Extreme isotopic heterogeneity in Samoan clinopyroxenes constrains sediment recycling

Jenna V Adams,Matthew G Jackson,Gareth Seward,Allison A Price,John M Cottle,Frank J Spera,Benjamin L Byerly

doi:10.1038/s41467-021-21416-9

Jenna V Adams, Matthew G Jackson + Show 5 more

Open Access

https://doi.org/10.1038/s41467-021-21416-9

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Abstract

Lavas erupted at hotspot volcanoes provide evidence of mantle heterogeneity. Samoan Island lavas with high 87Sr/86Sr (>0.706) typify a mantle source incorporating ancient subducted sediments. To further characterize this source, we target a single high 87Sr/86Sr lava from Savai’i Island, Samoa for detailed analyses of 87Sr/86Sr and 143Nd/144Nd isotopes and major and trace elements on individual magmatic clinopyroxenes. We show the clinopyroxenes exhibit a remarkable range of 87Sr/86Sr—including the highest observed in an oceanic hotspot lava—encompassing ~30% of the oceanic mantle’s total variability. These new isotopic data, data from other Samoan lavas, and magma mixing calculations are consistent with clinopyroxene 87Sr/86Sr variability resulting from magma mixing between a high silica, high 87Sr/86Sr (up to 0.7316) magma, and a low silica, low 87Sr/86Sr magma. Results provide insight into the composition of magmas derived from a sediment-infiltrated mantle source and document the fate of sediment recycled into Earth’s mantle.

Highlights

Lavas erupted at hotspot volcanoes provide evidence of mantle heterogeneity
It is generally accepted that mantle plumes ‘sample’ such recycled materials leading to a diverse range of geochemical signatures reflected in ocean island basalts (OIBs)[1,2,3]
Mantle isotopic heterogeneities are inferred by examining global OIB lavas, but the scale, origin, and compositions of the sources and/or derivative melts remain under intense investigation

Summary

Results and discussion

Mixing of the EM2 trachytic magma with more primitive Samoan basalt-like compositions reproduces the mixing trends observed in ALIA-D115 whole rock lavas (Fig. 1) as well as the range of 87Sr/86Sr and 143Nd/144Nd in Samoa clinopyroxene. The genesis of this high 87Sr/86Sr, trachytic magma is an outstanding question and is further explored in the discussion and Supplementary Text. The thinnest Fe and Mg lamella observed in clinopyroxene is about 15 μm thick

Methods

À C C1 À C0

Code availability