Geochemical characteristics of the La Réunion mantle plume source inferred from olivine-hosted melt inclusions from the adventive cones of Piton de la Fournaise volcano (La Réunion Island)
Résumé
Major and trace element compositions were
obtained for bulk rocks and melt inclusions hosted in olivine
crystals (Fo > 85) from the adventive cones of the Piton de
La Fournaise volcano (La Réunion Island). Ratios of highly
incompatible trace elements for these magmas are used to
identify the nature of the La Réunion mantle plume source.
Although adventive cone lavas display unusual major ele
-
ment compositions compared to the historical lavas of the
volcano (e.g., lower CaO/Al
2
O
3
), trace element data suggest
that the magmas emitted by the adventive cones originate
from a common chemical source. This source may corre
-
spond to either a homogeneous mixed source of different
mantle components or a near-primitive less-differentiated
mantle source. The melt inclusions display ratios of highly
incompatible elements (e.g., Th/La, Nb/La) which are simi
-
lar to primitive mantle values, and lower Nb/U ratios com
-
pared to most oceanic basalts. These results and previous
isotopic and trace element data suggest that La Réunion
plume samples a source which is intermediate between a
primitive-like mantle domain and a slightly depleted one
almost unaffected by the recycling processes. This source
could have originated from early depletion of the primitive
mantle. Assuming a depletion 4.45 Gyr ago, ~10% melting of this slightly depleted source could explain the enriched
trace element concentrations of the melt inclusions