OCGC Seminar - Tectonic Consequences of a Uniformly Hot Backarc and Why is the Cordillera Mountain Belt High?

   

Dr. R. D. Hyndman
Pacific Geoscience Centre, Geological Survey of Canada
School of Earth and Ocean Sciences, University of Victoria

 

 Thursday, November 6th, 2014

University of Ottawa
*Please note that this is the same seminar that will be presented at Carleton on the following
Monday, November 10th.

 

Why is the North American Cordillera Mountain Belt High?  We expect a thick crust to support high elevations by isostasy but, remarkably, the Cordillera crust is thin. There is no crustal root.  An important recent discovery is that the high elevation is supported by thermal expansion rather than by thickened crust.  The elevation of the Cordillera is only one consequence of the Cordillera being uniformly hot and having a thin lithosphere, in common with most other current and recent backarcs.  Some of the other tectonic consequences of the high temperatures (~800C at Moho) compared to the adjacent cool craton (~450C at Moho) include: The Cordillera and other backarcs are hot weak mobile belts that can be deformed by available plate tectonic forces, in contrast to stable cratons that cannot; there is widespread sporadic “backarc” volcanism; the high temperatures result in very low strength in the deep crust that allows lower crust detachment over large areas of the Cordilleran backarc; Cordilleran backarc lower crust weakness facilitates the development of large scale crustal oroclines that may be independent of the upper mantle; in hot backarcs globally, orogenic regional Barrovian metamorphism is concluded to be the result of the backarc high temperatures that predate collision orogeny.  No "heat of orogeny" is required.