There is no subduction of the crust of Venus (shown here).
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The Venus Lithosphere
Like the Earth's lithosphere, the lithosphere of Venus is the not-so-rigid part of the crust of Venus which is cooler than the interior of Venus, somewhat like the film on top of a cup of hot cocoa. Unlike the Earth, the lithosphere of Venus may be too thick to move.
arth, the lithosphere can be pushed aside in response to the warmth of the Earth. The lithosphere then subducts, melts, and becomes part of the warm rising magma again. Thus on Earth, the recycling of the lithosphere keeps the lithosphere from becoming
The shape of the volcanoes suggests that in its history, Venus, like Mars, has built a thick lithosphere. A thick lithosphere supresses the
motions of plates over a surface, even though the interior of the planet is warm enough for churning motions which cause material to rise from the deep interior.
Why would Venus, and not the Earth, have a thick lithosphere? The answer is that unlike the Earth, the rocky material which comprises the lithosphere of Venus does not contain enough trapped water to allow the lithosphere to deform and subduct. Thus
the lithosphere cannot make way for hot, rising magma from the interior and instead stays in place and thickens by cooling gradually.
Nevertheless, on Venus, there may be mechanisms for the surface to turn over.
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