A study of the minor element concentrations of spinels from two type B calcium-aluminum-rich inclusions: An investigation into potential formation conditions of calcium-aluminum-rich inclusions

We have conducted an electron microprobe study of minor element distributio ns among spinels from two type B1 calcium-aluminum-rich inclusions(CAIs): A llende TS-23 and Leoville 3537-2. We show that by maintaining the petrologi c context (edge, middle, and center of the inclusion plus their host silica te phase), four populations of spinels are resolvable based on their minor element contents. One population resides within the edge area (mainly mantl e melilite) and is characterized by the highest V contents. Unlike Leoville 3537-2, many edge grains from Allende TS-23 also have: high-Fe contents (u p to 4.0 wt%) and low-Cr values. Based on their V and Ti concentrations (wh ich is positively correlated), middle and center grains define a trend that is divided into three populations: spinels enclosed by melilite, fassaite, and anorthite. The overall range in Ti concentration based on fractional c rystallization should be much less than a factor of 2; however, the observe d range is considerably larger. The minor element contents of these grains are interpreted as recording alteration, primary fractional crystallization , and a complex igneous history that may involve remelting and recrystalliz ation. From our data, Allende TS-23 has experienced more alteration than Le oville 3537-2, which is consistent with previous petrologic studies of sili cates within these objects; yet both objects have likely been remelted (at least one additional melting event, possibly two, postdating the initial fo rmation of these CAIs). By Invoking a remelting history, the large range in Ti concentrations and the different populations of spinels can be explaine d. Although our data suggest that more than one generation of spinels exist within these objects, we are unable to establish any population of relic s pinel grains that predate the initial melting event.