The Assembly and Evolution of Eastern Laurentia: Evidence from the QM-III Experiment
Abstract:Eastern North America is an excellent region to test hypotheses about the evolution through time of tectonic processes, the growth of continental crust and the assembly of continents. Over a spatial scale of just a few hundred kilometres, the surface geology records almost 3 billion years of Earth history, with a transition from the Archean Superior craton through the Proterozoic Grenville orogenic belt to the Phanerozoic Appalachian terranes and the edge of the North American continent.
The boundaries between these major tectonic provinces have been mapped at the surface, and crustal-scale geophysical studies (e.g. LITHOPROBE) have been able to trace their complex signatures to the Moho and below in some parts of eastern Canada. Nevertheless, the nature of the boundaries across the region, and their continuation into the lithospheric mantle, remains enigmatic. The high wavespeed lithospheric keel of the Canadian Shield extends beneath the Proterozoic terranes; however it is still unclear whether this material represents a continuation of Archean lithosphere over which the Grenville terranes have been thrust, or whether the Grenville can be associated with its own thick keel. The transition from Proterozoic to Phanerozoic lithosphere beneath the Appalachian Front is likewise ambiguous.
To shed new light on the tectonic evolution of the region, and the nature of the major tectonic boundaries, a broadband seismograph network was installed in eastern Canada in 2012-2013 through the QM-III (Quebec-Maine Across Three Sutures) experiment; stations will remain in place for 2-3 years. The network consists of a dense NW-SE profile from the southern tip of Hudson Bay to coastal Maine, supplemented by existing more sparsely-distributed stations, and a 2D deployment across Maritime Canada.
Data acquisition is ongoing, but preliminary results from receiver function analysis, travel-time tomography and surface-wave dispersion are already showing some intriguing variations in structure across the region. Here we present an overview of the experiment, our initial analyses and our long-term goals.