Detrital zircon dating
The double-dating approach combined with the existing knowledge of the regional geology allows us to discriminate between magmatic cooled grains of extrusive and shallow intrusive rocks, exhumational cooled grains, and thermal reset grains.
We find that the erosion of both shallow and deep intrusive arc rocks dominate the detrital age signal, while syn-depositional extrusive grains are lacking.
The story often told is that radiometric dating produces dates that are super-reliable, because lab rates of radioactive decay don’t lie.
There are, however, two inconvenient and commonly ignored issues in geochronology-based sediment provenance: (1) detrital zircon U-Pb ages can cluster by grain size ; and (2) grain-size sorting is strongly influenced by the dynamics of sediment transport.
It is becoming increasingly clear that in order to resolve this, continuing to ignore statistically significant sources of natural systematic bias will only result in formulation of systematically misleading geological hypotheses.
simply dating more crystals per sample is not the only answer.
However, the character of the subducting slab has changed through time and has included subduction of normal oceanic crust, a spreading ridge, and an oceanic plateau.
The latter two resulted in a change of subduction mode by inducing a shallow subduction angle.