Semarkona: Lessons for chondrule and chondrite formation

TL;DR

This paper analyzes the Semarkona chondrite to understand chondrule formation, suggesting rapid melting and settling in the Solar Nebula, with implications for parent body formation and material filtering.

Contribution

It provides new insights into the formation and processing of chondrules and matrix material, emphasizing rapid melting and differential collisional properties.

Findings

Limited melting of matrix material in the Solar Nebula

Chondrules formed in surface layers and settled quickly

Filtering of unprocessed matrix during parent body formation

Abstract

We consider the evidence presented by the LL3.0 chondrite Semarkona, including its chondrule fraction, chondrule size distribution and matrix thermal history. We show that no more than a modest fraction of the ambient matrix material in the Solar Nebula could have been melted into chondrules; and that much of the unprocessed matrix material must have been filtered out at some stage of Semarkona's parent body formation process. We conclude that agglomerations of many chondrules must have formed in the Solar Nebula, which implies that chondrules and matrix grains had quite different collisional sticking parameters. Further, we note that the absence of large melted objects in Semarkona means that chondrules must have exited the melting zone rapidly, before the chondrule agglomerations could form. The simplest explanation for this rapid exit is that chondrule melting occurred in surface layers of the disk. The newly formed, compact, chondrules then settled out of those layers on short time scales.