Spatial variation of subduction zone fluids during progressive subduction: Insights from Serpentinite Mud Volcanoes
Spatial variation of subduction zone fluids during progressive subduction: Insights from Serpentinite Mud Volcanoes
复制标题
DOI：
10.1016/j.gca.2021.10.030
复制
发表时间：
2021-11
影响因子：
5
通讯作者：
C. Menzies;R. Price;J. Ryan;O. Sissmann;K. Takai;C. Geoffrey Wheat
中科院分区：
文献类型：
--
作者：
C. Menzies;R. Price;J. Ryan;O. Sissmann;K. Takai;C. Geoffrey Wheat
俯冲带的地质作用控制着地震活动、深成岩活动和火山活动，以及海洋、地壳和地幔之间的地球化学循环。下行板块经历变质作用，伴随的脱水作用和流体流动改变了板块界面和地幔楔的物理性质，控制了下行进入地幔的物质成分。任何直接研究板块在俯冲过程中的演变都受到这些过程发生的禁止深度的限制。为了研究这些过程，我们使用马里亚纳前弧中的蛇纹岩泥火山，可以对从俯冲通道上升的蛇纹岩材料及其孔隙沃茨水进行采样。我们提出了新的孔隙水化学数据从山顶和侧面的三个蛇纹岩泥火山，在国际海洋发现计划远征366期间，这是反映在地壳和地幔的反应，在早期，浅（<20公里）阶段的俯冲。我们表明，通过热力学模型，我们的新数据的孔隙水化学成分的演变反映了矿物学特征的主要玄武岩源下行太平洋板块。然而，沉积物来源的成分是可能的，特别是对于海沟附近的泥火山。其他潜在的板片衍生成分，如岩石圈蛇纹岩，富含碳酸盐的沉积物，或海山玄武岩与板内地球化学特征，不需要解释我们的结果。我们的研究结果表明，随着逐渐俯冲，在250 °C的硬铝石-绿帘石矿物转化边界可能有助于驱动板状碳酸盐的不稳定，尽管在这样的温度和预计压力（2300 °C和20.6 GPa）下它具有明显的热力学稳定性。新的溶解气体数据还指出，主要的热力学控制甲烷/乙烷生产的俯冲通道内的深度板增加。我们的研究结果提供了直接的证据，逐步矿物学和化学演化的俯冲大洋板块，释放一个逐步演变的流体相到俯冲通道。
Geological processes at subduction zones control seismicity, plutonism and volcanism, and geochemical cycling between the oceans, crust, and mantle. The down-going plate experiences metamorphism, and the associated dehydration and fluid flow alters the physical properties of the plate interface and mantle wedge, as well as controlling the composition of material descending into the mantle. Any direct study of slab evolution during subduction is inhibited by the prohibitive depths at which these processes occur. To examine these processes we use serpentinite mud volcanoes in the Mariana forearc, that permit sampling of serpentinite materials and their pore waters that ascend from the subduction channel. We present new pore water chemical data from the summit and flanks of three serpentinite mud volcanoes that were drilled during International Ocean Discovery Program Expedition 366 which are reflective of reactions within the crust and mantle during the early, shallow (<20 km) stages of subduction. We show, via thermodynamic modelling, that our new data on the evolution of pore water chemical compositions reflect mineralogical characteristics of a predominately basaltic source from the downgoing Pacific Plate. However, a component from sedimentary sources is likely, especially for those mud volcanoes near the trench. Other potential slab-derived constituents, such as lithospheric serpentinite, carbonate-rich sediments, or seamount basalts with an intraplate geochemical character, are not required to explain our results. Our results indicate that with progressive subduction the lawsonite-epidote mineral transformation boundary at ∼250 °C may help drive slab carbonate destabilisation, despite its apparent thermodynamic stability at such temperatures and projected pressures (∼300 °C and ∼0.6 GPa). New dissolved gas data also point to primary thermodynamic controls over methane/ethane production within the subduction channel as depths-to-slab increase. Our findings provide direct evidence for the progressive mineralogical and chemical evolution of a subducting oceanic plate, which liberates a progressively evolving fluid phase into the subduction channel.