INVESTIGATING THE TIMING OF POSTRIFT EXTENSION IN NORTHERN NEW ENGLAND: CROSSCUTTING STRUCTURES AT THE EARLY CRETACEOUS CUTTINGSVILLE COMPLEX, VERMONT

The eastern North American margin has experienced multiple episodes of postrift magmatism. Recent geochronological work has recognized that the postrift magmatism of northern New England spans at least 40 Ma during the Early Cretaceous. This extended duration of intraplate magmatism is inconsistent with a hot spot origin and edge-driven convection has been proposed as an alternate driving mechanism. The 103 Ma Cuttingsville plutonic complex of central Vermont is part of the ~110–100 Ma Taconic lobe magmatism that represents the youngest episode of postrift magmatism within the New England region.

In northern New England, Early Cretaceous postrift magmatism is linked to local changes in the regional extensional stress field (Cooper Boemmels et al., 2024). A field investigation of the Cuttingsville complex was conducted to gain a better understanding of the timing of local extensional events after 103 Ma. Field data were collected from structures crosscutting the quartz syenite and included fractures, faults, and crosscutting dikes. Oriented hand samples were collected from the quartz syenite unit and prepared into oriented thin sections for petrographic analysis of microfractures within quartz grains.

Multiple populations of fractures were observed to crosscut the Cuttingsville complex. NE–SW-striking fractures were recognized across the site and subparallel to a dike that crosscuts the quartz syenite. NE–SW-striking mesoscale normal faults were also observed crosscutting the quartz syenite. An E–W fracture network was associated with mineralized veins. In thin section, observed microfracture populations were similar to outcrop-scale fractures, and were associated with fluid inclusions within the quartz. The results of this investigation support an extensional stress field within the region after 103 Ma.