Tectonics of Miocene SW Japan Arc : Origin of Unusually High Temperature in the Mantle

中新世日本西南弧的构造:地幔异常高温的起源

• 批准号: 08404029
• 负责人: TATSUMI Yoshiyuki
• 金额: $ 20.42万
• 依托单位: KYOTO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (A)
• 财政年份: 1996
• 资助国家: 日本
• 起止时间: 1996 至 1998
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08404029/
• 关键词: Setouchi volcanic belt; Rotation of SW Japan arc; Thermal simulation; Slab melting; Sr-Nd-Pb isotopes; High-Mg andesite magma; 流紋岩質マグマ; 高Mg安山岩; 瀬戸内地域; 堆積物の融解; 西南日本弧; 中新世; テクトニクス; 異常高温; 日本海拡大; プレート融解; 同位体比

9.1 Timing of activity of Setouchi volcanic belt and the rotation of the SW Japan arcK-Ar dating and paleomagnetic investigations were conducted on lavas from the Setouchi volcanic rocks in SW Japan, in order to understand the tectonics of characteristic high-Mg andesite (HMA) magmatism. New 53 K-Ar ages confirm that the Setouchi volcanism occurred at 15-12 Ma, especially the volcanism of intermediate to mafic rocks including HMAs took place at 13 Ma. A paleomagnetic direction of 13.9 Ma was determined for the volcanic rocks in NE Shikoku area. This data and previous ones with the ages in this study indicates that NE Shikoku area rotated CW about 19。 between 13.9 and 12.8 Ma after the area experienced CW rotation at about 15 Ma as a part of SW Japan. Such additional CW rotations are inferred from paleomagnetic data in the east Shikoku and Osaka areas. The additional rotations possibly imply that rotations of faulted blocks occurred in the main part of SW Japan, or that a part of SW Jap … More an including the eastern Shikoku and Osaka areas rotated CW between about 15 and 12.8 Ma, for which rotation angle was larger than that for the CW rotation of the hole SW Japan at about 15 Ma9.2 Thermal structure of the upper mantle and the melting of the subducting slabCharacteristic high-Mg andesite magmas were produced in the SW Japan arc at 13-15 Ma that was synchronous with the commencement of subduction of a very young (<11 m.y.) lithosphere of the Shikoku Basin. Numerical simulation <deleted> suggests that temperature at the surface of such a young subducting plate is high enough for partial melting both of the subducting sediments and oceanic crust. High-Mg andesite magmas were likely to be produced by interaction between silicic slab melts and the overlying mantle wedge. HMA magmas may be commonly produced in the Archean subduction zones under relatively high mantle temperature conditions, contributing to making continental crusts.9.3 The slab-melting and Setouchi magma genesisIn order to evaluate the mechanism of production of unusual high-Mg andesite (HMA) magmas, Pb-Nd-Sr isotopic compositions were determined for HMAs and basalts from the Miocene Setouchi volcanic belt in the SW Japan arc. The isotopic compositions of Setouchi rocks form mixing lines between local oceanic sediments and Japan Sea backarc basin basalts, suggesting a significant contribution of the subducting sediment component to the HMA magma generation. Mixing calculations using compositions of an inferred original mantle and local oceanic sediments suggest that a sediment-derived melt, neither an H_2O-rich fluid nor an amphibolite/eclogite-derived melt, could have been produced first and served as a plausible metasomatic agent for the HMA magma source. The unusual tectonic setting, including subduction of a newly-borne hence hot plate, may be responsible for melting of subducting sediments. Less

9.1 Setouchi火山带活动的时机以及SW Japan Arck-Ar约会的旋转和古磁研究的旋转是在日本西南部的Setouchi火山岩的熔岩上进行的，以了解特征性的高含量高镁和斑点（HMA）磁岩的构造。新的53 k-ar时代证实，塞丘（Setouchi）火山症发生在15-12 Ma，尤其是包括HMA在内的中间岩石的火山，发生在13 mA。在NE Shikoku地区的火山岩确定了13.9 Ma的古磁方向。该数据和以前具有年龄的数据表明，NE Shikoku地区在该区域在SW Japan的一部分中经历了大约15 mA的CW旋转后，在13.9至12.8 mA之间旋转了CW。此类额外的CW旋转是从东shikoku和大阪地区的古磁数据中推断出来的。额外的轮换可能意味着故障块的旋转发生在西南部的主要部分，或者日本的一部分……更重要的是，包括东部的Shikoku和大阪地区，在大约15至12.8 Ma之间旋转CW旋转的CW旋转角度，其旋转角度大于日本的CW旋转，大约15 Ma9.2 MA9.2 MA99.2 MA的旋转量，并均高于梅尔的高级旋转，并呈融化的高度旋转，并呈融化的高度旋转。在SW Japan Arc以13-15 Ma的形式生产岩浆，这与Shikoku盆地非常年轻（<11 M.Y.）岩石圈的俯冲开始同步。数值模拟<deleted>表明，这种年轻的俯冲板表面的温度足够高，足以部分熔化的沉积物和海洋壳。高镁和有点岩浆很可能是通过硅平板融化与上覆的地幔楔之间的相互作用来产生的。 HMA岩浆可能在相对较高的地幔温度条件下通常在大代表的俯冲带中产生，这有助于进行大陆痉挛。9.3平板熔融和setouchi岩浆生殖器的命令，以评估不寻常的高mg和sr岩浆的生产机制，从在西南部日本弧线。 Setouchi岩石的同位素组成形成了局部海洋沉积物和日本海洋后盆地盆地之间的混合线，这表明俯冲沉积物成分对HMA岩浆产生产生了重要贡献。使用推断的原始地幔和局部海洋沉积物的组成进行混合，这表明沉积物衍生的熔体，即富含H_2O的液体，闪石/eclogite衍生的熔体，可以首先生产，并作为HMA Magma源的合理的化学剂。不寻常的构造环境，包括新生的俯冲，因此热板可能是导致俯冲沉积物融化的。较少的

项目成果

Tatsumi, Y.: "Trace element transport during dehydration processes in the subducted oceanic crust : 2, origin of chemcial and physical characteristics in arc magmatism." Earth Planet.Sci.Lett.148. 207-221 (1997)

Tatsumi, Y.：“俯冲洋壳脱水过程中的微量元素迁移：2，弧岩浆作用中化学和物理特征的起源。”

Tatsumi, Y.: "The petrology of melilite-olivine nephelinite from Hamada, SW Japan" Journal of Petrology. 40. 497-509

Tatsumi, Y.：“来自日本西南部滨田的黄长石-橄榄石霞石岩的岩石学”《岩石学杂志》。

巽 好幸: "地球惑星科学第10巻 地球内部ダイナミクス" 岩波書店(in press), (1997)

辰巳义之：《地球与行星科学第10卷：地球的内部动力学》岩波书店（正在出版），（1997年）

Tatsumi, Y.: "Subduction zone magmatism at depths to 2900 km : an overview" Bull.Volcanol.Soc.Japan. Spec.Vol.219-230 (1997)

Tatsumi, Y.：“2900 公里深处的俯冲带岩浆作用：概述”Bull.Volcanol.Soc.Japan。

Aizawa,Y.: "Element transport during dehydration of subducting sediments: experimental evidence for the origin of arc and ocean island basalts." The Island Arc. (in press).

Aizawa,Y.：“俯冲沉积物脱水过程中的元素传输：弧和洋岛玄武岩起源的实验证据。”