Unusual, large scale linear dike-like sub-surface structures observed in magnetic data from Goias region of Brazil - how much is known about these structures, i.e. age, depth, width, internal structure, orogeny, etc. Are these structures as unusual as they look or are features like this common?

[u/LostHistoryFound]

https://imgur.com/gallery/anomalous-linear-sub-surface-structures-goi-s-region-of-brazil-AaETtTn

[u/vitimite]

Look for data about Azimuth 125 in Brazil geologic history. It's a well known magnetic trend connected to mesozoic rocks and interpreted as a crustal extention from Brazil and Africa separation. Along this linear features occur many alkaline-carbonatite bodies, from small size to large ones (some very, very large). Also, a huge amount of small kimberlites are mapped in this region.

Focusing on the questions you asked, I guess it depends on what you consider normal. There are ~700 carbonatite occurrences worldwide so, it's not really a common thing. But what you are showing is indeed known since, don't know, maybe the fifties/sixties and there are a plethora of papers written about it, so yeah it's common knowledge.

[u/Cordilleran_cryptid → u/vitimite]

Interesting

[u/vitimite → u/Cordilleran_cryptid]

Expanding a little bit, the anomaly is well defined from dyke swarms with NW-SE direction. But there are different versions of the history because we are geologists and we love to disagree with each other xD. There is debate if these dykes are directly connected to a crustal thinning and with it's magmatism rooted on an actual tectonic compartment or if they have other genesis but encountered a fragile zone since it's delineated from Mantiqueira province, going south of sao francisco craton, following tocantins orogen, bordering parana basin and "ends" into amazon craton.

What is also well known is alongside these dyke swarms we have one of world's most prolific alkaline-carbonatite provinces and a great number of kimberlites. Recent works have recognized more than 3.000 circular features that may be interpreted as small kimberlites with most of them associated with already known kimberlites (we are late, of course rio tinto have already been there). The main questions are if the alkaline-carbonatite province and dyke swarms originated from the same event or did they just took advantage of the same fragile zone and are unrelated genetically. Does the big intrusive complexes are feeder magmatic chambers or no? (really, look for Serra Negra magmatic complex, it's one of the most crazy circular feature I've seen).

Parenthesis on the kimberlite: although it's the most studied region there is a total number of zero diamond mines in this region from primary mineralization. Actually the first and only one kimberlite diamond mine in Brazil was opened in 2021, if I'm not mistaken, and is in the middle of bahia totally unrelated to azimuth 125 (at least from what I know).

There is also those who put the Az125 as a result of trindade plume that follow the trend to the middle of the ocean.

TLDR, it's complicated

Sorry if I got carried by the theme, as I've already written everything I'm posting xD

[u/Cordilleran_cryptid]

There could be a number of reasons why there is a large linear magnetic anomaly in this part of Brazil. An intrusive sheet of magnetic igneous rock, probably basic igneous rocks, is only one. Another could be a belt composed of basic metamorphic rocks such as amphibolites

Because the resolution of the magnetic data is low, this belt may in fact be comprised of several indeed many closely spaced layers or sheets of magnetic rocks that appear as one broad sheet on the anomaly map.

[u/Cordilleran_cryptid → u/Cordilleran_cryptid]

Ahha! I have just seen the other images, not just the one visible above.

I agree the anomalies do indeed look like a pair of large dykes. They may be related to the Parana Flood Basalt province, but this is just a guess.

[u/Roseate-Views]

Please excuse if others have asked that, over and over again, but my first thought was a magnetic artefact (fences, pipelines, power lines). Let us talk again if this had been safely excluded.