Primordial and recycled helium isotope signatures in the mantle transition zone

Science ◽  
2019 ◽  
Vol 365 (6454) ◽  
pp. 692-694 ◽  
Author(s):  
S. Timmerman ◽  
M. Honda ◽  
A. D. Burnham ◽  
Y. Amelin ◽  
S. Woodland ◽  
...  
Keyword(s):  
Transition Zone ◽  
Critical Role ◽  
Crustal Contamination ◽  
Helium Isotope ◽  
Sr Isotope ◽  
Pb Isotope ◽  
Ocean Island Basalts ◽  
Zone Depth ◽  
Superdeep Diamond ◽  
Recycled Material

Isotope compositions of basalts provide information about the chemical reservoirs in Earth’s interior and play a critical role in defining models of Earth’s structure. However, the helium isotope signature of the mantle below depths of a few hundred kilometers has been difficult to measure directly. This information is a vital baseline for understanding helium isotopes in erupted basalts. We measured He-Sr-Pb isotope ratios in superdeep diamond fluid inclusions from the transition zone (depth of 410 to 660 kilometers) unaffected by degassing and shallow crustal contamination. We found extreme He-C-Pb-Sr isotope variability, with high 3He/4He ratios related to higher helium concentrations. This indicates that a less degassed, high-3He/4He deep mantle source infiltrates the transition zone, where it interacts with recycled material, creating the diverse compositions recorded in ocean island basalts.

scholarly journals Resolving Sediment Subduction and Crustal Contamination in the Lesser Antilles Island Arc: a Combined He–O–Sr Isotope Approach

2002 ◽  
Vol 43 (1) ◽  
pp. 143-170 ◽  
Author(s):  
MATTHIJS C. VAN SOEST ◽  
DAVID R. HILTON ◽  
COLIN G. MACPHERSON ◽  
DAVID P. MATTEY
Keyword(s):  
Crustal Contamination ◽  
Island Arc ◽  
Lesser Antilles ◽  
Sr Isotope

Clinopyroxene and bulk rock Sr–Nd–Hf–Pb isotope compositions of Raivavae ocean island basalts: Does clinopyroxene record early stage magma chamber processes?

2018 ◽  
Vol 482 ◽  
pp. 18-31 ◽  
Author(s):  
Takashi Miyazaki ◽  
Takeshi Hanyu ◽  
Jun-Ichi Kimura ◽  
Ryoko Senda ◽  
Bogdan Stefanov Vaglarov ◽  
...  
Keyword(s):  
Magma Chamber ◽  
Early Stage ◽  
Bulk Rock ◽  
Pb Isotope ◽  
Ocean Island ◽  
Magma Chamber Processes ◽  
Ocean Island Basalts

Lead isotope and trace element variation in Tenerife pumices: evidence for recycling within an ocean island volcano

1989 ◽  
Vol 53 (373) ◽  
pp. 519-525 ◽  
Author(s):  
J. A. Wolff ◽  
Z. A. Palacz
Keyword(s):  
Trace Element ◽  
Lead Isotope ◽  
Isotope Ratios ◽  
Volcanic Edifice ◽  
Sr Isotope ◽  
Isotopic Data ◽  
Pb Isotope ◽  
Pumice Fall ◽  
Element Variation ◽  
Fall Deposits

AbstractThree voluminous Quaternary phonolitic pumice fall deposits erupted from the compositionally-zoned Tenerife magma chamber exhibit variability in Sr and Pb isotope ratios. It has been previously argued that the Sr isotope variations are due to syn-eruptive interaction between magma and hydrothermal fluids (Palacz and Wolff, 1989). Pb compositions are not correlated with Sr, and are believed to reflect magmatic values. Pb isotope ratios exhibit regular variation with degree of fractionation, and one zoned deposit is heterogeneous in Pb. The highest values seem to characterize the most fractionated upper parts of the zoned system. This is unlikely to be a consequence of magmatic recharge. Isotopic and trace element behaviour is instead consistent with combined assimilation and fractional crystalliza- tion, involving the recycling of material containing relatively radiogenic Pb, from within the volcanic edifice. Assimilation of sediment intercalated within the submarine portion of the pile is ruled out by the isotopic data. The most probable contaminant is a felsic igneous rock. Early trachytes reported by Sun (1980) have the required Pb isotope compositions and may approximately represent the assimilant.

Sm–Nd, Pb–Pb, and Rb–Sr systematics of the basement in the Cigar Lake area, Saskatchewan, Canada

1993 ◽  
Vol 30 (4) ◽  
pp. 731-742 ◽  
Author(s):  
Maurice Pagel ◽  
Annie Michard ◽  
Martine Juteau ◽  
Laurent Turpin
Keyword(s):  
Isotope Geochemistry ◽  
Sedimentary Cover ◽  
Lake Area ◽  
Sr Isotope ◽  
Pb Isotope ◽  
Mineralizing Fluid ◽  
Isotope Data ◽  
Basement Rocks ◽  
Strong Contrast

The Sm–Nd, Pb–Pb, and Rb–Sr isotope geochemistry of graphitic metapelitic gneisses and their altered equivalents from the Cigar Lake area (Saskatchewan, Canada) has been investigated. Some granitic gneisses were also analyzed for Pb–Pb and Rb–Sr. Sm–Nd data show that the metapelitic gneisses are composed of detritus from heterogeneous, mainly mantle-derived Archean rocks (2.5–2.6 Ga) and that the Sm–Nd system has not been significantly perturbed during subsequent alteration and metamorphic events. The Pb–Pb age for samples of the less altered graphitic metapelitic gneisses is 1.77 ± 0.03 Ga. The crustal common Pb is located on the Pb–Pb isochron, but there are different zones with high and variable U/Pb ratios (μ = 15–280). The Pb–Pb age for the granitic gneisses is 1.79 ± 0.11 Ma. The Pb isotope data show that there has been no major uranium redistribution in the basement after the Hudsonian orogeny. However, there has been a strong perturbation of the U–Pb system in the regolithic zone beneath the Athabasca cover. In some samples, uranium was added during the mineralizing event. The Rb–Sr system in the graphitic metapelitic gneisses was also affected.The 87Sr/86Sr ratio in pitchblende is 0.709. At 1.3 Ga, there is a strong contrast between the 87Sr/86Sr ratio in the Athabasca sandstones (0.706–0.710) and the 87Sr/86Sr ratio in the metapelitic gneisses from the basement (0.725–0.775). The upper zone of the regolith is characterized by a low 87Sr/86Sr ratio (0.705–0.707). The Pb–Pb and Rb–Sr data are consistent with the circulation of a fluid with a low 87Sr/86Sr ratio, derived from the sedimentary cover; this fluid passed through the most permeable zones of the basement rocks, especially the regolith. The mineralizing fluid had a 87Sr/86Sr value typical of a fluid in equilibrium with the Athabasca sandstones.

Geology and geochemistry of the late Precambrian Coldbrook Group near Saint John, New Brunswick

1990 ◽  
Vol 27 (11) ◽  
pp. 1418-1430 ◽  
Author(s):  
K. L. Currie ◽  
G. N. Eby
Keyword(s):  
New Brunswick ◽  
Crustal Contamination ◽  
Geochemical Data ◽  
Bay Of Fundy ◽  
Sr Isotope ◽  
Magma Evolution ◽  
Volcanic Arc ◽  
Crustal Component ◽  
Pyroclastic Rocks ◽  
Late Precambrian

The late Precambrian Coldbrook Group comprises basal basaltic flows and pyroclastic rocks, fragmental andesitic to rhyolitic rocks, and minor capping sedimentary strata, all deformed and metamorphosed to prehnite–pumpellyite grade. Sr-isotope data indicate metasomatism, and probably deformation and metamorphism, took place long after deposition, possibly during major Carboniferous deformation of the Bay of Fundy region. Geochemical data suggest that the Coldbrook Group formed in a subduction-related ensialic volcanic-arc environment, although some specimens appear transitional to within-plate tholeiites. Magma evolution was dominated by fractionation of ilmenite, pyroxene, and plagioclase. Trace-element ratios suggest crustal contamination of virtually all Coldbrook Group rocks, with the amount of crustal component larger in the more salic portion. Comparison of data for the Coldbrook Group with data of other late Precambrian volcanic sequences in Atlantic Canada suggests that similar arc-related sequences underlie slightly younger, continental bimodal sequences in many Avalonian terranes.

scholarly journals The alkaline intraplate volcanism of the Antalya nappes (Turkey): a Late Triassic remnant of the Neotethys

2008 ◽  
Vol 179 (4) ◽  
pp. 397-410 ◽  
Author(s):  
René C. Maury ◽  
Henriette Lapierre ◽  
Delphine Bosch ◽  
Jean Marcoux ◽  
Leopold Krystyn ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Late Triassic ◽  
Primitive Mantle ◽  
Heavy Rare Earth Element ◽  
Alkali Basalts ◽  
Crustal Component ◽  
Ocean Island ◽  
Ocean Island Basalts ◽  
Enriched Mantle

AbstractLate Triassic submarine alkali basalts and hawaiites were collected from two superimposed tectonic slices belonging to the Kara Dere – Sayrun unit of the Middle Antalya nappes, southwestern Turkey. New determinations on conodont faunas allow to date this sequence to the Lower Carnian (Julian). The volcanic rocks show rather homogeneous compositions, with high TiO2 and relatively low MgO and Ni contents which suggest olivine fractionation. Their primitive mantle-normalised multi-elements plots show Nb and Ta enrichments relative to La, Pb negative anomalies and heavy rare earth element and Y depletions typical of intraplate ocean island basalts. These characteristics are consistent with the major and trace element compositions of their primary clinopyroxene phenocrysts, which do not show any feature ascribable to crustal contamination. The studied lavas display a restricted range of εNd (+4.6 to +5.2) which falls within the range of ocean island basalts. Their initial (143Nd/144Nd)i ratios are too low to be explained by a simple mixing line between depleted MORB mantle (DMM) and HIMU components. Their Pb and Nd isotopic compositions plot along a mixing line between HIMU component and an enriched mantle, the composition of which could be the result of the addition of about 5 to 8% of an EM2 component (recycled marine sediments) to DMM. The lack of evidence for any continental crustal component in their genesis could be consistent with their emplacement in an intra-oceanic setting.

scholarly journals Investigating influences on the Pb pseudo-isochron using three-dimensional mantle convection models with a continental reservoir

2021 ◽  
Author(s):  
James Panton ◽  
J. Davies ◽  
Tim Elliott ◽  
Morten Andersen ◽  
Donald Porcelli ◽  
...  
Keyword(s):  
Mantle Convection ◽  
Plate Tectonics ◽  
Three Dimensional ◽  
Isotope Ratios ◽  
Pb Isotope ◽  
Ocean Island Basalts ◽  
Mid Ocean Ridge ◽  
Subducted Oceanic Crust ◽  
Ocean Ridge ◽  
Relative Change

For mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs), measurements of Pb isotope ratios show broad linear correlations with a certain degree of scatter. In 207Pb/204Pb - 206Pb/204Pb space, the best fit line defines a pseudo-isochron age (τPb) of ~1.9 Gyr.Previous modelling suggests a relative change in the behaviours of U and Pb between 2.25-2.5 Ga, resulting in net recycling of HIMU (high U/Pb) material in the latter part of Earth's history, to explain the observed τPb. However, simulations in which fractionation is controlled by a single set of partition coefficients throughout the model runs fail to reproduce τPb and the observed scatter in Pb isotope ratios. We build on these models with 3D mantle convection simulations including parameterisations for melting, U recycling from the continents and preferential removal of Pb from subducted oceanic crust.We find that both U recycling after the great oxygenation event (GOE) and Pb extraction after the onset of plate tectonics, are required in order to fit the observed gradient and scatter of both the 207Pb/204Pb - 206Pb/204Pb and 208Pb/204Pb - 206Pb/204Pb arrays. Unlike much previous work, our model does not require accumulations of subducted oceanic crust to persist at the CMB for long periods of time in order to match geochemical observations.

The mineral chemistry and petrology of Tertiary pitchstones from Scotland

1998 ◽  
Vol 89 (2) ◽  
pp. 95-111 ◽  
Author(s):  
R. J. Preston ◽  
M. J. Hole ◽  
J. Still ◽  
H. Patton
Keyword(s):  
Trace Element ◽  
Major Element ◽  
Crustal Contamination ◽  
Mineral Chemistry ◽  
Lava Flows ◽  
Residual Glass ◽  
Pb Isotope ◽  
Isotope Data ◽  
Igneous Province ◽  
Basaltic Magmas

AbstractSub-silicic to silicic pitchstones are widespread throughout the British Tertiary Igneous Province (BTIP), with examples being found at all the major igneous centres. Both highly porphyritic and almost completely aphyric varieties occur, and take the form of sills, dykes and lava flows. Here we present previously unreported mineral chemistry data on phenocryst and microcrystallite populations from a number of pitchstones from throughout the BTIP. Phenocryst assemblages are completely anhydrous, comprising mixtures of plagioclase, sanidine, fayalite, orthopyroxene, pigeonite, ferroaugite, ferrohedenbergite and quartz. Microcrystallite assemblages are also diverse, consisting of sanidine, ferrohedenbergite, fayalite and, occasionally, almost pure end-member ferrosilite, as well as hydrous phases such as ferrohornblende and biotite. Textural and mineral chemistry observations support interpretations derived from whole-rock and residual glass major element analyses, together with whole-rock trace element and the available Sr-Nd-Pb isotope data, that the Tertiary pitchstones of Scotland are either the products of intimate mixing between a range of basaltic magmas with hydrous crustal melts, or were formed by the crustal contamination of basaltic magmas.

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