Petrogenesis of basaltic shergottite Northwest Africa 5298: Closed-system crystallization of an oxidized mafic melt

摘要: Abstract– Northwest Africa (NWA) 5298 is an evolved basaltic shergottite that has bulk characteristics and mineral compositions consistent with derivation from oxidized reservoir in Mars. Chemically zoned clinopyroxene (64.5%, augite pigeonite), interstitial lath-shaped plagioclase (29.4%, An40 to An55), constitutes the of this meteorite. The been converted by shock both isotropic maskelynite spherulitic, birefringent feldspar representing a quenched vesicular melt. remainder rock consists minor amounts Fe-Ti oxides (ilmenite titanomagnetite), phosphates (merrillite apatite), silica polymorph, fayalite, pyrrhotite, baddeleyite, hot desert weathering products (calcite barite). Oxygen fugacity derived oxide thermobarometry close quartz-fayalite-magnetite (QFM) buffer indicating late stage evolution magma occurred under more oxidizing condition than those recorded most other shergottites. Merrillite contains largest abundances rare earth elements (REE) all phases, thereby controlling REE budget NWA 5298. calculated pattern normalized CI chondrite relatively flat. patterns rock, clinopyroxene, plagioclase, phosphate closed-system chemical behavior no evidence crustal contamination or postcrystallization disturbance contents these phases.