caa a22 4500 465790968 CHVBK 20180323112024.0 cr unu---uuuuu 170327e19900301xx s 000 0 eng 10.1007/BF00321491 doi (NATIONALLICENCE)springer-10.1007/BF00321491 Sm−Nd and Pb isotopic study of mafic rocks associated with early Proterozoic continental rifting: the Peröpohja schist belt in northern Finland [Elektronische Daten] [Hannu Huhma, Robert Cliff, Vesa Perttunen, Matti Sakko] The Peräpohja schist belt in northern Finland rests unconformably on Archaean granitoids, and marks the early stages of Proterozoic crustal evolution in the Fennoscandian (Baltic) shield. 2440 Ma old layered mafic intrusions predate the supracrustal , and ca. 2200 Ma old sills of the gabbro-wehrlite association intrude the lowest quartzites and volcanics (Runkaus) of the sequence. The Sm-Nd mineral isochron of the Penikat layered intrusion gives an age of 2410±64 Ma. The initial ɛNd-values of the Penikat intrusion (ɛNd(2440) = −1.6) and the Runkausvaara sill (ɛNd(2200) ≈ 0) suggest that these mafic magmas were contaminated by older crustal material. The Sm-Nd and Pb isotopic results on the 2.44-2.2 Ga old Runkaus volcanics indicate mobility of Pb, fractionation of Sm/Nd during "late” greenschist facies metamorphism, and crustal contamination. The Pb-Pb data provide an age of 1972±80 Ma with a high initial 207Pb/204Pb ratio (μ1 = 8.49), while scattered Sm-Nd data result in an imprecise age of 2330±180 Ma, with an initial ɛNd-value of about zero. Secondary titanite gives an U-Pb age of ca. 2250 Ma. The Jouttiaapa basalts, in contrast, ascended from the mantle without interaction with older crust. These LREE depleted tholeiites mark a break in continental sedimentation, and yield a Sm-Nd age of 2090±70 Ma. Their initial ɛNd = + 4.2 ±0.5 implies that the subcontinental early Proterozoic mantle had been depleted in LREE for a long period of time. The first lava flows are strongly depleted in LREE, suggesting that their source was significantly more depleted than the source of mid-ocean ridge basalts today. Springer-Verlag, 1990 Huhma Hannu Geological Survery of Finland, SF-02150, Espoo, Finland aut Cliff Robert Department of Earth Sciences, University of Leeds, LS2 9JT, GB-Leeds, England aut Perttunen Vesa Geological Survey of Finland, SF-96101, Rovaniemi, Finland aut Sakko Matti Geological Survery of Finland, SF-02150, Espoo, Finland aut Contributions to Mineralogy and Petrology Springer-Verlag 104/3(1990-03-01), 369-379 0010-7999 104:3<369 1990 104 410 https://doi.org/10.1007/BF00321491 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00321491 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Huhma Hannu Geological Survery of Finland, SF-02150, Espoo, Finland aut NATIONALLICENCE 700 1- Cliff Robert Department of Earth Sciences, University of Leeds, LS2 9JT, GB-Leeds, England aut NATIONALLICENCE 700 1- Perttunen Vesa Geological Survey of Finland, SF-96101, Rovaniemi, Finland aut NATIONALLICENCE 700 1- Sakko Matti Geological Survery of Finland, SF-02150, Espoo, Finland aut NATIONALLICENCE 773 0- Contributions to Mineralogy and Petrology Springer-Verlag 104/3(1990-03-01), 369-379 0010-7999 104:3<369 1990 104 410 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer