On- and off-axis chemical heterogeneities along the South Atlantic Mid-Ocean-Ridge (5–11°S): Shallow or deep recycling of ocean crust and/or intraplate volcanism?

70 Ma chemical zonation of the Tristan-Gough hotspot track

“…Although there is good evidence that shallow recycling of continental lithosphere contributes to the origin of the enriched mantle (DUPAL) signature (e.g., Hanan et al, 2004;Hoernle et al, 2011), this is unlikely to be the source of the EM material in the South Atlantic hotspots. Geodynamic constraints show that only African lithosphere was likely to be located beneath the South Atlantic, but it does not have the appropriate composition to explain the composition of the Gough subtrack and other extreme DUPAL signatures in the South Atlantic (Class and Le Roex, 2011).…”

“…The origin of the EM-or DUPAL-type signature in the Southern Hemisphere is controversial. It has commonly been attributed to the shallow recycling of continental lithosphere (e.g., Hawkesworth et al, 1986;Hanan et al, 2004;Hoernle et al, 2011), but deep origins for this anomaly have also been proposed (Castillo, 1988;Class and Le Roex, 2011). An important question is to what extent the DUPAL geochemical anomaly in volcanic rocks from the South Atlantic and Indian Oceans is derived from the African superplume (Castillo, 1988).…”

Source components and magmatic processes in the genesis of Miocene to Quaternary lavas in western Turkey: constraints from HSE distribution and Hf–Pb–Os isotopes

“…With olivine and associated Os-bearing phases as the main fractionating phases, 187 Os/ 188 Os variations can be modeled by up to 15 % mineral separation and <2 % crustal contamination. It is notable that the amount of crustal material assimilated by the parental melts is quite small, but even this minor crustal (Zindler and Hart 1986;Hart et al 1992); and Atlantic MORB (Agranier et al 2005;Hoernle et al 2011). The parameter 208 Pb*/ 206 Pb* reflects radiogenic addition to the terrestrial lead defined as [( 208 Pb/ 204 Pb) measured − 29.476]/[( 206 Pb/ 204 Pb) measured − 9.307] (Galer and O'Nions 1985) input creates large differences in Os isotopic variations due to the large compositional contrast between the mantlederived melt and the contaminant crust.…”

A 1.5 Ma record of plume-ridge interaction at the Western Galápagos Spreading Center (91°40′–92°00′W)

“…Alternatively, it could reflect a random heterogeneity in the upper mantle beneath the ridge or could be upper, transition-zone or lower mantle material entrained by the plume during ascent. As is indicated by off-axis seamounts (e.g., Brandl et al 2012), Petit Spot volcanoes (Machida et al, 2009;2015), Pliocene volcanism on Christmas Island (Hoernle et al, 2011) and the isolated Godzilla seamount (Geldmacher et al, 2008), enriched components are present in the uppermost asthenospheric mantle and are tapped by low-degree melting in intraplate settings. Although the available data of 1.0-1.5 Ma WGSC off-axis crust are too few to constrain fully the origin and extent of the observed EMII flavor, we do however note that a component similar to samples from the <30 km group serve as one mixing component for the >30 km group.…”