UNDERSTANDING EARLY CRETACEOUS INTRAPLATE MAGMATISM IN NORTHERN NEW ENGLAND: A STRUCTURAL PERSPECTIVE

Recent geodynamic modeling has drawn attention to the difficulty of distinguishing magmatism from mantle plumes and edge-driven convection, largely because of the influence of lithospheric structure on the location of plume-related magmatism in continental lithosphere. The Early Cretaceous Ascutney plutonic complex in eastern Vermont may represent a location where both plume-related and edge-driven-convection-related magmatism occurred. The ~122 Ma age and general location of the Ascutney plutonic complex are broadly consistent with the Great Meteor hotspot track. However, the Ascutney plutonic complex also lies in the eastern portion of the Taconic lobe of the New England–Quebec igneous province. We have interpreted structural and geochronological data from the Taconic and Burlington lobes in western Vermont and eastern New York as consistent with magmatism from edge-driven convection.

We analyzed mapped mafic dike trends in the vicinity of Mount Ascutney using the mixed Bingham distribution cluster analysis method. N–S and NW–SE extensional stress fields were identified. Cluster analysis of mafic dikes crosscutting the plutonic complex yielded evidence for NW–SE extension. We interpret N–S extension as occurring prior to pluton emplacement and NW–SE extension after pluton emplacement. Our ongoing fieldwork in eastern Vermont includes observations of mesoscale faults and extension fractures supportive of NW–SE extension after pluton emplacement.

The stress fields and sequence of events in eastern Vermont are consistent with our observations in western Vermont and eastern New York. Our previous work identified N–S extension during ~140–130 Ma Burlington lobe magmatism and NW–SE extension during ~110–100 Ma Taconic lobe magmatism. We interpret the N–S and NW–SE extensional stress fields in the Ascutney region as contemporaneous with Burlington and Taconic lobe events supporting edge-driven convection as the driving mechanism for the Early Cretaceous mafic dike emplacement.