NDLI: Petrology of mafic lavas within the Onega plateau, central Karelia: evidence for 2.0 Ga plume-related continental crustal growth in the Baltic Shield

Content Provider	Springer Nature Link
Author	Puchtel, I. S. Arndt, N. T. Hofmann, A. W. Haase, K. M. Kröner, A. Kulikov, V. S. Kulikova, V. V. Garbe Schönberg, C. D. Nemchin, A. A.
Copyright Year	1998
Abstract	The Onega plateau constitutes part of a vast continental flood basalt province in the SE Baltic Shield. It consists of Jatulian-Ludikovian submarine volcanic, volcaniclastic and sedimentary sequences attaining in places 4.5 km in thickness. The parental magmas of the lavas contained ∼10% MgO and were derived from melts generated in the garnet stability field at depths 80–100 km. The Sm-Nd mineral and Pb-Pb whole-rock isochron ages of 1975 ± 24 and 1980 ± 57 Ma for the upper part of the plateau and a SHRIMP U-Pb zircon age of 1976 ± 9 Ma for its lower part imply the formation of the entire sequence within a short time span. These ages coincide with those of picrites in the Pechenga-Imandra belt (the Kola Peninsula) and komatiites and basalts in the Karasjok-Kittilä belt (Norway and Finnmark). Together with lithostratigraphic, chemical and isotope evidence, these ages suggest the derivation of the three provinces from a single large (∼2000 km in diameter) mantle plume. These plume-generated magmas covered ∼600,000 km2 of the Baltic Shield and represent a major contribution of juvenile material to the existing continental crust at 2.0 Ga. The uppermost Onega plateau lavas have high (Nb/Th)N = 1.4–2.4, (Nb/La)N= 1.1–1.3, positive ɛNd(T) of +3.2 and unradiogenic Pb-isotope composition (μ1 = 8.57), comparable with those of modern oceanic plume-derived magmas (oceanic flood basalt and ocean island basalt). These parameters are regarded as source characteristics. The lower sequences have (Nb/Th)N= 0.58–1.2, (Nb/La)N= 0.52–0.88 and ɛNd(T) =−2.6. They have experienced mixing with 10–30% of continental crust and resemble contaminated lavas from other continental flood basalt provinces. The estimated Nb/U ratios of 53 ± 4 in the uncontaminated rocks are similar to those found in the modern mantle (∼47) suggesting that by 2.0 Ga a volume of continental crust similar to the present-day value already existed.
Starting Page	134
Ending Page	153
Page Count	20
File Format	PDF
ISSN	00107999
Journal	Contributions to Mineralogy and Petrology
Volume Number	130
Issue Number	2
e-ISSN	14320967
Language	English
Publisher	Springer-Verlag
Publisher Date	1998-01-29
Publisher Place	Berlin/Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Content Type	Text
Resource Type	Article
Subject	Geochemistry and Petrology Geophysics

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