TESTING FOR SEDIMENTARY RECYCLING USING DETRITAL MONAZITE GEOCHRONOLOGY, ZIRCON “DOUBLE DATING”, AND TEXTURES IN PENNSYLVANIAN ARENITES OF THE CENTRAL APPALACHIAN BASIN, EASTERN KENTUCKY: IMPLICATIONS FOR SINGLE MINERAL SEDIMENTARY PROVENANCE ANALYSIS

Detrital monazite Th-Pb and detrital zircon U-Pb and U-Th/He double-dating coupled with sandstone petrography and exhumation rates can be used to test for sediment recycling in Pennsylvanian sandstones within the Alleghenian clastic wedge. The Alleghenian clastic wedge is a logical system in which to test for sediment recycling as four major collisional events (Grenville, Taconic, Acadian and Alleghenian orogenies) likely reworked the continental margin and recycled siliciclastic sediment. The combination of these geochronologic and thermochronologic methods provide a more accurate assessment of the proportion of recycled sediment in the Grundy Formation (sublitharenite) and the Corbin Sandstone (quartz arenite), which past studies and the use of standard zircon U-Pb alone could not distinguish. Recognition of sediment recycling is thus critical for sedimentary provenance studies, which assume a direct path from sediment source to depositional basin. Zircon U-Pb age modes for both formations include the dominant “Grenville doublet” along with a lesser component of Granite-Rhyolite and Taconic age modes. The Corbin Sandstone is temporally more expansive, with age modes associated with the Yavapai-Mazatzal and Kenoran orogenies not present in the Grundy Formation. Monazite Th-Pb age modes are younger than zircon U-Pb for both samples, with dominant modes in the Taconic, Acadian, and Alleghenian, and only minor age modes associated with the Grenville Orogeny. The extent of sediment recycling was quantified by the difference in crystallization ages and exhumation/cooling ages of detrital zircon. This difference in time (∆t) becomes higher in the case of recycling (\u3e ~300 Ma). A median 288 Ma ∆t cutoff value between first-cycle and multi-cycle Grenville aged zircons was calculated using post-Grenville exhumation rates. Furthermore, “detrital diagenetic monazite” grains older than the 312 Ma age of deposition are present in both the Grundy Formation and Corbin Sandstone and proves the occurrence of sediment recycling. In conclusion, most detrital grains of Grenville origin and older are likely multi-cycle, while detrital grains associated with the Taconic, Acadian, Neo-Acadian, and Alleghenian orogenies are likely first-cycle in origin