Temporal changes of isotopes in igneous rocks occurring in the ciucum Japan Sea regions

日本海地区火成岩中同位素的时间变化

基本信息

批准号：
05452086
负责人：
SHUTO Kenji
金额：
$ 3.46万
依托单位：
Niigata University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1994
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-05452086/
关键词：
Sr isotope Nd isotope Temporal change Northeast Japan arc High field strength elements HFS element depletion OIB source MORB source Zr Y比東北日本奥尻海嶺上部マントル白亜紀第三紀

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 to Quaternary volcanic rocks from the NE Japan arc, the mantle magma sources beneath the NE Japan arc can be divided into two regions ; one is the isotopically undepleted sub-island arc upper mantle and another is the depleted asthenosphere (called the depleted source) which was upwelled to the undepleted sub-island arc upper mantle at around 15 Ma.Temporal change of HFS element (high field strength element) character two different mantle parts beneath the NE Japan arc, the undepleted and depleted sources, is investigated using four HFS elements Nb, Ti, Y and Zr in 103 basalitc samples (MgO*5%, SiO2*53%) from the trench side (including some samples from the transitional zone) and 127 ones from the back-arc side. Systematic differences are observed in HFS element composition of the older basalts relative to the younger ones. Basaltic rocks derived from the u … More ndepleted source exhibit a gradual decrease in Zr/Y ratio and a gradual increase in Ti/Zr and Zr/Nb ratios with decreasing age from -35 Ma to the present, whereas those from the depleted source show similar variations in these HFS element ratios with decreasing age from -15 Ma to the present.Plotting of basalts with minimum Zr/Y ratio among respective basaltic rocks in 2Nb-Zr/4-Y diagram proposed by Meschede (1986) suggests that the undepleted source in the mantle wedge of the NE Japan arc has gradually changed its HFS element character, from a highly incompatible HFS element-enriched OIB source type through N-MORB source type to a highly incompatible HFS element-depleted IAB source type, with the decrease in age. Gradual depletions of HFS elements of greater incompatibility in the undepleted source may be due to the successive extraction of basaltic magmas from the source since -35 Ma ago. Examination of basalts derived from the depleted source in Meschede's diagram also indicates the changing from the source depleted slightly in Zr and enriched slightly in Nb compared with N-MORB source to that depleted slightly both in Zr and Nb compared with N-MORB source during -15 Ma to the present. Variations of Ti/Zr and Zr/Nb ratios of basaltic rocks from the NE Japan arc are not compatible with the presence of residual Ti, Nb-enriched minerals such as sphene, rutile and amphibole in the source mantle.(2) The initial ^<87>Sr/^<86>Sr and ^<143>Nd/^<144>Nd ratios (Sri and Ndi ratios) were determined for the late Miocene to Pliocene volcanic rocks from twenty-six locations in the NE Japan arc and a spatial-temporal variation of these ratios was also examined using the newly obtained and published isotope data. Sri and Ndi ratios of volcanic rocks except few samples during 12-0 Ma show linear trends across the NE Japan arc from the undepletedisotopic signature in the trench side volcanics to the depleted one in the back-arc side volcanics. This can be ascribed to a across-arc isotopic heterogeneity in their source mantle material due to mixing of isotopically undepleted island arc mantle with depleted asthenospheric mantle which was up-welled to the former beneath the back-arc side during the opening of the Japan Sea. Less

从该研究项目中获得的结果总结如下。（1）根据SR和ND的同位素数据，用于第四级的第四纪火山岩来自日本NE日本弧，日本NE弧下的地幔岩浆源可以分为两个区域；一种是同位素不合时的沿岛弧上地幔，另一个是耗尽的小层（称为耗尽的来源），该层上升至未恢复的次陆弧上地幔，处于15个以上的15个以上的HFS元素（高野外强度元素）的两种不同的ne ne ne ne ne Issed seples serection and ne ne ne ne eyples and the ebles and de ey eble de e Beal and ebles and de e Beal and de e Beal and de election and de election Arc and e Beal and a anc。使用四个HFS元素NB，Ti，Y和ZR中的103个基本样本（MGO*5％，Sio2*53％），从沟槽侧（包括过渡区的一些样品）和127个来自后弧侧的样品。在较旧玄武岩相对于年轻的玄武岩的HFS元素组成中观察到系统差异。源自U…更无能为力的来源的基底岩石的Zr/y比率下降，Ti/Zr和Zr/Nb的比例增加，随着年龄的降低，从-35 MA到现在，降低的年龄降低到现在，而这些HFS元素的质量降低了，而这些HFS元素的差异降低了，而质量为-15 MA的最小率降低，则是15 MA的最小差异。在1986年）中表明，日本NE Arc地幔楔中的未重新源已逐渐改变其HFS元素特征，从高度不相容的HFS HFS元素增强的OIB源类型通过N-MORB源类型到高度不相容的HFS HFS元素depted IAB源类型，年龄降低。自从-35 mA以来，玄武岩成功地从源中提取了玄武岩岩浆的成功提取。对Meschede图中耗尽源衍生的玄武岩的检查也表明，与NB中的NB略微富集的源相比，与N-MORB源相比，在-15 mA期间与N-Morb源相比，NB略微富集了NB。来自日本新日本的基底岩石的Ti/Zr和Zr/nb比的变化与源地壁中的残留Ti，NB富集的矿物质（如Sphene，Rutile和Amphibole）不兼容。确定了中新世晚期与来自日本NE日本二十六个位置的上新世火山岩的NDI比），并使用新获得和发表的同位素数据研究了这些比率的时空变化。除12-0 MA期间几个样品以外的火山岩外，SRI和NDI比率显示了日本NE日本的线性趋势，从趋势侧火山中未复制的二元签名到后北极侧火山的深度。这可以归因于由于将同位素未复制的岛弧形与脱离的运动层层甲层混合，因此在其源地幔材料中的跨弧度异质性归因于该材料，该地幔在日本大海开放期间被向前驶向前者的前者。较少的