Rio Grande Rise

Rio Grande Rise
The Rio Grande Rise separates the Brazilian (N) and Argentine Basins (S) and is itself separated from Vema Sill and Santos Plain (W) by the Vema Canal and from the Mid-Atlantic Ridge by the Hunter Canal (O ).
height	1000 m below sea level
location	east of Brazil
Coordinates	31 ° 0 ′ 0 ″  S , 35 ° 0 ′ 0 ″  W Coordinates: 31 ° 0 ′ 0 ″  S , 35 ° 0 ′ 0 ″  W
Type	Deep sea mountain

The Rio Grande Rise (Eng .: Rio Grande Ridge) is a seismically inactive mid-ocean ridge in the southern Atlantic , off the coast of Brazil . Together with the Walvis Ridge off Africa , the Rio Grande Rise forms a V-shaped structure of mirrored volcanic hotspot chains or chains of submarine mountains in the north of the South Atlantic. In 2013 Brazilian scientists published the discovery of large blocks of granite in the area of ​​the submarine mountains and concluded that they had found the remains of a submerged continent , a "Brazilian Atlantis" so to speak. however, most scientists reject this theory.

geology

The Rio Grande Rise separates the Santos Basin from the Pelotas Basin and clearly consists of a western and an eastern area with different geological compositions. The western part has numerous guyots and other deep-sea mountains and a base that was dated to an age of 80 to 87 million years. Volcanic breccias were found here and layers of ash are evidence of the intense volcanic activity during the Eocene . The rocks were formed at the same time as the rocks on the South American continent. The eastern part is determined by a fracture zone and may have been an area of expansion in the past .

As West Gondwana (South America) and Africa in the early Cretaceous period before 146 to 100 million. Years apart, the South Atlantic opened from south to north. In the course of this process, the massive continental flood basalts of the Paraná and Etendeka Traps in the area of ​​what is now Brazil and Namibia emerged . These events are linked to the Tristan-Gough Hotspot , which is now near the Mid-Atlantic Ridge , near Tristan da Cunha and the Gough Islands . During the Maastrichtian approx. 60 million years ago, the direction of the outflow changed, which is particularly noticeable on the African side and volcanism ended on the South American side. In the course of the process, the Tristan-Gough Seamount Chains (deep sea mountain chains) were created on both sides of the Tristan-Gough hotspot.

Paleoclimatic importance

A Brazilian-Japanese expedition in 2013 discovered granitic and metamorphic rock formations in situ on the Rio Grande Rise. This could indicate that the plateau consists partly of fragments of the continental crust (possibly even once a “micro-continent” itself, comparable to the Kerguelen Plateau in the Indian Ocean and Jan Mayen in the Arctic Ocean). The existence of such micro-continents is speculative, however, as their remains are usually covered by younger layers of lava and sediments. Nevertheless, there are also indications of islands scattered across the ocean based on the fossil record . For example, fossils of flightless birds such as Lavocatavis have been discovered, suggesting that during the Tertiary, several islands between Africa and South America allowed species to spread through island hopping.

At the beginning of the Maastrichtian there were immense differences between the water masses north and south of the complex of Rio Grande Rice and Walvis Ridge. During the Maastricht period, these differences disappeared, suggesting that the circulation patterns of the oceans changed during this time and that the middle and deeper water layers became unified. In the course of this process, the complex of Rio Grande Rise and Walvis Ridge broke apart and epicontinental inlets like the Tethys Sea disappeared. Thus disappeared the tropical habitats rudists and with them the benthic Inoceramidae clams.

The formation of today's circulation of cold deep water (big flush) probably began in the Eocene 55 to 40 million years ago. During this time, there were again strong tectonic shifts, such as the opening of the Northeast Atlantic and fracture zones that opened up in the Rio Grande Rise, causing cold water to flow from the Antarctic Weddell Sea north into the North Atlantic. 40 million years ago, the emergence of cold bottom water in the Antarctic led to the development of a pronounced cold water fauna (psychrospheric fauna), which today settled in water temperatures below 10 ° C in the Atlantic and already in the Tethys Sea. The global spread suggests that the Rio Grande Rise was broken up at that time, so cold, dense water could flow through a corridor from south to north, resulting in a change from a hot water circulation (thermospheric circulation) to a meridional thermohaline circulation occurred .

Individual evidence

1. ↑ Zenk, Morozov 2007: Fig. 1.
2. ^ O'Connor, Duncan 1990: Introduction, 17475.
3. ^ National Geographic News 2013.
4. ↑ ^{a b c} Sager 2014: 2-4.
5. ↑ Mourer-Chauviré, Tabuce, Mahboubi, Adaci, 2011: Abstract.
6. ^ Frank Arthur 1999: Conclusions, 115.
7. ↑ Berggren 1982: Cenozoic: 122-123.

literature

• WA Berggren: Role of ocean gateways in climatic change. In: Climate in Earth History. Geophysics Committee, Berger, WH; Crowell, J. C 1982: 118-125; <Studies in Geophysics> National Academy Press, Washington DC [1]
• TD Frank, MA Arthur: Tectonic forcings of Maastrichtian ocean-climate evolution. In: Paleoceanography. 1999 vol. 14, 2: 103-117. [2] (doi = 10.1029 / 1998PA900017 bibcode = 1999PalOc..14..103F)
• C. Mourer-Chauviré, R. Tabuce, M. Mahboubi, M. Adaci, M. Bensalah: A Phorhacoid bird from the Eocene of Africa. In: Natural Sciences. 2011 vol. 98, 10: 815-823. (doi = 10.1007 / s00114-011-0829-5 pmid = 21874523)
• JM O'Connor, RA Duncan: Evolution of the Walvis Ridge-Rio Grande Rise Hot Spot System: Implications for African and South American Plate motions over plumes. In: Journal of Geophysical Research: Solid Earth. 1990 vol. 95, B11: 17475-17502. [3] (doi = 10.1029 / jb095ib11p17475 bibcode = 1990JGR .... 9517475O)
• WW Sager: Scientific Drilling in the South Atlantic: Rio Grande Rise, Walvis Ridge and surrounding areas. In: US Science Support Program Workshop Report. [4]
• Ken Than: Lost Land Found by Scientists. National Geographic News May 11, 2013 [5]
• W. Zenk, E. Morozov: Decadal warming of the coldest Antarctic Bottom Water flow through the Vema Channel. In: Geophys. Res. Lett. 2007, vol. 34, 14: L14607. (doi = 10.1029 / 2007GL030340 bibcode = 2007GeoRL..3414607Z)