Les quatre isotopes du soufre dans les kimberlites de Sibérie, traceurs du recyclage de croûte océanique et de sédiments Archéens dans le manteau terrestre

Abstract : Inherited from the early atmosphere, anomalies in the relative abundances of sulfur isotopes (32S, 33S, 34S and 36S) are recorded in sediments older than 2.5 billion year (i.e. Archean). Here we test the robustness of sulfur isotopes to trace the early recycling of oceanic crust and sediments that may have been transferred to the deep mantle or stored in the lithospheric mantle since the onset of subduction. In Siberia, the lithospheric mantle has been naturally sampled by the Udachnaya-East kimberlite while it was erupting. Because it is extremely well preserved, rich in Na, K, Cl, S and contains remnants of oceanic crust recycled during the Archean, this kimberlite enables us to test : (1) the hypothesis of an early recycling of Archean atmospheric sulfur in the lithospheric mantle and/or the deeper source of the kimberlite; (2) the coherence between in situ (SIMS in sulfide minerals) and bulk methods (chemical extraction of sulfur from powdered rocks, followed by gas source mass-spectrometry) for measuring multiple sulfur isotopes. Our results, combined with measurements of Rb-Sr, Sm-Nd and lead (204Pb, 206Pb, 207Pb, 208Pb) isotopes, show that: (1) sulfates from the Udachnaya-East kimberlite and its nodules composed of chloride-carbonate have a deep, magmatic origin, uncontaminated by host sediments, suggesting the presence of sulfate-rich, oxidized domains in the mantle; (2) measurements of sulfur isotopes by bulk methods are consistent with the sulfide populations observed in situ; (3) sulfides from salty kimberlites are depleted in 34S with respect to the chondritic value and record small anomalies in sulfur isotopes ; (4) sheared peridotites contain another population of sulfides that are depleted in 34S and preserve 33S and 36S anomalies inherited from the Archean surface, despite resetting of the U-Pb chronometer during kimberlite eruption
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Theses
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http://docnum.univ-lorraine.fr/ulprive/DDOC_T_2018_0244_KITAYAMA.pdf
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Submitted on : Friday, May 10, 2019 - 4:34:39 PM
Last modification on : Friday, May 17, 2019 - 9:01:42 AM

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  • HAL Id : tel-02125867, version 1

Citation

Yumi Kitayama. Les quatre isotopes du soufre dans les kimberlites de Sibérie, traceurs du recyclage de croûte océanique et de sédiments Archéens dans le manteau terrestre. Géochimie. Université de Lorraine, 2018. Français. ⟨NNT : 2018LORR0244⟩. ⟨tel-02125867⟩

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