seismic reflection profiling in the proterozoic arunta block central australia processing for testing models of tectonic evolution abstract the region extending from the northern amadeus basin to the northern arunta province is characterised by a large change in bouguer gravity 1400 s 2 abrupt changes in teleseismic travel time residuals and large thrust structures in which rocks from the lower crust are now exposed at the surface deep seismic reflection data other geophysical data and geological mapping within this region have contributed to the development of a crustal model that would result from thick skinned tectonic processes in which deformation occurred along moderately dipping thrusts or shear zones that extended from the surface down to at least the crust mantle boundary two important features of this model have emerged with the help of unconventional stacking techniques the first is a series of reflections from the redbank deformed zone that can be traced from surface outcrop to depths of more than 30 km the second is evidence of a fault extending through the crust and displacing the moho

observations of a deep mixing event in crater lake oregon we present observations of the evolution of a deep mixing event in a deep temperate lake the observations were obtained from thermistors mounted on a long term mooring in the lake the event seems to have originated near 150 m depth and resulted in a plume or layer of cold water from the upper half of the lake that descended to the lake bottom 590 m over a 3 d period net mixing associated with this event resulted in an overall vertical heat exchange of nearly loi j and a volume exchange of 0 7 3 2 km 4 18 of the lake volume between the upper and lower portions of the lake the deep water displaced during the event is estimated to have carried 0 32 5 x lo6 mol of nitrate to the upper lake which accounts for a significant portion of the average annual nitrate flux 2 4 x 10 mol yr thought to be upwelled in this highly oligotrophic system

structure and evolution of the intracratonic basins of central australia summary the central australian geology is dominated by a series of parallel sedimentary intracratonic basins whose history spans time from the late proterozoic to the carboniferous the basins are separated by regions of exposed proterozoic crust that have a history of significant uplift the formation of the basins cannot be explained by conventional thermal or stretching mechanisms nor does the foreland basin model provide an adequate explanation for their occurrence the geophysical observations particularly gravity point to a structure whereby the crust is considerably thicker under the basins than it is under the regions where basement rock is exposed this suggests that the crust as a whole is involved in the process that led to the basin formation a mechanical model is developed which is based on the supposition that the lithosphere has been in a state of horizontal compression for long time intervals the lithosphere is considered as a viscoelastic plate that has been subjected to a small normal load distributed in an irregular manner under compression initial deflections due to this load are magnified according to the plate s physical properties the magnitude of the compressive force and the wavelength spectrum of the initial perturbations because of the viscosity the deflections grow with time at a rate that is determined by the balance of forces acting on the plate and by the lithosphere s rheology both the elastic and viscous deformations are much enhanced if erosion of the uplifted areas occurs with the sediments deposited into the downwarps these deformations take place at stresses that are much less than the buckling stresses as bending stresses increase with time failure by thrust faulting is predicted to occur within the basins with the exposed basement being thrust over the basins the model has been applied to the central australian region starting at about 900myr ago the first basins to develop are the officer and amadeus basins with uplift occurring in the intervening musgrave block initial rates of uplift and basin subsidence are small but they can increase rapidly with time if the compressive force is main

topography the geoid and compensation mechanisms for the southern rocky mountains the southern rockies of colorado are anomalously high elevations greater than 2800 m topographically rough implying active uplift and underlain by significant low velocity anomalies in the upper mantle that suggest an intimate relationship between mantle geodynamic processes and the surface topography the region is in isostatic equilibrium i e near zero free air gravity anomaly however the poor correlation between the high topography and crustal thickness makes the application of simple compensation models e g pure heiskanen or pratt hayford problematic knowledge of how the current topography of the rockies is isostatically compensated could provide constraints on the relative role of sublithospheric buoyancy versus lithospheric support here we evaluate the geoid and its relationship to the topography using the geoid to elevation ratio gtr in the spatial domain and the admittance in the frequency domain to constrain the mechanism of compensation we separate the upper mantle geoid anomalies from those with deeper sources through the use of spherical harmonic filtering of the egm2008 geoid we exploit the fact that at wavelengths greater than the flexural wavelength where features are isostatically compensated the geoid topography ratio can be used to estimate the depth of compensation and the elastic thickness of the lithosphere the results presented below indicate that the main tectonic provinces of the western united states have moderate geoid topography ratios between 3 5 and 5 5 m km 3 9 for the southern rockies 4 25 for the colorado plateau and 5 2 for the northern basin and range suggesting shallow levels of isostatic compensation in terms of the elastic thickness of the lithosphere our results indicate an elastic thickness of less than 20 km these value support the notion that a major portion of the buoyancy that has driven uplift resides at depths less than 100 km and that upper mantle processes such as small scale convection may play a significant role in the buoyant uplift of the southern rockies as well as other actively uplifting areas of the western united states further support for this hypothesis is provided by high coherence for the geoid topography relationship for nearly all wavelengths between 50 and 1000 km

teleseismic travel time anomalies and deep crustral structure in central australia summary teleseismic travel times have been recorded along two lines of instruments traversing the amadeus basin and southern arunta block of central australia for the purpose of examining the deep crustal and upper mantle structure underlying these features pronounced differential travel times approaching 1 5 s and with major azimuthal variation have been recorded most of the useful observations originated from events to the north japan marianas and to the east fiji tonga at epicentral distances of 40 65d a few observations of southerly azimuth events macquarie ridge and south sandwich islands were also recorded the inferred structure beneath the basin and block exhibits major lateral variations the essential aspects of which are 1 a zone of relatively high velocity material dipping steeply northwards such that the continuation of its southern edge to the surface coincides approximately with a mylonitic shear zone known as the redbank deformed zone 2 a steeply dipping zone of relatively low velocity material immediately to the south of this shear zone and partly underlying the high velocity zone if the travel times are interpreted in terms of an undulating moho variations in moho depth of 20 km occur over horizontal distances of less than 50 km with relatively shallow moho depths occurring immediately to the north of the redbank deformed zone such an interpretation is consistent with the gravity anomalies observed across the geological structures the inferred structure is out of hydrostatic equilibrium and departures from local isostasy approach 150 mpa these stress differences must have persisted during the 300 ma following the alice springs orogeny that led to the present crustal structure evidence in the form of the surface topography and seismicity suggests that some stress relaxation has occurred and still is occurring but not at the shear zone itself at the time of the orogeny the structure may have been close to isostatic equilibrium but as erosion took place complete local rebound did not occur either because horizontal compressive forces still operated or because the strength of the lithosphere increased with time

drivers of deep water renewal events observed over 13 years in the south basin of lake baikal lake baikal with a depth of 1637 m is characterized by deep water intrusions that bridge the near surface layer to the hypolimnion these episodic events transfer heat and oxygen over large vertical scales and maintain the permanent temperature stratified deep water status of the lake here we evaluate a series of intrusion events that reached the bottom of the lake in terms of the stratification and the wind conditions under which they occurred and provide a new insight into the triggering mechanisms we make use of long term temperature and current meter data 2000 2013 recorded in the south basin of the lake combined with wind data produced with a regional downscaling of the global ncep ra1 reanalysis product a total of 13 events were observed during which near surface cold water reached the bottom of the south basin at 1350 m depth we found that the triggering mechanism of the events is related to the time of the year that they take place we categorized the events in three groups 1 winter events observed shortly before the complete ice cover of the lake that are triggered by ekman coastal downwelling 2 under ice events and 3 spring events that show no correlation to the wind conditions and are possibly connected to the increased spring outflow of the selenga river

processes of deep water renewal in lake baikal deep water renewal in lake baikal siberia the world s deepest lake and largest lake by volume is relatively fast water age calculated from tritium and helium as well as from chlorofluorocarbons does not exceed 19 yr relative saturation of dissolved oxygen typically exceeds 80 the equation of state of baikal water was determined including the effect of dissolved ions and silicic acid based on nearly 600 ctd profiles taken between 1993 and 1995 two mechanisms of deep water mixing were identified 1 in spring cold and relatively saline water from the selenga the major inflow to the lake forms a density plume that reaches the bottom of the central basin during april and early may due to entrainment of lake water the plume transports about 125 km of water per year to the deepest part of the basin later in spring the river water forms the thermal bar observed along the eastern shore there are indications that parts of the selenga are also plunging to the deep part of the southern basin 2 at academician ridge separating the cold and saline water of the central basin from the warmer and slightly less saline water of the northern basin horizontal mixing results in a water mass that can sink on either side of the sill whereas in the central basin the water mass stays at intcrmediatc depth in the northern basin it sinks to the decpcst part more detailed data are needed to quantify this density flux no indication of a wind induced thermobaric instability was found

deep water renewal in lake issyk kul driven by differential cooling during two field campaigns on lake issyk kul in march and august 2001 179 high resolution conductivitytemperature depth profiles were measured along with profiles of dissolved oxygen and light transmission on the basis of this extensive data set we investigated the large scale vertical advective processes responsible for deepwater renewal in lake issyk kul at some locations sampled in march variable peak structures in the tracer profiles were observed that indicate horizontally localized intrusions these intrusions have their origin in density plumes that propagate along the bottom of the channels in the eastern shelf region the cold dense water at the bottom of the channels is most likely generated by differential cooling of the water in the shallow shelf regions during winter during summer vertical advective processes appear to be limited to the upper 200 m where upwelling in the open water leads to a doming structure the august data support the results of earlier investigations that suggested that dynamic forcing by a basinwide gyre is responsible for the upwelling in the open water

lithospheric shear zones and mantle crust connections abstract a crustal scale ductile shear zone network in the precambrian granulite facies crust of madagascar is examined to determine the nature of the connections between the mantle and lower crust based on three independent data sets field and satellite mapping c and o isotope geochemistry and gravimetry this crust is divided into three zones 1 outside of shear zones 2 minor shear zones that are 350 km long up to 1000 km and 20 35 km wide the mantle is uplifted by about 10 km beneath the major shear zones the major shear zones are rooted in and are inferred to be controlled by the mantle they directly tapped mantle derived co 2 the small scale minor shear zones were controlled by crustal processes and focused crustally derived h 2 o rich co 2 fluids the regular distribution of the shear zones on a crustal scale is in agreement with models of buckling of the continental lithosphere in a compressional context the propagation of these mechanical instabilities promoted and channelled fluid flow these major pan african shear zones thinned the crust and were reactivated during the subsequent drifting of madagascar and opening of the indian ocean during jurassic to cretaceous times they also controlled many of the brittle fault zones in the overlying sedimentary basins mantle rooted large scale shear zones are inferred to be a general feature of cratonic areas reactivated by shear zone systems

determination of crustal structure in central australia by inversion of traveltime residuals summary teleseismic traveltime anomalies for events recorded on portable seismograph arrays across the northern and southern margins of the amadeus basin in central australia are inverted to obtain a picture of the velocity structure at a scale on the order of 5 10 km a modifled srnr algorithm is used to iteratively redistribute traveltime anomalies along incoming ray paths subject to regularization constraints to obtain a direct estimate of the lithospheric velocity freld beneath the arrays model structure is assumed fo be 2 d based on the strong east ri est strike of surface geology and gravity structure in the area spurious structures commonly generated in snr inversions are suppressed using a filter based on the density ofrays a weighting towards near surface structure is also applied to test the robustness of the inference of deep structures the most prominent feature of the solutions for all three lines is a sharp interface between slow and fast regions dipping away from the basin and beneath the adjacent basement blocks the fastest region on the upper side of the interface corresponds to a belt of high grade metamorphic rocks where they crop out at the surface the interface between slow and fast regions extends to at least 50 km depth in all cases dipping at about 50 60 on the northern lines and 60 80 on the southern 1ine on the northern lines the interface can be correlated with the redbank thrust identified in deep seismic reflection data but the velocity interface seems to dip more steeply secondary features on the profiles include a possible change in dip of the interface on the southern line and a more complex structure on one of the northern lines suggesting that one or more steeper faults cut through the hanging wall of the thrust there predicted gravity profiles derived from the velocity sections using empirical velocitydensity relations resemble observed gravity surprisingly well in their style and approximate magnitude providing support for the general features of the models the results are consistent with a thick skinned thrusting model for the deformation of the central segment of the basin margins and indicate that the style of deformation in the late proterozoic cambrian compressional event at the southern edge of the amadeus basin was similar to that in the later alice springs orogeny in the north

nature of the crust below the southern granulite terrain sgt of peninsular india across the bavali shear zone based on analysis of gravity data abstract the bavali shear zone is a major proterozoic structure in the southern granulite terrain sgt of peninsular india a detailed gravity survey has been carried out in order to delineate the crustal structure and tectonics of the shear zone and adjacent areas the bouguer anomaly map of the region shows a number of features i an e w gravity gradient zone with an average gradient of 3 0 mgal km in the west and 0 4 mgal km in the east across the shear ii a broad gravity low with a relief of 20 mgal in the wynad plateau se of the shear iii a series of gravity lows in the southern part of the shear between kannur and vayittiri iv a broad gravity high of 30 40 mgal encircling the charnockite province in the nw part of the shear and v a sharp localised gravity high closure of 40 50 mgal towards coast at nileswaram spatially filtered gravity anomaly maps clearly exhibit contrasting gravity signatures on either side of the shear zone with relatively higher gravity values within the northern block crustal thickness estimates in general vary from 36 to 41 km with a thinning of 2 to 3 km towards the north below the shear zone using two dimensional crustal models determined from gravity anomaly profiles across the bavali shear zone it is interpreted that the shear zone extends downward close to a plane separating blocks of different crustal densities the shear zone dips steeply towards the south and its downward extension meets with a slight moho rise suggesting that the bavali shear zone is a crustal scale structure eastwards below the wynad plateau however the shear zone becomes less prominent suggesting local variations in its geometry the models also point out the presence of a thick high density body 2 98 g cc in the lower part of the crust below the northern charnockite province which narrows towards the wynad plateau region in the east the presence of such a high density body could be due to factors such as evolution together with the protoliths of overlying charnockitic rocks a dense lower crustal residual fraction during anorthosite genesis or emplacement during pan african later anorogenic events the models also indicate that the wynad plateau region is characterised by a relatively homogeneous crust

a three dimensional numerical model of deep ventilation in temperate lakes because of the variation in the temperature of maximum density with depth it is known that the upper above 250 m and lower water columns circulate separately in deep temperate lakes while near surface water overturns twice per year the deep waters often mix only partially during a complete annual cycle it is believed that deep convection is triggered by storm surge forcing of some of the relatively cold upper water column downward through its compensation depth so that it becomes unstable and sinks the scale and intensity of the resulting deep water forming plumes are studied numerically a high resolution model based on the nonhydrostatic boussinesq equations is used deep water formation is initiated by applying a statically unstable initial temperature profile over various regions of the domain at depths below 300 m the grid spacing is small enough to resolve individual plumes which carry surface water to the lake bottom the domain of study is also large enough that the geostrophic eady 1949 wave breakup of newly formed deep water can be observed it is found that when the initial instability is applied in midbasin remote from the solid sidewalls relatively little fresh deep water is formed and the fluid quickly reaches a geostrophic and hydrostatic balance vigorous vertical mixing ceases after 4 days and the resulting baroclinic fluid has a well defined and predictable scale in contrast when the initial instability is applied immediately adjacent to a solid boundary vigorous plume motion continues for the duration of the numerical simulations 12 days producing a much greater volume of fresh deep water a parametric study investigates the scale and intensity of this boundary mixing it is found that reduced surface water temperature coriolis acceleration or higher horizontal diffusion coefficients increase the rate of deep water renewal

teleseismic travel time anomalies and crustal structure in central australia abstract teleseismic p wave travel time anomalies of more than 0 5s have been recorded in central australia between sites separated by less than 100 km late arrivals occur at sites that are located within sedimentary basins and early arrivals occur at sites located on the exposed and eroded basement early arrivals correspond to relative gravity highs and late arrivals correspond to gravity lows the differential travel times cannot be attributed to near surface crustal structure alone the most straightforward interpretation is in terms of a moho whose depth varies by about 10 km from a mean value and which is deepest below the basins this interpretation is consistent with the intracratonic basin evolution model proposed by lambeck

thermal and structural evolution of the intracratonic arltunga nappe complex central australia the thermal and structural evolution of a paleozoic thrust system in central australia the arltunga nappe complex has been examined through field mapping petrographic microstructural and chemical analyses k ar and 40ar 39ar thermochronology and multi diffusion domain time temperature modeling of k feldspar 40ar 39ar data the arltunga nappe complex contains three distinct tectonic units bounded by regional faults and shear zones that have undergone contrasting deformational and metamorphic histories the cooling history of the three tectonic units has been constrained by k ar and 40ar 39ar isotopic age data from k feldspars micas and amphiboles results are consistent with a piggyback history of crustal imbrication spanning over 100 m y with the hottest rocks uplifted and cooled first and with imbrication acting progressively toward the foreland implications for the intracratonic paleozoic tectonics of central australia are 1 uplift within the structurally highest tectonic unit was initiated before 400 ma 2 continued piggyback imbrication footwall failure and uplift and exhumation of the crust resulted in duplexing in the lowest structural unit at approximately 325 300 ma 3 the contrast in thermal history between the tectonic units indicates that once widely separated crustal segments were juxtaposed during thrusting above a hinterland dipping megathrust resulting in 85 km of crustal shortening

geophysical evidence for thick skinned crustal deformation in central australia until now there has been no clear evidence from deep seismic reflection profiles of crustal faults that displace the moho new data from central australia show such a structure in a region characterized by large thrust structures large gravity anomalies and abrupt changes in teleseismic travel times here the principal thrust the redbank deformed zone cuts through the crust and the moho is significantly displaced across it the geological and geophysical evidence leads to a model of thick skinned crustal deformation which occurred in an intra cratonic environment in late devonian time

deep seismic profiling in central australia abstract deep seismic profiling undertaken in central australia comprised expanding spread reflection profiling long range refraction work and a small scale three dimensional refraction survey as well as the more usual near vertical incidence reflection profiling scismic reflection sections within the arunta block in central australia show abundant northerly dipping events that are interpreted as reflections from dipping faults many of which are evident in surface geological mapping the redbank deformed zone a major thrust feature has been imaged to depths of at least 30 km and defines a marked change in reflection character south of the redbank zone steep northerly dipping reflections are absent sub horizontal basement reflections are prevalent below the southern arunta province and amadeus basin seismic refraction profiles indicate that the crust is more than 50 km thick below both the boundary between the southern and central arunta provinces and the northern part of the amadeus basin expanding reflection spreads and a three dimensional refraction survey have added fine details to the results in regions of special geological interest and include the resolution of complicated velocity variations in the sedimentary rocks of the northern part of the amadeus basin and the measurement of anisotropy in the granulites of the central arunta province adjacent to the redbank zone

inversion for interface structure using teleseismic traveltime residuals summary an inversion method is presented for the reconstruction of interface geometry between two or more crustal layers from teleseismic traveltime residuals the method is applied to 2 d models consisting of continuous interfaces separating constant velocity layers the forward problem of determining ray paths and traveltimes between incident wave fronts below the structure and receivers located on the earth s surface is solved by an eycient and robust shooting method a conjugate gradient method is employed to solve the inverse problem of minimizing a least squares type objective function based on the diverence between observed and calculated traveltimes teleseismic data do not accurately constrain average vertical structure so a priori information in the form of layer velocities and average layer thicknesses is required synthetic tests show that the method can be used to reconstruct interface geometry accurately even in the presence of data noise tests also show that if layer velocities and initial interface positions are poorly chosen lateral structure is still recoverable the inversion method was applied to previously published teleseismic data recorded by an in line array of portable seismographs that traversed the northern margin of the musgrave block central australia the solution based on interface parametrization is consistent with models given by other studies that used the same data but diverent methods most notably the standard tomographic approach that inverts for velocity rather than interface structure

development of the late proterozoic to mid paleozoic intracratonic amadeus basin in central australia a key to understanding tectonic forces in plate interiors the intracratonic amadeus basin in central australia is a complex composite basin covering 17 000 km with at least nine distinct episodes of evolution between 900 and 300 ma these have been identified in neighboring central australian basins and are characterized by intervals of renewed subsidence followed by intervals of erosion and changes in basin shape several unconformities separating the tectonostratigraphic sequences represent periods of mild regional uplifts and correlate with major episodes of compressive tectonism at the evolving margin of the early australian plate in the absence of direct geological evidence for thermal events in the amadeus basin after the initial period of subsidence ended possibly at about 800 ma the correlations found between events in the amadeus basin those in the neighboring interconnected basins and tectonic events at the continental or plate margins emphasize that regional horizontal stress fields contribute significantly to primary basin forming mechanisms this suggests that stresses generated at continental or plate margins may propagate to the plate interior with the lithosphere acting as a stress guide throughout the history of the amadeus basin both periods when compressional stresses were dominant and when extensional tectonics controlled subsidence can be identified there were also transitional periods when neither compression nor extension dominated so that other processes masked the effects of weak horizontal stresses the most recent compressional thrust belt concentrated at the northern margin between 300 and 400 ma and has partly obscured the record of earlier basin shape and size

wind and buoyancy driven horizontal exchange in shallow embayments of a tropical reservoir lake argyle western australia many factors including depth vegetation density wind and gyres may act to influence the littoral exchange in a water body but very few studies have investigated the interaction between more than two of these factors at any time to investigate these controls on horizontal exchange in a large tropical reservoir we conducted a 9 d intensive field experiment in lake argyle western australia the experiment began with a 7 d cooling period that generated water in the shallows of the reservoir embayments that was persistently cooler than the interior this led to an underflow of dense water that moved from the lake boundary toward the center of the reservoir a three dimensional hydrodynamic model elcom was able to adequately reproduce this thermal structure and was used to demonstrate its sensitivity to wind sheltering effects and submerged macrophyte presence further analysis of the predictions indicated that when the ratio of the shear and buoyancy force averaged over 6 h b6h and 6 h averaged wind speed in the direction of the embayment u6h was 1 greater than 0 5 ms 1 and 4 5 ms 1 respectively the exchange was dominated by a topographic gyre formation 2 when 0 1 b6h 0 5 and 2 4 ms 1 u6h 4 5 ms 1 the resulting circulation was a combination of differential cooling flows and a topographic gyre circulation and 3 when u6h fell below 2 4 ms 1 purely buoyancy driven flow occurred but only if the buoyancy forces across the embayments were an order of magnitude greater than wind induced velocity shear

shortening of analogue models of the continental lithosphere new hypothesis for the formation of the tibetan plateau initial stages of compression produce periodic buckling of models analogous to a four layer continental lithosphere with further shortening amplification of the buckles occurs by thrust faulting at inflection points in both brittle layers of the upper crust and upper mantle the rescaled results suggest that a continental lithosphere under compression will buckle with a first order wavelength of about 200 km and a second order wavelength of 20 30 km continued shortening results in the amplification of undulations troughs sink and become compressional basins while deformation keeps going on major thrusts within the upper mantle thus giving rise to an irregular topography of the moho fifty percent shortening results in a 60 km thick continental crust we argue that this model history may explain the elevation and deep crustal structure of the tibetan plateau

role of lithosphere in intra continental deformation central australia abstract since the proterozoic there has been a set of deformation cycles in central australia culminating in the alice springs orogeny around 400 ma these events occurred away from plate boundaries and involved extension as well as compression although their precise history remains difficult to unravel from the geologic record much evidence of deformation is left in the central australian crust which features significant moho topography and an associated gravity signal in the past several mechanical models invoked crustal thickening and considerable compression to explain these geophysical characteristics however it is hard to envisage extensive deformation affecting the crust alone but leaving no deformation record in the sub crustal lithosphere in recent seismic tomography studies there is continuous seismically fast lithosphere in central australia below depths of about 100 km in this region the uppermost lithospheric mantle is seismically slow but exhibits no significant attenuation of seismic waves these new constraints make simple crustal thickening unlikely to be the main mechanism to generate variations of the moho depth in central australia here we propose a mechanical model of deformation that involves the entire lithosphere we make no strong assumptions about the history of deformation cycles our model does not require lithospheric thickening at any stage of the deformation cycle and results in a present day scenario compatible with shallow as well as deep constraints on the lithosphere structure

a teleseismic study of the lithospheric structure across the ladoga bothnian bay zone in finland abstract in order to study teleseismic arrivals times across the ladoga bothnian bay zone a proposed suture zone that separates the karelian region 2 7 ga from the svecofennian region 1 8 ga a seismic array of 22 event recorders was deployed along the sveka profile in central finland the p travel time delays are shown to vary by less than 0 2 s along the profile and consistent delay patterns are observed for the various earthquakes the travel time delays delineate zones that appear to correlate with different geological terrains a 2 d inversion of the data yields a tomographic image of the crust and lithosphere across the ladoga bothnian bay zone where 1 velocity variations are resolved the southwestern proterozoic crust is slower 0 15 s than the northeastern archean crust in agreement with a relatively thinner about 6 km archean crust a subcrustal lower velocity 0 8 dome like structure is present beneath the kuhmo block northern part of the profile and is bordered by a southwest dipping higher velocity 0 8 body that seems to connect to the surface trace of the kuhmo suomussalmi greenstone belt

the 520 km discontinuity although some of the earliest suggestions of a seismic discontinuity near 520 km depth in the upper mantle came from seismic studies of the structure to the north of australia results from more recent deployments of portable arrays of short period instruments are equivocal of the several hundred earthquakes recorded during these experiments only a small fraction provide data that could help to constrain the properties of the discontinuity of the few earthquake recordings that can address the question of whether such a discontinuity exists most indicate that it does not exist as a sharp feature i e less than 50 km thick at depths of less than 540 km the data do not however constrain the existence of a discontinuity at depths greater than 540 km furthermore the velocity increase could be distributed over a significant depth range even a 50 km transition would not appear in the short period observations and still provide sufficient reflectivity at near vertical incidence to be compatible with long period observations for waves traveling steeply in the mantle

investigation of the spring thermal regime in lake ladoga using field and satellite data we use a combination of field and satellite data to investigate the thermal regime in lake ladoga in spring 1992 the analysis concentrates mainly on the temperature structure in the convectively mixed region and the dynamics of a special thermo hydrodynamic phenomenon called thermal bar a zone of descending water with the temperature of maximum density equal to 4 c a theoretical model of the temperature distribution in the convectively mixed region temperatures 4 c and the thermal bar progression is also applied and compared with satellite data the study shows that the temperature offshore the 4 c isotherm in the convectively mixed region of the lake is almost depth constant because of strong convective mixing and that the horizontal heat flux seems to be of minor importance in this region the comparison between predictions from the simple theoretical model describing the temperature evolution and movement of the thermal bar with observations showed a fairly good agreement however calculations of the change of heat content in water columns along sections indicate heat transport from the nearshore stably stratified region toward the 4 c isotherm which will affect the movement of the thermal bar this effect has been incorporated in an improved model of the thermal bar progression a better agreement between predictions and observations was also obtained with this model

fluid rock interaction in the granulites of madagascar and lithospheric scale transfer of fluids abstract the nature of synmetamorphic fluids and their flow is examined in the granulitic lower crust of madagascar part of a precambrian crustal scale network of vertical ductile shear zones based on three independent data sets field and satellite mapping c o and h isotope geochemistry and gravimetry this crust is divided into three zones outside of shear zones minor shear zones 350 km long and 20 35 km wide the major shear zones are rooted in and are controlled by the mantle they tapped mantle derived co2 with carbon fluxes of the same order of magnitude as oceanic ridge degassing one major shear zone shows abundant phlogopite diopside apatite calcite mineralizations a well known paragenesis in mantle metasomatism due to mantle fluid infiltration and their interaction with the crust carbonatitic magmas possibly collected in the major shear zones at the base of the crust and may be the source for co2 upwellings as well as other metasomatic agents small scale minor shear zones were controlled by crustal deformation processes and focused crustally derived h2o rich fluids pervasive fluid circulation was restricted to the vicinity

isostatic response of the australian lithosphere estimation of effective elastic thickness and anisotropy using multitaper spectral analysis gravity and topography provide important insights regarding the degree and mechanisms of isostatic compensation the azimuthally isotropic coherence function be tween the bouguer gravity anomaly and topography evolves from high to low for increasing wavenumber a diagnostic that can be predicted for a variety of lithospheric loading models and used in inversions for flexural rigidity thereof in this study we investigate the isostatic response of continental australia we consider the effects of directionally anisotropic plate strength on the coherelce the anisotropic coherence function is calculated for regions of australia that have distinctive geological and geophysical properties the coherence estimation is performed by the thomson multiple slepian taper spectral analysis method extended to two dimensional fields our analysis reveals the existence of flexural anisotropy in central australia indicative of a weaker n s direction of lower te this observation is consistent with the suggestion that the parallel faults in that area act to make the lithosphere weaker in the direction perpendicular to them it can also be related to the n s direction of maximum stress and possibly the presence of e w running zones weakened due to differential sediment burial rates we also demonstrate that the multitaper method has distinct advantages for computing the isotropic coherence function the ability to make many independent estimates of the isostatic response that are minimally affected by spectral leakage results in a coherence that is more robust than with modified periodogram methods particularly at low wavenumbers our analysis elucidates the reasons for discrepancies in previous estimates of effective elastic thickness te of the australian lithosphere in isotropic inversions for te we obtain values that are as much as a factor of 2 less than those obtained in standard inversions of the periodogram coherence using bouguer gravity and topography but greater than those obtained by inversions that utilize free air rather than bouguer gravity and ignore the presence of subsurface loads however owing to the low spectral power of the australian topography the uncertainty on any estimate of te is substantial

the palaeozoic history of an unusual intracratonic thrust belt in central australia based on 40ar 39ar k ar and fission track dating intraplate thrusting involving reactivation of a mid proterozoic province boundary within the basement metamorphic rocks of the arunta block occurs at the northern margin of the late proterozoic to mid palaeozoic amadeus basin in central australia earlier geological and geophysical studies show that the thrust system referred to as the alice springs orogen is 9thick skinned9 in the central part of the thrust belt and was dominated by the crust cutting redbank thrust zone several episodes of thrusting defined stratigraphically began about 400 ma ago analysis and modelling of 40 ar 39 ar age spectra on k feldspar from the basement rocks combined with regional geological constraints point to cooling rates of 3 10 c ma and moderate overall exhumation rates of 100 400 m ma during the alice springs orogeny without appreciably increased heat flow however final uplift along the thrust front at 300 320 ma was rapid as the time of final closure of small domains in k feldspar approximates apatite fission track ages by using 40 ar 39 ar age data as a constraint together with available geological and geophysical data crustal shortening across the thrust belt is thought to be approximately 20 to 30 overall convergence rates of 0 6 3 km ma are slow compared with rates of 5 km ma for continent continent collision zones

moho geometry along a north south passive seismic transect through central australia abstract receiver functions from a temporary deployment of 25 broadband stations along a north south transect through central australia are used to retrieve crustal and uppermost mantle structural constraints from a combination of different methods using h k stacking as well as receiver function inversion overall thick crust with significant thickness variation along the profile 40 to 55 km is found bulk crustal v p v s values are largely in the felsic to intermediate range with the southernmost stations on the gawler craton exhibiting higher values in excess of 1 8 a common conversion point ccp stacking profile shows three major discontinuities of the crust mantle boundary 1 a two sided moho downwarp beneath the musgrave province which has previously been associated with the neoproterozoic to early cambrian petermann orogeny 2 a moho offset along the redbank shear zone further north attributed to the middle to late paleozoic alice springs orogeny and 3 another moho offset further north located at the boundary between the davenport and warramunga provinces which has not been imaged before in all cases the difference in crustal thickness between the two sides of the offset is 8 10 km unlike the two southern moho offsets the northernmost one does not coincide with a prominent gravity anomaly its location and the absence of known reactivation events in the region make it likely that it belongs to a proterozoic suture zone that marks a previously unknown block boundary within the north australian craton

ventilation and dissolved oxygen cycle in lake superior insights from a numerical model ventilation and dissolved oxygen in lake superior are key factors that determine the fate of various natural and anthropogenic inputs to the lake we employ an idealized age tracer and biogeochemical tracers in a realistically configured numerical model of lake superior to characterize its ventilation and dissolved o2 cycle our results indicate that lake superior is preferentially ventilated over rough bathymetry and that spring overturning following a very cold winter does not completely ventilate the lake interior while this is unexpected for a dimictic lake no part of the lake remains isolated from the atmosphere for more than 300 days our results also show that lake superior s oxygen cycle is dominated by solubility changes as a result the expected relationship between biological consumption of dissolved o2 and ventilation age does not manifest

deep ventilation of lake baikal waters due to spring thermal bars increase of density due to mixing cabbeling instability in a spring thermal bar in lake baikal results in the sinking of cold surface water t 3 2 3 4 c w 0 3 cm s 1 below the profile of tmd this density increase generates forced convection and subsequent movement of cold water along the underwater slope to maximum depths cooling of deep and near bottom waters caused by forced convection is compensated during other seasons of the year by eddy heat flux directed toward the bottom on a long term basis vertical temperature profiles in deep waters remain constant

isostatic response of the lithosphere with in plane stress application to central australia the relation between gravity and topography in central australia cannot be described by a conventional isostatic response function whether it assumes local or regional compensation or whether the crust behaves as an elastic or viscoelastic medium in particular the response function exhibits considerable anisotropy hence a theory for isostatic response has been developed for a crust in mechanical equilibrium of surface loads buoyancy and in plane forces and subject to erosion sedimentation and stress relaxation the observed north south response function exhibits extreme isostatic overcompensation at some wavelengths and this can be fully explained by the viscoelastic plate model with in plane compression the observed east west response function is consistent with models of regional or local isostatic compensation the response function implies an effective flexural rigidity of 5 10 1022 n m an effective maxwell relaxation time of 25 50 m y an in plane compression of 125 150 mpa and an erosion time constant of about 200 m y these parameters assume that the model evolved over a period of about 700 m y and are wholly consistent with the evolutionary model developed from geological observations

crustal structure of israel constraints from teleseismic and gravity data summary the structure of the crust in israel was studied using p wave traveltime residuals of 169 teleseisms recorded by a seismic network throughout the country independently of the teleseismic residuals the bouguer gravity anomalies were used as an additional aid to examine the structure of the crust the average time difference between the traveltime residuals in the north and in the south of israel is up to 0 2s three distinct provinces are observed in the teleseismic residuals with distinct boundareis at 31 5 n and 30 25 n similar differences of traveltime residuals were derived for each of the four principal azimuth quadrants most of the difference in traveltime residuals between northern and southern israel can be explained by changes in the sedimentary thickness we suggest that the structure of the northern province is significantly different from the central or the southern provinces if the moho shallows by about 13 15 km along the profile as was previously suggested by seismic refraction data a thickening of the sedimentary sequence to about 15 km in the northern province is needed to satisfy the traveltime residuals similar results are obtained if the bouguer gravity anomalies due to the thickening sediments and the rise of the moho depth are modelled in the eilat region the sedimentary sequence thins in the sse direction from the negev to the gulf of eilat implying a decrease of the moho in the southward direction by about 10 km in agreement with the crustal refraction studies

seismic p wave anisotropy in the subcrustal lithosphere of north west australia summary reduced p travel times from the archaean pilbara craton of north west australia show a strong correlation with azimuth which could be used as evidence of anisotropy however the azimuthal correlation could also be explained by a southerly dip of between 1 and 2 on the crustmantle boundary although the models from several reversed seismic profiles across the craton suggest a smaller dip a time term analysis of the p data yielded several models the preferred solution in which the dip on the crust mantle boundary is similar to that in the models from the reversed profiles has approximately 2 per cent anisotropy in the uppermost mantle with the direction of maximum velocity 30 east of north one possible cause of the anisotropy is that olivine crystals were aligned by syntectonic recrystallization and or power law creep in the tensional environment caused at the base of the lithosphere by flexure during loading of the lithosphere by the strata of the hamersley basin which overlies the pilbara craton a seismic discontinuity occurs about 15 km below the crust mantle boundary under the craton a qualitative analysis of all available seismic data suggests that the velocity below the boundary is probably also anisotropic with the direction of maximum velocity between north and 40 west of north the direction of minimum velocity below the sub moho boundary correlates loosely with the direction of basement lineaments in the proterozoic capricorn orogenic belt to the south of the craton suggesting that the anisotropy under the boundary may be younger than that immediately under the crustlmantle boundary this is consistent with the notion that the aichaean lithosphere was thinner than the present lithosphere

hillslope and wetland hydrodynamics in a tussock grassland south island new zealand previous research on two experimental catchments at the glendhu forest otago showed that runoff dynamics from this landscape differ substantially from other areas in new zealand in particular the recession curves from these catchments have two distinct phases a rapid decline for a period of several hours followed by a slow decline that may last many days to weeks in the current study soil water matric potential measurements indicated that perched saturated zones develop very rapidly in the surface 0 30 cm soil horizons deep 50 250 cm loess horizons remain moist throughout the year and may be near or at saturation at the bedrock contact and respond only slowly to rain events soils in the middle horizons are often drier than the surface soil above or the deep soils below throughflow measurements showed that storm runoff occurs primarily as interflow through a retentive but pervious mat of mosses litter and roots at the soil surface despite the presence of abundant earthworm burrows less water is transmitted through the soil horizon just below this surface mat only a small fraction of stormflow was transmitted through the deep mineral horizons however baseflow could be sustained for long periods up to 4 weeks from unsaturated flow of soil moisture stored in the deep loess horizons water storage in bog peats and associated riparian soils which are numerous in this area is insufficient to sustain baseflow for more than a few days the results from this study are consistent with previous hydrometric soils and isotopic observations and suggest that any land use practices that disrupt the surface soil horizons are likely to change the runoff characteristics of this area

the central australian seismic experiment 1985 preliminary results summary the major objective of the central australian seismic experiment is to investigate the structural evolution of the arunta block and the ngalia and amadeus basins a regional north south reflection line of 420 km length from the northern arunta province to the southern part of the amadeus basin was recorded in 1985 the most significant basement features are prominent bands of reflectors from beneath the northern arunta province and the ngalia basin at times of between 4 and 10 s that dip towards the north deep crustal features south of the ngalia basin are less clear except in the redbank zone bands of deep reflectors similar to those observed in the north occur at times of between 5 and 10 s beneath the southern part of the amadeus basin additional seismic profiling included a reflection line of 40 km length recorded across the northern margin of the redbank zone three expanding spread reflection profiles and a tomographic experiment an east west seismic refraction profile of 400 km length was recorded within the arunta block and suggests an average crustal thickness of 55 km

ausmoho the variation of moho depth in australia summary since 2004 more than 7000 km of full crustal reflection profiles have been collected across australia to give a total of more than 11000 km providing valuable new constraints on crustal structure a further set of hitherto unexploited results comes from 150 receiver functions distributed across the continent mostly from portable receiver sites these new data sets provide a dramatic increase in data coverage compared with previous studies and reveal the complex structure of the australian continent in considerable detail a new comprehensive model for moho depth across australia and its immediate environment is developed by utilizing multiple sources of information on shore and off shore refraction experiments are supplemented by receiver functions from a large number of portable stations and the recently augmented set of permanent stations and moho picks from the full suite of reflection transects the composite data set provides a much denser sampler of most of the continent than before though coverage remains low in the remote areas of the simpson and great sandy deserts the various data sets provide multiple estimates of the depth to moho in many regions and the consistency between the different techniques is high in a number of instances differences in estimates of moho depth can be associated with the aspects of the structure highlighted by the particular methods the new results allow considerable refinement of the patterns of moho depth across the continent some of the thinnest crust lies beneath the archean cratons in the pilbara and the southern part of the yilgarn thick crust is encountered beneath parts of the proterozoic in central australia and beneath the palaeozoic lachlan fold belt in southeastern australia the refined data indicate a number of zones of sharp contrast in depth to moho notably in the southern part of central australia

impact of lake level change on deep water renewal and oxic conditions in deep saline lake van turkey 1 changes in the hydrological regime of the saline closed basin lake van a large deep lake in eastern turkey resulted in a lake level increase by about 2 m between 1988 and 1995 followed by a 1 5 m decrease until 2003 and a relatively constant lake level thereafter based on measurements of transient tracers sulfur hexafluoride cfc 12 3h 3he 4he ne dissolved oxygen light transmission conductivity temperature depth profiles and thermistor data we investigate the implications associated with lake level fluctuations for deep water renewal and oxygenation our data suggest that deep water renewal was significantly reduced in lake van between 1990 and 2005 this change in mixing conditions resulted in the formation of a more than 100 m thick anoxic deep water body below 325 m depth apparently the freshwater inflows responsible for the lake level rise between 1988 and 1995 decreased the salinity of the surface water sufficiently that the generation of density plumes during winter cooling was substantially reduced compared to that in the years before the lake level rise significant renewal and oxygenation of the deep water did not occur until at least 2005 although by 2003 the lake level was back to almost the same level as in 1988 this study suggests that short term changes in the hydrological regime resulting in lake level changes of a couple of meters can lead to significant and long lasting changes in deep water renewal and oxic conditions in deep saline lakes

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

periodic instabilities during compression of the lithosphere 2 analogue experiments we have modeled the behavior of the continental and oceanic lithospheres under compression using materials with analogous properties in laboratory experiments to study the development of lithospheric buckling periodic instabilities which are a major deformation process during the compression of the lithosphere have already been described by several authors using an analytical perturbation method at small strains analogue experiments corroborate most of the results obtained by the perturbation method 1 the deformation modes geometrical relationships of interfaces and related wavelengths are mainly dependent on the spatial distribution of the brittle layer s and 2 the amplitude of buckling is an exponential function of the horizontal strain some departure from the perturbation method occurs when there are two instabilities growing concurrently the breakdown of the exponential growth occurs for strains of about 5 and is concomitant with the appearance of thrust faults in experiments including one brittle layer which model the compression of the oceanic lithosphere faults are regularly located at the inflection points of the folds in experiments including two brittle layers which model continental lithosphere faults form more complicated patterns with an asymmetrical deep thrust overlain by a fan shaped symmetrical thrust system in the upper brittle layer such fault geometries give some new highlights on typical compressive geological structures such as those encountered in central asia

physical and chemical properties of the waters of saline lakes and their importance for deep water renewal lake issyk kul kyrgyzstan the relationships between electrical conductivity temperature salinity and density are studied for brackish lake issyk kul these studies are based on a newly determined major ion composition which for the open lake shows a mean absolute salinity of 6 06 g kg 1 the conductivity temperature relationship of the lake water was determined experimentally showing that the lake water is about 1 25 times less conductive than seawater diluted to the same absolute salinity as that of the lake water based on these results an algorithm is presented to calculate salinity from in situ conductivity measurements applied to the field data this shows small but important vertical salinity variations in the lake with a salinity maximum at 200 m and a freshening of the surface water with increasing proximity to the shores the algorithm we adopt to calculate density agrees well with earlier measurements and shows that at 20 c and 1 atm lake issyk kul water is about 530 g m 3 denser than seawater at the same salinity the temperature of maximum density at 1 atm is about 0 15 c lower than that for seawater diluted to the same salinity despite its small variations salinity plays an important role together with temperature changes in the static stability and in the production of deep water in this lake changes in salinity may have had important consequences on the mixing regime and the fate of inflowing river water over geological time uncharged silicic acid is negligible for the stability of the water column except near an 15 m thick nepheloid layer observed at the bottom of the deep basin copyright 2002 elsevier science ltd

biological energy in landscape evolution traditional conceptual models of landscape evolution view topography as an outcome of endogenic forces uplift working against exogenic forces of denudation the energy considerations of these concepts have focused on the conversion of the potential energy of landscape relief to kinetic energy the concept of the biosphere as a planetary membrane for capturing and converting solar energy coupled with the critical geomorphic role of biota call for a consideration of biotic contributions to geomorphic work a review of estimates of global rates of kinetic energy of denudation and uplift and net primary production npp indicates that the energy density of npp is on average three to seven orders of magnitude greater than the others if even a tiny fraction of npp is geologically significant then the biological subsidy to the energy of landscape evolution must be considered on a par with that of geophysical and geochemical phenomena a case study in eastern kentucky shows that even if only 0 1 percent of npp is geomorphically significant it still far exceeds the energy inputs from uplift and conversion of potential to kinetic energy by denudation this is unlikely to be unique though the relative importance of biological and geophysical processes must obviously vary with climate tectonic setting and other factors results indicate that particularly where biological activity is significant geomorphic work performed by biota may be greater than that associated with endogenic processes and with the kinetic energy of denudation

the role of compressive forces in intracratonic basin formation and mid plate orogenies lithospheric buckling due to compressive forces requires excessively large stresses with some modifications of the elastic plate buckling problem significant deformation can occur at compressive stresses of a few kbars an order of magnitude less than required to induce elastic buckling three modifications are proposed i the plate is considered as an effective viscoelastic layer subjected to an initial perturbation ii when a compressive force is applied these perturbations are magnified and then grow with time iii uplifted areas are eroded and sediments are deposited in the downwarped areas this mechanism appears to be relevant to the formation of some intracratonic basins such as those in central australia the mechanism can lead to significant orogenies away from plate boundaries such as the petermann ranges orogeny and the alice springs orogeny of central australia

crustal heterogeneity in south australia earthquake evidence summary lateral velocity variations in the south australian crust have been mapped using the relatively new technique of seismic tomography the input data comprised p1 travel times from 1340 local earthquakes recorded on the south australian seismic network during the period 1978 1983 to reduce errors in the earthquake locations focal depths and origin times we used an averaging technique of dividing the area under consideration into a series of overlapping cylindrical cells all earthquakes and seismic stations were assigned to the centre of the nearest cell travel times between all centres were computed by averaging over all relevant cell pairs after first scaling all travel times by a factor equal to the distance between cell centres divided by the actual ray path length only ray paths appropriate to the p1 phase were considered starting with a first guess model based on the number of ray intersections with each cell the travel times were computed along all ray paths and compared with the observed averaged values the errors and residuals were back projected for each ray over all the chords along the ray and the average cell slowness adjusted in an iterative sense until the computed and observed travel times agreed within a specified error tolerance the areas with poor raypath coverage lack of earthquakes and or stations could not be imaged the area covered lies mostly within the adelaide geosyncline where there is believed to be a thick cover of proterozoic sediments the velocity image is of the upper 20 km of the crust so no direct correlation between the surface geology and the crustal velocity is to be expected results indicate a significant variation in crustal velocity from 5 9 to 6 5 km s 1 the velocities correlate remarkably with time terms computed in a separate study of moho refracted arrivals pn low time terms correspond to high crustal velocity and high time terms reflect anomalously low crustal velocity the residual component of the time terms can be explained in terms of variations in depth to the moho throughout the geosyncline of the order of 10 km the prominent features of the tomographic velocity map are a n s trending velocity low over the spencer gulf graben and a ridge of high velocity beneath the flinders ranges the velocity low can be associated with a region of low gravity aligned parallel to the torrens hinge zone which marks the western boundary of the geosyncline the northern end of the high velocity ridge coincides with a region of positive bouguer gravity teleseismic residuals from both earthquakes and nuclear explosions show a similar trend to the pn time terms and indicate lateral variability in crustal thickness and velocity a component of the residual must be attributed to mantle velocity inhomogeneity which extends to depths of 300 km

seismic and mechanical anisotropy and the past and present deformation of the australian lithosphere abstract we interpret the three dimensional seismic wave speed structure of the australian upper mantle by comparing its azimuthal anisotropy to estimates of past and present lithospheric deformation we infer the fossil strain field from the orientation of gravity anomalies relative to topography bypassing the need to extrapolate crustal measures and derive the current direction of mantle deformation from present day plate motion our observations provide the depth resolution necessary to distinguish fossil from contemporaneous deformation the distribution of azimuthal seismic anisotropy is determined from multi mode surface wave propagation mechanical anisotropy or the directional variation of isostatic compensation is a proxy for the fossil strain field and is derived from a spectral coherence analysis of digital gravity and topography data in two wavelength bands the joint interpretation of seismic and tectonic data resolves a rheological transition in the australian upper mantle at depths shallower than 150 200 km strong seismic anisotropy forms complex patterns in this regime the seismic fast axes are at large angles to the directions of principal shortening defining a mechanically coupled crust mantle lid deformed by orogenic processes dominated by transpression here seismic anisotropy may be considered frozen which suggests that past deformation has left a coherent imprint on much of the lithospheric depth profile the azimuthal seismic anisotropy below 200 km is weaker and preferentially aligned with the direction of the rapid motion of the indo australian plate the alignment of the fast axes with the direction of present day absolute plate motion is indicative of deformation by simple shear of a dry olivine mantle motion expressed in the hot spot reference frame matches the seismic observations better than the no net rotation reference frame thus seismic anisotropy supports the notion that the hot spot reference frame is the most physically reasonable independently from plate motion models seismic anisotropy can be used to derive a best fitting direction of overall mantle shear

some examples and mechanical aspects of continental lithospheric folding abstract recent theoretical and observational advances in understanding the dynamics of lithosphere processes have yielded strong evidence in favour of the existence of large scale lithosphere folds intraplate compressional stresses generated by plate tectonic forces can reach magnitudes that approach the plastic buckling strength of mechanical models of lithosphere with brittle ductile rheological stratification the models predict lower plastic buckling stresses for continental lithosphere than for oceanic lithosphere intraplate folding of relatively strong oceanic lithosphere documented extensively in the northeastern indian ocean occurs where stresses are concentrated by restricted geometric and dynamic conditions resulting in unusually high stress levels several hundreds mpa on continents where geophysical data suggest that lithosphere folding may have occurred during the development of sedimentary basins in northern canada and central australia buckling stresses can have magnitudes that are of a similar order to those thought typically to occur in the lithosphere several tens mpa folding of continental lithosphere although more difficult to document is likely to be an important mechanism of large scale continental deformation in particular thinned continental lithosphere with a history of superposition of thick sedimentary successions might be the preferential locus of such folding lithosphere folding could also be a controlling factor in the near surface deformation of rifted basins as reflected by tectonic basin inversion

a new chronology for the age of appalachian erosional surfaces determined by cosmogenic nuclides in cave sediments the relative chronology of landscape evolution across the unglaciated appalachian plateaus of kentucky and tennessee is well documented for more than a century geomorphologists have carefully mapped and correlated upland erosional surfaces inset by wide valley straths and smaller terraces constraining the timing of river incision into the appalachian uplands was difficult in the past due to unsuitable dating methods and poorly preserved surface materials today burial dating using the differential decay of cosmogenic 26al and 10be in clastic cave sediments reveals more than five million years of landscape evolution preserved underground multilevel caves linked hydrologically to the incision history of the cumberland river contain in situ sediments equivalent to fluvial deposits found scattered across the eastern highland rim erosional surface cave sediments correlate with 1 thick lafayette type gravels on the eastern highland rim deposited between c 5 7 and c 3 5 ma 2 initial incision of the cumberland river into the eastern highland rim after c 3 5 ma 3 formation of the parker strath between c 3 5 ma and c 2 0 ma 4 incision into the parker strath at c 2 ma 5 formation of a major terrace between c 2 0 ma and c 1 5 ma 6 shorter cycles of accelerated incision and base level stability beginning at c 1 5 ma and 7 regional aggradation at c 0 85 ma initial incision into the appalachian uplands is interpreted as a response to eustasy at 3 2 3 1 ma incision of the parker strath is interpreted as a response to eustasy at 2 5 2 4 ma a third incision event at c 1 5 ma corresponds with glacial reorganization of the ohio river basin widespread aggradation of cave passages at c 0 85 ma is interpreted as the beginning of intense glacial interglacial cycling associated with global climate change copyright 2006 john wiley sons ltd