TIMESCALES OF EPISODIC TECTONIC DENUDATION USING DETRITAL ZIRCON DOUBLE DATING IN THE AMAZON RIVER TO FAN SYSTEM (Invited Presentation)

Detrital zircon (DZ) geo-thermochronology applied to sediment routing systems linked to active orogenic hinterlands can help differentiate and refine conceptual and quantitative models of source-to-sink sediment transfer to flexural foreland basins and divergent or passive margins. This presentation integrates published DZ U-Pb geochronology with new DZ U-Pb and U-Th/He (ZHe) and new DZ U-Pb and zircon fission track (ZFT) double dates recovered from the Pleistocene Amazon fan. A deep-time thermotectonic history of crustal cooling along the active western margin of South America is archived in low-temperature cooling ages of DZs from the Amazon fan. Both ZHe and ZFT datasets display overall patterns in date frequencies that decay with age. Double-dating may inherently produce this decaying frequency as U-Pb dates describe an upper limit to ZHe and ZFT dates; while substantial exhumation can produce a young thermochronology age for any crystallization age, only old crystals with minimal exhumation can produce old cooling ages. Decaying age frequencies are an expected signal given the correlation between high exhumation rates and sediment flux from the Andes, a hypothesis that appears to closely replicate the broad trends in our dataset. Surprisingly, we note distinct populations of ZHe cooling ages that may record multiple active orogenic phases. New power spectra analysis of ZHe age data result in 57 Myr and 92 Myr periods (95% and 85% confidence intervals, respectively). This periodic signal recovered from the Amazon fan is broadly similar to previous studies using geochemical data in igneous and detrital zircons from the central and northern Andes. Thus, we hypothesize that these frequency patterns are linked by cyclicity of orogenic growth along the western margin of South America, driven by episodic lithospheric delamination, high-flux magmatism, and related orogenic shortening resulting in crustal cooling/exhumation and enhanced erosion and unroofing. These datasets reveal previously unrecognized patterns in DZ low-temperature thermochronometers that record signals of the Cordilleran hinterland in the marine passive-margin sedimentary record.