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

日本第四纪玄武岩微量元素丰度、同位素比与上地幔异质性

基本信息

批准号：
01302019
负责人：
AOKI Ken-ichiro
金额：
$ 4.48万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Co-operative Research (A)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1991
项目状态：
已结题

项目摘要

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.

为了阐明日本第四纪玄武质岩石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区物质的不均一性，我们测定了代表性火山岩及其上地幔和下地壳包体的主量元素、微量元素和Sr、Nd同位素比值及其主量元素。得到了以下几个重要结果和结论.东日本火山岩带的玄武岩和安山岩均具有典型的岛弧火山岩性质，在岩石/原始地幔不相容元素标准化模式中，Ba、K、Sr异常显著，Nb异常显著。从火山前缘到弧后盆地，Sr^<87>/Sr ^<86>逐渐降低，Nd^<143>/Nd^<144>逐渐升高.日本海侧碱性岩系的Sr^ /Sr^比值在0.7035 ~ 0.7050<87>之间<86>，不相容元素标准化模式具有大陆性，没有Ba、K、Nb、Sr异常.来自上地幔和下地壳的累积超镁铁质-镁铁质捕虏体的标准化模式和Sr、Nd同位素比值与该岛的捕虏体相似。9 rc玄武岩，并没有任何大陆或海洋玄武岩的性质。这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堆积岩组成的。