Geochemical evidence of the plume nature of Devonian mafic rocks of the Rudny Altai (Northwest of the Altai-Sayan folded area)

The research area is located in the north of the Rudno-Altai megatrough. Rudny Altai region borders on the east with the Altai-Sayan folded area, where the transregional Tuva-Minusinsk-West Siberian continental rift system was formed in the Early Devonian (Fig 1). Different magmatic facies are developed: intrusives are represented by gabbro, gabbro-pyroxenites, olivine pyroxenites; effusives are flow basalts; also subvolcanic dolerites. Fig. 1 – Structural-tectonic position of the Zmeinogorsk ore district Geochemical discrimination The presence of mantle geochemical signatures is visible in the Zr/Y – Nb/Y diagram [2] (Fig. 2a): 1) volcanic rocks points are located in the OPB area within the influence of the PM reservoir; 2) intrusive rocks points position is more ambiguous – gabbros fall predominantly in the OPB, pyroxenites are more inclined to the N-MORB and IAB. The La/Lu – Gd/Yb diagram [1] (Fig. 2b) illustrates: the effusives and intrusive mafic rocks are compactly located near the MORB field, only part of the Emsian basalts extend towards the IAB. The position of the points indicates a high degree of melting of the substance at a shallow melting depth. Apparently, this is caused by the impact of the plume's anomalous heat on the upper lithosphere. The La/Yb – Zr/Nb diagram [4] (Fig. 2c) illustrates: The figurative points are partially aligned along the mantle array, being in proximity to the E-MORM. Gabbro and pyroxenites are located outside the mantle array, but are close to N-MORB. Conclusion Gabbro and olivine pyroxenites have a dual nature – plume with IAB features, which may be due to the assimilation of host rock. Gabbro and basalts are associated with E-MORBB sources. Pyroxenites have an overall depleted background of trace elements and associated with N-MORB. The Emsian mafic rocks of the Aleisk granite-metamorphic dome are similar to the basalts of the Zmeinogorsk trough [3], synchronously erupting in the adjacent depression zone. 1 – pyroxenites (D1e); 2 – gabbro (D1e); 3 – gabbro-dolerite (D3f); 4 – basalts (D1е); 5 – subvolkanic dolerites (D2ef); 6 – compositional area of volcanics of the Zmeinogorsk trough; 7 – compositional area of intrusions of the Aleisk granite-metamorphic dome References: Boyce J.A., Nicholls I.A., Keays R.R., Hayman P.C. Variation in parental magmas of Mt Rouse, a complex polymagmatic monogenetic volcano in the basaltic intraplate Newer Volcanics Province, southeast Australia // Contributions to Mineralogy and Petrology. 2015. Vol. 169(11). DOI: 10.1134/S0869591121010082. Condie K.C. High field strength element ratios in Archean basalts: a window to evolving sources of mantle plumes? // Lithos. 2005. Vol. 79(3–4). P. 491–504. DOI: 10.1016/j.lithos.2004.09.014. Semiryakov A.S., Grinev O.M., Bestemyanova K.V., Grinev R.O., Morozova E.N., Adylbaev R.R. Plume component and geochemical convergence features of Emsian-Eifelian mafic rocks of the Northeastern Rudny Altai // Advances in Current Natural Sciences. 2023. № 11. P. 138–146. DOI: 10.17513/use.38155. (In Russian) Yang G., Li Y., Xiao W., Sun Y., Tong L. Petrogenesis and tectonic implications of the middle Silurian volcanic rocks in northern West Junggar, NW China // International Geology Review. 2014. Vol. 56(7). DOI: 10.1080/00206814.2014.905214.