| Popis: |
Crust forming processes in the Setesdalen area in the central part of southern Norway are dominated by the development of pre-Sveconorwegian supracrustal rocks (immature clastic sediments and bimodal volcanics) with an assumed depositional age of 1150–1100 Ma and by the emplacement of scattered infracrustal granitoids. The supracrustal rocks were deposited on a partly older than 1300 Ma gneissic basement including rocks which may have suffered one or more pre-Sveconorwegian orogeneses. During the Sveconorwegian orogeny, with the main upper greenschist to middle amphibolite facies high-temperature metamorphism and deformational phases in the period 1060–970 Ma, igneous activity comprising K-rich rocks high in elements such as P, Ti, La, Sr, Zr, and LREE and Ba was dominant. Significantly younger than this activity is the development of many REE pegmatites which are so characteristic for the region. The Precambrian geological activity terminated (at about 830 Ma?) with the development of E-W trending tholeiitic dolerites. |
