Jean Michot

UPb and RbSr geochronology of the eastern part of the south Rogaland igneous complex, southern Norway

Abstract The successive intrusive events in the eastern part of the south Rogaland anorthosito-mangeritic complex have been dated by the UPb method applied to zircon, sphene, monazite, uraninite and accessorily by the RbSr whole rock isochron method. The whole magmatic activity in that part of the complex takes place in a short time interval: between 955 m.y., the intrusion age of the Bjerkrem-Sogndal layered norites, and 910 m.y., the emplacement age of a pergmatite in the Lyngdal granodiorite. The UPb geochronological data are consistent with field and petrological data on origin and mutual relations of the intrusives. The RbSr data give incoherent results probably due to open system behaviour in some cases.

The 1160 ma hidderskog meta-charnockite - implications of this a-type pluton for the sveconorwegian belt in vest agder (sw norway)

Abstract The Hidderskog massif is a charnockitic intrusion located in the Rogaland-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 interpreted as the magmatic emplacement age. The Hidderskog charnockitic intrusion is deformed and at a large scale concordant with amphibolite facies gneisses. It has been partially transformed to amphibole-biotite gneiss during the main Sveconorwegian orogeny (1040mdash;980 Ma in Rogaland). Major and trace element composition as well as isotopic systems have been 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 correlated in age with the Gloppurdi and Botnavatnet intrusions of Rogaland and tentatively to the Hovdefjell and Gjeving charnockites of the Bamble sector. This group of charnockitic intrusions defines an intraplate anorogenic geodynamic environment prior to the main Sveconorwegian orogenic phase. These anorogenic charnockites are distinct from the charnockitic magmas spatially related to the Rogaland anorthosite complex, which intruded after the main Sveconorwegian orogeny within a short period of time, from around 950 to 930 Ma.

K-Rich Calc-Alkaline Augen Gneisses of Grenvillian Age in SW Norway: Mingling of Mantle-Derived and Crustal Components

Augen gneisses were emplaced as phenocryst-bearing granodiorites at

Pétrographie et géochronologie Rb-Sr de la transition calco-alcaline - alcaline fini-panafricaine dans l'Adrar des Iforas (Mali): accrétion crustale au Précambrien supérieur

1040 \pm 40 Ma

Anorthosites and their environment

to the west of the Sveconorwegian belt (Rogaland-Vest-Agder, SW Norway) just before the main Sveconorwegian (Grenvillian) metamorphic event. They define a typical K-rich calc-alkaline trend. Initial Sr and Nd isotopic ratios are close to Bulk Earth values at 1040 Ma: (

Acid leaching experiments on the mantle-derived vitim clinopyroxenes: implications for the role of clinopyroxenes in the mantle processes

I_{Sr} = 0.7036