SEISMIC CHARACTERISTICS OF THE EASTERN NORTH AMERICAN CRUST WITH PS CONVERTED WAVES: TERRANE ACCRETION AND MODIFICATION OF CONTINENTAL CRUST

Eastern North America recorded at least two complete episodes of supercontinent assembly and breakup over the past 1.3 Ga. Fundamental questions remain concerning the impact of the past tectonic events on the growth and modification of continental crust and mantle lithosphere. 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 659 broadband stations during 2010-2017, yielding high-resolution Moho depth distribution. The depths of the Moho and intra-crustal layers vary within and across the major tectonic units. Specifically, there are distinct differences in crustal thickness between the northern and southern Grenville Province. Further, a dipping intra-crustal feature can be seen within the central Grenville Province, with the depth increasing eastward from 5 km to 27 km. The Moho depth decreases southeastward across the Appalachian Mountains, 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 degrees of 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 Appalachian Mountains probably reflect along-strike variation of the sharpness of the subsurface boundary between Laurentia and accreted terranes with different intensities of post-orogenic modification.