High porosity fine-grained rims in CM Murchison revealed through sub-resolution XCT imaging with Xe gas

Abstract

Fine-grained rims (FGRs) are dust-sized material that surrounds chondrules and refractory inclusions in chondritic meteorites. Multiple lines of theoretical, experimental, and empirical evidence point to their formation from the accretion of nebular dust onto chondrule surfaces prior to the formation of chondrite parent bodies [e.g., 1-4]. Recently, we have applied X-ray computed tomography (XCT) to examine the 3D morphology of FGRs, finding that the chondrule size to rim volume relationship is consistent with their formation in a turbulent, rather than laminar, nebular setting [3]. Modeling studies have suggested that the internal porosity structure of the FGRs is also dependent on nebular conditions such as the degree of turbulence and grain charge [5, 6]. However, the size of pores within FGRs is submicronto micron-sized, and studies so far have utilized scanning electron microscopy (SEM) which limits the volume of observation and provides only a 2D picture of the porosity structure. As a 3D imaging technique, XCT is well suited to get around the 2D observational limitation, but the small size of the pores still necessitates a small volume (< ~1 mm) using traditional XCT imaging.