Seismic Characteristics of the Eastern North American Crust With Ps Converted Waves: Terrane Accretion and Modification of Continental Crust

Abstract

AbstractThe impact of past tectonic events on the formation and modification of continental lithosphere remains as an open question of fundamental importance. Eastern North America provides a complete record of supercontinent assembly and breakup over the past 1.3 Ga, serving as a natural laboratory for our understanding of continental crust and mantle lithosphere and for integrating geologic and geophysical observations. In this study, we used teleseismic Ps receiver functions to image the detailed distribution of crustal thickness beneath eastern North America. The radial‐component receiver functions were calculated from seismic waveforms recorded by a total of 659 broadband stations during 2010–2017, yielding a high‐resolution image of Moho depth distribution. The depths of the Moho and intracrustal layers vary within and across the major tectonic units. Specifically, there are distinct differences in crustal thickness between the northern and southern Grenville Province. A dipping intracrustal feature can be seen within the central Grenville Province, with the depth increasing eastward from 5 to 27 km. The Moho depth decreases southeastward across the Grenville‐Appalachian boundary, with a sharp Moho offset of up to 12–15 km in the central segment and a more gradual variation to the north and south. The thickness difference between the southern and northern Grenville‐aged crusts suggests different tectonic and/or exhumation histories during and after the Grenville Orogeny. The low‐angle eastward dipping crustal feature is interpreted to be a Grenville‐aged collisional structure. Differences in the steepness of the Moho offset along the strike of Appalachians probably reflect variation of the steepness of the subsurface boundary between Laurentia and accreted terranes with different intensities of postorogenic modification. The observed spatial relation between the geologically defined tectonic boundaries and crustal thickness variations provides new constraints on the depth extent of the tectonic units within the crust.