摘要:

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 fragmentatio

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1973.tb01247.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Electron microprobe analyses of olivine, orthopyroxene, clinopyroxene, plagioclase feldspar, chromite, whitlockite, apatite, troilite and metals indicate that the Vilna meteorite is a hypersthene chondrite belonging to the L5 or L6 subgroups.

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1973.tb01248.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

This paper describes a simple but satisfactory new method for the preparation of tiny, varied and specialized specimens for electron or ion‐microprobe analysis developed over the past five years. Microtektites, individual chondrules, single grains, blebs from lunar samples and meteoritic minerals have been prepared by this technique. A description of the preparation of these usually difficult samples from the initial mounting through the various polishing steps to their final polish is presented in detail. The procedures used to prevent any contamination of these specimens by the polishing agents and to prevent cross contamination to the other samples used for geochronology studies are presente

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1973.tb01249.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Periodic thermal excursions, even in a low‐temperature range, may cause internal stresses and give origin to some of the observed plastic and clastic deformations in stony meteorites.An experimental test confirms our hypothesis: lattice distortions, cleavage and cracking were artificially induced in specimens of two H‐chondrites (Mills and Bur‐Gheluai) by low‐temperature “thermal fatigue.” The observed effects appear to be increasing with increasing numbe

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1973.tb01250.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1973.tb01251.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

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 period

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1973.tb01252.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Roter Kamm, located in the Namib Desert of SW Africa, is an 8,000‐foot‐diameter crater developed essentially in Precambrian granitic rocks. Sand overburden is pervasive both inside ami outside the crater and the only significant rock exposures are high in the crater rim. In most cases these exposed rocks proved entirely normal when examined microscopically but two specimens were found which exhibited features compatible with, and suggestive of, shock pressures in the range of 50 to 100 kilobars. Both specimens are probably foreign to the rim environment and may represent remnants of ejecta from the crater formation. There is a strong negative residual gravity anomaly across the structure which reaches a maximum of −9.3 milligals. The size and shape of the anomaly are fully compatible with a meteorite impact structure of “normal” dimensions. It is more difficult to interpret the gravity data in terms of an explosive volcanic origin and neither is there any evidence of such an origin in the rim rock exposures. An impact origin for the crater is strongly suggested by all the evidence to date. Definitive evidence of shock metamorphism could perhaps be found by a further search for “exotic” roc

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1973.tb01253.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Both Fe and Ni were measured in microprobe analyses of a large copper metal rim that formed by exsolution from a large troilite grain contained within an iron‐nickel metal grain in the H‐group chondrite, Blansko. The Fe content of the copper can be accounted for largely by secondary fluorescence by Cu‐Kαof Fe radiation from the adjacent metal, however, fluorescence by Cu‐Kβof Ni radiation cannot significantly account for the observed Ni content. Therefore, the copper actually alloys up to 2% Ni, with a concentration gradient dropping to 0.7% away from the copper‐meta

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1973.tb01254.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

The Willowbar, Oklahoma meteorite was found by Kendall Rhoton in December, 1971, lat 36° 44′ N.; long 102° 12′ W. It is a shocked brecciated L6 chondrite (Fa‐24.3) with large black veins cutting areas of normal chondritic texture. It weighed

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1973.tb01255.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

The size distribution of 15,000 fragments from the Norton County meteorite was examined with size‐frequency histogram. The size is measured in phi units. The estimates of the moments β1and β2of the empirical distribution were used for approximating the latter with a theoretical frequency curve in terms of the Pearson system It was suggested that the beta distribution obtained from the Pearson system can be regarded as a superposition of two simpler distributions: a near to normal one, corresponding to a slower process of fragmentation, and a power‐law one, assumed to result from fast fragmentation process.… All meteorite falls are important but some are more important than others …… This fall was of outstanding importance because with its arrival the entire picture of the word meteorite as portrayed in the total of collections throughout the world was notably altered …H. H. Nininger, 1949. Significance of the Norton, Kansas, meteorite in Transactions of the Kansas Academy of Sc

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1973.tb01256.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY