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

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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.