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WATERS, C.L., DAY, J.M.D., WATANABE, S., SAYIT, K., ZANON, V., OLSON, K.M., HANAN, B.B., WIDOM, E. (2019) - Sulfide mantle source heterogeneity recorded in basaltic lavas from the Azores. Geochimica et Cosmochimica Acta, 268:422-445, doi:​​


New highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundance and Os isotopic compositions, along with major- and trace-element abundance and Sr-Nd-Hf-Pb isotope data are reported for high-MgO (>8–17 wt.%) lavas from the islands of São Miguel, Terceira, Pico and Faial in the Azores archipelago. The lavas span the range of Sr-Nd-Hf-Pb isotope and trace-element abundance variability reported previously for the islands. Pico and Faial lavas preserve distinct absolute and relative HSE abundances and 187Os/188Os (ƩHSE = 2 ± 2 ng g−1; 2SD; 187Os/188Os in lavas with > 50 pg g−1 Os = 0.1255 ± 31; 2SD) compared with São Miguel and Terceira lavas (ƩHSE = 5 ± 3 ng g−1; 187Os/188Os50pg = 0.1284 ± 48). Although HSE abundance variations in volcanic rocks from individual Azorean islands can be explained by sulfide crystallization, those between Pico and Faial and São Miguel and Terceira can only reasonably be attributed to partial melting of distinct mantle sources.

Pico and Faial lava compositions are consistent with high degrees of sulfide melting (90–100%) from a sulfide-depleted mantle source (<100 ppm) with relatively unradiogenic 187Os/188Os (<0.126). São Miguel and Terceira lavas likely derive from a sulfide-enriched (300–600 ppm) mantle source that underwent lesser degrees of sulfide melting (1–15%), with more radiogenic 187Os/188Os (>0.128). Radiogenic sulfides are not solely linked to the enriched lithophile isotope signature found in eastern São Miguel. Instead, São Miguel and Terceira magmatism may collectively result from metasomatism associated with the recycling of old subducted oceanic lithosphere. Abundances of sulfide-hosted HSE and 187Os/188Os are decoupled from silicate-hosted Sr-Nd-Hf-Pb isotope compositions in the mantle. Compositional variations of the HSE among global OIB suggest that, while distinct mantle domains are represented by heterogeneous sulfide mineralogy, comprising common metasomatic (enriched) and magmatic (depleted) compositions, these sulfide populations are distinct beneath different OIB due to their origin in different lithospheric materials (e.g., oceanic crust versus pelagic sediment), and to degree of partial melting caused by variable mantle potential temperature or lithospheric thickness.