关键词: 元素地球化学, Sr-Nd同位素, 玄武岩墙, 构造意义, 天池火山区, 长白山

Abstract: In order to further understand the origin and tectonic setting of basaltic dyke related to Middle and Late Pleistocene volcanic activities in the Heishigou area of Tianchi volcano, based on remote sensing interpretation and field geological investigation, the  geochemistry, whole rock Sr-Nd isotope and geochronology analysis of the basaltic dykes were carried out. The results show that: 1) The major elements of the dykes have relatively high MgO, CaO, K2O and relatively low Na2O, belonging to the series of potassium, metaaluminous and subalkaline basalts. They are enriched in LILEs, such as Li, Cs, Be, Rb, Ba and Sr, and weakly enriched in HFSEs, such as Nb, Ta, Zr, Hf, U and Th, and the corresponding ratios of Zr/Hf, Nb/Ta and Th/U are 40.92-45.10, 15.77-16.34 and 3.49-3.76, respectively. 2) The values of (87Sr/86Sr)i and (143Nd/144Nd)i in the whole rocks range from 0.704 570 to 0.704 690 and 0.512 552 to 0.512 571, respectively, the εNd (t) values range from 0.87 to 1.45. The K-Ar isotopic ages of (0.35-0.34 Ma) obtained by previous research in dykes and tectonic-magmatic evolution together suggest that the basaltic magmatism occurred in the Chibanian stage of Late Pleistocene, and the diagenetic parent magma has the characteristics of enriched Ⅰ-type mantle source, with a small amount of lower crust components were added during the ascent of the magma, showing the characteristic of ocean island basalt (OIB). The formation of the basalt dykes and the contemporaneous volcanic activities occurred in a compressional tectonic environment at 0.35-0.34 Ma, which may be related to the rollback or subsidence of the Pacific plate after it was subducted into the northeastern Eurasia continent.

Key words: element geochemistry, Sr-Nd isotope, basaltic dyke, tectonic significance, Tianchi volcanic area, Changbai Mountain ,