FRACTURE ANALYSIS OF THE LAKE CHAR FAULT ZONE IN SOUTHEASTERN CONNECTICUT: A PROGRESS REPORT FOR EDMAP 2000 AND THE AASG 2000 MENTORED FIELD RESEARCH EXPERIENCE

Structural data collected in the Lake Char fault region of southeastern Connecticut provide a first step towards understanding bedrock fracture systems that control the region's bedrock aquifers. In addition this data builds on the present understanding of the deformational history of the Lake Char fault. Field data were collected by Environmental Earth Science majors at Eastern Connecticut State University supported by the U.S. Geological Survey EDMAP program and by the AASG Mentored Field Research program.

The study area is roughly 4.5 x 2 km and straddles the west dipping Lake Char Fault. The footwall consists of Proterozoic Avalon terrane including porphyritic granitic gneisses and heterogeneous metavolcanic gneisses. The hanging wall consists of the Paleozoic Putnam Nashoba sequence and includes a mafic plutonic complex that intrudes metavolcanic and metasedimentary rocks.

Fractures within the footwall fall within three ranges of orientation, regardless of rock type. One set of fractures is parallel to the dominant S2 foliation and has a mean strike and dip of 165°/40°W in the northern area, and 200°/25°NW in the southern half of the field area. The other two groups of fractures are interpreted as a conjugate set with mean orientations of 055°/80°SE and 345°/60°NE. Several of the foliation-parallel fractures have slickensides with down dip lineations and normal offset. The foliation-parallel fractures are interpreted to have formed in part as shear fractures during brittle normal faulting along the LCF, and also as sheeting joints during unloading.

Fractures measured from non-foliated mafic rocks in the hanging wall fall into three groups with consistent strike directions, but with a wide variation in dip direction and dip angle. One group strikes WNW with steep to moderate dips to the NE and SW, the second group strikes N-S with moderate to shallow dips to the NE and SW, and the third group strikes N-S with steep dips to the west and steep to shallow dips to the east.