[meteorite-list] NWA 1152, Sahara 00182, Tagish Lake, MAC 88107, MAC 87300

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Sat Apr 23 17:01:42 2005
Message-ID: <DIIE.0000003000003755_at_paulinet.de>

SMITH C.L. et al. (2004) NWA 1152 and Sahara 00182: New primitive carbonaceous
chondrites with affinities to the CR and CV groups (MAPS 39-12, pp. 2009-2032):

Introduction (excerpts):

Among the five chondrite classes (carbonaceous, ordinary, enstatite, Rumuruti-like,
and Kakangari-like), the carbonaceous chondrites account for the greatest diversity
in chemical composition and texture. Although these meteorites have been extensively
studied, the relationships among and between the carbonaceous chondrite groups are
often obscure. Recent finds from Antarctica and the hot deserts have greatly increased
the number of carbonaceous chondrite samples within our collections. Correspondingly,
the chemical, mineralogical, and petrographic characteristics of recognized carbonaceous
chondrites have become more diverse, with the result that many samples may not easily
be assigned to one of the traditionally recognized classes. For example, the Antarctic
meteorites MacAlpine Hills (MAC) 87300 and MAC 88107 appear to be intermediate between
CM and CO meteorites on the basis of elemental abundance and CAI mineralogy, suggesting
a link between these classes (Russell et al. 2000).

Likewise, the unusual carbonaceous chondrite Tagish Lake shows characteristics similar to
both the C1 and CM groups on the basis of light element geochemistry (Grady et al. 2002)
and overall element abundance patterns (Mittlefehldt 2002), although in terms of its mineral-
ogy and petrography, it cannot be allied with either the C1s or the CMs (Zolensky et al. 2002).

The carbonaceous chondrite Acfer 094 is believed to be unique though it shows some similarities
with the both the CO and CM chondrites; the chemical composition and abundance of certain chon-
drule types suggests affinity with the CMs, whereas the lack of phyllosilicates and the oxygen
isotope composition is more consistent with a C03 classification (Newton et al. 1995).

Several workers have attempted to estimate the number of parent bodies required to supply the
total known range of carbonaceous chondrites and to determine genetic links between them using
the oxygen three-isotope system. Clayton and co-workers initially suggested that oxygen isotopes
can be used to indicate asteroidal sources - samples with different bulk DELTA 17 0 values being
likely to originate on different parent bodies (Clayton 1999). However, this picture is compli-
cated by the models of Clayton and Mayeda (1984) and Young et al. (1999) who have shown that the
differences in bulk DELTA 17 0 can plausibly be accounted for by differences in the degree of
aqueous alteration, provided that the water and rock sources have distinguishable oxygen isotope
compositions.

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Best wishes,

Bernd
Received on Sat 23 Apr 2005 05:01:40 PM PDT