CHARACTERIZING PALEOFLUIDS IN THE WESTERN VALLEY AND RIDGE PROVINCE OF WEST VIRGINIA: UNCOVERING THE FATE OF MIGRATING 'WARM' FLUIDS

Vein and host rock samples were collected from the Devonian Oriskany through Chemung Formations in the western portion of the Nittany anticlinorium and adjacent Appalachian structural front in northern West Virginia. Microthermometric studies, x-ray diffraction (XRD), and strontium isotope ratios were analyzed to characterize the paleofluids during the Alleghanian Orogeny. Microthermometric studies provide a constraint on paleotemperatures throughout the region. The rocks in the western Valley and Ridge Province contain aqueous inclusions that homogenize between 142 and 200°C with salinities of 6.1 to 18 wt % NaCl equivalent. Methane and light hydrocarbon inclusions that homogenize between -118 and -70°C were found to coexist with the brine inclusions. In contrast, veins from the same stratigraphic units in the eastern margin of the Appalachian Plateau have inclusions that homogenize between 60 and 109°C and have a relatively high NaCl equivalent content that ranges from 16-24 wt. %. Hydrocarbon inclusion in this region are determined to be methane-bearing that homogenize between -92 and -68°C and light hydrocarbon-bearing that homogenize between -1 and 30°C. Strontium isotope studies and XRD analyses have been undertaken to further illustrate the dichotomy of fluid migration evidence between the Valley and Ridge and Plateau provinces. To date, strontium isotope analyses have provided an 87Sr/86Sr ratio that is much higher than expected for an upper Devonian seawater source indicating the presence of 'exotic' fluids. XRD patterns, however, have not shown a clear difference in mineral composition between the two regions. The migrating 'warm' fluid that affected the Valley and Ridge province but not the Plateau province must have been prevented from advancing foreland by a structural discontinuity. Recent field mapping and prior work by others in the region have documented faults in this structural position. The abrupt change in fluid composition and temperature in this region leads to two theories on the fate of the migrating fluid. First, the migrating 'warm' fluids may have been transported along the fault(s) to the paleosurface. Second, the migrating 'warm' fluids may have been transported along the fault(s) to a stratigraphically high level, such as the Pennsylvanian Coal Sequence.