Investigation of the porosity of L/LL4 ordinary chondrite Bjurbole using synchrotron radiation microtomography and scanning electron microscopy: Implications for parent body evolution

Porosity is an essential property of chondritic meteorites and is closely related to the genesis, thermal evolution, metamorphism, and thermal properties of the meteorite parent bodies. We study porosity, its texture, and shapes at sub-micron resolution in 3D and 2D within a 0.35 cm3 sample of the L/LL4 ordinary chondrite (OC) Bjurbo center dot le using two techniques, synchrotron radiation microtomography (SR mu CT) and scanning electron microscopy (SEM). We employ automated segmentation tools that can be applied to both SR mu CT and SEM data. Successful segmentation results can be achieved by combining visual qualitative examination and machine learning algorithms. We report novel measurement results of three-dimensional porosity properties of Bjurbo center dot le, such as aspect ratio and connectivity of void spaces, and compare the results of 2D and 3D porosity analysis. The Bjurbo center dot le sample in this study is a complex, highly porous, and friable medium and the dominant type of porosity is intergranular, continuous porosity, which contains almost all porosity volume. The shapes of the void volumes have an important effect on the connectivity of the porosity and thermal transport properties. Positive correlations between void diameter and aspect ratio as well as void volume and connectivity are present in Bjurbo center dot le, which indicate that smaller voids have lower aspect ratios and lower connectivity. In Bjurbo center dot le, small, near-spherical voids with few connections have the highest relative frequency, whereas larger void spaces with higher aspect ratios and connectivity are significantly fewer. Completely isolated pores, i.e., voids surrounded by solid material, also have a high relative frequency, and they exist within the chondrules and the matrix. However, the volume percentage of these pores is negligible compared to that of the continuous porosity. Our results support the previously measured high porosities of Bjurbo center dot le. The volume percentage of intergranular void spaces, in particular in the matrix, and the measured high porosities are not in line with the results of thermal evolution and sintering models of chondritic parent bodies regarding petrologic type 4, which implies that Bjurbo center dot le originates from a parent body with an initial onion shell structure that fragmented during or after its metamorphic peak and quickly reaccreted into a rubble pile.

Automated summary

Porosity is an important property of chondritic meteorites and can be studied using synchrotron radiation microtomography (SR mu CT) and scanning electron microscopy (SEM). Our study on the Bjurbo sample reveals it to be a highly porous and complex medium, with intergranular continuous porosity as the dominant type. The shape of the void volumes affects the connectivity and thermal transport properties, with smaller voids having lower aspect ratios and connectivity. Completely isolated pores are present but have a lower relative frequency compared to continuous porosity.