12-7 Evidence for Dynamic Mantle Topography Associated with the Northern Appalachian Upper Mantle Anomaly Uplifting the Adirondack Mountains of Upstate New York

Session: New advances in geological and geophysical research on the Appalachian orogen. (II)

Presenting Author:

Authors:

Abstract:

The Adirondack Mountains of northern New York are an anomalous intracratonic dome of Grenvillian crust uplifted to elevations >1.6 km, and suggested to be rising at rates of 2–4 mm/yr. While glacial isostatic adjustment (GIA) contributes to present-day vertical motion, the persistence and magnitude of Adirondack relief suggest a mantle-driven component. In this study, we investigate the upper mantle structure beneath the Adirondacks using both receiver function analysis and a new P wave tomographic model of mantle structure beneath the northeastern U.S. We generate multi-taper spectral correlation receiver functions and apply a harmonic decomposition analysis that quantifies directionally dependent behavior. We identify a significant and sharp low-velocity contrast at ~100 km depth, accompanied by changes in anisotropic texture and geometry, at several long-running seismic stations across the Adirondack region. Additionally, the presence of coherent transverse component energy requires the low velocity feature to be dipping significantly, at a dip of ~30°-40°. We combine our receiver function results with a new P wave tomographic model that incorporates data from dense broadband seismic arrays recently deployed in New England and the surrounding region. We identify a broad low velocity zone directly beneath the Adirondacks at 100 km depth in the tomography; this low velocity zone appears to be physically connected to the Northern Appalachian Anomaly, located beneath New England, in the deeper part of the upper mantle. These datasets are consistent with a low velocity layer directly beneath the lithosphere-asthenosphere boundary, likely ~40-50 km thick and likely involving some degree of partial melting. We interpret the Adirondack Mountains as the western surface expression of the Northern Appalachian Anomaly (NAA), where dynamic mantle topography provides long-wavelength buoyant support and, together with GIA, provides a mechanism for ongoing uplift. Our model, which invokes a mantle contribution to ongoing Adirondack uplift, positions the Adirondacks as a key natural laboratory for probing the surface manifestations of upper mantle dynamics.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2, 2026

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