摘要:

Abstract—Currently, 44 distinct meteorites are recorded from the Nullarbor Region in Western Australia. Recovery data for the Billygoat Donga, Cardanumbi, Cocklebiddy, Forrest Lakes, Laundry East, Lookout Hill, North East Reid, North Reid, Reid, Webb, West Forrest, West Reid and Yayjinna meteorites are amended, and North Forrest is recognized as distinct from North West Forrest (H).Since 1971, the recovery of more than 500 specimens (predominantly ordinary chondrites) from the desert has made the Nullarbor Region one of the most productive areas of the world for meteorite recoveries and has caused major problems for meteorite nomenclature. To overcome a lack of geographical names, we have delineated a grid of 47 named ‘areas’ in the Nullarbor Region. Henceforth, distinct meteorites will take the name of the ‘area’ in which they are found and a number (e.g., 001) in order of discovery. In general, the names of past recoveries remain unchanged. The absence of transportation processes in the region, and accurate documentation of the distribution of finds allows ‘pairing’ of specimens to at least 90% level

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1989.tb00954.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract—The discovery of 34 new stony meteorites is reported from those areas of the Nullarbor Region, Western Australia named after Mundrabilla, Forrest, Reid and Deakin sidings on the Trans Australian Railway line. The recoveries include 15 H‐, and 15 L‐group equilibrated (types 4–6) ordinary chondrites, two distinct H3 chondrites (Mundrabilla 003 and Forrest 003), a genomict H‐group chondrite breccia (Reid 011) comprising types 3–6, and one structurally anomalous chondrite (Deakin 001). Seventy‐eight distinct meteorites are now known fr

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1989.tb00955.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract—Previous work indicates that Muong Nong‐type tektites from Indochina with low refractive indices and high silica contents contain relict mineral grains while those with high refractive indices and low silica contents do not. Instrumental Neutron Activation Analysis (INAA) was used to determine selected trace element concentrations for four Muong Nong‐type tektites with high refractive indices and no relict mineral inclusions and one with low refractive index and relict inclusions, to determine if there are any systematic differences in trace element compositions between the two groups. The data also were compared with published trace element data for sixteen Muong Nong‐type tektites which have low refractive indices and, therefore, should contain relict inclusions. Except for Ta which had lower concentrations in the high refractive index group, there is no consistent difference in trace element compositions between the two groups. We interpret these results to indicate a single, slightly heterogeneous source for the Muong Nong‐type tektites, rather than different sourc

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1989.tb00956.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract—The nature and isotopic composition of carbonaceous components in a variety of ordinary chondrites have been studied using stepped combustion. The samples were chosen to include falls, finds and Antarctic meteorites; specimens from all three chemical groups (H, L and LL) have been analysed. Effort was concentrated mostly on the low petrologic type meteorites (i.e., type 3); however, types 4–6 were also included in the study. Apart from terrestrial contaminants and weathering products, some of the unequilibrated ordinary chondrites appear to contain an indigenous organic component. In addition, most of the samples studied show evidence for an amorphous/graphitic component. This exists as C‐rich aggregates or as carbon associated with “Huss” matrix. There does not appear to be any difference in δ13C for this carbon between Antarctic and non‐Antarctic meteorites. In contrast, low temperature carbon in Antarctic samples is characterized by a13C‐enrichment. This is thought to be due to the influence of terrestrial weathering products introduced in the Antarctic. Curiously, the low temperature carbon in non‐Antarctic finds appears to be intermediate in δ13C between Antarctic finds and non‐Antarctic falls. This suggests that the weathering processes which are so obviously apparent from Antarctic samples may also extend, albeit in a more limited way, to non

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1989.tb00957.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1989.tb00958.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract—We derive values for the number and size distributions of meteorites landing on Earth from a study of photographic observations of bright fireballs with the Canadian camera network. The observations cover 11 years from 1974 to 1985. This analysis is an extension of a previous study and represents a 30% increase in the data base.The cumulative plot of numbers vs estimated mass of the largest fragment for each event shows a change in slope near 0.6 kg due to a deficiency of small meteorites surviving from the group of slow fireballs. The change can be explained by a mass dependence of the fraction of the incoming object that survives as the largest fragment. For larger falls, the main mass appears to represent a decreasing fraction of the total mass of the surviving meteorites and estimates of these effects are used to derive the final distribution of both main masses and total masses of meteoritic events. For total masses greater than 1 kg the population index is 1.82, close to previous estimates. About 9 events per year drop at least 1 kg of meteorites in an area of a million square km and the same area receives an annual influx of 54 kg from meteorite events with total masses between 0.01 and 100 kg.There is sufficient confidence in these results that they may be used for comparison of the present flux of meteorites with values inferred for other times, in particular the long accumulation times of the Antarctic meteorite collection

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1989.tb00959.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract—The size‐frequency distributions of chondrules in 11 CO3 chondrites were determined by petrographic analysis of thin sections. CO chondrites have the smallest chondrules of any major chondrite group. In order of decreasing chondrule size, chondrite groups can be arranged as CV ≥ LL>L>H ≥ CM ≥ EH>CO. Chondrule size varies significantly among different CO chondrites; there is a tendency for chondrules to increase in average size with increasing metamorphic grade of the whole‐rock. Different chondrule types in CO chondrites have distinct size‐frequency distributions: in order of decreasing chondrule size, BO>PO>PP>POP>RP = C. The large size of BO chondrules is problematic; however, PO chondrules are among the largest because ∼20% of them contain very coarse relict olivine grains that constitute 40–90 vol.% of the individual chondrules. PP chondrules may be larger than POP chondrules because some of them contain coarse relict pyroxene grains; a compound object consisting of a POP chondrule attached to a large relict pyroxene grain occurs in Lancé.The mean proportions of chondrule types in CO chondrites are estimated to be 69% POP, 18% PP, 8% PO, 2% BO, 2% RP, 1% C and<0.1% GOP. CO chondrites thus contain a smaller proportion of nonporphyritic chondrules than ordinary or EH chondrites, but a larger proportion than CV chondrites. Relative proportions of chondrule types vary with size interval: PO chondrules decrease fairly regularly in abundance with decreasing chondrule size, and RP chondrules appear to be most abundant in the small

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1989.tb00960.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract—A small (150 × 200‐μm‐size) clast consisting of 20 vol.% olivine microchondrules (with barred and granular textures) and 80 vol.% recrystallized silicate matrix material occurs in Krymka (LL3.1). This is the fourth microchondrule‐bearing clast to be described. The chondrules are zoned in FeO with concentrations increasing toward the surface. The clast most closely resembles a previously described radial‐pyroxene‐microchondrule‐bearing clast in Pian

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1989.tb00961.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1989.tb00962.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1989.tb00963.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY