Age and isotopic geochemical characteristics of Archean carbonatites and alkaline rocks of the Baltic shield

Abstract

Paradoxically, the lists of "proxies" of both plate-and plume-related settings are devoid of even a mention of the high-grade metamorphic rocks (granulite, amphibolite and high-temperature eclogite facies). However, the granulite-gneiss belts and areas which contain these rocks, have a regional distribution in both the Precambrian and the Phanerozoic records. The origin and evolution of the granulite-gneiss belts correspond to the activity of plumes expressed in vigorous heating of the continental crust; intraplate magmatism; formation of rift depressions filled with sediments, juvenile lavas, and pyroclastic flow deposits; and metamorphism of lower and middle crustal complexes under conditions of granulite and high-temperature amphibolite facies that spreads over the fill of rift depressions also. Granulite-gneiss complexes of the East European Craton form one of the main components of the large oval intracontinental tectonic terranes of regional or continental rank. Inclusion of the granulite-gneiss complexes from Eastern Europe, North and South America, Africa, India, China and Australia in discussion of the problem indicated in the title to this paper, suggests consideration of a significant change in existing views on the relations between the plate-and plume-tectonic processes in geological history, as well as in supercontinent assembly and decay. The East European and North American cratons are fragments of the long-lived supercontinent Lauroscandia. After its appearance at ~2.8 Ga, the crust of this supercontinent evolved under the influence of the sequence of powerful mantle plumes (superplumes) up to ~0.85 Ga. During this time Lauroscandia was subjected to rifting, partial breakup and the following reconstruction of the continent. The processes of plate-tectonic type (rifting with the transition to spreading and closing of the short-lived ocean with subduction) within Lauroscandia were controlled by the superplumes. Revision of the nature of the granulite-gneiss complexes has led to a fundamental new understanding of: a more important role than envisaged previously for mantle-plume processes in the juvenile additions to the continental crust, especially during the Neoarchaean-Proterozoic; the existence of the supercontinent Lauroscandia from ~2.80 to 0.85 Ga; the leading role of mantle plumes in the interaction of plate-and plume-tectonics in the Neoarchaean-Proterozoic history of Lauroscandia and perhaps of the continental crust as a whole. We propose that the evolution of the geodynamic settings of the Earth's crust origin can be represented as a spiral sequence: the interaction of mantle-plume processes and embryonic microplate tectonics during the Palaeo-Mezoarchaean (~3.8-2.8 Ga) → plume-tectonics and local plume-driven plate-tectonics (~2.80-0.55 Ga) → Phanerozoic plate tectonics along with a reduced role of mantle plumes.Key words: Precambrian; plate-tectonics; plume-tectonics; granulite-gneiss belts; supercontinent; intracontinent oval orogenRecommended by E.V. Sklyarov Аннотация: Ка...

Ore geochemistry, zircon mineralogy, and genesis of the Sakharjok Y-Zr deposit, Kola Peninsula, Russia

“…The U-Pb zircon age of nepheline syenite is esti mated at 2613 ± 35 Ma, and this date interpreted as the time of magma crystallization (Bayanova, 2004;Zozulya et al, 2007). Numerous U-Pb, Rb-Sr, and K-Ar determinations at 1810-1680 Ma (Batieva and Bel'kov, 1984;Zozulya et al, 2005) correspond to the superposed events of the Svecofennian regional meta morphism.…”

“…Numerous U-Pb, Rb-Sr, and K-Ar determinations at 1810-1680 Ma (Batieva and Bel'kov, 1984;Zozulya et al, 2005) correspond to the superposed events of the Svecofennian regional meta morphism. The zircon age of alkali syenite is 2682 ± 10 Ma (Zozulya et al, 2007) and thus suggests its genetic link to the Keivy alkali granites with reliable isotopic age of 2650-2670 Ma (Mitrofanov et al, 2000;Zozulya et al, 2005).…”

“…Third, zircon from the Sakharjok deposit is practically free of detrimental impurities. As follows from the U-Pb isotopic study, the U content in zircon is only 68-86 ppm (Zozulya et al, 2007), whereas zir con from rare metal alkali granites contains hundreds to a thousand ppm or higher (Kovalenko et al, 2004;Yarmolyuk et al, 2010;Kerr et al, 1993;Fetter and Goldberg, 1995;Zozulya et al, 2005;Abdalla et al, 2009).…”

U-Pb ID-TIMS age of the Tiksheozero carbonatite: expression of 2.0 Ga alkaline magmatism in Karelia, Russia

“…The majority, including the economically most important ones, formed in the Paleozoic but there are also several older generations reaching into the Paleoproterozoic and the Neoarchean [1][2][3][4][5][6][7][8]. Al- * E-mail: fernando.corfu@geo.uio.no kalic complexes witness episodes of mantle activity, generally related to extensional tectonic processes in the crust [e.g.…”

Britholite ores of the Sakharjok Zr–Y–REE deposit, Kola Peninsula: Geochemistry, mineralogy, and formation stages

“…The nepheline syenite, essexite, and alkali syenite of the Sakharjok Massif define U-Pb zircon ages of 2613 ± 35 Ma, 2666 ± 10 Ma, and 2682 ± 10 Ma (Bay anova, 2004;Zozulya et al, 2007), which indicates very ancient, Late Archean age of the alkaline magmatism of the Keivy terrane. In addition, ages within 1760-1810 Ma were obtained by U Pb dating on zircon, brit holite, and allanite and by Rb-Sr and K-Ar whole rock dating (Zozulya et al, 2005;Pushkarev et al, 1978), which presumably mark the overprint of the Sve cofennian regional metamorphism.…”