Origin and Regional Variation of the Magma in the Ryukyu Arc-Back Arc System

琉球弧背弧系岩浆成因及区域变化

• 批准号: 03640643
• 负责人: HONMA Hiroji
• 金额: $ 0.7万
• 依托单位: Institute for Study of the Earth's Interior
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1991
• 资助国家: 日本
• 起止时间: 1991 至 1992
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-03640643/
• 关键词: Ryukyu arc; Volcanic rocks; Trace element; Strontium isotope ratio; Neodymium isotope ratio; Magma genesis; Two-component mixing model; Alkaline rocks; 島弧マグマ; 微量元素組成; ストロウンチウム同位体; ネオジム同位体; 琉球系火山岩; 高苦土安山岩; 黄尾礁; アルカリ火山岩; ストロンチウム同位体

Contents of Rb, Sr, Nd and Sm and ^<87>Sr/^<86>Sr and ^<143>Nd/^<144>Nd ratios have been analyzed for Cenozoic volcanic rocks of the Ryukyu arc system. The distinctly low Sm contents and Sm/Nd ratios of hornblende-bearing rocks and the variation of Zr/Sr in rocks of the arc side with significantly low Zr/Sr ratios in relatively basic rocks clearly indicate the effects of the hornblende- and plagioclase-dominant fractionations, respectively, which most probably are related to crystallization differentiation of the magma. The Sr-Nd isotopic characteristics are best interpreted by the paired two-component mixing models, namely the 'source-mixing' and 'crustal-mixing' : (1)Strontium and Nd in the primary magmas consist mainly of the mixture derived from the MORB source-type peridotite and subducted sedimentary rocks. (2)Contribution of sedimentary components to the primary magma is distinctly lower in the back-arc side (27-30%). (3)Often magmas of both sides have been affected by considerable degree of isotopic modification by crustal materials during their evolution in the crust. (4)The ^<87>Sr/^<86>Sr and ^<143>Nd/^<144>Nd ratios also change with changing geological settings. (5)The high magnesian andesite has the high ^<143>Nd/^<144>Nd ratio compared to its ^<87>Sr/^<86>Sr ratio, and its primary magma should have originated from the different source material. (6)Alkaline basalts of the Obisyo characteristically have the isotopic signature of the plume-type basalts.Both the Zr-Sr and Sm/Nd-SiO_2 systematics and their accordance with each other strongly support the hypothesis that the difference in the melting degree (increase from back-arc side towards the arc side) should be the main controlling factor for the chemical difference of the primary magmas between both sides.

分析了琉球弧系新生代火山岩Rb、Sr、Nd、Sm含量及^<87>Sr/^<86>Sr和^<143>Nd/^<144>Nd比值。含角闪石岩石中Sm含量和Sm/Nd比值明显偏低，相对基性较低的弧侧岩石中Zr/Sr比值变化明显，表明角闪石和斜长石分别占主导作用，很可能与岩浆的结晶分异有关。Sr-Nd同位素特征最好用“源-混”和“壳-混”配对双组分混合模式来解释：①原生岩浆中的锶和Nd主要由源自MORB源型橄榄岩和俯冲沉积岩的混合组成；(2)沉积组分对原生岩浆的贡献在弧后侧明显较低（27 ~ 30%）。(3)两侧岩浆在地壳演化过程中经常受到地壳物质的相当程度的同位素改变的影响。(4) Sr <87> / Sr <86>和Nd <143> / Nd <144>的比值也随地质环境的变化而变化。(5)高镁安山岩的Nd/ Nd比值高于Sr/ Sr比值（<87>）和Sr比值（<86>），表明其原生岩浆来源不同。(6) Obisyo碱性玄武岩具有羽状玄武岩的同位素特征。Zr-Sr分系统和Sm/Nd-SiO_2分系统的一致性有力地支持了熔化程度的差异（从弧后向弧侧增加）是控制双方原生岩浆化学差异的主要因素的假设。

项目成果

HONMA,Hiroji: "Chronological and areal variation of Sr and Nd isotope ratios in Cenozoic volcanic rocks of the Ryukyu arc system,Southwest Japan." Contr.Min.Petrol.

HONMA，Hiroji：“日本西南部琉球弧系新生代火山岩中 Sr 和 Nd 同位素比值的年代和面积变化。”

Hiroji Honma: Geochemical Journal. 25. 121-136 (1991)

本间宏二：地球化学杂志。

Hiroji Honma: "Chronological and areal variation of Sr and Nd isotope ratios in Cenozoic volcanic rocks of the Rukyu arc system, Southwest Japan" Contr.Min.Petrol.

Hiroji Honma：“日本西南部流球弧系新生代火山岩中 Sr 和 Nd 同位素比率的年代和面积变化”Contr.Min.Petrol。

HONMA,Hiroji: "Across-arc variation of Rb,Sr,Nd and Sm contents and ^<87>Sr/^<86>Sr and ^<143>Nd ^<144>Nd ratios in Quatemary volcanic rocks from the Satsunan Islands area of the Ryukyu arc,Southwest Japan." 地質学雑誌.

HONMA，Hiroji：“萨南群岛第四纪火山岩中 Rb、Sr、Nd 和 Sm 含量以及 ^<87>Sr/^<86>Sr 和 ^<143>Nd ^<144>Nd 比率的跨弧变化日本西南部琉球岛弧区域。”地质杂志。

HONMA,Hiroji: "Rubidium,Sr,Nd and Sm contents and ^<87>Sr/^<86>Sr and ^<143>Nd ^<144>Nd ratios of Japanese sedimentary rocks." Geoche.J.

HONMA，Hiroji：“日本沉积岩的铷、Sr、Nd 和 Sm 含量以及 ^<87>Sr/^<86>Sr 和 ^<143>Nd ^<144>Nd 比率。”