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98-635: Due to subsidence, water depths range from 3000 m in the south near its mouth to 400 m in the north. The Porcupine Basin lies on the Caledonian metamorphic basement and preserves up to 12 km of sedimentary strata from Late Palaeozoic to Quaternary which includes significant hydrocarbon reservoirs. Sediment was likely sourced from the uplifted Caledonian metamorphic rocks of the Porcupine Median Ridge. The basin lent its name to Operation Seabight , an Irish drug-bust of November 2008. The basin

196-572: A NW-dipping one beneath Laurentia. About 430 Ma accretion in the Southern Uplands and Ireland switched from being orthogonal (at a right angle) to a sinistrally (left-lateral) transpressive one as indicated by cleavage transecting folds counterclockwise. Turbidite deposition in the oceanic trench overlapped onto the Lakesman-Leinster terrane. Laurentia-Avalonia convergence and Iapetus Ocean subduction ceased by C. 420 Ma as indicated by

294-780: A collision with a continental fragment. The Shelveian Orogeny occurred particularly in the Shelve area in Shropshire , in eastern Wales and in the English Midlands in the Late Ordovician and was related to the Taconic orogeny . It formed the Shelve Anticline and Rytton Castle Syncline and was the most important tectonic event in the area between the Cambrian and Devonian . Folding

392-732: A collisional orogeny). Orogeny typically produces orogenic belts or orogens , which are elongated regions of deformation bordering continental cratons (the stable interiors of continents). Young orogenic belts, in which subduction is still taking place, are characterized by frequent volcanic activity and earthquakes . Older orogenic belts are typically deeply eroded to expose displaced and deformed strata . These are often highly metamorphosed and include vast bodies of intrusive igneous rock called batholiths . Subduction zones consume oceanic crust , thicken lithosphere, and produce earthquakes and volcanoes. Not all subduction zones produce orogenic belts; mountain building takes place only when

490-497: A delamination of the orogenic root beneath them. Mount Rundle on the Trans-Canada Highway between Banff and Canmore provides a classic example of a mountain cut in dipping-layered rocks. Millions of years ago a collision caused an orogeny, forcing horizontal layers of an ancient ocean crust to be thrust up at an angle of 50–60°. That left Rundle with one sweeping, tree-lined smooth face, and one sharp, steep face where

588-645: A few square kilometers. Three distinct mound provinces are located in the Porcupine Seabight: More than a thousand mounds have been identified in the Porcupine Seabight. The mounds are most common in the northern section, near the Hovland and Magellan Provinces. These carbonate mounds are still not fully understood. Their formation and growth patterns have been hotly debated and multiple hypotheses have been proposed. One hypothesis connects their formation to

686-515: A late Caledonian phase and as having been driven by the closure of the Iapetus Ocean . However, there is also an argument that it would more appropriate to regard it as a proto- Variscan orogeny. This is because this Devonian event postdated the collision of Avalonia with Laurentia by 15–20 million years and was coeval with the early phase of the Variscan orogeny (Eo-Variscan or Ligerian) and because it

784-582: A major continent-continent collision, is called an accretionary orogen. The North American Cordillera and the Lachlan Orogen of southeast Australia are examples of accretionary orogens. The orogeny may culminate with continental crust from the opposite side of the subducting oceanic plate arriving at the subduction zone. This ends subduction and transforms the accretional orogen into a Himalayan -type collisional orogen. The collisional orogeny may produce extremely high mountains, as has been taking place in

882-468: A mid- Silurian weakening of deformation in the accretionary wedge. Magma production should be larger in convergent tectonic regimes during subduction and markedly reduced with the change to post-subduction collisional regimes. However, during Iapetus subduction (455–425 Ma) this was low and intrusive rocks were largely absent across all terranes in the concerned area in this period. Most Acadian magmatism occurred post-subduction (425-390 Ma) in

980-412: A noncollisional orogenic belt, and such belts are sometimes called Andean-type orogens . As subduction continues, island arcs , continental fragments , and oceanic material may gradually accrete onto the continental margin. This is one of the main mechanisms by which continents have grown. An orogen built of crustal fragments ( terranes ) accreted over a long period of time, without any indication of

1078-442: A pronounced linear structure resulting in terranes or blocks of deformed rocks, separated generally by suture zones or dipping thrust faults . These thrust faults carry relatively thin slices of rock (which are called nappes or thrust sheets, and differ from tectonic plates ) from the core of the shortening orogen out toward the margins, and are intimately associated with folds and the development of metamorphism . Before

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1176-420: A regional tectonic setting with alternating transpression and transtension phases. High rates of magma generation coincided with a c. 418–404 Ma Early Devonian sinistral transtension phase. This decreased during the 404–394 Ma Acadian transpression. In addition, the Southern Uplands accretionary wedge lacks evidence of the presence of a volcanic arc as usually found near subduction zones. This has led to

1274-569: A stretching lineation perpendicular to the fold hinges. The Southern Belt and the rest of the Central belt underwent sinistral transpression . This reflects a Late Ordovician – Silurian change from an orthogonal to an oblique tectonic plate collision. In the Central Belt the cleavage transects folds in a clockwise sense and is accompanied by a sub-horizontal stretching lineation. In the Southern belt

1372-521: A transition from orthogonal compression to transpression during the later stages of Acadian deformation. This makes the island more similar to the Southern Uplands terrane of Scotland than the Lake District inlier in this respect. In Ireland the Acadian Orogeny affected the four main terranes of the island: Grampian, Midland Valley, Longford-Down and Leinster. Tectonic deformation was mild as

1470-623: A westward direction. The combined convergence of this microcontinent and the two continents created continental collisions between them, the mentioned orogenic events and the closure of the Iapetus and Tornquist oceans. Continental collisions started in the Mid Silurian and mountain building and ended in the Early Devonian (420–405 Ma). The Grampian orogeny involved collisions between two landmasses of Laurentia and an oceanic island arc in

1568-578: Is a large basement massif. It is part of a magmatic belt which, starting from the Lake District , to the north of this massif, bears record of the subduction of part of the Tornquist Sea beneath Avalonia and its closure. The closure of the Rheic Ocean , which took place soon after, occurred through subduction along the southern margin of this massif. The Trans-European Suture Zone or Tornquist Zone

1666-436: Is an exposed N–S trending thrust zone which marks the western limit of intense Caledonian deformation. The dominant structures are interpreted as having resulted from sinistral transpression , which involved strain partitioning of regional deformation between sinistral strike-slip movements in the east and NW-directed oblique thrusting and folding further to the west. This orogenic event also affected Scotland and

1764-570: Is composed mainly of the Manx Group and the Dalby Group which were deformed in a sinistral transpression zone during the sinistral, oblique closure of the Iapetus Ocean. Folds are transected clockwise by their cleavage , major strike-parallel sinistral faults and ductile shear zones thought to be related to this transpression. All primary folds have the same style and are associated with

1862-936: Is indicated by the absence of orogenic structures or high-pressure metamorphic rocks , which are either not present or buried. This event occurred close to the end of the Ordovician , 440 Ma. It docked with the Baltica margins in southern Denmark , the south-western corner of the Baltic Sea and Poland . It came to comprise Silesia in Poland , northern Germany , the Netherlands , Belgium and part of north-eastern France (the Ardennes Mountains). The Anglo-Brabant massif or London-Brabant Massif in central and southern England and in Belgium

1960-446: Is initiated along one or both of the continental margins of the ocean basin, producing a volcanic arc and possibly an Andean-type orogen along that continental margin. This produces deformation of the continental margins and possibly crustal thickening and mountain building. Mountain formation in orogens is largely a result of crustal thickening. The compressive forces produced by plate convergence result in pervasive deformation of

2058-422: Is still in use today, though commonly investigated by geochronology using radiometric dating. Based on available observations from the metamorphic differences in orogenic belts of Europe and North America, H. J. Zwart (1967) proposed three types of orogens in relationship to tectonic setting and style: Cordillerotype, Alpinotype, and Hercynotype. His proposal was revised by W. S. Pitcher in 1979 in terms of

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2156-473: Is taking place today in the Southern Alps of New Zealand). Orogens have a characteristic structure, though this shows considerable variation. A foreland basin forms ahead of the orogen due mainly to loading and resulting flexure of the lithosphere by the developing mountain belt. A typical foreland basin is subdivided into a wedge-top basin above the active orogenic wedge, the foredeep immediately beyond

2254-575: Is the area of the suture of Baltica and Eastern Avalonia. It runs from a portion of the North Sea close to Denmark , through southern Denmark, a portion of the Baltic Sea between Denmark and Poland (by Germany's Rügen Island), and through Poland. It then follows the eastern margin of the Eastern Carpathian Mountains in western Ukraine . Finally, it runs to the Black Sea . However, in

2352-754: Is the toe end of the Southern Uplands turbidite accretionary wedge onlapping or thrust onto the Avalonia continental margin. The broad deformation style and age of the Manx Group are very similar to the equivalent features of the Skiddaw Group in the Lake District and the Ribband Group in SE Ireland. This group is thought to be their regional equivalent. It underwent two main deformation phases which also affected

2450-449: The Alpine type orogenic belt , typified by a flysch and molasse geometry to the sediments; ophiolite sequences, tholeiitic basalts, and a nappe style fold structure. In terms of recognising orogeny as an event , Leopold von Buch (1855) recognised that orogenies could be placed in time by bracketing between the youngest deformed rock and the oldest undeformed rock, a principle which

2548-647: The Anglo-Scottish border . It consists of a series of faults with no traces of subduction , such as ophiolite remnants or oceanic trench -derived rocks. The Iapetus Suture also extends along the margin of the Baltoscandian platform of the Fennoscandian Peninsula which collided with the eastern margin of Greenland along the eastern margin of Laurentia in the Scandian orogeny. According to some authors,

2646-685: The Avalonia microcontinent collided. The orogeny is named for Caledonia , the Latin name for Scotland . The term was first used in 1885 by Austrian geologist Eduard Suess for an episode of mountain building in northern Europe that predated the Devonian period . Geologists like Émile Haug and Hans Stille saw the Caledonian event as one of several episodic phases of mountain building that had occurred during Earth's history . Current understanding has it that

2744-879: The Great Glen Fault which affected the Moine Supergroup and the Dalradian rocks in Scotland and the Shetland Islands through the Walls Boundary Fault , which is the northeast-ward extension of the Great Glen Fault. As mentioned above, the British Isles were separated and belonged to two different tectonic plates: Laurentia ( Scotland and northern and western Ireland ) and Avalonia ( England and Wales and

2842-613: The Himalayas for the last 65 million years. The processes of orogeny can take tens of millions of years and build mountains from what were once sedimentary basins . Activity along an orogenic belt can be extremely long-lived. For example, much of the basement underlying the United States belongs to the Transcontinental Proterozoic Provinces, which accreted to Laurentia (the ancient heart of North America) over

2940-650: The Maritime Provinces of Canada has been applied to the early Devonian deformation phase in the British Caledonides by analogy with the one that occurred in what is now North America . Late Caledonian orogeny is another term used in reference to this phase. This phase involved a soft docking or soft collision rather an orogen -causing hard continental collision like the Eastern Avalonia docking with Baltica. This orogenic event has been interpreted as

3038-512: The Rodinia supercontinent . The majority of its bulk consisted of the landmass of Gondwana . Near the end of the Neoproterozoic, during the breakup of this supercontinent, Laurentia and Baltica rifted from the western ( Amazonian craton ) and northern (African) margins of Gondwana respectively. Laurentia first drifted westward away from Gondwana and then migrated northward. This led to

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3136-683: The San Andreas Fault , restraining bends result in regions of localized crustal shortening and mountain building without a plate-margin-wide orogeny. Hotspot volcanism results in the formation of isolated mountains and mountain chains that look as if they are not necessarily on present tectonic-plate boundaries, but they are essentially the product of plate tectonism. Likewise, uplift and erosion related to epeirogenesis (large-scale vertical motions of portions of continents without much associated folding, metamorphism, or deformation) can create local topographic highs. Eventually, seafloor spreading in

3234-628: The Scandinavian Caledonides . The first phase that is often included in the Caledonian orogeny is the Finnmarkian Orogeny, which was an early deformation event in Arctic (northern) Norway which preceded the Scandian phase (see below) in this area. Its onset has been dated at c. 500 Ma (Late Cambrian ). It continued to c. 460 Ma and was reactivated in the Scandian phase at ~425–415 Ma. According to van Roermund and Brueckner (2004), there

3332-637: The Sudetes Mountains and the Eastern Carpathians, it evolved through the Variscan and the Alpine orogenies, rather than the Caledonian one. The Scandian phase involved a collision between eastern Greenland on the eastern margin of Laurentia and the margin of the Baltoscandian platform of the Fennoscandian peninsula of Baltica. It involved the Scandinavian Caledonides in what is now Norway and

3430-634: The late Devonian (about 380 million years ago) with the Antler orogeny and continuing with the Sonoma orogeny and Sevier orogeny and culminating with the Laramide orogeny . The Laramide orogeny alone lasted 40 million years, from 75 million to 35 million years ago. Orogens show a great range of characteristics, but they may be broadly divided into collisional orogens and noncollisional orogens (Andean-type orogens). Collisional orogens can be further divided by whether

3528-516: The opening of the Iapetus Ocean between Laurentia, Baltica and Gondwana. Its initial opening phase was between the adjacent Laurentia and Baltica (to the West and East respectively) and caused the two to breakup c. 615 Ma or 590 Ma. Then the part between Laurentia and Gondwana (to the east), opened c. 550 Ma. Further spreading of the Iapetus Ocean also caused Laurentia and Baltica to move away from each other. Baltica drifted northward, too. This involved

3626-475: The Caledonian continental collisions involved another microcontinent, Armorica (southern Portugal , most of the north of France and parts of southern Germany and the Czech Republic ), even smaller than Avalonia. This microcontinent probably did not form one consistent unit, but was instead a series of fragments, of which the current Armorican and Bohemian Massifs are the most important. The ocean between

3724-506: The Caledonian orogeny encompasses a number of tectonic phases that can laterally be diachronous , meaning that different parts of the mountain range formed at different times. The name "Caledonian" can therefore not be used for an absolute period of geological time, it applies only to a series of tectonically related events. In the Neoproterozoic most of the Earth's landmasses were united in

3822-506: The Dalby Group: a) a pervasive slaty cleavage associated with gently to moderately plunging folds which also affected many of the minor igneous intrusions , b) a gently dipping crenulation cleavage associated with small folds verging towards the bedding dip direction. There are several ductile shear zones which run subparallel to the Manx Group northeast-oriented boundary faults which indicate predominantly sinistral shear and possibly

3920-564: The Hercynian orogeny. Orogeny Orogeny ( / ɒ ˈ r ɒ dʒ ə n i / ) is a mountain - building process that takes place at a convergent plate margin when plate motion compresses the margin. An orogenic belt or orogen develops as the compressed plate crumples and is uplifted to form one or more mountain ranges . This involves a series of geological processes collectively called orogenesis . These include both structural deformation of existing continental crust and

4018-469: The Iapetus Ocean orthogonally (at a right angle ). Its drift included an up to 55° counterclockwise rotation with respect to the subduction zone to its north, mainly in the 470–450 Ma timeframe. It moved significantly faster than Baltica but slowed down to a rate comparable to that of the latter in the Late Ordovician when it got close to it. The main phases of the Caledonian orogeny resulted from

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4116-535: The Iapetus Ocean outboard the main margin of the Laurentia tectonic plate (the future North America). There two Laurentian landmasses were Scotland and northern and western Ireland . The other parts of the British Isles ( England and Wales and the rest of Ireland) were part of the Avalonia microcontinent. Two parts of Avalonia have been distinguished, a western and an eastern one. The term Western Avalonia refers to

4214-537: The Lakesman terrane and north Wales . Transpression resulted in regionally clockwise transecting sinistral transpressive cleavages which were superimposed on pre-existing structures. Folding northwest of the Iapetus Suture is weak and this northward weakening of deformation may indicate that it is linked with Rheic Ocean subduction rather than Iapetus Ocean closure. The Lake District in north-western England

4312-620: The Late Jurassic crustal extension, but also by compressional deformation during the latest Jurassic–earliest Cretaceous. Inverted structures found in the basin formed may be related to the initial closure of the Alpine Tethys. The latest Jurassic to Cretaceous uplift, inversion and erosion observed in many basins in Western Europe may also be associated with this event. A large number and variety of sea life and cetaceans migrate through

4410-675: The NE into a marine basin which bridged the Avalonia and Laurentia margins. The tectonic contact between the two groups has been correlated either with the Windermere Supergroup (Lake District) turbidites or the Riccarton Group, ( Southern Uplands terrane ).The former hypothesis implies that the Dalby Group was originally deposited on the Manx Group and was subsequently faulted into its present day relationship. The latter one implies that it

4508-413: The Ordovician; these continents were by then further north. It also involved the consumption of both the Iapetus Ocean and the Tornquist Ocean along its northern margin. Avalonia's motion was related to slab pull created by the subduction of the Iapetus Ocean beneath the margin of Laurentia to its northwest and possibly also by ridge push created by the spreading of the Rheic Ocean. It migrated across

4606-425: The Pontesford-Linley fault system and folding in pre-Ashgill strata, uplift of the adjacent Towi Anticline and igneous activity. The main orogenic events or phases of the Caledonian orogenic cycle were related to the final closure of the Iapetus Ocean. They were, in sequential order, the Grampian phase, the docking of Eastern Avalonia with Baltica, the Scandian phase and the Acadian phase. The latter involved: A)

4704-460: The SE and east) ... and each tectonic event throughout this 200 million years can be considered as an orogenic phase." This includes tectonic events which were smaller, localised and predated the more well-known main phases of this orogeny. In this definition, the Taconic and Acadian orogenies in what today is North America are included in the phases of the Caledonian orogeny. Some early phases of deformation and metamorphism are recognised in

4802-412: The Swedish areas by its border. It occurred from the Wenlock Epoch of the Silurian to the Mid Devonian (430–380 Ma). Gee et al. (2013) and Ladenberger et al. (2012) propose a revised onset dating set at 440 Ma, however, there is no consensus about this. The Scandian orogenic event also led to the formation of mountains of Queen Louise Land (or Dronning Louise Land) in north-eastern Greenland . It

4900-452: The Tinure Fault is the surface expression of the Iapetus Suture zone. The Iapetus Suture is the lineament where the Caledonian collision closed the Iapetus Ocean. In Ireland it runs from the estuary of the River Shannon on the Atlantic coast to Clogherhead on the Irish Sea . It crosses this sea and is exposed in the Niarbyl Fault in the southern part of the northern coast of the Isle of Man . In Britain it runs roughly parallel to

4998-497: The acceptance of plate tectonics , geologists had found evidence within many orogens of repeated cycles of deposition, deformation, crustal thickening and mountain building, and crustal thinning to form new depositional basins. These were named orogenic cycles , and various theories were proposed to explain them. Canadian geologist Tuzo Wilson first put forward a plate tectonic interpretation of orogenic cycles, now known as Wilson cycles. Wilson proposed that orogenic cycles represented

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5096-463: The accretion of the Armorican terranes with the southern margin of Laurussia in the Carboniferous Variscan orogeny (about 340 million years ago). The Rhenohercynian basin , a back-arc basin , formed at the southern margin of Euramerica just after the Caledonian orogeny. According to these authors, a small rim from Euramerica rifted off when this basin formed. The basin closed when these Caledonian deformed terranes were accreted again to Laurussia during

5194-414: The active front, a forebulge high of flexural origin and a back-bulge area beyond, although not all of these are present in all foreland-basin systems. The basin migrates with the orogenic front and early deposited foreland basin sediments become progressively involved in folding and thrusting. Sediments deposited in the foreland basin are mainly derived from the erosion of the actively uplifting rocks of

5292-538: The area, which is regarded as a prominent habitat for them. This includes many fin whales and blue whales , the first confirmed sighting of the latter in Irish waters being made here as recently as 2008. The Porcupine Seabight contains some of the most well investigated deep-water carbonate mounds in the world. Carbonate mounds, which can reach heights of up to 600 m, are formed from the accumulation of cold-water corals that trap fine-grained sediment. These mounds can be found at depths of 500 to 1000 m over areas of

5390-400: The basin as a result of rotation of the Porcupine Ridge away from the Irish shelf. There are a number of unconformities found within the basin. Folding, uplift and related erosion during the Jurassic to Cretaceous produced the regional Base Cretaceous Unconformity in the northern section. Accommodation for the Early Cretaceous succession was not only generated by thermal subsidence following

5488-464: The basin. The presence of oil shown at different levels of the stratigraphy attests to the ability of fluids to move from deep to shallower levels in the Mesozoic and Cenozoic . Major igneous activity, of Early Cretaceous and Palaeogene times, is also likely to have produced fluid circulation patterns and some additional fluid transport channels along the flanks of volcanic centres, through associated dyke systems and compaction-associated faults above

5586-584: The collision is with a second continent or a continental fragment or island arc. Repeated collisions of the later type, with no evidence of collision with a major continent or closure of an ocean basin, result in an accretionary orogen. Examples of orogens arising from collision of an island arc with a continent include Taiwan and the collision of Australia with the Banda arc. Orogens arising from continent-continent collisions can be divided into those involving ocean closure (Himalayan-type orogens) and those involving glancing collisions with no ocean basin closure (as

5684-466: The collision was strongly oblique with sinistral transpression and without substantial crustal thickening . Devonian to Carboniferous rocks rest unconformably on Cambrian to Silurian folded and cleaved rocks. There were igneous intrusions with plutons and batholiths . The terrane has three relief belts. The northern belt and the northernmost part of the Central Belt underwent pure shear deformation with an axial planar cleavage and

5782-419: The combined continental mass of Laurentia, Baltica and Avalonia (called Euramerica, Laurussia or Old Red Continent ) and Armorica is called the Rheic Ocean . The paleogeographic position of the Armorica crustal fragments between the Ordovician and Carboniferous is highly disputed though. There are indications that the Bohemian Massif started moving northward from the Ordovician onward, but many authors place

5880-417: The convergence of Baltica, Laurentia and Avalonia which led to the closure of the Iapetus Ocean. McKerrow et al. (2000) give a definition of the Caledonian orogeny which includes "all the Cambrian , Ordovician , Silurian and Devonian tectonic events associated with the development and closure of those parts of the Iapetus Ocean which were situated between Laurentia (to the NW) and Baltica and Avalonia (to

5978-420: The course of 200 million years in the Paleoproterozoic . The Yavapai and Mazatzal orogenies were peaks of orogenic activity during this time. These were part of an extended period of orogenic activity that included the Picuris orogeny and culminated in the Grenville orogeny , lasting at least 600 million years. A similar sequence of orogenies has taken place on the west coast of North America, beginning in

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6076-539: The creation of new continental crust through volcanism . Magma rising in the orogen carries less dense material upwards while leaving more dense material behind, resulting in compositional differentiation of Earth's lithosphere ( crust and uppermost mantle ). A synorogenic (or synkinematic ) process or event is one that occurs during an orogeny. The word orogeny comes from Ancient Greek ὄρος ( óros )  'mountain' and γένεσις ( génesis )  'creation, origin'. Although it

6174-427: The crust of the continental margin ( thrust tectonics ). This takes the form of folding of the ductile deeper crust and thrust faulting in the upper brittle crust. Crustal thickening raises mountains through the principle of isostasy . Isostacy is the balance of the downward gravitational force upon an upthrust mountain range (composed of light, continental crust material) and the buoyant upward forces exerted by

6272-454: The dense underlying mantle . Portions of orogens can also experience uplift as a result of delamination of the orogenic lithosphere , in which an unstable portion of cold lithospheric root drips down into the asthenospheric mantle, decreasing the density of the lithosphere and causing buoyant uplift. An example is the Sierra Nevada in California. This range of fault-block mountains experienced renewed uplift and abundant magmatism after

6370-581: The development of geologic concepts during the 19th century, the presence of marine fossils in mountains was explained in Christian contexts as a result of the Biblical Deluge . This was an extension of Neoplatonic thought, which influenced early Christian writers . The 13th-century Dominican scholar Albert the Great posited that, as erosion was known to occur, there must be some process whereby new mountains and other land-forms were thrust up, or else there would eventually be no land; he suggested that marine fossils in mountainsides must once have been at

6468-565: The docking of England and Wales (which were part of eastern Avalonia) with eastern and southern Ireland with Scotland and the rest of Ireland (which were part of Laurentia). B) the amalgamation of terranes of Western Avalonia with the eastern margin of the main landmass of Laurentia (see Acadian orogeny article for this orogeny). During the final part of its northwestward migration, Avalonia converged with Baltica and Laurentia to its northeast and northwest respectively. After its amalgamation with Eastern Avalonia, Baltica converged with Laurentia in

6566-453: The edge of the uplifted layers are exposed. Although mountain building mostly takes place in orogens, a number of secondary mechanisms are capable of producing substantial mountain ranges. Areas that are rifting apart, such as mid-ocean ridges and the East African Rift , have mountains due to thermal buoyancy related to the hot mantle underneath them; this thermal buoyancy is known as dynamic topography . In strike-slip orogens, such as

6664-409: The final form of the majority of old orogenic belts is a long arcuate strip of crystalline metamorphic rocks sequentially below younger sediments which are thrust atop them and which dip away from the orogenic core. An orogen may be almost completely eroded away, and only recognizable by studying (old) rocks that bear traces of orogenesis. Orogens are usually long, thin, arcuate tracts of rock that have

6762-442: The hypotheses that arc rocks were eroded and thus have not been preserved, that the arc was displaced by lateral movement along strike-slip faults or that this is due to flat–slab subduction , which reduces magmatism rates. Nelison et al. (2009) propose an Iapetus Ocean subducting slab breakoff model to account for the intrusive rocks in the Grampian terrane being emplaced post-subduction. However, Miles at al. (2016) note that

6860-461: The intrusive rocks in the Trans-Suture Suite and in all the terranes in the region are similar in age and geochemistry. Thus, they argue that the common mechanism for the whole region involved an Iapetus Ocean slab which did not just break off. It also peeled back below the Iapetus Suture for c. 100 km to the SE below Avalonia. Thus they invoke a model of slab drop-off caused by lithospheric mantle delamination . The Lakesman terrane covers

6958-423: The main Jurassic source rocks in the Porcupine Basin are mature to overmature. Hydrocarbon generation started in Late Cretaceous times for the deepest Jurassic sequences, and is still ongoing today along the edges of the basin. The carbonate mounds found in the basin may in fact be surface expressions of an underlying active petroleum system. There are likely to be multiple potential fluid migration pathways within

7056-538: The mountain range, although some sediments derive from the foreland. The fill of many such basins shows a change in time from deepwater marine ( flysch -style) through shallow water to continental ( molasse -style) sediments. While active orogens are found on the margins of present-day continents, older inactive orogenies, such as the Algoman , Penokean and Antler , are represented by deformed and metamorphosed rocks with sedimentary basins further inland. Long before

7154-772: The north of England down to the Wensleydale in North Yorkshire and crosses the Irish Sea passing by the Island of Anglesey off Wales . Its continuation in eastern Ireland is the Leinster terrane. The combined terrane is termed Leinster-Lakesman terrane. It lies on the southern margin of the Iapetus Suture . It includes the Lake District and the Isle of Man . The Acadian Orogeny affected

7252-448: The northern margin of Gondwana ( Amazonia and northwest Africa) close to the original position of Baltica which had been to its north. Its rifting involved the opening and spreading of the Rheic Ocean to its south, which separated it from Gondwana. This rifting and opening were coeval with and may be related to subduction onset in the Iapetus Ocean. The drift of Avalonia was towards the positions where Baltica and Laurentia had been in

7350-416: The ocean basin comes to a halt, and continued subduction begins to close the ocean basin. The closure of the ocean basin ends with a continental collision and the associated Himalayan-type orogen. Erosion represents the final phase of the orogenic cycle. Erosion of overlying strata in orogenic belts, and isostatic adjustment to the removal of this overlying mass of rock, can bring deeply buried strata to

7448-619: The opening of the Tornquist Ocean which separated it from the northern margin of Gondwana to the south. The onset of Baltica rifting and the Tornquist Ocean opening are difficult to date due to insufficient palaeomagnetic data but must have occurred in similar times as those of Laurentia and the Iapetus Ocean. Either in the Late Precambrian or Early Ordovician , the Avalonia microcontinent started to drift northwestward from

7546-656: The outer Hebrides , causing thrusting in the Northern Highlands which culminated in the development of the Moine Thrust Belt , Ben Hope Thrust and Naver- Sgurr Beag Thrust (435–420 Ma) and led to igneous intrusion in Galloway and the Southern Uplands (c. 400 Ma) in Scotland and the enlargement of the Lake District batholith in northern England . All this spanned the Iapetus Suture zone (see below). It also caused northeast trending strike-slip faults, such as

7644-416: The periodic opening and closing of an ocean basin, with each stage of the process leaving its characteristic record on the rocks of the orogen. The Wilson cycle begins when previously stable continental crust comes under tension from a shift in mantle convection . Continental rifting takes place, which thins the crust and creates basins in which sediments accumulate. As the basins deepen, the ocean invades

7742-602: The rest of Ireland). The Early Devonian Acadian event in this area saw the amalgamation of these landmasses to form the British Isles as they are now. This occurred through NW-dipping subduction of Avalonian oceanic crust beneath the southern margins of the Laurentian landmasses. Since the 1980s the term Acadian , which referred to the Late Silurian to Early Devonian orogeny in the Northern Appalachians , and

7840-441: The rift zone, and as the continental crust rifts completely apart, shallow marine sedimentation gives way to deep marine sedimentation on the thinned marginal crust of the two continents. As the two continents rift apart, seafloor spreading commences along the axis of a new ocean basin. Deep marine sediments continue to accumulate along the thinned continental margins, which are now passive margins . At some point, subduction

7938-520: The same regional cleavage suggesting that they are roughly coeval. There is ductile deformation in some localities and a broad shear zone in the Langness Peninsula which deform the primary cleavage and are thought to have formed during or soon after the main deformation phase. The Dalby Group was overthrust onto the Manx Group, probably in the early Devonian. During the final stage of the Iapetus Ocean closure its turbidites were deposited from

8036-491: The sea-floor. Orogeny was used by Amanz Gressly (1840) and Jules Thurmann (1854) as orogenic in terms of the creation of mountain elevations, as the term mountain building was still used to describe the processes. Elie de Beaumont (1852) used the evocative "Jaws of a Vise" theory to explain orogeny, but was more concerned with the height rather than the implicit structures created by and contained in orogenic belts. His theory essentially held that mountains were created by

8134-444: The seepage of hydrocarbons, either along faults or from former gas-hydrate layers, as a response to glacial-interglacial changes in current patterns and sea levels. Another hypothesis relates their distribution to nutrient fluxes driven by specific oceanic conditions, notably the interaction of internal waves, formed at the boundary between different water masses, with the continental slope. Modelling of hydrocarbon generation shows that

8232-409: The south of the suture) which were at the Laurentia and Avalonia margins respectively. The emplacement of the plutons occurred after the subduction of the Iapetus Ocean ended. The Southern Uplands terrane is thought to be an accretionary wedge . Deep marine sedimentation here in response to subduction begun 455 Ma and marked the switch from an initial SE-dipping Iapetus subduction under Avalonia to

8330-414: The squeezing of certain rocks. Eduard Suess (1875) recognised the importance of horizontal movement of rocks. The concept of a precursor geosyncline or initial downward warping of the solid earth (Hall, 1859) prompted James Dwight Dana (1873) to include the concept of compression in the theories surrounding mountain-building. With hindsight, we can discount Dana's conjecture that this contraction

8428-423: The subduction produces compression in the overriding plate. Whether subduction produces compression depends on such factors as the rate of plate convergence and the degree of coupling between the two plates, while the degree of coupling may in turn rely on such factors as the angle of subduction and rate of sedimentation in the oceanic trench associated with the subduction zone. The Andes Mountains are an example of

8526-460: The surface. The erosional process is called unroofing . Erosion inevitably removes much of the mountains, exposing the core or mountain roots ( metamorphic rocks brought to the surface from a depth of several kilometres). Isostatic movements may help such unroofing by balancing out the buoyancy of the evolving orogen. Scholars debate about the extent to which erosion modifies the patterns of tectonic deformation (see erosion and tectonics ). Thus,

8624-449: The volcanic centres. The overall morphology of the basin, shallowing towards the margins and towards the northern section, is likely to have facilitated fluid migration in Cenozoic times towards these shallower regions. All of these point towards the movement of mantle-derived fluids within the basin, directed towards the basin margins. Caledonian orogeny The Caledonian orogeny

8722-799: The westernmost part of the microcontinent which amalgamated the east coast of the main part of the Laurentia tectonic plate (what is now North America) to the west in the area of the northern Appalachians and the Maritimes . Eastern Avalonia refers to a) the part which amalgamated with Baltica , b) England a Wales and eastern and south-eastern Ireland which amalgamated with Scotland and the north and west of Ireland (which were part of Laurentia). The easternmost part of Eastern Avalonia amalgamated with Baltica through an oblique soft docking governed by dextral strike-slip convergence and shear , rather than through an orogen-causing hard continental collision . This

8820-435: Was a mountain-building cycle recorded in the northern parts of the British Isles , the Scandinavian Caledonides , Svalbard , eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian , roughly 490–390 million years ago ( Ma ). It was caused by the closure of the Iapetus Ocean when the Laurentia and Baltica continents and

8918-681: Was a distinct orogenic event which was separate and slightly younger than that of the Finnmarkian one, which they dated at 455 Ma. They named it the Jämtlandian Orogeny . It involved the Seve Nappe Complex of the Swedish Caledonides in central Sweden , which is interpreted as the stretched outermost edge of Baltica. Contrary to the previous opinion that it had been subducted beneath an oceanic island arc , they propose that it involved

9016-608: Was accompanied by late stage igneous intrusions . The event caused a major unconformity in Shropshire with considerable erosion before the deposition of sediments in the Llandovery Epoch of the Silurian (444–443 Ma). There was no break in sediments in the area until the end of the Early Devonian , which was caused by the Acadian Orogeny in the British Isles . It was associated with dextral (right-lateral) strike-slip movement in

9114-591: Was at the north-western margin of the English part of Eastern Avalonia which converged and collided with Scotland and was thus involved in the Acadian phase. Generally, Acadian deformation metamorphosed mudrocks throughout various geologic formations of the district into slates by creating slaty cleavages . The Early Palaeozoic rocks in the Isle of Man in the Irish Sea crop out close to or probably on Iapetus suture . The island lies immediately to its SE. The island

9212-399: Was due to the cooling of the Earth (aka the cooling Earth theory). The cooling Earth theory was the chief paradigm for most geologists until the 1960s. It was, in the context of orogeny, fiercely contested by proponents of vertical movements in the crust, or convection within the asthenosphere or mantle . Gustav Steinmann (1906) recognised different classes of orogenic belts, including

9310-534: Was formed during numerous subsidence and rifting periods between the Late Carboniferous and Late Cretaceous . Repeated stages of uplift and subsidence were responsible for sediment input, the formation of accommodation space and the creation of steep basin margins: Extreme stretching of the lithosphere has been documented in the Porcupine Basin. This stretching is especially found in the southern part of

9408-459: Was not related to the Iapetus Ocean. It also has been argued that, although the Acadian orogeny in the British Isles involved the Iapetus Ocean closure, its driving force was actually a push from the south caused by the northward subduction of the Rheic Ocean which lied to the south of Avalonia and separated it from Gondwana . The closure of this ocean involved the (early) Eo-Variscan collision of Gondwana-related terranes in which Eastern Avalonia

9506-458: Was peripherally involved. Subduction of the Iapetus Ocean occurred beneath the Midland Valley terrane of Scotland. There is a Trans-Suture Suite of intrusive plutons which straddle both sides of the trace of the Iapetus Suture in the Southern Uplands terrane of Scotland (to the north of the suture) and the Lakesman-Leinster terrane of northern England and eastern Ireland (to

9604-494: Was used before him, the American geologist G. K. Gilbert used the term in 1890 to mean the process of mountain-building, as distinguished from epeirogeny . Orogeny takes place on the convergent margins of continents. The convergence may take the form of subduction (where a continent rides forcefully over an oceanic plate to form a noncollisional orogeny) or continental collision (convergence of two or more continents to form

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