Fluid-mobile and volatile element (Cl, B, and Li) cycling through the forearc: Case study of cold and thermal spring geochemistries from the Hikurangi accretionary prism, New Zeala

流体流动元素和挥发性元素（Cl、B 和 Li）在前弧循环：新西兰 Hikurangi 增生棱镜冷泉和温泉地球化学的案例研究

• 批准号: 1455432
• 负责人: Jaime Barnes
• 金额: $ 22.85万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1455432&HistoricalAwards=false
• 关键词: Fluid; mobile; volatile; element; Cl

A subduction zone is an area where two tectonic plates collide and the denser plate (also called a subducting slab, consisting of seafloor sediments, oceanic crust, and underlying mantle) is forced to sink into the mantle beneath the more buoyant plate. Hydrous minerals in the slab break down when exposed to the high temperatures encountered at depth, releasing fluids ultimately involved in the creation of arc magmas and explosive arc volcanoes. In addition, these fluids are also thought to influence seismic slip behavior and the manifestation of earthquakes. Therefore, determining the sources and amount of fluids released at depth within a subduction is critical for understanding volcanic and earthquake behavior along plate margins.Particular elements (for example, lithium, chlorine, and boron) are highly fluid-mobile, thereby making them excellent tracers of fluid source. These fluids impart diagnostic geochemical signatures to overlying material that can be used to trace mass transfer through subduction zones. This work will geochemically characterize cold and thermal spring waters from the Hikurangi (New Zealand subduction zone) accretionary prism to trace fluid sources along the fore-arc and quantify volatile flux through the fore-arc. Fluid sources to the fore-arc will be determined by examining variations in elemental concentrations (and ratios) and isotopic compositions. The data will be used to evaluate causal links between fluid sources and earthquake mechanics, such as shallow slow slip events. The Hikurangi margin is the ideal locality for this study due to the numerous exposed fore-arc springs, which allow a rare glimpse into the shallow part of the subduction zone, and the previously documented along arc variability in subduction parameters (e.g., amount of subducting sediment) and seismic slip behavior. Geochemical evidence for increased (or more shallow) dehydration reactions in the northern portion of the margin compared to the southern portion would support a link between dehydration reactions and shallow slow slip events.

俯冲带是两个构造板块碰撞的区域，密度较大的板块（也称为俯冲板块，由海底沉积物、洋壳和下面的地幔组成）被迫沉入浮力较大的板块下方的地幔。当板块中的含水矿物暴露在深处遇到的高温下时会分解，释放出最终参与创造弧岩浆和爆炸性弧火山的流体。此外，这些流体也被认为影响地震滑动行为和地震的表现。因此，确定俯冲带深处释放的流体的来源和数量，对于了解板块边缘沿着的火山活动和地震活动至关重要。某些元素（如锂、氯和硼）具有高度的流体流动性，因此成为流体来源的绝佳示踪剂。这些流体赋予上覆物质的诊断地球化学特征，可用于追踪俯冲带的物质转移。这项工作将从地球化学的特点冷和温泉沃茨Hikurangi（新西兰俯冲带）增生棱镜跟踪流体来源沿着弧前和量化挥发性通量通过弧前。弧前的流体来源将通过检查元素浓度（和比例）和同位素组成的变化来确定。这些数据将用于评估流体源和地震力学之间的因果关系，例如浅层缓慢滑动事件。Hikurangi边缘是这项研究的理想地点，因为有许多暴露的弧前泉水，这使得人们可以对俯冲带的浅部进行罕见的一瞥，以及先前记录的俯冲参数的沿着弧变化（例如，俯冲沉积物量）和地震滑动行为。地球化学证据表明，与南部相比，在陆缘的北方部分，脱水反应增加（或更浅），这将支持脱水反应与浅部缓慢滑动事件之间的联系。