IODP Phase 1 post cruise support for C Smith-Duque Expedition 344

构造板块俯冲是板块构造的基本过程之一，也是地球表面附近地震的最大震源。这一过程发生在会聚的边界上，在那里，一个构造板块沉入地幔，在另一个构造板块下方移动。尽管有大量研究致力于了解俯冲在地震孕育中的作用(地震成因)，但对俯冲带地震孕育区的直接采样一直超出了直接采样和观测的范围。我作为综合大洋钻探计划(IODP)探险344号国际科学家团队的一员航行，以恢复海底沉积物和下面的火山岩，它们构成了哥斯达黎加弧的俯冲洋板(Cocos-Nazca)和上板块(加勒比海)。344探险队在确定俯冲沉积物和基底的地质性质、科科斯板块向哥斯达黎加边缘俯冲的速度、哥斯达黎加边缘内流体-岩石相互作用的性质以及当俯冲系统进入孕震带时作用于俯冲系统的力如何变化方面取得了重要进展。在一个地点，对沉积物下面的火山岩进行了采样。在344次探险中发现的火山岩最初是在海底火山沿大洋中脊喷发期间形成的，但后来因海洋扩张而冷却，现在进入哥斯达黎加俯冲带。在大洋地壳的整个生命周期中，被称为热液蚀变的热驱动海水/岩石相互作用，导致元素和化合物交换，在空洞和矿脉中形成新的矿物，或局部取代岩石中的原始矿物。形成这些矿物的流体来自与洋壳在低温下相互作用的海水。随着洋壳的俯冲，温度和压力增加，以前束缚在次生矿物中的水向上迁移，这可能有助于俯冲带或其附近的热液活动。我们基于次生矿物碳酸钙的研究将被用来确定与俯冲相关的流体是否影响了即将俯冲的盆地的热液系统。碳酸钙中存在的锶元素非常有用，因为随着时间的推移，它在海水中的同位素组成是众所周知的。我们将使用碳酸钙中的锶同位素组成来估计有多少海水与大洋中脊玄武岩混合，而大洋中脊玄武岩又具有非常不同但定义明确的同位素比率。此外，我们将使用锶同位素来部分限制碳酸钙形成的时间。众所周知，温度控制着碳酸钙形成过程中氧(O)同位素吸收的偏好。因此，我们将使用碳酸盐岩中的氧同位素来确定地层温度，以估计地层的热环境。了解温度将有助于洞察某些流体或所有流体是否来自俯冲环境。我们将看到后来的脉化(随着地壳向俯冲带移动)是否会增加温度。这将表明俯冲过程正在影响进入的大洋地壳。流体中的痕量元素在形成过程中并入碳酸钙中，因此我们可以测量这些元素的浓度来估计流体的组成。然后将微量元素成分与其他俯冲带环境中的海水成分和孔隙流体成分进行比较，以估计流体可能来自哪里。我们的研究将对即将俯冲的洋壳内的蚀变性质提供新的见解，因此将有助于我们理解进入俯冲带的物质的组成和物理性质。

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 by sinking into the Earth's mantle. Despite the wealth of research that has been dedicated to understanding the role of subduction in earthquake generation (seismogenesis) direct sampling of the seismogenic region of subduction zones has been beyond the reach of direct sampling and observation.I sailed as part of an international team of scientists on Integrated Ocean Drilling Program (IODP) Expedition 344 to recover seafloor sediments and underlying volcanic rocks that make up the subducting oceanic plate (Cocos-Nazca) and the upper plate (Caribbean) of the Costa Rica Arc. Expedition 344 made important progress in determining the geological nature of subducting sediments and basement, the rate of subduction of the Cocos plate into the Costa Rican margin, the nature of fluid-rock interactions within the Costa Rican margin, and how the forces acting on the subduction system change as the subduction system enters the seismogenic zone. At one site, volcanic rock beneath sediment was sampled. The volcanic rocks recovered during Expedition 344 originally formed during the eruption of sub-sea volcanoes along mid-ocean ridges, but have since cooled, moved by ocean spreading, and are now entering the Costa Rican subduction zone.Throughout the lifetime of oceanic crust, thermally driven seawater/rock interaction known as hydrothermal alteration, results in exchange of elements and compounds to form new minerals within voids and veins, or locally replacing the original minerals in the rocks. Fluids that form these minerals are sourced from seawater that has interacted with oceanic crust at a low temperature. As oceanic crust subducts, temperatures and pressures increase such that water previously bound in secondary minerals migrates upwards and that it may contribute the hydrothermal activity at or near subduction zones. Our research, based on secondary mineral calcium carbonate will be used to determine if subduction-related fluids have influenced the hydrothermal system of imminently subducting basement.The element Strontium (Sr), present in calcium carbonate, is extremely useful since its isotopic composition in seawater through time is well known. We will use the Sr-isotopic composition in calcium carbonate to estimate how much seawater has mixed with mid-ocean ridge basalt, which in turn has a very different but well defined isotopic ratio. In addition we will use Sr isotopes to partially constrain the timing of calcium carbonate formation.Temperature is known to control the preference of Oxygen (O) isotopes uptake during calcium carbonate formation. We will therefore use O-isotopes in carbonates to determine the temperature of formation to estimate the thermal environment of formation. Knowing the temperature will provide insight into whether some or all of the fluids have come from subduction settings. We will see if later episodes of veining (as the crust moves towards the subduction zone) increase in temperature. This will indicate that subduction processes are influencing incoming ocean crust.Trace elements from fluids are incorporated in to calcium carbonate during its formation, therefore we can measure the concentrations of these elements to estimate the composition of the fluid. Trace element compositions will then be compared against seawater compositions and pore-fluid compositions from other subduction zone settings to estimate where fluids may have come from. Our research will offer new insight into the nature of alteration within imminently subducting ocean crust, and therefore will contribute to our understanding of the composition and physical properties of material that enters subduction zones.