Petrogenesis of Néma 001, an alkali-rich meteorite from the acapulcoite-lodranite parent body

Primitive achondrites are meteorites characterised by granoblastic textures evidencing high-temperature metamorphism and low degrees of partial melting. These include the acapulcoite and lodranite meteorites, which originated from a common parent body. Acapulcoites experienced low degrees of partial melting (ca. <1 to 5%) and lodranites experienced higher degrees of partial melting (∼5-20%). Meteorite collections also include a sample of their chondritic precursor, Grove Mountains 020043, as well as limited examples of partial melting products, such as the mm-sized gabbroic clasts in the Lewis Cliff 86220 transitional acapulcoite-lodranite and the 4.86 g pyroxene-plagioclase coarse-grained Frontier Mountain 93001 meteorite. This suite of samples, thus, provides us with a crucial snapshot into the transition from chondritic material to differentiated planetesimals. Here we propose that the 75.8 g alkali-rich Néma 001 meteorite, a coarse-grained igneous meteorite composed primarily of ortho- and clinopyroxene, plagioclase, and olivine, also originated from the acapulcoite-lodranite parent body. This is supported by a bulk oxygen isotope composition that is undistinguishable from that of the acapulcoites-lodranites and similar ferromagnesian mineral Fe/Mn ratios. Petrological modelling suggests that Néma 001 represents silicate melts formed by ∼15% melting of a chondritic precursor similar to Grove Mountains 020043. With the addition of Néma 001, we now have a comprehensive suite of samples from the acapulcoite-lodranite parent body, including chondritic precursor material, residues from ∼1-20% partial melting, and variably differentiated igneous rocks. This unique suite of samples is key to further investigate melting and differentiation processes of asteroids, and supports the existence of partially differentiated planetesimals.