Carbon dioxide released from subduction zones by fluid-mediated reactions
Carbon dioxide released from subduction zones by fluid-mediated reactions
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DOI：
10.1038/ngeo2143
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发表时间：
2014-05-01
影响因子：
18.3
通讯作者：
Nicolescu, Stefan
中科院分区：
文献类型：
--
作者：
Ague, Jay J.;Nicolescu, Stefan
含碳酸盐矿物的岩石俯冲到地幔中与二氧化碳通过火山和变质脱气返回大气之间的平衡(1-4) 对于碳循环至关重要。碳被认为主要是通过简单的脱挥发分反应从俯冲岩石中释放出来的(5-7)。然而，这些反应也会在俯冲板片内保留大量碳，并且难以解释火山弧排放的二氧化碳质量。因此，碳释放可能是通过碳酸钙的流体诱导溶解而发生的(8-10)。在这里，我们利用碳酸盐三角洲 O-18 和三角洲 C-13 系统学，结合岩石和流体包裹体矿物学和地球化学分析，研究了希腊锡罗斯岛和蒂诺斯群岛发掘的始新世基克拉迪俯冲杂岩的蚀变。我们发现，在俯冲过程中活跃的两个流体管道附近的大理石岩石中，接近管道时碳酸钙的丰度急剧减少，而硅酸盐矿物则增加。高达 60-90% 的二氧化碳从岩石中释放出来，远高于通过简单的脱挥发分反应所预期的量。碳酸盐矿物的 Delta O-18 比变质碳酸盐岩的典型值轻 5-10，这意味着同位素轻氧是通过周围流体渗透输送的。我们认为，流体介导的碳酸盐矿物去除，伴随着硅酸盐矿物沉淀，为俯冲带释放大量二氧化碳提供了机制。
The balance between the subduction of carbonate mineral-bearing rocks into Earth's mantle and the return of CO2 to the atmosphere by volcanic and metamorphic degassing(1-4) is critical to the carbon cycle. Carbon is thought to be released from subducted rocks mostly by simple devolatilization reactions(5-7). However, these reactions will also retain large amounts of carbon within the subducting slab and have difficulty in accounting for the mass of CO2 emitted from volcanic arcs. Carbon release may therefore occur via fluid-induced dissolution of calcium carbonate(8-10). Here we use carbonate delta O-18 and delta C-13 systematics, combined with analyses of rock and fluid inclusion mineralogy and geochemistry, to investigate the alteration of the exhumed Eocene Cycladic subduction complex on the Syros and Tinos islands, Greece. We find that in marble rocks adjacent to two fluid conduits that were active during subduction, the abundance of calcium carbonate drastically decreases approaching the conduits, whereas silicate minerals increase. Up to 60-90% of the CO2 was released from the rocks-far greater than expected via simple devolatilization reactions. The delta O-18 of the carbonate minerals is 5-10 lighter than is typical for metamorphosed carbonate rocks, implying that isotopically light oxygen was transported by fluid infiltration from the surroundings. We suggest that fluid-mediated carbonate mineral removal, accompanied by silicate mineral precipitation, provides a mechanism for the release of enormous amounts of CO2 from subduction zones.