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刘景波. 2019. 俯冲带变质过程中的含碳流体. 岩石学报, 35(1): 89-98
俯冲带变质过程中的含碳流体
作者单位
刘景波 中国科学院地质与地球物理研究所, 岩石圈演化国家重点实验室, 北京 100029
中国科学院大学地球与行星科学学院, 北京 100049 
基金项目:本文受国家自然科学基金项目(41372080)和岩石圈演化国家重点实验室自主研究课题(201707)联合资助.
摘要:
      俯冲带含碳岩石通过俯冲过程的变质反应生成了含碳水流体、富硅酸盐的超临界流体和含碳熔体。不同类型流体的形成与岩石成分和岩石经历的温压条件相关。岩石中碳酸盐矿物脱碳反应的温压条件取决于岩石起初的流体成分:有水存在时,反应发生在低温条件下。在高压条件下,碳酸盐矿物在水或含盐水流体的溶解是生成含碳流体重要的机制,其导致的碳迁移作用可能超过脱碳变质反应的作用。高温条件下,含碳岩石的部分熔融可以生成含碳的熔体,这在热俯冲环境和俯冲带岩石底辟到上覆地幔的情况下是碳迁移重要载体。富硅酸盐的超临界流体可能是在第二临界端点上形成的超临界流体,目前在超高压岩石中观察到的非花岗质成分的多相固体包裹体被认为是这种流体结晶的产物,然而对其理解尚存在很多问题,需要进一步的实验研究。地表含碳岩石在俯冲带被带到深部,俯冲带地温特征的不同导致了不同类型含碳流体的形成,这些流体运移至上覆地幔引起岩石部分熔融产生含碳的岛弧岩浆,岩浆喷出到地表释放了其中的碳,这构成了俯冲带-岛弧系统的碳循环。
英文摘要:
      Carbon-bearing rocks in subduction zones produce carbon-bearing aqueous fluids, silicate-rich supercritical fluids and carbon-bearing melts by metamorphic reactions during the subduction process. The formation of different fluid types relies on the compositions of rocks and the P-T conditions that the rocks suffered. The P-T conditions of carbonate devolatilization reactions depend on the initial compositions of fluids, and in the presence of H2O, the reactions occur at decreasing temperature conditions. At the high-pressure conditions, the dissolution of carbonate minerals in fluid is substantial mechanism for formation of carbon-bearing fluid, which parobably plays more important role than that of carbonate devolatilization reactions for carbon removal of rocks. In high-temperature circumstances such as hot subduction zones and in the case of diapirs of the rocks of subduction zones into mantle wedge, partial melting of carbon-bearing rocks can produce carbon-bearing melts that are responsible for carbon migration. Silicate-rich supercritical fluids probably form above the second critical endpoint, and multiphase solid inclusions observed in some minerals of UHP rocks were considered to be crystallized from such fluids. However, there are many open questions, and more experiments need for such interpretation. Carbon-bearing rocks in subduction zones were brought into deep mantle by subduction, and produce different types of carbon-bearing fluids in terms of different geotherms of subduction zones. The migration of carbon-bearing fluids into mantle wedge results in formation of carbon-bearing arc magmas, and subducted carbon is finally released to the surface in the eruptive process of the magmas, which makes the cycle of carbon in subduction zone-island arc system.
关键词:俯冲带  碳循环  含碳流体  多相包裹体  熔体包裹体
投稿时间:2018-09-11  修订日期:2018-11-18
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