The importance of talc and chlorite “hybrid” rocks for volatile recycling through subduction zones; evidence from the high-pressure subduction mélange of New Caledonia
The importance of talc and chlorite “hybrid” rocks for volatile recycling through subduction zones; evidence from the high-pressure subduction mélange of New Caledonia
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DOI：
10.1007/s00410-007-0236-2
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发表时间：
2008-02
影响因子：
3.5
通讯作者：
C. Spandler;J. Hermann;K. Faure;J. Mavrogenes;R. Arculus
中科院分区：
文献类型：
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作者：
C. Spandler;J. Hermann;K. Faure;J. Mavrogenes;R. Arculus
流体和微量元素从板片向地幔楔的转移不能用简单的板片脱挥发分模型来充分解释。新喀里多尼亚北方榴辉岩相混杂岩带代表了以前俯冲的洋壳，并含有大量与蛇纹岩有关的滑石和云母片岩。这些岩石中含有大量的H2O和CO2，并可能将挥发物输送到俯冲带的深层。滑石、钠长石片岩和蛇纹岩的体相和稳定同位素组成表明，蛇纹岩是俯冲前大洋岩石圈海水蚀变的产物，而滑石和钠长石片岩则是俯冲过程中镁铁质岩、超镁铁质岩和变质沉积岩混杂岩的流体交代产物。在俯冲带，滑石和钠片岩的脱水应发生在弧下深度，温度（约800°C）明显高于其他岩性（400-650°C）。在这些条件下释放的流体可以携带高的微量元素含量，并可能引发邻近的泥质岩和镁铁质岩的部分熔融，因此可能是至关重要的挥发性和微量元素转移到弧岩浆的源区。相比之下，这些混合岩石在俯冲过程中不太可能经历显著的脱碳作用，因此可能对碳循环到地幔深处很重要。
The transfer of fluid and trace elements from the slab to the mantle wedge cannot be adequately explained by simple models of slab devolatilization. The eclogite-facies mélange belt of northern New Caledonia represents previously subducted oceanic crust and contains a significant proportion of talc and chlorite schists associated with serpentinite. These rocks host large quantities of H2O and CO2and may transport volatiles to deep levels in subduction zones. The bulk-rock and stable isotope compositions of talc and chlorite schist and serpentinite indicate that the serpentinite was formed by seawater alteration of oceanic lithosphere prior to subduction, whereas the talc and chlorite schists were formed by fluid-induced metasomatism of a mélange of mafic, ultramafic and metasedimentary rocks during subduction. In subduction zones, dehydration of talc and chlorite schists should occur at sub-arc depths and at significantly higher temperatures (∼ 800°C) than other lithologies (400–650°C). Fluids released under these conditions could carry high trace-element contents and may trigger partial melting of adjacent pelitic and mafic rocks, and hence may be vital for transferring volatile and trace elements to the source regions of arc magmas. In contrast, these hybrid rocks are unlikely to undergo significant decarbonation during subduction and so may be important for recycling carbon into the deep mantle.