摘要:

The effects of chemical weathering on the Holbrook, Arizona chondrite were studied via major, minor, and trace element analysis along with noble gas measurements. Three samples of Holbrook were studied: a fresh specimen which fell in 1912, a specimen collected in 1931 and a specimen collected in 1968. The weathering of the meteorite produced changes in the Fe and Mg concentrations. The amount of metallic iron decreases with increasing degree of weathering. The MgO content decreases and the total iron content increases slightly with increasing weathering of the specimen, but these concentration differences are not necessarily due to weathering. Elemental concentrations for Ti, Ca, Al, P, Mn, Ni and Cr did not change significantly during weathering. Sodium may have been lost during weathering, whereas K showed a slight enrichment in abundance with terrestrial age. Trace elements C, Rb and Sr increased at least two‐fold during weathering of the meteorite. Abundances of the radiogenic and cosmogenic noble gases decreased with increasing terrestrial age. Concentration ratios of certain cosmogenic noble gas nuclides which are commonly used as indicators of gas loss and shielding in chondrites show unpredictable behavior in the weathered chondrit

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1978.tb00467.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Because of their short cosmic ray exposure ages, chondritic meteorites are more likely to have been broken off from parent bodies in Earth‐crossing orbits than from parent bodies in the asteroid belt. The radii of the objects now in the vicinity of the Earth (Apollo and Amor objects) are too small to be unfragmented asteroids of the theory for the origin of gas‐rich meteorites of Anders. Because of the abundant evidence for very heavy shock and reheating among L‐ and H‐chondrites, I conclude that the asteroidal origin for the ordinary chondrites is still the most likely. A cometary origin for the CI chondrites is examined. Regolith and megaregolith do not necessarily have to be formed by impacts on the cometary nucleus. The short‐period comet Encke receives about 1/10 the solar‐wind flux of a belt asteroid at 2.5 AU in its present orbit. The thickness of the megaregolith (C1 chondrites) is estimated between 0.1 and 0.3 km. Stirring of the megaregolith without substantial loss of dust from the comet might occur when the comet is transitional between “active” and “dead.” The consolidation of C1‐ “dust” into rock is somewhat problematic, but if liquid water and water vapor have played a role, then a crust rich in solar gases might form in the outer regions of a comet. A testable alternative explanation is suggested, namely that the solar gases in the C1 chondrites

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1978.tb00468.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

An eventual correlation between petrologic type and porosity can only be found if measurements are made on unshocked or slightly shocked chondrites. The main advantage of the method (described earlier in this journal) is that it offers the possibility of correlating on a very small scale porosity with structural and petrographical features along with punctual chemical and isotopic data. Moreover, the method is relatively unpolluting and non destructive, and requires very small amounts of matter. Porosity measurements have been carried out on polished thin section of five H chondrites, after sample impregnation with a fluorescent resin. The microscope images were analysed with a Quantimet. Two types of information have been derived. First, the macroporosity of the material ranges up to 13% in Sena (H5) but falls to 4% in samples that have undergone slight shock or compression. Second, approximately 25% by volume of the stones consist of zones of great permeability which were fissured or filled with loose debris. This has been observed in all cases but the well‐recrystallised Kernouve (H6) stone. Additional measurements are required to correlate petrology and porosity on a statistically significant basi

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1978.tb00469.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1978.tb00470.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1978.tb00471.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1978.tb00472.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1978.tb00473.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY