Mozambique belt

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Mozambique belt with crust domains and ages
Mozambique Belt Structural and metamorphic facies

The Mozambique Belt is a deformation belt that stretches along the east coast of central to South Africa and forms the southern branch of the East African orogen . Its formation began about 1,000 mya. Between 650 and 620 mya the belt was subject to the influences of the Pan-African orogeny , which was followed by the Kuunga orogeny from 570 to 530 mya with further tectono-thermal influences. Based on geophysical patterns, structural properties, and geochronology , it is believed that the Mozambique Belt may be a. continues in Madagascar .

Geographical extension, plate tectonic processes

The Mozambique belt connects to the south of the Arab-Nubian shield . It runs from southern Ethiopia , Kenya, Somalia , Tanzania , Malawi to central Mozambique . It consists of a large number of other mountain ranges .

The subduction of the Mozambique Ocean under the African east coast caused the separation of a coastal strip, Azania, with the formation of one or more crustal clods (terranos, microcontinents) archaic palaeoproterozoic age between Greater India ( India with NE Madagascar , Sri Lanka and the Seychelles ), the Tanzania craton , the then still connected Congo-São Francisco (Congo-SF) craton and the Bangweulu block.

Azania, an old name for areas of the East African coast, presumably extended from present-day Madagascar, Somalia, Ethiopia to the Afif Terrans on the Arab-Nubian Shield. It is believed that this separation was caused by the formation of oceanic island arcs with backarc and forearc basins and expansion of African continental crust. (Slab roll-back).

Between 650 and 620 mya, these crusts collided with the cratons Tanzania, Congo-SF and Bangweulu as a result of the approach of the Indian Shield.

Another orogen formation phase took place between 600 and 500 mya when East Antarctica and Australia approached the cratons Congo-SF, Tanzania and Bangweulu as well as Kalahari and Zimbabwe, collided with them and formed the Kuunga Belt.

Structural development, rocks, facies

The Mozambique Belt contains a large number of crustal domains, blocks and orrogens that have emerged in different ways and have evolved differently from one another. What they have in common, however, is the impact of the collision of these structures with Greater India as part of the Pan-African Orogeny.

Neoprotereozoic juvenile crustal domains

To the south of the Arab-Nubian Shield, the Eastern Granulite Nappe (EG) and Cabo Delgado Nappe (CD) complex, collectively known as EGCD, adjoin. Various tectonic units exist within this complex. The EGCD ​​runs from eastern Uganda through Kenya and Tanzania to central Mozambique.

Eastern Granulite Nappe and Cabo Delgado Nappe Complex

The EG contacts the Western Granulite Belt to the west, while the CD connects to the Marrupa Complex to the west.

The rocks that formed from approx. 990 mya are mostly classified as juvenile, i.e. i.e., newly formed oceanic crust similar to that of the Arab-Nubian shield. They were formed when the Mozambique Ocean opened up and ocean floor spreads formed backarc and forearc basins, island arches and other terranos . These crustal parts consist predominantly of metamagmatic and overlying metasedimentary (both metamorphically influenced) components and contain various other fragments, e.g. B. from anorthosites and gneisses of archaic or palaeoproterozoic age.

A special feature of this complex is the occurrence of marble-containing metasediments. The age of these sediments, around 800 to 600 mya, indicates that they were deposited on the edge of the Mozambique Ocean. This zone is interpreted as the passive continental margin that formed when Azania was separated from the East African flank. Alternatively, these metasediments are viewed as fragments of oceanic island arcs.

Between 650 and 620 mya they were subject to tectonic , thermal processes and now show highly metamorphic and deformed granulite facies . The collision processes also resulted in a thrust of the crusts formed on the westernmost basement in the form of tectonic ceiling or cliffs (engl .: Nappe).

Pre-Neoproterozoic reshaped crustal areas

As a result of the collision processes during the East African and Kuunga Orogeneses, pre-Neoproterozoic crustal areas on the eastern to southwestern edges of the cratons Congo-SF, Tanzania and Bangweulu as well as the northern and eastern edges of the cratons Kalahari and Zimbabwe were modified tectonically, thermally and structurally in different ways. This occurred in the Western Granulite Belt, Usagaran / Ubendian Belt, Irumide Belt, Southern Irumide Belt, Unango / Marrupa Complex and Nampula Block.

Western granulite belt

The Western Granulite Belt is located in SW Kenya and S Tanzania. It contacts the Congo-SF and Tanzania cratons and the Usagaran Belt to the west and the Eastern Granulite Nappe Complex to the east.

The only available data show an age of the belt base of 3,100 to 2,500 mya, comparable to that of the Tanzania craton. The granitoid gneisses date to 1,880 and 1,095 mya. Magmatic and sedimentary events occurred between 843 and 665 mya. The Pan-African influences produced a metamorphic granulite / amphibolite facies , 580 to 540 mya.

Usagaran and Ubendian belts

The Usagaran and Ubendian Belts run across Tanzania, Malawi and Zimbabwe. They lie between the southern area of ​​the Tanzania craton and the northwest of the Bangweulu block.

The base of this belt has an archaic age of 3,100 to 2,800 mya and corresponds to that of the Tanzania craton. Both paleoproterozoic belts correlate due to similar igneous ages.

The Usagaran Belt consists of two main tectonic units; a highly structured base containing 2,000 my old eclogites and a low metamorphic igneous-sedimentary overburden. Both are separated by a 1,920 my old fault . Most of the rocks consist of granitoids and granitoid gneisses that arose from intrusions between 1,900 and 1,730 mya mya .

The Ubendian Belt contains various terranes that have undergone multiple strike-slip deformations ( blade displacement ). There are mainly rocks with an early metamorphic granultite facies, 2,100 to 2,025 mya. They are associated with around 1,820 my old eclogites that originate from subduction zones. Metamorphic amphibolite facies and the formation of strike-slip-induced granitoids occurred between 1,960 and 1,800 mya.

Both belts show a pan-African metamorphosis from green slate to sub-green slate facies, 570 to 530 mya.

Irumide belt

The Irumide Belt stretches from central Zambia through northern Malawi to southern Tanzania and connects to the northwest of the Bangweulu Block and the Usangara and Ubendian Belts. In the SW he contacts the Lufilian arc . The Mugese shear zone separates this belt in the NE from the Ubendian belt. In the south, the Mwembeshi Shear Zone forms the tectonic boundary with the Southern Irumide Belt.

The basis of this belt is formed by granite gneiss with an age of 2,050 to 1,930 mya, overlaid by metasedimentary overburden, 1,880 to 1,550 mya. These two layers were intruded first between 1,650 and 1,550 mya and later with granitoids between 1,050 and 0.950 mya. The melt of the granitoids comes directly from the base crust. Associated with the last phase was also a high temperature / low pressure compression. According to the pan-African metamorphic, the rocks have a green slate to sub-green slate facies, 570 to 530 mya.

Southern Irumide Belt

The Southern Irumide Belt (SIG) is located in southern Tanzania. The south side encloses the northern flank of the Kalahari craton and the Nampula block. To the east, the Cabo Delgado Nappe complex forms the border.

The SIG represents a complex accretion zone of terrans derived from the Paleoproterozoic Usangara and Ubendian Belts, the Mesoproterozoic Irumide Belt and other Neoproterozoic crustal parts. These parts of the crust emerged as supra -subduction zone opiolites, i.e. that is, they have resided in convergent intra-ocean subduction zones, e.g. B. in Backarc and Forearc basins developed. The magmatism from this dates from 1,400 to 1,040 mya. Together with sedimentary deposits, these deposited on the southern edge of the Congo-SF craton. Migmatitic gneisses intruded around 1,055 to 1,000 mya . Local igneous granite is between 764 and 724 mya, comparable to occurrences in the Unango and Marrupa complexes.

The Mwembeshi Shear Zone separates the SIG from the north-trending Irumide Belt. The pan-African metamorphic influence produced granulite / amphibolite facies, 616 to 563 mya.

Unango and Marrupa complex

The Unango and Marrupa Complex (UMK) is located in the north and center of Mozambique. It lies between the Cabo Delgado Nappe Complex to the east and the Western Southern Irumide Belt. Lake Malawi is located between this and the UMK .

The UMK contains large volumes of mainly felsic orthogneiss, 1,062 to 946 mya, which presumably developed in continental rift valleys and accreted with the cratons Tanzania and Congo-SF. The formation of the granulite facies, 953 mya, is believed to be related to the orogeny of the Southern Irumide Belt. In the Neoproterozoic, minor magmatic events occurred in the form of plutons , 799 mya, from nepheline and syenite . Pan-African deformations and high-grade metamorphoses have been demonstrated in the Marrupa area, 555 mya, with amphibolite facies, and in the Unango area, 569 and 527 mya, with amphibolite to granulite facies. Postorogenic collisions with Felsic plutons, 549 and 486 mya, are only present in the Unango area.

Nampula block

The Nampula Block is in N Mozambique. To the north it is separated from the Southern Irumide Belt and the Cabo Delgado Nappe Complex by the Lurio Belt.

The oldest rocks, 1,127 mya, contain a polydeformed sequence of volcanic rocks consisting of gray gneisses and migmatites with upper amphibolite facies, into the Trondhjemit - and Tonalit -bearing, s. G. TTG complexes , granodiorites and granitic orthogneiss intruded. The geochemistry of these rocks suggests formation as a juvenile crust in the island arc environment. Various terranes formed, which then accreted.

During the last Mesoproterozoic activities, voluminous plutons and planar volcanic rocks appeared. They contain slate granites, eye gneiss and granitic orthogneiss. The age of this phase is dated to 1,075 mya. As a result of the Pan-African orogeny, the old rocks were tectonically and thermally metamorphic and are present as amphibolite facies, 550 to 500 mya.

Lurio belt

The Lurio Belt, also known as the Lurio Shear Zone, is located in the north of Mozambique and separates the Nampula Block from the Southern Irumide Belt to the north and the Cabo Delgado Nappe Complex in the west.

The Lurio belt originated during the Kibara orogeny, from 1,400 mya, and correlates with the formation of the Nampula belt. After the metamorphosis in the Kibara period, the rocks were tectonically and thermally reshaped again during the Pan-African orogeny. This resulted in a shift in the leaves between the adjacent blocks. Together with the Zambezi Belt and the Mwembeshi Shear Zone, they form a 3,000 km long discontinuity that is believed to run across South Africa to the coast of the South Atlantic .

In the west, the Mozambique Belt borders the Lufilian Arch .

literature

  • B. Bingen and others: Geochronology of the Precambrian crust in the Mozambique belt in NE Mozambique, and implications for Gondwana assembly. In: ScienceDirect Precambrian Research. Volume 170, Issues 3-4, May 2009, pp. 231-255. doi: 10.1016 / j.precamres.2009.01.005
  • H. Fritz, V. Tenczer and others: Central Tanzanian tectonic map: A step forward to decipher Proterozoic structural events in the East African Orogen. In: Tectonics. Vol. 24, TC6013, 2005. doi: 10.1029 / 2005TC001796
  • Harald Fritz and others: Hot granulite nappes - Tectonic styles and thermal evolution of the Proterozoic granulite belts in East Africa. In: ScienceDirect, Tectonophysics. Volume 477, Issues 3–4, November 15, 2009, pp. 160–173, Hot orogens, doi: 10.1016 / j.tecto.2009.01.021

Web links

Individual evidence

  1. ^ H. Fritz and others: Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution. In: ScienceDirect, Journal of African Earth Sciences. Volume 86, October 2013, pp. 65-106. doi: 10.1016 / j.jafrearsci.2013.06.004
  2. ↑ a b H. Fritz and others: East African and Kuunga Orogenies in Tanzania - South Kenya. bibcode : 2012EGUGA..14.8754F
  3. ^ Geological Framework and regional metallogeny of Tanzania. Full text ( memento from March 5, 2016 in the Internet Archive ) on: kilimanjarominingcompany.com (PDF; English)
  4. ^ Fernandez-Alonso et al : The proterozoic history of the Proto-Congo craton of Central Africa. Department of Earth Sciences, Royal Museum for Central Africa, B-3080 Tervuren, Belgium. ( Full text on: africamuseum.be ; PDF; English)
  5. ↑ LS Andersen, R. Unrug: Geodynamic evolution of the Bangweulu Block, northern Zambia. In: Precambrian Research. Volume 25, Issues 1-3, August 1984, pp. 187-212. doi: 10.1016 / 0301-9268 (84) 90032-9
  6. ^ Lecture Regional Geology of the Earth, Neoproterozoic 4, (Arabia, Egypt) WS 2006/07. ( Full text on: erdwissenschaften.uni-graz.at ; PDF)
  7. ↑ Tomoeki Nakakuki, Erika Mura: Dynamics of slab rollback and induced back-arc basin formation. In: Earth and Planetary Science Letters. Volume 361, January 2013, pp. 287-297. doi: 10.1016 / j.epsl.2012.10.031
  8. ↑ V. Tenczet and other: Anorthosites in the Eastern Granulites of Tanzania-New SIMS zircon U-Pb age data, petrography and geochemistry. In: ScienceDirect, Precambrian Research. Volume 148, No. 1-2, July 20, 2006, pp. 85-114. doi: 10.1016 / j.precamres.2006.03.004
  9. ^ G. Viola and others: Growth and collapse of a deeply eroded orogen: Insights from structural, geophysical, and geochronological constraints on the Pan-African evolution of NE Mozambique. In: Tectonics. Volume 27, TC5009. doi: 10.1029 / 2008TC002284
  10. ↑ Armin Zeh and others: Archean Accretion and Crustal Evolution of the Kalahari Craton — the Zircon Age and Hf Isotope Record of Granitic Rocks from Barberton / Swaziland to the Francistown Arc. In: Journal of Petrology. Volume 50, No. 5, May 1, 2009, pp. 933-966. doi: 10.1093 / petrology / egp027
  11. ↑ TM Kusky: Tectonic setting and terrane accretion of the Archean craton Zimbabwe. In: Geology. Volume 26, No. 2, February 1998 doi : 10.1130 / 0091-7613 (1998) 026 <0163: TSATAO> 2.3.CO; 2 ( full text ( Memento from February 19, 2016 in the Internet Archive ); English)
  12. ^ Andreas Möller and others: Crustal Age Domains and the Evolution of the Continental Crust in the Mozambique Belt of Tanzania: Combined Sm – Nd, Rb – Sr, and Pb – Pb Isotopic Evidence. In: Journal of Petrology. Volume 39, No. 4, pp. 749-783. doi: 10.1093 / petroj / 39.4.749
  13. ^ H. Fritz and others: Central Tanzanian tectonic map: A step forward to decipher Proterozoic structural events in the East African Orogen. In: Tectronics. Volume 24, TC6013, 2005. doi: 10.1029 / 2005TC001796 (full text on: erdwissenschaften.uni-graz.at. ) (English)
  14. ^ JL Lenoir and others: The Palaeoproterozoic Ubendian shear belt in Tanzania: geochronology and structure. In: Journal of African Earth Sciences. Vol. 19, No. 3, 1994, pp. 169-184. ( africamuseum.be: PDF ; English)
  15. ^ B. De Waele and others: "High-temperature, low-pressure tectono-thermal evolution of the Irumide Belt, central, Southern Africa: Lithosphere delamination during arc-accretion" Frontier Research on Earth Evolution Report 2002-2004. V2. ( bdewaele.be: PDF ; English)
  16. ↑ CA Hauzenberger and others: Termination of the Southern Irumide Belt in Tanzania: Zircon U / Pb geochronology. In: Precambrian Research. Volume 255, 12/2014, pp. 144-162. doi: 10.1016 / j.precamres.2014.09.021
  17. ↑ B. Bingen and others: Geochronology of the Precambrian crust in the Mozambiquebelt in NE Mozambique and implications for Gondwana assembly. In: Precambrian Research. Volume 170, Issues 3-4, May 2009, pp. 231-255. doi: 10.1016 / j.precamres.2009.01.005
  18. ^ PH Macey et al: Mesoproterozoic geology of the Nampula Block, northern Mozambique: Tracing fragments of Mesoproterozoic crust in the heart of Gondwana. In: Precambrian Research. Volume 182, Issues 1-2, September 2010, pp. 124-148. doi: 10.1016 / j.precamres.2010.07.005
  19. ^ R. Sacchi and others: Pan-African reactivation of the Lurio segment of the Kibaran Belt system: a reappraisal from recent age determinations in northern Mozambique. In: Journal of African Earth Sciences. Volume 30, Issue 3, April 2000, pp. 629-639. doi: 10.1016 / S0899-5362 (00) 00042-7
  20. ^ A. Kröner and others: Kibaran magmatism and Pan-African granulite metamorphism in northern Mozambique: single zircon ages and regional implications. In: Journal of African Earth Sciences. Volume 25, Issue 3, October 1997, pp. 467-484. doi: 10.1016 / S0899-5362 (97) 00117-6