Calcium-Aluminum-Rich Inclusions in Chondritic Meteorites

Abstract

Calcium-aluminum-rich inclusions (CAIs) are sub-mm- to cm-sized clasts in chondritic meteorites. They are composed almost entirely of CaO-Al2O3-MgO-SiO2-TiO2, and they contain the same minerals predicted by thermodynamic calculations to condense out of a gas of solar composition during cooling from very high temperatures. These features, together with ages of 4.567 Ga, suggest that CAIs are the oldest and most primitive solid objects formed at the time our solar system was born. CAIs possess endemic nuclear anomalies of nucleosynthetic origin, enrichment in 16O relative to other solar system materials, and also radiogenic anomalies from the in situ decay of short-lived nuclides such as 26Al and 10Be that existed when the CAIs (and solar system) formed. CAIs are complex objects whose petrologic and isotopic properties give clues to the events - and chronology of those events - that occurred during the first 1-2 million years of the solar system's existence. Reading that ancient record has been greatly enabled by recent and continuing advances in analytical laboratory instrumentation, and thus interest in CAIs remains very high. © 2014 Elsevier Ltd. All rights reserved.