Earliest rock fabric formed in the Solar System preserved in a chondrule rim

Abstract

Rock fabricsthe preferred orientation of grainsprovide a window into the history of rock formation, deformation and compaction. Chondritic meteorites are among the oldest materials in the Solar System 1 and their fabrics should record a range of processes occurring in the nebula and in asteroids, but due to abundant fine-grained material these samples have largely resisted traditional in situ fabric analysis. Here we use high resolution electron backscatter diffraction to map the orientation of sub-micrometre grains in the Allende CV carbonaceous chondrite: the matrix material that is interstitial to the mm-sized spherical chondrules that give chondrites their name, and finegrained rims which surround those chondrules. Although Allende matrix exhibits a bulk uniaxial fabric relating to a significant compressive event in the parent asteroid, we find that fine-grained rims preserve a spherically symmetric fabric centred on the chondrule. We define a method that

The early impact histories of meteorite parent bodies

“…, ; Blum ; Bland et al. ). The gentle manner in which dust grains must collide during planet formation probably leads to bodies with high porosities (Blum and Wurm ; Teiser and Wurm ).…”

“…Indeed, it is thought that the porous nature of early planetesimals is seen in the fabric of the Allende meteorite, with initial porosities reaching 60–70% (Bland et al. ).…”

“…These early bodies are likely to have contained a significant fraction of pore space (Dominik and Tielens ; Bland et al. ). Some planetesimals grew to protoplanets; the first stage of this growth is termed runaway growth (Greenberg et al.…”

Thermal and photophoretic properties of dust mantled chondrules and sorting in the solar nebula

“…Assuming that the material properties of the dust are the same on average, porosity of the dust rim is still a free parameter. The work by Bland et al (2011) suggests that mantle porosities are on the order of 0.7 or more. This is consistently on the same order of porosities to be expected from dust experiments (Teiser et al 2011).…”

“…As bare chondrules move through a dusty disk they would collect the dust. This dust is compressed to the observed rims, eventually (Bland et al 2011;Metzler et al 1992;Ormel et al 2008;Morfill et al 1998;Carballido 2011).…”