folding within seconds hypervelocity impacts of cosmic projectiles larger than 200 m diameter are capable of forming complex craters on earth at these craters shock loading shock damage and excavation flow are followed by a gravity driven collapse of the deep transient cavity such impact structures are characterized by a central uplift a flat crater floor and a terraced crater rim collapse induced deformation features like folds and brittle fault zones have many similarities to tectonic structures typical deformation patterns of complex terrestrial impact craters of 5 15 km diameter are compiled and analyzed with respect to their kinematic development unlike their tectonic counterparts deformation structures are always the result of non plane strain deformation and are formed in a single event that takes place in seconds to minutes to understand the high strain rate processes the microstructure of an impact induced fold of the crooked creek impact crater 7 km diameter missouri united states is investigated in detail a period of 20 30 s at the most is determined for the collapse phase of this crater the gross plastic deformation behavior of the fold is achieved by localized brittle deformation along millimeter to centimeter spaced fault zones forming a network of veins shock damage has fractured 40 of grain boundaries the onset of collapse and associated deformation started in rocks with a reduced cohesion and is friction controlled

the geologically recent giant impact basins at vesta s south pole since 17 july 2011 nasa s spacecraft dawn has been orbiting the asteroid vesta the second most massive and the third largest asteroid in the solar system see the cover russell et al p 684 1 use dawn s observations to confirm that vesta is a small differentiated planetary body with an inner core and represents a surviving proto planet from the earliest epoch of solar system formation vesta is also confirmed as the source of the howardite eucrite diogenite hed meteorites jaumann et al p 687 2 report on the asteroid s overall geometry and topography based on global surface mapping vesta s surface is dominated by numerous impact craters and large troughs around the equatorial region marchi et al p 690 3 report on vesta s complex cratering history and constrain the age of some of its major regions based on crater counts schenk et al p 694 4 describe two giant impact basins located at the asteroid s south pole both basins are young and excavated enough amounts of material to form the vestoids a group of asteroids with a composition similar to that of vesta and hed meteorites de sanctis et al p 697 5 present the mineralogical characterization of vesta based on data obtained by dawn s visual and infrared spectrometer revealing that this asteroid underwent a complex magmatic evolution that led to a differentiated crust and mantle the global color variations detailed by reddy et al p 700 6 are unlike those of any other asteroid observed so far and are also indicative of a preserved differentiated proto planet 1 lookup doi 10 1126 science 1219381 2 lookup doi 10 1126 science 1219122 3 lookup doi 10 1126 science 1218757 4 lookup doi 10 1126 science 1223272 5 lookup doi 10 1126 science 1219270 6 lookup doi 10 1126 science 1219088

metalliferous mining geophysics state of the art after a decade in the new millennium mining exploration was very active during the first decade of the twenty first century because there were numerous advances in the science and technology that geophysicists were using for mineral exploration development came from different sources instrumentation improvements new numerical algorithms and cross fertilization with the seismic industry in gravity gradiometry kept its promise and is on the cusp of becoming a key technology for mining exploration in potential field methods in general numerous techniques have been developed for automatic interpretation and 3d inversion schemes came into frequent use these inversions will have even greater use when geologic constraints can be applied easily in airborne electromagnetic em methods the development of time domain helicopter em systems changed the industry in parallel improvements in em modeling and interpretation occurred in particular the strengths and weaknesses of the various algorithms became better understood simpler imaging schemes came into standard use whereas layered inversion seldom is used in the mining industry today improvements in ground em methods were associated with the development of squid technology and distributed acquisition systems the latter also impacted ground induced polarization ip methods developments in borehole geophysics for mining and exploration were numerous borehole logging to measure physical properties received significant interest perhaps one reason for that interest was the desire to develop links between geophysical and geologic results which also is a topic of great importance to mining geologists and geophysicists

evidence for shock induced anhydrite recrystallization and decomposition at the unam 7 drill core from the chicxulub impact structure

structural geology of impact craters abstract the formation of impact craters is a highly dynamic and complex process that subjects the impacted target rocks to numerous types of deformation mechanisms understanding and interpreting these styles of micro meso and macroscale deformation has proved itself challenging for the field of structural geology in this paper we give an overview of the structural inventory found in craters of all size ranges on earth and look into the structures of craters on other planetary bodies structural features are discussed here that are caused by i extremely high pressures and temperatures that occur during the initial passage of the shock wave through the target rock and projectile ii the resulting flow field in the target that excavates and ejects rock materials and iii the gravitationally induced modification of the crater cavity into the final crater form a special focus is put on the effects that low angle impacting bodies have on crater formation we hope that this review will help both planetary scientists and structural geologists understand the deformation processes and resulting structures generated by meteorite impact

magnetic fabric of araguainha complex impact structure central brazil implications for deformation mechanisms and central uplift formation article i nfo the weakening mechanisms involved in the collapse of complex impact craters are controversial the ara guainha impact crater in brazil exposes a complex structure of 40 km in diameter and is an excellent object to address this issue its core is dominated by granite in addition to microstructural observations magnetic studies reveal its internal fabric acquired during the collapse phase all granite samples exhibit impact related planar deformation features pdfs and planar fractures pfs which were overprinted by cataclasis cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure fracture planes are systematically decorated by tiny grains b10 m of magnetite and hematite and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility ams and anhysteretic remanence aar are perfectly coaxial in all studied sites therefore we could track the orientation of deformation features which are decorated by iron oxides using the ams and aar the magnetic fabrics show a regular pattern at the borders of the cen tral peak with orientations consistent with the fabric of sediments at the crater s inner collar and complex in the center of the structure both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of complex im pact structures the widespread occurrence of cataclasis in the central peak and its orientations revealed by magnetic studies indicate that acoustic fluidization likely operates at all scales including the mineral scales the cataclastic flow made possible by acoustic fluidization results in an apparent plastic deformation at the macroscopic scale in the core

rock fluidization during peak ring formation of large impact structures large meteorite impact structures on the terrestrial bodies of the solar system contain pronounced topographic rings which emerged from uplifted target crustal rocks within minutes of impact to flow rapidly over large distances these target rocks must have weakened drastically but they subsequently regained sufficient strength to build and sustain topographic rings the mechanisms of rock deformation that accomplish such extreme change in mechanical behaviour during cratering are largely unknown and have been debated for decades recent drilling of the approximately 200 km diameter chicxulub impact structure in mexico has produced a record of brittle and viscous deformation within its peak ring rocks here we show how catastrophic rock weakening upon impact is followed by an increase in rock strength that culminated in the formation of the peak ring during cratering the observations point to quasi continuous rock flow and hence acoustic fluidization as the dominant physical process controlling initial cratering followed by increasingly localized faulting

the central pit and dome at cerealia facula bright deposit and floor deposits in occator crater ceres morphology comparisons and formation abstract the prominent bright deposit cerealia facula ceres coincides with the central depression or central pit of the recently formed 92 km wide complex crater occator the central pit is 9 10 km wide and up to 1 km deep and is partially filled with a 700 m high 2 km wide dome the upper surface of the central dome is densely fractured but the flanks are not indicating that uplift of the dome surface occurred after the bright deposit was emplaced and primarily through uplift of the surface from below by laccolithic intrusion or volume expansion the pit is rimless except for two prominent massifs that flank it to the east and west this pit dome morphology bears a strong resemblance in morphology topography and dimensions to central pit craters observed on ganymede and callisto but is essentially absent on the similar sized ice rich moons of uranus saturn and pluto the lack of pit craters on midsize icy moons and the possible lack of central pit craters at the cold poles of ceres suggest that temperature is a significant controlling factor in central pit formation beyond the canonical inverse gravity scaling of complex crater transitions while renewed modeling will benefit from these new constraints the mapping of central pits on ceres including occator suggests that either the rheologically layered target model or more likely the melted central uplift model may be the most probable explanation for central pit formation on ceres lack of similar high resolution imaging on the galilean icy satellites precludes definitive evaluation of models there large volumes of lobate floor fill material at least 600 m thick in some places cover large areas of the southern and eastern floor of occator and small outcrops of this unit are found perched high on closed topographic depressions on the occator terrace zone and other higher areas of the crater floor the swirling and knobby surface textures of these lobate deposits are essentially indistinguishable from those on impact melt sheets on large lunar craters such as tycho these observations indicate that this unit is most likely an impact melt sheet formed from melted water ice admixed with unmelted particulate or dissolved phyllosilicates salts and or carbonates and large quantities of fragmented debris melt of ice phases within ceres crust is also supported by independent numerical models of impact at occator and would provide a ready source of fluids to promote hydrothermal deposition of the observed bright na carbonates on the surface of the central pit at occator if the deposit formed within a million years or so of impact the central dome finds analogs in salt domes on earth and pingos frost mounds on earth and mars which form by water and solute migration and freeze expansion later freezing of a central reservoir of volatiles beneath the central pit at occator or mobilization of ice or other phases during the cooling and refreezing process could explain the uplift of the central dome finally no changes were detected in the cerealia and vinalia facula bright deposits during the course of the prime dawn mapping mission placing additional constraints on their formation time and limits on ongoing activity

tectonics of complex crater formation as revealed by the haughton impact structure devon island canadian high arctic the results of a systematic field mapping campaign at the haughton impact structure have revealed new information about the tectonic evolution of mid size complex impact structures these studies reveal that several structures are generated during the initial compressive outward directed growth of the transient cavity during the excavation stage of crater formation 1 sub vertical radial faults and fractures 2 sub horizontal bedding parallel detachment faults and 3 minor concentric faults and fractures uplift of the transient cavity floor toward the end of the excavation stage produces a central uplift compressional inward directed deformation results in the duplication of strata along thrust faults and folds it is notable that haughton lacks a central topographic peak or peak ring the gravitational collapse of transient cavity walls involves the complex interaction of a series of interconnected radial and concentric faults while the outermost concentric faults dip in toward the crater center the majority of the innermost faults at haughton dip away from the center complex interactions between an outward directed collapsing central uplift and inward collapsing crater walls during the final stages of crater modification resulted in a structural ring of uplifted intensely faulted sub vertical and or overturned strata at a radial distance from the crater center of 5 0 6 5 km converging flow during the collapse of transient cavity walls was accommodated by the formation of several structures 1 sub vertical radial faults and folds 2 positive flower structures and chaotically brecciated ridges 3 rollover anticlines in the hanging walls of major listric faults and 4 antithetic faults and crestal collapse grabens oblique strike slip i e centripetal movement along concentric faults also accommodated strain during the final stages of readjustment during the crater modification stage it is clear that deformation during collapse of the transient cavity walls at haughton was brittle and localized along discrete fault planes separating kilometer size blocks

ganymede crater dimensions implications for central peak and central pit formation and development the morphology of impact craters on the icy galilean satellites differs from craters on rocky bodies the differences are thought due to the relative weakness of ice and the possible presence of sub surface water layers digital elevation models constructed from galileo images were used to measure a range of dimensions of craters on the dark and bright terrains of ganymede measurements were made from multiple profiles across each crater so that natural variation in crater dimensions could be assessed and averaged scaling trends constructed the additional depth slope and volume information reported in this work has enabled study of central peak formation and development and allowed a quantitative assessment of the various theories for central pit formation we note a possible difference in the size morphology progression between small craters on icy and silicate bodies where central peaks occur in small craters before there is any slumping of the crater rim which is the opposite to the observed sequence on the moon conversely our crater dimension analyses suggest that the size morphology progression of large lunar craters from central peak to peak ring is mirrored on ganymede but that the peak ring is subsequently modified to a central pit morphology pit formation may occur via the collapse of surface material into a void left by the gradual release of impact induced volatiles or the drainage of impact melt into sub crater fractures

exploration for unconformity type uranium deposits with audiomagnetotelluric data a case study from the mcarthur river mine saskatchewan canada unconformity type deposits supply a significant amount of the world s uranium and consist of uranium that is generally codeposited with graphite in a fault zone the low resistivity of the graphite produces a significant contrast in electrical resistivity which can be located with electromagnetic em methods the athabasca basin in western canada hosts significant uranium deposits and exploration in deeper parts of the basin has required the application of new em methods this paper presents an evaluation of the audiomagnetotelluric amt exploration method at the mcarthur river mine in the athabasca basin amt data were collected at 132 stations on a grid and two dimensional 2d and three dimensional 3d inversions were used to generate resistivity models these models showed two major results 1 a significant conductor coincident with a major basement fault p2 and the uranium deposits this conductor begins at the unconformity at a depth of 550 m and extends to a depth of at least three km an

mid sized complex crater formation in mixed crystalline sedimentary targets insight from modeling and observation large impact crater formation is an important geologic process that is not fully understood the current paradigm for impact crater formation is based on models and observations of impacts in homogeneous targets real targets are rarely uniform for example the majority of earth s surface is covered by sedimentary rocks and or a water layer the ubiquity of layering across solar system bodies makes it important to understand the effect target properties have on the cratering process to advance understanding of the mechanics of crater collapse and the effect of variations in target properties on crater formation the first bridging the gap workshop recommended that geological observation and numerical modeling focussed on mid sized 15 30 km diameter craters on earth these are large enough to be complex small enough to be mapped surveyed and modelled at high resolution and numerous enough for the effects of target properties to be potentially disentangled from the effects of other variables in this paper we compare observations and numerical models of three 18 26 km diameter craters formed in different target lithology ries germany haughton canada and el gygytgyn russia based on the first order assumption that the impact energy was the same in all three impacts we performed numerical simulations of each crater to construct a simple quantitative model for mid sized complex crater formation in a subaerial mixed crystalline sedimentary target we compared our results with interpreted geological profiles of ries and haughton based on detailed new and published geological mapping and published geophysical surveys our combined observational and numerical modeling work suggests that the major structural differences between each crater can be explained by the difference in thickness of the pre impact sedimentary cover in each case we conclude that the presence of an inner ring at ries and not at haughton is because basement rocks that are stronger than the overlying sediments are sufficiently close to the surface that they are uplifted and overturned during excavation and remain as an uplifted ring after modification and post impact erosion for constant impact energy transient and final crater diameters increase with increasing sediment thickness

a balanced cross section of the 1994 northridge earthquake southern california the northridge earthquake of 17 january 19941 was the latest in a series of very damaging thrust fault generated earthquakes to strike california following the san fernando2 1971 coalinga3 1983 and whittier narrows4 5 1987 events like the last two of these the northridge event occurred along a fault that did not reach the surface and which had not been detected by traditional seismic hazard methods6 7 balanced cross sections8 9 which flatten and remove the crustal deformation can be used to identify and quantify the seismic hazard posed by thrust faults here we present a balanced cross section through the northridge portion of the transverse ranges fold and thrust belt10 which shows that the earthquake occurred on what we call the pico thrust a cross section of this sort constructed before the earthquake would have revealed the fault although it would not have predicted the earthquake cross sectional modelling of the pico thrust yields an average slip rate of 1 4 1 7 mm yr 1 and a recurrence interval of northridge sized mw 6 7 earthquakes every 1 500 1 800 years we show that the pico thrust is the back thrust to the 170 km elysian park thrust3 4 which underlies some of the most densely urbanized portions of the los angeles basin

radial transpression ridges a new structural feature of complex impact craters the gravity driven collapse of complex impact craters induces the mass transfer of large rock volumes in distal parts of a crater inward movements dominate whereas in the centre of an impact structure outward movements occur if the central uplift collapses the particle trajectory field is centro symmetric which signifies that the conditions for plane strain deformation are not fullfilled converging particle trajectories can be compensated either by a bulk thickening of inward sliding masses folding repetition of rock units along thrust faults plastic flow or by the formation of localised radial transpression ridges rtr at the edges of individual landslides in these transpression ridges material is uplifted to accommodate the converging mass flow different modes of uplift are possible including radial folding lateral overthrusting and the formation of positive flower structures a simple geometric model is used to estimate the amount of transpression thickening and bulk thickening of inward sliding masses on the base of volumetric considerations the existence of rtrs is confirmed by structural investigations at the siljan impact structure sweden as well as at other complex impact craters on earth

3d seismic reflection mapping of the silverpit multi ringed crater north sea the first comprehensive mapping of the silverpit multi ringed crater is presented based on five adjoining 3d seismic surveys that together provide 78 216 km2 areal coverage of the structure with spatial and depth sampling of 10 m the top cretaceous surface shows an excavated crater 3 km in diameter surrounded by 10 15 concentric ring structures out to a radius of 9 4 km seismic sequence stratigraphy and drilled wells indicate the lower age bound is a disconformity spanning 74 54 ma the upper bound is eocene termination of concentric ring fault growth ca 45 ma the inner rings are extensional faults defining rotated fault blocks that would be considered part of the crater in an impact structure interpretation giving a final impact crater diameter of 8 km the outer rings show a surprising variation in style from graben in the west to compressional structures in the east this may be explained by postcratering gravity spreading on easterly dipping intra cretaceous detachments within the crater the top cretaceous seismic reflector is disrupted and blocky but defines a central uplift with a slight crestal depression below this uplift the prominent base cretaceous seismic reflector shows jurassic strata rising into a cone 300 m high and 1 km wide characterized by radial faults this central uplift within the crater may structurally balance the inner ring fault blocks via a slumping model but we also identify low seismic velocity in the uplifted jurassic so fracturing may have contributed to growth of the central peak at a radius of 2 5 km base cretaceous shows a dish shaped depression that we interpret as marking either the extent of slumping toward the crater at this structural level or the limit of shockwave induced porosity collapse seismic reflectors above the top cretaceous excavated crater show differential compaction during the eocene accommodated by drape structure plus two conical faults that define narrow ring graben and represent the final phase of crater related tectonics

superimposed deformation in seconds breccias from the impact structure at kentland indiana usa abstract breccias from the central uplift at the kentland indiana impact structure have outcrop and microscopic characteristics that give insight into events that may occur in a carbonate dominated sedimentary sequence in the moments following hypervelocity impact three distinct types of brecciated rock bodies fault breccias breccia lenses and breccia dikes suggest multiple mechanisms of fragmentation the fault breccias occur along steeply dipping faults that coincide with compositional discontinuities in the stratigraphic succession the breccia lenses and dikes are less localized in occurrence and show no systematic spatial distribution or orientation the fault breccias and breccia lenses show no consistent cross cutting relationships but both are transected by the breccia dikes textural analysis reveals significant differences in particle size distributions for the different breccias the fault breccias are typically monomict coarsest and least uniform in grain size and yield the highest power law exponent fractal dimension in plots of particle size vs frequency the polymict dike filling is finest and most uniform in grain size has the lowest power law exponent and is locally laminated and size sorted sem images of the dike filling breccia show that fragmentation occurred to the scale of microns material within the breccia lenses has textural characteristics intermediate between the other two types but the irregular morphology of these bodies suggests a mechanism of formation different from that of either of the other breccia categories the breccia lenses and dikes both have sub mm scale spheroidal vugs that may have been formed by carbon dioxide bubbles released during sudden devolatilization of the carbonate country rock collectively these observations shed light on the processes that occur during the excavation and modification phases of crater formation in carbonate strata heterogeneous polyphase multiscale deformation accomplished over a time interval of seconds

folding by cataclastic flow at shallow crustal levels in the canyon range sevier orogenic belt west central utah abstract folds form by ductile deformation typically involving continuous flow in the elastico frictional regime such deformation may be accomplished by cataclastic flow involving collective movement on a population of fractures and zones the canyon range cr syncline part of the cr thrust sheet in west central utah developed in this regime the cr syncline is composed of thick bedded quartzite units with a small material contrast between layers limiting limb rotation by flexural slip alone thus fracture populations developed to accommodate fold tightening by limb rotation and thinning and the formation of transverse zones across the fold several generations of fracture and deformation zone dz networks are recognized from mesoscopic and microscopic evidence and can be related to stages of folding the net result of the large number of distributed fractures and deformation zones is a continuous deformation that is homogeneous at the scale of the outcrop all these lines of evidence suggest that large scale cataclastic flow accommodated folding by allowing rigid mesoscopic blocks to slide along bounding dzs along its length the cr syncline consists of several segments bounded by transverse zones with different mechanisms accommodating fold tightening in adjacent segments in one segment fold tightening progressed by limb rotation and then out of the core thrusting in contrast fold tightening in the adjoining segments occurred by rotation and thinning of one limb and possible hinge migration with the steeply dipping to overturned limb showing progressive thinning of units on a megascopic scale and progressive increase in the thickness and density of deformation zones at all scales

low angle collision with earth the elliptical impact crater matt wilson northern territory australia nearly all meteorite impact craters on earth are circular however 4 of craters should be formed by impacts at angles lower than 12 from the horizontal which should result in elongated crater structures the crater forming process that produces elliptical shapes is poorly understood we document the first elliptical crater on earth that contains a central uplift and that provides insights into the mechanisms of crater formation at a critical threshold angle of 10 15 the dimensions of the proterozoic matt wilson impact structure northern territory australia are 7 5 by 6 3 km corresponding to an aspect ratio of 1 2 with its long axis trending northeast southwest the exposed crater floor shows a preferred stacking of thrust sheets within the central uplift and in the surrounding syncline indicating northeast southwest shortening and a material transport top to the sw this is consistent with an up range to down range motion of rock caused by remnant horizontal momentum transferred from the impacting projectile to the target this preferential deformation interferes with a radially oriented convergent material flow characteristic for crater collapse the matt wilson crater provides evidence for the usefulness of structural asymmetries as a diagnostic tool to infer impact vectors the new impact crater is confirmed by the presence of planar deformation features planar fractures in quartz grains and its structural inventory

detection of alteration at the millennium uranium deposit in the athabasca basin a comparison of data from two airborne electromagnetic systems with ground resistivity data the millennium uranium deposit is located within the athabasca basin of northern saskatchewan the basement rocks comprised primarily of paleo proterozoic gneisses are electrically resistive however the deposit is associated with highly conductive graphitic metasediments that are intercalated with the gneisses an unconformity separates the basement rocks from the overlying horizontally stratified proterozoic sandstones of the athabasca group which are also highly resistive the strike extents of the graphitic metasedimenary packages are extensive and therefore electromagnetic em survey techniques are successful at identifying these zones but do not identify the specific locations where they are enriched in uranium through drilling it has been noted that hydrothermal processes associated with mineralization has altered the rocks in the vicinity of the deposits which should in theory result in a resistivity low a significant resistivity low has been mapped coincident with the millennium deposit using ground resistivity survey techniques however a comparison of the airborne em and ground resistivity results reveals that the two data sets have imaged different features the resistive limit on time windows of the megatem data show conductive features corresponding to lakes located to the west and south of the deposit the late time windows show a feature to the east of the deposit interpreted as being associated with the east dipping graphitic basement conductors similar to that observed in historical ground em data collected in this area the early time tempest windows delay times less than 0 2 ms show a broad resistivity low located at approximately the same location as where the alteration has been identified through drilling modelling the data is not easy but a response that decays prior to 0 3 ms is consistent with 500 m material in the sandstone a resistivity value close to the lower limit with respect to the hydrothermally altered athabasca group sediments in this area the megatem system does not see a conductive zone over the alteration as clearly but the high signal to noise ratio in the late time megatem data means that the conductive material at a greater depth is more coherently imaged

circular geological structures outcropping in the sedimentary basins of saudi arabia abstract a number of circular geological structures outcrop in the sedimentary basins of saudi arabia several are reviewed here to assess their mode of origin they are unrelated to each other are easily seen on aerial imagery and their origins are assessed here on the basis of new fieldwork and reflection seismic data the structures range in size from hundreds of meters to several kilometers in diameter jabal rayah 28 39 n 37 11 30 e is 5 km in diameter with ring faults and anomalously steep dips in siluro devonian strata reflection seismic data demonstrate that underlying strata are structureless and jabal rayah is interpreted as a probable impact structure ash shutbah 21 37 08 n 45 39 21 e is 2 3 km in diameter and consists of a zone of concentric sub horizontal folds in mesozoic carbonates surrounding a central area of disharmonic steeply plunging folds and a mass of stratigraphically anomalous sandstone there are dissolution structures in the vicinity and although this is a viable explanation the uniquely large and complex nature of ash shutbah suggests an alternative origin by impact reflection seismic data show that underlying strata in the vicinity of ash shutbah are structureless a province of at least 100 circular structures occurs in northeast saudi arabia aerial imagery and reflection seismic data shows that these structures are a mixture of bioherms and dissolution collapse features the kidan crater 22 06 53 n 53 26 38 e is a subcircular feature approximately 100 m in diameter exposed in quaternary sabkha between large sand dunes in the rub al khali field investigation reveals an unfaulted bowl with a slightly fractured floor in sabkha facies 3d reflection seismic data shows a small fault underlying the crater leading to a fluid escape interpretation for the depression

the theoretical plausibility of central pit crater formation via melt drainage central pit craters are seen in large craters on some icy satellites and on mars we investigate the hypothesis that central pits form when impact melt drains into fractures beneath the impact crater for this process to occur the volume of melt generated during the impact the volume of void space in fractures beneath the impact crater and the volume of melt able to drain before the fractures freeze shut all must exceed the volume of the observed central pits we estimate the volume of melt generated using results from previous numerical modeling studies the fracture volume is estimated using gravity anomalies over terrestrial craters to estimate the amount of melt able to drain before freezing we consider flow through plane parallel fractures these calculations all suggest that enough liquid water could drain into fractured ice beneath a crater on ganymede to form a central pit on earth and the moon silicate impact melt will freeze before a large volume is able to drain so we do not expect to see central pits in impact craters in targets with no ice in summary we find our calculations are consistent with observed central pits in craters on ganymede and the lack of central pits in craters on earth and the moon

structural geology the buried record of chicxulub impact craters often have asymmetric shapes which have been used to infer the direction and angle of impact but pre existing structural or topographic heterogeneities also play an important role in crater asymmetry