Despite the low recovery from the three holes drilled at Site 1117 (~5%), the structures observed in the rocks allow us to define four structural domains (Fig. F9). The four domains are from the top to the bottom: a fault gouge (Domain I) from 0 to 12.37 mbsf in Cores 180-1117A-1R and 2R; a mylonitic zone (Domain II) in Cores 180-1117A-2R through 7R and in Core 180-1117B-1R; a brecciated zone (Domain III) observed in Cores 180-1117A-8R to 12R and in Core 180-1117C-1R; and an undeformed zone (Domain IV) observed at the bottom of Hole 1117A (Cores 180-1117A-13R and 14R). A truly cohesive section was recovered from Cores 180-1117A-13R and 14R (gabbro); the overlap between Domains II and III is because of the presence of a few mylonitic pebbles in the breccia; the overlap of Domains III and IV is because of the presence of a few brecciated zones in the gabbro.
Domain I comprises Cores 180-1117A-1R and 2R. Core 180-1117A-1R, from 0 to 12.20 mbsf, recovered 4.07 m of soft, light colored clayey material containing few sparse clasts (see "Hole 1117A"). The initial attitude of an obvious preferential orientation in the fault gouge is difficult to assess because it has been folded during coring (Fig. F10). The mineralogy of this zone (pebbles and matrix), defined by XRD and microscope observation, gives a talc-serpentine-chlorite composition with minor quartz and amphibole present at the bottom of the zone (see "Hole 1117A"). Core 180-1117A-2R from 12.20 to 12.37 mbsf contains numerous cm-sized pebbles in a clayey material at the boundary between the fault gouge and the underlying igneous basic rocks. This intermediate unit is included in Domain I.
In Domain II from 18.60 to 57.07 mbsf (Hole 1117A) the recovered rocks show very well developed anastomosing foliation planes and shear bands (Fig. F11) and fibrous quartz pressure shadows around pyrite (Fig. F12) in greenschist basic rocks (see "Hole 1117A"). The foliation plane is defined by the alternation of epidote-rich layers and very fine grained layers made of epidote, quartz, and chlorite assemblages. Below 57.08 mbsf in Hole 1117A and at 0.09 mbsf in Hole 1117B, a few samples have an ultra-mylonitic texture characterized by the transposition of the planar structures where foliation plane and shear bands become parallel (see Fig. F4). In all the samples a network of calcite veins crosscut the foliation plane.
Domain III ranges from 61.60 to 96.06 mbsf (Sections 180-1117A-8R-1 to 12R-1) and is defined by the brecciation of gabbroic rock (Fig. F13). It consists of the fragmentation of plagioclase and clinopyroxene present as small clasts in a dark brown matrix made of very fine grained epidote, quartz, and clay assemblages. The intensity of the brecciation increases upward, and the number and size of the relics of clinopyroxene and plagioclase decrease upward. This is related to the presence of the mylonitization at the top of the sequence overprinting the breccia. In one sample (Fig. F14) the relationship between the breccia and the mylonitization of the rocks is demonstrated. The brecciated gabbros from Domain III are crosscut by epidote + quartz and quartz veins (Fig. F15A, F15B); the latter are subsequently reoriented into the mylonite as they form boudinaged quartz + epidote or quartz-rich layers.
Domain IV consists of an undeformed coarse-grained gabbro with no directional fabrics such as layering (F6; see "Hole 1117A"). This domain ranges from 105.2 mbsf (Section 180-1117A-13R-1) to the bottom of the hole (110.1 mbsf).
The fresh gabbroic rocks recovered at the bottom of Hole 1117A are thought to be the original basic rock that underwent ductile (mylonitization) to brittle (brecciation, fracturing) deformation and retrograde evolution from middle crustal level (plutonic conditions) to upper continental level (greenschist facies conditions). The tectono-metamorphic evolution could be related to the unroofing of the gabbro during extensional tectonics. Similar evolution has been described for the metadolerite recovered in Hole 1114. Indeed, at these two sites there is a massive brittle deformation (brecciation) associated with the development of greenschist minerals. At Sites 1114 and 1117 we observe the brecciation of the rocks (dolerite and gabbro) at the bottom of the sequence overprinted by a sheared zone giving rise to the development of an intense mylonitic fabric in the rocks. At both sites, the breccia formed by fluid-assisted fracturing (Fig. F16) of the rocks (gabbro and dolerite). At the earliest stage of the deformation and deeper in the gabbroic body, fluid should be siliceous as epidote + quartz occurs in veins. Later during the evolution and shallower in the gabbroic body, the fracturing is associated with carbonate-rich fluids as calcite occurs in veins.