Behavior of incompatible elements in rock-forming minerals under high temperature and high pressure

为了阐明高温高压条件下造岩矿物中不相容微量元素的地球化学和岩石学行为，我们测定了近3000个具有代表性的晚第三纪-第四纪火山岩及其来自上地幔和下地壳的包体及其主要成分矿物的常量和微量元素。1.日本东北部火山岩和伊豆-马里亚纳岛弧具典型的岩石/原始地幔不相容微量元素标准化模式的岛弧，具有显著的BA、K、Sr正异常和Nb负异常。日本西南部弧区火山前缘的火山岩虽然与扇形火山岩具有相同的特征，但碱性岩系由岛弧向大陆变化。大陆、洋岛和岛弧上地幔二辉橄榄岩包体及其组成矿物镁橄榄石、顽辉石、铬透辉石和铬尖晶石或镁铝榴石中不相容元素的浓度通常低于检测下限。因此，很难认为玄武岩岩浆中不相容元素的来源物质是这些二辉橄榄岩包体。日本群岛下地壳捕虏体及其主要矿物的归一化模式和稳定同位素比值与钙-氯-碱性火山岩相似，表明为积云成因。此外，Itinome-gata镁铁质包体的Rb-Sr测年结果表明其时代为前寒武纪。

In order to elucidate the geochemical and petrological behavior of incompatible trace elements in rock-foming minerals under the high temperature and high pressure conditions, we have determined major and trace elements of about 3000 representative late Tertiary-Quaternary volcanic rocks and their xenoliths derived from upper mantle and lower crust together with their major constituent minerals. The following several important results and conclusions have been clarified;1. All of the volcanic rocks in northeast Japan and Izu-Mariana arcs show the typical island arc of the rock/primitive mantle normalized pattern for incompatible trace elements, having the remarkable positive Ba, K and Sr anomalies and the negative Nb anomaly. Although, the volcanic rocks along the volcanic front in southwest Japan arc have the same characteristics as theose of the fanner, alkali series hange from island arc to continental patterns towards the continents.2. Concentration if incompatible elements in upper mantle iherzolite xenoliths in continents, oceanic islands and island arcs and their constituent minerals, forsterite, enstatite, chromian diopside and chromian spinel or pyrope is usually below the detection limit. Accordingly, it is very difficult to consider that the source materials of incompatible elements in basaltic magams are of these lherzolite xenoliths.3. Normalized patterns and stable isotope ratios of lower crustal xenoliths in Japanese Islands and their essential minerals are Similar to those of calc-cl-lkaline volcanic rocks, indicating the cumulus origin. Besides, the mafic xenoliths from Itinome-gata suggest the pre-Cambrian age by the Rb-Sr age dating.