Magmatic Response to Subduction Initiation, Part II: Boninites and Related Rocks of the Izu‐Bonin Arc From IODP Expedition 352
Magmatic Response to Subduction Initiation, Part II: Boninites and Related Rocks of the Izu‐Bonin Arc From IODP Expedition 352
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DOI：
10.1029/2020gc009093
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发表时间：
2020-11
期刊：
影响因子：
3.7
通讯作者：
J. Shervais;M. Reagan;M. Godard;J. Prytulak;J. Ryan;J. Pearce;R. Almeev;Hongyang Li;E. Haugen;T. Chapman;W. Kurz;W. Nelson;D. Heaton;M. Kirchenbaur;K. Shimizu;T. Sakuyama;S. Vetter;Yibing Li;S. Whattam
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文献类型：
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作者：
J. Shervais;M. Reagan;M. Godard;J. Prytulak;J. Ryan;J. Pearce;R. Almeev;Hongyang Li;E. Haugen;T. Chapman;W. Kurz;W. Nelson;D. Heaton;M. Kirchenbaur;K. Shimizu;T. Sakuyama;S. Vetter;Yibing Li;S. Whattam
国际海洋探索计划第352次对伊豆-博宁前弧的考察覆盖了超过800米的基底，包括博宁岩和博宁岩系列熔岩。这是迄今为止从原位海洋地壳中获得的最广泛、最受约束的博宁岩系熔岩套件。根据其SiO2 - MgO - TiO2的关系，将其分为高硅博云石（HSB）、低硅博云石（LSB）和玄武质博云石。三个系列的主要分选产物均为高镁安山岩（HMA）。海底250米以下的熔岩（mbsf）在弧前扩张轴上喷发，以LSB和HMA为主。小于250 mbsf的熔岩是离轴喷发的，以HSB为主。轴向和离轴熔岩在其主要、微量和同位素组成上具有明显的化学地层学趋势。离轴熔岩的化学性质与Chichijima类型地的boninite相似，具有凹向上的稀土元素模式。相比之下，更丰富的轴向熔岩具有明显的轻稀土元素耗尽模式，代表了一种新的，以前未采样的Chichijima型boninite熔岩的前身。岩石成因模拟表明，轴向熔岩是由难熔地幔（可能是弧前玄武岩提取的残留物）与角闪岩相熔体（来自俯冲蚀变的海洋地壳）相互作用形成的。上部离轴熔岩还需要沉积物衍生熔体的额外成分。这两个模型都与以前发表的同位素数据一致。
International Ocean Discovery Program Expedition 352 to the Izu‐Bonin forearc cored over 800 m of basement comprising boninite and boninite‐series lavas. This is the most extensive, well‐constrained suite of boninite series lavas ever obtained from in situ oceanic crust. The boninites are characterized as high‐silica boninite (HSB), low‐silica boninite (LSB), or basaltic boninite based on their SiO2‐MgO‐TiO2 relations. The principal fractionation products of all three series are high‐Mg andesites (HMA). Lavas recovered >250 meters below seafloor (mbsf) erupted at a forearc spreading axis and are dominated by LSB and HMA. Lavas recovered from <250 mbsf erupted off‐axis and are dominated by HSB. The axial and off‐axis lavas are characterized by distinct chemostratigraphic trends in their major, trace, and isotopic compositions. The off‐axis lavas are chemically similar to boninite from the type locality at Chichijima, with concave‐upward rare earth elements patterns. In contrast, the more abundant axial lavas have distinctly light rare earth element‐depleted patterns and represent a new, previously unsampled precursor to the Chichijima‐type boninite lavas. Petrogenetic modeling suggests that the axial lavas formed by fluxing of refractory mantle (likely the residue from forearc basalt extraction), with amphibolite‐facies melt derived from subducting altered oceanic crust. The upper, off‐axis lavas require an additional component of sediment‐derived melt in addition. Both models are consistent with previously published isotopic data.