and Japanese, have used their manned submersibles Nautile, Alvin and Shankai
respectively for this endeavor.
The first submersible cruise along the ultrafast EPR segment took place with
Nautile and its support ship N.O. LE NADIR. The cruise was organized and
conducted by scientists from IFREMER as part of the project Geocyatherm (short
for GEOlogy CYAna hydroTHERmalism). This cruise was divided into three legs
that were programmed on the previously surveyed area of the EPR where traces of
hydrothermal deposits were discovered. This was an ambitious French program to
understand and evaluate the metalliferous ore deposits along an ultrafast spreading
ridge segment.
The first Leg of Geocyarise Cruise headed by Vincent Renard as chief scientist
left Easter Island in January 1984 heading northward following the East Pacific
rise axis to the next port of call, which was Manzanillo in Mexico.
On board the N.O. Le Nadir there were scientists from French and US institutions. Dr. R. Ballard from WHOI and Emery Christoff from the ‘‘National Geographic Magazine’’ were invited in the framework of the French-American
collaboration on projects FAMOUS and CYAMEX. In addition, Dr. Harold Backer
from the German mining company ‘‘Preussag’’, who had previously explored and
mapped the area with the R.V. SONNE in 1979 was invited. He was also the first to
discover signs of hydrothermalism on this southern East Pacific Rise.
Field observations on ultrafast spreading centers in the south Pacific have
shown that some ridge segments are at different stages of development and were
also the sites of various types of tectonic, magmatic and hydrothermal activity.
This was confirmed during the first Leg of the GEOCYATHERM cruise submersible dives on four different short segments of the spreading ridge. The
ultrafast, short (3–15 km in length) spreading ridge segments were investigated
during six submersible dives. Three main types of ridge segments having a different structural evolution were chosen for diving (Renard et al. 1985) (Fig. 7.30):
(1) Two rifted segments with a relatively deep gashed ([50 m relief) graben at
21°26
0 S and 18°30
0 S), (2) moderately-rifted (20–40 m depth) segments at 20°S
and (3) a non-rifted segment at 17°30
0 S. The purpose was to understand the mode
of magmatic and hydrothermal fluid circulation in relation to the tectonics of
spreading. Furthermore the exploration helped to understand the cyclicity of
magmatic and tectonic events involved during ridge accretion as shown below.
Magmatic and Hydrothermal Cyclicity at Different Ridge
Segments
Magmato-tectonic processes in the lithosphere are responsible for the different
stages of evolution of the magmatic and hydrothermal activities on spreading ridge
segments. The compositional and the morphological changes observed in the
extrusion of lava are related to the dynamics of magma supply and residence time
240
7 Oceanic Spreading Ridges and Sea Floor Creation
respectively for this endeavor.
The first submersible cruise along the ultrafast EPR segment took place with
Nautile and its support ship N.O. LE NADIR. The cruise was organized and
conducted by scientists from IFREMER as part of the project Geocyatherm (short
for GEOlogy CYAna hydroTHERmalism). This cruise was divided into three legs
that were programmed on the previously surveyed area of the EPR where traces of
hydrothermal deposits were discovered. This was an ambitious French program to
understand and evaluate the metalliferous ore deposits along an ultrafast spreading
ridge segment.
The first Leg of Geocyarise Cruise headed by Vincent Renard as chief scientist
left Easter Island in January 1984 heading northward following the East Pacific
rise axis to the next port of call, which was Manzanillo in Mexico.
On board the N.O. Le Nadir there were scientists from French and US institutions. Dr. R. Ballard from WHOI and Emery Christoff from the ‘‘National Geographic Magazine’’ were invited in the framework of the French-American
collaboration on projects FAMOUS and CYAMEX. In addition, Dr. Harold Backer
from the German mining company ‘‘Preussag’’, who had previously explored and
mapped the area with the R.V. SONNE in 1979 was invited. He was also the first to
discover signs of hydrothermalism on this southern East Pacific Rise.
Field observations on ultrafast spreading centers in the south Pacific have
shown that some ridge segments are at different stages of development and were
also the sites of various types of tectonic, magmatic and hydrothermal activity.
This was confirmed during the first Leg of the GEOCYATHERM cruise submersible dives on four different short segments of the spreading ridge. The
ultrafast, short (3–15 km in length) spreading ridge segments were investigated
during six submersible dives. Three main types of ridge segments having a different structural evolution were chosen for diving (Renard et al. 1985) (Fig. 7.30):
(1) Two rifted segments with a relatively deep gashed ([50 m relief) graben at
21°26
0 S and 18°30
0 S), (2) moderately-rifted (20–40 m depth) segments at 20°S
and (3) a non-rifted segment at 17°30
0 S. The purpose was to understand the mode
of magmatic and hydrothermal fluid circulation in relation to the tectonics of
spreading. Furthermore the exploration helped to understand the cyclicity of
magmatic and tectonic events involved during ridge accretion as shown below.
Magmatic and Hydrothermal Cyclicity at Different Ridge
Segments
Magmato-tectonic processes in the lithosphere are responsible for the different
stages of evolution of the magmatic and hydrothermal activities on spreading ridge
segments. The compositional and the morphological changes observed in the
extrusion of lava are related to the dynamics of magma supply and residence time
240
7 Oceanic Spreading Ridges and Sea Floor Creation