NORTHWEST AFRICA 2797


L3.8
northwest africa 2797 photo
Purchased 2005
no coordinates recorded

A single unequilibrated chondrite weighing 1,211 g was found in the Sahara Desert and sold to G. Hupé in Erfoud, Morocco. This chondrite was analyzed and classified at Northern Arizona University (J. Wittke and T. Bunch) and was assigned to subtype L3.8.

In their modeling of the accretion and impact history of ordinary chondrites, Blackburn et al. (2017) calculated the timing of the catastrophic disruption of the H- and L-chondrite parent bodies to be ~60 m.y. after CAIs. This timing is consistent with two competing dating techniques—U–Pb (and Hf–W) chronometry and metallographic cooling rates (Ni diffusion profiles in Fe-metal)—which record cooling associated with both an onion shell structure prior to disruption and a rubble pile after disruption, respectively. Utilizing Pb–phosphate age data, Edwards et al. (2017) determined that the H and L chondrites of petrologic type 6 (i.e., those located at the greatest depths in a concentrically zoned body) show a similar timing for closure of the Pb-phosphate system of ~60 m.y. after CAIs; this age reflects the occurrence of ubiquitous quenching during parent body disruption. Employing thermal models, they constrained the timing of accretion for the two parent bodies to 2.0–2.35 m.y. after CAIs, and they derived an estimate for the minimum size of the two parent bodies of ~275 km in diameter.

Northwest Africa 2797 has a shock stage of S2 and a weathering grade of W2. The specimen shown above is a 3.2 g partial slice.