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Zinc Isotopes of the Mariana and Ryukyu Arc-Related Lavas Reveal Recycling of Forearc Serpentinites Into the Subarc Mantle
Journal of Geophysical Research: Solid Earth ( IF 3.9 ) Pub Date : 2021-11-01 , DOI: 10.1029/2021jb022261
Zuxing Chen 1, 2, 3 , Jiubin Chen 4 , Zhigang Zeng 1, 2, 3, 5 , Landry Soh Tamehe 6 , Ting Zhang 4 , Yuxiang Zhang 1, 2, 3 , Xuebo Yin 1, 2, 3 , Xiaoyuan Wang 1, 2, 3 , Shuai Chen 1, 2, 3 , Wangcai Shuai 4
Affiliation  

Mantle source heterogeneity of arc-related magmas was traditionally thought to be predominantly affected by slab-derived components. However, the role of forearc serpentinites in causing subarc mantle heterogeneity remains poorly constrained. Here, we present the first Zn isotope data for lavas from the Mariana and Ryukyu subduction zones. Notably, the δ66Zn values of basaltic lavas from the Mariana arc (0.16–0.18‰) and southern Okinawa Trough (0.15–0.17‰) are generally lower (∼0.10‰) than those of the mid-ocean ridge basalts (MORB) (0.27 ± 0.05‰). Since mantle melting and magmatic differentiation respectively induce heavy Zn isotope enrichment in primary and evolved magmas, while melt extraction yields the limited Zn isotope fractionation in the mantle, lavas with low δ66Zn values thus potentially indicate the addition of subducted components. The negative correlation between the δ66Zn values and the Ba/La ratios of the basaltic lavas suggests the involvement of isotopically light fluids in their mantle sources. Forearc serpentinites are typically characterized by extremely light Zn isotope compositions. Such forearc materials were likely dragged downward to subarc depths and released isotopically light Zn in fluids to modify the overlying mantle wedge, thereby producing low δ66Zn values in arc-related magmas. Beyond subarc depths, forearc serpentinites are broken down completely, so light Zn isotope fluids are absent. Accordingly, the basalts from the middle Mariana and Okinawa Trough display MORB-like δ66Zn values. Collectively, Zn isotope provides new insights into the role of the recycling of forearc serpentinites in generating chemical heterogeneity in the mantle source of subduction-related magmas.

中文翻译:

马里亚纳和琉球弧相关熔岩的锌同位素揭示前弧蛇纹石再循环到亚弧地幔

传统上认为弧相关岩浆的地幔源非均质性主要受板片衍生成分的影响。然而,弧前蛇纹岩在导致弧下地幔异质性方面的作用仍然受到很大限制。在这里,我们展示了来自马里亚纳和琉球俯冲带的熔岩的第一个 Zn 同位素数据。值得注意的是,来自马里亚纳弧(0.16-0.18‰)和冲绳海槽南部(0.15-0.17‰)的玄武质熔岩的δ 66 Zn值普遍低于(~0.10‰)洋中脊玄武岩(MORB) (0.27 ± 0.05‰)。由于地幔熔融和岩浆分异分别在原生岩浆和演化岩浆中诱导了大量的锌同位素富集,而熔体提取在地幔中产生了有限的锌同位素分馏,具有低δ 66 的熔岩因此,Zn 值可能表明添加了俯冲成分。δ 66 Zn 值与玄武岩熔岩的 Ba/La 比率之间的负相关表明同位素轻流体参与了它们的地幔源。Forarc 蛇纹岩通常以极轻的 Zn 同位素组成为特征。这种前弧物质很可能被向下拖曳到弧下深度,并在流体中释放同位素轻锌以改变上覆地幔楔,从而在弧相关岩浆中产生低 δ 66 Zn 值。在弧下深度之外,弧前蛇纹岩被完全分解,因此不存在轻锌同位素流体。因此,马里亚纳海槽中部和冲绳海槽的玄武岩显示出类似 MORB 的δ 66锌值。总的来说,锌同位素为弧前蛇纹岩的再循环在俯冲相关岩浆的地幔源中产生化学异质性的作用提供了新的见解。
更新日期:2021-11-17
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