Sub-arc xenolith Fe-Li-Pb isotopes and textures tell tales of their journey through the mantle wedge and crust
Sub-arc xenolith Fe-Li-Pb isotopes and textures tell tales of their journey through the mantle wedge and crust
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DOI：
10.1130/g45359.1
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发表时间：
2018-09
期刊：
影响因子：
5.8
通讯作者：
S. Turner;H. Williams;S. Piazolo;J. Blichert‐Toft;Mitchell Gerdes;J. Adam;Xiao-Ming Liu;B. Schaefer;R. Maury
中科院分区：
文献类型：
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作者：
S. Turner;H. Williams;S. Piazolo;J. Blichert‐Toft;Mitchell Gerdes;J. Adam;Xiao-Ming Liu;B. Schaefer;R. Maury
岛弧提供了对大陆地壳起源和再循环的见解，但问题仍然是源交代作用，分化的深度，角闪石分馏的潜在作用，以及所涉及的时间尺度。菲律宾巴坦岛的玄武安山岩中含有熔融-岩石反应生成的角闪石和辉长岩皮中包裹的≥150 Ma橄榄岩碎块。橄榄岩的δ 7 Li和δ 57 Fe值是地幔岩中最轻的。这些值是太分馏已经创建单独的平衡部分熔融，因此需要熔体耗尽和板流体添加的组合，并可能来自扩散改性熔体通道围岩。稳定同位素信号很容易被橄榄岩和寄主岩浆之间的扩散平衡所改变，因此，这里保存的轻δ 7 Li和δ 57 Fe表明岩浆的上升速率为10 km/yr−1。研究表明，在25-30 km深度的熔体-围岩反应导致角闪石（±斜长石）结晶，随后在27 km深度发生辉长岩分馏。前者提供了一个位置和机制的“隐”角闪石分馏观察到在这些和许多其他弧熔岩，并可能排除了分层的堆积的要求。
Island arcs provide insights into the origin and recycling of continental crust, but questions remain concerning source metasomatism, the depth of differentiation, the potential role of amphibole fractionation, and the time scales involved. Basaltic andesites on Batan Island (Philippines) contain ≥150 Ma peridotite fragments encased in hornblendite and gabbroic rinds produced via melt-rock reaction. The peridotites have some of the lightest δ7Li and δ57Fe values yet measured in mantle rocks. These values are too fractionated to have been created solely by equilibrium partial melting and thus require a combination of melt depletion and slab fluid addition and may be derived from diffusion-modified melt channel wall rocks. Stable isotope signals are easily modified by diffusive equilibration between peridotite and host magma, so the preservation of light δ7Li and δ57Fe here suggests magma ascent rates of ∼10 km yr−1. We show that melt–wall rock reactions at ∼25–30 km depth led to the crystallization of amphibole (± plagioclase) followed by gabbroic fractionation at ∼7 km depth. The former provides a location and mechanism for the “cryptic” amphibole fractionation observed in these and perhaps many other arc lavas and may obviate the requirement for delamination of cumulates.