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

• 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

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)根据东北日本弧第三纪-第四纪火山岩的Sr、Nd同位素资料，东北日本弧地幔岩浆源区可分为两个区域;一个是同位素未亏损的岛弧上地幔，另一个是亏损的软流圈15 Ma左右，上涌至未亏损的岛弧上地幔的HFS元素的时间变化本文用Nb、Ti、Y和Zr四种高场强元素在103个玄武岩样品中研究了日本东北弧下两个不同地幔部分（未亏损源和亏损源）的高场强元素特征（MgO* 5%，SiO2*53%），弧后侧127个。系统的差异，观察到的HFS元素组成的老玄武岩相对于年轻的。玄武质岩石是由 ...更多信息 亏损源的Zr/Y比值从-35 Ma到现在逐渐减小，Ti/Zr和Zr/Nb比值逐渐增大，而亏损源区的玄武岩在-15Ma到现在的时间段内，其HFS元素比值也呈现出类似的变化规律。1986）表明，随着年龄的减小，日本弧东北部地幔楔中的未亏损源区逐渐改变了其HFS元素特征，从高度不相容的HFS元素富集的OIB源区类型，经过N-MORB源区类型，转变为高度不相容的HFS元素亏损的IAB源区类型。在未贫化的源区中具有较大不相容性的HFS元素的逐渐贫化可能是由于自-35 Ma前以来从源区连续提取玄武质岩浆所致。对Meschede图解中亏损源区玄武岩的研究也表明，从-15Ma至今，源区经历了从相对于N-MORB源区略亏损Zr、略富集Nb到相对于N-MORB源区略亏损Zr和Nb的变化。东北日本弧玄武岩的Ti/Zr和Zr/Nb比值的变化与源区地幔中残留的富Ti、Nb矿物如斜长岩、金红石和角闪石的存在不一致。(2)测定<87><86><143><144>了日本东北弧26个地点晚中新世至上新世火山岩的初始^ Sr/^ Sr和^ Nd/^ Nd比值（Sri和Ndi比值），并利用新近获得和发表的同位素数据研究了这些比值的时空变化。除少数样品外，12-0 Ma期间火山岩的Sri和Ndi比值在整个东北日本弧上呈线性趋势，从海沟侧火山岩的未贫化同位素特征到弧后侧火山岩的贫化同位素特征。这可能是由于同位素未亏损的岛弧地幔与亏损的软流圈地幔混合而造成的弧间同位素不均匀性造成的。少

项目成果

Kenji Shuto: "Relationships between drastic change of Sr isotopes in magma sources beneath the NE Japan arc and the spreading of the Japan Sea back-arc basin" Mineralogy and Petrology. 49. 71-90 (1993)

Kenji Shuto：“日本东北弧下方岩浆源中锶同位素的剧烈变化与日本海弧后盆地扩张之间的关系”矿物学和岩石学。

Jun'ichi Ohki: "K-Ar ages of the Miocene Ryozen basalts from the northern margin of the Abukuma Highland, Japan" J.Min.Pet.Econ.Geol.88. 313-319 (1993)

Junichi Ohki：“日本阿武隈高原北缘中新世 Ryozen 玄武岩的 K-Ar 年龄”J.Min.Pet.Econ.Geol.88。

Naoki Watanabe: "K-Ar ages of the Miocene volcanic rocks from the Tomari area in the Shimokita Peninsula,Northeast Japan arc" 岩鉱. 88. 352-358 (1993)

Naoki Watanabe：“日本东北部下北半岛泊地区中新世火山岩的 K-Ar 年龄”《岩石矿山》，88. 352-358 (1993)。

Hiroo Kagami: "Temporal variation of Sr and Nd isotopic compositions of Jurassic to Miocene igneous rocks occurring in the Seto Inland Sea Kinki districts of the Ryoke belts, Southwest Japan arc" Memoirs Geol.Soc.Japan. 44 (submitted).

Hiroo Kagami：“日本西南弧 Ryoke 地带濑户内海近畿地区侏罗纪至中新世火成岩的 Sr 和 Nd 同位素组成的时间变化”Memoirs Geol.Soc.Japan。

Ohki Jyun-ichi: "K-Arages of the Miocene Ryoiecn baseets from the northern margin of the Abukuma Highland,Japan." 岩鉱. 88. 313-319 (1993)

Ohki Jyun-ichi：“日本阿武隈高原北缘的中新世 Ryoiecn 基群的 K-Arages。”88. Iwako (1993)。