LINEAMENTS AND IMPLICATIONS FOR ANCIENT AND MODERN FLUID FLOW: CASE STUDIES FROM CONNECTICUT AND PENNSYLVANIA

State-wide radar (SLAR) mapping of CT revealed: 1) a broad, poorly defined NE-trending (035°) regional lineament (the Pomperaug-Cherry Brook lineament or PCBL) bordering outliers of Mesozoic-aged rocks in western CT, 2) a strong, relatively sharp NNE-trending (015°) regional lineament (the Lantern Hill – Snake Meadow Brook or LH-SMB fault system) located in eastern CT, and 3) well-defined lineaments and fracture traces in the Killingworth dome in south-central CT.

The PCBL was field checked along its > 50-mile length within the "western highlands" and the Pomperaug and Hartford basins. It is characterized by steeply-dipping mesoscale fractures, rotated blocks, and breccia. Fractures commonly are filled by hydrothermal calcite and zeolites. In the region of the PCBL a number of NW-trending smaller lineaments occur. Mesoscale fractures within these are commonly characterized by quartz, galena, and sphalerite (Qtz-Pb-Zn) ± fluorite. One NW-trending lineament intersects the PCBL near Thomaston, CT. This intersection is the only locality along the PCBL where both mineral suites occur. This relationship is evidence for two distinct fluid flow events.

The LH-SMB fault system is characterized by steeply-dipping mesoscale fractures, rotated blocks, and breccia. Mesoscale fractures of the LH-SMB fault system are hydrothermally mineralized, dominantly by quartz. Stable isotopic data suggest that meteoric water dominated the mineralizing fluids. Fluid inclusion data indicate that fluid flow into the LH segment occurred at depth of ~6.5 km with a mean temperature of 265°C.

Water well data adjacent to lineaments of the Killingworth dome in south-central CT support the hypothesis that these radar linears are associated with elevated ground-water yields. This relationship is consistent with the occurrence of hydrothermal mineral deposits along lineaments (presumed fracture zones).

The use of lineaments has been advanced for natural gas exploration in Devonian shales in the Appalachians. SLAR lineament mapping in the Pennsylvania Ridge and Valley province has identified potential targets where the Everett-Bedford lineament transgresses such organic-rich shales. Ground-water prospecting and gas exploration rely on an assumption that lineaments represent fracture zones with high permeability.