Damara belt

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Relief map of Namibia
Traditional settlement area of ​​the Damara and Nama in Namibia

The Damara Belt ( English Damara Belt ) is a complex of folds and thrusts in the regional geology of South West Africa , which arose as a result of the collision between the then still intact Congo-São Francisco Craton (Congo-SF for short) and the Kalahari Craton.

The name of this belt is derived from the name for the African ethnic group Damara , which originally had their settlement area in the central west of Namibia .

The Damara Belt is the intra-continental branch of the Damara orogen. Both belong to the Neoproterozoic (1,000 to 541 million years ago, abbreviated mya ) Pan-African Orogenous System , which was an essential part of the formation of the supercontinent Pannotia .

The orogeny of the Damara belt was preceded by the separation of the Congo-SF craton from the Kalahari and Río de la Plata cratons from 780 mya. The cause were superplume events that led to the disintegration of the supercontinent Rodinias .

The main phase of the orogenic development of the Damara belt occurred from 560 to 510 mya with the collision of the cratons Congo-SF and Kalahari. Late orogenic intrusions occurred around 480 mya. Strong uplift processes took place up to the Triassic / Jura border.

The evolution of the Damara Belt from the breakup of the supercontinent Rodinia to the formation of rift breaks with oceans or seas and their subsequent closure as a result of subduction corresponds to the Wilson cycle .

Position and extent

The Damara Belt can be determined from the west coast of the South Atlantic to the interior of Namibia over a length of approx. 530 kilometers (abbreviated to km). To the east it is covered by younger sediments of the Kalahari with an irregular extent. On the Atlantic coast, the northern area of ​​the Damara belt in the Kunene region connects to the Kaoko belt with its Ugab zone. In the south, the Damara Belt borders the Gariep Belt in the ǁKaras region near the Namibian city of Lüderitz . This extension is approx. 600 km and represents the area of ​​the Damara belt in the narrower sense. In addition there are approx. 350 km for the northern platform reaching north and approx. 450 km for the Nama foreland basin in the south .

From a geological point of view, the Damara Belt has a southwest-northeast streak (longitudinal axis) on the southwestern area of ​​the Congo-SF craton and northwestern edge of the Kalahari craton. He is open-minded in central and southern Namibia . It continues under cover layers towards Botswana .

Based on similar tectonic developments, structural and metamorphic properties, it is believed that the Damara Belt is part of a larger orogen complex that stretches across southern Africa. This complex runs further east from the Damara Belt to the west to the Lufilian Arc , the Zambezi Belt to the Mozambique Belt and the Lurio Belt or to the Lurio Shear Zone .

Geodynamic development

Geological crust architecture of the Damara Belt in the Damara Orogen, schematic representation
Tectonic evolution of the Damara belt in the Damara orogen, schematic diagram

The reconstruction of the tectonic evolution of the Damara Belt is currently still marked by some uncertainties and ambiguities. These relate in particular to the configuration or location of continents and cratons (here relating to the Congo-SF and Kalahari), the formation of intra-continental rifts and ocean floor spreads , the formation, extent and size of oceans and seas that separate the land masses and the Subduction directions and velocities of the oceans (here relating to the Adamastor Ocean and the Khomas Sea).

On the basis of the previous geological investigation results as well as various assumptions about the uncertainties that have not yet been clarified, there are in part different hypotheses about the development of the Damara Belt. One of them is shown below.

The geodynamic evolution of the Damara Belt is related to the formation and disintegration of the Rodinia supercontinent. When this had formed around 900 mya, u. a. the cratons Kalahari , Río de la Plata and the Congo craton combined to form one land mass. The Congo Craton was connected to the São Francisco Craton (Congo SF for short).

Triple Junction using the example of the Afar Triangle , East Africa

In the period from 780 to 740 mya, the superplume events initiated intra-continental rifts (rifts) along a triple junction between the Congo-SF craton and the Kalahari and Río de la Plata cratons. First major igneous events can be seen as a sign of plume developments. The Adamastor Ocean formed between them.

On the western edges of the spreading cratons Kongo-SF and Kalahari, long-lasting extension- related plutons of granitoids , syenites and diorites as well as volcanic rocks with rhyolite lava flows and ash tuffs developed . Several kilometers thick layers were deposited. They form the basal layers of the sedimentary nosib group (see →  Nosib group ).

Schematic representation of Horst - Graben - (above) and Halbgraben (below) faults

Subsequently, two approximately parallel intra-continental rift breaks developed between the Congo SF and Kalahari cratons. The rift breaks formed basins in which various ditch - horst systems, half- ditches , ridges and faults developed.

Schematic section through a lake basin

First a northern rift valley opened followed by a southern rift valley. Today's tectono-stratigraphic division of the Damara Belt from the Northern Rim Zone to the Southern Rim Zone arose from them. From a displacement in the southern rift valley, a progressive subsidence (crust subsidence ) formed with increasing spread , in which the Khomas Rift, which is also known as the Khomas Trough, arose. The continued subsidence of the crust led to the flooding of the two basins with seawater from the Adamastor Ocean. The Outjo Sea formed in the northern rift valley and the Khomas Sea in the south.

A mid- ocean ridge and an ocean floor spreading probably arose in the Khomas trough . The approximately 350 km long Matchless Amphibolite Member (see → Matchless Amphibolite Member ) is seen as an indication of ocean floor spreading  . According to its current geographical location, this stretched eastwards from the Walvis Bay ( Walvis Bay ) to the north on the west Atlantic coast via the Lufilian Arch , the Zambezi Belt , the Katanga Copper Belt ( Copperbelt ) to the Lurio Belt in the Mozambique Belt of Central Mozambique .

For several million years, the rifts served as collecting basins for a wide variety of sediment material , which was mainly transported by rivers and deposited as fluviatiles sediments (river deposits). The rock spectrum consists mainly of siliciclastics with minor deposits of volcanic-sedimentary layers.

Several ice ages occurred during the rift phase . The first was the Kaigas Ice Age around 750 mya. It was followed by the Sturtic Ice Age at around 730 mya , which may have reached global proportions, known as Snowball Earth . Subsequent ice ages were the Marino Ice Age , from around 635 mya, also with global glaciation, and the Gaskiers Ice Age , around 580 mya. With the ice ages, especially the Sturtic Ice Age, sedimentation came to a standstill or was greatly reduced. During and after the formation of glaciers , the sea level changed drastically worldwide (see also → Eustasie ). With the melting of the mighty ice sheets , the enormous amounts of meltwater led to widespread flooding , in the course of which calcium carbonates and other sediments were formed as glacial diamictite or tillite deposits and sometimes transported far. These ice ages and their demonstrable effects on geological and climatic processes are important markers for the reconstruction of the geochronological development of the earth's history.

From 655 mya onwards, the divergence phase was followed by the convergence phase between the Cratonic African and South American continental floes. Between 595 and 560 mya the northern Adamastor Ocean closed, and between 550 and 540 mya the southern part of the Adamastor Ocean was also subducted westward under the Rio de la Plata craton. As a result, the cratons Río de la Plata and Kalahari collided.

Between 595 and 575 mya the Khomas Sea began to subduct northward under the Congo-SF craton. From 560 to 540 mya, the cratons Congo SF and Kalahari collided in a sinistral, that leftist slip fault (Engl. Strike-slip fault), and the Khomas sea had closed around 540 mya. On the Kraton Congo SF were formed north-west vergent inclined folds and thrust faults , while Southeast convergent trained on the Kalahri craton structures. It is believed that the Kalahari craton partially subducted under the Congo SF craton. The shifting of the leaves was accompanied by an expansion of the crusts in a northeast / southwest direction, which created various faults and shear zones .

Naukluft Mountains as seen from the Sesriem settlement

From 520 to 510 mya, the Congo-SF craton experienced a powerful thickening in the area of ​​the collision zone by up to 24 km with a corresponding increase in its crust relative to the southern zone. The sediments previously deposited were compressed, deformed into a high mountain range of folds and partially pushed onto the Congo-SF craton. They formed the still recent Khomashochland . The Naukluft Nappe Complex had pushed itself as a niche thrust on the northern continental margin of the Kalahari craton.

These compression processes were accompanied by intrusions of powerful plutons in the northern and central areas of the Damara Belt as well as deformations and metamorphoses of crustal areas that lasted up to 460 mya. After that, the Damara Belt had largely consolidated.

With the breakup of Gondwana and the opening of the South Atlantic from the Early Cretaceous onwards, powerful volcanic rocks intruded on the South American and African sides . In the Damara belt it was u. a. the Erongo , the Brandberg , the Spitzkoppe , the Messum Crater , the Brukkaros and Groot Paresis and several other igneous intrusions such as dykes , sills and kimberlite - vents (without diamonds ).

At the end of the Cretaceous the sediments of today's Kalahari were deposited in the Kalahari Basin . These range u. a. from Botswana westwards to about the middle of the Damara Belt.

The Namib desert probably developed between 16 and 15 mya . The cause was probably the formation of the Antarctic Circumpolar Current and the planetary circulation of the subtropical high pressure belt , which prevented significant precipitation over the Namib.

The developments that took place in the Damara Belt from the breakup to the reconfiguration of continental land masses, including the formation and closure of oceans and seas, are collectively referred to as the Wilson cycle .

Tectono-stratigraphic structure

Damara orogen with geological units of the Damara belt. Abbreviations: NZ Northern Zone; AF Autseib Fault; CZ Central Zone; OmSZ Omaruru Shear Zone; SZ Southern Zone; OkSZ Okahandja Shear Zone; SMZ Southern Margin Zone

The Damara belt is subdivided into several, approximately aligned tectonic-stratigraphic zones based on the tectonic development, stratigraphy , lithostratigraphy and the geological units. The boundaries of the zones result from faults , lineaments , faults or stratigraphic transitions. From north to south the zones are arranged as follows:

Northern platform

The Northern Platform is located on the southwestern area of ​​the Congo-SF craton. The large intra-continental Owambo Basin was formed there during the rift phase between the cratons Congo-SF, Kalahari and Río de la Plata. This basin stretches from northern Namibia to southern Angola . The western border of the Northern Platform is formed by the Sesfontein Thrust, which separates the Eastern and Central Zone of the Kaoko Belt . To the south, the Northern Platform is bounded by the Kamanjab Inlier and various outcrops of the Grootfontein Inlier.

This platform contains sediments from the Nosib Group, the Otavi Group, and the Mulden Group. The mighty, weakly metamorphic carbonate platform of the Otavi group and the molasses sediments of the Mulden group are particularly characteristic . The Otavi sediments formed the Otavi mountain range or the Otaviberge , which extends between the cities of Otavi (eponymous), Tsumeb and Grootfontein .

Northern edge zone

The Northern Margin Zone is a narrow, elongated, east- / northeast-trending mountain complex of metamorphic rocks, which extends along the northern Kamanjab Inlier and the western adjoining Northern Platform. To the south, the Khorixas-Gaseneirob Thrust, also called Outjo Thrust Belt, separates the area from the Northern Zone. In the west, the northern edge zone borders on the Epupa Metamorphic Complex. The communities of Outjo in the east and Khorixas in the west are on or at this thrust . It emerged from a fault that arose on the steep slope of the northern rift valley during the subsidence of the basin. This rift valley formed the northern area of ​​the Outjo Sea.

The Northern Rim contains a thick succession of sediments similar to that of the Northern Platform. During the collision of the cratons Kongo-SF and Kalahari, these were unfolded as thrust and folding belts in the direction of the Northern Platform. The vergence (tilting direction) of the folds is inclined in the northwest direction.

Northern zone

The Northern Zone extends between the Khorixas-Gaseneirob Thrust in the north and the Autseib Fault / Otjohorongo Thrust in the south. There the Northern Zone connects to the Central Zone. This fault runs east to the Grootfontein Inlier. It is named after the places Autseib and Otjohorongo in the Erongo region . In the west, the Epupa Metamorphic Complex forms the boundary.

The Northern Zone can be described as a northwardly directed, severely deformed belt of folds . Its folds are in principle upright to north Vergent, i. that is, they lean north, with an east-west trending trend. The strongest formation occurs in the south, while it subsides in the north.

The northern zone forms a deep rift basin with half-ditch structures, in which sediments from the Nosib, Swakop and regionally also the Mulden groups were deposited. The Swakop Group is characterized by mighty siliciclastic turbidites over which calcium carbonate and marine flyschoid sediments are deposited.

As a result of the formation of the rift valley, volcanic rocks developed between 756 and 746 mya , which penetrated the sediments of the Nosib group and thus defined the minimum age of the tectonics. The volcanic rocks consist of pyroclastic ash flows , tufa layers and lava flows . They form u. a. the majority of the approximately 150 km² Summas Mountains and the neighboring Mitten Folds. These mountain complexes are located southwest of Khorixas .

In the western part of the Northern Zone, thick granitoid plutonites or volcanic rocks intruded . These extend almost over the entire width and reach up to the central zone. They developed in two phases: the first sitting took place during the main deformation of the folds between 590 and 570 mya and penetrated these structures. The second phase occurred in the period from 550 to 510 mya and is assigned to the decaying north / south compression of the Damara belt. These plutonites typically form structures that have been formed from up to three intrusions and are often concentrically zoned. The magmas differ and can consist of syenitic to biotitic granites . Also aplitische Dykes took place.

Central zone

The Central Zone extends between the Autseib Fault / Otjohorongo Thrust of the Northern Zone and the Okahandja Lineament in the south. The Central Zone is divided into the Northern Central Zone and the Southern Central Zone, which are separated by the Omaruru Lineament and the Waterberg Thrust to the east. It is named after the municipality of Omaruru in the Erongo region and the Table Mountain Waterberg in the Otjozondjupa region , which mark the course of this fault up to the Grootfontein Inlier.

The Northern Central Zone is the continuation of the rift system beginning in the Northern Rim Zone with the Outjo Sea. The tectonic boundary is the Omaruru Lineament. The South Central Zone can be viewed as a geological nest in which several faults occurred. South of the eyrie is the rift system of the southern zone, in which the Khomas Sea was formed in the further development. The eyrie was flooded by both seas. In the southern central zone, dome-shaped inlays of the Khan River Detachment developed, which are surrounded by sediments (see →  Khan River Detachment ).

The sediments of the Central Zone are divided into the siliciclastics of the Nosib group and the calcium carbonates of the Swakop group. Tectonic and intrusive processes occurred in the period from 560 to 508 mya.

Okahandja lineament

The Okahandja Lineament is a linear geostructure that separates the Okahandja Lineament Zone from the north-lying South Central Zone. It can be traced aeromagnetically over a length of approx. 530 km from the Namib (desert) near the lower Kuiseb River via the municipality of Okahandja in the Otjozondjupa region and further on a SW / NE deletion . This tectonic fault initially represented the edge of the steep slope from the southern rift valley with the Khomas trough developing in it. The Okahandja Lineament thus probably represents the southern border of the Congo-SF craton during and after the formation of the rift.

The Okahandja Lineament forms a deep fracture zone in the earth's crust where shear displacements in vertical and horizontal directions between the central and southern zones take place. It can be viewed as a monoclinal-like, downward-facing part of a fold and represents one of the most important geological boundaries of the Damara orogen. The lineament can be recognized by a vertical fold structure with isoclinal fold legs that are almost parallel. On the basis of stratigraphic and geophysical surveys, it is assumed that along this lineament the Central Zone was raised by 20 to 24 km relative to the Southern Zone, or the crust of the Central Zone thickened by this amount. Felsic volcanic rocks similar to those in the Northern Zone emerged near the lineament .

During and after the tectonic collision phase with partial subduction of the Kalahri craton under the Kongo-SF craton, mighty granitoid plutons such as the Goas Diorit Suite, the Salem Granit Suite and the Habis Granit Suite intruded in the period from 565 to 495 mya . The suites consist of individual plutons of comparable petrography, mostly distributed over several areas in the central zone. In addition, post-tectonic dykes , volcanic vents and lava layers formed . The intrusiva are often composed of granite , granodiorite , quartz diorite , leukogranite and alaskite , a leukogranite variety, consisting mainly of quartz and alkali feldspar . The different petrography suggests different magma sources and their genesis history. The names of the volcanic rocks mostly refer to regional locations where they were first described or often occur.

Okahandja Lineament Zone

The Okahandja Lineament Zone connects to the Okahandja Lineament to the south and is between 25 and 40 km wide. This tectonic unit is interpreted as a geosuture between the cratons Congo-SF and Kalahari. During the subduction of the Khomas Sea, an accretion wedge attached itself to the Congo-SF craton, which is now considered to be its southern edge.

In this zone there is an abrupt change in the structural style, the vergence (inclination) of the structures, the geophysical signatures and the metamorphic facies between the southern zone and the southern central zone. The rock fabric is almost vertically aligned in NW-direction and parallel to the course of the zone due to strong cleavage geschiefert . The folds can be steep and dense to crowded (isoclinal).

At the southern edge of the Okahandja Lineament Zone, the Donkerhuk batholith intruded around 523 mya, which formed from a very large number of flat granitic effusions over a period of 20 to 20 million years. With a length of over 200 km and a width of up to 40 km, it is the largest individually formed batholith in Namibia.

Rocks of the basement and the sedimentary Nosib group are not exposed. However, sediments were deposited from the Swakop group known as turbidites down slid the steep slope to the deep pool of the Southern Zone.

Southern zone

The Southern Zone, also known as the Khomas Trough, extends between the Okahandja Lineament Zone in the north and the Gomab River Lineament in the south, where the southern edge zone begins. The southern zone emerged from the southern rift valley, which represents a basin structure that is about 20 km deep on the subducted plate edge (English. Slap) of the Kalahari craton. It is assumed that the edge of the plate tore off and did not completely submerge into the earth's mantle (slab break-off) (see also → Backarc basin ), which brought the subduction process to a standstill. The northern edge of this basin is formed by a steep slope of the Okahandja Lineament Zone.

In this basin encamped siliciclastic , flyschoide sediments of the Swakop group with widths of up to 10 km from. In the transition area of ​​the steep slope to the basin floor, extensive turbidite alluvial cones formed , the sediments of which originate from the southern central zone.

Matchless Amphibolite Member

The SW-NE trending zone of the Matchless Amphibolite Member represents an important geological unit within the Southern Zone. Its outcrop extends over a length of approx. 350 km southwest of the Walvis Bay seaport in the Erongo region north past Windhoek to Steinhausen in the Omaheke region .

This formation combines important tectonic and lithological features to understand the evolution of the Damara Belt. Tectonically, it is a major shear zone where displacements occur in a southeasterly direction. Geochemical studies show a basalt signature of a mid- ocean ridge for the Matchless Amphibolite Member . This mechanism includes subalkalinen and tholeiitic ocean floor basalts with metamorphic overprinted pillow lava , basaltic breccia (angular rock debris) and gabbro - lenses with embedded marbles and graphite - schists . During the partial subduction of the Kalahari craton, these rocks autopsied on the Congo-SF craton.

The Matchless Amphibolite Member is believed to be associated with the Mwembeshi Shear Zone present in the Zambezi Belt and the Lufilian Arc . Both would then form a trans-continental shear zone . However, the Zambezi Belt and the Lufilian Arc arose from so-called aulakogen rift breaks that did not develop into ocean floor spreads .

Southern edge zone

Hakos Mountains
Gamsberg

The Southern edge zone ( english Southern Margin zone ) adjoins the Southern Zone and extends between the gomab River lineament in the north and the Frontal Thrust in the south. The Gomab River Lineament, named after the Gomab River, sweeps south past Windhoek and further east. Similar to the Northern Rim, it was formed as an accretion wedge during the collision of the two cratons and subduction of the ocean floor . Rocks of the oceanic crust were pushed towards the Nama foreland basin on the Kalahari craton and unfolded into a thrust and folding belt .

The accretionary wedge or the folding belt consists of amphibolite facies with pelagic , hemipelagic and clastic sedimentary rocks output, in the lenses from metamorphic overprinted Basite are turned on. The result of this tectonics are the Hakos Mountains with the highest peak Gamsberg . The vergence (tilting direction) of the folds is inclined in the southeast direction.

Nama foreland basin

As a result of the partial subduction of the Kalahari craton under the Congo-SF craton, a section of the crust of the Kalahari craton sank due to the load of the continental block placed underneath and thus formed a lithospheric depression . From this, the nama foreshore pool originated, or Southern foreshore basin, which accordingly as Peripheral foreshore basin (engl. Peripheral foreland basin) is classified. As a result, the Nama foreland basin absorbed massive sediment deposits from the eroding surrounding mountains; with this reference it has become a sedimentary basin .

The southern edge zone was raised by 10 km compared to the southern zone by late orogenic processes. This was probably the initial event for the start of the Naukluft Nappe Complex - ceiling transport south to the Nama foreland basin with shearing from the subsoil and thrust onto the already deposited basin sediments. An allochtonic tectonic blanket is thus formed , about 80 km from the place of formation .

Geological floors

The Damara Belt contains crustal provinces of different ages, formed in different geological contexts and heterogeneously composed (English Geologic Province). They consist of the geologically older, folded and mostly highly metamorphic overprinted basement and the younger, mostly undeformed overburden . The basement consists of the Cratonic Floor, the Inlier and the Khan River Detachment. The overburden is formed by the sedimentary layer. Chronostratigraphically can be differentiated as follows:

Cratonic floor

The lowest floor of the Damara Belt is formed by the two predominantly archaic (4,000 to 2,500 mya) cratons Kongo-SF and Kalahari . The former is subject to the northern to central zones, the latter to the southern zones of the Damara Belt.

The kratonic storey in the central zone contains differently colored eye gneiss (larger mineral sprinkles embedded in a fine matrix) as a base layer. In metamorphic basalts (Metabasalt) are made of quartzite , calcium silicate -Gesteinen with rich mineral components at epidote and Skapolith , arkose and mica with various mineral proportions, which also occurs in the metasediments the Nosib- and Swakop groups.

Inlier

Connected to the kratonic floor are several inliers (enclaves). These are either partially exposed or covered by layers of sediment. The inliers probably form large expansions of the kratonic storey below the sedimentary cover layers.

Presumably these inliers originated on active continental margins during the development of the hypothetical supercontinent Columbia with rift formations during the Eburnean orogeny between about 2,200 and 2,000 mya and the Kibaran orogeny, which occurred between 1,400 and 1,000 mya led to the formation of Rodinia. The oldest parent rocks (protoliths) date back to more than 2,100 mya and come from an impoverished earth mantle spring, the original composition of which individual components were withdrawn as a result of magmatic differentiation .

The most important inliers are the Kamanjab inlier, the Grootfontein inlier and the Epupa-Metamorphic Complex, all of which accumulated as accretion wedges on the southwestern edge of the Congo-SF craton. This tectonic crustal growth took place from east to west. On the northwestern edge of the Kalahari craton the Rehoboth inlier accreted.

  • The Kamanjab Inlier was named after the village of Kamanjab in the Kunene region. It extends to the southeast of the Kaoko Belt and is surrounded to the north and east by the Northern Platform and south by the Northern Zone of the Damara Belt. The inlier appears over a large area as an outcrop or outcrop and is divided into three differently structured complexes.

The northern one is characterized by low-metamorphic volcanoclastic sequences with, among others, Felsic rhyolite lavas , ignimbrites and tuffites as well as sub-volcanic porphyries . The evolution of these rocks suggests a subduction zone on an active continental margin . The southern complex consists of highly metamorphic sediments and volcanic-clastic series, in which u. a. Gneisses , phyllites and quartzites , amphibolites and different forms of orthogneiss are included. Basic and felsic magmas intruded the deposits. Large-scale plutonic intrusions through to mighty batholiths made of coarse-grained granites , medium-grained quartz - monzonites (adamellites) and granodiorites form the third complex, which separates the northern and southern complexes.

The oldest paleoproterozoic (2,500 to 1,600 mya) metamorphic sequences with granitoids and granitic paragneisses date from 1,860 to 1,830 mya. During the Kibararian orogeny there were further igneous phases between about 1,500 and 1,300 mya. They are associated with tectono-metamorphic events. Metamorphic overprinting of the rocks produced migmatization , which caused them to be partially melted locally (see →  Anatexis ).

  • The Grootfontein Inlier got its name from the municipality of Grootfontein in the Otjozondjupa region . It is located east of the Kamanjab Inlier at the junction of the Northern Platform with the Northern Zone of the Damara Belt and only appears there as a small outcrop that has so far only been explored with drill cores and little. The rocks formed as plutonites , which mainly consist of an alkaline or tholeiitic (English Tholeiitic magma series) and calc-alkaline (English Calc-alkaline magma series) granitic and granodioritic composition with gabbros , diorites and granites (see →  Sub-alkaline magma ) . Aplites and pegmatites intruded into these . The geochemistry suggests an evolution at an active continental margin between 2,022 and 1,946 mya. The Grootfontein inlier is about 150 mya older than the Kamanjab inlier.
  • The Rehoboth Inlier is named after the town of Rehoboth in the Hardap region and can be understood as a block of crust that was deposited on the northwestern edge of the Kalahari craton as an accretion wedge . There it is located in the south of the Damara Belt as part of the Nama foreland basin. This inlier consists of two different tectonic sequences, the Rehoboth sequence and the Sinclair sequence. Both outcrops emerge on the railing surface.
    • The Sinclair sequence, which got its name from the type locality at the Sinclair Farm west of the village of Helmeringhausen (Namibia) , developed during the Kibari orogeny in the period from 1400 to 1000 mya in the regime of a continental rift event. The basement consists of granitoids with an age of 1,250 to 1,050 mya. In deposits formed consisting predominantly of a magmatic dominated sequence of felsic and mafic volcanic rocks , pyroclastic , extended intrusions as well as various composite sandstone - conglomerates . These deposits were covered from around 750 mya by layers of quartzites and schists . The Sinclair sequence extends west to northwest directly on the edge of the Kalahari craton.

Khan River Detachment

Khan-Rivier dry river

The Khan River Detachment is located on the Cratonic Floor in the South Central Zone of the Damara Belt. The name comes from the Khan-Rivier river in the Erongo region . The Detachment was created in a tectonic strain regime and forms as shearing a ductile shear zone that separates the granitic gneiss underground of cratonic floor of the metamorphic sedimentary floor. The layer thickness of this shear zone is between 50 m and 2 km. As a result of the sinistral transpressive collision of the cratons Kongo-SF and Kalahari, the rocks were subject to a dislocation metamorphosis and were mylonized (plastically deformed). Although not yet proven, a large or continuous shear zone is assumed.

Within the detachment, several inliers of different shapes were formed, which are known as domes. They appear as outcrops and often form linear areas, which are then referred to as inliners, such as B. the Abbabis inlier. This extends roughly between the municipalities of Karibib and Usakos in the Erongo region . Its name refers to the disused Abbabis train station about 15 km south-east of Karibib. The width of twelve domes examined varies at the base between about 2 and 30 km. The inclination of the dome points mainly in the SW direction, but occasionally also in the SSE, W or NNW direction.

A combination of north-west / south-east compression and south-west / north-east expansion of the crust is considered to be the cause of the formation of the dome, detaching the detachment from the ground and moving it in the direction of the south-west collision direction of the cratons.

The formation of the domes began with the compression and shortening of the kratonic floor, creating longitudinal folds parallel to the course of the Damara belt. This was followed by an additional compression and thickening in the transverse direction, which created the typical dome-shaped dome structure. Then the kratonic storey with the domes was stretched lengthways; the domes were elongated. In the last phase, the domes were pushed into kilometer-sized, longitudinal folds of the mantle as a result of thrusts. These plastic faults created a shear that detached the Khan River Detachment from the subsurface. During these processes, sediments were mainly deposited in the synclines (downward part of a fold) or crevices between the domes. Red quartz and feldspathic eye gneisses , porphyry , biotitic monzogranites are common.

Massive granitic intrusions penetrated the dome several times. The most common granite type is the non-layered pegmatitic leucogranite , also called alaskite. It intruded in the form of dykes or camp corridors . Otherwise gray, weakly stratified biotite-containing granites and diorites rose. The tectonic-volcanic development took place during the main collision phase of the cratons involved.

Sedimentary floor

The basement with the kratonic floor, the inlier and the Khan River Detachment are largely covered by a sedimentary floor, which is summarized under the names Damara supergroup or Damara sequence. It consists of Sometimes very different sediments that originated in terrestrial , limnic or marine sedimentation environments . They are lithostratigraphically divided into different groups , subgroups and formations . This reflects the lithological properties, areas and periods of formation of the sediments, which, however, are not equally present in all areas of the Damara Belt.

The information about the earliest sedimentation start of the Damara sequence varies between 1,000 and 850 mya. These relate to collision and disintegration processes of the supercontinent Rodinia . In a narrower sense, sediment formation and deposition began with the formation of rifts between the Congo-SF and Kalahari cartons around 780 mya.

The units of the Damara sequence are mostly discordant both on the basement units and on top of each other. They were subject to various deformations and metamorphoses caused by tectonically .

Web links

  • Atlas of Namibia, Chapter 2, Physical Geography, Research and Information Services of Namibia website. raison.com (PDF)
  • Nicole Grünert: The Damara sequence: the most significant geological unit in Namibia In: namibiana book depot, press releases / The Damara sequence: the most important geological unit in Namibia. namibiana.de
  • The Windhoek Green Belt Landscape, Geology. landscapesnamibia.org
  • Recordings of geological structures, Namibia 2015 Geology, Melting and melt transfer in the mid-crust: a record of two conference excursions. earth.ox.ac.uk
  • L. Tack, P. Bowden: Post-collisional granite magmatism in the central Damaran (Pan-African) Orogenic Belt, western Namibia. In: Journal of African Earth Sciences. 28, No. 3, April 1999, doi: 10.1016 / S0899-5362 (99) 00037-8 , pp. 653-674 ( researchgate.net )

Individual evidence

  1. ^ A b Christoffel Jasper Anthonissen: The mid-crustal architecture of a continental arc - a transect through the South Central Zone of the Pan-African Damara Belt, Namibia. In: Thesis presented in partial fulfillment of the requirements for the degree of Master of Science at the University of Stellenbosch, 2009. scholar.sun.ac.za
  2. ↑ Fold and thrust belt. In: Lexicon of Geosciences, Fold and Thrust Belt. Spectrum Academic Publishing House, Heidelberg ( Spektrum.de ).
  3. ↑ 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 ( researchgate.net full download possible).
  4. ↑ David R. Gray, David A. Foster, JG Meert, BD Goscombe and others: A Damara orogen perspective on the assembly of southwestern Gondwana . In: Geological Society - Special Publications . tape 294 , no. 1 . London, S. 257–278 , doi : 10.1144 / SP294.14 ( tekphys.geo.uni-mainz [PDF]).
  5. ^ ZX Li, SV Bogdanova, AS Collins, A. Davidson, B. De Waele and others: Assembly, configuration, and break-up history of Rodinia: A synthesis. In: ScienceDirect, Precambrian Research. 160, 2008, pp. 179-210, doi: 10.1016 / j.precamres.2007.04.021 ( bdewaele.be PDF).
  6. ↑ a b Armin Zeh, Axel Gerdes and 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 . tape 50 , no. 5 , 2009, ISSN  0022-3530 , p. 933-966 , doi : 10.1093 / petrology / egp027 .
  7. ↑ 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 . tape 100 , no. 2–3 , April 2011, ISSN  1437-3254 , pp. 201–220 , doi : 10.1007 / s00531-010-0580-8 .
  8. ^ A b Fernandez-Alonso and others: The Proterozoic History of the Proto-Congo Craton of Central Africa. In: Department of Earth Sciences, Royal Museum for Central Africa, B-3080 Tervuren, Belgium of Central Africa. ( africamuseum.be PDF).
  9. ↑ PP Hoffman, DP Hawkins, CE Isachsen and SA Bowring: Precise U-Pb zircon ages for early Damaran magmatism in the Summas Mountains and Welwitschia Inlier, northern Damara belt, Namibia Precise U-Pb zircon ages for early Damaran magmatism in the Summas Mountains and Welwitschia Inlier, northern Damara belt, Namibia. In: Communs geol. Surv. Namibia. 11, 1996, pp. 49-53 ( mme.gov.na PDF).
  10. ^ Hubertus Porada: Pan-African Rifting and Orogensis in Southern to Equatorial Africa and Eastern Brazil. In: Precambrian Research. August 1989, doi: 10.1016 / 0301-9268 (89) 90078-8 , pp. 103-136 ( researchgate.net ).
  11. ^ 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 . tape 7 , no. 3 , 2003, p. 685-699 , doi : 10.1016 / S1342-937X (05) 71056-X ( researchgate.net ).
  12. ^ H. Ahrendt, JC Hunziker, K. Weber: Age and Degree of Metamorphism and Time of Nappe Emplacement along the Southern Margin of the Damara Orogen, Namibia (Se Africa). In: Geologische Rundschau. 67, No. 2, June 1978. doi: 10.1007 / BF01802814 ( researchgate.net ).
  13. ↑ R. McG. Miller: Chapter 11 The owambo basin of northern namibia . In: Sedimentary Basins of the World . tape 3 , 1997, African Basins, pp. 237-268 , doi : 10.1016 / S1874-5997 (97) 80014-7 .
  14. ↑ a b c Ilka C. Kleinhanns, Thomas Fullgraf, Franziska Wilsky, Nicole Nolte and others: U – Pb zircon ages and (isotope) geochemical signatures of the Kamanjab Inlier (NW Namibia): constraints on Palaeoproterozoic crustal evolution along the southern Congo craton . In: Geological Society, London, Special Publications . tape 389 , no. 1 , August 2013, p. 165-195 , doi : 10.1144 / SP389.1 ( researchgate.net ).
  15. ↑ Débora Barros Nascimento, A. Ribeiro, RAJ Trouw, 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. 278, March 2016. doi: 10.1016 / j.precamres.2016.03.005 ( researchgate.net ).
  16. ↑ Ben Goscombe, David Gray and Martin Hand: Variation in Metamorphic Style along the Northern Margin of the Damara Orogen, Namibia. In: Oxford JournalsScience & Mathematics Journal of Petrology. Volume 45, No. 6, pp. 1261-1295. doi: 10.1093 / petrology / egh013 ( petrology.oxfordjournals.org ).
  17. Jump up ↑ PP Hoffman, DP Hawkins, CE Isachsen, SA Bowring: Precise U-Pb zircon ages for early Damaran magmatism in the Summas Mountains and Welwitschia Inlier, northern Damara belt, Namibia. In: Communs geol. Surv. Namibia. 11, 1996, pp. 49-53. ( mme.gov PDF).
  18. ^ A b Luke Longridge: Tectonothermal evolution of the Southwestern central zone, Damara Belt, Namibia. In: ETD Collection, Electronic Theses and Dissertations, January 31, 2013. ( core.ac PDF, alternatively wiredspace.wits.ac.za ).
  19. ↑ R. McG. Miller: The Okahandja Lineament, a fundamental tectonic boundary in the Damara Orogen of South West Africa / Namibia. In: Trans. Geo !. Soc. S. Afr., 82 (1979). 349-361. journals.co.za
  20. ↑ Christoffel Jasper Anthonissen: The mid-crustal architecture of a continental arc - a transect through the South Central Zone of the Pan-African Damara Belt, Namibia. In: Thesis presented in partial fulfillment of the requirements for the degree of Master of Science at the University of Stellenbosch, 2009. scholar.sun.ac.za
  21. ↑ JD Clemens, IS Buick, AFM Kisters and D. Frei: Petrogenesis of the granitic Donkerhuk batholith in the Damara Belt of Namibia: protracted, syntectonic, short-range, crustal magma transfer. In: Contributions to Mineralogy and Petrology, June 5, 2017. link.springer.com
  22. ^ Peter A. Kukla: Tectonics and Sedimentation of a late proterozoic damaran convergent continental Margin, Khomas Highland, Central Namibia. In: Ministry of Mines and Energy, Geological Survey of Namibia, Memoir 12, 1992. ( mme.gov PDF).
  23. ↑ Cecilia AM Jönsson: Geophysical ground surveys of the Matchless Amphibolite Belt in Namibia. In: Dissertation in Geology at Lund University, Master of Science thesis no.377 , Department of Geology Lund University, 2014. lup.lub.lu.se
  24. ↑ Michael Ian Hay Hardnady: The Structural Evolution of accretionary prism of Ancient in the Damara Belt, Namibia. In: Dissertation on obtaining a Master of Science in the Department of Geological Science, University of Cape Town, South Africa, September 2014. open.uct.ac.za
  25. ^ Geologic Province and Thermo-Tectonic Age Maps. In: Earthquake Hazards Program on the USGS website. earthquake.usgs.gov
  26. ^ A b R. Brandt: Preliminary Report on the Stratigraphy of the Damara Sequence and the Geology and Geochemistry of Damaran Granites in an Area between Walvis Bay and Karibib. In: Communs Geol. Surv. SW Afr./Namibia, 1, 1985, 31-44. mme.gov.na PDF
  27. ^ Emmanuel Egal, Denis Thiéblemont, Didier Lahondère, Catherine Guerrot and others: Late Eburnean granitization and tectonics along the western and northwestern margin of the Archean Kénéma – Man domain (Guinea, West African Craton) . In: Precambrian Research . tape 117 , no. 1–2 , July 2002, pp. 57-84 , doi : 10.1016 / s0301-9268 (02) 00060-8 .
  28. ↑ L. Tack, MTD Wingate, B. De Waele, J. Meert and others: The 1375Ma “Kibaran event” in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime . In: Precambrian Research . tape 180 , no. 1–2 , June 2010, pp. 63–84 , doi : 10.1016 / j.precamres.2010.02.022 .
  29. ↑ Nagel, Rudolf: One billion years of geological development on the NW edge of the Kalahari Kraton. In: Dissertation to obtain the doctoral degree of the mathematical and natural science faculties of the Georg-August-Universität zu Göttingen, Faculty for Geosciences and Geography (incl. GAUSS) [219], Göttingen 1999. ( ediss.uni-goettingen.de PDF).
  30. ↑ GJH Oliver: The Central Zone of the Damara Orogen, Namibia, as a deep metamorphic core complex. In: Communs geol. Surv. Namibia, 10 (1995), 33-42. ( mme.gov.na PDF).
  31. ^ RE Jacob, A. Kröner, AJ Burger: Areal extent and first U-Pb age of the Pre-Damaran Abbabis complex in the central Damara belt of South West Africa (Namibia) . In: Geologische Rundschau . tape 67 , no. 2 , June 1978, ISSN  0016-7835 , p. 706-718 , doi : 10.1007 / BF01802813 .
  32. ^ R. Brandt: A revised stratigraphy for the Abbabis Complex in the Abbabis Inlier, Namibia. In: S.-Afr.Tydskr. Geol. 90, No. 3, 1987, pp. 314-323. ( the-eis PDF).