<p>The melt-assisted destruction of thick continental lithosphere is a thermodynamically intensive process that requires a chemically altered lithosphere. Subduction is a convenient vehicle to introduce melts and fluids into the mantle and thus lower the solidus, yet many regions with thick crust - such as the Colorado Plateau, Arabian Plate, and Anatolia - exhibit continental volcanism and lithospheric foundering in the absence of active subduction. These locations share common geochemical signatures of a lithosphere that has been modified through ancient metasomatism, suggesting that these reactions have profound implications on modern cratonic stability. Arabian xenoliths provide direct evidence of three distinct metasomatic events and showcase the evolution of a progressively unstable lithosphere. These rocks allow an integrated petrographic and Sr-Nd-Pb isotopic characterization of silicate, hydrous fluid, and carbonate metasomatism. These modifications occurred between 400-1000 Ma yet the anomalously dense and fusible lithosphere remained “frozen” until the Miocene when fracture development perturbed the lithosphere and initiated foundering and lithospheric recycling. The effect of metasomatism upon lithospheric stability demonstrates that lithospheric differentiation and volcanism can occur beneath thick continental crust. This process is thus a potential explanation for lithospheric differentiation on both early earth and other solar bodies.</p>