1. Fluid properties and dynamics along the seismogenic plate interface
- Author
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Giulia Palazzin, Mathieu Mayoux, Laurent Jolivet, Asuka Yamaguchi, Vincent Famin, Claire Ramboz, Hugues Raimbourg, Institut des Sciences de la Terre d'Orléans - UMR7327 (ISTO), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Géodynamique - UMR7327, Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Bureau de Recherches Géologiques et Minières (BRGM) (BRGM)-Institut des Sciences de la Terre d'Orléans - UMR7327 (ISTO), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Bureau de Recherches Géologiques et Minières (BRGM) (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire GéoSciences Réunion (LGSR), Université de La Réunion (UR)-Institut de Physique du Globe de Paris, Department of Ocean Floor Geoscience, Ocean Research Institute, The University of Tokyo (UTokyo), ANR-10-LABX-0100,VOLTAIRE,Geofluids and Volatil elements – Earth, Atmosphere, Interfaces – Resources and Environment(2010), European Project: 290864,EC:FP7:ERC,ERC-2011-ADG_20110209,RHEOLITH(2012), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), and Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)
- Subjects
[SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics ,010504 meteorology & atmospheric sciences ,[SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph] ,Stratigraphy ,Drop (liquid) ,Geology ,Cathodoluminescence ,010502 geochemistry & geophysics ,Overburden pressure ,01 natural sciences ,law.invention ,Salinity ,law ,Fluid inclusions ,Seawater ,Crystallization ,Petrology ,Quartz ,0105 earth and related environmental sciences - Abstract
International audience; Fossil structures, such as exhumed accretionary prisms, are the only direct recorders of the fluids wetting the plate interface near the base of the seismo genic zone. By studying exhumed accretionary prisms, it is thus possible to determine the physicochemical properties of fluids and the geometry and dynamics of their circulation. We considered here two transects encompass ing the brittleplastic transition (BPT) zone, in the FrancoItalian Alps and the Shimanto Belt in Japan, and compared our data with a broader set of exam ples from the literature. On quartz that grew synkinematically at peak burial conditions, we inferred fluid properties indirectly from quartz traceelement concentrations (using cathodoluminescence [CL] imaging) and directly from fluidinclusion composition and PρT properties (using Raman and micro thermometry). At ~250 °C, quartz grew principally through fracturing and two types of quartz, a CLbrown and a CLblue, precipitated alternately. At ~350 °C, where plastic deformation and recrystallization is pervasive, only a single, ho mogeneously CLbrown quartz is present. The salinity of the fluid in the inclu sions shallower than the BPT is consistently of the order or lower than sea water, while salinities are very scattered deeper than the BPT and often exceed seawater salinity. The gas dissolved in the fluid is predominantly CH 4 shal lower than the BPT, and either CH 4 or CO 2 deeper than the BPT, depending on the nature of the host rock and in particular on the proportion of carbonates. Cathodoluminescence properties, salinity, and nature of the gas all point to a closedsystem behavior in rocks deeper than the BPT. In contrast, shallower than the BPT (i.e., at seismogenic depths), textures revealed by CLimaging evidence the episodic influx of an external fluid, leading to the crystallization of CLblue quartz. The scale of the circulation leading to the generation of the CLblue quartz, or its relationship with the seismic cycle, is still unclear. Be sides, the fluid pressure recorded in the abundant waterrich fluid inclusions is systematically much lower than the corresponding lithostatic pressure, ir respective of the depth domain considered. For inclusions trapped at large depth, the low fluid pressure recorded in the inclusions reflects postentrap ment reequilibration. For inclusions trapped at shallower conditions, typically at seismogenic depths, the low fluid pressure may as well be the result of large fluid pressure drop after earthquakes.
- Published
- 2018
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