Chemostratigraphic constraints on the time of deposition of carbonate rocks in the Karasjok Greenstone Belt, northern Norway.

The time of deposition of the rocks of the Karasjok Greenstone Belt, the most continuous and longest, linear Precambrian terrane in northern Norway, remains poorly dated. The belt is composed of several volcanic and sedimentary formations including a continuous unit of calcite and dolomite marbles. Most rocks have been strongly deformed and altered under amphibolite-facies metamorphism. Carbon isotope chemostratigraphy has been applied to provide an apparent depositional age of carbonate units and associated sedimentary and volcanic rocks. Thirty-eight samples representing marbles in four different locations in the northern part of the belt show high δ13Ccarb values, hence recording the Palaeoproterozoic Lomagundi-Jatuli isotopic event. The least-altered δ13Ccarb values suggest the presence of two isotopically different assemblages (+8 to +9‰ and +12 to +14‰) whose apparent time of deposition can be constrained between 2220 and 2140 Ma, and between 2220 and 2110 Ma, respectively. [ABSTRACT FROM AUTHOR]