MODIFICATION OF THE CONTINENTAL CRUST IN EASTERN NORTH AMERICA REVEALED BY PS CONVERTED WAVES

Eastern North America represents an iconic example of the Wilson cycle tectonics, which recorded at least two episodes of supercontinent assembly and breakup over the past 1.3 Ga. A long-term question remains about the impact of the past tectonic events on the growth and modification of the continental crust. In this study, we use teleseismic Ps receiver functions to image detailed distribution of the crustal thickness, as well as some distinctive intra-crustal features, beneath eastern North America. Our results show clear variations of the Moho depth within and across major tectonic units, which provides insights into the evolution of the crust during and after the major orogenic events in the eastern North America. More specifically, the Moho depth increases northwestward across the Appalachian front, with a west-east Moho offset of up to ~12-15 km. The gradient of the Moho offset varies along the Appalachian front, which probably reflects differences in the style and intensity of the Acadian, post-Acadian, and Alleghenian collisions. Along the Grenville front, a shallow Moho is seen in the northernmost part, while an abrupt Moho deepening appears along the southern front. The deepened Moho might be related to the collisions during the Grenville orogeny, or a combination of collisions and underplating due to failed rifts. The crustal thickness within the Grenville Province demonstrates a distinct difference between the northern part in Canada and the southern part in the United States. A portion of stations in the central Grenville Province of the United States show strong intra-crustal signals. The depth of this intra-crustal phase gradually increases eastward from the Grenville front to the Appalachian front over a distance of ~ 700 km. The heterogeneous seismic features observed within the Grenville crust may indicate a fundamental difference in the orogenic processes between the northern and southern parts.