Characteristics and origin of the magma generated in the fore-arc and accretionary regions

弧前和增生区岩浆的特征和来源

• 批准号: 06640583
• 负责人: HONMA Hiroji
• 金额: $ 1.34万
• 依托单位: Okayama University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1994
• 资助国家: 日本
• 起止时间: 1994 至 1996
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06640583/
• 关键词: fore-arc region; accretionary body; igneous activity; basalt magma; strontium isotope; granitoids of the Outer zone; neodimium isotope; oxygen isotope; 前弧部; 玄武岩; 花崗岩; ストロンチウム; ネオジム; 同位体

Sixty samples of granitoids, sedimentary rocks and xenoliths from Kii, Shikoku, Kyushu and Yakushima in the Outer zone of Southwest Japan and twenty-two samples of rocks of the olivine basalt-dolerite-olivine gabbro-granophyre-rhyolite association from Shionomisaki in the fore-arc region have been analyzed for majro elements, Rb-, Sr-, Nd, Sm- concentrations, and oxygen-, Sr- and Nd-isotope rations. Specific features of the mantle-derived magma and its behaviors in the crust and the genesis of per-aluminous granitoids were quantitatively discussed.(1) The basaltic magma generated in the mantle beneath the fore-arc region has characteristic MORB-type chemical and isotopic features that are distinctly different from common arc magmas'. This depends to the specific tectonic positio of the fore-arc region where the slab-derived component cannot incorporate to the genesis of original baslt magmas. (2) The Sr-Nd systematic of the basalt-rhyolite association of Shionomisaki well fits to the b … More ulk-mixing model of the olivine basalt-average Shimanto sedimentary rock end-members, indicating that the MORB-type magma uprised to the accretionary part could derived isotopically much evolved acid magma by reaction with sedimentary rocks which proceeded simultaneously to the crystallization of the magma.(3) Detailed studies of the chemical and isotopic change in each granite body and suite clearly discriminate the process of changing granitoid magma mass during uprise, crystallization and intrusion in the upper crust and the process of generation of varying parental granodioritic magmas in the depth. (4) The isotopic variation in granitoids is principally due to the local variation and internal heterogeneity of the parent granite magma mass, and its Sr-Nd isotopic systematics perfectly fits to the two-step two-component mixing model. This includes that the parental granite magma has been formed by 'mixing' of the mantle-derived arc magma and sedimentary rocks of the Shimanto Super Group.(5) The parental granitoid magmas should be generated by the reaction, including melting and assismilation, of mantle-derived magma with lower crustal rocks, and their chemical and isotopic features should principally controlled by the degree of contribution and nature of lower-crust substances. The per-aluminous granitoids like those of the Outer zone of Southwest Japan can only generated in the young accretionary regions where only the sedimentary rocks can be incorporated in the process of generation of parental granite magma. Less

对日本西南部外带Kii、四国岛、九州、雅居岛的60个花岗岩类、沉积岩和包体，以及弧前区Shionomisaki的22个橄榄质玄武岩-辉绿岩-橄榄辉长岩-流纹岩组合的岩石样品进行了主量元素、Rb-、Sr-、Nd、Sm含量和氧、锶、钕同位素比值的分析。定量地讨论了地幔岩浆的特征及其在地壳中的行为和全铝花岗岩类的成因：(1)弧前地区地幔中产生的玄武岩具有明显不同于普通弧岩浆的MORB型化学和同位素特征。这取决于弧前区特定的构造位置，在那里板岩派生的成分不能并入原始玄武岩岩浆的成因。(2)柴崎岩玄武岩-流纹岩组合的锶-钕体系与b-…很好地吻合。更多的橄榄玄武岩-平均石曼托沉积岩端元的ULK混合模式表明，上升到增生部分的MORB型岩浆可与沉积岩反应而产生大量同位素演化的酸性岩浆，并同时进行岩浆结晶。(3)详细的花岗岩体和岩套的化学和同位素变化研究清楚地区分了上地壳隆起、结晶和侵入过程中花岗岩类岩浆质量的变化过程和深部不同母质花岗闪长岩浆的形成过程。(4)花岗岩类中的同位素变化主要是由于母花岗岩岩浆体的局部变化和内部非均质性所致，其锶-钕同位素体系符合两步两组分混合模式。(5)母花岗岩岩浆是由地幔岩浆与下地壳岩的熔融和同化作用形成的，其化学和同位素特征主要受下地壳物质的贡献程度和性质控制。日本西南部外带的全铝花岗岩类只能在年轻的增积区产生，在母花岗岩岩浆的形成过程中只有沉积岩才能被合并。较少

项目成果

HONMA,Hiroji: "Genesis of granitoids in the mobile belt (the Ryoke belt) : with special refernce to the oxygen and strontium isotopic behaviors." Monthly 'The Earth', Spec.Vol.16. 99-106 (1996)

HONMA，Hiroji：“移动带（Ryoke 带）中花岗岩的成因：特别涉及氧和锶同位素行为。”

本間弘次: "High ammonium contents in the 3800 Ma Isua supracrustal rocks,central West Greenland" Geochimica et Cosmochimica Acta. 60(出版受理、1996、2.27). (1996)

Hiroji Homma：“西格陵兰中部 3800 Ma Isua 表壳岩石中的高铵含量”Geochimica et Cosmochimica Acta 60（已接受出版，1996 年，2.27）。

本間弘次: "変動帯(領家帯)花崗岩の形成過程:特に酸素及びストロンチウム同位体の挙動について" 月間 地球. 特別号No.16. 99-106 (1996)

Hirotsugu Homma：“变形带（Ryoke带）花岗岩的形成过程：特别是关于氧和锶同位素的行为”月刊特刊第16. 99-106号（1996）。

HONMA,Hiroji: "High ammonium contents in the 3800 Ma Isua supracrustal rocks, central West Greenland." Geochim.Cosmochim.Acta. Vol.60 No.12. 2173-2178 (1996)

HONMA，Hiroji：“西格陵兰岛中部 3800 Ma Isua 表壳岩石中的铵含量很高。”

Honma.H.: "High ammonium contents in the 3800 Ma Isua supracrustal rocks,central West Greenland" Geochimica et Cosmochimica Acta. 80. 2173-2178 (1996)

Honma.H.：“格陵兰岛西部中部 3800 Ma Isua 表壳岩石中铵含量较高”《地球化学与宇宙化学学报》。