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- Richat_Structure abstract "The Richat Structure, also known as the Eye of the Sahara and Guelb er Richat, is a prominent circular feature in the Sahara desert near Ouadane, west–central Mauritania. This structure is a deeply eroded, slightly elliptical, 40 km in diameter dome. The sedimentary rock exposed in this dome ranges in age from Late Proterozoic within the center of the dome to Ordovician sandstone around its edges. The sedimentary rocks comprising this structure dip outward at 10°–20°. Differential erosion of resistant layers of quartzite has created high-relief circular cuestas. Its center consists of a siliceous breccia covering an area that is at least 3 km in diameter.Exposed within the interior of the Richat Structure are a variety of intrusive and extrusive igneous rocks. They include rhyolitic volcanic rocks, gabbros, carbonatites and kimberlites. The rhyolitic rocks consist of lava flows and hydrothermally altered tuffaceous rocks that are part of two distinct eruptive centers, which are interpreted to be the eroded remains of two maars. According to field mapping and aeromagnetic data, the gabbroic rocks form two concentric ring dikes. The inner ring dike is about 20 m in width and lies about 3 km from the center of Richat Structure. The outer ring dike is about 50 m in width and lies about 7 to 8 km from the center of this structure. Thirty-two carbonatite dikes and sills have been mapped within the Richat Structure. The dikes are generally about 300 m long and typically 1 to 4 m wide. They consist of massive carbonatites that are mostly devoid of vesicles. The carbonatite rocks have been dated as having cooled between 94 to 104 million years ago. A kimberlitic plug and several sills have been found within the northern part of the Richat Structure. The kimberlite plug has been dated being about 99 million years old. These intrusive igneous rocks are interpreted as indicating the presence of a large alkaline igneous intrusion that currently underlies the Richat Structure and created it by uplifting the overlying rock.Spectacular hydrothermal features are a part of the Richat Structure. They include the extensive hydrothermal alteration of rhyolites and gabbros and a central megabreccia created by hydrothermal dissolution and collapse. The siliceous megabreccia is at least 40 m thick in its center to only a few meters thick along its edges. The breccia consists of fragments of white to dark gray cherty material, quartz-rich sandstone, diagenetic cherty nodules, and stromatolitic limestone and is intensively silicified. The hydrothermal alteration, which created this breccia, has been dated to have occurred about 98.2 ± 2.6 million years ago using the 40Ar/39Ar method.Initially interpreted as an asteroid impact structure because of its high degree of circularity, it is now argued to be a highly symmetrical and deeply eroded geologic dome. Despite extensive field and laboratory studies, geologists have found a lack of any credible evidence for shock metamorphism or any type of deformation indicative of a hypervelocity extraterrestrial impact. While coesite, an indicator of shock metamorphism, had initially been reported as being present in rock samples collected from the Richat Structure, further analysis of rock samples concluded that barite had been misidentified as coesite. In addition, the Richat Structure lacks the annular depression that characterizes large extraterrestrial impact structures of this size. Also, it is quite different from large extraterrestrial impact structures in that the sedimentary strata comprising this structure is remarkably intact and "orderly" and lacking in overturned, steeply dipping strata or disoriented blocks. A more recent multianalytical study on the Richat megabreccias concluded that carbonates within the silica-rich megabreccias were created by low-temperature hydrothermal waters, and that the structure requires special protection and further investigation of its origin.".
- Richat_Structure thumbnail Richat_Structure_-_SRTM.jpg?width=300.
- Richat_Structure wikiPageExternalLink ap021028.html.
- Richat_Structure wikiPageExternalLink view.php?id=2561.
- Richat_Structure wikiPageExternalLink earths-bulls-eye-the-eye-of-africa-landmark-for-astronauts-14-pics.
- Richat_Structure wikiPageExternalLink watch?v=pTTnYRaZ55A.
- Richat_Structure wikiPageID "377815".
- Richat_Structure wikiPageRevisionID "603695071".
- Richat_Structure hasPhotoCollection Richat_Structure.
- Richat_Structure subject Category:Adrar_Region.
- Richat_Structure subject Category:Geography_of_Mauritania.
- Richat_Structure subject Category:Geologic_domes.
- Richat_Structure subject Category:Geology_of_Mauritania.
- Richat_Structure subject Category:Regional_geology.
- Richat_Structure subject Category:Structural_geology.
- Richat_Structure subject Category:Tiris_Zemmour_Region.
- Richat_Structure point "21.124 -11.402".
- Richat_Structure type SpatialThing.
- Richat_Structure comment "The Richat Structure, also known as the Eye of the Sahara and Guelb er Richat, is a prominent circular feature in the Sahara desert near Ouadane, west–central Mauritania. This structure is a deeply eroded, slightly elliptical, 40 km in diameter dome. The sedimentary rock exposed in this dome ranges in age from Late Proterozoic within the center of the dome to Ordovician sandstone around its edges. The sedimentary rocks comprising this structure dip outward at 10°–20°.".
- Richat_Structure label "Estructura de Richat".
- Richat_Structure label "Estrutura de Richat".
- Richat_Structure label "Guelb er Richat".
- Richat_Structure label "Kalb ar-Riszat".
- Richat_Structure label "Richat Structure".
- Richat_Structure label "Richatstructuur".
- Richat_Structure label "Structure de Richat".
- Richat_Structure label "Struttura di Richat".
- Richat_Structure label "Структура Ришат".
- Richat_Structure label "تكوين الريشات".
- Richat_Structure label "リシャット構造".
- Richat_Structure label "理查特結構".
- Richat_Structure sameAs Guelb_er_Richat.
- Richat_Structure sameAs Estructura_de_Richat.
- Richat_Structure sameAs Structure_de_Richat.
- Richat_Structure sameAs Struktur_Richat.
- Richat_Structure sameAs Struttura_di_Richat.
- Richat_Structure sameAs リシャット構造.
- Richat_Structure sameAs Richatstructuur.
- Richat_Structure sameAs Kalb_ar-Riszat.
- Richat_Structure sameAs Estrutura_de_Richat.
- Richat_Structure sameAs m.0216l9.
- Richat_Structure sameAs 2376915.
- Richat_Structure sameAs Q744591.
- Richat_Structure sameAs Q744591.
- Richat_Structure lat "21.124".
- Richat_Structure long "-11.402".
- Richat_Structure wasDerivedFrom Richat_Structure?oldid=603695071.
- Richat_Structure depiction Richat_Structure_-_SRTM.jpg.
- Richat_Structure isPrimaryTopicOf Richat_Structure.