The geodynamics of Cordilleran mantle in northern Canada
Abstract
The Northern Canadian Cordillera (NCC) is characterized by a thin lithosphere (~ 50 km), high surface heat flow (>100 mW/m2) and shallow Curie depth, indicating a hot geotherm. It is bordered to the east by the North American Craton (NAC), which has a cooler (~50 mW/m2) and thicker lithosphere (~150 km). Elastic thickness, petrologic data, and receiver function imaging demonstrate the different lithospheric thickness between NCC and NAC, especially indicating the sharp boundary between them. The origin of thin NCC lithosphere is enigmatic. Seismic observations are consistent with a recent thinning event at 5-25 Ma, whereby the NCC mantle lithosphere detached as a coherent slab (i.e., delamination) that now appears as a dipping feature at 50-150 km depth below the NCC.
We use numerical models (SOPALE code) to investigate the 2D thermal-mechanical evolution of the lithosphere during a delamination event. Model experiments show that delamination occurs only if the deep NCC crust is relatively weak and contains high-density eclogite, perhaps formed during an earlier phase of crustal thickening. Once initiated, delamination proceeds quickly (over a few Ma), resulting in wholesale removal of the NCC mantle lithosphere and deep crust. Delamination is accompanied by rapid surface uplift and a more gradual increase in surface heat flow. It also produces widespread melting via decompression of the upwelling asthenosphere and rapid crustal heating, possibly explaining recent volcanism in the NCC. Future work will examine the effects of delamination on crustal deformation and NCC-NAC seismic structure.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T33C..03Y
- Keywords:
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- 1038 Mantle processes;
- GEOCHEMISTRY;
- 1209 Tectonic deformation;
- GEODESY AND GRAVITY;
- 7230 Seismicity and tectonics;
- SEISMOLOGY;
- 8178 Tectonics and magmatism;
- TECTONOPHYSICS