Behaviour of trace metals in the solid earth and atmosphere during subduction and volcanism

俯冲和火山作用期间固体地球和大气中痕量金属的行为

• 批准号: RGPIN-2019-03956
• 负责人: Canil, Dante
• 金额: $ 3.72万
• 依托单位: University of Victoria
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=750965
• 关键词: Behaviour; trace; metals; solid; earth

The upper surface of the Earth consists of tectonic plates. Where they collide, one plate is consumed, creating a flux of material to the deeper earth, as well as the addition of new magma to the surface of the other plate, expressed as a chain of volcanoes (arcs). The flux of elements into the deeper earth during subduction, and their return to the surface by volcanism, makes an important geochemical cycle critical to the evolution of the earth. Sulfur (S) and other elements that pair with it (chalcophile metals) are key components in this cycle that affect the composition and evolution of the atmosphere, and the endowment of the crust in metals required as nutrients by living organisms, or exploited by humans for technological use. This research program investigates the sequestration of S and allied trace metals in subducted rocks, and their release to overlying mantle and crust by fluids, melts and gases during plate convergence. The identity and stability of S-bearing minerals (sulfides) in the presence of fluids is investigated by laboratory experiments over the pressure-temperature regime experienced by subducted Ca-, Al- and Fe-rich rock compositions in the earth. The partitioning of S and chalcophile metals (As, Zn, Pb, Cu, Cd, Mo) into fluids measured during the experiments can be applied to natural rocks to understand how mass transfer deep beneath arcs can either sequester elements into the deeper earth, enrich the crust with ore metals, or control the composition of volcanic gases emitted to the atmosphere. The results of such experiments elucidate the stability and host for S and chalcophile element transfer expected from the subducted crust into the deep mantle as functions of many variables. The detailed examination of behaviour S and allied chalcophiles in fluids and solids will help answer a long standing question as to how the mantle beneath subduction zones can oxidize, or produce magmas with oxidized gases, controlling the evolution of oxygen in the atmosphere over time. The return flux of magma by subduction to the upper plate also emits gases. The output of toxic trace metals in these gases emitted to the atmosphere by volcanism will be investigated in the laboratory with a new apparatus that simulates natural volcanic vents. The apparatus will be used to measure the precipitation of trace metals from cooling volcanic gases into solid forms in vents and on volcanic ash particles. The overarching goal will be to isolate the variables in how metals are transported in a gas phase, in what species and what possible fractionations ensue during low pressure metal transport. The impact of these measurements will inform a better understanding of volcanic degassing processes and the formation of ore deposits and help quantify the toxicity of modern eruptions. Ultimately we can test if volcanic eruptions in the past loaded the surface environment with enough trace metals to influence living organisms or cause mass extinctions.

地球的上表面由构造板组成。在它们碰撞的地方，一块板被消耗，从而形成了更深的地球的材料通量，以及在另一盘表面上添加新的岩浆，以火山（弧）（弧）表示。在俯冲期间，元素进入更深地球的通量，并通过火山恢复到地面，使一个重要的地球化学循环对地球的进化至关重要。硫（s）和其他与之配对的元素（豆科植物金属）是该循环中影响大气组成和演变的关键组成部分，以及在生物体中所需的金属中地壳的质量，或者被人类所需要的金属所需的金属。用于技术使用。该研究计划研究了俯冲岩石中S和相关痕量金属的固相，并释放到板块收敛期间的液体，熔体和气体上覆盖地幔和地壳。通过实验室实验对地球上俯冲的Ca-，Al和Fe富含Fe的岩石组成所经历的压力温度制度研究，研究了在液体存在下的含矿物（硫化物）的身份和稳定性。可以将S和豆腐金属（AS，Zn，Pb，Cu，Cd，Mo）分配到实验期间测得的流体中矿石金属的外壳，或控制发射到大气的火山气体的成分。此类实验的结果阐明了S和Chalcophile元件转移的稳定性和宿主转移的稳定性，从俯冲地壳中预期到深幔中，这是许多变量的功能。对流体和固体中行为S和相关玉米菌的详细检查将有助于回答一个长期存在的问题，即俯冲带下的地幔如何可以氧化，或者用氧化气体产生岩浆，从而控制大气中氧气的演变。岩浆的回流通量通过俯冲到上板也发出了气体。通过模拟天然火山通风孔的新设备，将在实验室研究这些气体中这些气体中有毒痕量金属的输出。该设备将用于测量痕量金属从冷却火山气体和火山灰颗粒上的固体形式的沉淀。总体目标是将变量隔离在气相中金属的运输方式，在低压金属传输过程中发生什么物种以及可能的分馏。这些测量值的影响将使人们更好地了解火山脱水过程和矿床的形成，并有助于量化现代喷发的毒性。最终，我们可以测试过去的火山喷发是否用足够的痕量金属加载了表面环境，以影响活生物体或引起质量灭绝。