Paleostress Analysis of Normal faults and Early Cretaceous Sheet Intrusions in Northern New England: Evidence for a Dynamic Extensional Setting During the Early Cretaceous

Jennifer Cooper Boemmels, Southern Connecticut State University
Jean Crespi, University of Connecticut

Abstract

Postrift magmatism, uplift, and faulting have occurred along the eastern North American margin within a passive margin setting. In northern New England, postrift magmatism spanned at least 35 m.y. during the Early Cretaceous (Cooper Boemmels et al., 2021). Mineralization associated with faults and fractures spanned at least 40 m.y. during the Early and Late Cretaceous (Amidon et al., 2022). To understand the structural context for these events, we evaluated the stress fields associated with Early Cretaceous magmatism in northern New England.

Paleostress fields were determined using three datasets: (1) the mapped trends of Early Cretaceous sheet intrusions in western Vermont and eastern New York that overlap with the Burlington and Taconic lobes of the New England–Quebec igneous province (Dale, 1889; Fisher, 1985; Ratcliffe et al., 2011), (2) fault-slip data collected from the Burlington and Taconic lobes and vicinity, and (3) the orientation of Early Cretaceous sheet intrusions in the Mount Ascutney Quadrangle in eastern Vermont and western New Hampshire (Walsh et al., 2021). Dataset 1 was analyzed using cluster analysis through the program Orient (Vollmer, 1990, 1995, 2015), dataset 2 was analyzed using Zalohar and Vrabec's (2007) method of paleostress inversion, and dataset 3 was analyzed using the mixed Bingham distribution cluster analysis method of Yamaji and Sato (2011). Dataset 1 provides information on the stress fields at the time of ~140–130 Ma magmatism in the Burlington lobe and ~110–100 Ma magmatism in the Taconic lobe. Stress field compatibility and crosscutting relationships between faults and sheet intrusions were used to determine timing of the stress fields recorded by fault-slip data in dataset 2. Crosscutting relationships with the ~122 Ma Mount Ascutney pluton were used to determine relative timing of stress fields for dataset 3.

The datasets generally yielded consistent results. N–S and NW–SE extensional stress fields were identified from all three datasets and with each technique. The fault-slip dataset also yielded evidence for NE–SW extension. NE–SW extension likely represents the Early Cretaceous regional stress field while the N–S and NW–SE extensional stress fields are interpreted as occurring in association with the ~140–130 Ma Burlington lobe and ~110–100 Ma Taconic lobe episodes of magmatism, respectively. These results support a regional extensional setting during the Early Cretaceous and suggest episodes of sheet intrusion emplacement in the Burlington and Taconic lobes coincided with changes in the orientation of the extensional stress field.

Session

Session 6: Advances in Geology, Geochronology, Geophysics