The OCEANAUT Project: Mid Atlantic Ridge at 34°50
0 N
The objective of the OCEANAUT project was to study magmatic and dynamic
processes near 34°50
0 N. These processes are related to asthenosphere upwelling in
a relatively colder environment with less volcanic activity than in the FAMOUS
area and at a distance ([1,000 km) from the influence of the Azores hotspot
(Figs. 7.5, 7.8). From previous petrological, geophysical and geochemical investigation, it had been shown that the influence of the Azores hotspot was limited or
non-existent south of the Oceanographer transform fault. In addition, ‘‘cold areas’’,
with thin or absent basaltic crust, are ideal places for the exposure of deep-seated
upper mantle material such as peridotite.
This type of area is most appropriate for interpreting original structures and
their evolution over time (structural reconstruction) and for learning about the
asthenosphere-lithosphere interactions. Studying amagmatic areas and/or areas
that are poorly supplied by magma will help to: (a) determine the magmatic budget
for the whole crust and upper mantle, (b) be a way for us to model magmatic
upwelling and the mode of partial melting and (c) define the structure and composition of magmatic segregation through the upper mantle and lithosphere.
In the early 90s, several detailed geophysical investigations with modern
seismic equipment coupled with gravity studies had taken place along the North
Atlantic spreading ridge segments. They were intended to determine the existence
of magma upwelling zones and define the geometry of magma chambers along
several slow spreading ridge segments. Following an earlier seismic experiment
with fourteen three-component Ocean Bottom Seismometers (OBS) deployed for
46 days during November and December 1992 (Barclay et al. 1998) and after a
micro-seismicity experiment, six seismic refraction and tomography experiments
were carried out in October–November of 1996 (Detrick et al. 1995) in the same
area as the Oceanaut cruise at 34°50
0 N on the Mid-Atlantic Ridge. Because of the
international interest in this region, the 1991 FARA-Sigma cruise of the French
R.V. L’ATALANTE (Needham et al. 1992) had occurred in the framework of an
international cooperative program. Swath bathymetry, acoustic backscatter
(SIMRAD EM12 dual) and gravity data were systematically acquired with a track
spacing of 12–16 km (Detrick et al. 1995).
After these geophysical surveys, Daniel Bideau from the department of Marine
Geosciences at IFREMER was able to conduct a diving program in August 1995.
Daniel was a brilliant scientist who unfortunately died too young at the age of 55
in April 2006. I had followed his career while he was doing his research at
IFREMER. He did his PhD dissertation under my supervision and we shared the
same office and laboratory where we engaged in many conversations about
geology and life. I was impressed by his logical approach in dealing with scientific
problems. His main interest was the study of rocks that had undergone transformation (metamorphism) during tectonic and magmatic processes. Daniel was easy
going, friendly and had the type of personality, which makes people feel comfortable. This is an important quality for a chief scientist.
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7 Oceanic Spreading Ridges and Sea Floor Creation
0 N
The objective of the OCEANAUT project was to study magmatic and dynamic
processes near 34°50
0 N. These processes are related to asthenosphere upwelling in
a relatively colder environment with less volcanic activity than in the FAMOUS
area and at a distance ([1,000 km) from the influence of the Azores hotspot
(Figs. 7.5, 7.8). From previous petrological, geophysical and geochemical investigation, it had been shown that the influence of the Azores hotspot was limited or
non-existent south of the Oceanographer transform fault. In addition, ‘‘cold areas’’,
with thin or absent basaltic crust, are ideal places for the exposure of deep-seated
upper mantle material such as peridotite.
This type of area is most appropriate for interpreting original structures and
their evolution over time (structural reconstruction) and for learning about the
asthenosphere-lithosphere interactions. Studying amagmatic areas and/or areas
that are poorly supplied by magma will help to: (a) determine the magmatic budget
for the whole crust and upper mantle, (b) be a way for us to model magmatic
upwelling and the mode of partial melting and (c) define the structure and composition of magmatic segregation through the upper mantle and lithosphere.
In the early 90s, several detailed geophysical investigations with modern
seismic equipment coupled with gravity studies had taken place along the North
Atlantic spreading ridge segments. They were intended to determine the existence
of magma upwelling zones and define the geometry of magma chambers along
several slow spreading ridge segments. Following an earlier seismic experiment
with fourteen three-component Ocean Bottom Seismometers (OBS) deployed for
46 days during November and December 1992 (Barclay et al. 1998) and after a
micro-seismicity experiment, six seismic refraction and tomography experiments
were carried out in October–November of 1996 (Detrick et al. 1995) in the same
area as the Oceanaut cruise at 34°50
0 N on the Mid-Atlantic Ridge. Because of the
international interest in this region, the 1991 FARA-Sigma cruise of the French
R.V. L’ATALANTE (Needham et al. 1992) had occurred in the framework of an
international cooperative program. Swath bathymetry, acoustic backscatter
(SIMRAD EM12 dual) and gravity data were systematically acquired with a track
spacing of 12–16 km (Detrick et al. 1995).
After these geophysical surveys, Daniel Bideau from the department of Marine
Geosciences at IFREMER was able to conduct a diving program in August 1995.
Daniel was a brilliant scientist who unfortunately died too young at the age of 55
in April 2006. I had followed his career while he was doing his research at
IFREMER. He did his PhD dissertation under my supervision and we shared the
same office and laboratory where we engaged in many conversations about
geology and life. I was impressed by his logical approach in dealing with scientific
problems. His main interest was the study of rocks that had undergone transformation (metamorphism) during tectonic and magmatic processes. Daniel was easy
going, friendly and had the type of personality, which makes people feel comfortable. This is an important quality for a chief scientist.
186
7 Oceanic Spreading Ridges and Sea Floor Creation