Example, mid-Atlantic spreading must have started in middle of Pangea continent. It is an evolutionary thing, see fig 16.20 Basin and Range is another type of expression of tensional tectonics. Could also evolve into spreading. Trenches form where plates subduct. Characterized by large strato-volcanoes.
Subducted slab releases fluids, lowers solidus of overlying mantle wedge, which melts.
Produces basaltic magma that differentiates to andesite plus. Probably involved in continental crust formation. At least forms bouyant material that can later be accreted. Accretionary Wedge Material scraped off the downgoing plate just above the trench. The kind of deformation that occurs in accretinary prisms where the rocks are more coherent.