Abstract

Fluid inclusions are small relicts of fluid that are trapped in microscopic cavities inside a crystal during crystallization or during healing of cracks in a mineral. Fluid inclusions contain information about the pressure-temperature conditions that existed during mineral formation or rearrangement; this information can be used by geologists to understand, for example, the processes involved in orogenic uplift or in the genesis of ore deposits. Fluid inclusions are formed at temperatures above at least about 100°C and then cool during subsequent uplift of geological formations. The cooling of the fluid occurs, to a very good approximation, along an isochore, since the change in volume of the cavity in the crystal is small. During cooling, phase separation occurs at phase boundaries: for example, a vapor bubble nucleates or a salt crystal precipitates. Geologists use different techniques including microthermometry and Micro-Raman spectroscopy to obtain information about the density and composition of fluid inclusions. Microthermometry is used to measure the liquid-vapor homogenization temperature, the ice melting temperature, and the dissolution temperature of salt crystals. The first provides information about the density of the fluid while the latter two can be used to determine the salinity. In some fluid inclusions, metastable phase states—superstretched water without a vapor bubble or supersaturated solutions without a salt crystal—prevent such measurements. We address this problem by using single pulses from an amplified femtosecond laser to overcome these metastable phase states and to nucleate vapor bubbles, salt crystals, and ice [1], Figure 1 presents an example of nucleation of a vapor bubble in a natural one phase quartz fluid inclusion.

© 2007 IEEE