Thermal erosion alone would only create a volcanic dome,
such as Hoggar. We conclude that active rifting requires
also tensional forces in the lithosphere. Passive or active
rifting reflects some of the observed variety of rifts.
Another major factor is whether the lithosphere subjected
to rifting was homogeneous or already bearing scars,
namely, major shear bands, either thermal or geological,
for instance, the trace of a former subduction zone. With
respect to symmetrical rifting (Figure 1a, b), this would
favor asymmetrical rifting (Figure 1c). In this simple
model, the strength of a normal, homogeneous continental
lithosphere would be too high to yield, unless a flat-lying
weak zone is present. This would generate a cold detachment fault (Figure 1c). However, these models remain
very simple. There is also an evolution in time. As illustrated by the Red Sea evolution, the initiation of an oceanic rift in the North tends to be symmetrical, whereas in
the Southern Red Sea that is in a further stage of oceanic
10
0
20
30
a
b
c
d
40
km
SEAFLOOR SPREADING
EXHUMATION
10
0
20
30
40
km
THINNING
10
0
20
30
40
km
STRETCHING
10
0
20
30
40
km
upper continental crust
qtz-fsp rich middle - lower continental crust
upper - rigid
1. serpentinized mantle
embryonnic slow-spreading oceanic crust
pre-rift sediments
lower continental - mafic crust
post-rift sediments
syn-rift sediments
lower - plastic
asthenospheric mantle
poly-phase deformation structures
accommodating shear zones
ODP Sites
1300°C
lithospheric
mantle
2. upper lithospheric mantle
3. lower lithospheric mantle
4. infiltrated mantle
5. lithospheric / asthenospheric mantle
6. asthenospheric mantle
1.
2.
3.
4. 5.
6.
1070 899
897
1065 901
1277
1070
899
897
900 - 1067
1065
901
1069
1069
900
1068
1065 901
1065
901
1068
900
1067
1068
900
1067
1067
1069
1069
1277
897
899
1070
1277
1276
Oceanic Rifts, Figure 3 A new model for the mid-ocean rifting of the Atlantic Ocean, (a) and (b) from continental rifting, with
development of conjugate detachments and mantle uprise, (c) OCT between European margin in Galicia and American margin in
Newfoundland, with a new major detachment from the western margin and exhumation of lithospheric mantle, and (d) seafloor
spreading of the Atlantic Ocean (Pe ´ron-Pinvidic and Manatschal 2009).
570
OCEANIC RIFTS
such as Hoggar. We conclude that active rifting requires
also tensional forces in the lithosphere. Passive or active
rifting reflects some of the observed variety of rifts.
Another major factor is whether the lithosphere subjected
to rifting was homogeneous or already bearing scars,
namely, major shear bands, either thermal or geological,
for instance, the trace of a former subduction zone. With
respect to symmetrical rifting (Figure 1a, b), this would
favor asymmetrical rifting (Figure 1c). In this simple
model, the strength of a normal, homogeneous continental
lithosphere would be too high to yield, unless a flat-lying
weak zone is present. This would generate a cold detachment fault (Figure 1c). However, these models remain
very simple. There is also an evolution in time. As illustrated by the Red Sea evolution, the initiation of an oceanic rift in the North tends to be symmetrical, whereas in
the Southern Red Sea that is in a further stage of oceanic
10
0
20
30
a
b
c
d
40
km
SEAFLOOR SPREADING
EXHUMATION
10
0
20
30
40
km
THINNING
10
0
20
30
40
km
STRETCHING
10
0
20
30
40
km
upper continental crust
qtz-fsp rich middle - lower continental crust
upper - rigid
1. serpentinized mantle
embryonnic slow-spreading oceanic crust
pre-rift sediments
lower continental - mafic crust
post-rift sediments
syn-rift sediments
lower - plastic
asthenospheric mantle
poly-phase deformation structures
accommodating shear zones
ODP Sites
1300°C
lithospheric
mantle
2. upper lithospheric mantle
3. lower lithospheric mantle
4. infiltrated mantle
5. lithospheric / asthenospheric mantle
6. asthenospheric mantle
1.
2.
3.
4. 5.
6.
1070 899
897
1065 901
1277
1070
899
897
900 - 1067
1065
901
1069
1069
900
1068
1065 901
1065
901
1068
900
1067
1068
900
1067
1067
1069
1069
1277
897
899
1070
1277
1276
Oceanic Rifts, Figure 3 A new model for the mid-ocean rifting of the Atlantic Ocean, (a) and (b) from continental rifting, with
development of conjugate detachments and mantle uprise, (c) OCT between European margin in Galicia and American margin in
Newfoundland, with a new major detachment from the western margin and exhumation of lithospheric mantle, and (d) seafloor
spreading of the Atlantic Ocean (Pe ´ron-Pinvidic and Manatschal 2009).
570
OCEANIC RIFTS