New World (Help with Tectonics?)

[davoush]

It's not really plausible for a single plate to be subducted in multiple directions, you'd have to break it apart into at least two separate plates. You could also make E2 more-or-less surrounded by divergent boundaries like Antarctica, maybe something like this:

Attachment 106212

Thanks, yeah, I thought so - hence my previous question about oceanic plates splitting. Would it seem reasonable in this case? I.e. an oceanic plate splitting in two, spreading in the centre and subducting on either side? Are there (or have there been) any examples of this?

Alternatively, I could change the movement of E2 to follow the subduction more directly, in which case it looks like it is heading for an India-Style collision. As a continent moves towards a subduction zone, would there be island arcs? For example, imagine India had not yet collided with Eurasia, in the ocean 'gap' north of India, does anything happen, or is India just pulled into the subduction like a kind of conveyor-belt motion? (Wow, questions lead to more questions.)

[Charerg]

Thanks, yeah, I thought so - hence my previous question about oceanic plates splitting. Would it seem reasonable in this case? I.e. an oceanic plate splitting in two, spreading in the centre and subducting on either side? Are there (or have there been) any examples of this?

Alternatively, I could change the movement of E2 to follow the subduction more directly, in which case it looks like it is heading for an India-Style collision. As a continent moves towards a subduction zone, would there be island arcs? For example, imagine India had not yet collided with Eurasia, in the ocean 'gap' north of India, does anything happen, or is India just pulled into the subduction like a kind of conveyor-belt motion? (Wow, questions lead to more questions.)

I'd say the Pacific and Nazca is an example of an oceanic plate splitting and subducting on either side, in a sense. As to the collision, it depends. There weren't any island arcs on the Indian plate ofc, but there would have been some island arcs at the subduction zone itself on the Eurasian side. See Australia-Eurasia for a younger continent-continent collision, for example.

You could also check some vids from either CS Scotese or Earthbyte to answer most questions regarding Earth's tectonic past.

[Azélor]

While on the topic.
I hope I don't sound stupid saying this but apparently scientists just have confirmed the evidence on Africa splitting up.
It seems like we knew about this for a while though.

https://face2faceafrica.com/article/...t-valley-video

[davoush]

While on the topic.
I hope I don't sound stupid saying this but apparently scientists just have confirmed the evidence on Africa splitting up.
It seems like we knew about this for a while though.

https://face2faceafrica.com/article/...t-valley-video

Wow, an example of tectonics "in action". Dangerous for those living near the rift though...

After staring at my GPlates model for far too long, I've come up with the following present-day tectonic arrangement. Most of it seems coherent and consistent, only N1 bothers me the most.

I would explain it by saying: N1 was not connected to anything 200Mya, and is a semi-submerged continent like Australia. There was a subduction zone (maybe of an old polar ocean) along the coast of W1+W2 when they were joined, 200Mya, pulling N1 in this direction. Around 150Mya, the subduction was finished, and a rift opens between W1+2. N1 drifts slowly towards the rift, forming a triple junction. The rift becomes inactive by about 100Mya and N1's oceanic crusts begins to subduct beneath the new rift. The subduction zones to the north of W1+E1 (which is now basically one fused plate) could also be transform boundaries.

Edit: See latest post.

[davoush]

(Edit: See next post)

[davoush]

More or less final version. I think I'll leave the tectonics at that for now. I might update it at a later stage with a few more details. (Unless anybody spots anything terribly wrong/implausible!)

(I know I've missed some subduction triangles, use your imagination for those )

ReduxIslands10.png

[davoush]

Quick question about mountain ranges/elevation/rifting.

Where in a mountain range is rifting most likely to occur (assuming the range is 50-100 million years old) - I.e if India began rifting from Tibet, would the rift happen along Nepal’s border where the range rises steeply, or would it happen in the middle of the Tibetan plateau?

Is there any advice regarding placement of old mountain ranges? Would you expect rifted continents to have mountain ranges which ‘mirror’ each other on the sides which were once joined? Or can I place old ranges anywhere within reason?

Thanks

[Charerg]

Quick question about mountain ranges/elevation/rifting.

Where in a mountain range is rifting most likely to occur (assuming the range is 50-100 million years old) - I.e if India began rifting from Tibet, would the rift happen along Nepal’s border where the range rises steeply, or would it happen in the middle of the Tibetan plateau?

Rifting processes are somewhat poorly understood, it's a subject of ongoing research. Here's a study that suggests the South Atlantic rift originated at a former back-arc basin dating to the Pan-African orogeny. If this is accurate, then rifting would perhaps be more likely to occur somewhere in the Tibetan Plateau. Probably not near Nepal since the crust would be the thickest near the suture, the roots of the Himalayas go very deep underground (keep in mind that mountains grow a lot more "downward" than upward during continental collisions, what you see on the surface is only the "tip of the iceberg", so to speak).

Is there any advice regarding placement of old mountain ranges? Would you expect rifted continents to have mountain ranges which ‘mirror’ each other on the sides which were once joined? Or can I place old ranges anywhere within reason?

Thanks

Yes, there is such a thing as an Elevated Passive Continental Margin (EPCM): Brazil Highlands, Southern Africa, Greenland, Madagascar and Eastern Australia, to name some. The thinking in the past has been that those were formed as part of the rifting process (similar to the modern Ethiopian Plateau, as an example). However, there's some modern research which contests the idea (another study if you're interested). But the bottom line is that the coastal margins can often be elevated in passive boundaries (even if the exact mechanism of uplift isn't quite clear), and they tend to indeed be "mirrored" (with the exception of Eastern Australia though, so not always the case).

Other than that, old orogens are typically located at boundaries between cratons. However, those tend to be very eroded. Though there are exceptions to that rule as well, apparently active rifting can sort of "rejuvenate" old mountains because the increased buoyancy can lift their roots. This is thought to be the mechanism behind the Gamburtsev Range in Antarctica.

Mountains formed by intra-continental volcanism can be located more or less anywhere, and tend to have a somewhat characteristic "blob" shape (think Iceland or the Tibesti Mountains).

[davoush]

Thanks Charerg, that will help with my elevation map.

In the mean time, I have made a rough ocean currents map. I think most of them look about right. I was mostly unsure about the norther current being drawn down from the polar current. On the one hand it might draw a bit of warmth from the westerlies current, but also from the polar ocean. Would it more likely be 'mild/neutral' or very cold?

I'm beginning to think the Eastern continent looks too much like Eurasia even though I tried to avoid that...

[davoush]

Quick question about climates and the implications of a greater axial tilt (of about 27 degrees).

I know the tropics will cover a greater area (reaching 27 degrees), and the polar circle will also extend slightly further (to 63 degrees).

However, given that the ITCZ moves further each summer, does this mean the tropical rainforest climate will be decreased (since the monsoon affect of the ITCZ is larger)?

Also, although the tropical zone is larger, it seems like pressure belts would shift further north/south in summer/winter, so essentially the tropical zone shifts slightly.

What I'm struggling with is the seasonal variation and the Koppen climate classifications - it seems like some temperate areas will have mediterranean like summers, but far cooler winters. I don't think there is a classification which includes this variability?

I'm also unsure about where the 'horse latitudes' would fall with such an axial tilt.

Perhaps I would be better first determining the climates as if the tilt was the same as earth, then adjust them slightly?