COMPLETE IDENTIFICATION OF SEDIMENT DONOR TERRANES… CAREFUL WHOM YOU ASK

Acquisition of the crystallization ages of detrital zircon has attained routine status in modern provenance investigations. Detrital zircon-based studies have been successful for many interdisciplinary investigations including paleogeographic plate reconstructions, sedimentary basin characterization, and recognition of ancient sediment transport systems. However, detrital zircon has been shown to have limitations, particularly evident in Paleozoic sedimentary rocks derived from the Appalachian Mountains (Moecher and Samson 2006). The detrital zircon age spectra from these ancient sediments are, as an empirical rule, heavily skewed towards Grenville-aged sources with suppressed Paleozoic signals. A recent study (Hietpas et al 2010), comparing the ages of detrital zircon versus detrital monazite from modern river alluvium in the southern Appalachians, has shown that ages of detrital monazite more faithfully record the younger complex Paleozoic record as opposed to detrital zircon which is again strongly skewed towards Grenvillian ages. The differences between the ages recorded by the two mineral species are interpreted to be the result of the differences in the physical and petrogenetic properties of the two minerals. To further investigate the utility of detrital monazite as a provenance indicator we measured the crystallization ages of detrital monazite from several Pennsylvanian-Early Permian southern Appalachian-derived sandstones that have been previously characterized by detrital zircon ages. The results of this study demonstrate that detrital monazite provides a much more robust Paleozoic signal compared to zircon. Recording these younger events provides a more accurate assessment of the sediment donor terranes for each of the sedimentary units under investigation. In fact, for two of the sandstones, detrital monazite recorded multiple orogenic events that were completely missed by detrital zircon. The data show that monazite, as opposed to zircon, is more sensitive to events (i.e. sediment donor terranes) defined more by metamorphism than by magmatism. The results of this study have important implications for accurate assessment of sources of siliciclastic sediments and the tectonic conclusions reached by that assessment.