PAIRED RENAZZO-TYPE (CR) CARBONACEOUS CHONDRITES FROM THE SAHARA

被引:115
作者
BISCHOFF, A
PALME, H
ASH, RD
CLAYTON, RN
SCHULTZ, L
HERPERS, U
STOFFLER, D
GRADY, MM
PILLINGER, CT
SPETTEL, B
WEBER, H
GRUND, T
WEBER, D
ENDRESS, M
机构
[1] MAX PLANCK INST CHEM, W-6500 MAINZ, GERMANY
[2] OPEN UNIV, DEPT EARTH SCI, MILTON KEYNES MK7 6AA, BUCKS, ENGLAND
[3] UNIV COLOGNE, NUKL CHEM ABT, W-5000 COLOGNE, GERMANY
[4] NAT HIST MUSEUM, DEPT MINERAL, LONDON SW7 5BD, ENGLAND
[5] UNIV CHICAGO, ENRICO FERMI INST, CHICAGO, IL 60637 USA
关键词
D O I
10.1016/0016-7037(93)90014-N
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
Ten chondrites with chemical and mineralogical similarities to the carbonaceous chondrite Renazzo were recovered at two locations of the Sahara: Acfer 059, 087, 097, 114, 139, 186, 187, 209, 270, and El Djouf 001. Although the El Djouf location is more than 500 km away from the Acfer location, all samples appear to result from a single fall based on chemical and petrographic similarities and supported by light element stable isotope geochemistry, noble gas record, and similar Al-26 contents. The Acfer-El Djouf meteorite is classified as a CR (Renazzo-type) carbonaceous chondrite. This group presently comprises three non-Antarctic members (Al Rais, Renazzo, Acfer-El Djouf) and five Antarctic meteorites. The major lithological components of the Acfer-El Djouf meteorite are large chondrules (up to 1 cm in size; mean diameter: 1.0 +/- 0.6 mm), chondrule and mineral fragments, Ca,Al-rich inclusions, FeNi-metal (about 8-10 vol%), and dark inclusions embedded in a fine-grained fragment-bearing groundmass. Mineral compositions of the ten Acfer-El Djouf samples are similar to those of other CR chondrites. Most of the Ca,Al-rich inclusions are below 300 mum in size and rich in melilite and spinel. In some CAIs the rare phase CaAl4O7 is dominant. Fo-rich, Cr-bearing olivine (Fa0-4) and enstatite (Fs0-4) are the major phases of the chondrite. The meteorite is mildly shocked with a shock stage of S2 indicating a peak shock pressure of 5-10 GPa for the bulk meteorite. The oxygen isotopic compositions and carbon and nitrogen stable isotope geochemistry of the Acfer-El Djouf samples are very similar to those of the other CR-type chondrites. The major element composition of the Acfer-El Djouf meteorite is indistinguishable from CR chondrites. When compared to Renazzo the Acfer-El Djouf samples, however, have systematically lower contents of the moderately volatile elements Zn, Ga, As, Au, Sb, and Se, and the highly volatile elements Br, C, and N. This is thought to reflect primary differences between Renazzo and the Acfer-El Djouf meteorite.
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页码:1587 / 1603
页数:17
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