Petrological and geochemical aspects of the formation of Devonian plume-riftogenic volcanics of the Rastayskiy and Saralinskiy grabens (Kuznetskiy Alatau)

Abstract

The Saralinskiy and Rastayskiy grabens are the largest in the Kuznetsk-Alatau frame of the Minusinsk Trough. The peculiarity of their structural position is their location in the zone of juxtaposition of the axial depression zone (Minusinsk-Tuvinian) with the Kuznetsk-Alatau framing uplift (western shoulder) of the Devonian Altay-Sayan paleorift (Fig. 1). Fig. 1 – Tectonic scheme of morphostructures of the Devonian stage of development of the Kuznetsk Alatau and adjacent structures of the Minusinsk Trough   The volcanites of the studied grabens were formed under intraplate plume-riftogenic conditions under the influence of heat and plume fluids, which was expressed in their specialization in Al2O3, CaO, ΣFe2O3, Na2O, K2O, TiO2, as well as Cs, Rb, Ba, Sr, U, Th, Nb, Ta, Zr, REE characteristic of the rift systems of the world (Fig. 2). The mantle protolith generated high-aluminous, alkaline magmas at low degrees of its melting (up to 3 % at Rastay and up to 10 % at Sarala) (Fig. 2d). The composition of the protolith corresponded to spinel and spinel-garnet lherzolites (Fig. 2d). The magmogenesis system was animated by plume emanations involving fluid-magmatic interaction of plume matter and protolith. Within the lithosphere and crust, due to fluid saturation, the melts interacted with different depth lithospheric matter labelled E-MORB, EM2, IAB, and lower and middle crustal matter (Fig. 2), preserving plume labels. Fig. 2 – Source diagrams of the melting parameters and geodynamic setting of the Rastayskiy and Saralinskiy graben volcanism: a – [Kelemen et al., 2003]; b – [Condie, 2005]; c – [Tarun et al., 2015]; d – [Bi et al., 2015]; e-f – Rastayskiy (e) and Saralinskiy (f) [Pearce et al., 2021]. According to the proposed geochemical classification of plumes [Pears et al., 2021], the graben magmatites are clearly plume in nature (Fig. 2e, f). Differentials of primary magmas extend into the IAB and CAB quadrangle, characterizing the composition of metasomatized lithospheric mantle, corresponding to recycled back-arc oceanic basalts of subducted mantle and interacted with crustal matter. In this trend, they belong to type IIIab plume [Pears et al., 2021]. Bi J.-H., Ge W.-C., Yang H., Zhao G.-C., Xu W.-L., Wang, Z.-H. 2015. Geochronology, geochemistry and zircon Hf isotopes of the Dongfanghong gabbroic complex at the eastern margin of the Jiamusi Massif, NE China: Petrogensis and tectonic implications. Lithos, 234–235, 27-46, Condie K.C. High field strength element ratios in Archean basalts: a window to evolving sources of mantle plumes?, Lithos, 79, 491-504. Kelemen, P. B., Hanghøj, K., & Greene, A. R. 2003. One view of the geochemistry of subduction-related magmatic arcs, with an emphasis on primitive andesite and lower crust. Treatise on geochemistry, 3, 659. Khanna T.C., Sesha S.V.V., Bizimis M., A. Keshav Krishna K. 2015. Petrogenesis of basalt–high-Mg andesite–adakite in the Neoarchean Veligallu greenstone terrane: Geochemical evidence for a rifted back-arc crust in the eastern Dharwar craton, India. Precambrian Research, 258, 260-277. Pearce J.A., Ernst R.E., Peate D.W., Rogers C. 2021. LIP printing: Use of immobile element proxies to characterize Large Igneous Provinces in the geologic record. Lithos, 392–393,106068.