Olivine in EH Chondrites as an indicator of metamorphism in the enstatite chondrite parent body

High-Fe enstatite chondrites (EH chondrites) are samples of planetesimals accreted in a region of the solar nebula with very low oxygen fugacity [1]. A consequence of this reduction is that Fe exists as metal rather than as FeO in silicates, with pyroxene rather than olivine being the most common mineral (stabilized by low (FeO+MgO)/SiO2) [1, 2]. Like ordinary chondrites, EH chondrites are divided according to textural and limited geochemical criteria, with petrologic type 3 being unequilibrated nebular rocks and types 4-6 having been increasingly metamorphosed. Suggested mineralogical and geochemical criteria for classifying this process include the presence of disequilibrium mineral assemblages e.g. olivine and silica, which react according to Mg2SiO4 + SiO2 -> Mg2Si2O6 [3], and mineral geochemistry, particularly Cr in olivine [4]. We are attempting to consolidate these classification schemes with an investigation of mineral modal abundances and geochemistry.