Characterising devolatilisation beneath the Mariana Forearc

马里亚纳前弧下方的挥发分蒸发特征

• 批准号: NE/P020909/1
• 负责人: Damon Teagle
• 金额: $ 13.01万
• 依托单位: University of Southampton
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2016
• 资助国家: 英国
• 起止时间: 2016 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FP020909%2F1
• 关键词: Characterising; devolatilisation; beneath; Mariana; Forearc

There are two types of crust that make up the plates of the World; oceanic and continental, the former is thin and dense and underlies the oceans of the world; and the latter is considerably thicker and more buoyant and makes up the continents. Oceanic crust forms at divergent plate boundaries known as mid ocean ridges, chains of underwater volcanoes. As the newly formed crust ages and moves further from the ridge it cools, becomes denser and sinks. Where a convergent plate boundary occurs between oceanic and continental crust the denser oceanic crust sinks and subducts beneath the continental crust. Where convergence occurs between two oceanic plates, the older, denser plate sinks and subducts. Such boundaries are responsible for the deepest oceanic trenches on Earth, for example the Mariana Trench (deepest point 11,033 m).Subduction zones are the principal areas on Earth where crustal materials are transported into the mantle and therefore represent the fundamental recycling process in plate tectonic theory. Geological processes at these convergent margins control seismicity, plutonism and associated volcanism, and geochemical cycling between the ocean, crust and mantle. These margins commonly generate large, tsunamigenic earthquakes, thus understanding the physical properties controlling seismogenesis at the subduction interface is key to elucidating plate boundary behaviour. Sediments and crustal rocks experience changing pressures and temperatures as they subduct, minerals become unstable and breakdown to form new, denser minerals, and in doing so release fluids that are buoyant and rise into the faults above where earthquakes nucleate and interact with overlying mantle rocks. The chemical and physical changes that the subducting plate undergoes prior to the onset of melting controls earthquake behaviour, geochemical cycling and magmatism at these plate boundaries.To study these processes old pieces of subduction zones that have been uplifted onto the present day continental crust have been studied, but the chemical and physical changes that occurred during the transport of these sections of oceanic crust onto the continents are poorly constrained, and there are large errors on estimated pressures and temperatures of formation. Studying these processes in situ is difficult because they occur deep in the crust and in the some of deepest stretches of water on Earth. Subduction zones that are covered by thick piles of accreted sediments have been successfully drilled, but the thick sediment piles obscures signatures of deep fluids and so the deep subduction zone processes cannot be studied.At the Mariana convergent margin, the Pacific Plate subducts under the Mariana Plate where there is little sediment overburden. The Mariana Plate is faulted and these faults are associated with mud volcanoes. The mud volcanoes originate from the passage of fluids liberated from the subducting plate and carry material from this plate and chemically altered overlying mantle with them. This provides a unique opportunity to sample fluids generated during subduction and materials from the subducting plate without having to drill deep.We will use samples from the IODP Expedition 366 drilling into mud volcanoes in the Mariana forearc to analyse waters generated during subduction. Previous work shows that fluid chemistry changes as the plate moves deeper. We will measure the isotopic ratios of different chemical tracers in the fluids to document the evolution of these processes and metamorphic transformations in the downgoing rocks and the chemical reactions the fluids facilitate in the overlying mantle. This information will be combined with analyses of rocks that are transported with the fluids to quantify what is carried into the deeper subduction zone and what is liberated to the crust and ocean above. These analyses will help to constrain the reactions controlling the strength of materials where earthquakes nucleate.

构成世界板块的地壳有两种：海洋和大陆，前者稀薄而致密，位于世界海洋之下；后者更厚、更有浮力，构成了大陆。洋壳形成于不同的板块边界，称为大洋中脊，即水下火山链。随着新形成的地壳老化并远离山脊，它会冷却、变得更致密并下沉。在海洋和大陆地壳之间出现会聚板块边界的地方，较致密的海洋地壳下沉并俯冲到大陆地壳下方。在两个海洋板块之间发生汇聚的地方，较古老、密度较大的板块会下沉和俯冲。这些边界形成了地球上最深的海沟，例如马里亚纳海沟（最深点 11,033 m）。俯冲带是地球上地壳物质被输送到地幔的主要区域，因此代表了板块构造中的基本循环过程理论。这些汇聚边缘的地质过程控制着地震活动、深成作用和相关的火山作用，以及海洋、地壳和地幔之间的地球化学循环。这些边缘通常会产生大型海啸地震，因此了解控制俯冲界面地震发生的物理特性是阐明板块边界行为的关键。沉积物和地壳岩石在俯冲过程中会经历不断变化的压力和温度，矿物质变得不稳定并分解形成新的、密度更大的矿物质，并在此过程中释放出有浮力的流体并上升到地震成核并与上覆地幔岩石相互作用的断层中。俯冲板块在熔化开始之前经历的化学和物理变化控制着这些板块边界的地震行为、地球化学循环和岩浆活动。为了研究这些过程，已经隆起到当今大陆地壳上的旧俯冲带碎片已被研究。研究表明，这些洋壳部分向大陆迁移过程中发生的化学和物理变化很少受到约束，并且对地层压力和温度的估计存在较大误差。现场研究这些过程很困难，因为它们发生在地壳深处和地球上一些最深处的水域中。被厚厚的沉积物覆盖的俯冲带已被成功钻探，但厚厚的沉积物掩盖了深层流体的特征，因此无法研究深俯冲带过程。在马里亚纳辐合边缘，太平洋板块俯冲到马里亚纳之下几乎没有沉积物覆盖的板块。马里亚纳板块有断层，这些断层与泥火山有关。泥火山起源于从俯冲板块释放的流体通道，并携带来自该板块的物质以及化学改变的上覆地幔。这提供了一个独特的机会，无需深入钻探即可对俯冲过程中产生的流体和俯冲板块的材料进行采样。我们将使用 IODP Expedition 366 钻探马里亚纳弧前泥火山的样本来分析俯冲过程中产生的水。之前的研究表明，随着板块更深地移动，流体化学成分也会发生变化。我们将测量流体中不同化学示踪剂的同位素比率，以记录这些过程的演化和下降岩石中的变质转变以及流体在上覆地幔中促进的化学反应。这些信息将与随流体输送的岩石的分析相结合，以量化带入更深俯冲带的物质以及释放到上方地壳和海洋的物质。这些分析将有助于限制控制地震成核材料强度的反应。

项目成果

Supplementary material to "Fluid-rock interactions in the shallow Mariana forearc: carbon cycling and redox conditions"

补充材料

• DOI: 10.5194/se-2019-51-supplement
• 发表时间: 2019
• 作者: Albers E

Spatial variation of subduction zone fluids during progressive subduction: Insights from Serpentinite Mud Volcanoes

• DOI: 10.1016/j.gca.2021.10.030
• 发表时间: 2021-11
• 期刊: Geochimica et Cosmochimica Acta
• 影响因子: 5
• 作者: C. Menzies;R. Price;J. Ryan;O. Sissmann;K. Takai;C. Geoffrey Wheat

Mariana serpentinite mud volcanism exhumes subducted seamount materials: implications for the origin of life

• DOI: 10.1098/rsta.2018.0425
• 发表时间: 2020-02-21
• 期刊: PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
• 影响因子: 5
• 作者: Fryer, Patricia;Wheat, C. Geoffrey;Pomponi, Shirley
• 通讯作者: Pomponi, Shirley

Fluid-rock interactions in the shallow Mariana forearc: carbon cycling and redox conditions

马里亚纳弧前浅部的流体-岩石相互作用：碳循环和氧化还原条件

• DOI: 10.5194/se-2019-51
• 发表时间: 2019
• 作者: Albers E

Tracing the Evolution of Slab Fluids during Progressive Subduction: Insights from Serpentinite Mud Volcanoes in the Mariana Forearc

追踪渐进俯冲过程中板状流体的演化：来自马里亚纳弧前蛇纹岩泥火山的见解

• DOI: 10.5194/egusphere-egu21-15157
• 发表时间: 2021
• 作者: Menzies C