WEDGE FAULTING IN THE EARLY MESOZOIC HIGGANUM DIKE, PONSET, CONNECTICUT

The Higganum dike is a ~201 Ma, NNE-SSW-trending diabase intrusion that cuts metamorphic rocks to the east of the Hartford basin. Fault-slip data were collected from the Higganum dike in Ponset, Connecticut, as part of a larger project to understand early Mesozoic and more recent states of stress in southern New England, but the majority of the faults formed along cooling joint surfaces and slipped parallel to the cooling column axes. This indicates that the faults interacted and, therefore, classical paleostress inversion methods cannot be used to identify the reduced stress tensors that best describe the fault-slip data.

Faults that slip parallel to their common line of intersection are known as wedge faults while faults that do not have been termed residual faults. The following procedure was used to separate wedge faults from residual faults at the studied exposure of the Higganum dike. The poles to cooling joint surfaces were used to estimate the orientation of the contacts between the dike and the surrounding metamorphic rocks (204, 45 W). The pole to the dike contacts is considered the best estimate of the orientation of the common cooling column axis (114, 45). On the basis of the variation in orientation of the fault striae, wedge faults were classified as those with striae that lie at 25° or less to the common cooling column axis, and residual faults were classified as those with striae that lie at an angle of greater than 25° to this axis.

Future work will involve (1) use of Cosserat theory to analyze the wedge faults and the Gauss method to analyze the residual faults and (2) comparison of the results from the Higganum dike with the results of other studies of early Mesozoic and more recent states of stress in southern New England. Fault-slip data from the Higganum dike are among the first data that can be used to evaluate the techniques proposed to analyze wedge faults. Results of this analysis will provide additional information on the nature of rift and post-rift tectonics in southern New England and also contribute more broadly to the understanding of passive margin development in eastern North America.