LONG-LIVED AND LOCALIZED POST-OROGENIC MAGMATISM ON THE EASTERN NORTH AMERICAN MARGIN: INSIGHTS FROM ZIRCON U-PB GEOCHRONOLOGY
In order to precisely and accurately assess the variety of hypothesized causal mechanisms for both initiating and sustaining magmatism in each province, we conducted CA-ID-TIMS and LA-ICP-MS zircon U-Pb measurements on several units for both the WMMS and NEQ provinces, including: all major igneous centers associated with the WMMS; all igneous centers within the largest composite intrusion of this province, the White Mountain Batholith; and key units within the NEQ province.
Our results constrain the timing of the onset of the WMMS to be no younger than ~199 Ma, though we cannot rule out a potentially older initiation as some samples did not yield zircons. We also demonstrate that the main phase of WMMS magmatism lasted ~20 Myr, significantly shorter duration than published ages suggest.
The spatial and temporal proximity of the WMMS to the CAMP should motivate future examination of the a geodynamic link between the two. However, given the prolonged duration of WMMS magmatism well beyond the punctuated timing of the CAMP, a variety of processes are likely responsible for the generation, transport, and emplacement of these melts.
Our age constraints for the NEQ province demonstrate a relatively brief duration between magmatism in the Monteregian Hills (Québec) and Cretaceous White Mountains (New Hampshire) and provide the first zircon U-Pb chronological test of the Great Meteor Hotspot on land.
Our work provides the necessary boundary conditions for integrating high-precision geochronology, geochemistry, and geophysics to understand the tectono-magmatic history of the ENAM and evaluate to what extent such process had in producing geophysical anomalies (e.g, the Northern Appalachian Anomaly1) observed today.
1Menke et al., GRL. (2016).