HIGH RESOLUTION RECEIVER FUNCTION PROFILE BENEATH CONNECTICUT AND ITS IMPLICATIONS FOR THE TECTONIC HISTORY OF SOUTHERN NEW ENGLAND

The geology of southern New England has been shaped by a variety of past tectonic events, including Neoproterozoic continental rifting, multiple episodes of Paleozoic Appalachian orogenesis, and Mesozoic rifting. Southern New England shows diverse geologic features representing those past tectonic events. These include Proterozoic and early Paleozoic Laurentian units in the west, several Gondwanan-derived terranes that accreted during the Paleozoic to the east, and the Mesozoic Hartford Basin in the central portion of Connecticut. The Seismic Experiment for Imaging Structure beneath Connecticut (SEISConn) project involved the deployment of a dense array with 15 broadband seismometers across northern Connecticut from 2015 to 2019, in order to investigate how lithospheric structures beneath this region were deformed during these tectonic events and modified by subsequent events. The P-to-S receiver function analysis on SEISConn data shows that the westernmost part of Connecticut has a much deeper Moho than central and eastern Connecticut. The lateral transition shows as a vertical well-defined offset, with more than 15 km Moho depth reduction over ~20 km horizontal distance. The Moho step appears to be near the boundary between the Grenville orogenic belt to the west and the Gondwanan-derived Moretown terrane accreted during the Ordovician Taconic orogeny to the east, projected to the depth of the Moho. Receiver functions of the station CS03 located near the Moho step show Moho signals at multiple depths, suggesting that the Moho step is not simply the result of the juxtaposition of two landmasses with different crustal thickness. Possible models for its formation include over-thrusting of Grenville crust during the Moretown terrane accretion or modification by younger tectonic events after the Taconic orogeny. Another prominent feature imaged in this profile is a west-dipping positive velocity gradient in the lithospheric mantle, which is likely to be the Moho of a relict slab subducted during the later (Salinic, Acadian and/or perhaps Alleghanian) phases of the Appalachian orogenesis.