Evidence from Sr isotopes for long-lived heterogeneities in the upper mantle

Bell, Keith; Blenkinsop, John; Cole, T. J. S.; Menagh, D. P.

doi:10.1038/298251a0

Cited by 99 publications

(32 citation statements)

References 20 publications

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“…2). In addition, Sr and Pb isotopic data from North American carbonatites (ranging from 0.1 to 2.7 Ga) indicate derivation from a source region distinct from either primitive or MORB-like depleted mantle (Bell et al, 1982;Tilton and Bell, 1994). Alternatively, the negative £nf component may also reside in the subcontinental mantle .…”

Section: Resultsmentioning

confidence: 99%

Major element and isotope geochemistry (Sr Nd and Hf) of mantle derived peridotites carbonatites and kimberlites from Canada and Greeland insights into mantle dynamics

Bizzarro¹

2003

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Illhérité de la differentiation initiale de la Terre. Notre étude confirme donc qu'une telle hétérogénéité était toujours présente aux environ de 3 Ga, mais plus elusive dans les roches juvéniles d'âge <2.7 Ga. Les nouvelles données isotopiques de l'Hf ici présentées favorisent une source et origine communes pour les carbonatites, kimberlites et certain basaltes océaniques. IV ABSTRACTWe report on the major element composition of a suite of kimberlite-hosted peridotite xenoliths from the northern margin of the western Archean craton of Greenland, as well as the isotopic composition (Nd, Sr and Hf) of carbonatites and kimberlites from eastern Canada and southwestern Greenland.Our results indicate that the lithospheric mantle underneath the Sarfartoq area of southwestern Greenland extends to approximately 225 km, and consists of refractory (olivine Mg # >0.9) harzburgites and lherzolites. Moreover, the Sarfartoq peridotites are not characterized by the OPX enrichment observed in peridotites from the Kaapvaàl craton of South Africa, and show more affinity with peridotites from east Greenland (Wiedemann Fjord), Somerset Island (Canadian arctic) and Tanzania. Detailed analyses of constituent minerals reveal that the lithospheric mantle underneath the Sarfartoq area is compositionally layered as follows: (1) an internally stratified upper layer (70 to 180 km) consisting of coarse, un-deformed, refractory garnet-bearing and garnet-free peridotites and, (2) a lower layer (180 to 225 km) characterized by fertile, CPX-bearing, porphyroclastic garnet lherzolites. The stratification observed in the upper refractory harzburgite layer (70-180 km) is reflected by an increase in fertility (e.g. lower olivine abundance and fosterite content) with depth. The sharp nature of the stratification may indicate a two-step process for the formation of this lithosphère, i.e. multistage growth of the lithospheric root.In Sr values suggests that apatite and carbonate precipitated predominantly under non-equilibrium conditions. The isotopic variations observed within individual hand specimens may therefore reflect larger-(regional) scale open-system processes, possibly involving mixing of carbonatitic melts derived from distinct mantle sources, or from a common isotopically heterogeneous mantle. This analytical technique provides a rapid and effective approach to determine the extent of isotopic heterogeneity within a single sample or individual grains, with analytical precision approaching that obtained by conventional TIMS.High-precision Hf isotopic analyses and U-Pb ages of carbonatites and kimberlites from Greenland and eastern North America, including Earth's oldest known carbonatite (3 Ga), indicate derivation from an enriched mantle source. This previously unidentified mantle reservoir of unradiogenic Hf isotopic composition, preserved in the deep mantle for at least 3 billion years, may account for the mass imbalance in Earth's Hf-Nd budget. Our results show that the Early to mid-Archean terrestrial mantle was isotopically much more...

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Section: Resultsmentioning

confidence: 99%

Major element and isotope geochemistry (Sr Nd and Hf) of mantle derived peridotites carbonatites and kimberlites from Canada and Greeland insights into mantle dynamics

Bizzarro¹

2003

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“…The red line separates samples with > 10 wt% MgO.... 107 Eby (1984b;1985a) and Currie(1986). Only samples with MgO < 10 wt% are shown 108 Chen et al, 1994), a sedimentary formation from the St Lawrence platform (Trenton formation; Chakrabarti et al, 2007;Davies and Smith, 2006) and a granite gneiss from the Grenville basement (Bell, 1982). The thin lines represent degree of assimilation/ contamination ratios and small points illustrate the percent of contamination (R values).…”

Section: Figurementioning

confidence: 99%

“…Data sources: Appalachian data are from Chen et al (1994), Fisher (2006 and therein authors) and McDaniel and McLennan (1997). Grenville basement data are from McDaniel and McLennan (1997), Wareham et al (1998), Miller and Barr (2000) and Bell (1982). Lower crust data are from Griffin et al (1980a); ; ; Zhang (2002), and crust data is from Vervoort and Blichert-Toft (1999b).…”

Section: Figurementioning

confidence: 99%

Tracages isotopiques de l'origine et de l'évolution des magmas en milieu continental :

Roulleau¹

2010

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“…In North America, carbonatite and alkaline magmatism spans ~2.7 Ga [8,9], and Oka ( Figure 1) is one of the youngest carbonatite complexes on the basis of available geochronological data for various minerals and/or rock types. Apatite fission track ages reported for Oka vary between 118 ± 4 and 133 ± 11 Ma [10], whereas Shafiquall et al [11] document K-Ar ages that range between 107 and 119 Ma for the intrusive alnöites associated with the complex.…”

Section: Introductionmentioning

confidence: 99%

Evidence for the Multi-Stage Petrogenetic History of the Oka Carbonatite Complex (Québec, Canada) as Recorded by Perovskite and Apatite

Chen¹,

Simonetti²

2014

Minerals

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Abstract:The Oka complex is amongst the youngest carbonatite occurrences in North America and is associated with the Monteregian Igneous Province (MIP; Québec, Canada). The complex consists of both carbonatite and undersaturated silicate rocks (e.g., ijolite, alnöite), and their relative emplacement history is uncertain. The aim of this study is to decipher the petrogenetic history of Oka via the compositional, isotopic and geochronological investigation of accessory minerals, perovskite and apatite, using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The new compositional data for individual perovskite and apatite grains from both carbonatite and associated alkaline silicate rocks are highly variable and indicative of open system behavior. In situ Sr and Nd isotopic compositions for these two minerals are also variable and support the involvement of several mantle sources. U-Pb ages for both perovskite and apatite define a bimodal distribution, and range between 113 and 135 Ma, which overlaps the range of ages reported previously for Oka and the entire MIP. The overall distribution of ages indicates that alnöite was intruded first, followed by okaite and carbonatite, whereas ijolite defines a bimodal emplacement history. The combined chemical, isotopic, and geochronological data is best explained by invoking the periodic generation of small volume, partial melts generated from heterogeneous mantle.

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Evidence from Sr isotopes for long-lived heterogeneities in the upper mantle

Cited by 99 publications

References 20 publications

Major element and isotope geochemistry (Sr Nd and Hf) of mantle derived peridotites carbonatites and kimberlites from Canada and Greeland insights into mantle dynamics

Major element and isotope geochemistry (Sr Nd and Hf) of mantle derived peridotites carbonatites and kimberlites from Canada and Greeland insights into mantle dynamics

Tracages isotopiques de l'origine et de l'évolution des magmas en milieu continental :

Evidence for the Multi-Stage Petrogenetic History of the Oka Carbonatite Complex (Québec, Canada) as Recorded by Perovskite and Apatite

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