New World (Help with Tectonics?)

[davoush]

Ok, getting close to something usable I think. I don't know what I was thinking on my first attempt - I think I over estimated the influence of the axial tilt far too much. Thanks to Charerg's comments, I also now realise that evaporation rates play a large role, so rain shadow affect might not be as great in higher latitudes.

A few more questions/comments (hopefully there won't be too many more):

1) Semi-Arid > Cfb transition seems quite abrupt. Should there be a narrow band of Csa for transition, or does this simply just not occur inland? I think the Westerlies would be blowing around 30-40 latitude in winter, so maybe a band of Csa?

2) I changed this to Cfa, but then looking at the wind map, most of the winds are being diverted to the southern monsoon in winter, and this area is quite 'continental' with some highlands, so probably winter dry?

3) More or less the same question as 1). I have the Csa ending at a moderate highland region, with the other side being Cfa as East coast receives onshore winds in summer. Does this look ok?

4) This Himalaya-Tibetan plateau area is causing me the most difficulties. As Charerg pointed out, it is at quite higher latitudes than Tibet, so probably not as dry? That said, the westerlies do hit elevated highlands, but would the general moisture in the area mean it is fully humid? I have the high part of the plateau as tundra with the peaks as ET. This transitions into Dfc as elevation decreases. The semi-arid > Dfa transition doesn't seem quite right. I have included a basic elevation map.

5) I think there would be desert, but probably quite limited. I'm not sure if the transition here look right?

As an aside: Do you know why the Jurassic had high temperatures overall?

Many thanks for everyone's support and patience.

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[Charerg]

1) Semi-Arid > Cfb transition seems quite abrupt. Should there be a narrow band of Csa for transition, or does this simply just not occur inland? I think the Westerlies would be blowing around 30-40 latitude in winter, so maybe a band of Csa?

There could be a band of Cs climates, but Cfb->BS is also valid. I forgot to mention this the last time, but the same site that includes the Köppen map I previously linked also has some projected climate maps for 2100. Here's one from a high CO2 emission scenario: map. Those might be useful since they reflect a modelled situtation where the Earth is warmer than present.

Other than that, I might remark that a direct Csa->Cfb transition is slightly unrealistic. That is because the Ca/Cb and f/s letters are assigned based on different criteria. To make matters short, Ca/Cb describes the temperature pattern, while f/s describes the precipitation pattern. And of course it's a bit unlikely that the temperature based transition from a to b would 100% match the precipitation-based transition from s to f. It would probably be more likely to have either Csa->Csb->Cfb or Csa->Cfa->Cfb.

2) I changed this to Cfa, but then looking at the wind map, most of the winds are being diverted to the southern monsoon in winter, and this area is quite 'continental' with some highlands, so probably winter dry?

Yeah it could well be winter dry if the climate is similarly monsoonal as Asia.

3) More or less the same question as 1). I have the Csa ending at a moderate highland region, with the other side being Cfa as East coast receives onshore winds in summer. Does this look ok?

Looks ok to me.

4) This Himalaya-Tibetan plateau area is causing me the most difficulties. As Charerg pointed out, it is at quite higher latitudes than Tibet, so probably not as dry? That said, the westerlies do hit elevated highlands, but would the general moisture in the area mean it is fully humid? I have the high part of the plateau as tundra with the peaks as ET. This transitions into Dfc as elevation decreases. The semi-arid > Dfa transition doesn't seem quite right. I have included a basic elevation map.

It probably would be f yes (which means there is no distinct dry season btw, not necessarily that there is more rain per se). Dfa->BS is fine, but I would be more concerned about Cfb->Dfa or Cfb->Dfc. You would expect Cfa->Dfa->Dfb or Cfa->Cfb->Dfb for similar reasons as I described under point 1. This also applies to the Cwa->Dfa transition, it would work better as Cwa->Dwa->Dfa.

[Edit: It's also interesting to note that the Tibetan Plateau is projected to develop a Cwb/Dwb/Dwc climate in the "2100 high emission scenario" I linked.]

5) I think there would be desert, but probably quite limited. I'm not sure if the transition here look right?

Yes there should be a desert, the extent of which is basically up to you. It could potentially be larger. The transitions themselves are fine though I think the BS layer between BW and Cs climates should be more narrow, looking at the example of Earth's climates.

As an aside: Do you know why the Jurassic had high temperatures overall?

Hard to say with certainty. Continental arrangement was one big factor though: the chain of events leading to the present relatively cold climate started when Antarctica parked itself under the South Pole and became completely isolated. The buildup of Antarctic glaciers had a massive long term effect on the climate because it created a region that supplies basically all the world's oceans with their bottom water (colder water being denser and sinking to the bottom), the Antarctic Bottom Water or AABW. This had an effect of making the oceans much colder in the long run.

It's also thought that the CO2 levels in the atmosphere were much higher during the Jurassic, probably at least partially due to the ongoing breakup of Pangaea and the associated volcanic eruptions.

[davoush]

Well I think I am more or less finished with a (rough) climate map, unless anybody can spot anything very implausible or inaccurate?

I changed the transitions near the mountains in the south so Cwa > Dwa > Dwb > Dfb. Cfb also meets Dfb on the West of the continent, I explain this zone as where the mountains begin, oceanic influence is less, so Cfb > Dfb here. There is (basically) no Dfa on this continent now.

I am also a bit unsure about the deserts, especially the one in the northern continent as it is hotter/wetter - supposing I'm using the Holocene Climatic Optimum as a guide, perhaps they should be a bit less? Also regarding future Tibet climates, I expanded the Dwc area around the mountains a bit, but as the mountains are mostly between 50-70 latitudes and very high, I imagine there would still be significant tundra/ice?

I am also a bit unsure of the Cfa > Dfa transition on the southern subcontinent around 40 latitude. Should the Cfa extend a bit further? Bear in mind the east coast is receiving cold currents.

In the big southern continent, the BS band also a band of Cwa more or less in the middle, there aren't any high mountains or anything to 'shape' the area. Is this realistic? Is the 'transition' simply where the high pressure is no longer very strong?

Thanks!

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[davoush]

A few quick tectonics questions, as I started an elevation map (inspired b Charerg's), but realized I'm not too happy with some of the tectonics.

Must an oceanic plate subducting under a continental plate always cause mountains and/or islands? There's a coastline that I don't want to be Andes style mountains, but there is subduction of a large plate. I also don't really want an island chain.

Plate C (partially submerged continent) in the image has been causing me the most trouble. According to the earlier GPlates model, it was separated from plate A over 250mya. This means there should be some oceanic spreading between them? However, it has moved towards D, but I think this boundary can't be passive, so there has to be an intermediate plate (labelled question mark ?). D&E had also been spreading when C was moving in this direction, which I can't justify as it means there was a subduction opening up where D&E has spread. Not sure what to do with this. I don't mind changing the plate configurations, but I quite like the placement of the submerged continent.

Originally the polar ocean, now J and K was one plate, subducting under the top of H. My thinking was, it cracked along the middle, and is now also subducting under B & C. Is this too much subduction? Would it be more realistic to just have it as one plate?

G was originally part of A and F, but got rifted along the way. Maybe it is now basically part of B?

Thanks!

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[Charerg]

A few quick tectonics questions, as I started an elevation map (inspired b Charerg's), but realized I'm not too happy with some of the tectonics.

Must an oceanic plate subducting under a continental plate always cause mountains and/or islands? There's a coastline that I don't want to be Andes style mountains, but there is subduction of a large plate. I also don't really want an island chain.

I haven't looked through the rest in detail, but a quick comment on your question. A subduction zone is basically always associated with active volcanism, but how substantial the mountains or islands formed varies. In some cases like Sumatra and Java the mountain ranges are quite narrow. Which coastline are you referring to?

[davoush]

I see, thanks. I was talking about the northern coastline of H and A. The polar ocean is subducting here, but I didn't really want a long stretch of mountainous coast or island chains. I don't mind if they are more isolated. The large bay on northern H is probably continental shelf.

[davoush]

I am getting myself a bit tangled up with tectonics. I have a quick question:

Can an ocean which has been spreading become an oceanic plate in its own right? I.e. Could the Atlantic become 'The Atlantic Plate' not connected to Eurasia and Americas? If so, what would precipitate this?

[Charerg]

I am getting myself a bit tangled up with tectonics. I have a quick question:

Can an ocean which has been spreading become an oceanic plate in its own right? I.e. Could the Atlantic become 'The Atlantic Plate' not connected to Eurasia and Americas? If so, what would precipitate this?

Presumably yes, though it would perhaps be more likely that it would be "cut off" from one of the continents rather than both. For example, the convergence between Eurasia and Africa could cause a "subduction virus" where Atlantic lithosphere of the African Plate starts subducting beneath Eurasia, which could eventually evolve into a much larger subductice margin.

Similarly the Antilles trench could potentially initiate a "subduction virus" on the American side of the Atlantic.

Edit:
There could also be a combination of factors (and likely would be). For example, the North America-Pacific margin seems to be developing into a passive margin with the subduction of the Farallon plate (compressional tectonics being replaced with extensional tectonics, with the formation of the Basin and Range Province: here's a nice youtube vid about that). This could likewise contribute to a change in movement direction and hence possibly initiate the formation of a new subduction zone.

[davoush]

Thanks - I think that has helped solve some issues.

An update to the tectonics model with some change of land placement:

A, B & C were joined as supercontinent roughly 300mya. (Possibly G too?)

D, E & F were also joined as a supercontinent.

The ocean which was between A & D starts subducting under D, pulling A towards it, eventually colliding with a huge orogeny. This ocean was then basically closed, apart from J which is a small remnant still subducting. This also lead to the opening of the ocean between A & B.

Oceanic plate H starts to subduct. This was originally a spreading centre between the two super continents. It is subducting most strongly along the Western boundary, but has also split and is subducting in the other direction too (plate I).

The southern polar ocean begins subducting under B, dragging E into it. This means the spreading centre between D&E is the newest. E has collided recently with B, leading to a huge Himalaya-style orogeny. This subduction also caused C to rift from A, and F from D.

I am still unsure about G - should it just be part of plate A? I would like to add some more interesting plates along this subduction boundary, but I'm unsure. Perhaps there are can be fragments of rifted continental crust from the break up of A & B, which are now also colliding with the subduction zone? I don't know if that's realistic, however.

I also realize plate H is huge - is it OK to have such a massive oceanic plate?

Also, as a rifted continent moves, does it accrue continental crust on the 'active' margin? I.e. the southern margins of F and C might have gained some crust, or there will be a series of islands between them and the subduction zone which they are moving toward?

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[davoush]

Quick question (I feel like I could make a book out of my 'quick questions' at this point...).

Is it reasonable for the continent in the image to be rifting in two places? My explanation was that the rift formed at A is newer, and is because this piece is moving towards the subduction zone than the other, older rift to the East. The older rift is an eroded collision zone which happened about 100mya, hence the large lakes forming as the two pieces move apart. There is also subduction to the East, further motivating the rift. I don't know if this is too much rifting?

I am trying to understand what the terrain would be like so I can make a reasonably detailed elevation map, taking into account tectonic history and current processes.

Many thanks!

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