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

Ten chondrites with chemical and mineralogical similarities to the car bonaceous chondrite Renazzo were recovered at two locations of the Sah ara: Acfer 059, 087, 097, 114, 139, 186, 187, 209, 270, and El Djouf 0 01. Although the El Djouf location is more than 500 km away from the A cfer location, all samples appear to result from a single fall based o n chemical and petrographic similarities and supported by light elemen t stable isotope geochemistry, noble gas record, and similar Al-26 con tents. The Acfer-El Djouf meteorite is classified as a CR (Renazzo-typ e) carbonaceous chondrite. This group presently comprises three non-An tarctic members (Al Rais, Renazzo, Acfer-El Djouf) and five Antarctic meteorites. The major lithological components of the Acfer-El Djouf me teorite are large chondrules (up to 1 cm in size; mean diameter: 1.0 /- 0.6 mm), chondrule and mineral fragments, Ca,Al-rich inclusions, Fe Ni-metal (about 8-10 vol%), and dark inclusions embedded in a fine-gra ined fragment-bearing groundmass. Mineral compositions of the ten Acfe r-El Djouf samples are similar to those of other CR chondrites. Most o f the Ca,Al-rich inclusions are below 300 mum in size and rich in meli lite and spinel. In some CAIs the rare phase CaAl4O7 is dominant. Fo-r ich, Cr-bearing olivine (Fa0-4) and enstatite (Fs0-4) are the major ph ases of the chondrite. The meteorite is mildly shocked with a shock st age of S2 indicating a peak shock pressure of 5-10 GPa for the bulk me teorite. The oxygen isotopic compositions and carbon and nitrogen stab le isotope geochemistry of the Acfer-El Djouf samples are very similar to those of the other CR-type chondrites. The major element compositi on of the Acfer-El Djouf meteorite is indistinguishable from CR chondr ites. When compared to Renazzo the Acfer-El Djouf samples, however, ha ve systematically lower contents of the moderately volatile elements Z n, 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.