Petrology of a 2.41 Ga remarkably fresh komatiitic basalt lava lake in Lion Hills, central Vetreny Belt, Baltic Shield

Abstract

In the central Vetreny Belt, southeastern Baltic Shield, an areally extensive 110 m deep lava lake is exposed consisting of remarkably fresh differentiated komatiitic basalt. During eruption, the liquid had a temperature of 1380-1400 °C and contained &15% MgO. The lava ponded in a large topographic depression soon after eruption. The differentiation of the lava lake was controlled by settling of transported olivine and chromite phenocrysts and caused the origin of prominent internal layering. The last portions of the trapped liquid crystallized at temperatures of 1250-1070 °C. A Sm-Nd isochron of 2410$34 Ma for whole rock samples, olivine, augite and pigeonite separates from the lava lake provides a reliable estimate for the time of formation of the uppermost sequences in the Vetreny Belt. This age is in good agreement with the Sm-Nd and Pb-Pb isochron ages of 2449$35 and 2424$178 Ma for the volcanic rocks from the same stratigraphic level in the northwestern Vetreny Belt. Modeling of Nd-isotopes and major and trace elements shows that the komatiitic basalts at Lion Hills may have had a komatiite parent depleted in highly incompatible elements. It can be shown that this initial liquid I.S. Puchtel ( ) • A.

Komatiites constrain molybdenum isotope composition of the Earth's mantle

“…compositions of these chromites were also analyzed and are reported in Table S3; these are similar to 208 those reported in Puchtel et al (1996) …”

“…MgO content of the liquidus olivine in this system (i.e., ~48 wt.%, Puchtel et al, 1996), demonstrating …”

Geochronology of the Palaeoproterozoic Kautokeino Greenstone Belt, Finnmark, Norway: Tectonic implications in a Fennoscandia context

“…9A, B). Rare-earth (Balashov et al, 1993(Balashov et al, ), c. 2450 Ma plutons from the Belomorian Craton (Lobach-Zhuchenko et al, 1998), c. 2450-2428 Ma plutons from the Karelian Craton (Huhma et al, 1990;Amelin & Semenov, 1996;Perttunen & Vaasjoki, 2001;Hanski et al, 2001bHanski et al, ), c. 2450Hanski et al, -2410 Ma volcanic rocks from Vetreny Belt (Puchtel et al, 1996(Puchtel et al, , 1997(Puchtel et al, ), c. 2440 Onkamo Group volcanic rocks (Hanski & Huhma, 2005), c. 2403 Ma Ringvassøy dykes (Kullerud et al, 2006(Kullerud et al, ), c. 2504(Kullerud et al, , 2450(Kullerud et al, , 2310(Kullerud et al, and 2140 Ma dykes in the Karelian Craton (Amelin & Semenov, 1996;Mertanen et al, 2006;Stepanova et al, 2014Stepanova et al, , 2015, c. 2330 Ma Runkaus volcanic rocks in Peräpohja Schist Belt (Huhma et al, 1990), c. 2220 Ma Haaskalehto-type sills and dykes (Huhma et al, 1990;Hanski et al, 2010), 2137 ± 5 Ma amphibolite of Čáskejas Formation (deep pink; Krill et al, 1985) and davidite of the Bidjovagge deposit (pale pink; Bjørlykke et al, 1990) in the Kautokeino Greenstone Belt, c. 2090 Ma Jouttiaapa volcanic rocks in Peräpohja Schist Belt (Huhma et al, 1990(Huhma et al, ), c. 2085 Ma komatiites in the Karasjok Greenstone Belt (Henriksen, 1983;Krill et al, 1985), c. 2060 Ma Siilinjärvi volcanic rocks (Lahtinen et al, 2015b), c. 2060Ma Jeesiörova and Peuramaa komatiites in Savukoski Group in Central Lapland Greenstone Belt (Hanski et a...…”

“…They are interesting for a number of reasons. The mafic magmatic rocks provide a unique window into the evolution of the mantle during the Palaeoproterozoic (e.g., Puchtel et al, 1996). Sedimentary rocks record some of the conditions prevailing in the hydrosphere and atmosphere during the very specific period of the Earth's history when the atmosphere became oxidising (e.g., Melezhik et al, 2015b).…”

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

“…High-Mg basalts (basaltic komatiites) are less abundant. The section is completed with dacite and rhyolite dated at 2.44-2.42 Ga and 2.32 Ga subaerial andesite [Melezhik, Sturt, 1994;Smolkin et al, 1995;Amelin et al, 1995;Mints et al, 1996;Puchtel et al, 1996;Melezhik et al, 2012]. The geochemistry of the mafic volcanic rocks indicates relations to plume or T-MORB types.…”