Lubin, and arrived on the sea floor at 12:03 at 2795 m. Before we reached the
bottom, I was nervous and at the same time curious about what I was going to see.
We were going to the foot of the edifice on which the small islets are built, where
only 1 % of the structure has emerged on the surface. The secret of its origin
probably lies in the deep structural setting. After the CHALLENGER’s expedition
in 1873, here we were, looking at the sea floor in the middle of the Atlantic Ocean
where these islets were formed.
At about 11:50, as we approached the bottom, I started to turn around and lie
down on my stomach with my eyes glued to the starboard porthole waiting to see
the sea floor. The pilot turned on the floodlights and dropped 50 kg of weight from
each side of the submersible in order to slow down our descent. At 50 m above the
bottom, the water was a little blurry because of suspended particles in the water
column. We continued to approach the sea floor: 40, 30, 25 m. Now I could almost
see the bottom. There were no rocks but only sediment, no signs of current, and the
sediment was abundantly disturbed by animal dwellers, forming strange designs,
like circular thin ridges forming lines, small centimeter scale mounds and irregular
lines that looked like ‘‘hieroglyph’’ writing. The slope of the ridge was to our left
and our heading was N100° (that is, in a south-east direction). Patrick contacted
the surface on the R.V. Le Nadir to tell them that we had landed and give them our
depth.
After 4 min, the time needed to verify all instruments in the sphere, we started
to move towards the slope and we saw the first rocky outcrop sticking out of the
sediment. As soon as I saw this rocky outcrop, I asked Patrick to stop and take our
first sample at 2792 m depth. This was a loose prismatic fragment of rock showing
light and dark bands. Patrick turned the manipulating arm towards my side near the
porthole in order for me to have a closer look at the sample. The rock was coated
with a dark product but I could see alternating lighter bands. I knew then and there
that our sample was a veined peridotite. I was happy, because this meant that
further up we were going to find the outcrop from where the rock had slumped.
Also, in light of the fact that the emerged St. Peter’s and St. Paul’s Rocks massif
consisted of mantle peridotite, now we knew that the same material occurred all
away down to 2792 m and maybe even deeper.
We progressed further up the slope, which varied in relief from gentle (10–15°)
up to near vertical breaks (70–85°). At 13h09-13h12, we saw abundant avalanche
debris. Soon after we were on freshly fractured outcrops showing white veins
resembling gabbroic intrusions associated with talc-serpentinized peridotite and
mylonite that we sampled at 2670 m. At 13h27 at 2601 m depth, we arrived on
another near vertical scarp with a relief of about 100 m, made up of dark-colored
mylonitized peridotite showing signs of striations and a fractured surface. At 15:25
at 1915 m, we encountered a pink colored octopus swimming on top of an avalanche of gravel slumped down slope that was detached from another near vertical
outcrop that we were approaching. The color television was turned on to record a
video sequence. At 15h38 at 1843 m, we climbed the vertical faulted scarp where
the paved-like and foliated blocks of peridotite were at contact with prismatic and
columnar rock. The sample taken from this scarp turned out to be a dolerite
294
8 Fracture Zones and Transform Faults
bottom, I was nervous and at the same time curious about what I was going to see.
We were going to the foot of the edifice on which the small islets are built, where
only 1 % of the structure has emerged on the surface. The secret of its origin
probably lies in the deep structural setting. After the CHALLENGER’s expedition
in 1873, here we were, looking at the sea floor in the middle of the Atlantic Ocean
where these islets were formed.
At about 11:50, as we approached the bottom, I started to turn around and lie
down on my stomach with my eyes glued to the starboard porthole waiting to see
the sea floor. The pilot turned on the floodlights and dropped 50 kg of weight from
each side of the submersible in order to slow down our descent. At 50 m above the
bottom, the water was a little blurry because of suspended particles in the water
column. We continued to approach the sea floor: 40, 30, 25 m. Now I could almost
see the bottom. There were no rocks but only sediment, no signs of current, and the
sediment was abundantly disturbed by animal dwellers, forming strange designs,
like circular thin ridges forming lines, small centimeter scale mounds and irregular
lines that looked like ‘‘hieroglyph’’ writing. The slope of the ridge was to our left
and our heading was N100° (that is, in a south-east direction). Patrick contacted
the surface on the R.V. Le Nadir to tell them that we had landed and give them our
depth.
After 4 min, the time needed to verify all instruments in the sphere, we started
to move towards the slope and we saw the first rocky outcrop sticking out of the
sediment. As soon as I saw this rocky outcrop, I asked Patrick to stop and take our
first sample at 2792 m depth. This was a loose prismatic fragment of rock showing
light and dark bands. Patrick turned the manipulating arm towards my side near the
porthole in order for me to have a closer look at the sample. The rock was coated
with a dark product but I could see alternating lighter bands. I knew then and there
that our sample was a veined peridotite. I was happy, because this meant that
further up we were going to find the outcrop from where the rock had slumped.
Also, in light of the fact that the emerged St. Peter’s and St. Paul’s Rocks massif
consisted of mantle peridotite, now we knew that the same material occurred all
away down to 2792 m and maybe even deeper.
We progressed further up the slope, which varied in relief from gentle (10–15°)
up to near vertical breaks (70–85°). At 13h09-13h12, we saw abundant avalanche
debris. Soon after we were on freshly fractured outcrops showing white veins
resembling gabbroic intrusions associated with talc-serpentinized peridotite and
mylonite that we sampled at 2670 m. At 13h27 at 2601 m depth, we arrived on
another near vertical scarp with a relief of about 100 m, made up of dark-colored
mylonitized peridotite showing signs of striations and a fractured surface. At 15:25
at 1915 m, we encountered a pink colored octopus swimming on top of an avalanche of gravel slumped down slope that was detached from another near vertical
outcrop that we were approaching. The color television was turned on to record a
video sequence. At 15h38 at 1843 m, we climbed the vertical faulted scarp where
the paved-like and foliated blocks of peridotite were at contact with prismatic and
columnar rock. The sample taken from this scarp turned out to be a dolerite
294
8 Fracture Zones and Transform Faults