New Constraints on the Formation of Igneous Rims around Chon-

Introduction: It has long been recognized that igneous rims (IRs) around chondrules are indicative of a second heating event, occurring after a dustrich mantle was acquired [1-8,14,15]. The textures of IRs suggest they were formed by the same type of heating mechanism as the majority of chondrules [1-8]. IRs have igneous textures, and contain larger, less-ferroan mafic silicate grains than those found in fine-grained rims of matrix-like material [2]. As defined by [5], IRs show petrographic evidence that these rims experienced heating events resulting in an appreciable (> 20%) degree of silicate melting. According to [1], igenous rims surround ∼ 50% of the chondrules in CV3 meteorites, ∼ 10% in H-LLL3 meteorites, and ≤ 1% in CO3 meteoreites. A compositional relationship exists between the core (primary) and the rim (secondary), with both showing similar degrees of oxidation [3,5]. This suggests that the primary accreted its dust mantle after cooling, while still in the chondrule-forming region [6]. IRs around low-FeO chondrules show high degrees of melting (90 ± 10 %), and those around highFeO chondrules show a lesser degree of melting [35]. Low-FeO and high-FeO rims, therefore, seem to have experienced different thermal histories. Nevertheless, both types are consistent with formation in a high-temperature event, with peak temperature ≥ 1400K [5].