THE 1160 MA HIDDERSKOG META-CHARNOCKITE - IMPLICATIONS OF THIS A-TYPEPLUTON FOR THE SVECONORWEGIAN BELT IN VEST AGDER (SW NORWAY)

The Hidderskog massif is a chamockitic intrusion located in the Rogala nd-Vest Agder segment of the Sveconorwegian province of SW Norway. The U-Pb zircon age (1159 +/- 5 Ma) and the Rb-Sr whole-rock isochron age (1153 +/- 39 Ma) of this pluton are concordant. This age is interpret ed as the magmatic emplacement age. The Hidderskog charnockitic intrus ion is deformed and at a large scale concordant with amphibolite facie s gneisses. It has been partially transformed to amphibole-biotite gne iss during the main Sveconorwegian orogeny (1040-980 Ma in Rogaland). Major and trace element composition as well as isotopic systems have b een only weakly disturbed during this event. The Hidderskog intrusion displays A-type geochemical features. Most samples could correspond to mixing of a granitic liquid with feldspar crystals. It may be correla ted in age with the Gloppurdi and Botnavatnet intrusions of Rogaland a nd tentatively to the Hovdefjell and Gjeving charnockites of the Bambl e sector. This group of charnockitic intrusions defines an intraplate anorogenic geodynamic environment prior to the main Sveconorwegian oro genic phase. These anorogenic charnockites are distinct from the chamo ckitic magmas spatially related to the Rogaland anorthosite complex, w hich intruded after the main Sveconorwegian orogeny within a short per iod of time, from around 950 to 930 Ma.