The size of plume heterogeneities constrained by Marquesas isotopic stripes
TL;DR: In this paper, the authors present new Sr, Nd, Pb, Hf and Hf isotopes as well as trace element data on lavas from several Marquesas Islands and demonstrate that this archipelago consists of two adjacent and distinct rows of islands with significantly different isotopic compositions.
Abstract: The scale and geometry of chemical and isotopic heterogeneities in the source of plumes have important scientific implications on the nature, composition and origin of plumes and on the dynamics of mantle mixing over time. Here, we address these issues through the study of Marquesas Islands, one of the Archipelagoes in Polynesia. We present new Sr, Nd, Pb, Hf isotopes as well as trace element data on lavas from several Marquesas Islands and demonstrate that this archipelago consists of two adjacent and distinct rows of islands with significantly different isotopic compositions. For the entire 5.5 Ma construction period, the northern islands, hereafter called the Ua Huka group, has had systematically higher 87Sr/86Sr and lower 206Pb/204Pb ratios than the southern Fatu Hiva group at any given 143Nd/144Nd value. The shape and curvature of mixing arrays preclude the ambient depleted MORB mantle as one of the mixing end-members. We believe therefore that the entire isotopic heterogeneity originates in the plume itself. We suggest that the two Marquesas isotopic stripes originate from partial melting of two adjacent filaments contained in small plumes or "plumelets" that came from a large dome structure located deep in the mantle under Polynesia. Low-degree partial melting under Marquesas and other "weak" Polynesian hot spot chains (Pitcairn-Gambier, Austral-Cook, Society) sample small areas of the dome and preserve source heterogeneities. In contrast, more productive hot spots build up large islands such as Big Island in Hawaii or Reunion Island, and the higher degrees of melting blur the isotopic variability of the plume source.
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01 Dec 2008
TL;DR: In this article, the relationship between major elements and isotopes in ocean island basalts (OIBs) was analyzed based on the relationships between parent-daughter elements and radiogenic isotopes.
Abstract: Sr and Pb isotopes exhibit global trends with the concentrations of major elements (SiO 2 , TiO 2 , FeO, Al 2 O 3 and K 2 O) and major elements ratios (CaO/Al 2 O 3 and K 2 O/TiO 2 ) in the shield-stage lavas from 18 oceanic hotspots (including Hawaii, Iceland, Galapagos, Cook-Australs, St. Helena, Cape Verde, Cameroon, Canary, Madeira, Comoros, Azores, Samoa, Society, Marquesas, Mascarene, Kerguelen, Pitcairn, and Selvagen). Based on the relationships between major elements and isotopes in ocean island basalts (OIBs), we find that the lavas derived from the mantle end members, HIMU (or high ‘μ’ = 238 U/ 204 Pb), EM1 (enriched mantle 1), EM2 (enriched mantle 2), and DMM (depleted MORB [mid-ocean ridge basalt] mantle) exhibit distinct major element characteristics: When compared to oceanic hotspots globally, the hotspots with a HIMU (radiogenic Pb-isotopes and low 87 Sr/ 86 Sr) component, such as St. Helena and Cook-Australs, exhibit high CaO/Al 2 O 3 , FeO T , and TiO 2 and low SiO 2 and Al 2 O 3 . EM1 (enriched mantle 1; intermediate 87 Sr/ 86 Sr and low 206 Pb/ 204 Pb; sampled by hotspots like Pitcairn and Kerguelen) and EM2 (enriched mantle 2; high 87 Sr/ 86 Sr and intermediate 206 Pb/ 204 Pb; sampled by hotspots like Samoa and Societies) exhibit higher K 2 O concentrations and K 2 O/TiO 2 weight ratios than HIMU lavas. EM1 lavas exhibit the lowest CaO/Al 2 O 3 in the OIB dataset, and this sets EM1 apart from EM2. A plot of CaO/Al 2 O 3 vs K 2 O/TiO 2 perfectly resolves the four mantle end member lavas. Melting processes (pressure, temperature and degree of melting) fail to provide an explanation for the full spectrum of major element concentrations in OIBs. Such processes also fail to explain the correlations between major elements and radiogenic isotopes. Instead, a long, time integrated history of various parent–daughter elements appears to be coupled to major element and/or volatile heterogeneity in the mantle source. End member lava compositions are compared with experimental partial melt compositions to place constraints on the lithological characteristics of the mantle end members.
243 citations
TL;DR: The iron isotopic compositions of 93 well-characterized basalts from geochemically and geologically diverse mid-ocean ridge segments, oceanic islands and back arc basins were measured.
177 citations
Cites background from "The size of plume heterogeneities c..."
...…and are derived from three of the main geochemical mantle end-members: HIMU, EM1 and EM2 (Zindler and Hart, 1986) although their mantle source dynamics are still debated (e.g., Vidal et al., 1984; McNutt and Fischer, 1987; Hekinian et al., 1991; Chauvel et al., 1992, 2012; Huang et al., 2011b)....
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TL;DR: A model is presented that can explain the temporal evolution and origin of plume zonation for both the Tristan-Gough and Hawaiian hotspots, two end member types of zoned plumes, through processes taking place in the plume sources at the base of the lower mantle.
Abstract: Striped geochemical zonation has been observed along parts of hotspot tracks, although its origin is not well-understood. Here, the authors present Sr–Nd–Pb–Hf isotope data and present a model that can explain the evolution of zonation in both Tristan-Gough and Hawaiian hotspots, reflecting two end members.
112 citations
TL;DR: The mixing relationships inferred from the new He and Pb isotopic data provide the clearest picture yet of the geochemical geometry of a mantle plume, and are best explained by a high-3He/4He plume matrix that hosts, and mixes with, several distinct low- 3He/ 4He components.
Abstract: Hotspot lavas erupted at ocean islands exhibit tremendous isotopic variability, indicating that there are numerous mantle components1, 2 hosted in upwelling mantle plumes that generate volcanism at hotspots like Hawaii and Samoa3. However, it is not known how the surface expression of the various geochemical components observed in hotspot volcanoes relates to their spatial distribution within the plume4, 5, 6, 7, 8, 9, 10. Here we present a relationship between He and Pb isotopes in Samoan lavas that places severe constraints on the distribution of geochemical species within the plume. The Pb-isotopic compositions of the Samoan lavas reveal several distinct geochemical groups, each corresponding to a different geographic lineament of volcanoes. Each group has a signature associated with one of four mantle endmembers with low 3He/4He: EMII (enriched mantle 2), EMI (enriched mantle 1), HIMU (high µ = 238U/204Pb) and DM (depleted mantle). Critically, these four geochemical groups trend towards a common region of Pb-isotopic space with high 3He/4He. This observation is consistent with several low-3He/4He components in the plume mixing with a common high-3He/4He component, but not mixing much with each other. The mixing relationships inferred from the new He and Pb isotopic data provide the clearest picture yet of the geochemical geometry of a mantle plume, and are best explained by a high-3He/4He plume matrix that hosts, and mixes with, several distinct low-3He/4He components.
88 citations
69 citations
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TL;DR: In this paper, the authors compared the relative abundances of the refractory elements in carbonaceous, ordinary, and enstatite chondritic meteorites and found that the most consistent composition of the Earth's core is derived from the seismic profile and its interpretation, compared with primitive meteorites, and chemical and petrological models of peridotite-basalt melting relationships.
10,830 citations
TL;DR: The IUGS Subcommission on Geochronology (FOOTNOTE 4) as discussed by the authors recommended the adoption of a standard set of decay constants and isotopic abundances in isotope geology.
9,474 citations
TL;DR: In this paper, a digital bathymetric map of the oceans with a horizontal resolution of 1 to 12 kilometers was derived by combining available depth soundings with high-resolution marine gravity information from the Geosat and ERS-1 spacecraft.
Abstract: A digital bathymetric map of the oceans with a horizontal resolution of 1 to 12 kilometers was derived by combining available depth soundings with high-resolution marine gravity information from the Geosat and ERS-1 spacecraft. Previous global bathymetric maps lacked features such as the 1600-kilometer-long Foundation Seamounts chain in the South Pacific. This map shows relations among the distributions of depth, sea floor area, and sea floor age that do not fit the predictions of deterministic models of subsidence due to lithosphere cooling but may be explained by a stochastic model in which randomly distributed reheating events warm the lithosphere and raise the ocean floor.
4,433 citations
TL;DR: In this paper, the authors proposed a new constraint on mantle composition: the differentiated part of the mantle, chemically depleted after separation of the major portion of the continental crust, was subsequently internally rehomogenized.
1,475 citations
"The size of plume heterogeneities c..." refers result in this paper
...…worldwide data for ocean island basalts, showed that the Ce/Pb ratio of EM-type lavas is usually lower than the canonical “mantle” value of 25 [Hofmann et al., 1986] and that their Nb/U ratio is generally scattered and not significantly different from the value of 47 suggested by Hofmann et…...
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Max Planck Society1, Australian National University2, University of Grenoble3, National Taiwan University4, Australian Research Council5, University of Bristol6, Massachusetts Institute of Technology7, University of Hawaii8, Cardiff University9, Russian Academy of Sciences10, Shirshov Institute of Oceanology11, VU University Amsterdam12, Utrecht University13
TL;DR: Olivine phenocrysts' compositions record differences in the contributions of pyroxenite-derived melts in mid-ocean ridge basalts, which imply involvement of 2 to 20% (up to 28%) of recycled crust in mantle melting.
Abstract: Plate tectonic processes introduce basaltic crust (as eclogite) into the peridotitic mantle. The proportions of these two sources in mantle melts are poorly understood. Silica-rich melts formed from eclogite react with peridotite, converting it to olivine-free pyroxenite. Partial melts of this hybrid pyroxenite are higher in nickel and silicon but poorer in manganese, calcium, and magnesium than melts of peridotite. Olivine phenocrysts' compositions record these differences and were used to quantify the contributions of pyroxenite-derived melts in mid-ocean ridge basalts (10 to 30%), ocean island and continental basalts (many >60%), and komatiites (20 to 30%). These results imply involvement of 2 to 20% (up to 28%) of recycled crust in mantle melting.
1,226 citations