SIZE AND SPACIAL DISTRIBUTION IN METEORITIC SHOWERS

Size distribution in the Barwell, Bruderheim, Gibeon, Johnstown, Sikhote-Alin and Tenham showers is studied. On the assumption that the distribution follows the Gates-Gaudin-Schumann law, which describes artificially crushed material, it is estimated that 80% of the fine material of the Gibeon shower was not collected; for the other showers the figure varies between 52 and 61%. The spacial distribution pattern of the Barwell, Johnstown, Krymka, Kunashak, Leedey, Plainview (1917), and Sikhote-Alin meteoritic showers is studied. It is established that the patterns show considerable regularity and that the distribution pattern of fragments of any one size is a function of the sorting factor, which is the distance in kilometers between groups of fragments whose mass differs by an order of magnitude.     

NIOBIAN RUTILE IN AN APOLLO 14 KREEP FRAGMENT

Niobian rutile was found in a KREEP lithic fragment of basaltic texture. The niobian rutile contains 85.3% TiO₂, 7.1% Nb₂O₅, 2.65% Cr₂O₃, 0.70% ZrO₂, 0.61% SiO₂, 0.82% Al₂O₃ 0.61% FeO, 0.52% CaO, 0.22% V₂O₃ in addition to minor amounts of MnO, MgO, and CeO₂. Rare earth elements were not detected, in contrast with lunar niobian rutile of Marvin (1971). Coexisting minerals in the KREEP fragment are major amounts of plagioclase and orthopyroxene, and minor amounts of olivine, ilmenite, augite, barian K-feldspar, whitlockite, troilite, Ni-Fe, zirkelite and chromite     

MAJOR ELEMENT COMPOSITION OF GLASSES IN THREE APOLLO 15 SOILS

Approximately 180 glasses in each of three Apollo 15 soils have been analyzed for nine elements. Cluster analysis techniques allow the recognition of preferred glass compositions that are equated with parent rock compositions Green glass rich in Fe and Mg, poor in Al and Ti may be derived from deep seated pyroxenitic material now present at the Apennine Front. Fra Mauro basalt (KREEP) is most abundant in the LM soil and is tentatively identified as ray material from the Aristillus-Autolycus area. Highland basalt (anorthositic gabbro), believed to be derived from the lunar highlands, has the same composition as at other landing sites, but is less abundant. The Apennine Front is probably not true highland material but may contain a substantial amount of material with the composition of Fra Mauro basalt, but lacking the high-K content. Glasses with mare basalt compositions are present in the soils and four subgroups are recognized, one of which is compositionally equivalent to the large Apollo 15 basalt samples     

THE YIELD STRENGTH OF METEORITIC IRON

The compressive yield strength was determined on three meteorites using specimens 4 mm and 8 mm in length and strain magnifications of 10,000 and 2000 respectively, with an apparatus developed for testing small specimens of biological hard tissue. The flow stresses required to produce 0.2% plastic strain in a recrystallized Cañon Diablo specimen, in the Odessa octahedrite, and in the metal phase of a Brenham were 62.9 K psi, 46.6 K psi, and 62.7 K psi respectively. The flow stress of Cañon Diablo after heating in a vacuum for one hour at 871 °C and furnace cooling was 60.0 K psi. The microstructure and grain size of the heat treated specimen was virtually that of the untreated meteorite. Plastic deformation of the Odessa specimen produced wavy slip lines in kamacite on a previously polished and etched surface. Slip lines also developed in taenite and cracks occurred in the phosphide phase.     

FRAGMENTATION OF THE SIKHOTE-ALIN METEORITIC BODY

Based on the results of the study of regmaglyptic relief of individual specimens of the Sighote-Alin iron meteorite shower, three main stages of fragmentation have been established for a meteoritic body moving through the atmosphere with cosmic velocity. During the first stage, the fragmentation took place at a relatively high cosmic velocity, the fragments being subjected to a major aerodynamic influence. In the second stage, the velocity had decreased due to atmospheric resistance and the fragments were subjected to less drastic aerodynamic action in the regmaglyptic formation. During the third stage, fragments were further fragmented when their cosmic velocities had been almost completely absorbed and the new fracture surfaces were practically untouched by atmospheric influence. As a result of such a multistage fragmentation, the main scatter-ellipse was over-lapped by two secondary ellipses, thereby complicating the patterns of scattering of individual specimens of the meteorite shower, which turns out to contain a number of anomalies.     

CONCERNING THE METEORITIC ORIGIN OF THE PUCHEZH-KATUNKI CRATER

The geology of a disturbance in the Puchezh-Katunki region is reviewed and two recent hypotheses of origin are criticized. A meteoritic origin for the disturbance is proposed, since the structure and morphology of this region are similar to the sloping conical surface produced by an explosive meteor crater. The energy, mass, and size of the asteroid which could cause such a disturbance are estimated. It is shown that the probability of an impact of this size is finite [over geologic time]. The crater was formed between the end of the Triassic and the beginning of the Jurassic periods.     

ON THE BRITTLENESS OF GIBEON METEORITIC IRON

The iron-nickel alloy of the Gibeon octahedrite exhibited a transition from the normal ductile behavior to brittle behavior in tensile tests conducted below 103 °K. This result contradicts data published previously and implies that a temperature-induced transition could explain the fragmentation of a large parent metallic mass into meteorite-sized objects, since the micro-structures of existing octahedrites are consistent with brittle rather than ductile fracture events. Examination of the fractures and microstructures of the tensile specimens affirmed that the observed transition is consistent with meteoritic structures. It is concluded that the mechanical properties of Gibeon meteoritic iron are compatible with both the solid iron core and the metallic “raisin” models for the structure of the parent planet with respect to fragmentation mechanisms.     

A NEW CUTTING TECHNIQUE FOR METEORITIC IRONS

Small iron meteorites may be cut with high-speed plastic-bonded carborundum wheels, with hacksaws or automatic modifications of these, and with carbide-tipped wheels; to date, no simple method has been available for cutting large iron meteorites. The successful sectioning of a 20-ton meteorite involved the use of a mason's wire-saw, fed with a slurry of carborundum-grit. The slab produced measured 1.8 × 1.3 × 0.05 m and could be ground and polished for deep-etching, with a minimum of weight loss.     

THERMAL DEFORMATION AND FRACTURING IN OLIVINE-RICH SAMPLES

A study was made of the effect of low-temperature thermal fatigue on the generation of regular and irregular fractures in olivine-rich terrestrial rocks. The results appear to confirm the influence of thermal actions in the metamorphism of stony meteorites and lunar rocks.     

SOLID SOLUTION,SUBSOLIDUS REDUCTION AND COMPOSITIONAL CHARACTERISTICS OF SPINELS IN SOME APOLLO 15 BASALTS

Compositional data for spinels in the chromite-hercynite-ulvöspinel system from three large basalts and for spinels in 48 basalt particles in four soil samples show: (1) that the range of compositions are comparable to those of spinels in Apollo 12 basalts; (2) that the spinel series is complete between 0.75 FeCr₂O₄ 0.25 FeAl₂O₄ and Fe₂TiO₄; (3) that the Apollo 12 bimodal distribution is present insofar as chromite-rich and ulvöspinel-rich phases are more commonly present than compositions intermediate between these two end members; (4) well defined ionic relationships exist for those cations displaying high octahedral site preference energies in the spinel structure (viz. Cr vs Al and Ti vs Cr+ Al); (5) cations displaying low site preference energies (Fe²⁺, Mg) show poor correlation; and (6) the absence of a simple relationship between the divalent ions (Fe²⁺ and Mg), and the paucity (10% of 356 analyses) of intermediate compositions suggests a strong dependence on the structural stability of intermediate members of a normal (hercynite, chromite) — inverse (ulvöspinel) solid solution series     

URANIUM DISTRIBUTION and “EXCESSIVE” U-He AGES IN IRON METEORITIC TROILITE

Uranium was measured by fission track analysis in meteoritic troilite and graphite. The distribution is extremely heterogeneous, with a few high-U grains dominating the total abundances. U/He ages cannot be estimated from such a distribution pattern, and therefore previously reported excessive ages are not valid.     

A NEW MEASURE OF THE NICKEL CONTENT OF METEORITIC COPPER

A copper grain in the Mayfield chondrite surrounded by troilite contains up to 2.1% Ni. This provides a better measure of the Ni content in meteoritic Cu alloy than a former measurement which required a calculated correction for fluorescence effects from adjacent Fe-Ni alloy.     

METAL OF HIGH Co CONTENT IN LL CHONDRITES

Measurements on the metal of the LL chondrites Appley Bridge, Jelica, Olivenza, and Khanpur have shown that the Co: Ni ratio of the metal is near 1.24 and that Prior's law appears to be followed to some extent within the LL group.     

GRAIN-SIZE DISTRIBUTION AND MORPHOLOGY OF METAL IN E-CHONDRITES

The size distribution and morphology of metal grains have been examined in 11 sections of types I and II E-chondrites. The changes in the grain-size distribution and morphology of metal grains correspond with the petrologic types and define a series that reflects increase in thermal metamorphism in the following order: type I, Kota Kota-Indarch-South Oman-St. Mark's; and type II, Jajh deh Kot Lalu-Atlanta-Daniel's Kuil-Hvittis-Pillistfer-Khairpur-Blithfield. Concentrations of metal grains adjacent to the perimeters of chondrules are observable throughout the sequence and delineate relic chondritic structure in six of the seven type II E-chondrites; relic structures are absent from Blithfield.     

LAGUNA GUATAVITA: NOT METEORITIC,PROBABLE SALT COLLAPSE CRATER

Laguna Guatavita (Colombia), a crater 700 m across and 125 m deep containing a central lake, appears not to be a meteorite crater as widely supposed. The tectonic style is not that of an impact site and there is no raised rim or ejected debris. We could find no impactite, shock metamorphic effects or shock fractures (shatter cones). Most likely it is a collapsed crater caused by the solution and withdrawal of salt from an underlying anticline