Geochemical Controls on the Composition of Coexisting Vapors and Brines: A Novel Experimental Approach to Assess Aqueous Speciation in Subseafloor Hydrothermal Systems

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

Under this funding, the PIs will assess aqueous speciation in coexisting vapors and brines produced during subcritical boiling and supercritical brine condensation. The study will use pH and redox sensors together with a computer controlled Ti-flow reactor, which can maintain constant temperature, pressure and flow rates, while allowing simultaneous investigation of vapor and brine phases. Initially, the experimental study will focus on development of an internally consistent database for aqueous species in the NaCl-H2O system. Although both the vapor and brine phases will be instrumented, it is the vapor phase that will be utilized most to constrain the distribution of aqueous species in the coexisting brine. In effect, the distribution of aqueous species in the vapor buffers that of the brine and provides a novel experimental strategy for determining ion activities in the highly concentrated brine phase. Subsequently, mineral buffers will be added to the system to expand the compositional complexity necessary to model the chemical evolution of vapors and brines in subseafloor hydrothermal systems at mid-ocean ridges. The study will have numerous applications, including the speciation affecting Fe, Cu and Zn mineral solubility in vapors and brines, vapor-brine partitioning of boron and other mobile trace elements during phase separation/segregation processes, and others.