THE WESTERN NEW ENGLAND-QUEBEC IGNEOUS PROVINCE OF VERMONT AND NEW YORK: AN EXAMPLE OF POSTRIFT MAGMATISM AND NORMAL FAULTING FROM THE NORTHERN APPALACHIANS

Edge-driven convection is likely an important process associated with the evolution of the Eastern North American Margin. Geophysical evidence supports edge-driven convection beneath the New England region today. Mazza et al. (2017) linked Eocene magmatism and uplift within the central Appalachians to lithospheric delamination, foundering, and instability and Amidon et al. (2016) proposed edge-driven convection as a potential driving mechanism behind postrift Late Cretaceous uplift within New England. Our geochronological and geochemical data suggest the Early Cretaceous western New England-Quebec (NEQ) igneous province may represent an early expression of edge-driven convection along the Eastern North American Margin.

Our ⁴⁰Ar/³⁹Ar and U-Pb data indicate western NEQ magmatism was long-lived and spanned at least 35 Ma and is therefore inconsistent with magmatism induced by the Great Meteor hotspot track. Our major and trace element geochemistry for the sheet intrusions is bimodal and internally consistent throughout the study area, supporting a common source through time. The sheet intrusion geochemistry is also consistent with other examples of ENAM postrift magmatism.

Field observations and paleostress inversion of mesoscale fault-slip data indicate an extensional setting within the western NEQ during the Early Cretaceous. NW-SE extension dominated the region during the Early Cretaceous and normal faulting was likely coeval with magmatism. The Early Cretaceous timing of normal faulting is supported by slip along faults with cross-cutting relationships to dikes and dike contacts and by additional normal faults across the study area that are compatible with the dike emplacement stress field. The NE-SW trending dikes of southern VT display outcrop-scale evidence for emplacement in response to the Early Cretaceous stress field rather than emplacement controlled by preexisting structures. While NW-SE extension dominated the Early Cretaceous within the study area, evidence for an early phase of N-S extension and later E-W extension is also present.