Using electromagnetic geophysics to understand global tectonics and resource distribution

利用电磁地球物理学了解全球构造和资源分布

• 批准号: RGPIN-2020-04240
• 负责人: Unsworth, Martyn
• 金额: $ 3.72万
• 依托单位: University of Alberta
• 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=762600
• 关键词: Using; electromagnetic; geophysics; understand; global

Plate tectonics has shaped the surface of the Earth over the course of geological history. Many important processes occur at the boundaries where tectonic plates move relative to each other. Subduction zones are formed when two plates converge and an oceanic plate is forced downwards into the mantle. Subduction zones are important because they transport water into the mantle, generate molten rock that forms volcanoes, cause large earthquakes and also form important types of mineral deposit. A subduction zone is present in Western Canada beneath Vancouver Island and is responsible for both volcano and earthquake hazards. Subduction zones vary over time and sometimes the down going plate flattens out, stopping the volcanoes from erupting and changing the pattern of deformation. This behaviour occurs today beneath the Andes mountains where the Nazca Plate subducts beneath the South American Plate. In Peru a flat slab is present and grows southward. In Colombia, a previously flat slab has recently steepened, with volcanoes becoming active once again. This research program will investigate subduction zones by using geophysical imaging to map the location of fluids such as water and partial melt. Mapping fluid distribution within the Earth requires the use of geophysical data measured at the surface to determine the properties of rocks at depth. Seismic imaging uses acoustic waves but is not effective at imaging low concentrations of fluids. However, fluids dramatically change the electrical resistivity of a rock and this property can be determined with magnetotellurics (MT) - a geophysical exploration method that uses low frequency radio waves to image the subsurface to depths in excess of 200 km. In this proposal, MT will be used to study the processes that occur in subduction zones in Canada and South America. Measurements of the natural radio waves will be converted into 3-D images of the electrical resistivity of the Earth. From these 3-D models the distribution of water and molten rock will be determined. In Canada this will improve understanding of where water is present in the subduction zone beneath Vancouver Island and where the molten rock originates that is erupted in the volcanoes of the Garibaldi Belt. In Peru and Columbia the 3-D models will show how Earth structure changes when slabs flatten and steepen. In related research, the MT method will be used to investigate the tectonic events that occurred in the past as the North American continent was formed. The resulting models will be used to investigate how these past events formed mineral deposits. This process is being used to improve the methods used in mineral exploration by searching not just for mineral deposits, but regions of past fluid flow in the mineral systems approach to exploration. A major emphasis of the research program will be to train undergraduate and graduate students who will be qualified to work in academic research, hazard reduction and mineral exploration.

板块构造在地质历史进程中塑造了地球表面。许多重要的过程发生在构造板块相对运动的边界上。当两个板块汇合，一个大洋板块被强迫向下进入地幔时，俯冲带就形成了。俯冲带很重要，因为它们将水输送到地幔中，产生形成火山的熔岩，引发大地震，还形成重要类型的矿藏。加拿大西部温哥华岛下存在一个俯冲带，是火山和地震灾害的罪魁祸首。俯冲带随着时间的推移而变化，有时下行板块会变平，阻止火山喷发，改变变形模式。今天，这种行为发生在安第斯山脉之下，纳斯卡板块俯冲到南美板块之下。在秘鲁，出现了一块向南生长的平板。在哥伦比亚，随着火山再次活跃，以前平坦的板块最近变得陡峭起来。这项研究计划将通过使用地球物理成像来调查俯冲带，以绘制出水和部分熔体等流体的位置。绘制地球内部流体分布图需要使用在地表测量的地球物理数据来确定深部岩石的性质。地震成像使用声波，但在成像低浓度流体时无效。然而，流体极大地改变了岩石的电阻率，这一特性可以通过大地电磁(MT)来确定--这是一种地球物理勘探方法，使用低频无线电波对地下超过200公里的深度进行成像。在这项提议中，MT将被用来研究加拿大和南美洲俯冲带中发生的过程。对自然无线电波的测量将转换为地球电阻率的3D图像。根据这些三维模型，水和熔岩的分布将被确定。在加拿大，这将提高对温哥华岛下俯冲带中哪里有水，以及加里波迪带火山喷发的熔岩起源的了解。在秘鲁和哥伦比亚，3D模型将显示当板块变平和变陡时，地球结构是如何变化的。在相关研究中，将使用MT方法来调查北美大陆形成时过去发生的构造事件。由此产生的模型将被用于研究这些过去的事件是如何形成矿藏的。这一过程被用来改进矿产勘探中使用的方法，不仅寻找矿藏，而且寻找矿物系统中接近勘探的过去流体流动的区域。该研究计划的一个主要重点将是培养有资格从事学术研究、减灾和矿产勘探工作的本科生和研究生。