How much surface water do I need for plate-tectonics on a planet?

I want to build a habitable desert gas-giant moon and I´m not sure how little water I can give it and still get plate-tectonics instead of an Io-like lid-tectonic setup. I want plate tectonics because continental-continental divergent (East-African rift valley) and convergent (Himalayas) plate boundaries create way more interesting geological features than the uniform mountains and plains of Io-like lid-tectonics. Additionally, plate tectonics might be necessary to keep the planet habitable. Since no two papers, I read on the subject of what mass a planet needs to sustain plate-tectonics agreed on a mass range(either Earth is at the upper or lower boundary...), I settled on 0.2 to 5 earth masses and decided to call it a day. While even the role of water as a lubricant and thus its role in enabling plate-tectonics has been challenged, most sources consider it necessary. But how much water, specifically surface water, do I need on my planet in order to maintain plate tectonics? Earths oceans contain a lot of water, but the mantle and the crust might hold between 2 to 25 times the amount of water found in the oceans. So is ocean water even necessary?

My planet has the following, more or less fixed parameters.

• 10 to 20% global ocean cover

• ca. 0.3 Earth masses

• heavy volcanism due to tidal heating ( not Io-like but close)

• a similar composition to Earth

• first and biggest of the three moons of a super-jovian ( 12,6 Jupiter masses)

• super-jovian orbits an early F-Type star (1,15 solar masses) near the end of its 7 byr lifetime

• desert world with habitable poles

posted over 5 years ago

TheDyingOfLight‭

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