Collaborative Research: Expedition 322 Objective Research on the Nature and History of Subsurface Flow within the Nankai Sediments Prior to Subduction

知识价值：NanTroSEIZE是“发震带计划”的核心部分，旨在揭示俯冲巨型逆冲的水文过程。该项目的一个关键组成部分，也是IODP Exp. 322的目标，是在板块进入俯冲带之前，对进入的沉积地层和火成岩基底顶部进行表征。在四国盆地钻探了两个参考点（C0012和C0011），将其与之前在变形前沿向海钻探的其他地点（ODP腿131和190）进行了分析，为描述俯冲输入提供了理想的数据库。尽管这些输入仍然不受俯冲过程的影响，但它们受到深层脱水反应带的侧向流体运移的影响。限制这种水文机制是揭示流体和成岩反应对板块界面深部地质力学性质影响的关键。船上的结果指出了一种有趣的可能性，即来自不同来源的两种流体通过海沟向海方向的沉积地层迁移。一种状态（以流体新鲜化、甲烷和高级碳氢化合物的存在为特征）是由俯冲沉积物中的流体排出和俯冲输入区高渗透层的上倾运移驱动的。另一种流动形式（以深层存在硫酸盐为特征）是由一种类似海水的流体通过上部海洋地壳迁移到上覆沉积物的砂岩浊积岩中所驱动的。在两种流体状态的界面，微生物活动似乎受到刺激；新发现的深层甲烷活性厌氧氧化区（AOM）约为417 mbsf，其中甲烷浓度峰值与硫酸盐的完全消耗和孔隙水硫化物的显著增加相吻合。在这里，我们建议：1)在与其他船上科学家合作的项目中，利用孔隙水数据表征这些流动状态的性质；2)通过分析自生相（碳酸盐和重晶石）来推断这些发现，这些相包含流体来源（锶同位素）、代谢过程（碳和硫同位素）和地层温度（团块氧同位素）的记录。最近发展的团块氧同位素（即多重取代同位素）分析已被证明有效地将结晶温度限制在±2.4°C。测量井底附近的碳酸盐岩脉和胶结物将提供表征流体温度所需的关键数据：进入沉积物的状态属性；温度依赖性成岩反应；以及地下微生物群落。试验322期间未收集原位温度数据。除了提供进入板块下层的基本地球化学信息（Exp. 322的一个关键目标）之外，这里生成的数据集将用于进一步我们对新假设的和非常重要的主题的理解：1)进入板块下层的流动历史和性质，其中可能包括-尚未记录的-上部海洋地壳的流体流动制度；2)深层生物圈过程，其中包括新发现的AOM带，该带由含硫酸盐流体的上层基底流提供的电子受体维持。更广泛的影响：我们将收集的数据集将使我们能够提供关于流体在俯冲地层中地球化学、地质力学和地质生物过程中的作用的基本信息，这是这次考察的一个关键目标。我们的数据将与其他nantrocapture科学家共享，以充分整合和合作的努力。除了这些合作之外，不来梅大学的Peckman教授还同意免费分析碳酸盐岩中的生物标志物。该项目将直接支持2名研究生和1名本科生的论文研究。外展工作包括通过俄勒冈州立大学的SMILE项目（http://smile.oregonstate.edu/）、俄勒冈州的成人教育项目（http://literacyworks.org/ocean/）传播孕震带过程，以及通过亚利桑那州教育部的数学-科学合作项目为在职教师提供专业发展课程。

Intellectual merit: NanTroSEIZE, a central part of the Seismogenic Zone Initiative, is aimed at unraveling hydrologic processes at subduction megathrusts. A key component of the project, and the target of IODP Exp. 322, is the characterization of the incoming sedimentary strata and the top of igneous basement prior to the plate entering the subduction zone. Two reference sites (Sites C0012 and C0011) were drilled in the Shikoku Basin, which, when analyzed in the context of other sites previously drilled seaward of the deformation front (ODP Legs 131 and 190), provide an ideal database to characterize subduction inputs. Though still unaffected by subduction processes, these inputs are influenced by lateral fluid migration from zones of deeperseated dehydration reactions. Constraining this hydrologic regime is key to unraveling the effect of fluids and diagenetic reactions on the geomechanical properties of the plate interface at depth. Shipboard results point to the intriguing possibility of two fluids from different sources migrating through the sedimentary strata seaward of the trench. One regime (characterized by fluid freshening and the presence of methane and higher hydrocarbons) is driven by expulsion of fluids from the subducting sediment and up-dip migration through high permeability horizons in the subduction inputs. The other flow regime (characterized by the presence of sulfate at depth) is driven by migration of a seawater-like fluid through the upper oceanic crust into the sandstone turbidites of the overlying sediment. At the interface of both fluid regimes, microbial activity appears to be stimulated; with a newly discovered deep zone of active anaerobic oxidation of methane (AOM) at approximately 417 mbsf, where peak methane concentrations coincide with the complete consumption of sulfate and a marked increase in pore-water sulfide. Here we propose to: 1) characterize the nature of these flow regimes using pore water data in a collaborative program with other shipboard scientists; and 2) extrapolate these findings through time by analyses of authigenic phases (carbonates and barites), which contain a record of fluid sources (strontium isotopes), metabolic processes (carbon and sulfur isotopes) and formation temperatures (clumped oxygen isotopes). The recently developed clumped oxygen isotope (i.e. multiply-substituted isotopologues) analysis has been shown to effectively constrain temperatures of crystallization to ± 2.4 °C. Measurement on select carbonate veins and cements recovered near the bottom of the holes will provide key data on fluid temperatures needed to characterize: the state properties of the incoming sediments; temperature-dependent diagenetic reactions; and subsurface microbial communities. No in situ temperature data was collected during Exp. 322. In addition to providing information on basic geochemistry in the lower strata of the incoming plate (a key objective of Exp. 322), the data sets generated here will be used to further our understanding of newly postulated and highly significant topics: 1) history and nature of flow in the lower strata of the incoming plate, which may include an -as of yet undocumented- fluid flow regime in the upper oceanic crust; and 2) deep biosphere processes, which include a newly discovered AOM zone that is sustained by the electron acceptors supplied by an upper basement flow of sulfate bearing fluids. Broader impact: The data set we will assemble will allow us to provide fundamental information on the role of fluids on the geochemical, geomechanical and geobiological processes in the subducting strata, a key objective of the expedition. Our data will be shared with other NantroSeize scientists, in a fully integrated and cooperative effort. In addition to these collaborations, Prof. Peckman (U. of Bremen) has agreed to analyze biomarkers in the carbonates at no cost to this proposal. The project will directly support the thesis research of two graduate students, and an undergraduate research fellow. Outreach efforts include dissemination of Seismogenic zone processes through The SMILE program at Oregon State University (http://smile.oregonstate.edu/), Adult Education across the State of Oregon (http://literacyworks.org/ocean/) and professional development courses for in-service teachers through the Math-Science Partnership Program of the Arizona Department of Education.