Chapter 8
Fracture Zones and Transform Faults
Abstract Fracture zones are major discontinuities disrupting the linearity of
spreading ridge segments. They form depressions separating two regions of plates
that slip in opposite directions. The motion of the plates has gashed the lithosphere
down to more than 4000 m deep, often exposing deep mantle material. Fracture
zones vary in length from a few tens to hundreds of kilometers and are narrow, no
more than a few tens of kilometers wide. The seismically and tectonically active
portion of a fracture zone is also called a ‘‘transform fault’’. The area of the
Equatorial Atlantic between the African and South American continents located
between 5°N and 5°S corresponds to the highest concentration of closely spaced
fracture zones in the World’s ocean. That is where the St. Peter and St. Paul’s
Rocks Fracture Zone crosses the entire Atlantic Ocean from the Amazon basin at
the west through the coast of Liberia to the east. Most transforms are regions of
intense tectonic events but are deprived of volcanic activity, except for a few
transform faults associated with the fast spreading ridge systems in the Pacific
Ocean where recent volcanic activity has been detected.
Introduction
Fracture zones are oriented perpendicularly to the spreading ridge axis and represent large topographic irregularities, which interrupt the spreading ridge system
along its entire length. The fractures, extending across the ocean basins away from
the ridge axes, were called transcurrent faults by Tuzo Wilson (1965) and are more
commonly referred to as ‘‘fracture zones’’. The seismically active area of a fracture
zone displacing the immediate vicinity of the spreading ridge segments is called a
transform fault. The area that is more distant from the displaced spreading ridge
segment and which is seismically inactive and older is called a fracture zone (FZ).
One particularity of a fracture zone is to reveal a sliced portion of the oceanic
lithosphere, thereby creating steep and unstable scarps. Hence, one of the characteristics of a fracture zone is the abundance of broken rocks forming talus and
R. Hekinian, Sea Floor Exploration, Springer Oceanography,
DOI: 10.1007/978-3-319-03203-0_8,
Ó Springer International Publishing Switzerland 2014
255
Fracture Zones and Transform Faults
Abstract Fracture zones are major discontinuities disrupting the linearity of
spreading ridge segments. They form depressions separating two regions of plates
that slip in opposite directions. The motion of the plates has gashed the lithosphere
down to more than 4000 m deep, often exposing deep mantle material. Fracture
zones vary in length from a few tens to hundreds of kilometers and are narrow, no
more than a few tens of kilometers wide. The seismically and tectonically active
portion of a fracture zone is also called a ‘‘transform fault’’. The area of the
Equatorial Atlantic between the African and South American continents located
between 5°N and 5°S corresponds to the highest concentration of closely spaced
fracture zones in the World’s ocean. That is where the St. Peter and St. Paul’s
Rocks Fracture Zone crosses the entire Atlantic Ocean from the Amazon basin at
the west through the coast of Liberia to the east. Most transforms are regions of
intense tectonic events but are deprived of volcanic activity, except for a few
transform faults associated with the fast spreading ridge systems in the Pacific
Ocean where recent volcanic activity has been detected.
Introduction
Fracture zones are oriented perpendicularly to the spreading ridge axis and represent large topographic irregularities, which interrupt the spreading ridge system
along its entire length. The fractures, extending across the ocean basins away from
the ridge axes, were called transcurrent faults by Tuzo Wilson (1965) and are more
commonly referred to as ‘‘fracture zones’’. The seismically active area of a fracture
zone displacing the immediate vicinity of the spreading ridge segments is called a
transform fault. The area that is more distant from the displaced spreading ridge
segment and which is seismically inactive and older is called a fracture zone (FZ).
One particularity of a fracture zone is to reveal a sliced portion of the oceanic
lithosphere, thereby creating steep and unstable scarps. Hence, one of the characteristics of a fracture zone is the abundance of broken rocks forming talus and
R. Hekinian, Sea Floor Exploration, Springer Oceanography,
DOI: 10.1007/978-3-319-03203-0_8,
Ó Springer International Publishing Switzerland 2014
255