Richat Structure: Eye Of The Sahara
The Richat Structure, also known as the Eye of the Sahara, is a
prominent circular feature in the Sahara desert of west–central
Mauritania near Ouadane. Surrounded by thousands of square miles of
nearly featureless desert, this 40-50 km in diameter series of
concentric circles is readily visible from space. This prominent
circular feature in the Sahara desert has attracted attention since the
earliest space missions because it looks like a gigantic bull’s-eye.
Richat
Structure is not the site of an ancient meteor crater, as many people
originally postulated. These concentric circles are actually alternating
layers of sedimentary, metamorphic, and igneous rocks that were pushed
upward in a symmetrical anticline, geologic dome, from below due to a
small incursion of magma. The structure is a deeply eroded. The
sedimentary rock exposed in this dome range in age from Late Proterozoic
(2.5 billion years) within the center of the dome to Ordovician (480
million years) sandstone around its edges.
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 an
extraterrestrial impact.
In addition, the Richat structure lacks the annular depression that characterize 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.
