Program Overview
The Basic Energy Sciences (BES) Isotope Program at Berkeley Lab’s Energy Geosciences Division operations as the Center for Isotope Geochemistry (CIG), led by Don DePaolo.
Within the CIG, the isotope geochemistry group develops and applies knowledge of stable isotope fractionation processes to provide insights into the controls on mineral precipitation and material transport in fluid phases. Laboratory isotope experiments combined with field experiments and molecular modeling enable deeper understanding of the geological evolution of fluid-rock systems at the large spatial and ultraslow temporal timescales.
Molecular scale models of growth mechanisms in calcium carbonate developed by this group are in good agreement with experimental observations of the effects of ionic strength on Ca isotope incorporation and the Sr/Ca ratio in calcite.
An important topic of the groups is the behavior of isotopes and trace elements during mineral growth from aqueous solutions. This work seeks to
- build new models for isotopic fractionation factors as a function of growth conditions, so as to make isotopic and trace element measurements more robust for applications to natural systems, and
- using the isotopic fractionations to constrain the roles of mass transport, growth mechanisms, desolvation, and thermodynamics in controlling the complex processes at the mineral-fluid interface during crystal growth.
To achieve these objectives we need to perform carefully controlled laboratory experiments, to characterize the fluids and minerals with techniques such as AFM, TEM, and SIMS, and to make precise isotopic measurements on run products with TIMS and MC-ICPMS. In many cases, we can document isotopic fractionation effects, but we have difficulty uniquely identifying the mechanisms. To help in testing hypotheses regarding mechanisms, we are using Molecular Dynamics simulations and related computational approaches with appropriate collaborations. To evaluate the relevance of laboratory and theoretical approaches, and to access the much larger time and length scales needed to work with real Earth systems, we also include selected studies of natural systems, including both characterization and reactive transport modeling.