The passive margin of the eastern coast of the United States is known to be geologically active, with recently rejuvenated topography, intraplate seismicity, and volcanism of Eocene age. This study uses seismic data from the Mid-Atlantic Geophysical Integrative Collaboration (MAGIC) experiment to constrain lateral variations in the attenuation of teleseismic P waves beneath the central Appalachian Mountains to shed light on the structure and dynamics of the upper mantle at this “active” passive margin. We use a Monte Carlo approach to estimate variations in attenuation along with both data and model uncertainties. The quality factor of the upper mantle dramatically decreases over a distance of less than 50 km on the western side of the central Appalachian Mountains, where a low-velocity anomaly has been previously inferred. Extrinsic factors such as scattering or focusing are rejected as explanations for the observations on the basis of finite-difference waveform modeling experiments. The peak in attenuation beneath the crest of the Appalachian Mountains requires that near- to super-solidus conditions occur in the upper mantle and is co-located with volcanism of Eocene age. Our preferred interpretation is that the attenuation reflects the removal of the mantle lithosphere via delamination beneath the mountains, followed by ongoing small-scale convection.
Bibliographical noteFunding Information:
Funding for this study was provided by the University of Minnesota and by the National Science Foundation (NSF) under grant EAR-1827277 to the University of Minnesota, EAR-1251515 to Yale University, and EAR-1460257 to the College of New Jersey. Data from the MAGIC experiment (network code 7A) were used in this study and can be downloaded from the Incorporated Research Institutions for Seismology (IRIS) Data Management Center (DMC) at http://ds.iris.edu . Seismic instruments were provided by the IRIS PASSCAL Instrument Center at New Mexico Tech. The facilities of the IRIS Consortium are supported by NSF under Cooperative Agreement EAR-1261681 and the DOE National Nuclear Security Administration . The NSF I/D program helped support preparation of this manuscript. Any opinion, findings, and conclusions or recommendations expressed in this article are those of the authors and do not necessarily reflect the views of the National Science Foundation. Fig. 1 was prepared with the GMT/MATLAB toolbox ( Wessel and Luis, 2017 ). We thank two anonymous reviewers and Benjamin Murphy for providing thoughtful and constructive feedback on this manuscript. We extend our thanks to Zachary C. Eilon for making the code of Eilon et al. (2018) publicly available, as reference to this code was necessary to construct the inversion of this study.
- Appalachian Mountains
- passive margin