Serpentinization of New Caledonia peridotites: from depth to (sub-)surface
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(2020) 175:91
ORIGINAL PAPER
Serpentinization of New Caledonia peridotites: from depth to (sub‑) surface Marc Ulrich1 · Manuel Muñoz2 · Philippe Boulvais3 · Michel Cathelineau4 · Dominique Cluzel5 · Stéphane Guillot6 · Christian Picard7 Received: 14 February 2020 / Accepted: 2 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Serpentinization processes occur at geological settings notably during oceanic subduction and obduction, where mantle rocks interact with water. Different types of serpentine minerals form according to temperature and pressure conditions, and potentially chemical exchanges. Therefore, the characterization of serpentine minerals, and the possible occurrence of multiple serpentine generations in mantle rocks provide essential constraints on the conditions of fluid–rock interactions in the mantle. The serpentinite sole of the Peridotite Nappe of New Caledonia (Southwest Pacific) is the result of several superimposed serpentinisation events. The latter were discriminated using mineralogical and geochemical approaches and modeling. Lizardite represents more than 80% of the entire serpentine content of the ophiolite. It is crosscut by several veins of other serpentine species in the serpentinite sole. The relative chronology appears as follows: lizardite 1 → lizardite 2 → antigorite → chrysotile → polygonal serpentine. The transition from primary/magmatic minerals to lizardite 1 is almost isochemical. Then, the development of lizardite 2 yields an enrichment in fluid-mobile elements such as Cs, Rb, Ba, U and light rare-earth elements and an apparent increase of the Fe3+/FeT ratio. The modeling of δ18O values (1.9–13.9‰) and δD values (88–106‰) of all serpentine species through Monte-Carlo simulations show that New Caledonia serpentines were mainly formed in equilibrium with fluids released by the dehydration of altered oceanic crust (AOC) during subduction between 250 and 350 °C. AOC-derived fluids are not the unique source of fluids since a low temperature (100–150 °C) meteoric component is also predicted by the models. Thus, serpentine acts as a tape-recorder of fluid–rock interactions into the mantle from depth to (sub-)surface. Keywords Serpentinization · New Caledonia ophiolite · Subduction · Obduction · Serpentine geochemistry · Meteoric fluid circulation
Introduction
Communicated by Othmar Müntener. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00410-020-01713-0) contains supplementary material, which is available to authorized users. * Marc Ulrich [email protected] 1
Université de Strasbourg, CNRS, IPGS, UMR 7516, 67000 Strasbourg, France
2
Géosciences Montpellier, University Montpellier, CNRS, Montpellier, France
3
Géosciences Rennes‑UMR 6118, University Rennes, CNRS, 35000 Rennes, France
Serpentinization is a hydrothermal alteration process that leads to upper mantle hydration. Serpentine minerals are ubiquitous in ultramafic rocks from various geological settings and their crucial r
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