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Jean-Paul Liégeois
Earth Sciences
Geodynamics and mineral resources
Geodynamics and mineral resources
Publication details
Bolle, O., Diot, H., Liégeois, J.P. & Vander Auwera, J. 2010. ‘The Farsund intrusion (SW Norway): A marker of Late-Sveconorwegian (Grenvillian) tectonism emplaced along a newly defined major shear zone’. Journal of Structural Geology. Amsterdam : Elsevier. DOI: 10.1016/j.jsg.2010.04.003. I.F. 1.427.
Article in a scientific Journal / Article in a Journal
The ca. 930 Ma Farsund intrusion (SW Norway) belongs to a series of 0.99-0.92 Ga post22
collisional plutons from the Sveconorwegian (Grenvillian) orogen. It is made of two rock
facies (charnockite and quartz mangerite, and subordinate quartz monzonite and quartz
monzodiorite) that show mingling relationships. As shown elsewhere, these two facies
belong, respectively, to the two suites of A-type affinity recognized in the Sveconorwegian
post-collisional magmatism of Southern Norway, 26 namely the AMC and HBG suites. A
structural study of the Farsund intrusion, based on the anisotropy of magnetic susceptibility
(AMS) technique, is presented here. The AMS is controlled by the shape-preferred orientation
of low-Ti titanomagnetite grains and it can be used as a proxy for the global petrofabric. The
AMS data, when combined with micro- to macrostructural observations, unfold the
occurrence of a steeply-dipping shear zone, straddling the NE border of the pluton and
characterized by a likely strike-slip component of shearing. This high-strain zone is roughly
coincident with the boundary between the outcrop domains of the AMC and HBG suites, and
was formed or, more probably, reactivated during the gravitational collapse of the
Sveconorwegian orogen, in an extensional (possibly transtensional) tectonic regime. It would
have controlled the ascent and emplacement of the Farsund intrusion, and materializes as well
the structural weakness that would have channelled the magmas of the neighbouring and
coeval Rogaland anorthosite province (RAP). It is also suggested that vertical, gravity-driven
movements were recorded in the Farsund intrusion and its close surroundings. They would
have been induced in a very hot environment, akin to that prevailing in the Precambrian ultra41
hot orogens, but linked in the present case to the emplacement of anorthosites and
penecontemporaneous igneous bodies, including the Farsund intrusion.