it is the sort of topography that one would expect in a region where grinding tectonic plates beneath the sea are relentlessly pushing up a crazy quilt of irregular mountain
the whole sentence has ambiguity, what is the clear meaning of it?
I don't think the sentence is ambiguous, although it does show a partial understanding of where Tectonic Plates - Wikipedia, the free encyclopedia are, and what they do there.
'Topography', here, refers to a sort of landscape - having certain features; 'quilt' is a rather confusing metaphor. I think it is referring to a Patchwork quilt - Wikipedia, the free encyclopedia, rather than to a duvet . In pushing up (forming) mountains, the tectonic plates mix up the geological strata so that there is a 'patchwork' of different sorts of rock on the surface.