Okenyenya
| Okenyenya | ||
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 The Okenyenya (silhouette in the background) from the north of the Ugab seen from |
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| height | 1902 m | |
| location | Erongo Region , Namibia , Southern Africa | |
| Coordinates | 20 ° 50 ′ 18 ″ S , 15 ° 19 ′ 38 ″ E | |
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| rock | Essexit , Syenit , Gabbro | |
| Age of the rock | approx. 130 million years ( Lower Cretaceous ) | |
The Okenyenya or Okonjeje is a 1902 m high, striking mountain in northern Namibia . It is located around 60 kilometers northeast of the town of Uis in the Erongo region and towers over the surrounding area by around 1000 m.
geology
The Okenyenia is the highest peak of a ring-like mountain group, which extends over an area of around 20 km² and has a common geological origin. It is a complex basic pluton ( called Okenyenya igneous complex ), which in the Early Cretaceous Period in the Precambrian metamorphic basement (Damara sequence) and the overlying Upper Paleozoic -? Triassic table top mountains ( Karoo supergroup ) intruded , with part of the magma likely rising further from there and feeding a volcanic complex. In the course of millions of years, this pluton reached the surface of the earth as a result of an increase in the earth's crust (see → Great Escarpment ) with simultaneous attack by weathering and erosion , i.e. the Cretaceous volcanoes were eroded far below their base level. Finally, due to its higher resistance to erosion than the surrounding rocks , the pluton was gradually carved out of the subsoil like an island mountain . The Denudations amount since the Late Cretaceous is estimated m to around 4000th
On the conically shaped eastern and highest part of the Okenyenya, concentric, more or less cylindrical igneous rock bodies bite out. The innermost of these rock bodies forms the summit area and consists of oligoclase essexit , while andesine essexit connects to the outside or on the slopes below . The Essexit bodies are in turn surrounded by nepheline syenite ("Pulaskit"), which builds up the lower slopes on the north and east sides. The lower south-west and west slopes of the Okenyenia, including the western side summit called Adam's Shoulder ( 1590 m ), on the other hand, consist mainly of alkali gabbro . Consequently, almost the entire mountain is made up of alkaline igneous rocks . These represent the advanced (alkali gabbro) and late (nepheline syenite and essexite) main activity phases of Okenyenia magmatism. The concentric structure of the syenite-Essexit part of the body suggests that this is the plutonic expression of a caldera / shaft crater system ("multiple cauldron subsidence"). Contact metamorphic Karoo sediments are now only preserved to a large extent on the eastern flank in the form of the so-called Zbigniew Ridge . entire paragraph after
See also
Web links
Individual evidence
- ↑ a b c d e M. J. Raab, RW Brown, K. Gallagher, K. Weber, AJW Gleadow: Denudational and thermal history of the Early Cretaceous Brandberg and Okenyenya igneous complexes on Namibia's Atlantic passive margin. Tectonics. Vol. 24, No. 3, 2005, doi: 10.1029 / 2004TC001688
- ↑ Andrew Goudie, Heather Viles: Landscapes and Landforms of Namibia. Springer, 2015, ISBN 978-94-017-8020-9 , p. 32.
- ^ A b c R. T. Watkins, AP Le Roex: A reinvestigation of the Okenyenya igneous complex: a new geological map, structural interpretation and model of emplacement. Communications of the Geological Survey of Namibia. Vol. 9, 1994, pp. 13-22 ( PDF )
- ^ US Army Map Service Series 2201, Windhoek Sheet . US Army Topographic Command, Washington, DC 1970 ( online )
