Mantle wind, and why the Pacific is asymmetrical

[Tiluchi]

Wow, this is super helpful and answers some questions I'd had in my head about back-arc basins and how they form. FWIW as you say I don't think it's the *only* reason why back-arc basins form where they do; I think there used to be an Andes-style mountain range along the east coast of China until 80 million years ago or so before it got shut down by back-arc rifting, and the Andes used to have some back-arc basins. Thankfully it appears that my world mostly follows this rule, although I'm realizing now I do have a very high continental volcanic arc on the east coast of one continent that might make sense to turn into a back-arc basin. Will have to think about that one a little more...

[L1qu1dN1trog3n]

As far as I'm aware no-one's done a full mechanistic study of this phenomenon, just that there's a statistical significance to the dip angles of the various subduction zones around the world depending on if they are west or east facing, and my professor at least ascribes this to the influence of mantle wind. This is a very cutting edge area of geodynamics! You're also right to stress that it's fundamentally the balance of forces in the overlying wedge that determines the geomorphology, and therefore other factors can easily swamp the 'signal' of the mantle wind. That's why I think its better to think of it as a bias rather than a hard rule.

We're also in the somewhat odd position that the majority of subduction zones are oriented roughly NS, with the Aegean, Aleutian and Java trenches being the only ones I can think of that are oriented EW. This probably makes this phenomenon stand out a bit more on the modern Earth than, say, when the Tethys was in its main closure stage.