Richat Structure in Mauritania
I stumbled across this on Universe Today’s “Where in The Universe Challenge” and thought it made a very interesting geologic phenomenon to write about. (Apologies to Ron and the gang for potentially stealing an idea from the Where on Google Earth challenge.)
Source: Google Earth
What does the above photograph look like on your first impression? I immediately said an impact crater and was amazed at how well defined this was. Especially when you find out this feature has a diameter of 30 kilometers!
This interesting feature is known as the Richat Structure and is located in the African country of Mauritania. Below is an embedded Google Maps frame showing the location.
This structure is so big, that while zooming in to Mauritania on Google Maps, I was immediately able to see it on a rather zoomed out view.
Anyway, what exactly is this structure? It was originally thought to have been an impact crater when it was first seen on a large scale by scientists. More research eventually revealed that it was not actually an impact crater, but instead a a circular anticline whose crest has been eroded away.
Kim from All of My Faults Are Stress Related adds this comment after reading a paper linked in the Wikipedia article on the structure:
It’s not just a circular anticline – it’s a dome above a Cretaceous pluton. (The article describes the intrusion as a plug, but I wonder if we’re not looking at the top of a laccolith – like the Henry Mountains in Utah, but not eroded through to the pluton itself.)
The paper is titled “Resolving the Richat enigma: Doming and hydrothermal karstification above an alkaline complex,” by Matton G, Jébrak M, Lee JK:
The Richat structure (Sahara, Mauritania) appears as a large dome at least 40 km in diameter within a Late Proterozoic to Ordovician sequence. Erosion has created circular cuestas represented by three nested rings dipping outward from the structure. The center of the structure consists of a limestone-dolomite shelf that encloses a kilometer-scale siliceous breccia and is intruded by basaltic ring dikes, kimberlitic intrusions, and alkaline volcanic rocks. Several hypotheses have been presented to explain the spectacular Richat structure and breccia, but their origin remains enigmatic. The breccia body is lenticular in shape and irregularly thins at its extremities to only a few meters. The breccia was created during karst dissolution and collapse. Internal sediments fill the centimeter- to meter-scale cavities. Alkaline enrichment and the presence of Cretaceous automorphous neoformed K-feldspar demonstrate the hydrothermal origin of these internal sediments and their contemporaneity with magmatism. A model is proposed in which doming and the production of hydrothermal fluids were instrumental in creating a favorable setting for dissolution. The circular Richat structure and its breccia core thus represent the superficial expression of a Cretaceous alkaline complex with an exceptionally well preserved hydrothermal karst infilling at its summit.
For readers not familiar with anticlines, below is a cross section of an anticline to help visualize what might be going on.
Source: Wikipedia – Anticline
According to the website Google Sightseeing, there are a few other similar looking features that can be found in Africa: The Jebel Uwaynat that borders Sudan, Egypt and Libya and the Brandberg Intrusion in Namibia.
[Via Universe Today]
More Information
- Dark Roasted Blend – The Richat Structure, Eye of the Earth
- Universe Today – Where in The Universe Challenge #22
- Wikipedia – Richat Structure
Similar Posts on Geology News:
- Discovering Asteroid Impacts from Home
- Image of Nicholson Crater on Mars
- Meteor Impacts Helped Jump Start Life?
- Geology Links for August 28th, 2011
- Geology Links for March 6th, 2010
I followed the Wikipedia link, and found a recent Geology paper about it:
Matton, Jébrak, and Lee, 2005, Resolving the Richat enigma: Doming and hydrothermal karstification above an alkaline complex: Geology, v. 33, p. 665-668. ( doi:10.1130/G21542.1)
It’s not just a circular anticline – it’s a dome above a Cretaceous pluton. (The article describes the intrusion as a plug, but I wonder if we’re not looking at the top of a laccolith – like the Henry Mountains in Utah, but not eroded through to the pluton itself.)
Kim said:
“(The article describes the intrusion as a plug, . . . ”
===
It’s too bad that I’m not bringing this reply to a fresh discussion, but I believe the comment about the interesting physical anomaly by using the term “plug” is right on the money. This sin’t the only geologic feature to be mistaken as an impact crator, only to be later found with hydrothermal properties.
More an more evidence is suggesting that our planet earth in it’s early life was more of a minerotrophic system as opposed to the present ombrotrophic hydrological cycle we are familiar with today. It would also beautifully explain the complete peak abundance of both plant and animal life that once existed from pole to pole before the extinction event which changed it all forever.
Mummified wood tissues perfectly preserved for Oxygen Isotope studies for paleoclimate research are bearing this out that the chemical signature of the water was originally and strictly a deep hydrogical sprins environment and not originating from atmospherical cloud formations from off the world’s oceans. Very interesting indeed.
Thanks for the info.
Timeless
Cool!
This is a good article… would one of you kind folks please improve the Wikipedia article on this interesting formation? It is quite lame.
http://en.wikipedia.org/wiki/Richat_Structure
My opinion is purely speculative. I remember reading a biblical account of the Tower of Babel that indicated that it was a huge circular tower that housed nearly all of humanity at one time. This large tower was said to have one-third ultimately sink into the ground, another third was said to have exploded and one-third was said to remain above ground as a sort of testament to what mankind can create when we all work together. I thought it interesting that it has been noted that he rock of the Richat Structure does not match the rock of the surrounding area. Again, the biblical account of the Tower of Babel indicates that rather than use local materials, the buliders of the Tower made their own bricks. I would be interested to learn if anyone has conducted an expedition to the site to determine the actual nature of the Richat Structure.
Tower of Babel? Hmmm…ok…
I don’t care what anybody says, that’s an impact structure.
Is there any info on cores taken to support the notion that it is caused by a volcanic plug at depth?
Also, any iridium lying around out there?
It really is an interesting-looking place. I hope I am blessed to one day visit there.