Mineralogical studies of differentiated bodies in the early Solar System

Abstract

Although achondrites represent only 5% of the global collection, they offer insights into the early igneous and metamorphic processes that occurred on differentiated planetesimals and protoplanets in the early Solar System. I have studied achondrites, particularly focusing on the petrogenesis of HED meteorites (howardites, eucrites, and diogenites). HED meteorites are the largest group of differentiated achondrites that probably originated from the asteroid 4 Vesta. Based on the thermal history and geochemical characteristics of eucrites and diogenites, the crust of the HED parent body developed through lava eruptions and shallow intrusions of eucrites over a short period. Later, diogenite plutons intruded into the eucritic crust. These processes caused global crustal metamorphism and partial melting of the early crust. The presence of a few meteorites petrologically similar to eucrites but with different oxygen isotopic compositions suggests the existence of multiple protoplanets undergoing similar geologic processes in the early Solar System. The discovery of the oldest andesitic achondrite unveils new perspectives on the volcanism of differentiated meteorite parent bodies. The partial melting of chondritic meteorites likely produced Si- and Na-rich (i.e., andesitic) melts, yet such meteorites are extremely rare in global collections. It is inferred that the parent bodies of these achondrites have disrupted and did not survive. As the curator, I have been managing the Japanese Antarctic meteorite collection, making these valuable samples available to the scientific community. These meteorites provide crucial insights into the processes that took place in the early Solar System.