Isotopic composition, deposition ages and environemnts of Central Norwegian Caledonian marbles

摘要: The CO, 0-, and Sr-isotopic chemistry of 48 samples of Central Norwegian Caledonian marbles and metalimestones are used to constrain the extent of post-depositional fluid-carbonate and silicate-carbonate exchange and the sedimentary ages and environments. The marbles occur mainly at three tectonostratigraphical levels:(1) the Helgeland Nappe Complex (HNC) of the Uppermost Allochthon;(2) the Kbli-equivalent nappes (KN); and (3) the Seve-equivalent nappes (SN) of the Upper Allochthon. The carbonates in the KN and SN are closely associated with, and are generally deposited on, mafic metavolcanic rocks. The KN-rocks are generally in the greenschist facies and have undergone comparatively little deformation. The carbonates are partly fossiliferous and were deposited on Ordovician ophiolite and island arc fragments talling within two main age groups: 500-470 Ma and 443-437 Ma (Roberts et al. 1984, Pedersen et al. 1992).The SN-units in the Vestranden gneiss complex are metamorphosed in the amphibolite to granulite facies and have undergone extensive and complex deformation (Solli 1989). Most of the sampled SN-units occur as strongly flattened and isoclinally infolded bands in the basement gneisses. At several locations the marble units are tectonically thickened and thinned by plastic flow. Based on observations further east (in Sweden) the SN originated in the outermost part of the early passive margin of Baltica, and experienced metamorphism up to eclogite facies just prior to 500 Ma (Mark et al. 1985, Dallmeyer & Gee 1986, Andreasson & Gee 1989). The HNC includes two lithologically distinct groups:(1) nappes …