Infrared Spectroscopy of Quartz and Feldspar in Alpine Hydrothermal Veins

Abstract

With the aim of discerning fluid conditions present during hydrothermal activity associated with Alpine metamorphism, we present new results on the abundance and distribution of hydrous impurities in co-crystallizing hydrothermal feldspar and quartz crystals. The crystals were extracted from a hydrothermal vein in the Lepontine Zone of the Swiss Alps. Gemmy specimens of coexisting albite (Na-feldspar) and quartz are analyzed using infrared spectroscopy at high spatial resolution (100-μm spot sizes). We note the presence of distinctive absorption bands associated with each mineral type. We observe absorption at 3450, 3270, and 3100 cm-1 in all spot analyses of feldspar wafers. The abundances of the three bands range over an order of magnitude (100-1400 Abs/m at 3450 cm-1; 30-600 Abs/m at 3270 cm-1; and 20-200 Abs/m at 3100 cm-1)and co-vary smoothly with one another as our analytical traverses approach and cross structural features, including cleavage fractures and twin planes. Within the quartz crystal, abundances of HOH, LiOH, and AlOH (at 3400 cm-1, 3380 cm-1, and 3480 cm-1, respectively) also covary with one another. We explore the potential that infrared measurements have for discerning variations in fluid conditions present during and subsequent to crystal growth.