CONCLUSIONS

The following conclusions can be drawn from the present work:

  1. Holes 976B and 976E penetrated high-grade metamorphic rocks intersected by polymictic breccia and gouge intervals formed of high-angular and variable grain-sized clasts of nearby basement metamorphic lithologies. Fabrics at both meso- and microscopic scales indicate that breccias formed in situ by fracturing of the basement.
  2. Cataclastic flow-structures and cataclastic fabrics common in both breccias and gouges allow us to consider these rocks are cataclasites. Fabrics reveal intense brittle frictional sliding and multi-stage fracture processes. Additionally, tensional fractures and internal splint-breakage textures in porphyroclasts indicates that dilation accompanied the brittle fracturing of the basement. Extensive replacive- and displacive-dolomite growing over cataclastic fabrics is interpreted to be formed as a result of pervasive fluid circulation in fracture zones. The occurrence of neptunian dikes (filled with Serravallian sediments) at the top of the basement prove that brittle deformation occurred at least partially in a submarine environment.
  3. Intervals of breccia and gouges in Holes 976B and 976E mark zones of fault-related brittle deformation in the metamorphic basement. Logging data, together with macroscopic observations, reveal the occurrence of a thick fault zone with cataclastic rocks at 750-785 mbsf (Hole 976B) in the basement section. This fault zone coincides with a major change in basement lithology, which is richer in gneissic rocks downhole.
  4. On the basis of seismic images from the basement high, the brittle deformation have been related to middle Miocene (before 12 Ma) faulting accounted by antithetic or counter faults in a rollover basement structure. High-angle dip of fault zones and main foliation in metamorphic rocks may have originated from rotations in this rollover. The basement high drilled at Site 976 is interpreted as a faulted central high from the early to middle Miocene extensional fault-system occurred in the Western Alboran basin.

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