the active and passive margin regions (subduction trenches) where they are
thrusted, folded and exposed on a subaerial environment and/or subducted
underneath continental margins and volcanic arcs (Nicolas 1990). The model of
ophiolite emplacement over time covers the period from 570 Ma up to the Tertiary
and Cretaceous (50–40 Ma) belts in the Alps-Carpathians-Caucasus-and Himalaya
chains. This model suggests that ophiolite complexes have been formed episodically since the beginning of the Pangaea land break-up more than 200 million
years ago, when continents began colliding. Thus, several types of sections of
ophiolite provinces in the World (in Oman, Cyprus, Anatolia, the Alps, the
Apennines and in Vourinos, Greece) were exposed during the closure of the Tethys
Ocean.
Present Day Exposed Sea Floor
Cold areas with a thin or non-existent basaltic crust are ideal places for observing
the geological rock sequences. Such regions are magma-starved, and are located in
major depressions or deeps ([4000 m depths) associated with spreading ridge
segments and fracture zones.
In the North Atlantic, the crustal thickness varies considerably since under
Iceland it has a maximum depth of about 40 km (Darbyshire et al. 2000). On the
southern tip of the Reykjanes Ridge along the MAR, it was found that the crust is
about 9 km thick. The same crust thickness (9–10 km) was also found in the
Famous area near 37°N on the MAR (Whitmarsh 1973) where the intrusive zone is
about 3.5–1.6 km wide. In the equatorial Atlantic, it has been observed that there
is a deepening of the average spreading ridge’s axial bathymetric depth, which is
due to a decrease in magmatism and a less thick crust. This area of the equatorial
Atlantic corresponds to a region with a high concentration of fracture zones. The
4°N fracture zone, along with the St. Peter and Paul’s Rocks, the Romanche and
the Chain fracture zones are among the most prominent (see Chap. 8).
In the Pacific Ocean, similar situations are found in the equatorial region where
the Wilkes, Quebrada and Gofar transform faults occur. Other major fracture zones
in the Pacific include the Garrett and Eltanin FZ, which displace the East Pacific
Rise segments, and the Terevaka transform in the Easter Microplate (see Chap. 8)
(Fig. 4.6). If we hope to see the geological sequences that exist under the ocean
and within the crust, these are the areas where we should be looking.
Stratigraphic Columns
Although geologists have been able to observe and study land-based stratigraphic
sequences, very few oceanic sections of the crust and upper mantle have been
identified up to this day. In oceanic environments, we are obliged to use
100
4 Sea Floor Rocks
thrusted, folded and exposed on a subaerial environment and/or subducted
underneath continental margins and volcanic arcs (Nicolas 1990). The model of
ophiolite emplacement over time covers the period from 570 Ma up to the Tertiary
and Cretaceous (50–40 Ma) belts in the Alps-Carpathians-Caucasus-and Himalaya
chains. This model suggests that ophiolite complexes have been formed episodically since the beginning of the Pangaea land break-up more than 200 million
years ago, when continents began colliding. Thus, several types of sections of
ophiolite provinces in the World (in Oman, Cyprus, Anatolia, the Alps, the
Apennines and in Vourinos, Greece) were exposed during the closure of the Tethys
Ocean.
Present Day Exposed Sea Floor
Cold areas with a thin or non-existent basaltic crust are ideal places for observing
the geological rock sequences. Such regions are magma-starved, and are located in
major depressions or deeps ([4000 m depths) associated with spreading ridge
segments and fracture zones.
In the North Atlantic, the crustal thickness varies considerably since under
Iceland it has a maximum depth of about 40 km (Darbyshire et al. 2000). On the
southern tip of the Reykjanes Ridge along the MAR, it was found that the crust is
about 9 km thick. The same crust thickness (9–10 km) was also found in the
Famous area near 37°N on the MAR (Whitmarsh 1973) where the intrusive zone is
about 3.5–1.6 km wide. In the equatorial Atlantic, it has been observed that there
is a deepening of the average spreading ridge’s axial bathymetric depth, which is
due to a decrease in magmatism and a less thick crust. This area of the equatorial
Atlantic corresponds to a region with a high concentration of fracture zones. The
4°N fracture zone, along with the St. Peter and Paul’s Rocks, the Romanche and
the Chain fracture zones are among the most prominent (see Chap. 8).
In the Pacific Ocean, similar situations are found in the equatorial region where
the Wilkes, Quebrada and Gofar transform faults occur. Other major fracture zones
in the Pacific include the Garrett and Eltanin FZ, which displace the East Pacific
Rise segments, and the Terevaka transform in the Easter Microplate (see Chap. 8)
(Fig. 4.6). If we hope to see the geological sequences that exist under the ocean
and within the crust, these are the areas where we should be looking.
Stratigraphic Columns
Although geologists have been able to observe and study land-based stratigraphic
sequences, very few oceanic sections of the crust and upper mantle have been
identified up to this day. In oceanic environments, we are obliged to use
100
4 Sea Floor Rocks