Original paper

Geochemistry and isotopic systematics of Cenozoic alkaline volcanic rocks in Korea and NE China

Wee, Soo Meen

Abstract

Cenozoic alkaline volcanic rocks are distributed along the northeast margin of Eurasian plate, possibly the result of regional rifting which formed in response to the subduction of the western Pacific plate beneath the north eastern part of the Eurasian plate. Major, trace, rare earth elements concentrations and Sr, Nd, Pb isotopic systematics are reported for Cenozoic volcanic rocks from Korea (group I), Korea and China border (group II) and NE China (group III). These volcanic rocks are significantly enriched in highly incompatible elements, and are enriched relative to bulk silicate earth (BSE) based on 143Nd/144Nd vs. 87Sr/86Sr diagram. The clear negative and positive correlations are observed between 143Nd/144Nd and 87Sr/86Sr vs. 206Pb/204Pb ratios of the volcanic rocks. The 207Pb/204Pb and 208Pb/204Pb vs. 206Pb/204Pb plots show linear arrays parallel to the Northern Hemisphere Reference Line (NHRL), and 208Pb/204Pb data points are displaced considerably above NHRL in pattern similar to that of the oceanic island basalts (OIB) that show the Dupal signatures. Trace element ratios and isotopic signatures indicate that the group III rocks were derived from a different magma source which is more enriched compared to that of group I and II. Group I and II rocks have trace element signatures such as Rb/Sr, Sm/Nd, Ba/Nb and La/Nb ratios are similar to OIB, while group III rocks are characterized by high La/Nb, Th/Nb and Zr/Nb ratios similar to EM I OIB. Geochemical data including Sr, Nd and Pb isotopic compositions of the group I and II rocks suggest two mantle reservoirs in the origin of the rocks: asthenospheric MORB-like sources and EM I lithospheric component. Group III rocks are typical of magma derived from a reservoir predominantly consisting EM I component. The subcontinental lithospheric mantle source similar to the postulated EM1 component must have played a significant role in magma generation of group III rocks.

Keywords

koreane asiaisotopic signaturemantle reservoir