through the drake passage between the southern tip of south america and antarctica our results are based on an open ocean tracer release of trifluoromethyl sulphur pentafluoride we ascribe the increased mixing to turbulence generated by the deep reaching antarctic circumpolar current as it flows over rough bottom topography in the drake passage scaled to the entire circumpolar current the mixing we observe is compatible with there being a southern component to the global overturning in which about 20 sverdrups 1 sv 106 m3 s 1 upwell in the southern ocean with cross density mixing contributing a significant fraction 20 to 30 per cent of this total and the remainder upwelling along constant density surfaces the great majority of the diapycnal flux is the result of interaction with restricted regions of rough ocean floor topography

three dimensional collisional structure of the trans hudson orogen canada abstract the three dimensional structure of the eastern trans hudson orogen tho part of a paleoproterozoic continent continent collision zone in central north america is revealed through a network of lithoprobe seismic reflection profiles the seismic images are interpreted to delineate a series of stacked thrust sheets essentially confined to the crust e w profiles show strong e dipping reflections extending throughout the crust while n s profiles record events outlining antiformal and synformal structures this allows the identification of decollements that may have localized along pre existing structures e g possible basin bounding extensional faults and at major rheological boundaries e g basement cover contact upper middle crust transition the present topographic surface displays oblique crustal sections with 10 15 km of structural relief generated during post collisional intracontinental transpression of tho as a result of crustal scale folding and faulting

global abyssal mixing inferred from lowered adcp shear and ctd strain profiles abstract internal wave wave interaction theories and observations support a parameterization for the turbulent dissipation rate e and eddy diffusivity k that depends on internal wave shear vz2 and strain z2 variances its latest incarnation is applied to about 3500 lowered adcp ctd profiles from the indian pacific north atlantic and southern oceans inferred diffusivities k are functions of latitude and depth ranging from 0 03 10 4 m2 s 1 within 2 of the equator to 0 4 0 5 10 4 m2 s 1 at 50 70 diffusivities k also increase with depth in tropical and subtropical waters diffusivities below 4500 m depth exhibit a peak of 0 7 10 4 m2 s 1 between 20 and 30 latitudes where semidiurnal parametric subharmonic instability is expected to be active turbulence is highly heterogeneous though the bulk of the vertically integrated dissipation e is contributed from the main pycnocline hotspots in e show some correlation with small scale bottom roughness and near bottom flow at sites where st

high temperature low pressure metamorphism in the kisseynew domain trans hudson orogen crustal anatexis due to tectonic thickening the kisseynew domain within the central trans hudson orogen constitutes a high temperature t and low to medium pressure p metasedimentary belt characterized by uniform peak metamorphic conditions of 750 50 c and 5 6 kbar 1 kbar 100 mpa to investigate the thermal evolution of the kisseynew domain 1 dimensional thermal modelling was conducted for a range of thermal parameters including the effects of exhumation and incorporating current information about the crustal architecture the results show that tectonic thickening of the sedimentary pile to 40 km consistent with present day thickness estimates and erosional levels is capable of producing enough crustal heating to melt the base of the sedimentary pile advect heat to shallower crustal levels and produce the observed p t conditions deep seated mantle heat sources though not excluded are not required

strength of martian lithosphere beneath large volcanoes this paper provides an estimate of the thermal state of martian lithosphere established since the formation of the shield volcanoes comparison of the spherical harmonic models of martian topography derived using harmonics truncated at degrees 10 11 12 and 14 shows that the volcanoes have almost no contribution from harmonic coefficients of the topography less than degree 11 therefore intermediate scale surface topography and gravity anomalies of mars specified by harmonics of degree 11 50 are considered in this study these harmonics are dominated by shield volcanoes alba patera and isidis basin the central part of valles marineris is also well defined by these harmonics the strong correlation of the topography and gravity anomalies over these harmonics and the positive bouguer anomalies of the volcanoes suggest significant excess masses beneath these surface features in addition to their topographic masses this indicates that the martian lithosphere has been strong enough to support both the topography and the internal excess masses we determine the rigidity of the lithosphere beneath a given surface feature the lithosphere is modeled by a thin elastic spherical shell that overlies an inviscid interior of higher density and is subjected to both surface and internal loads the thickness of the shell and the magnitude of the internal load are calculated such that the deformed structure resulting from the flexure of the shell under both surface and internal loads gives rise to the observed topography and gravity anomaly it is shown that the lithosphere beneath elysium mons alba patera and the central part of valles marineris can be modeled by elastic shells subjected to topographic loads alone whereas the lithosphere beneath olympus and tharsis montes cannot internal excess masses of at least 40 and more likely 50 of the topographic masses are required and the lithosphere beneath must have an elastic core of 100 80 km to support these volcanoes the mean thermal gradient beneath this region of tharsis is estimated to be 7 10 k km on the basis of the strength envelopes calculated using diabase rheology for the crust of 50 km thickness and olivine rheology for the underlying mantle

geochemical and nd isotopic compositions of the metasedimentary rocks in the la ronge domain trans hudson orogen canada implications for evolution of the domain abstract metasedimentary rocks of greenschist to amphibolite facies occur in various belts in the paleoproterozoic la ronge domain of the trans hudson orogen metasedimentary rocks in the central metavolcanic greenstone belt are low to intermediate in sio2 contents have nd values of 2 3 to 4 5 with two rare earth element ree patterns of la yb n 8 5 respectively the predominant component meta arkoses of the overlying mclennan lake belt have distinctly high k2o and sio2 contents high la yb n ratios 11 46 large negative eu anomalies eu eu 0 1 0 58 and uniformly low nd values 0 8 to 0 2 the maclean lake belt is comprised of a variety of metasedimentary gneisses the volumetrically minor amphibole and diopside rich gneisses have high ferromagnesian element sc and co concentrations high nd values of 4 1 to 5 7 and flat ree patterns with no eu anomalies the predominant lithological unit in the maclean lake belt the psammitic gneisses is geochemically more variable the mafic psammitic gneiss samples in the maclean lake belt and the metasedimentary rocks in the central metavolcanic belt are similar in trace and major element geochemistry and nd isotope composition whereas those more felsic psammitic gneisses are similar to the mclennan lake meta arkoses geochemical data combined with lithological and geochronological evidence indicate that sediments in the central metavolcanic belt were derived mainly from contiguous volcanic debris with minor addition of felsic components from exotic sources in contrast the mclennan lake meta arkoses were derived from a distinct felsic source whereas the psammitic gneisses in the maclean lake belt are mixtures of volcanic materials in the central metavolcanic belt and meta arkoses like felsic components nd isotopic data and ages of detrital zircon suggest that proterozoic juvenile materials were dominant sources for metasedimentary rocks in the la ronge domain comparison of geochemical signatures of the metasedimentary rocks with those of the felsic plutonic rocks in the central metavolcanic belt suggests that the felsic materials in the mclennan lake and maclean lake belts could not have been derived predominantly from the plutonic rocks implying more distal sources topographic changes during collision may have resulted in a shift from mixing of both local and distal sources for the rocks in the maclean lake belt to the dominance of a more distal source for the mclennan lake meta arkoses

effect of leachate solutions from fly and bottom ash on groundwater quality abstract leaching experiments on fly and bottom ash for ca mg na k fe mn zn cu and pb indicated a potential for contamination of ground and surface water supplies due to the variability in chemical composition of coals it is difficult to make generalizations concerning the chemistry of leachate solutions from the ashes of the coals a decrease in concentration with time of leaching was observed for all elements except for ca which was released at a constant rate fly ash from a missouri coal generated a leachate enriched in pb zn cu fe mn and cd reflective of the high pb 1bzn mineralization present in the surrounding area with a ph of 3 0 this ash has the greatest potential for groundwater contamination conversely leachates from wyoming fly and bottom ashes exhibited low trace metal concentrations these same solutions were high in k na ca and mg and also showed strong pozzolanic behvior which will reduce the leachability of these ashes in most instances fly and bottom ash from kentucky and illinois coals yielded leachates intermediate in elemental composition to leachates of missouri and wyoming coal ashes leaching experiments indicate that it is not valid to predict the chemistry of leachates from fly and bottom ash based solely on the chemical composition of the ash from the limited number of parameters and sites examined in this study it is clear that many of the problems related to leachates from fly and bottom ash and gob piles are site specific as well as specific to the source of coal burned these results are nevertheless indicative of problems likely to be encountered in working with these materials

upb geochronology and tectonic development of the southern flank of the kisseynew domain trans hudson orogen canada abstract the southern flank of the kisseynew domain northern manitoba underwent polyphase deformation and metamorphism during the palaeoproterozoic trans hudson orogen and represents a lithological metamorphic and structural transition from greenschist grade volcano plutonic rocks of the flin flon domain to amphibolite grade paragneisses of the central kisseynew domain the timing of geological events has previously been constrained using widely dispersed sample sites but this study has integrated u pb geochronology with detailed lithological and structural mapping in the cleunion lake area pink gneisses interpreted as missi supracrustal rocks were deposited after 1855 ma but prior to 1835 ma and thus are similar in age to fluvial sedimentary rocks in the lower grade flin flon domain all the zircons in the pink gneisses appear to be inherited or resorbed during later amphibolite grade metamorphism and a late archaean component is also indicated corundum bearing gneisses in the missi group and leucosomes in burntwood river group rocks are deformed by f1 and are indicative of an early high t low p metamorphic event m1 that may have been synchronous with the intrusion of 1835 to 1827 ma intrusions and related to regional crustal extension the above rocks are folded during a continuous compressional deformation event d2 related to terminal collision between the palaeoproterozoic rocks of the trans hudson orogen and the superior province three main fold generations f1 f2 f3 have been identified which occurred during d2 a 1818 ma granitic vein is approximately synchronous with f2 and peak metamorphic m2 conditions in the cleunion lake area cooling uplift and intrusion of pegmatites during f3 at 1800 ma provides a time limit on the waning stages of compressional deformation the main phase of compressional deformation d2 in the southern flank of the kisseynew domain thus lasted for about 30 million years

heat flow and crustal thermal structure in the late archaean closepet granite batholith south india the late archaean closepet granite batholith in south india is exposed at different crustal levels grading from greenschist facies in the north through amphibolite and granulite facies in the south along a 400 km long segment in the dharwar craton two areas pavagada and magadi located in the main mass of the batholith best represent the granitoid of the greenschist and amphibolite facies crustal levels respectively heat flow estimates of 38 mw m 2 from pavagada and 25 mw m 2 from magadi have been obtained through measurements in deep 430 and 445 m and carefully sited boreholes measurements made in four boreholes of opportunity in pavagada area yield a mean heat flow of 39 4 s d mw m 2 which is in good agreement with the estimate from deep borehole the study therefore demonstrates a clear cut heat flow variation concomitant with the crustal levels exposed in the two areas the mean heat production estimates for the greenschist facies and amphibolite facies layers constituting the main mass of the batholith are 2 9 and 1 8 w m 3 respectively the enhanced heat flow in the pavagada area is consistent with the occurrence of a radioelement enriched 2 km thick greenschist facies layer granitoid overlying the granitoid of the amphibolite facies layer which is twice as thick as represented in the magadi area the crustal heat production models indicate similar mantle heat flow estimates in the range 12 14 mw m 2 consistent with the other parts of the greenstone granite gneiss terrain of the dharwar craton

heat flow in the trans hudson orogen of the canadian shield implications for proterozoic continental growth fourteen new heat flow and radiogenic heat production measurements have been obtained in the paleo proterozoic trans hudson orogen of the canadian shield this orogen which consists of several distinctive belts corresponds to a pulse of crustal growth through island arc magmatism between 1 9 and 1 8 ga the data now available include 17 previously published measurements heat flow variations that are related to the history of magmatism and internal differentiation of the belts provide constraints on the crustal assemblages in the different belts of the orogen the average and standard deviation of heat flow values for the entire orogen 425 11 mw m 2 are identical to those of the older superior province and of the younger grenville province for the orogen as a whole heat flow is weakly correlated to the heat production of surface rocks high heat flow values are found in the thompson belt consisting of metasedimentary rocks deposited on the ancient continental margin of the superior craton there the accumulation of sediments derived from older and differentiated continental upper crust has resulted in significant concentrations of rdioelements in large volumes of rocks the heat flow is low in the belts that expose juvenile proterozoic crust consisting mostly of arc related volcanic rocks in the flin flon snow lake belt the average heat flow is the same as the average of the orogen the low heat production and the lack of correlation between heat flow and heat production suggest that the supracrustal volcanics exposed a t the surface are thin and rest on a basement richer in radioelements in the lynn lake belt the heat flow is significantly lower than the average for the orogen although the surface heat production is not low the heat flow data require a thin 10 kin surface layer overlying the mid and lower crust depleted in ra dioelements around the town of lynn lake heat flow is consistently low over a distance of m40 kin the coincidence between this cold spot and anomalously thick crust suggests that deep crustal roots may be preserved because of the stronger rheology implied by the low temperatures the evolution of the trans hudson orogen exemplifies the interplay between the processes generating rocks of evolved composition which require crustal thickening and those forming normal continental crust with average thickness which require crustal flow and soft crustal rheology

lagrangian decomposition of the deacon cell the meridional overturning cells in the southern ocean are decomposed by lagrangian tracing using velocity and density fields simulated with an ocean general circulation model particular emphasis is given to the deacon cell the flow is divided into four major components 1 water circling around antarctica in the antarctic circumpolar current acc 2 water leaving the acc toward the north into the three world oceans 3 water coming from the north and joining the acc mainly consisting of north atlantic deep water nadw and 4 interocean exchange between the three world oceans without circling around antarctica the deacon cell has an amplitude of 20 sv of which 6 sv can be explained by the the east west tilt of the acc 5 sv by the east west tilt of the subtropical gyre and the remaining 9 sv by the differences of the slope and depth of the southward transport of nadw and its return flow as less dense water the diabatic or cross isopycnal deacon cell is only 2 sv

thermal regime of the lithosphere in the canadian shieldthis article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent geothermal studies were conducted within the framework of lithoprobe to systematically document variations of heat flow and surface heat production in the major geological provinces of the canadian shield one of the main conclusions is that in the shield the variations in surface heat flow are dominated by the crustal heat generation horizontal variations in mantle heat flow are too small to be resolved by heat flow measurements different methods constrain the mantle heat flow to be in the range of 12 18 mw m 2 most of the heat flow anomalies high and low are due to variations in crustal composition and structure the vertical distribution of radioelements is characterized by a differentiation index di that measures the ratio of the surface to the average crustal heat generation in a province determination of mantle temperatures requires the knowledge of both the surface heat flow and di mantle temperatures increase with an increase in surface heat flow but decrease with an increase in di stabi

kisseynew metasedimentary gneiss belt trans hudson orogen canada back arc origin and collisional inversion the kisseynew metasedimentary gneiss belt initially developed in a back arc setting the ages of detrital zircons and crosscutting plutons constrain turbidite sedimentation to 1 855 1 841 ga postdating early deformation and metamorphism associated with arc arc and arc continent collisions affecting much of the trans hudson orogen these turbidites are interpreted to have been deposited in a back arc basin behind a retreating subduction boundary the kisseynew domain and its southern flank are marked by 1 84 1 83 ga magmatic rocks that may be related to subduction of back arc basin oceanic crust collapse of the kisseynew basin by ductile fold and thrust deformation began during 1 84 1 83 ga magmatism and continued through peak metamorphism at ca 1 820 1 805 ga from authors

trans hudson orogen and williston basin in montana and north dakota new cocorp deep profiling results cocorp consortium for continental reflection profiling deep reflection profiling across the williston basin and underlying trans hudson orogen shows the following 1 there is no evidence for a precursor rift basin beneath the axis of the williston basin with the exception of small scale structures e g nesson and cedar creek anticlines the basement surface beneath the williston basin is smooth and has a dish shaped geometry 2 crustal penetrating reflections within the eastern trans hudson orogen dip eastward in apparent contradiction to the conventional view that the superior province underthrusts the eastern side of the orogen 3 basement reflections beneath the center of the orogen define a broad crustal scale antiform the axis of which coincides approximately with the depocenter of the overlying williston basin midcrustal reflections defining the crest and western flank of this antiform also coincide generally with the location and shape of the source of the north american central plains conductivity anomaly 4 crustal penetrating reflections beneath the western side of the orogen dip westward supporting the current view that subduction polarity was to the west beneath the wyoming province 5 the eastern edge of the wyoming province is marked by east dipping upper crustal reflections and subhorizontal lower crustal reflections that are truncated by the west dipping reflectivity of the trans hudson orogen

u pb zircon ages from the lynn lake and rusty lake metavolcanic belts manitoba two ages of proterozoic magmatism two ages of magmatism have been determined from zircon in felsic flows and plutons in the churchill province of manitoba a rhyolite flow from the lynn lake metavolcanic belt has a u pb age of and a rhyolite flow from the adjacent rusty lake metavolcanic belt has an age of tonalite and quartz diorite from two composite plutons emplaced into the volcanic rocks at lynn lake have ages of and indistinguishable from the age of the rusty lake belt rhyolite the arcuate domain of metavolcanic rocks that includes the rusty lake belt in the southeast the lynn lake belt in the north and the la ronge belt saskatchewan in the southwest has previously been considered a single structural sub province with similar ages throughout our results and published u pb ages from saskatchewan indicate that an older magmatism is represented by volcanic rocks in the lynn lake belt a younger magmatism by volcanic rocks in the rusty lake and la ronge belts and plutons in the lynn lake belt at lynn lake the older magmati

deep seismic profile across a proterozoic collision zone surprises at depth collisions between continents generate the world s most striking mountains the deep structure of these collision zones inferred from seismic reflection profiles1 3 can be equally dramatic if less well understood improved knowledge of the structure of ancient collisional belts now known to have developed through plate tectonic processes4 5 can provide important new insights into the mechanisms of crustal growth although many such belts have been partly destroyed by severe post collisional deformation6 7 or magmatism8 some have been preserved in the stable interiors of continents9 one example is the early proterozoic trans hudson orogen9 10 in western canada here we present seismic reflection images across the entire orogen which reveal a broadly symmetric structure with reflections linked to island arc rocks dipping beneath both bounding archaean cratons the observed reflection geometries imply a doubling of crustal thickness during the collision along crust penetrating faults the presence of a significant amount of archaean crust at depth the extent of which could not have been determined from surface mapping suggests the need for caution in inferring crustal growth rate from the surface area of juvenile crust11 12

new seismic images of the crust in the central trans hudson orogen of saskatchewan abstract a reprocessing program to enhance the correlation between the surface geology and the seismic data has been completed for seismic line 9 eastern 100 km and line 10 in the central region of the trans hudson orogen of saskatchewan canada the new seismic images through lateral continuity of reflectivity provide sufficient detail to resolve the discrepancy between the low dipping layer parallel and dextral reverse nature of the sturgeon weir shear zone line 9 observed in the field and its steeply dipping apparent normal displacement character interpreted on the basis of the initial processing furthermore the new interpretation provides a strong confirmation of the role of pelican thrust as a major detachment zone the main sole thrust along which juvenile allochthons have been carried across the archaean microcontinental block the images are also refined enough to suggest a a boundary within the pelican thrust between its internal and external suites b a possible boundary separating a lower older archaean basement from its upper younger counterpart and c sub moho events m2 which reveal possible involvement of the upper mantle in the collisional tectonic process in addition to the well defined moho m1 which probably represents the youngest of the post collisional detachments

a global analysis of heat flow from precambrian terrains implications for the thermal structure of archean and proterozoic lithosphere previous studies of heat flow from precambrian terrains have yielded two different relationships a global temporal relationship between heat flow and tectonic age and a regional spatial relationship between heat flow and the proximity of archean cratons we analyze heat flow from tectonically stable precambrian terrains worldwide to address questions associated with these two heat flow patterns 1 is the spatial relationship a global pattern 2 do the two heat flow relationships have a common underpinning in answer to the first question our data analysis reveals a widespread spatial pattern between heat flow and the proximity of archean cratons which is characterized by low heat flow in archean cratons and proterozoic terrains adjacent to cratonic margins and higher heat flow in proterozoic terrains that are more than a few hundred kilometers from a craton to address the second question we examine three previous interpretative models of precambrian heat flow 1 simple cooling of a thermal boundary layer 2 thicker lithosphere in archean terrains than in proterozoic and 3 greater heat production in proterozoic crust than in archean model 1 predicts essentially no change in heat flow in terrains older than 1 5 ga and therefore does not likely provide a common underpinning for the precambrian heat flow patterns models 2 and 3 when combined with the special structural configuration of sutures can independently yield both the spatial and temporal heat flow distributions and thus alone or together may be considered candidates to explain the precambrian heat flow patterns however thermal models of the lithosphere in which the heat flow patterns are explained entirely by variations in crustal heat production cannot satisfy constraints on upper mantle temperatures beneath archean cratons derived from xenolith thermobarometry the thermobarometry constraints can be satisfied by models in which differences in lithospheric thickness are the principal factor controlling the surface heat flow distributions if the heat flow patterns result primarily from variations in lithospheric thickness then a different temporal heat flow relationship for precambrian terrains can be proposed one in which heat flow varies inversely with the age of stabilization of the lithosphere

spatial and temporal variability of global ocean mixing inferred from argo profiles 1 the influence of turbulent ocean mixing transcends its inherently small scales to affect large scale ocean processes including water mass transformation stratification maintenance and the overturning circulation however the distribution of ocean mixing is not well described by sparse ship based observations since this mixing is both spatially patchy and temporally intermittent we use strain information from argo float profiles in the upper 2 000 m of the ocean to generate over 400 000 estimates of the energy dissipation rate indicative of ocean mixing these estimates rely on numerous assumptions and do not take the place of direct measurement methods temporally averaged estimates reveal clear spatial patterns in the parameterized dissipation rate and diffusivity distribution across all the oceans they corroborate previous observations linking elevated dissipation rates to regions of rough topography we also observe heightened estimated dissipation rates in areas of high eddy kinetic energy as well as heightened diffusivity in high latitudes where stratification is weak the seasonal dependence of mixing is observed in the northwest pacific suggesting a wind forced response in the upper ocean

heat production and thermal conductivity of rocks from the pikwitonei sachigo continental cross section central manitoba implications for the thermal structure of archean crust the pikwitonei and sachigo subprovinces of central manitoba provide a cross sectional view of the superior province crust in cross section the upper to mid level crust is composed of synformal greenstone belts surrounded by tonalitic gneisses both of which are intruded by granitoid plutons this crustal structure persists downward into the granulite facies where keels of the greenstone belts can be found to constrain thermal models of the crust we measured heat production and thermal conductivity in 60 rocks from this terrain using standard gamma ray spectrometry and divided bar techniques large vertical and lateral heterogeneities in heat production in the upper crust are evident heat production is high in granites and metasedimentary rocks intermediate in tonalite gneisses and low in the portions of greenstone belts dominated by mafic meta igneous rocks in the deeper granulite facies rocks heat production decreases by a factor of two in the tonalitic gneisses and remains low in the high grad

formation of 1 9 ga old trans hudson continental crust pb isotopic data pb isotopic data are reported for whole rock samples and feldspars from two parts of the 1 9 1 8 ga old trans hudson orogen in canada the reindeer zone in saskatchewan and the ottawa and belcher islands in hudson bay the first area contains a variety of volcanic granitoid and sedimentary rocks in several oceanic and magmatic arcs aligned parallel to the margin of the archean hearne craton the second is part of the circum superior belt a belt of oceanic basalts and sedimentary rocks that surrounds the superior craton in several regions pb pb isochrons gave ages generally consistent with available geochronological or geological data flin flon 1822 44 ma 2 peter lake complex 2710 220 ma ottawa islands 1790 80 ma belcher islands 1960 160 ma in other regions the pb pb age was too low reflecting disturbance of the pb system e g la ronge belt 1730 115 ma or too high perhaps because of contamination of certain samples with older crust e g wathaman batholith 2200 200 ma model values and th u ratios calculated from the pb data are interpreted in terms of variations in the compositions of mantle sources complicated by contamination with material from the upper or lower continental crust in the southern part of the reindeer zone and in volcanic rocks from the ottawa islands model values vary from 8 0 to 8 1 and correlate inversely with initial nd values this variation is thought to result from contamination of juvenile material 8 0 with material from archean upper crust which had low nd but relatively high in the northern part of the zone and in eskimo formation basalts from the belcher islands values remain constant or decrease as nd declines and this is attributed to contamination with u depleted lower crust calculated th u ratios vary from 1 34 to 6 67 the lowest values 1 4 1 8 come from mafic to felsic volcanic rocks of the flin flon and western la ronge belts these low th u values are like those in modern island arc volcanics and are attributed to enrichment of u in the source slightly higher values are calculated for oceanic basalts from the circum superior belt morb like basalts from the ottawa islands have a low th u of 2 5 reflecting depletion of th along with other incompatible elements higher values of 3 9 characterize the more enriched flaherty basalts the highest th u values which are found in samples with the lowest nd and low values wathaman batholith and eskimo basalts are thought to reflect the high th u of the u depleted lower crustal contaminant these results have several interesting implications the similarity between the isotopic and chemical characteristics inferred for these 1 9 ga old rocks and those of volcanics in modern convergent margin settings provides further indication that the tectonic and petrogenetic processes peculiar to modern subduction environments operated in the middle proterozoic the apparent presence of material from the lower and upper crust in the sources of the granitoids indicates that these rocks were not derived from subducting oceanic plate or the mantle wedge but probably formed and evolved within the crust itself

ground surface temperature history in central canada inferred from 10 selected borehole temperature profiles among the 57 temperature depth profiles recently measured in manitoba and saskatchewan canada only 10 are suitable for inferring recent changes in ground surface temperature many of the rejected temperature profiles show an apparent climatic signal but are affected by topography changes in vegetation or the proximity of lakes at the northernmost site near lynn lake manitoba shallow horizontal variations in temperature have been identified that are related to intermittent permafrost such variations can induce an apparent climatic perturbation in areas where lateral thermal conductivity contrasts have been measured heat refraction effects can also incorrectly be interpreted as ground surface temperature histories the analysis suggests that forest fires that occurred at some of the sites have had little influence on the temperature profiles the 10 selected temperature profiles cover a wide area in northern manitoba and saskatchewan they have been independently and jointly inverted by a singular value decomposition method the ground surface temperature history shows two main episodes a cold period tentatively identified as little ice age with a minimum around 1820 a d was followed by marked warming after 1920 these trends are similar to those recognized in eastern canada

rheological stratification of the lithosphere a direct inference based upon the geodetically observed pattern of the glacial isostatic adjustment of the north american continent 1 a sequence of new analyses of the process of glacial isostatic adjustment gia is described the focus is upon the resolution of a recognized flaw in the currently prevalent model of this process that denoted ice 5g vm2 the flaw concerns a previously noted inability of the model to simultaneously reconcile the vlbi and gps measured rates of vertical and horizontal motion in the region of the north american continent that lay outboard and to the south of the laurentide ice sheet lis at last glacial maximum this characteristic misfit of the model to the data has been suggested to be reconcilable only by recourse to models that explicitly incorporate the influence of lateral viscosity heterogeneity it is demonstrated herein that on the contrary this flaw is entirely and unambiguously attributable to the rheological stratification of the lithosphere an influence not previously accounted for in global models of the gia process but which must exist on a priori grounds

a microscale view of mixing and overturning across the antarctic circumpolar current abstractthe relative roles of isoneutral stirring by mesoscale eddies and dianeutral stirring by small scale turbulence in setting the large scale temperature salinity relation of the southern ocean against the action of the overturning circulation are assessed by analyzing a set of shear and temperature microstructure measurements across drake passage in a triple decomposition framework it is shown that a picture of mixing and overturning across a region of the antarctic circumpolar current acc may be constructed from a relatively modest number of microstructure profiles the rates of isoneutral and dianeutral stirring are found to exhibit distinct characteristic and abrupt variations most notably a one to two orders of magnitude suppression of isoneutral stirring in the upper kilometer of the acc frontal jets and an order of magnitude intensification of dianeutral stirring in the subpycnocline and deepest layers of the acc these variations balance an overturning circulation with meridional flo

heat flow heat generation and crustal temperatures in the northern canadian cordillera thermal control of tectonics 1 the heat flow in the northern canadian cordillera between 59 and 64 n is very high 105 22 mw m2 the average upper crust heat generation is 4 6 2 4 microw m3 giving a reduced deep heat flow of 59 mw m2 similar to the southern canadian cordillera 49 53 n estimated moho temperatures of 800 1000 c and lithosphere only 50 60 km thick are substantiated by slow upper mantle seismic velocities and by high elevations associated with crust only 32 35 km thick the new data support the conclusion that all of the north and south america cordilleras are hot the paleoproterozoic wopmay orogen to the east has a remarkably high heat flow of 90 15 mw m2 for such an old and stable region however basement samples indicate high heat generation and estimated deep temperatures are intermediate between the cordillera and the slave craton further to the east heat flow from the yellowknife area of the slave craton 53 mw m2 implies low lithosphere temperatures in agreement with kimberlite xenolith p t data the high temperatures in the cordillera result in a very thin and weak lithosphere and may allow a lower crust detachment the north and central cordillera have been inland of the coastal queen charlotte transform fault since subduction stopped in the eocene thus some process has maintained high temperatures in the former back arc for more than 40 ma

diapycnal and isopycnal transports in the southern ocean estimated by a box inverse model quantitative descriptions of circumpolar deep water upwelling and evolution into a lighter mode and heavier bottom waters in the southern ocean are still not well constrained here data from two occupations of eight hydrographic sections are combined and used in a box inverse model to estimate isopycnal and diapycnal transportsinthesouthernocean amixedlayerboxallowsdiapycnaltransportsinthesurfacemixedlayertobe estimated separately current velocity at 1000 dbar was constrained by the mean velocity field estimated from subsurfacefloatdriftdata theestimatedisopycnaltransportsarelargelyconsistentwithpastestimatesandwith outputs of three ocean general circulation models the estimated subduction and upwelling at the base of the southernoceanmixedlayershowthatuppercircumpolardeepwaterupwells 16615and17621sv where 1sv 10 6 m 3 s 21 by different inversion methods and evolves into heavier lower circumpolar deep water 5 6 13 and 6 6 18sv and bottom water 86 9a nd 86 13sv or lighter mode and intermediate waters 96 18 and 13 6 24sv meridional transport in the surface mixed layer is due to northward ekman transport and mostly southward eddy transport in seasonal ice covered areas near antarctica a significant 14 6 14sv southward transport was found the southward eddy transport is largest north of the antarctic circumpolar currentanddecreasespolewardbecauseofthepolewarddecreaseintheeddydiffusivity theinteriordiapycnal transports which can be either upward gaining buoyancy or downward gaining density are comparable in magnitude to the horizontal diapycnal transports within the surface mixed layer

a theory of deep stratification and overturning circulation in the ocean abstract a simple theoretical model of the deep stratification and meridional overturning circulation in an idealized single basin ocean with a circumpolar channel is presented the theory includes the effects of wind eddies and diapycnal mixing predicts the deep stratification in terms of the surface forcing and other problem parameters makes no assumption of zero residual circulation and consistently accounts for the interaction between the circumpolar channel and the rest of the ocean the theory shows that dynamics of the overturning circulation can be characterized by two limiting regimes corresponding to weak and strong diapycnal mixing the transition between the two regimes is described by a nondimensional number characterizing the strength of the diffusion driven compared to the wind driven overturning circulation in the limit of weak diapycnal mixing deep stratification throughout the ocean is produced by the effects of wind and eddies in a circumpolar channel and maintained even in the