brittle frictional mountain building 2 thermal structure and heat budget this paper describes a simple thermal model of an actively deforming critically tapered fold and thrust belt the model determines the steady state temperature distribution and heat flow as well as the pressure temperature time histories of rocks that outcrop at the surface the main parameters controlling the thermal structure are the accretion and erosion rates the undisturbed geothermal gradient at the toe and the amount of frictional heating both shear heating on the decollement fault and internal strain heating within the deforming brittle wedge are incorporated in a mechanically consistent manner and they dominate the effect of radiogenic heating except in fold and thrust belts with significantly overpressured pore fluids the mean stresses temperatures and surface heat flow all increase with an increase in the basal and internal coefficients of friction and this dependence is used to constrain the level of friction on the decollement fault beneath the steady state fold and thrust belt in taiwan rocks outcropping in the core of the central mountain range of taiwan experience maximum theoretical temperatures in excess of 400 c and maximum mean pressures in excess of 500 mpa if the coefficient of basal friction is b 0 5 qualitatively these conditions are in good agreement with the observed high greenschist facies metamorphism the theoretical surface heat flow which increases from 95 mw m2 at the front of the fold and thrust belt to 240 mw m2 at the rear is in excellent agreement with the results of a recent geothermal survey of taiwan and theoretical cooling histories are in good agreement with fission track and other geochronologic studies taken together these results provide strong evidence that sliding on the basal decollement fault beneath taiwan is governed by a coefficient of friction in the range of typical laboratory measurements b 0 5 0 2 approximately 35 of the total surface heat flux of 3 gw is heat conducted into the base of the wedge from the top of the basal decollement fault and somewhat more than 30 is heat advected into the toe by accretion the remaining heat is generated internally about 25 by internal strain heating and about 10 by radiogenic heating either an increase in the coefficient of basal friction b or a reduction in the pore fluid pressure ratio b leads to an increase in the surface heat flow because of the increased frictional heating within the wedge and on the basal decollement fault the overall balance of energy in a steady state fold and thrust belt is described by the equation e w g q where is the rate at which both mechanical and heat energy are added from external sources w g is the rate at which work is performed against gravitational body forces in a reference frame attached to the overriding plate and q is the rate at which waste heat flows out of both the upper and lower boundaries the total power input into the taiwan fold and thrust belt is approximately 4 2 gw the mechanical work being done on the base and front of the fold and thrust belt accounts for 3 of these 4 2 gw in addition 0 9 gw of heat are being advected from the subducting plate into the toe by accretion the remaining 0 3 gw are being supplied by in situ radiogenic heating the outgoing energy is dominated by the 3 gw of heat conducted out the top in the surface heat flow however another 0 8 gw are conducted down beneath the rear portion of the basal decollement fault to heat the underlying subducting slab only 0 4 of the incoming 4 2 gw do useful mechanical work against gravity within the wedge the efficiency of brittle frictional mountain building in taiwan is therefore 10

extension during continental convergence with application to the tibetan plateau the tibetan plateau is the product of crustal thickening caused by the collision between india and asia and is the largest active example of extensional tectonics in a zone of continental collision throughout most of the tertiary the tectonics of the plateau were dominated by north south shortening a significant proportion of which took place on east west striking thrust faults for the last 5 m y or so the plateau has been thinning by the mechanism of extension on north south trending normal faults previous investigations of the collision have been able to account for the large scale features of the tertiary deformation but have failed to explain the transition in the late tertiary to quaternary strain rate field of the plateau from north south compression to east west extension the transition could in principle be effected by a reduction in the rate of convergence between india and asia or by a uniform reduction in strength of the whole continental lithosphere of asia it could not however be effected by a reduction in strength of the elevated region alone this produces increased compressional strain rates in the weakened zone an alternative explanation for the transition to extension comes from considering the thermal evolution of thickened continental lithosphere the lower part of the lithosphere consists of a thermal boundary layer which when thickened by horizontal shortening is colder and denser than its surroundings convective instability of the thickened thermal boundary layer and its replacement by hot asthenosphere would rapidly raise the surface elevation and gravitational potential energy of the overlying part of the lithosphere the convective instability would happen in a time brief compared with the collision time scale 50 m y in the case of india and asia but would only occur after there had already been substantial thickening of the lithosphere numerical experiments show that for a range of lithospheric parameters the increase in surface height as much as 2 km and of potential energy 5 to 10 1012 n m 1 resulting from convective instability of the lower lithosphere are sufficient for east west extension to replace north south compression as the dominant feature of the stress field of the tibetan plateau

vertical averages of rheology of the continental lithosphere relation to thin sheet parameters abstract we calculate vertically averaged rheologies for continental lithosphere subject to biaxial states of stress corresponding to extensional compressional and strike slip regimes we assume that brittle deformation occurs by byerlee s law and that ductile deformation occurs by steady state creep mechanisms under these conditions the vertically averaged rheology may be approximated by a single power law over the range of strain rates from 10 13 to 10 17 s 1 this is true not only when either brittle or ductile behavior dominates the strength of the lithospere but also when the contributions of brittle and ductile behavior are comparable the value of the power law exponent n and the strength of the lithosphere depend on the depth and stress difference at the brittle ductile transition the temperature at the moho and the geothermal gradient in the range of vertically integrated stress between 1012 and 1013 n m 1n reaches a minimum of between 5 and 10 under other circumstancesn increases rapidly as brittle behavior dominates over ductile behavior the strength of the lithosphere depends most strongly on the thermal state of the upper mantle but also is influenced by the stress supported in brittle portions of the lithosphere

some thermal and mechanical consequences of rapid uplift an example from the southern alps new zealand abstract the thermal evolution of continental crust during active collision is modeled through numerical solutions of the two dimensional heat conduction equation for a rapidly moving medium the boundary conditions used in the modeling are derived from geological and geophysical observations from the active collision zone in the south island of new zealand the problem domain over which the solutions are obtained consists of a 40 km horizontal by 25 km vertical spatial plane with a vertical discontinuity at 10 km from the western boundary to the east of this discontinuity vertical uplift rates of up to 10 mm a occur over a timespan of up to 4 ma temperature distributions are calculated at 10 ka intervals over the 4 ma duration a two dimensional high temperature region is established upon initiation of uplift of the eastern block due to the advective component carrying heat upwards more rapidly than it can be dissipated laterally from the problem domain temperatures within the upper 5 km are greater than 400 c after 2 25 ma with geothermal gradients of up to 200 c km attained within the upper 3 km at times greater than 2 5 ma the vertical temperature distribution changes little while the anomalously high temperatures spread laterally into the stationary crust using rheological equations to describe the brittle behaviour of a water saturated upper crust and the ductile behaviour of a quartz dominated lower crust together with the thermal distribution of the conduction models the mechanical evolution of a collision zone is investigated in addition to high crustal temperatures and associated high heat flow rapid uplift produces a weakening of the crust by raising of the depth of transition from brittle to ductile behaviour within the zone of most rapid uplift the brittle ductile transition rises from 13 km to less than 5 km after 1 5 ma of uplift further uplift reduces the brittle layer to 3 km thickness and causes lateral spreading of the low strength zone the reductions in crustal strength caused by the thermal weakening produce a high strain zone within the region of maximum uplift which is incapable of sustaining large differential stresses this causes horizontal and vertical stress transfer and results in shallow seismicity increases in the adjacent crust as well as in intermediate depth seismicity within the high strength upper mantle because the thermal and mechanical anomalies discussed are a function of rapid uplift all regions of active continental collision may be expected to exhibit similar behaviour some mechanical and thermal characteristics of the himalayan collision zone are briefly examined in light of the numerical modeling

vp vs ratio along the voring margin ne atlantic derived from obs data implications on lithology and stress field a total of 13 regional ocean bottom seismograph obs profiles with an accumulated length of 2207 km acquired on the voring margin ne atlantic have been travel time modelled with regards to s waves the vp vs ratios are found to decrease with depth through the tertiary layers which is attributed to increased compaction and consolidation of the rocks the vp vs ratio in the intra campanian to mid campanian layer 1 75 1 8 in the central voring basin is significantly lower than for the layers above and beneath suggesting higher sand shale ratio this layer was confirmed by drilling to represent a layer of sandstone this mid cretaceous anomaly is also present in the northern voring basin as well as on the southern lofoten margin further north the vp vs ratio in the extrusive rocks on the voring plateau is estimated to be 1 85 conformable with mafic basaltic rocks landward of the continent ocean transition cot the vp vs ratio in the layer beneath the volcanics is estimated to be 1 67 1 75 these low values suggest that this layer represents sedimentary rocks and that the sand shale ratio might be relatively high here the vp vs ratio in the crystalline basement is estimated to be 1 67 1 75 in the basin and on the landward part of the voring plateau indicating the presence of granitic granodioritic continental crust in the lower crust the vp vs ratio in the basin decreases uniformly from southwest to northeast from 1 85 1 9 to 1 68 1 73 suggesting a gradual change from mafic gabbroic to felsic granodioritic lower crust significant 3 5 azimuthal s wave anisotropy is observed for several sedimentary layers as well as in the lower crust all these observations can be explained by invoking the presence of liquid filled microcracks aligned vertically along the direction of the present day maximum compressive stress nw se

on the initiation of subduction zones analysis of the relation between intraplate stress fields and lithospheric rheology leads to greater insight into the role that initiation of subduction plays in the tectonic evolution of the lithosphere numerical model studies show that if after a short evolution of a passive margin time span a few tens of million years subduction has not yet started continued aging of the passive margin alone does not result in conditions more favorable for transformation into an active margin

the steady state thermal structure of eroding orogenic belts and accretionary prisms an analytical expression derived in this paper for the steady state thermal structure of thrust belts and subduction systems shows that surface erosion rate basal accretion rate and upper plate heat production are extremely important in controlling the temperature and metamorphic history of orogenic belts and accretionary prisms especially where upper plate thickness h is large for example even at rapid erosion and accretion rates and with large upper plate heat productions temperatures near the toe of a thrust wedge e g at h 5 km are nearly the same as those that would be present in the absence of erosion accretion and upper plate heat production in thicker parts of the same wedge e g at h 30 km the combined effects of erosion accretion and upper plate heat production can be dramatic for sufficiently large magnitudes of upper plate heat production or sufficiently rapid erosion rates inverted negative geothermal gradients are produced in the lower part of the upper plate and the upper part of the lower plate although it is difficult to produce inverted geotherms where h 20 km the potential importance of erosion and accretion can be illustrated through two examples 1 beneath the himalayas increasing the upper plate radiogenic heat production from 0 to 2 5 mw m3 and increasing the rate of surface erosion from 0 to 1 mm yr raises the computed steady state temperatures on the main central thrust at h 30 km from 265 c to 600 c and produces a local temperature maximum of 635 c located 6 km above the fault and 2 within the upper plate of the peru trench increasing the rate of surface erosion and basal accretion from 0 to 2 4 mm yr or increasing the upper plate radiogenic heat production from 0 to 1 3 mw m3 increases the computed steady state surface heat flow at h 30 km from 10 to 33 mw m3 but only increases temperatures at the fault surface from 125 c to 170 c shear heating along thrust faults or subduction boundaries is not necessary to produce the high metamorphic temperatures or surface heat flows observed in these two examples and the generation of large amounts of heat by shear stresses on the faults more than a few tens of bars appears to be inconsistent with some of the observations made in these areas this study indicates that many of the major discrepancies between existing thermal models of overthrust belts and observed temperatures as inferred from field data can be attributed to neglect of horizontal and vertical advection of heat caused by surface erosion and by accretion of material from lower plate to upper plate across the fault surface

mass anomalies on ganymede abstract radio doppler data generated with nasa s galileo spacecraft during its second encounter with jupiter s moon ganymede are used to infer the locations and magnitudes of mass anomalies on ganymede we construct models for both surface and buried anomalies with only one flyby and no global coverage a solution for mass anomalies cannot be uniquely determined however we are able to constrain acceptable solutions for mass anomalies to four broad regions a near polar region and three that are roughly equatorial if the mass anomalies are constrained to lie at the surface the centers of the regions are located near the coordinates 77 n 333 w 36 n 0 w 33 n 130 w and 7 n 194 w if the mass anomalies are located at the deep ice rock interface 800 km below the surface the regions centers are approximately 65 n 17 w 32 n 30 w 37 n 175 w and 15 n 211 w for both models the regions are up to a few thousand kilometers across the magnitude of mass anomalies on the surface is on the order of 10 17 kg mass anomalies at the ice rock interface are on average no more than an order of magnitude larger 10 18 kg there are two positive and two negative mass anomalies in both the surface and ice rock interface models one of the positive mass anomalies at the surface is associated with galileo regio the other positive surface mass anomaly is located at high northern latitudes with no obvious geological association negative surface mass anomalies lie near uruk sulcus and between perrine regio and barnard regio near sicyan sulcus and phrygia sulcus the locations of the ice rock interface mass anomalies lie approximately radially below the surface anomalies positive mass anomalies at the surface could be associated with the silicate rich ice or accumulated silicate layers of the dark regions negative mass anomalies at the surface could be associated with the relatively clean low lying ice of sulci alternatively ganymede s mass anomalies could be associated with the topography or other mass concentrations at the deep ice rock interface

recent rapid uplift in the bolivian andes evidence from fission track dating apatite and zircon fission track cooling ages constrain the tertiary cooling and uplift history of the eastern cordillera and altiplano of bolivia fission track data are from two triassic plutons and surrounding paleozoic metasedimentary rocks in the eastern andes north of la paz zircon cooling ages indicate that the roof of the huayna potosi pluton was emplaced in the zircon partial annealing zone and that the zongo pluton was emplaced entirely in the zircon total annealing zone apatite cooling ages for both plutons record uplift in the past 5 15 m y and zircon cooling ages from the zongo pluton reflect uplift in the past 25 45 m y uplift rates calculated by these apatite and zircon cooling ages suggest that uplift rates were 0 1 0 2 mm yr between 20 and 40 ma and increased significantly between 10 and 15 ma by 3 ma uplift rates may have been as high as 0 7 mm yr

thermal effects of thrust faulting abstract calculations based on simple models of overthrust sheets in crystalline basement rocks show that significant thermal effects may result from their movements if rates are sufficiently high e g plate tectonic rates the thrust sheets sufficiently thick 5 10 and 15 km are modelled here the distances moved sufficiently large and for reasonable values of the coefficient of friction along the thrust plane overthrusting can cause metamorphic mineral zonations and heat flow anomalies observable in the field regions where large scale overthrusting has occurred should be characterized by a decrease with depth of grade of metamorphic mineral assemblages and anomalously low heat flow the theoretical effects are presented as a series of maximum temperature vs depth and heat flow vs time plots

some isostatic and thermal consequences of the vertical strain geometry in convergent orogens abstract the thermal and isostatic consequences of continental deformation particularly surface elevation horizontal buoyancy forces and metamorphism in the crust depend to a considerable extent on the way in which strain is distributed between the crust and the mantle lithosphere 1 since these vertical strains may be strongly decoupled by processes such as convective thinning or detachment of the lower thermal boundary layer 2 with the extent of this decoupling varying in space and time in an orogen 3 it is useful to parameterise the vertical strain on the scale of the crust c and lithosphere 1 respectively we illustrate this parameterisation by considering the thermal and isostatic consequences of a number of c 1 paths which may develop during the convergent deformation of a thermally stabilised lithosphere three qualitatively distinct c 1 paths in orogens are distinguished on the extent of decoupling between vertical strains in the crust and mantle lithosphere type 1 paths involve no decoupling so the vertical strain in the lithosphere is homogeneous for a given c type 1 paths result in relatively low surface elevation and low intermediate metamorphic temperatures appropriate for the development of glaucophane schist and barrovian metamorphic assemblages type 2 paths allow decoupling due to processes such as convective thinning of the mantle lithosphere on the orogenic timescale but only after considerable initial lithospheric thickening type 2 paths lead to relatively high surface elevations for a given c and intermediate to high metamorphic temperatures only after the mantle lithosphere is thinned the increase in potential energy associated with mantle lithospheric thinning resulting in an increase in buoyancy forces by as much as 10 13 nm 1 will quickly terminate convergent deformation with the result that metamorphic heating will postdate the thickening deformation and may induce extensional collapse of the orogen type 3 paths involve efficient mantle lithosphere thinning as the crust thickens with a consequence being particularly the possibility of relatively high metamorphic temperatures during active crustal thickening for a given driving force convergent deformation along a type 3 path will be terminated at relatively small c providing an appropriate setting for the development of high t low p metamorphic assemblages

new finite element techniques for modeling deformation histories of continents with stratified temperature dependent rheology previous techniques for modeling anelastic deformation of the lithosphere have included plane strain models restricted to two dimensional problems and quasi three dimensional plane stress or thin plate models that did not accurately include the effects of the shallow frictional layer or of kinematic detachment of crust from mantle this paper presents techniques to remedy these deficiencies of thin plate models an iteration strategy in which the rheology is linearized using artificial prestress and a particular effective viscosity tensor causes the calculation of horizontal velocities to converge monotonically even with a frictional layer at the top of the lithosphere a technique using two planar grids allows deformation and displacement to be different at the crust and mantle levels at far less cost than that of a three dimensional grid a finite element technique is developed for computing the changes in thickness of these layers caused by pure shear simple shear and pressure gradients a technique based on relaxation of perturbation eigenfunctions solves the heat equation in the lithosphere during deformation accuracy of component numerical methods is good for simple test problems but in realistic nonlinear problems utilizing all components only the precision can be determined because of the lack of analytic solutions precision of the combined program is tested with a realistic sample problem and presented as a function of the number of iterations in each velocity solution convergence factor 0 73 to 0 88 size of time step in the predictor corrector time integration convergence as t0 8 and number of degrees of freedom in the finite element grid convergence as n 0 5 to 0 8 for most variables overall cost of a simulation varies with the fractional precision as 3 3 a new consequence of kinematic detachment a moving wave of crustal thickness is found unfortunately the form of the wave depends on the finite element size this means that element size must be chosen to approximate the smoothing by flexural rigidity effects that were neglected because of cost

weathering instability and landscape evolution abstract the argument in this paper is that the fundamental control on landscape evolution in erosional landscapes is weathering the possibility of and evidence for instability in weathering at four scales is examined the four scales are concerned with weathering processes allocation of weathered products the interrelations of weathering and denudation and the topographic and isostatic responses to weathering limited denudation the regolith hillslope landscape unit and landscape scales respectively the stability conditions for each model and the circumstances under which the models themselves are relevant are used to identify scale related domains of stability and instability at the regolith scale the interactions among weathering rates resistance and moisture are unstable but there are circumstances over long timescales and where weathering is well advanced under which the instability is irrelevant at the hillslope scale the system is stable when denudation is transport rather than weathering limited and where no renewal of exposure via regolith stripping occurs at the level of landscape units the stability model is based entirely on the mutual reinforcements of weathering and erosion while this should generally lead to instability the model would be stable where other external controls of both weathering and erosion rates are stronger than the weathering erosion feedbacks at the broadest landscape scale the inclusion of isostatic responses destabilizes erosion topography uplift relationships thus if the spatial or temporal scale is such that isostatic responses are not relevant the system may be stable essentially instability is prevalent at local spatial scales at all but the longest timescales stability at intermediate spatial scales is contingent on whether weathering erosion feedbacks are strong or weak with stability being more likely at shorter and less likely at longer timescales at the broadest spatial scales instability is likely although stability may be present at intermediate temporal scales if weathering erosion feedbacks are weak the distinction is important because stability is associated with convergent evolution whereby the effects of initial variations or disturbances are reduced over time as the landscape converges toward a stable equilibrium state instability by contrast indicates divergent evolution increasing differentiation over time and the persistence and growth of disturbance effects and initial variations

modeling of dynamic uplift denudation rates and thermomechanical consequences of erosion in isostatically compensated mountain belts in this paper we present a simple one dimensional model to examine the interplay between dynamic uplift and denudation in response to simultaneous surface erosion and lithospheric deformation under the assumption that the surface elevation of a mountain belt is isostatically compensated and the lithosphere undergoes vertically homogeneous deformation we also discuss the dynamics of isostatically compensated mountain belts in relation to surface erosion based on a brace goetze lithospheric model consisting of a quartz dominated crust and an olivine dominated upper mantle the mechanical strength of such a lithosphere is governed by a combination of brittle failure and power law or dorn law creep assuming a simple linear dependence of erosion rate on elevation we find that contrary to previous suggestions the effect of high denudation rates on the mechanical strength of the lithosphere does not involve significant weakening of the lithosphere

finite strain calculations of continental deformation 2 comparison with the india asia collision zone numerical experiments on a thin viscous sheet model for deformation of continental lithosphere subjected to an indenting boundary condition yield distributions of crustal thickness of stress and strain rate and of latitudinal displacements that may be compared with observations in the india asia collision zone a simple indenting boundary condition applied to initially laterally homogeneous sheets obeying a power law rheology produces results that are in broad agreement with the observations provided that the power law exponent is three or greater and the sheet can support vertically integrated stress differences of 2 1013 5 1012 n m 1 in regions in front of the indenter under these conditions the calculated deformation shows accommodation of convergence primarily by crustal thickening to produce a plateau in front of the indenter palaeomagnetic data from india and tibet and the observed distribution of topography suggest that much of the post eocene convergence of india with asia has been taken up by deformation within asia that involved crustal thickening the principal difference between calculation and observation is the absence from the calculated strain rate fields of east west extension of the plateau in front of the indenting boundary the calculations show that once such a plateau is formed the buoyancy force associated with the crustal thickness contrast inhibits further thickening and the plateau strains at less than half the rate of its immediate surroundings seismically determined regional strain rates exhibit a similar distribution with the tibetan plateau straining at about one quarter the rate of the tien shan and ningxia gansu regions calculated principal compressive stress orientations and regional strain rates agree with the seismically determined quantities in the mongolia baikal tien shan tibet and ningxia gansu regions of asia to within the uncertainty of the latter the vertically integrated stresses that are calculated for the viscous sheet are comparable with those that can be supported by a theologically stratified continental lithosphere obeying laboratory determined flow laws we suggest that the thin viscous sheet model described in this paper and its companion gives a simple and physically plausible description of the observed deformation in central asia in this description the predominant mechanism of accommodation of continental convergence is diffuse crustal thickening with shear on vertical planes playing a subsidiary role once large crustal thickness contrasts have been established

crustal structure of the northern part of the voring basin mid norway margin from wide angle seismic and gravity data abstract three regional ocean bottom seismograph obs profiles with a total of fifteen recovered obss were acquired in the northern part of the voring basin mid norway margin in 1996 the data have been modelled by inversion and forward modelling of the obs vertical components p waves the velocity is found to increase downwards within the sedimentary layers due to increasing depth of burial confining pressure within the two deepest sedimentary layers there seems to be an increase of 0 5 1 km s in velocity northwestwards this increase is most likely caused by high velocity sill intrusions in the sedimentary rocks emplaced during the rift episode leading to early eocene opening of the ne atlantic the presence of significant amounts of sills seems to terminate close to the nyk high along profile 5 dip profile and close to a dome northwest of the shelf edge along profile 6 dip profile the velocity in the top of this dome is anomalously high 3 4 km s at only 1 km depth beneath the seafloor suggesting that the high consists of volcanic rocks or heavily intruded sedimentary rocks the relatively low velocities derived from within the upper crystalline crust 5 9 6 2 km s confirms that the crust is of continental origin within the lower crust there seems to be a clear increase in velocity northwestwards from about 7 0 km s to about 7 4 km s suggesting that the amount of high velocity intrusions underplating in the lower crust decreases landwards the modelling of the strike profile profile 7 suggests that the transition from a lower crust dominated by magmatic intrusions to a more undisturbed continental lower crust is located approximately beneath this profile the model for profile 7 ties closely southwestwards to the models derived from obs data acquired in 1992 and northeastwards to lofoten obs data acquired in 1988 the models indicate that the thick magmatic intrusions in the sedimentary rocks and lower crust extend further landwards in the area of the 1992 survey and that the transition zone is related to the surt lineament the distribution of magmatic rocks thus seems to correlate strongly with pre breakup structures in addition to the p wave modelling gravity modelling has been performed along all profiles the gravity modelling confirmed all main aspects of the obs models and provided constraints on the crustal structures towards the ends of the profiles

on uplift and exhumation during convergence a simple kinematic model is used to illustrate the vertical motions of rocks during convergent deformation and erosion at the surface it is shown that rocks may move upward or downward in the crust depending on the relative rates of erosion and thickening and depending on their initial depth in the crust exhumation during thickening can only occur if rapid denudation accompanies the thickening process during homogeneous thickening with erosion that is elevation dependent the initial depth from which rocks can be exhumed is only determined by the density distribution in the column and is independent of erosion or thickening rates the maximum initial depth from which rocks can be exhumed is of the order of 30 km or less there is therefore no conflict in the observation of synchronous exhumation and convergent deformation if the peak pressure of rocks is equivalent to no more than 30 km of burial it is also shown that uplift defined as vertical motion of the surface with respect to a reference level for example the geoid and exhumation defined as vertical motion of rocks with respect to the surface may follow different patterns in time and that the difference between the two evolutions may be a useful indicator of the exhumation process the model serves to emphasize the important differences between uplift and exhumation which are often not distinguished in the literature

constraints on geological strain rates arguments from finite strain states of naturally deformed rocks a summary of known finite strain states is presented longitudinal strains 1 e as measured in many rocks often range from 1 to 40 and 1 to 0 025 the time span available to produce such measureable strains in young orogenic zones seems to be less than 10 m y possibly less than 1 m y which constrains conventional strain rates into the range of 10 sup 13 s sup 1 to 10 sup 15 s sup 1 for both pure and simple shear the most efficient way and much less efficient way to accumulate incremental strains respectively the ellipticity of the finite strain ellipse increases in a nonlinear manner finite strain variations in adjacent layers which give rise to features such as cleavage refraction arise with only slight differences in the strain rates within these layers

finite strain calculations of continental deformation 1 method and general results for convergent zones a finite element method is used to calculate stresses and strain rates in a thin viscous sheet representing the continental lithosphere that is bordered in one part by an indenting boundary we calculate solutions for velocity fields crustal thickness distributions strain rates rotation time integrated vorticity and finite strain ellipsoids to show the dependence of these quantities on the controlling parameters the stress strain exponent n and the strength of the sheet relative to the gravitational forces which may be expressed as a dimensionless number the argand number ar for n 3 and ar between 1 and 10 a plateau of thickened crust is formed in front of the indenter the strain histories of individual elements within the viscous sheet may be quite complex and the finite strain at the end of deformation may bear no obvious relation to the principal stress orientations during the deformation the strain rate fields are interpreted in terms of the style of faulting that would be expected in the brittle upper crust if it were coupled to the ductile but stronger upper mantle in general the length scale of deformation increases with ar and time since the start of the collision and decreases with n for ar 3 the increase in length scale is accompanied by a change in the style of deformation from predominantly crustal thickening with thrust faulting in the brittle layer to predominantly transcurrent deformation strike slip faulting in the brittle layer

the scattering of shear waves in the crust the two major sources of scattering for shear waves in the crust interactions with the topography at the surface and the effective anisotropy of aligned cracks throughout the rockmass introduce first order changes to the shear wave particle motion at the surface shear waves are scattered by the topography within a wavelength or two of the recording site so that unless the effective incidence angle is less than the critical angle sin 1vs vp the recorded waveforms may bear little relationship to the waveforms of the incident wave within the rockmass shear waves are scattered by extensive dilatancy anisotropy eda the distribution of stress aligned fluid filled cracks microcracks and preferentially oriented pore space pervading most rocks in the crust analysis of this shear wave splitting yields new information about the internal structure of thein situ rockmass which is not otherwise available

mechanical consequences of granite emplacement during high t low p metamorphism and the origin of anticlockwise pt paths high temperature t low pressure p metamorphic belts preserve evidence of metamorphism under extremely perturbed and hence transient thermal regimes pt paths are commonly anticlockwise that is the maximumt was attained prior to or at the same time as the maximump with cooling at near constant or increasingp and in many terrains peak metamorphic temperatures prevailed during convergent deformation using a simple coupled thermal mechanical model that assumes a strongly temperature dependent rheology for the continental lithosphere we show that the coincidence of metamorphism with convergent deformation in high t low p terrains may reflect the thermal weakening attendant with rapid advective movement of heat within the lithosphere via granite magma ascent the model shows that the magnitude of the thermal weakening effect is sensitive to the critical temperature for granite segregation tm crit the depth of emplacement of the magmas and most importantly the granite forming mechanism during the prograde cycle material points attain maximum temperatures during a transient 3 ma high strain rate pulse withe up to 10 14 s 1 at levels near the site of granite emplacement the attainment of maximum pressures follows peak temperatures with rapid cooling paths that are close to isobaric or involve slight compression

crustal structure of the outer voring plateau offshore norway from ocean bottom seismic and gravity data four ocean bottom seismograph obs profiles acquired across the continent ocean transition zone of the outer voring plateau have been modeled by inversion and forward modeling of the obs vertical component traces p waves the thickness of the sedimentary layers deposited since the early eocene continental breakup varies from up to 2 2 km above the basaltic inner flows if to a minimum of 0 2 km about 20 km seaward of the voring escarpment ve with a velocity of 1 6 2 55 km s the thickness of the uppermost layer of basalt varies from 0 5 to 4 5 km and its velocity ranges from 3 4 to 5 km s the modeling of the two dip profiles suggests that strongly intruded preopening sedimentary rocks extend 40 km seaward of the ve farther seaward another layer of extrusives intrusives is found beneath the uppermost layer of basalt the lateral variations in velocity in the main crustal layer along the dip profiles indicate that the continent ocean transition extends over a 30 50 km wide zone in between strike profile 3 oceanic 6 6 7 35 km s and strike profile 4 continental 6 1 7 0 km s an up to 7 km thick lower crustal high velocity body 7 1 7 4 km s is interpreted in terms of intrusions in the lower crust beneath and landward of the continent ocean transition the total thickness of the normal oceanic crust is estimated to be 7 9 km the anomalously thick oceanic crust reaches a maximum thickness of about 25 km and the crustal thickness is estimated to be 17 22 km beneath the if gravity modeling of the profiles confirmed all main aspects of the velocity models and provided constraints on the crustal structures toward the ends of the profiles where the ray coverage was low

constraints on the location magnitude and dimensions of ganymede s mass anomalies abstract previously radio doppler data generated with nasa s galileo spacecraft during its second encounter with jupiter s moon ganymede were used to infer the locations and magnitudes of mass anomalies on ganymede using point mass models however the point mass solutions do not provide the vertical and horizontal extent of the anomalous mass concentrations here we provide the results of a new study using spherical cap disks to model ganymede s mass anomalies the spherical cap disk models not only provide the locations and magnitudes of the mass anomalies but also their vertical and horizontal dimensions the new models show that three disks a positive mass located at 53 0 n 127 0 w and two negative masses located at 22 0 n 87 0 w and 49 0 n 219 0 w can explain the data the magnitudes of the mass anomalies are on the order of 10 18 kg the diameters of the anomalies are a few thousand kilometers the positive anomaly is about 100 meters thick and both negative anomalies have a thickness of less than a kilometer we use the additional information provided by the disk models to investigate the viability of mass anomalies at ganymede s surface by comparing the diameters of the anomalies to the sizes of regiones and sulci and the anomalies thicknesses to accumulated layers of rock and clean ice on the surface we find that the dimensions of the mass anomalies could be explained by concentrations of rock in the regio and rock free ice in the sulci these results confirm that mass anomalies may reside on or near ganymede s surface and that positive mass anomalies are contained within areas of dark terrain and negative mass anomalies within bright terrain

on the relationship between surface uplift and gravitational extension this paper highlights the relationship between isostatically supported surface elevation and the lateral buoyancy forces of an orogen the former is a linear function the latter is a quadratic function of the thickness of the lithosphere thus surface elevation and lateral buoyancy forces may have differing evolutions in the development of an orogen indeed during the evolution of collisional orogens the qualitative relationship between these two parameters may reverse so that only in the early orogenic evolution topographically high regions exert a net lateral buoyancy force on topographically low regions later in the evolution this may change to a counterintuitive scenario in which there is a net lateral buoyancy force from the topographically lower regions toward the topographically higher regions to illustrate this fact we use a simple one dimensional kinematic model for an orogen which undergoes simultaneous thickening due to convergence and erosion at the surface it can be shown that for reasonable erosion and thickening rates surface elevation increases through time until a steady state is reached while the lateral buoyancy force changes from positive to negative giving rise to the inward collapse of an orogen in the field this may be recognized as the occurrence of two successive coaxial convergent deformation events present day examples may be the formation of back arc basins where extension in the low lying hinterland of an andean type mountain belt is caused by a gravitational compressive force exerted by the hinterland onto a belt of significantly higher surface elevation but possibly of lower potential energy

age dependence of oceanic intraplate seismicity and implications for lithospheric evolution we have determined depths for 16 oceanic intraplate earthquakes using body wave modeling a data set composed of these and 11 other well constrained depths shows that the maximum depth of seismicity deepens with increasing lithospheric age and appears to be bounded by a 700 800 c isotherm the maximum depth to which intraplate earthquakes occur is approximately equal to the flexural elastic thickness but much less than the seismic thickness from surface wave dispersion the maximum faulting depth is consistent with the predictions of rapid weakening at high temperatures for dry olivine rheologies determined by experimental rock mechanics oceanic intraplate earthquakes can occur at greater depths and temperatures than has previously been reported for continental crustal events presumably because oceanic lithosphere is stronger at high temperatures both the number of earthquakes and the cumulative seismic moment decrease with lithospheric age the cause of this trend is unclear possibilities include nonrandom location of preexisting weak zones with respect to the age provinces fault strengthening with age or a decrease in the stress level a decrease in intraplate stress with age is opposite that expected from ridge push stresses which increase with age but may result either from thermoelastic stresses which are greatest in young lithosphere or near ridge stress concentrations due to local heterogeneities in the spreading process

on the stability of isostatically compensated mountain belts the formation of convergent mountain belts is invariably accompanied by an increase in gravitational potential energy due to part of the work done by the forces driving convergence the evolution of potential energy stored in an orogen is dependent on 1 the density structure 2 the thermal evolution and 3 the way convergent deformation is partitioned between crust and mantle lithosphere it is now well recognized that this increase in potential energy associated with the mountain building process raises the possibility that significant extension or collapse may accompany the relaxation of the forces driving convergence provided the lithosphere is thermally weakened e g england 1987 in this paper we evaluate the stability of isostatically compensated mountain belts under the assumption that the strength of continental lithosphere is governed by a combination of frictional sliding and creep processes using the brace goetze model for the rheology of the lithosphere the reference lithosphere defined to be in potential energy and isostatic balance with the mid ocean ridges changes with different thermal parameters of the lithosphere the instantaneous extensional strain rate for thermally mature mountain belts is calculated by balancing the horizontal buoyancy force stored in the mountain belts measured relative to the reference state with the vertically integrated strength of the lithosphere for initial strengths spanning the probable natural range it is shown that horizontal buoyancy forces arising in isostatically balanced mountain belts are sufficiently large to induce the collapse at significant rates greater than a few times 10 16 s 1 and leading to significant finite extension providing the moho temperatures exceed about 650 700 c a condition only likely to be attained if the mantle lithosphere has not been thickened to the same extent as the overlying crust consequently processes that thin the mantle lithosphere as a consequence of convergent deformation such as the convective instability of a thickened lower thermal boundary layer greatly increase the possibility of collapse the calculations presented here suggest that near complete destruction of the mountain system by extensional collapse may be possible if such processes can reduce total lithospheric thickening to less than half the contemporary crustal thickening i e fl fc 2 where fl and fc are the lithospheric and crustal thickening factors

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

brittle frictional mountain building 1 deformation and mechanical energy budget an active fold and thrust belt is analogous to a wedge of soil or snow that forms in front of a moving bulldozer such wedges exhibit a critical taper and a regional state of stress that is everywhere on the verge of coulomb failure the width of such a critically tapered fold and thrust belt does not depend on its brittle strength or frictional properties but rather on the accretionary influx rate of fresh material at its toe and on the rate of erosion a steady state fold and thrust belt is one in which the accretionary influx is balanced by the erosive efflux rocks are accreted at the toe and then horizontally shortened as they are transported toward the rear those that enter lower in the accreted section are more deeply buried before being uplifted by erosion mass balance and isotropy constrain the kinematics of this large scale deformation enabling us to infer the trajectories residence times and stress strain histories of rocks incorporated into eroding fold and thrust belts a typical rock resides in the steady state taiwan wedge for 2 3 m y before it is uplifted and eroded during its motion through the wedge it experiences strain rates in the range 10 13 to 10 14 s 1 the mechanical energy budget of brittle frictional mountain building is described by the equation where is the rate of work performed on the base and front of the fold and thrust belt by the subducting plate is the rate at which energy is dissipated against friction on the decollement fault is the rate at which energy is dissipated by internal frictional processes within the deforming brittle wedge and is the rate of work performed against gravitational body forces in a reference frame attached to the overriding plate the total mechanical power being supplied by the subducting eurasian plate to the active fold and thrust belt in taiwan is slightly over 3 gw approximately 60 of this work of steady state mountain building is being dissipated against friction on the decollement fault and about another 25 is being dissipated against internal friction this leaves only 15 or roughly half a gigawatt available to do useful work against gravity in general fold and thrust belts with moderate pore fluid pressures are dominated by work done against friction on the decollement fault however those with nearly lithostatic pore fluid pressures may be dominated by work done against gravity internal frictional dissipation is always less than basal frictional dissipation as it is in taiwan an alternative and equivalent description of the mechanical energy balance of a steady state fold and thrust belt is provided by the equation in this version the quantity on the left is the rate at which work is performed on the back of the wedge by the overriding plate and is the rate of work performed against gravity in a reference frame attached to the subducting plate the latter quantity is always positive for any critically tapered fold and thrust belt whose decollement fault dips toward its rear in contradiction to the central premise of the gravity spreading theory of fold and thrust tectonics

rapid early miocene acceleration of uplift in the gangdese belt xizang southern tibet and its bearing on accommodation mechanisms of the india asia collision abstract five samples from a biotite hornblende granodiorite phase of the 42 5 ma quxu pluton gangdese batholith southern tibet have been collected at 250 m vertical intervals biotite from these rocks yields monotonically decreasing40ar 39ar isochron ages with decreasing elevation of 26 8 0 2 23 3 0 5 19 7 0 3 18 4 0 4 and17 8 0 1ma tc 335 c coexisting k feldspars have virtually identical minimum apparent40ar 39ar ages of 17 0 0 4ma tc 285 c these data indicate parts of southern tibet experienced a pulse of uplift in the early miocene with the rate of uplift rising from 0 07 to 4 4 mm year in the interval 20 to 17 ma an apatite fission track age of 9 9 0 9ma from this locality constrains the average uplift rate at this site to about 0 81 mm year between 17 and 9 9 ma and 0 30 mm year from 9 9 ma to present k feldspar from the dagze granite 30 km to the east near lhasa yields a minimum apparent40ar 39ar age of 35 9 0 9ma tc 227 c which indicates an average uplift rate there of 0 21 mm year since then the marked pulse of uplift of the quxu granodiorite and the difference in uplift history between the dagze and quxu plutons suggests southern tibet has experienced discrete pulses of uplift variable in both space and time these data are not consistent with models which require a large proportion of uplift of the tibetan plateau to have occurred in the last 2 ma the data support the suggestion that convergence between india and asia was largely accommodated by tectonic escape during the opening of the south china sea 32 to 17 ma ago and permit distributed shortening as a mechanism for crustal thickening and uplift of this part of the tibetan plateau subsequent to 20 ma

internal structure of rhea 1 we model the interior of rhea on the basis of observational constraints and the results from geodynamical models available in the literature ten main types of models are defined depending on the presence or absence of a high pressure ice layer ice ii and the extent of separation of the rock component from the volatiles the degree two gravity coefficients are computed for each of these models in order to assess which properties of the interior are likely to be inferred from cassini radio science measurements scheduled on 26 november 2005 c22 greater than 2 5 10 4 indicates that the satellite is undifferentiated except for a slight increase in density with depth resulting from material self compression c22 between 1 67 10 4 lower bound and 1 90 10 4 indicates the presence of a rocky core whose radius can be determined from the satellite s mass and ices densities for a given temperature profile for other values most of the ten models cannot be distinguished from each other however assumptions on the density of the rock phase presence or absence of ice ii and the degree of differentiation could allow a unique model to be determined in many cases while the calculation presented in this work assumes that rhea is in hydrostatic equilibrium it is likely that rhea gravity field is partly affected by nonhydrostatic anomalies

a regional shear wave velocity model in the central voring basin n norway using three component ocean bottom seismographs abstract a regional ocean bottom seismometer obs dataset was acquired in the central and northern part of the voring basin n norway in 1992 thirty three component obss were deployed along seven regional profiles and the shear waves recorded on the horizontal components have been modelled by use of 2 d ray tracing utilizing an established p wave model in the shallow sediments 1 4 km depth mean vp vs ratios of 2 1 2 2 and 2 3 2 5 are inferred along the nw se and ne sw trending profiles respectively the relatively high mean vp vs ratios in this interval are probably related to unconsolidated sediments in the uppermost layers the azimuthal variation in the vp vs ratios with the fast direction nw se indicates a shear wave anisotropy of 5 10 in this interval consistent with observations further north in the lofoten area in the 5 10 km depth interval high velocity sill intrusions in the sediments are mapped by the p wave modelling these high velocity intrusions act as efficient conversion interfaces confirmed by the shear wave modelling a regional decrease in the vp vs ratios to 1 7 1 8 are observed at 4 6 km depth possibly related to sand rich sediments in the middle cretaceous the upper crust is clearly mapped by the shear waves and the inferred vp vs ratio of 1 75 confirms that the crust in the voring basin is of continental origin an increase of the vp vs ratio 1 8 1 85 in the lower crust indicates a change in its composition possibly explained by a mixing of continental crust and magmatic underplating

discovery of mass anomalies on ganymede we present the discovery of mass anomalies on ganymede jupiter s third and largest galilean satellite this discovery is surprising for such a large icy satellite we used the radio doppler data generated with the galileo spacecraft during its second encounter with ganymede on 6 september 1996 to model the mass anomalies two surface mass anomalies one a positive mass at high latitude and the other a negative mass at low latitude can explain the data there are no obvious geological features that can be identified with the anomalies

lithospheric strength in compression initiation of subduction flake tectonics foreland migration of thrusting and an origin of displaced terranes compressive strength profiles through continental and oceanic lithosphere show under all likely conditions continental lithosphere to be significantly weaker than oceanic manifestations of this include subduction initiation within continental lithosphere north africa eastern japan and the existence of continental large scale strike slip faults these latter are associated with the production of displaced exotic terranes once failure has begun and crustal shortening occurs through thrusting reduction of the geotherm causes an increase in total compressive strength and burial of the strength maximum in the thickened section this result leads to a mechanistic view of flake tectonics such that the modified strength profile of the overriding thickened plate enables it to act as a chisel and strip the upper crust from an encroaching continent the increase in total strength leads to a horizontal strength gradient such that the most recently thrust shortened section is stronger than the as yet und

formation of the rocky mountains western united states a continuum computer model one hypothesis for the information of the rocky mountain structures in late cretaceous through eocene time is that plate of oceanic lithosphere was underthrust horizontally along the base of the north american lithosphere the horizontal components of the motion of this plate are known from paleomagnetism and the edge of the region of flat slab can estimated from reconstructed patterns of volcanism new techniques of finite element modeling allow prediction of the thermal and mechanical effects of horizontal subduction on the north american plate a model that has a realistic temperature dependent rheology and a simple plane layered initial condition is used to compute the consequences of horizontal underthrusting in the time interval 75 million to 30 million years before present successful prediction of this model include i the location amount and direction of horizontal shortening that has been inferred from laramide structures ii massive transport of lower crust from southwest to northeast iii the location and timing of the subsequent extension in metamorphic core complexes and the rio grande rift and iv the total area eventually involved in basin and range style extension in a broad sense this model has predicted the belt of laramide structures the transport of crust from the coastal region to the continental interior the subsequent extension in metamorphic core complexes and the rio grande rift and the geographic region of late tertiary basin and range extension its principal defects are that i many events are predicted about 5 million to 10 million years too late and ii the wave of crustal thickening does not travel far enough to the east reasonable modifications to the oceanic plate kinematics and rheologies that were assumed may correct these defects the correspondence of model predictions to actual geology is already sufficiently close to show that the hypothesis that horizontal subduction caused the laramide orogeny is probably correct the rocky mountain thrust and reverse faults formed in an environment of east west to northeast southwest compressive stress that was caused by the viscous coupling between the oceanic plate and the base of the north american crust nonuniform crustal thickening by simple shear transport also caused relative uplifts therefore this model is consistent with both of the range forming mechanisms that have been inferred 1 a new proposal that arises from this simulation is that horizontal subduction also caused the subsequent extensional basin and range taphrogeny by stripping away the mantle lithosphere so that the crust was exposed to hot asthenosphere after the oceanic slab dropped away

multiple scales in river basin morphology existing data reveal that the steepness s of many river basins with mountainous headwaters defined as the ratio of total relief to total length of a basin is related to the logarithm of basin size the relief of these same river basins is observed to be non linearly related to basin steepness with maximal values of relief occurring in basins for which the value of s is about 0 03 or equivalently in basins in which the average slope is about 2 these systematic relationships between size relief and steepness of some basins which span nine orders of magnitude of area are inter preted in terms of an intermediate limit process bounded by well separated spatial scales the lower limiting scale corresponds to a threshold between channel formation and significant mass wastage and the upper limiting scale corresponds to the size of the largest landmass if the observed relationships between basin size relief and steepness indeed reflect a limit process then they are independent of the details of the physics contributing to landscape development and instead result from the constraints imposed by the bounding spatial scales exceptions to the limiting relationships explored here are readily noted however and are interpreted to reflect regional geological and temporal controls the delineation of the importance of multiple scales provides a potentially powerful basis for the examination of morphological relation ships in river basins introduction river basins dominate the landscape and the study of their morphology reveals important information about their formation sediment yield and fill i examine here the quantitative relationship between the area and steepness of river basins which drain mountainous terrain in terms of the bounding and intermediate length scales imposed by geological process and form the steepness of a river basin is considered in terms of the ratio of its total relief to its total length this ratio is a dimensionless number that has found wide use in the comparison of basins schumm 1956 1963 and other landscape features such as alluvial fans melton 1965 which vary greatly in size its value represents the average slope of the longitudinal profile of a basin and thus represents the basin wide magnitude of the gravitational component of landscape forming processes in the next section i review ideas regarding the existence and separation of spatial scales in fluvial landscapes this is followed by a simple analysis of physical systems bounded exclusively by two well separated spatial scales the results of the analysis are then used to examine the relationships observed between river basin area steepness and relief additional points of interest are explored in the discussion these include the situation when an intermediate spatial scale is imposed by regional geological structure and the evaluation of a denudational time scale and its relationship to basin size i conclude with a summary of important findings separation of multiple bounding scales in river basin morphology montgomery and dietrich 1992 found a simple relationship between the length l of a drainage basin and its area a given by

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

local lunar gravity field analysis over the south pole aitken basin from selene farside tracking data 1 we present a method with which we determined the local lunar gravity field model over the south pole aitken spa basin on the farside of the moon by estimating adjustments to a global lunar gravity field model using selene tracking data our adjustments are expressed in localized functions concentrated over the spa region in a spherical cap with a radius of 45 centered at 191 1 e 53 2 s and the resolution is equivalent to a 150th degree and order spherical harmonics expansion the new solution over spa was used in several applications of geophysical analysis it shows an increased correlation with high resolution lunar topography in the frequency band l 40 70 and admittance values are slightly different and more leveled when compared to other global gravity field models using the same data the adjustments expressed in free air anomalies and differences in bouguer anomalies between the local solution and the a priori global solution correlate with topographic surface features the moho structure beneath the spa basin is slightly modified in our solution most notably at the southern rim of the apollo basin and around the zeeman crater