Trace element abundances and isotopic ratios of Japanese Quaternary basalts and heterogeneity of upper mantle

为了阐明日本第四纪玄武岩中不相容微量元素的地球化学和岩石学行为，以及上地幔源物质的非均质性，测定了日本第四纪玄武岩中具有代表性的上地幔和下地壳火山岩及其合并包体的主元素量、微量元素和Sr、Nd同位素比值。澄清了以下几个重要的结果和结论：东日本火山区玄武岩和安山岩均表现出典型的岛弧火山岩性质，在岩石/原始地幔不相容元素归一化模式中表现出显著的正Ba、K、Sr异常和负Nb异常。Sr^<87>/Sr^<86>比值逐渐减小，Nd^<143>/Nd^<144>比值从火山前缘向弧后盆地侧逐渐增大。日本海侧碱系Sr^<87>/Sr^<86>比值范围为0.7035 ~ 0.7050，大陆特征为不相容元素归一化模式，无Ba、K、Nb、Sr异常。来自上地幔和下地壳的累积超流体-基性捕虏体的归一化模式和Sr、Nd同位素比值与岛内相似。9rc玄武岩，没有任何大陆或海洋玄武岩性质。表明日本列岛的基底或上地幔和下地壳是由岛弧玄武岩的累积岩构成的。

In order to elucidate the geochemical and petrological behavior of incompatible trace elements in the Japanese Quaternary basaltic rocks, and the heterogeneity of the source materials in upper mantle, we have determined major and trace elements and Sr and Nd isotopic ratios of the representative volcanic rocks and their incorporated xenoliths derived from upper mantle and lower crust together with their major elements. The following several important results and conclusions have been clarified.1. All of the basalts and andesites from the East Japan volcanic zone exhibit the nature of typical island arc volcanic rocks'showing the remarkable positive Ba, K and Sr anomalies and the negative Nb anomaly in the rock/primitive mantle normalized pattern for the incompatible elements. Furthermore, their Sr^<87>/Sr^<86> ratios gradually decrease and Nd^<143>/Nd^<144> ratios increase from the volcanic front to the back arc basin side.2. Alkali series in Japan Sea side have the range of 0.7035 to 0.7050 for Sr^<87>/Sr^<86> ratios and continental characters for incompatible element normalized pattern without any Ba, K, Nb or Sr anomaly.3. Normalized patterns and Sr and Nd isotopic ratios of cumulative ultranafic to mafic xenoliths derived from upper mantle and lower crust are similar to those of the island. 9rc basalts, and do not have any continental or oceanic basalt natures. It indicates that the basement or uppermost mantle and lower crust of the Japanese islands are composed of cumulative rocks of the island arc basalts.