The Fukang pallasite: Characterization and implications for the history of the Main-group parent body

We report the results of a study of the Fukang pallasite that includes measurements of bulk composition, mineral chemistry, mineral structure, and petrology. Fukang is a Main-group pallasite that consists of semiangular olivine grains (Fo 86.3) embedded in an Fe-Ni matrix with 9-10 wt% Ni and low-Ir (45 ppb). Olivine grains sometimes occur in large clusters up to 11 cm across. The Fe-Ni phase is primarily kamacite with accessory taenite and plessite. Minor phases include schreibersite, chromite, merrillite, troilite, and low-Ca pyroxene. We describe a variety of silicate inclusions enclosed in olivine that contain phases rarely or not previously reported in Main-group pallasites, including clinopyroxene (augite), tridymite, K-rich felsic glass, and an unknown Ca-Cr silicate. Pressure constraints determined from tridymite (<0.4 GPa), two-pyroxene barometry (0.39 ± 0.07 GPa), and geophysical calculations that assume pallasite formation at the core-mantle boundary (CMB), provide an upper estimate on the size of the Main-group parent body from which Fukang originated. We conclude that Fukang originated at the CMB of a large differentiated planetesimal 400-680 km in radius.