by hand because the winch was broken. The connecting wire had traces of shark
teeth bites and was quite damaged. Luckily, the electronic engineer on board was
able to fix the cable. During our transit, the weather was sunny and the sea was
calm. We used our travel time to become better acquainted with the NADIR crew
and the members of the submersible team.
I was pleased to see some familiar faces from the submersible group, who were
involved in this expedition. For example, I saw Christian LeGuern, a mechanical
engineer and frogman, who did the same work as Charlie LeGuenn. Both men
were very handy and reliable, and could fix anything on board.
Before arriving on site we had another science meeting to discuss the operational orientation of the dives. The meeting was supposed to define our scientific
priorities and the order of the scientists for the first series of dives. Usually, the
chief scientist makes the first dive of a cruise. The reason for this is because the
first dive after the maintenance of the submersible is considered as being a testdive and things could go wrong. There are chances that the dive might be shorter
due to technical problems. For this reason, I was the person who was expected to
make the first dive on the presumed site of the exposed deep mantle peridotite.
Our first priority was to make detailed observations on the lower-crust/uppermantle formation of peridotite in one of the areas of the fastest spreading regions
in the World. Another important aspect was to determine if the transform fault was
the site of recent volcanic activity. Therefore, another target was to dive on the
flank and the top of one of the ellipsoidal shaped ridges crossing the transform
valley. This dive was assigned to Daniel Bideau whose competence in volcanology
was well known. The dive on the Median Ridge located at the center of the Garrett
transform where we were expecting to find outcrops of mantle material (peridotite)
was assigned to Mathilde Cannat and Rejean Hebert, who were respectively a
structural geologist and a petrologist. The fourth dive was assigned to Jean
Francheteau, a veteran of sea floor landscape and an expert in the geophysical
study of submarine structures. Jean was to dive on the northern wall of the
transform fault in order to determine the succession of tectonic events that had
constructed the 3000 m high wall. The fifth dive was scheduled to explore the
south wall of the Transform and its intersection with the transform valley in order
to find out if there was any symmetry between the north and south walls as far as
the type of lava formation was concerned. The second series of dives would be
scheduled during the middle of the cruise, after the first results were obtained.
We arrived on site on January 12, 1991. The weather conditions were good and
the crew and the navigators started to prepare the transponders for the following
day’s dive. The choice of the first dive’s site was where dredge samples containing
peridotites had first been taken by the FS SONNE in 1980. The samples had been
dredged from the deepest ([5000 m depth) area of the transform, an area where
tectonic activity was most prominent.
However, when arriving on the site we encountered a serious problem. The
satellite Global Positioning System (GPS) was not available all the time so on the
morning of the first dive, the bridge could not use this system. The reason for this
was that the Gulf War of 1991 was just beginning, therefore the US military had
260
8 Fracture Zones and Transform Faults
teeth bites and was quite damaged. Luckily, the electronic engineer on board was
able to fix the cable. During our transit, the weather was sunny and the sea was
calm. We used our travel time to become better acquainted with the NADIR crew
and the members of the submersible team.
I was pleased to see some familiar faces from the submersible group, who were
involved in this expedition. For example, I saw Christian LeGuern, a mechanical
engineer and frogman, who did the same work as Charlie LeGuenn. Both men
were very handy and reliable, and could fix anything on board.
Before arriving on site we had another science meeting to discuss the operational orientation of the dives. The meeting was supposed to define our scientific
priorities and the order of the scientists for the first series of dives. Usually, the
chief scientist makes the first dive of a cruise. The reason for this is because the
first dive after the maintenance of the submersible is considered as being a testdive and things could go wrong. There are chances that the dive might be shorter
due to technical problems. For this reason, I was the person who was expected to
make the first dive on the presumed site of the exposed deep mantle peridotite.
Our first priority was to make detailed observations on the lower-crust/uppermantle formation of peridotite in one of the areas of the fastest spreading regions
in the World. Another important aspect was to determine if the transform fault was
the site of recent volcanic activity. Therefore, another target was to dive on the
flank and the top of one of the ellipsoidal shaped ridges crossing the transform
valley. This dive was assigned to Daniel Bideau whose competence in volcanology
was well known. The dive on the Median Ridge located at the center of the Garrett
transform where we were expecting to find outcrops of mantle material (peridotite)
was assigned to Mathilde Cannat and Rejean Hebert, who were respectively a
structural geologist and a petrologist. The fourth dive was assigned to Jean
Francheteau, a veteran of sea floor landscape and an expert in the geophysical
study of submarine structures. Jean was to dive on the northern wall of the
transform fault in order to determine the succession of tectonic events that had
constructed the 3000 m high wall. The fifth dive was scheduled to explore the
south wall of the Transform and its intersection with the transform valley in order
to find out if there was any symmetry between the north and south walls as far as
the type of lava formation was concerned. The second series of dives would be
scheduled during the middle of the cruise, after the first results were obtained.
We arrived on site on January 12, 1991. The weather conditions were good and
the crew and the navigators started to prepare the transponders for the following
day’s dive. The choice of the first dive’s site was where dredge samples containing
peridotites had first been taken by the FS SONNE in 1980. The samples had been
dredged from the deepest ([5000 m depth) area of the transform, an area where
tectonic activity was most prominent.
However, when arriving on the site we encountered a serious problem. The
satellite Global Positioning System (GPS) was not available all the time so on the
morning of the first dive, the bridge could not use this system. The reason for this
was that the Gulf War of 1991 was just beginning, therefore the US military had
260
8 Fracture Zones and Transform Faults