25 API), natural radioactivity, and photoelectric factor (1 
m) values.
Intervals of breccia and clay-rich gouges in Holes 976B and 976E mark zones of brittle deformation. Their widespread occurrence largely determined the low total recovery at Site 976 (Fig. 3). In both holes, late Serravallian (Zone NN7, about 11-12 Ma) deposits overlie the brecciated basement (lithostratigraphic Unit IV; Shipboard Scientific Party, 1996)
On the mesoscopic scale, breccias correspond to a cemented or weakly cemented polymictic breccia formed of high-angular and variable grain-sized clasts of nearby basement metamorphic lithologies, which made up >50% of the whole rock (Pl. 1, fig. 1, fig. 2, fig. 4, fig. 6). Fabrics present in breccias are similar on both mesoscopic and microscopic scale, and shown a porphyroclastic texture where clasts (porphyroclasts) and particle-sized grains range from about 7 cm to microscopic. The breccias usually have a fine-grained matrix, formed by comminution and alteration of metamorphic rocks and a carbonate-rich "cement." Gouges are dark-colored, uncemented, or poorly cohesive rocks with a clay-rich groundmass or matrix and scattered angular porphyroclasts (<50%) of similar lithologies as in breccias. More cohesive gouges usually contain cataclastic foliation structures at mesoscopic scale (Pl. 1, fig. 3).
The uppermost breccia interval drilled at Hole 976B (Sections 161-976B-74X-1, through 75R-2; Pl. 1, fig. 1, fig. 2) is a coherent cemented breccia with angular to subrounded clasts of variable grain size (0.1-60 mm), formed of high-grade schist (>70%), quartzite (<25%), and minor grayish fine-grained marble (<5%). The matrix is dolomitic silty claystone, containing foraminifer ghosts, with frequent scattered biotite flakes and occasional single garnet crystals (<15%), including dolomite, calcite, ankerite, siderite, quartz, and clay minerals (from X-ray diffraction [XRD] data).
Sections 161-976B-79R-1 to 81R-2 correspond to basement rocks with discrete gouge and breccia intervals. Logging data reveal that these intervals extend from 702 to 708 mbsf (Fig. 3, Fig. 4). Breccia contains 0.1-10-mm fragments of schist (45%), quartzite (35%), and dolomite marble (20%) in a yellow dolomitic or clayey matrix. There is some evidence of oxidation, dissolution, and alteration in porphyroclasts and matrix as shown by abundant clay and oxide stains in pelitic fragments and solution cavities in dolomite fragments. Gouge occurs with up to 8 mm scattered porphyroclasts of high-grade schist and dolomite marble, and a clayey groundmass formed of ankerite, kaolinite, siderite, and quartz (XRD data).
Logging data suggest the occurrence of nonrecovered breccia or gouge intervals at 716-720 and 722-726 mbsf, which probably determined the low recovery from Cores 161-976B-81R and 82R (26% in both cases). Logging at these intervals is characterized by low resistivity, gamma-ray (25 API), natural radioactivity, and photoelectric factor (1 m) values.
An intensely fractured interval occurs through Cores 161-976B-86R to 88R (750-785 mbsf; Fig. 4). This interval (20-25 m thick) has abundant, poorly consolidated or cohesive clayey gouges (Shipboard Scientific Party, 1996). It most likely corresponds to a thick fracture zone, wherein we have distinguished several discrete brecciated zones, at 750-754, 758-765, and 767-785 mbsf (Fig. 4), corresponding to Sections 161-976B-86R-1 through 92R-1.
Gouges from this interval are polymictic, matrix-supported, poorly cemented rocks with variably-sized angular porphyroclasts. Porphyroclasts consist of biotite-rich schist and foliated gneiss (60%-70%, 1-60 mm); angular, white quartzite grains (20%-25%, up to 30 mm); and rounded and banded marble fragments (5%-20%, up to 40 mm). The silt-sized groundmass is formed of dolomite, calcite, kaolinite, and siderite, with minor biotite and quartz (XRD data). Logging data reveal a relatively consolidated (regular resistivity = <10 m) and dark zone (photoelectric factor = <3 barn/e-), with high gamma-ray values (70-75 API; Fig. 4). Geochemical profile done by logging along this interval shows a sharp increase in the concentration of Cl, Fe, and Si, which suggests extensive mobilization of these elements along the fracture zone. Representative macroscopic textures and structures in this fracture zone include multistage brecciation, crushed clasts (porphyroclasts), incipient cataclastic foliation surrounding crushed clasts, with occasional asymmetric fish-tails, and the presence of minor-scale fault planes with slickensides and ridge-in-groove lineations (Shipboard Scientific Party, 1996).
The lower 145 m of the basement section (from 785 to 930 mbsf) at Hole 976B has narrower (<5 m thick) breccia and gouge zones (Pl. 1, fig. 3), with similar lithologic and logging characteristics.
The brecciated intervals at Hole 976E (Pl. 1, fig. 4, fig. 5, fig. 6) have similar characteristics to those described in Hole 976B. Nevertheless, in Hole 976E breccia intervals are thinner (<150 cm) and dolomite-cemented marble breccia is more abundant. Marble breccia has angular clasts of calcitic or dolomitic marble (<40 mm long, up to 90%), biotite-rich high-grade schist (10%-40%), calc-silicate rocks, and minor quartzite (<10%) (Pl. 1, fig. 4). The matrix (size-grain fraction <2 mm) has abundant, finely comminuted biotite flakes. Matrix mineral components are dolomite with minor ankerite, quartz, and biotite (XRD data). The abundance of marble and calc-silicate rocks interlayered in the uppermost 40 m of the basement sequence (up to 690 mbsf; Fig. 3B), seems to account for the widespread occurrence of marble breccias in Hole 976E in contrast with Hole 976B.
The upper 75 m of Hole 976E (up to 715 mbsf; Fig. 3B) is also characterized by fine-laminated, particulated material (from sediments or finer comminuted matrix) filling fractures or fissures that cross-cut or follow the main foliation of the metamorphic rocks. Laminations are defined by oriented flakes of biotite and small schist fragments (Pl. 1, fig. 5). In some cases the fissures connect with breccia pocket intervals. The dominant orientation of these fractures is subvertical, with a maximum length of 30-40 cm and 1-15 mm thick.
Thin sections of polymictic cemented breccias from basement cores at Site 976 show complex fracturing and fabrics similar to that observed in hand samples. Microscopic features also indicate that breccias formed in situ. Photomicrographs of fabrics from representative breccia samples are shown in Plate 2, Plate 3, and Plate 4.
At Hole 976B, just overlying the brecciated basement sections, sediments consist of uncemented or weakly cemented, coarse-grained, poorly sorted, lithic silty sands and conglomeratic sands with pebbles of metamorphic rocks. In thin sections of cemented sandstones, siliciclastic components of the sand-sized fraction are quartz, biotite, glauconite, and fragments of schist and quartzite. The silt-sized matrix with similar siliciclastic components is cemented by euhedral to subhedral replacive dolomite crystals. The sandstone contains calcareous nannofossils and benthic and pelagic foraminifers (Shipboard Scientific Party, 1996; Pl. 2, fig. 1, fig. 2). In Hole 976E sediments just above the basement breccias consist of nannofossil-rich claystones. Breccias from the uppermost basement cores in Holes 976B and 976E (Cores 161-976B-74X and 75R, and Core 161-976E-16R) have matrixes largely consisting of those sediments that largely percolated into the previously brecciated basement from the overlying late Serravallian sequence (Pl. 2, fig. 3, fig. 4, fig. 5, fig. 6).
Microscopically, the breccia clasts appear to have derived from the metamorphic basement, as all clast lithologies in thin sections match those of the metamorphic host rocks. Breccias have high variability in clast and grain size, with fragments ranging from <1 mm to >5 cm in diameter (most are 0.1-4 cm). Large fragments (porphyroclasts) are generally broken with internal cracks cemented by dolomite or filled-up with the matrix.
The breccia fabric grades from grain-supported to clay- or dolomite-rich matrix-supported fabrics with a porphyroclastic texture, including randomly oriented highly angular pebble- to silt-sized clasts of different lithologies, and is characterized by a variety of deformational structures (Plate 3, Plate 4). Bedding is not apparent in thin sections, but several samples show elongated fragments parallel to the host rock wall (Pl. 4, fig. 1). Vague clusters of smaller fragments, or mica flakes, define laminations in the matrix (Pl. 3, fig. 1, fig. 5). Breccia clasts are unaltered, except within their outer margins, where they show grain dissolution or alteration by replacive dolomite crystals. Breccias are slightly veined or un-veined at microscopic scale.
Fabrics reveal intense cataclastic grain breakage (as much as 80%). Quartzite or quartz grains display internal splint-breakage texture (splintered quartz; Pl. 4, fig. 1, fig. 2, fig. 3). Commonly, fragments in lithoclasts or quartz grains can be fitted together, indicating grain dilation and disaggregation with no major rotation between the elements of each original porphyroclast (Pl. 3, fig. 1, fig. 6; Pl. 4, fig. 4). Cathodoluminescence microscopy allows clast correlation to distinguish smaller clastic fragments originating via cataclastic processes and reveals indications of grain-size reduction by grain breakage (Pl. 3, fig. 6; Pl. 4, fig. 3).
In thin section, the silt-sized matrix or groundmass consists of dark-gray, "clotted" clay and dolomicrite, very fine fragments of schist, fine-grained quartzite, quartz, biotite, chlorite, and sericite. At the uppermost basement cores, foraminifers have been found in the matrix (Pl. 2, fig. 4, fig. 5).
"Cements" largely comprise planar to nonplanar (see Sibley and Gregg, 1987) crystalline replacive dolomite. Replacive dolomite partially to almost completely (up to >90%) replaces the breccia matrix and porphyroclast borders (e.g., quartz, biotite) in many samples (Pl. 2, fig. 3, fig. 4; Pl. 3, fig. 2, fig. 4). Cathodoluminescence observations indicate at least two generations of dolomite growth, as denoted by recrystallization and replacement of former dolomite crystals. Replacive dolomite in breccia matrix display fine (<30 µm) to medium (<70 µm) subhedral to anhedral crystalline texture (Pl. 1, fig. 3, fig. 4, fig. 6). More rarely, dimensions in cements are larger than 200 µm; however, isopachous rims of bladed prismatic dolomite bounding clasts, locally changing to a central fill of blocky dolospar coarsening inward, have been noted in some samples (Pl. 3, fig. 4). Dolospar cement fill is not present everywhere, but some samples include saddle-shaped (curved crystal boundaries; Pl. 3, fig. 3) dolosparite. Complex, zoned saddle dolomite cements compose less than 5% of all dolomite cement in the samples studied. Dolomite crystallization produced replacement in quartz, feldspar, and biotite grain surfaces (Pl. 3, fig. 2, fig. 4). Displacive dolomite textures are also common, occurring as bladed- to planar-displacive dolomite crystals filling discrete veins or micro-fractures cross-cutting quartz, quartzite, and biotite grains (Pl. 4, fig. 1, fig. 2, fig. 6). Calcite cement is a minor component in breccia matrix, but it has been observed filling a few thin veins. There is no textural evidence of subaereal cements or weathering alterations in the studied breccias, as pendant or meniscus cements neither calcrete textures have been clearly recognized in thin sections. However, this point deserves to be explored by further geochemical studies.
Matrix composition and textures indicate a relatively broad spectrum of cemented-breccia types in basement cores. Two end-members of this spectrum can be considered as representative lithotypes of these breccias: (1) dolomite-cemented breccia and (2) clay-matrix cataclastic breccia.
