The presence of coexisting oxide phases has permitted the use of phase diagrams to fix temperatures of crystallization. This presents a problem for theories of crystallization for these ores which favor magmatic segregation with settling of the denser oxides to the base of the anorthosite complex. More recently it has been suggested the ores are the products of immiscible liquid segregation when the oxygen fugacity reaches a critical point. The oxides crystallize within the interstices of the older silicate phases. Eventually their density is sufficient to displace the silicate minerals upward causing the cataclastic fabric in the anorthosites.
Controversy remains about the narrow age constraints for anorthosite complexes.
One model suggests that the linear trend of the anorthosite belt is indicative of a rift system. However, rocks in active rifts today are rarely anorthosite so there must be additional complications to the model. The Earth's history prior to 1.5BY appears to be one of very stable cratonic land masses and little plate tectonics as we know it today. In fact, active rifting does not seem to have occurred until about 1 BY ago. Thus, the period from 1.5 to 1 BY may be one of transition.