These were originally basalt lava flows several meters to tens of meters thick.
In some outcrops pillow structures have been preserved, testimony to the basalt lavas having originally erupted and flowed under water onto the Creation Week ocean floor.
These are former sedimentary and volcanic strata that have been transformed by heat and pressure, possibly during the intense upheavals when the dry land was formed on Day 3 of Creation Week.
Among these metamorphosed volcanic strata are amphibolites, belonging to the Brahma Schist.
In other words, the decay of the parent radioisotopes was accelerated by different amounts, the decay of those yielding older "ages" (the alpha-decayers) having been accelerated more.