CHARACTERIZING THE UNIQUE CHEMICAL FINGERPRINT OF HIGH-TEMPERATURE, HYDROTHERMAL VEIN QUARTZ

Hydrothermal systems control the thermal and chemical evolution of metamorphic environments during mountain building events. Few geochemical techniques provide insights into the nature of fluid systems active at the time of metamorphism. Mullis et al. (1994) identified a pronounced thermal gradient in the fluid systems preserved along a north-south traverse of the Swiss Alps. They noted distinct changes in quartz crystal morphology that correlated with distinct changes in the temperature of crystal growth (based on fluid inclusion analyses). The highest temperature vein system (located at the southern end of their traverse) is characterized by quartz with tessin habit that grew at temperatures >300 °C. We collected single crystals of quartz with tessin habit from seven localities from Canton Ticino, Switzerland in order to characterize the chemistry of high temperature vein quartz. Micro-IR analyses provide a measure of the abundance and distribution of hydrous impurities within single crystals. The variations in concentrations of hydrous contaminants provide insights into morphologic evolution and growth timescales of individual crystals. We note the following three observations that are unique to the Ticino crystals: 1) All crystals exhibited the distinct tapering tessin habit; 2) All crystals lacked observable diffusion profiles in AlOH and HOH toward the m prism faces; and 3) All crystals are barren in LiOH species throughout the crystal, a finding not yet observed in other hydrothermal crystals analyzed from around the world. These unique geochemical characteristics of tessin crystals may be common to other quartz crystals grown in high temperature hydrothermal systems within orogenic belts, which we aim to test in future studies.