Torn Turbidite System

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Relief map of Namibia with the position of the outcrop of the Torn Turbidite System (highlighted in red)

The Torn Turbidite System ([ tsɛˈrɪsənə tɜːbəˌdaɪt ˌsɪstɪm ]; also known as the Torn Turbidite Complex ) is a multi-phase, folded , low-grade metamorphic sequence of predominantly siliciclastic turbiditic deposit rocks in northwestern Namibia . Its sedimentary and tectonic development spans a period from 750 to 530 million years ago (younger Neoproterozoic to older Cambrian ).

Position and extent

Surface geology of central Namibia with distortion of the position of the Ripped Turbidite System

The outcrop of the Torn Turbidite System, which extends over around 3000 km² (north-south extension approx. 40 km, east-west extension approx. 100 km), is located on the lower reaches of the Ugab River in the Kunene and Erongo regions and the historic ones Damaraland region . It is cut off in the west against the coast of the South Atlantic by the Ogden Rocks , a geological unit that also emerged from turbiditic sediments, but lies in a fossil ductile shear zone and is therefore mylonitized .

Regionaltektonisch the Shredded is Turbidite system in the overlapping region of two fold belt of the Pan-Orogensystem belonging Damara orogen : the NNW-SSE (parallel to the coast) oriented Kaoko-belt and the WSW-ENE (transverse to the coast) oriented to the hinterland Namibia withdrawing Damara belt . This area is still assigned to the Kaoko belt and called southern Kaoko Zone or Lower Ugab Domain (after the lower reaches of the Ugab). It is superficially cut off from the main part of the Kaoko belt , which emerges further to the north, by the Phanerozoic overburden , which consists mainly of early Cretaceous basalts , the morphological expression of which is the Etendeka plateau with its foothills. In the east, the Lower Ugab Domain is bounded by the Goantagab Domain. It also belongs to the Kaoko Belt and is also characterized by turbiditic, but apparently more proximally deposited sedimentary rocks and, above all, by a more intense and differently oriented tectonic deformation than the Lower Ugab. In the north and south, the Lower Ugab Domain is framed by sedimentary rocks of the Karoo supergroup (in the north by those of the Huab Basin), equivalents of the Etendeka basalts ( gobobosebbergs ) and also early Cretaceous igneous intrusive bodies such as the Brandberg batholite.

Geodynamic framework

In the wake of the disintegration of the Proterozoic supercontinent Rodinia , which (the roughly before 870 million years ago mya abbreviated) began, were made between 780 to 740 mya, starting from a triple junction (triple), intra-continental grave breaches between the cratons Congo -São-Fancisco (hereinafter abbreviated to Congo-SF, São-Fancisco-Kraton now located in Brazil), Kalahari and Río de la Plata (the latter is now located in Argentina). As a result of the continued expansion of the crust, these rift breaks eventually developed into oceanic spreading zones . The resulting, presumably narrow ocean basins are called Adamastor Ocean (between the "African" cratons and Río de la Plata) and Khomas Ocean (between Kalahari and Congo-SF). In these ocean basins, from around 750 mya, the sediments were deposited, which today form large parts of the Damara orogen as metasediments , including the metasediments of the Torn Turbidite System.

From 655 mya, the convergence phase of the ocean basins with subduction began initially only in the northern part of the Adamastor Ocean. From around 580 mya, the crust of the southern Adamastor and Khomas oceans were also in subduction. In the contact zone between the finally colliding cratons, complex deformation occurred, which is responsible, among other things, for today's tectonic structure of the Torn Turbidite System.

Geological structure

"Torn Mountains"
Ugab river.jpeg
False color satellite image of the western two thirds of the outcrop of the Torn Turbidite System. The formations can be roughly differentiated based on the colors (for details, see detailed image description ). Note also the elongated mountain ridges and valleys, which are mostly north-south trending, which are the morphological expression of the narrow main folds of the sedimentary rock layers. In the southeast corner of the picture - morphologically completely different because it is unfolded - the Gobobosebberge , a highland of Etendeka basalts, lined with Karoo sediments to the northwest. The white narrow band that meanders through the picture from east to west is the Ugab River, the white circle marks the location of the "Torn Hills".
In the hills near the Brandberg West Mine, steeply dipping layers of the Torn Turbidite System (view across strike ).
Another location near the Brandberg West Mine, here with a view almost parallel to the strike

Stratigraphy and Etymologies

The metasediments of the Zerrissene Turbidite System form a cyclic sequence of predominantly siliciclastic turbiditic deep-water deposits at least 1600 m thick . Carbonate rocks in the form of marbles occur on a larger scale in sections. The deposits of the Ripped Turbidite System are lithostratigraphically divided into five formations . The onset and release of extensive carbonate sedimentation are used to determine the formation boundaries.

  • The largely siliciclastic Amis River Formation is the youngest formation in the sequence and is at least 600 m thick. It is somewhat unfortunately named after a river that drains the Brandberg , but on whose banks there are no sedimentary rocks of the Torn Turbidite System. The Amis River Formation is particularly extensive in the east and west of the Lower Ugab Domain, whereas it is less widespread in the central part. It correlates with the Kuiseb Formation of the northern zone of the Damara Belt.
  • The partly carbonate-dominated Gemsbok River Formation is approx. 200 m thick. It is named after a southern tributary of the Ugab and is correlated with the Karibib Formation of the northern zone of the Damara Belt.
  • The siliciclastic Brak River formation is approx. 400 m thick. It is named after a southern tributary of the Ugab immediately west of the Brandberg West Mine (see below) and is correlated with the Ghaub Formation of the northern zone of the Damara Belt.
  • The Brandberg West Formation, which has a significant amount of carbonate, is very thin at only approx. 15 m. It is named after the Brandberg West Mine, a sloppy tin-tungsten open pit mine south of the Ugab River, and correlates with the Rössing Formation of the northern zone of the Damara Belt. Previously, it was a basal subformation (member) of the Brak River Formation.
  • The siliciclastic zebraput formation (also spelled zebrapütz ) is the oldest formation in the sequence and is at least 400 m thick. It is named after a water hole in the bed of the Ugab River and is correlated with the Okonguarri Formation of the northern zone of the Damara Belt. Its outcrop is largely restricted to the region north of the Ugab River.

In the absence of a concise generic term for these five formations, the South African geologist Roger Swart introduced the informal designation Torn Turbidite System in 1992 . It is derived from the Zerrissene Hills or Zerrissene (s) Mountains , an area in the western part of the Lower Ugab Domain south of the Ugab River that protrudes over the monotonous ridge and valley landscape. The part of the name "torn (s)" probably comes from the German colonial days of Namibia and was adopted by the South Africans after 1919.

The formations of the Broken Turbidite System and their "lateral" equivalents in the northern zone of the Damara Belt, northeast of the Lower Ugab Domain, are subordinated to the so-called Swakop Group, with the formations in the northern Damara Belt traditionally being understood as a shelf sequence. Because of this and because of the assumed time equivalence, the Torn Turbidite System was previously referred to as "turbiditic Swakop Group successions". In the meantime, the sequence is also delimited in the literature as the Zerrissene-Gruppe ( Zerrissene Group ) from the Swakop group, but still correlated with it. The Swakop Group (and Zerrissene Group) together with other neoproterozoic regional metasediments form the so-called Damara sequence .

Lithologies and sedimentology

The sequence of the Torn Turbidite System is determined by Psammit - Pelit - alternation , whereby the Psammites (predominantly Grauwacken ) show typical features of turbiditic sediments , such as gradation , parallel lamination, ripple stratification as well as load and (rarely) flow marks on the bed surfaces. The coarse fraction of the psammite consists mainly of quartz grains and furthermore of feldspar grains and (mini) fragments of crystalline rocks. The pelites represent the so-called background sediment that has settled in the periods between the turbidity flows.

Due to a metamorphic overprinting , the pelites are mostly in the form of biotite-rich phyllites and more carbon -based siliciclastics have an actinolite - tremolite association. The metamorphosis therefore probably took place under the conditions of the middle green schist facies . Garnets in the phyllites indicate upper green schist facies only locally . The metamorphosis went hand in hand with the folding in the late Neoproterozoic and Cambrian .

The sedimentary- facial characteristics of each of the five formations are briefly outlined below .

Amis River Formation

The Amis River Formation consists predominantly of an alternating layer of greywacke and pelite, but locally contains slightly carbonates and graded, coarse-grained quartz sandstones (quartzwacke). The turbidites in the sequence are clearly different in their western and eastern distribution area. While in the west they are generally relatively coarse-grained and the layer thicknesses are high, in the east both the mean grain size and the thicknesses are smaller. It is concluded that the western deposits are generally more proximal than the eastern ones, but both are assumed to be the outer to the marginal area of ​​a submarine fan .

Gemsbok River Formation

The Gemsbok River Formation consists of an alternating layer of hemipelagic pelites with turbiditic and hemipelagic carbonates. In the upper part, the hemipelagic carbonates (“blue marble”) dominate, in which locally coarse carbonate sediments can be embedded. This sequence is interpreted as material that was deposited in the basin of a developing ( progressive ) carbonate platform, with the clay slates forming the terrigenous background sediment and the carbonates from the platform area gravitationally in the form of debris flows and slowly draining fine-grained sludges ( peri platform oozes ). as more proximal or distal sediments were entered into the upstream, deeper basin.

Brak River Formation

The Brak River Formation is made up of an alternating layer of up to 10 m thick, laterally widely withstanding greywacke banks and pelites, which in the higher part contains isolated individual pebbles and conglomerate deposits. These are interpreted as dropstones or as suddenly unloaded rock cargo from icebergs. In the latter case, rubble is said to have accumulated on the iceberg above the waterline due to the melting of the ice. Simultaneous melting below the waterline led to a gradual shift of the center of gravity towards the tip of the iceberg until it finally became unstable, overturned and the debris that had accumulated up until then suddenly discharged into the sea. However, the pebbles are also seen as the result of turbiditic sedimentation. The highest part of the formation is pelit-dominated. The Grauwacken are interpreted as predominantly distal deposits of a submarine fan.

Brandberg West Formation

The Brandberg West Formation is very similar in structure to the Gemsbok River Formation. It also consists of hemipelagic pelites in alternation with turbiditic and hemipelagic carbonates ("blue marble"), whereby the proportion of the latter in the sequence to the top increases here as well. Debris stream deposits, such as those that occur in the Gemsbok River Formation, are missing, however. In fact, all individual layers show a high degree of lateral continuity. For the Brandberg West Formation, too, deposits in the basin area of ​​a carbonate platform are assumed.

Zebra formation

The zebraput formation in turn consists of pelites with greywacke switched on. Because of the dominance of fine-grained rocks and the average low thickness of the individual layers, this sequence is interpreted as deposits in the transition area between a submarine fan and the deep sea level .

Delivery area of ​​the Grauwacken and large tectonic framework of the deposit

The composition of the Grauwacken with u. a. Rock fragments of granitoids and crystalline slates as well as features of individual mineral grains contained, such as myrmekitic adhesions or perthitic segregation, indicate a continental delivery area, an exhumed crystalline complex of an (old) orogen. However, there are no indications of the presence of volcanic material (e.g. glass fragments) in the Grauwacken. This, like the paleomorphology of the deposit area, which can be reconstructed from the formation of the sediment bodies, indicates deposits on a passive continental margin . Geochemical investigations of the rock, however, showed that the detritic material originated from an active continental margin .

Contrary information is given in the literature on the position of the delivery area. While Swart (1992) in his palaeostream analysis locates the delivery area in western directions and thus in today's South America, other authors use the same methods to come to an exactly opposite position and suspect it to be in the area of ​​the Congo craton.

Sedimentological interpretation of the entire sequence

Strongly simplified representation of the formation of turbidites or submarine sediment fans

The sedimentation history of the Torn Turbidite System begins around 750 mya with the very distal turbiditic and (hemi-) pelagic siliciclastic sediments of the zebra formation, which after advanced divergence of the cratons Congo-São Francisco, Kalahari and Rio de la Plata on a fully formed, passive continental margin or at its transition into the deep sea level of the Adamastor Ocean, more on the western edge of the Congo than on the eastern edge of the Rio-de-la-Plata craton.

The Sedimentationsumschwung toward the carbonate -bearing layers of the Brandenberg-West formation is expected to increase the (relative) sea justified because high sea level generally favor the carbonate production. As a result of this rise in sea level, a carbonate platform with reef-like structures is likely to develop on the adjacent shelf (but only very remotely comparable to today's coral reefs), from which relatively fine-grained, detritic carbonate sediments were introduced into the deep "Torn Basin". The cause of the sea level rise is regional tectonics, i. H. assumed an increased rate of subsidence of the earth's crust in the region.

Then the relative sea level fell again. The carbonate sedimentation ebbed and with the Brak River Formation a siliciclastic, turbiditic deposit system was re-established, which, however, was somewhat closer to its delivery area than at the time of the Zebrapüts Formation. The Brak River Formation is correlated with the presumably glacial (more precisely: glaciomarine) Ghaub Formation (formerly Chuos Formation) of the Swakop Group. Insertions of volcanic ash in the layers of the Ghaub Formation have been dated to 635 mya, which roughly corresponds to the period of the Marino Ice Age , one of the postulated snowball-earth glaciations . Accordingly, the marine pebbles in the higher part of the Brak River Formation are also interpreted, although not unanimously, as glacial. The extensive clay sedimentation in the upper Brak River Formation and the subsequent renewed onset of carbonate deep-water deposits could then be achieved with a glacio-eustatic sea ​​level rise at the time of deposit of the upper Brak River Formation and a generally high eustatic sea level at the time the Gemsbok was deposited - Establish river formation.

Eventually the sea level sank again, and with the Amis River Formation a siliciclastic deposit system re-established itself for a second time. This time the delivery area was at least partially closer than in the “Brak River time”, which suggests an increasing narrowing of the ocean basin and therefore a general increase in the supply of sandy material into the “Torn Basin”.

Alternatively, the marbles of the Brandberg West and Gemsbok River Formations are also interpreted as deep-water equivalents of the cap carbonates of the initial post-sturtic or post-marine sedimentation. The change from siliciclastic to carbonatic systems would not have been caused by the revitalization of the “Carbonate Factory” as a result of a rise in sea level, but rather by interactions between the global climate and the chemical composition of the atmosphere and ocean (especially the CO 2 content).

Structural geology and deformation history

Tilted layers of the Torn Turbidite System up close. It is an infrared image in which the pelitic layers appear very dark. The light (brighter) layers are made of greywacke and / or marble. The image was taken near the Brandberg West Mine.
Satellite photo (above) and geological map (below) of the so-called Bushman folds in the northeast of the Lower Ugab Domain with a map of the D 1 and D 3 fold axes

Wrinkle and foliation generations

Three phases of deformation can be identified in the rocks of the Torn Turbidite System:

The first and most intense deformation (D 1 ) produced the narrow (isoclinal) fold on a kilometer scale with predominantly approximately north-south trending , approximately horizontal fold axes . They give the outcrop of the Torn Turbidite System or the Lower Ugab Domain its characteristic appearance in the aerial or satellite image. To the west of the Lower Ugab domain these wrinkles are west vergent , with folds axis planes with 20 to 70 degrees to the east come . The western fold legs are partly overturned. In the east of the Lower Ugab Domain, however, the folds stand upright or are East Vergent. In the metapelites, D 1 produced a penetrative , closely spaced foliation (S 1 ), which is designed as an axial plane foliation. In carbonate-rich clastics, it occurs in the form of parallel, more extensive, non-aging, anastomosing, muscovite and biotite- rich domains, particularly in the east of the Lower Ugab Domain in the Amis River Formation. In the Grauwacken there is usually no foliation. The spatial position of folds and foliation clearly shows a narrowing in an east-west direction. The shortening of the crust is estimated to be 40 to 60%. Boudinage and other indicators also show an expansion in the north-south direction of 10 to 40%.

The second deformation (D 2 ) can only be observed locally. It manifests itself in the form of obtuse-angled to acute-angled open folds in layers and S 1 on a centimeter scale. The D 2 fold axes have the same orientation in the entire Lower Ugab Domain as the D 1 fold axes (coaxial folding), with the D 2 and D 1 fold axis planes always intersecting at a large angle. S 2 schistoing in the form of rather extensive wrinkled schistoing (krenulation) is local, especially in pelitic layers .

The third generation of wrinkles (D 3 ) only occurs locally, but not only on a small, but also on a large scale. On a kilometer scale, it manifests itself in the form of obtuse-angled to acute-angled open, sometimes strongly asymmetrical folds that overprint the D 1 folds. Here, the obtuse-angled open folds tend to show east-west and the acute-angled open folds tend to have north-east-southwest trending fold axis planes. A relatively wide continuous S 3 -Schieferung occurs in the form of a Runzelschieferung preferably in pelitic layers.

Chronology and large-tectonic framework of the deformation

The three identified deformation phases fit relatively seamlessly into the deformation history generally determined for the Damara ore. The coaxial formation of the D 1 and D 2 folds and the fact that both folds took place under almost the same pressure and temperature conditions (stability range of biotite, readable from the mineralization of the cleavage surfaces) suggests that they refer to the same deformation event go back. It is conceivable here that D 2 started only locally from a certain point in time, while D 1 stopped in the other areas of the lower Ugab domain . The direction of foreshortening during this event was approximately east-west. D 1 is widely detectable in the Kaoko belt. The inversion of the Adamastor Ocean is assumed to be the cause of this deformation. For the following D 2 , a simultaneous northern transport of the Lower Ugab Domain is postulated in order to be able to explain the folding of the S 1 regardless of its orientation (shallow S 1 is folded by east-west shortening, steep S 1 becomes overprinted by activity of the basal shear zone and / or by collapse of the compressed crust with decreasing east-west shortening). The hypothesis of northern transport is consistent with the structural geology of the neighboring units (including the sinistral shear zone in the Ogden Rocks, dextral shear zone between Lower Ugab and Goagantab Domain) and is seen in connection with the closure of the Khomas Ocean that is now beginning.

The geometry of the non-coaxial D 3 structures mainly shows shortening in north-south and north-west-south-east directions, which is also related to the narrowing of the Khomas Ocean and the collision of the Congo-SF craton and the Kalahari- Kraton suggests. In addition, various small-scale deformation indicators in the rocks point to sinistral shear at least for certain D 3 folds during their formation. Since the intensity of the deformation is not the same in the entire Lower Ugab Domain, but is concentrated in certain areas (e.g. in the area of ​​the so-called Bushman folds), it is assumed that ductile shear zones in the basement were involved in D 3 . In addition, the D 3 structures evidently evade the two syenite - granite plutons in the northwest of the Lower Ugab Domain (Doros-Pluton and Voetspoor-Pluton) or attach themselves to them, which suggests that the plutons were already at the time of this deformation phase had taken their place in the rocks of the Ripped Turbidite System. The age of 540 to 530 Ma of the older (syenitic) parts of the Voetspoor pluton can thus serve as the maximum age for D 3 . The D 3 deformation is only detectable in the Damara belt and in the southern part of the Kaoko belt. For the most recent deformation in the northern part of the Kaoko belt, which corresponds to the D 1 -D 2 deformation, an age of around 550 Ma has been determined based on the dating of synkinematic intrusions there. It follows that the collision of the Kalahari craton with the Congo SF craton, unlike that of the Rio de la Plata craton with the Congo SF craton, was only completed well after the onset of the Cambrian.

Web links

Commons : Torn Turbidite System  - Collection of Pictures, Videos and Audio Files

Individual evidence

  1. ↑ David W. Peate: The Parana Etendeka Province. Pp. 217-245 in: John J. Mahoney, Millard F. Coffin (Eds.): Large Igneous Provinces: Continental, Oceanic, and Flood Volcanism. Geophysical Monograph 100. American Geophysical Union, Washington (DC) 1997, doi: 10.1029 / GM100p0217 (alternative full-text link : University of Iowa ( memento of August 9, 2017 in the Internet Archive )).
  2. ^ M. Fernandez-Alonso, L. Tack, A. Tahon, B. De Waele: The Proterozoic History of the Proto-Congo Craton of Central Africa. In: 23rd colloquium on African Geology - CAG23, Johannesburg. Book of abstracts. University of Johannesburg, Johannesburg 2011 ( PDF )
  3. ↑ Armin Zeh, Axel Gerdes, Jackson M. Barton, Jr .: 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, 2009, pp. 933–966, doi: 10.1093 / petrology / egp027 (Open Access)
  4. ↑ Pedro Oyhantçabal Siegfried Siegesmund, Klaus Wemmer: The Río de la Plata Craton: a review of units, boundaries, ages and isotopic signature. In: International Journal of Earth Sciences. Volume 100, No. 2, 2011, pp. 201–220, doi: 10.1007 / s00531-010-0580-8 (Open Access)
  5. ↑ a b David R. Gray, David A. Foster, Ben Goscombe, Cees W. Passchier, Rudolph AJ Trouw: 40Ar / 39Ar thermochronology of the Pan-African Damara Orogen, Namibia, with implications for tectonothermal and geodynamic evolution. In: Precambrian Research. October 2006. doi: 10.1016 / j.precamres.2006.07.003 (alternative full text link : ResearchGate ).
  6. ↑ Hartwig E. Frimmel, Peter G. Fölling: Late Vendian Closure of the Adamastor Ocean: Timing of Tectonic Inversion and Syn-orogenic Sedimentation in the Gariep Basin. In: Gondwana Research. Volume 7, No. 3, 2003 pp. 685-699, doi: 10.1016 / S1342-937X (05) 71056-X (alternative full text link : ResearchGate ).
  7. ↑ a b JFB Jeppe: The geology of the area along the Ugab River, west of the Brandberg. PhD-Thesis, Faculty of Engineering, University of Witwatersrand, 1952 ( online ), map sketch on p. 9 (Fig. 2) and p. 17.
  8. ↑ a b c d e f g h i j k l m n o Roger Swart: The Sedimentology of the Zerrissene Turbidite System, Damara Orogen, Namibia. In: Geological Survey of Namibia Memoir 13. Ministry of Mines and Energy, Windhoek 1992 ( PDF ), official publication of the PhD thesis of the same name from 1990, Rhodes University, Grahamstown ( PDF ).
  9. ↑ a b c d Fabio VP Paciullo, A. Ribeiro, Rudolph AJ Trouw, Cees W. Passchier: Facies and facies association of the siliciclastic Brak River and carbonate Gemsbok formations in the Lower Ugab River valley, Namibia, W. Africa. In: Journal of African Earth Sciences. Volume 47, No. 3, 2007, pp. 121-134, doi: 10.1016 / j.jafrearsci.2006.12.004 (alternative full-text link : AG Tektonophysik, Uni Mainz , unedited manuscript in the accepted version) and literature cited therein.
  10. ↑ The corresponding layers were previously known as the “Chuos Formation”. They were renamed when it turned out that there are two different ages (presumably) glacial horizons in the region. Only the older one kept the name "Chuos". See K.-H. Hoffmann, AR Prave: A preliminary note on a revised subdivision and regional correlation of the Otavi Group, based on glaciogenic diamictites and associated cap dolostones. In: Communications of the Geological Survey of Namibia. Volume 11, 1996, pp. 83-88 ( PDF ).
  11. ↑ a b c d Débora Barros Nascimento, A. Ribeiro, Rudolph AJ Trouw, Renata Da Silva Schmitt, Cees W. Passchier: Stratigraphy of the Neoproterozoic Damara Sequence in northwest Namibia: Slope to basin sub-marine mass-transport deposits and olistolith fields . In: Precambrian Research. Volume 278, 2016, pp. 108-125, doi: 10.1016 / j.precamres.2016.03.005 (alternative full-text link : ResearchGate ) and the literature cited therein.
  12. ↑ a b c d e f g h i j k Cees W. Passchier, Rudolph AJ Trouw, A. Ribeiro, Fabio VP Paciullo: Tectonic evolution of the southern Kaoko belt, Namibia. In: Journal of African Earth Sciences. Volume 35, No. 1, 2002, pp. 61-75, doi: 10.1016 / S0899-5362 (02) 00030-1 (alternative full-text link : AG Tektonophysik, Uni Mainz ) and literature cited therein.
  13. ^ KH Hoffmann, DJ Condon, SA Bowring, AR Prave, AE Fallick: Geochronological Constraints from the Ghaub Formation, Namibia: Implications for the Timing of Marinoan Glaciation. In: IGCP 493 Workshop - The Rise and Fall of the Vendian Biota, 30-31 August 2004, Prato. Abstracts volume. Monash University Prato Center, Prato 2004, p. 51 ( PDF 30 kB)
  14. ↑ Cees Passchier, Rudolph Trouw, Sara Coelho, Eric de Kemp, Renata Schmitt: Key-ring structure gradients and sheath folds in the Goantagab Domain of NW Namibia. In: Journal of Structural Geology. Volume 33, No. 3, 2011, pp. 280-291, doi: 10.1016 / j.jsg.2010.12.005 (alternative full-text link : ResearchGate ) and the literature cited therein.
  15. ↑ Barbara Seth, Martin Okrusch, Michael Wilde, Karl H. Hoffmann: The Voetspoor Intrusion, Southern Kaoko Zone, Namibia: Mineralogical, geochemical and isotopic constraints for the origin of a syenitic magma. In: Communications of the Geological Survey of Namibia. Volume 12, 2000, pp. 143-156 ( PDF ).
  16. ↑ Cees W. Passchier, Rudolph AJ Trouw, Ben Goscombe, David Gray, Alfred Kröner: Intrusion mechanisms in a turbidite sequence: the Voetspoor and Doros plutons in NW Namibia. In: Journal of Structural Geology. Volume 29, No. 3, 2007, pp. 481-496, doi: 10.1016 / j.jsg.2006.09.007 (alternative full-text link : ResearchGate , layouted proof sheet) and literature cited therein.