Elsevier

Precambrian Research

Volume 347, September 2020, 105803
Precambrian Research

Compositional heterogeneity of Archean mantle estimated from Sr and Nd isotopic systematics of basaltic rocks from North Pole, Australia, and the Isua supracrustal belt, Greenland

https://doi.org/10.1016/j.precamres.2020.105803Get rights and content

Highlights

  • MORBs and OIBs record the mantle differentiation-homogenization history in the Archean.

  • Archean basalts from Western Australia and West Greenland were chemically examined.

  • Results indicate efficient plate recycling and differentiation before ~3800 Ma.

  • Mantle-crust was then homogenized (to ~3460 Ma) with subsequent differentiation.

Abstract

Compositional variability found in modern mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) reflects differentiation processes associated with material recycling in the mantle-crust system. To investigate the timing at which this recycling system was established and how it transformed into the present-day system, we present geochemical analyses of the Archean basalts from North Pole (NP) in the East Pilbara Craton, Western Australia, and the Isua supracrustal belt (ISB), southern West Greenland. These rocks represent Archean accretionary complexes with ages of ~3.5 Ga and 3.7–3.8 Ga, respectively. We analyzed the trace element contents including rare earth elements (REEs), and Sr and Nd isotopic compositions of the basalts, which may represent MORBs and OIBs, from NP and ISB.

Their trace-element compositions are broadly similar, but show distinct geochemical characteristics particularly with respect to REEs that probably reflect differences in both the source mantle and degree of melting. Such differences are also evident in their initial Nd isotopic compositions, which were estimated based on equilibrium partitioning of REEs and well-defined isochron ages. In contrast, the Sr isotopic compositions of the NP and ISB basalts are highly variable and their isochron ages are inconsistent with previous studies. Furthermore, the partitioning of Rb and Sr in the NP basalts indicates disequilibrium, suggesting that the Rb-Sr system has been disturbed by post-igneous alteration and metamorphism.

Based on these observations, we propose the following model to explain the temporal variations in the geochemical composition of the Archean mantle: (i) ~3800 Ma: recycling of plate material and melting occurred quite readily and, therefore, MORBs and OIBs were produced from differentiated mantle sources; (ii) 3460 Ma to ~3800 Ma: mantle-crust mixing occurred as the result of an extreme event, such as mantle overturning, reducing the compositional variation of the mantle; and (iii) after ~3460 Ma: mantle heterogeneity gradually developed in the material-recycling system, re-establishing the compositional differences between MORBs and OIBs. This model requires an extreme event to drive the homogenization during stage (ii), which may provide new insights into the evolution of the crust-mantle system.

Introduction

Geochemical differences between mid-ocean ridge basalt (MORB) and ocean island basalt (OIB) are key to understanding the structure and differentiation history of the Earth’s mantle (e.g., Hofmann, 2003). Present-day MORBs have relatively high 143Nd/144Nd ratios and low 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios compared to OIBs, with some overlap in multi-dimensional spaces (Iwamori and Nakamura, 2015). Typically, these rocks also have distinct trace-element abundances and patterns, with lower abundances of more incompatible elements in MORBs. These characteristics indicate that a geochemically heterogeneous mantle has developed throughout Earth’s history via: (i) extraction of continental crustal components to create a depleted mantle as a MORB source; and (ii) recycling of various components, including subducted oceanic crusts, lithospheric mantle, and lower mantle/core components, that constitute rising plumes as OIB sources (e.g., Hofmann, 2003). The mechanisms by which such distinct source materials are physically distributed in the mantle are extensively debated. For example, shallow/deep origins of MORB/OIB source mantles might lead to layered mantle whereas shallow/deep melting of uniformly heterogeneous mantle involving marble cake mantle might have occurred (Ito and Mahoney, 2005). In any case, the differences between MORB and OIB in terms of geodynamic setting are key to discriminate the two distinct mantle sources; i.e., a depleted mantle source as a counterpart of continental crust, which is vastly melted adiabatically by passive upwelling of an average mantle of potential temperature beneath mid-ocean ridges associated with divergence of the plates (for MORB; McKenzie and Bickle, 1988), and an enriched or primitive mantle source as a recycled crustal component or undifferentiated mantle, which is melted by decompression melting of actively upwelling mantle plume of a relatively high potential temperature (for OIB; Watson and McKenzie, 1991). As long as a similar geodynamic system with plate tectonics and mantle convection with plumes operates, MORB and OIB may serve as geochemical probes looking into the mantle sources.

The geochemistry of Archean basaltic rocks is, therefore, important for providing direct information on the early evolution and near-initial conditions of the crust-mantle system. Numerous studies have focused on Archean rocks exposed in Canada (Bowring et al., 1989, Collerson et al., 1991, Koshida et al., 2016, Morino et al., 2017), Greenland (Nutman et al., 1997, Polat et al., 2002, Nutman et al., 2007, Rizo et al., 2012, Furnes et al., 2014), Australia (Fletcher et al., 1984, Van Kranendonk et al., 2003, Tessalina et al., 2010), and South Africa (Hegner et al., 1984, Blichert-Toft and Arndt, 1999, Puchtel et al., 2014). Much of this work has focused on isotopic analyses to understand the mantle evolution (e.g., Shirey and Hanson, 1986, Bennett et al., 1993, McCulloch, 1994, McCulloch and Bennett, 1994, Vervoort et al., 1996). These studies have shown that the Archean rocks show a wide compositional range including isotopic ratios (e.g., εNd ranging between −9 and +6 at 2.5 Ga, Bowring and Housh, 1995) and that the mantle has developed rapidly. The presence of highly enriched crustal materials (e.g., high µ signatures at 3.8 Ga, Kamber et al., 2003, and low 142Nd/144Nd values at 1.5 Ga, Upadhyay et al., 2009) and highly depleted early Archean rocks (e.g., an εNd value of approximately 3 at 3.8 Ga, Collerson et al., 1991, Bennett et al., 1993) indicate a significant degree of differentiation in the early Earth. Furthermore, the Sm-Nd system observed in several samples is indicative of post-magmatic processes (Polat et al., 2003).

To better understand the early geochemical evolution of the mantle, we report new geochemical analyses for Archean basaltic rocks from the North Pole region (NP) of the Pilbara Craton (3.5 Ga), Western Australia, and the Isua supracrustal belt (ISB), southern West Greenland (3.7–3.8 Ga). These rocks have similar lithostratigraphies to modern oceanic plates, from basaltic lava through pelagic sedimentary rocks to terrigenous sedimentary rocks. The basaltic rocks were, therefore, classified into MORB-type and OIB-type rocks based on their geological occurrence (Komiya et al., 2002a, Komiya et al., 2004). We measured the trace-element and isotopic compositions (87Sr/86Sr and 143Nd/144Nd) of the MORB-type and OIB-type rocks in NP and the ISB to assess the geochemical evolution of the Earth’s mantle during the Archean.

Section snippets

North Pole region

North Pole is located in the East Pilbara Craton, Western Australia (Fig. 1A). North Pole is underlain by the Mesoarchean monzogranite batholith and a greenstone belt that forms a domal structure due to the intrusion of the monzogranite at 3459 Ma (Thorpe et al., 1992). The Archean greenstone belt consists of predominant basaltic rock, subdominant bedded-chert intercalated with barite layers, and minor components of felsic volcanics, clastic sedimentary rocks, and siliceous dikes (Hickman, 1983

MORB- and OIB-type basalts in the North Pole area

On the basis of the classifications described in Section 2, we selected six NP-MORBs (sample IDs: E67, E148, E151, E152, E166, and E168) and six NP-OIBs (sample IDs: E109, E126, E137, E313, G275, and 95NP164) for further examination. All of the samples contain relatively unaltered and unmetamorphosed phenocrysts of clinopyroxene and magnetite together with relict minerals and/or pseudomorphs of phenocryst of plagioclase, with some chlorite, actinolite, epidote, albite, and magnetite as

Geochemical characteristics of the MORB and OIB-type rocks in the North Pole area

Trace element compositions of the NP basalts are shown in Table 1 and the primitive mantle normalized spidergrams are shown in Fig. 3A. These plots show highly-scattered Rb, Ba, K, Pb, and Sr mobile elements in comparison to immobile high field strength elements (HFSE) and rare earth elements (REE). In particular, the NP-OIBs are more variable in the mobile elements than the NP-MORBs; both positive and negative spikes are shown on the spidergrams of the NP-OIBs for Ba and K. Both basalts show

Secondary alteration of ancient basalts and their primary composition

The NP basalts show large positive spikes in Rb and Sr (Fig. 3A). Moreover, the partitioning of Rb and Sr between clinopyroxene and melt, respectively, is strongly deviated from the equilibrium relationships in the mantle-basalt-andesite system (Fig. 4B). This indicates significant modification from their original composition, which is consistent with the estimated isochron ages; the Rb-Sr isochron age for all of the samples in the 87Rb/86Sr–87Sr/86Sr diagram (Fig. 5A) is 3271 ± 0.0136 Ma

Conclusion

We analyzed the Sr and Nd isotopic compositions of the Archean MORBs and OIBs from the North Pole area of Pilbara (3460 Ma), Western Australia, and the Isua supracrustal belt (~3800 Ma), Greenland. These Archean basalts are thought to preserve their original REEs and Nd isotopic compositions based on (i) the strong correlation between 147Sm/144Nd and 143Nd/144Nd ratios; (ii) the consistency between isochron ages and U-Pb ages; and (iii) the equilibrium partitioning among relict igneous

Acknowledgements

The authors would like to thank Dr. J-I. Kimura, Dr. Q. Chang, Dr. T. Hanyu, and Dr. M. Hamada for their technical support and advice concerning analysis. We also thank Dr. M. Uno, Dr. T. Nishizawa, and K. Chiba for their help and discussion, and anonymous reviewers for their constructive comments and encouragements. We would like to thank Editage (www.editage.com) for English language editing.

Funding

This work was supported by JSPS KAKENHI [Grant Numbers 26247091; 26220713] from Japan Society for the Promotion of Science (JSPS).

References (124)

  • I.H. Campbell et al.

    A two-stage model for the formation of the granite-greenstone terrains of the Kalgoorlie-Norseman area, Western Australia

    Earth Planet. Sci. Lett.

    (1988)
  • C. Chauvel et al.

    The Sm-Nd age of Kambalda volcanics is 500 Ma too old! Earth Planet

    Sci. Lett.

    (1985)
  • K.D. Collerson et al.

    Nd and Sr isotopic crustal contamination patterns in an Archean meta-basic dyke from northern Labrador

    Geochim. Cosmochim. Acta

    (1984)
  • K.C. Condie

    Episodic continental growth and supercontinents: a mantle avalanche connection? Earth Planet

    Sci. Lett.

    (1998)
  • I.R. Fletcher et al.

    Sm-Nd geochronology of greenstone belts in the Yilgarn Block, Western Australia

    Precambrian Res.

    (1984)
  • H. Furnes et al.

    Four billion years of ophiolites reveal secular trends in oceanic crust formation

    Geosci. Front.

    (2014)
  • H. Furnes et al.

    Isua supracrustal belt (Greenland) a vestige of a 3.8 Ga suprasubduction zone ophiolite, and the implications for Archean geology

    Lithos

    (2009)
  • J.B. Gill

    Sr-Pb-Nd isotopic evidence that both MORB and OIB sources contribute to oceanic island arc magmas in Fiji

    Earth Planet. Sci. Lett.

    (1984)
  • M.G. Green et al.

    Growth and recycling of early Archean continental crust: geochemical evidence from the Coonterunah and Warrawoona Groups, Pilbara Craton, Australia

    Tectonophysics

    (2000)
  • G. Gruau et al.

    Age of the Archean Talga-Talga Subgroup, Pilbara Block, Western Australia, and early evolution of the mantle: new Sm-Nd isotopic evidence

    Earth Planet. Sci. Lett.

    (1987)
  • P.J. Hamilton et al.

    Sm-Nd Dating of Archean basic and ultrabasic volcanics

    Earth Planet. Sci. Lett.

    (1977)
  • B. Hamelin et al.

    Pb-Sr-Nd isotopic data of Indian Ocean ridges: new evidence of large-scale mapping of mantle heterogeneities

    Earth Planet. Sci. Lett.

    (1986)
  • P.J. Hamilton et al.

    Sm-Nd studies of Archean metasediments and metavolcanics from West Greenland and their implications for the Earth's early history

    Earth Planet. Sci.

    (1983)
  • A.R. Hastie et al.

    Eoarchean tectonics: new constraints from high pressure-temperature experiments and mass balance modelling

    Precambrian Res

    (2019)
  • E. Hegner et al.

    Age and isotope geochemistry of the Archean Pongola and Usushwana suites in Swaziland, southern Africa: a case for crustal contamination of mantle-derived magma

    Earth Planet. Sci. Lett.

    (1984)
  • G. Ito et al.

    Flow and melting of a heterogeneous mantle: 2. Implications for a chemically nonlayered mantle

    Earth Planet. Sci. Lett.

    (2005)
  • H. Iwamori et al.

    Isotopic heterogeneity of oceanic, arc and continental basalts and its implications for mantle dynamics

    Gondwana Res.

    (2015)
  • F.E. Jenner et al.

    Evidence for subduction at 3.8 Ga: geochemistry of arc-like metabasalts from the southern edge of the Isua Supracrustal Belt

    Chem. Geol.

    (2009)
  • S. Kagami et al.

    Chemical separation of Nd from geological samples for chronological studies using 146Sm-142Nd and 147Sm-143Nd systematics

    Anal. Chim. Ac.

    (2016)
  • T. Kato et al.

    Experimental determination of element partitioning between silicate perovskites, garnets and liquids: Constraints on early differentiation of the mantle

    Earth Planet. Sci. Lett.

    (1988)
  • T. Komiya

    Continental recycling and true continental growth

    Russian Geol. Geophys.

    (2011)
  • K. Koshida et al.

    Petrology and geochemistry of mafic rocks in the Acasta Gneiss Complex: Implications for the oldest mafic rocks and their origin

    Precambrian Res.

    (2016)
  • N. Machado et al.

    Determination of initial 87Sr/86Sr and 143Nd/144Nd in primary minerals from mafic and ultramafic rocks: Experimental procedure and implications for the isotopic characteristics of the Archean mantle under the Abitibi greenstone belt

    Canada. Geochim. Cosmochim. Acta

    (1986)
  • M.T. McCulloch

    Primitive 87Sr/86Sr from an Archean barite and conjecture on the Earth's age and origin

    Earth Planet. Sci. Lett.

    (1994)
  • M.T. McCulloch et al.

    Progressive growth of the Earth’s continental crust and depleted mantle: Geochemical constraints

    Geochim. Cosmochim. Acta

    (1994)
  • N.J. McNaughton et al.

    Constraints on the age of the Warrawoona Group, eastern Pilbara Block

    Western Australia. Precambrian Res.

    (1993)
  • P. Morino et al.

    Chemical stratification in the post-magma ocean Earth inferred from coupled 146,147Sm–142,143Nd systematics in ultramafic rocks of the Saglek block (3.25–3.9 Ga; northern Labrador, Canada)

    Earth Planet. Sci. Lett.

    (2017)
  • J.S. Myers

    Protoliths of the 3.7–3.8 Ga Isua greenstone belt

    West Greenland. Precambrian Res.

    (2001)
  • W. Nijman et al.

    Growth fault control of Early Archaean cherts, barite mounds and chert-barite veins, North Pole Dome, Eastern Pilbara, Western Australia

    Precambrian Res.

    (1998)
  • A.P. Nutman et al.

    ~3710 and ≥3790 Ma volcanic sequences in the Isua (Greenland) supracrustal belt; structural and Nd isotope implications

    Chem. Geol.

    (1997)
  • A.P. Nutman et al.

    New 1:20 000 scale geological maps, synthesisand history of investigation of the Isua supracrustal belt and adjacentorthogneisses, southern West Greenland: a glimpse of Eoarchean crust formationand orogeny

    Precambrian Res.

    (2009)
  • A.P. Nutman et al.

    Detrital zircon sedimentary provenance ages for the Eoarchean Isua supracrustal belt southern West Greenland: juxtaposition of an imbricated ca. 3700Ma juvenile arc against an older complex with 3920–3760Ma components

    Precambrian Res.

    (2009)
  • A.P. Nutman et al.

    Cross-examining Earth’s oldest stromatolites: Seeing through the effects of heterogeneous deformation, metamorphism and metasomatism affecting Isua (Greenland) ~3700 Ma sedimentary rocks

    Precambr. Res.

    (2019)
  • A. Polat et al.

    Alteration and geochemical patterns in the 3.7–3.8 Ga Isua greenstone belt

    West Greenland. Precambrian Res.

    (2003)
  • A. Polat et al.

    Boninite-like volcanic rocks in the 3.7–3.8 Ga Isua greenstone belt, West Greenland: geochemical evidence for intra-oceanic subduction zone processes in the early Earth

    Chem. Geol.

    (2002)
  • A. Polat et al.

    Contrasting geochemical patterns in the 3.7–3.8 Ga pillow basalt cores and rims, Isua greenstone belt, Southwest Greenland: Implications for postmagmatic alteration processes

    Geochim. Cosmochim. Acta

    (2003)
  • A. Polat et al.

    A review of structural patterns and melting processes in the Archean craton of West Greenland: Evidence for crustal growth at convergent plate margins as opposed to non-uniformitarian models

    Tectonophysics

    (2015)
  • I.S. Puchtel et al.

    Insights into early Earth from the Pt–Re–Os isotope and highly siderophile element abundance systematics of Barberton komatiites

    Geochim. Gosmochim. Acta

    (2014)
  • M. Rehkämper et al.

    Recycled ocean crust and sediment in Indian Ocean MORB

    Earth Planet. Sci. Lett.

    (1997)
  • S. Rino et al.

    Major episodic increases of continental crustal growth determined from zircon ages of river sands: implications for mantle overturns in the early Precambrian

    Phys. Earth Planet. Inter.

    (2004)
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    Present position: Tono Geoscience Center, Japan Atomic Energy Agency, 959-31, Jorinji, Izumicho, Toki-shi, Gifu 509-5102, Japan.

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