If that's the reason, it could be because the crust is about 25 kilometers thick, resembling continental crust, compared with the 5 to 10 kilometers of oceanic crust elsewhere. (sciencemag.org)
But here the sliver of continental crust lies on the Pacific plate, and it is the Australian plate that is being destroyed through subduction. (newscientist.com)
According to the paper's first author, Violaine Sautter, these primitive Martian crustal components bear a strong resemblance to a terrestrial rock type known to geologists as TTG (Tonalite - Trondhjemite - Granodiorite), rocks that predominated in the terrestrial continental crust in the Archean era (more than 2.5 billion years ago). (sciencedaily.com)