[ceribetoriate (OP)]

Hi all!

This is a very nice forum, thank you all who ARE it! And I'm sorry if I noob with a stoopid question in the wrong place and everything like that, but:

I wonder what the origin could be of that pretty perfectly circular shape of 35 km diameter, the center of which is  at about:

3 degrees 38' South
24 degrees 30' East.

Between the towns of Lodjo and Kindu in the territory of the Republic of Congo.

I ask because my neighbour is from that very place, and as we checked it out on Google Earth, she didn't know anything about there being this eery circle around her birthplace there...
 [:0]


[MOD EDIT - PLEASE FORMAT YOUR THREAD TITLES AS QUESTIONS, WHICH HELPS OTHERS TO FIND - AND ANSWER - ITEMS OF INTEREST. THANKS. CHRIS.]

[LeeE]

That's very interesting.

At very first glance, it looked more like an eroded impact crater to me, rather than anything else, but on looking at the elevations it turns out that the 'ring' is actually depressed and the interior bulges slightly.  There are no known/established no impact craters listed for the Republic of Congo.

I could just about imagine it being a collapsed caldera that has subsequently been refilled by a huge dome but the pdf linked to below (from the 41st Lunar and Planetary Science Conference of 2010) strongly suggests that it is indeed an impact crater and rules out volcanoes and salt-sinks due to the underlying geology.  Note that the pdf states that drilling and sampling will be necessary to prove its impact origin.

http://www.lpi.usra.edu/meetings/lpsc2010/pdf/1601.pdf

[ceribetoriate (OP)]

Wow! Splendid answers, and quickly. Great!

It surprises me that this ring structure, according to the conference paper above in the thread, hasn't been recorded until this year, since it is quite obvious to the eye. But then again, the Earth is a large place...

My interest in this stems from my neighbour who's an elderly lady born inside that "encircled" area. She speeks of how diamonds are abundant there. Peasants find diamonds when pulling potatoes out of the ground! Of course, such anecdotes feed themselves and I won't exactly go there to dig diamonds, but I am tempted to ask the question:

Are there any good reasons for why impact craters might be more diamond rich?
For example, does the impact energy help create diamonds?

I suppose that diamonds move with water flows, so the circular/radial river shape itself might possibly explain something, regardless of its origin.

[Mazurka]

Conventionally diamonds are found  as a result of Kimberlite eruptions, which are thought to originate from deeper in the mantle than the critical point where carbon is under sufficient pressure and temperature to keep carbon stable as diamond. 

Eruptions of kimberlite have not occurred for 100's of millions of years - it is theorised that this is because the volatile (gases and fluids) that are a key characteristic/ driver of such eruptions have degassed from the mantle whilst the earth was younger (and hotter).

The evidence from the diatremes (the volcanic pipe created by the eruption) is that these eruptions were very gaseous and the diatremes flare out towards the top as the eruption accelerates towards the surface as the confining pressure decreases.  Typically, they are up to 1km in diameter and I am not aware of any diatremes approaching 35km in diameter. (Which tends to favour the impact crater theory)

Diamonds are mined directly from diatremes and are also found in placer deposits, which are the result of the kimberlite being weathered and eroded so the diamonds are found in sediments down river.

Although diamond could form in a meteorite impact, these are going to have formed more or less instantly and  from a limited source of carbon so will be very (microscopically) small.

[LeeE]

Yeah, afaik diamonds are not normally associated with impact craters.  If it is an impact crater, and the impact formed a complex crater with uplift in the center you might come across some shatter cones there.

http://en.wikipedia.org/wiki/Shatter_cone

[Geezer]

Neil seems to think it was created by a gigantic conga line, but I'm not sure he's right about that.

[neilep]

dur nerr nerr nerr ner..NERR...dur nerr nerr nerr NERR...le la la la AY !!..etc etc :-)

[LeeE]

Look what has popped up in the news today:
 
Congo ring may be giant impact crater

Looks like the BBC has found that link I posted earlier (they cite the same Lunar & Planetary Conference)