The ''hot spots'' near Bristol, New Hampshire was an area of high fluid flow during metamorphism. In order to determine the mechanisms of fluid flow through the area, we made a detailed study of the Δ18O values of quartz from an outcrop of interlayered quartzites and schists. Results indicate that the permeability of the quartzite was low in comparison to that of the schist.

The Δ18Oqtz values from schist layers are remarkably homogeneous (15.5--15.8), in contrast to the Δ18Oqtz values of schist units outside of the hot spot, which vary widely. Quartz veins that cut the quartzites and pinch out in the schists have the same Δ18O values (15.7) as quartz from the schists. In the quartzites, Δ18Oqtz values immediately adjacent to the veins and schists are similar to those in the veins and schists, but decrease by ~1 permil in the center of the layer.

We interpet these results to indicate that fluid flow in the hot spot was mainly through the schists and fractures in the quartzites. The oxygen isotope exchange fronts in the quartzites prove that there was some flow from the schist and the fractures into the quartzites. Comparisons of the shapes of these exchange fronts with exchange fronts predicted by two different models of fluid flow in rocks indicate that fluid transport in the quartzite was predominantly by advection and that the kinetic rates of isotope exchange were fast relative to the advective velocity of the fluid infiltrating the system. Considering the slow rate of oxygen istope exchange between quartz and a fluid, this implies that fluid flow from the schist and vein fracture into the quartzite was extremly limited. ¿American Geophysical Union 1991