Deformation-related Paleozoic radiogenic lead and strontium additions in Proterozoic marbles from the Rombak-Sjangeli basement culmination, Scandinavian Caledonides

Godkänd; 1994; 20090116 (andbra)
The Sjangeli supracrustal belt occurs at the eastern margin of the Rombak-Sjangeli basement culmination that involves Proterozoic basement, which became incorporated into the Caledonian orogen as old basement faults were reactivated. The lead isotopic composition of early Proterozoic marbles from the Sjangeli supracrustal belt fall in the 206Pb/204Pb-207Pb/204Pb diagram on a linear array that is interpreted as a mixing line. Using the age of granite intrusion and Proterozoic metamorphism as source age for the lead (t1≈ 1.8 Ga), the corresponding mixing age is t1≈ 0.4 Ga, which suggests that the radiogenic lead was introduced during the Caledonian deformation of the marbles. The isotopic compositions of lead and strontium, which also is highly variable and radiogenic, are positively correlated, indicating that radiogenic lead and strontium were introduced together. Combining lead and strontium isotope data from the marbles and Paleozoic galena-calcite veins demonstrates that the lead and strontium were derived from local sources with isotopically distinct characteristics. Sample suites from deformed marbles that define linear arrays in the 206pb/204pb-207pb/204pb diagram probably represent mixing lines rather than secondary isochrons.

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