Water Concentration Preserved in Mantle Xenoliths from French Volcanoes

A new study by Konstantinos Thomaidis, Jannick Ingrin, Etienne Deloule, Lydéric France, and Huan Chen has been published in the European Journal of Mineralogy (volume 38, pages 477–489) in 2026, detailing how water remains trapped within mantle xenoliths during eruptions on the Massif Central in France ¹.

Mantle xenoliths are fragments of ultramafic peridotite or pyroxenites that become incorporated into magma as it ascends through the lithosphere. Their composition preserves a record of conditions they experienced deep beneath Earth’s surface. The authors focused on hydrous‑point‑defect pyroxenes—minerals that host water molecules inside their crystal lattice—as natural tracers to evaluate the water content before and after eruption ¹.

The research aimed to clarify two key questions long puzzling petrologists. First, what mechanism allows xenoliths to retain their original hydrogen signature when exposed to high temperatures and rapid cooling associated with lava emplacement? Second, does the mode of eruption—effusive versus explosive—affect the amount of water preserved once they reach the surface? By examining samples from Allègre and Ray Pic volcanoes, the team sought to quantify any changes in water concentration resulting from these processes ¹.

Although the paper does not report numerical values for water loss or retention rates, it provides an experimental framework for future studies.