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

大离子亲石（LIL），稀土（RE）和高场强（HFS）元素的含量测定的代表性岩石样品的火山在Moriyoshi和Chokai区，位于弧后侧的日本东北弧。在此基础上，结合本人的前期研究（资助号63540643），研究了岩浆源区不相容元素的跨弧不均匀性，发现岩浆岩套中玄武质岩段轻稀土/重稀土比值存在明显的跨弧变化，从沟侧到弧后侧，轻稀土/重稀土比值呈系统性增大。随着岩浆中硅质的富集，这种趋势变得越来越明显。由于普通岩浆源不同程度的部分熔融不能解释系统性变化，因此源幔区稀土元素存在跨弧变化似乎是合理的。此外，岩浆混合的作用是更重要的弧后火山岩浆演化过程中，与酸性端元岩浆遭受分馏（或残余）的一些HREE轴承矿物，如角闪石，单斜辉石，和garnet.Detailed考试的LIL-RE-HFS系统的同生岩浆套房在Kampu，Adatara，和Funagata火山揭示源的不相容元素地球化学方面的异质性。推断的交代添加剂的化学特征与Tatsumi提出的假设两个压力敏感脱水反应的两阶段逐步楔脱水模型（1989年）很好地吻合，强烈表明板状流体向地幔源的差异渗透是产生各种岩浆的关键过程。

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.