For the 14th dive, the objective is to complete the observations that have been made on the structure of the oceanic core-complex during the previous dives: Dive 09 on the front of the core-complex, dive 12 a little higher on the same front , and dive 11, which corresponds to a fault that cuts the internal structure of the core-complex. This dive is also positioned on a fault in the heart of the core-complex. The first part will be a transect along the fault, then join a ridge crest and follow it to the summit at -3840m.
Following a technical problem (a little water in a tube of electric cables, which are normally filled with oil), the departure is around 10H. We arrived at the bottom around 12H00 UTC, for 5 hours of observation.
The dive began on a flat and sedimented area. Beginning at a 4200 m immersion, we start the profile oriented ENE-WSW. At this depth a large breccia cliff appears (with a slope at about 80 °).
After 80m of vertical climbing, the breccia gave way to a rocky cliff of peridotite: a fault plan that we could follow until about -3970m. During the dive we discovered that the fault does not intersect the foliation, as for dive 11, but it is parallel and therefore corresponds to an exhumation plan. The direction of the fault plane is N140, with high temperature foliation subparallel to this plane. We also measured low-temperature fracturing plans and took samples in place, but we spent time there because the rocks were altered.
The end of this cliff looks like a surface of erosion, the surface is rounded. On the following part of the dive, we find blocks on sediments, and the entire portion of the ridge is completely covered with sediment. Arriving on the top of new rock blocks appear, as well as a few outcrops. Here the orientation of the foliation appears to have changed (N55).
After almost 5 hours of work at the bottom, and the collection of 16 samples (mainly peridotites), at 16:40 UTC we drop the ballast to get to the surface.
By M.-A. Kaczmarek