The Iapetus Suture is one of several major

geological fault Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

s caused by the collision of several ancient land masses forming a suture. It represents in part the remains of what was once the

Iapetus Ocean The Iapetus Ocean (; ) existed in the late Neoproterozoic and early Paleozoic eras of the geologic timescale (between 600 and 400 million years ago). It was in the southern hemisphere, between the paleocontinents of Laurentia, Baltica and Avalon ...

Iapetus In Greek mythology, Iapetus (; ; ), also Japetus, is a Titan, the son of Uranus and Gaia and father of Atlas, Prometheus, Epimetheus, and Menoetius. He was also called the father of Buphagus and Anchiale in other sources. Iapetus was linked ...

was the father of

Atlas An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets. Atlases have traditio ...

in Greek mythology, making his an appropriate name for what used to be called the 'Proto-Atlantic Ocean'. When the

Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

opened, in the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

period, it took a slightly different line from that of the Iapetus suture, with some originally

Laurentia Laurentia or the North American craton is a large continental craton that forms the Geology of North America, ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of ...

n rocks being left behind in north-west

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

and other,

Avalonia Avalonia was a microcontinent in the Paleozoic era. Crustal fragments of this former microcontinent are terranes in parts of the eastern coast of North America: Atlantic Canada, and parts of the East Coast of the United States, East Coast of the ...

n, rocks remaining as part of

Newfoundland Newfoundland and Labrador is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region of Labrador, having a total size of . As of 2025 the population ...

Background

The

was an ancient ocean which existed in the Southern Hemisphere approximately 600 million years ago and was bordered by several paleocontinents:

, Ganderia, Carolinia,

, and

Baltica Baltica is a paleocontinent that formed in the Paleoproterozoic and now constitutes northwestern Eurasia, or Europe north of the Trans-European Suture Zone and west of the Ural Mountains. The thick core of Baltica, the East European Craton, i ...

. During a series of geological events, the Salinic orogeny and

Caledonian progeny Caledonian is a geographical term used to refer to places, species, or items in or from Scotland, or particularly the Scottish Highlands. It derives from Caledonia, the Roman name for the area of modern Scotland. Caledonian is also used to refer t ...

, all three land masses began to converge upon each other, slowly diminishing the ocean by subducting the oceanic crust. By the end of the

Silurian period The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

, approximately 420 million years ago, the ocean had disappeared. The geological fault zone resulting from the continental collision is known as the Iapetus Suture, named after the ocean it replaced. The closure of Iapetus involved a complex and protracted collisional history of numerous

continental fragment Continental crustal fragments, partly synonymous with microcontinents, are pieces of continents that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin. Caus ...

volcanic arc A volcanic arc (also known as a magmatic arc) is a belt of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc ...

s and

back-arc basin A back-arc basin is a type of geologic Structural basin, basin, found at some convergent boundary, convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found ...

s that were accreted to

and Avalonia between the Early

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

and Late

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

. The notion of a single suture zone in a complex orogen such as the Appalachian/Caledonian is unrealistic as several temporal and spatial distinct suture zones are present.

In Canada

The Early Ordovician (Taconic) Baie Verte Line in

Quebec Quebec is Canada's List of Canadian provinces and territories by area, largest province by area. Located in Central Canada, the province shares borders with the provinces of Ontario to the west, Newfoundland and Labrador to the northeast, ...

and

marks the boundary between the continental margin of Laurentia and Iapetan oceanic rocks, while the Early Ordovician (Penobscot) GRUB Line defines the contact between the vestiges of Iapetus and Ganderia. The Middle Ordovician

Red Indian There is an ongoing discussion about the terminology used by the Indigenous peoples of the Americas to describe themselves, as well as how they prefer to be referred to by others. Preferred terms vary primarily by region and age. As Indigenous ...

Line is considered the main Iapetan suture zone in that it separates peri-Laurentian and peri-Gondwanan oceanic elements. The Dog Bay Line is a younger feature in the Appalachians and delineates the terminal Iapetan suture in Newfoundland as it marks the Early Silurian (Salinic) collisional zone between Ganderia and Laurentia.

In the United States

The suture runs through the north-eastern states of Maine, New Hampshire, Massachusetts and Connecticut. Rhode Island lies entirely to the east of the suture.

In Ireland

The estuary of the

River Shannon The River Shannon ( or archaic ') is the major river on the island of Ireland, and at in length, is the longest river in the British Isles. It drains the Shannon River Basin, which has an area of , – approximately one fifth of the area of I ...

(Ireland's largest river) follows the line of the Iapetus suture on the west coast. The suture reaches the east coast at

Clogherhead Clogherhead () is a fishing village in County Louth, Ireland. Located in a natural bay on the east coast it is bordered by the villages of Annagassan to the north and Termonfeckin to the south. It has a population of 2,145 according to the 2 ...

County Louth County Louth ( ; ) is a coastal Counties of Ireland, county in the Eastern and Midland Region of Republic of Ireland, Ireland, within the Provinces of Ireland, province of Leinster. Louth is bordered by the counties of County Meath, Meath to the ...

. Ireland's crust (and sedimentary rocks) to the north-west of the suture originally derives from Laurentia (proto-North America), while the crust to the south-east is Avalonian ("European").

On the Isle of Man (Niarbyl Fault)

Iapetus Suture - Niarbyl Fault - Isle of Man - kingsley - 23-JUN-09

The Niarbyl Fault is an exposed section of the Iapetus Suture as it crosses through the

Irish Sea The Irish Sea is a body of water that separates the islands of Ireland and Great Britain. It is linked to the Celtic Sea in the south by St George's Channel and to the Inner Seas off the West Coast of Scotland in the north by the North Ch ...

. It is readily visible in present-day Niarbyl on the southwest coast of

Isle of Man The Isle of Man ( , also ), or Mann ( ), is a self-governing British Crown Dependency in the Irish Sea, between Great Britain and Ireland. As head of state, Charles III holds the title Lord of Mann and is represented by a Lieutenant Govern ...

. The fault is manifested by two major rock groups which abut each other, both deposited by their respective, aforementioned continents – the Manx Group to the south-east and the Dalby Group to the north-west. The Niarbyl fault is evidence of two paleocontinents colliding:

on which present-day

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

is located and Laurentia which contains both present-day

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

and

Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...

. The fault is visible close to the shoreline downhill from the Niarbyl Cafe and Visitor Centre in Niarbyl.

In Great Britain

The Caledonian orogeny united the northern and southern portions of present-day

Great Britain Great Britain is an island in the North Atlantic Ocean off the north-west coast of continental Europe, consisting of the countries England, Scotland, and Wales. With an area of , it is the largest of the British Isles, the List of European ...

. The Iapetus Suture runs from the

Solway Firth The Solway Firth is an inlet on the west coast of Great Britain, forming part of the border between England and Scotland. The firth (a Scottish term for an inlet of the sea) divides Cumbria (including the Solway Plain) from Dumfries and Gallow ...

Lindisfarne Lindisfarne, also known as Holy Island, is a tidal island off the northeast coast of England, which constitutes the civil parishes in England, civil parish of Holy Island in Northumberland. Holy Island has a recorded history from the 6th centu ...

. The

Anglo-Scottish border The Anglo-Scottish border runs for between Marshall Meadows Bay on the east coast and the Solway Firth in the west, separating Scotland and England. The Firth of Forth was the border between the Picto- Gaelic Kingdom of Alba and the Angli ...

runs near and roughly parallel to the suture.

References

{{Reflist

External links

Animation by Manx Geological Survey

Niarbyl (Official Website of Manx National Heritage)
Historical oceans Silurian geology Geology of the United Kingdom Natural history of Europe Triple junctions Orogeny Suture zones