Stable isotope and trace element fractionation and implications for chemical weathering rates

Isotope geochemistry;Hydrogeology;Chemical weathering;Reactive transport modeling

Fernandez-Franzan, Nicole Marie

关键词: Isotope geochemistry;    Hydrogeology;    Chemical weathering;    Reactive transport modeling;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/107989/FERNANDEZ-FRANZAN-DISSERTATION-2020.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Application of stable isotopes and trace-element environmental tracers offers a promising approach in characterizing the underlying geochemical and hydrological processes giving rise to observed chemical weathering rates. Yet, to fully leverage these geochemical tools a better understanding of the fundamental mechanisms driving observed signatures is essential. This dissertation builds upon our current knowledge of stable isotope and trace element fractionation in low temperature, terrestrial environments through a combination of highly constrained laboratory experiments, geochemical models, and field analyses. Through this research, the extent of water–rock interactions and rate dependence of stable isotope and trace element fractionation during secondary mineral formation (a key fractionation pathway in weathering systems) is investigated. Further, the potential of stable Si isotopes to complement concentration –discharge relationships is explored through the development of a global dataset of silicon stable isotope–discharge relationships encompassing different lithologies and climates. Major findings from this thesis can be summarized as follows. First, metal stable isotopes and trace elements appear to be dependent on a variety of physio-chemical properties such as mineral surface area, solid to fluid ratios, and fluid solute compositions. Second, silicon, calcium, and strontium stable isotopes and germanium, strontium trace element ratios show a common, broadly consistent relationship between reaction rate and fractionation. Finally, the Si stable isotopes of stream water as a function of discharge are found to be sensitive to site-specific hydrogeochemical processes and are effective tracers of weathering intensity.