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Sulfide mantle source heterogeneity recorded in basaltic lavas from the Azores

TitleSulfide mantle source heterogeneity recorded in basaltic lavas from the Azores
Publication TypeJournal Article
Year of Publication2020
AuthorsWaters C.L, Day JMD, Watanabe S., Sayit K., Zanon V., Olson K.M, Hanan B.B, Widom E.
Date Published2020/01
Type of ArticleArticle
ISBN Number0016-7037
Accession NumberWOS:000500923500023
Keywordsabyssal; azores; elements; Geochemistry & Geophysics; Highly siderophile elements; island basalts; mantle heterogeneity; ocean island basalts; os isotope systematics; osmium isotopes; Pb isotope; peridotites; platinum-group; recycled oceanic lithosphere; sao-miguel; silicate melt; sulfides; u-235-pa-231 disequilibria

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 Sao 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 Os-187/Os-188 (Sigma(HSE) = 2 +/- 2 ng g(-1); 2SD; Os-187/Os-188 in lavas with > 50 pg g(-1) Os = 0.1255 +/- 31; 2SD) compared with Sao Miguel and Terceira lavas (Sigma(HSE) = 5 +/- 3 ng g(-1) ; Os-187/Os-188(50pg) = 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 Sao 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 Os-187/Os-188 (<0.126). Sao 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 Os-187/Os-188 (>0.128). Radiogenic sulfides are not solely linked to the enriched lithophile isotope signature found in eastern Sao Miguel. Instead, Sao Miguel and Terceira magmatism may collectively result from metasomatism associated with the recycling of old subducted oceanic lithosphere. Abundances of sulfide-hosted HSE and Os-187/Os-188 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 the degree of partial melting caused by variable mantle potential temperature or lithospheric thickness. (C) 2019 Elsevier Ltd. All rights reserved.

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