Two Contrasting Provenances of Prehistoric Obsidian Artifacts in South Korea: Mineralogical and Geochemical Characteristics

Abstract

Two provenances - Mount Baekdusan near Sino-Korean border and Kyushu of southwest Japan - are well known for Korean prehistoric obsidian artifacts. We examined the mineralogical and geochemical characteristics of the Baekdusan obsidians and the Kyushu obsidians. Though obsidians are of glassy material, microlites are easily found in the host matrix. Fe-oxides are the most abundant microlite phase, with a lesser amount of clinopyroxene, feldspar, and biotite. It is notable that the texture and chemical composition of the microlites in the Baekdusan obsidians are quite different from those in the Kyushu obsidians. Clinopyroxene in the Baekdusan obsidians occurs as oikocryst enclosing smaller Fe-oxides, and has the composition of hedenbergite to augite. On the other hand, clinopyroxene in the Kyushu obsidians is compositionally of clinoferrosilite, and shows intergrowth and/or overgrowth textures with Fe-oxides. Feldspar microlites in the Baekdusan obsidians are generally of sanidine to anorthoclase, whereas those in the Kyushu obsidians of oligoclase. Biotite microlites are often found in the Kyushu obsidians, but absent in the Baekdusan obsidians. Also, there exist prominent geochemical contrasts between the Baekdusan obsidians and the Kyushu obsidians. At the similar SiO2 range of 74 to 78 wt.% the host glasses of the Baekdusan obsidians have higher contents of TiO2, total FeO, K20, Nb, Hf, Zr, Ta, Y and rare earth elements (REEs) than those of the Kyushu obsidians. The overall mineralogical and geochemical contrasts for the Baekdusan and Kyushu obsidians seem to reflect different parental magma composition and crystallization environment. This distinction can be used to establish the provenance of the obsidian artifacts from the prehistoric sites in the Korean Peninsula as well as contiguous areas such as China, Japan, and Russia.