NORTHWEST AFRICA 735


CK4
standby for northwest africa 735 photo
Purchased January 1999
30° 37' N., 4° 07' W.

Several pieces of this meteorite having a combined weight of 161 g were purchased in Zagora, Morocco by American collector A. Lang. Northwest Africa 735 was classified by Dr. T. Mickouchi at the University of Tokyo as a CK4 carbonaceous chondrite with a shock stage of S3. Heavy weathering consistent with a W3 on the Wlotzka weathering scale (1993) has obscured many of the chondrules in this meteorite. A more useful weathering index (wi) was developed by Rubin and Huber (2005) for the highly oxidized meteorites of the more equilibrated CV members and the R chondrite group. This index is based on the modal abundance of brown-stained silicates as visually determined on a thin section in transmitted light at ~100× magnification.

Meteorites in the CK group were generally classified as such based on their lower abundances of refractory lithophile elements and their lack of CAIs and coarse-grained rims around chondrules compared to members of the CV group. 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 photo above shows a 3.69 g slice of NWA 735.