Ballard and had her first diving experience on the site of hot hydrothermal vents at
21°N on the EPR. Her PhD dissertation presented the first detailed mineralogical
and geochemical data compiled from the ocean floor’s hydrothermal system
(Février 1981). Michelle used mineral paragenesis to detect the sequences of
mineral precipitation in the water column and on the seafloor. Thus, it was found
that the origin of the sulfur binding the metallic phases and forming copper, zinc
and iron compounds came in part from seawater and in part from deep mantle
sources. The sulfur formed from seawater is released during a transformation of
sulfates due to seawater circulation and its reaction with the crustal material. The
work done on the hydrothermal material from the EPR has shown that the black
colored fluids spewing out of the chimneys have precipitated mainly high temperature metals such as chalcopyrite (copper rich sulfides) and sphalerite (zinc
sulfides), while the lighter, white colored fluids have precipitated silica and calcium enriched phases.
This early work revealed the fact that metal-enriched sulfide precipitates are
short lived and are inclined to alter within the seawater-oxygenated environment.
Thus, when the hydrothermal source is no longer being supplied, the deposits are
transformed into powdery products that can be easily dispersed by bottom currents
(see Chap. 6). The evolution of the individual hydrothermal chimneys was inferred
on the basis of the mineralogical studies. The size and composition of the crystals
will vary from the exterior towards the interior as the temperature of the exiting
fluid changes.
Long-Range Survey of the East Pacific Rise
After our exploration of fast (EPR 21°N) and slow (MAR 36°N) spreading ridge
segments and the discovery of hydrothermal precipitates, it seemed wise to conduct further exploration on accreting ridge axes. The rational behind the new
projects was to try to find out if hydrothermalism and volcanism were common
phenomena inherent to accreting spreading ridges. Our questions were concerned
with the extent of volcanism and its relationship to hydrothermalism. What was the
extent of hydrothermalism? How are volcanic events related to hydrothermal
activity and what is the relationship of volcanism to the geological setting of a
particular region?
Several large-scale bathymetric and topographic surveys along the crest of fast
spreading ridge systems were planned by the international scientific community,
especially French, German and U.S. institutions, prior to engaging more detailed
investigations with manned and unmanned diving engines on the sea floor.
In 1980, the first French long-range sea-going expedition along the axis of the
East Pacific Rise was called the SEARISE cruise. It was dedicated to exploring the
EPR axis between 21°N to 21°S, and then pursuing a further crossing over the
Pacific basin intraplate region all the way to Tahiti. The cruise was sponsored by
IFREMER and headed by Jean Francheteau on board the N.O JEAN CHARCOT.
East Pacific Rise at 21°N
203
21°N on the EPR. Her PhD dissertation presented the first detailed mineralogical
and geochemical data compiled from the ocean floor’s hydrothermal system
(Février 1981). Michelle used mineral paragenesis to detect the sequences of
mineral precipitation in the water column and on the seafloor. Thus, it was found
that the origin of the sulfur binding the metallic phases and forming copper, zinc
and iron compounds came in part from seawater and in part from deep mantle
sources. The sulfur formed from seawater is released during a transformation of
sulfates due to seawater circulation and its reaction with the crustal material. The
work done on the hydrothermal material from the EPR has shown that the black
colored fluids spewing out of the chimneys have precipitated mainly high temperature metals such as chalcopyrite (copper rich sulfides) and sphalerite (zinc
sulfides), while the lighter, white colored fluids have precipitated silica and calcium enriched phases.
This early work revealed the fact that metal-enriched sulfide precipitates are
short lived and are inclined to alter within the seawater-oxygenated environment.
Thus, when the hydrothermal source is no longer being supplied, the deposits are
transformed into powdery products that can be easily dispersed by bottom currents
(see Chap. 6). The evolution of the individual hydrothermal chimneys was inferred
on the basis of the mineralogical studies. The size and composition of the crystals
will vary from the exterior towards the interior as the temperature of the exiting
fluid changes.
Long-Range Survey of the East Pacific Rise
After our exploration of fast (EPR 21°N) and slow (MAR 36°N) spreading ridge
segments and the discovery of hydrothermal precipitates, it seemed wise to conduct further exploration on accreting ridge axes. The rational behind the new
projects was to try to find out if hydrothermalism and volcanism were common
phenomena inherent to accreting spreading ridges. Our questions were concerned
with the extent of volcanism and its relationship to hydrothermalism. What was the
extent of hydrothermalism? How are volcanic events related to hydrothermal
activity and what is the relationship of volcanism to the geological setting of a
particular region?
Several large-scale bathymetric and topographic surveys along the crest of fast
spreading ridge systems were planned by the international scientific community,
especially French, German and U.S. institutions, prior to engaging more detailed
investigations with manned and unmanned diving engines on the sea floor.
In 1980, the first French long-range sea-going expedition along the axis of the
East Pacific Rise was called the SEARISE cruise. It was dedicated to exploring the
EPR axis between 21°N to 21°S, and then pursuing a further crossing over the
Pacific basin intraplate region all the way to Tahiti. The cruise was sponsored by
IFREMER and headed by Jean Francheteau on board the N.O JEAN CHARCOT.
East Pacific Rise at 21°N
203