grown’’. On the edifice where the chain had been placed, a fragile, few millimeters
thin and 40 cm high tubular conduit had been built on top of the ‘‘chain measuring
device’’. The temperature probe inserted into the black smoker gave a reading of
314 °C. Two sulfide samples were collected from where the chain was located. At
11h27, after sampling at the foot of the edifice and recording the observations of
the site on videotape, Cyana left the site. Four hours later, when the submersible
returned once again to the same hydrothermal field, the divers witnessed a regrowth of the active vent. A thin, golden yellow metallic coating, which was
probably chalcopyrite or pyrite minerals, had been built, but it was so fragile, it
floated away in the water column as soon as the submersible’s mechanical arm
tried to grab it.
Hence, the first quantitative measurements were made on the growth of a
hydrothermal edifice on the ocean floor at the ‘‘Chain site’’. Based on the observations made during the Cyana dives, it was now possible to evaluate the growth
rate of a sulfide edifice. A cylindrical shaped chimney of 3 cm (internal diameter)
and 10 cm (external diameter) with an average density of 2.9 gms/cm
3 will
increase its mass by about 1.6 kg per day. It is known that sulfide edifices are
formed from the coalescence of several chimneys. Thus, edifices averaging about
six meters in height and three meters wide, weighing about 41 tons, could be built
over a period of seventy years. This is the average duration of a human’s lifetime.
Since then, the ‘‘Chain Site’’ has been used as a reference site by several other
expeditions, and has become an area where biologists and geochemists have also
conducted various in situ experiments.
More sophisticated methods of calculating growth rates based on the age of the
sulfide deposits were later performed by Claude Lalou (Lalou et al. 1985) in
Saclay at the Centre d’Energie Atomique (CEA). Several short-life radioactive
elements such as thorium (Th
238 = 75,000 yr), uranium as well as lead (Pb) and
radium (Ra) were used to determine the young age of the sulfide deposits. The
method is based on the fact that no Th
238 is present in the samples when they are
first formed, therefore any measurable thorium (Th
238 ) must have been the result
of the decay of radium (Ra
238 ). From the U/Th disequilibrium method (Lalou et al.
1985), it was calculated that the age of the gossans material and of the massive Fesulfide deposit found on the ‘‘Southeastern seamount’’ (near 12°43
0 N-103°50
0 W,
EPR) is about 30,000 years old. This age is much younger than that of the basement on which the seamount was formed (130000 years old, as predicted by the
magnetic anomalies). Other isotopic age-dating studies on samples from near 21°N
on the EPR show that massive sulfide deposits located at less than 10 km from the
axis are 2,000–5,000 years old. The oldest samples, consisting essentially of Feoxyhydroxides as products of sulfide chimney alteration, have an age of about
36,000 years old and were collected at a distance of 10 km from the ridge axis.
Hydrothermal activities are limited in time. For instance, in the Trans Atlantic
Geothermal (TAG) area on the MAR, intermittent hydrothermal activities have
lasted only during the past 40,000–50,000 years (Lalou et al. 1993).
Bryce canyon site. Further investigations along the spreading axis about 3 km
south of the Chain Site took place during dive Cy82-31 on February 25, 1982, with
Cyana Dives on the EPR at 12°50
0 N
221
thin and 40 cm high tubular conduit had been built on top of the ‘‘chain measuring
device’’. The temperature probe inserted into the black smoker gave a reading of
314 °C. Two sulfide samples were collected from where the chain was located. At
11h27, after sampling at the foot of the edifice and recording the observations of
the site on videotape, Cyana left the site. Four hours later, when the submersible
returned once again to the same hydrothermal field, the divers witnessed a regrowth of the active vent. A thin, golden yellow metallic coating, which was
probably chalcopyrite or pyrite minerals, had been built, but it was so fragile, it
floated away in the water column as soon as the submersible’s mechanical arm
tried to grab it.
Hence, the first quantitative measurements were made on the growth of a
hydrothermal edifice on the ocean floor at the ‘‘Chain site’’. Based on the observations made during the Cyana dives, it was now possible to evaluate the growth
rate of a sulfide edifice. A cylindrical shaped chimney of 3 cm (internal diameter)
and 10 cm (external diameter) with an average density of 2.9 gms/cm
3 will
increase its mass by about 1.6 kg per day. It is known that sulfide edifices are
formed from the coalescence of several chimneys. Thus, edifices averaging about
six meters in height and three meters wide, weighing about 41 tons, could be built
over a period of seventy years. This is the average duration of a human’s lifetime.
Since then, the ‘‘Chain Site’’ has been used as a reference site by several other
expeditions, and has become an area where biologists and geochemists have also
conducted various in situ experiments.
More sophisticated methods of calculating growth rates based on the age of the
sulfide deposits were later performed by Claude Lalou (Lalou et al. 1985) in
Saclay at the Centre d’Energie Atomique (CEA). Several short-life radioactive
elements such as thorium (Th
238 = 75,000 yr), uranium as well as lead (Pb) and
radium (Ra) were used to determine the young age of the sulfide deposits. The
method is based on the fact that no Th
238 is present in the samples when they are
first formed, therefore any measurable thorium (Th
238 ) must have been the result
of the decay of radium (Ra
238 ). From the U/Th disequilibrium method (Lalou et al.
1985), it was calculated that the age of the gossans material and of the massive Fesulfide deposit found on the ‘‘Southeastern seamount’’ (near 12°43
0 N-103°50
0 W,
EPR) is about 30,000 years old. This age is much younger than that of the basement on which the seamount was formed (130000 years old, as predicted by the
magnetic anomalies). Other isotopic age-dating studies on samples from near 21°N
on the EPR show that massive sulfide deposits located at less than 10 km from the
axis are 2,000–5,000 years old. The oldest samples, consisting essentially of Feoxyhydroxides as products of sulfide chimney alteration, have an age of about
36,000 years old and were collected at a distance of 10 km from the ridge axis.
Hydrothermal activities are limited in time. For instance, in the Trans Atlantic
Geothermal (TAG) area on the MAR, intermittent hydrothermal activities have
lasted only during the past 40,000–50,000 years (Lalou et al. 1993).
Bryce canyon site. Further investigations along the spreading axis about 3 km
south of the Chain Site took place during dive Cy82-31 on February 25, 1982, with
Cyana Dives on the EPR at 12°50
0 N
221