Phantom Archean crust in Mangaia hotspot lavas and the meaning of heterogeneous mantle

TitlePhantom Archean crust in Mangaia hotspot lavas and the meaning of heterogeneous mantle
Publication TypeJournal Article
Year of Publication2014
AuthorsHerzberg C., Cabral RA, Jackson MG, Vidito C., Day JMD, Hauri EH
JournalEarth and Planetary Science Letters
Volume396
Pagination97-106
Date Published2014/05
ISBN Number0012-821X
Accession NumberWOS:000336819900010
Keywordseclogite; fertile peridotite; garnet pyroxenite; hawaiian basalts; HIMU; isotope evidence; isotopes; ocean island basalts; Olivine; partial melting experiments; partition-coefficients; peridotite; phase-relations; pyroxenite; southern polynesia; trace-element
Abstract

Lavas from Mangaia in the Cook Austral island chain, Polynesia, define an HIMU (or high mu where mu = U-238/Pb-204) global isotopic end-member among ocean island basalts (OM) with the highest Pb-206,Pb-207,Pb-208/Pb-204. This geochemical signature is interpreted to reflect a recycled oceanic crust component in the mantle source. Mass independently fractionated (MIF) sulfur isotopes indicate that Mangaia lavas sampled recycled Archean material that was once at the Earth's surface, likely hydrothermally-modified oceanic crust. Recent models have proposed that crust that is subducted and then returned to the surface in a mantle plume is expected to transform to pyroxenite/eclogite during transit through the mantle. Here we examine this hypothesis for Mangaia using high-precision electron microprobe analysis on olivine phenocrysts. Contrary to expectations of a crustal component and, hence pyroxenite, results show a mixed peridotite and pyroxenite source, with peridotite dominating. If the isotopic compositions were inherited from subduction of recycled oceanic crust, our work shows that this source has phantom-like properties in that it can have its lithological identity destroyed while its isotope ratios are preserved. This may occur by partial melting of the pyroxenite and injection of its silicic melts into the surrounding mantle peridotite, yielding a refertilized peridotite. Evidence from one sample reveals that not all pyroxenite in the melting region was destroyed. Identification of source lithology using olivine phenocryst chemistry can be further compromised by magma chamber fractional crystallization, recharge, and mixing. We conclude that the commonly used terms mantle "heterogeneities" and "streaks" are ambiguous, and distinction should be made of its lithological and isotopic properties. (C) 2014 Published by Elsevier B.V.

DOI10.1016/J.Epsl.2014.03.065
Short TitleEarth Planet. Sci. Lett.
Alternate JournalEarth Planet Sc Lett
Integrated Research Themes: 
Student Publication: 
No