The N.O. LE NADIR sailed from Hanga Roa, Easter Island, on November 1,
1993, and returned on December 22, 1993. The Captain, Guénhaël Thibault, the
chief scientist, Jean Francheteau, and Norbert Compagnot, head of the submarine
group, were all on board. The submarine group included technicians, engineers
and pilots whom I knew from previous cruises. I was pleased be on another
mission with these men with whom I had previously navigated.
I was particularly pleased to see Charlie LeGuenn, who had been a frogman in
the past but who was now the person responsible for the mechanical up-keep of the
submersible. Charlie no longer dove in his wet suit, but he still accompanied the
divers in the zodiac when they went out to meet the submersible after it arrived on
the surface at the end of a day of diving.
Charlie is a person one could count on if something should go wrong with the
instruments. He was always keen to make sure that the technical gear was checked
and repaired on time. Twenty-one dives were made during the Pito cruise, four of
which were dedicated to exploring the deepest depression located in the Terevaka
Transform Fault (Fig. 8.12c).
PI 16 (Pito dive N°16) was the first dive in the Terevaka Transform. It took
place on November 22, 1993, and was made by Marc Constantin, a PhD student
doing his thesis on oceanic peridotite–gabbro at IFREMER-UBO. Marc was the
scientific observer accompanied by pilot Max Dubois and Henri Martinossi as copilot. The Nautile reached the bottom at 12:30 at 4910 m depth. It arrived at the
intersection of the transform valley and the north-facing wall (the southern wall
whose open face was directed to the north). This dive was aimed at reaching the
site of the dredge haul that had recovered peridotite-gabbro during a previous
cruise of the FS SONNE (Leg 80), and from there, the dive was supposed to start to
climb the wall of the transform. The floor was sedimented with small sedimentmounds and purple colored holothurians. At 12:42, they saw two parallel grooves
marked in the sediment, which were the traces of the dredge haul (DR83) made
during the FS SONNE expedition in 1992 (Fig. 8.13). A few minutes later, the
submersible stopped to have its first station and to collect a sample of rock from
the same area as the dredge. However, the samples were loose and partially buried
by sediment so they probably represented debris slumped from the wall. Luckily,
the sample that was collected was a peridotite and therefore likely to represent a
deeper portion of the exposed transform wall.
Going further up the wall, this discovery was confirmed by the presence of
in situ samples of peridotites up to about 3121 m depth. It was at about 3,190 m
that gabbroic veins intruding the peridotites were seen and recognized by Marc. He
observed this through the porthole on an outcrop on the vertical wall. Outcrops of
peridotites were seen, and in situ samples were taken up to 3190–3080 m along the
wall. These veins crossed each other in two major directions (N160° and N070°).
However the first veins of gabbro (10–20 cm thick) oriented in the N140° direction
were seen at 4700–4690 m between sample sites #3 and #4. Other peridotite rocks
veined with gabbro were observed at 4446 m and at 4304 m on sample site #5 and
near sample site #7 respectively. Peridotites containing veins of finer grained rocks
such as dolerites were observed at 4797 m and sampled (site #2) in a talus pile.
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8 Fracture Zones and Transform Faults
1993, and returned on December 22, 1993. The Captain, Guénhaël Thibault, the
chief scientist, Jean Francheteau, and Norbert Compagnot, head of the submarine
group, were all on board. The submarine group included technicians, engineers
and pilots whom I knew from previous cruises. I was pleased be on another
mission with these men with whom I had previously navigated.
I was particularly pleased to see Charlie LeGuenn, who had been a frogman in
the past but who was now the person responsible for the mechanical up-keep of the
submersible. Charlie no longer dove in his wet suit, but he still accompanied the
divers in the zodiac when they went out to meet the submersible after it arrived on
the surface at the end of a day of diving.
Charlie is a person one could count on if something should go wrong with the
instruments. He was always keen to make sure that the technical gear was checked
and repaired on time. Twenty-one dives were made during the Pito cruise, four of
which were dedicated to exploring the deepest depression located in the Terevaka
Transform Fault (Fig. 8.12c).
PI 16 (Pito dive N°16) was the first dive in the Terevaka Transform. It took
place on November 22, 1993, and was made by Marc Constantin, a PhD student
doing his thesis on oceanic peridotite–gabbro at IFREMER-UBO. Marc was the
scientific observer accompanied by pilot Max Dubois and Henri Martinossi as copilot. The Nautile reached the bottom at 12:30 at 4910 m depth. It arrived at the
intersection of the transform valley and the north-facing wall (the southern wall
whose open face was directed to the north). This dive was aimed at reaching the
site of the dredge haul that had recovered peridotite-gabbro during a previous
cruise of the FS SONNE (Leg 80), and from there, the dive was supposed to start to
climb the wall of the transform. The floor was sedimented with small sedimentmounds and purple colored holothurians. At 12:42, they saw two parallel grooves
marked in the sediment, which were the traces of the dredge haul (DR83) made
during the FS SONNE expedition in 1992 (Fig. 8.13). A few minutes later, the
submersible stopped to have its first station and to collect a sample of rock from
the same area as the dredge. However, the samples were loose and partially buried
by sediment so they probably represented debris slumped from the wall. Luckily,
the sample that was collected was a peridotite and therefore likely to represent a
deeper portion of the exposed transform wall.
Going further up the wall, this discovery was confirmed by the presence of
in situ samples of peridotites up to about 3121 m depth. It was at about 3,190 m
that gabbroic veins intruding the peridotites were seen and recognized by Marc. He
observed this through the porthole on an outcrop on the vertical wall. Outcrops of
peridotites were seen, and in situ samples were taken up to 3190–3080 m along the
wall. These veins crossed each other in two major directions (N160° and N070°).
However the first veins of gabbro (10–20 cm thick) oriented in the N140° direction
were seen at 4700–4690 m between sample sites #3 and #4. Other peridotite rocks
veined with gabbro were observed at 4446 m and at 4304 m on sample site #5 and
near sample site #7 respectively. Peridotites containing veins of finer grained rocks
such as dolerites were observed at 4797 m and sampled (site #2) in a talus pile.
276
8 Fracture Zones and Transform Faults