 As the rock enters the submetamorphic field, generally Zeolite facies metamorphism, clay minerals begin to recrystallize into low-temperature metamorphic phyllite minerals such as chlorite, prehnite, pumpellyite, glauconite and so forth.This liberates not only water but incompatible elements attached to the mineral and trapped within crystal lattices.Metals liberated from clay and carbonate minerals as they are changed from clays and low-pressure disordered carbonate forms enters the remaining pore fluid which by this time has become concentrated into what is known as a deep formation brine.