Formation of synthetic fluid inclusions in natural quartz

Abstract

Planes of water-rich fluid inclusions were created in natural quartz by partially annealing laboratory-induced fractures in a hydrothermal apparatus at 6(X)C and 2 kbar in the presence of water. The size, distribution, and morphology of the synthetic fluid inclusions show a remarkable similarity to fluid inclusions in quartz from metamorphic terranes. Fluid inclusion trains appear to be localized along former fracture-surface step litreations; their size varies proportionally and abundance inversely with the spacing of step lineations on the original fracture surface. Thin island-like inclusions grade to elongate ellipsoids with minimum di.mensions considerably greater than the original crack width and appear to have developed at the expense of the immediate crack walls. The surface of the unclosed portion of the crack appears unchanged, suggesting a preferential solution and precipitation phenomenon where the inclusions developed. Fluid density of the inclusions, determined by microthermometric measurement of the homogenization temperature, is in agreement with the fluid density under the experimental 4a1s4ling conditions. These observations suggest that the total density of the trapped fluid in the inclusions is the same as that of the homogeneous fluid phase present at the time of fluid inclusion formation.