DIFFERENTIAL SOURCE FERTILITY AND SEDIMENTARY RECYCLING: THE ACHILLES HEELS OF ACCURATE DETRITAL ZIRCON PROVENANCE ANALYSIS – HOW DETRITAL MONAZITE AND MUSCOVITE CAN HELP HEAL THE HEELS

Accurate provenance analysis of any type requires identification of the immediate sediment source. The perceived strengths of detrital zircon (DZ) U-Pb geochronology in provenance analysis are also limits on its utility. (1) Zircon is ultrastable – it will be recycled once it enters the clastic sedimentary system. (2) Zircon is refractory – it won’t record any of its post-magmatic history. (3) Differential zircon fertility - exceptionally zircon-fertile sources (e.g., high-Zr Grenville granites) generate 2-10 times as many zircon grains as typical collisional or arc granites. In Laurentian clastic systems, Paleozoic DZ source terranes will be swamped by the Grenville DZ grains in a sandstone, which are mostly recycled. DZ ages more likely correspond to the ultimate source of the zircon and not the bulk of the immediate sediment source. Detrital monazite (DMnz) Th-Pb and muscovite (DMu) ⁴⁰Ar-³⁹Ar ages are alternatives to DZ: their ages reflect metamorphic crystallization and/or cooling ages of immediate source rocks. The (U-Th)/He thermochronometer, when used in tandem with U-Th-Pb crystallization ages (“double dating”), also reflects the immediate source. For example, Pennsylvanian (Alleghenian) arenites of the Appalachian foreland basin exhibit DZ age spectra dominated by Grenville ages with minor Taconian (440-480 Ma) and Acadian (400-360 Ma) age modes, apparently implying a dominantly Grenville immediate source. However, DMnz and DMu spectra are dominated by Taconian and Acadian modes with minor Grenville modes, implying Grenville basement was a minor source. “Detrital diagenetic monazite”, which is distinguished texturally from metamorphic DMnz and proves recycling (Moecher et al. GSAB 2019), comprises a third of the DMnz signal. (U-Th)/He cooling ages for Grenville-aged DZs are also Taconian and Acadian. The combined DZ/DMnz/DMu age spectrum can be explained by a dominant initial source of Neoproterozoic-lower Cambrian sediments, which contained first cycle post-orogenic Grenville DZs and in which diagenetic Mnz formed, that were metamorphosed to produce metamorphic Mnz and Mu, and were then exhumed/eroded in the mid- to late Paleozoic. Taconian and Acadian granites are also documented sources of DZ, but syn-orogenic (Alleghenian) DZs are rare. Grenville DZs were recycled at least once.