HuBLE: The Hudson Bay Lithospheric Experiment

Abstract

We have carried out a broadband seismological study of the Hudson Bay region of northern Canada with the view to understanding better the reasons for the Bay’s existence, and the nature of the tectonic processes that shaped the Canadian shield during Precambrian times. Our 2007–2011 seismograph network consisted of up to 12 CMG-3T G¨uralp instruments with a combination of Taurus and DCM data loggers recording data at 20 Hz in both remote (solar powered) and community (mains powered) locations. Our work was carried out in conjunction with the Geological Survey of Canada who provided significant logistical and financial support beyond the scope of the original (2007-2009) NERC-funded proposal. Data quality from the HuBLE network was excellent, with percentage recovery good except during the long Canadian winters when stations powered down. A number of publications have resulted from analysis of the new dataset showing that: (i) the lithosphere in the region has retained a ∼1.8 Ga fossil fabric, providing strong evidence that modern-day-style plate tectonics was in operation by Paleoproterozoic times (the Trans Hudson Orogen). (ii) Crustal formation of the Canadian Shield likely evolved from one characterised by a hot ductile regime during the Paleoarchean, to one more closely resembling modern-day-style plate tectonics by the Paleoproterozoic. (iii) Crustal stretching (not a mantle down-welling, eclogitised lower-crust, or incomplete glacial rebound) is likely responsible for the presence of the Bay. (iv) There is no evidence for thinning or thickening of the mantle transition zone, with the implication that the mantle beneath Hudson Bay is neither characterized by a cold downwelling (potentially responsible for the formation of the Bay), or elevated temperatures due to the thermally insulating effects of the thick Canadian lithosphere.