Slab Transport of Fluids to Deep Focus Earthquake Depths—Thermal Modeling Constraints and Evidence From Diamonds
Slab Transport of Fluids to Deep Focus Earthquake Depths—Thermal Modeling Constraints and Evidence From Diamonds
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DOI：
10.1029/2020av000304
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发表时间：
2021-05
期刊：
影响因子：
8.4
通讯作者：
S. Shirey;L. Wagner;M. Walter;D. Pearson;P. V. van Keken
中科院分区：
文献类型：
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作者：
S. Shirey;L. Wagner;M. Walter;D. Pearson;P. V. van Keken
深源地震的性质和成因在地震学领域仍然是一个长期的未知数。我们提出了新的模型的俯冲板追溯到地幔过渡带的深度，允许板压力/温度（P/T）路径和水合/碳酸盐矿物相关系之间的详细比较的热结构。我们发现，能够将水输送到致密含水镁硅酸盐中过渡区深度的板块与在300-km深度以下（主要在500至700 km之间）产生地震活动的板块之间存在显着的相关性。这一深度范围也与P/T条件相吻合，在该条件下，冷板中的海洋地壳岩性预计将与含碳酸盐的玄武岩固相线相交，产生碳酸盐熔体。这两种形式的流体演化都很好地代表了岩石圈下的金刚石，其包裹体记录了来自水化或碳酸盐岩板的熔体，流体或超临界液体的存在，深度（300-700 km）通常与深源地震一致。我们认为，从这些深度的俯冲板释放的含水和碳酸盐流体导致流体触发的地震活动，流体迁移，金刚石沉淀和包裹体结晶。深源地震震源可以跟踪地幔深部流体释放、运移和金刚石形成的大致区域。地幔板块的热模拟和岩石圈下金刚石、深源地震和深部板块之间的相关性表明，碳和挥发物绕过浅层脱碳和脱水过程，存在一条通往地幔过渡区的深俯冲路径。
The nature and cause of deep earthquakes remain enduring unknowns in the field of seismology. We present new models of thermal structures of subducted slabs traced to mantle transition zone depths that permit a detailed comparison between slab pressure/temperature (P/T) paths and hydrated/carbonated mineral phase relations. We find a remarkable correlation between slabs capable of transporting water to transition zone depths in dense hydrous magnesium silicates with slabs that produce seismicity below ∼300‐km depth, primarily between 500 and 700 km. This depth range also coincides with the P/T conditions at which oceanic crustal lithologies in cold slabs are predicted to intersect the carbonate‐bearing basalt solidus to produce carbonatitic melts. Both forms of fluid evolution are well represented by sublithospheric diamonds whose inclusions record the existence of melts, fluids, or supercritical liquids derived from hydrated or carbonate‐bearing slabs at depths (∼300–700 km) generally coincident with deep‐focus earthquakes. We propose that the hydrous and carbonated fluids released from subducted slabs at these depths lead to fluid‐triggered seismicity, fluid migration, diamond precipitation, and inclusion crystallization. Deep focus earthquake hypocenters could track the general region of deep fluid release, migration, and diamond formation in the mantle. The thermal modeling of slabs in the mantle and the correlation between sublithospheric diamonds, deep focus earthquakes, and slabs at depth demonstrate a deep subduction pathway to the mantle transition zone for carbon and volatiles that bypasses shallower decarbonation and dehydration processes.