Acadian orogeny

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Paleogeographic development of Baltic and Laurentia from the Ordovician to the Devonian according to the “Greater Avalonia” hypothesis (surrounding continents are not shown). Bottom: Taconic phase in North America, Iapetus Ocean is still wide open. Middle: Main phase of the Caledonian orogeny in Europe (Scandinavian phase and formation of the North German-Polish Caledonids), Iapetus Ocean is already severely restricted, Acadian phase is imminent. Above: Iapetus Ocean is completely closed, the Acadian phase and with it Caledonian orogeny are complete.
The Central Devonian Schunemunk conglomerate in the US state of New York is considered to be the molasses of the Acadian fold belt.

A mountain formation or a tectonic deformation event that occurred in the early and middle Devonian ( Pragium - Eifelium ) on the eastern edge of present-day North America and in present-day northwestern Europe is referred to as the Acadian Orogeny or Acadian Phase (spelling also possible with "c" instead of "k") is demonstrable. The typical region of this folding event are the northern Appalachian Mountains . The Acadian orogeny was followed in time to the Taconic orogeny in the Ordovician (equivalent to Gram european orogeny to the British Isles ) and went the Alleghenischen orogeny in Carboniferous advance. *

etymology

The name was coined in 1923 by the American geologist Charles Schuchert and is derived from Akadien , the old name of the maritime provinces in eastern Canada.

Paleoplate tectonic models

The Acadian orogeny is considered to be the result of the collision of the Perigondwanian continental splinter Avalonia with the southeastern edge of the North American craton (Laurentia). The nature of this continental splinter is controversial, although two extreme positions can be contrasted. One regards Avalonia ("Avalonia sensu stricto ") as one of at least four Perigondwanic microcontinents (" crustal ribbons ") that were successively attached to the Laurentian continental margin between the middle Ordovician and the late Devonian. The other is based on a larger Perigondwian continental splinter (" composite Avalonia "), the north drift of which narrowed the so-called Iapetus Ocean more and more and at the rear of which the Rhine Ocean opened. According to this model, the eastern part of "Großavalonias" collided with the southwestern edge of the European craton (Baltica) in the late Ordovician and caused the formation of the North German-Polish Caledonids (see also →  Tornquist Zone ). In addition, the continental blocks Laurentias and Balticas collided in the late Silurian and early Devonian and formed a major continent called Laurussia until the Variscan Orogeny.

Yet another model moves away from the interpretation as a continent-continent collision event. Instead, it postulates that the closure of the Iapetus Ocean was already completed at the beginning of the Silurian, and that the Acadian phase was due to the upper plate deformation in a subduction zone of the Andean type on the northern edge of the Rheic Ocean or on the southern edge of Laurussia.

classification

Based on the “Greater Avalonia” model, the Acadian orogeny represents the final closure of the Iapetus Ocean , which opened in the late Neoproterozoic between the large southern continent of Gondwana and the smaller northern continents of Laurentia and Baltica. In this context, the Acadian orogeny is considered to be the last deformation event of the Caledonian orogeny , ** that orogeny cycle that includes all collisions on the northern edge or within the Iapetus Basin.

The consequence of an interpretation of the Acadian (and Neo-Acadian) orogeny as an upper plate deformation event as a result of the subduction of the Rheic Ocean under the Laurussian Bloc is that it must then no longer be seen as a Caledonian event, but rather as a "proto-Variscan" event.

Remarks

*Sometimes, between the Taconic and the Acadian, another, the Salinian orogeny, is postulated. This depends on how the information contained in the rocks is interpreted, which in turn often leads to different paleoplate tectonic models .
**According to the alternative model, after Avalonia's annexation to the Laurentian continental margin, another microcontinent called Meguma collides with Avalonia in the late Devonian. The term Neo-Acadian orogenesis is used for this deformation event.

Individual evidence

  1. ↑ J. Verniers, T. Pharaoh, L. André, TN Debacker, W. De Vos, M. Everaerts, A. Herbosch, J. Samuellson, M. Vecoli: The Cambrian to mid Devonian basin development and deformation history of Eastern Avalonia , east of the Midlands Microcraton: new data and a review. In JA Winchester, TC Pharaoh, J. Verniers (Eds.): Palaeozoic Amalgamation of Central Europe. Geological Society, London, Special Publications. Vol. 201, 2002, pp. 47-93, doi : 10.1144 / GSL.SP.2002.201.01.04
  2. ^ WS McKerrow, C. Mac Niocaill, JF Dewey: The Caledonian Orogeny redefined. Journal of the Geological Society. Vol. 157, 2000, pp. 1149–1154, doi : 10.1144 / jgs.157.6.1149 (alternative full text access : University of Oxford )
  3. ↑ John R. Mendum: Late Caledonian (Scandian) and Proto-Variscan (Acadian) orogenic events in Scotland. Journal of the Open University Geological Society. Vol. 33, No. 1, 2012, pp. 37–51 ( online )
  4. ↑ a b c J. Brendan Murphy, J. Duncan Keppie: The Acadian Orogeny in the Northern Appalachians. International Geology Review. Vol. 47, No. 7, 2005, pp. 663-687, doi : 10.2747 / 0020-6814.47.7.663
  5. ↑ a b c J. Brendan Murphy, J. Duncan Keppie, R. Damian Nance, Jaroslav Dostal: Comparative evolution of the Iapetus and Rheic Oceans: A North America perspective. Gondwana Research. Vol. 17, No. 2–3, 2010, pp. 482–499, doi : 10.1016 / j.gr.2009.08.009
  6. ↑ JA Winchester, TC Pharaoh, J. Verniers: Palaeozoic amalgamation of Central Europe: an introduction and synthesis of new results from recent geological and geophysical investigations. In JA Winchester, TC Pharaoh, J. Verniers (Eds.): Palaeozoic Amalgamation of Central Europe. Geological Society, London, Special Publications. Vol. 201, 2002, pp. 1–18, doi : 10.1144 / GSL.SP.2002.201.01.01 (free full text access )
  7. ↑ DM Chew, CJ Stillman: Late Caledonian orogeny and magmatism. In: Charles H. Holland, Ian S. Sanders (Eds.): The Geology of Ireland. 2nd edition, Dunedin Academic Press, Edinburgh 2009, ISBN 978-1-903765-72-2 , pp. 143-173 (free full text: Researchgate ).