The composition and distribution of the rejuvenated component across the Hawaiian plume: Hf‐Nd‐Sr‐Pb isotope systematics of Kaula lavas and pyroxenite xenoliths

Abstract

[1] Rejuvenated volcanism refers to the reemergence of volcanism after a hiatus of 0.5-2 Ma following the voluminous shield building stage of Hawaiian volcanoes. The composition of the rejuvenated source and its distribution relative to the center of the plume provide important constraints on the origin of rejuvenated volcanism. Near-contemporaneous lavas from the Kaula-Niihau-Kauai ridge and the North Arch volcanic field that are aligned approximately orthogonally to the plume track can constrain the lateral geochemical heterogeneity and distribution of the rejuvenated source across the volcanic chain. Nephelinites, phonolites and pyroxenite xenoliths from Kaula Island have radiogenic Hf, Nd and unradiogenic Sr isotope compositions consistent with a time-integrated depleted mantle source. The pyroxenites and nephelinites extend to the lowest 208 Pb/ 204 Pb reported in Hawaiian rocks. These data, along with new Pb isotope data from pyroxenites from the Salt Lake Crater (Oahu) redefine the composition of the depleted end-member of the Hawaiian rejuvenated source at 208 Pb/ 204 Pb¼37.3560.05, 206 Pb/ 204 Pb ¼ 17.7560.03, " Nd ¼ 9-10, " Hf $16-17 and 87 Sr/ 88 Sr <0.70305. The revised isotope composition also suggests that this depleted component may contribute to LOA and KEA trend shield stage Hawaiian lavas, consistent with the rejuvenated source being part of the Hawaiian plume and not entrained upper mantle. The isotope systematics of rejuvenated magmas along the Kaula-Niihau-KauaiNorth Arch transect are consistent with a larger proportion of the rejuvenated depleted component in the periphery of the plume track rather than along its axis.

Iron isotope tracing of mantle heterogeneity within the source regions of oceanic basalts

“…Some samples display ilmenite exsolutions within garnet (including samples NMNH-114959-20A and 77SL-582 analyzed here), majorite pseudomorphs and nanodiamonds and probably initially crystallized at >5 GPa (>150 km) (Keshav and Sen, 2001;Keshav et al, 2007), deeper than the 80-90 km seismically defined base of the lithosphere beneath Oahu (Li et al, 2004). The radiogenic Hf and Nd isotopic compositions of the pyroxenites analyzed thus far (Bizimis et al, 2013, including the high pressure pyroxenite NMNH-114959-20A, place them at the depleted end of the OIB array, suggesting an origin from a depleted mantle source, distinct from the isotopically enriched "eclogitic" component inferred for the Hawaiian plume (Hauri, 1996;Huang and Frey, 2005).…”

“…A location map is provided in Appendix A. In this study we focus on previously studied, well-characterized spinel lherzolite and garnet pyroxenite xenoliths (Bizimis et al, 2013(Bizimis et al, , 2004Sen et al, 2011) as well as some newly reported samples. The samples are from the Dale Jackson and Dean Presnall collections at the Smithsonian Institution.…”

“…The degree of partial melting was calculated following Hellebrand et al (2001). phlogopite. Based on major and trace element modeling and their Sr, Nd, Hf, Pb, and Os isotope compositions they have been largely interpreted as high pressure (>2 GPa, >60 km) cumulates near the base of the Pacific lithosphere from melts similar to the Hawaiian alkali rejuvenated lavas (Bizimis et al, 2013Keshav et al, 2007;Sen et al, 2010). Some samples display ilmenite exsolutions within garnet (including samples NMNH-114959-20A and 77SL-582 analyzed here), majorite pseudomorphs and nanodiamonds and probably initially crystallized at >5 GPa (>150 km) (Keshav and Sen, 2001;Keshav et al, 2007), deeper than the 80-90 km seismically defined base of the lithosphere beneath Oahu (Li et al, 2004).…”

“…The peridotites are considered to be fragments of 90-100 Ma Pacific oceanic lithosphere or even ancient recycled mantle material within the Hawaiian mantle plume (Bizimis et al, 2007(Bizimis et al, , 2004. The garnet pyroxenites are considered to be high-pressure cumulates from OIB-like melts that formed close to the lithosphereasthenosphere boundary (60-90 km) (Bizimis et al, 2013Sen et al, 2005Sen et al, , 2011, while some samples with majorite pseudomorphs (Keshav and Sen, 2001) and nanodiamonds (Wirth and Rocholl, 2003) potentially originated at depths >150 km. In this study, we use peridotite Fe isotope compositions to infer the Feisotope systematics of the peridotitic upper mantle and pyroxenites to explore the Fe-isotope systematics of mineralogically enriched (Beard et al, 2003); T-2008 (Teng et al, 2008).…”

“…Several studies have suggested that the Hawaiian plume mantle source contains longterm depleted and compositionally variable peridotitic components (Bizimis et al, 2013Pietruszka and Garcia, 1999;Ren et al, 2006;Stracke et al, 1999) and depleted components have also been invoked in the source of Reunion OIB (Vlastelic et al, 2006) and MORB. Evidence for the latter is provided by correlated Hf-Nd isotopes in MORB (Salters et al, 2011) and the radiogenic Hf isotope compositions of Gakkel Ridge abyssal peridotites , while mantle peridotites found at mid-oceanic spreading centers and as xenoliths in OIB provide some of the strongest evidence for the presence of ancient depleted peridotites in the convecting mantle (Bizimis et al, 2007;Burton et al, 2012;Liu et al, 2008;Stracke et al, 2011).…”