ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1988.tb00889.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—Among iron meteorites there is a simple relationship estimating, with two parameters, the production rates of spallation products of mass A, that range in ΔA from 2 to 36 (Cr to Ne), where ΔA is 56 — A. This paper describes further applications of this relation, extending it to chondrites, in terms of the effective ΔA. It is possible to systematize the production of common products in chondrites such as3He,26Al,22Ne,21Ne and38Ar. For this purpose, data on products determined in the metal phases of chondrites are useful in correlating stones to irons. For general application to stone meteorites, statistical treatments for multielement target systems are employed, except for the lowest energy reaction products. Statistical methods for spallation products are thus now applicable for all iron and stone mete

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1988.tb00890.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—Ningqiang is an anomalous CV chondrite (oxidized subgroup) containing a high abundance of aggregational inclusions (13.7 vol.%) and low abundances of refractory inclusions (1.0+1.0–0.5vol.%) and bulk refractory lithophiles (∼0.82 × CV). Ningqiang may have agglomerated after most refractory inclusions at the nebular midplane had already been incorporated into other objects. Coarse‐grained rims surround only ∼5% of Ningqiang chondrules, compared to ∼50% in normal CV chondrites. Aggregational inclusions appear to have formed by incipient melting of fine‐grained aggregates at relatively low temperatures in the solar nebula, possibly by the mechanism responsible for chondrule formation. Granoblastic porphyritic chondrules, which contain olivines forming 120° triple junctures and no mesostasis, probably formed in the solar nebula by incomplete melting of precursor materials that were olivine normative and had relatively low concentrations of Si, Ca

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1988.tb00891.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—The isotopic abundances of the noble gases in bulk samples of the Guangnan L6 chondrite and of the anomalous CV3 chondrite Ningqiang were measured. Guangnan yields a cosmic‐ray exposure age of 2.9 ± 0.4 Ma and belongs to the group of L chondrites with low exposure ages. Ningqiang, however, shows a cosmic‐ray exposure age of 42.2 ± 4.0 Ma, the highest for a CV3 chondrite. The concentrations of radiogenic4He and40Ar in Guangnan are the lowest observed in any ordinary chondrite. A U/Th‐4He age of 27 ± 16 Ma and a40K–40Ar age of 142 ± 14 Ma are calculated assuming L chondritic U, Th, and K concentrations. This assumption is justified considering the fact that a mineralogical composition typical for L chondrites was reported for this meteorite. The observed severe gas losses must have occurred at or before the onset of the exposure of the meteoroid to the cosmic radiation. For the Ningqiang carbonaceous chondrite concordant gas retention ages are obtained: The U/Th‐4He age is 4170 ± 160 Ma whereas the40K–40Ar age is 4260 ± 70 Ma, assuming average U, Th, and K concentration

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1988.tb00892.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—Following a brilliant daylight fireball at 10:10 a.m. (local time) on 30 September 1984, a single stone weighing 488.1 grams was recovered from Binningup beach (33°09′23″S, 115°40′35″E), Western Australia. Data from 23 reported sightings of the fireball indicate an angle of trajectory 20–40° from the horizontal, a flight‐path bearing N210°E and an end‐point (ca.32°39′S, 115°54.5′E) at a height of ∼20–30 km.A recrystallized chondritic texture and the presence of olivine and low‐Ca orthopyroxene with compositions of Fa18.4(PMD 1.1)and Fs16.1(PMD 1.1), respectively, show that Binningup is a typical member of the H‐group of ordinary chondrites. Uniform mineral compositions and the presence of generally microcrystalline plagioclase feldspar indicate that the meteorite belongs to petrologic type 5. Pervasive fracturing of silicates suggests mild pre‐terrestrial shock loading.Measurements (dpm kg−1) of cosmogenic radionuclides including22Na (61 ± 5),26Al (49 ± 3) and54Mn (66 ± 10)

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1988.tb00893.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—Compositions and morphologies of dolomites, breunnerites, Ca‐carbonates, Ca‐sulfates and Mg, Ni, Na‐sulfates, and their petrologic interrelations, in four CI chondrites are consistent with their having been formed by aqueous activity on the CI parent body. Radiochronometric data indicate that this activity took place very early in Solar‐System history. No evidence for original (“primitive”) condensates seems to be present. However, alteration apparently took place without change in bulk meteorit

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1988.tb00894.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—Microchondrules with apparent diameters of 2 to 150 μm are found in a black carbon—bearing inclusion in Mezö‐Madaras. Some are homogeneous (glassy or micro‐crystalline) others show two phases: mainly silica and a pyroxene‐rich glass. The bulk chemical composition of the inclusion is related to the host‐chondrite in which silica‐pyroxene chondrules are ubiquitous. Small black lumps of the same kind are dispersed in bulk Mezö‐Madaras. This L‐related carbon‐bearing material may represent a new specimen of C

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1988.tb00895.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—The Camel Donga eucrite is unique since it contains about 2% metallic iron. Chemical composition, mineralogy, and noble gas contents of Camel Donga are, however, indistinguishable from other eucrites. The bulk iron content and the composition of the metal show that the Camel Donga metal was formed by reduction of FeO and FeS, probably through loss of S2and SO2. Since coarse‐ and fine‐grained lithologies are affected it is likely that the reduction occurred after brecciation. The inhomogeneous distribution of metal suggests that reduction is limited to areas where sulfides were present. The fact that major parts of the meteorite still contain sulfides, in many cases associated with metal, indicates that the reduction process did not go to completion. A comparatively short heating period is suggested, perhaps in an ejecta bl

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1988.tb00896.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—We studied numerous specimens of the Norton County enstatite achondrite (aubrite) by optical microscopy, electron microprobe, and neutron‐activation analysis. Our main conclusions are the following:1. Norton County is a fragmental impact breccia, consisting of a clastic matrix made mostly of crushed enstatite, into which are embedded a variety of mineral and lithic clasts of both igneous and impact melt origin.2. The Norton County precursor materials were igneous rocks, mostly plutonic orthopyroxenites, not grains formed by condensation from the solar nebula.3. The Mg‐silicate‐rich aubrite parent body experienced extensive melting and igneous differentiation, causing formation of diverse lithologies, some of which have not been described previously. These lithologies include dunites (represented by forsterite crystals), plutonic orthopyroxenites (represented by most enstatite crystals in the matrix), plutonic pyroxenites (the pyroxenitic clasts), and plagioclase‐silica rocks (like the feldspathic clasts). Presence of impact melt breccias (the microporphyritic clasts and the diopside‐plagioclase‐silica clast) of still different compositions further attest to the lithologic diversity of the aubrit

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1988.tb00897.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—The partitioning of the rare earth elements (REE) between hibonite and silicate melt has been investigated at 1470 °C in the system calcium tschermak's molecule‐diopside. Oxygen fugacity was varied between air and the iron‐wustite buffer using conventional gas mixing, and to “infinitely reducing” using Sr2+as a surrogate for Eu2+. The partition coefficient (D) pattern is light REE enriched with D(La) = 7.15 and D(Yb) = 0.1. D(Eu) varied from about 2 in air to about 0.55 in an “infinitely reducing” atmosphere. Experiments were reversed for Eu and, by implication, a close approach to equilibrium was achieved for other elements. Absolute activity coefficients for REE in hibonite were estimated, yielding γLa= 330, γEu3+ = 1200, and γYb= 24 000. These results suggest that unless the principal phase(s) into which a trace element is dissolving and the activity—composition relationships for that trace element in that phase(s) are known, condensation temperatures based on assumed ideal solution behavior will ge

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1988.tb00898.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY