Cordillera thermal regime from Mexico to Alaska and tectonic implications
Roy Hyndman
Pacific Geoscience Centre, Geological Survey of Canada
- Date & Time
- Location
- Building 3, Rambo Auditorium
- Host
- Wayne Thatcher
- Summary
Numerous constraints to the Cordillera crust and upper mantle temperatures indicate remarkably uniformly hot from Mexico to Alaska, 800-850C at the Moho. The high temperatures are a consequence of the Cordillera being a current or recent backarc with shallow asthenosphere convection fluxed by water driven off the downgoing oceanic plates. A global compilation has shown that all continental backarcs are all similarly hot.
Some of the consequences of the uniformly hot backarc temperatures are:
1. The Cordillera is a high elevation mountain belt in spite of having a uniformly thin crust, avg. 33 km. The elevation results from thermal expansion.
2. The Cordillera is a mobile belt, hot enough to be deformed by normal plate tectonic forces (and resulting strong seismicity). Cratons and other stable areas are too strong for significant deformation.
3. The Cordillera (and other backarcs) have widespread lower crust horizontal detachment and also channel flow, especially indicated by the constant thickness crust in spite of a history of widespread crustal extension and crustal shortening.
4. The Cordillera and other backarcs have widespread sporadic backarc igneous activity. Temperatures are close to the upper mantle H2O-saturated first melting.
5. Finally, there are implications for: (a) the involvement of hot backarcs in continental collision orogeny, and (b) backarcs are the origin of most regional (Barrovian) metamorphism, not orogeny-related deformation heating.
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