Cooling and exhumation of the Shuswap Metamorphic Core Complex constrained by 40Ar/39Ar thermochronology

Research Article| February 01, 2003 Cooling and exhumation of the Shuswap Metamorphic Core Complex constrained by 40Ar/39Ar thermochronology Olivier Vanderhaeghe; Olivier Vanderhaeghe 1Université Henri Poincaré Nancy, UMR G2R, BP 239, 54506 Vandoeuvre, France, Department of Geology and Geophysics, University of Minnesota, Pillsbury Hall, Minneapolis, Minnesota 55455, USA and Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia Search for other works by this author on: GSW Google Scholar Christian Teyssier; Christian Teyssier 2Department of Geology and Geophysics, University of Minnesota, Pillsbury Hall, Minneapolis, Minnesota 55455, USA Search for other works by this author on: GSW Google Scholar Ian McDougall; Ian McDougall 3Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia Search for other works by this author on: GSW Google Scholar W. James Dunlap W. James Dunlap 3Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information Olivier Vanderhaeghe 1Université Henri Poincaré Nancy, UMR G2R, BP 239, 54506 Vandoeuvre, France, Department of Geology and Geophysics, University of Minnesota, Pillsbury Hall, Minneapolis, Minnesota 55455, USA and Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia Christian Teyssier 2Department of Geology and Geophysics, University of Minnesota, Pillsbury Hall, Minneapolis, Minnesota 55455, USA Ian McDougall 3Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia W. James Dunlap 3Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia Publisher: Geological Society of America Received: 15 May 2002 Accepted: 10 Jun 2002 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2003) 115 (2): 200–216. https://doi.org/10.1130/0016-7606(2003)115<0200:CAEOTS>2.0.CO;2 Article history Received: 15 May 2002 Accepted: 10 Jun 2002 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Olivier Vanderhaeghe, Christian Teyssier, Ian McDougall, W. James Dunlap; Cooling and exhumation of the Shuswap Metamorphic Core Complex constrained by 40Ar/39Ar thermochronology. GSA Bulletin 2003;; 115 (2): 200–216. doi: https://doi.org/10.1130/0016-7606(2003)115<0200:CAEOTS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The exhumation history of the Shuswap Metamorphic Core Complex (Shuswap MCC) is deciphered from structural analysis and 40Ar/39Ar thermochronology. With the exception of a few samples contaminated by excess argon, the analytical results indicate a consistent range of early Tertiary 40Ar/39Ar ages throughout the area. Hornblende yields ages ranging from ∼59–54 Ma; muscovite and biotite ages are clustered between 49.5 and 48 Ma, and are consistent with the timing of closure of K-feldspars, typically ranging from 50 to 43 Ma, except for samples in the immediate footwall of the Columbia River fault that yield ages as young as 26 Ma. These 40Ar/39Ar ages, combined with existing U/Pb ages on zircons and monazites, constrain the cooling history at several localities in the Shuswap MCC between Trans Canada Highway 1 and the Thor-Odin dome. The migmatitic core of the complex is affected by a rapid cooling event (∼700 °C to ∼300 °C), from crystallization of zircons through closure of argon diffusion in hornblende and micas, between ∼56 and ∼48 Ma. Based on our previous structural analysis, we propose that this first period of rapid cooling follows an exhumation event associated with the formation of the Shuswap MCC by activation of a low-angle detachment and ductile thinning of a previously thickened and partially molten crust. Multidiffusion-domain thermal modeling of K-feldspar constrains the lower temperature history from ∼350 °C to ∼150 °C and indicates a period of thermal stability from ∼48 to ∼45 Ma, and a cooling event at ∼45 Ma, except for the K-feldspars sampled in the immediate footwall of the Columbia River fault, which indicate rapid cooling at ∼33 Ma. These cooling events are attributed to exhumation accommodated by local activation of high-angle normal faults.Therefore, we distinguish two periods of exhumation in the Canadian Cordillera: (1) Exhumation in Paleocene time related to crustal thinning and tectonic denudation by activation of detachment zones at ∼60–50 Ma, which corresponds to gravitational collapse of the thickened and partially molten Cordilleran crust; and (2) Exhumation related to Eocene regional extension, Basin-and-Range style, at ∼45 Ma, with reactivation of the eastern boundary fault of the core complex, the Columbia River fault, in Oligocene time at ∼33 Ma. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

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