Chord - Yet Another tectonics/winds/climate/etc World Map Project

[AzureWings]

So I'd mentioned going through the processes mentioned by Azélor and Charerg et al. by hand a bit earlier. The first attempt I'd made towards the world with this name (Chord) had the problem that I realized well after proceeding a ways with the landforms I'd put together was that, while I'd modeled some degree of continental drift and placed things like mountain ranges based on plate movements, I'd made a map with pretty much no active orogenesis in the present time.

That seemed pretty implausible so I started over, and made a new map that I think is a little bit more tectonically reasonable (I don't personally need it to be that precise, just good enough). Proceeding along from there I found that the stage I was feeling the most uncertain of was the winds - so I'd like to ask about the reasonability of wind layouts. Something about the way different pressure zones are supposed to impact wind movements I seem to have difficulty compositing into something that feels satisfactory between multiple different influences on the wind patterns.

So - what might need tweaking in the winds laid out in the maps below? I'm a little bit more confident in the pressure zones than the winds themselves, but if there's something particularly glaring there I'd like to know that too. There's not too much that my heart's set on keeping constant so far, with one major exception - I've been trying to set things up so that the southern tip of the polar continent and many of those nearby islands in that sea have an at least livable (if still chilly) climate, rather than an arctic/E climate. Right now I have it under influence from a mild current by way of the winds that tend to go north-east-wards through that area, but might need to come up with something else if that doesn't seem to make sense.

Chord - July Winds (and Pressures):
chord-windsJul.png

Chord - January Winds (and Pressures):
chord-windsJan.png

Chord plates and rough movement directions, for the curious (plates over a pole can of course look like they're moving in very different directions even though it's supposed to be the same direction across a sphere). The large grey lines are the plates, and the thinner black lines are the actual landmasses (yellow lines are rough mountain range locations):
chord-plates.png

[davoush]

Hi Azurewings,

Nice to see another tectonics-type map project. I would like to comment on your tectonics map, but the colour scheme and lack of labelling makes it difficult to know what I'm looking at exactly. Perhaps if you update it with a clearer version?

[Mapsburgh]

It's a bit tough to talk about particular places on the map with no labels to refer to things, so hopefully this makes sense. On your tectonics map, you have a lot of island arcs, but they don't seem to line up with the types of plate boundaries they're on. For example, between the two western continents, you have a major island arc, but the plate boundary there is divergent. Meanwhile, the two oceanic plates in the center ocean seem to be converging near the equator, but there is no island arc there. That's basically backwards from how you'd find it in the real world. I'd advise going through your tectonics map and carefully marking which boundaries are divergent vs convergent vs transform. That will make it easier to see where there should be mountain-building on land and island arcs in the ocean (convergent), and where there shouldn't (divergent or transform).

[AzureWings]

Thanks for the feedback! I'd been operating under the assumption that divergent boundaries in oceanic areas could still cause island-forming volcanism, but I'm guessing then that even in such cases it is not so likely to form quite as dense, extended, and/or discrete chains as those I depicted in those areas?

I went through and labeled the boundaries, but am unsure about a few of the plate boundaries where adjacent plates are moving in similar directions. The below map uses red for convergent boundaries, blue for divergent, and yellow for transform boundaries; green denotes boundaries I was really unsure about. (The much thinner colored lines in the background are rough major landmass locations, and sorry about the misaligned gray lines with the plate boundaries - I rescaled slightly from the original source image I put together in GPlates).

chord-plateBoundaries.png

I added temporary plate labels for use to refer to locations since I don't yet have planned names for all of the regions or landmasses.

The places where I was unsure:

???-1 (F Plate/M Plate Boundary): I'd originally been thinking of having this be an Indian/Eurasian plate situation, but realized I have these two plates moving in similar directions to one another. Would the F Plate moving much faster (relatively speaking) than the M Plate be enough to have this still be a prominent subduction zone?

???-2 (A Plate/A2 Plate Boundary): These two plates look like they'd be diverging slowly, given that they're moving in similar but diverging directions. However, the placement of this boundary doesn't seem inclined to really be a divergent boundary as you move back along it, since it's roughly perpendicular to the directions these two plates are moving. What makes sense here?

???-3 (V2 Plate/E Plate Boundary): I'm really just not sure what would be happening here. It all seems to come down to the relative rate of movement of these two plates, but unlike the F Plate and the M Plate I hadn't had a particular relationship in mind. Given their general directions of movement would this be more likely to be a divergent or convergent boundary. It looks like an era down the line the two plates will only be sharing a transform boundary since the E Plate looks like it will move 'out of the way' of the V2 Plate (of course the V2 plate is probably going to be subducted under the V Plate by then).

Additionally, regarding the islands that were on the C2 Plate in my original landforms map; those in particular I hadn't imagined as caused directly by plate-boundary deformations so much as being pieces split off of the major landmasses on the S and C Plates (the C2 plate having originally been a part of one of the S or C plates and splitting off itself in a geologically relatively recent timescale). My understanding is fuzzy enough that I'm not sure how plausible this is, though.

[davoush]

I'm also working through the tectonic model of my second world, so here are some comments based on things I've learnt (although some more knowledgable members such as Charerg might be able give more detail). Of course, these are just suggestions as tectonics are a rabbit hole which can be very frustrating (and equally as fascinating) just to make something semi-plausible as I am experiencing myself...

Island arcs: Ocean spreading doesn't usually lead to island chains - look at the mid Atlantic ridge, there are very few island arcs along here. While smaller sections of landmasses can split off (i.e. back arc basins like Japan or smaller rifted landmasses like Madagascar), I think the extent of tiny islands you have here is quite difficult to explain.

Also: Long stretches of transform boundaries along oceanic plates basically don't generally occur - the ocean should either be subducting, or spreading along its boundaries as far as I'm aware (earth's current plate configuration attests to this).

???-1: Yes, I think they can be moving in a similar direction as long as the subducting plate is moving faster and colliding.

???-2: This doesn't look like it should be a divergent boundary. There is subduction to the East and rifting between A&V. I think A and A2 should be one plate moving to the East, having rifted from V. Maybe A2 was a failed rifted arm of a triple junction, but I can't see a motivation for a full 3-way rift here.

???-3: E Plate seems to be moving in a strange direction. It looks like it is colliding with V, but you indicate a movement which looks like rifting. V2 plate looks iike it could be a Juan de Fuca style minor plate subducting under E&V. The southern boundary should probably be divergent, or convergent if O Plate is also subducting under it.

The boundary between N and C looks a bit odd - N is oceanic and being subducted to the West, it shouldn't be rifting at the boundary with C. If you wanted rifting here, probably better to have the plate split, with an extra minor plate subducting under C too (i.e. see the East Pacific Rise).

(Also, it might be helpful if you include the landmasses a bit more clearly or filled with a colour, as they are barely visible in the map ).

[AzureWings]

Here's a version with a number of changes (as well as more-visible versions of the super-rough landmass shapes I'd based my others off of) generally in line with the mentioned suggestions.

chord-plateBoundaries2.png

I reduced the extents of oceanic transform boundaries (generally just a big issue along the boundaries of Plate S) - although I wonder a bit about its borders with other large plates (e.g. plates N and C) that are longitudinally wide as moving over the pole plate S is moving more towards them on one side and more away on the other.

I unified the A and A2 plates, although when drawing out more detailed landforms I may keep signs of partial rifting on the north side of the continent there where the border between those used to be.

Switched the boundary type on the V/E boundary, and marked V2 as subducting under both. Considered having O subduct under V2, but that made V2 have entirely convergent boundaries which seemed a little weird.

I added Plate N2, which has oceanic spreading with N and is subducting under C. I also expanded C2 a bit to hug the coastline of C's landmass a bit more closely; I noticed many of my continental boundaries near landmasses are a bit further offshore than a lot of Earth's. I do feel a little unsure about that multidirectional spreading rift area that formed, but everything there is kind of moving away from that point near the bottom of C2 (must be a pretty tectonically interesting spot then, spreading out oceanic crust in all directions).

Looking at the result suggests the locations for big, long island chains are the M/C boundary, the N/E boundary, and the V2/E and V2/V boundaries (along with a bunch of south-polar chains and the sea north of M). I think I'll still have a particularly large island landmass on the north of the V2 plate as in my original plan, as well as a number of islands on the C2 plate (though the big long chains extending out from there will be gone).

Locations for really major mountain ranges look like the F/M boundary, the M/M2 boundary, the western coast of the salmon-colored (C Plate) landmass, and the northern coasts of the green and pink landmasses. Additionally, from when I modeled their general movements in GPlates before, some historical collisions lead me to want to place mountain ranges on the southeastern coast of the salmon landmass and the eastern coast of the gray landmass. Looking at the way the plates are lined up and moving suggests that one or more of the F/M, north green, north pink and/or west salmon ranges should be the world's most extreme ones. Does that all sound reasonable?

[Charerg]

At a quick glance, the most glaring flaw of sorts is the convergent oceanic-oceanic boundary between C and M. I think it would work better if the border would follow the coastline of one continent or the other (probably M).

[AzureWings]

I played around with a few different approaches to the western hemisphere area centered on plate M.

chord-westernHemisPlates.png

This leaves plate M intact, just squaring the convergent boundary up to the coastline as you suggested.

I also played around with splitting plate M, although these might bring their own complications:

chord-westernhemisPlatesM3.png

The first approach I tried was splitting it into three plates, one (B) containing the majority of the southern oceanic area, M keeping most of the landmass, and a bit of the southern landmass on a smaller plate (M3) in the middle, but wasn't very satisfied with how it interacted with plate F and the F/O spreading ridge (had to be very specific about M3 being slower than O otherwise it would have a tiny convergent border in the middle of a spreading ridge which seemed like it would be very odd).

chord-westernhemisPlatesM2.png

Splitting plate M into two plates M and B seems like it might feel a bit better than the three plates but I still don't know if it's better than the single M plate version.

In the one-plate and two-plate cases I tweaked the F/M boundary: it's convergent where it is perpendicular to plate F's movement since it is faster than M and subducting under it there, but divergent where it isn't because in the axis perpendicular to plate F's movement plate M is moving away from it (the result being a sort of 'tearing' where F collides with M along one edge but M is rifting away along the other edge). I don't really know if that makes sense tectonically though.

Whatever else though I'm thinking this suggests the eastern region of the A Plate continent (i.e. the western hemisphere part seen in these snippets) is going to have some pretty extreme mountains near the north and east coastal areas.

[Pixie]

The one thing I think you are failing to consider, which is key, is how oceanic crust is formed.

It is formed in ridges because a plate is moving away from the ridge, and the "new" volcanic material gets added to the plate moving away. This means that a continent will have oceanic crust attached to it, opposite to where it is moving to. Unless, that is, that that oceanic crust was caught in some subduction, which means the entire plate is now pulled towards that subduction zone.

So, with this is mind:

F and O: F was pulled towards M, that's clear. The sea between them is rather recent, that's clear too. But then O has ocean crust on the other side as well, and is moving towards it. Which clearly indicates subduction at that end, as you have it.. but a mid ocean subduction?

M and C: if you want to have M moving westward, then it wouldn't be a bad idea to make the oceanic crust between the two belong to M and being pulled towards a subduction zone close to C. That would be the most natural, to my eyes.

[AzureWings]

The one thing I think you are failing to consider, which is key, is how oceanic crust is formed.

It is formed in ridges because a plate is moving away from the ridge, and the "new" volcanic material gets added to the plate moving away. This means that a continent will have oceanic crust attached to it, opposite to where it is moving to. Unless, that is, that that oceanic crust was caught in some subduction, which means the entire plate is now pulled towards that subduction zone.

Thank you so much! That makes a lot of sense and is probably something I should have been aware of, but that had not occurred to me. I've reworked a lot of my plate shapes and directions with that in mind (and remembering that it's subduction that drives movement if I recall right?), although there's probably still further to go.

chord-plateBoundaries3.png

F and O: F was pulled towards M, that's clear. The sea between them is rather recent, that's clear too. But then O has ocean crust on the other side as well, and is moving towards it. Which clearly indicates subduction at that end, as you have it.. but a mid ocean subduction?

Is a mid-ocean subduction that strange? Looking at Earth at least the Pacific and Australian plates seem to have this going on (on the non-Australian/large landmass side of that plate). Nonetheless I also note that subduction is a lot more common (because of crust type density) on oceanic/continental areas so I've reworked many of my convergent plate borders to fall more along the coastlines of major landmasses. Regarding Plate O in particular, I reworked that convergent boundary along with the boundary/directions of plates V2, E, and V although I still have some oceanic subduction where O hits the spreading zone between V and A.

M and C: if you want to have M moving westward, then it wouldn't be a bad idea to make the oceanic crust between the two belong to M and being pulled towards a subduction zone close to C. That would be the most natural, to my eyes.

In addition to that I tweaked M to be headed in a more westerly direction and less northwards (although this results in a bit more oceanic transform boundaries with M2...). It's a big plate now so I'm keeping the separate B plate I think. I also changed the direction of plate C a bit to correspond more to where it's being subducted (that shrinking sea area between it and V). I think the A plate must not be moving very fast since it isn't being pulled under any other plates (rather it's pulling M (to an extent) and B).