Brief Formation Interval for Calcium-aluminum-rich Inclusions in the Early Solar Sys- Tem

A recent studyof the Al-Mgchronometer (t1/2 ∼ 730,000 yr) in six bulk CAIs from the Allende carbonaceous chondrite indicated that these objects may have formed over a short time interval, possibly within 50,000 yr [1]. However, in situ Al-Mg data for CAIs from a number of carbonaceous chondrites suggest that these may have experienced a series of later transient heating events over ∼ 300,000 yr [2]. This is in contrast with chondrules, the most abundant component of chondritic meteorites, which appear to have formed over a time interval of ≥ 3 Myr [1,3]. To elucidate the timing of the CAI-forming event(s), we have extended our Al-Mg study of CAIs to other carbonaceous chondrites such as the Vigarano, SAH98044 and NWA779 meteorites. Rare earth elements (REE) analyses of a subset of these CAIs show they represent a wide range of types including objects with typical group II, III andVREEpatterns. We also report high-precision δ Mg* measurements [the per mil (h) excess in Mg/Mg due to the presence of radiogenic Mg (Mg*)] for terrestrial, lunar and martian samples, as well as chondrite meteorites, in order to assess the degree of Mg isotope heterogeneity in the inner Solar System.