Ca-Mg Isotopic Probe of Transport Processes in High Temperature Geochemical Systems

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

This project is aimed at using new analytical and experimental methods to determine the rates of chemical processes in magmas and in geothermal waters. This kind of information is important for understanding how magmas move under volcanoes and eventually erupt, and for estimating the fluid flow rates and lifetimes of geothermal systems. A second part of the research is directed toward understanding the material properties of silicate liquids and hydrothermal solutions, using novel measurements of isotopes of common chemical elements. The new methods will be used to determine whether minerals that crystallize from magma and hydrothermal solutions do so at chemical equilibrium. If not, as is likely according to preliminary data, the objective is to use measurements of isotopic abundances of Ca, Mg, and K to determine how fast such minerals grow, which will then provide other information about the speed of related natural processes. The proposed method for measuring mineral growth rates is based on isotopic measurements of the elements Ca, Mg, and K and will also include trace element measurements. Non-equilibrium isotopic effects will provide information about trace element fractionation processes, which are important for interpreting mineral chemistry. The research on liquid material properties uses mass-dependent isotopic changes that occur as elements and molecules diffuse through liquids. These subtle isotopic changes can now be monitored in key elements including Ca and Mg, as well as other chemical species like Ar and CO2. All of these species can exhibit mass-dependent isotopic changes related to diffusion. The changes depend on the viscosity, chemical composition, and chemical structure of the liquids, and the ways in which the each species is chemically bound to the liquid molecules. Consequently, diffusion-induced isotopic changes provide unique information about high temperature liquids that cannot be determined by any other method. Experiments will be augmented by study of natural rocks and minerals that formed under known conditions and at much slower rates than those of the laboratory experiments. The results of this research may have implications for materials science, volcanology, and geothermal energy production.