Source-derived heterogeneities in the composite (charnockite-granite) ferroan Farsund intrusion (SW Norway)

• The Farsund intrusion is made of two intermingled coeval facies.
• The two facies belong to the two Sveconorwegian late-orogenic magmatic suites.
• The Farsund intrusion was emplaced close to a shear zone and the opx-in isograd.
• Limited differentiation occurred within each facies in the upper crust.

The Sveconorwegian late-orogenic magmatism of southern Norway (970–916 Ma) consists of two magmatic suites: the Hornblende–Biotite–Granitoids (HBG) suite and the Anorthosite–Mangerite–Charnockite (AMC) suite of the Rogaland Anorthosite Province (RAP), characterized by opx-bearing lithologies. The Farsund body comprises elements of both suites that display mingling relationships. The main facies, mostly charnockitic, contains orthopyroxene whereas a subordinate granitic facies comprises hornblende and biotite. U–Pb (zircon) isotopic data show overlapping ages of 931 ± 2 Ma for the charnockitic facies and 926 ± 4 Ma for the granitic facies. Both facies display similar extent of differentiation demonstrating that the granitic facies was not derived by fractionation from the charnockitic one. Mineralogical, geochemical and petrological data indicate that the charnockitic facies belongs to the AMC suite and the granitic facies, to the HBG suite. Strontium, Nd and Pb isotopic data show that the Farsund intrusion was emplaced at the boundary between two different lithotectonic units that are separated by the Farsund-RAP shear zone. This shear zone likely favored the emplacement of the magmas. Most of the assimilation occurred in the lower crust whereas limited differentiation likely took place in the upper crust.