RECONSTRUCTION OF THE STATES OF STRESS SINCE RIFTING IN THE MESOZOIC USING FAULT-SLIP DATA FROM CRYSTALLINE BEDROCK IN 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, we have concentrated on brittle structures found in crystalline bedrock east of the Hartford Basin in Connecticut.

We collected 1,060 fault-slip data from various Paleozoic accreted terranes and the Early Jurassic Higganum Dike. Because the dataset is large and heterogeneous, we first processed it 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 ~N-S 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 indicate flattening strain in the basement during rifting. Phase 2 faults may have developed synchronously with structural inversion of the rift basins. Phase 3 faults are consistent with widespread observations for N-S compression in the region. Phase 4 stress orientations are parallel to the present-day state of stress. In total, our stress 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.