First-row transition elements in pyroxenites and peridotites: A promising tool for constraining mantle source mineralogy

Uranium-series disequilibria in MORB, revisited: A systematic numerical approach to partial melting of a heterogeneous mantle

“…Although volumetrically minor compared to the dominant ultramafic rocks, recycled and reworked mafic lithologies may play an outsized role in generating oceanic magmas due to their distinct melting behavior (e.g., Hirschmann and Stolper 1996;Lambart et al 2013;Stracke and Bourdon 2009;Stracke et al 2006). One reason for that incomplete understanding is that geochemical indicators of mantle melting, as recorded in basaltic lavas extracted from that mantle, are relatively ambiguous regarding the lithologic types involved in the partial melting process (e.g., Hirschmann and Stolper 1996;Lang and Lambart 2022;Mallik et al 2021;Stracke and Bourdon 2009). Partial melting is a prolonged and progressive process that occurs over a significant depth range (e.g., Asimow et al 1995), and the magmas thus produced are mixed and homogenized to an unknown degree prior to emplacement, processes which obscure subtle lithologic melting signals (e.g., Stracke and Bourdon 2009).…”

“…The global geochemical data set for MORBs includes a large number of major element, trace element, and longlived radiogenic isotope compositions, as well as a smaller (but globally-spanning) U-series disequilibrium data set (e.g., Elkins et al 2019;Gale et al 2013Gale et al , 2014 (Figure 1). Among these and other oceanic basalt data, a variety of major element and trace element characteristics have been proposed as possible indicators of pyroxenite melting in the mantle, including low SiO2 coupled with high FeO (Lambart et al 2009(Lambart et al , 2013, high TiO2 contents (Prytulak and Elliott, 2007), and a variety of elemental ratios (e.g., Mn/Fe, Zn/Fe, Ge/Si, Ba/Th, La/Nb, Sr/Nd, Ba/Ta, Nb/Zr) (e.g., Lang and Lambart 2022;Le Roux et al 2010;Stracke and Bourdon 2009;Yang et al 2019Yang et al , 2020. Likewise, although radiogenic isotope compositions may record more complex origins that could become decoupled from source lithology, it is expected that many pyroxenites have time-integrated isotope signatures that record incompatible element enrichment over long timescales, i.e., high 87 Sr/ 86 Sr, 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb, and low 143 Nd/ 144 Nd and 176 Hf/ 177 Hf, due to their posited recycled origins (e.g., Blichert-Toft et al 1999;Millet et al 2008;Salters and Dick 2002;Schiano et al 1997;Sobolev et al 2008).…”