Experimental reproduction of a surface-encircling olivine rim in barred olivine chondrules

Barred olivine (BO) chondrules, submillimeter-sized silicate spherules characterized by parallel olivine bars (tabular in 3D) and rims that enclose the surface, record high-temperature processing in the solar nebula. However, their thermal history remains unconstrained due to the lack of experimental reproduction of complete rim-bar textures. Here, we experimentally reproduce the characteristic rim-bar texture using a laser-heated gas-jet levitation system. Olivine bars crystallized from highly undercooled melts within seconds, followed by rim formation during holding at 1300 °C for several minutes to one hour. Gas flow continuously cools the melt surface, triggering rim crystallization, while prolonged thermal gradient between cold rim and hot inside causes the thickening of rims by the expense of nearby bar dissolution, which differs from the conditions for natural BO chondrules. Our results suggests that BO chondrules form through total melting at high temperature ( > 1700 °C), rapid cooling to ~1300 °C to form olivine bars, and subsequent slow cooling that promotes rim formation and further crystallization. Olivine rim formation in barred olivine chondrules requires the surface to be cooler than the interior, which may occur through evaporation and latent heat loss, according to experiments on simulated samples using a laser-heated gas-jet levitation system.