Noronha hotspot

Noronha hotspot is a hypothesized hotspot in the Atlantic Ocean. It has been proposed as the candidate source for volcanism in the Fernando de Noronha archipelago of Brazil, as well as of other volcanoes also in Brazil and even the Bahamas and the Central Atlantic Magmatic Province.

The presence of a mantle plume is controversial owing to equivocal seismic tomography images of the mantle and the inconsistent age progression in the volcanoes, especially the Brazilian ones.

Hotspots
Global map of hotspots; Noronha is number #9

General

The Noronha hotspot is also known as the Fernando hotspot.[1] The hotspot is located over the South America Plate, which moves west-southwestward at a rate of 45 millimetres per year (1.8 in/year),[2] and is considered to be part of a West African superplume.[3]

Candidate volcanoes

Fernando de Noronha

The Noronha hotspot is considered to be currently located beneath the Fernando de Noronha islands,[1] and age trends in the archipelago are consistent with a hotspot pattern.[4] Such a hotspot would presently be centered beneath the eastern part of the archipelago.[5] Mantle derived xenoliths found at Fernando de Noronha are consistent with the hotspot theory,[6] although their traits can be explained with non-hotspot theories as well.[7]

Rocas Atoll and Fernando de Noronha ridge

A series of volcanoes extend westwards away from Fernando de Noronha and may also be the consequence of hotspot volcanism.[5] Volcanic structures in this ridge include guyots, islands and seamounts.[8] The Rocas Atoll 137 kilometres (85 mi) from Fernando de Noronha has been proposed as another product of the Noronha hotspot.[9]

Brazilian continental

Activity of the hotspot has been used to explain alkaline Cenozoic volcanism in Brazil, such as Pico Cabugi[10][11] and the Fortaleza region.[5] The hotspot 30 million years ago passed by northeastern Brazil,[6] and some of the continental volcanics appear to have been erupted at the time of plume passage.[12] This interaction may be responsible for the high geothermal gradient in the region as well.[13] Oligocene-Eocene volcanic rocks in the offshore Potiguar basin may also be a product of a Noronha hotspot,[14] while volcanics in the offshore Boa Vista and Cubati basins probably have a different origin.[15] However, more recent chronological data have cast doubt on the plume origin of at least some of these volcanics.[16][15]

The mantle plume that feeds the Noronha hotspot appears to combine several different types of magma judging by the isotope ratios of the erupted rocks.[10] In addition, the plume material would have mixed with lithospheric melts to derive the rocks erupted by the continental volcanics.[12] Distinct mantle domains have been inferred to have contributed to magma genesis for some volcanoes underneath Brazil than for Fernando de Noronha, which calls into question the origin of these volcanoes over a Noronha hotspot.[17]

Caribbean and North America

If the Noronha hotspot is allowed to wander in the mantle,[18] it is possible to reconstruct a path where it runs through Louisiana, Florida and the Bahamas between 180 and 150 million years ago. In that case the Bahamas may be a subsided volcanic ridge with corals atop of it.[19] If the hotspot did not wander, it would have passed underneath Cuba and Hispaniola instead,[20] with Cuba above the hotspot 160-140 million years ago.[19]

Before 170 million years ago the hotspot was beneath Texas and Louisiana leaving no traces (maybe it was not active before then). If it followed a more southerly path, it may have been involved in the formation of the Gulf of Mexico.[21]

Alternatively, if it passed farther east it may be identical with the "Newark plume" that is considered responsible for the Central Atlantic Magmatic Province; generally speaking the position of the North America Plate is fairly uncertain before 130 million years ago.[22][23] The Cape Verde hotspot may also be related to the Central Atlantic Magmatic Province.[24] The opening of the central Atlantic Ocean may be the consequence of the activity of either hotspot.[25]

Alternative theories

One problem with the hotspot theory is that the geochronology of the Fernando de Noronha and mainland Brazil volcanics are not necessarily consistent with a mantle plume,[11][26] much of the volcanic activity in both regions was contemporaneous for example. Further, seismic tomography has not imaged a mantle plume,[27][28] although isolated seismic anomalies may reflect the existence of the hotspot.[29] There are also geochemical problems.[30] Several alternate theories have been proposed:

  • The volcanism of Fernando de Noronha may be a product of oceanic fracture zones. One argument in support of this view is that the strike of the hotspot path is consistent with that of fracture zones but not with that of well defined hotspot tracks such as the Rio Grande Rise, which trends more southeasterly.[31] The "Fernando de Noronha-Mecejana" volcano lineament has been attributed to such a transform fault.[32] It is also possible that such a fracture zone and a hotspot simultaneously contributed to the development of the volcanics.[8]
  • A mantle plume beneath the Paraná may feed both the Fernando de Noronha, the Martin Vaz and some continental volcanic fields.[26] Seismic tomography suggests that this mantle plume is actually the remnant of the plume associated with the Tristan hotspot.[33]
  • Edge-driven convection may be occurring at the margin of Brazil. This would be consistent with the volcanic activity not migrating over time, since edge-driven convection is tied to the continental block and "moves" along with it. However, an unrelated process must have enriched the mantle in the region in order to explain the composition of erupted volcanic rocks, which are inconsistent with melts derived from normal mantle.[34] Seismic tomography shows structures that are consistent with such a theory.[27]

References

  1. ^ a b Morgan 1983, p. 127.
  2. ^ Perlingeiro et al. 2013, p. 141.
  3. ^ Glišović, Petar; Forte, Alessandro M. (January 2015). "Importance of initial buoyancy field on evolution of mantle thermal structure: Implications of surface boundary conditions". Geoscience Frontiers. 6 (1): 12. doi:10.1016/j.gsf.2014.05.004. ISSN 1674-9871.
  4. ^ Morgan 1983, p. 133.
  5. ^ a b c Perlingeiro et al. 2013, p. 140.
  6. ^ a b Knesel et al. 2011, p. 38.
  7. ^ Rivalenti et al. 2007, p. 129.
  8. ^ a b Mohriak 2000, p. 280.
  9. ^ Sampaio, Cláudio L. S.; Nunes, José de Anchieta C. C.; Mendes, Liana F. (2004). "Acyrtus pauciradiatus, a new species of clingfish (Teleostei: Gobiesocidae) from Fernando de Noronha Archipelago, Pernambuco state, Northeastern Brazil". Neotropical Ichthyology. 2 (4): 206–208. doi:10.1590/S1679-62252004000400002. ISSN 1679-6225.
  10. ^ a b Rivalenti et al. 2007, p. 112.
  11. ^ a b Lopes, Rosana Peporine; Ulbrich, Mabel Norma Costas; Lopes, Rosana Peporine; Ulbrich, Mabel Norma Costas (2015). "Geochemistry of the alkaline volcanicsubvolcanic rocks of the Fernando de Noronha Archipelago, southern Atlantic Ocean". Brazilian Journal of Geology. 45 (2): 307–333. doi:10.1590/23174889201500020009. ISSN 2317-4889.
  12. ^ a b Fodor, Sial & Gandhok 2002, p. 199.
  13. ^ Fodor, Sial & Gandhok 2002, p. 211.
  14. ^ Morais Neto, J.M.; Hegarty, K.A.; Karner, G.D.; Alkmim, F.F. (August 2009). "Timing and mechanisms for the generation and modification of the anomalous topography of the Borborema Province, northeastern Brazil". Marine and Petroleum Geology. 26 (7): 1074. doi:10.1016/j.marpetgeo.2008.07.002. ISSN 0264-8172.
  15. ^ a b de Souza et al. 2013, p. 170.
  16. ^ Ngonge, Emmanuel Donald; de Hollanda, Maria Helena Bezerra Maia; Pimentel, Márcio Martins; de Oliveira, Diógenes Custódio (December 2016). "Petrology of the alkaline rocks of the Macau Volcanic Field, NE Brazil". Lithos. 266-267: 454–466. doi:10.1016/j.lithos.2016.10.008. ISSN 0024-4937.
  17. ^ Rivalenti, Giorgio; Mazzucchelli, Maurizio; Girardi, Vicente A. V.; Barbieri, M. Adelaide; Zanetti, Alberto; Goldstein, Steve L. (1999-03-01). "THE MANTLE LITHOSPHERE IN NORTHEASTERN BRAZIL AND FERNANDO DE NORONHA. PLUME-RELATED MANTLE METASOMATISM?". Ofioliti. 24 (1b): 159. ISSN 0391-2612.
  18. ^ Morgan 1983, p. 126.
  19. ^ a b Morgan 1983, p. 131.
  20. ^ Morgan 1983, p. 129.
  21. ^ Morgan 1983, p. 135.
  22. ^ Courtillot et al. 1999, p. 185.
  23. ^ Leitch, A.M.; Davies, G.F.; Wells, M. (September 1998). "A plume head melting under a rifting margin". Earth and Planetary Science Letters. 161 (1–4): 164. doi:10.1016/S0012-821X(98)00147-2. ISSN 0012-821X.
  24. ^ Sears, James W.; St. George, Gregory M.; Winne, J. Chris (March 2005). "Continental rift systems and anorogenic magmatism". Lithos. 80 (1–4): 151. doi:10.1016/j.lithos.2004.05.009. ISSN 0024-4937.
  25. ^ Courtillot et al. 1999, p. 189.
  26. ^ a b Knesel et al. 2011, p. 40.
  27. ^ a b Perlingeiro et al. 2013, p. 153.
  28. ^ Knesel et al. 2011, p. 47.
  29. ^ Colli, Lorenzo; Fichtner, Andreas; Bunge, Hans-Peter (September 2013). "Full waveform tomography of the upper mantle in the South Atlantic region: Imaging a westward fluxing shallow asthenosphere?". Tectonophysics. 604: 31. doi:10.1016/j.tecto.2013.06.015. ISSN 0040-1951.
  30. ^ Lopes, Rosana Peporine; Ulbrich, Mabel Norma Costas (20 June 2016). "Geoquímica das rochas vulcânicas-subvulcânicas alcalinas do Arquipélago de Fernando de Noronha, Oceano Atlântico Meridional". Brazilian Journal of Geology. 45 (2): 307–333. doi:10.1590/23174889201500020009. ISSN 2317-4692.
  31. ^ Knesel et al. 2011, p. 39.
  32. ^ de Souza et al. 2013, p. 160.
  33. ^ Knesel et al. 2011, p. 49.
  34. ^ Knesel et al. 2011, p. 48.

Sources

  • Courtillot, V; Jaupart, C; Manighetti, I; Tapponnier, P; Besse, J (March 1999). "On causal links between flood basalts and continental breakup". Earth and Planetary Science Letters. 166 (3–4): 177–195. doi:10.1016/S0012-821X(98)00282-9. ISSN 0012-821X.
  • de Souza, Zorano Sérgio; Vasconcelos, Paulo Marcos; Knesel, Kurt Michael; da Silveira Dias, Luiz Gustavo; Roesner, Eduardo Henrique; Cordeiro de Farias, Paulo Roberto; de Morais Neto, João Marinho (December 2013). "The tectonic evolution of Cenozoic extensional basins, northeast Brazil: Geochronological constraints from continental basalt 40Ar/39Ar ages". Journal of South American Earth Sciences. 48: 159–172. doi:10.1016/j.jsames.2013.09.008. ISSN 0895-9811.
  • Fodor, R.V; Sial, A.N; Gandhok, G (June 2002). "Petrology of spinel peridotite xenoliths from northeastern Brazil: lithosphere with a high geothermal gradient imparted by Fernando de Noronha plume". Journal of South American Earth Sciences. 15 (2): 199–214. doi:10.1016/S0895-9811(02)00032-9. ISSN 0895-9811.
  • Knesel, Kurt M.; Souza, Zorano S.; Vasconcelos, Paulo M.; Cohen, Benjamin E.; Silveira, Francisco V. (February 2011). "Young volcanism in the Borborema Province, NE Brazil, shows no evidence for a trace of the Fernando de Noronha plume on the continent". Earth and Planetary Science Letters. 302 (1–2): 38–50. doi:10.1016/j.epsl.2010.11.036. ISSN 0012-821X.
  • Mohriak (2000). Atlantic Rifts and Continental Margins. Geophysical Monograph Series. 115. Wiley Online Library. doi:10.1029/gm115. ISBN 978-0-87590-098-8.
  • Morgan, W Jason. (1 January 1983). "Hotspot Tracks and the Early Rifting of the Atlantic". Processes of Continental Rifting. Developments in Geotectonics. 19. pp. 123–139. doi:10.1016/B978-0-444-42198-2.50015-8. ISBN 9780444421982. ISSN 0419-0254.
  • Perlingeiro, Gabriela; Vasconcelos, Paulo M.; Knesel, Kurt M.; Thiede, David S.; Cordani, Umberto G. (January 2013). "40Ar/39Ar geochronology of the Fernando de Noronha Archipelago and implications for the origin of alkaline volcanism in the NE Brazil". Journal of Volcanology and Geothermal Research. 249: 140–154. doi:10.1016/j.jvolgeores.2012.08.017. ISSN 0377-0273.
  • Rivalenti, Giorgio; Zanetti, Alberto; Girardi, Vicente A.V.; Mazzucchelli, Maurizio; Tassinari, Colombo C.G.; Bertotto, Gustavo W. (March 2007). "The effect of the Fernando de Noronha plume on the mantle lithosphere in north-eastern Brazil". Lithos. 94 (1–4): 111–131. doi:10.1016/j.lithos.2006.06.012. ISSN 0024-4937.
Amazon Basin (sedimentary basin)

The Amazon Basin is a major 620,000 square kilometres (240,000 sq mi) large sedimentary basin located roughly at the middle and lower course of the Amazon River, south the Guiana Shield and north of the Central Brazilian Shield. It is bound to the west by the Púrus Arch, separating the Amazon Basin from the Solimões Basin and in the east by the Gurupá Arch, separating the basin from the Marajó Basin. The basin developed on a rift that originated possibly about 550 million years ago during the Cambrian. Parts of the rift were reactivated during the opening of the South Atlantic.The basin has an elongated shape with a WSW-ENE orientation. It long axis runs from the vicinity of Manaus to the area near the confluence of Xingu River with the Amazon River.

Boconó Fault

The Boconó Fault is a complex of geological fault located in the Eastern Ranges of northeastern Colombia and the Mérida Andes of northwestern Venezuela. The fault has a NE-SW orientation. Boconó Fault is a strike-slip fault and has a dextral relative movement. The fault extends over a length of 500 kilometres (310 mi). The fault, with a slip rate ranging from 4.3 to 6.1 millimetres (0.17 to 0.24 in) per year, has been active since the Early Holocene and earthquakes of 1610 and 1894 are associated with the Boconó Fault.

Fernando de Noronha

Fernando de Noronha (Portuguese pronunciation: [feʁˈnɐ̃du d(ʒ)i noˈɾoɲɐ]) is an archipelago of 21 islands and islets in the Atlantic Ocean, 354 km (220 mi) offshore from the Brazilian coast. The archipelago's name is a corruption of the name of the Portuguese merchant Fernão de Loronha, to whom it was given by the Portuguese crown for services rendered regarding wood imported from Brazil. Only the homonymous main island is inhabited; it has an area of 18.4 km2 (7.1 sq mi) and a population estimated at 2,718 in 2012. The archipelago's total area is 26 km2 (10 sq mi).

The islands are administratively unique in Brazil. They form a "state district" (Portuguese: distrito estadual) that is not part of any municipality and is administered directly by the government of the state of Pernambuco (despite being closer to the state of Rio Grande do Norte). The state district's jurisdiction also includes the very remote Saint Peter and Saint Paul Archipelago, located 625 kilometres (388 mi) northeast of Fernando de Noronha. 70% of the islands' area was established in 1988 as a national maritime park.

In 2001, UNESCO designated it as a World Heritage Site because of the importance of its environment. Its time zone is UTC−02:00 all year round.

Oca-Ancón Fault System

The Oca-Ancón Fault System (Spanish: Falla Oca-Ancón) is a complex of geological faults located in the northeastern Colombia and northwestern Venezuela near the Caribbean Sea. The fault system is of right-lateral strike-slip type and extends for an approximate length of 830 km (520 mi). The Oca-Ancón Fault System is part of the diffuse boundary between the Caribbean Plate and the South American Plate. The movement rate of the Oca-Ancón Fault System is estimated at 2 millimetres (0.079 in) each year, more than most Venezuelan faults.

Paraná Basin

The Paraná Basin (Portuguese: Bacia do Paraná, Spanish: Cuenca Paraná) is a large cratonic sedimentary basin situated in the central-eastern part of South America. About 75% of its areal distribution occurs in Brazil, from Mato Grosso to Rio Grande do Sul states. The remainder area is distributed in eastern Paraguay, northeastern Argentina and northern Uruguay. The shape of the depression is roughly elliptical and covers an area of about 1,500,000 km2 (580,000 sq mi).

The Paraná River, from which the Paraná Basin derived its name, flows along the central axis of the Paraná Basin and drains it.

Tectonic evolution of Patagonia

Patagonia comprises the southernmost region of South America, portions of which lie either side of the Chile–Argentina border. It has traditionally been described as the region south of the Rio Colorado, although the physiographic border has more recently been moved southward to the Huincul fault. The region's geologic border to the north is composed of the Rio de la Plata craton and several accreted terranes comprising the La Pampa province. The underlying basement rocks of the Patagonian region can be subdivided into two large massifs: the North Patagonian Massif and the Deseado Massif. These massifs are surrounded by sedimentary basins formed in the Mesozoic that underwent subsequent deformation during the Andean orogeny. Patagonia is known for their vast earthquakes and the damage.

The rocks comprising Patagonia occurred along the southwestern margin of the ancient supercontinent of Gondwana. During a period of continental rifting in the Cambrian period, a portion of Patagonia was separated from Gondwana, and the resulting passive margin that formed was a site of extensive sedimentation throughout the early-middle Paleozoic era. During the Devonian period, a transition to convergence resulted in the eventual collision of the Patagonian landmass in the late Paleozoic, with contact first occurring in the mid-Carboniferous. Several theories exist for the origin of the Patagonian landmass, though there are two that have greater consensus. The first of these theories cites an allochthonous origin of the Patagonian landmass from Gondwana during the Paleozoic, while the other argues that Northern Patagonia is an autochthonous component and that only the southern portion is allochthonous. The collision of Patagonia was succeeded by the rifting and eventual breakup of Gondwana during the early Mesozoic, a process which invoked large-scale rotation of the Patagonian landmass. Further extension through the Jurassic and Cretaceous periods formed the Rocas Verdes back-arc basin, while a transition to a compressional tectonic regime in the Cenozoic concurrent with the Andean orogeny resulted in formation of the foreland Magallanes basin.

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