Similar observations were made on top of the ‘‘Christèle’’ volcano as well as on
the most western ‘‘Fara’’ volcano (Dive OT07). These structures are compositionally similar to the surrounding oceanic crust. Hence, we could conclude that
they were formed during short-lived, localized magma upwelling.
Inside Corner-High Peridotite
Another task of the Oceanaut project was to determine the type of rocks that are
associated with the tips of the ridge rift valley segments, and to observe their
differences when compared to an adjoining spreading segment. Based on the sea
floor images observed with the side scan sonar, it was inferred that the rift valley’s
inside-corners of the spreading segment-ends showed semi-circular features with
steep slopes. The steepness of the slopes seemed to suggest the existence of an
uplifted crust. If this were the case, then we could expect to observe deep-seated
material, such as peridotite and/or gabbro, exposed on the sea floor.
Two dives (OT-08 and OT-14) were devoted to exploring the inside corner of
segment OH3 (Fig. 7.8b). The segment tips are marked by a deeper trough or
fracture, also called ‘‘non-transform’’. The tips are not a real transform fault, but
rather they seem to be a discontinuity or a break between two spreading ridge
segments.
Marc Constantin, as the scientific observer, Pierre Triger and Olivier Cipriani as
pilot and co-pilot respectively, were participants on dive OT08 on September 4. As
soon as the divers reached the first scarp of the rift valley’s inside-facing southwest
corner at 3836 m depth, they observed slumped material made up of dark looking
peridotite, which was detached from the upper part of the slope. At 12h38 at
3,543 m depth, Marc observed the presence of in situ peridotite together with a
dolerite dyke. Serpentinized peridotite was observed between 3836 m up to the
summit at 2550 m depth.
Confident with dive OT08
0 s discovery of exposed peridotite on one corner of
the rift valley, we decided to try to find out if the opposite, northern inside-corner
end of this rift valley segment would have the same geological setting. Thus, dive
OT14 was conducted on the northeast corner of the OH3 segment. The diving
party was composed of Pierre Triger and Olivier Cipriani, as pilot and co-pilot, and
I was the scientist on board. We touched down on the sea floor at 10h46, and found
the same general setting, which comforted our original ideas concerning the nature
of this particular type of spreading segment. We made a complete geological
profile from the rift valley floor upwards along the slope of this uplifted structure.
We reached a slightly sedimented area with pillow lava and lobated flows at
3,568 m depth. The lava flows were not as fresh as those encountered in the middle
of the rift segment during dive OT09. The lava flow extended all way to the
intersection with the inside corner’s high, at a depth of 3,300 meters. After traveling eastward for about 2 km, at 12h54, we arrived in front of a faulted scarp with
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7 Oceanic Spreading Ridges and Sea Floor Creation
the most western ‘‘Fara’’ volcano (Dive OT07). These structures are compositionally similar to the surrounding oceanic crust. Hence, we could conclude that
they were formed during short-lived, localized magma upwelling.
Inside Corner-High Peridotite
Another task of the Oceanaut project was to determine the type of rocks that are
associated with the tips of the ridge rift valley segments, and to observe their
differences when compared to an adjoining spreading segment. Based on the sea
floor images observed with the side scan sonar, it was inferred that the rift valley’s
inside-corners of the spreading segment-ends showed semi-circular features with
steep slopes. The steepness of the slopes seemed to suggest the existence of an
uplifted crust. If this were the case, then we could expect to observe deep-seated
material, such as peridotite and/or gabbro, exposed on the sea floor.
Two dives (OT-08 and OT-14) were devoted to exploring the inside corner of
segment OH3 (Fig. 7.8b). The segment tips are marked by a deeper trough or
fracture, also called ‘‘non-transform’’. The tips are not a real transform fault, but
rather they seem to be a discontinuity or a break between two spreading ridge
segments.
Marc Constantin, as the scientific observer, Pierre Triger and Olivier Cipriani as
pilot and co-pilot respectively, were participants on dive OT08 on September 4. As
soon as the divers reached the first scarp of the rift valley’s inside-facing southwest
corner at 3836 m depth, they observed slumped material made up of dark looking
peridotite, which was detached from the upper part of the slope. At 12h38 at
3,543 m depth, Marc observed the presence of in situ peridotite together with a
dolerite dyke. Serpentinized peridotite was observed between 3836 m up to the
summit at 2550 m depth.
Confident with dive OT08
0 s discovery of exposed peridotite on one corner of
the rift valley, we decided to try to find out if the opposite, northern inside-corner
end of this rift valley segment would have the same geological setting. Thus, dive
OT14 was conducted on the northeast corner of the OH3 segment. The diving
party was composed of Pierre Triger and Olivier Cipriani, as pilot and co-pilot, and
I was the scientist on board. We touched down on the sea floor at 10h46, and found
the same general setting, which comforted our original ideas concerning the nature
of this particular type of spreading segment. We made a complete geological
profile from the rift valley floor upwards along the slope of this uplifted structure.
We reached a slightly sedimented area with pillow lava and lobated flows at
3,568 m depth. The lava flows were not as fresh as those encountered in the middle
of the rift segment during dive OT09. The lava flow extended all way to the
intersection with the inside corner’s high, at a depth of 3,300 meters. After traveling eastward for about 2 km, at 12h54, we arrived in front of a faulted scarp with
196
7 Oceanic Spreading Ridges and Sea Floor Creation