Recycled Components in Mantle Plumes Deduced From Variations in Halogens (Cl, Br, and I), Trace Elements, and ³He/⁴He Along the Hawaiian‐Emperor Seamount Chain

Abstract

Halogens are primarily located within surface reservoirs of the Earth; as such they have proven to be effective tracers for the identification of subducted volatiles within the mantle. Subducting lithologies exhibit a wide variety of halogen compositions, yet the mantle maintains a fairly uniform signature, suggesting halogens may be homogenized during subduction to the mantle or during eruption. Here we present halogen (Cl, Br, and I), K, noble gas, and major and trace element data on olivines from three seamounts along the Hawaiian‐Emperor seamount chain to determine if the deep mantle source has retained evidence of halogen heterogeneities introduced through subduction. High Ni contents indicate that the Hawaiian‐Emperor mantle source contains a recycled oceanic crust component in the form of pyroxenite, which increases from the 46% in the oldest (Detroit) to 70% in the younger seamount (Koko). Detroit seamount retains mid‐ocean ridge basalts (MORB)‐like Br/Cl and I/Cl, while the Br/Cl and I/Cl of Suiko and Koko seamounts are higher than MORB and similar to altered oceanic crust and dehydrated serpentinite. Helium isotopes show a similar evolution, from MORB‐like values at Detroit seamount toward higher values at Suiko and Koko seamounts. The correlation between pyroxenite contributions, Br/Cl, I/Cl, and 3He/4He indicates that subducted material has been incorporated into the primordial undegassed Hawaiian mantle plume source. The identification of recycled oceanic crustal signatures in both the trace elements and halogens indicates that subduction and dehydration of altered oceanic crust may exert control on the cycling of volatile elements to the deep mantle.

Paroxysmal eruptions tracked by variations of helium isotopes: inferences from Piton de la Fournaise (La Réunion island)

“…3b). Similar cases of mixing between magmatic fluids coming from distinct components have been also reported at other hotspot volcanoes 1,45,51,52 . Our 4 He/ 40 Ar* data provide a new insight into the nature of this mixing of magmatic fluids.…”

“…At PdF, we do not find any correlation between 3 He/ 4 He and 87 Sr/ 86 Sr (Table 1; Fig. 6a) thus suggesting mixing between such distinct reservoirs 1,13,14,37,52,67,68 . Instead, decade-scale fluctuations of Sr isotopes have been documented for recent PdF lavas and attributed to the fertility of the source and induced melt channelization 43 (Fig.…”

Halogens in Eclogite Facies Minerals from the Western Gneiss Region, Norway

“…It has been argued that subduction does not introduce major halogen heterogeneity into the mantle [18]. However, this would require halogens to be decoupled from other volatile species, i.e., nitrogen, oxygen and sulphur that show heterogeneity in the mantle [124]. The high Br/Cl and I/Cl ratios of fluids in this study suggest, by analogy, that the SCLM may retain a significant quantity of devolatilised Br and I.…”