Shear wave structure in the Grenville Province beneath the lower Great Lakes region from Rayleigh wave tomography

Abstract

We have constructed a high resolution 3‐D shear wave velocity model of the upper mantle beneath the Grenville Province in the lower Great Lakes region. A two‐plane wave tomography method was applied to fundamental mode Rayleigh wave data recorded at 35 broadband seismic stations. Rayleigh wave phase velocities were obtained at 15 periods from 20 s to 143 s and then inverted for shear wave velocity variation. A high velocity lid to ~150 km depth is imaged beneath most of the studied Grenville Province. One low velocity anomaly of −4% appears at a failed rift in the northeast above 100 km depth, coinciding with the Great Meteor hot spot track and the high seismicity band, which can be interpreted as high temperature and high iron and/or volatile content related to the hot spot activity. Low velocity anomaly of ~2% at the depths of 100–200 km are found beneath the east of Lake Ontario and Lake Huron where the lithosphere is relatively thin. These anomalies follow the NW‐SE trend of the slow indentation imaged on the continental‐scale models. We conclude that the location of low velocity anomalies is not only related to the hot spot track but also controlled by the pre‐existing lithosphere morphology and strength. A high velocity column appears between southern Lake Ontario and the Appalachian front centered at ~100 km depth. It is likely caused by high Mg content at the formation of the lithosphere or the presence of ecologite or garnet phases generated during the opening and closure of the Iapetus Ocean.