Geochemical evidence of the plume nature of Devonian mafic rocks of the Rudny Altai (Northwest of the Altai-Sayan folded area)
Authors: Semiryakov Alexey , Grinev, Oleg , Bestemianova, Ksenia , Grinev Roman 
Published: March 2024

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 &#8211; Structural-tectonic position of the Zmeinogorsk ore district
Geochemical discrimination
The presence of mantle geochemical signatures is visible in the Zr/Y&#160;&#8211;&#160;Nb/Y diagram [2] (Fig. 2a): 1)&#160;volcanic rocks points are located in the OPB area within the influence of the PM reservoir; 2)&#160;intrusive rocks points position is more ambiguous &#8211; gabbros fall predominantly in the OPB, pyroxenites are more inclined to the N-MORB and IAB. The La/Lu&#160;&#8211;&#160;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&#160;&#8211;&#160;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 &#8211; 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 &#8211; pyroxenites (D1e); 2 &#8211; gabbro (D1e); 3 &#8211; gabbro-dolerite (D3f); 4 &#8211; basalts (D1&#1077;); 5 &#8211; subvolkanic dolerites (D2ef); 6 &#8211; compositional area of volcanics of the Zmeinogorsk trough; 7 &#8211; compositional area of intrusions of the Aleisk granite-metamorphic dome
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