glassy surface under the submersible’s lights. The older flow was duller looking.
The thin (\1 m thick) recent flows filling the interstices of the older pillows were
limited in their extent (only a few meters wide and a few tens of meters long).
Going further up the slope, which was made-up of staircase fault blocks between
4700 m and 3868 m depth, they crossed several other types of lithology.
This dive made a tremendous contribution to the project since they were able to
find the contact zone between the intrusive mantle-material (serpentinized peridotite) and the volcanic lava flows. At 15h36, at depths between 3940 to 3868 m,
the Nautile reached this boundary between the volcanic rocks and the exposed
mantle peridotite. Before reaching the mantle peridotite outcrops, the divers had
crossed between young volcanic rocks formed in the rift axis (at depths of 4630
and 4311 m), which had been moved aside during spreading. This series of lava
flows showed a radial jointing exposed on inward-looking (toward the rift valley)
faulted scarps and on talus piles at their feet. The most prominent (3) major fault
scarps, with a relief of up to 226 m, occurred along the wall. The top of the scarps
was covered with sediment and impressive, large talus piles, 15–74 m in height. At
12h44, the divers saw the first dyke, about 4 m thick and 8 m high, intruded into
brecciated (fragmented and partially consolidated) basaltic debris. Between 12h44
and 13h59, the divers crossed a field of dolerite dykes between 4211 and 4019 m
depth. These dykes were exposed during earthquakes related to the faulting and
uplift of the rift valley wall and were oriented N010° (dipping 070° W). The dykes
that had intruded into pillow lavas and volcanic breccia were 2–10 m in height and
1–4 m thick. Then, after a sudden break in the scarp, the submersible reached a
flattish sedimented area at 4019–3940 m depth, lying on top of a thin volcanic
pillow lava flow.
At 15h59, the submersible encountered the first serpentinized peridotite outcrop
at 3940 m depth. It was exposed on a steep scarp. Thus, between the dyke complex
and the mantle peridotite, there was only a 70 m-thick basaltic layer. The serpentinized peridotite continued to be observed during the continuation dive
(SP06), which was made to complete the profile along the same slope. However,
before continuing the profile to the top of the wall, we wanted to obtain more
visual data along the east wall of the rift valley.
Therefore, on the same day as the SP02 dive, December 26, 1997, after
recovering the Nautile, we planed to use our deep towed SCAMPI (#SC02) camera
in order to extend our sea floor observations further north along the wall. The
deep-towed camera was lowered to the bottom at a depth of 3890 m. Scampi’s
observations extended down to a depth of 4756 m at the foot of the rift valley. At
4150 m, the video camera showed an estimated bottom and then at around
4580 m, dark-colored massive fragmented blocks were observed which appeared
to be slumped peridotite, which had rolled down from shallower depths. Deeper
down slope ([4600 m), basaltic fragments forming large talus confirmed the
previous dive’s observations about the extent of volcanism as being all the way
down to the Intra-Transform Ridge’s rift valley floor.
I am not going to present the chronological order of the dives but rather I would
like to use the structural setting of this area of the SPPR Fracture Zone in
Diving in the Intra-Transform Ridges (ITR) of St. Peter and Paul’s Rocks
289
The thin (\1 m thick) recent flows filling the interstices of the older pillows were
limited in their extent (only a few meters wide and a few tens of meters long).
Going further up the slope, which was made-up of staircase fault blocks between
4700 m and 3868 m depth, they crossed several other types of lithology.
This dive made a tremendous contribution to the project since they were able to
find the contact zone between the intrusive mantle-material (serpentinized peridotite) and the volcanic lava flows. At 15h36, at depths between 3940 to 3868 m,
the Nautile reached this boundary between the volcanic rocks and the exposed
mantle peridotite. Before reaching the mantle peridotite outcrops, the divers had
crossed between young volcanic rocks formed in the rift axis (at depths of 4630
and 4311 m), which had been moved aside during spreading. This series of lava
flows showed a radial jointing exposed on inward-looking (toward the rift valley)
faulted scarps and on talus piles at their feet. The most prominent (3) major fault
scarps, with a relief of up to 226 m, occurred along the wall. The top of the scarps
was covered with sediment and impressive, large talus piles, 15–74 m in height. At
12h44, the divers saw the first dyke, about 4 m thick and 8 m high, intruded into
brecciated (fragmented and partially consolidated) basaltic debris. Between 12h44
and 13h59, the divers crossed a field of dolerite dykes between 4211 and 4019 m
depth. These dykes were exposed during earthquakes related to the faulting and
uplift of the rift valley wall and were oriented N010° (dipping 070° W). The dykes
that had intruded into pillow lavas and volcanic breccia were 2–10 m in height and
1–4 m thick. Then, after a sudden break in the scarp, the submersible reached a
flattish sedimented area at 4019–3940 m depth, lying on top of a thin volcanic
pillow lava flow.
At 15h59, the submersible encountered the first serpentinized peridotite outcrop
at 3940 m depth. It was exposed on a steep scarp. Thus, between the dyke complex
and the mantle peridotite, there was only a 70 m-thick basaltic layer. The serpentinized peridotite continued to be observed during the continuation dive
(SP06), which was made to complete the profile along the same slope. However,
before continuing the profile to the top of the wall, we wanted to obtain more
visual data along the east wall of the rift valley.
Therefore, on the same day as the SP02 dive, December 26, 1997, after
recovering the Nautile, we planed to use our deep towed SCAMPI (#SC02) camera
in order to extend our sea floor observations further north along the wall. The
deep-towed camera was lowered to the bottom at a depth of 3890 m. Scampi’s
observations extended down to a depth of 4756 m at the foot of the rift valley. At
4150 m, the video camera showed an estimated bottom and then at around
4580 m, dark-colored massive fragmented blocks were observed which appeared
to be slumped peridotite, which had rolled down from shallower depths. Deeper
down slope ([4600 m), basaltic fragments forming large talus confirmed the
previous dive’s observations about the extent of volcanism as being all the way
down to the Intra-Transform Ridge’s rift valley floor.
I am not going to present the chronological order of the dives but rather I would
like to use the structural setting of this area of the SPPR Fracture Zone in
Diving in the Intra-Transform Ridges (ITR) of St. Peter and Paul’s Rocks
289