Resetting of SmNd systematics during metamorphism of &gt; 3.7-Ga rocks: implications for isotopic models of early Earth differentiation

Gruau, Gérard; Rosing, Minik T.; Bridgwater, D.; Gill, R.C.O.

doi:10.1016/s0009-2541(96)00092-7

Cited by 121 publications

(55 citation statements)

References 35 publications

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“…The controversy has focussed more recently on the veracity of calculated initial compositions because of the potential of secondary resetting of isotopic systems including Sm-Nd (e.g. Gruau et al 1996). An additional aspect when using felsic rocks to determine mantle compositions is that, in general, granitoids in any tectonic setting have a range of initial isotopic compositions reflecting the complexity of granite forming processes.…”

Section: Depletion History Of the Pre-3850 Ma Mantle From 147 Sm-143 mentioning

confidence: 99%

∼3,850 Ma tonalites in the Nuuk region, Greenland: geochemistry and their reworking within an Eoarchaean gneiss complex

Nutman

Bennett

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et al. 2007

Contrib Mineral Petrol

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Hidaka, H. (2007). ~3,850 Ma tonalites in the Nuuk region, Greenland: geochemistry and their reworking within an Eoarchaean gneiss complex. Contributions to Mineralogy and Petrology, 154 (4), 385-408. ~3,850 Ma tonalites in the Nuuk region, Greenland: geochemistry and their reworking within an Eoarchaean gneiss complex AbstractThe Eoarchaean (>3,600 Ma) Itsaq Gneiss Complex of southern West Greenland is dominated by polyphase orthogneisses with a complex Archaean tectonothermal history. Some of the orthogneisses have c. 3,850 Ma zircons, and they vary from rare single phase metatonalites to more common complexly banded migmatites. This is due to heterogeneous strain, in situ anatexis and granitic veining superimposed during younger tectonothermal events. In the single-phase tonalites with c. 3,850 Ma zircon, oscillatory-zoned prismatic zircon is all 3,850 Ma old, but shows patchy ancient loss of radiogenic Pb. SHRIMP spot analyses and laser ablation ICP-MS depth profiling show that thin (usually < 10 μm) younger (3,590 Ma and Neoarchaean) shells of lower Th/U metamorphic zircon are present on these 3,850 Ma zircons. Several samples with this simple zircon population occur on islands near Akilia. In contrast, migmatites usually contain more complex zircon populations, with often more than one generation of igneous zircon present. Additional zircon dating of banded gneisses across the Complex shows that samples with c. 3,850 Ma igneous zircon are not just a phenomenon restricted to Akilia and adjacent islands. For example, migmatites from Itilleq (c. 65 km from Akilia) contain variable amounts of oscillatory-zoned 3,850 Ma and 3,650 Ma zircon, interpreted, respectively, as the rock age and the time of crustal melting under Eoarchaean metamorphism. With only 110-140 ppm Zr in the tonalites and likely magmatic temperatures of >850°C, zircon solubilitymelt composition relationships show that they were only one-third saturated in zircon. Any zircon entrained in the precursor magmas would thus have been highly soluble. Combined with the cathodoluminesence imaging, this demonstrates that the c. 3,850 Ma oscillatory zoned zircon crystallised out of the melt and hence gives a magmatic age. Thus the rare well-preserved tonalites and palaeosome in migmatites testify that c. 3,850 Ma quartzo -feldspathic rocks are a widespread (but probably minor) component in the Itsaq Gneiss Complex. C. 3,850 Ma zircon with negative Eu anomalies (showing growth in felsic systems) also occurs as detrital grains in rare c. 3,800 Ma metaquartzites and as inherited grains in some 3,660 Ma granites (sensu stricto). These demonstrate that still more c. 3,850 Ma rocks were present, but were recycled into Eoarchaean sediments and crustally derived granites. The major and trace element characteristics (e.g. LREE enrichment, HREE depletion, low MgO) of the best-preserved c. 3,850 Ma rocks are typical of Archaean TTG suites, and thus argue for crust formation processes involving important contributions from melting of hydrated mafic crust to the...

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Section: Depletion History Of the Pre-3850 Ma Mantle From 147 Sm-143 mentioning

confidence: 99%

∼3,850 Ma tonalites in the Nuuk region, Greenland: geochemistry and their reworking within an Eoarchaean gneiss complex

Nutman

Bennett

Friend

et al. 2007

Contrib Mineral Petrol

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“…Nitrogen commonly occurs in metamorphic fluids, and fluid inclusions representing synmetamorphic fluids that were derived either from crustal material (Glassley, 1984;Roskamp and Schultz, 1985;Kelley et al, 1986) or possibly from a mantle source (Kreulen and Schuiling, 1982) have been observed in highly metamorphosed rocks. Large-scale metasomatic activity in Isua (Rosing and Rose, 1993;Gruau et al, 1996;Rose et al, 1996;Rosing et al, 1996) could therefore have contributed nitrogen to these graphite sam- …”

Section: Strongly Retained Components In Graphitementioning

confidence: 99%

Nitrogen and argon isotopic signatures in graphite from the 3.8-Ga-old Isua Supracrustal Belt, Southern West Greenland

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Mathew

Wopenka

et al. 2005

Geochimica et Cosmochimica Acta

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“…The difficulty of dating basic rocks in a high grade terrane resides in that such rocks contain extremely small volumes of minerals suitable for high precision age determinations, and their isotopic systems are commonly affected at varied intensities during severe metamorphism, so the study of these systems will indicate varied levels of complexity, no matter if the tectonic evolution was polyphase or polycyclic (Frost and Frost, 1995;Gruau et al, 1996;Pidgeon and Wilde, 1998;Carson et al, 2002).…”

Section: Discussionmentioning

confidence: 99%

U–Pb and Sm–Nd geochronology of amphibolites from the Curaçá Belt, São Francisco Craton, Brazil: Tectonic implications

et al. 2007

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The Curaçá terrane is part of the Itabuna-Salvador-Curaçá (I-S-C) Paleoproterozoic orogen in the São Francisco craton, northeastern Brazil, and comprises supracrustal rocks, gneisses of their probable basement, amphibolites, and mafic-ultramafic Cu-bearing bodies (including the Caraíba Cu-Mine), all affected by D1-D3 deformation events associated to M1-M3 metamorphism under high-T granulite and amphibolite facies, and assisted by G1-G3 tonalitic-granodioritic-granitic intrusions. U-Pb and Sm-Nd Thermal Ionization Mass Spectrometry (TIMS) isotopic data from amphibolite, tonalite, and granite, sampled in a well-known outcrop, indicate partial reset and heterogeneous modification of the original isotopic systems, attributable to deformation and metamorphism. The ages obtained from these systems agree with each other, and also with other previously published U-Pb data, and imply that 2.6 Ga is the crystallization age of the protolith of the amphibolite. Together with key structural relationships, they also indicate a 2.08-2.05 Ga interval for M3 metamorphism, and make even a less precise age (2.2-2.3 Ga) acceptable, as it suggests contamination in the amphibolite with material in a syn-D2 tonalite crystallized 2248±36 Ma ago. The new data demonstrate the existence of Neoarchean fragments of both oceanic and continental crusts and constrain the Archean-Paleoproterozoic development of the Curaçá belt, the I-S-C orogen, and the São Francisco craton.

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Resetting of SmNd systematics during metamorphism of > 3.7-Ga rocks: implications for isotopic models of early Earth differentiation

Cited by 121 publications

References 35 publications

∼3,850 Ma tonalites in the Nuuk region, Greenland: geochemistry and their reworking within an Eoarchaean gneiss complex

∼3,850 Ma tonalites in the Nuuk region, Greenland: geochemistry and their reworking within an Eoarchaean gneiss complex

Nitrogen and argon isotopic signatures in graphite from the 3.8-Ga-old Isua Supracrustal Belt, Southern West Greenland

U–Pb and Sm–Nd geochronology of amphibolites from the Curaçá Belt, São Francisco Craton, Brazil: Tectonic implications

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