Chemical and isotopic evidence for widespread Eoarchean metasedimentary enclaves in southern West Greenland

Cates, N. L.; Mojzsis, Stephen J.

doi:10.1016/j.gca.2006.05.014

Cited by 52 publications

(23 citation statements)

References 113 publications

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“…Igneous rocks from Isua, Akilia, and Innersuartuut have close to chondritic Y/Ho ratio (average 27.44 ± 0.91, n = 73, Table 2, Fig. 7, and also data in McGregor and Mason, 1977;Nutman et al, 1996;Fedo and Whitehouse, 2002a;Polat et al, 2002;Komiya et al, 2004;Cates and Mojzsis, 2006). In Qtz-Px rocks from Akilia and Innersuartuut, the Y/Ho ratio is correlated with the logarithm of the Fe/Ti ratio (Fig.…”

Section: Ree + Ymentioning

confidence: 60%

“…Trace element concentrations were measured by ICP-MS on a Perkin-Elmer ELAN 5000. Because of its low concentration, there are few Ti measurements available in the literature of chemical sediments or metasomatic rocks from Akilia, Innersuartuut, and the ISB (McGregor and Mason, 1977;Appel, 1980;Nutman et al, 1984Nutman et al, , 1996Dymek and Klein, 1988;Dauphas et al, 2004a;Fedo and Whitehouse, 2002a;Cates and Mojzsis, 2006). For this reason, this element was measured separately on a Beckman DU 62 spectrophotometer after digestion in HF-HClO 4 (detection limit 0.0006 wt% TiO 2 ).…”

Section: Methodsmentioning

confidence: 99%

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Iron isotope, major and trace element characterization of early Archean supracrustal rocks from SW Greenland: Protolith identification and metamorphic overprint

Dauphas

Zuilen

Busigny

et al. 2007

Geochimica et Cosmochimica Acta

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Section: Ree + Ymentioning

confidence: 60%

Section: Methodsmentioning

confidence: 99%

Iron isotope, major and trace element characterization of early Archean supracrustal rocks from SW Greenland: Protolith identification and metamorphic overprint

Dauphas

Zuilen

Busigny

et al. 2007

Geochimica et Cosmochimica Acta

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“…Cates and Mojzsis (2006) reported whole rock (d 18 O WR = 7.4 ± 0.1&) and SIMS zircon (d 18 O Zr = from 6.9& ''core" to 8.5& ''rim") compositions for a single IGC banded tonalitic gneiss sample GR0083 (3617 ± 34 Ma). The 18 O-enriched, concordant, oscillatory zoned zircon overgrowths in this sample were interpreted as metamorphic zircon grown in equilibrium with crustal fluids (Cates and Mojzsis, 2006).…”

Section: Tonalite Samples G01/36 G01/113 G97/18 and 248228mentioning

confidence: 99%

In situ U–Pb, O and Hf isotopic compositions of zircon and olivine from Eoarchaean rocks, West Greenland: New insights to making old crust

Hiess

Bennett

Nutman

et al. 2009

Geochimica et Cosmochimica Acta

169

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In situ U-Pb, O and Hf isotopic compositions of zircon and olivine from Eoarchaean rocks, West Greenland: new insights to making old crust AbstractThe sources and petrogenetic processes that generated some of the Earth's oldest continental crust have been more tightly constrained via an integrated, in situ (U-Pb, O and Hf) isotopic approach. The minerals analysed were representative zircon from four Eoarchaean TTG tonalites and two felsic volcanic rocks, and olivine from one harzburgite/dunite of the Itsaq Gneiss Complex (IGC), southern West Greenland. The samples were carefully chosen from localities with least migmatisation, metasomatism and strain. Zircon was thoroughly characterized prior to analysis using cathodoluminescence, scanning electron, reflected and transmitted light imaging. The zircon from all but one sample showed only minor post-magmatic recrystallisation. (207)Pb/(106)Pb dating of oscillatory-zoned zircon using SHRIMP RG (n = 142) indicates derivation of the felsic igneous rocks from different batches of magma at 3. 88, 3.85, 3.81, 3.80 and 3.69 Ga. Analyses of (18)O/(16)O compositions of olivine from a harzburgite/dunite (n = 8) using SHRIMP II in multi-collector mode, indicate that the oxygen isotopic composition of this sample of Eoarchaean mantle (delta(18)O(OI) = 6.0 +/-0.4 parts per thousand) was slightly enriched in (18)O, but not significantly different from that of the modern mantle. Zircon delta(18)O measurements from the six felsic rocks (n = 93) record mean or weighted mean compositions ranging from 4.9 +/-0.7 parts per thousand to 5.1 +/-0.4 parts per thousand, with recrystallised domains showing no indication of oxygen isotopic exchange during younger tectonothermal events. delta(18)O(Zr) compositions indicate that the primary magmas were largely in equilibrium with the mantle or mantle-derived melts generated at similar high temperatures, while calculated tonalite delta(18)O(WR) compositions (6.7-6.9 parts per thousand) resemble those of modern adakites. LA-MC-ICPMS zircon (176)Hf/(177)Hf analyses were obtained from six samples (n = 122), Five samples record weighted mean initial epsilon(Hf) compositions ranging from to 0.5 +/-0.6 to -0.1 +/-0.7 (calculated using lambda(176)Lu = 1.867 x 10(-11) yr(-1)), while one sample records a composition of 1.3 +/-0.7, indicating the magmas were generated from a reservoir with a time averaged, near chondritic Lu/Hf. The derivation of TTG magmas from a chondritic Lu/Hf source implies either that there was not voluminous continental crustal growth nor major mantle differentiation leading to Lu/Hf fractionation during the Hadean or Eoarchaean, or alternatively that rapid recycling of an early formed crust allowed the early mantle to maintain a chondritic Lu/Hf. Previous studies have demonstrated that ancient TTG rocks were mostly produced by dehydration melting of mafic rocks within the stability field of garnet, probably in flatly-subducted or buried oceanic crust. The oxygen isotopic signatures measured here at high spatial resolution allow ...

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“…1). These enclaves are particularly common in the outer Godthåbsfjord area, south of Nuuk (McGregor and Mason 1977;Nutman et al 1996;Cates and Mojzsis 2006), and are generally believed to be older than enclosing gneisses, although tectonized boundaries make this difficult to prove in places (e.g. Whitehouse et al 2009).…”

Section: Geologic Settingmentioning

confidence: 99%

Metamorphic alteration, mineral paragenesis and geochemical re-equilibration of early Archean quartz–amphibole–pyroxene gneiss from Akilia, Southwest Greenland

Lepland

Whitehouse

2010

Int J Earth Sci (Geol Rundsch)

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Quartz-amphibole-pyroxene gneiss from the island of Akilia, Southwest Greenland has been claimed to contain the earliest traces of life on Earth in the form of biogenic carbonaceous matter encapsulated as inclusions in apatite crystals. Various lines of evidence, including petrography, geochronology, field relations, and geochemistry, have, however, been presented that challenge this interpretation. Textural relationships and geochemical signatures in this controversial gneiss presented here manifest a complex, spatially variable metamorphic history that includes granulite-and amphibolite-facies overprints and metasomatism. A peak metamorphic, granulite-facies, quartz-orthopyroxene-clinopyroxene-amphibole-magnetite assemblage is preserved in only a few centimeter-scale layers within the 5-m-thick, quartz-amphibole-pyroxene gneiss unit. Calcite veinlets that appear to postdate the peak metamorphism occur in pyroxene. The quartz-amphibolepyroxene gneiss unit has subsequently experienced isochemical (except hydration) amphibolite-facies alteration during which pyroxenes were retrogressed to amphiboles and magnetite, and calcite was consumed. Parts of the quartz-amphibole-pyroxene gneiss that contain texturally late hornblende have experienced metasomatic alteration by Al-carrying fluids. These fluids controlled the alteration of pyroxenes and amphiboles to hornblende, and modified the trace-element composition by remobilizing LREE and Eu. Apatite has variable REE composition and 87 Sr/ 86 Sr in the quartz-amphibole-pyroxene gneiss, but on the local scale (cm) is in equilibrium with co-existing silicates. Effective recrystallization of apatite crystals as well as co-existing silicates during several stages of the metamorphic history makes the intact preservation of diagenetic apatite with encapsulated primary carbonaceous matter implausible. Hence, it is highly unlikely that Akilia apatite could serve as repository of the earliest traces of life on Earth.

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Chemical and isotopic evidence for widespread Eoarchean metasedimentary enclaves in southern West Greenland

Cited by 52 publications

References 113 publications

Iron isotope, major and trace element characterization of early Archean supracrustal rocks from SW Greenland: Protolith identification and metamorphic overprint

Iron isotope, major and trace element characterization of early Archean supracrustal rocks from SW Greenland: Protolith identification and metamorphic overprint

In situ U–Pb, O and Hf isotopic compositions of zircon and olivine from Eoarchaean rocks, West Greenland: New insights to making old crust

Metamorphic alteration, mineral paragenesis and geochemical re-equilibration of early Archean quartz–amphibole–pyroxene gneiss from Akilia, Southwest Greenland

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