THE CRITICAL ROLE OF RECYCLING IN THE EVOLUTION OF DETRITAL ZIRCON AGE SYSTEMATICS IN A LONG-LIVED BASIN AND IMPORTANCE OF A MULTI-PROXY APPROACH TO PROVENANCE ANALYSIS: EVIDENCE FROM EASTERN LAURENTIA

Sedimentary provenance analysis is overfocused on detrital zircon (DZ) geochronology due to ease of analysis. Numerous studies call out the limitations of DZ as a sole provenance proxy but the accumulation rate of DZ ages only accelerates. The certitude that DZ is recycled makes it unable in long-lived Phanerozoic clastic systems to record the immediate sediment source - the goal of provenance analysis. More accurate constraints on immediate sources are obtained from low temperature thermochronometers: DZ (U-Th)/He; detrital metamorphic/diagenetic monazite Th-Pb; detrital muscovite Ar-Ar. The latter systems record the syn-orogenic unroofing of immediate source rocks in the orogen as a proxy for the time of release of grains into clastic systems. DZ double dating in tandem with detrital monazite (DM) geochronology and textures for Penn. lithic and quartz arenites of the Appalachian Basin (KY) indicate DZ ultimately sourced from Grenville basement was recycled at least five times. Cycle 1: post-Grenville (Neoproterozoic) clastic wedge – the “Great Grenville Sedimentation Episode”; Cycle 2: erosion of the Grenville clastic wedge and redistribution around the Laurentian margin in post-Rodinian rift basins; Cycle 3: reworking of Late Neoproterozoic clastics during the Cambrian transgression (formation of the “Great Unconformity”). Regional Taconian to Neo-Acadian metamorphism of Neoproterozoic-Cambrian clastic sequences formed metamorphic monazite and reset DZ (U-Th)/He ages. Cycle 4: Late Paleozoic exhumation of metaclastic sequences during Alleghanian orogenesis and formation of a Permo-Carboniferous pancontinental river system; Cycle 5: Mesozoic through Cenozoic exhumation to the modern erosion surface. Additional DZ data indicate some Grenville DZ was recycled at least 8 times. The presence of 1.9-1.6 Ga and 2.4-2.8 Ga DZ requires a distal source along strike in the Appalachian orogen as the Laurentian craton was covered and could not be an immediate source in the late Paleozoic. Neoproterozoic clastic sequences of the Scottish Caledonides with an eastern Grenville and N. Atlantic province provenance are proposed as extreme distal sources for the longitudinal alluvial system that mixed with transverse drainages delivering sediment from the southern Appalachian hinterland.