Mn-Cr


Mn and Cr both transition metals that have similar chemistries, but they are fractionated into different generally refractory (early-forming) minerals in meteorites.

53Mn decays to 53Cr by electron capture.

Mn-Cr method

The short-lived radioactive nuclide 53Mn was synthesised in a stellar interior or during a supernova event prior to formation of our solar system and is now extinct. Its decay products are preserved in some meteorites.

Enstatite chondrites are highly reduced, implying formation closer to Sun than the other classes of meteorites. They also have chondritic 55Mn/52Cr but have initial 53Cr/52Cr well below other meteorites. Based on 53Cr/52Cr measurements of different classes of meteorites and their inferred nebular formation environment, the 53Cr/52Cr ratio is observed to increase with radial distance from Sun. This variation in initial 53Cr/52Cr may be due to a radially heterogeneous distribution in initial 53Mn abundance (more plausible) or to the early Mn/Cr fractionation in the solar nebula (with initially homogeneneous 53Mn distribution). So these observations imply either that there was heterogeneous injection of 53Mn into the solar system, or that volatility-controlled Mn/Cr fractionation (redistribution of Mn outwards relative to Cr) occurred during condensation of an initially uniform nebula.