Direct observation of primary fluid-inclusion formation

Abstract

Observations of crystal growth in supersaturated KH 2 PO 4 solutions indicate that it duplicates natural crystallization processes and formation of fluid inclusions in free liquids similar to vein formation or igneous systems. Continuous crystal growth by surface nucleation results in elongate fluid inclusions forndng as hollow tubes within kinked growth steps. Large, flat fluid inclusions also form either by sealing of etch pits and other surface irregularities or along cracks propagated by crystal growth. Microscopic observation of real-time crystal growth documents the formation of fluid inclusions along a surface or within a plane, inclusions that would otherwise be identified as secondary. These primary fluid inclusions resemble pseudosecondary inclusions or secondary necked-down inclusions commonly observed in geologic samples. Furthermore, these fluid inclusions, and many or most in natural samples, are not generated by spiral growth processes. This simple analogue experiment serves as a model for crystal growth and fluid-inclusion entrapment in hydrothermal and igneous systems.