LITHOSPHERIC STRUCTURE ABOVE THE NORTHERN APPALACHIAN ANOMALY FROM RECEIVER FUNCTION ANALYSIS: CONSTRAINTS FROM THE NEST EXPERIMENT

The Northern Appalachian Anomaly (NAA) is a low-velocity region of the upper mantle beneath New England, centered near the border of New Hampshire and Vermont. The upper mantle anomaly is spatially correlated with Jurassic to Cretaceous magmatic activity and with accelerated exhumation during the Late Cretaceous. It is unclear, however, whether and how the present-day geophysical anomaly is linked to these past events. Possible explanations for the NAA include a thermal anomaly left over from the passage of the Great Meteor hotspot or a young mantle upwelling that may be associated with edge-driven convection or shear-driven upwelling. It also remains unclear to what extent the upper mantle anomaly may be involved in modification of the overlying lithosphere, perhaps thinning and/or “healing” the lithosphere through time. The recent deployment of broadband seismometers across Vermont, New Hampshire, and Maine, comprising the northern line of the New England Seismic Transects (NEST) array, is allowing for detailed imaging of the crust, mantle lithosphere, and asthenospheric upper mantle to address these questions.

Here we present preliminary results from P-to-S receiver function (RF) analysis of NEST data, which can identify major discontinuities such as the Mohorovicic discontinuity and the lithosphere-asthenosphere boundary (LAB). These constraints will allow us to characterize the present-day architecture of the crust and lithospheric mantle above the NAA, and to investigate to what extent dynamic processes in the upper mantle have modified that structure through time. Detailed constraints on intra-lithospheric structure from RF analysis can also shed light on whether structures related to Appalachian orogenesis are preserved, or whether such structures have been extensively modified by the NAA.