THE FORMATION HISTORY OF LAYERED CHONDRULES IN ACFER-139 (CR)

Chondrules are spherical grains made of silicates and metal that represent some of the oldest materials our solar system. Before they accumulated into their meteorite parent bodies, they existed as molten droplets condensing out of the protoplanetary disc. Acfer-139 (CR) is a carbonaceous chondrite with large multilayered chondrules. The multilayered chondrules are composed of a silicate core surrounded by alternating layers of silicate minerals and metal. Serial sectioning was used to analyze the sample in three dimensions. Electron Microprobe Analysis (EMPA) and Laser Ablation- Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) was used to create elemental maps of Acfer-139 (CR) and determine the geochemistry of silicate layers and metal layers of each thick section cut. X-ray computed tomography with a Phoenix v/tome/x CT scanner was used to construct a 3-D model of a large multilayered chondrule named Chondrule-1 with concentric layers of silicate and metal. The 3-D models allow for the determination of volumes of silicate layers and metal layers. A core to rim analysis of Chondrule-1 revealed increasing silica existing as olivine in the core and pyroxene at the edge. An increase in more volatile elements like Au and Ga occurred from core to rim as well as a decrease in refractory elements like Ni. While the formation of layered chondrules is still being examined, the concentric layers of silicates and metals combined with the changes in chemistry from core to rim support a formation consisting of silicate (olivine to pyroxene) and metal layers being accreted onto the high magnesium olivine silicate core in a cooling protoplanetary disc.