scholarly journals Remnants of early Earth differentiation in the deepest mantle-derived lavas

2020 ◽  
Vol 118 (1) ◽  
pp. e2015211118
Author(s):  
Andrea Giuliani ◽  
Matthew G. Jackson ◽  
Angus Fitzpayne ◽  
Hayden Dalton
Keyword(s):  
Mantle Source ◽  
Isotope Composition ◽  
Volcanic Rocks ◽  
Primitive Mantle ◽  
Early Earth ◽  
Apparent Contradiction ◽  
Ocean Island ◽  
Melt Extraction ◽  
Ocean Island Basalts ◽  
Isotopic Compositions

The noble gas isotope systematics of ocean island basalts suggest the existence of primordial mantle signatures in the deep mantle. Yet, the isotopic compositions of lithophile elements (Sr, Nd, Hf) in these lavas require derivation from a mantle source that is geochemically depleted by melt extraction rather than primitive. Here, this apparent contradiction is resolved by employing a compilation of the Sr, Nd, and Hf isotope composition of kimberlites—volcanic rocks that originate at great depth beneath continents. This compilation includes kimberlites as old as 2.06 billion years and shows that kimberlites do not derive from a primitive mantle source but sample the same geochemically depleted component (where geochemical depletion refers to ancient melt extraction) common to most oceanic island basalts, previously called PREMA (prevalent mantle) or FOZO (focal zone). Extrapolation of the Nd and Hf isotopic compositions of the kimberlite source to the age of Earth formation yields a143Nd/144Nd-176Hf/177Hf composition within error of chondrite meteorites, which include the likely parent bodies of Earth. This supports a hypothesis where the source of kimberlites and ocean island basalts contains a long-lived component that formed by melt extraction from a domain with chondritic143Nd/144Nd and176Hf/177Hf shortly after Earth accretion. The geographic distribution of kimberlites containing the PREMA component suggests that these remnants of early Earth differentiation are located in large seismically anomalous regions corresponding to thermochemical piles above the core–mantle boundary. PREMA could have been stored in these structures for most of Earth’s history, partially shielded from convective homogenization.

scholarly journals Tungsten-182 evidence for an ancient kimberlite source

2021 ◽  
Vol 118 (23) ◽  
pp. e2020680118
Author(s):  
Nao Nakanishi ◽  
Andrea Giuliani ◽  
Richard W. Carlson ◽  
Mary F. Horan ◽  
Jon Woodhead ◽  
...  
Keyword(s):  
Mantle Source ◽  
Upper Mantle ◽  
Primitive Mantle ◽  
Early Earth ◽  
The Core ◽  
Isotopic Compositions ◽  
Globally Distributed

Globally distributed kimberlites with broadly chondritic initial 143Nd-176Hf isotopic systematics may be derived from a chemically homogenous, relatively primitive mantle source that remained isolated from the convecting mantle for much of the Earth’s history. To assess whether this putative reservoir may have preserved remnants of an early Earth process, we report 182W/184W and 142Nd/144Nd data for “primitive” kimberlites from 10 localities worldwide, ranging in age from 1,153 to 89 Ma. Most are characterized by homogeneous μ182W and μ142Nd values averaging −5.9 ± 3.6 ppm (2SD, n = 13) and +2.7 ± 2.9 ppm (2SD, n = 6), respectively. The remarkably uniform yet modestly negative μ182W values, coupled with chondritic to slightly suprachondritic initial 143Nd/144Nd and 176Hf/177Hf ratios over a span of nearly 1,000 Mya, provides permissive evidence that these kimberlites were derived from one or more long-lived, early formed mantle reservoirs. Possible causes for negative μ182W values among these kimberlites include the transfer of W with low μ182W from the core to the mantle source reservoir(s), creation of the source reservoir(s) as a result of early silicate fractionation, or an overabundance of late-accreted materials in the source reservoir(s). By contrast, two younger kimberlites emplaced at 72 and 52 Ma and characterized by distinctly subchondritic initial 176Hf/177Hf and 143Nd/144Nd have μ182W values consistent with the modern upper mantle. These isotopic compositions may reflect contamination of the ancient kimberlite source by recycled crustal components with μ182W ≥ 0.

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 The influence of igneous processes on the chromium isotopic compositions of Ocean Island basalts

2020 ◽  
Vol 532 ◽  
pp. 116028 ◽  
Author(s):  
P. Bonnand ◽  
R. Doucelance ◽  
M. Boyet ◽  
P. Bachèlery ◽  
C. Bosq ◽  
...  
Keyword(s):  
Ocean Island ◽  
Ocean Island Basalts ◽  
Isotopic Compositions

Triple oxygen isotope constraints on the origin of ocean island basalts

2020 ◽  
Author(s):  
Xiaobin Cao ◽  
Huiming Bao ◽  
Yongbo Peng
Keyword(s):  
Theoretical Calculation ◽  
Oxygen Isotope ◽  
Mantle Source ◽  
Plate Tectonics ◽  
Unique Feature ◽  
Published Data ◽  
Ocean Island ◽  
Ocean Island Basalts ◽  
Geochemical Proxies ◽  
Subducted Oceanic Crust

<p> </p><p><span>Understanding the origin of ocean island basalts (OIB) has important bearings on Earth’s deep mantle. Although it is widely accepted that subducted oceanic crust, as a consequence of plate tectonics, contributes material to OIB’s formation, its exact fraction in OIB’s mantle source remains ambiguous largely due to uncertainties associated with existing geochemical proxies. We have shown, through theoretical calculation and examining published data, that unlike many known proxies, triple oxygen isotope compositions (i.e. Δ<sup>17</sup>O) in olivine samples are not affected by crystallization and partial melting. This unique feature allows olivine Δ<sup>17</sup>O values to identify and quantify the fractions of subducted ocean sediments and hydrothermally altered oceanic crusts in OIB’s mantle source. In this work, new Δ<sup>17</sup>O measurements for OIB will be presented, and the implications will be discussed.<span>  </span></span></p><p> </p>

Sr-Nd-Pb-Hf-Mg isotope geochemistry of volcanic rocks from Oldoinyo Lengai, Tanzania

2020 ◽  
Author(s):  
Sung Hi Choi ◽  
Seung Gi Jung ◽  
Kang Hyeun Ji
Keyword(s):  
Rift Valley ◽  
Source Region ◽  
Regression Line ◽  
Volcanic Rocks ◽  
Primitive Mantle ◽  
Geochemical Data ◽  
Stability Field ◽  
Crustal Material ◽  
Oldoinyo Lengai ◽  
Isotopic Compositions

<p>Oldoinyo Lengai is the only active carbonatite volcano within the East African Rift Valley in northern Tanzania. The volcano is dominated by peralkaline silicate rocks with natrocarbonatites. This study presents new mineralogical and geochemical data, including Sr–Nd–Pb–Hf–Mg isotopic compositions, for volcanic rocks at Oldoinyo Lengai and lavas from the nearby Gregory Rift Valley. The samples analyzed in this study include olivine melilitite, melanephelinite, wollastonite nephelinite, and phonolite. The olivine melilitites and melanephelinites have highly fractionated REE patterns with (La/Yb)<sub>N</sub> values of 26.4–64.9, suggesting that they formed from magmas generated by low-degree (up to ~7%) of partial melting within the garnet stability field. The wollastonite nephelinites have much higher (La/Sm)<sub>N</sub> values but lower (Sm/Yb)<sub>N</sub> values relative to typical OIB, with flat HREE patterns [(La/Yb)<sub>N</sub> = ~22]. The phonolites have elevated REE abundances but with patterns intermediate between the other two sample groups [(La/Yb)<sub>N</sub> = ~41]. All samples have primitive-mantle-normalized incompatible element patterns that are characterized by negative K and Rb anomalies but no significant Eu anomalies. They also have elevated Yb contents relative to the compositions of modeled garnet peridotite-derived melts, suggesting that they were derived from a sublithospheric source containing enriched HIMU-like recycled oceanic crustal material. However, the wollastonite nephelinites have significantly positive Ba, U, Sr, and Pb anomalies similar to those found within the Oldoinyo Lengai natrocarbonatites. The wollastonite nephelinites might have been sourced from a region of sub-continental lithospheric mantle (SCLM) that was previously metasomatized by interaction with carbonatite melts. The phonolites in the study area have also weakly positive Pb and Sr anomalies indicative of some interaction with the SCLM. All samples have d<sup>26</sup>Mg values (–0.39‰ ± 0.07‰) lighter than the composition of normal mantle material (–0.25‰ ± 0.04‰). In addition, a negative correlation between d<sup>26</sup>Mg values and MgO concentrations suggests derivation from a source region containing recycled carbonate. The samples from the study area define a mixing array between HIMU- and EM1-type OIB in Sr–Nd and Pb–Pb isotopic correlation diagrams, and have pronounced Nd–Hf isotopic decoupling, plotting below the mantle regression line in Nd–Hf isotopic space. The negative deviation from the Nd–Hf isotopic mantle array and the presence of an EM1-type mantle component in the Sr–Nd isotopic compositions of the Oldoinyo Lengai volcanic rocks can be generated by recycling of E-MORB-type oceanic crustal material with an age of 1.5–1.0 Ga.</p>

Subducted and recycled lithosphere as the mantle source of ocean island basalts from southern Polynesia, central Pacific

1989 ◽  
Vol 77 (1) ◽  
pp. 1-18 ◽  
Author(s):  
C. Dupuy ◽  
H.G. Barsczus ◽  
J. Dostal ◽  
P. Vidal ◽  
J.-M. Liotard
Keyword(s):  
Mantle Source ◽  
Central Pacific ◽  
Ocean Island ◽  
Ocean Island Basalts
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