Antarctic meteorites and micrometeorites as tracers of early solar system and planetary formation processes: Search for pre-solar grains in Antarctic meteorites

Abstract

Presolar grains are submicroscopic (some nms to some ?ms) mineral grains that formed before the solar system. They condensed in the stellar winds of stars in the late stadia of their evolution. Most presolar grains formed in low-mass stars, but some condensed in supernovae and novae ejecta. After residing in the interstellar medium, the presolar grains got incorporated in the dust and gas cloud that would later form our solar system. Some of these grains survived in interplanetary dust particles,
pristine meteorites and comets. As they formed in other stars where, due to nucleosynthesis, the isotopic composition in the stellar environment can deviate a lot from solar values, presolar grains can have an isotopic signature that differs significantly from the solar signature. This difference in isotopic composition is used to distinguish presolar grains from solar material. Presolar grains can have a very diverse mineralogy. Classically they are divided in carbonaceous (e.g. graphite, diamond, SiC) and oxygenous (oxides and silicates) grains. From all meteorites, presolar grains are most abundant in carbonaceous chondrites with up 235 ppm carbonaceous grains (Zhao et al., 2013) and 240 ppm oxygenous grains (Davidson et al., 2010). In ordinary chondrites they occur in much lower abundances with 41 ppm carbonaceous grains (Davidson et al., 2009) as a maximum. There is still
debate about the abundances in enstatite chondrites. Some studies point to similar values as ordinary chondrites (Zhao et al., 2010) and others point to much lower values (Ebata et al., 2006). In this study, presolar grains in the fine-grained matrix of the EH3 enstatite chondrite Yamato-691 (Y- 691) were researched. The sample was a polished thin section. Due to their small sizes, presolar grains occur in the fine-grained matrix of meteorites. First zones with high amount of fine-grained
matrix were located in the sample using scanning electron microscopy. The isotopic composition of these regions could then be researched using nanoSIMS.

Date of Award	30 Jun 2014
Original language	English
Awarding Institution	KU Leuven
Supervisor	Philippe Claeys (Promotor)