Cretaceous alkaline-ultramafic stocks in the northern Prince Charles Mountains (PCM) contain zircon xenocrysts entrained during magma ascent to the surface. These xenocrysts provide the only evidence for the age of the underlying crustal rocks in the area. The zircons display a range of ages from ca 2700 Ma to ca 300–260 Ma, with the most dominant ages of ca 900–800 Ma and ca 660–500 Ma. These data indicate that the presently exposed ca 1000–950 Ma metamorphic rocks in the northern PCM are underlain by other geological unit(s). The presence of ca 2700 Ma zircons indicates that a Neoarchaean component is present in the lower crust and that the presumed Proterozoic Rayner Province is not entirely composed of Proterozoic protoliths, but rather is a tectonic mixture of Neoarchaean and younger rocks. This finding questions a Cambrian (Kuunga-age) collisional suture running through the Ruker Province, which may thus be further south within the sub-ice terrain. Nevertheless, the presence of ca 900–800 Ma and ca 600–500 Ma zircons argue for more widespread post-1000 Ma metamorphic events than are observed at the surface. Ca 300–260 Ma zircons, which could not have been derived from any known crystalline rocks in this region, indicate within-crustal chambers parent to mafic dyke suites.