The Dynamics of Silica Deposition in Fractures: Oxygen Isotope Ratios in Hydrothermal Silica from Yellowstone Drill Core Y-13

Abstract

The 180 values of 22 samples of hydrothermal chalcedony and quartz from Y-13 drill core range from -7.5 to -1.3/°°. Most samples could not be in mineral water isotopic equilibrium under preset condition. Fluid inclusion homogenization temperatures in quartz indicate precipitation at or above temperatures measured during drilling. Most silica appears to have precipitated form water enriched in 180 relative to present thermal water. Inferred 180 enrichments are too large in many cases to be explained by boiling and steam separation. The apparent 180 enrichment in thermal water may represent a transient dynamic effect that occurs when new fractures open, as disequilibrium increases and the local system is temporarily perturbed. This interpretation is consistent with the observed sequence of mineral deposition and 180 within individual fractures.