NON-DARCIAN FLUID-FLOW DURING THE ALLEGHENIAN OROGENY

The late Paleozoic remagnetization of rocks in North America may in part related to the expulsion of 22,500 km3 of metamorphic fluids from beneath the Blue Ridge and Piedmont decollement. Fluid inclusions from veins and cements associated with this remagnetization event in the Valley and Ridge give temperatures 50-150-degrees-C higher than other indicators of peak temperatures. One explanation for the high temperatures is the passage of hot metamorphic fluids along 1-10 cm wide open fractures, which extended laterally 30-100 km. Using the above thermal constraints and a model for fluid flow in an open fracture, flow is found to be turbulent and to have mean velocities of 1-10 m/s. The duration of the flow ranged from approximately a day to a few years. These fluid velocities are seven orders of magnitude faster than the maximum velocities predicted by Darcian fluid flow models and the duration of flow is four to eight orders of magnitude shorter than those predicted by Darcian models.