detecting tides and gravity at europa from multiple close flybys 1 this paper presents the expected accuracy of the tides and gravity of europa that can be measured by tracking a spacecraft during close flybys of europa a reference trajectory was designed for flyby science observations and consists of a total of 36 flybys of europa at 100 km altitude earth based doppler measurements were created during 2 hours of each periapsis passage and were simulated with realistic dynamical and measurement assumptions the result shows that the degree 2 tidal love number k2 can be estimated to k2 0 045 and k2 0 009 1 sigma formal uncertainty assuming x band and ka band tracking capabilities respectively which is sufficient to confirm the existence of a global subsurface ocean

pseudotachylitic breccia from the dhala impact structure north central india texture mineralogy and geochemical characterization abstract pseudotachylitic breccia ptb occurs in a drill core from the crater floor of the 11 km diameter proterozoic dhala impact structure india ptbs were intersected in late archean granitoids between 348 15 m and 502 55 m depth in the mcb 10 drill core from the center of the dhala structure the breccias comprise both cataclastic matrix as well as melt breccias the presence of microlites and vesicles in the groundmass and a widely observed flow fabric in the ptb support the presence of melt in the groundmass of some samples clasts in ptb are derived from the archean granitoid basement ptb matrix the matrix of impact melt breccia also occurring between 256 50 m and 502 55 m depth and the target granitoids vary in terms of silica total alkali magnesium and iron oxide contents chondrite normalized ree patterns of ptb and target granitoids are similar but the elemental abundances in the ptb are lower the restricted size of ptb as veins and pods of up to 2 5 cm width their occurrence at varied depths over a core length of 150 m the clast population and the chemical relationships between ptb and their host rocks all suggest the derivation of these breccias locally from the fractured basement granitoids involving in situ melting we favor that this took place due to rapid decompression during the collapse and modification stage of impact cratering with locally additional energy input from frictional heating locally amphibolite and dioritic mylonite occur in the host granitoids and their admixture could have contributed to the comparatively more mafic composition of ptb alteration of these crater floor rocks could have involved preferential reduction of silica and alkali element abundances possibly due to impact induced hydrothermal activity at crater floor level this process too could have resulted in more mafic compositions

order or chaos origin and mode of emplacement of breccias in floors of large impact structures abstract breccias in the crater floor of large impact structures are pseudotachylites sensu largo authigenic monomict and polymict clastic matrix breccias so called footwall breccias and impact melt breccias pseudotachylite bodies in the center of large impact structures e g vredefort dome south africa appear to have a random distribution and orientation but most dip steeply or vertically large bodies of pseudotachylite in the more distal sectors of the 200 km diameter sudbury structure have been interpreted as ring and terrace collapse features in the vredefort dome networks of randomly distributed pseudotachylite veins accompany large mother lode pseudotachylite dikes in general pseudotachylites in the floors of central parts of impact craters may form through explosive transfer of thermal shock energy in a process that could be termed flash replacement melting whereas pseudotachylites at large distances from the centers of large impact structure are believed to have formed through friction leading to partial or complete melting similar to the formation of tectonic pseudotachylites in smaller structures e g ries and slate islands clastic matrix breccias instead of pseudotachylites occur as the most common breccias in the crater floors they have a chaotic distribution pattern their dips are commonly also steep to vertical melt breccia dikes in the target rocks of the crater floor are associated with melt sheets that fill the lower part of the excavation cavity at vredefort erosion has removed the coherent melt sheet but melt breccia dikes vredefort granophyre in the crater floor are preserved they are characterized by a remarkably homogeneous chemical composition and are believed to represent the initial undifferentiated impact melt near the vredefort collar the granophyre forms more or less concentric dikes in the more central parts of the dome their orientation is more random but in places may be controlled by the archean fabric of the crater basement the offset dikes of the sudbury structure are associated with the sudbury igneous complex that represents in total or in part a differentiated impact melt sheet the dikes in many aspects are similar to vredefort granophyres but their interpretation as undifferentiated bulk melt is problematic on geochemical and structural grounds chemically these dikes are not homogeneous and in places they contain massive sulfide deposits that are unlikely components of an undifferentiated impact melt differentiation and precipitation of massive sulfides are slow processes compared with the presumably high energy and fast emplacement of a supposedly undifferentiated melt pseudotachylites of the central impact crater apparently are mainly produced in the compression phase of the impact process whereas clastic matrix breccias form during the uplift and crater modification phases impact melt breccia dikes contain pseudotachylite bearing inclusions and cut across pseudotachylite bodies such impact melt breccia dikes were probably emplaced during uplift and crater modification

the history of danube loess research the loess paleosol sequences of the danube basin contain the longest and most complete terrestrial records of middle and late pleistocene paleoclimates in europe consequently it is no surprise that scientific research into european loess began in this region and has a long and distinguished history european loess research was initiated by count marsigli in the serbian vojvodina in the late 17th century formed the focus of the international loess commission which straddled both sides of the iron curtain from 1961 and culminated with george kukla s seminal studies in the 1970s correlating the loess archives with deep sea sediments the rise in popularity of the longer chinese loess sequences in the early 1980s shifted the international research focus away from europe and it was not until the change of century that scientific investigation intensified in the region this time with much more sophisticated tools for analysis despite its potential as one of europe s most valuable quaternary archives scientific research into danube loess has until recently been hindered both by landscape heterogeneity and the large number of countries it covers these have presented a major limiting factor in developing a unified research approach for decades regional national loess stratigraphic models were defined separately difficulties in correlating such schemes persist especially since these often change significantly with advances in dating methodologies a cooperative effort is necessary to synthesize the available data which requires not only the insights from but also the perspective provided by an appreciation of the history of the research in this study we present a critical historical overview of loess research in the danube region we classify the major research phases throughout the long tradition of danube loess investigations into five categories 1 the early period late 17th century until 1920 extending from marsigli to penck 2 the classic period 1920 1961 encompassing the contributions of milankovic and the development of pedostratigraphy 3 the modern period 1961 present which oversaw czech innovations and developments in geochronologic methods in particular amino acid racemisation aar and luminescence dating and 4 contemporary research from bronger s unified pedostratigraphy to orbitally tuned timescales finally 5 we present a vision of future danube loess research

an evaluation of geochemical weathering indices in loess paleosol studies abstract applying geochemical proxies as measure for the weathering intensity of paleosols and sediments such as loess the quaternary scientist is confronted with various element ratios that have been proposed in literature this paper gives an overview on the principle of geochemical weathering indices different types of indices are evaluated with respect to the suitability for loess paleosol sequences regarding the special characteristics of this type of sediments and paleosols case examples in this study are key sections in southeastern and eastern europe the loess paleosol sequences batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine which represent archives of the late and mid pleistocene climate change of the region considering element behavior during weathering or diagenesis the chemical proxy of alteration cpa i e the molar ratio al2o3 al2o3 na2o 100 is proposed as the most appropriate index for silicate weathering the cpa was evaluated against commonly used weathering indices including the chemical index of alteration cia the chemical index of weathering ciw the plagioclase index of alteration pia the index b of kronberg and nesbitt and the ba sr and rb sr ratio depth profiles of sr type indices e g ba sr rb sr are likely to be influenced by the dynamics of secondary carbonate on the other hand common na type indices e g cia pia ciw may suffer from uncertainties in separating carbonate ca from silicate ca or from biases due to k fixation illitization the cpa is insensitive against such effects additionally using the cpa as with other na type indices provides the possibility to evaluate the homogeneity of the parent material regarding the relevant host minerals via the a cn k diagram

shock barometry of the siljan impact structure sweden the siljan impact structure in sweden is the largest confirmed impact structure in western europe despite this the structure has been poorly studied in the past and detailed studies of shock metamorphic features in the target lithologies are missing here we present the results of a detailed systematic search for shock metamorphic features in quartz grains from 73 sampled localities at siljan at 21 localities from an area approximately 20 km in diameter located centrally in the structure the orientations of 2851 planar deformation feature sets in 1179 quartz grains were measured observations of shatter cones outside of the zone with shocked quartz extend the total shocked area to approximately 30 km in diameter the most strongly shocked samples recording pressures of up to 20 gpa occur at the very central part of the structure and locally in these samples higher pressures causing melting conditions in the affected rocks were reached pressures recorded in the studied samples decrease outwards from the center of the structure forming roughly circular envelopes around the proposed shock center based on the distribution pattern of shocked quartz at siljan the original transient cavity can be estimated at approximately 3238 km in diameter after correcting for erosion we conclude that the original rim to rim diameter of the siljan crater was somewhere in the size range 5090 km less

the loessic palaeolithic in south tadjikistan central asia its industries chronology and correlation abstract this paper starts with an introductory account of the loessic palaeolithic a term used by the author from 1987 to describe those palaeolithic sites which are associated with very thick loess palaeosol successions following a discussion on movius hypothesis on the lower palaeolithic industry of eurasia a brief description of four major palaeolithic sites in south tadjikistan is given the main sites are kuldara 0 8 ma karatau 1 0 2 ma lakhuti 1 0 13 ma and obi mazar 0 09 ma they represent different periods of slowly evolved pebble culture without new influence from other regions the main features of the stone age industry called karatau culture are as follows the clear pebble technique without prepared core bifacial and levallois techniques dispersion of the pebble tools choppers stone slices wedges unifaces and flakes which are not stable for this form and dimensions the blades are practically absent no series of the tools is observed and they are the side scrapers scrapers on occasion borers points carinate tools the karatau culture is similar to the lower palaeolithic industries of china the karatau culture in south tadjikistan has better geological context than other pebble industries of central and south asia

tectonic versus climatic control on the evolution of a loess paleosol sequence at beremend hungary an integrated approach based on paleoecological clay mineralogical and geochemical data the role of two major factors climate and tectonism in controlling loess paleosol evolution has been evaluated in the present study based on a multi proxy dataset comprising mollusc bulk and clay mineralogical and geochemical data a recent trend has been to use chemical indices such as the chemical index of alteration cia for paleoclimate reconstructions in loess paleosol sequences spanning several hundreds of thousands of years but without any tectonic interpretation possible effects of geodynamic factors on physical erosion chemical weathering and consequently weathering proxies are discussed clearly the relative rates of physical erosion and chemical weathering in a sedimentary environment could be significantly influenced by geodynamic factors and governed not just by climate intensifying tectonic uplift gives rise to enhanced physical erosion leading to increased supply of fresh mineral surfaces having less time to react with weathering agents in theory this process may point towards decreasing chemical weathering in a sequence without any real changes of climate in the studied loess paleosol sequence at beremend hungary a trend of decreasing chemical weathering has been observed which can be explained by a global climate deterioration and accelerating uplift in and around the sedimentary basin increasing dust sedimentation could theoretically also contribute to this process as a result of increasing aridification and wind strength reflecting climate change in weathering records following a non linear amplification the findings refer to the fact that the impact of tectonism should also be taken into consideration in tracing past chemical weathering trends on timescales of hundreds of thousands or millions of years this is because tectonic effects may impose on the cia signal and distort it suggesting a potential bias in reconstructing paleoclimate change based only on this proxy from certain loess sequences associated with young orogenic belts

the impact pseudotachylitic breccia controversy insights from first isotope analysis of vredefort impact generated melt rocks abstract besides impact melt rock several large terrestrial impact structures notably the sudbury canada and vredefort south africa structures exhibit considerable occurrences of a second type of impact generated melt rock so called pseudotachylitic breccia previously often termed pseudotachylite the term today reserved in structural geology for friction melt in shear or fault zones at the vredefort dome the eroded central uplift of the largest and oldest known terrestrial impact structure pseudotachylitic breccia is well exposed with many massive occurrences of tens of meters width and many hundreds of meters extent genesis of these breccias has been discussed variably in terms of melt formation due to friction melting melting due to decompression after initial shock compression decompression melting upon formation collapse of a central uplift or a combination of these processes in addition it was recently suggested that they could have formed by the infiltration of impact melt into the crater floor coming off a coherent melt sheet and under assimilation of wall rock even seismic shaking has been invoked field evidence for generation of such massive melt bodies by friction on large shear fault zones is missing also no evidence for the generation of massive pseudotachylitic breccias in rocks of low to moderate shock degree by melting upon pressure release after shock compression has been demonstrated the efficacy of seismic shaking to achieve sufficient melting as a foundation for massive pseudotachylitic melt generation as typified by the breccias of the sudbury and vredefort structures has so far remained entirely speculative the available petrographic and chemical evidence has thus been interpreted to favor either decompression melting i e in situ generation of melt upon central uplift collapse or the impact melt infiltration hypothesis importantly all the past clast population and chemical analyses have invariably supported an origin of these breccias from local lithologies only here the first rb sr sm nd and u pb isotopic data for vredefort pseudotachylitic breccias and their host rocks in comparison to data for vredefort granophyre impact melt rock are presented they strongly support that the pseudotachylitic breccias were exclusively formed from local precursor lithologies in agreement with earlier isotopic results for sudbury breccia and chemical results for vredefort pseudotachylitic breccias a contribution from a granophyre like impact melt component to form vredefort pseudotachylitic breccia is not indicated the most likely process for the genesis of voluminous pseudotachylitic breccias in large impact structures remains decompression melting upon formation and collapse of the central uplift during the modification stage of impact cratering

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

ice core evidence for a very tight link between north atlantic and east asian glacial climate 1 corresponding millennial scale climate changes have been reported from the north atlantic region and from east asia for the last glacial period on independent timescales only to assess their degree of synchrony we suggest interpreting greenland ice core dust parameters as proxies for the east asian monsoon systems this allows comparing north atlantic and east asian climate on the same timescale in high resolution ice core data without relative dating uncertainties we find that during dansgaard oeschger events north atlantic region temperature and east asian storminess were tightly coupled and changed synchronously within 5 10 years with no systematic lead or lag thus providing instantaneous climatic feedback the tight link between north atlantic and east asian glacial climate could have amplified changes in the northern polar cell to larger scales we further find evidence for an early onset of a younger dryas like event in continental asia which gives

new insights into the p and s wave velocity structure of the d discontinuity beneath the cocos plate summary broad band p and s waves from earthquakes in south america recorded at californian network stations are analysed to image lateral variations of the d discontinuity beneath the cocos plate we apply two array processing methods to the data set a simplified migration method to the p wave data set and a double array method to both the p and s wave data sets allowing us to compare results from the two methods the double array method images a dipping reflector at a depth range from 2650 to 2700 km in the southern part of the study area we observe a step like topography of 100 km to a shallower reflector at about 2600 km depth to the north as well as evidence for a second deeper reflector at a depth range from 2700 to 2750 km in the north results from the simplified migration agree well with those from the double array method similarly locating a large step in reflector depth in a similar location about 2650 km depth in the south and about 2550 km in the north as well as the additional deeper reflector at the depth of about 2750 km in the north waveform modelling of the reflected waves from both methods suggests a positive velocity contrast for s waves but a negative velocity contrast for p waves for the upper reflector in agreement with predictions from mineral physical calculations for a post perovskite phase transition the data also show some evidence for the existence of another deeper reflector that could indicate a double intersection of the geotherm with the post perovskite stability field that is the back transformation of post perovskite to perovskite close to the core mantle boundary

palaeoclimate records 60 8 ka in the austrian and swiss alps and their forelands abstract the european alps and their forelands provide a range of different archives and climate proxies for developing climate records in the time interval 60 8 thousand years ka ago we review quantitative and semi quantitative approaches for reconstructing climatic variables in the austrian and swiss sector of the alpine region within this time interval available quantitative to semi quantitative climate records in this region are mainly based on fossil assemblages of biota such as chironomids cladocerans coleopterans diatoms and pollen preserved in lake sediments and peat the analysis of oxygen isotopes in speleothems and lake sediment records the reconstruction of past variations in treeline altitude the reconstruction of past equilibrium line altitude and extent of glaciers based on geomorphological evidence and the interpretation of past soil formation processes dust deposition and permafrost as apparent in loess palaeosol sequences palaeoclimate reconstructions in the alpine region are affected by dating uncertainties increasing with age the fragmentary nature of most of the available records which typically only incorporate a fraction of the time interval of interest and the limited replication of records within and between regions furthermore there have been few attempts to cross validate different approaches across this time interval to confirm reconstructed patterns of climatic change by several independent lines of evidence based on our review we identify a number of developments that would provide major advances for palaeoclimate reconstruction for the period 60 8 ka in the alps and their forelands these include 1 the compilation of individual fragmentary records to longer and continuous reconstructions 2 replication of climate records and the development of regional reconstructions for different parts of the alps 3 the cross validation of different proxy types and approaches and 4 the reconstruction of past variations in climate gradients across the alps and their forelands furthermore the development of downscaled climate model runs for the alpine region 60 8 ka and of forward modelling approaches for climate proxies would expand the opportunities for quantitative assessments of climatic conditions in europe within this time interval

assessing the potential for measuring europa s tidal love number h 2 using radar sounder and topographic imager data abstract the tidal love number h 2 is a key geophysical measurement for the characterization of europa s interior especially of its outer ice shell if a subsurface ocean is present we performed numerical simulations to assess the potential for estimating h 2 using altimetric measurements with a combination of radar sounding and stereo imaging data the measurement principle exploits both delay and doppler information in the radar surface return in combination with topography from a digital terrain model dtm the resulting radar range measurements at cross over locations can be used in combination with radio science doppler data for an improved trajectory solution and for estimating the h 2 love number our simulation results suggest that the absolute accuracy of h 2 from the joint analysis of reason radar for europa assessment and sounding ocean to near surface surface return and eis europa imaging system dtm data will be in the range of 0 04 0 17 assuming full radio link coverage the error is controlled by the snr budget and dtm quality both dependent on the surface properties of europa we estimate that this would unambiguously confirm or reject the global ocean hypothesis and in combination with a nominal radio science based measurement of the tidal love number k 2 constrain the thickness of europa s outer ice shell to up to 15 km

high pressure phases in an ultramafic rock from mars abstract shock induced melt pockets in the martian meteorite chassigny are completely transformed into a set of high pressure mineral phases previously unknown from ultramafic rocks the major constituents of the earth s mantle ferropericlase amorphous mg fe sio 3 perovskite ringwoodite wadsleyite high pressure phosphate ca 3 po 4 2 and cati 2 o 4 structured chromite were formed by solid state transformation and fractional crystallization upon pressure release from 23 to 10 gpa during shock pressure release the temperatures in the melt pocket dropped to timescales of 10 2 to 10 3 s to allow preservation of the high pressure phases formation and preservation of these phases in chassigny depend on the duration of shock compression which increases with the pre impact burial depth of the meteorite below the martian surface the estimated burial depth of 25 to 250 m is in agreement with the sampling depth of potential source craters for the chassigny meteorite

a centennial reappraisal of the vredefort pseudotachylytes shaken not stirred by meteorite impact major pseudotachylyte zones constitute a spectacular component of the renowned c 2 023 ga vredefort impact structure south africa but it has always been difficult to explain how they were formed in his original account in 1916 shand interpreted the pseudotachylyte as due to cataclasis and frictional heating but pointed out two enigmas that have remained since there were no associated major faults and the pseudotachylyte volumes he observed were far greater than in similar rocks located within faults elsewhere on earth new observations show that the vredefort pseudotachylyte zones were indeed formed by cataclasis and frictional heating not by faulting but owing to impact induced seismic shaking initiated around temporarily loosened blocks in dendritic fracture systems progressive cataclasis of such loose blocks by intense high frequency oscillations of the country rock at the beginning of the cratering process led to size reduction rounding and comminution and frictional melting of feldspars and biotite in the comminuted parts most pseudotachylyte was thus not injected from anywhere but produced in situ the process of seismic shaking is well known from impacts on the moon and asteroids terrestrial earthquakes and nuclear tests but has largely been overlooked in terrestrial cratering except in the theoretical concept of acoustic fluidization

krems wachtberg excavations 2005 12 main profiles sampling stratigraphy and site formation abstract since 2005 detailed archaeological investigations have been carried out at the upper palaeolithic site of krems wachtberg in eastern austria where a well preserved gravettian find layer is embedded in an 8 m high late pleistocene loess sequence the excavations are accompanied by interdisciplinary sampling strategies applied on the main profiles entire sediment series as well as on selected locations within the archaeological context the latter include both evident anthropogenic structures an in situ occupation surface with hearths and burials and periglacial features that together determine the morphology and explain the formation of the main gravettian find horizon

pseudotachylyte controversy fact or friction high speed slip experiments performed on westerly granite using friction welding apparatus reveal that comminution is an essential precursor to melting by friction observations of slip surfaces via analytical scanning electron microscopy sem document the following sequence of events occurring in 2 s with increasing velocity up to 2 m s fracture progressive comminution surface melting of mineral fragments fragment to fragment adhesion and finally production of a fragment laden melt supported suspension explosive dehydration and melting of the epidote group mineral allanite indicates that temperatures of at least 1000 c were realized at the interface this is corroborated by calculation of the temperature rise for the known operating conditions contrary to earlier proposals these results show that comminution and frictional melting are complementary and not mutually exclusive processes depending on the velocity shear stress displacement relations prevailing during frictional slip rocks produced in seismogenic zones can be predominantly comminuted wall rock or fragment melt mixes pseudotachylytes

towards a revised chronostratigraphy of loess in austria with respect to key sections in the czech republic and in hungary abstract the stratigraphic ages of some well known and characteristic paleosols in austrian and hungarian loess sections have been questioned by several workers since the mid 1970s in particular a generally accepted correlation of austrian and hungarian loess stratigraphies with the well established czech loess stratigraphy has not been put forward this paper presents 41 new thermoluminescence tl dates and the first results from amino acid chronology of key sections in these areas the results are in agreement and suggest a new interregional correlation of loess paleosol sequences for loess older than the last interglacial quartz and feldspar inclusions yield more reliable tl ages than the polymineralic fine grain fraction

pseudotachylite in impact structures generation by friction melting and shock brecciation a review and discussion abstract fault related pseudotachylites are generated as the result of brittle or brittle ductile deformation related to seismic faulting it is generally accepted among tectonic workers that while cataclasis plays a role in pseudotachylite formation friction melting is involved in addition pseudotachylite and pseudotachylite like breccias have been repeatedly described from the basement exposures of impact and cryptoexplosion structures and as veinlets in shocked meteorites and lunar samples the relevant literature is reviewed with regard to controversial usage of the term pseudotachylite and attention is drawn to several problematic aspects 1 the term pseudotachylite is currently used both as a purely descriptive term and with genetic implications 2 no unambiguous criteria for comparison and distinction of tectonically and impact generated pseudotachylites have been identified 3 it needs to be considered that in impact structures pseudotachylite could be generated by two distinct processes namely by shock brecciation melting and by friction melting pseudotachylite in impact structures could be the result of either of these two processes or of both 4 it is recommended to adhere more stringently when describing breccias from impact or cryptoexplosion structures to nomenclature accepted for the description of fault rocks in tectonic environments this would help to avoid confusion when discriminating between melt rocks pseudotachylite impact melt rock fragmental breccias cataclasite fragmental impact breccia and mylonitic rocks 5 no criteria for the distinction of melt bearing impact breccias impact melt rock and pseudotachylite have been established either in order to solve these problems close interaction between structural geologists and impact workers is warranted it is suggested that the understanding of breccias in impact structures would be improved by paying particular attention to the temporal relationships between different breccia types this would facilitate recognition of possibly different formational processes for impact produced melt and fragmental breccias and their distinction from pre and post shock deformation products

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

numerical simulation of temperature effects at fissures due to shock loading the localized appearance of specific shock features in target rocks and meteorites such as melt veins and high pressure polymorphs suggests that regions with a local increase in pressure and temperature exist as a shock wave propagates through an inhomogeneous rock in this paper we investigate the effect of planar fissures on the local temperature distribution using numerical simulations time dependent parameters such as temperature pressure and displacement are evaluated the simulation model is based on a shock equation of state for the involved materials dunite and quartzite and simulates geometries that were also used in shock loading experiments an artificial gap between the materials simulates an open fissure at the interface a strong temperature increase occurs at a gap size of 0 1 mm which potentially can cause melting in a thin layer at the interfaces the temperature decreases with decreasing gap size temperature and pressure excursions at the interface are induced by the closure of the gap which causes a second shock wave to superpose the primary wave open fissures and fractures which occur ubiquitously in shallow buried target rocks and projectiles thus act as local pressure and temperature amplyfiers and may be responsible for thin melt vein formation in shocked rocks

paleoenvironments from robust loess stratigraphy using high resolution color and grain size data of the last glacial krems wachtberg record ne austria abstract the complex interplay of dust sedimentation pedogenesis and erosion reworking in the formation of loess paleosol sequences lps challenges paleoenvironmental proxies here we show that color and grain size are essential parameters characterizing loess profiles and support robust stratigraphies as a basis for reconstructions in the context of local geo ecological and large scale paleoclimatic evolution detailed paleoenvironmental records from the period since the arrival of anatomically modern humans to the last glacial maximum are scarce in the alpine surroundings the c 7 5 m thick lps krems wachtberg ne austria known for its well preserved upper paleolithic context at a depth of 5 5 m formed between 40 and 20 ka bp by quasi continuous dust sedimentation interrupted by phases of incipient pedogenesis and local reworking the new kw2015 composite is based on three sections studied and sampled at 2 5 cm resolution color and grain size data support a robust stratigraphy for reconstructions of the pedosedimentary evolution the marked transition from oxidized to reduced paleosols of kw2015 around 34 35 ka corresponds to the middle to upper pleniglacial transition as part of a general cooling trend from marine isotope stage mis 3 to 2 intensely modulated by millennial scale climatic fluctuations as recorded in the greenland ice core data the distinct response of kw2015 to these trends highlights that reconstructing lps evolution based on a robust stratigraphy is a prerequisite to paleoenvironmental proxy interpretation

austrian mis 3 2 loess palaeosol records key sites along a west east transect based on a w e transect through the northern loess regions of austria palaeoenvironmental studies were carried out in three loess palaeosol sequences gunderding krems wachtberg and stillfried b locus typicus to complement available results in the context of a multi methodological approach on the base of previously published datings our study concentrates on the mis 3 2 transition the results of detailed micromorphological investigations prove that palaeopedogenesis frost processes and sedimentation rates differ in their spatial occurrence in the loess belt of austria all three sequences are in line with the general trend of a reduced intensity of pedogenic and cryogenic features from western to south eastern europe which can be explained by lower atlantic moisture influence towards the east interstadial cambic horizons are well developed in the mis 3 sequence of western austria whereas the eastern loess profiles only show weak pedogenesis in all studied sequences frost processes were active during the upper mis 3 and mis 2 the studied mis 2 records are characterised by tundra soils with reductaquic horizons which is a clear sign for prolonged phases of permafrost on the spatial scale the sedimentation rate increases in the eastern loess regions and particularly the krems wachtberg sequence in the centre of the transect experienced an exceptionally high sedimentation rate and can thus be seen as one of the most important high resolution records for the mis 3 2 transition in european loess regions

ejection of martian meteorites we investigated the transfer of meteorites from mars to earth with a combined mineralogical and numerical approach we used quantitative shock pressure barometry and thermodynamic calculations of post shock temperatures to constrain the pressure temperature conditions for the ejection of martian meteorites the results show that shock pressures allowing the ejection of martian meteorites range from 5 to 55 gpa with corresponding post shock temperature elevations of 10 to about 1000 c with respect to shock pressures and post shock temperatures an ejection of potentially viable organisms in martian surface rocks seems possible a calculation of the cooling time in space for the most highly shocked martian meteorite allan hills alh 77005 was performed and yielded a best fit for a post shock temperature of 1000 c and a meteoroid size of 0 4 to 0 6 m the final burial depths of the sub volcanic to volcanic martian rocks as indicated by textures and mineral compositions of meteorites are in good agreement with the postulated size of the potential source region for martian meteorites during the impact of a small projectile 200 m as defined by numerical modeling artemieva and ivanov 2004 a comparison of shock pressures and ejection and terrestrial ages indicates that on average highly shocked fragments reach earth crossing orbits faster than weakly shocked fragments if climatic changes on mars have a significant influence on the atmospheric pressure they could account for the increase of recorded ejection events of martian meteorites in the last 5 ma

mid crustal granulite facies metamorphism in the central kaapvaal craton the bushveld complex connection abstract the numerous greenstone remnants which occur as inclusions in the archaean gneissic granitoid basement exposed in the core of the vredefort dome display evidence of very high grades of granulite facies metamorphism and an unusually complex three stage metamorphic history 1 in metapelites migmatites and refractory restites were produced in a mid crustal 0 5 gpa m1 anatectic event at temperatures in excess of 900 c in the restites 2 in the migmatites the peak metamorphic assemblages are variably overprinted by a high grade retrograde reaction which involved crystallizing anatectic melts m2 3 both the peak metamorphic assemblages and the retrogression textures are cross cut by pseudotachylitic breccia veins which mark a shock metamorphic event associated with the formation of the vredefort dome and 4 the peak metamorphic assemblages and the m2 retrogression textures are overprinted by new generations of remarkably fine grained post shock high grade phases which crystallised at a pressure some 0 25 gpa lower than that of both the peak metamorphic conditions and the retrogression m3 these data indicate an anticlockwise p t evolution where mid crustal anatexis most probably resulted from the intraplating of bushveld complex related ultramafic magmas at 2 06 ga a period of approximately isobaric cooling and retrogression was followed by the vredefort catastrophe which resulted from the impact of a large meteorite into the terrane at 2 02 ga this shock event halted the natural mid crustal metamorphic progression prior to the terrane cooling below 650 c and resulted in the rapid exhumation of the terrane by some 9 km in the process it provided a window into the deep levels of the central kaapvaal craton not seen elsewhere in the region

origin and paleoclimatic significance of late quaternary loess in nebraska evidence from stratigraphy chronology sedimentology and geochemistry muhs d r bettis iii e a aleinikoff j n mcgeehin j p beann j skipp g marshall b d roberts h m johnson w c benton r 2008 origin and paleoclimatic significance of late quaternary loess in nebraska evidence from stratigraphy chronology sedimentology and geochemistry gsa bulletin 120 11 12 1378 1407

probing europa s hidden ocean from tidal effects on orbital dynamics recent observations of europa suggest that the jovian satellite may have a liquid ocean underneath its icy surface geophysical models indicate that the tidal love number k2 has a strong dependence on the presence or absence of an ocean the k2 dependence on the ice shell thickness is also significant measurements of the static and tidal gravity fields through their dynamic effects on the trajectory of a low europan orbiter can be essential in the detection of an ocean and inference of other internal structures covariance analyses have been carried out to assess accuracies using simulated doppler tracking data with 15 days of tracking from 2 earth stations the uncertainties for k2 mantle libration amplitude and the epoch radial position of the spacecraft are expected to be 0 0004 2 8 arcsec and 5 7 m respectively these tight constraints will strongly contribute to ocean detection and ice thickness determination when combined with altimeter measurements

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

can cassini detect a subsurface ocean in titan from gravity measurements abstract recent models of titan s interior predict that the satellite contains an ocean of water and ammonia under an icy layer direct evidence for the presence of an ocean can be provided on the cassini mission only by radio science determination of titan love number k 2 simulations that use the five flybys t11 t22 t33 t45 and t68 the latter two belonging to the extended mission lead to the result that in the elastic case where the love number is real k 2 will be determined with a one sigma accuracy of 0 1 in the viscoelastic case where k 2 is complex the real and imaginary parts of k 2 will be determined with one sigma accuracies of 0 138 and 0 115 respectively ocean and oceanless models that include a viscoelastic rheology are built in the viscoelastic case there is a 93 probability to correctly predict the presence or absence of an ocean this probability improves to 97 in the elastic case

impact induced melting and the development of large igneous provinces abstract we use hydrodynamic modelling combined with known data on mantle melting behaviour to examine the potential for decompression melting of lithosphere beneath a large terrestrial impact crater this mechanism may generate sufficient quantity of melt to auto obliterate the crater melting would initiate almost instantaneously but the effects of such massive mantle melting may trigger long lived mantle up welling that could potentially resemble a mantle hotspot decompression melting is well understood it is the main method advocated by geophysicists for melting on earth whether caused by thinned lithosphere or hot rising mantle plumes the energy released is largely derived from gravitational energy and is outside but additive to the conventional calculations of impact modelling where energy is derived solely from the kinetic energy of the impacting projectile be it comet or asteroid the empirical correlation between total melt volume and crater size will no longer apply but instead there will be a discontinuity above some threshold size depending primarily on the thermal structure of the lithosphere we estimate that the volume of melt produced by a 20 km diameter iron impactor travelling at 10 km s may be comparable to the volume of melt characteristic of terrestrial large igneous provinces 106 km3 similar melting of the mantle beneath an oceanic impact was also modelled by roddy et al int j impact eng 5 1987 525 the mantle melts will have plume like geochemical signatures and rapid mixing of melts from sub horizontal sub crater reservoirs is likely direct coupling between impacts and volcanism is therefore a real possibility that should be considered with respect to global stratigraphic events in the geological record we suggest that the end permian siberian traps should be reconsidered as the result of a major impact at 250 ma auto obliteration by volcanism of all craters larger than 200 km would explain their anomalous absence on earth compared with other terrestrial planets in the solar system

microcomputed tomography and shock microdeformation studies on shatter cones one of the aspects of impact cratering that are still not fully understood is the formation of shatter cones and related fracturing phenomena yet shatter cones have been applied as an impact diagnostic criterion for decades without the role of shock waves and target rock defects in their formation having been elucidated ever we have tested the application of the nondestructive microcomputed tomography ct method to visualize the interior of shatter cones in order to possibly resolve links between fracture patterns and shatter cone surface features striations and intervening valleys shatter coned samples from different impact sites and in different lithologies were investigated for their ct suitability with a shatter cone in sandstone from the serra da cangalha impact structure brazil remaining as the most promising candidate because of the fracture resolution achieved to validate the obtained ct data the scanned specimen was cut into three orthogonal sets of thin sections scans with 13 m resolution were obtained ct scans and microscopic analysis unraveled an orientation of subplanar fractures and related fluid inclusion trails and planar fracture pf orientations in the interior of shatter cones planar deformation features pdf were observed predominantly near the shatter cone surface previously undescribed varieties of feather features ff in the form of lamellae emanating from curviplanar and curved fractures as well as an arrowhead like ff development with microlamellae originating from both sides of a pf were observed the timing of shatter cone formation was investigated by establishing temporal relations to the generation of various shock microscopic effects shatter cones are thus generated post or syn formation of pf ff subplanar fractures and pdf the earliest possible time for shatter cone formation is during the late stage of the compressional phase that is shock wave passage of an impact event

luminescence dating of the stratzing loess profile austria testing the potential of an elevated temperature post ir irsl protocol abstract feldspar infrared stimulated luminescence irsl signals saturate at 2000 gy i e 500 700 ka assuming a dose rate of 3 4 gy ka typical for loess and it is therefore theoretically possible to date middle pleistocene loess however the accuracy of age estimates is hampered by anomalous fading which leads to significant age underestimation fading corrections have been proposed but these corrections are reliant on inherent assumptions and in any case are inapplicable at large doses as the growth curve approaches saturation recent studies have identified a post ir irsl signal that shows less fading and is thus less dependent on accurate fading corrections this study builds upon these investigations and applies a post ir irsl sar dating protocol to polymineral fine grain samples of the loess palaeosol sequence in stratzing lower austria after a preheat at 320 c 60 s and an ir bleach at 50 c 200 s irsl was measured at 290 c for 200 s the same set of conditions were used to measure the response to a test dose recycling ratios recuperation and dose recovery tests show that this protocol is suitable for the loess under investigation although finite residual doses of up to 20 gy are observed for the oldest samples the natural signal is in or close to saturation indicating that fading is negligible in nature this observation is inconsistent with the measured laboratory fading rates of 1 1 5 decade and needs further investigation

osl chronologies of paleoenvironmental dynamics recorded by loess paleosol sequences from europe case studies from the rhine meuse area and the neckar basin abstract loess paleosol sequences lps represent an important terrestrial archive for the reconstruction of the paleoenvironmental evolution during the last glacial cycle in europe in the rhine meuse area and the southwestern germany there are only few numerical ages determined with state of the art luminescence methods which limits the robustness of established chronostratigraphies this study presents a comparative dating approach using quartz and feldspar post infrared pirir 290 optically stimulated luminescence osl from fine and medium grained samples of five loess paleosol sequences paleoenvironmental dynamics are reconstructed by high resolution grain size analysis the osl ages are evaluated as being robust and consistent with other records furthermore we show that ages for hillslope deposits are sometimes overestimated due to low frequency high magnitude erosive processes the integration of osl ages stratigraphy and high resolution grain size data contributes to a temporal more complete data record from western and central europe secondly we propose a combined stratigraphic model for lps of the last glacial cycle which is developed and discussed in the context of other key sites such as havrincourt schwalbenberg ii tonchesberg nussloch and dolni v stonice comparable chronologies and patterns in proxy data between sites with a large spatial distance suggest a possible semi synchronous response to climatic changes in europe by combining our data with the eifel laminated sediment archive elsa and the ngrip ice core a relationship of loess archives and large scale climatic signals is discussed and a proxydata based event stratigraphy is developed this model refines existing chronostratigraphic models and contributes to solve open discussion concerning the timing and demarcation of sedimentary units and sequences from for western and central europe

our oldest children age constraints for the krems wachtberg site obtained from various thermoluminescence dating approaches abstract we present several approaches to directly date the prehistoric human activity of lighting a fire at the early gravettian infant burial site of krems wachtberg austria by thermoluminescence tl methods blue thermoluminescence b tl from polymineral fine grain and orange red thermoluminescence r tl from fine grained quartz separates both extracted from the baked loess immediately underlying the hearth were employed the b tl dating followed the classic multiple aliquot additive dose maad protocol for r tl dating the multiple aliquot regenerative mar and a shortened single aliquot regeneration sar protocol were tested all thermoluminescence ages obtained agree within 1 uncertainties and assign a weighted mean age of 33 9 2 3 ka to the last use of the hearth and by inference to the infant burial anomalous fading is precluded due to the agreement of results from all luminescence protocols as well as with independent dating methods the tl ages are consistent with calibrated radiocarbon ages on associated charcoal osl dating of the sediment deposition and with age estimates obtained by two magnetic dating approaches

paleoenvironmental fluctuations as recorded in the loess paleosol sequence of the upper paleolithic site krems wachtberg abstract the loess paleosol sequence of krems wachtberg is famous for its archeological findings above all its gravettian infant burials it represents a complex system of paleoclimatic fluctuations which is nearly complete and thus enables the correlation with global paleoclimatic records this sequence comprises activity phases with dominant eolian and partly erosional processes as well as stable short periods of weak pedogenesis periglacial environment with drier climate conditions and high eolian sedimentation rates characterize the upper part of the sequence and in periods with lower sedimentation rates cryosols and permafrost induced structures are developed although the krems wachtberg site is situated at a slope position intensive erosional phases events can be excluded the basal parts of the sequence show signs of decalcification bioturbation organic inclusions as well as changes in element distribution pedogenic horizons are partly overprinted by permafrost related structures and are disturbed by redepositional processes to a minor degree remarkably the archeological horizon is not affected by permafrost in contrast to the layers below and above the focus of this study is deciphering stratigraphy by a combination of paleopedological sedimentological analyses with rock magnetic analyses on the chronological scale the sequence records a timespan from 35 ka to 20 ka altogether there is evidence of five pedogenic units and one archeological layer which are correlated with the greenland interstadials gi 7 to gi 2 however an equivalent of a mis 3 interstadial soil comparable with the lohne soil or stillfried b soil could not be detected

danube loess stratigraphy towards a pan european loess stratigraphic model abstract the danube river drainage basin is the second largest river catchment in europe and contains a significant and extensive region of thick loess deposits that preserve a record of a wide variety of recent and past environments indeed the danube river and tributaries may themselves be responsible for the transportation of large volumes of silt that ultimately drive loess formation in the middle and lower reaches of this large catchment however this vast loess province lacks a unified stratigraphic scheme european loess research started in the late 17th century in the danube basin with the work of count luigi ferdinand marsigli since that time numerous investigations provided the basis for the pioneering stratigraphic framework proposed initially by kukla 1970 1977 in his correlations of loess with deep sea sediments loess palaeosol sequences in the middle and lower reaches of the danube river basin were a key part of this framework and contain some of the longest and most complete continental climate records in europe covering more than the last million years however the very size of the danube loess belt and the large number of countries it covers presents a major limiting factor in developing a unified approach that enables continental scale analysis of the deposits local loess palaeosol stratigraphic schemes have been defined separately in different countries and the difficulties in correlating such schemes which often change significantly with advances in age dating have limited the number of basin wide studies a unified basin wide stratigraphic model would greatly alleviate these difficulties and facilitate research into the wider significance of these loess records therefore we review the existing stratigraphic schemes and define a new danube basin wide loess stratigraphy based around a synthetic type section of the mosorin and stari slankamen sites in serbia we present a detailed comparison with the sedimentological and palaeoclimatic records preserved in sediments of the chinese loess plateau with the oxygen isotope records from deep sea sediments and with classic european pleistocene stratigraphic subdivisions the hierarchy of danubian stratigraphic units is determined by climatically controlled environmental shifts in a similar way to the chinese loess stratigraphic scheme a new unified danube loess stratigraphic model has a number of advantages including preventing confusion resulting from the use of multiple national schemes a more transparent basis and the potential to set pleistocene palaeoenvironmental changes recorded in the danube catchment area into a global context the use of a very simple labelling system based on the well established chinese loess scheme facilitates interpretation of palaeoenvironmental information reported from the danube basin loess sites in a wider more accessible context that can be readily correlated world wide this stratigraphic approach also provides for the first time an appropriate framework for the development of an integrated pan european and potentially pan eurasian loess stratigraphic scheme

generation of fragment rich pseudotachylite bodies during central uplift formation in the vredefort impact structure south africa abstract target rocks underlying the central portions of large terrestrial impact structures are characterized by the pervasive presence of fragment rich pseudotachylite bodies debates regarding the formation of these bodies include the origin of pseudotachylitic melts i e friction versus shock induced melting melt mobility causes of target rock fragmentation and timing of fragmentation and melt emplacement with respect to stages of cratering comprehensive structural analysis of pre impact mineral fabrics and properties of fragment rich pseudotachylite in the vredefort dome suggests that melt is allochthonous and was emplaced at an advanced stage of cratering into tensional fracture zones within the crater floor both concentration of bending strains imparted on target rocks during central uplift formation and thermal stresses induced by the emplacement of allochthonous melt led to fragmentation of target rock tensional fracture zones formed in an overall dilational strain field towards the end of cratering likely during collapse of the central uplift and constitute low pressure zones into which melt was forcefully drawn melt may have been drained from the overlying impact melt sheet or from sites within the crater floor and transported into fragment rich dilation zones our field based analysis failed to identify the presence of bona fide shear faults that could potentially have generated in situ frictional melts and fragments rather target rock fragmentation and melt generation that resulted in fragment rich pseudotachylite bodies are processes separated in space and time during cratering

upper palaeolithic occupation in the wachtberg area of krems the evidence of surveys sections and core samples abstract the classic upper palaeolithic location of the wachtberg in krems eastern austria features a multitude of exposures in a limited area of about 50 000 m 2 in addition to gravettian sites which have been investigated in detail in the course of recent years using modern methods there are the records of old excavations several documented sections as well as a considerable number of core samples displaying heterogeneous documentation standards this paper provides an overview of these different sources of information and aims at synthesizing the data for a comprehensive understanding of the local loess sedimentation and palaeolithic occupation

the effects of laterally varying icy shell structure on the tidal response of ganymede and europa we use a finite element model to solve for the response of ganymede and europa to tidal forcing from jupiter using various icy shell models with laterally variable 3 d structure in all cases the shell is assumed to be underlain by a liquid water ocean icy shells with laterally varying thickness are derived from a thermal conduction model three dimensional shear modulus profiles for the shell are built either from a conduction model or for europa by assuming a hemispherical difference in composition icy shell structures with a nonglobal ocean are built for ganymede using these shell structures to calculate the tidal response of ganymede and europa we conclude the following 1 the presence of lateral variations in thickness or in shear modulus would not degrade future attempts to use tidal observations to decide on the existence or absence of a liquid ocean and to determine the mean icy shell thickness 2 given accurate enough observations the presence of lateral variations in thickness or in shear modulus could be determined by searching for nondegree 2 components in the tidal response 3 in the absence of significant viscous convective flow in the shell the effects of a laterally varying shear modulus on the tidal response would be smaller than those of a laterally varying shell thickness 4 if the shell is partially grounded tidal observations of either gravity or uplift would be able to roughly differentiate regions where the ice is grounded from those where it is floating

loess deposits and the conservation of the archaeological record the krems wachtberg example recent archaeological excavations at the upper palaeolithic open air site of krems wachtberg in eastern austria exposed a late pleistocene loess sequence an interdisciplinary sampling strategy was applied to the 8 m high north profile the extraordinary conservation of a gravettian living floor with several complex features is discussed in this paper

interior structure models and tidal love numbers of titan 1 interior models of a differentiated titan with an internal ammonia water ocean and chondritic radiogenic heat production in an undifferentiated rock iron core have been calculated we assume thermal and mechanical equilibrium and calculate the structure of the interior as a function of the thickness of an ice i layer on top of the ocean as well as the moment of inertia factor and the tidal love numbers for comparison with cassini gravity data the love numbers are linearly dependent on the thickness of the ice i shell at constant rheology parameters but decrease by one order of magnitude in the absence of an internal ocean ice shell thicknesses are between 90 and 105 km for models with 5 wt ammonia and for core densities between 3500 and 4500 kg m 3 for 15 wt ammonia the shell is 65 to 70 km thick we use a strongly temperature dependent viscosity parameterization of convective heat transport and find that the stagnant lid comprises most of the ice i shell tidal heating in the warm convective sublayer is of minor importance the internal ocean is several hundred kilometers thick and its thickness decreases with increasing thickness of the ice shell core sizes vary from 1500 to 1800 km radius with associated moment of inertia factors of 0 30 0 01

generation mobilization and crystallization of impact induced alkali rich melts in granitic target rocks evidence from the araguainha impact structure central brazil this paper provides important insights into the generation extraction and crystallization of clast laden impact melt rocks from the araguainha impact structure central brazil despite the mixed nature of the araguainha target rocks comprising a 2 km thick sequence of sedimentary rocks and underlying granitic basement the exposed melt bodies are characterised by an alkali rich granitic matrix embedding mineral and rock fragments derived only from the target granite the melt rocks occur in the form of a massive impact melt sheet overlying the eroded central uplift structure and as melt veins in the granite of the core of the central uplift bulk rock major and trace element data including platinum group elements indicate that the precursor melts were generated locally principally by partial melting of the target granite without any contribution from the sedimentary sequence or the projectile the dense network of melt veins was formed in isolation by selective melting of plagioclase and alkali feldspar within the granite target plagioclase and alkali feldspar melted discretely and congruently producing domains in the matrix of the melt veins which closely match the stoichiometry of these minerals the compositionally discrete initial melt phases migrated through a dense network of microfractures before being assembled into larger melt veins freezing of the melt veins was substantially fast and the melt components were quenched in the form of alkali feldspar and plagioclase schlieren in the matrix of the melt veins the overlying impact melt rock is in contrast characterised by a granophyric matrix consisting of albite sanidine quartz biotite and chlorite in this case melt components appear to have been more mobile and to have mixed completely to form a granitic parental melt we relate the melting of the minerals to post shock temperatures that exceeded the melting point of feldspars

a late mesoproterozoic 40ar 39ar age for a melt breccia from the keurusselka impact structure finland field investigations in the eroded central uplift of the 30 km keurusselka impact structure finland revealed a thin dark melt vein that intersects the autochthonous shatter cone bearing target rocks near the homestead of kirkkoranta close to the center of the impact structure the petrographic analysis of quartz in this melt breccia and the wall rock granite indicate weak shock metamorphic overprint not exceeding 8 10 gpa the mode of occurrence and composition of the melt breccia suggest its formation as some kind of pseudotachylitic breccia 40ar 39ar dating of dark and clast poor whole rock chips yielded five concordant late mesoproterozoic miniplateau ages and one plateau age of 1151 10 ma 11 ma 2 mswd 0 11 p 0 98 considered here as the statistically most robust age for the rock the new 40ar 39ar age is incompatible with 1 88 ga svecofennian tectonism and magmatism in south central finland and probably reflects the keurusselka impact followed by impact induced hydrothermal chloritization of the crater basement in keeping with the crosscutting relationships in the outcrop and the possible influence of postimpact alteration the late mesoproterozoic 40ar 39ar age of 1150 ma should be treated as a minimum age for the impact the new 40ar 39ar results are consistent with paleomagnetic results that suggested a similar age for keurusselka which is shown to be one of the oldest impact structures currently known in europe and worldwide

probing europa s interior with natural sound sources europa s interior structure may be determined by relatively simple and robust seismo acoustic echo sounding techniques the strategy is to use ice cracking events or impacts that are hypothesized to occur regularly on europa s surface as sources of opportunity a single passive geophone on europa s surface may then be used to estimate the thickness of its ice shell and the depth of its ocean by measuring the travel time of seismo acoustic reflections from the corresponding internal strata quantitative analysis is presented with full field seismo acoustic modeling of the europan environment this includes models for europan ambient noise and conditions on signal to noise ratio necessary for the proposed technique to be feasible the possibility of determining europa s ice layer thickness by surface wave and modal analysis with a single geophone is also investigated

sedimentation and erosion processes in middle to late pleistocene sequences exposed in the brickyard of langenlois lower austria abstract the correlation of sedimentary and pedogenetic processes in lower austria is difficult due to significant discontinuities and local variability in soil formation this hampers landscape reconstruction at a regional scale however at a local scale distinct landscape formation processes represented by a shift from fluvial to aeolian deposition can be observed in the brickyard of langenlois lower austria sedimentological and mineralogical analyses in combination with palaeontological finds suggest that the fluvial deposition took place during the middle pleistocene this attribution is confirmed by infra red stimulated luminescence irsl dating which gives a minimum age of 300 ka for the palaeosurface on which the fluvial sediments were deposited this is consistent with a small faunal assemblage including stephanorhinus sp dama sp and an alcine cervid such a fauna is previously unknown in austria it indicates a middle pleistocene interglacial period the low degree of weathering as well as cryosols found in the loess sequence point to loess accumulation during the last glacial the dating results 35 55 ka indicate prolonged loess deposition no signs of pedogenesis could be found this is surprising because in other areas this period is known for weak soil development the lack of soil formation seems to be specific to the western part of lower austria as is the complete erosion of the last glacial maximum lgm loess which can not be found at langenlois

new radiometric ages for the early upper palaeolithic type locality of brno bohunice czech republic comparison of osl irsl tl and 14c dating results new radiometric data are reported from the recent excavation of the type locality of the early upper palaeolithic entity of the bohunician recently obtained radiocarbon 14c data on charcoal are compared with new optically stimulated luminescence osl dating of sediment osl ages were determined on sediment from the archaeological occupation at brno bohunice as well as from the over and underlying loessic sediments multiple techniques were applied which all gave congruent results while a dual protocol post ir osl failed the quality criteria tests ages were obtained by multiple aliquot additive dose maad on polymineral material and single aliquot regeneration sar on fine grain quartz extract as well as on polymineral material fading tests show significant loss of infrared stimulated luminescence irsl after storage for 3 and 12 months for one sample but little or no fading for others the resulting uncorrected age estimates are smaller than those on quartz by osl methods the latter are considered to be more reliable estimates of the sedimentation age of these deposits the measured osl doses do not show a simple distribution and the lowest 5 was used for age calculation to represent the most likely sedimentation age the quartz from the loess overlying the archaeological layer is osl dated to 30 9 3 1 ka while the sediment for the paleosol which contains the archaeological layer gave an age of 58 7 5 8 ka the attribution of this paleosol to the hengelo interstadial is therefore questionable however if the hengelo interstadial is correlated with the dansgaard oeschger d o event 12 statistical agreement within 2 is achieved the osl result for the archaeological layer is in accordance with a weighted average tl date on heated flint artifacts of 48 2 1 9 ka from this layer as well as calibrated radiocarbon data calpal hulu 2007 from nearby locations however radiocarbon data on charcoal samples obtained during excavation at brno bohunice 2002 provide age estimates between 30 and 40 ka 14c years which translate to approximately 33 35 44 ka on the calendric time scale according to the hulu 2007 model for the underlying loess a depositional age of 104 3 10 6 ka was obtained by osl the presented osl ages indicate that a simple correlation of soil sequences between sites within a region has to be verified by chronometric dating

the tidal response of ganymede and callisto with and without liquid water oceans calculations of the tidal responses of ganymede and callisto reveal that tidal amplitudes on these bodies may be as large as a few meters if a liquid ocean exists to decouple the surface ice from the interior tides on ganymede s surface can exceed 7 m peak to peak variation while on callisto the tidal amplitude can exceed 5 m in the presence of a liquid ocean without an ocean tidal amplitudes are less than 0 5 m on ganymede and less than 0 3 m on callisto an orbiting spacecraft using an altimeter for crossover analysis and doppler tracking from earth should be able to achieve sufficient accuracy to identify the tidal amplitude to within about a meter over the course of a few months observing tens of tidal cycles

the nature distribution and genesis of the coesite and stishovite associated with the pseudotachylite of the vredefort dome south africa abstract the vredefort dome represents the uplift centre of a well known 2 00 ga old impact structure of unusually large magnitude shock features like shatter cones planar features and high pressure silica polymorphs are common the present study deals with the description mode of occurrence field distribution and post shock metamorphic alteration of coesite and stishovite which were poorly documented up to now these minerals occur as unusually large crystals in the quartzite of the wall rock in contact with very thin pseudotachylite veins in the pseudotachylite itself which can be interpreted as a friction and or a shock recovery melt fine needles of kyanite are ubiquitous it is proposed that these thin pseudotachylites a type formed during the transit of the shock wave they preceded the development of thick pseudotachylite and microbreccia veins b type which formed during the tensional period which immediately followed from comparison with the model of formation of high pressure polymorphs in porous sandstone it is suggested that higher pressure and stress was concentrated along the a type veins at the arrival of the shock front at this time the quartz was transformed into a high pressure phase which was probably poorly crystalline behind the shock front that is during the rarefaction the pressure was progressively released and the polymorphs crystallized from this initial high pressure phase stishovite crystallized first followed by coesite the high pressure conditions may have lasted an unusually long time due to the magnitude of the vredefort impact this long time probably about one second may account for the large size of the coesite and stishovite crystals most of the high pressure silica polymorphs are corroded to a variable degree by secondary quartz and preserved only in a restricted area of the impact structure this alteration is attributed to post shock metamorphism due to the temperature of the rock before impact plus the heat left after shock recovery some of the evidence put forward by authors against the impact model is discussed according to the facts arising from this investigation it is concluded that an origin by impact remains the simplest and most realistic model to explain the origin of the vredefort dome

luminescence based loess chronostratigraphy of the upper palaeolithic site krems wachtberg austria abstract the loess section krems wachtberg lower austria is well known for its upper palaeolithic find layer which contains a double and a single infant burial the layer containing the grave archaeological horizon ah 4 4 was dated to 26 580 160 14 c bp einwogerer et al 2006 corresponding to ca 31 ka cal bp and is embedded in an 8 m thick loess sequence in order to provide a chronostratigraphy of the entire section 38 samples for luminescence dating were taken at high resolution from below and above the find layer the samples were dated using the quartz coarse grain fraction the quartz fine grain fraction and or the polymineral fine grain fraction the resulting ages are in correct chronostratigraphic order and in case samples were measured with different protocols agree within errors with each other and with the radiocarbon age of the find layer the polymineral fine grain ages are systematically slightly lower than the quartz ages although no fading could be detected in laboratory experiments loess deposition at the site commenced ca 40 ka ago and reaches up to ca 22 ka the ages indicate nearly continuous loess sedimentation throughout this time span short breaks in sedimentation probably exist but cannot be resolved due to the uncertainties of luminescence ages

re os isotope and geochemical study of the vredefort granophyre clues to the origin of the vredefort structure south africa the origin of granophyric rock dikes the vredefort granophyre at the 2 ga vredefort structure in south africa has been controversial they have been interpreted as either impact melt or igneous intrusions most vredefort granophyre samples have considerably higher os contents than the country rocks and 187re 188os and 187os 188os ratios that scatter about a 2 ga isochron their initial 187os 188os ratios at 2 ga overlap the meteoritic data range indicating that all the granophyre samples contain some meteoritic os the re os isotopic composition of the granophyre is significantly different from that of local precursor rocks and indicates that up to 0 2 of a chondritic component could be contained in the granophyre our results confirm the interpretation that the vredefort granophyre represents an impact melt rock

changes in moc and gyre induced atlantic ocean heat transport anthropogenic change of the atlantic meridional ocean heat transport aoht is diagnosed from a large ensemble of climate simulations over the period 1940 2080 as well as its relation to changes in the meridional overturning circulation moc and the gyre circulation in the atlantic internal variability in aoht is closely associated with moc variability the anthropogenic change in aoht however does not follow the forced decrease in the moc thermohaline changes in the intermediate and deep water masses that are formed in the subpolar gyre cause the vertical temperature gradient near the western boundary to increase as a result the heat transport by the baroclinic gyre component largely compensates the decreased heat transport by the moc

thermal orbital evolution of io and europa coupled thermal orbital evolution models of europa and io are presented it is assumed that io europa and ganymede evolve in the laplace resonance and that tidal dissipation of orbital energy is an internal heat source for both io and europa while dissipation in io occurs in the mantle as in the mantle dissipation model of segatz et al 1988 icarus 75 187 two models for europa are considered in the first model dissipation occurs in the silicate mantle while in the second model dissipation occurs in the ice shell in the latter model ice shell melting and variations of the shell thickness above an ocean are explicitly included the rheology of both the ice and the rock is cast in terms of a viscoelastic maxwell rheology with viscosity and shear modulus depending on the average temperature of the dissipating layer heat transfer by convection is calculated using a parameterization for strongly temperature dependent viscosity convection both models are consistent with the present orbital elements of io europa and ganymede it is shown that there may be phases of quasi steady evolution with large or small dissipation rates in comparison with radiogenic heating phases with runaway heating or cooling and oscillatory phases during which the eccentricity and the tidal heating rate will oscillate europa s ice thickness varies between roughly 3 and 70 km dissipation in the silicate layer or 10 and 60 km dissipation in the ice layer suggesting that europa s ocean existed for geological timescales the variation in ice thickness including both convective and purely conductive phases may be reflected in the formation of different geological surface features on europa both models suggest that at present europa s ice thickness is several tens of km thick and is increasing while the eccentricity decreases implying that the satellites evolve out of resonance including lithospheric growth in the models makes it impossible to match the high heat flux constraint for io other heat transfer processes than conduction through the lithosphere must be important for the present io

experimental generation of shock induced pseudotachylites along lithological interfaces to understand the mechanism of formation of shock induced pseudotachylites and particularly the role that rock heterogeneities and interfaces play in their formation shock recovery experiments were carried out on samples consisting of two distinct lithologies dunite and quartzite it was possible to generate melt veins of 1 6 m width along lithological interfaces at moderate shock pressures 6 to 34 gpa the magnitudes of displacement along the interface strain rate and the kinetic heat production indicate that friction is an important heat source that largely contributes to the energy budget of the melt veins the experimentally produced veins resemble natural s type pseudotachylites the geometry of the veins depends on the orientation of the interface with respect to the shock front and includes strong variations in thickness formation of melt pockets and injection veins sudden changes in vein orientation and sharp vein margins two types of melt were observed vesicle free and vesicular melts dense vesicle free melt rock is likely to represent high pressure melts vesicular melts were also generated during shock compression but they remained in a molten state during pressure release and continued shearing intermingling of comminuted olivine and melt suggests that ultracataclasis of olivine induced by a dynamic tensile failure is a precursor stage to frictional melting shock wave interferences at the lithological interface provide the necessary stress conditions to start dynamic failure of olivine the composition of the frictional melts ranges from olivine normative to enstatite normative and is thus largely determined by olivine melting the validity of the sequence of friction melting susceptibilities of rock forming minerals inferred from tectonically produced pseudotachylites is confirmed and can now be applied to ultra high strain rates during shock compression

the influence of pretreatment chemistry on the radiocarbon dating of campanian ignimbrite aged charcoal from kostenki 14 russia the presence of an independently dated marker in an archaeological site offers rare opportunities for assessing the reliability of radiocarbon dates especially when these are close to the age limit of the technique two different pretreatment protocols routine aba and more rigorous abox sc were employed in the chemical preparation of the same charcoal sample from a layer closely associated to the campanian ignimbrite tephra at the russian palaeolithic site of kostenki 14 markina gora the aba treated fraction gave an age of 33 14c ka bp comparable to a previous determination from the same layer whereas the abox sc produced an older age of 35 14c ka bp this is the first radiocarbon determination of an archaeological sample to provide an age consistent with the calendar age for the ci tephra marker

formation of pseudotachylitic breccias in the central uplifts of very large impact structures scaling the melt formation abstract the processes leading to formation of sometimes massive occurrences of pseudotachylitic breccia ptb in impact structures have been strongly debated for decades variably an origin of these pseudotachylite friction melt like breccias by 1 shearing friction melting 2 so called shock compression melting with or without a shear component immediately after shock propagation through the target 3 decompression melting related to rapid uplift of crustal material due to central uplift formation 4 combinations of these processes or 5 intrusion of allochthonous impact melt from a coherent melt body has been advocated our investigations of these enigmatic breccias involve detailed multidisciplinary analysis of millimeter to meter sized occurrences from the type location the vredefort dome this complex archean to early proterozoic terrane constitutes the central uplift of the originally 250 km diameter vredefort impact structure in south africa previously results of microstructural and microchemical investigations have indicated that formation of very small veinlets involved local melting likely during the early shock compression phase however for larger veins and networks it was so far not possible to isolate a specific melt forming mechanism macroscopic to microscopic evidence for friction melting is very limited and so far chemical results have not directly supported ptb generation by intrusion of impact melt on the other hand evidence for filling of dilational sites with melt is abundant herein we present a new approach to the mysterium of ptb formation based on volumetric melt breccia calculations the foundation for this is the detailed analysis of a 1 5 3 0 04 m polished granite slab from a dimension stone quarry in the core of the vredefort dome this slab contains a 37 5 dm3 breccia zone the pure melt volume in 0 1 m3 ptb bearing granitic target rock outside of the several decimeter wide breccia zone in the granite slab was estimated at 5 2 dm3 this amount can be divided into 4 6 dm3 melt 88 for which we have evidenced a limited material transport at maximum 20 cm and 0 6 dm3 melt 12 with at most grain scale material transport which we consider in situ formed shock melt the breccia zone itself contains about 10 dm3 of matrix melt assuming melt exchange over 20 cm at the slab surface between breccia zone and surrounding melt bearing host rock volume the outer melt volume is calculated to contain the same amount of melt as contained by the massive breccia zone meso and microscopic observations indicate melt transport is more prominent from larger into smaller melt occurrences thus melt of the breccia zone could have provided the melt fill for all the small scale ptb veins in the surrounding target rock extrapolating this melt capacity calculation for 1 m3 ptb bearing host rock shows that a host rock volume of this dimension is able to take up some 52 dm3 melt scaling up 1000 fold to the outcrop scale reveals that exchange between a host rock volume of 2 m radius around a 37 m3 breccia zone could involve some 10 m3 melt these results demonstrate that large melt volumes i e large breccia zones can be derived in principle from local reservoirs however strong decompression would have to apply in order to exchange these considerable melt volumes which would only be realistic during the decompression phase of impact cratering upon central uplift formation or locally where compressive regimes acted during the subsequent down and outward collapse of the central uplift

exogenic and endogenic breccias a discussion of major problematics abstract pseudotachylitic breccias impact melt rock ultra cataclasites and even ultramylonites may macroscopically be of very similar appearance even detailed optical microscopic work may not suffice to identify the actual type of melt rock studied the difficulties to distinguish different tectonically produced breccias fault rocks and impact breccias for which no uniformly accepted nomenclature exists are examined and the various formational processes friction melting or shock melting at the macro and micro scales are discussed special emphasis is placed on the occurrence of different and multiple breccia types within impact structures where not only impact induced friction melt and impact melt may occur but where tectonically produced fault rocks that are not related to the impact event may further complicate the breccia situation melting on shatter cone surfaces and its likely formation the proposed origin as distal impact breccia of certain diamictites and problems with carbonate breccias and caused by metamorphic overprint on breccias are discussed it is cautioned not too easily to reach generalized conclusions for example with regard to the usage of the a and b type pseudotachylite terminology areas in need of further breccia studies if possible in close collaboration between impact and tectonic researchers are emphasized

galileo magnetometer measurements a stronger case for a subsurface ocean at europa on 3 january 2000 the galileo spacecraft passed close to europa when it was located far south of jupiter s magnetic equator in a region where the radial component of the magnetospheric magnetic field points inward toward jupiter this pass with a previously unexamined orientation of the external forcing field distinguished between an induced and a permanent magnetic dipole moment model of europa s internal field the galileo magnetometer measured changes in the magnetic field predicted if a current carrying outer shell such as a planet scale liquid ocean is present beneath the icy surface the evidence that europa s field varies temporally strengthens the argument that a liquid ocean exists beneath the present day surface

archean crustal structure of the kaapvaal craton south africa evidence from the vredefort dome abstract crystalline archean basement rocks in the core of the vredefort dome present a profile through a substantial part of the middle and lower crust of the kaapvaal craton previously this profile has been subdivided into two terranes with allegedly distinct lithologies and tectonometamorphic histories that were juxtaposed along a crustal scale late archean brittle ductile thrust zone lithological and structural mapping across the dome indicates however that the basement lithologies share a common polyphase tectonic history culminating in high grade metamorphism and melting at 3 1 ga no evidence was found of the postulated tectonic terrane boundary but the alleged boundary does coincide with a 1 2 km wide transition zone between upper amphibolite facies migmatitic gneisses and more restitic granulite facies gneisses the implications of these results for archean regional tectonic models for the kaapvaal craton are discussed

europa s differentiated internal structure inferences from four galileo encounters radio doppler data from four encounters of the galileo spacecraft with the jovian moon europa have been used to refine models of europa s interior europa is most likely differentiated into a metallic core surrounded by a rock mantle and a water ice liquid outer shell but the data cannot eliminate the possibility of a uniform mixture of dense silicate and metal beneath the water ice liquid shell the size of a metallic core is uncertain because of its unknown composition but it could be as large as about 50 percent of europa s radius the thickness of europa s outer shell of water ice liquid must lie in the range of about 80 to 170 kilometers

micromorphology of middle pleistocene palaeosols in northern italy two long term pleistocene palaeosol sequences oleggio and mezzomerico situated in northern italy were studied by a wide range of pedological methods in both palaeosol sequences six main pedogenic units were identified representing different stages of soil formation in the present study particular emphasis was placed on micromorphological analyses in order to acquire more information about the sequence of pedogenic processes the micromorphological results reveal more precise information about the complex sequence of soil forming processes that led to the formation of each palaeosol furthermore comparison of the micromorphological feature sets of the palaeosols which occur in the same pedogenic units provided an opportunity to refine a recently established pedostratigraphy

thermoluminescence electron spin resonance and14c dating of the late middle and early upper palaeolithic site of geisenklosterle cave in southern germany abstract thermoluminescence tl dating of burnt silex flint chert electron spin resonance esr dating of teeth and 14 c accelerator mass spectrometry ams dating of bones has been carried out on samples from the late middle palaeolithic and early upper palaeolithic levels of the geisenklosterle cave south germany esr dating on tooth enamel from the upper part of level iv which contains a very small undefined middle palaeolithic assemblage yields a mean age of 43 3 4 ka the overlying early aurignacian level iii is placed in the hengelo interstadial by palaeoecological analysis 14 c ams results give a mean age of 38 4 0 85 ka whereas a mean age of 40 2 1 5 ka is obtained by tl of burnt silex confirming the correlation of the early aurignacian level with the hengelo interstadial in oxygen isotope stage ois 3 14 c ams of bone samples from the aurignacian level ii resulted in a mean age of 33 5 0 35 ka whereas the tl ages on burnt silex are again older at c 37 ka these tl results can be taken as an indication of the age underestimation by 14 c caused by the lack of calibration the aurignacian level contains some of the most elaborate symbolic representations from the upper palaeolithic artwork of comparable quality is radiocarbon dated to 31 000 ka at the grotte chauvet thus being significantly younger furthermore the geisenklosterle cave provides evidence of the existence of early rock art in central europe although only small pieces survived erosion the gravettian assemblage of the geisenklosterle cave yielded a mean 14 c ams age of 29 0 0 25 ka

probing europa s third dimension jupiter9s moons are heated by tidal forces induced by its huge gravitational field the results can be spectacular as with io9s highly active volcanic behavior europa a moon farther away and heated less may support a water ocean larger than those on earth in his perspective chapman discusses recent efforts to understand europa9s surface by studying the impact craters that have been observed there the appearance of many craters could be explained if the surface ice layer were 10 to 15 kilometers thick according to recent computer simulations

combining shock barometry with numerical modeling insights into complex crater formation the example of the siljan impact structure sweden siljan central sweden is the largest known impact structure in europe it was formed at about 380 ma in the late devonian period the structure has been heavily eroded to a level originally located underneath the crater floor and to date important questions about the original size and morphology of siljan remain unanswered here we present the results of a shock barometry study of quartz bearing surface and drill core samples combined with numerical modeling using isale the investigated 13 bedrock granitoid samples show that the recorded shock pressure decreases with increasing depth from 15 to 20 gpa near the present surface to 10 15 gpa at 600 m depth a best fit model that is consistent with observational constraints relating to the present size of the structure the location of the downfaulted sediments and the observed surface and vertical shock barometry profiles is presented the best fit model results in a final crater rim to rim diameter of 65 km according to our simulations the original siljan impact structure would have been a peak ring crater siljan was formed in a mixed target of paleozoic sedimentary rocks overlaying crystalline basement our modeling suggests that at the time of impact the sedimentary sequence was approximately 3 km thick since then there has been around 4 km of erosion of the structure

chronology and paleoenvironment of marine isotope stage 3 from two high elevation speleothems austrian alps abstract a new high resolution stable isotope record from the alpine kleegruben cave 2165 m central alps is presented this record largely duplicates a previously reported speleothem record from this site high precision u series thermal ionization mass spectrometry dates constrain the growth history of this new sample 56 48 ka to the marine isotope stage mis 3 both stalagmites reveal highly similar variations in o isotopes that can be directly compared to o isotope variability associated with dansgaard oeschger interstadials recorded in the greenland ice cores greenland interstadials gis based on the new record we refine our previous age assignments of the gis during this time interval i e gis 15b at 55 7 ka gis 15a at 55 3 ka onset mid point of the prominent gis 14 at 54 5 yr and onset of gis 12 at 48 ka the overall uncertainties associated with these ages are 0 1 0 3 ka the timing of these dansgaard oeschger interstadials is within 0 2 ka of the newly proposed grip sfcp04 timescale the age data for both kleegruben stalagmites demonstrate that liquid water was at least seasonally present in the shallow sub surface allowing calcite precipitation to continue even during stadials of mis 3 given the present day low temperature 2 4 c we propose that these unusual speleothems formed in a karst system overlain by a warm based glacier

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

the formation of the sudbury breccia in the north range of the sudbury impact structure abstract in the north range of the ca 1 85 ga sudbury impact structure massive bodies of sudbury breccia cut across the archean levack gneiss complex and early proterozoic matachewan diabase dykes the complex underlies the sudbury igneous complex sic which represents an impact melt sheet that lined the floor of the impact crater the breccia occurs as 1 100 m wide irregular bodies that contain rounded clasts of diabase and tonalitic and dioritic levack gneiss within a fine grained to aphanitic black to dark grey matrix mineral chemical analyses and rietveld analyses based on x ray diffraction patterns show that the breccia matrix contains microclasts of magnesiohornblende oligoclase and quartz surrounded by metamorphic andesine laths actinolite kfeldspar albite and chlorite which crystallized during cooling of the sic on binary oxide sio2 diagrams breccia values plot on a compositional mixing line between those of the more felsic tonalitic gneiss and the more mafic dioritic gneiss and diabase the breccia has concentrations in rare earth elements rees intermediate between those of the dioritic and tonalitic gneisses and a ree pattern with a negative slope that is less pronounced than those of the gneisses this is due to the addition of a minor diabase component that has a slightly negative ree slope suggesting that the breccia is a mix of comminuted tonalitic gneiss dioritic gneiss and minor diabase comminution and cataclasis of these source rocks occurred along pre existing anisotropies and fractures that formed and were reactivated during the growth and collapse of the transient crater the comminuted materials mixed together as large bodies of breccia that were injected in dilational sites that opened during the upward expansion and collapse of the crater

tides on europa and the thickness of europa s icy shell 1 it has been shown previously that measurements of tides on jupiter s moon europa can be used to determine whether there is a liquid ocean beneath this moon s icy outer shell in this paper we examine the further possibility of constraining the thickness of the icy shell in the case where a liquid ocean exists by combining measurements of tidal gravity obtained from tracking an orbiting spacecraft with measurements of vertical tidal surface displacements obtained from a precise onboard altimeter by simulating a 1 month europa mapping mission we demonstrate that this combination of tidal measurements would provide a much better estimate of ice thickness than could be obtained using either tracking or altimeter measurements alone the thickness value inferred from the combined data would also require an estimate of the shear modulus of europa s icy shell this introduces an additional uncertainty in the thickness estimate that is approximately proportional to the uncertainty in the inverse of the shear modulus