Paleostress Inversion of Post-Alleghanian Brittle Faults in Paleozoic Accreted Terranes and the Early Mesozoic Higganum Dike, Eastern Connecticut

The passive margin of eastern North America contains reverse faults and folds in early Mesozoic basin-fill that are not characteristic of extension in the lithosphere during rifting. These observations deviate from the classical understanding of a passive margin and indicate other states of stress since rifting. To strengthen these observations, brittle faults were studied from the crystalline bedrock that is east of the Hartford Basin in Connecticut. Fault-slip data from 1,060 faults were collected from the Gander cover and Avalon terranes and from the early Mesozoic Higganum dike. Because the dataset is large and heterogeneous, it was first processed using stress orientations based on the trend of the Higganum dike in order to isolate faults representative of rifting. Paleostress inversion of the remaining faults in combination with age relations observed in the field identifies three additional phases of deformation. Phase 1 consists primarily of normal faults striking in a variety of directions but mainly ~NE-SW and displays a subvertical σ1. Faults in phase 2 have a variety of orientations but are dominated by a conjugate set of ~NNW-SSE and ~E-W-striking strike-slip faults and displays a NW-SE σ1. Phase 3 consists of a conjugate set of ~NW-SE and ~NE-SW-striking strike-slip faults and displays a N-S σ1. Phase 4 consists of a conjugate set of ~NE-SW and ~WNW-ESE-striking strike-slip faults and displays an ENE-WSW σ1. Phase 1 stress orientations represent the stress orientations during early Mesozoic rifting. Phase 2 faults are consistent with post-rift inversion that is oriented ~NW-SE in the southeastern United States. Phase 3 faults are consistent with post-rift inversion that is oriented ~N-S in the northeastern United States and Maritime Canada. Phase 4 stress orientations are parallel to the present-day state of stress. In total, the paleostress inversions for eastern Connecticut identify four tectonic phases and are consistent with other studies in eastern North America of the post-Paleozoic states of stress