GEOCHRONOLOGICAL DATING OF HYDROTHERMAL FLUID FLOW IN DETRITAL ZIRCONS

Geochronological Dating of Hydrothermal Fluid Flow in Detrital Zircons

Alexander Cerminaro, Erik Schoonover, Joshua Garber, Stephanie Mrozek, Renan Beckman, Jesse Reimink

Hydrothermal fluid flow is a key process that drives many critical features of geological systems. From ore deposit genesis to hydrocarbon mobilization and metamorphism, fluids are crucial drivers of reactions throughout the Earth system. Despite their importance, reliable dating methods that track fluid flow are lacking. Zircon is one of the premier geochronometers for the geosciences and is widely used to date high-temperature geological processes. The geochronometer fundamentally relies on the decay of U to Pb within the crystal lattice, which is a robust system for high-temperature geochronology. However, zircon can lose radiogenic Pb under certain situations, particularly when fluids are present or during metamorphism.

In this presentation we describe and test a method for dating fluid flow in sedimentary rocks using Pb-loss across a suite of detrital zircons in a single sedimentary sample. This method relies on a shared Pb-loss event from zircons with a range of crystallization ages. This Pb-loss, along with corresponding geochemical signatures of alteration, may allow us to determine fluid flow age and chemistry within sedimentary rocks.

We analyzed detrital zircons from a series of localities along well-known and assumed fluid flow and metamorphic pathways. Zircons were characterized by cathodoluminescence and electron backscatter imaging to characterize pristine and altered zones. Laser ablation split stream inductively coupled plasma mass spectrometry (LASS-ICPMS) was used to obtain simultaneous U-Pb and trace element concentrations from detrital zircons in these settings. The combined U-Pb and trace element data allows us to relate the degree of discordance to chemical signatures of alteration, with the possibility of tracing fluid or metamorphic reaction chemistries. In this presentation we demonstrate findings from these locations along with statistical tests of derived ages to evaluate the reliability of this technique for dating fluid flow in sedimentary rocks. We discuss scenarios where discordance dating may be useful for examining the ages of metamorphism and/or fluid flow in detrital sediments.