Oxygen and nitrogen isotopes as tracers of fluid activities in serpentinites and metasediments during subduction | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS

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  Oxygen and nitrogen isotopes as tracers of fluid activities in serpentinites and metasediments during subduction

Publication Type:

Journal Article

Source:

Mineralogy and Petrology, Volume 91, Issue 1-2, p.11-24 (2007)

ISBN:

0930-0708

Keywords:

ROCKS; ZONES; ELEMENT; MANTLE; WATER; CRUST; QUANTIFICATION

Abstract:

<p>
N and O isotope systematics of a suite of high-pressure (HP) and ultrahigh-pressure (UHP) metasediments of the Schistes Lustres nappe and metaperidotites of the Erro Tobbio Massif from the Alpine-Appennine system are compared with their unmetamorphosed or hydrothermally-altered equivalent from the same localities and from the South West Indian Ridge (SWIR). The HP and UHP rocks studied represent a sequence of pelagic sediments and altered ultramafic rocks subducted to different depths of down to 90km along a cold geothermal gradient (8 degrees C/km). Unmetamorphosed and HP metasediments show the same range in delta N-15 values irrespective of their metamorphic grade and bulk nitrogen concentrations. Together with several other geochemical features (K, Rb and Cs contents, delta D), this indicates that delta N-15 values were unaffected by metamorphism and N was not released during subduction. N isotope analysis of serpentinites coupled with delta O-18 systematics suggests the involvement of a mafic (crustal) component during partial deserpentinization of the subducted oceanic mantle at the depth locus of island arc magmatism. This does not imply large-scale fluxes as the metagabbros are spatially associated with the analyzed serpentinites. It rather indicates preservation of presubduction chemical and isotopic heterogeneities on a local scale as documented for the metasediments.</p>

Notes:

Mineral. Petrol.Philippot, P. Busigny, V. Scambelluri, M. Cartigny, P. 40 SPRINGER WIEN