TY - JOUR

T1 - 2.4 Ga Mafic Dikes and Sills of Northern Fennoscandia

T2 - Petrology and Crustal Evolution

AU - Erofeeva, K. G.

AU - Stepanova, A. V.

AU - Samsonov, A. V.

AU - Larionova, Yu O.

AU - Egorova, S. V.

AU - Arzamastsev, A. A.

AU - Kovalchuk, E. V.

PY - 2019/1/1

Y1 - 2019/1/1

N2 - New petrographic, geochemical, and Sm-Nd isotopic data provide constraints on the petrogenesis of ca. 2400 Ma gabbronorite, picrodolerite and dolerite mafic sills and dikes in the Liinakhamari and Sorvaranger areas, Kola–Norwegian terrane, Northern Fennoscandia. The sills are differentiated. Their chilled margins are composed of porphyritic picrodolerite with olivine (Fo 92-81 ) and clinopyroxene (Mg# = 85–80) phenocrysts enclosed by quenched groundmass with intergrows of fan-shaped branched plagioclase grains and clinopyroxenes. The bottom of the sills are usually composed of cumulative olivine gabbronorite upsection followed by olivine gabbro, gabbro, and quartz-bearing dolerites. Picrodolerite and dolerite dikes are close to chilled margins and evolved quartz-bearing dolerites from the upper parts of picrodolerite sills, correspondingly, in terms of mineral and chemical composition. The distribution of trace elements in sills sections is caused by fractionation crystallization of picrodolerite magma with a leading role of gravity settling of olivine phenocrysts. Variations of neodymium isotopic composition in the cumulative gabbronorites in the lower (ε Nd from –0.25 to +0.82) and dolerites in the upper (ε Nd from –0.85 to –2.4) parts of the sills are probably related with an addition of crustal contaminant into the magma after phenocrysts crystallization. Doleritic dikes have more radiogenic neodymium isotopic composition (ε Nd = –0.10) in comparison with dolerites of sills that suggests lower degrees of crustal contamination in dikes. Evaluation of conditions of phenocrysts crystallization using mineral thermobarometers and modelling of crystallization using alphaMELTS indicate that the main stage of the evolution of ca. 2400 Ma mafic melts was probably related with high degrees of fractional crystallization and crustal contamination of high-Mg (MgO ~ 18 wt %) primary melt in the upper crust at P =1–4 kbar. Ca. 2400 Ma mafic intrusions in the Kola–Norwegian terrane are similar with coeval mafic dikes in Troms area in the Northern Fennoscandia, basaltic komatiites of Vetreny Belt and doleritic dikes of Kostomuksha area in the Karelian Craton in terms of petrographic, geochemical and Sm-Nd isotopic characteristics. It suggests that studied mafic sills and dikes in the Kola–Norwegian terrane could be considered as a component of ca. 2400 Ma large igneous province in the Fennoscandia.

AB - New petrographic, geochemical, and Sm-Nd isotopic data provide constraints on the petrogenesis of ca. 2400 Ma gabbronorite, picrodolerite and dolerite mafic sills and dikes in the Liinakhamari and Sorvaranger areas, Kola–Norwegian terrane, Northern Fennoscandia. The sills are differentiated. Their chilled margins are composed of porphyritic picrodolerite with olivine (Fo 92-81 ) and clinopyroxene (Mg# = 85–80) phenocrysts enclosed by quenched groundmass with intergrows of fan-shaped branched plagioclase grains and clinopyroxenes. The bottom of the sills are usually composed of cumulative olivine gabbronorite upsection followed by olivine gabbro, gabbro, and quartz-bearing dolerites. Picrodolerite and dolerite dikes are close to chilled margins and evolved quartz-bearing dolerites from the upper parts of picrodolerite sills, correspondingly, in terms of mineral and chemical composition. The distribution of trace elements in sills sections is caused by fractionation crystallization of picrodolerite magma with a leading role of gravity settling of olivine phenocrysts. Variations of neodymium isotopic composition in the cumulative gabbronorites in the lower (ε Nd from –0.25 to +0.82) and dolerites in the upper (ε Nd from –0.85 to –2.4) parts of the sills are probably related with an addition of crustal contaminant into the magma after phenocrysts crystallization. Doleritic dikes have more radiogenic neodymium isotopic composition (ε Nd = –0.10) in comparison with dolerites of sills that suggests lower degrees of crustal contamination in dikes. Evaluation of conditions of phenocrysts crystallization using mineral thermobarometers and modelling of crystallization using alphaMELTS indicate that the main stage of the evolution of ca. 2400 Ma mafic melts was probably related with high degrees of fractional crystallization and crustal contamination of high-Mg (MgO ~ 18 wt %) primary melt in the upper crust at P =1–4 kbar. Ca. 2400 Ma mafic intrusions in the Kola–Norwegian terrane are similar with coeval mafic dikes in Troms area in the Northern Fennoscandia, basaltic komatiites of Vetreny Belt and doleritic dikes of Kostomuksha area in the Karelian Craton in terms of petrographic, geochemical and Sm-Nd isotopic characteristics. It suggests that studied mafic sills and dikes in the Kola–Norwegian terrane could be considered as a component of ca. 2400 Ma large igneous province in the Fennoscandia.

KW - BALTIC SHIELD

KW - COMPLEX

KW - GEOCHEMISTRY

KW - KARELIAN CRATON

KW - KOLA-PENINSULA

KW - Kola-Norwegian terrane

KW - LARGE IGNEOUS PROVINCE

KW - MANTLE

KW - Paleoproterozoic

KW - RUSSIA

KW - SCOURIE DYKE SWARM

KW - SM-ND

KW - large igneous province

KW - mafic sills

UR - http://www.scopus.com/inward/record.url?scp=85064549375&partnerID=8YFLogxK

U2 - 10.1134/S0869591119010016

DO - 10.1134/S0869591119010016

M3 - Article

AN - SCOPUS:85064549375

VL - 27

SP - 17

EP - 42

JO - Petrology

JF - Petrology

SN - 0869-5911

IS - 1

ER -