ASSESSING COMPATIBILITY OF DIKE-EMPLACEMENT AND FAULT-SLIP PALEOSTRESS CONDITIONS WITHIN THE NEW ENGLAND-QUEBEC IGNEOUS PROVINCE

The New England-Quebec igneous province (NEQ) consists of Early Cretaceous sheet intrusions and small plutons distributed within three lobes across Vermont, easternmost New York, and into the Montreal region. Other workers have suspected normal and strike-slip faults are genetically linked to the intrusions, yet the origins of both remain uncertain. We are investigating the genetic link between intrusions and faults by analyzing the stress field associated with dike emplacement and its compatibility with the stress field associated with fault slip.

The orientation of σ₃ for dike emplacement is determined from cluster analysis using Orient which provides a more quantitative assessment than interpretations relying exclusively on rose diagrams. Dikes from the NEQ Taconic and Burlington lobes were selected and limited to those outside the Eastern North America dolerite province to avoid inclusion of older intrusions (McHone, 1984). Dike azimuth data was obtained from the VT State Geologic Map (2011) and Dale (1889). Dip magnitude and direction were randomly generated because this information is known only for a limited number of dikes. Dip magnitudes ranged between 75° and 90°, consistent with field observations and the literature. Cluster analysis was performed for the entire selected NEQ dike population, the Taconic lobe, and the Burlington lobe. Five data sets were generated for each population and analyzed to determine repeatability of the results. Two populations of NEQ dikes were identified for the Taconic lobe with average azimuths of 041° and 109°, and two populations were identified for the Burlington lobe with average azimuths of 092° and 017°.

We are collecting fault-slip data for analysis using traditional paleostress inversion techniques to identify discrete fault populations and their associated reduced stress tensors. Forward modelling of the fault-slip data will also be performed to identify fault populations that are consistent with the stress fields associated with dike emplacement. These results, in combination with cross-cutting relationships, will refine our understanding of the relative and absolute timing of faulting associated with the NEQ.