Lithospheric Structure in the Northern Appalachian Mountains: A Detailed Examination of the Abrupt Change in Crustal Thickness in Northwestern Massachusetts

Abstract

The Appalachian Mountains were formed partially from multiple accretion of terranes along the Laurentia margin; these terranes were originally part of Gondwana. The present-day crustal structure holds a record of the tectonic history of the formation of the Appalachian Mountains. Previous geophysical studies identified an ~15 km vertical “Moho step” of the base of the crust in New England, USA along ~50 km horizontal distance and associated it with the surface boundary between Laurentia and the accreted terranes. Previous geochronological and thermochronological observations argue that the 60-km-thick crust in New England thickened during the assembly of the Appalachians and thinned during rifting and continental breakup.

Using data from 2018 to 2021 from the dense New England Seismic Transects (NEST) experiment, which placed seismic stations spaced ~10 km apart within the area of the Moho step, I used receiver function (RF) analysis to detect P to SV converted waves in records of P and PKP phases. Single composite RFs constructed for each station identify the changes of impedance with depth.