[WIP] Building a world from tectonics onward

[QED42]

Took a break from planet-scale things for a bit to work on a tiny corner of one continent to try and get my head around Wilbur. Definitely still have a lot to learn, but I've finally managed to get results that aren't facially ridiculous, so I'll consider that forward progress

Attachment 126427

This looks really cool, what process did you use for this?

[MrBragg]

Hey QED42, sorry I didn't see your post here until now. The process isn't really any special and is kind of an amalgamation of techniques I've seen on here. Basically I start in Gimp by making a few layers of high frequency grayscale noise; for each layer, I set the color levels to be between certain elevations (e.g. 0 - 150 m, 800 - 1000 m, 3700 - 4000 m, etc) and then give each one a layer mask. From there I can paint on the topography I want at each elevation by erasing the mask (using a variety of brushes I've collected), so it's basically a lot of time spent zoomed way in trying to paint features that make some amount of sense. Once I'm happy with how the large and medium scale things look, I read the heighmap into Wilbur for a little erosion and incise flow before sending it back to Gimp for the final color gradient.

Here's the latest piece I'm ~ done with for now.

Peninsula_bigger.png Peninsula_bigger_shaded.png

[Harrg]

I love your results. I see you are using a Wilbur shader for the shading. If you are using Photoshop you can achieve the same effect simply by using a heightmap. But get more control over it.
Copy the heightmap. Create an alpha channel. Insert your heightmap into the alpha channel. Create a new layer. Fill it with gray (half gray is sufficient). Choose filters, lighting effects. Choose endless light. In the settings, set the alpha channel with the height map. Move the sliders as you like. The most important thing is extrusion. In real time, you can extrude your map and make it three-dimensional. Now you can apply techniques to your map that real cartographers use for real maps, like Tom Patterson
https://www.shadedrelief.com/tutorials.html

[Charerg]

Nice to see you're still working on this! I see you've fallen into the rabbit hole of building up realistic-looking topography, and what you've showcased so far looks really great.

[NethanielShade]

I love this thread! Always great seeing other maps starting with tectonic plates. The ocean currents look really familiar, any chance you used Artifexian's tutorial whilst making those?

[MrBragg]

Thanks for all the kind words! It's definitely a rabbit hole, or maybe more of a black hole... ;-)

any chance you used Artifexian's tutorial whilst making those?

Glad you like the tectonics! I've actually revised things a bit since the last post about them, so at some point I should post the updated model. For the currents, I actually used the guide on this forum (https://www.cartographersguild.com/s...ad.php?t=27782) together with looking at maps of Earth's currents like this (https://upload.wikimedia.org/wikiped...erless%293.png).

[MrBragg]

So I've been fiddling around with tectonics some more (because masochism is fun!) and, since misery is much better with company, I wanted to solicit opinions on hypothetical scenarios.

Basically, I'm experimenting with having a "Tethys like" scenario early on during the supercontinent stage (~250 Mya), with a ridge that is destined to be subducted between the northern margin of the ocean between two halves of the supercontinent. When that subduction happens (~225 Mya), the northern margin of the southern continent should rift off and begin heading north. At around the same time--the precise timing doesn't appear to matter all that much--I also have the northern and southern halves of the supercontinent splitting, so a rift exists the entire way between them. Up until now, things seem fine.

01_snapshot_250.png 01_snapshot_225.png

After some time, there should be an oceanic-oceanic margin developing between the "A" and "B" fragments (~175 Mya). My inclination is that B should be subducting under A here as basically a continuation of the margin under the continent, though it also seems feasible that this could be more of a region of diffuse deformation and be more akin to a transform boundary. If either of those options seem wildly incorrect (or wildly correct!), I'd appreciate opinions. Lastly then, when the continental fragment on B collides with A (150 Mya), the question remains with what to do with that same pesky margin; if it's subducting, does subduction cease, or does it instead spread along the continent-ocean passive margin? If it's not, would the two plates basically fuse together? Again, opinions are appreciated

01_snapshot_175.png 01_snapshot_150.png

[Tiluchi]

Ah, nothing like the rabbithole of plate tectonics, where you can always make things more complicated!

It's always tough to suss things out without playing around on GPlates myself, but I think my instinct here would be to have the southern A/B margin as more or less a transform boundary, and have it running northwest to southeast, somewhat parallel to the direction of microcontinent B. The other option might be to have something like what you have at 150 Ma, with the subductive margin extending southwards beyond the continent; this is perfectly normal in plate tectonics as far as I know, though I might expect the subduction zone to keep moving to the west as there's no continental margin to stop it; this is more or less what happened with the Scotia Plate, and I think maybe the Greater and Lesser Antilles.

But these are all just guesses and I'm by no means an expert- getting a realistic tectonic history is a cycle of constant frustration for me, even though I find myself steadily happier with my results as I go on...

[Charerg]

You could also use the subduction of the ridge ca. 250 Mya as the driver for the breakup. I'm guessing this is more-or-less the scenario you were envisioning, with a hinge-type rotation between the separating landmasses. In essence the, eastern portion of the "southern plate" is subducting, while the western portion is diverging. After initial break-up, the rift would spread further east, with a piece of the southern plate breaking off. I guess the end result is largely the same, but I thought it was worth mentioning.

Concepts III.png

After the separating piece collides with the northern continent, it would be expected for the subduction zone to "jump over", and subduction to continue until the mid-oceanic ridge has been subducted. What happens beyond this point gets a bit complicated.

Concepts IV.png

The subduction might cease (depending on the relative montions of the plates), since slab-pull would no longer be a factor. However, unless the two continents merged into a single plate (with a mass of oceanic crust in the middle), a new rift would have to form. This would likely form over continental crust. Like you mentioned, another possibility is that the subduction continues, in which case the continents could return to the initial hinge-type movement, eventually colliding. It's also possible that another portion of the southern continent would break off, repeating the cycle.

[MrBragg]

getting a realistic tectonic history is a cycle of constant frustration for me, even though I find myself steadily happier with my results as I go on...

One of the truest things I've read in a long time

@Charerg, yep, we're definitely on the same page, you just said it better than me!

Appreciate both of your feedback! I actually tweaked things a bit and made a smaller Cimmeria-like block break off first rather than the bigger microcontinent; "Cimmeria" now collides with the northern continent before the cycle more or less repeats itself with the ridge subducting and then the rift jumping south and breaking off the microcontinent later (it will still eventually hit the north).

180.png

I've also followed the evolution a bit farther in time to the next big event happening in this region, which is a microcontinent-arc collision that happens around 100 Mya on the southwestern flank of the northern supercontinent (A). Given that the oceanic crust to the east of that arc is quite old, I have the subduction polarity reversing, placing A under slab pull and thus initiates breakup of the northern supercontinent. This part is more of a reach, but it also seemed reasonable that, which this change in direction of A, the subduction zone to the east of A might extend itself around to the west, consuming that old oceanic crust from both sides.

100_1.png 100_2.png