Exploring the decoupling and removal of dense material during lithospheric thickening as applicable to craton formation

Cratons are areas of continental crust and lithosphere that have not deformed for billions of years; thus, comprising the most stable regions on the Earth's surface. However, the processes that lead to craton formation introduce potential instabilities. For example, cratons formed via the stacking of buoyant oceanic lithosphere would pose some potentially serious buoyancy complications as the basaltic crust tends to transform into much denser eclogite at depth. Thus, if basaltic crust is a significant portion of buoyant oceanic lithosphere, the entire thickened package could be overwhelmed by the transition to eclogite. This could in turn promote instability, foundering and failure to produce thick cratonic lithosphere. Alternatively, forming thick cratonic lithosphere via the amalgamation of arc or continental material would also introduce instability. Achieving the required integrated buoyancy from island arc material also requires a secondary removal process of mafic/ultramafic cumulates during collision. This leads to several testable questions; how much dense material can the system maintain before becoming unstable? Does the relative depth of the dense material effect stability? Does the dense material need to be removed or can it be modified in some manner to maintain stability? If it can be modified, which process or processes can do so? We will present numerical models exploring one such modification process- the decoupling and removal of dense material during lithospheric thickening.