58Fe AND 54Cr IN EARLY SOLAR SYSTEM MATERIALS

Stepwise dissolution of primitive meteorites exhibits large 54Cr anomalies but no collateral effects on 58Fe and 48Ca, two other neutron-rich nuclides from the iron peak. These results suggest that 54Cr must have been produced in particular zones of the rare Type Ia supernovae or that 48Ca and/or 58Fe were produced together in Type II supernovae and were chemically separated into some mineral phase that favors Cr over Ca and Fe, and it is the dissolution properties of that phase that is driving the isotopic effect in leaching. The recent findings of nanometer-size oxide grains with very large 54Cr excesses favored the latter scenario for the origin of the mono-isotopic Cr isotopic effect. In addition, the absence of isotopic variations in the 58Fe/54Fe ratio at the mineral scale confirms that the short-lived nuclide 60Fe (T 1/2 = 2.62 Myr) was homogeneously distributed to a less than 15% dispersion in the early solar nebula.