Geochemical mapping of slab-derived fluid and source mantle along Japan arcs
Geochemical mapping of slab-derived fluid and source mantle along Japan arcs
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DOI：
10.1016/j.gr.2019.01.007
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发表时间：
2019-06
影响因子：
6.1
通讯作者：
Hitomi Nakamura;H. Iwamori;M. Nakagawa;T. Shibata;J. Kimura;T. Miyazaki;Q. Chang;B. Vaglarov;Toshiro Takahashi;Y. Hirahara
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文献类型：
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作者：
Hitomi Nakamura;H. Iwamori;M. Nakagawa;T. Shibata;J. Kimura;T. Miyazaki;Q. Chang;B. Vaglarov;Toshiro Takahashi;Y. Hirahara
虽然板片流体显着影响熔体的生成和俯冲带内的动力学，其数量和分布没有得到充分的限制，目前。在这里，我们使用同位素系统学的弧火山岩，俯冲物质，和内在地幔成分交代作用之前，量化的贡献板派生流体交代覆盖地幔楔下的整个地区的日本弧。同时应用几个多元统计分析（聚类分析和主/独立成分分析）的同位素数据集允许日本弧大致分为东部和西部的部分在第一顺序。此外，一个明确的高阶弧间分割观察，连同一些弧内的变化，可能对应于传入板块的异质性。弧间分割被示出为主要由板和弧的几何参数控制（例如，在大洋或大陆地壳之下的单一板块或双板块的俯冲），这导致地幔楔和板片热条件之间的差异。因此，千岛群岛和伊豆弧，其中有薄的弧壳（~20公里），表现出最低程度的板片衍生流体添加（0.1重量%）的地幔楔，而东北日本弧，弧壳较厚（高达36公里），具有较高的值为0.2重量%，虽然板片热参数为这三个弧基本上是相同的。由于太平洋和菲律宾海板块的重叠俯冲，日本中部弧显示出最高程度的板片衍生流体添加（>1.0重量%），而日本西南部和琉球弧的特征值为中等，约0.5重量%。此外，在日本西南部和日本海观测到了明显的外来烟羽带和斑点。除了板片流体成分的变化，地幔的内在成分（板片流体诱导交代作用之前）显示出明显的沿弧变化，这可能是由大规模的地幔流从大陆一侧。因此，板片衍生的流体添加和地幔成分的变化同样有助于弧间分割，这突出了本地和区域热流结构的板幔系统的重要性。
Although slab-derived fluid significantly affects melt generation and dynamics within subduction zones, its amount and distribution are not sufficiently constrained at present. Herein, we use isotopic systematics of arc volcanic rocks, subducting materials, and intrinsic mantle components prior to metasomatism, to quantify the contribution of the slab-derived fluid that metasomatizes the overlying mantle wedge beneath the entire area of Japan arcs. Simultaneous application of several multivariate statistical analyses (clustering analysis and principal/independent component analyses) to the isotopic data set allows Japan arcs to be broadly divided into eastern and western parts at the first order. Moreover, a clear higher-order inter-arc segmentation is observed, together with some intra-arc variations that possibly correspond to the heterogeneity of incoming plates. Inter-arc segmentation is shown to be primarily controlled by the geometrical parameters of the slab and the arc (e.g., subduction of a single plate or double plates beneath either oceanic or continental crust), which results in differences between mantle wedge and slab thermal conditions. Accordingly, the Kuril and Izu arcs, which have thin arc crusts (~20 km), exhibit the lowest extent of slab-derived fluid addition (0.1 wt%) to the mantle wedge, while the NE Japan arc, with a thicker arc crust (up to 36 km), features a higher value of 0.2 wt%, although the slab thermal parameters for these three arcs are essentially the same. The Central Japan arc shows the highest extent of slab-derived fluid addition (>1.0 wt%) because of the overlapping subduction of Pacific and Philippine Sea slabs, while the SW Japan and Ryukyu arcs feature moderate values of ~0.5 wt%. Moreover, a clear exotic plume zone and spots are observed in SW Japan and the Japan Sea. In addition to the variability of slab-derived fluid composition, the intrinsic mantle composition (before slab-derived fluid–induced metasomatism) shows a clear along-arc variation that is possibly caused by a large-scale mantle flow from the continental side. Thus, slab-derived fluid addition and mantle composition variability equally contribute to inter-arc segmentation, which highlights the importance of both local and regional thermal flow structures of slab-mantle systems.