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Horst (geology)

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Diagram of horsts and grabens

A horst, in physical geography and geology, is a raised fault block bounded by normal faults.[1] Horsts are typically found together with grabens. While a horst is lifted or remains stationary, the grabens on either side subside.[2] This is often caused by extensional forces pulling apart the crust. Horsts may represent features such as plateaus, mountains, or ridges on either side of a valley.[3] Horsts can range in size from small fault blocks up to large regions of stable continent that have not been folded or warped by tectonic forces.[2]

The word Horst, apart from being a common name, in general German refers to an "eagle's nest". The actual older meaning is "(wooded) hill top", "mass" or "heap", basically anything elevated. The term, as used in "Bergmannssprache", the special "language" of miners, was first adopted in the geological sense in 1883 by Eduard Suess in The Face of the Earth.[4][5][note 1]

Geomorphology

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Horsts may have either symmetrical or asymmetrical cross-sections. If the normal faults to either side have similar geometry and are moving at the same rate, the horst is likely to be symmetrical and roughly flat on top. If the faults on either side have different rates of vertical motion, the top of the horst will most likely be inclined and the entire profile will be asymmetrical. Erosion also plays a significant role in how symmetrical a horst appears in cross-section.[citation needed]

Horsts and hydrocarbon exploration

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Horsts can form structural petroleum traps.[6] In many rift basins around the world, the vast majority of discovered hydrocarbons are found in conventional traps associated with horsts.[citation needed] For example, much of the petroleum found in the Sirte Basin, Libya (of the order of tens of billions of barrels of reserves) are found on large horst blocks[7] such as the Zelten Platform and the Dahra Platform and on smaller horsts such as the Gialo High.[8]

Examples

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The Vosges Mountains in France and Black Forest in Germany are examples of horsts, as are the Table, Jura, the Dole mountains and the Rila – Rhodope Massif including the well defined horsts of Belasitsa (linear horst), Rila mountain (vaulted domed shaped horst) and Pirin mountain – a horst forming a massive anticline situated between the complex graben valleys of Struma and that of Mesta.[9][10][11]

Larger areas where the continent remains stable with horizontal table-land stratification can be considered horsts, such as the Russian Plain, Arabia, India and Central South Africa. This is in distinction to folded regions such as some mountain chains of Eurasia.[2]

The Midcontinent Rift System in North America is marked by a series of horsts extending from Lake Superior to Kansas.[12]

The Rwenzori Mountains in the East African Rift are an upthrown fault block, and are the highest non-volcanic, non-orogenic mountains in the world.[13][14]

The Vosges Mountains in France were formed by isostatic uplift in response to the opening of the Rhine Graben, a major extensional basin.[15]

Another example of a horst in France is the Canigou (or Canigó) massif, near the eastern end of the Pyrenees. It is underlain by Paleozoic granite and gneiss, and Ediacaran metasediments. Rising to an altitude of 2785 metres (over 9,000 feet), the massif is approximately 20 kilometres from north to south and 15 kilometres from west to east.[16] The Massif du Canigou rises distinctly, and in many places abruptly, from surrounding landscapes. In this respect, it is said to be "exceptional in France".[17] For example, it rises by more than 2000 metres from Vernet-les-Bains, at the north-western foot of the massif, to the summit, in less than seven kilometres. On all sides (except the south) normal faults lie close to the line of that prominent topographical change. Uplift of the Canigou massif has taken place during the past 30 million years, at variable rates. That is associated with tectonic extension during the same period, with such extension having also caused the development of nearby geological basins, such as that of the Roussillon Plain [fr].[18] Uplift of the Canigou massif may still be taking place.[19]

See also

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Notes

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  1. ↑ Originally published in 1883 in German as "Das Antlitz der Erde", translated and published in English in 1904

References

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  1. ↑ Fossen H. (2010-07-15). Structural Geology. Cambridge University Press. p. 154. ISBN 9781139488617.
  2. 1 2 3 Wikisource One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Horst". Encyclopædia Britannica. Vol. 13 (11th ed.). Cambridge University Press. p. 740.
  3. ↑ "Horst and Graben". National Park Service. 2020-04-22.
  4. ↑ "horst". Etymonline.
  5. ↑ Suess, Edward (1904). The Face of the Earth. Translated by Sollas, Hertha B C. Clarendon Press.
  6. ↑ "Hydrocarbon Traps". Geology In. 2014-12-05. Retrieved 2021-12-13.
  7. ↑ Parsons, M.G.; Zagaar, A.M.; Curry, J.J. (1980). "Hydrocarbon occurrences in the Sirte Basin, Libya". Facts and Principles of World Petroleum Occurrence Memoirs. 6: 723–732. Retrieved 28 June 2022.
  8. ↑ Selley, R. C. (1 January 1997). "Chapter 3 The sirte basin of libya". Sedimentary Basins of the World. 3: 27–37. doi:10.1016/S1874-5997(97)80006-8. ISBN 9780444825711.{{cite journal}}: CS1 maint: periodical has ISBN (link)
  9. ↑ Мичев (Michev), Николай (Nikolay); Михайлов (Mihaylov), Цветко (Tsvetko); Вапцаров (Vaptsarov), Иван (Ivan); Кираджиев (Kiradzhiev), Светлин (Svetlin) (1980). Географски речник на България [Geographic Dictionary of Bulgaria] (in Bulgarian). Sofia: Наука и култура (Nauka i kultura). p. 368.
  10. ↑ Димитрова (Dimitrova), Людмила (Lyudmila) (2004). Национален парк "Пирин". План за управление [Pirin National Park. Management Plan] (in Bulgarian). и колектив. Sofia: Ministry of Environment and Water, Bulgarian Foundation "Biodiversity". p. 53.
  11. ↑ Дончев (Donchev), Дончо (Doncho); Каракашев (Karakashev), Христо (Hristo) (2004). Теми по физическа и социално-икономическа география на България [Topics on Physical and Social-Economic Geography of Bulgaria] (in Bulgarian). Sofia: Ciela. pp. 128–129. ISBN 954-649-717-7.
  12. ↑ United States Geological Survey (1989). "Clastic Rocks Associated with the Midcontinent Rift System in Iowa" (PDF). U.S. Geological Survey Bulletin. 1989-I: 11. Retrieved Sep 3, 2018.
  13. ↑ Ring, Uwe (2008-08-27). "Extreme uplift of the Rwenzori Mountains in the East African Rift, Uganda: Structural framework and possible role of glaciations". Tectonics. 27 (4). Bibcode:2008Tecto..27.4018R. doi:10.1029/2007tc002176. ISSN 0278-7407. S2CID 129376195.
  14. ↑ "The Mountains of the Moon". Volcano Cafe. 20 February 2021.
  15. ↑ "horst and graben". Encyclopædia Britannica.
  16. ↑ Calvet, Marc; Delmas, Magali; Gunnell, Yanni; Laumonier, Bernard (2022). Geology and Landscapes of the Eastern Pyrenees: A Field Guide with Excursions. Springer International Publishing (Kindle Edition). Fig. 11.19.
  17. ↑ Guitard, G.; Laumonier, B.; Autran, A.; Bandet, Y.; Berger, G.M. (1998). Notice explicative, Carte géol. France (1/50 000), feuille Prades 1095) (pdf) (in French). Orléans: BRGM Éditions. p. 129.
  18. ↑ Milesi, G.; Monié, P.; Soliva, R.; Münch, P.; Valla, P.G.; Brichau, S. (2022). "Deciphering the Cenozoic exhumation history of the eastern Pyrenees along a crustal-scale normal fault using low-temperature thermochronology". Tectonics. 41, e2021TC007172.
  19. ↑ Laparade, Océane (2024-06-24). "Mesure du Canigó". L'Indépendant (in French). Perpignan. Retrieved 2026-08-06.
  20. ↑ The Aspres fault acted as a westward-moving thrust fault during the Pyrenees mountain-building period of the Eocene, but later, during the Neogene, it acted as a normal fault, raising the Canigou massif to the west. See: Laumonier, B. (2015). "Les Pyrénées alpines sud-orientales (France, Espagne) – essai de synthèse". Revue de Géologie pyrénéenne (in French). 2. Page 6 and Fig. 2.
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