Abstract
Three different models were developed to simulate the effect of contact metamorphism and fluid-rock interaction on the prograde mineralogical and O isotopic evolution of calcareous argillites from the Notch Peak aureole, Utah. All models assume local mineral-fluid equilibrium, a steady-state temperature profile corresponding to peak metamorphic values, and the thermodynamic data for minerals and fluid of Berman (1988). The preferred model, metamorphism with flow of a time-integrated fluid flux of 2 ± 0.5 · 104 mol/cm2 in the direction of increasing temperature, successfully reproduces the principal petrologic and isotopic features of the aureole: (1) occurrence and positions (in map view) of diopside-in, tremolite-out, grossular-in, wollastonite-in, and quartz-out isograds; (2) stable coexistence of tremolite + calcite + quartz + diopside over an ≈ 1 km distance between the diopside-in and tremolite-out isograds; (3) variable whole-rock 18O depletions of ≈6–9‰ adjacent to the contact; and (4) a gradual and irregular increase in δ18O with increasing distance from the pluton. One unsuccessful model considered interaction of rock with a tiny, stagnant, fluid-filled porosity with fluid pressure equal to either lithostatic or hydrostatic pressure. Regardless of fluid pressure, the model fails to predict the position of the tremolite-out isograd; the occurrence ofgrossular, wollastonite, and quartz-out isograds at any position; and 18O depletions >0.3‰. The other unsuccessful model, flow of magmatic fluid in the direction of decreasing temperature through the aureole, fails to predict the observed range of whole-rock isotopic compositions within 0.5 km of the contact, the observed position of the diopside isograd, and the observed spatial distribution of tremolite + calcite + quartz + diopside. Results demonstrate how isotopic and petrologic data for contact aureoles can be integrated to provide quantitative constraints on the magnitude and geometry of metamorphic fluid flow.
