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This study introduces an experimental approach using direct laser irradiation to simulate the virtually instantaneous melting of target rocks during meteorite impacts. We aim at investigating the melting and mixing processes of projectile (iron meteorite; steel) and target material (sandstone) under idealized conditions. The laser experiments ( LE) were able to produce features very similar to those of impactites from meteorite craters and cratering experiments, i.e., formation of lechatelierite, partial to complete melting of sandstone, and injection of projectile droplets into target melts. The target and projectile melts have experienced significant chemical modifications during interaction of these coexisting melts. Emulsion textures, observed within projectile-contaminated target melts, indicate phase separation of silicate melts with different chemical compositions during quenching. Reaction times of 0.6 to 1.4 s could be derived for element partitioning and phase-separation processes by measuring time-depended temperature profiles with a bolometric detector. Our LE allow (i) separate melting at high temperatures to constrain primary melt heterogeneities before mixing of projectile and target, (ii) quantification of element partitioning processes between coexisting projectile and target melts, (iii) determination of cooling rates, and (iv) estimation of reaction times. Moreover, we used a thermodynamic approach to calculate the entropy gain during laser melting. The entropy changes for laser-melting of sandstone and iron meteorite correspond to shock pressures and particle velocities produced during the impact of an iron projectile striking a quartz target at a minimum impact velocity of ~6 km s−1, inducing peak shock pressures of ~100 GPa in the target. [ABSTRACT FROM AUTHOR]

Definition and significance of suevite: By definition, suevite is a polymict impact breccia that contains impactderived melt particles in otherwise clastic material [1]. Glassy, lithic and mineral clasts are generally embedded in a particulate, clastic cum melt matrix. The presense of melt particles within polymict breccias is usually easy to identify, and therefore represents an important feature for the recognition of suevite as a proximal impactite in general, but specifically in the field. Suevite records various impact-related effects like rock comminution, different degrees of shock-metamorphism including melting, and the dynamics of crater formation. Furthermore, suevites, and specifically its lithic fragments, may record information on deeply buried lithologies. Suevite is a proximal impactite that occurs within or close to the impact structure. It is usually deposited in the upper part of the ejecta blanket, e.g. [2], [3], or impact melt sheet, e.g. [3], but it may also occur below the impact melt sheet, e.g. [4], [5], or as injections into the crater floor, e.g. [6]. Formation and emplacement models: Detailled studies in the recent years (including of the type example at Ries crater, Germany) have significantly improved our understanding of the formation and emplacement of suevite; however, many different hypotheses are still debated today. Some major hypotheses are (1) collapse of an ejecta plume, e.g. [7-9], (2) deposition via a density flow, e.g. [10], [11], (3) deposition from an impact melt flow, e.g. [12], (4) mixing between fragmented basement and impact melt during outflow, e.g. [4], [5], and (5) collapse of the post-impact phreatomagmatic plume(s) caused by fuel-coolant interaction (FCI) of an impact melt sheet with water or an aquifer, e.g. [13-15]. The co-existence of many different formation and emplacement models of suevite, some of which are controversial, may result from specific studies at different impact environments and conditions, the complexity of the formation process, the general lack of continuous outcrop of suevite deposits, and last not least, from some lack of understanding of the physical processes involved in the formation of such complex material in a highly dynamic environment. In this contribution to the Impact Cratering Workshop, the main existing genetic models of suevite formation will be reviewed and unresolved issues discussed, with some examples. [ABSTRACT FROM AUTHOR]

- We carried out hypervelocity cratering experiments with steel projectiles and sandstone targets to investigate the structural and mineralogical changes that occur upon impact in the projectile and target. The masses of coherent projectile relics that were recovered in different experiments ranged between 58% and 92% of their initial projectile masses. A significant trend between impact energy, the presence of water in the target, and the mass of projectile relics could not be found. However, projectile fragmentation seems to be enhanced if the target contains substantial amounts of water. Two experiments that were performed with 1 cm sized steel projectiles impacting at 3400 and 5300 m s−1 vertically onto dry Seeberger sandstone were investigated in detail. The recovered projectiles are intensely plastically deformed. Deformation mechanisms include dislocation glide and dislocation creep. The latter led to the formation of subgrains and micrometer-sized dynamically recrystallized grains. In case of the 5300 m s−1 impact experiment, this deformation is followed by grain annealing. In addition, brittle fracturing and friction-controlled melting at the surface along with melting and boiling of iron and silica were observed in both experiments. We estimated that heating and melting of the projectile impacting at 5300 m s−1 consumed 4.4% of the total impact energy and was converted into thermal energy and heat of fusion. Beside the formation of centimeter-sized projectile relics, projectile matter is distributed in the ejecta as spherules, unmelted fragments, and intermingled iron-silica aggregates. [ABSTRACT FROM AUTHOR]