Trace element characteristics of the fluid liberated from amphibolite-facies slab: Inference from the metamorphic sole beneath the Oman ophiolite and implication for boninite genesis
Trace element characteristics of the fluid liberated from amphibolite-facies slab: Inference from the metamorphic sole beneath the Oman ophiolite and implication for boninite genesis
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DOI：
10.1016/j.epsl.2005.09.049
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发表时间：
2005-12-01
影响因子：
5.3
通讯作者：
Masuda, T
中科院分区：
文献类型：
--
作者：
Ishikawa, T;Fujisawa, S;Masuda, T
通过对Wadi Tayin地区阿曼蛇绿岩地幔剖面下230 m厚的变质底壳中斜长角闪岩和石英岩的主量和微量元素组成的测定，探讨了俯冲斜长角闪岩相板片释放的含水流体的化学特征。流体不动元素组成表明，这些岩石的原岩是洋中脊玄武岩样拉斑玄武岩和深海硅质岩，这是一致的想法，这些岩石代表特提斯洋壳覆盖在早期，洋内逆冲阶段的阿曼蛇绿岩侵位。的斜长角闪岩的稀土元素（REE）和高场强元素的浓度显示有限的变化，在两个因素内，除了少数演变的样品，整个横断面的唯一。另一方面，流体活动元素，特别是B，Rb，K和Ba，在斜长角闪岩中的浓度在顶部30米的底部（>600摄氏度的峰值变质温度）高度升高，这表明在俯冲变质作用期间与演化的，B-Rb-K-Ba-富流体的平衡。在较低的150英寸（500至550摄氏度）的斜长角闪岩的比较表明，微量元素光谱的流体平衡与高级斜长角闪岩可能会有所不同，作为变质温度的函数。流体具有明显富集B、Rb、K、Ba和中、微量富集Sr、Li、Be、Pb的特征。在更高的温度下（高达700摄氏度），除了上述元素外，流体还显著富含轻PEE和Nb。估算的微量元素光谱与成熟的内弧玄武岩的成分不一致，但令人满意地解释了阿曼蛇绿岩中发现的低铅安山岩和玻安岩的特征。阿曼和其他地区的玻安岩之间的成分相似性表明，这里估计的流体很好地代表了角闪岩衍生的流体参与岩浆的未成熟，热，浅俯冲带。(C)2005 Elsevier B. V.保留所有权利。
Major and trace element compositions of amphibolites and quartzose rocks in the 230-m-thick metamorphic sole underlying the mantle section of the Oman ophiolite in Wadi Tayin area were determined to investigate the chemical characteristics of the hydrous fluid released from subducted amphiboltie-facies slab. The fluid-immobile element compositions indicate that protoliths of these rocks are mid-ocean ridge basalt-like tholeiite and deep-sea chert, which is consistent with the idea that these rocks represent Tethyan oceanic crust overridden during the early, intraoceanic thrusting stage of the Oman ophiolite emplacement. The rare-earth element (REE) and high field-strength element concentrations of the amphibolites show limited variations, within a factor of two except for a few evolved samples, throughout transect of the sole. On the other hand, concentrations of fluid-mobile elements, especially B, Rb, K and Ba, in amphibolites are highly elevated in tipper 30 m of the sole (>600 degrees C in peak metamorphic temperature), suggesting the equilibration with evolved, B-Rb-K-Ba-rich fluids during prograde metamorphism. The comparison with amphibolites in the lower 150 in (500 to 550 degrees C) demonstrates that the trace element spectra of the fluids equilibrated with the high-level amphibolites may vary as a function of metamorphic temperature. The fluids are characterized by striking enrichments of B, Rb, K and Ba and moderate to minor enrichments of Sr, Li, Be and Pb. At higher temperature (up to 700 degrees C), the fluids become considerably enriched in light PEE and Nb in addition to the above elements. The estimated trace element spectra of the fluids do not coincide with the compositions of basalts from matured intra-occanic arcs, but satisfactorily explain the characteristics of the low-Pb andesites and boninites found in the Oman ophiolite. Compositional similarity between the boninites of Oman and other localities suggests that the fluids estimated here well represent the amphibolite-derived fluids involved in the magmatism of immatured, hot, shallow subduction zones. (C) 2005 Elsevier B.V. All rights reserved.