New insights into the geology of high-grade Caledonian marbles based on isotope chemostratigraphy

Abstract

Despite abundant petrological and structural studies, as well as geological mapping, performed over several decades in the North-Central Norwegian Caledonides by both Norwegian and international research teams (Foslie 1946, 1949; Gustavson 1966, 1972, 1974a, 1974b; Bartley 1981; Boyd 1983; Boyd & Sovegjarto 1983; Boyd et al. 1986; Tull et al. 1985; Steltenpohl 1987; Steltenpohl & Bartley 1987; Steltenpohl et al. 1990; Tucker et al. 1990; Oliver & Krogh 1995; Andresen & Steltenpohl 1994; Coker et al. 1995; Northrup 1997), little research and detailed geological mapping has been done on marble formations in the Norwegian Caledonides. At the Geological Survey of Norway, a special project entitled ‘Carbonate formations of Norway: from basic research to industry’ has been launched to study depositional environments, metamorphism, stratigraphic correlation and ages of marble formations in selected regions of the Norwegian Caledonides. With the main goal of the project being to develop an exploration strategy for new marble deposits, a significant amount of basic research has been required in order to establish a reliable tectonostratigraphic base that aims at discriminating between the local and regional factors leading to the formation of carbonate deposits of different kinds. The Ofotenfjord area (Fig. 1) has been chosen as a first-priority target because of the presence there of a vast volume of marbles constituting part of the Uppermost Allochthon in that region. The main objectives of this contribution are (i) to illustrate the use of isotope stratigraphy for indirect dating, subdivision and correlation of high-grade marble sequences; and (ii) to demonstrate progress towards the production of a new generation of geological maps in highgrade metamorphic terranes, as based on detailed mapping combined with strontium and carbon isotope stratigraphy.