Isotopic record of Hadean crust in Western Australia

S. G. Tessalina, Pascal Philippot, Martin J. Van Kranendonk, Bernard Bourdon, J. L. Birck

Research output: Contribution to journalMeeting abstract

Abstract

Application of the 147Sm-143Nd and 146Sm-142Nd chronometers suggests that mantle depletion and related crust extraction had started during the first hundred million years of Earth history (Caro et al., 2006), but there is limited evidence for the presence of an enriched silicate reservoir before 4.0 Ga (Harrison et al., 2006). Here, we report new 147Sm-143Nd data from low-grade metamorphosed Paleoarchean volcanic and sedimentary rocks of the Warrawoona Group, Pilbara Craton, Western Australia. A Sm-Nd isochron age of 3.48 ± 0.09 Ga is in an agreement with the U-Pb zircon age from intercalated volcanoclastic rocks and indicates the preservation of their Sm-Nd isotope signature since the Archean. The initial HNd value of -3.3 ± 0.5 is out of the range (+1< HNd < +3) established for the Archean cratons based on whole-rock Sm- Nd isochrons with ages agreeing with independent chronological constraints. This data is best explained by the assimilation of older continental crust, as shown by significant Ta-Nb depletion associated with LILE, Th, U and LREE enrichment (Green et al., 2000). Geochemical modeling suggests the assimilation of 10% to 20% of crustal material that may be either Archean granites, shales, or average upper continental crust (Condie, 1993). Assimilation of this crustal material with HNd values of –6 (granite), –8 (shales) and/or –10 (upper CC) by a mantle-derived melt accounts for the observed Nd isotope composition of basalts. This crustal component, with 147Sm/144Nd ratios of 0.09–0.12, would have been isolated from the depleted mantle at 4.0–4.4 Ga, which is consistent with the Nd model ages derived from the studied rocks. Our observations, albeit indirect, clearly show the existence of a an Hadean crustal reservoir. Its presence is confirmed by negative HNd of Archean seawater, inferred from carbonate rocks with seawater-like REE patterns. The presence of a crustal basement involved in plume magmatism indicates eruption of flood basalts onto a submerged continental platform, analogous with the Phanerozoic Kerguelen plateau (Van Kranendonk and Pirajno, 2004). This could have been an important mode of crustal production in the Archean. References Caro G. et al. (2006) Geochim.Cosmochim.Acta 70, 164-191. Condie K.C. (1993) Chem. Geol. 104, 1-37. Green M.G. et al. (2000) Tectonoph. 322, 69-88. Harrison et al. (2006) Science 312, 1947-1950. Van Kranendonk M. and Pirajno F. (2004) Geochemistry: Exploration, Environment, Analysis 4, 253-278.
Original languageEnglish
Pages (from-to)A1015-A1015
Number of pages1
JournalGeochimica et Cosmochimica Acta
Volume71
Issue number15 supplement
Publication statusPublished - Aug 2007
Externally publishedYes
EventGoldschmidt Conference (17th : 2007) - Cologne, Germany
Duration: 19 Aug 200724 Aug 2007
Conference number: 17

Keywords

  • CONTINENTAL-CRUST
  • PILBARA CRATON

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