Pharusian Ocean
Encyclopedia
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.
era after rifting along the eastern margin of the West African craton
during the breakup of Rodinia
.
The ocean began to close around 730 million years ago with eastward subduction of the Tilemsi arc, which was accreted
against the Hoggar region of the Saharan Metacraton
.
The western part of the Hoggar massif is made of material from the Pharusian Ocean including oceanic basalts, arc volcanic and sedimentary rocks and sediments that were shed into the Pharusian Ocean by the West African craton and the eastern Hoggar.
Closure was completed when the West African and Saharan cratons collided around 635 million years ago at the start of the Pan-African orogeny
.
, extended into the Pharusian Ocean.
The Goiás Ocean closed during the final phases of formation of West Gondwana
. The southern portion of the Trans Brazilian Lineament
(TBL) marks the suture zone of this closure, while the northern Borborema portion of the TBL and the Trans-Saharan Belt, running from Algeria
to Benin
, mark the suture zone of the Pharusian Ocean closure.
These ocean closures and subsequent tectonic events were not simultaneous, but happened over an extended period of time.
In southwestern central Africa the granulite cooling ages range between 587 and 576 Ma, while in northeast Brazil they range from 568 to 500 Ma.
However, aeromagnetic and gravity data give evidence of continuity between the TBL lineament
, the Sobral fault
in northeastern Brazil, the Kandi fault zone
in Benin
and the Trans-Saharan Belt formed by closure of the Pharusian Ocean.
Rodinia
In geology, Rodinia is the name of a supercontinent, a continent which contained most or all of Earth's landmass. According to plate tectonic reconstructions, Rodinia existed between 1.1 billion and 750 million years ago, in the Neoproterozoic era...
supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
and the start of formation of the Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
supercontinent.
Opening and closure
The Pharusian Ocean opened around 800 million years ago in the NeoproterozoicNeoproterozoic
The Neoproterozoic Era is the unit of geologic time from 1,000 to 542.0 ± 1.0 million years ago. The terminal Era of the formal Proterozoic Eon , it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods...
era after rifting along the eastern margin of the West African craton
West African craton
The West African craton is one of the five large masses, or cratons, of the Precambrian basement rock of Africa that make up the African Plate, the others being the Kalahari craton, Congo craton, Saharan Metacraton and Tanzania craton. These land masses came together in the late Precambrian and...
during the breakup of Rodinia
Rodinia
In geology, Rodinia is the name of a supercontinent, a continent which contained most or all of Earth's landmass. According to plate tectonic reconstructions, Rodinia existed between 1.1 billion and 750 million years ago, in the Neoproterozoic era...
.
The ocean began to close around 730 million years ago with eastward subduction of the Tilemsi arc, which was accreted
Accretion (geology)
Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.-Description:...
against the Hoggar region of the Saharan Metacraton
Saharan Metacraton
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. Where 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...
.
The western part of the Hoggar massif is made of material from the Pharusian Ocean including oceanic basalts, arc volcanic and sedimentary rocks and sediments that were shed into the Pharusian Ocean by the West African craton and the eastern Hoggar.
Closure was completed when the West African and Saharan cratons collided around 635 million years ago at the start of the Pan-African orogeny
Pan-African orogeny
The Pan-African orogeny was a series of major Neoproterozoic orogenic events which related to the formation of the supercontinents Gondwana and Pannotia about 600 million years ago....
.
Southern extension
The Goiás Ocean, lying to the southwest between the Amazonian craton and the Congo cratonCongo craton
The Congo craton, covered by the Palaeozoic-to-recent Congo basin, is an ancient Precambrian craton that with four others makes up the modern continent of Africa. These cratons were formed between about 3.6 and 2.0 billion years ago and have been tectonically stable since that time...
, extended into the Pharusian Ocean.
The Goiás Ocean closed during the final phases of formation of West Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
. The southern portion of the Trans Brazilian Lineament
Trans Brazilian Lineament
The Trans Brazilian Lineament , 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...
(TBL) marks the suture zone of this closure, while the northern Borborema portion of the TBL and the Trans-Saharan Belt, running from Algeria
Algeria
Algeria , officially the People's Democratic Republic of Algeria , also formally referred to as the Democratic and Popular Republic of Algeria, is a country in the Maghreb region of Northwest Africa with Algiers as its capital.In terms of land area, it is the largest country in Africa and the Arab...
to Benin
Benin
Benin , officially the Republic of Benin, is a country in West Africa. It borders Togo to the west, Nigeria to the east and Burkina Faso and Niger to the north. Its small southern coastline on the Bight of Benin is where a majority of the population is located...
, mark the suture zone of the Pharusian Ocean closure.
These ocean closures and subsequent tectonic events were not simultaneous, but happened over an extended period of time.
In southwestern central Africa the granulite cooling ages range between 587 and 576 Ma, while in northeast Brazil they range from 568 to 500 Ma.
However, aeromagnetic and gravity data give evidence of continuity between the TBL lineament
Lineament
See also Line A lineament is a linear feature in a landscape which is an expression of an underlying geological structure such as a fault. Typically a lineament will comprise a fault-aligned valley, a series of fault or fold-aligned hills, a straight coastline or indeed a combination of these...
, the Sobral fault
Sobral fault
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....
in northeastern Brazil, the Kandi fault zone
Kandi fault zone
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...
in Benin
Benin
Benin , officially the Republic of Benin, is a country in West Africa. It borders Togo to the west, Nigeria to the east and Burkina Faso and Niger to the north. Its small southern coastline on the Bight of Benin is where a majority of the population is located...
and the Trans-Saharan Belt formed by closure of the Pharusian Ocean.