Selective contamination of basaltic magmas and buchite genesis (on the example of Shufan plateau, Primorye)

The article discusses the problem of large-scale contamination of the Shufan volcanic plateau’s basalts (Primorye) by selective melts from xenoliths. Silicic and alkaline liquids, selectively extracted from xenoliths, mix in a limited way with basaltic melts forming bands of granophyre that give lavas a taxitic structure. The article describes the unique compositions of buchites that were chemically modified by the diffusion interaction with basaltic magma and selectively molten politic xenoliths. Their mineral associations are represented by a high ferriferous cordierite (sekaninaite), ultra-ferriferous hercynite, (Al, Zr) Fe-armalcolite, Zr-ilmenite, mullite, sillimanite, high-lanthanum monazite, and barium-phosphate-aluminosilicate phase. The chemical and mineral compositions of buchites reflect the accumulation of refractory elements (Al, Fe, Ti, Zr, Ni, Cr) in the restite material of xenoliths. It is followed by the formation of ultra-alumina, ultra-ferruginous, initially immiscible metal-silicate composition. Low Pb isotopic ratios in Shufan basalts suggest a selective contamination by an ancient cratonic basement’s material. A consecutive increase of the isotopic ratios is observed the basalts contaminated by the upper crustal material, which is also shown by buchites’ isotopic composition.