Because the Iapetus Ocean was positioned between continental masses that would at a much later time roughly form the opposite shores of the
Atlantic Ocean, it can be seen as a sort of precursor of the Atlantic, and the process by which it opened shares many similarities with that of the Atlantic's initial opening in the
Jurassic.[2] The Iapetus Ocean was therefore named for the
titanIapetus, who in
Greek mythology was the father of
Atlas, after whom the Atlantic Ocean was named.[A]
Research history
At the start of the 20th century, American paleontologist
Charles Walcott noticed differences in early Paleozoic
benthictrilobites of
Laurentia (such as
Olenellidae, the so-called "Pacific fauna"), as found in
Scotland and western
Newfoundland, and those of Baltica (such as
Paradoxididae, often called the "Atlantic fauna"), as found in the southern parts of the
British Isles and eastern Newfoundland. Geologists of the early 20th century presumed that a large trough, a so-called
geosyncline, had existed between Scotland and England in the early Paleozoic, keeping the two sides separated.[4]
With the development of
plate tectonics in the 1960s, geologists such as
Arthur Holmes and
John Tuzo Wilson concluded that the Atlantic Ocean must have had a precursor before the time of
Pangaea. Wilson also noticed that the Atlantic had opened at roughly the same place where its precursor ocean had closed. This led him to his
Wilson cycle hypothesis.[4]
Geodynamic history
Neoproterozoic origin
In many spots in Scandinavia
basalticdikes are found with ages between 670 and 650 million years. These are interpreted as evidence that by that time,
rifting had started that would form the Iapetus Ocean.[5] In
Newfoundland and Labrador, the
Long Range dikes are also thought to have formed during the formation of the Iapetus Ocean.[6] It has been proposed that both the
Fen Complex in Norway and the
Alnö Complex in Sweden formed as consequence to mild
extensional tectonics in the ancient continent of
Baltica that followed the opening of the Iapetus Ocean.[7]
The eastern Iapetus Ocean is believed to have opened around 590 Ma with the emplacement of the Central Iapetus Magmatic Province between Laurentia and Baltica.[8] The southern Iapetus Ocean opened between Laurentia and southwestern
Gondwana (now South America) about 550 Ma, close to the end of the Ediacaran period. At the time it did so the
Adamastor Ocean further east
closed.[9] The opening of the Iapetus Ocean probably postdates the opening of the
Puncoviscana Ocean, which is believed to have opened around 700 Ma as Laurentia drifted away from Amazonia,[8] with the Iapetus Ocean being separated from the Puncoviscana Ocean by the ribbon-shaped
Arequipa-Antofallaterrane. However, the formation of both oceans seems unrelated.[10]
Paleozoic
Southwest of the Iapetus, a volcanic
island arc evolved from the early
Cambrian (540 million years ago) onward. This volcanic arc was formed above a
subduction zone where the
oceanic lithosphere of the Iapetus Ocean subducted southward under other oceanic
lithosphere. From Cambrian times (about 550 million years ago) the western Iapetus Ocean began to grow progressively narrower due to this subduction. The same happened further north and east, where Avalonia and Baltica began to move towards Laurentia from the
Ordovician (488–444 million years ago) onward.[5]
Trilobitefaunas of the
continental shelves of Baltica and Laurentia are still very different in the Ordovician, but
Silurian faunas show progressive mixing of species from both sides, because the continents moved closer together.[12]
In the west, the Iapetus Ocean closed with the
Taconic orogeny (480-430 million years ago), when the volcanic island arc
collided with Laurentia. Some authors consider the oceanic basin south of the island arc also a part of the Iapetus, this branch closed during the later
Acadian orogeny, when Avalonia collided with Laurentia.[citation needed]
Meanwhile, the eastern parts had closed too: the
Tornquist Sea between Avalonia and Baltica already during the late Ordovician,[14] the main branch between Baltica-Avalonia and Laurentia during the
Grampian and
Scandian phases of the Caledonian orogeny (440–420 million years ago).[citation needed]
At the end of the Silurian period (c. 420 million years ago) the Iapetus Ocean had completely disappeared and the combined mass of the three continents formed the "new" continent of
Laurasia,[15] which would itself be the northern component of the singular supercontinent of
Pangaea.[citation needed]
London-Brabant Massif – Ancient crystalline basement stretching across northern Belgium from Rhineland to East AngliaPages displaying short descriptions of redirect targets
Southern uplands of Scotland – Southernmost and least populous region of ScotlandPages displaying short descriptions of redirect targets
Ammonoosuc Volcanics - A metamorphosed rock unit that formed during the closure of the Iapetus Ocean.
Notes
^The name Iapetus was first used by
Harland & Gayer 1972, before that the ocean was referred to as the Proto-Atlantic.[3]
^In other words, what is at present the northern end of the Famatinian orogen would have been connected with what is currently the southern end of the Taconic orogen.
Gee D., Janák M., Majka J., Robinson P., van Roermund H., 2013, Subduction along and within the Baltoscandian margin during closing of the Iapetus Ocean and Baltica–Laurentia collision, Lithosphere, Vol. 5, pp. 169-178
[1]
Torsvik, T. H.; Smethurst, M. A.; Meert, J. G.; Van der Voo, R.; McKerrow, W. S.; Brasier, M. D.; Sturt, B. A.; Walderhaug, H. J. (1996). "Continental break-up and collision in the Neoproterozoic and Palaeozoic—a tale of Baltica and Laurentia". Earth-Science Reviews. 40 (3): 229–258.
Bibcode:
1996ESRv...40..229T.
doi:
10.1016/0012-8252(96)00008-6.
Windley, B. F. (1996). The Evolving Continents (3rd ed.). Wiley.
ISBN978-0-471-91739-7.