Kinetically driven successive sodic and potassic alteration of feldspar.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 34290248.
- Also identified by DOI 10.1038/s41467-021-24628-1 and PMC identifier 8295371.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The dynamic evolutions of fluid-mineral systems driving large-scale geochemical transformations in the Earth's crust remain poorly understood. We observed experimentally that successive sodic and potassic alterations of feldspar can occur via a single self-evolved, originally Na-only, hydrothermal fluid. At 600 °C, 2 kbar, sanidine ((K<sub>,</sub>Na)AlSi<sub>3</sub>O<sub>8</sub>) reacted rapidly with a NaCl fluid to form albite (NaAlSi<sub>3</sub>O<sub>8</sub>); over time, some of this albite was replaced by K-feldspar (KAlSi<sub>3</sub>O<sub>8</sub>), in contrast to predictions from equilibrium reaction modelling. Fluorine accelerated the process, resulting in near-complete back-replacement of albite within 1 day. These findings reveal that potassic alteration can be triggered by Na-rich fluids, indicating that pervasive sequential sodic and potassic alterations associated with mineralization in some of the world's largest ore deposits may not necessarily reflect externally-driven changes in fluid alkali contents. Here, we show that these reactions are promoted at the micro-scale by a self-evolving, kinetically-driven process; such positive feedbacks between equilibrium and kinetic factors may be essential in driving pervasive mineral transformations.