Ancient recycled mantle lithosphere in the Hawaiian plume: Osmium–Hafnium isotopic evidence fro.....IntroductionBackground informationThe O'ahu mantle xenolithsOs–Hf isotope systematics in peridotitesSample description and analytical methodsResultsMajor and trace element systematicsOs–Hf–Nd–Sr isotopic compositionsSr–Nd isotope systematicsNd–Hf isotope systematics187Os/188Os ratios and Hf–Os isotope systematicsDiscussionThe O'ahu peridotites as ancient residues of meltingOrigin of the SLC peridotitesImplications for the composition of the Hawaiian plume and erupted lavasErosion of the Pacific lithosphere by the Hawaiian plumeConclusionsAcknowledgmentsSupplementary dataReferencesAncient recycled mantle lithosphere in the Hawaiian plume:Osmium–Hafnium isotopic evidence fromperidotite mantle xenolithsMichael Bizimisa,⁎, Melanie Griselinb, John C. Lassiterb,1,Vincent J.M. Saltersa, Gautam SencaNational High Magnetic Filed Laboratory and Department of Geological Sciences, Florida State University,1800, E. Paul Dirac Dr., Tallahassee Fl, 32310, USAbMax Plank Institut für Chemie, Postfach 3060, D-55020 Mainz, GermanycDepartment of Earth Sciences, Florida International University, Miami Fl, 33199, USAReceived 11 September 2006; received in revised form 21 February 2007; accepted 22 February 2007Editor: R.W. CarlsonAvailable online 2 March 2007AbstractThe Emperor Seamount-Hawaiian island chain is thought to originate from melting of a heterogeneous mantle plume, but thecomposition of the plume has always been inferred from the compositions of the erupted lavas. It has been suggested that recycled (i.e.previously subducted) basaltic oceanic crust (with or without sediments) is part of this plume and responsible for the enriched isotopiccompositions of the Hawaiian lavas. Here we present the first combined Hf–Os isotopic study on peridotite mantle xenoliths from theisland of Oʻahu, Hawaiʻi. The clinopyroxene and spinel major element compositions overlap the global range of compositions of abyssalperidotites, suggesting that the Oʻahu peridotites are samples from the oceanic mantle and residues of variable degrees of melting. Theperidotite xenoliths from Salt Lake Crater have both highly unradiogenic Os (down to187Os/188Os=0.1138) and radiogenic Hf (up toεHf=114) isotopic compositions and minimum rhenium-depletion ages up to ∼ 2 Ga. Such extreme Hf and Os isotopic compositions arenot observed in Hawaiian lavas and are far removed from the composition of the depleted mantle, as it is sampled by mid oceanic ridgebasalts and abyssal peridotites. Importantly, both Hf and Os isotopic compositions correlate with degree of depletion, suggesting that theyare related to an ancient melting event. In contrast, peridotites from the Pali and Kaau vents have Os and Hf isotope ratios consistent withan origin from the ∼ 100 Ma Pacific lithosphere that lies beneath the Hawaiian islands. We suggest that the Salt Lake Crater peridotitesare fragments of an ancient (N 2 Ga) depleted and recycled mantle lithosphere that is part of the upwelling Hawaiian plume. Such depletedperidotites have higher solidus temperature than other more fertile mantle components, so that their contribution to the erupted lavascompositions is minor, if any. The recognition of such isotopically and compositionally depleted materials within the Hawaiian plumesuggests that depleted components are more common in mantle plumes than previously realized.© 2007 Elsevier B.V. All rights reserved.Keywords: recycling; peridotite; Hafnium; Osmium; plume; clinopyroxeneEarth and Planetary Science Letters 257 (2007) 259 – 273www.elsevier.com/locate/epsl⁎Corresponding author. Tel.: +1 850 644 2263; fax: +1 850 644 0827.E-mail address: [email protected] (M. Bizimis).1Present address: Geological Sciences Department, The University of Texas at Austin, 1, University Station C1100, Austin, TX, 78712-0254, USA.0012-821X/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.epsl.2007.02.0361. IntroductionGeneration of basaltic oceanic crust at divergentplate boundaries ( i.e. mid oceanic ridges) andrecycling of the lithospheric plate back into the Earth'smantle via subduction at convergent plate boundariesplay a principle role in the generation of long-livedchemical and isotopic heterogeneities in the mantle.Ocean island basalts (or OIB) are thought to representthe surface expression of localized mantle upwellings,or plumes, tha t ori gi nate p er hap s as dee p as the c or e–mantle boundary. The chemistry of OIB has thus beenused to map t he hete roge neit ie s of the Earth's mantleand constrain the proce sses that can cr ea te theseheterogeneities over t ime. Much of the trace elementand isotopic variability observed in OIB has beenattributed to mantle sources that contain various pro-portions of recycled oceanic basaltic crust, with orwithout sediments [1,2]. For example, the isotopicallyenriched endmember of the Hawaiian lavas , theKoʻolau lavas, has been argued to conta in recycledoceanic crust [3–5], possibly with pelagic sediments[6] in their source. However, the subduction processrequires that refractory components must be abundantinthemantlebecauseasubductedoceanicplatewillbevolumetrically dominated by the depleted lithosphericmantle, the residue of the basaltic crust e xtraction.Some rec e nt studies have proposed the pre se nce of adepleted component in OIB in part because of newHf [7,8] and Os [4,9] isotopic data. However, by theirnature, depleted or refractory mantle components aredifficult to stu dy th rough examination of mantl e-derived melts, both because such components contrib-ute proportionately less melt than more fertile compo-nents, and because they are depleted in the incompatibleelements (e.g. Sr–Nd–Pb–Hf) typically utilized to inferthe nature and origin of the mantle sources of oceanisland basalts.In this study we take a new approach to investigatethe presence and type of refractory material present inmantle plumes, with a detailed isotopic, trace and majorelement investigation of peridotite xenoliths fromOʻahu, Hawaiʻi. Earlier studies have suggested that theOʻahu peridotites repres ent metasomatized fragments ofthe Pacific lithosphere that underlies the Hawaiianislands [10–13]. The combined Hf and Os isotope datapresented in this study however, suggest that someperidotite xenoliths from the Salt Lake Crater ventcannot be fragm ents of the recent