Isotope Mass Balance as a Key to Geothermal and Crustal Hydrologies - Mixed and 1-dimensional Models

Abstract

Oxygen isotope 'clocks' for the measurement o f cumulative fluid-to-rock ratios are largely independent of mineralogical detail, and have the advantage of an even partition of the carrier element between fluid and rock. In measurinq fluid throughput, thermodynamic equilibrium is only a limiting condition, and mass balance is paramount. As evidence for external fluids, definite isotope shifts, and in the 1- dimensional case, isotope fronts, are required. The geochemical buffer capacity of solid rock is high and the high water throughputs of geothermal systems are exceptions in the crustal environment.