Geochronology and chemostratigraphy of the 2.47–1.96 Ga rift-related volcano-sedimentary succession in the Karasjok Greenstone Belt, northern Norway, and its regional correlation within the Fennoscandian Shield

Abstract

New geochronological data for the amphibolite-facies volcano-sedimentary Karasjok Greenstone Belt in northwestern Fennoscandia bracket its age between 2.47 and 1.96 Ga. The volcano-sedimentary units were deposited on the 3005 ± 24 to 2776 ± 69 Ma crystalline basement rocks of the Jergul Gneiss Complex. The lowermost Vuomegielas Formation contains rhyodacites dated at 2469 ± 12 Ma that were deposited in an intracratonic rift setting related to the Matachewan mantle plume event. The overlying Skuvanvárri Formation, correlative with the early Jatulian (c. 2.2 Ga) units on the Fennoscandian Shield, consists of siliciclastic sedimentary rocks deposited in coastal deltaic and shallow-marine settings. The overlying mid-Jatulian Gollebáiki Formation contains 2151 ± 5 Ma mafic intrusions and tholeiitic basalts related to a rifting event and breakup of the Superia supercraton that resulted in voluminous volcanic and shallow-marine deposits. The Ni-Cu-PGE-mineralized Porsvann intrusion, hosted by the Gollebáiki Formation, yielded an age of 2056 ± 10 Ma, which corresponds with other Ni-Cu-PGE-bearing intrusions on the Fennoscandian Shield. The uppermost Báhkilvárre Formation consists of basalts, komatiites, and andesitic lavas. A synvolcanic gabbro within the komatiites in the lower part of the formation yielded an age of 1984 ± 16 Ma. Andesites in the upper part of the same formation were dated at 1961 ± 1 Ma. They represent the final Paleoproterozoic magmatic event that affected large areas of the Fennoscandian Shield prior to the Lapland-Kola and Svecofennian orogenies. Carbon isotope values for carbonates of the Skuvanvárri and Gollebáiki formations range up to highly positive (+12.4 ‰) values, corresponding to the c. 2.22–2.06 Ga Lomagundi carbon isotope excursion. In contrast, carbonates from the Báhkilvárre Formation do not yield elevated δ13C values, indicating that it was deposited in the aftermath of the Lomagundi carbon isotope excursion. New geochronologic and chemostratigraphic data for the Karasjok Greenstone Belt support correlation with the early Paleoproterozoic sedimentary successions deposited on the eastern margin of the Superior craton and position the northern-northwestern margin of the Karelia-Kola craton against the eastern margin of the Superior craton between c. 2.5 and 2.05 Ga.