A young source for the Hawaiian plume

Abstract

Recycling of oceanic crust through subduction, mantle upwelling, and remelting in mantle plumes is a widely accepted mechanism to explain ocean island volcanism. The timescale of this recycling is important to our understanding of mantle circulation rates. Correlations of uranogenic lead isotopes in lavas from ocean islands such as Hawaii or Iceland, when interpreted as model isochrons, have yielded source differentiation ages between 1 and 2.5 billion years (Gyr). However, if such correlations are produced by mixing of unrelated mantle components they will have no direct age significance. Re-Os decay model ages take into account the mixing of sources with different histories, but they depend on the assumed initial Re/Os ratio of the subducted crust, which is poorly constrained because of the high mobility of rhenium during subduction. Here we report the first data on (87)Sr/(86)Sr ratios for 138 melt inclusions in olivine phenocrysts from lavas of Mauna Loa shield volcano, Hawaii, indicating enormous mantle source heterogeneity. We show that highly radiogenic strontium in severely rubidium-depleted melt inclusions matches the isotopic composition of 200-650-Myr-old sea water. We infer that such sea water must have contaminated the Mauna Loa source rock, before subduction, imparting a unique 'time stamp' on this source. Small amounts of seawater-derived strontium in plume sources may be common but can be identified clearly only in ultra-depleted melts originating from generally highly (incompatible-element) depleted source components. The presence of 200-650-Myr-old oceanic crust in the source of Hawaiian lavas implies a timescale of general mantle circulation with an average rate of about 2 (±1) cm yr(-1), much faster than previously thought.

Inherited Pb isotopic records in olivine antecryst-hosted melt inclusions from Hawaiian lavas

“…Previous studies of melt inclusions in olivine grains from Hawaiian lavas lead to the discovery of small-scale heterogeneity in the magma because of heterogeneous chemical and isotopic composition of the melt inclusions in the olivines (Sobolev et al, 2000(Sobolev et al, , 2011Norman et al, 2002;Kobayashi et al, 2004;Ren et al, 2005;Sobolev et al, 2011). These small-scale heterogeneities were attributed to changes in the mantle source of the melts.…”

“…This variation in melt inclusion composition is attributed to the heterogeneous nature of source mantle (Saal et al, 1998;Sobolev et al, 2000;Norman et al, 2002;Kobayashi et al, 2004;Saal et al, 2005;Sobolev et al, 2011), different degree of partial melting (Gurenko and Chaussidon, 1995;Nielsen et al, 1995;Laubier et al, 2007), and/or melt-rock reaction processes Shimizu, 1998;Sigurdsson et al, 2000;Danyushevsky et al, 2003Danyushevsky et al, , 2004Saal et al, 2005).…”

Cubic perovskite polymorph of strontium metasilicate at high pressures

“…This indicates that there are similar factors governing the compression behaviors in these alkaline earth oxide perovskites. Strontium (Sr) is of geochemical importance (Sobolev et al 2011). The identification of the SrSiO 3 cubic perovskite at high pressures provides experimental evidence to understand the occurrence of Sr atom in the Earth's lower mantle.…”

Extreme differences in 87Sr/86Sr between Samoan lavas and the magmatic olivines they host: Evidence for highly heterogeneous 87Sr/86Sr in the magmatic plumbing system sourcing a single lava

“…Their 79 results also show that 87 Sr/ 86 Sr in olivine-hosted melt inclusions can be significantly different 80 from the whole rock (by >6000 ppm). In a recent LA-ICP-MS study focusing on Hawaiian lavas, 81 Sobolev et al (2011) further demonstrated that the 87 Sr/ 86 Sr of olivine hosted melt inclusions can 82 vary dramatically (from 0.7021 to 0.7081) within a single lava. In summary, 87 Sr/ 86 Sr measured 83 in olivine-hosted melt inclusions reveal that isotopically heterogeneous components exist in OIB 84 that are not observed in whole rock analyses.…”