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Origin of acidic rocks
The acidic rocks associated with the Rogaland anorthositic complex are made of charnockites (i.e. farsundite) and of biotite/hornblende-bearing granites, these latter stretching along a 300 km long belt along the Mandal-Ustaoset line. Both types of rocks are characterized by high FeO/MgO and K2O contents and their origin remains problematic. Their ages and state of deformation (synemplacement magmatic or subsolidus deformation) are still poorly known but available data indicate that they are in general postcollisional and penecontemporaneous with the anorthositic complex of Rogaland. A petrological study of the farsundite and a selection of the biotite/hornblende bearing granites has been undertaken in order to compare their geochemical signatures and to better constrain their possible sources and conditions of crystallization. This petrological study involves major (XRF) and trace (ICPMS) elements geochemistry as well as isotopic geochemistry, experimental petrology (in collaboration with J. Longhi, Lamont-Doherty USA and B. Scaillet, CRSCM-CNRS, Orléans) and ASM (in collaboration with J.L. Bouchez, Toulouse, and H. Diot, La Rochelle). As these intrusions represent a very important volume of magma, deciphering their petrogenesis will improve our knowledge of the evolution of the Proterozoic continental crust.
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