The O-Isotope Compositions of Chondrules From an H3.1 Chondrite: The Origins of Chondrule Precursors and Implications for Grain Migration in the Early Solar System

In recent years, it has become increasingly evident that sub-mm sized-particles migrated within the early Solar System (e.g., [1–5]). However, the extent and direction(s) of grain migration throughout the protoplanetary disk are not well constrained. Different chondrite groups have distinct chemical and isotopic characteristics (e.g., [6]) and are believed to have formed at different heliocentric distances and at slightly different times [e.g., 7,8], making them valuable records of grain migration in the disk. In fact, studies of minimally altered chondrites have revealed compelling evidence for grain migration (e.g., [2–5,9–16]). Partially melted chondrules often preserve unmelted precursor silicates, known as relict grains, whose chemical and O-isotope compositions can be used to determine their origins. These relict grains may exhibit similarities to chondrule silicates from other chondrite groups and/or refractory inclusions, and thus imply potential grain migration in the protoplanetary disk (e.g., [3]). As part of our ongoing efforts to constrain the extent and direction(s) of grain migration throughout the protoplanetary disk, we have undertaken a search for chondrule precursors in multiple different chondrite groups [2–4,12,14–18]. Most of our work to date has focused on carbonaceous chondrite groups from the outer Solar System.

The unequilibrated ordinary chondrites (UOCs) formed in the inner Solar System [e.g., 7]. Some UOC chondrules contain olivine that is a unique compositional match to that from Comet Wild 2, ‘the forbidden triangle’; originally named so by [19]. This unique composition shared between UOCs and Comet Wild 2 may suggest that UOC chondrule fragments migrated from the UOC chondrule-forming region in the inner Solar System to the comet-forming region. Here we present O-isotope data for UOC chondrules from one of the least thermally altered H3 chondrites (an H3.1) to constrain the origins of their chondrule precursors and investigate the origin(s) of olivine from the so-called ‘forbidden triangle’.