seamount topography by least squares inversion of altimetric geoid heights and shipborne profiles of bathymetry and or gravity anomalies summary altimetric measurements of sea surface heights have long been used to locate uncharted marine features newly available data sets geosat gm ers 1 and topex poseidon now allow the topography of submarine volcanoes to be accurately restored and a method based upon inverse modelling is presented in this paper this method allows a joint assimilation of altimetric data and shipborne profiles of bathymetry and or gravity anomalies when available furthermore uncertainties can be computed together with the topography which constitutes a noticeable improvement since these parameters are still missing in the usual bathymetric data bases tests are performed using simulated data in order to characterize the errors which may or must occur with the modelled topography of a previously unknown volcano in particular the errors due to data uncertainties and the lack of precise knowledge of sensitive parameters that are used in the modelling these errors can be maintained under the 100 m level rms for altimetric data with a measurement noise of 5 cm rms or less which is achieved for geosat ers 1 and topex poseidon altimeters an example of inversion of seasat data is presented in the case of a seamount in french polynesia

holocene fringing reefs and sea level change in mangaia island southern cook islands abstract holocene relative sea levels in oceanic islands that are situated sufficiently far from glaciated regions provide basic information for the study of the melting histories of the continental ice sheets and of the rheological structure of the earth we have studied mangaia island south cooks as one such oceanic island located in the middle pacific ocean in addition to the usual geological and geomorphological observations of geomorphic features associated with former shorelines we have used a portable drilling sampler for shallow borings of coral reefs geological and geomorphological studies of the coast of mangaia island have revealed that there was a higher sea level than the present in the mid holocene the heights and ages of emerged microatolls on the emerged bench indicate that the sea reached a maximum level of 1 7 m around 4000 3400 yr b p and then emergence is considered to have occurred between 3400 and 2900 yr b p at the same time the reef crest formed in the period from 5000 to 3400 yr b p emerged above the sea and suffered erosion as a result of this change in sea level upward reef growth from the fore reef slope began to form a new reef crest by 2000 yr b p to seaward of the old reef crest the reef margin of mangaia grew outward intermittently with seaward jump of the reef front in accordance with a fall of sea level in the late holocene the presence of fossil reef crests or eroded algal ridges on modern reef flats is a rather common feature in the south pacific the geomorphic development of such features on reef flats can be explained by the effect of the late holocene fall in sea level

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

bias corrected population size distribution and impact hazard for the near earth objects abstract utilizing the largest available data sets for the observed taxonomic binzel et al 2004 icarus 170 259 294 and albedo delbo et al 2003 icarus 166 116 130 distributions of the near earth object population we model the bias corrected population diameter limited fractional abundances of the taxonomic complexes are a 0 2 c 10 d 17 o 0 5 q 14 r 0 1 s 22 u 0 4 v 1 x 34 in a diameter limited sample 30 of the neo population has jovian tisserand parameter less than 3 where the d types and x types dominate the large contribution from the x types is surprising and highlights the need to better understand this group with more albedo measurements combining the c d and x complexes into a dark group and the others into a bright group yields a debiased dark to bright ratio of 1 6 overall the bias corrected mean albedo for the neo population is 0 14 0 02 for which an h magnitude of 17 8 0 1 translates to a diameter of 1 km in close agreement with morbidelli et al 2002 icarus 158 2 329 342 coupling this bias corrected taxonomic and albedo model with the h magnitude dependent size distribution of stuart 2001 science 294 1691 1693 yields a diameter distribution with 1090 180 neos with diameters larger than 1 km as of 2004 june the spaceguard survey has discovered 56 of the neos larger than 1 km using our size distribution model and orbital distribution of stuart 2001 science 294 1691 1693 we calculate the frequency of impacts into the earth and the moon globally destructive collisions 10 21 j of asteroids 1 km or larger strike the earth once every 0 60 0 1 myr on average regionally destructive collisions with impact energy greater than 4 10 18 j 200 m diameter strike the earth every 56 000 6000 yr collisions in the range of the tunguska event 4 8 10 16 j occur every 2000 3000 yr these values represent the average time between randomly spaced impacts actual impacts could occur more or less closely spaced solely by chance as a verification of these impact rates the crater production function of shoemaker et al 1990 geological society of american special paper 247 has been updated by combining this new population model with a crater formation model to find that the observed crater production function on both the earth and moon agrees with the rate of crater production expected from the current population of neos

on geoid heights and flexure of the lithosphere at seamounts the sea surface height has now been mapped to an accuracy of better than 1 m by using radar altimeters on board orbiting satellites the major influence on the mean sea surface height is the marine geoid which is an equipotential surface we have carried out preliminary studies of how oceanic volcanoes which rise above the ocean floor as isolated seamounts and oceanic islands or linear ridges contribute to the marine geoid simple one and two dimensional models have been constructed in which it is assumed that the oceanic lithosphere responds to volcanic loads as a thin elastic plate overlying a weak fluid substratum previous studies based on gravity and bathymetry data and uplift subsidence patterns show that the effective flexural rigidity of oceanic lithosphere and the equivalent elastic thickness te increase with the age of the lithosphere at the time of loading the models predict that isolated seamounts emplaced on relatively young lithosphere on or near a mid ocean ridge crest will be associated with relatively low amplitude geoid anomalies about 0 4 0 5 m km of height while seamounts formed on relatively old lithosphere on ridge flanks will be associated with much higher amplitude anomalies 1 4 1 5 m km studies of the seasat altimetric geoid prepared by nasa s jet propulsion laboratory support these model predictions geoid amplitudes are relatively low over the mid pacific mountains and line islands which formed on or near a mid ocean ridge crest and relatively high over the magellan seamounts and wake guyots which formed off ridge direct modeling of the altimetric geoid over these features is complicated however by the wide spacing of the satellite tracks which can exceed 100 km and poor bathymetric control beneath individual satellite tracks in regions where multibeam bathymetric surveys are available models can be constructed that fit the altimetric geoid to better than 1 m studies of geoid anomalies over the emperor seamount chain for example suggest that these seamounts formed on 20 30 ma old oceanic lithosphere while anomalies over the louisville ridge and the hawaiian ridge suggest that these seamounts formed on lithosphere older than about 80 ma this indicates that geoid anomalies over bathymetrie features depend not only on the crustal structure prior to loading and the overall shape and density of the features but also on their tectonic setting we examine the implications of these results to studies which attempt 1 to separate temporal variations of the sea surface due to oceanographic effects 2 to predict seamounts directly from satellite derived gravity and geoid data and 3 to isolate the geoid effects of deep processes occurring beneath the lithosphere such as those due to mantle convection

a search for seamounts in the southern cook and austral region the existence of uncharted seamounts in the cook austral region of the south pacific has been investigated using geos 3 and seasat radar altimeter observations three previously uncharted submarine seamounts provisionally named geos a to geos c have been located between mauke and rimatara and a fourth geos d has been located east of rurutu this confirms that the aitutaki mauke islands of the southern cooks are a continuation of the austral chain a second group of uncharted seamounts has been provisionally located some 200 km south of rimatara and maria and this is suggestive of a second seamount chain south of the first that includes raratonga and mangaia fabert bank to the south of mangaia appears to be mislocated by about 2 sup 0 in longitude

nonuniform cratering of the terrestrial planets article history we estimate the impact flux and cratering rate as a function of latitude on the terrestrial planets using a model distribution of planet crossing asteroids and comets bottke w f morbidelli a jedicke r petit j m levison h f michel p metcalfe t s 2002 icarus 156 399 433 after determining the planetary impact probabilities as a function of the relative encounter velocity and encounter inclination the impact positions are calculated analytically assuming the projectiles follow hyperbolic paths during the encounter phase as the source of projectiles is not isotropic latitudinal variations of the impact flux are predicted the calculated ratio between the pole and equator is 1 05 for mercury 1 00 for venus 0 96 for the earth 0 90 for the moon and 1 14 for mars over its long term obliquity variation history by taking into account the latitudinal dependence of the impact velocity and impact angle and by using a crater scaling law that depends on the vertical component of the impact velocity the latitudinal variations of the cratering rate the number of craters with a given size formed per unit time and unit area is in general enhanced with respect to the equator the polar cratering rate is about 30 larger on mars and 10 on mercury whereas it is 10 less on the earth and 20 less on the moon the cratering rate is found to be uniform on venus the relative global impact fluxes on mercury venus the earth and mars are calculated with respect to the moon and we find values of 1 9 1 8 1 6 and 2 8 respectively our results show that the relative shape of the crater size frequency distribution does not noticeably depend upon latitude for any of the terrestrial bodies in this study nevertheless by neglecting the expected latitudinal variations of the cratering rate systematic errors of 20 30 in the age of planetary surfaces could exist between equatorial and polar regions when using the crater chronology method

the flux of small near earth objects colliding with the earth asteroids with diameters smaller than approximately 50 100 m that collide with the earth usually do not hit the ground as a single body rather they detonate in the atmosphere these small objects can still cause considerable damage such as occurred near tunguska siberia in 1908 the flux of small bodies is poorly constrained however in part because ground based observational searches pursue strategies that lead them preferentially to find larger objects a tunguska class event the energy of which we take to be equivalent to 10 megatons of tnt was previously estimated to occur every 200 300 years with the largest annual airburst calculated to be approximately 20 kilotons kton tnt equivalent ref 4 here we report satellite records of bolide detonations in the atmosphere over the past 8 5 years we find that the flux of objects in the 1 10 m size range has the same power law distribution as bodies with diameters 50 m from this we estimate that the earth is hit on average annually by an object with approximately 5 kton equivalent energy and that tunguska like events occur about once every 1 000 years

seamount loading and stress in the ocean lithosphere 2 viscoelastic and elastic viscoelastic models analytical solutions are presented for the deformation and stress state of a horizontally stratified earth subject to normal loads of size and wavelength that are characteristic of seamounts the models investigated include layered elastic plates homogeneous viscoelastic plates and elastic over viscoelastic models in all cases the composite models overlie an inviscid half space the principal advantage of the laminated elastic models over homogeneous elastic plates is that they can result in a substantial reduction in the maximum stress differences in those parts of the plate least capable of supporting large stress differences authors

thermal stresses and the bimodal distribution of elastic thickness estimates of the oceanic lithosphere observations of plate flexure beneath seamounts and at deep sea trenches suggest that the mechanical strength of the oceanic lithosphere increases with age the mechanical thickness h seems to follow the depth to a particular isotherm in the cooling plate model a detailed review of available estimates of elastic thickness te shows that the strength deduced from studies at seamounts is significantly different from the strength inferred at trenches and fracture zones whereas te beneath seamounts approximately follows the 400 c isotherm h at trenches follows the depth to the 700 800 c isotherms the cause of this bimodal distribution is not fully understood thermal bending stresses due to cooling of the lithosphere have been suggested to play an important role in the flexural deformation at transform faults and fracture zones and their distribution with depth is consistent with intraplate seismicity this paper evaluates the effects of thermal stresses on deformation beneath seamounts and at trenches and how their interaction with flexural stresses may modify plate strength the results indicate that thermal bending stresses will bias the moment curvature relationship such that a plate of a certain strength will appear relatively weaker beneath a seamount positive curvature but relatively stronger at a trench negative curvature this systematic bias appears to be in qualitative agreement with published te estimates for old lithosphere the theory predicts a diminishing amount of bias the general lack of sufficient te determinations from old ocean basins and the uncertainties associated with modeling of trenches prohibit a detailed analysis of this part of the te versus age relationship i conclude that the scatter in the elastic thickness estimates appears to be caused by a combination of lithospheric reheating during seamount emplacement bias introduced by thermal stresses and variable amount of yielding of the plate beneath seamounts in proportion to seamount size and lithospheric age at the time of loading

viscosity structure of the oceanic lithosphere inferred from the differential late quaternary sea level variations for the southern cook islands summary late quaternary sea level variations for the southern cook islands such as rarotonga and mangaia provide information on the time dependent crustal movement due to viscoelastic arching in response to loading by the pleistocene volcanic island of rarotonga the lithospheric responses to both external and internal loads have been investigated to estimate the viscosity of the lower part of the lithosphere and to examine the initial stage of swell formation detailed observations of sea level variations for the past 125 kyr indicate that the crustal uplift for mangaia is greater than 10 m while rarotonga was apparently stable for this period the following geophysical implications for the lithospheric rheology and loading model are derived from these observations the observed differential crustal movement implies that the viscous relaxation associated with this volcanic loading is still proceeding in the lithosphere the layer supporting stresses has therefore been migrating with time from weaker lower zones into the stronger upper zones for a lithosphere with a depth dependent viscosity structure this fact provides an important constraint on the viscosity of the lower part of lithosphere the observation that rarotonga has been apparently stable for this period is indicative of a local buoyant internal load in the upper mantle this load may be related to small scale and secondary convection in the asthenosphere surface uplift due to an internal load is therefore required to cancel the subsidence by volcanic loading this problem has been examined for two simplified background density models one is a model in which the density of the lithosphere is equal to that of the asthenosphere for this model very large mass anomalies which are 10 times larger than the external load are required beneath the lithosphere in order to explain the observed differential crustal movement of the islands for an earth model for which the density of the lithosphere is greater than that of the asthenosphere which is possible for mature oceanic lithosphere the observed differential crustal movement is explained for an internal load model with density anomalies of less than 20 kg m j the volume of the internal load is at most twice the volume of the external load a high viscosity layer with an effective viscosity of pa s and with a thickness of greater than 60 km is required beneath the top elastic layer with a thickness of 10 15 km the thickness of thermal lithosphere estimated by the plate age of this region is approximately 80 90 km regardless of the age thickness relationship adopted it is therefore suggested that the major part of the thermal lithosphere is composed of a viscoelastic layer with an effective viscosity of

nonuniform cratering of the moon and a revised crater chronology of the inner solar system abstract we model the cratering of the moon and terrestrial planets from the present knowledge of the orbital and size distribution of asteroids and comets in the inner solar system in order to refine the crater chronology method impact occurrences locations velocities and incidence angles are calculated semi analytically and scaling laws are used to convert impactor sizes into crater sizes our approach is generalizable to other moons or planets the lunar cratering rate varies with both latitude and longitude with respect to the global average it is about 25 lower at 65 n 90 e and larger by the same amount at the apex of motion 0 n 90 w for the present earth moon separation the measured size frequency distributions of lunar craters are reconciled with the observed population of near earth objects under the assumption that craters smaller than a few kilometers in diameter form in a porous megaregolith varying depths of this megaregolith between the mare and highlands is a plausible partial explanation for differences in previously reported measured size frequency distributions we give a revised analytical relationship between the number of craters and the age of a lunar surface for the inner planets expected size frequency crater distributions are calculated that account for differences in impact conditions and the age of a few key geologic units is given we estimate the orientale and caloris basins to be 3 73 ga old and the surface of venus to be 240 ma old the terrestrial cratering record is consistent with the revised chronology and a constant impact rate over the last 400 ma better knowledge of the orbital dynamics crater scaling laws and megaregolith properties are needed to confidently assess the net uncertainty of the model ages that result from the combination of numerous steps from the observation of asteroids to the formation of craters our model may be inaccurate for periods prior to 3 5 ga because of a different impactor population or for craters smaller than a few kilometers on mars and mercury due to the presence of subsurface ice and to the abundance of large secondaries respectively standard parameter values allow for the first time to naturally reproduce both the size distribution and absolute number of lunar craters up to 3 5 ga ago and give self consistent estimates of the planetary cratering rates relative to the moon

lithospheric response to volcanic loading in the southern cook islands abstract the response of the ocean lithosphere to volcanic island loading has been investigated for the southern cook islands of rarotonga mangaia and the aitutaki mauke group using 1 estimates of the change with distance from the load of uplift of islands located on the flexure created arch 2 geoid height perturbations as observed with the geos 3 and seasat radar altimeters and 3 bathymetric evidence for the moat and arch about the island loads the effective flexural rigidity for rarotonga is found to be higher than for the older and nearby islands of mangaia and aitutaki this together with an earlier result for tahiti 1 suggests that stress relaxation of the lithosphere has occurred and that this layer behaves as a viscoelastic material with an effective viscosity of about 5 10 10 25 poise the observations for the flexural rigidity do not indicate any dependence on the age of the lithosphere at the time the loading occurred this suggests that there are no significant differences in lithospheric properties for plates in the age range of 6 7 10 7 years altimeter passes to the east of mauke indicate that there may be an uncharted submarine extension of the aitutaki mauke chain

the geological significance of the geoid data are being used to study terrestrial phenomena at scales from tens of thousands of kilometers down to hundreds or even tens of kilometers this paper focuses on the interpretation of global gravity in the form of the geoid and concentrates on what has already been learned from it about the structure of the earth at long to intermed iate wavelengths the longest wavelengths of the gravity field are dominated by density distributions that must be supported by very large scale convective processes i attempt here to document the claim that these density anomalies are both deep and old at slightly shorter length scales the geoidal anomalies give very useful constraints on possible subduction processes and lead to the conclusion that density contrasts in the subducting slabs must be regionally partially compensated and supported from below at yet shorter length scales satellite altimetry results give insight into the thermal and mechanical structure of the oceanic litho sphere seeming to favor plate over thermal boundary layer models of cooling at the shortest length scales the location and mode of compen sation of individual seamounts can be studied

the support mechanism of the young foundation seamounts inferred from bathymetry and gravity summary the youngest volcanoes of the foundation volcanic chain were built on a plate less than 5 myr near the pacific antarctic ridge par axis the progressive approach of the spreading ridge to the hotspot during the last 10 myr resulted in the building of the edifices upon a progressively younger plate estimates of the effective elastic thickness te using two independent methods show that the elastic thickness of the plate diminishes towards the spreading ridge from 5 3 km to 2 0 km the spatial variation of te correlates with a significant change in both the morphology and the volume of the volcanoes suggesting an important control of the elastic thickness on the volcanic processes the reduction in te also explains conveniently the reduction in the distance between the north and the south systems the double volcanic line that characterizes the young part of the foundation chain in the direction of young loading ages the south system formed at the top of a flexural bulge created by the emplacement of the north system the main volcanic line the low te estimate for the south system and the shape of the bouguer anomalies confirm this model the effective elastic thicknesses obtained in this study are well matched by isotherms between 200 c and 300 c and support the hypothesis of a weak plate three mechanisms possibly acted to lower the plate rigidity re heating of a normal plate by the hotspot north system local fracturing south system and the creation of a thin lithosphere at the par axis by the coupling of a hotspot and the ridge related melting zones near ridge volcanoes

three dimensional seismic interpretation from the triangle zone of the frontal ouachita mountains and arkoma basin pittsburg county oklahoma analysis of 28 5 km 2 of three dimensional 3 d seismic reflection data from the triangle zone of the ouachita fold and thrust belt and the foreland arkoma basin reveals structural details not recognized previously in conventional two dimensional 2 d seismic data the data indicate that the frontal kiowa syncline in the arkoma basin has been passively uplifted by blind thrusting at the morrowan wapanucka limestone level and that smaller wavelength folds are produced by thrusting at shallower levels in the atoka formation faulting at deeper levels in the hunton and arbuckle groups has been traditionally interpreted as normal but our analysis of this data set indicates that in this area normal faults were reactivated during the ouachita orogeny as reverse faults and the changes in fault separation can be followed along strike these faults show the same trend as the overlying thrusts and are normal or have minor inversion where the overlying thrusts have small displacement these faults have been completely inverted where the overlying thrusts have more displacement suggesting a genetic relation between the wapanucka thrusts and the inversion of the hunton and arbuckle faults four reflections were chosen for analysis one reflection in the lower atoka formation two reflections repeated in the wapanucka limestone and a fourth reflection in the hunton group all of these surfaces exhibit the same geometry with the fold axes plunging to the southwest variations in bearing and plunge of fold axes in the wapanucka limestone can be directly correlated to changes in displacement and ramp height along strike the similarity between surface geometries suggests that the last deformation took place at deeper levels in the hunton and arbuckle groups and folded the overlying thrusts reactivation of atokan normal faults at deeper levels in the arkoma basin and ouachita subthrust play may be more widespread than previously recognized

late holocene sea level changes in the northwest tuamotu islands french polynesia abstract field surveys of several sea level indicators exposed in situ reef framework conglomerates coral colonies and tridacna shells in a growth position sea corrosion notches carried out on six atolls from the nw tuamotus mataiva rangiroa arutua kaukura apataki and takapoto and data from four subsurface boreholes drilled through mataiva show that during the late holocene mean sea level msl reached a maximum elevation at approximately 0 9 m it remained above the present msl from between 6000 and 5500 yr b p until at least 1200 yr b p human settlements on the atolls were extremely unlikely and probably impossible throughout this time the area investigated seems to have been tectonically quite stable during the late holocene a local curve of msl variations may be representative of the regional eustatic pattern

effects of a viscoelastic lithosphere on the isostatic bedrock response abstract the lithosphere responds to loading by elastic flexure which is followed by viscous relaxation the amount of which depends on the stress duration this study compares results of an earth model in which the lithosphere is modelled as a purely elastic layer and as a more general viscoelastic solid overlain by a rigid crust it shows the emergence of a noticeable difference in the short wavelength 1 102 5 102 km component of the bedrock deformation after loading durations of the order of 105 106 yr assuming a lower lithosphere viscosity of the order of 1023 1024 pa s in particular for the long term loading hypothesised to be imposed by the east antarctic ice sheet we find that a viscoelastic lithosphere yields a more local deformation pattern to which ice sheet dynamics are highly sensitive it confirms that modelling of the antarctic long term evolution would benefit from a fully coupled ice bedrock approach in which the lithosphere would be represented by a viscoelastic solid

a near earth asteroid population estimate from the linear survey i estimate the size and shape of the near earth asteroid nea population using survey data from the lincoln near earth asteroid research linear project covering 375 000 square degrees of sky and including more than 1300 nea detections a simulation of detection probabilities for different values of orbital parameters and sizes combined with the detection statistics in a bayesian framework provides a correction for observational bias and yields the nea population distribution as a function of absolute magnitude semi major axis eccentricity and inclination the nea population is more highly inclined than previously estimated and the total number of kilometer sized neas is 1227 90 170 1

genetic algorithms for geophysical parameter inversion from altimeter data summary a new approach for inverting several geophysical parameters at the same time from altimeter and marine data by implementing genetic algorithms gas is presented these original techniques of optimization based on non deterministic rules simulate the evolution of a population of candidate solutions for a given objective function to minimize they offer a robust and efficient alternative to gradient techniques for non linear parameter inversion here genetic algorithms are used for solving a discrete gravity problem of data associated with an undersea relief to retrieve seven parameters at the same time the elastic thickness the mean ocean depth the seamount location longitude latitude its amplitude radius and density from its observed gravity geoid signature this approach was also successfully used to adjust lithosphere parameters in the real case of the rarotonga seamount 21 2us 159 8uw in the southern cook islands region where ga simulations provided robust estimates of these seven parameters the ga found very realistic values for the mean ocean depth and the seamount amplitude and the precise geographical location of rarotonga island moreover the values of elastic thickness y14 15 km and seamount density y2850 2870 kg m x3 estimated by the ga are consistent with the ones proposed in earlier studies

abstract balanced cross section through wilburton gas field latimer county oklahoma implications for ouachita deformation and arbuckle cambro ordovician exploration in arkoma basin a computer balanced regional cross section allows several new interpretations for the structural development of the wilburton gas field the gas productive deep arbuckle structure is interpreted to be in the hanging wall of a high angle south dipping reverse fault this fault may be a reactivated normal fault based on pennsylvanian lower atokan thickness changes and by analogy to comparable extensional faults to the north overlying the arbuckle fault block is an imbricated thrust sheet containing pennsylvanian spiro and cromwell sandstone reservoirs where gas production has been established from both the hanging wall and footwall fault blocks the main thrust originates from a detachment zone within mississippian shales to the south and ramps over the deeper arbuckle fault block along the southern margin of the field minimum horizontal displacement of the hanging wall spiro cutoff is 2 3 mi 3 7 km this estimate is significantly smaller than that shown by previously published sections through the area yet is still too large to be adequately accommodated by blind thrusting north of wilburton field well and surface data indicate that much of the displacement instead may have been accommodated by north dipping backthrusts although poorly constrained at least some fault movement on the arbuckle reverse fault appearsmore to postdate the overlying thrust faulted structures less

geoid heights over the louisville ridge south pacific geoid heights over the louisville ridge seamount chain deduced from the seasat satellite altimeter data have been analyzed and interpreted two uncharted seamounts belonging to the chain have been detected the elastic thickness of the oceanic lithosphere has been determined along the chain this was done rigorously using the three dimensional geoid and bathymetry maps and was also computed approximately using spectral methods on geoid and bathymetry profiles a slightly increasing elastic thickness from the southeast to the northwest in the range 15 5 22 5 km has been estimated

the effective elastic lithosphere under the cook austral and society islands abstract we have determined the elastic thicknesste of the oceanic lithosphere along two volcanic chains of the south central pacific cook austral and society islands we used a three dimensional spatial method to model the lithospheric flexure assuming a continuous elastic plate the model was constrained by geoid height data from the seasat satellite along the cook austral chain the elastic thickness increases westward from 2 4 km at mcdonald hot spot to 14 km at rarotonga at mcdonald seamount however the data are better explained by a local compensation model the observed trend shows an increase ofte with age of plate at loading time however the elastic layer under the cook austral appears systematically thinner by several kilometers than expected for normal seafloor suggesting that substantial thermal thinning has taken place in this region considering the apparent thermal age of the plate instead of crustal age improves noticeably the results along the society chainte varies from 20 km under tahiti to 13 km under maupiti which is located 500 km westward when plotting together the society and cook australte results versus age of load we notice that within the first five million years after loading te decreases significantly while tending rapidly to an equilibrium value this may be interpreted as the effect of initial stress relaxation which occurs just after loading inside the lower lithosphere and suggests that the presently measured elastic thickness under the very young tahiti load 0 8 ma is not yet the equilibrium thickness

observed spectral properties of near earth objects results for population distribution source regions and space weathering processes abstract we present new visible and near infrared spectroscopic measurements for 252 near earth neo and mars crossing mc objects observed from 1994 through 2002 as a complement to the small main belt asteroid spectroscopic survey smass http smass mit edu combined with previously published smass results we have an internally consistent data set of more than 400 of these objects for investigating trends related to size orbits and dynamical history these data also provide the basis for producing a bias corrected estimate for the total neo population stuart and binzel 2004 icarus 170 295 311 we find 25 of the 26 bus 1999 phd thesis taxonomic types are represented with nearly 90 of the objects falling within the broad s q x and c complexes rare a and e types are more common in the mc than neo population about 5 compared to 3 orbits in terms of possible space weathering effects we see a size dependent transition from ordinary chondrite like q type objects to s type asteroids over the size range of 0 1 to 5 km where the transition is effectively complete at 5 km a match between the average surface age of 5 km asteroids and the rate of space weathering could constrain models for both processes however space weathering may proceed at a very rapid rate compared with collisional timescales in this case the presence or absence of a regolith may be the determining factor for whether or not an object appears space weathered thus 0 1 to 5 km appears to be a critical size range for understanding the processes timescales and conditions under which a regolith conducive to space weathering is generated retained and refreshed

precise location of unsurveyed seamounts in the austral archipelago area using seasat data summary seasat altimetric geoid data are used to detect uncharted seamounts in the austral archipelago area the various physical parameters which affect the geoid signature of a seamount are inspected to analyse their influence on the precision of the location these parameters are the shape of the seamount its density the crustal model the effective elastic thickness of the lithosphere and the distance between the seamount and sub satellite tracks respectively the results of the tests performed on synthetic data as well as on charted structures show that when a seamount is detected on at least two neighbouring tracks it is possible to locate it with good confidence and to give an estimation of its height if the correct elastic thickness is assumed the precision on the location is order 15 km ten previously unsurveyed seamounts have been located in the austral archipelago it appears that they are emplaced along two well defined azimuths n 1 10 e and n 150 e and that two parallel distinct volcanic chains form the austral archipelago

flexure modelling at seamounts with dense cores summary the lithospheric response to seamounts and ocean islands has been successfully described by deformation of an elastic plate induced by a given volcanic load if the shape and mass of a seamount are known the lithospheric flexure due to the seamount is determined by the thickness of an elastic plate te which depends on the load density and the age of the plate at the time of seamount construction we can thus infer important thermomechanical properties of the lithosphere from te estimates at seamounts and their correlation with other geophysical inferences such as cooling of the plate whereas the bathymetry i e shape of a seamount is directly observable the total mass often requires an assumption of the internal seamount structure the conventional approach considers the seamount to have a uniform density e g density of the crust this choice however tends to bias the total mass acting on an elastic plate in this study we will explore a simple approximation to the seamount s internal structure that considers a dense core and a less dense outer edifice although the existence of a core is supported by various gravity and seismic studies the role of such volcanic cores in flexure modelling has not been fully addressed here we present new analytic solutions for plate flexure due to axisymmetric dense core loads and use them to examine the effects of dense cores in flexure calculations for a variety of synthetic cases comparing analytic solutions with and without a core indicates that the flexure model with uniform density underestimates te by at least 25 per cent this bias increases when the uniform density is taken to be equal to the crustal density we also propose a practical application of the dense core model by constructing a uniform density load of same mass as the dense core load this approximation allows us to compute the flexural deflection and gravity anomaly of a seamount in the wavenumber domain and minimize the limitations recognized from the analytic tests then the dense core model is applied to predict the lithospheric flexure beneath howland island in the tokelau seamount chain these results are compared with the predictions of the uniform density model based on age dating of howland and the age of the seafloor traditional te versus age curves predict the elastic plate thickness beneath the seamount to be around 20 km which is comparable to the best dense core model of te 26 km however the best uniform density model is found at te 12 km which is significantly less than the predicted from our investigations of synthetic and real seamount cases we conclude that the dense core model approximates the true mass distribution of a seamount better than the uniform density model finally we suggest that the role of underplating in flexure modelling may need to be reexamined because the dense core model predicts substantially less deflections than the uniform density model without requiring additional buoyancy caused by underplated material

observations of flexure and the rheology of oceanic lithosphere the principal evidence for the long term i e 1 myr mechanical behaviour of the oceanic lithosphere has come from studies of how it deforms in response to large loads such as volcanoes and sediments a model widely used to explain the deformation is an elastic plate in which flexural rigidity depends on the thermal age of the lithosphere at the time of loading an elastic model however is time invariant and does not take into account temporal changes that may occur in the flexural rigidity as a consequence of loading there is evidence for example that the flexural rigidity of the oceanic lithosphere also depends on load age being large at short times and small at long times thus competing effects may exist between thermal cooling which strengthens the lithosphere and some form of load induced stress relaxation which weakens it in order to investigate the relative roles of these processes we have developed a multilayered viscoelastic model which is based on the results of experimental rock mechanics that creep in the lithosphere is a thermally activated process and on a thermal structure that is given by the plate cooling model by comparing the predictions of the model with a new compilation of flexural rigidity estimates we have found that if the upper mantle viscosity is 1020 pa s the activation energy that best describes the long term mechanical behaviour of the oceanic lithosphere is 120 kj mol 1 this parameter pair explains the dependence of flexural rigidity on both plate and load age it also helps account for the subsidence and uplift history of oceanic islands and the stratigraphic patterns that develop in the flexural moats that flank them at atolls a multilayered viscoelastic model explains the rapid subsidence that follows shield building and does not require that the age of the lithosphere that supports a volcano is thermally re set to a younger value our studies suggest that while the oceanic lithosphere has viscoelastic properties the viscosity of its upper layers is so much higher than that of its lower layers that in effect it behaves as a thin elastic plate on long timescales there will therefore be a certain permanence to the observations of oceanic flexure such that they may be used with some confidence to evaluate the tectonic setting of individual features of the seafloor and in some cases their age

ground truth for oblique impact processes new insight from the rio cuarto argentina crater field new evidence for an impact origin of oblong rimmed depressions near rio cuarto cordoba province argentina includes shocked silicate phases e g diaplectic glass thermal decomposition of high temperature mineral clasts e g baddeleyite from zircon rapid quenching very low water contents 0 1 wt and generation of identical glasses in hypervelocity laboratory impact experiments the results indicate that glasses with a wide range in major element concentrations can form from a single target type in a relatively small impact event impact glasses with the greatest volatile loss typically exhibit the greatest meteoritic contamination as defined by cr ni and ir abundances the different impact glass types and the different degrees of impactor contamination are proposed to reflect proximity to the projectile target interface during shallow penetration in an oblique impact consistent with laboratory simulations and planetary analogues

paleoshoreline record of relative holocene sea levels on pacific islands abstract understanding the history of relative holocene sea levels on pacific islands is important for constraining fundamental geodynamic theories interpreting the environments of early human occupation sites and forecasting future environmental conditions on the islands an observational paleoshoreline record is provided by emergent paleoshoreline indicators formed at higher relative sea levels hence standing at higher elevations than modern counterparts emergent paleoshoreline notches in limestone seacliffs record paleo high tide levels and emergent paleoreef flats record paleo low tide levels whereas emergent paleobeachrock locally records paleo intertidal levels both paleonotches and paleoreefs occur along the coasts of high standing islands exposing volcanic bedrock and uplifted reef complexes but low lying coralline atolls lack sufficient relief to preserve paleonotches controls on relative holocene sea level include global eustatic and regional hydro isostatic changes in ambient sea level relative to island landmasses and shifts in the elevations of islands relative to sea level caused by thermal subsidence of the oceanic lithosphere or thermally rejuvenated loci of hotspot volcanism by flexure of the lithosphere under the load of growing volcanic edifices hawaii samoa society islands by arching of the lithosphere over trench forebulges loyalty islands niue bellona rennell and by tectonism within forearc belts between active volcanic chains and trenches mariana islands tonga vanuatu the dominant pattern of relative sea level change where not overprinted by local tectonism or lithospheric flexure was a uniform early holocene rise in eustatic sea level followed by a regionally variable late holocene hydro isostatic drawdown in sea level the resultant was a mid holocene highstand in relative sea level that affected the development of shoreline morphology throughout the tropical pacific ocean the earliest human migrations into intra oceanic island groups of both the northwestern and southwestern pacific ocean followed close on the heels of the mid holocene sea level highstand and took advantage of newly attractive coastal environments engendered by sea level drawdown the effects of the mid holocene highstand were modified to varying degrees in different island groups by geodynamic uplift or subsidence

geological causes of recent 100 yr vertical land movement in the netherlands abstract geodetic levelling data record differential vertical movements of the top of the pleistocene sands of up to 1 5 mm year in the netherlands over the last century we compare these movements to a mean tectonic isostatic and compaction movements at time scales of millions of years obtained by backstripping of cenozoic stratigraphy and b estimates of recent 100 yr movements from process modelling of isostasy glacio and hydro isostasy and compaction the process rates at time scales of millions of years are insufficient to account for the geodetic observations by an order of magnitude the isostasy and compaction rates inferred for the last century are also insufficient they explain less than half of the observed movements this suggests that the residual observed rates less isostasy and compaction estimates which is interpreted to represent tectonic crustal deformation constitutes an important contribution to present day movements the surprisingly high rates of short term tectonic vertical movements in a region which is relatively inactive seismically indicate that correction of tide gauge records for the glacio isostatic signal alone does not yield an appropriate measure of eustatic sea level rise along the dutch coast

stress and relaxation time in the viscoelastic lithosphere inferred from the outer topographic rise the deformation of a thin viscoelastic plate is usually analyzed by use of an equation that is derived with an artificial assumption of the poisson s ratio equal to 1 2 it is shown in this paper that a simple treatment applicable to an arbitrary value of poisson s ratio is possible by introducing a new variable that represents the pressure gradient between the top and bottom of the plate in this treatment a one dimensional stationary deformation of moving plate is given by a simple analytic equation this equation is used to analyze the bathymetry of the outer topographic rise seaward of the deep sea trenches the analysis reveals that the lithosphere in the western pacific trenches is subject to an extensional horizontal force of 100 mpa or greater the horizontal force may be much less or even compressive in the eastern pacific trenches to prevent horizontal force and bending stress from being extraordinarily large the maxwell relaxation time of the plate must be 1 m y or shorter and the effective viscosity must be 1024 pa s or less

efficient disruption of small asteroids by earth s atmosphere accurate modelling of the interaction between the atmosphere and an incoming bolide is a complex task but crucial to determining the fraction of small asteroids that actually hit the earth s surface most semi analytical approaches have simplified the problem by considering the impactor as a strengthless liquid like object pancake models1 2 but recently a more realistic model has been developed that calculates motion aerodynamic loading and ablation for each separate particle or fragment in a disrupted impactor3 4 here we report the results of a large number of simulations in which we use both models to develop a statistical picture of atmosphere bolide interaction for iron and stony objects with initial diameters up to 1 km we show that the separated fragments model predicts the total atmospheric disruption of much larger stony bodies than previously thought in addition our data set of 1 000 simulated impacts combined with the known pre atmospheric flux of asteroids with diameters less than 1 km5 6 7 8 9 10 11 12 elucidates the flux of small bolides at the earth s surface we estimate that bodies 220 m in diameter will impact every 170 000 years

holocene changes in sea level and coastal environments on rarotonga cook islands south pacific ocean the holocene coastal plain of the island of rarotonga characterized by beach ridges and swamps is the best developed of the cook islands group which lies in eastern polynesia using geomorphic mapping excavation and coring and 14 c dating of these coastal deposits we have reconstructed a sea level curve and drawn maps of shoreline development for the middle to late holocene our sea level curve shows that sea level attained a position similar to that at present by 6000 6500 cal bp then gradually rose to a level of c 1 5 m above present sea level by c 4500 cal bp highstands possibly with fluctuations to lower levels occurred during the interval c 4500 to c 800 500 cal bp sea level has fallen to its present level since c 800 500 cal bp the sea level curve is similar to curves obtained elsewhere in polynesia hydro isostatic movement may have been responsible for the relative sea level change before c 800 500 cal bp whereas the sea level fall since then is in agreement with records from western polynesia that attribute such a fall to climatic change the coastal plain of rarotonga began to emerge c 4500 cal bp and prograded to the present coastline most conspicuously on the northeastern coast the formation of such a flat area on the coast associated with these mid to late holocene shoreline developments is likely to have influenced the pattern of human settlement in rarotonga

global distribution of seamounts inferred from gridded geosat ers 1 altimetry using a forward modeling approach based on an axisymmetric gaussian seamount i characterize the global seamount distribution by locating circular maxima in the gridded vertical gravity gradient field derived from altimetry collected by the geosat and ers 1 satellite missions the global seamount distribution is long tailed and resembles a power law distribution for seamounts in the height range 2 7 km smaller seamounts are not well isolated by my technique nor are they well resolved in the gridded data several factors are likely to influence the height of volcanic seamounts such as melt availability magma driving pressure and plate thickness the observed relationship between seamount gravimetric amplitudes and the age of the underlying seafloor implies that there is an upper limit on seamount heights whether a seamount will reach that height depends most likely on supply side factors such as melt availability and magma driving pressure but the limiting height itself seems more likely to be controlled by the strength of the oceanic plate specifically compressional stresses directly beneath the seamount as a consequence of the lithosphere s flexural response to loading may eventually exceed the magma driving pressure and prevent magma from reaching the surface thus limiting the growth of the seamount because oceanic plate strength primarily is controlled by plate age the limit on seamount height is inferred to be a simple function of plate age at the time of seamount emplacement using analytical solutions i present a simple flexural model that predicts the observed global height age relationship

the record of miocene impacts in the argentine pampas argentine pampean sediments represent a nearly continuous record of deposition since the late miocene 10 ma previous studies described five localized concentrations of vesicular impact glasses from the holocene to late pliocene two more occurrences from the late miocene are reported here one near chasico ch with an 40ar 39ar age of 9 24 0 09 ma and the other near baha blanca bb with an age of 5 28 0 04 ma in contrast with andesitic and dacitic impact glasses from other localities in the pampas the ch and bb glasses are more mafic they also exhibit higher degrees of melting with relatively few xenoycrysts but extensive quench crystals in addition to evidence for extreme heating 1700 c shock features are observed e g planar deformation features pdfs and diaplectic quartz and feldspar in impact glasses from both deposits geochemical analyses reveal unusually high levels of ba 7700 ppm in some samples which is consistent with an interpretation that these impacts excavated marine sequences known to be at depth these two new impact glass occurrences raise to seven the number of late cenozoic impacts for which there is evidence preserved in the pampean sediments this seemingly high number of significant impacts over a 10 6 km 2 area in a time span of 10 myr is consistent with the number of bolides larger than 100 m expected to enter the atmosphere but is contrary to calculated survival rates following atmospheric disruption the pampean record suggests therefore that either atmospheric entry models need to be reconsidered or that the earth has received an enhanced flux of impactors during portions of the late cenozoic evidence for the resulting collisions may be best preserved and revealed in rare dissected regions of continuous low energy deposition such as the pampas additionally the rare earth element ree concentrations of the target sediments and impact melts associated with the chasic event resemble the hna k australites of similar age this suggests the possibility that those enigmatic tektites could have originated as high angle distal ejecta from an impact in argentina thereby accounting for their rarity and notable chemical and physical differences from other australasian impact glasses

stability of the oceanic tectosphere a model for early proterozoic intercratonic orogeny resistance of modern oceanic tectosphere to the initiation of subduction can be evaluated by considering its flexural rigidity shear resistance in the subduction zone and the negative buoyancy force after mckenzie 13 these depend on the effective elastic thickness the depth to which shear stresses are appreciable and the tectospheric thickness respectively evaluation of these thicknesses and their variation with age allows development of a model in which oceanic tectosphere becomes progressively less stable with increasing age and spontaneously subducts at an age of 200 ma the same model applied to early proterozoic oceanic tectosphere distinguished only by having sub tectosphere temperatures 100 c higher than in the modern rquires that proterozoic ocean tectosphere subduct spontaneously at ages of about 75 ma the subduction of universally young oceanic tectosphere inhibits the production of juvenile magmas due to the release of volatiles from the descending slab at low pressures near the trench the model therefore accounts for the scarcity of subduction related magmas in many early proterozoic orogens it also predicts that ocean basins opening in the early proterozoic should have generally limited width that blueschist metamorphism should be rare and that early proterozoic oceanic crust should rarely be preserved at the earth s surface with progressive cooling of the mantle the proterozoic tectonic scheme may have changed gradually into the modern one by early phanerozoic time although parts of the pan african system may exhibit the characteristics of still unstable oceanic tectosphere

dynamics of cloud features on uranus abstract near infrared adaptive optics imaging of uranus by the keck 2 telescope during 2003 and 2004 has revealed numerous discrete cloud features 70 of which were used to extend the zonal wind profile of uranus up to 60 n we confirmed the presence of a north south asymmetry in the circulation karkoschka e 1998 science 280 570 572 and improved its characterization we found no clear indication of long term change in wind speed between 1986 and 2004 although results of hammel et al hammel h b rages k lockwood g w karkoschka e de pater i 2001 icarus 153 229 235 based on 2001 hst and keck observations average 10 m s less westward than earlier and later results and 2003 observations by hammel et al hammel h b de pater i gibbard s lockwood g w rages k 2005 icarus 175 534 545 show increased wind speeds near 45 n which we do not see in our 2003 2004 observations we observed a wide range of lifetimes for discrete cloud features some features evolve within 1 h many have persisted at least one month and one feature near 34 s termed s34 seems to have persisted for nearly two decades a conclusion derived with the help of voyager 2 and hst observations s34 oscillates in latitude between 32 s and 36 5 s with a period of 1000 days which may be a result of a non barotropic rossby wave it also varied its longitudinal drift rate between 20 day and 31 day in approximate accord with the latitudinal gradient in the zonal wind profile exhibiting behavior similar to that of the ds2 feature observed on neptune sromovsky l a limaye s s fry p m 1993 icarus 105 110 141 s34 also exhibits a superimposed rapid oscillation with an amplitude of 0 57 in latitude and period of 0 7 days which is approximately consistent with an inertial oscillation

cratering history and lunar chronology the moon is exceptional and important because it is the only planetary body besides the earth for which we have both a detailed stratigraphic history and datable rock samples that can be related to specific geomorphologic units fig 5 1 the moon has preserved much of its magmatic and impact record of at least the last 4 billion years while its endogenic history is of great interest for the fundamentals of planetary interiors and surfaces the moon has become a calibration plate for the cratering record of the earth moon system and by extrapolation of the entire inner solar system if one assumes a heliocentric origin for impactor populations these populations range from asteroids through long and short period comets to interplanetary dust and cover a size range from hundreds of kilometers to micrometers figure 5 1 telescopic view of the nearside of the earth s moon with landing sites of the apollo and luna missions this chapter reviews the presently available data sets in support of this paradigmatic assumption as follows 1 the phenomenology of lunar impact craters 2 the terrestrial record of the impact cratering process and the interpretation of terrestrial impactites as far as this ground truth is relevant for the interpretation of lunar impact craters and datable lunar impact breccias and melt rocks 3 the theory and numerical simulation of the cratering process and the characteristics of the earth moon crossing population of impactors asteroids and comets 4 the principles of relative age dating of lunar surface units and the general lunar stratigraphy 5 the stratigraphic significance and ages of lunar samples impactites and basalts and based on this data set the absolute ages of lunar surface units 6 the cratering rate of the moon as a function of time and 7 the time calibration of this cratering rate based on the

flexure of the ocean lithosphere from island uplift bathymetry and geoid height observations the society islands summary ln flexure models of the response of the ocean lithosphere to seamount loading three key unknowns must generally be considered the density distribution of the load the degree of fd in of the deflection created moat and the flexural rigidity the models are usually constrained by one of three types of observations gravity or geoicl height anomalies the moat and arch geometry and the amount of uplift of islands on this arch the determination of the model parameters from geoid anomalies is critically dependent on the interpretation of the broad and regional geoid rise that is seen over many of the younger seamount chains and likewise the flexure parameters deduced from the moat and arch geometry are a function of the interpretation of the associated bathymetric swell the uplift data require that the tectonic erosional and sea level history of the region be known although this requirement can be relaxed if rather than the uplift relative to sea level the change in uplift with distance from the load is used as the observed quantity all these types of observations have been used in this paper to constrain the flexure model for the society islands and while any one data type on its own does not lead to reliable flexure parameters a consistent solution is found when the three are taken together the results point to a relatively low load density of 2 5 g m apart from a high density core a moat that is partly fdled in with sediment or volcanic debris and a flexural rigidity of about 3 x dyne cm

current bombardment of the earth moon system emphasis on cratering asymmetries abstract we calculate the current spatial distribution of projectile delivery to the earth and moon using numerical orbital dynamics simulations of candidate impactors drawn from a debiased near earth object neo model we examine the latitude distribution of impactor sites and find that for both the earth and moon there is a small deficiency of time averaged impact rates at the poles the ratio between deliveries within 30 of the pole to that of a 30 band centered on the equator is small for earth 0 958 0 001 and somewhat greater for the moon 10 0 903 0 005 the terrestrial arrival results are examined to determine the degree of am pm asymmetry to compare with the pm excess shown in meteorite fall times we find that the average lunar impact velocity is 20 km s which has ramifications in converting observed crater densities to impactor size distributions we determine that current crater production on the leading hemisphere of the moon is 1 28 0 01 that of the trailing when considering the ratio of craters within 30 of the apex to those within 30 of the antapex and that there is virtually no nearside farside asymmetry in agreement with observations of rayed craters as expected the degree of leading trailing asymmetry increases when the moon s orbital distance is decreased

lithospheric flexure and thermal anomalies plots of effective elastic thickness te of the oceanic lithosphere as a function of age when elastically deformed show a general increase in te with the square root of age although there is much scatter some of the scatter can be eliminated by correcting for the effect of finite yield strength in rocks which makes te for more sharply bent plates underestimate the true depth tm to the rheological boundary at the base of the high strength mechanical lithosphere after converting effective values te to true thicknesses tm it appears that the mechanical lithosphere is always thinner beneath islands and seamounts compared to lithosphere of similar age flexed at subduction zones from several other lines of evidence such as depth anomalies seamount subsidence and heat flow data it has been suggested that the thermal structure in plates subjected to hot spot type volcanism is reset to values appropriate for much younger lithosphere the reduction in mechanical plate thickness beneath hot spot volcanoes is also consistent with this concept of thermal rejuvenation since the strength of rocks decreases exponentially with rising temperature this dependence implies that variations in mechanical plate thickness can be used to map temperature anomalies in the lithosphere since the mechanical plate thickness depends principally upon the temperature at one depth specifically the depth at which the temperature reaches 550 600 c depending on strain rate flexural data are particularly sensitive indicators of the vertical structure of lithospheric reheating compared to quantities dependent on depth integrals of temperature such as swell height and subsidence the thermal rejuvenation hypothesis predicts that the flexural profile should mimic viscoelastic relaxation in the first 10 ma after loading if initially reheating is confined to depths close to and below the 550 c isotherm the flexural data combined with depth anomaly information for hawaii point to extremely rapid reheating localized in the lower lithosphere rejuvenation in the society islands on the other hand is compatible with slower methods of heat injection involving the entire lithospheric column

stratigraphy and chronology of late pleistocene reefs in the southern cook islands south pacific the makatea islands in the southern cook islands consist of a degraded volcanic core surrounded by emergent makatea limestones while much of this reefal limestone is of tertiary age the seawardmost reefs are late pleistocene last interglacial reefs oxygen isotope substage 5e identified by u series dating reach 12 2 m on atiu mean age of three samples 126 000 5000 yr b p 9 8 m on mitiaro mean age of five samples 119 000 3000 yr b p 10 0 12 7 m on mauke mean age of four samples 128 000 5000 4 000 yr b p and 14 5 20 0 m on mangaia mean age of four samples 115 000 7000 yr b p on atiu mauke and mitiaro a lower reef unit has been identified and is separated from the overlying substage 5e reef by a sharp discontinuity often with a crust of coralline algae u series dating from atiu and mauke indicates that this is a stage 7 reef formed in the penultimate interglaciation the makatea islands have emerged as a result of flexure of the lithosphere in response to loading by the pleistocene volcanic island of rarotonga isolated outcrops of makatea limestone on rarotonga reach 3 5 m and are probably of substage 5e age elastic and viscoelastic models of lithospheric flexure predict that much of the compensatory movement should occur shortly after the emplacement of the load however the age and elevation of late quaternary reefs on the southern cook islands where a pleistocene volcanic island has loaded relatively old ocean floor 80 myr indicate that differential uplift has been continuing over the last 250 000 yr

passive roof duplexes under the rocky mountain foreland basin alberta seismic reflection data in the central alberta foothills near edson reveal the presence of small passive roof duplexes in upper cretaceous rocks within the otherwise undeformed foreland basin as much as 40 km northeast of the mountain front monocline the tops and bottoms of the duplexes are defined by backthrusts and sole thrusts which follow bedding planes within upper cretaceous strata overlying the structures is an essentially uncontracted 1 8 km thick section of upper cretaceous and tertiary rocks which is passively uplifted over the thickened duplexes the underlying autochthonous sequence of mesozoic and paleozoic rocks exhibits some minor folding but is also uncontracted our interpretation extends both the upper and lower detachments of the widely accepted triangle zone model more than 30 km farther under the foreland basin than has previously been supposed the seismic data illustrate relatively clearly the form of the leading edge of the last phase of rocky mountain thrusting we expect that similar features will be observed elsewhere in the rocky mountain foothills and probably at other mountain fronts worldwide

multiple episodes of volcanism in the southern austral islands flexural constraints from bathymetry seismic reflection and gravity data 1 at the southeastern end of the cook austral island chain in the vicinity of the currently active macdonald seamount multiple episodes of volcanism have left a diverse population of seamounts multichannel seismic reflection and shipboard gravity data provide observational constraints on the magnitude and wavelength of flexure and multibeam bathymetry obtained by r v ewing and f s sonne within the study area provides full spatial coverage of all volcanic loads three dimensional flexural modeling of closely spaced loads emplaced at discrete times performed both with analytical models of idealized loads and with fourier domain solutions of the observed volcanic loads partitioned into the younger and older seamounts is compared with seismic and gravity data this modeling provides a more complete view of the volcanic history than radiometric dating and geochemical analysis of sparse dredge samples alone wide angle seismic refraction data from ocean bottom hydrophones obhs and expendable sonobuoys are also consistent with the flexural modeling results volume estimates of the different volcanic episodes show that one half to two thirds of the material added to the abyssal seafloor by midplate volcanic processes is due to older volcanism that erupted on young lithosphere while the younger higher seamounts contributed the remainder

a study of the earth s response to surface loading with application to lake bonneville summary analytical solutions are presented for the deformation of a three layered plane earth with elastic viscoelastic rheology and subject to time dependent vertical surface loads the models investigated are 1 elastic or viscoelastic layers overlying an inviscid fluid 2 viscoelastic half space 3 elastic layer over a viscoelastic layer with different boundary conditions at the base of the second layer emphasis is given to the interdependence between the dominant parameters of thickness of the elastic layer the effective viscosity of the viscoelastic layer the change in viscosity with depth and the wavelength and duration of loading the models have been applied to the loading and unloading of the late pleistocene pluvial lake bonneville using the load histories given by crittenden the studies differ from earlier analyses of the bonneville uplift in several important aspects including a rigorous treatment of the horizontal and vertical coupling between the elastic and viscoelastic media the mantle is treated as viscoelastic rather than as a viscous medium the wavelength information has been introduced by using a more realistic model for the load geometry and the effect of the wasatch fault has been considered the models indicate that the two principal parameters defining the rebound are the effective viscosity of the upper mantle and the effective thickness of the elastic layer and that those two parameters can be separated only if both wavelength and amplitude information of the deformation is available at more than one epoch observations of uplift at one epoch are not sufficient to resolve the thickness of the elastic layer and the effective viscosity of the upper mantle but upper bounds for these quantities are well established as 30km and 1 2 10 poise respectively the uplift results do not confirm or deny the possibility of a low viscosity channel in the upper mantle but this can be resolved only if the uplift data are supplemented with observations of the present uplift rate the published rates are controversial but if valid they point to a thin 15 km elastic layer and a relatively narrow 200km low viscosity channel while the models predict uplift near the centre of the former lake they also predict that the peripheral regions should be subsiding appreciably if flow is confined into a shallow channel of low viscosity observations reported by anderson bucknam suggests such behaviour likewise the present rate of uplift changes sign at some distance from the centre of the lake and detailed observations of warping of the shorelines and repeated levelling in the area may yield further constraints on the rebound model copyright