The Precambrian core of North America was assembled in the Proterozoic by a series of collisions between Archean cratons. Among the orogenic belts, two stand out due to their significant spatial extent. The Paleoproterozoic Trans-Hudson Orogen (THO) and Mesoproterozoic Grenville Orogen extend for thousands of kilometers along-strike and hundreds of kilometers across-strike. Both have been compared to the present-day Himalayan-Karakoram-Tibetan Orogen (HKTO). Over the last 20–30 years, active and passive-source seismic studies have contributed a wealth of information about the present-day crustal structure and composition of the two orogens in Canada. The Proterozoic orogenic crust is generally thicker than that of neighboring Archean terranes, with a more variable Moho character, ranging from relatively sharp to highly diffuse. Both orogens have a prominent high-velocity lower-crustal layer, consistent with long-term preservation of a partially-eclogitized root at the base of the crust and similar to that inferred beneath the western HKTO. Crustal structure in the northern THO strongly resembles the lower-crustal structure of the HKTO, suggesting that Moho depths may have reached 60–70 km when the orogen was active. A prominent mid-crustal discontinuity beneath the central Grenville Province and changes in the patterns of seismic anisotropy in the THO crust beneath Hudson Bay provide geophysical evidence that lower-crustal flow likely played a role in the evolution of both orogens, similar to that inferred beneath the present-day HKTO. The seismic evidence from Canada supports the notion of tectonic uniformitarianism, at least as far back as the Paleoproterozoic.
Bibliographical noteIB acknowledges Leverhulme Trust research project grant RPG-2013-332. FD is supported by the Natural Sciences and Engineering Research Council of Canada through the Discovery Grants and Canada Research Chair programmes. Data for Portable Observatories for Lithospheric Analysis and Research Investigating Seismicity (POLARIS ) and Canadian National Seismograph Network stations are available from the Canadian National Data Centre and IRIS Data Management Center (DMC). Earth-Scope data, including the QM-III project, are available from the IRIS-DMC. POLAR IS and related stations were funded by the Canadian Foundation for Innovation, Natural Resources Canada and Industry Canada, with further contributions from the Natural Science and Environment Research Council and Fonds de Recherche: Nature et Technologies Quebec. The QM-III project was funded by the US National Science Foundation and instruments were provided by the IRIS-PASSCAL instrument pool. We thank Yu Jeﬀ Gu for his invitation to contribute to this special volume.
- Seismic studies
- Crustal structure
- Canadian Shield