J. Geophys. Res.http://doi.org/h3s (2012)

During periods of mountain building, parts of Earth's deep crust are thought to become so weak that they begin to flow, a process currently suspected to be occurring under the Himalaya. Seismic data from North America suggest that a channel of flowing crust may also have formed 1.8 billion years ago under the Trans-Hudson orogen, a mountain range that ran through the core of North America.

David Eaton at the University of Calgary and colleagues used measurements of Earth's microseismic background vibrations to analyse the structure of the rocks that once formed this ancient mountain range. The mountains have since subsided and now lie beneath Hudson Bay. The seismic data show that the rocks in the shallow parts of the crust retain the patterns of deformation imparted in them when they were thrust upwards to form high mountains. In contrast, a similar pattern of deformation cannot be identified in rocks from the deeper crust. The researchers suggest that the original pattern was overprinted in the later stages of mountain building, when the deeper rocks became so weak that they began to flow.

The patterns of deformation preserved in the rocks beneath Hudson Bay are remarkably similar to those found in the present day Himalayan mountains, suggesting that the same processes operated in both cases.