Preservation of the water concentration of mantle xenoliths in the Ray Pic volcano (FMC)
Résumé
The ability of xenoliths to preserve water lithospheric signatures remains an unsolved
question for many years. We report water content in olivine and pyroxenes of peridotite
xenoliths from Ray Pic volcano (Massif central, France). Xenoliths were sampled from
products of an explosive eruption (pyroclastic deposit) and an effusive eruption at five different
locations along the 10 km lava flow.
Water content in xenoliths from the lava flow is independent of its location in the lava:
ol < 1, opx 190-270 and cpx 430-640 wt. ppm H2O. Results suggest that the cooling and
solidification of the lava had no impact on water content.
The xenoliths from the explosive event have systematically more water: ol 3-12, opx
330-460 and cpx 810-890 wt. ppm H2O. These values are either comparable with or lower than
the values reported previously from the same locality (1). It shows that xenoliths recovered
from explosive eruptions have higher water content than the ones from effusive eruptions, but
also that water content can be different from one explosive event to another Conclusion is that
water content can rapidly be reset during magma degassing prior to eruption. Degassing
controls water content of xenoliths.
Among the xenoliths studied, two have spectral signatures different from others. This
different spectral signature has also been reported from other volcanoes (2, 3). The coexisting
of different spectral signatures, which have not been erased during degassing, are probably the
only OH signatures fully preserved from depth.
1 Azevedo-Vannson S.,et al. Chemical Geology 575 120257 (2021)
2 Denis C.M.M. et al. Lithos 226 256-274 (2015)
3 Patkó L. et al. Chemical Geology 507 23-41 (2019)
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