Evolved components in the eucrite parent body: Records in the layered eucrite Northwest Africa 8021

Yang He, Xiao-Wen Liu, Ai-Cheng Zhang

Version of Record online: 20 April 2022


“In this study, we report the petrography and mineralogy of a brecciated eucrite Northwest Africa (NWA) 8021, which shows a locally layered texture with one layer containing graphic clasts and Si,Ti-rich regions. The graphic clasts contain rod-like grains of silica phases, augite, K-feldspar, and Ca-phosphate minerals included in anorthite. Some of the clasts contain relatively coarse grains of quartz, K-feldspar, and augite, which are chemically different from the rod-like phases, indicating different origins. All of the augite grains in the graphic clasts have rare earth element (REE) concentrations higher than those in typical eucrites. The bulk Na2O+K2O contents of the graphic clasts are higher than typical eucrites. All of these chemical features indicate that the graphic clasts were probably derived from an evolved parent rock. Low-degree partial melting of the eucritic crust (<10%) is required to generate a melt equilibrated with the REE-rich rod-like pyroxene from the graphic clasts. The Si,Ti-rich regions contain high abundances of silica phases (~52 vol%) and ilmenite (~9 vol%), probably derived from an evolved Si,Ti-rich rock (dacite). The evolved components observed in NWA 8021 are different from other evolved components observed in howardites and indicate more diverse evolution in the eucrite parent body than previously thought.”