The concept of cryo-conditioning in landscape evolution — Comment to the paper published by Ivar Berthling and Bernd Etzelmüller,Quaternary Research 75 (2011) 378–384

The term “cryo-conditioning,” proposed by the authors for classifying specific landform association in periglacial landscapes, needs to be defined more precisely. A starting point could be the proper understanding of the term “Cryo-” in the various compound words found in various disciplines. This is also important for a correct understanding of the proposed concepts, since it concerns one of the most important processes in nature: the phase transition of water between solid and liquid. Cold-temperate transition surfaces in polythermal glaciers and at the permafrost base in their forelands can act as a specific hub between the glacial and periglacial domains.     

Impulse approximation improved

Improved formulas of impulse approximation method for stellar perturbations are derived. The method proposed involves a deflection of the stellar path. It is also applicable to an arbitrary time interval. A comparison of the classical vs improved method is presented both in qualitative discussion and numerical results for Oort cloud cometary orbits.     

Impact cratering and break up of the small bodies of the Solar System

We consider the largest impact craters observed on small satellites and asteroids and the impact disruption of such bodies. Observational data are considered from 21 impact-like structures on 13 satellites and 8 asteroids (target body radii in the range 0.7-265 km). If the radius of the target body is R and the diameter of the largest crater observed on this body D, the ratio D/R is then the main observational parameter of interest. This is found on the observed bodies and compared to data obtained in the laboratory. Taking the largest observed value for D/R as a proxy for the ratio Dc/R (where Dc is the diameter of the largest crater that can be formed on a body without shattering it) it was found that for the observed icy satellites Dc,icy≈1.2R and for the asteroids and the rocky satellites Dc,rocky≈1.6R. In laboratory experiments with ice targets at impactor speeds of 1 to 3 km s⁻¹ we obtained Dc,icy≈1.64R.     

Low‐Ir IAB irons from Morasko and other locations in central Europe: One fall,possibly distinct from IAB‐MG

Differences in texture and discovery location prompted us to analyze 16 irons from Morasko; one from Seeläsgen, known to have a similar composition; and a new mass found at Jankowo Dolne. These were analyzed in duplicate by instrumental neutron‐activation analysis (INAA). The results show that all 18 samples have very similar compositions, distinct from all other IAB irons except Burgavli; we conclude that they are all from a single shower. Eight of the samples were from regions with large amounts of cohenite (but were largely free of inclusions) and six were from samples with very little cohenite; we could find no resolvable difference in composition between these sets, a fact that suggests that the C contents of the metal phases were similar in the two areas. Although Morasko has been classified into the IAB main group (IAB‐MG), its Ir plots well outside the main group field on an Ir‐Au diagram. We considered the possibility that the low Ir reflected contamination by a melt from a IAB region that ponded and experienced fractional crystallization; however, because Morasko has Pt, W, and Ga values that are the same as the highest values in IAB‐MG, we rejected this model. We therefore conclude that Morasko formed from a different melt than the IAB‐MG irons; the Morasko melt was produced by impact heating, but one or more of the main Ir carriers did not melt, leaving much of the Ir in the unmelted residue. Copper is the only element that shows resolvable differences among Morasko samples. Most (13 of 18) samples have 149 ± 4 μg g^?1 Cu, but three have 213 ± 10 μg g^?1; we interpret this to mean that the low‐Cu samples have equilibrated with a Cu‐rich phase, whereas there was none of the latter phase within a few diffusion lengths of the samples with high Cu contents.     

Impact‐related noncoaxial deformation in the Pułtusk H chondrite inferred from petrofabric analysis

Petrofabrics in chondrites have the potential to yield important information on the impact evolution of chondritic parent asteroids, but studies involving chondritic petrofabrics are scarce. We undertook an analysis of the Pu?tusk H chondrite regolith breccia. Measurements of anisotropy of magnetic susceptibility and quantitative tomographic examination of metal grains are presented here and the results are compared with petrographic observations. The major fabric elements are in Pu?tusk shear fractures cutting the light‐colored chondritic clasts as well as brittly and semibrittly deformed, cataclased fragments in dark matrix of regolith breccia. Cataclasis is accompanied by rotation of silicate grains and frictional melting. Fabric of metal grains in chondrite is well defined and coherently oriented over the breccia, both in the clasts and in the cataclastic matrix. Metal grains have prolate shapes and they are arranged into foliation plane and lineation direction, both of which are spatially related and kinematically compatible to shear‐dominated deformational features. We argue that the fabric of Pu?tusk was formed in response to impact‐related noncoaxial shear strain. Deformation promoted brittle cataclastic processes and shearing of silicates, and, simultaneously, allowed for ductile metal to develop foliation and lineation. We suggest that plastic flow is the most probable mechanism for the deformation of metal grains in the shear‐dominated strain field. The process led also to the formation of large metal nodules and bands in the dark matrix of breccia.     

Layer silicates from a rodingite and its blackwall from Przemiłów (Lower Silesia, Poland): Mineralogical record of metasomatic processes during serpentinization and serpentinite recrystallization

Summary Minute inclusions of phlogopite and a chlorite-vermiculite intergrade mineral occur in the vesuvianite from rodingite at Przemiów (Lower Silesia). The same inclusions were found in its blackwall, i.e. outer metasomatic zone formed at the expense of adjacent ultrabasic rock. These findings demonstrate that potassium was released from the rodingite protolith during the Ca-metasomatism that accompanied low-temperature serpentinization and was consumed by phlogopite formed in the rodingite blackwall. Fresh phlogopite persists as small inclusions in vesuvianite. The abundant phlogopite-derived intergrade chlorite-vermiculite in the blackwall documents the potassium-rich composition of the protolith of the rodingite, though its primary chemistry is highly modified during metasomatic processes. The rodingite blackwall can be useful as tracer of the metamorphic and tectonic episodes obscured during complex geological evolution of the ophiolite.

---

Schichtsilikate von Rodingit- Blackwalls aus Przemiów (Niederschlesien, Polen): Mineralogische Dokumentation metasomatischer Prozesse während der Serpentinisierung und der Rekristallisation von Serpentinit

Zusammenfassung Winzige Einschlüsse von Phlogopit und einem K-führenden Chlorit-Vermiculit Mineral wurden in Vesuvian aus Rodingiten von Przemiów (Niederschlesien) gefunden. Dieselben Minerale treten in der sogenannten Blackwall, i.e. der äußeren metasomatischen Zone, die sich auf Kosten der angrenzenden Ultrabasite gebildet hat, auf. Diese Ergebnisse zeigen, daß Kalium aus dem Rodingit-Protolith während der Ca-Metasomatose, die die Niedrig-Temperatur 5erpentinisierung begleitete, freigesetzt wurde und von Phlogopit, der sich in der Blackwall bildete, konsumiert wurde. Frische kleine Phlogopite sind als Einschlüsse in Vesuvian erhalten geblieben. Das aus dem Phlogopit entstandene verbreitete Chlorit-Vermiculit Mineral belegt eine Kaliumreiche Zusammensetzung des Rodingit-Protoliths, obwohl die primäre Chemie durch metasomatische Prozesse stark verändert wurde.

---

---

With 7 Figures     

How selection and weighting of astrometric observations influence the impact probability. The case of asteroid (99942) Apophis

The aim of this paper is to show that in the case of a low probability of asteroid collision with the Earth, the appropriate selection and weighting of the data are crucial for the impact investigation and for analysing the impact possibilities using extensive numerical simulations. By means of the Monte Carlo special method, a large number of 'clone' orbits have been generated. A full range of orbital elements in the six-dimensional parameter space, that is, in the entire confidence region allowed by the observational material, has been examined. On the basis of 1000 astrometric observations of (99942) Apophis, the best solutions for the geocentric encounter distance of  6.065 ± 0.081 R_⊕  (without perturbations by asteroids) or  6.064 ± 0.095 R_⊕  (including perturbations by the four largest asteroids) were derived for the close encounter with the Earth on 2029 April 13. The present uncertainties allow for special configurations ('keyholes') during this encounter that may lead to very close encounters in future approaches of Apophis. Two groups of keyholes are connected with the close encounter with the Earth in 2036 (within the minimal distance of  5.7736−5.7763 R_⊕  on 2029 April 13) and 2037 (within the minimal distance of  6.3359–6.3488 R_⊕  ). The nominal orbits for our most accurate models run almost exactly in the middle of these two impact keyhole groups. A very small keyhole for the impact in 2076 has been found between these groups at the minimal distance of 5.97347   R_⊕  . This keyhole is close to the nominal orbit. The present observations are not sufficiently accurate to eliminate definitely the possibility of impact with the Earth in 2036 and for many years after.     

Evolution of close binaries and origin of Algol-type systems

The evolution of close binary systems was followed for ten systems with the initial mass of the primary in the range 1–4M and with different initial mass ratios and initial separations. A brief discussion of the evolution of the contact component is presented for two separate cases: when the primary reaches its Roche lobe during central hydrogen burning (case A) and after the exhaustion of hydrogen in the center (case B).The models obtained are compared with observed semi-detached systems separately for massive (with total mass greater than 5M ) and low mass (with total mass below 4M ) binaries. It is shown that the contact components of the observed massive binaries are probably burning hydrogen in the core. On the contrary, the majority of contact components of the observed low-mass binaries are burning hydrogen in the shell. The observed distribution of such binaries as a function of different luminosity excesses of contact components seems to indicate that their origin is connected with case A rather than with case B.