Massive recycling of nitrogen and other fluid-mobile elements (K, Rb, Cs, H) in a cold slab environment; evidence from HP to UHP oceanic metasediments of the Schistes Lustres Nappe (Western Alps, Europe)

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doi: 10.1016/S0012-821X(03)00453-9
Authors:Busigny, Vincent; Cartigny, Pierre; Philippot, Pascal; Ader, Magali; Javoy, Marc
Author Affiliations:Primary:
Institut de Physique du Globe de Paris, Laboratoire de Géochimie des Isotopes Stables, Paris, France
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 215(1-2), p.27-42. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:2003
Note:In English. Inst. Phys. Globe de Paris, Contrib. No. 1941. 70 refs.; illus., incl. 3 tables, geol. sketch map
Summary:Nitrogen and hydrogen isotopic compositions together with N, K, Rb, Cs and H2O contents were measured on several high-pressure (HP) to ultrahigh-pressure (UHP) metasediments from the Schistes Lustres nappe (western Alps) and on unmetamorphosed sedimentary protoliths from the Apennines (Italy). These samples represent a sequence of pelagic sediments subducted to different depths down to 90 km along a "cold" geothermal gradient (∼8°C/km). Nitrogen isotopic composition (δ15N between +2.6 and +4.8 per mil) does not show any specific evolution with increasing metamorphic conditions and can be considered constant during subduction. Large variations of the N content (between 169 and 1721 ppm N) together with K, Rb and Cs content are observed but the constancy of K/N (14), K/Rb (385) and K/Cs (10 190) molar ratios in protoliths and metamorphic rocks indicates that none of these fluid-mobile elements was lost through devolatilization processes. This suggests that fluid circulation was limited to sample scale and that the rocks behaved as closed systems during subduction. This interpretation is also supported by the small range of δD values (from -54.1 to -78.0 per mil). The present results indicate that N, K, Rb and Cs were retained in the subducted sedimentary veneer at least down to the depth locus of island arc magmatism. Based on the correlation between N and K contents, the flux of sedimentary N recycled in subduction zones is estimated at 7.6×1011 g/yr. Mass balance calculations strongly support the fact that nitrogen is efficiently recycled to the deeper mantle. Abstract Copyright (2003) Elsevier, B.V.
Subsections:Metamorphism: regional, dynamic; Metamorphism: thermal, metasomatic
Subjects:Alkali metals; Cesium; Chemical fractionation; Cretaceous; D/H; Depositional environment; Deuterium; Experimental studies; Geochemical cycle; Geochemistry; High pressure; Hydrogen; Infrared spectra; Isotope ratios; Isotopes; Jurassic; Marine environment; Mass balance; Mesozoic; Metals; Metamorphic rocks; Metamorphism; Metasedimentary rocks; Mobility; Nappes; Nitrogen; P-T conditions; Paragenesis; Pelagic environment; Potassium; Pressure; Protoliths; Rubidium; Sediment-water interface; Sedimentary rocks; Slabs; Spectra; Stable isotopes; Subduction zones; Temperature; Ultrahigh pressure; Volatilization; Alps; Apennines; Europe; France; French Alps; Italy; Northern Apennines; Southern Europe; Western Alps; Western Europe; Schistes Lustres
Coordinates:N440000 N460000 E0090000 E0060000
Abstract Numbers:04M/4787
Record ID:2004082837
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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