Rare-earth-element compositions of rocks from Quaternary volcanoes in Northeast Japan arc and their magmagenetic implications.

日本东北部第四纪火山岩石的稀土元素组成及其岩浆成因意义。

基本信息

批准号：
02640620
负责人：
FUJINAWA Akihiko
金额：
$ 1.28万
依托单位：
Ibaraki University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1992
项目状态：
已结题

项目摘要

Contents of large-ion-lithophile (LIL), rare earth (RE), and high-field-strength (HFS) elements are determined for representative rock samples from volcanoes at Moriyoshi and Chokai zones, situated in back-arc side of Northeast Japan arc. Based on these results together with the preceeding research made by myself ( Grant-in-aid No. 63540643 ), across-arc inhomogeneity in magma source region with respect to incompatible elements is investigated.Across-arc variation in respect of lighter REE / heavier REE ratios is clearly recognized among basaltic members of the magma suites; the ratios increase systematically from trench side toward back-arc side zone. This tendency becomes distinct more and more as the relevant magmas enrich in silica. Since different degrees of partial melting of common magma source can not account for the systematic variations, it seems plausible that across-arc variation with regard to REE exists within source mantle region. Further, role of magma mixing is more important in magmatic evolution process for back-arc side volcanoes, with acidic end-member magma suffering fractionation ( or remnant ) of some HREE-bearing minerals such as amphibole, clinopyroxene, and garnet.Detailed examination of the LIL-RE-HFS systematics for concurring magma suites at Kampu, Adatara, and Funagata volcanoes revealed source heterogeneity in respect of incompatible element geochemistry. The inferred chemical characteristics for metasomatically added agent(s) are well-reconciled with the two-stage stepwise wedge dehydration model postulating two pressuresensitive dehydration reactions ( proposed by Tatsumi; 1989 ), suggesting strongly that differential infiltration of slabderived fluid into the mantle source is a crucial process in producing a variety of magmas.

确定位于日本东北部弧的后面的莫里伊岛和Chokai区的代表性岩石样品，确定了大离子岩石噬菌体（LIL），稀土（RE）和高场强（HFS）元素的含量。基于这些结果以及我自己所做的先前研究（第63540643号赠款），研究了岩浆源区域中关于不兼容元素的跨弧度不均匀性。在Magma Suites basaltic spaltic中，较轻的REE /重的REE比率在较轻的REE /重的REE率方面得到了较轻的REE /重ree率的差异；该比率从沟渠侧到后弧侧区域有系统地增加。随着相关的岩浆丰富在二氧化硅中，这种趋势变得越来越独特。由于常见岩浆源的不同程度的部分熔化无法解释系统的变化，因此与REE有关REE的跨源地幔区域内的跨核变化似乎是合理的。此外，岩浆混合的作用在岩浆进化过程中的作用更为重要关于不兼容元件地球化学的源异质性。代理添加的剂的推断化学特性与两阶段的逐步楔形脱水模型相连，该模型假设两个压力敏感的脱水反应（提出了Tatsumi; 1989），这表明，强烈表明将slabdivedived的流体浸入了壁炉质量的过程中，这是一种杂志的杂物。