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The opening of the North Atlantic Ocean is a
geological event A geological event is a temporally and spatially heterogeneous and dynamic (diachronous) happening in Earth history that contributes to the transformation of Earth system and the formation of geological strata. Event stratigraphy was first propo ...
that has occurred over millions of years, during which the supercontinent Pangea broke up. As modern-day Europe ( Eurasian plate) and North America ( North American Plate) separated during the final breakup of Pangea in the early
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configurat ...
Era, they formed the North
Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth#Surface, Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Afr ...
. Geologists believe the breakup occurred either due to primary processes of the
Iceland plume The Iceland hotspot is a hotspot which is partly responsible for the high volcanic activity which has formed the Iceland Plateau and the island of Iceland. Iceland is one of the most active volcanic regions in the world, with eruptions occur ...
or secondary processes of lithospheric extension from plate tectonics.


Description

Rocks from the North Atlantic Igneous Province have been found in Greenland, the Irminger Basin,
Faroe Islands The Faroe Islands ( ), or simply the Faroes ( fo, Føroyar ; da, Færøerne ), are a North Atlantic archipelago, island group and an autonomous territory of the Danish Realm, Kingdom of Denmark. They are located north-northwest of Scotlan ...
, Vøring Plateau (off Norway), Faroe-Shetland Basin, Hebrides, Outer Moray Firth and Denmark. The supercontinent known as Pangea existed during the late Paleozoic and early Mesozoic eras and began to
rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben wi ...
around 200 million years ago. Pangea had three major phases of breakup. The first major phase began in the Early-Middle Jurassic, taking place between North America and Africa. The second major phase of breakup began in the Early Cretaceous. The South Atlantic Ocean opened around 140 million years ago as Africa separated from South America, and about the same time, India separated from Antarctica and Australia, forming the central Indian Ocean. The final major phase of breakup occurred in the early
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configurat ...
, as Laurentia separated from Eurasia. As the two plates broke free from each other, the
Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth#Surface, Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Afr ...
continued to expand.


Iceland plume theory

The
Iceland plume The Iceland hotspot is a hotspot which is partly responsible for the high volcanic activity which has formed the Iceland Plateau and the island of Iceland. Iceland is one of the most active volcanic regions in the world, with eruptions occur ...
is a mantle plume under Iceland that carries hot material from the deep within Earth's mantle upwards to the crust. The rising hot material weakens the lithosphere, making the separation of plates easier. The flow of hot plume material creates volcanism under the
continental lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of up to thousands of years o ...
. Iceland extends across the
Mid-Atlantic Ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent or constructive plate boundary) located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. In the North Atlantic, the ridge separates the North Ame ...
. The Mid-Atlantic Ridge is a divergent plate boundary, and it separates the Eurasian and North American plates. The ages of the earliest volcanic rocks from this plume lie in the late Paleocene, and both sides of the Atlantic Ocean contain these rocks. Since these rocks have been dated to the late Paleocene, this lines up with the time of breakup of the North Atlantic continent, so some think it could have been a contributing factor.


Plate tectonics

This theory views volcanism as the resultant of lithospheric processes rather than heat from the mantle rising up. Instead of heat coming up from deep in the mantle, volcanic anomalies come from a shallow source. Volcanism thus occurs where the crust is easier to break up because it has been stretched by lithospheric extension, allowing melt to reach the surface. Volcanic anomalies are created by plate tectonics such as spreading plate boundaries or subduction zones. The location of the volcanism is governed by the stress field in the plate and the amount of melt is governed by the fusibility of the mantle beneath. Plate tectonics can explain most of the volcanism on Earth.


Active vs. passive plates

Active rifting, such as is formed by the
Iceland plume The Iceland hotspot is a hotspot which is partly responsible for the high volcanic activity which has formed the Iceland Plateau and the island of Iceland. Iceland is one of the most active volcanic regions in the world, with eruptions occur ...
, is driven by hotspot or mantle plume activity. From deep within the Earth, hot mantle rises to force doming of the crust. This causes thinning of the crust and lithosphere, then melting and
underplating Magmatic underplating occurs when basaltic magmas are trapped during their rise to the surface at the Mohorovičić discontinuity or within the crust. Entrapment (or 'stalling out') of magmas within the crust occurs due to the difference in re ...
occur. Finally, there is rifting at the crest of the domed crust and volcanism occurs. In passive rifting, driven by plate tectonics, the crust and lithosphere extend as a result of plate boundary forces such as
slab pull Slab pull is a geophysical mechanism whereby the cooling and subsequent densifying of a subducting tectonic plate produces a downward force along the rest of the plate. In 1975 Forsyth and Uyeda used the inverse theory method to show that, of the ...
. Far field stresses thin the crust and lithospheric mantle, and hot asthenospheric mantle passively enters the thinned area. The upwelling of
asthenosphere The asthenosphere () is the mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, at a depth between ~ below the surface, and extends as deep as . However, the lower boundary of the asthenosphere is not ...
is not involved in the actual rifting process. The upward flow of the asthenosphere results in
decompression melting Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma ...
, magmatic underplating and some volcanism that may occur in the rift area.


See also

* North Atlantic Igneous Province


References

{{Reflist Plate tectonics Cenozoic geology Geology of the Atlantic Ocean