DaG 275

standby for dar al gani 275 photo
Found March 24, 1997
27° 21.74′ N., 16° 05.38′ E. Two fragments of this formerly Karoonda-type carbonaceous chondrite were found in the Libyan Sahara weighing a total of 492 g. Dar al Gani 275 has been weakly shocked to stage S2, and has been highly weathered to grade W4 on the Wlotzka weathering scale (1993). Another similar meteorite of petrologic type 4/5, DaG 250, was also found in the Sahara. However, DaG 275 has a different cosmic-ray exposure age (35.2 m.y.) compared to DaG 250 (27 m.y.), and the noble gas data do not exclude separate parent bodies.

The CK chondrites were designated as a separate group in 1990, named for the only observed fall at the time in Karoonda, Australia (a second CK4 fall occurred in Kobe, Japan in 1999). Members of the CK group were previously distinguished from the CO and CV groups based on the following characteritics: 1) low chondrule/matrix ratio; 2) intermediate chondrule size; 3) lack of chondrule rims; 4) low abundance of refractory inclusions; 5) low C content; 6) intermediate abundance of refractory lithophiles; 7) O-isotopic composition. However, in a study of the CK group conducted by Greenwood et al. (2003), it was proposed that these characteristics are evidence of the highly metamorphosed nature of most members of this group. They found that CK bulk compositions are similar to those of CV chondrites, and that the other defining criteria could be explained in terms of higher degrees of metamorphic alteration. Furthermore, they argued that the few CK3 members that have been identified are more similar to oxidized CV3 members, thus questioning whether CK chondrites actually represent a unique carbonaceous chondrite group.

To that goal, a petrologic study was conducted by Chaumard et al. (2009) comparing the CK chondrites to the oxidized subgroup of CV chondrites. They found that matrix, chondrule and CAI abundances in CK chondrites are similar to those characteristics in some oxidized CV members. Moreover, dark inclusions commonly present in the CV group are also abundant in the CK group. They also determined that CK chondrites have an olivine chemistry that is correlated with the textural equilibration of the matrix. Taking these findings into consideration, the investigators suggest that the CK group might represent a metamorphic continuum beginning with the oxidized CV subgroup rather than representing a separate parent body.

After in-depth analyses of many CV and CK meteorites having a wide range of petrologic types was conducted by Wasson et al. (2013), they presented a reasoned argument for merging the CK and CV groups into a single unified group. The geochemical and petrological justification for such a reclassification of the CK chondrites, along with details of their proposed taxonomic scheme, can be found on the Dhofar 015 page. Subsequent studies have demonstrated a high likelihood for separate parent bodies. One such study conducted by Dunn et al. (2016) compared magnetite in a number of CK and CV chondrites. They presented geochemical, mineralogical, and petrographic evidence which is more consistent with separate CV and CK parent bodies. Another study conducted by Yin et al. (2017) utilized a coupled Δ17O vs. ε54Cr diagram to plot several CK and CV chondrites. Through this technique they demonstrated that these two meteorite groups derive from separate parent bodies. Details of these studies can also be found on the Dhofar 015 page. The specimen of DaG 275 shown above is a 15.2 g complete slice.

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