Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

Geological Magazine

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (6) Citing Articles via Google Scholar Google Scholar Articles by KENDRICK, M. A. Articles by OSMUNDSEN, P. T. Search for Related Content GeoRef GeoRef Citation

The Middle to Late Devonian Høybakken detachment, central Norway: ⁴⁰Ar–³⁹Ar evidence for prolonged late/post-Scandian extension and uplift

The Geological Survey of Norway, Leiv Eirikssons Vei 39, 7491 Trondheim, Norway

^* Author for correspondence: mark.kendrick{at}unimelb.edu.au

The regionally significant 0.5–2 km thick Høybakken detachment in central Norway bounds the southern margin of the Central Norway Basement Window and exhibits a well-developed top-to-the-WSW fabric characteristic of late Scandian, Devonian ductile extension. ⁴⁰Ar–³⁹Ar data obtained from hornblende, mica and K-feldspar mineral separates of rocks collected in a transect through the Høybakken detachment yield well-defined plateau and isochron mineral ages. Early Devonian exhumation and cooling of the Høybakken detachment footwall is recorded by hornblende ages of ~ 400 Ma and mica ages of ~ 390 Ma. The mylonitic fabric overlying the footwall records younger Middle Devonian mica crystallization ages of 384–381 Ma that are among the youngest extensional ductile fabrics dated in the Caledonides and suggest prolonged extensional activity on the Høybakken detachment. After inferred cessation of ductile extension at 381 Ma, the rate of uplift and cooling was reduced, and the footwall records Late Devonian to Early Carboniferous K-feldspar ages of 371–356 Ma. Prolonged extensional activity at Høybakken is compatible with recent U–Pb ages of deformed titanite crystals and established Rb–Sr ages of white mica in shear-related pegmatites, both from the southwestern part of the Fosen Peninsula, and ⁴⁰Ar–³⁹Ar ages of syn-tectonic mica overgrowth from the adjacent Hitra–Snasa Fault. Together, these ages suggest the onset of ductile extension soon after ~ 401 Ma, and with the Middle Devonian crystallization ages determined here, suggest that ductile extension on the Høybakken detachment had a duration of 11–20 Ma. The youngest age of 320 Ma was obtained from a K-feldspar in a cataclastic granite of the Høybakken detachment’s hangingwall and is considered to date a phase of post-Scandian brittle deformation that overprinted the mylonitic shear fabric.

Key Words: Caledonian Orogeny • ductile deformation • extension • geochronology • thermochronology • ⁴⁰Ar–³⁹Ar

This article has been cited by other articles:

				J. A. Gilotti and W. C. McClelland Geometry, kinematics, and timing of extensional faulting in the Greenland Caledonides--A synthesis Geological Society of America Memoirs, January 1, 2008; 202(0): 251 - 271. [Abstract] [Full Text] [PDF]

				P.T. Osmundsen, E.A. Eide, N.E. Haabesland, D. Roberts, T.B. Andersen, M. Kendrick, B. Bingen, A. Braathen, and T.F. Redfield Kinematics of the Hoybakken detachment zone and the More-Trondelag Fault Complex, central Norway Journal of the Geological Society, March 1, 2006; 163(2): 303 - 318. [Abstract] [Full Text] [PDF]

				O.M. Saether, D. Roberts, and C. Reimann Structural control of strontium concentrations in stream sediments: an example from major fault zones in central Norway Geochemistry: Exploration, Environment, Analysis, May 1, 2005; 5(2): 183 - 188. [Abstract] [Full Text] [PDF]