Early fracturing and impact residue emplacement: Can modelling help to predict their location in major craters?

This paper reviews major findings of the Multidisciplinary Experimental and Modeling Impact Crater Research Network (MEMIN). MEMIN is a consortium, funded from 2009 till 2017 by the German Research Foundation, and is aimed at investigating impact cratering processes by experimental and modeling approaches. The vision of this network has been to comprehensively quantify impact processes by conducting a strictly controlled experimental campaign at the laboratory scale, together with a multidisciplinary analytical approach. Central to MEMIN has been the use of powerful two‐stage light‐gas accelerators capable of producing impact craters in the decimeter size range in solid rocks that allowed detailed spatial analyses of petrophysical, structural, and geochemical changes in target rocks and ejecta. In addition, explosive setups, membrane‐driven diamond anvil cells, as well as laser irradiation and split Hopkinson pressure bar technologies have been used to study the response of minerals and rocks to shock and dynamic loading as well as high‐temperature conditions. We used Seeberger sandstone, Taunus quartzite, Carrara marble, and Weibern tuff as major target rock types. In concert with the experiments we conducted mesoscale numerical simulations of shock wave propagation in heterogeneous rocks resolving the complex response of grains and pores to compressive, shear, and tensile loading and macroscale modeling of crater formation and fracturing. Major results comprise (1) projectile–target interaction, (2) various aspects of shock metamorphism with special focus on low shock pressures and effects of target porosity and water saturation, (3) crater morphologies and cratering efficiencies in various nonporous and porous lithologies, (4) in situ target damage, (5) ejecta dynamics, and (6) geophysical survey of experimental craters.

“…The MEMIN experiments yielded results that are very similar to observations in nature, e.g., at Meteor Crater and the Wabar craters (Kearsley et al. ; Mittlefehldt et al. ; Hamann et al.…”

Section: Projectile–target Interactionsupporting

confidence: 74%

Experimental impact cratering: A summary of the major results of the MEMIN research unit

Kenkmann

Deutsch

Thoma

et al. 2018

“…1976; Hörz et al. 1989), Monturaqui crater (e.g., Bunch and Cassidy 1972; Kearsley et al. 2004), and Kamil crater (D’Orazio et al.…”

Section: Discussionmentioning

confidence: 99%

“…In impact melts of Meteor Crater (Arizona, USA), Hörz et al. (2002) and Kearsley et al. (2004) described a decrease in Fe/Ni in meteoritic droplets compared with the composition of the Canyon Diablo meteorite, and a complementary increase in this ratio in the surrounding target melt.…”

Section: Discussionmentioning

confidence: 99%

Chemical modification of projectile residues and target material in a MEMIN cratering experiment

Ebert

Hecht

Deutsch

et al. 2013

Abstract-In the context of the MEMIN project, a hypervelocity cratering experiment has been performed using a sphere of the iron meteorite Campo del Cielo as projectile accelerated to 4.56 km s, and a block of Seeberger sandstone as target material. The ejecta, collected in a newly designed catcher, are represented by (1) weakly deformed, (2) highly deformed, and (3) highly shocked material. The latter shows shock-metamorphic features such as planar deformation features (PDF) in quartz, formation of diaplectic quartz glass, partial melting of the sandstone, and partially molten projectile, mixed mechanically and chemically with target melt. During mixing of projectile and target melts, the Fe of the projectile is preferentially partitioned into target melt to a greater degree than Ni and Co yielding a Fe ⁄ Ni that is generally higher than Fe ⁄ Ni in the projectile. This fractionation results from the differing siderophile properties, specifically from differences in reactivity of Fe, Ni, and Co with oxygen during projectile-target interaction. Projectile matter was also detected in shocked quartz grains. The average Fe ⁄ Ni of quartz with PDF (about 20) and of silica glasses (about 24) are in contrast to the average sandstone ratio (about 422), but resembles the Fe ⁄ Ni-ratio of the projectile (about 14). We briefly discuss possible reasons of projectile melting and vaporization in the experiment, in which the calculated maximum shock pressure does not exceed 55 GPa.

“…Recently, Son and Koeberl (2007) reported detail analyses of 67 impact melt samples collected from the ejecta blanket around the crater rim, but no enrichment of any meteoritic component was seen. Kearsley et al (2004), however, reported the presence of small (<10 µm) iron-nickel particles with a wide range of Fe/Ni ratios (0.02-14.4) within vesicles of Lonar impact melts, but it is not clear whether these fragments represent an indigenous component (may be reduced during impact) or an extraterrestrial contamination (Osae et al 2005). Further work by Son and Koeberl (2007), however, does not confirm any presence of iron-nickel particles within Lonar impact melts.…”

Section: Introductionmentioning

confidence: 92%

Geochemical identification of impactor for Lonar crater, India

Misra

Newsom

Prasad

et al. 2009

available online at http://meteoritics.org Abstract-The only well-known terrestrial analogue of impact craters in basaltic crusts of the rocky planets is the Lonar crater, India. For the first time, evidence of the impactor that formed the crater has been identified within the impact spherules, which are ~0.3 to 1 mm in size and of different aerodynamic shapes including spheres, teardrops, cylinders, dumbbells and spindles. They were found in ejecta on the rim of the crater. The spherules have high magnetic susceptibility (from 0.31 to 0.02 SI-mass) and natural remanent magnetization (NRM) intensity. Both NRM and saturation isothermal remanent magnetization (SIRM) intensity are ~2 Am 2 /kg. Demagnetization response by the NRM suggests a complicated history of remanence acquisition. The spherules show schlieren structure described by chains of tiny dendritic and octahedral-shaped magnetite crystals indicating their quenching from liquid droplets. Microprobe analyses show that, relative to the target basalt compositions, the spherules have relatively high average Fe 2 O 3 (by ~1.5 wt%), MgO (~1 wt%), Mn (~200 ppm), Cr (~200 ppm), Co (~50 ppm), Ni (~1000 ppm) and Zn (~70 ppm), and low Na 2 O (~1 wt%) and P 2 O 5 (~0.2 wt%). Very high Ni contents, up to 14 times the average content of Lonar basalt, require the presence of a meteoritic component in these spherules. We interpret the high Ni, Cr, and Co abundances in these spherules to indicate that the impactor of the Lonar crater was a chondrite, which is present in abundances of 12 to 20 percent by weight in these impact spherules. Relatively high Zn yet low Na 2 O and P 2 O 5 contents of these spherules indicate exchange of volatiles between the quenching spherule droplets and the impact plume. Geochemical identification of impactor for Lonar crater, India