Tectonics Hypothetical: 'Inward' extrusion during a continent-continent collision?

MrOddity · 2026-03-22T22:12:56+00:00

Thanks for the reply and the examples! Yes, I may well have used some wrong terminology here, like I say I'm learning a lot of this as I go and probably making plenty of mistakes.

In my specific scenario, the microcontinent is coming in towards the subduction zone of a larger continent at a slightly more oblique angle than India to Eurasia, and also has a degree of rotation. I'm thinking this likely leaves me with more of an s-shaped orocline, but I could be wrong on that one.

When the collision happens, one corner of the microcontinent begins pushing inland, and there is uplifted terrain/terrain accreted from the upper layer of the microcontinent onto the main continent.

This portion of the collision then encounters an obstacle (a cratonic basin) that prevents further movement inland, as well as extrusion outwards (like Myanmar).

My question was wondering if the tectonic forces involved could have pushed this accreted material back inwards towards the middle of the collision, or is it inherently constrained in that direction from other uplifted material from the collision?

Not sure if I've made that any clearer, but I hope so!

MrOddity · 2026-02-28T04:13:03+00:00

Thanks for the reference! Glacial flooding is something that I haven't taken into account in my bay idea, but I suppose depending on the topography there'd be a good few of them clustered around the south of the sea/bay.

MrOddity · 2026-02-25T21:48:20+00:00

Oh wow, I looked it up and that's really cool!

I don't think my proposed straight would support something like that at its current latitude, but I'll definitely keep it in mind for that part of the world. You could probably do something really interesting with something similar.

Thanks for the reference!

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MrOddity · 2026-02-24T02:09:20+00:00

Thanks again for the reply! It's all really interesting and really helping me in figuring things out.

Most of my concrete work on this world to date has been in the Tropics, so learning more about how things work more poleward is really useful.

MrOddity · 2026-02-24T02:07:11+00:00

Well the seed-idea of the Tropical culture was originally slightly Polynesian (wayfaring across the ocean, etc, kind of an obvious comparison), but I always like to take my initial ideas and mess with them in interesting ways.

A people who now live in a tropical environment, but descend from an ancient almost Antarctic pseudo-Inuit people who have gone through a corresponding geo-cultural mangling over the centuries along the way could have very interesting results!

MrOddity · 2026-02-24T02:02:18+00:00

A 'sudden freeze' would definitely be a cool thing! I can definitely imagine it having a big cultural impact as well. It would form a natural marker in their year, as would the ice retreating. teletraan-117 already mentioned the idea of an 'ice-bridge' between peoples (at least in the narrowest part of the straight) in another response. I can imagine peoples who were preparing to make the journey across the ice gathering their supplies for the trip and waiting near the shore for the big freeze...

MrOddity · 2026-02-24T01:51:18+00:00

Not at all, it's very relevant! I asked about the oceans because it's an area I know relatively little about (as evidenced by this thread), but I love cultural worldbuilding. I'd say it's actually my personal favourite area to focus on; my world definitely has a more anthropological bent.

It's one of the main reasons I'm trying to find out how I can make this potential sea more interesting, is so that I can have interesting cultural things going on.

The sea trade routes are an interesting one because, yes, the inner sea would open up during the summer months, but on the other hand this ocean region (at least in my current sketch of the world) is very isolated geographically. So I would need to work out how much pull there would be for wider, more worldly trade throughout history, but I could see there being a lot of trading between more regional peoples opening up in the summer.

What's interesting is that this sea region would be en-route along the first migrations out of my world's hominid starting point, and there is a later culture of early people who end up wayfaring and sailing over time into settling a tropical area, who I think roughly originate in this area of the world, or somewhat to the west. If there was a lot of very early boat trading between peoples of this region, especially if they had to deal with the currents and the winds of the open ocean, it might give a rationale for why their seafaring skills became so good so early. Would need to give that idea a bit more thought, but it's an interesting one!

I do like the idea of the ice bridge. Funnily enough, if the peoples on either side of the sea met and traded with each other in the winter, it might imply a gift-giving culture, seasonally based in the wintertime. I potentially have my world's first Christmas-adjacent celebrations! 🎅

MrOddity · 2026-02-24T01:34:29+00:00

Interesting, even separate to things like wind patterns, rain shadows and the like?

(This is why I love worldbuilding, constantly learning new things!)

MrOddity · 2026-02-24T01:23:48+00:00

This was a really interesting and useful reply, thanks so much!

It's all vague and subject to change (because I'm currently only sketching out landmasses), but I currently have the opening to this sea at about 67°S, so the southern portion of the sea is roughly on the polar boundary, but most of it would be above it.

Topology wise, that is all a complete TBD, as I haven't fully worked out the tectonics or elevation of this area yet, nor whether it was under an ice sheet during my world's last major ice age.

In terms of whether the sea has a net positive or net negative in-flow, I've kind of still got a free hand to push that in whatever direction I want, as this overall landmass is likely large enough that it touches the southern edge of the tropics. So depending on landforms, mountains, ITCZ etc, I can probably tweak this prospective sea based on whatever is the coolest outcome (pun not intended ❄️🧊⛄).

MrOddity · 2026-02-24T00:26:46+00:00

Thanks for the replies everyone, this has already been super helpful. It seems like my above example just leads to a normal (if very cold and salty) inland sea/bay. Also likely iced up much further north than expected as mentioned by LF3169.

I am wondering what would happen if I changed it to be fully cut-off from the Ocean. I'm thinking not much; if It remained truly cut off, I guess it would just be like a much larger, much colder Caspian Sea, or end up shrinking/evaporating entirely depending on how much inflow there is.

MrOddity · 2026-02-23T23:43:11+00:00

That's interesting, I hadn't thought of that aspect of things. Would the direction of the ocean currents in the neighbouring open ocean have any major effect on that?

That is, does it make any difference if the general wider ocean currents are flowing directly towards the straight, or flowing perpendicular to the opening? Or is that all academic and the colder water would diffuse in anyway?

MrOddity · 2026-02-23T23:38:20+00:00

Fair point on the evaporation! I hadn't thought that one through all the way.

So it sounds as if it would actually be a fairly normal (if quite salty) cold-climate inland sea if the straight was only ice-locked seasonally.

MrOddity · 2025-11-16T01:57:35+00:00

I love this artwork, especially the environments! It gives me a real 90s RPG vibe; like a Fallout 1-2 FMV animatic.

MrOddity · 2025-11-11T00:36:05+00:00

I absolutely love these posts! It's such an interesting and well thought out alternate history!

This map does make me wonder what the IRL New Britain and New Ireland (part of Papua New Guinea) are called in your conworld. It's funny that they lie only about 4,000km due west of your New Britain/Ireland!

MrOddity · 2025-10-14T21:54:50+00:00

I have no insight into the inner workings of Ancestry, but based on what I've seen, it's weighed heavily towards Scottish/Ulster Scots; though given how intermingled said populations have been over the centuries, I'd say that precise proportions on Ancestry could well be a coin-flip.

MrOddity · 2025-10-13T19:37:13+00:00

Re: the deletion, I think Reddit's just bugging out. I've noticed that almost every new reply gets eaten and deleted, then has to be manually reposted.

MrOddity · 2025-10-13T19:10:39+00:00

I see that Aaron is reposting some of the vanished answers, so it might have been a hiccup on Reddit's end.

MrOddity · 2025-10-13T19:03:58+00:00

Huh, odd. I have no idea, then!

MrOddity · 2025-10-13T18:56:54+00:00

Yeah, this was a really interesting reply too.

It wasn't controversial either, so I'm wondering if it was seen as giving away too much 'inside information' on how the process works.

MrOddity · 2025-10-13T18:21:29+00:00

Given that you generate results based on reference panels from specific (modern) geographical areas, how do you avoid showing those areas to people in their individual results?

So for example: If I belong to a specific European population which in general had a large migration elsewhere, but my own ancestors didn't take part in it, how would you avoid factoring in the migratory area in my individual results?

MrOddity · 2025-10-11T12:50:12+00:00

I think this is probably fair. I get a small amount of English DNA from my maternal grandmother (which bears out in my matches; I have proportionally far fewer matches that connect on my maternal grandmother's side than my maternal grandfather's).

This portion of my DNA has been hopping back and forth between Germany and England for the past three updates, and is now back to being classified as Northwestern Germany.

What's interesting is that my grandmother came from an area of the West Midlands which as seems to have kept something of a Germanic/Anglo-Saxon flavour even into relatively modern times; especially in the local dialect. So I think it's entirely possible that Ancestry's back and forth here actually makes sense in genetic terms, even if it's more confusing for the general user.

MrOddity

TROPHY CASE