kinematic models of fluvial terraces over active detachment folds constraints on the growth mechanism of the kashi atushi fold system chinese tian shan during detachment folding the relationship between differential uplift and shortening depends on the mechanism of fold growth such as limb rotation or hinge migration and may vary over the lifetime of a fold thus neither long term shortening rates nor the present fold geometry unambiguously constrain the kinematics of fold growth where rivers cut through growing anticlines flights of abandoned fluvial terraces act as passive kinematic markers as shortening progresses the terraces become deformed and thereby preserve critical information about the kinematics and evolution of active fold growth to constrain recent fold growth across three detachment folds in the kashi atushi fold system in the sw tian shan china we surveyed flights of deformed terraces and compared them with geometric models of successively emplaced horizontal unconformities terraces across pregrowth strata deformed by hinge migration limb rotation and a combination of the two migration of angular hinges and curved hinge zones were also compared each kinematic model predicts both a distinct geometry for the deformed terraces and contrasting angular relationships between the terraces and the pregrowth strata notably limb rotation and migration of curved hinge zones result in progressively rotated terraces that cut across pregrowth strata whereas all limb lengthening models result in parallelism between pregrowth strata and terrace straths across much of the fold the kashi atushi terraces show clear evidence of abandoned axial surfaces concentrated deformation near the core of the folds and progressive tilting with age when compared to the model predictions the folds are likely growing by a combination of limb rotation in the tight cores of the folds and hinge zone migration of pregrowth strata across the flanks of the folds

detachment folding in the southwestern tian shan tarim foreland china shortening estimates and rates abstract geologic observations of the chinese tian shan foreland reveal active contractional deformation along the entire margin to quantify the amount of shortening and understand the structural style we mapped the stratigraphy and structure of four folds expressed at the western end of the foreland north of kashi in this region upper tertiary through quaternary sediments are conformable but an abrupt transition from parallel to unconformable bedding in the uppermost strata suggests a transition from pre fold strata to strata deposited on a growing fold the folds have very steep 60 90 limbs and are box like to isoclinal suggestive of detachment folding total north south shortening across the center of the region is 9 km of which 5 7 km occurred in the kashi atushi fold system shortening estimates determined with excess area methods for individual folds decrease from a maximum of 6 8 km in the northwest to a minimum of 0 7 km in the southeast timing derived from a paleomagnetic study shows that the transition to syn folding strata occurred 1 2 ma in the middle of the study area resulting in an average shortening rate for the kashi atushi fold system of 5 mm yr if folding was coeval the shortening rate is high compared with foreland deformation east of the study area suggesting that the regional stresses or response of the foreland stratigraphy are unique to the kashi atushi fold system kinematics

structural characteristic and origin of intra continental fold belt in the eastern sichuan basin south china block abstract the fold and thrust belt in the eastern sichuan basin is represented by a series of subparallel chevron anticlines under the orogenic tectonic setting within the south china block in meso cenozoic period and the influence of the multi layer detachment fault the deformation of the thrust belt exhibits remarkably layered and large scale intracontinental thrusting structural characteristics in this paper we focus on the structural geometry and deformational mechanisms using the latest two dimensional 2d and three dimensional 3d seismic reflection data in combination with well and outcrop data the multi layer detachment faults especially the upper gypsum bearing detachment in the middle triassic jialingjiang formation and lower detachment with gypsum or shale in the lower middle cambrian system directly control the deformational styles of the study area interpretation of seismic sections indicates that the fold and thrust belt has various deformational styles during folding including fault propagation fold fault bend fold and detachment fold with box fold or pop up structural geometry regional location and structural boundaries play significant roles in controlling the deformational styles and distinct differences exist among the different anticlines the huayingshan anticline located at the front of the thrust belt shows intense structural deformation with northwestward thrusting direction and a relatively weak opposite southeastward thrusting in addition the anticlines exhibit structural differences along strike and the fold and thrust belt in the northern segment is influenced by the north china block

the velocity description of deformation paper 2 sediment geometries associated with fault bend and fault propagation folds abstract a general tectono sedimentary forward modelling equation is used to derive two dimensional numerical models of sediment geometries associated with developing fault bend and fault propagation folds these styles of folding are described in terms of velocity models of deformation and are linked with syn tectonic erosion transport and sedimentation the resultant two dimensional numerical models simulate pre growth and growth strata in both submarine and subaerial settings the geometries and relationships produced by the models are broadly similar to those seen in natural examples however complex stratal geometries may be generated which are significantly different to those produced by previous models growth strata associated with fault bend and fault propagation folds are also compared and the distinguishing features of each mode of folding discussed the forward models presented in this paper have predictive capabilities in terms of possible sediment geometries associated with fault bend and fault propagation folds and also in terms of the amount of deformation or erosion that a part of a structure may have undergone

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

stratigraphic and kinematic modeling of thrust evolution northern apennines italy we present a quantitative kinematic model of thrust evolution that allows detailed interpretation of the stratigraphic record of foreland basins simulation of thrusting and syntectonic sedimentation shows that changes in the relative rate of thrusting and mode of thrust activation can be determined by their expression in basin stratigraphy truncations and offlaps reflect thrust activity and hinterland migration of basin depocenters indicates out of sequence thrusting forward modeling of the stratigraphic record of the pliocene quaternary po basin italy enables the quantitative reconstruction of the displacement sequence of the thrust sheets prograding into the basin during the pliocene deep seated middle pliocene thrusting accompanied by out of sequence thrusting provides a consistent explanation for the observed stratigraphic record of the po piggyback basins

bed by bed fold growth by kink band migration sant llorenc de morunys eastern pyrenees ahstract rowth strata deposited over and against the flank of the sant llorenc de morunys fold during its final stages of deformation have been mapped at high resolution as the basis for unraveling the kinematics of fold growth we use restoration techniques based on normal balancing assumptions to decipher the detailed kinematic history of folding the progressive restorations as well as balanced forward modeling show that the last few hundred meters of fold growth were dominated by kink band migration of a sort that is typical of much faultrelated folding the kink band migration has produced complex anticlinal hinge zone geometry including segmented fold hinges linked by disconformities and unconformities which has direct and detailed explanation in terms of fluctuations in deposition rate relative to curved hinge kink band migration rate large fluctuations in the convolution of non steady sedimentation and deformation are demonstrated although the absolute fluctuations in deformation and sedimentation are unknown at a length scale of 100 m kink band migration with little or no deposition is interspersed with sedimentation with little or no deformation at the length scale of 500 m deposition ranges from 200 to 50 of uplift 0 1997 elsevier science ltd all rights reserved

a model for low amplitude detachment folding and syntectonic stratigraphy based on the conservation of mass equation abstract this paper presents a model for the structural evolution of low strain detachment folds in which rock is treated as an incompressible deformable material and its kinematics is governed by the continuity equation the model also considers the following boundary conditions i the vertical flux across the core of the fold is described by a cosine function ii the horizontal flux due to transport along a basal detachment remains constant with depth and iii the depth of the detachment remains fixed upon finding analytical expressions for the velocity field of this deformation process a model for the accumulation of growth strata and the degradation of the topography created by folding is then derived these processes are approximated by means of the transport diffusion equation solutions of these two models are in excellent agreement with geometric and stratigraphic relations documented in fold and thrust belts and analog experiments moreover the model indicates that fold growth in this class of structures is a self affine process a compilation of detachment folds around the world indicates that these structures share a common profile moreover fold amplitude and wavelength of these folds are scaled by different amounts confirming this result the stratigraphy obtained with the growth strata model exhibits the typical thinning and truncation of timelines toward the core of the anticline cross cutting relations often observed in seismic cross sections and field data

kinematics of fault related folding derived from a sandbox experiment we analyze the kinematics of fault tip folding at the front of a fold and thrust wedge using a sandbox experiment the analog model consists of sand layers intercalated with low friction glass bead layers deposited in a glass sided experimental device and with a total thickness h 4 8 cm a computerized mobile backstop induces progressive horizontal shortening of the sand layers and therefore thrust fault propagation active deformation at the tip of the forward propagating basal decollement is monitored along the cross section with a high resolution ccd camera and the displacement field between pairs of images is measured from the optical flow technique in the early stage when cumulative shortening is less than about h 10 slip along the decollement tapers gradually to zero and the displacement gradient is absorbed by distributed deformation of the overlying medium in this stage of detachment tip folding horizontal displacements decrease linearly with distance toward the foreland vertical displacements reflect a nearly symmetrical mode of folding with displacements varying linearly between relatively well defined axial surfaces when the cumulative slip on the decollement exceeds about h 10 deformation tends to localize on a few discrete shear bands at the front of the system until shortening exceeds h 8 and deformation gets fully localized on a single emergent frontal ramp the fault geometry subsequently evolves to a sigmoid shape and the hanging wall deforms by simple shear as it overthrusts the flat ramp system as long as strain localization is not fully established the sand layers experience a combination of thickening and horizontal shortening which induces gradual limb rotation the observed kinematics can be reduced to simple analytical expressions that can be used to restore fault tip folds relate finite deformation to incremental folding and derive shortening rates from deformed geomorphic markers or growth strata

interplay between tectonics climate and fluvial transport during the cenozoic evolution of the ebro basin ne iberia 1 three dimensional modeling that integrates fluvial sediment transport crustal scale tectonic deformation and lithospheric flexural subsidence is carried out to simulate the landscape and drainage evolution of the ebro sedimentary basin ne iberia the ebro basin underwent a long period of closed intramountain drainage as a result of tectonic topography generation at the pyrenees the iberian range and the catalan coastal range in the late oligocene the catalan coastal range underwent extension leading to the formation of the valencia trough nw mediterranean but the ebro basin remained closed for nearly 15 myr more before the ebro river cut through the remnants of the topographic barrier this drainage opening caused widespread basin incision that shaped spectacular outcrops of the syntectonic and posttectonic infill here we investigate the processes controlling these major drainage changes the modeling results constrained by a large data set on the tectonic and transport evolution of the area predict a closed phase characterized by a large lake in the central eastern ebro basin dry climatic conditions probably lowered the lake level and contributed together with rift flank uplift to prolong this endorheic basin stage the age and amount of reworked sediment after the opening are consistent with an onset of basin incision between 13 and 8 5 ma as a result of lake capture by escarpment erosion and lake level rise associated with sediment accumulation and wetter climatic conditions sea level changes in the mediterranean had no major impact in the large scale drainage evolution of the ebro basin index terms 1625 global change geomorphology and weathering 1824 1886 1815 hydrology erosion and sedimentation 3210 mathematical geophysics modeling 3344 meteorology and atmospheric dynamics paleoclimatology 8102 tectonophysics continental contractional orogenic belts keywords pyrenees drainage evolution lake sediment budget erosion flexure

consequences of large impacts on enceladus core shape the intense activity on enceladus suggests a differentiated interior consisting of a rocky core an internal ocean and an icy mantle however topography and gravity data suggests large heterogeneity in the interior possibly including significant core topography in the present study we investigated the consequences of collisions with large impactors on the core shape we performed impact simulations using the code isale2d considering large differentiated impactors with radius ranging between 25 and 100 km and impact velocities ranging between 0 24 and 2 4 km s our simulations showed that the main controlling parameters for the post impact shape of enceladus rock core are the impactor radius and velocity and to a lesser extent the presence of an internal water ocean and the porosity and strength of the rock core for low energy impacts the impactors do not pass completely through the icy mantle subsequent sinking and spreading of the impactor rock core lead to a positive core topographic anomaly for moderately energetic impacts the impactors completely penetrate through the icy mantle inducing a negative core topography surrounded by a positive anomaly of smaller amplitude the depth and lateral extent of the excavated area is mostly determined by the impactor radius and velocity for highly energetic impacts the rocky core is strongly deformed and the full body is likely to be disrupted explaining the long wavelength irregular shape of enceladus core by impacts would imply multiple low velocity 2 4 km s collisions with deca kilometric differentiated impactors which is possible only after the lhb period

a unified kinematic model for the evolution of detachment folds abstract detachment folds represent a major structural element in a number of fold belts they are common in the jura mountains the zagros fold belt the central appalachian fold belt the wyoming fold belt the brooks range the parry islands fold belt and parts of the subandean belt these structures form in stratigraphic packages with high competency contrasts among units the competent upper units exhibit parallel fold geometries whereas the weak lower unit displays disharmonic folding and significant penetrative deformation two distinct geometric types disharmonic detachment folds and lift off folds have been recognized however these structures commonly represent different stages in the progressive evolution of detachment folds the structures first form by symmetric or asymmetric folding with the fold wavelength controlled by the thickness of the dominant units volumetric constraints require sinking of units in the synclines and movement of the ductile unit from the synclines to the anticlines continuing deformation results in increasing fold amplitudes and tighter geometries resulting from both limb segment rotation and hinge migration initially limb rotation occurs primarily by flexural slip folding but in the late stages of deformation the rotation may involve significant internal deformation of units between locked hinges the folds eventually assume tight isoclinal geometries resembling lift off folds variations in the geometry of detachment fold geometry such as fold asymmetry significant faulting and fold associated with multiple detachments are related to variations in the mechanical stratigraphy and pre existing structure

unstable extension of enceladus lithosphere abstract regions near enceladus equator sarandib and diyar planitia contain extensive sets of parallel ridges and troughs that may be diagnostic of the region s formation conditions we present photoclinometry profiles across these ridges and troughs which indicate that they are periodic low slope features with dominant wavelengths of 3 to 4 km and amplitudes between 100 and 400 m the morphology of these terrains is consistent with formation via unstable extension of the lithosphere our numerical modeling demonstrates that unstable extension can generate large scale topography under enceladus like conditions comparison of our photoclinometry profiles with the dominant wavelengths produced by our numerical model permits estimation of the background heat flow at the time the sarandib diyar province formed we estimate heat flows of 110 to 220 mw m 2 suggesting that resurfacing of the planitiae was accompanied by strong localized heating the extension necessary to produce the ridges and troughs may have been caused by now inactive diapirs internal phase changes or other mechanisms our heat flux estimates imply elastic thickness at the time of resurfacing of 0 4 to 1 4 km which are sufficient to have allowed satellite reorientation if the province was underlain by a low density region it is therefore plausible that enceladus has experienced multiple heating events each leading to localized resurfacing and global reorientation

obliquity tides do not significantly heat enceladus recently tyler tyler r h 2009 geophys res lett 36 l15205 tyler r 2011 icarus 211 770 779 proposed that the tide due to an obliquity of greater than 0 1 might drive resonant flow in a liquid ocean at enceladus and that dissipation of the ocean s kinetic energy may be an alternate source for the observed global heat flux while there is currently no measurement of enceladus obliquity dissipation is expected to drive the spin pole to a cassini state under this assumption we find that enceladus should occupy cassini state 1 and that the obliquity of enceladus should be less than 0 0015 for values of the degree 2 gravity coefficient c2 2 between 1 0 10 3 and 2 5 10 3 unless there is a

solid tidal friction above a liquid water reservoir as the origin of the south pole hotspot on enceladus abstract earth jupiter s moon io and saturn s tiny moon enceladus are the only solid objects in the solar system to be sufficiently geologically active for their internal heat to be detected by remote sensing interestingly the endogenic activity on enceladus is only located on a specific region at the south pole from which jets of water vapor and ice particles have been observed spencer j r and 9 colleagues 2006 science 311 1401 1405 porco c c and 24 colleagues 2006 science 311 1393 1401 the current polar location of the thermal anomaly can possibly be explained by diapir induced reorientation of the satellite nimmo f pappalardo r t 2006 nature 441 614 616 but the thermal anomaly triggering and the heat power required to sustain it over geological timescales remain problematic using a three dimensional viscoelastic numerical model simulating the response of enceladus to tidal forcing we explore the effect of a low viscosity anomaly in the ice shell localized to the south polar region on the tidal dissipation patterns we demonstrate that only interior models with a liquid water layer at depth can explain the observed magnitude of dissipation rate and its particular location at the south pole moreover we show that tidally induced heat must be generated over a relatively broad region in the southern hemisphere and it is then transferred toward the south pole where it is episodically released during relatively short resurfacing events as large tidal dissipation and internal melting cannot be induced in the south polar region in the absence of a pre existing liquid decoupling layer we propose that liquid water must have been present in the interior for a very long period of time and possibly since the satellite formation owing to the orbital equilibrium requirement meyer j wisdom j 2007 icarus 188 535 539 sustaining some liquid water at depth is impossible if heat is continuously emitted at a rate of 4 8 gw at the south pole based on that requirement we propose that the current thermal emission is not in equilibrium with the heat production and that the thermal emission rate is abnormally high at present time alternatively continuous dissipation at a rate of 1 2 gw in the ice shell at the south pole should be sufficient to induce internal melting and it could sustain a layer of liquid water at depth over geologic timescales

estimating the detachment depth in cross sections involving detachment folds this paper evaluates four different methods that have been proposed for the estimation of the detachment depth beneath detachment folds guidelines are presented in order to use the most suitable method in a particular region deformed by detachment folds these guidelines are constructed considering the assumptions of each method the influence of different parameters on the estimation of the detachment depth folding mechanisms cross sectional area variations position and orientation of the regional datum number of stratigraphic horizons bed length and thickness dip and position of the bounding lines initial thickness of the ductile unit single anticlines or fold trains and the available data ductile unit thickness regional datum detachment depth moreover a new simple method based on two previous methods is presented the advantages of this new method are that the calculations are extremely simple and it uses information from more than one stratigraphic horizon therefore it does not depend strongly on the accuracy of the data at one level the precision of the proposed methods is tested by their application to a number of natural and experimental single anticlines and fold trains it appears that better predictions are obtained when analysing a complete detachment fold train than when dealing with a single detachment anticline the reason might be that ductile material flow beneath the folds along the cross sectional plane is taken into account when dealing with a long enough cross section we also suggest some hypotheses concerning what the shape and dimensions of the detachment folds indicate about the detachment depth in those cases where insufficient data are available to apply the methods proposed

structural mapping of enceladus and implications for formation of tectonized regions global structural mapping of high resolution cassini images of enceladus reveals a richly varied surface most notable are three main regions of deformation each containing multiple structural units in addition to the well known south polar terrain spt there are two other large regions of deformation that we term leading hemisphere terrain lht and trailing hemisphere terrain tht each of these three terrains includes a circumferential belt that encloses one or more other structurally deformed units areal extents range from about 80 000 km2 spt to 195 000 km2 lht or 160 to 250 km equivalent circular radius based on relative crater densities the tht is inferred to be older than the lht the geologically active spt is the youngest the overall similarities in shape and dimension of the three tectonized terrains suggest similar formational processes plausibly related to broad loading of a thin elastic shell a viable scenario is that each tectonized terrain formed above a large scale region of warm upwelling ice with subsequent downwarping triggered by cooling and or subsurface melting however differences in morphological detail suggest that the specific evolution of each tectonized terrain has been different

three layered models of ganymede and callisto compositions structures and aspects of evolution abstract three layered structural models are determined for ganymede and callisto each consists of a rock core a mixed ice rock lower mantle and a pure ice upper mantle this structure results from differentiation subsequent to accretional melting attention is given to evaluating various candidates for the rock component and three alternatives representing various degrees of silicate hydration and oxidation are modeled and incorporated structures are calculated on the basis of a 250 k isotherm which is a reasonablev approximation to the gentle adiabats expected to occur in icy satellites differentiation of an ice rock satellite generally involves an increase in radius and the three layered approach allows this process to be examined in some detail it is determined that satellite expansion is most significant early in the process and much less so as differentiation proceeds to completion if tectonics are due to global expansion distinguishing on this basis between a completely differentiated satellite and one that is only partially differentiated is difficult the postaccretional global expansion of ganymede which may have left a tectonic record was probably limited to 1 in radius in agreement with observed limits useful quantities such as silicate mass and volume fraction uncompressed density j2 c22 binding energy and surface heat flow are also determined nonhydrostatic contributions to j2 and c22 are estimated and shown to be nonnegligible encounters with jupiter orbiting spacecraft are unlikely to determine callisto s degree of central condensation we conclude by calculating the relative likelihood of postaccretional melting caused by radiogenic heating three layered satellites have generally hotter interiors because additional thermal boundary layers divide the separately convecting upper and lower mantles inhibiting heat transport ganymedes and callistos that are less than about 1 3 differentiated by mass should experience a second episode of melting as these boundary layers are either above the level of the water ice minimum melting temperature or intersect the melting curve at deeper levels runaway differentiation to at least a depth corresponding to a pressure in the ice v stability field is likely the main point here is that if satellite tectonics are tied to differentiation by melting or its aftermath as in the instability following ocean closure of kirk and stevenson moderate or small amounts of accretional differentiation are unlikely to explain an absence of tectonics as in callisto because extensive differentiation ultimately occurs

friction of ice the frictional strength of ice seems to be well below that for all other rocks triaxial testing of cylinders of pure water ice containing a 45 inclined sawcut at temperatures of 77 t 115 k and confining pressures 0 1 p 250 mpa reveals the frictional laws 0 20 n 8 3 mpa for p 10 mpa and 0 55 n 1 0 mpa for p 5 mpa where and n are the shear and normal stresses on the sawcut surface friction is independent of t and over the one order of magnitude tested of average sliding velocity the sliding behavior is invariably stick slip examination of sliding surfaces shows only minor gouge development a curious arrangement of densely packed short vertical fractures occurs primarily in samples with anomalously low strength these results apply to models of near surface tectonic activity on jupiter s three large icy moons europa callisto and ganymede they indicate for example that a global expansion on ganymede of 3 linear percent will cause extensional movement on preexisting faults at depths to 7 3 km

saturn s icy satellites thermal and structural models abstract thermal histories of the small icy saturnian satellites mimas tethys dione rhea and iapetus are constructed by assuming that they formed as homogeneous ice silicate mixtures the models include effects of radiogenic and accretional heating conductive and subsolidus convective heat transfer and lithospheric growth accretional heating is unlikely to have melted the water ice in the interiors of these bodies and solid state creep of the predominately ice material precludes melting by radiogenic heating mimas is so small that its thermal evolution is essentially purely conductive at present it is a cold nearly isothermal body any subsolidus convection or thermal activity in mimas would have been confined to a brief period in its early history and would have been due to a warm formation the four largest satellites are big enough and contain sufficient heat producing silicates that solid state convection beneath a rigid lithosphere is inevitable independent of initial conditions dione and rhea have convective interiors for most of their thermal histories while tethys and iapetus have mainly conductive thermal histories with early periods of convective 0activity the thermal histories of the five satellites for the last 4 by are independent of initial conditions at present they have cold conductive interiors the model thermal histories are qualitatively consistent with the appearances of these satellites mimas has an ancient heavily cratered surface tethys and probably iapetus have both heavily cratered and more lightly cratered areas and dione and rhea have extensively modified surfaces because of their similar sizes and densities mimas and enceladus are expected to have similar surfaces and thermal histories but instead enceladus has the most modified surface of all the small icy saturnian satellites our results suggest a heat source for enceladus in addition to radiogenic and accretional heating tidal dissipation is a possibility because the water ice in these bodies does not melt resurfacing must be accomplished by the melting of a low melting temperature minor component such as ammonia hydrate

the velocity description of deformation paper 1 theory abstract there are several advantages in using velocities to describe the deformation of the crust and lithosphere induced by extension compression isostasy and other processes 1 the method is very general any deformation style can be described in this way simple examples are pure shear inclined or vertical simple shear bulk rotation airy or flexural isostasy and compaction 2 velocity fields can be combined to model more complex deformation 3 the syn tectonic evolution of parameters such as temperature pressure hydrocarbon maturity and porosity are easily modelled once the deformation velocities are specified 4 the syn tectonic evolution of sedimentary architectures can be modelled using a general tectono sedimentary forward modelling equation which incorporates the deformation velocities these advantages are illustrated by a computer model which simulates clastic sediments prograding into an active half graben formed by extension above a listric fault processes included in this model are compaction of the sediments hanging wall deformation by inclined simple shear and simultaneous footwall deformation to avoid space problems the velocity field for the hanging wall block above the non rigid footwall must obey a simple contact condition

short note a velocity description of shear fault bend folding this short note presents a derivation of the velocity description of deformation for the geometric models of pure shear and simple shear fault bend folding this allows the calculation of rates of displacement uplift and limb rotation associated with such structures and their comparison with classical fault bend folds using this velocity description we examine the differences between pure shear and simple shear fault bend folds in terms of uplift limb rotation and particle trajectories resulting from deformation

a model for the interior structure evolution and differentiation of callisto abstract the recently measured dimensionless moment of inertia moi factor for callisto of 0 3549 0 0042 anderson et al 2001 icarus 153 157 161 poses a problem its value cannot be explained by a model in which callisto is completely differentiated into an ice shell above a rock shell and an iron core such as its neighboring satellite ganymede nor can it be explained by a model of a homogeneous undifferentiated ice rock satellite we show that callisto may be incompletely differentiated into an outer ice rock shell in which the volumetric rock concentration is close to the primordial one at the surface and decreases approximately linearly with depth an ice mantle mostly depleted of rock and an about 1800 km rock ice core in which the rock concentration is close to the close packing limit the ice rock shell thickness depends on uncertain rheology parameters and the heat flow and can be roughly 50 to 150 km thick we show that if callisto accreted from a mix of metal bearing rock and ice and if the average size of the rocks was of the order of meters to tens of meters then callisto may have experienced a gradual but still incomplete unmixing of the two components an ocean in callisto at a depth of 100 200 km is difficult to obtain if the ice is pure h2o and if the ice rock lithosphere is 100 km or more thick a water ocean is more plausible for ice contaminated by ammonia methane or salts or for pure h2o at a depth of 400 600 km

relief and shortening in detachment folds we present new thickness relief methods for determining shortening s z mean shortening s z and curvimetric shortening sc z as a function of height in well imaged structures thickness relief measurements allow us to constrain the fractions of the deformation that are layer parallel pure shear simple shear and flexural and to measure the excess area ae of fold cores caused for example by flow of evaporites the key measurements are made in the thickness domain which allows for more certain determination of regional stratigraphic gradients which is required for reliable separation of structural relief from primary stratigraphic thickness variations we apply these methods to a diverse set of active detachment folds from the fronts of the nankai trough japan cascadia accretionary wedge oregon southern tianshan china and agbami anticline deep water niger delta three of these folds can be approximated by pure shear detachment fold models because more than 95 of the shortening is by layer parallel heterogeneous pure shear plus horizontal compaction for this reason curvimetric shortening is one to two orders of magnitude less than total shortening in contrast agbami anticline shows layer parallel stretching above the excess area of the fold core in all examples the layer parallel simple shear component is negligible or absent 2006 elsevier ltd all rights reserved

multispectral analysis of asteroid 3 juno taken with the 100 inch telescope at mount wilson observatory abstract high resolution multispectral images of main belt asteroid 3 juno were taken at visible and near ir wavelengths with the 100 inch telescope at mount wilson observatory equipped with an adaptive optics system the images show spectral features that may represent a large relatively recent impact that deeply excavated the coarse grained olivine pyroxene rich crust of the asteroid

enceladus extreme heat flux as revealed by its relaxed craters 1 enceladus cratered terrains contain large numbers of unusually shallow craters consistent with deformation by viscous relaxation of water ice under conditions of elevated heat flow here we use high resolution topography to measure the relaxation fraction of craters on enceladus far from the active south pole we find that many craters are shallower than expected with craters as small as 2 km in diameter having relaxation fractions in excess of 90 these measurements are compared with numerical simulations of crater relaxation to constrain the minimum heat flux required to reproduce these observations we find that enceladus nominal cold surface temperature 70 k and low surface gravity strongly inhibit viscous relaxation under such conditions less than 3 relaxation occurs over 2 ga even for relatively large craters diameter 24 km and high constant heat fluxes 150 mw m 2 greater viscous relaxation occurs if the effective temperature at the top of the lithosphere is greater than the surface temperature due to insulating regolith and or plume material even for an effective temperature of 120 k however heat fluxes in excess of 150 mw m 2are required to produce the degree of relaxation observed simulations of viscous relaxation of enceladus largest craters suggest that relaxation is best explained by a relatively short lived period of intense heating that decayed quickly we show that infilling of craters by plume material cannot explain the extremely shallow craters at equatorial and higher northern latitudes thus like enceladus tectonic terrains the cratered regions of enceladus have experienced periods of extreme heat flux

radar enabled recovery of the sutter s mill meteorite a carbonaceous chondrite regolith breccia doppler weather radar imaging enabled the rapid recovery of the sutter s mill meteorite after a rare 4 kiloton of tnt equivalent asteroid impact over the foothills of the sierra nevada in northern california the recovered meteorites survived a record high speed entry of 28 6 kilometers per second from an orbit close to that of jupiter family comets tisserand s parameter 2 8 0 3 sutter s mill is a regolith breccia composed of cm mighei type carbonaceous chondrite and highly reduced xenolithic materials it exhibits considerable diversity of mineralogy petrography and isotope and organic chemistry resulting from a complex formation history of the parent body surface that diversity is quickly masked by alteration once in the terrestrial environment but will need to be considered when samples returned by missions to c class asteroids are interpreted

enceladus s ice shell structure as a window on internal heat production abstract its extraordinary level of geologic activity its potential for habitability and the prospects of returning samples from its plume of erupting water ice make saturn s small 500 km diameter moon enceladus a high priority target for future exploration and a key to our developing understanding of icy ocean worlds the structure of its outer ice shell is particularly important as it relates to the global heat budget the global scale response to tidal forces and the nature of the ongoing eruptions it is also diagnostic of how and where heat is dissipated internally here using the most recent shape model and a new approach to modeling isostasy we obtain a shell structure that simultaneously accommodates the shape gravity and libration observations and suggests that tidal dissipation near the base of the ice shell is likely an important mode of internal heating the implied conductive heat loss is greater than the heat loss associated with the eruptions but is nevertheless compatible with the condition of steady state

the shape of enceladus as explained by an irregular core implications for gravity libration and survival of its subsurface ocean 1 enceladus global shape is not consistent with a simultaneously hydrostatic and fully differentiated body but its geophysical hyperactivity strongly implies that it is differentiated enceladus surface conforms to a triaxial shape consistent with relaxation to a global geoid but its rocky core need not be hydrostatic a modestly irregular core either in terms of topography or density and dynamically aligned would act to enhance the global geoid explaining the full global shape of enceladus requires 10 km of excess core polar flattening and 4 km of excess core equatorial distortion for a uniform density core the stresses associated with this excess topography can be sustained indefinitely but because the rocky core is not hydrostatic enceladus degree 2 gravity coefficients j2 and c22 will not conform to the hydrostatic ratio of 10 3 testable by cassini gravity notably core polar axes could be depressed by up to 4 6 km with respect to internal isobars such a topographic variation could help preserve polar ocean remnants for example if enceladus ocean undergoes secular freezing it will first ground near the tidal axes polar seas would be the last to freeze and survival of a south polar sea may be one reason why enceladus activity today is concentrated at high southern latitudes isostatic variations in the thickness or density of a floating ice shell may also contribute to enceladus nonhydrostatic shape but a strength supported nonisostatic icy lithosphere is argued here to be unlikely given enceladus record of regional high heat flows faulting and viscous relaxation

experimental constraints on the chemical evolution of large icy satellites abstract we derive experimental constraints on the interior structure and mineralogy of large icy satellites by reacting material of chondritic chemistry with water at a pressure of 1 5 gpa temperatures between 300 c and 800 c and a range of oxygen fugacities our results document the existence of three chemical processes that probably occur in large icy satellites as a result of high pressure hydrothermal processing 1 the formation of low density hydrated silicates 2 the alloying of iron and sulfur to form fes dominated cores and 3 the instability of organic material relative to carbonates we construct new internal models of the thermal and structural state of ganymede and infer that the magnetic field of this body arises from convection within a mostly iron sulfide core simple thermochemical calculations are conducted to further explore the likely effects of composition and oxygen fugacity on the high pressure chemistry undergone by organic material within icy satellites both experimental and calculated results show that primordial organics are likely to have been largely oxidized to carbonates through hydrothermal processing early in ganymede s history potentially sterilizing ganymede s h 2 o layer

effect of enceladus s rapid synchronous spin on interpretation of cassini gravity enceladus s degree 2 gravity determined by cassini is nominally nonhydrostatic to 3 j2 c22 3 38 3 63 as opposed to 10 3 iess et al 2014 interpret this in terms of a hydrostatic interior core and isostatic not hydrostatic floating ice shell enceladus s rapid 1 37 d synchronous spin and tide distorts its shape substantially though enough that the predicted hydrostatic j2 c22 is not 10 3 but closer to 3 25 this leads to the following revision to the internal picture of enceladus compared with iess et al 1 the satellite s core is somewhat smaller and slightly denser 190 km radius and 2450 kg m3 2 the compensation depth shell thickness of the global degree 2 ice shell is 50 km rather close to the base of the modeled ice water layer and 3 the compensation depth shell thickness beneath the south polar terrain from j3 remains shallower thinner at 30 km independent of but influenced by the degree 2 solution

tectonics on iapetus despinning respinning or something completely different abstract saturn s moon iapetus is unique in that it has apparently despun while retaining a substantial equatorial bulge stresses arising from such a non hydrostatic shape should in principle cause surface deformation tectonics as part of a search for such a tectonic signature lineaments linear surface features on iapetus were mapped on both its bright and dark hemispheres lineament orientations were then compared to model stress patterns predicted for spin down from a rotation period of 16 5 h or less to its present synchronous period and for a range of lithospheric thicknesses many lineaments are straight segments of crater rimwalls which may be faults or joints reactivated during complex crater collapse most striking are several large troughs on the bright trailing hemisphere these troughs appear to be extensional and are distinctive on that hemisphere because the interior floors and walls of the troughs contain dark material globally no specific evidence of strike slip or thrust offsets are seen but this could be due to the age and degraded nature of any such features we find that observed lineament orientations do not correlate with predicted patterns due to despinning on either hemisphere the equatorial ridge was specifically excluded from this analysis and is considered separately modest evidence for preferred orientations 40 from north could be construed as consistent with respinning which is not necessarily far fetched assuming the rigidity of unfractured ice predicted maximum lithospheric differential stresses from despinning range from 1 mpa to 160 mpa for the elastic spheroid and thin lithosphere limits respectively although it is only for thicker elastic lithospheres that we expect a nonhydrostatic state to be maintained over geologic time against lithospheric failure the tectonic signature of despinning may have been obscured over time because the surface of iapetus is very ancient iapetus thick lithosphere may have inhibited the full tectonic expression of despinning or both several prominent lineaments strike e w and are thus parallel to the equatorial ridge though not physically close to it but a tectonic or volcanic origin for the ridge is highly problematic

one hundred km scale basins on enceladus evidence for an active ice shell 1 stereo derived topographic mapping of 50 of enceladus reveals at least 6 large scale ovoid depressions basins 90 175 km across and 800 to 1500 m deep and uncorrelated with geologic boundaries in contrast the south polar depression is larger and apparently shallower and correlates with active resurfacing the shape and scale of the basins is inconsistent with impact geoid surface deflections or with dynamically supported topography isostatic thinning of enceladus ice shell associated with upwellings and tidally driven ice melting can plausibly account for these basins thinning implies upwarping of the base of the shell of 10 20 km beneath the depressions depending on total shell thickness loss of near surface porosity due to enhanced heat flow may also contribute to basin lows alternatively the basins may overly cold inactive and hence denser ice but thermal isostasy alone requires thermal expansion more consistent with clathrate hydrate than water ice

enceladus an active ice world in the saturn system enceladus one of the mid sized icy moons of saturn has an importance to planetary science far greater than its modest 504 km diameter would suggest intensive exploration of enceladus by the cassini saturn orbiter has revealed that it is the only known icy world in the solar system with ongoing deep seated geological activity active tectonic fractures at enceladus s south pole dubbed tiger stripes warmed by internal tidally generated heat spew supersonic jets of water vapor other gases and ice particles into circum saturnian space a subsurface saltwater sea probably exists under the south pole between the ice shell and the silicate core because of evidence that liquid water is probably present at the jet sources enceladus is also of great astrobiological interest as a potential habitat for life

convection in enceladus ice shell conditions for initiation 1 observations of enceladus by the cassini spacecraft indicate that this tiny saturnian moon is geologically active with plumes of water vapor and ice particles erupting from its southern polar region this activity suggests that tidal dissipation has become spatially localized perhaps due to a compositional rheological and or thermal anomaly in its ice shell here we examine the role that solid state convection may have played in enceladus prolific activity by creating a suitable rheological and thermal anomaly we find convection can only initiate in the pure water ice i shell of a differentiated enceladus if the ice grain size is less than 0 3 mm which is quite small but may be realistic if non water ice impurities and or tidal stresses keep grains from growing this grain size restriction becomes more severe for lower basal ice temperatures which implies that any ammonia present has not become strongly concentrated in a thin basal ocean while convection occurs for a maximally thick pure ice shell and underlying ocean convective heat flows are 7 11 mw m 2 for ice grain sizes of 0 1 0 3 mm compared with the 100 mw m 2 measured for enceladus south polar terrain from cassini cirs observations thus whereas solid state convection may be a prerequisite for enceladus geological activity the observed heat flow requires strong tidal dissipation within the convecting region and possibly that convection reaches the surface

enceladus s and dione s floating ice shells supported by minimum stress isostasy enceladus gravity and shape have been explained in terms of a thick isostatic ice shell floating on a global ocean in contradiction of the thin shell implied by librations here we propose a new isostatic model minimizing crustal deviatoric stress and demonstrate that gravity and shape data predict a 38 4km thick ocean beneath a 23 4km thick shell agreeing with but independent from libration data isostatic and tidal stresses are comparable in magnitude south polar crust is only 7 4km thick facilitating the opening of water conduits and enhancing tidal dissipation through stress concentration enceladus resonant companion dione is in a similar state of minimum stress isostasy its gravity and shape can be explained in terms of a 99 23km thick isostatic shell overlying a 65 30km thick global ocean thus providing the first clear evidence for a present day ocean within dione

excess area and depth to detachment a plot of the excess area in cross section vs the depth to a reference level for several stratigraphic horizons in a compressional fold produces a curve that gives the depth to detachment the curve is a straight line for detachment folds the slope of the line is the displacement on the lower detachment and the depth intercept where excess area zero is the depth to detachment for a fault bend fold the result is a line that abruptly changes slope at the position corresponding to the upper detachment the difference in slope between the two parts of the line is the displacement on the upper detachment added layer parallel shear produces a curve on the graph tested on detachment folds from the jura mountains the method accurately predicts the depth to detachment he tip top field anticline in the wyoming thrust belt is found to be interpretable as either a detachment anticline with a basal detachment close to the top of the basement or as a fault bend fold with a basal detachment at the base of the triassic the excess area diagram is useful for testing a cross section for balance determining the structural style detachment anticline vs fault bend fold and for examining alternatives in the construction of cross sections

geometries of syntectonic sediments associated with single layer detachment folds abstract three kinematic models have been proposed to account for the geometry and kinematics of detachment folds involving a homogeneous competent layer detached over a ductile unit model 1 variable limb dip constant limb length model 2 constant limb dip variable limb length and model 3 variable limb dip variable limb length because the same fold shape can be generated by any of the above mechanisms fold kinematics are best determined by the geometries of syntectonic sediments in single layer detachment folds growth strata patterns are controlled by axial surface activity limb rotation limb lengthening fold uplift rates sedimentation rates and deformation mechanisms of the syntectonic sediments asymmetric kink folds have been modelled and compared with natural examples from the southern spanish pyrenees under conditions of high sedimentation rates model 1 folds produce characteristic fanning growth stratal wedges that initially onlap and then progressively overlap the detachment anticline whereas at low sedimentation rates anticlines with fanning growth wedges on both limbs are formed model 2 folds under conditions of high syntectonic sedimentation rates form anticlines with growth strata largely parallel to the pre growth units and thinned over the fold crest in contrast at low sedimentation rates model 2 folds show offlapping growth strata onto both limbs model 3 growth folds under conditions of high syntectonic sedimentation rates form anticlines with intermediate features from model 1 and model 2 at low sedimentation rates anticlines are formed with offlapping growth structures

tidal dynamical considerations constrain the state of an ocean on enceladus abstract in previous work solutions to the non dissipative laplace tidal equations lte were used to provide bounds on the heat generated by the response of a subsurface ocean on enceladus to an obliquity component of tidal forces here we improve these bounds using solutions from the lte with a generic dissipation term explicitly added we find solutions for a wider range of ocean tidal responses that include both unstratified barotropic and stratified baroclinic flow responses to obliquity as well as eccentricity components of the tidal forces we consolidate the results in three ocean tidal scenarios on enceladus that can explain the high heat fluxes 7 mw m 2 globally averaged inferred from measurements by the cassini spacecraft 1 a deep 1 50 km barotropic ocean responding to obliquity tidal forces where obliquity is at least 0 1 2 a shallow 360 m barotropic ocean responding to eccentricity tidal forces 3 a stratified baroclinic ocean responding to eccentricity tidal forces where the density weighted equivalent depth typically much smaller than the ocean s physical depth is near 360 m the ocean is assumed to be global but extensions for a semi global case are also described a more general result which is independent of the specific scenarios proposed is that an ocean attempting to freeze with an associated decrease in its liquid depth which affects the ocean s dynamical response to the tidal forcing must first pass through resonant configurations with a greatly increased generation of ocean tidal heat exceeding 1 w m 2 to 1 kw m 2 that would act to halt further freezing and stagnate the ocean state in this configuration so long as there is still orbital energy to provide the tidal forces with an additional assumption that the ocean has evolved from a more energetic state where the depth of the liquid ocean was greater we obtain the three scenarios proposed

geometry and growth kinematics of salt pillows in the southern north sea abstract low amplitude salt pillow structures can potentially reveal important details of the physical behaviour of salt and overburden from their growth histories this is because the initial characteristic wavelengths are likely to be preserved beds are more easily traceable across the tops of the structures and original salt thicknesses can be accurately estimated for these reasons a detailed analysis of depth converted seismic data was undertaken to gain insight into the formation growth and spatial distribution of salt pillows in the southern north sea basin around quadrant 44 this area contains a permian zechstein salt interval which has undergone widespread halokinesis to the pillow stage since triassic times but with the main movement during the tertiary perhaps due to inversion the wavelength of the pillows decreases northwards from over 24 to 1 km and estimated original salt thickness also decreases northwards from 1300 to 800 m and there is a strong positive relationship between salt thickness and pillow wavelength pillows appear to be spaced at a characteristic wavelength as they are not directly related to faults and the wavelength varies smoothly through the area however there is a strong alignment of some pillows parallel with the underlying nw se fault trend suggesting that their axis of elongation was controlled by faulting average vertical growth rates of the pillows vary from 40 m ma in the north to less than 10 m ma in the central part of the area measured over vertical distances up to 1250 m most of the growth occurred in the tertiary although a few pillows initiated in the triassic in the north of the area the northern pillows appear to have slowed or even stopped growing during the jurassic and cretaceous and then restarted in the tertiary assuming rayleigh taylor instability controlled the initial pillow wavelengths and using the calculated original salt overburden thicknesses ratios the viscosity ratio between the overburden and the salt can be estimated across the area and was found to vary from 6000 to less than 100 the pillows which moved earliest had the lowest inferred viscosity ratios which is probably because the sediments were less lithified at the time of movement

shapes of the saturnian icy satellites and their significance the sizes and shapes of six icy saturnian satellites have been measured from cassini imaging science subsystem iss data employing limb coordinates and stereogrammetric control points mimas enceladus tethys dione and rhea are well described by triaxial ellipsoids iapetus is best represented by an oblate spheroid all satellites appear to have approached relaxed equilibrium shapes at some point in their evolution but all support at least 300 m of global wavelength topography the shape of enceladus is most consistent with a homogeneous interior if enceladus is differentiated its shape and apparent relaxation require either lateral inhomogeneities in an icy mantle and or an irregularly shaped core iapetus supports a fossil bulge of over 30 km and provides a benchmark for impact modification of shapes after global relaxation satellites such as mimas that have smoother limbs than iapetus and are expected to have higher impact rates must have relaxed after the shape of iapetus was frozen

a kinematic model for the formation of duplex systems with a perfectly planar roof thrust we present a cross sectional kinematic forward model for the formation of duplexes with a perfectly planar roof thrust the major assumptions are a constant dip and constant spacing of the ramps in the undeformed state and sequential deformation in the direction of tectonic transport with equal displacement along each ramp the model is based on a coordinate transformation that simulates flexural slip parallel to the active fault surface this causes angular parallel folds and keeps the layer thickness constant except in the forelimbs of the horses attempts by previous workers to simulate the formation of duplexes with a perfectly planar roof thrust on the other hand were based on the assumptions of constant bed thickness and bed length or a different topology of the axial planes delimiting the forelimbs of the horses and resulted in corrugated roof thrusts we show that it is not possible to form a flat roof duplex type and preserve the forelimb thickness of the horses under flexural slip parallel to the active fault we describe duplexes by three parameters which are the separation s between ramps the ramp length l and the displacement u along the ramps in a us vs ls diagram duplexes with a perfectly planar roof thrust resulting from numerical experiments with our kinematic algorithm occupy specific families of straight lines our results are independent of the dip or internal geometry of the thrust ramps

a general method for morphologic dating of hillslopes morphologic dating of hillslopes is the determination of the age of a hillslope by its morphology current methods match the observed morphology with the morphology predicted by the diffusion equation model for hillslope evolution the morphologic dating method presented here requires no specific model for evolution but is only applicable to transport limited hillslopes on which the downslope debris flux is some scale and time independent function of slope angle if these conditions are met changes in morphology with scale e g height for a set of hillslopes of a fixed age are identical to changes in morphology with time for a hillslope of a fixed scale this fact provides the basis for a simple generally applicable method for morphologically dating such hillslopes with any initial morphology this new dating method may be applied to a wide variety of vegetated hillslopes in temperate humid regions and is an improvement over previous morphologic dating methods that relied on the diffusion equation model

an oceanic composition on early and today s enceladus 1 the oceanic composition on saturn s moon enceladus is evaluated through calculations of thermochemical equilibria at hydrothermal and freezing settings conditions of rock alteration are constrained from assumptions and models for the moon s interior composition and thermal evolution and from the composition of enceladus plume results show that an early ocean was an alkaline na cl hco3 solution underlying altered rocks consisted of mg phyllosilicates magnetite fe and ni sulfides and carbonates subsequent freezing of oceanic water caused the deposition of a nacl hydrate na k and ca carbonates and the formation of a salt free ice shell if an aqueous phase exists on today s enceladus it could consist of eutectic na cl hco3 brine that at least locally decouples the ice shell and facilitates tidal heating a lack of firm detection of na and cl at enceladus is consistent with the accumulation of salts at the ice rock boundary and implies the plume formation via sublimation in the ice shell

geometry and kinematics of single layer detachment folds detachment folds form above below or above and below bed parallel thrusts where thrust displacement is transferred into folding geometric and kinematic models are developed for individual single layer detachment folds formed above the tip line of a thrust we analyze three different detachment fold shapes kink bands chevron and box detachment folds and consider three principal detachment fold models 1 constant limb dip where the detachment fold grows by limb lengthening 2 constant limb length where the detachment fold grows by limb rotation and 3 variable limb length and variable limb dip where the detachment fold grows by both limb rotation and limb lengthening the allowance for variable forelimb thickness and excess layer parallel shear enables us to de elop a wide range of possible detachment fold geometry the geometric validity fields for folds with excess parallel shear are reduced when forelimb thinning takes place folds formed with constant limb length are likely to lock up in the initial amplification stages whereas larger amounts of shortening can be taken up by folds formed with variable limb length the manner in which a fold evolves affects the fracture and porosity features of the folded strata therefore determining which mechanism operated to form a specific detachment fold is of particular importance in hydrocarbon exploration the models we present are aimed at permitting more accurate geometric and kinematic interpretations of individual detachment folds examples of detachment folds are analyzed to illustrate the po ential benefits and limitations of the geometric model presented

keeping enceladus warm abstract despite its small size enceladus emits considerable heat especially at its south pole even long after simple thermal models predict it should be frozen several sources of energy have been proposed as responsible for this heating such as tidal dissipative heating tdh convection and shearing in the ice shell and exothermic chemical reactions e g serpentine formation crater relaxation simulations suggest that episodic heating events have occurred over long stretches of enceladus history thermal history and hydrothermal simulations reported here show that a combination of steady plus episodic tdh heating could maintain at least a polar ocean to the present time hydrothermal circulation can play a significant role in mining enceladus internal heat facilitating the persistence of an ocean even to the present by focusing internal heat to the polar regions

tidally induced melting events as the origin of south pole activity on enceladus abstract the intense activity at the south pole of enceladus hints at an internal water reservoir however there is no direct evidence of liquid water at present and its long term stability in the interior remains problematic by modeling heat production and transfer in the ice shell in a spherical geometry we show that tidal heating naturally leads to a concentration of convective hot upwellings in the south polar region favoring the preservation of liquid water at depth we show that large volumes of water are produced within the ice shell at the south pole during periods of elevated orbital eccentricity 3 5 times the present day value strong lateral variations in the melt production and crystallization rates result in stress concentration in the south polar region thus providing an explanation for the tectonic activity observed today we predict that an internal ocean may be sustained over the long term as the consequence of repeated periods with elevated orbital eccentricity leading to episodic melting and resurfacing events

tidal heating and the long term stability of a subsurface ocean on enceladus abstract tidal dissipation has been suggested as the heat source for the south polar thermal anomaly on enceladus we find that under present day conditions and assuming maxwellian behavior tidal dissipation is negligible in the silicate core dissipation may be significant in the ice shell if the shell is decoupled from the silicate core by a subsurface ocean we have run a series of self consistent convection and conduction models in 2d axisymmetric and 3d spherical geometry in which we include the spatially variable tidal heat production we find that in all cases the shell removes more heat from the interior than can be produced in the core by radioactive decay resulting in cooling of the interior and the freezing of any ocean under likely conditions a 40 km thick ocean made of pure water would freeze solid on a 30 ma timescale an ocean containing other chemical components will have a lower freezing point but even a water ammonia eutectic composition will only prolong the freezing not prevent it if the eccentricity of enceladus were higher e 0 015 in the past the increased dissipation in the ice shell may have been sufficient to maintain a liquid layer we cannot therefore rule out the presence of a transient ocean as a relic of an earlier era of greater heating if the eccentricity is periodically pumped up the ocean may have thickened and thinned on a similar timescale as the orbital evolution provided the ocean never froze completely we conclude that the current heat flux of enceladus and any possible subsurface ocean is not in steady state and is the remnant of an epoch of higher eccentricity and tidal dissipation

cassini observes the active south pole of enceladus cassini has identified a geologically active province at the south pole of saturn s moon enceladus in images acquired by the imaging science subsystem iss this region is circumscribed by a chain of folded ridges and troughs at 55 s latitude the terrain southward of this boundary is distinguished by its albedo and color contrasts elevated temperatures extreme geologic youth and narrow tectonic rifts that exhibit coarse grained ice and coincide with the hottest temperatures measured in the region jets of fine icy particles that supply saturn s e ring emanate from this province carried aloft by water vapor probably venting from subsurface reservoirs of liquid water the shape of enceladus suggests a possible intense heating epoch in the past by capture into a 1 4 secondary spin orbit resonance

self consistent generation of single plume state for enceladus using non newtonian rheology the thermal dichotomy of enceladus suggests an asymmetrical structure in its global heat transfer so far most of the models proposed that obtained such a distribution have prescribed an a priori asymmetry i e some anomaly in or below the south polar ice shell we present here the first set of numerical models of convection that yield a stable single plume state for enceladus without prescribed mechanical asymmetry using the convection code stagyy in a 2 d spherical annulus geometry we show that a non newtonian ice rheology is sufficient to create a localized single hot plume surrounded by a conductive ice mantle we obtain a self sustained state in which a region of small angular extent has a sufficiently low viscosity to allow subcritical to weak convection to occur due to the stress dependent part of the rheological law we find that the single plume state is very unlikely to remain stable if the rheology is newtonian confirming what has been found by previous studies in a second set of numerical simulations we also investigate the first order effect of tidal heating on the stability of the single plume state tidal heating reinforces the stability of the single plume state if it is generated in the plume itself lastly we show that the likelihood of a stable single plume state does not depend on the thickness of the ice shell

mechanisms of active folding of the landscape southern tian shan china 1 we explore the kinematic mechanisms of active large scale folding based on analysis of two adjacent major anticlines in tian shan central asia that share an acceleration of shortening rate leading to topographic emergence and folded geomorphic surfaces their folding mechanisms are fundamentally different yakeng anticline is a gentle pure shear detachment fold with 1200 m of shortening and a well constrained history of growth beginning at 5 5 ma with an order of magnitude increase in shortening rate from 0 16 to 1 2 1 6 mm yr at 0 16 0 21 ma the shape of the deformed topographic surface and of subsurface horizons deposited during deformation is a linearly proportional image at reduced amplitude of the deeper structure which shows that instantaneous uplift rates have been pointwise linearly proportional to the current finite fold amplitude in contrast quilitak anticline is a complex fault bend fold with uplift rates proportional to the sine of the fault dip showing discontinuities in uplift rate across active axial surfaces the 10 to 20 km wide anticline is topographically emergent only in a central 5 to 7 km wide mountainous uplift the abrupt southern edge of which is marked by 600 to 700 m high triangular facets that result from active folding of a pediment across an active axial surface the giant facets are shown to form by kink band migration and record postemergence deformation since an order of magnitude acceleration in shortening rate from 0 6 to 4 5 mm yr apparently contemporaneous with yakeng sections logged across the active 115 m wide hinge zone show that recent strata provide a bed by bed record of fold scarp growth which is quantitatively deciphered by fitting bed shapes to a finite width kink band migration model

modeling the shortening history of a fault tip fold using structural and geomorphic records of deformation 1 we present a methodology to derive the growth history of a fault tip fold above a basal detachment our approach is based on modeling the stratigraphic and geomorphic records of deformation as well as the finite structure of the fold constrained from seismic profiles we parameterize the spatial deformation pattern using a simple formulation of the displacement field derived from sandbox experiments assuming a stationary spatial pattern of deformation we simulate the gradual warping and uplift of stratigraphic and geomorphic markers which provides an estimate of the cumulative amounts of shortening they have recorded this approach allows modeling of isolated terraces or growth strata we apply this method to the study of two fault tip folds in the tien shan the yakeng and anjihai anticlines documenting their deformation history over the past 6 7 myr we show that the modern shortening rates can be estimated from the width of the fold topography provided that the sedimentation rate is known yielding respective rates of 2 15 and 1 12 mm yr across yakeng and anjihai consistent with the deformation recorded by fluvial and alluvial terraces this study demonstrates that the shortening rates across both folds accelerated significantly since the onset of folding it also illustrates the usefulness of a simple geometric folding model and highlights the importance of considering local interactions between tectonic deformation sedimentation and erosion

kinematic model of detachment folding including limb rotation fixed hinges and layer parallel strain abstract detachment anticlines formed above a stratigraphically fixed detachment horizon and without thinning in the syncline will in general require layer parallel shortening a kinematic model for detachment folds is presented that has planar limbs and is area balanced but requires bed length changes that can be expressed as layer parallel strain the fold grows primarily by limb rotation not by limb lengthening at constant dip the kinematic evolution of the geometry and strain is examined fold geometry is well predicted and the strain estimated in applications of the model to two map scale detachment folds a triangle zone from the front of the wyoming thrust belt and a duplex cored anticline from the appalachian plateau

coupling mantle convection and tidal dissipation applications to enceladus and earth like planets 1 anelastic dissipation of tidal forces likely contributes to the thermal budget of several satellites of giant planets and earth like planets closely orbiting other stars in order to address how tidal heating influences the thermal evolution of such bodies we describe here a new numerical tool that solves simultaneously mantle convection and tidal dissipation in a three dimensional spherical geometry since the two processes occur at different timescales tidal dissipation averaged over a forcing period is included as a volumetric heat source for mantle dynamics for the long term flow a purely viscous material is considered whereas a maxwell like formalism is employed for the tidal viscoelastic problem due to the strongly temperature dependent rheological properties of both mechanisms the coupling is achieved via the temperature field the model is applied to two examples enceladus and an earth like planet for enceladus our new 3 d method shows that the tidal strain rates are strongly enhanced in hot upwellings when compared with classical methods moreover the heat flux at the base of enceladus ice shell is strongly reduced at the poles thus favoring the preservation of a liquid reservoir at depth for earth like planets tidal dissipation patterns are predicted for different orbital configuration thermal runaway is observed for orbital periods smaller than a critical value e g 30 days for an eccentricity of 0 2 and 3 2 resonance this is likely to promote large scale melting of the mantle and io like volcanism

the effect of an asymmetric core on convection in enceladus ice shell implications for south polar tectonics and heat flux 1 enceladus exhibits a strong tectonic contrast between its south polar terrain spt which is young and geologically active and its northern hemisphere which is relatively ancient and stable previous global three dimensional 3 d spherical models of convection exhibit patterns that are symmetrical around the equator and fail to explain the formation of a hemispheric dichotomy here we present global 3 d spherical models of convection in enceladus ice shell to show that convection in enceladus ice shell with plasticity and irregular core geometry can self consistently generate a hemispheric dichotomy in tectonics and heat flux with a spherical core convection produces global overturning which cannot explain the regional confinement of enceladus current tectonic activity to the spt models with appropriate nonspherical core geometry and plasticity tend to produce overturning confined to the spt or regional overturning in different regions at different times which can explain the tectonic dichotomy and local age differences on enceladus our models predict heat flows up to 5 10 gigawattts gw during active episodes consistent with cassini observations

role of membrane stresses in the support of planetary topography the principal purpose of this paper is to examine whether membrane stresses can support topographic loads on planetary elastic lithospheres it is found that the ability of a spherical shell to support loads through membrane stresses is determined by the nondimensional parameter ed gr2 where d is the thickness of the elastic lithosphere is the density difference between the mantle and crust and r is the radius of the planetary body when this parameter is large membrane stresses can fully support topographic loads without flexure and when it is small the influence of membrane stresses can be neglected solutions of the equation governing the behavior of a spherical shell are obtained for a topographic load expressed in terms of spherical harmonics spherical harmonic expansions of the measured gravity and topography for mars and the moon are compared with the theory it is found that for mars the support of topography is primarily due to membrane stresses for n 8 and for the moon for n 17 for mars the data for 4 n 7 give 0 5 for the moon the data have considerable scatter that is attributed to the mascons but generally correlate with 0 5 if bending stresses are neglected the governing equation for the deflection of the spherical shell is legendre s equation a general solution is obtained for an axisymmetric load this solution is applied to the tharsis region on mars the 60 65 compensation of this region requires that 0 6 the well defined fracture pattern surrounding the tharsis region is attributed to tensional membrane stresses

shell thickness variations and the long wavelength topography of titan the long wavelength topography of titan has an amplitude larger than that expected from tidal and rotational distortions at its current distance from saturn this topography is associated with small gravity anomalies indicating a high degree of compensation both observations can be explained if titan has a floating isostatically compensated ice shell with a spatially varying thickness the spatial variations arise because of laterally variable tidal heating within the ice shell models incorporating shell thickness variations result in an improved fit to the observations and a degree two tidal love number h2t consistent with expectations without requiring titan to have moved away from saturn our preferred models have a mean shell thickness of 100 km in agreement with the observed gravity anomalies and a heat flux appropriate to a chondritic titan shell thickness variations are eliminated by convection we therefore conclude that titan s ice shell is not convecting at the present day

convection driven compaction as a possible origin of enceladus s long wavelength topography 1 the long wavelength surface topography of enceladus shows depressions about 1 km in depth and 102 km wide one possible cause of this topography is spatially variable amounts of compaction of an initially porous ice shell driven by spatial variations in heat flux here we show that the heat flux variations associated with convection in the shell can quantitatively match the observed features we develop a simple model of viscous compaction that includes the effect of porosity on thermal conductivity and find that an initial shell porosity of at least 20 25 is required to develop the observed topography over 1 ga this mechanism produces topographic depressions not rises above convective upwellings and does not generate detectable gravity anomalies unlike transient dynamic topography it can potentially leave a permanent record of ancient convective processes in the shallow lithospheres of icy satellites

enceladus an estimate of heat flux and lithospheric thickness from flexurally supported topography fluxes of 200 270 mw m 2 at the time of formation the heat fluxes are comparable to average heat flux values measured in enceladus active south polar region and they are consistent with estimates derived via models of unstable extension of the lithosphere at this location surface porosity can reduce the obtained heat fluxes to an estimated minimum of 45 60 mw m 2 c rater size frequency counts fix the time of formation from presentday of the rift zone at either 3 5 0 4 0 1 ga assuming an

fault related folding in sandbox analogue models of thrust wedges abstract the nucleation and growth of thrust fault related folds has been simulated using high resolution sandbox coulomb wedge type analogue models thrust related anticlines grew progressively from initial layerparallel shortening to decollement folding thrust tip folding and eventually thrust ramp folding thrust ramps nucleated in the central sector of the overturned forelimb of decollement folds as a consequence of limb thinning thrust tip folding occurred during outward migration of the ramp tips the fault propagation rate was greater at the lower ramp tip which quickly joined the basal thrust flat while folding continued beyond the upper tip the development of the analogue model thrust fault related folds by progressive changes in kinematics from decollement folding to thrust tip folding and finally thrust ramp folding compares well with analyses of naturally occurring thrust fault related folds

geometric and numerical model of progressive limb rotation in detachment folds a simple area balanced geometric model of progressive limb rotation in detachment folds allows the quantification of displacement uplift and rotation and the assessment of their effect upon growth strata geometries translation of this geometric model into a velocity model of deformation allows the modeling of associated growth strata resulting from background sedimentation and local erosion transport and deposition we show that with constant displacement and sedimentation rate this model predicts a progressive unconformity indicating the onlap and eventual overlap of the fold limb caused by a decreasing uplift rate this decrease is a consequence of the kinematics of progressive limb rotation increases in displacement rate with sedimentation rate kept constant can lead to offlap and angular unconformities although subsequent onlap does not necessarily reflect a return to a lower displacement rate modeled growth strata geometries exhibit many of the features reported from the literature

kinematic modeling of cross sectional deformation sequences by computer simulation we derive a kinematic algorithm which permits simulation of postulated cross sectional deformation sequences in sedimentary rocks affected by faulting fault related folding and simple shear the transformations are to a more deformed state and are formulated analytically in terms of the less deformed configuration forward modeling lagrangian description the medium is subdivided into domains of constant dip and homogeneous displacement vector fields which are delimited by the axial planes of the fault inflections the displacement trajectory is of constant length for all the displaced particles throughout the medium and parallel to the underlying active fault segment as a consequence the deformation path is continuous but not smooth and causes an angular style of parallel folding except at the deformation front where the layer thickness is not conserved the inhomogeneity of the displacement vector field across axial planes introduces longitudinal and angular shear strains whereas the area of the medium remains constant these strains which are superposed on the externally applied simple shear make the mapping transformation unconformal we define the stratigraphic layering of the undeformed medium by an approximating body of finite quadrilateral elements evaluate the defined displacement functions for the grid nodes and graph the deformed mesh eventually we create with the algorithm synthetic deformation sequences for simple boundary conditions and try in a specific case study to match the resulting synthetics with the available observational and experimental data

unfolding an inverse approach to fold kinematics preservedfoldshapesusuallyreveallittleabouttheirkinematicevolution syntectonic strata preserved in growth synclines in contact with a fold however can permit unfolding a sequential reconstruction of fold growth backward through time from a geometry observed at present to an initial undeformed state such reconstructions can define the kinematics of fold growth growth strata associated with anticlinal forelimbs in the ebro basin exhibit depositional tapering of beds on fold flanks and progressive limb rotation unfoldingawell dateddetachmentfolddefinesitskinematicevolutionandcoevallyvarying rates of shortening forelimb uplift and forelimb rotation interplay of these rates with sedimentation rates controls onlap and offlap relations

detachment folding in the central and eastern zagros fold belt iran salt mobility multiple detachments and late basement control abstract detachment folding has been studied on the basis of field and subsurface examples from the central and eastern zagros iran we discuss different aspects of detachment folding well illustrated in the studied area in particular we focus on salt mobility multiple decollements and late basement control salt mobility concerns the hormuz basal detachment and the gachsaran upper detachment for the latter it is shown that mobility results not only from folding related diapirism but also from early gravity driven migration from growing anticlines towards intervening synclines concentric folding between two detachment levels is directly observed in the izeh zone central zagros where it is shown that the wave length depends on the distance between the two active decollements and that the fold shape is a function of the level of erosion throughout the zagros detachment folds mainly developed during an initial thin skinned phase of deformation which was followed by the current thick skinned stage this succession is particularly well expressed in the eastern zagros where basement faults cut early detachment folds obliquely

fault related folding a review of kinematic models and their application abstract folding that is directly related to fault activity is an important deformation feature that occurs all over the world in mountain belts accretionary wedges fold and thrust belts and intra plate settings in either strike slip compressional or extensional regimes due to their widespread occurrence knowledge about the development of these structures is important to a broad spectrum of geoscience sub disciplines such as structural geology seismology geomorphology petroleum geology and quaternary geology fault related folding has been analyzed intensively over the last 140 years for the sake of this review we divide the folds according to the way the faults and the folds form that is into detachment fault bend and fault propagation folds all fault related folds are caused by changes in fault parameters the simplest method to produce folds is to transport material along faults that have stepped flat ramp flat geometries fault bend fold alternatively the slip can decrease along the length of the fault and depending on whether the fault remains within a detachment layer or steps up through mechanical stratigraphy either a detachment fold or a fault propagation fold is formed respectively detachment folding was first investigated in the early 20th century whereas the full significance of fault propagation folds was recognized quite late in the 1980s seminal work on fault related folding was carried out in the 1930s but quantitative kinematic models have only been available in the last 30 years these models are extremely valuable because they allow a comprehensive understanding of the evolution of fault related folds and lead to more accurate predictions of the sub surface structure from the mid 1990s onwards numerical simulations have been used to identify how fault parameters such as dip and fault bend angle propagation to slip ratio and shape of the trishear zone influence the geometry of the related folding this is directly applicable to the analysis of the shape of anticlines produced however this does not mean that fold geometry is uniquely related to fault geometry on the contrary different kinematic approaches can lead to a similar fold shape

geophysical implications of the long wavelength topography of the saturnian satellites 1 we use limb profiles to quantify the long wavelength topography of the saturnian satellites the degree 2 shapes of mimas enceladus and tethys are not consistent with hydrostatic equilibrium we derive 2 d topographic maps out to spherical harmonic degree 8 there is a good correlation with topography derived from stereo techniques if uncompensated topography at degree 3 and higher is large enough to be detectable during close spacecraft flybys if not properly accounted for this topography may bias estimates of a satellite s degree 2 gravity coefficients which are used to determine the moment of inertia we also derive a one dimensional variance spectrum a measure of how roughness varies with wavelength for each body the short wavelength spectral slope is 2t o 2 5 similar to silicate bodies however unlike the terrestrial planets each satellite spectrum shows a reduction in slope at longer wavelengths if this break in slope is due to a transition from flexural to isostatic support the globally averaged elastic thickness te of each satellite may be derived we obtain te values of 5 km 1 5 5 km 5 km and 5 km for tethys dione rhea and iapetus respectively for europa we obtain te 1 5 km these estimates are generally consistent with estimates made using other techniques for enceladus intermediate wavelengths imply te 0 5 km but the variance spectrum at wavelengths greater than 150 km is probably influenced by long wavelength processes such as convection or shell thickness variations impact cratering may also play a role in determining the variance spectra of some bodies citation nimmo f b g bills and p c thomas 2011 geophysical implications of the long wavelength topography of the saturnian satellites j geophys res 116 e11001 doi 10 1029 2011je003835

hydrostatic interfaces in bodies with nonhydrostatic lithospheres below the lithospheres of the terrestrial planets dwarf planets and moons density interfaces adjust over geologic time to align with surfaces of constant gravitational potential it is well known that the shape of such hydrostatic surfaces is controlled by the pseudo rotational potential tidal potential and the induced potential of nonspherical density interfaces in the body when a lithosphere is present however additional gravitational terms must be considered that arise from for example surface relief and crustal thickness variations a first order formalism is presented for calculating the shape of hydrostatic density interfaces beneath the lithosphere when the gravity field and surface shape of the body are known using an arbitrary discretized density profile the shapes are obtained by solving a simple matrix equation as examples lithospheric gravity anomalies account for about 10 of the relief along hydrostatic interfaces in mars whereas for the moon the lithospheric gravity is the dominant contributor to the core shape spherical harmonic degree 1 mass anomalies in the lithosphere generate degree 1 relief along the core mantle boundary and for mars and the moon the core is offset from the center of mass of the body by about 90 m the moments of inertia of the core of these bodies are also misaligned with respect to the principal moments of the entire body an improved crustal thickness map of mars is constructed that accounts for gravity anomalies beneath the lithosphere and the consequences of core relief on the martian free core nutation are quantified plain language summary the shapes of the solid planets and moons are largely hydrostatic and are determined by their rotation rate if the body has gravity anomalies that arise from within a rigid lithosphere these will act to perturb the shape of hydrostatic density interfaces beneath the lithosphere such as the core mantle boundary we present a method to compute the shape of density interfaces beneath the lithosphere when the gravity field of the body is known as examples of our technique we compute the shape of the core mantle boundary for mars and the moon both of which are shown to have important contributions that arise from the lithosphere we also generate a new crustal thickness map that accounts for gravity anomalies generated beneath the lithosphere

diapir induced reorientation of saturn s moon enceladus the recent discovery of active water venting from the surface of saturn s icy moon enceladus has caused a ripple of excitement as it suggests the possibility of subsurface liquid water geologically enceladus poses problems one the reason why the hotspot of geological activity is centred precisely on the south pole has been tackled by francis nimmo and robert t pappalardo they identify reorientation of enceladus s rotation axis as the likely cause and an upwelling of low density material to the surface as the cause of that reorientation comparison of the distribution of impact craters on the leading and trailing hemispheres will be a good test of the reorientation part of the theory enceladus is a small icy satellite of saturn its south polar region consists of young tectonically deformed terrain and has an anomalously high heat flux1 2 this heat flux is probably due to localized tidal dissipation within either the ice shell3 or the underlying silicate core4 the surface deformation is plausibly due to upwelling of low density material diapirism5 as a result of this tidal heating here we show that the current polar location of the hotspot can be explained by reorientation of the satellite s rotation axis because of the presence of a low density diapir if the diapir is in the ice shell then the shell must be relatively thick and maintain significant rigidity elastic thickness greater than 0 5 km if the diapir is in the silicate core then enceladus cannot possess a global subsurface ocean because the core must be coupled to the overlying ice for reorientation to occur the reorientation generates large 10 mpa tectonic stress patterns6 that are compatible with the observed deformation of the south polar region2 we predict that the distribution of impact craters on the surface will not show the usual leading hemisphere trailing hemisphere asymmetry a low density diapir also yields a potentially observable negative gravity anomaly

enceladus south polar sea recent observations of the south pole of saturn s moon enceladus by the cassini spacecraft have revealed an active world powered by internal heat in this paper we propose that localized subsurface melting on enceladus has produced an internal south polar sea evidence for this localized sea comes from the shape of enceladus which does not match a differentiated body at its current orbital position we show that melting induced by the observed heat flow at the south pole produces a large enough pit to match the shape of enceladus with a differentiated rock and ice interior numerical modeling of melting and ice flow shows that the sea produced beneath the south pole is stable against inflow of ductile ice from its surroundings for the duration of the heating the shape modification due to melting also produces a negative degree two gravity anomaly which can reorient the spin axis of enceladus in order to place the sea at the pole

a 1 5d model of the steady state thermal structure of detachment folds abstract we present a 1 5d steady state model of thermal perturbations in the core of detachment anticlines the model incorporates the effects of heat conduction advection by folding radiogenic sources and conversion of work into heat by viscous dissipation we work out analytical solutions of model s equations for heat flow and temperature field for the case of low amplitude detachment folds growing in a thick homogeneous stratigraphy our analytical solutions for the simplest case of no heat sources show that detachment folds develop a thermal boundary layer conduction of heat dominates inside the layer whereas advection of heat by folding prevails outside the boundary layer we also find that heat flow in a growing detachment fold decays exponentially with the square of the thickness of the detached stratigraphic section when heat sources are included into the problem we find that radiogenic heat generates thermal anomalies at the crest of the anticlines whereas viscous dissipation produces thermal anomalies at the core of the detachment fold we analyze three cases of geological interest detachment folds growing in evaporitic sequences marine carbonates and shaley sediments for a typical uplift rate of 2 mm yr conduction dominates in the first class of rocks viscous dissipation dominates in folds growing in limestone due to its high viscosity advection and the generation of heat by radiogenic isotopes dominate the growth of detachment folds in shale additionally the cooling histories of lagrangian particles embedded in the fold for the last two cases are analyzed the core of the fold is characterized by rapid cooling whereas the limbs cool at slower rates than the core thus the development of detachment anticlines may either accelerate maturation of source rocks and expand the maturation window or halt it by removing source rocks from the generating window

reverse modelling of detachment folds application to the pico del aguila anticline in the south central pyrenees spain abstract a simple method to estimate fold amplification and thrust movement rates for detachment folds is documented and illustrated by its application to a symmetrical detachment fold in the southern pyrenees spain the technique provides a complete record of the kinematic evolution of detachment folds and is based on the application of equations for detachment folds involving limb rotation the method uses the stratal pattern of the syntectonic sediments and assumes that these growth strata were deposited horizontally that the folds involve a homogeneous competent unit detached over a ductile horizon and that the folds can be represented by chevronkink bands the procedure is applicable to any detachment fold with associated growth strata that display wedge geometries progressive unconformities indicating limb rotation through time this method can be used for both detachment folds formed with constant limb length or variable limb length and it can also accommodate undecompacted or decompacted growth strata

modal mineralogy of carbonaceous chondrites by x ray diffraction and mossbauer spectroscopy carbonaceous chondrites are among the most analyzed geological materials on earth however despite this attention and unlike most terrestrial rocks little is known on the abundance of individual phases within them here we show how a combination of several novel x ray diffraction xrd techniques including a high brightness x ray microsource and mssbauer spectroscopy allows a complete modal mineralogy to be ascertained from even the most highly unequilibrated fine grained chondrites for all minerals of abundance 1 wt knowledge of the modal mineralogy of a sample also allows us to calculate grain density we analyzed allende murchison tagish lake and orgueil based on our modal data the grain density estimates for allende murchison and orgueil are close to literature values in the case of tagish lake there is no published grain density although a bulk density measurement does exist taking our estimate of grain density and the measured bulk density we calculate an exceptionally high porosity of 41 for this meteorite similar to some chondritic idps and in line with a porosity calculated from an entry model for the tagish lake fireball although it is an oxidized cv magnetite is present in allende at a level of 0 5 wt or 0 3 vol a result that is substantiated by several other instrumental studies this may be an oxidized meteorite but that oxidation is not manifested in abundant magnetite in addition we note appreciable fayalitic olivine in orgueil detected by both xrd and mossbauer we employed microsource xrd to look at heterogeneity in mineral abundance in orgueil and found substantial variation with phyllosilicates varying inversely with olivine the data suggest that orgueil was initially composed primarily of anhydrous materials which have been partially but not completely altered although the data are preliminary comparison between our xrd modal assessment bulk chemistry grain density and mossbauer data suggests that our estimates of mineral abundance are robust the advent of microsource xrd allows similar modal data to be acquired from samples as small as a few hundred micrograms

is titan s shape caused by its meteorology and carbon cycle 1 titan s shape is characterized by a difference between the long equatorial radius and the polar radius that is several hundred meters larger than that predicted by the flattening due to its spin rate the north polar region is covered by large mare filled with hydrocarbons including ethane moreover global circulation models predict ethane precipitation on the polar areas this study shows that the shape of titan can be explained by the subsidence associated with the substitution of methane with ethane rich liquids percolating into the crust which as suggested by evolution models may be composed of methane clathrate hydrates such substitutions have been observed in laboratory experiments this process would provide an additional methane source as required for sustaining the presence of this constituent in titan s atmosphere through its history a 270 m subsidence of the polar caps is explained by the circulation of 1 5 to 6 1018kg of ethane in the top three kilometers of an initially methane clathrate crust this process would have operated during the last 300 1200 myr at the present ethane production rate

north atlantic fracture zone distribution and patterns shown by multibeam sonar fracture zone distribution in the north atlantic ocean varies from closely spaced about 50 km to widely spaced 300 km between the equator and the azores hotspot across the mid atlantic ridge north of the azores hotspot seamount chains predominate in place of fracture valleys the fracture zone trends are taken from a data base with the ability to show fracture valleys of several kilometres width whereas the past 200 m y of kinematic history in the atlantic may be recorded in the magnetic lineations these lineations are not adequate to show actual spreading flow lines and in fact cloud the actual bathymetry of fracture valley orientation