22 April 2013 – Seminar

When: 4pm on Monday, 22 April 2013
Where: DIAS, Geophysics Section, 5 Merrion Square, Dublin 2, (library)

Speaker: Prof. Ian Bastow (Imperial College London)
Title: Precambrian plate tectonics: seismic evidence from northern Hudson Bay

Abstract

Much of the geological record on Earth can be interpreted in the context of active processes occurring at the plate boundaries. For Phanerozoic (younger than 570 Ma) rocks this is well established, but during the Precambrian (older than 570 Ma), when the oldest rocks were forming, Earth conditions were likely very different, so analogies with modern-day tectonics are less certain. For example, 40 yr after the advent of plate tectonic theory, the precise onset of continental drift remains ambiguous: in the past 5 yr its onset has been estimated as early as ca. 4.1 Ga (e.g., Hopkins et al., 2008), or as late as ca. 1 Ga (Stern, 2005). Gathering geological evidence preserved deep within the plates in stable Precambrian regions (shields) is thus essential to improve our understanding of the early Earth. The geological record of northern Canada spans more than 2 b.y. of the Precambrian (ca. 3.9–1.7 Ga; Hoffman, 1988), and the region is underlain by a large continental root (e.g., Hoffman, 1990). It comprises several Archean terranes that are thought to have been brought together during a series of Paleoproterozoic collisions (e.g., Hoffman, 1988), culminating in the Trans-Hudson orogen, an ~1.8 b.y. old mountain building event that is thought to have been similar in scale and nature to the present-day Himalaya-Karakoram-Tibetan orogen of Asia (St-Onge et al., 2006). To address questions concerning Precambrian plate tectonics and the assembly of the Canadian shield, the Hudson Bay Lithospheric Experiment operated broadband seismograph stations between 2007-2011. I will describe the salient results of HuBLE and their implications for Precambrian plate tectonics, as well as the reasons for the existence of the Hudson Bay basin.