The Rise and Erosion of the South Eastern Canadian Cordillera - Cenozoic Cooling, Exhumation and Elevation of the Columbia Mountains and Southern Rocky Mountains in Western Canada from Low-Temperature Thermochronology
posted on 2016-11-14, 11:16authored byAnnika Szameitat
The North American Cordillera influences climate on a local and global
scale, by forming a distinct barrier to Pacific moisture reaching the continental
interior. The extent to which this climatic pattern existed in the past is uncertain,
so improving our understanding of the elevation history of the Cordillera is critical
to determining the controls on climate change within the Northern Hemisphere
[e.g. Foster et al. 2010]. In western Canada, the Cordillera comprises two parallel
mountain chains separated by a high elevation (~1100 m) intermontane plateau.
The Cenozoic exhumation history of the western range, the Coast Mountains, has
been well studied [e.g. Parrish, 1983; O'Sullivan and Parrish, 1995; Farley et al.,
2001], while the Cenozoic history of the eastern Cordillera remains poorly
constrained.
This study presents a comprehensive new apatite (U-Th)/He, apatite fission
track and zircon (U-Th)/He dataset of the south-eastern Canadian Cordillera and
constrains the Cenozoic cooling, exhumation and elevation history of the area.
Cooling ages show rapid cooling (>10°C/Ma) from peak metamorphic
temperatures (>500°C) to below 120°C during the Cretaceous to Eocene (75-40
Ma) followed by a period of slow cooling (<1°C/m.y.) and a later phase of rapid
cooling (>10°C/m.y.) to below 70°C since the Miocene (10-0 Ma). Corresponding
exhumation phases modelled using age-elevation relationships of numerous
vertical profiles show 1-5 km of erosion between 70-35 Ma and up to ~2.5 km in
current valleys since ~10 Ma. Paleo-surface reconstructions and Paleo-mean
elevations estimated from isostasy indicate a high elevation (~2.5 km) but low
relief plateau at the end of orogeny (~45 Ma), which gradually lowered in mean
elevation by ~1.5 km until ~10 Ma. A later Neogene increase lifted the peaks a
further ~2.5 km to their current height, while incising up to 2.5 km of relief. The
main causes for both exhumation phases are found to be a combination of
lithosphere delamination, asthenosphere upwelling and thermal expansion, while
the last phase of incision and surface uplift was further enhanced by glacial
incision and isostasy.