How would a Larger Planet with a Thicker Crust than Earth affect Tectonic Activity

Question

The basics are the planet is larger in both mass and size, but lower in density than the Earth.

In a previous question I asked about methods of reducing said Density which involved thickening the mantle and crust and it lead me to another question: how would a thicker crust and mantle affect tectonic activity?

Assuming that for all other intents and purposes, tectonics are basically function like on Earth, how would the thicker crust change the way plates behave? ie. Would there be fewer, slower plates or vice versa, and would it affect volcanic activity (eg. volcanoes are less likely because there is more material the magma has to rise through, or perhaps the pressure is more likely to mount causing more explosive eruptions)

I'd be interested to know the results.

Answer 1

Assuming that tectonics would function basically like on Earth is a bad assumption. This sort of thing has been studied in simulation, and any combination of significantly higher gravity, significantly thicker crust, and significantly more ductile crust results in pipe tectonics, rather than plate tectonics. Venus is an example of thicker, more ductile crust. Mars is an example of thicker, rigid crust. (Sadly, we have no examples of higher gravity rocky worlds in our solar system.)

Pipe tectonics is dominated by volcanic hotspot features--large dome volcanoes and supervolcanoes. With a rigid crust like Mars, you don't get much relative crustal motion at all, so hotspots can stay in place and build huge volcanic structures, and the major tectonic processes are deposition of volcanic material and recycling of melted crust that is pushed down into the mantle by the weight of overlying deposition. With a more ductile crust like Venus, you can get regions of crust with differential motion, producing folds, faults, and rifts, but there are no continuous boundaries delineating distinct plates; boundary regions undergoing tension or shear mostly just stretch rather than fracturing.

Answer 2

My knowledge of geology is limited, but here you go.

Just kinda thicker

You're going to get tectonics that are fairly Earthlike, but probably much slower, since plate tectonics are fueled by the mantle, which is further away from the surface in your example. Subduction will also probably be slower, unless there's also a significant increase in density, which I doubt.

Much thicker

Your tectonics will certainly be much, much slower, and you may get pipe tectonics instead of plate tectonics (as the previous answer said). This is harder to work out, and less interesting from a xenobiology and worldbuilding perspective, since there's less change. So if you do want a thicker crust, don't make it *too* thick.