Solar nebula magnetic fields recorded in chondrules from the Murchison CM chondrite

Paleomagnetic studies of chondritic meteorites in recent years have revealed strong magnetic fields in the protoplanetary disk, suggesting amplification through magnetohydrodynamic instabilities. Further, paleointensities from different carbonaceous chondrite groups appear to show large contrasts across a factor of >102. Although age differences may account for some of this spread, these results suggest heterogeneous magnetic fields in the outer solar system, potentially representing a novel method to establish affinities in the formation regions of different chondrite groups. Simultaneously, whether chondrules and their host chondrites formed in the same nebular region remains uncertain, with inner solar system geochemical affinities reported in carbonaceous chondrite chondrules.

We extracted and conducted paleomagnetic analyses of dusty olivine-bearing chondrules from the Murchison CM chondrite. This type of chondrules has been the subject of previous studies on LL and CO group chondrites because they contain abundant sub-micrometer scale Fe metal that can reliably record ancient magnetic fields. Nebular field paleointensities retrieved from these Murchison chondrules can be compared to existing LL, CO, CV, CR, and ungrouped chondrite data to identify which samples formed in similar magnetic environments. Further, analysis of Murchison chondrules offers a unique opportunity to directly compare non-zero chondrule and matrix-derived paleointensities for the first time, since a previous study recovered paleointensities of >2 µT from CM matrix.

Our alternating field demagnetization of five dusty olivine-bearing chondrules shows that at least three samples carry a high coercivity component of magnetization that passes a paleomagnetic conglomerate test (Fig. 1). Preliminary paleointensity estimates suggest that these chondrules experienced strong, >100 µT magnetic fields during their formation, consistent with paleointensities of CO chondrules but higher than values recorded by CM matrix. Ongoing analysis of more chondrules will determine robust paleointensities to test a common formation environment for CM chondrules, other carbonaceous chondrite chondrules, and CM chondrite matrix.