Northwest Africa 13669, a reequilibrated nakhlite from a previously unsampled portion of the nakhlite igneous complex

Abstract

AbstractNorthwest Africa (NWA) 13669 is a recently found nakhlite and here, we use 2‐D and 3‐D mineralogy and texture, quantitative textural analysis of pyroxene, bulk rock and mineral major and trace element compositions, and melt inclusion analyses to assess its formation and emplacement. Using these combined results, we determine that NWA 13669 is derived from a depleted mantle source common to nakhlites and modeled parental melt compositions from olivine‐ and pyroxene‐hosted melt inclusions record similar major element trends to other nakhlites, including an alkali enrichment. Homogeneous pyroxene and olivine and diffusive reequilibration of trace elements in melt inclusions provide evidence for magma storage in a crystal mush within the nakhlite plumbing system and suggest NWA 13669 has undergone extensive reequilibration. Quantitative textural analysis of NWA 13669, including crystal size distribution (CSD) profiles, CSD slope and intercepts, and residence times, are similar to the Yamato nakhlite group, and indicate that NWA 13669 likely experienced similar emplacement conditions. However, differences in bulk rock and mineral compositions suggest NWA 13669 represents a new flow or sill from a previously unsampled portion of the nakhlite igneous complex, further increasing the diversity of the nakhlite suite.