Subduction and Exhumation of the Western Gneiss Region, Norway: Application of Zircon U-Pb Geochronology
Abstract
Ultrahigh-pressure (UHP) terranes, such as those exposed in the Western Gneiss Region (WGR), Norway, provide an excellent natural laboratory for studying collisional orogenesis and its subsequent effects on Earth processes. UHP terranes range in size, from less than a few km2 in area and a few km thick to greater than 50,000 km2 and >30 km thick. The timing of terrane formation appears to be linked to size; larger terranes form more slowly than smaller ones. Because larger terranes expose more material and undergo a more protracted genesis, they afford the opportunity to study the spatio-temporal evolution of such terranes, and thus to understand how large portions of cold, buoyant, crust respond structurally to subduction to mantle depths. The (U)HP rocks of the WGR are a result of the Laurentia-Baltica collision during the Caledonian Orogeny. Westward subduction and eastward exhumation of Baltica created and the present (U)HP terrane, which spans 50,000 km2. Thermobarometric results from the WGR report peak P-T conditions of 3.5 GPa/800°C for the west, and 2.0 GPa/~400°C for the east. An east-to-west younging of both white mica and titanite ages reflect a contiguous exhumation of the WGR from amphibolite-facies conditions. Current geochronologic data from eclogite-facies assemblages in the western WGR define a range of 420-398 Ma for the time spent at HP conditions, but as of yet, little data have been produced from eastern eclogites. This study aims to test whether the WGR was subducted as one, large, coherent slab or the subduction of several, small, independent slabs exhumed together as one. Comparison between new U-Pb zircon age ranges of (U)HP eclogite from the central and eastern WGR (this study) to known ages of the western WGR will resolve the true timing of subduction and duration of peak P-T conditions experienced by both the foreland and the hinterland of the WGR, and determine the geometry and structural integrity of large subducted slabs.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.V13D2391G
- Keywords:
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- 1199 GEOCHRONOLOGY / General or miscellaneous;
- 3654 MINERALOGY AND PETROLOGY / Ultra-high pressure metamorphism;
- 8199 TECTONOPHYSICS / General or miscellaneous