Siberian meimechites: origin and relation to flood basalts and kimberlites

Abstract

Here we combine petrological-geochemical and thermomechanical modeling techniques to explain origin of primary magmas of both Maimecha–Kotui meimechites and the Gudchikhinskaya basalts of Norilsk region, which represent, respectively, the end and the beginning of flood magmatism in the Siberian Trap Province. We have analyzed the least altered samples of meimechites, their olivine phenocrysts, and melt inclusions in olivines, as well as samples of dunites and their olivines, from boreholes G-1 and G-3 within the Guli volcanoplutonic complex in the Maimecha–Kotui igneous province of the northern Siberian platform. The Mn/Fe and Ni/MgO ratios in olivines indicate a mantle peridotite source of meimechites. Meimechite parental magma that rose to shallow depths was rich in alkalis and highly magnesian (24 wt.% MgO), largely degassed, undersaturated by sulfide liquid and oxidized. At greater depths, it was, likely, high in CO2 (6 wt.%) and H2O (2 wt.%) and resulted from partial melting of initially highly depleted and later metasomatized harzburgite some 200 km below the surface. Trace-element abundances in primary meimechite magma suggest presence of garnet and K-clinopyroxene, in the mantle source and imply for genetic link to the sources of the early Siberian flood basalts (Gudchikhinskaya suite) and kimberlites. The analyzed dunite samples from the Guli complex have chemistry and mineralogy indicating their close relation to meimechites. We have also computed thermomechanical model of interaction of a hot mantle plume with the shield lithosphere of variable thickness, using realistic temperature- and stress-dependent visco-elasto-plastic rocks rheology and advanced finite element solution technique. Based on our experimental and modeling results we propose that a Permian–Triassic plume, with potential temperature of about 1650 °C transported a large amount of recycled ancient oceanic crust (up to 15%) as SiO2-oversaturated carbonated eclogite. Low-degree partial melting of eclogite at depths of 250–300 km produced carbonate-silicate melt that metasomatized the lithospheric roots of the Siberian shield. Further rise of the plume under relatively attenuated lithosphere (Norilsk area) led to progressive melting of eclogite and formation of reaction pyroxenite, which then melted at depths of 130–180 km. Consequantly, a large volume of melt (Gudchikhinskaya suite) penetrated into the lithosphere and caused its destabilization and delamination. Delaminated lithosphere that included fragments of locally metasomatized depleted harzburgite subsided into the plume and was heated to the temperatures of the plume interior with subsequent generation of meimechite magma. Meimechites showed up at the surface only under thicker part of the lithosphere aside from major melting zone above because otherwise they were mixed up in more voluminous flood basalts. We further suggest that meimechites, uncontaminated Siberian flood basalts and kimberlites all share the same source of strongly incompatible elements, the carbonated recycled oceanic crust carried up by hot mantle plume.

Origin of spinel-free dunite veins from northern Oman ophiolite: Possible involvement of a komatiitic melt

“…On the basis of the discrimination diagram of Hanski et al (2001), a picritic origin is precluded since picrite olivines are characterized by higher TiO 2 and Al 2 O 3 contents. A meimechitic origin is also unlikely, even with Cr 2 O 3 content of olivines closer to that measured in our dunite samples, because the olivine TiO 2 content in this type of melt is also remarkably high, reflecting the primary high -Ti character of the magma (e.g., Sobolev et al, 2009). Although boninites share appreciable chemical resemblances with our dunites (Hanski et al, 2001), their involvement is significantly weakened by the spinel -free character of some of our dunites.…”

The mechanism of magma ascent through the solid lithosphere and relation between mantle and crustal diapirism: numerical modeling and natural examples

“…The temperature of a heat source was inferred to be about 300 °C higher than the adiabatic temperature conditions at the same depth at the base of the cratonic lithosphere. This temperature estimate was substantiated in the works of Sobolev et al (2009) and Griffin et al (2013) based on the compositions of ultramafic magmas from the Maimecha-Kotui and Seiland igneous provinces. At the lateral boundaries, the horizontal velocity and heat flow were set to zero, i.e., the effect of the lateral boundaries was of minor importance.…”

Petrogenises of Triassic gabbroic and basaltic rocks from Chukotka, NE Russia: Eastern end of the ‘arc–type’ Siberian LIP?

“…Siberian LIP is one of the most voluminous (~4 × 10 6 km 3 ; Ivanov, 2007) and the representative examples of IABtype LIPs, because of the majority of the erupted low-Ti basalts are characterized by IAB-type trace element pat-terns (Puffer, 2001;Ivanov, 2007). The high-Ti series rocks (e.g., meimechites; Arndt et al, 1998;Sobolev et al, 2009) are volumetrically insignificant and commonly display OIB-type geochemical features. The IAB-type geochemical feature of the low-Ti basalts of Siberian LIP are traditionally attributed to a fingerprint of lithospheric contamination (Lightfoot et al, 1993;Reichow et al, 2005).…”