Trans Brazilian Lineament

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The Trans Brazilian Lineament (TBL), or Transbrasiliano Lineament, is a major shear zone that developed in the Precambrian period, and that has been reactivated several times since then, mostly recently during the Mesozoic. Movement along the shear zone helps explain how the South American continent could have fitted tightly to the African continent before the breakup of Gondwana. [1]

Contents

Formation and location

The TBL was formed when the Goiás Ocean, lying between the Amazonian craton and the Congo / Sao Francisco craton, was closed during the formation of West Gondwana around 600 million years ago. [2] The lineament extends from the northeast coast of Brazil in a southwesterly direction through Paraguay and into Argentina, where it is dissipated in the Salado and Colorado extension basins. [1]

The Trans-Saharan Belt (TSB), running from Algeria to Benin, was created in the same period. It marks the line where the Pharusian Ocean, linked to the Goiás Ocean, was closed as the West African craton collided with the Saharan Metacraton. [2] The TSB includes the Hoggar belt, which splays into the Kandi fault zone in Benin, corresponding to the Sobral fault at the north of the TBL. Given the correspondence of faults, which is widely accepted, the TBL and TBS form perhaps the longest coherent shear zone on the Earth. [3]

Gondwana breakup

Towards the north of the lineament in Brazil, a series of splay faults show where the crust has extended, and these faults match corresponding faults in Africa. Thus the Pernambuco fault in Brazil matches the Foumban fault zone in Cameroon, and other Brazilian faults match the Benue Trough in Nigeria. The extension caused by these splay faults causes a poor fit between South America and Africa around the Niger Delta region. [1] However, after allowing for a sinistral shear movement of about 100 km of the crust to the east of the TBL, there is an excellent fit between South America and Africa both to the south and the west of the Niger Delta. [4]

See also

Related Research Articles

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See also Line (geometry)

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This is a list of articles related to plate tectonics and tectonic plates.

Saharan Metacraton Large area of continental crust in the north-central part of Africa

The Saharan Metacraton is a term used by some geologists to describe a large area of continental crust in the north-central part of Africa. Whereas a craton is an old and stable part of the lithosphere, the term "metacraton" is used to describe a craton that has been remobilized during an orogenic event, but where the characteristics of the original craton are still identifiable. The geology of the continent has only been partially explored, and other names have been used to describe the general area that reflect different views of its nature and extent. These include "Nile Craton", "Sahara Congo Craton", "Eastern Saharan Craton" and "Central Saharan Ghost Craton". This last term is because the older rocks are almost completely covered by recent sediments and desert sands, making geological analysis difficult.

Tuareg Shield geological formation between the West African craton and the Saharan Metacraton in West Africa

The Tuareg Shield is a geological formation lying between the West African craton and the Saharan Metacraton in West Africa. Named after the Tuareg people, it has complex a geology, reflecting the collision between these cratons and later events. The landmass covers parts of Algeria, Niger and Mali.

Benue Trough Major geological structure underlying a large part of Nigeria and extending from the Bight of Benin to Lake Chad

The Benue Trough is a major geological structure underlying a large part of Nigeria and extending about 1,000 km northeast from the Bight of Benin to Lake Chad. It is part of the broader West and Central African Rift System.

The Pharusian Ocean is an ancient ocean that existed from 800 to 635 million years ago, between the break-up of the Rodinia supercontinent and the start of formation of the Gondwana supercontinent.

The Kandi fault zone is a southern extension of the Hoggar fault zone in West Africa, with splays in Benin, Togo and southeastern Ghana. It lies at the southern end of the Trans Saharan belt, a lineament that extends in a southwest direction from Algeria to Benin. The Kandi fault zone is identified with the Sobral fault in northeastern Brazil, considered to be the northern section of the Trans Brazilian Lineament.

The Sobral fault is a major fault in the Borborema geological province of northeastern Brazil, a part of the Transbrasiliano lineament. It is commonly correlated with the Kandi fault in Benin, east of the West African craton. The fault lies in the northwest of Ceará state. It appears to have formed late in the orogeny when the West African craton engaged with the Congo craton, and to have allowed significant dextral strike-slip movement. It was reactivated when South America was breaking away from Africa. In this later phase, a sinistral shear movement of about 100 km seems to have taken place during and after the break-up.

The Foumban Shear Zone, or Central Cameroon Shear Zone (CCSZ), is a fault zone in Cameroon that has been correlated with the Pernambuco fault in northeastern Brazil, which splays from the Trans-Brazilian Lineament. It is part of the Central African Shear Zone (CASZ) and dates to at least 640 million years ago. The zone was rejuvenated several times, usually with a dextral movement, before and during the opening of the South Atlantic in the Cretaceous period.

The Pernambuco Fault or Pernambuco Shear Zone in northeastern Brazil is a fault radiating from the Trans Brazilian Lineament eastwards to the coast, a major geological feature.

Brasiliano orogeny

Brasiliano orogeny or Brasiliano cycle refers to a series of orogenies of Neoproterozoic age exposed chiefly in Brazil but also in other parts of South America. The Brasiliano orogeny is a regional name for the larger Pan-African/Brasiliano orogeny that extended not only in South America but across most of Gondwana. In a wide sense the Brasiliano orogeny includes also the Pampean orogeny. Almeida et al. coined the term Brasiliano Orogenic Cycle in 1973. The orogeny led to the closure of several oceans and aulacogens including the Adamastor Ocean, the Goianides Ocean, the Puncoviscana Ocean and the Peri-Franciscano Ocean.

The Adamastor Ocean was a "proto-Atlantic" ocean that formed with the break-up of the Rodinia supercontinent c. 780-750 Ma. It separated the Río de la Plata Craton from the Congo Craton. The inversion of the Adamastor Ocean began about 640 Ma with the development of a large back-arc basin along the western margin of the Kalahari Craton, and the ocean closed when Río de la Plata collided with Kalahari about 545 Ma along the sinistral Sierra Ballena Shear Zone. The São Francisco Craton and the Río de la Plata Craton amalgamated 630–620 Ma, closing the Adamastor Ocean on the South American side and forming the Mantiqueira Mountains around 600 Ma.

The geology of Brazil includes very ancient craton basement rock from the Precambrian overlain by sedimentary rocks and intruded by igneous activity, as well as impacted by the rifting of the Atlantic Ocean.

References

  1. 1 2 3 J D Fairhead, Nasreddine Bournas and M Chaker Raddadi (2007). "The Role of Gravity and Aeromagnetic Data in Mapping Mega Gondwana Crustal Lineaments: the Argentina - Brazil – Algeria (ABA) Lineament" (PDF). SEG. Archived from the original (PDF) on 2011-07-11. Retrieved 2011-01-30.
  2. 1 2 Robert D. Hatcher (2007). 4-D framework of continental crust. Geological Society of America. p. 316. ISBN   978-0-8137-1200-0.
  3. ↑ Attoh, K.; Brown, L. D. (2008). "The Neoproterozoic Trans-Saharan/Trans-Brasiliano shear zones: Suggested Tibetan Analogs". AGU Spring Meeting Abstracts. American Geophysical Union. 2008: S51A–04. Bibcode:2008AGUSM.S51A..04A.
  4. ↑ Gillian R. Foulger (2005). Plates, plumes, and paradigms. Geological Society of America. p. 545. ISBN   0-8137-2388-4.
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