PRESOLAR GRAIN ABUNDANCE VARIATION IN THE MILLER RANGE 090019 CO3.1 CHONDRITE

Presolar grains condensed in the outflows of evolved red giant stars and the ejecta of supernovae (SNe) and novae. These grains have greatly anomalous isotopic compositions compared to solar system material, reflecting their stellar origins [1]. They have been identified in primitive meteorites, interplanetary dust particles (IDPs), Antarctic micrometeorites, and comet Wild 2 samples returned by NASA’s Stardust mission. Presolar silicates are one of the most abundant presolar phases and their concentrations extend up to 1.5% in primitive IDPs believed to derive from comets [2]. These grains are highly susceptible to alteration and destruction by secondary processing in the interstellar medium, nebula, and asteroid or comet parent body. Presolarsilicate abundance variations between primitive meteorites and chemical and mineralogical studies provide indications of the extent of secondary hydrothermal alteration [3, 4]. The abundance of presolar SiC grains is generally consistent among chondrites, but lower abundances in some meteorites have been attributed to thermal alteration [5, 6]. Presolar grain abundance variations attributed to localized alteration have also been reported within different regions of a chondrite [e.g., 7].Carbonaceous chondrites from the CO and CR groups have the highest abundances of presolar silicates among meteorites, attesting to their primitive nature. The CO3 chondrite Dominion Range (DOM) 08006 has the highest presolar O-rich grain abundance of ~260 ppm [8, 9]. MillerRange (MIL) 090019 is classified as a CO3.1 chondrite and has affinities to Acfer 094, DOM 08004/6 and Allan Hills (ALH) 77307. These chondrites have high presolar silicate abundances and contain high abundances of various types of refractory inclusions. We previously conducted detailed studies of CAIs in MIL 090019 [10, 11]. Here we evaluate its presolar grain inventory to assess the degree of parent body alteration and compare to other chondrites