Cruise support for Dr Christopher Smith-Duque to sail as a Petrologist on IODP Expedition 344 - CRISP II

构造板块的俯冲是板块构造的基本过程之一，也是地球表面附近地震最有力的来源。这一过程发生在一个构造板块移动到另一个构造板块下沉入地幔的会聚边界。尽管有大量的研究致力于了解俯冲作用在地震发生（造震）中的作用，但到目前为止，对俯冲带的发震区进行直接采样还无法进行直接采样和观测。综合海洋钻探计划（IODP）远征344是一个雄心勃勃的项目的组成部分，该项目旨在了解控制俯冲带大地震形成和破裂的过程。我们将从哥斯达黎加奥萨半岛近海的中美洲边缘的4个地点收集沉积物和基底岩心，横跨俯冲之前的区域，一直到孕震带上方的区域，为之后的勘探和取样做准备。在船上，我将成为一个国际科学家团队的一员，使用多学科的方法来描述海底沉积物的地质性质，潜在的火山岩，以及构成俯冲海洋板块（科科斯-纳斯卡）和哥斯达黎加上部（加勒比）板块的沉积和基底。哥斯达黎加的侵蚀性俯冲系统是目标，因为大多数俯冲系统都是侵蚀性的（上部板块物质被侵蚀并卷入俯冲），这是一个强烈的地震活动地区，关键的是，该地区的地震成核发生在足够浅的深度，可以通过海洋钻探进行采样。IODP 344考察队将确定：1)俯冲沉积物和基底的地质性质，包括它们的组成、结构和物理性质。2)大洋板块的俯冲速率和哥斯达黎加俯冲系统上板块的侵蚀作用3)上板块内部流体和岩石之间的相互作用。4)当俯冲系统进入发震带时，作用在俯冲系统上的力是如何变化的。作为第344远征队的岩石学家，我的职责是描述和描述发生在俯冲海洋地壳沉积物下方和上部板块基底内的火成岩起源的岩石。俯冲板块和上板块的火山物质分别形成于数百万年前的洋中脊和弧后火山活动时期。在远征344期间对这些岩石的描述和分析将使我能够推断出原始喷发过程的风格并对它们进行分类。被称为热液蚀变的热驱动化学过程导致海水和岩石之间的元素和化合物交换，在岩石碎片之间的空隙中，在冷却的裂缝中，以及在被称为小泡的气泡中形成新的矿物质，这些气泡曾经被火山喷发时从岩浆中逸出的气体占据。在上板块，火山成因的基底（如增生的海山）在就位之前可能经历了类似的海底蚀变过程。然而，一个额外的考虑将是在增生和俯冲期间发生的化学交换过程，这是地震形成的一个潜在的重要因素。我将解释344号探险期间发现的火成岩中的热液蚀变特征，以确定海水和俯冲相关流体分别如何与海洋基底和上板块基底相互作用。我的工作将有助于我们了解俯冲带的水文地质系统，这将有助于我们了解地震形成的环境。

The subduction of tectonic plates is one of the fundamental processes of plate tectonics, and the most potent source of earthquakes near the Earth's surface. The process occurs at convergent boundaries where one tectonic plate moves under another tectonic plate sinking into the Earth's mantle. Despite the wealth of research that has been dedicated to understand the role of subduction in earthquake generation (seismogenesis) direct sampling of the seismogenic region of subduction zones has, until now been beyond the reach of direct sampling and observation.Integrated Ocean Drilling Program (IODP) Expedition 344 forms an integral part of an ambitious project to understand the processes that control the formation and rupture of large earthquakes at subduction zones. We will collect sediment and basement cores from 4 sites across the Central American margin offshore the Osa Peninsula of Costa Rica, spanning the area immediately preceding subduction through to the area above the seismogenic zone preparing the groundwork for a later expedition to drill and sample this zone.Aboard ship, I will be part of an international team of scientists using a multi-disciplinarily approach to characterise the geological nature of seafloor sediments, underlying volcanic rocks and accreted sediment and basement that make up the subducting oceanic plate (Cocos-Nazca) and the upper (Caribbean) plate of Costa Rica. The erosive Costa Rican subduction system is targeted since the majority of subduction systems are erosive (Upper plate material is eroded and drawn into subduction), it is an area of intense seismic (earthquake) activity, and crucially earthquake nucleation in this region occurs at a sufficiently shallow depth to be sampled by ocean drilling.IODP Expedition 344 will determine:1) The geological nature of subducting sediments and basement, including their composition, texture and physical properties.2) The rate of subduction of the oceanic plate and erosion of the upper plate of the Costa Rican subduction system3) The interactions between fluids and rock within the upper plate.4) How the forces acting on the subduction system change as the subduction system enters the seismogenic zone. My role as a petrologist on Expedition 344 will be to describe and characterise rocks of igneous origin that occur beneath the sediments of the subducting oceanic crust and within the upper plate basement. The volcanic material in the subducting plate and the upper plate originally formed millions of years ago at mid-ocean ridges and during back-arc volcanism respectively. Describing and analysing these rocks during Expedition 344 will allow me to infer the styles of the original eruptive processes and classify them.Thermally driven chemical processes known as hydrothermal alteration, results in the exchange of elements and compounds between seawater and rock to form new minerals in voids between fragments of rock, in cooling fractures, and within bubbles known as vesicles that were once occupied by gases escaping from the magmas during eruption. In the upper plate, basement of volcanic origin (e.g., accreted seamounts) may have been subjected to similar seafloor alteration processes prior to their emplacement. However, an additional consideration will be the chemical exchange processes that have taken place during accretion and during subduction, a potentially significant factor in how earthquakes form. I will interpret hydrothermal alteration features within igneous rock recovered during Expedition 344 to determine how seawater and subduction-related fluids interacted with oceanic basement and upper plate basement respectively. My work will contribute to our understanding of the hydrogeological system of the subduction zone which will help us to understand the setting at which earthquakes can form.