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| Titel |
Water-serpentine interactions and deformation in subduction zones |
| VerfasserIn |
Hélène Pilorgé, Anne-Céline Ganzhorn, Gilles Montagnac, Hervé Cardon, Sylvie Le Floch, Bruno Reynard |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250143795
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| Publikation (Nr.) |
 EGU/EGU2017-7549.pdf |
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| Zusammenfassung |
| The circulation of substantial amounts of fluids in subduction zones results in volcanism,
tremors, brine springs and electrically conductive zones, in particular above the subducting
slab and in the mantle wedge. The mantle wedge is serpentinized by fluids coming from the
dehydration of the slab at pressure and temperature conditions that favor the formation the
antigorite species of serpentine. The evolution of the mantle wedge is linked to the
interactions between the aqueous fluids and antigorite. In order to investigate these
interactions in detail, we reacted antigorite powder with liquid D2O at high pressure and high
temperature in a Belt apparatus in the range 1.5 to 3.0 GPa and from 315˚ C to
540˚ C, corresponding to the conditions of the mantle wedge. Antigorite samples
were then analyzed by Raman micro-spectrometry, from which D/(D+H) maps
were calculated, in order to quantify the exchanges between hydrogen (H) from
the hydroxyl (OH) groups of antigorite and deuterium (D) from the liquid water
(D2O). Solid state diffusion was previously characterized on single-crystals, and
we obtained a solid-state diffusion law for D/H inter-diffusion in antigorite. At
the aggregate scale, we observe zones where the exchange between antigorite and
water is much more important than expected for solid-state diffusion. These zones
correspond to highly micro-cleaved antigorites, with up to tens of open fractures per
micrometer. The high amount of cleavages raises the reactional surface between water and
antigorite and allows fluids to interact much more with micro-fractured grains than with
non-fractured grains. The highly fractured zones displaying high D/H exchanges
correspond to shear zones that form in response to the non-hydrostatic conditions in
the belt apparatus. Deformation creates fractures sub-parallel to the cleavage of
antigorite, and to the foliation of the serpentinite. Our observations indicate that
sheared antigorite serpentinites are highly permeable and reactive with aqueous
fluids.
The serpentinized subduction interface is a zone of intense deformation just above the
slab, and deformation with veins is observed in natural samples from the micrometer
to the outcrop scale. We discuss applications of our experimental observations to
subduction zones and in particular to high deformed serpentinite layers above the slab. |
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