The fate of magmas in planetesimals and the retention of primitive chondritic crusts

- We model the fate of volatiles and magmas in igneous planetesimals.
- We find that free volatiles are readily lost as gases and supercritical fluids.
- The dry melts on CV and CM parent bodies were negatively buoyant.
- This supports the survival of CV and CM chondrites on differentiated bodies.
- Our findings support a relationship between the largest E-type asteroids and aubrites.

High abundances of short-lived radiogenic isotopes in the early solar system led to interior melting and differentiation on many of the first planetesimals. Petrologic, isotopic, and paleomagnetic evidence suggests that some differentiated planetesimals retained primitive chondritic material. The preservation of a cold chondritic lid depends on whether deep melts are able to ascend and breach the chondritic crust. We evaluate the likelihood of melt ascent on a range of chondritic parent bodies. We find that, due to the efficient ascent of free volatiles in the gas and supercritical fluid phases at temperatures still below the solidus for silicates and metals, mobile silicate melts on planetesimals were likely volatile-depleted. By calculating the densities of such melts, we show that silicate melts likely breached crusts of enstatite chondrite compositions but did not ascend in the CV and CM parent bodies. Ordinary chondrite melts represent an intermediate case. These predictions are consistent with paleomagnetic results from CV and CM chondrites as well as spectral observations of large E-type asteroids.