Rhenium-osmium isotopes and highly siderophile elements in ultramafic rocks from the Eoarchean Saglek Block, northern Labrador, Canada: implications for Archean mantle evolution

Ishikawa, Akira; Suzuki, Katsuhiko; Collerson, K. D.; Liu, Jingao; Pearson, D. Graham; Komiya, Tsuyoshi

doi:10.1016/j.gca.2017.07.023

Cited by 22 publications

(11 citation statements)

References 118 publications

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“…Major, trace, and platinum group element compositions of these mantle fragments closely resemble those hosted within the IGC (cf. Collerson et al 1991;Bennett et al 2002;Friend et al 2002;Ishikawa et al 2017;van de Löcht et al 2018). This resemblance further supports the contention that ultramafic enclaves south of the ISB may be representative of Eoarchean lithospheric mantle.…”

Section: Nature Of Crust/mantle Fragments In the Igcsupporting

confidence: 72%

“…These potential lithospheric mantle fragments in the IGC have similarities with Eoarchean TTG-hosted ultramafic enclaves in the Saglek-Hebron area of northeastern Labrador (e.g., Collerson et al 1991;Ishikawa et al 2017)-an eastern extension of the North Atlantic Craton. Major, trace, and platinum group element compositions of these mantle fragments closely resemble those hosted within the IGC (cf.…”

Section: Nature Of Crust/mantle Fragments In the Igcmentioning

confidence: 89%

“…Dymek et al 1988;Bennett et al 2002;Friend et al 2002;Rollinson 2007;Friend and Nutman 2011;Szilas et al 2015;van de Löcht et al 2018). The same uncertainty surrounds the origin of Eoarchean ultramafic rocks from other crustal terranes (Morino et al 2017;Ishikawa et al 2017). This uncertainty may, in part, be due to the alteration and metamorphism experienced by these rocks, as their ancient crustal residence time (> 3.65 Ga) means that they have typically undergone at least one phase of high-grade metamorphism, arguably altering many geochemical characteristics and obscuring petrogenetic indicators (Rollinson 2007).…”

Section: Introductionmentioning

confidence: 99%

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Implications for the origins of Eoarchean ultramafic rocks of the North Atlantic Craton: a study of the Tussaap Ultramafic complex, Itsaq Gneiss complex, southern West Greenland

McIntyre

Pearson

Szilas

et al. 2019

Contrib Mineral Petrol

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Ultramafic rocks found within the ~ 3.81 Ga Itsaq Gneiss Complex (IGC) have some mantle-like geochemical characteristics that have led to them being used to directly constrain the nature of the Eoarchean mantle. The discrimination of mantle peridotites that are the residues of partial melting, from cumulate peridotites generated by crystal accumulation from mantle-derived magmas can be difficult in ancient, altered ultramafic rocks whose field relations have been obscured by multiple tectonic episodes. Hence it is important to scrutinize significant individual occurrences of Eoarchean ultramafic rocks in some detail prior to using them to constrain the nature of Earth's early mantle. Here we present mineral chemistry, whole rock major-, trace-, and platinum-group-element abundances, and Re-Os isotope compositions of a previously unstudied large ultramafic enclave in the IGC-the Tussaap Ultramafic Complex (TUC)-with the aim of documenting its origin. High FeO contents of up to 15.5 wt% and correlations between MgO and Os provide strong evidence that the TUC evolved through fractional crystallization rather than partial melt extraction. In addition, co-variations of major elements in the TUC lithologies can be modeled via fractional crystallization of picritic basalts using MELTS. Later alteration and metasomatism of these ultramafic rocks has largely overprinted primary mineral chemistry and resulted in a redistribution of light rare earth elements, rendering these tools ineffective for ascertaining the origin of the TUC or quantifying some of the petrogenetic processes that formed the body. In addition, it is clear that many geochemical features used to identify residual mantle peridotites can also be produced by cumulate or alteration processes, such as some variations in olivine and chromite chemistry, whole rock Al/Si vs Mg/Si systematics, and trace and platinum group element patterns. Finally, combined discrimination diagrams for high field strength elements and moderately high 187 Os/ 188 Os ratios suggest the parental melt of the TUC partially assimilated basaltic crust prior to precipitating the TUC cumulates. As such, these rocks represent a variably obscured record of Eoarchean crystal fractionation from mantle-derived melts. Despite not being prima facie mantle rocks, it is possible that such early formed ultramafic cumulates in nascent continents found their way into the later-stabilized roots of Archean cratons, helping to explain the high compositional variability of cratonic peridotites. Keywords Eoarchean • Itsaq gneiss complex • Ultramafic cumulates • Platinum group elements • Re-Os isotopes Communicated by Timothy L. Grove.

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Section: Nature Of Crust/mantle Fragments In the Igcsupporting

confidence: 72%

Section: Nature Of Crust/mantle Fragments In the Igcmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

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Implications for the origins of Eoarchean ultramafic rocks of the North Atlantic Craton: a study of the Tussaap Ultramafic complex, Itsaq Gneiss complex, southern West Greenland

McIntyre

Pearson

Szilas

et al. 2019

Contrib Mineral Petrol

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“…These gneisses have been interpreted to intrude the supracrustal rocks and therefore would represent a minimum age for the supracrustal rocks. Younger ages for these rocks have however also been proposed, ranging between 3612 ± 130 Myr (Re-Os, Ishikawa et al, 2017) and 3782 ± 93 Myr (Sm-Nd, Morino et al, 2017). The complex has undergone a complicated protracted thermal history with several magmatic and metamorphic episodes (Komiya et al 2017;Kusiak et al 2017).…”

Section: Saglek Blockmentioning

confidence: 99%

Widespread occurrences of variably crystalline 13C-depleted graphitic carbon in banded iron formations

Dodd

She

Manikyamba

et al. 2019

Earth and Planetary Science Letters

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Almost all evidence for the oldest traces of life on Earth rely on particles of graphitic carbon preserved in rocks of sedimentary protolith. Yet, the source of carbon in such ancient graphite is debated, as it could possibly be non-biological and/or non-indigenous in origin. Here we describe the co-occurrence of poorly crystalline and crystalline varieties of graphitic carbon with apatite in ten different and variably metamorphosed banded iron formations (BIF) ranging in age from 1,800 to >3,800 Myr. In Neoarchean to Palaeoproterozoic BIF subjected to low-grade metamorphism, 13 C-depleted graphitic carbon occurs as inclusions in apatite, and carbonate and arguably represents the remineralisation of syngenetic biomass. In BIF subjected to high-grade metamorphism, 13 C-depleted graphite co-occurs with poorly crystalline graphite (PCG), as well as apatite, carbonate, pyrite, amphibole and greenalite. Retrograde minerals such as greenalite, and veins cross-cutting magnetite layers contain PCG. Crystalline graphite can occur with apatite and orthopyroxene, and sometimes it has PCG coatings. Crystalline graphite is interpreted to represent the metamorphosed product of syngenetic organic carbon deposited in BIF, while poorly crystalline graphite was precipitated from CO -H fluids partially sourced from the syngenetic carbon, along with fluid-deposited apatite and carbonate. The isotopic signature of the graphitic carbon and the distribution of fluiddeposited graphite in highly metamorphosed BIF is consistent with carbon in the fluids being derived from the thermal cracking of syngenetic biomass deposited in BIF, but, extraneous sources of carbon cannot be ruled out as a source for PCG. The results here show that apatite + graphite is a common mineral assemblage in metamorphosed BIF. The mode of formation of this assemblage is, however, variable, which has important implications for the timing of life's emergence on Earth.

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“…They obtained Sm-Nd isochrons with ages of 4017 ± 194 Ma and 3815 ± 121 for the rocks they interpreted as metakomatiites and mantle slivers respectively. However, Re-Os analyses on equivalent suites of rocks yielded younger isochron ages of respectively 3612 ± 130 Ma and 3096 ± 170 Ma (Ishikawa et al, 2017). In contrast, Morino et al (2017) suggested that all SHC ultramafic rocks are consistent with an origin as komatiite lavas.…”

Section: 12) Saglek-hebron Complexmentioning

confidence: 95%

The nature of Earth’s first crust

et al. 2019

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Recycling of crust into the mantle has left only small remnants at Earth's surface of crust produced within a billion years of Earth formation. Few, if any, of these ancient crustal rocks represent the first crust that existed on Earth. Understanding the nature of the source materials of these ancient rocks and the mechanism of their formation has been the target of decades of geological and geochemical study. This traditional approach has been expanded recently through the ability to simultaneously obtain U-Pb age and initial Hf isotope data for zircons from many of these ancient, generally polymetamorphic, rocks. The addition of information from the short-lived radiometric systems 146 Sm-142 Nd and 182 Hf-182 W allows resolution of some of the ambiguities that have clouded the conclusions derived from the long-lived systems. The most apparent of these is clear documentation that Earth experienced major chemical differentiation events within the first tens to hundreds of millions of years of its formation, and that Earth's most ancient crustal rocks were derived from these differentiated sources, not from primitive undifferentiated mantle. Eoarchean rocks from the North Atlantic Craton and the Anshan Complex of the North China Craton have sources in an incompatible-elementdepleted mantle that dates to 4.4-4.5 Ga. Hadean/Eoarchean rocks from two localities in Canada show the importance of remelting of Hadean mafic crust to produce Eoarchean felsic crust. The mafic supracrustal rocks of the Nuvvuagittuq Greenstone Belt are a possible example of the Hadean mafic basement that is often called upon to serve as the source for the high-silica rocks that define continental crust. Many, but not all, ancient terranes show a shift in the nature of the sources for crustal rocks, and possibly the physical mechanism of crust production, between 3.0-3.6 Ga. This transition may reflect the initiation of modern plate tectonics. Eoarchean/Hadean rocks from some terranes, however, also display compositional characteristics expected for convergent margin volcanism suggesting that at least some convergent margin related magmatism began in the Hadean. The persistence of isotopic variability in 142 Nd/ 144 Nd into the mid-Archean, and the eventual reduction in that variability by the end of the Archean, provides new information on the efficiency by which mantle convection recombined the products of Hadean silicate-Earth differentiation. The rate of crust production and recycling in the Hadean/Archean, however, is not resolved by these data beyond the observation that extreme isotopic compositions, such as expected for Hadean evolved, continent-like, crust are not observed in the preserved Eoarchean rock record. The lack of correlation between 142 Nd/ 144 Nd and 182 W/ 184 W variation in Archean rocks suggests that these two systems track different processes; the Sm-Nd system mantle-crust differentiation while Hf-W is dominated by core formation. The major silicate differentiation controlling Sm/Nd fractionation occurred at ~4.4 Ga, po...

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Rhenium-osmium isotopes and highly siderophile elements in ultramafic rocks from the Eoarchean Saglek Block, northern Labrador, Canada: implications for Archean mantle evolution

Cited by 22 publications

References 118 publications

Implications for the origins of Eoarchean ultramafic rocks of the North Atlantic Craton: a study of the Tussaap Ultramafic complex, Itsaq Gneiss complex, southern West Greenland

Implications for the origins of Eoarchean ultramafic rocks of the North Atlantic Craton: a study of the Tussaap Ultramafic complex, Itsaq Gneiss complex, southern West Greenland

Widespread occurrences of variably crystalline 13C-depleted graphitic carbon in banded iron formations

The nature of Earth’s first crust

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