摘要:

The Colony meteorite is an accretionary breccia containing several millimeter‐to centimeter‐size chondritic clasts embedded in a chondritic host. Colony is one of the least equilibrated CO3 chondrites; it has an unrecrystallized texture and contains compositionally heterogeneous olivine and low‐Ca pyroxene, kamacite with low Ni and Co and high Cr, amoeboid inclusions with low FeO and MnO, a fine‐grained silicate matrix with very high FeO, and numerous small chondrules with clear pink glass. However, Colony differs from normal CO chondrites in several respects: Although Al, Sc, V, Cr, Ir, Fe, Au and Ga abundances are consistent with a CO chondrite classification, certain lithophiles (Mg and Mn), siderophiles (Ni and Co) and chalcophiles (Se and Zn) are depleted by factors of 10–40%. The shape of Colony's thermoluminescence (TL) glow curve is similar to that of Allan Hills A77307 (another unequilibrated chondrite with CO3 petrological characteristics) and different from those of normal CO chondrites. [ALHA77307 also resembles Colony in having low Mg, Mn, Ni and Co, compared to normal CO chondrites, but it possesses CO‐CV levels of Se and Zn and nearly CV levels of Cd.]Colony is badly weathered; it contains 22.7 wt.% Fe2O3and 5.7 wt.% H2O. Recalculating the analysis on an H2O‐free basis with all Fe2O3, NiO and CoO converted to metal, yields an inferred original metallic Fe, Ni abundance of ∼ 19 wt.%. This is similar to that of Kainsaz (an unweathered CO3 fall), but much higher than that of all other CO3 chondrites (<6.3 wt.%). Although it is possible that Colony and either ALHA77307 or Kainsaz constitute distinct CO3 chemical subgroups, the weathered nature of Colony and ALHA77307 preclude the drawing of firm conclusions. Nevertheless, it is clear that CO3 chondrites vary more in compositional and petrological properties than was previo

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1985.tb00859.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abee clast samples, a matrix sample, a dark inclusion, magnetic and nonmagnetic samples, and bulk samples were analyzed by neutron activation analysis (NAA). The REE were determined by radiochemical NAA. Na, K, Sc, Cr, Mn, Fe, Co, Ni, Zn, As, Se, Sm, Ir, Au were determined by instrumental NAA.High abundances of As, Ir, and Au in the magnetic separate and the correlation of their abundances with the metal content of the clasts indicate that As, Ir, and Au chiefly occur in the metal. Correlations for Zn and Sc indicate that they chiefly occur in niningerite, but a significant amount of Sc may also occur in oldhamite. The dark inclusions do not follow the As and Zn correlations, suggesting that the dark inclusions and clasts are not equilibrated with each other. Correlation of the REE and oldhamite abundances for both the clasts and dark inclusions indicates that the REE chiefly occur in oldhamite.In view of the INAA and mineralogical evidence for non‐equilibration among the clasts and a dark inclusion (Sears et al., 1981), the similar REE patterns for clasts (3,3) and dark inclusion (5,1), and the similar mineral composition of oldhamite in clast (3,3) and dark inclusion (5,1), suggest that the oldhamite in the clasts and dark inclusions is of a common origin, which Sears et al. (1981) showed could be formed by condensation.A Tb anomaly of a factor of 2 was found in sample (2,9 and 9,2), and a La anomaly of a factor of 2 was found in clast (3,3). The only other REE anomaly in Abee, a factor of 3.5 for Yb, was found by Nakamura and Masuda(1973). In view of the evidence for equilibration among the clasts, this anomaly must have been introduced shortly before the brecciation process and indicates that no significant reheating has occurred. This concurs with the findings of Sugiura and Strangeway (1981) and Bogard et al. (1982

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1985.tb00860.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Based on optical microscopy and electron microprobe analyses, eight previously undescribed or poorly known chondrites were classified into compositional groups, petrologic types, and degree of shock alteration. These chondrites are: Leander, L4b; Nazareth(a), L6d; La Villa, H4b; Mereta, H4c; Gail, H4d; Shafter Lake, H5a; Uvalde, H5d; and Howe, H5d.

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1985.tb00861.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Amphibole and spinel occur in the Shergotty and Zagami meteorites only in magmatic inclusions in pigeonite. The trapped magma is essentially identical to the parental magmas for Shergotty and Zagami. The amphibole is a kaersutite with minimal halogen content; by inference, it must have been hydrous. If so, the Shergotty and Zagami melts contained at least 0.2 wt % H2O and were probably H2O‐undersaturated. Pressures in excess of 1 kilobar seem necessary for the formation of amphibole. Spinel replaces magnetite in the inclusions, and olivine replaces magnetite elsewhere in the meteorites. To stabilize spinel, the melt in the inclusions must have become enriched in Al during fractionation, possibly because the small volume of the inclusions made nucleation of plagioclase unlikely. Pervasive replacement of magnetite through reduction reactions suggests that Shergotty and Zagami interacted with hydrogen‐rich fluids during their cool

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1985.tb00862.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Bells and Sharps have some mineralogical and chemical peculiarities that make their classification uncertain. For Bells, the40Ar content at 890 × 10−8cm3STP/g is greater than the highest C1 chondrite value (Ivuna; 640), but close to the mean value for C2's (880). The21Ne‐exposure age of 0.38 ± 0.07 Ma is very short, and coincides with the distinctive cluster of five C2's (0.17 to 0.76 Ma). Very likely Bells belongs to the same cluster, in which case it comes from the C2 parent body. Hence the C2 parent body seems to contain transitional C1‐C2 material, like Bells, within a few km of the region of C2 chondrites proper. Thus the radiogenic and especially the cosmogenic gases link Bells to the C2 group. For Sharps, the elemental concentrations of primordial Ar, Kr and Xe (127, 0.76 and 0.59, all 10−8cc/g) are ∼ 3 x higher than for any other H3 chondrite. While Sharps is classified as 3.4 based on five indicators of metamorphism, the very high concentration of remaining two parameters of the Sears et al. (1980) scheme — C and primordial36Ar — (together with the high concentration of the volatile trace elements Bi, In and Tl) implies a classification of 3.0 for its volatile element content. The21Ne‐exposure age is 25.5 ± 2.5 Ma, placing Sharps in the second largest peak of the H‐chondrite distribution. The nominal K‐Ar and U, Th‐He ages are 4.6 ± 0.2 and 4.2 ± 1.5 Ga, suggesting that Sharps has remained at low tempera

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1985.tb00863.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Bocaiuva is a unique meteorite consisting of major metal having a high Ge/Ga ratio and minor (∼ 50 mg/g) silicates. The silicates are generally chondritic and consist of major olivine (Fa.7.7) and orthopyroxene (Fs7.6) and minor plagioclase (Ab49, An49) and clinopyroxene (Fs4.5, Wo42). The low alkali content of the silicates is the only property inconsistent with a chondritic composition. Based on metal composition Bocaiuva seems distantly related to certain iron meteorites having similar Ge contents and similar Ge/Ga ratios, but detailed comparison with six such irons shows none to be closely related to Bocaiuva. Perhaps most closely related is Cold Bay, a member of the Eagle‐Station trio of pallasites, but its composition is too different to suggest formation on the same parent body. Oxygen‐isotope data show that Bocaiuva silicates are closely related to those in the Eagle‐Station pallasites and to the CO and CV chondrites. The composition and texture of the Bocaiuva metal‐silicate assembly indicate mixing in an impact event. We suggest that the Eagle‐Station pallasites were also formed by impact heating rather than by a long‐lived interna

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1985.tb00864.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1985.tb00865.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1985.tb00866.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY