Limitations of provenance diagnoses and maximum-depositional-age constraints based on detrital-zircon geochronology: the fertility bias

Abstract

Detrital zircon U–Pb geochronology (DZG) is widely used in the provenance analysis and calculating maximum depositional ages (MDAs) of strata. To assess the geologic limitations of this approach, we conducted DZG coupled with bulk-petrology and heavy-mineral analyses of Miocene volcaniclastic and non-volcanic siliciclastic sandstones from the SW Tarim Basin. Although these two sandstone types display greatly different bulk-petrography and heavy-mineral signatures, they exhibit similar detrital-zircon-age spectra, and thus represent a less common case in which interpretations based on DZG alone may misalign with bulk-sediment provenance. Most zircon-based MDAs of volcaniclastic sandstones range from 12.3 to 14.8 Ma, deviating from their ca. 11 Ma true depositional age constrained previously. The similarity of zircon-age spectra in volcaniclastic and siliciclastic sandstones and the 1–4 M.y. the error of the zircon-based MDAs is ascribed to the low zircon fertility of coeval alkaline magmatic sources. This study emphasizes the importance of an integrated approach to provenance analysis and chronostratigraphy.