Precambrian Processes, the Trans-Hudson Orogen, and Cratonic Keels: Insights From Teleseismic Tomography in Northern Hudson Bay, Canada

Abstract:

Earth conditions in the Precambrian, and their effect upon the formation of cratons and orogenies from that era, are not fully understood. For example, the precise onset of modern plate tectonics remains ambiguous; it has been hypothesised to have begun anywhere from ~4.1Ga (Hopkins, 2008) to ~1Ga (Stern, 2005). Also, the exceptional depth to which fast wave-speed and geoid anomalies extend beneath some cratons points to the existence of thick “cratonic keels”, the origin of which remains unexplained. To improve our understanding of the early Earth processes, geological evidence preserved within ancient plates that have remained largely unchanged since the Precambrian can be used. The rocks of northern Hudson Bay include Archean domains, the Paleoproterozoic Trans-Hudson Orogen (THO), and lie atop one of the largest cratonic keels on Earth (Bastow et al., 2013), making this region an ideal laboratory for study of Precambrian processes.

Here, we use seismological data recorded at Canadian POLARIS and Hudson Bay Lithospheric Experiment (HuBLE) stations to perform a relative arrival-time study of northern Hudson Bay region and the THO. Waveforms are aligned using the adaptive stacking routine of Rawlinson et al. (2004), and inversions are produced using the Fast Marching Tomography (FMTOMO) inversion code of Rawlinson et al. (2006). Our inversions provide an improved velocity model of the lithosphere and upper mantle of northern Canada, suggesting updated boundaries between lithospheric blocks at mantle depths and constituting new body-wave constraints on their structure. The results are used to address a number of outstanding questions regarding the processes that formed the THO and the Laurentian Keel of North America.