DATING SEDIMENTARY REACTIVE FLUID FLOW USING ZIRCON

Hydrothermal fluid flow controls the distribution of certain elements that are vital to our economy and society. However, geologic fluid flow is difficult to accurately date, and therefore difficult to completely understand. In particular, the timing of fluid flow may be protracted, punctuated, and driven by potential external drivers such as magmatic intrusion, thermal cycling, and tectonics. Determining the age of fluid flow would be extremely useful for many disciplines of geosciences, but few reliable tools exist.

The Alta Stock is surrounded by a very well-studied metamorphic reaction aureole as a result, zircons in metamorphosed sediments experienced high and low-temperature fluid flow. Here, we present results from an attempt to use detrital zircon discordance to accurately quantify the age of lead (Pb) loss from rocks surrounding the Alta Stock in Utah. Using uranium-lead data from hydrothermally altered detrital zircon we accurately placed age constraints on hydrothermal alteration in Alta contact aureole. The Alta, Utah area experienced hydrothermal fluid from around 30-23 Ma. Our results agree well with other chronometric data from the area. We quantify the uncertainty in our analysis using detrital zircons, by applying a bootstrap resampling model that allows us to test the sensitivity of our technique for geochronology. We also examine the chemical effects of both fluid flow and metamorphism within zircons that have experienced Pb-loss. We evaluate whether metamorphism or fluid flow, or a combination, are drivers of Pb-loss and are therefore datable using our approach.

We will discuss the implications of the data for the applicability of our discordance dating technique for other fluid-flow and/or metamorphic settings.