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

Vanderhaeghe, O., Teyssier, C., McDougall, I. and Dunlap, W. J. (2003) Cooling and exhumation of the Shuswap Metamorphic Core Complex constrained by 40Ar/39Ar thermochronology. Bulletin of the Geological Society of America, 115 2: 200-216. doi:10.1130/0016-7606(2003)115


Author Vanderhaeghe, O.
Teyssier, C.
McDougall, I.
Dunlap, W. J.
Title Cooling and exhumation of the Shuswap Metamorphic Core Complex constrained by 40Ar/39Ar thermochronology
Journal name Bulletin of the Geological Society of America   Check publisher's open access policy
ISSN 0016-7606
1943-2674
Publication date 2003-02
Sub-type Article (original research)
DOI 10.1130/0016-7606(2003)115
Volume 115
Issue 2
Start page 200
End page 216
Total pages 17
Editor Jill Rothenberg
Place of publication Boulder, CO., U.S.A.
Publisher Geological Society of America
Language eng
Subject 0404 Geophysics
0403 Geology
Formatted 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.

Keyword Argon thermochronology
Canadian Cordillera
Exhumation
Metamorphic core complex
Shuswap
Tectonics
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
School of Earth Sciences Publications
 
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Created: Thu, 08 Apr 2010, 11:58:28 EST by June Temby on behalf of Faculty of Science