High field strength element depletions in the mantle beneath island arc

岛弧下方地幔中的高场强元素损耗

基本信息

批准号：
07404026
负责人：
SHUTO Kenji
金额：
$ 22.85万
依托单位：
Niigata University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07404026/
关键词：
Northeast Japan arc Sr and Nd isotopes source mantle HFS element depletion basalt magma OIB source MORB source 北海道北部 HFS元素玄武岩 Sr同位体比 Nb同位対比マントルプリューム Nd同位体比

项目摘要

The results obtained from this research project are summarized as follows.1) On the basis of Sr and Nd isotopic data for Tertiary and Quaternary volcanic rocks from the NE Japan arc, two isotopically different mantle sources have been proposed by the present workers. One is an undepleted sub-island arc upper mantle from which -35 Ma to -15 Ma basaltic magmas in the back-arc side and -21 Ma to the present basalts in the trench side and transitional zone were extracted. The other is depleted asthenosphere which upwelled and intruded the undepleted subisland arc upper mantle beneath the back-arc side of the NE Japan arc at around 15 Ma.2) The temporal change in HFS element (high field strength element) character of two different parts of the mantle beneath the NE Japan arc was investigated using Nb, Ti, Y and Zr in 103 basaltic samples (MgO*5%, SiO2*53%) from the trench side (including some samples from the transitional zone) and 127 samples from the back-arc side. Systematic differences … More are observed in the HFS element contents of older basalts relative to younger ones. Basaltic rocks derived from the subisland arc upper mantle exhibit a gradual decrease in Zr/Y and a gradual increase in Ti/Zr with decreasing age from -35 Ma to the present, whereas those from the upwelled asthenospheric mantle show different HFS element variations with decreasing age from -15 Ma to the present.3) Basalts with the lowest Zr/Y ratios have been plotted on the 2Nb-Zr/4-Y diagram of Meschede (1986), which shows that the sub-island arc upper mantle of the NE Japan arc has gradually changed its HFS element character from a highly incompatible HFS element-enriched OIB source, to an N-MORB source, to a highly incompatible HFS element-depleted IAB source, with decreasing in age. The gradual depletion in HFS elements with greater incompatibility in the sub-island arc upper mantle may be due to the successive extraction of basaltic magmas from the source since -35 Ma ago. On of Meschede's (1986) diagram basalts derived from the upwelled asthenospheric mantle show a change in the source from slightly depleted in Zr and slightly enriched in Nb compared to N-MORB,to a source slightly depleted both in Zr and Nb compared to N-MORB during the last 15 Ma. Less

从该研究项目中获得的结果总结如下。1）根据SR和ND同位素数据的第三纪和第四纪火山岩的同位素数据，目前的工人提出了两个同位素不同的不同地幔来源。一个是一个不合时的次陆弧上地幔，后弧侧的-35 mA至-15 mA玄武岩岩浆，在沟槽侧和过渡区提取到当前玄武岩的-21 mA。另一个被耗尽的哮喘层，上升并侵入了日本新日本的背面侧面的未复制的sibisland弧形上地幔，大约在15 ma。从沟渠侧（包括过渡区的一些样本）和来自后弧侧的127个样本的Sio2*53％）。系统的差异……在较幼年的HFS元素含量中观察到更多的差异。源自subisland弧形地幔衍生的基底岩石Zr/y的年级下降，Ti/Zr的成绩增加，年龄从-35 mA到现在，年龄降低，而在跨层层层上升的HFS元素的元素变化随着-15 MA的范围下降到现在。 2Nb-Zr/4-Y diagram of Meschede (1986), which shows that the sub-island arc upper mantle of the NE Japan arc has gradually changed its HFS element character from a highly incompatible HFS element-enriched OIB source, to an N-MORB source, to a highly incompatible HFS element-depleted IAB source, with decreasing in age.自35 MA以前以来，在次国弧形上地幔中具有更大不兼容的HFS元素的分级部署可能是由于成功地从源头中提取了玄武岩岩浆。在梅切德（Meschede，1986年）的底层图中，从上流的软圈地幔中得出的玄武岩显示，与在NB中相比，与NB相比，与NB相比，与NB相比，与n-morb相比，与NB相比，与NB相比，与NB的源相比，与NB相比，与NB的源相比，与NB的源相比，与NB相比，与NB相比，与NB相比，与NB相比，与NB相比，与NB相比，与NB相比，与NB相比略有富集。较少的