Evaluating episodicity of high-temperature venting within seafloor hydrothermal vent fields

Abstract

Hydrothermal episodicity refers to the cycle of cessation and reactivation of hydrothermal venting at the seafloor and is often considered a common characteristic of high-temperature seafloor hydrothermal systems. With few exceptions, evidence for episodicity at the vent field scale and at timescales of hydrothermal systems (1000s to 100,000s of years) is primarily derived from interpretation of the age distribution of rock samples collected from hydrothermal vent fields and dated using U-series disequilibrium techniques. Using this approach, significant age gaps between dated samples have been interpreted as hiatuses in the venting of fluids that form the deposits that accumulate at the vent fields. Here, we use Monte Carlo simulations to show that the maximum time gaps in the observed age distributions are similar to those predicted by modeling random sampling of a logarithmic age distribution. These simulation results indicate that large time gaps between dated samples do not indicate episodic venting, and/or the numbers of dated samples are not high enough to confidently distinguish between continuous and episodic venting. The lack of geochronological evidence for episodicity suggests that, although fluid temperature and composition within a vent field can vary over time, hydrothermal fluid circulation may be continuous over the lifespans of vent fields.