Modification of fluid inclusions in quartz by deviatoric stress I: experimentally induced changes in inclusion shapes and microstructures

Abstract

Fluid inclusions in quartz are known to modify their shapes and microstructures (textures) during weak plastic deformation. However, such changes have not been experimentally demonstrated and criteria are not available to relate them to paleostress conditions. To address these issues, quartz crystals containing natural CO 2 -H 2 O-NaCl fluid inclusions have been experimentally subjected to compressive deviatoric stresses of 90-250 MPa at 700°C and *600 MPa confining pressure. Strains of up to 1% cause the inclusions to develop irregular shapes and to generate microcracks in crystallographic planes oriented subperpendicular to the major compression axis, r 1 . The uniform alignment of the microcracks imparts a planar fabric to the samples. The microcracks heal and form swarms of tiny satellite inclusions. These new inclusions lose H 2 O by diffusion, thereby triggering plastic deformation of the surrounding quartz via H 2 O-weakening. Consequently, the quartz samples deform plastically only in domains originally rich in inclusions. This study shows that fluid inclusions deformed by deviatoric stresses may indeed record information on paleostress orientations and that they play a key role in facilitating crystal-plastic deformation of quartz.

CO 2 flow during orogenic gravitational collapse: Syntectonic decarbonation and fluid mixing at the ductile-brittle transition (Lavrion, Greece)

“…At room temperature, the carbonic phase (a car ) is around 80 vol.% and dominated by carbonic liquid. Type Ia are (i) dismembered ( Fig.3c; Diamond et al, 2010;Tarantola et al, 2010Tarantola et al, , 2012Diamond and Tarantola, 2015), (ii) accumulated along quartz subgrain boundaries (Fig.3c;Kerrich, 1976;Wilkins and Barkas, 1978), (iii) distributed as 'en-echelon'…”

Uranium mobilization by fluids associated with Ca–Na metasomatism: A P–T–t record of fluid–rock interactions during Pan-African metamorphism (Western Zambian Copperbelt)

“…The large range of shapes and bulk homogenization temperatures of the type-I inclusions is interpreted to result from such successive deformation driven modifications affecting quartz grains (Kerrich, 1976;Johnson and Hollister, 1995;Tarantola et al, 2010Tarantola et al, , 2012. However, Eglinger et al (2014) demonstrated that there is a link between the local intensity of hostquartz plastic deformation, the bulk homogenization mode and the temperature of homogenization.…”

High stresses stored in fault zones: example of the Nojima fault (Japan)

“…Therefore, we may infer that quartz behaves as an isotropic material during the dispersion of large fluid inclusions into tiny ones and that this phenomenom is (Pêcher, 1981;Tarantola et al, 2010) and with similar natural fluid inclusions (Diamond and Tarantola, 2015), alignments of tiny fluid inclusions are tentatively interpreted as 15 decrepitated large former fluid inclusions in an anisotropic stress regime. Decrepitation or dispersion of the former large fluid inclusions was probably accompanied by contamination of the primary fluid by the laumontite-bearing fluid circulating in microfractures and characterizing the first period of seismic activity of the Nojima fault.…”

“…It is believed that decrepitation of large fluid inclusions and microfracturing occurred during the 20 seismic stage, and that healing of alignments of tiny fluid inclusions took place during the post-seismic stage. If healing is a slow mechanism at the experimental time-scale (several days or weeks; Pêcher, 1981;Brantley, 1992 ;Tarantola et al, 2010), it may contribute to the relatively fast post-seismic strengthening and seismic velocity recovery observed along active faults during a few months after an earthquake (Brenguier et al, 2008).…”

“…In their experiments, Tarantola et al (2010) have demonstrated that alignments of tiny fluid inclusions form in a plane 25 perpendicular to the maximum compressive stress. Actually, the direction of the alignments of tiny fluid inclusions in the NOJ220 sample is roughly parallel to kink-bands in biotite ( Figure S1), which themselves form also perpendicular to the maximum compressive stress (Cummings, 1965).…”