A Geological Marvel: The Richat Structure
Since the dawn of the new millennium, the most widely accepted scientific explanation asserts that the Richat Structure is a colossal volcanic dome from the Cretaceous period (about 100 million years ago) that collapsed after millions of years of erosion. The rocks within this structure vary in age from the Proterozoic to the Ordovician period as one moves away from the center.
Uncovering the Layers of the Richat Structure
The varying degrees of erosion within this structure are determined by the presence of different levels of quartzite. Within the structure, the presence of various intrusive and effusive igneous rocks has been detected, including gabbro rocks, rhyolites, kimberlites, and carbonates. In the 1950s, scientists visited this structure, and subsequently, the Gemini space mission photographed and collected data from space. Due to its unmistakable appearance, astronauts consider it a landmark.
Interpretation of the Richat Structure
The structure was first described in the 1930s and 1940s as the Richât Crater or Richât Button. Richard Molard (1948) considered it the result of a laccolithic uplift. A geological expedition in Mauritania led by Théodore Monod in 1952 recorded four "crater-like or circular irregularities" in the area, including Er Richât, Aouelloul, Temimichat Ghallaman, and Tenoumer. Initially, it was considered an impact structure, but a more detailed study conducted in the 1950s and 60s suggested it could have been formed by terrestrial processes.
Further Studies and Discoveries
After several field and laboratory studies in the 1960s, no significant evidence of shock metamorphism or other deformations indicative of an extraterrestrial impact was found. Coesite, a shock metamorphism indicator, was initially reported present in the rock samples from the structure. However, further analysis in 1969 concluded that barite had been wrongly identified as coesite.
In the 1990s, the first studies on the dating of the structure took place. A study on the formation of the Richat Structure by Matton, et al. (2005, 2008), concluded that it was not an impact structure. Further analysis of the deep structure beneath the surface, including aeromagnetic and gravimetric mapping, determined an origin of the structure caused by the motion of ring faults above a magma intrusive body.
The molten rock rose to the surface without reaching the bottom of the structure, forming layers of rock denoting its pimple-like shape. Consequently, fault lines were formed that cross and surround the eye. Near the center of the structure, the limestone was melted by the molten rock, causing it to collapse and thus forming a typical rock called arms. About a hundred million years ago, the Richat eye underwent a violent explosion that partially collapsed the bubble. Subsequent erosion contributed to the typical formation of the Eye as we observe it today.
The Richat Structure: A Geological Heritage Site
The International Union of Geological Sciences (IUGS) in October 2022 included the Richat Structure in the 100 sites of the world geological heritage, defining it as a "key place containing geological elements and/or processes of international scientific relevance, giving a substantial historical contribution to the development of geological sciences".
In conclusion, the Eye of Sahara is a fascinating example of complex concentric alkaline magmatic complex and a testament to the ever-evolving landscape of our planet. The journey of understanding and interpreting the Richat Structure continues, adding to the richness of geological knowledge and the wonder of natural formations. As we delve deeper into the past, the Richat structure remains a captivating subject of study, reminding us of the Earth's dynamic, ever-changing nature.
This article was written by GERD DANI for FreeAstroScience.com.
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