Program > Browse abstracts by speaker > Li Huijuan

Lunar apatite has been shown to have volatiles concentrations (F, Cl and H2O) comparable to terrestrial apatite. However, in comparison to Earth, the Moon is believed to be volatile-depleted. The prevailing theory advanced to explain such a paradoxical phenomenon is fractional crystallization (Boyce et al., 2014). One clear distinction between lunar and terrestrial apatite is their sulfur composition. While their reported S contents cover similar ranges (up to several thousand ppm), it is in fact S2- in lunar apatite, whereas terrestrial apatite generally contains less than ~100 ppm S2- under reduced conditions (due to the incompatible nature of S2- in apatite), with higher S contents corresponding to S6+ in an oxidized environment. We demonstrate experimentally that fractional crystallization can produce the high S2- contents observed in lunar apatite, thus providing experimental support for the fractional crystallization theory. In combination with fractional crystallization modelling, we propose that the distinct difference in S compositions between lunar and terrestrial apatite results from depletion of H2O in lunar magma in comparison to its terrestrial counterpart. Such a depletion reflects both the depletion of H2O in the lunar mantle source, and the extensive degassing experienced by lava flows on the lunar surface.