impact melt rocks from the ries structure germany an origin as impact melt flows abstract the production of impact melt rocks and glasses is a characteristic feature of hypervelocity impact events on earth and other planetary bodies this investigation represents the first detailed study of an unusual series of coherent impact melt rocks intermittently exposed around the periphery of the 24 km diameter 14 5 ma ries impact structure germany optical and analytical scanning electron microscopy sem reveals that the groundmass comprises sanidine plagioclase quartz and ilmenite decreasing order of abundance with the interstices filled by either fresh or devitrified glassy mesostasis primary crystallites display skeletal dendritic and or spherulitic textures indicating rapid crystallization from a melt the mesostasis is characterized by extreme chemical heterogeneity e g feo and al 2 o 3 contents from 1 to 62 80 wt this is likely due to a combination of crystal liquid fractionation during rapid cooling and crystallization of an originally incompletely homogenized melt vapor phase crystallization of sanidine and cristobalite occurred in miarolitic cavities during late stage cooling of the impact melts the most likely protolith for the impact melt rocks are granitic rocks present in the crystalline basement target the high volatile content of the mesostasis suggests that a large volatile component was retained from this protolith field observations together with analytical data and micro textures indicate that the ries impact melt rocks were molten at the time of and after deposition field relations with other impactites also suggest that these rocks were emplaced subsequent to the excavation stage of crater formation and that they are not therefore ballistic ejecta thus it is proposed that the ries impact melt rocks were emplaced as ground hugging impact melt flows that emanated from different regions of the evolving transient cavity during the modification stage of crater formation this is consistent with and in fact predicted by field relations which indicate that these rocks overlie unequivocal ejecta this represents the first recognition of impact melt flows near the rim of a terrestrial impact structure and is consistent with observations of such features on the moon and venus

effects of asteroid and comet impacts on habitats for lithophytic organisms a synthesis asteroid and comet impacts can have a profound influence on the habitats available for lithophytic microorganisms using evidence from the haughton impact structure nunavut canadian high arctic we describe the role of impacts in influencing the nature of the lithophytic ecological niche impact induced increases in rock porosity and fracturing can result in the formation of cryptoendolithic habitats in some cases and depending upon the target material an increase in rock translucence can yield new habitats for photosynthetic cryptoendoliths chasmoendolithic habitats are associated with cracks and cavities connected to the surface of the rock and are commonly increased in abundance as a result of impact bulking chasmoendolithic habitats require less specific geological conditions than are required for cryptoendolithic habitats and their formation is likely to be common to most impact events impact events are unlikely to have an influence on epilithic and hypolithic habitats except in rare cases where for example the formation of impact glasses might yield new hypolithic habitats we present a synthetic understanding of the influence of asteroid and comet impacts on the availability and characteristics of rocky habitats for microorganisms

a high precision 40 ar 39 ar age for the nordlinger ries impact crater germany and implications for the accurate dating of terrestrial impact events abstract 40ar 39ar dating of specimens of moldavite the formation of which is linked to the ries impact in southern germany with a latest generation argus vi multi collector mass spectrometer yielded three fully concordant plateau ages with a weighted mean age of 14 808 0 021 ma 0 038 ma including all external uncertainties 2 mswd 0 40 p 0 67 this new best estimate age for the nordlinger ries is in general agreement with previous 40ar 39ar results for moldavites but constitutes a significantly improved precision with respect to the formation age of the distal ries produced tektites separates of impact glass from proximal ries ejecta suevite glass from three different surface outcrops and partially melted feldspar particles from impact melt rock of the subo 18 enkingen drill core failed to produce meaningful ages these glasses show evidence for excess 40ar introduction which may have been incurred during interaction with hydrothermal fluids only partially reset 40ar 39ar ages could be determined for the feldspathic melt separates from the enkingen core the new 40ar 39ar results for the ries impact structure constrain the duration of crater cooling during the prevailing hydrothermal activity to locally at least 60 kyr with respect to the dating of terrestrial impact events this paper briefly discusses a number of potential issues and effects that may be the cause for seemingly precise but on a kyr scale inaccurate impact ages

devolatilization or melting of carbonates at meteor crater az we have investigated the carbonates in the impact melts and in a monolithic clast of highly shocked coconino sandstone of meteor crater az to evaluate whether melting or devolatilization is the dominant response of carbonates during high speed meteorite impact both melt and clast carbonates are calcites that have identical crystal habits and that contain anomalously high sio2 and al2o3 also both calcite occurrences lack any meteoritic contamination such as fe or ni which is otherwise abundantly observed in all other impact melts and their crystallization products at meteor crater the carbon and oxygen isotope systematics for both calcite deposits suggest a low temperature environment 100 c for their precipitation from an aqueous solution consistent with caliche we furthermore subjected bulk melt beads to thermogravimetric analysis and monitored the evolving volatiles with a quadrupole mass spectrometer co2 yields were 5 wt with typical values in the 2 wt range also total co2 loss is positively correlated with h2o loss an indication that most of these volatiles derive from the secondary calcite also transparent glasses considered the most pristine impact melts yield 100 wt element totals by empa suggesting complete loss of co2 the target dolomite decomposed into mgo cao and co2 the co2 escaped and the cao and mgo combined with sio2 from coexisting quartz and feo from the impactor to produce the dominant impact melt at meteor crater although confined to meteor crater these findings are in stark contrast to osinski et al 2008 who proposed that melting of carbonates rather than devolatilization is the dominant process during hypervelocity impact into carbonate bearing targets including meteor crater

post impact alteration of surficial suevites in ries crater germany hydrothermal modification or weathering processes alteration of surficial suevites at ries crater germany was studied by means of x ray diffraction and scanning electron microscopy here we discuss the origin of hydrous silicate clay phases in these suevites that have been previously interpreted as resulting from post impact hydrothermal processes the results of this study indicate that the dominant alteration phases are dioctahedral al fe montmorillonite and halloysite which are typical low temperature clay minerals we suggest that the surficial suevites are not altered by hydrothermal processes and that alteration occurred by low temperature subsurface weathering processes if the surficial suevites were indeed hydrothermally modified during the early stages of post impact cooling then the alteration was of limited character and is completely masked by later weathering

melt in the impact breccias from the eyreville drill cores chesapeake bay impact structure usa the center of the 35 3 ma chesapeake bay impact structure 85 km diameter was drilled during 2005 2006 in an icdp usgs drilling project the eyreville drill cores include polymict impact breccias and associated rocks 1397 1551 m depth tens of melt particles from these impactites were studied by optical and electron microscopy electron microprobe and microraman spectroscopy and classified into six groups m1 clear or brownish melt m2 brownish melt altered to phyllosilicates m3 colorless silica melt m4 melt with pyroxene and plagioclase crystallites m5 dark brown melt and m6 melt with globular texture these melt types have partly overlapping major element abundances and large compositional variations due to the presence of schlieren poorly mixed melt phases partly digested clasts and variable crystallization and alteration the different melt types also vary in their abundance with depth in the drill core based on the chemical data mixing calculations were performed to determine possible precursors of these melt particles the calculations suggest that most melt types formed mainly from the thick sedimentary section of the target sequence mainly the potomac formation but an additional crystalline basement schist gneiss precursor is likely for the most abundant melt types m2 and m5 sedimentary rocks with compositions similar to those of the melt particles are present among the eyreville core samples therefore sedimentary target rocks were the main precursor of the eyreville melt particles however the composition of the melt particles is not only the result of the precursor composition but also the result of changes during melting and solidification as well as postimpact alteration which must also be considered the variability of the melt particle compositions reflects the variety of target rocks and indicates that there was no uniform melt source original heterogeneities resulting from melting of different target rocks may be preserved in impactites of some large impact structures that formed in volatile rich targets because no large melt body exists in which homogenization would have taken place

a tem investigation of shock metamorphism in quartz from the vredefort dome south africa the origin of the vredefort structure in south africa is still debated several causes have been discussed namely asteroid impact internal gas explosion or tectonic processes evidence of dynamic rock deformation is pervasive in the form of planar features in quartz grains shatter cones veins of pseudotachylite and occurrence of coesite and stishovite high pressure quartz polymorphs a number of these characteristics is widely believed to support an impact origin however the planar features in quartz which are generally considered as one of the strongest indicators of impact are in the vredefort case considered as anomalous when compared with those from accepted impact structures we have investigated by optical and transmission electron microscopy tem the defect microstructures in quartz grains from different lithologies sampled at various places at the vredefort structure whatever the locality only thin mechanical brazil twin lamellae in the basal plane are observed by tem so far such defects have only been found in quartz from impact sites but always associated with sets of thin glass lamellae in rhombohedral planes 10 1n with n 1 2 3 and 4 at the scale of the optical microscope brazil twins in 0001 are easily detected in vredefort quartz grains because of the numerous tiny fluid inclusions which decorate them similar alignments of tiny fluid inclusions parallel to other planes are also detected optically but at the tem scale no specific shock defects are detected along their traces if these inclusion alignments initially were shock features they are now so severely weathered that they can no longer be recognized as unambiguous shock lamellae fine grained coesite was detected in the vicinity of narrow pseudotachylite veinlets in a quartzite specimen but stishovite was not found even in areas where its occurrence was previously reported finally definite evidence of high temperature annealing was observed in all the samples these observations lead us to the conclusion that our findings regarding microdeformation in quartz are consistent with an impact origin for the vredefort structure most of the original shock defects are now overprinted by an intense post shock annealing episode only the thin mechanical twin lamellae in the basal plane have survived

40ar 39ar laser probe age determination confirms the ries impact crater as the source of glass particles in graupensand sediments grimmelfingen formation north alpine foreland basin mineralogical and chemical characteristics of reworked suevite material recovered from graupensand deposits grimmelfingen formation north alpine foreland basin middle miocene are identical to those recorded in ries suevite 40ar 39ar laser probe analyses of two glass particles from graupensand components and of a glass fragment from the ries suevite yielded ages ranging between 14 3 and 14 4 ma identical within analytical uncertainties hitherto the ries impact event was dated at 15 ma conventional k ar and 40ar 39ar methods whereas the graupensande have been placed into the ottnangian around 18 5 ma on the basis of mammal biostratigraphy small sample masses involved in laser probe technique allowed rigorous preselection of highly pure glass particles thus reducing possible age determination errors through partly molten or even unmolten mineral fragments from the variscan crystalline basement our results reconfirm previous statements considering the graupensande as reworked products of the ries impact ejecta blanket thus placing the age of the grimmelfingen formation into the badenian of middle miocene rather than into the ottnangian early miocene

lateral transport of suevite inferred from 3d shape fabric analysis evidence from the ries impact crater germany the transport mechanism of suevite parti cles during impact cratering is poorly under stood and was studied at the 15 ma ries crater in southern germany two emplace ment modes of suevite deposits are generally discussed 1 fallback of plume material into the crater and its periphery upon collapse of an ejecta plume and 2 horizontal transport of ejected material akin to emplacement of pyroclastic deposits erupting from volcanic centers in order to differentiate between the two emplacement modes of suevite deposition we analyzed the shape fabrics of suevite components from two localities out side the ries crater by fishape fabric ellipsoids to measured shape fabric ellipses and by applying high resolution x ray computed tomography to analyze the three dimensional shape and orientation of the suevite particles we show that the preferred orientation of long axes of elongate particles is disposed either radially or concentrically with respect to the crater center our obser vations indicate that suevite material was not only derived from an ejecta plume but was transported by lateral fl ow under viscous conditions upon fallback this fl ow regime resembles that known from pyroclastic fl ows

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

scaling impact melting and crater dimensions implications for the lunar cratering record abstract the dimensions of large craters formed by impact are controlled to a large extent by gravity whereas the volume of impact melt created during the same event is essentially independent of gravity this differential scaling fosters size dependent changes in the dynamics of impact crater and basin formation as well as in the final morphologies of the resulting structures a variety of such effects can be observed in the lunar cratering record and some predictions can be made on the basis of calculations of impact melting and crater dimensions among them are the following 1 as event magnitude increases the volume of melt created relative to that of the crater will grow and more will be retained inside the rim of the crater or basin 2 the depth of melting will exceed the depth of excavation at diameters that essentially coincide with both the inflection in the depth diameter trend and the simple to complex transition 3 the volume of melt will exceed that of the transient cavity at a cavity diameter on the order of the diameter of the moon this would arguably correspond to a moon melting event 4 small lunar craters only rarely display exterior flows of impact melt because the relatively small volumes of melt created can become choked with clasts increasing the melt s viscosity and chilling it rapidly larger craters and basins should suffer little from such a process 5 deep melting near the projectile s axis of penetration during larger events will yield a progression in cen tral structure morphology with growing event magnitude this sequence should range from single peaks through multiple peaks to peak rings 6 the minimum depth of origin of central peak material should co incide with the maximum depth of melting the main central peak in a crater the size of tycho should have had a preimpact depth of close to 15 km

the ries impact a double layer rampart crater on earth the ejecta blankets of impact craters formed on a planetary body that is free of significant quantities of volatiles show substantial differences from those formed on a volatile rich planetary body craters in volatile rich environments often have layered ejecta blankets with lobe like ramparts and long runout flows as seen for martian impact craters under volatile free conditions present on the moon and mercury radial textures and patterns and a gradational decrease in ejecta thickness with distance can be observed the ries crater in germany is one of the rare impacts on earth with a preserved ejecta blanket this crater was previously regarded as an analogue for impact formation on the moon here we demonstrate for the first time that the recent ries ejecta blanket contains a massive and continuous rampart structure at 1 45 2 12 crater radii from the crater center ejecta distribution and thickness as well as the ejecta fabric indicate the presence of fluids during the emplacement process although mars differs in atmospheric pressure and water distribution from earth the ries crater shows striking similarities to martian craters in particular those with double layered ejecta consequently terrestrial impact craters can be better used as analogues for understanding impact formation on mars than for planetary bodies with volatile free conditions as seen on the moon and mercury

distribution petrography and shock metamorphism of the ejecta of the ries crater in germany a review abstract the lithologies and distribution of the various ejecta formations from the ries crater germany are described they may be subdivided into 1 low shock level 10 gpa represented by polymict crystalline breccias fall out suevites crater suevite and tektites moldavites the ejecta from the mesozoic sedimentary column do not show effects of shock pressures exceeding 10 gpa and only basement gneisses were shock melted to yield suevite glasses it is therefore concluded that the maximum impact energy was transferred from the impactor to the target rocks at a depth of at least 1000 m below ground level where a complex of gneisses underlies shallower granitic intrusions the estimated depth of the transient crater was about 2700 m and its diameter was 12 13 km bunte breccia megablocks of sedimentary rocks and crystalline breccias and megablocks were ejected in ballistic trajectories and form the earliest ejecta deposits extending up to a radius of 22 km fall out suevites are understood to have been lofted from the transient crater by an expanding plume of vaporized rocks and deposited outside the crater as fluidized turbulent masses on top of the earlier ejecta in contrast the crater suevite never left the crater cavity it represents the main mass of suevite moldavites are understood to have been formed during the first encounter of the impactor with the ground by condensation from vaporized and ionizised tertiary sands covering the surface of the target area

ca rich majorite derived from high temperature melt and thermally stressed hornblende in shock veins of crustal rocks from the ries impact crater germany shock veins up to 1 1 mm thick were found within non porous lithic clasts from suevite breccia of the nordlinger ries impact structure these veins were studied by optical microscopy in transmitted and reflected light and by scanning electron microscopy in shocked amphibolites two types of ca rich majorite occur within and adjacent to the veins the first type crystallized from shock induced melts within the veins si contents of these majorites suggest dynamic pressure of 15 17 gpa implying minimum temperatures in the range of 2 150 2 230 c the second type of majorite was formed adjacent to the shock veins within pargasitic hornblende this majorite contains significant amounts of h2o 0 7 0 9 wt based on the textural setting the shrinkage cracks and the chemical compositions of both phases a solid state mechanism is deduced for the hornblende to majorite phase transition both genetic types of ca rich majorite are described for the first time from a terrestrial impact crater along with stishovite majorite constitutes the second silicate mineral displaying sixfold coordination of si at ries using micro raman spectroscopy jadeite coesite and jadeite grossular were identified within local melt glasses of alkali feldspar and plagioclase composition respectively stishovite aggregates produced by solid state reaction along with shock induced high pressure melt glasses of almandine composition were also detected in shock veins of a garnet cordierite sillimanite restite the quenched homogeneous almandine glasses point to melting temperatures of more than 2 500 c for the veins our findings demonstrate that terrestrial shock veins can give valuable information on shock induced mineral transformations and transient high pressures of host rocks during a natural impact event

establishing a 14 6 0 2 ma age for the nordlinger ries impact germany a prime example for concordant isotopic ages from various dating materials abstract 40ar 39ar dating of recrystallized k feldspar melt particles separated from partially molten biotite granite in impact melt rocks from the approximately 24 km nordlinger ries crater southern germany yielded a plateau age of 14 37 0 30 0 32 ma 2 this new age for the nordlinger ries is the first age obtained from 1 monomineralic melt 2 separated from an impact metamorphosed target rock clast within 3 ries melt rocks and therewith extends the extensive isotopic age data set for this long time studied impact structure the new age goes very well with the 40ar 39ar step heating and laser probe dating results achieved from mixed glass samples suevite glass and tektites and is slightly younger than the previously obtained fission track and k ar and ages of about 15 ma as well as the k ar and 40ar 39ar age data obtained in the early 1990s taking all the 40ar 39ar age data obtained from ries impact melt lithologies into account data from the literature and this study we suggest an age of 14 59 0 20 ma 2 as best value for the ries impact event

simulating groundwater flow in multi aquifer systems with analytical and numerical dupuit models abstract analytic dupuit solutions for multi aquifer flow are compared to exact solutions for two dimensional flow in the vertical plane to determine the error in discharge that is introduced by adopting the dupuit approximation specifically the problem of flow in the bottom aquifer of a two aquifer system is studied where flow is caused by a piecewise constant head in the top aquifer the difference between the exact and dupuit solutions is small if the leakage factor a characteristic length of the aquifer system is large relative to the thickness of the aquifer even for anisotropic hydraulic conductivities the accuracy of discharges obtained with a dupuit solution improves when the aquifer is divided up in a number of layers separated by leaky layers representing the vertical resistance to flow of the aquifer in a second comparison analytic dupuit solutions are compared to numerical dupuit solutions obtained with the finite difference method to determine reasonable cell sizes and domain sizes for finite difference models accurate discharges were obtained with the finite difference method when the cell size is chosen equal to or smaller than the smallest leakage factor and the domain size is at least six times the largest leakage factor both a two aquifer system with one leakage factor and a three aquifer system with two leakage factors were studied

geological overview and cratering model for the haughton impact structure devon island canadian high arctic the haughton impact structure has been the focus of systematic multi disciplinary field and laboratory research activities over the past several years regional geological mapping has refined the sedimentary target stratigraphy and constrained the thickness of the sedimentary sequence at the time of impact to 1880 m new 40ar 39ar dates place the impact event at 39 ma in the late eocene haughton has an apparent crater diameter of 23 km with an estimated rim final crater diameter of 16 km the structure lacks a central topographic peak or peak ring which is unusual for craters of this size geological mapping and sampling reveals that a series of different impactites are present at haughton the volumetrically dominant crater fill impact melt breccias contain a calcite anhydrite silicate glass groundmass all of which have been shown to represent impact generated melt phases these impactites are therefore stratigraphically and genetically equivalent to coherent impact melt rocks present in craters developed in crystalline targets the crater fill impactites provided a heat source that drove a post impact hydrothermal system during this time haughton would have represented a transient warm wet microbial oasis a subsequent episode of erosion during which time substantial amounts of impactites were removed was followed by the deposition of intracrater lacustrine sediments of the haughton formation during the miocene present day intracrater lakes and ponds preserve a detailed paleoenvironmental record dating back to the last glaciation in the high arctic modern modification of the landscape is dominated by seasonal regional glacial and niveal melting and local periglacial processes the impact processing of target materials improved the opportunities for colonization and has provided several present day habitats suitable for microbial life that otherwise do not exist in the surrounding terrain

hf zr and ree partition coefficients between ilmenite and liquid implications for lunar petrogenesis hf zr and ree partition coefficients between ilmenite and coexisting liquid were determined under near lunar conditions ilmenite was synthesized at 1125 c under low oxygen fugacity fo2 10 12 4 from glass of a high ti mare basalt composition doped with 50 100 g g of ree and hf and 500 1000 g g of zr the partition coefficients d of ilmenite for hf and zr obtained by isotope dilution analysis are 0 41 and 0 33 respectively these values are significantly lower than those of ilmenite 3 0 and 1 8 respectively from a kimberlite megacryst fujimaki et al 1984a dree for the synthesized ilmenite are slightly smaller than those of ilmenite from the kimberlite megacryst and the dlu is 0 056 these results suggest that ilmenite may have played an important role in the lu hf evolution of lunar mare basalts using newly determined dlu and dhf for ilmenite the lu hf evolution or lunar cumulates and the coexisting magma was examined for several different crystallization sequences by a model calculation the lu hf variation trend of most high ti mare basalts is well explained by a small degree less than 5 of partial melting of the cumulates however a higher degree of partial melting is required to explain the variation of very low ti basalts green glass and apollo 12 low ti basalts apollo 15 low ti basalts could not be produced by simple partial melting but may require chromite crystallization as well

co2 release due to impact devolatilization of carbonate results of shock experiments a study of pure single crystal calcite shocked to pressures from 9 0 to 60 8 gpa was conducted to address contradictory data for carbonate shock behavior the recovered materials were analyzed optically and by transmission electron microscopy tem as well as by thermogravimetry tga x ray diffraction xrd and raman spectroscopy in thin section progressive comminution of calcite is observed although grains remain birefringent to at least 60 8 gpa tga analysis reveals a positive correlation between percent of mass loss due to shock and increasing shock pressure r 0 77 and suggests that shock loading leads to the modest removal of structural volatiles in this pressure range xrd patterns of shocked iceland spar samples produce peaks that are qualitatively and quantitatively less intense more diffuse and shift to lower o2 however the regularity observed in these shocked powder patterns suggests that structures with very uniform unit cell separations persist to shock pressures as high as 60 8 gpa raman spectral analyses indicate no band asymmetry and no systematic peak shifting or broadening tem micrographs display progressively diminishing crystallite domain sizes selected area electron diffraction saed patterns reveal no signatures of amorphous material these data show that essentially intact calcite is recovered at shock pressures up to 60 8 gpa with only slight mass loss 7 this work suggests that the amount of co2 gas derived from shock devolatilization of carbonate by large meteorite impacts into carbonate targets has been substantially overestimated

the nature of the groundmass of surficial suevite from the ries impact structure germany and constraints on its origin surficial suevites from the ries impact structure have been investigated in the field and using optical and analytical scanning electron microscopy the groundmass of these suevites comprises calcite clay minerals impact melt glass crystallites plagioclase garnet and pyroxene francolite and ba phillipsite the latter zeolite is a secondary phase abundant textures have been observed intricate flow textures between the various groundmass phases globules of each phase in the other phases spheroids of pyrrhotite in calcite the budding off of clay globules into silicate glass and or calcite euhedral overgrowths of francolite on apatite clasts and quench textured crystallites in the groundmass groundmass forming calcite displays higher feo mno and sio2 contents than limestone target material the composition of suevite clay minerals is highly variable and not always consistent with montmorillonite three types of glasses are distinguished in the groundmass type 1 glasses are sio2 rich and are clearly derived from sandstones in the sedimentary cover while the protoliths of the other two glass types remains unclear analytical data and micro textures indicate that the calcite silicate glass francolite and clay minerals of the groundmass of the ries suevites represent a series of impact generated melts that were molten at the time of and after deposition on cooling plagioclase pyroxene and garnet crystallized from the groundmass these results are at variance with the current traditional descriptive definition of suevite given that ries is the original type occurrence of suevite some modification to the traditional definition may be in order as the results of this study are most consistent with the groundmass of ries surficial suevites representing a mix of several types of impact generated melts we suggest that a possible origin for these suevites is as some form of impact melt flow s that emanated from different regions of the evolving crater

ries crater and suevite revisited observations and modeling part i observations we report results of an interdisciplinary project devoted to the 26 km diameter ries crater and to the genesis of suevite recent laboratory analyses of crater suevite occurring within the central crater basin and of outer suevite on top of the continuous ejecta blanket as well as data accumulated during the past 50 years are interpreted within the boundary conditions imposed by a comprehensive new effort to model the crater formation and its ejecta deposits by computer code calculations artemieva et al 2013 the properties of suevite are considered on all scales from megascopic to submicroscopic in the context of its geological setting in a new approach we reconstruct the minimum maximum volumes of all allochthonous impact formations 108 116 km3 of suevite 14 22 km3 and the total volume of impact melt 4 9 8 0 km3 produced by the ries impact event prior to erosion these volumes are reasonably compatible with corresponding values obtained by numerical modeling taking all data on modal composition texture chemistry and shock metamorphism of suevite and the results of modeling into account we arrive at a new empirical model implying five main consecutive phases of crater formation and ejecta emplacement numerical modeling indicates that only a very small fraction of suevite can be derived from the primary ejecta plume which is possibly represented by the fine grained basal layer of outer suevite the main mass of suevite was deposited from a secondary plume induced by an explosive reaction fuel coolant interaction of impact melt with water and volatile rich sedimentary rocks within a clast laden temporary melt pool both melt pool and plume appear to be heterogeneous in space and time outer suevite appears to be derived from an early formed melt rich and clast poor plume region rich in strongly shocked components melt clasts and originating from an upper more marginal zone of the melt pool crater suevite is obviously deposited from later formed clast rich and melt poor plumes dominated by unshocked and weakly shocked clasts and derived from a deeper central zone of the melt pool genetically we distinguish between primary suevite which includes dike suevite the lower sublayer of crater suevite and possibly a basal layer of outer suevite and secondary suevite represented by the massive upper sublayer of crater suevite and the main mass of outer suevite

a case study of impact induced hydrothermal activity the haughton impact structure devon island canadian high arctic the well preserved state and excellent exposure at the 39 ma haughton impact structure 23 km in diameter allows a clearer picture to be made of the nature and distribution of hydrothermal deposits within mid size complex impact craters a moderate to low temperature hydrothermal system was generated at haughton by the interaction of groundwaters with the hot impact melt breccias that filled the interior of the crater four distinct settings and styles of hydrothermal mineralization are recognized at haughton a vugs and veins within the impact melt breccias with an increase in intensity of alteration towards the base b cementation of brecciated lithologies in the interior of the central uplift c intense veining around the heavily faulted and fractured outer margin of the central uplift and d hydrothermal pipe structures or gossans and mineralization along fault surfaces around the faulted crater rim each setting is associated with a different suite of hydrothermal minerals that were deposited at different stages in the development of the hydrothermal system minor early quartz precipitation in the impact melt breccias was followed by the deposition of calcite and marcasite within cavities and fractures plus minor celestite barite and fluorite this occurred at temperatures of at least 200 c and down to 100 120 c hydrothermal circulation through the faulted crater rim with the deposition of calcite quartz marcasite and pyrite occurred at similar temperatures quartz mineralization within breccias of the interior of the central uplift occurred in two distinct episodes 250 down to 90 c and 80 c appreciation of the structural features of impact craters has proven to be key to understanding the distribution of hydrothermal deposits at haughton

diverse lithologies and alteration events on the rim of noachian aged endeavour crater meridiani planum mars in situ compositional evidence we report the results of geological studies by the opportunity mars rover on the endeavour crater rim four major units occur in the region oldest to youngest the matijevic shoemaker grasberg and burns formations the matijevic formation consisting of fine grained clastic sediments is the only pre endeavour impact unit and might be part of the noachian etched units of meridiani planum the shoemaker formation is a heterogeneous polymict impact breccia its lowermost member incorporates material eroded from the underlying matijevic formation the shoemaker formation is a close analog to the bunte breccia of the ries crater although the average clast sizes are substantially larger in the latter the grasberg formation is a thin fine grained homogeneous sediment unconformably overlying the shoemaker formation and likely formed as an airfall deposit of unknown areal extent the burns formation sandstone overlies the grasberg but compositions of the two units are distinct there is no evidence that the grasberg formation is a fine grained subfacies of the burns formation the rocks along the endeavour crater rim were affected by at least four episodes of alteration in the noachian and early hesperian i vein formation and alteration of preimpact matijevic formation rocks ii low water rock alteration along the disconformity between the matijevic and shoemaker formations iii alteration of the shoemaker formation along fracture zones and iv differential mobilization of fe and mn and caso 4 vein formation in the grasberg and shoemaker formations episodes ii and iii possibly occurred together but i and iv are distinct from either of these

fluidization and hydrothermal alteration of the suevite deposit at the ries crater west germany and implications for mars the formation cooling and alteration of the impact ejecta deposits at the ries crater are an analog for impact processes and the formation of regoliths and soils on mars we have studied the suevite deposit an impact melt bearing breccia found outside of the crater rim this suevite contains large numbers of chimney like degassing pipes apparently formed by high gas pressures in the hot 500 c fluidized suevite immediately after deposition of the suevite the likely sources of the gas are volatiles from the melted and shocked basement inclusions the suevite outside of the crater rim contains about 15 wt clay indicating a large amount of alteration of the suevite the clay is an fe rich montmorillonite with less than 5 interstratified illite indicating that the temperature at which most of the alteration occurred was less than 100 130 c the duration of this low temperature period may have been extended by additional heating from the exothermal alteration reactions the surfaces of the degassing pipes are not altered to clays however but have a thin fe rich oxide or hydroxide coating the absence of alteration in the pipes suggests that the main alteration event outside the crater occurred under unsaturated conditions such that the walls of the pipes were dry suevite deposits are likely to exist on mars because of the presence of volatile rich target rock martian suevites may have also been fluidized and hydrothermally altered contributing significantly to the formation of the clay like phases inferred to exist in the martian soil

mineralogy and petrology of melt rocks from the popigai impact structure siberia the late eocene popigai impact structure of siberia comprises a 0 5 1 5 km thick 100 km diameter sequence of clast rich and clast poor andesitic to rhyolitic impact melt rocks and impact breccias underlain by archean to proterozoic crystalline basement and proterozoic to phanerozoic sedimentary rocks the fine grained to cryptocrystalline texture of the more melt rich rocks despite their occurrence in bodies locally in excess of 800 m thick and 28 km long suggests that the melt crystallized in response to 1 cooling by the clast load and or 2 rapid nucleation on finely brecciated clasts which have since been assimilated and or 3 crystallization enhanced by the relatively low water contents of the melts rapid crystallisation of the melt is indicated by the lack of zoning in minerals the presence of glass the lack of strain recovery features in clasts and the lack of evidence for fractionation in the major and trace elements including the rare earth elements optical and analytical electron microscopy reveal that the previously reported division of the melt rocks into high and low temperature variants based on hand sample appearance or glass content is not warranted clasts within the melt rich rocks exhibit a wide range of shock metamorphic features though they are not distributed in the impact melts in a systematic manner this indicates that the melt rich rocks were well mixed during their formation thus juxtaposing unshocked with shocked material injection of mesostasis melt into partially melted checkerboard plagioclase and orthopyroxene clasts also occurred during this mixing stage

igneous rocks formed by hypervelocity impact abstract igneous rocks are the primary building blocks of planetary crusts most igneous rocks originate via decompression melting and or wet melting of protolith lithologies within planetary interiors and their classification and compositional petrographic and textural characteristics are well studied as our exploration of the solar system continues so too does the inventory of intrusive and extrusive igneous rocks settings and processes the results of planetary exploration have also clearly demonstrated that impact cratering is a ubiquitous geological process that has affected and will continue to affect all planetary objects with a solid surface whether that be rock or ice it is now recognized that the production of igneous rocks is a fundamental outcome of hypervelocity impact the goal of this review is to provide an up to date synthesis of our knowledge and understanding of igneous rocks formed by hypervelocity impact following a brief overview of the basics of the impact process we describe how and why melts are generated during impact events and how impact melting differs from endogenic igneous processes while the process may differ we show that the products of hypervelocity impact can share close similarities with volcanic and shallow intrusive igneous rocks of endogenic origin such impact melt rocks as they are termed can display lobate margins and cooling cracks columnar joints and at the hand specimen and microscopic scale such rocks can display mineral textures that are typical of volcanic rocks such as quench crystallites ophitic porphyritic as well as features such as vesicles flow textures and so on historically these similarities led to the misidentification of some igneous rocks now known to be impact melt rocks as being of endogenic origin this raises the question as to how to distinguish between an impact versus an endogenic origin for igneous like rocks on other planetary bodies where fieldwork and sample analysis may not be possible and all that may be available is remote sensing data while the interpretation of some impact melt rocks may be relatively straightforward e g for clast rich varieties and those with clear projectile contamination we conclude that distinguishing between impact and endogenic igneous rocks is a non trivial task that ultimately may require sample investigation and analysis to be conducted caution is therefore urged in the interpretation of igneous rocks on planetary surfaces

40ar 39ar laser probe dating of the central european tektite producing impact event a new 40ar 39ar data set is presented for tektites from the central european strewn field moldavites this is the only strewn field that is entirely situated in a continental environment and still characterized by scattered ages 14 15 3 myr the main objectives of the study were to define more precisely the moldavite formation age and provide a good calibration for a glass standard proposed for fission track dating the laser total fusion ages obtained on chips from 7 individual specimens from the southern bohemian and moravian subfields are restricted to a narrow interval of time with an average of 14 34 0 08 myr relative to the 27 95 0 09 myr of the fish canyon tuff biotite this result gives a more precise age not only for the tektite field but also for its producing impact if the genetic link between the moldavites and the nordlinger ries impact crater is maintained then this new age has to be considered a reliable estimate for the ries crater also this new value places the formation of central european tektites within the lower serravallian period in the latest geologic timescales evidence of their impact products such as glass spherules or shocked minerals can therefore be sought in sedimentary marine formations in a more precisely defined age interval

shock re equilibration of fluid inclusions in crystalline basement rocks from the ries crater germany this study examines the effects of shock metamorphism on fluid inclusions in crystalline basement target rocks from the ries crater germany the occurrence of two phase fluid inclusions decreases from shock stage 0 to shock stage 1 while single phase inclusions increase likely as a result of re equilibration in shock stages 2 and 3 both two phase and single phase inclusions decrease with increasing shock stage indicating that fluid inclusion vesicles are destroyed due to plastic deformation and phase changes in the host minerals however quartz clasts entrained in shock stage 4 melts contain both single phase and two phase inclusions demonstrating the rapid quenching of the melt and the heterogeneous nature of impact deformation inclusions in naturally shocked polycrystalline samples survive at higher shock pressures than those in single crystal shock experiments however fluid inclusions in both experimental and natural samples follow a similar trend in re equilibration at low to moderate shock pressures leading to destruction of inclusion vesicles in higher shock stages this suggests that shock processing may lead to the destruction of fluid inclusions in many planetary materials and likely contributed to shock devolatilization of early planetesimals

impact melting on venus some considerations for the nature of the cratering record abstract modeling the volume of impact melt and its variation with the size of the impact event indicates that for similar sized final craters venusian impacts create about 25 more impact melt than terrestrial impacts more significantly venusian impacts result in approximately a factor of three more impact melt than lunar events producing equivalent sized craters this difference is due to the higher average impact velocity and higher ambient temperatures on venus which enhance impact melt production combined with higher planetary gravity which inhibits crater growth for a given impact event the initial higher intrinsic temperature of incorporated clastic debris also contributes to impact melts with higher initial temperatures lower viscosities and longer cooling times on venus with respect to lunar impact melts the enhanced production of relatively hot low viscosity impact melts under venusian impact conditions may account for the long exterior runout flows and also for the radar smooth interior floors of some venusian craters we also argue that the anomalously deep character of cleopatra may be attributed to drainage of its interior impact melt pool to form the smooth deposits in the adjacent fortuna tessera increasing depth of melting with increasing cavity size resulting in the progressive weakening of transient cavity floor material is offered as a possible explanation for the replacement of uplifted central peaks by rings with increasing crater diameter a consequence of this process is that interior rings will increase in diameter relative to the diameter of the final crater s rim crest with increasing crater size a trend observed on venus and other terrestrial planets this weakening of the target due to relatively enhanced impact melt production in the venusian environment makes it unlikely that orientale style impact basins ever formed on venus

terrestrial chondrules glass spherules and accretionary lapilli from the suevite ries crater germany abstract until recently no terrestrial analogues of meteoritic and lunar chondrules were known only rare glass spherules from the lonar crater india and black magnetic spherules from various localities have been recorded the impact breccia suevite of the no rdlinger ries crater germany contains both chondrules and glass spherules and in addition accretionary lapilli all of which are found imbedded within the fine grained matrix of the suevite the chondrules display many of the textural features characteristic of meteoritic and lunar chondrules lithic chondrules and fluid drop chondrules are present the latter having a composition quite similar to that of glass bombs and glass fragments in the suevite fluid drop chondrules developed from glass spherules by slow devitrification in the hot suevite ejecta masses after deposition on the whole fluid drop chondrules lithic chondrules and glass spherules are rare in the suevite with fluid drop chondrules prevailing detection of chondrules from a terrestrial impact crater supports theories of an impact origin for meteoritic and lunar chondrules accretionary lapilli also represent material formed as a result of impact

shock experiments up to 30 gpa and their consequences on microstructures and magnetic properties in pyrrhotite 1 shock experiments with pressures ranging from 3 to 30 gpa have been conducted on a mixed assemblage of hexagonal and monoclinic pyrrhotite all samples were studied with respect to their particular shock induced microstructures and magnetic properties at high and low temperatures up to 8 gpa microstructures in shocked pyrrhotite are characterized by mechanical deformation producing a damage of the crystal structure at pressures of 20 gpa and upward amorphization and mechanical twinning are the dominant structural features induced by shock within the lower pressure range coercivity saturation isothermal remanent magnetization and coercivity of remanence increase with shock pressures in agreement with more single domain sd like behavior simultaneously the peak of hexagonal pyrrhotite decreases and the 34 k transition of monoclinic pyrrhotite broadens and is depressed magnetic hardening is triggered by grain size reduction but also by the formation of sd within discrete multidomain grains planar deformation features subdivide such multidomain grains into lath shaped domains with average sizes lying in the sd range the planar deformation features disappear at 20 gpa and irregular nanometer sized amorphous domains occur instead pressure release from 30 gpa finally triggers partial melting of pyrrhotite the sharp interfaces between molten and crystalline pyrrhotite document a rapid change of thermal conditions within molten pyrrhotite quenched iron crystals occur the presence of native iron strongly influences the magnetic properties depending on the particular amount in the studied sample and likely affects the magnetic properties of impact lithologies on earth and extraterrestrial material

modeling the ries steinheim impact event and the formation of the moldavite strewn field using detailed geological petrographic geochemical and geographical constraints we have performed numerical modeling studies that relate the steinheim crater apparent diameter da 3 8 km the ries crater da 24 km in southern germany and the moldavite tektite strewn field in bohemia and moravia czech republic lusatia east germany and lower austria the moldavite strewn field extends from 200 to 450 km from the center of the ries to the east northeast forming a fan with an angle of 57 an oblique impact of a binary asteroid from a west southwest direction appears to explain the locations of the craters and the formation and distribution of the moldavites the impactor must have been a binary asteroid with two widely separated components some 1 5 and 0 15 km in diameter respectively we carried out a series of three dimensional hydrocode simulations of a ries type impact the results confirm previous results suggesting that impacts around 30 50 from the horizontal are the most favorable angles for near surface melting and consequently for the formation of tektites finally modeling of the motion of impact produced tektite particles through the atmosphere produces in the downrange direction a narrow angle distribution of the moldavites tektites in a fan like field with an angle of 75 an additional result of modeling the motion of melt inside and outside the crater is the preferred flow of melt from the main melt zone of the crystalline basement downrange towards the east northeast rim this explains perfectly the occurrence of coherent impact melt bodies some tens of meters in size in a restricted zone of the downrange rim of the ries crater the origin of these melt bodies which represent chemically a mixture of crystalline basement rocks similar to the main melt mass contained as melt particles 0 5 m in size in the suevite do not occur at any other portion of the ries crater rim and remained enigmatic until now although the calculated distribution of moldavites still deviates to some degree from the known distribution our results represent an important step toward a better understanding of the origin and distribution of the high velocity surface melts and the low velocity deep seated melt resulting from an oblique impact on a stratified target

the suevite conundrum part 1 the ries suevite and sudbury onaping formation compared the term suevite has been applied to various impact melt bearing breccias found in different stratigraphic settings within terrestrial impact craters suevite was coined initially for impact glass bearing breccias from the ries impact structure germany which is the type locality various working hypotheses have been proposed to account for the formation of the ries suevite deposits over the past several decades with the most recent being molten fuel coolant interaction mfci between an impact melt pool and water this mechanism is also the working hypothesis for the origin of the bulk of the onaping formation at the sudbury impact structure canada in this study the key characteristics of the ries suevite the onaping formation and mfci deposits from phreatomagmatic volcanic eruptions are compared the conclusion is that there are clear and significant lithological stratigraphic and petrographic observational differences between the onaping formation and the ries suevite the onaping formation however shares many key similarities with mfci deposits including the presence of layering their well sorted and fine grained nature and the predominance of vitric particles with similar shapes and lacking included mineral and lithic clasts these differences argue against the viability of mfci as a working hypothesis for genesis of the ries suevite and for a required alternative mechanism for its formation

bunte breccia of the ries continuous deposits of large impact craters the ries crater an impact structure of 26 km diameter in south germany is the largest terrestrial crater where substantial amounts of ejecta are preserved on occasion 100 m deep further the target stratigraphy is well known and it is possible to relate specific clasts and breccia lithologies to initial target depth as a consequence the continuous deposits of the ries also known as bunte breccia may be studied with exceptional field control we report field observations and laboratory analyses obtained from 560 m core materials taken at nine different locations that range from 16 to 37 km in radial distance from the impact center the objective is to relate the ries observations to ejection and to emplacement processes of large scale planetary crater deposits the observations regarding the modal stratigraphic characteristics of the bunte breccia may be summarized as follows only 600 m some 0 7 is composed of triassic clasts originating from 300 to 600 m depths lower and middle jurassic horizons approximately 300 150 m constitute some 2 3 and upper jurassic 0 150 m makes up some 31 5 in addition the bunte breccia contains tertiary materials in the form of 1 cm clasts 29 1 and as highly comminuted fine grained matrix 10 gpa constitute 0 1 weight of the entire deposit which indicates that bunte breccia was emplaced at essentially ambient temperatures when possible the above observations are quantified via linear regressions throughout the text all of these observations are consistent with if not predicted by a ballistic emplacement scenario as postulated by oberbeck and co workers primary crater ejecta are expelled ballistically and will form secondary craters in the local substrate a mixture of primary and secondary ejecta results and combines into a highly turbulent ground hugging debris surge as the final phase of ejecta emplacement total emplacement time for the bunte breccia 200 km is estimated to be of the order of 5 min only these findings are compared with cratering theory relating to a number of ejecta thickness decay models and with the so called z model addressing material flow during various stages of crater formation qualitative to fair agreement of observations and predictions results an initial crater radius of 6 5 km an excavation depth of 1650 m an excavation volume of 136 km and an associated transient cavity volume of aproximately 230 km appear to be reasonable estimates approximately 170 km of material was involved in slumping and restoration of the transient cavity for the above radius and z 2 7 the modal composition of ries ejecta with regard to preimpact target stratigraphy indicates that materials contained in the continuous deposits of large complex planetary craters are predominantly derived from depths as small as one hundredth the apparent crater diameter a number of implications are addressed regarding remote sensing of planetary surfaces and investigation of lunar and meteoritic impact breccias

definition of sinkhole triggers and susceptibility based on hydrogeomorphological analyses sinkholes represent a geological risk that is often underrated mainly due to its very localized nature in fact sinkholes occur only under particular circumstances and typically affect relatively small areas despite these characteristics the difficulty in forecasting the precise location and timing of their sudden collapse creates serious problems for civil protection authorities and urban planners in this framework identifying the mechanism and thus the triggering factor of sinkholes is strategically pivotal in developing management plans the present paper addresses the sinkhole prone area of il piano elba island central italy the integration of hydrogeological surveys coupled with a thorough study of historical maps and aerial photographs suggests that the main triggering factor in this area may not be related to water pumping from the karst aquifer as initially hypothesized instead sinkholes appear to be caused by ravelling and erosive processes occurring entirely in the sedimentary cover when heavy rainfall induces water overpressure within the superficial aquifer

impact glasses in fallout suevites from the ries impact structure germany an analytical sem study t impact generated glasses from fallout suevite deposits at the ries impact structure have been investigated using analytical scanning electron microscopy approximately 320 analyses of glass clasts were obtained four glass types are distinguished on the basis of composition and microtextures type 1 glasses correspond to the aerodynamically shaped glass bombs studied previously by many workers major oxide concentrations indicate the involvement of granitic rocks amphibolites and minor al rich gneisses during melting type 2 glasses are chemically heterogeneous even within individual clasts with variations of several wt in most of the major oxides e g 57 70 wt sio2 this suggests incomplete mixing of 1 mineral derived melts or 2 whole rock melts from a wide range of lithologies aluminium rich clinopyroxene and fe mg rich plagioclase quench crystals are present in type 1 and 2 glasses respectively type 3 glasses contain substantial amounts of h2o 12 17 wt low sio2 50 53 wt high al2o3 17 21 wt and high cao 5 7 wt contents this suggests an origin due to shock melting of part of the sedimentary cover type 4 glasses form a ubiquitous component of the suevites based on their high sio2 content 85 100 wt the only possible protolith are sandstones in the lowermost part of the sedimentary succession calcite forms globules within type 1 glasses with which it develops microtextures indicative of liquid immiscibility unequivocal evidence also exists for liquid immiscibility between what are now montmorillonite globules and type 1 2 and 4 glasses indicating that montmorillonite was originally an impact melt glass clearly the melt zone at the ries must have incorporated a substantial fraction of the sedimentary cover as well as the underlying crystalline basement rocks impact melts were derived from different target lithologies and these separate disaggregated melts did not substantially mix in most cases type 2 3 and 4 glasses and carbonate melts

the melt rocks of the boltysh impact crater ukraine ussr the 100 12 m y 25 km diameter boltysh impact crater was formed in precambrian granites and granite gneisses of the ukrainian shield the crater deposits have undergone minimal post impact erosion and it is possible to study a complete vertical section of the underlying 200 m thick melt sheet the melt rocks as sampled in two drill holes can be subdivided into two major textural classes microcrystalline and glassy the microcrystalline melt rocks form an uppermost and two lowermost units with the glassy variety occupying the middle of the melt sheet the microcrystalline units contain 25 zoned plagioclase phenocrysts set in a microcrystalline matrix of intergrown alkali feldspar and quartz pyroxene has been replaced by sheet silicates mineral and lithic clasts make up 5 15 and show varying degrees of shock and resorption the glassy melt rocks are characterized by 10 30 zoned plagioclase and 5 10 orthopyroxene set in a fresh to partially devitrified glassy matrix clast content is 5 chemically the melt rocks are relatively homogeneous and correspond to a mixture of kirovograd granites and gneisses in the ratio of 5 to 1 with ni ir and cr showing slight enrichments over the target rocks there are minor differences in the fe2o3 feo ratio and the alkalis between the microcrystalline and glassy varieties the increase in matrix crystallinity at the upper and lower contacts is contrary to observations at other impact melt sheets where greater matrix crystallinity occurs in the interiors of the melt sheets one possible explanation is that the melt matrix was originally glassy throughout due to its high sio2 content and the microcrystalline matrix is the result of extensive devitrification involving minor alkali exchange with circulating ground waters

stable isotope composition of impact glasses from the nordlinger ries impact crater germany abstract the ries impact which today is represented by a 24 km diameter complex crater occurred at 15 ma it is estimated that a projectile of about 1 km diameter formed a transient crater of 6 to 7 km radius and 2 8 km depth impact melt glasses investigated are found within the suevite the breccia that forms the uppermost layers of the ejecta blanket around the crater the glasses are considered to represent quenched melts produced as a result of the impact the oxygen isotope compositions of several glasses sampled from widely spaced localities are very homogeneous with 18 o values in the range of 6 7 to 7 4 and 17 o of 3 3 to 3 7 with increasing devitrification and alteration the 18 o values increase up to 15 8 17 o up to 8 1 water content also increases with devitrification from fresh glasses with about 1 3 wt to 3 8 wt in devitrified glass d values decrease with increasing water content from about 87 to 127 whole rock oxygen isotope compositions of the sedimentary cover sequence range from 17 to 27 and crystalline basement rocks range from 8 8 to 13 5 for granites and gneisses whereas amphibolites have 18 o values of 5 2 and 6 1 models suggesting that the glass in the suevite represents a mixed melt derived from all the rocks present in the suevite in proportion of their occurrence engelhardt 1997 do not agree with the oxygen isotope composition of the glass the simplest explanation for the homogeneous chemical and oxygen isotope composition is that the glass represents quenched melts from a few closely spaced lithologies only high fe and ni contents in the glass cr ni and cr co ratios and relatively low 18 o values indicate involvement of amphibolites during melting the balance of the melt was made up of spatially associated granites or gneisses as indicated by the major element and rare earth element geochemistry the best agreement between major element and oxygen isotope composition of the glass and model melts is obtained by mixtures of amphibolite and granite in proportions similar to their average occurrence in the fallout suevite

shock experiments on pre heated α and β quartz ii x ray and tem investigations quartz single crystals pre heated to different temperatures 20 275 540 and 630 c were experimentally shocked to pressures ranging from 20 to 40 gpa with the shock front propagating parallel to 1010 or 0001 shocked quartz pre heated to 630 c is nearly x ray amorphous at 26 gpa while quartz shocked at room temperature still displays several x ray diffraction lines up to 30 gpa all samples that were still crystalline when shocked above 25 gpa exhibit lattice expansion internal strain and reduced crystallite sizes lattice expansion was up to 1 for the constants a o and co and up to 3 for the cell volume v o quartz shocked parallel to 1010 always shows larger lattice constants and is more strained than quartz shocked parallel to 0001 indicating that shock effects are controlled by the structural anisotropy internal strain is anisotropic with minimum strain in the planes belonging to 1012 the dominant shock defect revealed by tem are sets of parallel lamellae consisting of pure sio 2 glass so called planar deformation features pdfs below 25 gpa pdfs are extremely rare and thin 30 nm at pressures above 25 gpa however pdfs occur frequently and are about ten times thicker this qualitative observation of increasing pdf frequency and thickness with increasing pressure is quantified by calculations of the amount of glass using x ray and density data the results of this study substantiate the crucial role of pdfs for the lattice expansion of quartz and the formation of diaplectic glass and lechatelierite lattice expansion is ascribed to the enormous expansion of pdfs during decompression leading to elastic stretching in adjacent crystalline areas the observation that pdfs occur predominantly parallel to 1012 where minimum strain is present supports this hypothesis the increasing amount of pdfs above 25 gpa is interpreted as the cause for the formation of diaplectic glass shock temperature calculations support the assumption that these pdfs consist under compression of superheated melt the heat is possibly sufficient to melt crystalline areas adjacent to the superheated pdfs at enhanced pressures such molten bands coalesce to a total melt which is quenched upon decompression thus diaplectic glass represents a quenched high pressure melt while lechatelierite sio 2 glass with a fluidal texture is interpreted as quenched low pressure melt

the first day of the cenozoic highly expanded cretaceous paleogene k pg boundary section from the chicxulub peak ring recovered by international ocean discovery program iodp international continental scientific drilling program icdp expedition 364 provides an unprecedented window into the immediate aftermath of the impact site m0077 includes 130 m of impact melt rock and suevite deposited the first day of the cenozoic covered by

the distribution of megablocks in the ries crater germany remote sensing field investigation and statistical analyses the ries crater is a well preserved complex impact crater that has been extensively used in the study of impact crater formation processes across the solar system however its geologic structure especially the megablock zone still poses questions regarding crater formation mechanics the megablock zone located between the inner crystalline ring and outer morphologic crater rim consists of allochthonous crystalline and sedimentary blocks bunte breccia deposits patches of suevite and parautochthonous sedimentary blocks that slumped into the crater during crater modification our remote sensing detection method in combination with a shallow drilling campaign and geoelectric measurements at two selected megablocks proved successful in finding new megablock structures 25 m mean diameter within the upper approximately 1 5 m of the subsurface in the megablock zone we analyzed 1777 megablocks of the megablock zone 81 of which are new discoveries in our statistical analysis we also included 2318 ejecta blocks 25 m beyond the crater rim parautochthonous megablocks show an increase in total area and size toward the final crater rim the sizes of allochthonous megablocks generally decrease with increasing radial range but inside the megablock zone the coverage with postimpact sediments obscures this trend the size frequency distribution of all megablocks obeys a power law distribution with an exponent between approximately 1 7 and 2 3 we estimated a total volume of 95 km3 of bunte breccia and 47 km3 of megablocks ejecta volume calculations and a palinspastic restoration of the extension within the megablock zone indicate that the transient cavity diameter was probably 14 15 km

suevite breccia of the ries impact crater germany petrography chemistry and shock metamorphism of crystalline rock clasts clasts of deep seated crystalline basement rocks in suevites of the ries crater germany were catalogued lithologically and classified with regard to their degree of shock metamorphism the sample suite consisted of 806 clasts from 10 outcrops in fallout suevites and 447 clasts from drill cores encountering crater suevite in the crater interior these clasts can be grouped into seven types of metamorphic and nine types of igneous rocks one hundred forty three clasts representing these lithologies were analyzed for major element bulk composition the fallout suevite contains on average 4 vol of crystalline basement clasts 0 4 vol of sedimentary rocks 16 vol of glass bodies some of them aerodynamically shaped and 79 vol of groundmass on average 52 of all crystalline clasts are from metamorphic sources and 42 are of igneous origin using the shock classification of stoffler 1974 8 of all crystalline clasts appear unshocked 10 gpa and 34 30 and 27 of clasts are shocked to stages i 10 35 gpa ii 35 45 gpa and iii 45 60 gpa respectively the bulk composition of suevite glasses is consistent with the modal proportions of crystalline rock types observed in the clast populations this indicates that the glasses originate by shock fusion of a similarly composed basement the crater suevite contains the same crystalline rock types that occur in the fallout suevites the bore hole nordlingen 1973 yields an average of 62 vol metamorphic and 38 vol igneous rocks the crater suevite differs from fallout suevites by a higher clast glass ratio by preponderance 65 95 of clasts shocked to stage i only and by the absence of aerodynamically shaped glass bodies the source of crystalline clasts and melt particles of suevites is a volume of rocks located deep in the crystalline basement to which the projectile transmittted most of its energy so that only rocks of the basement were shocked by pressures exceeding 10 gpa deep burst impact model fallout suevites were ejected propelled by an expanding plume of vaporized rock and withdrew preferentially from this volume melt and highly shocked clasts leaving in the transient cavity the crater suevite with more clasts of modest shock levels and less melt

coeval argon 40 argon 39 ages of moldavites from the bohemian and lusatian strewn fields 40ar 39ar ages of four tektites moldavites from southern bohemia near cesk budejovice czech republic and a tektite from lusatia near dresden germany have been determined by 11 step degassing experiments the purpose of the study was to enlarge the 40ar 39ar data base of moldavites and to check the age relations of the bohemian and lusatian samples the mean plateau age of the bohemian samples which range from 14 42 to 14 70 ma is 14 50 0 16 0 42 2 ma errors in parentheses include age error and uncertainty of standard monitor age the plateau age of the lusatian sample of 14 38 0 26 0 44 2 ma confirms the previously published 40ar 39ar age of 14 52 0 08 0 40 2 ma and demonstrates that the fall of lusatian and bohemian tektites were contemporaneous because of their geochemistry and their ages there is no doubt that the lusatian tektites are moldavites accepting that moldavites are ejecta from the nrdlinger ries impact the new ages also date the impact event this age is slightly younger about 0 2 0 3 ma than the age suggested by earlier k ar determinations

suevite of the ries crater germany source rocks and implications for cratering mechanics suevites are impact breccias with a montmorillonitic matrix that contains shocked and unshocked mineral and rock fragments from the crystalline basement glass inclusions and a small amount of sedimentary clasts data are given of the modal composition of fall out suevites deposited at isolated points around the crater and crater suevite forming a layer below post impact lake sediments in the crater cavity fall out suevites contain aerodynamically shaped bombs which are absent in crater suevite taking into account not only large glass fragments and bombs but also the finer fractions the glass content of fall out and crater suevites amounts to 47 and 29 vol respectively crystalline clasts in suevites consist of all igneous and metamorphic rock types that constitute the local basement which consists of an upper layer of igneous rocks mainly granites and a lower series of gneisses and amphibolite based on a collection of 1 200 clasts from 13 suevite occurrences the average crystalline clast population of suevites was determined suevites contain on the average 46 igneous and 54 metamorphic clasts in constrast weakly shocked and unshocked crystalline ejecta of the ries structure consist of 82 igneous and 18 metamorphic rocks

carbonate silicate liquid immiscibility upon impact melting ries crater germany the 24 km diameter ries impact crater in southern germany is one of the most studied impact structures on earth the ries impactor struck a triassic to upper jurassic sedimentary sequence overlying hercynian crystalline basement at the time of impact 14 87 0 36 ma storzer et al 1995 the 350 m thick malm limestone was present only to the south and east of the impact site to the north and west the malm had been eroded away exposing the underlying dogger and lias the largest proportion of shocked target material is in the impact melt bearing breccia suevite the suevite had been believed to be derived entirely from the crystalline basement calcite in the suevite has been interpreted as a postimpact hydrothermal deposit from optical inspection of 540 thin sections of suevite from 32 sites i find that calcite in the suevite shows textural evidence of liquid immiscibility with the silicate impact melt textural evidence of liquid immiscibility between silicate and carbonate melt in the ries suevite includes carbonate globules within silicate glass silicate globules embedded in carbonate deformable and coalescing carbonate spheres within silicate glass sharp menisci or cusps and budding between silicate and carbonate melt fluidal textures and gas vesicles in carbonate schlieren a quench crystallization sequence of the carbonate spinifex textured quenched carbonate separate carbonate spherules in the suevite mineral fragment matrix and inclusions of mineral fragments suspended in carbonate blebs given this evidence of liquid immiscibility the carbonate in the suevite therefore has like the silicate melt a primary origin by impact shock melting evidence of carbonate silicate liquid immiscibility is abundant in the suevites from the southwest to east of the ries crater the rarer suevites to the west to northeast of the crater are nearly devoid of carbonate melts this correspondence between the occurrence of outcropping limestones at the target surface and the formation of carbonate melt indicates that the malm limestones are the source rocks of the carbonate impact melt this correspondence shows that the suevites preserve a compositional memory of their source rocks from the regional distribution of suevites with or without immiscible carbonate melts it is inferred that the ries impactor hit the steep albtrauf escarpment at its toe in an oblique impact from the north

impacts do not initiate volcanic eruptions eruptions close to the crater many papers on meteorite impact suggest that large impacts can induce volcanic eruptions through decompression melting of the underlying rocks we perform numerical simulations of the impact of an asteroid with a diameter of 20 km striking at 15 km s 1 into a target with a near surface temperature gradient of 13 k km 1 cold case or 30 k km 1 hot case the impact creates a 250 300 km diameter crater with 10 000 km3 of impact melt however the crater collapses almost flat and the pressure field returns almost to the initial lithostat even an impact this large cannot raise mantle material above the peridotite solidus by decompression statistical considerations also suggest that impacts cannot be the common initiator of large igneous provinces any time in post heavy bombardment earth history

effect of volatiles and target lithology on the generation and emplacement of impact crater fill and ejecta deposits on mars impact cratering is an important geological process on mars and the nature of martian impact craters may provide important information as to the volatile content of the martian crust terrestrial impact structures currently provide the only ground truth data as to the role of volatiles and an atmosphere on the impact cratering process recent advancements based on studies of several well preserved terrestrial craters have been made regarding the role and effect of volatiles on the impact cratering process combined field and laboratory studies reveal that impact melting is much more common in volatile rich targets than previously thought so impact melt rocks melt bearing breccias and glasses should be common on mars consideration of the terrestrial impact cratering record suggests that it is the presence or absence of subsurface volatiles and not the presence of an atmosphere that largely controls ejecta emplacement on mars furthermore recent studies at the haughton and ries impact structures reveal that there are two discrete episodes of ejecta deposition during the formation of complex impact craters that provide a mechanism for generating multiple layers of ejecta it is apparent that the relative abundance of volatiles in the near surface region outside a transient cavity and in the target rocks within the transient cavity play a key role in controlling the amount of fluidization of martian ejecta deposits this study shows the value of using terrestrial analogues in addition to observational data from robotic orbiters and landers laboratory experiments and numerical modeling to explore the martian impact cratering record

compositional variation and mixing of impact melts on microscopic scales we investigated the compositional characteristics of schlieren rich holohyaline impact glasses from ries wabar and meteor crater using a cameca sx 100 scanning electron microprobe this instrument is capable of producing detailed maps of major elements at spatial resolutions of 10 m the objective was to characterize the composition of an unusually large number of individual schlieren and to evaluate details of the process that causes melts of lithologically diverse target rocks to mix on scales of micrometers the ries and meteor crater impacts involved lithologically heterogeneous targets whereas wabar crater formed in relatively uniform dune sand texturally heterogeneous schlieren rich glasses from the ries crater illustrate that schlieren of highly variable color can be surprisingly similar in composition as first detailed by stahle 1972 consistent with these earlier findings most schlieren represent mixtures of diverse rock melts their compositions deviate only subtly from the average melt and do not resemble monomineralic melts nor binary mixtures of major rock forming minerals a specific population of schlieren is enriched in mafic elements mg fe and ca which suggests incomplete homogenization of an amphibolite progenitor in the case of wabar crater a compositionally simple melt of dune sand mixed with projectile iiia iron meteorite materials and specific schlieren are variable mixtures of these two progenitors the optically homogeneous glass from meteor crater is compositionally homogeneous as well which suggests ideal mixing of such diverse lithologies as platform carbonates sandstone and a class iiia iron meteorite the mixing of projectile and target melts at wabar and meteor crater unambiguously demonstrates that melts initially produced in distinctly different stratigraphic structural locations will undergo wholesale mixing if not homogenization also the projectile melts unquestionably formed relatively early in the cratering process and their dissemination throughout the prospective melt volume albeit at variable concentration levels suggests that the entire mixing process may be an early cratering feature this also follows from the fact that we investigated ballistic melt ejecta which thereby eliminates all of those mixing processes that may additionally operate during the pooling and generation of massive melt ponds following gravitational collapse of large structurally complex craters substantial turbulence ranging from field dimensions to microscopic scales seems inescapable to accomplish the observed degree of mixing yet this is not readily inferred from current models of macroscopic material motions during hypervelocity impact