摘要:

In several ordinary chondrites showing slight shock deformation, the shock effects in diopsidic pyroxene have been characterized, using transmission electron microscopy. Narrow twin lamellae, and slip planes, in (100) orientation are abundant. These are comparable with the effects of experimental deformation at low strain‐rates. The absence of (001) twinning indicates different conditions from those in shock experiments and in many natural shock events. Predominance of the (100) features is thought to indicate a particularly mild type of shock, in which the stresses generated within a crystal are lo

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1980.tb00514.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

There are two types of planetary noble gases: One, containing isotopically “anomalous” argon, krypton and xenon but isotopically “normal” helium and neon, was derived from outer stellar regions. The other, consisting almost entirely of isotopically “normal” argon, krypton and xenon, with little or no helium or neon, was derived from inner stellar regions.Mixing of nucleosynthesis products from different regions of a supernova is responsible for the observed correlations between elemental and isotopic ratios of planetary noble gases in different classes of meteorites. The solar system condensed directly from the chemically and isotopically heterogeneous debris of a single supernova.There is no convincing evidence, however, of separate nucleogenetic components in neon. Fractionation and spallation can account for all previously identified components of trapped meteoritic neon, Ne‐A, Ne‐B, Ne‐C, Ne‐D, Ne‐E, Ne‐Al, Ne‐A2, Ne‐E(L), Ne‐E(H) and Ne‐O, and this same mechanism also explains differences between the isotopic compositions of meteoritic, atmospheric, and solar wind neon.Variations in the abundance pattern of planetary noble gases are primarily the result of stellar fusion reactions and physical adsorpt

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1980.tb00515.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Nepheline and sodalite have been found in association with glass in a barred olivine chondrule from the Allende C3V meteorite. The major minerals of the chondrule are olivine (Fo80–88), bronzite (En85Fs12Wo3), and chromite. Olivine bars are separated by glass of nearly pure plagioclase composition (An81–99). Olivine composition is more Fe‐rich than predicted by olivine‐liquid equilibria (Fo96). Conditions of non‐equilibrium are implied from this and the presence of plagioclase glass and small amounts of subcalcic diopside (En75Fs12Wo13) in the chondrule. The properties of this chondrule are consistent with liquid condensation, but melting of an amoeboid olivine aggregate or similar object could also have generated the chondrule‐forming liquid. Nepheline and sodalite appear to have crystallized from this liquid under non‐equilibri

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1980.tb00516.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

A 701 kg iron meteorite has recently been discovered near the Mount Manning Range in Western Australia. The meteorite has a fan‐shaped or delta wing configuration, one side being smooth and slightly concave with a well‐defined fusion crust, whilst the other side is rough, convex and possesses numerous regmaglypts. It is probable that the meteorite pentrated much of the earth's atmosphere in an aerodynamically stable orientation, typical of the stalled attitude of delta wing aircraft. The meteorite is a member of Chemical Group 1C. A comparison of the chemical composition, surface features, microstructure and location of this meteorite with the Mount Dooling meteorite confirms that the find is a larger specimen of Mount Dooling. It is possible that other fragments of the Mount Dooling meteorite may be found in the Mount Manning Range reg

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1980.tb00517.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

From orbital, aviation and geologic documents, four circular depressions on the Sahara sedimentary platform were selected for field investigation because of their possible impact origin. Our results can be summarized as follows: Amguid Crater (26° 05′N; 004° 23.5′E; 450 m diameter, 30 m deep) is perfectly circular, with a steep wall, a raised rim and an ejecta blanket. The strata are uplifted, outward dipping, dislocated and locally overturned at the rim crest. Large blocks are scattered around the rim. There is petrological evidence of shock by planar elements in quartz. Amguid is a well preserved impact crater probably no older than 100,000 years. Talemzane (33° 19′N; 004° 02′E; 1.7 km diameter, 70 m deep) is also perfectly circular and displays a raised rim. The strata are uplifted, outward dipping, and locally highly fractured. Numerous breccia veins are clearly exposed in the crater wall. Consolidated ejected debris form a continuous blanket more than 500 m outward from the rim. Reworked mixed breccias are exposed at the base of the crater wall. Planar elements are observed in quartz clasts in the mixed breccia. Talemzane is an impact crater on the order of 0.5 to 3 million years old. El Mouilah (33° 51′N; 002° 03′E; 4.5 km diameter, 130 m deep) is almost perfectly circular, the walls are steep and there is a central dome. In spite of a promising morphology, there is no field evidence of impact. El Mouilah is possibly a recent collapse structure due to dissolution in the thick underlying limestone and gypsum formations or purely erosional in origin. Aflou (34° 00′N; 002° 03′E) is not circular (3 × 5 km) but was selected because it appears in the literature as a probable impact crater, the main argument being the existence of fused materials in the center (Marks et al., 1972). We found no evidence of impact, but several occurrences of igneous rocks along an E‐W direction suggest a structurally controlled volcanic activity. A volcanic activity is also supported by the existence of a local magnetic anomaly centered on the depression. Aflou is neither an impact structure nor a crater. Located on a probable structural dome, at the intersection of several structural trends, the formation of the depression can be due to erosion and/or dissolution in the thick underlying limes

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1980.tb00518.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1980.tb00519.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1980.tb00520.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1980.tb00513.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY