become the site of volcanic activity. In such cases, it will be called a ‘‘leaky’’
transform fault. Several transform domains have been recognized as being magmatically active. Examples of these types of ‘‘leaky transforms’’ are found in the
equatorial Pacific at 3°–8°S, near 13°S (Garrett F.Z.) and 15°N (Siqueiros F.Z.)
(Lonsdale 1978; Searle 1983; Fox and Gallo 1989; Hekinian et al. 1992).
Nomenclature of a fracture zone:
A seismically active transform fault consists of several tectonic domains:
(1) The Transform Domain (TD) limits the width of the main transform fault
bounded by two walls forming the displaced lithospheric plates between two
spreading segments. (2) The active tectonic zone (ATZ) consists of the region
where the most recent sheering and faulting is taking place in the Transform
Domain, also called the transform fault zone (Arcyana 1975). The ATZ runs
parallel to the strike of the transform. (3) The Transform Valley (TV) is the
floor of the transform bounded by the Active Tectonic Zone (ATZ). (4) The
Transverse Ridge (TR), when present, is an uplifted structure that is shallower than the surrounding displaced lithospheric plate and forms the
exterior walls of the transform fault. The TR is the result of large vertical
uplift during compression caused by the tectonics of thrust faulting within
the transform domain (TD).
Garrett Transform Fault
The Garrett transform is the fastest-slipping transform in the World with a lateral
slip rate of about 145 km/million years. The transform separates two segments of
the ultra-fast EPR near 13°28
0 S–112°W by a distance of about 130 km (Fig. 8.1).
Bathymetry and structural data have shown that the Garrett Transform is composed of a deep ([4000 m) transform valley, 24 km wide from wall to wall at the
3000 m contour interval. Within this transform valley, there is a transform domain,
which is about 10 km wide and deeper than 3000 m. This is where most of the
tectonic and volcanic activity takes place. Another peculiarity of the Garrett
Transform Fault is that it is one of a few fracture zones where recent volcanic
activity has been reported but never observed in its geological context prior to the
Garrett cruise. Other transforms with evidence of recent volcanism were reported
from the Siqueiros transform (15°N) (Natland 1989; Casey et al. 1991; Perfit et al.
1994) and from a region comprising several transforms between 2°S and 8°S along
the East Pacific Rise (Lonsdale 1989).
After preliminary surface-ship exploration of the Garrett Transform was carried
out by the international scientific community, the area was then ready to be
explored in more detail by submersible. It was important for the success of our
mission that we had been able to obtain the SeaBeam bathymetry coverage and
Introduction
257
transform fault. Several transform domains have been recognized as being magmatically active. Examples of these types of ‘‘leaky transforms’’ are found in the
equatorial Pacific at 3°–8°S, near 13°S (Garrett F.Z.) and 15°N (Siqueiros F.Z.)
(Lonsdale 1978; Searle 1983; Fox and Gallo 1989; Hekinian et al. 1992).
Nomenclature of a fracture zone:
A seismically active transform fault consists of several tectonic domains:
(1) The Transform Domain (TD) limits the width of the main transform fault
bounded by two walls forming the displaced lithospheric plates between two
spreading segments. (2) The active tectonic zone (ATZ) consists of the region
where the most recent sheering and faulting is taking place in the Transform
Domain, also called the transform fault zone (Arcyana 1975). The ATZ runs
parallel to the strike of the transform. (3) The Transform Valley (TV) is the
floor of the transform bounded by the Active Tectonic Zone (ATZ). (4) The
Transverse Ridge (TR), when present, is an uplifted structure that is shallower than the surrounding displaced lithospheric plate and forms the
exterior walls of the transform fault. The TR is the result of large vertical
uplift during compression caused by the tectonics of thrust faulting within
the transform domain (TD).
Garrett Transform Fault
The Garrett transform is the fastest-slipping transform in the World with a lateral
slip rate of about 145 km/million years. The transform separates two segments of
the ultra-fast EPR near 13°28
0 S–112°W by a distance of about 130 km (Fig. 8.1).
Bathymetry and structural data have shown that the Garrett Transform is composed of a deep ([4000 m) transform valley, 24 km wide from wall to wall at the
3000 m contour interval. Within this transform valley, there is a transform domain,
which is about 10 km wide and deeper than 3000 m. This is where most of the
tectonic and volcanic activity takes place. Another peculiarity of the Garrett
Transform Fault is that it is one of a few fracture zones where recent volcanic
activity has been reported but never observed in its geological context prior to the
Garrett cruise. Other transforms with evidence of recent volcanism were reported
from the Siqueiros transform (15°N) (Natland 1989; Casey et al. 1991; Perfit et al.
1994) and from a region comprising several transforms between 2°S and 8°S along
the East Pacific Rise (Lonsdale 1989).
After preliminary surface-ship exploration of the Garrett Transform was carried
out by the international scientific community, the area was then ready to be
explored in more detail by submersible. It was important for the success of our
mission that we had been able to obtain the SeaBeam bathymetry coverage and
Introduction
257