Petrogenesis and mantle source characteristics of the late Cenozoic Baekdusan (Changbaishan) basalts, North China Craton

Abstract

Late Cenozoic intraplate basaltic rocks in northeastern China have been interpreted as being derived from a mantle source composed of DMM and EM1 components. To constrain the origin of the enriched mantle component, we have now determined the geochemical compositions of basaltic rocks from the active Baekdusan volcano on the border of China and North Korea. The samples show LREE-enriched patterns, with positive Eu and negative Ce anomalies. On a trace element distribution diagram, they show typical oceanic island basalt (OIB)-like LILE enrichments without significant Nb or Ta depletions. However, compared with OIB, they show enrichments in Ba, Rb, K, Pb, Sr, and P. The Nb/U ratios are generally within the range of OIB, but the Ce/Pb ratios are lower than those of OIB. Olivine phenocrysts are characterized by low Ca and high Ni contents. The radiogenic isotopic characteristics (Sr-87/Sr-86 =0.70449 to 0.70554; epsilon(Nd) = -2.0 to +1.8; epsilon(Hf) = -1.7 to +6.1; Pb-206/Pb-204 = 17.26 to 18.12) suggest derivation from an EM1-like source together with an Indian MORB-like depleted mantle. The Mg isotopic compositions (delta Mg-26 = -0.39 +/- 0.17 parts per thousand) are generally lower than the average upper mantle, indicating carbonates in the source. The Sr-87/Sr-86 ratios decrease with decreasing delta Mg-26 values whereas the Nd-143/Nd-144 and (Nb/La)(N) ratios increase. These observations suggest the mantle source of the Baekdusan basalts contained at least two components that resided in the mantle transition zone (MTZ): (1) recycled subducted ancient (similar to 2.2-1.6 Ga) terrigenous silicate sediments, possessing EM1-like Sr-Nd-Pb-Hf isotopic signatures and relatively high values of delta Mg-26; and (2) carbonated eclogites with relatively MORB-like radiogenic isotopic compositions and low values of delta Mg-26. These components might have acted as metasomatizing agents in refertilizing the asthenosphere, eventually influencing the composition of the MTZ-derived plume that produced the Baekdusan volcanism. (c) 2019 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.