Inversely Zoned Chondrules: Clues to Early Solar System Formation

Chondrules are among the oldest solid components of our solar system and provide important clues to its early development. Especially inversely zoned chondrules (IZ chondrules) have been little studied so far and could provide new insights into the formation processes of the solar nebula. In this study, we make additionally analyse to the chemical and structural composition of IZ chondrules using optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), backscattered electron imaging (BSE), electron backscatter diffraction (EBSD) and Raman spectroscopy. Our investigations show that IZ chondrules have a core of Mg-rich pyroxene surrounded by an olivine rim. The high Fe content of the olivines (Fa 39-41 %), which is significantly higher than that of other chondrites, is remarkable. The core consists of radially arranged pyroxene crystals, with Mg-rich olivines (Fa34) occasionally occurring in the interior. The textural and chemical zoning indicates that these chondrules were formed in the earliest stages of the solar system and differ from classical chondrules. The formation of the pyroxene core is probably due to a rapid cooling of the protoplanetary nebula (500-2500 K/h). This was followed by a reheating to 1600-1800 K, which formed the olivine mantle. Another possibility was a subtle change in the composition of the chondrule, which may cause a shift in the liquidus phases from low ca pyroxene to iron-containing olivine. These results provide new insights into the diversity of chondrule formation processes and contribute to a better understanding of the early evolution of our solar system.